KR19980073316A - Method for producing pulp-shaped superabsorbent polymer - Google Patents

Abstract

After the polymerization was carried out by adjusting the viscosity and the stirring speed by adding a hydrophilic monomer solution containing a polymerization initiator in a solution obtained by dispersing a dispersant having an HLB of 8-12 in an organic solvent, the water content in the polymer was 55 weights by azeotropic distillation. A pulp-shaped superabsorbent polymer manufacturing method comprising the step of crosslinking for 1 to 3 hours by adding a crosslinking agent aqueous solution while maintaining the temperature in the reactor at 40 to 85 ° C. or less and filtering and drying is provided. The water absorbent resin prepared by the method of the present invention has a form similar to pulp, and has excellent kneading property with absorbents of sanitary materials such as pulp or pulp, and has excellent physical properties such as absorption amount, absorption rate, and attraction force for salt water. Satisfies the particle size distribution standard of the sanitary products, while the narrow particle size distribution is easy to handle it can be usefully used for sanitary products.

Description

Method for producing pulp-shaped superabsorbent polymer

The present invention relates to a method for producing a pulp-shaped superabsorbent polymer which can be usefully used for the production of hygiene products due to its excellent absorption ability and kneading with pulp.

Absorbent materials consist of natural materials such as sponges, pulp and paper, and synthetic materials made by partial neutralization of salts with hydrophilic groups such as -OH, -NH ₂ and -COOH. Conventionally, natural materials such as sponges, pulp and paper have been used as materials for hygiene products. However, since these natural materials suck water by physical methods, there is a problem in that the absorbed water escapes not only with low water absorption but also with a slight pressure.

In order to solve this problem, synthetic materials having a mechanism of sucking water by physical and chemical methods have been required, and saponified starch-acrylonitrile graft copolymer (JP 49-43395), saponified starch Acrylic acid graft copolymers (JP 51-125468), saponified acrylonitrile or acrylamide copolymers (JP 53-15959), crosslinked acrylate polymers (JP 55-84304), and the like. It is used not only in the field of sanitation, civil engineering and horticulture such as dragon napkin, but also in various fields for the purpose of agglomeration of sediment, dehydration in oil and prevention of dew condensation of building materials.

As a manufacturing method of such a water absorbing resin, mass polymerization, aqueous solution polymerization, spray polymerization, reverse phase emulsion polymerization, reverse phase suspension polymerization, etc. are known a lot. However, manufacturing processes through bulk polymerization or aqueous solution polymerization require not only a special type of reactor, but also have a grinding process in order to have a particle size distribution (typically 100-850 µm) in accordance with the specification. Therefore, the crushing process causes a wider particle size distribution and generates a large amount of fine powder (100 μm or less). For this reason, reverse phase emulsion polymerization (US Pat. No. 3,284,393) or reverse suspension suspension polymerization (US Pat. No. 4,340,706) is widely used, except that manufacturing facilities are simpler than aqueous solution polymerization or bulk polymerization and are easier to control the heat of polymerization. Particle shape or particle size to be produced has a problem that it is inappropriate to be used for hygiene products.

In more detail, the main use of the absorbent polymer is in the field of hygiene, such as diapers, sanitary napkins, and in particular, the diaper is in the spotlight as the main field of use. The diaper is made of an absorbent material such as pulp in addition to the absorbent resin as an absorbent material. Therefore, due to the capillary phenomenon, pulp having excellent water diffusion rate and absorbent resin having excellent absorption amount and urination force have a complementary relationship. In order to achieve such a complement, even distribution of the absorbent resin in the pad composed of the pulp and the absorbent resin is required. However, spherical absorbent resins prepared by the reverse phase emulsion polymerization or the reverse phase suspension polymerization of the above-mentioned patents are difficult to handle due to their small particle size. In the kneading process, it is not fixed in the pad and falls, so that the absorbent resin loss in the pad fabrication process increases, and the absorbent resin fixed on the pulp is also unevenly distributed in the pad.

Therefore, the present inventors have continued to research a superabsorbent polymer having a narrow particle size distribution and a pulp-like form by improving the disadvantages of the reverse phase suspension polymer, and thus, a dispersant having a hydrophilic lypophilic balance (HLB) of 8-12 By adjusting the viscosity and agitation power appropriately when performing reverse phase suspension polymerization, it was found out that a pulp-like polymer having excellent water absorption was produced by the phase transition phenomenon, thereby leading to the completion of the present invention.

Accordingly, an object of the present invention is to easily handle because the particle size distribution is narrow even within the range while satisfying the particle size distribution standard (100-850 µm) of the general sanitary ware use, and excellent physical properties such as the amount of absorption, absorption rate and suction force to the brine. The present invention provides a method for producing a superabsorbent polymer suitable for use in hygiene products, having excellent kneading ability with an absorbent material of a sanitary material such as pulp or pulp in a form similar to a non-spherical pulp in shape.

1 is a micrograph (magnification: 100, 340 times, respectively) of a super absorbent polymer having a pulp shape in the form of pea shell prepared by the method of the present invention,

2 is a micrograph (magnification: 100, 340 times, respectively) of a superabsorbent polymer having a needle-like pulp shape prepared by the method of the present invention,

Figure 3 is a micrograph (magnification: 100, 340 times, respectively) of the square superabsorbent polymer produced by the method of the present invention,

Figure 4 is a micrograph (magnification: 100, 340 times) of the superabsorbent polymer in the form of spherical particulates prepared by a conventional reverse phase suspension polymerization method.

In order to achieve the above object, in the present invention, a hydrophilic monomer aqueous solution containing a polymerization initiator dissolved in a solution obtained by dispersing a dispersing agent having a hydrophilic lypophilic balance (HLB) of 8-12 in an organic solvent is added to adjust the viscosity and stirring rate. After performing, by azeotropic distillation, the water content in the polymer is 55% by weight or less, and the crosslinking agent is added for 1 to 3 hours while maintaining the temperature in the reactor at 40-85 ° C, followed by filtration and drying. It provides a pulp-shaped superabsorbent polymer production method.

The dispersant having an HLB value of 8-12 used in the present invention is generally known to be very unstable in the water in oil (W / O) system, which is a reverse phase emulsion polymerization and a reverse phase suspension polymerization. As the viscosity rises sharply by the viscosity effect (Trommsdorff effect), a phase transition occurs. This phenomenon is believed to be due to the following two phenomena.

1) a phenomenon in which a phase shifts from a large mechanical force due to agitation to an area balanced with a viscous force and then to a large dynamic force due to agitation;

2) The phase transition to the hydrophilic and water equilibrium phase system in the hydrophobic system, where the main phase is hydrophobic.

Therefore, by appropriately adjusting the viscosity at the time when the phase transition phenomenon occurs, it is possible to obtain a water-absorbent resin of various states depending on the viscosity and the degree of mechanical force.

At this time, the viscosity adjusting factors include the following.

(1) Monomer concentration in monomer aqueous solution (monomer partially neutralized with water-soluble monomer)

(2) Increasing heat transfer rate or externally important efficiency of initiator

(3) polymerization temperature

(4) Ratio of organic solvent and aqueous monomer solution

(5) Feeding rate of aqueous monomer solution

(6) degree of neutralization of aqueous monomer solution

(7) Type and amount of dispersant

In addition, the following factors control the stirring force.

(1) stirring speed

(2) ratio of reactor diameter to stirrer diameter

(3) agitator type

In the present invention, by uniformly applying the above factors in an organic relationship with each other, a uniform superabsorbent polymer having a pulp shape was prepared.

Specifically, an initiator (alone or oxidation) is prepared in a monomer solution prepared by adjusting the neutralization degree of the water-soluble monomer, the monomer concentration of the monomer aqueous solution, and the ratio of the monomer aqueous solution to the organic dispersion medium in the organic solvent in which the dispersing agent of HLB is 8-12. -The aqueous solution (1) in which the reduction system is dissolved is shot fed at high speed and dispersed in an organic solvent. At this time, the temperature control of the inner and outer heating medium of the reactor is as follows. First, the monomer aqueous solution (1) is introduced at a high rate in a state where the temperature inside the reactor is high, and then the temperature of the external heat medium is maintained as it is, or second, after the aqueous solution (1) is introduced in the state where the temperature inside the reactor is low, the external heat medium The polymerization rate is increased by increasing the heat transfer rate applied from the outside by increasing the temperature of. In view of reaction heat control, the first method is more preferable. Nitrogen may be added before and after shot feeding of the aqueous solution 1 to remove dissolved oxygen in the system to increase polymerization efficiency of the initiator. Here, the input rate of the aqueous monomer solution is adjusted so that the temperature in the reactor is lowered by more than 8 ℃ than the first.

When the polymerization is carried out as described above, due to the relatively high monomer concentration at the time of the polymerization and the increase in the heat transfer rate or the efficiency of the initiator in the system, the polymerization rate is increased and the physical entanglement increases as the molecular weight of the polymer chain increases. Due to the increase in viscosity and the decrease in diffusion rate of the polymer, the termination rate is very slow compared to the development rate, resulting in the formation of high molecular weight polymer chains and more severe physical entanglement, resulting in pseudocrosslinking. At this time, the phase transition time at which the dispersion medium and the resulting polymer aqueous solution become one phase is reached. In this case, if a suitable stirring force is applied, a pulp-shaped polymer can be obtained, not a spherical size.

Then, by using azeotropic distillation, the water content is 55% by weight or less, the aqueous solution of the water-soluble crosslinking agent is added, crosslinked at 40-85 ° C, and dried at 80-180 ° C so that the water content is 10% or less. It is possible to obtain a pulp-shaped superabsorbent resin which is excellent in mixing with pulp or pulp-like materials.

As the water-soluble monomer used in the present invention, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, meth Monomers having carboxylic acid groups such as methoxypolyethylene glycol (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate and anhydrides thereof or ester derivatives thereof ; Amides such as (meth) acrylamide and N, N-dimethylaminopropyl (meth) acrylamide or N-substituted (meth) acryl amides and salts thereof; Those having sulfonic acid groups such as 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid and vinylsulfonic acid It can be used individually or in mixture of 2 or more.

Such a water-soluble monomer is used by neutralizing with an alkali metal such as sodium hydroxide so as to have an electrolyte characteristic of the anion, and the degree of neutralization is 20 to 95 mol%, preferably 40 to 75 mol%. If the neutralization degree is less than 40 mol%, the electrolyte ion concentration in the polymer is small, so that the charge density difference with water or physiological saline is small, so that the penetration pressure is low, and thus an absorbent resin having excellent absorption ability cannot be obtained. If the degree of neutralization is greater than 75 mol%, a sufficient viscosity is not reached at the time of phase transition, so that a sufficient shear force in the flow direction due to the applied mechanical force is not obtained, thereby obtaining an absorbent resin having a shape close to a spherical shape.

In addition, the monomer concentration in the aqueous monomer solution after neutralization is 30 to 50% by weight, preferably 35 to 45% by weight. If the monomer concentration is less than 30% by weight, it is difficult to obtain a desired pulp shape due to the low viscosity at the phase transition point, and the lower the degree of neutralization, the higher the viscosity at the phase transition point. On the other hand, when the monomer concentration exceeds 50% by weight, regardless of the degree of neutralization, the viscosity at the point of phase transition is too high to cause agglomeration phenomenon (Weissenberg effect), resulting in unstable reaction.

The organic solvents used in the present invention are aliphatic or aromatic hydrocarbons having a boiling point of 30 to 200 ° C., for example, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, methylcyclohexane, citrooctane, Decalin and its derivatives, benzene, xylene, toluene and the like can be used alone or in combination of two or more. The amount of the organic solvent used is preferably 0.5-5.0 times, preferably 1-3 times the weight of the aqueous monomer solution, and it is preferable to determine the amount of the dispersion medium in conjunction with the concentration of the aqueous monomer so that the polymer content is 10-25 wt%. Do. If the polymer content is less than 10% by weight, the viscosity is low, not only can not be obtained the water absorbent resin of the desired shape, but also economical, and if it exceeds 25% by weight the particle production process becomes unstable.

As a dispersant, a nonionic dispersant having a HLB (hydrophilic lypophilic balance) value of 8-12 may be used to exhibit the effect to be obtained in the present invention. Examples thereof include sorbitan monolaurate and rotosugar ester S-970. Can be.

In the present invention, polymerization initiators include sulfate-based compounds such as potassium persulfate, sodium persulfate and ammonium persulfate; Hydroxide compounds such as hydrogen peroxide, t-butyl hydroperoxide and cumene hydroperoxide; And water-soluble initiators such as azo compounds, such as 2,2'-azo-bis-2-aminopropane dihydrochloride, may be used alone or in combination of two or more, and include sulfite, L-ascorbic acid and ferric salts. It can be used in combination with a reducing agent.

The polymerization temperature in the manufacturing process of the present invention depends on the type of the polymerization initiator and the combination of the reducing agent, but generally it is preferable to induce the polymerization reaction at 40-90 ℃, 40 ℃ when used in combination with the reducing agent It is also possible at the following temperatures.

In the present invention, it is necessary to control the moisture content in the polymer in order to optimize the absorption and suction force, the dehydration process for this is carried out by azeotropic distillation during and after the polymerization. The water content should be 5 to 55% by weight of the total amount of the polymer and the water contained therein, so that crosslinking by the crosslinking agent is effective, and the water absorption and gel strength are lowered outside the above range.

In the present invention, in order to improve the crosslinking efficiency, a crosslinking agent having an unsaturated group or a reactor capable of two or more reactions is mixed as an aqueous solution in an aqueous monomer solution or poured into an absorbent resin polymer dispersed in an organic dispersion medium after polymerization, followed by swelling and crosslinking. React. Examples of the crosslinking agent include N, N'-methylenebis (methyl) acrylamide, N-methylol (methyl) acrylamide, ethylene glycol (methyl) acrylate, polypropylene glycol (methyl) acrylate, polyethylene glycol (methyl) acrylate , Glycerol tri (methyl) acrylate, glycerol mono (methyl) acrylate, trimethylolpropane tri (methyl) acrylate, triarylamine, triarylcyanolate, triarylisocyanolate, triarylphosphate, glycy And diyl (methyl) acrylate. Examples of the crosslinking agent having a reactive group include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, polyglycerol, propylene glycol, diethanolamine, and triethanol. Polyhydric alcohol derivatives such as amines; Polyglycols such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, sorbitol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether Cydyl derivatives; 2,2-bishydroxymethylbutanol-tri [3- (1-aziridinyl) propionate], 1,6-hexamethylene-diethylene urea, diphenylmethane-bis-4,4'-N, Aziridine derivatives such as N'-diethylene urea; Haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; Polyaldehydes such as glutaraldehyde and glyoxal; Polyamine derivatives, such as ethylenediamine, diethylene triamine, triethylene tetraamine, tetraethylene pentaamine, pentaethylene hexaamine, polyethylene hexaamine, etc. are mentioned.

The crosslinking agent is used in an amount of 0.01 to 5.0% by weight based on the weight of the monomer in the aqueous monomer solution. In addition, the amount of water used with the crosslinking agent is preferably 0.5 to 10% by weight based on the weight of the aqueous monomer solution.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these Examples are only for illustrating the present invention, the present invention is not limited to these.

Example 1

180 g of cyclohexane and 0.30 g of Rotosugar ester S-970 (HLB = 9) were added to a 500 ml four-necked reactor equipped with a stirrer, a Dean-Stark condenser, a pressure regulating panel and a temperature measuring device, and stirred at 460 rpm. The temperature in the reactor was maintained at 73 ° C. Thereafter, pressure adjustment was carried out in a reactor in which a monomer aqueous solution having a neutralization degree of 60% and a monomer content of 37% in which sodium persulfate was dissolved in 120 g in which 26.64 g of sodium acrylate salt and 17.76 g of acrylic acid was dissolved was maintained at 73 ° C. It was injected at high speed by using the panel to make the reactor internal temperature reaches 57 ° C., and then polymerization was performed by external heat supply and self-heating. 64.5 g of water was removed by azeotropic distillation during the polymer formation process and after the polymerization so that the water content in the polymer was 20% by weight, followed by ethylene glycol diglycidyl ether (EX-810, manufactured by NAGASE CHEMICALS) 0.35 An aqueous solution dissolved in 3.5 g of distilled water was added and crosslinked at 70 ° C. for 2 hours. After crosslinking reaction, the polymer was filtered and dried to obtain a pulp-shaped superabsorbent polymer. The attraction force, absorption performance, and particle shape of the prepared resin were measured, and the results are shown in Table 2.

Example 2

A pulp-like superabsorbent polymer was obtained in the same manner as in Example 1 except that nitrogen gas was sufficiently injected in order to remove dissolved oxygen before and after polymerization and was polymerized while maintaining the temperature in the reactor at 70 ° C. The attraction force, absorption performance, and particle shape of the prepared resin were measured, and the results are shown in Table 2.

Example 3

A pulp-like superabsorbent polymer was obtained in the same manner as in Example 1 except that the temperature of the external heat medium was increased by 8 ° C. immediately after the monomer aqueous solution was added at a rapid rate while the temperature inside the reactor was maintained at 70 ° C. The attraction force, absorption performance, and particle shape of the prepared resin were measured, and the results are shown in Table 2.

Examples 4-7

The monomer content in the aqueous monomer solution, the amount of dispersant (Rotosugar ester S-970), the aqueous monomer solution, and the solvent (cyclohexane) were used as shown in Table 1 below, and the water content was 20% by weight based on the polymer. Water was removed before crosslinking as in Example 7, except that the crosslinking agent was crosslinked with 0.5g of crosslinking agent (EX-810) and 4.0g of water in Example 7. The results are shown in Table 2.

Example 4 5 6 7 Monomer content (% by weight) 36 38 39 43 Dispersant (g) 0.1 0.4 0.6 1.2 Monomer aqueous solution (g) 120 120 120 90 Cyclohexane (g) 180 180 180 180 Water removed before crosslinking (g) 65.25 63.0 61.5 43.3

Examples 8-12

The neutralization degree of the aqueous monomer solution having a monomer content of 37% was performed in the same manner as in Example 1 except that the neutralization degree was 35%, 40%, 45%, 50%, and 55%, and the results are shown in Table 2.

Examples 13 and 14

The polymerization process was carried out in the same manner as in Example 1, except that polymerization was performed at 76 ° C. and 79 ° C., and the results are shown in Table 2.

Example 15

The polymerization was carried out in the same manner as in Example 1 except that the monomer aqueous solution was added so as to drop to 65 ° C., and the results are shown in Table 2.

Examples 16 and 17

The polymerization was carried out in the same manner as in Example 1 except that the stirring speed was set to 430 and 480 rpm, respectively, and the results are shown in Table 2.

Example 18

After polymerization, 69 g of water was removed so that the water content in the polymer was 13% by weight, and the crosslinking reaction was performed in the same manner as in Example 1 except that 0.5 g of ethylene glycol diglycidyl ether and 4.0 g of distilled water were used. The results are shown in Table 2.

Comparative Example 1

The polymerization process was carried out in the same manner as in Example 1, except that the polymerization was carried out in a state where the temperature in the reactor was maintained at 70 ° C., and the results are shown in Table 2.

Comparative Example 2

The polymerization was carried out in the same manner as in Example 1 except that the monomer aqueous solution was added at a slow rate so that the temperature inside the reactor dropped to 68 ° C., and the results are shown in Table 2.

Comparative Example 3

The polymerization was carried out in the same manner as in Example 1, except that the monomer concentration in the aqueous monomer solution was 43%, and the results are shown in Table 2.

Comparative Example 4

Except for polymerization at a stirring speed of 300 rpm was carried out in the same manner as in Example 1 and the results are shown in Table 2.

Attraction pressure under normal pressure ^* (ml / g) Absorption after 30 minutes ^* (g / g) Particle shape 1 minute later 5 minutes later Example One 7.5 14.2 51 Pulp Shape (Pea Peel Form) 2 5.6 12.4 63 Pulp Shape (Needle Type) 3 5.8 13.1 49 Pulp Shape (Needle Type) 4 4.0 10.2 48 Pulp Shape (Needle Type) 5 8.1 16.0 50 Pulp Shape (Needle Type) 6 7.5 14.5 55 Square 7 10.2 14.5 49 Pulp Shape (Pea Peel Form) 8 4.8 13.1 40 Pulp Shape (Needle Type) 9 5.2 13.1 55 Pulp Shape (Needle Type) 10 6.0 14.6 43 Pulp Shape (Needle Type) 11 5.5 15.0 48 Pulp Shape (Needle Type) 12 5.7 14.5 47 Pulp Shape (Needle Type) 13 6.4 14.1 50 Pulp Shape (Needle Type) 14 5.9 13.5 50 Pulp Shape (Needle Type) 15 5.7 13.1 53 Pulp Shape (Needle Type) 16 6.3 13.4 60 Pulp Shape (Pea Peel Form) 17 6.7 14.4 58 Pulp Shape (Pea Peel Form) 18 6.8 14.2 48 Pulp Shape (Pea Peel Form) One 2.5 3.6 77 Spherical particles 2 3.4 8.2 72 Spherical particles 3 - - - Bundling (Weissenberg Effect) 4 7.1 12.8 37 Spherical particles

* Both suction and absorption were measured in 0.9% NaCl aqueous solution.

It was measured using the column method, the absorption was measured by the molecular sieve method.

The water absorbent resin prepared according to the present invention has a form similar to pulp that could not be prepared by the conventional reverse phase suspension polymerization method, and has excellent kneading ability with the absorbent material of pulp or other sanitary materials, and the absorption amount and absorption rate for brine. And it is excellent in physical properties such as suction force and the particle size distribution is narrow while satisfying the particle size distribution standard of the general sanitary products use is easy to handle it can be usefully used in sanitary products.

Claims (16)

After the polymerization was carried out by adjusting the viscosity and the stirring speed by adding a hydrophilic monomer solution containing a polymerization initiator in a solution obtained by dispersing a dispersant having an HLB of 8-12 in an organic solvent, the water content in the polymer was 55 weights by azeotropic distillation. Pulp-shaped superabsorbent polymer production method comprising the step of cross-linking for 1 to 3 hours by adding a crosslinking agent aqueous solution while maintaining the temperature in the reactor at 40-85 ° C or less. The method of claim 1, The viscosity control is carried out by controlling the monomer concentration in the aqueous monomer solution, the external heat transfer rate, the efficiency of the polymerization initiator, the polymerization temperature, the weight ratio of the organic solvent and the aqueous monomer solution, the rate and neutralization of the monomer aqueous solution, the type and amount of the dispersant Characterized in that the method. The method of claim 2, The external heat transfer rate control is such that the monomer aqueous solution is rapidly added at a high temperature inside the reactor and the temperature of the external heat medium is maintained until the polymerization is completed, or the monomer aqueous solution is kept at a low temperature inside the reactor. Method to be carried out by increasing the temperature of the external heating medium after the addition. The method of claim 2, The efficiency of the polymerization initiator is increased by adding nitrogen before and after polymerization to remove dissolved oxygen. The method of claim 2, And a rate of introduction of the aqueous monomer solution so that the temperature in the reactor drops by at least 8 ° C. than before the addition of monomer. The method of claim 1, The dispersant is sorbitan monolaurate or Rotosugar ester S-970, characterized in that used in an amount of 0.01 to 0.5% by weight of the aqueous monomer solution. The method of claim 1, The organic solvent has a boiling point of 30-200 ° C. and consists of n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, methylcyclohexane, citrooctane, decalin and derivatives thereof, benzene, xylene and toluene At least one selected from the group. The method of claim 7, wherein The amount of the organic solvent is characterized in that 0.5 to 5 times the weight of the aqueous monomer solution. The method of claim 1, Wherein the aqueous hydrophilic monomer solution is prepared to neutralize the hydrophilic monomer with an alkali metal salt of 20 to 95 mol% and then have a monomer concentration of 30 to 50 wt%. The method of claim 9, The hydrophilic monomer is acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth ) Acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate and anhydride or ester derivatives thereof; (Meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide or N-substituted (meth) acrylamide and salts thereof; At least one selected from the group consisting of 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid and vinylsulfonic acid Characterized in that the method. The method of claim 1, The polymerization initiator consists of potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide and 2,2'-azo-bis-2-aminopropane dihydrochloride At least one selected from the group. The method of claim 11, Using said polymerization initiator in combination with sulfite, L-ascorbic acid or ferric salt. The method of claim 1, The polymerization reaction is carried out at a temperature of 40 to 90 ℃. The method of claim 1, The crosslinking agent is N, N'-methylenebis (methyl) acrylamide, N-methylol (methyl) acrylamide, ethylene glycol (methyl) acrylate, polypropylene glycol (methyl) acrylate, polyethylene glycol (methyl) acrylate , Glycerol tri (methyl) acrylate, glycerol mono (methyl) acrylate, trimethylolpropane tri (methyl) acrylate, triarylamine, triarylcyanolate, triarylisocyanolate, triarylphosphate, glycy Dyl (methyl) acrylate, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, polyglycerol, propylene glycol, diethanolamine, triethanolamine, ethylene glycol diglycidyl ether, polyethylene glycol Diglycidyl ether, glycerol polyglycidyl ether, sorbitol polyglycidyl ether, propylene Glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 2,2-bishydroxymethylbutanol-tri [3- (1-aziridinyl) propionate], 1,6-hexamethylene-di Aziridine derivatives such as ethylene urea and diphenylmethane-bis-4,4'-N, N'-diethylene urea; Epichlorohydrin, α-methylchlorohydrin, glutaraldehyde, glyoxal, ethylenediamine, diethylene triamine, triethylene tetraamine, tetraethylene pentaamine, pentaethylene hexaamine and polyethylene hexaamine At least one method. The method of claim 14, The crosslinking agent is used in an amount of 0.01 to 5.0% by weight based on the weight of the monomer in the aqueous monomer solution. The method of claim 1, The amount of water used with the crosslinking agent is 0.5 to 10% by weight based on the aqueous monomer solution.