JP2008133396A - Manufacturing method for water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-absorbing resin with a high water-retaining ability and a high water-absorbing ability capable of being preferably used for a sanitation material, and to provide its manufacturing method. <P>SOLUTION: In the method for manufacturing the water-absorbing resin by polymerizing a water-soluble ethylenic unsaturated monomer, a polymerization reaction of the water-soluble ethylenic unsaturated monomer is performed in the presence of a diamine compound represented by the formula (I) (wherein R<SP>1</SP>represents a 1-6C straight alkylene group or a phenylene group, and R<SP>2</SP>, R<SP>3</SP>, R<SP>4</SP>and R<SP>5</SP>each independently represent a methyl group, an ethyl group or a hydrogen atom) or its salt and a water-soluble radical polymerization initiator, and after the polymerization reaction, a cross-linking agent is added to perform a cross-linking reaction. The water-absorbing resin obtained by the method is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water absorbent resin and a method for producing the same. More specifically, the present invention relates to a water absorbent resin that can be suitably used for sanitary materials such as disposable diapers, incontinence pads, sanitary napkins and the like, and a method for producing the same.

  Water-absorbing resins are widely used in various fields such as sanitary materials such as disposable diapers and sanitary goods, agricultural and horticultural materials such as water retention materials and soil improvement materials, water-proofing materials for cables, and anti-condensation materials. Examples of such a water-absorbing resin include a hydrolyzate of starch-acrylonitrile graft copolymer, a neutralized product of starch-acrylic acid graft polymer, a saponified product of vinyl acetate-acrylic acid ester copolymer, and polyacrylic acid. Partially neutralized products are known.

  In recent years, sanitary materials such as disposable diapers and sanitary napkins tend to make the absorbent body thinner from the viewpoint of comfort during use. In this case, it is necessary to reduce the content of hydrophilic fibers having a high bulkiness and a low water absorption capacity, and to increase the proportion of the water absorbent resin having a high water absorption capacity. Properties desired for such an absorbent body and a water-absorbent resin used in a water-absorbent article using the absorber include a high water retention capacity when contacting with an aqueous liquid, an appropriate water absorption speed, particularly high water absorption under pressure. Noh.

  However, there is a contradictory relationship between water retention capacity, water absorption capacity under pressure and water absorption speed. In general, in order to obtain a water-absorbing resin having a high water-retaining ability, it is necessary to lower the cross-linking density of the water-absorbing resin. However, if the cross-linking density is lowered, the gel strength becomes weak and the water-absorbing ability under pressure is reduced. Furthermore, due to an increase in the amount of uncrosslinked components, the water absorption rate tends to decrease due to the mamako state when in contact with the liquid.

  On the other hand, in order to increase the water absorption capacity under pressure, it is necessary to increase the cross-linking density. Therefore, in the absorbent article using such a water absorbent resin, the absorption capacity of the entire absorbent article is reduced.

  On the other hand, the acrylic acid-based monomer having α-hydrogen, which is widely used as a monomer of the water-absorbing resin, easily forms a crosslinked structure by the monomer itself depending on the polymerization conditions, such as potassium persulfate as a polymerization initiator. When this persulfate is used, this self-crosslinking tends to occur without using a crosslinking agent. Therefore, it is difficult to lower the crosslink density of the water absorbent resin itself, and it is difficult to obtain a water absorbent resin having both high water absorption ability and gel strength.

  In order to solve the above-described problems, a water-absorbing resin precursor is obtained by performing aqueous solution polymerization in the presence of phosphorous acid and / or a salt thereof, and then the water-absorbing resin precursor and a surface cross-linking agent are mixed and heated. (Refer to Patent Document 1), reverse-phase suspension polymerization in the presence of hypophosphorous acid to obtain a water-absorbent resin precursor, and then surface-crosslinking the water-absorbent resin (refer to Patent Document 2). Are known.

However, the water-absorbent resin obtained by these methods has a drawback that the performance cannot be sufficiently satisfied. For this reason, development of a water-absorbing resin excellent in water retention ability and water absorption ability under pressure is desired.
JP-A-9-124710 JP-A-2-255804

  An object of the present invention is to provide a water-absorbing resin that has a high water-holding capacity and high water-absorbing capacity under pressure and can be suitably used for sanitary materials, and a method for producing the same.

  The present invention is a method for producing a water-absorbent resin by polymerizing a water-soluble ethylenically unsaturated monomer, which comprises the formula (I):

(In the formula, R ¹ represents a linear alkylene group having 1 to 6 carbon atoms or a phenylene group, and R ² , R ³ , R ⁴ and R ⁵ each independently represents a methyl group, an ethyl group or a hydrogen atom)
In the presence of a diamine compound or a salt thereof and a water-soluble radical polymerization initiator, the water-soluble ethylenically unsaturated monomer is subjected to a polymerization reaction, and after the polymerization reaction, a crosslinking agent is added to perform a crosslinking reaction. The present invention relates to a method for producing a water-absorbent resin, and a water-absorbent resin obtained by the method.

  According to the production method of the present invention, a water-absorbing resin having a high water retention capacity and high water absorption capacity under pressure can be obtained.

  The present invention specifies a polymerization reaction of a water-soluble ethylenically unsaturated monomer in a method for producing a water-absorbent resin by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of a radical polymerization initiator. This is characterized in that it is carried out in the presence of the diamine compound, and after the polymerization reaction, a crosslinking agent is added to carry out the crosslinking reaction. Although the details of the action of the diamine compound in the present invention are not clear, it is presumed to be related to the control of self-crosslinking that occurs in the polymerization of the water-soluble ethylenically unsaturated monomer. That is, due to the presence of the diamine compound, self-crosslinking during polymerization is moderately suppressed, and by performing a crosslinking reaction after polymerization, the surface layer of the water-soluble ethylenically unsaturated monomer polymer is crosslinked, It is considered that a water-absorbing resin having a high water retention capacity and high water absorption capacity under pressure can be obtained.

Examples of the water-soluble ethylenically unsaturated monomer used in the present invention include (meth) acrylic acid and alkali salts thereof (in this specification, “acrylic” and “methacrylic” together with “(meth) acrylic”). 2- (meth) acrylamide-2-methylpropanesulfonic acid and its alkali salts; (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate , N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate and other nonionic monomers; N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, and diethylaminopropyl Examples include amino group-containing unsaturated monomers such as (meth) acrylamide and quaternized products thereof. These may be used alone or in combination of two or more. Of these, acrylic acid and its alkali salts, methacrylic acid and its alkali salts, acrylamide, methacrylamide and N, N-dimethylacrylamide are preferred from the viewpoint of easy industrial availability. Examples of the alkali salt include salts of alkali metals such as lithium, sodium and potassium.

  Examples of the water-soluble radical polymerization initiator used in the present invention include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, peroxides such as hydrogen peroxide, 2,2′-azobis [2- ( N-phenylamidino) propane] dihydrochloride, 2,2′-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2′-azobis {2-methyl-N- [1,1-bis ( Droxymethyl) -2-hydroxyethyl] propionamide}, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 4,4′-azobis (4-cyanovaleric acid), etc. These azo compounds may be used, and these may be used alone or in combination of two or more. Among these, from the viewpoint of easy availability and easy handling, persulfates are preferable, and potassium persulfate, ammonium persulfate, and sodium persulfate are more preferable.

  The water-soluble radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, L-ascorbic acid and the like.

  The amount of the water-soluble radical polymerization initiator used is preferably 0.005 to 1 part by weight, preferably 0.05 to 0.5 parts per 100 parts by weight of the water-soluble ethylenically unsaturated monomer, from the viewpoint of promoting appropriate progress of the polymerization reaction. Part by weight is more preferred. The 100 parts by weight of the water-soluble ethylenically unsaturated monomer means the total amount of the water-soluble ethylenically unsaturated monomer used for the polymerization reaction unless otherwise specified.

  The diamine compound used in the present invention has the formula (I):

(In the formula, R ¹ represents a linear alkylene group having 1 to 6 carbon atoms or a phenylene group, and R ² , R ³ , R ⁴ and R ⁵ each independently represents a methyl group, an ethyl group or a hydrogen atom)
It is represented by

  Examples of the diamine compound represented by the formula (I) include N-position unsubstituted compounds such as diaminomethane, ethylenediamine, 1,6-hexamethylenediamine, o-phenylenediamine, and p-phenylenediamine: N-methylethylenediamine, N -N-substituted mono-substituents such as ethylethylenediamine, N-methyl-1,3-propanediamine, N-methyl-o-phenylenediamine, N-methyl-p-phenylenediamine: N, N-dimethylethylenediamine, N, N -N-disubstituted compounds such as diethylethylenediamine, N, N-dimethyl-o-phenylenediamine, N, N-dimethyl-p-phenylenediamine, N, N-diethyl-p-phenylenediamine: N, N'-dimethyl N, N'-position mono-substitution such as ethylenediamine, N, N'-dimethyl-1,3-propanediamine : N, N, N′-trimethyldiethylamine, N, N-dimethyl-N′-ethylethylenediamine, N, N, N′-triethylethylenediamine, N, N, N′-trimethyl-1,3-propanediamine, etc. N-disubstituted N′-monosubstituted: N, N, N ′, N′-tetramethyldiaminomethane, N, N, N ′, N′-tetramethylethylenediamine, N, N, N ′, N′— Tetraethylethylenediamine, N, N, N ′, N′-tetramethyl-1,3-propanediamine, N, N, N ′, N′-tetraethyl-1,3-propanediamine, N, N, N ′, N '-Tetramethyl-1,4-butanediamine, N, N, N', N'-tetramethyl-1,6-hexanediamine, N, N, N ', N'-tetramethyl-p-phenylenediamine, etc. N, N Position disubstitution, and the like. Examples of the salt of the diamine compound include hydrochloride, sulfate, oxalate and the like. Among these, ethylenediamine, N, N, N ′, N′-tetramethylethylenediamine, N, N′-dimethyl are used from the viewpoint of being easily industrially available and easily mixed with water-soluble ethylenically unsaturated monomers. Ethylenediamine and their salts are preferred. These compounds may be used alone or in combination of two or more.

  The amount of the diamine compound used is preferably 0.001 to 0.5 parts by weight, and 0.01 to 0.2 parts by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer, from the viewpoint of reducing residual monomers and water-soluble components. More preferred.

  In the present invention, a method for polymerizing a water-soluble ethylenically unsaturated monomer in the presence of a diamine compound and a water-soluble radical polymerization initiator is not particularly limited, and is a typical method, reverse phase suspension weight. A combination method, an aqueous solution polymerization method, or the like is used. In the reverse phase suspension polymerization, for example, an aqueous solution of a water-soluble ethylenically unsaturated monomer, a water-soluble radical polymerization initiator, and, if necessary, a crosslinking agent are mixed to obtain a surfactant and / or polymer protective colloid. Polymerization is carried out by heating in a hydrocarbon solvent in the presence of. In the aqueous solution polymerization method, polymerization is carried out by mixing an aqueous solution of a water-soluble ethylenically unsaturated monomer, a water-soluble radical polymerization initiator, and, if necessary, a crosslinking agent and heating.

  Hereinafter, the reverse phase suspension polymerization method will be described in more detail as an example of the polymerization method of the water-soluble ethylenically unsaturated monomer.

  The concentration of the monomer in the aqueous solution of the water-soluble ethylenically unsaturated monomer is preferably in the range of 20% by weight to the saturated concentration.

  In addition, when the water-soluble ethylenically unsaturated monomer has an acid group such as (meth) acrylic acid or 2- (meth) acrylamide-2-methylpropanesulfonic acid, the acid group is neutralized by an alkali compound or the like. You can keep it together. Examples of the alkali compound used for neutralization include sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like. These alkali compounds may be used alone or in combination.

  The degree of neutralization of all acid groups by the alkali compound is to increase the osmotic pressure of the resulting water-absorbent resin to increase the absorption capacity, and from the presence of excess alkali compound, the viewpoint of preventing problems such as safety Therefore, 10 to 100 mol% is preferable, and 30 to 80 mol% is more preferable.

  As necessary, the crosslinking agent mixed with the aqueous solution of the water-soluble ethylenically unsaturated monomer before the polymerization reaction (hereinafter also referred to as “internal crosslinking agent”) has, for example, two or more polymerizable unsaturated groups. A compound or the like is used. Specific examples thereof include, for example, (poly) ethylene glycol [in this specification, for example, “polyethylene glycol” and “ethylene glycol” are collectively referred to as “(poly) ethylene glycol”. The same shall apply hereinafter), (poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, di- or tri (meth) acrylates of polyols such as (poly) glycerin; Unsaturated polyesters obtained by reacting unsaturated acids such as acid and fumaric acid; Bisacrylamides such as N, N′-methylenebis (meth) acrylamide; Obtained by reacting polyepoxide and (meth) acrylic acid Di (meth) acrylic acid esters obtained by reacting polyisocyanate such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth) acrylate; allyl Modified starch, allylated cellulose Diallyl phthalate, N, N ', N "- triallyl isocyanate, divinyl benzene, and the like.

  Further, as the internal cross-linking agent, in addition to the compound having two or more polymerizable unsaturated groups, a compound having two or more other reactive functional groups can also be used. Specific examples thereof include, for example, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, glycidyl group-containing compounds such as (poly) glycerin diglycidyl ether, (poly) ethylene glycol, (poly) propylene Examples include glycol, (poly) glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate, and these may be used alone or in combination of two or more.

  As the internal cross-linking agent, (poly) ethylene glycol diacrylate, (poly) ethylene glycol diglycidyl ether and N, N′-methylenebisacrylamide are preferable because of excellent reactivity.

  The amount of the internal crosslinking agent used is preferably 3 parts by weight or less and more preferably 1 part by weight or less with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer from the viewpoint of water absorption performance.

  Examples of the surfactant include sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene Alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, Polyethylene glycol fatty acid ester, alkyl glucoside, N-alkyl gluconamides Polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, and the like. These may be used alone or in combination of two or more. Among these, sorbitan fatty acid ester, polyglycerin fatty acid ester and sucrose fatty acid ester are preferable.

  The amount of the surfactant used is preferably from 0.1 to 5 parts by weight, preferably from 0.3 to 3 parts by weight, based on 100 parts by weight of the aqueous solution of the water-soluble ethylenically unsaturated monomer, from the viewpoint of suspension stability during polymerization. Is more preferable.

  Examples of polymer protective colloids include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified EPDM (ethylene / propylene / diene / terpolymer), and maleic anhydride. Acid-modified polybutadiene, ethylene / maleic anhydride copolymer, ethylene / propylene / maleic anhydride copolymer, butadiene / maleic anhydride copolymer, oxidized polyethylene, ethylene / acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose These may be used singly or in combination of two or more. Among these, from the viewpoint of dispersion stability of the aqueous monomer solution, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, oxidized polyethylene, and ethylene / acrylic acid copolymer. Coalescence is preferred.

  The amount of the polymeric protective colloid used is preferably from 0.1 to 5 parts by weight, preferably from 0.3 to 3 parts by weight, based on 100 parts by weight of the aqueous solution of the water-soluble ethylenically unsaturated monomer, from the viewpoint of suspension stability during polymerization. Part is more preferred.

  Examples of the hydrocarbon solvent include aliphatic hydrocarbons such as n-hexane, n-heptane, n-octane, and ligroin, alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, and methylcyclohexane, benzene, and toluene. And aromatic hydrocarbons such as xylene, and the like. These may be used alone or in combination of two or more. Among these, n-hexane, n-heptane, and cyclohexane are preferable from the viewpoint of industrial availability, stable quality, and low cost.

  The amount of the hydrocarbon solvent used is preferably 50 to 600 parts by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer from the viewpoint of suspension stability of the water-soluble ethylenically unsaturated monomer. 80 to 550 parts by weight is more preferable.

  In addition, when polymerizing by the reverse phase suspension polymerization method, a polymerization method in which a water-soluble ethylenically unsaturated monomer as a raw material monomer is added at once to perform a polymerization reaction, a water-soluble ethylenically unsaturated monomer is Any method of the multistage polymerization method in which the polymerization reaction is carried out by adding in several parts can be adopted, but from the viewpoint of excellent economic efficiency, the water-soluble ethylenically unsaturated monomer is added in several parts Thus, a multistage polymerization method in which a polymerization reaction is performed is preferable. When performing by the multistage polymerization method, the diamine compound may be present from the first stage or from the second stage, but from the viewpoint of increasing the water absorption rate of the resulting water-absorbent resin, the second and subsequent stages. It is preferable to make it exist. The water-soluble ethylenically unsaturated monomer used in the second and subsequent stages may be the same as or different from the monomer used in the first stage.

  The reaction temperature during the polymerization reaction is preferably 20 to 110 ° C., more preferably 40 to 90 ° C., from the viewpoint of promoting appropriate progress of the reaction. In addition, the reaction time varies depending on the type of raw material used and the like, and thus cannot be determined unconditionally, but is preferably about 0.1 to 2 hours. The polymerization reaction is preferably performed in an inert gas atmosphere such as nitrogen gas. The completion of the polymerization reaction of the water-soluble ethylenically unsaturated monomer can be confirmed by, for example, maximizing the reaction temperature due to a temperature rise due to reaction heat.

  In the present invention, after the polymerization reaction of the water-soluble ethylenically unsaturated compound, a crosslinking agent (hereinafter also referred to as “post-crosslinking agent”) is added to carry out the crosslinking reaction.

  The post-crosslinking agent is not particularly limited as long as it can react with the carboxyl group of the polymer of the water-soluble ethylenically unsaturated compound.For example, (poly) ethylene glycol diglycidyl ether, (poly) glycerol (poly) Glycidyl group-containing compounds such as glycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) ethylene glycol, (poly) propylene glycol, (poly) glycerin, pentaerythritol, ethylenediamine, polyethyleneimine These may be used singly or in combination of two or more. Among these, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether are preferable from the viewpoint of reactivity.

  The amount of the post-crosslinking agent varies depending on the type and cannot be determined unconditionally. From the viewpoint of improving the water absorption capacity under pressure with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer. 0.01 parts by weight or more is preferable, and from the viewpoint of improving water retention capacity, 5 parts by weight or less is preferable. From these viewpoints, the amount of the post-crosslinking agent used is preferably 0.01 to 5 parts by weight, more preferably 0.02 to 4 parts by weight, and 0.03 to 3 parts by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer. Part is more preferable.

  The time for adding the post-crosslinking agent is not particularly limited as long as it is after completion of the polymerization reaction of the monomer. The post-crosslinking agent is preferably added in the presence of water. The amount of water when adding the post-crosslinking agent is preferably 5 parts by weight or more from the viewpoint of improving water absorption capacity under pressure with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer. From the viewpoint of improving the content, 300 parts by weight or less is preferable. From these viewpoints, the amount of water used is preferably 5 to 300 parts by weight, more preferably 10 to 100 parts by weight, and 10 to 50 parts by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer. Further preferred. The amount of water means the total amount of water contained in the polymerization reaction system and water used as necessary when adding the post-crosslinking agent. Excess water, hydrocarbon solvent in the polymerization reaction system When such a solvent is contained, it is preferable to distill off the solvent as appropriate before adding the crosslinking agent.

  The reaction temperature at the time of the crosslinking reaction varies depending on the type of post-crosslinking agent used and the like, and therefore cannot be determined unconditionally. In the case where the diamine compound used in the present invention has a primary amino group (-NH2) and / or a secondary amino group (monosubstituted amino group) at the terminal, from the viewpoint of promoting the progress of an appropriate reaction, 50 ° C or higher Preferably, 150 ° C. or lower is preferable from the viewpoint of preventing the diamine compound from acting as a crosslinking agent. From these viewpoints, the reaction temperature is preferably 50 to 150 ° C, more preferably 70 to 130 ° C.

  In addition, when the diamine compound used in the present invention has a tertiary amino group (disubstituted amino group) at the terminal, the reaction temperature of the crosslinking reaction is preferably 50 ° C. or more from the viewpoint of promoting an appropriate progress of the reaction, From the viewpoint of preventing thermal decomposition, 250 ° C. or lower is preferable. From these viewpoints, the reaction temperature is preferably 50 to 250 ° C, more preferably 70 to 180 ° C.

  The reaction time of the cross-linking reaction varies depending on the post-crosslinking agent used, and thus cannot be determined unconditionally, but is preferably about 30 minutes to 6 hours. After completion of the crosslinking reaction, the water-absorbent resin of the present invention is obtained by distilling off a solvent such as water or a hydrocarbon solvent used for the polymerization reaction or the crosslinking reaction.

In the present invention, when using a diamine compound having a primary amino group (—NH ₂ ) and / or a secondary amino group (monosubstituted amino group) at the terminal, the temperature at which the solvent is distilled off after the polymerization reaction or after the crosslinking reaction Is preferably 60 ° C. or higher from the viewpoint of quickly distilling off the solvent, and preferably 150 ° C. or lower from the viewpoint of preventing the diamine compound from acting as a crosslinking agent. From these viewpoints, the temperature when the solvent is distilled off is preferably 60 to 150 ° C, more preferably 80 to 130 ° C.

  Further, when using a diamine compound having a tertiary amino group (disubstituted amino group) at the terminal, the temperature at which the solvent is distilled off is preferably 60 ° C. or higher from the viewpoint of quickly distilling off the solvent. From the viewpoint of preventing internal crosslinking and thermal decomposition of the obtained polymer, it is preferably 250 ° C. or lower. From these viewpoints, the temperature when the solvent is distilled off is preferably 60 to 250 ° C, more preferably 80 to 180 ° C.

  The average particle diameter of the water absorbent resin of the present invention is preferably 100 to 600 μm, and more preferably 300 to 500 μm, from the viewpoint of the water absorption rate when used in a water absorbent article. When the water-soluble ethylenically unsaturated monomer is polymerized by reversed-phase suspension polymerization, the particle size of the resulting polymer can be adjusted by adjusting the stirring speed of the reaction solution. In addition, when the polymer is obtained in a lump like aqueous solution polymerization, it is preferably subjected to a crosslinking reaction after previously adjusting to a desired particle size by pulverization or the like.

  The water retention capacity and the water absorption capacity under pressure required for the water-absorbent resin of the present invention differ depending on the intended use, and thus cannot be determined unconditionally. For example, the water-absorbent resin of the present invention can be determined for hygiene for infants such as disposable diapers. When used as a material, from the viewpoint of reducing the amount of liquid returned from the absorber under load, the physiological saline retention capacity under no load is preferably 40 g / g or more, under pressure under a load of 2.07 kPa. The physiological saline water absorption capacity is preferably 25 ml / g or more. The physiological saline is a 0.9% by weight sodium chloride aqueous solution.

  On the other hand, when the water-absorbent resin of the present invention is used for an adult sanitary material such as an incontinence pad or a sanitary napkin, from the same viewpoint as described above, the physiological saline retention capacity under no load is preferably 30 g / The physiological saline water absorption capacity under pressure with a load of 4.14 kPa or more is preferably 20 ml / g or more.

  Furthermore, the water absorption rate of the water absorbent resin is preferably 20 to 80 seconds, and more preferably 30 to 60 seconds, for the same reason as described above. Further, the water soluble content of the water absorbent resin is preferably 25% by weight or less, and more preferably 15% by weight or less.

  In addition, you may add additives, such as a lubricant, a deodorizer, an antibacterial agent, to the water absorbing resin of this invention further according to the objective.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such examples.

Example 1
An Erlenmeyer flask having an internal volume of 1 liter was charged with 92 g of an 80% by weight aqueous acrylic acid solution, and 102.2 g of a 30% by weight aqueous sodium hydroxide solution was added dropwise while cooling with ice from the outside to neutralize 75% by mole of acrylic acid. Further, 54.4 g of water was added to prepare a 37 wt% partially neutralized acrylic acid aqueous salt solution. In the obtained aqueous solution of partially neutralized acrylic acid, 8.3 mg of N, N′-methylenebisacrylamide as an internal cross-linking agent, 0.11 g of potassium persulfate as a water-soluble radical polymerization initiator, and N, N, N ′, N ′ -0.046 g of tetramethylethylenediamine was added to make a polymerization solution.

  321 g of n-heptane was added to a 5-liter cylindrical round bottom flask with an internal volume of 2 liters equipped with a stirrer, a stirring blade, a reflux condenser, a dropping funnel and a nitrogen gas inlet, and sucrose stearate (Mitsubishi Chemical Foods). Product name: Ryoto Sugar Ester S-370 (0.92 g) and maleic anhydride modified ethylene / propylene copolymer (Mitsui Chemicals, High Wax 1105A) (0.92 g) were added and dissolved. The polymerization solution was added and suspended under stirring, and the system was replaced with nitrogen gas. Subsequently, the temperature was raised in a water bath at 70 ° C. and held for 1 hour to carry out reverse phase suspension polymerization.

  After completion of the polymerization, the temperature of the reaction solution was raised in an oil bath at 125 ° C., 120 g of water was removed out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water, and a post-crosslinking agent. 3.0 g of a 2 wt% ethylene glycol diglycidyl ether aqueous solution was added, and the mixture was kept at 80 ° C. for 2 hours. Further, water and n-heptane were distilled off at 125 ° C. to obtain 93 g of a water absorbent resin.

Example 2
An Erlenmeyer flask having an internal volume of 1 liter was charged with 92 g of an 80% by weight aqueous acrylic acid solution, and 102.2 g of a 30% by weight aqueous sodium hydroxide solution was added dropwise while cooling with ice from the outside to neutralize 75% by mole of acrylic acid. Further, 54.4 g of water was added to prepare a 37 wt% partially neutralized acrylic acid aqueous salt solution. To the resulting aqueous solution of partially neutralized acrylic acid salt, 8.3 mg of N, N′-methylenebisacrylamide as an internal crosslinking agent and 0.11 g of potassium persulfate as a water-soluble radical polymerization initiator are added, and this is used for the first stage polymerization. It was set as the solution.

  321 g of n-heptane was added to a 5-liter cylindrical round bottom flask with an internal volume of 2 liters equipped with a stirrer, a stirring blade, a reflux condenser, a dropping funnel and a nitrogen gas inlet, and sucrose stearate (Mitsubishi Chemical Foods). Product name: Ryoto Sugar Ester S-370 (0.92 g), maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemicals, High Wax 1105A) (0.92 g) was added and dissolved. The total amount of the first stage polymerization solution prepared above was added and suspended under stirring, and the system was replaced with nitrogen gas. Subsequently, the temperature was raised to 70 ° C. and maintained for 1 hour to carry out the first-stage reverse phase suspension polymerization.

  Separately, 128g of 80wt% acrylic acid aqueous solution was placed in an Erlenmeyer flask with an internal volume of 1 liter, and 142.9g of 30wt% sodium hydroxide aqueous solution was added dropwise with ice cooling to neutralize 75mol% of acrylic acid. did. Further, 33.9 g of water was added to prepare a 42% by weight aqueous solution of partially neutralized acrylic acid. To the resulting partially neutralized acrylic acid aqueous solution, 0.15 g of potassium persulfate and 0.064 g of N, N, N ′, N′-tetramethylethylenediamine were added as a water-soluble radical polymerization initiator, and this was added to the second stage. A polymerization solution was obtained.

  After completion of the first-stage reversed-phase suspension polymerization, the reaction solution is cooled to room temperature, and the whole amount of the second-stage polymerization solution prepared above is added dropwise thereto. Replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C. and held for 2 hours to carry out the second-stage reverse phase suspension polymerization.

  After completion of the polymerization, the temperature of the reaction solution was raised in an oil bath at 125 ° C., and 260 g of water was removed from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. 8.14 g of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added and held at 80 ° C. for 2 hours. Further, water and n-heptane were distilled off at 125 ° C. to obtain 230 g of a water absorbent resin.

Example 3
In the preparation of the second stage polymerization solution of Example 2, 0.033 g of ethylenediamine was used instead of N, N, N ′, N′-tetramethylethylenediamine, and water and n-heptane were distilled off at 110 ° C. 229 g of a water-absorbent resin was obtained in the same manner as in Example 2 except that

Example 4
In the preparation of the second-stage polymerization solution of Example 2, 0.049 g of N, N′-dimethylethylenediamine was used instead of N, N, N ′, N′-tetramethylethylenediamine, and water and n-heptane were further used. Was carried out in the same manner as in Example 2 except that 229 g of a water absorbent resin was obtained.

Example 5
In the preparation of the first-stage polymerization solution of Example 2, 0.035 g of N, N′-dimethylethylenediamine was added to the aqueous solution of partially neutralized acrylic acid salt together with the internal crosslinking agent and the water-soluble radical polymerization initiator. In the preparation of the eye polymerization solution, 0.049 g of N, N′-dimethylethylenediamine was used instead of N, N, N ′, N′-tetramethylethylenediamine, and water and n-heptane were distilled off at 120 ° C. 228 g of a water-absorbent resin was obtained in the same manner as in Example 2 except that

Example 6
Into a 5-liter cylindrical round bottom flask with an internal volume of 2 liters equipped with a stirrer, stirring blade, reflux condenser, dropping funnel and nitrogen gas inlet, put 184 g of 80% by weight acrylic acid aqueous solution, and 11.4 wt. 540 g of an aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% of acrylic acid to prepare a 25 wt% aqueous partially neutralized acrylic acid salt solution. In the obtained aqueous solution of partially neutralized acrylic acid, 18.4 mg of N, N′-methylenebisacrylamide as an internal crosslinking agent, 0.184 g of potassium persulfate as a water-soluble radical polymerization initiator, and N, N, N ′, N ′ -After adding 0.092 g of tetramethylethylenediamine and replacing the inside of the system with nitrogen gas, the solution was kept in a water bath at 50 ° C for 1 hour to carry out an aqueous solution polymerization reaction.

  The resulting polymerization reaction product was coarsely pulverized with a SUS meat chopper and then dried with a hot air dryer at 140 ° C. for 1 hour. Next, the dried product was pulverized with a rotor speed mill and classified with a JIS standard sieve having an opening of 850 μm, and particles having a size of 850 μm or less were obtained as a precursor of a water absorbent resin.

  The total amount of the obtained water-absorbent resin precursor was placed in a flask having an internal volume of 2 liters equipped with a stirrer, a stirring blade, a cooler, and a gas introduction tube. On the other hand, 18.4 g of water and 6.4 g of 2% by weight ethylene glycol diglycidyl ether aqueous solution as a post-crosslinking agent were added to the precursor of the water-absorbent resin by spraying and heated in an oil bath at 130 ° C. for 30 minutes. A crosslinking reaction was performed to obtain 172 g of a water absorbent resin.

Comparative Example 1
92 g of water-absorbent resin was obtained in the same manner as in Example 1 except that N, N, N ′, N′-tetramethylethylenediamine was not used in Example 1.

Comparative Example 2
In the same manner as in Example 2 except that N, N, N ′, N′-tetramethylethylenediamine was not used in Example 2, 228 g of a water absorbent resin was obtained.

Comparative Example 3
A water-absorbing resin 173 g was obtained in the same manner as in Example 6 except that N, N, N ′, N′-tetramethylethylenediamine was not used in Example 6.

  The water-absorbent resin obtained in each example and comparative example was evaluated by the following method. Table 1 shows the evaluation results of the following items (1) to (5).

(1) Physiological saline water retention capacity 2.00 g of water-absorbing resin is put into a cotton bag (Membroad No. 60, width 100 mm x length 200 mm) and placed in a 500 mL beaker. 500 g of physiological saline is poured into the cotton bag, the opening is tied with a rubber band, and left for 1 hour. Thereafter, the cotton bag was dehydrated for 1 minute using a dehydrator having a centrifugal force of 167G (manufactured by Centrifuge Co., Ltd., product number: H-122), and the weight Wa (g ). The same operation is performed without adding the water-absorbent resin, the wet hourly space mass Wb (g) of the cotton bag is measured, and the physiological saline water retention capacity is calculated by the following formula.
Saline retention capacity (g / g) = [Wa-Wb] (g) / mass of water absorbent resin (g)

(2) Saline water absorption capacity under pressure The physiological saline water absorption capacity of a water-absorbing resin under pressure of 2.07 kPa or 4.14 kPa is measured using a measuring device X whose schematic configuration is shown in FIG. .

  The measuring apparatus X shown in FIG. 1 includes a burette unit 1, a conduit 2, a measuring table 3, and a measuring unit 4 placed on the measuring table 3. The burette unit 1 has a rubber stopper 14 connected to the upper part of the burette 10, an air introduction pipe 11 and a cock 12 connected to the lower part, and a cock 13 located on the upper part of the air introduction pipe 11. A conduit 2 is attached from the burette part 1 to the measuring table 3, and the diameter of the conduit 2 is 6 mm. At the center of the measuring table 3, there is a hole with a diameter of 2mm, and the conduit 2 is connected. The measuring unit 4 includes a cylinder 40, a nylon mesh 41 attached to the bottom of the cylinder 40, and a weight 42. The inner diameter of the cylinder 40 is 2.0 cm. The nylon mesh 41 is formed to 200 mesh (aperture 75 μm). A predetermined amount of the water-absorbing resin 5 is uniformly distributed on the nylon mesh 41. The weight 42 has a diameter of 1.9 cm and a weight of 59.8 g or 119.5 g. This weight 42 is placed on the water-absorbent resin 5, and a 2.07kPa load is applied uniformly to the water-absorbent resin 5 by a weight of 59.8g and a load of 4.14kPa by a weight of 119.5g. Be able to.

  In the measuring apparatus X having such a configuration, first, the cock 12 and the cock 13 of the burette unit 1 are closed, and physiological saline adjusted to 25 ° C. is poured from the upper part of the burette 10, and the stopper at the upper part of the burette is plugged with the rubber plug 14. Then, the cock 12 and the cock 13 of the burette unit 1 are opened. Next, the height of the measurement table 3 is adjusted so that the tip of the conduit 2 at the center of the measurement table 3 and the air introduction port of the air introduction tube 11 have the same height.

  On the other hand, 0.10 g of the water absorbent resin 5 is uniformly spread on the nylon mesh 41 of the cylinder 40, and the weight 42 is placed on the water absorbent resin 5. The measuring part 4 is placed so that the center part thereof coincides with the conduit port of the central part of the measuring table 3.

From the time when the water absorbent resin 5 starts to absorb water, the amount of decrease in physiological saline in the burette 10 (the amount of physiological saline absorbed by the water absorbent resin 5) Wc (mL) is read. The water absorption capacity under pressure of the water absorbent resin 5 after 60 minutes from the start of water absorption is calculated from the following equation.
Water absorption capacity (mL / g) = Wc / 0.10

(3) Water absorption speed
In a 100 ml beaker, put 50 ± 0.1 g of physiological saline at a temperature of 25 ± 0.2 ° C., and adjust the rotation speed to 600 r / min using a magnetic stirrer bar (8 mmφ × 30 mm). Next, 2.0 ± 0.002 g of water-absorbing resin is quickly added to the beaker, and the stopwatch is started as soon as the addition is completed. The time (seconds) until the water-absorbing resin absorbs physiological saline and the vortex disappears is measured with a stopwatch, and is defined as the water absorption rate.

(4) Water-soluble component
In a 500 mL beaker, weigh 500 ± 0.1 g of physiological saline, add a magnetic stirrer bar (without 8mmφ × 30mm ring), and adjust it to rotate at 600r / min using a magnetic stirrer. .

  Next, 2.0 ± 0.002g of water-absorbent resin classified by JIS-Z8801-1982 standard sieve (mesh size 500μm, 300μm) and particle size adjustment (500μm or less, 300μm or more) is added to the beaker. Stir for 3 hours. The water-absorbent resin-dispersed water after stirring for 3 hours is filtered with a standard sieve (aperture 75 μm), and the obtained filtrate is further filtered with suction using a Kiriyama funnel (filter paper No. 6).

  The obtained filtrate is weighed 80 ± 0.1 g into a 100 mL beaker and dried with a hot air dryer (model number: FV-320, manufactured by ADVANTEC, Inc.) at 140 ° C. until it reaches a constant weight, and the weight Wd (g ).

On the other hand, it carries out similarly to the said operation, without using a water absorbing resin, measures the weight We (g) of filtrate solid content, and calculates a water-soluble content from following Formula.
Water-soluble content (% by weight) = [[(Wd−We) × (500/80)] / 2] × 100

(5) Average particle diameter 0.5 g of amorphous silica (manufactured by Degussa Japan Co., Ltd., Sipernat 200) is mixed with 100 g of water-absorbent resin particles as a lubricant.

  From the top of the JIS standard sieve, sieve with an opening of 600 μm, sieve with an opening of 500 μm, sieve with an opening of 355 μm, sieve with an opening of 300 μm, sieve with an opening of 250 μm, sieve with an opening of 180 μm, sieve with an opening of 106 μm, and tray Combine, put the water-absorbent resin on the top sieve, and shake for 20 minutes using a low-tap shaker.

  Next, the weight of the water-absorbent resin particles remaining on each sieve is calculated as a percentage by weight with respect to the total amount, and by integrating in order from the smaller particle diameter, the sieve weight and the weight percentage remaining on the sieve are integrated. Plot the relationship with the values on a logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle diameter corresponding to the cumulative weight percentage of 50% by weight is taken as the average particle diameter.

  From the results shown in Table 1, the water-absorbing resins obtained in the examples compared with the water-absorbing resins obtained in the comparative examples have the ability to retain physiological saline and absorb physiological saline under pressure. It can be seen that the water absorption rate is high, the water absorption rate is low, and the water-soluble content is small.

  The water-absorbent resin obtained by the method of the present invention can be suitably used for sanitary materials such as paper diapers, incontinence pads, sanitary napkins, especially paper diapers.

It is a schematic diagram which shows schematic structure of the apparatus for measuring the water absorption ability under pressure.

Explanation of symbols

X Measuring device 1 Bullet part 10 Bullet 11 Air introduction pipe 12 Cock 13 Cock 14 Rubber stopper 2 Conduit 3 Measuring table 4 Measuring part 40 Cylinder 41 Nylon mesh 42 Weight 5 Water absorbing resin

Claims (6)

A method for producing a water-absorbent resin by polymerizing a water-soluble ethylenically unsaturated monomer, which comprises the formula (I):

(In the formula, R ¹ represents a linear alkylene group having 1 to 6 carbon atoms or a phenylene group, and R ² , R ³ , R ⁴ and R ⁵ each independently represents a methyl group, an ethyl group or a hydrogen atom)
In the presence of a diamine compound or a salt thereof and a water-soluble radical polymerization initiator, the water-soluble ethylenically unsaturated monomer is subjected to a polymerization reaction, and after the polymerization reaction, a crosslinking agent is added to perform a crosslinking reaction. A method for producing a water-absorbent resin characterized by comprising:   The production method according to claim 1, wherein the amount of the diamine compound or a salt thereof used is 0.001 to 0.5 parts by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer.   The production method according to claim 1 or 2, wherein the water-soluble radical polymerization initiator is a persulfate.   The water absorbing resin obtained by the method in any one of Claims 1-3.   The water-absorbent resin according to claim 4, wherein the physiological saline water retention capacity is 40 g / g or more, and the physiological saline water absorption capacity under pressure at a load of 2.07 kPa is 25 ml / g or more.   The water-absorbent resin according to claim 4, wherein the physiological saline water retention capacity is 30 g / g or more, and the physiological saline water absorption capacity under pressure at a load of 4.14 kPa is 20 ml / g or more.

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