JP2022114909A - Silica scale preventive - Google Patents

Abstract

To provide a silica scale preventive that has a greater ability to inhibit silica scale than that of the conventional art and can be used suitably as an inhibitor for, for example, silica scale.SOLUTION: A silica scale preventive contains a (meth)acrylic acid copolymer that has a (meth)acrylic acid (salt)-derived constitutional unit and a sulfonic acid (salt) group-containing monomer-derived constitutional unit, wherein, relative to 100 mol% of all the monomer-derived structures, the sulfonic acid (salt) group-containing monomer-derived constitutional unit is 11 mol% or more; at least one end of the backbone of the copolymer is provided with a sulfonic acid (salt) group; and the weight average molecular weight is 20000 or more.SELECTED DRAWING: None

Description

The present invention relates to silica scale inhibitors. More particularly, it relates to a silica scale inhibitor used for suppressing silica scale generated during various water treatment processes.

For example, in geothermal power generation, industrial cooling water, desalination of seawater, and the like, generation of scale such as calcium carbonate and silica poses a problem.
For example, the structural unit derived from the sulfonic acid group-containing monomer described in Patent Document 1 is 5 mol% or more and 22 mol% or less, and the structural unit derived from (meth)acrylic acid (salt) is 78 mol% or more and 95 mol % or less, and having a sulfonic acid (salt) group at at least one main chain end and a weight average molecular weight of 13,000 to 50,000 has excellent gel resistance and high calcium ion chelating ability. , and that it can be suitably used as a water treatment agent such as a scale inhibitor. For example, the copolymer described in Patent Document 2 improves the dispersibility of hydrophobic particles and exhibits excellent chelating ability to calcium ions, so it is extremely good for the piping and inside of the geothermal power generation device. It is disclosed that it can be suitably used as an anti-scaling agent for geothermal power generation equipment because it is possible to exhibit a high anti-scaling ability.

JP 2012-188586 A JP 2016-064382 A

As described above, water treatment agents such as scale inhibitors have been proposed, but there is a demand for further improving the ability to suppress silica scale, and polymers produced using easily available general-purpose monomers. Therefore, a silica scale inhibitor that can be applied to prevent silica scale in various water treatment applications has been desired. An object of the present invention is to provide a (meth)acrylic acid-based copolymer that can be suitably used as, for example, a silica scale inhibitor because of its excellent ability to suppress silica scale.

In order to achieve the above object, the inventor conducted various studies and came up with the present invention.
That is, the scale inhibitor of the present disclosure is a copolymer containing a structural unit derived from (meth)acrylic acid (salt) and a structural unit derived from a sulfonic acid (salt) group-containing monomer, Structural units derived from a sulfonic acid (salt) group-containing monomer are 11 mol% or more relative to 100 mol% of the structure derived from the polymer, and at least one main chain end of the copolymer has a sulfonic acid (salt) group and a (meth)acrylic acid-based copolymer characterized by having a weight average molecular weight of 20,000 or more.

The silica scale inhibitor containing the (meth)acrylic acid-based copolymer of the present disclosure can be preferably used as a silica scale inhibitor by exhibiting a good ability to suppress silica scale.

The present invention will be described in detail below.
A combination of two or more of the individual preferred embodiments of the invention described below is also a preferred embodiment of the invention.

[Copolymer of the present disclosure]
The copolymer of the present disclosure is a copolymer containing a structural unit derived from (meth)acrylic acid (salt) and a structural unit derived from a sulfonic acid (salt) group-containing monomer, Structural units derived from a sulfonic acid (salt) group-containing monomer are 11 mol% or more relative to 100 mol% of the structure derived, and a sulfonic acid (salt) group is added to at least one main chain end of the copolymer and having a weight average molecular weight of 20,000 or more. In addition, the said copolymer may be called the copolymer of this indication.

<Structural unit derived from (meth)acrylic acid (salt)>
In the present disclosure, (meth)acrylic acid refers to acrylic acid, methacrylic acid, and salts thereof.
Examples of the salt include, but are not limited to, alkali metal salts, alkaline earth metal salts, transition metal salts, and ammonium salts.
In the present disclosure, a structural unit derived from (meth)acrylic acid (salt) represents a structural unit in which the carbon-carbon double bond of (meth)acrylic acid (salt) is replaced with a carbon-carbon single bond. For example, in the case of acrylic acid, CH ₂ =CH(COOH), the structural unit derived from acrylic acid can be represented by -CH ₂ -CH(COOH)-. A structural unit derived from (meth)acrylic acid (salt) can be formed, for example, by radical polymerization of (meth)acrylic acid (salt). The structural unit derived from (meth)acrylic acid (salt) may have the same structure as the structure in which the carbon-carbon double bond of (meth)acrylic acid (salt) is replaced with a carbon-carbon single bond. It is not limited to structural units formed by polymerization of acrylic acid (salt), and may be structural units formed by post-reaction after polymerization, for example.

The content of structural units derived from (meth)acrylic acid (salt) in the copolymer of the present disclosure is based on 100 mol% of structural units derived from all monomers constituting the copolymer of the present disclosure, It is preferably 50 mol % or more, more preferably 60 mol % or more, still more preferably 70 mol % or more. Also, it is preferably 89 mol % or less, more preferably 86 mol % or less, and still more preferably 82 mol % or less. The content of structural units derived from (meth)acrylic acid (salt) is calculated in terms of (meth)acrylic acid. (Meth)acrylic acid conversion refers to mass calculation as (meth)acrylic acid even when a structural unit derived from (meth)acrylic acid (salt) is a structural unit derived from (meth)acrylate. Within the above range, the silica scale suppressing ability of the scale prevention of the present disclosure tends to be improved.

<Structural unit derived from sulfonic acid (salt) group-containing monomer>
In the present disclosure, a sulfonic acid (salt) group-containing monomer refers to a compound containing at least one carbon-carbon double bond and a sulfonic acid (salt) group. The at least one carbon-carbon double bond is usually radically polymerizable.
Examples of the salt include, but are not limited to, alkali metal salts, alkaline earth metal salts, transition metal salts, and ammonium salts.
In the present disclosure, a structural unit derived from a sulfonic acid (salt) group-containing monomer is a structural unit in which at least one carbon-carbon double bond of the sulfonic acid (salt) group-containing monomer is replaced with a carbon-carbon single bond. represents The structural unit derived from the sulfonic acid (salt) group-containing monomer has the same structure as the structure in which at least one carbon-carbon double bond of the sulfonic acid (salt) group-containing monomer is replaced with a carbon-carbon single bond. It is not limited to a structural unit formed by polymerization of a sulfonic acid (salt) group-containing monomer, and may be, for example, a structural unit formed by a post-reaction after polymerization.
Examples of sulfonic acid (salt) group-containing monomers include vinylsulfonic acid and its salts, styrenesulfonic acid and its salts, (meth)allylsulfonic acid and its salts, and 3-(meth)allyloxy-2-hydroxypropane. Sulfonic acid and its salts, 3-(meth)allyloxy-1-hydroxypropanesulfonic acid and its salts, 2-(meth)allyloxyethylenesulfonic acid and its salts, 2-acrylamido-2-methylpropanesulfonic acid and its salts etc.

（一般式（１）中、Ｒ_１は、水素原子またはメチル基を表し、ＸおよびＹは、それぞれ独立
に水酸基またはスルホン酸（塩）基を表す（但し、Ｘ、Ｙのうち少なくとも一方はスルホ
ン酸（塩）基を表す。スルホン酸（塩）とは、スルホン酸、スルホン酸塩をいう。スルホン酸塩における塩とは、金属塩、アンモニウム塩、有機アミン塩である。具体的には、ナトリウム塩、リチウム塩、カリウム塩等のアルカリ金属塩；マグネシウム塩、カルシウム塩等のアルカリ土類金属塩；鉄の塩等の遷移金属塩；モノエタノールアミン塩、ジエタノールアミン塩、トリエタノールアミン塩等のアルカノールアミン塩；モノエチルアミン塩、ジエチルアミン塩、トリエチルアミン塩等のアルキルアミン塩；エチレンジアミン塩、トリエチレンジアミン塩等のポリアミン等の有機アミンの塩；等が挙げられる。この中でもナトリウム塩、カリウム塩が特に好ましい。アスタリスクは、一般式（１）で表される構造単位が結合している同種もしくは異種の他の構造単位に含まれる原子を表す。）上記アスタリスクが表す原子が含まれる構造単位としては、特に制限はないが、単量体由来の構造単位、開始剤由来の構造単位、連鎖移動剤に由来する構造単位等が例示される。
本開示のスケール抑制剤のスケール抑制能が向上する傾向にあることから、３－（メタ）アリルオキシ－２－ヒドロキシプロパンスルホン酸及びその塩であることが好ましく、より好ましくは、３－アリルオキシ－２－ヒドロキシプロパンスルホン酸及びそのナトリウム塩である For example, a structural unit derived from a sulfonic acid (salt) group-containing monomer is represented by the following general formula (1).

(In general formula (1), R ₁ represents a hydrogen atom or a methyl group, and X and Y each independently represent a hydroxyl group or a sulfonic acid (salt) group (provided that at least one of X and Y is a sulfone Represents an acid (salt) group.Sulfonic acid (salt) refers to sulfonic acid and sulfonate.Salts in sulfonate include metal salts, ammonium salts, and organic amine salts.Specifically, alkali metal salts such as sodium salts, lithium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; transition metal salts such as iron salts; Alkanolamine salts, alkylamine salts such as monoethylamine salts, diethylamine salts and triethylamine salts, organic amine salts such as polyamines such as ethylenediamine salts and triethylenediamine salts, etc. Of these, sodium salts and potassium salts are particularly preferred. The asterisk represents an atom contained in another structural unit of the same or different type to which the structural unit represented by the general formula (1) is bonded.) As the structural unit containing the atom represented by the above asterisk, Examples include, but are not limited to, monomer-derived structural units, initiator-derived structural units, and chain transfer agent-derived structural units.
3-(meth)allyloxy-2-hydroxypropanesulfonic acid and salts thereof are preferable, and 3-allyloxy-2 - hydroxypropanesulfonic acid and its sodium salt

In the copolymer of the present disclosure, the content of structural units derived from sulfonic acid (salt) group-containing monomers is 100% by mass of structural units derived from all monomers constituting the copolymer of the present disclosure. On the other hand, it is 11 mol % or more, preferably 12 mol % or more, more preferably 13 mol % or more. Also, it is preferably 40 mol % or less, preferably 30 mol % or less, more preferably 25 mol % or less. The content of structural units derived from the sulfonic acid (salt) group-containing monomer is calculated in terms of sodium salt. The calculation in terms of sodium salt means that even if the sulfonic acid (salt) group contained in the structural unit derived from the sulfonic acid (salt) group-containing monomer is, for example, an acid-type sulfonic acid group, the sodium of the sulfonic acid group It means to calculate as if it is salt.
Within the above range, the silica scale inhibiting ability of the scale inhibitor of the present disclosure tends to be improved. For example, within the above range, a polymer containing many sulfonic acid (salt) groups is easily adsorbed to silica particles, thereby improving the dispersibility of silica particles and suppressing aggregation of silica particles.

<Structural units derived from other monomers>
The copolymer of the present disclosure, if desired, a structural unit derived from a (meth)acrylic acid (salt)-derived structural unit, a structural unit derived from a monomer other than a sulfonic acid (salt) group-containing monomer (also referred to as structural units derived from other monomers).
In the present disclosure, structural units derived from other monomers represent structural units in which at least one carbon-carbon double bond of another monomer is replaced with a carbon-carbon single bond. In addition, the structural unit derived from other monomers may have the same structure as the structure in which at least one carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond. The structural units are not limited to those formed by polymerization, and may be, for example, structural units formed by post-reaction after polymerization.
In the copolymer of the present disclosure, the content of structural units derived from other monomers is 0 mol with respect to 100 mol% of structural units derived from all monomers constituting the copolymer of the present disclosure. % or more and 15 mol% or less, preferably 0 mol% or more and 10 mol% or less, more preferably 0 mol% or more and 5 mol% or less, still more preferably 0 mol% or more and 3 mol% or less, It is particularly preferably 0 mol % or more and 2 mol % or less, and most preferably 0 mol %.

Examples of the other monomers include carboxyl group-containing monomers such as maleic acid, itaconic acid, and salts thereof; unsaturated alcohols such as (meth)allyl alcohol and isoprenol; and monomers obtained by adding alkylene oxide thereto. polyalkylene glycol chain-containing monomers such as (meth)acrylic acid esters of alkoxyalkylene glycols; vinyl aromatic monomers having heterocyclic aromatic hydrocarbon groups such as vinylpyridine and vinylimidazole; dimethylamino Dialkylaminoalkyl (meth)acrylates such as ethyl acrylate, dimethylaminoethyl methacrylate and dimethylaminopropyl acrylate, dialkylaminoalkyl (meth)acrylamides such as dimethylaminoethylacrylamide, dimethylaminoethyl methacrylamide and dimethylaminopropylacrylamide, diallylamine, diallyl Amino group-containing monomers such as allylamine such as diallylalkylamine such as dimethylamine, and quaternized products thereof; N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylformamide, N -N-vinyl monomers such as vinyl-N-methylacetamide and N-vinyloxazolidone; (meth)acrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, amide monomers such as t-butylacrylamide; (Meth) allyl alcohol, hydroxyl group-containing monomers such as isoprenol; butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, etc. (meth) acrylic acid alkyl ester monomers; 2- Hydroxy (meth)acrylates such as hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyhexyl (meth)acrylate Alkyl-based monomers; vinylaryl monomers such as styrene, indene and vinylaniline; isobutylene, vinyl acetate and the like; ether bond-containing monomers such as vinyl ethers such as ethyl vinyl ether, butyl vinyl ether and benzyl vinyl ether; , butyl methallyl ether, benzyl methallyl ether, and other (meth)allyl ethers; ethyl isoprenyl ether, butyl isoprenyl ether, benzyl iso Examples include isoprenyl ethers such as prenyl ethers.

<Other structural units>
The copolymers of the present disclosure are characterized by having a sulfonic acid (salt) group on at least one end of the polymer backbone. Having a sulfonic acid (salt) group at at least one end of the main chain of a polymer means having a sulfonic acid (salt) group at one or more main chain ends. For example, in the case of a linear polymer, there are two main chain ends, one or both of which may have a sulfonic acid group. The main chain terminals described above may be present, and one or more of them may have a sulfonic acid group. Having a sulfonic acid (salt) group at at least one chain end improves the ability to inhibit silica scale. The mass% of the sulfonic acid group at the main chain end of the copolymer is preferably 0.01% or more and 10% or less, more preferably 0.01% or more and 5% or less, relative to 100% by mass of the copolymer. . Incidentally, conversion of sulfonic acid group shall be calculated with acid group.

<Physical properties, etc. of the copolymer of the present disclosure>
The copolymer of the present disclosure preferably has a weight average molecular weight (Mw) of 20,000 or more, more preferably 30,000 or more, and even more preferably 37,000 or more. It is preferably 100,000 or less, more preferably 80,000 or less, even more preferably 60,000 or less. Within the above range, the silica scale inhibiting ability of the scale inhibitor of the present disclosure tends to be further improved.
Although the copolymers of the present disclosure contain acid groups such as carboxylic acid (salt) groups and sulfonic acid (salt) groups, the acid groups of the copolymers of the present disclosure may be neutralized. The total neutralization rate of acid groups is preferably 1 mol % or more and 90 mol % or less. The above neutralization rate can be calculated, for example, by ordinary acid-base titration.

<Method for producing the copolymer of the present disclosure>
The method for producing the copolymer of the present disclosure is not particularly limited, but usually (meth) acrylic acid (salt), a sulfonic acid (salt) group-containing monomer, and optionally other monomers. It is preferably produced by polymerizing the structural units. In the production process of the copolymer of the present disclosure, a polymerization initiator can be used in the polymerization of the monomers. A chain transfer agent can be used as necessary for adjusting the molecular weight in the production process of the copolymer of the present disclosure.

<Chain transfer agent of the present disclosure>
The chain transfer agents of the present disclosure can be used for molecular weight control. For example, bisulfites (salts) such as bisulfite, metabisulfite, sodium bisulfite, potassium bisulfite, sodium metabisulfite, potassium metabisulfite, mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionic acid, Thiol-based chain transfer agents such as 3-mercaptopropionic acid, thiomalic acid, octyl thioglycolate, octyl 3-mercaptopropionate, 2-mercaptoethanesulfonic acid, n-dodecylmercaptan, octylmercaptan, butyl thioglycolate; Halides such as carbon chloride, methylene chloride, bromoform, bromotrichloroethane; secondary alcohols such as isopropanol and glycerin; phosphorous acid, hypophosphorous acid, and salts thereof (sodium hypophosphite, hypophosphite potassium etc.). Among these, bisulfites (salts) can be used in the production of the copolymer according to the present disclosure because they contain a sulfonic acid group at at least one end of the main chain. A sulfonic acid group can be efficiently introduced to at least one terminal of the main chain of the resulting copolymer. One type of chain transfer agent may be used, or two or more types may be used. The amount of the chain transfer agent to be added is not limited as long as it is an amount that allows the monomers to be favorably polymerized. The following are preferred.

<Polymerization initiator of the present disclosure>
A polymerization initiator is typically used in the process of producing the copolymers of the present disclosure. A known polymerization initiator can be used. Persulfates such as sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, 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(isobutyrate)dimethyl, 4,4′-azobis(4-cyanovaleric acid), 2,2′-azobis(2-methylpropionamidine) dihydrochloride, 2,2′-azobis [N-(2-carboxyethyl)-2-methylpropionamidine]n-hydrate, 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2′- Azo compounds such as azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate, 1,1′-azobis(cyclohexane-1-carbonitrile), benzoyl peroxide, lauroyl peroxide , peracetic acid, di-t-butyl peroxide, and cumene hydroperoxide. Among these, persulfates are preferred, and by combining with the chain transfer agent, a sulfonic acid group can be efficiently introduced to the end of the main chain of the polymer.

[Applications of the copolymer of the present disclosure]
The copolymer of the present disclosure can exhibit high performance in water-based applications, such as geothermal power generation processes, oil and gas well processes, seawater desalination processes or waste liquid concentration processes using forward or reverse osmosis membranes, and boiler water circulation systems. , it can be preferably applied as a scale inhibitor used in a cooling water circulation system.
The copolymer of the present disclosure can be preferably applied as, for example, a silica scale or calcium carbonate scale inhibitor. In particular, it is most preferably applied as a silica scale inhibitor because of its excellent ability to suppress silica scale.

[Silica scale inhibitor of the present disclosure]
Silica scale inhibitors of the present disclosure comprise copolymers of the present disclosure. The silica scale inhibitor of the present disclosure preferably contains the copolymer of the present disclosure in an amount of, for example, 1% by mass or more and 100% by mass or less. It is more preferably 1% by mass or more and 80% by mass or less, and even more preferably 1% by mass or more and 50% by mass or less.
The silica scale inhibitor of the present disclosure may contain components other than the copolymer of the present disclosure. Components other than the copolymer of the present disclosure include solvents such as water; pH adjusters such as alkalis and acids; oxygen absorbers; anticorrosive agents; chelating agents; - Phosphonic acids (salts) such as diphosphonic acid and salts thereof; carboxy group-containing polymers other than the copolymers of the present disclosure; surfactants; antifoaming agents; pitch control agents; .

[Water treatment agent of the present disclosure]
Water treatment chemicals of the present disclosure include scale inhibitors of the present disclosure. The water treatment agent of the present disclosure preferably contains the copolymer of the present disclosure in an amount of, for example, 1% by mass or more and 70% by mass or less. More preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, particularly preferably 1% by mass or more and 30% by mass or less, 1% by mass or more, It is most preferable to contain 20% by mass or less. The water treatment chemical of the present disclosure may contain ingredients other than the scale inhibitor of the present disclosure. Components other than the scale inhibitor of the present disclosure include solvents such as water; pH adjusters such as alkalis and acids; oxygen absorbers; anticorrosive agents; chelating agents; - Phosphonic acids (salts) such as diphosphonic acid and salts thereof; carboxy group-containing polymers other than the copolymers of the present disclosure; surfactants; antifoaming agents; pitch control agents; .

[Silica scale prevention method of the present disclosure]
The silica scale prevention method of the present disclosure uses the silica scale inhibitor of the present disclosure or the copolymer of the present disclosure. The silica scale prevention method of the present disclosure preferably includes the step of adding the silica scale inhibitor of the present disclosure or the copolymer of the present disclosure to the system to be targeted for silica scale prevention. Moreover, it preferably includes a step of controlling the amount of the copolymer of the present disclosure in the system targeted for silica scale prevention so that it falls within a predetermined range. The content of the copolymer of the present disclosure in the system targeted for silica scale prevention is preferably 0.1 ppm or more and 500 ppm or less, more preferably 0.1 ppm or more and 300 ppm.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited only to these examples. Unless otherwise specified, "part" means "mass part" and "%" means "mass %".
<Conditions for measuring weight average molecular weight (GPC)>
Apparatus: HLC8320 manufactured by Tosoh Corporation
Column: Showa Denko Co., Ltd. SHODEX Asahipak GF-310-HQ,
GF-710-HQ, GF-1G-7B
Column temperature: 40°C
Flow rate: 0.5ml/min
Calibration curve: Polyacrylic acid standard manufactured by American Polymer Standards Corporation
Eluent: 0.1N sodium acetate

<Synthesis Example 1>
251.5 g of pure water and 0.031 g of Mohr's salt were charged into a 3 L SUS reaction vessel equipped with a reflux condenser and a stirrer (paddle blade), and the temperature was raised to 85° C. while stirring to form a polymerization reaction system. . Next, 517.5 g of an 80% acrylic acid aqueous solution (hereinafter also referred to as "80% AA") and sodium 3-allyloxy-2-hydroxypropanesulfonate were added to a polymerization reaction system maintained at 85° C. with stirring. 40% aqueous solution (hereinafter also referred to as “40% HAPS”) 533.2 g, 15% sodium persulfate aqueous solution (hereinafter also referred to as “15% NaPS”) 179.3 g, and 32.5% hydrogen sulfite 18.6 g of sodium aqueous solution (hereinafter also referred to as "32.5% SBS") was dropped from separate nozzles. The dropping time of each solution was 180 minutes for 80% AA, 140 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 32.5% SBS. Further, the dropping rate of each solution was constant, and the dropping of each solution was performed continuously. After the dropwise addition of 15% NaPS was completed, the reaction solution was kept at 85° C. for an additional 30 minutes (aging) to complete the polymerization. Thus, an aqueous polymer solution (1) having a solid concentration of 44.8% was obtained. The weight average molecular weight of polymer (1) was 37,000. In addition, the composition ratio of the charged polymer and the produced polymer is the same.

<Synthesis Example 2>
250.78 g of pure water and 0.031 g of Mohr's salt were charged into a 3 L SUS reaction vessel equipped with a reflux condenser and a stirrer (paddle blade), and the temperature was raised to 85° C. while stirring to form a polymerization reaction system. and Next, 508.9 g of 80% AA, 524.3 g of 40% HAPS, 176.3 g of 15% NaPS, and 39.7 g of 10% SBS were added to the polymerization reaction system maintained at 85°C with stirring from separate nozzles. Dripped. The dropping time of each solution was 180 minutes for 80% AA, 140 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 10% SBS. Further, the dropping rate of each solution was constant, and the dropping of each solution was performed continuously. After the addition of 15% NaPS was completed, the reaction solution was kept at 85° C. for an additional 30 minutes (aged) to complete the polymerization. Thus, an aqueous polymer solution (2) having a solid concentration of 44.5% was obtained. The weight average molecular weight of polymer (2) was 49,000. In addition, the composition ratio of the charged polymer and the produced polymer is the same.

<Synthesis Example 3>
250.8 g of pure water and 0.031 g of Mohr's salt were charged into a 3 L SUS reaction vessel equipped with a reflux condenser and a stirrer (paddle blade), and the temperature was raised to 85° C. while stirring to form a polymerization reaction system. and Next, 457.2 g of 80% AA, 609.7 g of 40% HAPS, 165.2 g of 15% NaPS, and 17.2 g of 32.5% SBS were separately added to the polymerization reaction system maintained at 85° C. under stirring. dripped from the nozzle. The dropping time of each solution was 180 minutes for 80% AA, 140 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 32.5% SBS. Further, the dropping rate of each solution was constant, and the dropping of each solution was performed continuously. After the addition of 15% NaPS was completed, the reaction solution was kept at 85° C. for an additional 30 minutes (aged) to complete the polymerization.
Thus, an aqueous polymer solution (3) having a solid concentration of 43.6% was obtained. The weight average molecular weight of polymer (3) was 37,000. In addition, the composition ratio of the charged polymer and the produced polymer is the same.

<Synthesis Example 4>
462.6 g of pure water and 0.031 g of Mohr's salt were charged into a 3 L SUS reaction vessel equipped with a flow cooler and a stirrer (paddle blade), and the temperature was raised to 85° C. while stirring to form a polymerization reaction system. and Next, 674.3 g of 80% AA, 238.0 g of 40% HAPS, 103.1 g of 15% NaPS, and 21.9 g of 32.5% SBS were separately added to a polymerization reaction system maintained at 85°C under stirring. dripped from the nozzle. The dropping time of each solution was 180 minutes for 80% AA, 155 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 32.5% SBS. Further, the dropping rate of each solution was constant, and the dropping of each solution was performed continuously. After the dropwise addition of 80% AA was completed, the above reaction solution was kept at 85° C. for an additional 30 minutes (aging) to complete the polymerization. Thus, an aqueous polymer solution (4) having a solid concentration of 43.6% was obtained. The weight average molecular weight of polymer (4) was 44,000. In addition, the composition ratio of the charged polymer and the produced polymer is the same.

<Synthesis Example 5>
611.3 g of ion-exchanged water was introduced into a 5 L SUS reaction vessel equipped with a reflux condenser and a stirrer, and the temperature was raised to the boiling point reflux state while stirring. Then, while stirring, 57.6 g of 80% AA, 1145.9 g of 37% sodium acrylate (hereinafter also referred to as "37% SA"), 502.9 g of 40% HAPS, and 132.2 g of 15% NaPS were added to the polymerization reaction system in the boiling point reflux state. , 35% hydrogen peroxide water (hereinafter also referred to as “35% H ₂ O ₂ ”) 19.0 g, and ion-exchanged water 367.9 g were dropped from separate nozzles. The dropping time of each solution was 120 minutes for 80% AA and 37% SA, 90 minutes for 40% HAPS and deionized water, 140 minutes for 15% NaPS, and 120 minutes for 35% H ₂ O ₂ . Thus, an aqueous polymer solution (5) having a solid content of 50.2% was obtained. The weight average molecular weight of polymer (5) was 5,000. In addition, the composition ratio of the charged polymer and the produced polymer is the same.

<Synthesis Example 6>
1,620 g of ion-exchanged water was introduced into a 5-liter SUS reaction vessel equipped with a reflux condenser and a stirrer, and the temperature was raised to the boiling point reflux state while stirring. Then, while stirring, 455 g of 80% AA and 133 g of 15% NaPS were added dropwise from separate nozzles into the polymerization reaction system in the boiling point reflux state. The dropping time of each solution was 180 minutes for 80% AA, 185 minutes for 15% NaPS, and 170 minutes for deionized water. After the dropwise addition of the 15% NaPS solution was completed, the above reaction solution was maintained (aged) at the boiling point reflux state for an additional 30 minutes to complete the polymerization. Thus, an aqueous polymer solution (6) having a solid content of 45.7% was obtained. The weight average molecular weight of polymer (6) was 10,000. In addition, the composition ratio of the charged polymer and the produced polymer is the same.

<Silica scale suppression rate evaluation test>
Sodium silicate aqueous solution: To 2.129 g of sodium metasilicate nonahydrate (manufactured by Aldrich), deionized water is added to adjust the total amount to 150 g.
Magnesium sulfate aqueous solution: Deionized water is added to 8.115 g of magnesium sulfate heptahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) to make a total of 1000 g.
Borate buffer: 7.42 g of boric acid (manufactured by Kanto Chemical Co., Ltd.) and 19.07 g of sodium borate decahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed to prepare a borate buffer.
73 g of deionized water was placed in a container, and 2 g of the boric acid buffer, 10 g of the sodium silicate aqueous solution, 5 g of the polymer aqueous solution diluted to a polymer concentration of 1000 ppm, and 10 g of the magnesium sulfate aqueous solution were added while stirring. C. and left for 5 hours. After standing for 5 hours, the test solution was suction-filtered using a filter paper with 0.1 μm openings in a suction filtration device. The obtained filtrate was measured by XR-F to measure the Si concentration in terms of SiO ₂ .
Silica scale suppression rate (%) = SiO ₂ after test (ppm) / SiO ₂ concentration before test (ppm) x 100
The silica scale suppression rate was determined according to the following criteria.
<Suppression Rate Evaluation Criteria>
90% or more: ◎
70-90%: ○
30-70%: △
Less than 30%: ×
<Example 1>
5 g of the 1000 ppm aqueous solution of polymer (1) obtained in Synthesis Example 1 was subjected to the above silica scale inhibition rate test.
<Example 2>
5 g of the 1000 ppm aqueous solution of polymer (2) obtained in Synthesis Example 2 was subjected to the above silica scale inhibition rate evaluation test.
<Example 3>
5 g of the 1000 ppm aqueous solution of polymer (3) obtained in Synthesis Example 3 was subjected to the above silica scale inhibition rate evaluation test.
<Comparative Example 1>
5 g of the 1000 ppm aqueous solution of polymer (4) obtained in Synthesis Example 4 was subjected to the above silica scale inhibition rate evaluation test.
<Comparative Example 2>
5 g of the 1000 ppm aqueous solution of polymer (5) obtained in Synthesis Example 5 was subjected to the above silica scale inhibition rate evaluation test.
<Comparative Example 3>
5 g of the 1000 ppm aqueous solution of polymer (6) obtained in Synthesis Example 6 was subjected to the above silica scale inhibition rate evaluation test.
<Comparative Example 4>
An evaluation test was conducted in the same manner as the above silica scale inhibition rate evaluation test except that the aqueous polymer solution was not added.

Experimental results of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1.

表１中、「組成」は、アクリル酸（塩）に由来する構造単位／スルホン酸（塩）基に由来する構造単位を表す。
表１の結果から、本開示の共重合体は、シリカスケール抑制能に優れることがわかった。

In Table 1, "composition" represents structural units derived from acrylic acid (salt)/structural units derived from sulfonic acid (salt) groups.
From the results in Table 1, it was found that the copolymer of the present disclosure is excellent in silica scale suppressing ability.

Claims (4)

A copolymer containing a structural unit derived from (meth)acrylic acid (salt) and a structural unit derived from a sulfonic acid (salt) group-containing monomer, relative to 100 mol% of the structure derived from all monomers , the structural unit derived from a sulfonic acid (salt) group-containing monomer is 11 mol% or more, the copolymer has a sulfonic acid (salt) group at at least one main chain end, and the weight average molecular weight is 20000 A silica scale inhibitor containing a (meth)acrylic acid-based copolymer characterized by the above. The silica scale inhibitor according to claim 1, wherein the structural unit derived from the sulfonic acid (salt) group-containing monomer is represented by general formula (1).

(In general formula (1), R ₁ represents a hydrogen atom or a methyl group, and X and Y each independently represent a hydroxyl group or a sulfonic acid (salt) group (provided that at least one of X and Y is a sulfonic acid represents a (salt) group.The asterisk represents an atom contained in another structural unit of the same or different type to which the structural unit represented by general formula (1) is bonded.) The structural unit derived from the sulfonic acid (salt) group-containing monomer is a structural unit derived from 3-allyloxy-2-hydroxypropanesulfonic acid or a salt thereof, according to any one of claims 1 and 2. Silica scale inhibitor. A water treatment agent containing the silica scale inhibitor according to any one of claims 1 to 3