JP2574882B2 - Salt resistant water swelling material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a water swelling material useful as a sealing material for filling gaps between various structures and sealing them. More specifically, when in contact with an aqueous liquid containing salts, particularly polyvalent metal ions, it rapidly swells, absorbs a large amount of the aqueous liquid, and the swelling ratio does not decrease over time, and The present invention relates to a salt-resistant water-swelling material useful as a water-stopping material or the like that can completely prevent leaching of the aqueous liquid.

(Prior Art) Conventionally, many techniques have been proposed for preparing a water-swellable composition by dispersing a water-absorbing substance in a thermoplastic resin or rubber and using the composition as a water-stopping material. However, these are all poor in salt tolerance, and when they come into contact with aqueous liquids containing high concentrations of salts, especially polyvalent metal ions, or when they come in contact with aqueous liquids containing new salts continuously for a long time even at low concentrations, There was a drawback that the swelling ratio was reduced and a sufficient water stopping effect could not be exhibited.

The present inventors, as a water swelling material improved the above disadvantages,
It has been proposed that a water-absorbing resin comprising a sulfoalkyl (meth) acrylate-based crosslinked product is dispersed in a base material comprising rubber and / or a thermoplastic resin (Japanese Patent Laid-Open No. 61-31450).
issue). It has also been proposed to disperse a nonionic water-absorbing resin such as polyethylene oxide in a substrate.
However, this salt-resistant water swelling material does not have a sufficient swelling speed when it comes into contact with an aqueous liquid, and in particular, when the amount of the water-absorbing resin added is small in order to obtain a water swelling material having a low swelling ratio, the water swelling speed becomes low. There is a problem that it is small and cannot withstand practical use. In addition, if the amount of the water-absorbing resin is increased to increase the water swelling rate to a practically preferable level, it becomes difficult to disperse the lipophilic thermoplastic resin or rubber, and as a water-stopping material, a long-term contact with the aqueous liquid occurs. There is also a problem that durability is impaired such as insufficient water stopping effect and strength.

On the other hand, as a water-absorbing material having an improved water swelling rate, a method has been proposed in which a water-absorbent resin and water-swellable urethane are kneaded with rubber or a soft resin (Japanese Patent Application Laid-Open No. 59-120563). However, the water-absorbing resin and the water-swellable urethane compounded in this water-absorbing material both have poor affinity with rubber or soft resin, so the above-mentioned durability problem still remains. Since water-swellable urethane gradually elutes from the water-absorbing material into the aqueous liquid after water-swelling, there is also a problem that the water-swelling ratio decreases with time.

(Problems to be Solved by the Invention) The present inventors have improved the above-mentioned problems, and have a salt-resistant water-swelling material which has a high swelling speed when in contact with an aqueous liquid and has excellent durability as a water-stopping material. As a result of intensive studies for the purpose of obtaining the present invention, the present invention has been completed.

(Means and Actions for Solving the Problems) The present invention relates to a base material (I) made of rubber and / or a thermoplastic resin, which has a general formula (However, R ¹ is a hydrogen or methyl group, R ² is a C 2-4
X represents NH or O, and Y represents hydrogen, an alkali metal, an alkaline earth metal, an ammonium group or a substituted ammonium group. A) a sulfonic acid group-containing unsaturated monomer represented by the formula (A):
5 to 80 parts by weight of a water-absorbent resin (II) obtained by polymerizing a monomer component comprising 100% by weight and 0 to 90% by weight of another water-soluble monomer (B) in the presence of a crosslinking agent; General formula (However, R ³ represents an alkylene group having 3 to ⁴ carbon atoms, R ⁴ represents a hydrocarbon group having 1 to 8 carbon atoms and 1 to 5 valent, and n represents 2 to 2000
And m is an integer of 1 to 5. The urethane prepolymer (II) obtained by reacting a non-water-miscible polyether represented by
I) It is to provide a salt-resistant water swelling material obtained by mixing and dispersing 1 to 50 parts by weight.

The sulfonic acid group-containing unsaturated monomer (A) used in the present invention is represented by the above general formula, for example, 2-acrylamido-2-methylpropanesulfonic acid,
2-sulfoethyl (meth) acrylate, 3-sulfopropyl (meth) acrylate, 1-sulfopropane-2
-Yl (meth) acrylate, 2-sulfopropyl (meth) acrylate, 1-sulfobutan-2-yl (meth) acrylate, 2-sulfobutyl (meth) acrylate, 3-sulfobutan-2-yl (meth) acrylate, etc. Examples thereof include saturated sulfonic acids and their alkali metal salts, alkaline earth metal salts, ammonium salts and substituted ammonium salts, and one or more of these can be used.

The water-absorbing resin (II) used in the present invention may be a polymer obtained by polymerizing the sulfonic acid group-containing unsaturated monomer (A) alone, but may be used in combination with another water-soluble monomer (B). Polymerized materials may be used. Other water-soluble monomers (B) include, for example, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and alkali metal salts and alkaline earths thereof. Carboxyl group-containing unsaturated monomers such as metal salts, ammonium salts or substituted ammonium salts; water-soluble (meth) acrylates such as hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polyethylene glycol monomethyl ether mono (meth) acrylate; ) Acrylate; or (meth) acrylamide, and one or more of these can be used.

The ratio of the monomer (B) used is preferably the monomer (A)
The proportion is at most 90% by weight, more preferably at most 60% by weight, based on the total amount of the monomer and the monomer (B). If the amount of the monomer (B) is more than 90% by weight, the resulting water-absorbent resin (II) may have a reduced salt resistance. Further, even when the monomer is a water-insoluble monomer, the monomer (A)
If it can be copolymerized with water, the resulting water-absorbent resin (I
It can be used in a range that does not significantly reduce the water absorption of I). Use of a water-insoluble monomer in combination may be preferable in terms of increasing the affinity of the resulting water-absorbent resin (II) with the substrate (I).

In the present invention, the water-absorbent resin (II) is obtained by polymerizing the monomer component in the presence of a cross-linking agent. The cross-linking agent controls the cross-link density at the time of polymerizing the monomer component. This is essential to obtain a super absorbent polymer (II). Even in the polymerization in the absence of a crosslinking agent, the monomer component partially self-crosslinks, but does not become a highly water-absorbent resin (II) to such an extent that it can be generally used as a water-absorbent resin. By appropriately selecting and using the type and amount of the crosslinking agent, a water-absorbent resin (II) having excellent salt resistance can be obtained.

Examples of the crosslinking agent in the present invention include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, and polyethylene glycol di (meth) acrylate.
In one molecule of acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, N, N-methylenebisacrylamide, triallyl isocyanurate, trimethylolpropane diallyl ether, etc. Having two or more ethylenically unsaturated groups; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, triethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbit, Polyhydric alcohols such as sorbitan, glucose, mannitol, mannitan, sucrose, glucose, etc .; ethylene glycol Diglycidyl ether, glycerin diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether,
Examples thereof include polyepoxy compounds such as trimethylolpropane triglycidyl ether and glycerin triglycidyl ether, and one or more of these can be used. When a polyhydric alcohol is used as a cross-linking agent, it is preferable to carry out heat treatment after polymerization at 150 ° C. to 250 ° C., and when using a polyepoxy compound at 50 ° C. to 250 ° C. The amount of the cross-linking agent to be used is preferably in the range of 0.00001 to 0.1 in molar ratio with respect to the monomer component.

If the amount is less than 0.00001, the cross-linking density of the obtained water-absorbent resin may be low, and only a water-swellable material having a large amount of water-soluble components and poor durability may be finally obtained. Also, 0.1
If the amount exceeds the above range, the resulting water-absorbent resin may have too high a cross-linking density, so that only a water-swelling material having a small water-swelling ratio may be finally obtained.

The polymerization method for obtaining the water-absorbent resin (II) in the present invention may be any conventionally known method, including a method using a radical polymerization catalyst, a method of irradiating radiation, an electron beam, an ultraviolet ray, and the like. . Radical polymerization catalysts include peroxides such as hydrogen peroxide, benzoyl peroxide and cumene hydroperoxide, azo compounds such as azobisisobutyronitrile, and radical generation such as persulfates such as ammonium persulfate and potassium persulfate. And redox initiators obtained by combining these with reducing agents such as sodium bisulfite, L-ascorbic acid and ferrous salts. As the polymerization solvent, for example, water, methanol, ethanol, acetone, dimethylformamide, dimethylsulfoxide and the like, and a mixture thereof can be used. The temperature at the time of polymerization varies depending on the type of catalyst used.
Is preferred because of its high molecular weight. However, in order to complete the polymerization, the temperature is preferably in the range of 20 ° C. or more and 100 ° C. or less. As described above, since the crosslinking density of the water-absorbent resin (II) obtained by using the crosslinking agent can be freely controlled,
The concentration of the monomer component of the polymerization system is not particularly limited, but in consideration of the ease of control of the polymerization reaction and the yield / economical efficiency, the concentration is 20 to
Preferably it is in the range of 80% by weight. Although various forms can be adopted as the polymerization form, there is a method in which a hydrogel polymer is subdivided by shearing force of a reversed-phase suspension polymerization, a casting polymerization, and a double-arm kneader (Japanese Patent Application Laid-Open No. 57-34101). Is preferred.

The water-absorbent resin (II) obtained by the above method is a base material (I)
It is preferable to dry and pulverize the powder before dispersing it. The average particle size of the pulverized product is preferably 100 μm or less, particularly preferably 30 μm or less.

Urethane prepolymer (III) used in the present invention
Is obtained by reacting a non-water-miscible polyether with a polyisocyanate, and the isocyanate group content is preferably in the range of 0.01 to 5 mg equivalent / g. 0.0
If it is less than 1 mg equivalent / g, it is difficult to obtain a water-swelling material having excellent durability, and if it exceeds 5 mg equivalent / g, the workability during mixing and dispersion with the substrate may be poor.

The polyether used as a raw material of the urethane prepolymer (III) must be non-water miscible so that it does not become transparent when completely mixed with water at a temperature of 25 ° C. With a hydrophilic urethane prepolymer obtained using a polyether having miscibility with water, a water swelling material having excellent durability cannot be obtained.

Accordingly, the polyether used in the present invention is represented by the above general formula and has non-water miscibility. Examples thereof include polypropylene glycol, polytetramethylene ether glycol, and polybutylene glycol. One or two or more can be used. Further, as long as it has non-water miscibility, a polyether obtained by copolymerizing ethylene oxide such as an ethylene oxide / propylene oxide copolymer can also be used, but in such an ethylene oxide copolymer, The content of the ethylene oxide component is generally not more than 10% by weight.

The polyisocyanate used as another raw material of the urethane prepolymer (III) is not particularly limited, and examples thereof include tolylene diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate. One or more of these are used. be able to.

The average molecular weight of the urethane prepolymer (III) is 300 to 10
Preferably it is in the range of 0,000. If it is less than 300, the swelling speed and durability of the resulting water-swellable material may not be sufficiently improved, and if it exceeds 100,000, the workability during mixing and dispersion with the substrate (I) may be poor.

The number of isocyanate groups in the urethane prepolymer (III) is preferably 1 to 5 particularly preferably 2 to 3 in one molecule, and the isocyanate group content is as described above.
Those in the range of 0.01 to 5 mg equivalent / g are preferred. In the case of a urethane prepolymer having an isocyanate group content exceeding 5 mg equivalent / g, the prepolymers react with each other and tend to gel, which makes it difficult to mix and disperse them in a base material or a water absorbent resin.

In the present invention, the base material (I) into which the water absorbent resin (II) and the urethane prepolymer (III) are mixed and dispersed can be appropriately selected from various thermoplastic resins and / or rubbers.

Examples of the thermoplastic resin used in the present invention include ethylene-vinyl acetate copolymer, saponified ethylene-vinyl acetate copolymer, ethylene-isobutylene copolymer, ethylene-acrylate copolymer, and vinyl chloride polymer. Coalescing, polyurethane, polyethylene, polypropylene,
Examples include polystyrene, ABS resin, polyamide, and polyvinyl acetate.

As the rubber, for example, ethylene-propylene rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, chloroprene rubber, fluorine rubber, silicon rubber, urethane rubber, polysulfide rubber, acrylic rubber Butyl rubber, epichlorohydrin rubber, natural rubber and the like.

The salt-resistant water-swelling material of the present invention comprises a water-absorbent resin (II) and a urethane prepolymer (III) which are made of a thermoplastic resin and / or
Alternatively, it can be obtained by uniformly mixing and dispersing the rubber base material (I) by a mechanical method. The dispersion method is not particularly limited. For example, a method of kneading the water-absorbent resin (II), the urethane prepolymer (III) and the base material (I) with a commonly used mixing device such as a roll or a Banbury mixer, a base material ( Water-absorbent resin (II) and urethane prepolymer (II)
A method of performing a polymerization or curing reaction after dispersing I) can be mentioned.

The mixing ratio of the water-absorbent resin (II) to the base material (I) in the salt-resistant water-swellable material of the present invention varies depending on the type of the base material (I) used and the method of dispersing the water-absorbent resin (II). However, the ratio is generally 5 to 80 parts by weight of the water absorbent resin (II) based on 100 parts by weight of the base material (I). If the amount of the water-absorbent resin (II) is less than 5 parts by weight, the resulting water-swelling material cannot exhibit a sufficient swelling ratio when in contact with an aqueous liquid. On the other hand, if the amount exceeds 80 parts by weight, the strength and durability of the obtained water swelling material become insufficient, and the effect of improving the swelling speed using the urethane prepolymer (III) becomes insignificant.

The mixing ratio of the urethane prepolymer (III) to the base material (I) in the salt-resistant water-swellable material of the present invention differs depending on the type of the base material (I) and the type of the urethane prepolymer (III) used. However, in general, the urethane prepolymer (III) is used for 100 parts by weight of the base material (I).
It is a ratio of 1 to 50 parts by weight. Urethane prepolymer (II
When the amount of I) is less than 1 part by weight, the obtained water swelling material does not show a sufficient water swelling speed when it comes into contact with an aqueous liquid, and the water swelling material containing a large amount of water absorbent resin (II) The durability becomes insufficient. Conversely, if it exceeds 50 parts by weight, not only is it difficult to obtain a water-swelling material having a large swelling ratio, but also the durability may be deteriorated.

The water swelling material of the present invention includes fillers such as carbon black, calcium silicate, calcium carbonate, zinc oxide, white carbon, and clay; modifiers such as rosin, petroleum resin, coumarone resin, and phenol resin; Vulcanizing agents such as sulfurized rubber; vulcanization accelerators such as 2-mercaptobenzothiazole and dibenzothiazyl disulfide; stabilizers; anti-aging agents; pigments; processing aids; In addition, water-absorbing resins other than the water-absorbing resin (II) may be added in a range not impairing the performance of a water-swelling material capable of obtaining a crosslinked product of sodium polyacrylate or polyethylene oxide. A hydrophilic polyalkylene polyether such as an ethylene oxide / propylene oxide copolymer may be added.
Further, the water-swelling material of the present invention may be formed into a desired shape by various molding methods such as press molding.

(Effect of the Invention) The salt-resistant water swelling material of the present invention swells large and quickly even when it comes into contact with an aqueous liquid containing a high concentration of salt, and even when it comes into contact with an aqueous liquid containing a polyvalent metal ion, Since the decrease in the swelling ratio is small, it can be used to prevent water retention or passage of an aqueous liquid containing salt, particularly seawater.

In addition, the salt-resistant water-swelling material of the present invention can easily disperse a water-absorbing resin in a substrate at the time of its production, and thus has practically sufficient strength and durability, for example, for civil engineering and construction. It can be effectively used as a waterproof material, a seal material between tunnel construction segments, a seal material for connecting fume pipes, a water retention bed for agricultural and horticultural use, a medical sanitary material, and the like.

(Examples) Hereinafter, the present invention will be described in detail with reference to examples, but the scope of the present invention is not limited only to these examples.

Reference Example 1 172.8 g (0.80 mol) of 2-sulfoethyl methacrylate sodium salt was placed in a 500-ml cylindrical separable flask.
3.6 g (0.05 mol) of acrylic acid, sodium acrylate 1
4.1 g (0.15 mol), N, N-methylenebisacrylamide
0.308 g (0.002 mol) and 260 g of water were charged, stirred and uniformly dissolved to prepare an aqueous monomer solution. After purging with nitrogen, the mixture was heated to 40 ° C. in a water bath, 1.0 g of a 10% aqueous ammonium persulfate solution and 0.5 g of a 1% aqueous L-ascorbic acid solution were added, and stirring was stopped to carry out polymerization. It generates heat after the start of polymerization,
After one minute, the temperature rose to 68 ° C. After confirming that the temperature of the polymerization system had begun to decrease, the temperature of the hot water bath was raised to 90 ° C., and the system was further heated for 1 hour. The resulting water-absorbent resin hydrogel was finely divided, dried in a hot air dryer at 150 ° C. for 5 hours, and pulverized to obtain a water-absorbent resin (1) having an average particle diameter of 20 μm.

Reference Example 2 220 ml of n-hexane was charged into a 1000 ml four-necked flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen gas inlet tube, and 1.8 g of sorbitan monostearate was added and dissolved, followed by replacement with nitrogen. 218 g of sodium 2-acrylamido-2-methylpropanesulfonate (0.
95 mol), 115 g (0.05 mol) of ethoxy polyethylene glycol monoacrylate (containing an average of 50 ethylene oxide units per molecule), 0.348 g (0.002 mol) of ethylene glycol diglycidyl ether, 368 g of water and 0.05 g of potassium persulfate Was added and dissolved, and nitrogen gas was blown in to remove oxygen present in the aqueous solution. Next, the contents of the dropping funnel were added to the four-necked flask and dispersed, and the polymerization reaction was continued for 3 hours while maintaining the temperature of the polymerization system at 60 to 65 ° C. with a hot water bath while slightly introducing nitrogen gas. . Thereafter, n-hexane was distilled off under reduced pressure, and the remaining hydrogel of the crosslinked polymer was dried under reduced pressure at 90 ° C.
25 μm of the water absorbent resin (2) was obtained.

Reference Example 3 21.6 g (0.10 mol) of sodium salt of 2-sulfoethyl methacrylate as an aqueous monomer solution, 25.8 g of methacrylic acid
(0.30 mol), sodium methacrylate 21.6 g (0.20 mol), acrylamide 28.4 g (0.40 mol), N, N-methylenebisacrylamide 0.154 g (0.001 mol) and water 150
A water-absorbent resin (3) having an average particle diameter of 10 µm was obtained in the same manner as in Reference Example 1 except that the resin consisting of g was used.

Reference Example 4 300 g of polypropylene glycol (average molecular weight 3000) obtained by ring-opening addition of propylene oxide to glycerin was used.
After charging into a 500 ml four-necked flask, 52.2 g of tolylene diisocyanate was added, uniformly stirred, and heated to 60 ° C. After maintaining at the same temperature for 24 hours under stirring, the mixture was cooled and taken out to obtain a urethane prepolymer (1). In addition, the content of the isocyanate group in this urethane polymer (1) is
It was 0.835 mg equivalent / g, and when 50 g of the used polypropylene glycol was mixed with 50 g of water, a transparent mixture was not obtained.

Reference Example 5 Polytetramethylene ether glycol (average molecular weight) was used instead of polypropylene glycol in Reference Example 4.
2000) A urethane prepolymer (2) having an isocyanate group content of 0.826 mg equivalent / g was obtained in the same manner as in Reference Example 4 except that 300 g was used. When 50 g of the used polytetramethylene ether glycol was mixed with 50 g of water, a transparent mixture was not obtained.

Comparative Reference Example 1 Same as Reference Example 4 except that an ethylene oxide / propylene oxide copolymer (average molecular weight 3000) obtained by ring-opening addition of ethylene oxide and propylene oxide to glycerin was used instead of polypropylene glycol in Reference Example 4. And the isocyanate group content
0.821 mg equivalent / g of the comparative urethane prepolymer (1) was obtained. When 50 g of the ethylene oxide / propylene oxide copolymer used was mixed with 50 g of water, a transparent mixture was formed.

Comparative Reference Example 2 18.0 g of acrylic acid in a 500 ml cylindrical separable flask
(0.25 mol), sodium acrylate 70.5 g (0.75 mol), N, N-methylenebisacrylamide 0.154 g (0.001 mol)
Mol) and 121 g of water, 1.0 g of a 10% by weight aqueous solution of ammonium persulfate and 0.1% of a 1% by weight aqueous solution of L-ascorbic acid.
Using 5 g, polymerization, drying and pulverization were performed in the same manner as in Reference Example 1 to obtain a comparative water-absorbent resin (1) having an average particle size of 20 μm.

Example 1 100 g of chloroprene rubber, 30 g of the water absorbent resin (1) obtained in Reference Example 1, 7 g of the urethane prepolymer (1) obtained in Reference Example 4, polyethylene glycol (average molecular weight: 100
0) 3 g, kaolin clay (Tsuchiya Kaolin) 50 g, zinc white (No. 1) 5 g, magnesium oxide 4 g, stearic acid 3 g and 2-mercaptoimidazoline 0.5 g were kneaded with a roll for 15 minutes, and then pressed at 160 ° C. for 30 minutes. It was vulcanized to obtain a salt-resistant water-swelling material (1) of the present invention formed into a sheet having a thickness of 1 mm. The change over time in the water swelling ratio when this water swelling material (1) was immersed in a 0.05% by weight aqueous solution of calcium chloride was measured. The results are shown in Table 1.

Example 2 In Example 1, 20 g of the water-absorbent resin (2) obtained in Reference Example 2 was used instead of the water-absorbent resin (1), and the urethane obtained in Reference Example 5 was used instead of the urethane prepolymer (1). Example 1 except that 20 g of prepolymer (2) was used.
In the same manner as in the above, a salt-resistant water-swelling material (2) of the present invention was obtained.
Table 1 shows the measurement results of the water swelling ratio of the water swelling material (2).

Example 3 In Example 1, except that 60 g of the water-absorbent resin (3) obtained in Reference Example 3 was used instead of the water-absorbent resin (1), and the amount of the urethane prepolymer (1) used was changed to 2.5 g. In the same manner as in Example 1, a salt-resistant water-swelling material (3) of the present invention was obtained. The measurement result of the water swelling ratio of this water swelling material (3)
It is shown in the table.

Comparative Example 1 A comparative water swelling material (1) was obtained in the same manner as in Example 1 except that the urethane prepolymer (1) was not used. Table 1 shows the measurement results of the water swelling ratio of this comparative water swelling material (1).

Comparative Example 2 Comparative water swelling was performed in the same manner as in Example 1 except that 30 g of the comparative water absorbent resin (1) obtained in Comparative Reference Example 2 was used instead of the water absorbent resin (1). Lumber (2)
I got Table 1 shows the measurement results of the water swelling ratio of this comparative water swelling material (2).

Comparative Example 3 Comparative water swelling was performed in the same manner as in Example 2 except that 20 g of the comparative urethane prepolymer (1) obtained in Comparative Reference Example 1 was used instead of the urethane prepolymer (2). Material (3) was obtained. Table 1 shows the measurement results of the water swelling ratio of this comparative water swelling material (3).

 ──────────────────────────────────────────────────続 き Continuation of the front page Examiner Miyako Kaneo (56) References JP-A-2-15553 (JP, A)

Claims (1)

(57) [Claims] (1) 100 parts by weight of a base material (I) comprising a rubber and / or a thermoplastic resin, (However, R ¹ is a hydrogen or methyl group, R ² is a C 2-4
X represents NH or O, and Y represents hydrogen, an alkali metal, an alkaline earth metal, an ammonium group or a substituted ammonium group. A) a sulfonic acid group-containing unsaturated monomer represented by the formula (A):
5 to 80 parts by weight of a water-absorbent resin (II) obtained by polymerizing a monomer component comprising 100% by weight and 0 to 90% by weight of another water-soluble monomer (B) in the presence of a crosslinking agent; General formula (However, R ³ represents an alkylene group having 3 to ⁴ carbon atoms, R ⁴ represents a hydrocarbon group having 1 to 8 carbon atoms and 1 to 5 valent, and n represents 2 to 2000
And m is an integer of 1 to 5. The urethane prepolymer (II) obtained by reacting a non-water-miscible polyether represented by
I) A salt-resistant water-swelling material obtained by mixing and dispersing 1 to 50 parts by weight.