KR101023587B1 - Method for treating a substrate - Google Patents

Abstract

A method of treating a substrate, and a product produced by the method,

According to one aspect the method comprises applying a polymer coating to a substrate and contacting the polymer coating with a heated surface while the coating is wet, optionally wherein the polymer coating comprises a crosslinkable material and Crosslinkers can be used to promote crosslinking, and the polymeric coating replicates the heated surface and is characterized by having a void below the surface in the coating of the product.

Description

Substrate processing method {METHOD FOR TREATING A SUBSTRATE}

The present invention relates to a method of treating a substrate with a polymer film-forming composition. More particularly, the present disclosure relates to a method of making paper or paperboard comprising the step of applying a polymer film-forming coating to a substrate and bringing the polymer coating into contact with the heated surface while the polymer coating is still wet. The polymer layer obtained has a smooth surface with voids (eg bubbles) just below the surface. In certain embodiments the polymer coating may comprise a crosslinkable hydrogel, and the crosslinking solution may be applied to the polymer coating on the substrate surface to form at least partially crosslinked polymer coating and placed in contact with the heated surface. . The invention also relates to a treated base product.

Paper is originally manufactured in a continuous manufacturing process, in which a dilute aqueous slurry of cellulose fibers flows into the wet end of the paper machine, while an indefinite length of the consolidated dried web is the paper machine dry end. Coming out continuously. The wet end of the paper machine includes one or more headboxes, drains and presses. State-of-the-art paper machine drying ends include a plurality of steam heated rotating shell cylinders distributed along a serpentine web that traverses under a heat confining hood structure. For each of these paper machine sections a number of variations can be made to the design, but the most commercially important deformation machine is a fourdrinier machine, where the headbox is slurry on a very fine mesh moving screen. Emits a large injection.

The screen consists of an endless belt carried on a plurality of support rolls or foils and moves. The pressure difference across the screen from the side in contact with the slurry causes the screen portion to move along the table portion of the screen path rotation, drawing water out of the slurry through the screen. By drawing the slurry dilution water the fibrous portion of the slurry accumulates on the screen surface as a wet but practically consolidated mat. Upon reaching the screen turn table length distal end, the mat accumulates at an effective mass and tensile strength to carry a short physical distance between the screen and the first press roll. The first press roll carries the mat to the first press nip and most of the volume of water remaining on the mat is removed by squeegeeing the roll nip. One or more additional compression nips may follow.

The mat continuum from the crimp is generally characterized by a web entering the dryer section of the paper machine to thermodynamically remove residual water.

Generally speaking, the most important fibers in the manufacture of paper are obtained from softwood and hardwood wood varieties. However, the fibers obtained from straw or bagasse were used in special cases. Both chemical and mechanical defiberizing processes, well known in the prior art, are used to separate papermaking fibers from naturally occurring compositions. The papermaking fibers obtained by the chemical gripping dissociation process and method are generally called chemical pulp, and the papermaking fibers derived by the mechanical gripping dissociation method may be referred to as groundwood pulp or mechanical pulp. There is also a combined phage dissociation method such as semichemical, thermochemical or thermomechanical. Any tree species can be phage dissociated by chemical or mechanical methods. However, some types and phage dissociation methods are more economical or functional matches than others.

An important difference between chemical and mechanical pulp is that mechanical pulp can pass directly from the phage dissociation step to the paper machine. On the other hand, chemical pulp should be mechanically dissociated, washed and screened at least after chemical decomposition. Chemical pulp is also generally mechanically refined after screening and before papermaking. In addition, the average fiber length of the mechanical pulp is usually shorter than the length of the chemical pulp. However, the fiber length also varies greatly depending on the type of wood from which the fiber is derived. Soft wood fibers are typically about three times longer than hard wood fibers.

The ultimate characteristics of a particular paper are largely determined by the method of treating these raw materials in papermaking and web forming processes and the type of raw materials used. Important operating factors for the mechanism of paper web formation are the headbox and screen.

Coated paper or paperboard used for printing and packing should typically have high levels of gloss, excellent smoothness and excellent printability, as well as certain strength and stiffness properties.

The high stiffness of the coated paper or paperboard allows the paper to pass smoothly through high-speed printing or packaging machines with less paper jams in the feed. High rigid paper can be advantageous for use as books, magazines and catalogs, as it provides a feel of hardness or weight similar to hardcover books. High stiffness in packaging is essential to maintain the structural integrity of the cardboard product during filling and subsequent use.

Stiffness is highly related to the basis weight and density of the paper. Increasing basis weight increases stiffness, and increasing paper density generally decreases stiffness. Stiffness and other properties can be improved by increasing basis weight. However, this can result in products using more fibers, which can increase cost and weight. Therefore, coated paper or paperboard with high rigidity but moderate basis weight is preferred. Paper having a good basis weight is also more economical because it uses less raw material (fiber). In addition, the weight-based transportation costs are also less for low basis weight paper.

In addition to high stiffness, coated paper or paperboard to be printed often requires high gloss and smoothness. For coated paper or paperboard with these quality characteristics, it is common to have some density high to have a printing surface available. Smoothness is typically obtained by calendaring. However, calendaring typically reduces the caliper, resulting in a corresponding decrease in stiffness. The calendering process significantly reduces the calipers and increases their density, which degrades the stiffness of the paper. Base sheets for conventional coated board grades are significantly densified by calendering to provide surface roughness low enough to produce an industrially acceptable final coated smoothness. This calendaring process, including wet stack treatment, can increase the density by 20% to 25%.

Thus the relationship between gloss and stiffness and smoothness and stiffness is usually inversely proportional to one another in the amount of fiber given per unit of area. Packaging grades are marketed based on calipers because manufacturing processes that reduce calipers (increasing board density) reduce the selling price. This saves material costs by inducing fewer calipers. Calipers are measured in "points" with 1 point = 0.001 inches. For example, conventional methods for manufacturing 10-point boards need to use boards having a thickness greater than 12 points prior to calendering. It would be desirable to be able to produce a finished board of approximately the same thickness as in the starting material.

Improvements in the calendering process, including moisture gradient calendering, hot calendering, soft calendering, and belt calendering, slightly improve the stiffness for a given caliper, but do not change the basic ratio between calipers, stiffness, smoothness, and printing characteristics. Do not.

Various schemes have been established to improve the stiffness of coated paper or cardboard without calendaring in printing. For example, some schemes include high soft wood content in raw materials, the addition of specially formulated fibers to the raw materials, the addition of high branched polymers to the raw materials, and high glass transition temperatures in coating formulations (commonly referred to as "Tg"). A large amount of starch or copolymer latex having

A potential drawback of this method of stiffness improvement, however, is the possibility of degrading the smoothness, gloss and / or printability of the coated paper obtained, despite being useful for improving paper stiffness.

For the reasons mentioned above it is very difficult to obtain satisfactory smoothness of the paper without increasing the density. Other methods can be used to change paper and cardboard grades and density / smoothness relationships. Applying a paper coating is a very common method for enhancing the surface properties of a paper without significantly increasing the paper density typically associated with the level of calendering required to achieve a certain level of smoothness.

It would therefore be desirable to provide a paper or cardboard product having the desired properties while minimizing density increase or maintaining the initial density of the sheet. It would also be desirable to provide paper or paperboard that exhibits improved smoothness without the accompanying increase in density associated with conventional methods of making smoothness. Cast coating methods exist for producing very smooth surfaces, but such methods typically run at slower manufacturing speeds than the speed of several paper machines.

Summary of the Invention

In one embodiment the article is disclosed to include a substrate having a coating on the substrate. The coating includes a water soluble polymer and a release agent. There is a void formed in the coating.

In another embodiment the article is disclosed to include a substrate having a coating on the substrate. The coating includes a water soluble polymer and does not inherently contain an elastomeric material. There is a void formed in the coating.

In another embodiment the article is disclosed to include a substrate having a coating on the substrate. The coating includes a surface, the surface having Sheffield Smoothness of about 300 units or less. There is a void formed under the surface of the coating.

In another embodiment the article is disclosed to include a substrate having a coating on the substrate. The coating includes a water soluble polymer and a release agent and does not inherently contain an elastomeric material. The coating has a surface, the surface having a Sheffield smoothness of about 300 units or less. There is a void formed under the surface of the coating.

In another embodiment, a method of treating a substrate is disclosed. A wet film of aqueous polymer solution is applied to the substrate. The aqueous polymer solution is moved in contact with the heated surface to induce the aqueous polymer solution to boil, and at least a portion of the aqueous polymer solution is dried and fixed.

In another embodiment, a substrate treatment method is disclosed. A wet film of aqueous polymer solution is applied onto the substrate. The aqueous polymer solution is allowed to boil by contacting the aqueous polymer solution to form a void remaining in the aqueous polymer solution, and at least some of the aqueous polymer solution is dried and fixed.

In another embodiment, a substrate treatment method is disclosed. The coating of the 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 brought into contact with the surface heated to a temperature of about 150 ° C. or more for about 3 seconds or less to boil the aqueous polymer solution, voids are formed in the film, and at least a portion of the film is dried and fixed.

In another embodiment, a substrate treatment method is disclosed. A coating of aqueous polymer solution is applied on the substrate as a wet film. The coating includes an aqueous solution polymer and essentially no elastomeric material. The film is brought into contact with the surface heated to a temperature above about 150 ° C. for about 3 seconds or less to allow the aqueous polymer solution to boil and to form voids in the film, and at least a portion of the film is dried and fixed.

In another embodiment, a substrate treatment method is disclosed. The coating of the aqueous polymer solution is applied to the substrate as a wet film. The coating includes a water soluble polymer and does not inherently contain an elastomeric material. The film is brought into contact with the surface heated to a temperature of about 150 ° C. or more for about 3 seconds or less to boil the aqueous polymer solution and cause voids to form in the film, and at least a portion of the film is dried and fixed. After drying, the coating surface has a Sheffield smoothness of about 300 units or less.

In another embodiment, a substrate treatment method is disclosed. The coating of the aqueous polymer solution is applied to the substrate as a wet film. The coating includes a water soluble polymer and a release agent and does not inherently contain an elastomeric material. The film is brought into contact with the surface heated to a temperature above about 150 ° C. for about 3 seconds or less to boil the aqueous polymer solution to form voids in the film, and at least a portion of the film is dried and fixed. After drying, the coating surface has a Sheffield smoothness of about 300 units or less.

In another embodiment, a cellulose based treatment process is disclosed. A wet film of aqueous polymer solution is applied to the substrate. The aqueous polymer solution comprises at least about 60% water soluble polymer by dry weight and up to about 10% release agent by dry weight. The aqueous polymer solution is brought into contact with the surface heated to a temperature above about 150 ° C. for about 3 seconds or less to boil the aqueous polymer solution to form voids in the film, and at least a portion of the aqueous polymer solution is dried and fixed.

1 is a schematic diagram of an apparatus for treating a substrate with a polymer coating in accordance with one embodiment of the present invention.

2-9 show the shape of a sample prepared according to one embodiment of the invention, which is a cross-sectional area of an electron micrograph with a top coating.

10-12 are cross-sectional views of electron micrographs showing the shape of a sample made in accordance with one embodiment of the present invention.

13-14 are surface photographs of electron microscopes prepared with an electron scanning microscope showing the form of a sample prepared according to one embodiment of the present invention.

15-16 are surface photographs of electron microscopes made with a reflective electron microscope, showing the form of a sample prepared according to one embodiment of the present invention.

FIG. 17 is a graph showing the distribution of void diameters in samples prepared according to one embodiment of the present invention. FIG.

Detailed description of the invention

In describing in the preferred embodiment, specific terminology will be used to clarify. This terminology includes not only the recited embodiments, but also all technical equivalents using similar methods for similar purposes for obtaining similar results. The citation of any document is not considered to be permitted by the prior art relating to the present invention. All weights, percentages, and ratios are by weight unless otherwise noted.

Detailed description of the invention relates to a method of treating a substrate with a polymer film-forming coating. More particularly, this detailed description relates to a method of making paper or paperboard comprising applying a polymer coating to a substrate and contacting the heated surface with the polymer coating while the polymer coating is still wet. Boiling water in the polymer coating forms voids under the surface, but the film surface is smooth. Paper or cardboard made 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 comprise a crosslinkable material and the crosslinking solution may be applied to the polymer coating on the substrate surface to form at least a portion of the crosslinked polymer film-forming composition. In such cases it may be customary to first apply the polymer coating to the web and then to apply the crosslinkable solution before contacting the treated web with the heated surface. For weakly crosslinked polymers it is possible to provide a crosslinkable solution in the coating itself.

One advantage of treating the substrate with the polymer film-forming coating according to the invention is an improvement in the smoothness and / or flatness that can be obtained without reducing the caliper of the sheet or significantly increasing the density. Excessive calendaring of the cellulose paper web associated with the prior art is not required to produce paper having print characteristics similar to conventional coated paper. In addition, when the cellulose paper web is flat, lower pressure may be applied to provide similar printing properties on paper with increased stiffness. According to certain embodiments of the present invention, the cellulose paper web is flat such that the caliper is reduced to about 7% or less, and typically about 2% to 5%. In comparison, conventionally coated papers are typically calendered before coating at higher pressures, resulting in an increase in density of about 20-25%. According to one aspect of the invention the cellulose paper web may be calendared with Parker Print Surf smoothness of about 2 to 6 microns prior to application of the polymer film. However, substrates with high Parker Print Surf values can be used. For example, a substrate having a Parker Print Surf smoothness of about 9 microns can be used. Parker Print Surf smoothness is measured according to TAPPI Standard T 555 om-99.

1 depicts an apparatus 10 useful in certain current embodiments of the present invention. Substrate 12 treats crosslinkable polymer coating 14 on one surface thereof to form polymer coating layer 16 on substrate 12. While the polymer coating is still wet, an optional crosslinking solution 18 is applied to the polymer coating layer 16 to form a crosslinked polymer coating 20 on the substrate 12. The polymer coating 20 is typically at least partially crosslinked. The polymer coating is still wet before pressing the web 12 against the drum surface with a squeeze roll 24 to contact the hotly polished drum 22. The heat from the drum surface causes the wet polymer coating to boil and form voids in the polymer under the surface. With the crosslinking solution, the polymer coating is substantially crosslinked into a continuous layer or film and becomes a gel. Typically the film obtained will exhibit improved strength on the base sheet. The polymer treated sheet may not be completely dried and may be transferred through the second heater 26. Any type of second heating device can be used to dry the treated sheet without adversely affecting the sheet properties. The treated sheet emerges from the second heater 26 such that the polymer film treated substrate 28 has improved flatness and smoothness characteristics. Optionally, additional coating process 30 (and other processes such as coatings, gloss calendering, etc.) may be used to make coated article 32.

As shown in FIG. 1, the web covers much of the hotly polished drum 22. The amount of wrapping may vary depending on operating conditions such as web speed, moisture content of the polymer film forming composition 20, temperature of the drum and other process factors. Even shortening the contact time with the hotly polished drum 22 may be effective. In addition to providing a substrate in the form of a web, it may also be provided in the form of a sheet.

Crosslinkable polymer coatings and optional crosslinking solutions can be used in a number of techniques such as dip-coating, rod coating, doctor blast coating, gravure roll coating, reverse roll coating, metered size press, flat roll coating, extrusion coating, curtain It can apply | coat by coating, spray coating, etc. The crosslinkable polymer coating and the crosslinking solution may be applied by the same coating technique, or different methods may be used respectively.

One embodiment according to the invention is based on the gelling or flocculation occurring between polyvinyl alcohol and borax. According to this type of system polyvinyl alcohol (PVOH) is an example of a crosslinkable polymer and borax solution is an example of a corresponding crosslinker. Application of PVOH solution 14 results in a crosslinker solution 16 having a coverage of approximately 25% solids and about 5 g / m ² dry matter and a crosslinker solution 16 exhibiting borax coverage of at least about 0.1 g / m ² dry matter. Apply with The wet, crosslinked polymer film 20 then compresses the web 12 against the drum surface with a squeeze roll 24 to contact the hotly polished drum 22. The drum surface temperature is at least about 150 ° C., or according to certain embodiments, at least about 190 ° C. to allow the coating to dry and to fall off the drum surface. The contact time of the polymer film to the drum may be up to about 3.0 seconds or less, more particularly in the range of about 0.5 to 2.0 seconds. This time is sufficient time for the polymer film to be fixed and solidified to have a flat smooth finish that reflects the drum surface. Immobilization of the polymer film includes at least partially drying the film. The coating does not need to be completely dry when falling off the drum, and additional drying 26 may be required. The web then proceeds continuously through the process and may receive additional coating layers, such as conventional coatings, prior to bending. The polymeric coating can be applied as a single layer or as two or more layers. Only heated drums and the like, as a polymer film can be obtained using the squeeze roll 24 to squeeze the web 12 against the hot drum 22 without the need for the web to further wrap around the hot drum. It has also been proposed in limited experiments that it can be immobilized or solidified by instantaneous contact. However, it is contemplated that the wrapping of the hot drum may be performed several times, and may optionally help to compress the web to contact the hot drum using felt 23. The felt 23 may be used to help compress the web for contact with the hot drum and then the felt 23 may be run between the squeeze roll 24 and the heated drum 22.

The contact between the polymer film and the hot drum boils the polymer film, creating voids or bubbles in the film. Nip conditions should be adjusted to allow boiling. Satisfactory experimental results were obtained with a nip load of about 2 to 15 pounds per linear inch and an elastic crimp roll, i.e. a 9 "wide web. The hardness of the crimp roll and the diameter of the hot drum and crimp roll The conditions should be adjusted accordingly.

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, soy protein and alginate. One or more polymers selected from the group consisting of those recited above may be used. Crosslinkable polymers are typically applied in solution form, usually as an aqueous solution. The concentration of the polymer in the solution is not particularly limited but can be easily determined by those skilled in the art. For example, about 20% starch solution can be used as described below. Crosslinkable polymers may be applied to provide a surface coverage (based on dry matter) of about 3 to about 15 gsm (g / m ² ), more particularly about 4 to about 8 gsm. According to certain embodiments of the present invention, the crosslinkable polymer may be used in an amount ranging from about 60% to about 100% by weight based on the dry matter.

Specific examples of crosslinkers include borate, aldehydes, ammonium salts, calcium compounds and derivatives thereof. If used, the crosslinker is usually applied in the form of a solution, usually as an aqueous solution. The concentration of the crosslinker in the solution is not particularly limited but can be easily determined by those skilled in the art. Crosslinkers can be used to provide a surface coverage (dry basis) of about 0.1 to about 0.5 gsm, more particularly about 0.2 to about 0.3 gsm.

The heated surface temperature typically exceeds that used for gaseous coatings. Higher temperatures should allow for higher running speeds. It is anticipated that the paper or cardboard provided in accordance with certain embodiments of the present invention may be produced at a rate of about 750 to 3000 fpm, more particularly about 1500 to 1800 fpm. Although not supported by theory, the high temperature and residence time are selected such that the coating composition is heated to its boiling point temperature and, when the coating material is boiling, the contact area between the coating material and the drum increases. Increasing contact results in a heated surface of the polymer film that exhibits improved smoothness and gloss. The treated surface is also ink receptive. Boiling the coating to smooth the heated drum surface smoothly improves the gloss and smoothness of the final polymer film treated substrate.

The polymeric coating on the base is typically pressed against the heated surface for a sufficient time to allow the coating to boil and then establish a flat, glossy finish. According to certain embodiments the contact time of the formed polymer film with the drum is in the range of about 3.0 seconds or less, more particularly about 2.0 seconds or less, most preferably about 0.5 seconds or less.

The polymeric 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 amorphous silica, amorphous silica or finely divided silica. It includes. Organic pigments may also be used.

The crosslinkable polymer coating and / or crosslinking solution may further comprise 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 stearate, long chain alkyl derivatives such as fatty esters, fatty amides, fatty amines, fatty acids and fats. 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 for use in a particular application. Typically the coating material may contain about 0.3 to 10% by weight of release agent, more particularly about 2 to 5% by weight. Instead of or in addition to the release agent in the coating material, the release agent may be applied on the surface of the coating material or applied to the heated drum surface. If a non-tacky surface can be provided on a heated drum, it is not necessary to apply the release agent on the coating or coating surface by a release agent or other means.

Polymeric coatings applied to certain embodiments of the present invention generally contain at least the polymers described above and are generally prepared in the form of an aqueous composition. The suitable ratio between the components depends on the polymer composition, the application conditions and the like, but is not particularly limited as long as the treated paper produced can satisfy the quality required for its application. Further polymeric coatings according to certain embodiments according to the invention may optionally contain adducts, such as dispersants, moisture retainers, thickeners, antifoams, preservatives, colorants, waterproofing agents, wetting agents, drying agents, initiators, plasticizers, fluorescent salt furnaces, ultraviolet absorbers. , Release agents, lubricants and cationic polyelectrolytes.

According to certain embodiments of the present invention, the substrate is treated with a polymer coating in proximity to the central region of the paper machine, such as the size crimp position. Additionally, a device for applying a polymer coating to a substrate may be positioned proximate to the paper machine to apply a polymer film to the surface of the formed paper web. More particularly, a polymer film can be applied to each side of the paper web formed using one device.

With the above advantages it is possible to use weakly calendered paper or paperboard, thus preserving stiffness while providing good printing properties.

The base sheet is conventionally made from fibers conventionally used for this purpose, and according to certain embodiments comprises unbleached or bleached kraft pulp. The pulp may be composed of hard wood or soft wood or combinations thereof. The basis weight of the cellulose fiber layer may range from about 30 to about 500 gsm, more particularly from about 150 to about 350 gsm. The base sheet may also contain organic and inorganic fillers, size agents, retention agents, and other auxiliaries known in the art. The final paper product may contain one or more cellulose-fiber layers, a polymer film layer and other functional layers according to certain embodiments.

In accordance with certain embodiments, the present invention provides a coating of one or two sides for printing or packaging having a Parker Print Surf smoothness value of about 2-3 microns or less after coating and finishing process as measured according to TAPPI paper and pulp test method number 5A. Provide paper or cardboard.

The paper or cardboard described herein may be provided with one or more additional coatings. Top coatings containing conventional components may be provided to improve certain properties of paper or cardboard. Examples of such conventional components include pigments, binders, fillers and other special additives. If present, the top coating can be applied to provide less print weight but similar print characteristics than conventional coatings. The top coating weight may thus be about 4 to 9 gsm, such as a single coating layer, or about 8 to 18 gsm, such as two coating layers. In contrast, conventional coated papers typically require about 10-20 gsm, such as a single coating layer, or 18-30 gsm, such as two coating layers, to provide similar surface properties. Paper or cardboard may also be coated on the side of the sheet having a non-treated surface.

The description will now be given by means of specific embodiments which, given the description of the detailed description of the invention, are not intended to limit the claims in any way.

A base sheet having about 10 points of caliper, about 9 microns of Parker Print Surf (PPS) (10 kg pressure with soft baking) and Sheffield smoothness of about 310 was processed in accordance with certain embodiments of the present invention so that only the calipers It is possible to provide a treated sheet with minimal reduced smoothness. The base sheet can be treated by applying a PVOH solution with approximately 25% solids to the base sheet to provide a coverage of about 5 g / m ² drying. The crosslinker solution may then be applied at a rate and solution solids to indicate borax coverage of at least about 0.1 g / m ² dryness. The wet crosslinked polymer film can be contacted with the hot polished drum by pressing the sheet onto the drum surface. The drum surface temperature may be at least about 190 ° C. The coating is dried and separated from the drum surface. The contact time of the polymer film to the drum may typically range from about 0.5-2.0 seconds. The caliper of the treated sheet is about 9.6 to 10.0 points, the PPS thin is about 2.4 to 3.0 and the Sheffield smoothness is about 140-170.

In a preferred embodiment, the starch solution can be used as the polymer material of the polymer coating.

One aspect of the detailed description relates to a method of making paper or cardboard. According to one embodiment of the invention the method comprises the steps of applying a polymer coating comprising a crosslinkable hydrogel to a substrate, a polymer film crosslinked at least in part by applying a crosslinking solution to the polymer coating on the substrate surface- Forming a forming coating and contacting the heated surface with the polymer film-forming coating while the polymer film-forming coating is still wet. The heated surface may be a hot polished drum with a flat and flat finish. The temperature of the heated surface is typically in the range of about 150 ° C to about 240 ° C. High temperatures can be used, for example about 300 ° C. or less. The temperature of the heated surface according to certain embodiments ranges from 180 ° C. to about 200 ° C., and according to certain embodiments is at least about 190 ° C.

According to certain embodiments of the invention, the crosslinkable polymer may be selected from the group consisting of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soy protein and alginate. According to certain aspects of the invention, the crosslinkable polymer may be used in an amount ranging from about 60% to about 100% by weight based on the dry matter.

As some indications the crosslinker may be a borate or a borate derivative such as borax, sodium tetraborate, boric acid, phenyl boronic acid or butyl boronic acid. Crosslinking agents can be used in amounts ranging from about 1 to about 12% based on the crosslinkable polymer.

The invention also refers to a treated paper produced according to the method described herein. Treated paper is characterized by improved smoothness with a relatively small increase in density compared to the original sheet.

The coating material can be moisturized, for example, by applying water, since a wet coating material is preferred upon contact with the heated drum. One method is to spray water onto the coating prior to contacting the hot drum. However, in certain embodiments it may also be practiced without any additional moisturizing.

In certain embodiments starch may be used as a soluble polymer. In certain embodiments the starch-based coating can proceed successfully without crosslinkers and good results can be obtained without gelation (or also known as agglomeration).

The starch solution containing 2-5% of the release agent is contacted with a heated drum under the conditions described above. If it is necessary to moisturize the coating material under certain conditions, water can be used by spraying alone, and good polishing surface reproduction is achieved. A 20% solid starch coating is applied to the web and contacted with a heated drum to reproduce it well.

Starch coatings were also found to have 25% and 30% solids. Both of these coatings fall off the drum without stickiness but do not have good surface reproduction. The 25% solids coating mediates the reproduction, but the 30% solids coating is not so smooth. A defined amount of moisture present on the surface can help to deliver the boiling over the entire coating. Under a defined amount of surface moisture, the local surface area is effectively boiled to improve the reproduction of the drum surface but not the other surface. Thus, the percentage of the area that reproduces the smooth drum surface without moisturizing the surface with water spray, such as raising solids above 20%, increased the coating until approximately 30% coating solids were obtained with little or no surface smoothness reproduction. Reduced to solids. Full surface reproduction can be obtained by spraying enough water on the surface of the 30% solids coating material before contacting the heated drum. It can be expected that this relationship may be affected by rawstock absorptivity, coat weight, coating viscosity and process speed. Further experiments should be able to confirm the effects of these parameters.

The embodiment described above runs with a chrome surface on a heated drum. The examples described below proceed after resurfacing the drum with a tungsten carbide coating. In each of these examples some "runs" were run to collect the results. The run proceeds by heating the drum to approximately 190 ° C., setting the degree of spraying, applying the coating to the web by the metered rod method, and optionally followed by a moisturizing spray (which may optionally contain a crosslinker). The web then comes into contact with the drum at 35 fpm. The temperature of the drum during the run is varied from 180 ° C to 190 ° C. The variability changed during the run is the coating weight applied by the metering rod. Changes in coating type, coating solids, or spray level consist of different experimental runs on the equipment. Coat weights are measured in several weights and are reported as bone-dry. Some experiments are carried out with crosslinking agents on their own coatings that are not strongly crosslinked, for example when using materials such as starch.

Example 1

A very compact pressed base sheet having a basis weight of 111 lb / 3000 ft ² is used as the substrate to which the simple coating composition is applied and treated. The first coating is 95% CELVOL 203S polyvinyl alcohol (PVOH) by dry weight, Emtal 50 VCS, 5% triglycerides used as a release agent. The coating solids is 20% by weight. The coating is applied by metered rods. The table lists the samples and the test conditions. Sample 1.1 was prepared by spraying the coating with a crosslinking solution containing 1% by weight of sulfonated castor oil and 3% by weight of borax as a release agent. Spray rate is 48 milliliters per minute. Samples replicate in drum wells and fall off the drums without stickiness. Significant improvements in smoothness were obtained with minimal loss of calipers. For sample 1.2, the conditions are the same except that borax was not used in the spray solution. When crosslinking polyvinyl alcohol without borax, the coating material does not fall off the surface, and some film remains on the drum surface. This experiment clearly demonstrates the benefits of crosslinking of polyvinyl alcohol.

In another run, carboxymethyl cellulose (CMC) is replaced with polyvinyl alcohol to compare polymer efficacy. Carboxymethyl cellulose is FINFIXX 30, which can only proceed at 7% solids due to the coating viscosity. The coating is formulated with 95% polymer and 5% Emtal. Samples 1.3 and 1.4 have two different coat weights sprayed with Borax spray at 48 ml / min. The coating replicates in the drum surface wells and completely falls off the drum. Smoothness improved with minimal loss of caliper but smoothness was not as good as for polyvinyl alcohol. In the process for preparing Sample 1.5, borax was not used for spraying. The coating replicates in the drum surface wells and completely falls off the drum. Smoothness was improved by removing borax. The non-crosslinked coatings can be replicated and can be seen to fall from the drum, indicating that materials other than crosslinkable materials can be used in the present invention.

Example 2

A very compact pressed base sheet having a basis weight of 111 lb / 3000 ft ² is used as the substrate to which the simple coating composition is applied and treated. The first coating material was 95% CLEER-COTE 625 starch (viscosity modified wax cone starch) by dry weight, Emtal 50 VCS used as a release agent, ie 5% triglycerides. The coating solids is 20% by weight. The coating is applied by metered rods. Sample 2.1 was prepared by spraying the coating with a crosslinking solution containing 1% by weight of sulfonated castor oil and 3% by weight of borax as a release agent. The spray rate is 46 milliliters per minute. Samples replicate in drum wells and fall off the drums without stickiness. Significant improvements in smoothness were obtained with minimal caliper loss. Samples 2.2, 2.3, 2.4 and 2.5 were prepared with different coat weights of the same coating and the spray did not contain borax. All samples are replicated in surface wells and completely dropped from the drum. Samples 2.6 and 2.7 were run without any spraying. Samples replicate in surface wells and fall off completely. Although the smoothness was not well improved, the sample showed markedly improved smoothness at minimal caliper reduction. It can be seen above that the process can proceed without any moisturizing spray.

Example 3

This experiment is a continuation of Example 2 to illustrate the effect of coating solids. Samples 3.1 and 3.2 were run on 23% coating solids without moisturizing spray. Good replication and fall were obtained. In samples 3.3 and 3.4 the coating solids increased to 25.7% when reapplied without moisturizing spray. It fell perfectly, but the replication on the surface was not perfect. Visually observed, only about 90-95% of the surface was replicated in the drum. The same 25.7% solids coating above proceeded for samples 3.5 and 3.6 and a 48 ml / min moisturizing spray was applied. Surface replication was perfect and smoothness was greatly improved. For samples 3.7 to 3.12 a 30% solids coating was used. When no moisturizing spray was used (3.7), it dropped perfectly but only a small percentage of the surface was replicated. Replication was greatly improved when the moisturizing spray 48 ml / min was used (3.8), but the surface was spotted as having a poor replication area. When the moisturizing spray was raised to 98 ml / min (3.9, 3.10, 3.11 & 3.12) the replication was perfect and the smoothness was greatly improved with a minimum reduction in calipers. The coating solids are then reduced. For 17.5% coating solids (3.13, 3.14) without a moisturizing spray, they dropped well and replicated perfectly. At 10% solids (3.15) without moisturizing spray, the coating weight was reduced due to the low coating viscosity and the coating uptake into the sheet resulted in poor replication.

Samples of smooth products made from starch as a polymer coating, at 20% solids, were coated with a conventional colored clay coating (approximately 10 lb / 3000 ft ² of a latex binder applied on a smooth polymer layer). Top coated with about 3 minutes 2 clay and 3 minutes 1 carbonate). This sample was then cut into sections to examine the shape of the coating layer. Cross sectioning was performed by freezing the sample in liquid nitrogen and then cracking (freeze fracturing) the sample into two. The cracked edge (eg cross-sectional area) of the sample was then observed under a microscope.

Photomicrographs confirmed the voids present in the polymer coating layer as shown in FIG. 2 (indicated by the measurement bar to indicate the ratio). In Figures 2-5, the microscope magnification is 1000 and the measurement bar is 20 microns long. As an embodiment the structure shown in FIG. 2 includes a cardboard substrate 110. The substrate thickness typically extends below the micrograph area. The substrate 110 shown in the micrographs sometimes separates or partially separates from the polymer layer 120 due to the freeze crushing process. Thus, the upper boundary of the substrate 110 is roughly represented by the distance in square brackets representing the substrate.

In this embodiment the polymer coating layer 120 was applied onto the substrate 110 and dried against a heated drum as previously described. The top coat 130 is then applied and dried. The term "polymer coating" is used to refer to a layer that is applied as described above and then contacted while in a wet state with respect to the heated drum. The term "top coating" is used to describe the outer layer that is applied as one layer. Obviously the "top coating" can be applied in more layers and can be composed of coating materials other than those used here.

The voids 121 are evident in the polymer coating layer 120 as shown in FIGS. 2-9. For example, FIG. 2 shows several voids 121 of polymer coating layer 120 having voids appearing approximately 5 to 20 microns in horizontal length. It is assumed that their size entering the "crushed sample" is in about the same range. These voids enter the sample thickness and typically appear somewhat flat in the "vertical" direction. The voids also appear to have relatively "walls" that are relatively smooth and generally thin. These thin walls are mostly identifiable as appearing between adjacent voids. Although the void wall is adjacent to the top coating 130, it is difficult to determine its thickness, but their presence can be estimated by the smooth bottom outline of the top coating 130 adjacent to the void.

3 is a sample micrograph showing several voids 121 in the polymer coating layer. The voids extend over an area equal to at least half of the coated surface area. The polymer coating layer does not show clear boundaries with this micrograph.

4 is a sample micrograph showing several voids 121 in the polymer coating layer 120. The walls of the voids appear relatively thin, as can be seen by the somewhat transparent appearance of the two void walls.

5-9 the microscope magnification is 500 and the measurement bar is 50 microns long. 5 shows several voids 121 of the polymer layer 120, each measuring bar representing the width of the selected void, for example, generally moving from left to right, the vertical distance is 10.5 microns, the horizontal distance is 36 microns, The vertical distance is measured at 10.6 microns and the horizontal distance is measured at 36.3 microns. Again the voids appear to extend over an area approximately equal to about half of the coated surface area.

Figure 6 is another sample with similar measurement bars, for example moving from left to right, the vertical distance is 8.66 microns, the horizontal distance is 32.1 microns, the vertical distance is 11.8 microns, and the horizontal distance is 22.7 microns. Such measurements in FIGS. 5 and 6 were collected for use in the graphs described later in FIG. 17.

FIG. 7 shows the voids 121 in the polymer layer 120 comprising a few generally showing flat sides. The voids appear to extend on an area corresponding to almost all coated surface areas. 8 shows another similarly unfolded sample. Several void wall areas are visible. 9 shows another sample extending over an area corresponding to almost all coated surface areas where voids 121 appear.

No other samples of smooth products prepared using starch as polymer coating at 20% solids were not top-coated. This sample was cut into sections to check the shape of the coating layer. Section cutting was performed by freezing the sample in liquid nitrogen and cracking (freezing crushing) the sample into two. The cracked edges (eg cross-sectional area) of the samples were checked under a microscope as shown in FIGS. 10-12 (indicated by the measurement bars to indicate their proportions). The microscope magnification is 1000 and the measurement bar is 20 microns long. 10 shows a polymer layer 120 containing voids 121 and having a very smooth outer surface. The polymer layer is on the cardboard substrate 110 and represents one of the cellulose fibers 112. The substrate thickness typically extends below the area of the micrograph.

11 and 12 show additional micrographs of samples that are polymer coated but not top-coated. As with the voids 121 below, the smoothness of the polymer layer 120 is apparent. The void walls often coincide with the polymer coating surface.

Figures 13 (200x magnification) and Figures 14 (500x magnification) show the surface of the sample as seen under a scanning electron microscope. Such a sample does not have a top coating (130). The largest yarn-like structure 112 is the cellulose fiber of the substrate 110. The smallest cell-like structure 122 that appears as a fine network or mesh is the individual voids of the polymer layer 120. The polymer layer here is inherently transparent except for the walls of the voids.

15 and 16 show the surface of a sample confirmed by a reflective scanning electron microscope. Such a sample does not have a top coating (130). The largest yarn-like structure 112 is the cellulose fiber of the substrate 110. The small cell-like structure 122, represented by a fine network or mesh, is a wall of individual voids in the polymer layer 120. The polymer layer here is inherently transparent except for the void walls. The voids appear to be distributed over the entire surface.

FIG. 17 is a graph showing the distribution of void sizes based on approximately 90 measurements of each of void width (horizontal length) and height (vertical length in a micrograph). The measurement represents an average void width of about 19 microns (measured in a direction parallel to the sample thickness) with a standard deviation of about 9 microns. The measurements represent an average void height (measured in the direction of the sample thickness) of about 10 microns with a standard deviation of about 4 microns.

This void length is representative of the sample studied here. This does not mean, however, that limitations can arise in other lengths due to changes in material or process conditions.

It is hypothesized that steam bubbles create these voids while the coating is in contact with the heated drum, and the bubbles can help maintain contact between the drum and the coating. The resulting voids typically help to bridge the distance between the other rough substrate layer 110 and the smooth surface of the heated drum. Thus, the dried polymer coating has a smoother replicating surface that is smoother than the substrate layer 110. Many or most voids appear to remain intact when the top coating 130 is applied. The top coating is therefore smoother, due to the relatively smooth underlying polymer layer 120. It has been found that this is advantageously obtained by the present invention. In addition to the supposed effect that voids help to create smooth replica surfaces, voids may also contribute to low density in the product.

Nip conditions between the squeeze roll 24 and the hot drum 22 can affect the presence or absence of voids in the polymer coating. It is necessary to adjust the nip loading (e.g. PLI loading on the nip) in order to boil the nip that produces voids by the squeeze roll hardness and the diameter of the squeeze roll and hot drum.

The polymer-coated paper or cardboard produced by the present invention can be used when a smooth substrate or final product is desired. Polymer-coated paper or cardboard may be used as is (eg, as shown in FIGS. 10-16), or additional coatings or other treatments applied thereto (eg, towers shown in FIGS. 2-9). Coating material 130, or other coating material]. Additional final materials or processes may be applied to polymer-coated paper or cardboard with or without additional coating. For example, one or more additional coatings can be applied as conventional coatings, top coatings, and triple coatings of conventional paper or cardboard substrates. The calendering process can be applied before or after the optional further coating. For example, one or more additional coatings may be applied and the gloss calendaring process may proceed.

The method of using and preparing the polymer-coated material according to the invention should be clearly understood from the simple details of the materials and processes provided herein. Thus, there is no need for further explanation or discussion of the material or method.

While describing and describing preferred embodiments of the invention, various modifications of the embodiments and implementations of the invention may be possible without departing from the spirit or scope of the invention. While the preferred embodiments described herein are described in connection with paper or cardboard substrates, such embodiments are not limited to fabrics, nonwovens, fibrous materials, polylactic acid substrates, and porous films, and other structures are readily available according to the invention. You can run

Thus, it is to be understood that the invention is not limited to the specific embodiments described herein (or as apparent from the description), but only to the claims appended hereto.

Claims (162)

A product comprising a substrate and a first coating material on the substrate, The first coating includes a water soluble polymer and a release agent; Sheffield smoothness of the surface of the first coating material has a range of 200 units or less; And the first coating includes a surface, wherein at least 50% of the first coating surface has a void below the surface having a transverse dimension of at least 5 microns. The method of claim 1, The water soluble polymer comprises at least one selected from the group consisting of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soy protein and alginate. A product comprising a substrate and a first coating material on the substrate, The first coating includes a water soluble polymer and a release agent and does not contain an elastomeric material inherently; Sheffield smoothness of the surface of the first coating material has a range of 200 units or less; Said first coating comprising a surface, wherein at least 50% of said first coating surface has a void below the surface having a transverse diameter of at least 5 microns. A product comprising a substrate and a first coating material on the substrate, The first coating includes a water soluble polymer and does not contain an elastomeric material inherently; Sheffield smoothness of the surface of the first coating material has a range of 200 units or less; The first coating comprises a surface, wherein at least 50% of the surface of the first coating has a void below the surface having a transverse diameter of at least 5 microns The method according to claim 1 or 4, Further comprising a second coating on the first coating. delete delete delete The method of claim 1, The first coating material is inherently free of elastomeric materials. The method according to any one of claims 1, 3 and 4, The first coating material comprises a crosslinking agent. The method according to any one of claims 1, 3 and 4, The first coating material comprises, by dry weight, at least 60% water soluble polymer and up to 10% release agent. The method according to claim 3 or 4, The first coating material comprises at least one selected from the group consisting of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soy protein and alginate. delete delete As a processing method of a base material, Applying a first coating material of an aqueous polymer solution to the substrate as a film, the first coating material comprising a water-soluble polymer and a release agent; And The process of immobilizing the aqueous polymer solution by contacting the aqueous polymer solution with a heated surface to boil the aqueous polymer solution and forming voids remaining in the aqueous polymer solution (the immobilization process causes some or all of the aqueous polymer solution to dry). Including the step of making a; Sheffield smoothness of the surface of the first coating material has a range of 200 units or less; The first coating comprises a surface, wherein at least 50% of the first coating surface has a void below the surface having a transverse diameter of at least 5 microns. The method of claim 15, The film is contacted with the heated surface for a time interval of 3 seconds or less. The method of claim 15, And contacting the film of aqueous polymer solution with a heated surface having a temperature of at least 150 ° C. for up to 3 seconds. delete As a method of treating a substrate, Applying a first coating of an aqueous polymer solution as a film to the substrate, the first coating comprising a water soluble polymer and not necessarily including an elastomeric material; And Contacting the surface heated to a temperature above 150 [deg.] C. for 3 seconds or less to boil the aqueous polymer solution and to form voids in the film to immobilize the film (the immobilization process involves drying part or all of the film). Inclusive); Sheffield smoothness of the surface of the first coating material has a range of 200 units or less; The first coating comprises a surface, wherein at least 50% of the first coating surface has a void below the surface having a transverse diameter of at least 5 microns. The method of claim 19, Wherein the crosslinking agent is applied to or included in the first coating prior to contacting the film with the heated surface. delete delete The method of claim 15, The film is in contact with the heated surface for less than 2 seconds; The substrate comprises a web or sheet and comprises one or more selected from the group consisting of cellulose, paper, cardboard, fabric, fiber material, porous material, porous film or polylactic acid; The aqueous polymer solution comprises a crosslinkable polymer, essentially free of elastomeric material; The crosslinker is included in or applied to the first coating prior to contacting the film with the heated surface; The crosslinking agent comprises at least one selected from the group consisting of borax, borate, aldehydes, ammonium salts, calcium compounds and derivatives thereof; The first coating comprises at least 60% water soluble polymer and up to 10% release agent by dry weight; The release agent is a wax, petroleum wax, vegetable wax, animal wax, synthetic wax, fatty acid metal soap, metal stearate, long chain alkyl derivatives, fatty esters, fatty amides, fatty amines, fatty acids, fatty alcohols, polymers, polyolefins, silicone polymers At least one selected from the group consisting of fluoropolymers, natural polymers, fluorinated compounds, fluorinated fatty acids and combinations thereof; The first coating includes at least one selected from the group consisting of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soy protein and alginate; Further comprising applying a second coating material after part or all of the film is dried, wherein the second coating material comprises at least one selected from the group consisting of pigments, binders, and fillers. As a method of treating a substrate, Applying a first coating of an aqueous polymer solution as a film to the substrate, the first coating comprising a water soluble polymer and a release agent, essentially no elastomeric material; And Contacting the surface heated to a temperature of at least 150 ° C. for up to 3 seconds to immobilize the aqueous polymer solution to boil and form voids in the film; The immobilization process comprises drying part or all of the film; Sheffield smoothness of the surface of the first coating material has a range of 200 units or less; The first coating comprises a surface, wherein at least 50% of the first coating surface has a void below the surface having a transverse diameter of at least 5 microns. The method of claim 24, The film is in contact with the heated surface for less than 2 seconds; The substrate comprises a web or sheet and comprises one or more selected from the group consisting of cellulose, paper, cardboard, fabric, fiber material, porous material, porous film or polylactic acid; Water soluble polymers include crosslinkable polymers; The crosslinker is included in or applied to the first coating prior to contacting the film with the heated surface; Crosslinking agents include at least one selected from the group consisting of borax, borate, aldehydes, ammonium salts, calcium compounds and derivatives thereof; The first coating includes, by dry weight, at least 60% water soluble polymer and up to 10% release agent; The release agent is a wax, petroleum wax, vegetable wax, animal wax, synthetic wax, fatty acid metal soap, metal stearate, long chain alkyl derivatives, fatty esters, fatty amides, fatty amines, fatty acids, fatty alcohols, polymers, polyolefins, silicone polymers At least one selected from the group consisting of fluoropolymers, natural polymers, fluorinated compounds, fluorinated fatty acids and combinations thereof; The first coating includes at least one selected from the group consisting of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soy protein and alginate; Further comprising applying a second coating material after part or all of the film is dried, wherein the second coating material comprises at least one selected from the group consisting of pigments, binders, and fillers. As a method of treating a substrate, Providing a cellulose substrate; Applying a first coating of an aqueous polymer solution as a film to the substrate, the aqueous polymer solution comprising at least 60% water soluble polymer by dry weight and up to 10% release agent by dry weight; Contacting the surface heated to a temperature of at least 150 ° C. for 3 seconds or less to boil the aqueous polymer solution and to form voids in the aqueous polymer solution to immobilize the aqueous polymer solution (the immobilization process is part or all of the aqueous polymer solution). And drying the same); Sheffield smoothness of the surface of the first coating material has a range of 200 units or less; The first coating comprises a surface, wherein at least 50% of the first coating surface has a void below the surface having a transverse diameter of at least 5 microns. The method of claim 19, And further comprising applying a second coating material after drying part or all of the film. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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