JP2007002033A - Method for manufacturing highly water holding and water absorptive resin of spherical type and large particle size - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a water absorptive resin with high water absorbing magnification capable of exercising enough water absorptive capacity even at a small amount of the resin, when used as an absorbent such as sanitary materials. <P>SOLUTION: This absorptive resin is manufactured by polymerizing an aqueous monomer solution containing an ammonium unsaturated carboxylate under a condition satisfying following requirements of (1)-(4): (1) the ammonium unsaturated carboxylate is ≥50 mole% based on a 100 mole% radical-polymerizable monomer component in the aqueous monomer solution, (2) a monomer concentration is >40 wt% in the aqueous monomer solution, (3) a nonionic surfactant of an HLB of 4.5-12 is used, and (4) a reversed phase suspension polymerization is conducted in which the aqueous monomer solution is suspended in an organic solvent to be polymerized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an absorptive resin mainly composed of a polymer obtained by polymerizing an acid group-containing monomer having an ammonium cation as a counter cation. More specifically, it provides an absorbent resin that has high absorption performance, is spherical and has a large particle size, and is suitable for use in various applications including sanitary materials such as paper diapers, sanitary napkins, and incontinence pads. The present invention relates to a method for producing a functional resin.

  In recent years, a water-absorbing resin that gels by absorbing a large amount of water has been developed as a kind of synthetic polymer, and is widely used in the field of sanitary materials such as disposable diapers and sanitary napkins, agriculture and forestry, and civil engineering. Yes. Examples of such a water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product (for example, see Patent Document 1), a hydrolyzate of starch-acrylonitrile graft polymer (for example, see Patent Document 2), and starch-acrylic acid. Neutralized graft polymer (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 Many are known (for example, refer to Patent Document 5). The properties that these water-absorbent resins should have include conventionally a high water absorption ratio and excellent absorption rate when in contact with aqueous liquids such as body fluids, liquid permeability, gel strength of swollen gels, and groups containing aqueous liquids. A suction amount for sucking water from the material is required.

  In recent years, the demand for disposable diapers for the elderly has been increasing with the increase in the average lifespan. Furthermore, in recent years, there has been a growing demand for thinner and lighter sanitary materials due to design problems, distribution problems, and dust problems. In order to cope with this, as a method generally used in the current sanitary material, there is a method in which the absorbent resin supporting carrier in the sanitary material such as fiber is reduced and a large amount of the absorbent resin is used.

  The hygienic material with a reduced ratio of hydrophilic fibers and increased absorbent resin is a preferable direction from the viewpoint of simply storing liquid, but it is related to the distribution and diffusion of liquid in actual diaper usage. I have a problem that performance drops. That is, there is a problem that a large amount of absorbent resin becomes a soft gel due to water absorption, and a so-called gel blocking phenomenon that greatly hinders liquid diffusion occurs.

  For this reason, the absorbent resin used preferably has a high gel strength in order to prevent gel blocking. However, in general, an absorbent resin having a high gel strength has a low water retention because the number of cross-linking points between polymer chains increases. For this reason, in order to supplement the water retention capacity, it has become necessary to use a larger amount of absorbent resin in such an absorbent body than when mixed with a large amount of fibers.

  In addition, as a means for preventing gel blocking that occurs when fibers are reduced and a large amount of absorbent resin is used, a method using two types of absorbent resins with different absorption performances (for example, see Patent Document 6), cationic ions A method using a composition comprising an exchange hydrogel-forming polymer and an anionic ion-exchange hydrogel-forming polymer (see, for example, Patent Document 7), a method using an absorbent resin having a high surface crosslinking density (see, for example, Patent Document 8), A method of foaming and extruding a mixture of an absorbent resin and a thermoplastic resin to form a sheet (for example, see Patent Document 9) has been proposed. In any case, an absorbent resin with reduced absorption performance is used. Thus, there is a problem that the performance as an absorber is expressed.

  As a method for solving these problems, a method of fixing an absorbent resin to a support carrier has been studied. For example, a method of embossing the absorbent body, a method of including a thermoplastic binder fiber in an absorbent body composed of an absorbent resin and a hydrophilic fiber and heat-sealing the absorbent body, a synthetic resin having a high recovery rate from strain A method of heat-sealing the absorbent by containing it in an absorbent comprising an absorbent resin and a hydrophilic fiber (see, for example, Patent Document 10 and Patent Document 11), a cationic polymer on the surface of the absorbent resin having an anionic group Coating and fixing the particles to each other at the time of swelling (for example, see Patent Document 12 and Patent Document 13), a method of fixing the absorbent resin and the hydrophilic fiber using an emulsion binder, a hot melt adhesive (For example, refer to Patent Document 14 and Patent Document 15) and the like.

  By adopting these methods, it is possible to use a normal absorbent resin having a low crosslink density and a high absorbability as the absorbent resin. However, at present, the absorbent resin mainly composed of poly (sodium acrylate) has a limit value of about 60 g / g in 0.9% physiological saline absorption capacity, which makes the absorbent body lighter and thinner. There is a problem of not progressing.

  On the other hand, in the manufacture of sanitary materials including absorbent bodies, fine particles of absorbent resin are always a problem. This includes health problems caused by workers inhaling fine powders, environmental problems, and adverse effects on manufacturing equipment. For this reason, various methods have been studied conventionally. For example, an increase in the size of particles by agglomeration by a two-stage polymerization method (for example, see Patent Document 16) has been proposed. However, the production process in which the polymerization is performed in two stages has a lower production efficiency than the polymerization in one stage. Moreover, the reverse phase suspension polymerization method (for example, refer patent documents 17-20) by using a special surfactant is mentioned. However, it is pointed out in the literature that the surfactant used is not a commonly available surfactant, and the stability of the emulsion in polymerization is unstable, and the absorption capacity is still low. There are problems such as not being a highly water-absorbing absorbent resin (see, for example, Patent Document 16).

  In order to achieve light weight and thinness as an absorbent body, it is a simple means to use an absorbent resin with high absorbent performance and to maximize its high absorbent performance in the absorbent body. Things do not exist in the world. This is achieved by arranging an absorbent resin having a reduced crosslink density with a high absorption performance as much as possible in a state with as few contact points and / or contact surfaces between the resins as possible (a state in which gel blocking is difficult). That is, a highly water-retaining, spherical, and large-sized absorbent resin has not been obtained so far.

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 2001-252307 A International Publication No. 98/037149 Pamphlet Japanese Patent Laid-Open No. 06-057010 International Publication No. 01/64153 Pamphlet JP-A-10-118114 JP-A-10-118115 JP-A-5-31362 JP-A-6-370 JP 2000-238161 A Japanese National Patent Publication No. 10-510447 JP-A-9-77810 Japanese Examined Patent Publication No. 6-6612 Japanese Patent Publication No. 1-17482 Japanese Patent Publication No. 63-36322 Japanese Examined Patent Publication No. 63-36321

  Accordingly, an object of the present invention is to provide a method for producing an absorbent resin having a high water absorption capacity that can exhibit a sufficient water absorption capacity even when used in an absorbent body such as a sanitary product, and also a spherical and small amount of fine powder. It is providing the manufacturing method of the water absorbing resin which is a particle diameter.

As a result of intensive studies to achieve the above object, the present inventors have found that a high concentration monomer aqueous solution containing 50 mol% or more of unsaturated ammonium carboxylate in an organic solvent in a W / O type reverse phase. It has been found that by using a specific surfactant during polymerization by suspension polymerization, a water-absorbing resin having a high water absorption capacity and a spherical and large particle diameter can be produced, and the present invention has been completed.
That is, the present invention includes the following [1] to [5].
[1] A method for producing an absorptive resin, characterized in that an absorptive resin is obtained by polymerizing an aqueous monomer solution containing an unsaturated ammonium carboxylate under conditions satisfying the following requirements (1) to (4): .
(1) The ratio of unsaturated ammonium carboxylate to 100 mol% of the radically polymerizable monomer component in the monomer aqueous solution is 50 mol% or more. (2) The monomer concentration of the monomer aqueous solution is 40% by weight. To exceed.
(3) Use a nonionic surfactant of HLB4.5-12.
(4) Use reverse phase suspension polymerization in which polymerization is suspended in an organic solvent.
[2] The method for producing an absorbent resin according to [1], wherein the surfactant is a sorbitan fatty acid ester.
[3] The method for producing an absorbent resin as described in [1], wherein the surfactant is sorbitan monolaurate.
[4] The method for producing an absorbent resin as described in [1] to [3], wherein the organic solvent is an aliphatic hydrocarbon.
[5] The method for producing an absorbent resin as described in [4], wherein the aliphatic hydrocarbon solvent is cyclohexane.
[6] The ratio according to [1] to [5], wherein the ratio of unsaturated ammonium carboxylate to 100 mol% of the radically polymerizable monomer component in the monomer aqueous solution is 95 to 100 mol%. Manufacturing method of absorbent resin.
[7] The method for producing an absorbent resin as described in [1] to [6], wherein the unsaturated ammonium carboxylate is ammonium (meth) acrylate.

  The absorptive resin obtained by the production method of the present invention is an absorptive resin per unit weight that is particularly excellent in water retention among the absorptive performance, has a small amount of fine powder, and is most effective for bringing out the water absorptive performance as a water absorbent. It has a feature that it has a spherical shape and a large particle diameter with few adhesion points and / or adhesion surfaces (gel blocking hardly occurs).

Hereinafter, the present invention will be described in more detail.
In the present invention, as the polymerization method, a reverse phase suspension polymerization method is used in which an aqueous monomer solution containing an unsaturated ammonium carboxylate is suspended in an organic solvent for polymerization. The type of the reactor is not particularly limited, and may be either batch type or continuous type. For example, a loop reactor, a general stirring tank, etc. are mentioned.

  The monomer aqueous solution may contain an unsaturated carboxylic acid alkali metal salt and / or other monomer in an amount of less than 50 mol% based on the total monomer components. In addition, a radical polymerizable crosslinking agent may be added as an internal crosslinking agent. However, when a high concentration monomer aqueous solution exceeding 50% by weight is used, for example, if the internal crosslinking agent is used, the water retention amount tends to decrease. is there. It is desirable that the concentration of the monomer in the aqueous monomer solution exceeds 50% by weight and is not more than the solubility of the monomer in water. For example, in the case of ammonium acrylate, the concentration is preferably 40 to 80% by weight, more preferably 50 to 70% by weight.

  The higher the monomer concentration in the aqueous monomer solution, the larger the particle diameter of the water-absorbing resin produced, which is preferable because the fine powder is reduced. Further, the higher the monomer concentration, the more easily the self-crosslinking reaction proceeds, the amount of the internal crosslinking agent used can be reduced, and the water absorption capacity of the produced water-absorbing resin becomes very high, which is preferable. Further, in the solvent separation described later, the higher the concentration of the monomer in the aqueous solution, the easier the filtration separation between the hydrous gel to be produced and the solvent is possible, and a simple process can be adopted. Conversely, gels with a high water content have high tackiness, and the gel is fixed and integrated when filtered and separated, so if the concentration of the monomer in the aqueous solution is low, the solvent is evaporated and azeotropic dehydration is performed at the same time. There is a problem that the gel must be recovered after the moisture content has been reduced.

  The monomer aqueous solution may be polymerized after being suspended in advance in an organic solvent, or may be polymerized while being added to the organic solvent as needed. In addition, as long as the intended absorption performance and particle size are within the range where the surfactant is obtained, the whole amount of the surfactant of HLB4.5-12 is added to the organic solvent used as the suspension solvent in advance. Or may be added at any time during the polymerization process.

  The polymerization initiation method is not particularly limited, and polymerization by a radical polymerization initiator, polymerization by irradiation with radiation, an electron beam, or ultraviolet polymerization by a photosensitizer can also be performed. Examples of the initiator used for such radical polymerization include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; hydrogen peroxide; organics such as cumene hydroperoxide, t-butyl hydroperoxide and peracetic acid. Well-known initiators, such as a peroxide, are mentioned. When an oxidizing radical polymerization initiator is used, a reducing agent such as L-ascorbic acid or Rongalite may be used in combination.

  It is preferable to perform a deoxygenation operation of 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. The atmosphere in the reactor is preferably replaced with an inert gas such as nitrogen or helium. The inside of the polymerization reactor may be any of reduced pressure, normal pressure, and increased pressure. The polymerization start temperature is usually 0 to 70 ° C.

  The polymerization initiation temperature is preferably 10 to 50 ° C. The temperature in the reactor during the polymerization reaction may be determined depending on the situation, and the temperature may be controlled from the outside by cooling or heating. The reaction temperature may be controlled by the boiling point of the solvent. When controlling the reaction temperature based on the boiling point of the solvent, it is preferable to adjust the boiling point by adjusting the pressure of the gas phase. It is a preferable method to control the polymerization by changing the temperature of the reaction from the start of the polymerization to the end of the polymerization. For example, it is a very preferable method to suppress the runaway reaction by suppressing the runaway reaction at a relatively low temperature at the beginning of the reaction, and to increase the degree of polymerization and / or reduce the residual monomer at the end of the reaction.

After completion of the polymerization reaction, the produced hydrogel is recovered. Separation of the solvent and the hydrous gel includes filtration fractionation, fractionation by centrifugation, removal of the solvent by heating, and the like, and any method may be used.
The drying method is not particularly limited, and usually vacuum drying or hot air drying is used. The drying temperature is preferably in the range of 70 ° C to 180 ° C, particularly preferably 90 to 140 ° C. Multi-stage heating may be performed. If the drying temperature is too low, it takes too much time to dry, which is not economical. If the drying temperature is too high, the water-absorbing resin is decomposed, resulting in a decrease in water absorption performance.

  After drying, the water-absorbent resin may be subjected to a heat treatment to liberate ammonia, and the ammonia neutralization rate may be controlled to an arbitrary ratio. It is also within the scope of the present invention to perform a so-called surface crosslinking treatment by impregnating a compound containing two or more functional groups capable of reacting with a carboxyl group at the same time and causing a crosslinking reaction by heating.

(Unsaturated ammonium carboxylate)
The unsaturated ammonium carboxylate in 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.

  The amount of unsaturated ammonium carboxylate used is the total molar amount of radical polymerizable monomers (this is the sum of the respective molar amounts of unsaturated ammonium carboxylate, unsaturated carboxylic acid alkali metal salt and unsaturated carboxylic acid). )) In the raw material liquid for polymerization in the range of 50 to 100 mol%. In order to improve the absorption capacity of the absorbent resin produced from the raw material liquid for polymerization, it is preferable that the content of mol% of the unsaturated ammonium carboxylate is high, and it is preferably in the range of 80 to 100 mol%. More preferably, it is 90 to 100%, and particularly preferably 95 to 100%.

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.

(Production method of unsaturated ammonium carboxylate)
The unsaturated ammonium carboxylate in the present invention may be produced by any production method. As the manufacturing 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.

Moreover, 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. 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 purify and 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 such a method, for example, distillation may be carried out as described in JP-A-6-56931. The amount of impurities is preferably reduced to 1000 ppm or less, more preferably 500 ppm or less, further preferably 300 ppm or less, and most preferably 100 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. As described in JP-A-6-56931 and JP-B-7-49449, neutralization is performed under the condition that the neutralization rate of acrylic acid exceeds 100 mol% for at least one period during the neutralization step. May be. 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 generated.

(Description of organic solvent used in suspension polymerization)
The organic solvent used in the present invention needs to be an organic solvent that is mixed with an equal amount of water, and then separated into two layers as a stationary state, and does not significantly inhibit the radical polymerization reaction of the raw material monomer. That is, there is no need to limit the type and amount of functional groups, constituent atoms, and the like. Usually, as a process solvent, a solvent having a small latent heat of vaporization, good separability from water, and hardly forming a chemical bond with a surfactant is preferably used. Specifically, a hydrocarbon solvent is preferable. More preferably, it is an aliphatic hydrocarbon solvent. Most preferred is a saturated aliphatic hydrocarbon solvent.

  The saturated aliphatic hydrocarbon solvent may have a linear structure, a branched structure, or a cyclic structure. Of course, a compound having a plurality of structures of a linear structure, a branched structure, and a cyclic structure in one molecule may be used. Specific examples of the saturated aliphatic hydrocarbon solvent include cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, cyclooctane and the like, as saturated aliphatic hydrocarbon solvents having a cyclic structure, n-pentane, Examples of saturated aliphatic hydrocarbons having a chain structure include n-hexane, n-heptane, n-octane, and ligroin. Of these, cyclopentane, cyclohexane, cyclooctane, n-pentane, and n-hexane are preferable, and cyclohexane is most preferable because of the stability of the obtained emulsion and various physical properties such as the boiling point and specific gravity of the solvent.

(Unsaturated carboxylic acid alkali metal salt)
The unsaturated carboxylic acid alkali metal salt in the present invention refers to a compound having both an unsaturated bond and a carboxylic acid alkali metal group. This may contain many unsaturated bonds and alkali metal 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.

  Representative examples of such unsaturated carboxylic acids that form alkali metal salts include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and cinnamic acid. Among these alkali metal salts of unsaturated carboxylic acids, alkali metal acrylates and alkali metal methacrylates are preferred from the viewpoints of polymerizability and polymer absorbability. Further, as the alkali metal, lithium is preferable for improving the absorption capacity of the produced resin, and sodium is preferable from the viewpoint of safety when used as a sanitary material.

  The amount of unsaturated carboxylic acid alkali metal salt used is the total amount of radical polymerizable monomers (this is the sum of the molar amounts of unsaturated ammonium carboxylate, unsaturated carboxylic acid alkali metal salt and unsaturated carboxylic acid). In the raw material liquid for polymerization in the range of 0 to 45 mol%. In order to improve the absorptivity of the absorbent resin produced from the raw material liquid for polymerization, the content of the unsaturated carboxylic acid alkali metal salt is preferably as low as possible, and may be in the range of 0 to 20 mol%. preferable. More preferably, it is 0 to 10%.

(Unsaturated carboxylic acid)
The unsaturated carboxylic acid in the present invention refers to a compound having both an unsaturated bond and a carboxylic acid group. This may contain a large number of unsaturated bonds and carboxylic acid 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 include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, cinnamic acid, and the like. Among these unsaturated carboxylic acids, acrylic acid and methacrylic acid are preferable from the viewpoints of polymerizability and polymer absorbability.

  The amount of unsaturated carboxylic acid used is the total molar amount of radical polymerizable monomers (this is the amount of each of unsaturated ammonium carboxylate, unsaturated carboxylic acid alkali metal salt, unsaturated carboxylic acid and other monomers). It is contained in the raw material liquid for polymerization in the range of 0 to 45 mol% with respect to the total amount. In order to improve the absorptivity of the absorbent resin produced from the raw material liquid for polymerization, the content of the unsaturated carboxylic acid alkali metal salt is preferably as low as possible, and may be in the range of 0 to 20 mol%. preferable. More preferably, it is 0 to 10%.

(Other monomers)
Other monomers in the present invention are mainly monofunctional unsaturated monomers, such as (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, crotonic acid, vinyl sulfonic acid, Acid group-containing hydrophilic monofunctional typified by styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, etc. Unsaturated monomers and salts thereof, acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide Amido group-containing hydrophilic monofunctional unsaturated monomer represented by 2-hydroxyethyl ( TA) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, esterified hydrophilic unsaturated monomer represented by polyethylene glycol mono (meth) acrylate, vinylpyridine, N- Vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N atom-containing hydrophilic monofunctional unsaturated monomers represented by N-dimethylaminoethyl (meth) acrylamide and quaternary salts thereof, styrene, vinyl chloride, butadiene, isobutene, ethylene, propylene, alkyl (meth) Acry It can be mentioned hydrophobic monofunctional unsaturated monomers over bets, etc.. 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.

  The content of these monomers in the raw material solution for polymerization is the total molar amount of radical polymerizable monomers (this includes unsaturated carboxylic acid ammonium, unsaturated carboxylic acid alkali metal salt, unsaturated carboxylic acid and other It is the range of 0 to 45 mol% with respect to the total molar amount of each monomer. Since these are used for the modification of the absorbent resin according to various purposes, the optimum use amount varies depending on the purpose, but in order to suppress the decrease in the absorption capacity of the absorbent resin, it is a small amount. Is preferable, the range of 0 to 20 mol% is preferable, and the range of 0 to 5 mol% is more preferable.

(Surfactant with HLB 4.5-12)
As the surfactant used in the present invention, any nonionic surfactant having an HLB of 4.5 to 12 can be used. A surfactant having a high HLB has a high stability in the production of relatively large particles, and therefore a surfactant having an HLB of 8 to 12 is preferred. Specific examples of the surfactant include sorbitol fatty acid ester type, sorbitol fatty acid ester ether type, sorbitan fatty acid ester type, sorbitan fatty acid ester ether type and the like. Of these, sorbitan fatty acid ester and sorbitan fatty acid ester ethers are preferred surfactant systems. Accordingly, sorbitan monolaurate or oxyethylene sorbitan monostearate ether having an HLB of 8 to 12 is a specific example of a preferable surfactant. Most preferred is sorbitan monolaurate.

  The amount of the surfactant used is suitably in the range of 0.1 to 15% by weight, preferably 0.2 to 5% by weight, based on the monomer. Even if the amount used is too small, a stable emulsion state cannot be maintained, and even if it exceeds 15% by weight, the resulting good results cannot be obtained.

(Radical polymerizable crosslinking agent)
In the present invention, a crosslinked structure can be introduced into the interior using a radical polymerizable crosslinking agent in addition to the monofunctional unsaturated monomer in the polymerization. The radical polymerizable 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 compound, an internal cross-linked structure can be formed without using a radical polymerizable cross-linking agent.

  Examples of the radical polymerizable crosslinking agent include N, N-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and trimethylolpropane tri (meth) acrylate. , Trimethylolpropane di (meth) acrylate, glycerin (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triary Multiple in one molecule typified by lucyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane Compounds having an unsaturated bond, (poly) ethylene glycol diglycidyl ether, a compound having a plurality of epoxy groups in one molecule represented by glycerol diglycidyl ether, and glycidyl (meth) acrylate. These radical polymerizable crosslinking agents may be used alone or in combination of two or more.

(Compound capable of reacting with carboxyl group)
Examples of the compound containing two or more functional groups capable of reacting with a carboxyl group in the present invention include ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, (poly) glycerin polyglycidyl ether, diglycerin polyglycidyl ether, and propylene glycol. Glycidyl ether compounds such as diglycidyl ether; (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, penta Various polyhydric alcohols typified by lithitol, sorbitol, etc .; polyvalent amines such as ethylenediamine, diethylenediamine, polyethyleneimine, hexamethylenediamine; 2,2-bishydroxymethylbutanol-tris (3- (1-aziridinyl) Multivalent aziridine compounds such as propionate), 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,6-dimethyl-1,3-dioxolane-2- Various alkylene carbonate compounds typified by ON, various polyvalent aldehyde compounds typified by glyoxal, polyvalent oxazoline compounds typified by 2,4-tolylene diisocyanate, haloepoxy compounds typified by epichlorohydrin; zinc, calcium, Magnesium, al Such as multivalent ions, and the like represented by chloride or the like.

  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. The content of the carboxylic acid-reactive crosslinking agent in the polymerization raw material solution is a radical polymerizable monomer (unsaturated carboxylic acid ammonium, unsaturated carboxylic acid alkali metal salt, unsaturated carboxylic acid and other simple quantities). Body) and the radically polymerizable crosslinking agent in a total molar amount of 0 to 10 mol%. If the amount of the carboxylic acid-reactive crosslinking agent is too large, a hard gel is formed, and the absorption capacity is remarkably lowered.

Gel hardness can be adjusted with the combination of a radically polymerizable crosslinking agent and this carboxylic acid reactive crosslinking agent. Therefore, the radical polymerizable crosslinking agent is converted into a radical polymerizable monomer (unsaturated ammonium carboxylate, unsaturated carboxylic acid alkali metal salt, unsaturated carboxylic acid and other monomers) and the total molar amount of the radical polymerizable crosslinking agent. In the case of using a small amount in the range of 0.001 to 0.09 mol%, the carboxylic acid reactive crosslinking agent is preferably used in the range of 0.01 to 5 mol%, more preferably 0. The range is from 0.05 to 3 mol%.
Moreover, you may superpose | polymerize by adding a foaming agent, a chain transfer agent, 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)
Examples of the initiator used for radical polymerization in the production method of the present invention include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; hydrogen peroxide; cumene hydroperoxide, t-butyl hydroperoxide, Well-known initiators, such as organic peroxides, such as peracetic acid, are mentioned. When an oxidizing radical polymerization initiator is used, a reducing agent such as L-ascorbic acid or Rongalite may be used in combination.
Only one type of initiator may be used, or two or more types may be used in combination.

Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following examples.
(Water absorption performance measuring method; Tea bag method)
A water-absorbing resin A (g) (about 0.5 g) is uniformly placed in a non-woven tea bag bag (7 × 9 cm), and immersed in 500 cc of physiological saline at a liquid temperature of 25 ° C. until equilibrium swelling is reached. After a predetermined time, the tea bag type bag is pulled up and drained naturally for 10 minutes, and then the weight B (g) of the tea bag type bag is measured. The same operation as a blank is performed using only a tea bag type bag without adding a water-absorbing resin, and the weight C (g) is measured. The water absorption ratio is obtained from the following formula.
Water absorption magnification (g / g) = (B (g) -C (g)) / A (g)

[Production Example 1]
(Preparation of ammonium acrylate by hydrolysis of acrylonitrile)
Acrylonitrile was hydrolyzed according to the method of Example 4 by preparing a biocatalyst according to the method of Example 1 of Japanese Patent Application Laid-Open No. 2004-305062.

(Preparation of biocatalyst)
Acinetobacter sp. AK226 (FERM BP-08590) having nitrilase activity was added to 0.1% sodium chloride, 0.1% potassium dihydrogen phosphate, 0.05% magnesium sulfate heptahydrate, and iron sulfate heptahydrate. A medium prepared by adjusting pH = 7 to an aqueous solution containing 005%, manganese sulfate pentahydrate 0.005%, ammonium sulfate 0.1%, and potassium nitrate 0.1% (both by weight%). 5% by weight 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). Subsequently, 2.5% in a mixed solution of acrylamide, N, N′-methylenebisacrylamide, 5% N, N, N ′, N′-tetramethylethylenediamine aqueous solution, cell suspension, and 30 mM phosphate buffer. A potassium persulfate aqueous solution was mixed to obtain a heavy product. The final composition is 3% dry cell concentration, 52% 30 mM phosphate buffer (pH = 7), 18% acrylamide, 1% methylenebisacrylamide, 5% N, N, N ′, N′-tetramethylethylenediamine. An aqueous solution of 12% and a 2.5% potassium persulfate aqueous solution of 14% (both by weight) were used. The polymer was cut into about 1 × 3 × 3 mm square particles to obtain immobilized cells. The immobilized cells were washed with 30 mM phosphate buffer (pH = 7) to prepare an immobilized cell catalyst (hereinafter referred to as biocatalyst).

(Hydrolysis with biocatalyst)
Distilled water (400 g) was placed in an Erlenmeyer flask having an internal volume of 500 ml, and the above-mentioned biocatalyst (1 g) (corresponding to 0.03 g of dry cells) was placed in a wire mesh basket and set in the liquid, and sealed with a rubber stopper. Then, it was immersed in a constant temperature water tank, the internal temperature was kept at 20 degreeC, and it stirred with the stirrer.
Acrylonitrile was intermittently fed in an amount of 2% by weight (acrylonitrile concentration was controlled at 0.5% by weight or more), and an accumulation reaction of ammonium acrylate was carried out, and 30% by weight could be accumulated.
The obtained aqueous solution of ammonium acrylate was colorless and transparent. 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 30% by weight ammonium acrylate aqueous solution was obtained. To this aqueous solution, 200 ppm of methoxyquinone was added, and concentrated to 70% by weight under light-shielding reduced pressure, and used for polymerization.

[Example 1]
A special grade acrylic acid manufactured by Wako Pure Chemicals was distilled, 36 g of acrylic acid purified by removing the polymerization inhibitor was weighed into a 100 ml flask, and 36 g of 23.6% by weight ammonia water was added dropwise with stirring while cooling. 72 g of 100 mol% neutralized ammonium acrylate aqueous solution was produced. To this, 0.0368 g of ammonium persulfate dissolved in 0.5 g of water was added and dissolved by stirring.
In a 500-ml separable flask with a reflux condenser tube whose atmosphere was previously replaced with nitrogen, 180 g of cyclohexane and 0.36 g of sorbitan monolaurate as a surfactant were charged and dissolved by stirring at room temperature. The suspension was added and sufficiently stirred at 250 rpm while flowing nitrogen. Thereafter, the polymerization was started by putting a water bath at 45 ° C., and the mixture was held for 2 hours while maintaining the stirring speed at 250 rpm to obtain an emulsion containing a hydrous gel.
The produced hydrogel was recovered by filtration and recovered by vacuum drying at 100 ° C. The produced water-absorbent resin had an average particle size of 730 μm, and no particles having a size of 212 μm or less were generated. The water absorption ratio by the Tea bag method was 84.0 times.

[Example 2]
Polymerization was carried out under the same conditions as in [Example 1] except that 72 g of ammonium acrylate in [Example 1] was changed to 63.6 g of an aqueous ammonium acrylate solution in [Production Example 1].
The produced water-absorbent resin had an average particle diameter of 1 mm, and particles having a size of 212 μm or less were not generated. The water absorption by the Tea bag method was 101 times.

[Example 3]
A special grade acrylic acid made by Wako Pure Chemicals was distilled, 36 g of purified acrylic acid removed from the polymerization inhibitor was weighed into a 100 ml flask, and 27.5 g of 31 wt% aqueous ammonia was added dropwise with stirring while cooling. 63.5 g of 100 mol% neutralized ammonium acrylate aqueous solution was produced. To this, 0.0004 g of N, N′-methylenebisacrylamide dissolved in 0.2 g of water and 0.0368 g of ammonium persulfate dissolved in 0.3 g of water were added and dissolved by stirring.
In a 500-ml separable flask with a reflux condenser tube whose atmosphere was previously replaced with nitrogen, 180 g of cyclohexane and 0.36 g of sorbitan monopalmitate as a surfactant were charged and dissolved by stirring at room temperature. The suspension was added and sufficiently stirred at 250 rpm while flowing nitrogen. Thereafter, the polymerization was started by putting a water bath at 45 ° C., and the mixture was held for 2 hours while maintaining the stirring speed at 250 rpm to obtain an emulsion containing a hydrous gel.
The produced hydrogel was recovered by filtration and recovered by vacuum drying at 100 ° C. The produced water-absorbent resin had an average particle size of 650 μm, and only 2.1% by weight of particles having a size of 212 μm or less was generated. The water absorption ratio according to the Tea bag method was 88 times.

[Example 4]
Polymerization was carried out under the same conditions as in [Example 1] except that the surfactant in [Example 1] was changed to EO 3 mol adduct oxyethylene sorbitan monostearate ether.
The produced water-absorbent resin had an average particle size of 1.2 mm, and no particles having a size of 212 μm or less were generated. The water absorption ratio by the Tea bag method was 100 times.

[Example 5]
Polymerization was performed under the same conditions as in [Example 1] except that cyclohexane in [Example 1] was changed to cyclooctane.
The produced water-absorbent resin had an average particle size of 0.9 mm and no particles having a size of 212 μm or less were generated. The water absorption rate by the Tea bag method was 88.4 times.

[Example 6]
We distilled special grade acrylic acid manufactured by Wako Pure Chemicals, removed the polymerization inhibitor and weighed 36 g of purified acrylic acid into a 100 ml flask, dropped 23.5 g of 36 wt% ammonia water with stirring while cooling, 59.5 g of 100 mol% neutralized ammonium acrylate aqueous solution was produced. To this, 0.0368 g of ammonium persulfate dissolved in 0.5 g of water was added and dissolved by stirring.
In a 500-ml separable flask with a reflux condenser tube whose atmosphere was previously replaced with nitrogen, 180 g of cyclohexane and 0.36 g of sorbitan monopalmitate as a surfactant were charged and dissolved by stirring at room temperature. The suspension was added and sufficiently stirred at 250 rpm while flowing nitrogen. Thereafter, the polymerization was started by putting a water bath at 45 ° C., and the mixture was held for 2 hours while maintaining the stirring speed at 250 rpm to obtain an emulsion containing a hydrous gel.
The produced hydrogel was recovered by filtration and recovered by vacuum drying at 100 ° C. The produced water-absorbent resin had an average particle diameter of 700 μm, and particles of 212 μm or less were only 1.3% by weight. The water absorption ratio according to the Tea bag method was 93 times.

[Comparative Example 1]
Wako Pure Chemicals special grade acrylic acid was distilled, 12 g of purified acrylic acid removed from the polymerization inhibitor was weighed into a 100 ml flask, and 12 g of 23.6 wt% ammonia water was added dropwise with stirring while cooling. 50.2 g was added to produce 74.2 g of a 100 mol% neutralized ammonium acrylate aqueous solution. To this, 0.04 g of N, N′-methylenebisacrylamide dissolved in 0.2 g of water and 0.0122 g of ammonium persulfate dissolved in 0.3 g of water were added and dissolved by stirring.
In a 500-ml separable flask with a reflux condenser tube whose atmosphere was previously replaced with nitrogen, 180 g of cyclohexane and 0.12 g of sorbitan monolaurate as a surfactant were added and dissolved by stirring at room temperature. The suspension was added and sufficiently stirred at 250 rpm while flowing nitrogen. Thereafter, a water bath at 60 ° C. was started to initiate polymerization, and the mixture was held for 2 hours while maintaining the stirring speed at 250 rpm, to obtain an emulsion containing a hydrous gel.
The produced hydrogel was recovered by filtration and recovered by vacuum drying at 100 ° C. The produced water-absorbent resin had an average particle size of 489 μm, and 6% by weight of particles having a size of 212 μm or less were generated. The water absorption magnification by the Tea bag method was 52.8 times.

[Comparative Example 2]
We distilled special grade acrylic acid manufactured by Wako Pure Chemicals, removed the polymerization inhibitor and weighed 36 g of purified acrylic acid into a 100 ml flask, dropped 23.5 g of 36 wt% ammonia water with stirring while cooling, 59.5 g of 100 mol% neutralized ammonium acrylate aqueous solution was produced. To this, 0.0368 g of ammonium persulfate dissolved in 0.5 g of water was added and dissolved by stirring.
In a 500-ml separable flask with a reflux condenser tube whose atmosphere was previously replaced with nitrogen, 180 g of cyclohexane and 0.36 g of sorbitan tristearate as a surfactant were charged and dissolved by stirring at room temperature. The suspension was added and sufficiently stirred at 250 rpm while flowing nitrogen. Thereafter, polymerization was started with a 55 ° C. water bath, but the water phase portions were united immediately and mass polymerization occurred, and a stable emulsion could not be obtained.

[Comparative Example 3]
Wako Pure Chemical's special grade acrylic acid was distilled, 12 g of purified acrylic acid removed from the polymerization inhibitor was weighed into a 100 ml flask, and 24.7 g of 18.9% by weight sodium hydroxide aqueous solution was added with stirring while cooling. The solution was added dropwise to produce 36.7 g of a 70 mol% neutralized sodium acrylate aqueous solution. To this, 0.04 g of N, N′-methylenebisacrylamide dissolved in 0.2 g of water and 0.0122 g of ammonium persulfate dissolved in 0.3 g of water were added and dissolved by stirring.
In a 500-ml separable flask with a reflux condenser tube whose atmosphere was previously replaced with nitrogen, 180 g of cyclohexane and 0.12 g of sorbitan monolaurate as a surfactant were charged and dissolved by stirring at room temperature. The suspension was added and sufficiently stirred at 250 rpm while flowing nitrogen. Thereafter, a water bath at 60 ° C. was started to initiate polymerization, and the mixture was held for 2 hours while maintaining the stirring speed at 250 rpm, to obtain an emulsion containing a hydrous gel.
The produced hydrogel was recovered by filtration and recovered by vacuum drying at 100 ° C. The produced water-absorbent resin had an average particle size of 389 μm, and 15% by weight of particles having a size of 212 μm or less was generated. The water absorption ratio by the Tea bag method was 55.3 times.

  In Comparative Example 1, the monomer concentration of the aqueous monomer solution is 19.9% by weight, which is less than the monomer concentration defined in the present invention, 40% by weight. In Comparative Example 2, the surfactant HLB is 2. 1 and outside the range of HLB4.5 to 12 specified in the present invention, and since Comparative Example 3 does not use unsaturated ammonium carboxylate as a monomer, it is compared with those of Examples. The water absorption ratio was low or a water absorbent resin could not be obtained.

  The method for producing a water-absorbing resin of the present invention is a method for producing a water-absorbing resin having a high water-absorbing ratio that can exhibit a sufficient water-absorbing ability even when used in an absorbent body such as a sanitary product, or a small amount of fine powder. The water-absorbing agent can be suitably used in the field of producing a water-absorbing resin having a spherical shape and a large particle diameter, which makes it easy to optimally arrange the absorptive resin for obtaining the best water-absorbing performance.

Claims (7)

A method for producing an absorptive resin, characterized in that an absorptive resin is obtained by polymerizing an aqueous monomer solution containing an unsaturated ammonium carboxylate under conditions satisfying the following requirements (1) to (4).
(1) The proportion of unsaturated ammonium carboxylate with respect to 100 mol% of the radically polymerizable monomer component in the monomer aqueous solution is 50 mol% or more.
(2) The monomer concentration of the aqueous monomer solution exceeds 40% by weight.
(3) Use a nonionic surfactant of HLB4.5-12.
(4) Use reverse phase suspension polymerization in which polymerization is suspended in an organic solvent.   The method for producing an absorbent resin according to claim 1, wherein the surfactant is a sorbitan fatty acid ester.   The method for producing an absorbent resin according to claim 1, wherein the surfactant is sorbitan monolaurate.   The said organic solvent is an aliphatic hydrocarbon, The manufacturing method of the absorptive resin in any one of Claims 1-3 characterized by the above-mentioned.   The method for producing an absorbent resin according to claim 4, wherein the aliphatic hydrocarbon solvent is cyclohexane.   The absorbency according to any one of claims 1 to 5, wherein the ratio of unsaturated ammonium carboxylate to 100 mol% of the radical polymerizable monomer component in the monomer aqueous solution is 95 to 100 mol%. Manufacturing method of resin.   The method for producing an absorbent resin according to claim 1, wherein the unsaturated ammonium carboxylate is ammonium (meth) acrylate.