JPH10251309A - Production of water-absorbing resin having high water-absorbing rate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject resin having high water-absorption rate, enabling easy drying and requiring little load in crushing by copolymerizing an aqueous monomer solution having high viscosity and containing a mixture of a water-soluble unsaturated monomer and a crosslinking monomer in a state containing dispersed bubbles in the solution. SOLUTION: An aqueous solution of a monomer having a viscosity of >=10cp and containing a mixture of a water-soluble unsaturated monomer such as (meth)acrylic acid and a crosslinking monomer such as ethylene glycol di(meth) acrylate is preferably incorporated with a surfactant. An inert gas is introduced into the solution and the mixture is copolymerized in a state containing the dispersed bubbles of the gas, preferably in a state to give the bubble-dispersed monomer solution having a volume corresponding to >=1.02 times the volume of the non-dispersed solution. The objective resin obtained by this process is suitable for various uses necessitating water-absorption and water-retention, e.g. a sanitary material field such as sanitary goods and paper diaper, an agricultural and horticultural field, a food field for keeping freshness and an industrial field such as condensation preventing agent and cold-reserving agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a water-absorbing resin having a high water absorption rate. To elaborate,
The present invention relates to a method for producing a water-absorbent resin which has a high absorption rate under no pressure and under pressure, is easy to dry, and has a small load during pulverization.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been developed which absorb water tens to hundreds of times as much as their own weight. Various water-absorbing resins have been used for applications requiring water absorption and water retention, such as in the field, industrial fields such as dew condensation prevention and cooling materials.

[0003] As such a water-absorbing resin, for example,
Hydrolyzate of starch-acrylonitrile graft polymer (JP-B-49-43395) and neutralized product of starch-acrylic acid graft polymer (JP-A-51-125468)
No.), saponified vinyl acetate-acrylate copolymer (JP-A-52-14689), hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (JP-B-53-15959), or a mixture thereof. Cross-linked product, self-cross-linked sodium polyacrylate obtained by reverse phase suspension polymerization (JP-A-53-46389), cross-linked polyacrylic acid partially neutralized product (JP-A-55-84304)
No.) etc. are known.

The performance required of the water-absorbent resin differs depending on the application to be used, but the desired properties of the water-absorbent resin for sanitary materials include an absorption capacity under high pressure when in contact with an aqueous liquid. , Fast absorption rate, large liquid permeability and the like. However, the relationship between these properties does not always show a positive correlation, and it has been difficult to improve these properties at the same time.

[0005] As an attempt to increase the absorption rate of a water-absorbing resin, for example, in order to increase the surface area, an attempt has been made to reduce the particle size, granulate or scaly. However, in general, when the water-absorbent resin is formed to have a small particle size, the water-absorbent resin particles form so-called "mamako" upon contact with the aqueous liquid, and the absorption rate is reduced. When the water-absorbent resin is formed in the granulated material, a phenomenon occurs in which the granulated material itself changes into a “mamako” state by contact with the aqueous liquid, and the absorption rate is rather reduced. When the water-absorbent resin is formed into flakes, the absorption rate is improved, but the absorption rate is not sufficient to induce gel blocking. The resulting water-absorbent resins are necessarily bulky and uneconomical because they require larger transportation and storage facilities.

Further, a technique has been proposed in which molecular chains near the surface of the water-absorbent resin are cross-linked to increase the cross-linking density of the surface layer, thereby preventing generation of mamako and improving the absorption rate. Such a technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 57-44627.
No., JP-A-58-42602, JP-B-60-1869.
0, JP-A-58-180233, JP-A-59-62
665 and JP-A-61-16903. These techniques have provided some improvement in absorption rates. However, these water-absorbent resins actually contain a considerable proportion of fine powder finer than the desired optimum particle size. Therefore, even when such a water-absorbent resin is used, a sufficient absorption rate cannot be obtained, and a decrease in liquid permeability due to gel blocking occurs.

In the improvement of the water absorption rate by a foaming agent, which is a method of forming bubbles inside by the thermal decomposition, foaming starts due to the heat of polymerization generated by the polymerization. Difficult, the quality of the obtained polymer is not uniform, especially the amount of water-soluble component is large, the pore size of the obtained foam and its distribution are not stable, and therefore the control of the water absorption rate is insufficient. There was such a problem.

In the method using an azo-based polymerization initiator, it is necessary to increase the amount of the initiator in order to form a sufficient amount of air bubbles to improve the water absorption rate. The amount of the soluble component tended to increase. Also, the method using an azo-based polymerization initiator also has a problem that the volume change during polymerization is large as in the case of using a foaming agent, so that it is not easy to control the pore diameter and distribution thereof.

In the method in which the polymerization is carried out under the dispersion of a water-insoluble blowing agent such as a volatile organic compound, the polymerization can be carried out relatively stably. However, since the volatile organic compound is used, a special method is required from the viewpoint of safety. Requires a polymerization unit,
Further, the used volatile organic compounds are exhausted out of the system, so that they are wasteful in terms of energy and costly, so that they are not practical.

However, these water-absorbing resins have insufficient water absorption rates under no pressure and under pressure, are difficult to dry, and have a large load at the time of pulverization.
In addition, there is a problem that the pore size is not uniform and the water-soluble component of the water-absorbent resin is large.

On the other hand, according to the method of the present invention, the pore size and the distribution of the cell pores of the foam are uniform, so that the water absorption rate under no pressure and under pressure is high, drying is easy, and the load during pulverization is small. It has become possible to provide a method for producing a conductive resin.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a water-absorbing resin having a high water absorption rate.

Another object of the present invention is to provide a method for producing a water-absorbent resin which has a high water absorption rate under no pressure and under pressure, is easy to dry, and has a small load during pulverization.

Still another object of the present invention is to provide a method for producing a water-absorbing resin having a large water absorption and a small water-soluble component content of the water-absorbing resin.

[0015]

The above object is achieved by the following (1).
(9) is achieved.

(1) In a state where bubbles of an inert gas are dispersed in an aqueous monomer solution having a viscosity of 10 cP or more containing a mixture of a water-soluble unsaturated monomer and a crosslinkable monomer, the mixture is copolymerized. A method for producing a water-absorbent resin having a high water absorption rate, wherein

(2) The water-absorbent resin according to (1), wherein the volume of the aqueous monomer solution in which the inert gas bubbles are dispersed is at least 1.02 times the volume of the non-dispersed state. Production method.

(3) The method for producing a water-absorbing resin having a high water absorption rate according to the above (1) or (2), wherein the aqueous monomer solution contains a surfactant.

(4) The amount according to (3), wherein the amount of the surfactant is 0.0001 to 10 parts by weight per 100 parts by weight of the total amount of the water-soluble unsaturated monomer and the crosslinkable monomer. Water absorption rate A method for producing a water absorbent resin.

(5) The method according to any one of (1) to (4) above, wherein the volume of the aqueous monomer solution in which the inert gas bubbles are dispersed is 1.08 times or more the volume of the non-dispersed state. High water absorption rate Production method of water absorbent resin.

(6) The dispersion of bubbles is carried out by introducing an inert gas into an aqueous solution as described in (1) to (5) above.
The method for producing a water-absorbent resin having a high water absorption rate according to any one of the above.

(7) The method for producing a water-absorbent resin having a high water absorption rate according to any one of the above (1) to (6), wherein the dispersion of the bubbles is carried out by high-speed strong stirring of the aqueous solution.

(8) The bubbles are dispersed by adding a foaming agent to an aqueous solution before polymerization.
(7) The method for producing a high water absorption rate water absorbent resin according to any one of (7).

(9) A method for producing a water-absorbing resin having a high water-absorbing rate, wherein the water-absorbing resin according to any one of (1) to (8) is further treated with a surface crosslinking agent.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method for dispersing an inert gas bubble in an aqueous monomer solution having a viscosity of 10 cP or more containing a mixture of a water-soluble unsaturated monomer and a crosslinking monomer.
A method for producing a superabsorbent resin, comprising copolymerizing the mixture.

Examples of these water-soluble unsaturated monomers include (meth) acrylic acid, (anhydride) maleic acid, fumaric acid, crotonic acid, itaconic acid, 2- (meth) acryloylethanesulfonic acid, (Meth) acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid, and other anionic monomers and salts thereof; (meth) acrylamide, N-substituted ( Meth) acrylamide, 2-
Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, N-vinylpyrrolidone,
Nonionic hydrophilic group-containing monomers such as N-vinylacetamide; N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) Specific examples include amino group-containing unsaturated monomers such as acrylamide, and quaternized products thereof. In addition, in an amount that does not extremely impair the hydrophilicity of the obtained polymer, for example, acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, vinyl acetate, and propionic acid A hydrophobic monomer such as vinyl may be used. One or more of these can be selected and used as the monomer component. However, considering the water absorption properties of the finally obtained water absorbing material, (meth) acrylic acid (salt), 2- (meth) acryloylethanesulfonic acid (salt), 2- (meth) acrylamido-2-methylpropanesulfonic acid (salt),
One or more selected from the group consisting of (meth) acrylamide, methoxypolyethylene glycol (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate or a quaternary compound thereof are preferable, and (meth) acrylic acid (salt Is more preferable. In this case, 30 to 90 mol% of (meth) acrylic acid
Is most preferably neutralized with a basic substance.

Examples of the crosslinkable monomer include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, and polyethylene glycol di (meth) acrylate. )
Acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate,
Pentaerythritol tetra (meth) acrylate,
There are two ethylenically unsaturated groups in one molecule such as N, N'-methylenebis (meth) acrylamide, triallyl isocyanurate, trimethylolpropanedi (meth) allyl ether, triallylamine, tetraallyloxyethane, glycerolpropoxytriacrylate and the like. Compounds having at least one compound; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, 1,
4-butanediol, 1,5-pentanediol, 1,
Polyhydric alcohols such as 6-hexanediol, neopentyl alcohol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbit, sorbitan, glucose, mannitol, mannitol, sucrose, glucose; ethylene glycol diglycidyl ether; Polyglycidyl ethers such as polyethylene glycol diglycidyl ether and glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; polyaldehydes such as glutaraldehyde and glyoxal; polyamines such as ethylenediamine; Calcium, calcium chloride, calcium carbonate, calcium oxide, magnesium borax,
Hydroxides, halides, carbonates, oxides, borates such as borax, metals such as magnesium oxide, aluminum chloride, zinc chloride, nickel chloride, etc. And one or more of these can be used in consideration of reactivity. However, a compound having two or more ethylenically unsaturated groups in one molecule may be used. Most preferably, it is used as a crosslinking agent.

The ratio of the crosslinkable monomer used in the present invention is 0.00 0.00 parts by weight per 100 parts by weight of the water-soluble unsaturated monomer.
It is 1 to 2 parts by weight, preferably 0.005 to 1 part by weight. That is, when the amount is less than 0.001 part by weight, the ratio of the water-soluble component in the obtained water-absorbent resin is large, so that the water absorption under sufficient pressure may not be maintained. The crosslink density is too high,
The water absorption of the resulting water-absorbent resin may be insufficient.

In the method of the present invention, the concentration of the total amount of the water-soluble unsaturated monomer and the crosslinking monomer in water is not particularly limited as long as the water-soluble unsaturated monomer can be dissolved. , Generally from 15 to 50% by weight, preferably from 25 to 40% by weight.

In the method of the present invention, the copolymerization reaction may be carried out in the presence of a surfactant. By using the surfactant, bubbles of the inert gas can be stably dispersed. Examples of such a surfactant include the following.

Examples of the anionic surfactant include fatty acid salts such as mixed fatty acid sodium soap, semi-hardened tallow fatty acid sodium soap, sodium stearate soap, potassium oleate soap and castor oil potassium soap; sodium lauryl sulfate, higher alcohol sodium sulfate Alkylsulfonates such as sodium, sodium lauryl sulfate and triethanolamine lauryl sulfate; alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate; alkylnaphthalenesulfonates such as sodium alkylnaphthalenesulfonate; alkylsulfosuccinates such as sodium dialkylsulfosuccinate Acid salts; alkyl diphenyl ether disulfonates such as sodium alkyl diphenyl ether disulfonate; alkyls such as potassium alkyl phosphate Polyoxyethylene alkyl (or alkylallyl) sulfuric acid such as sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, triethanolamine polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate Ester salt; special reaction type anionic surfactant; special carboxylic acid type surfactant; sodium salt of β-naphthalene sulfonic acid formalin condensate, naphthalene sulfonic acid formalin condensate such as sodium salt of special aromatic sulfonic acid formalin condensate A special polycarboxylic acid type polymer surfactant; and polyoxyethylene alkyl phosphate.

Examples of the nonionic surfactant include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether,
Polyoxyethylene alkyl ethers such as polyoxyethylene oleyl ether and polyoxyethylene higher alcohol ether, polyoxyethylene alkylaryl ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene derivatives; sorbitan monolaurate, sorbitan monopalmitate; Sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, sorbitan sesquioleate, sorbitan distearate, and other sorbitan fatty acid esters; polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monolaurate, Polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene Ren sorbitan tristearate,
Polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbite tetraoleate; glycerol monostearate, glycerol monooleate, self Glycerin fatty acid esters such as emulsified glycerol monostearate; polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate; polyoxyethylene alkylamine; poly Oxyethylene hydrogenated castor oil; alkyl alkanolamides and the like.

Examples of the cationic surfactant and the double-sided surfactant include alkylamine salts such as coconutamine acetate and stearylamine acetate; lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride and distearyldimethylammonium. Quaternary ammonium salts such as chloride and alkylbenzyldimethylammonium chloride; alkyl betaines such as lauryl betaine, stearyl betaine and lauryl carboxymethyl hydroxyethyl imidazolinium betaine; and amine oxides such as lauryl dimethylamine oxide.

Further, as the surfactant, a fluorine-based surfactant and an organometallic surfactant can also be used. By using these surfactants, bubbles of the inert gas can be stably dispersed in the aqueous monomer solution for a long time. It is also easy to control the amount of bubbles and the pore size. The resulting water-absorbent resin becomes a porous foam and has a high absorption rate. As the fluorine-based surfactant used in the present invention, there are various ones. For example, a perfluoroalkyl group obtained by replacing hydrogen of a lipophilic group of a general surfactant with fluorine is used. Is much stronger.

When the hydrophilic group of the fluorinated surfactant is changed,
4 types of anionic, nonionic, cationic and amphoteric
Although there are types, a fluorocarbon chain having the same structure is often used for the hydrophobic group. Moreover, the carbon chain which is a hydrophobic group can be used whether it is linear or branched. The following are typical fluorine-based surfactants.

Fluoroalkyl (C ₂ -C ₁₀ ) carboxylic acid, N-perfluorooctanesulfonyl glutamate disodium, 3- [fluoroalkyl (C ₆ -C ₁₁ )
Oxy] -1-alkyl (C ₃ ~C ₄₎ sodium sulfonate, 3- [.omega.-fluoroalkanoyl (C ₆ ~
C ₈₎ -N- ethylamino] -1-sodium sulfonate, N-[3- (perfluorooctane sulfonamide) propyl] -N, N-dimethyl -N- carboxymethylene ammonium betaine, fluoroalkyl (C ₁₁ -C ₂₀₎ carboxylic acids, perfluoroalkyl carboxylic acids (C ₇ ~C _13), perfluorooctane sulfonic acid diethanolamide, perfluoroalkyl (C ₄ ~
C ₁₂₎ sulfonate (Li, K, Na), N-propyl-N-(2-hydroxyethyl) perfluorooctane sulfonamide, perfluoroalkyl (C ₆ -C ₁₀₎
Al Hong amidopropyl trimethyl ammonium salts, perfluoroalkyl (C ₆ -C ₁₀₎ -N- ethylsulfonyl glycine salt (K), phosphate bis (N- perfluorooctylsulfonyl -N- ethylamino ethyl), monoperfluoroalkyl Alkyl (C ₆ -C ₁₆ ) ethyl phosphate, perfluoroalkyl quaternary ammonium iodide (trade name: Florade FC-135, cationic fluorine-based surfactant manufactured by Sumitomo 3M Limited), perfluoroalkyl alkoxylate (product Name Florard F
C-171, a nonionic surfactant manufactured by Sumitomo 3M Ltd.), and potassium perfluoroalkylsulfonic acid (trade names: Florade FC-95 and FC-98, an anionic surfactant manufactured by Sumitomo 3M Limited).

The organometallic surfactant refers to a substance having a metal such as Si, Ti, Sn, Zr, or Ge in the main chain of the molecule.

Representative organometallic surfactants include those represented by the following formulas (1) to (19) (Yoshida, Kondo, Ogaki,
Yamanaka, “New Edition Surfactant Handbook”, Engineering Books (1996), p. 34).

[0039]

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[0040]

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[0041]

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[0042]

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[0043]

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[0044]

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[0045]

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[0046]

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[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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[0055]

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[0056]

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[0057]

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The metal contained in the main chain of the organometallic surfactant represented by the above formulas (1) to (19) includes S
Sn, Zr, Ge, or the like can be used instead of i or Ti.

These surfactants have a total (mixture) amount of the water-soluble unsaturated monomer and the crosslinkable monomer of 1 used.
The amount is 0.0001 to 10 parts by weight, preferably 0.0003 to 5 parts by weight, per 100 parts by weight. That is, 0.000
If the amount is less than 1 part by weight, a sufficient effect of increasing the water absorption rate may not be obtained. On the other hand, if the amount exceeds 10 parts by weight, the effect corresponding to the added amount may not be obtained, which is uneconomical. It is.

Conventionally, it has been known to use a surfactant in aqueous solution polymerization, but such a known technique does not improve the water absorption rate at all.

In the method of the present invention, a monomer aqueous solution containing a mixture of the water-soluble unsaturated monomer and the crosslinkable monomer is prepared, for example, by dissolving the mixture in an aqueous medium.

The viscosity of the aqueous monomer solution thus prepared may be at least 10 cP, but is preferably at least 10 cP.
It is 100,000 cP, more preferably 20 to 3000 cP. By setting the viscosity of the monomer aqueous solution to 10 cP or more, bubbles of the inert gas can be stably dispersed in the monomer aqueous solution for a long time. If the viscosity is higher than 100,000 cP, bubbles in the aqueous monomer solution become large, and it may be difficult to obtain a polymer having a high water absorption rate.

If necessary, a thickener may be added to the aqueous monomer solution. The thickener may be a water-soluble polymer, for example, polyacrylic acid (salt), polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyethylene oxide, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose and the like. Further, a water-absorbing resin such as colloidal silica or crosslinked polyacrylic acid (salt) can also be used. These water-soluble polymers used as thickeners have an average molecular weight of 10,000 or more, preferably 100,000 or more. If the average molecular weight is less than 10,000, the amount of the thickener to be added becomes large, and the water absorption performance may be undesirably reduced. The viscosity of the monomer aqueous solution is 10 cP.
If it is above, there is no particular limitation,
Generally, it is in the range of 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the mixture (monomer) of the water-soluble unsaturated monomer and the crosslinkable monomer. If the amount is less than 0.01% by weight, the viscosity may not be 10 cP or more, and if it exceeds 10% by weight, the water absorption performance may be undesirably reduced.

To carry out the method of the present invention, for example, a mixture of the above-mentioned water-soluble unsaturated monomer and the above-mentioned crosslinkable monomer,
Further, if necessary, the above-mentioned thickener is dissolved in an aqueous medium to prepare a monomer aqueous solution having a viscosity of 10 cP or more, and a required amount of a polymerization initiator is added thereto. In the presence, in the state where bubbles are dispersed, aqueous solution copolymerization is performed by heating to a predetermined temperature if necessary. As the monomer aqueous solution, an aqueous solution having a viscosity of 10 cP or more in which polymerization is partially started may be used.

Then, the obtained hydrogel polymer is shredded as necessary, and further dried, and the resulting dried product is pulverized to obtain a high-water-absorbing-speed water-absorbing resin.

When a mixture of a water-soluble unsaturated monomer and a crosslinkable monomer is copolymerized in an aqueous solution, either continuous polymerization or batch polymerization may be employed. ,
It may be carried out under any normal pressure. The polymerization is preferably performed under a stream of an inert gas such as nitrogen, helium, argon, or carbon dioxide.

In the case of aqueous solution copolymerization, it is more preferable that the radical polymerization initiator is previously dissolved or dispersed in the aqueous monomer solution. Specific examples of the radical polymerization initiator include azo compounds such as 2,2'-azobis (2-amidinopropane) dihydrochloride; ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, and hydrogen peroxide. Peroxides such as benzoyl oxide, cumene hydroperoxide and di-t-butyl peroxide; and the above peroxides and reducing agents such as sulfites, bisulfites, thiosulfates, formamidinesulfinic acid and ascorbic acid. And a redox initiator obtained by combining the above.
These radical polymerization initiators may be used alone or in combination of two or more.

The amount of the radical polymerization initiator used relative to the total amount of the water-soluble unsaturated monomer and the crosslinkable monomer depends on the combination of the monomer and the radical polymerization initiator. It is preferably in the range of 0.001 to 5 parts by weight, more preferably in the range of 0.01 to 1 part by weight, based on 100 parts by weight of the total amount of the unsaturated monomer and the crosslinkable monomer. When the use amount of the radical polymerization initiator is less than 0.001 part by weight, the amount of unreacted unsaturated monomers increases, and therefore, the amount of residual monomers in the obtained water-absorbing resin increases, which is preferable. Absent. On the other hand, if the amount of the radical polymerization initiator exceeds 5 parts by weight, the amount of water-soluble components in the obtained water-absorbing resin increases, which is not preferable.

The temperature at the start of polymerization depends on the type of radical polymerization initiator used, but is preferably in the range of 0 to 50 ° C., and more preferably in the range of 10 to 40 ° C. The polymerization temperature during the reaction depends on the type of radical polymerization initiator used, but is preferably in the range of 20 to 110 ° C, and more preferably in the range of 30 to 90 ° C. When the temperature at the start of polymerization or the polymerization temperature during the reaction is out of the above range, (a) the amount of residual monomers in the obtained water-absorbing resin increases, and (b) foaming by the blowing agent described below. If it is performed, it becomes difficult to control it. (C)
An excessive self-crosslinking reaction may proceed to cause inconvenience such as a decrease in the water absorption of the water-absorbing resin.

The reaction time may be set according to the combination of the unsaturated monomer, the crosslinking agent and the radical polymerization initiator, or the reaction conditions such as the reaction temperature, and is not particularly limited.

The aqueous solution copolymer according to the present invention has a viscosity of 10
It is essential to carry out the reaction in a state in which bubbles of an inert gas are dispersed in an aqueous monomer solution having a cP or more. The volume of the aqueous monomer solution in which the inert gas bubbles are dispersed at that time is at least 1.02 times, preferably at least 1.08 times, more preferably at least 1.11 times the volume of the non-dispersed state. Preferably it is 1.2 times or more.

In the conventional polymerization reaction operation under stirring, some bubbles may be mixed in. However, according to the confirmation of the present inventors, even if bubbles are mixed in the normal operation, the mixture may be mixed. The volume change is less than 1.01 times.
The change in volume of 1.02 times or more is the result of performing an operation of intentionally mixing bubbles using a monomer aqueous solution having a viscosity of 10 cP or more, and the performance of the resin obtained by this operation is also improved. . Since the volume change of the aqueous solution of the crosslinkable monomer in the reaction vessel appears as a change only in the height of the waterline,
The rate of volume change can be easily confirmed. Since the transparency of the aqueous solution is reduced as a result of a more conscious foam mixing operation,
The dispersion state of the bubbles in the aqueous solution can also be confirmed visually. Although the use of an aqueous monomer solution thickened by a thickener for polymerization is a conventionally known technique, it is not known to polymerize a monomer in a state in which bubbles are dispersed.

As a method of dispersing bubbles of the inert gas in the aqueous monomer solution, a method of introducing an inert gas into the aqueous solution, a method of rapidly stirring the aqueous solution at a high speed, a method of previously adding a foaming agent, and the like. There is a method of combining two or more of the methods. Examples of the method of high-speed strong stirring include strong stirring using a stirrer or a stirring blade, and strong stirring using a high-speed homogenizer or an ultrasonic homogenizer.

The aqueous solution polymerization according to the present invention can be carried out while foaming the obtained copolymer. Foaming can be performed by a known method. For example, a solution containing a carboxylic acid monomer or a water-soluble salt thereof and a crosslinking agent is prepared, a carbonate-based blowing agent and a polymerization initiator are added to the solution to form a carbonated monomer solution, and the solution is polymerized. A method of forming a microporous hydrogel, pulverizing and drying the microporous hydrogel, and treating the surface with a crosslinking agent to obtain a superabsorbent polymer (Japanese Patent Laid-Open No. 5-23737)
No. 8 and JP-A-7-185331), a method of producing a microporous water-absorbent resin by polymerizing a water-soluble monomer while dispersing a volatile organic compound such as toluene (US Pat.
No. 354,290), a water-insoluble foaming agent is dispersed in a reaction mixture comprising a water-soluble monomer, a cross-linking agent and a water-soluble solvent using a surfactant, then foamed, and the monomer and the cross-linking agent are further reacted. Methods for producing superabsorbent resins (U.S. Pat.
No. 38,766) A method for producing a superabsorbent water-absorbent resin by copolymerizing a water-soluble monomer and a crosslinking agent using an azo initiator having a 10-hour half-life of 30 to 120 ° C. (WO95 / 17455), a method of obtaining a water-absorbing resin by copolymerizing a water-soluble monomer and a crosslinking agent in the presence of a blowing agent comprising an acrylate complex of an azo compound (WO96 / 17884), and the like.

Further, foaming is performed by adding an inert gas to the aqueous solution,
For example, it is carried out by introducing nitrogen, carbon dioxide, air or the like, or by stirring the aqueous solution at high speed and vigorously. Foaming is also performed by adding a foaming agent to the aqueous solution before polymerization.

Examples of such foaming agents include sodium carbonate, potassium carbonate, ammonium carbonate, magnesium carbonate, calcium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, ammonium hydrogencarbonate, magnesium hydrogencarbonate, calcium hydrogencarbonate, zinc carbonate, Examples thereof include carbonates such as barium carbonate, water-soluble azo polymerization initiators such as azobisamidinopropane dihydrochloride, dicarboxylic acids such as malonic acid, and volatile organic solvents such as trichloroethane and trifluoroethane. When a foaming agent is added, the amount of the foaming agent used is 10 in total of the water-soluble unsaturated monomer and the crosslinkable monomer.
0 to 5 parts by weight per 0 parts by weight, more preferably 0 to 5 parts by weight
A range of １1 part by weight is appropriate.

The above-mentioned hydrogel containing cells is broken into fragments of about 0.1 mm to about 50 mm by a predetermined method during or after the reaction, if necessary. Next, in order to foam the foam more efficiently, the hydrogel containing cells is dried. In addition, foaming with a foaming agent can be performed not at the time of reaction but at the time of drying.

The drying temperature is not particularly limited, but may be, for example, in the range of 100 to 250 ° C., more preferably in the range of 120 to 200 ° C. The drying time is not particularly limited, but is preferably about 10 seconds to 5 hours. Prior to drying, the hydrogel resin may be neutralized, or may be further crushed and fragmented.

The drying method includes heating drying, hot air drying,
Various methods such as reduced-pressure drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration with a hydrophobic organic solvent, and high-humidity drying using high-temperature steam can be employed, and are particularly limited. Not something. Of the drying methods exemplified above, hot air drying and microwave drying are more preferred. When microwaves are applied to the hydrogel containing bubbles,
Since the bubbles expand several times to several tens times, it is possible to obtain a water-absorbing resin with a further improved water absorption speed.

When the hydrogel containing bubbles is microwave-dried, the thickness of the crushed hydrogel is preferably 3 mm or more, more preferably 5 mm or more, and more preferably 10 mm or more. More preferred. When the hydrogel is subjected to microwave drying, it is particularly preferable to form the hydrogel into a sheet having the above thickness.

By the above-mentioned polymerization, that is, by the above-mentioned production method, the water-absorbing resin having a high water absorption rate according to the present invention can be easily obtained at low cost. The above water-absorbent resin has an average pore diameter in the range of 10 to 500 μm, more preferably 20 to 4 μm.
Within the range of 00 μm, more preferably 30 to 300 μm
, Most preferably in the range of 40 to 200 μm. The average pore diameter is determined by performing image analysis of a cross section of the dried water-absorbent resin using an electron microscope. That is, a histogram representing the pore size distribution of the water-absorbent resin is created by performing image analysis, and the number average of the pore sizes is calculated from the histogram, whereby the average pore size is obtained.

The water-absorbing resin obtained by the above method is
Since it is porous with a large number of pores inside and on its surface, under no pressure and under pressure, the liquid conducting space necessary for the aqueous liquid to migrate into the water absorbent resin is sufficiently secured. I have. Therefore, it is excellent in liquid permeability and diffusibility of the aqueous liquid, and can improve a water absorption rate, a water retention ability, and the like by a capillary phenomenon. Further, since the water-absorbent resin of the present invention is porous, even when the shape of the water-absorbent resin is particulate, it is possible to maintain liquid permeability when the aqueous liquid passes between the particles. . If the average pore diameter is smaller than 10 μm, there is a possibility that the liquid permeability and the diffusivity of the aqueous liquid may deteriorate. In addition, the average pore size is 50
If it is larger than 0 μm, the water absorption rate may not be sufficiently improved.

The water-absorbent resin may be treated with a surface cross-linking agent to form a covalent bond (secondary cross-link), thereby further increasing the cross-link density near the surface. The surface cross-linking agent is not particularly limited as long as it is a compound having a plurality of functional groups capable of forming a covalent bond by reacting with a carboxyl group of the water-absorbing resin. By treating the water-absorbent resin with a surface cross-linking agent, the liquid-permeability, water-absorption rate, water-absorption amount under pressure, and liquid-permeability of the water-absorbent resin are further improved.

As the surface cross-linking agent, specifically, for example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3
-Propanediol, dipropylene glycol, 2,
3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin,
2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-
Polyhydric alcohol compounds such as cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether; Epoxy compounds such as glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether and glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylene Hexamine, polyethylene Polyamine compounds such as imines and polyamide polyamines; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin; condensates of the above polyamine compounds with the above haloepoxy compounds; -Tolylene diisocyanate,
A polyvalent isocyanate compound such as hexamethylene diisocyanate; a polyvalent oxazoline compound such as 1,2-ethylenebisoxazoline; a silane coupling agent such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 3-dioxolan-2
-One, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, -Ethyl-1,3-dioxolan-2-one, 4
-Hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,
3-dioxan-2-one, 4,6-dimethyl-1,3
-Dioxan-2-one, 1,3-dioxoban-2-
Alkylene carbonate compounds such as on; and the like, but are not particularly limited thereto.

Among the surface cross-linking agents exemplified above, polyhydric alcohol compounds, epoxy compounds, polyvalent amine compounds, condensates of polyvalent amine compounds and haloepoxy compounds, and alkylene carbonate compounds are more preferable.

These surface crosslinking agents may be used alone or in combination of two or more. When two or more surface crosslinking agents are used in combination, the solubility parameter (S
By combining the first surface cross-linking agent and the second surface cross-linking agent having different P values), it is possible to obtain a water-absorbing resin having even more excellent water-absorbing properties. The above-mentioned solubility parameter is a value generally used as a factor indicating the breadth of a compound.

The first surface cross-linking agent is a compound having a solubility parameter of 12.5 (cal / cm ³ ) ^1/2 or more, which can react with a carboxyl group of the water-absorbing resin.
For example, glycerin and the like correspond. The second surface cross-linking agent can react with a carboxyl group of the water-absorbing resin,
A compound having a solubility parameter of less than 12.5 (cal / cm ³ ) ^1/2 , such as ethylene glycol diglycidyl ether.

The amount of the surface cross-linking agent used with respect to the water-absorbing resin depends on the combination of the water-absorbing resin and the surface cross-linking agent.
Within the range of 01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight.
It may be within the range of parts by weight. By using the surface cross-linking agent within the above range, the water absorbing properties for body fluids (aqueous liquids) such as urine, sweat, menstrual blood, etc. can be further improved. If the amount of the surface crosslinking agent is less than 0.01 parts by weight,
The crosslink density near the surface of the water-absorbent resin can hardly be increased. If the amount of the surface cross-linking agent is more than 5 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical and may make it difficult to control the cross-linking density to an appropriate value.

The treatment method for treating the water-absorbent resin with a surface crosslinking agent is not particularly limited. For example, a method of mixing a water-absorbing resin and a surface crosslinking agent without a solvent, a method of dispersing the water-absorbing resin in a hydrophobic solvent such as cyclohexane or pentane, and then mixing the surface crosslinking agent,
After dissolving or dispersing the surface crosslinking agent in the hydrophilic solvent,
A method of spraying or dropping the solution or dispersion onto the water-absorbent resin and mixing the solution or the dispersion may be used. The hydrophilic solvent is preferably water or a mixture of water and an organic solvent soluble in water.

Examples of the organic solvent include, for example, methyl alcohol, ethyl alcohol, n
-Propyl alcohol, iso-propyl alcohol,
n-butyl alcohol, iso-butyl alcohol, t
Lower alcohols such as -butyl alcohol; ketones such as acetone; ethers such as dioxane, ethylene oxide (EO) adduct of monohydric alcohol, and tetrahydrofuran; amides such as N, N-dimethylformamide and ε-caprolactam; And sulfoxides such as sulfoxide. These organic solvents may be used alone or in combination of two or more.

The amount of the hydrophilic solvent used for the water-absorbing resin and the surface cross-linking agent depends on the combination of the water-absorbing resin, the surface cross-linking agent, and the hydrophilic solvent.
200 parts by weight or less, more preferably 0.1 part by weight based on parts by weight.
001 to 50 parts by weight, more preferably 0.1 to 50 parts by weight.
The amount may be in the range of from 50 to 50 parts by weight, particularly preferably in the range of from 0.5 to 20 parts by weight.

When the secondary crosslinking is carried out with the above-mentioned surface crosslinking agent, a heat treatment is carried out, if necessary, depending on the type of the surface crosslinking agent, to crosslink the vicinity of the surface of the water-absorbing resin. By performing the secondary crosslinking, it is possible to obtain a water-absorbent resin having an excellent absorption capacity under pressure.

The mixing device used for mixing the water-absorbing resin and the surface cross-linking agent preferably has a large mixing force in order to uniformly and surely mix the two. Examples of the mixing device include a cylindrical mixer, a double-walled conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluidized furnace rotary desk type. Mixers, air-flow mixers, double-arm kneaders, internal mixers, pulverizing kneaders, rotary mixers, screw-type extruders and the like are preferred.

The treatment temperature and treatment time for treating the water-absorbent resin with the surface cross-linking agent may be appropriately selected and set according to the combination of the water-absorbent resin and the surface cross-linking agent, the desired crosslinking density, and the like. Although not particularly limited, for example, the processing temperature is preferably in the range of 0 to 250 ° C.

The above-mentioned water-absorbing resin may be further added to a deodorant, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a plasticizer, a pressure-sensitive adhesive, a surfactant, if necessary. Fertilizers, oxidizing agents, reducing agents, water, salts, and the like may be added to impart various functions to the water-absorbing resin.

Examples of the inorganic powder include substances inert to aqueous liquids and the like, for example, fine particles of various inorganic compounds and fine particles of clay minerals. The inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water. Specifically, for example, metal oxides such as silicon dioxide and titanium oxide, silicic acids (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay,
Bentonite and the like can be mentioned. Among them, silicon dioxide and silicic acid (salt) are more preferable, and silicon dioxide and silicic acid (salt) having an average particle diameter of 200 μm or less as measured by the Coulter counter method are more preferable.

The amount of the inorganic powder used for the water-absorbing resin is as follows:
Although it depends on the combination of the water-absorbent resin and the inorganic powder,
The amount may be in the range of 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water absorbent resin. The mixing method of the water-absorbent resin and the inorganic powder,
There is no particular limitation, and for example, a dry blending method, a wet mixing method, or the like can be employed. However, it is preferable to employ a dry blending method.

The water-absorbing resin composition is compounded (combined) with a fibrous material such as pulp, for example.
It is an absorbent article.

Examples of absorbent articles include sanitary materials (body fluid absorbent articles) such as disposable diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials, etc .; absorbent articles such as urine for pets; Materials for civil engineering and construction such as water retention materials, water stop materials, packing materials, gel blisters, etc .; Food products such as drip absorbents, freshness retention materials, cold insulation materials; oil / water separation materials, dew condensation prevention materials,
Various industrial articles such as coagulants; agricultural and horticultural articles such as water retention materials such as plants and soil; and the like are not particularly limited. In addition, for example, a disposable diaper is formed by laminating a back sheet (back material) made of a liquid-impermeable material, the above-described water-absorbent resin composition, and a top sheet (surface material) made of a liquid-permeable material in this order. And a gather (elastic portion) or a so-called tape fastener or the like is attached to the laminate. Further, the disposable diaper also includes pants with a disposable diaper used when disciplining urination and defecation for infants.

The water absorbent resin thus obtained has a water absorption of 10 to 100 g / g, preferably 20 to 80 g / g.
g.

[0101]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to these Examples. Further,% in Examples and Comparative Examples means% by weight unless otherwise specified, and parts means parts by weight.

The amount of water absorbed, the rate of water absorption, and the amount of water-soluble components of the water-absorbing resin were measured by the following methods.

(1) Water Absorption of Water Absorbent Resin 0.2 g of the water absorbent resin was poured into a tea bag type bag (6 cm × 6 c
m), heat-sealing the opening,
It was immersed in a 9% aqueous sodium chloride solution (physiological saline). After 60 minutes, the tea bag bag was lifted up, drained at 250 G for 3 minutes using a centrifuge, and then the weight W ₁ (g) of the bag was measured. The same operation was performed without using a water-absorbing resin, and the weight W ₀ (g) at that time was measured. From these weights W ₁ and W ₀ , the water absorption (g / g) was calculated according to the following equation: water absorption (g / g) = (W ₁ −W ₀ ) / weight (g) of water-absorbing resin.

(2) Water absorption rate of water-absorbent resin A water-absorbent resin (600 μm in advance by a sieve) was placed in a bottomed cylindrical polypropylene cup having an inner diameter of 50 mm and a height of 70 mm.
A portion having a particle diameter in the range of ３００300 μm was collected and used as a sample. Next, 28 g of physiological saline was poured into the cup. Then, the time from when the physiological saline was poured to when the physiological saline was completely absorbed by the water-absorbent resin and disappeared was measured. The measurement was repeated three times, and the average value was taken as the water absorption rate (second).

(3) Amount of water-soluble component of water-absorbent resin 0.5 g of the water-absorbent resin was dispersed in 1000 ml of deionized water, stirred for 16 hours, and filtered with a filter paper. Then, the obtained filtrate was titrated by colloid titration to determine the amount (%) of a water-soluble component in the water absorbent resin.

(Average Particle Diameter of Water Absorbent Resin) The average particle diameter is as shown below (850 μm, 600 μm, 30 μm).
(0 μm, 150 μm, 106 μm), the water absorbent resin was sieved and classified, and the residual percentage R was plotted on log probability paper, and the particle size corresponding to R = 50% was defined as the average particle size.

Example 1 In a 5 liter beaker, 306 g of acrylic acid, 37%
A monomer aqueous solution containing 3240 g of sodium acrylate, 8.2 g of polyethylene glycol (n = 8) diacrylate, 12 g of hydroxyethyl cellulose (trade name: SP-850, manufactured by Daicel Chemical Industries, Ltd.) and 1420 g of pure water was prepared. The viscosity of the monomer aqueous solution is 63 cP
Met. Nitrogen was blown into the monomer aqueous solution to remove dissolved oxygen in the solution, and then the mixture was rapidly and vigorously stirred at 6,000 rpm using a homodisper under a nitrogen stream to disperse a large amount of nitrogen bubbles in the monomer aqueous solution. When the nitrogen gas was uniformly dispersed in the monomer aqueous solution and the volume became 1.3 times, the monomer aqueous solution in which bubbles were dispersed was poured into a 10-liter double-arm kneader, and stirred under stirring. 10 g of a 10% aqueous sodium persulfate solution and 10 g of a 10% aqueous sodium bisulfite solution were added, and polymerization was immediately started. Subsequently, the mixture was allowed to stand still at a temperature of 25 to 75 ° C. for 2 hours while the bubbles were dispersed. After the polymerization, a sponge-like hydrated gel-like polymer containing a large amount of air bubbles was removed from a 10 mm square to
It was crushed to a size of mm square, and then dried in a hot air dryer at 160 ° C. for 1 hour. The average diameter of the bubbles in the sponge-like hydrogel polymer was 300 μm. The dried product was pulverized with a pulverizer, and the material passed through a sieve having an opening of 850 μm was fractionated to obtain a water-absorbent resin (1) of the present invention having an average particle diameter of 480 μm. The water absorption amount, water absorption rate and water-soluble component amount of the water-absorbent resin (1) of the present invention were 340.0 g / g, 42 seconds and 9.2%, respectively.

Example 2 In a 5 liter beaker, 306 g of acrylic acid, 37%
A monomer aqueous solution containing 3240 g of sodium acrylate, 8.2 g of polyethylene glycol (n = 8) diacrylate, 12 g of hydroxyethyl cellulose (trade name: SP-850, manufactured by Daicel Chemical Industries, Ltd.) and 1420 g of pure water was prepared. The viscosity of the monomer aqueous solution is 63 cP
Met. Then, a fluorine-based surfactant (trade name: Florard FC-135, manufactured by Sumitomo 3M Limited) 0.3
g, nitrogen is blown into the monomer aqueous solution to remove dissolved oxygen in the solution, and high-speed and strong stirring is performed at 6000 rpm using a homodisper under a nitrogen stream to disperse a large amount of nitrogen bubbles in the monomer aqueous solution. I was sorry. When the nitrogen gas was uniformly dispersed in the monomer aqueous solution and the volume became 1.35 times, the monomer aqueous solution in which the bubbles were dispersed was poured into a 10-liter double-arm kneader, and stirred for 10 minutes. 10% aqueous sodium persulfate solution and 10% aqueous sodium bisulfite solution 1
0 g was added and the polymerization was started immediately. Continued
With the air bubbles dispersed, static polymerization was performed at a temperature of 25 to 75 ° C. for 1 hour. After the polymerization, a sponge-like hydrogel polymer containing a large amount of air bubbles was kneaded from a 10 mm square to 50 mm with a kneader.
The pieces were crushed into corners, and then dried in a hot air dryer at 160 ° C. for 1 hour. The average diameter of the bubbles in the sponge-like hydrogel polymer was 140 μm. The dried product was pulverized with a pulverizer, and the material passed through a sieve having an opening of 850 μm was collected to obtain a water-absorbent resin (2) of the present invention having an average particle diameter of 400 μm. The water absorption amount, water absorption rate and water soluble component amount of the water absorbent resin (2) of the present invention were 40.2 g / g, 28 seconds and 9.8, respectively.
%Met.

Example 3 In a 5 liter beaker, 306 g of acrylic acid, 37%
A monomer aqueous solution containing 3240 g of sodium acrylate, 8.2 g of polyethylene glycol (n = 8) diacrylate, 3 g of hydroxyethyl cellulose (trade name: SP-850, manufactured by Daicel Chemical Industries, Ltd.) and 1420 g of pure water was prepared. The viscosity of the aqueous monomer solution was 12 cP. Then, after adding 3 g of polyoxyethylene sorbitan monostearate (trade name: Reodol TW-S120, manufactured by Kao Corporation), nitrogen is blown into the aqueous monomer solution to remove dissolved oxygen in the solution, and then under a nitrogen stream. Using a homodisper, high-speed and strong stirring was performed at 6000 rpm to disperse a large amount of nitrogen bubbles in the aqueous monomer solution. Nitrogen gas is uniformly dispersed in the aqueous monomer solution, and its volume is 1.38.
At this point, the aqueous monomer solution in which bubbles were dispersed was poured into a 10-liter double-arm kneader, 10 g of a 10% aqueous sodium persulfate solution and 10 g of a 10% aqueous sodium bisulfite solution were added with stirring, and polymerization was immediately performed. Started. Subsequently, the temperature is 25 to 75 ° C. in a state where the air bubbles are dispersed.
For 1 hour. After the polymerization, a sponge-like hydrogel polymer containing a large amount of air bubbles was reduced to 10 mm by a kneader.
It was crushed to a size of 50 mm square from the corner, and then dried in a hot air dryer at 160 ° C. for 1 hour. The average diameter of the bubbles in the sponge-like hydrogel polymer was 128 μm. The dried product is pulverized by a pulverizer, and the material having passed through the sieve having an opening of 850 μm is fractionated to obtain a water-absorbent resin (3) of the present invention having an average particle diameter of 410 μm.
I got The water absorption amount, water absorption rate and water-soluble component amount of the water-absorbent resin (3) of the present invention are 42.2 g / g and 29, respectively.
Seconds and 8.8%.

Comparative Example 1 In a 5 liter beaker, 306 g of acrylic acid, 37%
3,240 g of sodium acrylate, 8.2 of polyethylene glycol (n = 8) diacrylate, and 14 pure water
An aqueous monomer solution containing 20 g was prepared. The viscosity of the aqueous monomer solution was 3 cP. Nitrogen was blown into the aqueous monomer solution to remove dissolved oxygen in the solution, and then the mixture was vigorously stirred at 6000 rpm using a homodisper under a nitrogen stream.
When the volume becomes 1.1 times, the aqueous monomer solution having bubbles dispersed therein is poured into a 10-liter double-arm kneader, and 10 g of a 10% aqueous sodium persulfate solution and 10 g of a 10% aqueous sodium persulfate solution are stirred.
10 g of a 10% aqueous solution of sodium hydrogen sulfite was added, polymerization was started immediately, and static polymerization was carried out at a temperature of 25 to 75 ° C. for 1 hour. After the polymerization, the hydrogel polymer was crushed into a size of 10 to 50 mm square by a kneader.
It was dried in a hot air dryer at 60 ° C. for 1 hour. Almost no bubbles were found in the hydrogel polymer. The dried product was pulverized with a pulverizer, and the material passed through a sieve having an opening of 850 μm was fractionated to obtain a comparative water absorbent resin (1) having an average particle diameter of 460 μm. The water absorption amount, water absorption rate and water-soluble component amount of the comparative water absorbent resin (1) were 42.0 g / g, 128 seconds and 8.9%, respectively.
Met.

[0111]

According to the present invention, since the present invention is constituted as described above, the water absorption rate under no pressure and under pressure is high, the amount of water absorption is large, and the amount of water-soluble components is small. High water absorption rate water absorption that can be suitably used for various applications that require water absorption or water retention, such as sanitary material fields, agricultural and horticultural fields, food fields such as freshness retention, industrial fields such as dew condensation prevention and cold insulation, etc. Resin can be manufactured.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hideyuki Tahara 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo

Claims (5)

[Claims] 1. A mixture containing a mixture of a water-soluble unsaturated monomer and a crosslinkable monomer and having a viscosity of 10 cP or more in a state in which bubbles of an inert gas are dispersed in a monomer aqueous solution. A method for producing a water-absorbent resin having a high water-absorption rate, characterized in that: 2. The method for producing a water-absorbent resin having a high water absorption rate according to claim 1, wherein the volume of the aqueous monomer solution in which the inert gas bubbles are dispersed is at least 1.02 times the volume of the non-dispersed state. . 3. The method according to claim 1, wherein the aqueous monomer solution contains a surfactant. 4. The method for producing a water-absorbent resin having a high water absorption rate according to claim 1, wherein the bubbles are dispersed by introducing an inert gas into the aqueous solution. 5. The method for producing a water-absorbent resin having a high water absorption rate according to claim 1, wherein the dispersion of the bubbles is carried out by high-speed strong stirring of the aqueous solution.