Title of Invention

ABSORBENT COMPOSITION MATERIAL AND METHOD FOR MANUFACTURING THE SAME

Abstract An absorbent composite comprising: a base material and water-absorbent resin particles; wherein the following conditions (1) to (4) are fulfilled: (1) the weight ratio of water-absorbent resin relative to the total weight of the base material and water- absorbent resin is 65 to 99 wt%, (2) the water-absorbent resin particles adhering directly to the base material constitute 50 wt% or more of the total water-absorbent resin particles; (3) the average absorption capacity of the water-absorbent resin particles is 50 g/g or more; and (4) the amount of residual monomers in the water-absorbent resin is 200 ppm or less.
Full Text A0501 VP32W/YA
ABSORBENT COMPOSITE MATERIAL AND METHOD FOR MANUFACTURING
THE SAME
TECHNICAL FIELD
[0001] The present invention relates to a thin, lightweight sheet-shaped
absorber, and to a method for manufacturing the same. Because this absorber is an
absorbent composite with excellent water-absorbing capability, absorption speed and
high-dispersion properties, it is suitable for use in hygiene products such as
disposable diapers and sanitary napkins. The present invention also relates to an
environmentally-friendly absorber which is capable of reducing the amount of pulp,
water-absorbent resin and the like commonly used in sanitary materials.
BACKGROUND ART
[0002] Disposable diapers, sanitary napkins and other sanitary materials have an
absorber body for absorbing bodily fluids and other liquids, a soft, liquid-permeable
top sheet on the side that contacts the body, and a liquid-impermeable back sheet on
the side away from the body. The absorber is normally made from a mixture of pulp
or another fibrous substance and a water-absorbent resin.
There has been increasing demand in recent years for thinner, more
lightweight sanitary materials to resolve problems of design, distribution, garbage
disposal and the like. The most common method currently used to meet these
demands in sanitary materials is to reduce the amount of fiber or other support
material for the water-absorbent resin in the sanitary material and use larger amounts
of water-absorbent resin. Such sanitary materials having a smaller proportion of
hydrophilic fiber and a higher proportion of water-absorbent resin may be better at
simply storing liquid, but are not necessarily good at distributing and dispersing the
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liquid when the diaper is actually used. That is, the large amount of water-absorbent
resin turns into a soft gel when it absorbs liquid, resulting in a phenomenon called gel
blocking which greatly inhibits dispersal of the liquid. Once gel blocking occurs the
resin no longer performs properly, and not only does it absorb less water but
absorption speed decreases.
[0003] The proportions of hydrophilic fiber and water-absorbent resin must both be
restricted in order to avoid this problem and maintain the absorbent properties of the
absorber, so there are limits on reducing the hydrophilic fiber and reducing the
thickness of the sanitary material. Moreover, pulp is most commonly used as the
fiber in sanitary materials, especially virgin pulp is normally used because of its
cleanliness, therefore the use of large quantities of fiber increase of burdens on
forest resources.
[0004] Methods that have been proposed for preventing the gel blocking that occurs
when amount of fiber is reduced and large amounts of water-absorbent resin are
used include a method using two different water-absorbent resins with different
absorption abilities (see for example Patent Document 1), a method using a
composition containing a cationic ion-exchange hydrogel-forming polymer and an
anionic ion-exchange hydrogel-forming polymer (see for example Patent Document
2) a method using a water-absorbent resin crosslink density on the surface of which
is high (see for example Patent Document 3), a method using a water-absorbent
resin the salt density of which near the surface is lower than the overall salt density
(see for example Patent Document 32), and a method extruding and foaming a
mixture of a water-absorbent resin and a thermoplastic resin into a sheet (see for
example Patent Document 4). However, these suffer from such problems as high
cost and inadequate absorption properties for use in an absorber with a high water-
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absorbent resin concentration. Moreover, because these methods reduce the
relative amount of hydrophilic fiber, which serves to hold the water-absorbent resin,
the particles of absorbent resin tend to become unevenly distributed before use or to
move around during use. The absorbent product loses its shape when the water-
absorbent resin shifts from its intended position in this way, and the excreted urine or
other liquid does not contact the water-absorbent resin in the absorbent product,
resulting in leakage.
[0005] In another method, the method of mixing the fiber and water-absorbent resin is
fine-tuned so as to prevent uneven distribution and blocking of one part of the water-
absorbent resin by another part (see for example Patent Document 5). In this
method, the degree of mixing is high because the water-absorbent resin and pulp are
first mixed in water and then dry mixed with hydrophilic fiber and formed into a web
with air. However, the problem is that the water-absorbent resin may clog the web
during the process of air formation. Once this occurs, it becomes necessary to
remove it from the drum, decreases productivity. It is also preferable to use a
relatively hard absorbent resin in order to prevent clogging and facilitate removing
when clogging occurs. In general, hard water-absorbent resins tend to have low
absorption capacity, making it necessary to use a large quantity of water-absorbent
resin in order to absorb the target amount of liquid. This method is also
unsatisfactory in terms of preventing movement and uneven distribution of the water-
absorbent resin in the product.
[0006] In order to resolve these problems, particularly the problem of movement and
uneven distribution of the water-absorbent resin, methods of bonding the water-
absorbent resin onto a support have been studied. Examples include a method of
embossing an absorber, a method in which a thermoplastic binder fiber is included in
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an absorber comprising a water-absorbent resin and hydrophilic fiber, and the
absorbent body is then thermally fused, a method in which a synthetic resin with high
recovery from deformation is included in an absorbent body comprising a water-
absorbent resin and hydrophilic fiber, and the absorbent body is then thermally fused
(see for example Patent Documents 6 and 7), a method in which the surface of a
water-absorbent resin having anionic groups is coated with a cationic polymer, so
that the particles adhere and are fixed to one another as the resin swells (see for
example Patent Document 8 and 9), a method of using an emulsion binder to fix the
water-absorbent resin and hydrophilic fiber, and a method of using a hot melt
adhesive to fix the water-absorbent resin to a base material (see for example Patent
Document 10 and 11) and the like. Because in such examples the particles of water-
absorbent resin are stacked on each other on the support so as to increase the
proportion of water-absorbent resin, the blocking effect is greater and a large quantity
of binder must be used. When a large quantity of binder is used to fix the water-
absorbent resin on the base material in this way, moreover, the binding force itself
may restrict the swelling of the water-absorbent resin. In particular, the inherent
absorbent abilities of the water-absorbent resin may not be fully exploited if the
water-absorbent resin, hydrophilic fiber and the like are fixed with a thermoplastic
binder or emulsion.
[0007] Techniques for reducing restrictions on the swelling of the water-absorbent
resin when it is fixed on a support include a water absorbable composite material
comprising a water-absorbent resin part of which is held within a bulky nonwoven
fabric, while the exposed surface of the resin is coated with fine cellulose fiber and
the outer surface of the composite is covered with a fibrillated hot melt (see for
example Patent Document 12) and an absorbent composite sheet comprising a
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water-absorbent resin part of which is held within a bulky nonwoven fabric and part of
which is exposed on the surface, wherein the outer surface of the resin is coated with
a fiber net-like double hot melt layer consisting of two layers with different sized mesh
(see for example Patent Document 13). However, although swelling is less restricted
with these methods, the absorption properties are affected by the fixing process. As
has already been shown, the absorption properties of water-absorbent resin include
not only the absorption capacity, absorption speed, absorption capacity under
pressure, dispersion-absorption capacity under pressure and liquid permeability of
the swollen gel, but also the capillary absorption factor, which is an absorption
property based on the capillary force in the gaps between particles (see for example
Patent Document 14 and 15). It has been shown that this capillary absorption
capacity and other absorption properties of water-absorbent resin are greatly affected
by conventional fixing means. That is, even using highly functional water-absorbent
resins the absorption properties of absorbent bodies obtained by fixing those resins
often have not reflected the inherent absorption properties of the water-absorbent
resins. It has also been said that it is not necessary to insist so much on the
performance of the water-absorbent resin as long as it fulfills a minimum performance
requirement (see for example Patent Document 16), and differences in the
absorption properties of water-absorbent resin have in fact been hard to distinguish
when the resin is made into an absorbent body, making it hard to differentiate
absorbent bodies.
[0008] In some cases, an adhesive has been used to bond an absorbent gel to a
chemically strengthened cellulose fiber (see for example Patent Document 17). In
this method the chemically strengthened cellulose fiber ensures a space for swelling
of the absorbent gel, effectively separating the water-absorbent resin particles and
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allowing the resin to function more easily. However, the fibers are not fixed to each
other, and the fiber inevitably moves inside the absorbent body, resulting in a
corresponding movement of the absorbent gel. Also, large quantities of cellulose
need to be used because the absorbent gel must be enveloped in cellulose fiber to
ensure space for swelling, and the swelling space itself is not adequate. A large
quantity of adhesive must also be used, which inevitably restricts swelling. Adhesion
has also been accomplished using a base material and a crosslinking agent (see for
example Patent Document 18). In this method, it appears that an absorbent
composite with good liquid permeability has been obtained by using a crosslinking
agent which does not restrict swelling of the gel, along with a low weight of particles
to prevent gel blocking. However, a crosslinking agent is required for adhesion, and
the absorption capacity of the particles could be reduced when some of them are
crosslinked. Moreover, it is also said that performance under load is improved when
the degree of surface crosslinking is increased, but in this case the blocking
prevention effect would not be adequate. In addition, the absorption capacity of the
composite is low because a low weight of particles is used.
[0009] In some cases, a water-absorbent resin has also been fixed to a base material
without using a binder. In one method, absorbent polymer particles are bonded to a
fibrous base material during polymerization, and polymerization is performed on the
fibrous base material (see for example Patent Document 19). In this method, the
fibrous base material penetrates between the polymer particles and the particles are
strongly fixed, but it is difficult to complete the reaction in the base material, and there
is likely to be considerable residual monomer and residual crosslinking agent. In
another example, a certain amount or more of an aqueous monomer solution is
carried as fine particles on a raised nonwoven fabric, and then polymerized and
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thermally compressed (see for example Patent Document 20). The absorption
performance of the composite is high in this case because of the large quantity of
water-absorbent resin, and because a nonwoven fabric is used there is less
movement than with pulp. However, because polymerization is performed in a
nonwoven fabric there is still the problem of residual monomers. Another method is
to re-impregnate a water-absorbent resin with an aqueous solution of unpolymerized
monomer, apply it to a base material and polymerize the impregnated monomer to
thereby bond the water-absorbent resin to the base material (see for example Patent
Document 31), but it is difficult to completely polymerize the residual monomer after it
adheres to the base material, and large quantities of residual monomers occur.
[0010] In a similar example, the water-absorbent resin is made into a slurry
and applied to a base material (see for example Patent Document 21). Productivity
is certainly improved by applying a slurry, but expensive microfibril fiber must be used
as the dispersion medium, and the adhesive force may not be adequate. In thin
sanitary materials and other absorbent materials with a higher proportion of water-
absorbent resin, because more water-absorbent resin is used the resin can swell and
become rather bulky after absorbing water depending on how it is positioned. The
more strongly the water-absorbent resin is fixed, the more it presses on the body
when it becomes bulky.
[0011] A method has also been proposed of printing drops of low-viscosity aqueous
monomer solution on fabric, and then performing a polymerization reaction with the
fabric to thereby provide gaps between polymerized particles and prevent gel
blocking (see for example Patent Document 30). In this case, large amounts of
residual monomers and low-molecular-weight components remain because of the
difficulty of achieving complete polymerization on a base material. This not only
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makes the product undesirable for use as a sanitary material, but also reduces the
absorption speed. When arranging resin on both sides of one sheet of fabric in an
effort to achieve the desired level of absorption relative to area, moreover, the resin
must have a large particle size of 550 urn or more, and the extremely small surface
area/volume of the spherical, semi-spherical and deformed spherical particles
obtained by this method does not provide sufficient absorption speed for actual use.
[0012] From the standpoint of comfort, it is important to prevent not only leakage but
also dampness in a hygiene product. Absorbent products have been proposed in
which dampness is reduced by controlling the rise in humidity that occurs during use
(see for example Patent Document 22 and 23). In the techniques described in these
publications, the absorbent bodies contain absolute dry pulp, a large quantity of
highly-absorbent polymer and a hygroscopic material such as silica gel or lithium
chloride, in combination with a moisture permeable back sheet. Some absorbent
products also use a moisture permeable back sheet (see for example Patent
Document 24). Another technique combines two moisture permeable sheets in order
to prevent liquid from seeping through the moisture permeable back sheet even
under pressure. However, because in these methods the secreted bodily fluid
remains unfixed between the fibers of the paper or pulp, when a large amount of
bodily fluid is excreted the unfixed liquid may produce steam, resulting in dampness.
[0013] There have also been proposed a sanitary napkin wherein rewetting from the
absorbent body is prevented through the use of an absorbent body in which the
centrifugal holding capacity after equilibrium absorption swelling of false blood and
the false blood permeating speed are at or above a fixed value (see for example
Patent Document 25), a multilayer absorbing paper having a surface layer to be first
contacted with a liquid and made of mixed bulky cellulose fiber and one or more base
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material layers laminated to the surface layer (see for example Patent Document 26),
and an absorbent sheet comprising hydrophilic fine fibers or a hydrophilic fine
powder contained in an absorbent sheet comprising a highly-absorbent polymer and
bulky cellulose fiber (see for example Patent Document 27). However, these
publications do not describe the configuration of an absorbent article that allows
steam to be dramatically controlled and humidity to be dramatically suppressed even
when the amount of excretion (amount of liquid to be absorbed) is large.
[0014] Another method for controlling dampness uses fiber with a low water-holding
capacity for the absorbent layer (see for example Patent Document 28). There is
certainly less dampness with this method, but because the fiber functions hardly at all
as an absorbent body, absorption is dependent entirely on an absorbent resin with a
slow absorption speed, resulting in slower absorption. Because the fiber expands
very little as it swells, moreover, gel blocking is likely and it is difficult for the water-
absorbent resin to perform properly.
[0015] It has been reported that the absorbent capability of a water-absorbent resin is
affected by the shape of the particles (see for example Patent Document 29).
Commonly used water-absorbent resin particles are not especially long and thin and
have a particle diameter of about 45 to 850 urn with a mass median particle diameter
of about 200 to 370 urn, but the absorbent capability of a structure and the effective
capability of the water-absorbent resin in it were improved by means of a relatively
large particle size distribution, with a median particle diameter of 400 to 700 urn.
Conventionally, however, when the absorbent capability is improved the effect of
blocking cannot be avoided because there is more contact between particles.
Because of the low proportion of water-absorbent resin, moreover, the absorbent
capability of the absorbent body is low.
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[0016] Thus, most absorbent bodies in which a water-absorbent resin is bonded to a
base material use adhesion by monomer polymerization (raising the issue of residual
monomers) or adhesion using an adhesive (which restricts swelling), and no
satisfactory adhesion method currently exists. Moreover, only absorbent bodies with
poor performance have been produced because the resin is not in a state that allows
high absorption performance after adhesion. That is, no thin, lightweight absorbent
body has been obtained having high liquid holding capability and absorption speed,
high liquid dispersibility and high stability of the absorbent body.
[0017]
[Patent Document 1] Japanese Patent Application Laid-open No.2001 -252307
[Patent Document 2] WO98/037149
[Patent Document 3] Japanese Patent Application Laid-open No.06-057010
[Patent Document 4] WO01/64153
[Patent Document 5] Japanese Patent Application Laid-open No.5-230747
[Patent Document 6] Japanese Patent Application Laid-open No. 10-118114
[Patent Document 7] Japanese Patent Application Laid-open No.10-118115
[Patent Document 8]. Japanese Patent Application Laid-open No.5-31362
[Patent Document 9] Japanese Patent Application Laid-open No.6-370
[Patent Document 10] Japanese Patent Application Laid-open No.2000-238161
[Patent Document 11] Japanese Translation of PCT International Publication No. 10-
510447
[Patent Document 12] Japanese Patent Application Laid-open No.2001-96654
[Patent Document 13] Japanese Patent Application Laid-open No.2001-171027
[Patent Document 14] Japanese Patent Application No.2002-72476
[Patent Document 15] Japanese Patent Application No.2001-375375
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[Patent Document 16] Japanese Patent Application Laid-open No.2001-96654
[Patent Document 17] Japanese Patent Application Laid-open No. 10-512183
[Patent Document 18] Japanese Translation of PCT International Publication No. 10-
508528
[Patent Document 19] Japanese Patent Application Laid-open No.2003-11118
[Patent Document 20] Japanese Patent Application Laid-open No.2004-124303
[Patent Document 21] Japanese Patent Application Laid-open No. 11-137600
[Patent Document 22] Japanese Patent Application Laid-open No.6-218007
[Patent Document 23] Japanese Patent Application Laid-open No.7-132126
[Patent Document 24] Japanese Translation of PCT International Publication No. 10-
508521
[Patent Document 25] Japanese Patent Application Laid-open No.7-184956
[Patent Document 26] Japanese Patent Application Laid-open No.6-287886
[Patent Document 27] Japanese Patent Application Laid-open No.9-156013
[Patent Document 28] Japanese Patent Application Laid-open No.2002-165837
[Patent Document 29] Japanese Patent Application No.2904791
[Patent Document 30] US2003/0205318 A1
[Patent Document 31] Japanese Patent Application Laid-open No.9-239912
[Patent Document 32] Japanese Patent Application Laid-open No.2005-200630
DISCLOSURE OF INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0018] It is an object of the present invention to provide a thin, lightweight absorbent
body and bodily fluid-absorbing article with high absorption capability, absorption
speed and dispersibility. In particular, it is an object of the present invention to
provide an absorber and bodily fluid-absorbing article that can be used favorably in
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disposable diapers, sanitary napkins, incontinence pads and the like. More
particularly, it is an object of the present invention to provide an absorber and bodily
fluid-absorbing article which can absorb stably with almost no movement or uneven
distribution of the absorber in a sanitary product, and that can absorb liquid to be
absorbed with a minimum amount of material used. In addition, it is an object of the
present invention to provide an environmentally-friendly absorber and bodily fluid-
absorbing article whereby the pulp and other resources commonly used in hygiene
products can be conserved.
MEANS FOR SOLVING THE PROBLEMS
[0019] As a result of exhaustive research to address the above-identified problem, we
found that high absorption capability could be achieved with a small amount of water-
absorbent resin while reducing the amount of other materials by using an absorbent
composite wherein a base material and water-absorbent resin particles are made into
a composite as the absorber, and the base material and water-absorbent resin
particles are combined in specific proportions and in a specific arrangement.
[0020] That is, the following absorbent composite, method for manufacturing the
absorbent composite and device for manufacturing the absorbent composite are
provided.
An absorbent composite comprising: a base material and water-absorbent
resin particles: wherein the following conditions (1) to (4) are fulfilled:
(1) the weight ratio of water-absorbent resin relative to the total weight of
the base material and water-absorbent resin is 65 to 99 wt%,
(2) the water-absorbent resin particles adhering directly to the base
material constitute 50 wt% or more of the total water-absorbent resin particles;
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(3) the average absorption capacity of the water-absorbent resin particles
is 50 g/g or more; and
(4) the amount of residual monomers in the water-absorbent resin is 200
ppm or less.
[0021] A method for manufacturing an absorbent composite comprising a base
material and water-absorbent resin particles, comprising making the base material
and/or the water-absorbent resin absorb water, followed by removing water from and
drying the base material and water-absorbent resin while making them be in contact
with each other.
[0022] A device for manufacturing an absorbent composite comprising a base
material and water-absorbent resin particles, comprising: a base material feed part; a
rotating drum for adhering the resin particles to the base material: a part for supplying
the resin particles to the rotating drum: a drying part for removing water from the
base material with the resin particles adhered thereto: and a part for supplying a
specific amount of moisture to the base material and/or resin particles: wherein the
device has the following features (1) and (2):
(1) the rotating drum has multiple dimples on its surface, and
(2) teach of the dimples has a ventilation hole at its bottom, through which
a gas can be blow out from the inside of the rotating drum.
EFFECT OF THE INVENTION
[0023] The present invention is an integrated absorbent composite comprising many
water-absorbent resin particles adhered onto a base material, thereby providing a
thin absorber with high liquid dispersibility and liquid holding capability. By using this
absorber in a sanitary material or other bodily fluid-absorbing article, the process of
manufacturing the sanitary material can be simplified, and the water-absorbent resin
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is utilized efficiently, thus the amount of the water-absorbent resin and paper, fabric
and other materials used in the absorber can be reduced. As a result,
unprecedented thin, lightweight sanitary materials and other bodily fluid-absorbing
articles can be provided.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024] The present invention is explained in more detail below.
1. Overview of the structure and performance of the absorbent composite of the
present invention
In the present invention, an absorbent composite means a combination of a
water-absorbent resin and a base material. In this composite, 50 wt% or more of the
water-absorbent resin particles adhered directly to the base material, thus there is
little change in the positions of the resin particles. Consequently, the base material
maintains its sheet shape. The absorption capability as an absorber of this
absorbent composite is preferably adjusted by mixing pulp or other short fibers or
other sheet-shaped materials into the absorbent composite.
[0025] In the present invention, the water-absorbent resin particles are preferably
relatively large particles (particle diameter 550 urn to 2100 urn) [hereinafter referred
to as "large particles"], as the absorbent composite using these particles has high
absorption capacity per area and the absorption speed that allows the composite to
be used as a sanitary material. Large particles have conventionally been avoided in
absorber for sanitary materials because of their slow absorption speed, but when
they are directly adhere to the fibers of a base material, the liquid can be transported
inside the particles via the adhered fibers, a stress resulting from morphological
change of fibers in contacting with water are loaded on the adhering large particles,
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and the absorption speed of large particles is dramatically improved, thus allowing
them to be used as constituents of an absorbent product for sanitary materials.
[0026] In arranging the resin particles on the base material, it is preferable to
maintain an area occupancy rate of the large particles to be 1 to 30% on at least one
side, as the swollen resin particles will bump against each other and block each other
from swelling and the resin in the composite will not absorbed adequately if sufficient
space is not provided for the particles to swell in a direction parallel to the plane of
the base material. In this case, it is more preferable to arrange the particles so as to
prevent them from contacting each other, and it is more preferable to space out the
water-absorbent resin particles. Preferably, the water-absorbent resin particles are
arranged in a single layer so that they do not overlap each other. Moreover, the
large particles are preferably arranged on both sides, and maintain the area
occupancy rate of the large particles in the range of 1 to 30% on both sides. If the
composite also contains relatively small particles, they will only swell down below the
large particles without greatly blocking the large particles from swelling, so it is
possible and preferable to adjust the absorption speed to the required speed for the
absorber by adding such small particles. When such relatively small water-absorbent
resin particles are added to adjust the absorption speed, the total surface area
coefficient (explained in detail below) is preferably adjusted to the range of 0.3 to 3 in
order to provide a good balance between absorption capacity and absorption speed
in the composite.
[0027] Since a relatively high absorption capacity is required for purposes of a
sanitary material, the weight ratio of the water-absorbent resin relative to the total
weight of the water-absorbent resin and the base material must be between 65 and
99 wt%.
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[0028] The reason why gel blocking does not occur even with such a high weight
ratio is that 50 wt% or more of the resin particles adhere to the base material, thereby
ensuring a certain space between the resin particles. The proportion of the adhering
resin particles is preferably at least 60 wt%, more preferably at least 70 wt% ,or
further more preferably at least 90 wt% or ideally 95 wt% or more. It is preferable
that the water-absorbent resin particles adhere to the base material, because it can
prevent the water-absorbent resin particles from moving during transportation or
absorption of bodily fluid.
[0029] The method for directly adhering the water-absorbent resin particles to the
base material is not particularly limited. It is preferable that some of the fibers of the
base material are incorporated into the water-absorbent resin particles. It is
preferable that at least 50 wt% of the directly adhering water-absorbent resin
particles are adhere with incorporating some of the fibers therein, and preferably at
least 70%, more preferably at least 90 wt% or still more preferably at least 95% of the
water-absorbent resin are adhere in such a manner. When the water-absorbent
resin particles adhere with incorporating some of the fibers therein, the fibers act as a
conduit when the water-absorbent resin absorbs bodily fluid, the absorption capacity
of the resin particles under pressure as well as the absorption speed increase.
[0030] It is impossible to achieve a high absorption capacity of the absorber merely
by using large particles and thus increasing volume of resin relative to area, and the
resin particles must also have a high absorption capacity. That is, the average
absorption capacity of the water-absorbent resin particles used must be at least 50
g/g. Water-absorbent resin particles having such a high absorption capacity are
generally liable to gel blocking, and their swelling may also be greatly blocked when
the resin particles bump against each other, so an absorbent composite meeting with
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various requirements cannot be achieved just by using a composite with a high resin
proportion of more than 50 wt%. Consequently, in the past it has been necessary to
use hard resin particles with a high degree of crosslinking on the surface and inside
which have a high absorbing capability under pressure and a low absorption capacity.
In the present invention, the water-absorbent resin particles are arranged so as to
avoid gel blocking, and due to the presence of conduits in the resin in some cases,
high absorbing capability under pressure can be achieved even using soft resin
particles with a high absorption capacity. As a result, the absorbent composite has
high absorption capability under pressure or under no pressure.
[0031] Moreover, because the absorbent composite of the present invention has high
bodily fluid dispersibility and makes all of the water-absorbent resin maximize its
absorption capability, an excess of water-absorbent resin need not to be used and
the absorbent composite can be made lightweight. To improve the absorption
capacity of the composite it is preferable to increase the proportion of highly
absorbent resin, and it is more preferable to use a highly absorbent resin with a
higher absorption capacity.
[0032] As is regulated by the voluntary standards of the Japan Hygiene Products
Industry Association regarding the water-absorbent resin, reductions of residual
monomers is required. One feature of the absorbent composite of the present
invention is that the residual monomers in the water-absorbent resin have been
reduced to a dramatically low value of 200 ppm or less. Such a value is hard to
achieve by polymerizing resin on a base material that is commonly used method to
adhere resin directly to a base material. This low level of residual monomers can be
achieved by polymerizing the water-absorbent resin in advance followed by using the
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resin with a specific low level of residual monomers as the water-absorbent resin of
the composite.
[0033] 2. Adhesion
In the present invention, it is preferable that at least 60 wt%, preferably at least
70 wt%, more preferably at least 90 wt%, or still more preferably at least 99 wt% of
the total water-absorbent resin particles are adhere to the base material at the time
when the absorbent composite is used.
In the present invention, the status in which the water-absorbent resin
particles adhere to the base material means the status in which the water-absorbent
resin particles are fixed on the base material, and positional relationship between the
base material and the water-absorbent resin particles does not essentially change.
Specifically, adhering particles means that the particle that is not detached after
shaking back and forth the absorbent composite with the surface having the adhering
particles underneath for one minute at a rate of 2 complete (back and forth) shakes
per second with a shake distance of 20 cm (back (20cm) and forth (20cm)), while
holding the edge of the absorbent composite by hand.
[0034] If the positional relationship between the base material and water-absorbent
particles does not change, the absorption capability of the absorbent composite will
not change due to transportation before use, and this is also preferable from the
standpoint of repeated absorption.
The percentage of adhering particles can be determined by detaching the
adhering particles by force with tweezers or the like and measuring the weight of
them.
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In the present invention, at least 50 wt% of the total water-absorbent particles
adhere directly to the base material at the time when the absorbent composite is
used. Preferably, at least 60 wt%, more preferably at least 70 wt%, still more
preferably at least 90 wt% or ideally at least 99 wt% adhere directly to the base
material.
[0035] Adhere directly, as used herein, means that they adhere without using any
components such as adhesive other than the components including the base
material, the water-absorbent resin particles and derivatives thereof. However, they
are still considered to adhere directly if an adhesive is used to such an extent as not
to inhibit swelling.
The percentage of directly adhering particles can be determined by measuring
the amount of water-absorbent resin particles still adhering after 1 hour of immersion
of the absorbent composite in a solvent that dissolves the adhesive.
[0036] The method for adhering directly is not particularly limited, and includes
adhesion by chemical bonding between the base material and the water-absorbent
resin particles, adhesion by physical interaction and adhesion by incorporating the
fiber into the water-absorbent resin.
Of these, adhesion by incorporating the fiber into the water-absorbent resin is
preferred. Specifically, it is preferable that at least 50 wt% of the total water-
absorbent resin particles adhere with fibers incorporated into the water-absorbent
resin. Preferably at least 60 wt%, more preferably at least 70 wt% or still more
preferably at least 90 wt% of the particles adhere in this manner.
[0037] Fibers incorporated into the water-absorbent resin means that fibers of the
base material are present in the water-absorbent resin matrix. There are no
particular limitations on the shape and length of the incorporated fibers. Because
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water can be taken up into the water-absorbent resin via the fibers, adhesion of this
type provides superior absorption capability from the standpoint of absorbed volume
and absorption speed. An electron microscope can be used to determine whether
the particles adhere with fibers incorporated into the water-absorbent resin. The
proportion can be determined by selecting 30 adhering particles at random,
detaching them by force from the base material, and observing them with an electron
microscope.
[0038] In the present invention, the method of adhesion of the remaining water-
absorbent resin particles does not matter as long as at least 50 wt% of the total
water-absorbent resin particles adhere directly to the base material.
However, it is preferable not to use adhesive from the standpoint of preventing
the blocking of swelling when liquid is absorbed. It is not preferable to use adhesive
because it may block the water-absorbent resin from swelling. Examples of
adhesives include thermoplastic fibers and polymers, emulsion binders, hot melt
adhesives and the like.
[0039] The adhering large particles are preferably arranged with a resin area
occupancy rate (described below) of 1 to 30%. The absorption capability of the large
particles is facilitated if they are arranged in such a way that they do not come in
contact with each other when they absorb the expected amount of liquid. The large
particles may adhere only to one side of the base material or may adhere to both
sides of the base material. It is preferable that they adhere to both sides is desirable
because it increases the absorption amount per unit area.
[0040] 3. Absorbent resin weight ratio
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The weight ratio of the water-absorbent resin in the present invention is given
as the weight percentage of the water-absorbent resin relative to the total weight of
the base material and the water-absorbent resin, and is specifically determined by
the following formula (Formula 1):
(Formula 1)
Weight ratio (wt%) of resin = A/B x 100
(wherein the weight of the water-absorbent resin in the absorbent composite is A (g)
and the total weight of the base material and the water-absorbent resin is B (g)).
[0041] The weight ratio must be at least 65 wt% and not more than 99% at the time
when the absorbent composite is used, and is preferably at least 70 wt% and not
more than 99 wt% or more preferably at least 80 wt% and not more than 99wt%.
The higher the weight ratio, the higher the total amount absorbed by the composite.
The weight of the water-absorbent resin is measured after having detached all of the
particles.
[0042] 3. Resin area occupancy rate
The resin area occupancy rate of the water-absorbent resin particles in the
particle size range from 550 to 2100 urn (that is, large particles) in the present
invention is an indicator of possibility of contact between particles when the
absorbent resin particles have absorbed a liquid. In the present invention, the resin
area occupancy rate of the large particles is measured as follows.
A photograph of the surface of the absorbent composite is taken with an
optical microscope or electron microscope. The measurement conditions and
magnification are set so that the water-absorbent resin can be distinguished from the
base material, and that 10 or more water-absorbent resin particles with a diameter of
21

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550 to 2100 urn (that is, large particles) appear in one photograph. The enlarged
photocopy of the photograph is prepared, the parts corresponding to the water-
absorbent resin particle are cut out from the parts corresponding to the base, and the
large particles are selected from the water-absorbent resin particle parts. The
following method is used for selection.
Square paper corresponding to a 500 µm - square of on the composite is
prepared by calculating based on the magnification of the photograph and the
magnification of the enlarged copy. Square paper corresponding to a 2500 µm -
square is also prepared in the same way. The large particles are selected by laying
each part of the copy of the water absorbent resin particles over these squares and
excluding those particles whose copies are small enough to fit within the 500 µm -
square or large enough to protrude even slightly from the 2500 µm -square.
The weight of selected cutout parts corresponding to large particles and whole
enlarged copy are weighed, and the resin area occupancy rate of large particles is
calculated based on the following formula (Formula 2). Any five or more points on
the absorbent composite or photographed, and the average is determined to be the
area occupancy rate. When water-absorbent resin particles are adhere to both sides
of the base material, the occupancy rate of each side is determined respectively.
(Formula 2)
Resin area occupancy rate (%) = weight of cutout parts corresponding to large
particles/weight of whole enlarged copy x 100
[0043] The resin area occupancy rate is preferably 1 to 30(%), more preferably 2 to
25, or still more preferably 3 to 20 at the time when the absorbent composite is used.
If the area occupancy rate is too high, the water-absorbent resin particles will contact
with each other when they swell, resulting in blocking so that the water-absorbent
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resin cannot maximize its absorption capability. If the resin area occupancy rate is
too low, the amount of absorption per unit area of the absorbent composite will be
undesirably low.
[0044] 4. Total surface area coefficient
In the present invention, the total surface area coefficient is an indicator of the
surface area of water-absorbent resin particles per unit area of the absorbent
composite. A greater total surface area coefficient is preferable, as the greater the
total surface area coefficient, the faster the absorption speed of the absorbent
composite.
[0045] The total surface area coefficient is preferably about 0.1 to 3, and when
especially rapid absorption is required in the early stages (within first 1 minute after
initiation of use), it is preferably 0.3 to 3, more preferably 0.4 to 3 or still more
preferably 0.5 to 3 at the time when the absorbent composite is used.
[0046] The total surface area coefficient in the present invention is determined
according to (Formula 3) by collecting the water-absorbent resin particles used in the
absorbent composite, classifying them by particle size, measuring the weight and
the bulk density of particles in respective particle size range.
(Formula 3)
Total surface area coefficient =
(wherein Wr is the total weight (g) of water-absorbent resin particles of particle size r
(cm), Cr is the bulk density (g/cm2) of water-absorbent particles of particle size r (cm)
and S is the area (cm2) of the absorbent composite).
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The water-absorbent resin particles are taken out (by peeling when they
adhere to the base material) and collected to measure particle size and bulk density
of the water-absorbent resin particles, and where fibers or the like adheres to the
surfaces of the water-absorbent resin particles, they are removed before
measurement. Where fibers are incorporated into the water-absorbent resin particles,
the fibers on the particle surfaces are cut off before measurement. Where adhesive
or the like has been applied to the surfaces of the water-absorbent resin particles, the
adhesive is removed using a solvent that is not absorbed by the water-absorbent
resin.
The particle size of the water-absorbent resin particles is measured by sieving
them with sieves with a sieve opening of mesh of 106 µm, 212 µm, 300 µm, 425 µm,
500 µm, 600 µm, 710 µm, 850 µm, 1000 µm, 1180 µm, 1400 µm, 1700 µm and 2500
µm. In the present invention, the particle size is determined to be an intermediate
value between the value of sieve opening of two sieves through which a particle
passes and through which it does not pass. The particle size of particles that passes
through a sieve with a sieve opening of 106 µm is determined to be 53 urn, and the
particle size of particles that remains on a sieve with a sieve opening of 2500 µm is
determined to be 2700 µm. By this operation, the particles are classified into particle
sizes of 53 µm, 159 µm, 256 µm, 362.5 µm, 462.5 µm, 550 µm, 655 µm, 780 µm, 925
µm, 1090 µm, 1290 µm, 1550 µm, 1850 µm, 2100 µm and 2700 µm.
The bulk density of the water-absorbent resin particles is determined by
measuring out a 2 cm3 of water-absorbent resin using a 2 cm3 measurement flask,
and dividing the weight in two. The bulk density is measured 5 times, and the
average value is taken. Bulk density is measured for particles in each particle size
grade after having been sieve-classified.
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[0047] 5. Water-absorbent resin particles
(Water-absorbent resin)
The water-absorbent resin constituting the water-absorbent resin particles in
the present invention is explained first.
In the present invention, the water-absorbent resin preferably have a residual
monomer concentration of 200 ppm or less, more preferably 100 ppm or less, further
more preferably 50 ppm or less or still more preferably 10 ppm or less relative to the
weight of the water-absorbent resin. It is not preferable that the water-absorbent
resin include residual monomer in high concentration, as they elute during liquid
absorption.
[0048] Residual monomers can be reduced by completing polymerization by heat
treatment either during or after manufacturing the absorbent composite. The residual
monomer concentration of the absorbent resin before contacting with the base
material is preferably 5% or less, more preferably 1 % or less, further more preferably
0.1% or less or still more preferably 0.05% or less. It is not preferable to use the
water-absorbent resin with many residual monomers as a starting material, as it
becomes difficult to complete polymerization during manufacturing the composite,
and a large quantity of residual monomers still remain at the end. The texture of the
base material may also be adversely affected by the polymerization reaction method.
[0049] For such reasons, in the present invention, it is preferable to use amorphous
particles manufactured by a method comprising aqueous solution polymerization
followed by pulverization and/or particles manufactured by reverse-phase suspension
polymerization.
[0050] The amount of residual monomers can be measured by the following method.
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The water-absorbent resin is added to 0.9% saline in the amount of 250 times
the weight of the resin, the residual monomers are extracted for 6 hours by stirring at
room temperature, and filtered. The amount of residual monomers of the filtrate is
determined by liquid chromatography.
[0051] In the present invention, the type of water-absorbent resin is not particularly
limited, and any kind of water-absorbent resin can be used. A water-absorbent resin
having acid groups in the side chains is preferred, and a resin having carboxylic acid
groups in the side chains is especially preferred. It is desirable that 50% or more of
the acid groups are neutralized in the form of salts, and especially desirable that 50%
or more of the acid groups are neutralized in the form of ammonium salts. A water-
absorbent resin having acid groups in the side chain is preferred because the
absorption speed is enhanced due to static repulsion between the acid groups during
liquid absorption. It is desirable for the acid groups to be neutralized because
thereby the liquid is absorbed into the inside of the water-absorbent resin by osmotic
pressure. It is preferable that the acid groups are neutralized in the form ammonium
of salts, because ammonium salts have a high affinity for water and are therefore
more absorbent.
[0052] Many types of water-absorbent resin are known, including crosslinked
partially-neutralized polyacrylic acid (see for example Japanese Patent Application
Laid-open No. S55-84304), hydrolyzed starch-acrylonitrile graft polymer (see for
example Japanese Patent Publication No. S49-43395), neutralized starch-acrylic
acid graft polymer (see for example Japanese Patent Application Laid-open No. S51-
125468), saponified vinyl acetate-acrylic acid ester copolymer (see for example
Japanese Patent Application Laid-open No. S52-14689), hydrolyzed acrylonitrile
copolymer or acrylamide copolymer (see for example Japanese Patent Publication
26

A0501 VP32W/YA
No. S53-15959), polyglutamic acid salts (see for example Japanese Patent
Application Laid-open No. 2003-192794) and the like.
Polyacrylic acid salt copolymers and crosslinked partially-neutralized
polyacrylic acid, which are commonly used for sanitary materials, are preferred from
the standpoint of absorption performance and cost.
[0053] Crosslinked polyacrylic acid is explained below as a desirable example of a
water-absorbent resin, along with a manufacturing method the same.
In crosslinked polyacrylic acid, preferably at least 50 mol%, more preferably at
least 80 mol% or still more preferably at least 90 mol% of the repeating units in the
polymer molecule chains are carboxyl group-containing units. It is not preferable that
the proportion of the carboxyl group-containing unit in the repeating units is 50 mol%
or less because absorption capability is adversely affected.
It is preferable that the carboxyl groups in the polymer molecule chains are
partially neutralized, and alkali metal salt including sodium, potassium and lithium;
and nitrogen-containing basic substance including ammonia may be used as a salt.
Preferably at least 50% and more preferably at least 70% of the carboxyl groups are
neutralized. In terms of the kind of salt, it is preferable that the carboxyl groups are
partially neutralized with at least one salt including ammonia, and it is most
preferable that the carboxyl groups are partially neutralized with ammonia alone.
From the standpoint of absorption capability, at least 50 mol%, more preferably at
least 70 mol%, still more preferably at least 90 mol% or ideally all of the carboxyl
group neutralized salts in the polymer molecule chains are ammonia salts. It is
preferable that the proportion of ammonia salts is high from the standpoint of
absorption capacity and adhesiveness to the base material. The proportion of
ammonia salts in the water-absorbent resin can be calculated from the total amount
27

A0501 VP32W/YA
of nitrogen atoms in the water-absorbent resin. The total amount of nitrogen atoms
in the water-absorbent resin can be determined by the Kjeldahl method.
[0054] The monomers constituting the water-absorbent resin may be neutralized salts
of unsaturated carboxylic acid monomers such as (meth)acrylic acid, ethacrylic acid,
itaconic acid, maleic acid, crotonic acid, fumaric acid, sorbic acid, cinnamic acid and
anhydrides thereof, and preferably a neutralized salt of (meth)acrylic acid is used.
The neutralized salt is preferably alkali metal salt including lithium, sodium and
potassium or nitrogen-containing basic substance including ammonia. Other
monomers may also be copolymerized, and examples of unsaturated monomers that
may be copolymerized include anionic unsaturated monomers such as (meth)acrylic
acid, ethacrylic acid, itaconic acid, maleic acid, crotonic acid, sorbic acid, cinnamic
acid , anhydrides thereof, vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid,
vinyltoluenesulfonic acid, 2-(meth)acrylicamide-2-methylpropanesulfonic acid, 2-
(meth)acryloyl ethanesulfonic acid, 2-(meth)acryloyl propanesulfonic acid, 2-
hydroxylethylacryloylophosphate, 2-hydroxylethyl methacryloyl phosphate, phenyl-2-
acryloyloxyethyl phosphate and vinyl phosphoric acid and salts thereof, nonionic
hydrophilic group-containing unsaturated monomers such as acrylamide,
methacrylamide, N-ethyl (meth)acrylamide, N-n-propyl (meth)acrylamide, N-isopropyl
(meth)acrylamide, N,N-dimethyl (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, 2-
hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate,
polyethylene glycol mono(meth)acrylate, N-vinylpyrrolidone, N-acryloylpiperidine and
N-acryloylpyrrolidine and, and hydrophilic monomers that yield water-absorbing
property by hydrolysis of the functional groups after polymerization such as methyl
(meth)acrylate, ethyl (meth)acrylate and vinyl acetate that form. Hydrophobic
monomers that may be used in combination include styrene, vinyl chloride, butadiene,
28

A0501 VP32W/YA
isobutene, ethylene, propylene, stearyl (meth)acrylate, lauryl (meth)acrylate and the
like, and these may be used singly, or in combination of two or more thereof.
A crosslinking agent may be used with the monomers, and the resin may be
crosslinked by reacting a condensation crosslinking agent with functional groups in
the resin, by copolymerizing a polymerizable crosslinking agent with unsaturated
monomers or by exposing the resin to electron beams or radiation or the like. A
preferred crosslinking method is using a condensation crosslinking agent and a more
preferred crosslinking method is copolymerizing a polymerizable crosslinking agent
with unsaturated monomers in the presence of a condensation crosslinking agent
that reacts with functional groups in the resin.
Examples of condensation crosslinking agents include glycidyl ether
compounds such as ethylene glycol diglycidyl ether, trimethylol propane triglycidyl
ether, (poly)glycerine polyglycidyl ether, diglycerine polyglycidyl ether and propylene
glycol diglycidyl ether; polyvalent alcohols such as (poly)glycerine, (poly)ethylene
glycol, propylene glycol, 1,3-propanediol, polyoxyethylene glycol, triethylene glycol,
tetraethylene glycol, diethanolamine and triethanolamine; polyvalent amines such as
ethylenediamine, diethylenediamine, polyethylenimine and hexamethylenediamine;
and polyvalent ions such as zinc, calcium, magnesium and aluminum, and these
crosslinking agents may be used in combination of two or more.
[0056] Examples of polymerizable crosslinking agents that copolymerize with
unsaturated monomers include diethylene glycol diacrylate, N,N'-
methylenebisacrylamide, polyethylene glycol diacrylate, polypropylene glycol
diacrylate, trimethylol propane diallyl ether, allylglycidyl ether, pentaerythritol triallyl
ether, pentaerythritol diacrylate monostearate, bisphenol diacrylate, isocyanuric acid
29

A0501 VP32W/YA
diacrylate, tetraallyloxyethane and diallyloxyacetic acid salt, and these crosslinking
agents may be used in combination of two or more.
[0057] The solvent for the monomer solution is not particular limited as long as it has
excellent dissolving properties. Water alone is particularly desirable, but hydrophilic
solvents such as ethanol, methanol and acetone may also be used either singly or in
combination of two or more. A salt such as sodium chloride, a basic compound such
as ammonia for controlling pH, or a suspending agent in the case of reverse-phase
suspension polymerization may also be added as necessary.
[0058] The method of polymerizing the unsaturated monomers is not particularly
limited, and a commonly used method such as aqueous solution polymerization,
reverse-phase suspension polymerization, reverse-phase emulsion polymerization,
spray polymerization, belt polymerization or the like may be used. The
polymerization initiation method is also not particularly limited, and polymerization
may be initiated by using a radical polymerization initiator, by exposure to radiation,
electron beams or the like, or by using a photosensitizer in ultraviolet polymerization.
The initiator used in radical polymerization may be a known initiator such as for
example a persulfate such as potassium persulfate, ammonium persulfate or sodium
persulfate; hydrogen peroxide; or an organic peroxide such as cumene
hydroperoxide, t-butyl hydroperoxide, peracetic acid or the like. When using an
oxidizing radical polymerization initiator, a reducing agent such as L-ascorbic acid or
Rongalite may also be added.
[0059] An oxygen removal operation is preferably carried out in the monomer solution
prior to initiating polymerization. An example is removing dissolved oxygen by
bubbling or the like with an inactive gas for a sufficient period of time. The
atmosphere in the reaction container is preferably substituted by an inactive gas such
30

A0501 VP32W/YA
as nitrogen or helium. The inside of the reaction container may be under reduced
pressure, normal pressure or increased pressure. The polymerization initiation
temperature is generally preferably in the range of 0 to 100°C or more preferably in
the range of 20 to 70°C. If the initiation temperature is too high, polymerization
occurs due to heat before adding the initiator, which is not desirable. A low initiation
temperature is undesirable because reaction initiation takes longer. The temperature
inside the container may be let follow its course during the reaction, or may be
controlled by cooling or heating. The rate of temperature increase and maximum
temperature during polymerization may not be strictly controlled, and the maximum
temperature may exceed 100°C. The maximum temperature during polymerization is
generally in the range of 20 to 140°C or preferably 40 to 120°C. The concentration of
the monomer solution is preferably 10 to 80% or more preferably 30 to 70%. It is not
preferable that the concentration is too high because the reaction tends to get out of
control. It is not preferable that the concentration is too low because the reaction
takes to much time and the subsequent drying step becomes more difficult. It is
preferable to terminate the polymerization when the reaction solution ceases to
generate heat. Since polymerization is followed by heating process, such as drying,
crosslinking and the like, polymerization may also be terminated before the reaction
solution ceases to generate heat. The solution may also be heated or kept warm
after it ceases to generate heat.
[0060] The polymer obtained after above-mentioned polymerization is dried when it is
a wet gel. The drying method is not particularly limited. Azeotropic drying, fluidized
drying, hot air drying, vacuum drying or the like can be preferably used, and hot air
drying or vacuum drying is particularly desirable. The polymer is dried until the water
content become 30 wt% or less or preferably 10 wt% or less. A wet gel may be dried
31

A0501 VP32W/YA
in any form, it is preferable to dry the polymer after having increased the surface area
by grounding them coarsely. The drying temperature is preferably in the range of
70°C to 180°C or more preferably 100 to 140°C.
[0061] The particle size of the dried polymer is adjusted as necessary by operations
such as pulverization or classification. When crosslinked polyacrylic acid is used, the
dried polymer may be pulverized into a specific particle size and then be heated. It is
preferable to add a compound having 2 or more functional groups that are capable of
reacting with the carboxyl groups used during this heat treatment. The compound
having 2 or more functional groups capable of reacting with carboxyl groups may be
added before polymerization, or may be added to the particles before heat treatment.
When the compound is added before heat treatment, it is preferable that the
compound is added by dissolving it in a hydrophilic solvent such as water, alcohol or
ether, and dispersing the solution on the surface. The heat treatment temperature is
not particularly limited, and is preferably in the range of 120 to 250°C, more
preferably 150 to 240°C or still more preferably 170 to 230°C. Heat treatment may
be carried out continuously in the same unit after drying, or may be an independent
step from the drying step.
An ordinary dryer or furnace may be used for this heat treatment, and for
example a channel dryer, rotary drier, disc dryer, fluidized bed dryer, air current dryer,
infrared dryer or the like may be used.
[0062] Deodorants, perfumes, various inorganic powders, foaming agents, pigments,
dyes, antibacterial agents, hydrophilic short fibers, plasticizers, adhesives,
surfactants, fertilizers, oxidizing agents, reducing agents, chelating agents,
antioxidants, thermal stabilizers, ultraviolet absorbers, light stabilizers, water, salts
and the like may be added to the water-absorbent resin as necessary.
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Examples of above-mentioned inorganic powders include fine particles of
various inorganic compounds that are inactive with water and hydrophilic organic
solvents and fine particles of clay minerals. Inorganic powders that have a certain
affinity for water but are insoluble or poorly soluble in water are particularly desirable
as inorganic powders, and examples include metal oxides such as silicon dioxide,
titanium; silicic acids (salts) such as natural zeolite, synthetic zeolite; kaolin; talc;
clay; bentonite and the like.
The amount of inorganic powder that is used is normally 0.001 to 10 weight
parts or preferably 0.01 to 5 weight parts per 100 weight parts of water-absorbent
resin. The method of mixing the water-absorbent resin and inorganic powder is not
particularly limited and may be dry blending, wet mixing or the like.
[0063] (Particle shape)
The water-absorbent resin particles may be of any shape, and may be in the
form of spherical particles widely used in absorbent compositions, amorphous
particles, aggregated particles, short fibers, long fibers or particle with sheet shape.
Amorphous particle obtained by pulverization, particle aggregates (such as grape
clusters), particle with scale shape, granules and the like may also used. Preferred
particles include aggregated particles, spherical particles or amorphous particles.
However, a water-absorbent resin that is used as large particles is preferably
in the form of amorphous particles manufactured by polymerization by aqueous
solution polymerization followed by pulverization, and/or particle aggregates
manufactured by reverse-phase suspension polymerization. This is because that it is
hard to achieve a satisfactory absorption speed for sanitary materials with spherical
particles due to their extremely low specific surface area even if the absorption speed
is increased due to the composite effect with the base material,
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A0501 VP32W/YA
[0064] (Salt concentration near the surface)
The salt concentration of the water-absorbent resin particles near the surface
before adhering to the base material (hereinafter referred as "surface salt
concentration") is preferably at least 50 mol%, more preferably at least 60 mol%,
further more preferably 70 mol% or still more preferably at least 80 mol%. The
adhesiveness of the particles is low if the surface salt concentration before adhering
to the base material is too low.
[0065] The ultimate surface salt concentration of the water-absorbent resin particles
in the absorbent composite after adhering to the base material is not particularly
limited , but it is preferably 90 mol% or less, more preferably 80 mol% or less or still
more preferably 60 mol% or less. It is advantageous that the surface salt
concentration of the water-absorbent resin particles in the final composite is low
because it reduces stickiness of the product that is exposed to humid air. This is also
extremely desirable because the dispersibility of aqueous solution in the absorbent
composite can thus remain high even if the particles contact each other during
swelling after the composite absorbs an aqueous solution. To maintain a high
absorption capacity, it is necessary to increase the salt concentration of the
absorbent resin particles as a whole, but to maintain high liquid dispersibility in the
composite, it is better to have a lower salt concentration near the surface. That is, it
is desirable that the surface salt concentration is reduced while the internal salt
concentration is increased. Specifically, the surface salt concentration is preferably
at least 10 mol% lower, more preferably at least 20 mol% lower or further more
preferably at least 30 mol% lower than the salt concentration at the center of the
resin. "Near the surface" means the outer layer of a thickness of about 1 um from the
surface of the resin. It is desirable to adjust the salt concentration near the surface at
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A0501 VP32W/YA
the same time as the resin is adhered to the base material because a high level of
balance between adhesiveness and absorbability can thus be obtained.
[0066] The water-absorbent resin normally consists of acid groups such as carboxyl
groups, sulfonic acid groups and neutralized salts thereof, and basic groups such as
amino groups and neutralized salts thereof and the like. The surface salt
concentration of the water-absorbent resin particles means the proportion of
neutralized groups of the surface part of the water-absorbent resin particles. In the
present invention, the salt concentration near the surface of the resin particles can be
determined by microscopic ATR, a method of infrared absorption analysis. Since
ATR generally provides structural information about the surface layer to a depth of 1
urn, the degree of neutralization of the resin particle surfaces can be measured
directly by microscopic ATR. The degree of neutralization of the inner part is
measured by microscopic ATR after cutting open the resin and exposing the center
by using an ultramicrotome (Reichert, Ultracut N). A Bio-Rad FTS-575 is used for
measurement.
[0067] A polyacrylic acid water-absorbent resin is used as an example below. In
order to determine the ratio of carboxylic acid and carboxylate, the peak area ratio
(1695/1558 cm-1) of peak area at 1695 cm-1 (carboxylic acid v C=O base materialise
1774-1616 cm-1) and peak area at 1558 cm-1 (carboxylate v COO- base materialise
1616-1500 cm-1) was calculated. The ratio is determined based on calibration curve
that was prepared by measuring standard samples of partially crosslinked polyacrylic
acid neutralized by 10 mol%, 30 mol%, 50 mol%, 70 mol%, 90 mol% or 100 mol%
with ammonia.
[0068] (Surface strength)
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The water-absorbent resin particles before being adhered to the base material
preferably have a surface strength of 0.1 to 5.5 N, more preferably 0.1 to 5 N, further
more preferably 0.2 to 4 N or still more preferably 0.2 to 3 N. A surface strength is a
parameter indicating the tendency to be deformed of the particle surfaces. When
water-absorbent resin particles that have absorbed to certain times and have swollen
are placed in a container and subjected to load, the gel moves and deforms so as to
fill in the gaps between the water-absorbent resin particles, which are packed in the
container with gaps between them. Since surface strength is the elastic module of
the water-absorbent particles when they have absorbed liquid and become to their
actual volume, it signifies the degree of interaction between gel particles and the
tendency to be deformed on their surface. If the surface strength of the water-
absorbent resin particles is high, it means that the water-absorbent resin particles are
not easily deformed. If the particles are not easily deformed, a strong negative force
against swelling is generated when the water-absorbent resin particles absorb liquid,
and thereby decrease the absorption capacity. If the surfaces are not easily
deformed, the area of adhesion between the resin and base material is reduced, and
thereby yield detachment of the particles from the composite. The surface strength
of the water-absorbent resin particles of the present invention is determined as
follows.
Equipment: Shimadzu Autograph AG-1
Sample: 0.10 g of water-absorbent resin particles are weighed precisely
and distributed uniformly on the bottom of a cylindrical container with a height of 50
mm and an inner diameter of 20.5 mm on the bottom of which is pasted a nylon
sheet with a pore size of 75 µm. A Petri dish with a diameter of 50 mm is prepared
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A0501 VP32W/YA
and filled with 0.90 g of saline, and the cylindrical container containing the water-
absorbent resin particles is left in the Petri dish to absorb and swell for 1 hour.
Measurement: 1 kN load cell is prepared, and a cylindrical shaft with a
diameter of 19.7 mm is attached to it. The measurement range is set at 0.2 kN, and
starting from the height at which there is no load on the load cell, it is set to descent
at a fixed rate of 0. 6 mm/minute. The pressure loaded on the load cell is measured
over time. Surface strength is indicated by the load (N) at the point when the
particles become actual volume. The actual volume of the water-absorbent resin
particles was calculated based on the relative density of saline of 1.010 g/cm3 and
the relative density of the water-absorbent resin particles.
[0069] (Absorption capacity)
In the present invention, the average absorption capacity of the water-
absorbent particles in the composite must be at least 50 g/g, and is preferably at
least 60 g/g or more preferably at least 70 g/g.
In the water-absorbent resin particles of the present invention, moreover, the
absorption capacity of the water-absorbent resin under load or pressure of 0.8 psi is
preferably at least 20 g/g, more preferably at least 25 g/g or still more preferably at
least 30 g/g. It is desirable for the water-absorbent resin particles to have a high
absorption capacity because the quantity of water-absorbent resin particles used can
then be reduced.
[0070] In the present invention, the absorption capacity of the water-absorbent resin
particles means the amount of 0.9% saline that the water-absorbent resin particles
can absorb by freely swelling under the condition that no loads is loaded on the
water-absorbent particles. The absorption capacity of the water-absorbent resin
particles is measured by the following method.
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0.05 g of water-absorbent resin particles are placed uniformly in a nonwoven
pouch similar to a tea bag (60 x 40 mm), and immersed in 0.9% saline at 23°C. 180
minutes later, the tea bag is taken out, and obliquely-suspended with its corners fixed
for 10 minutes to drip, and the weight is measured. A same measurement is carried
out for the sample without water-absorbent resin particles, and the measured weight
is given as the blank. The absorption capacity is calculated using (Formula 4). The
value is measured 3 times, and the average of them is given as the absorption
capacity.
(Formula 4)
Absorption capacity of water-absorbent resin particles (g/g) = {(weight of tea
bag after absorption) - (weight of blank tea bag after absorption) - (weight of water-
absorbent resin particles)}/(weight of water-absorbent resin particles).
[0071] The absorption capacity under pressure of the water-absorbent resin particles
of the present invention is measured as follows. 0.02 g of water-absorbent resin
particles are placed in an acrylic resin tube with a inner diameter of 25 mm and a
height of 30 mm having a 250-mesh nylon nonwoven fabric on the bottom, a
smoothly moving cylinder is placed in the tube to make it the measurement device,
and the weight is measured. Load is applied by placing a 278.33 g load
(corresponding to 0.8 psi) on top of the cylinder of the measurement device, and the
device is placed in a 120 mm Petri dish containing 60 g of 0.9% saline. After 60
minutes the measurement device is taken out and left for 3 seconds on a Kimtowel to
drain off water, the device is weighed after unloading the load, and the absorption
capacity under pressure is calculated according to (Formula 5).
(Formula 5)
38

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Absorption capacity (g/g) of water-absorbent resin particles under load =
(weight (g) of the device after absorption - weight (g) of the device before
absorption)/(weight of water-absorbent resin particles)
An absorbent composite with a tensile breaking strength of 0.6 (N/20 mm) or
more comprising water-absorbent resin particles with an absorbent capacity of 70 g/g
or more and an absorbent capacity under load of 0.8 psi of 20 g/g or more is
desirable for sanitary material applications such as disposable diapers because it
exhibits excellent absorption properties both under no pressure and under pressure.
Preferably the water-absorbent composite consists of water-absorbent resin particles
and paper and/or fabric, and more preferably each water-absorbent resin particle is
arranged with a space between each other so that blocking of the particles does not
occur, and still more preferably 90 wt% or more of the water-absorbent resin particles
adhere to paper and/or fabric. Water-absorbent resin particles having an absorption
capacity under no pressure of 70 g/g or more and an absorption capacity under load
of 0.8 psi of 20 g/g or more can be obtained by the following methods. They can be
obtained by polymerizing unsaturated carboxylic acid monomers 70% or more of
which are acrylic acid, wherein 50% or more of the carboxyl groups are neutralized
as ammonium salts and 70% or more of the total monomers are neutralized. In this
case, monomers include a compound having 2 or more unsaturated groups in one
molecule that acts as a crosslinking agent in the amount of 0.0005 to 0.1 mol% of the
total monomer components. 0.1 to 3 weight parts of a compound having two or more
functional groups that can react with carboxyl groups may be used during any step
either before or after polymerization. Radical polymerization is carried out by using a
redox-type initiator, and the radical polymerization initiator is used in the amount of
0.005 to 0.5 mol% of the amount of unsaturated monomers. Reducing agent is used
39

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in the amount of 0.0001 to 1 g per 1 mole of monomer. Heating is also carried out as
necessary under the conditions that fulfill (Formula 6) below. This heating is
preferably carried out on the absorbent composite during the manufacturing process
of it rather than on the water-absorbent resin particles alone.
(Formula 6)
Y = -1.6X + 345
(wherein Y is the heating time (minutes) and X is the heating temperature (°C)).
As the water-absorbent resin particles obtained in this way have a tendency to
cause blocking, they show inferior results especially in the absorption speed and
absorption capacity under pressure if they are measured by a conventional method in
which the water-absorbent resin particles are in close contact with each other.
However, the water-absorbent resin particles show excellent results in any of
absorption speed, absorption capacity under no pressure and absorption capacity
under pressure if they are measured by the above-mentioned method of the present
invention in which they can maximize their absorption capability.
[0072] (Particle size)
The weight-average particle size of the water-absorbent resin particles used in
the present invention is preferably 100 to 2700 µm, more preferably 100 to 2100 µm
or still more preferably 200 to 2100 µm or ideally 200 to 1400 µm. It is not preferable
that the average particle size is too small from the standpoint of absorption capability.
On the other hand, it is not preferable that the average particle size is too large, as it
is difficult to adjust the total surface area coefficient within the desired range.
[0073] In the present invention, the particle size of the water-absorbent resin particles
is determined by sieve classifying with sieves with a sieve-opening of 106 µm, 212
µm, 300 µm, 425 µm, 500 µm, 600 µm, 710 µm, 850 µm, 1000 µm, 1180 µm, 1400
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µm, 1700 µm and 2500 µm. In the present invention, the particle size is determined
to be the intermediate value between the values for sieve-openings in the sieves
through which the particles pass and through which they cannot pass. The particle
size of particles that pass through a sieve with a sieve-opening of 06 µm is
determined to be 53 µm, and the particle size of particles that remains on a sieve
with a sieve-opening of 2500 µm is determined to be 2700 µm. By this operation,
the particles are classified into 53 µm, 159 µm, 256 µm, 362.5 µm, 462.5 µm, 550 µm,
655 µm, 780 µm, 925 µm, 1090 µm, 1290 µm, 1550 µm, 1850 µm, 2100 µm or 2700
µm.
[0074] The proportion of the water-absorbent resin particles in the composite of the
present invention that pass through a sieve with a sieve-opening of 300µm is
preferably 50% or less, more preferably 40% or less. The proportion of particles that
cannot pass through a sieve with a sieve-opening of 3000 µm is preferably 10% or
less, more preferably 5% or less.
[0075] The particle size distribution of the water-absorbent resin particles in the
absorbent composite of the present invention is closely related to the absorption
capability of the absorbent composite. For example, the absorption speed tends to
increase as the average particle size decrease, and the degree of swelling in the
direction perpendicular to the base material and the absorption amount per unit area
tend to increase as the average particle size increase. Comparing resin particles of
the same weight, the area occupancy rate of the resin tends to decrease as the
average particle size increases, and thus blocking of swelling is less likely to occur.
The absorption speed of particles alone is too slow if the particle size is too large, but
the absorption speed of large particles in the composite of the present invention is
enhanced by the combination effect with fibers, thus it is preferable to use relatively
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large particles. From the standpoint of both absorption capacity and absorption
speed, it is desirable to use both relatively large particles with a particle size of 550
urn or more and relatively small particles with a particle size of 300 µm or less, and
preferably there are two or more peaks in the particle size distribution of the particles
in the composite. The particle sizes of the two peaks preferably differ by a factor of 2
or more, more preferably 3 or more or still more preferably 4 or more. If there is a
difference in the particle size, the particles are packed as close as closest packing,
and the large particles and the small particles do not contact with each other when
they swell, and each particle will be able to maximize its absorption capability.
[0076] (Large particles)
Large particles are preferably used in the absorbent composite of the present
invention. Large particles are particles with a particle size of 550 to 2100 µ. Larger
particles are more desirable for purposes of increasing the absorption capacity of the
absorbent composite per unit area, but the absorption speed become very slow if the
particles are too large, and they may cause a problem of pain or the like by sticking
out when they are used in the absorber of a hygiene product. Consequently, the size
of the large particles is preferably 655 to 1850 µm, more preferably 780 to 1550 µm
or still more preferably 925 to 1290 µm.
[0077] Since the absorption speed of these large particles is greatly affected by their
shape, they are preferably pulverized amorphous particles produced by a method
comprising pulverization, and/or aggregated particles produced by reverse-phase
suspension polymerization. Particles other than pulverized amorphous particles or
aggregated particles whose specific surface area (surface area/volume) is smaller
than these may cause a reduction in the absorption speed.
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[0078] Aggregated particles used herein means aggregate formed by aggregation of
two or more particles with an average particle size in the range of 10 to 550 µm
(hereinafter refers as primary particles). The particle size distribution of the primary
particles does not need to be uniform, and the primary particles may include partiµcles
with a particle size of exceeding 550 µm or below 10 µm. That is, it is sufficient that
the average particle size of the primary particles before aggregation be in the range
of 10 to 550 µm. It is desirable that the average particle size of the primary particle is
small because it increases the absorption speed of the large particles. On the other
hand, it is desirable that the average particle size of the large particle is large
because it reduces the particle surface area after swelling, thereby reducing the
contact area of the water-absorbent resin with the external and preventing the users
from feeling coldness of the water-absorbent resin. This is also desirable because it
prevents swollen resin from penetrating through the sheet between the absorbent
composite and the body to the skin even when the swollen primary particles become
detached. Consequently, the most desirable average particle size of the primary
particles is 200 to 500 µm.
[0079] The salt concentration near the surface of the large particles is preferably 10
mol% or more, more preferably 20 mol% or more, or still more preferably 30 mol% or
more lower than the salt concentration at the center of the resin. Where pulverized
amorphous particles are used, it is particularly preferable to increase the absorption
speed by transporting water into the inside of the particles using ion osmotic effect
caused by a salt concentration difference between the surface and the center,
because the specific surface area of large particles is smaller than that of aggregated
particles. It is also preferable to crosslink the surface of the particles in order to
reduce the blocking effect that blocks liquid from dispersing into the inside of the
43

A0501 VP32W/YA
particles caused by swelling of the particle near its surface during absorption. When
aggregated particles are used as the large particles, the absorption speed may be
reduced by gel blocking effect of the constituent primary particles that prevent water
from penetrating into inside of the large particles. Consequently, it is desirable to
reduce the gel blocking effect by making the surface of the swollen particle dry by
reducing the salt concentration near the surface of the primary particles, or by
crosslinking near the surface of the primary particles.
[0080] In the absorbent composite of the present invention, the absorption capacity
and absorption speed of the absorbent composite are preferably adjusted by using
both large particles and other water-absorbent resin particles, and in this case the
average particle size of the mixed resin particles is preferably in the range of 10 to
2700 µm, more preferably 100 to 1000 µm or still more preferably 200 to 550 µm.
When resin particles other than large particles are included in the composite of the
present invention for the purpose of improving absorption speed, it is desirable to
include many water-absorbent resin particles with relatively small particle size. In this
case, the content of particles that pass through a sieve with a sieve opening size of
300 µm is preferably 10 to 50 wt% based on the total water-absorbent resin particles
in the absorbent composite. If the water-absorbent resin particles are too small the
absorbent capability will be lower, therefore the content of water-absorbent resin
particles with a particle size of less than 100 µm is preferably 10 wt% or less. More
preferably, the content of water-absorbent resin particles with a particle size of less
than 212 µm is preferably 10 wt% or less.
[0081] 6. Base material
A base material in the present invention means a material that can maintain a
sheet form.
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(Material)
In the present invention, the base material may be of any material that is in
sheet form, but preferably it is of paper and/or fabric. Paper used herein means
paper broadly defined by JISP0001, and fabric is a general term for sheet-shaped
fiber products as defined by JISL0206. Fabric is classified into woven fabric, knitted
fabric, lace, mesh and nonwoven fabric depending on the means of forming the sheet.
Woven, knitted or nonwoven fabric is preferably used in the present invention and
nonwoven fabric is particularly preferable. Paper and/or fabric are desirable because
they have morphologic stability, unlike pulp and other short fibers. Nonwoven fabric
is defined by JIS L 0222.
[0082] The material of the base material is not particularly limited, and more than one
material may be combined. The base material fibers may be natural fibers or
synthetic fibers, and multiple types of fibers may also be combined. The fibers may
be either long or short. They may also be treated to increase strength or
hydrophilicity. Hydrophilic fibers are more desirable than hydrophobic fibers from the
standpoint of liquid absorption and water permeability. Continuous long fibers are
also desirable than short fibers because they are excellent in liquid permeability.
Of the hydrophilic base materials, a cellulose base material is particularly
desirable. In the present invention, a cellulose base material means a fabric and/or
paper that are made mainly from cellulose, and a fabric and/or paper made of
cellulose fiber, especially a nonwoven cellulose fabric, is desirable. A cellulose
derivative obtained by esterification or etherification can be used as the cellulose. It
may also be mixed with other fibers. Kinds of cellulose include natural fibers such as
cotton and hemp, and reclaimed fibers such as rayon, polynosic, Lyocell and cupra
45

A0501 VP32W/YA
and the like. A reclaimed fiber, especially reclaimed fiber made from the annual
cottonseed, is preferred.
[0083] (Shape)
The shape of the base material is not particularly limited, and the thickness is
preferably 0.001 mm to 1 cm, more preferably 0.01 mm to 5 mm, still more preferably
0.05 mm to 3 mm or ideally 0.1 mm to 1 mm. The weight is preferably 0.1 g/m2 to 1
kg/m2, more preferably 0.5 g/m2 to 500 g/m2 or still more preferably 1 g/m2 to 100
g/m2. From the standpoint of strength, the material that is too thin or too light is not
preferable.
[0084] (Tensile breaking strength)
In the present invention, the tensile breaking strength after absorption of saline
is preferably at least 0.6 N/20 mm, more preferably 0.6 to 5000 N/20 mm, still more
preferably 0.7 to 500 N/20 mm or yet more preferably 0.85 to 100 N/20 mm or ideally
1 to 100 N/20 mm.
[0085] In the present invention, the direction in which the strength of the material is
maximum is defined as lengthwise direction and the direction perpendicular to this
direction is defined as crosswise direction, and the strength is preferably within the
aforementioned range in the crosswise direction (that is, both in the lengthwise
direction and in the crosswise direction).
[0086] In the present invention, the tensile breaking strength of the base material
after absorption of saline means the tensile breaking strength that is measured after
having made the base material absorb saline. A sanitary material sometimes
continues to be used after having absorbed liquid without being changed. It may
also be required to absorb liquid multiple times after having once absorbed liquid. If
the absorber continues to be used after having absorbed liquid, it becomes to be in
46

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the same situation where it is under load with keeping water in it. If the base material
breaks due to the load, the liquid permeability and liquid dispersion properties are
adversely affected, and the absorption capability is adversely affected. It is
preferable that the base material maintains its strength even after having absorbed
saline from the standpoint of durability of the absorber. It is preferable that the base
material has high strength, because it is disadvantageous to have low strength when
the manufacturing process of the composite includes a process in which the base
material absorbs water. However, the absorption capability does not further
improved by using an excessively strong base material.
[0087] The tensile breaking strength after absorption of saline is determined as
follows.
Sample: 15 cm x 2 cm rectangular base material (various kinds with
different directions are prepared)
Equipment: Tensile Tester (Shimadzu Autograph)
Methods: 700 g of 0.9% saline is taken in a 1 L beaker, and the base
material is immersed therein for 10 minutes. The base material is pulled out and left
on a Kim towel for 1 minute, then is fixed on the equipment at the points 2.5 cm
inside from each edge so that the space between the points to be pulled is 10 cm,
and the base material is pulled at a speed of 10 mm/minute until it breaks. The force
at the time of break is recorded, and the maximum value is determined to be strength
N/20 mm. If the base material has different strength depend on measurement
direction, measurements are carried out for some different measurement directions.
[0088] (Absorption capacity, absorption speed)
Absorption capacity and absorption speed are indicators of the hydrophilicity
and liquid permeability of the base material. These are explained below.
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In the present invention, the absorption capacity of the base material means
the factor by which the base material increases in weight after having absorbed 0.9%
saline over 60 minutes, and is specifically measured as follows.
A circular piece with a diameter of 59.5 mm is cut out from the base material
and weighed, and a wire is passed through it 1 cm inside from the edge. 500 g or
more of saline is provided at 23°C in a 1 L beaker, and the base material is immersed
in the saline together with the wire. After 60 minutes, the base material is taken out
from the saline together with the wire, and suspended for 10 minutes without
contacting with anything else. After 10 minutes, the wire is removed and the total
weight of the wet base material and water adhering thereto is measured.
[0089] The absorption capacity of the base material is shown by (Formula 7).
(Formula 7)
Absorption capacity of base material (g/g) = weight after absorption (g)/weight
before absorption (g)
In the present invention, the absorption capacity of the base material is
preferably at least 6 g/g and not more than 200 g/g, more preferably at least 8 g/g
and not more than 100 g/g, still more preferably at least 10 g/g and not more than 50
g/g or ideally at least 12 g/g and not more than 30 g/g.
Because in the absorbent composite the fiber has a faster absorption speed
than the water-absorbent resin particles, the base material absorbs in the early stage
of absorption and the water-absorbent resin particles absorbs in the late stage of
absorption. It is desirable for the base material to have a higher absorption capacity
because this means a faster liquid absorption speed in the early stage. Because the
base materials generally absorb by capillary action, the liquid may be released under
load, causing humidity during use. However, if the resin particles adhered with the
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fibers of the base incorporated therein, the water-absorbent resin absorbs liquid by
capturing liquid from the base. As a result, there is little rewetting under load or
steaminess during use.
[0090] In the present invention, the absorption speed of the base material means the
speed at which the base with a width of 2cm absorbs 0.9% saline in perpendicular
direction.
The absorption speed of the base material is preferably at least 0.35 mg/sec
and not more than 100 mg/sec, more preferably at least 0.45 mg/sec and not more
than 50 mg/sec, further more preferably at least 0.55 mg/sec and not more than 30
mg/sec or still more preferably at least 0.65 mg/sec and not more than 10 mg/sec.
[0091] Specifically, the absorption speed of the base material is measured as follows.
Sample: 10 cm x 2 cm rectangular base
2 or more samples are prepared with different directions if it has a lengthwise
direction and a crosswise direction.
Equipment: Electronic scale, 90 mm dia. Petri dish
Methods: The Petri dish is placed on the electronic scale, and the base
material is suspended vertically 10 cm above the Petri dish. The Petri dish is taken
out from the scale, and filled with 60 g of 0.9% saline which was measured out with
another scale. The Petri dish is replaced on the scale with the bottom of the base
material being held by hand not to be in contact with the saline, and the scale is set
to 0. The base material is carefully immersed in the saline, and the value of the scale
is measured over time. The time (seconds) and the absolute value (mg) of the scale
are plotted on a graph, and the gradient (mg/sec) between 120 and 240 seconds is
determined to be the absorption speed. If the base material has directions, several
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measurements are carried out for different directions, and the fastest value is
determined to be the absorption speed.
[0092] It is preferable that the absorption speed of the base material is different
depend on directions. This is because in this case, liquid permeability is excellent in
a particular direction and liquid disperses easily in the particular direction, thus the
balance of absorption can be controlled in the absorber.
[0093] (Ratio of tensile breaking elongation and strength in the lengthwise direction
and in the crosswise direction)
When the base material has directions, the strength and elongation are
different depend on direction. As mentioned above, in the present invention, the
direction in which the strength is maximum refers to as the lengthwise direction and
the direction perpendicular to the lengthwise direction refers to as the crosswise
direction.
The ratio of tensile breaking strength in the length direction and the crosswise
direction is preferably at least 1.2:1, more preferably at least 1.5:1 and still more
preferably at least 2:1, but not more than 10:1.
The ratio of tensile breaking elongation in the lengthwise direction and
crosswise direction is preferably at least 1:1.2, more preferably at least 1:1.5 and still
more preferably at least 1:2, but not more than 1:10. The elongation and strength of
the base material can be determined in the same way as the strength of the base
material after having absorbed saline by tensile testing with the base material in a dry
state, not immersed in saline. The tensile test is continued until the base material
breaks, and the force at which it exhibits maximum strength is determined to be the
strength of the base material and the elongated distance at that time is determined to
be the elongation.
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[0094] (Contact angle)
The base used in the present invention is preferable a nonwoven fabric with a
contact angle of 130° or less.
In the present invention, the contact angle is defined as the angle formed after
a 44% aqueous ammonium polyacrylate solution with a viscosity of 74 cps is made
be in contact with the base material at room temperature for 10 minutes. The angle
is measured using a contact angle meter (CA-X150) made by FACE (Kyowa
Interface Science). The solution is prepared by adjusting the viscosity of a 44%
aqueous ammonium polyacrylate solution (70 to 110 cp) from Wako Pure Chemical
with water. Viscosity is measured with a rotating disc viscometer.
The contact angle is preferably 130° or less , more preferably 120° or less, still
more preferably 110° or less or ideally 100° or less. The affinity between the base
material and water and the affinity between the base material and water-absorbent
resin increase as the contact angle decreases, and thereby increase the absorption
capability and adhesiveness.
[0095] 7. Method for manufacturing absorbent composite
The absorbent composite of the present invention is made from water-
absorbent resin particles and a base material, and is preferably manufactured by a
method including a step of adhering the water-absorbent resin particles to the base
material.
The adhering method is not particularly limited, and may be one that fulfills the
conditions mentioned above.
Examples of adhering methods including methods in which the water-
absorbent resin is entangled with the base material and methods using adhesives,
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A0501 VP32W/YA
and a preferred method is one in which the water-absorbent resin and/or the base
material is made to absorb 10 to 3000 weight parts of water per 100 weight parts of
water-absorbent resin, and the water is then removed while the water-absorbent
resin is in contact with the base material. The amount of water is preferably 20 to
2000 weight parts or more preferably 50 to 1000 weight parts per 100 weight parts of
water-absorbent resin particles. This method of adhering is preferred because it
does not require an adhesive, which becomes an impurity. In this method some of
the fibers are also incorporated into the water-absorbent resin, which is desirable
from the standpoint of absorption speed and absorption capacity. It is preferable to
use more water, as it increases adhesiveness, but using too much water is inefficient
because it takes longer to dry.
[0096] The water to be absorbed may contain impurities. Examples of impurities
include cations such as sodium ions, ammonium ions and water-soluble organic
compounds such as iron ions, and chlorine ions and other anions, and acetone,
alcohols, ethers and amines. An acidic or basic substance may be used to adjust the
pH of the water-absorbent resin and/or absorbent composite. From the standpoint of
contact between the water-absorbent resin and base material and absorption
capability, it is desirable to use ion-exchange water or distilled water without
impurities alone.
[0097] It is preferable to dissolve and/or disperse a substance having a deodorant or
other function in the water to thereby functionalize the resulting absorbent composite.
Examples of deodorants that can be used in this case include organic and inorganic
deodorants. When using a deodorant that is insoluble in water, it is desirable to use
a dispersant or surfactant as necessary. An inorganic deodorant can also be
dispersed in water without using a dispersant by reducing the particle size to the
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A0501 VP32W/YA
nanometer level, therefore it is preferable to use a fine-particle inorganic deodorant
without a dispersant.
[0098] The wetting method is not particularly limited, and examples include
immersing in a water bath, spraying with water, making be in contact with a wet body,
exposing to humidification and the like. Of these, the water spraying method is most
preferred because it is industrially simple and easy to adjust the water content. It is
preferable to use a water spraying system which provides a uniform water content in
the fabric or other base material. If the water content varies widely with location of
the base material, the particle size of the resin in the dried water absorbent
composite become nonuniform, as the amount of water the water-absorbent resin
particles absorb after they come in contact with the base material and before the
drying step starts differ by location, and the foaming behaviors caused by removal of
water in the drying step will differ by location The texture of the absorbent
composite with nonuniformly-sized resin particles may not good.
[0099] In wetting the base material and adhering to the water-absorbent resin
particles, the water content of the base material is preferably in the range of 50 to
500 wt%. It is preferable to increase a water content to increase the adhesiveness
between the water-absorbent resin particles and the base material, but if the water
content is too large, the drum used in manufacturing method mentioned below will
be covered with large amount of water and it will cause the problem that the water-
absorbent resin particles adhere to other parts of the drum than the dimples. Of
course, if the water content is too low, adhesiveness between the base material and
the resin will be adversely affected. Therefore, the water content is preferably in the
range of 50 to 200 wt% or more preferably 80 to 150 wt%.
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[0100] In order to wet the base material, the water-absorbent resin particles may
contain water for adhering, but since this makes the water-absorbent resin more
likely to adhere to other objects than the base, the water-absorbent resin particles
before adhering are preferably dried to the extent that they do not adhere to other
objects or to other resin particles. The water content of the water-absorbent resin
particles in this case is preferably 1 to 50 wt% or more preferably 5 to 30 wt%.
[0101] Examples of contacting methods include scattering the water-absorbent resin
particles on the base material from above, holding the water-absorbent resin particles
in the dimples on the surface of a drum followed by transferring the water-absorbent
particles in the dimples to the surface of the base material, and filling the inside of a
drum roll having surface dimples with water-absorbent resin particles followed by
expelling the particles from the drum and putting them onto the base material with
pressure. A Preferred method is the one that allows the water-absorbent resin
particles to be arranged so that they do not contact with each other after swelling,
because it maximize the absorption capability of the water-absorbent resin particles.
[0102] Any method can be used for removal of water. Examples include drying by
heating, blowing dry air or nitrogen, vacuum drying, freeze drying, azeotropic drying,
fluid drying, microweb drying and the like, and drying by heating is preferred. The
heating conditions are preferably 1 to 1000 seconds at 70 to 350°C, more preferably
1 to 1000 seconds at 100 to 340°C, still more preferably 1 to 1000 seconds at 120 to
330°C or ideally 1 to 1000 seconds at 150 to 300°C. The higher the temperature the
shorter the drying time, but the absorption capability of some types of resin may be
adversely affected by long-term heating at high temperatures. Surface treatment
such as crosslinking may be applied at the same time as drying. Removal of water
may be carried out at any stage before completion of the final product, and is
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preferably carried out shortly after wetting in order to avoid deterioration of the water-
absorbent resin.
[0103] (Preferred method for manufacturing the absorbent composite)
One desirable example of a method for manufacturing the absorbent
composite of the present invention is explained below.
Figure 1 is an explanatory diagram of a desirable manufacturing device for
manufacturing the absorbent composite of the present invention. The base material
supplied from the original fabric roll (a) is made into wet base material (c) using a
device such as a water sprayer (b). Then resin particles are blown onto one surface
of the wet base material from a rotating drum for adhering resin particles (e1) in the
dimples on which resin particles (f) supplied from resin particle feed part (d1) are
placed. Then resin particles are blown onto another surface of the wet base material
from a rotating drum for adhering resin particles (e2) in the dimples on which resin
particles (f) supplied from resin particle feed part (d2) are placed. Then small-sized
resin particles are dispersed uniformly from small resin particle feed part (i) to adjust
the absorption capabilities of the absorbent composite, and the base material with
resin particles adhere to both surfaces is dried by passing through drying part (g) to
give a composite with resin particles strongly adhere thereto.
In the method described above, the structure of the rotating drum for adhering
resin particles which arranges the water-absorbent resin particles on the base
material is important. The drum surfaces have, at pre-determined positions, multiple
dimples into which the water-absorbent resin particles can be inserted. These
dimples are preferably arranged so as to reduce the probability that the water-
absorbent resin particles come in contact with each other. There is an optimal
arrangement of dimples that maximizes the absorption capability of the absorbent
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composite. This is an arrangement whereby spaces are provided between adjacent
resin particles to allow them to swell by absorption, and whereby more water-
absorbent resin particles can be arranged on the base material.
[0104] In this manufacturing method, the outer diameter of the opening of the dimples
on the surface of the drum is preferably 1 to 3 times, more preferably 1.2 to 2 times
the maximum diameter of the supplied water-absorbent resin particles. The outer
diameter of the opening of the dimple on the drum as used in this explanation means
the largest value of the distances between any two points on the peripheral border of
the opening on the surface of the drum.
[0105] If the outer diameter of an opening is too large, it is difficult to operate stably,
as multiple water-absorbent resin particles may be inserted into a single dimple or
the water-absorbent resin particles once inserted in the dimple will be more likely to
fall out of the dimples . On the other hand, if the outer diameter of the opening is too
small, water-absorbent resin particles in the dimples may be removed in removing
water-absorbent resin particles that adhere to other parts than the dimples due to
static electricity or the like even when the particles are held into the dimples with
sucking force.
[0106] Regarding the structure of the dimple, the peripheral border on the surface of
the drum surface may take any form including non-angular shape such as circular
and oval, angular shape such as triangular, rectangular and pentagonaland infinite
shape. A definite non-angular or angular shape is preferable from the standpoint of
manufacturing the drum, and a non-angular shape is desirable from the standpoint of
manufacturing the drum and inserting and removing the particles from the dimples.
[0107] Regarding the structure of the dimple from the peripheral border on the
surface of the drum towards the inside of the drum, the dimples may have the same
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space from the surface to the inside, or may be wider on the inside than on the
surface, or may be narrower on the inside than on the surface. From the standpoint
of ease of insertion and removal of the water-absorbent resin particles, it is desirable
that the space of the dimples be narrower on the inside than on the surface.
[0108] The depth of each dimple on the drum is preferably 0.3 to 2 times, more
preferably 0.5 to 1.5 times or still more preferably 0.7 to 1.2 times the average
particle size of the water-absorbent resin particles supplied to the drum. If the
dimples are too shallow, water-absorbent resin particles in the dimples may be
removed in removing water-absorbent resin particles that adhere to other parts than
the dimples due to static electricity or the like even when the particles are held into
the dimples with sucking force. If the dimples are too deep, multiple water-absorbent
resin particles may be inserted into one dimple, making it difficult to adjust the
amount of resin adhere to the resulting absorbent composite, and it may also be
more difficult to remove the water-absorbent resin particles after insertion, interfering
with stable operation.
[0109] The drum used in this manufacturing method preferably has a hole at the
bottom of each dimple on the surface of the drum through which the gas which is
used to blow out the water-absorbent resin particles can pass. The inner diameter of
the hole is preferably smaller than the size of the small-sized particles of water-
absorbent resin supplied to the drum. If the holes are larger than the small-sized
particles, particles smaller than the holes may pass through the holes into the inside
of the drum instead of being blown onto the base material, and may be accumulated
in the drum and cause problems for operation. The holes may be of any structure as
long as they can let the gas through effectively from the inside of the drum to the
outside of the drum. In order to avoid clogging of holes with the water-absorbent
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resin particles, it is preferable that the holes have the structure wider towards the
inside of the drum.
[0110] In inserting the water-absorbent resin particles into the drum, it is preferable
that the particles are inserted under suction condition by depressurizing the inside of
the drum. The pressure difference between the outside and inside of the drum in this
case is preferably in the range of 0.01 to 500 Torr. If this pressure difference is too
small, the particles inserted into the dimples fall out easily. On the other hand, if it is
too large, too many particles enter the dimples and they are hard to expel. Therefore,
this pressure difference is preferably in the range of 0.05 to 100 Torr, more preferably
0.1 to 50 Torr or still more preferably 0.5 to 5 Torr. This method with suction is
extremely desirable because it not only increase the probability of the water-
absorbent resin particles being inserted into the dimples, but also can prevent water-
absorbent resin particles in the dimples from falling out in removing particles
adhering to other parts than the dimples on the drum after inserting the particles into
the dimples until blowing out them onto a hydrophilic fabric support.
[0111] For this manufacturing method, it is preferable to provide a system for
removing the water-absorbent resin particles that adhere to other parts of the drum
than the dimples after inserting the water-absorbent resin particles into dimples on
the drum until blowing out them onto the base material. The removal method is not
particularly limited, and examples include sweeping with a brush, blowing a gas and
using vibration. Of these methods, blowing a gas is most desirable.
[0112] It is preferable to provide a device for removing static electricity from the drum,
because the drum generates static electricity which destabilize the movement of the
water-absorbent resin particles during operation.
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It is preferable to apply the water-absorbent resin of various particle sizes to
adjust the total surface area coefficient and the like after having arranged the large
particles with large particle size using the drum. These particles may be applied to
only one surface, or may be applied to the both surfaces of the fabric by reversing
the fabric followed by applying the particles to another surface as well. To avoid
detachment of the particles, it is desirable to once again apply water to the base
material before said application of the particles. The method for applying particles
is not particularly limited and is preferably one that can apply them uniformly.
[0113] It is preferable to convey the base material in this manufacturing method. The
method of conveying the base material in this case is not particularly limited.
Examples of the method of conveying the base material include those in which the
base material is conveyed without any support from above or below and those in
which the base material is conveyed along with a conveyor belt or other support that
supports it from below. When the water-absorbent resin particles adhere to both
surfaces of the base material, it is preferable to introduce a conveyor belt system for
the step to convey the surface of the base material to which the particles adhere later
under the surface of the drum for adhering. This is because it can prevent resin
already adhering to the reverse surface of the base material from falling off when the
water-absorbent resin particles are being blown out from the drum. It is also
desirable to use a conveyor belt system during the final step of removing water and
drying. This is because it can minimize the shrinkage of the base material that may
occur during removing water from and drying the base material.
[0114] It is preferable that the water-absorbent resin particles used in this
manufacturing method have a high salt concentration on the particle surfaces
because this results in stronger adhesion when they are blowing out onto the base
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material. However, it is not preferable that the salt concentration of the surface is too
high in the final product. That is, it is desirable to adjust the salt concentration of the
particle surface of the water-absorbent resin particles after having adhered the water-
absorbent resin to the base material. From the standpoint of productivity, it is better
to adjust the salt concentration simultaneously with the drying step rather than
separately after the drying step. The salt concentration of the particle surfaces is
preferably at least 10% less, more preferably at least 20% less or more preferably at
least 30% less compared to the concentration before the treatment.
[0115] 8. Performance of absorbent composite
(Absorption capacity)
In the present invention, the absorption capacity of the absorbent composite
means the amount of 0.9% saline absorbed during 3 hours of free absorption.
Specifically, a circular absorbent composite with a diameter of 59.5 mm is prepared,
and the absorption capacity is measured by the same methods used to measure the
absorption capacity of the base material. When there are water-absorbent resin
particles that do not adhere or when detachment of the particles has occurred, the
water-absorbent resin particles are collected by filtration and left for 10 seconds on a
Kimwipe to remove excess water, and count their weight into the measurement. In
measuring the capacity of the absorbent composite in which almost 50 wt% of the
water-absorbent resin particles do not adhered, the absorbent composite is placed in
a T-Bag and measured according to the method for measuring the absorption
capacity of the water-absorbent resin particles.
The absorption capacity of the absorbent composite is preferably at least 40
g/g, more preferably at least 45 g/g or still more preferably at least 50 g/g.
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[0116] (Absorption amount per unit area)
Absorption amount per unit area is important as an indicator of the absorption
capability of the absorbent composite. Absorption amount per unit area is calculated
according to (Formula 8) based on the measurement results above.
(Formula 8)
Absorption amount per unit area (g/cm2) = (total weight after absorption (g) -
weight of the absorbent composite (g))/area of the absorbent composite (cm2)
It is preferable that the absorption amount per unit area is high, and it is
preferable to be not less than 0.4 g/cm2, more preferably not less than 0.7 g/cm2, or
further more preferably not less than 1 g/cm2.
[0117] (Absorption capacity under pressure)
The absorption capacity of the absorbent composite of the present invention
under pressure is represented as the amount of 0.9% saline absorbed during 3 hours
of absorption under load. Specifically, it is measured as follows using a circular
absorbent composite with a diameter of 59.5 mm.
The measurement device is explained roughly with reference to Figure 2. As
shown in Figure 2, the measurement unit comprises scale 1, container 2 placed on
the scale 1, outer air suction pipe 3, conduit 4, glass filter 6 and measurement part 5,
which is placed on glass filter 6. Container 2 has opening 2a at the top and opening
2b on the side. Outer air suction pipe 3 is inserted into opening 2a, while conduit 4 is
attached to opening 2b. Container 2 also contains a predetermined amount of saline
12. The lower end of outer air suction pipe 3 is immersed in saline 12. Glass filter 6
is formed with a diameter of 70 mm. Container 2 and glass filter 6 are connected to
each other via conduit 4. The position of glass filter 6 is adjusted so that its height to
be the same as the lower end of outer air suction pipe 3. As shown in Figure 3,
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measurement part 5 has filter paper 7, support cylinder 9 and weight 11. Advantec
No. 2 with a diameter of 60 mm is used for filter paper 7. In measurement part 5,
filter paper 7 and support cylinder 9 are placed on glass filter 6 in this order, with
weight 11 placed inside of support cylinder 9. Support cylinder 9 has an inner
diameter of 60 mm. The weight of weight 11 is adjusted so that it can apply a
uniform load of 0.8 psi on absorbent composite 13. The absorbent capacity under
pressure of an absorbent composite was measured using a measurement unit of this
configuration. The measurement method is explained below. First, the necessary
preparations were made including filling container 2 with a predetermined amount of
saline 12, and inserting outer air suction pipe 3 into container 2. Filter paper 7 was
then placed on glass filter 6. Concurrently, absorbent composite 13 was placed
inside of support cylinder 9, and weight 11 was placed on this absorbent composite
13. Next, support cylinder 9 was placed so that its center was aligned with the center
of glass filter 6. After placing support cylinder 9, the weight W (g) of the saline 12
absorbed by absorbent composite 13 was measured every 10 seconds using scale 1.
The absorption capacity under pressure of the absorbent composite was determined
according to (Formula 9).
(Formula 9)
Absorption capacity under pressure of absorbent composite (g/g) = weight W
(g)/weight of absorbent composite (g)
[0118] The absorption capacity under pressure of the absorbent composite under
load of 0.8 psi is preferably at least 15 g/g, more preferably at least 16 g/g or still
more preferably at least 18 g/g. The absorption amount per unit area can also be
determined in the same way of the absorption amount per unit area under no
pressure. The absorption amount per unit area under pressure of 0.8 psi is
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preferably 0.1 g/cm2, more preferably at least 0.15 g/cm2 or still more preferably at
least 0.2 g/cm2.
[0119] An absorbent composite with an absorption capacity of 40 g/g or more, an
absorption capacity under pressure of 15 g/g or more under load of 0.8 psi and a
tensile breaking strength of 0.6 (N/20 mm) or more is highly absorbent and strong
and can be used favorably in disposable diapers and other sanitary materials. The
absorption capacity is preferably at least 45 g/g, more preferably at least 50 g/g or
still more preferably at least 55 g/g. The absorption capacity under pressure of 0.8
psi is preferably at least 16.5 g/g, more preferably at least 18 g/g or still more
preferably at least 20 g/g.
[0120] (Absorption capacity after 1 minute)
The absorption capacity after 1 minute is an indicator of the initial liquid
absorption speed. Because in sanitary material applications such as disposable
diapers, bodily fluid needs to be absorbed instantly, it is preferable to have higher
absorption capacity after 1 minute. The absorption capacity after 1 minute is
determined according to (Formula 10). Specifically, it is measured by the following
method.
A piece with a length of 2 cm and a width of 7 cm is cut out from the
absorbent composite, and weighed. A 1000 cc glass beaker is filled with 700 cc of
saline. A T-Bag with a length of 80 cm and width of 70 cm is weighed, and the T-Bag
alone is made to absorb water for 1 minute, centrifuged, and then weighed. This
weight is divided by the weight of the T-Bag before absorption to give the absorption
capacity after 1 minute of the T-Bag. A T-Bag of the same size is weighed and the
absorbent composite is placed therein. In order that the T-Bag can be quickly pulled
out from the liquid, a clip with a string attached is prepared and attached to the T-Bag,
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which is then carefully and quickly immersed in the liquid so that the fabric does not
bend or twist. After 1 minute of immersion, it is quickly pulled out by pulling the string.
The clip is removed, and the bag is centrifuged at 150 G for 3 minutes and then
weighed. The absorption capacity after 1 minute is determined by subtracting the
amount absorbed by the T-Bag from the total weight, and dividing the result by the
weight of the absorbent composite before absorption. Centrifugation is initiated
within 15 seconds after the absorbent composite is pulled out from the liquid.
(Formula 10)
Absorption capacity after 1 minute (g saline/g) = (weight after centrifugation
(g) - weight of T-bag (g) * absorption capacity after 1 minute of T-Bag)/weight of
absorbent composite (g)
[0121] (Bending resistance)
The bending resistance of the absorbent composite is determined by the
bending resistance D method (heart loop method) described in JIS L1096. The
values of front surface and back surface are different when the particle sizes and
distribution are different on the front and back, and in the present invention the value
of softer one, or in other words the higher value, is determined to be the bending
resistance. The bending resistance is preferably 90 mm or less or more preferably
85 mm or less.
[0122] 9. Method for using absorbent composite
A preferred method for using the absorbent composite of the present invention
is using as a constituent element of a bodily fluid-absorbing article. The use of the
composite as a constituent element of a bodily fluid-absorbing article is explained
below.
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[0123] (Bodily fluid-absorbing article)
In the present invention, the bodily fluid-absorbing article means a bodily fluid-
absorbing article comprising a liquid-permeable sheet, a liquid impermeable sheet,
and the absorbent composite sandwiched between them, and it includes all articles
with the ability to absorb bodily fluids. There are no particular limitations on the
bodily fluids absorbed in the present invention, and examples include urine,
menstrual blood, mother's milk, soft stool and the like. There are also no particular
limitations on the shape of the article, and desirable examples include pads, tapes,
pants and the like. Examples include diapers, sanitary napkins, incontinence pads,
lactation pads and the like.
[0124]When combined with a liquid-permeable sheet and a liquid-impermeable sheet,
the absorbent composite of the present invention can form part of a bodily fluid-
absorbing article that has a high bodily fluid-absorbing capability while being thin and
lightweight. Because there is little risk of the absorber moving or slipping in the
bodily fluid-absorbing article during use, moreover, it can stably absorb bodily fluid.
In addition, because the proportion of water-absorbent resin is higher than that in
conventional bodily fluid-absorbing articles, the amount of absorbed liquid that is
released under load (rewetting) is small, and the worn part remains comfortable.
[0125] In the present invention, the liquid-permeable sheet may be anything as long
as it is in sheet shape and water poured on the sheet permeates through it, and
preferably it is a fabric such as that defined by JIS L0206. Fabric is classified as
woven fabric, knit fabric, lace, mesh and nonwoven fabric according to the means of
forming the sheet, and preferred fabric used in the liquid-permeable sheet of the
present invention includes woven, knitted or nonwoven fabric and more preferred
fabric is nonwoven. It is preferable to use a sheet with a low water-absorbing ability
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made of polyethylene, polypropylene or other polyolefin in order to reduce feel of the
moisture and improve feel of the sheet against user's skin, and it is preferable to use
a sheet made of polyolefin that has been given a water-permeability or hydrophilicity
by treatment in order to rapidly transport bodily fluid.
[0126] A liquid-impermeable sheet in the present invention can be anything that is in
sheet form and is impermeable to water. A material with good gas permeability is
preferred for preventing dampness.
[0127] It is sufficient for the bodily fluid-absorbing article of the present invention to
have at least a liquid-permeable sheet, a liquid-impermeable sheet and an absorbent
composite sandwiched between them, but other materials may also be present
between the liquid-permeable sheet and the absorbent composite and/or between
the liquid-impermeable sheet and the absorbent composite. Another material may
also be present outside the liquid-impermeable sheet or liquid-impermeable sheet.
Materials that can be used in this case include fibrous materials such as pulp,
particulate materials such as water-absorbent resins, sheet-shaped materials such
as tissue, fabric, paper, and the like. These materials may also adhere to the water-
absorbent composite of the present invention. These materials may adhere with
adhesive, or they may adhere directly to the water-absorbent resin particles of the
absorbent composite of the present invention. A bodily fluid-absorbing article
preferably includes tape or elastic for fixing the article to the user's body, gathers for
preventing leakage from the side and the like.
[0128] The shape of the bodily fluid-absorbing article of the present invention may be
a square or circle, a rectangle or oval or a combination of trapezoids, or may have an
irregular shape. A rectangle or oval or a similar shape having a longer direction and
a shorter direction (direction perpendicular to the longer direction) is desirable when it
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is used for a diaper, sanitary napkin, incontinence pad or the like, as they fit to the
crotch of user. Figure 4 shows an illustrative example of the shape of an absorbent
composite having a longer direction. There may also be a part that serves as an
overlap width for jointing the composite to another part.
[0129] Where the absorbent composite include an overlap width that does not contain
water-absorbent resin thereon, it is preferable that the proportion of the water-
absorbent resin and the area occupancy rate of the absorbent composite are
adjusted to the desired range not counting the overlap width.
[0130] The absorbent composites may be used singly or in the combination of two or
more in the articles more than one. It is preferable to use only one composite in
order to make a thin product. In order to make a product with greater absorbing
ability, it is preferable to use more than one. When more than one composite are
used, they can be used in piles or in lines. They may also be of exactly the same
shape or different shapes. To improve the absorbing capability efficiently, they are
preferably overlapped only in the areas where bodily fluids are excreted to, and in
order to prevent leakage, they are overlapped in the areas where leakage is likely to
occur.
[0131] There are no particular limitations on the posture of the absorbent composite
in the bodily fluid-absorbing article, and the absorbent composite sheet may be
completely spread out, or may be wrinkled or folded.
[0132] (Folding of absorbent composite in bodily fluid-absorbing article)
When the absorbent composite of the present invention is used as a
constituent element of a bodily fluid-absorbing article, the edge of the absorbent
composite is preferably folded over to prevent leakage of bodily fluid from the edge.
The edge used herein means the area within 15 cm from the periphery of the
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absorbent composite sheet. The folded part is not particularly limited as long as it is
within 15 cm from the periphery and it is preferably within 12 cm, more preferably 8
cm or still more preferably 5 cm or ideally 3 cm. In the present invention, the posture
that the absorbent composite is folded over means that a part of the absorbent
composite is not on the same plane of the absorbent composite, when the absorbent
composite is stretched without using excess force and attached to a board with
thumb tacks.
[0133] The fold may be towards the liquid-permeable sheet as shown in Figure 5 or
towards the liquid-impermeable sheet as shown in Figure 6. When another part is on
a still different plane from the first fold as shown in Figure 7, that part is called the
second fold.
[0134] The composite may be folded once, twice, or many times. Multiple folds are
more effective for preventing leakage, but result in extra thickness, so the number of
folds should be set so as not to detract from the shape of the composite. When
multiple folds are used, their directions and angles can be determined at will. They
may be alternating concertina folds as in Figure 8, or continuous folds in the same
direction as in Figure 9. A part that has been folded once can be folded over again to
form a double fold as in Figure 10. A triple or greater fold is also possible. As shown
in Figure 11, the fold does not have to be a flat fold.
[0135] A fold along the edge of the absorbent composite prevents leakage because it
has thickness and acts as a physical barrier for the dispersing liquid. Moreover, the
folded part can also prevent leakage of liquid after the liquid has reached it, because
the folded part has a higher absorption capability than the unfolded part.
[0136] The absorbent composite may be folded around the full circumference, or only
part Where the shape of the absorbent composite has a long direction and a short
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direction, such as a rectangle, oval or similar shape, leakage is more likely to occur in
the shorter direction, and leakage can therefore be prevented with the minimum
amount of folding by folding only the long sides of the absorbent composite. In this
case the absorbent composite is preferably either formed with a part for folding as in
Figure 12 A, or with slits to allow folding as in Figure 12 B. When it is known where
bodily fluid needs to be absorbed, it is effective to locate the fold on the edge near
that area. In Figure 12, the dotted area is the folded area.
[0137] The length of the folded part is not particularly limited but is preferably at least
2 cm, more preferably at least 5 cm, still more preferably at least 7 cm or ideally at
least 10 cm. The longer the fold, the greater the leakage-prevention effect.
Folding may be at one location or at more than one location. The folds may
be continuous, or there may be multiple folded areas with gaps between.
The folds may be of any width, but the overlapping part formed by the fold is
preferably 0.1 to 100 mm, more preferably 1 to 70 mm, still more preferably 5 to 40
mm or ideally 5 to 20 mm in width. If the fold is too narrow it will have little leakage
control effect, on the other hand and little advantage is gained by making it too wide.
In the present invention, when the bodily fluid-absorbing article is spread out
on a flat board without excess force and the four corners are fixed with thumb tacks,
the angle of folding is the angle between the plane of the bodily fluid-absorbing
particle and a straight line between the point immediately before the folds leaves the
plane of the bodily fluid-absorbing article and the furthest point from that plane.
When there are multiple folds, only the first fold is considered. Angles of folding are
shown in Figures 5, 6 and 11. The angle of folding is preferably greater than 0°C and
is more preferably at least 30° or still more preferably at least 60° or ideally at least
90°.
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[0138] The folded part may be fixed with an adhesive. Fixing the folded part with an
adhesive is desirable because it prevents slippage of the absorbent composite. The
adhesive may be applied on the inside of the folded part to attach the absorbent
composite to itself, or may be applied on the outside to attach the absorbent
composite to the liquid-permeable sheet, to the liquid-impermeable sheet or to
another member.
[0139] The absorbent composite may be folded alone, or with the other members.
When the absorbent composite is folded with the other members, it is preferable that
the other material is in sheet form.
[0140] (Adhesive used in bodily fluid-absorbing article)
The adhesive is preferably applied lineally in the effectively lengthwise
direction or in other words in the longer direction between the liquid-permeable sheet
and/or liquid-impermeable sheet and the absorbent composite. Another sheet-
shaped substance may also be present between the absorbent composite and the
liquid permeable sheet and/or liquid-impermeable sheet. In this case, the adhesive
may be applied on the absorbent composite itself, or on another sheet, or on the
liquid-permeable sheet and/or liquid impermeable sheet. In the present invention,
the absorbent composite has a stable shape of a sheet, and is less likely to move or
shift in the bodily fluid-absorbing article during use, thus it allows bodily fluid to be
stably dispersed and absorbed. The applied adhesive serves as a barrier against
the bodily fluid, thereby controls the flow of bodily fluid and allows it to disperse
preferentially in the longer direction of the bodily fluid-absorbing article. Normally the
bodily fluid-absorbing article has a longer direction and a shorter direction, and if the
bodily fluid disperses preferentially in the longer direction, the usage efficiency of the
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absorbent composite is improved and bodily fluid is less likely to leak in the shorter
direction.
[0141] The properties of the adhesive used herein are not particularly limited, and it
may be either liquid or solid. Adhesive may be used singly, or in combination of two
or more. The type of adhesive is also not particularly limited, and examples include
solvent type, water dispersion type, hot melt adhesives, reactant type and the like,
specifically urea resin adhesives, melamine resin adhesives, phenol resin adhesives,
resorcinol adhesives, alpha-olefin adhesiveness, water-soluble polymer-isocyanate
adhesives, vinyl acetate resin emulsion adhesives, acrylic emulsion adhesives, vinyl
acetate resin adhesives, chloroprene rubber adhesives, nitrile rubber adhesives,
SBR adhesives, natural rubber adhesives, epoxy resin adhesives, cyanoacrylate
adhesives, polyurethane adhesives, acrylic resin adhesives, anaerobic adhesives,
denatured silicone adhesives, inorganic adhesives, paste and the like. Because
hydrophilic adhesives disperse easily, and make it difficult to control the surface of
the adhesive, a hydrophobic adhesive is preferably used. A hot melt adhesive is
preferably used to facilitate the manufacturing process. A hot melt adhesive refers to
any adhesive that is solid at room temperature and melts and spreads by heating
and consolidates and adhere by cooling, and specific examples are those containing
ethylene vinyl acetate copolymer resin, polyamide, polyester, atactic polypropylene,
thermoplastic elastomers or the like as principal components, with rosin resin,
petroleum resin or the like as tackifiers, as well as waxes, antioxidants, inorganic
fillers, plasticizers and the like.
[0142] The amount of adhesive may be any amount that provides adhesive effects.
The amount of adhesive per unit length is preferably 0.000001 to 0.1 g/cm, more
preferably 0.00001 to 0.01 g/cm or still more preferably 0.00003 to 0.0045 g/cm. The
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applied amount of adhesive per unit area of the absorbent composite is preferably
0.2 to 1000 g/m2, more preferably 2.0 to 100 g/m2. If too much adhesive is applied
on the absorbent composite, it will impede the water-absorbent resin from swelling
and decrease the absorption capability, and impair the texture. On the other hand, it
is not preferable to apply too little adhesive from the standpoint of adhesive strength.
[0143] In the present invention the adhesive may be applied in a commonly used
pattern such as wavy lines, dots, vertical stripes or the like. When the longer
direction of the bodily-fluid absorbing article or the absorbent composite is defined as
the lengthwise direction, and the shorter direction is defined as the crosswise
direction, it is preferable that the adhesive is applied so as to cause liquid to flow
preferentially in the lengthwise direction rather than the crosswise direction, in which
leakage is most likely to occur, as it reduce leakage. Examples of shape and
directionality in absorbent composites are shown in Figure 4 with the arrows showing
the lengthwise direction, but they are not limited to these examples. It is desirable to
apply the adhesive in a pattern that forms barriers extending in the lengthwise
direction as a method of making liquid flow preferentially in the lengthwise direction.
The flow of liquid is altered by the pattern of the adhesive, as the liquid can not flow
over the adhesives, when the liquid disperses to reach to the adhesive. In the
present invention, an adhesive pattern that preferentially directs this alteration of flow
in the direction of length rather than the direction of width is a pattern of lines
extending lengthwise with spaces between them. Desirable examples of such
adhesive patterns are shown in Figure 13, but they are not limited to these examples.
In Figure 13 A, the adhesive is applied linearly in the lengthwise direction. Each line
may be a straight line or may be a curved line as in Figure 13 B. The lines may be
continuous, or may be short lines as in Figures 13 C and D or patterns of dots as in
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Figures 13 E and F. Preferably at least 60%, more preferably at least 80% of each
line is at angles of within 45° to the longer direction. 60% or 80% means the total
percentage of the lengths of the straight lines that are at angles of within 45° to the
longer direction relative to the total lengths of all the lines. Where the lines are
curved, the overall vector of the lines is preferably at angle of within 45° to a straight
line in the lengthwise direction. The lines are preferably spaced at intervals of 0.001
to 10 cm, more preferably 0.01 to 5 cm or further more preferably 0.1 to 2 cm.
Helical patterns which are arranged in the lengthwise direction as shown in Figure 13
G is also preferable. The vector of a helical pattern is preferably at an angle of within
45° to the longer direction. The vectors of each helical pattern are preferably spaced
at intervals of 0.001 to 10 cm, more preferably 0.01 to 5 cm or further more preferably
0.1 to 2 cm. A single pattern may be used, or multiple patterns may be combined as
shown in Figure 13 H. A pattern of intersecting lines can also be used as in Figure
13 1. In this case, preferably at least 60% or more preferably at least 80% of the total
lines of adhesive are spaced at intervals of 0.001 to 10 cm.
[0144] (Evaluating the capability of a bodily fluid-absorbing article)
Evaluation of liquid return (rewetting), liquid dispersion distance
A sufficiently wide wooden board is placed on a laboratory table, and the four
corners of a bodily fluid-absorbing article are stretched but not getting wrinkled and
fixed with thumb tacks. A cylindrical pipe with a diameter of 60 mm and a weight of
53.5 g is placed on the center of the absorbent composite. 80 g of saline warmed to
37°C is dripped through the pipe onto the center of the absorbent composite at a rate
of 7 to 8 ml/second. After the saline is no longer visible on the upper surface of the
top sheet, the pipe is removed. 5 minutes after the start of dripping, the distance of
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dispersion in the lengthwise direction is measured and determined to be the liquid
dispersion distance.
[0145] 1 minute after the dripping started, a 10 cm square piece that is cut out from
Advantec No. 2 filter paper with a diameter of 150 mm are stacked on the dripping
position so that the total weight become about 90 g, and a 3.5 kg load is immediately
applied on the filter papers. 3 minutes after the load was applied, the load is
removed, the filter papers are taken out from the article and weighed. The amount of
the weight of the filter papers increased from the original weight is determined to be
the first rewet amount.
9 minutes after the dripping started, the cylinder is replaced. 10 minutes after
the dripping started, 80 g more of saline is dripped and the same procedures as the
first dripping are repeated. The amount of the weight of the filter papers increased
after these procedures is then determined to be the second rewet amount.
19 minutes after the first dripping started, the pipe is replaced, and 20 minutes
after the first dripping started, 80 g more of saline is dripped and the same
procedures are repeated. The amount of the weight of the filter papers increased
after these procedures is then determined to be the third rewet amount.
[0146] The rewet amount is an indicator of rewetting or in other words of the feeling
of the bodily fluid-absorbing article during use. If the rewet amount is large, the skin
will become wet and the article will be unpleasant to wear. The rewet amount is
preferably as small as possible to keep the surface of the article dry and make it
comfortable to wear. The repeated rewet amounts indicate the feeling of the bodily
fluid-absorbing article when it is worn continuously and absorbs bodily fluid
repeatedly. The larger the second and third rewet amounts, the more comfortable the
article will be when it is used continuously. The first rewet amount is preferably not
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more than 30 g, more preferably not more than 20 g, further more preferably not
more than 10 g or still more preferably not more than 3 g. The second rewet amount
is preferably not more than 40 g, more preferably not more than 30 g, further more
preferably not more than 25 g or still more preferably not more than 20 g. The third
rewet amount is preferably not more than 50 g, more preferably not more than 45 g,
further more preferably not more than 40 g or still more preferably not more than 30 g.
[0147] The liquid dispersion distance means the distance of the portion that was used
to absorb the liquid in the absorbent composite, and the longer the liquid dispersion
distance, the higher the usage efficiency of the absorbent composite. If the usage
efficiency of the absorbent composite is high, the necessary absorption capability can
be attained with a small quantity of absorbent composite, allowing for conservation of
resources. If the liquid dispersion distance is long, the absorbent layer after liquid
absorption become thin, the likelihood of displacement of the absorbent composite
decrease, and the absorbent composite become more comfortable to wear. The
liquid dispersion distance is preferably at least 200 mm, more preferably at least 240
mm, further more preferably at least 270 mm or still more preferably at least 300 mm.
[0148].Evaluation of lengthwise dispersion, distribution area
A sufficiently wide wooden board is placed on a laboratory table, and the four
corners of a bodily fluid-absorbing article are stretched but not getting wrinkled and
fixed with thumb tacks. 50 cc of saline is continuously dripped at a rate of 1
ml/second onto the center of the absorbent composite. 2 minutes after completion of
dripping, the length and width of the part into which the liquid dispersed are
measured. Lengthwise dispersion is calculated according to Formula 11, and
distribution area according to Formula 12.
(Formula 11)
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Lengthwise dispersion = length of dispersion in the lengthwise direction
(cm)/length of dispersion in the crosswise direction (cm)
(Formula 12)
Distribution area = length of dispersion in the lengthwise direction (cm) x
length of dispersion in the crosswise direction (cm)
[0149] In a bodily fluid-absorbing article, leakage is normally more likely in the
crosswise direction, in which the article generally is shorter. It is preferable that the
lengthwise dispersion is high, as it makes liquid flow more readily in the lengthwise
direction, and reduces leakage. A higher lengthwise dispersion is also desirable
because it increases the usage efficiency of the absorbent composite. The
lengthwise dispersion is preferably at least 1.4, more preferably at least 1.7, further
more preferably at least 2.0 or still more preferably at least 2.5. In an absorbent
composite with good dispersibility, the liquid may disperse as far as it reaches to the
lateral edge. Leakage usually does not occur immediately after the liquid reaches to
the edge, or is prevented by gathers or the like. However, it is preferable that the
length of dispersion in the crosswise direction is shorter than the width of the article,
as leakage may occur if a large quantity of liquid is further added.
[0150] The distribution area is an indicator of the liquid dispersibility of the article, and
it is preferable to use the absorbent composite with higher distribution area in order
to increase the usage efficiency of the absorbent composite. If the amount of liquid
to be absorbed is kept constant, the absorbent composite with higher distribution
area changes less in thickness after absorption and is more stable, because the
amount of liquid to be absorbed per unit area decrease as the distribution area
increase. If the absorbent composite change little in thickness, moreover, the article
is more comfortable to wear without a feeling of pressure to the user. The
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distribution area is preferably at least 150 cm2, more preferably at least 200 cm2,
further more preferably at least 250 cm2 or still more preferably at least 300 cm2.
[0151]•Evaluating leakage
In the present invention, leakage is measured as follows. The center of the
absorbent composite part in the bodily fluid-absorbing article is marked with a cross
mark with a size of about 1 cm. The absorbent composite is fixed with thumb tacks
to a horizontal board over a line drawn parallel to the short direction from the center
as shown in Figure 14. When the absorbent composite has gathers or the like, the
gathers are also fixed so that the edges of the absorbent composite can be seen
from above. A plastic board is then inserted as shown in Figure 15, and an article is
fixed with tape so that they form an angle of 30° at the fixed point. In this case the
absorbent composite is stretched but not getting wrinkled.
[0152] Saline dyed with edible red is dripped at a rate of 0.1 ml/second onto the point
marked with a cross mark. The amount of liquid dripped at the point when the
dispersed liquid begins to disperse outside of the edge of the absorbent composite is
determined to be the leakage drip amount.
[0153] The leakage drip amount is preferably at least 100 ml, more preferably at least
120 ml, further more preferably at least 135 ml or still more preferably at least 150 ml.
The leakage drip amount can be increased by increasing the thickness and weight of
the absorbent composite, but the article itself is preferably thin and lightweight. In the
present invention, therefore, the leakage coefficient as an indicator of leakage
resistance per unit area is determined according to (Formula 13) below based on the
leakage drip amount, the weight of the absorbent composite and the area of the
absorbent composite.
(Formula 13)
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Leakage coefficient = leakage drip amount (ml)/(the weight of the absorbent
composite (g)/the area of the absorbent composite (cm2))
The weight and area of the absorbent composite are determined by measuring
the absorbent composite as a whole. In absorbent composites with the same weight
and area, the greater the leakage coefficient, the greater the resistance to leakage.
The leakage coefficient is preferably at least 1000, more preferably at least 2000,
further more preferably at least 3000 or still more preferably at least 4000. It is
preferable that the absorbent composite has both the leakage coefficient within this
range and the leakage drip amount within the range described above.
EXAMPLES
[0154] Specific examples of the present invention are given below together with
comparative examples, and the present invention is not limited to these examples.
[0155] (Manufacturing 1)
Acrylic acid of special grade reagent from Wako Pure Chemical was purified
by distillation and used. 100 g of this acrylic acid was dissolved in 91.02 g of water.
This aqueous solution was cooled in an ice bath and maintained at a liquid
temperature of 30°C or less, and 117.94 g of 25 wt% aqueous ammonia solution
were gradually added to the solution with stirring to give a 40 wt% ammonium
acrylate aqueous solution (neutralization rate 100%).
90 g of this 40 wt% ammonium acrylate aqueous solution and 0.0187 g of
N,N'-methylenebisacrylamide were added to a 300 ml separable flask. The flask was
immersed in a water bath so as to maintain a liquid temperature of 30°C. The water
bath was deoxygenated by bubbling with nitrogen gas to substitute the reaction
system with nitrogen. 0.43 g of 42 wt% aqueous glycerin solution was then added
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with a syringe and thoroughly stirred, and 0.0917 g of 30 wt% aqueous hydrogen
peroxide solution and 0.0415 g of Rongalite, each dissolved in 1 g of water, were
added to initiate polymerization. 5 minutes after the start of the reaction, the internal
temperature had risen to 100°C from the initial temperature of 30°C. This was then
heated for 3 hours in a water bath so as to maintain an internal temperature at 70°C.
The gel was then taken out from the separable flask, coarsely grounded and dried for
4 hours at 100°C in an inert oven. After completion of drying, it was pulverized with a
homogenizer and classified by sieving into sizes of under 106 µm, 106 to 212 µm,
212 to 300 µm, 300 to 425 µm, 425 to 500 µm, 500 to 600 µm, 600 to 710 µm, 710 to
850 µm, 850 to 1200 µm, 1200 to 1400 µm, 1400 to 1700 µm, 1700 to 2500 µm,
2500 to 3000 µm and over 3000 µm. These were used as water-absorbent resin
particles 1. The surface strength of these resin particles was 0.5 N. The overall
ammonium salt concentration was 96%, the salt concentration of the surface was
90% and the salt concentration at the center was 97%.
[0156] (Manufacturing 2)
The water-absorbent resin particles 1 manufactured in Manufacturing 1 were
heat-treated for 10 minutes in an inert oven at 180°C, and used as water-absorbent
resin particles 2. The surface strength was 2.7 N. The overall ammonium salt
concentration was 70%, the salt concentration of surface was 30% and the salt
concentration at the center was 95%.
[0157] (Manufacturing Example 3)
81.73 g of acrylic acid of special grade reagent from Wako Pure Chemical,
185.71 g of water and 31.78 g of sodium hydroxide were slowly added to a 300 ml
flask while the flask was being cooled so that the liquid temperature did not exceed
30°C (salt concentration 70%). 90 g of this monomer solution and 0.0561 g of N,N'-
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methylenebisacrylamide were added to a 300 ml separable flask. The flask was
immersed in a water bath so as to maintain a liquid temperature at 30°C. The water
bath was deoxygenated by bubbling with nitrogen gas to substitute the reaction
system with nitrogen. 0.0826 g of 30 wt% of and 0.0518 g of Rongalite, each
dissolved in 1 g of water, were added to initiate polymerization. After 10 minutes, the
internal temperature had risen to 70°C from the initial temperature of 30°C. 5
minutes after the internal temperature has reached to the maximum temperature, the
solution was heated for 3 hours in a water bath so as to maintain an internal
temperature at 75°C. After a lapse of predetermined time, the gel was taken out from
the separable flask, coarsely grounded and dried for 4 hours at 100°C in an inert
oven. After completion of drying, it was pulverized with a homogenizer and classified
by sieving into sizes of under 106 µm, 106 to 212 µm, 212 to 300 µm, 300 to 425 µm,
425 to 500 µm, 500 to 600 µm, 600 to 710 µm, 710 to 850 µm, 850 to 1200 µm, 1200
to 1400 µm, 1400 to 1700 µm, 1700 to 2500 µm, 2500 to 3000 µm and over 3000 µm.
These were used as water-absorbent resin particles 3. The surface strength of the
resin was 0.9 N.
[0158] (Manufacturing 4)
A mixture of 0.6 g of isopropyl alcohol, 0.02 g of glycerin and 0.06 g of water
was prepared, and dispersed uniformly over 2 g of the water-absorbent resin
particles 2 manufactured in Manufacturing 3. These were heated for 10 minutes at
180°C in an inert oven, and used as water-absorbent resin 4. The surface strength
of the resin was 5.9 N.
[0159] (Manufacturing 5)
81.73 g of acrylic acid of reagent special grade from Wako Pure Chemical,
185.71 g of water and 21.8 g of sodium hydroxide were slowly added to a 300 ml
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flask while cooling the flask with ice so as to keep the liquid temperature not to
exceed 30°C (salt concentration 48%). 90 g of this monomer solution and 0.0561 g
of N,N'-methylenebisacrylamide were added to a 300 ml separable flask. The flask
was immersed in a water bath so as to maintain a liquid temperature at 30°C. The
water bath was deoxygenated by bubbling with nitrogen gas to substitute the reaction
system with nitrogen. 0.0826 g of 30 wt% aqueous hydrogen peroxide solution and
0.0518 g of Rongalite, each dissolved in 1 g of water, were added to initiate
polymerization. After 10 minutes, the internal temperature had risen to 70°C from the
initial temperature of 30°C. 5 minutes after the internal temperature has reached to
the maximum temperature, the solution was heated for 3 hours in a water bath so as
to maintain an internal temperature at 75°C. After a lapse of predetermined time, the
gel was taken out from the separable flask, coarsely grounded and dried for 4 hours
at 100°C in an inert oven. After completion of drying, it was pulverized with a
homogenizer and classified by sieving into sizes of under 106 µm, 106 to 212 µm,
212 to 300 µm, 212 to 300 µm, 300 to 425 µm, 425 to 500 µm, 500 to 600 µm, 600 to
710 µm, 710 to 850 µm, 850 to 1200 µm, 1200 to 1400 µm, 1400 to 1700 µm, 1700
to 2500 µm, 2500 to 3000 µm and over 3000 µm. These were used as water-
absorbent resin particles 5. The surface strength of the resin was 1.1 N.
[0160] (Manufacturing 6)
A mixture of 0.6 g of isopropyl alcohol, 0.02 g of glycerin and 0.06 g of water
was prepared, and dispersed uniformly over 2 g of the water-absorbent resin
particles 5 manufactured in Manufacturing 5. These were heated for 10 minutes at
180°C in an inert oven, and used as water-absorbent resin particles 6. the surface
strength of the resin was 6 N.
[0161] (Manufacturing 7)
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Acrylic acid of reagent special grade from Wako Pure Chemical was purified
by distillation. 753 g of the purified acrylic acid was cooled in an ice bath and
maintained at a liquid temperature at 30°C or less, and 625 g of 25 wt% aqueous
ammonia solution of reagent special grade from Wako Pure Chemical was added
gradually while stirring the solution to give a 66 wt% ammonium acrylate aqueous
solution (neutralization rate 100%). 0.0395 g of N,N'-methylenebisacrylamide
dissolved in 1 g of water was added and dissolved by stirring the solution, and the
mixture was deoxygenated by bubbling with nitrogen gas.
4.3 L of cyclohexane and 7.8785 g of sorbitan monostearate as a surfactant
were added to a 12 L autoclave with a nitrogen atmosphere already in the system,
and dissolved by stirring at room temperature, and the reaction system was
deoxygenated under reduced pressure of 65 kPa. The reaction system was heated,
still under reduced pressure, to an internal temperature of 60°C. An aqueous
solution of 0.7186 g of ammonium persulfate dissolved in 50 g of water was added to
the aforementioned ammonium acrylate aqueous solution. After the internal
temperature of the reaction system had reached 60°C, the prepared ammonium
acrylate aqueous solution was added to the system, and suspended by stirring at
120 rpm in a flow of nitrogen. Polymerization was initiated in the reaction system
maintained at 65 kPa, and at internal temperature of 60°C, and the reaction system
was stirred at a stirring speed of 120 rpm for 2 hours to give an emulsion containing a
wet gel. The inside of the reaction system was returned to normal pressure with
nitrogen, sealed, and heated at an internal temperature of 80°C, the stirring speed
was set to 400 rpm, and a mixed solution of 108.8 g of ethanol from Wako Pure
Chemical and 8.35 g of glycerin was added over 15 minutes. The system was
pressurized with nitrogen, heated to an internal temperature of 110°C and maintained
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with stirring for 30 minutes. The pressure was then lowered to normal pressure, and
the resulting wet gel was washed three times with 2 L of cyclohexane at 40°C.
The resulting wet gel was collected by filtration, dried in a 70°C full vacuum
and collected. The gel was dried for 6 hours in an inert oven at 70°C. After
completion of drying, it was grounded coarsely with a homogenizer and classified by
sieving into sizes of under 106 µm, 106 to 212 µm, 212 to 300 µm, 300 to 425 µm,
425 to 500 µm, 500 to 600 µm, 600 to 710 µm, 710 to 850 µm, 850 to 1400 µm, 850
to 1200 µm, 1200 to 1400 µm, 1400 to 1700 µm, 1700 to 2500 µm, 2500 to 3000 µm
and over 3000 µm. These were used as water-absorbent resin particles 7. The
absorption capacity of these resin particles was 70x. The surface strength of these
resin particles was 0.4 N. The overall ammonium salt concentration was 95%, the
surface salt concentration was 88% and the center salt concentration was 97%.
The water-absorbent resin particles 7 manufactured in Manufacturing 7 were
heat treated for 10 minutes in an inert oven at 180°C. The conditions for this
operation are the same as the heat treatment conditions for forming a composite with
the base material in the following examples. As a result, the surface salt strength of
the water-absorbent resin was 2.5 N, with an overall ammonium salt concentration of
70%, and the salt concentration of the surface of 32% and a the salt concentration at
the center of 94%.
[0162] (Manufacturing 8)
The same operations were carried out as in Manufacturing 7 except that the
stirring speed during polymerization was changed from 120 rpm to 400 rpm. The
resulting particles were water-absorbent resin particles 8. The absorption capacity of
these resin particles was 80x. The surface strength of the resin particles was 0.4 N.
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The overall ammonium salt concentration was 95%, the salt concentration of the
surface was 87% and the salt concentration at the center was 97%.
The water-absorbent resin particles 8 manufactured in Manufacturing 8 were
heat-treated for 10 minutes in an inert oven at 180°C. The conditions for this
operation are the same as the heat treatment conditions for forming a composite with
the base material in the following examples. As a result, the surface salt strength of
the water-absorbent resin was 2.2 N, with an overall ammonium salt concentration of
68%, the salt concentration of the surface of 33% and the salt concentration at the
center of 93%.
[0163] (Manufacturing 9)
Acrylic acid of reagent special grade from Wako Pure Chemical was prepared.
2557.8 g of the reagent acrylic acid was dissolved in 2087.3 g of water. The
aqueous solution was cooled in an ice bath, and 3507.0 g of 40.5 wt% aqueous
NaOH solution was added gradually with stirring while keeping the liquid temperature
at 30°C or less to give a 40 wt% sodium acrylate aqueous solution.
1733.0 g of the sodium acrylate aqueous solution obtained above was
dissolved in 341.5 g of water. 227.7 g of acrylic acid was added to this sodium
acrylate aqueous solution to give 2302.2 g of a 40 wt% sodium acrylate/acrylic acid =
70/30 aqueous solution. 2.5 g of N,N'-methylenebisacrylamide was added and
dissolved as a crosslinking agent, and the mixture was deoxygenated by bubbling
with nitrogen gas.
4.3 L of cyclohexane and 7.8785 g of sorbitan monostearate as a surfactant
were added to a 12 L autoclave substituted with nitrogen in advance, and dissolved
by stirring the solution at room temperature, and the reaction system was
deoxygenated under reduced pressure of 65 kPa. The reaction system was heated,
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still under reduced pressure, to an internal temperature of 60°C. An aqueous
solution of 0.7186 g of ammonium persulfate dissolved in 50 g of water was added to
the aforementioned sodium acrylate aqueous solution. After the internal temperature
of the reaction system had reached 60°C, the prepared sodium acrylate aqueous
solution was added to the system, and suspended by stirring at 400 rpm in a flow of
nitrogen. Polymerization was initiated in the reaction system maintained at 65 kPa,
internal temperature 60°C, and the reaction system was stirred at a stirring speed of
400 rpm for 2 hours to give an emulsion containing a wet gel. The inside of the
reaction system was returned to normal pressure with nitrogen, sealed, and heated
at an internal temperature of 80°C, the stirring speed was set to 400 rpm, and a
mixed solution of 108.8 g of ethanol from Wako Pure Chemical and 4.2 g of glycerin
was added over 15 minutes. The system was pressurized with nitrogen, heated to
an internal temperature of 110°C and maintained with stirring for 30 minutes. The
pressure was then lowered to normal pressure, and the resulting wet gel was washed
three times with 2 L of cyclohexane at 40°C.
The resulting wet gel was collected by filtration, dried in a 70°C full vacuum
and collected. After completion of drying, it was grounded with a homogenizer and
classified by sieving into sizes of under 106 µm, 106 to 212 µm, 212 to 300 µm, 300
to 425 µm, 425 to 500 µm, 500 to 600 µm, 600 to 710 µm, 710 to 850 µm, 850 to
1200 µm, 1200 to 1400 µm, 1400 to 1700 µm, 1700 to 2500 µm, 2500 to 3000 µm
and over 3000 µm. These were used as water-absorbent resin particles 9. The
absorption capacity of these resin particles was 55x. The surface strength of these
resin particles was 1.2 N.
[0164] (Manufacturing 10)
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Acrylic acid of reagent special grade from Wako Pure Chemical was purified
by distillation. 753 g of the purified acrylic acid was cooled in an ice bath and
maintained at a liquid temperature of 30°C or less, and 625 g of 25 wt% aqueous
ammonia solution of reagent special grade from Wako Pure Chemical was added
gradually with stirring to give a 66 wt% ammonium acrylate aqueous solution
(neutralization rate 100%). This was then deoxygenated by bubbling with nitrogen
gas.
4.3 L of cyclohexane and 7.53 g of sorbitan monolaurate as a surfactant were
added to a 12 L autoclave substituted with a nitrogen atmosphere in advance, and
dissolved by stirring at room temperature, and the reaction system was
deoxygenated under reduced pressure of 30 kPa. This was heated, still under
reduced pressure, to an internal temperature of 40°C. An aqueous solution of 0.7699
g of ammonium persulfate dissolved in 50 g of water was added to the
aforementioned ammonium acrylate aqueous solution. After the internal temperature
of the reaction system had reached 40°C, the prepared ammonium acrylate aqueous
solution was added to the system, and suspended by stirring at 400 rpm in a flow of
nitrogen. Polymerization was initiated in the reaction system maintained at 30 kPa,
internal temperature 40°C, and the reaction system was stirred at a stirring speed of
400 rpm for 2 hours to give an emulsion containing a wet gel. The pressure was then
lowered to normal pressure, and the resulting wet gel was washed three times with 2
L of cyclohexane at 40°C.
The resulting wet gel was collected by filtration, dried in a 70°C full vacuum
and collected. After drying, this was grounded with a homogenizer and classified by
sieving into sizes of under 106 µm, 106 to 212 µm, 212 to 300 µm, 300 to 425 µm,
425 to 500 µm, 500 to 600 µm, 600 to 710 µm, 710 to 850 µm, 850 to 1200 µm, 1200
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A0501 VP32W/YA
to 1400 µm, 1400 to 1700 µm, 1700 to 2500 µm, 2500 to 3000 µm and over 3000 µm.
These were used as water-absorbent resin particles 10. The absorption capacity of
these resin particles was 80x. The surface strength of these resin particles was 0.6
N. The overall ammonium salt concentration was 97%, the salt concentration of the
surface was 91% and the salt concentration at the center was 98%.
The water-absorbent resin particles 10 manufactured in Manufacturing 10
were heat treated for 10 minutes in an inert oven at 180°C. The conditions for this
operation are the same as the heat treatment conditions for forming a composite with
the base material in the following examples. As a result, the surface salt strength of
the water-absorbent resin was 2.8 N, with an overall ammonium salt concentration of
70%, the salt concentration of the surface of 29% and the salt concentration at the
center of 95%.
[0165] (Manufacturing 11)
Acrylic acid of reagent special grade from Wako Pure Chemical was prepared.
2557.8 g of the reagent acrylic acid was dissolved in 2087.3 g of water. This
aqueous solution was cooled in an ice bath, and 3507.0 g of 40.5 wt% aqueous
NaOH solution was added gradually with stirring while keeping the liquid temperature
at 30°C or less to give a 40 wt% sodium acrylate aqueous solution.
1733.0 g of the sodium acrylate aqueous solution obtained above was
dissolved in 341.5 g of water. 227.7 g of acrylic acid was added to this sodium
acrylate aqueous solution to give 2302.2 g of a 40 wt% sodium acrylate/acrylic acid =
70/30 aqueous solution. 2.5 g of N,N'-methylenebisacrylamide was added and
dissolved as a crosslinking agent, and the mixture was deoxygenated by bubbling
with nitrogen gas.
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4.3 L of cyclohexane and 7.8785 g of sorbitan monostearate as a surfactant
were added to a 12 L autoclave substituted with a nitrogen atmosphere in advance,
and dissolved by stirring at room temperature, and the reaction system was
deoxygenated under reduced pressure of 65 kPa. This was heated, still under
reduced pressure, to an internal temperature of 60°C. An aqueous solution of 0.7186
g of ammonium persulfate dissolved in 50 g of water was added to the
aforementioned sodium acrylate aqueous solution. After the internal temperature of
the reaction system had reached 60°C, the prepared sodium acrylate aqueous
solution was added to the system, and suspended by stirring at 400 rpm in a flow of
nitrogen. Polymerization was initiated with the reaction system maintained at 65 kPa,
internal temperature 60°C, and the reaction system was stirred at a stirring speed of
400 rpm for 2 hours to give an emulsion containing a wet gel. The inside of the
reaction system was returned to normal pressure with nitrogen, sealed, and heated
at an internal temperature of 80°C, the stirring speed was set to 400 rpm, and 108.8
g of ethanol from Wako Pure Chemical was added over 15 minutes. The system was
pressurized with nitrogen, heated to an internal temperature of 110°C and maintained
with stirring for 30 minutes. The pressure was then lowered to normal pressure, and
the resulting wet gel was washed with 2 L of cyclohexane three times at 40°C.
The resulting wet gel was collected by filtration, dried in a 70°C full vacuum
and collected. After completion of drying, it was grounded with a homogenizer and
classified by sieving into sizes of under 106 urn, 106 to 212 µm, 212 to 300 µm, 300
to 425 µm, 425 to 500 µm, 500 to 600 µm, 600 to 710 µm, 710 to 850 µm, 850 to
1400 µm, 850 to 1200 µm, 1200 to 1400 µm, 1400 to 1700 µm, 1700 to 2500 µm,
2500 to 3000 µm and over 3000 µm. These were used as water-absorbent resin
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particles 11. The absorption capacity of these resin particles was 57x. The surface
strength of these resin particles was 1.1 N.
[0166] The material properties of the water-absorbent resin particles 1 to 11
manufactured in Manufacturing 1 to 11 are shown in Table 1.
Table 1

Average
absorption
capacity (g/g) Absorption
capacity under
pressure (g/g) Residual
monomers
(ppm)
Water-absorbent resin particles 1 76 28 170
Water-absorbent resin particles 2 83 35 Water-absorbent resin particles 3 61 26 200
Water-absorbent resin particles 4 54 21.6 160
Water-absorbent resin particles 5 53 23 190
Water-absorbent resin particles 6 43 12.3 160
Water-absorbent resin particles 7 70 Water-absorbent resin particles 8 80 Water-absorbent resin particles 9 55 Water-absorbent resin particles 10 80 Water-absorbent resin particles 11 57 Water-absorbent resin particles 12 76 28 170
Water-absorbent resin particles 13 76 28 170
[0167] (Example 1)
A portion of a circle with a diameter of 59.5 mm was cut out from Bemliese®
from Asahi Kasei Fibers Corp. (material properties shown in Table 2) , and the
weight of the portion was 0.0796 g. Bemliese® is a nonwoven fabric made from
100% cellulose continuous-filament. Because it is a cellulose nonwoven fabric, it has
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excellent absorption properties. Because it is made from the continuous filaments, it
is sufficiently strong when containing water and has excellent liquid dispersibility.
Of the water-absorbent resin particles 1 synthesized in Manufacturing 1, 0.164
g of particles with a particle size of 850 to 1200 urn were arranged on Teflon sheet
with a diameter of 59.5mm so that the particles were not closely packed. This was
called Teflon (1). Another Teflon sheet was prepared in the same way and called
Teflon (2). The Bemliese® was placed on Teflon (1), and sprayed with 3 ml of water
with an atomizer. Teflon (1) was placed upside-down on Teflon (2) with the
Bemliese® side of Teflon (1) on top of the particle side of Teflon (2). This was
pressed down lightly by hand, left for 1 minute, and heated for 10 minutes at 180°C in
an inert oven. The weight as measured immediately after heating was 0.4061 g.
The weight ratio of the water-absorbent resin in the composite is calculated as 80.4%.
All of the water-absorbent resin particles were strongly adhered to Bemliese®, and
none of the water-absorbent resin became detached when rubbed by hand. It was
observed with a scanning electron microscope (JEOL JSM-5300) that all the particles
adhere to Bemliese® with fibers incorporated inside the water-absorbent resin.
Figure 16 is an electron microscope image of the configuration of adhesion (150x
enlargement), which was taken from the side at an angle, rather than from above the
particles, so that the adhesion configuration appears in the image. This composite
was called Example 1.
In Figure 16, the part inside the circle is an adhering bond between the water-
absorbent resin and fibers. The water-absorbent resin particles appear to the upper
right of the black part and the fiber part of the base material to the lower left, and the
fibers appear black, showing that they are bonded inside the water-absorbent resin
particles.
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[0168] (Example 2)
An experiment was carried out in the same way as in Example 1 except that
resin particles 7 with a particle size of 850 to 1200 µm manufactured in
Manufacturing 7 were used. The evaluation results are shown in Table 3.
(Example 3)
An experiment was carried out in the same way as in Example 1 except that
resin particles 8 with a particle size of 850 to 1200 µm manufactured in
Manufacturing 8 were used. The evaluation results are shown in Table 3.
(Example 4)
An experiment was carried out in the same way as in Example 1 except that
resin particles 9 with a particle size of 850 to 1200 µm manufactured in
Manufacturing 9 were used. The evaluation results are shown in Table 3.
(Example 5)
An experiment was carried out in the same way as in Example 1 except that
resin particles 10 with a particle size of 850 to 1200 µm manufactured in
Manufacturing 10 were used. The evaluation results are shown in Table 3.
(Example 6)
An experiment was carried out in the same way as in Example 1 except that
resin particles 11 with a particle size of 850 to 1200 µm manufactured in
Manufacturing 11 were used. The evaluation results are shown in Table 3.
[0169] (Comparative Example 1)
81.73 g of reagent acrylic acid (Wako Pure Chemical, reagent special grade),
185.71 g of water and 31.78 g of sodium hydroxide were gradually added in a 300 ml
flask with ice cooling so that the liquid temperature did not exceed 30°C (salt
concentration 70%). 90 g of this monomer solution was poured into an atomizer in a
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nitrogen box, and 0.0561 g of N,N'-methylenebisacrylamide was added. The
aqueous solution was deoxygenated by bubbling with nitrogen gas. 1 ml of a
solution of 0.022 g of iron chloride (III) hexahydrate dissolved in 100 g of water, 1 ml
of 30 wt% hydrogen peroxide solution, and a solution of 0.12 g of L-ascorbic acid
dissolved in 1ml of water were rapidly added and stirred, and the mixture was
sprayed over Spun Bond EltasCrimp® PC8020 from Asahi Kasei Fibers Corp..
Whole set of this including nonwoven fabric was heated to 60°C with a hot plate, and
polymerized for 1 hour, then the temperature was raised to 120°C and maintained for
30 minutes to complete polymerization. It was vacuum dried at 100°C, the residual
monomer level was measured as 1000 ppm or more.
[0170] (Comparative Example 2)
A composite was prepared in the same way as Example 1 using the water-
absorbent resin particles 2 prepared in Manufacturing 2. Particles with a particle size
of 850 to 1200 urn were used. Because the ammonium salt concentration near the
surface was as low as 30%, only about 35% of the resin particles adhered. The area
occupancy rate was measured immediately after heating before the resin had
detached. Because the ratio of the particles adhering is low, it was difficult to obtain
stable performance. The evaluation results are shown in Table 3.
[0171] (Comparative Example 3)
A composite was prepared in the same way as Example 1 using the water-
absorbent resin particles 6 obtained in Manufacturing 6. Particles with a particle size
of 850 to 1200 urn were used. The surface strength was as high as 6 N, and only
about 25% of the resin adhered. The area occupancy rate was measured
immediately after heating before the resin detached. The evaluation results are
shown in Table 3.
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(Comparative Example 4)
A composite was prepared in the same way as Example 1 except that no
water was added. The particles did not adhere.
[0172] (Example 7)
A composite was prepared in the same way as Example 1 except that 15 g of
water was used. Because water remained after 10 minutes heating, it was heated for
a further 10 minutes.
(Example 8)
A composite was prepared in the same way as Example 1 except that the
drying conditions were 60°C, 5 hours.
(Example 9)
A composite was prepared in the same way as Example 1 except that the
drying temperature was 370°C. Because it would burn if it was over heated, the dry
conditions was checked every few seconds, and heating was terminated at the time
when the drying was completed.
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[0173] The physical properties of the absorbent composites of Examples 1 to 9 and
Comparative Examples 2 and 3 are shown in Table 3.
Table 3
Water-
absorbent
resin Absorbent composite
Particles
No. Weight
ratio
(%) Adhesion
rate (%) Total
surface
area
coefficient Area
occupancy
rate of
large
particles
(%) Absorption
capacity
(g/g) Absorption
capacity
after 1
minute (g/g)
Example 1 1 80 100 0.16 12 55.1 7
Example 2 7 80 100 0.19 13 51.3 8
Example 3 8 80 100 0.18 14 55.2 10
Example 4 9 80 100 0.15 14 41 8
Example 5 10 80 100 0.2 9 58.6 4
Example 6 11 80 100 0.17 14 42.4 5
Example 7 1 80 100 0.16 12 54 7
Example 8 1 80 100 0.19 13 55 7
Example 9 1 80 100 0.16 12 52 7
Comparative
Example 2 2 80 35 0.16 12 51 4
Comparative
Example 3 6 80 25 0.19 13 30 2
Comparative
Example 4 1 80 0 0.16 12 50 4
5 [0174] (Example 10)
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An experiment was carried out in the same way as in Example 1 except that
the water-absorbent resin particles 1 with a particle size of 500 to 600(jm
manufactured in Manufacturing 1 were used and the weight ratio of resin in the
absorbent composite was 67.6%. The evaluation results are shown in Table 4.
(Example 11)
An experiment was carried out in the same way as in Example 1 except that
the water-absorbent resin particles 1 with a particle size of 710 to 850 urn
manufactured in Manufacturing 1 were used and the weight ratio of resin in the
absorbent composite was 72.6%. The evaluation results are shown in Table 4.
(Example 12)
An experiment was carried out in the same way as in Example 1 except that
rayon spun lace was used as the base material (physical properties of rayon span
lace shown in Table 2), and the weight ratio of resin in the absorbent composite was
81.5%. The evaluation results are shown in Table 4.
(Example 13)
An experiment was carried out in the same way as in Example 1 except that
the water-absorbent resin particles 1 with a particle size of 1700 to 2500 urn
manufactured in Manufacturing 1 were used and the weight ratio of resin in the
absorbent composite was 89.2%. The evaluation results are shown in Table 4.
(Example 14)
An experiment was carried out in the same way as in Example 1 except that
the water-absorbent resin particles 1 with a particle size of 710 to 850 urn
manufactured in Manufacturing 1 were used and the weight ratio of resin in the
absorbent composite was 72.8%. The evaluation results are shown in Table 4.
(Example 15)
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An experiment was carried out in the same way as in Example 1 except that
the weight ratio of resin in the absorbent composite was 66.6%. The evaluation
results are shown in Table 4.
(Example 16)
An experiment was carried out in the same way as in Example 8 except that
the weight ratio of resin in the absorbent composite was 71.6%. The evaluation
results are shown in Table 4.
(Example 17)
An experiment was carried out in the same way as in Example 1 except that
the water-absorbent resin particles 7 with a particle size of 850 to 1200 manufactured
in Manufacturing 7 were used and the weight ratio of resin in the absorbent
composite was 80.0%, and rayon spun lace was used as the base material. The
evaluation results are shown in Table 4.
[0175] (Comparative Example 5)
An experiment was carried out in the same way as in Example 1 except that
the water-absorbent resin particles 1 with a particle size of 300 to 425 urn
manufactured in Manufacturing 1 were used and the weight ratio of resin in the
absorbent composite was 64%. The evaluation results are shown in Table 4.
The physical properties of the absorbent composites of Examples 10 to 17
and Comparative Example 5 are shown in Table 4.
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[0176] (Example 18)
A composite of Example 18 was prepared in the same way as Example 1
except that the particles of a mixture of 50 wt% of the water-absorbent particles 1
with a particle size of 850 to 1200 urn manufactured in Manufacturing 1 and 50 wt%
of the water-absorbent particles 1 with a particle size of 100 to 300 urn manufactured
in Manufacturing 1 was used. 98% of the particles adhered, with fibers incorporated
into the water-absorbent resin in all adhesion.
(Example 19)
A composite of Example 19 was prepared in the same way as Example 1
except that the particles of a mixture of 30% of the water-absorbent particles 1 with a
particle size of 850 to 1200 urn manufactured in Manufacturing 1 and 70% of the
water-absorbent particles 1 with a particle size of 100 to 300 urn sized particles
manufactured in Manufacturing 1 was used. 98% of the particles adhered, with fibers
incorporated into the water-absorbent resin in all adhesion.
[0177] (Example 20)
A composite of Example 20 was prepared in the same way as Example 1
except that the particles of a mixture of 30% of the water-absorbent particles 1 with a
particle size of 850 to 1200 urn manufactured in Manufacturing 1, 20% of the water-
absorbent particles 1 with a particle size of 3000 urn or larger manufactured in
Manufacturing 1 and 50% of the water-absorbent particles 1 with a particle size of
100 to 300 urn manufactured in Manufacturing 1 was used. 98% of the particles
adhered, with fibers incorporated into the water-absorbent resin in all cases.
(Example 21)
A composite of Example 21 was prepared in the same way as Example 1
except that the water-absorbent particles 3 with a particle size of 850 to 1200 urn
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manufactured in Manufacturing 3 were used. All of the water-absorbent resin
adhered strongly to Bemliese®, with fibers incorporated into the water-absorbent
resin. Compared with the water-absorbent resin particles 1 of Manufacturing 1, the
absorption amount absorbed by the composite was slightly lower because absorption
amount absorbed by the resin particles was less.
[0178] (Example 22)
A composite of Example 22 was prepared in the same way as Example 1
except that the water-absorbent resin particles 4 with a particle size of 850 to 1200
urn manufactured in Manufacturing 4 were used. Adhesiveness was somewhat
weaker because of the higher surface strength, and 67% of the particles adhered.
(Example 23)
A composite of Example 23 was prepared in the same way as Example 1
except that Asahi Kasei Fibers nylon Spun Bond® (physical properties shown in
Table 2) was used instead of Bemliese®. The particles with a particle size of 850 to
1200 µm were used. 92% of the particles adhered.
[0179] (Example 24)
A composite of Example 24 was prepared in the same way as Example 1
except that Oji Kinocloth KS-40® manufactured by Oji Kinocloth, (physical properties
shown in Table 2) was used instead of Bemliese®. Oji Kinocloth is a dry pulp
nonwoven fabric. The particles with a particle size of 850 to 1200 urn were used. All
of the water-absorbent resin particles adhered with fibers incorporated into the water-
absorbent resin. Because the strength of pulp is low, the particles easily detached
together with the pulp fibers with tweezers.
(Example 25)
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A composite of Example 25 was prepared in the same way as Example 1
except that Asahi Kasei Fibers PET Spunbond® (physical properties shown in Table
2) was used instead of Bemliese®. The particles with a size of 850 to 1200 µm were
used. The adhesive force was weak and only 62% of the particles adhered.
[0180] (Example 26)
A composite of Example 26 was prepared in the same way as Example 1
except that Asahi Kasei Fibers polypropylene Spunbond Eltas® P03020 (physical
properties shown in Table 2) was used instead of Bemliese®. The particles with a
particle size of 850 to 1200 urn were used. The adhesive force was weak, and only
51 % of the particles adhered.
(Example 27)
A composite of Example 27 was prepared in the same way as Example 1
except that Toyo Co. toilet paper "Piason" singles were used instead of Bemliese®.
The particles with a particle size of 850 to 1200 µm were used. Because the strength
was low when it was wet, it readily tore while being handled.
(Example 27-2)
A composite of Example 27-2 was prepared in the same way as Example 1
except that the ratio of resin was 94%, the water-absorbent resin particles 1 with a
particle size of 850 to 1200 urn manufactured in Manufacturing 1 were used. 95% of
the water-absorbent resin particles adhered. The absorbent resin particles were
densely packed. Some particles detached after absorption, because some of the
particles overlapped with each other.
[0181] (Reference Example 1)
The liquid permeability of "Saran Wrap" from Asahi Kasei Life & Living Co., Ltd.
was measured. The water could not pass through the wrap. It is not preferable to
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use a completely water-impermeable film for sanitary material, because it can be
used only for one side.
[0182] (Comparative Example 7)
A mixture of pulp and water-absorbent resin was taken out from absorber of a
Pampers Cotton Care® M size from P & G Co., Ltd., and used as Comparative
Example 7. The water-absorbent resin did not adhere to the pulp, and the pulp was
cottony and did not maintain its shape. The weight ratio of the resin could not be
measured by the method of the present invention. Because there was no base
material, the area occupancy rate could not be measured.
(Comparative Example 8)
A top sheet and back sheet were separated from a Rifure Anshin Pad®, 150 cc
size from Livedo Corporation, and the absorber alone was taken out. A circular piece
of with a diameter of 59.5 mm was cut out from the center of this. The water-
absorbent resin adhered to the base material with an adhesive and they did not
directly adhere to the base material. This was given as Comparative Example 8.
[0183] (Comparative Example 9)
Acrylic acid of special grade reagent from Wako Pure Chemical was used after
being purified by distillation. 10 g of the reagent acrylic acid was dissolved in 91.02 g
of water. This aqueous solution was chilled in an ice bath and maintained at a liquid
temperature of 30°C or less and 117.94 g of 25 wt% aqueous ammonia solution was
added gradually with stirring to give a 40 wt% ammonium acrylate aqueous solution.
A simple nitrogen box was prepared, and all subsequent operations were
carried out in a nitrogen-substituted nitrogen box. 90 g of the 40 wt% ammonium
acrylate aqueous solution and 0.0187 g of N,N'-methylenebisacrylamide were added
in a 300 ml flask. The aqueous solution was deoxygenated by bubbling with nitrogen
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gas. The internal temperature at this time was 20°C. 0.43 g of 42 wt% glycerin
aqueous solution was then added with a syringe and thoroughly stirred, and 0.0917 g
of 30 wt% hydrogen peroxide aqueous solution and 0.0415 g of Rongalite, each
dissolved in 1 g of water, were added to initiate polymerization. After the internal
temperature began to rise from 20°C, 50 g of the reaction liquid was poured over 3 g
of Bemliese® prepared in a tray. This was left for 3 hours, taken out from the
nitrogen box, and then dried for 4 hours at 100°C in an inert oven. This was given as
Comparative Example 9. This absorbent composite was hard and difficult to cut or
bend. Because it was difficult to measure the absorption capacity of the absorbent
composite directly, it was first pulverized in the same way as water-absorbent resin
particles and sieve-classified to a size of 106 to 850 urn before being measured. The
weight ratio of the resin and area occupancy rate could not be measured for this
composite, as it had been pulverized into particles.
[0184] (Comparative Example 10)
A composite was prepared in the same way as Example 1 except that the
water-absorbent resin particles 1 with a particle size of 850 to 1200 µm manufactured
in Manufacturing 1 were used, and the weight ratio of the resin was 25%. This was
given as Comparative Example 10. All the water-absorbent resin particles adhered.
(Comparative Example 12)
A composite was prepared in the same way as Example 1 except that the
water-absorbent resin particles 1 with a particle size of 850 to 1200 µm manufactured
in Manufacturing 1 were used, and the ratio of the resin was 55%. This was given as
Comparative Example 12. All the water-absorbent resin particles adhered.
[0185] The physical properties of the absorbent composites (absorbers) of Examples
18 to 27-2 and Comparative Examples 7 to 12 are shown in Table 5.
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[0186] (Manufacturing 12)
Water-absorbent resin particles 12 were manufactured in the same way as
Manufacturing 1 except that the particles were classified by sieving using sieves with
a sieve opening of 106 µm, 212 µm, 300 µm, 425 µm, 500 µm, 600 µm, 710 µm, 850
µm, 1000 µm, 1180 µm, 1400 µm, 2000 µm and 2500 µm.
(Manufacturing 13)
Water-absorbent resin particles 13 were manufactured in the same way as in
Manufacturing 3 except that the particles were classified by sieving using sieves with
a sieve opening of 106 µm, 212 µm, 300 µm, 425 µm, 500 µm, 600 µm, 710 µm, 850
µm, 1000 µm, 1180 µm, 1400 µm, 2000 µm and 2500 µm.
[0187] (Example 28)
A piece with a length of 27 cm and a width of 8 cm was cut out from Bemliese®
from Asahi Kasei Fiber. Bemliese® is a nonwoven fabric made of 100% cellulose
continuous-filament. As it is a cellulose nonwoven fabric, it has excellent absorption
properties. Because it is made of continuous filaments, it is sufficiently strong when
containing water and has excellent liquid dispersibility. A piece with a length of 27
cm and a width of 8 cm was cut out from Teflon® sheet, and a line with a length of 25
cm and a width of 6 cm was drawn on it. Another of the same was prepared. 1.5 g
of the water-absorbent resin particles 12 that remained on the 1000 µm sieve from
Manufacturing 12 were scattered uniformly on the inside of the line on the sheet
using a 1180 µm sieve. 1.5 g of the resin particles that remained on the 212 µm
sieve were scattered uniformly in the same way using a 300 µm sieve. 1.5 g of the
resin particles that remained on the 1000 µm sheet were scattered in the same way
on another sheet. 1.2 g of water was sprayed with an atomizer onto the Bemliese®,
then it was placed on the prepared sheets to adhere the resin to both surfaces. It was
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dried for 10 minutes at 180°C in an inert oven with the portion with no resin being
pressed with weights to prevent shrinkage of the Bemliese®. This was given as
Example 28.
[0188] (Examples 29 to 32)
Composites were manufactured in the same way as Example 28 except to
change the particle size and the used amount of the water-absorbent resin particles
12.
1.5 g of the resin particles that remained on the 500 µm sieve were used on
each side for Example 29.
1.5 g of the resin particles that remained on the 850 µm sieve were used on
each side and 1.5 g of the resin particles that remained on the 212 µm sieve were
used on one side for Example 30.
1.05 g of the resin particles that remained on the 710 µm sieve were used on
each side and 2.4 g of resin particles that remained on the 300 µm sieve on one side
for Example 31.
1.05 g of the resin particles that remained on the 710 µm sieve were used on
each side and 0.975 g of resin particles that remained on the 300 µm sieve on one
side for Example 32.
[0189] (Example 33)
A composite of Example 33 was prepared in the same way as Example 28
except that the water-absorbent resin particles 13 of Manufacturing 13 were used.
The absorption amount of the composite was slightly less, as the resin particles were
not in the form of ammonium salts and absorbed less compared with the water-
absorbent resin of Manufacturing 12. Some particles detached after manufacturing,
as the salt concentration of the surface was slightly less than that of ammonium salts.
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(Example 34)
A composite of Example 34 was manufactured in the same way as Example
28 except that nylon Spunbond® from Asahi Kasei Fiber was used instead of
Bemliese®. This was given as Example 34.
[0190] (Example 35)
A composite of Example 35 was manufactured in the same way as Example
28 except that Oji Kinocloth KS-40® from Oji Kinocloth was used instead of
Bemliese®. Oji Kinocloth® is a nonwoven fabric of dry pulp. Because pulp is weak,
the particles could be easily detached together with the pulp fibers with tweezers.
(Example 36)
A composite of Example 36 was manufactured in the same way as Example
28 except that PET Spunbond® from Asahi Kasei Fibers was used instead of
Bemliese®. The adhesive force was slightly weak.
[0191] (Example 37)
A composite was manufactured in the same way as Example 28 except to
change the particle size and the used amount of the resin particles using resin
particles 7 of Manufacturing 7.
1.5 g of resin particles that passed through a 1400 µm sieve but remained on
a 850 urn sieve were used on each sides and 1.5 g of resin particles that passed
through a 300 urn sieve but remained on a 212 urn sieve were used on one side to
give the composite of Example 37.
(Example 38)
A composite was manufactured in the same way as Example 28 except to
change the particle size of resin particles using the resin particles 8 of Manufacturing
8.
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1.5 g of resin particles that passed through a 1400 µm sieve but remained on
a 850 urn sieve were used on each sides and 1.5 g of resin particles that passed
through a 300 µm sieve but remained on a 212 urn sieve were used on one side to
give the composite of Example 38.
[0192] (Example 39)
A composite was manufactured in the same way as Example 28 except to
change the particle size of resin particles using the resin particles 7 and 8 of
Manufacturings 7 and 8.
1.5 g of resin particles that passed through a 1400 µm sieve but remained on
a 850 urn sieve of the resin particles 7 manufactured in Manufacturing 7 were used
on each sides and 1.5 g of resin particles that passed through a 300 µm sieve but
remained on a 212 µm sieve of the resin particles 8 manufactured in Manufacturing 8
were used on one side to give the composite of Example 39.
[0193] The physical properties of the absorbent composites of Examples 28 to 39 are
shown in Table 6.
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[0194] (Example 40)
The apparatus shown in Figure 17 was prepared, (a) is a fabric roll (base
material) of Bemliese® from Asahi Kasei Fiber with a width of 500 mm. The
measured density of this fabric was 28 g/m2. Gas line and water line were attached
to the spray nozzle of water atomizer (b). The sprayed amount of water was
adjusted by adjusting the gas pressure and the water pressure in the spray nozzle. A
water-absorbent resin particle hopper (d1) (supply part) was provided. Gas blower
(i1) was provided on the top of drum (e1) to blow off water-absorbent resin particles
from hopper (d1) that adhered to other parts than the dimples on the drum. Dry
warm air blower (j1) was provided to dry the surface of the drum before it came into
contact with the particles. Drum (e1) had a diameter of 500 mm and a width of 500
mm. The structure of the dimples on the drum surface is shown in Figures 18 and 19.
Figure 18 shows the positional relationship of the dimples as seen from above the
drum surface. The dimples were arranged such that the distance between the
centers of adjacent dimples was about 3.1 mm. Figure 19 is a cross-section view of
a dimple in the depth direction, showing a hole structure extending from the surface
of the drum to the inside of the drum, wherein the opening on the drum surface is a
circle with a diameter of 1.5 mm and narrows towards the inside of the drum to a
diameter of 0.7 mm at a depth of 0.8 mm, and then maintains a diameter of 0.7 mm
to the inside of the drum.
[0195] Fabric (c), which passed under drum (e1) and to one surface of which the
resin particles (f) adhere, then passes between press rolls (I), which strengthens the
adhesion between the resin particles and the fabric. The same equipment mentioned
above was used for drum (e2), upper hopper (d2), gas blower (i2) and dry warm air
blower 02) as for drum (e1), hopper (d1), gas blower (i1) and dry warm air blower (j1),
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respectively. The fabric was conveyed by conveyer belt (k) from beneath drum (e2)
to the exit of dryer (g). In dryer (g), a distance that the fabric travels is about 2 m,
and warm air was blown from the fabric exit towards the fabric entrance. Final take-
up roll (h) was operated by hand in order to control the rotational speed so as to
maintain a roughly constant deflection of the fabric between the belt conveyer and
the final roll.
[0196] Figure 20 shows a structure including internal structure of drum (e1).
The interior of drum (e1) is divided by partition (o1) into reduced pressure
space (q1) and normal pressure space. Gas blower (ml) is fixed to the position
where the drum contacts the fabric, and emits gas to blow out particles in holes that
pass the gas blower (ml). Drum (e1) also has another gas blower (n1), which emits
gas to blow out particles that were not blown onto the fabric into residual resin
container (p1).
[0197] Figure 21 shows a structure including internal structure of drum (e2).
The interior of drum (e2) is divided by partition (o2) into reduced pressure
space (q2) and normal pressure space. Gas blower (m2) is fixed to the position
where the drum contacts the fabric, and emits gas to blow out particles in holes that
pass the of gas blower (m2). Drum (e2) also has another gas blower (n2), which
emits gas to blow out residual resin that were not blown onto the fabric onto the
fabric once again.
The water-absorbent resin particles used here were 850 to 1200 urn sized
particles manufactured by the method given in Manufacturing 1. 1 kg of these resin
particles was placed in each hopper (d1) and hopper (d2). Every time the amount of
resin in each hopper decreased to about 300 g during operation, resin was added to.
the hopper up to 1 kg of resin. This operation was repeated to prevent the resin in
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the hoppers from being exhausted during operation. Reduced pressure spaces (q1)
and (q2) were depressurized from near the axis so as to maintain the pressure of
about 700-750 mmHg. Air was blown from gas blowers (i1) and (i2), and the volume
of blown air was adjusted so as to bring most of the resin adhere to other parts than
the dimples back to the hoppers. Warm dry air was blown from dry warm air blowers
(j1) and (j2) to dry the surfaces of the drums. Gas was blown from gas blowers (ml),
(m2), (n1) and (n2). Nitrogen gas at 180°C was supplied through dryer (g) from the
exit towards the entrance at a rate of 50 m3/hr. The amount of water sprayed by the
water sprayer was adjusted so that the water content of the Bemliese would be 20g
water/m2 when the rate of movement of the Bemliese was 0.2 m/minute.
Drums (e1) and (e2) and conveyer belt (k) were rotated so as to ensure the
fabric move smoothly, and operation was initiated after adjusting the speed of the
fabric to about 0.3 m/minute.
During operation, composite roll (h) was operated by hand so as to maintain a
roughly constant deflection between conveyer belt (k) and composite roll (h).
The fabric coming out from the roll 20 to 60 minutes after the initiation of
operation was evaluated in various ways.
[0198] (Evaluation of manufactured absorbent composite: adhesion between resin
and fabric)
A 10cm square piece was cut out from the absorbent composite manufactured
in Example 40 and the mode of adhesion between the fibers in the nonwoven fabric
and the absorbent resin was observed with an optical microscope. The fibers passed
through the resin.
[0199] (Evaluation of manufactured absorbent composite: the weight ratio of resin of
absorbent composite)
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Part of the absorbent composite manufactured in Example 40 was divided into
pieces with a length of 50 cm and 10 pieces of these were selected to measure the
ratio of the resin. The ratio of the resin was between 82 and 86 wt%. That is, there
was little variation in the weight ratio of the resin in the manufactured absorbent
composite. This absorbent composite was divided into pieces with a length of 50 cm
and 10 pieces of these were selected at random to measure the ratio of the resin
content. The ratio of the resin varied greatly between 70 wt% and 90 wt%, showing
that the fabric did not have a stable weight ratio of resin. The weight ratio of the resin
in the absorbent composite was calculated by the same methods used in Example 42
below.
[0200] (Evaluation of manufactured absorbent composite: adhesion between
absorbent resin and fabric)
A piece with a length of 50 cm was cut out from the absorbent composite
manufactured in Example 40 and was hanged on a bar fixed at about 1m in height,
and the bar was shaken up and down for 60 seconds at a rate of 15 cm/second with
a shaking width of 30 cm. The weight ratio of the resin of the absorbent composite
was 84 wt%, and only 5 resin particles fell off.
[0201] (Evaluation of manufactured absorbent composite: absorption amount under
no pressure)
The amount absorbed under no pressure by the absorbent composite
manufactured in Example 40 was 61 g/g. The absorption capacity per unit area was
1 g/cm2.
[0202] (Example 41)
The operation was carried out in the same way as Example 40 except that the
water-absorbent resin particles of Manufacturing 3 were used.
113

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(Evaluation of manufactured absorbent composite: area occupancy rate of absorbent
composite)
The area occupancy rate per one surface of the absorbent composite
manufactured in Example 41 was 15.5%.
[0203] (Evaluation of manufactured absorbent composite: adhesion between water-
absorbent resin and fabric)
A piece with a length of 50 cm was cut out from the absorbent composite
manufactured in Example 41 and was hanged on a bar fixed at about 1 m high, and
the bar was shaken for 60 seconds up and down at 15 cm/second with a shaking
range of 30 cm. The weight ratio of the resin of the absorbent composite was 85 wt%,
and only 20 particles of resin fell off.
(Example 42)(The water content of the base material is less than 0.5 wt%)
The operation was carried out in the same way as Example 40 except that the
amount of water sprayed by the atomizer was reduced so as to adjust the water
content of the Bemliese after having passed under the water atomizer to 0.3 wt%.
The fabric coming out from the machine 20 to 60 minutes after the initiation of
operation was used. A piece with a length of 50 cm was cut out from this absorbent
composite and was hanged on a bar fixed at about 1 m high, and the bar was
shaken 60 times at 30 cm/second with a shaking range of 30 cm. The weight ratio of
resin of the absorbent composite was 30 wt% or less. Few resin particles adhered to
the fabric that had a low water content. The amount of resin of the absorbent
composite is determined by subtracting the weight of the fabric in the absorbent
composite from the total weight of the absorbent composite. The weight of the fabric
in the absorbent composite was determined by multiplying 0.25 m2 by the density of
the fabric in the dry state before use (g/m2) which was measured in advance with the
114

A0501 VP32W/YA
assumption that area of the piece with a length of 50 cm which was cut out for this
measurement is 0.25 m2. The weight ratio of the resin in the absorbent composite is
given as a percentage and is obtained by dividing the weight of resin in the absorbent
composite as calculated by the aforementioned method by the total weight of the
absorbent composite.
[0204] (Example 43) (The water-absorbent resin particles containing more than
50 wt% water were used)
1 kg of the water-absorbent resin particles were placed in a 10 L Teflon
container, and 2 kg of water was added all at once with stirring vigorously. After
almost all of the water had been absorbed by the water-absorbent resin particles, it
was stop to be stirred. The operation was carried out in the same way as Example 40
except that these were used as the water-absorbent resin particles. The fabric
coming out from the machine 20 to 60 minutes after the initiation of operation was
used. This absorbent composite was divided into pieces with a length of 50 cm and
10 of these pieces were taken at random and the weight ratios of the resin were
measured. They varied greatly between 70 wt% and 90 wt%, showing that the
weight ratio of the resin was not steady. The weight ratio of the resin of the
absorbent composite was calculated by the same methods as in Example 42.
[0205] (Example 44) (The outer diameter of the dimples on the drum surface
of coating machine was larger than 3 times the average particle size of the water-
absorbent resin)
The operation was carried out in the same way as Example 40 except that
drums having surface dimples with an outer diameter of 4 mm were used as drums
(e1) and (e2). The fabric coming out from the machine 20 to 60 minutes after the
initiation of operation was used. This absorbent composite was divided into pieces
115

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with a length of 50 cm and 10 of these pieces were taken at random and the weight
ratios of the resin were measured. They varied greatly between 92 wt% and 75 wt%,
showing that the weight ratio of the resin was not steady. The weight ratio of the
resin of the absorbent composite was calculated by the same methods as in Example
42.
[0206] (Example 45) (The depth of the dimples on the drum surface of coating
machine was larger than 2 times the average particle size of the water-absorbent
resin)
The operation was carried out in the same way as Example 40 except that
drums having surface dimples with a depth of 4 mm rather than 0.8 mm were used as
drums (e1) and (e2). The fabric coming out from the machine 20 to 60 minutes after
the initiation of operation was used. This absorbent composite was divided into
pieces with a length of 50 cm and 10 of these pieces were taken at random and the
weight ratios of the resin were measured, they varied greatly between 92 wt% and 75
wt%, showing that the weight ratio of the resin was not steady. The weight ratio of
the resin of the absorbent composite was calculated by the same methods as in
Example 42.
[0207] (Example 46) (PET nonwoven fabric was used)
The coating machine was operated in the same way as Example 40 except
that PET nonwoven fabric was used as the fabric. The fabric coming out from the
machine 20 to 60 minutes after the initiation of operation was used. A piece with a
length of 50 cm was cut out from this absorbent composite and hanged on a bar at
about 1 m high and the bar was shaken up and down for 60 seconds at a rate of 15
cm/second with a shaking range of 30 cm. The weight ratio of the resin of the
absorbent composite was 30 wt% or less, and few resin particles adhered to the PET
116

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nonwoven fabric. The weight ratio of the resin of the absorbent composite was
calculated as in Example 42.
[0208] (Example 47) ( PP nonwoven fabric was used)
The coating machine was operated in the same way as Example 40 except
that PP nonwoven fabric was used as the fabric. The fabric coming out from the
machine 20 to 60 minutes after the initiation of operation was used. A piece with a
length of 50 cm length was cut out from this absorbent composite and hanged on a
bar fixed at about 1 m high and the bar was shaken 60 times at a rate of 30
cm/second with a shaking range of 30 cm. The weight ratio of the resin of the
absorbent composite was 30 wt% or less, and few resin particles adhered to the PP
nonwoven fabric. The weight ratio of the resin of the absorbent composite was
calculated as in Example 42.
[0209] (Example 48)
A piece with a length of 37 cm and with a width of 21cm was cut out from
Bennl'iese®. A piece with a length of 37 cm and with a width of 21cm was cut out from
Teflon® in the same way, and a line with a length of 35 cm and a width of 19 cm was
drawn on it. Another of the same was prepared. 6.6 g of the particles with a particle
size of 1000 to 1180 µm of Manufacturing 1 were used as the large particles and
scattered uniformly on the inside of the line on the sheet using a 1180 µm sieve.
Likewise, 6.65 g of the particles with a particle size of 212 to 300 µm of
Manufacturing 1 were used as the small particles and scattered uniformly using a
300 urn sieve. 6.7 g of the particles with a particle size of 1000 to 1180 µm were
scattered in the same way on another sheet. 8 g of water was applied with an
atomizer over the Bemliese®, then it was placed and pressed on the resin particles.
A further 2 g of water was then applied to the Bemliese®, and adhere the resin
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particles to the reverse surface. 3 g of water was sprayed on the Bemliese®, and it
was dried for 10 minutes at 180°C in an inert oven with the portion with no resin
being pressed with weights to prevent shrinkage of the Bemliese®.
A Munee Nobiru Fit® M size diaper from Unicharm Co., Ltd. was prepared, the
top sheet and back sheet were separated from by melting the hot melt adhesive with
the heat of dryer. A piece with a length of 33 cm and a width of 17 cm was cut out
from the manufactured absorbent composite and was sandwiched between the
sheets, and the edges of the top sheet and the back sheet that were not in contact
with the absorbent composite were adhered to each other with the non-corrosive
quick-drying adhesive seal material TSE397 from GE Toshiba Silicones Co., Ltd. to
give a bodily fluid-absorbing article of Example 48.
[0210] (Example 49)
The absorber of a Munee Nobiru Fit® M size diaper from Unicharm Co., Ltd.
was broken apart and the pulp and water-absorbent resin were simultaneously set in
a screened shaker. The pulp was collected with tweezers, as it aggregated. This
operation was repeated to completely separate the water-absorbent resin from the
pulp. An absorbent composite was prepared in the same way as Example 48, and
the 3 g of pulp was scattered thereon using a sieve. This was sandwiched between
the top sheet and the back sheet in the same way as Example 48 to give a bodily
fluid-absorbing article. The feeling of the article was improved by introducing a pulp
layer.
[0211] (Example 50)
A bodily fluid-absorbing article was prepared in the same way as Example 48
except that the particle size of the large particles was changed from 500 to 600 urn to
1000 to 1180 µm, and small particles were not used. This was used as Example 50.
118

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(Example 51)
A bodily fluid-absorbing article was prepared in the same way as Example 48
except that the particle size of the large particles was changed to 710 to 850 µm and
the used mount of the large particles was changed to 4.65 g per one side and the
particle size of the small particles was changed to 300 to 425 urn and the used mount
of the small particles was changed to 10 g. This was used as Example 51.
(Example 52)
A bodily fluid-absorbing article was prepared in the same way as Example 48
except that the resin of Manufacturing 3 was used. This was used as Example 52.
[0212] (Example 53)
A bodily fluid-absorbing article was prepared in the same way as Example 48
except that the absorbent composite and water-impermeable sheet were adhered to
each other with water-repellent hot melt adhesive ME117 from Japan NSC Co., Ltd.
as shown in Figure 22. This was used as Example 53. The adhesive was spread
vertically and horizontally on the absorbent composite as shown in Figure 22. The
absorbent composite was stable and did not shift in the article.
(Example 54)
A bodily fluid-absorbing article was prepared in the same way as Example 48
except that the resin particles with a particle size of 710 to 850 µm were used as the
large particles on both sides, 6.1 g per one side, and 4g of the resin particles with a
particle size of 212 to 300 urn were used as the small particles. This was used as
Example 54.
[0213] (Comparative Example 13)
119

A0501 VP32W/YA
A Unicharm Co. M-size Munee Nobiru Fit® diaper was used as Comparative
Example 13. The absorber, which was a mixture of pulp and water-absorbent resin,
was thick and had low absorption ability.
(Comparative Example 14)
An M-size Pampers Cotton Care® diaper from P&G Co., Ltd. was used as
Comparative Example 14. The absorber, which was a mixture of pulp and water
absorbent resin, was thick and had low absorption capability.
[0214] The physical properties of the bodily fluid-absorbing articles of Examples 48 to
54 and Comparative Examples 13 and 14 are shown in Table 7.
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Table 7

Absorbent
resin Absorbent composite Bodily fluid-absorbing article

Particle No. Weight
(g) Weight
ratio
(%) Adhesion
rate
(%) Absorption
capacity
(g/g) Absorption
capacity
After
1 min.
(g/g) Bending
resistance
(mm) Rewetting
(g) Liquid
dispersion
distance
(mm)








1st 2nd 3rd

Ex.48 1 16 90 100 55 15 70 0.4 8 18 280
Ex.50 1 12 87 100 53 15 80 0.3 9 19 260
Ex. 51 1 14 89 100 60 14 69 0.8 14 21 270
Ex.52 3 17 90 100 50 10 70 5 17 24 275
Ex 53 1 16 90 100 55 15 70 0.3 7 17 270
Ex.54 1 13 88 100 68 14 74 0.3 10 20 285
CE13 *d 28 - 0 21 7 - 12 40 51 210
CE14 *e 24 - 0 21 9 - 1.6 28 40 180
*d: Absorbent resin from absorber of Munee Nobiru Fit®
*e: Absorbent resin from absorber of Pampers Cotton Care®
121

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[0215] (Example 55)
A bodily fluid-absorbing article of Example 55 was prepared in the same way
as Example 48 except for the following changes.
Pieces with a length of 37 cm and a width of 25 cm were cut from the
Bemliese® and Teflon sheet. A line with a length of 35 cm and a width of 23 cm was
drawn on the Teflon sheet. 8.0 g and 8.1 g of large particles were dispersed on the
front surface and the back surface, respectively, and 8 g of small particles were
dispersed.
A piece with a length of 33 cm and a width of 21 cm was cut from the
manufactured composite, and inserted between the top sheet and the back sheet
with being folded as shown in Figure 23.
[0216] (Example 56)
A bodily fluid-absorbing article was prepared in the same way as Example 55
except that the particle size of the large particles was changed to 500 to 600 µm, and
no small particles were used. This was used as Example 56.
(Example 57)
A bodily fluid-absorbing article was prepared in the same way as Example 55
except that the water-repellent hot-melt adhesive ME117 from Japan NSC Co., Ltd.
was used as the adhesive.
[0217] The physical properties of the bodily fluid-absorbing articles of Examples 55 to
57 are shown in Table 8. This was used as Example 57.
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Table 8

Absorbent
resin Absorbent composite Bodily fluid-absorbing article

Particles
No. Weight
(g) Weight
ratio
(%) Adhesion
rate
(%) Absorption
capacity
(g/g) Absorption
capacity
after
1 min
(g/g) Rewetting
(g) Liquid
dispersion
distance
(mm) Wetting
drip volume
(ml) Wetting
coefficient







1st 2nd 3rd



Ex.55 1 20 90 100 55 15 0.2 6 16 300 160 5300
Ex.56 1 15 87 100 55 15 0.5 7 18 275 140 6000
Ex.57 1 20 90 100 55 15 0.2 6 15 310 165 5100
CE 13 *d 28 -- 0 21 7 12 40 51 210 42 800
CE 14 *e 24 -- 0 21 9 1.6 28 40 180 55 800
*d: Absorbent resin from absorber of Munee Nobiru Fit®
*e: Absorbent resin from absorber of Pampers Cotton Care®
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[0218] (Example 58)
A bodily fluid-absorbing article of Example 58 was prepared in the same way
as Example 48 except that the absorbent composite was adhered to the water-
permeable sheet and water-impermeable sheet in the pattern shown in Figure 24.
(Example 59)
A bodily fluid-absorbing article of Example 59 was prepared in the same way
as Example 58 except that the water-repellent hot-melt adhesive ME117 from Japan
NSC Co., Ltd. was used as the adhesive. (Example 60)
A bodily fluid-absorbing article of Example 60 was prepared in the same way
as Example 50 except that the absorbent composite was adhered to the water-
permeable sheet and water-impermeable sheet in the pattern shown in Figure 24.
[0219] The physical properties of the bodily fluid-absorbing articles of Examples 58 to
60 are shown in Table 9.
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Table 9

Absorbent
resin Absorbent composite Bodily fluid-absorbing article

Particles
No. Weight
(g) Weight
ratio
(%) Adhesion
rate
(%) Absorption
capacity
(g/g) Absorption
capacity
after
1 min
(g/g) Rewetting
(g) Liquid
dispersion
distance
(mm) Lengthwise
dispersion Distribution
area
(cm2)







1st 2nd 3rd



Ex.58 1 16 90 100 55 15 0.3 7 18 300 2.8 300
Ex. 59 1 16 90 100 55 15 0.2 7 16 310 3 360
Ex.60 1 12 87 100 53 15 0.5 8 19 275 2.7 270
CE 13 *d 28 -- 0 21 7 12 40 51 210 1.1 90
CE 14 *e 24 -- 0 21 9 1.6 28 40 180 1.1 80
*d: Absorbent resin from absorber of Munee Nobiru Fit®
*e: Absorbent resin from absorber of Pampers Cotton Care®
125

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DESCRIPTION OF THE DRAWINGS
[0220] Figure 1 is an explanatory diagram of a desirable manufacturing device for
manufacturing the absorbent composite of the present invention.
Figure 2 is an explanatory diagram of a measurement unit for measuring the
absorption capacity of an absorbent composite under pressure in the present invention.
Figure 3 shows an enlarged explanatory view of the measurement part 5 in
Figure 2.
Figure 4 shows examples of shapes of absorbent composites with the longer
directions.
Figure 5 shows an example of folding of an absorbent composite.
Figure 6 shows an example of folding of an absorbent composite.
Figure 7 shows an example of folding of an absorbent composite.
Figure 8 shows an example of folding of an absorbent composite.
Figure 9 shows an example of folding of an absorbent composite.
Figure 10 shows an example of folding of an absorbent composite.
Figure 11 shows an example of folding of an absorbent composite.
Figure 12 shows an example of folding of an absorbent composite.
Figure 13 shows an example of an adhesive application pattern.
Figure 14 is an explanatory diagram of a leakage evaluation test.
Figure 15 is an explanatory diagram of a leakage evaluation test.
Figure 16 is an electron microscope image showing adhesion with the fibers
penetrating the absorbent resin.
Figure 17 is an explanatory diagram of one example of a manufacturing device
for manufacturing the absorbent composite of the present invention.
126



A0501 VP32WYA
Figure 18 is a simplified diagram showing the arrangement of dimples on the
drum surface in the device of Figure 17.
Figure 19 is a simplified diagram showing the dimples on the drum surface in the
device of Figure 17 in the direction of depth.
Figure 20 is a simplified diagram showing the first drum in the device of Figure 17.
Figure 21 is a simplified diagram showing the second drum in the device of
Figure 17.
Figure 22 shows the pattern of adhesive on the bodily fluid-absorbing article of
Example 53.
Figure 23 is a simplified diagram of the structure of the bodily fluid-absorbing
article of Example 55.
Figure 24 is a simplified diagram of the structure of the bodily fluid-absorbing
article of Example 58.
127

A0501 VP32W YA
CLAIMS
We claim:
1. An absorbent composite comprising: a base material and water-absorbent
resin particles;
wherein the following conditions (1) to (4) are fulfilled:
(1) the weight ratio of water-absorbent resin relative to the total weight of the
base material and water-absorbent resin is 65 to 99 wt%,
(2) the water-absorbent resin particles adhering directly to the base material
constitute 50 wt% or more of the total water-absorbent resin particles;
(3) the average absorption capacity of the water-absorbent resin particles is
50 g/g or more; and
(4) the amount of residual monomers in the water-absorbent resin is 200 ppm
or less.

2. The absorbent composite according to Claim 1, wherein the resin area
occupancy rate of the water-absorbent resin particles in the particle size range of from
550 µm to 2100 µm is 1 to 30% on at least one side of the base material.
3. The absorbent composite according to Claim 1 or 2, wherein the total
surface area coefficient is 0.3 to 3.
4. The absorbent composite according to any of Claims 1 through 3, wherein
the salt concentration of the surface of the water-absorbent resin particles in the particle
size range of from 550 µm to 2100 µm after having been adhered to the base material is
at least 10 mol% lower than the salt concentration at the center of them.
5. The absorbent composite according to any of Claims 1 through 4, wherein
the surfaces of the water-absorbent resin particles in the particle size range of from 550
urn to 2100 µm are crosslinked.
128

A0501 VP32WYA
6. The absorbent composite according to any of Claims 1 through 5, wherein
the particle size distribution of the water-absorbent resin particles fulfills the following
conditions (1) and (2):
(1) particles that can pass through a sieve with a sieve opening of 300 µm
constitute 10 to 50 wt% of the total weight of water-absorbent resin; and
(2) Particles that cannot pass through a sieve with a sieve opening of 3000
urn constitute 10 wt% or less of the total weight of water-absorbent resin.

7. The absorbent composite according to any of Claims 1 through 6, wherein
the water-absorbent resin particles are amorphous resin particles manufactured by
aqueous solution polymerization followed by pulverization and/or resin particles
manufactured by reverse-phase suspension polymerization.
8. The absorbent composite according to any of Claims 1 through 7, wherein
the surface strength of the water-absorbent resin particles before being adhered to the
base material is 0.1 to 5.5 N.
9. The absorbent composite according to any of Claims 1 through 8, wherein
the absorption capacity under pressure of the water-absorbent resin particles is 20 g/g
or more.

10. The absorbent composite according to any of Claims 1 through 9, wherein
the water-absorbent resin constituting the water-absorbent resin particles is a resin
having carboxylic acid groups in the side chains, and 50% or more of the acid groups in
the water-absorbent resin before being adhered to the base material are neutralized in
the form of ammonium salts.
11. The absorbent composite according to any of Claims 1 through 10,
wherein the water-absorbent resin constituting the water-absorbent resin particles is a
copolymer consisting primarily of a polyacrylic acid salt.
129

A0501 VP32WYA
12. The absorbent composite according to any of Claims 1 through 11,
wherein the contact angle of the base material with an aqueous ammonium polyacrylate
solution with a solution viscosity of 74 cps is 130° or less.
13. The absorbent composite according to any of Claims 1 through 12,
wherein the tensile breaking strength of the base material after having absorbed saline
is 0.6 N/20 mm or more in either the lengthwise or the crosswise direction.
14. The absorbent composite according to any of Claims 1 through 13,
wherein the base material is fabric and/or paper.
15. The absorbent composite according to any of Claims 1 through 14,
wherein the base material fulfills the following conditions (1) and (2):

(1) the ratio between the tensile breaking elongation in the lengthwise
direction and that in the crosswise direction is 1:1.2 to 1:10; and
(2) the ratio between the tensile breaking strength in the lengthwise direction
and that in the crosswise direction is 1.2:1 to 10:1.

16. The absorbent composite according to any of Claims 1 through 15,
wherein the absorption capacity of the base material is 6 g/g or more.
17. The absorbent composite according to any of Claims 1 through 16,
wherein the absorption speed of the base material is 0.35 mg/second or more.
18. The absorbent composite according to any of Claims 1 through 17,
wherein the base material is paper and/or fabric consisting of cellulose fibers.
19. The absorbent composite according to Claim 18, wherein the base
material is cellulose non-woven fabric.
20. The absorbent composite according to any of Claims 1 through 19,
wherein the edges are folded and fixed.
130

A0501 VP32WYA
21. The absorbent composite according to any of Claims 1 through 20,
wherein an adhesive is applied linearly in the longer direction.
22. The absorbent composite according to Claim 21, wherein the adhesive is a
hot-melt adhesive.
23. A method for manufacturing an absorbent composite comprising a base
material and water-absorbent resin particles, comprising: making the base material
and/or the water-absorbent resin absorb water, followed by removing water from and
drying the base material and the water-absorbent resin while making them be in contact
with each other.
24. The method for manufacturing an absorbent composite according to Claim
23, comprising the following steps (1) to (3):

(1) making the water-absorbent resin particles and/or the base material
absorb water in the amount of 10 to 3000 wt% of the water-absorbent resin particles to
be adhered;
(2) making the base material be in contact with the water-absorbent resin
particles; and
(3) removing water from and drying the base material and the water-absorbent
resin particles.
25. The method for manufacturing an absorbent composite according to Claim
23 or 24, wherein drying is carried out under heat conditions at a heating temperature of
70 to 350°C with a treatment time of 1 to 1000 seconds.
26. The method for manufacturing an absorbent composite according to Claim
25, wherein the water-absorbent particles used are particles where the salt
concentration on the surface has been reduced by drying treatment with heating by 10%
or more compared to the value before treatment.
131

A0501VP32WYA
27. A device for manufacturing an absorbent composite comprising a base
material and water-absorbent resin particles, comprising: a base material feed part; a
rotating drum for adhering the resin particles to the base material; a part for supplying
the resin particles to the rotating drum; a drying part for removing water from the base
material with the resin particles adhered thereto; and a part for supplying a specific
amount of moisture to the base material and/or resin particles;
wherein the device has the following features (1) and (2):
(1) the rotating drum has multiple dimples on its surface, and
(2) each of the dimples has a ventilation hole at its bottom, through which a
gas can blow out from the inside of the rotating drum.
28. A method for manufacturing an absorbent composite using the
manufacturing device described in Claim 27 comprising: adhering the water-absorbent
resin particles to a base material followed by drying the water-absorbent resin particles
and the base material;
wherein the method fulfills the following conditions (1) to (5):
(1) the water content of the base material before spraying is 50 to 500 wt%;
(2) the water content of the water-absorbent resin particles before spraying is
1 to 50 wt%;
(3) the water-absorbent resin particles are adhered to the base material by
spraying the water-absorbent resin particles placed in advance in the dimples of the
rotating drum onto the base material while making the cloth-like base material be in
contact with the surface of the rotating drum;
(4) the outer diameter of the openings of the dimples on the surface of the
rotating drum is 1 to 3 times the maximum particle diameter of the water-absorbent resin
particles used; and
132

A0501 VP32W YA
(5) the depth of the dimples on the rotating drum is 0.3 to 2 times the average
particle size of the water-absorbent resin particles used.
133
29. A bodily fluid-absorbing article comprising a liquid-permeable sheet, a
liquid-impermeable sheet, and the absorbent composite according to any of Claims 1
through 22 between said two sheets.
30. The bodily fluid-absorbing article according to Claim 29, further comprising
pulp between the liquid-permeable sheet and the liquid-impermeable sheet.

An absorbent composite comprising: a base material and water-absorbent resin
particles; wherein the following conditions (1) to (4) are fulfilled: (1) the weight ratio of
water-absorbent resin relative to the total weight of the base material and water-
absorbent resin is 65 to 99 wt%, (2) the water-absorbent resin particles adhering
directly to the base material constitute 50 wt% or more of the total water-absorbent resin
particles; (3) the average absorption capacity of the water-absorbent resin particles is
50 g/g or more; and (4) the amount of residual monomers in the water-absorbent resin is
200 ppm or less.

Documents:

04326-kolnp-2007-abstract.pdf

04326-kolnp-2007-claims.pdf

04326-kolnp-2007-correspondence others.pdf

04326-kolnp-2007-description complete.pdf

04326-kolnp-2007-drawings.pdf

04326-kolnp-2007-form 1.pdf

04326-kolnp-2007-form 2.pdf

04326-kolnp-2007-form 3.pdf

04326-kolnp-2007-form 5.pdf

04326-kolnp-2007-gpa.pdf

04326-kolnp-2007-international search report.pdf

04326-kolnp-2007-pct priority document notification.pdf

04326-kolnp-2007-pct request form.pdf

04326-kolnp-2007-translated copy of priority document.pdf

4326-KOLNP-2007-(20-08-2014)-ABSTRACT.pdf

4326-KOLNP-2007-(20-08-2014)-CLAIMS.pdf

4326-KOLNP-2007-(20-08-2014)-CORRESPONDENCE.pdf

4326-KOLNP-2007-(20-08-2014)-DESCRIPTION (COMPLETE).pdf

4326-KOLNP-2007-(20-08-2014)-DRAWINGS.pdf

4326-KOLNP-2007-(20-08-2014)-FORM-1.pdf

4326-KOLNP-2007-(20-08-2014)-FORM-2.pdf

4326-KOLNP-2007-(20-08-2014)-OTHERS.pdf

4326-KOLNP-2007-(20-08-2014)-PETITION UNDER RULE-137.pdf

4326-KOLNP-2007-(24-12-2012)-CORRESPONDENCE.pdf

4326-KOLNP-2007-(24-12-2012)-FORM 3.pdf

4326-KOLNP-2007-(29-11-2012)-ANNEXURE TO FORM 3.pdf

4326-KOLNP-2007-(29-11-2012)-CORRESPONDENCE.pdf

4326-KOLNP-2007-CORRESPONDENCE OTHERS 1.1.pdf

4326-KOLNP-2007-CORRESPONDENCE OTHERS 1.2.pdf

4326-kolnp-2007-form 18.pdf

4326-KOLNP-2007-OTHERS.pdf

4326-KOLNP-2007-PRIORITY DOCUMENT.pdf

abstract-04326-kolnp-2007.jpg


Patent Number 265064
Indian Patent Application Number 4326/KOLNP/2007
PG Journal Number 06/2015
Publication Date 06-Feb-2015
Grant Date 04-Feb-2015
Date of Filing 13-Nov-2007
Name of Patentee ASAHI KASEI CHEMICALS CORPORATION
Applicant Address 1-2, YURAKU-CHO 1-CHOME, CHIYODA-KU, TOKYO
Inventors:
# Inventor's Name Inventor's Address
1 TAMOTSU KODAMA 1-2, YURAKU-CHO, 1-CHOME, CHIYODA-KU, TOKYO 100-8440
2 TSUTOMU AKIYAMA 1-2, YURAKU-CHO, 1-CHOME, CHIYODA-KU, TOKYO 100-8440
3 MASATAKA NISHI 1-2, YURAKU-CHO, 1-CHOME, CHIYODA-KU, TOKYO 100-8440
4 HIROSHIGE OKAMOTO 1-2, YURAKU-CHO, 1-CHOME, CHIYODA-KU, TOKYO 100-8440
PCT International Classification Number B32B 7/04,A61F 13/49
PCT International Application Number PCT/JP2006/309536
PCT International Filing date 2006-05-12
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2005-144837 2005-05-18 Japan
2 2005-279976 2005-09-27 Japan
3 2005-141371 2005-05-13 Japan