JP2000053719A - Production of acrylic polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an acrylic polymer in which the content of unreacted residual monomer is reduced while retaining basic properties such as appropriate viscosity, non-discoloring property, or the like by adding a redox-type polymerization initiator to a specific water-containing gel-like polymer. SOLUTION: The objective polymer (e.g. an acrylic acid/sodium acrylate/ sodium methacrylate copolymer) is obtained by adding (B) a redox-type polymerization initiator (including an oxidizing agent and a reducer as essential ingredients) to (A) a water soluble water-containing gel-like polymer obtained by polymerizing an acrylic monomer having carboxylic group in an aqueous solution till the reaction has completed. The method is pref. conducted by preparing an aqueous solution of a polymerizable monomer [e.g. (meth)acrylic acid, a (meth)acrylate or the like] so as to have a preferred concentration by sufficiently substituting dissolved oxygen with nitrogen, adding a radical polymerization initiator and, optionally heating and irradiating ultraviolet-light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a base material for a poultice,
The present invention relates to a method for producing an acrylic polymer excellent in applicability to a thickener, a pressure-sensitive adhesive, a papermaking agent, a polymer flocculant and the like, in which the content of unreacted residual monomers is reduced.

[0002]

2. Description of the Related Art Among water-soluble acrylic polymers containing a carboxyl group, those having a high degree of polymerization such that they become gel-like due to water content have been conventionally used as a base material for a poultice, a thickener, It is used for adhesives, papermaking chemicals, polymer flocculants and the like. Examples of the method for producing the polymer include various radical polymerization methods such as an aqueous solution polymerization method, a slurry polymerization method, a suspension polymerization method, and an emulsion polymerization method, and the production process is simple, such as removal or removal of an organic solvent. The application of the aqueous solution polymerization method is common in view of the advantage that the reaction operation is easy without any problem. Examples of application of the aqueous solution polymerization method include, for example, preparing an aqueous solution of a polymerizable monomer such as (meth) acrylic acid or (meth) acrylic acid salt at a predetermined concentration, sufficiently displacing dissolved oxygen with nitrogen, and then performing radical polymerization. A method in which an initiator is added, and a polymerization reaction is performed by appropriately heating or irradiating ultraviolet rays as necessary, and as the polymerization reaction proceeds, the aqueous solution of the (meth) acrylic acid (salt) -based polymer becomes very viscous. When the polymerization reaction is completed, it is usually obtained as a hydrogel polymer. If necessary, the hydrogel is shredded, dried by hot air drying, reduced pressure drying, indirect heating drying, and the like, and further pulverized to obtain a powdery polymer.
However, the polymer thus obtained usually contains a large amount of unreacted residual monomers in excess of 0.1% by weight based on the polymer pure content. The materials, thickeners, adhesives, papermaking agents, and polymer flocculants were not satisfactory enough.

[0003] In order to solve the above-mentioned problems, studies have been made on the following methods for reducing residual monomers. For example, a method of separating and removing residual monomers by ultrafiltration or the like after obtaining a polymer (Japanese Patent Application Laid-Open No. 8-217802), a method of increasing the amount of a polymerization initiator added during a polymerization reaction, and the like. Of the above, the former method cannot sufficiently remove the residual monomer, or if an attempt is made to increase the removal rate of the residual monomer, the equipment becomes excessively large and the productivity is significantly reduced. There is no solution yet. Further, in the latter method, although the residual monomer can be reduced, the degree of polymerization of the polymer is lowered, and the physical properties of the polymer are largely changed with time, and it is difficult to apply the method to a base material for a poultice. Furthermore, in order to solve the problem of the latter method, a method of reducing the residual initiator content (Japanese Patent Application Laid-Open No. 9-124467) has been proposed, but insolubilization and coloring of the polymer due to severe processing Has become a problem and is not yet a fundamental solution.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its main objects are to provide a base material for cataplasms, a thickener, a pressure-sensitive adhesive, a chemical for papermaking, When applied to molecular coagulants, etc., suitable viscosity, solubility,
An object of the present invention is to provide a method for producing an excellent acrylic polymer having a reduced content of unreacted residual monomers while maintaining basic physical properties such as no coloring.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, in a production method for obtaining an acrylic polymer containing a carboxyl group by an aqueous solution polymerization method, first, a polymerization was carried out. Only by adding a redox-based polymerization initiator to the hydrogel polymer after the polymerization reaction is substantially completed to obtain a hydrogel polymer by the reaction, and the polymerization reaction is substantially completed, the solubility is good. While maintaining the basic physical properties of no coloring,
The inventors have found that an excellent acrylic polymer having a reduced content of unreacted residual monomers can be obtained, thereby completing the present invention.

That is, the present invention relates to a water-soluble, water-containing gel polymer obtained by reacting an acrylic monomer having a carboxyl group in an aqueous solution until the polymerization reaction is substantially completed. And a method for producing an acrylic polymer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The acrylic polymer having a carboxyl group according to the present invention is a water-soluble polymer having a linear or branched molecular structure, and is a main monomer constituting the polymer. The body may be a (meth) acrylic acid (salt) such as acrylic acid and its salts, methacrylic acid and its salts, and even if these are only one kind of homopolymer, two or more kinds may be copolymerized as necessary. May be used. Specific examples of the acrylic polymer, for example,
Poly (meth) acrylic acid having a linear or branched molecular structure, poly (meth) acrylate, (meth) acrylic acid /
(Meth) acrylic acid (salt) such as (meth) acrylate copolymer
-Based polymers, among which (meth) acrylic acid / (meth) acrylate copolymer is preferred, acrylic acid / (meth) sodium acrylate copolymer is more preferred, acrylic acid / sodium acrylate / Sodium methacrylate copolymer is most preferred. Further, specific examples of preferred composition ratios of the copolymer include acrylic acid / sodium acrylate / sodium methacrylate in a proportion of 5 to 80/2, respectively.
0 to 95/0 to 10 mol% is preferable, and 25 to 65/35.
-75 / 0-5 mol% is more preferable, and 45-55 / 42.
~ 52/0 ~ 3 mol% is most preferred. In addition to the above, the production method of the present invention can be effectively used for copolymers obtained by copolymerizing other polymerizable monomers as long as the effects intended by the present invention are not impaired. Specific examples of other polymerizable monomers include, for example, maleic acid, itaconic acid, unsaturated carboxylic acids such as fumaric acid and salts thereof, 2-acrylamido-2-methylpropanesulfonic acid, (meth) allylsulfonic acid , Unsaturated sulfonic acids such as styrenesulfonic acid and salts thereof, (meth) acrylamide, N-isopropylacrylamide, N, N-dimethylacrylamide, etc.
(Meth) acrylamide derivative, dimethylaminoethyl
Examples thereof include quaternary ammonium salts and neutralized salts of (meth) acrylate, and one or more of these may be used as necessary.

A preferred acrylic polymer obtained by the present invention is 0.2% by weight of the polymer.
The aqueous solution viscosity of the concentration (in terms of solid content) was measured at 30 rp with a B-type viscometer.
m, measured at 30 ° C. (hereinafter abbreviated as 0.2% viscosity)
Is in the range of 100 to 800 cps, a more preferable acrylic polymer is 250 to 700 cps, and a particularly preferable one is 480 to 600 cps. If the 0.2% viscosity is out of the range of 100 to 800 cps, the degree of polymerization is too high to be insolubilized, or conversely, the degree of polymerization is too low for base materials for cataplasms, thickeners, adhesives, and papermaking. In some cases, sufficient performance as a drug, a polymer flocculant or the like cannot be obtained. For these uses, usually those having a molecular weight of hundreds of thousands to tens of millions are used.

According to the production method of the present invention, an acrylic polymer having an unreacted residual monomer content of 0.1% by weight or less based on the pure polymer content in the polymer can be easily obtained.
Preferred acrylic polymers for the present invention have a residual monomer content of 0.05% by weight or less, and more preferably have a residual monomer content of 0.02% by weight or less. If the unreacted residual monomer content exceeds 0.1% by weight, for example,
When applied as a base material for a poultice, the adhesiveness required as a poultice is insufficient, or the properties of the gel plaster, which is the adhesive portion of the poultice, change over time, or the gel plaster to the support In some cases, problems such as exudation of the body and deterioration of the adhesiveness may occur. Also, in other uses, there may be a case where the viscosity is insufficient, the tackiness and the cohesiveness are insufficient, and the safety is a problem due to the irritability of the residual monomer.

In the aqueous solution polymerization method to which the present invention is applied, for example, an aqueous solution of a polymerizable monomer such as (meth) acrylic acid or (meth) acrylate is prepared at a predetermined concentration, and dissolved oxygen is sufficiently reduced by nitrogen. After the substitution, a method of performing a polymerization reaction by adding a radical polymerization initiator and appropriately heating or irradiating ultraviolet rays as necessary, and the like, as the polymerization reaction proceeds
The aqueous solution of the (meth) acrylic acid (salt) -based polymer becomes very viscous, and is usually obtained as a hydrogel polymer when the polymerization reaction is completed. If necessary, the hydrogel is shredded, dried by hot air drying, reduced pressure drying, indirect heating drying, and the like, and further pulverized to obtain a powdery polymer. However, the polymer thus obtained is
Usually, the unreacted residual monomer is 0.1 to the polymer pure content.
Since it is contained in excess of% by weight, the acrylic polymer aimed at by the present invention is insufficient in this state. Therefore, in the production method of the present invention, it is necessary to include an operation of additionally adding a redox polymerization initiator to the hydrogel polymer obtained by the polymerization reaction as a method for reducing the residual monomer.

The hydrated gel polymer is a hydrated gel polymer which is obtained after the polymerization reaction is substantially completed. The polymer after the polymerization reaction is substantially completed is a polymer after most of the chain formation of the acrylic polymer is completed by the polymerization reaction.For example, in the case of polymerization in an adiabatic system, at least the polymerization heat Is a polymer after the temperature rise in the reaction system is completed and reaches the maximum temperature, and usually has a reaction rate of 95% or more, preferably 98% or more. If a polymerization initiator is added before the polymerization reaction is substantially completed, the degree of polymerization of the acrylic polymer may be significantly reduced, and a base material for a poultice, a thickener, a pressure-sensitive adhesive, an agent for papermaking, An acrylic polymer which does not sufficiently obtain the performance expected as a polymer flocculant is obtained.

[0012] The polymerization initiator additionally added to the hydrogel polymer must be a redox-based polymerization initiator capable of suppressing the residual oxidizing agent. When the oxidizing agent remains in the polymer, the polymer may be oxidatively degraded and colored,
This may cause a problem by insolubilizing the polymer or lowering the degree of polymerization.

The redox polymerization initiator is a polymerization initiator comprising as essential components at least one of (A) an oxidizing agent and (B) at least one of a reducing agent.
The molar ratio of the additional amount of (B) is usually 0.1 to 200.
The oxidizing agent and the reducing agent are not particularly limited, and known agents can be used. Examples of the oxidizing agent include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, benzoyl peroxide, and lauroyl peroxide. Among them, organic peroxides and hydrogen peroxide are used, and among them, persulfates which have a high initiator efficiency and relatively hardly cause oxidative deterioration of the polymer are particularly preferable. One or more of these oxidizing agents can be used as necessary.
Examples of the reducing agent include sulfites such as sodium sulfite, potassium sulfite, and ammonium sulfite, and bisulfites such as sodium bisulfite, potassium bisulfite, and ammonium bisulfite; Sodium phosphite, potassium hypophosphite, hypophosphites such as ammonium hypophosphite and the like are used. Among them, the remaining oxidizing agent can be effectively suppressed, and Sulfites and hydrogen sulfites, which hardly cause a decrease in the degree of polymerization, are particularly preferred. One or more of these reducing agents can be used as necessary. The molar ratio of the additional amount of the reducing agent to the oxidizing agent is usually 0.1 to 200, preferably 1.5 to 10
0, and more preferably 3 to 40. If the molar ratio of the amount of the reducing agent to the oxidizing agent is out of the range of 0.1 to 200, the effect of the redox polymerization initiator is not sufficiently exhibited, and the residual monomer may be reduced to 0.1% by weight or less. In some cases, the polymer may not be colored, or the polymer may be insolubilized or the degree of polymerization may be reduced, and the good polymer properties expected in the present invention may not be maintained.

Of the redox polymerization initiators, the amount of the oxidizing agent added is desirably the minimum amount necessary to sufficiently reduce the residual monomers, and is usually 1 to the pure polymer content.
The concentration is from 1000 to 1000 ppm, preferably from 5 to 500 ppm, more preferably from 10 to 300 ppm. 1 ppm of oxidizer added
If the amount is less than 0.1% by weight, the residual monomer cannot be reduced to less than 0.1% by weight. If the amount exceeds 1000 ppm, the coloring of the polymer or the insolubilization of the polymer or the decrease in the degree of polymerization is caused, which is expected in the present invention. In some cases, good polymer properties cannot be maintained. Of the redox-based polymerization initiators, the amount of the reducing agent to be added is usually 1 to 1000 with respect to the pure polymer.
0 ppm, preferably 5 to 2000 ppm, more preferably 20 to 1000 ppm. When the amount of the reducing agent added is less than 1 ppm, the amount of the residual monomer cannot be reduced to 0.1% by weight or less, or the coloring of the polymer, the insolubilization of the polymer or the decrease in the degree of polymerization may be caused by the present invention. In some cases, the desired good polymer physical properties cannot be maintained.
When the content exceeds ppm, the stability with time of the polymer is deteriorated, and the quality and performance of the polymer may vary, which may cause a problem.

Accordingly, a preferable application example of the production method of the present invention is, for example, to obtain a hydrogel polymer by an aqueous solution polymerization method as described above, and then to obtain a hydrogel obtained after the polymerization reaction is substantially completed. After or while additionally adding a redox-based polymerization initiator to the polymer, the hydrogel is shredded with a gel grinder or the like. The hydrogel that has been shredded by the gel crusher is almost uniformly mixed with the polymerization initiator at the same time, so the unreacted residual monomer is reduced by drying and crushing the obtained shredded gel as it is. The present invention is completed by obtaining an acrylic polymer. Further, if necessary, mixing and aging operations can be performed before drying the shredded gel.

When the acrylic polymer in the present invention is used as a poultice, it is used as a crosslinked product, but the crosslinking of the acrylic polymer is caused by the unreacted residual monomer content obtained as described above. Is preferable to crosslink an acrylic polymer containing 0.1% by weight or less of a carboxyl group based on the polymer pure content with a polyvalent metal compound in the state of a hydrogel. The cross-linking method is applied as a method for producing a gel plaster.

The gel plaster is a hydrogel-like pressure-sensitive adhesive constituting a poultice. The essential components are acrylic polymer, polyvalent metal compound, water, and additives such as water retention agent and inorganic powder. And medicinal ingredients, etc., and are obtained by kneading after adding or mixing the components at once or sequentially so as to have a predetermined mixing ratio. Specific examples of the preferable mixing ratio of the gel plaster include, for example, 1 to 20% by weight of an acrylic polymer such as a (meth) acrylic acid / (meth) acrylate copolymer based on the total amount of the gel plaster. 1 to 30% by weight of a water retention agent such as glycerin; 0.001 to 3% by weight of a polyvalent metal compound such as aluminum hydroxide; 1 to 10% by weight of an inorganic additive such as kaolin; ~
10% by weight and water content of 40 to 80% by weight. Since the cross-linking reaction of the acrylic polymer by the polyvalent metal compound proceeds with time after the preparation of the gel plaster, the gel plaster applied and spread on the support surface has an appropriate degree as the cross-linking reaction proceeds. It cures at a rapid rate and has excellent adhesion and base strength to complete crosslinking.

Examples of the polyvalent metal compound include, for example, aluminum hydroxide, aluminum chloride, aluminum sulfate, aluminum silicate, aluminum phosphate,
Examples thereof include aluminum / magnesium hydroxide and aluminum glycinate, which may be used alone or in combination. Further, these polyvalent metal compounds may be water-soluble or hardly soluble.

The amount of the polyvalent metal compound in the gel plaster varies depending on the degree of polymerization and the amount of the acrylic polymer, the type of the polyvalent metal compound, other compounds, and the like. 0.001 to 3% by weight based on the total weight of the gel plaster
, Preferably 0.001 to 1% by weight, more preferably 0.01 to 0.5% by weight.

The mixing amount of the acrylic polymer in the gel plaster is preferably 1 to 20% by weight based on the total weight of the gel plaster.
And more preferably 5 to 15% by weight. If the blending amount of the polymer is less than 1% by weight, the tackiness, viscosity increase and formability are reduced, and if it exceeds 20% by weight, the effect of the poultice expected in the present invention is obtained because the viscosity increases too much. May not be.

[0021]

The present invention will be specifically described below with reference to examples and comparative examples. In addition, physical property test methods used in Examples and Comparative Examples are also described. [Amount of residual monomer] Dissolve the polymer sample in pure water,
A polymer solution having a concentration of 1.0% by weight (in terms of solid content) is prepared, 2 g of the polymer solution is poured into 20 ml of methanol, and the polymer is precipitated by stirring with a stirrer for 30 minutes. After 30 minutes, the supernatant was collected and the amount of residual monomer was measured by high performance liquid chromatography (column: Hitachi HPL).
(C packed column # 3056, eluent: 0.1% phosphate buffer, detector: UV 195 nm). [0.2% viscosity] A polymer sample was dissolved in pure water to obtain a 0.2% viscosity.
A polymer solution having a concentration of 2% by weight (in terms of solid content) was prepared.
The 0.2% viscosity at 30 rpm and 30 ° C. was measured with a mold viscometer. [Insoluble content] A polymer sample was dissolved in pure water to obtain 0.2
A 400% by weight polymer solution (solid content conversion) was prepared, and the entire amount of the solution was filtered through a 83-mesh sieve having a diameter of 20 cm, washed with water, and the insoluble material remaining on the sieve was collected and taken into a cylinder. The capacity was measured. [Polymer coloring] A polymer sample was visually observed to evaluate the presence or absence of coloring of the polymer. In the three-step evaluation, the evaluation criteria were as follows. ：: No coloring (white) △: Slightly coloring (slightly yellowing) ×: Strongly coloring (yellowing) [Spinnability] A polymer sample was dissolved in pure water to a concentration of 1.0% by weight (solid content conversion). ) Was prepared in a beaker, the temperature was adjusted to 25 ° C., a glass ball having a diameter of 10 mm was immersed in the solution to a depth of about 20 mm, and the beaker was cooled to 5 mm / s.
The time T (sec) from the time when the lower end of the glass ball reached the surface of the dissolving solution by lowering at a speed of ec until the stringing was broken was measured, and the spinning property was calculated by the following equation. Spinnability (mm) = 5 × T This spinnability measurement is an objective method for evaluating the shapeability of a polymer. In the case of polymers having similar viscosities, the spinning length is The smaller the size, the better the shapeability of the polymer.

Example 1 An aqueous solution of sodium acrylate, an aqueous solution of acrylic acid and an aqueous solution of sodium methacrylate were placed in a stainless steel Dewar bottle at 46.4 mol%, 51.22 mol%, and 2.38 mol%, respectively.
Molar% composition, total weight 1kg, monomer concentration 30% by weight
Ion-exchanged water was added such that After adjusting the temperature of the aqueous monomer solution to 10 ° C., nitrogen was introduced and degassed for 60 minutes. As a polymerization initiator, azobisamidinopropane hydrochloride, ammonium persulfate, sodium sulfite, and Elbit-N were added at 500 ppm, 10
Polymerization was started by adding 0 ppm, 100 ppm, and 20 ppm.
After 8 hours, the polymerization was completed, and the obtained hydrogel polymer was taken out, and ammonium persulfate and sodium sulfite were added as additional redox-based polymerization initiators at 60 ppm and 300 ppm, respectively, based on the polymer pure content.
The hydrogel polymer was placed in a small chopper and cut into minced meat. The obtained shredded gel was dried in a hot air drier at 100 ° C. for 5 hours, and the dried product was pulverized to obtain a polymer A.

Comparative Example 1 A polymer a was obtained in the same manner as in Example 1, except that no additional polymerization initiator was added. Comparative Example 2 To a monomer aqueous solution prepared and degassed in the same manner as in Example 1,
Azobisamidinopropane hydrochloride, ammonium persulfate, sodium sulfite, and Elbit-N were added at 500 ppm, 100 ppm, 100 ppm,
At the same time as the addition of 0 ppm, ammonium persulfate and sodium sulfite were added to the aqueous monomer solution before the start of polymerization and before the formation of the hydrous gel in an amount of 30 ppm and 100 ppm, respectively, based on the total monomer weight. Started. 8
After a period of time, the polymerization was completed, and the obtained hydrogel polymer was taken out, cut into small pieces with a chopper, dried and pulverized to obtain a polymer b. Comparative Example 3 A monomer aqueous solution prepared and degassed in the same manner as in Example 1 was added to
Azobisamidinopropane hydrochloride, ammonium persulfate, sodium sulfite, and Elbit-N were added at 500 ppm, 100 ppm, 100 ppm,
Polymerization was started by adding 0 ppm. Four hours later, when the reaction rate reached about 40%, ammonium hydrosulfate and sodium sulfite were added to the hydrogel polymer before the polymerization was completed, based on the total monomer weight at the time of monomer preparation. 10
After additional addition of 0 ppm and 300 ppm, the hydrogel polymer was mixed with a handy mixer, and polymerization was continued. After 2 hours, the polymerization was completed, so the obtained hydrogel polymer was taken out, shredded with a small chopper, dried and pulverized to obtain a polymer c.

Examples 2 to 7 and Comparative Examples 4 and 5 In Example 1, the formulation of the additional addition of the polymerization initiator is shown in Table 1.
Polymer B was prepared in the same manner except that the reaction was carried out under the conditions shown in
To G and polymers de to e. The physical properties tests were performed on the polymers thus obtained in Examples and Comparative Examples. The results are summarized in Table 1.

[0025]

[Table 1]

As is apparent from Table 1, the polymers of Comparative Examples 1 to 4 are problematic due to the high residual monomer content.
Although the amount of the residual monomer was reduced to 1000 ppm or less, the polymer of No. 3 had a large amount of insoluble matter, and the polymer was significantly colored, which was a problem. On the other hand, the polymer of the example is 0.1.
While maintaining suitable values for 2% viscosity, spinnability, and insoluble content, the amount of residual monomer was reduced to 1000 ppm or less, and the polymer was excellent in physical properties without coloring.

評 価 Crosslinkability evaluation test Next, the crosslinkability of these polymers was examined. The evaluation of the cross-linkability is based on the change in hardness of the gel plaster for cataplasm.
(Curing speed) was measured over time over one week. A gel plaster was prepared according to the formulation shown in Table 2. First, the polymer A obtained in Example 1 was uniformly dispersed in glycerin, and this was dispersed in 50 parts of the total amount of the gel plaster.
Dissolved in water by weight. On the other hand, kaolin, titanium oxide, methyl salicylate, 1-
Add menthol, dl-camphor and peppermint oil and mix,
Further, a mixture obtained by adding aluminum hydroxide gel and uniformly stirring and mixing was added to the above polymer solution, and kneaded to prepare a gel plaster. Similarly, gel plasters were prepared using Polymers BE and Polymers ad. About these gel plasters,
The curing speed was evaluated as follows. First, the gel plaster immediately after preparation as a sample was packed into a cylindrical container having an inner diameter of 55 mm and a depth of 20 mm so as to be completely filled, and at the same time the surface was leveled and flattened. The hardness of the gel plaster was measured by a viscoelasticity measurement device (Rheometer Max RX-1700 manufactured by Eye Techno Engineering Link Co., Ltd.) by constant-speed compression and tensile motion (100 mm /
Minute: φ30 mm flange). After the measurement, seal the container at 25 ° C
And the hardness of the gel plaster was similarly measured every predetermined time. The results are summarized in Table 3.

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

As is evident from Table 3, the polymer gel of the comparative example has a slow curing speed, whereas the polymer gel of the present invention has a significantly improved curing speed. It showed good crosslinkability, and also had high strength of the gel plaster itself, showing excellent performance as a base material for a poultice. As described above, according to the present invention, an excellent acrylic polymer having a reduced content of unreacted residual monomers can be easily obtained. Further, the acrylic polymer obtained by the production method of the present invention has a suitable viscosity, good solubility, and,
Since there is no coloring, it is excellent in applicability to thickeners, pressure-sensitive adhesives, papermaking chemicals, polymer flocculants, and the like. Furthermore, by applying as a base material for a poultice, a highly safe poultice having excellent adhesiveness and stability over time and improved skin irritation can be obtained.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinzo Narimatsu 2-4-1 Showa-cho, Sakaide-shi, Kagawa F-term in the Sakaide Plant of Toa Gosei Co., Ltd. 4J100 AJ02P AK08P CA01 GB01

Claims (1)

[Claims] 1. A redox polymerization initiator is added to a water-soluble hydrogel polymer obtained by reacting an acrylic monomer having a carboxyl group in an aqueous solution until the polymerization reaction is substantially completed. A method for producing an acrylic polymer.