CA1330868C

CA1330868C - Water-absorbent resin composition

Info

Publication number: CA1330868C
Application number: CA000538781A
Authority: CA
Inventors: Shigeji Obayashi; Morio Nakamura; Takushi Yamamoto; Hitoshi Tanaka; Yuji Sakamoto
Original assignee: Seitetsu Kagaku Co Ltd
Current assignee: Sumitomo Seika Chemicals Co Ltd
Priority date: 1986-06-04
Filing date: 1987-06-03
Publication date: 1994-07-26
Anticipated expiration: 2011-07-26
Also published as: CN87104090A; US4972019A; CN1007729B; EP0249391A3; BR8702835A; MX169620B; EP0249391B1; US4863989A; ES2033311T3; EP0249391A2; DE3778429D1

Abstract

Abstract:
The present invention is directed to a water-absorbent resin composition having superior gel stability which comprises a water-absorbent resin, at least one oxygen-containing reducing inorganic salt and, optionally, at least one organic antioxidant. The water-absorbent resin composition is suitable for water-absorbent articles for example diapers, tampons, sanitary napkins and the like.

Description

t33~8 Water-absorbent resin composition The present invention relates to a water-absorbent resin composition. More particularly, it relates to a water-absorbent resin composition having an improved stability to body fluids e.g. urine, catamenial S blood, secretaions and the like, and further relates to a water-absorbent resin composition having an improved stability to an aqueous solution containing an electrolyte in addition to an improved stability to body fluids.
Recently, various water-absorbent resins have been developed (for example, see U.S. Patent No. 4,340,706, U.S. Patent No. 4,093,776, U.S. Patent No. 4,459,396, U.S.
~atent No. 3,980,663 and U.S. Patent No. 4,552,938) and ~ -used extensively in various water-absorbent articles for example diapers, tampons, sanitary napkins and the like.
Theeeby, the water-absorbent properties of such articles are improved. For example, liquid retention characteris~
tics are improved and liquid leak is diminished. Further, the water-absorbent articles are comfortable to wear even after body fluids have been absorbed. Accordingly, such a water-absorbent article tends to be kept on for a longer period of time.
On the other hand, it has been found that the gel which results from the absorption of fluids e.g. urine, catamenial blood, secretions and the like by a water-absorbent article crumbles out of shape because, ingeneral, the water-absorbent resin of the gel is decom-posed by the body fluids with time. Accordingly, the ,.' ': . - : ; : .
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longer the water-absorbent article is worn, the lower the liquid retention characteristics of the article become.
This results in an increase in liquid leak, discomfort for the wearer and the like. In view of this, it is necessary to develop a water-absorbent resin which has an improved gel stability to body fluids.
Increasing the crosslinking density of the water-absorbent resin has been employed as a means for improving gel stability. However, as the crosslinking density becomes higher, the water-absorption capacity becomes lower and therefore it is necessary to increase the amount of the resin used. This is less economical and adversely affects other properties of the water-absorbent article.
The present inventors have been searching to obtain a water-absorbent resin having improved gel stability to body fluids. As a result, it has been found that the gel stability to body fluids of a water-absorbent resin can be sufficiently improved without the above disadvantages by incorporating an oxygen-containing reducing inorganic salt. Further, it has been found that, in addition to gel stability to body fluids, gel stability of a water-absorbent resin to an aqueous solution con-taining an electrolyte can also be sufficiently improved while maintaining its high water-absorption capacity by incorporating an organic antioxidant together with the oxygen-containing reducing inorganic salt.
One object of the present invention is to provide a water-absorbent resin composition having improved gel stability to body fluids and which is suitable for water-absorbent articles.
Another object of the present invention is toprovide a water-absorbent resin composition having improved gel stability to an aqueous solution containing an electro-lyte as well as to body fluids and which is suitable for water-absorbent articles.

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- 2a -In one aspect of the present invention, there is provided a water-absorbent resin composition which comprises crosslinked polyacrylic acid salts, crosslinked copolymers of vinyl alcohol-acrylic acid salt, crosslinked saponification products of starch-acrylonitrile graft copolymer, crosslinked starch-acrylic acid salt copolymer, crosslinked products of polyvinyl alcohol grafted with maleic anhydride, or crosslinked carboxymethyl cellulose alkali metal salts and at least one oxygen-containing reducing inorganic salt selected from the group consisting of sulfites, bisulfites, pyrosulfites, dithionites, trithionates, tetrathionates, thiosulfates, and nitrites.
This water-absorbent resin composition of the present invention has an improved gel stability to body fluids, e.g.
urine, catamenial blood, secretions and the like.
In another aspect of the present invention, there is provided a water-absorbent resin composition which comprises:
(a) crosslinked polyacrylic acid salts, crosslinked copolymers of vinylalcohol-acrylic acid salt, crosslinked saponification products of starch-acrylonitrile graft copolymer, crosslinked starch-acrylic acid salt copolymer, crosslinked pxoducts of polyvinylacohol grafted with maleic anhydride, or crosslinked carboxymethyl cellulose alkali metal salts; (b) at least one oxygen-containing reducing inorganic salt selected from the group consisting of sulfites, bisulfites, pyrosulfites, dithionites, trithionates, tetrathionates, thiosulfates, and nitrites; and (c) at least one organic antioxidant selected from the group consisting of ascorbic acid and its derivatives, gallic acid and its derivatives, benzothiazoles, dithionates, thiurams, benzimidazoles, formaldehyde sulfoxylates and phenothiazines.
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The water-absorbent composition of the present invention has improved stability to an aqueous solution containing an electrolyte in addition to improved stability to body fluids.
In the present invention, although an account of the mechanism of the oxygen-containing reducing inorganic salt and the organic antioxidant in the water-absorbent resin composition is unclear, properties of water-absorbent articles can be remarkably improved simply by incorporating a small amount of these materials into the water-absorbent resin without any sanitary problems.
By using the composition of the present invention, there can be obtained various water-absorbent articles having improved properties e.g., improved liquid retention characteristics with good prevention of liquid leak and a comfortable feeling for the wearer. Further, the composition of the present invention can be broadly used in the field where an aqueous solution containing an electrolyte is involved.
The water-absorbent resin used in the composition of the present invention is not limited to a specific one and any conventional water-absorbent resin can be used.
Examples of suitable water-absorbent resins include cross-linked polyacrylic acid salts, crosslinked copolymers of vinyl alcohol-acrylic acid salts, crosslinked saponifica-tion products of starch-acrylonitrile graft copolymers, e~

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In one aspect of the present invention, the water-absorbent resin is incorporated with the oxygen-containing reducing inorganic salt to improve its gel stability to body fluids e.g. urine, catamenial blood, secretions, etc.
As the oxygen-containing reducing inorganic salt in the present invention, particularly, there can be used at least one member selected from the group consisting of sulfites, bisulfites, pyrosulfites, dithionites, trithion-ates, tetrathionates, thiosulfates and nitrites. Specific examples of these oxygen-containing reducing inorganic salts include sulfites e.g., sodium sulfite, potassium sulfite, calcium sulfite, zinc sulfite, ammonium sulfite, etc.; bisul~ite, e.g., sodium bisulfite, potassium bisulfite, calcium bisulfite, ammonium bisulfite, etc.;
pyrosulfites e.g., sodium pyrosulfite, potassium pyro-sulfite, ammonium pyrosulfite, etc.; dithionites e.g.
sodium dithionite, potassium dithionite, ammonium di-thionite, calcium dithionite, zinc dithionite, etc.;
trithionates e.g. potassium trithionate, sodium trithio- -~
nate, etc.; tetrathionates e.g., potassium tetrathionate, sodium tetrathionate, etc.; thiosulfates e.g., sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, etc.; and nitrites e.g., sodium nitrite, potassium nitrite, calcium nitrite, zinc nitrite, etc. They can be used alone or in combination thereof. Among them, from the sanitary and gel stability points of view, sodium sulfite, sodium bisulfite, sodium pyrosulfite, sodium dithionite and sodium nitrite are preferred.
In the present invention, the oxygen-containing reducing inorganic salt is used in an amount of 0.001 to 10 parts by weight, preferably, 0.01 to 5 parts by weight per 100 parts by weight of the water-absorbent resin.
When the amount of the reducing inorganic salt is less - . ... ..
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than 0.001 part by weight per 100 parts by weight of the water-absorbent resin, the gel stability to body fluids of the water-absorbent resin scarcely improves. On the other hand, when the amount is more than 10 parts by weight, the water-absorption capacity of the resulting composition is lowered, even though the gel stability is improved.
In another aspect of the present invention, the water-absorbent resin is incorporated with both the oxygen-containing reducing agent and the organic antioxidant to improve its gel stability to both body fluids and an aqueous solution containing an electrolyte for example, a physiological saline solution, artificial urine and the like.
In this aspect, the above-described oxygen-containing reducing agent can be used in an amount of the same range as described above.
As the organic antioxidant, particularly, therecan be used at least one member selected from the group ~-~ consisting of ascorbic acid and its derivatives, gallic acid and its derivatives, benzothiazoles, dithionates, thiurams, benzimidazoles, formaldehyde sulfoxylates and phenothiazines. Specific examples of these organic anti-oxidants include ascorbic acid and its derivatives e.g.
L-ascorbic acid, sodium L-ascorbate, isoascorbic acid, sodium isoascorbate, etc.; gallic acid and its derivatives e.g. gallic acid, methyl gallate, ethyl gallate, n-propyl gallate, isoamyl gallate, octyl gallate, lauryl gallate, etc.; benzothiazoles e.g. mercaptobenzothiazole, sodium mercaptobenzothiazole, zinc mercaptobenzothiazole, etc.;
dithionates e.g. zinc methyldithiocarbamate, zinc diethyl-dithiocarbamate, zinc di-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate, etc.; thiurams e.g. tetra-methylthiuram disulfide, tetraethylthiuram sulfide, tetra-butylthiuram disulfide, tetramethylthiuram monosulfide, etc.; benzimidazoles e.g. 2-mercaptobenzimidazole, etc.;
formaldehyde sulfoxylates e.g. sodium formaldehyde ..--.
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sulfoxylate, etc.; and phenothiazines e.g. phenothiazine, 2-methoxyphenothiazine, etc. They can be used alone or in combination thereof. Among them, from the sanitary and gel stability points of view, ~-ascorbic acid, sodium L-ascorbate, isoascorbic acid, sodium isoascorbate and n-propyl gallate are preferred.
In the present invention, the organic antioxidant is used in an amount of 0.0001 to 10 parts by weight, preferably, 0.001 to 5 parts by weight per 100 parts by weight of the water-absorbent resin. When the amount of the antioxidant is less than 0.0001 part by weight per 100 parts by weight of the water-absorbent resin, the improve-ment in the gel stability of the water-absorbent resin to an aqueous solution containing an electrolyte is insuffic-ient. On the other hand, when the amount is more than 10parts by weight, the gel stability of the water-absorbent resin becomes inferior. Further, when the water-absorbent resin is incorporated with only the antioxidant without incorporation of the oxygen-containing reducing inorganic salt, the gel stability of the water-absorbent resin is lowered and therefore, in the present invention, the -antioxidant should be used together with the inorganic salt.
The water-absorbent resin composition of the present invention can be prepared by blending the water-absorbent resin with the oxygen-containing reducing inorganic salt and, if necessary, the organic antioxidant.
The blending method is not limited to a specific one and any known method can be employed. For example, the inor-ganic .salt and the antioxidant can be added to a polymeriz-ation reaction mixture of the water-absorbent resin.
Further, they can be blended with the dried water-absorbent resin by dry blending.
The water-absorbent resin composition of the present invention can be used for the production of various water-absorbent articles according to any conventional method.

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The following Preparations, Comparative Examples and Examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof.
PREPARATIONS
Preparation 1 Cyclohexane (213 g) was placed in a 500 ml four necked round bottom flask equipped with a stirrer, a reflux condenser, a dropping funnel and a nitrogen gas inlet. To the flask was charged sorbitan monolaurate having HLB of 8.6 (manufactured and sold by Nippon Oil and Fats Co., Ltd., Japan under the trade mark of Nonion LP-20R) (1.9 g).
After dissolution of the surfactant with stirring at room temperature, dissolved oxygen was purged with nitrogen gas.
Separately, an 80% (w/w) aqueous solution of acrylic acid (48.8 g) was placed in a 200 ml conical flask and a 25.9~ (w/w) aqueous solution of sodium hydroxide (66.7 g) was added dropwise with cooling to neutralize 80 mole ~ of the acrylic acid. Potassium persulfate (0.13 g) was added to the mixture.
The resulting partially neutralized acrylic acid solution was added to the above four necked round bottom flask and the mixture was thoroughly purged with nitrogen gas. The mixture was heated and subjected to a polymeriza-tion reaction for 3 hours while maintaining the bath temperature at 55 to 60C.
Water and cyclohexane were distilled off and the residue was dried to obtain a fine granular water-absorbent resin (48.5 g).
Preparation 2 n-Heptane (280 ml) was placed in a 500 ml four necked round bottom flask equipped with a stirrer, a reflux condenser, a dropping funnel and a nitrogen gas inlet. To the flask was charged hexaglyceryl monobehenirate having HLB of 13.1 (manufactured and sold by Nippon Oil and Fats, Co., Ltd., Japan under the trade mark Nonion G~-106) (0.75 g).

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, ' - ~ -After dispecsion of the surfactant, dissolved oxygen was purged with nitrogen gas. The temperature was raised to 50C to dissolve the surfactant and then the mixture was cooled to 30C.
Separately, an 80% (w/w) aqueous solution of acrylic acid (37.5 g) was placed in a 200 ml conical flask and a 25.4% (w/w) aqueous solution of sodium hydroxide (49.3 g) was added dropwise with ice-cooling to neutralize 75 mole % of the acrylic acid. Potassium persulfate (0.045 g) was added to the mixture. -~
The resulting partially neutralized acrylic acid ~
solution was added to the above four necked round bottom ;
flask and the mixture was thoroughly purged with nitrogen gas. The mixture was heated and subjected to a polymer-ization reaction for 2 hours while maintaining the bath temperature at 55 to 60C.
Water and n-heptane were distilled off and the ~
residue was dried to obtain a water-absorbent resin -~-(40.2 g).
Preparation 3 A water-absorbent resin (40.3 g) was obtained according to the same manner as described in Preparation 2 except that ethylene glycol diglycidyl ether (0.038 g) was added to the polymerization reaction mixture.
COMPARATIVE EXAMPLES AND EXAMPLES
In the following Comparative Examples and Examples, absorbency, evaluation of gel stability to a saline solution (0.9% (w/w) aqueous solution of sodium chloride), preparation of an absorbent article and evaluation of gel stability to human urine were carried out as follows.
Absorbency A water-absorbent resin (1 g) was dispersed in a 0.9% (w/w) aqueous solution of sodium chloride (200 ml) to thoroughly swell. After 4 hours or 15 hours, the swollen resin was filtered through a 100 mesh metallic wire gauze and the volume of the swollen resin obtained as a filter cake was measured and the value was taken as the absorbency.
_aluation of qel stability to a saline solution The swollen resin obtained in the above measure-ment of the absorbency was pressed with the fingers to organoleptically evaluate its gel stability according to the following four criteria.
A: Gel was not crumbled even by pressing strongly.
B: Gel was crumbled by pressing strongly.
C: Gel was observed but readily crumbled.
D: No gel form was retained.
Preparation of an absorbent article A pulp having the basis weight of 150 g/m2 was cut out to form a sheet (20 cm x 10 cm) and a water-absorbent resin or a water-absorbent resin composition ~3 g) was uniformly scattered thereon. Further, the same sheet as described above was laminated thereon and pressed by uniformly applying a pressure of 1 kg/cm2 to obtain an absorbent article.
Evaluation of gel stability to human urine ; Human urine (120 ml) was poured on the center part of the above-prepared absorbent article over 1 minute and the article was allowed to stand for 5 minutes. Then, the absorbent article which absorbed human urine was packed in a polyethylene bag and the bag was placed in an incubator at 37C. After 4 hours or 15 hours, the absorbent article was taken out of the bag and pressed with the fingers to organoleptically evaluate its gel stability according to the following four criteria.
A: Gel was not crumbled even by pressing strongly.
B: Gel was crumbled by pcessing strongly.
C: Gel was observed but readily crumbled.
D: No gel form was retained.
Comparative Examples 1 to 5 By using the water-absorbent resins obtained in ~t~
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the above Preparations 1 to 3 and commercially available water-absorbent resins, Arasorb* 720 (crosslinked poly-acrylic acid salt manu~actured and sold by Arakawa Chemical Co., Ltd., Japan) and Sanwet* IM-1000 (crosslinked starch-acrylic acid salt graft copolymer manufactured and sold by Sanyo Chemical Industries Co., J.td., Japan~, the above measurements of absorbency, evaluation of gel stability to a saline solution, and evaluation of gel stability to human urine were carried out. The results are shown in Table 1.
Comparative Example 6 A water-absorbent resin composition was prepared by thoroughly blending the water-absorbent resin powder (40.0 g) obtained in the above Preparation 2 with L-ascorbic acid powder (0.4 g). By using the water-absor~ent resin composition, the above measurement of absorbency, evaluation of gel stability to a saline solution, and evaluation of gel stability to human urine were carried out. However, no desired results could be obtained.

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Table 1 Comp. Water- Absorbency Evaluation of gel stability Ex. No. absorbent (g/g) resin Aqueous Aqueous Human urine 0.9% NaCl 0.9% NaCl 4 hrs.15 hrs. 4 hrs. 15 hrs. 4 hrs. 15 hrs.
1 Prep. 1 85 85 B B D D
2 Prep. 2 70 70 A A C D

3 Prep. 3 50 50 A A B C

4 Arasorb* 62 62 B B C D

Sanwet* 75 75 B B D D

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Examples l_t_ 24 Various water-absorbent resin compositions were prepared by thoroughly blending the water-absorbent reslns used in the above Comparative Examples with oxygen-containing reducing inorganic salts in various ratios. Byusing the water-absorbent resin compositions thus obtained, measurements of absorbency, evaluation of gel stability to a saline solution, and evaluation of gel stability to ~
human urine were carried out. The resuls are shown in -Tables 2A and 2B.
Example 25 A water-absorbent resin composition (40.5 g) was obtained by addition of sodium sulfite (0.4 g) to the polymerization mixture of the above Preparation 2. By using the water-absorbent resin composition thus obtained, an evaluation of gel stability to human urine was carried out. As a result, both evaluations after 4 hours and 15 hours were A.

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Table 2A
Ex. No. Water-absorbent resin composition Water- Oxygen-containing reducing absorbent inorganic salt resin Salt Amount (parts) 1 Prep. 1 sodium sulfite 0.5 2 Prep. 1 sodium dithionite , 1.5 3 Prep. 1 potassium nitrite4.0 4 Prep. 1 potassium pyrosulfite 1.5 Prep. 1 sodium bisulfite 4.0 ~ Prep. 2 potassium bisulfite 0.5 7 Prep. 2 sodium nitrite 4.5 8 Prep. 2 calcium nitrite 5.0 9 Prep. 2 sodium pyrosulfite 2.0 Prep. 2 potassium bisulfite 0.1 11 Prep. 3 sodium bisulfite 1.0 12 Arasor~ 720 potassium sulfite0.5 13 Arasorb 720 sodium dithionite3.5 14 Sanwet IM-1000 sodium sulfite 0.05 Sanwet IM-1000 sodium sulfite 1.0 Sanwet IM-1000 sodium sulfite 5.0 17 Prep. 1 potassium bisulfite 5.0 18 Prep. 1 sodium dithionite1.5 19 Prep. 2 sodium sulfite 4.0 Prep. 2 calcium nitrite 0.5 * Trade Mark ~ ~ -r . ~

Table 2A (continued) Ex. No. Water-absorbent resin composition Water- Oxygen-containing reducing absorbent inorganic salt resin Salt Amount (parts) 21 Prep. 3 sodium pyrosulfite 1.0 22 Prep. 3 sodium bisulfite 0.1 23 Arasorb 720 sodium sulfite 3.5 24 Sanwet IM-1000 sodium sulfite 2.0 Note: * parts by weight per 100 parSs by weight of the water-absorbent resin * Trade Mark " ~ , .:.:: ... .

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Table 2B
Ex. No. Absorbency Evaluation of gel stability (g/g) Aqueous Aqueous Human urine 0.9~ NaCl 0.9% NaCl 4 hrs. 15 hrs. 4 hrs. 15 hrs. 4 hrs. 15 hrs.
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Table 2B (continued) Ex. No. Absorbency Evaluation of gel stability (g/g) Aqueous Aqueous Human urine 0.9~ NaCl 0.9% NaCl 4 hrs. 15 hrs. 4 hrs. 15 hrs. 4 hrs. 15 hrs.

Note: ** variance in absorbency is larger, gel is more unstable.

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Examples_26 to 38 Various water-absorbent resin compositions were prepared by thoroughly blending the water-absorbent resins used in the above Comparative Examples with oxygen-containing reducing inorganic salts and organic anti-oxidants in various ratios. By using the water-absorbent resin compositions thus obtained, measurements of absor-bency, evaluation of gel stability to a saline solution, and evaluation of gel stability to human urine were carried out. The results are shown in Tables 3A and 3B.

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Table 3A
Ex. Water-absorbent resin compostion No.
Water Oxygen-containing Organic absorbent reducing antioxidant resin inorganic salt Salt Amount Compound Amount (parts) (parts) 26 Prep. 1 potassium 5.0 L-ascorbic 0.002 bisulfite acid 27 Prep. 1 sodium l.O L-ascorbic 0.02 sulfite acid 28 Prep. l ammonium 2.8 zinc ethyl- 1.3 pyrosulfite phenyldithio-carbamate 29 Prep. 2 sodium 4.0 phenothiazine 0.8 sulfite Prep. 2 sodium l.O n-propyl 5.0 sulfite gallats 31 Prep. 2 calcium 0.5 n-propyl l.O
nitrite gallate 32 Prep. 2 calcium 4.7 n-propyl l.O
nitrite gallate 33 Prep. 3 sodium l.O mercapto- 0.3 pyrosulfite benzothi-azole 34 ~rep. 3 sodium 0.1 2-mercapto- 0.1 bisulfite benzimidazole Arasorb potassium 3.5 tetramethyl-3.0 - 720 sulfite thiuram disulfide 36 Arasorb sodium l.l sodium 4.8 720 dithionite formaldehyde sulfoxylate * Trade Mark f~
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Table 3A (continued) Ex. Water-absorbent resin compostion No.
Water Oxygen-containing Organic absorbent reducing antioxidant resin inorganic salt Salt Amount Compound Amount (parts) (parts) 37 Sanwe~ sodium 2.0 sodium 0.005 IM-1000 sulfite isoascorbate 38 Sanwe~ sodium 2.0 sodium 0.1 IM-1000 sulfite isoascorbate Note: * parts by weight per 100 parts by weight of the water-absorbent resin * Trade Mark ,. . , , ':

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Ex. No. Absorbency** Evaluation of gel stability (g/g) Aqueous Aqueous Human urine 0.9% NaCl 0.9% NaCl 4 hrs. 15 hrs. 4 hrs. 15 hrs. 4 hrs. 15 hrs.

Note: ** variance in absorbency is larger, gel is ~ore unstable.

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`` $ ~ `5`33 ~ $ '~' 8 As seen from Tables 1, 2A and 2B, the water-absorbent resin composition of the present invention comprising the water-absorbent resin and the oxygen-containing reducing inorganic salt has superior gel stability to body fluids in comparison with the water absorbent resin alone. Further, as seen from Table 1, 3A and 3B, the water-absorbent resin composition of the present invention comprising the water-absorbent resin, the oxygen-containing reducing inorganic salt and the organic antioxidant has superior gel stability to both body fluids and an aqueous solution containing an electrolyte in comparison with the water absorbent resin alone.

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Claims

1. A water-absorbent resin composition which comprises crosslinked polyacrylic acid salts, crosslinked copolymers of vinyl alcohol-acrylic acid salt, crosslinked saponification products of starch-acrylonitrile graft copolymer, crosslinked starch-acrylic acid salt copolymer, crosslinked products of polyvinyl alcohol grafted with maleic anhydride, or crosslinked carboxymethyl cellulose alkali metal salts and at least one oxygen-containing reducing inorganic salt selected from the group consisting of sulfites, bisulfites, pyrosulfites, dithionites, trithionates, tetrathionates, thiosulfates, and nitrites.

2. A water-absorbent resin composition according to claim 1, wherein the composition contains the oxygen-containing reducing inorganic salt in an amount of 0.001 to 10 parts by weight per 100 parts by weight of the water-absorbent resin.

3. A water-absorbent resin composition which comprises:
(a) crosslinked polyacrylic acid salts, crosslinked copolymers of vinylalcohol-acrylic acid salt, crosslinked saponification products of starch-acrylonitrile graft copolymer, crosslinked starch-acrylic acid salt copolymer, crosslinked products of polyvinylacohol grafted with maleic anhydride, or crosslinked carboxymethyl cellulose alkali metal salts;
(b) at least one oxygen-containing reducing inorganic salt selected from the group consisting of sulfites, bisulfites, pyrosulfites, dithionites, trithionates, tetrathionates, thiosulfates, and nitrites; and (c) at least one organic antioxidant selected from the group consisting of ascorbic acid and its derivatives, gallic acid and its derivatives, benzothiazoles, dithionates, thiurams, benzimidazoles, formaldehyde sulfoxylates and phenothiazines.

4. A water-absorbent resin composition according to claim 3, wherein the composition contains the oxygen-containing reducing inorganic salt in an amount of 0.001 to 10 parts by weight per 100 parts by weight of the water-absorbent resin.

5. A water-absorbent resin composition according to claim 3, wherein the composition contains the organic antioxidant in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the water-absorbent resin.