Indian Patents
Title of Invention

AN AQUARIUM
Abstract The present invention provides a liquid tank, a viewing device for under-liquid observation, and an optical film, each excellent in visibility and durability and being easy to clean. The present invention is a liquid tank having a transparent wall, including, on an internal surface of the wall, a first moth-eye layer having a moth-eye structure, and a protective layer covering the moth-eye structure, in this order from the wall side, and preferably, further including, on an external surface of the wall, a second moth-eye layer having a moth-eye structure, and the second moth-eye layer being disposed in a region facing the first moth-eye layer.
Full Text

DESCRIPTION
LIQUID TANK, VIEWING DEVICE FOR UNDER-LIQUID OBSERVATION, AND
OPTICAL FILM
TECHNICAL FIELD
[0001]
The present invention relates to liquid tanks, viewing
devices for under-liquid observation, and optical films. More
particularly, the present invention relates to: a liquid tank
such as an aquarium tank and a tank with a liquid volume meter,
suitably used as a container the inside of which is viewed through
a transparent wall; a viewing device for under-liquid observation
suitably used as a viewing device for underwater observation;
and an optical film for the liquid tank or the viewing device.
BACKGROUND ART
[0002]
The liquid tank includes an aquarium or observation
container, and particularly tanks for raising and breeding fishes
and the like thereinside are common. Such tanks are usually
composed of a transparent material. In an aquarium tank
containing water 21 as shewn in Fig. 9, for example, ambient
light is reflected on the external and internal (outer and inner
surfaces) of an observer-side transparent plate (the transparent
wall 11) , and this makes it difficult for the observer to clearly
view the inside of the tank and also to photograph it clearly
because strobe 1 ight is reflected. With a view to clearly observe
aquarium or food fishes raised or bred in the tank from the outside,
modifications and improvements have been made not only for the
tank itself such as a viewing window and a transparent wall but
for maintenance tools installed on the tank, including an air
pump and a cleaning tool.
[0003]
For example, as a way of more clearly viewing underwater

objects, it is commonly known that an anti-reflection thin film
is coated on the external surface of a glass or acrylic resin
transparent wall constituting a tank, or alternatively, an
anti-reflection film is attached to it, thereby preventing
reflection of ambient light on the external surface of the wall
(hereinafter, also referred to as "external
surface-reflection").
[0004]
With regard to a technology for preventing reflection on
an interface between a content of the tank and the internal surface
(the interior of the tank) of the wall (hereinafter, also referred
to as "internal surface-reflection") in addition to the external
surface-reflection, for example, Patent Document 1 discloses
that at least an observer-side one of the transparent walls
constituting the tank has an anti-reflection function on its
both surface.
[0005]
Examples of the liquid tank also include a tank equipped
with a window (viewing window) used as a liquid volume meter
and through which objects present in the liquid can be viewed.
Also in such a tank, reflection on the external and internal
surfaces of the viewing window occurs in the matter of the
above-described tank, so that an observer has a difficulty in
accurately measuring the volume of the liquid.
[0006]
In the tank inside which fishes are raised and bred, there
is required to minimize or completely prevent adhesion of algae
to the wall surface, thereby maintaining the wall surface clean
and keeping the fishes in captivity healthy. As a technology
of achieving it, for example, Patent Document 2 discloses a film
for lining a water tank, provided with a tacky layer having the
transparency and water resistance on one surface of a transparent
resin film, further a release sheet or a sheet of paper on the
surface thereof and a peeling off means for peeling at least
one end of the release sheet or paper.

[0007]
Similarly in the liquid tanks, the clear under-liquid
observation is difficult also in viewing devices for under-liquid
observation, including goggles andaquascopes. In goggles, for
example, reflection on a lens surface might occur.
[0008]
As a technology of preventing such surface reflection,
a "moth-eye structure", a kind of nanostructure, is known in
the field of optical materials. The moth-eye structure includes
a great number of nanometer-sized conical protrusions formed
on a transparent substrate surface, for example. As disclosed
in Patent Documents 3 to 6, the moth-eye structure allows
continuous change of the refractive index from air to the
transparent substrate, so that incident light does not recognize
the interface as an optical surface, and as a result, reflection
of the light can be significantly decreased.
[0009]
[Patent Document 1]
Japanese Kokai Publication No. 2003-319733
[Patent Document 1]
Japanese Kokai Publication No. Hei-09-322 674
[Patent Document 1]
Japanese Kokai Publication No. 2003-43203
[Patent Document 1]
Japanese Kokai Publication No. 2005-156695
[Patent Document 1]
WO 2006/059686
[Patent Document 1]
Japanese Kokai Publication No. 2001-264520
DISCLOSURE OF INVENTION
[0010]
When optical films having a surface with a nanostructure
such as a moth-eye structure are used under water or another
liquid of the tank, under-liquid life such as microorganism and

algae tend to adhere to the film surface. This might look like
stains and deteriorate the appearance, and further lead to a
reduction in transmittance. For example, when a moth-eye
structure 16 is used, a stain 31 such as underwater life is fixed
to the features (the moth-eye structure 16) as illustrated in
Fig. 10, and this stain is very difficult to remove, for example,
even by washing with a cloth and the like because a fiber 32
of the cloth is generally much larger than the structure 16.
Also in a viewing window-including tank or a viewing device each
including the optical film, stains are easy to adhere to the
film but it is difficult to remove them therefrom. When the
technology disclosed in Patent Document 2 is employed as a measure
against this stain, the release sheet or the sheet of paper for
preventing this stain is disposed on the moth-eye structure,
so that the anti-reflection function derived from the moth-eye
structure can not be exhibited. Further, ambient light is
reflected on the interface between media with different
refractive indexes, i.e., water and the release sheet or the
paper, and the viewing is significantly deteriorated as a result.
Thus in the use of the nanostructure such as a moth-eye structure
for the purpose of preventing the surface reflection on an
aquarium or observation container, the film with the
nanostructure is required to prevent the surface reflection and
further suppress the stains that are generated due to the content
of the container and to allow easy removal of the stains. Also
in the use of the nanostructure such as a moth-eye structure
for anti-surface reflection of the viewing device, the film with
the nanostructure is required to prevent the surface reflection
and further suppress the stains from adhering to a transparent
window of the viewing device and to allow easy removal of the
stains.
[0011]
The technology of Patent Document 1 does not suffer from
such a problem relating to the stains peculiar to the
nanostructure because instead of the nanostructure, the

multi-layer anti-reflection film is used. However, this
multi-layer structure leads to poor wavelength dispersion
characteristic of the anti-reflection film to cause coloring
of reflected light. Further, unlike the film with the moth-eye
structure, the multilayer anti-reflection film can not decrease
the reflectance to such a level that almost no surface reflection
occurs. When disposed on the internal surface of a transparent
wall or the external surface of a transparent window, for example,
the multi-layer anti-reflection film is readily damaged by hit
of fishes to the wall or window. That is, the multi-layer
anti-reflection film usually has poor durability. As mentioned
above, in the use of the multi-layer anti-reflection film for
the purpose of anti-surface reflection, the film is required
to provide further improved visibility by suppressing the
coloring and reducing the reflectance and to show enhanced
durability. The multi-layer anti-reflection film is an
expensive material and requires complicated production steps,
and therefore it might be lack in versatility.
[0012]
The present invention is devised considering the
aforementioned situations. An object of the present invention
is to provide a liquid tank, a viewing device for under-liquid
observation, and an optical film, each excellent in visibility
and durability and being easy to clean.
[0013]
The present inventors made various investigations on a
liquid tank excellent in visibility and durability and easy to
clean, and noted a moth-eye structure. The inventors found that
the following effects can be achieved when not only the moth-eye
structure but also a protective layer covering it are disposed
on the internal surface of a transparent wall constituting the
tank. First, the surface reflection, especially the internal
surface-reflection, can be markedly decreased while the coloring
is suppressed. Secondly, the durability on the internal surface
of the tank is improved. Finally, the internal surface of the

tank can be readily cleaned. Thus, the present inventors have
found the solution of the aforementioned problems and arrived
at the present invention,
[0014]
The present invention is a liquid tank: having a transparent
wall, including, on an internal surface of the wall,
a first moth-eye layer having a moth-eye structure,
and
a protective layer covering the moth-eye structure, in
this order from the wall side. This liquid tank is excellent
in visibility and durability and easy to clean. Further, the
liquid tank can be produced at a much lower cost than in use
of other anti-reflection films such as a multi-layer
anti-reflection film.
[0015]
The liquid tank of the present invention may or may not
include other components as long as it essentially includes the
above-mentioned components, and the configuration thereof is
not especially limited.
The following will mention preferable embodiments of the
liquid tank of the present invention in detail. The following
embodiments may be appropriately employed in combination.
[0016]
With a view to significantly decrease the external
surface-reflection and further improve the visibility, it is
preferable that the liquid tank further includes, on an external
surface of the wall, a second moth-eye layer having a moth-eye
structure, and the second moth-eye layer being disposed in a
region facing the first moth-eye layer.
[0017]
For further improvement in durability, it is preferable
that the protective layer contains a fluorine-containing resin.
The fluorine-containing resin generally has a refractive index
of about 1. 3 to 1. 4, so that the refractive index of the protective
layer containing such a resin can be readily made substantially

equivalent to that of water. That is, according to this, the
liquid tank of the present invention can be suitably used as
a water tank.
[0013]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of a liquid to be stored
in the tank. According to this, the effects of the present
invention can be more surely exhibited.
[0019]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of water. According to
this, the liquid tank of the present invention can be suitably
used as a water tank.
[0020]
It is preferable that the protective layer has a refractive
index smaller than that of each of the transparent wall and the
first moth-eye layer. According to this, the transparent wall
and the first moth-eye layer can be composed of the respective
appropriate materials, and the refractive index of a liquid to
be stored in the tank can be readily made substantially equivalent
to that of the protective layer.
r002l]
It is preferable that the protective layer has a refractive
index of 1.28 to 1.38. According to this, the liquid tank of
the present invention can be suitably used as a water tank.
[0022]
The present invention is also an optical film attached
to an internal surface of a liquid tank having a transparent
wall, the film including a moth-eye layer having a moth-eye
structure and a protective layer covering the moth-eye structure
(hereinafter, also referred to as a "first optical film of the
present invention"} . The liquid tank of the present invention
can be easily and inexpensively provided by attaching the first
optical film of the present invention to the internal surface
of the transparent wall.

[0023]
The first optical film may or may not include other
components as long as it essentially includes the above-mentioned
components, and the ccnfiguraticn thereof is not especially
limited.
The following will mention preferable embodiments of the
first optical film of the present invention. The following
embodiments may be appropriately employed in combination.
[0024]
For further improvement in durability, it is preferable
that the protective layer contains a fluorine-containing resin.
The fluorine-containing resin generally has a refractive index
of about 1. 3 to 1.4, so that the refractive index of the protective
layer containing such a resin can be easily made substantially
equivalent to of water. That is, according to this, the liquid
tank including the first optical film of the present invention
attached thereto can be suitably used as a water tank.
[0025]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of a liquid to be stored
in the tank. According to this, the effects of the present
invention can be more surely exhibited.
[0026]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of water. According to
this, the liquid tank including the first optical film of the
present invention attached thereto can be suitably used as a
water tank.
[0027]
It is preferable that the protective layer has a refractive
index smaller than that each of the transparent wall and the
moth-eye layer. According to this, the transparent wall and
the moth-eye layer can be composed of the respective appropriate
materials, and the refractive index of a liquid to be stored
in the tank including the first optical film of the present

invention can be readily made substantially equivalent to that
of the protective layer.
[0028]
It is preferable that the protective layer has a refractive
index of 1.28 to 1.38. According to this, the liquid tank
including the first optical film of the present invention
attached thereto can be suitably used as a water tank.
[0029]
The present invention is also a viewing device having a
transparent window for under-liquid observation,
the device including, on an outer surface of the window,
a first moth-eye layer having a moth-eye structure, and
a protective layer covering the moth-eye structure, in this order
from the window side. This viewing device is excellent in
visibility and durability and easy to clean. Further, the
viewing device including such layers can be produced at a much
lower cost than in use of other anti-reflection films such as
a multi-layer anti-reflection film.
[0030]
The viewing device of the present invention may or may
not include other components as long as it essentially includes
the above-mentioned components, and the configuration thereof
is not especially limited.
The following will mention preferable embodiments of the
viewing device of the present invention. The following
embodiments may be appropriately employed in combination.
[0031]
With a view to markedly decrease reflection of ambient
light on the internal surface of the transparent window to further
improve the visibility, it is preferable that the viewing device
further includes, on an inner surface of the window, a second
moth-eye layer having a moth-eye structure, and
the second moth-eye layer being disposed in a region facing
the first moth-eye layer.
[0032]

For further improvement in durability, it is preferable
that the protective layer contains a fluorine-containing resin.
The fluorine-containing resin generally has a refractive index
of about 1. 3 to 1. 4, so that the refractive index of the protective
layer containing such a resin can be easily made substantially
equivalent to that of water. That is, according to this, the
viewing device of the present invention can be suitably used
as a device for underwater observation.
[0033]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of a liquid to be in contact
with the device. According to this, the effects of the present
invention can be more surely exhibited.
[0034]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of water. According to
this, the viewing device of the present invention can be suitably
used as a device for underwater observation.
[0035]
It is preferable that the protective layer has a refractive
index smaller than that of each of the transparent window and
the first moth-eye layer. According to this, the transparent
window and the first moth-eye layer can be composed of the
respective appropriate materials, and the refractive index of
a liquid to be in contact with the device can be readily made
substantially equivalent to that of the protective layer.
[0036]
It is preferable that the protective layer has a refractive
index of 1.28 to 1.38. According to this, the viewing device
of the present invention can be suitably used as a device for
underwater observation.
[0037]
The present invention is also an optical film attached
to an outer surface of a viewing device having a transparent
window for under-liquid observation,

the film including a moth-eye layer having a moth-eye
structure and a protective layer covering the moth-eye structure
(hereinafter, also referred to as a "second optical film of the
present invention"). The viewing device of the present
invention can be readily and inexpensively provided by attaching
the second optical film of the present invention to the external
surface of the window.
[0038]
The second optical film of the present invention may or
may not include other components as long as it includes the
above-mentioned components, and the configuration thereof is
not especially limited.
The following will mention preferable embodiments of the
second optical film of the present invention. The following
embodiments may be appropriately employed in combination.
[0039]
For further improvement in durability, it is preferable
that the protective layer contains a fluorine-containing resin.
The fluorine-containing resin generally has a refractive index
of about 1. 3 to 1. 4, so that the refractive index of the protective
layer containing such a resin can be easily made substantially
equivalent to that of water. That is, according to this, the
viewing device including the second optical film of the present
invention attached thereto can be suitably used as a device for
underwater observation.
[0040]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of a liquid to be in contact
with the device. According to this, the effects of the present
invention can be more surely exhibited.
[0041]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of water. According to
this, the viewing device including the second optical film of
the present invention attached thereto can be suitably used as

a device for underwater observation.
It is preferable that the protective layer has a refractive
index smaller than that of each of the transparent window and
the moth-eye layer. According to this, the transparent window
and the moth-eye layer can be composed of the respective optimum
materials, and the refractive index of a liquid to be in contact
with the viewing device including the second optical film of
the present invention can be readily made substantially
equivalent to that of the protective layer.
[0043]
It is preferable that the protective layer has a refractive
index of 1.28 to 1.38. According to this, the viewing device
including the second optical film of the present invention
attached thereto can be suitably used as a device for underwater
observation.
EFFECT OF THE INVENTION
[0044]
The liquid tank and the first optical film of the present
invention can provide a liquid tank excellent in visibility and
durability and easy to clean. More specifically, the use of
the liquid tank and the first optical film of the present invention
allows a marked decrease in coloring and an improvement in
durability of the internal surface of the liquid tank, and further
allows easily cleaning the internal surface of the tank. Further,
the refractive index of the protective layer can be easily made
substantially equivalent to that of a liquid to be stored in
the tank. As a result, the reflection on the surfaces,
particularly on the internal surface of the tank can be markedly
decreased. Inaddition, the protective layer andair are usually
different in refractive index, so that the liquid level in the
tank can be readily determined by being viewed from the outside
through the transparent wall.
[0045]

The viewing device and the second optical film of the
present invention can provide a viewing device for under-liquid
observation excellent in visibility and durability and easy to
clean. More specifically, the use of the viewing device and
the second optical film of the present invention allows a marked
decrease in coloring and an improvement in durability of the
external surface of the viewing device, and further allows easily
cleaning the external surface of the device. Further, the
refractive index of the protective layer can be easily made
substantially equivalent to that of a liquid to be in contact
with the device. As a result, the reflection of ambient light
on the surfaces, particularly on the external surface, of the
device can be markedly decreased.
BRIEF DESCRIPTION OF DRAWINGS
[0046]
[Fig. 1]
Fig. 1 is a schematic view showing a liquid tank of Example
1. Fig. 1(a) is an overall cross-sectional view of the tank.
Fig. 1(b) is an enlarged view of a region (side surface) surrounded
by the broken line of Fig. 1(a).
[Fig. 2]
Fig. 2 is a cross-sectional view schematically showing
a moth-eye layer of the liquid tank of Example 1.
[Fig. 3]
Fig. 3 is a cross-sectional view schematically showing
the moth-eye layer and a protective layer in the liquid tank
of Example 1.
[Fig. 4]
Fig. 4 is an explanation view of refractive index change
in the liquid tank of Example 1. Fig. 4(a) is a side
cross-sectional view of the tank. Fig. 4 (b) is a graph showing
refractive index change on a side surface of the tank.
[Fig. 5]
Fig. 5 is a schematic view showing the liquid tank of Example

2. Fig. 5(a) is an overall cross-sectional view of the tank.
Fig. 5(b) is an enlarged viewof a region (side surface) surrounded
by the broken line of Fig. 5(a).
[Fig. 6]
Fig. 6 is a perspective view schematically showing a liquid
tank of Example 3.
[Fig. 7]
Fig. 7 is an explanation view of refractive index change
in the liquid tank of Example 3. Fig. 7 (a) is a cross-sectional
view of a liquid volume meter portion of the tank. Fig. 7(b)
is a graph showing refractive index change in the liquid volume
meter portion.
[Fig. 8]
Fig. 8 is an explanation view of a moth-eye structure (the
view for explaining the principle of continuous refractive index
change from the surface and the marked reflection decrease on
the interface). Fig. 8(a) is a schematic view showing a
cross-section of the moth-eye structure. Fig. 8(b) shows
refractive index change in the structure.
[Fig. 9]
Fig. 9 is a cross-sectional view schematically showing
a conventional aquarium tank.
[Fig. 10]
Fig. 10 is a cross-sectional view schematically showing
a state where a stain has adhered to a conventional moth-eye
structure.
[Fig. 11]
Fig. 11 is a cross-sectional view schematically showing
a viewing device for under-liquid observation of Example 4.
[Fig. 12]
Fig. 12 is an explanation view of refractive index change
in the viewing device of Example 4. Fig. 12(a) is a
cross-sectional viewof thedevice. Fig. 12(b) is a graph showing
refractive index change in the device.
[Fig. 13]

Fig. 13 is a cross-sectional view schematically showing
the device of Example 4 in accordance with a modified example.
[Fig. 14]
Fig. 14 is a cress-sectional view schematically showing
the device of Example 4 in accordance with another modified
example.
[Fig. 15]
Fig. 15 is a cross-sectional view schematically showing
a viewing device for under-liquid observation of Example 5.
[Fig. 16]
Fig. 16 is an explanation view of refractive index change
in the device of Example 5. Fig. 16(a) is a cross-sectional
view of the device. Fig. 16(b) is a graph showing refractive
index change in the device.
BEST MODES FOR CARRYING OUT THE INVENTION
[0047]
The present invention will be explained in more detail
below on the basis of Embodiments, with reference to accompanying
drawings. The present invention, however, is not limited to
these Embodiments.
[0048]
In the present description, when one member has a
refractive index substantially equivalent to that of another
member, the refractive indices thereof is not necessarily
completely the same and may be substantially the same to such
a degree that the effects of the present invention are exhibited.
[0049]
In the present description, the refractive index is
expressed as a value measured at a wavelength of 589 nm (D ray)
at a room temperature (25°C).
[0050]
Embodiment 1
The liquid tank of Embodiment 1 has a transparent wall,
and on the internal surface of the wall, a first moth-eye layer

having a moth-eye structure and a protective layer covering the
moth-eye structure are disposed in this order from the wall side.
[0051]
Inside the tank of the present Embodiment, a material
containing at least a liquid is stored. An observer views the
content of the tank, such as under-liquid objects (e.g., living
creatures) , the liquid level, the liquid itself from the outside
through the transparent wall. Thus, the tank of the present
Embodiment is suitably used as an aquarium or observation tank,
including a water tank and a tank with a viewing window.
[0052]
According to the tank of the present Embodiment, the first
moth-eye layer having a moth-eye structure allows markedly
reducing light reflection on the interface between the first
moth-eye layer and the protective layer (e.g., a reflectance
of 0.1 % or lower). The transparent wall and the liquid
(hereinafter, also referred to as a "content liquid") to be stored
in the tank are usually different in refractive index. The
material for the first moth-eye layer can be appropriately
selected from those having a refractive index substantially
equivalent to that of the transparent wall. The material for
the protective layer can be appropriately selected from those
having a refractive index substantially equivalent to that of
the content liquid. Specifically, the first moth-eye layer
ensures the refractive index compatibility with the transparent
wall, and the protective layer ensures that with the content
liquid. As a result, the refractive index can be continuously
changed from the content liquid to the transparent wall, so that
the internal-surface reflection in a region below the liquid
level can be markedly decreased (e.g., a reflectance of 0.1%
or lower).
[0053]
Patent Document 6 discloses a reflection preventing film
that includes a transparent layer composed of hardened matter
of an ionizing radiation-setting resin composition. On one

surface of the transparent layer, a structure provided with a
projecting and recessing part on which count less fine project ions
and recessions are formed with a pitch shorter than the wavelength
of light. Further, a layer (coating layer 4) composed of a resin
composition and having a refractive index lower than that of
the transparent layer is laminated on the fine projections and
recessions. It is also disclosed that the material with a
refractive index of 1.3 to 1.4 is used for the surface layer
4. However, reflection of about 2% occurs on the interface
between air (refractive index of 1) and this surface layer 4
(refractive index of 1,35}. for example, when the layer 4 has
a refractive index of 1.35. Thus, this anti-reflection film
is poor in the effect of reducing unnecessary reflection.
[0054]
The anti-reflection mechanism derived from the moth-eye
structure excludes A/4 conditions unlike in the use of the
multi-layer anti-reflection film, and therefore coloring can
be almost completely prevented.
[0055]
The liquid tank includes the protective layer covering
the moth-eye structure in addition to the first moth-eye layer,
and materials excellent in durability can be appropriately
determined as a material for the protective layer. Accordingly,
the durability of the internal surface of the tank can be improved.
[0056]
Since the moth-eye structure is covered by the protective
layer, adherence of stains to the moth-eye structure, from which
the stains are difficult to remove, can be prevented. The shape
of a portion to be in contact with the content liquid (surface
shape) of the protective layer is not especially limited, and
therefore the surface can be formed to be more flat than the
moth-eye structure. Even when adhered to the protective layer,
the stains can be readily removed therefrom.
[0057]
The refractive index of the protective layer, which is

substantially equal to that of the content liquid, is usually
different from that of air. In the region below the content
liquid level, the reflective indices of the respective members
are made substantially equal to each other. In the region above
the level (generally the region exposed to air) , the refractive
indices of the respective members are not matched and as a result
of this, the internal surface-reflection occurs . Based on this
difference in occurrence of the internal-surface reflection
between the regions below and above the content liquid, the
position (level) of the content liquid can be readily determined
by being viewed from the outside through the transparent wall.
[0058]
The moth-eye structure of the present invention can be
formed, for example, by coating a UV-curable resin on a base
film or a mold surface, pressing the film against the mold, and
curing the resin coating by UV radiation through the base film.
This allows producing the liquid tank dramatically inexpensively
in comparison to use of other anti-reflection films such as a
multi-layer film (multi-layer anti-reflection film) requiring
expensive processes involving two or more coating processes,
deposition processes, and the like.
[0059]
It is preferable that the liquid tank includes, on the
external surface of the transparent wall, a secondmoth-eye layer
having a moth-eye structure, and the second moth-eye layer is
disposed in a region facing the f irst moth-eye layer. This second
moth-eye layer allows markedly reducing the external
surface-reflection (e.g., a reflectance of 0.1% or lower) . As
a result of this, the reflection on the region where the first
and secondmoth-eye layers overlap with each other can be further
decreased. The first and second moth-eye layers are disposed
so as to overlap with each other in the viewing direction.
Between the first and secondmoth-eye layers, the shape, size,
and location thereof may be the same or different but preferably
the same.

[0060]
The location of the first and second moth-eye layers and
the protective layer is not especially limited as long as they
can be viewed from an observer. Examples thereof include a side
surface, an upper surface, and a bottom surface of the tank.
The first and second moth-eye layers and the protective layer
may be formed over the entire or part of the transparent wall,
but preferably formed on at least part through which the observer
views the content of the tank. Specifically, when the liquid
tank of the present Embodiment is used in an application where
the viewing direction is predetermined, the first and second
moth-eye layers and the protective layer may be disposed only
on the transparent wall facing the observer, not on all the walls .
[0061]
The moth-eye structure is not especially limited as long
as it includes a large number of nanometer-sized protrusions.
Specifically, the moth-eye structure includes, but is not
especially limited to, a large number of protrusions each having
a height (depth) of 1 nm or larger and smaller than 1 µm ( = 1000
nm) . More specifically, the moth-eye structure preferably
includes protrusions whose pitch (a distance between tops of
adjacent ones of the protrusions) and height are each smaller
than a visible light wavelength (380 nm to 780 nm), and more
preferably includes substantially conical protrusions each of
which has a pitch of 50 nm to 300 nm and a height of 50 nm to
300 nm. The thickness of each of the first and second moth-eye
layers is generally, but not limited to, about 1 µm to 30 µm.
[0062]
This surface structure is typically called "moth-eye
structure" and a film with this structure is known as an ultra-low
reflection film allowing a reflectance of 0.1% or lower for
visible light, for example. Fig. 8 is an explanation view of
a moth-eye structure (the view for explaining the principle of
continuous refractive index change from the surface and the
marked reflection decrease on the interface). Fig. 8(a) is a

schematic view showing a cross-sect ion of the moth-eye structure.
Fig. 8 (b) shows refractive index change in the moth-eye structure.
Fig. 8 shows the case where the moth-eye structure is exposed
to air. The moth-eye structure-including film typically has
protrusions 19 smaller than a visible light wavelength (380 run
to 780 nm) as shown in Fig. 8(a), and as shown in Fig. 8(b),
the interface refractive index can be regarded to gradually and
continuously increase from the refractive index of the medium
(air) on the film surface (refractive index of air is 1.0) to
a value equivalent to the refractive index of a material
constituting the film (for example, a refractive index of a resin
is ordinarily about 1.5). As a result, no refractive index
interface substantially exists, and the reflectance on the
interface is significantly decreased.
[0063]
The moth-eye structure can be formed by nanoimprint,
including UV nanoimprint and thermal imprinting. Particularly
preferably, an aluminum substrate with nanometer-sized cavities
formed on its surface by anodization is used as a mold. More
specifically, the mold with nanometer-sized cavities can be
prepared by cut-polishing an outer circumference surface of a
conical or cylindrical aluminum tube formed by extruding, and
alternately repeating, for example, three times, anodization
and etching for the cut-polished aluminum surface (outer
circumference surface). According to this method involving
anodizing, nanometer-sized recesses can be formed in a random
placement and in a uniform distribution, and seamless
nanostructures needed for continuous production can be formed
on a columnar or cylindrical mold roller surface. Accordingly,
the seamless nanostructures can be continuously transferred to
a workpiece (for example, a UV-curable or thermocurable resin
film).
[0064]
The materials for the first and second moth-eye layers
are not especially limited. It is preferable that the refractive

index of each of the first and second moth-eye layers is
substantially equivalent to that of the transparent wall. More
specifically, the difference in refractive index between the
transparent wall and the first and second moth-eye layers is
preferably 0.05 (more preferably 0.03) or smaller, and in this
case, the reflection on the both interfaces can be hardly
recognized,
[0065]
The other optical characteristics of the first and second
moth-eye layers are not especially limited and may be the same
as those of common moth- eye films . The first and second moth-eye
layers are preferably transparent to such a degree that an
observer can view the content of the tank. More specifically,
it is preferable that: the light transmittance is 90% (more
preferably 95%) or higher; the haze is preferably 10% (more
preferably 1%) or lower; the refractive index is 1.45 to 1.55
(more preferably 1.47 to 1.53).
[0066]
In view of readily preparing the first and second moth-eye
layers by the above-mentioned nanoimprint, resins that can be
cured by energy beams, e.g., electromagnetic waves such as UV
light and visible light or thermocurable resins are preferably
used as the material for the first and second moth-eye layers.
[0067]
Each of the first and second moth-eye layers may be (1)
formed on the transparent wall with a base film therebetween
or may be (2) directly formed on the transparent wall.
[0068]
According to the embodiment (1), an optical film including
the moth-eye structure-containing layer and the protective layer
covering the moth-eye structure; and an optical film having a
moth-eye structure-including layer can be preferably used.
Specifically, mass-produced films formed by nanoimprint can be
used, which allows an improvement in productivity of the liquid
tank of the present Embodiment.

[0069]
Another Embodiment of the present invention provides such
an optical film. The present Embodiment provides an optical
film (film for the tank internal surface) attached to the internal
surface of the liquid tank of Embodiment 1, i.e., the liquid
tank having a transparent wall, the optical film including a
moth-eye layer having a moth-eye structure (the above-mentioned
first moth-eye layer) and a protective layer covering the
moth-eye structure (the moth-eye structure of the
above-mentioned first moth-eye layer).

[0070]
The base film is a base for supporting a material (for
example, a UV-curable or thermocurable resin) for the (first
and/or second) moth-eye layer during the production steps. It
is preferable that the base film has transparency, and
resistances to water and solvent (liquid). The base film
preferably has a refractive index substantially equivalent to
that of each of the first and second moth-eye layers and the
transparent wall. More specifically, the difference in
refractive index among them is preferably 0.05 or smaller (more
preferably 0.03 or smaller), and in this case, the reflection
on the both interfaces can be hardly recognized. From the same
viewpoint, the difference in refractive index between adjacent
ones of these members is preferably 0.05 or smaller (more
preferably 0.03 or smaller).
[0071]
The other optical characteristics of the base film are
not especially limited and may be the same as those of a base
for common optical films. The base film is preferably
transparent to such a degree that an observer can recognize the
contents of the tank. More specifically, it is preferable that
the base film has a light transmittance of 90% (more preferably
95%) or higher, a haze of 10% (preferably 1%) or lower, and a
refractive index of 1. 55 to 1. 45 (more preferably 1. 53 to 1. 47) .
[0072]

The optical film of the present Embodiment is preferably
a transparent film with transparency, waterproof property, and
resistances to water and solvent (liquid). The optical
characteristics of the entire optical film of the present
Embodiment are not especially limited. The optical film is
preferably transparent to such a degree that an observer can
recognize the contents of the tank. More specifically, it is
preferable that the optical film has a light transmittance of
90% (more preferably S5%) or higher and a haze of 10% (more
preferably 1%) or lower.
[0073]
Specific examples of the base film include ZEONOR by ZEON
Corp., ARTON by JSR Corp., COC and TPX each by Mitsui Chemicals,
Inc. Olefin films are preferably used as the base film. The
thickness of the base film is generally, but not limited to,
about 30 µm to 100 µm.
[0074]
According to the embodiment (1), it is preferable that
the optical film of the present Embodiment has an adhesive paste
on a (first or second) moth-eye layer-free-side surface of the
base film. The adhesive paste (adhesive) is used for attaching
the optical film of the present Embodiment to the interior of
the tank easily, and preferably has transparency and water
resistance. Specifically, the adhesive paste can be disposed
by coating an acrylic adhesive and the like on a single surface
of the base film by a publicly known method, and the thickness
of the paste can be appropriately determined. According to the
embodiment (1) , the optical film of the present Embodiment may
further include an easy-peelable laminate film on the adhesive
paste.
[0075]
The embodiment (2) excludes use of the members such as
the base film and the adhesive paste, which permits a reduction
in cost of the liquid tank of the present Embodiment. Neither
reflection nor reduction in light transmittance caused by the

base film and the adhesive paste occur, resulting in further
improvement in visibility of the liquid tank. The embodiment
(2) can be achieved by, for example, coating a UV-curable or
thermocurable resin directly on a transparent wall and then
transferring moth-eye structures of a soft mold to the resin
coating by the above nanoimprint.
[0076]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of a liquid (content
liquid) to be stored in the tank. According to this, the effects
of the present Embodiment can be more surely exhibited. More
specifically, the difference in refractive index between the
protective layer and the content liquid is 0 . 05 (more preferably
0.03) or smaller. In this case, the reflection on the interface
between the protective layer and the content liquid can be hardly
recognized. The refractive index of the protective layer is
preferably within a range of the refractive index of the content
liquid ±0.05 (more preferably ± 0.03).
[0077]
It is preferable that the protective layer has a refractive
index substantially equivalent to that of water. According to
this, the liquid tank of the present Embodiment can be preferably
used as a tank for storing water, i.e., as a water tank. More
specifically, the difference in refraetive index between the
protective layer and water is 0.05 (more preferably 0.03) or
smaller. In this case, the reflection on the interface between
the protective layer and the water can be hardly recognized.
[0078]
The refractive index of water is about 1.33, and so it
is preferable that the protective layer has a refractive index
of 1. 2 8 to 1. 38 (more preferably 1. 3 to 1. 36) in view of suitably
using the liquid tank of the present invention as a water tank.
[0079]
According to the present Embodiment, the transparent
members having a refractive index of about 1.5 such as a glass

or transparent resin material can be preferably used as a material
for the transparent wall. Further, transparent members having
a refractive index of about 1.5 such as a transparent resin
material can be suitably used as a material for the first moth-eye
layer. These transparent members each have a refractive index
higher than that of the content liquid (e.g., 1.33 of water
refractive index), generally. With a view to form the
transparent wall and the first moth-eye layer by the respective
optimum materials and to easily make the refractive index of
the content liquid substantially equivalent to that of the
protective layer, it is preferable that the protective layer
has a refractive index smaller than that each of the transparent
wall and the moth-eye layer.
[0080]
The other optical characteristics of the protective layer
are not especially limited. The optical film is preferably
transparent to such a degree that an observer can recognize the
contents of the liquid tank. More specif ically, it is preferable
that: the light transmittance is 90% (more preferably 95%) or
higher; and the haze is preferably 10% (more preferably 1%) or
lower.
[0081]
It is preferable the protective layer contains a
fluorine-containing resin. According to this, the protective
layer can more surely protect the moth-eye structure, which is
commonly poor in durability, and as a result, the durability
of the liquid tank of Embodiment 1 can be more improved. Since
the refractive index of the fluorine-containing resin is
generally about 1. 3 to 1. 4, the refractive index of the protective
layer containing a fluorine-containing resin can be easily made
substantially equal to that of water. That is, according to
this, the liquid tank of the present Embodiment can be preferably
used as a water tank. The protective layer can be formed by
coating a material for the protective layer on the first moth-eye
layer by a common coating method (including, spray, spin coating,

die coating, slit coating, and the like) , and drying the coating
if necessary.
[0082]
The fluorine-containing resin is a resin including a
carbon-fluorine bond, and the resin itself has water repellency.
CYTOP CTX BGSAby ASAHI Glass Co. , Ltd. , is mentioned as a specific
example of the fluorine-containing resin. The thickness of the
protective layer is generally, but not limited to, about 1 urn
to 5 µm.
[0083]
The adhesion of the protective layer possibly deteriorates
when a resin material (a polymer material) is used for the first
moth-eye layer and a fluorine-containing resin material
(fluorine resin material) is coated on the first moth-eye layer
as a material for the protective layer. In view of this, it
is preferable that prior to the coating of the protective layer
material, the first moth-eye layer surface is treated with a
primer.
[0084]
The flatness of the protective layer surface is not
especially limited as long as it is more flat than the moth-eye
structure of the first moth-eye layer. It is preferable that
the protective layer surface is flat to such a degree that stains
on the surface can be removed by a common washing way (e.g.,
wiping or rubbing) with a common tool (e.g., cloth or brush).
There is no problem in that the protective layer surface has
a flatness that is allowed when the protective layer is composed
of a resin material by a common coating method such as spraying,
spin coating, die coating, and slit coating.
[0085]
The transparent wall is transparent to such a degree that
an observer can view the under-liquid objects therethrough, and
can be composed of a material commonly used in typical water
tanks or viewing windows. More specifically, it is preferable
that the transparent wall has a light transmittance of 90% (more

preferably 95%) or higher and a haze of 10% (more preferably
1%) or lower. The refractive index of the transparent wall is
preferably, but not limited to, substantially equivalent to that
of the base film of the moth-eye layer or the resin constituting
the moth-eye structure. According to this, the effects of the
present Embodiment can be sufficiently exhibited.
[0086]
Examples of the material for the transparent wall include,
but not limited to, various glass materials and transparent resin
(e.g., acrylic resin) materials. Such materials include those
generally used for water tanks or viewing windows.
[0037]
The transparent wall constitutes the entire or part of
the liquid tank of the present Embodiment. Specifically, the
transparent wall may be a transparent window.
[0088]
As long as the liquid tank is a container (appreciation
or observation container) the interior of which is viewed from
the outside, the application thereof is not especially limited.
Particularly preferable are aquarium tanks in which fishes are
raised and bred and tanks having as a liquid volume meter a window
(viewing window) through which the content is viewed.
[0089]
The liquid (the content liquid) stored in the tank is in
contact with at least part of the protective layer, preferably.
The kind and refractive index of the content liquid can be
appropriately determined according to the application of the
tank and are not especially limited. Preferably, the content
liquid is water. The content of the tank is not especially
limited to liquid materials and include underwater life such
as fishes and microorganism, and ornamentals.
[0090]
Embodiment 2
The viewing device for under-liquid observation of
Embodiment 2 includes a transparent window, and on the external

surface of the window, a first moth-eye layer having a moth-eye
structure and a protective layer covering the moth-eye structure
are disposed in this order from the window side.
[0091]
The external surface of the transparent window means a
surface on the side opposite to the observer side.
[0092]
Thus, in Embodiment 2, the first moth-eye layer and the
protective layer mentioned in Embodiment 1 are applied to a
viewing device for under-liquid observation. Embodiment 2 is
mentioned below mainly with reference to embodiments and effects
different from those in Embodiment 1, and the same contents are
omitted.
[0093]
The viewing device of the present Embodiment is used with
at least the transparent window being in contact with liquid.
Through this transparent window, the observer views under-liquid
objects.
[0094]
The viewing device of the present Embodiment includes the
first moth-eye layer having a moth-eye structure, so that the
reflection on the interface between the first moth-eye layer
and the protective layer can be markedly decreased (e.g., a
reflectance of 0.1 % or lower) . The transparent window and the
liquid in contact with the viewing device (transparent window)
(hereinafter, also referred to simply "liquid") are usually
different in refractive index. The material for the first
moth-eye layer can be appropriately selected from those having
a refractive index equivalent to that of the transparent window.
The material for the protective layer can be appropriately
selected from those having a refractive index substantially
equivalent to that of the liquid. Specifically, the first
moth-eye layer ensures the refractive index compatibility with
the transparent window, and the protective layer ensures that
with the liquid. As a result, the refractive index can be

continuously changed from the liquid to the transparent wall,
so that reflection of ambient light on the external surface of
the window can be markedly decreased (e.g., a reflectance of
.
[0095]
For the same reasons as in Embodiment 1 the viewing device
of Embodiment 2 can exhibit the following effects:
[0096]
coloring can be almost completely suppressed;
[0097]
the durability of the external surface of the transparent
window can be improved; and
[0098]
adhesion of stains to the moth-eye structure can be
prevented. Moreover, the shape of the liquid-contacting
portion (surface) of the protective layer is not especially
limited, so that it can be made more flat than the moth-eye
structure. Therefore, even when adhered to the protective layer,
the stains can be readily removed therefrom.
[0099]
Further, it is possible to produce the liquid tank
dramatically inexpensively in comparison to the case where other
anti-reflection films such as a multi-layer film (multi-layer
anti-reflection film) are used.
[0100]
It is preferable that the viewing device includes, on the
internal surface of the transparent window, a second moth-eye
layer having a moth-eye structure, and the second moth-eye layer
is disposed in a region facing the first moth-eye layer.
[0101]
The internal surface of the transparent window means a
surface on the observer side.
[0102]
This second moth-eye layer allows markedly reducing
reflection of ambient light on the window internal surface (e.g.,

a reflectance of 0.1% or less). As a result of this, the
reflection on the region where the first and second moth-eye
layers overlap with each other can be further decreased. The
first and second moth-eye layers are disposed so as to overlap
with each other in the viewing direction. Between the first
and second moth-eye layers, the shape, size, and location thereof
may be the same or different but preferably the same,
[0103]
The location of the first and second moth-eye layers and
the protective layer is not especially limited as long as they
can be viewed from an observer. The first and second moth-eye
layers and the protective layer may be formed over the entire
or part of the transparent window, but preferably at least on
a portion through which the user views the observation objects.
It is preferable that the first and second moth-eye layers and
the protective layer are disposed over the entire (surface) of
the transparent window in order to improve the visibility in
a range as wide as possible.
[0104]
The materials for the first and second moth-eye layers
are not especially limited. It is preferable that the refractive
index of each of the first and second moth-eye layers is
substantially equivalent to that of the transparent window.
More specifically, the difference in refractive index between
the transparent wall and the first and second moth-eye layers
is preferably 0.05 (more preferably 0.03) or smaller, and in
this case, the reflection on the both interfaces can be hardly
recognized.
[0105]
The other optical characteristics of the first and second
moth-eye layers are not especially limited and may be the same
as those of common moth-eye films. The first and second moth-eye
layers are preferably transparent to such a degree that the user
can view the observation objects. More specifically, it is
preferable that: the light transmittance is 90% (more preferably

95%) or higher; the haze is preferably 10% (more preferably 1%)
or lower; the refractive index is 1.45 to 1.55 (more preferably
1.47 to 1.53) .
[0106]
Each of the first and second moth-eye layers may be (1)
formed on the transparent window with a base film therebetween
or may be (2) directly formed en the transparent window, from
the same viewpoint as in Embodiment 1.
[0107]
Another Embodiment of the present invention provides such
an optical film. The present Embodiment provides an optical
film attached to the external surface of the viewing device of
Embodiment 2, i.e., the viewing device having a transparent
window, the optical film including a moth-eye layer having a
moth-eye structure (the above-mentioned first moth-eye layer)
and a protective layer covering the moth-eye structure (the
moth-eye structure of the above-mentioned first moth-eye layer) .
[0108]
The base film is preferably transparent to such a degree
that the user can view the under-liquid objects. More
specifically, it is preferable that the base film has a light
transmittance of 90% (more preferably 95%) or higher, a haze
of 10% (more preferably 1%) or lower, and a refractive index
of 1.45 to 1.55 (more preferably 1.47 to 1.53).
[0109]
The optical film of the present Embodiment is preferably
a transparent film with transparency, waterproof property, and
resistances to water and solvent (liquid). The optical
characteristics of the entire optical film of the present
Embodiment are not especially limited. The optical film is
preferably transparent to such a degree that the user can view
the under-liquid objects. More specifically, it is preferable
that the optical film has a light transmittance of 90% (more
preferably 95%) or higher and a haze of 10% (more preferably
1%) or lower.

[0110]
According to the embodiment (1), it is preferable that
the optical film of the present Embodiment has an adhesive paste
on a (first cr second) moth-eye layer-free-side surface of the
base film, from the same viewpoint as in Embodiment 1. The
adhesive paste (adhesive) is used for attaching the optical film
of the present Embodiment to the viewing device readily, and
preferably has transparency and water resistance.
[0111]
It is that the protective layer has a refractive index
substantially equivalent to that of a liquid to be in contact
with the device. According to this, the effects of the present
Embodiment can be more surely exhibited. More specifically,
the difference in refractive index between the protective layer
and the liquid is 0.05 (more preferably 0.03) or smaller. In
this case, the reflection on the interface between the protective
layer and the liquid can be hardly recognized. The refractive
index of the protective layer is preferably within a range of
the refractive index of liquid to be in contact with the viewing
device + 0.05 (more preferably ± 0.03).
[0112]
The protective layer has a refractive index substantially
equivalent to that of water. According to this, the viewing
device of the present Embodiment can be preferably used as a
device for observing underwater objects, i.e., a device for
underwater observation. More specifically, the difference in
refractive index between the protective layer and water is 0.05
(more preferably 0. 03) or smaller. In this case, the reflection
on the interface between the protective layer and the water can
be hardly recognized.
[0113]
The refractive index of water is about 1.33, and so it
is preferable that the protective layer has a refractive index
of 1.2 8 to 1.38 (more preferably 1. 3 to 1.36) in view of suitably
using the viewing device of the present Embodiment as a device

for underwater observation.
[0114]
According to the present Embodiment, the transparent
members having a refractive index of about 1.5 such as a glass
or transparent resin material can be preferably used as a material
for the transparent window. Further, transparent members
having a refractive index of about 1.5 such as a transparent
resin material can be suitably used for the first moth-eye layer.
These transparent members each have a refractive index larger
than that of the liquid (e.g., 1.33 of water refractive index) ,
generally. With a view to form the transparent window and the
first moth-eye layer by the respective optimum materials and
to easily make the refractive index of the content liquid
equivalent to that of the protective layer, it is preferable
that the protective layer has a refractive index smaller than
that of each of the transparent window and the first moth-eye
layer (transparent window).
[0115]
The other optical characteristics of the protective layer
is not especially limited. The protective layer is preferably
transparent to such a degree that the user can view the
under-liquid objects. More specifically, it is preferable
that: the light transmittance is 90% (more preferably 95%) or
higher; and the haze is preferably 10% (more preferably 1%) or
lower.
[0116]
It is preferable the protective layer contains a
fluorine-containing resin. According to this, the protective
layer can more surely protect the moth-eye structure, which is
commonly poor in durability, and as a result, the durability
of the viewing device of Embodiment 2 can be more improved. Since
the refractive index of the fluorine-containing resin is
generally about 1. 3 to 1. 4, the refractive index of the protective
layer containing a fluorine-containing resin can be easily made
equal to that of water. That is, according to this, the viewing

device of the present Embodiment can be preferably used as a
device for underwater observation.
[0117]
The transparent window is transparent to such a degree
that the user can view the under-liquid objects therethrough,
and can be formed of a lens or a transparent plate commonly used
in typical goggles or aquascopes. More specifically, it is
preferable that the transparent window has a light transmittance
of 90% (more preferably 95%) or higher and a haze of 10% (more
preferably 1%) or lower. The refractive index of the transparent
window is preferably, but net limited to, substantially
equivalent to that of the base film of the moth-eye layer or
the resin constituting the moth-eye structure. According to
this, the effects of the present Embodiment can be sufficiently
exhibited.
[0118]
Examples of the material for the transparent window include,
but not limited to, various glass materials and transparent resin
(e.g., acrylic resin) materials. Such materials include those
generally used for goggles or aquascopes.
[0119]
The transparent window constitutes the entire or part of
the viewing device of the present Embodiment.
[0120]
As long as the user can view the under-liquid objects
through the transparent window of the viewing device, the
application of the device is not especially limited.
Particularly preferable are a device for observing under-liquid
objects from above the liquid level and a goggle. The former
device preferably includes aquascopes. In the former device,
the transparent window may be a transparent plate, and in the
latter one, the transparent window may be a transparent lens.
The viewing device may be a window or wall for underwater
observation with which ships, in-water facilities, and the like
are provided.

[0121]
The kind and refractive index of the liquid are not
especially limited andmay be appropriately determined according
to applications of the viewing device. Water, seawater,
solvents, and the like are mentioned.
[0122]
Example 1
Fig. 1 is a schematic view showing a liquid tank of Example
1. Fig. 1(a) is an overall cross-sectional view of the tank.
Fig. 1(b) is an enlarged view of a region (side surf ace) surrounded
by the broken line of Fig. 1(a) . Fig. 2 is a cross-sectional
view schematically showing a moth-eye layer of the liquid tank
of Example 1. Fig. 3 is a cross-sectional view schematically
showing the moth-eye layer and a protective layer in the liquid
tank of Example 1.
The present Example relates to an embodiment in which the
liquid tank of the present invention is used as a water tank.
The water tank of the present Example has a multi-layer structure,
as shown in Fig. 1, composed of: a transparent wall 11 constituting
a container storing a content liquid, or water 21; a moth-eye
layer (moth-eye film) 12 attached to the external surface
(hereinafter, also referred to as an "A surface") of the
transparent wall 11, which faces an observer 23; a moth-eye layer
(moth-eye film) 13 attached to the internal surface (hereinafter,
also referred to as a "B surface") of the wall 11; and a protective
layer 14 coating the moth-eye layer 13. The transparent wall
11 is composed of a transparent glass plate. The moth-eye layer
12 has a moth-eye structure. The moth-eye layer 13 has a moth-eye
structure and faces the moth-eye layer 12 . The protective layer
14 is composed of a fluorine-containing resin (fluorine resin) .
The transparent wall 11 has a refractive index of about 1.5.
The protective layer 14 has a refractive index of 1.28 to 1.38.
The water 21 has a refractive index of 1.33.
[0123]
The moth-eye layer 12 can prevent a mismatch in refractive

index between air outside the water tank (refractive index of
1) and the transparent wall 11. Also on the internal side of
the wall 11, the refractive index matching between the water
21 and the transparent wall 11 can be achieved. As a result,
the observer 23 feels as if no wail of the water tank exists
and experiences a feeling of being inside the tank. Further,
when the water tank is photographed from the outside by strobe
photography, the strobe light is not reflected on the refractive
index interface. This can obviate the need of moving the camera
close to the tank. Thus, the matching in refractive index can
be achieved well when the moth-eye structure is formed on the
B surface. On the other hand, the moth-eye structure has a
surface very excellent in biocompatibility, so that underwater
life easily adhere to the surface or stains on the surface are
difficult to remove. This problem can be solved by coating a
material whose refractive index is almost equivalent to that
of the water 21 on the B surface of the moth-eye layer 13. As
a result, the refractive index matching between the water 21
and the transparent glass wall 11 is achieved, and adhesion of
stains including underwater life can be minimized. Even if once
adhered to the wall 11, the stains can be easily removed therefrom
with a commercially available cloth and the like. Moreover,
the fluorine-containing resin layer protects the surface of the
moth-eye layer 13 (the moth-eye structure), which is poor in
durability, whereby the water tank can be used as a durable
aquarium or observation tank. Since the refractive index of
the fluorine-containing resin is generally about 1.3 to 1.4,
the refractive index of the protective layer 14 containing a
fluorine-containing resin can be easily made substantially equal
to that of the water 21.
[0124]
The moth-eye structure 16, with which the moth-eye layers
12 and 13 are provided, has protrusions. It is preferable that
the protrusions are formed with a pitch of 50 nm to 300 nm and
a height of 50 nm to 300 nm. The moth-eye layers 12 and 13 are

each made of a material whose refractive index is substantially
equivalent to that of the material for the transparent wall 11
of a glass or resin material.
[0125]
In the present Example, CYTOP CTX809A (produced by ASAHI
Glass Co., LLd.) is used as the fluorine-containing resin
material (fluorine coating material) for the protective layer
14. This resin is coated on the moth-eye layer 13 to form a
layer with 0.5 um in thickness. CYTOP CTX809A has a refractive
index of 1.34, which is almost equivalent to that of water, or
1.33. Although in the single use of the moth-eye layer 13 the
stains still easily adhere to the internal wall of the tank,
the fluorine resin coating on the internal wall of the tank
suppresses the stain adhesion and makes it easier to remove the
stains from the wall. The adhesion between the moth-eye layer
13 and the protective layer 14 might be insufficient when the
moth-eye layer 13 is composed of a polymer material and thereon
the fluorine-resin coating is formed. In view of this, it is
preferable that the moth-eye layer 13 surface is treated with
a primer prior to the formation of the fluorine-resin coating.
In this Example, a primer (CT-P10, by ASAHI Glass Co., Ltd.)
exclusively for CYTOP CTX809A can be used.
[0126]
Between the transparent wall 11 and each of the moth-eye
layers 12 and 13, there are provided a base film 15 and an adhesive
paste 17 disposed on the transparent wall 11-side main surface
of the base film 15 as illustrated in Fig. 2. Thus each of the
moth-eye layers 12 and 13 is formed by subjecting to
nanoimprinting a film of a UV-curable resin and the like formed
on the base film 15 and then attached to the transparent wall
11 with the adhesive paste 17. The moth-eye structure 16 of
the layer 13 is coated with the protective layer 14 of a
fluorine-containing resin (fluorine resin) as illustrated in
Fig. 3. As mentioned above, attached is an optical film (film
for the tank internal surface) composed of the protective layer

14, the moth-eye layer 13, the base film 15, and the adhesive
paste 17 to the internal surface of the transparent wall 11;
and to the external surface thereof, an optical film (film for
the tank external surface) composed of the moth-eye layer 12,
the base film 15, and the adhesive paste 17 is attached. When
a moth-eye layer is disposed on the B surface side, the moth-eye
layer 13, which is located on the internal side of the tank,
preferably includes a material with excellent solvent resistance
because it is under the presence of a solvent (solution) such
as water. The base film 15 preferably is a film with transparency,
water resistance, and solvent (liquid) resistance.
Specifically, olefin films, including the above-mentioned
commercially available ones, are suitably used. The refractive
index of the base film 15 is preferably designed to be
substantially equivalent to that of the transparent wall 11.
[0127]
Fig. 4 is an explanation view of refractive index change
in the liquid tank of Example 1. Fig. 4(a) is a side
cross-sectional view of the tank. Fig. 4 (b) is a graph showing
refractive index change on a side surface of the tank. In the
tank of the present Example, as shown in Figs. 4(a) and 4(b),
the moth-eye layers 12 and 13 are disposed at a portion facing
the observer of the A and B surfaces of the transparent wall
11 respectively whereby the refractive index matching can be
ensured with the solution (the water 21) being charged in the
tank. Particularly the refractive index matching on the B
surface side is achieved using a fluorine-containing material
with a low refractive index for the protective layer 14. Thus,
the protective layer 14 can be coated successfully while a
mismatch of the refractive index on the interface between the
water and the resin layer is minimized. Further, the treatment
for the refractive index matching with the solution (the water
21) and the moth-eye structure enable the refractive index to
continuously change from air 22 (the refractive index is 1) to
the water 21 (the refractive index is 1.33), and as a result,

the portion facing the observer of the wall 11 behaves as if
no interface existed. Reflected light on this portion have a
very flat wavelength dispersion characteristic and is less
colored. Thus the coloring hardly occurs because the moth-eye
structure requires no A/4 conditions unlike the multi-layer film
and because the refractive index continuously changes from the
surface of the moth-eye structure to the inside thereof. The
reflectance on the moth-eye structure surface can be extremely
decreased because the light does not recognize the moth-eye
structure surface as a refractive index interface. Moreover,
the fluorine-containing resin layer (with a refractive index
substantially equivalent to that of the solvent (e.g., 1.33 when
the solvent is water) ) is disposed on the B surface, which can
ease the poor resistance to stains such as underwater life and
the difficulty in removal of the stains of the nanostructure
(nanometer-sized protrusions) of the moth-eye structure and
which can dramatically increase the durability of the B surface.
[0128]
Example 2
Fig. 5 is a schematic view showing the liquid tank of Example
2. Fig. 5(a) is an overall cross-sectional view of the tank.
Fig. 5(b) is an enlarged view of a region (side surface) surrounded
by the broken line of Fig. 5(a).
The present Example employs exactly the principle of
Example 1, but the films for the tank internal surface and for
the tank external surface are each disposed on part of the tank
by patterning. Specifically, as shown in Fig. 5, the moth-eye
layer 12 on the A surface, and the moth-eye layer 13 and the
protective layer 14 on the B surface, each of which is disposed
on the transparent wall 11 with the base film and the adhesive
paste therebetween, are patterned into the same planar shape.
As a result, the observer 23 feels as if no transparent wall
11 existed at the pattern portion and he could enter the tank.
Thus the display effects like this can be obtained.
[0129]

The pattern shape includes, but not limited to, a circular
or square shape in consideration of the viewing window shape.
Alternatively, thelayers arepatternedtoexpress some character
or logo for advertisement, for example. When the layers are
patterned to express some character, it looks as if no interface
exists on the layer-provided portion, but therearound, light
reflection occurs. This difference between the two portions
brings higher display effects.
[0130]
Example 3
Fig. 6 is a perspective view schematically showing a liquid
tank of Example 3. Fig. 7 is an explanation view of refractive
index change in the liquid tank of Example 3. Fig. 7(a) is a
cross-sectional view of a liquid volume meter portion of the
liquidtank. Fig. 7(b) is a graph showing refractive index change
in the liquid volume meter portion.
In the present Example, the liquid tank of the present
invention is applied to a tank equipped with a viewing window
as a liquid volume meter through which the liquid level can be
determined. A liquid volume meter 18 is disposed at part of
the tank, as shown in Fig. 6. The films for tank internal and
external surfaces are each attached to the liquid volume meter
portion, similarly to Example 1. More specif ically, the liquid
volume meter portion of the tank of the present Example has a
multi-layer structure composed of: a transparent wall 11; a
moth-eye layer 12 attached to the external surface (A surface)
of the transparent wall 11 and having a moth-eye structure; a
moth-eye layer 13 attached to the internal surface (B surface)
of the wall 11 and disposed in a region facing the moth-eye layer
12; and the protective layer 14 coating the moth-eye layer 13
and composed of a fluorine-containing resin (fluorine resin).
Fig. 7 illustrates that the level of the content liquid (the
water 21) reaches a certain level of the liquid volume meter
18.
[0131]

The B surface allows refractive index matching below the
liquid level (the water 21 level) , but does not allow it thereabove,
i.e. , at the portion exposing to air 22, as shown in Fig. 7 (b) .
Specifically, the reflection is suppressed in the region below
the liquid level where the refractive index is matched, and on
the other hand, the reflection occurs in the region thereabove
where the refractive index is mismatched. This difference in
occurrence of the reflection makes it easy to determine the height
of the liquid level. The A surface is also provided with the
moth-eye structure, so that the external-surface reflection can
be almost completely prevented and as a result, the liquid level
height can be more easily determined.
[0132]
When the protective layer 14 is not disposed on the moth-eye
layer 13, the moth-eye structure is directly exposed to air above
the liquid level. This region also continuously changes the
refractive index to diminish the reflected light. As a result,
the internal-surface reflection is suppressed both above and
below the liquid level, and the interface between the liquid
and air becomes unclear. In contrast to this, when the protective
layer 14 is disposed on the moth-eye layer 13, the light reflection
occurs on the interface between the air 22 and the protective
layer 14 above the liquid level. Thus, the liquid level can
be clearly determined as mentioned above.
[0133]
When the liquid volume meter is not equipped with the films
for tank internal and external surfaces, the mismatch of the
refractive index occurs both above and below the liquid level.
The degree of the mismatch is different between the two regions,
resulting in a difference in reflectance therebetween. In this
case, therefore, the liquid level is not so clearly viewed as
in the liquid volume meter of Example 3, although barely
determined.
[0134]
As mentioned above, in Examples 1 to 3, the matching of

refractive index on the side surface of the transparent wall
of the tank can be achieved with the moth-eye structure and the
resin with a low refractive index. The light reflection can
be suppressed as much as possible, and thus objects (aquarium
fishes, liquid level, and the like) inside the tank can be clearly
observed.
[0135]
Example 4
Fig. 11 is a cross-sectional view schematically showing
a viewing device for under-liquid observation of Example 4 . Fig.
12 is an explanation view of refractive index change in the viewing
device of Example 4. Fig. 12(a) is a cross-sectional view of
the device. Fig. 12(b) is a graph showing refractive index change
in the device. Figs. 13 and 14 are cross-sectional views each
schematically the device of Example 4 in accordance with a
modified example.
In the present Example, the viewing device of the present
invention is applied to a device through which a user views
under-liquid objects above the liquid level. The device of the
present Example has the followingmulti-layer structure composed
of: a transparent plate-like base (transparent window) 24;
a moth-eye layer 12 attached to the surface exposed to air (the
top) of the base 24 and having a moth-eye structure; a moth-eye
layer 13 attached to the liquid (water)-side surface (the bottom)
of the base 24 and disposed in a region facing the moth-eye layer
12; and a protective layer 14 of a fluorine-containing resin
(fluorine resin) coating the moth-eye layer 13. The base 24
is made of a glass or resin material and the like, and has a
refractive index of about 1.5. The device of the present Example
is used with the protective layer 14 being in contact with the
liquid and the moth-eye layer 12 being in contact with the
atmosphere. Accordingly, it is preferable that the respective
members of the present Example are made of materials with a
specific gravity lower than that of the liquid.
[0136]

In the present Example, the moth-eye films are attached
to the respective surfaces of the base 24, and on the moth-eye
film that is to be exposed to liquid, the protective layer 14
of a resin with a low refractive index is disposed. When this
device is floated on the surface of the liquid, as shown in Fig.
12, the both surface allow the refractive index matching, and
the refractive index continuously changes from air (refractive
index of 1) to water 21 (refractive index of 1.33} . Thus the
refractive index mismatch on the liquid surface can be solved.
As a result, underwater objects can be clearly viewed from above
the liquid level. Further, since this Example employs the
fluorine resin as a material for the protective layer 14,
similarly to Examples 1 to 3, the device can suppress from being
contaminated by the liquid and can achieve the refractive index
matching also on the bottom thereof.
[0137]
A float 25 with a lower specific gravity than that of the
liquid may be disposed around the device of the present Example
(for example, around the base 24), as shown in Fig. 13. This
allows using materials with a higher specific gravity than that
of the liquid for the members such as the base 24.
[0138]
The device of the present Example may be equipped with
a light-shielding cylindrical member 26 as shown in Fig. 14 to
be used as an aquascope. One opening of the cylindrical member
26 is closed with a transparent portion such as the base 24.
This can suppress incident of ambient light into the transparent
portion so that observation objects can be more clearly viewed.
Further, the gravity of the cylindrical member 26 can be made
lower than that of the liquid, whereby materials with a specific
gravity higher than that of the liquid can be used for the members
such as the base 24.
[0139]
The application of the device of the present Example is
not especially limited. The device may be used for underwater

or undersea observation, or alternatively, for viewing an
indicator inside an apparatus containing a solvent or checking
behavior of such an apparatus.
[0140]
Example 5
Fig. 15 is a cross-sectional view schematically showing
a viewing device for under-liquid observation of Example 5. Fig.
16 is an explanation view of refractive index change in the device
of Example5. Fig. 16(a) is a cross-sectional view of the device.
Fig. 16(b) is a graph showing refractive index change in the
device.
In the present Example, the viewing device of the present
invention is applied to goggles. The lens part of the goggles
of the present Example has the following multi-layer structure
composed of a transparent base (transparent window) 27; a
moth-eye layer 12 attached to the internal surface of the base
27 (the user 27-side surface) and having a moth-eye structure;
amoth-eye layer 13 attachedto the liquid (water 21) -side surface
(the external surface) thereof and disposed in a region facing
the moth-eye layer 12; and the protective layer 14 of a
fluorine-containing resin (fluorine resin) coating the moth-eye
layer 13. The base 27 is composed of a glass or resin material,
and the like, and has a refractive index of about 1. 5. The goggles
of the present Example are used with the protective layer 14
being in contact with the liquid and the moth-eye layer 12 being
with air.
[0141]
In the present Example, the moth-eye films are attached
to the respective surfaces of the base 27, and on the moth-eye
film that is to be exposed to liquid, the protective layer 14
of a resin with a low refractive index is disposed. In underwater
observation by means of the goggles of the present Example, as
shown in Fig. 16, the both surface can achieve the matching of
the refractive index, and the refractive index can be
continuously changed from the water 21 (the refractive index

is 1.33) to air (the refractive index of 1), finally to just
in front of user's (observer's) eyes. The user can view objects
present in the water naturally and clearly like fishes do.
[0142]
The moth-eye layer 12 surface may be provided with a
water-shedding treatment to such a degree that the moth-eye
structure does not completely lose its undulated pattern,
although the above effects can be exhibited without the treatment.
This allows easy removal of water from the lens inner surface.
[0143]
The moth-eye layer 12 surface may be provided with
hydrophilicity. In this case, even when water enters the inside
of the lens part and comes in contact with the moth-eye layer
12, the water can be spread over the layer 12 surface to form
a water film thereon. Thus, fogging of the goggles can be
suppressed.
[0144]
The goggles of the present Example may be those for athletic
use, hobby use, or fishing industries, and the application
thereof is not especially limited.
[0145]
Also in Examples 4 and 5, a base film and an adhesive paste
are disposed in this order on the base 24 or 27-side main surface
of each of the moth-eye layers 12 and 13, similarly to Examples
1 to 3. Thus, the optical film composed of the protective layer
14, the moth-eye layer 13, the base film, and the adhesive paste
is attached to the bottom of the base 24 or the external surface
of the base 27, and on the top of the base 24 or the internal
surface of the base 27, the optical film composed of the moth-eye
layer 12, the base film, and the adhesive paste is attached.
[0146]
The present application claims priority to Patent
Application No. 2008-329996 filed in Japan on December 25, 2008
under the Paris convention and provisions of national law in
a designated State, the entire contents of which are hereby

incorporated by reference.
EXPLANATION OF NUMERALS AND SYMBOLS
[0147]
11: Transparent wall
12: Moth-eye layer
13:' Moth-eye layer
14: Protective layer
15: Base film
16: Moth-eye structure
17: Adhesive paste
18: Liquid volume meter
19: Protrusion
21: Water
22: Air
23: Observer
24, 27: Base
25: Float
36: Cylindrical member
27: User
31: Stain
32: Fiber

CLAIMS
1. A liquid tank having a transparent wall,
comprising, on an internal surface of the wall,
a first moth-eye layer having a moth-eye structure,
and
a protective layer covering the moth-eye structure, in
this order from the wall side.
2. The liquid tank according to Claim 1,
further comprising, on an external surface of the wall,
a second moth-eye layer having a moth-eye structure, and
the second moth-eye layer being disposed in a region facing
the first moth-eye layer.
3. The liquid tank according to Claim 1 or 2,
wherein the protective layer contains a
fluorine-containing resin.
4. The liquid tank according to any one of Claims 1 to
3,
wherein the protective layer has a refractive index
substantially equivalent to that of a liquid to be stored in
the tank.
5. The liquid tank according to any one of Claims 1 to
4,
wherein the protective layer has a refractive index
substantially equivalent to that of water.
6. The liquid tank according to any one of Claims 1 to
5,
wherein the protective layer has a refractive index smaller
than that of each of the transparent wall and the first moth-eye
layer.

7. The liquid tank according to any one of Claims 1 to
6,
wherein the protective layer has a refractive index of
1.28 to 1.38.
8. An optical film attached to an internal surface of
a liquid tank having a transparent wall,
the film comprising a moth-eye layer having a moth-eye
structure andaprotective layer covering themoth-eye structure.
9. The optical film according to Claim 8,
wherein the protective layer contains a
fluorine-containing resin.
10. The optical film according to Claim 8 or 9,
wherein the protective layer has a refractive index
substantially equivalent to that of a liquid to be stored in
the tank.
11. The optical film according to any one of Claims 8
to 10,
wherein the protective layer has a refractive index
substantially equivalent to that of water.
12. The optical film according to any one of Claims 8
to 11,
wherein the protective layer has a refractive index smaller
than that each of the transparent wall and the moth-eye layer.
13. The optical film according to any one of Claims 8
to 12,
wherein the protective layer has a refractive index of
1.28 to 1.38.

14. 7A viewing device having a transparent window for
under-liquid observation,
the device comprising, on an outer surface of the window,
a first moth-eye layer having a moth-eye structure, and
a protective layer covering the moth-eye structure, in
this order from the window side.
15. The viewing device according to Claim 14,
further comprising, on an inner surface of the window,
a second moth-eye layer having a moth-eye structure, and
the second moth-eye layer being disposed in a region facing
the first moth-eye layer.
16. The viewing device according to Claim 14 or 15,
wherein the protective layer contains a
fluorine-containing resin.
17. The viewing device according to any one of Claims
14 to 16,
wherein the protective layer has a refractive index
substantially equivalent to that of a liquid to be in contact
with the device.
18. The viewing device according to any one of Claims
14 to 17,
wherein the protective layer has a refractive index
substantially equivalent to that of water.
19. The viewing device according to any one of Claims
14 to 18,
wherein the protective layer has a refractive index smaller
than that of each of the transparent window and the first moth-eye
layer.
20. The viewing device according to any one of Claims

14 to 19,
wherein the protective layer has a refractive index of
1.28 to 1.38.
21. An optical film attached to an outer surface of a
viewing device having a transparent window for under-liquid
observation,
the film comprising a moth-eye layer having a moth-eye
structure and a protective layer covering themoth-eye structure.
22. The optical film according to Claim 21,
wherein the protective layer contains a
fluorine-containing resin.
23. The optical film according to Claim 21 or 22,
wherein the protective layer has a refractive index
substantially equivalent to that of a liquid to be in contact
with the device.
24. The optical film according to any one of Claims 21
to 23,
wherein the protective layer has a refractive index
substantially equivalent to that of water.
25. The optical film according to any one of Claims 21
to 24,
wherein the protective layer has a refractive index smaller
than that of each of the transparent window and the moth-eye
layer.
26. The optical film according to any one of Claims 21
to 25,
wherein the protective layer has a refractive index of
1.28 to 1.38.


The present invention provides a liquid tank, a viewing
device for under-liquid observation, and an optical film, each
excellent in visibility and durability and being easy to clean.
The present invention is a liquid tank having a transparent wall,
including, on an internal surface of the wall, a first moth-eye
layer having a moth-eye structure, and a protective layer
covering the moth-eye structure, in this order from the wall
side, and preferably, further including, on an external surface
of the wall, a second moth-eye layer having a moth-eye structure,
and the second moth-eye layer being disposed in a region facing
the first moth-eye layer.

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Patent Number 279800
Indian Patent Application Number 2423/KOLNP/2010
PG Journal Number 05/2017
Publication Date 03-Feb-2017
Grant Date 31-Jan-2017
Date of Filing 02-Jul-2010
Name of Patentee SHARP KABUSHIKI KAISHA
Applicant Address 22-22, NAGAIKE-CHO, ABENO-KU, OSAKA-SHI, OSAKA 5458522, JAPAN
Inventors:
# Inventor's Name Inventor's Address
1 YAMADA, NOBUAKI C/O. SHARP KABUSHIKI KAISHA 22-22, NAGAIKE-CHO, ABENO-KU, OSAKA-SHI, OSAKA 5458522, JAPAN
PCT International Classification Number G02B5/30
PCT International Application Number PCT/JP2009/070198
PCT International Filing date 2009-12-01
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2008-329996 2008-12-25 Japan