Title of Invention	SUBSTRACTS COATED WITH A POLYMER COMPOSITION
Abstract	A method for treating a substrate is described. In accordance with one aspect, the method includes applying a polymer coating to a substrate, and bringing the polymer coating into contact with a heated surface while the coating is still in a wet state. Optionally the polymer coating may include a crosslinkable material, and a crosslinking agent may be used to promote crosslinking. The polymer coating replicates the heated surface. A product produced in accordance with thedescribed method is also disclosed. The product is characterized by having subsurface voids within the coating.

Title of Invention

SUBSTRACTS COATED WITH A POLYMER COMPOSITION

Abstract

A method for treating a substrate is described. In accordance with one aspect, the method includes applying a polymer coating to a substrate, and bringing the polymer coating into contact with a heated surface while the coating is still in a wet state. Optionally the polymer coating may include a crosslinkable material, and a crosslinking agent may be used to promote crosslinking. The polymer coating replicates the heated surface. A product produced in accordance with thedescribed method is also disclosed. The product is characterized by having subsurface voids within the coating.

Full Text	REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of priority under 35 U.S.C. § 119(e) of provisional application serial number 60/776,114 filed on February 23, 2006, which is hereby incorporated by reference in its entirety. BACKGROUND OF THE INVENTION [0002] The present disclosure relates to a method for treating a substrate with a polymer film-forming composition. More particularly, the disclosure relates to a paper or paperboard manufacturing method comprising the steps of applying a polymer film-forming coating to a substrate, and, bringing the polymer coating into contact with a heated surface while the polymer coating is still in a wet state. The resulting polymer layer has a smooth surface with voids (e.g., bubbles) just below the surface. In certain embodiments, the polymer coating may comprise a crosslinkable hydrogel, and a crosslinking solution may be applied to the polymer coating on the substrate surface thereby forming at least a partially crosslinked polymer coating then placed into contact with a heated surface. The present disclosure also relates to a treated substrate product. [0003] Paper is manufactured by an essentially continuous production process wherein a dilute aqueous slurry of cellulosic fiber flows into the wet end of a paper machine and a consolidated dried web of indefinite length emerges continuously from the paper machine dry end. The wet end of the paper machine comprises one or more headboxes, a drainage section and a press section. The dry end of a modern paper machine comprises a multiplicity of steam heated, rotating shell cylinders distributed along a serpentine web traveling route under a heat confining hood structure. Although there are numerous design variations for each of these paper machine sections, the commercially most important of the variants is the fourdrinier machine wherein the headbox discharges a wide jet of the slurry onto a moving screen of extremely fine mesh. [0004] The screen is constructed and driven as an endless belt carried over a plurality of support rolls or foils. A pressure differential across the screen from the side in contact with the slurry to the opposite side draws water from the slurry through the screen while that section of the screen travels along a table portion of the screen route circuit. As slurry dilution water is extracted, the fibrous constituency of the slurry accumulates on the screen surface as a wet but substantially consolidated mat. Upon arrival at the end of the screen circuit table length, the mat has accumulated sufficient mass and tensile strength to carry a short physical gap between the screen and the first press roll. This first press roll carries the mat into a first press nip wherein the major volume of water remaining in the mat is removed by roll nip squeezing. One or more additional press nips may follow. [0005] From the press section, the mat continuum, now generally characterized as a web, enters the dryer section of the paper machine to have the remaining water removed thermodynamically. [0006] Generally speaking, the most important fibers for the manufacture of paper are obtained from softwood and hardwood tree species. However, fibers obtained from straw or bagasse have been utilized in certain cases. Both chemical and mechanical defiberizing processes, well known to the prior art, are used to separate papermaking fiber from the composition of natural growth. Papermaking fiber obtained by chemical defiberizing processes and methods is generally called chemical pulp whereas papermaking fiber derived from mechanical defiberizing methods may be called groundwood pulp or mechanical pulp. There also are combined defiberizing processes such as semichemical, thermochemical or thermomechanical. Any of the tree species may be defiberized by either chemical or mechanical methods. However, some species and defiberizing processes are better economic or functional matches than others. [0007] An important difference between chemical and mechanical pulp is that mechanical pulp may be passed directly from the defiberizing stage to the paper machine. Chemical pulp on the other hand must be mechanically defiberized, washed and screened, at a minimum, after chemical digestion. Usually, chemical pulp is also mechanically refined after screening and prior to the paper machine. Additionally, the average fiber length of mechanical pulp is, as a rule, shorter than that of chemical pulp. However, fiber length is also highly dependent upon the wood species from which the fiber originates. Softwood fiber is generally about three times longer than hardwood fiber. [0008] The ultimate properties of a particular paper are determined in large part by the species of raw material used and the manner in which the paper machine and web forming process treat these raw materials. Important operative factors in the mechanism of forming the paper web are the headbox and screen. [0009] Coated paper or paperboard used for printing and for packaging is generally required to have high level of gloss, excellent smoothness, and excellent printability, as well as certain strength and stiffness characteristics. [0010] If the coated paper or paperboard has a high stiffness, it can pass smoothly through high-speed printing or packaging machines with less feeding jams. Higher stiffness paper can be advantageously used in books, magazines, and catalogues, because it provides a feel of hardness or heaviness similar to a hardcover book. For packaging, high stiffness is necessary for maintaining the structural integrity of the paperboard product during filling and in subsequent use. [0011] Stiffness has close relationship to the basis weight and density of paper. There is a general trend that stiffness increases as the basis weight increases, and decreases as the paper density increases. Stiffness and other properties can be improved by increasing basis weight. However, this would result in a product utilizing more fibers, which add cost and weight. Therefore, coated paper or paperboard with high stiffness but moderate basis weight is desirable. Paper with moderate basis weight is also more economical because less raw material (fiber) is utilized. In addition, shipping costs based on weight are less for low basis weight paper. [0012] In addition to high stiffness, coated paper or paperboard which must be printed is often required to have high gloss and smoothness. For coated paper or paperboard to have such quality characteristics, density typically must be increased to some extent to allow for a usable printing surface. Smoothness is normally achieved by calendering. However, calendering will cause a reduction in caliper, which typically results in a corresponding reduction in stiffness. The calendering process deteriorates the stiffness of paper by significantly reducing caliper and increasing the density. The base sheet for conventional coated board grades typically is heavily densified by calendering to provide a surface roughness low enough to produce final coated smoothness acceptable to the industry. These calendering processes, including wet stack treatment, may increase density by as much as 20% to 25%. [0013] Thus, the relationship between gloss and stiffness and between smoothness and stiffness are generally inversely proportional to each other, for a given amount of fiber per unit area. Packaging grades are sold based on caliper, so manufacturing processes that reduce the caliper (increasing the density of the board) decrease the selling price. Processes that cause less caliper reduction save material costs. Caliper is measured in "points", where a point = 0.001 inches. For example, the conventional method for making a 10-point board requires the use of a board having a thickness of greater than 12 points prior to calendering. It would be desirable to be able to produce a finished board having approximately the same thickness as the starting substrate. [0014] Improvements in the calendering process including moisture gradient calendering, hot calendering, soft calendering, and belt calendering slightly improved stiffness for a given caliper but did not change the fundamental ratio between caliper, stiffness, smoothness, and printing properties. [0015] Various proposals have been made to improve the stiffness of coated paper or paperboard without calendering for printing. For example, several proposals include high softwood content in the raw stock, addition of specially engineered fibers in the raw stock, addition of highly branched polymers within the raw stock, and high amounts of starch or copolymer latex with a high glass transition temperature (commonly referred to as "Tg") within the coating formulation. [0016] However, potential drawbacks to these methods of stiffness improvement are that although they are useful in improving paper stiffness, they could potentially degrade the smoothness, gloss, and/or printability of the coated paper obtained. [0017] For the reasons mentioned above, it has been very difficult to obtain satisfactory paper smoothness without increasing density. Other methods can be used for changing the density/smoothness relationship in paper and paperboard grades. Applying a paper coating is a very common way to enhance the surface properties of paper without causing the drastic increases in paper density typically associated with the levels of calendering required to obtain a certain level of smoothness. Preferably, the final coated surface should be uniform to provide acceptable appearance and printing properties. [0018] Therefore, it would be desirable to provide a paper or paperboard product having the desired properties while maintaining the initial density of the sheet or minimizing the increase in density. Furthermore, it would be desirable to provide a paper or paperboard exhibiting improved smoothness without the concomitant increase in density associated with conventional methods for creating smoothness. Cast coating methods exist for producing a very smooth surface, but these methods are typically run at production rates slower than the speed of many paper machines. WO 96/29199A (D1) to Rutledge (MacMillan Bloedel) discloses coating a substrate with swelled super absorbent particles having a minimum dimension of at least 5 microns to obtained desired porosity and roughness in the finished coating, to produce a coated surface having a roughness in the macro as opposed to the micro range. EP 1,197,503 (D2) to Bardman (Rohm and Haas) discloses a coating with core polymer having an average size of 0.05 to 2 microns, preferably 0.15 to 0.5 microns. EP 0,218,956 (D3) to Otouma (Asahi Glass) discloses a coating containing porous particles, the coating having voids up to 100 microns in size between the particles. EP 0,959,176 (D4) to Blankenship (Rohm and Haas) discloses the use of hollow sphere pigment in coatings. The polymer particles having diameters of about 0.6 microns. GB 1,331,816 (D5) to Penick and Ford discloses a bubble coating, with the bubbles having an average size less than 10 microns, preferably less than 2 microns in diameter. GB 1,287,919 (D6) to Arthur Little discloses a bubble coating, with the 'bubbles' 0.1-1 microns. US 2006/057358 Al (D7) to Miyake Kazuhito (Fuji) discloses a coating with particles having voids therein, but the particles are 2 microns or less. US 3,480,455 (D8) to Richardson (Blandin Paper) discloses a bubble coating utilizing a volatile liquid hydrocarbon in the 'bubbles' which after drying become air bubbles. Bubble coatings are stated to have bubbles in the one micron range. "Introduction to bubble coatings" (D9) by JJ Clancy et al (1 October 1965; TAPPI, GA, pages 51A - 53A) discloses, bubble coatings have bubbles of 1-2 microns. US 4,617,239 (D10) to Maruyama (Kuraray) discloses a paper coating, but does not disclose any subsurface voids. US 6,991,706 (D11) to Lindsay (Kimberly Clark) discloses a paper with patterns made on the paper by the forming fabric and relates to absorbent disposable paper products. US 6,332,953 (D12) to Singh (International Paper) discloses use of shoe nip calendaring to provide a product of improved print performance and/or bulk. US 2003/198885 (D13) to Tamagawa (Fuji)) discloses coating materials for a image-reproducing material and does not disclose any subsurface voids. SUMMARY OF THE DISCLOSURE [0019] In one embodiment, a product is disclosed that includes a substrate with a coating on the substrate. The coating includes a water soluble polymer and a release agent. There are voids formed within the coating. [0020] In another embodiment, a product is disclosed that includes a substrate with a coating on the substrate. The coating includes a water soluble polymer and essentially no elastomeric material. There are voids formed within the coating. [0021] In another embodiment, a product is disclosed that includes a substrate with a coating on the substrate. The coating includes a surface, and the surface has a Sheffield Smoothness of less than about 300 units. There are voids formed under the surface of the coating. [0022] In another embodiment, a product is disclosed that includes a substrate with a coating on the substrate. The coating includes a water soluble polymer, a release agent, and essentially no elastomeric material. The coating includes a surface, and the surface has a Sheffield Smoothness of less than about 300 units. There are voids formed under the surface of the coating. [0023] In another embodiment, a process is disclosed for treating a substrate. A wet film of aqueous polymer solution is applied to the substrate. The aqueous polymer solution is immobilized by bringing it into contact with a heated surface to cause the aqueous polymer solution to boil, and to at least partially dry the aqueous polymer solution. [0024] In another embodiment, a process is disclosed for treating a substrate. A wet film of aqueous polymer solution is applied to the substrate. The aqueous polymer solution is immobilized by bringing it into contact with a heated surface to cause the aqueous polymer solution to boil and form voids that remain in the aqueous polymer solution, and to at least partially dry the aqueous polymer solution. [0025] In another embodiment, a process is disclosed for treating a substrate. A coating of aqueous polymer solution is applied to the substrate as a wet film. The coating includes a water soluble polymer and a release agent. The film is immobilized by bringing it into contact for less than about 3 seconds with a heated surface with a temperature above about 150°C so as to cause the aqueous polymer solution to boil and form voids in the film, and to at least partially dry the film. [0026] In another embodiment, a process is disclosed for treating a substrate. A coating of aqueous polymer solution is applied to the substrate as a wet film. The coating includes a water soluble polymer and essentially no elastomeric material. The film is immobilized by bringing it into contact for less than about 3 seconds with a heated surface with a temperature above about 150°C so as to cause the aqueous polymer solution to boil and form voids in the film, and to at least partially dry the film. [0027] In another embodiment, a process is disclosed for treating a substrate. A coating of aqueous polymer solution is applied to the substrate as a wet film. The coating includes a water soluble polymer and essentially no elastomeric material. The film is immobilized by bringing it into contact for less than about 3 seconds with a heated surface with a temperature above about 150°C so as to cause the aqueous polymer solution to boil and form voids in the film, and to at least partially dry the film. The coating surface after drying has a Sheffield Smoothness of less than about 300 units. [0028] In another embodiment, a process is disclosed for treating a substrate. A coating of aqueous polymer solution is applied to the substrate as a wet film. The coating includes a water soluble polymer, a release agent, and essentially no elastomeric material. The film is immobilized by bringing it into contact for less than about 3 seconds with a heated surface with a temperature above about 150°C so as to cause the aqueous polymer solution to boil and form voids in the film, and to at least partially dry the film. The coating surface after drying has a Sheffield Smoothness of less than about 300 units. [0029] In another embodiment, a process is disclosed for treating a cellulosic substrate. A wet film of aqueous polymer solution is applied to the substrate. The aqueous polymer solution includes at least about 60% water soluble polymer by dry weight, and up to 10% release agent by dry weight. The aqueous polymer solution is immobilized by bringing it into contact for less than about 3 seconds with a heated surface with a temperature above about 150°C so as to cause the aqueous polymer solution to boil and form voids in the aqueous polymer solution, and to at least partially dry the aqueous polymer solution. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS [0030] FIG. 1 is a schematic view of an apparatus for treating a substrate with a polymer coating in accordance with one embodiment of the present invention. [0031] FIGs. 2 - 9 are cross section micrographs showing the morphology of samples made in accordance with one embodiment of the invention, and having a top coating. [0032] FIGs. 10-12 are cross section micrographs showing the morphology of samples made in accordance with one embodiment of the invention. [0033] FIGs. 13-14 are surface micrographs made by scanning electron microscope showing the morphology of samples made in accordance with one embodiment of the invention. [0034] FIGs. 15-16 are surface micrographs made by backscatter scanning electron microscope showing the morphology of samples made in accordance with one embodiment of the invention. [0035] FIG. 17 is a graph showing distribution of void dimensions in samples made in accordance with one embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION [0036] In describing the preferred embodiments, certain terminology will be utilized for the sake of clarity. It is intended that such terminology include not only the recited embodiments but all technical equivalents that operate in a similar manner, for a similar purpose, to achieve a similar result. The citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. Unless indicated otherwise or unless the context suggests otherwise, all weights, percentages, and ratios are by weight. [0037] The present disclosure relates to a method for treating a substrate with a polymer film-forming coating. More particularly, the disclosure relates to a paper or paperboard manufacturing method comprising the steps of applying a polymer coating to a substrate, and bringing the polymer coating into contact with a heated surface while the polymer coating is still in a wet state. Boiling of water in the polymer coating causes voids to form under the surface, but the surface of the film is smooth. The paper or paperboard produced in accordance with certain embodiments of the present invention exhibits desirable levels of surface flatness and smoothness without significant densification of the base paper. In certain embodiments, the polymer coating may include a crosslinkable material and a crosslinking solution may be applied to the polymer coating on the substrate surface thereby forming at least a partially crosslinked polymer film-forming composition. In such cases, the polymer coating may typically be applied to the web first and then the cross linking solution applied before the treated web contacts the heated surface. For weakly cross linking polymers, it may be possible to provide the cross linking solution in the coating itself. [0038] One advantage of treating a substrate with a polymer film-forming coating in accordance with the present invention relates to the improvement in smoothness and/or flatness that can be obtained without significantly increasing the density or decreasing the caliper of the sheet. The heavy calendering of the cellulose paper web associated with conventional techniques is not required to produce a paper having print properties comparable to conventional coated papers. Furthermore, even when the cellulose paper web is smoothed, much lower pressures can be applied to provide similar printing properties on papers with increased stiffness. In accordance with certain embodiments of the present invention, the cellulose paper web is smoothed such that the caliper decreases not more than about 7% and typically is decreased by between about 2% and 5%. By comparison, conventional coated papers are typically calendered before coating at much higher pressures, which cause an increase in density of from about 20 to 25%. In accordance with one aspect of the invention, the cellulose paper web may be calendered to a Parker Print Surf smoothness of between about 2 and 6 microns prior to application of the polymer film. However, substrates with higher Parker Print Surf values may be used. For example, a substrate with a Parker Print Surf smoothness of about 9 microns may be used. Parker Print Surf smoothness is determined in accordance with TAPPI standard T 555 om-99. [0039] FIG. 1 illustrates an apparatus 10 useful in practicing certain embodiments of the invention. A substrate 12 is subjected to treatment on one surface thereof with crosslinkable polymer coating 14 to form a layer of polymer coating 16 on substrate 12. While the polymer coating is still wet, an optional crosslinking solution 18 may be applied to the layer of polymer coating 16 thereby forming a cross linked polymer coating 20 on substrate 12. The polymer coating 20 is typically at least partially crosslinked. The polymer coating is still in a wet state before being brought into contact with hot polished drum 22 by pressing the web 12 against the drum surface with a press roll 24. Heat from the drum surface causes boiling within the wet polymer coating, so that voids form in the polymer under the surface. The crosslinking solution causes the polymer coating to crosslink and gel into a substantially continuous layer or film. Typically, the resulting film will exhibit improved strength over the base sheet. The polymer treated sheet may not be fully dried so it may be conveyed through a secondary heater 26. Any type of secondary heating device can be used that is capable of drying the treated sheet without adversely affecting the properties of the sheet. The treated sheet emerges from secondary heaters 26 as a polymer film treated substrate 28 characterized by improved flatness and smoothness. Optionally, additional coating processes 30 (and other processes such as coating, gloss calendering, etc) may be used to form a coated product 32. [0040] As shown in FIG. 1, the web wraps a substantial portion of hot polished drum 22. The amount of wrap may depend on operating conditions such as web speed, moisture content of the polymer film forming composition 20, temperature of the drum, and other process factors. It is possible that a small amount of contact time with hot polished drum 22 may be sufficient. Besides providing the substrate in web form, it may also be provided in sheet form. [0041] The crosslinkable polymer coating and the optional crosslinking solution may be applied by any number of techniques, such as dip-coating, rod coating, doctor blade coating, gravure roll coating, reverse roll coating, metered size press, smooth roll coating, extrusion coating, curtain coating, spray coating and the like. The crosslinkable polymer coating and crosslinking solutions may be applied by the same coating technique or different methods may be used for each. [0042] One embodiment in accordance with the present invention is based on the coagulation or gelling that occurs between polyvinyl alcohol and borax. In accordance with this type of system polyvinyl alcohol (PVOH) is an example of a crosslinkable polymer and a borax solution is an example of a corresponding crosslinker. Once the PVOH solution 14 is applied, at approximately 25% solids and coverage of about 5 g/m2 dry, the crosslinker solution 16 is applied at a rate and solution solids to give a borax coverage of at least about 0.1 g/m2 dry. This wet, crosslinked polymer film 20 is then brought into contact with a hot polished drum 22 by pressing the web 12 against the drum surface with a press roll 24. The drum surface temperature is at least about 150°C, or in accordance with certain embodiments, at least about 190°C so that the coating can be dried and release from the drum surface. The contact time of the polymer film to the drum may be in the range of up to about 3.0 seconds, more particularly between about 0.5 - 2.0 seconds. This is sufficient time for the polymer film to immobilize and solidify, giving the surface of the polymer film a flat smooth finish mirroring the surface of the drum. Immobilizing the polymer film includes at least partially drying the film. The coating is not necessarily completely dry when it leaves the drum, so additional drying 26 may be needed. The web then continues on through the process and may receive additional coating layers, for example conventional coatings, prior to being wound up. The polymer coating may be applied as a single layer or as two or more layers. Limited experiments also suggest that a polymer film may be immobilized or solidified with just momentary contact with the heated drum, as may be achieved by using a press roll 24 to press the web 12 against the hot drum 22, without any additional wrap of web around the hot drum. However, it is contemplated that some wrap of the hot drum may be practiced, and that optionally a felt 23 may be used to help press the web into contact with the hot drum. If a felt 23 is used to help press the web into contact with the hot drum, then the felt 23 may be carried between the press roll 24 and the heated drum 22. [0043] The contact between the polymer film and the hot drum causes boiling to occur in the polymer film, creating voids or bubbles in the film. Nip conditions should be adjusted so that boiling may occur. Satisfactory lab results were obtained with a resilient press roll, a 9" wide web, and nip loads between about 2 to about 15 pounds per linear inch. Depending on press roll hardness and the diameters of the hot drum and press roll, conditions may have to be adjusted. [0044] Specific examples of crosslinkable polymers useful in certain embodiments of the present invention include crosslinkable hydrogels. The following crosslinkable hydrogels are particularly useful: starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soybean protein, and alginates. One or more polymers selected from the above-recited ones can be used. The crosslinkable polymer typically is applied in solution form and usually as an aqueous solution. The concentration of the polymer in solution is not particularly limited but can be easily determined by one of ordinary skill in the art. For example, a solution of about 20% starch may be used as described below. The crosslinkable polymer may be applied to provide a surface coverage (dry basis) of from about 3 to about 15 gsm (g/m2) more particularly from about 4 to about 8 gsm. In accordance with particular embodiments of the present invention, the crosslinkable polymer may be used in an amount ranging from about 60% to about 100% by weight of the dry materials. [0045] Specific examples of crosslinkers include borates, aldehydes, ammonium salts, calcium compounds and derivatives thereof. The crosslinker if used typically may be applied in solution form and usually as an aqueous solution. The concentration of the crosslinker in solution is not particularly limited but can be easily determined by one of ordinary skill in the art. The crosslinker may be applied to provide a surface coverage (dry basis) of from about 0.1 to about 0.5 gsm more particularly from about 0.2 to about 0.3 gsm. [0046] The temperature of the heated surface is in excess of that typically used for cast coating. The higher temperature should allow for higher run speeds. It is anticipated that paper or paperboard produced in accordance with certain embodiments of the present invention may be produced at speeds in the range of about 750 to 3000 fpm, more particularly from about 1500 to 1800 fpm. Although not wishing to be bound by theory, the higher temperature and the dwell time are selected such that the coating composition is heated to its boiling temperature and it appears that when the coating boils there is an increase in contact area between the coating and the drum. The increased contact results in a polymer film heated surface that exhibits improved smoothness and gloss. Furthermore, the treated surface is ink receptive. Boiling of the coating as it is being smoothed on the polished drum surface appears to significantly improve gloss and smoothness of the finished polymer film treated substrate. [0047] The polymer coating on the substrate is typically pressed against the heated surface for a sufficient period of time to allow the coating to boil and then set to a smooth, glossy finish. In accordance with particular embodiments, the contact time of the forming polymer film to the drum is within the range of up to about 3.0 seconds, more particularly up to about 2.0 seconds, and most particularly up to about 0.5 seconds. [0048] The polymer coating may also include one or more pigments. Examples of useful pigments include, but are not limited to, kaolin, talc, calcium carbonate, calcium acetate, titanium dioxide, clay, zinc oxide, alumina, aluminum hydroxide and synthetic silica such as noncrystalline silica, amorphous silica or finely divided silica are examples thereof. Organic pigments may also be used. [0049] The crosslinkable polymer coating and/or the crosslinking solution may further include one or more release agents. Specific examples of release agents useful herein include, without limitation, waxes, such as petroleum, vegetable, animal and synthetic waxes, fatty acid metal soaps, such as metal stearates, long chain alkyl derivatives, such as fatty esters, fatty amides, fatty amines, fatty acids, and fatty alcohols, polymers, such as polyolefins, silicone polymers, fluoropolymers, and natural polymers, fluorinated compounds, such as fluorinated fatty acids and combinations thereof. One of ordinary skill in the art can readily determine the amount of release agent to use in a particular application. Typically, the coating may contain from about 0.3 to 10 percent release agent, more particularly from about 2 to 5 percent by weight. Instead of or in addition to release agent in the coating, release agent may be sprayed onto the coating surface, or applied to the heated drum surface. If a non-sticking surface can be provided on the heated drum, whether by a release agent or other means, then application of a release agent in the coating or onto the coating surface may not be needed. [0050] The polymer coating employed in certain embodiments of the present invention, wherein at least the aforementioned polymer is contained, is generally prepared in the form of an aqueous composition. An appropriate ratio between those ingredients is different depending on the polymer composition, the application conditions and so on, but it has no particular limitation as far as the treated paper produced can satisfy the quality required for the intended use thereof. Further, the polymer coating according to certain embodiments of the present invention can optionally contain additives, such as a dispersant, a water retaining agent, a thickening agent, an anti-foaming agent, a preservative, a colorant, a waterproofing agent, a wetting agent, a drying agent, an initiator, a plasticizer, a fluorescent dye, an ultraviolet absorbent, a release agent, a lubricant and a cationic polyelectrolyte. [0051] In accordance with a particular embodiment of the present invention, the substrate is treated with the polymer coating near a central region of the paper machine, such as the size press position. Furthermore, the apparatus for applying the polymer coating to the substrate may be positioned relative to the paper machine so as to apply the polymer film to either surface of the forming paper web. More than one apparatus may be employed to apply a polymer film to each side of the forming paper web. [0052] These advantages allow the use of lightly calendered paper or paperboard, thus preserving stiffness while providing good printing properties. [0053] The base sheet is typically formed from fibers conventionally used for such purpose and, in accordance with the particular embodiments, includes unbleached or bleached kraft pulp. The pulp may consist of hardwood or softwoods or a combination thereof. The basis weight of the cellulose fiber layer may range from about 30 to about 500 gsm, and more particularly, from about 150 to about 350 gsm. The base sheet may also contain organic and inorganic fillers, sizing agents, retention agents, and other auxiliary agents as is known in the art. The final paper product can contain one or more cellulose-fiber layers, polymer film layers and, in accordance with certain embodiments, other functional layers. [0054] The present invention in accordance with certain embodiments, provides one or two-sided coated paper or paperboard for printing or packaging whose Parker Print Surf smoothness value after the coating and finishing processes, when measured according to TAPP1 paper and pulp test method No. 5A, is lower than about 2-3 microns. [0055] The paper or paperboard described herein may further be provided with one or more additional coatings. A top coating containing conventional components may be provided to improve certain properties of the paper or paperboard. Examples of such conventional components include pigments, binders, fillers and other special additives. The top coating, when present, may be applied at much lower coat weights than conventional coatings and yet provide similar print properties. Accordingly, the top coating weight may be about 4 to 9 gsm as a single coating layer or about 8 to 18 gsm as two coating layers. By contrast, conventional coated papers typically require about 10 to 20 gsm as a single coating layer or 18 to 30 gsm as two coating layers to provide comparable surface properties. The paper or paperboard may also be coated on the side of the sheet having the non-treated surface. [0056] Having given the teachings of the present disclosure, it will now be illustrated by means of specific examples which should not be considered as limiting the scope of the claims in any way. [0057] A base sheet having a caliper of about 10 points, a Parker Print Surf (PPS) value of about 9 microns (10kg pressure with a soft backing) and a Sheffield smoothness of about 310 can be treated in accordance with certain embodiments of the present invention to provide a treated sheet having improved smoothness with only a minimal decrease in caliper. The base sheet may be treated by applying a PVOH solution at approximately 25% solids to the base sheet to provide a coverage of about 5 g/m2 dry. Next, the crosslinker solution may be applied at a rate and solution solids to give a borax coverage of at least about 0.1 g/m2 dry. The wet, crosslinked polymer film can be brought into contact with a hot polished drum by pressing the sheet against the drum surface. The drum surface temperature may be at least about 190°C. The coating would be dried and released from the drum surface. The contact time of the pblymer film to the drum would typically be in the range of between about 0.5 - 2.0 seconds. The treated sheet would have a caliper of between about 9.6 and 10.0 points, a PPS value of about 2.4 to 3.0 and a Sheffield smoothness of about 140-170. [0058] In a preferred embodiment, a starch solution may be used as the polymeric material in the polymer coating. [0059] One aspect of the disclosure relates to a paper or paperboard manufacturing method. In accordance with one embodiment of the invention, the method includes applying a polymer coating comprising a crosslinkable hydrogel to a substrate, applying a crosslinking solution to the polymer coating on the substrate surface thereby forming at least a partially crosslinked polymer film-forming coating and bringing the polymer film-forming coating into contact with a heated surface while the polymer film-forming coating is still in a wet state. The heated surface may be a hot polished drum having a flat smooth finish. The temperature of the heated surface typically is within a range of from about 150°C to about 240°C. Higher temperatures may be used, for example up to about 300°C. The temperature of the heated surface in accordance with certain embodiments is within a range of from 180°C to about 200°C, and in accordance with certain embodiments is at least about 190°C. [0060] In accordance with particular embodiments of the invention, the crosslinkable polymer may be selected from the group consisting of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soybean protein, and alginates. In accordance with certain aspects of the present invention, the crosslinkable polymer may be used in amounts ranging from about 60 to about 100% by weight of the dry materials. [0061] In some manifestations, the crosslinker may be a borate or borate derivative such as borax, sodium tetraborate, boric acid, phenyl boronic acid, or butyl boronic acid. The crosslinker may be used in amounts ranging from about 1 to about 12% based on the crosslinkable polymer. [0062] The present invention is also directed to treated papers produced in accordance with the method described herein. The treated papers are characterized by improved smoothness in conjunction with relatively minor increases in density compared to the original sheet. [0063] As it is desirable to have the coating in a wet state when it contacts the heated drum, the coating may be moistened for example by applying water. One method is to spray water onto the coating before it contacts the hot drum. However, in certain embodiments, it may also be possible to operate without any additional moistening. [0064] In certain embodiments, starch may be used as the soluble polymer. In certain embodiments, starch-based coatings can be run successfully without a crosslinker, and good results may be obtained without gelling (also called coagulating). [0065] A starch solution containing 2-5% of a release agent was brought into contact with a heated drum under conditions described above. In certain conditions, if moistening of the coating is desired, water alone may be used as the spray and yield a good reproduction of the polished surface. If the coating solids are low enough, the process works without a moistening water spray. A 20% solids starch coating was applied to the web and brought into contact with a heated drum, and gave good reproduction. [0066] Starch coatings were also tested having 25% and 30% solids. Both of these coatings released from the drum without any sticking, but without good surface reproduction. The 25% solids coating gave moderate reproduction, but the 30% solids coating was not very smooth. It appears that a certain amount of water present at the surface may help to propagate boiling throughout the entire coating. Below a certain amount of surface water, localized surface areas may still have sufficient boiling to give good reproduction of the drum surface, but other surface areas do not. Thus, without moistening of the surface with a water spray, as solids increase above 20%, the percentage of the area that reproduces the smooth drum surface decreases with increasing coating solids, until at about 30% coating solids, little or no surface smoothness reproduction is achieved. If sufficient water is sprayed on the surface of the 30% solids coating before it contacts the heated drum, complete surface reproduction can be obtained. We would expect this relationship to also be affected by rawstock absorptivity, coat weight, coating viscosity and process speed. It should be possible to establish the effects of these parameters by further experiments. [0067] The examples described above were run with a chrome surface on the heated drum. The examples described below were run after the drum was resurfaced with a tungsten carbide coating.' In each of these examples, several "runs" were made to collect the data. A run consists of the drum being heated to approximately 190°C, the spray level being set, coating being applied to the web by a metered rod method, optionally followed by moistening spray (which optionally may contain a cross linking agent), and then by the web being brought into contact with the drum at 35 fpm. The drum temperature during a run varied between 180°C and 190°C. During a run, the only variable that was changed was the coating weight applied by the metering rod. Changes in coating type, coating solids, or spray level were made in different experimental runs on the equipment. Coat weight was measured by differential weight and is reported as bone-dry. Some of experiments were run with cross linker in the coating itself, for example when a material such as starch was used, which does not strongly cross link. [0068] Example 1 [0069] A minimally pressed base sheet with a basis weight of 111 lb/3000 ft2 was used as a substrate on which to apply and treat simple coating compositions. The first coating was 95% by dry weight CELVOL 203S polyvinyl alcohol (PVOH) and 5% Emtal 50 VCS, a triglyceride used as a release agent. The coating solids were 20% by weight. The coating was applied by a metering rod. The Table is a list of samples and test conditions. Sample 1.1 was made by spraying the coating with a crosslinking solution containing 3% by weight borax and 1% by weight of a sulfonated castor oil as a release agent. The spraying rate was 48 milliliters per minute. The sample replicated the drum well and released from the drum without sticking. Significant improvements in smoothness were obtained with minimal loss of caliper. For sample 1.2, the conditions were the same except that no borax was used in the spray solution. Without the borax to crosslink the polyvinyl alcohol, the coating did not release from the surface, and part of the film remained on the drum surface. This experiment clearly showed the benefit of crosslinking the polyvinyl alcohol. [0070] In another run, carboxymethyl cellulose (CMC) was substituted for the polyvinyl alcohol to compare polymer performance. The carboxymethyl cellulose was FINFIXX 30, which could only be run at 7% solids due to coating viscosity. The coating was formulated with 95% polymer and 5% Emtal. Samples 1.3 and 1.4 are two different coat weights sprayed with 48 ml/min of borax spray. The coating replicated the drum surface well and released completely from the drum. Smoothness was improved with minimal loss of caliper, but smoothness was not as good as for polyvinyl alcohol. For the run that produced Sample 1.5, no borax was used in the spray. The coating replicated the drum surface well and released completely from the drum. Smoothness was improved by removing the borax. This showed that a non- crosslinked coating could replicate and release from the drum, which indicates that materials other than crosslinkable materials can be used in this process. [0071] Example 2 [0072] A minimally pressed base sheet having a basis weight of 1111b/3000 ft2 was used as a substrate on which to apply and treat simple coating compositions. The first coating was 95% by dry weight CLEER-COTE 625 starch (a viscosity modified waxy corn starch) and 5% Emtal 50 VCS, a triglyceride used as a release agent. The coating solids were 20% by weight. The coating was applied by a metering rod. Sample 2.1 was made by spraying the coating with a crosslinking solution containing 3% by weight borax and 1% by weight of a sulfonated castor oil as a release agent. The spraying rate was 46,milliliters per minute. The sample replicated the drum well and released from the drum without sticking. Significant improvements in smoothness were obtained with minimal loss of caliper. Samples 2.2, 2.3, 2.4 and 2.5 were made with different coat weights of the same coating, but the spray did not contain borax. All samples replicated the surface well and released completely from the drum. Samples 2.6 and 2.7 were run without any spray at all. The samples replicated the surface well and completely released. Smoothness values were not quite as good, but samples still had significantly improved smoothness with minimal reduction in caliper. This demonstrates that the process can work without any moistening spray. [0073] Example 3 [0074] This experiment was a continuation of Example 2 exploring the effect of coating solids. Samples 3.1 and 3.2 were run at 23% coating solids without any moistening spray. Good replication and release were obtained. For samples 3.3 and 3.4, coating solids were increased to 25.7%, again applied with no moistening spray. Complete release was obtained, but incomplete replication of the surface was achieved. Based on visual inspection, only about 90-95% of the surface replicated the drum. For samples 3.5 and 3.6, this same 25.7% solids coating was run and a moistening spray of 48ml/min was applied. The surface replication was complete and the smoothness values were greatly improved. For Samples 3.7 through 3.12. a 30% solids coating was used. When no moistening spray was used (3.7), complete release was achieved, but only a small percentage of the surface was replicated. When 48 ml/min of moistening spray was used (3.8), the replication was greatly improved, but the surface was still mottled with areas of poor replication. When the moistening spray was increased to 98 ml/min (3.9, 3.10, 3.11 & 3.12), the replication was complete and smoothness was greatly improved with minimal reduction in caliper. Next, the coating solids were lowered. At 17.5% coating solids (3.13, 3.14) with no moistening spray applied, good release and complete replication were obtained. At 10% solids (3.15) with no moistening spray applied, the low coating viscosity led to reduced coat weight and increased coating absorption into the sheet, so poor replication occurred. [0075] Samples of the smooth products, produced using starch as the polymer coating, at 20% solids, were top coated with a conventional pigmented clay coating (about two-thirds clay and one third carbonate, with a latex binder, applied in a single coat of approximately 10 lb/ 3000ft2) applied over the smooth polymer layer. These samples then were cross sectioned to examine the morphology of the coating layer. Cross sectioning was done by freezing the samples in liquid nitrogen, then cracking the samples in two (freeze fracturing). The cracked edges of the samples (e.g., the cross sections) were then viewed under a microscope. [0076] Micrographs revealed that voids exist in the polymer coating layer, as shown in FIGs. 2 through 9, which include measurement bars to indicate their scale. For FIGs. 2-5, the microscope magnification was 1000, and the measurement bars are 20 microns long. In FIG. 2 as an example, the structure as shown includes a paperboard substrate 110. The substrate thickness generally extends below the area of the micrograph. Because of the freeze fracturing process, the substrate 110 as shown in the micrographs is sometimes separated or partly separated from polymer layer 120. Therefore the upper boundary of substrate 110 may be only approximately shown by the bracketed distance denoting the substrate. [0077] In these samples, the polymer coating layer 120 had been applied onto substrate 110, and dried against a heated drum, as described previously. Then a top coating 130 was applied and dried. The term "polymer coating" is used here to describe that layer applied as described above, then contacted while wet against a heated drum. The term "top coating" is used to describe the outer layer, which was applied as one layer. Obviously the "top coating" could be applied in more than layer and could be of coating materials other than those used here. [0078] Voids 121 are evident in the polymer coating layer 120, as seen in FIGs. 2-9. FIG. 2 for example shows several voids 121 in polymer coating layer 120, with the voids appearing to be approximately 5 to 20 microns in lateral dimension. It is assumed that their size going "into" the fractured sample is in approximately the same range. The voids typically appear to be somewhat "flattened" in the "vertical" direction, that is, going into the sample thickness. The voids also appear to have "walls" that are relatively smooth, and generally thin. These thin walls are most apparent as seen between adjacent voids. Where a void wall is adjacent to the top coating 130, its thickness may be difficult to see but its presence may be deduced by the smooth lower contour of the top coating 130 adjacent to the void. [0079] FIG. 3 is an example micrograph showing several voids 121 in the polymer coating layer. The voids appear to extend over an area equivalent to more than half the coated surface area. The polymer coating layer is not well defined in this micrograph. [0080] FIG. 4 is an example micrograph showing several voids 121 in polymer coating layer 120. The walls of the voids appear to be relatively thin, as evidenced by a somewhat translucent appearance in the walls of two of the voids. [0081] For FIGs. 5-9, the microscope magnification was 500 and the measurement bars are 50 microns long. FIG. 5 shows several voids 121 in polymer layer 120, with individual measurement bars showing dimensions of the selected voids, for example, moving generally from left to right, measurements of 10.5 microns in vertical distance, 36 microns in lateral distance, 10.6 microns in vertical distance, and 36.3 microns in lateral distance. Again the voids appear to extend over an area equivalent approximately half the coated surface area. [0082] FIG. 6 shows another sample with similar measurement bars, for example, moving generally from left to right, measurements of 8.66 microns in vertical distance, 32.1 microns in lateral distance, 11.8 microns in vertical distance, and 22.7 microns in lateral distance. Measurements such as these in FIGs. 5 and 6 were collected for use in the graph discussed later in FIG. 17. [0083] FIG. 7 shows voids 121 in polymer layer 120, including several showing a generally flattened aspect. The voids appear to extend over an area equivalent to nearly all the coated surface area. FIG. 8 shows another sample with similar widespread voids 121. The wall areas of several voids are visible. FIG. 9 shows yet another sample where the voids 121appear to extend over an area equivalent to nearly all the coated surface area. [0084] Other samples of the smooth products, produced using starch as the polymer coating, at 20% solids, were not top-coated. These samples were cross sectioned to examine the morphology of the coating layer. Cross sectioning was done by freezing the samples in liquid nitrogen, then cracking the samples in two (freeze fracturing). The cracked edges of the samples (e.g., the cross sections) were then viewed under a microscope as shown in FIGs. 10 to 12, which include measurement bars to indicate their scale. The microscope magnification was 1000, and the measurement bars are 20 microns long. FIG. 10 shows the polymer layer 120, which contains voids 121 and has a very smooth outer surface. The polymer layer is on paperboard substrate 110, and one of the cellulose fibers 112 is denoted. The substrate thickness generally extends below the area of the micrograph. [0085] FIGs. 11 and 12 show additional micrographs of samples that were polymer coated but not top-coated. Again the smoothness of the polymer layer 120 is evident, as are the underlying voids 121. The walls of the voids often coincide with the surface of the polymer coating. [0086] FIG. 13 (at 200x magnification) and FIG. 14 (at 500x magnification) show the surface of samples as seen under a scanning electron microscope. These samples were not given top coating 130. The larger string-like structures 112 are cellulose fibers of the substrate 110. The smaller cell-like structures 122 that appear as a fine network or mesh are individual voids in polymer layer 120. The polymer layer here appears essentially transparent, except for the walls of the voids. [0087] FIGs. 15 and 16 show the surface of samples as seen under a backscatter scanning electron microscope. These samples were not given top coating 130. The larger string-like structures 112 are cellulose fibers of the substrate 110. The smaller cell-like structures 122 that appear as a fine network or mesh are the walls of individual voids in polymer layer 120. The polymer layer here appears essentially transparent, except for the walls of the voids. The voids appear to be distributed over the entire surface. [0088] FIG. 17 is a graph showing the distribution of void sizes based on approximately 90 measurements each of void width (lateral dimension) and height (vertical dimension in the micrographs). The measurements show an average void width (measured in the direction parallel to the thickness of the sample) of about 19 microns, with a standard deviation of about 9 microns. The measurements show an average void height (measured in the direction going "into" the sample thickness) of about 10 microns, with a standard deviation of about 4 microns. [0089] These void dimensions appear to be representative of the samples studied here. However, they are not meant to be limiting as changes in materials or processing conditions might give other dimensions. [0090] It is hypothesized that steam bubbles create these voids while the coating is in contact with the heated drum, and that the bubbles may provide a force to help keep the coating in contact with the drum. The resulting voids typically help bridge the gap between an otherwise rough substrate layer 110, and the smooth surface of the heated drum. Thus the dried polymer coating has a smooth replicated surface, which is smoother than the substrate layer 110. It appears that many or most of the voids remain intact when top coating 130 is applied. Therefore the top coating may end up smoother because of the relatively smooth underlying polymer layer 120. This is seen as an advantage achieved by the invention. Besides the hypothesized influence of the voids on help creating a smooth replicated surface, the voids may also contribute to a lower density in the product. [0091] The conditions in the nip between press roll 24 and hot drum 22 may influence whether voids form in the polymer coating. Depending on press roll hardness, and the diameters of the press roll and hot drum, it may be necessary to adjust the nip loading (for example, the PLI loading on the nip) in order to achieve boiling in the nip which creates the voids. [0092] The polymer-coated paper or paperboard created by this process may be used wherever a smooth substrate or finished product is desired. The polymer-coated paper or paperboard may be used as-is (e.g., as shown in FIGS. 10-16), or it may be used as a substrate for additional coatings or other treatments to be applied (for example the top coating 130 shown in FIGs. 2-9, or other coatings) thereon. Additional finishing materials or processes may be applied to the polymer-coated paper or paperboard, with or without additional coatings. For example, one or more additional coatings may be applied, as is typical with base coating, top coating, and triple coating of conventional paper or paperboard substrates. Calendering processes may be applied, before or after optional additional coating. For example one or more additional coatings may be applied, followed by a gloss calendering step. [0093] Methods of making and using polymer-coated material in accordance with the invention should be readily apparent from the mere description of the material and process as provided herein. No further discussion or illustration of such material or methods, therefore, is deemed necessary. [0094] While preferred embodiments of the invention have been described and illustrated, it should be apparent that many modifications to the embodiments and implementations of the invention can be made without departing from the spirit or scope of the invention. Although the preferred embodiments illustrated herein have been described in connection with a paper or paperboard substrate, these embodiments may easily be implemented in accordance with the invention in other structures, including without limitation textiles, non-woven fabrics, fibrous materials, polylactic acid substrates, and porous films. [0095] It is to be understood therefore that the invention is not limited to the particular embodiments disclosed (or apparent from the disclosure) herein, but only limited by the claims appended hereto. We Claim: 1. A substrate coated with polymer composition, comprising: a substrate and a first coating on the substrate, wherein the first coating includes a surface having a Sheffield Smoothness of less than 300 units, and wherein voids are formed under said surface of the first coating; wherein at least 50% of the first coating surface has subsurface voids having a transverse dimension of at least 5 µm. 2. The substrate coated with polymer composition as claimed in claim 1, wherein the surface has a Sheffield Smoothness of less than 200 units. 3. The substrate coated with polymer composition as claimed in claim 1, wherein the surface has a Sheffield Smoothness of less than, 150 units. 4. The substrate coated with polymer composition as claimed in claim 1, wherein the substrate comprises at least one of cellulose, paper, paperboard, fabric, fibrous material, porous material, porous film, or polylactic acid. 5. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating includes a water soluble polymer. 6. The substrate coated with polymer composition as claimed in claim 5, wherein the first coating includes a release agent. 7. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating contains essentially no elastomeric material. 8. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating includes a cross linking agent. 9. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating includes by dry weight at least about 60% water soluble polymer and up to 10% release agent. 10. The substrate coated with polymer composition as claimed in claim 5, wherein the water soluble polymer includes a cross linkable polymer. 11. The substrate coated with polymer composition as claimed in claim 5, wherein the water soluble polymer includes at least one of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soybean protein, and alginate. 12. The substrate coated with polymer composition as claimed in claim 9, wherein the release agent includes at least one of wax, petroleum wax, vegetable wax, animal wax, synthetic wax, fatty acid metal soap, metal stearates, long chain alkyl derivatives, fatty esters, fatty amides, fatty amines, fatty acids, fatty alcohols, polymers, polyolefins, silicone polymers, fluoropolymers, natural polymers, fluorinated compounds, fluorinated fatty acids, and combinations thereof. 13. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating includes a water soluble polymer and essentially no elastomeric material. 14. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating includes a cross linkable polymer and essentially no elastomeric material. 15. The substrate coated with polymer composition as claimed in claim 1, wherein said substrate sheet is paper or paperboard and further comprising a second coating on the first coating. 16. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating includes a water soluble polymer, a release agent, and essentially no elastomeric material. 17. The substrate coated with polymer composition as claimed in claim 8, wherein the cross linking agent comprises at least one of borax, borates, aldehydes, ammonium salts, calcium compounds, and derivatives thereof. 18. The substrate coated with polymer composition as claimed in claim 17, wherein the second coating includes at least one of pigments, binders, and fillers. 19. The substrate coated with polymer composition as claimed in claim 1, wherein the first coating includes by dry weight at least 60% water soluble polymer and up to 10% release agent. 20. The substrate coated with polymer composition as claimed in claim 1, wherein the voids are bounded by walls formed from the first coating. 21. The substrate coated with polymer composition as claimed in claim 1, wherein said substrate comprises a sheet or a web. ABSTRACT A method for treating a substrate is described. In accordance with one aspect, the method includes applying a polymer coating to a substrate, and bringing the polymer coating into contact with a heated surface while the coating is still in a wet state. Optionally the polymer coating may include a crosslinkable material, and a crosslinking agent may be used to promote crosslinking. The polymer coating replicates the heated surface. A product produced in accordance with thedescribed method is also disclosed. The product is characterized by having subsurface voids within the coating.

Full Text

REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority under 35 U.S.C. § 119(e) of
provisional application serial number 60/776,114 filed on February 23, 2006, which is
hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present disclosure relates to a method for treating a substrate with a
polymer film-forming composition. More particularly, the disclosure relates to a
paper or paperboard manufacturing method comprising the steps of applying a
polymer film-forming coating to a substrate, and, bringing the polymer coating into
contact with a heated surface while the polymer coating is still in a wet state. The
resulting polymer layer has a smooth surface with voids (e.g., bubbles) just below the
surface. In certain embodiments, the polymer coating may comprise a crosslinkable
hydrogel, and a crosslinking solution may be applied to the polymer coating on the
substrate surface thereby forming at least a partially crosslinked polymer coating then
placed into contact with a heated surface. The present disclosure also relates to a
treated substrate product.
[0003] Paper is manufactured by an essentially continuous production process
wherein a dilute aqueous slurry of cellulosic fiber flows into the wet end of a paper
machine and a consolidated dried web of indefinite length emerges continuously from
the paper machine dry end. The wet end of the paper machine comprises one or more
headboxes, a drainage section and a press section. The dry end of a modern paper
machine comprises a multiplicity of steam heated, rotating shell cylinders distributed
along a serpentine web traveling route under a heat confining hood structure.
Although there are numerous design variations for each of these paper machine
sections, the commercially most important of the variants is the fourdrinier machine
wherein the headbox discharges a wide jet of the slurry onto a moving screen of
extremely fine mesh.
[0004] The screen is constructed and driven as an endless belt carried over a
plurality of support rolls or foils. A pressure differential across the screen from the
side in contact with the slurry to the opposite side draws water from the slurry through
the screen while that section of the screen travels along a table portion of the screen
route circuit. As slurry dilution water is extracted, the fibrous constituency of the

slurry accumulates on the screen surface as a wet but substantially consolidated mat.
Upon arrival at the end of the screen circuit table length, the mat has accumulated
sufficient mass and tensile strength to carry a short physical gap between the screen
and the first press roll. This first press roll carries the mat into a first press nip
wherein the major volume of water remaining in the mat is removed by roll nip
squeezing. One or more additional press nips may follow.
[0005] From the press section, the mat continuum, now generally characterized as a
web, enters the dryer section of the paper machine to have the remaining water
removed thermodynamically.
[0006] Generally speaking, the most important fibers for the manufacture of paper
are obtained from softwood and hardwood tree species. However, fibers obtained
from straw or bagasse have been utilized in certain cases. Both chemical and
mechanical defiberizing processes, well known to the prior art, are used to separate
papermaking fiber from the composition of natural growth. Papermaking fiber
obtained by chemical defiberizing processes and methods is generally called chemical
pulp whereas papermaking fiber derived from mechanical defiberizing methods may
be called groundwood pulp or mechanical pulp. There also are combined defiberizing
processes such as semichemical, thermochemical or thermomechanical. Any of the
tree species may be defiberized by either chemical or mechanical methods. However,
some species and defiberizing processes are better economic or functional matches
than others.
[0007] An important difference between chemical and mechanical pulp is that
mechanical pulp may be passed directly from the defiberizing stage to the paper
machine. Chemical pulp on the other hand must be mechanically defiberized, washed
and screened, at a minimum, after chemical digestion. Usually, chemical pulp is also
mechanically refined after screening and prior to the paper machine. Additionally, the
average fiber length of mechanical pulp is, as a rule, shorter than that of chemical
pulp. However, fiber length is also highly dependent upon the wood species from
which the fiber originates. Softwood fiber is generally about three times longer than
hardwood fiber.
[0008] The ultimate properties of a particular paper are determined in large part by
the species of raw material used and the manner in which the paper machine and web

forming process treat these raw materials. Important operative factors in the
mechanism of forming the paper web are the headbox and screen.
[0009] Coated paper or paperboard used for printing and for packaging is generally
required to have high level of gloss, excellent smoothness, and excellent printability,
as well as certain strength and stiffness characteristics.
[0010] If the coated paper or paperboard has a high stiffness, it can pass smoothly
through high-speed printing or packaging machines with less feeding jams. Higher
stiffness paper can be advantageously used in books, magazines, and catalogues,
because it provides a feel of hardness or heaviness similar to a hardcover book. For
packaging, high stiffness is necessary for maintaining the structural integrity of the
paperboard product during filling and in subsequent use.
[0011] Stiffness has close relationship to the basis weight and density of paper.
There is a general trend that stiffness increases as the basis weight increases, and
decreases as the paper density increases. Stiffness and other properties can be
improved by increasing basis weight. However, this would result in a product
utilizing more fibers, which add cost and weight. Therefore, coated paper or
paperboard with high stiffness but moderate basis weight is desirable. Paper with
moderate basis weight is also more economical because less raw material (fiber) is
utilized. In addition, shipping costs based on weight are less for low basis weight
paper.
[0012] In addition to high stiffness, coated paper or paperboard which must be
printed is often required to have high gloss and smoothness. For coated paper or
paperboard to have such quality characteristics, density typically must be increased to
some extent to allow for a usable printing surface. Smoothness is normally achieved
by calendering. However, calendering will cause a reduction in caliper, which
typically results in a corresponding reduction in stiffness. The calendering process
deteriorates the stiffness of paper by significantly reducing caliper and increasing the
density. The base sheet for conventional coated board grades typically is heavily
densified by calendering to provide a surface roughness low enough to produce final
coated smoothness acceptable to the industry. These calendering processes, including
wet stack treatment, may increase density by as much as 20% to 25%.

[0013] Thus, the relationship between gloss and stiffness and between smoothness
and stiffness are generally inversely proportional to each other, for a given amount of
fiber per unit area. Packaging grades are sold based on caliper, so manufacturing
processes that reduce the caliper (increasing the density of the board) decrease the
selling price. Processes that cause less caliper reduction save material costs. Caliper
is measured in "points", where a point = 0.001 inches. For example, the conventional
method for making a 10-point board requires the use of a board having a thickness of
greater than 12 points prior to calendering. It would be desirable to be able to
produce a finished board having approximately the same thickness as the starting
substrate.
[0014] Improvements in the calendering process including moisture gradient
calendering, hot calendering, soft calendering, and belt calendering slightly improved
stiffness for a given caliper but did not change the fundamental ratio between caliper,
stiffness, smoothness, and printing properties.
[0015] Various proposals have been made to improve the stiffness of coated paper
or paperboard without calendering for printing. For example, several proposals
include high softwood content in the raw stock, addition of specially engineered fibers
in the raw stock, addition of highly branched polymers within the raw stock, and high
amounts of starch or copolymer latex with a high glass transition temperature
(commonly referred to as "Tg") within the coating formulation.
[0016] However, potential drawbacks to these methods of stiffness improvement are
that although they are useful in improving paper stiffness, they could potentially
degrade the smoothness, gloss, and/or printability of the coated paper obtained.
[0017] For the reasons mentioned above, it has been very difficult to obtain
satisfactory paper smoothness without increasing density. Other methods can be used
for changing the density/smoothness relationship in paper and paperboard grades.
Applying a paper coating is a very common way to enhance the surface properties of
paper without causing the drastic increases in paper density typically associated with
the levels of calendering required to obtain a certain level of smoothness. Preferably,
the final coated surface should be uniform to provide acceptable appearance and
printing properties.

[0018] Therefore, it would be desirable to provide a paper or paperboard product
having the desired properties while maintaining the initial density of the sheet or
minimizing the increase in density. Furthermore, it would be desirable to provide a
paper or paperboard exhibiting improved smoothness without the concomitant
increase in density associated with conventional methods for creating smoothness.
Cast coating methods exist for producing a very smooth surface, but these methods
are typically run at production rates slower than the speed of many paper machines.
WO 96/29199A (D1) to Rutledge (MacMillan Bloedel) discloses coating a
substrate with swelled super absorbent particles having a minimum dimension of at
least 5 microns to obtained desired porosity and roughness in the finished coating, to
produce a coated surface having a roughness in the macro as opposed to the micro
range.
EP 1,197,503 (D2) to Bardman (Rohm and Haas) discloses a coating with core
polymer having an average size of 0.05 to 2 microns, preferably 0.15 to 0.5 microns.
EP 0,218,956 (D3) to Otouma (Asahi Glass) discloses a coating containing
porous particles, the coating having voids up to 100 microns in size between the
particles.
EP 0,959,176 (D4) to Blankenship (Rohm and Haas) discloses the use of hollow
sphere pigment in coatings. The polymer particles having diameters of about 0.6
microns.
GB 1,331,816 (D5) to Penick and Ford discloses a bubble coating, with the
bubbles having an average size less than 10 microns, preferably less than 2 microns in
diameter.
GB 1,287,919 (D6) to Arthur Little discloses a bubble coating, with the 'bubbles'
0.1-1 microns.
US 2006/057358 Al (D7) to Miyake Kazuhito (Fuji) discloses a coating with
particles having voids therein, but the particles are 2 microns or less.
US 3,480,455 (D8) to Richardson (Blandin Paper) discloses a bubble coating
utilizing a volatile liquid hydrocarbon in the 'bubbles' which after drying become air
bubbles. Bubble coatings are stated to have bubbles in the one micron range.
"Introduction to bubble coatings" (D9) by JJ Clancy et al (1 October 1965;
TAPPI, GA, pages 51A - 53A) discloses, bubble coatings have bubbles of 1-2
microns.

US 4,617,239 (D10) to Maruyama (Kuraray) discloses a paper coating, but does
not disclose any subsurface voids.
US 6,991,706 (D11) to Lindsay (Kimberly Clark) discloses a paper with patterns
made on the paper by the forming fabric and relates to absorbent disposable paper
products.
US 6,332,953 (D12) to Singh (International Paper) discloses use of shoe nip
calendaring to provide a product of improved print performance and/or bulk.
US 2003/198885 (D13) to Tamagawa (Fuji)) discloses coating materials for a
image-reproducing material and does not disclose any subsurface voids.
SUMMARY OF THE DISCLOSURE
[0019] In one embodiment, a product is disclosed that includes a substrate with a
coating on the substrate. The coating includes a water soluble polymer and a release
agent. There are voids formed within the coating.
[0020] In another embodiment, a product is disclosed that includes a substrate with
a coating on the substrate. The coating includes a water soluble polymer and
essentially no elastomeric material. There are voids formed within the coating.
[0021] In another embodiment, a product is disclosed that includes a substrate with
a coating on the substrate. The coating includes a surface, and the surface has a
Sheffield Smoothness of less than about 300 units. There are voids formed under the
surface of the coating.
[0022] In another embodiment, a product is disclosed that includes a substrate with
a coating on the substrate. The coating includes a water soluble polymer, a release
agent, and essentially no elastomeric material. The coating includes a surface, and the
surface has a Sheffield Smoothness of less than about 300 units. There are voids
formed under the surface of the coating.
[0023] In another embodiment, a process is disclosed for treating a substrate. A wet
film of aqueous polymer solution is applied to the substrate. The aqueous polymer
solution is immobilized by bringing it into contact with a heated surface to cause the
aqueous polymer solution to boil, and to at least partially dry the aqueous polymer
solution.
[0024] In another embodiment, a process is disclosed for treating a substrate. A wet
film of aqueous polymer solution is applied to the substrate. The aqueous polymer
solution is immobilized by bringing it into contact with a heated surface to cause the

aqueous polymer solution to boil and form voids that remain in the aqueous polymer
solution, and to at least partially dry the aqueous polymer solution.
[0025] In another embodiment, a process is disclosed for treating a substrate. A
coating of aqueous polymer solution is applied to the substrate as a wet film. The
coating includes a water soluble polymer and a release agent. The film is
immobilized by bringing it into contact for less than about 3 seconds with a heated
surface with a temperature above about 150°C so as to cause the aqueous polymer
solution to boil and form voids in the film, and to at least partially dry the film.
[0026] In another embodiment, a process is disclosed for treating a substrate. A
coating of aqueous polymer solution is applied to the substrate as a wet film. The
coating includes a water soluble polymer and essentially no elastomeric material. The
film is immobilized by bringing it into contact for less than about 3 seconds with a
heated surface with a temperature above about 150°C so as to cause the aqueous
polymer solution to boil and form voids in the film, and to at least partially dry the
film.
[0027] In another embodiment, a process is disclosed for treating a substrate. A
coating of aqueous polymer solution is applied to the substrate as a wet film. The
coating includes a water soluble polymer and essentially no elastomeric material. The
film is immobilized by bringing it into contact for less than about 3 seconds with a
heated surface with a temperature above about 150°C so as to cause the aqueous
polymer solution to boil and form voids in the film, and to at least partially dry the
film. The coating surface after drying has a Sheffield Smoothness of less than about
300 units.
[0028] In another embodiment, a process is disclosed for treating a substrate. A
coating of aqueous polymer solution is applied to the substrate as a wet film. The
coating includes a water soluble polymer, a release agent, and essentially no
elastomeric material. The film is immobilized by bringing it into contact for less than
about 3 seconds with a heated surface with a temperature above about 150°C so as to
cause the aqueous polymer solution to boil and form voids in the film, and to at least
partially dry the film. The coating surface after drying has a Sheffield Smoothness of
less than about 300 units.

[0029] In another embodiment, a process is disclosed for treating a cellulosic
substrate. A wet film of aqueous polymer solution is applied to the substrate. The
aqueous polymer solution includes at least about 60% water soluble polymer by dry
weight, and up to 10% release agent by dry weight. The aqueous polymer solution is
immobilized by bringing it into contact for less than about 3 seconds with a heated
surface with a temperature above about 150°C so as to cause the aqueous polymer
solution to boil and form voids in the aqueous polymer solution, and to at least
partially dry the aqueous polymer solution.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0030] FIG. 1 is a schematic view of an apparatus for treating a substrate with a
polymer coating in accordance with one embodiment of the present invention.
[0031] FIGs. 2 - 9 are cross section micrographs showing the morphology of
samples made in accordance with one embodiment of the invention, and having a top
coating.
[0032] FIGs. 10-12 are cross section micrographs showing the morphology of
samples made in accordance with one embodiment of the invention.
[0033] FIGs. 13-14 are surface micrographs made by scanning electron microscope
showing the morphology of samples made in accordance with one embodiment of the
invention.
[0034] FIGs. 15-16 are surface micrographs made by backscatter scanning electron
microscope showing the morphology of samples made in accordance with one
embodiment of the invention.
[0035] FIG. 17 is a graph showing distribution of void dimensions in samples made
in accordance with one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] In describing the preferred embodiments, certain terminology will be utilized
for the sake of clarity. It is intended that such terminology include not only the
recited embodiments but all technical equivalents that operate in a similar manner, for
a similar purpose, to achieve a similar result. The citation of any document is not to
be construed as an admission that it is prior art with respect to the present invention.

Unless indicated otherwise or unless the context suggests otherwise, all weights,
percentages, and ratios are by weight.
[0037] The present disclosure relates to a method for treating a substrate with a
polymer film-forming coating. More particularly, the disclosure relates to a paper or
paperboard manufacturing method comprising the steps of applying a polymer coating
to a substrate, and bringing the polymer coating into contact with a heated surface
while the polymer coating is still in a wet state. Boiling of water in the polymer
coating causes voids to form under the surface, but the surface of the film is smooth.
The paper or paperboard produced in accordance with certain embodiments of the
present invention exhibits desirable levels of surface flatness and smoothness without
significant densification of the base paper. In certain embodiments, the polymer
coating may include a crosslinkable material and a crosslinking solution may be
applied to the polymer coating on the substrate surface thereby forming at least a
partially crosslinked polymer film-forming composition. In such cases, the polymer
coating may typically be applied to the web first and then the cross linking solution
applied before the treated web contacts the heated surface. For weakly cross linking
polymers, it may be possible to provide the cross linking solution in the coating itself.
[0038] One advantage of treating a substrate with a polymer film-forming coating in
accordance with the present invention relates to the improvement in smoothness
and/or flatness that can be obtained without significantly increasing the density or
decreasing the caliper of the sheet. The heavy calendering of the cellulose paper web
associated with conventional techniques is not required to produce a paper having
print properties comparable to conventional coated papers. Furthermore, even when
the cellulose paper web is smoothed, much lower pressures can be applied to provide
similar printing properties on papers with increased stiffness. In accordance with
certain embodiments of the present invention, the cellulose paper web is smoothed
such that the caliper decreases not more than about 7% and typically is decreased by
between about 2% and 5%. By comparison, conventional coated papers are typically
calendered before coating at much higher pressures, which cause an increase in
density of from about 20 to 25%. In accordance with one aspect of the invention, the
cellulose paper web may be calendered to a Parker Print Surf smoothness of between
about 2 and 6 microns prior to application of the polymer film. However, substrates
with higher Parker Print Surf values may be used. For example, a substrate with a

Parker Print Surf smoothness of about 9 microns may be used. Parker Print Surf
smoothness is determined in accordance with TAPPI standard T 555 om-99.
[0039] FIG. 1 illustrates an apparatus 10 useful in practicing certain embodiments of
the invention. A substrate 12 is subjected to treatment on one surface thereof with
crosslinkable polymer coating 14 to form a layer of polymer coating 16 on substrate
12. While the polymer coating is still wet, an optional crosslinking solution 18 may
be applied to the layer of polymer coating 16 thereby forming a cross linked polymer
coating 20 on substrate 12. The polymer coating 20 is typically at least partially
crosslinked. The polymer coating is still in a wet state before being brought into
contact with hot polished drum 22 by pressing the web 12 against the drum surface
with a press roll 24. Heat from the drum surface causes boiling within the wet
polymer coating, so that voids form in the polymer under the surface. The
crosslinking solution causes the polymer coating to crosslink and gel into a
substantially continuous layer or film. Typically, the resulting film will exhibit
improved strength over the base sheet. The polymer treated sheet may not be fully
dried so it may be conveyed through a secondary heater 26. Any type of secondary
heating device can be used that is capable of drying the treated sheet without
adversely affecting the properties of the sheet. The treated sheet emerges from
secondary heaters 26 as a polymer film treated substrate 28 characterized by improved
flatness and smoothness. Optionally, additional coating processes 30 (and other
processes such as coating, gloss calendering, etc) may be used to form a coated
product 32.
[0040] As shown in FIG. 1, the web wraps a substantial portion of hot polished
drum 22. The amount of wrap may depend on operating conditions such as web
speed, moisture content of the polymer film forming composition 20, temperature of
the drum, and other process factors. It is possible that a small amount of contact time
with hot polished drum 22 may be sufficient. Besides providing the substrate in web
form, it may also be provided in sheet form.
[0041] The crosslinkable polymer coating and the optional crosslinking solution
may be applied by any number of techniques, such as dip-coating, rod coating, doctor
blade coating, gravure roll coating, reverse roll coating, metered size press, smooth
roll coating, extrusion coating, curtain coating, spray coating and the like. The

crosslinkable polymer coating and crosslinking solutions may be applied by the same
coating technique or different methods may be used for each.
[0042] One embodiment in accordance with the present invention is based on the
coagulation or gelling that occurs between polyvinyl alcohol and borax. In
accordance with this type of system polyvinyl alcohol (PVOH) is an example of a
crosslinkable polymer and a borax solution is an example of a corresponding
crosslinker. Once the PVOH solution 14 is applied, at approximately 25% solids and
coverage of about 5 g/m2 dry, the crosslinker solution 16 is applied at a rate and
solution solids to give a borax coverage of at least about 0.1 g/m2 dry. This wet,
crosslinked polymer film 20 is then brought into contact with a hot polished drum 22
by pressing the web 12 against the drum surface with a press roll 24. The drum
surface temperature is at least about 150°C, or in accordance with certain
embodiments, at least about 190°C so that the coating can be dried and release from
the drum surface. The contact time of the polymer film to the drum may be in the
range of up to about 3.0 seconds, more particularly between about 0.5 - 2.0 seconds.
This is sufficient time for the polymer film to immobilize and solidify, giving the
surface of the polymer film a flat smooth finish mirroring the surface of the drum.
Immobilizing the polymer film includes at least partially drying the film. The coating
is not necessarily completely dry when it leaves the drum, so additional drying 26
may be needed. The web then continues on through the process and may receive
additional coating layers, for example conventional coatings, prior to being wound up.
The polymer coating may be applied as a single layer or as two or more layers.
Limited experiments also suggest that a polymer film may be immobilized or
solidified with just momentary contact with the heated drum, as may be achieved by
using a press roll 24 to press the web 12 against the hot drum 22, without any
additional wrap of web around the hot drum. However, it is contemplated that some
wrap of the hot drum may be practiced, and that optionally a felt 23 may be used to
help press the web into contact with the hot drum. If a felt 23 is used to help press the
web into contact with the hot drum, then the felt 23 may be carried between the press
roll 24 and the heated drum 22.
[0043] The contact between the polymer film and the hot drum causes boiling to
occur in the polymer film, creating voids or bubbles in the film. Nip conditions
should be adjusted so that boiling may occur. Satisfactory lab results were obtained

with a resilient press roll, a 9" wide web, and nip loads between about 2 to about 15
pounds per linear inch. Depending on press roll hardness and the diameters of the hot
drum and press roll, conditions may have to be adjusted.
[0044] Specific examples of crosslinkable polymers useful in certain embodiments
of the present invention include crosslinkable hydrogels. The following crosslinkable
hydrogels are particularly useful: starch, waxy maize, protein, polyvinyl alcohol,
casein, gelatin, soybean protein, and alginates. One or more polymers selected from
the above-recited ones can be used. The crosslinkable polymer typically is applied in
solution form and usually as an aqueous solution. The concentration of the polymer
in solution is not particularly limited but can be easily determined by one of ordinary
skill in the art. For example, a solution of about 20% starch may be used as described
below. The crosslinkable polymer may be applied to provide a surface coverage (dry
basis) of from about 3 to about 15 gsm (g/m2) more particularly from about 4 to about
8 gsm. In accordance with particular embodiments of the present invention, the
crosslinkable polymer may be used in an amount ranging from about 60% to about
100% by weight of the dry materials.
[0045] Specific examples of crosslinkers include borates, aldehydes, ammonium
salts, calcium compounds and derivatives thereof. The crosslinker if used typically
may be applied in solution form and usually as an aqueous solution. The
concentration of the crosslinker in solution is not particularly limited but can be easily
determined by one of ordinary skill in the art. The crosslinker may be applied to
provide a surface coverage (dry basis) of from about 0.1 to about 0.5 gsm more
particularly from about 0.2 to about 0.3 gsm.
[0046] The temperature of the heated surface is in excess of that typically used for
cast coating. The higher temperature should allow for higher run speeds. It is
anticipated that paper or paperboard produced in accordance with certain
embodiments of the present invention may be produced at speeds in the range of
about 750 to 3000 fpm, more particularly from about 1500 to 1800 fpm. Although not
wishing to be bound by theory, the higher temperature and the dwell time are selected
such that the coating composition is heated to its boiling temperature and it appears
that when the coating boils there is an increase in contact area between the coating
and the drum. The increased contact results in a polymer film heated surface that
exhibits improved smoothness and gloss. Furthermore, the treated surface is ink

receptive. Boiling of the coating as it is being smoothed on the polished drum surface
appears to significantly improve gloss and smoothness of the finished polymer film
treated substrate.
[0047] The polymer coating on the substrate is typically pressed against the heated
surface for a sufficient period of time to allow the coating to boil and then set to a
smooth, glossy finish. In accordance with particular embodiments, the contact time of
the forming polymer film to the drum is within the range of up to about 3.0 seconds,
more particularly up to about 2.0 seconds, and most particularly up to about 0.5
seconds.
[0048] The polymer coating may also include one or more pigments. Examples of
useful pigments include, but are not limited to, kaolin, talc, calcium carbonate,
calcium acetate, titanium dioxide, clay, zinc oxide, alumina, aluminum hydroxide and
synthetic silica such as noncrystalline silica, amorphous silica or finely divided silica
are examples thereof. Organic pigments may also be used.
[0049] The crosslinkable polymer coating and/or the crosslinking solution may
further include one or more release agents. Specific examples of release agents useful
herein include, without limitation, waxes, such as petroleum, vegetable, animal and
synthetic waxes, fatty acid metal soaps, such as metal stearates, long chain alkyl
derivatives, such as fatty esters, fatty amides, fatty amines, fatty acids, and fatty
alcohols, polymers, such as polyolefins, silicone polymers, fluoropolymers, and
natural polymers, fluorinated compounds, such as fluorinated fatty acids and
combinations thereof. One of ordinary skill in the art can readily determine the
amount of release agent to use in a particular application. Typically, the coating may
contain from about 0.3 to 10 percent release agent, more particularly from about 2 to
5 percent by weight. Instead of or in addition to release agent in the coating, release
agent may be sprayed onto the coating surface, or applied to the heated drum surface.
If a non-sticking surface can be provided on the heated drum, whether by a release
agent or other means, then application of a release agent in the coating or onto the
coating surface may not be needed.
[0050] The polymer coating employed in certain embodiments of the present
invention, wherein at least the aforementioned polymer is contained, is generally
prepared in the form of an aqueous composition. An appropriate ratio between those

ingredients is different depending on the polymer composition, the application
conditions and so on, but it has no particular limitation as far as the treated paper
produced can satisfy the quality required for the intended use thereof. Further, the
polymer coating according to certain embodiments of the present invention can
optionally contain additives, such as a dispersant, a water retaining agent, a thickening
agent, an anti-foaming agent, a preservative, a colorant, a waterproofing agent, a
wetting agent, a drying agent, an initiator, a plasticizer, a fluorescent dye, an
ultraviolet absorbent, a release agent, a lubricant and a cationic polyelectrolyte.
[0051] In accordance with a particular embodiment of the present invention, the
substrate is treated with the polymer coating near a central region of the paper
machine, such as the size press position. Furthermore, the apparatus for applying the
polymer coating to the substrate may be positioned relative to the paper machine so as
to apply the polymer film to either surface of the forming paper web. More than one
apparatus may be employed to apply a polymer film to each side of the forming paper
web.
[0052] These advantages allow the use of lightly calendered paper or paperboard,
thus preserving stiffness while providing good printing properties.
[0053] The base sheet is typically formed from fibers conventionally used for such
purpose and, in accordance with the particular embodiments, includes unbleached or
bleached kraft pulp. The pulp may consist of hardwood or softwoods or a
combination thereof. The basis weight of the cellulose fiber layer may range from
about 30 to about 500 gsm, and more particularly, from about 150 to about 350 gsm.
The base sheet may also contain organic and inorganic fillers, sizing agents, retention
agents, and other auxiliary agents as is known in the art. The final paper product can
contain one or more cellulose-fiber layers, polymer film layers and, in accordance
with certain embodiments, other functional layers.
[0054] The present invention in accordance with certain embodiments, provides one
or two-sided coated paper or paperboard for printing or packaging whose Parker Print
Surf smoothness value after the coating and finishing processes, when measured
according to TAPP1 paper and pulp test method No. 5A, is lower than about 2-3
microns.

[0055] The paper or paperboard described herein may further be provided with one
or more additional coatings. A top coating containing conventional components may
be provided to improve certain properties of the paper or paperboard. Examples of
such conventional components include pigments, binders, fillers and other special
additives. The top coating, when present, may be applied at much lower coat weights
than conventional coatings and yet provide similar print properties. Accordingly, the
top coating weight may be about 4 to 9 gsm as a single coating layer or about 8 to 18
gsm as two coating layers. By contrast, conventional coated papers typically require
about 10 to 20 gsm as a single coating layer or 18 to 30 gsm as two coating layers to
provide comparable surface properties. The paper or paperboard may also be coated
on the side of the sheet having the non-treated surface.
[0056] Having given the teachings of the present disclosure, it will now be
illustrated by means of specific examples which should not be considered as limiting
the scope of the claims in any way.
[0057] A base sheet having a caliper of about 10 points, a Parker Print Surf (PPS)
value of about 9 microns (10kg pressure with a soft backing) and a Sheffield
smoothness of about 310 can be treated in accordance with certain embodiments of
the present invention to provide a treated sheet having improved smoothness with
only a minimal decrease in caliper. The base sheet may be treated by applying a
PVOH solution at approximately 25% solids to the base sheet to provide a coverage
of about 5 g/m2 dry. Next, the crosslinker solution may be applied at a rate and
solution solids to give a borax coverage of at least about 0.1 g/m2 dry. The wet,
crosslinked polymer film can be brought into contact with a hot polished drum by
pressing the sheet against the drum surface. The drum surface temperature may be at
least about 190°C. The coating would be dried and released from the drum surface.
The contact time of the pblymer film to the drum would typically be in the range of
between about 0.5 - 2.0 seconds. The treated sheet would have a caliper of between
about 9.6 and 10.0 points, a PPS value of about 2.4 to 3.0 and a Sheffield smoothness
of about 140-170.
[0058] In a preferred embodiment, a starch solution may be used as the polymeric
material in the polymer coating.

[0059] One aspect of the disclosure relates to a paper or paperboard manufacturing
method. In accordance with one embodiment of the invention, the method includes
applying a polymer coating comprising a crosslinkable hydrogel to a substrate,
applying a crosslinking solution to the polymer coating on the substrate surface
thereby forming at least a partially crosslinked polymer film-forming coating and
bringing the polymer film-forming coating into contact with a heated surface while
the polymer film-forming coating is still in a wet state. The heated surface may be a
hot polished drum having a flat smooth finish. The temperature of the heated surface
typically is within a range of from about 150°C to about 240°C. Higher temperatures
may be used, for example up to about 300°C. The temperature of the heated surface
in accordance with certain embodiments is within a range of from 180°C to about
200°C, and in accordance with certain embodiments is at least about 190°C.
[0060] In accordance with particular embodiments of the invention, the
crosslinkable polymer may be selected from the group consisting of starch, waxy
maize, protein, polyvinyl alcohol, casein, gelatin, soybean protein, and alginates. In
accordance with certain aspects of the present invention, the crosslinkable polymer
may be used in amounts ranging from about 60 to about 100% by weight of the dry
materials.
[0061] In some manifestations, the crosslinker may be a borate or borate derivative
such as borax, sodium tetraborate, boric acid, phenyl boronic acid, or butyl boronic
acid. The crosslinker may be used in amounts ranging from about 1 to about 12%
based on the crosslinkable polymer.
[0062] The present invention is also directed to treated papers produced in
accordance with the method described herein. The treated papers are characterized by
improved smoothness in conjunction with relatively minor increases in density
compared to the original sheet.
[0063] As it is desirable to have the coating in a wet state when it contacts the
heated drum, the coating may be moistened for example by applying water. One
method is to spray water onto the coating before it contacts the hot drum. However,
in certain embodiments, it may also be possible to operate without any additional
moistening.

[0064] In certain embodiments, starch may be used as the soluble polymer. In
certain embodiments, starch-based coatings can be run successfully without a
crosslinker, and good results may be obtained without gelling (also called
coagulating).
[0065] A starch solution containing 2-5% of a release agent was brought into
contact with a heated drum under conditions described above. In certain conditions, if
moistening of the coating is desired, water alone may be used as the spray and yield a
good reproduction of the polished surface. If the coating solids are low enough, the
process works without a moistening water spray. A 20% solids starch coating was
applied to the web and brought into contact with a heated drum, and gave good
reproduction.
[0066] Starch coatings were also tested having 25% and 30% solids. Both of these
coatings released from the drum without any sticking, but without good surface
reproduction. The 25% solids coating gave moderate reproduction, but the 30%
solids coating was not very smooth. It appears that a certain amount of water present
at the surface may help to propagate boiling throughout the entire coating. Below a
certain amount of surface water, localized surface areas may still have sufficient
boiling to give good reproduction of the drum surface, but other surface areas do not.
Thus, without moistening of the surface with a water spray, as solids increase above
20%, the percentage of the area that reproduces the smooth drum surface decreases
with increasing coating solids, until at about 30% coating solids, little or no surface
smoothness reproduction is achieved. If sufficient water is sprayed on the surface of
the 30% solids coating before it contacts the heated drum, complete surface
reproduction can be obtained. We would expect this relationship to also be affected
by rawstock absorptivity, coat weight, coating viscosity and process speed. It should
be possible to establish the effects of these parameters by further experiments.
[0067] The examples described above were run with a chrome surface on the heated
drum. The examples described below were run after the drum was resurfaced with a
tungsten carbide coating.' In each of these examples, several "runs" were made to
collect the data. A run consists of the drum being heated to approximately 190°C, the
spray level being set, coating being applied to the web by a metered rod method,
optionally followed by moistening spray (which optionally may contain a cross
linking agent), and then by the web being brought into contact with the drum at 35

fpm. The drum temperature during a run varied between 180°C and 190°C. During a
run, the only variable that was changed was the coating weight applied by the
metering rod. Changes in coating type, coating solids, or spray level were made in
different experimental runs on the equipment. Coat weight was measured by
differential weight and is reported as bone-dry. Some of experiments were run with
cross linker in the coating itself, for example when a material such as starch was used,
which does not strongly cross link.
[0068] Example 1
[0069] A minimally pressed base sheet with a basis weight of 111 lb/3000 ft2 was
used as a substrate on which to apply and treat simple coating compositions. The first
coating was 95% by dry weight CELVOL 203S polyvinyl alcohol (PVOH) and 5%
Emtal 50 VCS, a triglyceride used as a release agent. The coating solids were 20% by
weight. The coating was applied by a metering rod. The Table is a list of samples and
test conditions. Sample 1.1 was made by spraying the coating with a crosslinking
solution containing 3% by weight borax and 1% by weight of a sulfonated castor oil
as a release agent. The spraying rate was 48 milliliters per minute. The sample
replicated the drum well and released from the drum without sticking. Significant
improvements in smoothness were obtained with minimal loss of caliper. For sample
1.2, the conditions were the same except that no borax was used in the spray solution.
Without the borax to crosslink the polyvinyl alcohol, the coating did not release from
the surface, and part of the film remained on the drum surface. This experiment
clearly showed the benefit of crosslinking the polyvinyl alcohol.

[0070] In another run, carboxymethyl cellulose (CMC) was substituted for the
polyvinyl alcohol to compare polymer performance. The carboxymethyl cellulose
was FINFIXX 30, which could only be run at 7% solids due to coating viscosity. The
coating was formulated with 95% polymer and 5% Emtal. Samples 1.3 and 1.4 are
two different coat weights sprayed with 48 ml/min of borax spray. The coating
replicated the drum surface well and released completely from the drum. Smoothness
was improved with minimal loss of caliper, but smoothness was not as good as for
polyvinyl alcohol. For the run that produced Sample 1.5, no borax was used in the
spray. The coating replicated the drum surface well and released completely from the
drum. Smoothness was improved by removing the borax. This showed that a non-
crosslinked coating could replicate and release from the drum, which indicates that
materials other than crosslinkable materials can be used in this process.
[0071] Example 2
[0072] A minimally pressed base sheet having a basis weight of 1111b/3000 ft2 was
used as a substrate on which to apply and treat simple coating compositions. The first
coating was 95% by dry weight CLEER-COTE 625 starch (a viscosity modified waxy
corn starch) and 5% Emtal 50 VCS, a triglyceride used as a release agent. The
coating solids were 20% by weight. The coating was applied by a metering rod.
Sample 2.1 was made by spraying the coating with a crosslinking solution containing
3% by weight borax and 1% by weight of a sulfonated castor oil as a release agent.
The spraying rate was 46,milliliters per minute. The sample replicated the drum well
and released from the drum without sticking. Significant improvements in
smoothness were obtained with minimal loss of caliper. Samples 2.2, 2.3, 2.4 and 2.5
were made with different coat weights of the same coating, but the spray did not
contain borax. All samples replicated the surface well and released completely from
the drum. Samples 2.6 and 2.7 were run without any spray at all. The samples
replicated the surface well and completely released. Smoothness values were not
quite as good, but samples still had significantly improved smoothness with minimal
reduction in caliper. This demonstrates that the process can work without any
moistening spray.
[0073] Example 3

[0074] This experiment was a continuation of Example 2 exploring the effect of
coating solids. Samples 3.1 and 3.2 were run at 23% coating solids without any
moistening spray. Good replication and release were obtained. For samples 3.3 and
3.4, coating solids were increased to 25.7%, again applied with no moistening spray.
Complete release was obtained, but incomplete replication of the surface was
achieved. Based on visual inspection, only about 90-95% of the surface replicated the
drum. For samples 3.5 and 3.6, this same 25.7% solids coating was run and a
moistening spray of 48ml/min was applied. The surface replication was complete and
the smoothness values were greatly improved. For Samples 3.7 through 3.12. a 30%
solids coating was used. When no moistening spray was used (3.7), complete release
was achieved, but only a small percentage of the surface was replicated. When 48
ml/min of moistening spray was used (3.8), the replication was greatly improved, but
the surface was still mottled with areas of poor replication. When the moistening
spray was increased to 98 ml/min (3.9, 3.10, 3.11 & 3.12), the replication was
complete and smoothness was greatly improved with minimal reduction in caliper.
Next, the coating solids were lowered. At 17.5% coating solids (3.13, 3.14) with no
moistening spray applied, good release and complete replication were obtained. At
10% solids (3.15) with no moistening spray applied, the low coating viscosity led to
reduced coat weight and increased coating absorption into the sheet, so poor
replication occurred.
[0075] Samples of the smooth products, produced using starch as the polymer
coating, at 20% solids, were top coated with a conventional pigmented clay coating
(about two-thirds clay and one third carbonate, with a latex binder, applied in a single
coat of approximately 10 lb/ 3000ft2) applied over the smooth polymer layer. These
samples then were cross sectioned to examine the morphology of the coating layer.
Cross sectioning was done by freezing the samples in liquid nitrogen, then cracking
the samples in two (freeze fracturing). The cracked edges of the samples (e.g., the
cross sections) were then viewed under a microscope.
[0076] Micrographs revealed that voids exist in the polymer coating layer, as shown
in FIGs. 2 through 9, which include measurement bars to indicate their scale. For
FIGs. 2-5, the microscope magnification was 1000, and the measurement bars are 20
microns long. In FIG. 2 as an example, the structure as shown includes a paperboard
substrate 110. The substrate thickness generally extends below the area of the

micrograph. Because of the freeze fracturing process, the substrate 110 as shown in
the micrographs is sometimes separated or partly separated from polymer layer 120.
Therefore the upper boundary of substrate 110 may be only approximately shown by
the bracketed distance denoting the substrate.
[0077] In these samples, the polymer coating layer 120 had been applied onto
substrate 110, and dried against a heated drum, as described previously. Then a top
coating 130 was applied and dried. The term "polymer coating" is used here to
describe that layer applied as described above, then contacted while wet against a
heated drum. The term "top coating" is used to describe the outer layer, which was
applied as one layer. Obviously the "top coating" could be applied in more than layer
and could be of coating materials other than those used here.
[0078] Voids 121 are evident in the polymer coating layer 120, as seen in FIGs. 2-9.
FIG. 2 for example shows several voids 121 in polymer coating layer 120, with the
voids appearing to be approximately 5 to 20 microns in lateral dimension. It is
assumed that their size going "into" the fractured sample is in approximately the same
range. The voids typically appear to be somewhat "flattened" in the "vertical"
direction, that is, going into the sample thickness. The voids also appear to have
"walls" that are relatively smooth, and generally thin. These thin walls are most
apparent as seen between adjacent voids. Where a void wall is adjacent to the top
coating 130, its thickness may be difficult to see but its presence may be deduced by
the smooth lower contour of the top coating 130 adjacent to the void.
[0079] FIG. 3 is an example micrograph showing several voids 121 in the polymer
coating layer. The voids appear to extend over an area equivalent to more than half
the coated surface area. The polymer coating layer is not well defined in this
micrograph.
[0080] FIG. 4 is an example micrograph showing several voids 121 in polymer
coating layer 120. The walls of the voids appear to be relatively thin, as evidenced by
a somewhat translucent appearance in the walls of two of the voids.
[0081] For FIGs. 5-9, the microscope magnification was 500 and the measurement
bars are 50 microns long. FIG. 5 shows several voids 121 in polymer layer 120, with
individual measurement bars showing dimensions of the selected voids, for example,
moving generally from left to right, measurements of 10.5 microns in vertical

distance, 36 microns in lateral distance, 10.6 microns in vertical distance, and 36.3
microns in lateral distance. Again the voids appear to extend over an area equivalent
approximately half the coated surface area.
[0082] FIG. 6 shows another sample with similar measurement bars, for example,
moving generally from left to right, measurements of 8.66 microns in vertical
distance, 32.1 microns in lateral distance, 11.8 microns in vertical distance, and 22.7
microns in lateral distance. Measurements such as these in FIGs. 5 and 6 were
collected for use in the graph discussed later in FIG. 17.
[0083] FIG. 7 shows voids 121 in polymer layer 120, including several showing a
generally flattened aspect. The voids appear to extend over an area equivalent to
nearly all the coated surface area. FIG. 8 shows another sample with similar
widespread voids 121. The wall areas of several voids are visible. FIG. 9 shows yet
another sample where the voids 121appear to extend over an area equivalent to nearly
all the coated surface area.
[0084] Other samples of the smooth products, produced using starch as the polymer
coating, at 20% solids, were not top-coated. These samples were cross sectioned to
examine the morphology of the coating layer. Cross sectioning was done by freezing
the samples in liquid nitrogen, then cracking the samples in two (freeze fracturing).
The cracked edges of the samples (e.g., the cross sections) were then viewed under a
microscope as shown in FIGs. 10 to 12, which include measurement bars to indicate
their scale. The microscope magnification was 1000, and the measurement bars are
20 microns long. FIG. 10 shows the polymer layer 120, which contains voids 121 and
has a very smooth outer surface. The polymer layer is on paperboard substrate 110,
and one of the cellulose fibers 112 is denoted. The substrate thickness generally
extends below the area of the micrograph.
[0085] FIGs. 11 and 12 show additional micrographs of samples that were polymer
coated but not top-coated. Again the smoothness of the polymer layer 120 is evident,
as are the underlying voids 121. The walls of the voids often coincide with the
surface of the polymer coating.
[0086] FIG. 13 (at 200x magnification) and FIG. 14 (at 500x magnification) show
the surface of samples as seen under a scanning electron microscope. These samples
were not given top coating 130. The larger string-like structures 112 are cellulose

fibers of the substrate 110. The smaller cell-like structures 122 that appear as a fine
network or mesh are individual voids in polymer layer 120. The polymer layer here
appears essentially transparent, except for the walls of the voids.
[0087] FIGs. 15 and 16 show the surface of samples as seen under a backscatter
scanning electron microscope. These samples were not given top coating 130. The
larger string-like structures 112 are cellulose fibers of the substrate 110. The smaller
cell-like structures 122 that appear as a fine network or mesh are the walls of
individual voids in polymer layer 120. The polymer layer here appears essentially
transparent, except for the walls of the voids. The voids appear to be distributed over
the entire surface.
[0088] FIG. 17 is a graph showing the distribution of void sizes based on
approximately 90 measurements each of void width (lateral dimension) and height
(vertical dimension in the micrographs). The measurements show an average void
width (measured in the direction parallel to the thickness of the sample) of about 19
microns, with a standard deviation of about 9 microns. The measurements show an
average void height (measured in the direction going "into" the sample thickness) of
about 10 microns, with a standard deviation of about 4 microns.
[0089] These void dimensions appear to be representative of the samples studied
here. However, they are not meant to be limiting as changes in materials or
processing conditions might give other dimensions.
[0090] It is hypothesized that steam bubbles create these voids while the coating is
in contact with the heated drum, and that the bubbles may provide a force to help keep
the coating in contact with the drum. The resulting voids typically help bridge the gap
between an otherwise rough substrate layer 110, and the smooth surface of the heated
drum. Thus the dried polymer coating has a smooth replicated surface, which is
smoother than the substrate layer 110. It appears that many or most of the voids
remain intact when top coating 130 is applied. Therefore the top coating may end up
smoother because of the relatively smooth underlying polymer layer 120. This is seen
as an advantage achieved by the invention. Besides the hypothesized influence of the
voids on help creating a smooth replicated surface, the voids may also contribute to a
lower density in the product.

[0091] The conditions in the nip between press roll 24 and hot drum 22 may
influence whether voids form in the polymer coating. Depending on press roll
hardness, and the diameters of the press roll and hot drum, it may be necessary to
adjust the nip loading (for example, the PLI loading on the nip) in order to achieve
boiling in the nip which creates the voids.
[0092] The polymer-coated paper or paperboard created by this process may be
used wherever a smooth substrate or finished product is desired. The polymer-coated
paper or paperboard may be used as-is (e.g., as shown in FIGS. 10-16), or it may be
used as a substrate for additional coatings or other treatments to be applied (for
example the top coating 130 shown in FIGs. 2-9, or other coatings) thereon.
Additional finishing materials or processes may be applied to the polymer-coated
paper or paperboard, with or without additional coatings. For example, one or more
additional coatings may be applied, as is typical with base coating, top coating, and
triple coating of conventional paper or paperboard substrates. Calendering processes
may be applied, before or after optional additional coating. For example one or more
additional coatings may be applied, followed by a gloss calendering step.
[0093] Methods of making and using polymer-coated material in accordance with
the invention should be readily apparent from the mere description of the material and
process as provided herein. No further discussion or illustration of such material or
methods, therefore, is deemed necessary.
[0094] While preferred embodiments of the invention have been described and
illustrated, it should be apparent that many modifications to the embodiments and
implementations of the invention can be made without departing from the spirit or
scope of the invention. Although the preferred embodiments illustrated herein have
been described in connection with a paper or paperboard substrate, these
embodiments may easily be implemented in accordance with the invention in other
structures, including without limitation textiles, non-woven fabrics, fibrous materials,
polylactic acid substrates, and porous films.
[0095] It is to be understood therefore that the invention is not limited to the
particular embodiments disclosed (or apparent from the disclosure) herein, but only
limited by the claims appended hereto.

We Claim:
1. A substrate coated with polymer composition, comprising:
a substrate and
a first coating on the substrate,
wherein the first coating includes a surface having a Sheffield Smoothness of less
than 300 units, and
wherein voids are formed under said surface of the first coating;
wherein at least 50% of the first coating surface has subsurface voids having a
transverse dimension of at least 5 µm.
2. The substrate coated with polymer composition as claimed in claim 1, wherein the
surface has a Sheffield Smoothness of less than 200 units.
3. The substrate coated with polymer composition as claimed in claim 1, wherein the
surface has a Sheffield Smoothness of less than, 150 units.
4. The substrate coated with polymer composition as claimed in claim 1, wherein the
substrate comprises at least one of cellulose, paper, paperboard, fabric, fibrous material,
porous material, porous film, or polylactic acid.
5. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating includes a water soluble polymer.
6. The substrate coated with polymer composition as claimed in claim 5, wherein the
first coating includes a release agent.
7. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating contains essentially no elastomeric material.
8. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating includes a cross linking agent.

9. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating includes by dry weight at least about 60% water soluble polymer and up to
10% release agent.
10. The substrate coated with polymer composition as claimed in claim 5, wherein the
water soluble polymer includes a cross linkable polymer.
11. The substrate coated with polymer composition as claimed in claim 5, wherein the
water soluble polymer includes at least one of starch, waxy maize, protein, polyvinyl
alcohol, casein, gelatin, soybean protein, and alginate.
12. The substrate coated with polymer composition as claimed in claim 9, wherein the
release agent includes at least one of wax, petroleum wax, vegetable wax, animal wax,
synthetic wax, fatty acid metal soap, metal stearates, long chain alkyl derivatives, fatty
esters, fatty amides, fatty amines, fatty acids, fatty alcohols, polymers, polyolefins,
silicone polymers, fluoropolymers, natural polymers, fluorinated compounds, fluorinated
fatty acids, and combinations thereof.
13. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating includes a water soluble polymer and essentially no elastomeric material.
14. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating includes a cross linkable polymer and essentially no elastomeric material.
15. The substrate coated with polymer composition as claimed in claim 1, wherein said
substrate sheet is paper or paperboard and further comprising a second coating on the first
coating.
16. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating includes a water soluble polymer, a release agent, and essentially no
elastomeric material.
17. The substrate coated with polymer composition as claimed in claim 8, wherein the
cross linking agent comprises at least one of borax, borates, aldehydes, ammonium salts,

calcium compounds, and derivatives thereof.
18. The substrate coated with polymer composition as claimed in claim 17, wherein the
second coating includes at least one of pigments, binders, and fillers.
19. The substrate coated with polymer composition as claimed in claim 1, wherein the
first coating includes by dry weight at least 60% water soluble polymer and up to 10%
release agent.
20. The substrate coated with polymer composition as claimed in claim 1, wherein the
voids are bounded by walls formed from the first coating.
21. The substrate coated with polymer composition as claimed in claim 1, wherein said
substrate comprises a sheet or a web.

ABSTRACT

A method for treating a substrate is described. In accordance with one aspect, the
method includes applying a polymer coating to a substrate, and bringing the polymer coating
into contact with a heated surface while the coating is still in a wet state. Optionally the
polymer coating may include a crosslinkable material, and a crosslinking agent may be used
to promote crosslinking. The polymer coating replicates the heated surface. A product
produced in accordance with thedescribed method is also disclosed. The product is
characterized by having subsurface voids within the coating.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=HNLxCMf/WgXx/FNV8yyztw==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

270198

Indian Patent Application Number

3040/KOLNP/2008

PG Journal Number

49/2015

Publication Date

04-Dec-2015

Grant Date

30-Nov-2015

Date of Filing

28-Jul-2008

Name of Patentee

MEADWESTVACO CORPORATION

Applicant Address

11013 WEST BROAD STREET, GLEN ALLEN, VIRGINIA

Inventors:

#	Inventor's Name	Inventor's Address
1	STANLEY H. MCGREW JR.	5428 LANGSTON PARK DRIVE, N. CHARLESTON, SC 29420
2	STEVEN P. METZLER	525 SOUTHMONT DRIVE, CLAYTON, NC 27527
3	TERRELL J. GREEN	9401 CLUBVALLEY WAY, RALEIGH, NC 27617
4	GARY P. FUGITT	55 INDIAN LANDING DRIVE, PITTSBORO, NC 27312
5	JOHN W. STOLARZ	437 N. COURT STREET, CIRCLEVILLE, OH 43313
6	ROBERT W. CARLSON	5128 HUNTINGDON DRIVE, RALEIGH, NC 27606
7	SCOTT E. GINTHER	140 EDMONDSON DRIVE, WILLOW SPRING, NC 27592

PCT International Classification Number

C09J 103/00

PCT International Application Number

PCT/US2007/004742

PCT International Filing date

2007-02-22

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/776,114	2006-02-23	U.S.A.