JPH11199602A - Water absorbing polymer and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a water absorbing polymer by carrying out aqueous solution polymerization in the presence of a surfactant, causing no reduction in water absorbing characteristics of the water absorbing polymer in a final product, having no problem of safety and to obtain a water absorbing polymer having excellent water absorbing characteristics free from problem of safety. SOLUTION: In this method for producing a water absorbing polymer by subjecting a monomer convertible to a water absorbing polymer by polymerization to aqueous solution polymerization, the polymerization is characteristically carried out in the presence of a polymerizable surfactant, preferably foams, to give the objective amorphous ground particle-like water absorbing polymer in which the surfactant is bonded to the polymer by a covalent bond.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a water-absorbing polymer and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, water-absorbing polymers having high water-absorbing properties have been developed and compounded with fiber substrates such as cotton, pulp, paper and sponge, and have been put to practical use as disposable diapers, sanitary napkins and the like. Examples of the water-absorbing polymer include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, a neutralized product of a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylate copolymer, A hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer, a crosslinked product thereof, a crosslinked polymer of a cationic monomer, and the like are known.

[0003] As a method for producing such a water-absorbing polymer, from the viewpoint of the performance of the obtained resin and the ease of controlling the polymerization,
In general, aqueous polymerization is performed using a monomer as an aqueous solution. In this case, a surfactant may be used for the purpose of increasing the dispersibility of the polymer during polymerization and preventing the stirring blades and particles from adhering to each other. In addition, when polymerizing the monomer aqueous solution in a state containing bubbles, it is necessary to stably disperse the bubbles in the monomer aqueous solution, but since the surfactant can be stabilized, the bubbles are uniformly contained. The obtained hydrogel polymer can be obtained. Therefore, the obtained water-absorbing polymer can secure a large surface area, so that a higher water absorption rate can be obtained. Furthermore, the amount of bubbles in the hydrogel and the size thereof can be easily controlled by the amount of the surfactant added. As such a surfactant, a known anionic surfactant,
Nonionic surfactants, cationic surfactants and the like are used.

[0004] However, such surfactants remain in the polymer even after polymerization and are contained in final products such as disposable diapers as they are, and thus flow out of the polymer by external pressure or aging. For this reason, there is a problem that the interfacial tension of the liquid to be absorbed is reduced and the water absorbing property of the water-absorbing polymer is reduced. Further, depending on the type of the surfactant, it may not be preferable from the viewpoint of safety.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a water-absorbing polymer which is polymerized in the presence of a surfactant, and which does not deteriorate the water-absorbing properties of the water-absorbing polymer in the final product. Another object of the present invention is to provide a production method which does not cause a safety problem, and a water-absorbing polymer which is excellent in water absorption properties and has no safety problem as obtained by the production method.

[0006]

In order to solve the above problems, the present invention has the following arrangement. (1) A method for producing a water-absorbing polymer by polymerizing a monomer which can be converted into a water-absorbing polymer by polymerization in an aqueous solution, wherein the polymerization is carried out in the presence of a polymerizable surfactant. .

(2) performing polymerization in a state containing bubbles,
The method for producing a water-absorbing polymer according to the above (1). (3) An irregularly crushed water-absorbing polymer in which a surfactant is bonded to a polymer by a covalent bond. (4) The water-absorbing polymer according to the above (3), which contains bubbles inside.

(5) The water-absorbing polymer according to the above (3) or (4), wherein the vicinity of the surface is crosslinked.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The water-absorbing polymer of the present invention is a polymer which absorbs and swells a large amount of water, physiological saline, urine and the like to form a substantially water-insoluble hydrogel. A typical example of such a water-absorbing polymer is a hydrophilic polymer having a crosslinked structure obtained by polymerizing a hydrophilic monomer containing acrylic acid or a salt thereof as a main component. Such products include, for example, partially neutralized cross-linked polyacrylic acid, cross-linked and partially neutralized starch-acrylic acid graft polymer, isobutylene-maleic acid copolymer, saponified vinyl acetate-acrylic acid copolymer, acrylamide (co ) Polymer hydrolysates, acrylonitrile polymer hydrolysates, and the like are disclosed. Among them, preferred is a crosslinked polyacrylate. As the crosslinked polyacrylate, 50 to 95 mol% of the acid groups in the polymer
Is preferably neutralized, and more preferably 60 to 90 mol% is neutralized. Examples of the salt include an alkali metal salt, an ammonium salt, an amine salt and the like. This neutralization may be performed with a monomer before polymerization or with a hydrogel polymer during or after polymerization.

The monomer used in the present invention is not particularly limited as long as it is a monomer which can be converted into the above-mentioned water-absorbing polymer by polymerization. For example, acrylic acid, methacrylic acid, maleic acid, vinyl sulfonic acid, Styrenesulfonic acid, 2- (meth) acrylamide-2-
Anionic unsaturated monomers such as methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, N- n-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) Acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-
Vinylpyrrolidone, N-acryloylpiperidine, N-
Nonionic hydrophilic group-containing unsaturated monomers such as acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N And N-dimethylaminopropyl (meth) acrylamide and cationic unsaturated monomers such as quaternary salts thereof.
Among these, it is preferable to use acrylic acid as a main component, and the amount of other monomers besides acrylic acid is usually 0 to less than 50 mol%, preferably 0 to 30 mol%, but not limited to all monomers. It is not something to be done.

The present invention is characterized in that a polymerizable surfactant is used as a surfactant when performing aqueous solution polymerization using a monomer as an aqueous solution. Since the polymerizable surfactant can be copolymerized by radical polymerization with a monomer that can be converted to a water-absorbing polymer, it is covalently bonded to the resulting water-absorbing polymer. Therefore, since it does not flow out of the polymer due to external pressure or aging, the water absorption properties of the water-absorbing polymer in the final product are not reduced and safety is not a problem. Further, when the polymerization is carried out in a state containing bubbles, the specific surface area of the obtained water-absorbing polymer can be controlled without causing the above-mentioned problem of surfactant outflow, and the water absorption rate can be reduced. Can be improved.

The polymerizable surfactant includes, in one molecule, a hydrophilic group and a hydrophobic group which are basic structural elements of the surfactant,
It has a radically polymerizable ethylenically unsaturated double bond. Examples of the functional group having a radically polymerizable ethylenically unsaturated double bond in the surfactant include allylic, (meth) acrylic, (meth) acrylamide,
Styryl, butadiene, itaconic acid and the like can be mentioned. Further, as the hydrophilic group, any of anionic groups, cationic groups, nonionic groups, and amphoteric groups similar to ordinary surfactants are possible. Representative polymerizable surfactants include those represented by the following formulas (1) to (16) (“Development and application of novel reactive monomers”, edited by Endo, CMC (19)
93), p. 308).

[0013]

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[0014] (A is an alkylene group having 2 to 4 carbon atoms, R ₁
Is a hydrogen atom or a methyl group; R ₂ is a hydrocarbon group or an acyl group having 8 to 24 carbon atoms; m is an integer of 0 to 50;
M is a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group or a hydroxylammonium group having 1 to 4 carbon atoms. )

[0015]

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(R ₁ and R ₂ represent a hydrogen atom or a methyl group;
₃ is an alkyl or alkenyl group having 7 to 21 carbon atoms,
M is an alkali metal or ammonium group. )

[0017]

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(A is an alkylene group having 2 or more carbon atoms;
₁ is a hydrogen atom or a methyl group, m is an integer of 2 to 30, M
Is a hydrogen atom, an alkali metal or an ammonium group. )

[0019]

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[0020] (A is an alkylene group having 2 to 4 carbon atoms, R ₁
Is a hydrogen atom or a methyl group; R ₂ is a hydrocarbon group or an acyl group having 8 to 24 carbon atoms; m is an integer of 0 to 50;
M is a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group or a hydroxylammonium group having 1 to 4 carbon atoms. )

[0021]

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(R is a hydrocarbon group, a hydrocarbon group having a substituent or an organic group containing an oxyalkylene group, and M is an alkali metal, an alkaline earth metal, an ammonium group or an organic quaternary ammonium base.)

[0023]

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(A is an alkylene group or a substituted alkylene group having 2 to 4 carbon atoms, R ₁ is an alkyl group, alkenyl group or aralkyl group having 6 to 18 carbon atoms, R ₂ is a hydrogen atom or an alkyl group having 6 to 18 carbon atoms. Group, alkenyl group or aralkyl group, m is an integer of 1 to 200, and M is an alkali metal, ammonium group or alkanolamine residue.)

[0025]

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[0026] (A is an alkylene group having 2 to 4 carbon atoms, R ₁
Is a hydrogen atom or a methyl group, R ₂ is a hydrocarbon group having 8 to 24 carbon atoms, and m and n are 0 wherein m + n is an integer of 0 to 100.
Integer of -100, M is a hydrogen atom, an alkali metal, an ammonium group or an alkanol ammonium group. )

[0027]

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(A is an alkylene group having 2 to 4 carbon atoms,
R ₁ and R ₃ represent a hydrogen atom or a methyl group, and R ₂ has 8 to 8 carbon atoms.
24 hydrocarbon groups, m and n are integers of 0 to 100 where m + n is an integer of 0 to 100, and M is a hydrogen atom, an alkali metal, an ammonium group or an alkanol ammonium group. )

[0029]

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(R is a hydrocarbon group having 8 to 22 carbon atoms, and M is an alkali metal or ammonium group.)

[0031]

Embedded image

(A is an alkylene group having 2 to 4 carbon atoms, R ₁
Is a hydrogen atom or a methyl group; R ₂ is a hydrocarbon group or an acyl group having 8 to 24 carbon atoms; m is an integer of 0 to 50;
It is an integer of １００100. )

[0033]

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(E is -CH ₂ CH ₂ O-, P is -CH (C
H ₃ ) CH ₂ O—, R ₁ and R ₂ represent a hydrogen atom or a methyl group,
l, m, n are 0 to 100 such that 1 ≦ l + m + n ≦ 100
Is an integer. )

[0035]

Embedded image

(A is an alkylene group having 2 to 4 carbon atoms, R ₁
Is a hydrogen atom or a methyl group; R ₂ is a hydrocarbon group or an acyl group having 8 to 24 carbon atoms; m is an integer of 0 to 50;
It is an integer of １００100. )

[0037]

Embedded image

(A is an alkylene group or substituted alkylene group having 2 to 4 carbon atoms, R ₁ is an alkyl group, alkenyl group or aralkyl group having 6 to 18 carbon atoms, R ₂ is a hydrogen atom or an alkyl group having 6 to 18 carbon atoms. Group, alkenyl group or aralkyl group, m is an integer of 1 to 200.)

[0039]

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(A represents an alkylene group having 2 to 4 carbon atoms or a substituted alkylene group; R ₁ and R ₂ represent a hydrogen atom or a carbon atom having 1 carbon atom;
To 36 hydrocarbon groups or acyl groups. When both R ₁ and R ₂ are hydrogen atoms, m and n are integers of 1 or more; otherwise, m is 0 or a positive integer. However, m + n ≧ 3)

[0041]

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[0042] (A is an alkylene group having 2 to 4 carbon atoms, R ₁
Is a hydrogen atom or a methyl group, R ₂ is a hydrocarbon group or an acyl group having 8 to 24 carbon atoms, m is an integer of 0 to 50, and X is a hydrogen atom or a nonionic or anionic hydrophilic group. )

[0043]

Embedded image

(A is an alkylene group having 2 to 4 carbon atoms, R ₁
Is a hydrogen atom or a methyl group, R ₂ is a hydrocarbon group or an acyl group having 8 to 24 carbon atoms, m is an integer of 0 to 50, and X is a hydrogen atom or a nonionic or anionic hydrophilic group. These polymerizable surfactants can be used alone or in combination of two or more. In addition, a normal surfactant having no polymerizability may be used in combination with the polymerizable surfactant as long as the effects of the present invention are not impaired.

The amount of the polymerizable surfactant used is preferably in the range of 0.0001 to 30 parts by weight, more preferably 0.001 to 10 parts by weight, per 100 parts by weight of the total amount of the monomer which can be converted into the water-absorbing polymer. Range of parts. When the amount is within this range, the dispersibility and tackiness of the hydrogel formed during the polymerization can be improved, and the stability of the bubbles can be sufficiently ensured. , The water absorption rate of the resulting water-absorbing polymer can be easily controlled. If the amount is less than 0.0001 part by weight, it is difficult to control the tackiness of the obtained polymer, which may lead to a decrease in water absorption properties during production or an inability to control the water absorption rate. On the other hand, when the amount is more than 30 parts by weight, not only the effect corresponding to the added amount is not obtained but also the water absorption properties such as the water absorption capacity, the water absorption speed and the amount of the water-soluble component are sometimes undesirably reduced.

In order to carry out the polymerization containing bubbles, for example, nitrogen, argon, helium,
Examples thereof include a method of introducing an inert gas such as carbon dioxide gas and a method of adding a foaming agent to an aqueous monomer solution before polymerization. In order to introduce the inert gas into the monomer aqueous solution, for example, a method of fluidly mixing the monomer aqueous solution and the inert gas is preferable. Examples of the foaming agent include sodium carbonate, potassium carbonate, ammonium carbonate, magnesium carbonate, calcium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, magnesium bicarbonate, calcium bicarbonate, zinc carbonate, and barium carbonate. Salts, dicarboxylic acids such as malonic acid, and azo compounds.

The amount of bubbles dispersed in the aqueous monomer solution is such that the volume of the aqueous monomer solution in which the bubbles are dispersed is in the range of 1.02 to 30 times, preferably 1.05 to 10 times, the volume of the non-dispersed state. , More preferably 1.11 to
It is preferable to disperse the bubbles in the monomer aqueous solution so as to have a range of 5 times. When the volume of the monomer aqueous solution in which the bubbles are dispersed is smaller than 1.02 times the volume of the non-dispersed state, the water absorbing rate of the obtained water-absorbing polymer may be insufficiently improved. If it is too large, the mechanical strength of the resulting water-absorbing polymer may be undesirably reduced.

In the present invention, potassium persulfate, ammonium persulfate, sodium persulfate, t-
Butyl hydroperoxide, hydrogen peroxide, 2,2 '
Radical polymerization initiators such as -azobis (2-amidinopropane) dihydrochloride, active energy rays such as ultraviolet rays and electron beams, and the like can be used. When an oxidizing radical polymerization initiator is used, redox polymerization may be performed by using a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid in combination. The amount of the polymerization initiator used is usually 0.001 to the monomer component.
To 2 mol%, preferably 0.01 to 0.5 mol%.

The cross-linking structure of the water-absorbing polymer may be a self-cross-linking type using no cross-linking agent, or an internal cross-linking agent having two or more polymerizable unsaturated groups or two or more reactive groups. A reacted type is exemplified, and a type having a crosslinked structure obtained by copolymerizing or reacting an internal crosslinking agent is more preferable. Specific examples of these internal crosslinking agents include, for example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropanetri (Meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa ( (Meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene Glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol,
Examples thereof include propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate.
Further, two or more of these internal crosslinking agents may be used. Above all, it is preferable to use a compound having two or more polymerizable unsaturated groups as an internal cross-linking agent indispensably from the viewpoint of the water absorbing properties of the obtained water-absorbing polymer. To 3 mol%, more preferably 0.01 to 1.5 mol%.

The shape of the water-absorbing polymer obtained by the above-mentioned aqueous solution polymerization is irregularly crushed. When the polymerization is carried out in a state containing bubbles, a sponge-like or porous water-absorbing polymer containing bubbles therein can be obtained. Water-absorbing properties can be further enhanced by further crosslinking the vicinity of the surface of the water-absorbing polymer. For the surface cross-linking treatment, a cross-linking agent capable of reacting with a functional group of the water-absorbing polymer, for example, an acidic group may be used. When the functional group of the water-absorbing polymer is a carboxyl group, for example, a polyhydric alcohol compound, a polyvalent epoxy compound, a polyvalent amine compound, a polyvalent isocyanate compound, a polyvalent oxazoline compound, an alkylene carbonate compound, a haloepoxy compound, a silane Coupling agents, polyvalent metal compounds and the like can be used. These surface cross-linking agents may be used alone or in combination of two or more.

The water-absorbing polymer obtained by the present invention is compounded with a fiber substrate such as cotton, pulp, paper, and sponge,
It can be suitably used as a sanitary material such as disposable diapers and sanitary products. Other uses include medical fields such as body fluid absorbents, civil engineering and construction fields such as sealing materials (water blocking materials) and anti-condensation materials, and freshness preserving materials. In the field of food, industrial fields such as dehydrating agents for removing water from solvents, and agricultural and horticultural fields such as greening.

[0052]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. In the present invention, various performances were measured by the following methods. (1) Water absorption capacity of water-absorbing polymer 0.2 g of water-absorbing polymer was added to a tea bag type bag (6 cm ×
6cm), heat-seal the opening,
It was immersed in a 0.9% aqueous sodium chloride solution (physiological saline). After 60 minutes, the tea bag type bag was pulled up, and after draining at 250 G for 3 minutes using a centrifuge, the weight W1 (g) of the bag was measured. The same operation was performed without using a water-absorbing polymer, and the weight W0
(G) was measured. From these weights W1 and W0, the water absorption capacity (g / g) was calculated according to the following equation: water absorption capacity (g / g) = (W1−W0) / weight (g) of water-absorbing polymer. (2) Water absorption rate of water-absorbing polymer A cylindrical polypropylene cup with a bottom of 50 mm in inner diameter and 70 mm in height is filled with a water-absorbing polymer (600
A particle diameter portion in the range of μm to 300 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-absorbing polymer 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 polymer 0.5 g of the water-absorbing polymer 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-absorbing polymer. (4) Surface tension 150 g of 0.1 g of 3 g of the water-absorbing polymer was stirred at high speed.
Dispersed in 9% aqueous sodium chloride solution (physiological saline)
After 10 seconds, the mixture was filtered with a glass filter. The surface tension of the obtained filtrate was measured using a FACE CBVP-A3 type surface tensiometer (manufactured by Kyowa Interface Science Co., Ltd.). (5) Return amount of the water-absorbing polymer 1.0 g of the water-absorbing polymer was sprayed on a glass petri dish having a diameter of 9 cm and a height of 2 cm. Was.
After standing for 5 minutes, a non-woven fabric made of polyolefin having a diameter of 9 cm was placed thereon, and further weighed in advance.
5 mm filter paper (No.
2) After placing (5 sheets) (W1g), put a weight of 55 mm in diameter and a load of 21.0 g / cm ^{2 on} the center of the filter paper.
0 seconds. Then, the weight (W2
g) was weighed. The return amount was calculated from W1 and W2 by the following equation: return amount (g) = W2 (g) -W1 (g). It is evaluated that the smaller the amount of return, the better the performance.

Example 1 30.5 g of acrylic acid, 323.0 g of 37% by weight of sodium acrylate, 0.4 g of polyethylene glycol (n = 8) diacrylate, 20% by weight (a propenyl group-introduced product of polyoxyethylene alkylphenyl ether) )
A monomer aqueous solution containing 0.15 g (trade name: Aqualon RN-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 142.3 g of pure water was prepared. After degassing the monomer with nitrogen, the temperature of the aqueous monomer solution is set to 20 ° C., and bubbles of nitrogen gas are generated and dispersed in the aqueous monomer solution stably so that the volume becomes 1.05 times that of the non-dispersed bubble state. While stirring
0.34 g of 10% by weight aqueous sodium persulfate solution 0.34 g of 10% by weight aqueous solution of 2,2-azobisamidinopropane dihydrochloride and 0.61 g of 1% by weight aqueous solution of L-ascorbic acid, 0.1% by weight hydrogen peroxide 2.44 g of an aqueous solution were added. Approximately 3 minutes after the addition of the polymerization initiator, the monomer aqueous solution gelled, and thus the stirring was stopped, and the stationary polymerization was performed as it was. About 30 minutes after the addition of the polymerization initiator, the polymerization temperature reached a peak of 82 ° C., and was left standing for about 30 minutes after the peak to complete the polymerization.

The sponge-like hydrogel polymer containing a large amount of air bubbles thus obtained was cut into 15 mm squares with scissors, and then dried in a hot air drier at 160 ° C. for 60 minutes. The dried product is pulverized with a tabletop pulverizer and the opening is 85
The material having passed through the 0 μm sieve was fractionated to obtain a water-absorbing polymer (1) having an average particle size of 440 μm. The surface tension, water absorption capacity, water absorption rate and amount of water-soluble component of the obtained water-absorbing polymer (1) were 67.3 dyn / cm and 57.7 g /, respectively.
g, 33 seconds and 16%.

Example 2 Functionality capable of reacting with a carboxyl group consisting of 0.03 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, 3 parts of pure water and 2 parts of isopropanol with respect to 100 parts of the water-absorbing polymer (1). An aqueous liquid containing a compound having a plurality of groups was added, and the mixture was heated at 185 ° C. for 60 minutes to obtain a water-absorbing polymer (2) whose surface was crosslinked near the surface. The amount of return, surface tension, water absorption capacity, water absorption rate and amount of water-soluble component of the obtained water-absorbing polymer (2) were 0.21 g, 67.0 dyn / cm, and 43.4 g /, respectively.
g, 33 seconds and 16%.

Comparative Example 1 51.0 g of acrylic acid, 334.8 g of 37% by weight sodium acrylate, 0.5 g of polyethylene glycol (n = 8) diacrylate, polyoxymethylene sorbitan monostearate (trade name: Rheodol TW-S12)
0, manufactured by Kao Corporation) and a monomer aqueous solution containing 1.8 g of a 1% by weight aqueous solution and 107.4 g of pure water.
After degassing the monomer with nitrogen, raise the temperature of the monomer aqueous solution to 25.
C. and 0.41 g of a 10% by weight aqueous solution of sodium persulfate while stirring at a high speed so that nitrogen gas bubbles are stably generated and dispersed in the monomer aqueous solution and the volume thereof is 1.05 times that of the bubble non-dispersed state. 0.41 g of a 10% by weight aqueous 2,2-azobisamidinopropane dihydrochloride solution
And 0.73 g of a 1% by weight aqueous L-ascorbic acid solution,
2.92 g of a 0.1% by weight aqueous hydrogen peroxide solution was added.
Approximately 2 minutes after the addition of the polymerization initiator, the monomer aqueous solution gelled, so the stirring was stopped and the polymerization was allowed to proceed as it was. About 12 minutes after the addition of the polymerization initiator, the polymerization temperature reached a peak of 78 ° C., and was left standing for about 30 minutes after the peak to complete the polymerization.

The sponge-like hydrogel polymer containing a large amount of air bubbles thus obtained was cut into 15 mm squares with scissors, and then dried in a hot air drier at 160 ° C. for 60 minutes. The dried product is pulverized with a tabletop pulverizer and the opening is 85
The material having passed through the sieve having a size of 0 μm was collected to obtain a water-absorbing polymer (3) having an average particle size of 320 μm. The surface tension, water absorption capacity, water absorption rate and water-soluble component amount of the obtained water-absorbing polymer (3) were 44.2 dyn / cm and 55.9 g / cm, respectively.
g, 40 seconds and 16%.

Comparative Example 2 Functionality capable of reacting with a carboxyl group consisting of 0.03 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, 3 parts of pure water and 2 parts of isopropanol per 100 parts of the water-absorbing polymer (3). An aqueous liquid containing a compound having a plurality of groups was added, and the mixture was heated at 185 ° C. for 60 minutes to obtain a water-absorbing polymer (4) whose surface was crosslinked. The return amount, surface tension, water absorption capacity, water absorption rate and water-soluble component amount of the obtained water-absorbing polymer (4) were 1.94 g, 44.1 dyn / cm, and 38.0 g /, respectively.
g, 40 seconds and 16%.

[0059]

According to the present invention, since a surfactant is used, it is possible to enhance the dispersibility at the time of polymerization and prevent the stirring blades and particles from adhering to each other. Moreover, since the surfactant is covalently bonded to the water-absorbing polymer, it does not flow out of the polymer due to external pressure or aging. Therefore, the water absorbing property of the water absorbing polymer is not reduced in the final product, and there is no safety problem. Further, even when the polymerization is carried out in a state containing bubbles, the specific surface area of the obtained water-absorbing polymer can be controlled without causing the above-described problems, and the water absorption rate can be improved. it can.

Claims (5)

[Claims] 1. A method for producing a water-absorbing polymer by aqueous polymerization of a monomer which can be converted to a water-absorbing polymer by polymerization, wherein the polymerization is carried out in the presence of a polymerizable surfactant. Production method. 2. The method for producing a water-absorbing polymer according to claim 1, wherein the polymerization is carried out in a state containing bubbles. 3. An irregularly crushed water-absorbing polymer in which a surfactant is bound to a polymer by a covalent bond. 4. The water-absorbing polymer according to claim 3, which contains bubbles inside. 5. The water-absorbing polymer according to claim 3, wherein the vicinity of the surface is crosslinked.