JP2024092400A - Aqueous emulsion, aqueous resin composition, and method for producing coating film - Google Patents

Abstract

[Problem] To provide an aqueous emulsion that can be used as a material for an aqueous resin composition that can form a coating film that exhibits good adhesion even when cured at room temperature without using a curing agent. [Solution] The aqueous emulsion contains a copolymer (X), a polyepoxy compound (Y) that has no ethylenically unsaturated bonds and has two or more epoxy groups in one molecule, and an aqueous medium (Z), in which (X) contains a structural unit derived from a (meth)acrylic acid ester (A) and a structural unit (b) derived from an ethylenically unsaturated monomer (B) having a carboxy group, at least one of (B) being an ethylenically unsaturated monomer (B1) having two or more carboxy groups, the content of carboxy groups in the structural unit (b1) derived from (B1) out of the total number of carboxy groups in the structural unit (b) is 25 mol % or more, and the content of (Y) relative to 100 parts by mass of the total amount of (X) is 1.0 part by mass or more and 67 parts by mass or less. [Selected Figure] None

Description

The present invention relates to an aqueous emulsion, a method for producing an aqueous emulsion, an aqueous resin composition, and a method for producing a coating film.

Generally, the surface of metal products is treated. In particular, metal products that are used outdoors and metal products that are expected to be exposed to moisture often have their surface painted to prevent rust.

Traditionally, paints containing organic solvents have been used to coat the surfaces of metal products. However, when applying paints containing organic solvents to the surface of metal products, measures must be taken to protect workers and the surrounding environment from volatile organic compounds (VOCs). For this reason, there has been a growing trend to use water-based paints instead of paints containing organic solvents when coating the surfaces of metal products.

Patent Document 1 describes a coating composition for thick coating, which contains an emulsion composition in which polymer particles are dispersed in an aqueous medium, and an aggregate. The polymer particles described in Patent Document 1 are produced by emulsion polymerization of a constituent unit formed by polymerizing an alkyl (meth)acrylate monomer having an alkyl group with 4 to 14 carbon atoms, a constituent unit formed by polymerizing an ethylenically unsaturated carboxylic acid monomer, and a constituent unit formed by polymerizing other monomers, in the presence of a compound having at least two epoxy groups in one molecule and a basic catalyst.

Patent document 2 describes a composition that includes an aqueous dispersion of thermoplastic polymer particles imbibed with a thermosetting compound having oxirane groups. Patent document 2 also describes that the polymer particles have a sufficient concentration of anti-agglomeration functional groups to stabilize the latex against agglomeration.

Patent Document 3 describes how an acrylate resin emulsion is mixed with an epoxy emulsion to form an acrylate resin that has absorbed an epoxy compound (acrylic/epoxy latex).

Patent Document 4 describes an aqueous resin composition that includes an aqueous resin emulsion (α) that includes a copolymer (X) that includes a structural unit derived from a (meth)acrylic acid ester and a structural unit derived from an ethylenically unsaturated carboxylic acid, a polyepoxy compound (Y), a curing agent (β), and a curing accelerator (γ). Patent Document 4 also describes the use of a polyamine as the curing agent (β).

JP 2011-89092 A JP 2014-65914 A International Publication No. 2017/112018 International Publication No. 2021/112042

Traditionally, amine-based hardeners have been widely used as hardeners for aqueous emulsions containing epoxy compounds. However, when mixing an amine-based hardener with an aqueous emulsion to prepare a paint, and when applying the prepared paint, a strong odor is generated. In addition, amine-based hardeners can cause a rash if they come into contact with the skin.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an aqueous emulsion that can be used as a material for an aqueous resin composition that can form a coating film exhibiting good adhesion even when cured at room temperature without using a curing agent, and a method for producing the same.
An object of the present invention is to provide an aqueous resin composition containing the aqueous emulsion of the present invention, and a method for producing a coating film using the same.

The configurations of the present invention to achieve the above objective are as follows [1] to [13].

[1] A copolymer (X), a polyepoxy compound (Y) having no ethylenically unsaturated bond and having two or more epoxy groups in one molecule, and an aqueous medium (Z),
The copolymer (X) contains a structural unit (a) derived from a (meth)acrylic acid ester (A) and a structural unit (b) derived from an ethylenically unsaturated monomer (B) having a carboxy group,
the content of the structural unit (a) derived from the (meth)acrylic acid ester (A) in the copolymer (X) is 10 mol % or more and 99.9 mol % or less;
the content of the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group in the copolymer (X) is 0.1 mol % or more and 20 mol % or less;
At least one of the ethylenically unsaturated monomers (B) having a carboxy group is an ethylenically unsaturated monomer (B1) having two or more carboxy groups,
a content of carboxy groups of the structural unit (b1) derived from the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups of the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group is 25 mol % or more,
The content of the polyepoxy compound (Y) relative to 100 parts by mass of the total amount of the copolymer (X) is 1.0 part by mass or more and 67 parts by mass or less.

[2] The aqueous emulsion according to [1], containing emulsified particles containing the copolymer (X) and the polyepoxy compound (Y).
[3] The aqueous emulsion according to [1] or [2], wherein at least one of the ethylenically unsaturated monomers (B1) having two or more carboxy groups is maleic acid, itaconic acid, fumaric acid, mesaconic acid, citraconic acid, glutaconic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, 3-butene-1,2,3-tricarboxylic acid, or ethylenetetracarboxylic acid.

[4] The aqueous emulsion according to [1] or [2], wherein at least one of the ethylenically unsaturated monomers (B1) having two or more carboxy groups is an ethylenically unsaturated monomer having two carboxy groups.
[5] The aqueous emulsion according to [1] or [2], wherein at least one of the ethylenically unsaturated monomers (B1) having two or more carboxy groups is maleic acid.
[6] The aqueous emulsion according to [1] or [2], wherein at least one of the polyepoxy compounds (Y) is a bisphenol-type epoxy compound, a hydrogenated bisphenol-type epoxy compound, a diglycidyl ether, a triglycidyl ether, a tetraglycidyl ether, a diglycidyl ester, a triglycidyl ester, or a tetraglycidyl ester.

[7] The method includes an emulsion polymerization step of emulsion-polymerizing a monomer raw material including a (meth)acrylic acid ester (A) and an ethylenically unsaturated monomer (B) having a carboxy group in an aqueous medium (Z) in the presence of a polyepoxy compound (Y) having no ethylenically unsaturated bond and having two or more epoxy groups in one molecule,
the content of the (meth)acrylic acid ester (A) in the monomer raw material is 10 mol % or more and 99.9 mol % or less,
the content of the ethylenically unsaturated monomer (B) having a carboxy group in the monomer raw material is 0.1 mol % or more and 20 mol % or less,
At least one of the ethylenically unsaturated monomers (B) having a carboxy group is an ethylenically unsaturated monomer (B1) having two or more carboxy groups,
a content of carboxy groups of the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups of the ethylenically unsaturated monomer (B) having a carboxy group is 25 mol % or more,
a content of the polyepoxy compound (Y) relative to 100 parts by mass of the monomer raw material is 1.0 part by mass or more and 67 parts by mass or less.

[8] An aqueous resin composition comprising the aqueous emulsion (α) according to [1] or [2].
[9] The aqueous resin composition according to [8], wherein the aqueous resin composition does not contain a curing agent.

[10] A method for producing a coating film, comprising applying the aqueous resin composition according to [8] to a surface to be coated.
[11] The method for producing a coating film according to [10], wherein the aqueous resin composition applied to the surface to be coated is cured at a temperature of 20°C to 40°C.

According to the present invention, it is possible to provide an aqueous emulsion that can be used as a material for an aqueous resin composition that can form a coating film exhibiting good adhesion even when cured at room temperature without using a curing agent, and a method for producing the aqueous emulsion.
Since the aqueous resin composition of the present invention contains the aqueous emulsion of the present invention, it can form a coating film that exhibits good adhesion even when cured at room temperature without using a curing agent.

In the method for forming a coating film of the present invention, the aqueous resin composition of the present invention may be applied to the surface to be coated and cured at room temperature. This allows the formation of a coating film that exhibits good adhesion without the use of a curing agent.

The aqueous emulsion of the present invention, its production method, aqueous resin composition, and coating film production method will be described in detail below.
The present invention is not limited to the following embodiments. For example, the number, type, position, amount, ratio, material, configuration, and the like can be added, omitted, substituted, or changed without departing from the spirit of the present invention.

Here, the following terms used in this specification will be explained.
"(Meth)acrylic" is a general term for acrylic and methacrylic.
"(Meth)acrylate" is a general term for acrylate and methacrylate.
The term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability, unless otherwise specified.
The "weight average molecular weight" is a value calculated in terms of standard polystyrene measured by gel permeation chromatography (GPC).

In a polymer using a compound having an ethylenically unsaturated bond, a structural unit derived from the compound having an ethylenically unsaturated bond means a structural unit in which the chemical structure of the portion other than the ethylenically unsaturated bond in the compound having an ethylenically unsaturated bond is the same as the chemical structure of the portion in the polymer other than the portion corresponding to the ethylenically unsaturated bond of the structural unit. The ethylenically unsaturated bond of the compound is converted into a single bond when forming a polymer. For example, in a polymer of methyl methacrylate, the structural unit derived from methyl methacrylate is represented by -CH ₂ -C(CH ₃ )(COOCH ₃ )-.

In the case of a polymer of a compound having an ionic functional group and an ethylenically unsaturated bond, for example, a structural unit having an ionic functional group such as a carboxy group is considered to be a structural unit derived from the same ionic compound, regardless of whether a part of the functional group has been ion-exchanged or not. For example, a structural unit represented by -CH ₂ -C(CH ₃ )(COONa)- may also be considered to be a structural unit derived from methacrylic acid.

Furthermore, after polymerization, if the portion other than the chain structure corresponding to the ethylenically unsaturated bond in the polymer, for example a functional group such as a carboxyl group, no longer corresponds to the chemical structure of the monomer due to a chemical reaction, the structural unit of the polymer is made to be a structural unit derived from the compound having an ethylenically unsaturated bond in the polymer. For example, if vinyl acetate is polymerized and then saponified, the structural unit of the polymer is made to be a structural unit derived from vinyl alcohol, not a structural unit derived from vinyl acetate, based on the chemical structure of the polymer.

"Cure" refers to the process in which molecules contained in the raw material bond together through a chemical reaction to form a polymer network structure.
The "coating film" consists of a cured product formed by curing the resin component contained in the aqueous resin composition of this embodiment, and is integrated with the surface to be coated, obtained by a method such as applying the aqueous resin composition to the surface to be coated and drying the medium.

[1. Aqueous emulsion (α)]
The aqueous emulsion (α) contains a copolymer (X), a polyepoxy compound (Y) having no ethylenically unsaturated bond and having two or more epoxy groups in one molecule, and an aqueous medium (Z).
The aqueous emulsion (α) is capable of forming a coating film exhibiting good adhesion and rust prevention properties even when the aqueous emulsion (α) described below is prepared into an aqueous resin composition, which is then applied to a surface to be coated and cured at room temperature (20° C. to 40° C.).

The aqueous emulsion (α) may contain emulsion particles containing the copolymer (X) and the polyepoxy compound (Y). The emulsion particles containing the copolymer (X) and the polyepoxy compound (Y) are emulsions obtained by emulsion polymerization of the monomer raw material that will become the structural unit of the copolymer (X) in the aqueous medium (Z) in the presence of the polyepoxy compound (Y).

The aqueous emulsion (α) may contain emulsion particles containing a copolymer (X) and emulsion particles containing a polyepoxy compound (Y). In such an aqueous emulsion (α), the emulsion particles containing a copolymer (X) dispersed in the aqueous medium (Z) and the emulsion particles containing a polyepoxy compound (Y) are electrically repelled. For this reason, it is presumed that the emulsion particles containing a copolymer (X) and the emulsion particles containing a polyepoxy compound (Y) dispersed in the aqueous medium (Z) do not aggregate in the aqueous medium (Z) and are uniformly dispersed.

When the aqueous emulsion (α) contains emulsion particles containing copolymer (X) and polyepoxy compound (Y), it can be used as a material for an aqueous resin composition that can form a coating film that exhibits good adhesion and rust prevention properties compared to when it contains emulsion particles containing copolymer (X) and emulsion particles containing polyepoxy compound (Y). When the aqueous emulsion (α) contains emulsion particles containing copolymer (X) and polyepoxy compound (Y), the coating film obtained by curing the aqueous resin composition has smaller and more densely distributed domains derived from each of copolymer (X) and polyepoxy compound (Y). As a result, it is presumed that the low water resistance of the domains derived from copolymer (X) is reduced and good adhesion and rust prevention properties are exhibited.

<1-1. Copolymer (X)>
The copolymer (X) contains a structural unit (a) derived from a (meth)acrylic acid ester (A) and a structural unit (b) derived from an ethylenically unsaturated monomer (B) having a carboxy group. At least one of the ethylenically unsaturated monomers (B) having a carboxy group is an ethylenically unsaturated monomer (B1) having two or more carboxy groups.

The copolymer (X) may be one consisting of the structural unit (a) and the structural unit (b) (referred to as copolymer (X1)). The copolymer (X) may be one containing the structural unit (a), the structural unit (b), and further a structural unit (c) derived from an ethylenically unsaturated aromatic compound (C) having a benzene ring and an ethylenically unsaturated bond (referred to as copolymer (X2)). The copolymer (X2) may be one consisting only of the structural units (a) to (c). The copolymer (X) may have a structural unit (d) (referred to as a structural unit derived from another monomer (D)) other than the structural units (a) to (c).

[(Meth)acrylic acid ester (A)]
The (meth)acrylic acid ester (A) preferably contains an alkyl (meth)acrylic acid ester, and more preferably consists of an alkyl (meth)acrylic acid ester. The alkyl group of the alkyl (meth)acrylic acid ester is more preferably a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isobornyl (meth)acrylate. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester (A) may also include a (meth)acrylic acid ester (A1) in which the moiety derived from an alcohol has 2 or less carbon atoms.
The (meth)acrylic acid ester (A1) is a (meth)acrylic acid ester having a (meth)acryloyloxy group (CH ₂ ═CR-COO-, where R represents hydrogen or a methyl group) and having 2 or less carbon atoms in the portion derived from an alcohol, i.e., the portion other than the (meth)acryloyloxy group. The number of carbon atoms in the portion other than the acryloyloxy group may be, for example, 1 or 2.

Examples of the (meth)acrylic acid ester (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, and the like. The (meth)acrylic acid ester (A1) is preferably a (meth)acrylic acid alkyl ester having 2 or less carbon atoms in the alcohol-derived portion, and more preferably methyl methacrylate.

The (meth)acrylic acid ester (A) may contain a (meth)acrylic acid ester having an epoxy group. This is because the rust prevention properties of the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment are improved.

Examples of the (meth)acrylic acid ester having an epoxy group include glycidyl (meth)acrylate, β-methyl glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, and 3,4-epoxycyclohexylpropyl (meth)acrylate. These (meth)acrylic acid esters having an epoxy group may be used alone or in combination of two or more. Among these (meth)acrylic acid esters having an epoxy group, it is preferable to include glycidyl (meth)acrylate.

Furthermore, the (meth)acrylic acid ester (A) may be any other (meth)acrylic acid ester that is neither an alkyl (meth)acrylic acid ester nor a (meth)acrylic acid ester having an epoxy group. Examples of other (meth)acrylic acid esters include (meth)acrylic acid esters having a hydroxy group and (meth)acrylic acid esters having a benzene ring.

Examples of the (meth)acrylic acid ester having a hydroxy group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, mono(meth)acrylic acid esters of polyethylene glycol, and mono(meth)acrylic acid esters of polyalkylene glycol such as mono(meth)acrylic acid esters of polypropylene glycol. These (meth)acrylic acid esters having a hydroxy group may be used alone or in combination of two or more.

Examples of (meth)acrylic acid esters having a benzene ring include benzyl (meth)acrylate.

In the present embodiment, a compound that can be classified as both the (meth)acrylic acid ester (A) and the ethylenically unsaturated monomer having a carboxy group (B) described later is regarded as being classified as the ethylenically unsaturated monomer having a carboxy group (B). For example, a (meth)acrylic acid ester having a carboxy group is classified as the ethylenically unsaturated monomer having a carboxy group (B).
In addition, a compound that can be classified as both a (meth)acrylic acid ester (A) and an ethylenically unsaturated aromatic compound (C) having a benzene ring and an ethylenically unsaturated bond described below is considered to be classified as a (meth)acrylic acid ester (A). For example, benzyl (meth)acrylate is classified as a (meth)acrylic acid ester (A).

The structural unit (a) derived from the (meth)acrylic acid ester (A) may be only a structural unit derived from one type of compound selected from these compounds, or may contain two or more types of structural units derived from two or more types of compounds.

In this embodiment, the content of structural units derived from the compounds used as monomers in copolymer (X) is a value calculated based on the amount of substance of the compounds used as monomer raw materials for copolymer (X). Specifically, for example, the content of structural units (a) derived from (meth)acrylic acid ester (A) in copolymer (X) means the ratio (mol %) of the amount of substance of (meth)acrylic acid ester (A) used as a raw material for copolymer (X) to the total amount of substance of the compounds used as monomer raw materials for copolymer (X).

The content of the structural unit (a) derived from the (meth)acrylic acid ester (A) in the copolymer (X) is 10 mol% or more. This is because, in the manufacturing method of the aqueous emulsion (α) described later, it is possible to improve the dispersibility between the monomer raw material that becomes the structural unit of the copolymer (X) and the polyepoxy compound (Y) described later. From this viewpoint, the content of the structural unit (a) derived from the (meth)acrylic acid ester (A) in the copolymer (X) is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and particularly preferably 50 mol% or more.

The content of structural units (a) derived from the (meth)acrylic acid ester (A) in the copolymer (X) is 99.9 mol% or less. This is because if the content of structural units (a) exceeds 99.9 mol%, the dispersibility of the aqueous emulsion (α) tends to decrease. From this viewpoint, the content of structural units (a) derived from the (meth)acrylic acid ester (A) in the copolymer (X) is preferably 98.5 mol% or less, and more preferably 98.0 mol% or less.

When copolymer (X) is composed only of structural unit (a) and structural unit (b), i.e., copolymer (X1), the following ratio is preferable from the viewpoint of improving the dispersibility of the monomer raw material that becomes the structural unit of copolymer (X1) and polyepoxy compound (Y). That is, the content of structural unit (a) derived from (meth)acrylic acid ester (A) in copolymer (X1) is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more.

When copolymer (X) has structural unit (a), structural unit (b), and structural unit (c), i.e., when copolymer (X) is copolymer (X2), the dispersibility of the aqueous emulsion (α) tends to decrease, so the following ratio is preferable. The content of structural unit (a) derived from (meth)acrylic acid ester (A) in copolymer (X2) is preferably 89.9 mol% or less, more preferably 80 mol% or less, even more preferably 70 mol% or less, and particularly preferably 60 mol% or less.

When introducing structural unit (a1) derived from (meth)acrylic acid ester (A1) in which the number of carbon atoms in the alcohol-derived portion is 2 or less into copolymer (X), the content is preferably 10 mol% or more, and more preferably 15 mol% or more. This is because the dispersibility of the aqueous emulsion (α) becomes good. In addition, the content of structural unit (a1) may be 50 mol% or more, or may be 60 mol% or more.

The upper limit of the content of the structural unit (a1) derived from the (meth)acrylic acid ester (A1) in the copolymer (X1) is the same as the upper limit of the content described for the structural unit (a) derived from the (meth)acrylic acid ester (A). That is, the upper limit is 99.9 mol% or less, preferably 98.5 mol% or less, and more preferably 98.0 mol% or less.

[Carboxy group-containing ethylenically unsaturated monomer (B)]
The ethylenically unsaturated monomer (B) having a carboxy group includes an ethylenically unsaturated monomer (B1) having two or more carboxy groups. The ethylenically unsaturated monomer (B1) having two or more carboxy groups may be used alone or in combination of two or more.

At least one of the ethylenically unsaturated monomers (B1) having two or more carboxy groups is preferably an ethylenically unsaturated monomer having two carboxy groups.
Specifically, at least one of the ethylenically unsaturated monomers having two carboxy groups is preferably maleic acid, itaconic acid, fumaric acid, mesaconic acid, citraconic acid, glutaconic acid, or cis-4-cyclohexene-1,2-dicarboxylic acid. As the ethylenically unsaturated monomer having three or more carboxy groups, 3-butene-1,2,3-tricarboxylic acid or ethylenetetracarboxylic acid is preferred. In order to improve the adhesion of the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment, at least one of the ethylenically unsaturated monomers having two or more carboxy groups (B1) is preferably maleic acid.

The ethylenically unsaturated monomer (B) having a carboxy group may be only an ethylenically unsaturated monomer (B1) having two or more carboxy groups, or may contain an ethylenically unsaturated monomer (B2) having one carboxy group. Therefore, the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group may be a structural unit (b1) derived only from an ethylenically unsaturated monomer (B1) having two or more carboxy groups, or may contain a structural unit (b2) derived from an ethylenically unsaturated monomer (B2) having one carboxy group.

Examples of the ethylenically unsaturated monomer (B2) having one carboxy group include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, and alkyl esters of the ethylenically unsaturated monomer (B1) having two or more carboxy groups, which have only one carboxy group. Among these ethylenically unsaturated monomers (B2) having one carboxy group, methacrylic acid is preferred. This is because the aqueous resin composition containing the aqueous emulsion (α) of this embodiment has good pigment compatibility and blend stability. The ethylenically unsaturated monomer (B2) having one carboxy group may be used alone or in combination of two or more.

The structural unit (b) derived from the ethylenically unsaturated aromatic compound (B) may be only a structural unit derived from one type of compound selected from these compounds, or may contain two or more types of structural units derived from two or more types of compounds.

The content of the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group in the copolymer (X) is 0.1 mol% or more. This is because the dispersibility of the copolymer (X) in the aqueous emulsion (α) is good. From this viewpoint, the content of the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group in the copolymer (X) is preferably 1.0 mol% or more, more preferably 2.0 mol% or more. The content of the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group in the copolymer (X) may be 2.5 mol% or more, or may be 3.0 mol% or more.

The content of structural units (b) derived from ethylenically unsaturated monomer (B) having a carboxy group in copolymer (X) is 20 mol% or less. This is to prevent copolymer (X) from becoming gelled in a high-temperature environment and to improve the high-temperature stability of aqueous emulsion (α). From this viewpoint, the content of structural units (b) derived from ethylenically unsaturated monomer (B) having a carboxy group in copolymer (X) is preferably 17 mol% or less, more preferably 15 mol% or less, even more preferably 10 mol% or less, and particularly preferably 5 mol% or less.

Next, the content of carboxy groups in the structural unit (b1) derived from the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups in the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group will be described with reference to examples.
The above content is calculated by the following formula, for example, when the ethylenically unsaturated monomer (B) having a carboxy group comprises maleic acid which is an ethylenically unsaturated monomer (B1) having two carboxy groups and methacrylic acid which is an ethylenically unsaturated monomer (B2) having one carboxy group, and contains 3 mol of maleic acid and 4 mol of methacrylic acid.
(B1)*2/[(B1)*2+(B2)]={3*2/(3*2+4)}×100=60 mol%

The content of carboxy groups in the structural unit (b1) derived from the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups in the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group is 25 mol% or more, preferably 30 mol% or more, more preferably 35 mol% or more, even more preferably 40 mol% or more, and particularly preferably 50 mol% or more. This is because the adhesion of the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment to the metal surface is improved.

The content of carboxy groups in the structural unit (b1) derived from the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups in the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group is preferably 85 mol% or less, more preferably 80 mol% or less. This is because the aqueous resin composition containing the aqueous emulsion (α) of this embodiment has good pigment compatibility and compounding stability.

[Ethylenically unsaturated aromatic compound (C)]
The ethylenically unsaturated aromatic compound (C) is a compound that does not fall under either the (meth)acrylic acid ester (A) or the ethylenically unsaturated monomer having a carboxy group (B) and has a benzene ring and an ethylenically unsaturated bond, except that the ethylenically unsaturated aromatic compound (C) does not include a maleimide compound described later.

The ethylenically unsaturated aromatic compound (C) is preferably an aromatic vinyl compound. Examples of aromatic vinyl compounds include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, tert-butoxystyrene, vinyltoluene, divinyltoluene, vinylnaphthalene, monochlorostyrene, dichlorostyrene, monobromostyrene, dibromostyrene, tribromostyrene, fluorostyrene, styrenesulfonic acid and its salts, α-methylstyrenesulfonic acid and its salts, p-hydroxystyrene, m-hydroxystyrene, o-hydroxystyrene, p-isopropenylphenol, m-isopropenylphenol, and o-isopropenylphenol. Among these ethylenically unsaturated aromatic compounds (C), styrene is particularly preferred because it provides better compounding stability of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment.

The structural unit (c) derived from the ethylenically unsaturated aromatic compound (C) may be only a structural unit derived from one type of compound selected from these compounds, or may contain two or more types of structural units derived from two or more types of compounds.

When the copolymer (X) contains the structural unit (c) derived from the ethylenically unsaturated aromatic compound (C), that is, when the copolymer (X) is the copolymer (X2), the content of the structural unit (c) in the copolymer (X2) is preferably 10 mol% or more. This is because the water resistance of the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment is improved, and better rust prevention properties are obtained. From this viewpoint, the content of the structural unit (c) in the copolymer (X2) is more preferably 20 mol% or more, and even more preferably 30 mol% or more.

When the copolymer (X) is the copolymer (X2), the content of the structural unit (c) in the copolymer (X2) is preferably 89.9 mol% or less. This is because the aqueous resin composition containing the aqueous emulsion (α) of this embodiment has better pigment miscibility and blend stability. From this perspective, the content of the structural unit (c) in the copolymer (X2) is more preferably 80 mol% or less, and even more preferably 70 mol% or less.

[Other Monomers (D)]
The other monomer (D) is a compound which does not fall under any of the (meth)acrylic acid ester (A), the ethylenically unsaturated monomer having a carboxy group (B), and the ethylenically unsaturated aromatic compound having a benzene ring and an ethylenically unsaturated bond (C), and which has an ethylenically unsaturated bond and is copolymerizable with the compound used in the synthesis of the copolymer (X).
Examples of the other monomer (D) include a conjugated diene compound, a maleimide compound, and a vinyl compound having a cyano group.

Examples of the conjugated diene compounds include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, and chloroprene (2-chloro-1,3-butadiene). These conjugated diene compounds may be used alone or in combination of two or more.

Examples of the maleimide compounds include maleimide, N-methylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-dodecylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(4-methylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-diethylphenyl)maleimide, N-(2-methoxyphenyl)maleimide, N-benzylmaleimide, N-(4-hydroxyphenyl)maleimide, N-naphthylmaleimide, and N-cyclohexylmaleimide. These maleimide compounds may be used alone or in combination of two or more.

Examples of the vinyl compounds having a cyano group include acrylonitrile, methacrylonitrile, α-ethylacrylonitrile, α-isopropylacrylonitrile, α-chloroacrylonitrile, and α-fluoroacrylonitrile. These vinyl compounds having a cyano group may be used alone or in combination of two or more.

The amount of copolymer (X) contained in the aqueous emulsion (α) can be selected arbitrarily, but is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, based on the total amount of the aqueous emulsion (α). The amount of copolymer (X) contained in the aqueous emulsion (α) is preferably 60% by mass or less, more preferably 57% by mass or less, based on the total amount of the aqueous emulsion (α). However, it is not limited to these examples.

<1-2. Polyepoxy compound (Y)>
The polyepoxy compound (Y) is a compound having no ethylenically unsaturated bond and having two or more epoxy groups in one molecule. Only one type of polyepoxy compound (Y) may be used, or two or more types may be used.

Specific examples of the polyepoxy compound (Y) include diglycidyl ether of bisphenol A, diglycidyl ether of hydrogenated bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of hydrogenated bisphenol F, glycerin polyglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diglycidyl ester of phthalic acid, 1,4-cyclohexanedimethanol diglycidyl ether, 1,3-cyclohexanedimethanol diglycidyl ether, and diglycidyl ester of hexahydrophthalic acid.

At least one of the polyepoxy compounds (Y) is preferably a bisphenol type epoxy compound, a hydrogenated bisphenol type epoxy compound, a diglycidyl ether, a triglycidyl ether, a tetraglycidyl ether, a diglycidyl ester, a triglycidyl ester, or a tetraglycidyl ester. The polyepoxy compound (Y) is more preferably a bisphenol type epoxy compound and/or a hydrogenated bisphenol type epoxy compound, even more preferably a bisphenol A type epoxy compound and/or a hydrogenated bisphenol A type epoxy compound, and even more preferably a bisphenol A type epoxy compound. This is because the water resistance and rust prevention of the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment is further improved.

The weight average molecular weight of the polyepoxy compound (Y) is not particularly limited, but is preferably 1000 or less, more preferably 800 or less, and even more preferably 500 or less. This is because the compatibility of the polyepoxy compound (Y) with the copolymer (X) is improved, resulting in an aqueous emulsion (α) with excellent dispersibility and storage stability. The lower limit of the weight average molecular weight of the polyepoxy compound (Y) can be selected arbitrarily and may be, for example, 200 or 300, but is not limited thereto.

The epoxy equivalent of the polyepoxy compound (Y) (mass of the polyepoxy compound (Y) per 1 mol of epoxy groups) is preferably 500 g/mol or less, more preferably 350 g/mol or less, even more preferably 250 g/mol or less, and particularly preferably 200 g/mol or less. This is because the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment has high strength. The lower limit of the epoxy equivalent can be selected arbitrarily and may be, for example, 70 g/mol or more or 120 g/mol or more, but is not limited to these examples.

The content of polyepoxy compound (Y) per 100 parts by mass of copolymer (X) is 1.0 part by mass or more. This is because the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of this embodiment has excellent rust prevention properties even when cured at room temperature. From this viewpoint, the content of polyepoxy compound (Y) per 100 parts by mass of copolymer (X) is preferably 11 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 33 parts by mass or more.

The content of the polyepoxy compound (Y) is 67 parts by mass or less per 100 parts by mass of the total amount of the copolymer (X). This is because the aqueous emulsion (α) of the present embodiment has excellent dispersibility in the aqueous resin composition containing the aqueous emulsion (α). From this viewpoint, the content of the polyepoxy compound (Y) is preferably 50 parts by mass or less, more preferably 47 parts by mass or less per 100 parts by mass of the total amount of the copolymer (X).
In the present embodiment, 100 parts by mass of the total amount of copolymer (X) is regarded as 100 parts by mass of the total amount of the monomer raw materials used in the polymerization of copolymer (X).

<1-3. Aqueous medium (Z)>
The aqueous medium (Z) may be any medium, and is preferably water. However, as long as the dispersibility of the aqueous emulsion (α) of the present embodiment is not impaired, for example, a water-soluble solvent may be added to water. The resulting solution may be used as the aqueous medium (Z). The hydrophilic (water-soluble) solvent to be added to water can be arbitrarily selected, and examples thereof include methanol, ethanol, and N-methylpyrrolidone.

<1-4. Method for producing aqueous emulsion (α)>
(First manufacturing method)
When the aqueous emulsion (α) contains emulsified particles containing the copolymer (X) and the polyepoxy compound (Y), it can be produced, for example, by the method shown below.

The aqueous emulsion (α) containing emulsion particles containing the copolymer (X) and the polyepoxy compound (Y) can be produced by an emulsion polymerization method. Specifically, the aqueous emulsion (α) can be produced by a method in which an emulsion polymerization step is carried out in which a monomer raw material (i.e., all monomers that become structural units of the copolymer (X)) containing a (meth)acrylic acid ester (A), an ethylenically unsaturated monomer (B) having a carboxy group, and an optional ethylenically unsaturated aromatic compound (C) and/or other monomers (D) is emulsion-polymerized in an aqueous medium (Z) in the presence of the polyepoxy compound (Y).

When an aqueous emulsion (α) containing emulsion particles containing a copolymer (X) and a polyepoxy compound (Y) is produced using an emulsion polymerization method, an emulsifier, a polymerization initiator, a basic substance, a chain transfer agent, etc. may be contained in the solution to be emulsion polymerized, which contains the monomer raw material, the polyepoxy compound (Y), and the aqueous medium (Z). The emulsifier and/or the basic substance may be added to the aqueous emulsion (α) obtained after the emulsion polymerization.

The content of each raw material in the total raw materials used to produce the aqueous emulsion (α) of this embodiment is the same as the content of the components derived from each raw material in the aqueous emulsion (α) obtained after emulsion polymerization. Therefore, the content of each monomer component in the monomer raw material used to produce the aqueous emulsion (α) is the same as the content of the structural units derived from each monomer in the structural units of the copolymer (X) contained in the emulsion particles containing the copolymer (X) and the polyepoxy compound (Y) contained in the aqueous emulsion (α).

(emulsifier)
The emulsifier improves the dispersion stability of the solution during emulsion polymerization and/or the aqueous emulsion (α) obtained after emulsion polymerization. The emulsifier that may be used in the emulsion polymerization step is preferably a non-polymerizable surfactant. The non-polymerizable surfactant is a surfactant that does not have a polymerizable unsaturated bond in its chemical structure. The surfactant that may be used in the emulsion polymerization step is preferably an anionic surfactant and/or a nonionic surfactant.

Examples of the anionic surfactant include alkyl sulfate, alkyl benzene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, polyoxyalkylene alkyl sulfate, and polyoxyalkylene alkyl phosphate.
Examples of the nonionic surfactant include polyoxyalkylene alkyl ethers, polyoxyalkylene alkylphenol ethers, polyoxyalkylene fatty acid esters, and polyoxyalkylene sorbitan fatty acid esters.

These emulsifiers may be used alone or in combination of two or more. Of these emulsifiers, it is preferable to use a combination of an alkylbenzene sulfonate and a polyoxyalkylene alkyl ether. As the alkylbenzene sulfonate, it is preferable to use sodium dodecylbenzene sulfonate, and as the polyoxyalkylene alkyl ether, it is preferable to use a polyoxyethylene alkyl ether. This is because the dispersion stability of the aqueous emulsion (α) is improved.

(Polymerization initiator)
The polymerization initiator used in the emulsion polymerization step may be, for example, a peroxide, or a combination of a peroxide and a reducing agent. Examples of the peroxide include persulfates such as potassium persulfate and ammonium persulfate, and hydrogen peroxide. Examples of the reducing agent include sodium hydrogen sulfite, sodium sulfoxylate formaldehyde, ascorbic acid, sulfites, tartaric acid or a salt thereof, and the like.

(Chain Transfer Agent)
In the above emulsion polymerization step, a chain transfer agent is used to adjust the molecular weight of the copolymer (X) obtained by emulsion polymerization. Examples of the chain transfer agent that can be used include alcohols such as methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol, and mercaptans such as n-dodecyl mercaptan, tert-dodecyl mercaptan, and n-butyl mercaptan.

(Basic substances)
In the above emulsion polymerization step, the acidic components contained in the raw materials used to produce the aqueous emulsion (α) are neutralized by adding a basic substance. As a result, the pH of the solution during emulsion polymerization and/or the aqueous emulsion (α) after emulsion polymerization is in an appropriate range. Therefore, the stability of the solution during emulsion polymerization and/or the aqueous emulsion (α) after emulsion polymerization is improved.

Examples of basic substances include ammonia, triethylamine, ethanolamine, sodium hydroxide, lithium hydroxide, etc. These basic substances may be used alone or in combination of two or more.

In the emulsion polymerization process for producing an aqueous emulsion (α) containing emulsion particles including a copolymer (X) and a polyepoxy compound (Y), the components including the monomer raw materials used to produce the aqueous emulsion (α) may be charged all at once in a reaction vessel and emulsion-polymerized, or the components including the monomer raw materials may be continuously fed to the reaction vessel and emulsion-polymerized. The emulsion polymerization is preferably carried out while stirring the solution in the reaction vessel during emulsion polymerization.

In the first manufacturing method, the emulsion polymerization for producing the aqueous emulsion (α) containing the emulsion particles containing the copolymer (X) and the polyepoxy compound (Y) can be carried out at any temperature. The temperature of the emulsion polymerization can be, for example, 30°C to 90°C, preferably 40°C to 85°C, and more preferably 40°C to 70°C. When the temperature of the emulsion polymerization is 30°C or higher, the emulsion polymerization reaction is promoted. Therefore, the emulsion particles containing the copolymer (X) and the polyepoxy compound (Y) can be efficiently produced. In addition, when the temperature of the emulsion polymerization is 90°C or lower, the emulsion polymerization step can suppress the reaction between the carboxy group in the compound contained in the monomer raw material and the epoxy group contained in the polyepoxy compound (Y).

According to the first production method, an aqueous emulsion (α) is obtained in which emulsified particles, in which a polyepoxy compound (Y) is dispersed in particles made of a copolymer (X), are dispersed in an aqueous medium (Z).
In this embodiment, the state in which "polyepoxy compound (Y) is dispersed in particles made of copolymer (X)" does not necessarily mean that copolymer (X) and polyepoxy compound (Y) are compatible with each other, but it is sufficient that domains of polyepoxy compound (Y) are present without bias both at the center side and the surface side of particles made of copolymer (X).

(Second manufacturing method)
When the aqueous emulsion (α) contains emulsion particles containing the copolymer (X) and emulsion particles containing the polyepoxy compound (Y), it can be produced, for example, by the method shown below.
In the second production method, an emulsion containing emulsified particles containing the copolymer (X) and an emulsion containing emulsified particles containing the polyepoxy compound (Y) are separately produced.

The emulsion containing emulsified particles including copolymer (X) can be produced by emulsion polymerization of monomer raw materials (i.e., all monomers that become structural units of copolymer (X)) including (meth)acrylic acid ester (A), ethylenically unsaturated monomer having a carboxy group (B), and optional ethylenically unsaturated aromatic compound (C) and/or other monomers (D) in an aqueous medium (Z).

In this case, the solution to be emulsion-polymerized containing the monomer raw material and the aqueous medium (Z) may contain an emulsifier, a polymerization initiator, a basic substance, a chain transfer agent, etc. The emulsifier and/or the basic substance may be added to the emulsion containing the emulsion particles containing the copolymer (X) obtained after the emulsion polymerization. The emulsifier, polymerization initiator, basic substance, and chain transfer agent may be the same as those that can be used in producing the aqueous emulsion (α) containing the emulsion particles containing the copolymer (X) and the polyepoxy compound (Y) in the first production method.

In the emulsion polymerization for producing an emulsion containing emulsion particles including copolymer (X), the components including the monomer raw materials may be charged into a reaction vessel all at once and emulsion polymerization may be performed, or the components including the monomer raw materials may be continuously fed into the reaction vessel and emulsion polymerization may be performed. It is preferable to carry out the emulsion polymerization while stirring the reaction solution in the reaction vessel.

Emulsion polymerization for producing an emulsion containing emulsion particles containing copolymer (X) can be carried out at any temperature. The temperature of emulsion polymerization can be, for example, 30°C to 90°C, preferably 40°C to 85°C, and more preferably 40°C to 80°C. When the temperature of emulsion polymerization is 30°C or higher, the emulsion polymerization reaction is promoted. Therefore, emulsion particles containing copolymer (X) can be produced efficiently. In addition, when the aqueous medium (Z) is water, it is preferable that the temperature of emulsion polymerization is 90°C or lower, because it is possible to produce an emulsion without boiling the aqueous medium (Z).

The emulsion containing emulsified particles containing the polyepoxy compound (Y) can be produced by dispersing the polyepoxy compound (Y) in the aqueous medium (Z) by a known method. When dispersing the polyepoxy compound (Y) in the aqueous medium (Z), an emulsifier may be used as necessary. The emulsifier may be the same as that which can be used in producing the aqueous emulsion (α) containing emulsified particles containing the copolymer (X) and the polyepoxy compound (Y) in the first production method.

As the emulsion containing emulsified particles containing polyepoxy compound (Y), commercially available products may be used. For example, an emulsion containing emulsified particles containing bisphenol A type epoxy, which is polyepoxy compound (Y) (solid content 47%; content of polyepoxy compound (Y) in the emulsion 45 to 49% by mass; manufactured by ADEKA Corporation; product name: ADEKA RESIN EM-101-50), an emulsion containing emulsified particles containing bisphenol A type epoxy (solid content 53%; epoxy equivalent of polyepoxy compound (Y): 990; manufactured by Daicel-Allnex Corporation; product name: BECKOPOX EP386w/52WA), an emulsion containing emulsified particles containing bisphenol A type epoxy (solid content 46%; epoxy equivalent of polyepoxy compound (Y): 4200; manufactured by Daicel-Allnex Corporation; product name: BECKOPOX EP2307w/45WAMP), etc. may be mentioned.

Next, the emulsion containing the emulsion particles containing the copolymer (X) and the emulsion containing the emulsion particles containing the polyepoxy compound (Y) are mixed using a known method. This results in an aqueous emulsion (α) in which the emulsion particles containing the copolymer (X) and the emulsion particles containing the polyepoxy compound (Y) are dispersed in the aqueous medium (Z).

In the second production method, the content of each raw material in the total raw materials used to produce the aqueous emulsion (α) (the sum of the raw materials for the emulsion containing emulsion particles containing the copolymer (X) and the raw materials for the emulsion containing emulsion particles containing the polyepoxy compound (Y)) is the same as the content of the components derived from each raw material in the aqueous emulsion (α) obtained after production.

<1-5. Characteristics of aqueous emulsion (α)>
[pH of aqueous emulsion (α)]
The pH of the aqueous emulsion (α) is preferably 2 to 10, and more preferably 5 to 9. When the pH is within this range, the mechanical stability and chemical stability of the aqueous emulsion (α) are improved. The pH is a value measured at a liquid temperature of 23° C. using a pH meter with a hydrogen ion concentration indicator having a glass electrode as a standard electrode.

The pH can be adjusted, for example, by adding a basic substance to the solution during or after emulsion polymerization for producing an aqueous emulsion (α) containing emulsified particles containing copolymer (X) and polyepoxy compound (Y) in the first production method, or to the solution during or after emulsion polymerization for producing an emulsion containing emulsified particles containing copolymer (X) in the second production method.

[Non-volatile content concentration of aqueous emulsion (α)]
The non-volatile content of the aqueous emulsion (α) is preferably 10 to 65% by mass, more preferably 20 to 60% by mass, and even more preferably 30 to 55% by mass. The non-volatile content of the aqueous emulsion (α) can be appropriately determined in consideration of the workability in the step of applying the aqueous resin composition to the surface to be coated. The non-volatile content of the aqueous emulsion (α) can be appropriately adjusted by adjusting the amount of the aqueous medium (Z) added.

The non-volatile content of the aqueous emulsion (α) can be determined by the following method. 1 g of the aqueous emulsion (α) is weighed out onto an aluminum dish with a diameter of 5 cm, and dried at 105°C for 1 hour in a dryer at atmospheric pressure while circulating air. The mass of the resulting residue is then measured. The ratio (mass%) of the measured mass of the residue to the mass of the aqueous emulsion (α) before drying is calculated as the non-volatile content of the aqueous emulsion (α).

[Viscosity of aqueous emulsion (α)]
In this embodiment, the viscosity of the aqueous emulsion (α) is measured at 23° C. The viscosity of the aqueous emulsion (α) is measured using a B-type viscometer at a rotation speed of 60 rpm, with a rotor selected according to the viscosity of the aqueous emulsion (α). For example, when the viscosity of the aqueous emulsion (α) is about several mPa·s to several hundred mPa·s, the measurement is performed using rotor No. 1. When the aqueous emulsion (α) contains emulsion particles containing a copolymer (X) and emulsion particles containing a polyepoxy compound (Y), the viscosity of the aqueous emulsion (α) means the viscosity measured immediately after mixing the emulsion particles containing the copolymer (X) and the emulsion particles containing the polyepoxy compound (Y) (in other words, immediately after producing the aqueous emulsion (α)).

The viscosity of the aqueous emulsion (α) may be, for example, 0.1 to 1000 mPa·s, 1 to 100 mPa·s, 3 to 50 mPa·s, or 5 to 25 mPa·s. When the viscosity of the aqueous emulsion (α) is 0.1 to 1000 mPa·s, the aqueous resin composition containing it is easy to apply, and the components are mixed uniformly.

[2. Aqueous resin composition]
The aqueous resin composition of the present embodiment includes the aqueous emulsion (α) of the above-mentioned embodiment. The aqueous resin composition of the present embodiment may consist of the aqueous emulsion (α) of the above-mentioned embodiment.

The aqueous resin composition according to this embodiment may contain, in addition to the aqueous emulsion (α), other components as necessary depending on the intended use of the aqueous resin composition.
Other components may include additives such as pigments, thickeners, primary rust inhibitors, coupling agents, fillers, organic or inorganic hollow balloons, pigment dispersants, surfactants, defoamers, preservatives (e.g., biocides, mildewcides, fungicides, algaecides, combinations thereof, etc.), flow agents, leveling agents, neutralizing agents (e.g., hydroxides, amines, ammonia, carbonates, etc.).

Examples of pigments that may be included in the aqueous resin composition include titanium oxide, talc, barium sulfate, carbon black, red iron oxide, calcium carbonate, silicon oxide, talc, mica, kaolin, clay, ferrite, and silica sand. The pigment may contain only one type of compound, or may contain two or more types of compounds. The pigment is preferably included in the aqueous resin composition in an amount of 0.1 to 50% by mass, and more preferably 1 to 40% by mass. This is to improve the hiding power of the coating film.

As the pigment dispersant, for example, amino alcohols, polycarboxylic acid surfactants such as polycarboxylates, and the like can be used.
As the thickener, for example, hydroxyethyl cellulose, polyether polyol-based urethane polymer, etc. can be used.
As the primary rust inhibitor, for example, sodium nitrite, benzotriazole, etc. can be used.
As the surfactant, for example, the same emulsifier as that usable in producing the aqueous emulsion (α) can be used.

As the coupling agent, it is preferable to use a silane coupling agent. Examples of the silane coupling agent include epoxy silane compounds. Specific examples include 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

When the aqueous resin composition contains a silane coupling agent, the content of the silane coupling agent is preferably 0.1 to 5 mol %, and more preferably 0.5 to 4 mol %, relative to the amount of epoxy groups contained in the polyepoxy compound (Y). This is because the aqueous resin composition after curing has improved rust resistance and adhesion to metal materials.

The aqueous resin composition according to the present embodiment can form a coating film exhibiting good adhesion even when cured at room temperature without using a curing agent. Therefore, it is preferable that the aqueous resin composition does not contain a curing agent. However, the aqueous resin composition according to the present embodiment may contain a curing agent and/or a curing accelerator as necessary.
When the aqueous resin composition contains a curing agent, it may contain a known curing agent, but it is preferable that the aqueous resin composition does not contain an amine-based curing agent because a strong odor is generated during the process of preparing the aqueous resin composition by mixing with the aqueous emulsion and during the process of applying the prepared aqueous resin composition.

At least one of the curing agents may be a polyamine having active hydrogen reactive to epoxy groups. In this embodiment, the term "polyamine" refers to a compound having two or more amino groups in one molecule. At least one of the polyamines is preferably a compound having an amino group that is unsubstituted or has only one substituent. It is more preferable that at least two of the amino groups of the polyamine having active hydrogen are either primary amino groups (-NH ₂ (no substituent)) or secondary amino groups (-NHR (R is a substituent)). The type of polyamine having active hydrogen reactive to epoxy groups contained in the curing agent may be only one type, or may be two or more types.

Examples of polyamines include aliphatic polyamines, alicyclic polyamines, and aromatic polyamines.
Examples of the aliphatic polyamine include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and modified products thereof.
Examples of aromatic polyamines include m-xylylenediamine, diaminodiphenylmethane, m-phenylenediamine, diaminodiphenylsulfone, and modified products thereof.

As the hardener, commercially available products may be used. Examples of commercially available hardeners include ADEKA Hardener EH-8051 (polyamine) (manufactured by ADEKA Corporation); Fujicure FXI-919, Tomide TXH-674-B and TXS-53-C (manufactured by T&K Toka Corporation); Gaskamine 328 (Mitsubishi Gas Chemical Company, Inc.); Jeffamine D-230 and Jeffamine ED-600 (Huntsman Japan Co., Ltd.).

The smaller the amount of curing agent contained in the aqueous resin composition, the better. The amount of curing agent contained in the aqueous resin composition is preferably such that the chemical equivalent of the active hydrogen in the polyamine contained in the curing agent relative to the epoxy groups contained in the aqueous emulsion (α) is 1.5 equivalents or less, more preferably 1.3 equivalents or less, even more preferably 1.2 equivalents or less, and most preferably no curing agent is contained. This is because it improves the working environment in the work of mixing with the aqueous emulsion to prepare the aqueous resin composition and in the work of applying the prepared aqueous resin composition.

The amount of curing agent used in the aqueous resin composition is preferably 0.10 equivalents or more, more preferably 0.20 equivalents or more, even more preferably 0.50 equivalents or more, and particularly preferably 0.60 equivalents or more, relative to the epoxy groups in the aqueous emulsion (α). This is because the crosslinking reaction between the polyepoxy compound (Y) and the curing agent in the aqueous resin composition proceeds sufficiently, resulting in a coating film in which the penetration of water and ions is more suppressed. In addition, the increased reaction rate of the epoxy groups results in a coating film with better adhesion to metal materials. For these reasons, by using an amount of curing agent such that the active hydrogen in the polyamine is 0.10 equivalents or more, the coating film made of the cured product of the aqueous resin composition exhibits rust prevention properties for a long period of time.

The curing accelerator has the function of accelerating the curing of the aqueous resin composition and forming a coating film with high hardness and water resistance. The curing accelerator is preferably a tertiary amine that does not have an active hydrogen on the nitrogen that is reactive to an epoxy group. The tertiary amine in this embodiment is a compound represented by NR ¹¹ R ²² R ³³ (wherein R ¹¹ R ²² R ³³ are substituents, and may be different from each other or may contain two or more of the same. R ¹¹ R ²² R ³³ may be bonded to each other to form a ring.).

At least one of the curing accelerators is preferably a tertiary aliphatic amine, a tertiary alicyclic amine, or a tertiary heteroaromatic amine. This is to increase the nucleophilicity of the curing accelerator and efficiently advance the curing reaction of the aqueous resin composition.

Examples of the tertiary aliphatic amine include triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-sec-butylamine, and tri-n-hexylamine.
Examples of the tertiary alicyclic amine include 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,8-diazabicyclo[5.4.0]undec-7-ene.
As the tertiary heteroaromatic amine, it is preferable to use a compound having an imidazole skeleton, and specific examples thereof include imidazole, 2-methylimidazole, and 2-ethyl-4-methylimidazole.

The curing accelerator may be a tertiary aromatic amine having a phenyl group that is not directly bonded to a nitrogen atom of the tertiary amine (NR ¹¹ R ²² R ³³ ). Such tertiary aromatic amines include dimethylbenzylamine, diethylbenzylamine, tribenzylamine, 2,4,6-trisdimethylaminomethylphenol, 2-phenylimidazole, and the like.

Among these curing accelerators, it is particularly preferable to use the following compounds (i) and/or (ii).
(i) A tertiary alicyclic amine which does not have an active hydrogen atom on the nitrogen that is reactive with an epoxy group and has a saturated ring structure in which two nitrogen atoms are bonded to each other by three substituents of an amino group.
(ii) A tertiary heteroaromatic amine which does not have an active hydrogen reactive with an epoxy group and has a heteroaromatic ring structure containing two or more nitrogen atoms.

(i) Tertiary alicyclic amines include, for example, 1,4-diazabicyclo[2.2.2]octane (DABCO). (ii) Tertiary heteroaromatic amines include, for example, imidazole.
The curing accelerators may be used alone or in combination of two or more.

The amount of curing accelerator used in the aqueous resin composition is preferably 0.0070 equivalents or more, more preferably 0.010 equivalents or more, even more preferably 0.05 equivalents or more, and particularly preferably 0.10 equivalents or more, in terms of chemical equivalent to the epoxy groups contained in the aqueous emulsion (α). This is because the coating film made of the cured product of the aqueous resin composition of this embodiment has a high crosslink density, high adhesion to the substrate, and exhibits rust prevention properties for a long period of time.

The amount of the curing accelerator is preferably 1.5 equivalents or less, more preferably 0.70 equivalents or less, even more preferably 0.44 equivalents or less, and particularly preferably 0.38 equivalents or less, relative to the epoxy groups contained in the aqueous emulsion (α). This is because the cured product of the aqueous resin composition of this embodiment becomes a coating film with good adhesion to metal materials. Furthermore, when the content of the curing accelerator is 1.5 equivalents or less, it is possible to prevent the aqueous resin composition from gelling in a short period of time, and a coating film made of a cured product with good rust resistance is obtained.

When the aqueous resin composition contains other components, the aqueous resin composition of this embodiment may be produced by mixing and stirring the aqueous emulsion (α) with the other components and/or the curing agent by a known method. This produces the aqueous resin composition of this embodiment in which each component is dispersed.

Stirring during mixing can be performed, for example, using Robomics (manufactured by Primix Corporation). In order to thoroughly disperse each component contained in the aqueous resin composition of this embodiment, the stirring time during mixing is preferably 5 minutes or more. In addition, in order to prevent the resin components contained in the aqueous resin composition from hardening, the stirring time is preferably within 1 hour.

The aqueous resin composition of this embodiment contains the aqueous emulsion (α) of this embodiment. Therefore, even when curing at room temperature without using a curing agent, a coating film that exhibits good adhesion can be formed.

More specifically, the copolymer (X) contained in the aqueous emulsion (α) contains a structural unit (b) derived from an ethylenically unsaturated monomer (B) having a carboxy group, the content of the structural unit (b) in the copolymer (X) is 0.1 mol% or more and 20 mol% or less, and the content of the carboxy group of the structural unit (b1) derived from an ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups of the structural unit (b) is 25 mol% or more. Therefore, the copolymer (X) contains a sufficient amount of carboxy groups. This improves the dispersibility of the copolymer (X) in the aqueous emulsion (α). Moreover, the copolymer (X) contains an appropriate amount of the structural unit (b1). The two or more carboxy groups of the structural unit (b1) can interact with metal materials such as iron. Specifically, the two or more carboxy groups of the structural unit (b1) can be coordinated to metal ions such as iron ions at two or more locations (multidentate coordination). This allows the coating film made of the cured product of the aqueous resin composition containing the aqueous emulsion (α) of the present embodiment to have excellent adhesion to the surface of the metal material, thereby preventing water from penetrating between the coating film and the metal material and providing excellent rust prevention properties.
Moreover, the aqueous resin composition of the present embodiment has excellent dispersion stability compared to an aqueous resin composition containing a curing agent, and therefore can ensure a sufficient application time (pot life) compared to, for example, a coating material containing an aqueous emulsion containing an epoxy compound and an amine-based curing agent.

[3. Coating film manufacturing method]
Next, a method for producing a coating film made of a cured product of the aqueous resin composition of this embodiment will be described in detail. In the method for producing a coating film of this embodiment, the aqueous resin composition of this embodiment is applied to a surface to be coated (application step).

Examples of materials forming the surface to be coated include metal materials such as iron, etc. The surface to be coated may be previously subjected to a surface treatment such as a primer or undercoat.
A known method can be used as a method for applying the aqueous resin composition. Examples of the application method include, but are not limited to, a method using a brush, a roller, a spray, etc. In addition, in order to prevent the resin component contained in the aqueous resin composition from curing before the application process is completed, the application process is preferably completed within 4 hours after the preparation of the aqueous resin composition, and more preferably within 3 hours.

In the method for producing a coating film according to the present embodiment, it is preferable to cure the resin composition applied to the surface to be coated (curing step) after the application step.
In the curing step, for example, the surface of the substrate to which the aqueous resin composition is applied is dried and cured to cure the resin component contained in the aqueous resin composition. The curing time varies depending on the temperature of the curing atmosphere. For example, it can be 10 to 17 days at 10°C, 7 to 14 days at 20°C, 5 to 12 days at 30°C, and 3 to 10 days at 40°C.

The aqueous resin composition of this embodiment can be cured at room temperature. Therefore, in the curing step of this embodiment, the aqueous resin composition applied to the surface to be coated is preferably cured at a temperature of 20° C. to 40° C., more preferably at a temperature of 20° C. to 30° C. This is because, after the aqueous resin composition is applied to the surface to be coated of a coating object installed outdoors, the aqueous resin composition can be dried and cured in the outdoor atmosphere.
In this embodiment, an example has been described in which the aqueous resin composition applied to the surface to be coated is cured at a temperature of 20°C to 40°C. However, in order to shorten the curing time in the curing step, the aqueous resin composition applied to the surface to be coated may be heated.

In the coating film manufacturing method of this embodiment, even when the aqueous resin composition of this embodiment is cured at room temperature without using a curing agent, a coating film with good adhesion to metal materials is obtained. Therefore, even if the curing process is performed at a temperature of 20°C to 40°C, a coating film with excellent rust prevention properties is obtained.

[4. Coating film]
The coating film of the present embodiment is made of a cured product of the aqueous resin composition of the present embodiment. The coating film of the present embodiment can be formed by the above-mentioned method for producing a coating film.
The coating film of the present embodiment may be one layer of a coating film having a multi-layer structure. That is, the coating film of the present embodiment may be laminated with a coating film consisting of an undercoat layer provided under the coating film consisting of the cured product of the aqueous resin composition of the present invention, and/or a topcoat layer provided on the upper layer, if necessary. When the coating film of the present embodiment is one layer of a coating film having a multi-layer structure, it is preferably the layer in contact with the surface to be coated of the coating film having the multi-layer structure.

The coating film of this embodiment is made of a cured product of the aqueous resin composition of this embodiment. Therefore, the coating film of this embodiment can be cured at room temperature, and is therefore suitable as a coating film that is used outdoors, for example on steel towers, bridges, ships, port facilities, etc., and is formed by a method of applying and curing outdoors. In addition, the coating film of this embodiment has good adhesion and rust prevention properties. Therefore, it is suitable as a coating film formed on the surface of metal products.

5. Fields of application
The aqueous emulsion, its production method, aqueous resin composition, and coating film production method of the present invention are useful in various fields.
In particular, the aqueous resin composition of the present invention is suitable for use as an anticorrosive coating applied to the surfaces of metal products used outdoors, such as steel towers, bridges, ships, and port facilities.

The article on which a coating film made of a cured product of the aqueous resin composition of the present invention is formed, i.e., the object to which the aqueous resin composition of the present invention is applied, can be selected arbitrarily. Specific examples of the object to which the composition is applied include metal products used outdoors, such as steel towers, bridges, ships, and port facilities, various household items, home appliances such as refrigerators, play equipment installed in amusement parks and parks, sporting goods, buildings (interiors, exteriors, etc.), various industrial products and parts thereof, including transport machinery and machine tools, automobile bodies and chassis, railroad car bodies and underfloor equipment, marine containers, and aircraft.

The present invention will be described in detail below using examples. Note that the following examples do not limit the present invention in its entirety, and all implementations that do not deviate from the content of this description are included in the technical scope of the present invention.

<1. Synthesis of aqueous emulsion (α)>
(Aqueous emulsion (α-1))
A separable flask equipped with a cooling tube, a thermometer, a stirrer, and a dropping funnel was charged with 190 parts by mass of ion-exchanged water, and the temperature was raised to 60°C. Nitrogen gas was blown into the contents of the separable flask to deoxygenate them. An emulsion containing methyl methacrylate, 2-ethylhexyl acrylate, maleic acid, and methacrylic acid as monomer raw materials that are structural units of the copolymer (X), bisphenol A-type epoxy as the polyepoxy compound (Y), sodium dodecylbenzenesulfonate as an emulsifier, polyoxyethylene alkyl ether, and 231 parts by mass of ion-exchanged water was dropped into the flask over a period of 3 hours in the amounts (parts by mass) shown in Table 1.

At the same time as the emulsion, 1.5 parts by mass of potassium persulfate, an oxidizing agent, dissolved in 38 parts by mass of ion-exchanged water, and 0.5 parts by mass of sodium hydrogen sulfite, a reducing agent, dissolved in 19 parts by mass of ion-exchanged water, were added dropwise at 60°C over 3.3 hours as a polymerization initiator, and polymerization was carried out. After the emulsion and polymerization initiator were added dropwise, the temperature of the solution was kept at 60°C and the solution was stirred for 1.5 hours to mature. The solution was then cooled to room temperature, and 3.3 parts by mass of 25% ammonia water was added as a basic substance to obtain an aqueous emulsion (α-1) containing emulsified particles containing copolymer (X) and polyepoxy compound (Y).

(Aqueous emulsions (α-2) to (α-5))
Aqueous emulsions (α-2) to (α-5) containing emulsified particles containing copolymer (X) and polyepoxy compound (Y) were synthesized in the same manner as for aqueous emulsion (α-1), except that each material shown in Table 1 was used in the amount (parts by mass) shown in Table 1.

The amounts of each material used in the synthesis of the aqueous emulsions (α-1) to (α-5) are shown in Table 1.
The column "parts by mass" indicates the amount of each raw material used in parts by mass. The column "mol % of copolymer (X)" indicates the ratio of the amount of each raw material to the total amount of the amounts of the monomer raw materials used in copolymer (X).
The value of "ion-exchanged water" shown in Table 1 indicates the content of ion-exchanged water contained in the synthesized aqueous emulsions (α-1) to (α-5).
The value for "ammonia water" shown in Table 1 is the content of 25 mass% ammonia water, and indicates the total amount of water and ammonia contained in the ammonia water.

As the polyepoxy compound (Y) shown in Table 1, bisphenol A type epoxy (epoxy equivalent: 190 g/mol; manufactured by Mitsubishi Chemical Corporation; product name: JER828) was used.

For the aqueous emulsions (α-1) to (α-5), the content (mol %) of the carboxy group derived from the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups derived from the ethylenically unsaturated monomer (B) having a carboxy group, calculated based on the amount of each material used in the synthesis, is shown in Table 2.
In addition, for the aqueous emulsions (α-1) to (α-5), the content of polyepoxy compound (Y) per 100 parts by mass of the total amount of the monomer raw materials used in the synthesis of copolymer (X), i.e., per 100 parts by mass of the total amount of copolymer (X), calculated based on the amount of each material used in the synthesis, is shown in Table 2.

2. Evaluation of aqueous emulsion (α)
The aqueous emulsions (α-1) to (α-5) were evaluated for the following items, respectively, and the results are shown in Table 3.
In the following description, the aqueous emulsions (α-1) to (α-5) may be collectively referred to as aqueous emulsion (α).

<2-1. Residual rate of epoxy groups>
The residual epoxy group ratio of the aqueous emulsion (α) is the ratio of the amount of epoxy groups N ₁ [mol/g] contained in the aqueous emulsion (α) after synthesis to the total amount of epoxy groups N ₂ [mol/g] contained in the components (including raw materials, initiators, solvents, other additives, etc.) used in the synthesis of the aqueous emulsion (α).

The amount of epoxy groups N ₁ [mol/g] of the aqueous emulsion (α) after synthesis was measured by the method shown below. Excess hydrogen chloride was added to the total amount of epoxy groups contained in the components (raw materials) used in the synthesis of the aqueous emulsion (α) to react with the epoxy groups. Next, the amount of remaining hydrogen chloride was confirmed by titrating the unreacted hydrogen chloride with potassium hydroxide. At this time, potassium hydroxide is consumed by reaction with acidic components such as carboxylic acids contained in the aqueous emulsion (α). For this reason, the amount of acidic components was titrated in advance by a blank measurement without using hydrogen chloride, and the result of this measurement was corrected. The specific measurement procedure is as follows (i) to (ii).

(i) Blank measurement (confirmation of the amount of acidic components)
Aqueous emulsion (α) was weighed out in an amount of W ₁ [g] (5 g in this example) into a 100 mL Erlenmeyer flask, 25 g of tetrahydrofuran (THF) was added, and the mixture was stirred with a magnetic stirrer to obtain a homogeneous solution. 0.15 mL of a 0.1% by mass aqueous solution of cresol red was added to this solution as an indicator. The solution was titrated with a 0.1 M potassium hydroxide/ethanol solution while stirring. The point at which the purple color persisted for 30 seconds after the potassium hydroxide/ethanol solution was dropped was taken as the equivalence point. The amount of potassium hydroxide/ethanol solution used in the titration was taken as V _KOH1 [mL].

(ii) Main Measurement Aqueous emulsion (α) was weighed out in an amount of W ₂ [g] (5 g in this example) into a 100 mL Erlenmeyer flask, 25 g of THF was added, and the mixture was stirred with a magnetic stirrer to dissolve. A 0.2 M hydrogen chloride/dioxane solution was added to the emulsion, and the mixture was stirred for 1 hour to obtain a homogeneous solution. The amount of hydrogen chloride/dioxane solution added here was V _HCl [mL] (25 mL in this example). 0.15 mL of a 0.1% by mass cresol red aqueous solution was added to the solution as an indicator. The solution was titrated with a 0.1 M potassium hydroxide/ethanol solution while stirring. After the potassium hydroxide/ethanol solution was dropped, the point at which the purple color lasted for 30 seconds was defined as the equivalence point. The amount of potassium hydroxide/ethanol solution used in the titration here was V _KOH2 [mL].

From the values obtained in (i) and (ii), the amount of epoxy groups N ₁ [mol/g] per 1 g of the aqueous emulsion (α) was calculated according to the following formula (1).
N ₁ = (0.2 × V _HCl / 1000 - 0.1 × V _{KOH 2} / 1000) / W ₂ + (0.1 × V _{KOH 1} / 1000) / W ₁ ... (1)

The total amount _N2 [mol/g] of epoxy groups contained in the components (raw materials) used in the synthesis of aqueous emulsion (α) is calculated from the mass m _i [parts by mass] (i = 1, 2, 3, ...) of each component and the epoxy equivalent EP _i [g/mol] by the following formula (2): The components used in the synthesis of aqueous emulsion (α) refer to all the components listed in Table 1 as raw materials for aqueous emulsion (α).
_N2 = Σ( _mi / _EPi )/ _Σmi ... (2)

For compounds that do not contain an epoxy group, such as methyl methacrylate and ion-exchanged water, 1/EP _i =0.
From the amount of epoxy groups thus determined, the residual ratio of epoxy groups in the aqueous emulsion (α) is expressed as 100×N ₁ /N ₂ [mol %].

<2-2. pH>
The pH at 23° C. was measured using a pH meter (glass electrode type hydrogen ion concentration indicator HM-30G, manufactured by DKK-TOA Corporation).

<2-3. Non-volatile content>
1 g of the aqueous emulsion (α) was weighed out onto an aluminum dish having a diameter of 5 cm, and dried in a dryer at atmospheric pressure with air circulation at 105° C. for 1 hour. The mass of the residue obtained after drying was measured, and the ratio (mass %) of the mass after drying to the mass of the aqueous emulsion (α) before drying was calculated and defined as the non-volatile content concentration.

<2-4. Viscosity>
The viscosity of the aqueous emulsion (α) was measured under the following conditions using the following device.
Temperature: 23°C
Measuring equipment: B-type viscometer Rotor: No. 1
Rotation speed: 60 rpm

<2-5. Dispersion stability>
The state of the aqueous emulsion (α) immediately after synthesis was visually observed and evaluated according to the following criteria.
◯ (Fair): None of aggregation, precipitation, separation, or gelation was observed.
× (unacceptable): At least one of aggregation, precipitation, separation, and gelation was observed.

<2-6. Evaluation results>
As shown in Table 3, all of the aqueous emulsions (α-1) to (α-5) had good dispersibility and stability.

<3. Preparation of aqueous resin composition>
Example 1
In a polypropylene (PP) container, 100 parts by mass of ion-exchanged water, 60 parts by mass of pigment dispersant, 2.4 parts by mass of titanium oxide and 11.1 parts by mass of talc as pigments, 49.3 parts by mass of thickener, and 0.5 parts by mass of 10% aqueous sodium nitrite solution as a primary rust inhibitor were placed and stirred for 10 minutes. 100 parts by mass of aqueous emulsion (α-1) shown in Table 1 was added thereto and stirred for 10 minutes to prepare the aqueous resin composition of Example 1.

(Examples 2 to 6 and Comparative Examples 1 and 2)
The aqueous resin compositions of Examples 2 to 6 and Comparative Examples 1 and 2 were synthesized in the same manner as the aqueous resin composition of Example 1, except that the materials shown in Table 4 were used in the amounts (parts by mass) shown in Table 4.

The materials shown in Table 4 are as follows.
Pigment dispersant: polycarboxylic acid surfactant, Demol EP (Kao Corporation)
Titanium oxide: Tipaque CR-97 (Ishihara Sangyo Kaisha, Ltd.)
Talc: PKP-80 (Fuji Talc Industry Co., Ltd.)
Thickener: polyether polyol-based urethane polymer, ADEKA NOL UH-420 (ADEKA Corporation)
Primary rust inhibitor: 10% aqueous solution of sodium nitrite. Hardener: EH-8051 (product name: ADEKA HARDENER EH-8051, manufactured by ADEKA Corporation). The equivalent weight of active hydrogen reactive with epoxy groups contained in ADEKA HARDENER EH-8051 is 180 g/mol.

In Table 4, the "equivalent of active hydrogen to epoxy group" in the curing agent is a numerical value indicating the equivalent of active hydrogen contained in the polyamine contained in the curing agent to 1 equivalent of epoxy group contained in the aqueous emulsion (α), calculated based on the amount of each material used in the production of the aqueous resin composition.
The "equivalent weight relative to epoxy groups" of the curing accelerator is a numerical value indicating the equivalent weight (mol number) of the curing accelerator relative to 1 equivalent weight of epoxy groups contained in the aqueous emulsion (α), calculated based on the amount of each material used in producing the aqueous resin composition.

<4. Evaluation of adhesion of coating film>
Coating films were formed by the method described below using the aqueous resin compositions of Examples 1 to 6 and Comparative Examples 1 and 2, respectively, and the adhesion was evaluated. The results are shown in Table 4. The coating films of Examples 1 to 6 and Comparative Examples 1 and 2 were formed by applying the aqueous resin composition to the surface to be coated within 1 hour after the aqueous resin composition was prepared.

The aqueous resin composition was applied to a cold-rolled steel plate (thickness 800 μm) (hereinafter referred to as "substrate") using an air spray so that the coating weight was 280 g/ ^m2 . The substrate after application was dried at 23° C. for 7 days to form a coating film on the substrate surface. This resulted in the formation of a rectangular test piece having a length of 70 mm and a width of 150 mm and having a coating film on its surface. The test area was a rectangular area having a length of 45 mm and a width of 125 mm in the coating film of the test piece. The thickness of the coating film of the test piece was about 100 μm.

According to JIS K-5400 (1990) "Section 8.5.2 Cross-cut tape method", a steel plate on which a coating was formed was used as a test piece, and 100 cross-cuts (1 mm apart) were cut with a cutter so as to penetrate the coating, and Cellophane Tape (registered trademark) was applied to the test piece. After 1 hour, the Cellophane Tape (registered trademark) was peeled off, and the number of squares that remained on the steel plate without peeling off the coating was counted to evaluate the adhesion of the coating to the metal material.

5. Evaluation Results
As shown in Table 4, the aqueous resin compositions of Examples 1 to 6 containing the aqueous emulsions (α-1) to (α-3) were all good in the adhesion evaluation, with 90 or more of 100 squares remaining without peeling.

In contrast, as shown in Table 4, the aqueous resin compositions of Comparative Example 1 containing aqueous emulsion (α-4) and Comparative Example 2 containing aqueous emulsion (α-5) had less than 70 masses that remained unpeeled, and were inferior in adhesion to the aqueous resin compositions of Examples 1 to 6. In addition, the aqueous resin compositions of Examples 1 and 3 had good adhesion equivalent to the aqueous resin composition of Example 2 containing the curing agent and curing accelerator, and the aqueous resin compositions of Examples 4 and 5 containing the curing agent and/or curing accelerator.

The present invention provides an aqueous emulsion that can be used as a material for an aqueous resin composition that can form a coating film that exhibits good adhesion even when cured at room temperature without using a curing agent, an aqueous resin composition set, and a method for producing the aqueous emulsion.

Claims (11)

The composition comprises a copolymer (X), a polyepoxy compound (Y) having no ethylenically unsaturated bond and having two or more epoxy groups in one molecule, and an aqueous medium (Z),
The copolymer (X) contains a structural unit (a) derived from a (meth)acrylic acid ester (A) and a structural unit (b) derived from an ethylenically unsaturated monomer (B) having a carboxy group,
the content of the structural unit (a) derived from the (meth)acrylic acid ester (A) in the copolymer (X) is 10 mol % or more and 99.9 mol % or less;
the content of the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group in the copolymer (X) is 0.1 mol % or more and 20 mol % or less;
At least one of the ethylenically unsaturated monomers (B) having a carboxy group is an ethylenically unsaturated monomer (B1) having two or more carboxy groups,
a content of carboxy groups of the structural unit (b1) derived from the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups of the structural unit (b) derived from the ethylenically unsaturated monomer (B) having a carboxy group is 25 mol % or more,
The content of the polyepoxy compound (Y) relative to 100 parts by mass of the total amount of the copolymer (X) is 1.0 part by mass or more and 67 parts by mass or less. The aqueous emulsion according to claim 1, which contains emulsified particles containing the copolymer (X) and the polyepoxy compound (Y). The aqueous emulsion according to claim 1 or 2, wherein at least one of the ethylenically unsaturated monomers (B1) having two or more carboxy groups is maleic acid, itaconic acid, fumaric acid, mesaconic acid, citraconic acid, glutaconic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, 3-butene-1,2,3-tricarboxylic acid, or ethylenetetracarboxylic acid. The aqueous emulsion according to claim 1 or 2, wherein at least one of the ethylenically unsaturated monomers (B1) having two or more carboxy groups is an ethylenically unsaturated monomer having two carboxy groups. The aqueous emulsion according to claim 1 or 2, wherein at least one of the ethylenically unsaturated monomers (B1) having two or more carboxy groups is maleic acid. The aqueous emulsion according to claim 1 or 2, wherein at least one of the polyepoxy compounds (Y) is a bisphenol-type epoxy compound, a hydrogenated bisphenol-type epoxy compound, a diglycidyl ether, a triglycidyl ether, a tetraglycidyl ether, a diglycidyl ester, a triglycidyl ester, or a tetraglycidyl ester. The method includes an emulsion polymerization step of emulsion-polymerizing a monomer raw material including a (meth)acrylic acid ester (A) and an ethylenically unsaturated monomer (B) having a carboxy group in an aqueous medium (Z) in the presence of a polyepoxy compound (Y) having no ethylenically unsaturated bond and having two or more epoxy groups in one molecule,
the content of the (meth)acrylic acid ester (A) in the monomer raw material is 10 mol % or more and 99.9 mol % or less,
the content of the ethylenically unsaturated monomer (B) having a carboxy group in the monomer raw material is 0.1 mol % or more and 20 mol % or less,
At least one of the ethylenically unsaturated monomers (B) having a carboxy group is an ethylenically unsaturated monomer (B1) having two or more carboxy groups,
a content of carboxy groups of the ethylenically unsaturated monomer (B1) having two or more carboxy groups in the total number of carboxy groups of the ethylenically unsaturated monomer (B) having a carboxy group is 25 mol % or more,
a content of the polyepoxy compound (Y) relative to 100 parts by mass of the monomer raw material is 1.0 part by mass or more and 67 parts by mass or less. An aqueous resin composition comprising the aqueous emulsion (α) according to claim 1 or 2. The aqueous resin composition according to claim 8, wherein the aqueous resin composition does not contain a curing agent. A method for producing a coating film, comprising applying the aqueous resin composition according to claim 8 to a surface to be coated. The method for producing a coating film according to claim 10, wherein the aqueous resin composition applied to the surface to be coated is cured at a temperature of 20°C to 40°C.