JP2023166452A - Aqueous resin composition, coating, and method for forming coating - Google Patents

Abstract

To provide an aqueous resin composition that yields a cured product with superior adhesion to a metal material and a high coating yield strength.SOLUTION: An aqueous resin composition comprises a specific aqueous resin emulsion (α), a curing agent (β), and a curing accelerator (γ), wherein the aqueous resin emulsion (α) comprises a copolymer (X), a polyepoxy compound (Y) having no ethylenically unsaturated bonds and having two or more epoxy groups in the molecule, and an aqueous medium (Z), the curing agent (β) comprises a compound having, in the molecule, two or more functional groups (F) having reactivity with epoxy groups, and the curing accelerator (γ) comprises a tertiary amine not having any of the functional groups (F) in the molecule and/or a tertiary amine having only one of the functional groups (F) in the molecule.SELECTED DRAWING: None

Description

The present invention relates to an aqueous resin composition, a film, and a method for forming the film.
This application claims priority based on Japanese Patent Application No. 2019-218183 filed in Japan on December 2, 2019, the contents of which are incorporated herein.

Generally, the surface of metal products is subjected to surface treatment. In particular, metal products used outdoors and metal products expected to be exposed to moisture are often surface-coated to prevent rust from forming.

Conventionally, paints containing organic solvents have been used to paint the surfaces of metal products. However, when applying a paint containing an organic solvent to the surface of a metal product, measures against volatile organic compounds (VOCs) are required for workers and the surrounding environment. Therefore, there is an active movement to use water-based paints instead of paints containing organic solvents for paints used for surface painting of metal products.

Patent Document 1 describes a thick coating coating composition containing 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 structural units formed by polymerizing an alkyl (meth)acrylate monomer having an alkyl group having 4 to 14 carbon atoms, and a structural unit formed by polymerizing an ethylenically unsaturated carboxylic acid monomer. Manufactured by emulsion polymerization of a structural unit consisting of a structural unit formed by polymerization of other monomers, and a structural unit formed by polymerization of other monomers in the presence of a compound having at least two epoxy groups in one molecule and a basic catalyst. It is.

Patent Document 2 describes a composition comprising an aqueous dispersion of thermoplastic polymer particles adsorbed with a thermosetting compound having oxirane groups. Also, Patent Document 2 describes that the polymer particles have a sufficient concentration of anti-aggregation functional groups to stabilize the latex against agglomeration.

Patent Document 3 describes that an acrylate resin (acrylic/epoxy latex) that has absorbed an epoxy compound is formed by mixing an epoxy emulsion with an emulsion of an acrylate resin.

Japanese Patent Application Publication No. 2011-89092 Japanese Patent Application Publication No. 2014-65914 International Publication No. 2017/112018

However, films made of cured products of conventional aqueous resin compositions have insufficient film yield strength. For this reason, in conventional aqueous resin compositions, it is required to improve the yield strength of the film obtained by curing them.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aqueous resin composition that has good adhesion to metal materials and yields a cured product having high film yield strength.
Another object of the present invention is to provide a film having a high film yield strength and comprising a cured product of the aqueous resin composition of the present invention.
Another object of the present invention is to provide a method for forming a film made of a cured product of the aqueous resin composition of the present invention.

The configurations of the present invention to achieve the above object are as follows [1] to [15].
The first aspect of the present invention is the following aqueous resin composition.

[1] Contains an aqueous resin emulsion (α), a curing agent (β), and a curing accelerator (γ),
The aqueous resin emulsion (α) comprises a copolymer (X), a polyepoxy compound (Y) having no ethylenically unsaturated bonds and having two or more epoxy groups in one molecule, and an aqueous medium (Z). ) and,
The content of the polyepoxy compound (Y) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 1 to 40% by mass,
The copolymer (X) contains a structural unit derived from (meth)acrylic acid ester (A) and a structural unit derived from ethylenically unsaturated carboxylic acid (B),
The content of the structural unit derived from the (meth)acrylic ester (A) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 20 to 98% by mass,
The content of the structural unit derived from the ethylenically unsaturated carboxylic acid (B) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 0.1 to 10% by mass,
The structural unit derived from the (meth)acrylic ester (A) includes a structural unit derived from a hydrophilic (meth)acrylic ester (A1) in which the alcohol-derived moiety has 2 or less carbon atoms,
The content of the structural unit derived from the hydrophilic (meth)acrylic acid ester (A1) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 15 to 98% by mass,
One or both of the copolymer (X) and the polyepoxy compound (Y) contain a carboxyl group,
The curing agent (β) is made of a compound having a functional group (F) that is reactive with epoxy groups,
The content of the functional group (F) contained in the curing agent (β) is 0.010 equivalent or more and 3.0 equivalent or less with respect to 1 equivalent of epoxy group contained in the aqueous resin emulsion (α). ,
The curing accelerator (γ) is made of a tertiary amine that does not have a functional group that is reactive with epoxy groups,
The content of the curing accelerator (γ) in the aqueous resin composition is 0.0070 mol or more and 1.5 mol or less with respect to 1 equivalent of epoxy group contained in the aqueous resin emulsion (α).

The aqueous resin composition of the first aspect of the present invention preferably includes the features described in [2] to [12] below. It is also preferable to combine two or more of these features.
[2] The aqueous resin composition according to [1], wherein the (meth)acrylic acid ester (A) is an alkyl (meth)acrylic ester.
[3] The ethylenically unsaturated carboxylic acid (B) is at least one of the group consisting of α,β-unsaturated monocarboxylic acid, α,β-unsaturated dicarboxylic acid, and a vinyl compound containing a carboxy group. The aqueous resin composition according to [1] or [2], which contains seeds.

[4] The polyepoxy compound (Y) is selected from bisphenol-type epoxy compounds, hydrogenated bisphenol-type epoxy compounds, diglycidyl ethers, triglycidyl ethers, tetraglycidyl ethers, diglycidyl esters, triglycidyl esters, and tetraglycidyl esters. The aqueous resin composition according to any one of [1] to [3], which is at least one type of water-based resin composition.

[5] The copolymer (X) consists of a structural unit derived from the (meth)acrylic acid ester (A) and a structural unit derived from the ethylenically unsaturated carboxylic acid (B), [1] to [4] ] The aqueous resin composition according to any one of the above.
[6] The copolymer (X) contains a structural unit derived from an ethylenically unsaturated aromatic compound (C) having a benzene ring and an ethylenically unsaturated bond, any one of [1] to [4] The aqueous resin composition described.
[7] The aqueous resin composition according to [6], wherein the ethylenically unsaturated aromatic compound (C) is an aromatic vinyl compound.

[8] The curing agent (β) contains at least one selected from the group consisting of an unsubstituted or one-substituted amino group, a carboxy group, and a mercapto group, according to [1] to [7]. The aqueous resin composition according to any one of the above.
[9] The curing accelerator (γ) is at least one compound selected from the group consisting of tertiary aliphatic amines, tertiary alicyclic amines, and tertiary heteroaromatic amines, [1 ] to [8]. The aqueous resin composition according to any one of [8].

[10] The aqueous resin emulsion (α) is prepared by emulsion polymerization in the aqueous medium (Z) in which the monomers serving as the structural units of the copolymer (X) undergo emulsion polymerization in the presence of the polyepoxy compound (Y). The aqueous resin composition according to any one of [1] to [9], which is an emulsion.
[11] The content of carboxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is 0.10×10 ⁻⁴ mol/g or more [1] to [10] ] The aqueous resin composition according to any one of the above.
[12] The content of epoxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is 0.50×10 ⁻⁴ mol/g or more [1] to [11] ] The aqueous resin composition according to any one of the above.

The second aspect of the present invention is the following cured product.
[13] A film comprising a cured product of the aqueous resin composition according to any one of [1] to [12].
A third aspect of the present invention is a method of forming a film described below.
[14] A film comprising a coating step of applying the aqueous resin composition according to any one of [1] to [12] to a surface to be coated, and a curing step of curing the applied aqueous resin composition. How to form.

According to the present invention, it is possible to provide an aqueous resin composition that has good adhesion to metal materials and yields a cured product having high film yield strength.
Further, according to the present invention, a film having a high film yield strength made of a cured product of the aqueous resin composition of the present invention can be provided.
Further, according to the present invention, it is possible to provide a method for forming a film formed of a cured product of the aqueous resin composition of the present invention.

Hereinafter, the aqueous resin composition, film, and film forming method of the present invention will be explained in detail.
Note that the present invention is not limited only to the embodiments shown below. In the present invention, for example, additions, omissions, substitutions, changes, etc. can be made in the number, type, position, amount, ratio, material, configuration, etc., without departing from the spirit of the invention.

Here, the following terms used in this specification will be explained.
"(Meth)acrylate" means acrylate or methacrylate. Moreover, "(meth)acrylic" means acrylic or methacrylic.
"Ethylenically unsaturated bond" means a double bond between carbon atoms excluding carbon atoms forming an aromatic ring.
The "weight average molecular weight" is a standard polystyrene equivalent value measured by gel permeation chromatography (GPC).

In a polymer using a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having an ethylenically unsaturated bond refers to the chemical structure of the portion other than the ethylenically unsaturated bond in the compound, and the above-mentioned structural unit derived from the compound having an ethylenically unsaturated bond. It may mean a unit in which the chemical structure of the structural unit other than the portion corresponding to the ethylenically unsaturated bond in the polymer is the same. The ethylenically unsaturated bond of the compound may be 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 addition, in the case of a polymer of a compound having an ionic functional group and an ethylenically unsaturated bond, for example, a structural unit (b) derived from an ethylenically unsaturated carboxylic acid (B) described below. , for structural units having ionic functional groups such as carboxy groups, structural units derived from the same ionic compound even if some of the functional groups are ion-exchanged or not ion-exchanged. may be used as For example, the structural unit represented by -CH ₂ -C(CH ₃ )(COONa)- may also be considered to be a structural unit derived from methacrylic acid.

Further, for a compound having a plurality of independent ethylenically unsaturated bonds, one or more ethylenically unsaturated bonds may remain inside the structural unit as a structural unit of a polymer of the compound. A plurality of independent ethylenically unsaturated bonds may mean a plurality of ethylenically unsaturated bonds that do not form a conjugated diene with each other. For example, in the case of a divinylbenzene polymer, the structural unit derived from divinylbenzene has a structure that does not have ethylenically unsaturated bonds (the moieties corresponding to the two thylenically unsaturated bonds of divinylbenzene are both in the polymer chain). It may be a structure having one ethylenically unsaturated bond (a form in which only the portion corresponding to one ethylenically unsaturated bond is incorporated into the polymer chain).

"Curing" refers to the bonding of molecules contained in raw materials through a chemical reaction to form a network-structured polymer.
Unless otherwise specified, "coating film" means a coating film formed by coating the aqueous resin composition of the present embodiment, drying the medium, and curing the resin component.

<1. Water-based resin composition>
The aqueous resin composition of this embodiment includes an aqueous resin emulsion (α), a curing agent (β), and a curing accelerator (γ). The aqueous resin composition of this embodiment is produced by mixing an aqueous resin emulsion (α), a curing agent (β), and a curing accelerator (γ), as described below.

[1-1. Water-based resin emulsion (α)]
The aqueous resin emulsion (α) consists of a copolymer (X), a polyepoxy compound (Y) having no ethylenically unsaturated bonds and having two or more epoxy groups in one molecule, and an aqueous medium (Z). including. The aqueous resin emulsion (α) is an emulsion obtained by emulsion polymerization of a monomer serving as a structural unit of a copolymer (X) in an aqueous medium (Z) in the presence of a polyepoxy compound (Y). This is because when mixed with a curing agent (β) to be described later and cured, a coating film with high strength and high elongation can be obtained.

<1-1-1. Copolymer (X)>
The copolymer (X) has a structural unit (a) derived from (meth)acrylic acid ester (A) and a structural unit (b) derived from ethylenically unsaturated carboxylic acid (B). Note that the structural unit (a) derived from the (meth)acrylic ester (A) includes a structural unit (a1) derived from the hydrophilic (meth)acrylic ester (A1).

The copolymer (X) may consist of only the structural unit (a) and the structural unit (b) (referred to as copolymer (X1)). The copolymer (X) comprises a structural unit (a), a structural unit (b), and 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 consist only of structural units (a) to (c). The copolymer (X) may have a structural unit (d) (a structural unit derived from another monomer (D)) other than the structural units (a) to (c).

The amount of copolymer (X) contained in the aqueous resin emulsion (α) can be selected arbitrarily, but it is preferably 10% by mass or more, and 20% by mass based on the total amount of the aqueous resin emulsion (α). It is more preferably at least 25% by mass, and even more preferably at least 25% by mass. The amount of copolymer (X) contained in the aqueous resin emulsion (α) can be arbitrarily selected, but it is preferably 60% by mass or less, and 50% by mass based on the total amount of the aqueous resin emulsion (α). It is more preferably at most 40% by mass, even more preferably at most 40% by mass. However, it is not limited to these examples.

The content of the copolymer (X) relative to the total amount of the copolymer (X) and the polyepoxy compound (Y) described below is preferably 50% by mass or more, and preferably 60% by mass or more. More preferably, it is 65% by mass or more. The content of the copolymer (X) relative to the total amount of the copolymer (X) and the polyepoxy compound (Y) described below is preferably 99% by mass or less, and preferably 94% by mass or less. The content is more preferably 88% by mass or less.

[(meth)acrylic acid ester (A)]
As the (meth)acrylic acid ester (A), one or more types can be arbitrarily selected, but it is preferably composed of (meth)acrylic acid alkyl ester. As an example of the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms is more preferable. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-ethylhexyl. Examples include (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isobornyl (meth)acrylate. These may be used alone or in combination of two or more.

Examples of the (meth)acrylic ester (A) may also include examples of the hydrophilic (meth)acrylic ester (A1) described below. Note that the (meth)acrylic ester having a carboxyl group is not included in the (meth)acrylic ester (A), but is included in the ethylenically unsaturated carboxylic acid (B) described below.

The (meth)acrylic ester (A) preferably contains a compound with low hydrophilicity. This is to improve the rust prevention properties of the paint film. For the same reason, the (meth)acrylic ester (A) may include a (meth)acrylic ester having an epoxy group.

Examples of the (meth)acrylic ester having an epoxy group include glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and 3,4-epoxycyclohexyl. Examples include methyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, and 3,4-epoxycyclohexylpropyl (meth)acrylate.
The structural unit (a) may contain a structural unit derived from only one type of these compounds, or may contain a structural unit derived from two or more types of these compounds. Furthermore, among these compounds, the structural unit (a) preferably contains a structural unit derived from glycidyl (meth)acrylate.

Furthermore, the (meth)acrylic ester (A) may be a (meth)acrylic ester that is neither an alkyl (meth)acrylate ester nor a compound having an epoxy group. Examples of such (meth)acrylic esters include (meth)acrylic esters having a hydroxy group.

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

The content of the structural unit (a) derived from the (meth)acrylic ester (A) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 20% by mass or more. This is because the dispersion stability of the monomer of the copolymer (X) and the polyepoxy compound (Y) can be improved in the method for producing an aqueous resin emulsion described later. From this point of view, the content of the structural unit (a) derived from the (meth)acrylic acid ester (A) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) should be 35% by mass or more. The content is preferably 45% by mass or more, more preferably 60% by mass or more.

The content of the structural unit (a) derived from the (meth)acrylic acid ester (A) relative to the total amount of the copolymer (X) is preferably 40% by mass or more, more preferably 60% by mass or more. It is preferably at least 75% by mass, more preferably at least 90% by mass. This is because within the above range, the water resistance swelling rate of the film produced using the aqueous resin composition can be lowered. The content of the structural unit (a) derived from the (meth)acrylic acid ester (A) with respect to the total amount of the copolymer (X) is preferably 99% by mass or less.

Furthermore, in the present embodiment, the content of structural units derived from a compound may mean the proportion (% by mass) of the compound used. For example, the content of the structural unit (a) derived from (meth)acrylic acid ester (A) with respect to the total amount of copolymer (X) and polyepoxy compound (Y) means It may mean the mass ratio (mass %) of the (meth)acrylic acid ester (A) used in the production of the compound (X).

Furthermore, when the copolymer (X) is composed of only the structural unit (a) and the structural unit (b), that is, the copolymer (X1), from the viewpoint of similarly improving dispersion stability, the following Preferably, it is a percentage. That is, the content of the structural unit (a) derived from the (meth)acrylic ester (A) with respect to the total amount of the copolymer (X1) and the polyepoxy compound (Y) is 50% by mass or more. More preferably, the content is particularly preferably 60% by mass or more. The preferable upper limit of the content is the same as that for copolymer (X).

The content of the structural unit (a) derived from the (meth)acrylic ester (A) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 98% by mass or less. This is because if the content does not exceed 98% by mass, the dispersion stability of the aqueous resin emulsion will not deteriorate. From this point of view, the content of the structural unit (a) derived from the (meth)acrylic acid ester (A) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) should be 92% by mass or less. is preferable, and more preferably 87% by mass or less.

Furthermore, the copolymer (X) has a structural unit (a), a structural unit (b), and a structural unit (c). When copolymer (X) is copolymer (X2), from the same viewpoint, the following proportions are preferred. It is more preferable that the content of the structural unit (a) derived from the (meth)acrylic ester (A) to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 75% by mass or less. , 65% by mass or less is particularly preferred. The preferable lower limit of the content is the same as that for copolymer (X).

[Hydrophilic (meth)acrylic acid ester (A1)]
The structural unit derived from the (meth)acrylic ester (A) includes a structural unit derived from the hydrophilic (meth)acrylic ester (A1).

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

Examples of the hydrophilic (meth)acrylic ester (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. The hydrophilic (meth)acrylic ester (A1) is preferably an alkyl (meth)acrylic ester in which the alcohol-derived moiety has 2 or less carbon atoms, and more preferably methyl methacrylate.

The content of the structural unit (a1) derived from the hydrophilic (meth)acrylic acid ester (A1) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 15% by mass or more. This is because, as described above, when the content of the hydrophilic (meth)acrylic ester is low, gelation proceeds rapidly when the aqueous resin emulsion (α) is mixed with a curing agent containing a polyamine.

The content of the structural unit (a1) derived from the hydrophilic (meth)acrylic acid ester (A1) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 15% by mass or more, and 20% by mass. It is preferably at least 30% by mass, more preferably at least 30% by mass, even more preferably at least 40% by mass. This is because the water resistance and rust prevention properties of the cured coating film are further improved. The content may be 45% by mass or more or 50% by mass or more.

The upper limit of the content of the structural unit (a1) derived from the hydrophilic (meth)acrylic ester (A1) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is the (meth)acrylic ester. This is the same as the upper limit of the content rate described in (a) of the structural unit derived from (A). That is, the upper limit is 98% by mass or less, preferably 92% by mass or less, and more preferably 87% by mass or less. However, if the polyepoxy compound (Y) described below is a hydrophobic compound such as a bisphenol-type epoxy compound, a hydrogenated bisphenol-type epoxy compound, or a phenol novolac-type epoxy compound, the structural unit (a1) that occupies the structural unit (a) ) is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less. This is to improve the affinity between the copolymer (X) and the polyepoxy compound (Y).

[Ethylenically unsaturated carboxylic acid (B)]
Ethylenically unsaturated carboxylic acid (B) is a compound having an ethylenically unsaturated bond and a carboxy group. Ethylenically unsaturated carboxylic acid (B) includes α,β-unsaturated monocarboxylic acid, α,β-unsaturated dicarboxylic acid, monoalkyl ester of α,β-unsaturated dicarboxylic acid, and vinyl containing a carboxy group. It is preferable to include at least one of the group consisting of compounds, and at least one of the group consisting of α,β-unsaturated monocarboxylic acids, α,β-unsaturated dicarboxylic acids, and vinyl compounds containing a carboxyl group. It is more preferable to include one type. Examples of α,β-unsaturated mono- or dicarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, citraconic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, and the like. Examples of the vinyl compound containing a carboxyl group include monohydroxyethyl (meth)acrylate phthalate, monohydroxypropyl (meth)acrylate oxalate, and the like.

The structural unit (b) may be a structural unit derived from only one type of these compounds, or may include a structural unit derived from two or more types. Among these compounds, the ethylenically unsaturated carboxylic acid (B) includes a compound having a (meth)acryloyl group and a carboxyl group, or consists only of a compound having a (meth)acryloyl group and a carboxyl group. is preferred. It is also preferable that the ethylenically unsaturated carboxylic acid (B) contains (meth)acrylic acid or consists only of (meth)acrylic acid. The structural unit (b) preferably consists only of structural units derived from a compound having a (meth)acryloyl group and a carboxy group, and further preferably includes a structural unit derived from (meth)acrylic acid.

The content of the structural unit (b) derived from the ethylenically unsaturated carboxylic acid (B) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 0.1% by mass or more. This is to improve the dispersion stability of the aqueous resin emulsion (α). From this point of view, the content of the structural unit (b) derived from the ethylenically unsaturated carboxylic acid (B) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) should be 0.3% by mass or more. The content is preferably 0.5% by mass or more, and more preferably 0.5% by mass or more. The content may be 0.8% by mass or more, or 1.0% by mass or more. The content of the structural unit (b) derived from the ethylenically unsaturated carboxylic acid (B) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 10% by mass or less. This is to suppress the copolymer (X) from becoming gel-like in a high-temperature environment and improve the high-temperature stability of the aqueous resin emulsion (α). From this point of view, the content of the structural unit (b) derived from the ethylenically unsaturated carboxylic acid (B) is 7% by mass or less with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y). The content is preferably 5% by mass or less, and more preferably 5% by mass or less. The content may be 4% by mass or less, or 3% by mass or less.

In addition, the content of the structural unit (b) derived from ethylenically unsaturated carboxylic acid (B) with respect to the total amount of the copolymer (X) is preferably 0.2% by mass or more, and 0.5% by mass. The content is more preferably 0.8% by mass or more, and even more preferably 0.8% by mass or more. The content of the structural unit (b) derived from ethylenically unsaturated carboxylic acid (B) relative to the total amount of the copolymer (X) is preferably 12% by mass or less, more preferably 8% by mass or less. It is preferably at most 5% by mass, more preferably at most 3% by mass.

[Ethylenically unsaturated aromatic compound (C)]
The ethylenically unsaturated aromatic compound (C) does not fall under either a (meth)acrylic acid ester (A) or an ethylenically unsaturated carboxylic acid (B), and has a benzene ring and an ethylenically unsaturated bond. It is a compound. The ethylenically unsaturated aromatic compound (C) is preferably an aromatic vinyl compound.

Examples of the aromatic vinyl compound as the ethylenically unsaturated aromatic compound (C) 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, styrene sulfone Acids and their salts, α-methylstyrenesulfonic acid and its salts, p-hydroxystyrene, m-hydroxystyrene, o-hydroxystyrene, p-isopropenylphenol, m-isopropenylphenol, o-isopropenylphenol, etc. Can be mentioned. The structural unit (c) may be derived from only one type of these compounds, or may include a structural unit derived from two or more types. Among these, the structural unit (c) is more preferably a structural unit derived from a hydrocarbon, and particularly preferably a structural unit derived from styrene.

When the copolymer (X) contains a structural unit (c) derived from the ethylenically unsaturated aromatic compound (C), that is, when the copolymer (X) is a copolymer (X2), the copolymer The content of the structural unit (c) relative to the total amount of (X2) and the polyepoxy compound (Y) is preferably 5% by mass or more. This is to improve the water resistance of the coating film. From this point of view, the content of the structural unit (c) with respect to the total amount of the copolymer (X2) and the polyepoxy compound (Y) is more preferably 10% by mass or more, and more preferably 15% by mass or more. Even more preferred. The content may be 18% by mass or more, 20% by mass or more, or 23% by mass or more.

When the copolymer (X) is a copolymer (X2), the content of the structural unit (c) with respect to the total amount of the copolymer (X2) and the polyepoxy compound (Y) is 50% by mass or less. It is preferable that there be. This is because the weather resistance of the coating film is improved. From this point of view, the content of the structural unit (c) relative to the total amount of the copolymer (X2) and the polyepoxy compound (Y) is more preferably 40% by mass or less, and more preferably 35% by mass or less. is even more preferable. The content may be 33% by mass or less, 30% by mass or less, or 28% by mass or less.

The content of the structural unit (c) relative to the total amount of the copolymer (X2) is preferably 5% by mass or more, more preferably 15% by mass or more, and further preferably 25% by mass or more. preferable. The content of the structural unit (c) relative to the total amount of the copolymer (X2) is preferably 55% by mass or less, more preferably 45% by mass or less, and further preferably 35% by mass or less. preferable.

[Other monomers (D)]
The other monomer (D) does not fall under any of (meth)acrylic acid ester (A), ethylenically unsaturated carboxylic acid (B), or ethylenically unsaturated aromatic compound (C), and It is a compound having an ethylenically unsaturated bond that can be copolymerized with the compound used to synthesize the copolymer (X). Examples of the other monomer (D) include conjugated diene compounds, maleimide compounds, vinyl ether compounds, allyl ether compounds, dialkyl esters of unsaturated dicarboxylic acids, and vinyl compounds having a cyano group.

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

Examples of the maleimide compound 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-hydroxy) (phenyl)maleimide, N-naphthylmaleimide, N-cyclohexylmaleimide, and the like. These maleimide compounds may be used alone or in combination of two or more.

Examples of the vinyl ether compound include alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether, and hydroxyl group-containing alkyl vinyl ethers in which some hydrogen atoms are substituted with hydroxyl groups.

Examples of the allyl ether compound include allyl alkyl ethers such as allyl methyl ether and allyl ethyl ether, allyl alkyl ethers containing hydroxyl groups in which some hydrogen atoms are substituted with hydroxyl groups, and allyl glycidyl ethers.

Examples of dialkyl esters of unsaturated dicarboxylic acids include unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, and tetrahydrophthalic anhydride. Examples include dialkyl esters of These dialkyl esters may be used alone or in combination of two or more. These unsaturated compounds may be used alone or in combination of two or more.

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

<1-1-2. Polyepoxy compound (Y)>
The polyepoxy compound (Y) is a compound that does not have ethylenically unsaturated bonds and has two or more epoxy groups in one molecule.

The polyepoxy compound (Y) is at least one selected from bisphenol-type epoxy compounds, hydrogenated bisphenol-type epoxy compounds, diglycidyl ethers, triglycidyl ethers, tetraglycidyl ethers, diglycidyl esters, triglycidyl esters, and tetraglycidyl esters. Preferably it is a seed.

Examples of compounds having two or more epoxy groups in one molecule include diglycidyl ether of bisphenol A, diglycidyl ether of hydrogenated bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of hydrogenated bisphenol F, and 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 Examples include glycidyl ether and diglycidyl ester of hexahydrophthalic acid. It may contain one kind or two or more kinds of these compounds.

The polyepoxy compound (Y) is more preferably a bisphenol type epoxy compound or a hydrogenated bisphenol type epoxy compound, more preferably a bisphenol A type epoxy compound or a hydrogenated bisphenol A type epoxy compound, and a bisphenol A type epoxy compound. More preferably, it is an epoxy compound. This is because the water resistance and rust prevention properties of the cured coating film are 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. The compatibility of the polyepoxy compound (Y) with the copolymer (X) is improved, and an emulsion with excellent dispersion stability and storage stability can be obtained. The lower limit of the molecular weight can be arbitrarily selected, 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 mol of epoxy group) is preferably 500 g/mol or less, more preferably 350 g/mol or less, and 250 g/mol It is more preferably at most 200 g/mol, particularly preferably at most 200 g/mol. This is because the strength of the coating film obtained by curing the aqueous resin composition described below becomes higher. The lower limit of the epoxy equivalent can be arbitrarily selected, 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 the polyepoxy compound (Y) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 1% by mass or more. This is because the aqueous resin composition is cured and a coating film having excellent rust prevention properties is obtained. From this point of view, the content of the polyepoxy compound (Y) relative to the total amount of the copolymer (X) and the polyepoxy compound (Y) is preferably 5% by mass or more, and preferably 8% by mass or more. is more preferable, and even more preferably 10% by mass or more. If necessary, the content may be 12% by mass or more, or 20% by mass or more. The content of the polyepoxy compound (Y) based on the total amount of the copolymer (X) and the polyepoxy compound (Y) is 40% by mass or less. This is to obtain an aqueous resin emulsion (α) with high dispersion stability. From this point of view, the content of the polyepoxy compound (Y) relative to the total amount of the copolymer (X) and the polyepoxy compound (Y) is preferably 35% by mass or less, and preferably 30% by mass or less. is more preferable.

The amount of polyepoxy compound (Y) contained in the aqueous resin emulsion (α) is preferably 1% by mass or more, more preferably 3% by mass or more, based on the total amount of the aqueous resin emulsion (α). The content is preferably 4% by mass or more, and more preferably 4% by mass or more. The amount of polyepoxy compound (Y) contained in the aqueous resin emulsion (α) is preferably 30% by mass or less, more preferably 20% by mass or less, based on the total amount of the aqueous resin emulsion (α). The content is preferably 15% by mass or less, and more preferably 15% by mass or less.

<1-1-3. Aqueous medium (Z)>
The aqueous medium (Z) can be arbitrarily selected, and it is preferable to use water. However, as long as the dispersion stability of the copolymer (X) and the polyepoxy compound (Y) is not impaired, for example, water to which a water-soluble solvent is added may be used as the aqueous medium (Z). The hydrophilic solvent to be added to water can be arbitrarily selected and includes methanol, ethanol, N-methylpyrrolidone, and the like.

The amount of the aqueous medium (Z) in the aqueous resin emulsion (α) can be selected as necessary, but is preferably 20% by mass or more, more preferably 30% by mass or more, and 40% by mass or more. It is more preferable that The amount of the aqueous medium (Z) in the aqueous resin emulsion (α) can be selected as required, but is preferably 80% by mass or more, more preferably 70% by mass or more. The concentration may be 50 to 70% by weight or 55 to 65% by weight.

<1-1-4. Method for producing aqueous resin emulsion (α)>
The method for producing the aqueous resin emulsion (α) according to the present embodiment involves using a monomer containing a (meth)acrylic acid ester (A) and an ethylenically unsaturated carboxylic acid (B) in the presence of a polyepoxy compound (Y). (That is, the monomer for constituting the copolymer (X)) can be emulsion polymerized in an aqueous medium (Z). According to the above manufacturing method of the present embodiment using this method, an aqueous resin emulsion (α) in which the polyepoxy compound (Y) is uniformly dispersed in the particles of the produced copolymer (X) can be obtained. Conceivable. Here, "uniformly existing" does not necessarily mean that the copolymer (X) and the polyepoxy compound (Y) are compatible with each other; It is sufficient that the domains of the polyepoxy compound (Y) are evenly present on both the surface side and the surface side. As a specific emulsion polymerization method, a method of charging each component including a monomer at once, a method of polymerizing while continuously supplying each component, etc. can be used. Stirring is preferred during the polymerization reaction.

The content of each raw material in the total raw materials used for manufacturing the aqueous resin emulsion (α) is the same as the content of structural units derived from the raw materials or compounds corresponding to the raw materials in the aqueous resin emulsion (α). .

The polymerization is preferably carried out at an arbitrarily selected temperature, for example, at a temperature of 30 to 90°C, more preferably at a temperature of 40 to 80°C, even more preferably at a temperature of 40 to 70°C. . This is to prevent the carboxy group contained in the monomer from reacting with the epoxy group contained in the polyepoxy compound (Y).

The emulsifier used in the emulsion polymerization can be arbitrarily selected, and includes, for example, nonionic surfactants such as polyoxyalkylene alkyl ether, polyoxyalkylene alkylphenol ether, polyoxyalkylene fatty acid ester, polyoxyalkylene sorbitan fatty acid ester, and alkyl sulfate esters. Examples include anionic surfactants such as salts, alkylbenzene sulfonates, alkyl sulfosuccinates, alkyldiphenyl ether disulfonates, polyoxyalkylene alkyl sulfates, and polyoxyalkylene alkyl phosphates. These may be used alone or in combination of two or more. Preferred as these emulsifiers are alkylbenzenesulfonates, and it is more preferred to use sodium dodecylbenzenesulfonate.

In emulsion polymerization, it is preferable to use a polymerization initiator. As the polymerization initiator, it is preferable to use, for example, peroxide. Examples of the peroxide used as a polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate, hydrogen peroxide, and the like. It is also possible to use a redox initiator in combination with a peroxide and a reducing agent. Examples of the reducing agent include sodium sulfoxylate formaldehyde, ascorbic acid, sulfite, tartaric acid or a salt thereof, and the like. Furthermore, alcohols and mercaptans may be used as chain transfer agents, if necessary.

<1-1-5. Characteristics of water-based resin emulsion (α)>
[pH of aqueous resin emulsion (α)]
The pH of the aqueous resin emulsion (α) is preferably 2 to 10, more preferably 5 to 9. When the pH is within this range, the mechanical stability and chemical stability of the aqueous resin emulsion (α) can be improved. The pH is a value measured at a liquid temperature of 25° C. using a pH meter with a hydrogen ion concentration indicator using a glass electrode as a standard electrode. For example, the pH can be adjusted by adding a basic substance to the aqueous resin emulsion (α) during or after emulsion polymerization. Examples of basic substances used for pH adjustment include ammonia, triethylamine, ethanolamine, caustic soda, and the like. These may be used alone or in combination of two or more.

[Nonvolatile content concentration of aqueous resin emulsion (α)]
The nonvolatile content concentration of the aqueous resin emulsion (α) is preferably 10 to 65% by mass, more preferably 15 to 60% by mass, and even more preferably 20 to 55% by mass. The concentration may be 30-50% by weight, or 35-45% by weight. The non-volatile content concentration in the aqueous resin emulsion (α) is determined in the mixing process of the aqueous resin emulsion (α), a curing agent (β), a curing accelerator (γ), etc., which will be described later, or in the coating process of the aqueous resin composition. It can be determined as appropriate considering workability. The nonvolatile content concentration in the aqueous resin emulsion (α) can be adjusted as appropriate by adjusting the amount of the aqueous medium (Z) added.

In addition, the nonvolatile content concentration of the aqueous resin emulsion (α) was determined by the method shown below. 1 g of aqueous resin emulsion (α) was weighed into an aluminum dish with a diameter of 5 cm, and after drying at 105°C for 1 hour at atmospheric pressure in a dryer with air circulation, the mass of the resulting residue was measured. . The ratio (mass %) of the mass of the measured residue to the mass of the aqueous resin emulsion (α) before drying was determined as the nonvolatile content concentration of the aqueous resin emulsion (α).

[Viscosity of water-based resin emulsion (α)]
In this embodiment, the viscosity of the aqueous resin emulsion (α) is measured at 23°C. The viscosity of the aqueous resin emulsion (α) was measured using a B-type viscometer, and the value was measured at a rotation speed of 60 rpm and a rotor selected according to the viscosity of the aqueous resin emulsion. For example, when the viscosity of the aqueous resin emulsion (α) is about several mPa·s to several hundred mPa·s, rotor No. Measure using 1. The viscosity may be, for example, 0.1 to 300 mPa·s, 1 to 100 mPa·s, 3 to 50 mPa·s, or 5 to 25 mPa·s. .

[Glass transition point of copolymer (X)]
The glass transition point Tg of the copolymer (X) is calculated based on the glass transition point of the homopolymer of each monomer used in the synthesis of the copolymer (X). The specific method for calculating the glass transition point _Tg of the _copolymer (X) is as follows: , the mass fraction of monomer i in all monomers, X _i (ΣX _i (total monomers)=1), is calculated by the following formula (1). In equation (1), both Tg and Tg _i are calculated using absolute temperature (K) values.
1/Tg=Σ(X _i /Tg _i )...(1)

The glass transition point Tg of the copolymer (X) is preferably -30°C (243K) or higher. This is because the strength of the coating film is improved. From this point of view, it is more preferable that the glass transition point Tg of the copolymer (X) is −10° C. (263 K) or higher. More preferably, the temperature is 0°C (273K) or higher. This is because, in the case of such a range, the strength of the coating film after curing is improved. The glass transition point Tg of the copolymer (X) may be 5°C or higher, or 10°C or higher. The glass transition point Tg of the copolymer (X) is preferably 100°C (373K) or lower, more preferably 80°C (353K) or lower. This is because the adhesion of the coating film to the base material is improved. From this viewpoint, the glass transition point Tg of the copolymer (X) is more preferably 60°C (333K) or lower, particularly preferably 50°C (323K) or lower. This is because within such a range, the flexibility of the cured coating film can be improved. The glass transition point Tg of the copolymer (X) may be 40°C or lower, or 30°C or lower.

[Content of epoxy groups in aqueous resin emulsion (α)]
The content of epoxy groups in the aqueous resin emulsion (α) is the ratio of the number of moles of epoxy groups contained in 1 g of the aqueous resin emulsion (α). The method for determining the amount N ₁ [mol/g] of epoxy groups contained per 1 g of the aqueous resin emulsion (α) is as explained in the Examples below.

[Content of epoxy groups in the total amount of copolymer (X) and polyepoxy compound (Y)]
As described above, the polyepoxy compound (Y) contained in the aqueous resin emulsion (α) in this embodiment contains an epoxy group. The content of epoxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is preferably 0.50×10 ⁻⁴ mol/g or more, and 1.0×10 ⁻⁴ It is more preferably at least mol/g, even more preferably at least 4.0×10 ⁻⁴ mol/g, even more preferably at least 6.0×10 ⁻⁴ mol/g. This is because the water resistance, rust prevention, and adhesion of the cured coating film to the substrate can be improved.

The content of epoxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is preferably 50×10 ⁻⁴ mol/g or less, and 30×10 ⁻⁴ mol/g or less More preferably, it is 20×10 ⁻⁴ mol/g or less. Even if the content of epoxy groups in the total amount of copolymer (X) and polyepoxy compound (Y) is 15×10 ⁻⁴ mol/g or less, or 10×10 ⁻⁴ mol/g or less good.

[Content of epoxy groups in nonvolatile components of aqueous resin emulsion (α)]
The content of epoxy groups in the nonvolatile components of the aqueous resin emulsion (α) is preferably 0.50×10 ⁻⁴ mol/g or more, and preferably 3.0×10 ⁻⁴ mol/g or more. More preferably, it is 5.0×10 ⁻⁴ mol/g or more. This is because the water resistance, rust prevention, and adhesion of the cured coating film to the substrate can be improved. The content of epoxy groups in the nonvolatile components of the aqueous resin emulsion (α) may be 1.0×10 ⁻⁴ mol/g or more, or 6.0×10 ⁻⁴ mol/g or more.

The content of epoxy groups in the nonvolatile components of the aqueous resin emulsion (α) is preferably 50×10 ⁻⁴ mol/g or less, more preferably 30×10 ⁻⁴ mol/g or less, and 20 More preferably, it is not more than ×10 ⁻⁴ mol/g. The content of epoxy groups in the nonvolatile components of the aqueous resin emulsion (α) may be 15×10 ⁻⁴ mol/g or less, or 10×10 ⁻⁴ mol/g or less.

The content R _EP [mol/g] of epoxy groups in the nonvolatile components of the aqueous resin emulsion (α) is a value determined as follows. If the nonvolatile content concentration of the aqueous resin emulsion (α) is C _S [mass %] and the amount of epoxy groups contained per 1 g of the aqueous resin emulsion (α) is N ₁ [mol/g], then the content of epoxy groups R _EP is expressed as in equation (2). The method for determining N ₁ will be described later in the Examples.
R _EP [mol/g]=N ₁ /(C _S /100)...(2)

[Carboxy group content in aqueous resin emulsion (α)]
The content of carboxy groups in the aqueous resin emulsion (α) is the ratio of the number of moles of carboxy groups contained in 1 g of the aqueous resin emulsion (α). The method for determining the number of moles of carboxyl groups contained per 1 g of the aqueous resin emulsion (α) is as explained in the Examples below.

[Content of carboxy groups in the total amount of copolymer (X) and polyepoxy compound (Y)]
In this embodiment, one or both of the copolymer (X) and the polyepoxy compound (Y) contained in the aqueous resin emulsion (α) contain a carboxyl group, and the copolymer (X) contains a carboxyl group. It is preferable to include. The content of carboxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is preferably 0.10×10 ⁻⁴ mol/g or more, and 0.50×10 ⁻⁴ mol It is more preferably at least 1.0×10 ⁻⁴ mol/g, and even more preferably at least 1.0×10 −4 mol/g. This is because aggregation of the copolymer (X) can be suppressed during polymerization and during storage of the aqueous resin emulsion (α) after polymerization.

The content of carboxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is preferably 10×10 ⁻⁴ mol/g or less, and 5.0×10 ⁻⁴ mol/g. It is more preferable that it is less than g. It may be 3.0×10 ⁻⁴ mol/g or less, 2.5×10 ⁻⁴ mol/g or less, or 2.0×10 ⁻⁴ mol/g or less.

[Carboxy group content in nonvolatile components of aqueous resin emulsion (α)]
The content of carboxy groups in the nonvolatile components of the aqueous resin emulsion (α) is preferably 0.10×10 ⁻⁴ mol/g or more, and preferably 0.50×10 ⁻⁴ mol/g or more. More preferably, it is 1.0×10 ⁻⁴ mol/g or more. This is because aggregation of the copolymer (X) can be suppressed during polymerization and during storage of the aqueous resin emulsion (α) after polymerization.

The content of carboxyl groups in the nonvolatile components of the aqueous resin emulsion (α) is preferably at most 10×10 ⁻⁴ mol/g, more preferably at most 5.0×10 ⁻⁴ mol/g. . It may be 3.0×10 ⁻⁴ mol/g or less, 2.5×10 ⁻⁴ mol/g or less, or 2.0×10 ⁻⁴ mol/g or less.

Here, the above-mentioned carboxy group includes not only -COOH but also a structure in which a cation other than a hydrogen ion and -COO ^- are bonded. The content of carboxyl groups in the nonvolatile matter of the aqueous resin emulsion (α) is determined from the content of carboxyl groups in the raw materials by the polymerization of the functional groups that react with the carboxyl groups in the raw materials, as shown in the formula below. It is calculated from the value obtained by subtracting the amount of decrease before and after. The raw material refers to the component used in the synthesis of the aqueous resin emulsion (α). Furthermore, in the present invention, the functional group that reacts with a carboxy group is an epoxy group, and a hydroxy group is not considered to be a functional group that reacts with a carboxy group.

Hereinafter, how to determine the content R _CX [mol/g] of carboxy groups in the nonvolatile components of the aqueous resin emulsion (α) will be explained in detail. The total amount of carboxy groups in the raw materials (including initiators, solvents, other additives, etc.) is N ₃ [mol/g], and the total amount of epoxy groups in the raw materials (including initiators, solvents, other additives, etc.) is N ₂ [mol/g], and the amount of epoxy groups contained per 1 g of the aqueous resin emulsion (α) is N ₁ [mol/g]. The nonvolatile content concentration of the aqueous resin emulsion (α) is defined as C _S [% by mass]. At this time, the carboxy group content R _CX is expressed as shown in formula (3). How to determine N ₁ and N ₂ will be described later in the examples. _N2 can be obtained by calculation.
R _CX [mol/g]={N ₃ -(N ₂ -N ₁ )}/(C _S /100)...(3)

[1-2. Hardening agent (β)]
The curing agent (β) is composed of a compound having a functional group (F) that is reactive with epoxy groups. The functional group (F) can be an unsubstituted amino group (-NH ₂ (no substituent), an amino group with only one substituent (-NHR (R is a substituent)), a carboxy group, or a mercapto group. Preferably, it is selected from the group consisting of:
The number of types of functional groups (F) having reactivity with epoxy groups contained in the curing agent (β) may be only one type, or two or more types.

Examples of the curing agent (β) having an amino group that is unsubstituted or has only one substituent include polyamines. Polyamine is a compound having an unsubstituted amino group (-NH ₂ ) and/or an amino group having only one substituent (-NHR (R is a substituent)), and includes, for example, aliphatic polyamine, fatty Examples include cyclic polyamines and aromatic polyamines.

Examples of aliphatic polyamines include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and modified products thereof. Examples of the alicyclic polyamine include isophorone diamine, menthanediamine, N-aminoethylpiperazine, diaminodicyclohexylmethane, and modified products thereof. Examples of the aromatic polyamine include m-xylylene diamine, diaminodiphenylmethane, m-phenylene diamine, diaminodiphenylsulfone, and modified products thereof.

As the curing agent (β) having a carboxyl group, a compound having two or more carboxyl groups in the molecule is preferable. Examples include phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, pyromellitic acid, benzophenonetetracarboxylic acid, and 1,2,3,4-butanetetracarboxylic acid.

As the curing agent (β) having a mercapto group, a compound having two or more mercapto groups in the molecule is preferable. Examples include condensates of thioglycolic acid and polyhydric alcohols, polysulfides, and the like.

These curing agents (β) may be used alone or in combination of two or more. As the curing agent (β), it is preferable to use a polyamine curing agent.

As the curing agent (β), a commercially available one may be used. Examples of commercially available curing agents include ADEKA Hardener EH-8051 (polyamine) (manufactured by ADEKA Co., Ltd.); Fuji Cure FXI-919; Tomide TXH-674-B and TXS-53-C (manufactured by T&K TOKA Co., Ltd.); Examples include Rikacid BTW (manufactured by New Japan Chemical Co., Ltd.); and Karenz MT BD-1 (manufactured by Showa Denko Co., Ltd.).

The content of the functional group (F) having reactivity with the epoxy group contained in the curing agent (β) is 0.010 equivalent or more with respect to 1 equivalent of the epoxy group contained in the aqueous resin emulsion (α), It is preferably 0.10 equivalent or more, and more preferably 0.20 equivalent or more. This is because the rust prevention properties and adhesion to metal materials of the aqueous resin composition after curing are improved. Here, in calculating the equivalent weight of the functional group (F), when the functional group (F) has two active hydrogens like an unsubstituted amine, the number of functional groups (F) is counted as two.

The content of the functional group (F) having reactivity with the epoxy group contained in the curing agent (β) is 3.0 equivalents or less with respect to 1 equivalent of the epoxy group contained in the aqueous resin emulsion (α), It is preferably 2.0 equivalents or less, more preferably 1.5 equivalents or less, even more preferably 1.0 equivalents or less, even more preferably 0.80 equivalents or less, and even more preferably 0.50 equivalents. It is more preferable that the amount is equal to or less than the equivalent amount. This is because the strength of the coating film is improved.

[1-3. Curing accelerator (γ)]
The curing accelerator (γ) has the function of accelerating the curing of the aqueous resin composition and forming a film with high film yield strength. The curing accelerator (γ) consists of a tertiary amine that does not have a functional group that is reactive with epoxy groups. The tertiary amine in this embodiment is NR ¹ R ² R ³ (wherein R ¹ R ² R ³ is a substituent and may be different from each other, or two or more of the same one may be included) R ¹ R ² R ³ may be bonded to each other to form a ring.

The curing accelerator (γ) is directly bonded to the nitrogen atom of a tertiary aliphatic amine, a tertiary alicyclic amine, a tertiary heteroaromatic amine, or a tertiary amine (NR ¹ R ² R ³ ). At least one compound selected from the group consisting of tertiary aromatic amines having no phenyl group is preferred. This is to increase the nucleophilicity of the curing accelerator (γ) and efficiently advance the curing reaction.

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, 1,8 -diazabicyclo[5.4.0]undec-7-ene, and the like.

As the tertiary heteroaromatic amine, it is preferable to use a compound having an imidazole skeleton, and specific examples thereof include imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and the like.

Examples of tertiary aromatic amines having a phenyl group that is not directly bonded to the nitrogen atom of the tertiary amine (NR ¹ R ² R ³ ) include dimethylbenzylamine, diethylbenzylamine, tribenzylamine, 2,4, Examples include 6-trisdimethylaminomethylphenol and 2-phenylimidazole.

Among these curing accelerators (γ), it is particularly preferable to use the following compounds (i) and/or (ii).
(i) Tertiary alicyclic amine that does not have a functional group (F) that is reactive with epoxy groups 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 that does not have a functional group (F) that is reactive with an epoxy group and has a heteroaromatic ring structure containing two or more nitrogen atoms.

(i) Examples of the tertiary alicyclic amine include 1,4-diazabicyclo[2.2.2]octane (DABCO). (ii) Examples of the tertiary heteroaromatic amine include imidazole.
The curing accelerator (γ) may be used alone or in combination of two or more.

The content of the curing accelerator (γ) is 0.0070 mol or more, preferably 0.070 mol or more, and 0.18 mol or more per equivalent of the epoxy group contained in the aqueous resin emulsion (α). It is more preferable that the amount is present, and even more preferably that it is 0.30 mol or more. This is because a cured product with high film yield strength can be obtained.

The content of the curing accelerator (γ) is 1.5 mol or less, preferably 1.0 mol or less, and 0.70 mol or less per equivalent of epoxy group contained in the aqueous resin emulsion (α). More preferably, the amount is at most 0.44 mol, even more preferably at most 0.40 mol, particularly preferably at most 0.38 mol. This is because it is possible to suppress gelation of the aqueous resin composition in a short time. This is also because a cured product with good rust prevention properties can be obtained.

[1-4. Other ingredients]
The aqueous resin composition according to this embodiment may contain a pigment. Examples of the pigment 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 content of the pigment in the aqueous resin composition is preferably 0.1 to 50% by mass, more preferably 1 to 40% by mass. This is to improve the hiding property of the coating film. Depending on the need, the pigment may be 0.1 to 3% by weight, 3 to 6% by weight, 6 to 10% by weight, 10 to 20% by weight, 20 to 35% by weight, or 35 to 50% by weight. %, etc., in the aqueous resin composition.

The aqueous resin composition includes a filler, an organic or inorganic hollow balloon, a dispersant (for example, amino alcohol, polycarboxylate, etc.), a surfactant, a coupling agent (for example, a silane coupling agent, etc.), a defoaming agent, Preservatives (e.g., biocides, fungicides, fungicides, algaecides, and combinations thereof, etc.), flow agents, leveling agents, neutralizing agents (e.g., hydroxides, amines, ammonia, carbonates, etc.) etc.) may also be included.

As the coupling agent, it is preferable to use a silane coupling agent. Examples of the silane coupling agent include epoxysilane compounds. Specific examples include 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexy)ethyl Examples include trimethoxysilane.

The amount of the silane coupling agent added can be arbitrarily selected, but is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 3 parts by weight, based on 100 parts by weight of the aqueous resin emulsion. . This is because the rust prevention properties and adhesion to metal materials of the aqueous resin composition after curing are improved.

<1-1-6. Method for producing aqueous resin composition>
The aqueous resin emulsion (α), the curing agent (β), the curing accelerator (γ), and other components contained as necessary are mixed. Regarding the mixing step, for example, there is a method described later in Examples, but the method is not limited thereto.

<2. Film formation method>
Next, a method for forming a film made of a cured product of the aqueous resin composition of this embodiment will be described in detail.

In the film forming method of this embodiment, first, an aqueous resin emulsion (α), a curing agent (β), a curing accelerator (γ), and other components contained as necessary are mixed. By this, the aqueous resin composition of this embodiment is prepared (mixing step). Next, the aqueous resin composition obtained in the mixing step is applied to the surface to be painted (coating step).

In the mixing step, the aqueous resin emulsion (α), the curing agent (β), the curing accelerator (γ), and other components contained as necessary are mixed and stirred. By this, an aqueous resin composition in which each component is dispersed is obtained. Stirring in the mixing step can be performed by any method or device, for example, by a device such as Robomics (manufactured by Primix Co., Ltd.). In order to sufficiently disperse each component, stirring in the mixing step is preferably performed for 5 minutes or more. Furthermore, in order to prevent the resin component from curing, the stirring time is preferably within 1 hour.

In the coating step, the aqueous resin composition is applied to the surface of the object to be coated. The material forming the surface to be painted can be arbitrarily selected, and examples include metal materials. The surface to be painted may be previously subjected to a surface treatment such as a primer or an undercoat. Methods for applying the aqueous resin composition include, but are not limited to, methods using brushes, rollers, and the like. Furthermore, in order to prevent the resin component from curing before the coating process is completed, the coating process is preferably completed within one hour after the mixing process is completed.

In the coating film forming method of this embodiment, after the coating step, it is preferable to perform a curing step of curing the coating film obtained by applying it to the surface to be coated.
In the curing step, the resin component contained in the aqueous resin composition can be cured by, for example, drying and curing the surface of the object to be coated to which the aqueous resin composition has been applied. The curing time varies depending on the temperature of the curing atmosphere. For example, at 20°C it is preferably 5 hours or more, at 40°C it is preferably 1 hour or more, and at 60°C it is preferably 5 minutes or more. Whether or not it has hardened may be determined by, for example, touching it with a finger.

<3. Film＞
The film of this embodiment is made of a cured product of the aqueous resin composition of this embodiment. The film of this embodiment can be formed by the film forming method described above.

The film of the present embodiment may optionally include a film consisting of an undercoat layer provided on the lower layer of the film made of the cured product of the aqueous resin composition of the present invention, and/or a top coat layer provided on the upper layer. They may be provided in a stacked manner.

The aqueous resin composition of this embodiment includes an aqueous resin emulsion (α), a curing agent (β), and a curing accelerator (γ). Therefore, a cured product having high film yield strength can be obtained.

In addition, in the film forming method of the present embodiment, an aqueous resin composition is prepared by mixing an aqueous resin emulsion (α), a curing agent (β), and a curing accelerator (γ), and the aqueous resin composition is coated with the aqueous resin composition. Apply to painted surface. As a result, the film of this embodiment made of a cured product having a high film yield strength can be obtained.

<4. Application fields>
The aqueous resin composition of the present invention is useful in various fields, and is particularly suitable for use as a paint applied to the surface of metal products. The article on which a film formed of the cured product of the aqueous resin composition of the present invention is formed, that is, the object to be coated with the aqueous resin composition of the present invention, can be arbitrarily selected. Examples of applicable objects include, for example, various household goods, home appliances such as refrigerators, play equipment installed in amusement parks, sports equipment, buildings (interiors, exteriors, etc.), transportation machinery, etc. Examples include various industrial products and their parts including machine tools, automobile bodies and chassis, railway vehicle bodies and underfloor equipment, ships, marine containers, aircraft, etc.

Hereinafter, the present invention will be explained in detail using Examples. Note that the following examples do not limit the present invention in its entirety, and all examples implemented within the scope of the contents of this description are included in the technical scope of the present invention.

<1. Synthesis of aqueous resin emulsion (α)>
(Aqueous resin emulsion (α-1))
A separable flask equipped with a cooling tube, a thermometer, a stirrer, and a dropping funnel was charged with 158 parts of ion-exchanged water, and the temperature was raised to 60°C. Nitrogen gas was blown into the contents of the separable flask to remove oxygen. Here, an emulsion consisting of methyl methacrylate, 2-ethylhexyl acrylate, methacrylic acid, hydrogenated bisphenol A type epoxy, sodium dodecylbenzenesulfonate as an emulsifier, and 356 parts by mass of ion-exchanged water is shown in Table 1. was added dropwise over 3 hours. At the same time as the emulsion, 1.2 parts by mass of potassium persulfate was dissolved in 41 parts by mass of ion-exchanged water as an oxidizing agent, and 0.4 parts by mass of sodium bisulfite was dissolved in 21 parts by mass of ion-exchanged water as a reducing agent. was added dropwise at 60° C. over 3.3 hours to polymerize. After the addition was completed, the mixture was aged for 1.5 hours. Thereafter, it was cooled, and 0.8 parts by mass of ammonia water as a basic substance was added to obtain an aqueous resin emulsion (α-1).

Table 1 shows the amounts (parts by mass) of each material used in the synthesis of the aqueous resin emulsion (α-1). The numerical value of "ion-exchanged water" shown in Table 1 indicates the content of ion-exchanged water contained in the synthesized aqueous resin emulsion (α-1). In addition, the numbers in parentheses for the usage amounts of copolymer (X) and polyepoxy compound (Y) in Table 1 are the total amount (100%) of copolymer (X) and polyepoxy compound (Y). The ratio (mass%) of each material is shown.

As the polyepoxy compound (Y) shown in Table 1, the following was used.
Hydrogenated bisphenol A epoxy (epoxy equivalent: 215 g/mol; manufactured by Kyoei Chemical Co., Ltd.; Epolite 4000)
Bisphenol A epoxy (epoxy equivalent: 190 g/mol; manufactured by Mitsubishi Chemical Corporation; JER828)
Glycerin polyglycidyl ether (epoxy equivalent: 143 g/mol; manufactured by Sakamoto Pharmaceutical Co., Ltd.; SR-GLG)
1,6-hexanediol diglycidyl ether (epoxy equivalent: 160 g/mol; manufactured by Kyoei Chemical Co., Ltd.; Epolite 1600)

(Aqueous resin emulsion (α-2) to (α-7))
Aqueous resin emulsions (α-2) to (α-7 ) was synthesized. In addition, in the aqueous resin emulsions (α-2) to (α-7), the values for “ion exchange water” shown in Table 1 are the same as in the synthesized aqueous resin emulsion (α-1). The content of ion-exchanged water contained in the aqueous resin emulsions (α-2) to (α-7) is shown.

<2. Evaluation of aqueous resin emulsion (α)>
The following items were evaluated for each of the aqueous resin emulsions (α-1) to (α-7). The results are shown in Table 2. Note that the aqueous resin emulsion (α-7) was not evaluated because it aggregated during synthesis.
In the following description, when aqueous resin emulsions (α-1) to (α-7) are collectively referred to, they may be written as aqueous resin emulsion (α).

<2-1. Non-volatile content>
1 g of the aqueous resin emulsion (α) was weighed into an aluminum dish with a diameter of 5 cm, and dried at 105° C. for 1 hour at atmospheric pressure in a dryer while circulating air. The mass of the residue obtained after drying was measured, and the ratio (% by mass) of the mass after drying to the mass of the aqueous resin emulsion (α) before drying was determined.

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

The amount N ₁ [mol/g] of epoxy groups in the aqueous resin 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 to synthesize the aqueous resin emulsion (α) to react with the epoxy groups. Next, the amount of remaining hydrogen chloride was confirmed by titrating unreacted hydrogen chloride with potassium hydroxide. At this time, potassium hydroxide is consumed by reaction with acidic components such as carboxylic acid contained in the aqueous resin emulsion (α). For this reason, the amount of acidic components was titrated in advance by blank measurement without using hydrogen chloride, and the results of the main measurement were corrected. The specific measurement procedures are as follows (i) to (ii).

(i) Blank measurement (confirmation of acidic component amount)
Weigh W ₁ [g] (5 g in the present example and comparative example) of the aqueous resin emulsion (α) into a 100 mL Erlenmeyer flask, add 25 g of tetrahydrofuran (THF), and stir with a magnetic stirrer to make a homogeneous mixture. It was made into a solution. To this solution, 0.15 mL of a 0.1% by mass cresol red aqueous solution was added 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 dropping the potassium hydroxide/ethanol solution was defined as the equivalence point. Here, the amount of potassium hydroxide/ethanol solution used for titration is defined as V _KOH1 [mL].

(ii) Main measurement Weigh out the aqueous resin emulsion (α) in an amount of W ₂ [g] (5 g in this example and comparative example) into a 100 mL Erlenmeyer flask, add 25 g of THF, and stir with a magnetic stirrer to dissolve. Ta. A 0.2M hydrogen chloride/dioxane solution was added to this and stirred for 1 hour to form a homogeneous solution. The amount of the hydrogen chloride/dioxane solution added here is defined as V _HCl [mL] (25 mL in this example and comparative example). To this solution, 0.15 mL of a 0.1% by mass cresol red aqueous solution was added 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 dropping the potassium hydroxide/ethanol solution was defined as the equivalence point. Here, the amount of potassium hydroxide/ethanol solution used for titration is defined as V _KOH2 [mL].

From each value obtained in (i) and (ii), the amount N ₁ [mol/g] of epoxy groups per 1 g of aqueous resin emulsion (α) was calculated using the following formula (4).
N ₁ = (0.2×V _HCl /1000-0.1×V _KOH2 /1000)/W ₂ + (0.1×V _KOH1 /1000)/W ₁ …(4)

The total amount N ₂ [mol/g] of epoxy groups contained in the components (raw materials) used for the synthesis of the aqueous resin emulsion (α) is the mass m _i [parts by mass] of each component (i=1, 2, 3, ...) and the epoxy equivalent EP _i [g/mol] using the following formula (5). The components used in the synthesis of the aqueous resin emulsion (α) here mean all the components listed in Table 1 as raw materials for the aqueous resin emulsion (α).
N ₂ = Σ(m _i /EP _i )/Σm _i …(5)

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

<2-3. Content of epoxy groups in nonvolatile matter, content of epoxy groups in component (X) + (Y)>
From the nonvolatile content concentration C _S [mass %], the epoxy group content N ₁ in the aqueous resin emulsion (α), and the total amount of epoxy groups in the raw materials N ₂ determined by the above method, the amount of the aqueous resin emulsion (α) The content R _EP [mol/g] of epoxy groups in the nonvolatile components was determined based on the formula (2) explained above.
R _EP =N ₁ /(C _S /100)...(2)

In addition, the epoxy group content _N1 in the aqueous resin emulsion (α) determined by the above method, the total mass α [g] of all components (raw materials) used in the synthesis of the aqueous resin emulsion (α), and the copolymer Using the mass X [g] of the raw material used for coalescence (X) and the mass Y [g] of the raw material used for the polyepoxy compound (Y), calculate the proportion of components (X) + (Y) based on the following formula. The epoxy group content R _EP [mol/g] was calculated.
R _EP in (X) + (Y) = N ₁ / {(X + Y) / α}

<2-4. Content of carboxy groups in nonvolatile matter, content of carboxy groups in component (X) + (Y)>
The total amount N ₃ [mol/g] of carboxyl groups contained in the components (raw materials) used for the synthesis of the aqueous resin emulsion (α) is the mass m _i [parts by mass] of each component (i=1, 2, 3, ...) and the carboxy equivalent CX _i [g/mol] using the following formula (6). The components used in the synthesis of the aqueous resin emulsion (α) here mean all the components listed in Table 1 as raw materials for the aqueous resin emulsion (α).
N ₃ =Σ(m _i /CX _i )/Σm _i …(6)
From the N ₃ determined here, the content R _CX [mol/g] of carboxy groups in the nonvolatile components of the aqueous resin emulsion (α) was determined based on the formula (3) explained above.
R _CX = {N ₃ - (N ₂ - N ₁ )}/(C _S /100)...(3)

In addition, the epoxy group content N ₁ in the aqueous resin emulsion (α) determined by the above method, the total amount of epoxy groups in the raw materials N ₂ , the content of epoxy groups in the components (raw materials) used for the synthesis of the aqueous resin emulsion (α), The total amount of carboxyl groups _N3 , the total mass α [g] of all components (raw materials) used in the synthesis of the aqueous resin emulsion (α), the mass X [g] of the raw materials used for the copolymer (X), Using the mass Y [g] of the raw material used for the polyepoxy compound (Y), calculate the content R _CX [mol/g] of carboxy groups in component (X) + (Y) based on the following formula: did.
(X) + R _CX in (Y) = {N ₃ - (N ₂ - N ₁ )}/{(X+Y)/α}

<2-5. pH＞
It was measured using a pH meter (manufactured by DKK Toa Co., Ltd., glass electrode hydrogen ion concentration indicator HM-30G).

<2-6. Viscosity＞
The viscosity of the aqueous resin emulsion (α) was measured using the following conditions and equipment.
Temperature: 23℃
Measuring equipment: B-type viscometer Rotor: No. 1
Rotation speed: 60rpm

<2-7. Glass transition point>
The glass transition point Tg of the copolymer (X) is a value calculated using the above formula (1).

<2-8. Dispersion stability>
The state of the aqueous resin emulsion (α) immediately after synthesis was visually observed and evaluated according to the following criteria.
○ (Acceptable): No aggregation, precipitation, separation, or gelation was observed.
× (impossible): At least one of aggregation, precipitation, separation, and gelation was observed.

<2-9. High temperature stability>
The high temperature stability of the aqueous resin emulsion (α) was evaluated as follows. First, the aqueous resin emulsion (α) was put into a 70 ml glass bottle, the bottle was tightly stoppered, and the bottle was allowed to stand at 60° C. for 7 days. Thereafter, the state of the aqueous resin emulsion (α) in the glass bottle was visually observed and evaluated according to the following criteria.
○ (Acceptable): No aggregation, thickening, precipitation, separation, or gelation was observed.
× (impossible): At least one of aggregation, thickening, precipitation, separation, and gelation was observed.

<2-10. Evaluation results＞
As shown in Table 2, all of the aqueous resin emulsions (α-1) to (α-6) had good high temperature stability.
From the above, the amount of (meth)acrylic acid ester (A) added to the total amount of monomer and polyepoxy compound (Y) is 20 to 98% by mass, and the total amount of monomer and polyepoxy compound (Y) is 20 to 98% by mass. The amount of the ethylenically unsaturated carboxylic acid (B) added to the amount is 0.1 to 10% by mass, and the amount of the polyepoxy compound (Y) added to the total amount of the monomer and the polyepoxy compound (Y) is 1 to 10% by mass. It was found that the aqueous resin emulsion (α) having a concentration of 40% by mass has excellent high temperature stability.
On the other hand, in the aqueous resin emulsion (α-7) in which the polyepoxy compound (Y) was added in an excessive amount, the polymer was not dispersed but aggregated.

<3. Examples 1 to 17 and Comparative Examples 1 to 2 (Preparation of aqueous resin composition)>
100 parts by mass of the aqueous resin emulsion (α) shown in Tables 3 and 4 (nonvolatile content 40% by mass), 60 parts by mass of ion-exchanged water, and the curing agent (β) shown in Tables 3 and 4. A curing accelerator (γ) was added in the amounts (parts by mass) shown in Tables 3 and 4 and stirred for 10 minutes to prepare aqueous resin compositions of Examples 1 to 17 and Comparative Examples 1 to 2. .

In Tables 3 and 4, the "equivalent to epoxy group" in each curing agent (β) refers to the reactivity of the epoxy group contained in the curing agent (β) to 1 equivalent of epoxy group contained in the aqueous resin emulsion (α). This is a numerical value indicating the equivalent weight of the functional group (F) having
The "equivalent to epoxy group" in each curing accelerator (γ) is a numerical value indicating the number of moles of the curing accelerator (γ) with respect to 1 equivalent of epoxy group contained in the aqueous resin emulsion (α).
As the polyamine shown in Tables 3 and 4, ADEKA Hardener EH-8051 (manufactured by ADEKA Corporation) was used. The amine equivalent of the polyamine used as the curing agent (β) is 187 g/mol. The carboxy group equivalent of 1,2,3,4-butanetetracarboxylic acid is 58.5 g/mol.

<4. Evaluation of film (paint film)>
Using the aqueous resin compositions of Examples 1 to 17 and Comparative Examples 1 to 2, films (coating films) were formed by the method shown below, and evaluated on the following items. The results are shown in Tables 3 and 4.

<4-1. Measuring method of film yield strength>
The aqueous resin composition was applied by drooling so as to spread over the entire surface of a rectangular flat plate of polyethylene film with a length of 90 mm and a width of 190 mm, which was placed horizontally. This was dried at 23° C. for 72 hours and then cured at 50° C. for 24 hours to produce a cured coating film (cured product). The resulting coating film was peeled off from the flat plate. The peeled coating film was cut into a rectangle with a width of 10 mm and a length of 30 mm, and was used as a test piece.

The following tests were conducted with the longitudinal direction of this test piece as the tensile direction. The thickness of the test piece was measured using Quick Micro (registered trademark) MDQ-MX manufactured by Mitutoyo Co., Ltd. Measurements were performed at three locations on each test piece, and the average value of the measurement results at the three locations was taken as the thickness t [mm] of the test piece.

The film yield strength test was conducted using Autograph AG-X (manufactured by Shimadzu Corporation) by the method shown below. Both sides of the test piece in the longitudinal direction were gripped with chucks with a distance between chucks of 10 mm. The test piece was pulled at a speed of 100 mm/min in an atmosphere with a temperature of 23° C. and a relative humidity (RH) of 50%.

If the distance between the chucks is L [mm] and the change in length of the test piece (the difference between the distance between the chucks during the test and the distance between the chucks before the test) is ΔL [mm], the strain S is 100 It is calculated as ×ΔL/L [%]. In addition, the load applied to the test piece (measured load) is F [N], the maximum value of the load until the test piece breaks is F _max [N], and the following conditions are set at the beginning of the test. The point where this is satisfied is defined as the yield point Y (S _y , F _y ).

(Yield point conditions)
Strain S is 2% or more (S _y ≧2%).
As the strain S increases, the amount of change in the load F changes from increasing to decreasing.
dF/dS<0 continues until F=F _y −0.01F _max .
When S≦S _y +0.05%, there is no point where F>F _y .

The film yield strength, which is the stress σ _y applied to the test piece at the yield point Y, is calculated by the formula shown below.
σ _y [N/mm ² ]=F _y /(W×t)
(W in the formula is the width [mm] of the test piece, and t is the thickness [mm] of the test piece.)

<4-2. Water resistance swelling rate>
A coating film was formed on a flat plate made of polyethylene film in the same manner as in the measurement of the yield point above. The resulting coating film was peeled off from the flat plate. The peeled coating film was cut into a square with a length of 10 mm and a width of 10 mm.

After weighing the cut out coating film, it was immersed in ion-exchanged water at 23° C. for 24 hours. The immersed coating film was taken out from the ion-exchanged water, and immediately after that, the coating film was weighed, and this was taken as the weight of the coating film before drying. Thereafter, the coating film was dried at 105° C. for 3 hours, and the coating film was weighed again, and this was taken as the weight of the coating film after drying. The water resistance swelling ratio was determined from the mass of the coating film before drying and the mass of the coating film after drying using the following formula (4).

Water resistance swelling rate (%) = {(mass of coating film before drying - mass of coating film after drying)/mass of coating film after drying} x 100...(4)

<4-3. Rust prevention>
The aqueous resin composition was applied to a cold rolled steel plate (hereinafter referred to as "base material") using a brush so that the basis weight was 50 g/m ² . The coated base material was dried in a constant temperature bath at 60° C. for 10 minutes to form a coating film on the surface of the base material.

A rectangular area measuring 30 mm long and 45 mm wide on the coating film formed on the surface of the substrate was used as the test area. A notch consisting of two intersecting straight lines (that is, an X-shape) was formed in the coating film so as to form a diagonal of the rectangle forming the test area, and a test piece was obtained. The cut was made using a cutter knife so that it reached from the top of the coating to the base material. A neutral salt spray test (Section 4.2.1) was conducted on the test specimen in which the cuts were formed based on JIS Z-2371 (2000).

In the test specimen after the neutral salt spray test, the area [area %] occupied by the blisters in the coating film in the test area, the size of the blisters [mm], and the size [mm] of flowing rust from the notches were measured. The size of the bulge was determined as the longest dimension in the area occupied by one independent bulge. In addition, the size of the flowing rust was determined as the maximum width of the rust centered on the cross-cut portion.

<4-4. Adhesion of coating film to metal materials>
A coating film was formed on the surface of a cold rolled steel sheet in the same manner as in the above evaluation of rust prevention properties. According to JIS K-5400 (1990) "Section 8.5.2 Cross-cut tape method," a steel plate with a coating film is used as a test piece, and a cutter is used to make cuts in a grid pattern at 1 mm intervals so as to penetrate the coating film. (100 squares), and Cellotape (registered trademark) was attached. After 1 hour, the cellotape (registered trademark) was peeled off, and the adhesion of the coating film to the metal material was evaluated by counting the number of squares that remained without peeling off the coating film from the steel plate.

<4-5. Evaluation results＞
As shown in Tables 3 and 4, aqueous resin emulsions (α-1) to (α-6), a curing agent (β) which is a polyamine or 1,2,3,4-butanetetracarboxylic acid, and 1 , 4-diazabicyclo[2.2.2]octane (DABCO) or imidazole as the curing accelerator (γ). /mm ² ] or more, and the yield strength of the film was high. Further, the cured products of the aqueous resin compositions of Examples 1 to 17 had low water swelling ratios, good water resistance, and good adhesion to metal materials. Further, the cured products of the aqueous resin compositions of Examples 1 to 4, 6 to 9, and 11 to 17 had little swelling and had good rust prevention properties.

On the other hand, the cured products of the aqueous resin compositions of Comparative Examples 1 and 2, which do not contain the curing accelerator (γ), have a higher film yield than the cured products of the aqueous resin compositions of Examples 1 to 17. The strength was inferior.

According to the present invention, it is possible to provide an aqueous resin composition that yields a cured product with high film yield strength, water resistance, and high adhesion to metal materials.

Claims (15)

Contains an aqueous resin emulsion (α), a curing agent (β), and a curing accelerator (γ),
The aqueous resin emulsion (α) is
Copolymer (X) and
A polyepoxy compound (Y) having no ethylenically unsaturated bonds and having two or more epoxy groups in one molecule,
an aqueous medium (Z);
including;
The content of the polyepoxy compound (Y) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 1 to 40% by mass,
The copolymer (X) is
(meth)acrylic acid ester (A)-derived structural unit,
A structural unit derived from ethylenically unsaturated carboxylic acid (B),
The content of the structural unit derived from the (meth)acrylic ester (A) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 20 to 98% by mass,
The content of the structural unit derived from the ethylenically unsaturated carboxylic acid (B) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 0.1 to 10% by mass,
The structural unit derived from the (meth)acrylic ester (A) includes a structural unit derived from the hydrophilic (meth)acrylic ester (A1) in which the alcohol-derived moiety has 2 or less carbon atoms, and the hydrophilic (Meth)acrylic acid ester (A1) is methyl (meth)acrylate or ethyl (meth)acrylate,
The content of the structural unit derived from the hydrophilic (meth)acrylic acid ester (A1) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 15 to 98% by mass,
One or both of the copolymer (X) and the polyepoxy compound (Y) contain a carboxyl group,
The curing agent (β) is made of a compound having a functional group (F) that is reactive with epoxy groups,
The content of the functional group (F) contained in the curing agent (β) is 0.010 equivalent or more and 3.0 equivalent or less with respect to 1 equivalent of epoxy group contained in the aqueous resin emulsion (α). ,
The curing accelerator (γ) is made of a tertiary amine that does not have a functional group that is reactive with epoxy groups,
The content of the curing accelerator (γ) in the aqueous resin composition is 0.0070 mol or more and 1.5 mol or less with respect to 1 equivalent of epoxy group contained in the aqueous resin emulsion (α). The aqueous resin composition according to claim 1, wherein the (meth)acrylic acid ester (A) is an alkyl (meth)acrylic ester. The ethylenically unsaturated carboxylic acid (B) contains at least one member from the group consisting of α,β-unsaturated monocarboxylic acid, α,β-unsaturated dicarboxylic acid, and a vinyl compound containing a carboxyl group. , the aqueous resin composition according to claim 1 or claim 2. The polyepoxy compound (Y) is at least one selected from bisphenol-type epoxy compounds, hydrogenated bisphenol-type epoxy compounds, diglycidyl ethers, triglycidyl ethers, tetraglycidyl ethers, diglycidyl esters, triglycidyl esters, and tetraglycidyl esters. The aqueous resin composition according to any one of claims 1 to 3, which is a seed. Any one of claims 1 to 4, wherein the copolymer (X) consists of a structural unit derived from the (meth)acrylic acid ester (A) and a structural unit derived from the ethylenically unsaturated carboxylic acid (B). The aqueous resin composition according to item 1. The copolymer (X) contains a structural unit derived from an ethylenically unsaturated aromatic compound (C) having a benzene ring and an ethylenically unsaturated bond, according to any one of claims 1 to 4. water-based resin composition. The aqueous resin composition according to claim 6, wherein the ethylenically unsaturated aromatic compound (C) is an aromatic vinyl compound. Any one of claims 1 to 7, wherein the curing agent (β) contains at least one selected from the group consisting of an unsubstituted or one-substituted amino group, a carboxy group, and a mercapto group. The aqueous resin composition described in . The curing accelerator (γ) is at least one compound selected from the group consisting of a tertiary aliphatic amine, a tertiary alicyclic amine, and a tertiary heteroaromatic amine. Item 8. The aqueous resin composition according to any one of Item 8. The aqueous resin emulsion (α) is an emulsion obtained by emulsion polymerization of monomers serving as structural units of the copolymer (X) in the aqueous medium (Z) in the presence of the polyepoxy compound (Y). The aqueous resin composition according to any one of claims 1 to 9. Any one of claims 1 to 10, wherein the content of carboxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is 0.10 x 10 ^-4 mol/g or more. The aqueous resin composition according to item 1. Any one of claims 1 to 11, wherein the content of epoxy groups in the total amount of the copolymer (X) and the polyepoxy compound (Y) is 0.50 x 10 ^-4 mol/g or more. The aqueous resin composition according to item 1. The content of the structural unit derived from the hydrophilic (meth)acrylic ester (A1) with respect to the total amount of the copolymer (X) and the polyepoxy compound (Y) is 30 to 98% by mass,
The aqueous resin composition according to any one of claims 1 to 12. A film comprising a cured product of the aqueous resin composition according to any one of claims 1 to 13. A coating step of applying the aqueous resin composition according to any one of claims 1 to 13 to a surface to be painted;
a curing step of curing the applied aqueous resin composition;
A method of forming a film, including: