JPH08253597A - Method for granulating highly water-absorptive resin - Google Patents

Abstract

PURPOSE: To obtain a highly water-absorptive resin containing less fine powder and having a low bulk density, by mixing a highly waterabsorptive resin, a crosslinking agent, water, and a specified silicon dioxide followed by drying. CONSTITUTION: This method for granulating a highly water-absorptive resin comprises mixing a highly water-absorptive resin, a crosslinking agent, water, and a silicon dioxide having a specific surface area of 250m<2> /g or more measured by the nitrogen adsorption method followed by drying. Preferably the highly water-absorptive resin and the crosslinking agent are previously mixed homogeneously and then water and the silicon dioxide having a specific surface area of 250m<2> /g or more measured by the nitrogen adsorption method are mixed therewith. More preferably, the highly water-absorptive resin and the crosslinking agent are mixed in an organic solvent, the organic solvent is distilled off, the mixture is mixed homogeneously, and water and the silicon dioxide having a specific surface area of 250m<2> /g or more measured by the nitrogen adsorption method are mixed therewith.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for granulating a highly water-absorbent resin, and more particularly to a method for granulating a highly water-absorbent resin having a small amount of fine powder and a low bulk density.

[0002]

2. Description of the Related Art Superabsorbent resins are generally prepared by synthesizing a polymer by a reverse phase suspension polymerization method, a reverse phase emulsion polymerization method, a static polymerization method or the like, and then drying the polymer as it is or by drying it. After that, it is manufactured by crushing.
In addition to acrylic polymerization methods, superabsorbent polymers other than acrylic resins are manufactured by a suspension polymerization method, an emulsion polymerization method, or the like. However, the super absorbent resin produced by these methods generally contains a considerable amount of fine powder that can pass through a standard sieve of 100 mesh or less, and therefore has the following problems.

(A) Dust is liable to be generated, which tends to deteriorate the working environment and reduce the amount of products. (B) Poor mixability and dispersibility when blending with other substances. (C) When water is absorbed, so-called “mamako” is likely to be generated, in which particles stick to each other and uniform water absorption is hindered. (D) Because of poor fluidity, bridge formation in the hopper,
Flash phenomenon is likely to occur. As a method for solving these problems, a method of removing fine powder and a method of granulating are considered.

However, the former method is economically disadvantageous and is not preferable. Various methods have been proposed for the latter method. For example, JP-A-62-1329
Japanese Unexamined Patent Publication (Kokai) No. 5-17509 discloses a method of granulating by adding a surfactant, water, an inert solvent and a powdery inorganic substance to a super absorbent resin. A method is disclosed in which an acrylic acid-based monomer is added and polymerized to a water-containing superabsorbent resin slurry liquid by a suspension polymerization method to aggregate and granulate particles. Further, JP-A-3-137129 discloses a method of granulating a polymer powder with an oxyalkylene group-containing polyvinyl alcohol, which is disclosed in JP-A-61-29.
Japanese Patent No. 322 discloses a method in which a specific crosslinking agent and water are added to a mixture of a superabsorbent resin and an inert inorganic powder to carry out a crosslinking reaction and water distillation. Further, although the action and effect are different, JP-A-2-238035 discloses a method of adding specific silicon dioxide to a superabsorbent resin.

[0005]

However, in the techniques disclosed in Japanese Patent Laid-Open No. 62-132936 and Japanese Patent Laid-Open No. 5-17509, the generation of fine powder is small and the above (a) to
Although the phenomenon shown in (d) is improved, the particle size distribution of the obtained superabsorbent resin granules becomes broader, and when used in hygiene products such as paper diapers and sanitary napkins, leakage is particularly noticeable. There was a problem that it occurred. Further, the bulk density of the obtained superabsorbent resin granules becomes large, and the granules become hard in practical use, so that the granules are easily broken, the handleability is poor, and the entanglement with the pulp (fiber) is poor. There was a problem of being bad. Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 3-137129, although the amount of fine powder is small and the particle size distribution is sharp, the problem that the bulk density of the obtained granules of the superabsorbent resin becomes large remains. It was JP 61-
In the disclosed technology of Japanese Patent No. 29322, as seen in Example 1, silicon dioxide (Aerosil 2 having a small specific surface area) is disclosed.
No. 00 has a specific surface area of about 200 m ² / g), and there is a problem that a good particle size distribution cannot be obtained as is apparent from the comparative examples of the present invention.

In the technique disclosed in Japanese Patent Laid-Open No. 2-238035, since only the powdery super absorbent resin and silicon dioxide are simply mixed and dispersed, the effects of improving hygroscopicity, cohesiveness, metal adhesion resistance and the like can be seen. However, when focusing on the granulation effect as in the present invention, there was a problem that the granulation effect was not exhibited, the amount of fine powder increased considerably, and the bulk density also increased.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that
Cross-linking agent, specific surface area by adsorption of water and nitrogen is 250m ² / g
After mixing the above silicon dioxide, it is possible to produce a granule of a superabsorbent resin having a small amount of fine powder and low bulk density by performing drying, and in particular, the superabsorbent resin and the cross-linking agent are preliminarily uniformly mixed. After that, it was found that a more remarkable effect can be obtained by mixing water and the silicon dioxide and then drying, and the present invention has been completed. The present invention is described in detail below.

The highly water-absorbent resin to which the present invention is applied include acrylic acid type crosslinked products, saponified products of acrylic acid ester-vinyl acetate copolymer crosslinked products, starch-acrylic acid salt graft copolymer crosslinked products, Saponification products of starch-acrylonitrile graft copolymers, cross-linked polyvinyl alcohol-modified products, and the like can be mentioned. Among these, acrylate-based polymer cross-linking that has excellent physical properties such as water absorption rate when made into products such as diapers. And a highly water-absorbent resin made of a crosslinked polyvinyl alcohol modified product are preferable.

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 stationary 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; acetyl peroxide, lauroyl peroxide, stearoyl peroxide, amyl peroxide such as 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.

In carrying out the polymerization method, the water-soluble crosslinking agents used are (meth) acrylic acid and (meth)
10 to 2000 pp relative to the total amount of acrylic acid water-soluble salt
m, preferably 50 to 1000 ppm, and examples of such a crosslinking agent include 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 (meth) acrylate, (meth) acrylic acid polyvalent metal salt, trimethylolpropane tri (meth) acrylate, triallylamine, triallyl cyanurate, Triallyl isocyanurate, triallyl phosphate,
Examples thereof include glycidyl (meth) acrylate, ethylene glycol diglycidyl ether, glycerin tri (di) glycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether.

Further, the superabsorbent resin comprising a cross-linked 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.

The cross-linking agent used in the granulation of the present invention is a carboxyl group or carboxylate group present in the superabsorbent resin modified by the present invention, preferably other than this, a hydroxyl group, a sulfone group or an amino group. It is a cross-linking agent having a functional group capable of reacting with a group or the like, and such a cross-linking agent can be used without particular limitation. Examples of the cross-linking agent include diglycidyl ether compounds, haloepoxy compounds, aldehyde compounds and isocyanate compounds. Among these, diglycidyl ether compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, and glycerol polyglycidyl ether are suitable, and among these, , Diethylene glycol diglycidyl ether is most suitable because of its reactivity with the carboxyl group or carboxylate group in the super absorbent polymer.

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 include 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 100 parts by weight of 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.

In the present invention, it is also necessary to add water at the time of granulation, and the super absorbent polymer before adding water may contain water, and the preferable water content is 2
It is 0 to 80% by weight. The amount of water added is preferably 10 to 70 parts by weight of water with respect to 100 parts by weight of water-free superabsorbent resin. More preferably 20 to 6
0 parts by weight.

If the amount added is less than 10 parts by weight, the crosslinking will not be carried out efficiently, and if it exceeds 70 parts by weight, the superabsorbent resin will agglomerate to form lumps, making it difficult to carry out uniform crosslinking. Become. The timing of adding water to the superabsorbent resin is not particularly limited, but it is preferable to add water at the same time as or before the addition of silicon dioxide. The method of adding water to the superabsorbent resin is not particularly limited as long as it is a method of adding as uniformly as possible to the superabsorbent resin, and specifically, it may be added with stirring, spraying or You can add it by steaming,
You may add the organic solvent which disperse | distributed water in the organic solvent containing a superabsorbent resin. Further, it is possible to separately charge water. Alternatively, a predetermined amount of water may be added to water during the production of the superabsorbent resin so as to obtain the above water content, and the superabsorbent resin containing water obtained by reverse phase suspension polymerization is once subjected to azeotropic dehydration. The water content may be adjusted to the above water content by distilling off the water with.

The most characteristic feature of the present invention is that a specific silicon dioxide having a specific surface area of 250 m ² / g or more by the nitrogen adsorption method is used together with the above-mentioned cross-linking agent and water during granulation of the super absorbent polymer. Is. The specific surface area is 25
If it is less than 0 m ² / g, the granulation effect is small and unsuitable.
It is preferably 250 to 800 m ² / g. More preferably, it is 250 to 490 m ² / g.

Although such silicon dioxide may be produced by any method, it can be produced by, for example, a sol-gel method. The specific method will be described below. First, bulk silicon dioxide is neutralized with an aqueous solution of sodium silicate with an acid such as concentrated hydrochloric acid, and the obtained silica sol is gelled, filtered, and dried, or obtained by drying, such as tetramethoxysilane or tetraethoxysilane. Tetraalkoxysilane is hydrolyzed in the presence of an inorganic acid or an organic acid, and the obtained silica sol is gelated and filtered, and dried under atmospheric pressure and vacuum, or supercritical drying. For example, when drying at atmospheric pressure, it is usually 60 to 300 ° C, preferably 100 to 200 ° C.
It is preferable that the content of silicon dioxide is 80% by weight or more, and preferably 90% by weight or more after dehydration and drying. Regarding the drying temperature, if it is lower than 60 ° C., there is a problem that the dehydration and drying rates are significantly slowed down. Although there is no particular problem if the dehydration / drying temperature is higher than 300 ° C, the process economy is deteriorated. Further, regarding the drying temperature, if the silicon dioxide content is lower than 80% by weight, problems such as volume expansion, foaming, and adhesion to the vessel wall may occur.

Next, the dehydration and drying steps are started. The larger the content of silicon dioxide in the dehydration and drying steps, the smaller the particle size of the produced silicon dioxide, and the particle size of the produced silicon dioxide is adjusted by adjusting the content of this silicon dioxide. be able to. For example, when the content of silicon dioxide is 80 to 85% by weight, the particle size of the produced silicon dioxide is about 2 to 6 nm, and when the content of silicon dioxide is 95% by weight or more, the particles of the produced silicon dioxide are The diameter is 2 nm or less. Next, the sintering process is started. Water treatment may be performed before the sintering step. The sintering step can be performed in the same manner as a conventionally known method, and usually 5
It is carried out at a sintering temperature of 00 to 1300 ° C, preferably 800 to 1200 ° C, usually for 1 to 8 hours, preferably for 3 to 6 hours. Even if the sintering temperature is longer than 8 hours, the physical properties of the product,
There is no big change in the properties.

The silicon dioxide of the present invention is preferably in the form of fine particles which are adsorbed on the surface of the highly water-absorbent resin, and the preferable particle size is 20 μm or less, particularly preferably 10 μm.
It is the following. The amount of silicon dioxide used in the present invention is 0.05 to 5 parts by weight, preferably 0.1 to 3 parts by weight, based on 100 parts by weight of the water-free superabsorbent resin. If it is less than 0.01 part by weight, the granulation effect is small and it is not preferable. On the other hand, if the amount exceeds 5 parts by weight, the amount of fine powder increases, resulting in poor handling, which is not preferable.

The silicon dioxide of the present invention preferably has a pore volume of 3 ml / g or less measured by a mercury porosimeter. More preferably, it is 0.4 to 1.8 ml / g. Further, the silicon dioxide of the present invention is manufactured according to JIS K 510.
The oil absorption by Method 1 is preferably 350 ml / 100 g or less, more preferably 200 to 100 ml / 1.
It is 00 g.

Next, the granulation method of the super absorbent polymer will be specifically described. The present invention has a specific surface area of 250 m ² / g as measured by the superabsorbent resin, crosslinking agent, water and nitrogen adsorption method as described above.
After mixing the above silicon dioxide, characterized by performing drying and granulation, a super absorbent resin, a cross-linking agent,
The order of addition of water and silicon dioxide having a specific surface area of 250 m ² / g or more measured by a nitrogen adsorption method is not particularly limited, and they may be added in any order or may be added all at once. From this point of view, it is preferable that the superabsorbent resin and the crosslinking agent are uniformly mixed in advance, and then water and silicon dioxide having a specific surface area of 250 m ² / g or more by the nitrogen adsorption method are mixed.

The method for uniformly mixing the superabsorbent resin and the crosslinking agent is not particularly limited as long as the superabsorbent resin and the crosslinking agent are in a uniformly dispersed and mixed state. A method of distilling off the organic solvent after mixing and stirring, a method of directly sprinkling the cross-linking agent on the super absorbent polymer, a method of dispersing or dissolving the cross-linking agent in water and sprinkling on the super absorbent resin, and the like. However, a method of uniformly mixing and stirring an organic solvent as a solvent and then distilling off the organic solvent is preferable, and the method will be described more specifically.

At this time, the organic solvent used is not particularly limited as long as it is inert to the crosslinking reaction during the crosslinking treatment and can dissolve or disperse the crosslinking agent. 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 monoethers such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether. And the like.

The organic solvent may be added in an amount sufficient to be mixed with the super absorbent polymer, and is preferably 20 to 2000 parts by weight with respect to 100 parts by weight of the super absorbent resin containing no water. It is more preferably 40 to 600 parts by weight.

The method of mixing with the organic solvent is a method of mixing the superabsorbent resin and the crosslinking agent and then adding the organic solvent, or a method of adding the organic solvent to the superabsorbent resin and mixing and then adding the crosslinking agent and mixing. Method, a method of adding and mixing a superabsorbent resin after adding an organic solvent to the crosslinking agent and mixing, a superabsorbent resin,
Examples include a method of adding an organic solvent to each of the cross-linking agents, mixing and then blending and mixing, a method of mixing the super-water-absorbent resin and the cross-linking agent in the organic solvent separately or in a batch, and the like. Even with the method, after mixing and stirring uniformly,
It is necessary to distill off the organic solvent. The distillation of the organic solvent is preferably carried out under reduced pressure and low temperature in order to suppress the crosslinking reaction, and the pressure is suitably selected from the range of 150 to 250 torr and the temperature of 20 to 50 ° C.

Next, the specific surface area by water and nitrogen adsorption method is 25
Although 0 m ² / g of silicon dioxide is added, the addition may be carried out directly, but considering the dispersibility of the powder, it is better to add water first. Finally, the superabsorbent resin, the cross-linking agent, and the specific surface area of water and nitrogen adsorption method of 25 were obtained.
A mixture of 0 m ² / g of silicon dioxide is dried. The conditions of the drying treatment at this time are 50 to 150 ° C., preferably 70 to 100 ° C. for about 30 minutes to 5 hours, although it cannot be said depending on the kind of the crosslinking agent. Thereafter, if necessary, the drying treatment is performed again at 105 to 150 ° C. for about 0.5 to 5 hours to obtain the superabsorbent polymer granules of the present invention.

The superabsorbent resin obtained by such a method produces less fine powder, and has a small bulk density of 0.90 g / ml or less, so there is little fine powder, so that it is easy to handle and has no entanglement with pulp. It can be widely used for sanitary materials such as paper diapers and sanitary napkins, soil water retention agents, seed coating agents, water blocking agents, thickeners, anti-condensation agents, desiccants, humidity control agents and the like.

[0031]

In the present invention, since the silicon dioxide having a specific surface area is used in the granulation of the super absorbent polymer, a granulated body of the super absorbent resin having a small bulk density and a small amount of fine powder is produced. You can do it.

[0032]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, “%” is based on weight unless otherwise specified. Further, the evaluation of the granules of the super absorbent polymer was performed according to the following procedure.

(Measurement of Particle Size Distribution) By a dry sieve analysis using a Tyler mesh standard wire mesh, the content of coarse particles of 20 mesh on and fine particles of 100 mesh pass were shown by weight%. (Measurement of bulk density) The measurement was performed according to JIS-K6721.

Example 1 190 g of a super absorbent polymer (water content 23%) obtained by usual reverse phase suspension polymerization using cyclohexane as a solvent and 250 ppm of a bifunctional oil as a crosslinking agent with respect to the super absorbent resin. Cyclic epoxy compound (trade name "Celoxide 202
1 ", manufactured by Daicel Chemical Industries, Ltd. and 76 g of cyclohexane were charged into a 1-liter twin-arm kneader, and after stirring 76 g of cyclohexane at 210 torr and 45 ° C., the mixture was mixed for 60 minutes. Then, 8% of water was added to the superabsorbent resin, and 30 minutes after that, 12% of water was added to the superabsorbent resin. 15 minutes later, 0.
14 g (0.1% by weight) of silicon dioxide (specific surface area 432 m ² / g by nitrogen adsorption method, pore volume 1 by mercury porosimeter 1, 12 ml / g, pore peak radius by nitrogen adsorption 4.1 nm) were added. While stirring in a kneader under atmospheric pressure, it was dried at 70 ° C. for 1 hour, and then statically dried at 110 ° C. for 3 hours to give about 1% of granules having a water content of 5%.
60 g was obtained. The particle size distribution and bulk density of the obtained granules of the super absorbent polymer were measured.

Examples 2 to 3 and Comparative Examples 1 to 4 The superabsorbent resin was granulated in the same manner as in Example 1 except that the type and addition amount of silicon dioxide were changed as shown in Table 1, and the particle size distribution was similarly obtained. The bulk density was measured. Table 2 shows the measurement results of Examples and Comparative Examples.

[0036]

[Table 1] SiO ₂ specific surface area Pore volume Pore peak Oil absorption Added amount (m ² / g) (ml / g) Radius (nm) (ml / 100g) (%) Example 1 432 1.15 4. 1 170 0.1 Example 2 432 1.15 4.1 170 1 Example 3 432 1.15 4.1 170 5 Comparative Example 1 −−−−−−−−−−−−− 0 Comparative Example 2 1901 .15 4.1 170 0.1 Comparative Example 3 190 3.13 12.3 170 0.1 Comparative Example 4 190 1.15 4.1 4.1 237 0.1

[0037]

[Table 2] Particle size distribution of the obtained resin Bulk density 20 mesh 20 100 100 Larger than 100 mesh (g / ml) Smaller than mesh Example 1 23 74 3 0.89 Example 2 20 76 4 0.90 Example 3 15 80 5 0.90 Comparative Example 1 1 84 15 1.02 Comparative Example 2 2 90 8 0.95 Comparative Example 3 5 85 10 0.99 Comparative Example 4 2 83 15 1.00

[0038]

INDUSTRIAL APPLICABILITY In the present invention, since the silicon dioxide having a specific specific surface area is used in the granulation of the super absorbent polymer, the granules of the super absorbent polymer having a small bulk density and a small bulk density are produced. Can be manufactured.

Claims (6)

[Claims] 1. A granulation of a superabsorbent resin, which comprises mixing a superabsorbent resin, a crosslinking agent, water, and silicon dioxide having a specific surface area of 250 m ² / g or more by a nitrogen adsorption method, and then drying the mixture. Law. 2. A highly water-absorbent resin and a cross-linking agent are uniformly mixed in advance, and then the specific surface area is 250 m ² by a water and nitrogen adsorption method.
2. The method for granulating a super absorbent polymer according to claim 1, wherein the amount of silicon dioxide is not less than 1 g / g. 3. A highly water-absorbent resin and a cross-linking agent are mixed in an organic solvent, the organic solvent is distilled off and uniformly mixed, and then a specific surface area of 250 m ² / g or more by water and nitrogen adsorption method is obtained. The method for granulating a highly water-absorbent resin according to claim 2, wherein silicon is mixed. 4. The granulation of super absorbent polymer according to claim 1, wherein the specific surface area of silicon dioxide measured by a nitrogen adsorption method is 250 m ² / g or more and 800 m ² / g or less. Law. 5. The granulation of superabsorbent resin according to claim 1, wherein the specific surface area of silicon dioxide measured by a nitrogen adsorption method is 250 m ² / g or more and 490 m ² / g or less. Law. 6. The composition according to claim 1, wherein the mixing amount of silicon dioxide is 0.05 to 5 parts by weight with respect to 100 parts by weight of the water-free superabsorbent resin. Granulation method of water absorbent resin.