JPH08157531A - Production of highly water-absorbing resin - Google Patents

Abstract

PURPOSE: To produce a highly water-absorbing resin being excellent in water- absorbing power under a load and not forming agglomerates of insufficiently wet particles. CONSTITUTION: A highly water-absorbing resin having carboxylate groups and a water content of 3-50wt.%, a sucrose/fatty acid ester and/or a sorbitan/fatty acid ester, a cross-linking agent having at least two functional groups reactive with the carboxylate groups, and a water-insoluble inorganic powder are mixed together in the presence of an organic solvent, which is then distilled off from the mixture, and the residue is subjected to cross-linking by heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a highly water-absorbent resin, and more particularly to a method for producing a highly water-absorbent resin which is excellent in water absorption under load and does not produce "Mamako".

[0002]

BACKGROUND OF THE INVENTION Super absorbent polymers are useful as a body fluid absorbent for absorbing and preventing leakage of body fluids in sanitary products. In addition, a water retention agent for soil, a seed coating agent, a water blocking agent, a thickener, It is used for anti-condensation agents, desiccants, humidity control agents, etc. However, these super absorbent resins are
When water is absorbed, particles stick to each other and uniform water absorption is impeded, so-called "mamako" occurs, the water absorption rate decreases without water spreading throughout the water absorbent resin, and load that is important for sanitary material applications. Some of them have a drawback that they have a low water absorption capacity below.

As a technique for improving these drawbacks, a method of adding a polyhydric alcohol or its oxyalkylene ether to a highly water-absorbent resin (JP-A-58-183754),
A method in which a superabsorbent resin is crosslinked by absorbing a crosslinking agent and water in the presence of an inorganic powder (JP-A-60-16395).
No. 6), sucrose fatty acid ester is added to the superabsorbent resin, and a crosslinking agent is used in the presence of water to crosslink (JP-A-3-28203). Water and inorganic substances are added to the superabsorbent resin. A method of crosslinking using a crosslinking agent in a hydrophilic inert solvent in the presence of powder (JP-A-60-147475), a crosslinking agent previously dispersed in a hydrophobic organic solvent in the presence of a surfactant. A method of adding to a suspension in which a superabsorbent resin is dispersed in a hydrophobic organic solvent (JP-A-1-207327), the superabsorbent resin in the presence of water and a surfactant,
A method (Japanese Patent Publication No. 6-43500) in which water and an inert solvent are distilled off after adding a powdered inorganic substance in an inert solvent is known.

[0004]

However, although the technique disclosed in Japanese Patent Laid-Open No. 183754/1983 leads to the prevention of the formation of "Mamako", the decrease of the water absorption under load cannot be avoided, and JP-A-60-63956, JP-A-3-28203 and JP-A-60-14
In the technology disclosed in Japanese Patent No. 7475, since the crosslinking is carried out in the presence of a large amount of water, the superabsorbent resin absorbs part of the water, and the effect of adding the crosslinking agent cannot be sufficiently obtained. It has the drawback that "Mamako" is generated and the water absorption capacity is lowered under load, and further, it is disclosed in JP-A-1-207327 and JP-B-6.
The technology disclosed in JP-A-43500 has a drawback in that it is difficult to obtain a sufficient effect of improving water absorption under load, which suppresses the formation of "Mamako" when in contact with an aqueous liquid, and Therefore, a method for producing a highly water-absorbent resin excellent in water absorption is desired.

[0005]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that the water content is 3 to 50.
A highly water-absorbent resin having a weight percent and a carboxylate group, a sucrose fatty acid ester and / or a sorbitan fatty acid ester, a crosslinking agent having two or more functional groups capable of reacting with a carboxylate group, and a water-insoluble inorganic powder are organic. After mixing in the presence of a solvent, the organic solvent was distilled off, and then "Mamako" was not formed by heating and performing a crosslinking treatment, and it was found that it has good water absorption even under load, The present invention has been completed. The present invention is described in detail below.

The superabsorbent resin to which the present invention is applied is not specified as long as it has a carboxylate group in its molecule. Specifically, it has a carboxylate group and absorbs a large amount of water in water. It is a resin that swells and forms a hydrogel. Here, the carboxylate group means a carboxyl group and / or a carboxylate group. Various resins are known as such a resin, for example, a hydrolyzate of a starch-acrylonitrile graft copolymer, a neutralized product of a starch-acrylic acid graft polymer, an acrylic acid ester-vinyl acetate copolymer. Saponified product, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer, crosslinked polyvinyl alcohol modified product, self-crosslinking polyacrylic acid neutralized product, polyacrylic acid salt crosslinked product, crosslinked isobutylene-
Examples thereof include, but are not limited to, neutralized products of maleic anhydride copolymers, but among them, polyacrylic acid salt crosslinked products and superabsorbent resins composed of crosslinked polyvinyl alcohol modified products are important. .

The highly water-absorbent resin composed of the crosslinked polyacrylic acid salt is usually obtained by polymerizing a monomer composed of a mixture of (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid. Examples of the water-soluble salt include sodium salt, potassium salt, ammonium salt and the like. The mixing ratio of (meth) acrylic acid and the water-soluble salt of (meth) acrylic acid is preferably selected from the range of 10/90 to 50/50 in terms of molar ratio. If it deviates from this range, the absorption characteristics of the resulting superabsorbent polymer will deteriorate. A mixture of (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid is
It is usually obtained by partially neutralizing (meth) acrylic acid with an alkali such as sodium hydroxide, potassium hydroxide or ammonia. In addition to these monomers, other vinyl monomers such as (meth) acrylic acid ester, unsaturated sulfonic acid or its salt, (meth) acrylamide,
A small amount of (meth) acrylonitrile, vinyl ester, vinyl ether, etc. can be used together.

In carrying out the polymerization, any known method can be adopted, and any of aqueous solution polymerization (static polymerization), emulsion polymerization (reverse phase emulsion polymerization), suspension polymerization (reverse phase suspension polymerization) and the like can be used. Although possible, reverse phase suspension polymerization or static polymerization is preferable. The polymerization method will be described more specifically below. When carrying out reverse phase suspension polymerization, an aqueous solution containing (meth) acrylic acid, a water-soluble salt of (meth) acrylic acid, preferably a crosslinking agent such as a polyfunctional vinyl monomer is dispersed in an organic solvent that is insoluble in water. Polymerization is performed in the presence of a radical polymerization initiator. At that time, it is possible to improve the stability of the polymerization by coexisting a known dispersion stabilizer or surfactant. As the organic solvent, cyclohexane,
Alicyclic hydrocarbons such as cyclopentane, n-pentane, n
Examples thereof include aliphatic hydrocarbons such as -hexane, n-heptane and ligroin, and aromatic hydrocarbons such as benzene, toluene and xylene. Judging from the melting point, boiling point, price, and industrial availability of the solvent, n-hexane and cyclohexane are the most practical. It is suitable that the polymerization temperature is 50 to 90 ° C. and the polymerization time is 0.5 to 5 hours. After completion of the polymerization, the superabsorbent resin is obtained by filtering the produced particles, washing and drying according to a conventional method.

Next, in order to carry out static polymerization, water, (meth) acrylic acid, water-soluble salt of (meth) acrylic acid and radical polymerization initiator are uniformly mixed, and no stirring or kneading is performed thereafter. Polymerization is carried out, and the obtained solid is pulverized and dried. Industrially, the above uniform mixed solution is put in a bucket conveyor, supplied on a belt having weirs at both ends, supplied in a tube, or charged in a container having an arbitrary shape and 40 After kneading at a temperature of about 100 ° C for 0.03 to 5 hours, polymerization is allowed to proceed while keeping no mixing. The resin solid matter having reached a predetermined polymerization rate is cut to a size of a pellet or a particle size smaller than that, pulverized and dried. It is desirable to continuously perform this series of operations.

In carrying out the above-mentioned polymerization method, the polymerization initiator used is an azonitrile such as azobisisobutyronitrile; an alkyl peroxide such as t-butyl peroxide or cumene hydroperoxide; di- Dialkyl peroxides such as t-butyl peroxide; amyl peroxides such as acetyl peroxide, lauroyl peroxide, stearoyl peroxide, benzoyl peroxide; t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t
Examples include peroxyesters such as butyl peroxypivalate; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; hydrogen peroxide solution; ammonium persulfate; potassium persulfate; and cerium salts. The amount of the initiator added is about 200 to 5000 ppm based on the total amount of (meth) acrylic acid and the water-soluble salt of (meth) acrylic acid.

During the reverse phase suspension polymerization, it is practical to add a surfactant to keep the system stable.
Examples of the activator include polyoxyethylene alkyl ether, polyoxyethylene acyl ester, polyoxyethylene sorbitan fatty acid ester, sorbitan fatty acid ester, oxyethyleneoxypropylene block copolymer, sucrose fatty acid ester, higher alcohol sulfate ester salt, and alkylbenzene sulfone. A nonionic surfactant such as an acid salt or polyoxyethylene sulfate, or an anionic surfactant is used alone or in combination. Further, in order to exert a high water absorbing property, a water-soluble crosslinking agent (different from a crosslinking agent having two or more functional groups capable of reacting with a carboxylate group) is usually used together during polymerization.

The water-soluble crosslinking agent is 10 to 2 relative to the total amount of (meth) acrylic acid and (meth) acrylic acid water-soluble salt.
000 ppm, preferably 50 to 1000 ppm is used, and as an example of such a water-soluble crosslinking agent, N, N '
-Methinebis (meth) acrylamide, N-methylol (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, glycerin tri (meth) acrylate, glycerin (meth) acrylate, (Meth) acrylic acid polyvalent metal salt, trimethylolpropane tri (meth) acrylate, triallylamine, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, glycidyl (meth) acrylate,
Examples thereof include ethylene glycol diglycidyl ether, glycerin tri (di) glycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether.

Further, the superabsorbent resin comprising a crosslinked polyvinyl alcohol-modified product has a maleic acid monoester content of 0.2 to 15 mol% and a saponification degree of 70 to 100 mol% vinyl acetate-maleic acid monoester. It can be obtained by irradiating the saponified copolymer with an electron beam or radiation of 0.1 to 50 Mrads in a water-containing state, or by heat treatment at 100 ° C. or higher.

In the present invention, it is an essential condition that the water content of the super absorbent polymer having a carboxylate group as described above is 3 to 50% by weight. Water content is 3% by weight
If it is less than 50% by weight, the crosslinking is not performed efficiently, and if it exceeds 50% by weight, the superabsorbent polymer agglomerates to form a lump, which makes it difficult to perform uniform crosslinking. Preferably 18 to 3
It is 5% by weight. Examples of the method of obtaining the water-absorbing superabsorbent resin include a method of adding water to the superabsorbent resin, a method of containing water during the production of the superabsorbent resin, and the like, and a method of adding water to the superabsorbent resin. As, as long as it is a method of adding as uniformly as possible to the super absorbent polymer, it is not particularly limited, specifically, it may be added by spraying or steaming, in an organic solvent containing super absorbent resin. In addition, an organic solvent in which water is dispersed may be added. Further, as a method for obtaining a superabsorbent resin which contains water uniformly when it is made to contain water during the production of the superabsorbent resin, preferably the superabsorbent resin powder containing water obtained by reverse phase suspension polymerization is subjected to azeotropic dehydration. By distilling off the water with
There is a method of adjusting the water content within the above range.

Examples of the sucrose ester used by adding to the superabsorbent resin in the present invention include mono-, di- or triesters of sucrose and fatty acids such as stearic acid, palmitic acid, lauric acid and oleic acid. ,In particular,
Sucrose stearate, sucrose palmitate, sucrose laurate and the like are used. Among them, sucrose stearate which has a HLB value of 10 or less and is solid at room temperature is preferable. The sorbitan fatty acid ester used in the present invention is preferably solid at room temperature, and examples thereof include sorbitan monopalmitate, sorbitan monostearate, sorbitan sesquistearate, and sorbitan tristearate. Of these, sorbitan monostearate that has a HLB value of 6 or less and is solid at room temperature is preferable.

The amount of the above sucrose fatty acid ester or sorbitan fatty acid ester to be added is not particularly limited, but it is preferably 0.001 to 10 parts by weight with respect to 100 parts by weight of the water-free superabsorbent resin. , And more preferably 0.01 to 1 part by weight. When the amount of the ester used is less than 0.001 part by weight, the effect of addition is poor,
The super absorbent polymer powder causes agglomeration, and the expected effect cannot be obtained. If it exceeds 10 parts by weight, not only the effect commensurate with the addition amount cannot be obtained, but also the water absorption amount and water absorption speed are remarkably lowered, which is not preferable. The above-mentioned esters can be used alone or in combination, and the amount used in that case is also the same as above.

The cross-linking agent having two or more functional groups capable of reacting with the carboxylate used in the present invention is a carboxylate group present in the superabsorbent resin modified by the present invention, preferably other than this. Further, it is a cross-linking agent having two or more functional groups capable of reacting with a hydroxyl group, a sulfone group, an amino group and the like, and such a agent can be used without particular limitation. As the cross-linking agent,
For example, diglycidyl ether compounds, haloepoxy compounds, aldehyde compounds, isocyanate compounds and the like can be mentioned. Among these, for example (poly)
Diglycidyl ether compounds such as ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether are suitable, and among these, diethylene glycol diglycidyl ether is a carboxy in the superabsorbent resin. Most suitable because of its reactivity with the rate group.

Specific examples of the haloepoxy-based compound include epichlorohydrin, epibromohydrin, α-methylepochlorohydrin and the like, aldehyde-based compounds such as glutaraldehyde and glyoxal, and isocyanate-based compounds such as 2,4-triphenyl. Examples thereof include rendi diisocyanate and hexamethylene diisocyanate. The amount of the crosslinking agent used is preferably 0.001 to 1 part by weight, and more preferably 0.005 to 0.1 part by weight, based on the water-free superabsorbent resin. If the amount of the cross-linking agent used is less than 0.001 part by weight, the effect of addition will be small, and if it exceeds 1 part by weight, excessive crosslinking will be carried out and the water absorption amount will be significantly reduced, such being undesirable.

Examples of the water-insoluble inorganic powder used in the present invention include silicon dioxide, aluminum oxide, titanium dioxide, talc, bentonite, zeolite and other metal oxides, but silicon dioxide is preferably used. Further, these water-insoluble inorganic powders are preferably fine particles that can be adsorbed on the surface of the highly water-absorbent resin, and the preferable particle diameter is 200 μm or less, particularly preferably 10 μm.
It is 0 μm or less. The amount of the water-insoluble inorganic powder used is preferably 0.005 to 2 parts by weight, and particularly preferably 0.05 to 1 part by weight, based on the water-free superabsorbent resin.

The organic solvent used in the present invention is inert to the crosslinking reaction during the crosslinking treatment and dissolves a crosslinking agent having two or more functional groups capable of reacting with the carboxylate group in the presence of a surfactant. Alternatively, it is not particularly limited as long as it can be dispersed. Specifically, saturated hydrocarbons such as cyclohexane and n-hexane, lower alcohols such as methanol, ethanol and isopropyl alcohol, ethers such as acetone and methyl ethyl ketone, ethylene glycol monomethyl ether such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether. Examples thereof include ethers. The amount of the organic solvent added may be an amount that can be sufficiently mixed with the superabsorbent polymer, and is preferably 20 to 2000 parts by weight, more preferably 100 parts by weight of the superabsorbent resin containing no water. 40 to 600 parts by weight.

Next, a method for crosslinking the super absorbent polymer will be specifically described. The present invention comprises a water-containing superabsorbent resin, a sucrose fatty acid ester and / or a sorbitan fatty acid ester, a water-insoluble inorganic powder, a cross-linking agent having two or more functional groups capable of reacting with a carboxylate group, and an organic solvent. Cross-linking treatment is carried out by distilling off an organic solvent, and a sucrose fatty acid ester and / or sorbitan fatty acid ester, a water-insoluble inorganic powder, and a cross-linking agent having two or more functional groups capable of reacting with a carboxylate group. The addition order of the organic solvent and the organic solvent is not particularly limited, and they may be added in any order, or may be added all at once, but from the viewpoint of the mixing property, the following order is preferable.

First, the superabsorbent resin whose water content is adjusted to 3 to 50% by weight and the above ester are uniformly dispersed in an organic solvent, or the superabsorbent resin obtained by the polymerization reaction is partially removed. The solvent is dehydrated to adjust the above water content, and the above ester is uniformly dispersed in a state of being dispersed in an organic solvent. During these operations, if necessary, 30 to 13
It is also possible to heat to about 0 ° C. Next, the above-mentioned cross-linking agent or an organic solvent solution containing the cross-linking agent is added, the mixture is uniformly mixed and stirred, and then the organic solvent is distilled off. At this time, in order to suppress the crosslinking reaction, it is desirable to carry out under reduced pressure and low temperature, and the pressure is suitably selected from the range of 150 to 250 torr and the temperature of 20 to 50 ° C. When an organic solvent liquid in which a cross-linking agent is previously dissolved or dispersed in an organic solvent is added, the content of the cross-linking agent in the solvent is 20 to 100 parts by weight based on 100 parts by weight of water-free super absorbent resin. Is preferred. It goes without saying that the organic solvent in the organic solvent liquid is also included in the amount of the organic solvent used.

Next, the water-insoluble inorganic powder is added. The addition may be carried out directly. However, considering the dispersibility of the powder, like the above-mentioned crosslinking agent, it is uniformly dispersed in an organic solvent beforehand. After this, it is preferable to add. It goes without saying that the organic solvent in the organic solvent liquid is also included in the amount of the organic solvent added. In distilling off the organic solvent,
The content of the organic solvent is 100% water-free super absorbent resin.
It is desirable that the amount is 5 parts by weight or less with respect to parts by weight. After the distillation, depending on the type of the cross-linking agent, it cannot be said that it is 50 to 15
Heat treatment is performed at 0 ° C., preferably 70 to 100 ° C. for about 30 minutes to 5 hours. Then, if necessary, 105-1
The superabsorbent resin of the present invention is obtained by performing a drying treatment at 50 ° C for about 0.5 to 5 hours.

The highly water-absorbent resin obtained by such a method does not form "Mamako" upon absorption, and also has excellent water-absorbing performance under load, such as sanitary materials such as paper diapers and sanitary napkins, and water-retaining soil. Agent, seed coating agent, water blocking agent,
It can be widely used as a thickener, anti-condensation agent, desiccant, humidity control agent and the like.

[0025]

In the present invention, the superabsorbent resin containing a specific amount of water, the water-insoluble inorganic powder, the specific surfactant and the cross-linking agent are mixed in an organic solvent, and the organic solvent is distilled off, followed by heat treatment. Therefore, it is possible to produce a highly water-absorbent resin that has excellent water absorption under load and does not generate "Mamako".

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, “part” and “%” are based on weight unless otherwise specified. In addition, the evaluation of the super absorbent polymer was performed according to the following procedure. (Water absorption under load) Connect a 50 ml capacity burette with a branch with a cock to a branch and a funnel with a glass filter with an inner diameter of 55 mmφ with a tube with an inner diameter of 6 mmφ. We arranged them so that they would be at the height of, and left them. The buret was filled with artificial urine, and the top of the buret was sealed with a rubber stopper. On the glass filter of the funnel with a glass filter, put 0.25 g of super absorbent polymer through a non-woven fabric, and put a weight of 453 g of cylindrical weight having a bottom diameter of 54 mmφ on it.
A load of 20 g / cm ² was applied to the super absorbent resin on the glass filter. On the other hand, a tube (6 mmφ) was attached to the end of the funnel with a glass filter, and a burette with a branch of 50 ml capacity was placed vertically on the other end of the tube so that the upper surface of the glass filter and the center position of the branch pipe of the buret were at the same height. , Put artificial urine. This state was left for 60 minutes, and the water absorption amount (ml / g) of the highly water-absorbent resin was measured.

(Presence or absence of "Mamako") Immediately after measuring the water absorption under the above-mentioned load, the presence or absence of "Mamako" (glue of superabsorbent resin particles) of the superabsorbent resin on the glass filter is visually observed. did. The artificial urine used in the above evaluation was urea 20
g, sodium chloride 8.2 g, anhydrous magnesium sulfate 0.57 g, and anhydrous calcium chloride 0.64 g were dissolved in ion-exchanged water 1000 g, and used.

Example 1 50 equipped with a stirrer, a reflux condenser and a nitrogen gas introducing tube
After charging 40 g of acrylic acid in a 0 ml separable flask, sodium hydroxide having a purity of 95% was added to 53 g of water.
The solution in which 9 g was dissolved was added dropwise with stirring and cooling to neutralize. Nitrogen bubbling was performed for 30 minutes to replace oxygen in the system. Then, 0.4 g of a 1% ammonium persulfate aqueous solution which had been subjected to nitrogen bubbling in advance and 0.5% N, N'-
Add 0.2 g of methylenebisacrylamide aqueous solution,
After sufficiently mixing, stirring was stopped. 60 in a flask
When immersed in a warm bath at ℃ and started the polymerization without stirring,
After reaching a maximum of 80 ° C after 10 minutes, the internal temperature returned to 60 ° C. Further, this temperature was maintained for 1 hour and then cooled to room temperature to terminate the polymerization. The content was taken out of the flask, cut into small pieces, dried at 100 ° C. for 2 hours, pulverized with a pulverizer and sieved to obtain superabsorbent resin particles (A) having a particle diameter of 350 to 74 μm. 24 g of the particles (A) were charged into a double-arm kneader reactor, and 16 g of water was sprayed with stirring using a manual sprayer to give a highly water-absorbent resin having a water content of 40% by weight. Further, after adding 20 g of n-hexane, 0.008 g of sorbitan monostearate and SiO ₂ fine powder
(Manufactured by Nippon Silica Industry Co., Ltd., trade name "Nipseal L"
p ”(average particle size 9 μm)) and diethylene glycol diglycidyl ether 0.004 g were added and mixed for 30 minutes. Then, while stirring, the mixture was heated to 40 ° C. under reduced pressure to distill off n-hexane. Then return to normal pressure 7
The mixture was heated to 0 ° C. to carry out a crosslinking reaction for 1 hour. Then, it was heated in an open state at 120 ° C. for 2 hours and dried to obtain a highly water-absorbent resin of the present invention.

Comparative Example 1 A superabsorbent resin was prepared in the same manner as in Example 1 except that the amount of water added by spraying was 0.74 g and the water content of the superabsorbent resin was 2% by weight. Obtained. Comparative Example 2 In Example 1, the amount of water added by spraying was 36 g,
A super absorbent polymer was obtained in the same manner as in Example 1 except that the water content of the super absorbent resin was 60% by weight.

Example 2 In the same manner as in Example 1, except that the bifunctional alicyclic epoxy compound (manufactured by Daicel Chemical Industries, Ltd., trade name “Celoxide 2021”) was used as the crosslinking agent. ,
A super absorbent resin was obtained.

Comparative Example 3 The procedure of Example 1 was repeated except that n-hexane was not used, and diethylene glycol diglycidyl ether 0.0 was used as a crosslinking agent.
A highly water-absorbent resin was obtained in the same manner as in Example 1 except that 04 g of water was dissolved in 8 g of water and added while spraying.

Comparative Example 4 Cyclohexane 800 was placed in a separable flask (flask A) equipped with a stirrer, a reflux condenser and a nitrogen gas inlet tube.
ml, as a protective colloid agent, sucrose fatty acid ester (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name "DK Ester F-7"
0 ") 0.78 g and sorbitan monostearate 0.7
8 g was charged and nitrogen bubbling was performed to replace the dissolved oxygen in the system. Another separable flask (flask B)
After charging 260 g of 80% acrylic acid aqueous solution into the
% Sodium hydroxide aqueous solution (310 g) was gradually added dropwise under cooling to neutralize. Then, 8 g of a 5% N, N′-methylenebisacrylamide aqueous solution and 4 g of a 10% ammonium persulfate aqueous solution were added, and nitrogen bubbling was performed while stirring to replace the dissolved oxygen. After the temperature of Flask A was raised to 73 ° C., the solution of Flask B was added dropwise over 1.5 hours. The rotation speed of the stirrer during the polymerization was set to 350 rpm. Then, the jacket was kept at 95 ° C. to azeotrope cyclohexane and water, and 230 ml of water was distilled off. here,
Sucrose fatty acid ester (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name "DK Ester F-7", containing 37.2 parts by weight of water per 100 parts by weight of super absorbent polymer (water content 27% by weight).
0 ") and sorbitan monostearate 0.00
A cyclohexane dispersion liquid (dispersion liquid B) of a super absorbent resin containing 256.5 g of a super absorbent resin in which 6 parts by weight and 243 parts by weight of cyclohexane were mixed was obtained. 2.56 g of this dispersion B and fine powder SiO ₂ (trade name “Nipseal Lp” (average particle size 9 μm), manufactured by Nippon Silica Industry Co., Ltd.) are added at 120 ° C.
After heating for 3 hours, water and cyclohexane were distilled off to obtain a dried super absorbent polymer.

Example 3 To the dispersion B obtained in Comparative Example 4, 0.0385 g of a bifunctional alicyclic epoxy compound (manufactured by Daicel Chemical Industries, Ltd., trade name "Celoxide 2021") was added as a crosslinking agent. And stirred well. Then, the mixture was heated to 40 ° C. under reduced pressure to remove cyclohexane. After returning to normal pressure, 1 at 70 ℃
After heating for a period of time to carry out a crosslinking reaction, the temperature was further raised to 120 ° C., and the temperature was kept for 3 hours and dried to obtain a super absorbent polymer of the present invention.

Example 4 A highly water-absorbent resin of the present invention was obtained in the same manner as in Example 3 except that the water content of the highly water-absorbent resin before the dispersion B was obtained in Example 3 was adjusted to 20%. . Regarding the SAPs obtained in the above Examples and Comparative Examples, the water absorption capacity under load and "Mamako"
Table 1 shows the evaluation results of the presence or absence of.

[0035]

[Table 1] Moisture content * Crosslinking agent ** Water absorption under load Presence / absence of Mamako (% / ml) Example 1 40 a 28 None Example 2 40 b 30 None Example 3 27 b 32 None Example 4 20 a 34 None Comparative Example 1 2 a 5 Yes Comparative Example 2 60 a 10 Yes Comparative Example 3 40 a 14 Yes Comparative Example 4 27 a 12 Yes * High before adding surfactant, cross-linking agent, water-insoluble inorganic powder Water content of water-absorbent resin ** Abbreviations of cross-linking agents are as follows: a: Diethylene glycol diglycidyl ether b: Bifunctional alicyclic epoxy compound (manufactured by Daicel Chemical Industries, Ltd., trade name "Ceroxide 2021")

[0036]

INDUSTRIAL APPLICABILITY In the present invention, a highly water-absorbent resin containing a specific amount of water, a water-insoluble inorganic powder, a specific surfactant and a crosslinking agent are mixed in an organic solvent, and then the organic solvent is distilled off, Since it is heat-treated, it is possible to produce a highly water-absorbent resin that has excellent water absorption under load and does not generate "Mamako".

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[Procedure amendment]

[Submission date] December 25, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

[0035]

[Table 1] Moisture content * Crosslinking agent ** Water absorption under load Presence / absence of Momako (% / ml) Example 1 40 a 30 None Example 2 40 b 32 None Example 3 27 b 34 None Example 4 20 a 36 None Comparative Example 1 2 a 9 Yes Comparative Example 2 60 a 14 Yes Comparative Example 3 40 a 18 Yes Comparative Example 4 27 No 13 Yes * Water content of super absorbent resin before adding surfactant, cross-linking agent and water-insoluble inorganic powder ** Abbreviation of cross-linking agent is as follows: a: Diethylene glycol diglycidyl ether b: Bifunctional alicyclic epoxy compound (Daicel Chemical Industry Co., Ltd., trade name "Celoxide 2021")

Claims (10)

[Claims] 1. A highly water-absorbent resin having a water content of 3 to 50% by weight and having a carboxylate group, sucrose fatty acid ester and / or sorbitan fatty acid ester, and two or more functional groups capable of reacting with a carboxylate group. A method for producing a highly water-absorbent resin, which comprises mixing the crosslinking agent and the water-insoluble inorganic powder in the presence of an organic solvent, distilling off the organic solvent, and then heating to carry out a crosslinking treatment. 2. The method for producing a superabsorbent resin according to claim 1, wherein the superabsorbent resin having a carboxylate group is a polyacrylate crosslinked product or a crosslinked polyvinyl alcohol-modified product. 3. The method for producing a superabsorbent resin according to claim 1, wherein the superabsorbent resin having a carboxylate group has a water content of 18 to 35% by weight. 4. The addition amount of sucrose fatty acid ester and / or sorbitan fatty acid ester is 0.001 to 10 parts by weight with respect to 100 parts by weight of a water-free superabsorbent resin. 1. The method for producing the super absorbent polymer according to 1. 5. The superabsorbent polymer according to claim 1, wherein the crosslinking agent having two or more functional groups capable of reacting with a carboxylate group is diethylene glycol diglycidyl ether or a bifunctional alicyclic epoxy compound. Resin manufacturing method. 6. The addition amount of a crosslinking agent having two or more functional groups capable of reacting with a carboxylate group is 0.001 to 1 part by weight based on 100 parts by weight of a water-free superabsorbent resin. The method for producing a highly water-absorbent resin according to claim 1 or 5, wherein 7. The method for producing a highly water-absorbent resin according to claim 1, wherein the water-insoluble inorganic powder is silicon dioxide. 8. The amount of the water-insoluble inorganic powder added is 0.005 to 100 parts by weight of water-free superabsorbent resin.
It is 2 weight part, The manufacturing method of the super absorbent resin of Claim 1 or 7 characterized by the above-mentioned. 9. The particle size of the water-insoluble inorganic powder is 200 μm.
It is m or less, The manufacturing method of the super absorbent resin of Claim 1, 7 or 8 characterized by the above-mentioned. 10. The production of a super absorbent polymer according to claim 1, wherein the added amount of the organic solvent is 20 to 2000 parts by weight with respect to 100 parts by weight of the super absorbent polymer containing no water. Law.