JP3068840B2 - Method for producing water absorbent resin - Google Patents

Description

The present invention relates to a method for producing a water absorbent resin.

More specifically, the present invention has a wide range of uses in various fields such as the agricultural and horticultural fields and the food field, including sanitary materials such as disposable diapers and sanitary products, has a low residual monomer, and has a water absorption capacity and a suction force under pressure. The present invention relates to a method for producing a water-absorbent resin which is excellent in various water-absorbing properties, such as water-absorbing resin, and has good stability over time of a swollen gel.

(Prior Art) In recent years, water-absorbing resins have been utilized in various water-absorbing materials such as diapers, sanitary products, soil water retention agents, sealants, etc., taking advantage of their properties.

Examples of such a water-absorbent resin include carboxymethylcellulose cross-linked products (JP-A-56-15458), cross-linked polyvinyl alcohol-modified products (JP-A-54-20093),
Crosslinked isobutylene-maleic anhydride copolymer (JP-A-56
JP-A-36,504), saponified acrylate-vinyl acetate copolymer (JP-B-53-13,495), partially cross-linked polyethylene oxide (JP-A-61-130,324), starch-acrylonitrile graft copolymer A hydrolyzate of the union (JP-B-49-43,395), a starch-acrylic acid graft copolymer (JP-B-53-46,199), and a crosslinked product of acrylic acid or methacrylate polymer (JP-A No.
Japanese Patent Application Laid-Open No. 55-84,304 and Japanese Patent Application Laid-Open No. 55-19,243) are known. However, the water-absorbent resins obtained by these production methods have drawbacks such as low absorption capacity, and inferior suction power or absorption capacity under pressure even if the absorption capacity is high. Was also high in residual monomer content.

(Problems to be Solved by the Invention) As a method for improving various well-absorbing properties of a water-absorbent resin such as absorption capacity, suction power, and absorption capacity under pressure, the surface of the water-absorbent resin is crosslinked with a hydrophilic crosslinking agent. Methods are known (JP-A-58-180,233, JP-A-59-189,103).
JP-A-61-16,903, JP-A-57-44,627, JP-A-58-117,222, etc.).

These techniques can improve the suction power, the absorption capacity under pressure, etc., but the residual monomer of the water-absorbent resin is not reduced at all, but rather, the case where the residual monomer increases by performing a crosslinking reaction is also recognized. Was done.

In addition, the methods reported as a technique for reducing the residual monomer of the water-absorbent resin are roughly classified into the following three, similar to the techniques that have been used for water-soluble polymers for a long time.

(1) A method of increasing or dividing and adding a polymerization initiator (JP-A-56-72,005) (2) Extraction with a solvent or the like (JP-A-1-292,003) (3) Addition to a double bond Method for leading the remaining monomer to another derivative by using a reducing substance or the like (Japanese Patent Laid-Open No. 1-62,317, Japanese Patent Publication No. 3724709, etc.) Among these methods for reducing the remaining monomer, the method (1) above In this case, a decrease in the molecular weight of the polymer, a decrease in absorption capacity accompanying an excessive self-crosslinking reaction, an increase in water-soluble components, and the like are observed, and although the remaining monomers are reduced, the properties of the water-absorbent resin are reduced.

The method (2) also requires a large amount of solvent, the recovery cost is very high, and is not a preferable method.

In the method of (3) described in JP-A-1-62,317, the reduction rate of the residual monomer is still low according to the results of the present inventors, and the method disclosed in West German Patent Publication No. In the method of Japanese Patent No. 3724709, although the residual monomer was reduced, it was also recognized that the obtained water-absorbent resin swelled gel lacked the stability over time depending on the type and amount of the additional substance used. In addition, when the method described in West German Patent Publication No. 3724709 is applied to a water-absorbing resin having well-balanced water-absorbing properties obtained by treating the surface portion with a hydrophilic cross-linking agent as described above, the resin becomes It was revealed that various properties of water absorption, such as absorption capacity, absorption capacity under pressure, and suction force, which were originally possessed, were significantly reduced. This is because, in the method, 50 parts by weight of the water-absorbent resin powder is used.
It is considered that since a large amount of water of up to 500 parts by weight is used, the highly crosslinked layer on the surface thereof is deteriorated and destroyed due to swelling due to water during mixing. Further, in this case, a drying step is required later, and the process becomes expensive.

Conversely, when the surface of the water-absorbent resin obtained by the above method (3) with reduced residual monomers is cross-linked with a hydrophilic cross-linking agent based on the above-mentioned known technology, the production process becomes longer and once reduced. In some cases, the amount of the residual monomer increased during the cross-linking reaction, or the swollen gel of the obtained resin was in a state lacking in stability over time.

(Means for Solving the Problems) In view of the above-mentioned circumstances, the present inventors have conducted intensive studies and as a result, have found that a water-absorbent resin powder having a carboxyl group has two functional groups capable of reacting with the carboxyl group in a specific amount of water. By mixing an aqueous liquid obtained by dissolving a cross-linking agent having at least one reducing agent and a reducing substance, and performing an industrially simple method of performing a heating reaction, the above-described problem is completely solved, and the residual monomer is eliminated. The present inventors have found that a water-absorbent resin which is efficiently reduced, has excellent water-absorbing properties, and has excellent stability over time of the swollen gel can be obtained, thereby completing the present invention.

According to the present invention, a crosslinking agent (2) having at least two functional groups capable of reacting with a carboxyl group and a reducing substance (3) are dissolved in 100 parts by weight of a water-absorbing resin powder having a carboxyl group (1). A water-absorbent resin characterized by mixing and heating an aqueous liquid containing up to 50 parts by weight of water (5)
And a method for producing the same.

In addition, the present invention relates to a cross-linking agent having two or more functional groups capable of reacting with a carboxyl group per 100 parts by weight of a water-absorbent resin powder having a carboxyl group (1), 0.01 to 10 wt. ) And 5 to 50 parts by weight of water,
Water-absorbent resin characterized by being crosslinked by heating at 0 ° C. (5)
And a method for producing the same.

The water-absorbent resin powder (1) that can be used in the present invention includes:
It is a conventionally known resin that absorbs a large amount of water in water and swells to form a hydrogel, and needs to have a carboxyl group. For example, a hydrolyzate of a starch-acrylonitrile graft copolymer, a (partially) neutralized product of a starch-acrylic acid graft polymer, a saponified product of an acrylate-vinyl acetate copolymer, an acrylonitrile copolymer or an acrylamide copolymer A hydrolyzate of the union or a crosslinked product thereof, a carboxyl group-containing crosslinked polyvinyl alcohol modified product, a self-crosslinked polyacrylic acid (partially) neutralized product, a crosslinked product of a partially neutralized polyacrylic acid,
Examples include a neutralized product of a crosslinked isobutylene-maleic anhydride copolymer (part).

Considering the various properties of water absorption of the finally obtained resin, a crosslinked polymer of a water-soluble ethylenically unsaturated monomer containing acrylic acid (salt) as a main component is preferable. The amount of the carboxyl group having the water-absorbent resin powder (1) is not particularly limited, but usually, it is preferable that the carboxyl group is present in an amount of 0.01 equivalent or more per 100 g of the water-absorbent resin powder (1).

Examples of the polymerization method for obtaining the water-absorbent resin powder (1) include aqueous solution polymerization and reversed-phase suspension polymerization, but are not particularly limited.

The water content in these water absorbent resin powders (1) is usually
Those having 30% or less, more preferably 15% or less can be suitably used in the present invention.

In the present invention, the thus obtained water-absorbent resin powder having a carboxyl group (1) (which usually contains 100 to 3000 ppm of a residual monomer in many cases) has two functional groups capable of reacting with the carboxyl group. By mixing an aqueous liquid containing a specific amount of water in which the crosslinking agent (2) having the above and the reducing substance (3) are dissolved, and subjecting the mixture to heat treatment, excellent water absorption properties are obtained.
The resin (5) having high stability over time of the swollen gel and having a significantly reduced residual monomer content can be obtained.

The crosslinking agent (2) having two or more functional groups capable of reacting with a carboxyl group that can be used in the present invention is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, Glycerin, polyglycerin, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer Polyhydric alcohol compounds such as coalesce, polyvinyl alcohol, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol poly Glycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether,
Polyvalent glycidyl compounds such as propylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether; 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate], 1,
Polyvalent aziridine compounds such as 6-hexamethylene diethylene urea and diphenylmethane-bis-4,4 '-, N, N'-diethylene urea; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; ethylenediamine, diethylenetriamine, triethylenetetramine ,
Examples thereof include polyvalent amine compounds such as tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine; and polyvalent isocyanate compounds such as 2,4-toluylene diisocyanate and hexamethylene diisocyanate. Particularly preferred are polyhydric alcohol compounds and polyglycidyl compounds, and most preferred are polyhydric alcohol compounds. Among these, compounds having a molecular weight of 100 or more are preferred in the present invention in that the water-absorbent resin (5) having excellent water-absorbing properties is provided.

The amount of the cross-linking agent (2) used depends on the type thereof, but is generally based on 100 parts by weight of the water-absorbent resin powder (1).
A suitable amount is 0.01 to 10 parts by weight, preferably 0.5 to 5 parts by weight. When the amount is less than 0.01 part by weight, the surface crosslinking effect is not exhibited, and when it exceeds 10 parts by weight, the water absorption capacity may be extremely reduced.

The reducing substance (3) that can be used in the present invention includes sulfurous acid (salt), bisulfite, phosphorous acid (salt), hypophosphorous acid (salt), thiosulfuric acid (salt), ammonia, amines , Amino acids and the like.

Specific examples include sodium sulfite, potassium sulfite, calcium sulfite, ammonium sulfite, sulfurous acid,
Potassium bisulfite, sodium bisulfite, ammonium bisulfite, sodium thiosulfate, ammonium thiosulfate, potassium thiosulfate, magnesium thiosulfate, sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, sodium phosphite, Potassium phosphite, ammonium phosphite, ammonia, ammonium chloride, methylamine, ethyleneamine, butylamine,
Dimethylamine, diethylamine, cyclohexylamine, benzylamine, morpholine, glycine, alanine, valine, leucine, serine, threonine, cysteine, cystine, tyrosine, aspartic acid, glutamic acid, lysine, arginine and the like can be used. One or more kinds can be used in consideration of the reactivity with the crosslinking agent (2) used above.

Among these, from the viewpoint of the reduction rate of the residual monomer, sulfite (salt) bisulfite ammonia and amino acid salt are preferred, and sulfite (salt) and sulfite are most preferred because they also promote the cross-linking reaction of the surface portion. It is a hydrogen salt.

In the present invention, the crosslinking agent (2) is used in combination with the reducing substance (3).
, The stability of the gel is improved in each step as compared with the case where the crosslinking agent (2) is not used. The amount of the reducing substance (3) to be used depends on the amount of residual monomers remaining in the water-absorbent resin powder (1), but is generally 0.001 to 5 parts by weight, preferably 100 parts by weight of the water-absorbent resin (1). Is from 0.005 to 0.5 part by weight, most preferably from 0.01 to 0.1 part by weight. When the amount of the reducing substance (3) exceeds 5 parts by weight, various properties of the water-absorbent resin powder (1) including the stability of the gel are reduced, or the reducing substance (3) remains in the resin. There is. On the other hand, 0.
If the amount is less than 001 parts by weight, the effect of reducing the residual monomer may be hardly recognized.

In the present invention, the amount of water contained in the aqueous liquid mixed with the water-absorbent resin powder (1) by simultaneously dissolving the cross-linking agent (2) and the reducing substance (3) is as follows. 100
It is 5 to 50 parts by weight, preferably 7 to 30 parts by weight based on parts by weight. When the amount of water exceeds 50 parts by weight, the absorption capacity of the water-absorbent resin after heat treatment and the absorption capacity under pressure are significantly reduced, and depending on the heat treatment conditions, the swelling gel of the obtained resin is stable over time. It may be lacking in gender. 5
If the amount is less than parts by weight, the reduction ratio of the residual monomer is low.

Further, when a water-miscible hydrophilic organic solvent is contained in the aqueous liquid, a water-absorbing resin having excellent water-absorbing properties and having efficiently reduced residual monomers can be obtained, which is even more preferable.

Examples of the hydrophilic organic solvent in this case include methanol, ethanol, isopropanol, butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, acetone, and methyl ethylene ketone. Among them, ethanol and isopropanol are preferred.

The amount used when the hydrophilic organic solvent is used depends on the amount of water used and the solubility of the reducing substance, but is usually 0.1 to 50 parts by weight, preferably 100 to 100 parts by weight of the water-absorbent resin powder (1).
0.5 to 8 parts by weight. If the amount is less than 0.1 part by weight, the effect of using the organic solvent is unlikely to appear. If the amount exceeds 50 parts by weight, not only is it economically disadvantageous, but also the residual monomer is not efficiently reduced.

On the other hand, if the amount of the hydrophilic organic solvent in the aqueous liquid exceeds 40% by weight, the rate of reduction of the residual monomer is undesirably low. Preferably not more than 20% by weight, most preferably 10-20
% By weight.

As a specific example showing an embodiment of the production method in the present invention, the following method can be usually mentioned.

(1) A method in which an aqueous solution in which a crosslinking agent (2) and a reducing substance (3) are dissolved is added to the water-absorbent resin powder (1), mixed uniformly, and heat-treated.

(2) A hydrophilic organic solvent is further added to an aqueous solution in which the crosslinking agent (2) and the reducing substance (3) are dissolved in the water-absorbing resin powder (1) as long as the solubility of the reducing substance (3) is not hindered. A method in which an aqueous liquid is added, mixed uniformly, and heat-treated.

(3) The water-absorbent resin powder (1) is dispersed in a hydrophobic organic solvent containing a surfactant or a dispersion stabilizer, and
A method in which an aqueous solution in which a crosslinking agent (2) and a reducing substance (3) are dissolved is added, and the inside of the system is heat-treated.

(4) An aqueous solution in which a crosslinking agent (2) and a reducing substance (3) are dissolved is added to the water-absorbent resin powder (1), and the mixture is mixed uniformly. Heat treatment after giving.

As a mixer used for the addition and mixing, an ordinary stirrer, mixer and kneader can be used. For example, cylindrical mixer, double conical mixer, fluidized mixer, V-type mixer, ribbon-type mixer, screw-type mixer, rotating disk-type mixer, air-flow-type mixer, double-arm kneader Examples include a Japanese machine, an internal mixer, a muller-type kneader, a roll mixer, and a screw-type extruder, which further enhance the effect of uniformly and significantly modifying the surface of the resin to reduce residual monomers, thereby increasing productivity. Also has a high-speed rotating pattle to obtain,
A mixer having a large mechanical mixing force is more preferable. Further, a method in which a water-absorbent resin powder (1) powder is allowed to flow down, droplets of an aqueous liquid are sprayed thereon, and the two liquids are brought into contact in a co-current state to mix them without mechanical mixing force can also be used in the present invention. . In addition, in order to perform the most uniform reforming of the resin surface and the reduction of residual monomers, up to a heating treatment after mixing, at a low temperature, preferably 20-
It is preferable to leave at 40 ° C. for a certain period of time. This standing time is usually about 1 to 60 minutes, preferably about 3 to 30 minutes.

Further, for the heat treatment for causing a crosslinking reaction after mixing, a usual dryer or heating furnace can be used. For example, a channel-type stirring dryer, a rotary dryer, a disk dryer, a kneading dryer, a fluidized-bed dryer, a flash dryer, an infrared dryer, and the like. In that case, the heat treatment temperature is 60 to 250 ° C, preferably 90 ° C.
~ 230 ° C. If the temperature is higher than 250 ° C., the absorption capacity may be too low or the residual monomer may not be efficiently reduced, which is not preferable. On the other hand, when the temperature is lower than 60 ° C., the crosslinking reaction is difficult to be carried out smoothly.

Further, at the time of addition of the aqueous liquid in which the crosslinking agent (2) and the reducing substance (3) are dissolved, a deodorant, a fragrance, a drug, a fertilizer, a dye, a content, a short fiber, and the like are further interposed in the aqueous liquid. New functions can be imparted to the resulting water-absorbent resin.

(Examples) Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

Various physical properties and various properties of the water-absorbing resin were determined as follows.

(A) 100 ml of deionized water was added to a beaker of 200 ml of residual monomer, and 1.0 g of a water-absorbent resin was added thereto with stirring to gel the whole amount of deionized water. One hour later, the gel was shrunk by adding 5 ml of an aqueous phosphoric acid solution. After stirring, the water-absorbent resin dispersion was filtered using a filter paper, and the filtrate was analyzed by high performance liquid chromatography.

On the other hand, a calibration curve obtained by similarly analyzing a monomer standard solution having a known concentration was used as an external standard, and the amount of residual monomer in the water-absorbent resin was determined in consideration of the dilution ratio of the filtrate.

(B) Absorption ratio 0.2 g of absorbent resin in a non-woven tea bag bag (40 mm
× 150mm), immersed in 0.9% by weight aqueous sodium chloride solution, 30 minutes later, lifted up this tea bag type bag, drained it for a certain period of time, measured its weight, and calculated the water absorption capacity by the following formula did.

(C) Absorbency under load FIG. 1 is a cross-sectional view for explaining an apparatus for measuring the absorbency under pressure of a water-absorbent resin. The absorption capacity under pressure is measured using the apparatus shown in FIG. The upper port 2 of the burette 1 is plugged, and the measuring table 4 and the air port 5 are set at the same height. A filter paper 7, a water-absorbent resin 9 (0.2 g) and a filter paper 7 'are placed on a glass filter (NO.1) 6 having a diameter of 70 mm in a measuring table 4, and a weight 8 of 20 g / cm ² is further placed thereon. Artificial urine (composition: urea 1.9%, NaCl 0.8%, CaCl ₂ 0.1
%, Deionized water containing 0.1% MgSO ₄ ) were expressed as absorption capacity under pressure (ml / g).

(C) Suction force 20 ml of artificial urine is poured on a tissue paper (55 mm x 75 mm, 16 layers) with a syringe to create a base material containing artificial urine, and 1.0 g of water-absorbent resin is placed on the base material. placed. After 10 minutes, the swollen gel was collected, and its weight was measured to determine the suction force of the liquid from the tissue paper.

 At the same time, the presence or absence of mamako in the water absorbent resin was observed.

(D) Stability over time of swollen gel 2 g of water-absorbent resin was swollen with 50 ml of adult urine, sealed in a container, and left at 40 ° C. for 16 hours. Take out this sealed container,
The stability over time of the swollen gel was evaluated on the following three levels by examining the fluidity of the gel by closing the container.

O: gel does not flow △: gel flows slightly X: gel flows Reference Example 141 parts of sodium acrylate, 36.1 parts of acrylic acid and 0.093 part of N, N'-methylenebisacrylamide are dissolved in 329 parts of deionized water. Then, nitrogen gas was blown into this to expel dissolved oxygen. The aqueous solution of this monomer was kept at 30 ° C. Next, 0.5 parts of sodium perfluate and 0.02 parts of l-ascorbic acid were added and the mixture was left to stand for polymerization to obtain a gel-like hydropolymer.

This was dried with hot air at 150 ° C. and then pulverized with a hammer type pulverizer to obtain a water-absorbent resin powder (a) having passed through a 20 mesh. The residual monomer in the water-absorbent resin powder (a) was 210 ppm. The water content of the water-absorbent resin powder (a) was 6%.

Example 1 An aqueous liquid was prepared by dissolving 4 parts of trimethylolpropane as a crosslinking agent and 0.2 parts of sodium hydrogen sulfite as a reducing substance in 10 parts of water and 3 parts of isopropanol.

100 parts of the water-absorbent resin powder (a) obtained in Reference Example 1 and the above aqueous liquid were mixed using a high-speed rotary paddle-type mixer and brought to room temperature.
After standing for 30 minutes, the mixture was heated at 180 ° C. for 30 minutes with stirring to obtain the water-absorbent resin (1) of the present invention. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Example 2 0.1 part of ethylene glycol diglycidyl ether as a cross-linking agent and 0.1 part of sodium sulfite as a reducing substance in water
An aqueous liquid dissolved in 20 parts and 5 parts of isopropanol was prepared.

100 parts of the water-absorbent resin powder (a) obtained in Reference Example 1 and the above-mentioned aqueous liquid were mixed using a high-speed rotary paddle-type mixer and brought to room temperature.
After standing for a minute, the mixture was heated at 120 ° C. for 40 minutes with stirring to obtain a water-absorbent resin (2) of the present invention. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Example 3 An aqueous liquid was prepared by dissolving 4 parts of 1.6-hexanediol as a crosslinking agent and 0.05 part of sodium hydrogen sulfite as a reducing substance in 30 parts of water and 4 parts of ethanol.

100 parts of the water-absorbent resin powder (a) obtained in Reference Example 1 and the above aqueous liquid were mixed using a high-speed rotary paddle type mixer, and the mixture was added at room temperature for 15 minutes.
After standing for minutes, the mixture was heated at 180 ° C. for 40 minutes with stirring to obtain a water-absorbent resin (3) of the present invention. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Example 4 An aqueous liquid prepared by dissolving 5 parts of polyglycerin as a crosslinking agent, 15 parts of ammonia as a reducing substance in 15 parts of water, and 3 parts of ethanol was prepared.

100 parts of the water-absorbent resin powder (a) obtained in Reference Example 1 and the above aqueous liquid were mixed using a high-speed paddle-type mixer, and the mixture was cooled to room temperature.
After standing for minutes, the mixture was heated at 180 ° C. for 40 minutes with stirring to obtain a water-absorbent resin (4) of the present invention. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Example 5 An aqueous liquid was prepared by dissolving 2 parts of glycerin as a crosslinking agent and 0.07 part of sodium sulfite as a reducing substance in 8 parts of water and 2 parts of isopropanol.

100 parts of the water-absorbent resin (a) obtained in Reference Example 1 and the above aqueous liquid were mixed using a high-speed paddle-type mixer, allowed to stand at room temperature for 10 minutes, and then heat-treated at 180 ° C for 30 minutes with stirring. The water-absorbent resin (5) of the invention was obtained. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Comparative Example 1 A comparative water-absorbent resin (1) was obtained in the same manner as in Example 1, except that sodium bisulfite was not used.
Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Comparative Example 2 Comparative Example 1 was repeated by mixing an aqueous liquid without using the cross-linking agent trimethylolpropane and the water-absorbent resin powder (a) with a high-speed rotating paddle-type mixer and then heating at 110 ° C. for 30 minutes. Water absorbent resin (2) was obtained. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Comparative Example 3 100 parts of the comparative water-absorbent resin (1) obtained in Comparative Example 1 and an aqueous solution in which 0.2 part of sodium bisulfite was dissolved in 50 parts of water were mixed by a high-speed rotary paddle-type mixer.
By heating at 120 ° C. for 1 hour, a comparative water absorbent resin (3) was obtained. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Comparative Example 4 An aqueous liquid composed of 4 parts of trimethylolpropane, 10 parts of water and 3 parts of isopropanol was mixed with 100 parts of the comparative water absorbent resin (2) obtained in Comparative Example 2 using a high-speed paddle type mixer. The mixture was heated at 180 ° C. for 30 minutes with stirring to obtain a comparative water absorbent resin (4). Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Comparative Example 5 A comparative water-absorbent resin (5) was obtained in the same manner as in Example 1, except that water was changed to 60 parts. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

Comparative Example 6 A comparative water-absorbent resin (6) was obtained in the same manner as in Example 1 except that water was changed to 3 parts. Physical properties and the like of the obtained resin were measured by the methods described above, and the results are shown in Table 1.

(Effects of the Invention) According to the present invention, a water-absorbing resin having excellent water absorption properties such as an absorption capacity, an absorption capacity under pressure, and a suction force, and also having a remarkably reduced residual monomer, has a crosslinking agent and a reducing physical property. At the same time, it has been clarified that an aqueous liquid containing a specific amount of water dissolved therein can be mixed with a water-absorbent resin powder and subjected to heat treatment to produce the first liquid.

Further, according to the present invention, since the crosslinking agent is also distributed in the vicinity of the reducing substance added to the water-absorbing resin after mixing, even when the type or amount of the reducing substance is changed, even when swollen, the stability with time is high. A water-absorbing resin can be manufactured stably.

Therefore, the water-absorbent resin obtained by the present invention, taking advantage of its features, absorbents for sanitary materials such as disposable diapers and sanitary napkins, medical water retention agents, horticultural water retention agents, and water absorption of other industrial dehydrating agents It can be suitably used for applications requiring water retention and water retention.

[Brief description of the drawings]

FIG. 1 is a sectional view for explaining an apparatus for measuring the absorption capacity of a water-absorbent resin under pressure. DESCRIPTION OF SYMBOLS 1 ... Burette 2 ... Upper end of burette 3 ... Plug 4 ... Measurement table 5 ... Air hole 6 ... Glass filter 7.7 '... Filter paper 8 ... Weight 9 ... Water absorbent resin

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshio Irie 992, Nishioki, Okahama-ku, Himeji-shi, Hyogo Pref. Address No. 1 Himeji Laboratory, Nippon Shokubai Chemical Industry Co., Ltd. (56) References JP-A-64-62317 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 8/00- 8/14

Claims (12)

(57) [Claims] 1. A crosslinking agent (2) having at least two functional groups capable of reacting with a carboxyl group and a reducing substance (3) are dissolved in 100 parts by weight of a water-absorbent resin powder having a carboxyl group (1). A water-absorbent resin characterized by mixing and heating an aqueous liquid containing 5 to 50 parts by weight of water (5)
Manufacturing method. 2. A cross-linking agent having two or more functional groups capable of reacting with a carboxyl group per 100 parts by weight of a water-absorbent resin powder having a carboxyl group (1), 0.01 to 10 parts by weight of a cross-linking agent (2) and a reducing substance (3) 5) 50 to 50 parts by weight of 0.001 to 5 parts by weight
The method according to claim 1, wherein an aqueous liquid containing parts by weight of water is mixed and heat-treated at a temperature of 60 to 250C. 3. The method according to claim 1, wherein the aqueous liquid contains a hydrophilic organic solvent. 4. A water-absorbent resin powder (1) based on 100 parts by weight
The method according to claim 1, wherein water is used in a ratio of 7 to 30 parts by weight and a hydrophilic organic solvent is used in a ratio of 0.5 to 8 parts by weight. 5. The method according to claim 4, wherein the proportion of the hydrophilic organic solvent in the aqueous liquid is 40% by weight or less. 6. The method according to claim 1, wherein the reducing substance (3) is sulfite (salt) or bisulfite. 7. The method according to claim 1, wherein the crosslinking agent (2) is a polyhydric alcohol compound or a polyhydric glycidyl compound. 8. The method according to claim 7, wherein the crosslinking agent (2) is a polyhydric alcohol compound. 9. The method according to claim 8, wherein the heat treatment is performed at a temperature of 90 to 230 ° C. 10. The method of claim 1, wherein the mixing is performed by a high speed paddle type mixer. 11. A carboxyl group-containing water-absorbent resin powder (1) 100 parts by weight of a crosslinking agent (2) having at least two functional groups capable of reacting with a carboxyl group (2) 0.01 to 10 parts by weight, a reducing substance (3) ) And 5 to 50 parts by weight of water,
A method for producing a water-absorbent resin (5), characterized in that the composition is crosslinked by heating at a temperature of ° C. 12. A cross-linking agent having two or more functional groups capable of reacting with a carboxyl group per 100 parts by weight of a water-absorbent resin powder having a carboxyl group (1), 0.01 to 10 parts by weight of a cross-linking agent (2) and a reducing substance (3) 5) 50 to 50 parts by weight of 0.001 to 5 parts by weight
The method according to claim 11, wherein an aqueous liquid containing parts by weight of water is mixed and heat-treated at a temperature of 60 to 250 ° C.