JP4476822B2 - Ammonium salt-containing water-absorbent resin and method for producing the same - Google Patents

Description

  The present invention relates to a water-absorbent resin suitably used for sanitary materials such as disposable diapers and incontinence pads, and a method for producing the same. More specifically, the present invention relates to a water-absorbent resin, a water-absorbent resin composition, and a method for producing the same, having a high water absorption ratio, excellent water absorption characteristics under a high load, and little residual monomer. In addition, under the use conditions of the absorbent body where there is little contact between the water-absorbent resins, the water-absorbing magnification in a no-load state and the water-absorbing property under a high load are high, and even after absorbing an aqueous liquid, The present invention relates to a water-absorbent resin and an absorbent resin composition with little resin position change.

Conventionally, water-absorbing resins have been widely used as sanitary materials such as disposable diapers and incontinence pads for the purpose of absorbing body fluids as constituent materials.
As such a water-absorbing resin, a crosslinked polyacrylic acid partially neutralized product (see, for example, Patent Document 1), a hydrolyzate of starch-acrylonitrile graft polymer (see, for example, Patent Document 2), and a starch-acrylic acid graft polymer. Neutralized product (for example, see Patent Document 3) Saponified vinyl acetate-acrylic acid ester copolymer (for example, see Patent Document 4), hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (for example, see Patent Document 5) ) Etc. are known.

  As a recent demand for paper diapers, there is a reduction in the thickness of paper diapers. In order to cope with this, as a method generally used in paper diapers at present, there is a method of using a large amount of water-absorbent resin by reducing the water-absorbent resin support carrier in diapers such as pulp. In such a paper diaper, the water-absorbing resin is in a dense state. As performance required for the water-absorbent resin used in such a paper diaper, physical properties such as liquid permeability between the water-absorbent resins and gel strength of the swollen gel are emphasized. In recent years, demand for disposable diapers for the elderly has been increasing with the aging of the average lifespan. Since disposable diapers for elderly people have more excretion per time than for infants, in addition to the above physical properties, it is necessary to have a high water absorption capability in a non-pressurized state. In addition, the disposable diaper for elderly people has a larger load on the disposable diaper than that for infants, so it has excellent absorption characteristics under high load that can fully exhibit water absorption capacity even under weight. Is also strongly sought after. However, liquid permeability between water-absorbent resins, physical properties such as gel strength of the swollen gel, absorption characteristics under high load, and water absorption capacity in a non-pressurized state do not show a positive correlation. For example, the higher the absorption capacity in the non-pressurized state, the liquid permeability, gel strength, and the physical properties such as the absorption characteristics under high load tend to decrease, conversely the liquid permeability, gel strength, under high load If importance is attached to the absorption characteristics, etc., the absorption capacity in the non-pressurized state is lowered. In other words, the compatibility of water absorption capacity under no pressure and water absorption characteristics under high load, liquid permeability, gel strength and other conflicting properties is a challenge, especially water absorption capacity under high pressure and high load. There is a strong demand for improving the balance of water absorption characteristics below.

As a method for improving the water absorption properties of such a water absorbent resin in a well-balanced manner, a technique of crosslinking the vicinity of the surface of the water absorbent resin is known, and various methods have been proposed so far.
For example, a method using a polyhydric alcohol as a crosslinking agent (see, for example, Patent Documents 16 and 7), a method using a polyvalent glycidyl compound, a polyvalent aziridine compound, a polyvalent amine compound, and a polyvalent isocyanate compound (see, for example, Patent Document 8). ), A method using glyoxal (for example, see Patent Document 9), a method using a polyvalent metal (for example, see Patent Documents 10 and 11), a method using a silane coupling agent (for example, see Patent Documents 12 to 14), and the like. ing.

  In addition, a method in which a crosslinking agent is uniformly distributed on the surface of the water-absorbent resin during the crosslinking reaction, and an inert inorganic powder is present when adding the crosslinking agent as an attempt to perform uniform surface crosslinking (see, for example, Patent Documents 15 and 16). Also known are a method in which a dihydric alcohol is present (see, for example, Patent Document 17), a method in which water and an ether compound are present (see, for example, Patent Document 18), and a method in which phosphoric acid is present (see, for example, Patent Document 19). Yes. Further, as an application example of the above method, there is also known a method in which a neutralized monomer having a specific composition is mixed with the above crosslinking agent for the purpose of reducing residual monomer and surface crosslinking is performed while heat treatment (see, for example, Patent Documents 20 and 21). ing. However, although the balance of various physical properties of the water-absorbent resin is improved by these methods, it is still not sufficient, and further higher quality is required.

  As a method for improving the physical properties of other water-absorbent resins in a well-balanced manner, a polyfunctional unsaturated compound that becomes a crosslinking agent during polymerization and a compound that becomes a condensation type crosslinking agent are added to a monomer obtained by partially neutralizing acrylic acid with sodium. There is also a method of controlling the maximum reaction temperature by starting polymerization with a redox polymerization initiator (see, for example, Patent Document 22). According to this method, although a water-absorbing resin having a small amount of water-soluble component that causes a decrease in water-absorbing ability is obtained, the value of the absorbing ability is not sufficient. Moreover, even if it tries to superpose | polymerize by adding the compound used as a condensation type crosslinking agent to the aqueous solution of acrylic acid / acrylic acid sodium salt, monomer aqueous solution will gelatinize during nitrogen substitution performed before adding a polymerization initiator, There is a problem in the control of polymerization.

  Other requirements for the water-absorbent resin include reduction of residual monomers. At present, among water-absorbent resins, a cross-linked copolymer of acrylic acid / sodium acrylate is mainly used from the viewpoint of performance and cost, but in this acrylic acid-based water-absorbing resin, usually 100 ppm or more. Monomer remains, and it seems that about several hundred ppm of monomer remains in the commercial product. Residual monomers may cause deterioration of the water-absorbent resin, which is not preferable for the product.

  Conventionally, many methods for reducing the residual monomer of the water-absorbent resin have been proposed. For example, (1) a method of improving the polymerization rate by changing reaction conditions, (2) a method of adding an additive to the polymer after polymerization to reduce the residual monomer, (3) a method of extracting the residual monomer, (4) a microorganism Are known, such as a method of decomposing the residual monomer by adding water, (5) a method of volatilizing the residual monomer at high temperature, and (6) a method of using a monomer obtained by a specific neutralization method. However, no method has been found that has a practically sufficient effect because it is insufficient, has safety problems, or is industrially difficult.

  In recent years, a method has been proposed in which the residual monomer of the water-absorbent resin can be reduced by reducing impurities derived from the starting acrylic acid (see, for example, cited references 23 to 25). According to this method, not only the residual monomer during polymerization can be reduced, but also an increase in residual monomer during heat treatment after polymerization can be suppressed. However, in order to reduce impurities derived from acrylic acid as a raw material, it is possible to use acrylic acid immediately after distillation purification, and in the neutralization step, the neutralization rate exceeds 100 mol% for at least one period. For example, the use of such monomers as soon as possible is highly restrictive, and it is not economically preferable to add equipment and the like for industrial implementation.

  As another method, a monomer obtained by neutralizing a part of acrylic acid with an ammonium salt or a monomer obtained by partially or completely neutralizing acrylic acid with a nitrogen compound is used. A method of reducing is proposed (see Patent Documents 26 and 27). According to this method, it is possible to provide a water-absorbing resin with a small amount of residual monomer and little increase in residual monomer even under various use conditions. However, there are several problems with this method. In general, when acrylic acid or an alkali metal acrylate is the main component, the extraction reaction of alpha hydrogen in the main chain is likely to occur during radical polymerization as compared with the case where ammonium acrylate is the main component. For this reason, chain transfer to the main chain occurs during polymerization, resulting in uncontrolled intramolecular crosslinking. As a result, the molecular weight between cross-linking points is reduced, and the gel capacity and thus the absorption capacity is lowered. If it is completely neutralized with an ammonium salt, such side reactions can be suppressed and the absorption capacity can be increased. However, in ordinary radical polymerization, the molecular weight distribution is large, and even when polymerized with 100% ammonium salt, many low molecular weight components are contained. These low molecular weight components cannot contribute to water absorption, resulting in a decrease in water absorption performance. In other words, these methods are not satisfactory in actual use conditions because of their low water absorption performance even if the amount of residual monomers is small.

A method has also been proposed in which the residual monomer of the water-absorbent resin is reduced by using ammonium acrylate obtained by hydrolyzing acrylonitrile (see Patent Document 28), but even in this case, the residual monomer is 100 ppm. It remains nearby and the effect is not enough.
Thus, it is difficult to obtain a water-absorbing resin with a small amount of residual monomer, which is difficult due to various restrictions, and has a high water absorption capacity under no pressure and excellent water absorption characteristics under high load. A functional resin was not obtained.

JP 55-84304 A Japanese Patent Publication No.49-43395 Japanese Patent Laid-Open No. 51-125468 JP-A-52-14689 Japanese Patent Publication No.53-15959 JP 58-180233 A JP-A 61-16903 JP 59-189103 A JP 52-117393 A JP 51-136588 A JP-A-61-257235 JP-A-61-211305 JP-A 61-252212 JP 61-264006 A JP-A-60-163958 JP 60-255814 A JP-A-1-292004 Japanese Patent Laid-Open No. 2-153903 Japanese National Patent Publication No. 8-508517 JP-A-6-122707 JP-A-6-122708 JP-A-8-188602 JP-A-6-56931 JP-A-6-122707 JP 2000-26538 A Japanese Patent No. 3259143 Special table 2001-524557 Japanese Patent Application No. 2003-117838

  The object of the present invention can be suitably used for sanitary materials such as disposable diapers, sanitary napkins, incontinence pads, etc., has a high water absorption capacity under no load conditions, and has excellent absorption characteristics under high loads, and It is an object of the present invention to provide a water-absorbing resin with little residual monomer, a water-absorbing resin composition, and a method for producing the same. Also, under the conditions of use of the absorbent body with little contact with the water-absorbent resin, the water absorption capacity under high load and the water absorption characteristic under high load are particularly high, and the hydrophilic fiber and resin inside the absorbent body are absorbed even after absorbing the aqueous liquid. An object of the present invention is to provide an absorbent body with little change in position.

As a result of diligent studies to achieve the above-mentioned problems, hydroperoxide was used in the presence of a compound having two or more functional groups capable of reacting with a carboxyl group using unsaturated ammonium carboxylate as a polymerization monomer. It was found that the above problems can be solved by polymerizing at least two or more reducing agents as a radical polymerization initiator, followed by heat treatment after drying to produce a water-absorbent resin, and completed the present invention.

  By the above production method, it is possible to produce a water-absorbent resin having a high water absorption ratio in a non-pressurized state and excellent in water absorption characteristics under a high load and having little residual monomer. Preferably, a water absorbent resin satisfying the heating condition of Y ≦ −1.6X + 345 (Y is the heating time (minutes), X is the heating temperature (° C.)) is preferable.

  In addition, deformation of a gel in which the carboxylate ammonium salt is 50% or more, the residual monomer is 50 ppm or less, the soluble content is 1 to 30%, and the gel is swollen to 10 times its own weight with physiological saline. The water-absorbent resin having a repulsive pressure of 0.1 to 5.5 N and satisfying that the transverse relaxation time in 1H-NMR is 5 to 22 milliseconds is an absorber having less contact between resins due to its unique structure. Under the conditions of use, it was discovered that the water absorption characteristics under high loads were improved without changing the water absorption capacity under no load conditions, and the balance between the water absorption capacity under no pressure conditions and the water absorption characteristics under high loads could be further improved. I found it. Furthermore, by using this resin, it is possible to create an absorbent body in which the position of the hydrophilic fibers and the resin inside the absorbent body is small even after absorbing the aqueous liquid.

That is, the present invention has a configuration as described below.
(1) A method for producing a water-absorbent resin characterized by satisfying the following a) to c) in a method for producing a water-absorbent resin including a polymerization step, a drying step, and a heating step.
a) 60-100 mol% (meth) ammonium acrylate is used as a raw material monomer for polymerization.
b) The raw material monomer for polymerization contains a compound having two or more functional groups capable of reacting with a carboxyl group.
c) Hydroperoxide and two or more reducing agents are used as radical initiators.
(2) (meth) ammonium acrylate (meth) acrylonitrile and / or (meth) acrylic amide produced by the hydrolytic by microorganisms (meth) impurities that can be the ammonium acrylate and / or decomposed to acrylic acid, the amount is 500ppm or less (meth) acrylic acid neutralized by ammonia (meth) ammonium acrylate, the (1) according to one of the reducing agent being a reducing metal component A method for producing a water-absorbent resin.
( 3 ) The method for producing a water-absorbent resin according to any one of (1) to (2) , wherein the heating condition satisfies the following mathematical formula in the heating step.
Y ≦ −1.6X + 345
Y is heating time (minutes)
X is the heating temperature (° C)
( 4 ) The method for producing a water-absorbent resin according to any one of (1) to (3), wherein the hydroperoxide is hydrogen peroxide.
( 5 ) The method for producing a water absorbent resin according to any one of the above (1) to (4) , wherein one kind of the reducing agent is a formaldehyde derivative of sulfoxylate.
( 6 ) The above-mentioned (1) to (5), wherein a compound having two or more unsaturated groups in one molecule serving as a crosslinking agent at the time of polymerization is contained in an amount of 0.1 mol% or less based on the total monomer components. ) . The method for producing a water-absorbent resin according to any one of the above.

  According to the present invention, it is possible to obtain a water-absorbent resin having a high water absorption capacity in a non-pressurized state, excellent water absorption characteristics under a high load, and little residual monomer. Such a water-absorbing resin is suitable for sanitary material applications such as disposable diapers. By using a resin that has a high water absorption capacity in a non-pressurized state and excellent water absorption characteristics under a high load, the amount of water-absorbing resin used in the absorbent composition can be reduced. In such a state where there is little contact between the water-absorbing resins, the water-absorbing resin that is particularly excellent in water absorption capacity under no pressure, water-absorbing characteristics under high load, and further the hydrophilic inside the absorber even after absorbing the aqueous liquid It is possible to provide an absorbent body in which the positional change between the conductive fiber and the resin is small. If there are few changes in the position of the hydrophilic fibers and the resin inside the absorber, it is stable inside the absorber even after urine has been absorbed once, and can accommodate multiple urines.

  The present invention will be described in detail below. In the present invention, a compound containing two or more functional groups capable of reacting with an unsaturated ammonium carboxylate and a carboxylic acid is used as a raw material, and hydroperoxide is used as a radical initiator in the presence of two or more reducing components. It is essential to polymerize. Unsaturated ammonium carboxylates are produced by microbial hydrolysis of unsaturated nitriles and / or unsaturated amides, and / or unsaturated carboxylic acids obtained by neutralizing unsaturated carboxylic acids that have been purified to remove impurities with ammonia. Reductant and hydroperoxide different from the reducing component contained in this raw material in the presence of a compound containing two or more functional groups capable of reacting with carboxylic acid, using ammonium acid added with a trace reducing component Is preferably used as a radical initiator.

(Description of unsaturated ammonium carboxylate species)
The unsaturated ammonium carboxylate of the present invention refers to a compound having both an unsaturated bond and an ammonium carboxylate group. This may contain many unsaturated bonds and ammonium carboxylate groups. The unsaturated bond means a bond containing a double bond (ethylene bond) or a triple bond (acetylene bond) in a bond between carbon atoms. Typical examples of such unsaturated carboxylic acids that form ammonium salts include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and cinnamic acid. Of these ammonium salts of unsaturated carboxylic acids, ammonium acrylate and ammonium methacrylate are preferred from the viewpoints of polymerizability and polymer absorbability.

This unsaturated ammonium carboxylate may partially contain an unsaturated carboxylic acid amide. An unsaturated amide refers to a compound containing both an unsaturated bond and a functional group represented by the general formula R—CONH ₂ (R is an alkyl group, an aryl group, etc.) in the molecule. Examples of such compounds include Cinnamamide, acrylamide, and methacrylamide, and acrylamide and methacrylamide are preferable, and acrylamide is particularly preferable.

(Description of production method of unsaturated ammonium carboxylate)
The unsaturated ammonium carboxylate of the present invention may be produced by any production method. For example, a. A method of subjecting an unsaturated nitrile and / or an unsaturated amide to a hydrolysis reaction by a microorganism; b. A method of neutralizing unsaturated carboxylic acid with ammonia is raised.

a. Hydrolysis by microorganisms Unsaturated nitriles subjected to hydrolysis reactions by microorganisms refer to compounds containing both unsaturated bonds and cyan groups in the molecule. It may contain many unsaturated bonds and cyan groups. The unsaturated bond means a bond containing a double bond (ethylene bond) or a triple bond (acetylene bond) in a bond between carbon atoms. Examples of such compounds include acrylonitrile, methacrylonitrile, crotonnitrile, cinnamate nitrile and the like. Of these, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is particularly preferable.

The unsaturated amide used for the hydrolysis reaction by microorganisms is a compound containing both an unsaturated bond and a functional group represented by the general formula R-CONH ₂ (where R is an alkyl group, aryl group, etc.) in the molecule. I mean. Examples of such compounds include Cinnamamide, acrylamide, and methacrylamide, and acrylamide and methacrylamide are preferable, and acrylamide is particularly preferable.

  There are no particular limitations on the hydrolysis conditions of unsaturated nitrile and / or unsaturated amide by microorganisms, but microorganisms capable of producing an aqueous solution of unsaturated ammonium carboxylate having a concentration of 20% by weight or more are preferable. As such a microorganism, it is preferable to use at least one selected from the group consisting of Acinetobacter, Alkagenes, Corynebacterium, Rhodococcus, and Gordona. Among the above-mentioned microorganisms, microorganisms belonging to the genus Acinetobacter are preferable, and among them, the microorganism is Acinetobacter sp. AK226 strain (Mikken Kenki No. 8271) or Acinetobacter sp. Most preferred. In addition, the microbiological properties of Acinetobacter sp. AK226 strain (Microtechnological Bacteria No. 8271) and Acinetobacter sp. AK227 strain (Microtechnological Bacteria No. 8272) are as shown in JP-B 63-2596. It is.

Since the unsaturated ammonium carboxylate aqueous solution produced by the hydrolysis method using this microorganism has a very small amount of impurities such as dimers and / or hydrates of unsaturated carboxylic acid, the production method is a preferable method. .
Specific examples of the impurities include, in the case of acrylic acid, β-acryloyloxypropionic acid which is a dimer of acrylic acid, β-hydroxypropionic acid which is a hydrate of acrylic acid, and salts thereof. Can be mentioned.

b. Method for neutralizing unsaturated carboxylic acid with ammonia As the unsaturated carboxylic acid used in the method for neutralizing unsaturated carboxylic acid with ammonia, the same unsaturated carboxylic acid as described above is used.

  This unsaturated carboxylic acid may be produced by any method. When such an unsaturated carboxylic acid contains a large amount of impurities, it is preferable to produce them to reduce the impurities. The impurity here refers to a compound that can be decomposed to become a monomer component. For example, in the case of acrylic acid, such as hydrated unsaturated bonds and oligomers, β-hydroxypropionic acid and β-acryloyloxypropionic acid can be used. The purification method may be any method as long as the amount of impurities can be reduced to a predetermined amount or less, and the means is not particularly limited. As a method, for example, it may be performed by distillation as in Patent Document 23. The amount of impurities is preferably reduced to 500 ppm or less, more preferably 300 ppm or less, still more preferably 100 ppm or less, and most preferably 50 ppm or less. If the amount of impurities is large, the resulting water-absorbent resin has a large amount of residual monomer, and the residual monomer increases in the subsequent manufacturing process. Further, various physical properties of the polymer may be insufficient, which is not preferable.

  The neutralization method is not particularly limited. Ammonia water may be used, or ammonia gas may be used. You may neutralize on the conditions which the neutralization rate of acrylic acid passes through the state which exceeds 100 mol% at least one time in the neutralization process like patent documents 24-25. In the neutralization step, the temperature is preferably maintained at 0 to 50 ° C. by cooling. An excessively high temperature is not preferable because β-hydroxypropionic acid and oligomers are produced.

(Compounds with multiple functional groups that can react with carboxyl groups)
The compound containing two or more functional groups capable of reacting with a carboxyl group is ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, (poly) glycerin polyglycidyl ether, diglycerin polyglycidyl ether, propylene glycol diglycidyl ether. Glycidyl ether compounds such as (poly) glycerin, (poly) ethylene glycol, (poly) propylene glycol, 1,3-propanediol, polyoxyethylene glycol, triethylene glycol, tetraethylene glycol, 1,6-hexanediol, Trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol, Various polyhydric alcohols represented by bitol, etc .; polyhydric amines such as ethylenediamine, diethylenediamine, polyethyleneimine, hexamethylenediamine; 2,2-bishydroxymethylbutanol-tris (3- (1-aziridinyl) propionate) And the like, 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,6-dimethyl-1,3-dioxolan-2-one, etc. Alkylene carbonate compounds typified by glyoxal, polyvalent aldehyde compounds typified by glyoxal, polyvalent oxazoline compounds typified by 2,4-tolylene diisocyanate, haloepoxy compounds typified by epichlorohydrin; zinc, calcium, magnesium Representative for aluminum, etc. Such as multivalent ions, and the like to be. Among such carboxylic acid reactive cross-linking agents, it is preferable to use one or more selected from the group consisting of polyhydric alcohols, polyhydric glycidyl compounds, polyhydric amines, and alkylene carbonates. In addition, the usage-amount of a carboxylic acid reactive crosslinking agent is 0.01-10 weight part with respect to 100 weight part of solid content of the polymer particle after drying, Preferably it is 0.05-5 weight part. More preferably, it is 0.1 to 3 parts by weight.

(About resin composition)
The water-absorbent resin obtained by the production method of the present invention preferably comprises a (meth) acrylic acid ammonium unit, a (meth) acrylic acid alkali metal salt unit, and a (meth) acrylic acid unit as main components.

  In the present invention, only ammonium (meth) acrylate may be used as a monofunctional unsaturated monomer in the polymerization, or a part thereof may be converted to an alkali metal (meth) acrylate. Moreover, you may add monofunctional unsaturated monomers other than ammonium (meth) acrylate as needed. Preferred monofunctional unsaturated monomer composition in the polymerization is 40 to 100 mol% of ammonium (meth) acrylate, 0 to 90 mol% of alkali metal (meth) acrylate, and other monofunctionalities. The unsaturated monomer is 0 to 50 mol%. More preferably, ammonium (meth) acrylate is 50 to 100 mol%, alkali metal (meth) acrylate is 0 to 80 mol%, and other monofunctional unsaturated monomers are 0 to 40 mol%. Most preferably, ammonium (meth) acrylate is 60 to 100 mol%, alkali metal (meth) acrylate is 0 to 70 mol%, and other monofunctional unsaturated monomers are 0 to 30 mol%.

  Examples of other monofunctional unsaturated monomers include (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, crotonic acid, vinyl sulfonic acid, styrene sulfonic acid, and 2- (meth) sulfonic acid. ) Hydrophilic monofunctional unsaturated monomers containing acid groups represented by acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and the like Contains amide groups such as salt, acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide Hydrophilic monofunctional unsaturated monomers, 2-hydroxyethyl (meth) acrylate, 2-hydroxy Esterified hydrophilic unsaturated monomers represented by roxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloyl Piperidine, N-acryloylpyrrolidine, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminoethyl ( Hydrophobic properties such as N-containing hydrophilic monofunctional unsaturated monomers such as meth) acrylamide and quaternary salts thereof, styrene, vinyl chloride, butadiene, isobutene, ethylene, propylene, alkyl (meth) acrylate, etc. Monofunctional It can be mentioned unsaturated monomers. Among these, (meth) acrylic acid (salt), 2- (meth) acryloylethanesulfonic acid (salt), 2- (meth) acrylamido-2-methylpropanesulfonic acid (salt), methoxypolyethylene glycol (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate and (meth) acrylamide are preferred.

(Internal crosslinking agent)
In the present invention, it is desirable to introduce a cross-linked structure into the interior using an internal cross-linking agent in addition to the monofunctional unsaturated monomer during the polymerization. The internal crosslinking agent may be a compound having a plurality of polymerizable unsaturated groups and / or reactive groups in one molecule. It is preferable to use a highly hydrophilic compound as the internal cross-linking agent because the water absorption performance of the resin is improved. In the case where the monofunctional unsaturated monomer is a self-crosslinking type compound, an internal cross-linked structure can be formed without using an internal cross-linking agent.

  Examples of the internal cross-linking agent include N, N-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tri Methylolpropane di (meth) acrylate, glycerin (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate , Triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, etc. A compound having a plurality of epoxy groups in one molecule, represented by (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, etc., represented by ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, etc. And a compound having a plurality of hydroxyl groups in one molecule, a compound having a plurality of amino groups in one molecule typified by ethylenediamine, polyethyleneimine, and the like, and glycidyl (meth) acrylate. These internal cross-linking agents may be used alone or in combination of two or more.

The amount of the internal crosslinking agent used is preferably 0.005 to 3 mol%, more preferably 0.01 to 1.5 mol%, most preferably 0, based on the total amount of monofunctional unsaturated monomers. 0.01 to 0.09 mol%. When the amount of the internal cross-linking agent is small, the soluble content of the polymer is remarkably increased. When the amount of the internal cross-linking agent is large, the gel becomes hard and the water absorption performance is remarkably lowered.
Moreover, you may superpose | polymerize by adding a foaming agent, a chain transfer agent, surfactant, a chelating agent, etc. other than the said monofunctional unsaturated monomer and an internal crosslinking agent as needed.

(Description of radical initiator and reducing agent)
In the polymerization of the present invention, it is necessary to use two or more reducing agents and hydroperoxide as a radical polymerization initiator. The reducing agent may be originally contained in the monomer raw material for polymerization or may be added at the time of polymerization. A reducing agent refers to a substance that can cause reduction. Examples of such reducing components include hydrogen and relatively unstable hydrogen compounds such as hydrogen sulfide, lower oxides such as carbon monoxide, sulfite, and bisulfite, or salts of lower oxides, sodium sulfide, and the like. Sulfur compounds, alkali metals, magnesium, calcium, aluminum, electropositive metals such as zinc, or their amalgams, low atoms such as iron (II), tin (II), titanium (III), chromium (II) There are organic salts with low oxidation stages such as metal salts in the valence state, aldehydes, saccharides, formic acid and the like. Other examples include sodium thiosulfate, hydrazine hydrate, ascorbic acid, erythorbic acid, and formaldehyde derivatives of sulfoxylate. These reducing agents include a reducing agent that changes irreversibly when self is oxidized, such as an organic compound, and a reducing agent that has a reducing action by changing the valence of a metal or the like and can be regenerated. It is preferable that at least one of the reducing agents is a renewable reducing agent, and at least one of them is an irreversibly changing reducing agent. The renewable reducing agent is preferably a metal salt in a low valence state, particularly iron (II) or manganese (II). These low-valent metals may be added in any form, but for example, iron (II) such as iron (II) sulfate, iron (II) chloride, sodium ferrocyanide, etc. As a salt, manganese (II) can be added as a salt of manganese (II) chloride, manganese (II) sulfate, potassium permanganate, manganese carbonate (II), or the like, or a hydrate of those salts. . These salts may be added directly to the monomer, and are derived from the biocatalyst from the culture medium or preservation solution of the biocatalyst when the unsaturated nitrile and / or unsaturated amide is hydrolyzed by the biocatalyst. May be brought in, but is preferably derived from a biocatalyst. The amount of these reducing agents is preferably 1 g or less, more preferably 0.1 g or less, and most preferably 0.01 g or less with respect to 1 mol of the monomer component. The concentration of the metal acting as a reducing agent such as iron (II) or manganese (II) in the aqueous monomer solution can be examined by ion chromatography. The reducing agent that changes irreversibly is preferably a reducing agent having a reducing power stronger than that of a renewable reducing agent. Of these, compounds selected from alkali metal sulfites, alkali metal bisulfites, ammonium sulfites, ammonium bisulfites, ascorbic acid, erythruvic acid, and formaldehyde derivatives of sulfoxylate are preferred, and formaldehyde derivatives of sulfoxylate are most preferred. preferable. Of the formaldehyde derivatives of sulfoxylate, sodium, formaldehyde, sulfoxylate is particularly preferable. The amount of these reducing agents is 0.000001 g to 10 g, preferably 0.00001 g to 5 g, more preferably 0.0001 to 1 g with respect to 1 mol of the monomer component. The total amount of the reducing agent is preferably 0.000001 to 11 g, more preferably 0.00001 to 5 g, and more preferably 0.0001 to 1 g with respect to 1 mol of the monomer component. Such a combination of reducing agents causes a distribution in radical generation. In particular, a reducible reducing agent is considered to have an effect of reducing residual monomers because radicals can be effectively generated in the latter stage of polymerization by changing the valence.

  Hydroperoxide refers to a compound represented by the general formula ROOH (R is hydrogen, an alkyl group, other organic and / or inorganic atomic groups). Examples of such compounds include hydrogen peroxide, methyl hydroperoxide, allyl hydroperoxide, benzyl hydroperoxide, cumene hydroperoxide, tert-butyl hydroperoxide, and the like. Of these, hydrogen peroxide is preferable. Such hydroperoxides may be used alone or in combination of two or more. By using hydroperoxide as an initiator, the initiator end of the main chain becomes an OH group and can react with a carboxyl group in another main chain, so that it has an apparently high molecular weight, so the water absorption capacity is increased. It is done. Moreover, you may use together radical polymerization initiators other than a hydroperoxide. Examples of such radical polymerization initiators include known initiators such as persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, and 2,2′-azobis (2-amidinopropane) dihydrochloride. It is done. The amount of radical polymerization initiator other than hydroperoxide is preferably less than the amount of hydroperoxide, more preferably 50% by weight or less, more preferably the weight of hydroperoxide. It is 10% by weight or less, and most preferably 1% by weight or less based on the weight of the hydroperoxide. If the amount of initiator other than hydroperoxide is too large, the number of polymer terminals other than OH groups will increase, making it impossible to obtain a water absorbent resin having a high water absorption ratio. The amount of hydroperoxide to be used is preferably 0.001 to 2 mol%, more preferably 0.01 to 0.5 mol%, based on the total amount of short-functional unsaturated monomers. If the amount of the initiator is too small, too few radicals are generated and a large amount of unreacted monomer remains. Even if the amount of the initiator is too large, it hardly affects the amount of residual monomer and water absorption performance, but it is not preferable because impurities after polymerization increase.

  When hydroperoxide and two or more kinds of reducing components are used as a polymerization initiator, each reducing agent has a different reducing power. Therefore, the radical generation is distributed and reacts with the remaining monomer even in the latter half of the polymerization. It is considered that the residual monomer is reduced. In addition, the terminal of the low molecular weight component generated by the reaction also becomes an OH group, and can react with the carboxyl group in the main chain in the subsequent heating step, and the apparent high molecular weight as a whole increases the absorption capacity. It is done.

(Polymerization conditions)
Although there is no restriction | limiting in particular in the polymerization method of a monofunctional unsaturated monomer, Aqueous solution polymerization and reverse phase suspension polymerization are used preferably. Reaction conditions such as reaction temperature and reaction time may be appropriately selected according to the type and concentration of the monofunctional unsaturated monomer, and are not particularly limited.

  It is preferable to perform a deoxygenation operation in the monomer solution in advance before the start of polymerization. As a specific method, there is a method of removing dissolved oxygen by bubbling with an inert gas for a sufficient time. In addition, it is preferable that the atmosphere in the reactor is replaced with an inert gas such as nitrogen or helium. The inside of the reactor may be any of reduced pressure, normal pressure, and increased pressure. The polymerization initiation temperature is usually preferably in the range of 0 to 70 ° C. More preferably, it is the range of 10-40 degreeC. If the starting temperature is too high, polymerization by heat occurs before the initiator is added, which is not preferable. On the other hand, if the starting temperature is too low, it takes too much time to start the reaction, which is not preferable. The temperature in the reactor during the reaction may depend on the outcome, and the temperature may be controlled by cooling or heating from the outside. The temperature rising rate and the maximum temperature during the polymerization are not particularly problematic, and there is no problem even if the maximum temperature exceeds 100 ° C. The maximum temperature during polymerization is usually 20 to 140 ° C, preferably 40 ° C to 120 ° C. The concentration of the monomer solution is preferably 10 to 70%, and most preferably 30 to 50%. If the concentration is too high, the reaction tends to run away, which is not preferable. If the concentration is too low, it takes too much time for the reaction, and the subsequent drying process is also burdened, which is not preferable. The polymerization time is preferably set in the vicinity of the time when heat generation from the reaction solution stops. Since there are heating processes such as a drying process and a post-crosslinking process as post-processes after the polymerization, the polymerization may be terminated before the heat generation from the reaction solution stops. Moreover, you may heat for several hours after completion | finish of heat_generation | fever.

(Drying process)
When the polymer obtained after the polymerization is a hydrogel, drying is performed. Although this drying method is not particularly limited, for example, azeotropic dehydration, fluidized drying, hot air drying, vacuum drying and the like are preferably used, and hot air drying and vacuum drying are particularly preferable. The moisture content is 30% by weight or less, preferably 10% by weight or less. Drying may be performed with any form of hydrogel, but it is preferable to dry after coarsely crushing to increase the surface area. The drying temperature is preferably in the range of 70 ° C to 180 ° C, particularly preferably 100 to 140 ° C.

  The particle size of the polymer after drying is adjusted by operations such as pulverization and classification as required. The shape may be various shapes such as spherical, scaly, irregularly crushed, and granular, but the weight average particle size is 10 to 3000 μm, preferably 40 to 2000 μm, more preferably 50 to 1500 μm, Still more preferably, it is 100-850 micrometers, and the most preferable 300-700 micrometers. If the particle size is too small, it becomes fine powder, and it becomes easy to scatter. Further, the amount of ammonia that volatilizes during heating increases, resulting in a decrease in water absorption performance, which is not preferable. When the particle size is too large, there are problems such as a decrease in water absorption rate and unevenness of the water absorbent resin in the absorbent article.

  In the present invention, it is necessary to heat the polymer after drying controlled to a predetermined particle size. The temperature of this heat treatment is in the range of 163 to 250 ° C., although it depends on the type of compound having two or more functional groups capable of reacting with the carboxyl group used. Preferably it is 163-240 degreeC, More preferably, it is 163-230 degreeC. If the heat treatment temperature is too low, sufficient post-crosslinking reaction will not occur and the performance as a water absorbent resin will be insufficient. If the heat treatment temperature is too high, the polymer will be thermally deteriorated and the performance as a water absorbent resin will be insufficient.

The heat treatment time preferably satisfies the following mathematical formula.
Y ≦ −1.6X + 345
Where X is the heating temperature (° C) and Y is the heat treatment time (minutes)
More preferably, the following mathematical formula is satisfied.
Y ≦ −1.6X + 335

  Through the heat treatment step, ammonia is released from some ammonium carboxylate units in the polymer, and a water-absorbing resin containing carboxylic acid units is obtained. Examples of the water-absorbing resin thus obtained include 9 to 100 mol% of an ammonium carboxylate unit, 0 to 90 mol% of a carboxylic acid metal salt unit, 1 to 50 mol% of a carboxylic acid unit, and other simple units. It is preferable that a functional unsaturated monomer unit is 0-50 mol%. More preferably, the ammonium carboxylate unit is 15 to 90 mol%, the carboxylic acid metal salt unit is 0 to 80 mol%, the carboxylic acid unit is 5 to 45 mol%, and other monofunctional unsaturated monomer units. Is 0 to 40 mol%, more preferably 20 to 80 mol% of ammonium carboxylate units, 0 to 70 mol% of carboxylic acid metal salt units, 10 to 40 mol% of carboxylic acid units, and other than these The monofunctional unsaturated monomer unit is 0 to 30 mol%.

  For the above heat treatment, a normal dryer or a heating furnace can be used. For example, a groove type mixer / dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, an infrared dryer, etc. Can be mentioned.

(Other additives)
In the water-absorbing resin thus obtained, if necessary, deodorants, fragrances, various inorganic powders, foaming agents, pigments, dyes, antibacterial agents, hydrophilic short fibers, plasticizers, adhesives, surfactants, Fertilizers, oxidizing agents, reducing agents, chelating agents, antioxidants, heat stabilizers, UV absorbers, light stabilizers, water, salts, etc. may be added.

Examples of the inorganic powder include fine particles of various inorganic compounds that are inert to water and hydrophilic organic solvents, fine particles of clay mineral, and the like. In particular, the inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water, such as metal oxides such as silicon dioxide and titanium oxide, natural zeolite, synthetic zeolite, etc. Silicic acid (salt), kaolin, talc, clay, bentonite and the like.
The usage-amount of the said inorganic powder is 0.001-10 weight part normally with respect to 100 weight part of water absorbing resin, Preferably it is 0.01-5 weight part. There is no restriction | limiting in particular in the mixing method of water absorbing resin and inorganic powder, It carries out by the dry blend method, the wet mixing method, etc.

(Classification)
In the present invention, the particle diameter of the water absorbent resin is finally adjusted by operations such as pulverization and classification as required. The shape may be various shapes such as spherical, scaly, irregularly crushed, and granular, but the weight average particle size is 10 to 3000 μm, preferably 40 to 2000 μm, and more preferably 50 to 1500 μm. Still more preferably, it is 100-850 micrometers, Most preferably, it is 300-700 micrometers.

(Usage of water-absorbing resin)
The absorbent article which sandwiched between the top sheet and the back sheet the absorbent layer containing the water-absorbent resin obtained on the basis of the production method of the present invention and the absorbent mainly composed of hydrophilic fibers can be obtained. Specific examples of such absorbent articles include various sanitary materials such as paper diapers, sanitary napkins, and incontinence pads.

(Absorbent resin)
Furthermore, the present invention provides a resin having high absorption performance when used as a constituent component of the absorber and having high internal structure retention even after absorption of an aqueous liquid.
That is, in the water-absorbent resin having a crosslinked structure obtained by polymerizing an unsaturated carboxylic acid monomer, the carboxylate ammonium salt is 50% or more, and the residual monomer is 50 ppm or less, preferably 20 ppm or less, more preferably 10 ppm or less, most preferably 5 ppm or less, the soluble content is 1 to 30%, and the deformation repulsion pressure of the gel swollen 10 times its own weight with physiological saline is 0.1 to 5.5 N And a water-absorbing resin characterized by having a transverse relaxation time in 1H-NMR of 5 to 22 milliseconds and exhibiting high absorption performance in the state of use of the absorber. The inventors have found that high structure retention is exhibited, and completed the present invention. By using the resin of the present invention, under the conditions of use of the absorbent body with less resin contact, it exhibits high absorption performance (balance), and even after absorbing an aqueous liquid, the position of the hydrophilic fiber and the resin inside the absorbent body is changed. Less absorber can be created. Such a water-absorbent resin can be obtained by performing polymerization that satisfies the following conditions. Among unsaturated carboxylic acid monomers, 70% or more is acrylic acid, 50% or more of acid groups are neutralized as ammonium salts, and a total of 65% or more is neutralized. use. 0.1 to 3 parts by weight of a compound having two or more functional groups capable of reacting with a carboxyl group in a monomer, and a compound having two or more unsaturated groups in one molecule On the other hand, a monomer containing 0.01 to 0.1 mol% is used. The amount of the compound that can be decomposed into a monomer in the monomer is 50 ppm or less. When performing radical polymerization using a redox initiator, 50% or more of the compound that generates radicals is used as a radical polymerization initiator, and the amount is 0.01 to the amount of the unsaturated monomer. Use ~ 0.5 mol%. At least two types of reducing agents are used, at least one of which is a reducing metal, the amount is 0.01 g or less per mole of monomer, and at least one type of reducing organic compound is used as a monomer The amount is 0.0001 to 1 g with respect to 1 mol. The total amount of the reducing agent is 0.0001 to 1 g with respect to 1 mol of the monomer. The obtained resin is heat-treated under the following temperature conditions.
Y ≦ −1.6X + 335
Y is the heat treatment time (minutes), X is the heating temperature (° C.), and the heating temperature is 163 ° C. or higher.

(1) Residual monomer: Transfer 1.00 g of water-absorbing resin to a beaker, add 200 ml of 0.9% physiological saline, add a stir bar and stir at 500 rpm for 120 minutes. The mixture is allowed to stand for 5 minutes after the stirring is stopped, and the residual monomer in the upper layer solution is measured by HPLC.

(2) Water absorption ratio: 0.20 g of water-absorbing resin is uniformly placed in a non-woven tea bag bag (60 × 40 mm) and immersed in 0.9% physiological saline at 23 ° C. The bag is taken out after 30 minutes, suspended for 10 minutes, drained, and then weighed. The same operation is performed without using the water absorbent resin, the weight is measured, and the water absorption magnification is calculated according to the following formula.

(3) Water absorption capacity under pressure: 0.16 g of water-absorbing resin is placed in an acrylic resin cylinder with an inner diameter of 25 mm, a height of 30 mm and a 250 mesh nylon nonwoven fabric at the bottom, and a smoothly moving cylinder is placed in the cylinder. Use a measuring device to measure the weight. A load of 278.33 g is placed on the upper part of the cylinder of the measuring device to obtain a load, which is then placed in a petri dish with an inner diameter of 120 mm containing 60 g of 0.9% physiological saline. After 60 minutes, it is taken out and left on a Kim towel for 3 seconds to drain water, the weight of the device after removing the load is measured, and the water absorption capacity under pressure is calculated according to the following formula.

(4) Balance of water absorption performance: The balance of water absorption capacity in the non-pressurized state and the balance of water absorption characteristics under load is as follows when the water absorption capacity in (2) is A and the water absorption capacity in (3) is B: It shall be expressed as The higher this value, the better the balance. The water absorption balance is preferably 55 or more, and more preferably 60 or more.
Balance of water absorption performance = 0.65 × A + B

(5) Quantification of ammonium acrylate units The total amount of nitrogen atoms in the water-absorbent resin was determined by the Kjeldahl method, and the amount of ammonium acrylate structural units (mol%) was determined. When the carboxylic acid ammonium salt is 50% or more, a gradient structure of carboxyl groups during drying can be expected. When there is too much soluble content, the water absorption magnification is reduced by the amount that is dissolved in water.

(6) Measurement of transverse relaxation time T2 The transverse relaxation time was measured by the following procedure with reference to Patent Document 26.
Preparation of sample: The dried water-absorbent resin is classified to 355 μm to 500 μm. 5 mg of this resin was placed in a 5 mmφ NMR tube, and heavy water was added to make the total amount 500 mg. In order to swell the resin uniformly, the mixture was lightly stirred with a thin stick and allowed to stand at room temperature for 24 hours under light shielding to cause equilibrium swelling.
Device: α-400 made by JEOL
Measurement: The CPMG (Carr-Purcell Meiboom-Gillsequence) method was used. A spin echo signal is obtained by repeating the -τ-180 degree pulse-τ-unit in the pulse sequence n times. At this time, τ is set to 250 μs or less, and the 90-degree pulse is set to 30 μs or less. The main chain in the resin consists of CH2 and CH skeletons, and the relaxation times of the 1H nuclei are different, but for the sake of convenience, the combined signal intensity of both is used.
1H-NMR lateral relaxation time is a parameter related to the mobility of molecular chains. The shorter the lateral relaxation time (relaxes faster), the more the polymer chains constituting the resin particles are entangled or cross-linked. It means big. If this entanglement or cross-linking is too small, it will dissolve in water, but if it is too large, it will be difficult to absorb water and spread the molecular chain, resulting in a small amount of water absorption. In the present invention, the 1H-NMR transverse relaxation time is preferably 5 to 22 (milliseconds), more preferably 8 to 20 (milliseconds) or more, and most preferably 10 to 16 (milliseconds). .

(7) Measurement of deformation repulsion pressure of gel With reference to Patent Document 26, the deformation repulsion pressure of the gel was measured as follows.
Equipment: Shimadzu Autograph AG-1
Sample: The dried water-absorbent resin was classified so as to have a particle diameter of 355 μm to 500 μm. Of these, 0.10 g was precisely weighed and uniformly placed in the bottom of a cylindrical container having an inner diameter of 20.5 mm and a height of 50 mm, with a nylon sheet having a pore diameter of 75 μm attached to the bottom surface. A 50φ petri dish was prepared, 0.90 g of physiological saline was added, and the cylindrical container containing the water-absorbent resin was left to stand for absorption and swelling for 1 hour.
Measurement: A 1 kN load cell was used, and a cylindrical shaft having a diameter of 19.7 mm was attached. The measurement range is set to 0.2 kN, and is set so that the load cell is lowered at a constant speed of 0.6 mm / min according to the height at which no load is applied to the load cell. The pressure applied to the load cell was recorded over time. Here, the deformation repulsion pressure represents the load (N) at the time when the actual volume is reached. The actual volume of the gel was calculated using the specific gravity of physiological saline 1.010 g / cm ³ and the specific gravity of the water absorbent resin. The specific gravity of the water-absorbent resin this time was 1.515 g / cm ³ .
The deformation repulsion pressure is a parameter related to the surface strength of the gel. When a gel that has swollen after absorbing water at a specific magnification is placed in a container and a load is applied, the gel moves and deforms so as to fill the gap between the filled gel with a gap in the container. The deformation repulsion pressure represents the elastic modulus when the gel reaches an actual volume, and means the magnitude of interaction between gel particles and the ease of surface deformation. A large deformation repulsion pressure indicates that the gel particles are difficult to deform. The fact that it is difficult to deform means that the particles absorb water and swell, whereas the negative force is strong, and thus the absorption capacity is lowered. In the present invention, the deformation repulsion pressure is preferably 0.1 to 5.5 N, more preferably 0.1 to 5 N or less, and most preferably 0.2 to 4 N / mm ³ or less.

(8) Measurement of soluble content The soluble content was measured by a colloid titration method. 0.5 g of water-absorbing resin was dispersed in 1000 g of distilled water, stirred for 1 hour, and then filtered through filter paper. Next, 50 g of the obtained filtrate was placed in a 100 ml beaker, and 1 ml of 0.1N sodium hydroxide aqueous solution, 10 ml of N / 200-methylglycol chitosan aqueous solution, and 4 drops of 0.1% toluidine blue aqueous solution were added to the filtrate. Next, the solution of the beaker was colloidally titrated with an aqueous N / 400 potassium potassium sulfate solution, and the titration (ml) was determined with the time when the color of the solution changed from blue to reddish purple as the end point of titration. Moreover, the same operation was performed using 50 g of distilled water instead of 50 g of the filtrate, and a titration amount (ml) was obtained as a blank. Then, the water-soluble amount (% by weight) was calculated according to Equation 3 from these titration amounts and the average molecular weight of the monomers constituting the water-absorbent resin.

(9) Absorption capacity under practical pressure Measurement was performed in the same manner as the measurement of absorption capacity under pressure except that the sample amount was 0.02 g. The absorption capacity under pressure represents the water absorption performance under load in a state close to the state in an absorbent article such as a paper diaper in which water-absorbing resins are not directly adhered to each other.

(10) Other physical properties The water-absorbent resin of the present invention can have various other characteristics according to the specifications of the sanitary material by controlling the degree of crosslinking. In the present invention, the degree of crosslinking can be freely and simply controlled by changing the amount and type of crosslinking agent and heating conditions. By increasing the degree of cross-linking, it is possible to increase the absorbency under load, and to exhibit desirable characteristics for hygiene material applications that are classified into the physical properties a group. In the present invention, it is also possible to balance with the characteristics classified into the absorption force and physical properties b group under no pressure, which usually must be sacrificed when trying to exhibit these characteristics. Furthermore, in the present invention, it is possible to provide additional properties as shown in the physical property group c and the physical property group d. The physical properties a group, physical property b group, physical property c group, physical property d group can be said to be preferable if any one of the physical properties classified as follows is satisfied. It is more preferable to satisfy all the measurement items of any one physical property group among the physical property a group, the physical property b group, the physical property c group, and the physical property d group, and it is most preferable to balance all the physical properties at a high level.

Physical Properties Group A Physical properties such as those listed in Physical Group a can generally be improved by increasing the degree of crosslinking. In the water absorbent resin of the present invention, the amount of crosslinking inside the resin and the amount of crosslinking on the surface portion can be freely controlled. Therefore, these physical property groups can be improved while maintaining the non-pressurized absorption capacity at a high level. These physical properties can be further improved by increasing the degree of crosslinking. Moreover, these physical properties are closely related to the blocking of the water-absorbent resin. In addition to improving the degree of crosslinking, blocking prevention can also be achieved by making the surface hydrophobic or adding additives. In the water-absorbent resin of the present invention, the carboxylate concentration of the resin surface portion is reduced by heating, and the same effect as the surface hydrophobization can be expressed without surface treatment. These physical properties can be improved without sacrificing absorbency.

1. Diffusion absorption factor: Measurement can be performed according to (Patent Document 28). The diffusion absorption ratio preferably satisfies 15 (g / g) or more after 20 minutes, 20 (g / g) or more after 30 minutes, and 30 (g / g) or more after 60 minutes. More preferably, it is 17 (g / g) or more after 20 minutes, 28 (g / g) or more after 30 minutes, 33 (g / g) or more after 60 minutes, and most preferably 20 (g / g) after 20 minutes. As described above, 30 (g / g) or more after 30 minutes and 35 (g / g) or more after 60 minutes.

2. Performance under pressure: Measurement can be performed according to (Patent Document 29). The pressure performance is preferably 25 (g / g) or more, more preferably 29 (g / g) or more, more preferably 33 (g / g) or more, and most preferably 35 (g / g) or more. is there.

3. Permeation time after 1 minute under load: Measurement can be performed according to (Patent Document 30). The liquid permeation time is preferably ≦ 150 seconds / 10 ml, more preferably 100 seconds / 10 ml, more preferably ≦ 50 seconds / 10 ml, most preferably ≦ 40 seconds / 10 ml.

4). Liquid permeation time: Measurement can be performed according to (Patent Document 31). The liquid permeation time is preferably 50 seconds or shorter, more preferably 40 seconds or shorter, and most preferably 30 seconds or shorter.

5. Absorption capacity under high pressure: Measurement can be performed according to (Patent Document 32). The absorption capacity under high pressure is preferably 23 g / g or more, more preferably 25 g / g or more, and most preferably 27 g / g or more.

6). Pressure-resistant water absorption ratio: The pressure-resistant water absorption ratio can be calculated according to (Patent Document 32) together with the absorption ratio under high pressure. The pressure-resistant water absorption ratio is preferably 0.7 or more, more preferably 0.75 or more, and most preferably 0.8 or more.

7). Absorption under pressure for 5 minutes: Measurement can be performed according to (Patent Document 33). The absorption after 5 minutes under pressure is preferably 20 g / g or more at 200 g load, 16 g / g or more at 300 g load, more preferably 24 g / g at 200 g load, 20 g / g or more at 300 g load, most preferably It is 28 g / g or more at a 200 g load and 24 g / g or more at a 300 g load.

8). Absorption efficiency: Measurement can be performed according to (Patent Document 34). The absorption efficiency is preferably 0.6 or more, more preferably 0.7 or more, further preferably 0.8 or more, and most preferably 0.9 or more. The absorption capacity under pressure of the upper layer is preferably 20 g / g or more, more preferably 25 g / g or more, and most preferably 30 g / g or more.

Physical property b property Physical property The physical property of the b group can generally be improved as the gel capacity increases. The gel capacity is closely related to the degree of crosslinking, particularly the molecular weight between crosslinking points, and the gel capacity can be increased by reducing the degree of crosslinking. However, if the degree of cross-linking is reduced too much, conversely, the performance under load and the performance of the physical properties a group are extremely lowered. As a method of satisfying these simultaneously, there is, for example, a method of increasing the molecular weight of the main chain skeleton of the polymer and reducing the crosslinking points to increase the molecular weight between the crosslinking points. In the present invention, by using hydroperoxide as an initiator, the terminal OH group reacts with the carboxyl group in the polymer, so that it can be made to have a high molecular weight in addition to the ammonium salt content. Since there are many side reactions, such as self-crosslinking, since it is many, resin with a large gel capacity can be manufactured. For this reason, the water-absorbent resin of the present invention exhibits a high physical property b group value. By lowering the degree of cross-linking, higher values of the physical property b group can be achieved. As another means for improving the physical property b group, a crosslinking agent having a long distance between crosslinking points can be used.

1. Differential inflection point absorption: Measurement can be performed according to (Patent Document 35). When the limit absorption amount is exceeded, the shear pressure of the gel rapidly decreases, so it is considered that the differential inflection point absorption amount is correlated with the non-pressurized absorption amount. The differential inflection point absorption is preferably 40 g / g or more, more preferably 50 g / g or more, still more preferably 60 g / g or more, and most preferably 70 g / g or more. At this time, the gel friction index is about 15 to 30.

2. Water retention amount: Measurement can be performed according to (Patent Document 36). It can be said that the water retention amount tends to increase as the non-pressurized absorption capacity increases and the soluble content increases. The water retention amount is preferably 35 g / g or more, preferably 45 g / g or more, and most preferably 60 g / g or more.

3. Absorption capacity reduction degree: Measurement can be performed according to (Patent Document 37). The degree of absorption reduction is preferably 3 g / g or less, more preferably 1 g / g or less. Depending on the absorption rate, it may be negative.

4). High viscosity liquid absorption: Measurement can be performed according to (Patent Document 38). High-viscosity liquid absorption shows a tendency similar to that of a normal non-pressurized absorption amount. Preferably it is 40 g / g or more, More preferably, it is 50 g / g or more, Most preferably, it is 70 g / g or more.

Physical property c group Physical property The physical property of the c group is a physical property group that cannot be generally correlated only with the degree of cross-linking, but can exhibit favorable performance in the water-absorbent resin of the present invention.

1. Ventilation resistance: The measurement can be carried out according to (Patent Document 39), but the measurement is carried out by setting the time of immersion in raw food as 30 minutes and the time of standing under load as 3 minutes. The ventilation resistance is preferably 20 kPa · sec / m or less, more preferably 10 kPa · sec / m or less, and most preferably 5 kPa · sec / m or less.

2. Return rate: The return rate can be measured as follows. 0.16 g of a water-absorbing resin is placed in an acrylic resin cylinder having an inner diameter of 25 mm, a height of 30 mm, and a nylon nonwoven fabric having a 250 mesh mesh at the bottom, and the weight is measured. Each measuring apparatus is placed in a petri dish with an inner diameter of 120 mm containing 60 g of 0.9% physiological saline. After 60 minutes, it was taken out and left on a Kim towel for 3 seconds to drain water, the weight of the device after removing the load was measured, and the water absorption ratio A was calculated according to the following formula.
Absorption capacity A (g / g) = (final weight (g) −device weight before water absorption (g)) / particle weight (g)
Prepare 50 pieces of 90φ Advantech No. 2 filter paper, place each measuring device on top of it, put a weight of 278.33 g and leave it for 1 hour. Thereafter, the weight of each weight is measured, and the water absorption magnification B is calculated according to the following formula.
Absorption capacity B (g / g) = (weight measured with weight after 1 hour (g) −device weight before water absorption (g) −278.33) / particle weight (g)
Return rate = absorption magnification B / absorption magnification A × 100
The return rate is preferably 40% or less, more preferably 25% or less, and most preferably 15% or less. When the return amount is small, it indicates that it is difficult to discharge the liquid even when a load is applied.

3. Ratio of transverse relaxation time T2 and non-pressurized absorption amount: Measurement of transverse relaxation time T2 and non-pressurized absorption amount are performed by the method described above. The smaller the lateral relaxation time, the more restricted the molecular motion. It can be said that the direction in which molecular motion is constrained is excellent in stability as a gel. However, the water absorption magnification is more likely to increase as the restraint is smaller. That is, it can be said that the stability of the gel and the water absorption are generally contradictory properties. Thus, as an index representing this feature, the ratio between the pressureless absorption ratio and T2 can be taken. The pressureless absorption capacity / T2 is preferably 3.2 to 9.3, more preferably 4.2 to 8.7, and most preferably 4.4 to 5.5. If it falls within this range, it can be said that the stability of the gel and the water absorption ratio are balanced.

Physical property group d Physical property property group d is also a physical property that cannot be correlated only with the degree of crosslinking.

1. Viscosity measurement: Measurement can be performed according to (Patent Document 40). The viscosity is preferably 20000 mPa · s or more, and more preferably 25000 mPa · s or more.

2. Static deterioration, dynamic deterioration: Measurement can be performed according to (Patent Document 41). Sexual deterioration (1) is preferably 15 or more, and more preferably 17 or more. Sexual deterioration (4) is preferably 5 or more, more preferably 8 or more. The dynamic deterioration is preferably 13 or more, more preferably 16 or more.

3. Coloration degree: Measurement can be performed according to (Patent Document 42). The degree of coloring is preferably 50 or less.

4). L value, a value, b value: Measurement can be performed according to (Patent Document 43). The L value is preferably 100 or less, the a value is 3.5 or less, and the b value is 13.5 or less.

5. Vortex method water absorption rate: Measurement can be performed according to (Patent Document 44). Vortex method water absorption speed is affected by particle diameter, surface area, gel strength and the like. The smaller the particle size and the larger the surface area, the faster the vortex method water absorption rate, but the stronger the gel strength, the slower the vortex method water absorption rate. The water absorption rate of the vortex method is preferably 110 seconds or less, and more preferably 50 seconds or less.

6). Gel layer flow rate: The measurement can be performed according to (Patent Document 45). Gel layer permeation rate correlates with gel strength, absorption, surface structure, and the like. The more surface irregularities, the shorter the tendency. The gel layer flow rate is preferably 130 seconds or less.

7). Absorption swelling pressure: Measurement can be performed according to (Patent Document 46). The absorption swelling pressure is preferably 2000 Pa after 10 seconds and 30000 Pa or more after 300 seconds.

JP-A-6-56931 JP-A-6-56931 JP 7-49449 JP 2001-106728 A JP 2003-88552 A Patent 2918808 Patent 3330959 JP 2003-176421 A JP 2003-135524 A JP 11-60975 JP 2003-192732 A JP 10-265582 A JP2003-335970 JP 2003-102732 A JP-A 8-188602 JP2002-315783 JP 2002-45395 A JP 2003-88554 A JP 2000-463 A JP 11-322846 JP 11-71529 A JP 2003-135524 A JP 2001-89527 A JP 2003-88553 A

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, it is not limited to this.

Production Example 1
Preparation of ammonium acrylate by hydrolysis of acrylonitrile Hydrolysis of acrylonitrile was carried out by preparing a biocatalyst according to the method of Example 1 of Japanese Patent Application No. 2003-101199 and performing hydrolysis according to the method of Example 4.

Preparation of biocatalyst Acinetobacter sp. AK226 (FERM BP-2451) having nitrilase activity 0.1% sodium chloride, 0.1% potassium dihydrogen phosphate, 0.05% magnesium sulfate heptahydrate, 7 water iron sulfate A medium prepared by adjusting pH = 7 to an aqueous solution containing 0.005% Japanese, 0.005% manganese sulfate pentahydrate, 0.1% ammonium sulfate, and 0.1% potassium nitrate (both by weight). As a medium, 0.5% by weight of acetonitrile was added and cultured aerobically at 30 ° C. This was washed with a 30 mM phosphate buffer (pH = 7.0) to obtain a cell suspension (dry cell 15% by weight).

Hydrolysis with biocatalyst 400 g of distilled water was put into an Erlenmeyer flask having an internal volume of 500 ml, and the above biocatalyst 0.2 g (corresponding to 0.03 g of dry cells) was suspended therein, and sealed with a rubber stopper. The inner temperature was kept at 20 ° C. by immersion in a constant temperature water bath, and the mixture was stirred with a stirrer.
Acrylonitrile was intermittently fed in an amount of 1% by weight (the acrylonitrile concentration was controlled at 2% by weight or less), and an accumulation reaction of ammonium acrylate was carried out. As a result, it was possible to accumulate up to 40% by weight. This liquid was centrifuged at 15000 rpm for 30 minutes to recover only the supernatant. In addition, when 5 L of the reaction solution was prepared under the same conditions and purified using a UF membrane (Asahi Kasei Pencil type module SIP-0013), no clogging or other phenomena were observed, and the entire solution could be processed. A highly pure 40 wt% ammonium acrylate aqueous solution was obtained. In addition, β-hydroxypropionic acid (salt) and β-acryloyloxypropionic acid (salt) were not detected in the monomer (detection limit: 0.1 ppm). Moreover, when metal analysis was performed, iron 0.2ppm, manganese 0.17ppm, and magnesium 0.84ppm were contained. These metal components are considered to have been introduced through the biocatalyst from the time of culturing the microorganism, and act as a reducing agent during the polymerization.

Production Example 2
Preparation of Ammonium Acrylate by Neutralization of Acrylic Acid Acrylic acid was manufactured by distilling and purifying a reagent-grade product manufactured by Wako Pure Chemical. 100 g of reagent acrylic acid was dissolved in 91.02 g of water. This aqueous solution was cooled in an ice bath, and while maintaining the liquid temperature at 30 ° C. or lower, 117.94 g of a 25 wt% aqueous ammonia solution was gradually added with stirring to obtain a 40 wt% aqueous ammonium acrylate solution.

Example 1
To a 300 ml separable flask, 90 g of 40 wt% ammonium acrylate aqueous solution of Production Example 1 and 0.0187 g of N, N′-methylenebisacrylamide are added. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.43 g of 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of 30 wt% aqueous hydrogen peroxide solution dissolved in 1 g of water each and Rongarit (sodium, formaldehyde, sulfo Polymerization is started by adding 0.0415 g of xylate trade name). The internal temperature starts from 30 ° C and rises to 100 ° C in 5 minutes from the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 170 ° C. in an inert oven for 30 minutes under a nitrogen atmosphere. The water absorbent resin obtained as described above is designated as a water absorbent resin (1).

Example 2
0.0273 g of iron sulfate heptahydrate, 0.0750 g of manganese sulfate pentahydrate, and 7.209 g of magnesium sulfate heptahydrate were weighed into a 2 L flask, and distilled water was added to make 1000 g. This was diluted 1000 times with distilled water. To a 300 ml separable flask, 1.0 g of this metal solution, 90 g of 40 wt% ammonium acrylate aqueous solution of Production Example 2 and 0.0374 g of N, N′-methylenebisacrylamide are added. In the monomer, 7.8 ppm of magnesium, 0.06 ppm of iron (II), and 0.19 ppm of manganese (II) are present, and these act as a reducing agent during polymerization. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.86 g of a 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of a 30 wt% aqueous hydrogen peroxide solution dissolved in 1 g of water and 0.0415 g of Rongalite were added to initiate polymerization. The internal temperature starts from 30 ° C and rises to 100 ° C in 4 minutes from the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 180 ° C. for 15 minutes in an inert oven under a nitrogen atmosphere. The water absorbent resin obtained as described above is designated as a water absorbent resin (2). The average particle size was 450 μm. Table 3 shows the physical properties of this water-absorbent resin.

Example 3
To a 300 ml separable flask, 90 g of 40 wt% ammonium acrylate aqueous solution of Production Example 1 and 0.0561 g of N, N′-methylenebisacrylamide are added. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.86 g of a 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of a 30 wt% aqueous hydrogen peroxide solution dissolved in 1 g of water and 0.0415 g of Rongalite were added to initiate polymerization. The internal temperature starts from 30 ° C and rises to 103 ° C in 4 minutes from the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated in an inert oven at 170 ° C. for 20 minutes in a nitrogen atmosphere. The water absorbent resin obtained as described above is designated as a water absorbent resin (3).

Example 4
To a 300 ml separable flask, 90 g of 40 wt% ammonium acrylate aqueous solution of Production Example 1 and 0.0187 g of N, N′-methylenebisacrylamide are added. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.86 g of a 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of a 30 wt% aqueous hydrogen peroxide solution dissolved in 1 g of water and 0.0415 g of Rongalite were added to initiate polymerization. The internal temperature starts from 30 ° C and rises to 101 ° C in 6 minutes from the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 170 ° C. in an inert oven for 30 minutes under a nitrogen atmosphere. The water absorbent resin obtained as described above is designated as a water absorbent resin (4).

Example 5
While cooling 115.81 g of acrylic acid distilled and purified in a 300 ml flask, 193.40 g of water, 16.03 g of 30 wt% NaOH aqueous solution and 109.38 g of 25 wt% aqueous ammonia, the liquid temperature does not exceed 30 ° C. Slowly added.
90 g of the monomer aqueous solution and 0.0378 g of N, N′-methylenebisacrylamide are added to a 300 ml separable flask. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.86 g of 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0953 g of 30 wt% aqueous hydrogen peroxide dissolved in 1 g of water and 0.0419 g of Rongalite were added to initiate polymerization. The internal temperature started from 30 ° C and increased to 105 ° C 5 minutes after the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed and then dried at 100 ° C. for 4 hours using an inert oven in a nitrogen atmosphere. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 170 ° C. in an inert oven for 30 minutes under a nitrogen atmosphere. The water absorbent resin thus obtained is designated as water absorbent resin (5).

Example 6
0.0187 g of N, N′-methylenebisacrylamide was added as a crosslinking agent to 90 g of a 40 wt% ammonium acrylate aqueous solution obtained by the biocatalyst of Production Example 1 and dissolved. This solution was transferred to a 300 ml separable flask and purged with nitrogen at 30 ° C. for 30 minutes while stirring. 0.263 g of erythritol was added thereto, 0.0414 g of Rongalite was further added, and 0.092 g of a 30% by weight aqueous hydrogen peroxide solution was subsequently added to initiate polymerization. The temperature rose from 1 minute after the start, and the maximum temperature reached 102 ° C. After polymerization for 1 hour, the hydrogel was crushed to about 5 mm square and dried at 100 ° C. for 2 hours in an inert oven with a nitrogen atmosphere. The dried polymer was pulverized with a homogenizer, and further dried at 100 ° C. in an inert oven for 2 hours. The polymer after drying was classified to 106 to 850 μm. Thereafter, heating was performed at 170 ° C. for 30 minutes. The water absorbent resin obtained as described above is designated as a water absorbent resin (6).

Example 7
In a 300 ml flask, 97.66 g of reagent acrylic acid (manufactured by Wako Pure Chemical, special grade reagent), 126.55 g of water, and 81.35 g of 25 wt% aqueous ammonia are slowly cooled so that the liquid temperature does not exceed 30 ° C. Added. Further, 7.8 g of activated carbon was added, stirred for 1 hour under light shielding, and the activated carbon was removed by filtration to obtain a 90% neutralized ammonium acrylate aqueous solution.
To a 300 ml separable flask, 90 g of 90% neutralized ammonium acrylate aqueous solution and 0.0198 g of N, N′-methylenebisacrylamide are added. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.86 g of 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0953 g of 30 wt% aqueous hydrogen peroxide dissolved in 1 g of water and 0.0419 g of Rongalite were added to initiate polymerization. The internal temperature started from 30 ° C. and increased to 102 ° C. 5 minutes after the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed and then dried at 100 ° C. for 4 hours using an inert oven in a nitrogen atmosphere. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 170 ° C. in an inert oven for 30 minutes under a nitrogen atmosphere. The water absorbent resin thus obtained is designated as water absorbent resin (7).

Example 8
A resin produced in the same manner as in Example 1 except that the heating condition is set at 180 ° C. for 15 minutes is referred to as a water absorbent resin (8).

Example 9
A resin produced in the same manner as in Example 1 except that the heating condition is 190 ° C. for 5 minutes is referred to as a water absorbent resin (9).

Example 10
To a 300 ml separable flask, 90 g of 40 wt% ammonium acrylate aqueous solution of Production Example 1 and 0.0187 g of N, N′-methylenebisacrylamide are added. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.43 g of 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of 30 wt% aqueous hydrogen peroxide solution dissolved in 1 g of water and 0.0280 g of sodium bisulfite were added to initiate polymerization. To do. The internal temperature starts from 30 ° C. and rises to 106 ° C. 7 minutes after the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 180 ° C. for 10 minutes in an inert oven in a nitrogen atmosphere. The water absorbent resin obtained as described above is designated as a water absorbent resin (10).

Example 11
75 parts by weight of the water absorbent resin (1) and 25 parts by weight of pulverized wood pulp were dry-mixed using a mixer. Into an acrylic cylindrical container having an outer diameter of 70 mm, an inner diameter of 59.5 mm, and a 250 mesh nylon nonwoven fabric at the bottom, 1.5 g of the obtained mixture is put. The whole acrylic cylindrical container is put into a 120 mm petri dish containing 200 g of 0.9% physiological saline and allowed to absorb water for 60 minutes. After water absorption, the acrylic cylindrical container is allowed to stand on a Kim towel for 1 minute. Thereafter, the container was set on a reciprocating shaker, shaken at 40 rpm for 10 minutes, and when the water-containing resin hydrous gel and pulp were changed in shape by visual observation, the shape and position of the gel and pulp were hardly changed. .

Comparative Example 1
100 g of reagent acrylic acid was dissolved in 91.02 g of water. This aqueous solution was cooled in an ice bath, and while maintaining the liquid temperature at 30 ° C. or lower, 117.94 g of a 25 wt% aqueous ammonia solution was gradually added with stirring to obtain a 40 wt% aqueous ammonium acrylate solution. The amount of β-hydroxypropionic acid (salt) in the monomer was 50 ppm, and the amount of β-acryloyloxypropionic acid (salt) was 540 ppm. 90 g of this 40 wt% ammonium acrylate aqueous solution and 0.0187 g of N, N′-methylenebisacrylamide are added to a 300 ml separable flask. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, after adding 0.43 g of 42 wt% glycerin aqueous solution with a syringe and stirring well, 0.0917 g of 30 wt% aqueous hydrogen peroxide solution and 0.0415 g of Rongalite each dissolved in 1 g of water are added to initiate polymerization. . The internal temperature starts from 30 ° C and rises to 100 ° C in 7 minutes from the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 180 ° C. for 15 minutes in an inert oven under a nitrogen atmosphere. The water absorbent resin obtained as described above is referred to as a comparative water absorbent resin (1).

Comparative Example 2
To a 300 ml separable flask, 90 g of 40 wt% ammonium acrylate aqueous solution of Production Example 2 and 0.0374 g of N, N′-methylenebisacrylamide are added. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.86 g of a 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of a 30 wt% aqueous hydrogen peroxide solution dissolved in 1 g of water and 0.0415 g of Rongalite were added to initiate polymerization. The internal temperature starts from 30 ° C and rises to 100 ° C in 6 minutes from the start of the reaction. Then, it heats in a water bath for 3 hours so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 180 ° C. for 15 minutes in an inert oven under a nitrogen atmosphere. The water absorbent resin thus obtained is referred to as comparative water absorbent resin (2).

Comparative Example 3
To a 300 ml separable flask, 90 g of 40 wt% ammonium acrylate aqueous solution of Production Example 1 and 0.0374 g of N, N′-methylenebisacrylamide are added. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deoxygenated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, after adding 42 wt% ethylene glycol aqueous solution with a 0.86 g syringe and stirring well, 0.0615 g of ammonium persulfate dissolved in 1 g of water and 0.0007 g of L-ascorbic acid are added to initiate polymerization. The internal temperature starts from 30 ° C and increases to 70 ° C in 5 minutes from the start of the reaction. Heat in a water bath for 3 hours so that the internal temperature is maintained at 75 ° C. 5 minutes after recording the maximum temperature. After a predetermined time has elapsed, the gel is taken out from the separable flask and roughly crushed, and then dried at 100 ° C. using an inert oven for 4 hours. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. This is heated at 170 ° C. in an inert oven for 30 minutes under a nitrogen atmosphere. The water absorbent resin obtained as described above is referred to as a comparative water absorbent resin (3).

Comparative Example 4
Except not adding glycerol aqueous solution before superposition | polymerization, superposition | polymerization, drying, and grinding | pulverization were performed like Example 1, and 106-850 micrometers was collect | recovered by sieving. An aqueous liquid composed of 1 part by weight of glycerin, 3 parts by weight of water and 30 parts by weight of isopropyl alcohol is added to and mixed with 100 parts by weight of the particles, and the resulting mixture is heated at 170 ° C. for 30 minutes. The water absorbent resin thus obtained is referred to as comparative water absorbent resin (4).

Comparative Example 5
To a 300 ml flask, 81.73 g of reagent acrylic acid (manufactured by Wako Pure Chemical, special grade reagent), 185.71 g of water, and 31.78 g of sodium hydroxide were slowly added while cooling with ice so that the liquid temperature did not exceed 30 ° C. . The amount of β-hydroxypropionic acid (salt) in the monomer was 60 ppm, and the amount of β-acryloyloxypropionic acid (salt) was 550 ppm. 90 g of this monomer solution and 0.0561 g of N, N′-methylenebisacrylamide are added to a 300 ml separable flask. The flask is bathed in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deoxygenated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Polymerization is initiated by adding 0.0826 g of 30 wt% and 0.0518 g of Rongalite dissolved in 1 g of water. The internal temperature starts from 30 ° C and increases to 70 ° C in 10 minutes from the start of the reaction. Heat in a water bath for 3 hours so that the internal temperature is maintained at 75 ° C. 5 minutes after recording the maximum temperature. After a predetermined time has elapsed, the gel is taken out from the separable flask and roughly crushed, and then dried at 100 ° C. using an inert oven for 4 hours. After drying, the mixture is pulverized with a homogenizer, and 100 to 850 μm is collected by sieving. An aqueous liquid composed of 1 part by weight of glycerin, 3 parts by weight of water and 30 parts by weight of isopropyl alcohol is added to and mixed with 100 parts by weight of the particles, and the resulting mixture is heated at 170 ° C. for 30 minutes. The water absorbent resin thus obtained is referred to as comparative water absorbent resin (5).

Comparative Example 6
In Example 1, a resin produced in the same manner except that drying and drying after classification are not performed is referred to as a comparative water absorbent resin (6).

Comparative Example 7
The commercially available Pampers L (Cotton Care) was disassembled and only the water-absorbing resin was recovered. This water absorbent resin is referred to as comparative water absorbent resin (7).

Comparative Example 8
75 parts by weight of the comparative water absorbent resin (4) and 25 parts by weight of pulverized wood pulp were dry-mixed using a mixer. Into an acrylic cylindrical container having an outer diameter of 70 mm, an inner diameter of 59.5 mm, and a 250 mesh nylon nonwoven fabric at the bottom, 1.5 g of the obtained mixture is put. The whole acrylic cylindrical container is put into a 120 mm petri dish containing 200 g of 0.9% physiological saline and allowed to absorb water for 60 minutes. After water absorption, the acrylic cylindrical container is allowed to stand on a Kim towel for 1 minute. After that, the container was set on a reciprocating shaker and shaken at 40 rpm for 10 minutes. The shape change of the water-absorbent resin hydrogel and pulp was visually observed, and the shape and positional relationship of the water-absorbent resin and pulp changed. Was.

Comparative Example 9
The same operation as in Comparative Example 8 was performed except that the comparative water absorbent resin (7) was used. When the state of the water absorbent resin and the pulp was confirmed, the shape and positional relationship of the water absorbent resin and the pulp were changed.

The characteristics of the water-absorbent resin obtained above are shown in Tables 1 to 3 below. Table 3 shows the physical properties of the water absorbent resin (2).

The water-absorbing resin and the method for producing the same of the present invention can be suitably used in the field of producing a highly water-absorbing resin and a highly water-absorbing composition that are required for high water-absorbing performance used in sanitary materials and the like.

Claims (6)

In the method for producing a water absorbent resin including a polymerization step, a drying step, and a heating step, the following a) b)
The manufacturing method of the water-absorbent resin characterized by satisfying c).
a) 60-100 mol% (meth) ammonium acrylate is used as a raw material monomer for polymerization.
b) The raw material monomer for polymerization contains a compound having two or more functional groups capable of reacting with a carboxyl group.
c) Hydroperoxide and two or more reducing agents are used as radical initiators. (Meth) ammonium acrylate (meth) acrylonitrile and / or (meth) the amount of impurities produced by the hydrolytic action of microorganisms acrylic amide (meth) ammonium acrylate, and / or decompose can be the acrylic acid 500ppm The water-absorbent resin according to claim 1, which is ammonium (meth) acrylate obtained by neutralizing (meth) acrylic acid with ammonia, wherein one of the reducing agents is a reducing metal component. Manufacturing method. In the heating step, the manufacturing method of the water-absorbent resin according to any one of claims 1-2 where the heating condition is to satisfy the following equation.
Y ≦ −1.6X + 345
Y is heating time (minutes)
X is the heating temperature (° C.), X ≧ 163 (° C.) The method for producing a water absorbent resin according to any one of claims 1 to 3 , wherein the hydroperoxide is hydrogen peroxide. Method for producing a water-absorbent resin according to any one one reducing agent of claims 1 to 4 formaldehyde derivative sulfoxylate salt. According to claim 1, characterized in that it contains less 0.1 mol% of the compound in one molecule of crosslinking agent during polymerization with an unsaturated group at least two relative Zentan monomer component A method for producing a water-absorbent resin.