WO2017204293A1

WO2017204293A1 - Method for forming cured electrodeposition coating film

Info

Publication number: WO2017204293A1
Application number: PCT/JP2017/019524
Authority: WO
Inventors: 金子　敏雄; 裕久加納; 澄穂西岡; 勝青木
Original assignee: 日本ペイント・インダストリアルコーティングス株式会社
Priority date: 2016-05-27
Filing date: 2017-05-25
Publication date: 2017-11-30
Also published as: CN109477235B; KR102316870B1; JP2017210668A; CN109477235A; KR20190013755A; JP6058191B1

Abstract

The present invention addresses the problem of providing a method for forming a cured electrodeposition coating film in which the glossiness thereof is adjusted, such as a low-gloss coating film having low specular gloss or a mat coating film. The present invention provides a method for forming a cured electrodeposition coating film, wherein the method includes an electrodeposition coating step for dipping an object to be coated in an anion electrodeposition coating material composition and forming an electrodeposition coating film, and a thermal curing step for heating and curing the electrodeposition coating film formed in the coating step, the anion electrodeposition coating material composition including an acrylic resin (A), a curing agent (B), a water-dispersion-type gloss adjuster (C), and a curing catalyst (D), the water-dispersion-type gloss adjuster (C) being a water dispersion of one or more types of wax selected from the group consisting of natural wax and a polyolefin wax, the wax configuring the water-dispersion-type gloss adjuster (C) having a softening point (T_m) of 100°C or higher and a density in the range of 0.91-1.10, the solid content mass of the water-dispersion-type gloss adjuster (C) included in the anion electrodeposition coating material composition being 6-20 parts by mass with respect to 100 parts by mass of resin solid content of the anion electrodeposition coating material composition, and the coating film viscosity at 50°C of the electrodeposition coating film formed in the electrodeposition coating step being in the range of 10,000-100,000 Pa∙s.

Description

Method for forming cured electrodeposition coating film

The present invention relates to a method for forming a cured electrodeposition coating film using an anionic electrodeposition coating composition.

Electrodeposition coating is a coating method performed by immersing an object to be coated in an electrodeposition coating composition and applying a voltage. This method can be applied to the details even if the object has a complicated shape, and can be applied automatically and continuously, so it is widely used as an undercoating method for various objects. It has been. There are two types of electrodeposition coating compositions, a cationic electrodeposition coating composition and an anionic electrodeposition coating composition. In general, a cationic electrodeposition coating composition can form a cured electrodeposition coating film having better rust prevention and corrosion resistance. On the other hand, an anionic electrodeposition composition is often used for an aluminum material. The aluminum material is superior to the aluminum material by first forming an anodized film (anodized film) by anodizing treatment and then performing anion electrodeposition coating using the anion electrodeposition composition. This is because corrosion resistance can be imparted.

In anionic electrodeposition coating, for example, in the case of aluminum sash coating, a coated object provided with a low gloss coating or matting coating with a low specular gloss can generally give a calm visual impression, Moreover, since a high-class feeling is also felt, the request | requirement to the coating method which can form such a coating film is increasing in recent years.

As a matte anion electrodeposition coating composition, for example, JP-A-2002-188044 (Patent Document 1) uses a polymerizable unsaturated monomer in the presence of acrylic resin (I), water and an emulsifier. An emulsion polymer produced by emulsion polymerization in multiple stages, wherein the polymerizable unsaturated monomer is an alkoxysilyl group-containing polymerizable unsaturated monomer based on the total monomer weight used in multiple stages. A coating composition containing an alkoxysilyl group-containing emulsion polymer (II) and a crosslinking agent (III) in a proportion of 5 to 40% by weight, comprising the acrylic resin (I) and the alkoxysilyl group-containing emulsion polymer The blending ratio of (II) and crosslinking agent (III) is 20 to 70% by weight of (I), 5 to 40% by weight of (II), and 20 to 60 of (III) with respect to the total solid content of these resins. Anionic-type matte electricity characterized by the weight percent Coating composition are described (claim 1). JP-A-2005-307161 (Patent Document 2) discloses an emulsion polymer produced by emulsion polymerization in multiple stages using a polymerizable unsaturated monomer in the presence of water and an emulsifier. A core / shell type emulsion containing an alkoxysilyl group-containing polymerizable unsaturated monomer as the polymerizable unsaturated monomer in a ratio of 1 to 40% by weight based on the total weight of monomers used in multiple stages ( An anionic electrodeposition paint containing A), an acrylic resin (B), and a curing agent (C) is described. However, the cured electrodeposition coating films obtained with these anion electrodeposition coating compositions vary greatly in gloss depending on the coating conditions and / or the shape of the object to be coated, so-called gloss unevenness. There was a problem that occurred.

Japanese Patent Application Laid-Open No. 5-039445 (Patent Document 3) discloses a matte electrodeposition coating composition in which a matte electrodeposition coating composition is diluted and electrodeposited. 5) to 50% by weight of a water-soluble fluorine-containing copolymer resin having a carboxyl group and a hydroxyl group; (B1) 5 to 60% by weight of a water-soluble or water-dispersible acrylic copolymer resin having an alkoxysilane group; A method for forming a matte coating film comprising 20 to 60% by weight of an agent is described (claim 1). The matte electrodeposition coating composition in Patent Document 3 has an insoluble gel structure when (B1) a water-soluble or water-dispersible acrylic copolymer resin having an alkoxysilane group is crosslinked, and the insoluble gel particles Is different from the method of the present invention in that it provides a matting effect.

In Japanese Patent Laid-Open No. 8-113735 (Patent Document 4), in the presence of a water-soluble or water-dispersible vinyl copolymer (A) having a carboxyl group and a hydroxyl group in the side chain, (a) α, β-ethylenically unsaturated carboxylic acid hydroxyalkyl-containing ester monomer, (b) α, β-ethylenically unsaturated carboxylic acid alkoxysilane group-containing ester monomer, (c) copolymer having no carboxyl group After adding the amino resin (E) to the copolymer (D) obtained by copolymerizing the monomer mixture (B) of the polymerizable vinyl group-containing monomer, the wax (F) is mixed and partially mixed with an organic amine. A method for producing a resin composition for a matte electrodeposition coating material, characterized in that after neutralization, water is added to form an emulsion (claim 1). However, the matte cured electrodeposition coating film obtained by using the resin composition for electrodeposition coatings obtained by this production method, the glossiness of the resulting cured electrodeposition coating film varies greatly depending on the heat curing temperature, A cured electrodeposition coating film having a desired glossiness may not be obtained.

By the way, due to further demands for environmental load reduction such as energy saving and CO ₂ emission reduction in recent years, it is required to lower the heat curing temperature in coating film formation. On the other hand, by lowering the heat curing temperature, the resulting cured electrodeposition coating film has a low cross-linking density, and there is a possibility that the coating film properties such as coating film hardness or corrosion resistance may be decreased.

JP 2002-188044 A JP 2005-307161 A Japanese Patent Laid-Open No. 5-039445 Japanese Patent Laid-Open No. 8-113735

The present invention solves the above-mentioned conventional problems, and the object of the present invention is to form a cured electrodeposition coating film with adjusted glossiness, such as a low-gloss coating film or matte coating film with low specular gloss. It is to provide a method.

In order to solve the above problems, the present invention provides the following aspects.
[1]
A method of forming a cured electrodeposition coating film, wherein the method is
An electrodeposition coating process in which an object to be coated is immersed in an anionic electrodeposition coating composition, and an electrodeposition coating film is formed by applying a voltage; and
A heat curing step for forming a cured electrodeposition coating by heat curing the electrodeposition coating formed in the electrodeposition coating step;
Including
The anion electrodeposition coating composition includes an acrylic resin (A), a curing agent (B), a water-dispersed gloss adjusting agent (C), and a curing catalyst (D).
The water-dispersed gloss modifier (C) is an aqueous dispersion of one or more waxes selected from the group consisting of natural waxes and polyolefin waxes,
The wax constituting the water-dispersed gloss adjusting agent (C) has a softening point (T _m ) of 100 ° C. or higher and a density in the range of 0.91 to 1.10.
The solid content mass of the water-dispersed gloss adjusting agent (C) contained in the anion electrodeposition coating composition is 6 to 20 parts by mass with respect to 100 parts by mass of the resin solid content of the anion electrodeposition coating composition.
The electrodeposition coating film formed in the electrodeposition coating step has a coating film viscosity at 50 ° C. in the range of 10,000 to 100,000 Pa · s.
Method.
[2]
The above method wherein the heating temperature (T _h ) in the heat curing step is 110 to 160 ° C.
[3]
The above method, wherein the softening point (T _m ) is in the range of 100 to 140 ° C.
[4]
The method as described above, wherein the electrodeposition coating film formed in the electrodeposition coating step has a coating film viscosity at 80 ° C. in the range of 1,000 to 10,000 Pa · s.
[5]
The acrylic resin (A) is an acrylic resin having a carboxyl group and a hydroxyl group,
The curing agent (B) is one or more selected from the group consisting of amino resins and blocked isocyanate compounds.
The above method.
[6]
The method as described above, wherein the difference (ΔT) between the softening point (T _m ) and the heating temperature (T _h ) is 10 ° C. or more and 50 ° C. or less and T _h > T _m .
[7]
The above-mentioned method, wherein the cured electrodeposition coating film formed by the above-described forming method has a 60 ° specular gloss of 70 or less.

In this specification, an uncured electrodeposition coating before heat curing is referred to as an “electrodeposition coating”, and a coating after heat curing is referred to as a “cured electrodeposition coating” or simply “curing coating”. It is called “membrane”.

According to the method of the present invention, it is possible to obtain a cured electrodeposition coating film with adjusted glossiness, such as a low gloss coating film or matte coating film with low specular gloss. By the method of the present invention, it is possible to obtain a cured electrodeposition coating film having no gloss unevenness such as a glossiness change due to a heat curing temperature change and having an excellent finished appearance. In the method of the present invention, a cured electrodeposition coating film having good hardness can be obtained even when an electrodeposition coating film is formed and then heat-cured under low-temperature curing conditions.

The method for forming the cured electrodeposition coating film of the present invention comprises the following steps:
An electrodeposition coating process in which an object to be coated is immersed in an anionic electrodeposition coating composition, and an electrodeposition coating film is formed by applying a voltage; and
A heat curing step for forming a cured electrodeposition coating film by heating and curing the electrodeposition coating film formed in the electrodeposition coating step;
Is included. Hereinafter, the method of the present invention will be described in detail.

The object to be coated in the forming method of the present invention is not particularly limited as long as it is a conductive substrate. Examples of the objects to be coated include metal materials such as iron, stainless steel, aluminum, copper, zinc, tin and alloys thereof, molded products of these metal materials, and conductive plastics and surface treated products thereof. it can. The metal material may be a base material that has been plated. In the present invention, examples of the object to be coated include iron substrates such as iron and stainless steel, and aluminum substrates such as aluminum and aluminum alloys.

Anionic electrodeposition coating composition The anionic electrodeposition coating composition in the present invention comprises an acrylic resin (A), a curing agent (B), a water-dispersed gloss adjusting agent (C) and a curing catalyst (D).

Acrylic resin (A)
The acrylic resin (A) contained in the anion electrodeposition coating composition is a film-forming resin. The acrylic resin (A) is preferably an acrylic resin having a carboxyl group and a hydroxyl group. Examples of such an acrylic resin (A) include a carboxyl group-containing radical polymerizable unsaturated monomer (a-1) and a hydroxyl group-containing radical polymerizable unsaturated monomer (a-2), and if necessary, And acrylic resins obtained by radical polymerization of these monomers using other radically polymerizable unsaturated monomers (a-3).

The carboxyl group-containing radical polymerizable unsaturated monomer (a-1) is a compound having at least one carboxyl group and polymerizable unsaturated bond in one molecule. Examples of the carboxyl group-containing radical polymerizable unsaturated monomer (a-1) include (meth) acrylic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, maleic acid monoester, itaconic acid monoester, Examples thereof include vinyl polymerizable α, β-unsaturated fatty acids such as crotonic acid and citraconic acid, caprolactone-modified carboxyl group-containing (meth) acrylic monomers, and mixtures thereof. As the carboxyl group-containing radical polymerizable unsaturated monomer (a-1), it is preferable to use at least one selected from the group consisting of acrylic acid and methacrylic acid.
In the present specification, (meth) acrylic acid represents acrylic acid or methacrylic acid.

The hydroxyl group-containing radical polymerizable unsaturated monomer (a-2) is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule. Examples of the hydroxyl group-containing radical polymerizable unsaturated monomer (a-2) include (meth) acrylic such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and hydroxybutyl (meth) acrylate. Hydroxyalkyl acids; (meth) acrylic acid (poly) ethylene glycol, (meth) acrylic acid (poly) propylene glycol and other (meth) acrylic acid (poly) alkylene glycols; and hydroxyl group-containing acrylic monomers And lactone compounds such as β-propiolactone, dimethylpropiolactone, butyrolactone, γ-valerolactone, γ-caprolactone, γ-caprolactone, γ-lauryllactone, ε-caprolactone, and δ-caprolactone. And reactants. Commercially available products may be used as such reactants. For example, Plaxel FM1 (trade name, caprolactone-modified (meth) acrylic acid hydroxyesters manufactured by Daicel Chemical Industries), Plaxel FM2 (same as left), Plaxel FM3 (same as left) Plaxel FA1 (same as left), Plaxel FA2 (same as left), Plaxel FA3 (same as left), and the like.

The other radical polymerizable unsaturated monomer (a-3) includes the above-mentioned carboxyl group-containing radical polymerizable unsaturated monomer (a-1) and hydroxyl group-containing radical polymerizable unsaturated monomer (a-2). And a monomer having at least one radical polymerizable unsaturated bond in one molecule. Other radical polymerizable unsaturated monomers (a-3) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, (meth) C _1-8 alkyl ester of (meth) acrylic acid such as hexyl acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate or C _3-8 cycloalkyl esters; aromatic polymerizable monomers such as styrene, α-methylstyrene, vinyltoluene; (meth) acrylic acid amide, N-butoxymethyl (meth) acrylamide, N-methylol (meth) acrylamide, etc. (Meth) acrylamide and derivatives thereof; (meth) acrylonitrile compounds; γ Alkoxysilyl group-containing polymerizable monomers such as (meth) acryloxypropyltrimethoxysilane, γ- (meth) acryloxypropylmethyldimethoxysilane, γ- (meth) acryloxypropyltriethoxysilane, vinyltrimethoxysilane; Etc.

As a method for subjecting the monomers (a-1), (a-2) and (a-3) to a radical copolymerization reaction, a solution polymerization method, an emulsion polymerization method and the like which are usually used by those skilled in the art can be used. In preparing the acrylic resin (A),
The carboxyl group-containing radically polymerizable unsaturated monomer (a-1) is preferably 3 to 30% by mass, more preferably 4 to 20% by mass, based on the total mass of the monomers.
The hydroxyl group-containing radically polymerizable unsaturated monomer (a-2) is preferably 3 to 40% by weight, more preferably 5 to 30% by weight, and other radically polymerizable unsaturated monomers (a-2) based on the total weight of the monomers. The saturated monomer (a-3) is preferably 30 to 90% by mass, more preferably 40 to 85% by mass, based on the total mass of the monomers.
It is preferable to use within the range.

The acid value of the acrylic resin (A) is preferably 15 to 150 mgKOH / g, and more preferably 40 to 80 mgKOH / g. When the acid value of the acrylic resin (A) is 15 mgKOH / g or more, the water dispersibility of the resin is increased, and a uniform paint can be produced. Moreover, when it is 150 mgKOH / g or less, there exists an advantage that the corrosion resistance of a cured coating film, acid resistance, etc. increase.

The acrylic resin (A) preferably has a hydroxyl group value of 30 to 200 mgKOH / g, more preferably 50 to 150 mgKOH / g. When the hydroxyl value of the acrylic resin (A) is 30 mgKOH / g or more, the curing reaction occurs sufficiently and the original coating film performance can be obtained. Moreover, when it is 200 mgKOH / g or less, there exists an advantage that an unreacted hydroxyl group does not remain in a coating film, and corrosion resistance, acid resistance, etc. are not reduced.
In addition, in this specification, an acid value and a hydroxyl value represent a solid content acid value and a solid content hydroxyl value, respectively, and can be measured by the method described in JIS K0070.

The acrylic resin (A) preferably has a weight average molecular weight (Mw) of 5,000 to 100,000, and more preferably 10,000 to 50,000. When the weight average molecular weight (Mw) of the acrylic resin (A) is 5000 or more, there are advantages such as improved coating performance such as corrosion resistance and acid resistance. Moreover, in the case of 100,000 or less, there exists an advantage that the flow property of an electrodeposition coating film improves and the cured electrodeposition coating film with a favorable coating-film external appearance is obtained.
In the present specification, the weight average molecular weight (Mw) is a value in terms of polystyrene measured by gel permeation chromatography (GPC).

In the anionic electrodeposition coating composition in the present invention, the acrylic resin (A) is water-soluble or water-dispersible by neutralizing a carboxyl group with a basic substance (for example, triethylamine, dimethylethanolamine, ammonia, etc.). It is preferable to use as the resin. In such neutralization of the acrylic resin (A), the neutralization rate is preferably 30 to 100%, and more preferably 50 to 80%. When the neutralization rate is within the above range, the acrylic resin (A) can be favorably dispersed in the anion electrodeposition coating composition.

In the anion electrodeposition coating composition in the present invention, the content of the acrylic resin (A) is 50 to 80 mass with respect to 100 mass% of the total resin solid content of the acrylic resin (A) and the curing agent (B). % Is preferred. By being 50 mass% or more, chemical resistance such as acid resistance and alkali resistance and corrosion resistance are enhanced. Moreover, when it is 80 mass% or less, an electrodeposition coating film fully hardens | cures and desired coating-film performance is obtained.

The coating composition of the present invention may contain other coating film forming resins as needed other than the acrylic resin (A). Examples of other coating film forming resins include polyester resins, urethane resins, epoxy resins, butadiene resins, phenol resins, xylene resins, and the like. From the viewpoint of improving the corrosion resistance of the cured electrodeposition coating film, an epoxy resin is preferred. Further, the content in the case of using such other coating film-forming resin is preferably less than 20% by mass, preferably less than 10% by mass with respect to the resin solid content contained in the coating composition. More preferred.

Curing agent (B)
The anion electrodeposition coating composition in this invention contains a hardening | curing agent (B). The curing agent (B) is preferably one or more selected from the group consisting of amino resins and blocked isocyanate compounds.

Amino resin is a condensate obtained by modifying a condensate of an amino compound such as melamine, urea or benzoguanamine with an aldehyde compound such as formaldehyde or acetaldehyde using a lower alcohol such as methanol, ethanol, propanol or butanol. It is. Specific examples of such amino resins include, for example, fully alkyl type methyl / butyl mixed etherified melamine resin, methylol group type methyl / butyl mixed etherified melamine resin, imino type methyl / butyl mixed etherified melamine resin, fully alkyl type Mention may be made of methylated melamine resins and imino group-type methylated melamine resins.

Commercial products may be used as amino resins. Examples of commercially available products include fully alkyl type methyl / butyl mixed etherified melamine resins such as Cymel 232, Cymel 232S, Cymel 235, Cymel 236, Cymel 238, Cymel 266, Cymel 267, and Cymel 285; Type methyl / butyl mixed etherified melamine resin; Cymel 202, Cymel 207, Cymel 212, Cymel 253, Cymel 254 and other imino type methyl / butyl mixed etherified melamine resins; Cymel 300, Cymel 301, Cymel 303, Cymel 350, etc. Immediately alkyl type methylated melamine resin; Cymel 325, Cymel 327, Cymel 703, Cymel 712, Cymel 254, Cymel 253, Cymel 212, Cymel 1128, etc. Group type methylated melamine resin (manufactured by Aulnay box Japan), U-VAN 20SE60 (manufactured by Mitsui Chemicals, Inc., butyl etherified melamine resins).

As the blocked isocyanate compound, the following 1) to 3):
1) Aliphatic diisocyanates such as trimethylene diisocyanate and hexamethylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate,
2) Bifunctional or higher polyisocyanates obtained by reacting the above diisocyanates with polyhydric alcohols such as ethylene glycol, trimethylolpropane, pentol,
3) Isocyanurate bond-containing trifunctional isocyanate obtained by reacting 3 moles of the diisocyanates of 1) above;
A blocked isocyanate compound obtained by reacting a blocking agent with at least one selected from the group consisting of
Examples of the blocking agent include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol and methylphenyl carbinol; ethylene glycol monohexyl Cellosolves such as ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type double-end diols such as polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol phenol; ethylene glycol, propylene glycol, 1,4-butanediol and the like Polyester-type double-ended polyols obtained from diols and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, sebacic acid; para-t Phenols such as butylphenol and cresol; oximes such as dimethylketoxime, methylethylketoxime, methylisobutylketoxime, methylamylketoxime, and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam are preferable. Used.

Specific examples of commercially available polyisocyanate compounds include Bihijoule VPLS 2186 (manufactured by Sumika Bayer Urethane Co., Ltd.).

As the curing agent (B), a mixture of the amino resin and the blocked isocyanate compound may be used. As said hardening | curing agent (B), it is more preferable to use an amino resin from the point which can acquire the effect of this invention effectively.

In the anionic electrodeposition coating composition of the present invention, the content of the curing agent (B) is 20 to 50 masses with respect to 100 mass% of the total resin solid content of the acrylic resin (A) and the curing agent (B). % Is preferred. In the case of 20% by mass or more, the curing reaction sufficiently proceeds and desired coating film performance is obtained. Moreover, in the case of 50 mass% or less, the adhesiveness and flexibility of a coating film increase.

Water-dispersed gloss modifier (C)
The anion electrodeposition coating composition in the present invention contains a water-dispersed gloss adjusting agent (C). The water-dispersed gloss modifier (C) is an aqueous dispersion of one or more waxes selected from the group consisting of natural waxes and polyolefin waxes. This wax is required to have a softening point (T _m ) of 100 ° C. or higher and a density in the range of 0.91 to 1.10.
Among the waxes, specific examples of natural waxes include wood wax, carnauba wax, petroleum-based microcrystalline wax, paraffin wax, and mineral-based montan wax. Specific examples of the polyolefin wax include polyolefin waxes such as polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, chlorinated polyethylene, and chlorinated polypropylene.
As an example of a method for preparing an aqueous dispersion of the wax, for example,
A method in which the wax is dissolved in a hydrophilic organic solvent and then mechanically dispersed in an aqueous solvent;
A method of dispersing the wax in an aqueous solvent using a surfactant or a polymer emulsifier, and the like, and
A method of emulsifying and dispersing in an aqueous solvent by reacting the wax with an α, β-unsaturated carboxylic acid to introduce a carboxyl group, and then neutralizing the introduced carboxyl group with an organic amine or an inorganic base;
Etc.
In these preparation methods, it is preferable to use polyethylene, polypropylene, polyethylene oxide, polypropylene oxide or the like as the wax.

In the present invention, a wax having a softening point (T _m ) of 100 ° C. or higher is used as the wax constituting the water-dispersed gloss adjusting agent (C). When the softening point (T _m ) of the wax constituting the water-dispersed gloss adjusting agent (C) is less than 100 ° C., a sufficient gloss adjusting effect cannot be obtained. Further, there is a problem that gloss unevenness occurs in the cured electrodeposition coating film. The softening point (T _m ) of the wax constituting the water-dispersed gloss adjusting agent (C) is preferably within the range of 100 to 140 ° C.

The softening point (T _m ) of the wax constituting the water-dispersed gloss modifier (C) is softened by heating in the solid state before the wax constituting the water-dispersed gloss modifier (C) is water-dispersed. It can be determined by measuring the temperature at the time. Specifically, the measurement of the softening point (T _m ) of the wax constituting the water-dispersed gloss adjusting agent (C) is used for the preparation of the water-dispersing gloss adjusting agent (C), and the above-mentioned state before water dispersion. It can be measured by a method based on JIS K 2207 using wax. In the above measurement, the aqueous medium is evaporated in the water dispersion type gloss adjusting agent (C) instead of the solid state before the water constituting the water dispersion type gloss adjusting agent (C) is dispersed in water, and the wax is solid. It is also possible to use what is in a state.

In the present invention, the wax constituting the water-dispersed gloss adjusting agent (C) has a density in the range of 0.91 to 1.10. The density of the wax constituting the water-dispersed gloss adjusting agent (C) is preferably in the range of 0.92 to 1.05. When the density of the wax that constitutes the water-dispersed gloss adjusting agent (C) is out of the above range, there is a possibility that a defect may occur in the appearance of the cured coating film in the obtained cured electrodeposition coating film.

The density of the wax constituting the water-dispersed gloss modifier (C) can be measured by a method based on JIS K7112.

The water-dispersed gloss adjusting agent (C) is preferably an anion-dispersed type. When the water-dispersed gloss adjusting agent (C) is an anion-dispersing type, there are advantages such as improved coating stability of the resulting anionic electrodeposition coating composition.

A commercially available product may be used as the water-dispersed gloss adjusting agent (C). Commercially available products include, for example, HI-DISPER ^(trademark) series manufactured by Gifu Shellac, AQUACER ^(trademark) series and AQUAMAT ^(trademark) series, manufactured by Big Chemie Japan, Chemipearl W ^(trademark) series, manufactured by Mitsui Chemicals, and Unitika. The Arrow Base ^(trademark) series made by the company is mentioned.

In the present invention, the solid content mass of the water-dispersed gloss adjusting agent (C) contained in the anionic electrodeposition coating composition is 6 to 20 masses per 100 parts by mass of the resin solid content of the anionic electrodeposition coating composition. Part. The solid content mass of the water-dispersed gloss adjusting agent (C) is preferably 7 to 20 parts by mass, and more preferably 10 to 15 parts by mass. When the solid content mass of the water-dispersed gloss adjusting agent (C) exceeds 20 parts by mass, the hardness of the resulting cured electrodeposition coating film may decrease. Moreover, when the solid content mass of the water-dispersed gloss adjusting agent (C) is less than 6 parts by mass, a sufficient gloss adjusting effect cannot be obtained.
In the present specification, the “resin solid content of the anion electrodeposition coating composition” refers to the resin solid content of the coating film-forming resin contained in the electrodeposition coating composition. Specifically, the acrylic resin (A) , Curing agent (B), and resin solid content of other coating film forming resin as required.

Curing catalyst (D)
The anion electrodeposition coating composition in the present invention contains a curing catalyst (D). Examples of the curing catalyst (D) include n-butylbenzenesulfonic acid, amylbenzenesulfonic acid, octylbenzenesulfonic acid, dodecylbenzenesulfonic acid, octadecylbenzenesulfonic acid, dibutylbenzenesulfonic acid, i-propylnaphthalenesulfonic acid, p -Sulfonic acid catalysts such as toluenesulfonic acid, dodecylnaphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and amine neutralized products of these sulfonic acid catalysts; dioctyltin dilaurate, dioctyltin dibenzoate, dibutyl Tin compound catalysts such as tin dibenzoate; and the like.

The sulfonic acid catalyst is more preferably used as the curing catalyst (D), and is selected from the group consisting of dodecylbenzenesulfonic acid, p-toluenesulfonic acid, dodecylnaphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. More preferably, one or more of the above are used. By using such a curing catalyst (D) in the anion electrodeposition coating composition in the present invention, the heating temperature in the heat curing step is relatively low temperature, for example, 100 to 160 ° C., preferably 110 to 160 ° C. Can be set in the condition. Further, there is an advantage that a cured electrodeposition coating film having good performance such as scratch resistance can be formed even when the heating temperature in the heat curing step is relatively low as described above.

The amount of the curing catalyst (D) contained in the anionic electrodeposition coating composition is based on the solid content of the curing catalyst (D) based on the total solid content of 100 parts by mass of the acrylic resin (A) and the crosslinking agent (B). The amount is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and still more preferably 0.2 to 4 parts by mass. By using it in the above range, a cured electrodeposition coating film having good performance such as scratch resistance can be formed.

The anion electrodeposition coating composition in the present invention such as other components is an aqueous coating composition and contains water as a main solvent. On the other hand, the anion electrodeposition coating composition in the present invention may contain an organic solvent as necessary. Specific examples of the organic solvent include alcohols such as methanol, isopropanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and methoxypropanol, ethers such as ethylene glycol monobutyl ether, propylene glycol monobutyl ether and diethylene glycol monobutyl ether, and acetylacetone. Ketones such as, esters such as ethylene glycol monoethyl ether acetate, hexane and the like. These organic solvents may use only 1 type and may use 2 or more types together. However, from the viewpoint of VOC emission regulation, the amount of the organic solvent is preferably as small as possible.

The anion electrodeposition coating composition according to the present invention includes a colorant, a pigment, a film-forming aid, a drying delay aid, a viscosity modifier, an antiseptic, an antifungal agent, an antiseptic, an antifoaming agent, a light as necessary. Other additives known in the art such as stabilizers (for example, hindered amine light stabilizers), antioxidants, ultraviolet absorbers, pH adjusters and the like may be included.

The anion electrodeposition coating composition in the present invention may contain a pigment as necessary. The pigment is not particularly limited. For example, extender pigments such as barium sulfate, talc, calcium carbonate, and barium sulfate; phosphorus molybdate-based rust preventives such as aluminum zinc phosphomolybdate, zinc phosphomolybdate and calcium phosphomolybdate Examples thereof include pigments, rust preventive pigments such as molybdate salt rust preventive pigments and phosphate rust preventive pigments; and color pigments commonly used in the paint field.

When the anionic pigment dispersion paste contains a pigment in the anionic electrodeposition coating composition, it is preferable to prepare the pigment in the form of a pigment dispersion paste from the viewpoint of easy dispersion of the pigment. An anionic pigment dispersion paste can be prepared by dispersing a pigment in an anionic pigment dispersion resin.
As the anionic pigment dispersion resin, for example, a modified acrylic resin prepared using an acrylic ester, acrylic acid, an azonitrile compound, or the like can be used.
The anionic pigment dispersion paste is prepared by mixing an anionic pigment dispersion resin, a pigment, an aqueous medium, and, if necessary, a neutralizing base, until the particle diameter of the pigment in the mixture reaches a predetermined uniform particle diameter. It can be prepared by dispersing using a commonly used dispersing apparatus such as a ball mill or a sand grind mill.
Examples of the neutralizing base include ammonia; organic amines such as diethylamine, ethylethanolamine, diethanolamine, monoethanolamine, monopropanolamine, isopropanolamine, ethylaminoethylamine, hydroxyethylamine, diethylenetriamine, triethylamine; sodium hydroxide, hydroxide And basic compounds such as alkali metal hydroxides such as potassium. In general, the anionic pigment dispersion paste is prepared to a solid content of 35 to 70% by mass, preferably 40 to 65% by mass.

A commercially available anionic colored paste may be used as the anionic pigment dispersion paste. Examples of commercially available products include WAJ-AAT-907 black, WAJ-AAT-825 violet, WAJ-AAT-731 blue (above, manufactured by Toyochem), Emacol NS Ocher 4622 (manufactured by Sanyo Dye).

Preparation of anion electrodeposition coating composition The anion electrodeposition coating composition in the present invention is the above-mentioned acrylic resin (A), curing agent (B), water-dispersed gloss modifier (C), curing catalyst (D), and further necessary. Can be prepared by dispersing an anionic pigment-dispersed paste in an aqueous medium. The aqueous medium is water or a mixture of water and the above organic solvent. As water, ion-exchanged water is preferably used. Here, you may use the said neutralization base as needed.

The amount of the neutralizing base used is an amount sufficient to neutralize at least 30%, preferably 50 to 120% of the anionic group (carboxyl group) of the coating film-forming resin such as acrylic resin (A). preferable. Moreover, you may adjust the pH of an anionic electrodeposition coating-material composition using a neutralizing base. The pH of the anionic electrodeposition coating composition is preferably 7.0 to 9.0, and more preferably 7.0 to 8.5.

Formation of cured electrodeposition coating film The method of the present invention comprises the following steps:
An electrodeposition coating process in which an object to be coated is immersed in an anionic electrodeposition coating composition, and an electrodeposition coating film is formed by applying a voltage; and
A heat curing step for forming a cured electrodeposition coating film by heating and curing the electrodeposition coating film formed in the electrodeposition coating step;
Is included.
In this method, the anion electrodeposition coating composition is used, and the coating viscosity at 50 ° C. of the electrodeposition coating film formed in the electrodeposition coating step is in the range of 10,000 to 100,000 Pa · s. Therefore, the glossiness of low-gloss or matte coatings with low specular glossiness is adjusted, which is not accompanied by defects such as gloss differences due to differences in heating temperature or poor matting effect. A cured electrodeposition coating film can be obtained.

Electrodeposition coating of the anion electrodeposition coating composition is performed by immersing the object to be coated in the anion electrodeposition coating composition and then applying a voltage of usually 1 to 400 V to the cathode. . The coating temperature of the anion electrodeposition coating composition during electrodeposition coating is preferably 10 to 45 ° C, more preferably 15 to 30 ° C. The time for applying the voltage can be arbitrarily selected according to the electrodeposition coating conditions, and can be, for example, 30 seconds to 5 minutes. By applying a voltage, an electrodeposition coating film is formed on the surface of the object to be coated. The formed electrodeposition coating film may be washed with water as necessary.

In the method of the present invention, the coating film viscosity at 50 ° C. of the electrodeposition coating film formed in the electrodeposition coating step is within the range of 10,000 to 100,000 Pa · s. When the coating film viscosity at 50 ° C. of the electrodeposition coating film is within the above range, the water-dispersed gloss modifier (C) contained in the anionic electrodeposition coating composition in the present invention has a good gloss control function. Thus, the gloss of the obtained cured electrodeposition coating film can be designed in a low range (60 ° specular gloss is 70 or less).

In the present invention, the reason for measuring the viscosity of the electrodeposition coating film at 50 ° C. is as follows. An electrodeposition coating film is a coating film deposited on the surface of an object to be coated by application of a voltage. The electrodeposition coating is generally designed to have a higher viscosity (high Tg). Therefore, when the viscosity of the electrodeposition coating film is measured at a general electrodeposition bath temperature (for example, 30 ° C.), the measurement may be impossible due to the very high viscosity. For this reason, it is difficult to measure the viscosity of the electrodeposition coating film at 30 ° C. On the other hand, the deposited electrodeposition coating film undergoes a heat flow by heating, and the viscosity is once reduced. By further heating, the coating film forming resins such as the acrylic resin (A) and the curing agent (B) contained in the electrodeposition coating film undergo a crosslinking reaction, and the coating film viscosity rapidly increases. As a result, the electrodeposition coating film is cured to form a cured electrodeposition coating film. That is, the viscosity of the electrodeposition coating film is temporarily reduced by heating, and then the viscosity increases.

Furthermore, at the time of electrodeposition coating, Joule heat is generated, and the vicinity of the object to be coated is raised to about 40-50 ° C. That is, it can be said that the viscosity measurement at 50 ° C. is a state in which the physical properties at the time of electrodeposition coating deposition are reproduced. From the above, the temperature of 50 ° C. is a temperature preferable for the measurement of the viscosity of the coating film from the above properties of the electrodeposition coating composition, and is a temperature at which no crosslinking of the coating film forming resin occurs, that is, an uncured electrodeposition coating film. It is considered that the temperature is appropriate for judging the properties at the time of precipitation.

When the coating film viscosity at 50 ° C. of the electrodeposition coating film is less than 10,000 Pa · s, the heat flow property of the deposited electrodeposition coating film is improved, and thus the resulting cured electrodeposition coating film has high glossiness. Become. On the other hand, when the coating film viscosity at 50 ° C. of the electrodeposition coating film exceeds 100,000 Pa · s, the appearance of the cured coating film becomes poor due to a decrease in flowability of the obtained electrodeposition coating film.

In the present invention, the electrodeposition coating film formed in the electrodeposition coating step preferably has a coating film viscosity at 80 ° C. in the range of 1,000 to 10,000 Pa · s. When the coating film viscosity at 80 ° C. of the electrodeposition coating film is within the above range, the finished appearance of the cured electrodeposition coating film is made uniform while designing the glossiness of the resulting cured electrodeposition coating film to be in a low range. be able to. This temperature of 80 ° C. can be said to be a temperature just before the start of the curing reaction of the acrylic resin (A) and the curing agent (B) contained in the electrodeposition coating film. Under such temperature conditions, the coating viscosity at 80 ° C. of the electrodeposition coating film is in the above range, so that the flowability of the electrodeposition coating film by heating does not increase excessively, and the cured electrodeposition has low gloss. A coating film can be formed, and a poor appearance of the cured electrodeposition coating film can be avoided.

The coating film viscosity at 50 ° C. and the coating film viscosity at 80 ° C. of the electrodeposition coating film can be measured as follows. First, electrodeposition coating is carried out for 180 seconds so that the film thickness becomes about 20 μm to form an electrodeposition coating film, which is washed with water to remove the extra electrodeposition coating composition. Next, after removing excess moisture adhering to the surface of the electrodeposition coating film, the coating film is taken out immediately without drying to prepare a sample. By measuring the viscosity of the sample thus obtained using a dynamic viscoelasticity measuring apparatus, the coating film viscosity at 50 ° C. and 80 ° C. can be measured.

By heating the electrodeposition coating film formed at the said coating process, an electrodeposition coating film will harden | cure and a cured electrodeposition coating film will be obtained (heat-hardening process). In the method of the present invention, the heating temperature (T _h ) in this heat curing step is preferably 110 to 160 ° C.
The difference (ΔT) between the softening point (T _m ) and the heating temperature (T _h ) is more preferably 10 ° C. or more and 50 ° C. or less. Regarding the softening point (T _m ) and heating temperature (T _h ),
T _h > T _m and
The difference ΔT between the softening point (T _m ) and the heating temperature (T _h ) is 10 ° C. or more and 50 ° C. or less,
It is more preferable that
The ΔT is more preferably 10 ° C. or higher and 30 ° C. or lower.

When the heating temperature (T _h ) in the heat curing step is within the above range, the difference from the softening point (T _m ) of the wax constituting the water-dispersed gloss adjusting agent (C) is in an appropriate range, and is obtained. There is an advantage that the gloss of the cured electrodeposition coating film can be designed well in a low range (60 ° specular gloss is 70 or less), and further the occurrence of uneven gloss can be suppressed.

The heating time of the electrodeposition coating can be appropriately selected depending on the size of the object to be coated and the heating temperature (T _h ). The heating time is, for example, 5 to 60 minutes, preferably 10 to 30 minutes.

The film thickness of the cured electrodeposition coating film formed in the method of the present invention is preferably 5 to 30 μm, more preferably 10 to 25 μm.

The cured electrodeposition coating film formed by the method of the present invention preferably has a 60 ° specular gloss of 70 or less. The 60 ° specular gloss is an index generally referred to as 60 ° gloss (Gs (60 °)), and the specular reflected light flux (ψs) is measured by irradiating the coating surface with light from a light source with an incident angle of 60 °. Then, a numerical value [Gs (60 °) = ψs / ψos × 100 (%)] expressed as a ratio with respect to a specular reflection light beam (ψos) of a glass surface having a refractive index n = 1.567 under the same conditions. It is a value measured by a method based on JIS Z 8741. The 60 ° specular gloss can be measured by using a gloss meter such as Uni-Gross 60 (manufactured by Konica Minolta).

By the method of the present invention, a cured electrodeposition coating film adjusted to have a low glossiness can be formed without causing uneven glossiness. Such a technical effect is not limited by theory, but it controls the softening point (T _m ) of the wax constituting the water-dispersed gloss modifier (C) contained in the anionic electrodeposition coating composition. In addition, by controlling the viscosity of the electrodeposition coating film at 50 ° C. within a specific range, it is possible to control the change in the coating state that occurs during the heat curing of the electrodeposition coating film. This is thought to be because it was possible to suppress the occurrence of uneven gloss in the formation of a cured electrodeposition coating film having a high degree.

In the method of the present invention, a cured electrodeposition coating film is further formed under a low temperature condition as compared with the heat curing step in normal electrodeposition coating, such as a heating temperature in the heat curing step of 100 to 160 ° C., for example. However, there exists an advantage which can form the coating film which has sufficient coating-film hardness. Thereby, there exists an advantage that an environmental load can be reduced in a painting process.

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on mass unless otherwise specified.

Production Example 1 Production of acrylic resin (A) 700 parts of isopropyl alcohol was charged into a 2 L reaction vessel equipped with a stirrer, a cooling pipe, a nitrogen introduction pipe, and a thermometer connected to a temperature controller, and the temperature was 80 ° C. under a nitrogen atmosphere. Heated. In this reaction vessel, 322 parts of methyl methacrylate (MMA), 140 parts of butyl acrylate (nBA), 105 parts of styrene (St), 84 parts of hydroxyethyl methacrylate (HEMA), 49 parts of acrylic acid (AA), azoisopropyl A mixed solution of 7 parts of tyronitrile was dropped at a constant rate over 3 hours, and then kept at 80 ° C. for 2 hours, whereby acrylic acid having an acid value of 55 mgKOH / g, a hydroxyl value of 52 mgKOH / g, and a weight average molecular weight of 30,000 was obtained. Resin (A) was obtained.

Example 1 Production of Anion Electrodeposition Coating Composition 328 parts of acrylic resin (A) prepared in Production Example 1 (solid content concentration 50%), Cymel 235 (Ornex Japan Co., Ltd.) which is a melamine resin as a curing agent (B) Manufactured, solid content concentration 100%) 86 parts and triethylamine 11 parts while mixing and stirring, 3.75 parts of dinonylnaphthalenesulfonic acid (curing catalyst (D)) in the amount shown in the following table and the following table 71.4 parts of water dispersion type gloss adjusting agent (C) of the kind and amount were added and mixed. The obtained mixture was diluted to 10% solid content using ion exchange water to obtain an anionic electrodeposition coating composition.
The amount of the water-dispersed gloss adjusting agent (C) shown in the following table is a solid content part by mass with respect to 100 parts by mass of the total resin solid content of the acrylic resin (A) and the curing agent (B) as the coating film forming resin. .

Formation of cured electrodeposition coating film A SUS430 plate as an object to be coated is immersed in the anion electrodeposition coating composition obtained as described above, and a DC voltage of a coating voltage of 80 to 200 V is applied for 2.5 minutes to form a cured film. Electrodeposition was applied so that the thickness was 20 μm, and an electrodeposition coating film was provided. Three painted plates were prepared.
A coating plate having an electrodeposition coating film is heated at a temperature 10 ° C, 30 ° C and 50 ° C higher than the softening point (Tm) of the water-dispersed gloss adjusting agent (C) used in the preparation of the anion electrodeposition coating composition (respectively, 145 ° C., 165 ° C., and 185 ° C.) for 30 minutes each to obtain a coated plate having a cured electrodeposition coating film.

Example 2 and Comparative Examples 1-5
In the preparation of the anion electrodeposition coating composition, in the same manner as in Example 1 except that the type and amount of the water-dispersed gloss modifier (C) and the amount of the curing catalyst (D) were changed as shown in the table below, An anionic electrodeposition coating composition was prepared.
Using the obtained anionic electrodeposition coating composition, electrodeposition coating was performed in the same manner as in Example 1 to obtain a coated plate having a cured electrodeposition coating film.

Comparative Example 6
An anionic electrodeposition coating composition was prepared in the same manner as in Example 2, except that the water-dispersed gloss modifier (C) was not used in the preparation of the anionic electrodeposition coating composition.
Using the resulting anionic electrodeposition coating composition, electrodeposition coating was carried out in the same manner as in Example 1, and baked at 120 ° C., 140 ° C. and 160 ° C. for 30 minutes, respectively, and a coated plate having a cured electrodeposition coating film Got.

Evaluation was performed according to the following criteria using the coated plates obtained in the above examples and comparative examples. The evaluation results are shown in the following table.

Measurement of electrodeposition coating film viscosity at 50 ° C. and 80 ° C. of the electrodeposition coating film Using the anion electrodeposition coating composition obtained by the above Examples and Comparative Examples, the film thickness is about 20 μm on the object to be coated. Electrodeposition coating was performed for 180 seconds to form an electrodeposition coating film, which was washed with water to remove excess electrodeposition coating composition. Next, after removing moisture, the coating film was taken out immediately without drying to prepare a sample. The sample thus obtained was subjected to frequency-dependent measurement in dynamic viscoelasticity using a Rheosol G-3000 (manufactured by UBM), which is a rotary dynamic viscoelasticity measuring device, with a strain of 0.5 deg and a frequency of 0.02 Hz. The setting conditions were used. The prepared sample was set and the measurement temperature was kept at 50 ° C. After the measurement was started, the viscosity of the coating film was measured when the electrodeposition coating film was spread uniformly in the cone plate. The coating film viscosity at 80 ° C. was measured in the same manner as described above except that the measurement temperature was changed.

Evaluation of gloss change due to heating temperature change Measurement of 60 ° specular gloss and gloss evaluation The 60 ° specular gloss of the coated plate obtained above was measured using Uni-Gross 60 (manufactured by Konica Minolta). .
When the 60 ° specular gloss is 70 or less, the low gloss range is evaluated as “◯”, and when it exceeds 70, the low gloss range is not adjusted and “×” ".

Difference in glossiness caused by changes in heating temperature The 60 ° specular glossiness of each of the coated plates heat-cured at the above various heating temperatures is compared, and the minimum value is subtracted from the maximum value of the 60 ° specular glossiness. The difference was calculated and evaluated according to the following criteria.
○: The difference in glossiness is 20 or less. X: The difference in glossiness exceeds 20. It can be determined that the larger this difference is, the more easily the glossiness change depending on the change in heating temperature. When the difference in glossiness exceeds 20, the difference in glossiness can be clearly recognized even in visual evaluation.
When the glossiness change depending on the heating temperature is likely to occur, for example, when heat-curing an electrodeposition coating film provided on a large-scale coating material or a coating material of different thickness, each part of the coating material When the heating temperature varies in the case, there is a problem that uneven gloss occurs.

Coating Film Appearance Evaluation The cured electrodeposition coating film obtained by heating at a temperature of the softening point of the water-dispersed gloss modifier (C) + 30 ° C. was visually evaluated based on the following criteria.
○: A coating film appearance defect such as a stirring mark is not recognized ×: A coating film appearance defect such as a stirring mark is recognized

* Stirring trace: poor coating appearance, recognized as a streak-like trace on the cured electrodeposition coating, which is thought to be derived from stirring of the electrodeposition coating composition during the formation of the electrodeposition coating.

Evaluation of Horizontal Appearance Unevenness Using the electrodeposition coating compositions described in each Example and Comparative Example, electrodeposition coating was performed by placing a substrate in a horizontal state in an unstirred electrodeposition coating composition. The obtained electrodeposition coating film was cured by heating for 30 minutes at a temperature of the softening point of the water-dispersed gloss modifier (C) + 30 ° C. The coating film appearance after baking of the obtained coated plate was visually observed, and the difference in appearance between the upper surface and the lower surface was visually evaluated according to the following criteria.

○: No difference is recognized by visual observation, and it is judged that the appearance is good.
X: Since it is recognized that the matte degree of the upper and lower surfaces is different by visual observation, it is determined that the appearance is poor.

Measurement of Pencil Hardness Using a cured electrodeposition coating film obtained by heating at a temperature of the softening point of the water-dispersed gloss modifier (C) + 30 ° C., in accordance with JIS K 5600-5-4 The pencil hardness was measured. Specifically, a pencil (Mitsubishi Pencil Co., Ltd .: for scratch hardness test of Japan Paint Inspection Association) is pressed against the surface of the cured electrodeposition coating so that the scratch angle is 45 °. Was observed visually.
For example, in the case of a test using a pencil of H, when there was no generation of a scar, it was judged as H or more. It was judged as H when the occurrence of a slight dent was visually recognized in one test out of five tests. Then, in the case where there was a dent twice or more during the five tests, it was judged that it was less than H, and the evaluation was performed in the same manner by lowering by one step.
When the pencil hardness is less than F, it can be determined that the hardness and scratch resistance are poor.

The water-dispersed gloss modifier (C) used in the above examples and comparative examples is as follows.

(C1) Example 1, Comparative Examples 3 and 4: AQUAMAT 208 manufactured by Big Chemie Japan (solid content concentration (NV) = 35%, softening point (T _m ) = 135 ° C., density = 1.00)
(C2) Example 2: Arrow Base SD-1010 manufactured by Unitika (NV = 20%, T _m = 105 ° C., density = 0.93)
(C3) Comparative Example 1: Arrow Base SB-1010 manufactured by Unitika (NV = 25%, T _m = 80 ° C., density = 0.93)
(C4) Comparative Example 2: Chemipearl WP-100 manufactured by Mitsui Chemicals (NV = 40%, T _m = 148 ° C., density = 0.90)
(C5) Comparative Example 5: AQUACER 531 (nonionic emulsion wax, NV = 45%, T _m = 130 ° C., density = 0.98) manufactured by Big Chemie Japan

As shown in the above evaluation results, in the cured electrodeposition coating film formation using the anion electrodeposition coating composition obtained in the examples, the change in glossiness caused by the change in heating temperature is small, and the coating film appearance is poor. It was confirmed that it was not accompanied.
Comparative Example 1 is an experimental example in which the softening point (T _m ) of the wax constituting the water-dispersed gloss adjusting agent (C) is less than 100 ° C. In this case, the glossiness of the obtained cured electrodeposition coating film was increased overall, and the difference in glossiness caused by changes in heating temperature was increased. Furthermore, there was a problem that the hardness of the cured electrodeposition coating film was lowered.
Comparative Example 2 is an experimental example in which the density of the wax constituting the water-dispersed gloss adjusting agent (C) is less than 0.91. In this case, the difference in glossiness caused by the change in heating temperature became large. Moreover, generation | occurrence | production of the horizontal external appearance nonuniformity was confirmed. This is because the water-dispersed gloss adjusting agent (C) does not disperse well in the anion electrodeposition coating composition due to the low density of the wax constituting the water-dispersing gloss adjusting agent (C), and electrodeposition It is considered that the water-dispersed gloss adjusting agent (C) was not uniformly present on the upper and lower surfaces of the base material in the electrodeposition coating film and the cured electrodeposition coating film in the coating process and the heat curing process.
Comparative Example 3 is an experimental example in which the amount of the water-dispersed gloss adjusting agent (C) is small. In this case, the glossiness of the obtained cured electrodeposition coating film was increased overall, and the difference in glossiness caused by changes in heating temperature was increased. Furthermore, coating film appearance unevenness was confirmed.
Comparative Example 4 is an experimental example in which the amount of the water-dispersed gloss adjusting agent (C) is large. In this case, the glossiness value was low, but the glossiness difference caused by the heating temperature change was large. Furthermore, there was a problem that the hardness of the cured electrodeposition coating film was lowered.
Comparative Example 5 is an experimental example in which the electrodeposition coating film has a coating film viscosity at 50 ° C. of less than 10,000. In this case, the difference in glossiness caused by the change in heating temperature became large.
Comparative Example 6 is an experimental example that does not include the water-dispersed gloss adjusting agent (C). In this case, the gloss of the cured electrodeposition coating film was very high.

According to the method of the present invention, a cured electrodeposition coating film with adjusted glossiness, such as a low-gloss coating film or matte coating film with low specular glossiness, is accompanied by uneven glossiness such as a glossiness change due to a change in heating temperature. There is an advantage that it can be formed without any problems. The method of the present invention further has an advantage that a cured electrodeposition coating film having good hardness can be obtained even when the electrodeposition coating film is formed and then heat-cured under low-temperature curing conditions.

Claims

A method of forming a cured electrodeposition coating film, the method comprising:
An electrodeposition coating process in which an object to be coated is immersed in an anionic electrodeposition coating composition, and an electrodeposition coating film is formed by applying a voltage; and
A heat curing step for forming a cured electrodeposition coating film by heating and curing the electrodeposition coating film formed in the electrodeposition coating step;
Including
The anion electrodeposition coating composition includes an acrylic resin (A), a curing agent (B), a water-dispersed gloss adjusting agent (C), and a curing catalyst (D).
The water-dispersed gloss modifier (C) is an aqueous dispersion of one or more waxes selected from the group consisting of natural waxes and polyolefin waxes,
The wax constituting the water-dispersible gloss modifier (C) has a softening point (T m ) of 100 ° C. or higher and a density in the range of 0.91 to 1.10.
The solid content mass of the water-dispersed gloss adjusting agent (C) contained in the anion electrodeposition coating composition is 6 to 20 parts by mass with respect to 100 parts by mass of the resin solid content of the anion electrodeposition coating composition.
The electrodeposition coating film formed in the electrodeposition coating step has a coating film viscosity at 50 ° C. in the range of 10,000 to 100,000 Pa · s.
Method.
The method according to claim 1, wherein the heating temperature (T h ) in the heat curing step is 110 to 160 ° C.
The method according to claim 1 or 2, wherein the softening point (T m ) is in the range of 100 to 140 ° C.
The method according to any one of claims 1 to 3, wherein the electrodeposition coating film formed in the electrodeposition coating step has a coating film viscosity at 80 ° C in the range of 1,000 to 10,000 Pa · s.
The acrylic resin (A) is an acrylic resin having a carboxyl group and a hydroxyl group,
The curing agent (B) is one or more selected from the group consisting of amino resins and blocked isocyanate compounds.
The method according to any one of claims 1 to 4.
The difference (ΔT) between the softening point (T m ) and the heating temperature (T h ) is 10 ° C. or more and 50 ° C. or less, and T h > T m is set. the method of.
The method according to any one of claims 1 to 6, wherein the cured electrodeposition coating film formed by the forming method has a 60 ° specular gloss of 70 or less.