JPH04120111A - Water absorbing resin composition and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject composition excellent in safety and useful as sanitary materials, etc., by adding a reducing substance and a radical scavenger to a specified water absorbing resin, e.g. at a stage of drying after polymerization and reducing remaining monomers, etc. CONSTITUTION:To a water absorbing resin obtained by polymerization of a water-soluble monomer such as (meth)acrylic acid, a polysaccharide such as starch and/or a crosslinking agent such as bis(meth)acrylamide, one or more reducing substance selected from sulfites, bisulfites, ferrous iron, ascorbic acid, amines and reducing sugars and a radical scavenger such as hydroquinone are added respectively in an amount of 0.001-5wt.% based on the total amount of the monomer and the crosslinking agent at an arbitrary stage such as drying or crushing after polymerization so as to reduce the remaining monomer content and the water-soluble component content respectively to <=500ppm and <=7wt.%. An objective composition is obtained thereby. In addition, the ratio of the reducing substances to the radical scavenger is preferably (1/0.01-3) on weight base.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a water-absorbing resin composition and a method for producing the same. More specifically, the present invention relates to a water-absorbing resin composition with a reduced residual monomer content and a reduced amount of water-soluble components, and a method for producing the same.

[Prior Art] Conventionally, methods such as addition of reducing substances, addition of peroxides and/or azo compounds, and ultraviolet irradiation have been proposed as methods for reducing residual monomers in water-absorbing resins.

[Problems to be Solved by the Invention] However, although these methods can reduce residual monomers, at the same time as the addition reaction and repolymerization reaction due to the generation of radical species, the main chain polymer of the water-absorbing resin due to the generated excess radicals. It causes side reactions such as cleavage of , cleavage of crosslinking points, etc.

As a result, there are problems such as a decrease in absorption capacity due to a decrease in the molecular weight of the water-absorbing resin and an increase in the amount of water-soluble components.

[Means for Solving the Problems] The present inventors have made extensive studies to solve the above problems, and as a result, have discovered the present invention.

That is, the present invention adds a reducing substance and a radical scavenger to a water-absorbing resin obtained by polymerizing a water-soluble monomer, a polysaccharide, and/or a crosslinking agent at any stage of drying or pulverization after polymerization. A method for producing a water absorbent resin with a reduced residual monomer content and a reduced amount of water-soluble components; and a water-absorbent resin composition obtained by polymerizing a water-soluble monomer, a polysaccharide, and/or a crosslinking agent. , containing a reducing substance and a radical scavenger at any stage of drying or pulverization after polymerization, and having a residual monomer content of 500 ppm or less and a water-soluble component amount of 7x or less. In the resin composition of the present invention, water-soluble monomers include monomers that are water-soluble or become water-soluble by hydrolysis. Examples of water-soluble monomers include acid group-containing polymerizable monomers containing carboxylic acid groups, polymerizable monomers containing sulfonic acid groups, and polymerizable monomers containing phosphoric acid groups. Monomers and salts thereof are included.

Examples of the polymerizable monomer containing a carboxylic acid group include unsaturated mono- or polycarboxylic acids [(meth)acrylic acid (referring to acrylic acid and/or methacrylic acid. The same description will be used hereinafter), ethacrylic acid , crotonic acid, sorbic acid, maleic acid, itaconic acid, cinnamic acid, and their anhydrides [maleic anhydride, etc.].

Examples of polymerizable monomers containing sulfonic acid groups include fatty acids or aromatic vinylsulfonic acids (vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, etc.), (meth)acrylsulfonic acid [(meth) ) sulfoethyl acrylate, sulfopropyl (meth)acrylate, etc. (meth)acrylamide sulfonic acid [2-acrylamido-2-methylpropanesulfonic acid, etc.].

As a polymerizable monomer containing a phosphate group, (meth)
Acrylic acid hydroxyalkyl phosphate monoester [2
-hydroxyethyl (meth)acryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate and the like.

Monomers containing these acid groups may be used alone (
, or two or more types may be used in combination.

Among these, preferred are polymerizable monomers containing a carboxylic acid group or a sulfonic acid group, and particularly preferred are polymerizable monomers containing a carboxylic acid group.

Monomers containing acid groups can also be used as water-soluble salts, examples of which include alkali metal salts (salts such as sodium, potassium, lithium, etc.), alkaline earth metal salts (salts such as calcium, magnesium, etc.). ), ammonium salts and amine salts (alkylamine salts such as methylamine and trimethylamine; alkanolamine salts such as triethanolamine and jetanolamine), and two or more thereof. Preferred among these are sodium and potassium salts.

The degree of neutralization of monomers containing acid groups is 5% of the acid groups in the polymer.
It is 0 to 90 mol%, preferably 60 to 80%.

When the degree of neutralization is less than 50%, the resulting hydrogel polymer has high stickiness, making it difficult to produce a water absorbent resin with good workability. If it exceeds 30 mol%, the pl of the obtained polymer
'l becomes high, which poses a problem in terms of safety for human skin.

This neutralization may be performed at any stage of producing the water-absorbing resin, for example, neutralization at the stage of polymerizable monomers, or neutralization at the state of a hydrogel which is a polymerization product. There is a way.

Examples of monomers that become water-soluble through hydrolysis are (
Examples include meth)acrylonitrile, alkyl esters of unsaturated carboxylic acids, (meth)acrylamide, and vinyl acetate.

In the present invention, cationic water-soluble monomers having a tertiary amine group or a quaternary ammonium base can also be used.

Examples of tertiary amine group-containing monomers include dialkylaminoalkyl (meth)acrylate, dialkylaminohydroxyalkyl (meth)acrylate, dialkylaminoalkyl (meth)acrylamide, and dialkylaminehydroxyalkyl (meth)acrylamide. It will be done.

Examples of the monomer containing a quaternary ammonium group include a reaction product of the monomer containing a tertiary amine group and an alkyl halide or dialkyl sulfuric acid, ethylkylvinylpyridinium halide, trialkylallylammonium halide, etc. .

In the present invention, examples of polysaccharides include starch and cellulose. Examples of starch include modified starches such as sweet potato starch, potato starch, wheat starch, corn starch, and rice starch: oxidized starch, dialdehyde starch, alkyl etherified starch, starch etherified with starch, alkylated starch oxene, and aminoethyl ether. Examples include modified starches such as modified starches.

Examples of cellulose include cellulose obtained from wood, leaves, stems, gin bark, seed hair, etc.; and processed cellulose such as alkyl etherified cellulose, acid esterified cellulose, oxidized cellulose, and hydroxyalkyl etherified cellulose.

The amount of polysaccharide relative to water-soluble monomer is usually θ on a weight basis.
-30%, preferably 3-20%. If the amount of polysaccharide exceeds 30%, the absorption performance of the obtained water absorbent resin will decrease.

In the present invention, the crosslinking agent includes (1) a compound having at least two polymerizable double bonds and (2) a functional group having at least one polymerizable double bond and reactive with the monomer. Examples include compounds having a small number of (both 1).

Examples of the compound (1) include the following.

■Bis(meth)acrylamide: N,N'-alkylene (CI"Ca)bis(meth)
Acrylamide such as N,N'-methylenebisacrylamide.

■Di- or polyester of polyols and unsaturated mono- or polycarboxylic acids: Polyols [ethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol,
Di- or tri-(meth)acrylic esters such as polyoxypropylene glycol: Unsaturated polyesters [co- and di- or tri-(meth)acrylic esters obtained by reaction of the above polyols with unsaturated acids such as maleic acid [ obtained by the reaction of polyepoxide and (meth)acrylic acid], etc.

■Carbamyl ester: Polyisocyanate [tolylene diisocyanate, hexamethylene diinsinate, 4,4'-diphenylmethane diisocyanate and NCO group-containing prepolymer (
(obtained by the reaction of the above-mentioned polyinsinate with an active hydrogen atom-containing compound) and the like, and a carbamyl ester obtained by the reaction of hydroxyethyl (meth)acrylate.

■ Polyvinyl compounds such as divinylbenzene, divinyltoluene, divinyl ether, divinyl ether, divinyl ketone, trivinylbenzene, etc.

■Di- or poly(meth)allyl ether of polyols: Polyols [alkylene glycol, glycerin, polyalkylene glycol, polyalkylene polyol,
Di- or poly-(meth)allyl ethers such as hydrocarbons such as polyethylene glycol diallyl ether and allylated starches, allylated celluloses.

■ Di- or poly-allyl ester of polycarboxylic acid: diallyl phthalate, diallyl adipate, etc.

■Esters of unsaturated mono- or poly-carboxylic acids and mono(meth)allyl ethers of polyols (meth)acrylic acid esters of polyethylene glycol monoallyl ethers, etc.

■Allyloxyalkanes: Tetraallyloxyethane etc.

The compound (2) includes groups reactive with (meth)acrylic acid and/or other copolymerizable monomers, such as carboxyl groups, groups reactive with carboxylic acid anhydride groups (hydroxyl groups, epoxy groups, cationic groups, etc.). ethylenically unsaturated compounds containing (e.g., chemical groups). Specifically, unsaturated compounds containing nonionic groups, such as unsaturated compounds containing hydroxyl groups [co- and epoxy group-containing unsaturated compounds such as tomethylol (meth)acrylamide [glycidyl (meth)acrylate, etc.], and unsaturated compounds containing cationic groups. Saturated compounds, such as quaternary ammonium base-containing unsaturated compounds [1
f,N,N-trimethylto(meth)acryloyloxyethyltrimethylammonium chloride, N,N,N
-) riethyl-N-(meth)acryloyloxyethylammonium chloride, etc., and unsaturated compounds containing a tertiary amino group [dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, etc.]. .

Two or more of the above crosslinking agents (1) and (2) may be used in combination.

Among the crosslinking agents, preferred are the crosslinking agents (1), and more preferred are bis(meth)acrylamide, di- or polyesters of polyols and unsaturated monocarboxylic acids, and allyloxyalkanes. Particularly preferred are N,N'-methylenebisacrylamide, ethylene glycol diacrylate, trimethylolpropane triacrylate and tetraallyloxyethane.

The amount of crosslinking agent is usually 0.0001-10%, preferably 0.000%, based on the total weight of water-soluble monomer and crosslinking agent.
It is 1 to 5%, more preferably 0.0I to 2%. If the amount of the crosslinking agent is less than 0.0001%, the resulting resin will have a low gel strength upon water absorption and will become sol-like. On the other hand, if it exceeds 10%, the gel strength becomes excessive and the absorption performance decreases.

In the present invention, other polymerizable monomers may be used together with the acid group-containing monomer or its salt, for example, unsaturated carboxylic acids [monocarboxylic acids such as (meth)acrylic acid, maleic acid] , polycarboxylic acids such as fumaric acid], hydroxyalkyl esters, aromatic vinyl hydrocarbons [such as styrene, aliphatic vinyl hydrocarbons [ethylene, propylene, butene, etc.], unsaturated nitriles (acrylonitrile, etc.), (meth)acrylamide, etc.

The amount of other polymerizable monomers used if necessary is usually 30% based on the total weight of water-soluble monomer and crosslinking agent.
It is preferably 10% or less.

The polymerization method in the present invention may be a conventionally known method, and examples thereof include an aqueous solution polymerization method using a radical polymerization catalyst, a suspension polymerization method, a reversed-phase suspension polymerization method, and the like. Alternatively, a method of irradiating with radiation, electron beams, ultraviolet rays, etc. can also be used.

In the method using a radical polymerization catalyst, examples of this catalyst include azo compounds [azobisisobutyronitrile,
Azobiscyanovaler iL 212'-7 Zobis(2-
(amidinopropane) hydrochloride, inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides (benzoyl peroxide, dibutyl peroxide, cumene hydroperoxide, Succinic acid peroxide, di(2-
co- and redox catalysts such as (ethoxyethyl) peroxydicarbonate [alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite,
A combination of a reducing agent such as ascorbic acid, an ethyl potash metal persulfate, an ammonium persulfate, an oxidizing agent such as a peroxide], and two or more thereof.

Further, a redox catalyst consisting of a combination of hydrogen peroxide and ascorbic acid, or a combination of sodium persulfate and sodium bisulfite, etc. can also be used.

The amount of catalyst may be the same as usual, for example, usually 0°0001 to 5% based on the total weight of all polymerizable monomers and crosslinking agent.
%, preferably 0.0005 to 1%.

Other polymerization conditions, such as polymerization concentration, polymerization initiation temperature, polymerization time, aging temperature, etc., may be conventionally known conditions.

The hydrogel polymer thus obtained has a molecular weight of 11,000
Normally, pp -110000 pp of unreacted monomer remains, but as in the present invention, by adding a reducing substance and a radical scavenger at any stage of drying or pulverization after polymerization, the remaining monomer can be removed. It is possible to obtain a water-absorbing resin with a reduced amount of water-soluble components.

Examples of reducing substances include inorganic salts [sulfites (ammonium sulfite, etc.), bisulfites (ammonium bisulfite, sodium bisulfite, etc.), ferrous salts (ferrous chloride, ferrous sulfate, etc.), Cuprous salts (cuprous chloride, cuprous sulfate, etc.), ascorbic acid, amines (ammonia, monoethanolamine, etc.), reducing sugars (glucose, etc.)
etc., and two or more of these. Among these, preferred reducing substances are bisulfite, sulfite and ascorbic acid.

The amount of these reducing substances added is usually (1001 to 5%, preferably 0.01 to 3%) based on the total weight of the polymerizable monomer and crosslinking agent. If the amount exceeds 5%, it is necessary to add a large amount of the radical scavenger described below, and even if a large amount is added, the main chain polymer and crosslinking points will not be completely cleaved. As a result, the absorption performance of the water absorbent resin decreases.

The radical scavenger used in the present invention may be any conventionally known compound having the ability to inhibit radical chains.

Examples of such radical scavengers include quinones such as) lambda hydroquinone, methylhydroquinone, hydroquinone methyl ether, benzoquinone, and phenanthraquinone; polyhydric phenols such as catechol, pyrogallol, and resorcin; and polyphenols such as gallic acid. Carboxylic acid derivatives of phenols and their condensates, flavonoid derivatives,
Amine compounds such as diphenylpicrylhydrazyl, p-phenylenediamine, thiourea, hydrazopenzole, nitroso-β-naphthol, m-dinitropenzole, 0-dinitrocresol, 2,4-dinitrophenol, 2, Examples include 4-dinitrodolol and two or more thereof. Among these, preferred are quinones, polyhydric phenols and their carboxylic acid derivatives,
It is an amine compound.

Particularly preferred are quinones.

The amount of the radical scavenger added is usually 0.001% to 5%, preferably 0.01 to 3%, based on the total weight of the polymerizable monomer and crosslinking agent. If the amount added is less than 0.001%, the effect of suppressing the cutting of the water absorbent resin main chain and/or crosslinking point caused by the addition of the reducing substance is poor,
As a result, the absorption performance decreases and the amount of water-soluble components increases. When the amount added exceeds 5%, the radical scavenger inhibits the residual monomer reduction reaction, which is the objective of the present invention.

The ratio of reducing substance to radical scavenger is usually 1 on a weight basis.
:0.01-3, preferably l:o, I~! It is.

The amount of radical scavenger is 0.01 per liter of reducing substance.
If the amount of the radical scavenger exceeds 3, the effect of suppressing the cutting of the water absorbent resin main chain and/or crosslinking point caused by the addition of the reducing substance will be poor, and if the amount of the radical scavenger exceeds 3, the effect of reducing the residual monomer will be poor. inhibit.

In the present invention, the reducing substance and the radical scavenger may be added to the water absorbent resin at any stage after polymerization. If added before or during polymerization, the radical scavenger may inhibit polymerization.

The steps to be added after polymerization include the step after polymerization and before drying;
Examples include a stage during drying, a stage after drying before pulverization, a stage during pulverization, and a stage after pulverization before reaching a product. Preferably, it is a stage after polymerization but before drying and a stage after pulverization before reaching a product.

In the present invention, the reducing substance and radical scavenger may be added in the form of powder or stock solution, but in order to ensure uniform addition, they are usually added in the form of an aqueous solution or aqueous dispersion. At the time of addition, the reducing substance solution and the radical scavenger solution may be added separately, or the two types of solutions may be added at the same time. Alternatively, a mixed solution of a reducing substance and a radical scavenger may be added.

As for the method of adding at the stage after polymerization and before drying, any method may be used as long as it can be added uniformly, for example, a method of immersing a hydrous gel in the aqueous solution or dispersion,
Examples include a method of spraying onto a hydrogel, a method of stirring and mixing, and the like.

At the time of addition, it is preferable to crush the hydrogel using a crusher if necessary, since this allows uniform addition to the hydrogel.

The size after crushing is usually 50 mm or less, preferably 20 mm.
It is less than or equal to m+a. If the size after crushing exceeds 50 ml, the aqueous solution to be added will not penetrate sufficiently into the gel. As a result, the desired residual monomer content may not be sufficiently reduced, or it takes time for the aqueous solution to penetrate.

In addition, as a method of adding to the pearl-like hydrogel obtained by reverse-phase suspension polymerization, an aqueous solution of a reducing substance and a radical scavenger is added to the suspension after stirring and before removing the solvent. It can be added to the hydrogel by spraying or the like after the solvent has been removed.

Various methods can be used to add the powder to the granular polymer at the stage after drying and before pulverization, during pulverization, and before reaching the pulverized product, such as Nauta mixer, ribbon mixer, paddle mixer, kneader air, etc. Methods include using a mixer such as a mixer or a conical blender. In this case, it is preferable to spray or drop an aqueous solution or dispersion of the reducing substance and radical scavenger onto the stirred granular polymer, but the method is not limited to this method as long as uniform addition is possible.

In the present invention, when adding a reducing substance and a radical scavenger to reduce residual monomer, the water content of the water-absorbing resin is an important point.

The water content of the water absorbent resin is usually 5% to 95%, preferably 2
It is 0% to 85%. If the water content is less than 5%, even if an aqueous solution of a reducing substance and a radical scavenger is added, it will not penetrate sufficiently into the hydrogel polymer.

If the moisture content exceeds 95%, subsequent drying will take a long time.

Methods for adjusting the water content include methods such as adjusting the water content of the hydrogel polymer by adjusting the polymerization concentration, polymerization conditions, etc., adjusting by drying, and adjusting by adding water to a dried product.

When an aqueous solution or an aqueous dispersion of a reducing substance and a radical scavenger are added and mixed, they are dried by heating if necessary. The heat drying temperature is usually 100 to 230" C1, preferably 120"
-100°C. However, when drying under reduced pressure,
It is also possible to use drying temperatures below 100°C. The heat drying method may be a known method, such as a perforated plate, a wire mesh, a flat plate,
Methods of laminating on a belt and drying with hot air in batches or continuously, methods of drying with hot air in a rotary kiln or fluidized fluidized drying oven, methods of heating and drying by contacting with the surface of a hot plate or heated roller, methods of heating and drying under reduced pressure, etc. can be mentioned.

In the present invention, the surface of the obtained water absorbent resin powder is
Surface crosslinking may be carried out by a conventional method using a crosslinking agent such as a polyglycidyl ether compound or a polyvalent metal compound.

The residual monomer content and water-soluble component content of the water-absorbing resin composition of the present invention thus obtained is usually 500 ppn.
+ or less, and 7% or less. By selecting preferable conditions, the residual monomer content is 30 Qpl)m or less and the water-soluble component content is 5% or less.

[Examples] The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Note that the residual monomer content, water-soluble component amount, and absorption amount shown in the following Examples and Comparative Examples are the values determined by the following operations. Add 1 g of water absorbent resin composition and
．． Add 243 g of 9% salt solution and stir with a magnetic stirrer for 3 hours. The filtrate after the water-absorbing gel was filtered off with a filter paper was used as a sample solution.

(Measurement) Inject the sample solution into liquid chromatography and determine the peak area of the remaining monomer. Separately, a calibration curve (relationship between the amount of seven monomers and the peak area) is obtained from a monomer solution with a known concentration.
was created, and the residual upper Zimmer content was determined from this calibration curve.

Amount of water-soluble components> 3
The amount of water-soluble components after time extraction was measured.

<Absorption amount> Accurately weigh 1.00 g of the sample into a tea bag made of 250 mesh nylon net, soak it in physiological saline for 1 hour, drain for 15 minutes, and then measure the weight (a) in g. A similar measurement was carried out using a tea bag without a sample, the weight (b) g was measured, and the absorption amount was determined using the following formula.

Absorption amount (g/g) = ((a) −(b) ) −
1 Example 1 ■Contents: 80 g of sodium acrylate, 20 g of acrylic acid, 1 N in a stainless steel separable flask with contents of 1 yen.
.

N'-methylenebisacrylamide 0.1g and water 4
00g was charged, and the temperature of the contents was maintained at 40°C by heating from the outside of the flask while stirring. After purging the system with nitrogen, 0.1 g of 2.2'azobis(2-amitsunopropane) hydrochloride was added and mixed to initiate polymerization. Polymerization was completed in about 1 hour to obtain a hydrogel polymer.

The hydrogel polymer was taken out from the flask and the surface temperature was 1.
It was dried using a drum dryer heated to 50°C.

The obtained dried product was pulverized to a particle size of 20 mesh or less using a household mixer to obtain a pulverized product.

■Pour 100g of the crushed material into a small conical blender, add 0.5g of sodium bisulfite prepared in advance and 5g of water.
and 0.3 g of hydroquinone dissolved in 5 g of water.
were added sequentially and blended for 5 minutes. The obtained hydrogel polymer was dried under reduced pressure to obtain a water absorbent resin composition of the present invention. The residual monomer content of this resin,
The amount of water-soluble components and absorption amount were measured.

The results are shown in Table 1.

Example 2 To 100 g of the pulverized material obtained in Example 1, a mixed aqueous solution of 0.5 g of sodium bisulfite and 0.3 g of hydroquinone dissolved in water]Og was added and blended for 5 minutes. did. The obtained hydrogel polymer was dried under reduced pressure to obtain a water absorbent resin composition of the present invention. The residual content of the resin, the amount of water-soluble components, and the amount of absorption were measured.

The results are shown in Table 1.

Examples 3 to 7 The water-absorbing resin composition of the present invention was prepared in the same manner as in Example 1, except that the types and amounts of the reducing substance and radical scavenger added to the hydrogel polymer in Example 1 are shown in Table 1. I got it. The residual monomer content, water-soluble component amount, and absorption amount of the obtained water-absorbent resin were measured.

The results are shown in Table 1.

Example 8 (1) 196 g of acrylic acid, 0.05 g of methylene bisacrylamide, and 236 g of deionized water were mixed to prepare a polymerizable monomer solution. While keeping the temperature of this mixture below 50°C, add 68g of 48% sodium hydroxide aqueous solution.
was gradually added to neutralize 74% of the acrylic acid.

Dissolved oxygen lpp in the solution by introducing nitrogen gas
m or less, 0.05 g of V-50 (azo catalyst manufactured by Wako Pure Chemical Industries, Ltd.) was added and mixed for 1 minute. This solution was heated to 30°C, filled with nitrogen gas and sealed with polyethylene film.
0II was injected into a stainless steel vat measuring 1 m x 200 mm x 100 mm. This stainless steel panto is about 5
It was immersed in a 0°C hot bath and polymerized for about 1 hour to obtain a hydrogel polymer.

(2) A previously prepared aqueous solution of 1.2 g of ascorbic acid dissolved in 12 g of water and an aqueous solution of 0.72 g of hydroquinone methyl ether dissolved in 72 g of water were uniformly sprayed onto the surface of 600 g of this hydrogel polymer.

This gel was crushed using a gel crusher (manufactured by Horai Tekko) and then dried at 130°C using a hot air dryer.

The obtained dried product was pulverized to a particle size of 20 mn or less using a household mixer to obtain a water absorbent resin composition of the present invention. Table 1 shows the residual monomer content, water-soluble component amount, and absorption amount of this resin.

Example 9 After crushing the hydrogel polymer obtained in Example 8 (■) into particles with a particle diameter of 5 mm using a gel crusher, 100 g of this gel was mixed with an aqueous solution in which 0.2 g of ascorbic acid was dissolved in 2 g of water. Then, an aqueous solution of 0.12 g of hydroquinone methyl ether dissolved in 12 g of water was sprayed uniformly.

This gel was dried and pulverized to obtain a water absorbent resin composition of the present invention. Table 1 shows the residual content, amount of water-soluble components, and absorption amount of this resin.

Example 10 To 397 g of acrylic acid, 74 mol % neutralized with sodium hydroxide, 0.05 g of methylenebisacrylamide5
0.05 g of v-so was added and mixed with 800 g of deionized water. After introducing nitrogen gas to reduce the amount of dissolved oxygen in this solution to 1 ppm or less, a double-arm kneader (100 mm x 15 hm x 150 mm) with grooves for nitrogen gas was introduced.
injected into. While stirring, heat the jacket to 50”C.
Polymerization was carried out by passing hot water for a period of ].

Add an aqueous solution of 2.0 g of sodium bisulfite dissolved in 20 g of water and an aqueous solution of 1.2 g of hydroquinone dissolved in 20 g of water to the hydrogel polymer, which has been crushed into particle sizes of about 5 to 20 mm by stirring. After mixing, the mixture was taken out from the kneader.

This gel was dried with hot air at 130°C and pulverized to obtain a water absorbent resin composition of the present invention. Table 1 shows the residual monomer content, water-soluble component amount, and absorption amount of this resin.

Example 11 ■ In a 2001 flask, 32.7 g of acrylic acid,
A polymerizable monomer solution was prepared by mixing 0.01 g of methylenebisacrylamide and 39.3 g of deionized water. While cooling the mixture, 28.0 g of a 48% aqueous sodium hydroxide solution was gradually added dropwise to neutralize 4% of the acrylic acid. Next, 0.1 g of potassium persulfate was added and dissolved at room temperature, and then nitrogen gas was introduced to reduce the dissolved oxygen in the solution to 1 ppm or less.

Add 4 liters of n-hexane to a 1-liter flask fitted with a reflux condenser.
After dissolving 5 g of sorbitan monostearate at room temperature, dissolved oxygen in the flask was expelled by introducing nitrogen gas. Next, while maintaining the temperature at approximately 60°C in a hot bath and introducing nitrogen gas little by little,
The aforementioned potassium persulfate-containing polymerizable monomer solution was added dropwise overnight, and polymerization was carried out for about 2 hours to obtain a pearl-like hydrogel polymer.

(2) A previously prepared aqueous solution of 0.2 g of sodium bisulfite and 0.12 g of hydroquinone methyl ether dissolved in 20 g of water was dropped into the flask and mixed for 20 minutes.

After n-hexane was removed under reduced pressure, the mixture was dried with hot air at 130'C to obtain a water absorbent resin composition of the present invention. Table 1 shows the results of measuring the residual monomer content, water-soluble component amount, and absorption amount of this resin.

Example 12 The pearly hydrogel polymer obtained in Example 11 (2) was taken out after n-hexane was removed.

50g of pearl-like gel taken out, 0 sodium bisulfite,
An aqueous solution of tg dissolved in 5 g of water and an aqueous solution of 0.0 g of hydroquinone methyl ether dissolved in 6 g of water were uniformly sprayed and then dried with hot air at 130° C. to obtain a water absorbent resin composition of the present invention. Table 1 shows the results of measuring the residual monomer content, water-soluble component amount, and absorption amount of this resin.

Comparative Example 1 Table 1 shows the results obtained when sodium bisulfite and hydroquinone were not added and mixed in Example 1.

Comparative Example 2 Table 1 shows the results when only sodium bisulfite was added and mixed in Example 1.

Comparative Example 3 Table 1 shows the results obtained when ascorbic acid and hydroquinone methyl ether were not added and mixed in Example 8.

Comparative Example 4 Table 1 shows the results when only ascorbic acid was added and mixed in Example 8.

Comparative Example 5 Table 1 shows the results when sodium bisulfite and hydroquinone were not added in Example 10. Comparative Example 6 Table 1 shows the results when only sodium bisulfite was added in Example 10.

Comparative Example 7 Table 1 shows the results obtained in Example 11 without adding sodium bisulfite and hydroquinone methyl ether.

Comparative Example 8 Table 1 shows the results obtained when only sodium bisulfite was added in Example 11.

[Effects of the Invention] As is clear from Table 1, the production method of the present invention makes it possible to produce a highly safe water-absorbing resin composition with extremely low residual monomer content and water-soluble component content.

Because it exhibits the above effects, the water absorbent resin composition obtained by the production method of the present invention can be used as absorbent materials, sanitary materials (disposable diapers for children and adults, sanitary napkins, sanitary cotton, bandages, incontinence pads, Applications that come into contact with the human body, such as paper towels, etc.;
Applications include freshness preservation agents for fruits and vegetables that may come into contact with food; l' IJ knob absorbers for meat and seafood; water retention agents for plants and soil; sludge coagulants; anti-condensation agents used in interior building materials, etc. , useful for various industrial applications.

One eleven one

Claims (1)

[Claims] 1. A reducing substance and a radical scavenger are added to the water-absorbing resin obtained by polymerizing a water-soluble monomer, a polysaccharide, and/or a crosslinking agent at any stage of drying or pulverization after polymerization. 1. A method for producing a water-absorbing resin with reduced residual monomer content and reduced amount of water-soluble components. 2. The method for producing a water absorbent resin according to claim 1, wherein the reducing substance is at least one selected from the group consisting of sulfites, bisulfites, ferrous salts, ascorbic acid, amines, and reducing sugars. . 3. The method for producing a water-absorbing resin according to claim 1 or 2, wherein the amount of the reducing substance added is 0.001 to 5% based on the total weight of the polymerizable monomer and the crosslinking agent. 4. Claim 1, wherein the amount of the radical scavenger added is 0.001 to 5% based on the total weight of the polymerizable monomer and crosslinking agent.
3. The method for producing a water absorbent resin according to any one of 3 to 3. 5. The ratio of reducing substance to radical scavenger is 1 on a weight basis.
:0.01-3. The method for producing a water-absorbing resin according to any one of claims 1 to 4. 6. Obtained by the production method according to any one of claims 1 to 5,
A water-absorbing resin composition characterized in that the residual monomer content is 500 ppm or less and the amount of water-soluble components is 7% or less.