WO2024203343A1 - (meth)acrylic acid copolymer, method for producing same, water treatment agent and scale inhibitor - Google Patents

Abstract

A (meth)acrylic acid copolymer according to the present invention contains (a) a monomer unit derived from at least one substance selected from (meth)acrylic acid and salts thereof, (b) a monomer unit derived from at least one substance selected from 2-acrylamide-2-methylpropanesulfonic acid and salts thereof, and (c) a monomer unit derived from at least one monomer selected from aromatic vinyl monomers and vinyl monomers having a solubility of 7g or less in 100mL of water at 20°C or 30°C in the following proportions: 65.1-95.8 mass%, 4.1-34.8 mass%, and 0.1-4.9 mass%.

Description

(Meth)acrylic acid copolymer and method for producing the same, water treatment agent, and scale adhesion inhibitor

The present invention relates to a water treatment agent or anti-scaling agent that sufficiently inhibits the formation of scale containing at least silica out of the group consisting of silica, calcium phosphate, calcium carbonate, and calcium sulfate, as well as a (meth)acrylic acid-based copolymer suitable as the main component thereof, and a method for producing the same.

　Traditionally, water has been used in various industries, and water is usually transported through pipes. However, repeated transport or retention of water can cause scale to form on the inner surface of the pipes, including silicon compounds, calcium compounds, magnesium compounds, zinc compounds, etc., and treatment agents (water treatment agents) are used to suppress this scale formation.

For example, Patent Document 1 describes a method for preventing the prevalence of silica or silicate formation in an aqueous system, comprising: adding to the system a) a water-soluble copolymer or terpolymer of (meth)acrylic acid or maleic acid or a salt thereof having a weight average molecular weight of about 1,000 to about 25,000, wherein the copolymer is composed of 1) about 20 to about 85% by weight of (meth)acrylic acid or maleic acid, and 2) from about 11 to about 80% by weight of (meth)acrylamidomethylpropanesulfonic acid or styrenesulfonic acid, or 3) from about 5 to about 30% by weight of (meth)acrylamide or a substituted (meth)acrylamide, or 4) from about 30 to about 60% by weight of isobutylene or diisobutylene, and the terpolymer is composed of 1) about 30 to about 80% by weight of (meth)acrylic acid or maleic acid, and 2) from about 11 to about 65% by weight of (meth)acrylamidomethylpropanesulfonic acid or styrenesulfonic acid. A method is disclosed which comprises adding an effective amount of a scale inhibitor selected from the group consisting of styrene sulfonic acid, 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, esters of vinyl or allyl alcohol, vinyl esters, styrene, isobutylene or diisobutylene, or 5) about 3 to about 30% by weight of styrene sulfonic acid when (meth)acrylaminomethylpropane sulfonic acid is present, b) magnesium ions, c) a mixture of said copolymer or terpolymer with aluminum ions or magnesium ions, and d) a mixture of poly(meth)acrylic acid or polymaleic acid or a salt thereof having a weight average molecular weight of about 1000 to about 25000 with aluminum ions or magnesium ions.

Patent Document 2 describes a method for stabilizing an aqueous system by suppressing precipitation of inorganic salts, which comprises adding to the aqueous system: (a1) 40 to 60% by weight of an unsaturated sulfonic acid selected from one or more of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, 3-methacrylamido-2-hydroxy-1-propanesulfonic acid, or salts thereof; and (b1) a water-soluble polymer having a weight average molecular weight of about 3,000 to about 10,000 and having monomer units of 40 to 60% by weight of an unsaturated carboxyl monomer selected from acrylic acid or methacrylic acid, or a salt thereof; or (a2) 1 or more of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, 3-methacrylamido-2-hydroxy-1-propanesulfonic acid, or salts thereof. (b2) 30 to 60% by weight of an unsaturated sulfonic acid selected from the above; (b3) 35 to 65% by weight of an unsaturated carboxyl monomer selected from acrylic acid or methacrylic acid or a salt thereof; and (c2) a water-soluble polymer having a weight average molecular weight of about 3,000 to about 12,000 and having monomer units of 0.1 to 10% by weight of an unsaturated non-ionizable 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 includes inorganic ions selected from one or more of iron, zinc, calcium, phosphate, or molybdate ions; and the aqueous system is maintained at a temperature of greater than about 80°C.

Patent Document 3 discloses an acrylic acid-based copolymer that contains a structural unit (x) derived from acrylic acid or a sodium salt thereof and a structural unit (y) derived from 2-acrylamido-2-methylpropanesulfonic acid or a sodium salt thereof, and the contents of the structural unit (x) and the structural unit (y) are 35 to 90% by mass and 10 to 65% by mass, respectively, when the total of the two is taken as 100% by mass, and the content of the acrylic acid-based copolymer having a weight average molecular weight Mw of 2,000 to 30,000 and a molecular weight of 70,000 or more is 0.30% by mass or less relative to the total amount of all polymers. It also discloses that this acrylic acid-based copolymer is suitable as a component of a water treatment agent that has an effect of suppressing scale formation on calcium phosphate.

Patent Document 4 also discloses a calcium phosphate and silica scale inhibitor that is a copolymer of (meth)acrylic acid, (meth)acrylamidomethylpropanesulfonic acid, and a (meth)acrylamide derivative having an alkyl group with 1 to 8 carbon atoms, in which, out of 100% by weight of structural units derived from all monomers, the copolymer contains 40 to 70% by weight of structural units derived from (meth)acrylic acid, 15 to 40% by weight of structural units derived from (meth)acrylamidomethylpropanesulfonic acid, and 5 to 25% by weight of structural units derived from a (meth)acrylamide derivative having an alkyl group with 1 to 8 carbon atoms, and the polymer chain contains a skeleton derived from a hypophosphorous compound.

Japanese Patent Application Publication No. 4-356580 Japanese Patent Application Publication No. 8-224597 International Publication No. 2016/047267 JP 2018-130702 A

Water treatment agents used to inhibit scale formation are usually aqueous solutions, and it is preferable for such water treatment agents to be transparent, since it is easy to visually determine whether or not they have acted on the water to be treated.Furthermore, since the scale formation inhibiting effect of active ingredients such as polymers is easily exerted, it is preferable for the water treatment agent to be less likely to generate foaming when mixed with water containing precursor components that form scale components, such as silica, calcium phosphate, calcium carbonate, or calcium sulfate.
An object of the present invention is to provide a (meth)acrylic acid-based copolymer which, when made into an aqueous solution, provides a water treatment agent and a scale adhesion inhibitor which have excellent transparency, are less likely to generate foam when mixed with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate, calcium sulfate, etc., and which satisfactorily suppresses the formation of scale containing at least silica out of the silica, calcium phosphate, calcium carbonate, and calcium sulfate scales in the mixed liquid, and a method for producing the same.

The inventors have found that when a (meth)acrylic acid-based copolymer containing a specific ratio of monomer units derived from at least one monomer selected from the group consisting of (meth)acrylic acid and its salts, and at least one monomer selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and its salts, each of which has a solubility of more than 7 g in 100 mL of water at 20°C or 30°C, is dissolved in water, a transparent aqueous solution can be obtained, and when this aqueous solution is used as a water treatment agent and contacted with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate, or calcium sulfate, foaming is unlikely to occur, and the formation of scale containing these compounds is suppressed in each mixture of the water treatment agent and each water to be treated.

The present invention is illustrated below.
[1] A (meth)acrylic acid-based copolymer comprising the following monomer units (a), (b) and (c):
(a) a monomer unit derived from at least one monomer (ma) selected from the group consisting of (meth)acrylic acid and salts thereof; (b) a monomer unit derived from at least one monomer (mb) selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and salts thereof; and (c) a monomer unit derived from at least one monomer (mc) 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. The (meth)acrylic acid-based copolymer has the following contents, when the total of the monomer units (a), (b) and (c) is taken as 100 mass%, the contents of the monomer units (a), (b) and (c) are 65.1 to 95.8 mass%, 4.1 to 34.8 mass% and 0.1 to 4.9 mass%, respectively.
[2] The (meth)acrylic acid-based copolymer according to the above [1], wherein the monomer (mc) is at least one selected from the group consisting of styrene, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and N-tert-butylacrylamide.
[3] The (meth)acrylic acid-based copolymer according to the above [1] or [2], having a weight average molecular weight of 1,500 to 20,000.
[4] The (meth)acrylic acid-based copolymer according to any one of [1] to [3] above, wherein the content of the (meth)acrylic acid-based copolymer having a molecular weight of 1,000 or less is 15.0 mass% or less, and the content of the (meth)acrylic acid-based copolymer having a molecular weight of 200,000 or more is 0.10 mass% or less, based on the total amount of the (meth)acrylic acid-based copolymer.
[5] A method for producing the (meth)acrylic acid-based copolymer according to any one of [1] to [4] above,
a preparation step of preparing a monomer mixture containing the monomer (ma), the monomer (mb), the monomer (mc) and water;
a polymerization step of continuously supplying the monomer mixture, a polymerization initiator, and an optional chain transfer agent to a reactor to polymerize the monomers;
The method for producing a (meth)acrylic acid-based copolymer includes the steps of:
[6] The method for producing a (meth)acrylic acid-based copolymer according to the above [5], wherein in the polymerization step, the supply time of the monomer mixture to the reactor is 2 to 12 hours.
[7] The method for producing a (meth)acrylic acid-based copolymer according to [5] or [6] above, wherein in the polymerization step, polymerization of the monomer is carried out while maintaining a residual concentration of the monomer (mc) in the reactor of 0.3 g/100 mL or less in total.
[8] A water treatment agent containing the (meth)acrylic acid-based copolymer according to any one of [1] to [4] above.
[9] An agent for preventing adhesion of calcium phosphate scale, calcium carbonate scale, calcium sulfate scale, and silica scale, comprising the (meth)acrylic acid-based copolymer according to any one of [1] to [4] above.

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 the polymer are values calculated as standard sodium polyacrylate measured by gel permeation chromatography (hereinafter also referred to as "GPC"). In addition, the term "(meth)acrylic" refers to acrylic and methacrylic.

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 contacted with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate or calcium sulfate, foaming is unlikely to occur, and in the mixed liquid of the water treatment agent and each water to be treated, the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate and calcium sulfate can be suitably suppressed. Therefore, the (meth)acrylic acid copolymer of the present invention can also be used as a drug component that prevents the adhesion of scale containing at least silica among silica, calcium phosphate, calcium carbonate and calcium sulfate to the inner surface of a pipe or the like that comes into contact with water (water to be treated) containing precursor components that form scale.
According to the method for producing a (meth)acrylic acid-based copolymer of the present invention, a (meth)acrylic acid-based copolymer having the above-mentioned effects can be efficiently produced.

The (meth)acrylic acid-based copolymer of the present invention (hereinafter referred to as "(meth)acrylic acid-based copolymer (P)") is characterized in that it comprises the following monomer units (a), (b) and (c), and the contents of the 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, when the total of the monomer units (a), (b) and (c) is taken as 100% by mass.
(a) a monomer unit derived from at least one monomer (ma) selected from the group consisting of (meth)acrylic acid and salts thereof; (b) a monomer unit derived from at least one monomer (mb) selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and salts thereof; and (c) a monomer unit derived from at least one monomer (mc) 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.

The monomer unit (a) constituting the (meth)acrylic acid-based copolymer (P) of the present invention is derived from at least one type of monomer (ma), and is a monomer unit derived from at least one selected from acrylic acid, acrylic acid salts, methacrylic acid, and methacrylic acid salts.

Examples of the above monomer (ma) include acrylic acid, sodium acrylate, potassium acrylate, magnesium acrylate, calcium acrylate, methacrylic acid, sodium methacrylate, potassium methacrylate, magnesium methacrylate, calcium methacrylate, etc.

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

In the present invention, the content of the monomer unit (a) constituting the (meth)acrylic acid-based copolymer (P) is 65.1 to 95.8% by mass, assuming that the total of the monomer units (a), (b) and (c) is 100% 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.

The monomer unit (b) constituting the (meth)acrylic acid-based copolymer (P) of the present invention is derived from at least one type of monomer (mb), and is a monomer unit derived from at least one selected from 2-acrylamido-2-methylpropanesulfonic acid and its salts.

Examples of the above monomer (mb) include 2-acrylamido-2-methylpropanesulfonic acid, sodium 2-acrylamido-2-methylpropanesulfonate, etc.

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 2-acrylamido-2-methylpropanesulfonate.

In the present invention, the content of the monomer unit (b) constituting the (meth)acrylic acid-based copolymer (P) is 4.1 to 34.8% by mass, assuming that the total of the 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.

The monomer unit (c) constituting the (meth)acrylic acid-based copolymer (P) of the present invention is derived from at least one type of monomer (mc), and is at least one type selected from the group consisting of vinyl monomers having a solubility of 7 g or less in 100 mL of water at 20° C. or 30° C., and aromatic vinyl monomers.
Examples of vinyl monomers having 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, N-tert-butylacrylamide (TBAM), etc. In the present invention, vinyl monomers having a solubility of 3 g or less are preferred, vinyl monomers having a solubility of 2 g or less are more preferred, vinyl monomers having a solubility of 1 g or less are even more preferred, and vinyl monomers having a solubility of 0.1 g or less are particularly preferred.
Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, β-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinyltoluene, vinylxylene, and vinylnaphthalene.

In the present invention, from the viewpoints of the water solubility of the (meth)acrylic acid-based copolymer (P), the transparency of the resulting aqueous solution, and the inhibition of the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate, it is preferable that the monomer unit (c) contains a monomer unit derived from ethyl acrylate, n-butyl acrylate, isobutyl acrylate, N-tert-butylacrylamide (TBAM), or styrene.

In the present invention, the content of the monomer unit (c) constituting the (meth)acrylic acid-based copolymer (P) is 0.1 to 4.9% by mass, assuming that the total of the 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.

Specific examples of the (meth)acrylic acid-based copolymer (P) of the present invention are shown below.
(1) Acrylates/2-acrylamido-2-methylpropanesulfonate/styrene copolymer (2) Acrylates/2-acrylamido-2-methylpropanesulfonate/ethyl acrylate copolymer (3) Acrylates/2-acrylamido-2-methylpropanesulfonate/n-butyl acrylate copolymer (4) Acrylates/2-acrylamido-2-methylpropanesulfonate/isobutyl acrylate copolymer (5) Acrylates/2-acrylamido-2-methylpropanesulfonate/N-tert-butylacrylamide (TBAM) copolymer

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

The Mw of the (meth)acrylic acid-based 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 inhibiting the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate. In addition, 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.

The (meth)acrylic acid copolymer (P) of the present invention can have the above-mentioned preferred Mw by assembling copolymers having different molecular weights. 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)") and 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, but the content of the (meth)acrylic acid copolymer (P1) is preferably 15.0 mass% or less, more preferably 10.0 mass% or less, and even more preferably 5.0 mass% or less, based on the total amount of the (meth)acrylic acid copolymer (P) of the present invention, and the content of the (meth)acrylic acid copolymer (P2) is preferably 0.10 mass% or less, more preferably 0.05 mass% or less, based on the total amount of the (meth)acrylic acid copolymer (P) of the present invention.

The (meth)acrylic acid copolymer (P) of the present invention contains a specific monomer unit at a specific content ratio and has the above-mentioned preferred Mw, so that an aqueous solution with excellent transparency can be obtained. When this aqueous solution is used as a water treatment agent and contacted with water (water to be treated) containing precursor components that form silica, calcium phosphate, calcium carbonate, or calcium sulfate, foaming is unlikely to occur, and the formation of scale containing at least silica among silica, calcium phosphate, calcium carbonate, and calcium sulfate can be suppressed in a mixture of the water treatment agent and each water to be treated. The inventors presume that the reason why foaming is unlikely to occur when the water treatment agent is mixed with the water to be treated is because the monomer unit (c) has a hydrophobic group, and therefore in the (meth)acrylic acid copolymer (P) containing 0.1 to 4.9 mass% of this monomer unit (c), the balance between the hydrophobic group and the hydrophilic group can be controlled within a range that does not act as a surfactant.

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

The method for producing the (meth)acrylic acid-based copolymer (P) of the present invention (hereinafter referred to as the "production method of the present invention") sequentially comprises 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, respectively, and polymerizing the monomers. Note that when the monomers to be polymerized contain at least (meth)acrylic acid, i.e., (meth)acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, and a (meth)acrylic acid-based copolymer (P) containing monomer units derived from (meth)acrylic acid salts and/or monomer units derived from 2-acrylamido-2-methylpropanesulfonic acid salts is produced, it is preferable to subject the copolymer obtained by the polymerization step to a neutralization reaction (neutralization step) after the polymerization step. In addition, a step of removing unreacted monomers can be provided after either the polymerization step or the neutralization step.

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

The amounts of each monomer and water used in the above preparation steps are as follows.
The amount of the monomer (ma) used is 65.1 to 95.8% by mass based on the total amount of the 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 the monomer (mb) used is 4.1 to 34.8% by mass based on the total amount of the 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 the monomer (mc) used is 0.1 to 4.9% by mass based on the total amount of the 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.
The amount of water used is preferably 5 to 80 parts by mass, and more preferably 20 to 60 parts by mass, relative to 100 parts by mass of the total of the monomers (ma), (mb) and (mc).

Next, in the polymerization step, the monomer mixture obtained in the preparation step, the polymerization initiator, and an optional chain transfer agent are each continuously supplied to a reactor, and the monomers are polymerized, preferably while stirring the reaction system. At this time, water may also be continuously supplied, if necessary. As the reactor, a reactor (reaction device) of a conventional, publicly known configuration, equipped with a means for supplying a monomer mixture, a means for supplying a chain transfer agent, a means for supplying a polymerization initiator, a stirring means, a means for adjusting the temperature of the reaction system, a reflux cooling means, a means for supplying a neutralizing agent, a means for discharging the reaction liquid, etc., can be used.

In the polymerization process of the present invention, a copolymer with the 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 polymerization process is usually not completed at the same time as the completion of the supply of the monomer mixture.

It is also preferable that the feed rate of the monomer mixture to the reactor is constant, but the feed rate may be changed while checking the change in the polymerization conversion rate over time.

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), 2,2'-azobis(2-methyl Examples of the azo compounds include 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] dihydrochloride, 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-carbonitrile); and organic peroxides such as benzoyl peroxide, lauroyl peroxide, peracetic acid, di-t-butyl peroxide, and cumene hydroperoxide. These may be used alone or in combination of two or more.

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

The method of using the polymerization initiator is not particularly limited, but it is preferable to start the supply of the polymerization initiator at the same time as the monomer mixture, or to start the supply of the polymerization initiator after the supply of the monomer mixture. In addition, the supply of the polymerization initiator is terminated preferably 5 minutes or more, and particularly preferably 10 minutes or more later than the completion of the supply of the monomer mixture.

Chain transfer agents include phosphorous acid, hypophosphorous acid, and salts thereof (sodium hypophosphite, potassium hypophosphite, etc.); sulfurous acid, hydrogen sulfite, dithionite, metabisulfite, and salts thereof (sodium hydrogen sulfite, potassium hydrogen sulfite, sodium dithionite, potassium dithionite, sodium metabisulfite, potassium metabisulfite, etc.); mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, thiomalic acid, octyl thioglycolate, octyl 3-mercaptopropionate, 2-mercaptoethanesulfonic acid, n-dodecyl mercaptan, octyl mercaptan, butyl thioglycolate, and other thiols. These may be used alone or in combination of two or more.

The amount of the 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 of the monomers (ma), (mb) and (mc).

The method of using the chain transfer agent is not particularly limited, but the supply of the chain transfer agent should be terminated preferably at least 10 minutes, and more preferably at least 20 minutes, earlier than the completion time of the supply of the monomer mixture.

In the polymerization process, the presence of polyvalent metal ions in the reaction system can promote the decomposition of the polymerization initiator and the chain transfer agent during the polymerization reaction. Materials that form such polyvalent metal ions include ammonium iron (III) sulfate or its hydrate, iron (III) sulfate or its hydrate, iron (II) sulfate or its hydrate, etc.

In the polymerization process, it is preferable to store water in the reactor before supplying each raw material to the reactor. This allows the raw materials supplied to the reactor to be mixed efficiently and the polymerization reaction to proceed smoothly. The contents can be water only, water containing a chain transfer agent, or water containing polyvalent metal ions, etc.

The polymerization temperature of the monomers in the polymerization process (the 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 in which no side reactions occur, the temperature is preferably close to the boiling point of the polymerization solvent (water), and is particularly preferably the boiling point of the polymerization solvent (water). When the supply of the polymerization initiator begins after the supply of the monomer mixture begins, the temperature of the reaction system at the start of the supply of the monomer mixture may be lower than the specified polymerization temperature. When set in this way, the temperature can be adjusted to the specified polymerization temperature after the supply of the polymerization initiator begins.

In the polymerization process of the present invention, the residual concentration (total concentration) of the monomer (mc) per 100 mL of reaction liquid in the reactor can be adjusted to preferably 0.3 g or less, more preferably 0.1 g or less, throughout the entire process from the start of polymerization to the end of the supply of the polymerization initiator, so that a (meth)acrylic acid-based copolymer (P) having the desired physical properties can be efficiently produced. It is preferable to end the polymerization process a maximum of 13 hours after the completion of the supply of the monomer mixture.

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

When performing the neutralization step, the pH of the reaction solution is preferably adjusted to 7.0 or less, and more preferably to a range of 1.0 to 5.0.

The manufacturing method of the present invention makes it possible to efficiently manufacture a (meth)acrylic acid-based copolymer (P) 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-based copolymers (P1) and (P2) are all as small as possible.

　When water is not removed from the reaction liquid after the polymerization step and neutralization step in the production method of the present invention, the reaction liquid usually consists of an aqueous solution of the (meth)acrylic acid copolymer (P). Using this aqueous solution, it is possible to easily produce a water treatment agent that suppresses scale formation in cooling water systems, boiler water systems, geothermal power generation water systems, seawater desalination equipment, pulp dissolving pots, black liquor concentrating pots, etc., and a scale adhesion inhibitor that prevents scale adhesion to the inner surface of cooling water piping, the heat transfer surface of a heat exchanger, etc. Furthermore, since the aqueous solution of the (meth)acrylic acid copolymer (P) can be made clear and transparent, the water treatment agent and scale adhesion inhibitor obtained using this aqueous solution can also be transparent and easy to handle.

The water treatment agent of the present invention contains a (meth)acrylic acid-based copolymer (P) and is preferably in the form of a liquid (aqueous solution). The content of the (meth)acrylic acid-based copolymer (P) in this aqueous solution is preferably 1 to 1000 mg/L, more preferably 5 to 100 mg/L, since the effect as a water treatment agent, i.e., the effect of inhibiting scale formation, can be sufficiently obtained.

The water treatment agent of the present invention may contain, as necessary, conventionally known scale formation inhibitors, bactericides, anticorrosive agents, slime inhibitors, defoamers, etc., such as polyacrylic acid or its salts, polymaleic acid or its salts, other (meth)acrylic acid copolymers, and styrene-maleic acid copolymers.

The water treatment agent of the present invention is suitable for application to water (water to be treated) containing at least a precursor component for forming silica scale among silica scale, calcium phosphate scale, calcium carbonate scale, and calcium sulfate scale. For example, in an open circulation cooling water system, in order to reduce the amount of cooling water discharged outside the system from the viewpoint of water and resource saving, the cooling water may be concentrated and poorly soluble salts such as calcium phosphate and calcium carbonate may be formed. In such a case, the use of the water treatment agent of the present invention can suppress problems such as a decrease in heat exchange efficiency and blockage of piping. In addition, in a cooling water system, boiler water system, or geothermal power generation water system that is equipped with a heat exchanger, a refrigerator, etc. and performs a highly concentrated operation, silica scale may be formed. When silica scale adheres to the components of the equipment, it is often difficult to remove it, so the use of 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.

When using the water treatment agent of the present invention, for example, it is added to water (water to be treated) containing the precursor components that form the above-mentioned scale materials, and stirred as necessary.

The scale adhesion inhibitor of the present invention contains a (meth)acrylic acid-based copolymer (P) and is preferably in the form of a liquid (aqueous solution). The content of the (meth)acrylic acid-based copolymer (P) in this aqueous solution is preferably 1 to 1000 mg/L, more preferably 5 to 100 mg/L, since the effect as a scale adhesion inhibitor can be sufficiently obtained, for example, the effect of preventing scale adhesion on structural members such as condensers, heat exchangers, and piping that come into contact with water such as industrial water, tap water, and groundwater.

When using the scale adhesion inhibitor of the present invention, for example, it is added to water (water to be treated) containing the precursor components that form the above-mentioned scale materials, and stirred as necessary.

The present invention will be explained in detail below with reference to examples. However, the present invention is not limited to these examples. In the following, % and ppm are by mass unless otherwise specified.

1. Raw Materials for Producing (Meth)acrylic Acid-Based Copolymers Various polymers were produced using the following raw materials.

1-1. Monomer 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.

1-2. Polymerization initiator: Sodium persulfate

1-3. Chain transfer agent Sodium bicarbonate

1-4. Neutralizing agent: 50% aqueous solution of sodium hydroxide

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

2-2. Quantitative analysis of unreacted monomers contained in (meth)acrylic acid copolymers (1)
AA or its sodium salt, and ATBS were measured by high performance liquid chromatography (hereinafter referred to as "HPLC") using a Shimadzu Corporation "LC-20AD" (model name).
<HPLC measurement conditions>
Column: Tosoh ODS-80Ts
Eluent: 0.17% aqueous tetrabutylammonium hydrogen sulfide solution:acetonitrile = 90:10
Column temperature: 40°C
Detector: UV-vis (205 nm)

2-3. Quantitative analysis of unreacted monomers contained in (meth)acrylic acid copolymers (2)
St, EA, BA, IBA and TBAM were measured by gas chromatography (hereinafter referred to as "GC") using a Shimadzu Corporation "GC-2014AF" (model name).
<GC measurement conditions>
Column: Tosoh HR-1
Carrier gas: He
Sample injection port temperature: 250°C
Temperature rise conditions: 70°C → 150°C (heat rise rate: 20°C per minute)
Detector: FID
Detector temperature: 250°C

3. Production of (meth)acrylic acid-based copolymers Production examples of various (meth)acrylic acid-based copolymers are shown below.

Example 1-1
First, 1.4 g of styrene (St) was dissolved in 475 g of acrylic acid (AA), and 496 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (ATBS) and 14 g of pure water were added to this mixture, followed by thorough stirring to obtain a monomer mixture.
Then, 420 g of pure water was charged into a reactor equipped with a reflux condenser, and the temperature was raised to 75° C., and 9 g of a 30% aqueous solution of sodium bicarbonate was added while stirring the inside of the reactor. Then, the above-mentioned monomer mixture, a 5% aqueous solution of sodium persulfate, and a 30% aqueous solution of sodium bicarbonate were continuously fed into the reactor to carry out a polymerization reaction. The feed amount and feed time of the monomer mixture were 4.1 g/min and 4 hours, respectively. The feed amount and feed time of the 5% aqueous solution of sodium persulfate were 0.3 g/min and 4 hours and 10 minutes, respectively. The feed amount and feed time of the 30% aqueous solution of sodium bicarbonate were 0.7 g/min and 3 hours and 40 minutes, respectively. During the polymerization reaction, the temperature in the reactor was maintained at 75° C. In addition, the residual concentration of styrene (St), which is the monomer (mc), per 100 mL of the reaction liquid was maintained at less than 0.1 g. After the supply of the 5% aqueous solution of sodium persulfate was completed, the reaction solution was heated to 85° C. and held for 1 hour. The pH of the reaction solution was then adjusted to 2.3 using a neutralizing agent to obtain an aqueous solution of a (meth)acrylic acid-based copolymer (hereinafter also referred to as “copolymer (E1)”) with a solid content of 42%. This aqueous solution was clear and transparent.

When a sample taken one hour after the start of polymerization was subjected to gas chromatography (GC), the residual concentration of monomer (mc) was found to be less than 0.1 g/100 mL (see Table 1).

Then, copolymer (E1) was subjected to gel permeation chromatography (GPC), and the Mw was 9,570, the Mn was 4,830, and the Mw/Mn was about 2.0. The content of (meth)acrylic acid-based copolymers having a molecular weight of 1,000 or less in copolymer (E1) was 0.6%, and the content of (meth)acrylic acid-based copolymers having a molecular weight of 200,000 or more was 0.0% (see Table 1).

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

Examples 1-2 to 1-9
Using monomers having the compositions shown in Table 1, (meth)acrylic acid-based copolymers (E2) to (E9) were produced in the same manner as in Example 1-1 (see Table 1).

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.
Then, 420 g of pure water was charged into a reactor equipped with a reflux condenser, and the temperature was raised to 75° C., and 9 g of a 30% aqueous solution of sodium bicarbonate was added while stirring the inside of the reactor. Then, the above-mentioned monomer mixture, a 5% aqueous solution of sodium persulfate, and a 30% aqueous solution of sodium bicarbonate were continuously fed into the reactor to carry out a polymerization reaction. The feed amount and feed time of the monomer mixture were 4.1 g/min and 4 hours, respectively. The feed amount and feed time of the 5% aqueous solution of sodium persulfate were 0.3 g/min and 4 hours and 10 minutes, respectively. The feed amount and feed time of the 30% aqueous solution of sodium bicarbonate were 0.7 g/min and 3 hours and 40 minutes, respectively. During the polymerization reaction, the temperature inside the reactor was maintained at 75° C. After the supply of the 5% aqueous solution of sodium persulfate was completed, the reaction liquid 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-based copolymer (hereinafter also referred to as "copolymer (EE1)") having a solid content of 45%. This aqueous solution was clear and not turbid.

Then, the copolymer (EE1) was subjected to gel permeation chromatography (GPC), and the Mw was 6730, the Mn was 4130, and the Mw/Mn was about 1.6. The content of (meth)acrylic acid-based copolymers with a molecular weight of 1000 or less in this copolymer (EE1) was 0.8%, and the content of (meth)acrylic acid-based copolymers with a molecular weight of 200000 or more was 0.0% (see Table 1).

In addition, a quantitative analysis of the unreacted monomers contained in the copolymer (EE1) revealed that AA and its sodium salt were 66 ppm, and ATBS was 123 ppm (see Table 1).

Comparative Example 1-2
First, 35 g of styrene (St) was dissolved in 315 g of acrylic acid (AA), and 774 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (ATBS) and 14 g of pure water were added to this mixture, followed by thorough stirring to obtain a monomer mixture.
Then, 420 g of pure water was charged into a reactor equipped with a reflux condenser, and the temperature was raised to 75° C., and 9 g of a 30% aqueous solution of sodium bicarbonate was added while stirring the inside of the reactor. Then, the above-mentioned monomer mixture, a 5% aqueous solution of sodium persulfate, and a 30% aqueous solution of sodium bicarbonate were continuously fed into the reactor to carry out a polymerization reaction. The feed rate and feed time of the monomer mixture were 4.7 g/min and 4 hours, respectively. The feed rate and feed time of the 5% aqueous solution of sodium persulfate were 0.3 g/min and 4 hours and 10 minutes, respectively. The feed rate and feed time of the 30% aqueous solution of sodium bicarbonate were 0.7 g/min and 3 hours and 40 minutes, respectively. During the polymerization reaction, the temperature inside the reactor was maintained at 75° C. After the supply of the 5% aqueous solution of sodium persulfate was completed, the reaction liquid 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-based copolymer (hereinafter referred to as "copolymer (EE2)") having a solid content of 42%. This aqueous solution was turbid and opaque.

When a sample taken one hour after the start of polymerization was subjected to gas chromatography (GC), the residual concentration of monomer (mc) was found to be less than 0.1 g/100 mL (see Table 1).

Then, copolymer (EE2) was subjected to gel permeation chromatography (GPC), and the Mw was 7700, the Mn was 4640, and the Mw/Mn was about 1.7. The content of (meth)acrylic acid-based copolymers with a molecular weight of 1000 or less in this copolymer (EE2) was 0.5%, and the content of (meth)acrylic acid-based copolymers with a molecular weight of 200000 or more was 0.0% (see Table 1).

In addition, quantitative analysis of the unreacted monomers contained in the copolymer (EE2) revealed that AA and its sodium salt were 66 ppm, and ATBS was 628 ppm (see Table 1).

Comparative Example 1-3
First, 70 g of styrene (St) was dissolved in 469 g of acrylic acid (AA), and 357 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (ATBS) and 14 g of pure water were added to this mixture, followed by thorough stirring to obtain a monomer mixture.
Then, 420 g of pure water was charged into a reactor equipped with a reflux condenser, and the temperature was raised to 75° C., and then 9 g of a 30% aqueous solution of sodium bicarbonate was added while stirring the inside of the reactor. Then, while maintaining the temperature in the reactor at 75° C., the amount and time of the monomer mixture fed into the reactor were 3.8 g/min and 4 hours, respectively, the amount and time of the 5% aqueous solution of sodium persulfate were 0.3 g/min and 4 hours 10 minutes, respectively, and the amount and time of the 30% aqueous solution of sodium bicarbonate were 0.7 g/min and 3 hours 40 minutes, respectively, and a polymerization reaction was started, but during the polymerization reaction, a precipitate was formed in the reactor, and the production of a (meth)acrylic acid-based copolymer (hereinafter referred to as "copolymer (EE3)") was stopped.

4. Evaluation of Water Treatment Agents (1) Scale Inhibition Test for Silica, Calcium Phosphate, Calcium Carbonate, and Calcium Sulfate The aqueous solutions of the (meth)acrylic acid copolymers obtained in the above Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-2 were adjusted to a concentration of the (meth)acrylic acid copolymer of 1000 ppm to prepare water treatment agents (S), and the scale formation inhibition effect for 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 test, calcium carbonate scale inhibition test, and calcium sulfate scale inhibition test, "blank" refers to the test result of a solution in which no water treatment agent (S) is added and inorganic salts are present at a specified concentration.

<Silica scale inhibition test>
Using the water treatment agent (S) and sodium silicate, 240 mL of a solution having a concentration of 150 mg/L of (meth)acrylic acid copolymer and a concentration of 351 mg/L of sodium silicate was prepared and left at 70 ° C for 30 minutes. Then, while stirring this solution, 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. Next, while stirring this mixed solution, 40 mL of 0.21% sodium bicarbonate aqueous solution was added, and the pH was adjusted to 8.0 with 1 mol/L hydrochloric acid aqueous solution. After that, after leaving it at 70 ° C for 3 hours, the presence or absence of turbidity and precipitation of the solution due to silica was visually observed, and the scale inhibition was evaluated according to the following criteria.
◎: No precipitation was observed, but the liquid was slightly cloudy. ◯: No precipitation was observed, but the liquid was heavily cloudy. ×: Precipitation was observed.

<Calcium phosphate scale inhibition test>
Using the water treatment agent (S), disodium hydrogen phosphate, and calcium chloride, 360 mL of a solution having a concentration of 20 mg/L of (meth)acrylic acid-based copolymer, a concentration of 90 mg/L of disodium hydrogen phosphate, and a concentration of 375 mg/L of calcium chloride was prepared. 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 a 0.1 mol/L sodium hydroxide aqueous solution. After that, the solution was left at 60°C for 3 hours, and the presence or absence of turbidity and precipitation due to calcium phosphate was visually observed, and the scale inhibition was evaluated according to the following criteria.
◎: No turbidity or precipitation was observed. ◯: Turbidity and precipitation were observed, but the Ca concentration in the supernatant after filtration was higher than that in the blank. ×: Turbidity and precipitation were observed, but there was no difference in the Ca concentration in the supernatant after filtration compared to the blank.

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

<Calcium sulfate scale inhibition test>
Using the water treatment agent (S), sodium sulfate, and calcium chloride, 400 mL of a solution having a (meth)acrylic acid copolymer concentration of 4 mg/L, a sodium sulfate concentration of 6000 mg/L, and a calcium chloride concentration of 6200 mg/L was prepared. After leaving it at 60° C. for 3 hours, the solution was visually observed for turbidity and precipitation due to calcium sulfate, and the scale inhibition ability was evaluated according to the following criteria.
◎: No turbidity or precipitation was observed. ◯: Turbidity and precipitation were observed, but the Ca concentration in the supernatant after filtration was higher than that in the blank. ×: Turbidity and precipitation were observed, but there was no difference in the Ca concentration in the supernatant after filtration compared to the blank.

(2) Foaming Evaluation Test The aqueous solutions of the (meth)acrylic acid copolymers obtained in the above Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-2 were adjusted to a concentration of 1% to prepare a water treatment agent (T), and 10 g of the aqueous solution was placed in a resin disposable cup (volume: 1 L, size: upper diameter 122 mm, lower diameter 102.5 mm, height 147 mm) manufactured by AS ONE, and stirred at maximum speed for 30 seconds using a SCARLETT hand mixer "SUPER HAND MIXER MODEL HE-133" (attachment is beater type). The foaming height immediately after the start of stirring and the time from the start of stirring until the generated foam disappeared were measured, and the foaming property was evaluated according to the following criteria. The results are shown in Table 2.
◎: Almost no foaming immediately after stirring (approximately 1 cm or less), 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 of stirring

Examples 2-1 to 2-4 are examples using (meth)acrylic acid-based copolymers E1 to E4 with a content of monomer unit (a) of 70% or less, and showed particularly excellent performance in all areas of silica deposition inhibition, calcium phosphate formation inhibition, calcium carbonate formation inhibition, and calcium sulfate formation inhibition. Examples 2-1 to 2-3 are examples using (meth)acrylic acid-based copolymers E1 to E3 with a content of monomer unit (c) of 2.0% or less, and showed excellent results in foaming evaluation, with foaming immediately after stirring being suppressed.

Examples 2-5 to 2-9 are examples using (meth)acrylic acid copolymers E5 to E9, which showed a certain effect in suppressing silica deposition, and demonstrated excellent performance in suppressing calcium phosphate formation, calcium carbonate formation, and calcium sulfate formation. Furthermore, in Examples 2-5 to 2-7, foaming immediately after stirring was suppressed in the foaming evaluation, demonstrating excellent results.

On the other hand, no silica deposition inhibition effect was obtained in Comparative Examples 2-1 and 2-2. The (meth)acrylic acid-based copolymers EE2 and EE3 of Comparative Examples 2-2 and 2-3 are not sufficiently water-soluble and cannot be used as a water treatment agent or a component of a scale adhesion inhibitor that has an effect of inhibiting scale adhesion to components of equipment in cooling water systems, boiler water systems, or geothermal power generation water systems.

The (meth)acrylic acid-based copolymer of the present invention is suitable as a component of a water treatment agent having excellent effects of inhibiting scale formation, including at least silica, among silica, calcium phosphate, calcium carbonate, and calcium sulfate, or a scale adhesion inhibitor having excellent effects of inhibiting scale adhesion to components of equipment in cooling water systems, boiler water systems, or geothermal power generation water systems.

Claims (9)

A (meth)acrylic acid-based copolymer comprising the following monomer units (a), (b) and (c):
(a) a monomer unit derived from at least one monomer (ma) selected from the group consisting of (meth)acrylic acid and salts thereof; (b) a monomer unit derived from at least one monomer (mb) selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and salts thereof; and (c) a monomer unit derived from at least one monomer (mc) 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. The (meth)acrylic acid-based copolymer has the following contents, when the total of the monomer units (a), (b), and (c) is taken as 100 mass%, the contents of the monomer units (a), (b), and (c) are 65.1 to 95.8 mass%, 4.1 to 34.8 mass%, and 0.1 to 4.9 mass%, respectively. The (meth)acrylic acid copolymer according to claim 1, wherein the monomer (mc) is at least one selected from styrene, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, and N-tert-butylacrylamide. The (meth)acrylic acid copolymer according to claim 1 or 2, having a weight average molecular weight of 1,500 to 20,000. Relative to the total amount of the (meth)acrylic acid-based copolymer,
The content of the (meth)acrylic acid-based copolymer having a molecular weight of 1,000 or less is 15.0% by mass or less,
The (meth)acrylic acid-based copolymer according to any one of claims 1 to 3, wherein the content of the (meth)acrylic acid-based copolymer having a molecular weight of 200,000 or more is 0.10 mass% or less. A method for producing the (meth)acrylic acid-based copolymer according to any one of claims 1 to 4, comprising the steps of:
a preparation step of preparing a monomer mixture containing the monomer (ma), the monomer (mb), the monomer (mc) and water;
a polymerization step of continuously supplying the monomer mixture, a polymerization initiator, and an optional chain transfer agent to a reactor to polymerize the monomers;
The method for producing a (meth)acrylic acid-based copolymer includes the steps of: The method for producing a (meth)acrylic acid-based copolymer according to claim 5, wherein the monomer mixture is supplied to the reactor for 2 to 12 hours in the polymerization step. The method for producing a (meth)acrylic acid-based copolymer according to claim 5 or 6, wherein in the polymerization step, the monomer (mc) is polymerized while maintaining the residual concentration of the monomer (mc) in the reactor at 0.3 g/100 mL or less in total. A water treatment agent containing the (meth)acrylic acid copolymer according to any one of claims 1 to 4. An anti-adhesion agent for calcium phosphate scale, calcium carbonate scale, calcium sulfate scale, and silica scale, comprising the (meth)acrylic acid-based copolymer according to any one of claims 1 to 4.