JP7358722B1 - Coating agent for forming hydrogel sheet and hydrogel sheet - Google Patents

Abstract

[Problem] A water-containing product that has a pH that is not in the strongly acidic region, has a sufficient pot life, and gelation progresses sufficiently in a short period of time, making it possible to roll it up during coating, resulting in excellent productivity. To provide a coating agent for forming a gel sheet. [Solution] Contains at least a partially neutralized water-soluble or water-swellable carboxyl group-containing polymer (A), an oxazoline compound or a carbodiimide compound, and water, and has a pH of 4 or more and less than 11, after 24 hours at 25°C. A coating agent for forming a hydrogel sheet, which has a viscosity increase rate of 100% or less. [Selection diagram] None

Description

The present invention relates to a coating agent for forming a hydrogel sheet and a hydrogel sheet.

The hydrogel sheet, which has moderate adhesive strength, low skin irritation, moisture retention, and cushioning properties, can be used as a laminate in which a gel layer is laminated on a base material, such as medical poultices, medical electrode fixing materials, and sheet skin. It is widely used as cooling materials, wound dressings, sheet cosmetic packs, temporary fixing materials, vibration isolators, conductive materials, agricultural sheets, etc.

The gel layer of a hydrogel sheet is made by swelling a crosslinked or insolubilized hydrophilic polymer with water, and there are various types depending on the type of hydrophilic polymer and the method of crosslinking or insolubilization. As polymers used in the gel layer, carboxy group-containing polymers such as non-crosslinked polyacrylic acid or its salt, crosslinked polyacrylic acid or its salt, and carboxymethyl cellulose or its salt are known. A known method for crosslinking carboxy group-containing polymers is to form an ionic bond complex with polyvalent metal cations such as aluminum hydroxide or aluminum sulfate, and this method is often used industrially. ing.

For example, Patent Document 1 discloses a solid contact medium in which an adhesive layer and a non-adhesive gel layer are laminated (Claim 6, FIG. It is disclosed that the composition contains (meth)acrylates, polyvalent inorganic salts, alcohols, and a polymeric crosslinking agent that binds to the carboxy group (Claim 1).
Further, Patent Document 2 states that the polymer contains a carboxyl group-containing polymer and a crosslinking agent that ionically bonds with the carboxyl group-containing polymer, has a pH of 1 or more and less than 3, and has a moisture content of 1 to 30% by mass. A water-containing gel sheet is disclosed.

JP 2021-151298 Publication Patent No. 6593566

When the above-mentioned polyvalent metal cations, which have been commonly used in the past, are mixed with an aqueous solution of a carboxyl group-containing polymer, a crosslinking reaction proceeds rapidly at room temperature and a gel is formed. The period (hereinafter referred to as "pot life") during which a coating agent for forming a hydrous gel sheet containing (hereinafter sometimes simply referred to as "coating agent") can be maintained in a fluid state becomes shorter.
Therefore, even if you try to apply a coating agent containing an aqueous solution of a carboxyl group-containing polymer and a polyvalent metal cation onto a substrate using a roll coater or the like, the coating agent must be adjusted before being applied to the coating device. There was a problem in that the crosslinking reaction had already progressed and the fluidity had disappeared by the time it was supplied, making it impossible to coat.
Although it is not a coating agent for forming a hydrous gel sheet, for example, the stock solution for forming the adhesive layer in the solid contact medium described in Patent Document 1 is a crosslinking agent that crosslinks a carboxyl group-containing polymer and poly(meth)acrylates. As such, polyvalent inorganic salt is an essential component, and it is thought that it is difficult to obtain a sufficient pot life.

In order to solve this problem, a chelating agent such as ethylenediaminetetraacetic acid (EDTA) or its sodium salt is added to the coating agent as a gelling rate regulator. A coating agent to which a gelation rate regulator has been added is coated onto a substrate using a roll coater etc. after preparation of the coating agent, in order to delay the gelation reaction and have sufficient fluidity during coating. It becomes possible to paint. However, since the effect of delaying the gelation reaction remains even after coating, it is necessary to keep the coated material for a long time without deforming it (hereinafter referred to as "seasoning") until gelation sufficiently progresses. There was a problem that it was considered.
Therefore, when applying a coating agent to a single sheet of substrate, there is a problem in that production equipment is required to wait for the completion of the crosslinking reaction without deforming the single sheet of water-containing gel sheet after coating. .

When coating a coating agent on a long web-like substrate rather than a single sheet, the crosslinking reaction can be completed without deforming the long hydrogel sheet after coating without winding it up as a long sheet. There was a problem in that even larger special production equipment was required for waiting. If you try to wind up a long coated hydrogel sheet into a roll before cross-linking has fully progressed, the pressure during winding will cause the applied coating agent to curl around the edges of the rolled hydrogel sheet. This may cause problems such as protruding from the surface.
If it were possible to wind up a long web-like hydrous gel sheet into a roll without seasoning, it would be possible to transport it in a roll to the next processing step such as slitting or punching, which would simplify the manufacturing process and improve the quality of the product. It is also possible to supply gel sheets in rolls, which significantly improves productivity compared to single-wafer hydrogel sheets.

Patent Document 2 discloses the problem of improving pot life and productivity during coating.
However, the gel sheet described in Patent Document 2 is strongly acidic, and there are concerns that it may be irritating or corrosive to adherends. Depending on the chemical structure of the components, problems may arise such as denaturation or decomposition.

The problem to be solved by the present invention is to have a pH that is not in the strongly acidic region, a sufficient pot life, and gelation that progresses sufficiently in a short period of time so that it can be rolled up at the time of coating. An object of the present invention is to provide a coating agent for forming a hydrogel sheet that has excellent productivity.

As a result of intensive studies to solve the above-mentioned problems, the present inventor found that the above-mentioned problems could be solved, and completed the present invention.

That is, the present invention comprises an at least partially neutralized water-soluble or water-swellable carboxyl group-containing polymer (A), an oxazoline compound or a carbodiimide compound, and water, has a pH of 4 or more and less than 11, and is heated at 25° C. 24 The present invention relates to a coating agent for forming a hydrous gel sheet, which has a viscosity increase rate of 100% or less after a period of time.

The present invention also relates to the above-mentioned coating agent for forming a hydrogel sheet, which has a viscosity at 25° C. of 100 mPa·s or more and less than 50,000 mPa·s.

Furthermore, the present invention relates to a hydrogel layer formed from the coating agent for forming a hydrogel sheet and having a moisture content of 1% by mass or more and less than 30% by mass.

Furthermore, the present invention relates to a hydrous gel sheet in which the hydrous gel layer described above is laminated on at least one surface of a sheet-like base material.

Furthermore, the present invention relates to the above hydrogel sheet, characterized in that it is wound up into a roll.

The present invention has a pH that is not in the strongly acidic region, has a sufficient pot life, and gelation progresses sufficiently in a short period of time, making it possible to roll up during coating, resulting in excellent productivity. Now we can provide a coating agent for forming hydrogel sheets.

Embodiments of the present invention will be described in detail below.

The coating agent for forming a hydrogel sheet of the present invention is a water-soluble or water-swellable carboxyl group-containing polymer (A) that is at least partially neutralized (hereinafter simply referred to as "carboxy group-containing polymer (A)" or "polymer (A)"). ), contains an oxazoline compound or carbodiimide compound and water, has a pH of 4 or more and less than 11, and has a viscosity increase rate of 100% or less after 24 hours at 25°C, that is, within twice the original viscosity. It is a coating agent.

The at least partially neutralized water-soluble or water-swellable carboxyl group-containing polymer (A) used in the present invention is (meth)acrylic acid ("acrylic acid" and "methacrylic acid" are collectively referred to as "( Synthetic polymers such as homopolymers and copolymers of meth)acrylic acid, polysaccharides such as hyaluronic acid, carrageenan, pectin, gum arabic, xanthan gum, gellan gum, agar, and gum tragacanth, glycinin (soy protein ) and other proteins. As the carboxyl group-containing polymer, one type or two or more types of components can be used. Among these, polyacrylic acid is preferably used.

As the polymer (A) used in the present invention, both non-crosslinked polymers and crosslinked polymers can be used as appropriate. A non-crosslinked polymer is a polymer obtained from a monofunctional monomer and has a linear structure. A crosslinked polymer is a polymer obtained from a monomer group including a polyfunctional monomer, and has a crosslinked structure.

The weight average molecular weight of the non-crosslinked carboxyl group-containing polymer used in the present invention is preferably 20,000 or more, more preferably 150,000 or more. Further, the upper limit of the mass average molecular weight is not particularly limited, but is generally 5 million or less. By using a non-crosslinked polymer having a mass average molecular weight of 20,000 or more, the gel strength necessary for forming a sheet can be obtained.

The crosslinked carboxyl group-containing polymer preferably has a 0.2% neutralized viscosity at 25°C of 1,500 mPa·s or more and 35,000 mPa·s or less, and 2,000 mPa·s or more and 30,000 mPa·s or less. It is more preferable that Alternatively, the 0.5% neutralized viscosity at 25°C is preferably 5,000 mPa·s or more and 75,000 mPa·s or less, more preferably 5,400 mPa·s or more and 70,000 mPa·s or less. . By using a crosslinked carboxyl group-containing polymer with a 0.2% neutralized viscosity at 25°C of 1,500 mPa·s or more, or a 0.5% neutralized viscosity at 25°C of 5,000 mPa·s or more. Gel strength can be improved. By using a crosslinked carboxyl group-containing polymer with a 0.2% neutralized viscosity at 25°C of 35,000 mPa・s or less, or a 0.5% neutralized viscosity at 25°C of 75,000 mPa・s or less Deterioration in handling properties due to increase in coating fluid viscosity can be suppressed. Incidentally, "0.2% neutralized viscosity" means the viscosity when an aqueous solution containing 0.2% by mass of a crosslinked carboxyl group-containing polymer is neutralized, and represents a value measured by a B-type viscometer. Sodium hydroxide can be offered as a neutralizing agent.

Furthermore, for the same reason as above, those having a 0.2% neutralized viscosity at 20°C of 1,500 mPa·s or more and 35,000 mPa·s or less are also preferably used, and 2,000 mPa·s or more and 30,000 mPa・Those which are less than s are more preferably used. Alternatively, those having a 0.5% neutralized viscosity at 20°C of 5,000 mPa·s or more and 75,000 mPa·s or less are also preferably used, and those having a 0.5% neutralized viscosity of 5,400 mPa·s or more and 70,000 mPa·s or less are also preferably used. More preferably used.

In addition to the above-mentioned carboxy group-containing polymers, emulsion-type polymers also exist, but emulsion-type polymers refer to polymers in which polymer particles are suspended in water, and are neither water-soluble nor water-swellable. Since this is not applicable, the at least partially neutralized water-soluble or water-swellable carboxyl group-containing polymer (A) does not include an emulsion type polymer.

An oxazoline compound or a carbodiimide compound is a compound having one or more oxazoline groups or carbodiimide groups in the same molecule, and is used for the purpose of reacting with the carboxyl group-containing polymer to form a crosslinked structure. A compound having a moiety is preferable. These compounds include 2,2'-bis(2-oxazoline), 1,3-phenylenebis(2-oxazoline), 1,4-phenylenebis(2-oxazoline), and 1,4-di(2-oxazoline). -2-yl)piperazine, 1,1'-(1,3-propanediyl)bis(3-tert-butylcarbodiimide), and the like. Further, it may be a polymer compound having a plurality of oxazoline groups or carbodiimide groups. As the oxazoline compound or the carbodiimide compound, one type or two or more types of components can be used. Among these, polymer compounds such as polyoxazoline and polycarbodiimide are preferably used.

Any amount of the oxazoline compound or carbodiimide compound can be used, but it is preferably 0.1 parts by mass or more and less than 50 parts by mass, and 0.5 parts by mass based on 100 parts by mass of the carboxyl group-containing polymer (A). More preferably, the amount is less than 40 parts by mass. When the amount of the oxazoline compound or carbodiimide compound used is 0.1 parts by mass or more, gelation proceeds rapidly as the moisture content of the coating agent decreases, and when the amount is less than 50 parts by mass, the coating agent for forming a hydrous gel sheet is A water-containing gel sheet that has a sufficient pot life and does not contain excessive oxazoline compounds or carbodiimide compounds can be obtained.

The hydrogel sheet may further contain a hydrophilic polymer other than the carboxyl group-containing polymer (A), an oxazoline compound, and a carbodiimide compound, an emulsion type polymer, and other additives, as necessary.

Hydrophilic polymers include nonionic synthetic polymers such as polyvinyl alcohol and polyvinylpyrrolidone;
Cationic synthetic polymers such as polyallylamine or its salt, polyethyleneimine or its salt, polyacrylamide or its salt, polydiallyldimethylammonium, polyvinylpyridine;
Anionic synthetic polymers such as polystyrene sulfonic acid or its salts;
Nonionic polysaccharides such as starch, locust bean gum, guar gum, and tamarind seed gum;
Examples include cationic polysaccharides such as chitosan.
Although these hydrophilic polymers do not contribute to the reaction with the crosslinking agent, they can adjust the rheology of the coating liquid and the physical properties such as gel strength and adhesive force of the gel layer formed depending on the type and amount of the added polymer. I can do it.

Any emulsion type polymer can be used as the emulsion type polymer. When the water-containing gel sheet is applied to human skin, an acrylic emulsion that has been used on human skin is preferably used in view of safety, but it is not limited to acrylic emulsions. For example, in a dispersion medium mainly composed of water, an alkyl (meth)acrylate such as n-butyl (meth)acrylate or 2-ethylhexyl (meth)acrylate is used as the main monomer, and a copolymerizable ( Emulsion polymerization of the main monomer alone using a conventional method using a carboxy group-containing monomer such as meth)acrylic acid, a hydroxyl group-containing monomer such as 2-hydroxyethyl (meth)acrylate, or an amide group-containing monomer such as dimethylacrylamide as a secondary monomer. Alternatively, it can be obtained by emulsion polymerization of a main monomer and a submonomer.
Moreover, an emulsion type polymer can be obtained without using emulsion polymerization, for example, by a method in which water is added after solution polymerization and further solvent removal is performed.

Other additives include drying adjusters, pH adjusters, antioxidants, preservatives, ultraviolet absorbers, lubricants, colorants (dyes or pigments), chemicals, fillers (particles or fibers), and conductivity imparting agents. Examples include.

As the drying regulator, a hydrophilic compound having a weight average molecular weight of 10,000 or less, which has a small influence on the viscosity of the coating liquid, can be preferably used. Examples include compounds that are liquid at room temperature, such as glycerin and polyethylene glycol, and sugars. By using a drying conditioner, it is possible to suppress a decrease in the usability of the gel due to excessive water evaporation in the drying process, and it is also possible to suppress a change in the moisture content after producing a hydrous gel sheet.

The amount of the drying regulator used is preferably 10 to 95% by mass, more preferably 15 to 92% by mass, based on the total amount of the gel layer excluding water. When the content is 10% by mass or more, overdrying can be suppressed, and when the content is 95% by mass or less, the gel has sufficient strength.

As the pH adjuster, any component that can adjust the pH of the coating agent to 4 or more and less than 11 can be used. Examples of pH adjusting agents include acetic acid, formic acid, lactic acid, tartaric acid, oxalic acid, benzoic acid, glycolic acid, malic acid, citric acid, hydrochloric acid, nitric acid, sulfuric acid, sodium hydroxide, calcium hydroxide, methylamine, ethylamine, propylamine. , dimethylamine, diethylamine, dipropylamine, trimethylamine, triethylamine, tripropylamine, monomethanolamine, monoethanolamine, monopropanolamine, dimethanolamine, diethanolamine, dipropanolamine, trimethanolamine, triethanolamine, tripropanol Examples include amine, citrate buffer, phosphate buffer, glycine buffer, acetate buffer, and the like. Any amount of pH adjuster can be added.

The pH of the coating agent is 4 or more and less than 11. By setting the pH to 4 or more, excessive production of molecular carboxy groups contributing to the crosslinking reaction is suppressed, and a good pot life can be obtained. Moreover, by setting the pH to less than 11, molecular carboxy groups necessary for gelation can be ensured, and good winding properties can be obtained. More preferably, the pH is 6 or more and less than 9. Note that the term "molecular carboxy group" refers to a non-ionized carboxy group.

The coating agent for forming a hydrous gel sheet of the present invention preferably has a viscosity at 25° C. of 100 mPa·s or more and less than 50,000 mPa·s, more preferably 500 mPa·s or more and less than 30,000 mPa·s. If the viscosity is too low, there is a risk of repelling when applied to a release sheet that has been treated with silicone, etc. If the viscosity is too high, it will be difficult to stir, and the liquid transportability will decrease during coating. Problems such as roughening of the coated surface occur.
Further, the nonvolatile content concentration of the coating agent is preferably 20% by mass or more and less than 70% by mass.

It is important that the coating agent has a viscosity increase rate of 100% or less after 24 hours at 25°C, preferably 50% or less.
When the viscosity increase rate after 24 hours at 25° C. is 100% or less, a sufficient pot life necessary for coating can be ensured, and stable coating can be achieved.
Note that the viscosity increase rate of 100% means that the viscosity of the coating agent, for example, was 100 mPa·s and became 200 mPa·s.

By applying the coating agent of the present invention onto a substrate and drying to volatilize and remove a portion of the water, crosslinking of the polymer (A) rapidly progresses and a hydrogel layer is obtained. There are no particular limitations on the substrate to which the coating agent is applied, but examples thereof include sheet-like substrates, block-shaped or uneven metal or plastic molded articles, and the like.

The method for applying the coating agent is not particularly limited as long as it is a method that can apply a fluid material, but examples include a roll coater, knife coater, gravure coater, bar coater, die coater, dip coater, spray coater, etc. Examples of methods used include: The amount of coating agent applied is not particularly limited, but it is preferably 1 to 2000 g/m ² as a coating amount.

There are no particular restrictions on the method of drying the coating agent to volatilize and remove a portion of the water, but examples include methods such as air drying and heating. The heating temperature is not particularly limited, but is preferably 50°C to 200°C, more preferably 80°C to 120°C. By heating the atmosphere at a temperature of 50°C or higher, the coating agent can be dried efficiently in a timely manner, and by heating at a temperature of 200°C or lower, rapid changes in moisture content can be suppressed, resulting in poor appearance due to air bubbles and damage to the hydrogel layer. Non-uniformity can be prevented.

The moisture content of the hydrogel layer formed by the coating agent is preferably 1% by mass or more and less than 30% by mass, more preferably 2% by mass or more and less than 25% by mass. The flexibility of the hydrogel layer can be ensured because the water content of the hydrogel layer is 1% by mass or more. Furthermore, gelation proceeds rapidly when the moisture content is less than 30% by mass. The moisture content of the hydrogel layer can be measured using a Karl Fischer moisture meter. A commercially available device can be used, such as a coulometric Karl Fischer moisture meter model CA-200 (manufactured by Mitsubishi Chemical Analytech).

The pH of the hydrogel layer is 4 or more and less than 11. The pH of the hydrogel layer reflects the pH of the coating agent forming it. The pH of the hydrogel layer can be measured using a pH meter with a flat sensor. Commercially available devices can be used, such as LAQUAtwin <pH-22B> (manufactured by Horiba, Ltd.).

There are the following two methods for applying a coating agent to obtain a hydrogel sheet in which a hydrogel layer is laminated on at least one surface of a sheet-like base material.
(1) Direct coating: A coating agent is applied onto a base material such as a resin film, and after the drying process, the surface is peeled off to protect the formed hydrogel layer, if necessary. How to paste sheets together.
(2) Transfer coating: A coating agent is applied onto a release sheet that is a support during coating, and after a drying process, a base material such as a resin film is attached to the surface, forming a hydrogel layer. and a base material.

Transfer coating described in (2) above does not apply heat to the base material, and strong tension derived from the structure of the coating machine is not applied to the base material. It is often used in the manufacture of products that use highly elastic base materials.

As the base material of the hydrogel sheet, resin films, natural fibers, semi-synthetic fibers, synthetic fibers, fabrics or knitted fabrics made of composite fibers thereof, nonwoven fabrics, paper, synthetic paper, etc. can be used. These base materials may be subjected to surface treatments such as primer treatment and water repellent/hydrophilic treatment, and may be composited with base materials of the same type or different types. Among these, polyurethane, nonwoven fabrics, and composite substrates thereof are preferably used because they have good adhesion to the hydrogel layer formed by the coating agent, but as mentioned above, when using these materials as substrates, It is preferable to use transfer coating.
Note that the type of release sheet is not particularly limited, and a sheet whose surface has been subjected to release treatment with silicone resin or the like can be used. The thickness of the base material and release sheet is not particularly limited, but is preferably 5 to 3000 μm.

A water-containing gel sheet is obtained by attaching a release sheet in the case of direct coating, or a base material in the case of transfer coating, to the coated film from which a portion of the water has been removed by heating and drying. These can be wound up into a roll if necessary. For winding, a normal winder can be used.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.
<Raw materials>
The raw materials for the coating agents used in the Examples and Comparative Examples shown in Tables 1 to 3 are as follows.
<<Carboxy group-containing polymer (A)>>
・Jurimer AC-10SH: non-crosslinked polyacrylic acid, mass average molecular weight 1 million, aqueous solution with non-volatile content concentration 10% by mass, manufactured by Toagosei Co., Ltd. ・Jurimer AC-10L: non-crosslinked polyacrylic acid, mass average molecular weight 2 .50,000, aqueous solution with a nonvolatile content concentration of 40% by mass, manufactured by Toagosei Co., Ltd., Aqualic AS58: non-crosslinked polyacrylic acid, mass average molecular weight 800,000, powder, manufactured by Nippon Shokubai Co., Ltd., Aqualic HL-415 : Non-crosslinked polyacrylic acid, mass average molecular weight 10,000, aqueous solution with non-volatile content concentration 45% by mass, manufactured by Nippon Shokubai Co., Ltd., Aronbis SX: Non-crosslinked sodium polyacrylate, mass average molecular weight 4.5 million, powder, Toa Junron PW-120, manufactured by Gosei Co., Ltd.: Cross-linked polyacrylic acid, 0.2% neutralized viscosity 8,000-20,000 mPa・s/25°C, powder, manufactured by Toagosei Co., Ltd., Akupec HV-505ED: Crosslinked polyacrylic acid, 0.2% neutralized viscosity 15,000-30,000 mPa・s/20°C, 0.5% neutralized viscosity 40,000-70,000 mPa・s/20°C, powder, Sumitomo Seika Co., Ltd., Rheosic 260H: cross-linked sodium polyacrylate, 0.2% neutralized viscosity 7,000-13,000 mPa・s/25°C, powder, manufactured by Toagosei Co., Ltd.

<<Oxazoline compound or carbodiimide compound>>
- Epocross WS-300: Polyoxazoline, oxazoline group weight 7.7 mmol/g (as an active ingredient), non-volatile content concentration 10% by mass, manufactured by Nippon Shokubai Co., Ltd. - Epocross WS-700: Polyoxazoline, oxazoline group weight 4. 5 mmol/g (as an active ingredient), non-volatile content concentration 25% by mass, manufactured by Nippon Shokubai Co., Ltd. Epocross K-2010E: Polyoxazoline, oxazoline group weight 1.8 mmol/g (as an active ingredient), non-volatile content concentration 40 mass %, emulsion type, manufactured by Nippon Shokubai Co., Ltd., Carbodilite V-02: Polycarbodiimide, NCN equivalent (chemical formula weight per 1 mol of carbodiimide group; as an active ingredient) 590, non-volatile content concentration 40% by mass, manufactured by Nisshinbo Co., Ltd., Carbodilite E -02: Polycarbodiimide, NCN equivalent (chemical formula weight per mol of carbodiimide group; as an active ingredient) 445, nonvolatile content concentration 40% by mass, emulsion/dispersion type, manufactured by Nisshinbo Co., Ltd.

<<Acrylic emulsion>>
・TOCRYL FSK-6649T: Alkyl acrylate copolymer emulsion, nonvolatile content 58% by mass, pH 7.1, manufactured by Toyochem Co., Ltd.
<<Hydrophilic polymer>>
・GOHSENOL EG-40: Polyvinyl alcohol, 4% viscosity 43.0 mPa・s/20°C, powder, manufactured by Nippon Gosei Kagaku Co., Ltd.
<<Drying agent>>
・Glycerin: Reagent grade, manufactured by Kishida Chemical Co., Ltd.
<<pH adjuster>>
<<Solvent>>
・Purified water: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
<<Base material>>
・Base material 1: Polyurethane film with a thickness of approximately 11 μm ・Base material 2: Nonwoven fabric with a thickness of approximately 180 μm

<Coating agent>
According to the formulation shown in Tables 1 to 3, a predetermined amount of raw materials are dissolved or dispersed in purified water at room temperature, and sodium hydroxide and hydrochloric acid are added as pH adjusters to achieve the viscosity and pH shown in Tables 1 to 3. An arbitrary amount was added to obtain a coating agent.
The pH, viscosity, pot life, and coatability of the obtained coating agent were evaluated according to the methods described below.

<Hydrogel layer, hydrogel sheet>
Using the obtained coating agent, a hydrogel layer and a hydrogel sheet were prepared according to the method described below, and the pH, moisture content, degree of gelation, and film-forming state of the hydrogel layer were evaluated.

[pH of coating agent]
The pH of the coating agent was measured at 25° C. using LAQUAtwin <pH-22B> (manufactured by Horiba, Ltd.).

[Viscosity of coating agent]
The viscosity of the coating agent was measured at 25° C. within 1 hour after blending using a TVB10/15 type B viscometer (manufactured by Toki Sangyo Co., Ltd.).

[Pot life of coating agent]
The viscosity increase rate of the coating agent was evaluated after being left at 25° C. for 24 hours after blending. Evaluation was performed based on the following criteria. In addition, for the comparative examples that received an evaluation of ×, subsequent evaluations were discontinued.
◎: Increase rate of 50% or less. (Extremely good)
○: Increase rate is greater than 50% and less than 80%. (Good)
△: Increase rate is greater than 80% and less than 100%. (Practical lower limit)
×: Increase rate is greater than 100%, or gelation occurs and coating is not possible. (Bad)

[Applicability of coating agent]
The coating agent was applied onto a silicone release-treated polyethylene terephthalate (PET) film as a release sheet using a knife coater in an amount of about 100 g/m ² , and the state of the coating was visually observed. Evaluation was performed based on the following criteria.
◎: No repellency or selvage is observed, and the thickness of the film is uniform throughout. (Extremely good)
○: The ears are slightly high, but there is no repellency, and there is no effect on performance or productivity. (Good)
△: The edges are obviously high, but most of the film maintains the expected film thickness, and the impact on productivity is slight. Alternatively, the coating method is limited due to the high viscosity, but it can be coated using an appropriate coating method. (Practical lower limit)
×: Repellency spreads over the entire coating film, making the film thickness non-uniform, or circular repellency is formed randomly, or the viscosity of the coating solution is high and coating is difficult. (Bad)

[pH of hydrogel layer]
The coating agent was applied onto a silicone release-treated polyethylene terephthalate (PET) film as a release sheet using a knife coater in an amount of about 100 g/m ² , and dried at 100°C for 1.5 minutes to form a hydrogel. formed a layer. Using LAQUAtwin <pH-22B> (manufactured by Horiba, Ltd.), a flat sensor was applied to the surface of the formed hydrogel layer to measure the pH of the hydrogel layer.
In Examples 36 to 42, the same coating agent as in Example 1 was used, but the drying conditions were changed. The drying conditions are as follows. Example 36 at 100°C for 30 minutes, Example 37 at 100°C for 20 minutes, Example 38 at 100°C for 5 minutes, Example 39 at 100°C for 3 minutes, Example 40 at 100°C for 2 minutes, Example 41 was heated to 100°C for 0.5 minutes, and Example 42 was heated to 100°C for 0.3 minutes.

[Moisture content of hydrogel layer]
The moisture content of the gel layer described in the case of pH measurement was measured using a Karl Fischer moisture meter model CA-200 (manufactured by Mitsubishi Chemical Analytech).

[Gelification degree of hydrogel layer]

(Gelification degree of hydrogel layer)
Peel off the hydrous gel layer described in the case of pH measurement from the release sheet within 1 hour after formation, measure the mass, then immerse in purified water at 40°C for 24 hours, dry at 100°C for 1 hour, and calculate the mass of the remaining components. The degree of gelation was calculated using the following formula. The degree of gelation of the hydrogel layer is related to the state of film formation and influences whether it can be wound into a roll.
Gelation degree (%) = Mass of remaining components after immersion (g) / Mass of hydrogel layer before immersion (g) x 100

[Hydrogel layer formation state 1 (expansion of coating width)]
After applying the coating agent to the release sheet according to the method described in the case of pH measurement, drying under each condition, compare the coating width immediately after coating (before drying) and after drying, and evaluate using the following criteria. did.
◎: Coating width change is less than 1 mm compared to immediately after coating (extremely good).
○: Coating width change is 1 mm or more and less than 5 mm (good) compared to immediately after coating.
Δ: Coating width change is 5 mm or more and less than 10 mm (practical lower limit) compared to immediately after coating.
×: Compared to immediately after coating, the coating width changed by 10 mm or more, and the film thickness was not stable (poor).

[Film formation state 2 of hydrogel layer (lifting of the end portion of base material 1)]
After applying the coating agent to the release sheet according to the method described in the case of pH measurement, it was dried under each condition, the base material 1 was attached to the hydrous gel layer, and it was rolled for 30 m at a winding tension of 100 N (per 1000 mm). A sample roll was prepared. After being stored at 25° C. for one week, the condition of the end in the width direction of the middle portion of the roll (approximately 15 m from the end of the roll) was visually evaluated.
◎: No lifting occurred even after unwinding (extremely good).
○: Although some floating occurs when unrolled, it is within an acceptable range (good).
△: When unrolled, some lifting is seen at the ends, but most of the material is in close contact with the base material and can be used (practical lower limit).
×: When unrolled, most of the film was not in close contact with the base material and could not be used (defective).

[Film formation state 3 of hydrogel layer (back stain of hydrogel layer on base material 2)]
After applying the coating agent to the release sheet according to the method described in the case of pH measurement, drying under each condition, attaching the base material 2 to the hydrous gel layer, and winding it for 30 m at a winding tension of 100 N (per 1000 mm). A sample roll was prepared. After storage at 25° C. for one week, the roll was unwound and the state of the gel layer seeping out to the back of the base material 2 was evaluated.
◎: The hydrous gel layer did not ooze out from the back of the base material 2 from the end of the roll to the beginning of the roll (extremely good).
Good: At the beginning of winding of the roll, the hydrous gel layer almost reaches the back of the base material 2, and dotted discoloration is observed in several places, but there is no stickiness to the touch (good).
△: At the beginning of winding of the roll, the hydrous gel layer oozes out from the back of the base material 2, and some spot-like discoloration is observed, and it is slightly sticky to the touch, but there is no large area other than the beginning of winding. The water-containing gel layer does not ooze out from the part, and it can be used (lower practical limit).
×: The hydrous gel layer oozed out from the back of the base material 2 from the end of the roll to the beginning of the roll, and it was sticky (defect).

In all of Examples 1 to 42, the pot life of the coating agent is sufficiently long, there is no coating defect in the coating process, and the degree of gelation of the hydrogel layer is above a certain level, so the film formation state is excellent. We were able to create a hydrous gel sheet that could be rolled up. On the other hand, in Comparative Examples 1 to 3, problems were found in any of the pot life of the coating agent, the coating properties, the degree of gelation of the hydrogel layer, and the film formation state of the hydrogel layer.

Claims (5)

It contains at least a partially neutralized water-soluble or water-swellable , non-crosslinked or crosslinked polyacrylic acid (A), an oxazoline compound or a carbodiimide compound, and water, and has a pH of 4 or more and less than 11, and has a pH of 4 or more and less than 11, and has a pH of 25 A coating agent for forming a hydrogel sheet, which has a viscosity increase rate of 100% or less after 24 hours at °C. The coating agent for forming a hydrogel sheet according to claim 1, having a viscosity at 25° C. of 100 mPa·s or more and less than 50,000 mPa·s. A hydrogel layer having a moisture content of 1% by mass or more and less than 30% by mass, which is formed from the coating agent for forming a hydrogel sheet according to claim 1 or 2 . A hydrous sheet comprising the hydrous gel layer according to claim 3 laminated on at least one surface of a sheet-like base material. The hydrous gel sheet according to claim 4 , which is wound up into a roll.