JPH09143210A - Water-absorbing resin and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the subject resin having high and stable absorbability of salt-containing water by polymerizing a water-soluble ethylenic unsaturated monomer by polymerization operations including three steps. SOLUTION: (A) An aqueous solution of a water-soluble ethylenic unsaturated monomer [preferably (meth)acrylic acid, etc.] is subjected to reverse-phase suspension polymerization in (B) a hydrocarbon solvent in the presence of (C) a surfactant and/or a polymeric protecting colloid. The action of the component C is eliminated after the polymerization. The polymerization reaction system is incorporated with (D) an aqueous solution of a water-soluble ethylenic unsaturated monomer containing nonionic macromonomer and again subjected to reverse-phase suspension polymerization. The final stage is preferably repeated twice or more. The macromonomer of the component D is preferably selected from carbamyl esters of the formula [R<1> is H or methyl; R<2> is H, methyl or ethyl; R<3> is a 1-8C hydrocarbon group; (n) is 1-500 on an average; (m) is 0-200 on an average; n>=m; Σ(n+m)=1 to 500], etc.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water-absorbent resin and a method for producing the same, and more particularly to a water-absorbent resin having excellent salt water-absorbent ability and a method for producing the same.

[0002]

2. Description of the Related Art As water-absorbent resins, various substances such as a hydrolyzate of starch-acrylonitrile graft polymer and a partially neutralized product of crosslinked polyacrylic acid have been known for a long time. Generally, such a water-absorbent resin can exhibit a high water-absorbing ability several hundred to several thousand times its own weight with respect to fresh water, but its water-absorbing ability with respect to water containing salts is extremely small. Therefore, in the field of water-absorbent resins, various attempts have been made to improve the water-absorbing ability with respect to water containing salts.

As a water-absorbent resin having an improved ability to absorb water containing salts, a combination of an ionic water-absorbent resin having a small salt resistance and a nonionic water-absorbent resin having a large salt resistance is considered. Has been.

As such a water-absorbent resin, for example, the following have been proposed. (1) A water-swellable polymer composed of a copolymer of an ethylenically unsaturated monomer containing a carboxyl group and a salt thereof and a polyoxyalkylene glycol allyl ether having a hydrophobic group at one end (JP-A-62-27408).
issue). (2) Ethylenically unsaturated monomer containing a carboxyl group and its salt, and alkyl polyoxyalkylene glycol mono (meth) having an alkyl group at one end
A water-swellable polymer composed of a copolymer with an acrylate (JP-A-3-93815). (3) Water absorption obtained by mixing an ionic polymer containing a carboxyl group and its salt with polyvinyl alcohol and polyethylene oxide, which are nonionic polymers, and adding a peroxide radical initiator to this mixture to heat-crosslink the mixture. Resin (JP-A-1-92226). (4) A water-absorbent resin obtained by uniformly mixing an ionic water-absorbent resin and crosslinked polyethylene oxide in the presence of an organic solvent, and then removing the solvent by evaporation (JP-A-63-31).
539). (5) A water absorbent resin comprising an ionic water absorbent resin fine powder, a nonionic water absorbent resin fine powder and a resin binder (JP-A-63-315230).

[0005]

Among the various water-absorbing resins described above, the ionic water-absorbing resin has advantages such as high water-absorbing ability and high-speed water-absorbing ability, and non-ionic water-absorbing resin has advantages such as salt resistance. Are simultaneously exhibited, and the low salt resistance of the ionic water absorbing resin and the low water absorbing property of the nonionic resin are improved to some extent. However, with these water-absorbent resins, the water-absorbing ability decreases with time, and good water-absorbing ability with respect to water containing salts cannot be stably maintained.

An object of the present invention is to enhance and stabilize water absorption of water containing a salt in a water absorbent resin.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a water-soluble ethylenically unsaturated monomer having a carboxyl group or a carboxylic acid salt is subjected to reverse phase suspension. Polymerization is carried out in a liquid by the first-stage polymerization reaction to obtain a polymer gel, and then the obtained polymer gel is allowed to absorb an aqueous solution of a water-soluble monomer containing a nonionic monomer as a main component to obtain a polymer gel of the second stage. It was found that the water-absorbent resin obtained by carrying out the polymerization reaction contains both ionic components and non-ionic components, has a high water-absorbing property with respect to water containing salts, and is stable and hardly deteriorates. The present invention has been completed.

That is, the water-absorbent resin according to the present invention is a reversed-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer aqueous solution in a hydrocarbon solvent in the presence of a surfactant and / or a polymer protective colloid. Of the first step, a second step of eliminating the action of the surfactant and / or the polymeric protective colloid after the first step, and a nonionic macromolecule in the polymerization reaction system after the second step. A third step of adding a water-soluble ethylenically unsaturated monomer containing a monomer and further performing a reverse phase suspension polymerization is obtained by a polymerization operation. In the polymerization operation, the third step may be repeated twice or more.

In this water absorbent resin, the reverse phase suspension polymerization in the above-mentioned first step and / or the above-mentioned third step is carried out, for example, in the presence of a crosslinking agent.

The water-soluble ethylenically unsaturated monomer aqueous solution used in the first step and the third step is, for example, at least one selected from the group consisting of acrylic acid, methacrylic acid and alkali salts thereof. Is.

Further, the nonionic macromonomer used in the third step is, for example, a carbamyl ester represented by the following general formula (1) or a carbamyl ester represented by the following general formula (2). At least selected from the group consisting of an alkyl polyoxyalkylene glycol (meth) acrylate represented by the following general formula (3) and an alkyl polyoxyalkylene glycol (meth) allyl ether represented by the following general formula (4). It is one kind. (Note that in this specification, “acrylic” and “methacrylic” are collectively referred to as “(meth) acrylic”.)

[0012]

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In the general formulas (1), (2), (3) and (4), R ¹ is hydrogen or a methyl group, R ² is hydrogen,
A methyl group or an ethyl group, and R ³ each represents a hydrocarbon group having 1 to 8 carbon atoms. n has an average value of 1 to 500, and m has an average value of 0 to 20.
0. n and m are n ≧ m and Σ (n + m) = 1
The condition of ~ 500 is satisfied.

The water absorbent resin according to the present invention has a surface layer portion rich in nonionic water absorbing component and a central portion rich in ionic water absorbing component.

The method for producing a water-absorbent resin according to the present invention is a reverse phase suspension of a water-soluble ethylenically unsaturated monomer aqueous solution in a hydrocarbon solvent in the presence of a surfactant and / or a polymeric protective colloid. The first step of polymerizing, the second step of eliminating the action of the surfactant and / or the polymeric protective colloid after the first step, and the polymerization reaction system that has completed the second step is nonionic A third step of adding a water-soluble ethylenically unsaturated monomer containing a macromonomer and further performing reverse phase suspension polymerization.

In this manufacturing method, the third step is
May be repeated more than once.

In this production method, the reverse phase suspension polymerization in the first step and / or the third step is carried out, for example, in the presence of a crosslinking agent.

Further, the concentration of the monomer in the aqueous solution of the water-soluble ethylenically unsaturated monomer used in the first step and the water-soluble ethylenically unsaturated monomer containing the nonionic macromonomer used in the third step The monomer concentration in the aqueous solution is usually 25% by weight or more.

Further, the water-soluble ethylenically unsaturated monomer aqueous solution containing the nonionic macromonomer used in the third step is usually the same as the water-soluble ethylenically unsaturated monomer aqueous solution used in the first step. It is set to 50 to 300% by weight.

Further, the water-soluble ethylenically unsaturated monomer aqueous solution used in the first step and the third step is, for example,
It is at least one selected from the group consisting of acrylic acid, methacrylic acid and alkali salts thereof.

Further, the nonionic macromonomer used in the third step is, for example, a carbamyl ester represented by the following general formula (1) or a carbamyl ester represented by the following general formula (2). At least selected from the group consisting of an alkyl polyoxyalkylene glycol (meth) acrylate represented by the following general formula (3) and an alkyl polyoxyalkylene glycol (meth) allyl ether represented by the following general formula (4). It is one kind.

[0022]

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In the general formulas (1), (2), (3) and (4), R ¹ , R ² , R ³ , n and m are the same as described above.

The surfactant used in the first step is, for example, a nonionic surfactant or a combination of a nonionic surfactant and an anionic surfactant.

The surfactant may be, for example, a sorbitan fatty acid ester, a polyglycerin fatty acid ester, a sucrose fatty acid ester, a sorbitol fatty acid ester, a polyoxyethylene alkylphenyl ether, and a hydrophobic group consisting of a dodecyl glycol group at one or both ends. It is at least one selected from the group consisting of poly (oxyethylene) glycol / dodecyl glycol block copolymers which have and are formed by polyoxyethylene chains.

Further, the surfactant is, for example, a polymerizable surfactant represented by the following general formula (5).

[Chemical 6] In the general formula (5), R ⁴ represents a hydrocarbon group having at least 9 carbon atoms, and R ⁵ represents an acryloyl group, a methacryloyl group or a maleoyl group. Also, l is 30 to 70.

The polymer protective colloid used in the first step is, for example, ethyl cellulose, ethyl hydroxyethyl cellulose, oxidation modified polyethylene, maleic anhydride modified polyethylene, maleic anhydride modified polybutadiene, maleic anhydride modified ethylene propylene diene It is at least one selected from the group consisting of terpolymers.

In the second step, for example, the surfactant and / or the polymer protective colloid are deposited by a cooling operation to eliminate the action of the surfactant and / or the polymer protective colloid.

The hydrocarbon solvent used in the first step is
For example, it is at least one selected from the group consisting of n-hexane, n-heptane, cyclohexane, toluene and xylene.

When a crosslinking agent is used, examples of the crosslinking agent include ethylene glycol diglycidyl ether,
Polyethylene glycol diglycidyl ether, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, or N, N′-methylenebisacrylamide is used.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION The water absorbent resin according to the present invention can be manufactured by the following manufacturing method. The manufacturing method will be described below.

First, a water-soluble ethylenically unsaturated monomer aqueous solution is subjected to reverse phase suspension polymerization in a hydrocarbon solvent (first step). The hydrocarbon solvent used here is an aliphatic hydrocarbon solvent, an alicyclic hydrocarbon solvent or an aromatic hydrocarbon solvent. Examples of the aliphatic hydrocarbon solvent include n-pentane, n-hexane, n-heptane, ligroin and the like. As the alicyclic hydrocarbon solvent, for example,
Examples thereof include cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane and the like. Examples of aromatic hydrocarbon solvents include benzene, toluene and xylene. Among these hydrocarbon solvents, preferable ones are n-hexane, n-heptane, cyclohexane, toluene and xylene, which have industrially constant quality and are easily available and inexpensive.

The above hydrocarbon solvents may be used as a mixture of two or more kinds.

The water-soluble ethylenically unsaturated monomer constituting the water-soluble ethylenically unsaturated monomer aqueous solution used in this step is not particularly limited, and various kinds can be used. Specific examples of the water-soluble ethylenically unsaturated monomer include (meth) acrylic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid and alkali salts thereof, diethylaminoethyl (meth).
Examples thereof include amino group-containing unsaturated monomers such as acrylate, diethylaminopropyl (meth) acrylate, and dimethylaminopropyl (meth) acrylamide, and quaternary compounds thereof. Two or more kinds of such water-soluble ethylenically unsaturated monomers may be mixed and used.

The above water-soluble ethylenically unsaturated monomers include (meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide, 2-
Nonionic monomers such as hydroxyethyl (meth) acrylate and N-methylol (meth) acrylamide may be mixed.

The water-soluble ethylenically unsaturated monomer used in this step is preferably acrylic acid, methacrylic acid or an alkali salt thereof.

The concentration of the above-mentioned water-soluble ethylenically unsaturated monomer aqueous solution used in this step is not particularly limited as long as it is equal to or lower than the saturation concentration of the monomer used. However, the polymerization reaction efficiency represented by the energy required to heat up to the polymerization start temperature and the product acquisition rate per volume of the polymerization tank, the thermal energy required to dry the polymer, and the particles of the product polymer powder. In terms of the size of the diameter and the like, it is generally preferable that the concentration is set to 25% by weight to the saturated concentration.

When the above aqueous suspension of the water-soluble ethylenically unsaturated monomer is subjected to reverse phase suspension polymerization, a surfactant or a polymeric protective colloid is present in a hydrocarbon solvent. The surfactant and the polymeric protective colloid may be used in combination.

The surfactant used here is not particularly limited as long as it is capable of reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer aqueous solution. Specific examples of usable surfactants include sorbitan fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, sorbitol fatty acid ester and polyoxyethylene alkylphenyl ether, and a hydrophobic group consisting of dodecyl glycol residue at one or both ends. And nonionic surfactants such as poly (oxyethylene) glycol / dodecylglycol block copolymers which have the formula: and are formed by polyoxyethylene chains. Two or more kinds of such nonionic surfactants may be mixed and used.

Further, such a nonionic surfactant is
It can also be used in combination with an anionic surfactant. Examples of the anionic surfactant include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfate ester salts, polyoxyethylene alkyl ether sulfonates, and the like.

Further, as the surfactant, those represented by the following general formula (5) may be used.

[0042]

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In the general formula (5), R ⁴ is a hydrocarbon group having at least 9 carbon atoms, and examples thereof include an alkylphenyl group and an alkylnaphthyl group. More specifically, for example, nonylphenyl. Groups. R ⁵
Is a radically polymerizable group, specifically, an acryloyl group, a methacryloyl group or a maleoyl group.
Further, l, which indicates the condensation degree of the ethylene oxide moiety, is 30
~ 70.

On the other hand, as the polymer protective colloid, various kinds can be used as long as they are capable of reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer aqueous solution. For example, ethyl cellulose, ethyl hydroxyethyl cellulose, oxidation-modified polyethylene, maleic anhydride-modified polyethylene, maleic anhydride-modified polybutadiene, maleic anhydride-modified EPDM (ethylene propylene diene terpolymer), polyvinyl alcohol, polyvinyl pyrrolidone, etc. are used. The polymer protective colloid can also be used in combination with the above-mentioned anionic surfactant.

The amount of the surfactant and / or polymer protective colloid used is usually 0.1 to 5% by weight, preferably 0.1% by weight of the aqueous solution of the water-soluble ethylenically unsaturated monomer used in this step. It is 2-3% by weight.

In this step, a crosslinking agent may be further used if desired. When a cross-linking agent is used, the gel strength of the resulting water absorbent resin at the time of absorbing water is improved and the stability of the water absorbent gel with time is improved.

The cross-linking agent which can be used in this step is
It has two or more polymerizable unsaturated groups or reactive functional groups. Examples of the cross-linking agent having two or more polymerizable unsaturated groups include ethylene glycol, propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, polyglycerin, and other polyols such as di- or tri (meth) acryl. Acid esters, unsaturated polyesters obtained by reacting the above polyols with unsaturated acids such as maleic acid and fumaric acid, bisacrylamides such as N, N′-methylenebisacrylamide, polyepoxides and (meth) Di or tri (meth) acrylic acid esters obtained by reacting with acrylic acid, polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate, and di (meth) acrylate obtained by reacting hydroxyethyl (meth) acrylate Examples thereof include carbamyl acrylic acid esters, allylated starch, allylated cellulose, diallyl phthalate, N, N ′, N ″ -triallyl isocyanurate, and divinylbenzene.

Preferred cross-linking agents having two or more polymerizable unsaturated groups are ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol diacrylate. Methacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, diallyl phthalate, N, N ′, N ″ -triallyl isocyanurate,
N, N'-methylenebisacrylamide.

On the other hand, as the cross-linking agent having two or more reactive functional groups, for example, a diglycidyl ether compound, a haloepoxy compound, an isocyanate compound or the like can be used, and among them, the diglycidyl ether compound is preferable. Specific examples of the diglycidyl ether compound include, for example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, polyglycerin diglycidyl ether, and the like. . Of these, particularly preferred is ethylene glycol diglycidyl ether.

Examples of the haloepoxy compound include epichlorohydrin, epibromhydrin, α-methylepichlorohydrin and the like. Furthermore, examples of the isocyanate compound include 2,4-tolylene diisocyanate and hexamethylene diisocyanate.

The above-mentioned cross-linking agent can improve the gel strength of the water-absorbent resin at the time of absorbing water as described above. However, if the amount used is excessive, the water-absorbing ability may be deteriorated. Need to be set appropriately. For this reason,
The amount of the crosslinking agent used is usually set to 0.001 to 5% by weight of the water-soluble ethylenically unsaturated monomer used in this step.

When carrying out the reverse phase suspension polymerization in the first step, a radical polymerization initiator is usually used. As the radical polymerization initiator, it is preferable to use a commonly used water-soluble radical polymerization initiator such as potassium persulfate, ammonium persulfate and sodium persulfate. Such a radical polymerization initiator can also be used as a redox type initiator in combination with sulfite or the like.

As the radical polymerization initiator, an oil-soluble radical polymerization initiator can be used. However,
When an oil-soluble radical polymerization initiator is used, the resulting polymer is generally water-soluble, and therefore the above-mentioned crosslinking agent must be used in order to obtain the water absorbent resin of the present invention. In addition,
As the oil-soluble radical polymerization initiator, it is preferable to use benzoyl peroxide, azobisisobutyronitrile or the like.

The amount of the radical polymerization initiator used is usually 0.005 to 1.0 mol% of the water-soluble ethylenically unsaturated monomer used in this step. If it is less than 0.005 mol%, the polymerization reaction will take a long time, and if it exceeds 1.0 mol%, a rapid polymerization reaction will occur, which is dangerous.

The reverse phase suspension polymerization in the first step can be carried out by a usual method using the above-mentioned various materials. At this time, the polymerization temperature varies depending on the polymerization initiator used, but is usually 20 to 110 ° C., preferably 40 to 8
0 ° C. When the polymerization temperature is lower than 20 ° C., the polymerization rate decreases and the polymerization time becomes long, which is not economical. On the contrary, when the temperature is higher than 110 ° C, it becomes difficult to remove the heat of polymerization, and it becomes difficult to carry out a smooth polymerization reaction.

After the completion of the first step as described above, the action of the surfactant and / or the polymeric protective colloid used in the first step is eliminated (second step). When the process proceeds to the third step described later without losing the action of the surfactant and / or the polymer protective colloid, the monomer used in the third step is absorbed in the hydrous gel obtained in the first step. The resin finally obtained is a water-absorbent resin powder containing the ionic monomer used in the first step as a main component and the nonionic macromonomer used in the third step because the resin is in a suspended state before being treated. It is simply a mixture with a water-absorbent resin powder containing as a main component. That is, when the process moves to the third step without passing through the second step, the water-absorbent resin intended by the present invention cannot be obtained.

As a method for eliminating the action of the surfactant and / or the polymer protective colloid, usually, the solution obtained after the completion of the first step is cooled to remove the surfactant and / or the polymer protective colloid. The method of precipitation is adopted. The precipitated surfactant or polymer protective colloid may be removed by filtration if desired.

The cooling temperature for depositing the surfactant and / or polymer protective colloid varies depending on the type of surfactant or polymer protective colloid or the type of solvent.
For example, in the case of using hexaglyceryl monobehenylate and n-heptane, 38 to 40 ° C., and in the case of using hexaglyceryl monobehenylate and cyclohexane, 27 to 40 ° C.
30 ° C., 29 to 31 ° C. when using sorbitan monostearate and n-heptane.

When the surfactant represented by the above general formula (5) is used as the surfactant, the surfactant itself has a radically polymerizable group, and therefore the surfactant itself has the first group. In the step (2), it is polymerized with the water-soluble ethylenically unsaturated monomer, and its action disappears after completion of the polymerization.

After completion of the above steps, a surfactant and / or
Alternatively, a water-soluble ethylenically unsaturated monomer aqueous solution containing a nonionic macromonomer is added to the polymerization reaction system from which the action of the polymer protective colloid has disappeared, and then reverse phase suspension polymerization is performed (third step).

The water-soluble ethylenically unsaturated monomer used in this step is selected from the group of water-soluble ethylenically unsaturated monomers which can be used in the first step. The water-soluble ethylenically unsaturated monomer used in the third step may be the same as or different from the one used in the first step, but usually, for example, in terms of economy. Also, from the viewpoint of reaction operation, it is preferable to use the same one as used in the first step.

On the other hand, examples of the nonionic macromonomer contained in the aqueous solution of the water-soluble ethylenically unsaturated monomer include, for example, a polymerizable ethylenically unsaturated group at one end and a carbon number at the other end. Is used having 1 to 8 hydrocarbon chains. Examples of such a nonionic macromonomer include carbamine esters (general formula (1) below), which are urethane reaction products of propenoic acid isocyanate ethyl ester and polyalkylene glycol, and benzene-1- (1-isocyanate- 1-
Carbamine esters (general formula (2) below) which are urethane reaction products of methylethyl) -3 (or 4)-(1-methylethenyl) and polyalkylene glycol, polyalkylene glycol (meth) acrylate (following General formula (3)) and polyalkylene glycol (meth) allyl ether (the following general formula (4))
Can be exemplified.

[0063]

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In the general formulas (1) to (4), R ¹ represents hydrogen or a methyl group, and R ² represents hydrogen, a methyl group or an ethyl group. R ³ represents a hydrocarbon group having 1 to 8 (preferably 1 to 5) carbon atoms. The average value of n is 1 to 500, and the average value of m is 0 to 200. Further, n and m satisfy n ≧ m and satisfy the condition of Σ (n + m) = 1 to 500.

When R ³ has 9 or more carbon atoms,
Since the hydrophobicity of the hydrocarbon group becomes large, the nonionic macromonomer containing such a group itself exerts a surface active action. If this happens, the aqueous solution containing the nonionic macromonomer will not be absorbed by the hydrogel obtained in the first step during the polymerization reaction in this step, and will itself undergo reverse phase suspension polymerization in the solvent. become. Further, the water-absorbent resin produced by using such a nonionic macromonomer has a low compatibility with water,
Since water is easily repelled in the initial stage of water absorption, the water absorption speed becomes slow. On the other hand, as described above, when the carbon number of R ³ is 8 or less, particularly 5 or less, the nonionic macromonomer does not exhibit surface activity and has an appropriate compatibility with water. Therefore, the water-absorbent resin thus obtained has less stickiness on the surface even at high humidity, has good free-flowability, and has a high water-absorption rate because it is difficult to repel water.

Among the nonionic macromonomers represented by the above general formulas (1) to (4), the nonionic macromonomers represented by the general formulas (2) and (4) are hydrolyzable. Are better. For this reason, the water-absorbent resin produced using these macromonomers is less likely to deteriorate its water retention capacity even under a water-containing state, and can exhibit stable water-absorption performance for a long time. Furthermore, since the macromonomer represented by the general formula (2) has a polymerizability similar to that of acrylic acid or its salt, acrylic acid or its salt is used as the water-soluble ethylenically unsaturated monomer. If so, the polymerization reaction in this step can proceed extremely smoothly.

Two or more kinds of the above-mentioned nonionic macromonomers may be used in combination.

The above-mentioned nonionic macromonomer is used by mixing it with a water-soluble ethylenically unsaturated monomer aqueous solution. In a water-soluble ethylenically unsaturated monomer aqueous solution containing such a nonionic macromonomer, when the content ratio of the nonionic macromonomer is small, the nonionic water-absorbing component of the surface layer of the resulting water-absorbent resin In some cases, the ratio becomes small and the water absorbent resin does not show sufficient salt resistance. Therefore, the proportion of the nonionic macromonomer is usually preferably set to 0.01 to 100 mol per mol of the water-soluble ethylenically unsaturated monomer,
It is more preferable to set it to 02 to 10 mol. This ratio may vary depending on the degree of condensation of the oxyalkylene group contained in the nonionic macromonomer.

Further, this aqueous solution contains (meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide and 2-hydroxyethyl (meth).
A nonionic monomer such as acrylate or N-methylol (meth) acrylamide may be contained. Especially,
When a monomer such as N, N-dimethylacrylamide or N-isopropylacrylamide is contained, it can be heated to a specific temperature to obtain a heat-sensitive water-absorbent resin whose water-absorption capacity largely changes at that temperature.

The amount of the water-soluble ethylenically unsaturated monomer aqueous solution containing the nonionic macromonomer used in this step is 50 to 50% of that of the water-soluble ethylenically unsaturated monomer aqueous solution used in the first step. It is preferably set to 300% by weight. If this amount is less than 50% by weight, it is difficult to obtain the desired water absorbent resin. On the contrary, when it exceeds 300% by weight, a part of the aqueous solution may not be absorbed in the hydrogel obtained in the first step, and as a result, the unit amount contained in the unabsorbed aqueous solution may be decreased. The body polymerizes and agglomerates in a hydrocarbon solvent in which the action of the surfactant and / or the polymeric protective colloid has disappeared by itself,
Alternatively, a very large coarse-grained water absorbent resin is easily produced.

The reverse phase suspension polymerization in this step can be carried out under the same conditions as in the case of the first step. Here, a crosslinking agent may be used as in the case of the first step, and the same radical polymerization initiator as that used in the first step may be used. The radical polymerization initiator is added as an aqueous solution together with the above-mentioned ethylenically unsaturated monomer aqueous solution.

In the third step, the water-soluble ethylenically unsaturated monomer aqueous solution containing the nonionic macromonomer is absorbed in the hydrous gel obtained in the first step, Is polymerized with. Therefore, in the water absorbent resin of the present invention produced by such a method, the surface layer portion was rich in the nonionic water absorbing component obtained in the third step, and the central portion was obtained in the first step. Resin particles rich in ionic water-absorbing component, in other words, in the form of particles that gradually change from the surface layer part to the center part to the state of being rich in nonionic water-absorbing resin, and being rich in ionic water-absorbing resin To be

In this manufacturing method, the above-mentioned third step may be repeated twice or more. When the third step is repeated in this manner, a water absorbent resin powder having a large particle size can be obtained.

When water containing salts (hereinafter referred to as salt water) is absorbed by the water absorbent resin of the present invention, first, salt water is absorbed by the surface layer of the water absorbent resin particles. As the absorbed salt water passes through the surface layer portion rich in the nonionic water-absorbent resin component, the ions contained in the salt water are gradually blocked. As a result, salt water having a small content of the ions gradually penetrates into the central portion of the water absorbent resin particles. That is, the concentration of the salt water gradually decreases as it moves to the central portion. The salt water that has permeated into the central portion in this manner has a reduced salt concentration, and is efficiently absorbed by the central portion that is rich in ionic water-absorbing resin.

The water-absorbent resin of the present invention is, for example, sanitary items, sanitary items such as paper cleats, water-retaining materials for agriculture and horticulture, water-stopping materials in the field of electric cables and civil engineering, sludge coagulating materials, desiccants, oils. It can be widely used as a moisture remover and other uses.

[0076]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Production Example 1 (Production of Nonionic Macromonomer
Concrete) stirrer, Dean Stark trap, condenser, thermometer, providing a reaction vessel equipped with a gas inlet tube and a purge tube, this contains an average of 40 oxyethylene units and toluene 300 g n-Butokishipori (ethyleneoxy ) Ethanol (380 g, 0.2 mol) was added. This solution was heated to about 110 ° C. under reflux, and trace water was removed azeotropically to the outside of the system.

This solution was cooled to 90 ° C., 3.0 g of 28% bismuth octoate (catalyst) was added and mixed well. Then, isopropenyl-α, α-dimethylbenzyl isocyanate (m-TM manufactured by Cytec Co., Ltd.
42 g of I) was further added and reacted at 90 ° C. for 1.5 hours. After the reaction solution was cooled to 70 ° C., 2,6-di-tert
-4-Methylphenol (polymerization inhibitor) 0.1 g was added and mixed.

The obtained mixed liquid was transferred to a rotary evaporator to remove the solvent and cooled. As a result, waxy n-butoxypoly (ethyleneoxy) ₄₀ ethylisopropenyl-α, α-dimethylbenzylcarbamyl ester was obtained.

Production Example 2 (Production of nonionic macromonomer)
( Preparation) Prepare a reaction vessel equipped with a stirrer, condenser, and Dean Stark trap, and add 300 g of toluene,
380 g of n-butoxypoly (ethyleneoxy) ethanol containing an average of 40 oxyethylene units (0.2
Mol), methacrylic acid 17.2 g (0.2 mol), p-
3.0 g of toluenesulfonic acid (catalyst) and 1.0 g of methoxyhydroquinone were charged. It was heated to reflux temperature and continued to reflux for 1.5 hours. The water produced by the esterification reaction during reflux was collected in a Dean Stark trap.

Next, the obtained reaction mixture was cooled, neutralized with anhydrous sodium carbonate (solid) and then filtered. Then, the solvent toluene was vacuum stripped. This gave a slightly yellow waxy n-butoxypoly (ethyleneoxy) ₄₀ ethylmethacrylate.

Production Example 3 (Production of Nonionic Macromonomer
( Preparation) A reaction vessel equipped with a stirrer, a condenser, a Dean Stark trap and a thermometer was prepared, and 550 g (0.2 mol) of iso-propoxypoly (ethyleneoxy) ethanol containing an average of 60 oxyethylene units was prepared. And 300 g of xylene were charged and heated with stirring to dehydrate by azeotropic distillation.

10.8 g (0.2 mol) of sodium methoxide (30% methanol solution) in terms of pure content
After addition and heating to reflux temperature, all the methanol formed was removed by distillation. Thereafter, the reaction mixture was cooled to 60 ° C., and 15.5 g (0.2 mol) of allyl chloride was carefully added thereto little by little. Heat this to 110 ℃ 1
Hold at this temperature for hours.

After 1 hour, the reaction mixture was transferred to a rotary evaporator via a filter and the xylene was removed under vacuum at 100 ° C. The final product was cooled to give waxy iso-propoxy poly (ethyleneoxy) ₆₀ ethyl allyl ether.

Production Example 4 (Production of Nonionic Macromonomer)
Concrete) isopropenyl-.alpha., alpha-dimethyl benzyl isocyanate 42g instead of 2-methacryloyloxyethyl isocyanate (manufactured by Showa Denko) except using 26g performs a similar procedure as in Production Example 1, waxy n -Butoxy poly (ethyleneoxy) ₄₀ ethyl methacryloyloxyethylcarbamyl ester was obtained.

Production Examples 5 to 7 (Nonionic macromonomer
Instead of manufacturing) contains an average of 40 oxyethylene units n- Butokishipori (ethyleneoxy) ethanol 380 g, the production example except that using alcohol defined by the general formula (6) and Table 1 below The same operation as in 1 was performed to obtain waxy carbamyl esters.

[0087]

Embedded image

[0088]

[Table 1]

The carbamyl esters obtained here were methoxypoly (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethyl isopropenyl-α, α-dimethylbenzylcarbamyl ester (Production Example 5), ethoxypoly (ethylene Oxy) ₅₀ (propyleneoxy) ₁₀ ethyl isopropenyl-α, α-dimethylbenzylcarbamyl ester (Production Example 6) and n-butoxypoly (ethyleneoxy) ₃₀ (propyleneoxy) ₁₀ ethyl isopropenyl-α, α- It is dimethylbenzylcarbamyl ester (Production Example 7).

Production Examples 8 to 10 (Nonionic macromonomer
Production of over) contains an average of 40 oxyethylene units n- Butokishipori (instead of ethyleneoxy) ethanol 380 g, except using the alcohol defined by the general formula (6) and Table 2 Production Example The same operation as in 4 was performed to obtain waxy carbamyl esters.

[0091]

[Table 2]

The carbamyl esters obtained here were methoxypoly (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethyl methacryloyloxyethylcarbamyl ester (Production Example 8), ethoxypoly (ethyleneoxy) ₅₀ (propylene Oxy) ₁₀ ethyl methacryloyloxyethylcarbamyl ester (Production Example 9) and n-butoxypoly (ethyleneoxy) ₃₀ (propyleneoxy) ₁₀ ethyl methacryloyloxyethylcarbamyl ester (Production Example 10).

Production Examples 11 to 13 (nonionic macromono)
Production of mer) Production Example except that alcohols defined by the above general formula (6) and Table 3 were used instead of 380 g of n-butoxypoly (ethyleneoxy) ethanol containing an average of 40 oxyethylene units. The same operation as in 2 was performed to obtain waxy methacrylates.

[0094]

[Table 3]

The methacrylates obtained here were methoxypoly (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethyl methacrylate (Production Example 11), ethoxypoly (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethylmethacrylate (Production Example). 12) and n-butoxypoly (ethyleneoxy) ₃₀ (propyleneoxy) ₁₀ ethylmethacrylate (Production Example 13).

Production Example 14 (of nonionic macromonomer
Production) Acrylic acid 14.4 instead of methacrylic acid 17.2 g
The same operation as in Production Example 2 was performed except that g was used to obtain waxy n-butoxypoly (ethyleneoxy) ₄₀ ethyl acrylate.

Production Examples 15 to 17 (nonionic macromono)
Production of mer) Production Example except that alcohols defined by the above general formula (6) and Table 4 were used in place of 380 g of n-butoxypoly (ethyleneoxy) ethanol containing an average of 40 oxyethylene units. The same operation as in 14 was performed to obtain waxy acrylates.

[0098]

[Table 4]

The acrylates obtained here are
Methoxypoly (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethyl acrylate (Production Example 15), ethoxypoly (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethylacrylate (Production Example 16) and n-butoxypoly (ethyleneoxy) ₃₀ (Propyleneoxy) _{It is 10} ethyl acrylate (Production Example 17).

Production Examples 18 to 20 (nonionic macromono)
Manufacture of mer), except that 550 g of iso-propoxypoly (ethyleneoxy) ethanol containing an average of 60 oxyethylene units was replaced with alcohols defined by the above general formula (6) and Table 5 The same operation as in Example 3 was performed to obtain waxy allyl ether macromonomers.

[0101]

[Table 5]

The acrylates obtained here are
Methoxypoly (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethyl allyl ether (Preparation 18), Etokishipori (ethyleneoxy) ₅₀ (propyleneoxy) ₁₀ ethyl allyl ether (Preparation 19) and n- Butokishipori (ethyleneoxy) ₃₀ (Propylene Oxy) ₁₀ ethylallyl ether (Production Example 20).

Example 1 (Production of Water-Absorbent Resin) (First Step) 550 ml of n-heptane was added to a 1 liter cylindrical round bottom flask equipped with a stirrer, a reflux condenser, a dropping funnel and a nitrogen gas introducing tube. In addition, the HLB is 1
3.1 Hexaglyceryl monobehenylate (smooth surface-active agent: NOF GV-106 manufactured by NOF CORPORATION)
38 g was added and the temperature was raised to 50 ° C. with stirring to dissolve. Then, the contents of the flask were cooled to 30 ° C.

On the other hand, 92 g of an acrylic acid aqueous solution having a concentration of 80% by weight was added to a 500 ml Erlenmeyer flask, and 15.2 g of an aqueous sodium hydroxide solution having a concentration of 20% by weight was added dropwise while cooling from the outside to add 75 mol of acrylic acid. % Neutralized. Add ethylene glycol diglycidyl ale 1 to this liquid.
8.4 mg was added, and further potassium persulfate 0.11 g
Was added and dissolved.

Next, the 75 mol% partially neutralized acrylate aqueous solution containing the polymerization initiator and the cross-linking agent, obtained as described above, was added to the contents of the above cylindrical round bottom flask, and the mixture was stirred. The solution was dispersed in an n-heptane solution containing a surface-active agent, and the inside of the system was sufficiently replaced with nitrogen. Then, the temperature was raised by heating, the bath temperature was set at 70 ° C., and the temperature was kept for 30 minutes to carry out a polymerization reaction.

(Second Step) The polymer-containing slurry liquid obtained in the first step was cooled to 20 ° C. to eliminate the action of the surfactant.

(Third step) Using a 500 ml Erlenmeyer flask, 24 g of a partially neutralized sodium acrylate aqueous solution having a degree of neutralization of 75 mol% was prepared from 9.2 g of an acrylic acid aqueous solution having a concentration of 80% by weight according to the method described above. Prepared. To this, 100 g of n-butoxypoly (ethyleneoxy) ₄₀ ethyl isopropenyl-α, α-dimethylbenzylcarbamyl ester obtained in Production Example 1, 10 mg of ethylene glycol diglycidyl ether and 15 parts of deionized water were added.
0 g was added and mixed, and further potassium persulfate 0.05 g
Was added and dissolved.

274 g of the partially neutralized sodium acrylate / macromonomer mixed aqueous solution containing the polymerization initiator and the cross-linking agent thus obtained was slowly added to a polymer slurry liquid kept at 20 ° C. after the completion of the second step. The mixture was added dropwise, and the mixed solution was absorbed by the polymer over 30 minutes. Then, the inside of the flask was sufficiently replaced with nitrogen, and the content was heated to 70 ° C. and kept for 30 minutes to carry out a second stage polymerization reaction.

Subsequently, the solvent (n-heptane) and water were removed by vacuum drying. As a result, 196 g of a spherical polymer powder was obtained.

[0110]Examples 2 to 20 (Production of water absorbent resin)  The composition shown in Table 6 is obtained as the mixed aqueous solution used in the third step.
The same procedure as in Example 1 was carried out except that a spherical one was used.
A polymer powder having a narrow particle size distribution was obtained.

[0111]

[Table 6]

[0112]

[Table 7]

Example 21 (Production of Water-Absorbent Resin) (First Step) A 1-liter cylindrical round-bottom flask reactor equipped with a stirrer, a reflux condenser, a dropping funnel and a nitrogen gas inlet tube was charged with n-heptane. Modified polyethylene obtained by adding 550 ml and adding maleic anhydride thereto (polymer protective colloid: Hi-wax 11 manufactured by Mitsui Petrochemical Co., Ltd.).
05A) 0.92 g was added and dissolved.

On the other hand, in a 500 ml Erlenmeyer flask, 92 g of an 80% by weight aqueous solution of acrylic acid was neutralized with 152 g of a 20% by weight aqueous sodium hydroxide solution to obtain a neutralization degree of 7
A 5 mol% aqueous sodium acrylate solution was obtained. To this, 5.5 g of 1% aqueous potassium persulfate solution, 2% concentration
1.84g of ethylene glycol diglycidyl ether
And maleic acid ester of nonylphenol ethylene oxide adduct containing an average of 50 oxyethylene units (Aerosol ME M- manufactured by Cytec Co., Ltd.
0.46 g of NP50) was added.

The partially neutralized sodium acrylate aqueous solution containing the polymerization initiator, the cross-linking agent and the polymer protective colloid thus obtained was added little by little to the above flask reactor while stirring, and at the same time, the inside of the flask reactor was flushed with nitrogen. Subsequent replacement with a water phase reverse phase suspension was formed. Then, the temperature is set to 70 ° C.
The temperature was raised to, and the polymerization reaction was carried out while maintaining this temperature for 30 minutes.

(Second Step) After the polymerization reaction, the content of the flask reactor was cooled to 45 ° C. to eliminate the action of the polymer protective colloid.

(Third step) In a 500 ml Erlenmeyer flask, 9.2 g of an 80% by weight aqueous solution of acrylic acid was neutralized with 15.2 g of a 20% by weight aqueous sodium hydroxide solution, and the degree of neutralization was 75 mol%. An aqueous solution of sodium acrylate was obtained. To this, 100 g of n-butoxypoly (ethyleneoxy) ₄₀ ethyl isopropenyl-α, α-dimethylbenzylcarbamyl ester obtained in Production Example 1 was added at a concentration of 2
% Ethylene glycol diglycidyl ether 1.84
g, 150 g of deionized water and 5.5 g of a 1% aqueous potassium persulfate solution were added to obtain a partially neutralized sodium acrylate / macromonomer mixed aqueous solution containing a polymerization initiator and a crosslinking agent. This mixed aqueous solution was cooled to 10 ° C. and stored.

The 1 liter cylindrical round-bottom flask reactor containing the polymer slurry having a temperature of 45 ° C. obtained after the second step as a content was replaced with nitrogen, and the above mixed aqueous solution was slowly added while stirring. And dropped into the flask reactor,
The mixed aqueous solution was absorbed by the polymer in the flask reactor at a temperature of 45 ° C. for 30 minutes. Next, raise the temperature to 70 ° C.
The temperature was raised to 2, and the second stage polymerization reaction was carried out for 30 minutes.

After the completion of the polymerization reaction, the content in the flask reactor was dried under reduced pressure to remove n-heptane and water. As a result, 203 g of a spherical polymer powder having an average particle size of 370 μm was obtained. In addition, the obtained polymer powder,
No fine powder was included that passed through a 100 μm sieve.

Comparative Example (Production of Water-Absorbent Resin) As the mixed aqueous solution used in the third step, 174 g of the partially neutralized sodium acrylate / macromonomer mixed aqueous solution containing a polymerization initiator and a crosslinking agent was used in place of the first aqueous solution. Used in the process,
244 g of 75 mol% neutralized sodium acrylate aqueous solution (concentration = 37% by weight) containing 0.11 g of potassium persulfate and 18.4 mg of ethylene glycol diglycidyl ether
175 g of spherical polymer powder was obtained in the same manner as in Example 1 except that was used.

Evaluation Regarding the polymer powders obtained in each Example and Comparative Example,
The properties (water absorption performance and water absorption rate) as the water absorbent resin were evaluated. The evaluation method is as follows. Table 9 shows the results.
Shown in

(Water Absorption Performance) Deionized water absorption, salt water absorption and seawater absorption were evaluated.

Absorption of deionized water 0.2 g of a sample was placed in a 250-mesh nylon bag, and this nylon bag was immersed in 1,000 ml of deionized water obtained by ion-exchange treatment for 4 hours, and then taken out. Drained for minutes. After that, the weight was measured, and the deionized water absorption amount (g /
g).

Absorption of salt water 1 g of a sample was added with a 0.9% sodium chloride aqueous solution of 1,000 m.
After being dispersed in 1 l to absorb water and swelling, it was filtered using a wire mesh of 200 mesh. The sample was drained for 15 minutes, and the weight of the resulting swollen and water-absorbent sample on the wire net was measured. The weight increased by swelling was defined as 0.9% saline absorption (g / g).

Absorption of seawater 1,000 g of a sample of synthetic seawater having the composition shown in Table 8 below.
After being dispersed in ml and sufficiently swollen with water, it was filtered using a wire mesh of 200 mesh. After draining for 15 minutes, the weight of the swollen and water-absorbing sample on the wire net was measured. The weight increased by swelling was taken as the seawater absorption (g / g).

[0126]

[Table 8]

(Water absorption rate) 5 g of the sample was spread to about 3.5 cmφ in a petri dish, and a pipette was used to add 0.9%.
2 cc of saline was added dropwise. The time until the dripped saline solution was completely absorbed was measured, and this was defined as the water absorption rate (water wettability).

[0128]

[Table 9]

In addition, in Examples 1, 2, 9 and 17 and Comparative Example, the aging stability of the swollen gel was also evaluated.
Here, 90 g of 0.9% saline was added to 10 g of the sample to absorb water to obtain a swollen gel, and the swollen gel was placed in a black polyethylene bag and stored in a room kept at 18 ° C. Was observed over time. The evaluation criteria are as follows. Table 10 shows the results.

A: Hard gel. B: Soft gel. C: Flowable gel.

[0131]

[Table 10]

[0132]

As described above, the water-absorbent resin according to the present invention functions as a surfactant and / or a polymeric protective colloid after reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer aqueous solution. Since it is manufactured by eliminating it and subsequently adding an aqueous solution of a water-soluble ethylenically unsaturated monomer containing a nonionic macromonomer, and performing reverse phase suspension polymerization in the same manner, it has high water absorption for water containing salts. And it is stable.

In the method for producing a water absorbent resin according to the present invention, the action of the surfactant and / or the polymeric protective colloid is carried out by reverse phase suspension polymerization of the water-soluble ethylenically unsaturated monomer aqueous solution as described above. , Followed by the reverse phase suspension polymerization by adding a water-soluble ethylenically unsaturated monomer aqueous solution containing a nonionic macromonomer, resulting in high and stable water absorption for water containing salts. A water absorbent resin can be manufactured.

Claims (20)

[Claims] 1. A first step of reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer aqueous solution in a hydrocarbon solvent in the presence of a surfactant and / or a polymeric protective colloid, After the first step, a second step of eliminating the action of the surfactant and / or the polymeric protective colloid, and a water-soluble solution containing a nonionic macromonomer in the polymerization reaction system which has completed the second step. A water-absorbent resin obtained by a polymerization operation including the third step of adding an aqueous solution of an ethylenically unsaturated monomer and further performing reverse phase suspension polymerization. 2. The water absorbent resin according to claim 1, which is obtained by repeating the third step twice or more. 3. The water absorbent resin according to claim 1, wherein the reverse phase suspension polymerization in the first step and / or the third step is carried out in the presence of a crosslinking agent. 4. The water-soluble ethylenically unsaturated monomer aqueous solution used in the first step is at least one selected from the group consisting of acrylic acid, methacrylic acid and alkali salts thereof. The water absorbent resin according to 1, 2 or 3. 5. The nonionic macromonomer used in the third step is a carbamyl ester represented by the following general formula (1) or a carbamyl ester represented by the following general formula (2). At least selected from the group consisting of an alkyl polyoxyalkylene glycol (meth) acrylate represented by the following general formula (3) and an alkyl polyoxyalkylene glycol (meth) allyl ether represented by the following general formula (4). The water absorbent resin according to claim 1, 2, 3 or 4, which is one kind. Embedded image (In the general formulas (1), (2), (3) and (4), R ¹
Represents hydrogen or a methyl group, R ² represents hydrogen, a methyl group or an ethyl group, R ³ represents a hydrocarbon group having 1 to 8 carbon atoms, and n has an average value of 1 to 500, m Has an average value of 0 to 200, and n and m satisfy the conditions of n ≧ m and Σ (n + m) = 1 to 500. ) 6. A water absorbent resin comprising a surface layer portion rich in a nonionic water absorbing component and a central portion rich in an ionic water absorbing component. 7. A first step of performing reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer aqueous solution in a hydrocarbon solvent in the presence of a surfactant and / or a polymeric protective colloid, After the first step, a second step of eliminating the action of the surfactant and / or the polymeric protective colloid, and a water-soluble solution containing a nonionic macromonomer in the polymerization reaction system which has completed the second step. A third step of adding an ethylenically unsaturated monomer and further performing reverse phase suspension polymerization, and a method for producing a water absorbent resin. 8. The method for producing a water absorbent resin according to claim 7, wherein the third step is repeated twice or more. 9. The method for producing a water absorbent resin according to claim 7, wherein the reverse phase suspension polymerization in the first step and / or the third step is performed in the presence of a crosslinking agent. 10. The water-soluble ethylenic containing the monomer concentration in the water-soluble ethylenically unsaturated monomer aqueous solution used in the first step and the nonionic macromonomer used in the third step. The method for producing a water absorbent resin according to claim 7, 8 or 9, wherein the monomer concentration in the unsaturated monomer aqueous solution is 25% by weight or more. 11. The water-soluble ethylenically unsaturated monomer used in the first step, wherein the water-soluble ethylenically unsaturated monomer aqueous solution containing the nonionic macromonomer used in the third step is used. The method for producing a water absorbent resin according to claim 7, 8, 9 or 10, wherein the content is set to 50 to 300% by weight of the aqueous solution. 12. The water-soluble ethylenically unsaturated monomer aqueous solution used in the first step and the third step is at least one selected from the group consisting of acrylic acid, methacrylic acid and alkali salts thereof. A species, claim 7,
The method for producing the water absorbent resin according to 8, 9, 10 or 11. 13. The nonionic macromonomer used in the third step is a carbamyl ester represented by the following general formula (1) or a carbamyl ester represented by the following general formula (2). At least selected from the group consisting of an alkyl polyoxyalkylene glycol (meth) acrylate represented by the following general formula (3) and an alkyl polyoxyalkylene glycol (meth) allyl ether represented by the following general formula (4). The method for producing a water absorbent resin according to claim 7, 8, 9, 10, 11 or 12, which is one kind. Embedded image (In the general formulas (1), (2), (3) and (4), R ¹
Represents hydrogen or a methyl group, R ² represents hydrogen, a methyl group or an ethyl group, R ³ represents a hydrocarbon group having 1 to 8 carbon atoms, and n has an average value of 1 to 500, m Has an average value of 0 to 200, and n and m satisfy the conditions of n ≧ m and Σ (n + m) = 1 to 500. ) 14. The surface active agent is a nonionic surface active agent or a combination of a nonionic surface active agent and an anionic surface active agent, as claimed in claim 7, 8, 9, 10, 11, 12.
Or the method for producing a water absorbent resin according to item 13. 15. The surfactant has a sorbitan fatty acid ester, a polyglycerin fatty acid ester, a sucrose fatty acid ester, a sorbitol fatty acid ester, a polyoxyethylene alkylphenyl ether, and a hydrophobic group consisting of a dodecyl glycol group at one or both ends. And at least one member selected from the group consisting of poly (oxyethylene) glycol / dodecyl glycol block copolymers formed by a polyoxyethylene chain. 7. 13. The method for producing the water absorbent resin according to 13. 16. The surfactant has the following general formula (5):
A polymerizable surfactant represented by:
The method for producing a water absorbent resin according to 8, 9, 10, 11, 12 or 13. Embedded image (In the general formula (5), R ⁴ represents a hydrocarbon group having at least 9 carbon atoms, R ⁵ represents an acryloyl group, a methacryloyl group or a maleoyl group, and l
Is 30 to 70. ) 17. The polymer protective colloid is selected from the group consisting of ethyl cellulose, ethyl hydroxyethyl cellulose, oxidation modified polyethylene, maleic anhydride modified polyethylene, maleic anhydride modified polybutadiene, maleic anhydride modified ethylene propylene diene terpolymer. 9. At least one selected from the above,
The method for producing a water absorbent resin according to 9, 10, 11, 12, 13, 14, 15 or 16. 18. In the second step, the surfactant and / or the polymer protective colloid is precipitated by a cooling operation to eliminate the action of the surfactant and / or the polymer protective colloid. Item 7, 8,
The method for producing a water absorbent resin according to 9, 10, 11, 12, 13, 14, 15, 16 or 17. 19. The hydrocarbon solvent is n-hexane, n
-At least one member selected from the group consisting of heptane, cyclohexane, toluene and xylene, 7, 8, 9, 10, 11, 12, 13, 14, 15, 1.
The method for producing the water absorbent resin according to 6, 17 or 18. 20. The crosslinking agent is ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, or N, N′-methylenebis. Acrylamide, Claims 9, 10, 11, 12, 13, 14,
The method for producing the water absorbent resin according to 15, 16, 17, 18 or 19.