JP5656702B2 - (Meth) acrylic acid copolymer and method for producing the same - Google Patents

Description

The present invention relates to a (meth) acrylic acid copolymer suitably used for, for example, a scale inhibitor, a dispersant, a detergent builder, and the like, and a method for producing the same.

Conventionally, among water-soluble polymers such as (meth) acrylic acid-based polymers, low molecular weight ones use dispersants and scales such as inorganic pigments and metal ions by utilizing their excellent chelating ability and dispersing ability. It is suitably used for an inhibitor or a detergent builder. However, for example, scale inhibitors are used in highly concentrated cooling water systems to save resources and save water, used in water systems with high hardness for reasons such as deterioration of water quality, or high salt such as seawater. In such a case, there is a problem that the polymer gels and precipitates, and the scale preventing ability is remarkably lowered.

  In Patent Document 1, the structural unit (a) derived from the (meth) acrylic acid monomer (A) represented by the following general formula (1) and the (meth) acrylic acid monomer (A) are copolymerized. A copolymer having a structural unit (b) derived from a possible monoethylenically unsaturated monomer (B), and at least one of the ends of the main chain, a sulfonic acid group (provided that the sulfonic acid group is ammonium A (meth) acrylic acid copolymer having a salt, an alkali metal salt, or a salt of an organic amine group, wherein the structural unit (b) has the following general formula: It contains at least the structural unit (b1) derived from the (meth) allyl ether monomer (B1) represented by (2), and the mutual proportion of the structural unit (a) and the structural unit (b1) Unit (a) 70-95 mol%, said structural unit (b1) 5-30 A le%, gelation resistance degree of gelation resistance test in an aqueous system containing calcium ions is 100 to 1500 (meth) acrylic acid copolymer is disclosed.

(In the formula, R ¹ represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, a metal atom, an ammonium group, or an organic amine group.)

(Wherein R ² represents a hydrogen atom or a methyl group, and Y and Z each independently represent a hydroxyl group or a sulfonic acid group (provided that the monovalent metal salt, divalent metal salt, ammonium salt, or organic amine group) It may be a salt.))
In Patent Document 1, the copolymer is a synergistic effect of a sulfonic acid group in a side chain, which is a structural unit derived from the (meth) allyl ether monomer, and a sulfonic acid group introduced at the end of the main chain. Thus, it is disclosed that the gel resistance performance is remarkably improved.

  However, in order to meet the demands of more demanding customers as, for example, detergent builders and water treatment agents, the above-mentioned copolymer prevents insolubilization of the surfactant by calcium ions and improves detergency. In order to suppress the generation of scale by trapping ions, there is room for improving the calcium trapping ability.

JP 2002-3536 A

As described above, although various polymers have been reported in the past, the present situation is that they are not sufficiently met with requirements for water-based applications such as detergent builders and water treatment applications. Specifically, for example, in water treatment applications, at high hardness, in addition to the ability to suppress gelation and precipitation (gel resistance), chelating ability to capture calcium ions in water in order to suppress the formation of scale Is strongly requested.
Therefore, the present invention provides a copolymer having improved gel resistance and a high calcium ion chelating ability when used in the above-mentioned aqueous applications, and a method for producing the same. Objective.

As a result of intensive studies on various polymers / copolymers to achieve the above object, the present inventors have found that a specific (meth) acrylic acid-based copolymer has excellent gel resistance and chelating ability. I learned that I have Based on the above findings, the present invention has been completed.
That is, the copolymer of the present invention has a structure derived from a monomer represented by the following general formula (1) of 5 mol% to 22 mol% with respect to 100 mol% of the structure derived from all monomers. A copolymer having the unit (a) and a structural unit (b) derived from (meth) acrylic acid (salt) in an amount of 78 mol% or more and 95 mol% or less as an essential structural unit, and having at least one main chain terminal A (meth) acrylic acid copolymer having a sulfonic acid (salt) group and a weight average molecular weight of 13,000 to 50,000.

In general formula (1), R ₂ 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 sulfonic acid) (Salt) group).

Another copolymer of the present invention comprises a structural unit (a) derived from the monomer represented by the general formula (1) and a structural unit (b) derived from (meth) acrylic acid (salt) as essential structures. A copolymer having as a unit,
The copolymer has a weight average molecular weight of 13,000 to 50,000,
The copolymer has a sulfonic acid (salt) group at at least one main chain end,
The composition (A mass%) of the structural unit (a) derived from the monomer represented by the general formula (1) with respect to the structural unit derived from the weight average molecular weight (Mw) of the copolymer and all monomers. The (meth) acrylic acid copolymer is characterized in that the relationship satisfies the following formula.

Since the copolymer of the present invention exhibits excellent gel resistance and chelating ability, it can be suitably used for detergent additives (particularly detergent builders) and water treatment agents (particularly scale inhibitors).

Hereinafter, the present invention will be described in detail.

[(Meth) acrylic acid copolymer (also referred to as a copolymer of the present invention)]
The copolymer of the present invention essentially has a specific proportion of the structural unit (a) derived from the monomer represented by the following general formula (1).

In general formula (1), R ₂ 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 sulfonic acid) (Salt) group).
The sulfonic acid (salt) refers to sulfonic acid and sulfonate.
The salt in the sulfonate is a metal salt, an ammonium salt, or an organic amine salt. Specifically, alkali metal salts such as sodium salt, lithium salt and potassium salt; alkaline earth metal salts such as magnesium salt and calcium salt; transition metal salts such as iron salt; monoethanolamine salt, diethanolamine salt, Alkanolamine salts such as ethanolamine salts; alkylamine salts such as monoethylamine salts, diethylamine salts, and triethylamine salts; salts of organic amines such as polyamines such as ethylenediamine salts and triethylenediamine salts; Of these, sodium salts and potassium salts are particularly preferable.
In general formula (1), it is preferable that any one of X and Y is a sulfonic acid (salt) group.

  The structural unit (a) derived from the monomer represented by the general formula (1) is specifically represented by the following general formula (2).

In general formula (2), R ₂ 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 sulfonic acid) (Salt) group).
When the copolymer of the present invention has “structural unit (a) derived from the monomer represented by the general formula (1)”, the finally obtained polymer has the general formula (2). Is included.
When the copolymer of the present invention has a predetermined amount of the structural unit (a) derived from the monomer represented by the general formula (1), the gel resistance is remarkably improved. Since the structural unit (a) does not contain an ester group or an amide group, it is highly stable even under conditions in the production process of the polymer and in the production process of various products containing the polymer. It is possible to improve.

  In the copolymer of the present invention, the structural unit (a) derived from the monomer represented by the general formula (1) is 5 mol% or more and 22 mol% with respect to 100 mol% of the structure derived from all monomers. It is preferable to have the following proportions. In the present invention, the structure derived from all monomers refers to the structural unit (a) derived from the monomer represented by the general formula (1), the structure derived from (meth) acrylic acid (salt), and the like. The structure derived from the monomer. When the structural unit (a) represented by the general formula (1) is within the above range, the gel resistance of the copolymer is excellent. Moreover, since the structural unit (b) derived from (meth) acrylic acid (salt) contains a carboxyl group to some extent efficiently, it also exhibits good chelating ability. The ratio of the structural unit (a) to 100 mol% of the structure derived from all monomers is more preferably 8 mol% or more and 18 mol% or less, still more preferably 9 mol% or more and 15 mol% or less, particularly preferably. Is 10 mol% or more and 13 mol% or less.

  The copolymer of the present invention preferably contains a predetermined amount of the structural unit (a) represented by the general formula (1) per molecule of the polymer. Specifically, the composition of the structural unit (a) derived from the monomer represented by the general formula (1) with respect to the weight average molecular weight (Mw) of the copolymer and the structural unit derived from all monomers (A The mass%) relationship preferably satisfies the following formula.

In the above formula, when calculating the composition (A mass%) of the structural unit (a) derived from the monomer represented by the general formula (1) relative to the structural unit derived from all monomers, In the case where contains a salt of an acid group, it is calculated as the corresponding acid (acid type conversion). Moreover, when a monomer contains the salt of an amino group, it calculates as a corresponding amine (amine conversion). For example, if it is a structural unit derived from sodium acrylate, a ratio (mass%) is calculated as a structure derived from the corresponding acid, acrylic acid.
In the above formula, “molecular weight of the structural unit (a)” is also calculated in terms of acid type.
In the above formula, the weight average molecular weight (Mw) of the copolymer is a numerical value measured under measurement conditions by gel permeation chromatography described later.
When the above formula is satisfied, each polymer molecule has an appropriate amount of the structural unit (a), and the gel resistance of the copolymer is good.

<Structural unit derived from (meth) acrylic acid (salt)>
The copolymer of the present invention essentially has a specific proportion of structural units (b) derived from (meth) acrylic acid (salt) (also referred to as monomer (B)).
(Meth) acrylic acid (salt) refers to acrylic acid, acrylate, methacrylic acid, and methacrylate. The salt in (meth) acrylic acid (salt) is the same as the salt in the sulfonate. Similarly, (meth) acrylic acid (salt) is particularly preferably a sodium salt or potassium salt of (meth) acrylic acid.

The structural unit (b) derived from (meth) acrylic acid (salt) is a structure in which the unsaturated double bond of (meth) acrylic acid (salt) is a single bond. For example, (meth) acrylic acid ( When the salt is sodium acrylate, the structural unit (b) can be represented by —CH ₂ —CH (COONa) —. The copolymer of the present invention has “structural unit (b) derived from (meth) acrylic acid (salt)” means that the finally obtained polymer has no (meth) acrylic acid (salt). It is meant to include structural units in which saturated double bonds are replaced with single bonds.

In the copolymer of the present invention, the structural unit (b) derived from (meth) acrylic acid (salt) is from 78 mol% to 95 mol% with respect to 100 mol% of the structure derived from all monomers. It is essential to have. In the present invention, the structure derived from all monomers is derived from the structural unit (a) derived from the monomer represented by the general formula (1) and (meth) acrylic acid (salt) as described above. The structural unit (b) derived from other monomers.
If the structural unit (b) derived from (meth) acrylic acid (salt) is within the above range, the gel resistance and chelating ability of the copolymer will be excellent. The ratio of the structural unit (b) to 100 mol% of the structure derived from all monomers is preferably 82 mol% or more and 92 mol% or less, more preferably 85 mol% or more and 91 mol% or less, particularly preferably. It is 87 mol% or more and 90 mol% or less. When the structural unit (b) derived from (meth) acrylic acid (salt) is lower than the above range, the chelating ability of the copolymer is lowered.

<Structural units derived from other monomers>
In addition to the structural unit (a) represented by the above general formula (1) and the structural unit (b) derived from (meth) acrylic acid (salt), the copolymer of the present invention contains other monomers (units). You may have the structural unit (c) derived from a monomer (C).
The other monomer is preferably a monomer copolymerizable with the structural unit (a) represented by the general formula (1) and / or (meth) acrylic acid (salt).
The other monomer may be a salt, and the salt in that case is the same as the salt in the sulfonate. Similarly, when it is a salt, sodium salt and potassium salt are particularly preferable.

The structural unit (c) derived from the other monomer is a structure in which the unsaturated double bond of the other monomer is a single bond. For example, when the monomer (C) is methyl acrylate, The structural unit (c) derived from another monomer can be represented by —CH ₂ —CH (COOCH ₃ ) —.
The copolymer of the present invention has “structural unit (c) derived from other monomer” means that the finally obtained polymer has an unsaturated double bond of another monomer as a single unit. Means including structural units replaced by bonds.

  The copolymer of the present invention has structural units (c) derived from other monomers at a ratio of 0 mol% or more and 17 mol% or less with respect to 100 mol% of the structure derived from all monomers. May be. In the present invention, the structure derived from all monomers is as described above. When the structural unit (c) derived from other monomer exceeds the above range, it is not preferable because both gel resistance and chelating ability cannot be achieved or the scale preventing ability of calcium carbonate tends to be lowered. . The proportion of the structural unit (c) with respect to 100 mol% of the structure derived from all monomers is preferably 0 mol% or more and 10 mol% or less, more preferably 0 mol% or more and 6 mol% or less, particularly preferably. It is 0 mol% or more and 3 mol% or less.

Other monomers (C) are not particularly limited, and are appropriately selected depending on the desired effect. Specifically, unsaturated monocarboxylic acids other than the monomer (B) and salts thereof such as crotonic acid, α-hydroxyacrylic acid, α-hydroxymethylacrylic acid and derivatives thereof; itaconic acid, fumaric acid Acids, maleic acids, unsaturated dicarboxylic acids such as 2-methyleneglutaric acid and their salts; vinylsulfonic acid, 1-acrylamido-1-propanesulfonic acid, 2-acrylamido-2-propanesulfonic acid, 2- (meth) Acrylamido-2-methyl-1-propanesulfonic acid, (meth) allyloxybenzenesulfonic acid, styrenesulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, (meth) allylsulfonic acid, isoprenesulfonic acid, and Sulfonic acid group-containing monomers other than the monomer (A) such as these salts; A) Monomers obtained by adding alkylene oxide to allyl alcohol, isoprenol, polyalkylene glycol chain-containing monomers such as (meth) acrylic acid esters of alkoxyalkylene glycol; N-vinylpyrrolidone, N-vinylformamide, N-vinyl N-vinyl monomers such as acetamide, N-vinyl-N-methylformamide, N-vinyl-N-methylacetamide, N-vinyloxazolidone; (meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide, etc. Amide monomers; (meth) allyl alcohol and other allyl ether monomers; isoprenol and other isoprene monomers; butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate Etc. ) Acrylic acid alkyl ester monomers; hydroxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4 -Hydroxyalkyl (meth) acrylates such as hydroxybutyl (meth) acrylate, α-hydroxymethylethyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyneopentyl (meth) acrylate, hydroxyhexyl (meth) acrylate, etc. Mer: vinyl aryl monomer such as styrene, indene and vinylaniline, isobutylene, vinyl acetate; heterocyclic aromatic hydrocarbon group such as vinylpyridine and vinylimidazole, and amino group Vinyl aromatic amino group-containing monomers and quaternized products and salts thereof; aminoalkyl (meth) acrylates such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl acrylate, and aminoethyl methacrylate; Grades and salts; Allylamines such as diallylamine and diallyldimethylamine and their quaternizations and salts; (i) (ii) Dimethyl on the epoxy ring of (meth) allyl glycidyl ether, isoprenyl glycidyl ether, vinyl glycidyl ether Dialkylamines such as amine, diethylamine, diisopropylamine and di-n-butylamine, alkanolamines such as diethanolamine and diisopropanolamine, aminocarboxylic acids such as iminodiacetic acid and glycine , Morpholine, quaternary compound or salt amine of monomers and obtained by reacting such cyclic amines pyrrole etc., etc., it can be mentioned.
Moreover, the said other monomer (C) may be used individually by 1 type, or may be used with the form of a 2 or more types of mixture.

<Other structural units>
The copolymer of the present invention is characterized by having a sulfonic acid (salt) group at the end of at least one main chain of the polymer molecule. Having a sulfonic acid (salt) group at at least one main chain terminal means having one or two or more main chain terminals having a sulfonic acid (salt) group, for example, a linear polymer molecule. 2 may have a sulfonic acid (salt) group at the terminal end of the main chain, and may have a sulfonic acid (salt) group at three or more main chain terminals as long as it is a branched polymer molecule. . Having a sulfonic acid (salt) group at at least one main chain terminal is preferable because gel resistance is improved. The ratio (mass%) of the sulfonic acid group at the main chain terminal of the polymer molecule with respect to 100 mass% of the total mass of the copolymer is preferably 0.01 mass% or more and 5 mass% or less. In addition, when calculating the mass% of the sulfonic acid group at the molecular terminal with respect to the total mass of the copolymer, it is calculated in terms of acid, and if applicable, it is calculated in terms of amine.

As a method for forming a structural unit containing a sulfonic acid group at the molecular end of a copolymer, a monomer containing monomers (A), (B), etc. is converted into bisulfite (salts) (sulfurous acid, bisulfite). , Dithionic acid, metabisulfite, and salts thereof) is preferably used. In the above case, the bisulfite (salt) acts as a chain transfer agent or the like, whereby the sulfonic acid group is incorporated into the polymer molecule.
The sulfonic acid group at the molecular end of the copolymer can be measured, for example, by ¹ HNMR.

<Molecular weight of (meth) acrylic acid copolymer>
The weight average molecular weight Mw of the (meth) acrylic acid polymer according to the present invention is 13,000 to 50000, preferably 16000 to 45000, and more preferably 20000 to 40000. If the weight average molecular weight is within this range, the (meth) acrylic acid polymer tends to improve the chelating ability. Therefore, it can be used more suitably for applications such as scale inhibitors and detergent builders. When the weight average molecular weight of the (meth) acrylic acid polymer is less than 13,000, the chelating ability of calcium carbonate tends to decrease.
In addition, if the weight average molecular weight Mw is in the above range, the number of molecules per certain mass is small compared to the case where Mw is small, so that the low gel property is high even when the composition of the structural unit (a) is set low. Can be maintained.

  The dispersity (Mw / Mn) of the (meth) acrylic acid polymer according to the present invention is 1.5 to 10.0, preferably 1.8 to 8.0, more preferably 2.0 to 6. .0. When the degree of dispersion is less than 1.5, the synthesis becomes complicated. On the other hand, when the dispersity exceeds 10.0, components effective in performance are reduced, and there is a risk of performance degradation.

  In addition, the said weight average molecular weight (Mw) and number average molecular weight (Mn) are measured by the method described in the below-mentioned Example.

<Gel resistance of copolymer>
In the gel resistance test of the present invention, pure water, boric acid-sodium borate pH buffer solution, aqueous copolymer solution, and calcium chloride solution are sequentially added to a 500 mL conical beaker, and the copolymer is added at a solid content concentration of 100 mg. / L of test solution of pH8.5 containing, by changing the calcium concentration (by increasing the concentration of 100MgCaCO ₃ / L every 100mgCaCO ₃ / L) were each prepared, a thermostat seal to 90 ° C. with a polyvinylidene chloride film The minimum concentration of the test solution in which white turbidity was caused to stand for 1 hour was evaluated as the degree of gelation resistance. That is, it can be said that the greater the degree of gelation resistance, the higher the gel resistance.
The copolymer of the present invention preferably has a gelation resistance of 400 mg CaCO ₃ / L or more. By being the said range, it can use preferably as additives, such as a detergent composition and a water treatment agent. More preferably, it is 500 mgCaCO ₃ / L or more. No particular limitation to the upper limit of the gelation resistance degree, but for example 10000mgCaCO ₃ / L or less.

<Calcium scavenging ability of copolymer>
The (meth) acrylic acid copolymer of the present invention exhibits good calcium capturing ability.
The calcium ion scavenging ability (mgCaCO ₃ / g) is defined as the number of mg obtained by converting the calcium ion captured by 1 g of the water-soluble polymer into the amount of calcium carbonate, and how much the water-soluble polymer has the calcium ion in the water. It is an index indicating whether to capture. For example, a surfactant used as a main component in applications such as a detergent composition is insolubilized when combined with calcium ions in water, and the surfactant effect is significantly reduced. Here, when a water-soluble polymer having a high calcium ion scavenging ability is used together with the surfactant, the insolubilization of the surfactant is prevented, and the effect of improving the detergency is increased and sufficiently exerted. In addition, when added to a water treatment agent, it is possible to suppress the generation and growth of scale by capturing calcium ions in water or adsorbing them to crystal nuclei that form the scale.
In the present invention, the calcium ion scavenging ability is a value measured by the method and conditions described in Examples described later.
The copolymer of the present invention preferably has a calcium ion scavenging ability of 180 mgCaCO ₃ / g or more. By being the said range, it can use preferably as additives, such as a detergent composition and a water treatment agent. More preferably 200mgCaCO ₃ / g or more, further preferably 220mgCaCO ₃ / g or greater. There is no particular limitation on the upper limit of the calcium ion trapping ability, is, for example 500mgCaCO ₃ / g or less.

[Method for producing (meth) acrylic acid copolymer]
<Monomer composition>
The production method of the copolymer of the present invention is 5 mol% or more and 22 mol% or less with respect to 100 mol% of all monomers (total of monomers (A), (B) and (C)) used. The monomer represented by the general formula (1) (monomer (A)) and (meth) acrylic acid in an amount of 78 mol% to 95 mol% with respect to 100 mol% of the total monomer used It is preferable to copolymerize (salt) (monomer (B)) as an essential component.
In the method for producing a copolymer of the present invention, the monomer (A) and the monomer (B) may be used alone or in combination of two or more. In the method for producing a copolymer of the present invention, in addition to the monomer (A) and the monomer (B), the other monomer (C) may be further copolymerized as necessary. .
The proportion of the monomer (E) used in the method for producing a copolymer of the present invention is 100 mol% with respect to 100 mol% of all monomers (total of monomers (A), (B) and (E)). It is preferable to set it to 0 mol% or more and 17 mol% or less. Also when using the monomer (C) which is the said arbitrary component, 1 type may be used or 2 types may be used.
The method for producing a copolymer of the present invention is such that each of the monomers used in producing the copolymer is from the viewpoint that the obtained copolymer exhibits more preferable gel resistance and calcium carbonate scale-preventing ability. The composition ratio of the monomer (A) is 8 mol% or more and 18 mol% or less, the monomer (B) is 82 mol% or more and 92 mol% or less, with respect to 100 mol% of all monomers. The monomer (C) is more preferably 0 to 10 mol%. More preferably, the monomer (A) is 9 to 15 mol%, the monomer (B) is 85 to 91 mol%, and the monomer (C) is 0 to 6 mol. Particularly preferably, the monomer (A) is 10 mol% or more and 13 mol% or less, the monomer (B) is 87 mol% or more and 90 mol% or less, and the monomer (C) is Is 0 to 3 mol%. The total amount of the monomers (A), (B) and (C) is 100 mol%.

<Initiator>
In the method for producing a copolymer of the present invention, the monomers (A), (B), and (C) (sometimes referred to as a monomer composition) are polymerized in the presence of a polymerization initiator. preferable.
As the initiator, known ones can be used, for example, hydrogen peroxide; persulfates such as sodium persulfate, potassium persulfate, ammonium persulfate; dimethyl 2,2′-azobis (2-methylpro Pionate), 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-Methylpropionamidine) dihydrochloride, 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] n hydrate, 2,2′-azobis [2- (2- Imidazoline- 2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 1,1′-azobis (cyclohexane-1-carbohydrate) Suitable are azo compounds such as nitrile); organic peroxides such as benzoyl peroxide, lauroyl peroxide, peracetic acid, di-t-butyl peroxide, cumene hydroperoxide, and the like. Among these polymerization initiators, since the gel resistance of the resulting polymer tends to be improved, it is preferable to use a persulfate as described later.
The amount of the initiator used is not particularly limited as long as it is an amount capable of initiating copolymerization of the monomers (A) and (B) and, if necessary, other monomers (C). Except for cases, it is 15 g or less, more preferably 1 to 12 g, based on 1 mol of all monomer components consisting of monomers (A) and (B) and other monomer (C) if necessary. Preferably there is.

<Chain transfer agent>
In the method for producing a copolymer of the present invention, a chain transfer agent may be used as a molecular weight regulator of the polymer as long as it does not adversely affect polymerization. Specific examples of the chain transfer agent include mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropion, 3-mercaptopropion, thiomalic acid, octyl thioglycolate, octyl 3-mercaptopropionate, 2- Thiol chain transfer agents such as mercaptoethanesulfonic acid, n-dodecyl mercaptan, octyl mercaptan, butylthioglycolate; halides such as carbon tetrachloride, methylene chloride, bromoform, bromotrichloroethane; Secondary alcohol; phosphorous acid, hypophosphorous acid, and salts thereof (sodium hypophosphite, potassium hypophosphite, etc.), sulfurous acid, bisulfite, dithionite, metabisulfite, and salts thereof ( Sodium bisulfite, potassium bisulfite, sub Sodium dithionite, potassium dithionite, sodium metabisulfite, metabisulfite potassium, etc.) and the like, and the like lower oxides and salts thereof. The chain transfer agent may be used alone or in the form of a mixture of two or more.
The use of a chain transfer agent has the advantage that the copolymer to be produced can be prevented from having a higher molecular weight than necessary, and a low molecular weight copolymer can be produced efficiently. Among these, in the copolymerization reaction according to the present invention, it is preferable to use bisulfites as described above. Thereby, it becomes possible to introduce a sulfonic acid group quantitatively to the end of the main chain of the copolymer to be obtained, and it is possible to improve the gel resistance. Further, it is preferable to use bisulfites as the chain transfer agent because the color tone of the copolymer (composition) can be improved.
In the production method of the present invention, the addition amount of the chain transfer agent is not limited as long as the monomer (A), (B) and, if necessary, the other monomer (C) is polymerized satisfactorily. Unless otherwise specified below, it is preferably 1 to 1 mol of all monomer components consisting of monomers (A) and (B), and other monomer (C) if necessary. -20 g, more preferably 2-15 g.

<Preferable combination of initiator and chain transfer agent (also referred to as initiator system)>
In the method for producing a copolymer of the present invention, it is preferable to use a combination of one or more persulfates and bisulfites as an initiator system. As a result, a sulfonic acid group is quantitatively introduced into a terminal or a side chain, and a low molecular weight water-soluble polymer having excellent gel resistance in addition to dispersibility and chelating ability is obtained. Can be expressed. By adding bisulfites to the initiator system in addition to the persulfate, it is possible to suppress the resulting polymer from having a higher molecular weight than necessary, and to efficiently produce a low molecular weight polymer.

Specific examples of the persulfate include sodium persulfate, potassium persulfate, and ammonium persulfate.
In the present invention, bisulfites are as described above, and specific examples include sodium bisulfite, potassium bisulfite, and ammonium bisulfite.
When the above-mentioned persulfate and bisulfite are used in combination, the addition ratio of 0.1 to 5 parts by weight, preferably 0.2 to 3 parts by weight of bisulfite is 1 part by weight of persulfate. Preferably it exists in the range of 0.2-2 mass parts. When the amount of bisulfite is less than 0.1 part by mass with respect to 1 part by mass of persulfate, the effect of bisulfite tends to decrease. Therefore, the introduction amount of the sulfonic acid group at the terminal of the polymer is lowered, and the gel resistance of the copolymer tends to be lowered. Further, the weight average molecular weight of the (meth) acrylic acid copolymer tends to be high. On the other hand, when the amount of bisulfite exceeds 5 parts by mass with respect to 1 part by mass of persulfate, the bisulfite is excessively supplied in the polymerization reaction system in such a state that the effect of bisulfite is not obtained as much as the addition ratio. Tend to be used (wasted). For this reason, excess bisulfites are decomposed in the polymerization reaction system, and a large amount of sulfurous acid gas is generated. In addition, many impurities in the (meth) acrylic acid copolymer are generated, and the performance of the resulting (meth) acrylic copolymer tends to be lowered. In addition, impurities tend to precipitate during holding at a low temperature.

  When using the above-mentioned persulfate and bisulfite, the total amount of persulfate and bisulfite is 2 to 20 g, preferably 2 to 15 g, more preferably, per mole of monomer. 3 to 10 g, more preferably 4 to 8 g. When the addition amount of the persulfate and bisulfite is less than 2 g, the molecular weight of the resulting polymer tends to increase. In addition, the sulfonic acid group introduced into the terminal of the resulting (meth) acrylic acid copolymer tends to decrease. On the other hand, when the addition amount exceeds 20 g, the effects of persulfate and bisulfite cannot be obtained as the addition amount increases, and conversely, the purity of the resulting (meth) acrylic acid copolymer decreases. There is a tendency.

  The persulfate may be added in the form of a persulfate solution (preferably an aqueous solution) dissolved in a solvent described later, preferably water. The concentration when used as the persulfate solution (preferably an aqueous solution) is 1 to 35% by mass, preferably 5 to 35% by mass, and more preferably 10 to 30% by mass. Here, when the concentration of the persulfate solution is less than 1% by mass, the concentration of the product decreases, and transportation and storage become complicated. On the other hand, when the concentration of the persulfate solution exceeds 35% by mass, handling becomes difficult.

  The bisulfites may be added in the form of a bisulfite solution (preferably an aqueous solution) after being dissolved in a solvent described later, preferably water. The concentration when used as the bisulfite solution (preferably an aqueous solution) is 10 to 42% by mass, preferably 20 to 42% by mass, and more preferably 32 to 42% by mass. Here, when the concentration of the bisulfite solution is less than 10% by mass, the concentration of the product is lowered, and transportation and storage become complicated. On the other hand, when the concentration of the bisulfite solution exceeds 42% by mass, handling becomes difficult.

<Other additives>
In the method for producing a copolymer of the present invention, as an additive other than an initiator and a chain transfer agent that can be used in a polymerization reaction system when the monomer is polymerized in an aqueous solution, the action of the present invention An appropriate amount of an appropriate additive can be added within a range that does not affect the effect. For example, heavy metal concentration adjusting agents, pH adjusting agents and the like are used.
The heavy metal concentration adjusting agent is not particularly limited, and a polyvalent metal compound or a simple substance can be used. Specifically, vanadium oxytrichloride, vanadium trichloride, vanadyl oxalate, vanadyl sulfate, vanadic anhydride, ammonium metavanadate, ammonium sulfate hypovanadas [(NH4) 2SO4 · VSO4 · 6H2O], ammonium sulfate vanadas [(NH4 ) V (SO4) 2 · 12H2O], copper (II) acetate, copper (II), copper (II) bromide, copper (II) acetyl acetate, cupric ammonium chloride, ammonium copper chloride, copper carbonate, copper chloride (II), copper citrate (II), copper formate (II), copper hydroxide (II), copper nitrate, copper naphthenate, copper oleate (II), copper maleate, copper phosphate, copper sulfate (II ), Cuprous chloride, copper (I) cyanide, copper iodide, copper (I) oxide, copper thiocyanate, iron acetyl acetonate, iron ammonium citrate, Ferric ammonium oxalate, ammonium iron sulfate, ammonium ferric sulfate, iron citrate, iron fumarate, iron maleate, ferrous lactate, ferric nitrate, iron pentacarbonyl, ferric phosphate, Water-soluble polyvalent metal salts such as ferric pyrophosphate; polyvalent metal oxides such as vanadium pentoxide, copper (II) oxide, ferrous oxide, ferric oxide; iron (III) sulfide, iron sulfide ( II), polyvalent metal sulfides such as copper sulfide; copper powder and iron powder.

  In the method for producing a copolymer of the present invention, it is desirable that the obtained (meth) acrylic acid copolymer has a heavy metal ion concentration of 0.05 to 10 ppm. It is desirable to add an appropriate amount. Furthermore, the inventors of the present invention made a reaction vessel made of glass lining having excellent corrosion resistance on the inner wall surface of a reaction vessel made of existing steel or copper-based alloy, a vessel made of SUS (slenless), and a stirrer. In the production conditions of the present invention, an appropriate amount of heavy metal ions as defined above, particularly iron ions, was eluted (supplied) into the reaction solution from SUS, which is a material such as a container. . This is advantageous in terms of cost effectiveness. In the production method of the present invention, when such a reaction apparatus such as a SUS reaction vessel or a stirring blade is used, the same operational effects as in the case of adding the heavy metal concentration adjusting agent can be obtained. Although there is no problem even if the reaction vessel is made of existing steel or copper base alloy, there is a possibility that a heavy metal ion concentration is eluted. In such a case, since a color due to heavy metal appears, an operation for removing such heavy metal ions is necessary, which is uneconomical. Moreover, there is no problem even if the reaction vessel is subjected to glass lining processing or the like, and a heavy metal concentration adjusting agent may be used if necessary.

<Polymerization solvent>
In the method for producing the copolymer of the present invention, the above monomers are usually polymerized in a solvent. In this case, the solvent used in the polymerization reaction system is water, alcohol, glycol, glycerin, polyethylene glycol. Aqueous solvents such as the like are preferred, and water is particularly preferred. These may be used alone or in combination of two or more. Moreover, in order to improve the solubility of the monomer in the solvent, an organic solvent may be appropriately added as long as it does not adversely affect the polymerization of each monomer.
Specifically, the organic solvent is selected from one or more types selected from lower alcohols such as methanol and ethanol; amides such as dimethylformaldehyde; ethers such as diethyl ether and dioxane; sell.
The amount of the solvent used is in the range of 40 to 200 mass%, preferably 45 to 180 mass%, more preferably 50 to 150 mass%, based on the total amount of monomers. When the amount of the solvent used is less than 10% by mass, the molecular weight becomes high. On the other hand, when the usage-amount of this solvent exceeds 200 mass%, the density | concentration of the manufactured (meth) acrylic-acid type copolymer will become low, and solvent removal will be needed depending on the case. It should be noted that most or all of the solvent may be charged into the reaction vessel at the initial stage of polymerization. For example, a part of the solvent may be added (dropped) appropriately into the reaction system alone during the polymerization. The monomer component, the initiator component, and other additives may be appropriately added (dropped) into the reaction system during the polymerization together with these components in the form of being previously dissolved in a solvent.

<Polymerization temperature>
The polymerization temperature in the polymerization of the monomer is not particularly limited. Since a polymer can be produced efficiently, the polymerization temperature is preferably 50 ° C. or higher, and more preferably 70 ° C. or higher. The polymerization temperature is preferably 99 ° C. or lower, and more preferably 95 ° C. or lower. In addition, since the polymerization time takes too long, productivity is lowered. On the other hand, when the polymerization temperature is 99 ° C. or lower, it is preferable that bisulfite can be prevented from being decomposed and generating a large amount of sulfurous acid gas when bisulfite is used as an initiator system. The polymerization temperature here refers to the temperature of the reaction solution in the reaction system.

  In particular, in the case of the method of starting polymerization from room temperature (room temperature starting method), for example, when polymerization is performed in 180 minutes per batch (180 minute formulation), within 70 minutes, preferably 0 to 50 It is made to reach the set temperature (within the range of the polymerization temperature defined above, preferably 70 to 90 ° C., more preferably about 80 to 90 ° C.) in minutes, more preferably 0 to 30 minutes. Thereafter, it is desirable to maintain the set temperature until the polymerization is completed. When the temperature rise time is out of the above range, the resulting (meth) acrylic acid copolymer may have a high molecular weight. In addition, although the example of the polymerization time is shown as 180 minutes, if the prescription of the polymerization time is different, referring to the example, the temperature increase time is set so that the ratio of the temperature increase time to the polymerization time is the same. Is desirable.

<Reaction system pressure, reaction atmosphere>
When polymerizing the monomer, the pressure in the reaction system is not particularly limited. The pressure may be any of normal pressure (atmospheric pressure), reduced pressure, and increased pressure. Preferably, when bisulfite is used as the initiator system, the polymerization is carried out under normal pressure or under pressure in order to prevent the release of sulfurous acid gas during polymerization and to reduce the molecular weight. It is good. In addition, when polymerization is performed under normal pressure (atmospheric pressure), it is not necessary to provide a pressurizing device or a decompressing device, and it is not necessary to use a pressure-resistant reaction vessel or pipe. For this reason, normal pressure (atmospheric pressure) is preferable from the viewpoint of production cost. That is, optimal pressure conditions may be set as appropriate depending on the intended use of the resulting (meth) acrylic acid copolymer.
The atmosphere in the reaction system may be maintained in an air atmosphere, but an inert atmosphere is preferable. For example, it is desirable to replace the inside of the system with an inert gas such as nitrogen before the start of polymerization. Thereby, atmospheric gas (for example, oxygen gas etc.) in the reaction system dissolves in the liquid phase and acts as a polymerization inhibitor. As a result, the initiator (persulfate, etc.) is prevented from being deactivated and reduced, and the molecular weight can be further reduced.

<Neutralization degree during polymerization>
In the production method of the present invention, the polymerization reaction of the monomer is preferably performed under acidic conditions. By carrying out under acidic conditions, the increase in the viscosity of the aqueous solution of the polymerization reaction system can be suppressed, and a low molecular weight (meth) acrylic acid copolymer can be produced satisfactorily. In addition, since the polymerization reaction can proceed under a higher concentration condition than before, the production efficiency can be significantly increased. In particular, by reducing the degree of neutralization during polymerization to 0 to 25 mol%, the effect of reducing the initiator amount can be synergistically increased, and the effect of reducing impurities can be significantly improved. Furthermore, it is desirable to adjust the reaction solution during polymerization so that the pH at 25 ° C. is 1-6. By carrying out the polymerization reaction under such acidic conditions, the polymerization can be carried out at a high concentration and in one stage. Therefore, it is possible to omit the concentration step which was necessary in some cases in the conventional manufacturing method. Therefore, the productivity of the (meth) acrylic acid copolymer is greatly improved, and an increase in production cost can be suppressed.

  Among the above acidic conditions, the pH of the reaction solution during polymerization at 25 ° C. is 1 to 6, preferably 1 to 5, and more preferably 1 to 4. When the pH is less than 1, for example, when bisulfite is used as an initiator system, generation of sulfurous acid gas and corrosion of the apparatus may occur. On the other hand, when the pH exceeds 6, when bisulfites are used as the initiator system, the efficiency of bisulfites decreases and the molecular weight increases.

  Examples of the pH adjuster for adjusting the pH of the reaction solution during the polymerization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth metal waters such as calcium hydroxide and magnesium hydroxide. Examples thereof include oxides, organic amine salts such as ammonia, monoethanolamine, and triethanolamine. These may be used alone or in combination of two or more. Among these, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are preferable, and sodium hydroxide is particularly preferable. In the present invention, these may be simply referred to as “pH adjusting agent” or “neutralizing agent”.

  The degree of neutralization during the polymerization is 0 to 25 mol%, preferably 1 to 15 mol%, more preferably 2 to 10 mol%. If the degree of neutralization during the polymerization is within such a range, it is possible to perform the copolymerization best, to reduce impurities, and to produce a polymer having good gel resistance. Moreover, the viscosity of the aqueous solution of the polymerization reaction system does not increase, and a low molecular weight polymer can be produced satisfactorily. In addition, since the polymerization reaction can proceed under a higher concentration condition than before, the production efficiency can be significantly increased. On the other hand, when the degree of neutralization during polymerization exceeds 25 mol%, the chain transfer efficiency of bisulfites may decrease and the molecular weight may increase. In addition, as the polymerization proceeds, the viscosity of the aqueous solution in the polymerization reaction system increases significantly. As a result, the molecular weight of the resulting polymer increases more than necessary, and a low molecular weight polymer cannot be obtained. Furthermore, the effect of reducing the degree of neutralization cannot be fully exhibited, and it may be difficult to significantly reduce impurities.

  The neutralization method here is not particularly limited. For example, a salt of (meth) acrylic acid such as sodium (meth) acrylate may be used as a part of the raw material, and an alkali metal hydroxide such as sodium hydroxide is used as a neutralizing agent. You may neutralize during superposition | polymerization and you may use these together. Moreover, the addition form of the neutralizing agent at the time of neutralization may be solid, or may be an aqueous solution dissolved in an appropriate solvent, preferably water. The concentration of the aqueous solution when the aqueous solution is used is 10 to 60% by mass, preferably 20 to 55% by mass, and more preferably 30 to 50% by mass. When the concentration of the aqueous solution is less than 10% by mass, the concentration of the product decreases, and transportation and storage become complicated. On the other hand, when it exceeds 60 mass%, there exists a possibility of precipitation, and since a viscosity also becomes high, liquid feeding becomes complicated.

<Additional conditions of raw materials>
In the polymerization, the monomer, initiator, chain transfer agent and other additives are previously dissolved in a suitable solvent (preferably the same solvent as the solvent for the liquid to be dropped), As an initiator solution, a chain transfer agent solution, and other additive solutions, with respect to the (aqueous) solvent charged in the reaction vessel (adjusted to a predetermined temperature if necessary) at a predetermined dropping time. It is preferable to polymerize while dropping continuously. Further, a part of the aqueous solvent may be added dropwise later, separately from the initially charged solvent prepared in advance in a container in the reaction system. However, the production method of the present invention is not limited to these. For example, regarding the dropping method, it may be dropped continuously or may be dropped in several portions intermittently. One or two or more of the monomers may be initially charged in part or in whole (that is, it can be considered that all or part of the monomer is added dropwise at the start of polymerization). Also, the dropping rate (dropping amount) of one or more monomers may be dropped constantly (constant amount) from the start to the end of dropping, or may be dropped over time depending on the polymerization temperature or the like. The dropping speed (dropping amount) may be changed. Moreover, even if it does not dripping all the dripping components similarly, you may shift the start time and the end time for every dripping component, or you may shorten or extend dripping time. Thus, the manufacturing method of this invention can be changed suitably in the range which does not impair the effect of this invention. Moreover, when each component is dripped in the form of a solution, you may heat a dripped solution to the same extent as the polymerization temperature in a reaction system. In this way, when the polymerization temperature is kept constant, temperature variation is small and temperature adjustment is easy.

  When bisulfites are used as the initiator system, the molecular weight at the initial stage of polymerization of bisulfites greatly affects the final molecular weight. For this reason, in order to lower the initial molecular weight, 5 to 20% by mass of bisulfite or a solution thereof is added (dropped) within 60 minutes, preferably within 30 minutes, more preferably within 10 minutes from the start of polymerization. desirable. In particular, as described later, this is effective when the polymerization is started from room temperature.

  Moreover, about the dripping time of a bisulfite or its solution in the case of using bisulfite as an initiator system among the dripping components in the case of superposition | polymerization, from the completion | finish of dripping of a monomer (A) and (B) Is preferably 1 to 30 minutes, preferably 1 to 20 minutes, more preferably 1 to 15 minutes. Thereby, the amount of bisulfites after completion | finish of superposition | polymerization can be reduced, and generation | occurrence | production of sulfurous acid gas by this bisulfites and formation of an impurity can be suppressed effectively. For this reason, after the polymerization is completed, impurities formed by dissolving the sulfurous acid gas in the gas phase in the liquid phase can be significantly reduced. When bisulfite remains after the completion of the polymerization, impurities are generated, leading to deterioration of the performance of the polymer and precipitation of impurities when kept at a low temperature. Therefore, it is desirable that the initiator containing the bisulfite is consumed and does not remain at the end of the polymerization.

  Here, when the dropping end time of the bisulfite (solution) can be advanced by less than 1 minute from the dropping end time of the monomers (A) and (B), May remain. In such cases, the end of dropping of the bisulfite or the solution thereof and the end of dropping of the monomers (A) and (B) are simultaneous, or the end of dropping of the bisulfite (solution) is more simple. The case where it is later than the end of dropping of the monomers (A) and (B) is included. In such a case, it tends to be difficult to effectively and effectively suppress the generation of sulfurous acid gas and the formation of impurities, which may adversely affect the thermal stability of the polymer from which the remaining initiator is obtained. On the other hand, when the completion time of the addition of the bisulfite or the solution thereof is more than 30 minutes earlier than the completion time of the addition of the monomers (A) and (B), the bisulfite is consumed by the end of the polymerization. I'm stuck. For this reason, the molecular weight tends to increase. In addition, during the polymerization, the dropping rate of bisulfites is faster than the dropping rate of the monomers (A) and (B), and many of them are dropped in a short time. Tend to occur frequently.

  In addition, among the dropping components in the polymerization, when the bisulfite is used as the initiator system, the dropping end time of the persulfate (solution) is the dropping end time of the monomers (A) and (B). 1 to 30 minutes, preferably 1 to 25 minutes, more preferably 1 to 20 minutes. Thereby, the amount of monomer components remaining after the completion of polymerization can be reduced, and impurities caused by the remaining monomers can be significantly reduced.

  Here, in the case where the dropping end time of the persulfate (solution) can be delayed by less than 1 minute from the dropping end time of the monomers (A) and (B), the monomer component after the completion of the polymerization May remain. In such cases, the end of dropping of the persulfate (solution) and the end of dropping of the monomers (A) and (B) are simultaneous, or the end of dropping of the persulfate (solution) is simpler. The case where it is earlier than the end of dropping of the monomers (A) and (B) is included. In such a case, it tends to be difficult to effectively and effectively suppress the formation of impurities. On the other hand, in the case where the dropping end time of the persulfate (solution) is more than 30 minutes later than the dropping end time of the monomers (A) and (B), the persulfate or the decomposition product thereof is It may remain and form impurities.

<Polymerization time>
In the polymerization, even when bisulfite is used as an initiator system at a low polymerization temperature, it is more important to suppress the generation of sulfurous acid gas and prevent the formation of impurities. For this reason, the total dropping time during the polymerization is preferably 150 to 600 minutes, preferably 180 to 450 minutes, more preferably 210 to 300 minutes. When the total dropping time is less than 150 minutes, the effect of the persulfate solution and the bisulfite solution added as the initiator system tends to decrease. Therefore, the amount of sulfur-containing groups such as sulfonic acid groups introduced into the terminals and side chains tends to decrease with respect to the obtained (meth) acrylic acid copolymer. As a result, the weight average molecular weight of the polymer tends to increase. Moreover, it may occur that bisulfite exists excessively by being dripped in the reaction system in a short time. For this reason, such excessive bisulfite is decomposed to generate sulfurous acid gas, which may be released out of the system or may form impurities. However, it tends to be improved by carrying out the polymerization temperature and the initiator amount in a specific range that is low. On the other hand, when the total dropping time exceeds 600 minutes, the generation of sulfurous acid gas is suppressed, so that the resulting polymer has good performance. However, the productivity of the (meth) acrylic acid copolymer is lowered, and the use application may be limited. The total dropping time here means the time from the start of dropping the first dropping component (not necessarily one component) to the completion of dropping the last dropping component (not necessarily one component).

<Polymerization concentration>
The solid content concentration in the aqueous solution (that is, the polymerization solid content concentration of the monomer) at the time when the dropping of the above components is completed and the polymerization reaction in the polymerization reaction system is completed is preferably 35% by mass or more, more preferably It is 40-70 mass%, More preferably, it is 45-65 mass%. Thus, if the solid content concentration at the end of the polymerization reaction is 35% by mass or more, the polymerization can be carried out at a high concentration and in one stage. Therefore, a low molecular weight (meth) acrylic acid copolymer can be obtained efficiently. For example, the concentration step that was necessary in some cases in the conventional manufacturing method can be omitted. Therefore, the manufacturing efficiency can be greatly increased. As a result, the productivity of the (meth) acrylic acid copolymer is greatly improved, and an increase in production cost can be suppressed.

  Here, when the solid-formation concentration is less than 35% by mass, the productivity of the (meth) acrylic acid copolymer may not be significantly improved. For example, it becomes difficult to omit the concentration step.

  When the solid content concentration is increased in the polymerization reaction system, the viscosity of the reaction solution increases remarkably with the progress of the polymerization reaction, and the weight average molecular weight of the resulting polymer tends to increase significantly. However, by carrying out the polymerization reaction on the acidic side (pH at 25 ° C. is 1 to 6 and the neutralization degree of carboxylic acid is in the range of 0 to 25 mol%), the viscosity of the reaction solution accompanying the progress of the polymerization reaction can be reduced. The rise can be suppressed. Therefore, a polymer having a low molecular weight can be obtained even when the polymerization reaction is carried out under a high concentration condition, and the production efficiency of the polymer can be greatly increased.

  Here, the time point when the polymerization reaction is completed may be a time point when the dropping of all of the dropping components is completed, but preferably refers to a time point when a predetermined aging time has elapsed (polymerization is completed). .

<Aging process>
The aging time is usually 1 to 120 minutes, preferably 5 to 90 minutes, more preferably 10 to 60 minutes. When the aging time is less than 1 minute, the monomer component may remain due to insufficient aging, which may cause impurities due to the residual monomer, resulting in performance degradation. On the other hand, when the aging time exceeds 120 minutes, the polymer solution may be colored. In addition, since the polymerization has already been completed, it is uneconomical to apply a further polymerization temperature.

  Further, during the aging, the polymerization temperature is applied because it is within the polymerization reaction period and is included in the polymerization. Therefore, the temperature here may also be maintained at a constant temperature (preferably the temperature at the end of dropping), or the temperature may be changed over time during aging. Therefore, the polymerization time refers to the above total dropping time + ripening time, and refers to the time required from the first titration start point to the ripening end point.

<Process after polymerization>
In the method for producing a (meth) acrylic acid copolymer according to the present invention, the polymerization is preferably performed under acidic conditions as described above. Therefore, the neutralization degree (carboxylic acid final neutralization degree) of the carboxylic acid of the (meth) acrylic acid copolymer to be obtained is determined by appropriately adding an appropriate alkaline component as a post-treatment as needed after the polymerization is completed. You may set to a predetermined range by adding.

  The final neutralization degree is not particularly limited because it varies depending on the intended use. For example, when used as a detergent builder for a weakly acidic detergent said to be gentle to the skin, it may be used without being neutralized while remaining acidic. Moreover, when using it for a neutral detergent, an alkaline detergent, etc., you may neutralize with an alkali component as a post-process, and you may use after neutralizing to carboxylic acid neutralization degree 90 mol% or more. In particular, the final neutralization degree of carboxylic acid when used as an acidic polymer is preferably 0 to 75 mol%, more preferably 0 to 70 mol%. When used as a neutral or alkaline polymer, the degree of final neutralization of carboxylic acid is preferably 75 to 100 mol%, more preferably 85 to 99 mol%. Further, when the final neutralization degree when used as a neutral or alkaline polymer exceeds 99 mol%, the aqueous polymer solution may be colored.

  Examples of the alkali component include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; ammonia, monoethanolamine, diethanolamine, Examples thereof include those represented by organic amines such as triethanolamine. Only one type of alkali component may be used, or a mixture of two or more types may be used.

  In addition, when the reaction system is used without being neutralized as described above, since the reaction system is acidic, toxic sulfurous acid gas (SO2 gas) remains in the atmosphere in the reaction system. There may be. In such a case, it is desirable to decompose by adding a peroxide such as hydrogen peroxide or to expel it by introducing (blowing) air or nitrogen gas.

<Other manufacturing conditions>
The (meth) acrylic acid-based copolymer of the present invention may be produced in a batch manner or in a continuous manner.

[Copolymer composition of the present invention]
The copolymer composition of the present invention contains the (meth) acrylic acid copolymer of the present invention as an essential component, and may contain only the copolymer of the present invention. Contains one or more selected from agent residues, residual monomers, by-products during polymerization, and moisture. It is preferable that the copolymer composition of this invention contains 1-100 mass% of copolymers of this invention with respect to 100 mass% of copolymer compositions of this invention. One of the forms of a preferable copolymer composition is a form which contains 40-60 mass% of copolymers, and contains 40-60 mass% of water.

[Usage of copolymer and copolymer composition of the present invention]
The copolymer (or copolymer composition) of the present invention comprises a water treatment agent, a fiber treatment agent, a dispersant, a detergent builder (or a detergent composition), a scale inhibitor (scale inhibitor), and a metal ion sealing agent. , Thickeners, various binders, emulsifiers, skin care agents, hair care agents and the like. As a detergent builder, it can be used by adding to detergents for various uses such as clothing, tableware, residential, hair, body, toothpaste, and automobile.

<Water treatment agent>
The copolymer (or copolymer composition) of the present invention can be used as a water treatment agent. If necessary, the water treatment agent may contain a polymerized phosphate, phosphonate, anticorrosive, slime control agent, and chelating agent as other compounding agents.

  The water treatment agent is useful for scale prevention in a cooling water circulation system, a boiler water circulation system, a seawater desalination apparatus, a reverse osmosis membrane treatment apparatus, a pulp digester, a black liquor concentration tank, and the like. Further, any appropriate water-soluble polymer may be included as long as it does not affect the performance and effects.

<Fiber treatment agent>
The copolymer (or copolymer composition) of the present invention can be used as a fiber treatment agent. The fiber treatment agent includes at least one selected from the group consisting of a dye, a peroxide, and a surfactant, and the copolymer (or copolymer composition) of the present invention.

  The content of the copolymer of the present invention in the fiber treatment agent is preferably 1 to 100% by weight, more preferably 5 to 100% by weight, based on the entire fiber treatment agent. Further, any appropriate water-soluble polymer may be included as long as the performance and effects are not affected.

  Below, the compounding example of the fiber processing agent which is closer to embodiment is shown. This fiber treatment agent can be used in the steps of refining, dyeing, bleaching and soaping in fiber treatment. Examples of dyeing agents, peroxides and surfactants include those usually used for fiber treatment agents.

  The blending ratio of the copolymer of the present invention and at least one selected from the group consisting of a dye, a peroxide and a surfactant is, for example, for improving the whiteness, color unevenness, and dyeing tempering of the fiber. Includes 0.1 to 100 weight percent of at least one selected from the group consisting of a staining agent, a peroxide and a surfactant with respect to 1 weight part of the copolymer of the present invention in terms of a pure amount of the fiber treatment agent. It is preferable to use a composition blended at a ratio of parts as a fiber treatment agent.

  Arbitrary appropriate fiber can be employ | adopted as a fiber which can use the said fiber processing agent. Examples thereof include cellulosic fibers such as cotton and hemp, chemical fibers such as nylon and polyester, animal fibers such as wool and silk, semi-synthetic fibers such as human silk, and woven fabrics and blended products thereof.

  When the fiber treatment agent is applied to the refining process, it is preferable to blend the copolymer of the present invention with an alkali agent and a surfactant. When applied to the bleaching step, it is preferable to blend the copolymer of the present invention, a peroxide, and a silicic acid-based agent such as sodium silicate as a decomposition inhibitor for the alkaline bleaching agent.

<Inorganic pigment dispersant>
The copolymer (or copolymer composition) of the present invention can be used as an inorganic pigment dispersant. In the inorganic pigment dispersant, condensed phosphoric acid and its salt, phosphonic acid and its salt, and polyvinyl alcohol may be used as other compounding agents as required.

  The content of the copolymer of the present invention in the inorganic pigment dispersant is preferably 5 to 100% by weight with respect to the whole inorganic pigment dispersant. Further, any appropriate water-soluble polymer may be included as long as it does not affect the performance and effect.

  The inorganic pigment dispersant can exhibit good performance as a dispersant for heavy or light calcium carbonate or clay inorganic pigment used in paper coating. For example, by adding a small amount of an inorganic pigment dispersant to an inorganic pigment and dispersing it in water, high concentration calcium carbonate having low viscosity and high fluidity and good aging stability of their performance. High concentration inorganic pigment slurries such as slurries can be produced.

  When the inorganic pigment dispersant is used as a dispersant for an inorganic pigment, the amount of the inorganic pigment dispersant used is preferably 0.05 to 2.0 parts by weight with respect to 100 parts by weight of the inorganic pigment. When the amount of the inorganic pigment dispersant used is within the above range, a sufficient dispersion effect can be obtained, and an effect commensurate with the addition amount can be obtained, which can be economically advantageous.

<Detergent Builder>
The copolymer and copolymer composition of the present invention can be used as a detergent builder. As a detergent builder, it can be used by adding to detergents for various uses such as clothing, tableware, residential, hair, body, toothpaste, and automobile.

(Detergent composition)
The copolymer (or copolymer composition) of the present invention can also be added to a detergent composition.

  The content of the copolymer in the detergent composition is not particularly limited. However, from the viewpoint that excellent builder performance can be exhibited, the content of the copolymer is preferably 0.1 to 15% by mass, more preferably 0.3%, based on the total amount of the detergent composition. It is 10 mass%, More preferably, it is 0.5-5 mass%.

  Detergent compositions used in detergent applications usually include surfactants and additives used in detergents. Specific forms of these surfactants and additives are not particularly limited, and conventionally known knowledge can be appropriately referred to in the detergent field. The detergent composition may be a powder detergent composition or a liquid detergent composition.

  The surfactant is one or more selected from the group consisting of an anionic surfactant, a nonionic surfactant, a cationic surfactant and an amphoteric surfactant. When two or more kinds are used in combination, the total amount of the anionic surfactant and the nonionic surfactant is preferably 50% by mass or more, more preferably 60% by mass with respect to the total amount of the surfactant. Or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

  Examples of the anionic surfactant include alkylbenzene sulfonate, alkyl ether sulfate, alkenyl ether sulfate, alkyl sulfate, alkenyl sulfate, α-olefin sulfonate, α-sulfo fatty acid or ester salt, alkane sulfonate. , Saturated fatty acid salt, unsaturated fatty acid salt, alkyl ether carboxylate, alkenyl ether carboxylate, amino acid type surfactant, N-acyl amino acid type surfactant, alkyl phosphate ester or salt thereof, alkenyl phosphate ester or Its salts are preferred. An alkyl group such as a methyl group may be branched from the alkyl group or alkenyl group in these anionic surfactants.

  Nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene alkenyl ethers, polyoxyethylene alkyl phenyl ethers, higher fatty acid alkanolamides or alkylene oxide adducts thereof, sucrose fatty acid esters, alkyl glycoxides, fatty acid glycerin mono Esters, alkylamine oxides and the like are preferred. An alkyl group such as a methyl group may be branched from the alkyl group or alkenyl group in these nonionic surfactants.

  As the cationic surfactant, a quaternary ammonium salt or the like is suitable. As the amphoteric surfactant, a carboxyl type amphoteric surfactant, a sulfobetaine type amphoteric surfactant, and the like are suitable. The alkyl group and alkenyl group in these cationic surfactants and amphoteric surfactants may be branched from an alkyl group such as a methyl group.

  The blending ratio of the surfactant is usually 10 to 60% by mass, preferably 15 to 50% by mass, more preferably 20 to 45% by mass, particularly preferably based on the total amount of the detergent composition. Is 25-40 mass%. If the surfactant content is too small, sufficient detergency may not be achieved, and if the surfactant content is too high, the economy may be reduced.

  Additives include anti-redeposition agent to prevent redeposition of contaminants such as alkali builder, chelate builder, sodium carboxymethyl cellulose, stain inhibitor such as benzotriazole and ethylene-thiourea, soil release agent, color transfer Inhibitors, softeners, alkaline substances for pH adjustment, fragrances, solubilizers, fluorescent agents, colorants, foaming agents, foam stabilizers, polishes, bactericides, bleaching agents, bleaching aids, enzymes, dyes A solvent or the like is preferable. In the case of a powder detergent composition, it is preferable to blend zeolite.

  The detergent composition may contain other detergent builders in addition to the copolymer (or copolymer composition) of the present invention. Examples of other detergent builders include, but are not limited to, alkali builders such as carbonates, hydrogen carbonates, and silicates, tripolyphosphates, pyrophosphates, bow glass, nitrilotriacetate, ethylenediaminetetraacetate, Examples thereof include acid salts, (meth) acrylic acid copolymer salts, acrylic acid-maleic acid copolymers, chelate builders such as fumarate and zeolite, and carboxyl derivatives of polysaccharides such as carboxymethylcellulose. Examples of the counter salt used in the builder include alkali metals such as sodium and potassium, ammonium and amine.

  The total blending ratio of the additive and other builder for detergent is usually preferably 0.1 to 50% by mass with respect to 100% by mass of the cleaning composition. More preferably, it is 0.2-40 mass%, More preferably, it is 0.3-35 mass%, Most preferably, it is 0.4-30 mass%, Most preferably, it is 0.5-20 mass% or less. It is. If the additive / other detergent builder content is less than 0.1% by mass, sufficient detergent performance may not be achieved, and if it exceeds 50% by mass, the economy may be reduced.

  In addition, the concept of the above-mentioned detergent composition includes specific detergents such as synthetic detergents for household detergents, textile industry and other industrial detergents, hard surface cleaners, and bleaching detergents that enhance one of the components. Detergents that are only used are also included.

  When the detergent composition is a liquid detergent composition, the amount of water contained in the liquid detergent composition is usually preferably 0.1 to 75% by mass, more preferably based on the total amount of the liquid detergent composition. Is 0.2 to 70% by mass, more preferably 0.5 to 65% by mass, even more preferably 0.7 to 60% by mass, particularly preferably 1 to 55% by mass, Preferably it is 1.5-50 mass%.

  When the detergent composition is a liquid detergent composition, the detergent composition preferably has a kaolin turbidity of 200 mg / L or less, more preferably 150 mg / L or less, and even more preferably 120 mg / L or less. Especially preferably, it is 100 mg / L or less, Most preferably, it is 50 mg / L or less.

<Measurement method of kaolin turbidity>
A sample (liquid detergent) uniformly stirred in a 50 mm square cell having a thickness of 10 mm was removed and air bubbles were removed. Then, a NDU2000 manufactured by Nippon Denshoku Co., Ltd. Kaolin turbidity: mg / L) is measured.
Proteases, lipases, cellulases, and the like are suitable as enzymes that can be incorporated into the cleaning composition. Of these, proteases, alkaline lipases, and alkaline cellulases that are highly active in an alkaline cleaning solution are preferred.
The amount of the enzyme added is preferably 5% by mass or less with respect to 100% by mass of the cleaning composition. If it exceeds 5% by mass, improvement in detergency cannot be seen, and the economy may be reduced.
As the alkali builder, silicate, carbonate, sulfate and the like are preferable. As the chelate builder, diglycolic acid, oxycarboxylate, EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), STPP (sodium tripolyphosphate), citric acid and the like are preferable. Other water-soluble polycarboxylic acid-based polymers other than the copolymer in the present invention may be used.
The above detergent composition should be a detergent with excellent dispersibility, extremely high quality agent performance and excellent stability that is less likely to cause performance degradation when stored for a long time and precipitation of impurities when held at low temperatures. Can do.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by mass” and “%” means “% by mass”.
The determination of the monomer and the measurement and evaluation of the weight average molecular weight of the copolymer were carried out according to the following methods.

<Monomer determination method>
The measurement of the content of monomers and the like was performed using liquid chromatography under the following conditions.
Apparatus: L-7000 series detector manufactured by Hitachi, Ltd .: UV detector L-7400 manufactured by Hitachi, Ltd.
Column: Shodex RSpak DE-413L manufactured by Showa Denko KK
Flow rate: 1.0 ml / min
Column temperature: 40 ° C
Mobile phase: 0.1% aqueous phosphoric acid solution.

<Measurement conditions of weight average molecular weight>
Equipment: HLC-8320GPC manufactured by Tosoh Corporation
Detector: RI
Column: Shodex Asahipak GF-310-HQ, GF-710-HQ, GF-1G 7B manufactured by Showa Denko KK
Column temperature: 40 ° C
Flow rate: 0.5 ml / min
Calibration curve: POLYACRYLIC ACID STANDARD made by Soka Science Co., Ltd.
Eluent: 0.1N sodium acetate aqueous solution.

<Measurement of solid content>
In an oven heated to 120 ° C., the copolymer of the present invention (1.0 g of the copolymer composition of the present invention plus 1.0 g of water) was allowed to stand for 2 hours for drying treatment. From the weight change before and after drying, the solid content (%) and the volatile component (%) were calculated.

<Measurement of gel resistance>
It measured by the above-mentioned gel resistance test.

<Measurement of chelating ability (calcium ion capturing ability)>
In a beaker with a capacity of 100 cc, 50 g of a 0.001 mol / L calcium chloride aqueous solution was sampled, and 10 mg of the copolymer was added in terms of solid content. Next, the pH of this aqueous solution was adjusted to 9-11 with dilute sodium hydroxide. Then, 1 ml of 4 mol / L potassium chloride aqueous solution was added as a calcium ion electrode stabilizer under stirring.
Using an ion analyzer (EA920 type, manufactured by Orion) and a calcium ion electrode (93-20 type, manufactured by Orion), free calcium ions were measured, and how many milligrams of calcium in terms of calcium carbonate per 1 g of copolymer. Whether ions were chelated (calcium ion capturing ability, which is one type of chelating ability) was calculated. The unit of calcium ion scavenging ability is “mgCaCO ₃ / g”.

<Example 1>
In a 2.5 L SUS316 separable flask equipped with a thermometer, reflux condenser, and stirrer, 355.0 g of pure water and 0.0319 g of molle salt (the mass of iron (II) relative to the total charged amount (here The total charge refers to the weight of all inputs including the neutralization step after completion of polymerization. The same shall apply hereinafter.) 3 ppm) was added, and the temperature was raised to 87 ° C. with stirring (initial value). Preparation).
Next, in a polymerization reaction system at a constant temperature of 87 ° C. under stirring, 522.7 g (5.8 mol) of an 80% by weight aqueous acrylic acid solution (hereinafter referred to as 80% AA), 40% by weight 3-allyloxy-2-hydroxy-1 -431.6 g (0.79 mol) of sodium propanesulfonate aqueous solution (hereinafter referred to as 40% HAPS), 176.0 g of 15 mass% sodium persulfate aqueous solution (hereinafter referred to as 15% NaPS), 35 mass% sodium bisulfite aqueous solution 28.3 g (hereinafter referred to as 35% SBS) was dropped from separate dropping nozzles. The dropping time was 80 minutes AA for 180 minutes, 40% HAPS for 150 minutes, 35% SBS for 170 minutes, and 15% NaPS for 200 minutes. Moreover, regarding the dripping start time, all dripping liquids started dripping simultaneously. For 40% HAPS, 107.9 g was continuously dropped at a constant dropping rate in 0-20 minutes, and the remaining 323.7 g was continuously dropped at a constant dropping rate in 20-150 minutes. As for 15% NaPS, 88.0 g was continuously dropped at a constant dropping rate from 0 to 130 minutes, and the remaining 88.0 g was continuously dropped at a constant dropping rate from 130 to 200 minutes. 80% AA and 35% SBS were continuously dropped at a constant dropping rate during each dropping time.
After completion of the dropwise addition, the reaction solution was kept at 87 ° C. for 60 minutes to complete the polymerization. Thus, the copolymer composition (polymer composition (1)) of the present invention having a solid content concentration of 45% by mass was obtained (the copolymer contained is referred to as polymer (1)).
The obtained copolymer composition (1) was dried under reduced pressure at room temperature to distill off water, and then ¹ HNMR measurement was performed using heavy water as a solvent. As a result, the polymer main chain terminal was found to be 2.6 ppm and 3.0 ppm. The peaks of methylene and methine groups derived from the introduction of sulfonic acid groups were confirmed.

<Examples 2 to 4 >
In Example 1, except having changed the conditions described in Table 1, it carried out similarly to Example 1, and obtained polymer composition (2)-( 4 ) (The copolymer contained is a polymer (2 ) To ( 4 )).

<Comparative Example 1>
In a 2.5 L SUS316 separable flask equipped with a thermometer, a reflux condenser, and a stirrer, when converted to a mass of iron (II) with respect to 273.2 g of pure water and 0.0267 g of Mole salt (total amount charged) 3 ppm) and the temperature was raised to 87 ° C. with stirring (initial charge).
Next, under stirring, 80% AA 418.9 g (4.7 mol), 40% HAPS 345.2 g (0.63 mol), 15% NaPS 141.0 g, and 35% SBS 90.6 g were placed in a polymerization reaction system at a constant temperature of 87 ° C. It dripped from the separate dripping nozzle. The dropping time was 80 minutes AA for 180 minutes, 40% HAPS for 120 minutes, 35% SBS for 170 minutes, and 15% NaPS for 200 minutes. Moreover, regarding the dripping start time, all dripping liquids started dripping simultaneously. For 40% HAPS, 85.8 g was continuously dropped at a constant dropping rate in 0-15 minutes, and the remaining 259.4 g was continuously dropped at a constant dropping rate in 15-120 minutes. As for 15% NaPS, 70.5 g was continuously dropped at a constant dropping rate from 0 to 130 minutes, and the remaining 70.5 g was continuously dropped from 130 to 200 minutes at a constant dropping rate. 80% AA and 35% SBS were continuously dropped at a constant dropping rate during each dropping time.
After completion of the dropwise addition, the reaction solution was kept at 87 ° C. for 60 minutes to complete the polymerization. In this way, a comparative polymer composition (comparative polymer composition (1)) having a solid content concentration of 46% by mass was obtained (referred to as the comparative polymer (1)).
The obtained comparative polymer composition (1) was dried at room temperature under reduced pressure to distill off water, and ¹ HNMR measurement was carried out using heavy water as a solvent. As a result, the polymer main chain terminal was found to be 2.6 ppm and 3.0 ppm. The peaks of methylene and methine groups derived from the introduction of sulfonic acid groups were confirmed.

<Comparative Examples 2-3 , 5 >
In Comparative Example 1, comparative polymer compositions (2) to (3) were obtained in the same manner as Comparative Example 1 except that the conditions described in Table 2 were changed. (2) to (3)).
Further, a comparative polymer composition (5) was obtained in the same manner as in Example 1 except that the conditions described in Comparative Example 5 in Table 2 were changed (in each case, the copolymer contained was compared with Comparative Polymer (5). And).

<Comparative Example 4>
Into a 2.5 L SUS316 separable flask equipped with a thermometer, reflux condenser, and stirrer was charged 119.4 g of pure water and 97.3 g (0.18 mol%) of 40% HAPS, and refluxed under boiling with stirring. The temperature was raised until it reached a state (initial charge).
Next, 41.1 g (0.46 mol) of 80% AA, 1040.7 g (4.1 mol) of 37% sodium acrylate (hereinafter referred to as 37% SA), 40% HAPS340 in a polymerization reaction system in a boiling point reflux state with stirring. 4 g (0.63 mol), 140.7 g of 15% NaPS, and 46.7 g of 35% hydrogen peroxide (hereinafter referred to as 35% HP) were dropped from separate dropping nozzles. The dropping time was 80% AA and 37% SA for 120 minutes, 40% HAPS for 90 minutes, 15% NaPS for 200 minutes, and 35% HP for 120 minutes. Moreover, regarding the dripping start time, all dripping liquids started dripping simultaneously. As for 15% NaPS, 66.6 g was continuously dropped at a constant dropping rate from 0 to 90 minutes, and the remaining 74.1 g was continuously dropped at a constant dropping rate from 90 to 140 minutes. 80% AA, 40% HAPS, and 35% SBS were dripped continuously at a constant drip rate during each drip time.
After completion of the dropwise addition, the reaction solution was maintained at the boiling point reflux state for an additional 30 minutes and aged to complete the polymerization. In this way, a comparative polymer composition (comparative polymer composition (4)) having a solid content concentration of 37% by mass was obtained (referred to as the comparative polymer (4)).
The obtained comparative polymer composition (4) was dried at room temperature under reduced pressure to distill off water, and then ¹ HNMR measurement was carried out using heavy water as a solvent. As a result, a sulfonic acid group was introduced at the end of the polymer main chain. The peak derived from was not confirmed.

<Example 6>
Using the obtained polymers (1) to ( 4 ) and comparative polymers (1) to ( 5 ), measurement of respective molecular weights and gel resistance (degree of gelation resistance) by the methods described above. The calcium scavenging ability (Ca scavenging ability) was evaluated. The results are shown in Table 4 below.

From the above evaluation results, it has been clarified that the copolymer of the present invention has better gel resistance and chelating ability (calcium scavenging ability) than conventional polymers.

  The copolymer of the present invention has high gel resistance and chelating ability. Therefore, when it uses for additives, such as a water treatment agent (especially scale inhibitor), a builder for detergents, a detergent composition, a dispersing agent, a washing | cleaning agent, it can exhibit the especially outstanding performance.

Claims (3)

For 100 mol% structure derived from all monomers,
9 to 15 mol% of structural unit (a) derived from the monomer represented by the following general formula (1),
8 5 mol% 9 1 mol% or less of (meth) other than the structural units derived from an acrylic acid (salt) (b),
A copolymer in which the proportion of structural units derived from other monomers (c) is 0 mol% relative to 100 mol% of structural units derived from all monomers,
Having at least one sulfonic acid (salt) group at the end of the main chain;
A (meth) acrylic acid copolymer having a weight average molecular weight of 13,000 to 50,000.

In general formula (1), R ₂ 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 sulfonic acid) (Salt) group). For 100 mol% of all monomers,
9 mol% or more and 15 mol% or less of the monomer (A) represented by the following general formula (1)
Other than 8 5 mol% 9 1 mol% or less of (meth) acrylic acid (salt) (B),
The proportion of the other monomer (C) is 0 mol% with respect to 100 mol% of structural units derived from all monomers,
The method for producing a (meth) acrylic acid copolymer according to claim 1, wherein the copolymerization is carried out in the presence of bisulfite (salt).

In general formula (1), R ₂ 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 sulfonic acid) (Salt) group). A water treatment agent, a fiber treatment agent, an inorganic pigment dispersant, a detergent builder or a detergent composition comprising the (meth) acrylic acid copolymer according to claim 1.