JP6617709B2 - Acrylic acid polymer aqueous solution and method for producing the same - Google Patents

Description

  The present invention relates to an aqueous solution containing an acrylic acid polymer suitable as a water treatment agent and a method for producing the same.

  It is known that a low molecular weight polymer having a structural unit derived from acrylic acid or a salt thereof is suitable for suppressing scale formation in piping, boilers, heat exchangers and the like.

As a method for producing an acrylic acid-based low molecular weight polymer, the following methods are known.
In Patent Document 1, acrylic acid or methacrylic acid, sodium bisulfite that is a chain transfer agent, and 3-allyloxy-2-hydroxy-1-propanesulfonic acid are dropped into a reaction system, and the weight average molecular weight is 4400 or A method for producing 3600 copolymers is disclosed.
In Patent Document 2, in an aqueous solvent containing 80% by weight or more of water, maleic acid is initially charged at 80% by weight or more with respect to the total amount of maleic acid used, and the remainder is dropped, and acrylic acid is added to the total amount thereof. 90% by weight or more is dropped relative to the amount used, the rest is initially charged, and as a polymerization initiator, hydrogen peroxide and sodium persulfate are used for dropping 80% by weight or more of the predetermined amount, and the rest are used for initial charging. The polymerization reaction monomer composition liquid at the initial charging stage has a pH of 8 to 12 and a degree of neutralization of 50 to 95 mol%, and polymerization is started. The solid content concentration during the polymerization reaction is 40 The pH is adjusted to 4 to 8 and the solid content concentration is adjusted to the range of 40 to 60% by weight at the stage where the dripping of all the monomer compositions is completed. Polymerized to have a weight average molecular weight of 4900 to 9000 Method for producing a maleic acid-based water-soluble copolymer of time is disclosed.

In Patent Document 3, acrylic acid or acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid and sodium persulfate are dropped into a reaction system, and both produce polymers having a weight average molecular weight of 2000. A method is disclosed.
In Patent Document 4, acrylic acid and / or 2-acrylamido-2-methylpropanesulfonic acid and sodium persulfate are added dropwise in the presence of maleic acid to produce a copolymer having a weight average molecular weight of 700 to 18,000. A method is disclosed.
Patent Document 5 discloses a method for producing a copolymer having a number average molecular weight of 2580 by polymerizing a monomer mixture containing acrylic acid, methacrylic acid and mercaptopropionic acid using a specific azo initiator. .

JP 2002-3536 A JP 2000-355615 A JP 11-181479 A Japanese Patent Laid-Open No. 10-25684 JP 2011-82512 A

A water treatment agent for the purpose of suppressing scale formation is usually transparent. Although the pH may be adjusted in the range of 3 to 5, the water treatment agent is not preferred to cause corrosion of metal pipes or the like, and to be turbid or colored during use. Yes. However, it has been found that these defects depend on the production raw material and production method of the acrylic acid polymer.
For example, the polymer obtained by the method described in Patent Documents 1 to 4 has a sulfonic acid group or a sulfate ester group derived from a monomer, a chain transfer agent, an initiator, and the like, and has the above pH. Use of a water treatment agent may corrode metals, alloys, and the like.
Further, the copolymer described in Patent Document 5 does not have a sulfonic acid group or a sulfate ester group, but an aqueous solution containing the copolymer may generate turbidity under low temperature conditions. In the climate, when the water treatment agent is stored, it can no longer be used.
In view of the above, there is a demand for a method for producing an aqueous solution containing an acrylic acid-based polymer that has reduced effects on metals, alloys, and the like and does not generate turbidity under low temperature conditions.

The present invention is shown below.
[1] A method for producing an aqueous solution containing an acrylic acid polymer having a weight average molecular weight of 1500 or less, comprising at least one chain transfer selected from hypophosphorous acid and a salt thereof and phosphorous acid and a salt thereof Characterized by comprising a polymerization step of polymerizing a monomer containing acrylic acid in a reaction system comprising an agent, at least one polymerization initiator selected from azo compounds and peroxides, and water, A method for producing an acrylic acid polymer aqueous solution.
[2] The method for producing an acrylic acid polymer aqueous solution according to the above [1], wherein the amount of the chain transfer agent used is 12 to 35 parts by mass when the monomer is 100 parts by mass.
[3] The acrylic acid according to [1] or [2], wherein in the polymerization step, the monomer and the polymerization initiator are continuously supplied to a reaction system containing the water and the chain transfer agent. For producing an aqueous polymer solution.
[4] The acrylic polymer aqueous solution according to any one of [1] to [3], further including a pH adjusting step for adjusting the pH of the reaction solution to 3.0 or more after the polymerization step. Manufacturing method.
[5] An acrylic acid polymer aqueous solution obtained by the method according to any one of [1] to [4] above.
In this specification, the weight average molecular weight (hereinafter also referred to as “Mw”) of the polymer is a standard sodium polyacrylate conversion value measured by gel permeation chromatography (hereinafter also referred to as “GPC”). . The description of “(meth) acryl” means acryl and methacryl.

  According to the present invention, an aqueous solution containing an acrylic acid-based polymer having a phosphate group can be efficiently produced by using a specific chain transfer agent, and this aqueous solution has a small effect on metals, alloys, etc. Turbidity is also suppressed under low temperature conditions. Therefore, the acrylic acid polymer aqueous solution obtained by the production method of the present invention can be suitably used as a water treatment agent.

  The present invention relates to a method for producing an aqueous solution containing an acrylic acid polymer having an Mw of 1500 or less, and at least one chain transfer agent selected from hypophosphorous acid and salts thereof and phosphorous acid and salts thereof And a polymerization step of polymerizing a monomer containing acrylic acid in a reaction system comprising at least one polymerization initiator selected from azo compounds and peroxides and water.

In the polymerization step according to the production method of the present invention, the monomer containing acrylic acid is composed of at least one chain transfer agent selected from hypophosphorous acid and its salt and phosphorous acid and its salt, an azo compound, and Polymerization is performed in a reaction system including at least one polymerization initiator selected from peroxides and water.
The monomer may be only acrylic acid, or may contain a compound having a polymerizable unsaturated bond (hereinafter referred to as “other monomer”) that can be copolymerized with acrylic acid. Other monomers include salts of acrylic acid, unsaturated monocarboxylic acids having 4 or more carbon atoms or salts thereof, unsaturated dicarboxylic acids or anhydrides or salts thereof, (meth) acrylic acid alkyl esters, (meth ) Acrylic acid hydroxyalkyl ester, amino group-containing vinyl compound, amide group-containing vinyl compound, sulfonic acid group-containing vinyl compound, polyoxyalkylene group-containing vinyl compound, alkoxyl group-containing vinyl compound and the like. These compounds may be used alone or in combination of two or more. The “salt” may be an alkali metal salt such as sodium or potassium, an alkaline earth metal salt such as calcium or magnesium, an organic amine salt such as ammonium salt, monoethanolamine, or triethanolamine. As other monomers, among them, the scale inhibiting ability and the solubility in water are good, so that a salt of acrylic acid, an unsaturated monocarboxylic acid having 4 or more carbon atoms or a salt thereof, unsaturated Dicarboxylic acids or anhydrides or salts thereof and sulfonic acid group-containing vinyl compounds are preferred.
The proportion of acrylic acid contained in the monomer is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass.

Examples of the unsaturated monocarboxylic acid having 4 or more carbon atoms include methacrylic acid, crotonic acid, isocrotonic acid, α-hydroxyacrylic acid and the like.
Examples of the unsaturated dicarboxylic acid or its anhydride include maleic acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid, citraconic acid and the like.
Examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate.
Examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and the like.

  Examples of amino group-containing vinyl compounds include dimethylaminomethyl (meth) acrylate, diethylaminomethyl (meth) acrylate, 2-dimethylaminoethyl (meth) acrylate, 2-diethylaminoethyl (meth) acrylate, and (meth) acrylic. 2- (di-n-propylamino) ethyl acid, 2-dimethylaminopropyl (meth) acrylate, 2-diethylaminopropyl (meth) acrylate, 2- (di-n-propylamino) propyl (meth) acrylate , (Meth) acrylic acid 3-dimethylaminopropyl, (meth) acrylic acid 3-diethylaminopropyl, (meth) acrylic acid 3- (di-n-propylamino) propyl, and the like.

  Examples of the amide group-containing vinyl compound include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N-methylol (meth) acrylamide and the like.

  Examples of the sulfonic acid group-containing vinyl compound include methallylsulfonic acid, acrylamide-2-methyl-2-propanesulfonic acid, and the like.

  Examples of the polyoxyalkylene group-containing vinyl compound include (meth) acrylic acid esters of alcohols having a polyoxyethylene group and / or a polyoxypropylene group.

  Examples of the alkoxyl group-containing vinyl compound include 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2- (n-propoxy) ethyl (meth) acrylate, 2- (meth) acrylic acid 2- ( n-butoxy) ethyl, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate, 2- (n-propoxy) propyl (meth) acrylate, 2- (n)-(meth) acrylate Butoxy) propyl and the like.

  The chain transfer agent is at least one selected from hypophosphorous acid and salts thereof and phosphorous acid and salts thereof. As hypophosphites and phosphites, sodium salts (sodium hypophosphite, disodium hydrogen phosphite), potassium salts, lithium salts, calcium salts, magnesium salts, barium salts and the like can be used. . Among these, an acrylic acid polymer having an Mw of 1500 or less is efficiently generated, the action of the acrylic acid polymer on metals, alloys, and the like is suppressed, and turbidity does not occur under low temperature conditions. A sodium salt is preferable because an aqueous solution containing an acrylic acid polymer is obtained.

  In the present invention, the amount of the chain transfer agent used is an aqueous solution containing an acrylic acid polymer that efficiently produces an acrylic acid polymer having an Mw of 1500 or less and does not generate turbidity under low temperature conditions. Therefore, when the amount of the monomer is 100 parts by mass, the amount is preferably 12 parts by mass or more, more preferably 12 to 35 parts by mass, and still more preferably 15 to 30 parts by mass. In addition, when there is too little usage-amount of the said chain transfer agent, it may become easy to generate | occur | produce turbidity at low temperature.

  The polymerization initiator is at least one selected from an azo compound and a peroxide. These compounds may be used alone or in combination of two or more. The peroxide according to the present invention excludes sulfur-containing compounds such as persulfuric acid and salts thereof.

Examples of the azo compound include 2,2′-azobis (isobutyronitrile), 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile), dimethyl-2,2′-azobisisobutyrate, 4,4′-azobis (4-cyanovaleric acid), 1,1′-azobis (1- Acetoxy-1-phenylethane), 2,2′-azobis (2-methylbutyramide), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (2 -Methylpropionamidine) dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane], 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propion Mido], 2,2′-azobis (2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2′-azobis (N-butyl-2-methylpropionamide), 2, 2'-azobis (N-cyclohexyl-2-methylpropionamide) and the like.
The peroxide is preferably an organic peroxide, such as t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, or the like; Oxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, 2.5-dimethyl-2,5-di (t-butylperoxy) hexane, di (2-t -Butylperoxyisopropyl) benzene, dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexene-3; diisobutyryl peroxide, bis (3,5,5-trimethyl- 1-oxohexyl) peroxide, dilauroyl peroxy Diacyl peroxides such as dimethyl and dibenzoyl peroxides; Ketone peroxides such as methyl ethyl ketone peroxide, cyclohexanone peroxide and acetylacetone peroxide; Peroxydicarbonates such as diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, di (4-t-butylcyclohexyl) peroxydicarbonate T-hexyl peroxyneodecanoate, t-butylperoxyneodecanoate, t-butylperoxyneoheptanoate, t-hexy Peroxyesters such as peroxy-2-ethylhexanoate and t-butylperoxy-2-ethylhexanoate; 1,1-di (t-hexylperoxy) cyclohexane, 1,1-di (t-butyl) Peroxyketals such as peroxy) -2-methylcyclohexane and n-butyl 4,4-di- (t-butylperoxy) valerate; peracetic acid, persuccinic acid and the like.

  The amount of the polymerization initiator used is preferably 0.2 to 5.0 mass when the monomer is 100 mass parts because an acrylic polymer having an Mw of 1500 or less can be obtained efficiently. Part, more preferably 0.5 to 3.5 parts by weight, still more preferably 0.8 to 1.4 parts by weight.

In the polymerization step, the reaction system for polymerizing the monomer containing acrylic acid contains a chain transfer agent, a polymerization initiator, and water. When synthesizing an acrylic acid polymer, the whole amount of monomers, chain transfer agent, polymerization initiator and water is added to the reaction system separately or in a batch, or continuously or intermittently. Method of polymerizing a monomer; a monomer is polymerized by charging the remaining raw material components separately or collectively or continuously or intermittently into a reaction system containing specific raw material components in advance. It can be a method or the like.
In the present invention, water and a chain transfer agent are previously stored in a reactor and heated to the polymerization temperature, while continuously supplying the monomer and the polymerization initiator, Polymerization is preferably performed. When supplying a monomer and a polymer, a chain transfer agent can also be supplied simultaneously.

  The polymerization temperature of the monomer in the polymerization step is appropriately selected depending on the type of the polymerization initiator, but is usually 80 ° C. or higher, preferably 90 ° C. or higher, and more preferably 95 ° C. or higher. The upper limit of the polymerization temperature is the boiling point of the reaction solution, and is usually about 110 ° C.

  According to the polymerization step, a reaction solution in which an acrylic acid polymer having an Mw of 1500 or less is dissolved in water and the pH is usually in the range of 3.0 to 5.0 is obtained. The Mw of this acrylic acid polymer is preferably 700 to 1400, more preferably 900 to 1200.

  When the pH of the reaction solution obtained by the polymerization step is in the range of 3.0 to 5.0, this reaction solution can be used as it is as a water treatment agent or the like, but the pH is less than 3.0. In some cases, the production method of the present invention can further include a pH adjustment step for adjusting the pH of the reaction solution to 3.0 or more, preferably 3.5 to 5.0. In this pH adjustment step, hydroxides, chlorides or carbonates of alkali metals such as sodium and potassium; hydroxides, chlorides or carbonates of alkaline earth metals such as calcium and magnesium; ammonia; monoethanolamine, An aqueous solution in which an organic amine such as diethanolamine or triethanolamine is dissolved as it is or in water can be used. The said compound may be used independently and may be used in combination of 2 or more type.

  The concentration of the acrylic acid polymer having an Mw of 1500 or less in the aqueous acrylic acid polymer solution obtained by the production method of the present invention is not particularly limited, but is preferably 40 to 65% by mass, more preferably 50 to 60% by mass. %. This acrylic acid polymer aqueous solution does not act on metals, alloys, etc., and especially under low temperature conditions, the acrylic acid polymer is less likely to aggregate and the occurrence of turbidity is suppressed. Suitable for use in satisfying environment (cold region etc.).

  The aqueous acrylic acid polymer solution of the present invention is suitable as a water treatment agent, and the aqueous solution may be used as it is as a water treatment agent, and if necessary, polymaleic acid or a salt thereof, (meth) acrylic acid type Other components such as a copolymer, a styrene / maleic acid copolymer, and other scale inhibitors, bactericides, anticorrosives, slime inhibitors, antifoaming agents and the like may be blended to form a water treatment agent. By using such a water treatment agent, for example, problems such as a decrease in heat exchange efficiency and blockage of piping in a cooling water system, a boiler water system, a seawater desalination apparatus, and the like can be suppressed.

  Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to this embodiment. In the following, “part” and “%” are based on mass unless otherwise specified.

1. Example 1 Production of Acrylic Acid Copolymer
A flask equipped with a stirrer and a condenser was charged with 250 g of water and 20 g of sodium hypophosphite and heated to 95 ° C. Thereafter, while stirring the aqueous solution, a mixture of 1200 g of 80% acrylic acid aqueous solution (hereinafter also referred to as “80% AA”) and 140 g of sodium hypophosphite, and 50 g of 20% azobisisobutyric acid amidine hydrochloride aqueous solution (Hereinafter, also referred to as “20% V-50”) was fed into the flask for 4 hours to conduct polymerization. Thereafter, the mixture was further aged at 95 ° C. for 1 hour. Then, the reaction liquid is cooled, and water and a 48% sodium hydroxide aqueous solution (hereinafter also referred to as “48% NaOH”) are added thereto, so that the solid content concentration of the acrylic acid polymer is 60%, An acrylic acid polymer aqueous solution (E1) having a pH of 3.8 was obtained (see Table 1).

Subsequently, when the acrylic acid polymer was subjected to gel permeation chromatography (GPC) under the following conditions, Mw was 1200.
<GPC measurement conditions>
Apparatus: HLC8020 system manufactured by Tosoh Corporation Detection: RI
Column: Tosoh G4000PWxl, G3000PWxl and G2500PWxl are connected. Eluent: 0.1M NaCl + phosphate buffer (pH 7)
Standard: Sodium polyacrylate manufactured by Soka Science Co., Ltd.

Examples 2-5
Except that the amounts of water, sodium hypophosphite and 80% AA used were changed as shown in Table 1, the same operation as in Example 1 was performed, and the solid content concentration of the acrylic acid polymer was 60%. Acrylic acid polymer aqueous solutions (E2) to (E5) were obtained (see Table 1).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in each aqueous solution was performed, and Mw was also shown in Table 1.

Example 6
The same polymerization initiator as in Example 1 except that 40 g of 70% t-butyl hydroperoxide aqueous solution (hereinafter also referred to as “70% TBHP”) was used instead of 50 g of 20% V-50. Operation was performed to obtain an acrylic acid polymer aqueous solution (E6) having a solid content concentration of acrylic acid polymer of 60% and a pH of 3.8 (see Table 1).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the aqueous acrylic acid polymer solution (E6) was performed, and Mw was also shown in Table 1.

Example 7
Except that the amount of 70% TBHP used was changed to 20 g, the same operation as in Example 6 was performed, and an aqueous acrylic acid polymer solution (E7) having a solid content concentration of 60% and a pH of 3.8 was obtained. Obtained (see Table 1).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the acrylic acid polymer aqueous solution (E7) was performed, and Mw was also shown in Table 1.

Example 8
180 g of disodium hydrogen phosphite pentahydrate was used instead of 20 g of sodium hypophosphite, and 100 g of disodium hydrogen phosphite pentahydrate was used instead of 140 g of sodium hypophosphite. The acrylic acid polymer aqueous solution (E8) having a solid content concentration of 60% and a pH of 4.0 was obtained in the same manner as in Example 1 except for (Table 1). reference).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the acrylic acid polymer aqueous solution (E8) was performed, and Mw was also shown in Table 1.

Example 9
A flask equipped with a stirrer and condenser was charged with 250 g of water, 20 g of sodium hypophosphite, 160 g of maleic anhydride and 30 g of 48% NaOH and heated to 95 ° C. Thereafter, while stirring this aqueous solution, a mixture of 1000 g of 80% AA and 140 g of sodium hypophosphite and 50 g of 20% V-50 were each fed into the flask over 4 hours to polymerize. Went. Thereafter, the mixture was further aged at 95 ° C. for 1 hour. Then, the reaction liquid is cooled, water and 48% NaOH are added thereto, and the acrylic acid polymer aqueous solution (the solid content concentration of the acrylic acid polymer is 50% and the pH is 4.3) ( E9) was obtained (see Table 1).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the acrylic acid polymer aqueous solution (E9) was performed, and Mw was also shown in Table 1.

Comparative Example 1
The same operation as in Example 1 was performed except that 30 g of 30% aqueous sodium persulfate solution (hereinafter also referred to as “30% NPS”) was used in place of 50 g of 20% V-50 as a polymerization initiator. An acrylic acid polymer aqueous solution (C1) having a solid content concentration of acrylic acid polymer of 60% and a pH of 3.8 was obtained (see Table 2).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the aqueous acrylic acid polymer solution (C1) was performed, and Mw was also shown in Table 2.

Comparative Example 2
The procedure of Example 1 was repeated except that 100 g of sodium bisulfite was used instead of 20 g of sodium hypophosphite, and 180 g of sodium bisulfite was used instead of 140 g of sodium hypophosphite. An acrylic acid polymer aqueous solution (C2) having a solid content concentration of 50% and a pH of 3.8 was obtained (see Table 2).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the aqueous acrylic acid polymer solution (C2) was performed, and Mw was also shown in Table 2.

Comparative Example 3
Except for changing the amount of sodium hypophosphite used, the same operation as in Example 1 was performed, and an acrylic acid polymer aqueous solution (C3) having a solid content of 60% and a pH of 3.8 was obtained. Obtained (see Table 2).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the acrylic acid polymer aqueous solution (C3) was performed, and Mw was also shown in Table 2.

Comparative Example 4
A flask equipped with a stirrer and a condenser was charged with 250 g of water and heated to 95 ° C. Thereafter, while stirring the hot water, 1200 g of 80% AA and 200 g of 20% V-50 were respectively supplied into the flask over 10 hours to carry out polymerization. Thereafter, the mixture was further aged at 95 ° C. for 1 hour. Then, the reaction liquid is cooled, and water and a 48% sodium hydroxide aqueous solution (hereinafter also referred to as “48% NaOH”) are added thereto, so that the solid content concentration of the acrylic acid polymer is 45%. An aqueous acrylic acid polymer solution (C4) having a pH of 3.8 was obtained (see Table 2).
Thereafter, in the same manner as in Example 1, GPC measurement of the acrylic acid polymer contained in the aqueous acrylic acid polymer solution (C4) was performed, and Mw was also shown in Table 2.

2. Evaluation of Acrylic Acid Polymer Aqueous Solution The acrylic acid polymer aqueous solutions obtained in Examples 1 to 9 and Comparative Examples 1 to 4 were subjected to the following evaluations. The results are shown in Tables 1 and 2.
(1) Low-temperature stability test 500 g of an acrylic acid polymer aqueous solution was placed in a glass container and allowed to stand in a thermostatic bath at 0 ° C., and the number of days until the aqueous solution became cloudy was visually observed until 60 days passed. .
(2) Material test The surface of the test piece made of SUS304 (70 mm × 15 mm × 2 mm) was treated with acetone to remove oil, and the mass of the test piece was measured. Subsequently, this test piece and 25 mL of acrylic acid polymer aqueous solution whose acrylic acid polymer content is 10 g were put in a 50 mL test tube and sealed. This was left still for 30 days in a thermostat set to 60 ° C. Then, the test piece was taken out and washed with water, and the surface appearance was visually observed and the mass was measured.
(3) Polymer aggregation inhibition test Using an acrylic acid polymer aqueous solution and calcium chloride dihydrate, the concentration of acrylic acid polymer is 100 mg / L, and the concentration of calcium chloride dihydrate is 5000 mg / L. After obtaining an aqueous solution, the pH was adjusted to 8.5 using sodium hydroxide. This was left still for 3 days in a thermostat set to 60 ° C. Thereafter, the components precipitated in the aqueous solution were filtered off, and the carbon concentration in the filtrate was measured with a total organic carbon meter “TOC-5000” manufactured by Shimadzu Corporation. Thereby, the polymer aggregation suppression rate was calculated. The aggregation suppression rate of 100% is a state where the acrylic acid polymer is not aggregated and maintains a concentration of 100 mg / L. A high polymer agglomeration inhibition rate means that calcium is difficult to precipitate.

As is apparent from Table 2, Comparative Example 1 is an example in which sodium persulfate was used as the polymerization initiator instead of the azo compound or peroxide, and the results of the material test were not sufficient. Comparative Example 2 was an example in which sodium hydrogen sulfite was used as the chain transfer agent instead of a phosphorus compound such as hypophosphorous acid, and the results of the material test were not sufficient. Comparative Example 3 is an example in which the amount of chain transfer agent used was reduced, and Mw of the obtained acrylic acid polymer exceeded 1500, and the results of the low-temperature stability test and polymer aggregation suppression test were not sufficient. It was. Moreover, the comparative example 4 is the example which superposed | polymerized without using a chain transfer agent, and the result of the low-temperature stability test and the polymer aggregation suppression test was not enough.
On the other hand, as is apparent from Table 1, Examples 1 to 9 are examples of the acrylic acid polymer aqueous solution of the present invention, and excellent results were obtained in any of the low temperature stability test, material test and polymer aggregation inhibition test. was gotten.

  The acrylic acid polymer aqueous solution obtained by the present invention is used in an environment (such as a cold district) that satisfies the temperature condition because the acrylic acid polymer is less likely to aggregate under low temperature conditions and the occurrence of turbidity is suppressed. It is suitable as a water treatment agent.

Claims (4)

A method for producing an aqueous acrylic acid polymer solution having a weight average molecular weight of 1500 or less,
It contains at least one chain transfer agent selected from hypophosphorous acid and salts thereof and phosphorous acid and salts thereof, at least one polymerization initiator selected from azo compounds and peroxides, and water. The reaction system includes a polymerization step for polymerizing a monomer containing acrylic acid,
The method for producing an aqueous acrylic acid polymer solution, wherein the chain transfer agent is used in an amount of 12 to 35 parts by mass when the monomer is 100 parts by mass.   The acrylic acid polymer according to claim 1, wherein in the polymerization step, a raw material composition containing the monomer and the polymerization initiator is continuously supplied to a reaction system containing the water and the chain transfer agent. A method for producing an aqueous solution. The reaction system is preheated to the polymerization temperature,
The method for producing an aqueous acrylic acid polymer solution according to claim 2, wherein the raw material composition also includes the chain transfer agent.   The method for producing an aqueous acrylic acid polymer solution according to any one of claims 1 to 3, further comprising a pH adjusting step of adjusting the pH of the reaction solution to 3.0 or more after the polymerization step.