JPH08120019A - Production of highly water-absorbing resin - Google Patents

Abstract

PURPOSE: To obtain stably a highly water-absorbing resin suppressed in the formation of fine particles and having an easily handleable suitable mean particle diameter (of about 200-350-/μm) and a sharp particle diameter distribution. CONSTITUTION: A process for producing a highly water-absorbing resin by subjecting an aqueous solution of a water-soluble unsaturated monomer comprising a partially neutralized salt of (meth)acrylic acid in the presence of a free- radical polymerization initiator and in the presence or absence of a crosslinking agent, wherein the polymerization reaction is performed in the presence of a gummy polysaccharide such as xanthan gum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stably producing a highly water-absorbent resin in which generation of fine particles is suppressed, which has an appropriate average particle size for easy handling and has a sharp particle size distribution. is there.

[0002]

BACKGROUND OF THE INVENTION Super absorbent polymers having the property of absorbing a large amount of water are useful as a body fluid absorbent that absorbs body fluids and prevents leakage in sanitary and sanitary products. It is also used in applications such as seed coating agents, waterstops, thickeners, anti-condensation agents, sludge coagulants, desiccants, and humidity control agents.

As the super absorbent polymer, various kinds of starch-acrylonitrile graft polymer partially hydrolyzate, polyacrylic acid partially neutralized salt, polyethylene oxide system, polyacrylonitrile system, polyvinyl alcohol system, or cross-linking system thereof are used. Among them, from the viewpoint of quality and performance, among them, (meth) acrylic acid and (meth) acrylic acid water-soluble salt were obtained by reverse phase suspension polymerization in a hydrocarbon solvent. Partially neutralized salts of polyacrylic acid are particularly useful.

When reverse phase suspension polymerization of (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid in a hydrocarbon solvent is carried out in the presence of a surfactant as a dispersion stabilizer. Is normal. As the surfactant for this purpose, sorbitan fatty acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene acyl ester, polyoxyethylene sorbitan fatty acid ester, oxyethylene-oxypropylene block copolymer is used. The starting surfactants are used.

In the reverse phase suspension polymerization, a water-soluble polymer may coexist with or in place of the surfactant as exemplified above. The purpose of coexistence with the water-soluble polymer is to provide a protective colloid, thickening or grafting, and it is expected that the effects such as improvement of suspension stability and regulation of particle size can be obtained.

[0006] When the reverse phase suspension polymerization of (meth) acrylic acid and the water-soluble salt of (meth) acrylic acid in a hydrocarbon solvent is carried out, coexistence of a water-soluble polymer is disclosed in the following applications. There is something like.

Japanese Unexamined Patent Publication No. 2-153907 discloses an HL
It is disclosed that a mixed surfactant of a sorbitan fatty acid ester having a B value in the range of 1 to 8 and a sucrose fatty acid ester having an HLB value in the range of 1 to 6 coexists. , Sorbitan monostearate and sucrose fatty acid ester are coexistent with hydroxyethyl cellulose.

In JP-A-2-196802, a sucrose fatty acid ester and / or a polyglycerin fatty acid ester is used as a dispersant, and in order to adjust the viscosity of a water-soluble ethylenically unsaturated monomer aqueous solution, a hydroxy compound is used. Ethyl cellulose, hydroxypropyl cellulose,
It is described that a thickener such as methylcellulose, carboxymethylcellulose, polyethylene glycol, polyacrylamide, polyethyleneimine, polyacrylic acid, polyacrylic acid (partial) neutralized product crosslinked product, dextrin, sodium alginate can be used,
In the example, an example in which hydroxyethyl cellulose or sodium polyacrylate is present in the aqueous monomer solution is given.

JP-A-3-195713 discloses that an acrylic acid-based monomer containing (meth) acrylic acid and its salt as a main component is used as a dispersant in the presence of a water-soluble radical polymerization initiator and hydroxyethyl cellulose. HLB3
It has been shown to polymerize by the water-in-oil type reverse phase suspension polymerization method using sorbitan fatty acid ester of ~ 6.

JP-A-56-76419 discloses that an aqueous solution of an alkali metal acrylate containing hydroxyethyl cellulose is dispersed in the presence of a sorbitan fatty acid ester of HLB 3 to 6 and polymerized in the absence of a crosslinking agent. A method of making a water-swellable polymer is shown.

In JP-A-60-36534, sorbitan fatty acid ester, cellulose ether (ethyl cellulose, benzyl cellulose, etc.), cellulose ester (cellulose acetate, cellulose butyrate) is used as a protective colloid for reverse phase suspension polymerization. , Cellulose acetate butyrate, etc.) and polymer dispersants (maleinated polybutadiene, maleated polyethylene, maleated α-olefin, etc.) can be used.

JP-A-63-118308 describes that graft polymerization may be carried out in the presence of a monomer component such as a partially neutralized salt of acrylic acid and starch, cellulose or a derivative thereof, polyvinyl alcohol or the like. There is.

In JP-A-60-186506, in suspension polymerization of an aqueous solution of poly (meth) acrylate in a hydrocarbon or a halogenated aromatic hydrocarbon, oil-soluble cellulose ester or a protective ester is used as a protective colloid. It has been shown to use cellulose ethers.

JP-A-4-120111 and JP-A-4-120112 disclose that a water-soluble monomer is polymerized with a polysaccharide (starch, cellulose) and / or a crosslinking agent. Examples using polysaccharides, including Example 11 (both publications) relating to reverse phase suspension polymerization, are not mentioned.

[0015]

In the production of superabsorbent resin, if a large amount of fine particles are produced or the particle size distribution is wide, the yield of the target particle size is reduced, and the productivity is lowered. Especially when a large amount of fine particles are generated, it is difficult to smoothly perform various processes such as decantation, filtration, and drying.
Dust is also generated during handling, which is a significant disadvantage in terms of workability.

Also in terms of the performance of the super absorbent polymer, when the particle size distribution is wide, the powder performance varies greatly. In addition, when the particle size is small, the Mamako phenomenon occurs when it comes into contact with water or body fluid, and when it is used in combination with a material with coarse mesh such as non-woven fabric, the particles may leak from the eyes of the material. It will cause troubles during use.

Therefore, it is strongly desired that the formation of fine particles is suppressed during the reverse phase suspension polymerization, particles having an appropriate average particle size of about 200 to 350 μm are obtained, and that the particle size distribution at that time is sharp. .

However, although the method disclosed in Japanese Patent Laid-Open No. 2-153907 has succeeded in increasing the average particle size, it has a relatively wide particle size distribution and contains a considerable amount of fine particles. However, there is a problem in that the acquisition rate of the product decreases, and processes such as filtration and drying cannot be performed smoothly. The particles obtained in Comparative Example 6 according to an example in which hydroxyethyl cellulose coexisted with sorbitan monostearate and sucrose fatty acid ester had an average particle size of 490 μm, which was too large, and had a tendency to aggregate. There are various drawbacks such as low speed and low water retention.

The method disclosed in JP-A-2-196802 is
Particles with a particle size of about 150 to 550 μm can be obtained, but the allowable range of manufacturing conditions is narrow, and there is a tendency for them to agglomerate due to slight differences in the conditions such as the shape of the stirring blade and reaction vessel, stirring conditions, and the amount dropped. There is a problem that it is difficult to adopt industrially. In addition, in the method of this publication, there is a disadvantage that scaling easily occurs on the wall of the polymerization reactor and the stirring blades, and one of the causes is considered to be the thickener added for viscosity adjustment. .

The method disclosed in JP-A-3-195713 is
Although particles of 202 to 355 μm are obtained in the examples, since the particle size distribution is wide, fine particles are also generated in a considerable proportion, and the obtained particles are actually aggregates of small particles and are not classified as primary particles. The particle size itself is small, for example, when it is applied to a disposable diaper, it has a fine particle size of 1 when absorbing urine.
There is a problem that the particles return to the next particles and leak out from the eyes of materials such as nonwoven fabric.

There is no description of the particle size of the superabsorbent resin obtained in JP-A-60-36534, and it is disclosed in JP-A 4-1.
Although there is no description in JP-A No. 20111 and JP-A No. 4-120112 about the particle size of the super absorbent polymer obtained by reverse phase suspension polymerization, the particle size is appropriately large and the particle size distribution is sharp in each case. Things are hard to come by. In JP-A-56-76419, the particle size is 10 to 300.
A highly water-absorbent resin of about μm is obtained, and there is a problem that the proportion of fine particles is too large. In JP-A-60-186506, since an oil-soluble cellulose ester or cellulose ether is used and dissolved in the hydrocarbon side, there is a risk of agglomeration due to a slight difference in conditions. Although particles having a median particle diameter of about 100 to 350 μm are obtained, there is a problem that a large proportion of particles having a small particle diameter is large. In Japanese Patent Laid-Open No. 63-118308, a super absorbent polymer is obtained in small pieces, which are then cut and further pulverized.

The present invention has the following background.
When reverse-phase suspension polymerization of an aqueous solution of a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components in a hydrocarbon solvent, a specific water-soluble polymer is allowed to coexist. This suppresses the generation of fine particles,
A method for stably producing a highly water-absorbent resin having a moderate average particle size (about 200 to 350 μm) and a sharp particle size distribution that is easy to handle, and also causes scaling to a reactor or a stirring blade during its polymerization. It is intended to provide a difficult method.

[0023]

The method for producing a superabsorbent resin of the present invention is to crosslink an aqueous solution of a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components. In producing a superabsorbent polymer by reverse phase suspension polymerization in a hydrocarbon solvent using a radical polymerization initiator in the presence or absence of an agent, the reverse phase suspension polymerization of gum polysaccharide It is characterized in that it is performed in the coexistence.

The present invention will be described in detail below.

In the present invention, a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components is used as the monomer. This monomer can be obtained by partially neutralizing (meth) acrylic acid with an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, ammonium hydroxide or amines.

The mixing ratio of (meth) acrylic acid and water-soluble salt of (meth) acrylic acid is 30:70 to 10: 9 by weight.
It is preferably 0. That is, the degree of partial neutralization of (meth) acrylic acid is 70 to 90 of the total (meth) acrylic acid.
Preferably it is mol%. When the degree of partial neutralization is too small, the water absorption capacity and water absorption rate of the resulting superabsorbent resin decreases, and product particles have a difficulty in exhibiting acidity, while when the degree of partial neutralization is too large, After all, the water absorption capacity and the water absorption speed are lowered, and it is difficult for the product particles to be alkaline.

The cross-linking agent may or may not be present, but it is desirable to use a small amount of cross-linking agent. Examples of the crosslinking agent when the crosslinking agent is used include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth).
Acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, N, N'-methylenebis (meth) acrylamide,
Examples thereof include triallyl isocyanurate, (poly) ethylene glycol diglycidyl ether, glycerin polyglycidyl ether, sorbitol polyglycidyl ether and pentaerythritol polyglycidyl ether. The amount of the cross-linking agent used is 0.0001 to the monomer component.
It is often about 0.5% by weight.

Examples of the radical polymerization initiator include azobisisobutyronitrile, t-butyl peroxide, cumene hydroperoxide, di-t-butyl peroxide, acetyl peroxide, lauroyl peroxide, stearoyl peroxide and benzoyl peroxide. Examples include oxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, methyl ethyl ketone peroxide, cyclohexanone peroxide, hydrogen peroxide, ammonium persulfate, potassium persulfate, and cerium salt. Those that are water-soluble are particularly preferable. The amount of the radical polymerization initiator used is often about 0.01 to 1% by weight with respect to the monomer component.

As the hydrocarbon solvent, cyclohexane,
Alicyclic hydrocarbons such as cyclopentane and methylcyclohexane, n-pentane, n-hexane, n-heptane, n
Examples thereof include aliphatic hydrocarbons such as oritan and ligroin, aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene, and halogenated hydrocarbons such as chlorobenzene and carbon tetrachloride. Among these, n-hexane and cyclohexane are particularly important in consideration of the boiling point, melting point, cost, and industrial availability of the solvent.

As described above, an aqueous solution of a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as a main component is added to a radical polymerization initiator in the presence or absence of a crosslinking agent. Is used for reverse phase suspension polymerization in a hydrocarbon solvent. At this time, it is suitable to set the polymerization temperature to 50 to 90 ° C. and the polymerization time to about 0.5 to 5 hours.

In the present invention, the above-mentioned reverse phase suspension polymerization is carried out in the coexistence of a gum polysaccharide. This is the point of the present invention. The gum polysaccharide is dissolved on the side of the aqueous solution of the water-soluble unsaturated monomer.

Xanthan gum is preferably used as the gum polysaccharide, and tragacanth gum, karaya gum, arabia gum, guar gum, tara gum, locust bean gum, tamarind gum and curdlan can also be used.

The coexisting amount of the gum polysaccharide in the reverse phase suspension polymerization is 0.001 to 5% by weight based on the water-soluble unsaturated monomer,
It is preferably set to 0.002 to 2% by weight, and more preferably 0.005 to 1% by weight. When the amount is too small, it is not possible to sufficiently achieve the intended purpose of suppressing the generation of fine particles, obtaining particles having an appropriate average particle diameter, and sharpening the particle size distribution, while the amount is too small. When the amount is large, the gum polysaccharide is not uniformly dispersed or dissolved in the solution, which may result in a broad particle size distribution.

In addition to the above limitation on the coexisting amount of the gum polysaccharide, it is desirable to consider the following points. That is,
When the gum polysaccharide is dissolved in an aqueous solution of a water-soluble unsaturated monomer and reverse phase suspension polymerization is performed in a hydrocarbon solvent,
The difference between the interfacial tension γ _g of a water-soluble unsaturated monomer solution containing a gum polysaccharide and a hydrocarbon solvent and the interfacial tension γ ₀ of a water-soluble unsaturated monomer solution containing no gum polysaccharide and a hydrocarbon solvent (γ _g − γ ₀ ) is 0.4 dyne / cm or more, especially 0.5
It is desirable to set the type of hydrocarbon solvent, the type of gum polysaccharide, and the coexisting amount thereof so that the dyne / cm 2 or more, and perform the above-mentioned reverse phase suspension polymerization. Difference in interfacial tension (γ _g −
If γ ₀ ) is less than 0.4 dyne / cm, the effect of suppressing the generation of fine particles and the effect of narrowing the particle size distribution may not be sufficiently exhibited.

In addition to the gum polysaccharide, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, dextrin, sodium alginate, polyvinyl alcohol, polyacrylamide, within a range not impairing the gist of the present invention.
Even if other water-soluble polymers such as polyethylene glycol and polyethyleneimine are used together, there is no particular problem.

In the reverse phase suspension polymerization, it is usual to coexist with an oil-soluble surfactant having an HLB of 10 or less (preferably 9 or less). Typical examples of such oil-soluble surfactants include sorbitan fatty acid ester (sorbitan monopalmitate, sorbitan monostearate, sorbitan sesquistearate, sorbitan tristearate, etc.), sucrose fatty acid ester (sucrose and stearin). Acid, palmitic acid, lauric acid, mono-, di- or triester with fatty acid such as oleic acid) and the like. This oil-soluble surfactant is dissolved on the hydrocarbon solvent side. The coexisting amount of the oil-soluble surfactant is 5% by weight or less with respect to the water-soluble unsaturated monomer, usually 0.05 to 3% by weight,
Especially, it is often set to 0.1 to 2% by weight. The use of oil-soluble surfactants is advantageous in preventing particle size reduction or agglomeration.

After completion of the polymerization, decantation, filtration,
The produced particles are separated by centrifugation or the like, and then washed and dried. Thereby, generation of fine particles is suppressed, and a highly water-absorbent resin having an appropriate particle size (about 200 to 350 μm) and a sharp flow distribution can be obtained. Moreover, in the present invention in which the gum polysaccharide is coexistent, scaling does not easily occur in the reactor and the stirring blade during the polymerization.

The highly water-absorbent resin obtained by the method of the present invention is particularly useful as a body fluid absorbent for absorbing body fluids and excrements and preventing leakage in sanitary products and sanitary products. In addition, soil water retention agent, seed coating agent, water blocking agent, thickening agent, dew condensation preventive agent, dehydrating agent, desiccant, humidity control agent, coagulant for sludge and liquid waste, heavy metal adsorbent, drug, aromatic agent It can also be used for applications such as sustained-release preparations and poultices.

[0039]

In the present invention, the reverse phase suspension polymerization of the aqueous solution of the water-soluble unsaturated monomer is devised so as to be carried out in the coexistence of the gum polysaccharide (or this and the oil-soluble surfactant).
It is possible to industrially produce a highly water-absorbent resin in which generation of fine particles is suppressed, which has an appropriate average particle size (about 200 to 350 μm) that is easy to handle, and which has a sharp flow distribution. In addition, in the present invention in which a gum polysaccharide is coexistent, it is difficult for scaling to occur in the reactor and the stirring blade during polymerization.

[0040]

EXAMPLES The present invention will be further described with reference to examples. Hereinafter, "%" means% by weight. The average particle size is a particle size determined based on the mesh size when 50% passes when sieving is performed using a standard sieve.

Example 1 A polyacrylic acid partially neutralized salt-based highly water-absorbent resin was produced by the reverse phase suspension polymerization method described in detail below.

In a 2 liter separable flask A equipped with a stirrer, a reflux condenser and a nitrogen gas introduction tube, 800 g of cyclohexane and 0.8 g of sorbitan monostearate.
And 0.8 g of sucrose fatty acid ester ("DK Ester F-70" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was charged and nitrogen bubbling was performed for 30 minutes to expel the dissolved air and the air in the flask. This is designated as solution A.

After 260 g of 80% acrylic acid was charged in another separable flask B, 310 g of 28% sodium hydroxide aqueous solution was gradually added dropwise under cooling for neutralization. Then, 8 g of 0.5% N, N'-methylenebisacrylamide aqueous solution and 1.5 g of xanthan gum (“Kelzan” manufactured by Sansho Co., Ltd.) as an example of a gum polysaccharide (approximately 0.5% with respect to the monomer) were added. And dissolved. After dissolution, 1
4 g of a 0% ammonium persulfate aqueous solution was added, and nitrogen bubbling was performed while stirring to expel the dissolved air. This is designated as solution B.

The interfacial tension γ _{g of} liquid B with respect to liquid A is
3.9 dyne / cm, interfacial tension γ of solution B against solution A (only the addition of xanthan gum was omitted when preparing solution B)
₀ is 3.3 dyne / cm, and the difference (γ _g −γ ₀ ) between them is 0.6 dyn.
It was e / cm.

After the temperature of Flask A was raised to 73 ° C., the solution in Flask B was added dropwise over 1.5 hours. The rotation speed during polymerization was set to 350 rpm. Then, the warm water in the jacket was kept at 95 ° C., azeotrope with cyclohexane and 230 ml of water was expelled (the dehydration rate of water was 70%). After that, decantation was performed, and the produced particles were dried at a temperature of 105 ° C. for 3 hours to obtain the target highly water-absorbent resin particles. Almost no scaling was observed on the flask wall and the stirring blade used for the polymerization.

The average particle size of this particle is 317 μm, 105
The proportion of fine particles below μm is 3.1%, and the water absorption capacity is 8% for pure water.
80 g / g and 0.9% saline were 72 g / g.

Comparative Example 1 Example 1 was repeated except that the addition of xanthan gum was omitted. The average particle size of the resulting superabsorbent resin particles is 173.
The proportion of fine particles having a size of μm or less than 105 μm was 17.7%, and the water absorption capacity was 920 g / g for pure water and 73 g / g for 0.9% saline.

Comparative Example 2 Hydroxyethyl cellulose instead of xanthan gum
Example 1 was repeated except that 0.3 g was added. At this time, some scaling was observed on the flask wall and the stirring blade. The average particle size of the resulting super absorbent polymer particles is 1
The proportion of fine particles of 84 µm or less and 105 µm or less was 16.3%, and the water absorption capacity was 920 g / g for pure water and 73 g / g for 0.9% saline.

Comparative Example 3 By repeating the procedure of Comparative Example 2 except that the amount of hydroxyethyl cellulose added was changed to 1.5 g, superabsorbent resin particles having substantially the same properties as those of Comparative Example 2 were obtained. And the scaling to the stirring blade was significant.

Comparative Example 4 Sodium polyacrylate 0.3 in place of xanthan gum
Example 1 was repeated except that g was added. The average particle size of the resulting super absorbent resin particles was 179 μm, the proportion of fine particles of 105 μm or less was 17.3%, and the water absorption capacity was 930 g / pure water.
The g and 0.9% saline were 73 g / g.

Comparative Example 5 Carboxymethyl cellulose was used instead of xanthan gum.
Example 1 was repeated except that 0.3 g was added. The average particle diameter of the resulting super absorbent polymer particles is 175 μm, 105 μm.
The proportion of fine particles of m or less is 17.5%, and the water absorption capacity is 92% for pure water.
The amount of 0 g / g and 0.9% saline was 74 g / g.

Comparative Example 6 Example 1 was repeated except that 1.5 g of pullulan was added instead of xanthan gum. The superabsorbent resin particles obtained had an average particle size of 175 μm, the ratio of fine particles of 105 μm or less was 17.0%, and the water absorption capacity was 910 g / g of pure water and 73 g / g of 0.9% saline. The interfacial tension γ _g of solution B with respect to solution A is 3.4 dyne / cm, and the interfacial tension γ ₀ of solution B'with respect to solution A (without adding pullulan when preparing solution B) is 3.3 dyne / cm. And the difference between them (γ _g −γ ₀ ) is 0.
It was only 1 dyne / cm.

Examples 2-9 Instead of xanthan gum, tragacanth gum (Example 2), karaya gum (Example 3), arabia gum (Example 4), guar gum (Example 5), tara gum (Example 6), locust bean. Example 1 was repeated except that the gum (Example 7), tamarind gum (Example 8) and curdlan (Example 9) were each added at 1.0% to the monomer. Scaling adhering to the flask wall and stirring blades subjected to the polymerization was not so noticeable. The average particle size of the resulting super absorbent resin particles, particle size distribution,
The water absorption capacity was similar to that in Example 1.

[0054]

INDUSTRIAL APPLICABILITY In the present invention, reverse phase suspension polymerization of an aqueous solution of a water-soluble unsaturated monomer is devised so as to be carried out in the coexistence of a gum polysaccharide (or a gum-soluble polysaccharide and an oil-soluble surfactant). It is possible to stably obtain a highly water-absorbent resin whose generation is suppressed, has an appropriate average particle size (about 200 to 350 μm) and is easy to handle, and has a sharp flow distribution.

Therefore, the yield of the target particle size is increased and the productivity is improved, and various processes such as decantation, filtration, and drying can be smoothly performed, and the generation of dust during handling is small, and the work can be performed. The property becomes good. Further, the obtained particles do not cause a mamako phenomenon when they come into contact with water or body fluid, and do not cause troubles such as leakage even when they are used in combination with a rough material such as a nonwoven fabric.

In addition, according to the present invention, since the gum polysaccharide is used, there is an advantage that scaling does not easily occur in the reactor and the stirring blade during the polymerization.

Claims (5)

[Claims] 1. An aqueous solution of a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components in the presence or absence of a crosslinking agent using a radical polymerization initiator. In producing a highly water-absorbent resin by reverse-phase suspension polymerization in a hydrocarbon solvent, a method for producing a highly water-absorbent resin characterized in that the above-mentioned reverse-phase suspension polymerization is carried out in the coexistence of a gum polysaccharide. . 2. The gum polysaccharide is at least one polysaccharide selected from the group consisting of xanthan gum, tragacanth gum, karaya gum, arabia gum, guar gum, tara gum, locust bean gum, tamarind gum and curdlan. Manufacturing method. 3. The method according to claim 1, wherein the gum polysaccharide is xanthan gum. 4. The method according to claim 1, wherein the coexisting amount of the gum polysaccharide is 0.001 to 5% by weight based on the water-soluble unsaturated monomer. 5. The method according to claim 1, wherein the reverse phase suspension polymerization is carried out in the coexistence of 5% by weight or less of an oil-soluble surfactant having an HLB of 10 or less with respect to the water-soluble unsaturated monomer. .