JPH01210463A - Water-absorptive resin composition of excellent stability - Google Patents

Abstract

PURPOSE:To obtain the title resin composition which can retain good water- absorptive performances and is improved in gel strength upon swelling an long- term stability of swollen gel, by mixing a water-absorptive resin with a radical chain inhibitor and a metal chelating agent in a specified ratio. CONSTITUTION:A water-absorptive resin composition is obtained by mixing a resin formed by crosslinking a water-absorptive resin, for example, polyactylate with N-N'-methylene-bisacrylamide with a radical chain inhibitor (A) such as a gallic ester or thiourea (preferably one having a solubility in water at 25 deg.C of 0.1g/100g or above) and a chelating agent (B) such as citric acid or 1,10-phenanthroline. It is preferable that the content of each of components A and B in the composition is 0.1-10wt.% based on the dry resin, and the total of components A and B is 10% or below. This composition can be desirably used as water-retaining agents for agriculture and horticulture, water cut-off agents for civil engineering and building, dehydrating agents, sanitary napkins, disposable diapers, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] 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.

Generally, the performance of water-absorbing resins 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, JP-A-57-158210, JP-A-59-62665, JP-A-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, and as the gel strength increases, 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 will no longer retain its form within a few hours, and its water absorbing and water retaining functions will be lost. Furthermore, a water-absorbing resin that has swollen after absorbing urine may also undergo similar deterioration, and may no longer be able to maintain its swollen gel form.

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, the present invention was achieved.

That is, the present invention contains a water-absorbing resin, a radical chain inhibitor, and a metal chelating agent as essential components, and the content of the radical chain inhibitor is 0.01% based on the dry water-absorbing resin.
The present invention provides a highly stable water absorbent resin composition characterized in that the metal chelating agent content is 0.01 to 10 weight percent based on the dry water absorbent resin. be.

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 M 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 regarding the polymerization method or copolymerization components.

Next, the radical chain inhibitor used in the present invention may be any compound having the ability to inhibit radical chains, and examples thereof include conventionally known antioxidants, polymerization inhibitors, radical scavengers, and the like. Among these radical chain inhibitors, especially 25°
It is desirable that C dissolves 1 g or more of O per 100 g of water.

Such radical chain inhibitors include those obtained from hydroquinone, p-methoxyphenol, benzoquinone, methylhydroquinone, L-butylhydroquinone, pyrogallol, gallic acid, methyl gallate, ethyl gallate, propyl gallate, pentate or gallic acid. Tannic acid and its salts, lignin sulfonates, such as hydrolyzed tannins obtained from the United States and condensed tannins obtained from Gambia, etc.
Preferred examples include flavonoids and their salts such as quercetin and ellagic acid, phenolic compounds and their derivatives such as catechol and resorcin, amine compounds such as N-nitrosophenylhydroxyamine ammonium salts, and thiourea. It is not limited to.

Among these, particularly preferred are pyrogallol, gallic acid, gallic acid ester, tannic acid, flavonoids, thiourea, and the like.

These may be used alone or in combination of two or more.

Next, examples of the metal chelating agent used in the present invention include compounds having metal chelating ability and having a bidentate or higher ligand that binds to metal ions to form a chelate compound. Among these, those having a solubility of 0.1 g or more in 100 g of water at 25° C. are particularly desirable. Such metal chelating agents include, for example, inorganic acids such as phosphoric acid; oxycarboxylic acids such as tartaric acid, gluconic acid, citric acid, and salicylic acid; dioxylic acids such as glycol and glycerin; ethylenediamine, 1,10-phenanthroline, 2 .2-Amine compounds such as bipyridine and terpyridine; condensed phosphates such as tripolyphosphate; ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid,
Examples include, but are not limited to, polyaminocarboxylic acids such as triethylenetetramine hexaacetic acid and ethylenediaminebis0-hydroxyphenylacetic acid, and salts thereof; and dicarboxylic acids such as oxalic acid. These may be used alone or in combination of two or more.

The present invention significantly improves the stability of a swollen gel over time by incorporating specific amounts of the above-mentioned radical chain inhibitor and metal chelating agent into a water-absorbing resin, without reducing water-absorbing performance and gel strength during swelling. It is something.

The content of the radical chain inhibitor (a) and the metal chelating agent (b) in the composition of the present invention is in the range of 0.01 to 10% by weight, respectively, based on the dry water absorbent resin. (a
If the content of component () and (b) is less than 0.01% by weight, the above-mentioned effect of improving stability against light, heat, oxygen oxidation, etc. will be poor, and if it exceeds 10% by weight, water absorption will be reduced. The water absorption performance of the resin composition decreases, which is not the intention of the present invention.

In addition, radical chain inhibitor (a) and metal chelating agent (b)
) can be arbitrarily selected within the above range, but the total amount of components (a) and (b) is preferably 15% by weight or less, more preferably 10% by weight based on the dry water absorbent resin. It is as follows.

In the present invention, the method of adding the radical chain inhibitor and metal chelating agent is not particularly limited as long as it does not interfere with the production of the resin, and these additives are directly added during or after the production process of the water absorbent resin. , or by adding a solution in a solvent capable of dissolving them, preferably water, ethanol, etc., mixing, and then drying.

[For production]

In this way, the water-absorbing resin composition of the present invention containing a specific amount of a radical chain inhibitor and a metal chelating agent,
The stability of the swollen gel state after water absorption is significantly improved, and this form can be maintained for a long period of time.

The effects of these two different types of components can be considered as follows.

In other words, even if radical species are generated due to the action of light, heat, oxygen, etc., the radical chain inhibitor effectively captures them, and metal chelates can remove trace amounts of transition metals derived from resins, urine, etc. Since the agent effectively captures these metals, the generation of radical species is suppressed, which is thought to prevent undesirable reactions such as decomposition and cutting of the resin caused by these radical species. .

〔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 is dispersed in a large excess of physiological saline, allowed to swell sufficiently, and then filtered through an 80-mesh wire mesh, the weight (W) of the swollen resin obtained is measured, and this value is calculated as that of the unswollen, i.e. This is the value obtained by dividing by the initial resin weight (IAo).

In other words, water absorption amount (g/g) = W/Wo.

In addition, 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, the stability of the swollen gel was evaluated using light and heat as follows.

Evaluation of Light Resistance> A resin that had been swollen to equilibrium saturation with ion-exchanged water was placed in a glass bottle, and an acceleration test was conducted by adding a small amount of iron ions. That is,
Add and mix an aqueous solution of ferrous sulfate FeSO4.7!1□0 (amount of 11,000 pp per dry resin) dissolved in a small amount of ion-exchanged water to the above resin. An irradiation test was conducted using a Model B (manufactured by Suga Test Instruments) (inner temperature 60°C), and the appearance of the gel was observed over time.

Heat Resistance Evaluation> The resin was saturated and swollen with ion-exchanged water and placed in a glass bottle, and the state of the gel was orally observed in a thermostat at 80°C.

The evaluation scale for the light resistance and heat resistance 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 resins (1) and (n)) 2 equipped with a stirring device, reflux condenser, dropping funnel, and nitrogen gas introduction pipe
! - 1.150a of cyclohexane in a round bottom flask for 4 days
Z, 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 dissolved in 200 g of ion-exchanged water while cooling from the outside.
Neutralized with 8% caustic soda. Then potassium persulfate 0.
33g and N,N'-methylenebisacrylamide 0.
After adding and dissolving 015 g, the mixture was transferred to the above-mentioned dropping funnel. This was added dropwise to the above-mentioned 4-hole flask over 1 hour. Even after the dropwise addition was completed, the temperature was kept at 75°C and the reaction continued for 1 hour. 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 (
II) was obtained.

Example 1 100g of water-absorbing resin (If) was placed in a double-arm kneader, and while stirring, 1g of citric acid and 0% of propyl gallate were added.
．． An aqueous solution of 1 g dissolved in 100 g water was sprayed. These resins were then dried under reduced pressure.

Example 2 100 g of water-absorbing resin (I) (however, the amount converted to the dry product) was placed in a double-arm kneader, and a solution of 0.1 g of 1.10-phenanthroline and 5 g of thiourea dissolved in 100 g of ethanol was added. , stirred and mixed.

These resins were then dried under reduced pressure.

Comparative Example 1 Comparative Example 1 was a water-absorbing resin (n) to which neither a radical chain inhibitor nor a metal chelating agent was added.

Comparative Example 2 100g of water absorbent resin (II) was placed in a double-arm kneader,
While stirring, an aqueous solution of 1 g of citric acid dissolved in 100 g of water was sprayed. These resins were then dried under reduced pressure.

Comparative Example 3 100 g of a water-absorbing resin <n) was placed in a double-arm kneader, and an aqueous solution of 0.1 g of propyl gallate dissolved in 100 g of water was sprayed with stirring. These resins were then dried under reduced pressure.

Comparative Example 4 100 g of water absorbent resin (1) (the amount calculated as a dry product) was placed in a double-arm kneader, and a solution of 0.1 g of l,10-phenanthroline dissolved in 100 g of ethanol was added and stirred. These resins were then dried under reduced pressure.

Comparative Example 5 100g of water absorbent resin (1) (however, the amount converted to dry product) was placed in a double-arm kneader, and 5g of thiourea was added to 100g of water absorbent resin (1).
A solution of 5 g dissolved in ethanol was added and mixed with stirring.

These resins were then dried under reduced pressure.

Example 3 100 g of water absorbent resin (I) (however, the amount converted to dry product) was placed in a double-arm kneader, and 0.25 g of a 40% aqueous solution of diethylenetriamine pentaacetic acid/Na salt and 0.1 g of propyl gallate were added. An aqueous solution dissolved in 100 g of water was added and stirred. These resins were then dried under reduced pressure.

Example 4 100g of water absorbent resin (1) (however, the amount converted to dry product) was placed in a double-arm kneader, and 0.1g of triethylenetetramine hexaacetic acid and 0.1g of propyl gallate were added to 10g of water absorbent resin (1).
An aqueous solution dissolved in 0 g of water was added and stirred. after that,
These resins were dried under reduced pressure.

Comparative Examples 6-7 100 g of water absorbent resin (1) (however, the amount converted to the dry product) was placed in a double-arm kneader, and 0.25 g of a 40% aqueous solution of diethylenetriamine pentaacetic acid/Na salt was added (Comparative Example 6)
or triethylenetetramine hexaacetic acid 0.1g (Comparative Example 7
) dissolved in 100 g of water was added and stirred.

These resins were then dried under reduced pressure.

The water absorbent resin compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 7 were evaluated for water absorption amount, water absorption rate, light resistance, and heat resistance. 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 absorption properties and durability.

〔Effect of the invention〕

As specifically shown in the examples, the water-absorbing resin composition of the present invention has excellent water-absorbing performance, and also has good stability of the gel shape when swollen, even under the effects of light, heat, and the like.

Therefore, the water-absorbing resin composition of the present invention can be suitably used for applications such as water retention agents for agriculture and horticulture, water supply materials for civil engineering and construction, dehydration agents, and absorbent materials for sanitary products such as sanitary napkins and disposable diapers. can.

Claims (1)

[Claims] 1. Contains a water absorbent resin, a radical chain inhibitor, and a metal chelating agent as essential components, and the content of the radical chain inhibitor is 0.01 to 10% by weight based on the dry water absorbent resin.
A highly stable water-absorbing resin composition, characterized in that the content of the metal chelating agent is 0.01 to 10% by weight based on the dry water-absorbing resin. 2. The water-absorbing resin composition with excellent stability according to claim 1, wherein the water-absorbing resin is a crosslinked polyacrylate.