JPH04120112A - 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 applying ultraviolet rays to a water absorbing resin synthesized by polymerization of a water-soluble monomer and a polysaccharide, etc., in the presence of a radical scavenger, 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 (used preferably in an amount of 3-20wt.% based on monomer) such as starch and/or a crosslinking agent (used preferably in an amount of 0.01-2wt.% based on total weight of monomer and crosslinking agent) such as bis(meth)acrylamide, ultraviolet rays are applied in the presence of a scavenger such as hydroquinone preferably in an amount of 0.01-3wt.% 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.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a water absorbent resin composition and a method for producing the same.

More specifically, the present invention relates to a water-absorbing resin composition with reduced residual monomer content and reduced amount of water-soluble components, and a method for producing the same.

[Prior Art] Conventionally, methods such as adding a reducing substance, adding a peroxide and/or an azo compound, and irradiating ultraviolet rays have been proposed as methods for reducing the residual residual content in a water-absorbing resin.

[The problem that the invention attempts to solve! i! ]however,
Although these methods can reduce residual monomer,
At the same time as addition reactions and repolymerization reactions due to the generation of radical species, side reactions such as cleavage of the polymer main chain of the water-absorbing resin and cleavage of crosslinking points are caused by the generated excess radicals.

As a result, there have been problems such as a decrease in water absorption performance due to a decrease in the molecular weight of the water absorbent resin and an increase in the amount of water-soluble components.

[Means for Solving the Problems] The present inventors conducted extensive studies to solve the above problems, and as a result, they came up with the present invention.

That is, in the present invention, a water-absorbing resin obtained by polymerizing a water-soluble monomer, a polysaccharide, and/or a crosslinking agent is exposed to ultraviolet rays in the presence of a radical scavenger at any stage of drying or pulverization after polymerization. A method for producing a water-absorbing resin with reduced amounts of residual monomer and water-soluble components, characterized by irradiation; and a water-absorbing resin composition obtained by polymerizing a water-soluble monomer, a polysaccharide, and/or a crosslinking agent. The material is irradiated with ultraviolet rays in the presence of a radical scavenger at any stage of drying or pulverization after polymerization, and the residual monomer content is 500 ppm or less and the amount of water-soluble components is 7% or less. It is a water absorbent resin composition.

In 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-based monomers containing carboxylic acid groups, polymerizable monomers containing sulfonic acid groups, and polymerizable monomers containing phosphoric acid groups. monomers and their salts.

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)acrylicsulfonic acid [(metal) ) sulfoethyl acrylate, sulfopropylene (meth)acrylate, (meth)acrylamidosulfonic 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, etc.].

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, such as alkali metal salts (salts of sodium, potassium, lithium, etc.), alkaline earth metal salts (salts of calcium, magnesium, etc.). ), ammonium salts and amine salts (alkylamine salts such as methylamine and trimethylamine; salts of alkanolamines such as triethanolamine and jetanolamine), and two or more thereof. Preferred among these are sodium salts and potassium salts.

The degree of neutralization of the monomer containing acid groups is usually 50 to 90 mol%, preferably 60 to 80 mol% of the acid groups in the polymer. When the degree of neutralization is less than 50 mol %, the resulting hydrogel polymer has high stickiness and it is difficult to produce a water absorbent resin with good workability. When the degree of neutralization exceeds 90%, the pH of the obtained polymer 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, neutralization at the state of a hydrogel that is a polymerization product, etc.). There is a way.

Examples of monomers that become water-soluble through hydrolysis include (
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 amino group-containing monomers include dialkylaminoalkyl (meth)acrylate, dialkylaminohydroxyalkyl (meth)acrylate, dialkylaminoalkyl (meth)acrylamide, and sialkylaminohydrokinealkyl (meth)acrylamide. can be mentioned.

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

In the present invention, examples of polysaccharides include starch and cellulose. Examples of starches include raw starches such as sweet potato starch, potato starch, wheat starch, corn starch, and rice starch; oxidized starch, dialdehyde starch, alkyl etherified starch, aryl etherified starch, oxyalkylated starch, 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.; processed cellulose such as alkyl etherified cellulose, eic acid esterified cellulose, oxidized cellulose, and hydroquine alkyl etherified cellulose. .

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

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

Examples of the compound (1) include the following.

■Bis(meth)acrylamide: N,N'-alkylene (C+ to Cs) 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 acid esters such as polyoxypropylene glycol: Unsaturated polynisterol Co- and di- or tri-(meth)acrylic esters obtained by the reaction of the above polyols with unsaturated acids such as maleic acid [polyepoxides] and (meth)acrylic acid.

■Carbamyl ester: Polyisocyanate [tolylene diisocyanate, hexamethylene insinate, 4.4''-diphenylmethane diisocyanate, NCO group-containing prepolymer (obtained by reaction of the above polyisone unsaturated compound with an active hydrogen atom-containing compound), etc. Co and hydroxyethyl (meth)
Carbamyl ester obtained by reaction with acrylate.

■Di- or polyvinyl compounds such as divinylbenzene, divinyltoluene, divinylxylene, 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: such as tetraallyloxyethane.

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 (hydroquinyl groups, epoxy groups, cationic groups, etc.). Examples include ethylenically unsaturated compounds that contain a chemical group, etc. Specifically, nonionic group-containing unsaturated compounds such as hydroxy group-containing unsaturated compounds [N-methylol (meth)acrylamide, etc.]
and unsaturated compounds containing evoquine group [glycidyl (meth)
acrylates, etc.] and unsaturated compounds containing cationic groups, such as quaternary ammonium base-containing unsaturated compounds I
N,N,N-trimethyl-N-(meth)acryloyloxyethyltrimethylammonium chloride, N,N,
N-)limethyl-N-(meth)acryloyloxyethylammonium chloride, etc., and unsaturated compounds containing tertiary amino groups [(meth)methylaminoethyl acrylate, diethylaminoethyl (meth)acrylate, etc. It will be done. .

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 poly-esters of polyols and unsaturated monocarboxylic acids and allyloxyalkanes, particularly preferred are N,N'-methylenebisacrylamide,
Ethylene glycolone acrylate, trimethylolpropane triacrylate and tetraaryloquinethane.

The amount of crosslinking agent is usually 0.000%, preferably 0.000%, based on the total weight of water-soluble monomer and crosslinking agent.
It is 1 to 5%. More preferably, it is 0.01 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 too high 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, Alkyl (C+ to C+Q) esters of polycarboxylic acids such as fumaric acid, hydroxyalkyl esters, aromatic vinyl hydrocarbons [styrene, etc.], 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% or less, preferably 10% or less, based on the total weight of the water-soluble monomer and crosslinking agent.

The polymerization method in the present invention may be any conventionally known method, and includes, for example, 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,
Azobiscyanovaleric acid, 2,2'-azobis(2-amidinopropane) hydrochloride, etc., inorganic peroxides, hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc., organic peroxides [peroxide Co- and redox catalysts such as benzoyl, dibutyl peroxide, cumene hydroperoxide, succinic peroxide, di(2-ethoxyethyl) peroxydicarbonate [alkali metal sulfites or bisulfites, ammonium sulfite, bisulfite] Examples include combinations of reducing agents such as ammonium sulfate and ascorbic acid and oxidizing agents such as alkali metal persulfates, ammonium persulfates, and peroxides, and combinations of two or more of these.

Further, redox catalysts consisting of combinations of hydrogen peroxide and ascorbic acid, 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 I%.

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, unreacted monomers of pp to 10,000 pp11 remain, but by irradiating with ultraviolet rays in the presence of a radical scavenger, the residual monomers are reduced and a water-absorbing resin with a small amount of water-soluble components is produced. can get.

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 hydroquinone, methylhydroquinone, hydroquinone methyl ether, benzoquinone, and phenanthraquinone; polyphenols such as catechol, pyrogallol, and resorcin; and polyphenols such as gallic acid. carboxylic acid derivatives and their condensates, flavonoid derivatives, nophenylpicrylhydrazyl, p-phenylenediamine, amine compounds such as thiourea, hydraazopenzole, nitroso-β-naphthol, m-dinitropenzole, Examples include 0-dinitrocresol, 2,4-dinitrophenol, 2,4-dinitrodolol, and the like. Among these, preferred are quinones, polyhydric phenols and their carboxylic acid derivatives, and amine compounds, and particularly preferred are quinones.

The amount of these radical scavengers added is usually 0.00W% to 5%, based on the total weight of the polymerizable monomer and crosslinking agent.
Preferably it is 0.01 to 3%. The amount added is 0°001
If it is less than %, the water-absorbing resin main chain etc. will be cut when irradiated with ultraviolet rays, resulting in a decrease in absorption performance and an increase in the amount of water-soluble components. If the amount added exceeds 5%, the radical scavenger inhibits the reaction for reducing residual residual zimmer, which is the objective of the present invention.

In the present invention, the radical scavenger may be added to the water absorbent resin at any stage after polymerization.

When added before or during polymerization, the radical scavenger inhibits polymerization.

Examples of the stage of addition after polymerization include the stage after polymerization before drying, the stage during drying, the stage after drying, the stage before pulverization, the stage during pulverization, and the stage after pulverization before reaching the 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 radical scavenger may be added in the form of powder or stock solution, but in order to ensure uniform addition, it is usually added in the form of an aqueous solution or dispersion. Examples of this method include a method of immersing the hydrogel in the aqueous solution or dispersion, a method of spraying the hydrogel, and a method of stirring and mixing the hydrogel with crushed hydrogel if necessary.

In addition, methods for adding radical scavengers to the burr-shaped hydrogel obtained by reverse-phase suspension polymerization include adding radical scavengers to the suspension after polymerization and before removing the solvent; Examples include a method of spraying onto a crowbar-shaped hydrogel in a step.

In the present invention, ultraviolet irradiation is performed in a state in which a radical scavenger is added. The irradiation step may be any step after the radical scavenger is added and contained. Examples include the stage of a hydrogel polymer obtained by polymerization, the semi-drying stage during drying, and the stage after drying.

For ultraviolet irradiation, an ordinary ultraviolet lamp or the like may be used (the irradiation intensity and irradiation time vary depending on the residual monomer content in the water-absorbing resin. Usually, for example, when an ultraviolet lamp is used, 10W to 5θON/cm, preferably 30
W -300W/cm, irradiation time 1 second - 10 minutes,
Distance between ultraviolet lamp and water-absorbing resin: 0.5mm~]00m
+n.

The irradiation method used in the present invention may be a stationary method or a moving method using a belt conveyor, as long as ultraviolet irradiation can be performed under the above conditions.

In the present invention, when irradiating ultraviolet rays after adding and containing a radical scavenger, the water content and particle size of the water absorbent resin are important points.

The water content of the water absorbent resin is usually 5 to 95%, preferably 2
It is 0-85%. If the water content is less than 5%, the ultraviolet rays will not penetrate into the water-absorbing resin, so the residual monomer, which is the objective of the present invention, will not be sufficiently reduced.If it exceeds 95%, it will take a long time to dry afterwards. .

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.

The particle size is preferably 50 mm or less, more preferably 2
It is 0mn+ or less. If the particle size exceeds 50), the ultraviolet rays will not sufficiently penetrate into the interior of the water-containing water-absorbent resin when irradiated with ultraviolet rays, so that the desired reduction of residual monomers will not be achieved sufficiently.

When a polymerization method is adopted in which a sheet-like hydrogel polymer is obtained in the polymerization step, the thickness of the sheet is preferably 50 mm or less, more preferably 20II11 or less.

The hydrogel polymer obtained by adding the radical scavenger and then irradiating it with ultraviolet rays is dried by heating if necessary. The heat drying temperature is usually 100 to 230°C, preferably 1
20 to +90°C. However, when drying under reduced pressure, the drying temperature can be lower than 100"C. The drying method may be any known method, and may be laminated on a perforated plate, a wire mesh, a flat plate, or a belt for batch drying. Alternatively, methods include continuous drying, hot air drying in a rotary kiln or fluidized drying oven, heating drying by contacting with the surface of a hot plate or hot roller, and heating reduced pressure drying.

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 polygrindyl ether compound or a polyvalent metal compound.

The residual monomer content and water-soluble component amount of the water-absorbent resin composition of the present invention obtained in this way is usually 500 pp.
m or less and 7% or less. By selecting preferable conditions, the residual monomer content is 300 ppm 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.

In addition, 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 procedure. <Residual monomer content> (Preparation of sample solution) Add 1g of resin and 0.9
Add 249g of % salt solution and stir with a magnetic stirrer.
Stir for an hour. 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 area of the peak of the remaining monomer. Separately, a calibration curve (relationship between the amount of heptamers and the area of the peak) was created from a monomer solution of a known concentration, and the residual monomer content was determined from this calibration curve.

Amount of water-soluble components> The amount of water-soluble components after extraction for 3 hours was measured by the method described in JP-A-82-54751.

<Absorption amount> 1 water absorbent resin in 250 mesh nylon teabag
．． Weigh out 00g accurately, soak in 0.9% saline solution 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 (1) 196 g of acrylic acid 1 0.05 g of methylenebisacrylamide 236 g of deionized water were mixed to prepare a polymerizable monomer solution. While keeping the temperature of this mixed solution below 50°C, 48% hydroxide is added) IJum aqueous solution 168
g was gradually added to neutralize 74 mol% of the acrylic acid. 1 p of dissolved oxygen in the solution by introducing nitrogen gas
After setting the temperature to below pa+, 0.05 g of V-SO (azo catalyst manufactured by Wako Pure Chemical Industries, Ltd.) was added and mixed for 1 minute. This solution was injected into a 300 mm x 20 hm x 100 mm stainless steel vat filled with nitrogen gas and sealed with polyethylene film. This stainless steel bat 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 0.72 g of hydroquinone dissolved in 14 g of water was uniformly sprayed onto the surface of 600 g of this hydrogel polymer.

This gel was placed on a mobile belt conveyor and
Using an AS ultraviolet lamp, ultraviolet light was irradiated for 10 seconds with a distance of 10 cm between the ultraviolet lamp and the gel.

This gel was crushed using a gel crusher (manufactured by Seimetsu Tekko) and then dried with hot air at a temperature of 130°C.

The obtained dried product was pulverized to a particle size of 20 mesh 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.

Examples 2 to 7 A water-absorbing resin composition of the present invention was obtained in the same manner as in Example 1 except for the type and amount of the radical scavenger added to the hydrogel polymer and the ultraviolet irradiation time. . The amount of residual water-soluble components and absorption amount of the obtained water absorbent resin were measured.

The results are shown in Table 1.

Example 8 An aqueous solution of 0.12 g of hydroquinone methyl ether dissolved in 12 g of water was added to 100 g of the hydrogel obtained by chopping the hydrogel polymer obtained in Example 1 to 5 m+o or less in particle size using a meat chopper. sprayed on.

This gel was irradiated with ultraviolet rays under the same conditions as in Example 2, then dried 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 9 ■ 0.05 g of methylene bisacrylamide was added to 397 g of acrylic acid whose 74 mol% was neutralized with sodium hydroxide.
, 0.05 g of V-50, 600 g of deionized water
was added and mixed.

By introducing nitrogen gas, the amount of dissolved oxygen in this solution was reduced to 1 ppa.
After reducing the temperature to less than
+*). 5 into the jacket while stirring.
Polymerization was carried out for about 1 hour by passing warm water at 0°C to obtain a hydrogel polymer.

Hydroquinone methyl ether 1.2
An aqueous solution prepared by dissolving 120 g of water in 120 g of water was added by spraying, mixed, and then taken out from the kneader.

This gel was heated at 80W/c1 on a mobile belt conveyor.
Ultraviolet rays were irradiated for 180 seconds using an ultraviolet lamp No. 1 with a distance of 1OCI11 between the gel and the ultraviolet lamp.

After drying and pulverizing the gel irradiated with ultraviolet rays, a water-absorbing resin composition of the present invention was obtained, and the amount of residual monomer, water-soluble component, and absorption amount were measured. The results are shown in Table 1.

Example 10 The hydrogel polymer obtained in Example 9 (1) was crushed into pieces of 5 mm or less using a gel crusher (manufactured by Shisai Tekkosho).

After spraying an aqueous solution of 0.12 g of hydroquinone methyl ether dissolved in 12 g of water to this long hydrogel, irradiation with ultraviolet rays was performed for 30 seconds, followed by drying and pulverization 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 water-absorbing resin.

Example 11 In a 2001 flask, acrylic acid 32, 7g1
A polymerizable monomer solution was prepared by mixing 0.01 g of methylenebisacrylamide and 39.3 g of deionized water. While cooling this mixture, add 48% sodium hydroxide aqueous solution 2.
8.0 g was gradually added dropwise to neutralize 74 mol% of 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 n-hex 7 to a 1U flask equipped with a reflux condenser.
After charging 400 g of sorbitan monostearate and 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 about 60"C in a hot bath and introducing nitrogen gas little by little, the solution in which potassium persulfate was dissolved was added dropwise.
Polymerization was carried out for a period of time to obtain a pearl-like hydrogel polymer.

Hydroquinone methyl ether prepared in advance 0.
An aqueous solution of 11 g dissolved in 11 g water was added dropwise into the flask and mixed for 10 minutes.

After removing n-hexane under reduced pressure, the remaining burl-shaped gel was taken out and heated at 80 W/c on a mobile belt conveyor.
Ultraviolet rays were irradiated for 30 seconds using an ultraviolet ray lamp with a distance of IOcw between the gel and the ultraviolet lamp.

Next, this burl-shaped gel was dried with hot air at 130°C to obtain a water absorbent resin composition of the present invention. The residual monomer content, water-soluble component amount, and absorption amount of this resin were measured.

The results are shown in Table 1.

Example 12 The water-absorbing resin composition of the present invention was prepared under the same conditions as in Example 11, except that n-hexane was removed, the pearly hydrogel was taken out, and hydroquinone methyl ether was added by spraying. Obtained. The residual monomer content, water-soluble component amount, and absorption amount of this resin were measured.

The results are shown in Table 1.

Example 13 10 g of a water-absorbing resin obtained by drying and pulverizing the hydrogel polymer obtained in Example 1 (■) in the same manner as in Example 1 was placed in a petri dish (diameter: 10 cm), and pre-adjusted hydroquinone 0.
．． A water-absorbing resin composition of the present invention was obtained by uniformly spraying an aqueous solution prepared by adding water to 0.3 g and irradiating it with ultraviolet rays under the same conditions as the others except that the irradiation time was 10 seconds. The residual monomer content, water-soluble component amount, and absorption amount of this resin were measured. The results are shown in Table 1.

Example 14 In Example 11, addition of hydroquinone methyl ether and irradiation with ultraviolet rays were performed after hot air drying to obtain a water absorbent resin composition of the present invention. The residual monomer content, water-soluble component amount, and absorption amount of this resin were measured. The results are shown in Table 1.

Comparative Example 1 Table 1 shows the results obtained in Example 1 without adding hydroquinone and without irradiating ultraviolet rays.

Comparative Examples 2 to 4 Table 1 shows the results when UV rays were irradiated in Examples 1 to 3 without adding hydroquinone.

Comparative Example 5 Table 1 shows the results obtained in Example 9 without adding hydroquinone methyl ether and without irradiating ultraviolet rays.

Comparative Example 6 Table 1 shows the results when ultraviolet rays were irradiated in Example 9 without adding hydroquinone methyl ether.

Comparative Example 7 Table 1 shows the results obtained in Example 11 without adding hydroquinone methyl ether and without irradiating ultraviolet rays.

Comparative Example 8 Table 1 shows the results when ultraviolet rays were irradiated in Example 11 without adding hydroquinone methyl ether.

[Effects of the Invention] As is clear from Table 1, the production method of the present invention makes it possible to produce highly safe water-absorbing resins 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 for absorbent materials, sanitary materials (disposable diapers for children and adults, sanitary napkins, sanitary cotton, bandages,
Applications that come into contact with the human body, such as incontinence pads, paper towels, etc. Applications such as freshness preservation agents for fruits and vegetables that may come into contact with food, and trip absorbents for meat and seafood; Water retention agents for plants and soil; It is suitable for various industrial applications, such as as a dew-preventing agent for interior building materials.

Claims (1)

[Claims] 1. A water-absorbing resin obtained by polymerizing a water-soluble monomer, a polysaccharide, and/or a crosslinking agent is treated in the presence of a radical scavenger at any stage of drying or pulverization after polymerization. A method for producing a water-absorbing resin with a reduced amount of residual monomer and water-soluble components, which comprises irradiating with ultraviolet rays. 2. The method for producing a water absorbent resin according to claim 1, wherein the amount of the radical scavenger is 0.001 to 5% based on the total weight of the polymerizable monomer and the crosslinking agent. 3. A water-absorbing resin composition obtained by the production method according to any one of claims 1 to 2, which has a residual monomer content of 500 ppm or less and a water-soluble component content of 7% or less.