JPH10114801A - Water-absorbing resin with high water absorption rate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-absorbing resin with a high water absorption rate by dispersing inert gas bubbles in an aq. soln. of a mixture of a water-soluble unsatd. monomer and a water-soluble cross-linking monomer and conducting the copolymn. of the monomers at a specified ratio of the vol. of the soln. contg. the bubbles to the vol. of the soln. before dispersing the bubbles therein. SOLUTION: An aq. monomer soln. with a concn. of 15-50wt.% is prepd. by mixing 100 pts.wt. water-soluble unsatd. monomer (e.g. acrylic acid or sodium acrylate), 0.001-2 pts.wt. water-soluble cross-linking monomer, a fluorine-based cationic surfactant in an amt. of 0.0001-10wt.% of the sum of the monomers, and a certain amt. of water. The soln. is stirred at a high speed in an nitrogen atmosphere to homogeneously disperse a large amt. of nitrogen bubbles having an average bubble size of 10-500μm in the soln. When the vol. of the soln. contg. the bubbles reaches 1.02-5 times that of the soln. before dispersing the bubble, a redox catalyst comprising Na2 S2 O8 , an aq. soln. of NaHSO3 , etc., in an amt. of 0.001-5wt.% of the sum of the monomer is added to the soln. and the monomers are copolymerized at 20-110 deg.C. The resultant spongy hydrogel polymer is thermally dried and ground to give the a water-absorbing resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high water absorption rate water absorbing resin and a method for producing the same. More specifically, the present invention relates to 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, and a method for producing the same.

[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 conductive resin and a method for producing the same.

[0012]

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

Another object of the present invention is to provide 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, and a method for producing the same. Still another object of the present invention is to provide a water-absorbent resin having a large amount of water absorption and a small amount of a water-soluble component of the water-absorbent resin, and a method for producing the same.

[0014]

The above object is achieved by the following (1).
(15).

(1) Inert gas bubbles are dispersed in a monomer aqueous solution comprising a mixture of a water-soluble unsaturated monomer and a water-soluble crosslinkable monomer, and the monomer having the inert gas bubbles dispersed therein is dispersed in the monomer solution. A method for producing a water-absorbent resin having a high water absorption rate, wherein the mixture is copolymerized within a range of 1.02 to 5 times the volume of a non-dispersed body aqueous solution.

(2) The method for producing a water-absorbent resin having a high water absorption rate according to the above (1), wherein the inert gas bubbles are dispersed so that the dispersed inert gas gas has an average pore diameter of 10 to 500 μm. .

(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 method for producing a water-absorbent resin having a high water absorption rate according to the above (3), wherein the surfactant is a fluorinated surfactant.

(5) The above (3) or (3) wherein the amount of the surfactant is 0.0001 to 30 parts by weight per 100 parts by weight of the total amount of the water-soluble unsaturated monomer and the water-soluble crosslinkable monomer. The method for producing a high water absorption rate water absorbent resin according to 4).

(6) The water-soluble unsaturated monomer is (meth) acrylic acid (salt), 2- (meth) acryloylethanesulfonic acid (salt), 2- (meth) acrylamido-2-methylpropanoic acid (salt) ), (Meth) acrylamide and methoxypolyethylene glycol (meth) acrylate,
At least one selected from the group consisting of N, N-dimethylaminoethyl (meth) acrylate and quaternary compounds thereof;
The method for producing a high-water-absorbing-speed water-absorbing resin according to any one of the above (1) to (5), which is of a kind.

(7) The above (1), wherein the water-soluble unsaturated monomer contains (meth) acrylic acid (salt) as an essential component.
The method for producing a water-absorbent resin having a high water absorption rate according to any one of (1) to (6).

(8) The high water absorption rate as described in any one of (1) to (7) above, wherein the water-soluble crosslinkable monomer is a compound having two or more ethylenically unsaturated groups in one molecule. A method for producing a water absorbent resin.

(9) The method according to any one of (1) to (8), wherein the volume of the aqueous monomer solution in which the inert gas bubbles are dispersed is 1.08 to 4 times the volume of the non-dispersed state. Method for producing a water-absorbent resin having a high water absorption rate.

(10) The dispersion of the bubbles is carried out by introducing an inert gas into the aqueous solution.
(9) The method for producing a high water absorption rate water absorbent resin according to any one of (9). (11) The method for producing a water-absorbent resin having a high water absorption rate according to any one of the above (1) to (9), wherein the dispersion of the bubbles is performed by high-speed strong stirring of the aqueous solution.

(12) Dispersion of bubbles is carried out by adding a foaming agent to an aqueous solution before polymerization.
(9) The method for producing a high water absorption rate water absorbent resin according to any one of (9).

(13) The method for producing a water-absorbent resin having a high water absorption rate according to any one of the above (1) to (12), wherein the copolymerization is carried out using a redox polymerization initiator.

(14) A method for producing a water-absorbent resin having a high water-absorbing rate, wherein the water-absorbent resin according to any one of the above (1) to (12) is further treated with a surface crosslinking agent.

(15) A water-absorbent resin having a high water absorption rate produced by the method according to any one of the above (1) to (14).

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, an inert gas bubble is dispersed in a monomer aqueous solution comprising a mixture of a water-soluble unsaturated monomer and a water-soluble crosslinkable monomer. The volume of the dispersed monomer is 1.02 to 5
A method for producing a superabsorbent resin, characterized in that the mixture is copolymerized in a range of 2 times.

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 water-soluble crosslinking 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. (Meth) acrylate, trimethylolpropanedi (meth)
Acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, N, N'-methylenebis (meth) acrylamide,
Compounds having two or more ethylenically unsaturated groups in one molecule such as triallyl isocyanurate, trimethylolpropanedi (meth) allyl ether, triallylamine, tetraallyloxyethane, glycerolpropoxytriacrylate; ethylene glycol, diethylene glycol, triethylene Ethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl alcohol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol Polyhydric alcohols such as pentaerythritol, sorbitol, sorbitan, glucose, mannitol, mannitol, sucrose, glucose; Glycol diglycidyl ether, polyethylene glycol diglycidyl ether,
Polyglycidyl ethers such as glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; glutaraldehyde;
Polyaldehydes such as glyoxal; polyamines such as ethylenediamine; Periodic Table Groups 2A and 3B such as calcium hydroxide, calcium chloride, calcium carbonate, calcium oxide, magnesium borax, magnesium oxide, aluminum chloride, zinc chloride and nickel chloride , 8
Group metal hydroxides, halides, carbonates, oxides,
Borates such as borax; and polyvalent metal compounds such as aluminum isopropylate. One or more of these can be used in consideration of reactivity.
Most preferably, a compound having two or more ethylenically unsaturated groups in the molecule is used as a crosslinking agent.

The ratio of the water-soluble crosslinking monomer used in the present invention is 0.001-2 parts by weight, preferably 0.005-1 part by weight, per 100 parts by weight of the water-soluble unsaturated monomer. . 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 crosslinking density may be too high, and 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 water-soluble crosslinkable monomer in water is 15 to 50% by weight, preferably 25 to 40% by weight. In the method of the present invention, the copolymerization reaction may be performed 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, there is a fluorine-based surfactant. By using the fluorine-based surfactant, 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 (C6 -C16) ethyl phosphate, perfluoroalkyl quaternary ammonium iodide (trade name: Florado FC-135, cationic fluorine-based surfactant manufactured by Sumitomo 3M Limited), perfluoroalkyl alkoxylate (trade 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).

These surfactants are used in a total amount of water-soluble unsaturated monomer and water-soluble crosslinkable monomer of 100%.
0.0001 to 10 parts by weight per part by weight, preferably 0.1 to 10 parts by weight.
0003 to 5 parts by weight, most preferably 0.0005 to 5 parts by weight
0.3 parts by weight. That is, if the amount is less than 0.0001 part by weight, it may not be possible to obtain a sufficient effect of increasing the water absorption rate, whereas if it exceeds 10 parts by weight, the effect corresponding to the added amount may not be obtained. It is uneconomical, and the surfactant may permeate when absorbing water, which may increase wet back and the like.

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

To carry out the method of the present invention, the above-mentioned water-soluble unsaturated monomer, water-soluble crosslinkable monomer and surfactant are dissolved in an aqueous medium to prepare an aqueous monomer solution. A necessary amount of a polymerization initiator is added, and if necessary, the mixture is heated to a predetermined temperature to carry out aqueous solution copolymerization. Next, the obtained hydrogel polymer is shredded as necessary, and further dried, and the resulting dried product is pulverized to obtain a water-absorbent resin having a high water absorption rate in powder form. When the aqueous solution of the water-soluble unsaturated monomer and the water-soluble crosslinkable monomer is copolymerized, any of continuous polymerization and batch polymerization may be employed.
You may implement under any pressure of pressurization and normal pressure. In addition,
The polymerization is preferably carried out 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 to previously dissolve or disperse the radical polymerization initiator 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.

Among them, redox-based polymerization initiators are preferred. By using the redox-based polymerization initiator, the monomer can be polymerized without breaking the bubbles and holding the bubbles. In addition, a water-absorbing resin having a high water-absorbing speed and a high strength can be obtained.

The amount of the radical polymerization initiator used relative to the total amount of the water-soluble unsaturated monomer and the water-soluble crosslinkable monomer depends on the combination of these monomers and the radical polymerization initiator. 0.001 to 5 based on 100 parts by weight of the total amount of the water-soluble unsaturated monomer and the water-soluble crosslinkable monomer
It is preferably in the range of parts by weight, more preferably in the range of 0.01 to 1 part by weight. The amount of the radical polymerization initiator used is 0.
If the amount is less than 001 parts by weight, the amount of unreacted unsaturated monomers increases, and therefore, the amount of residual monomers in the obtained water-absorbing resin is undesirably increased. 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.

It is essential that the aqueous monomer copolymerization of the monomer according to the present invention is carried out in a state in which bubbles of an inert gas are dispersed in the aqueous monomer solution. And the volume of the aqueous monomer solution in which the inert gas bubbles are dispersed at that time is 1.02 to 5 times, preferably 1.08 to 4 times the volume of the non-dispersed state,
More preferably 1.11 to 3 times, most preferably 1.2 times
~ 2.5 times.

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 an operation of intentionally mixing bubbles, and the performance of the resin obtained by this operation is also improved. Since the change in volume of the aqueous solution of the crosslinkable monomer in the reaction vessel appears as a change only in the height of the waterline, the ratio of the change in volume can be easily confirmed. Further, since the transparency of the aqueous solution is reduced as a result of the intentional operation of mixing the bubbles, the dispersion state of the bubbles in the aqueous solution can be visually confirmed.

If the volume of the aqueous monomer solution in which the inert gas bubbles are dispersed exceeds 5 times, the pore diameter of the bubbles dispersed therein becomes large, and the resulting water-absorbent resin becomes brittle. Moreover, it may become a very fine powder or a scaly water-absorbing resin.

As a method of dispersing bubbles of an inert gas in an aqueous monomer solution, a method of introducing an inert gas into an aqueous solution, a method of rapidly stirring an aqueous solution at a high speed, a method of adding a foaming agent in advance, 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.

In the present invention, the dispersed inert gas gas has an average pore diameter of 10 to 500 μm, preferably 50 to 200 μm.
It is preferable to disperse the inert gas bubbles in the range of m. If the average pore size is smaller than 10 μm, the resulting water-absorbent resin may have a poor water absorption rate. On the other hand, if it is larger than 500 μm, the water absorption rate may be poor or the strength may be brittle.

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 hydrogen carbonate, potassium hydrogen carbonate, ammonium hydrogen carbonate, magnesium hydrogen carbonate, calcium hydrogen carbonate, 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 used is in the range of 0 to 5 parts by weight, more preferably 0 to 1 part by weight, per 100 parts by weight of the total amount of the water-soluble unsaturated monomer and the water-soluble crosslinkable monomer. Is appropriate.

The above-mentioned hydrogel containing cells may be 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.

Drying methods include 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 high-water-absorbing-speed water-absorbing resin according to the present invention can be easily obtained at low cost. Most of them have a closed cell structure. The above water absorbent resin has an average pore diameter of 10 to 5
In the range of 00 μm, more preferably in the range of 20 to 400 μm, even more preferably in the range of 30 to 300 μm,
Most preferably, it is 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 crosslinking 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-cyclohexanediol, trimethylolpropane, diethanolamine,
Polyhydric alcohol compounds such as triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl Epoxy compounds such as ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, polyamidepolyamine, etc. Polyvalent amine compound; epichlorohydrid , Epibromohydrin, alpha-haloepoxy compound methyl epichlorohydrin and the like; condensates of the polyvalent amine compound and the haloepoxy compound; 2,4-tolylene diisocyanate, a polyhydric isocyanate compound such as hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one,
-Methyl-1,3-dioxolan-2-one, 4,5-
Dimethyl-1,3-dioxolan-2-one, 4,4-
Dimethyl-1,3-dioxolan-2-one, 4-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-dioxane-
Alkylene carbonate compounds such as 2-one and 1,3-dioxoban-2-one; and the like, but are not particularly limited. 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 cross-linking 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,
Solubility parameter is 12.5 (cal / cm ³ ) ^1/2
, For example, ethylene glycol diglycidyl ether and the like.

The amount of the surface cross-linking agent used for 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 when 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 above 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 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, so that the vicinity of the surface of the water-absorbent resin is crosslinked. 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-absorbent 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 when 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, such as 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, for example,
By combining (combining) with a fibrous material such as pulp, an absorbent article is obtained.

As absorbent articles, for example, sanitary materials (body fluid absorbing articles) such as disposable diapers, sanitary napkins, incontinence pads, wound protecting materials, wound healing materials; absorbent articles such as urine for pets; building materials and soil 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.

[0077]

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-absorbent 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 pulled out and drained at 250 G for 3 minutes using a centrifuge, and then the weight W1 (g) of the bag was measured. The same operation was performed without using a water-absorbing resin, and the weight W0 (g) at that time was measured. The water absorption (g / g) was calculated from the weights W1 and W0 according to the following equation: water absorption (g / g) = (W1−W0) / weight (g) of the water-absorbing resin.

(2) Water Absorption Rate of Water Absorbent Resin A water-absorbent resin (600 μm previously passed through 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-absorbing resin 0.5 g of the water-absorbing 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.

(4) Average Particle Size of Water Absorbent Resin The average particle size is as follows:
(μm, 300 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.

(5) Average pore diameter of dispersed inert gas gas The hydrogel polymer after polymerization is thinly sliced, the feret diameter is determined with an optical microscope, and a histogram representing the pore diameter distribution of bubbles is created. The average pore diameter was determined by calculating the number average of the pore diameters from the histogram.

Example 1 153 parts of acrylic acid, 37% sodium acrylate 16
15 parts, 4.9 parts of polyethylene glycol (n = 8) diacrylate, 0.75 part of a fluorinated cationic surfactant (trade name: Florade FC-135, manufactured by Sumitomo 3M Limited), and 710 parts of pure water An aqueous monomer solution was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse a large amount of nitrogen bubbles in the aqueous monomer solution. When the nitrogen gas was uniformly dispersed in the monomer aqueous solution and the volume became 1.58 times, 10% aqueous sodium persulfate
And 10 parts of a 5% aqueous solution of sodium bisulfite were added, polymerization was immediately started, and the mixture was allowed to stand still at a temperature of 25 to 75 ° C. for 2 hours while bubbles were dispersed. The sponge-like hydrogel polymer containing a large amount of air bubbles obtained after the polymerization is treated with 1
Cut from 0mm square to 50mm square, then 15mm
It was dried in a hot air dryer at 0 ° C. for 1 hour. The average pore size of the bubbles in the hydrogel polymer was 90 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 (1) of the present invention having an average particle size of 220 μm. The water absorption amount, water absorption rate, and water-soluble component amount of the water-absorbent resin (1) of the present invention were 31.1 g / g, 26 seconds, and 5.5%, respectively.

Example 2 153 parts of acrylic acid, 37% sodium acrylate 16
Monomer aqueous solution containing 15 parts, 4.9 parts of polyethylene glycol (n = 8) diacrylate, 1.5 parts of lauryl betaine surfactant (trade name: Amphitol 20BS, manufactured by Kao Corporation) and 710 parts of pure water Was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse a large amount of nitrogen bubbles in the aqueous monomer solution. When the nitrogen gas was uniformly dispersed in the monomer aqueous solution and the volume became 1.20 times, 10 parts of a 10% aqueous solution of sodium persulfate and 10%
10 parts of an aqueous solution of sodium hydrogen sulfite was added, polymerization was immediately started, and the temperature was 25 to 75 in a state where bubbles were dispersed.
The polymerization was carried out at room temperature for 1 hour. The hydrogel polymer containing bubbles obtained after the polymerization was cut into a size of 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C. The average pore size of the bubbles in the hydrogel polymer was 200 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 are each 38.7 g /.
g, 50 seconds and 6.6%.

Example 3 153 parts of acrylic acid, 37% sodium acrylate 16
15 parts, 4.9 parts of polyethylene glycol (n = 8) diacrylate, 0.075 part of a fluorinated cationic surfactant (trade name: Florade FC-135, manufactured by Sumitomo 3M Limited), and 710 parts of pure water An aqueous monomer solution was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse a large amount of nitrogen bubbles in the aqueous monomer solution. When the nitrogen gas was uniformly dispersed in the monomer aqueous solution and the volume became 1.20 times, 10% aqueous sodium persulfate solution
0 parts and 10 parts of a 10% aqueous solution of sodium bisulfite were added, polymerization was immediately started, and static polymerization was carried out at 25 to 75 ° C. for 3 hours in a state where bubbles were dispersed. The hydrogel polymer containing bubbles obtained after the polymerization was cut into a size of 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C. The average pore size of the bubbles in the hydrogel polymer is 130.
μm. The dried product is pulverized with a pulverizer, and the opening is 850.
The product having passed through the sieve having a size of μm was collected to obtain a water absorbent resin (3) of the present invention having an average particle size of 320 μm. The water absorption amount, water absorption rate, and water-soluble component amount of the water-absorbent resin (3) of the present invention were 36.0 g / g, 33 seconds, and 6.9%, respectively.

Example 4 100 parts of the water-absorbent resin (3) of the present invention obtained in Example 3 was mixed with ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.).
0.2 parts, pure water 9 parts, isopropyl alcohol 10 parts,
A crosslinker aqueous solution consisting of 2 parts of lactic acid and 0.02 part of polyoxyethylene sorbitan monostearate (trade name: Reodol TW-S120, manufactured by Kao Corporation) is added and mixed, and the mixture is heat-treated at 120 ° C. for 30 minutes, followed by the present invention. Water-absorbent resin (4) was obtained. Water absorption of the water absorbent resin (4) of the present invention,
The water absorption rate and the amount of the water-soluble component were 30.0 g /
g, 26 seconds and 5.9%.

Example 5 153 parts of acrylic acid, 37% sodium acrylate 16
A monomer aqueous solution containing 15 parts, 4.9 parts of polyethylene glycol (n = 8) diacrylate and 710 parts of pure water was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse nitrogen bubbles in the monomer aqueous solution. When the nitrogen gas was uniformly dispersed in the aqueous monomer solution and the volume became 1.07 times, 10 parts of a 10% aqueous sodium persulfate solution and 10 parts of a 10% aqueous sodium bisulfite solution were added under high-speed strong stirring. And immediately start the polymerization, at a temperature of 25 with the air bubbles dispersed.
Static polymerization was performed at -75 ° C for 2 hours. The hydrogel polymer containing bubbles obtained after the polymerization was cut into a size of 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C.
The average pore size of the bubbles in the hydrogel polymer was 250 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 (5) of the present invention having an average particle diameter of 430 μm. The water absorption amount, water absorption rate and water-soluble component amount of the water-absorbent resin (5) of the present invention are each 31.5.
g / g, 98 seconds and 3.9%.

Example 6 153 parts of acrylic acid, 37% sodium acrylate 16
15 parts, 4.8 parts of polyethylene glycol (n = 8) diacrylate, 0.8 part of an anionic surfactant (trade name: Emal 20C, manufactured by Kao Corporation) and pure water 710
A monomer aqueous solution containing a part was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse a large amount of nitrogen bubbles in the aqueous monomer solution.
When the nitrogen gas was uniformly dispersed in the aqueous monomer solution and the volume became 1.52 times, 10 parts of a 30% aqueous sodium persulfate solution and 10 parts of a 30% aqueous sodium bisulfite solution were stirred under high-speed strong stirring. The polymerization was started immediately after the addition, and the mixture was allowed to stand still at a temperature of 25 to 75 ° C. for 3 hours in a state where bubbles were dispersed. The hydrogel polymer containing a large amount of air bubbles obtained after the polymerization was cut into a size of 10 mm square to 30 mm square, and then dried in a hot air dryer at 150 ° C for 1 hour. The average pore size of the bubbles in the hydrogel polymer is 100 μm
Met. The dried product is pulverized with a pulverizer and the opening is 850 μm
Was filtered to obtain a water-absorbent resin (6) of the present invention having an average particle diameter of 200 μm. The water absorption amount, water absorption rate and water soluble component amount of the water absorbent resin (6) of the present invention are each 3
4.8 g / g, 17 seconds and 15.6%.

Example 7 153 parts of acrylic acid, 37% sodium acrylate 16
15 parts, 2.4 parts of polyethylene glycol (n = 8) diacrylate, 0.33 part of a fluorine-based nonionic surfactant (trade name: Florard FC-171, manufactured by Sumitomo 3M Limited), and 710 parts of pure water An aqueous monomer solution was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse nitrogen bubbles in the monomer aqueous solution. When the nitrogen gas was uniformly dispersed in the monomer aqueous solution and the volume became 1.09 times, 10 parts of a 10% aqueous sodium persulfate solution and 10 parts of a 10% aqueous sodium bisulfite solution were added under high-speed strong stirring. Add,
Polymerization was started immediately, and the temperature was increased to 2 with the bubbles dispersed.
Static polymerization was performed at 5 to 75 ° C for 1 hour. The hydrogel polymer containing bubbles obtained after the polymerization was cut into a size of 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C.
The average pore size of the bubbles in the hydrogel polymer was 200 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 (7) of the present invention having an average particle diameter of 360 μm. The water absorption amount, water absorption rate, and water-soluble component amount of the water-absorbent resin (7) of the present invention were 45.0, respectively.
g / g, 61 seconds and 13.6%.

Example 8 153 parts of acrylic acid, 37% sodium acrylate 16
15 parts, 6.9 parts of polyethylene glycol (n = 8) diacrylate, 0.27 parts of a fluorine-based anionic surfactant (trade name: Florado FC-95, manufactured by Sumitomo 3M Limited), and 710 parts of pure water An aqueous monomer solution was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse nitrogen bubbles in the monomer aqueous solution. When the nitrogen gas was uniformly dispersed in the monomer aqueous solution and the volume became 1.09 times, 10 parts of a 10% aqueous sodium persulfate solution and 10 parts of a 10% aqueous sodium bisulfite solution were added under high-speed strong stirring. Add,
Polymerization was started immediately, and the temperature was increased to 2 with the bubbles dispersed.
Static polymerization was carried out at 5 to 75 ° C for 2 hours. The hydrogel polymer containing bubbles obtained after the polymerization was cut into a size of 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C.
The average pore size of the bubbles in the hydrogel polymer was 150 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 (8) of the present invention having an average particle diameter of 420 μm. The water absorption amount, water absorption rate and water-soluble component amount of the water-absorbent resin (8) of the present invention are each 31.1.
g / g, 102 seconds and 4.1%.

Example 9 153 parts of acrylic acid, 37% sodium acrylate 16
15 parts, 4.9 parts of polyethylene glycol (n = 8) diacrylate, 0.0099 parts of a fluorine-based cationic surfactant (trade name: Florade FC-135, manufactured by Sumitomo 3M Limited), and 710 parts of pure water An aqueous monomer solution was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse nitrogen bubbles in the monomer aqueous solution. When the nitrogen gas is uniformly dispersed in the monomer aqueous solution and its volume becomes 1.09 times, 10% sodium persulfate aqueous solution
And 10 parts of a 10% aqueous solution of sodium bisulfite were added, polymerization was immediately started, and static polymerization was carried out at a temperature of 25 to 75 ° C. for 3 hours in a state in which bubbles were uniformly dispersed. The hydrogel polymer containing bubbles obtained after the polymerization was cut into a size of 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C. The average pore size of the bubbles in the hydrogel polymer is 1
It was 80 μm. The dried product is pulverized with a pulverizer,
The 50 μm sieved product was collected to obtain a water-absorbent resin (9) of the present invention having an average particle size of 420 μm. The water absorption amount, water absorption rate and water soluble component amount of the water absorbent resin (9) of the present invention were 36.6 g / g, 63 seconds and 5.6%, respectively.

Example 10 153 parts of acrylic acid, 37% sodium acrylate 16
Monomer containing 15 parts, 4.9 parts of polyethylene glycol (n = 8) diacrylate, 1.5 parts of nonionic surfactant (trade name: Reodol TW-S120, manufactured by Kao Corporation) and 710 parts of pure water An aqueous solution was prepared. Dissolved oxygen in the aqueous solution was replaced with nitrogen while rapidly stirring the aqueous solution under a nitrogen stream to disperse nitrogen bubbles in the monomer aqueous solution. When the nitrogen gas is uniformly dispersed in the aqueous monomer solution and the volume becomes 1.10 times, 10%
10 parts of an aqueous sodium persulfate solution and 10 parts of a 4% L-ascorbic acid aqueous solution were added, polymerization was immediately started, and static polymerization was carried out for 2 hours at a temperature of 25 to 75 ° C. in a state where bubbles were dispersed. The hydrogel polymer containing bubbles obtained after the polymerization was cut into a size of 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C. 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 (10) of the present invention having an average particle diameter of 300 μm. The water absorption amount, water absorption rate, and water-soluble component amount of the water-absorbent resin (10) of the present invention were 40.8 g / g, 69 seconds, and 8.6%, respectively.

Comparative Example 1 153 parts of acrylic acid, 37% sodium acrylate 16
A monomer aqueous solution containing 15 parts, 4.9 parts of polyethylene glycol (n = 8) diacrylate, and 710 parts of pure water was prepared. Under a nitrogen stream, dissolved oxygen in the aqueous solution was removed, and then 10 parts of a 10% aqueous sodium persulfate solution and 10 parts of a 10% aqueous sodium bisulfite solution were added without vigorous stirring. Polymerization was carried out at a temperature of 25 to 75 ° C. for 2 hours, with no bubbles mixed in and the volume was the same as in the normal state. The hydrogel polymer obtained after the polymerization was cut into a size of about 5 mm square, and then dried for 1 hour in a hot air dryer at 150 ° C. 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 420 μm.
The water absorption amount, water absorption rate and water-soluble component amount of the comparative water-absorbent resin (1) were 37.5 g / g, 112 seconds and 6.1%, respectively.

[0095]

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. It can be suitably used for various applications that require water absorption or water retention, such as the field of sanitary materials, etc., the field of agriculture and horticulture, the food field such as keeping freshness, and the industrial field such as dew condensation prevention and cooling materials.

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C08F 20/34 C08F 20/34 20/38 20/38 20/56 20/56 // A61F 13/00 301 A61F 13/00 301M 13/15 13/18 307B A61L 15/60 307A (72) Inventor Hideyuki Tahara 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo Japan Nippon Shokubai Co., Ltd.

Claims (15)

[Claims] An inert gas bubble is dispersed in a monomer aqueous solution comprising a mixture of a water-soluble unsaturated monomer and a water-soluble crosslinkable monomer, and said inert gas bubble is dispersed in said monomer. A method for producing a water-absorbent resin having a high water absorption rate, wherein the mixture is copolymerized in a range of 1.02 to 5 times the volume of an aqueous solution in a non-dispersed state. 2. A dispersed inert gas gas having an average pore diameter of 1
The method for producing a water-absorbent resin having a high water absorption rate according to claim 1, wherein the inert gas bubbles are dispersed so as to have a range of 0 to 500 µm. 3. The method according to claim 1, wherein the aqueous monomer solution contains a surfactant. 4. The method according to claim 3, wherein the surfactant is a fluorinated surfactant. 5. The surfactant according to claim 3, wherein the amount of the surfactant is 0.0001 to 30 parts by weight per 100 parts by weight of the total of the water-soluble unsaturated monomer and the water-soluble crosslinkable monomer. Method for producing a water-absorbent resin having a high water absorption rate. 6. The water-soluble unsaturated monomer is (meth) acrylic acid (salt), 2- (meth) acryloylethanesulfonic acid (salt), or 2- (meth) acrylamide-2-methylpropanoic acid (salt). , (Meth) acrylamide and methoxypolyethylene glycol (meth) acrylate, N, N
The method for producing a water-absorbent resin having a high water absorption rate according to any one of claims 1 to 5, wherein the resin is at least one member selected from the group consisting of -dimethylaminoethyl (meth) acrylate or a quaternary compound thereof. 7. The method for producing a water-absorbent resin having a high water absorption rate according to claim 1, wherein the water-soluble unsaturated monomer contains (meth) acrylic acid (salt) as an essential component. . 8. The compound according to claim 1, wherein the water-soluble crosslinkable monomer is a compound having two or more ethylenically unsaturated groups in one molecule.
7. The method for producing a water-absorbent resin having a high water absorption rate according to any one of items 7 to 7. 9. The 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 1.08 to 4 times the volume of the non-dispersed state. A method for producing a water absorbent resin. 10. 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. 11. 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 performed by high-speed and strong stirring of the aqueous solution. 12. The method for producing a water-absorbing resin having a high water absorption rate according to claim 1, wherein the foam is dispersed by adding a foaming agent to an aqueous solution before polymerization. 13. The method for producing a water-absorbing resin having a high water absorption rate according to claim 1, wherein the copolymerization is carried out using a redox polymerization initiator. 14. A method for producing a water-absorbing resin having a high water-absorbing rate, wherein the water-absorbing resin according to claim 1 is further treated with a surface crosslinking agent. 15. A high water absorption rate water absorbent resin produced by the method according to claim 1. Description: