JPH0625209B2 - Water absorbent resin and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water-absorbent resin and a method for producing the same, and more specifically, it has an average particle size in a specific range and a particle size distribution of A water-absorbent resin whose narrow surface has been uniformly modified,
Especially excellent in water absorption capacity, water absorption speed, suction force, gel strength, etc.
In addition, the present invention relates to a water-absorbent resin which is excellent in balance between these water-absorbing properties and has little elution of a water-soluble resin (hereinafter referred to as a water-soluble component), which is suitable as a sanitary material, etc. . Furthermore, the present invention relates to a novel water-absorbent resin having a non-spherical non-spherical shape, excellent in handleability, and having a modified surface, and a method for producing the water-absorbent resin.

[Conventional technology and its problems]

Heretofore, attempts have been made to use a water-absorbent resin as an absorbent of sanitary materials such as sanitary cotton, disposable diapers and other body fluids. Examples of such a water-absorbent resin include a hydrolyzate of a starch-acrylonitrile graft polymer (Japanese Patent Publication No. 49-43395) and a neutralized product of a starch-acrylic acid graft polymer (Japanese Patent Publication-Sho 54). −
No. 125468), a saponified product of vinyl acetate-acrylic acid ester copolymer (Japanese Patent Publication No. Sho 52-14689).
No.), a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer (Japanese Patent Publication No. Sho 53-15).
959), or a crosslinked product thereof or a partially neutralized polyacrylic acid crosslinked product (Japanese Patent Publication-SHO-55-84304).
No.) etc. By the way, as properties desired for the water-absorbent resin, a high water-absorption capacity and an excellent water-absorption rate when in contact with an aqueous liquid, a high gel strength of a water-containing swelling gel, and for sucking water from a substrate containing an aqueous liquid, It has excellent suction power. These water absorption characteristics have conventionally lacked balance. That is, the relationship between these characteristics does not necessarily show a positive correlation, and in particular, there is a contradictory relationship between the water absorption capacity and the water absorption rate, the gel strength and the suction force, and the higher the water absorption capacity, the other physical properties deteriorate. There was a tendency to end up. In addition, some of the high water absorption ratios form so-called "mamako" when they come into contact with an aqueous liquid, and the water does not diffuse throughout the water-absorbent resin particles, resulting in an extremely low water-absorption rate. It was Further, the water-soluble component contained in the water-absorbent resin, when these water-absorbent resin is used in the absorbent body of the sanitary material, the absorption amount of the absorbent body affects the diffusion of the liquid in the absorbent body, etc. In particular, a water-absorbent resin having a particularly high water-absorption capacity has a large elution amount of a water-soluble component and has a problem that it cannot be suitably used as a sanitary material.

As a method for improving the above properties in a well-balanced manner, a method is proposed in which the surface of the obtained water-absorbent resin is cross-linked to improve the performance such as the water-absorption rate without impairing the water absorption capacity of the water-absorbent resin itself. Has been done. For example, a method of dispersing a water-absorbent resin in a hydrophilic organic solvent or a hydrophobic organic solvent in the presence of water and adding a crosslinking agent (aqueous solution) to react (Japanese Patent Publication Nos. 61-48521 and 60-18690).
No.) or a water-absorbent resin powder and a liquid mixture containing a cross-linking agent or a cross-linking agent are mixed and heat-treated (Japanese Patent Publication Nos. Sho 58-180233, Sho 59-189103, Sho 61-169903). ) Etc. In this case, it is preferable that the cross-linking agent is uniformly dispersed on the surface of the water-absorbent resin and proper penetration into the vicinity of the surface is important, and the process is industrially advantageous.

However, the above-mentioned conventional method has a problem in that respect. That is, the former method of dispersing the water-absorbent resin powder in the solvent to carry out the crosslinking reaction requires a large amount of the solvent, and its recovery process is industrially disadvantageous. Particularly when the treatment is carried out in a hydrophobic organic solvent, the distribution of the cross-linking agent on the resin surface tends to be non-uniform, and therefore the cross-linking on the surface tends to be non-uniform. On the other hand, the latter method of mixing and heat-treating the water-absorbent resin powder and the liquid mixture containing the crosslinking agent is a very advantageous method industrially, but the particle diameter of the water-absorbent resin powder is small. In some cases or when the particle size distribution is wide, the powders may associate with each other due to the composition of the liquid mixture mixed with the water-absorbent resin powder to form a large lump, and uniform surface cross-linking may be difficult. Further, although physical properties such as water absorption rate and suction force can be improved to some extent by carrying out these treatments, the treatment is insufficient at all, and elution of water-soluble components is hardly prevented. As described above, there has been no sufficiently satisfactory method for improving the water absorption properties of the water absorbent resin in a well-balanced manner.

[Means and Methods for Solving the Problems]

The present inventors have reached the present invention as a result of intensive research to solve the above problems.

That is, the present invention relates to a water-absorbent resin having an average particle diameter of 100 to 600 μm, a particle diameter distribution of logarithmic standard deviation value σζ of 0.35 or less, and a particle surface cross-linked, and a method for producing the same. The other is a non-spherical non-spherical particle having a ratio of the average major axis to the average minor axis of the particles of 1.5 to 20, and the particle surface is cross-linked, and relates to a method for producing the same. is there.

Since the surface of the water absorbent resin of the present invention is uniformly modified, it has excellent water absorption capacity, water absorption speed, suction force and gel strength, and has a small amount of water-soluble components. Further, the water-absorbent resin having a ratio of the average major axis to the average minor axis of 1.5 to 20 has good handleability.

In the method for producing a water absorbent resin of the present invention, the average particle size is 100 to 6
Water-absorbing polymer powder having a particle size distribution of 100 μm and a logarithmic standard deviation value σζ of 0.35 or less, or a non-spherical water-absorbing polymer having a ratio of an average major axis to an average minor axis of 1.5 to 20 and no corners. It crosslinks the surface of the polymer powder.

The method for obtaining the water-absorbing polymer powder having the above-mentioned average particle size and particle size distribution used in the present invention is to perform aqueous solution polymerization of a water-soluble ethylenically unsaturated monomer, and then to obtain the above-mentioned average particle size and particle size distribution. Examples include a method of pulverizing and classifying so as to fall within the range of, and a method of performing reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer under specific conditions. In order to obtain a water-absorbing polymer powder having a diameter distribution or a novel shape, the water-soluble ethylenically unsaturated monomer or its aqueous solution is suspended and dispersed in a hydrophobic organic solvent to carry out radical polymerization. When performing reverse phase suspension polymerization with an initiator, the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution is selected to be 15 cps or more by Brookfield rotational viscometer (25 ° C., 0.6 rpm), Sucrose fatty acid as a dispersant Most preferred systems using ether and / or polyglycerin fatty acid ester.

In the case of carrying out the above-mentioned manufacturing method, if the viscosity defined as above is adjusted to 15 to 5,000 cps, the average particle diameter is 100 to 600 μm and the index (logarithmic standard deviation) showing the particle diameter distribution. A polymer powder having a value) σζ of 0.35 or less can be obtained.

Furthermore, when carrying out the above manufacturing method, the viscosity defined as above is adjusted to 5,000 to 1,000,0.
If the sucrose fatty acid ester is used as the dispersant only, the ratio of the average major axis to the average minor axis of the particles is in the range of 1.5 to 20, and the non-spherical non-spherical particles are used. The polymer powder can be obtained in good yield.

Examples of the water-soluble ethylenically unsaturated monomer constituting the polymer used in the present invention include acrylic acid, methacrylic acid, 2-
(Meth) acryloylethanesulfonic acid, 2- (meth)
Anionic monomers such as acryloyl propane sulfonic acid, 2- (meth) acrylamide-2-methyl propane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid and salts thereof; (meth) acrylamide, N-substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate,
Nonionic hydrophilic group-containing monomers such as polyethylene glycol (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) Examples thereof include cationic monomers such as aarylate and N, N-dimethylaminopropyl (meth) acrylamide, quaternary compounds thereof, and the like, and one kind or a mixture of two or more kinds thereof can be used. Preferably, acrylic acid, methacrylic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acrylamide-
2-Methylpropanesulfonic acid and salts thereof, N, N
-One or two or more selected from the group consisting of dimethylaminoethyl (meth) acrylate and its quaternary compounds, methoxypolyethylene glycol (meth) acrylate and (meth) acrylamide. The monomer concentration in the aqueous monomer solution is generally variable over a wide range, but is preferably 20% by weight or more to the saturated concentration.

The water-absorbing polymer powder used in the present invention is a self-crosslinking type which does not use a crosslinking agent, or a small amount of a crosslinking agent having two or more polymerizable unsaturated groups or reactive functional groups at the time of polymerization. It may be one.

Examples of these cross-linking agents include those having a polymerizable unsaturated group, such as N, N'-methylenebis (meth).
Acrylamide, N-methylol (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, (meth) acrylic acid polyvalent Metal salts, trimethylolpropane tri (meth) acrylate, triallylamine, triallyl cyanurate,
Triallyl isocyanurate, triallyl phosphate, glycidyl (meth) acrylate, and those having a reactive functional group, for example, ethylene glycol, diethylene glycol, triethylene glycol when the unsaturated monomer has a carboxyl group. , Tetraethylene glycol, polyethylene glycol, glycerin,
Polyhydric alcohols such as polyglycerin, propylene glycol, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol, sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol Polyvalent glycidyl compounds such as polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether; -Bishydroxymethylbutanol-
Tris [3- (1-aziridinyl) propionate],
Polyvalent aziridines such as 1,6-hexamethylenediethyleneurea, diphenylmethane-bis-4,4'-N, N'-diethyleneurea; epichlorohydrin, α-
Haloepoxy compounds such as methyl chlorohydrin;
Multivalent aldehydes such as glutaraldehyde, glyoxal, etc .; ethylenediamine, diethylenetriamine,
Triethylenetetramine, tetraethylenepentamine,
Polyvalent amines such as pentaethylenehexamine and polyethyleneimine; Polyisocyanates such as 2,4-toluylene diisocyanate and hexamethylene diisocyanate, aluminum chloride, magnesium chloride,
Examples thereof include polyvalent metal salts such as calcium chloride, aluminum sulfate, magnesium sulfate, calcium sulfate and the like. These crosslinking agents may be used as a mixture of two or more in consideration of reactivity and the like, but it is usually more preferable to use a crosslinking agent having a polymerizable unsaturated group as an essential component. The amount of these cross-linking agents used is generally from 0.01 to 1 based on the water-soluble ethylenically unsaturated monomer.
It is about 0 mol%.

In order to obtain a polymer that can be suitably used in the present invention, the aqueous solution viscosity of the water-soluble ethylenically unsaturated monomer is adjusted to 15 cps or more, and sucrose fatty acid ester and / or
Alternatively, a method of reverse phase suspension polymerization using polyglycerin fatty acid ester is also preferable, but in this case, the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution is measured by a Brookfield rotational viscometer (25 ° C, 0.6 rpm). It is necessary to adjust the above viscosity (hereinafter, simply referred to as viscosity) to be 15 cps or more. Viscosity is 15 cp
When it is lower than s, the average particle size obtained by polymerization is small and the particle size distribution is wide.

In addition, the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution is 15
It is possible to obtain a spherical polymer which can be suitably used in the present invention having an average particle size in the range of 100 to 600 μm and a very narrow particle size distribution depending on its viscosity by controlling the viscosity within a range of up to 5000 cps. it can. Further, generally, under the same conditions, the higher the viscosity of the aqueous monomer solution is, the larger the average particle size of the obtained resin is, and various average particle sizes can be obtained by a simple operation of adjusting the viscosity. The average particle size of the obtained polymer powder varies depending on its use, but when it is used for sanitary materials, the average particle size is usually 100 to 600 μm, preferably 150 to 600 μm.
About 400 μm, in which case the viscosity of the water-soluble monomer is 15 to 5000 cps, preferably 20 to 3000
It is obtained by adjusting to cps. The polymer powder thus obtained has a very narrow particle size distribution. For example, when the particle size distribution is plotted on a logarithmic probability paper, the logarithmic standard deviation value σζ which is an index showing the uniformity of the distribution cannot be obtained by the conventional method of 0.35 or less, preferably 0.30 or less. A polymer having a narrow particle size distribution is obtained.

On the other hand, when the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution is adjusted to the range of 5,000 to 1,000,000 cps, it depends on the stirring conditions, but the average major axis of the particles is determined as follows. And the average minor axis ratio is 1.5 to 20
In this range, a non-spherical non-spherical powder, for example, a wiener sausage-like powder is obtained. This polymer is
The major axis is 100 to 10,000 μm, preferably 1000
To 10,000 μm, the minor axis is 10 to 2000 μm, preferably 100 to 2000 μm, and the ratio of the average major axis to the average minor axis is within the range of 1.5 to 20 as described above. It is extremely easy to handle because it does not easily fall off, and the range of combinations with various base materials is expanded. The diameter for expressing the shape of the polymer powder having this novel shape is defined as follows.

Even within the above viscosity range of 5,000 cps, when the viscosity is 5,000 to 20,000 cps, the non-spherical polymer and the spherical polymer are mixed, and when the viscosity is higher than 20,000 cps, the non-spherical polymer is almost non-spherical. Only coalesced is obtained. If the viscosity is higher than 1,000,000 cps, it may be difficult to supply the monomer aqueous solution to the reactor.

Examples of the thickener that can be used for adjusting the viscosity as described above include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyacrylamide, polyethyleneimine, polyacrylic acid, polyacrylic acid (partial) neutralization. And polyacrylic acid crosslinked products, polyacrylic acid (partial) neutralized product crosslinked products, dextrin, sodium alginate and the like, but preferably hydroxyethyl cellulose, polyacrylamide, polyacrylic acid, polyacrylic acid (partial) Neutralized product, polyacrylic acid (partial) neutralized product crosslinked product. When a water-soluble neutralized product of polyacrylic acid (partial) is used, the viscosity of the 5% aqueous solution thereof is preferably 30 cps or more. When a water-insoluble material such as a crosslinked material is used, its particle size is 30
A powdery material having a size of about μm or less is preferable.

In order to thicken a water-soluble liquid to a predetermined viscosity using these thickeners, it depends on the type and concentration of the monomer and the molecular weight of the thickener, but the thickener is used as a monomer. On the other hand, it is generally preferable to use it in the range of 0.05 to 20% by weight.

The dispersant used in this case is sucrose fatty acid ester and / or polyglycerin fatty acid ester.
Examples of the sucrose fatty acid ester include mono-, di-, and triesters of sucrose and one or more fatty acids selected from stearic acid, palmitic acid, lauric acid, oleic acid, and the like. On the other hand, as the polyglycerin fatty acid ester, polyglycerin having a condensation degree of 10 or less and at least one kind of fatty acid selected from stearic acid, palmitic acid, lauric acid, oleic acid, ricinoleic acid, etc., mono-, di- and triether, etc. Can be given. Among these nonionic surfactants, those having an HLB of 2 to 6 are particularly preferable. The amount of the dispersant used is generally 0.05 to 10% by weight, preferably 0.5 to 5% by weight, based on the water-soluble ethylenically unsaturated monomer.

In addition, one of the polymers that can be preferably used in the present invention,
In order to obtain a non-spherical non-spherical water-absorbing polymer, it is necessary to use only sucrose fatty acid ester as a dispersant, and other dispersants cannot obtain a water-absorbent resin having such a good shape. .

In order to obtain the polymer powder used in the present invention, when the reversed phase suspension polymer is adopted as described above, the non-polymerizable hydrophobic organic solvent used is, for example, n-pentane, n-hexane, n. -Aliphatic hydrocarbons such as heptane and n-octane; Alicyclic hydrocarbons such as cyclohexane, cyclooctane, methylcyclohexane and decalin; Aroma which may have a substituent such as benzene, ethylbenzene, toluene and xylene Group hydrocarbons; halogenated hydrocarbons such as chlorobenzene, brombenzene, carbon tetrachloride, 1,2-dichloroethane and the like can be mentioned, and one kind or a mixture of two or more kinds thereof can be used, but particularly preferably, They are n-hexane, n-heptane, cyclohexane, methylcyclohexane, toluene, xylene and carbon tetrachloride.

The ratio of the organic solvent to the water-soluble ethylenically unsaturated monomer is generally preferably 1: 1 to 5: 1 from the viewpoint of removal of heat of polymerization, control of temperature, or stable dispersibility.

The radical polymerization initiator can be used without limitation as long as it is one commonly used in the art, and a water-soluble one is particularly preferable. Specifically, for example, persulfates such as potassium persulfate, sodium persulfate, ammonium persulfate; hydrogen peroxide, t-butyl hydroperoxide,
Hydroperoxides such as cumene hydroperoxide; azo compounds such as 2,2′-azobis-2-amidinopropane dihydrochloride. These polymerization initiators can be used as a mixture of two or more kinds, and further, a redox type initiator in combination with a reducing agent such as sulfite, l-ascorbic acid, ferric salt, etc. should be used. You can also

When the reverse-phase suspension polymerization as described above is performed to obtain the water-absorbent polymer used in the present invention, a drying step is performed after the polymerization, so that the obtained polymer is a bead-like or sausage-like powder. It can be taken out as a body. As this drying step, a method of distilling off water by azeotropy with the hydrophobic organic solvent used for the polymerization, or filtration of the hydrous gel-like material, and then using a normal hot air dryer, a vacuum dryer or a fluidized bed dryer. There are methods such as drying.

Further, in order to obtain a polymer powder that can be used in the present invention, not only the above-mentioned reversed-phase suspension polymerization method, but also a hydrogel obtained by aqueous solution polymerization carried out by a known method is dried, pulverized, and classified. In doing so, the average particle size may be adjusted to 100 to 600 μm, and the particle size distribution may be adjusted to have a logarithmic standard deviation value σζ of 0.35 or less.

In the production method of the present invention, a polymer and / or a sausage-like polymer having an average particle diameter within a specific range and having a narrow particle diameter distribution obtained by the above-mentioned method is surface-treated by a conventionally known method. By doing so, the surface of the polymer is uniformly modified.

As a more preferable method of the surface treatment, a cross-linking agent having in the molecule two or more groups reactive with the functional group in the polymer powder, which is obtained by drying the polymer powder until the water content is less than 10% After mixing with 0.005 to 20% by weight (based on the polymer powder), the mixture is heated and reacted to uniformly crosslink the vicinity of the surface of the polymer powder. When mixing the cross-linking agent and the polymer powder, water and a hydrophilic organic solvent may be contained.

In carrying out this surface cross-linking treatment, if the treatment conditions are selected to be the following specific ones, the treatment effect will be excellent, and it will be advantageous in terms of the process. That is, a polymer powder having a water content of less than 10%, a crosslinking agent, water and a hydrophilic organic solvent are added to the polymer powder in an amount of 0.005 to 20 respectively.
It is a method in which the polymer powder is cross-linked in the vicinity of the surface by mixing with a treatment solution containing the polymer powder in an amount of 0.1% by weight, 0.1% by weight to 5% by weight and 0.01% by weight to 6% by weight.

When having an average particle size in a specific range obtained by the procedure, and mixing a polymer powder having a narrow particle size distribution with a treatment solution having a specific composition containing a crosslinking agent, no lumps are generated at the time of mixing, The treatment solution is uniformly dispersed on the surface of the polymer powder, and appropriately penetrates into the vicinity of the surface of the powder to uniformly and efficiently crosslink the vicinity of the surface. Thus, it is possible to obtain a water absorbent resin having a high water absorption capacity, an excellent water absorption speed and suction force, and a very small amount of water-soluble components eluted from the resin, which is suitable as a sanitary material. In the method for producing the water absorbent resin of the present invention, first, the water content of the polymer obtained by the above-mentioned reverse phase suspension polymerization or the like is adjusted to 1 by the same drying step as described above.
It is necessary to keep it below 0%, preferably below 7%. When the water content is 10% or more, when mixed with a cross-linking agent or a treatment solution containing the cross-linking agent, the mixing property is poor and the cross-linking agent excessively penetrates into the resin, and the resulting water-absorbent resin has a water absorption ratio of It may become smaller.

The crosslinking agent that can be used in the present invention is not particularly limited as long as it is a compound having two or more functional groups capable of reacting with the functional group of the polymer, but is preferably hydrophilic, more preferably water-soluble. A compound, for example, when the polymer has a carboxyl group and / or a carboxylate group as a functional group, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, Polyhydric alcohols such as triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol Polyglycidyl ether such as diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, etc. Compounds; 2,2-bishydroxymethylbutanol-
Tris [3- (1-aziridinyl) propionate],
Polyvalent aziridines such as 1,6-hexamethylenediethyleneurea, diphenylmethane-bis-4,4'-N, N'-diethyleneurea, etc .; epichlorohydrin, α
-Haloepoxy compounds such as methyl chlorohydrin; polyvalent aldehydes such as glutaraldehyde, glyoxal; polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine Examples include polyvalent isocyanates such as 2,4-toluylene diisocyanate and hexamethylene diisocyanate; polyvalent metal salts such as aluminum chloride, magnesium chloride, calcium chloride, aluminum sulfate, magnesium sulfate, calcium sulfate and the like. it can. Particularly preferred are polyhydric alcohols, polyhydric glycidyl compounds, polyvalent amines, and polyvalent metal salts. The amount of these crosslinking agents used is 0.005 to 20% by weight, preferably 0.005 to 5% by weight, and more preferably 0.01 to 1% by weight, based on the polymer powder. If this amount is less than 0.005% by weight, the surface treatment effect does not appear, and even if it is used in excess of 20% by weight, the effect corresponding to the amount of the cross-linking agent used cannot be obtained, and the water absorption capacity is remarkably high. It may become smaller.

Further, in the present invention, when the crosslinking agent is mixed with the polymer powder,
It is more preferable to use a treatment solution containing water and a hydrophilic organic solvent in order to enhance the treatment effect. In this case, the amount of water constituting the treatment solution is 0.1 to 5% by weight based on the polymer powder.
Is. If this amount is less than 0.1% by weight, it becomes difficult for the cross-linking agent to properly permeate into the vicinity of the powder surface, and the surface cross-linking layer is not properly formed. The water absorption capacity may decrease.

The hydrophilic organic solvent that constitutes the treatment solution is not particularly limited as long as it dissolves the crosslinking agent and does not affect the performance of the water absorbent resin. Examples thereof include methyl alcohol, ethyl alcohol, n-
Propyl alcohol, iso-propyl alcohol, n
-Butyl alcohol, iso-butyl alcohol, t-
Examples thereof include lower alcohols such as butyl alcohol, ketones such as acetone and methyl ethyl ketone, ethers such as dioxane and tetrahydrofuran, amides such as N, N-dimethylformamide, and sulfoxides such as dimethyl sulfoxide. The amount of the hydrophilic organic solvent used is 0.1 to 6% by weight based on the polymer powder. When the amount of the hydrophilic organic solvent used is less than 0.1% by weight,
Mixing of the polymer and treatment solution may be non-uniform.
Further, even if the amount exceeds 6% by weight, the effect commensurate with the amount used cannot be obtained and only the cost is increased, which is not industrially preferable. Although it depends on the kind of the hydrophilic organic solvent, it is generally preferable to use 0.3 to 4% by weight based on the polymer powder.

In the present invention, as a method of mixing the treatment solution containing the crosslinking agent with the polymer powder, it is general to spray or drop / mix the polymer powder with the treatment solution. As a mixer used for mixing, a mixer having a large mixing force is preferable for uniform mixing, but a normal mixer or a kneader can be used. For example, a cylinder type mixer, a double cone type mixer, a V type mixer, a ribbon type mixer, a screw type mixer, a fluidizing type mixer, a rotary disc type mixer, an air flow type mixer, a double arm type kneader. Japanese-style machines, internal mixers, muller type kneaders, roll mixers, screw type extruders and the like. To heat the mixture obtained by mixing the polymer powder with the treatment solution containing these crosslinking agents, a usual dryer or heating furnace can be used. For example, a groove-type stirring dryer, a rotary dryer, a disk dryer, a kneading dryer, a fluidized bed dryer, a stream dryer, an infrared dryer, a dielectric heating dryer and the like. Heat treatment temperature is 40
To 250 ° C, preferably 80 to 200 ° C.

〔The invention's effect〕

The water-absorbent resin of the present invention has an average particle diameter in a specific range and has a narrow particle diameter distribution, has a high water-absorption capacity, an excellent water-absorption rate and a suction force, and has a water-absorbing property present inside the resin. Elution of soluble components from the resin surface is extremely small, and when used as a sanitary material, it is particularly excellent in liquid diffusivity and safety. Such a water-absorbent resin is, as described above,
A water-soluble ethylenically unsaturated monomer aqueous solution adjusted to a specific viscosity with a thickener was subjected to reverse phase suspension polymerization using sucrose fatty acid ester and / or polyglycerin fatty acid ester as a dispersant to obtain a heavy polymer. When the combined product is dried, mixed with a treatment solution containing a cross-linking agent having a specific composition, and heated, it is possible to effectively produce the compound with the highest yield. In addition, since the method of treating the surface portion in this case does not require a large amount of organic solvent, it is an economically and industrially advantageous method, and an excellent water-absorbent resin with high safety as a sanitary material and various water retention agents. Can be obtained by a very advantageous method in terms of manufacturing method.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited to these Examples. Unless otherwise specified, "%" means "% by weight" and "part" means "part by weight".

The water absorption performance of the water absorbent resin was measured by the method described below.

(1) Average particle size and particle size distribution The average particle size is a polymer powder using a JIS standard sieve (20 mesh, 32 mesh, 48 mesh, 60 mesh, 100 mesh, 145 mesh, 200 mesh, 350 mesh). After sieving, the residual percentage R
Was plotted on a logarithmic probability paper, and the particle diameter corresponding to R = 50% was taken as the average particle diameter.

As for the particle size distribution, the logarithmic standard deviation value σζ represented by the following formula was used as the index. Here, the smaller the value of σζ, the narrower the particle size distribution.

(X ₁ is the particle diameter when R = 84.1% and x ₂ is the particle diameter when R = 15.9%) (2) Water absorption ratio 0.2 g of water-absorbent resin is a non-woven tea bag bag (4
(0 mm × 150 mm), dipped in a 0.9 wt% sodium chloride aqueous solution for 10 minutes and 30 minutes, then pull up this tea bag type bag, drain it for a certain period of time, and measure its weight. The water absorption capacity was calculated by the formula. The water absorption weight when only the tea bag type bag was immersed was set as the blank.

(3) Water absorption rate 1.0 g of water-absorbent resin was added to 20 ml of artificial urine (containing 1.9 wt% urea, 0.8 wt% sodium chloride, 0.1 wt% calcium chloride, and 0.1 wt% magnesium sulfate). In addition, the water absorption rate was defined as the time taken for the water absorbent resin to absorb all artificial urine and the fluidity of the swollen gel disappeared.

(4) Suction power Artificial urine 2 on tissue paper (55 mm x 75 mm)
0 ml was added to prepare a base material containing artificial urine, and 1.0 g of the water absorbent resin was placed on the base material. After 10 minutes, the swollen gel was sampled and the weight thereof was measured to obtain the force of sucking the liquid from the tissue paper. In addition, the presence or absence of Mamako of the water absorbent resin added at the same time was observed.

(5) Amount of water-soluble component eluted from resin surface A commercially available children's paper diaper (weight: 72 g) consisting of a non-woven fabric, cotton-like pulp, water-absorbent paper and a waterproof film is cut in half,
2.5 g of the polymer was evenly dispersed between the cotton-like pulp and the absorbent paper, 120 ml of the artificial urine was added, and the mixture was allowed to stand at 37 ° C. for 16 hours. After 16 hours, only the cotton-like pulp on the upper part of the polymer was taken, the water-soluble component transferred to this pulp was extracted with 1000 ml of pure water, filtered with filter paper, and the polymer content in the filtrate was measured by acid-base titration. Then, the total amount of the soluble water-soluble components (% by weight) with respect to the water absorbent resin was determined.

Example 1 Cyclohexane 1.0 was placed in a 2-necked separable flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube and a dropping funnel, and sucrose fatty acid ester as a dispersant (Daiichi Kogyo) 4.0 g of DK-ester F-50, HLB = 6, manufactured by Pharmaceutical Co., Ltd. was added and dissolved, and nitrogen gas was blown in to expel dissolved oxygen. Separately, 84.6 g of sodium acrylate and 2 acrylic acid in a flask.
1.6 g and 0.016 g of N, N'-methylenebisacrylamide were dissolved in 197 g of ion-exchanged water, and further hydroxyethyl cellulose (manufactured by Daicel Chemical Industries, Ltd.)
Manufactured by HEC-Daicel EP-850) was dissolved to prepare an aqueous monomer solution having a monomer concentration of 35% by weight and a viscosity of 40 cps. After 0.15 g of potassium persulfate was added to and dissolved in this monomer aqueous solution, nitrogen gas was blown in to expel oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in this flask was added to the above separal flask and stirred at 230 rpm for dispersion. Then, the bath temperature was raised to 60 ° C. to start the polymerization reaction, and then the temperature was maintained for 2 hours to complete the polymerization. After completion of the polymerization, water in the hydrous gel was distilled off by azeotropic dehydration with cyclohexane, filtered, and dried under reduced pressure at 80 ° C. to obtain spherical polymer powder [A01]. The water content of the obtained polymer powder [A01] was 5.6%.

A treatment solution consisting of 0.3 part of diethylene glycol, 4 parts of water and 0.5 part of isopropanol was mixed with 100 parts of the polymer powder [A01] using a paddle type mixer. No large lumps were generated at the time of mixing, and when the mixture was passed through a 20-mesh wire mesh (opening 840 μm), all of the mixture passed. The resulting mixture is paddle-dried at 18
Water-absorbent resin [A1
1] was obtained. Various properties of the resulting water absorbent resin [A11] are summarized in Table 1.

Example 2 Polymerization was carried out under the same conditions as in Example 1 except that 2.2 g of hydroxyethyl cellulose (SP-600 manufactured by Daicel Chemical Industries, Ltd.) was used as a thickener. The viscosity of the aqueous monomer solution was 800 cps, and the obtained spherical polymer powder [A02] had a water content of 6.8%.

A treatment solution consisting of 0.1 part of ethylene glycol glycidyl ether, 3 parts of water and 6 parts of methanol was mixed with 100 parts of the polymer powder [A02] with a paddle type mixer. The mixture was passed through a 20 mesh wire mesh and all the mixture passed. The resulting mixture is paddle-dried for 10
Water-absorbent resin [A1
2] was obtained. The measurement results of the various performances are shown in Table 1.

Example 3 Polymerization was carried out in the same manner as in Example 1 except that 3.5 g of hexaglycerin condensed ricinoleate (manufactured by Kao Corporation, Step RP-6) was used as a dispersant, and a spherical polymer powder [A03] was used. Got The water content of the obtained polymer powder [A03] was 6.3%.

A treating solution consisting of 0.08 part of epichlorohydrin, 2 parts of water and 4 parts of methanol was mixed with 100 parts of the polymer powder [A03] by a V-type mixer. When the mixture was passed through a wire mesh of 20 mesh, all the mixture passed and no lump was generated during mixing. The resulting mixture was heat treated with a paddle dryer at 100 ° C. for 1 hour to obtain a water absorbent resin [A13]. The measurement results of the various performances are shown in Table 1.

Example 4 Cyclohexane 1.0 was placed in a two-necked four-separable flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introduction tube and a dropping funnel, and sucrose fatty acid ester (Daiichi Kogyo Seiyaku Co., Ltd.) was used as a dispersant. DK-ester F manufactured by Co., Ltd.
-20) 4.0 g was added and dissolved, and nitrogen gas was blown in to expel dissolved oxygen.

Separately, in a flask, 65.8 g of sodium acrylate, 21.6 g of acrylic acid and 0.076 g of polyethylene glycol diacrylate (n = 14) and sodium polyacrylate as a thickener (Aqualic OM manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) 1.5 g of a 5% aqueous solution of -100, 25 ° C and a viscosity of 150 cps) was dissolved in 250 g of ion-exchanged water to prepare a monomer aqueous solution having a viscosity of 20 cps.

Then, after adding and dissolving 0.12 g of sodium persulfate, the same operation as in Example 1 was performed to obtain a spherical polymer powder [A04]. The water content of the obtained polymer powder [A04] was 4.8%.

A treatment solution consisting of 1 part of glycerin, 5 parts of water and 1 part of isopropanol was mixed with 100 parts of the polymer powder [A04] by a paddle type mixer. The mixture passed through a 20-mesh wire mesh and no lumps were generated during mixing. Then, the obtained mixture was heated with a paddle dryer at 180 ° C. for 1.5 hours to obtain a water absorbent resin [A14]. The measurement results of the various performances are shown in Table 1.

Example 5 Sodium polyacrylate (produced by Nippon Shokubai Kagaku Kogyo Co., Ltd., Aqualic FH, 2 as a thickener in Example 4)
The same operation as in Example 4 was carried out except that 1.0 g of a 1% aqueous solution having a viscosity of 2 × 10 ⁴ cps at 5 ° C. was used to obtain a polymer powder [A05] having a water content of 5.8%. At this time, the viscosity of the aqueous monomer solution was 27 cps.

100 parts of the obtained polymer powder [A05] was added to 0.05 part of glyceryl glycidyl ether, 4 parts of water, and 0.1 part of ethanol.
The treatment solution consisting of 8 parts was mixed with a ribbon mixer. The mixture passed through a 20-mesh wire mesh and no lumps were generated during mixing. The resulting mixture in a fluid bed dryer,
Water absorbent resin [A1
5] was obtained.

Example 6 Hydroxyethyl cellulose added to the monomer aqueous solution in Example 1 (manufactured by Daicel Chemical Industries, Ltd., HEC-
Polymerization was carried out under the same conditions as in Example 1 except that the amount of Daicel EP-850) was changed to 1.6 g and the viscosity of the aqueous monomer solution was adjusted to 2000 cps to obtain a polymer powder [A06] having a spherical shape. Obtained. The obtained polymer powder [A0
6] had a water content of 6.4%.

This polymer powder [A06] was surface-crosslinked in the same manner as in Example 1 to obtain a water absorbent resin [A16]. The various properties of the water absorbent resin are summarized in Table 1.

Example 7 Hydroxyethyl cellulose added to the aqueous monomer solution in Example 2 (manufactured by Daicel Chemical Industries, Ltd., HEC-
Polymerization was performed under the same conditions as in Example 2 except that the amount of Daicel CP-600) was set to 0.3 g and the viscosity of the aqueous monomer solution was adjusted to 17 cps, to obtain a polymer powder [A07] having an all spherical shape. . The water content of the obtained polymer powder [A07] was 5.9%.

This polymer powder [A07] was surface-crosslinked in the same manner as in Example 1 to obtain a water absorbent resin [A17]. The various properties of the water absorbent resin are summarized in Table 1.

Example 8 In a four-neck separable flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing tube and a dropping funnel, 1.0 was charged with cyclohexane, and sucrose fatty acid ester (Daiichi Kogyo Seiyaku Co., Ltd.) was used as a dispersant. DK-ester F manufactured by Co., Ltd.
-50, HLB = 6) 4.0 g was added and dissolved, and nitrogen gas was blown in to expel dissolved oxygen. Separately, 84.6 g of sodium acrylate and 2 acrylic acid in a flask.
2. 1.6 g and 0.016 g of N, N'-methylenebisacrylamide were dissolved in 197 g of ion-exchanged water, and hydroxyethyl cellulose (HEC-Daicel EP-850 manufactured by Daicel Chemical Industries, Ltd.) was used as a thickener.
2 g was dissolved, the monomer concentration was 35% by weight, the viscosity was 35,
A 000 cps aqueous monomer solution was prepared. After 0.15 g of potassium persulfate was added to and dissolved in this monomer aqueous solution, nitrogen gas was blown in to expel oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in the flask was added to the separable flask and stirred at 230 rpm to disperse the monomer solution. Then, the bath temperature was raised to 60 ° C. to start the polymerization reaction, and then the temperature was maintained for 2 hours to complete the polymerization. After completion of the polymerization, water in the hydrous gel was distilled off by azeotropic dehydration with cyclohexane, filtered and dried under reduced pressure at 80 ° C. to obtain a slightly elongated Wiener sausage-like polymer powder having an average major axis of 3000 μm and an average minor axis of 550 μm. The body [A08] was obtained.

This polymer powder was surface-crosslinked in the same manner as in Example 1 to obtain a water absorbent resin [A18].

Example 9 Polymerization was performed under the same conditions as in Example 2 except that the amount of hydroxyethyl cellulose (manufactured by Daicel Chemical Industries, Ltd., EP-850) as a thickener was changed to 5.3 g. The viscosity of the aqueous monomer solution was 240,000 cps. After completion of the polymerization, azeotropic dehydration, filtration, and drying under reduced pressure at 80 ° C., the average major axis is 3500 μm and the average minor axis is 600 μm. A slender Wiener sausage-like polymer powder [A09] was obtained.

This polymer powder was surface-crosslinked in the same manner as in Example 2 to obtain a water absorbent resin [A19].

Example 10 141 g of sodium acrylate, 36.1 g of acrylic acid
And N, N'-methylenebisacrylamide 0.11
8 g was dissolved in 329 g of ion-exchanged water, 0.68 g of ammonium persulfate and 0.025 of sodium bisulfite.
Using g, static polymerization was performed in a nitrogen atmosphere at 55 to 80% to obtain a gel-like hydropolymer. 180% of this gel-like hydropolymer
After drying with a hot air dryer at ℃, crush with a hammer crusher,
A crushed polymer powder [A010] was obtained by taking a portion which passed through the 28-mesh wire net and did not pass through the 60-mesh wire net.

Comparative Example 1 Various properties of the polymer powder [A01] of Example 1 were measured and shown in Table 1.

Comparative Example 2 The same polymerization as in Example 1 was carried out except that 3.5 g of sorbitan monostearate (Reodol SP-S10 manufactured by Kao Corporation) was used as the dispersant in place of sucrose fatty acid ester. Water content 6.2%, average particle size 8
Comparative polymer powder of 0 μm, σζ, 0.43 [B01]
Got

The obtained comparative polymer powder [B01] was mixed with the same treatment solution as in Example 1 using a paddle type mixer. At the time of mixing, 8.6% of lumps which did not pass through the 20-mesh wire mesh were formed. The mixture that passed through the obtained 20-mesh wire net was subjected to heat treatment with a paddle dryer at 180 ° C. for 1 hour to obtain a comparative water absorbent resin [B11]. The measurement results of the various performances are shown in Table 1.

Comparative column 3 The same operation as in Example 1 was carried out except that hydroxyethyl cellulose was not added to the aqueous monomer solution, and the comparative polymer powder [B02 having a water content of 4.7%, an average particle size of 100 μm and σζ = 0.41] was used. ) Got. At this time, the viscosity of the aqueous monomer solution was 7 cps.

The comparative polymer powder [B02] thus obtained was mixed with the same treatment solution as in Example 2 using a paddle type mixer. At the time of mixing, 8.2% of lumps which did not pass through the 20-mesh wire mesh were formed. The resulting mixture was heat-treated in a fluidized bed dryer at 100 ° C. for 1 hour to obtain a comparative water absorbent resin [B12]. The measurement results of the various performances are shown in Table 1.

Comparative Example 4 In Example 1, except that 4.0 g of tetraglycerin monostearate (Riken Vitamin Co., Ltd., Poem J-4010) instead of sucrose fatty acid ester was used as a dispersant, hydroxyethyl cellulose was not added to the monomer aqueous solution. The same operation was performed to obtain a comparative polymer powder [B03] having a water content of 5.9%, an average particle size of 150 μm, and σζ = 0.40.

The obtained comparative polymer powder [B03] was mixed with the same treatment solution as in Example 1 using a paddle type mixer. At the time of mixing, 7.6% of lumps which did not pass through the 20-mesh wire mesh were formed. The resulting mixture was heat treated with a paddle dryer at 180 ° C. for 1 hour to obtain a comparative water absorbent resin [B13]. The measurement results of the various performances are shown in Table 1.

Comparative Example 5 Various properties of the polymer powder [A08] of Example 8 were measured and shown in Table 1.

Comparative Example 6 A polymer powder for comparison [B04] was obtained by taking only the portion passing through the 28-mesh wire net in Example 10.

The comparative polymer powder was surface-crosslinked in the same manner as in Example 1 to obtain a comparative water absorbent resin [B14].

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle structure of the water absorbent resin (A16) obtained in Example 6. FIG. 2 is an electron micrograph showing the particle structure of the wiener sausage-like water absorbent resin (A18) obtained in Example 8. FIG. 3 shows a comparative water absorbent resin (B1 obtained in Comparative Example 3).
It is an electron micrograph showing the particle structure of 2).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Shimomura 5-8 Nishimitabicho, Suita City, Osaka Prefecture Kazutaka Itabashi Examiner, Central Research Laboratory, Nippon Shokubai Chemical Co., Ltd.

Claims (13)

[Claims] 1. A water-absorbent resin having an average particle diameter of 100 to 600 μm, a particle diameter distribution of logarithmic standard deviation value σζ of 0.35 or less, and having a particle surface cross-linked. 2. The ratio of the average major axis to the average minor axis of the particles is 1.5 to.
A water-absorbent resin having a non-spherical shape of 20 and having a particle surface cross-linked. 3. In Claim 2, the major axis of particles is 100.
A water absorbent resin having a particle size of ˜10,000 μm and a minor axis of 10 to 2,000 μm. 4. A method for producing a water absorbent resin, wherein the surface of a polymer powder having an average particle size of 100 to 600 μm and a particle size distribution of logarithmic standard deviation σζ 0.35 or less is subjected to a crosslinking treatment. 5. The ratio of the average major axis to the average minor axis of the particles is 1.5 to.
A method for producing a water absorbent resin, wherein the surface of a non-spherical polymer powder having no corners at 20 is subjected to a crosslinking treatment. 6. A method for producing a water absorbent resin according to claim 4 or 5, wherein the water content of the polymer powder is less than 10% by weight. 7. The polymer powder according to claim 4, 5 or 6, wherein the polymer powder is a Brookfield rotational viscometer (25.degree.
A water-soluble ethylenically unsaturated monomer aqueous solution having a viscosity of 15 cps or more at 6 rpm) is dispersed in a polymerization-inert hydrophobic organic solvent by using sucrose fatty acid ester and / or polyglycerin fatty acid ester as a dispersant. A method for producing a water absorbent resin, which is obtained by suspending and polymerizing with a radical polymerization initiator. 8. A method for producing a water-absorbent resin according to claim 7, wherein the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution is adjusted to 15 to 5,000 cps. 9. In claim 7, the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution is 5,000 to 1,000,0.
A method for producing a water absorbent resin, which is adjusted to 00 cps and uses only sucrose fatty acid ester as a dispersant. 10. Claims 4, 5, 6, 7, 8 or 9 wherein, in the cross-linking treatment, a cross-linking agent having two or more groups reactive with a functional group of the polymer in the molecule is used. Of producing water absorbent resin. 11. The method for producing a water-absorbent resin according to claim 10, wherein the crosslinking agent is used in the form of a treatment solution obtained by mixing the crosslinking agent with water and a hydrophilic organic solvent. 12. The compounding ratio of a cross-linking agent, water and a hydrophilic organic solvent in a treatment solution according to claim 11 is 0.005 to 20% by weight and 0.1 to 0.1% by weight based on the polymer powder.
A method for producing a water-absorbent resin, which comprises 5% by weight and 0.01 to 6% by weight. 13. A water-absorbent resin according to claim 11 or 12, wherein a polymer powder is mixed with a treatment solution and then heated at 40 to 250 ° C. to crosslink the surface of the polymer powder. Production method.