JPH02284902A - Production of moisture-absorbing resin fine particles - Google Patents

Abstract

PURPOSE:To obtain the title fine particles of high dispersion and high water absorption speed by adding under stirring an inert hydrophobic organic solvent containing a dispersant to an aqueous solution of a water soluble monomer to form an oil-in-water type suspension, then reversing it into the water-in-oil type suspension and polymerizing the monomer. CONSTITUTION:A polymerization-inert hydrophobic organic solvent such as cyclohexane containing a dispersant such as sorbitan monostearate is added under stirring to an aqueous solution of a water-soluble ethylenically unsaturated monomer such as sodium acrylate to form an oil-in-water type suspension. Additionally, the hydrophobic solvent is added to cause phase reversion into the water-in-oil type suspension. The suspension is heated up to 60 deg.C to polymerize the monomer whereby the subject fine particles of a water-absorption resin is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing water-absorbing resin fine particles. More specifically, the present invention relates to a method for efficiently producing particulate water-absorbing resin that has excellent dispersibility and water absorption speed during various processing operations without going through complicated steps.

(Conventional technology) In recent years, water-absorbing resins that absorb tens to hundreds of times their own weight in water have been developed, and are used as absorbents for sanitary products and disposable diapers, as water retention agents for agriculture and horticulture, and for sludge removal. It is being developed for use as a coagulant, anti-condensation agent for building materials, water stopper for civil engineering, desiccant, etc.

Examples of such water-absorbing resins include, for example, hydrolysates of starch-acrylonitrile graft polymers (Japanese Patent Publication No. 4
9-43395), neutralized product of starch acrylic acid graft polymer (JP-A-51125468), saponified product of vinyl acetate-acrylic acid ester copolymer (JP-A-52
-14689), hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (Japanese Patent Publication No. 5315
No. 959), crosslinked products thereof, and partially neutralized polyacrylic acid crosslinked products (Japanese Patent Application Laid-open No. 84304/1983) are known.

In addition, many technologies have been developed to mix water-absorbing resins with rubber or soft resins such as polyurethane to impart water-swelling and hygroscopic properties to rubber and soft resins, thereby producing water-stopping materials and anti-condensation materials. There is.

Therefore, in order to improve the dispersibility and uniform mixing properties of water-absorbing resins into base materials such as rubber and soft resins, and the water absorption of the resulting water-stopping materials and anti-condensation materials, Efforts have been made to make the particle size of water absorbent resin as fine as possible.

As a method for efficiently obtaining a water-absorbing resin with a relatively small particle size, a method of reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer that forms a water-absorbing resin by polymerization in a hydrophobic organic solvent (e.g. JP-A No. 53-46389) has been proposed. However, in this method, the particle size is usually 50
Only a water-absorbing resin with a thickness of about 1,000 μm was obtained, and the above-mentioned problems when mixing a water-absorbing resin with a base material could not be solved.

Therefore, the practice has been to re-pulverize water-absorbing resins having a particle size of about 50 to 1000 μm and classify the fine particles before use. However, such a method is economically and industrially disadvantageous considering the cost required for pulverization and the yield of classification.

Therefore, as a method to solve these problems, a hydrophobic car end body that forms a polymer that becomes a water-absorbing resin by saponification is suspended in water, and a powerful A method of obtaining microparticles of water-absorbing resin by carrying out immersion and suspension polymerization in which the droplet size of the monomer is adjusted to a desired size using shearing force, and saponifying the obtained polymer (a special method). 63-186751) has been proposed. However, this method requires careful control of the mechanical shearing force using a homomixer, etc. in order to obtain fine particles of about 10 μm, and the operation is complicated, so the method is still unsatisfactory from a process standpoint. Moreover, there are also limitations on the hydrophobic monomers that can be used, making it difficult to obtain water-absorbing resin fine particles with sufficient water-absorbing properties.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems when mixing a water-absorbing resin with a base material.

Therefore, an object of the present invention is to produce fine water-absorbing resin microparticles with an average particle diameter of several micrometers, which are excellent in dispersibility and uniform mixing properties in a substrate, with a simple operation and in good yield.

(Means and effects for solving the problem) As a result of extensive research in view of the above circumstances, the present inventors have discovered that when producing a water-absorbing resin using a reversed-phase suspension polymerization method, a hydrophobic resin containing a dispersant is prepared in advance. By adding an organic solvent to an aqueous solution of a water-soluble ethylenically unsaturated monomer to form an oil-in-water suspension, and then adding a hydrophobic organic solvent to perform phase inversion, the particle size can be adjusted. The present inventors have discovered that water-absorbing resin fine particles with a narrow distribution have very little adhesion to the side walls of a reactor, are stable, and can be easily obtained industrially, and have completed the present invention.

That is, in the present invention, a polymerization-inactive hydrophobic paid solvent containing a dispersant is added to an aqueous solution of a water-soluble ethylenically unsaturated monohung material under stirring to form an oil-in-water suspension. Subsequently, the oil-in-water suspension is phase inverted to a water-in-oil suspension,
The present invention relates to a method for producing water-absorbing resin fine particles, which comprises polymerizing the monomer in a suspended state.

The water-soluble ethylenically unsaturated monomer used in the present invention is not particularly limited as long as it is a water-soluble monomer that forms a water-absorbing resin by polymerization, such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) Maleic acid, fumaric acid, itaconic acid, 2-(meth)acryloylethanesulfonic acid, 2
-(meth)acryloylpropanesulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid,
Anionic monobases such as vinyl sulfonic acid, styrene sulfonic acid, etc. and their salts: N,N-dimethylaminoethyl (
meth)acrylate, N,N-dimethylaminepropyl(meth)acrylate, N.

Cationic monomers such as N-dimethylaminopropyl (meth)acrylamide and their quaternized products: (meth)acrylamide, N-substituted (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl ( Examples include nonionic parent wood group-containing monolayers such as meth)acrylate, polyethylene glycol mono(meth)acrylate, meth-hexypolyethylene glycol(meth)acrylate-1 and the like, and one or two of these The above can be used. Among them, acrylic acid, methacrylic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, and salts thereof, N,N-dimethylaminoethyl (meth)acrylate and its quaternary compound,
One or more selected from the group consisting of methoxypolyethylene glycol (meth)acrylate and (meth)acrylamide are preferred.

In addition, when obtaining a water-absorbing resin in the present invention, the water-soluble monomer may be polymerized without using a cross-linking agent to obtain a self-crosslinking type water-absorbing resin, or it may be polymerized in the presence of a cross-linking agent. A water-absorbing resin may also be obtained.

Examples of such crosslinking agents include compounds that have two or more reactive functional groups or polymerizable unsaturated groups in the molecule that can react with the functional groups of the water-soluble ethylenically unsaturated single prisoner. , N'-methylenebis(meth)acrylamide, N
- Methylol (meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, glycerin di(meth)acrylate, (meth)acrylic acid polyhydric Metal salts, trimedylolpropane tri(meth)acrylate, triallylamine, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, glycidyl (meth)acrylate, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl Examples include ether, polyethylene glycol diglycidyl ether, etc. One or two of these
More than one species can be used.

Further, the amount of the crosslinking agent used is generally preferably about 0.001 to 5 mol% based on the water-soluble ethylenically unsaturated monomer.

The concentration of the water-soluble ethylenically unsaturated monomer aqueous solution is preferably in the range of 30% by weight to saturated concentration in terms of industrial productivity. If the i11 degree is lower than 30% by weight, the productivity per unit reaction volume will decrease and the drying process will take a long time, which is not preferred from an industrial standpoint.

In the present invention, a conventionally known water-soluble polymerization initiator is used to form a water-absorbing resin by polymerizing the water-soluble ethylenically unsaturated 11H). The monomer may be dissolved in advance in an aqueous solution, or a hydrophobic organic solvent may be added to the monomer aqueous solution (9) and added to an oil-in-water suspension. Good too.

As the water-soluble polymerization initiator, any one commonly used in the field can be used without restriction, such as persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; hydrogen peroxide, t-butylhydrochloride, etc. Hydroperoxides such as peroxide and cumene hydroperoxide; azo compounds such as 2°2'-azobis-2-amidinopropane dihydrochloride; and the like. These polymerization initiators can be used as a mixture of two or more, and can also be used as a redox initiator in combination with a reducing agent such as sulfite, 1-ascorbic acid, or ferric salt. Good too.

Further, in the present invention, a surfactant may be dissolved or dispersed and contained in the water-soluble ethylenically unsaturated monohung body aqueous solution, if necessary. By including this surfactant in the monomer aqueous solution, the phase inversion accompanying the addition of the hydrophobic organic solvent may occur more uniformly, resulting in a narrower particle size distribution of the final water absorbent resin. be.

Examples of these surfactants include nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, polyoxyethylene acyl ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and sucrose fatty acid ester. or anionic surfactants such as higher alcohol sulfate ester salts, alkylnaphthalene sulfonates, alkyl polyoxyethylene sulfate salts, and dialkyl sulfosuccinates. . Among these, nonionic surfactants or anionic surfactants with an HLB of 8 or more are preferred.

In the present invention, examples of the dispersant used by dissolving or dispersing in a hydrophobic organic solvent include nonionic surfactants such as sorbitan fatty acid ester, glycerin fatty acid ester, sucrose fatty acid ester, and polyglycerin fatty acid ester; cellulose ester; , cellulose derivatives such as cellulose ether; carboxyl group-containing polymers such as copolymers of α-olefin and maleic anhydride or derivatives thereof; one or more of these may be used. I can do it. Depending on the type of dispersant used, a double emulsion etc. may be formed and phase inversion may not be performed uniformly, but nonionic surfactants with an HLB of 2 to 7, and more preferably sorbitan fatty acid esters with an HLB of 2 to 7, are preferred. This is desirable because there is no such concern and a water-absorbing resin with a smaller particle size can be obtained.

The amount of dispersant used is generally 0.05 to 10% by weight, preferably 0.5 to 5% by weight based on the water-soluble ethylenically unsaturated monomer.
Weight%.

The hydrophobic organic solvent used in the present invention is not particularly limited as long as it is immiscible with the aqueous monomer solution and forms two phases, such as n-pentane, n-hexane, n-hebutane, n- Aliphatic hydrocarbons such as octane; alicyclic hydrocarbons that may have substituents such as cyclohexane, cyclooctane, methylcyclohexane, and decalin; benzene,
Examples include aromatic hydrocarbons which may have substituents such as ethylbenzene, toluene, and xylene, and one type or a mixture of two or more of these can be used. Particularly preferred are n-hexane, n-hebutane, cyclohexane, methylcyclohexane, toluene or xylene.

In the present invention, by adding a hydrophobic organic solvent containing a dispersant to a water-soluble ethylenically unsaturated monomer aqueous solution while stirring, an oil-in-water type in which a hydrophobic organic solvent is suspended in a monomer aqueous solution is produced. A suspension is first formed and then an aqueous monomer solution in an organic solvent is subsequently formed from the oil-in-water suspension! ! A phase inversion occurs to a cloudy water-in-oil suspension.

Through such phase inversion, uniform and fine droplets of the monomer aqueous solution are stably formed. in this case,
By selecting the type of dispersant, suspension, and stirring conditions, the average particle size and particle size distribution of the droplets can be controlled to a desired value. In particular, in order to uniformly perform phase inversion, the ratio of the hydrophobic organic solvent to the monomer aqueous solution is 3:2 to 4:
Uniformity is preferred. Further, after the phase inversion is completed, a dispersant or a hydrophobic organic solvent may be newly added.

In the present invention, after phase inversion, the monomer polymerization is completed in a suspended state by heating in the same manner as in normal reversed-phase suspension polymerization, and a drying process such as azeotropic dehydration is then carried out. After that, the water-absorbing resin can be taken out as primary fine particles without agglomeration.

The water-absorbing resin fine particles thus obtained have an average particle diameter of 30 μm or less, preferably 1 μm or less, although this varies depending on the type of dispersant used during phase inversion and the stirring conditions during suspension or phase inversion.
They are very fine particles with a diameter of less than 0μ, and their particle size distribution is also narrow.

Furthermore, the water-absorbing resin fine particles obtained in this way are
The surface portion can be crosslinked by a known method to prevent the formation of mako and to slow down the water absorption rate, and it can also be dispersed in a specific solvent and used as a slurry of water absorbent resin.

(Effects of the Invention) The water-absorbing resin fine particles thus obtained by the production method of the present invention have a much finer particle size than conventional ones, and a very narrow particle size distribution. Therefore,
When composited with base materials such as rubber, plastic, paint vehicles, etc., the dispersibility in the base material is good, and the water absorption rate of products such as water stop materials obtained by composite can be high.

Furthermore, according to the present invention, water-absorbing resin can be stably obtained as primary fine particles without agglomeration without any complicated operations such as mechanical crushing or classification, and moreover, it is possible to obtain the water-absorbing resin stably as primary fine particles without any agglomeration, and moreover, it does not adhere to the side wall of the reaction vessel during polymerization. Kimono is hardly seen, and water-absorbing resin fine particles can be produced very economically and industrially efficiently.

(Examples) Hereinafter, the present invention will be explained in detail with reference to Examples, but the scope of the present invention is not limited only to these Examples.

In addition, the average particle size and particle size distribution of the obtained water absorbent resin were determined using a Shimadzu laser diffraction particle size distribution analyzer.

Example 1 84.6 g of sodium acrylate, 21.6 g of acrylic acid (1 and N, N, '-methylenebisacrylamide 0.0
An aqueous solution prepared by dissolving 74 g of a monomer mixture in 197 g of ion-exchanged water was charged, and polyoxyethylene nonylphenyl ether (HL, B) was added as a surfactant.
= 12.3) 0.5q and 0.16 potassium persulfate as polymerization initiator! After adding J and dissolving it, nitrogen gas was blown in to drive out dissolved oxygen.

Take cyclohexane 11 in another flask and add sorbitan monostearate (HLB=4.
7) After dissolving 4.20 and blowing nitrogen gas to drive out dissolved oxygen, this was charged into a dropping funnel.

By dropping 60 ml of the cyclohexane solution in the dropping funnel into the four separable flasks with stirring at 23 Orpm, the cyclohexane solution was dispersed in the monomer aqueous solution to obtain an oil-in-water suspension. . Further, the cyclohexane solution was continued to be added, and around the time when 300- was added dropwise, a phase inversion occurred and a water-in-oil suspension was obtained.

After the cyclohexane solution was completely added, the bath temperature was raised to 60°C to start the polymerization reaction, and this temperature was maintained for 2 hours to complete the polymerization.

After the completion of polymerization, the water in the hydrous gel was distilled off by azeotropic dehydration with cyclohexane, and then dried under reduced pressure at 80°C to obtain water-absorbing resin fine particles (1) with an average particle size of 6.3 μm and a particle size distribution of 1 to 15 μm. I got it. Note that no deposits were observed on the side walls of the four-loaf flask.

Example 2 In Example 1, the dispersant sorbitan monostearate was replaced with simi sugar fatty acid ester (HL B, =6.0)4
．． 0! The same operation was performed except that I+ was used to obtain water-absorbing resin fine particles (2) having an average particle diameter of 10.3 μm and a particle size distribution of 3 to 25 μm. Note that no deposits were observed on the side walls of the four-loaf flask.

Example 3 In Example 1, the surfactant polyethylene nonyl phenyl ether was not added to the monomer aqueous solution.
Water-absorbing resin fine particles (3) of 25 μm were obtained. In addition, a slight amount of deposit was observed on the side wall of the four-loaf flask.

Comparative Example 1 Cyclohexane 11 was placed in a 21 four-piece separable flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube, and a dropping funnel, and sorbitan monostearate (HLB = 4) was added there as a dispersant. .7) 4.2
a was dissolved and nitrogen gas was blown into the solution to drive out the dissolved oxygen.

In another flask, take an aqueous solution of a monomer mixture consisting of 84.6 Q of sodium acrylate, 21.6 CI of acrylic acid, and 0.0741 J of N,N'-methylenebisacrylamide dissolved in 197 g of ion-exchanged water. After adding and dissolving polyoxyethylene nonylphenyl ether <HLB=12.3) 0,5a as a surfactant and potassium persulfate 0.16111, nitrogen gas was blown into the aqueous solution to eliminate the oxygen dissolved in the aqueous solution. chased out.

Next, by dropping the monomer aqueous solution in this flask from the dropping funnel into the separable flask at 230 rOIIl with stirring, the monomer aqueous solution is dispersed in the cyclohexane solution without going through an oil-in-water suspension. A water-in-oil suspension was obtained.

After dropping the entire amount of the aqueous solution of Monoshuite, the bath temperature was raised to 60° C. to initiate the polymerization reaction, and this humidity was maintained for 2 hours to complete the polymerization.

After the completion of polymerization, the water in the hydrous gel was distilled off by azeotropic dehydration with cyclohexane, and then dried under reduced pressure at 80°C to obtain comparative water-absorbing resin particles (1) with an average particle size of 63 μm and a particle size distribution of 6 to 150 μm. Obtained. In addition, deposits were observed on the side walls of the four-loaf flask.

Comparative Example 2 In Comparative Example 1, the dispersant sorbitan monostearate was mixed with sucrose fatty acid ester (HLB=6.0) 4.0 (
], except that the average particle size was 85 μm.
Comparative water absorbent resin particles (2) having a particle size distribution of 15 to 200 μm were obtained. In addition, some deposits were observed on the side wall of the four-loaf flask.

Comparative Example 3 The same operation as in Comparative Example 1 was performed except that polyoxyethylene nonylphenyl ether was not added to the monomer aqueous solution, and the average particle size was 80 μm and the particle size distribution was 20 to 150.
Comparative water absorbent resin particles (3) of μm were obtained. In addition, deposits were observed on the side walls of the four-loaf flask.

Example 4 Into the same four-loaf flask as used in Example 1 was added 129.6 kg of the sodium salt of 2-sulfoethyl methacrylate. J.
Acrylic acid 2.2 (1, sodium acrylate 11.3
0 and polyethylene glycol diacrylate 0.0
An aqueous solution of 58 g of a monomer mixture dissolved in 180 g of ion-exchanged water was charged, and polyoxyethylene sorbitan monostearate (HL B) was added as a surfactant.
= 9.6) 0.9 g and 0.9 g of 2-2'-azobis-2-aminodibroban hydrochloride as a polymerization initiator.
After adding and dissolving 22a, nitrogen gas was blown in to drive out dissolved oxygen.

Using the single solid aqueous solution thus obtained and the cyclohexane solution prepared in the same manner as in Example 1, the operations of phase inversion, polymerization, azeotropic dehydration, and vacuum drying were performed in the same manner as in Example 1. , average particle size 3.1 μm, particle size distribution 1-6
Water-absorbing resin fine particles (4) of μm in size were obtained. Note that no deposits were observed on the side walls of the four-loaf flask.

Example 5 The same operation as in Example 4 was carried out except that the surfactant polyoxyethylene sorbitan monostearate was not added to the monomer aqueous solution, and the average particle size was 4.5.
Water-absorbing resin fine particles with a particle size distribution of 1 to 10 μm (μm)
5) was obtained. In addition, a slight amount of deposit was observed on the side wall of the fourth flask.

Claims (1)

[Claims] 1. A polymerization-inactive hydrophobic organic solvent containing a dispersant is added to an aqueous solution of a water-soluble ethylenically unsaturated monomer under stirring to form an oil-in-water suspension. A method for producing water-absorbing resin microparticles, which comprises subsequently performing phase inversion from an oil-in-water suspension to a water-in-oil suspension, and polymerizing the monomers in a suspended state. 2. The method for producing water-absorbing resin fine particles according to claim 1, wherein the dispersant is a nonionic surfactant with an HLB of 2 to 7. 3. The method for producing water-absorbing resin fine particles according to claim 2, wherein the nonionic surfactant is a sorbitan fatty acid ester. 4. The method for producing water-absorbing resin fine particles according to claim 1, wherein the aqueous solution of the water-soluble ethylenically unsaturated monomer contains a surfactant. 5. The method for producing water-absorbing resin fine particles according to claim 4, wherein the surfactant is a nonionic surfactant or anionic surfactant with an HLB of 8 or higher. 6. The method for producing water-absorbing resin fine particles according to any one of claims 1 to 5, wherein the monomer concentration of the water-soluble ethylenically unsaturated monomer aqueous solution is in the range of 30% by weight to saturated concentration.