JP2017133066A - Acrylic resin emulsion for metal surface treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acrylic resin emulsion for metal surface treatment excellent in safety.SOLUTION: An acrylic resin emulsion has a hydrophobic (meth)acrylic acid ester polymer (Tg≥10°C)(A), and a reactive surfactant (B) expressed by formula (I): [R is formula (II); m is an integer of 1-3; D is formula (III);AO is an oxyalkylene group of C2-4; n is an integer of 0-100; X is H, -SOM, -COOM or -POM; and M is an alkali metal, an alkaline earth metal or an ammonium group].SELECTED DRAWING: None

Description

  The present invention relates to an acrylic resin emulsion for metal surface treatment.

  The surface of a metal plate such as an electromagnetic steel plate may be subjected to a coating treatment for the purpose of punchability, rust prevention or the like. Such a coating treatment method includes an insulating coating treatment liquid (hereinafter referred to as “chromic acid salt”, a phosphate (for example, a polyvalent metal salt such as aluminum phosphate), and an acrylic resin emulsion as a binder. , Also referred to as “treatment liquid”).

For example, Patent Document 1 discloses, as a treatment liquid, an aqueous solution of an inorganic film forming substance mainly composed of chromate, a methacrylic ester polymer fine powder, and a carboxylic acid component-containing polymer having a carboxy group. An electrical steel sheet insulating film-forming composition containing an aqueous emulsion is disclosed.
Patent Document 2 discloses a process for forming an electrical steel sheet insulating coating comprising a metal phosphate and an organic resin emulsion having a hydroxyl value of 5 mg to 40 mg KOH / g and a particle diameter of 0.01 μm to 0.5 μm. A liquid is disclosed.
Further, Patent Document 3 was obtained by polymerizing a monomer such as a (meth) acrylic acid ester monomer in the presence of an emulsifier for emulsion polymerization containing a compound having a specific structure as an acrylic resin emulsion. A polymer dispersion is disclosed.

Japanese Patent No. 2769730 Japanese Patent No. 3435080 International Publication No. 2013/108588

However, since the carboxy group is ionized in water and has a negative charge, it easily interacts with the positive charge of the metal ion derived from the metal salt. Therefore, in a treatment liquid containing a resin emulsion having a carboxy group, such as a carboxylic acid component-containing polymer aqueous emulsion described in Patent Document 1, the resin is likely to aggregate due to the influence of metal ions, resulting in poor stability. There is.
On the other hand, there is a resin emulsion that does not have a carboxy group, such as the organic resin emulsion described in Patent Document 2. However, a resin emulsion having only a hydroxyl group as a hydrophilic group may cause a phenomenon that micelles are destroyed by metal ions derived from a metal salt, and its use is preferable from the viewpoint of the stability of the treatment liquid. I can't say that.
When a metal surface is treated using a treatment liquid that is inferior in stability, a uniform film cannot be formed, so that it is difficult to impart functions such as rust prevention.

  According to the emulsifier for emulsion polymerization containing a compound having a specific structure described in Patent Document 3, it is said that the stability of the polymer dispersion can be improved. It means mechanical stability that emulsion particles are not easily broken by stirring, which is different from chemical stability. Therefore, even if the emulsifier for emulsion polymerization described in Patent Document 3 is used, it is considered that aggregation of resin and destruction of micelles due to metal ions that can occur in the emulsions described in Patent Document 1 and Patent Document 2 cannot be suppressed. .

  This invention is made | formed in view of the above situations, and makes it a subject to provide the acrylic resin emulsion for metal surface treatments which is excellent in stability.

Specific means for solving the problems include the following aspects.
<1> Resin particles are dispersed in an aqueous medium, and the resin is represented by a structural unit (A) derived from a hydrophobic (meth) acrylate monomer and the following general formula (I) An acrylic resin for metal surface treatment, having a structural unit (B) derived from a reactive surfactant and having a glass transition temperature of 10 ° C. or higher of a compound obtained by removing the structural unit (B) from the resin Emulsion.

In the formula, R represents a substituent represented by the following general formula (II), and m represents an integer of 1 to 3. D represents a polymerizable unsaturated group represented by the following general formula (III). AO represents an oxyalkylene group having 2 to 4 carbon atoms, and n represents an integer of 0 to 100. X represents a hydrogen atom or an anionic hydrophilic group selected from —SO ₃ M, —COOM, and —PO ₃ M, and M represents an alkali metal atom, an alkaline earth metal atom, or an ammonium group.

<2> The acrylic resin emulsion for metal surface treatment according to <1>, wherein the acid value of the compound obtained by removing the structural unit (B) from the resin is 40 mgKOH / g or less.
<3> The metal surface treatment according to <1> or <2>, wherein the proportion of the structural unit (B) is 0.5% by mass to 15% by mass with respect to the total mass of all the structural units in the resin. Acrylic resin emulsion.
<4> The acrylic resin emulsion for metal surface treatment according to any one of <1> to <3>, wherein the resin further includes a structural unit derived from an aromatic monovinyl compound.
<5> The acrylic resin emulsion for metal surface treatment according to any one of <1> to <4>, which is used for electrical steel sheet treatment.

  ADVANTAGE OF THE INVENTION According to this invention, the acrylic resin emulsion for metal surface treatments which is excellent in stability can be provided.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention. be able to.

In the present specification, a numerical range indicated using “to” means a range including the numerical values described before and after “to” as a minimum value and a maximum value, respectively.
In this specification, the amount of each component in the acrylic resin emulsion for metal surface treatment is such that when there are a plurality of substances corresponding to each component in the acrylic resin emulsion for metal surface treatment, unless otherwise specified, the metal surface It means the total amount of a plurality of substances present in the acrylic resin emulsion for treatment.

  In the present specification, “(meth) acrylate” is a term including both acrylate and methacrylate, “(meth) acryl” is a term including both acrylic and methacrylic, and “(meth) acryloyl group” "Is a term that encompasses both acryloyl and methacryloyl groups.

  In this specification, the term “process” is not limited to an independent process, and is included in this term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes. It is.

[Acrylic resin emulsion for metal surface treatment]
In the acrylic resin emulsion for metal surface treatment (hereinafter also referred to as “acrylic resin emulsion”) of the present invention, resin particles (hereinafter also referred to as “resin particles”) are dispersed in an aqueous medium. Structural unit (A) derived from hydrophobic (meth) acrylic acid ester monomer (hereinafter also referred to as “structural unit (A)”), and reactive interface represented by general formula (I) described later A compound having a structural unit (B) derived from an activator (hereinafter also referred to as “structural unit (B)”) and having a glass transition temperature of 10 from which the structural unit (B) is removed from the resin. It is an acrylic resin emulsion at ℃ or higher.
In the present specification, resin particles dispersed in an aqueous medium are referred to as “resin emulsion particles”.

In general, a carboxy group is ionized in water and has a negative charge, and thus easily interacts with a positive charge of a metal ion derived from a metal salt. Therefore, the processing liquid containing the resin emulsion which has the conventional carboxy group tends to aggregate resin under the influence of a metal ion, and is inferior to stability. Since the processing solution having poor stability cannot form a uniform film on the metal surface, it is difficult to impart functions such as rust prevention. On the other hand, a treatment liquid containing a resin emulsion that does not have a carboxy group and has only a hydroxyl group as a hydrophilic group is also known, but the phenomenon that micelles are destroyed by metal ions derived from metal salts may occur. The stability is not enough.
In contrast, the acrylic resin emulsion of the present invention has a structural unit (A) derived from a hydrophobic (meth) acrylic acid ester monomer and a reactive surface activity represented by the general formula (I) described later. Particles of a resin having a structural unit (B) derived from the agent and having a glass transition temperature of 10 ° C. or higher of a compound obtained by removing the structural unit (B) from the resin is dispersed in an aqueous medium. The present embodiment exhibits excellent stability.
The reason why the acrylic resin emulsion of the present invention can exhibit such an effect is not clear, but the present inventors presume as follows.

A normal emulsifier (hereinafter also referred to as “non-reactive surfactant”) physically adsorbs to the resin particles. The non-reactive surfactant physically adsorbed on the resin particles is detached from the resin particles or re-adsorbed on the resin particles, so the resin emulsion particles formed using the non-reactive surfactant are unstable. It becomes.
Conventional general reactive surfactants form resin particles by chemically bonding (covalently bonding) with other monomers forming the resin. Since reactive surfactants and other monomers chemically bond, resin emulsion particles formed using reactive surfactants are formed by physical adsorption of non-reactive surfactants on resin particles. It becomes stable when compared with the resin emulsion particles. However, the polymerizable group possessed by the general reactive surfactant is not sufficiently reactive with the (meth) acrylate monomer, so it was formed using a general reactive surfactant. In the acrylic resin emulsion, the reactive surfactant present in a free state without forming resin particles increases. Reactive surfactants form a hydrated layer in resin emulsions, but if there are few reactive surfactants that form resin particles, the particles in resin emulsions become unstable and micelles are generated by metal ions derived from metal salts. Are easily broken and agglomerated.
On the other hand, in the acrylic resin emulsion of the present invention, the reactive surfactant represented by the general formula (I) described later is a 1-propenyl group having high reactivity with the (meth) acrylic acid ester monomer. And a substituent represented by the general formula (II) described later, resin particles are formed in which the reactive surfactant and the (meth) acrylic acid ester monomer are strongly chemically bonded (covalently bonded). The When the bond between the reactive surfactant and the (meth) acrylic acid ester monomer is strong, the hydrated layer in the resin emulsion becomes stable. Resin emulsion particles having a stable hydrated layer are less susceptible to micelle destruction and aggregation due to metal ions derived from the metal salt, and are represented by the general formula (I) described below from the structural unit of the resin. By setting the glass transition temperature of the compound having a structure excluding the structural unit (B) derived from the reactive surfactant within a specific range, it is considered that the compound is excellent in stability when used for metal surface treatment.

Moreover, since the acrylic resin emulsion formed using the conventional general reactive surfactant has many reactive surfactant which exists in a free state, foaming will arise when it coats on the surface of a metal. When foaming occurs, the coating cannot be performed uniformly, the appearance of the metal surface after coating is impaired, and good performance cannot be obtained.
On the other hand, since the acrylic resin emulsion of the present invention has a high reactivity with the (meth) acrylic acid ester monomer, the 1-propenyl group of the reactive surfactant represented by the general formula (I) described later is high, It is considered that the reactive surfactant present in a free state without forming resin particles is reduced. Therefore, according to the acrylic resin emulsion of the present invention, it is possible to achieve an effect that foaming hardly occurs when coating on a metal surface.

〔resin〕
In the acrylic resin emulsion of the present invention, a structural unit (A) derived from a hydrophobic (meth) acrylic acid ester monomer and a structure derived from a reactive surfactant represented by the general formula (I) described later Resin particles (resin particles) having units (B) are dispersed in an aqueous medium. The glass transition temperature of the compound obtained by removing the structural unit (B) from the resin is 10 ° C. or higher.
First, each structural unit that the resin has will be described.

<Structural unit (A)>
The structural unit (A) is a structural unit derived from a hydrophobic (meth) acrylic acid ester monomer.
In the present specification, the “structural unit derived from a hydrophobic (meth) acrylate monomer” means a structural unit formed by addition polymerization of a hydrophobic (meth) acrylate monomer. To do.
The kind of hydrophobic (meth) acrylic acid ester monomer is not particularly limited.
Examples of the hydrophobic (meth) acrylic acid ester monomer include alkyl (meth) acrylate, alkylene glycol di (meth) acrylate, fluorine-containing alkyl (meth) acrylate and the like.
Among these, the hydrophobic (meth) acrylic acid ester monomer is at least selected from the group consisting of alkyl (meth) acrylates and alkylene glycol di (meth) acrylates from the viewpoint of the hardness of the particles of the resin emulsion. One is preferred.

  The alkyl part of the alkyl (meth) acrylate may be linear, branched or cyclic. The carbon number of the alkyl moiety is preferably in the range of 1 to 25, more preferably in the range of 1 to 8. When the carbon number of the alkyl moiety is within the above range, the resulting coating is excellent in flexibility and robustness.

  Specific examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylate, t -Butyl (meth) acrylate, n-octyl (meth) acrylate, i-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, i-nonyl (meth) acrylate, n-decyl (Meth) acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate and the like.

The alkylene moiety of the alkylene glycol that forms the alkylene glycol moiety of the alkylene glycol di (meth) acrylate may be linear, branched, or cyclic. Carbon number of an alkylene part becomes like this. Preferably it is the range of 2-6, More preferably, it is the range of 2-3. When the number of carbon atoms in the alkylene moiety is within the above range, the resulting coating has excellent fastness.
Specific examples of the alkylene glycol di (meth) acrylate include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,3-butanediol di (meth) acrylate, and 1,4-butanediol di (Meth) acrylate, 1,6-hexanediol di (meth) acrylate and the like can be mentioned.

The proportion of the structural unit (A) is preferably 50 mass with respect to the total mass of all structural units in the resin (excluding the structural unit (B)), for example, from the viewpoint of copolymerizability during polymerization. % Or more, more preferably 60% by mass or more, and still more preferably 65% by mass or more.
The proportion of the structural unit (A) is preferably 100% by mass or less with respect to the total mass of all structural units in the resin (excluding the structural unit (B)).

  The resin may have one type of structural unit (A) or two or more types.

<Structural unit (B)>
The structural unit (B) is a structural unit derived from a reactive surfactant represented by the following general formula (I).

In general formula (I), R represents a substituent represented by the following general formula (II). m represents an integer of 1 to 3, and is preferably 2 from the viewpoint of surface activity.
D represents a polymerizable unsaturated group represented by the following general formula (III).

In general formula (I), AO represents an oxyalkylene group having 2 to 4 carbon atoms. Specific examples of the oxyalkylene group having 2 to 4 carbon atoms include an oxyethylene group, an oxypropylene group, and an oxybutylene group.
Among these, as AO, an oxyethylene group is preferable. Since the oxyethylene group has higher hydrophilicity than other oxyalkylene groups and can form a resin emulsion having a dense hydrated layer, the stability of the acrylic resin emulsion can be further improved.
n represents the average number of repeating oxyalkylene units (that is, the average number of moles of oxyalkylene group added). n is an integer of 0 to 100, and is preferably an integer of 5 to 50, more preferably an integer of 5 to 30 from the viewpoint of the stability of the acrylic resin emulsion.

In general formula (I), X represents a hydrogen atom or an anionic hydrophilic group selected from —SO ₃ M, —COOM, and —PO ₃ M.
M represents an alkali metal atom, an alkaline earth metal atom, or an ammonium group. Examples of the alkali metal atom include a sodium atom and a potassium atom. Examples of the alkaline earth metal atom include a calcium atom and a barium atom.
X is preferably a hydrogen atom, —SO ₃ NH ₄ , —SO ₃ Na, or —SO ₃ K, more preferably —SO ₃ NH ₄ from the viewpoint of the water resistance of the coating.

The proportion of the structural unit (B) is preferably 0.5% by mass or more and more preferably 1% by mass with respect to the total mass of all structural units in the resin, for example, from the viewpoint of the stability of the acrylic resin emulsion. % Or more, and more preferably 5% by mass or more.
Further, the proportion of the structural unit (B) is preferably 15% by mass or less, more preferably 12% by mass with respect to the total mass of all the structural units in the resin, for example, from the viewpoint of fastness of the resulting coating % Or less, and more preferably 10% by mass or less.

  The resin may have one type of structural unit (B), or two or more types.

<Other structural units>
The resin is also referred to as a structural unit derived from a monomer other than the structural unit (A) and the structural unit (B) (hereinafter also referred to as “other monomer”) (hereinafter referred to as “other structural unit”). ).
The kind of other monomer is not particularly limited.
As other monomers, for example, a monomer having a carboxy group such as (meth) acrylic acid or a monomer having no carboxy group may be used. From the viewpoint of properties, a monomer having no carboxy group is preferred.

As the monomer having no carboxy group, from the viewpoint of the stability of the acrylic resin emulsion, a hydrophilic group having a hydrophilic group other than the carboxy group and an ethylenically unsaturated double bond (hereinafter simply referred to as “hydrophilic”). Also referred to as “monomer”).
The kind of the hydrophilic monomer having a hydrophilic group other than a carboxy group and an ethylenically unsaturated double bond is not particularly limited.

The hydrophilic group other than the carboxy group is not particularly limited, and may be a dissociable group or a nonionic group.
Examples of the dissociable group include a sulfonic acid group and a phosphoric acid group.
Examples of the nonionic group include a hydroxyl group, an amide group in which the nitrogen atom is unsubstituted, a group derived from an alkylene oxide polymer (polyethylene oxide, polypropylene oxide, etc.), a group derived from a sugar alcohol, and the like.
Among these, as the hydrophilic group other than the carboxy group, a hydroxyl group is preferable from the viewpoint of the stability of the acrylic resin emulsion.
The number of hydrophilic groups other than the carboxy group possessed by the hydrophilic monomer may be one or plural.

The ethylenically unsaturated double bond is not particularly limited as long as it is a functional group capable of radical reaction using a polymerization initiator.
Examples of the ethylenically unsaturated double bond include (meth) acryloyl group, vinyl group, allyl group, isopropenyl group, 1-propenyl group, allyloxy group, and styryl group. Among these, as an ethylenically unsaturated double bond, a (meth) acryloyl group is preferable from a reactive viewpoint, for example.
The number of ethylenically unsaturated double bonds that the hydrophilic monomer has may be one or plural, and preferably one.

  Examples of the hydrophilic monomer having a hydrophilic group other than a carboxy group and an ethylenically unsaturated double bond include alkyl (meth) acrylates having a hydrophilic group other than a carboxy group, and poly having a hydrophilic group other than a carboxy group. Examples include alkylene glycol (meth) acrylate.

The alkyl moiety of the alkyl (meth) acrylate having a hydrophilic group other than a carboxy group may be linear, branched or cyclic.
The carbon number of the alkyl moiety is preferably in the range of 1 to 25, more preferably in the range of 1 to 3. When the carbon number of the alkyl moiety is within the above range, the hydrophilic group sufficiently contributes to the stability of the acrylic resin emulsion, so that the stability of the acrylic resin emulsion is excellent.

  Examples of the alkylene glycol that forms the polyalkylene glycol portion of the polyalkylene glycol (meth) acrylate having a hydrophilic group other than a carboxy group include ethylene glycol, propylene glycol, a combination of ethylene glycol and propylene glycol.

Examples of hydrophilic monomers having a hydrophilic group other than a carboxy group and an ethylenically unsaturated double bond include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 3-hydroxypropyl (meth). Acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate 1,1-dimethyl-3-hydroxybutyl (meth) acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2- Ethyl-3-hydroxyhexyl Meth) acrylate, glycerin mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, poly (ethylene glycol - propylene glycol) mono (meth) acrylate.
Among these, as a hydrophilic monomer having a hydrophilic group other than a carboxy group and an ethylenically unsaturated double bond, from the viewpoint of compatibility and copolymerization with other monomers, 2-hydroxyethyl (Meth) acrylate is preferred.

When the resin has a structural unit derived from a hydrophilic monomer, the proportion of the structural unit is, for example, from the viewpoint of stability of the acrylic resin emulsion, all structural units in the resin (however, the structural unit (B) Is preferably 0.1% by mass or more, and more preferably 1% by mass or more, based on the total mass of
Moreover, the ratio of the structural unit derived from the hydrophilic monomer excludes all structural units (however, the structural unit (B) in the resin from the viewpoint of suppressing the hydrophilicity of the film from becoming too high. ) Is preferably 30% by mass or less, and more preferably 20% by mass or less.

Other monomers include aromatic monovinyl compounds (styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, vinyltoluene, etc.) in addition to the hydrophilic monomers described above. And vinyl cyanide compounds (acrylonitrile, methacrylonitrile, etc.), vinyl ester compounds (vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, etc.), various derivatives of these monomers, and the like.
Among these, as another monomer, an aromatic monovinyl compound is preferable and styrene is more preferable. When the resin contains a structural unit derived from an aromatic monovinyl compound, the water resistance and alkali resistance of the acrylic resin emulsion and the smoothness of the coating are further improved.

  The resin may have one type of structural unit derived from another monomer, or may have two or more types.

(Glass-transition temperature)
The glass transition temperature (Tg) of the compound obtained by removing the structural unit (B) from the resin is 10 ° C. or higher, preferably 15 ° C. or higher, more preferably 20 ° C. or higher.
When the Tg of the resin is 10 ° C. or higher, the micelles are not easily broken and aggregated by metal ions, and the stability is excellent. Also, for example, when the acrylic resin emulsion of the present invention is used for electrical steel sheet treatment, the particles of the resin emulsion are exposed to high-temperature heat, but if the Tg of the resin is 10 ° C. or higher, Can be suitably used.
Although the upper limit of Tg of resin is not specifically limited, For example, it is 100 degrees C or less.

  In the present specification, the “compound from which the structural unit (B) is removed from the resin” means a compound having a structure corresponding to a portion in which the structural unit (B) is removed from all the structural units forming the resin. For example, the structural unit (A) derived from a hydrophobic (meth) acrylic acid ester monomer, a structural unit derived from a hydrophilic monomer, and the above-described general formula (I) When formed from the structural unit (B) derived from the reactive surfactant, it means a copolymer of a hydrophobic (meth) acrylic acid ester monomer and a hydrophilic monomer. .

Tg of the compound obtained by removing the structural unit (B) from the resin is all or part of the monomer that forms the resin (excluding the reactive surfactant represented by the general formula (I)). By using a monomer having a Tg of 10 ° C. or higher when a homopolymer (homopolymer) is used, the monomer can be adjusted to 10 ° C. or higher.
Monomers having a Tg of 10 ° C. or higher as a homopolymer include methyl methacrylate (103 ° C.), styrene (90 ° C.), acrylic acid (163 ° C.), methacrylic acid (185 ° C.), and methacrylic acid. 2-hydroxyethyl (55 degreeC) etc. are mentioned.

  In addition, "Tg when it is set as a homopolymer" means Tg of the homopolymer manufactured by polymerizing the monomer independently. The Tg of the homopolymer was determined by using a differential scanning calorimeter (DSC) (model number: EXSTAR6000, manufactured by Seiko Instruments Inc.) in a nitrogen stream and measuring the 10 mg sample at a heating rate of 10 ° C. / The inflection point of the DSC curve obtained by measuring under the conditions of minutes is defined as the Tg of the homopolymer.

  The Tg of the compound obtained by removing the structural unit (B) from the resin is a value obtained by converting the absolute temperature (K) obtained by calculation from the following formula into Celsius temperature (° C.).

In the formula, Tg1, Tg2,..., Tg (k-1), and Tgk are monomers that form a resin (however, the reactive surfactant represented by the general formula (I) is excluded). Of the glass transition temperature represented by the absolute temperature (K) of the homopolymer. w1, w2,..., w (k-1), wk are the mass fractions of the monomers forming the resin (excluding the reactive surfactant represented by the general formula (I)). Each rate is expressed as w1 + w2 +... + W (k−1) + wk = 1.
The absolute temperature (K) can be converted to Celsius temperature (° C) by subtracting 273 from the absolute temperature (K), and the Celsius temperature (° C) can be converted to absolute temperature (K) by adding 273 to the Celsius temperature (° C). Can be converted to

(Acid value)
From the viewpoint of the stability of the acrylic resin emulsion, the resin forming the particles of the resin emulsion does not have a carboxy group, or even if it has a carboxy group, the amount of the carboxy group may be small. preferable.
Since the carboxy group has a small acid dissociation constant and a strong interaction with metal ions, if the particles of the resin emulsion have a carboxy group, aggregation and generation of foreign matters are likely to occur.
On the other hand, in a treatment liquid containing a resin emulsion having a carboxy group (a resin emulsion containing a structural unit derived from acrylic acid), it is known that foaming when applied to a metal surface is suppressed (for example, Patent Document 1).
In the acrylic resin emulsion of the present invention, the 1-propenyl group of the reactive surfactant represented by the general formula (I) is highly reactive with the (meth) acrylic acid ester monomer, so that the surface of the metal It is considered that foaming can be suppressed even if the resin emulsion particles do not have a carboxy group because the reactive surfactant present in a free state, which can cause foaming when coated on the resin emulsion, is reduced.

The amount of the carboxy group in the resin forming the particles of the resin emulsion can be, for example, an index of the acid value of the resin.
In the acrylic resin emulsion of the present invention, since the reactive surfactant represented by the general formula (I) does not have a carboxy group, the acid value of the compound in which the structural unit (B) is removed from the resin. Is an indicator of the amount of carboxy groups in the resin forming the particles of the resin emulsion.
From the viewpoint of the stability of the acrylic resin emulsion, the acid value of the compound from which the structural unit (B) is removed from the resin is preferably 40 mgKOH / g or less, more preferably 30 mgKOH / g or less, and still more preferably 20 mgKOH. / G or less, particularly preferably 0 mgKOH / g.

  In this specification, “the acid value of the compound in which the structural unit (B) is removed from the resin” is determined by the following calculation formula. In the following calculation formula, 56.1 is the molecular weight of KOH.

  When there are two or more monomers having a carboxy group used in the resin, the acid value is determined according to the above formula for each monomer, and the obtained values are summed to determine the acid value. Find the price.

<Aqueous medium>
The aqueous medium is not particularly limited and can be appropriately selected depending on the purpose.
Examples of the aqueous medium include water, a mixed solution of water and an alcohol solvent, and the like. From the viewpoint of the stability of the acrylic resin emulsion, water is preferable as the aqueous medium.
Content of the aqueous medium in an acrylic resin emulsion is not restrict | limited in particular, Preferably it is 20 mass%-80 mass%, More preferably, it is 30 mass%-70 mass%, More preferably, it is 50 mass%-60 mass%. % By mass.

<Other ingredients>
The acrylic resin emulsion of the present invention may contain other components other than those described above, if necessary, within a range not impairing the effects of the present invention.
Examples of other components include various additives such as an antioxidant, an antistatic agent, a pH adjuster, and an antifoaming agent.

[Average particle diameter of resin particles]
The average particle diameter of the resin particles is preferably 50 nm to 500 nm, more preferably 100 nm to 300 nm, and still more preferably 100 nm to 200 nm, from the viewpoint of the stability of the resin particles and the smoothness of the coating.
In the present specification, the “average particle diameter of resin particles” means “New Experimental Chemistry Course 4 Basic Technology 3 Light (II)” pages 725 to 741 (July 20, 1977 Maruzen ( It is a value measured by the dynamic light scattering method described in “Issuance”). The specific method is as follows.
The acrylic resin emulsion was diluted with distilled water and sufficiently stirred and mixed. Then, 5 ml was collected in a 10 mm square glass cell using a Pasteur pipette, and this was collected using a dynamic light scattering photometer “Zetasizer 1000HS” [Sysmex ( Set to “Made by Co., Ltd.”. After adjusting the concentration of the acrylic resin emulsion dilution so that the decay rate count rate is 150 Cps to 200 Cps, the results measured under the conditions of a measurement temperature of 25 ° C. ± 1 ° C. and a light scattering angle of 90 ° are processed by a computer. By doing this, the average particle diameter of the resin particles in the acrylic resin emulsion is obtained.

[Use]
The acrylic resin emulsion of this invention can be used suitably for an electromagnetic steel plate process, for example.
A film containing chromate, metal phosphate (aluminum phosphate, magnesium phosphate, calcium phosphate, zinc phosphate, etc.) is formed on the surface of the electrical steel sheet for the purpose of rust prevention and the like. In order to satisfactorily impart functions such as rust prevention, it is required that the film formed on the surface of the electromagnetic steel sheet is uniform.
The acrylic resin emulsion of the present invention is excellent in stability, and even when it comes into contact with metal ions, the resin particles and the metal ions are hardly bonded, and aggregation and generation of foreign substances are difficult to occur. Further, in the acrylic resin emulsion of the present invention, since there are very few reactive surfactants present in a free state without forming a resin, foaming hardly occurs when applied. Therefore, according to the treatment liquid using the acrylic resin emulsion of the present invention as a binder such as chromate or metal phosphate, a uniform film can be formed.
That is, the acrylic resin emulsion of the present invention is less likely to cause agglomeration and generation of foreign matter even when a large amount of metal salts such as chromates and metal phosphates are blended, and also less likely to foam when applied. Therefore, it is possible to form a uniform film, and in particular, it can be suitably used as a treatment liquid for treatment of electrical steel sheets containing a high concentration of metal salt.

[Method for producing acrylic resin emulsion]
The manufacturing method of the acrylic resin emulsion of this invention should just manufacture the above-mentioned acrylic resin emulsion, and is not restrict | limited in particular.
As a method for producing the acrylic resin emulsion of the present invention, the method for producing an acrylic resin emulsion of the present embodiment described below is preferable.

  The method for producing an acrylic resin emulsion of the present embodiment (hereinafter also referred to as “production method of the present embodiment”) is at least hydrophobic in the presence of the reactive surfactant represented by the general formula (I) ( A compound obtained by polymerizing a monomer selected from a (meth) acrylic acid ester (hereinafter also referred to as a hydrophobic "(meth) acrylic acid ester monomer") and removing the structural unit (B) from the resin; An emulsion polymerization step of obtaining particles of a resin emulsion having a glass transition temperature of 10 ° C. or higher.

Hereafter, the process in the manufacturing method of this embodiment is demonstrated in detail.
In addition, since it is as having described in the item of the above-mentioned acrylic resin emulsion about the specific example of a component used at each process, and a preferable aspect, description is abbreviate | omitted here.

<Emulsion polymerization process>
In the emulsion polymerization step, in the presence of the reactive surfactant represented by the general formula (I), at least a monomer selected from hydrophobic (meth) acrylic acid ester is polymerized to form a structural unit (B ) Is a step of obtaining resin emulsion particles having a glass transition temperature of 10 ° C. or higher.
In the emulsion polymerization step, at least the hydrophobic (meth) acrylic acid ester monomer and the reactive surfactant represented by the general formula (I) are copolymerized and hydrated by the reactive surfactant. Resin emulsion particles having a layer formed thereon are obtained.

The polymerization method is not particularly limited. For example, in a reaction vessel equipped with a thermometer, a stirring rod, a reflux condenser, a dropping funnel, etc., at least a hydrophobic (meth) acrylate monomer and a general formula After charging the reactive surfactant represented by (I) and an aqueous medium such as water and raising the temperature inside the reaction vessel, a polymerization initiator, a reducing agent, etc. are added as appropriate, and the emulsion polymerization reaction proceeds. A method (so-called batch charging method), after charging at least the reactive surfactant represented by the general formula (I) and an aqueous medium such as water into the reaction vessel and raising the temperature in the reaction vessel The monomer component [at least hydrophobic (meth) acrylic acid ester monomer] is dropped, and a polymerization initiator, a reducing agent, etc. are added as appropriate, and the emulsion polymerization reaction proceeds (so-called monomer dropping method). ), The monomer component at least in general formula (I) After emulsifying with a reactive surfactant and an aqueous medium such as water to obtain a pre-emulsion, the obtained pre-emulsion is dropped into the reaction vessel, and a polymerization initiator, a reducing agent, etc. are added appropriately. And a method of causing the emulsion polymerization reaction to proceed (so-called emulsion monomer dropping method).
Among these, as a polymerization method, the emulsion monomer dropping method is preferable from the viewpoint of industrial productivity.

The polymerization temperature is, for example, 50 ° C to 80 ° C, preferably 60 ° C to 80 ° C.
The polymerization time is, for example, 6 hours to 12 hours, preferably 6 hours to 8 hours.

The amount of the reactive surfactant represented by the general formula (I) is the total amount of monomers other than the reactive surfactant represented by the general formula (I) from the viewpoint of the stability of the acrylic resin emulsion. Preferably it is 1 mass part or more with respect to 100 mass parts, More preferably, it is 3 mass parts or more, More preferably, it is 5 mass parts or more.
Moreover, the usage-amount of the reactive surfactant represented by general formula (I) is monomers other than the reactive surfactant represented by general formula (I) from the viewpoint of the fastness of the film obtained. The total amount is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and still more preferably 10 parts by mass or less.

  In the emulsion polymerization process, when using the other monomers described above, the amount of the other monomers used is the reactive surface activity represented by the general formula (I) from the viewpoint of copolymerizability during polymerization. Preferably it is 55 mass parts or less with respect to 100 mass parts of total amounts of monomers other than an agent, More preferably, it is 45 mass parts or less, More preferably, it is 35 mass parts or less.

  In the emulsion polymerization step, various additives such as a polymerization initiator, a reducing agent, a chain transfer agent, and a pH adjuster may be used.

(Polymerization initiator)
Any polymerization initiator can be used without particular limitation as long as it can be used for ordinary emulsion polymerization. Examples of the polymerization initiator include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, organic peroxides such as t-butyl hydroperoxide and cumene hydroperoxide, and hydrogen peroxide.
When using a polymerization initiator in an emulsion polymerization process, a polymerization initiator may be used individually by 1 type, and may be used in combination of 2 or more type.

  The polymerization initiator is used in an amount usually used. The amount of the polymerization initiator used is, for example, 0.1 parts by mass to 2 parts by mass, preferably 0.3 parts by mass to 1.5 parts by mass with respect to 100 parts by mass of the total amount of monomers as raw materials. It is.

(Reducing agent)
In the emulsion polymerization step, a reducing agent may be used together with the above polymerization initiator.
Examples of the reducing agent include sodium metabisulfite, sodium sulfite, sodium hydrogen sulfite, sodium pyrosulfite, sodium pyrophosphate, thioglycolic acid, sodium thiosulfate, ascorbic acid, tartaric acid, citric acid, and glucose.
When using a reducing agent in an emulsion polymerization process, a reducing agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  The reducing agent is used in an amount usually used. The amount of the reducing agent used is, for example, 0.1 parts by mass to 2 parts by mass, preferably 0.3 parts by mass to 1.5 parts by mass with respect to 100 parts by mass of the total amount of monomers as raw materials. is there.

<Other processes>
The manufacturing method of this embodiment may have processes other than an emulsion polymerization process as needed.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the following examples as long as the gist thereof is not exceeded.

  The average particle diameter of the resin particles in the acrylic resin emulsion produced in this example was determined by measurement using the method described above.

In this example, the glass transition temperature (Tg) and the acid value of the compound obtained by removing the structural unit (B) from the resin were calculated by the methods described above.
The Tg of the homopolymer is -57 ° C for butyl acrylate, 103 ° C for methyl methacrylate, 90 ° C for styrene, 163 ° C for acrylic acid, and 185 for methacrylic acid. ° C, 2-hydroxyethyl methacrylate is 55 ° C, and 2-ethylhexyl acrylate is -76 ° C.
The results are shown in Tables 1 and 2.

[Manufacture of acrylic resin emulsion]
[Example 1]
In a reaction vessel equipped with a thermometer, a stirring bar, a reflux condenser, and a dropping funnel, 43.3 parts by mass of deionized exchange water was charged, and the temperature in the reaction vessel was raised to 60 ° C. while purging with nitrogen.
Meanwhile, in another container, 76.8 parts by mass of deionized exchange water and 5.0 parts by mass of surfactant (a) (reactive surfactant represented by the following structural formula (a)) are placed. Then, 38.0 parts by mass of butyl acrylate (BA), 30.0 parts by mass of methyl methacrylate (MMA), and 30. styrene (St, other monomer). A pre-emulsion was prepared by adding and stirring 0 parts by mass and 2.0 parts by mass of acrylic acid (AA: acrylic acid, other monomer).
Next, while maintaining the internal temperature of the reaction vessel at 60 ° C., 3% by mass (6.2 parts by mass) of the pre-emulsion prepared above was added to the reaction vessel, and then a 10% by mass ammonium persulfate aqueous solution. 0.14 parts by mass and 0.14 parts by mass of a 10% by mass aqueous sodium metabisulfite solution were added to initiate the emulsion polymerization reaction.
After the internal temperature of the reaction vessel reached 62 ° C., the remaining total amount of the pre-emulsion prepared above, 0.36 parts by mass of a 2.5% by mass ammonium persulfate aqueous solution (polymerization initiator), and 2.5% by mass An aqueous solution of sodium metabisulfite (reducing agent) 0.36 parts by mass was uniformly added successively over 4 hours to effect emulsion polymerization. After completion of the sequential addition, the obtained emulsion polymer was aged at 62 ° C. for 2 hours and then cooled to room temperature to obtain an acrylic resin emulsion having a pH of 2.3. Solid content of the obtained acrylic resin emulsion was 42 mass%.

[Example 2]
In Example 1, 76.8 parts by mass of deionized water and 5.0 parts by mass of the surfactant (a) were added and stirred, and then 35.0 parts by mass of butyl acrylate (BA). And 30.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), and 5.0 mass of 2-hydroxyethyl methacrylate (2HEMA: 2-hydroxyethyl methacrylate, other monomers) An acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that a pre-emulsion was prepared by adding and stirring. Solid content of the obtained acrylic resin emulsion was 42 mass%.

Example 3
In Example 1, 76.8 parts by mass of deionized water and 10.0 parts by mass of a surfactant (b) (reactive surfactant represented by the following structural formula (b)) were added and stirred. After that, 30.0 parts by mass of butyl acrylate (BA), 35.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), and 2-hydroxyethyl methacrylate (2HEMA) An acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that 5.0 parts by mass and stirring were added to prepare a pre-emulsion. Solid content of the obtained acrylic resin emulsion was 42 mass%.

Example 4
In Example 1, 76.8 parts by mass of deionized water and 5.0 parts by mass of the surfactant (a) were added and stirred, and then further 2-ethylhexyl acrylate (2EHA: 2 -ethylhexyl acrylate) 35.0 parts by weight, methyl methacrylate (MMA) 30.0 parts by weight, styrene (St) 30.0 parts by weight, and 2-hydroxyethyl methacrylate (2HEMA) 5.0 parts by weight , And stirred to obtain an acrylic resin emulsion having a pH of 2.3 in the same manner as in Example 1 except that a pre-emulsion was prepared. Solid content of the obtained acrylic resin emulsion was 42 mass%.

Example 5
In Example 1, 76.8 parts by mass of deionized water and 5.0 parts by mass of the surfactant (b) were added and stirred, and then 30.0 parts by mass of butyl acrylate (BA). And 37.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), and 3.0 parts by mass of methacrylic acid (MAA: methacrylic acid). An acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that the emulsion was prepared. Solid content of the obtained acrylic resin emulsion was 42 mass%.

Example 6
In Example 1, 76.8 parts by mass of deionized water and 5.0 parts by mass of the surfactant (a) were added and stirred, and then 40.0 parts by mass of butyl acrylate (BA). And Example, except that 59.0 parts by mass of methyl methacrylate (MMA) and 1.0 part by mass of 2-hydroxyethyl methacrylate (2HEMA) were added and stirred to prepare a pre-emulsion. In the same manner as in Example 1, an acrylic resin emulsion having a pH of 2.3 was obtained. Solid content of the obtained acrylic resin emulsion was 42 mass%.

Example 7
In Example 1, 76.8 parts by mass of deionized water, 5.0 parts by mass of the surfactant (a), and 5.0 parts by mass of the surfactant (b) were added and stirred. Further, 35.0 parts by mass of butyl acrylate (BA), 30.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), and 2-hydroxyethyl methacrylate (2HEMA) 5. An acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that 0 part by mass was added and stirred to prepare a pre-emulsion. Solid content of the obtained acrylic resin emulsion was 42 mass%.

Example 8
In Example 1, 76.8 parts by mass of deionized water and 5.0 parts by mass of the surfactant (b) were added and stirred, and then 30.0 parts by mass of butyl acrylate (BA). Then, 35.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), and 5.0 parts by mass of acrylic acid (AA) are added and stirred to prepare a pre-emulsion. Except that, an acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1. Solid content of the obtained acrylic resin emulsion was 42 mass%.

Example 9
In Example 1, 76.8 parts by mass of deionized water and 1.0 part by mass of the surfactant (a) were added and stirred, and then 35.0 parts by mass of butyl acrylate (BA). And 30.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), and 5.0 parts by mass of 2-hydroxyethyl methacrylate (2HEMA), and stirring, An acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that a pre-emulsion was prepared. Solid content of the obtained acrylic resin emulsion was 42 mass%.

[Comparative Example 1]
In Example 1, 76.8 parts by mass of deionized water and 5.0 parts by mass of the surfactant (a) were added and stirred, and then 49.5 parts by mass of butyl acrylate (BA). And 49.5 parts by mass of styrene (St) and 1.0 part by mass of acrylic acid (AA) were added and stirred in the same manner as in Example 1 except that the pre-emulsion was prepared. An acrylic resin emulsion having a pH of 2.3 was obtained. Solid content of the obtained acrylic resin emulsion was 42 mass%.

[Comparative Example 2]
In Example 1, 76.8 parts by mass of deionized water and a surfactant (c) [reactive surfactant represented by the following structural formula (c), trade name: Aqualon (registered trademark) KH-10 , Active ingredient: polyoxyethylene-1- (allyloxymethyl) alkyl ether ammonium sulfate, active ingredient: 99% by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], and stirred, 2-ethylhexyl acrylate (2EHA) 40.0 parts by mass, methyl methacrylate (MMA) 15.0 parts by mass, styrene (St) 40.0 parts by mass, 2-hydroxyethyl methacrylate (2HEMA) An acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that 5.0 parts by mass and stirring were added to prepare a pre-emulsion. Solid content of the obtained acrylic resin emulsion was 42 mass%.

[Comparative Example 3]
In Example 1, 76.8 parts by weight of deionized water and a surfactant (d) [non-reactive surfactant represented by the following structural formula (d), trade name: Haitenol (registered trademark) NF -13, active ingredient: polyoxyethylene distyryl phenyl ether sulfate ammonium salt, m≈2, n = 13, active ingredient: 98% by mass, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.] 5.1 parts by mass Then, 35.0 parts by mass of butyl acrylate (BA), 30.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), 2-hydroxyethyl methacrylate ( 2HEMA) 5.0 parts by mass and stirring, an acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that a pre-emulsion was prepared. Solid content of the obtained acrylic resin emulsion was 42 mass%.

[Comparative Example 4]
In Example 1, 76.8 parts by mass of deionized water and 5.0 parts by mass of the surfactant (c) were added and stirred, and then 35.0 parts by mass of butyl acrylate (BA). And 30.0 parts by mass of methyl methacrylate (MMA), 30.0 parts by mass of styrene (St), and 5.0 parts by mass of 2-hydroxyethyl methacrylate (2HEMA), and stirring, An acrylic resin emulsion having a pH of 2.3 was obtained in the same manner as in Example 1 except that a pre-emulsion was prepared. Solid content of the obtained acrylic resin emulsion was 42 mass%.

[Evaluation]
1. Stability The stability of the acrylic resin emulsions of Examples 1 to 9 and Comparative Examples 1 to 4 was evaluated by the following method.
5 parts by mass of an acrylic resin emulsion, 10 parts by mass of an aluminum phosphate 50% by mass aqueous solution, and 1 part by mass of glycerin were weighed into a reagent bottle, and the reagent bottle was shaken up and down 10 times. The state of the liquid after shaking was visually observed, and the stability of the acrylic resin emulsion was evaluated according to the following evaluation criteria. The results are shown in Tables 1 and 2.
Those practically acceptable are classified into “AA”, “A”, and “B”.

-Evaluation criteria-
AA: No foreign matters or lumps are observed, and no separation occurs.
A: Some foreign matter is observed, but aggregation or separation does not occur.
B: A large amount of foreign matter was observed, and separation occurred over time.
C: A lot of lumps were observed, and the fluidity was lost (gelled) over time.

2. Foamability About the acrylic resin emulsions of Examples 1 to 9 and Comparative Examples 1 to 4, the foamability was evaluated by the following method.
The acrylic resin emulsion was diluted 3 times with deionized water. 30 ml of the obtained diluted solution was weighed out into a 200 ml measuring cylinder (Shiba Kagaku Co., Ltd.). The opening of the graduated cylinder was sealed with a wrap film so that the diluent did not leak, and then the graduated cylinder was vigorously shaken for 15 seconds. The total volume of liquid and foam immediately after shaking was measured by reading the scale of the graduated cylinder. Based on the total volume of the measured liquid and foam, the foamability of the acrylic resin emulsion was evaluated according to the following evaluation criteria. The results are shown in Tables 1 and 2.
In addition, it shows that foamability is so low that the total volume of a liquid and a bubble is small.

-Evaluation criteria-
A: The total volume of liquid and foam is 100 mL or less.
B: The total volume of liquid and foam is more than 100 mL and less than 200 mL.
C: The total volume of liquid and foam is 200 mL or more.

In Tables 1 and 2, “-” means that the corresponding component is not blended.
In Tables 1 and 2, “the glass transition temperature (Tg) of the compound in which the structural unit (B) is removed from the resin” is simply expressed as “Tg”. Further, “the acid value of the compound in which the structural unit (B) is removed from the resin” is simply expressed as “acid value”.

As shown in Table 1, the acrylic resin emulsions of Examples 1 to 9 were all excellent in stability.
Moreover, it was confirmed that the acrylic resin emulsions of Examples 1 to 9 all have low foaming properties.

On the other hand, as shown in Table 2, the acrylic resin emulsions of Comparative Example 1 and Comparative Example 2 in which the Tg of the compound obtained by removing the structural unit (B) from the resin was less than 10 ° C. were poor in stability.
The acrylic resin emulsions of Comparative Examples 2 and 4 having structural units derived from a reactive surfactant, but the reactive surfactant is not a reactive surfactant represented by the general formula (I): The stability was bad.
The acrylic resin emulsion of Comparative Example 3 having a structural unit derived from a non-reactive surfactant instead of the structural unit (B) derived from the reactive surfactant represented by the general formula (I) is stable. The nature was bad.
Moreover, it was confirmed that the acrylic resin emulsions of Comparative Examples 2 to 4 have high foamability.

Claims (5)

Resin particles are dispersed in an aqueous medium,
A structural unit (A) derived from a hydrophobic (meth) acrylic acid ester monomer, and a structural unit (B) derived from a reactive surfactant represented by the following general formula (I): And having
The acrylic resin emulsion for metal surface treatment whose glass transition temperature of the compound by which the said structural unit (B) was remove | excluded from the said resin is 10 degreeC or more.

[In formula, R represents the substituent represented by the following general formula (II), and m represents the integer of 1-3. D represents a polymerizable unsaturated group represented by the following general formula (III). AO represents an oxyalkylene group having 2 to 4 carbon atoms, and n represents an integer of 0 to 100. X represents a hydrogen atom or an anionic hydrophilic group selected from —SO ₃ M, —COOM, and —PO ₃ M, and M represents an alkali metal atom, an alkaline earth metal atom, or an ammonium group. ]

  The acrylic resin emulsion for metal surface treatment according to claim 1, wherein the acid value of the compound obtained by removing the structural unit (B) from the resin is 40 mgKOH / g or less.   The ratio of the said structural unit (B) is 0.5 mass% or more and 15 mass% or less with respect to the total mass of all the structural units in the said resin, The metal surface treatment of Claim 1 or Claim 2 Acrylic resin emulsion.   The acrylic resin emulsion for metal surface treatment according to any one of claims 1 to 3, wherein the resin further has a structural unit derived from an aromatic monovinyl compound.   The acrylic resin emulsion for metal surface treatment of any one of Claims 1-4 used for an electromagnetic steel plate process.