JPH04227705A - Production of salt-resistant water absorbing resin - Google Patents

Abstract

PURPOSE:To inexpensively produce a water absorbing resin having high gel strength, small change of absorption magnification with salt concentration of aqueous solution to be absorbed and excellent salt resistance. CONSTITUTION:The objectives can be attained by production of a salt-resistant water absorbing resin wherein an aqueous solution of at least one monomer component (A) selected from a group consisting of an unsaturated carboxylic acid and a salt thereof is subjected to aqueous solution polymerization in the presence of 1-30 pts.wt. water absorbing resin (B) based on 100 pts.wt. of the monomer component.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a salt-resistant water-absorbing resin. More specifically, the present invention relates to a method for producing a water-absorbing resin that has high gel strength and improved salt resistance.

0002

BACKGROUND OF THE INVENTION Water-absorbing resins have been used in various water-absorbing materials such as diapers, sanitary products, soil water retention agents, and sealants.

[0003] Such water-absorbing resins are roughly divided into those having electrolyte structures such as carboxyl groups and those having nonionic hydrophilic segments.The former include, for example, crosslinked acrylic acid (salt) polymers. (Unexamined Japanese Patent Publication No. 55-8
4,304, etc.), hydrolysates of starch-acrylonitrile graft copolymers (Japanese Patent Publication No. 49-43,395), neutralized products of starch-acrylic acid graft copolymers (Japanese Patent Publication No. 53-46, etc.) , No. 199), saponified product of acrylic acid ester-vinyl acetate copolymer (Japanese Patent Publication No. 53-1
3,495), but the latter include cross-linked polyvinyl alcohol modified products (JP-A-54-20093) and polyethylene oxide partially cross-linked products (JP-A-61-130).
, No. 324), etc. are known.

[0004] Water-absorbent resins are widely used in industrial fields for the purpose of absorbing various aqueous solutions due to their characteristics, but the absorption capacity varies greatly depending on the type of liquid to be absorbed. For example, when used in diapers, The absorption capacity changes due to changes in the salt concentration in urine, leading to quality fluctuations, and the swelling volume changes depending on the salt concentration, which limits its use in the fields of agriculture, horticulture, and water-stopping agents. There was a case.

For example, the former water-absorbing resin having an electrolyte structure such as a carboxyl group generally has a high gel strength and exhibits a very high absorption capacity in pure water (deionized water), etc. When used as a solution, there is a problem that the absorption capacity is significantly lowered and so-called salt tolerance is low.

The latter water-absorbent resin having a nonionic hydrophilic segment has a small decrease in absorption capacity for electrolyte solutions and is excellent in terms of salt resistance, but its gel strength is weak, its water absorption rate is slow, and its absolute absorption capacity is low. The value is also low.

[0007] In addition, as a resin with excellent salt resistance, a water-absorbing resin (Japanese Patent Laid-Open No. 6-117) into which a sulfonic acid group, which is a strong electric modification, has been introduced is also used.
Publication No. 1-36,309, JP-A-56-161,412
Although it is known that it exhibits excellent salt resistance against liquids containing multivalent ions, it exhibits excellent salt resistance against liquids containing monovalent ions, similar to acrylate crosslinked products. It has poor salt tolerance. Moreover, since a monomer having a sulfonic acid group is used as a raw material, it is expensive.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for producing a salt-resistant water-absorbing resin.

Another object of the present invention is to provide a gel with high gel strength;
Another object of the present invention is to provide a method for inexpensively producing a water-absorbing resin with excellent salt resistance and a small change in absorption capacity depending on the salt concentration of an aqueous solution to be absorbed.

0010

[Means for Solving the Problems] The above objects are achieved by preparing an aqueous solution of at least one monomer component (A) selected from the group consisting of unsaturated carboxylic acids and salts thereof.
A) This is achieved by a method for producing a salt-resistant water-absorbing resin, which comprises polymerizing the water-absorbing resin (B) in an aqueous solution in an amount of 1 to 30 parts by weight per 100 parts by weight.

[0011]

[Function] The salt-resistant water-absorbing resin obtained by the production method of the present invention is extremely excellent in both salt resistance and gel strength. In addition, in the present invention, a resin having a specific particle size range contained in the obtained salt-resistant water-absorbing resin is further added to the water-absorbing resin (B).
For example, when a resin with a fine particle size range is used as the water-absorbing resin (B), the resulting product has a significantly reduced amount of fine powder of, for example, 149 μm or less, and has improved absorption properties and economy. Not only does it have excellent properties, but there is no fear of fine powder scattering when it is processed into various absorbent products such as disposable diapers and sanitary cotton.
It also has the advantage of eliminating problems in terms of occupational health. Therefore, the salt-resistant water-absorbent resin obtained by the present invention can be used in diapers, sanitary products, etc. by taking advantage of its properties.
It can be effectively used for agricultural and horticultural purposes, as a sealant, as a lubricant for propulsion methods, to prevent slippage of mud in ground excavation, as a fixing agent for muddy water, as a carpet underlay, as a coating for agriculture, etc.

Examples of the unsaturated carboxylic acids used in the present invention include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, etc., and salts of unsaturated carboxylic acids include these. Alkali metal salts, ammonium salts, substituted ammonium salts, and the like can be mentioned, and one or more of these can be used.

However, in order to obtain a water-absorbing resin with excellent salt resistance, it is preferable to use acrylic acid and/or acrylate as an essential component as the unsaturated carboxylic acid and/or its salt. In particular acrylic acid 10-70 mol%, preferably 20-40 mol% and acrylate salt 9
Preferably, the content is 0 to 30 mol%, preferably 80 to 60 mol%.

The monomer component (A) may contain other unsaturated monomers in addition to the unsaturated carboxylic acid and/or its salt.

Examples of other unsaturated monomers include 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, sulfoethyl (meth)acrylate, and sulfopropyl (meth)acrylate. ) Unsaturated sulfonic acids and their salts such as acrylate and vinyltoluenesulfonic acid; Unsaturated amine compounds and their salts such as N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate ;Hydroxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxypolyethylene glycol mono(meth)acrylate, methoxypolypropylene glycol (Meth)acrylic acid esters such as mono(meth)acrylate, methyl (meth)acrylate, and ethyl (meth)acrylate; (meth)acrylamide, N-hexyl (meth)acrylamide, N-
Methylol (meth)acrylamide, N,N dimethyl (
Unsaturated amides such as meth)acrylamide; styrene, α
- Styrene or its derivatives such as methylstyrene, o-methylstyrene, p-methylstyrene; (meth)acrylonitrile, vinyl acetate, etc., and one or more of these may be used as the monomer component (A ), preferably less than 40% by weight.

The water-absorbing resin (B) used in the present invention is not particularly limited as long as it is a water-insoluble resin that can absorb water and become a water-containing gel, such as crosslinked carboxymethylcellulose, modified crosslinked polyvinyl alcohol, and crosslinked isobutylene. Maleic anhydride copolymer, saponified crosslinked acrylic acid ester-vinyl acetate copolymer, partially crosslinked polyethylene oxide, hydrolyzate of starch-acrylonitrile graft copolymer, crosslinked starch-acrylic acid graft copolymer neutralized products, crosslinked products of partially neutralized (meth)acrylic acid polymers, and the like.

Preferably, a crosslinked product of partially neutralized (meth)acrylic acid polymer is used, for example, JP-A-56-93,716, JP-A-56-131,608, JP-A-56
-147,806, JP 58-71907, JP 58-117,222, JP 54-
30,710, Japanese Patent Publication No. 54-37,994, Japanese Patent Publication No. 53-46,200, U.S. Patent No. 4,0
The water absorption capacity disclosed in Publication No. 41,228 is 100~
Any 1000 times more water-absorbent resin can be preferably used as the water-absorbent resin (B) of the present invention. Among them, in order to obtain an excellent salt-resistant water-absorbent resin by uniformly absorbing monomer components and swelling, and efficiently creating an IPN structure and grafting, the water-absorbent resin (B) has a water content of 0. .1-10
% by weight in powder form is preferred. In addition, the monomer component (
In order to cause the water absorption of A) to occur promptly, 90 to 100% by weight of the water absorbent resin (B) has a diameter of 1 to 149 μm,
In particular, it is preferable to have a particle size of 1 to 74 μm.

The original monomer components (A) constituting the water absorbent resin (B) may be the same or different;
The physical properties of the water-absorbing resin finally obtained and as described later,
Considering the case where the operation of the present invention is repeated, it is preferable that the composition be the same. Further, the polymerization method for obtaining the water-absorbent resin (B) may be aqueous solution polymerization or other polymerization method, but considering the case where the operation of the present invention is repeated, aqueous solution polymerization is preferred. It is preferable. Further, the unsaturated carboxylic acid polymer has a carboxyl group of 0.3 to 0.9 equivalent, preferably 0.6 to 0.8 equivalent.
It may be equivalently neutralized. As such a water-absorbing resin (B), a water-absorbing resin obtained by a normal manufacturing method, or a water-absorbing resin with a specific particle size range selected as necessary may be used. Alternatively, the water-absorbing resin (B) contained in the salt-resistant water-absorbing resin obtained by drying and classifying the aqueous solution polymerization of the production method of the present invention. The resin (C) having the same particle size range may be removed and used repeatedly as the water absorbent resin (B). Also,
The water absorbent resin (B) may be treated to increase the crosslinking density of the surface portion of the particles.

The amount of water-absorbing resin (B) to be used is preferably 1 to 30 parts by weight per 100 parts by weight of monomer component (A) in order to efficiently obtain a water-absorbing resin with particularly excellent salt resistance. is 5 to 20 parts by weight. If this amount exceeds 30 parts by weight, the water-absorbing resin (B) cannot be uniformly dispersed and swollen in the monomer component (A), and the resin precipitates, resulting in a desired high absorption capacity. A salt-resistant water-absorbing resin cannot be obtained. Also,
If it is less than 1 part by weight, the salt tolerance intended by the present invention will not be achieved. In addition, the monomer component (A) of the water absorbent resin (B)
) is generally added before the start of polymerization of monomer component (A), but if the system still maintains fluidity after the start of polymerization, it may be added at this time. A water-absorbing resin (B) can also be added thereto.

According to the production method of the present invention, even if the monomer component (A) is polymerized in an aqueous solution in the presence of the water-absorbing resin (B) without using a crosslinking agent, the monomer component (A) It is presumed that a salt-resistant water-absorbing resin can be obtained because it is polymerized while taking a graft or IPN structure on the absorbent resin (B), but in addition, a water-absorbing resin with better gel strength can be obtained. Therefore, it is preferable to allocate a crosslinking agent to the monomer component (A) during polymerization.

Examples of crosslinking agents that can be used 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, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(
meth)acrylate, N,N'-methylenebis(meth)
Compounds having two or more ethylenically unsaturated groups in one molecule such as acrylamide, triallyl isocyanurate, trimethylolpropane di(meth)allyl ether; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, Polyhydric alcohols such as propylene glycol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbitol, sorbitan, glucose, mannitol, mannitan, sucrose, glucose; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, Polyglycidyl ethers such as glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; polyaldehydes such as glutaraldehyde and glyoxal; polyamines such as ethylenediamine; calcium hydroxide, calcium chloride, calcium carbonate, and oxidized Hydroxides, halides, carbonates, oxides of metals in Groups 2A, 3B, and 8 of the Periodic Table such as calcium, magnesium chloride, magnesium oxide, aluminum chloride, zinc chloride, and nickel chloride, boric acid such as borax, etc. salts, polyvalent metal compounds such as aluminum isopropylate, etc., and one or more of these can be selected and used as appropriate after considering the reactivity. Most preferably, a compound having two or more groups is used as a crosslinking agent.

[0022] These crosslinking agents are used in a proportion of 0.001 to 0.001 to the monomer component (A) in order to exhibit the necessary and sufficient effect.
More preferably, it is used in an amount of 0.1 mol%, particularly preferably 0.01 to 0.05 mol%. If it exceeds 0.1 mol %, the absorption capacity itself may decrease, so care must be taken.

In the present invention, it is essential to use water-soluble polymerization as the polymerization method. In other polymerization methods, such as reverse-phase suspension polymerization, spray polymerization, and precipitation polymerization, the water-absorbing resin (B) cannot be stably dispersed and uniformly present in the monomer component (A). The desired salt tolerance effect cannot be obtained.

[0024] Furthermore, the aqueous solution polymerization is preferably carried out under stirring and mixing in order to uniformly disperse the water-absorbing resin (B) in the monomer component (A) and to carry out the grafting reaction efficiently. For this purpose, it is more preferable to carry out the polymerization in a reaction vessel having a rotating stirring shaft while fragmenting the gel-like material produced during polymerization by the shearing force of the rotating stirring shaft. No. 101, US-A-4,
Most preferably, a kneader is used as the reaction vessel with multiple rotating stirring shafts, as disclosed in EP 0 343,919.

Examples of methods for initiating polymerization include a method using a radical polymerization initiation catalyst and a method of irradiating active energy rays. Examples of radical polymerization initiation catalysts include peroxides such as hydrogen peroxide and benzoyl peroxide; azo compounds such as 2-2'-azobis-2-amidinopropane dihydrochloride and azobisisobutyronitrile;
Radical generators such as persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, and combinations of these radical generators with sodium bisulfite, L-ascorbic acid,
A redox initiator in combination with a reducing agent such as a ferrous salt is used. The amount used is based on the monomer component (
0.01 to 1.0% by weight, preferably 0.01 to 1.0% by weight based on A).
05 to 0.5% by weight. During aqueous solution polymerization,
It is preferable to use only water as the polymerization solvent, but methanol, ethanol, isopropanol,
A hydrophilic organic solvent such as acetone, dimethylformamide, dimethyl sulfoxide, etc. may be added to water.

The concentration of the monomer component (A) during aqueous solution polymerization is not particularly limited and can be set within a wide range, but in consideration of ease of controlling the polymerization reaction and yield, (A):Water ratio of 1:9 to 7:3 (weight ratio), especially 3
It is preferable to set it as the range of :7-5:5.

[0027] In the present invention, salt tolerance means that the degree of change in absorption capacity is small depending on the salt concentration in the aqueous solution to be absorbed, and salt tolerance = absorption capacity of physiological saline/pure water (deionized water). It is defined as the absorption capacity of

If the salt resistance of the water-absorbing resin is improved, for example, when used as an absorbent in disposable diapers or sanitary products, it will be less affected by the salt concentration in urine, and will have a stable absorption capacity and absorb liquid. Furthermore, when used as a sealant for seawater, etc., there is an advantage that the sealing effect is less affected by salt concentration.

[0029]

EXAMPLES The present invention will be explained in detail below with reference to Examples, but the scope of the present invention is not limited in any way by these Examples.

The absorption capacity and gel strength of the salt-resistant water-absorbing resin were measured by the following methods.

(1) Absorption capacity of pure water (deionized water): Approximately 0.05 g of salt-resistant water-absorbing resin is uniformly placed in a non-woven tea bag type bag (40 mm x 150 mm), and a large excess of pure water ( The sample was immersed in deionized water for 30 minutes, pulled out and drained on paper, and the weight after absorbing the liquid was measured. The absorption capacity of pure water (deionized water) was calculated according to the following formula using the weight of an empty tea bag itself as a blank after absorbing the liquid in the same manner. Absorption capacity of pure water (deionized water) (g/g) = (weight after absorption g - blank g) / (
Weight of salt-resistant resin (g) (2) Absorption capacity of physiological saline; salt-resistant water-absorbent resin approximately 0.
2g in a non-woven tea bag type bag (40mm x 150mm)
mm), immersed in a large excess of physiological saline (0.9% by weight NaCl) for 30 minutes to swell, pulled out, drained on paper, and measured the weight after absorbing the liquid. The absorption capacity of pure water was calculated according to the following formula using the weight of an empty tea bag itself as a blank after absorbing the liquid in the same manner.

Absorption capacity of physiological saline (g/g) = (weight after absorption g - blank g) / (weight of salt-resistant resin g) Note that salt tolerance = absorption capacity of physiological saline /Pure water(
It is expressed as the absorption capacity of deionized water).

(3) Gel strength: The swollen hydrogel was measured using a stress rheometer equipped with a disk with a radius of 2.5 cm.
The measurement was performed under the conditions that the sample thickness was 0.1 cm and the vibration frequency was 1.0 Hz. The shear modulus of the swollen hydrogel was defined as gel strength. The swollen hydrogel was prepared by mixing a salt-resistant water-absorbing resin with artificial urine (1.9% by weight of urea, 0.0% by weight of NaCl).
8% by weight, CaCl2 0.1% by weight, MgSO4
0.1% by weight) for 1 hour to swell, and then excess artificial urine was removed with a filter paper.

Example 1 A jacketed stainless steel double-arm kneader having an internal volume of 10 liters and having two sigma-type blades with a rotating diameter of 120 mm was charged with a mixture of 75 mol% sodium acrylate and 25 mol% acrylic acid. 4400 g of an aqueous solution of monomer component (A) (concentration of monomer component 37% by weight), 2.72 g of trimethylmethylolpropane acrylate as a crosslinking agent (0.05 mol% to monomer component (A)) was added and nitrogen gas was blown into the reaction system to replace the inside of the reaction system with nitrogen. Next, while rotating the two sigma-type blades, a water-absorbing resin (Nippon Shokubai Kagaku Kogyo Co., Ltd., Aqualic CA) was crushed with a hammer mill, and
Particle size 1 to 14 obtained by passing through a wire mesh of 0 mesh
162 g of a 9 μm water-absorbing resin (B) (10% by weight vs. monomer component (A)) was added, and while heating the inside of the reaction diameter by passing 30°C hot water through the jacket, 11 g of sodium persulfate was added as an initiator. .20g and 1 sodium bisulfite
．． 10g was added. The gel polymer obtained by continuing the polymerization reaction for another 60 minutes after the start of the polymerization reaction was subdivided into fine particles with a diameter of about 3 mm. The obtained gel polymer was dried with hot air on a wire mesh at a temperature of 150° C. for 2 hours. This dried product was pulverized using a hammer mill to obtain a salt-resistant water-absorbing resin. Table 1 shows the performance of the obtained salt-resistant water-absorbing resin.

Example 2 In Example 1, water absorbent resin (B
) was changed to 407 g (25% by weight vs. monomer component (A)), but the same operation as in Example 1 was repeated to obtain a salt-resistant water-absorbing resin. Table 1 shows the performance of this salt-resistant water absorbent resin.

Example 3 A salt-resistant water-absorbing resin was obtained by repeating the same operations as in Example 2, except that no crosslinking agent was used in Example 2. Table 1 shows the performance of this salt-resistant water absorbent resin.

Example 4 In a double-arm kneader similar to that used in Example 1, 2490 g of an aqueous solution of monomer component (A) consisting of 282 g of sodium acrylate, 108 g of acrylic acid, and 606 g of sodium salt of sulfoethyl acrylate was added. (concentration of monomer component 40% by weight) and 0.888 g of trimethylmethylolpropane triacrylate as a crosslinking agent (0.04 mol% vs. monomer component (A))
and nitrogen gas was blown into the reaction system to replace the inside of the reaction system with nitrogen. Next, while rotating the two sigma-type blades, 97 g (10
% by weight vs. monomer component (A)) and put 30% by weight into the jacket.
While heating the reaction system by passing hot water at ℃,
0.9 g of sodium persulfate and 0.038 g of L-ascorbic acid were added as polymerization initiators. The gel polymer obtained by continuing the polymerization reaction for an additional 90 minutes after the start of the polymerization reaction was subdivided into fine particles with a diameter of about 3 mm. The obtained gel polymer was dried with hot air on a wire mesh at a temperature of 150° C. for 2 hours. This dried product is crushed using a hammer mill,
A salt-resistant water absorbent resin was obtained. Table 1 shows the performance of the obtained salt-resistant water-absorbing resin.

Example 5 A salt-resistant water-absorbing resin was obtained by repeating the same procedure as in Example 4, except that no crosslinking agent was used. Table 1 shows the performance of this salt-resistant water absorbent resin. Example 6 In Example 4, water absorbent resin (B
) was changed to 49.8 g (5% by weight vs. monomer component (A)), but the same operation as in Example 4 was repeated to obtain a salt-resistant water-absorbent resin. Table 1 shows the performance of this salt-resistant water absorbent resin.

Example 7 In Example 1, water absorbent resin (B
) with a particle diameter of 1 to 84 that passed through a 20 mesh wire mesh.
A salt-resistant water-absorbing resin was obtained by repeating the same operation as in Example 1 except that the powder had a particle size of 0 μm. Table 1 shows the performance of this salt-resistant water absorbent resin.

Comparative Example 1 In Example 1, water absorbent resin (B
) amount to 3256g (50% by weight vs. monomer component (A))
A comparative resin was obtained by repeating the same operation as in Example 1 except for the following. The performance of this comparative resin is shown in Table 1.

Comparative Example 2 In Example 1, water absorbent resin (B
) was not used, but the same operation as in Example 1 was repeated to obtain a comparative resin. The performance of this comparative resin is shown in Table 1.

Comparative Example 3 In Example 1, the amount of crosslinking agent was changed to 27
．． A comparative resin was obtained by repeating the same operation as in Example 1, except that the amount was 2 g (0.5 mol % vs. monomer component (A)) and the water-absorbing resin (B) was not used. The performance of this comparative resin is shown in Table 1.

Comparative Example 4 20 parts of a polyethylene oxide resin having an average molecular weight of 100,000 and 0.05 part of triethylenediamine, which had been thoroughly dehydrated using a vacuum drying method, were added to 280 parts of acetonitrile, and the mixture was heated to 30 to 40°C in a nitrogen atmosphere. After completely dissolving the mixture, 0.2 part of 1,4-phenylene diisocyanate was added and the reaction was carried out at 70°C for 5 hours to obtain a uniform water-insoluble resin solution. This reaction product was cast into a glass Petri dish, vacuum dried at 40°C, and pulverized to obtain a comparative resin. The performance of this comparative resin is shown in Table 1.

Comparative Example 5 In Example 3, water absorbent resin (B
) was not used, but the same operation as in Example 3 was repeated to obtain a comparative resin. The performance of this comparative resin is shown in Table 1.

Comparative Example 6 1.0 liter of cyclohexane was placed in a 2 liter four-necked separable flask equipped with a stirrer, reflux condenser, thermometer, nitrogen gas inlet tube and dropping funnel, and sorbitan monostearate was added as a dispersant. 3
．． 0 g was added and dissolved, and nitrogen gas was blown in to drive out the dissolved oxygen.

Separately, in a flask, add 88% of sodium acrylate.
4.6 g, 21.6 g of acrylic acid and N as a crosslinking agent.
, N'-methylenebisacrylamide 0.0925g (
0.05 mol% of monomer component (A)) in ion-exchanged water 1
97g of the water-absorbing resin (B) used in Example 1.
) 10.6 g (10% by weight vs. monomer component (A)) was added to prepare an aqueous monomer solution.

Add 0.1 potassium persulfate to this monomer aqueous solution.
After adding and dissolving 5 g, nitrogen gas was blown into the aqueous solution to drive out oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in this flask was added to the separable flask and dispersed by stirring. Thereafter, the bath temperature was raised to 65° C. to initiate the polymerization reaction, and this temperature was maintained for 2 hours to complete the polymerization. After the polymerization was completed, the water in the hydrous gel was distilled off by azeotropic dehydration with cyclohexane, and then filtered to obtain a comparative resin. The performance of this comparative resin is shown in Table 1.

[0049]

[Table 1]

[0050]

Effect of the invention: At least one monomer component selected from the group consisting of unsaturated carboxylic acids and salts thereof of the present invention (
By a method for producing a salt-resistant water-absorbing resin, which comprises polymerizing an aqueous solution of A) in a ratio of 1 to 30 parts by weight of the water-absorbing resin (B) per 100 parts by weight of the monomer component (A). When the obtained salt-resistant water-absorbing resin with improved salt resistance is used as an absorbent in disposable diapers or sanitary products, for example, it is less affected by the salt concentration in urine, has a stable absorption capacity, and can be used as a liquid absorbent. It has excellent absorbency, and when used as a sealant for seawater, etc., it has the advantage that the sealing effect is less affected by salt concentration.

Claims (18)

[Claims] Claim 1: An aqueous solution of at least one monomer component (A) selected from the group consisting of unsaturated carboxylic acids and salts thereof is added to a water-absorbing resin (per 100 parts by weight of the monomer component (A)). B) A method for producing a salt-resistant water-absorbing resin, which comprises polymerizing in an aqueous solution in the presence of 1 to 30 parts by weight. 2. The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein the aqueous solution polymerization is carried out under stirring and mixing. 3. The method for producing a salt-resistant water-absorbing resin according to claim 2, wherein the aqueous solution polymerization is carried out under stirring and mixing in a reaction vessel having a plurality of rotating stirring shafts. 4. The method for producing a salt-resistant water-absorbing resin according to claim 3, wherein the reaction vessel having a plurality of rotating stirring shafts is a kneader. [Claim 5] 0 crosslinking agent is added to the monomer component (A).
．． The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein the salt-resistant water-absorbing resin is used in an amount of 0.001 to 0.1 mol%. 6. The salt-resistant water absorbent according to claim 1, wherein the aqueous solution polymerization is carried out in the presence of 5 to 20 parts by weight of the water absorbent resin (B) per 100 parts by weight of the monomer component (A). Method of manufacturing resin. [Claim 7] The water content of the water absorbent resin (B) is 0.1.
The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein the amount is 10% by weight. 8. The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein 90 to 100% by weight of the water-absorbing resin (B) has a particle size of 1 to 149 μm. 9. The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein the water-absorbing resin (B) is obtained by aqueous solution polymerization. 10. The water-absorbing resin (B) comprises a monomer component (
Claim 1, which is obtained by polymerizing A)
A method for producing a salt-resistant water-absorbing resin as described in . 11. The monomer component (A) is at least one member selected from the group consisting of (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and salts thereof. The method for producing a salt-resistant water-absorbing resin according to claim 1. 12. Production of the salt-resistant water-absorbing resin according to claim 1, wherein the monomer component (A) is at least one member selected from the group consisting of (meth)acrylic acid and salts thereof. Method. 13. The monomer component (A) comprises 10 to 70 mol % of (meth)acrylic acid and 90 to 30 mol % of an acrylic acid salt.
13. The method for producing a salt-resistant water-absorbing resin according to claim 12, wherein the salt-resistant water-absorbing resin is composed of mol%. 14. The method for producing a salt-resistant water-absorbing resin according to claim 13, wherein the crosslinking agent is used in an amount of 0.001 to 0.1 mol % based on the monomer component (A). 15. The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein the water-absorbing resin (B) is a crosslinked product of a partially neutralized acrylate polymer. 16. The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein the water-absorbing resin (B) is obtained by aqueous solution polymerization of the monomer component (A) according to claim 13. . 17. The water-absorbing resin (B) contains a crosslinking agent of 0.0%.
16. The salt-resistant water absorbent according to claim 15, which is a crosslinked product of a monomer polymer containing 0.001 to 0.1 mol% and neutralized with 0.3 to 0.9 equivalents of carboxyl groups in acrylic acid. Method of manufacturing resin. 18. The water-containing water absorbent resin obtained by aqueous solution polymerization is dried, and then classified to produce the water absorbent resin (B).
2. The method for producing a salt-resistant water-absorbing resin according to claim 1, wherein the water-absorbing resin (C) having a particle size range of .