JP2009052009A - Method for producing water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing water-absorbing resins excellent in an absorption rate by solving a problem that water-absorbing resins produced by conventional methods do not always satisfy absorbing abilities, particularly absorption rates, and provide a water-absorbing resin. <P>SOLUTION: The method for producing the water-absorbing resin is to prepare a water-absorbing resin composition through a process for mixing a crosslinked polymer (A) comprising (meth)acrylic acid (salt) and a crosslinking agent (b) as essential ingredients, with a foaming agent (B) generating a gas by heating, and further heat the composition, wherein the mixing process comprises one or more steps selected from a group consisting of the following first step to the forth step: the first step of mixing (B) and a water-containing gel of (A), the second step of mixing (B) and the water-containing gel of (A) by drying the latter, the third step of mixing (B) and the dried (A) by crushing the latter, and the fourth step of mixing (B) and resin particles (A1) comprising (A). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a water absorbent resin.

Conventionally, in order to improve the water absorption capacity of water-absorbent resin, especially to improve the water-absorption rate, a production method that increases the cross-linking density of the particle surface has been proposed to prevent gel blocking between water-absorbent resin particles and increase liquid permeability. (Patent Document 1). Moreover, in order to enlarge the surface area of a water-absorbent resin particle, the manufacturing method to granulate is proposed (patent document 2). Furthermore, a production method in which water-absorbent resin particles are foamed and made porous has been proposed (Patent Documents 3 and 4).
JP 57-44627 A International Publication No. 93/24153 Pamphlet International Publication No. 96/17884 Pamphlet JP-T 9-507085

  However, the water-absorbing resin obtained by these production methods cannot always satisfy the absorption capacity, particularly the absorption rate. An object of this invention is to provide the manufacturing method of the water absorbing resin excellent in the absorption rate.

The present invention comprises a mixing step of a cross-linked polymer (A) having (meth) acrylic acid (salt) and a cross-linking agent (b) as essential constituent units and a foaming agent (B) that generates gas by heating. A method for producing a water absorbent resin obtained by further heating a water absorbent resin composition, wherein the mixing step includes one step or two or more steps selected from the group consisting of the following first to fourth steps. This is a method for producing a water-absorbent resin.
1st process: The process of mixing the hydrogel of (A) and (B) 2nd process: The process of mixing with (B), drying the hydrogel of (A) 3rd process: Drying (A) Step of mixing with (B) while pulverizing Fourth step: Step of mixing resin particles (A1) and (B) comprising (A)

  The method for producing a water-absorbent resin of the present invention produces an effect that it is possible to produce a water-absorbent resin that is extremely excellent in the absorption rate of water, saline, and the like.

In the present invention, (meth) acrylic acid means acrylic acid and / or methacrylic acid, and "... acid (salt)" means "... acid" and / or "... acid salt". means. Examples of the salt include alkali metal salts such as potassium, sodium and lithium, alkaline earth metal salts such as calcium, and onium salts.
As the onium salt, those described in JP-A Nos. 2003-251178 and 2005-95357 can be used, and examples of the onium cation include a quaternary ammonium cation (I) and a tertiary phosphonium cation ( II), quaternary phosphonium cation (III), tertiary oxonium cation (IV) alkylpyridinium cation (V), ammonium cation (VI) excluding quaternary ammonium cation, etc. (Omitted).

  The quaternary ammonium (I) includes an aliphatic quaternary ammonium (I1) having 4 to 30 or more carbon atoms having an alkyl and / or alkenyl group, an aromatic quaternary having 9 to 30 or more carbon atoms. Quaternary ammonium (I2), alicyclic quaternary ammonium (I3) having 6 to 30 or more carbon atoms, imidazolinium (I4) having 6 to 30 or more carbon atoms, 5 to 30 or more carbon atoms Of imidazolium (I5), tetrahydropyrimidinium having 6 to 30 or more carbon atoms (substituents may be combined to form a bicyclo ring), (I6), 6 to 30 or more carbon atoms Dihydropyrimidinium (I7) and guanidinium (I8) having an imidazolinium skeleton having 8 to 30 or more carbon atoms.

  Examples of the aliphatic quaternary ammonium (I1) having 4 to 30 or more carbon atoms having an alkyl and / or alkenyl group include tetramethylammonium, tetraethylammonium, trimethylpropylammonium, dimethylpropylammonium and the like.

  Examples of the aromatic quaternary ammonium (I2) having 9 to 30 or more carbon atoms include trimethylphenylammonium, triethylphenylammonium, benzyltrimethylammonium and the like.

  Examples of the alicyclic quaternary ammonium (I3) having 6 to 30 or more carbon atoms include N, N-dimethylpyrrolidinium, N, N-diethylpyrrolidinium, N, N dimethylmorpholinium and the like. It is done.

  Examples of the imidazolinium (I4) having 6 to 30 or more carbon atoms include 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium and the like.

  Examples of the imidazolium (I5) having 5 to 30 or more carbon atoms include 1,3-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1,2,3,4-tetramethylimidazolium and the like. It is done.

  Tetrahydropyrimidinium having 6 to 30 or more carbon atoms (a substituent may be bonded to form a bicyclo ring) (I6) includes 1,3-dimethyltetrahydropyridinium, 1,2,3- Examples thereof include trimethyltetrahydropyridinium, 1,2,3,4-tetramethyltetrahydropyridinium and the like.

  As dihydropyrimidinium (I7) having 6 to 30 or more carbon atoms, 1,3-dimethyl-2,4- or -2,6-dihydropyrimidinium [these are 1,3-dimethyl-2, This is expressed as 4, (6) -dihydropyrimidinium, and the same expression is used hereinafter. 1,2,3-trimethyl-2,4, (6) -dihydropyrimidinium, 1,2,3,4-tetramethyl-2,4, (6) -dihydropyrimidinium and the like. .

  Examples of guanidinium (I8) having an imidazolinium skeleton having 8 to 30 or more carbon atoms include 2-dimethylamino-1,3,4-trimethylimidazolinium and 2-diethylamino-1,3,4-trimethylimidazole. Examples include linium.

Examples of the ammonium cation (VI) excluding the quaternary ammonium cation include tertiary ammonium (VI1), secondary ammonium (VI2), primary ammonium (VI3), and ammonium cation (VI4).
Examples of tertiary ammonium (VI1) include alkylammonium (trimethylammonium, triethylammonium, etc.), alkanol ammonium (trimethanolammonium, triethanolammonium, etc.), pyridinium, and the like.
Secondary ammonium (VI2) includes alkylammonium (dimethylammonium, diethylammonium, etc.) and alkanolammonium (dimethanolammonium, diethanolammonium, etc.).
Examples of the primary ammonium (VI3) include alkyl ammonium (monomethyl ammonium, monoethyl ammonium, etc.) and alkanol ammonium (monomethanol ammonium, monoethanol ammonium, etc.).

  Among these, the preferred onium cation is (I), and more preferably (I1), (I4) and (I5). These onium cations may be used alone or in combination of two or more.

Content of (meth) acrylic acid (salt) is 99.0-99 with respect to the total weight of (meth) acrylic acid (salt) and a crosslinking agent (b) from a viewpoint of the absorptivity of a water absorbing resin. It is preferably 0.95% by weight, more preferably 99.2 to 99.90% by weight, and particularly preferably 99.4 to 99.85% by weight.
The molar ratio ((meth) acrylic acid: (meth) acrylate) of (meth) acrylic acid to (meth) acrylate is 70:30 to 0: 100 from the viewpoint of the absorption capacity of the water absorbent resin. It is preferably 60:40 to 5:95, more preferably 50:50 to 10: 90% by weight.

  The crosslinking agent (b) includes at least two polymerizable double bonds and a crosslinking agent (b1) having no functional group having reactivity with a carboxyl group, at least one polymerizable double bond, A crosslinking agent (b2) having a functional group reactive with at least one carboxyl group and a crosslinking agent having a functional group reactive with at least two carboxyl groups without having a polymerizable double bond ( b3).

  Examples of the polymerizable double bond include an acryloyl group, an allyl ether group, and a vinyl ether group. The functional group having reactivity with a carboxyl group is a functional group that reacts with a carboxyl group to form an ester bond or an amide bond, and examples thereof include a hydroxyl group, an epoxy group, and an amino group.

  As the crosslinking agent (b1), a crosslinking agent (b11) having two or more (meth) acryloyl groups, a crosslinking agent (b12) having two or more vinyl ether groups, and a crosslinking agent having two or more allyl ether groups (B13) etc. are mentioned. These crosslinking agents may be used alone or in combination of two or more.

Examples of the crosslinking agent (b11) include N, N′-methylenebisacrylamide, ethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and pentaerythritol di (meth). ) Copolymerizable cross-linking agents having 2 to 10 acryloyl groups in the molecule such as acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate and polyglycerin (degree of polymerization 3 to 13) polyacrylate Can be mentioned.
Among the crosslinking agents (b11), N, N′-methylenebisacrylamide, ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) are used from the viewpoint of the absorbability of the water absorbent resin. Acrylates are preferred, more preferably N, N′-methylenebisacrylamide, ethylene glycol di (meth) acrylate and trimethylolpropane tri (meth) acrylate, particularly preferably N, N′-methylenebisacrylamide and trimethylolpropane tri ( (Meth) acrylate.

  Examples of the crosslinking agent (b12) include ethylene glycol divinyl ether, 1,4-butanediol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, 1,6-hexanediol divinyl ether, polyethylene glycol divinyl ether (degree of polymerization of 2 5), bisphenol A divinyl ether, pentaerythritol trivinyl ether, sorbitol trivinyl ether, polyglycerol (degree of polymerization 3 to 13) polyvinyl ether and the like.

  As the crosslinking agent (b13), there are two allyl ether groups in the molecule and no hydroxyl group, and 3-10 allyl ether groups in the molecule and no hydroxyl group. A crosslinking agent (b132) etc. are mentioned.

As the crosslinking agent (b131) having two allyl ether groups in the molecule and having no hydroxyl group, diallyl ether, 1,4-cyclohexanedimethanol diallyl ether, alkylene (2 to 5 carbon atoms) glycol diallyl ether, And polyethylene glycol (weight average molecular weight: 100 to 4000) diallyl ether and the like.
Examples of the cross-linking agent (b132) having 3 to 10 allyl groups in the molecule and having no hydroxyl group include trimethylolpropane triallyl ether, glyceryl triallyl ether, pentaerythritol tetraallyl ether, and tetraallyloxyethane. Can be mentioned.

Examples of the crosslinking agent (b2) having at least one polymerizable double bond and at least one functional group having reactivity with a carboxyl group include JP-A-1-103615 and JP-A-2000-26510. Can be used, and examples thereof include a crosslinking agent (b21) having a nonionic group and a crosslinking agent (b22) having a cationic group. These crosslinking agents may be used alone or in combination of two or more.
As the crosslinking agent (b21), a crosslinking agent (b211) having 2 allyl groups and 1 to 5 hydroxyl groups in the molecule, 3 to 10 allyl groups in the molecule and 1 to 3 hydroxyl groups. Cross-linking agent (b212) having one, cross-linking agent (b213) having no allyl group in the molecule and having a hydroxyl group {N-methylol (meth) acrylamide, etc.} and hydroxyethyl (meth) acrylate, and allyl group in the molecule And a crosslinking agent (b214) having no epoxy and having an epoxy group, such as {glycidyl (meth) acrylate}.

As a crosslinking agent (b211) having two allyl groups and 1 to 5 hydroxyl groups in the molecule, glycerin diallyl ether, trimethylolpropane diallyl ether, pentaerythritol diallyl ether, polyglycerin (degree of polymerization: 2 to 5) Examples include diallyl ether.
As the crosslinking agent (b212) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule, pentaerythritol triallyl ether and diglyceryl triallyl ether, sorbitol triallyl ether, polyglycerol (degree of polymerization) 3-13) and polyallyl ether.
Examples of the crosslinking agent (b213) having no allyl group in the molecule and having a hydroxyl group include N-methylol (meth) acrylamide and hydroxyethyl (meth) acrylate.
A glycidyl (meth) acrylate etc. are mentioned as a crosslinking agent (b214) which does not have an allyl group in a molecule | numerator and has an epoxy group.

  As the crosslinking agent (b22), a crosslinking agent having a quaternary ammonium salt {N, N, N-trimethyl-N- (meth) acryloyloxyethylammonium salt (carbonate, carboxylate, etc.) and N, N , N-triethyl-N- (meth) acryloyloxyethylammonium salt (carbonate, carboxylate, etc.)} and a cross-linking agent having a tertiary amino group {dimethylaminoethyl (meth) acrylate and (meth) And diethylaminoethyl acrylate}.

  The crosslinking agent (b2) is preferably (b21), more preferably (b211) and (b212), more preferably (b212), particularly preferably an allyl group of 3 to 3, from the viewpoint of the absorbability of the water absorbent resin. A crosslinking agent having 5 and 1 to 3 hydroxyl groups, most preferably pentaerythritol triallyl ether and sorbitol triallyl ether.

Examples of the crosslinking agent (b3) having no polymerizable double bond and having a functional group reactive with at least two carboxyl groups are described in JP-A-1-103615 and JP-A-2000-26510. Can be used. Examples thereof include a polyvalent glycidyl compound (b31), a polyvalent isocyanate compound (b32), a polyvalent amine compound (b33), and a polyhydric alcohol compound (b34). These crosslinking agents may be used alone or in combination of two or more.
Examples of the polyvalent glycidyl compound (b31) include ethylene glycol diglycidyl ether, glycerin diglycidyl ether, and sorbitol polyglycidyl ether.
Examples of the polyvalent isocyanate compound (b32) include 4,4′-diphenylmethane diisocyanate.
Examples of the polyvalent amine compound (b33) include ethylenediamine.
Examples of the polyhydric alcohol compound (b34) include (poly) alkylene glycol, glycerin and sorbitol.
Of the crosslinking agent (b3), the polyvalent glycidyl compound (b31) is preferable, and ethylene glycol diglycidyl ether is more preferable.
When the cross-linking agent (b3) is used, it is general that the cross-linking reaction proceeds by heating at 100 to 230 ° C., more preferably 120 to 160 ° C. at any stage after the addition of the cross-linking agent. Further, the crosslinking agent (b3) may be used in combination of two or more in a predetermined amount range, and further in combination with (b1) and (b2).

  (B) is preferably (b1) and (b3), more preferably (b11), (b13) and (b3) from the viewpoint of the absorbability of the water absorbent resin. These crosslinking agents may be used alone or in combination of two or more.

  The ratio of the crosslinking agent (b) constituting the crosslinked polymer (A) is from the viewpoint of the absorbent capacity of the water-absorbent resin to a value of 0. 0 to the total weight of (meth) acrylic acid (salt) and (b). The content is preferably 0.5 to 1% by weight, more preferably 0.1 to 0.8% by weight, and particularly preferably 0.1 to 0.6% by weight.

In the present invention, other ethylenically unsaturated monomers (a) can be used as long as they can be copolymerized with (meth) acrylic acid (salt). The other ethylenically unsaturated monomer (a) is not particularly limited as long as it is copolymerizable with (meth) acrylic acid (salt), but is preferably water-soluble.
Other unsaturated monomers (a) include carboxylic acid (salt) monomers such as maleic acid (salt), fumaric acid (salt) and itaconic acid (salt); 2-acrylamido-2-methylpropanesulfone Sulfonic acid (salt) monomers such as acid (salt), sulfoalkyl (meth) acrylate and 4-vinylbenzenesulfonic acid (salt); (meth) acrylamide, N-alkyl (carbon number 1 to 3) substitution (meta ) Amide monomers such as acrylamide [N-methylacrylamide, N, N-dimethylacrylamide, etc.] and N-vinylacetamide; alcohol monomers such as monohydroxyalkyl (1 to 3 carbon atoms) mono (meth) acrylate; Polyethylene glycol (polymerization degree: 2 to 100) mono (meth) acrylate, polypropylene glycol (polymerization degree: 2 to 100) mono (meth) acrylate Examples include relate, ether monomers such as methoxypolyethylene glycol (polymerization degree: 2 to 100) mono (meth) acrylate; ester monomers such as alkyl (1 to 5 carbon atoms) (meth) acrylate and vinyl acetate. be able to. These (a) may use 2 or more types together.
The content of (a) is preferably 0.1 to 50% by weight based on the total weight of (meth) acrylic acid (salt) and (b) from the viewpoint of the absorbability of the water absorbent resin of the present invention. More preferably, it is 0.5 to 40% by weight, particularly preferably 1 to 30% by weight.

(B) which generates gas by heating, when (B) is heated to a temperature of 70 to 210 ° C., for 1 to 300 minutes, (B) 1 to 1 g of (B) 50 to 300 ml amount (0 ° C., 1 atm) ) Means a gas generating compound.
From the viewpoint of the absorbability of the water-absorbent resin of the present invention, the temperature at which (B) generates the gas is preferably 80 to 190 ° C, more preferably 90 to 170 ° C. Moreover, it is preferable that (B) generate | occur | produces the said gas by the heating for 2-120 minutes from a viewpoint of the absorptivity of this water absorbing resin. Moreover, from the viewpoint of the absorbability of the water absorbent resin, the amount of gas generated is preferably 60 to 290 ml / g, more preferably 70 to 280 ml / g, and particularly preferably 80 to 250 ml / g.

Examples of the foaming agent (B1) include an azo compound (B11), a sulfonyl hydrazide compound (B12), and a nitroso compound (B13). These foaming agents may be used alone or in combination of two or more.
Examples of the azo compound (B11) include azodicarbonamide and azobisisobutyronitrile.
Examples of the sulfonyl hydrazide compound (B12) include p-toluenesulfonyl hydrazine and p, p′-oxybis (benzenesulfohydrazide).
Examples of the nitroso compound (B13) include N, N′-dinitrosopentamethylenetetramine.
Among (B1), from the viewpoint of the absorbability of the water-absorbent resin, (B11) and (B12) are preferable, and azodicarbonamide and p, p′-oxybis (benzenesulfohydrazide) are more preferable.

  Examples of the foaming agent (B2) include ammonium carbonate and sodium hydrogen carbonate.

Among (B2), sodium hydrogen carbonate is preferable from the viewpoint of the absorbability of the water absorbent resin. As the foaming agent (B), (B1) is preferable from the viewpoint of the absorbability of the water absorbent resin.
In addition, (B1) and / or (B2) may be used alone or in combination of two or more.

  The amount of the foaming agent (B) used is preferably 0.1 to 20% by weight based on the total weight of the (meth) acrylic acid (salt) and (b) from the viewpoint of the absorbability of the water absorbent resin. More preferably, it is 0.5 to 15% by weight, particularly preferably 1.0 to 13% by weight, and most preferably 2.0 to 10% by weight.

  The hydrogel of (A) is prepared by using (meth) acrylic acid (salt) and crosslinking agent (b) and, if necessary, other ethylenically unsaturated monomer (a) by a conventionally known method (JP-A-1-103615). JP, 2000-26510, 2001-220415, etc.) and the like. The water-absorbing resin composition is obtained by drying and / or pulverizing the hydrous gel of (A) in (1) a drying step and (2) a pulverizing step. If necessary, before the step (1), (3) a step of neutralizing the hydrogel of (A), after the step of (2), (4) a step of performing a surface crosslinking treatment, (6) additional You may implement the process of drying, and the process of (7) additional grinding | pulverization. Further, if necessary, (5) the step of mixing various additives is performed either before the step (1), between the steps (1) and (2), or after the step (2). May be.

The crosslinked polymer (A) can be obtained by polymerizing (meth) acrylic acid (salt) and the crosslinking agent (b) as essential constituent units.
A known polymerization method can be applied as the polymerization method, and examples thereof include aqueous solution polymerization, suspension polymerization, bulk polymerization, reverse phase suspension polymerization, and emulsion polymerization.
Among these polymerization methods, aqueous solution polymerization, suspension polymerization, reverse phase suspension polymerization and emulsion polymerization are preferable from the viewpoint of the absorbability of the water absorbent resin of the present invention, and more preferably aqueous solution polymerization, reverse phase suspension polymerization and emulsion. Polymerization, particularly preferably aqueous solution polymerization. For these polymerizations, known polymerization initiators, chain transfer agents and / or solvents can be used.
Most preferred is an aqueous solution polymerization method in which a crosslinking agent (b) is added and dissolved in an aqueous monomer solution mainly composed of (meth) acrylic acid (salt). With this polymerization method, it is possible to obtain a water-absorbing resin excellent in absorbability.
The method of polymerizing (meth) acrylic acid (salt) by an aqueous solution polymerization method may be a normal method, for example, a method of polymerizing using a radical polymerization initiator, a method of irradiating with radiation, ultraviolet rays, electron beams or the like. .
When a radical polymerization initiator is used, the initiator includes an azo compound [azobisisovaleronitrile, azobisisobutyronitrile, 4,4'-azobis (4-cyanovaleric acid), 2,2'- Azobis [2-methyl-N- (2-hydroxyethyl) propionamide, 2,2′-azobis (2-amidinopropane) hydrochloride, etc.], inorganic peroxides [hydrogen peroxide, potassium persulfate, ammonium persulfate, Sodium persulfate, etc.], organic peroxides [di-t-butyl peroxide, cumene hydroperoxide, etc.], redox initiators [alkali metal sulfites or bisulfites, ammonium sulfites, ammonium bisulfites, L- Reducing agents such as ascorbic acid, alkali metal persulfate, ammonium persulfate, hydrogen peroxide, etc. Combination etc. peroxides. Two or more of these may be used in combination.

The polymerization temperature varies depending on the type of initiator used, but is preferably −10 ° C. to 100 ° C., more preferably −10 ° C. to 80 ° C. from the viewpoint of the degree of polymerization.
The amount of the initiator is not particularly limited, but from the viewpoint of the degree of polymerization with respect to the total weight of the unsaturated monomer {ie, (meth) acrylic acid (salt), (b) and (a)}. , Preferably 0.000001-3.0%, more preferably 0.000001-0.5%.

  In the case of aqueous solution polymerization, the polymerization concentration (% by weight) of the unsaturated monomer {ie, (meth) acrylic acid (salt), (b) and (a)} varies depending on the polymerization conditions, but the water absorption From the viewpoint of the resin absorbability and ease of adjusting the polymerization temperature, 10 to 40% by weight is preferable, and 10 to 30% by weight is more preferable. Moreover, about -10-100 degreeC regarding polymerization temperature, -10-80 degreeC is more preferable. The amount of dissolved oxygen during polymerization depends on the amount of radical initiator added and the like, but is preferably 0 to 2 ppm, more preferably 0 to 0.5 ppm from the viewpoint of the degree of polymerization.

The degree of neutralization of (meth) acrylic acid at the time of polymerization is not particularly limited as long as a predetermined amount of (b) can be completely dissolved in the monomer aqueous solution, but the water solubility of (b) is particularly poor. ) Since the solubility in acrylic acid (salt) aqueous solution is very low and (b) may be separated from the aqueous monomer solution even if a predetermined amount of (b) is added, the predetermined cross-linking may not be performed. The degree of neutralization of the acid is 0 to 30 mol%, and the polymerization is preferably carried out after the polymerization if necessary, and more preferably after the polymerization in an unneutralized state and after the polymerization if necessary.
In addition, (meth) acrylic acid is polymerized under the same conditions. Since the degree of polymerization tends to increase when the degree of neutralization is low, in order to increase the degree of polymerization of the polymer, the degree of neutralization is low. It is preferable to perform polymerization.
When neutralizing (meth) acrylic acid, an alkali (C) is mixed to obtain a neutralized product. Alkali (C) includes alkali metal hydroxide, alkali metal carbonate, onium cation hydroxide and onium cation carbonate.
Examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. Examples of the alkali metal carbonate include sodium carbonate and sodium bicarbonate. Examples of the onium cation hydroxide include tetraethylammonium hydroxide. Examples of the onium cation carbonate include 1,2,3,4-tetramethylimidazolinium monomethyl carbonate.

In the production of the crosslinked polymer (A), the average degree of polymerization of the polymer when the polymer is produced under exactly the same polymerization conditions except that no crosslinking agent is used, is preferably 5,000 to 1,000,000. It is more preferred to polymerize under polymerization conditions (type of initiator, amount of initiator, polymerization concentration of unsaturated monomer, polymerization temperature, dissolved oxygen amount, etc.) that are preferably 10,000 to 1,000,000.
When the polymerization is carried out under the condition that the average degree of polymerization is 5,000 or more, the absorbability of the water absorbent resin is further improved by using an appropriate amount of the crosslinking agent. The average degree of polymerization can be measured by gel permeation chromatography (GPC).

The crosslinked polymer (A) obtained by aqueous solution polymerization is obtained as a gel containing water (hydrous gel). The hydrogel is neutralized and broken if necessary, and is usually dried and then used as a water absorbent resin.
When neutralizing the hydrogel, alkali (C) is mixed into the hydrogel of (A) to obtain a neutralized product of the hydrogel. The neutralization degree of the water-containing gel obtained in this step is preferably 60 to 80 mol% of the carboxyl group in (A) from the viewpoint of the adhesiveness of the water-containing gel and the safety of the water-absorbent resin to the human skin, Preferably it is 65-78 mol%.
As a method of neutralizing the hydrogel of (A) with alkali (C), an aqueous solution of alkali (C) or (C) is added while chopping the hydrogel of (A) into small pieces of about 1 cm ³ or less. The method of mixing is mentioned.

As a mixing device with (C), a vertical slitting machine equipped with a cutter blade conventionally used in this step, a horizontal slitting machine equipped with a cutter blade, a cutter type crusher equipped with a rotary blade, a predetermined diameter A meat chopper equipped with an eye plate and a rotating blade can be used.
The temperature at the time of mixing may be a range conventionally used in this step, and is preferably 10 to 80 ° C. Moreover, the shearing to mix may be a conventionally well-known method, and the rotation speed of an apparatus becomes like this. Preferably it is 20-100 rpm.

When breaking the hydrous gel, a vertical slitting machine equipped with a cutter blade conventionally used in this process, a horizontal slitting slitter equipped with a cutter blade, a cutter type crusher equipped with a rotary blade, a predetermined diameter A meat chopper equipped with an eye plate and a rotating blade can be used.
The temperature at the time of fracture may be in the range conventionally used in this step, and is preferably 10 to 80 ° C. Moreover, the shearing to mix may be a conventionally well-known method, and the rotation speed of an apparatus becomes like this. Preferably it is 20-100 rpm.

  Regarding the drying method of the hydrogel, the hydrogel is subdivided to some extent with a meat chopper or cutter type crusher (the level of subdivision is about 0.5 to 20 mm square) or noodles, and if necessary, an alkali metal hydroxide, etc. After neutralizing the water-containing gel by adding air permeation drying (laminate the water-containing gel on the punching metal or screen, forcibly ventilate with hot air of 80-210 ° C) and air drying Examples include a method of putting a hydrogel into a container, aerating and circulating hot air, drying, and further drying the gel while further subdividing the gel with a machine such as a rotary kiln. Among these, air drying is preferable because efficient drying can be performed in a short time.

  Other drying methods of the hydrogel include, for example, a contact drying method in which the hydrogel is compressed and stretched on a drum dryer, and the hydrogel is poor in heat conduction. It is necessary to create a thin film of hydrogel.

In the present invention, the drying temperature at the time of drying the hydrogel varies depending on the dryer used, the drying time, and the like, but is preferably 80 to 210 ° C, more preferably 100 to 180 ° C. When the drying temperature is 210 ° C. or lower, the polymer is difficult to crosslink due to heat at the time of drying, the degree of cross-linking does not increase excessively due to thermal cross-linking, and the amount of absorption does not decrease. When the temperature is 80 ° C. or higher, drying does not take a long time and it is efficient. The drying time also varies depending on the model of the dryer to be used, the drying temperature, and the like, but is preferably 5 to 300 minutes, more preferably 5 to 120 minutes.
The dried product of the crosslinked polymer (A) thus obtained is pulverized and powdered as necessary. The pulverization method may be a normal method, and can be performed by, for example, an impact pulverizer (pin mill, cutter mill, skiller mill, ACM pulverizer, etc.) or an air pulverizer (jet pulverizer, etc.).
The weight average particle diameter of the resin particles (A1) obtained by pulverization is 10 to 1000 μm, preferably 20 to 800 μm, and 90% by weight or more of the particles is preferably in the range of 10 to 850 μm.

  The resin particles (A1) obtained by pulverization can be further crosslinked with a compound (D) having at least two groups capable of reacting with a carboxyl group and / or a carboxylate salt. In this method, compound (D) is added to A1), mixed, heated, subjected to a crosslinking reaction, and pulverized to obtain a particulate water-absorbing resin.

  As the compound (D), those described in JP-A-1-103615 can be used. Examples thereof include a compound (D1) having at least two functional groups selected from an epoxy group, a hydroxyl group, an amino group or an isocyanate group, and a polyvalent metal compound (D2) capable of forming an ionic bridge.

As the compound (D1) having at least two functional groups selected from an epoxy group, a hydroxyl group, an amino group or an isocyanate group, a polyepoxy or polyglycidyl ether compound (D11), a polyol compound (D12), a (poly) alkylene polyamine A compound (D13) etc. are mentioned.
Examples of the polyepoxy or polyglycidyl ether compound (D11) include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether, polyethylene glycol diglycidyl ether, and bisphenol A-epichlorohydrin type epoxy resin. Can be mentioned.
Examples of the polyol compound (D12) include glycerin, ethylene glycol, and propylene glycol.
Examples of the (poly) alkylene polyamine compound (D13) include ethylenediamine.

Examples of the polyvalent metal compound (D2) capable of forming ionic crosslinking include hydroxides, salts (halides, sulfates, carbonates) of alkaline earth metals (calcium, magnesium, etc.), zinc, aluminum, titanium, etc. Salt, acetate, etc.).
Specific examples include calcium chloride, zinc diacetate, and aluminum sulfate.

  Of these, polyglycidyl ether compounds and polyvalent metal compounds capable of forming ionic crosslinks are preferred.

  The addition amount of the compound (D) is preferably 0.005 to 3% by weight, more preferably 0.01 to 2% by weight, particularly preferably from the weight of (A1), from the viewpoint of the absorbability of the water absorbent resin. Is 0.05 to 1% by weight.

  As an example of a method of further crosslinking with the compound (D) having at least two functional groups, for example, the compound (D) is added to and mixed with the resin particles (A1), and the crosslinking reaction is performed by heating as necessary. If necessary, it is pulverized to obtain a particulate water-absorbing resin.

  Compound (D) is added and mixed as an aqueous solution if necessary, and is usually carried out in a kneader such as a kneader or a universal mixer. The heating method may be a normal method such as a method of heating with hot air at a temperature of 100 to 230 ° C., a thin film drying method using a drum dryer heated to 100 to 230 ° C., a reduced pressure drying method, a freeze drying method, or the like. Further, the water-absorbent resin obtained by surface cross-linking is sieved and pulverized to adjust the particle size as necessary. The pulverization method is not particularly limited, and is the same as that described above.

  The weight average particle diameter of the obtained water-absorbent resin is preferably 10 to 1000 μm, more preferably 20 to 800 μm, and more preferably 90 to 90% by weight of particles in the range of 10 to 850 μm, from the viewpoint of the water absorption capacity of the water absorbent resin. Preferably there is.

The manufacturing method of the water-absorbing resin of the present invention includes one step or two or more steps selected from the group consisting of the following first step to fourth step in this conventionally known method for manufacturing a water-absorbing resin by aqueous solution polymerization. The foaming agent (B) is mixed with (A).
1st process: The process of mixing the hydrogel of (A) and (B) 2nd process: The process of mixing with (B), drying the hydrogel of (A).
Third step: Step of mixing dried (A) with pulverizing (B) Fourth step: Step of mixing resin particles (A1) and (B) comprising (A)

The first step is a step of mixing the hydrogel (A) and (B).
This step may be performed simultaneously with the step (3) of neutralizing the hydrous gel of (A).
In this step, the mixing method of (B) includes a method of adding and mixing the dispersion liquid of (B) or (B) while chopping the hydrogel of (A) into small pieces of about 1 cm ³ or less. .
When the step of mixing the hydrogel of (A) and (B) is performed simultaneously with the step of neutralizing the hydrogel of (A), the step immediately before mixing the hydrogel of (A) and (C) , (A) The water-containing gel may be neutralized, or (A) the water-containing gel may be neutralized immediately after neutralization.

When the dispersion liquid (B) is used, the concentration of (B) is preferably 10 to 70% by weight, more preferably 20 to 60% by weight, particularly preferably 30 to 30% by weight based on the weight of the dispersion liquid (B). 50% by weight.
As a mixing device, a vertical slitter with a cutter blade used in the process of mixing a conventional hydrogel and (C), a transverse slitter with a cutter blade, a cutter type crusher with a rotary blade A meat chopper equipped with a machine, a pan with a predetermined diameter and a rotary blade can be used.
The temperature at the time of mixing may be a range performed in the step of mixing the conventional hydrogel and (C), and is preferably 10 to 80 ° C. Moreover, the shear to mix may be the same as the case where the conventional hydrogel and (C) are mixed, and the rotation speed of an apparatus becomes like this. Preferably it is 20-100 rpm.

In the present invention, when the hydrogel of (A) is crushed and dried, the adhesion of the hydrogels of (A) to each other and the mixing device, and for the purpose of preventing the adhesion of the hydrogel of (A) to the dryer, as necessary You may mix a well-known mold release agent with the dispersion liquid of (B).
Release agents include inorganic powders [calcium carbonate, aluminum hydroxide, aluminum oxide, silicon dioxide, hydrophobized silicon dioxide, titanium oxide, etc.], natural product-derived powders [wheat flour, rice flour, starch, carboxymethylcellulose] , Hydroxyethyl cellulose, hydroxypropyl cellulose, etc.], synthetic polymer or synthetic resin powder [polyvinyl alcohol, polyester, silicone resin, fluorine resin, polyethylene, polypropylene, acrylic resin, etc.], anionic surfactant [lauryl sulfate] Triethanolamine, sodium lauryloxypolyethyleneoxysulfate, sodium lauryl sulfosuccinate, sodium lauroyl sarcosine, sodium α-olefin sulfonate, sodium lauryl phosphate, N- 椰Oil fatty acid acyl-L-glutamate monosodium, sodium lauryl sulfoacetate, etc.], nonionic surfactants [1: 1 type coconut oil fatty acid diethanolamide, lauryl dimethylamine oxide, glyceryl monostearate, polyethylene glycol monostearate, Polyethylene glycol distearate, sorbitan monolaurate, polyoxyethylene sorbitan monolaurate, nonylphenol polyoxyethylene, octylphenol polyoxyethylene, dodecylphenol polyoxyethylene, etc.], cationic surfactants [stearyltrimethylammonium chloride, distearyldimethylammonium chloride] , Ethyl sulfate lanolin fatty acid aminopropyl ethyl dimethyl ammonium, etc.], amphoteric activator [coconut oil fatty acid acid Dopropyldimethylaminoacetic acid betaine, lauryldimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, etc.], polymer activator [cationized cellulose, polyethylene glycol, polypropylene glycol, polyacryl Examples thereof include sodium acid surfactants, and known silicon surfactants and fluorine surfactants. Among these release agents, inorganic powders, anionic surfactants and nonionic surfactants are preferred.

  When the release agent is in powder form, the amount of release agent added is reduced in dust generation and absorption performance of the water-absorbent resin composition with respect to the total weight of (meth) acrylic acid (salt) and (b). From the viewpoint, it is 0 to 50% by weight, preferably 0.001 to 30% by weight. In addition, when a powder-form mold release agent is used, you may isolate | separate and collect | recover an excess mold release agent in the arbitrary steps after gel crushing. When the release agent to be added is liquid, the addition amount is 0 to 5% by weight, preferably from the total weight of (meth) acrylic acid (salt) and (b), from the viewpoint of the absorbability of the water-absorbent resin. Is 0.0001 to 3% by weight.

  In the second step, the hydrogel of (A) is contact-dried (such as by compressing and stretching the hydrogel on a drum dryer), and air-permeable drying (the hydrogel is laminated on a punching metal or a screen to force (For example, dry by blowing hot air of 80 to 210 ° C.) and dry by drying (Put water-containing gel in a container, dry by circulating hot air, dry it with a machine such as a rotary kiln) It is the process of mixing with (B), drying with the method of this. Among these, air drying is preferable because efficient drying can be performed in a short time.

  The drying temperature varies depending on the dryer to be used, the drying time, and the like, but is preferably 80 to 210 ° C, more preferably 100 to 180 ° C, from the viewpoint of the drying time and the absorbability of the water absorbent resin. The drying time varies depending on the model of the dryer to be used, the drying temperature, and the like, but is preferably 5 to 300 minutes, more preferably 5 to 120 minutes, from the viewpoint of the drying time and the absorbability of the water absorbent resin.

In this step, examples of the mixing method (B) include a method of adding and mixing the dispersion liquid (B) or (B) while drying the hydrogel of (A).
When mixing (B) with the hydrogel of (A), the stage immediately before drying the hydrogel of (A), the stage of drying the hydrogel of (A), and drying the hydrogel of (A) Mixing may be performed at any of the immediately following stages, and is preferably the stage immediately before drying the hydrogel of (A).
When the dispersion liquid (B) is used, the concentration of (B) is preferably 10 to 70% by weight, more preferably 20 to 60% by weight, particularly preferably 30 to 30% by weight based on the weight of the dispersion liquid (B). 50% by weight.

As a mixing device, in the case of the stage immediately before drying the hydrogel of (A), it is equipped with a vertical slitting slitter equipped with a cutter blade used in the process of mixing the conventional hydrogel and (C), and a cutter blade. A cross-cut slitter, a cutter-type crusher equipped with a rotary blade, a meat chopper equipped with a pan with a predetermined diameter and a rotary blade can be used. The temperature at the time of mixing may be a range performed in the step of mixing the conventional hydrogel and (C), and is preferably 10 to 80 ° C. Moreover, the shear to mix may be the same as the case where the conventional hydrogel and (C) are mixed, and the rotation speed of an apparatus becomes like this. Preferably it is 20-100 rpm.
The mixing apparatus at the stage of drying the hydrogel of (A) is not particularly limited as long as the dried hydrogel of (A) and (B) can be mixed uniformly. For example, in a conventional drying process, It is possible to use an apparatus such as adding a charging line (B) to the dryer to be used. The temperature at the time of mixing may be in the range used in the conventional drying process.
The stage immediately after drying the hydrogel of (A) is not particularly limited as long as the dried hydrogel of (A) and (B) can be uniformly mixed. For example, in the transfer line immediately after the conventional drying process. An apparatus for adding a preparation line (B) and the like can be used. The temperature at the time of mixing may be in the range used in the conventional drying process.

The third step is a step of mixing dried (A) with (B) while crushing.
The pulverization method may be a conventionally known method, for example, an impact pulverizer (pin mill, cutter mill, skiller mill, ACM pulverizer, etc.) or an air pulverizer (jet pulverizer, etc.).
In this step, the mixing method (B) includes a method in which the dispersion (B) is added and mixed while pulverizing the dried (A) into small pieces of about 1 mm ³ or less.
When mixing (B) with dried (A) while pulverizing, the stage immediately before pulverizing dried (A), the stage pulverizing dried (A), immediately after pulverizing dried (A) Mixing may be carried out at any of the stages, preferably the stage immediately before pulverizing the dried (A) and the stage pulverizing the dried (A).
The concentration of the dispersion (B) is preferably 10 to 70% by weight, more preferably 20 to 60% by weight, and particularly preferably 30 to 50% by weight based on the weight of the dispersion (B).
The mixing device for mixing at the stage immediately before pulverization is not particularly limited as long as the dried (A) and (B) can be mixed uniformly. For example, in a conventional pulverizer, immediately before pulverizing the dried (A). (B) preparation line can be provided in this part, and the apparatus of addition etc. can be used. The temperature at the time of mixing may be within the range performed in the conventional step of pulverizing the dried (A).
The apparatus for mixing the dried (A) while pulverizing is not particularly limited as long as the pulverized resin particles (A1) and (B) can be mixed uniformly, but the pulverizer used in the conventional pulverization process is not limited. An apparatus such as adding a charging line (B) can be used. The temperature and shear at the time of mixing may be within a known range performed in the conventional step of pulverizing the dried (A).
As a mixing device for mixing at the stage immediately after pulverization, a Nauter type mixer, a kneader type mixer, a paddle type mixer, a V type mixer, a ribbon type mixer, a screw type mixer, an airflow type mixer, etc. are used. it can. The temperature and shear at the time of mixing may be in a known range conventionally used in the surface crosslinking step.

The fourth step is a step of mixing the resin particles (A1) and (B) made of (A).
This step may be performed simultaneously with the step (4) of performing the surface crosslinking treatment.
In this step, examples of the mixing method (B) include a method in which the resin particles (A1) and (B) made of (A) and the dispersion liquid of (B) are added and mixed.
As the step of mixing (B) with the resin particles (A1) comprising (A), when (A1) is subjected to surface crosslinking, (A1) is subjected to surface crosslinking immediately before surface crosslinking. May be mixed in any of the steps immediately after the surface crosslinking of (A1), preferably the step immediately before the surface crosslinking of (A1) and the step of (A1) surface crosslinking, Preferably, it is the step immediately before surface cross-linking (A1). When (A1) is not surface-crosslinked, it may be carried out at any stage as long as it is a process after obtaining (A1).
When the dispersion liquid (B) is used, the concentration of (B) is preferably 10 to 70% by weight, more preferably 20 to 60% by weight, particularly preferably 30 to 30% by weight based on the weight of the dispersion liquid (B). 50% by weight.
As a mixing apparatus at the stage of surface cross-linking (A1), a Nauter type mixer, a kneader type mixer, a paddle type mixer, a V type mixer, a ribbon type mixer, a screw type, which are conventionally used in this process. A mixer, an airflow type mixer, etc. can be used. The temperature and shear at the time of mixing may be within a known range in the conventional surface crosslinking step.
The mixing apparatus at the stage immediately before and after the surface crosslinking of (A1) is the same as the mixing apparatus that can be used at the stage of (A1) surface crosslinking, and the conditions for mixing are also the same.

  Of these, as the step of mixing (A) and (B), the first step and the fourth step are preferable, and the first step is more preferable.

The step of heating after mixing (B) may be at any timing, and the heating device is not particularly limited, and a normal heating dryer such as a hot air dryer, fluidized bed dryer, nauter dryer, rotary kiln, etc. Etc. can be used. The heating temperature varies depending on the model to be used, the heating time, etc., but is 70 to 210 ° C., and preferably 80 to 190 ° C. from the viewpoint of the efficiency of generating gas from (B) and the absorbent capacity of the water absorbent resin. More preferably, it is 90-170 degreeC. The heating time also varies depending on the model used and the drying temperature, but is preferably 1 to 300 minutes, more preferably 2 to 120 minutes.
When mixing before a drying process, since a drying process can be utilized as this heating process, the process of heating especially is unnecessary.
Moreover, when mixing before the process of surface-crosslinking treatment, since the heating process of surface crosslinking treatment can be utilized as a heating process, the process of heating in particular is unnecessary.

  The water-absorbent resin obtained by the production method of the present invention preferably has a 0.9M / vol% saline absorption rate of 0.80 to 5.0 g / g / s, more preferably 1.0 to 5.0 g. / G / s, particularly preferably 1.2 to 3.6 g / g / s, most preferably 1.6 to 2.5 g / g / s. Within this range, when used in a paper diaper or sanitary napkin, dry feeling and leakage prevention are further improved.

The 0.9M / vol% saline absorption rate is measured by the following method.
<Measurement method of 0.9M / vol% saline absorption rate>
The 0.9M / vol% saline absorption rate is measured according to JIS K7224-1996.

  The water-absorbent resin composition obtained by the production method of the present invention preferably has an apparent density of 0.48 to 0.63 g / ml, more preferably 0.50 to 0, from the viewpoints of dry feeling and leakage prevention. 0.62 g / ml, particularly preferably 0.52 to 0.60 g / ml.

The apparent density is measured by the following method.
<Measurement method of apparent density>
The apparent density is measured according to JIS K3362-1998.

  The water-absorbent resin composition obtained by the production method of the present invention preferably has a fractal order of 1.87 to 1.92, more preferably 1.89 to 1.91, from the viewpoint of dry feeling and leakage prevention. Particularly preferred is 1.90 to 1.91.

  In the present invention, the fractal order is one of indices indicating the shape of particles, that is, the irregularities of the particle surface. A small fractal order means that the external surface area of the particles is large. The fractal order is 2 if the resin particles are truly spherical with no irregularities on the surface.

In addition, said fractal order can be measured with the following method described in Unexamined-Japanese-Patent No. 2001-2935.
<Fractal order measurement method>
Using a scanning electron microscope (for example, JSM-7000F manufactured by JEOL Datum), a photograph of one water-absorbent resin particle is taken at each magnification of 25, 30, 50, and 100 times. For each of these photographs, the particle contour length and the particle projected area are determined using image analysis software (WinROOF manufactured by Mitani Corporation). Next, the common logarithm of the particle contour length and the particle projected area of each photograph is obtained. The obtained values are plotted in an XY coordinate diagram with the common logarithm of the particle contour length as the X axis and the common logarithm of the particle projection area as the Y axis, and a straight line is drawn by the method of least squares. The above straight line is drawn for each of the five water-absorbing resin particles taken out at random, and the average value of the slopes is taken as the fractal order.

  Since the water-absorbent resin obtained by the production method of the present invention has an excellent absorption rate, it can be suitably used for applications such as disposable diapers, sanitary napkins, freshness-keeping materials, and water-stopping materials. When the water-absorbent resin obtained by the production method of the present invention is used for these applications, the method of use is the same as the method of using a conventionally known water-absorbent resin.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to this.

Example 1
In a 2-liter beaker, 200 g of acrylic acid, 0.16 g of pentaerythritol triallyl ether, 0.72 g of trimethylolpropane triacrylate, and 880 g of ion-exchanged water are mixed with stirring to prepare an aqueous acrylic acid solution, and the temperature is kept at 8 ° C. Adjusted.
The acrylic acid aqueous solution was put into a 1.5 liter adiabatic polymerization tank, and the dissolved oxygen amount in the acrylic acid aqueous solution was adjusted to 0.1 ppm or less through nitrogen in the aqueous solution. To this heat insulation polymerization layer, 0.62 g of 1.0 wt% aqueous hydrogen peroxide, 0.62 g of 1.0 wt% L-ascorbic acid aqueous solution, 10 wt% 2,2′-azobis (2-amidinopropane) hydrochloride (Product name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 6.2 g of aqueous solution and 0.32 g of 0.1 wt% iron (II) sulfate heptahydrate aqueous solution were added, and the solution was in the aqueous solution until polymerization started. Continued nitrogen aeration. After confirming that the polymerization started and the viscosity of the acrylic acid aqueous solution started to rise, the nitrogen aeration was stopped and the polymerization was carried out for 6 hours. When the temperature of the aqueous acrylic acid solution was measured with a hot spot thermometer, the maximum temperature reached was 63 ° C.
After taking out the block-like crosslinked hydrous gel from the adiabatic polymerization tank and using a small meat chopper (Royal) to subdivide the gel into noodles with a thickness of 3 to 10 mm at 60 rpm at room temperature. , 167 g of a 48% by weight aqueous solution of sodium hydroxide (special grade reagent) (neutralization degree 72 mol%) was added to neutralize the carboxyl group of the polyacrylic acid in the cross-linked polymer under the same conditions as above. A hydrogel was obtained. Further, 31.9 g of azodicarbonamide (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: VINYHALL AC # 3) {13% by weight with respect to the total weight of acrylic acid (salt) and cross-linking agent} was added. And kneaded uniformly into the hydrous gel.
This hydrogel was laminated on a SUS screen having an aperture of 850 μm with a thickness of 5 cm, and using a small air-permeable dryer (manufactured by Yako Electric Manufacturing Co., Ltd.), the supply air temperature was 205 ° C. and the air speed was 1. Under a condition of 0.5 m / sec, the hydrated gel was allowed to pass through for 30 minutes, and the hydrated gel was dried by heating to obtain a dried product having a moisture content of about 4%.
The obtained dried product was pulverized using a home mixer, and a particle having a particle size of 32 to 710 μm (400 to 22 mesh) was collected using a sieve to obtain the water absorbent resin (1) of the present invention. .

Example 2
In the same manner as in Example 1, a water-containing gel after neutralization was obtained. 500 g of the hydrous gel after neutralization is laminated on a SUS screen with an opening of 850 μm at a thickness of 1 cm, and dried at 160 ° C. for 15 minutes using a smooth air dryer (manufactured by Tabai Espec Co., Ltd.). Thereafter, 50 wt% p, p′-oxybis (benzenesulfohydrazide) (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: Neocerbon N # 5000) dispersion 29.3 g {based on the total weight of acrylic acid (salt) and crosslinking agent 15% by weight} is sprinkled on the water-containing gel being dried, and then dried by heating at 160 ° C. for 45 minutes using a smooth air dryer (manufactured by Tabai Espec Co., Ltd.). Got.
The obtained dried product was pulverized using a home mixer, and a particle having a particle size of 32 to 710 μm (400 to 22 mesh) was collected using a sieve to obtain the water absorbent resin (2) of the present invention. .

Example 3
Except not adding azodicarbonamide to the hydrous gel after neutralization in Example 1, the same operation as in Example 1 was performed to obtain a dried product.
While pulverizing 200 g of the obtained dried product using a household mixer, 3.8 g of 50 wt% p, p′-oxybis (benzenesulfohydrazide) dispersion {total weight of acrylic acid (salt) and crosslinking agent 1.0 wt%} was added and pulverized and mixed. Using a sieve, collect 100g of particles with a particle size of 32 to 710μm (400 mesh to 22 mesh) and add a solution consisting of 0.12g of ethylene glycol diglycidyl ether, 4.5g of water and 2.5g of diethylene glycol while stirring. After mixing, a water-absorbing resin (3) of the present invention was obtained by performing a heating reaction at 160 ° C. for 40 minutes using a smooth air dryer (manufactured by Tabai Espec Co., Ltd.).

Example 4
Except not adding azodicarbonamide to the hydrous gel after neutralization in Example 1, the same operation as in Example 1 was performed to obtain a dried product. The obtained dried product was pulverized using a home mixer, and 100 g of particles having a particle size of 32 to 710 μm (400 mesh to 22 mesh) were collected using a sieve to obtain resin particles.
While stirring 100 g of the obtained resin particles, 0.12 g of ethylene glycol diglycidyl ether, 4.5 g of water, 2.5 g of diethylene glycol and 50 wt% p, p′-oxybis (benzenesulfohydrazide) dispersion 3 .8 g {2.0% by weight with respect to the total weight of acrylic acid (salt) and crosslinking agent} was added and mixed using a Nauter mixer (manufactured by Hosokawa Micron Corporation) at room temperature and 50 rpm. Then, a water-absorbing resin (4) of the present invention was obtained by performing a heating reaction at 160 ° C. for 40 minutes using a smooth air dryer (manufactured by Tabai Espec Co., Ltd.).

Example 5
In Example 1, 24.5 g of azodicarbonamide was changed to 24.5 g of azobisisobutyronitrile {10% by weight with respect to the total weight of acrylic acid (salt) and the cross-linking agent}. Thus, a water absorbent resin (5) of the present invention was obtained.

Example 6
In Example 1, 24.5 g of azodicarbonamide was changed to 24.5 g of p-toluenesulfonylhydrazine {10% by weight based on the total weight of acrylic acid (salt) and cross-linking agent}. Thus, a water absorbent resin (6) of the present invention was obtained.

Example 7
In Example 1, 24.5 g of azodicarbonamide was changed to 24.5 g of N, N′-dinitrosopentamethylenetetramine {10% by weight based on the total weight of acrylic acid (salt) and crosslinking agent}. In the same manner as in Example 1, a water absorbent resin (7) of the present invention was obtained.

Example 8
In a 2-liter beaker, 300 g of acrylic acid, 1.0 g of pentaerythritol triallyl ether and 660 g of ion-exchanged water were mixed with stirring to prepare an aqueous acrylic acid solution, and the temperature was adjusted to 8 ° C.
The acrylic acid aqueous solution was put into a 1.5 liter adiabatic polymerization tank, and the dissolved oxygen amount in the acrylic acid aqueous solution was adjusted to 0.1 ppm or less through nitrogen in the aqueous solution. To this heat insulation polymerization layer, 2.0 wt% 2,2′-azobis {2-methyl-N- (2-hydroxyethyl) -propionamide} (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086) 4.65 g of aqueous solution, 1.23 g of 1.0 wt% aqueous hydrogen peroxide, 4.65 g of 1.0 wt% L-ascorbic acid aqueous solution and 0.45 g of 0.1 wt% iron (II) sulfate heptahydrate aqueous solution And nitrogen bubbling into the aqueous solution was continued until polymerization started. After confirming that the polymerization started and the viscosity of the acrylic acid aqueous solution started to rise, the nitrogen aeration was stopped and the polymerization was carried out for 6 hours. When the temperature of the aqueous acrylic acid solution was measured with a hot spot thermometer, the highest temperature reached 98 ° C.
After taking out the block-like crosslinked hydrous gel from the adiabatic polymerization tank and using a small meat chopper (Royal) to subdivide the gel into noodles with a thickness of 3 to 10 mm at 60 rpm at room temperature. Then, 250 g of a 48 wt% sodium hydroxide (reagent special grade) aqueous solution (neutralization degree 72 mol%) was added, and the carboxyl group of the polyacrylic acid in the crosslinked polymer was neutralized under the same conditions as in the above apparatus. Further, 36.7 g of p, p′-oxybis (benzenesulfohydrazide) (manufactured by Eiwa Kasei Kogyo: Neocerbon N # 5000) {10% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent} The water-containing gel was uniformly kneaded under the same conditions as in the above apparatus.
This hydrogel was laminated on a SUS screen having an opening of 850 μm with a thickness of 5 cm, and a small air-permeable dryer (manufactured by Yako Electric Manufacturing Co., Ltd.) was used to supply a supply air temperature of 160 ° C. and a wind speed of 1 Under a condition of 0.5 m / sec, the water-containing gel was passed through for 40 minutes, and the water-containing gel was dried by heating to obtain a dried product having a water content of about 4%.
The dried product was pulverized using a home mixer, and a particle having a particle size of 32 to 710 μm (400 to 22 mesh) was collected using a sieve to obtain resin particles.
While stirring 100 g of the obtained resin particles, a solution consisting of 0.01 g of ethylene glycol diglycidyl ether, 0.9 g of water, and 0.46 g of propylene glycol was used at room temperature using a Nauter mixer (manufactured by Hosokawa Micron Corporation). The mixture was added and mixed under the condition of 50 rpm, and subjected to a heating reaction at 140 ° C. for 40 minutes using a smooth air dryer (manufactured by Tabai Espec Co., Ltd.) to obtain the water absorbent resin (8) of the present invention.

Example 9
In Example 8, p, p′-oxybis (benzenesulfohydrazide) was changed to 73.4 g {20% by weight based on the total weight of acrylic acid (salt) and the cross-linking agent}. Thus, a water absorbent resin (9) of the present invention was obtained.

Example 10
In Example 8, except that p, p′-oxybis (benzenesulfohydrazide) is 1.84 g {0.5% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent} Similarly, the water absorbent resin (10) of the present invention was obtained.

Example 11
To the water-absorbent resin (8) obtained in Example 8, 2% by weight of silicon dioxide {manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil 200PE} is added and uniformly blended. A water absorbent resin (11) was obtained.

Example 12
The same operation as in Example 8 was performed, and the obtained water-absorbent resin was pulverized using a household mixer, and a sample having a particle size of 106 to 300 μm (145 mesh to 48 mesh) was collected using a sieve. The water absorbent resin (12) of the invention was obtained.

Example 13
To the water-absorbent resin (12) obtained in Example 12, 2% by weight of silicon dioxide {manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil 200PE} is added and blended uniformly. A water absorbent resin (13) was obtained.

Example 14
In a 1 liter beaker, 100 g of acrylic acid, 272.2 g of ion-exchanged water and 0.13 g of ethylene glycol diglycidyl ether were added and mixed to obtain a uniform solution. While cooling the beaker with an ice bath, 100 g of 40% sodium hydroxide aqueous solution was added to neutralize a part (72 mol%) of acrylic acid. After the neutralized monomer solution was cooled to 5 ° C., 0.2 g of potassium persulfate was added as a polymerization initiator to prepare a monomer aqueous solution.
In a 2 liter separable flask equipped with a stirrer and a condenser (cooler), 1000 ml of cyclohexane and polyoxyethylene octyl phenyl ether phosphate as a dispersant (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Prisurf A210G) 2 0.5 g was added and stirred while adjusting the temperature to 60 ° C. using a hot water bath to dissolve the dispersant in cyclohexane.
After reducing the dissolved oxygen of cyclohexane to 0.1 ppm or less through nitrogen in a cyclohexane liquid in a separable flask, stirring the cyclohexane using a stirrer, and then adding 400 g of the monomer aqueous solution at 6.6 g / min using a dropping funnel. Dropped over 1 hour, reverse phase suspension polymerization was carried out at a polymerization temperature of 60 ° C., and after completion of dropping of the monomer aqueous solution, the temperature was further adjusted to 60 ° C. for 2 hours to complete the suspension polymerization, and then up to 30 ° C. Upon cooling, a spherical hydrous gel was obtained in cyclohexane.
After the rotation of the stirrer was stopped and the produced hydrogel was allowed to settle, cyclohexane was removed by decantation, and the remaining hydrogel was washed twice with cyclohexane to remove the dispersant adhering to the hydrogel.
The obtained spherical water-containing gel was spread on a release paper, and dried for 2 hours with a 80 ° C. vacuum dryer (degree of vacuum: 10,000 to 20,000 Pa).
To 100 g of the obtained dried product, 48.3 g of an aqueous dispersion of 30 wt% azodicarbonamide {15 wt% based on the total weight of acrylic acid (salt) and crosslinking agent} was added, and a small air-permeable dryer was used. After air permeation for 30 minutes under the conditions of a supply air temperature of 205 ° C. and a wind speed of 1.5 m / sec, the mixture is pulverized using a home-use mixer, and the particles are 32 to 710 μm (400 to 22 mesh) using a sieve. The thing of diameter was extract | collected and the water absorbing resin (14) of this invention was obtained.

Comparative Example 1
A comparative water absorbent resin (H1) was obtained in the same manner as in Example 1 except that 24.5 g of azodicarbonamide was not added.

Comparative Example 2
In Example 8, a comparative water-absorbent resin (H2) was obtained in the same manner except that 73.4 g of p, p′-oxybis (benzenesulfohydrazide) was not added.

Comparative Example 3
A comparative water-absorbing resin (H3) was obtained in the same manner as in Example 12 except that 73.4 g of p, p′-oxybis (benzenesulfohydrazide) was not added.

Comparative Example 4
A comparative water-absorbing resin (H4) was obtained in the same manner as in Example 13 except that 73.4 g of p, p′-oxybis (benzenesulfohydrazide) was not added.

Comparative Example 5
In Example 1, instead of “putting acrylic acid aqueous solution into 1.5 liter adiabatic polymerization tank”, “put 24.5 g of acrylic acid aqueous solution and azodicarbonamide into 1.5 liter adiabatic polymerization tank”, and A comparative water absorbent resin (H5) was obtained in the same manner as in Example 1 except that azodicarbonamide was not added after neutralization.

  Table 1 summarizes the measurement results of 0.9M / vol% saline solution absorption rate, apparent density, and fractal order of the resins prepared in the above Examples and Comparative Examples.

  The water-absorbing resins of Examples 1 to 14 obtained by the production method of the present invention have an excellent absorption rate as compared with Comparative Examples 1 to 5.

  By the method for producing a water-absorbent resin of the present invention, a water-absorbent resin having an excellent absorption rate can be obtained. Therefore, when the water-absorbent resin obtained by the production method of the present invention is used as a sanitary material such as a paper diaper or a sanitary napkin, a sanitary material excellent in absorption capacity such as absorption rate and diffusibility can be created. In addition, when the water-absorbent resin obtained by the production method of the present invention is used for a freshness-keeping material, a water-stopping agent, or the like, a freshness-holding material, a water-stopping agent, etc. excellent in absorbability such as an absorption rate can be created.

Claims (5)

A water-absorbent resin composition obtained by mixing a cross-linked polymer (A) having (meth) acrylic acid (salt) and a cross-linking agent (b) as essential constituent units and a foaming agent (B) that generates gas by heating. A method for producing a water absorbent resin obtained by further heating a product, wherein the mixing step comprises one step or two or more steps selected from the group consisting of the following first to fourth steps. Manufacturing method of resin.
1st process: The process of mixing the hydrogel of (A) and (B) 2nd process: The process of mixing with (B), drying the hydrogel of (A) 3rd process: Drying (A) Step of mixing with (B) while pulverizing Fourth step: Step of mixing resin particles (A1) and (B) comprising (A)   The production method according to claim 1, wherein the amount of (B) used is 0.1 to 20% by weight relative to (A).   The production method according to claim 1 or 2, wherein the water absorbent resin has a 0.9 M / vol% saline absorption rate of 0.80 to 5.0 g / g / s.   The manufacturing method according to claim 1, wherein the water absorbent resin is porous.   The apparent density of the water-absorbent resin is 0.48 to 0.63 g / ml, and the fractal order is 1.87 to 1.92. The production method according to any one of claims 1 to 4.