JPH0626668B2 - Water absorbing material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water absorbent material made of a water absorbent resin.

[Prior Art] Conventional water-absorbing materials made of water-absorbent resins include cross-linked polyacrylate, cross-linked starch-polyacrylate polymer, hydrolyzed vinyl acetate-methyl methacrylate copolymer, and isobutylene. -Crosslinked products of maleic anhydride are known, and all of them are anionic polyelectrolytes having a carboxyl group.

Therefore, although these water-absorbing materials show high water absorption for deionized water, ionic cross-linking proceeds for polyelectrolyte aqueous solutions containing Mg ²⁺ ions, Ca ²⁺ ions, Al ³⁺ ions, etc. Then, there is a problem that the water absorption capacity is extremely lowered, and also there is a problem that the water absorption capacity for the acidic aqueous solution is extremely low.

As a product with improved water absorption capacity for this polyelectrolyte aqueous solution,
A copolymer obtained by copolymerizing a vinyl monomer having a carboxyl group and a vinyl monomer having a tertiary amino group in the coexistence of 0.005 to 0.5% by weight of a divinyl compound has been proposed (JP-A-58-154710). There is.

[Problems to be Solved by the Invention] However, although this improved product exhibits a certain degree of water absorption ability to monovalent electrolyte aqueous solutions such as Na ⁺ ions and K ⁺ ions, it is a polyvalent electrolyte aqueous solution or acidic aqueous solution. In terms of water absorption capacity and water absorption gel strength, it is not yet sufficiently satisfactory. In addition, as a manufacturing problem, this improved product is produced by polymerizing a vinyl monomer having a tertiary amino group [for example, dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate] in the presence of water. In that case, there is also a problem that hydrolysis occurs during the polymerization to prevent the polymerization and the molecular weight is difficult to increase.

[Means for Solving Problems] The inventors of the present invention have a high water-absorbing ability not only for a monovalent electrolyte aqueous solution but also for a polyvalent electrolyte aqueous solution and an acidic aqueous solution, and a water-absorbing material made of a resin having excellent water-absorbing gel strength. As a result of intensive studies to obtain a material, the present invention has been achieved. That is, the present invention is a cationic vinyl monomer having a quaternary ammonium salt group.
(A), an anionic vinyl monomer having a carboxyl group and / or a sulfone group (B), a copolymerizable cross-linking agent (C) and optionally a nonionic water-soluble vinyl monomer (D),
(A) :( B) (molar ratio) = 85: 15 to 15:85, and (C)
(A), (B) and (D) is polymerized with an aqueous solution or aqueous dispersion containing 0.01 to 10% with respect to the total weight,
A water-absorbing material (first invention) characterized by comprising a polymer (1) partially neutralized with an acid group to become an alkali metal base if necessary; and this polymer (1)
A water absorbing material (second invention) comprising a polymer (2) obtained by crosslinking with a compound (E) having at least two groups capable of reacting with the functional group in (1).

In the present invention, the cationic vinyl monomer (A) is a reaction product of a dialkylaminoalkyl (meth) acrylate and an alkyl halide or dialkyl sulfuric acid [eg (meth) acryloyloxyethyltrimethylammonium chloride or bromide, (meth) Acryloyloxyethyltrimethylammonium sulfate, (meth) acryloyloxyethyldimethylethylammonium chloride, (meth) acryloyloxyethyldiethylmethylammonium chloride, (meth) acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloyloxypropyltrimethylammonium chloride, (Meth) acryloyloxypropyltrimethylammonium sulfate, etc.]; dia Reaction product of a kylaminohydroxyalkyl (meth) acrylate with an alkyl halide or dialkylsulfate [eg (meth) acryloyloxyhydroxyethyltrimethylammonium chloride or bromide, (meth) acryloyloxyhydroxyethyltrimethylammonium sulfate, (meth) acryloyloxyhydroxy) Propyltrimethylammonium chloride, etc.]; Reaction product of dialkylaminoalkyl (meth) acrylamide with alkyl halide or dialkylsulfuric acid [eg chloride or bromide of trimethylaminoethyl (meth) acrylamide, chloride of trimethylaminopropyl (meth) acrylamide, Diethylmethylaminopropyl (meth) acrylamide chloride, etc.]; dial Reaction products of ruaminohydroxyalkyl (meth) acrylamides with alkyl halides or dialkylsulfates [eg chloride of trimethylaminohydroxyethyl (meth) acrylamide, chloride of trimethylamidohydroxypropyl (meth) acrylamide, diethylmethylaminohydroxypropyl ( (Meth) acrylamide chloride, etc.]; N-alkylvinylpyridinium halides [eg N-methyl-2-vinylpyridinium chloride or bromide, N-methyl-4-vinylpyridinium chloride, etc.]; Trialkylallylammonium halides [eg trimel Allyl ammonium chloride or bromide, triethyl allyl ammonium chloride, etc.] and the like. These may be used alone or in combination of two or more.

In the present invention, among the vinyl monomers (B) having a carboxyl group and / or a sulfone group, the anionic vinyl monomer having a carboxyl group is an unsaturated mono- or polycarboxylic acid [(meth) acrylic acid (acrylic acid And / or methacrylic acid. The same shall apply hereinafter), crotonic acid, sorbic acid, maleic acid, itaconic acid, cinnamic acid, etc.], and their anhydrides [maleic anhydride, etc.] and the like.

Among the anionic vinyl monomers having a sulfo group among (B), aliphatic or aromatic vinyl sulfonic acids [vinyl sulfonic acid, allyl sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, etc.]; (meth) acrylic Examples thereof include sulfonic acid [sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate]; (meth) acrylamidesulfonic acid [2-acrylamido-2-methylpropanesulfonic acid, etc.].

The vinyl monomer (B) may be used as a water-soluble salt.
These salts include alkali metal salts (salts such as sodium, potassium and lithium), alkaline earth metal salts (salts such as calcium and magnesium), ammonium salts and amine salts (alkylamine salts such as methylamine and trimethylamine). Alkanolamine salts such as triethanolamine and diethanolamine) and two or more of these. Preferred of these are the sodium and potassium salts.

As the anionic vinyl monomer (B), those exemplified above may be used alone or in combination of two or more kinds. Among these, a vinyl monomer having a carboxyl group is preferable.

If necessary, a nonionic water-soluble vinyl monomer (E) can be used in combination with the cationic vinyl monomer (A) and the anionic vinyl monomer (B). Examples of (D) include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, (meth) acrylamide, and vinylpyrrolidone.

In the present invention, as the copolymerizable cross-linking agent (C), (C-1) a compound having at least two polymerizable double bonds; and (C-2) having one polymerizable double bond And a compound having at least one group capable of reacting with the functional group of the cationic vinyl monomer and / or the anionic vinyl monomer. Examples of the compound (C-1) include the following.

Bis (meth) acrylamide: N, N-alkylene (C1
-C6) Bis (meth) acrylamide such as N, N-methylenebisacrylamide.

Di- or polyesters of polyols and unsaturated mono- or polycarboxylic acids: Di- or tri- (meth) acrylic acid of polyols [ethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, etc.] Esters: unsaturated polyesters [obtained by reaction of the above polyols with unsaturated acids such as maleic acid] and di
-Or tri- (meth) acrylic acid ester [obtained by reaction of polyepoxide with (meth) acrylic acid]
Such.

Carbamyl ester: polyisocyanate [tolylene diisocyanate, hexamethylene diisocyanate,
Carbamyl ester obtained by reacting 4,4'-diphenylmethane diisocyanate and an NCO group-containing prepolymer (obtained by the reaction of the above polyisocyanate with an active hydrogen atom-containing compound) and hydroxyethyl (meth) acrylate .

Di or polyvinyl compound: divinylbenzene, divinyltoluene, divinylxylene, divinyl ether,
Divinyl ketone, trivinyl benzene, etc.

Di- or poly- (meth) allyl ethers of polyols: Di- or poly- (meth) allyl ethers of polyols [alkylene glycol, glycerin, polyalkylene glycol, polyalkylene polyols, carbohydrates etc.] such as polyethylene glycol diallyl ether and Allylated starch, allylated cellulose.

Di- or poly-allyl esters of polycarboxylic acids: diallyl phthalate, diallyl adipate and the like.

Esters of unsaturated mono- or polycarboxylic acids with mono (meth) allyl ethers of polyols: (meth) acrylic acid esters of polyethylene glycol monoallyl ether and the like.

Polyallyloxyalkanes: Tetraallyloxyethane and the like.

Examples of the compound (C-2) include an ethylenically unsaturated compound having a group reactive with a carboxyl group, a sulfone group or a quaternary ammonium salt group (hydroxyl group, epoxy group, tertiary amino group, etc.). . Specifically, a hydroxyl group-containing unsaturated compound [N-methylol (meth) acrylamide, etc.]; an epoxy group-containing unsaturated compound [glycidyl (meth) acrylate, etc.]; a tertiary amino group-containing unsaturated compound [(meth) acrylic acid Dimethylaminoethyl, diethylaminoethyl (meth) acrylate, etc.] and the like.

Among the copolymerizable cross-linking agent (C) preferred is (C-1), especially N,
N-methylenebisacrylamide, ethylene glycol diacrylate, trimethylolpropane triacrylate and tetraallyloxyethane.

The molar ratio of the cationic vinyl monomer (A) and the anionic vinyl monomer (B) can be variously changed depending on the conditions such as the solution to be water-absorbed and the required water-absorbing performance.
(A): (B) = 85:15 to 15:85, and considering the water absorption capacity for polyelectrolyte solution and acidic solution, (A): (B) = 70:30 ~
A range of 30:70 is preferred.

Nonionic water-soluble vinyl monomer used together as necessary
The amount of (D) is usually based on the total weight of (A), (B) and (D)
It is 30% or less, preferably 10% or less.

The amount of the copolymerizable cross-linking agent (C) in the present invention is usually 0.01 to 10%, preferably 0.1 to 5%, based on the total weight of (A), (B) and (D) optionally used in combination. Especially, it is 0.6 to 3%. When the content of (C) is less than 0.01%, the obtained resin has a low gel strength when absorbing water and becomes a sol. On the other hand, if it exceeds 10%, on the contrary, the gel strength becomes excessive and the water absorption capacity decreases.

(A), (B), (C) and optionally a method for polymerizing an aqueous solution or an aqueous dispersion containing (D) may be a conventionally known method, for example, polymerization using a radical polymerization catalyst. And a usual method of irradiating with radiation, electron beam, ultraviolet ray and the like.

Examples of the radical polymerization catalyst include azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid, 2,2'-
Azobis (2-amidinopropane) hydrochloride, etc.], inorganic peroxides [hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.], organic peroxides [benzoyl peroxide, di-t-butyl peroxide] , Cumene hydroperoxide, succinic acid peroxide, di (2-ethoxyethyl) peroxydicarbonate, etc.]; redox catalysts [reduction of alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite, ascorbic acid, etc. Agent and an oxidizing agent such as alkali metal persulfate, ammonium persulfate, and peroxide]; and a combination of two or more thereof.

The method of polymerizing using this catalyst is not particularly limited, and for example, the temperature can be variously changed depending on the type of the catalyst used, but is usually 0 to 150 ° C, preferably 5 to 100 ° C. The amount of the catalyst may be the same as usual, and is usually 0.0005 to 5%, preferably 0.001 to 2%, based on the total weight of all the polymerizable vinyl monomers and the copolymerizable crosslinking agent.

The polymerization is carried out in an aqueous solvent or dispersion. Examples of this solvent include water, methanol, ethanol, acetone, N, N-dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, and a mixture of two or more thereof. The preferred solvent is water.

In addition, after dissolving all polymerizable vinyl monomers and copolymerizable cross-linking agent in an aqueous solvent to make an aqueous solution, if necessary, in the presence of a dispersant, in a hydrophobic solvent (eg, hexane, cyclohexane, toluene, chlorobenzene, etc.). A so-called reverse layer suspension polymerization method of dispersing and suspending in and polymerizing is also applicable. The total concentration of all the polymerizable vinyl monomers and the copolymerizable crosslinking agent when using a solvent is not particularly limited, but is usually 10% or more, preferably 15 to 80% by weight. When the concentration is less than 10%, the water absorption capacity of the obtained resin becomes low and the energy cost required for drying the polymer increases, which is uneconomical.

The polymer (1) may be a polymer obtained by the above-mentioned polymerization method, and if necessary, the acid groups in the polymer may be further neutralized (by adding an alkali metal compound) to partially It may be an alkali metal base such as sodium base, potassium base or lithium base.

Examples of the alkali metal compound include alkali metal hydroxides (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.), alkali metal carbonates (sodium carbonate, sodium bicarbonate, etc.), and two or more thereof. Preferred of these are sodium hydroxide, potassium hydroxide and sodium bicarbonate. As a method of neutralizing with an alkali metal compound, a method of adding the water solubility of the alkali metal compound while chopping the gel-like polymer obtained by polymerization into small pieces with a kneader, a universal mixer or the like, and further kneading Can be mentioned.

The degree of neutralization of acid groups in the polymer (1) is 90 mol% or less, preferably 50 to 80 mol%. If the degree of neutralization exceeds 90 mol%, the PH of the obtained resin will be high, which poses a problem in terms of safety for human skin.

The water absorbing material of the present invention comprising the polymer (1) is usually obtained by drying the polymer obtained as described above by a method as described below,
It is composed of the polymer (1) in a pulverized form.

In the present invention, the polymer (2) is obtained by further crosslinking the polymer (1) with a compound (E) having at least two groups capable of reacting with the functional group in the polymer (1). The polymer (2) has a higher gel strength than the polymer (1) and is more stable in the water-absorbing gel.

Examples of the compound (E) include a compound having at least two groups such as an epoxy group, a hydroxyl group and an isocyanate group, and a polyvalent metal compound capable of forming an ionic bridge.

Specific examples of the compound having at least two groups such as epoxy group, hydroxyl group, and isocyanate group are polyepoxy or polyglycidyl ether compounds (ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3-di). Examples thereof include glycidyl ether, polyethylene glycol diglycidyl ether, bisphenol A-epichlorohydrin type epoxy resin), polyols (glycerin, ethylene glycol, propylene glycol, etc.).

Examples of polyvalent metal compounds include alkaline earth metals (calcium, magnesium, etc.), hydroxides, halides, salts (sulfates, carbonates, acetates, etc.) of zinc, aluminum, titanium and the like, specifically Examples include calcium hydroxide, magnesium chloride, zinc diacetate, and aluminum sulfate.

Of these, preferred are polyglycidyl ether compounds and polyvalent metal compounds.

The addition amount of the compound (E) can be variously changed depending on the degree of crosslinking of the polymer (1) by the copolymerizable crosslinking agent (C), the water absorption capacity required for the water absorbing material, and the gel strength. Polymer (2)
The amount is usually 5% or less, preferably 0.001 to 3%, based on the total weight of all the monomers that are the constituent units.

The compound (E) is added to the polymer (1), kneaded, dried and pulverized to obtain a water-absorbent material of the present invention, which is a dried and pulverized product of the polymer (2). Addition / kneading is carried out by adding an aqueous solution, if necessary, and usually using a kneader such as a kneader or a universal mixer.

The drying method is usually a method of drying by heating with hot air having a temperature of 100 to 200 ° C., a thin film drying method by using a drum dryer or the like usually heated to 100 to 200 ° C., a reduced pressure drying method, a freeze drying method, etc. The method is good. Alternatively, a method in which polymerization is performed using a high-concentration aqueous solution and water is evaporated by the generated heat of polymerization to directly pulverize without a drying step can be selected.

The crushing method is also not particularly limited, and a normal crusher such as a hammer crusher, an impact crusher, a roll crusher, or a jet stream crusher can be used.

[Examples] The present invention will be further described with reference to Examples below, but the present invention is not limited thereto. Parts in the examples are parts by weight. The water absorption amount for each solution in the examples was measured by the following operation. That is, put 1 g of the sample in a 250 mesh nylon tea bag, immerse it in a large excess of the test solution for 60 minutes, hang it vertically for 15 minutes to drain the sample, and measure the increased weight of the sample. did. Further, the gel strength was evaluated by touching the water-absorbing gel with fingers and evaluating it in four grades of ⊚, ◯, Δ, and ×.

Example 1 22 parts of methacryloyloxyethyl trimethylammonium chloride, 8 parts of acrylic acid, 0.35 part of trimethylolpropane triacrylate and 70 parts of water were placed in an openable and closable closed container, and the liquid temperature was adjusted to 15 ° C. under a nitrogen atmosphere.
When 1 part of 0.5% ammonium persulfate aqueous solution and 1 part of 0.5% sodium hydrogen sulfite aqueous solution were added and polymerized, a gel was formed with heat generation. Five hours after the initiation of polymerization, the closed container was opened, and the produced gel-like water-containing crosslinked polymer was taken out. The gel was shredded with, dried with a drum dryer heated to 150 ° C., and pulverized to have a particle size of 32 to 145 mesh to obtain the water absorbing material of the present invention. The performance measurement results of this product are shown in Table 1.

Example 2 A gel-like water-containing crosslinked polymer polymerized in the same manner as in Example 1 was shredded with a kneader, and then 50% aqueous sodium hydroxide solution was used.
The mixture was neutralized by adding 6.6 parts. The neutralized product was dried with a drum dryer heated to 150 ° C. and pulverized to a particle size of 32 to 145 mesh to obtain a water absorbing material of the present invention. The performance measurement results of this product are shown in Table 1.

Example 3 To a neutralized product prepared in the same manner as in Example 2, 1.8 parts of a 5% aqueous solution of ethylene glycol diglycidyl ether was further added and kneaded uniformly, and then dried with a drum dryer heated to 150 ° C. Then, it was pulverized to a particle size of 32 to 145 mesh to obtain the water absorbing material of the present invention. The performance measurement results of this product are shown in Table 1.

Example 4 In Example 1, 23.5 parts of methacryloyloxyethylene trimethyl ammonium chloride and acrylic acid
23.5 parts of methacryloyloxyethyl dimemethylbenzyl ammonium chloride and acrylic acid instead of 8 parts
A water absorbent of the present invention was obtained in the same manner as in Example 1 except that 6.5 parts of Sakae was used and the amount of trimethylolpropane triacrylate was 0.24 parts. The performance measurement results of this product are shown in Table 1.

Example 5 In Example 1, 23.5 parts of methacryloyloxyethyl trimethyl ammonium chloride and acrylic acid 8
N-methyl-2-vinylpyridinium chloride instead of 1
A water absorbent of the present invention was obtained in the same manner as in Example 1 except that 3 parts and 17 parts of 2-acrylamido-2-methylpropanesulfonic acid were used. The performance measurement results of this product are shown in Table 1.

Example 6 A gel-like water-containing crosslinked polymer obtained by polymerization in the same manner as in Example 5 was shredded, and 1.8 parts of a 5% aqueous solution of glycerin 1,3-diglycidyl ether was added to homogenize the mixture. After kneading, dry with a drum dryer heated to 150 ℃,
The water absorbing material of the invention was obtained by pulverizing to a particle size of ˜145 mesh.
The performance measurement results of this product are shown in Table 1.

Example 7 In Example 1, 15 parts of methacryloyloxyethyltrimethylammonium chloride and acrylic acid were used, and the same amount of N, N-methyllenbisacrylamide was used instead of the copolymerizable cross-linking agent trimethylolpropane triacrylate. A water absorbent of the present invention was obtained in the same manner as in Example 1 except that it was used. The performance measurement result of this thing
Shown in the table.

Comparative Example 1 A comparative water absorbing material was obtained in the same manner as in Example 3, except that 0.35 part of trimethylolpropane triacrylate, which is a copolymerizable cross-linking agent, was not used. The performance measurement results of this product are also shown in Table 1.

Comparative Example 2 23.5 parts of dimethylaminoethyl methacrylate (a vinyl monomer having a tertiary amino group) and 6.5 parts of acrylic acid were dissolved in 70 parts of water, and about 6 g of 35% hydrochloric acid was added to adjust the pH to 4.
Further, 0.1 part of N, N-methylenebisacrylamide was added and uniformly dissolved. Transfer this aqueous solution to a closed container that can be opened and closed, and set the liquid temperature to 15 ° C under a nitrogen atmosphere. Then, add 1 part of 0.5% ammonium persulfate aqueous solution and 0.5% as an initiator.
When 1 part of an aqueous sodium hydrogen sulfite solution was added and polymerized, a gel was formed with heat generation. 5 from the start of polymerization
After a lapse of time, the closed container was opened, and the produced gel-like water-containing crosslinked polymer was taken out. The gel was shredded, dried with a drum dryer heated to 150 ° C., and pulverized to have a particle size of 32 to 145 mesh to obtain a comparative water absorbent material. The performance measurement results of this product are also shown in Table 1.

Comparative Example 3 A commercially available anionic water-absorbent resin "AQUALIC CA" (crosslinked sodium polyacrylate, manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) was used as a comparative water-absorbing material, and the results of performance comparison are also shown in Table 1.

[Effects of the Invention] The water absorbing material of the present invention has the following effects.

It has a high water absorption capability not only for monovalent electrolyte solutions but also for polyvalent electrolyte solutions. In particular, compared with the conventional anionic water-absorbing material, it has a remarkably high water-absorbing ability for a polyelectrolyte solution containing a large amount of Mg ²⁺ ions, Ca ²⁺ ions, Al ³⁺ ions and the like.

It has a high water absorption capacity even for acidic solutions such as sulfuric acid aqueous solution. This is an improvement of the problem that conventional anionic water-absorbing materials show almost no water-absorbing ability in an acidic solution.

It is a resin with a large molecular weight that has solved the conventional problems.

The water absorbent of the present invention is stable to sunlight and ultraviolet rays even after absorbing water.

The water-absorbent material of the present invention further crosslinked with the compound (E) has further improved gel strength, and also has improved stability of the water-absorbent gel against sunlight and ultraviolet rays and long-term storage stability.

Since the water-absorbing material of the present invention exhibits the above-mentioned effects, the water-absorbing material is used for absorbing urine or blood such as water-absorbing materials, sanitary materials (paper diapers for children and adults, sanitary napkins, incontinence pads, etc.); industrial waste Use as a solidifying agent for water-containing substances that contain high concentrations of electrolytes such as sewage, sewage, and sludge; a water retention agent for plants and soil; a sealing agent for civil engineering and seabed that requires high swelling power against seawater and hard water. It has a wide range of uses such as water-stopping agents for cables; sulfuric acid battery applications that require absorption of high-concentration acid solutions; water-absorbing / water-retaining agents when exposed to sunlight, such as dew condensation prevention building materials and paints. It is possible.

Claims (3)

[Claims] 1. A cationic vinyl monomer (A) having a quaternary ammonium salt group, an anionic vinyl monomer (B) having a carboxyl group and / or a sulfone group, a copolymerizable cross-linking agent (C) and If necessary, the nonionic water-soluble vinyl monomer (D) is added to (A) :( B) (molar ratio) = 85:15 to 15:85.
And the content of (C) in an amount of 0.01 to 10% with respect to the total weight of (A), (B) and (D) is polymerized, and if necessary, an acid group A water-absorbing material, characterized by comprising a polymer (1) which is partially converted to an alkali metal base. 2. A cationic vinyl monomer (A) having a quaternary ammonium salt group is a reaction product of a dialkylaminoalkyl (meth) acrylate and an alkyl halide or dialkylsulfate, a dialkylaminohydroxyalkyl (meth) acrylate and an alkyl. Reaction product of halide or dialkyl sulfuric acid, reaction product of dialkylaminoalkyl (meth) acrylamide with alkyl halide or dialkyl sulfuric acid, reaction product of dialkylaminohydroxyalkyl (meth) acrylamide with alkyl halide or dialkyl sulfuric acid, N-alkyl vinyl The water absorbing material according to claim 1, which is at least one selected from the group consisting of pyridinium halides and trialkylallylammonium halides. 3. A cationic vinyl monomer (A) having a quaternary ammonium salt group, an anionic vinyl monomer (B) having a carboxyl group and / or a sulfone group, a copolymerizable cross-linking agent (C) and If necessary, the nonionic water-soluble vinyl monomer (D) is added to (A) :( B) (molar ratio) = 85:15 to 15:85.
And (C) is contained in an amount of 0.01 to 10% with respect to the total weight of (A), (B) and (D). A polymer (1) which is partially converted to an alkali metal base, and further the polymer (1)
A water-absorbing material comprising a polymer (2) obtained by crosslinking with a compound (E) having at least two groups capable of reacting with the functional groups therein.