JP5076864B2 - Acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous solution of acrylic acid (salt)/maleic acid (salt) based copolymer with an excellent temporal stability and a method for producing the same. <P>SOLUTION: The aqueous solution of acrylic acid (salt)/maleic acid (salt) based copolymer including a copolymer obtained by polymerizing in an aqueous medium monomers in which a part or all of acrylic acid is neutralized and monomers in which a part or all of maleic acid is neutralized, and the aqueous medium includes 50 ppm or less of hydrogen peroxide. Since the hydrogen peroxide content is extremely low, the aqueous solution of the polymer shows less temporal coloring, can be stored for a long period of time and is useful as a dispersant, a detergent builder, a fiber treatment agent, a dyeing auxiliary, a scale controller and the like. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

The present invention provides an aqueous solution of an acrylic acid (salt) / maleic acid (salt) copolymer having excellent stability over time and a method for producing the same. The acrylic acid (salt) / maleic acid (salt) copolymer of the present invention is useful for dispersants, detergent builders, fiber treatment agents, dyeing assistants, scale control agents, and the like.
In the present invention, acrylic acid or a part or all of which is neutralized is referred to as acrylic acid (salt), and maleic acid or a part or all of which is neutralized is referred to as maleic acid (salt).

When a monomer mixture containing acrylic acid (salt) and maleic acid (salt) is polymerized in an aqueous solution, it is common to use hydrogen peroxide as a polymerization initiator. Furthermore, since hydrogen peroxide has a slow decomposition rate, it is known that a reducing agent is used in combination to accelerate polymerization, or metal ions are added to promote decomposition of hydrogen peroxide.
For example, according to Patent Document 1 (Japanese Patent Laid-Open No. Sho 62-218407), in the polymerization of unsaturated dicarboxylic acid, the pH is maintained at about 40 ° C. to 150 ° C. while maintaining the pH at 2 to 7 in the presence of metal ions. A method for reducing the residual monomer by reacting is described. However, this method has a problem that a large amount of undecomposed hydrogen peroxide is contained in the polymerization solution. In addition, when the reaction is carried out at a high temperature, hydrogen peroxide is reduced.

  In addition, according to Patent Document 2 (Japanese Patent Laid-Open No. 5-29503), in a method of polymerizing a monomer mixture containing maleic acid by adding iron, vanadium or copper ions, hydrogen peroxide and hypophosphorous acid Describes a method for improving the biodegradability and molecular weight distribution of a copolymer by polymerizing the polymer under a pH of 2 or less. However, when an aqueous polymer solution is produced by this method, there is a problem that a large amount of undecomposed hydrogen peroxide is contained in the aqueous solution.

  Patent Document 3 (International Application WO96 / 18714) describes a method in which a monomer mixture containing maleic acid is polymerized with hydrogen peroxide and persulfate, and the pH at the start of polymerization is 13 to 14, It is described that the polymerization in the presence of a valent metal ion improves the prevention of iron particle deposition and the stability of calcium ions. However, when an aqueous polymer solution is produced by this method, there is a problem that a large amount of undecomposed hydrogen peroxide is contained in the aqueous solution. If more persulfate is used and hydrogen peroxide is reduced, the amount of hydrogen peroxide contained in the product will be reduced, but conversely, since a large amount of persulfate is used, the decomposition product of persulfate contained in the product There is a problem that a large amount is included. Furthermore, although it is described that it is preferable to make the supply time of hydrogen peroxide shorter than the supply time of the monomer, in this method, the reaction of maleic acid (salt) supplied at the end stage is difficult to proceed, There is a problem that a large amount of unreacted maleic acid (salt) exists.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2000-53729) discloses a method for polymerizing a monomer mixture containing maleic acid, by using a combination of hydrogen peroxide and a metal ion to polymerize clay dispersibility. A method for improving calcium ion scavenging ability is described. However, the aqueous polymer solution produced by this method has a problem that a large amount of undecomposed hydrogen peroxide is contained. When polymerized at a high temperature, hydrogen peroxide is reduced, but coloring in the product becomes a problem because the coloring becomes remarkable.

As described above, in the production method in which a conventional monomer mixture containing acrylic acid (salt) and maleic acid (salt) is polymerized in an aqueous solution, the polymer aqueous solution contains a large amount of undecomposed hydrogen peroxide.
On the other hand, in order to deactivate hydrogen peroxide, a method of adding an equal amount or more of a reducing sulfur compound is known. Here, the reducing sulfur compound is a compound containing a sulfur atom having an oxidation number of 5 or less, and examples thereof include sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, and sodium hydrosulfite. If such a reducing sulfur compound is added in an amount equal to or greater than the amount of hydrogen peroxide present, the hydrogen peroxide can be deactivated, but the reducing sulfur compound remains. In addition, if the reducing sulfur compound remains, there is a problem of adverse effects when used as a dispersant, a detergent builder, a fiber treatment agent, a dyeing aid, or a scale control agent.
In addition, if a reductive sulfur compound equivalent to the equivalent amount of hydrogen peroxide contained in the aqueous polymer solution is added, theoretically, a reductive sulfur compound free from hydrogen peroxide should be obtained. However, a very strict addition amount is required, and such an adjustment method is extremely difficult in a manufacturing apparatus on an industrial production scale.
JP 62-218407 A JP-A-5-295033 International Application WO 96/18714 JP 2000-53729 A

  An object of the present invention is to provide an acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution obtained by polymerizing a monomer mixture containing acrylic acid (salt) and maleic acid (salt) in an aqueous medium. It is an object of the present invention to provide an aqueous solution with little coloration and viscosity increase over time even when the storage period is long.

In order to solve the above problems, the present inventor paid attention to the amount of hydrogen peroxide and reducing sulfur compound present in the aqueous solution after the completion of the polymerization reaction, and by making these present in a specific range or less, It has been found that an acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution with little coloration and viscosity increase over time can be obtained.
In addition, the present inventor is characterized by adding a compound containing iron ions after completion of the supply of hydrogen peroxide as a method of effectively reducing hydrogen peroxide present in the aqueous solution after the completion of the polymerization reaction, The present inventors have found a method for producing an acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution.

The invention for solving the above problems is described below.
The first invention is a monomer {acrylic acid (salt)} in which acrylic acid or a part or all thereof is neutralized and a monomer {maleic acid (salt) in which maleic acid or a part or all thereof is neutralized )} In an aqueous medium, comprising a copolymer obtained by polymerization using hydrogen peroxide as a polymerization initiator and an aqueous medium, and potassium alum is added after the addition of the hydrogen peroxide. The method for producing an aqueous solution of an acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution having a hydrogen peroxide content of 50 ppm or less.
According to a second aspect of the present invention, the amount of hydrogen peroxide used is 1 to 8 parts by mass with respect to 100 parts by mass of the total monomers. Acrylic acid (salt) / maleic acid according to the first aspect of the present invention This is a method for producing a (salt) copolymer aqueous solution .
According to a third aspect of the present invention, there is provided a process for producing an aqueous solution of an acrylic acid (salt) / maleic acid (salt) copolymer according to the first or second aspect of the invention, wherein potassium alum is added even before the start of polymerization. It is.
Furthermore, the fourth invention is the acrylic acid (2) according to the second invention, characterized in that the potassium alum added after the addition of hydrogen peroxide is 20 to 500% by mass of the potassium alum added before the start of polymerization. Salt) / maleic acid (salt) copolymer aqueous solution .

  The aqueous solution of acrylic acid (salt) / maleic acid (salt) copolymer of the present invention contains a small amount of hydrogen peroxide, so there is no coloration even when stored for a long time, and the viscosity increases with time. In addition, since a large amount of unreacted monomer does not exist, the metal container does not become pressurized even when stored in the metal container. Further, since the remaining reducing sulfur compound is extremely small, there is no deterioration over time such as dispersion performance. Therefore, the acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution of the present invention is excellent in long-term storage when used as a dispersant, detergent builder, fiber treatment agent, dyeing aid, scale control agent, etc. To express the effect.

Hereinafter, embodiments of the present invention will be described in detail.
Hydrogen peroxide contained in the acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution of the present invention is 50 ppm or less of the acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution.
If the hydrogen peroxide content exceeds 50 ppm, the viscosity of the aqueous copolymer solution tends to change with time and the liquid tends to be colored, and the stored container tends to be in a pressurized state, causing inconvenience for long-term storage.
The amount of hydrogen peroxide contained depends on the value measured by a color development method that measures absorbance as described later.

Furthermore, the amount of the reducing sulfur compound contained in the acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution is 1 ppm or less of the acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution. It is desirable to be. The reducing sulfur compound is a compound containing a sulfur atom having an oxidation number of 5 or less, and examples thereof include sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, and sodium hydrosulfite. If the content of the reducing sulfur compound exceeds 1 ppm, the viscosity of the aqueous copolymer solution tends to change with time.
The amount of the reducing sulfur compound contained is a value measured by ion chromatography as will be described later.

In the acrylic acid (salt) / maleic acid (salt) copolymer in the present invention, acrylic acid and maleic acid are essential components as monomers, and other monomers are copolymerized as necessary. Also good. Maleic acid and acrylic acid may be partially or wholly neutralized. Maleic anhydride may be used as maleic acid.
Examples of the acrylate include alkali metal acrylates such as sodium acrylate and potassium acrylate, ammonium acrylate, and salts of organic amines of acrylic acid.
Examples of maleates include alkali metal maleates such as sodium maleate and potassium maleate, and salts of ammonium maleate and organic amines of maleate.
The acrylate and maleate are prepared by reacting acrylic acid or maleic acid with an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an organic amine such as ammonia or monoethanolamine. Can be manufactured.

Acrylic acid or a part or all of which is neutralized (hereinafter referred to as acrylic acid (salt)) and maleic acid or a part or all of which is neutralized (hereinafter referred to as maleic acid (salt)) As a ratio, it is preferable that the usage-amount of maleic acid (salt) is 10-80 mass parts with respect to 100 mass parts of all monomers, 20-70 mass parts is still more preferable, It is 30-60 mass parts. Most preferred. When the ratio of maleic acid (salt) is less than 10 mass, there is a possibility that the performance of a dispersant or the like may not be exhibited, and when it exceeds 80 mass parts, the copolymerizability is deteriorated.
Moreover, it is preferable that it is 1-90 mass parts with respect to 100 mass parts of all monomers, and, as for the usage-amount of acrylic acid (salt), 10-80 mass parts is more preferable, and it is 20-70 mass parts. Is most preferred. When the ratio of acrylic acid (salt) is less than 1 part by mass, the copolymerizability may be deteriorated, and when it exceeds 90 parts by mass, the performance of a dispersant or the like may not be exhibited.

Further, monomers other than acrylic acid (salt) and maleic acid (salt) include unsaturated acids such as methacrylic acid and itaconic acid and salts thereof, unsaturated acid anhydrides such as itaconic anhydride, 2-acrylamide- Unsaturated sulfonic acids such as 2-methylpropane sulfonic acid, styrene sulfonic acid, sulfoethyl acrylate, and allyl sulfonic acid and salts thereof, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, etc. Examples include (meth) acrylic acid alkyl esters, (meth) acrylic acid hydroxyalkyl esters, acrylamides, and (meth) acrylic acid esters containing a polyalkylene oxide skeleton in the ester. Two or more of these can be used in combination.
These monomers are preferably 0 to 50 parts by mass, more preferably 0 to 40 parts by mass with respect to 100 parts by mass of all monomers. If it exceeds 50 parts by mass, the copolymerizability may be deteriorated.

  Regarding the supply of monomer to the reactor, maleic acid (salt) is poorly copolymerizable compared to other monomers, and therefore it is preferable to add the whole amount to the reactor in advance at the start of the reaction. Moreover, it is preferable that the maleic acid is partially neutralized in advance before the start of polymerization. The partially neutralized product of maleic acid can be prepared, for example, by adding maleic anhydride to a reactor containing water and adding alkali. The amount of alkali added is preferably 90 to 110% of maleic anhydride. As the alkali, sodium hydroxide is preferable because it is inexpensive and easy to handle.

Monomers other than maleic acid (salt) are preferably dripped continuously into the reactor from the viewpoint of safety and copolymerization with maleic acid (salt). A part of the monomer other than maleic acid (salt) may be added to the reactor in advance, and the reaction may be started while the remainder is continuously added. The time for continuous dropping is not particularly limited, but it is preferably 2 to 6 hours. If it is longer than 6 hours, the coloring will be remarkable due to the iron content in the reaction solution, which may affect the product.
On the other hand, if it is less than 2 hours, it is difficult to remove the polymerization heat, which may cause a problem in safety.

In the present invention, it is necessary to use hydrogen peroxide as an initiator for the polymerization reaction. The amount of hydrogen peroxide to be used is preferably 1 to 8 parts by mass, more preferably 2 to 6 parts by mass with respect to 100 parts by mass of all monomers. When hydrogen peroxide is used in excess of 8 parts by mass, an effect commensurate with the hydrogen peroxide used may not be exhibited, and the remaining amount of hydrogen peroxide in the final product may increase. If it is less than the part, a large amount of unreacted monomer may remain.
In the polymerization reaction, persulfate can be used in combination with hydrogen peroxide. When persulfate is used, it is preferably used in a range of 200% by mass or less of hydrogen peroxide. When the amount of persulfate exceeds 200% by mass of hydrogen peroxide, a large amount of persulfate decomposition products are contained in the polymer aqueous solution, which may cause deterioration in performance in various applications. Examples of the persulfate include sodium persulfate, potassium persulfate, and ammonium persulfate.

In the present invention, it is preferable to add iron ions before the start of the polymerization reaction in order to promote the decomposition of hydrogen peroxide. The amount of iron ions added is preferably 0.005 to 0.1% by mass of hydrogen peroxide, more preferably 0.01 to 0.05% by mass.
If the iron ion exceeds 0.1% by mass of the amount of hydrogen peroxide, the aqueous solution may become colored as the polymerization reaction proceeds. On the other hand, if it is less than 0.005% by mass, decomposition of hydrogen peroxide does not proceed. Therefore, the polymerization reaction may not proceed.
Examples of compounds containing iron ions include potassium alum, ammonium iron sulfate (II), ammonium iron sulfate (III), iron sulfate (II), iron sulfate (III), iron chloride (II), and iron chloride (III). . Among these, potassium alum and ammonium iron sulfate (III) are preferable, and potassium alum is more preferable.

  The polymerization temperature is not particularly limited and can be carried out in a wide range, but the polymerization temperature is preferably 80 to 100 ° C. (the boiling point of the polymerization reaction solution). When it is less than 80 ° C., the polymerization reaction is slow, which is not preferable in terms of productivity. The reaction can also be carried out under pressure or reduced pressure, but it is preferable to carry out the reaction at normal pressure because of the cost required to make equipment for pressure or reduced pressure reaction.

  It is preferable that the monomer and hydrogen peroxide which are continuously dropped are started to be dropped at the same time and dropped at the same time. When the dropping of hydrogen peroxide is terminated first, the polymerization reaction of the monomer supplied at the end of the reaction becomes difficult to proceed. Conversely, when the dropping of the monomer is terminated first, it tends to remain in the aqueous polymer solution of hydrogen peroxide supplied thereafter. It should be noted that there is no problem in tracking the persulfate after the dropping of the monomer and hydrogen peroxide is completed.

In the present invention, it is necessary to add potash after completion of the dropwise addition of hydrogen peroxide. By adding potassium alum after dropwise addition of hydrogen peroxide, it becomes possible to efficiently reduce hydrogen peroxide in the reaction solution. It is preferable that the potassium alum added after the dropwise addition of hydrogen peroxide is 20 to 500% by mass of the iron ions added before the start of the polymerization reaction.
If it is less than 20% by mass, the effect of addition is small, and hydrogen peroxide may not be efficiently reduced. On the other hand, if it exceeds 500 mass%, the aqueous solution may be colored due to the influence of iron.

After adding the potassium alum , the reaction solution is preferably held at a temperature of 80 to 100 ° C. (boiling point of the polymerization reaction solution) for 0.5 to 3 hours, more preferably at a temperature of 85 to 95 ° C. Hold for ~ 2 hours.
When the holding temperature is less than 80 ° C., decomposition of hydrogen peroxide is not promoted, and it becomes difficult to control the amount of hydrogen peroxide of the present invention to 0.1 to 50 ppm. On the other hand, if it is pressurized, it can be maintained at a temperature exceeding 100 ° C., but there is a risk that the cost of the equipment increases and the operation operation becomes complicated, and the aqueous solution is kept at a high temperature. There is a possibility that coloring may become remarkable under the influence of iron.
On the other hand, when the holding time is less than 0.5 hours, the decomposition of hydrogen peroxide is not accelerated, and it becomes difficult to control the amount of hydrogen peroxide of the present invention to 0.1 to 50 ppm. On the other hand, if the holding time exceeds 3 hours, the aqueous solution may be markedly colored due to the iron content in the aqueous solution.

  According to the production method of the present invention, the acrylic acid (salt) / maleic acid (salt) copolymer obtained usually has a weight average molecular weight of 1000 to 50000, and the dispersity (weight average molecular weight ÷ number average molecular weight) is usually 2.0 to 7.0. The weight average molecular weight is measured by GPC (gel permeation chromatography).

  The acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution obtained in the present invention can be used alone as a dispersant, detergent builder, fiber treatment agent, dyeing assistant, scale inhibitor, etc. Accordingly, various conventionally known additives can be blended.

Hereinafter, the present invention will be described in more detail by way of examples. Unless otherwise specified,% means mass%, and part means mass part.
<Example 1>
After 700 kg of deionized water, 0.2 kg of potassium alum, 500 kg of maleic anhydride and 450 kg of 48% sodium hydroxide solution were charged into a SUS tank reactor, the temperature was raised to 90 ° C. Next, 500 kg of acrylic acid, 200 kg of 35% hydrogen peroxide and 30%
80 kg of aqueous sodium persulfate solution was dropped into the reactor over 4 hours. After the addition, 0.2 kg of potassium alum was added, and the reaction solution was kept at 90 ° C. for 2 hours. Subsequently, 48% sodium hydroxide aqueous solution (850 kg) was added and neutralized. An acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution having a solid content concentration of 43 mass% and a pH of 7 was obtained.

About the aqueous solution obtained above, hydrogen peroxide content and APHA were measured by the following method. Furthermore, in order to evaluate the dispersion performance, the dispersion viscosity immediately after dispersion and after 7 days was measured.
(Measurement of hydrogen peroxide content)
Measurement was carried out by a color development method measuring absorbance at 407 nm using a sample obtained by diluting 2 g of a polymer aqueous solution and 10 g of a 30% titanium (IV) sulfate solution with distilled water to 100 mL. A blank was prepared by diluting 2 g of the aqueous solution and 10 g of 25% sulfuric acid to 100 mL with distilled water.
(Measurement of reducing sulfur compounds)
Sulfite ions were measured by ion chromatography (8000 series manufactured by Tosoh Corporation).
(Measurement of APHA)
The aqueous polymer solution was placed in a 50 mL colorimetric tube and visually compared with the colorimetric tube containing the APHA standard solution. The color number of the standard solution closest to the polymer aqueous solution was read.
In order to measure the color change over time, APHA was also measured for an aqueous polymer solution placed in a plastic container and left in a dryer at 50 ° C. for 1 month.

(Measurement of dispersion viscosity)
0.4 parts (solid content) of the obtained copolymer and 23 parts of distilled water were stirred and dissolved uniformly to prepare a dispersant aqueous solution. To this dispersant aqueous solution, 77 parts of light calcium carbonate powder was added, and the mixture was stirred and dispersed at 4000 rpm for 15 minutes using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). The viscosity was measured immediately after dispersion and after standing at 25 ° C. for 7 days. The viscosity was measured using a BL type viscometer at 25 ° C. and 60 rpm.
(Storage test in drums)
In order to examine whether the obtained polymer aqueous solution can be safely stored in a drum can, the polymer aqueous solution was filled in a drum can (made of steel and coated with epoxy resin on the inner surface) and stored outdoors for half a year. The appearance was observed.

<Example 2>
The polymerization reaction was carried out in the same manner as in Example 1 except that the potassium alum added after the completion of dropping of the monomer, hydrogen peroxide and sodium persulfate was changed to 0.1 kg, the solid content concentration was 43% by mass, and the pH was 7 acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution was obtained.

<Example 3>
A polymerization reaction was carried out in the same manner as in Example 1 except that the amount of 35% hydrogen peroxide was 250 kg and a 30% sodium persulfate aqueous solution was not used. Acrylic acid (salt) / solid content of 43% by mass and pH of 7 / A maleic acid (salt) copolymer aqueous solution was obtained.

<Example 4>
The polymerization reaction was conducted in the same manner as in Example 1 except that 250 kg of acrylic acid and 250 kg of 2-acrylamido-2-methylpropanesulfonic acid (ATBS) were used in place of 500 kg of acrylic acid as the monomer, and the solid concentration was An acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution having a mass of 43% by mass and a pH of 7 was obtained.

< Comparative Example 5 >
A polymerization reaction was carried out in the same manner as in Example 1 except that 0.1 kg of sodium sulfite was added instead of potassium alum which was added after the dropwise addition of the monomer, hydrogen peroxide and sodium persulfate, and the solid content concentration was 43 mass. % Aqueous solution of acrylic acid (salt) / maleic acid (salt) copolymer having a pH of 7.
The aqueous solution was less colored with time due to the effect of the remaining sodium sulfite, but on the contrary, the dispersion performance was inferior due to the effect of sodium sulfite.

< Comparative Example 6 >
A polymerization reaction was carried out in the same manner as in Example 1 except that 10 kg of sodium sulfite was added instead of potassium alum added after the dropwise addition of the monomer, hydrogen peroxide and sodium persulfate, and the solid content concentration was 43% by mass. An acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution having a pH of 7 was obtained.
The aqueous solution was less colored with time due to the effect of the remaining sodium sulfite, but on the contrary, the dispersion performance was inferior due to the effect of sodium sulfite.

<Comparative Example 1>
A polymerization reaction was performed in the same manner as in Example 1 except that potassium alum was not added at the end of the dropwise addition of the monomer and the aqueous hydrogen peroxide solution, and the acrylic acid (salt) / solid content concentration was 43% by mass and pH was 7. A maleic acid (salt) copolymer aqueous solution was obtained.
A phenomenon that the drum filled with the aqueous solution swells after 3 months was observed.

<Comparative example 2>
A polymerization reaction was carried out in the same manner as in Example 1 except that potassium alum was not added at the end of the dropwise addition of the monomer and aqueous hydrogen peroxide, and the mixture was held at 90 ° C. for 8 hours. 7 acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution was obtained. The aqueous solution was remarkably colored.
In addition, a phenomenon that the drum filled with the aqueous solution swells after 3 months was observed.

<Comparative Example 3>
The polymerization reaction was carried out in the same manner as in Example 1 except that the potassium alum added after completion of the dropwise addition of the monomer, hydrogen peroxide and sodium persulfate was changed to 0.05 kg, the solid content concentration was 43% by mass, and the pH was 7 acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution was obtained.
A phenomenon that the drum filled with the aqueous solution swells after 3 months was observed.

  Table 1 shows the polymerization conditions and measurement results of Examples 1 to 6 and Comparative Examples 1 to 3.

Since the acrylic acid (salt) / maleic acid (salt) copolymer aqueous solution of the present invention does not contain a reducing agent and the content of hydrogen peroxide is 50 ppm or less, there is little coloring over time, The viscosity increases little, and even when stored in a metal container such as a drum can, it is not in a pressurized state, and has the characteristics of not causing deterioration in dispersion performance due to the remaining reducing agent.
Therefore, the polymer aqueous solution is useful as a dispersant, a detergent builder, a fiber treatment agent, a dyeing aid, a scale control agent, and the like.

Claims (4)

Acrylic acid or monomer partially or completely neutralized and maleic acid or monomer partially or fully neutralized in aqueous medium using hydrogen peroxide as a polymerization initiator Acrylic acid (salt) / maleic acid having a hydrogen peroxide content of 50 ppm or less, comprising a copolymer obtained by polymerization and an aqueous medium, wherein potassium alum is added after the addition of hydrogen peroxide A method for producing an acid (salt) copolymer aqueous solution. 2. The acrylic acid (salt) / maleic acid (salt) system according to claim 1, wherein the amount of hydrogen peroxide used is 1 to 8 parts by mass with respect to 100 parts by mass of all monomers. A method for producing an aqueous polymer solution. 3. The method for producing an aqueous solution of acrylic acid (salt) / maleic acid (salt) copolymer according to claim 1 or 2, wherein potassium alum is added even before the start of polymerization. The acrylic acid (salt) / maleic acid (salt) according to claim 3, wherein the potassium alum added after the hydrogen peroxide addition is 20 to 500% by mass of the potassium alum added before the start of polymerization. A method for producing an aqueous copolymer solution.