(meth)acrylic acid copolymer and its manufacturing method, water treatment agent and scale inhibitor

Abstract

The present invention provides a water treatment agent that is less likely to generate foam when mixed with water to be treated, and that sufficiently suppresses the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate, as well as a (meth)acrylic acid copolymer suitable as the main component thereof and a method for producing the same. [Solution] The (meth)acrylic acid copolymer of the present invention contains a) monomer units derived from at least one selected from (meth)acrylic acid and its salts, b) monomer units derived from at least one selected from 2-acrylamido-2-methylpropanesulfonic acid and its salts, and c) monomer units derived from at least one selected from vinyl monomers and aromatic vinyl monomers having a solubility of 7 g or less in 100 mL of water at 20°C or 30°C, in proportions of 65.1 to 95.8% by mass, 4.1 to 34.8% by mass, and 0.1 to 4.9% by mass.

Description

Technical Field

[0001] The present invention relates to a water treatment agent or a scale adhesion preventive agent in which the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate is sufficiently suppressed, a (meth)acrylic acid-based copolymer suitable as a main component thereof, and a method for producing the same.

Background Art

[0002] Conventionally, water has been used in various industries, and the liquid feeding of water is usually performed through a pipe. However, since scale containing a silicon compound, a calcium compound, a magnesium compound, a zinc compound, etc. is formed on the inner surface of the pipe by repeating liquid feeding or retention, a treatment agent (water treatment agent) for suppressing such scale formation has been used.

[0003] For example, Patent Document 1 describes a method for preventing the proliferation of silica or silicate formation in an aqueous system, wherein the system comprises a) a water-soluble copolymer or terpolymer of (meth)acrylic acid or maleic acid or salts thereof having a weight-average molecular weight of about 1000 to about 25000, wherein the copolymer consists of 1) about 20 to about 85% by weight of (meth)acrylic acid or maleic acid, 2) more than 11 to about 80% by weight of (meth)acrylamide methylpropanesulfonic acid or styrenesulfonic acid, or 3) about 5 to about 30% by weight of (meth)acrylamide or substituted (meth)acrylamide, or 4) about 30 to about 60% by weight of isobutylene or diisobutylene, and the terpolymer consists of 1) about 30 to about 80% by weight of (meth)acrylic acid or maleic acid, and 2) more than 11 to about 65% by weight of (meth)acrylaminomethylpropanesulfonic acid or A method is disclosed characterized by adding an effective amount of a scale inhibitor selected from the group consisting of styrene sulfonic acid and 3) about 5 to about 30% by weight of (meth)acrylamide or substituted (meth)acrylamide, or 4) about 5 to about 30% by weight of vinyl alcohol, allyl alcohol, vinyl or allyl alcohol esters, vinyl esters, styrene, isobutylene or diisobutylene, or 5) about 3 to about 30% by weight of styrene sulfonic acid if (meth)acrylaminomethylpropanesulfonic acid is present, b) magnesium ions, c) a mixture of the copolymer or terpolymer and aluminum ions or magnesium ions, and d) a mixture of poly(meth)acrylic acid or polymaleic acid or salts thereof with a weight-average molecular weight of about 1000 to about 25000 and aluminum ions or magnesium ions.

[0004] Patent Document 2 describes a method for stabilizing an aqueous system by suppressing the precipitation of inorganic salts, wherein the aqueous system comprises: (a1) 40-60% by weight of an unsaturated sulfonic acid selected from one or more of 2-acrylamide-2-methyl-1-propanesulfonic acid, 2-methacrylamide-2-methyl-1-propanesulfonic acid, 3-methacrylamide-2-hydroxy-1-propanesulfonic acid or salts thereof; and (b1) 40-60% by weight of an unsaturated carboxyl monomer selected from acrylic acid or methacrylic acid or salts thereof, and a water-soluble polymer having a weight-average molecular weight of about 3,000 to about 10,000, or (a2) one of 2-acrylamide-2-methyl-1-propanesulfonic acid, 2-methacrylamide-2-methyl-1-propanesulfonic acid, 3-methacrylamide-2-hydroxy-1-propanesulfonic acid or salts thereof. The invention provides for adding a water-soluble polymer having a weight-average molecular weight of about 3,000 to about 12,000, comprising monomer units of 30-60% by weight of an unsaturated sulfonic acid selected from the above; (b2) 35-65% by weight of an unsaturated carboxyl monomer selected from acrylic acid or methacrylic acid or salts thereof; and (c2) 0.1-10% by weight of an unsaturated nonionizing monomer selected from one or more of tert-butylacrylamide, tert-octylacrylamide, dimethylacrylamide, acrylamide, acryloylmorpholine, styrene, ethyl acrylate, butyl acrylate, hydroxyethyl methacrylate, or hydroxypropyl acrylate; the aqueous system comprises an inorganic ion selected from one or more of iron, zinc, calcium, phosphate, or molybdate ions; and a method for maintaining the aqueous system at a temperature above about 80°C is disclosed.

[0005] Patent Document 3 discloses an acrylic acid copolymer comprising structural unit (x) derived from acrylic acid or its sodium salt and structural unit (y) derived from 2-acrylamido-2-methylpropanesulfonic acid or its sodium salt, wherein the content ratios of structural unit (x) and structural unit (y) are 35-90% by mass and 10-65% by mass, respectively, when the total of both is 100% by mass, and the content ratio of the acrylic acid copolymer having a weight-average molecular weight Mw of 2000-30000 and a molecular weight of 70000 or more is 0.30% by mass or less of the total amount of all polymers. It is also stated that this acrylic acid copolymer is suitable as a component of a water treatment agent that has an inhibitory effect on scale formation on calcium phosphate.

[0006] Furthermore, Patent Document 4 discloses a calcium phosphate and silica scale inhibitor as an active ingredient, which is a copolymer of (meth)acrylic acid, (meth)acrylamide methylpropanesulfonic acid, and a (meth)acrylamide derivative having an alkyl group having 1 to 8 carbon atoms, wherein, out of 100% by weight of total monomer-derived structural units, 40 to 70% by weight are structural units derived from (meth)acrylic acid, 15 to 40% by weight are structural units derived from (meth)acrylamide methylpropanesulfonic acid, and 5 to 25% by weight are structural units derived from the (meth)acrylamide derivative having an alkyl group having 1 to 8 carbon atoms, and the polymer chain contains a skeleton derived from a hypophosphorous compound. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 4-356580 [Patent Document 2] Japanese Patent Application Publication No. 8-224597 [Patent Document 3] International Publication No. 2016 / 047267 [Patent Document 4] Japanese Patent Publication No. 2018-130702 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Water treatment agents used to suppress scale formation are usually aqueous solutions. Such water treatment agents are preferably transparent so that it is easy to visually determine whether or not they have acted on the water being treated. Furthermore, it is preferable that they do not easily produce foam when mixed with water containing precursor components that form scale components, such as silica, calcium phosphate, calcium carbonate, or calcium sulfate, as this facilitates the expression of the scale formation suppression effect by active ingredients such as polymers. The object of the present invention is to provide a (meth)acrylic acid copolymer and a method for producing the same, which provides a water treatment agent and a scale adhesion inhibitor that exhibits excellent transparency when prepared as an aqueous solution, is less prone to foaming when mixed with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate, calcium sulfate, etc., and in the mixed solution, sufficiently suppresses the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate. [Means for solving the problem]

[0009] The inventors have found that when a (meth)acrylic acid copolymer containing these three monomer units in a specific ratio is dissolved in water, a transparent aqueous solution can be obtained. This aqueous solution is used as a water treatment agent and comes into contact with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate, or calcium sulfate. The copolymer consists of monomer units derived from at least one monomer selected from the group consisting of (meth)acrylic acid and its salts, which have a solubility of more than 7 g in 100 mL of water at 20°C or 30°C, and at least one monomer selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and its salts, respectively, and monomer units derived from at least one monomer selected from the group consisting of vinyl monomers and aromatic vinyl monomers, which have a solubility of 7 g or less in 100 mL of water at 20°C or 30°C.

[0010] The present invention is shown below. [1] A (meth)acrylic acid copolymer comprising the following monomer units (a), (b), and (c), (a) Monomer units derived from at least one monomer (ma) selected from the group consisting of (meth)acrylic acid and its salts. (b) Monomer units derived from at least one monomer (mb) selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and its salts (c) Monomer units derived from at least one monomer (mc) selected from the group consisting of vinyl monomers and aromatic vinyl monomers, which have a solubility of 7 g or less in 100 mL of water at 20°C or 30°C. A (meth)acrylic acid copolymer in which, when the sum of the above monomer units (a), (b), and (c) is taken as 100% by mass, the content ratios of the above monomer units (a), (b), and (c) are 65.1 to 95.8% by mass, 4.1 to 34.8% by mass, and 0.1 to 4.9% by mass, respectively. [2] The (meth)acrylic acid copolymer described in [1] above, having a weight-average molecular weight of 1,500 to 20,000. [3] The (meth)acrylic acid copolymer according to [2] above, wherein the content of (meth)acrylic acid copolymers having a molecular weight of 1,000 or less is 15.0% by mass or less, and the content of (meth)acrylic acid copolymers having a molecular weight of 200,000 or more is 0.10% by mass or less, based on the total amount of the (meth)acrylic acid copolymers. [4] A method for producing the (meth)acrylic acid copolymer described in [1] above, A preparation step for preparing a monomer mixture containing the above monomer (ma), the above monomer (mb), the above monomer (mc), and water, A polymerization step is performed in which the monomer mixture, polymerization initiator, and a chain transfer agent as an optional component are continuously supplied to a reactor to carry out polymerization of the monomers. A method for producing a (meth)acrylic acid copolymer comprising the following, in sequence. [5] A method for producing a (meth)acrylic acid-based copolymer according to [4], wherein the supply time of the monomer mixture to the reactor in the polymerization step is 2 to 12 hours. [6] A method for producing a (meth)acrylic acid copolymer according to [5], wherein the polymerization of the monomer is carried out in the polymerization step while maintaining the total residual concentration of the monomer (mc) in the reactor to 0.3 g / 100 mL or less. [7] A water treatment agent containing the (meth)acrylic acid copolymer described in [1] above. [8] An anti-adhesion agent for calcium phosphate scale, calcium carbonate scale, calcium sulfate and silica scale, comprising the (meth)acrylic acid copolymer described in [1] above.

[0011] In this specification, the weight-average molecular weight (hereinafter also referred to as "Mw") and number-average molecular weight (hereinafter also referred to as "Mn") of polymers are standard sodium polyacrylate equivalent values ​​measured by gel permeation chromatography (hereinafter also referred to as "GPC"). Furthermore, the term "(meth)acrylic" refers to acrylic and methacrylic. [Effects of the Invention]

[0012] When the (meth)acrylic acid copolymer of the present invention is dissolved in water, a transparent aqueous solution can be obtained. When this aqueous solution is used as a water treatment agent and brought into contact with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate, or calcium sulfate, foaming is less likely to occur, and the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate can be suitably suppressed in the mixture of the water treatment agent and each water to be treated. Therefore, the (meth)acrylic acid copolymer of the present invention can also be used as a chemical agent to prevent the adhesion of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate to the inner surface of pipes and the like that come into contact with water (water to be treated) containing precursor components that form scale. According to the method for producing (meth)acrylic acid copolymers of the present invention, (meth)acrylic acid copolymers having the above-mentioned effects can be produced efficiently. [Modes for carrying out the invention]

[0013] The (meth)acrylic acid copolymer of the present invention (hereinafter referred to as "(meth)acrylic acid copolymer (P)") consists of the following monomer units (a), (b), and (c), and is characterized in that when the total of these monomer units (a), (b), and (c) is taken as 100% by mass, the content ratios of monomer units (a), (b), and (c) are 65.1 to 95.8% by mass, 4.1 to 34.8% by mass, and 0.1 to 4.9% by mass, respectively. (a) Monomer units derived from at least one monomer (ma) selected from the group consisting of (meth)acrylic acid and its salts. (b) Monomer units derived from at least one monomer (mb) selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and its salts (c) Monomer units derived from at least one monomer (mc) selected from the group consisting of vinyl monomers and aromatic vinyl monomers, which have a solubility of 7 g or less in 100 mL of water at 20°C or 30°C.

[0014] The monomer unit (a) constituting the (meth)acrylic acid copolymer (P) of the present invention is derived from at least one of the monomers (ma), and is a monomer unit derived from at least one selected from acrylic acid, acrylate, methacrylic acid, and methacrylate.

[0015] Examples of the monomer (ma) include acrylic acid, sodium acrylate, potassium acrylate, magnesium acrylate, calcium acrylate, methacrylic acid, sodium methacrylate, potassium methacrylate, magnesium methacrylate, calcium methacrylate, and the like.

[0016] In the present invention, from the viewpoint of the transparency of the aqueous solution of the (meth)acrylic acid copolymer (P), it is preferable that the monomer unit (a) contains a monomer unit derived from an acrylate.

[0017] In the present invention, when the total of the monomer units (a), (b), and (c) is 100% by mass, the content ratio of the monomer unit (a) constituting the (meth)acrylic acid copolymer (P) is 65.1 to 95.8% by mass. The lower limit is preferably 66.0% by mass, more preferably 67.0% by mass. The upper limit is preferably 80% by mass, more preferably 70% by mass.

[0018] The monomer unit (b) constituting the (meth)acrylic acid copolymer (P) of the present invention is derived from at least one of the monomers (mb), and is a monomer unit derived from at least one selected from 2-acrylamido-2-methylpropane sulfonic acid and its salts.

[0019] Examples of the monomer (mb) include 2-acrylamido-2-methylpropane sulfonic acid, sodium 2-acrylamido-2-methylpropane sulfonate, and the like.

[0020] In the present invention, from the viewpoint of improving the solubility of the copolymer, it is preferable that the monomer unit (b) contains a monomer unit derived from a 2-acrylamido-2-methylpropane sulfonate.

[0021] In the present invention, the content of monomer unit (b) constituting the (meth)acrylic acid copolymer (P) is 4.1 to 34.8% by mass, where the total of monomer units (a), (b), and (c) is 100% by mass. The lower limit is preferably 10% by mass, more preferably 20% by mass. The upper limit is preferably 34.0% by mass, more preferably 33.0% by mass.

[0022] The monomer unit (c) constituting the (meth)acrylic acid copolymer (P) of the present invention is derived from at least one monomer (mc), and is at least one selected from the group consisting of vinyl monomers and aromatic vinyl monomers having a solubility of 7 g or less in 100 mL of water at 20°C or 30°C. Examples of vinyl monomers with a solubility of 7 g or less in 100 mL of water at 20°C or 30°C include ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, butylene, isobutylene, and N-tert-butylacrylamide (TBAM). In the present invention, vinyl monomers with a solubility of 0.1 g or less are preferred. Furthermore, examples of aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, β-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinyltoluene, vinylxylene, and vinylnaphthalene.

[0023] In the present invention, from the viewpoint of the water solubility of the (meth)acrylic acid copolymer (P), the transparency of the resulting aqueous solution, and the ability to suppress scale formation, which includes at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate, the monomer unit (c) preferably contains monomer units derived from ethyl acrylate, n-butyl acrylate, isobutyl acrylate, N-tert-butylacrylamide (TBAM), or styrene.

[0024] In the present invention, the content of monomer units (c) constituting the (meth)acrylic acid copolymer (P) is 0.1 to 4.9% by mass, where the total of monomer units (a), (b), and (c) is 100% by mass. The lower limit is preferably 0.2% by mass, more preferably 0.4% by mass. The upper limit is preferably 3.0% by mass, more preferably 2.0% by mass.

[0025] Specific examples of the (meth)acrylic acid copolymer (P) of the present invention are shown below. (1) Acrylate, 2-acrylamido-2-methylpropanesulfonate, and styrene copolymer (2) Acrylate, 2-acrylamido-2-methylpropanesulfonate, and ethyl acrylate copolymer (3) Acrylate, 2-acrylamido-2-methylpropanesulfonate, n-butyl acrylate copolymer (4) Acrylate, 2-acrylamido-2-methylpropanesulfonate, isobutyl acrylate copolymer (5) Acrylate, 2-acrylamido-2-methylpropanesulfonate, N-tert-butylacrylamide (TBAM) copolymer

[0026] The structure of the (meth)acrylic acid copolymer (P) of the present invention is not particularly limited, but is preferably a random copolymer.

[0027] The Mw of the (meth)acrylic acid copolymer (P) of the present invention is preferably 1,500 to 20,000, more preferably 2,000 to 15,000, and even more preferably 3,000 to 10,000, from the viewpoint of suppressing scale formation, which includes at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate. Furthermore, the polydispersity, which is the ratio of Mw to Mn (Mw / Mn), is preferably 1.2 to 2.5, and more preferably 1.2 to 2.0.

[0028] The (meth)acrylic acid copolymer (P) of the present invention can be formed by the aggregation of copolymers with different molecular weights to have the above-mentioned preferred Mw. In the present invention, a (meth)acrylic acid copolymer having a molecular weight of 1,000 or less (hereinafter referred to as "(meth)acrylic acid copolymer (P1)") or a (meth)acrylic acid copolymer having a molecular weight of 200,000 or more (hereinafter referred to as "(meth)acrylic acid copolymer (P2)") may be included. The content of (meth)acrylic acid copolymer (P1) is preferably 15.0% by mass or less, more preferably 10.0% by mass or less, and even more preferably 5.0% by mass or less, relative to the total amount of (meth)acrylic acid copolymer (P) of the present invention, and the content of (meth)acrylic acid copolymer (P2) is preferably 0.10% by mass or less, more preferably 0.05% by mass or less, relative to the total amount of (meth)acrylic acid copolymer (P) of the present invention.

[0029] The (meth)acrylic acid copolymer (P) of the present invention contains specific monomer units in specific proportions and has the above-mentioned preferred Mw, thereby enabling the production of highly transparent aqueous solutions. When this aqueous solution is used as a water treatment agent and brought into contact with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate, or calcium sulfate, foaming is less likely to occur, and the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate can be suppressed in the mixture of the water treatment agent and each water to be treated. The inventors estimate that the reason why foaming is less likely to occur when the water treatment agent is mixed with the water to be treated is that the monomer unit (c) has a hydrophobic group, and in the (meth)acrylic acid copolymer (P) containing 0.1 to 4.9% by mass of this monomer unit (c), the balance between hydrophobic and hydrophilic groups can be controlled within a range where it does not act as a surfactant.

[0030] The (meth)acrylic acid copolymer (P) of the present invention can be produced by conventionally known methods. In order to obtain a preferred composition of the (meth)acrylic acid copolymer (P), not only monomers may be polymerized, but the reaction product obtained by polymerization may also be purified.

[0031] The method for producing a (meth)acrylic acid copolymer (P) in the present invention (hereinafter referred to as "the production method of the present invention") comprises, in order, a preparation step of preparing a monomer mixture containing monomer (ma), monomer (mb), monomer (mc), and water, and a polymerization step of continuously supplying the obtained monomer mixture, a polymerization initiator, and an optional chain transfer agent to a reactor to perform polymerization of the monomers. When producing a (meth)acrylic acid copolymer (P) in which the monomers subjected to polymerization contain at least (meth)acrylic acid of (meth)acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, and monomer units derived from (meth)acrylate salts and / or monomer units derived from 2-acrylamido-2-methylpropanesulfonic acid salts, it is preferable to subject the copolymer obtained by the polymerization step to a neutralization reaction (neutralization step) after the polymerization step. Furthermore, a step to remove unreacted monomers may be included after either the polymerization step or the neutralization step.

[0032] The method for obtaining the monomer mixture in the above preparation step is not particularly limited. In the present invention, since a hydrophobic monomer (mc) is used, it is preferable to first dissolve monomer (mc) in monomer (ma), and then mix the resulting solution with monomer (mb) and water. The mixing method is not particularly limited.

[0033] The amounts of each monomer and water used in the above preparation process are as follows: The amount of monomer (ma) used is 65.1 to 95.8% by mass relative to the total amount of monomers (ma), (mb), and (mc). The lower limit is preferably 66.0% by mass, more preferably 67.0% by mass. The upper limit is preferably 80% by mass, more preferably 70% by mass. The amount of monomer (mb) used is 4.1 to 34.8% by mass relative to the total amount of monomers (ma), (mb), and (mc). The lower limit is preferably 10% by mass, more preferably 20% by mass. The upper limit is preferably 34.0% by mass, more preferably 33.0% by mass. The amount of monomer (mc) used is 0.1 to 4.9% by mass relative to the total amount of monomers (ma), (mb), and (mc). The lower limit is preferably 0.2% by mass, more preferably 0.4% by mass. The upper limit is preferably 3.0% by mass, more preferably 2.0% by mass. Furthermore, the amount of water used is preferably 5 to 80 parts by mass, more preferably 20 to 60 parts by mass, assuming the total amount of monomers (ma), (mb), and (mc) is 100 parts by mass.

[0034] Next, in the polymerization step, the monomer mixture obtained in the preparation step, a polymerization initiator, and a chain transfer agent as an optional component are continuously supplied to the reactor, and preferably, the monomers are polymerized under stirring of the reaction system. At this time, water may also be continuously supplied as needed. As the reactor, a conventionally known reactor (reaction apparatus) can be used, which is equipped with means for supplying the monomer mixture, means for supplying the chain transfer agent, means for supplying the polymerization initiator, stirring means, means for adjusting the temperature of the reaction system, reflux cooling means, means for supplying neutralizing agents, means for discharging the reaction solution, etc.

[0035] In the polymerization process according to the present invention, copolymers with desired physical properties can be efficiently produced by setting the supply time of the monomer mixture to the reactor within a specific range. The supply time of the monomer mixture is preferably 2 to 12 hours, more preferably 2 to 10 hours, and even more preferably 2 to 6 hours. Note that the end of the polymerization process is not usually simultaneous with the completion of the supply of the monomer mixture.

[0036] Furthermore, while it is preferable that the supply rate of the monomer mixture to the reactor be constant, the supply rate may be changed while monitoring the change in polymerization conversion rate over time.

[0037] Polymerization initiators include hydrogen peroxide; persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; dimethyl 2,2'-azobis(2-methylpropionate), 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyric acid)dimethyl, 4,4'-azobis(4-cyanovaleric acid), and 2,2'-azobis(2-methylpropionate). Examples include azo compounds such as ropionamidine dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]n-hydrate, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate, and 1,1'-azobis(cyclohexane-1-carbonitride); and organic peroxides such as benzoyl peroxide, lauroyl peroxide, peracetic acid, di-t-butyl peroxide, and cumenehydroperoxide. These may be used individually or in combination of two or more.

[0038] The amount of polymerization initiator used is preferably 0.1 to 10.0 parts by mass, more preferably 0.1 to 2.0 parts by mass, per 100 parts by mass of the total monomers (ma), (mb), and (mc).

[0039] The method of using the polymerization initiator is not particularly limited, but it is preferable to start supplying the polymerization initiator at the same time as the monomer mixture, or to start supplying the polymerization initiator after supplying the monomer mixture. Furthermore, the end time of supplying the polymerization initiator is preferably 5 minutes or more, and particularly preferably 10 minutes or more, later than the end time of supplying the monomer mixture.

[0040] Examples of chain transfer agents include phosphorous acid, hypophosphorous acid and their salts (sodium hypophosphorous acid, potassium hypophosphorous acid, etc.); sulfurous acid, bisulfite, dithionite, metabisulfite and their salts (sodium bisulfite, potassium bisulfite, sodium dithionite, potassium dithionite, sodium metabisulfite, potassium metabisulfite, etc.); mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionine, 3-mercaptopropionine, thiomalic acid, octyl thioglycolate, octyl 3-mercaptopropionate, 2-mercaptoethanesulfonic acid, n-dodecyl mercaptan, octyl mercaptan, butyl thioglycolate, and other thiols. These may be used individually or in combination of two or more.

[0041] The amount of chain transfer agent used is preferably 0.1 to 30 parts by mass, more preferably 1 to 15 parts by mass, per 100 parts by mass of the total monomers (ma), (mb), and (mc).

[0042] The method of using the chain transfer agent is not particularly limited, and the time when its supply is completed is preferably 10 minutes or more earlier, and particularly preferably 20 minutes or more earlier, than the time when the monomer mixture supply is completed.

[0043] In the polymerization process, the presence of polyvalent metal ions in the reaction system can promote the decomposition of polymerization initiators and chain transfer agents during the polymerization reaction. As materials that form such polyvalent metal ions, ammonium iron(III) sulfate or its hydrate, iron(III) sulfate or its hydrate, iron(II) sulfate or its hydrate, etc., can be used.

[0044] In the polymerization process, it is preferable to pre-fill the reactor with water before supplying each raw material. This ensures that the raw materials supplied to the reactor are efficiently mixed and that the polymerization reaction proceeds smoothly. The contents of the water can be water only, water containing a chain transfer agent, or water containing polyvalent metal ions, etc.

[0045] The polymerization temperature of the monomers in the polymerization process (temperature of the reaction system) is appropriately selected depending on the type of polymerization initiator, etc., and is not particularly limited. A preferred polymerization temperature is 70°C or higher. In a reaction system where no side reactions occur, it is preferably near the boiling point of the polymerization solvent (water), and particularly preferably at the boiling point of the polymerization solvent (water). If the polymerization initiator is supplied after the monomer mixture is supplied, the temperature of the reaction system at the start of the monomer mixture supply may be lower than the predetermined polymerization temperature. In this case, the temperature can be adjusted to the predetermined polymerization temperature after the start of the polymerization initiator supply.

[0046] In the polymerization process according to the present invention, the residual concentration (total concentration) of monomer (mc) per 100 mL of reaction solution in the reactor can be adjusted to preferably 0.3 g or less, more preferably 0.1 g or less, from the start of polymerization until the end of supplying the polymerization initiator, thereby enabling the efficient production of a (meth)acrylic acid copolymer (P) with desired physical properties. It is preferable to terminate the polymerization process a maximum of 13 hours after the completion of supplying the monomer mixture.

[0047] If the manufacturing method of the present invention includes a neutralization step after the polymerization step, an alkaline agent or aqueous solution thereof can be used, such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; ammonia; or organic amine salts such as monoethanolamine and triethanolamine. As the alkaline agent, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are preferred, and sodium hydroxide is particularly preferred.

[0048] When performing the neutralization step, the pH of the reaction solution is preferably adjusted to 7.0 or lower, more preferably in the range of 1.0 to 5.0.

[0049] According to the manufacturing method of the present invention, a (meth)acrylic acid copolymer (P) can be efficiently produced in which the content ratios of monomer units (a), (b), and (c) are within a predetermined range, and the content of unreacted monomers (ma), (mb), and (mc), as well as the content of the above-mentioned (meth)acrylic acid copolymers (P1) and (P2), are all kept to the minimum possible extent.

[0050] In the manufacturing method of the present invention, if water is not removed from the reaction solution after the polymerization and neutralization steps, the reaction solution usually consists of an aqueous solution of (meth)acrylic acid copolymer (P). Using this aqueous solution, a water treatment agent that suppresses scale formation in cooling water systems, boiler water systems, geothermal power generation water systems, seawater desalination plants, pulp dissolving kettles, black liquor concentration kettles, etc., and a scale-preventing agent that prevents scale adhesion to the inner surface of cooling water pipes, heat transfer surfaces of heat exchangers, etc., can be easily manufactured. Furthermore, since the aqueous solution of (meth)acrylic acid copolymer (P) can be made clear and transparent, the water treatment agent and scale-preventing agent obtained using this aqueous solution can also be transparent and easy to handle.

[0051] The water treatment agent of the present invention contains a (meth)acrylic acid copolymer (P), and its preferred state is liquid (aqueous solution). The content ratio of the (meth)acrylic acid copolymer (P) in this aqueous solution is preferably 1 to 1000 mg / L, more preferably 5 to 100 mg / L, in order to obtain sufficient effect as a water treatment agent, i.e., a scale formation suppression effect.

[0052] The water treatment agent of the present invention may optionally contain conventionally known scale formation inhibitors, disinfectants, corrosion inhibitors, slime inhibitors, defoaming agents, etc., such as polyacrylic acid or its salts, polymaleic acid or its salts, other (meth)acrylic acid copolymers, and styrene-maleic acid copolymers.

[0053] The water treatment agent of the present invention is suitable for application to water (water to be treated) containing at least one precursor component that forms silica scale, among silica scale, calcium phosphate scale, calcium carbonate scale, and calcium sulfate. For example, in open-circulation cooling water systems, in order to reduce the amount of cooling water discharged outside the system from the viewpoint of water conservation and resource conservation, the cooling water may be concentrated and sparingly soluble salts such as calcium phosphate and calcium carbonate may be formed. In such cases, using the water treatment agent of the present invention can suppress problems such as a decrease in heat exchange efficiency and blockage of pipes. Furthermore, in cooling water systems, boiler water systems, or geothermal power generation water systems equipped with heat exchangers, refrigerators, etc., and operating in a highly concentrated state, silica scale may form. Since silica scale is often difficult to remove once it adheres to the components of the equipment, the water treatment agent of the present invention can suitably suppress the formation of silica scale. The pH and temperature of the water (water to be treated) are not particularly limited.

[0054] When using the water treatment agent of the present invention, for example, it is added to water (water to be treated) containing the precursor component that forms the scale material described above, and stirred as necessary.

[0055] The scale inhibitor of the present invention contains a (meth)acrylic acid copolymer (P), and its preferred state is liquid (aqueous solution). The content ratio of the (meth)acrylic acid copolymer (P) in this aqueous solution is preferably 1 to 1000 mg / L, more preferably 5 to 100 mg / L, in order to obtain sufficient effectiveness as a scale inhibitor, for example, in preventing scale adhesion to structural members that come into contact with water such as industrial water, tap water, and groundwater, such as condensers, heat exchangers, and piping.

[0056] When using the scale inhibitor of the present invention, for example, it is added to water (water to be treated) containing the precursor components that form the scale material, and stirred as necessary. [Examples]

[0057] Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples in any way. In the following, % and ppm are based on mass unless otherwise specified.

[0058] 1. Raw materials for the production of (meth)acrylic acid copolymer Using the following raw materials, various polymers were produced.

[0059] 1-1. Monomers AA: Acrylic acid ATBS: Sodium 2-acrylamido-2-methylpropanesulfonate St: Styrene EA: Ethyl acrylate The solubility in 100 mL of water at 20 °C is 1.5 g. BA: n-Butyl acrylate The solubility in 100 mL of water at 20 °C is 0.14 g. IBA: Isobutyl acrylate The solubility in 100 mL of water at 20 °C is 0.79 g. TBAM: N-tert-Butylacrylamide The solubility in 100 mL of water at 30 °C is 0.1 g.

[0060] 1-2. Polymerization initiator Sodium persulfate

[0061] 1-3. Chain transfer agent Sodium metabisulfite

[0062] 1-4. Neutralizing agent 50% aqueous solution of sodium hydroxide

[0063] 2. Evaluation method for (meth)acrylic acid copolymer or its aqueous solution 2-1. Measurement of molecular weight distribution of (meth)acrylic acid copolymer The Mw and Mn of the (meth)acrylic acid copolymer were measured by GPC using "LC-20AD" (model name) manufactured by SHIMADZU Corporation. <GPC measurement conditions> Column: Connected Tosoh's G4000PWxl, G3000PWxl and G2500PWxl Eluent: 0.1M - NaCl + phosphate buffer (pH 7) Detector: RI Column temperature: 40 °C Standard substance: Sodium polyacrylate manufactured by Sowa Kagaku Co., Ltd.

[0064] [[ID=1​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ First, 1.4 g of styrene (St) was dissolved in 475 g of acrylic acid (AA). To this mixture, 496 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (ATBS) and 14 g of pure water were added and the mixture was thoroughly stirred to obtain a monomer mixture. Subsequently, 420g of pure water was charged into a reactor equipped with a reflux condenser, and after raising the temperature to 75°C, 9g of a 30% aqueous solution of sodium bisulfite was added while stirring the reactor. Then, the monomer mixture, a 5% aqueous solution of sodium persulfate, and a 30% aqueous solution of sodium bisulfite were continuously supplied to the reactor to carry out the polymerization reaction. The supply rate and supply time for the monomer mixture were 4.1g / min and 4 hours, respectively. The supply rate and supply time for the 5% aqueous solution of sodium persulfate were 0.3g / min and 4 hours 10 minutes, respectively. The supply rate and supply time for the 30% aqueous solution of sodium bisulfite were 0.7g / min and 3 hours 40 minutes, respectively. The temperature inside the reactor was maintained at 75°C during the polymerization reaction. In addition, the residual concentration of styrene (St), which is the monomer (mc), was maintained at less than 0.1g per 100mL of the reaction solution. After the supply of the 5% aqueous solution of sodium persulfate was exhausted, the reaction solution was heated to 85°C and held there for 1 hour. Next, the pH of the reaction solution was adjusted to 2.3 using a neutralizing agent to obtain an aqueous solution of a (meth)acrylic acid copolymer (hereinafter also referred to as "polymer (E1)") with a solid content of 42%. This aqueous solution was clear and transparent.

[0068] When samples taken one hour after the start of polymerization were subjected to gas chromatography (GC), the residual concentration of monomer (mc) was less than 0.1 g / 100 mL (see Table 1).

[0069] Subsequently, when copolymer (E1) was subjected to gel permeation chromatography (GPC), the Mw was 9570, Mn was 4830, and Mw / Mn was approximately 2.0. Furthermore, the content of (meth)acrylic acid copolymers with a molecular weight of 1000 or less in copolymer (E1) was 0.6%, and the content of (meth)acrylic acid copolymers with a molecular weight of 200,000 or more was 0.0% (see Table 1).

[0070] Furthermore, quantitative analysis of unreacted monomers contained in copolymer (E1) revealed that AA and its sodium salt were present at 55 ppm, ATBS at 125 ppm, and St was below the detection limit (1 ppm) (see Table 1).

[0071] Examples 1-2 to 1-9 (Meth)acrylic acid copolymers (E2) to (E9) were produced in the same manner as in Example 1-1 using monomers having the compositions listed in Table 1 (see Table 1).

[0072] Comparative Example 1-1 First, 473 g of acrylic acid (AA), 496 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (ATBS), and 14 g of pure water were thoroughly stirred to obtain a monomer mixture. Subsequently, 420g of pure water was charged into a reactor equipped with a reflux condenser, and after raising the temperature to 75°C, 9g of a 30% aqueous solution of sodium bisulfite was added while stirring the reactor. Then, the monomer mixture, a 5% aqueous solution of sodium persulfate, and a 30% aqueous solution of sodium bisulfite were continuously supplied to the reactor to carry out the polymerization reaction. The supply rate and supply time for the monomer mixture were 4.1g / min and 4 hours, respectively. The supply rate and supply time for the 5% aqueous solution of sodium persulfate were 0.3g / min and 4 hours 10 minutes, respectively. The supply rate and supply time for the 30% aqueous solution of sodium bisulfite were 0.7g / min and 3 hours 40 minutes, respectively. The temperature inside the reactor was maintained at 75°C during the polymerization reaction. After the supply of the 5% aqueous solution of sodium persulfate was completed, the reaction solution was heated to 85°C and maintained at that temperature for 1 hour. Next, the pH of the reaction solution was adjusted to 2.3 using a neutralizing agent to obtain an aqueous solution of a (meth)acrylic acid copolymer (hereinafter also referred to as "polymer (EE1)") with a solid content of 45%. This aqueous solution was clear and transparent.

[0073] Subsequently, when the copolymer (EE1) was subjected to gel permeation chromatography (GPC), the Mw was 6730, the Mn was 4130, and the Mw / Mn ratio was approximately 1.6. Furthermore, the content of (meth)acrylic acid copolymers with a molecular weight of 1000 or less in this copolymer (EE1) was 0.8%, and the content of (meth)acrylic acid copolymers with a molecular weight of 200,000 or more was 0.0% (see Table 1).

[0074] Furthermore, quantitative analysis of unreacted monomers contained in the copolymer (EE1) revealed that AA and its sodium salt were present at 66 ppm, and ATBS at 123 ppm (see Table 1).

[0075] Comparative Example 1-2 First, 35 g of styrene (St) was dissolved in 315 g of acrylic acid (AA). To this mixture, 774 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (ATBS) and 14 g of pure water were added and the mixture was thoroughly stirred to obtain a monomer mixture. Subsequently, 420g of pure water was charged into a reactor equipped with a reflux condenser, and after raising the temperature to 75°C, 9g of a 30% aqueous solution of sodium bisulfite was added while stirring the reactor. Then, the monomer mixture, a 5% aqueous solution of sodium persulfate, and a 30% aqueous solution of sodium bisulfite were continuously supplied to the reactor to carry out the polymerization reaction. The supply rate and supply time for the monomer mixture were 4.7g / min and 4 hours, respectively. The supply rate and supply time for the 5% aqueous solution of sodium persulfate were 0.3g / min and 4 hours 10 minutes, respectively. The supply rate and supply time for the 30% aqueous solution of sodium bisulfite were 0.7g / min and 3 hours 40 minutes, respectively. The temperature inside the reactor was maintained at 75°C during the polymerization reaction. After the supply of the 5% aqueous solution of sodium persulfate was completed, the reaction solution was heated to 85°C and maintained at that temperature for 1 hour. Next, the pH of the reaction solution was adjusted to 2.6 using a neutralizing agent to obtain an aqueous solution of a (meth)acrylic acid copolymer (hereinafter referred to as "polymer (EE2)") with a solid content of 42%. This aqueous solution was turbid and opaque.

[0076] When samples taken one hour after the start of polymerization were subjected to gas chromatography (GC), the residual concentration of monomer (mc) was less than 0.1 g / 100 mL (see Table 1).

[0077] Subsequently, when the copolymer (EE2) was subjected to gel permeation chromatography (GPC), the Mw was 7700, the Mn was 4640, and the Mw / Mn ratio was approximately 1.7. Furthermore, the content of (meth)acrylic acid copolymers with a molecular weight of 1000 or less in this copolymer (EE2) was 0.5%, and the content of (meth)acrylic acid copolymers with a molecular weight of 200000 or more was 0.0% (see Table 1).

[0078] Furthermore, quantitative analysis of unreacted monomers contained in the copolymer (EE2) revealed that AA and its sodium salt were present at 66 ppm, and ATBS at 628 ppm (see Table 1).

[0079] Comparative Examples 1-3 First, 70 g of styrene (St) was dissolved in 469 g of acrylic acid (AA). To this mixture, 357 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (ATBS) and 14 g of pure water were added and the mixture was thoroughly stirred to obtain a monomer mixture. Subsequently, 420g of pure water was charged into a reactor equipped with a reflux condenser, and after raising the temperature to 75°C, 9g of a 30% aqueous solution of sodium bisulfite was added while stirring the reactor. Then, while maintaining the temperature inside the reactor at 75°C, the polymerization reaction was started by supplying the monomer mixture at a rate and time of 3.8g / min and 4 hours, respectively, the 5% aqueous solution of sodium persulfate at a rate and time of 0.3g / min and 4 hours and 10 minutes, respectively, and the 30% aqueous solution of sodium bisulfite at a rate and time of 0.7g / min and 3 hours and 40 minutes, respectively. However, during the polymerization reaction, precipitates formed inside the reactor, and the production of the (meth)acrylic acid copolymer (hereinafter referred to as "polymer (EE3)") was stopped.

[0080] [Table 1]

[0081] 4. Evaluation of water treatment agents (1) Scale suppression tests for silica, calcium phosphate, calcium carbonate, and calcium sulfate The aqueous solutions of the (meth)acrylic acid copolymers obtained in Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-2 were adjusted to a concentration of 1000 ppm of (meth)acrylic acid copolymer to form water treatment agents (S), and their effect on inhibiting scale formation against silica, calcium phosphate, calcium carbonate, and calcium sulfate was confirmed by the following method. The results are shown in Table 2. In the following calcium phosphate scale inhibition tests, calcium carbonate scale inhibition tests, and calcium sulfate scale inhibition tests, "blank" refers to the test results of a solution containing an inorganic salt at a specified concentration without the addition of a water treatment agent (S).

[0082] <Silica scale suppression test> Using a water treatment agent (S) and sodium silicate, a 240 mL solution was prepared with a (meth)acrylic acid copolymer concentration of 150 mg / L and a sodium silicate concentration of 351 mg / L. This solution was left to stand at 70°C for 30 minutes. Then, while stirring, 44 mL of 0.5% magnesium chloride aqueous solution, 31.6 mL of 0.5% calcium chloride aqueous solution, and 36 mL of 0.5% sodium bicarbonate aqueous solution were added to this solution. Next, while stirring this mixture, 40 mL of 0.21% sodium bicarbonate aqueous solution was added, and the pH was adjusted to 8.0 with a 1 mol / L hydrochloric acid aqueous solution. After standing at 70°C for 3 hours, the turbidity and presence of precipitation due to silica were visually observed, and the scale suppression performance was evaluated according to the following criteria. ◎: No precipitate was observed, but the liquid was slightly cloudy. ○: No precipitate was observed, but the liquid was highly turbid. ×: Precipitation was observed.

[0083] <Calcium phosphate scale inhibition test> Using a water treatment agent (S), disodium hydrogen phosphate, and calcium chloride, 360 mL of a solution was prepared with a concentration of (meth)acrylic acid copolymer of 20 mg / L, a concentration of disodium hydrogen phosphate of 90 mg / L, and a concentration of calcium chloride of 375 mg / L. Next, while stirring this solution, 40 mL of 0.21% sodium bicarbonate aqueous solution was added, and the pH was adjusted to 8.5 with 0.1 mol / L sodium hydroxide aqueous solution. After standing at 60°C for 3 hours, the turbidity and presence of precipitate due to calcium phosphate were visually observed, and the scale suppression performance was evaluated according to the following criteria. ◎: No turbidity or sedimentation was observed. ○: Turbidity and sedimentation were observed, but the Ca concentration in the supernatant after filtration was higher compared to the blank. ×: Turbidity and sedimentation were observed, but there was no difference in Ca concentration in the supernatant after filtration compared to the blank.

[0084] <Calcium carbonate scale inhibition test> Using a water treatment agent (S), sodium bicarbonate, and calcium chloride, 400 mL of a solution was prepared with a concentration of (meth)acrylic acid copolymer of 10 mg / L, a concentration of sodium bicarbonate of 420 mg / L, and a concentration of calcium chloride of 375 mg / L. Next, the pH of this solution was adjusted to 8.5 with a 1 M sodium hydroxide aqueous solution. After standing at 60°C for 20 hours, the turbidity and presence of precipitate due to calcium carbonate were visually observed, and the scale suppression performance was evaluated according to the following criteria. ◎: No turbidity or sedimentation was observed. ○: Turbidity and sedimentation were observed, but the Ca concentration in the supernatant after filtration was higher compared to the blank. ×: Turbidity and sedimentation were observed, but there was no difference in Ca concentration in the supernatant after filtration compared to the blank.

[0085] <Calcium sulfate scale inhibition test> Using a water treatment agent (S), sodium sulfate, and calcium chloride, 400 mL of solution was prepared with a concentration of (meth)acrylic acid copolymer of 4 mg / L, a sodium sulfate concentration of 6000 mg / L, and a calcium chloride concentration of 6200 mg / L. After standing at 60°C for 3 hours, the turbidity and presence of precipitate due to calcium sulfate were visually observed, and the scale suppression performance was evaluated according to the following criteria. ◎: No turbidity or sedimentation was observed. ○: Turbidity and sedimentation were observed, but the Ca concentration in the supernatant after filtration was higher compared to the blank. ×: Turbidity and sedimentation were observed, but there was no difference in Ca concentration in the supernatant after filtration compared to the blank.

[0086] (2) Foaming evaluation test Each aqueous solution of the (meth)acrylic acid copolymer obtained in Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-2 was adjusted to a concentration of 1% of the (meth)acrylic acid copolymer to form a water treatment agent (T). 10 g of this agent was placed in an AS ONE disposable plastic cup (volume: 1 L, size: top diameter 122 mm, bottom diameter 102.5 mm, height 147 mm), and stirred at maximum speed for 30 seconds using a SCARLETT hand mixer "SUPER HAND MIXER MODEL HE-133" (with a beater attachment). The foaming height immediately after the start of stirring and the time until the generated foam disappeared were measured, and the foaming ability was evaluated according to the following criteria. The results are shown in Table 2. ◎: There was almost no foaming immediately after stirring (approximately less than 1 cm), and the foam disappeared immediately (within approximately 15 seconds). ○: The foam disappeared within approximately 1 minute of stirring. ×: The foam did not disappear within approximately 1 minute after stirring.

[0087] [Table 2] [Industrial applicability]

[0088] The (meth)acrylic acid copolymer of the present invention is suitable as a component of a water treatment agent that has an excellent effect in suppressing scale formation, containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate, or as a scale adhesion inhibitor that has an excellent effect in suppressing scale adhesion to equipment components in cooling water systems, boiler water systems, or geothermal power generation water systems.

Claims

1. A (meth)acrylic acid copolymer comprising the monomer units (a), (b), and (c) described below, (a) Monomer units derived from at least one monomer (ma) selected from the group consisting of (meth)acrylic acid and its salts (b) Monomer units derived from at least one monomer (mb) selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and its salts (c) Monomer units derived from at least one monomer (mc) selected from the group consisting of vinyl monomers and aromatic vinyl monomers, which have a solubility of 7 g or less in 100 mL of water at 20°C or 30°C. (meth)acrylic acid copolymer, wherein when the sum of monomer units (a), (b), and (c) is 100% by mass, the content ratios of monomer units (a), (b), and (c) are 65.1 to 95.8% by mass, 4.1 to 34.8% by mass, and 0.1 to 4.9% by mass, respectively.

2. The (meth)acrylic acid-based copolymer according to claim 1, wherein the weight-average molecular weight is 1,500 to 20,000.

3. With respect to the total amount of the (meth)acrylic acid copolymer, The content of (meth)acrylic acid copolymers with a molecular weight of 1,000 or less is 15.0% by mass or less. The (meth)acrylic acid copolymer according to claim 2, wherein the content of the (meth)acrylic acid copolymer having a molecular weight of 200,000 or more is 0.10% by mass or less.

4. A method for producing a (meth)acrylic acid copolymer according to claim 1, A preparation step of preparing a monomer mixture containing the monomer (ma), the monomer (mb), the monomer (mc), and water, A polymerization step is performed in which the monomer mixture, polymerization initiator, and a chain transfer agent as an optional component are continuously supplied to a reactor to perform polymerization of the monomers. A method for producing a (meth)acrylic acid copolymer comprising the following, in sequence.

5. The method for producing a (meth)acrylic acid-based copolymer according to claim 4, wherein the supply time of the monomer mixture to the reactor in the polymerization step is 2 to 12 hours.

6. The method for producing a (meth)acrylic acid copolymer according to claim 5, wherein the polymerization of the monomer is carried out in the polymerization step while maintaining the total residual concentration of the monomer (mc) in the reactor to 0.3 g / 100 mL or less.

7. A water treatment agent containing the (meth)acrylic acid copolymer described in claim 1.

8. An anti-adhesion agent for calcium phosphate scale, calcium carbonate scale, calcium sulfate, and silica scale, comprising the (meth)acrylic acid copolymer described in claim 1.

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