JPH01223161A - Water-absorptive resin composition - Google Patents

Abstract

PURPOSE:To obtain the title composition with high water absorptivity, excellent in gel strength when swollen and stability with time of the swollen gel therefrom, thus suitable for absorptive materials for hygienic articles etc., by incorporating a water-absorptive resin with a specified amount of a reductive substance. CONSTITUTION:The objective composition comprising, as the essential components, (A) a water-absorptive resin, pref. a polyacrylic acid salt crosslinked form and (B) a reductive substance, pref. a compound selected from sulfur-contg. inorganic compounds and marcaptan compounds. This composition can be obtained by the following process: 0.01-10pts.wt., based on 100pts.wt. of the component A (on a dry basis), of the component B is incorporated in the component A directly or in the form of an aqueous or ethanol (or the like) solution, and furthermore, if needed, followed by incorporation of a phenolic antioxidant, a radical chain reaction inhibitor, a metal chelating agent etc. The resultant blend is then dried.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a water-absorbing resin composition that quickly absorbs a large amount of aqueous liquid and has excellent stability in a swollen state.

More specifically, the present invention relates to a highly stable water-absorbing resin composition that can maintain a swollen gel state after absorbing an aqueous liquid for a long time under normal usage conditions.

[Conventional technology]

In recent years, water-absorbent resins with excellent water absorption and water retention properties have been developed, which absorb and retain large amounts of water.They are used in sanitary products such as sanitary napkins and disposable diapers, and in agriculture and horticulture as water retention agents, etc. In the construction field, it is widely used as a sludge coagulant, anti-condensation agent, water-stopping agent, etc.

Examples of such water-absorbing resins include hydrolysates of starch-acrylonitrile graft polymers, starch-acrylic acid graft polymers, hydrolysates of vinyl acetate-acrylic acid ester copolymers, and crosslinked polyacrylates. , carboxymethylated cellulose, etc. have been proposed.

-m, the performance of the water-absorbing resin is evaluated by water absorption amount, water absorption rate, gel strength when swollen, etc. Among these, many proposals have been made for improving water absorption performance such as water absorption amount and water absorption speed (for example, Japanese Patent Application Laid-Open Nos. 57-158210, 59-62665, and 61-973).
Publication No. 01, etc.).

On the other hand, the gel strength during swelling has a negative correlation with the amount of water absorption; for example, if the gel strength is increased by increasing the crosslinking density, the amount of water absorption tends to decrease. An ideal water-absorbing resin would be one that satisfies both the above-mentioned water-absorbing performance and gel strength upon swelling, but at present such a resin has not yet been obtained.

[Problem to be solved by the invention]

When the water-absorbing resin described above absorbs water and becomes a swollen gel, it is not only subject to mechanical forces such as swelling pressure, but also environmental factors such as exposure to high temperatures or sunlight, and even oxygen in the air. There is a problem that the gel-like resin deteriorates due to factors such as the influence of. In extreme cases, the swollen gel can no longer maintain its shape within a few hours and loses its water-absorbing and water-retaining functions.A similar deterioration occurs even with the water-absorbent resin used in disposable diapers that absorbs urine and swells. may occur, and the swollen gel form may not be maintained.

Such a phenomenon becomes a major hindrance when water-absorbing resins are used for various purposes, and there is a desire to develop water-absorbing resins with excellent stability of swollen gels over time.

[Means to solve the problem]

The present inventors have made extensive studies in order to solve the above-mentioned problems and obtain a water-absorbing resin that maintains good water-absorbing performance and has excellent gel strength during swelling and stability of the swollen gel over time. As a result, it was discovered that the above object can be achieved by incorporating a specific amount of a reducing substance into a water-absorbing resin, leading to the present invention.

That is, the present invention contains a water-absorbing resin and a reducing substance as essential components, and the content of the reducing substance is 6.01 to 10 parts by weight based on 100 parts by weight of the dry water-absorbing resin. The present invention provides a water absorbent resin composition characterized by:

The present invention will be explained in detail below.

Examples of water-absorbing resins that can be used in the present invention include hydrolysates of starch-acrylonitrile graft polymers, starch-acrylic acid graft polymers,
Examples include vinyl acetate-acrylic acid ester copolymer hydrolyzate, polyacrylate crosslinked product, isobutylene-maleic anhydride copolymer crosslinked product, carboxymethylated cellulose, etc., and these are preferable for the present invention. Can be used. Particularly preferred is a crosslinked polyacrylate from the viewpoint of water absorption performance, and there are no particular limitations on the polymerization method or copolymerization components.

In the present invention, the water-absorbing resin as described above is made to contain a specific amount of a reducing substance.

Conventionally, when producing water absorbent resins, it has been known to use reducing agents such as sulfites and hydrogen sulfites together with oxidative radical polymerization initiators to act as redox polymerization initiators. This is based on the discovery that water-absorbing resin compositions obtained by incorporating a reducing substance into water-absorbing resins produced by various methods have excellent stability of swollen gels over time.

The reducing substance used in the present invention may be any substance that has a reducing effect, and includes, for example, sulfur-containing inorganic compounds such as sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, and sodium dithionite; cysteine;
Examples include mercaptan compounds such as glutathione, thioglycolic acid, and 2-mercaptoethanol; aldehydes such as formaldehyde and acetaldehyde; sugars, formic acid, and Schellaic acid. Among these, those selected from sulfur-containing inorganic compounds and mercaptan compounds are preferred.

Each of the above reducing substances may be used alone, or two or more types may be used in combination.

The content of the reducing substance in the composition of the present invention is 0.01 to 10 parts by weight based on 100 parts by weight of the dry water absorbent resin. If it is less than 0.01 parts by weight, the effect of improving stability will be poor, and if it exceeds 10 parts by weight, the water absorption performance will decrease, which is not the intention of the present invention.

The method of adding the reducing substance is not particularly limited, but it may be added directly to the water-absorbing resin, or by adding a solution in a solvent that can dissolve them, preferably water, ethanol, etc. This is achieved by drying after mixing.

The water-absorbing resin composition of the present invention has a water-absorbing resin and a reducing substance as essential components, but may contain other additives as necessary.

Among them, radical chain inhibitors such as phenolic antioxidants, gallic acid, gallic acid esters, tannic acid, and flavonoids; and metal chelating agents such as phosphoric acid, condensed phosphates, oxycarboxylic acids, and polyaminocarboxylic acids are used in combination. There is an advantage that the stabilizing effect of the swollen gel, which is the object of the present invention, is enhanced.

[For production]

In this way, the water-absorbing resin composition of the present invention containing a specific amount of a reducing substance has significantly improved stability in the state of a swollen gel after water absorption, and can maintain that form for a long period of time. Can be done.

The effect of the present invention is to suppress the oxidation-reduction reaction of minute amounts of transition metals, such as iron, which are present inside the swelling gel and are derived from the resin or absorbed aqueous liquid, and these metals intervene to generate radicals. This is thought to prevent the generation of seeds and the occurrence of undesirable reactions such as decomposition and cutting of the resin. Therefore, it is thought that the magnitude of the oxidation-reduction potential between the transition metal such as iron and the reducing substance used is related to the effect of the present invention, but the details are not clear.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Synthesis Examples, Examples, and Comparative Examples, but the present invention is not limited to these Examples.

In addition, the amount of water absorption in the following examples and comparative examples is a value determined by the following operation.

That is, 1 g of the resin was dispersed in a large excess of physiological saline, allowed to swell sufficiently, and then filtered through an 80-mesh wire mesh. This is the value obtained by dividing by the resin weight (-〇).

In other words, water absorption amount (g/g) -11/W. It is.

Moreover, the water absorption rate was expressed as the amount of physiological saline absorbed by 1 g of resin in 20 minutes.

On the other hand, stability was evaluated in an accelerated test by adding a small amount of iron.

That is, 300 ppm ferrous sulfate Fe5On” 7H
The resin, which had been swollen to equilibrium saturation with physiological saline in which tO was dissolved, was placed in a glass bottle, and the appearance of the gel was observed over time in a 40°C constant temperature bath.

The stability evaluation scale was set to the following three levels.

O: The swollen particles maintain their original shape.

Δ...Dissolution does not occur, but the shape of the swollen particles becomes unclear.

×: Partial dissolution occurred and liquid was observed.

Synthesis Example 1 (Synthesis of water absorbent resin (1), (If)) 2 equipped with a stirring device, reflux condenser, dropping funnel, and nitrogen gas introduction pipe
1.150 m of cyclohexane in a round bottom flask,
Ethyl cellulose N-200 (manufactured by Vercules) 9
．． 0 g was charged, nitrogen gas was blown in to drive out dissolved oxygen, and the temperature was raised to 75°C.

Separately, in a flask, 150 g of acrylic acid was cooled externally and neutralized with 65.8 g of 98% caustic soda dissolved in 200 g of deionized water, followed by potassium persulfate.
．． 33g and N,N'-methylenebisacrylamide 0.
After adding and dissolving 0.015 g, the mixture was transferred to the above-mentioned dropping funnel.

This was added dropwise to the above-mentioned 4-hole flask over a period of 1 hour. Even after the completion of 0 dropwise addition, the reaction was continued for 1 hour while maintaining the temperature at 75°C. The water-containing water-absorbing resin dispersed in this solvent is added to the water-absorbing resin (1
).

Thereafter, the cyclohexane was distilled off under reduced pressure, and the remaining water-containing water-absorbent resin was dried under reduced pressure to form a powdery water-absorbent resin (
n) was obtained.

Synthesis Example 2 (Synthesis of water-absorbing resin (III)) In Synthesis Example 1, N
, Bunacol I instead of N'-methylenebisacrylamide! Synthesis and drying were carried out according to Synthesis Example 1 except that 0.038 g of X-810 (ethylene glycol diglycidyl ether manufactured by Nagase Sangyo ■) was used, and water absorbent resin (II
I) was obtained.

Example 1 100 g of water-absorbing resin (I) (in terms of dry product) was placed in a double-arm Nigu, and while stirring, 100 g of a 1.0% by weight aqueous solution of sodium bisulfite was added and mixed with stirring. Thereafter, the resin was filtered off and dried under reduced pressure.

Example 2 100g of water-absorbing resin (II) was placed in a double-armed knee gun,
While stirring, add 1.0% by weight aqueous solution of sodium sulfite.
00g was sprayed and mixed with stirring. Thereafter, it was dried under reduced pressure.

Example 3 100g of water-absorbing resin (In) was put into a double-armed knee gun,
While stirring, 200 g of a 1.0% by weight cysteine ethanol solution was added and mixed with stirring. Thereafter, the resin was filtered off and dried under reduced pressure.

The water absorbent resin compositions obtained in Examples 1 to 3 above were evaluated for water absorption amount, water absorption rate, and stability. Display the results -
Shown in 1.

Comparative Example 1.2 Water-absorbing resin without adding reducing substances (■) (Comparative Example 1)
The water absorbent resin (■) (Comparative Example 2) was evaluated for water absorption amount, water absorption rate, and stability in the same manner as in the examples.

The results are shown in Table-1.

Comparative Example 3 A water absorbent resin was synthesized and dried in the same manner as in Synthesis Example 2, except that the amount of Bunacol IEX-810 used was 0.15 g, and the crosslinking density was increased compared to the water absorbent resin (III). A water absorbent resin (IV) was obtained, and its water absorption amount, water absorption rate, and stability were evaluated in the same manner as in the examples.

The results are shown in Table-1.

Table 1 From the results shown in Table 1, it is clear that the water absorbent resin composition of the present invention has excellent water absorption performance and excellent stability of the swollen gel.

In addition, although the water-absorbing resin shown in Comparative Example 3 with only an increased crosslinking density slightly improves the stability of the swollen gel, both the water absorption amount and the water absorption rate decrease, which is not suitable for the purpose of the present invention. do not.

〔Effect of the invention〕

As is clear from the results of the Examples, the water-absorbing resin composition of the present invention has excellent water-absorbing performance and stability of the swollen gel.

Therefore, it can be suitably used for applications such as water retention agents for agriculture and horticulture, water stop materials for civil engineering and construction, dehydration agents, and absorbent materials for sanitary products such as sanitary napkins and disposable diapers.

Applicant's agent Kaoru Furutani

Claims (1)

[Claims] 1. Water-absorbing resin 10 that contains a water-absorbing resin and a reducing substance as essential components and has a dry content of the reducing substance.
A water-absorbing resin composition characterized in that the amount is 0.01 to 10 parts by weight relative to 0 parts by weight. 2. Claim 1, wherein the reducing substance is selected from the group consisting of sulfur-containing inorganic compounds and mercaptan compounds.
The water absorbent resin composition described above. 3. The water-absorbing resin composition according to claim 1 or 2, wherein the water-absorbing resin is a crosslinked polyacrylate.