JP7650771B2 - Multi-layer coating method - Google Patents

Description

The present invention relates to a method for forming a multi-layer coating film.

The application of inkjet painting to automobile exterior panels is already known. For example, Patent Document 1 discloses a painting method in which a base coating, a drawing coating, and a clear coating are formed in that order on the surface of the object to be painted.

When paints for forming each coating are applied using one coating machine, the paints may mix together inside the machine and cause cratering. In inkjet coating machines, taking into consideration problems such as dents and cratering caused by paint contamination, one type of paint is applied per machine, and when forming multi-layer coatings, multiple machines are used to apply the paint, corresponding to the number of coatings. For example, when applying a clear coating over a base coating, which is a colored coating, the colored paint is applied using inkjet equipment, and the clear paint is applied using another inkjet equipment or by hand spray. In order to avoid such cumbersome processes, sometimes only the colored paint is applied and the application of the clear paint is omitted.

Patent Publication No. 9-314039

It is desirable to suppress the occurrence of cissing in a multi-layer coating film formed by curing a colored coating formed by inkjet coating and a clear coating formed on top of the colored coating by inkjet coating. In addition, since weather resistance may be insufficient when only a colored coating is applied, it is preferable that the resulting coating film also has excellent weather resistance.

The object of the present invention is to provide a method for forming a multi-layer coating film that can form a multi-layer coating film with excellent cissing resistance and weather resistance.

As a result of intensive research into solving the above problems, the inventors discovered that by making the resin composition of the colored paint similar to that of the clear paint, it is possible to form a multi-layer coating film with good cissing resistance, and thus completed the present invention.

The present invention includes the following:

Item 1. Step (1): A step of ink-jet coating a one-liquid type water-based colored coating composition (Y) containing a hydroxyl-containing acrylic resin emulsion (y1), a hydroxyl-containing polyester resin (y2), a polyurethane resin (y3), a curing agent (y4) and a color pigment (y5) on a substrate to form an uncured colored coating film;
Step (2): A step of ink-jet coating a one-liquid type water-based clear coating composition (Z) containing a hydroxyl-containing acrylic resin emulsion (z1), a hydroxyl-containing polyester resin (z2), a polyurethane resin (z3), and a curing agent (z4) on the uncured colored coating film to form an uncured clear coating film; and Step (3): A step of simultaneously curing the uncured colored coating film and the uncured clear coating film by heating them to 60 to 140°C.
A method for forming a multilayer coating film comprising the steps of:
the hydroxyl-containing acrylic resin emulsion (y1) and the hydroxyl-containing acrylic resin emulsion (z1) are the same hydroxyl-containing acrylic resin emulsion,
the hydroxyl-containing polyester resin (y2) and the hydroxyl-containing polyester resin (z2) are the same hydroxyl-containing polyester resin,
The polyurethane resin (y3) and the polyurethane resin (z3) are the same polyurethane resin, and
The curing agent (y4) and the curing agent (z4) are the same curing agent;
A method for forming multi-layer coating films.

The multilayer coating film obtained using the multilayer coating film forming method of the present invention has good cissing resistance and has superior weather resistance compared to a coating film formed only with a colored coating film. In addition, the colored paint and the clear paint can be applied using the same coating machine. In such a case, the colored paint can be applied using inkjet equipment and then the clear paint can be applied using the same coating machine, simplifying the coating process compared to using two coating machines.

The method for forming a multilayer coating film of the present invention comprises the steps of:
Step (1): A step of ink-jet coating a one-liquid type water-based colored coating composition (Y) containing a hydroxyl-containing acrylic resin emulsion (y1), a hydroxyl-containing polyester resin (y2), a polyurethane resin (y3), a curing agent (y4) and a color pigment (y5) on a substrate to form an uncured colored coating film;
Step (2): A step of ink-jet coating a one-liquid type water-based clear coating composition (Z) containing a hydroxyl-containing acrylic resin emulsion (z1), a hydroxyl-containing polyester resin (z2), a polyurethane resin (z3), and a curing agent (z4) on the uncured colored coating film to form an uncured clear coating film; and Step (3): A step of simultaneously curing the uncured colored coating film and the uncured clear coating film by heating them to 60 to 140°C.
A method for forming a multilayer coating film comprising the steps of:
the hydroxyl-containing acrylic resin emulsion (y1) and the hydroxyl-containing acrylic resin emulsion (z1) are the same hydroxyl-containing acrylic resin emulsion,
the hydroxyl-containing polyester resin (y2) and the hydroxyl-containing polyester resin (z2) are the same hydroxyl-containing polyester resin,
The polyurethane resin (y3) and the polyurethane resin (z3) are the same polyurethane resin, and
The curing agent (y4) and the curing agent (z4) are the same curing agent.

Step (1)
According to the method for forming a multilayer coating film of the present invention, first, a one-liquid type aqueous colored coating composition (Y) containing a hydroxyl-containing acrylic resin emulsion (y1), a hydroxyl-containing polyester resin (y2), a polyurethane resin (y3), a curing agent (y4) and a color pigment (y5) is inkjet-coated on a substrate to form an uncured colored coating film.

The substrate to which the one-liquid type aqueous colored coating composition (Y) is applied is not particularly limited. Examples of the substrate include the outer plate parts of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts such as bumpers; and the outer plate parts of household electrical appliances such as mobile phones and audio equipment. Among these, the outer plate parts of automobile bodies and automobile parts are preferred.

The material of these substrates is not particularly limited. For example, metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, mixtures of these resins, plastic materials such as various fiber reinforced plastics (FRP); inorganic materials such as glass, cement, concrete; wood; fibrous materials such as paper, cloth, etc. Among these, metal materials and plastic materials are preferred. The substrate may also be a combination of the above metal materials and plastic materials.

The above-mentioned substrate may be a metal surface of the above-mentioned metal material or a car body formed from it, which has been subjected to a surface treatment such as phosphate treatment, chromate treatment, composite oxide treatment, etc., and may further have a coating film formed thereon.

Examples of substrates on which a coating film is formed include those in which a substrate is surface-treated as necessary and an undercoat coating film is formed thereon. The undercoat coating film is usually formed for the purpose of imparting corrosion resistance, adhesion to the substrate, and ability to conceal unevenness on the substrate surface (sometimes referred to as "undercoat concealment"). The undercoat paint used to form the undercoat coating film may be a known one. For example, for conductive substrates such as metals, it is preferable to use cationic electrodeposition paint or anionic electrodeposition paint from the viewpoint of corrosion resistance of the multilayer coating film to be formed, and it is preferable to use cationic electrodeposition paint from the viewpoint of chipping resistance and adhesion.

After application, the undercoat paint may be cured by heating, air blowing, or other means, or may be dried to a degree that does not cause curing. When using a cationic electrodeposition paint or anionic electrodeposition paint as the undercoat paint, it is preferable to cure the undercoat paint by heating after application of the undercoat paint in order to prevent inter-layer mixing between the undercoat paint film and the paint film subsequently formed on the undercoat paint film and to form a multi-layer paint film with excellent appearance.

One-component water-based colored paint composition (Y)
The one-liquid type aqueous colored coating composition (Y) contains a hydroxyl-containing acrylic resin emulsion (y1), a hydroxyl-containing polyester resin (y2), a polyurethane resin (y3), a curing agent (y4) and a color pigment (y5).

The one-liquid type aqueous colored coating composition (Y) is an aqueous coating. In this specification, the term "aqueous coating" is used in contrast to organic solvent-based coatings, and generally refers to a coating in which a film-forming resin or the like is dispersed and/or dissolved in water or a medium whose main component is water (aqueous medium).

The content of water in the one-component aqueous colored coating composition (Y) is preferably within the range of 10 to 500 parts by mass, more preferably within the range of 50 to 450 parts by mass, and even more preferably within the range of 100 to 400 parts by mass, based on 100 parts by mass of the resin solid content of the one-component aqueous colored coating composition (Y). The content of the organic solvent as a solvent in the one-component aqueous colored coating composition (Y) is preferably within the range of 0 to 100 parts by mass, more preferably within the range of 0 to 90 parts by mass, and even more preferably within the range of 0 to 80 parts by mass, based on 100 parts by mass of the resin solid content of the one-component aqueous colored coating composition (Y).

Hydroxyl-containing acrylic resin emulsion (y1)
The hydroxyl-containing acrylic resin emulsion (y1) is prepared by emulsifying and dispersing a hydroxyl acrylic resin in an aqueous medium.

As the hydroxyl group-containing acrylic resin, a water-soluble or water-dispersible acrylic resin that has been conventionally used in water-based paints can be used.

The hydroxyl-containing acrylic resin can be produced, for example, by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer (a) and another polymerizable unsaturated monomer (b) that is copolymerizable with the hydroxyl-containing polymerizable unsaturated monomer by a method known per se, such as a solution polymerization method in an organic solvent or an emulsion polymerization method in water.

The hydroxyl-containing polymerizable unsaturated monomer (a) is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in one molecule. Examples of the hydroxyl-containing polymerizable unsaturated monomer (a) include monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having polyoxyethylene chains whose molecular terminals are hydroxyl groups. However, in the present invention, monomers corresponding to "(xvii) polymerizable unsaturated monomer having an ultraviolet absorbing functional group" described later should be defined as "other polymerizable unsaturated monomer (b) copolymerizable with the above hydroxyl group-containing polymerizable unsaturated monomer" and are excluded from "hydroxyl group-containing polymerizable unsaturated monomer (a)". These can be used alone or in combination of two or more kinds.

As the other polymerizable unsaturated monomer (b) copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer, for example, the following monomers (i) to (xx) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more kinds.
(i) Alkyl or cycloalkyl (meth)acrylates: for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and the like.
(ii) Polymerizable unsaturated monomers having an isobornyl group: isobornyl (meth)acrylate, etc.
(iii) Polymerizable unsaturated monomers having an adamantyl group: adamantyl (meth)acrylate, etc.
(iv) Polymerizable unsaturated monomers having a tricyclodecenyl group: tricyclodecenyl (meth)acrylate, etc.
(v) Aromatic ring-containing polymerizable unsaturated monomers: benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, and the like.
(vi) Polymerizable unsaturated monomers having an alkoxysilyl group: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, and the like.
(vii) Polymerizable unsaturated monomers having a fluorinated alkyl group: perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; fluoroolefins, and the like.
(viii) Polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group.
(ix) Vinyl compounds: N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, etc.
(x) Carboxyl group-containing polymerizable unsaturated monomers: (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl (meth)acrylate, etc.
(xi) Nitrogen-containing polymerizable unsaturated monomers: (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, methylene bis(meth)acrylamide, ethylene bis(meth)acrylamide, adducts of glycidyl (meth)acrylate and amine compounds, and the like.
(xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, etc.
(xiii) Epoxy group-containing polymerizable unsaturated monomers: glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, and the like.
(xiv) (meth)acrylates having a polyoxyethylene chain with an alkoxy group at the molecular terminal.
(xv) Polymerizable unsaturated monomers having a sulfonic acid group: 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allylsulfonic acid, 4-styrenesulfonic acid, and the like; sodium salts and ammonium salts of these sulfonic acids.
(xvi) Polymerizable unsaturated monomers having a phosphoric acid group: acid phosphooxyethyl (meth)acrylate, acid phosphooxypropyl (meth)acrylate, acid phosphooxypoly(oxyethylene)glycol (meth)acrylate, acid phosphooxypoly(oxypropylene)glycol (meth)acrylate, and the like.
(xvii) Polymerizable unsaturated monomers having an ultraviolet absorbing functional group: 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, and the like.
(xviii) Light-stable polymerizable unsaturated monomers: 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, and the like.
(xix) Polymerizable unsaturated monomers having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), and the like.
(xx) Polymerizable unsaturated monomers having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride, etc.

In this specification, a polymerizable unsaturated group means an unsaturated group that can undergo radical polymerization. Examples of such polymerizable unsaturated groups include vinyl groups and (meth)acryloyl groups.

In this specification, "(meth)acrylate" means acrylate or methacrylate. "(meth)acrylic acid" means acrylic acid or methacrylic acid. "(meth)acryloyl" means acryloyl or methacryloyl. "(meth)acrylamide" means acrylamide or methacrylamide.

From the viewpoint of weather resistance of the multilayer coating film formed, the hydroxyl-containing acrylic resin emulsion (y1) preferably contains a hydroxyl-containing acrylic resin emulsion (y1') having a core/shell multilayer structure composed of a core of a copolymer (I-1) obtained by copolymerizing a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule, and a shell of a copolymer (II-1) obtained by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer (a), a hydrophobic polymerizable unsaturated monomer (e), and a polymerizable unsaturated monomer (f) other than the hydroxyl-containing polymerizable unsaturated monomer (a) and the hydrophobic polymerizable unsaturated monomer (e).

The core of the copolymer (I-1) is obtained by copolymerizing 0.1 to 30 mass% of the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and 70 to 99.9 mass% of the polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule, based on the total mass of the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and the polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule, and the shell of the copolymer (II .... It is more preferable that the copolymer is obtained by copolymerizing 1 to 35% by mass of the hydroxyl-containing polymerizable unsaturated monomer (a), 5 to 60% by mass of the hydrophobic polymerizable unsaturated monomer (e), and 5 to 94% by mass of the polymerizable unsaturated monomer (f) other than the hydroxyl-containing polymerizable unsaturated monomer (a) and the hydrophobic polymerizable unsaturated monomer (e), based on the total mass of the hydroxyl-containing polymerizable unsaturated monomer (a), the hydrophobic polymerizable unsaturated monomer (e), and the polymerizable unsaturated monomer (f) other than the hydroxyl-containing polymerizable unsaturated monomer (a) and the hydrophobic polymerizable unsaturated monomer (e).

Examples of polymerizable unsaturated monomers (c) having at least two polymerizable unsaturated groups per molecule that constitute the core include allyl (meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,2-hexanediol di(meth)acrylate. acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerol di(meth)acrylate, 1,1,1-trishydroxymethylethane di(meth)acrylate, 1,1,1-trishydroxymethylethane tri(meth)acrylate, 1,1,1-trishydroxymethylpropane tri(meth)acrylate, triallyl isocyanurate, diallyl terephthalate, divinylbenzene, etc., which can be used alone or in combination of two or more.

The polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule can be used in an amount of preferably 0.1 to 30% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass, based on the total mass of monomer (c) and monomer (d).

The polymerizable unsaturated monomer (d) having one polymerizable unsaturated group per molecule that constitutes the core is a polymerizable unsaturated monomer that can be copolymerized with the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups per molecule, and includes compounds that contain one polymerizable unsaturated group per molecule, such as a vinyl group, a (meth)acryloyl group, an allyl group, etc.

Specific examples of polymerizable unsaturated monomers (d) having one polymerizable unsaturated group per molecule include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, la alkyl or cycloalkyl (meth)acrylates such as uryl (meth)acrylate, stearyl (meth)acrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, etc.; polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate; polymerizable unsaturated monomers having an adamantyl group such as adamantyl (meth)acrylate, etc. Saturated monomers: vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene; monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified products of the monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms; allyl alcohol; polyoxyethylene chains having hydroxyl groups at the molecular terminals; Examples of such monomers include hydroxyl group-containing polymerizable unsaturated monomers such as (meth)acrylates having a hydroxyl group; carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; and nitrogen-containing polymerizable unsaturated monomers such as (meth)acrylonitrile, (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, and adducts of glycidyl (meth)acrylate and amines. These can be used alone or in combination of two or more.

The polymerizable unsaturated monomer (d) having one polymerizable unsaturated group per molecule can be used in an amount of preferably 90 to 99.9% by mass, more preferably 90 to 99.5% by mass, and even more preferably 95 to 99% by mass, based on the total mass of monomer (c) and monomer (d).

On the other hand, as described above, examples of the hydroxyl-containing polymerizable unsaturated monomer (a) constituting the shell include monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms; allyl alcohol; and (meth)acrylates having polyoxyethylene chains whose molecular terminals are hydroxyl groups. These can be used alone or in combination of two or more.

The hydroxyl group-containing polymerizable unsaturated monomer (a) can be used in an amount of preferably 1 to 35% by mass, more preferably 5 to 25% by mass, and even more preferably 8 to 20% by mass, based on the total mass of monomer (a), monomer (e) and monomer (f).

In addition, the hydrophobic polymerizable unsaturated monomer (e) constituting the shell includes polymerizable unsaturated monomers containing linear, branched or cyclic saturated or unsaturated hydrocarbon groups having 6 or more carbon atoms, specifically, for example, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, "isostearyl acrylate" (product name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, Examples of the monomers include alkyl or cycloalkyl (meth)acrylates such as tert-butylcyclohexyl (meth)acrylate and cyclododecyl (meth)acrylate; polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate; polymerizable unsaturated monomers having an adamantyl group such as adamantyl (meth)acrylate; vinyl aromatic compounds such as styrene, α-methylstyrene and vinyl toluene, each of which can be used alone or in combination of two or more. Among these, vinyl aromatic compounds are preferred from the viewpoint of the smoothness and image clarity of the formed coating film, and styrene is particularly preferred.

The hydrophobic polymerizable unsaturated monomer (e) can be used in an amount of preferably 5 to 60% by mass, more preferably 8 to 40% by mass, and even more preferably 11 to 25% by mass, based on the total amount of monomer (a), monomer (e) and monomer (f).

In addition, examples of the polymerizable unsaturated monomer (f) other than the hydroxyl group-containing polymerizable unsaturated monomer (a) and the hydrophobic polymerizable unsaturated monomer (e) constituting the shell include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and tert-butyl (meth)acrylate; and carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate, which may be used alone or in combination of two or more.

The polymerizable unsaturated monomer (f) other than the hydroxyl group-containing polymerizable unsaturated monomer (a) and the hydrophobic polymerizable unsaturated monomer (e) preferably contains a carboxyl group-containing polymerizable unsaturated monomer (g) as at least a part of its components, in order to ensure the smoothness of the formed coating film.

Examples of the carboxyl group-containing polymerizable unsaturated monomer (g) include (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate, and among these, (meth)acrylic acid is preferred.

From the viewpoints of the stability of the hydroxyl-containing acrylic resin emulsion (y1') in an aqueous medium and the smoothness and weather resistance of the formed coating film, the carboxyl-containing polymerizable unsaturated monomer (g) is preferably used in an amount of 1 to 40% by mass, more preferably 6 to 25% by mass, and even more preferably 11 to 19% by mass, based on the total mass of the monomers (a), (e) and (f).

From the viewpoint of the weather resistance of the multi-layer coating film to be formed, the hydroxyl group-containing acrylic resin emulsion (y1') preferably has a hydroxyl value within the range of 1 to 200 mgKOH/g, more preferably 5 to 180 mgKOH/g, and even more preferably 7 to 130 mgKOH/g.

The hydroxyl-containing acrylic resin emulsion (y1') preferably has an acid value in the range of 1 to 130 mgKOH/g, more preferably 5 to 100 mgKOH/g, and even more preferably 7 to 70 mgKOH/g, from the viewpoints of storage stability, weather resistance and cissing resistance of the multilayer coating film to be formed. Furthermore, from the viewpoints of weather resistance and cissing resistance of the multilayer coating film to be formed, it is preferable to use polymerizable unsaturated monomers having only one polymerizable unsaturated group per molecule as monomer (a), monomer (e) and monomer (f), and to make the shell of the hydroxyl-containing acrylic resin emulsion (y1') of the non-crosslinked type.

The hydroxyl-containing acrylic resin emulsion (y1') is prepared by, for example, emulsion polymerization of a monomer mixture (I) containing 0.1 to 30% by mass of a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and 70 to 99.9% by mass of a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule, based on the total mass of the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and the polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule. It can be obtained by adding a monomer mixture (II) containing 1 to 35% by mass of hydroxyl-containing polymerizable unsaturated monomer (a), 5 to 60% by mass of hydrophobic polymerizable unsaturated monomer (e), and polymerizable unsaturated monomer (f) other than the hydroxyl-containing polymerizable unsaturated monomer (a) and the hydrophobic polymerizable unsaturated monomer (e), and further polymerizing the monomer mixture (II).

The emulsion polymerization of the monomer mixture can be carried out by a method known per se, for example, by using a polymerization initiator in the presence of an emulsifier.

As the emulsifier, an anionic emulsifier or a nonionic emulsifier is suitable. Examples of the anionic emulsifier include sodium salts and ammonium salts of organic acids such as alkylsulfonic acid, alkylbenzenesulfonic acid, and alkylphosphoric acid. Examples of the nonionic emulsifier include polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, and polyoxyethylene sorbitan monolaurate.

Polyoxyalkylene group-containing anionic emulsifiers having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule, or reactive anionic emulsifiers having the anionic group and a radically polymerizable unsaturated group in one molecule may be used, and among these, reactive anionic emulsifiers are preferably used.

Examples of the reactive anionic emulsifier include sodium salts and ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups such as (meth)allyl groups, (meth)acryloyl groups, propenyl groups, and butenyl groups. Among these, ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups are preferred because they provide excellent water resistance to the coating film that is formed. Examples of the ammonium salts of sulfonic acid compounds include commercially available products such as "Latemul S-180A" (product name, manufactured by Kao Corporation).

Among the above ammonium salts of sulfonic acid compounds having a radically polymerizable unsaturated group, ammonium salts of sulfonic acid compounds having a radically polymerizable unsaturated group and a polyoxyalkylene group are more preferred. Examples of ammonium salts of sulfonic acid compounds having a radically polymerizable unsaturated group and a polyoxyalkylene group include commercially available products such as "Aqualon KH-10" (product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and "SR-1025A" (product name, manufactured by Asahi Denka Kogyo Co., Ltd.).

The emulsifier can be used in an amount of preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass, based on the total amount of all monomers used.

The polymerization initiator may be either oil-soluble or water-soluble, and examples of such initiators include organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxy laurate, tert-butyl peroxy isopropyl carbonate, tert-butyl peroxy acetate, and diisopropylbenzene hydroperoxide; azobisisobutyronite; azo compounds such as azobis(2,4-dimethylvaleronitrile), azobis(2-methylpropiononitrile), azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutanoic acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}; and persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These can be used alone or in combination of two or more.

If necessary, the above polymerization initiator may be used in combination with a reducing agent such as sugar, sodium formaldehyde sulfoxylate, or an iron complex to form a redox polymerization system.

The polymerization initiator is preferably used in an amount of 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, based on the total mass of all monomers used. The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on the type and amount. For example, the polymerization initiator may be included in the monomer mixture or aqueous medium in advance, or may be added all at once or dropwise during polymerization.

The hydroxyl-containing acrylic resin emulsion (y1) can be obtained by adding the monomer mixture (II) to the emulsion obtained as described above and then polymerizing the mixture.

The monomer mixture (II) may contain, as necessary, the polymerization initiator, chain transfer agent, reducing agent, emulsifier, and other components as listed above.

Although the monomer mixture (II) can be dropped as it is, it is preferable to disperse the monomer mixture (II) in an aqueous medium and drop it as a monomer emulsion. In this case, the particle size of the monomer emulsion is not particularly limited.

The polymerization of the monomer mixture (II) can be carried out, for example, by adding the monomer mixture (II), which may be emulsified, all at once or dropwise to the above emulsion and heating to an appropriate temperature while stirring.

The hydroxyl-containing acrylic resin emulsion (y1') obtained as described above can have a core/shell type multilayer structure in which the core is a copolymer (I-1) formed from a monomer mixture (I) containing a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule, and the shell is a copolymer (II-1) formed from a monomer mixture (II) containing a hydroxyl-containing polymerizable unsaturated monomer (a), a hydrophobic polymerizable unsaturated monomer (e), and a polymerizable unsaturated monomer (f) other than the monomers (a) and (e).

The hydroxyl-containing acrylic resin emulsion (y1') may be made into resin particles consisting of three or more layers by adding a step of supplying a polymerizable unsaturated monomer (one type or a mixture of two or more types) that forms another resin layer and carrying out emulsion polymerization between the steps of obtaining copolymer (I-1) and obtaining copolymer (II-1).

In the present invention, the "shell" of the hydroxyl-containing acrylic resin emulsion (y1') means a polymer layer present in the outermost layer of the resin particle, the "core" means a polymer layer in the inner layer of the resin particle excluding the shell portion, and the "core/shell structure" means a structure having the core and shell. The core/shell structure is generally a layer structure in which the core is completely covered by the shell, but depending on the mass ratio of the core and the shell, the amount of monomer in the shell may be insufficient to form a layer structure. In such a case, it is not necessary to have a complete layer structure as described above, and the shell may be a structure in which a part of the core is covered by the shell, or a structure in which a polymerizable unsaturated monomer, which is a component of the shell, is graft-polymerized to a part of the core. The concept of a multilayer structure in the core/shell structure also applies to the case in which a multilayer structure is formed on the core in the hydroxyl-containing acrylic resin emulsion (y1').

The ratio of copolymer (I-1) to copolymer (II-1) in the hydroxyl-containing acrylic resin emulsion (y1') having a core/shell type multilayer structure is, in terms of the solid content mass ratio of copolymer (I-1)/copolymer (II-1), preferably within the range of 10/90 to 90/10, more preferably 50/50 to 85/15, and even more preferably 65/35 to 80/20, from the viewpoint of the water resistance and adhesion of the multilayer coating film to be formed.

The hydroxyl-containing acrylic resin emulsion (y1') obtained as described above preferably has an average particle size within the range of 10 to 1000 nm, and particularly preferably 20 to 500 nm. The average particle size of the hydroxyl-containing acrylic resin is a value measured by the Coulter Counter method at a measurement temperature of 20°C. This measurement can be performed, for example, using a "COULTER N4 type" (product name, manufactured by Beckman Coulter, Inc.).

In order to improve the mechanical stability of the resulting aqueous dispersion particles of the hydroxyl-containing acrylic resin emulsion (y1'), it is desirable to neutralize the acidic groups, such as carboxyl groups, contained in the hydroxyl-containing acrylic resin emulsion (y1') with a neutralizing agent. The neutralizing agent can be any neutralizing agent that can neutralize the acidic groups, and examples of such neutralizing agents include sodium hydroxide, potassium hydroxide, trimethylamine, 2-(dimethylamino)ethanol, 2-amino-2-methyl-1-propanol, triethylamine, and aqueous ammonia. It is desirable to use these neutralizing agents in an amount such that the pH of the aqueous dispersion of the hydroxyl-containing acrylic resin emulsion (y1') after neutralization is about 6.5 to about 9.0.

The proportion of the hydroxyl-containing polymerizable unsaturated monomer used in producing the hydroxyl-containing acrylic resin emulsion (y1) is preferably 1 to 50% by mass, more preferably 1 to 40% by mass, and even more preferably 1 to 30% by mass, based on the total amount of the monomer components.

From the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the hydroxyl value of the hydroxyl-containing acrylic resin emulsion (y1) is preferably 1 to 200 mgKOH/g, more preferably 5 to 180 mgKOH/g, and even more preferably 7 to 130 mgKOH/g.

In addition, from the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the acid value of the hydroxyl-containing acrylic resin emulsion (y1) is preferably 1 to 130 mgKOH/g, more preferably 5 to 100 mgKOH/g, and even more preferably 7 to 70 mgKOH/g.

From the viewpoint of the weather resistance of the multilayer coating film formed, the content of the hydroxyl-containing acrylic resin emulsion (y1) in the one-component water-based colored coating composition (Y) is preferably 2 to 70 mass %, more preferably 5 to 60 mass %, and even more preferably 10 to 55 mass %, based on the resin solid content in the one-component water-based colored coating composition (Y).

In this specification, solid content means non-volatile content, and refers to the residue remaining after removing volatile components such as water and organic solvents from a sample. The solid content can be calculated by multiplying the mass of the sample by the solid content concentration. The solid content concentration can be measured by dividing the mass of the residue obtained by drying 3 grams of a sample at 105°C for 3 hours by the mass before drying.

Hydroxyl-containing polyester resin (y2)
As the hydroxyl group-containing polyester resin (y2), any known water-soluble or water-dispersible polyester resin that has been conventionally used in water-based paints can be used.

The hydroxyl-containing polyester resin (y2) can usually be produced by an esterification reaction or transesterification reaction between an acid component and an alcohol component.

As the acid component, compounds that are commonly used as acid components in the production of polyester resins can be used. Examples of such acid components include aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids.

The above-mentioned aliphatic polybasic acids are generally aliphatic compounds having two or more carboxyl groups in one molecule, acid anhydrides of the aliphatic compounds, and esters of the aliphatic compounds. Examples of the aliphatic polybasic acids include aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, octadecanedioic acid, citric acid, and butanetetracarboxylic acid; anhydrides of the aliphatic polybasic acids; and esters of the aliphatic polybasic acids with lower alkyls having about 1 to 4 carbon atoms. The above-mentioned aliphatic polybasic acids can be used alone or in combination of two or more kinds.

From the viewpoint of the smoothness of the resulting coating film, it is preferable to use adipic acid and/or adipic anhydride as the aliphatic polybasic acid.

The alicyclic polybasic acids are generally compounds having one or more alicyclic structures and two or more carboxyl groups in one molecule, acid anhydrides of the compounds, and esters of the compounds. The alicyclic structures are mainly 4- to 6-membered ring structures. Examples of the alicyclic polybasic acids include alicyclic polycarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; anhydrides of the alicyclic polybasic acids; and esters of the alicyclic polybasic acids with lower alkyls having about 1 to 4 carbon atoms. The alicyclic polybasic acids can be used alone or in combination of two or more.

The aromatic polybasic acids are generally aromatic compounds having two or more carboxyl groups in one molecule, acid anhydrides of the aromatic compounds, and esters of the aromatic compounds, such as aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of the aromatic polycarboxylic acids; and esters of the aromatic polycarboxylic acids with lower alkyls having about 1 to 4 carbon atoms. The aromatic polybasic acids can be used alone or in combination of two or more kinds.

As the aromatic polybasic acid, it is preferable to use phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, and trimellitic anhydride.

In addition, acid components other than the above-mentioned aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids can also be used. Such acid components are not particularly limited, and examples thereof include fatty acids such as coconut oil fatty acid, cottonseed oil fatty acid, hempseed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, and safflower oil fatty acid; monocarboxylic acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid, and 10-phenyloctadecanoic acid; and hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethoxybenzoic acid. These acid components can be used alone or in combination of two or more.

As the alcohol component, a polyhydric alcohol having two or more hydroxyl groups in one molecule can be suitably used. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricyclohexane Examples of such compounds include dihydric alcohols such as rodecanedimethanol, hydroxypivalic acid neopentyl glycol ester, hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; polylactone diols obtained by adding lactone compounds such as ε-caprolactone to these dihydric alcohols; ester diol compounds such as bis(hydroxyethyl)terephthalate; polyether diol compounds such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol; trihydric or higher alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris(2-hydroxyethyl)isocyanuric acid, sorbitol, and mannitol; polylactone polyol compounds obtained by adding lactone compounds such as ε-caprolactone to these trihydric or higher alcohols; and fatty acid esters of glycerin.

Alcohol components other than the above polyhydric alcohols can also be used. Examples of such alcohol components include, but are not limited to, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; and alcohol compounds obtained by reacting monoepoxy compounds such as propylene oxide, butylene oxide, and "Cardura E10P" (trade name, manufactured by HEXION, glycidyl ester of synthetic highly branched saturated fatty acid) with an acid.

The method for producing the hydroxyl-containing polyester resin is not particularly limited, and can be carried out according to a conventional method. For example, the hydroxyl-containing polyester resin can be produced by heating the acid component and the alcohol component in a nitrogen stream at about 150 to 250°C for about 5 to 10 hours to carry out an esterification reaction or an ester exchange reaction between the acid component and the alcohol component.

When the acid component and alcohol component are subjected to an esterification reaction or an ester exchange reaction, they may be added to a reaction vessel at once, or one or both may be added in several portions. Alternatively, a hydroxyl-containing polyester resin may first be synthesized, and then the resulting hydroxyl-containing polyester resin may be reacted with an acid anhydride to half-esterify it to form a carboxyl- and hydroxyl-containing polyester resin. Alternatively, a carboxyl-containing polyester resin may first be synthesized, and then the alcohol component may be added to form a hydroxyl-containing polyester resin.

In the esterification or transesterification reaction, a catalyst known per se, such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, or tetraisopropyl titanate, can be used as a catalyst to promote the reaction.

The hydroxyl-containing polyester resin can be modified with a fatty acid, a monoepoxy compound, a polyisocyanate compound, an acrylic resin, or the like during or after the preparation of the resin.

Examples of the fatty acids include coconut oil fatty acids, cottonseed oil fatty acids, hemp seed oil fatty acids, rice bran oil fatty acids, fish oil fatty acids, tall oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, and safflower oil fatty acids. An example of the monoepoxy compound that can be suitably used is "Cardura E10P" (trade name, manufactured by HEXION, glycidyl ester of synthetic highly branched saturated fatty acid).

Examples of the polyisocyanate compounds include aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate; aliphatic diisocyanate compounds such as hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), and 1,3-(isocyanatomethyl)cyclohexane. Examples of suitable polyisocyanates include cyclic diisocyanate compounds; aromatic diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, and diphenylmethane diisocyanate; organic polyisocyanates themselves, such as trivalent or higher polyisocyanates such as lysine triisocyanate; adducts of these organic polyisocyanates with polyhydric alcohols, low molecular weight polyester resins, water, and the like; cyclic polymers of these organic polyisocyanates (e.g., isocyanurates), biuret-type adducts, and the like. These polyisocyanate compounds can be used alone or in combination of two or more.

The hydroxyl group-containing polyester resin can be modified with an acrylic resin by known methods, such as a method of polymerizing a mixture of a polymerizable unsaturated group-containing polyester resin and a polymerizable unsaturated monomer, or a method of reacting a hydroxyl group-containing polyester resin with an acrylic resin.

From the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the hydroxyl group-containing polyester resin (y2) preferably has a hydroxyl value of 1 to 250 mgKOH/g, more preferably 2 to 200 mgKOH/g, and even more preferably 5 to 200 mgKOH/g.

When the hydroxyl group-containing polyester resin (y2) further contains a carboxyl group, from the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the acid value is preferably 1 to 150 mgKOH/g, more preferably 2 to 100 mgKOH/g, and even more preferably 3 to 80 mgKOH/g.

The weight average molecular weight of the hydroxyl group-containing polyester resin (y2) is preferably 3,000 to 100,000, more preferably 4,000 to 50,000, and even more preferably 5,000 to 30,000, from the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed.

In this specification, the average molecular weight is a value calculated from a chromatogram measured by gel permeation chromatography, based on the molecular weight of standard polystyrene. The gel permeation chromatograph used was "HLC8120GPC" (manufactured by Tosoh Corporation). Four columns, "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (all product names manufactured by Tosoh Corporation), were used, and the measurement was performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 mL/min, detector: RI.

From the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the content of the hydroxyl-containing polyester resin (y2) in the one-component water-based colored coating composition (Y) is preferably 2 to 70 mass %, more preferably 5 to 50 mass %, and even more preferably 10 to 40 mass %, based on the resin solid content in the one-component water-based colored coating composition (Y).

Polyurethane resin (y3)
The polyurethane resin (y3) can be obtained by a conventional method, for example, by reacting a polyol with a polyisocyanate compound. After the reaction, the chain can be extended in the presence of a chain extender, which is a low molecular weight compound having at least two active hydrogens in one molecule, such as a diol or diamine. The resin can be modified with an acrylic resin or the like during or after preparation.

Examples of the polyols include low molecular weight dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and hexamethylene glycol, and trihydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol. Examples of high molecular weight polyols include polyether polyols, polyester polyols, acrylic polyols, and epoxy polyols. Examples of polyether polyols include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of polyester polyols include polycondensates of the above-mentioned dihydric alcohols, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol, and dibasic acids such as adipic acid, azelaic acid, and sebacic acid, lactone ring-opening polymer polyols such as polycaprolactone, and polycarbonate diols. In addition, carboxyl group-containing polyols such as 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid can also be used. The above polyols can be used alone or in combination of two or more.

Examples of polyisocyanate compounds that can be reacted with the above polyols include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and methylcyclohexane-2,4-(or -2,6-)diisocyanate. alicyclic diisocyanates such as 1,3-(or 1,4-)di(isocyanatomethyl)cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, and 1,2-cyclohexane diisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, aromatic diisocyanate compounds such as 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-)phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, bis(4-isocyanatophenyl)sulfone, and isopropylidene bis(4-phenylisocyanate); and polyisocyanates thereof. Examples include biuret-type adducts and isocyanurate ring adducts of isocyanates; polyisocyanates having three or more isocyanate groups in one molecule, such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, and 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanate compounds.

Examples of diols that can be used as chain extenders include ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and cyclohexanediol, and examples of diamines include ethylenediamine, propylenediamine, xylylenediamine, and N-(2-hydroxyethyl)ethylenediamine.

The polyurethane resin (y3) may be a polyurethane resin that does not contain hydroxyl groups, or may be a polyurethane resin that contains hydroxyl groups.

From the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the polyurethane resin (y3) preferably has a hydroxyl value of 0 to 250 mgKOH/g, more preferably 0 to 200 mgKOH/g, and even more preferably 0 to 150 mgKOH/g.

In addition, from the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the polyurethane resin (y3) preferably has an acid value of 1 to 100 mgKOH/g, more preferably 2 to 50 mgKOH/g, and even more preferably 2 to 30 mgKOH/g.

The weight average molecular weight of the polyurethane resin (y3) is preferably 3,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more.

From the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed, the content of polyurethane resin (y3) in one-component water-based colored coating composition (Y) is preferably 2 to 70 mass%, more preferably 5 to 50 mass%, and even more preferably 10 to 40 mass%, based on the resin solid content in the one-component water-based colored coating composition (Y).

Hardener (y4)
The one-liquid type aqueous colored coating composition (Y) may contain a curing agent (y4). The curing agent (y4) is a compound that can react with the crosslinkable functional groups in the binder components, the hydroxyl-containing acrylic resin emulsion (y1) and the hydroxyl-containing polyester resin (y2), and is a compound that can form a crosslinked structure by the reaction. It is preferable that the crosslinkable functional group in the binder component (A) is a hydroxyl group, and the curing agent (y4) is a compound that is reactive with a hydroxyl group.

Specific examples of the curing agent (y4) that can be suitably used include polyisocyanate compounds, blocked polyisocyanate compounds, and amino resins. In particular, from the viewpoint of the cissing resistance of the coating film to be formed, it is preferable that the curing agent (y4) contains an amino resin.

The polyisocyanate compound is a compound having at least two isocyanate groups in one molecule, and examples of the polyisocyanate compound include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, aromatic aliphatic polyisocyanate compounds, aromatic polyisocyanate compounds, and derivatives of the polyisocyanate compounds.

Examples of the aliphatic polyisocyanate compounds include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate), isocyanate); aliphatic triisocyanate compounds such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

Examples of the alicyclic polyisocyanate compounds include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), 2-methyl-1,3-cyclohexylene diisocyanate, Alicyclic diisocyanate compounds such as cyclohexanediisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or mixtures thereof, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), and norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl) -2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)- Examples of alicyclic triisocyanate compounds include 2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

Examples of the aromatic aliphatic polyisocyanate compounds include aromatic aliphatic diisocyanate compounds such as methylene bis (4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; and aromatic aliphatic triisocyanate compounds such as 1,3,5-triisocyanatomethylbenzene.

Examples of the aromatic polyisocyanate compound include aromatic diisocyanate compounds such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4-TDI) or 2,6-tolylene diisocyanate (common name: 2,6-TDI) or mixtures thereof, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, etc.; aromatic triisocyanate compounds such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, etc.; and aromatic tetraisocyanate compounds such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate, etc.

In addition, examples of derivatives of the polyisocyanate compounds include dimers, trimers, biurets, allophanates, uretdione, uretoimine, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the above-mentioned polyisocyanate compounds.

The above polyisocyanate compounds and their derivatives may be used alone or in combination of two or more.

As the polyisocyanate compound, from the viewpoint of the weather resistance of the coating film formed, it is preferable to use at least one selected from aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, and derivatives thereof. From the viewpoint of high solid content of the resulting one-component water-based colored coating composition, the finished appearance and scratch resistance of the coating film formed, etc., it is more preferable to use an aliphatic polyisocyanate compound and/or its derivative.

As the above-mentioned aliphatic polyisocyanate compound and/or its derivative, from the viewpoints of high solid content of the resulting one-liquid type aqueous colored coating composition, the finished appearance and scratch resistance of the formed coating film, etc., it is preferable to use an aliphatic diisocyanate compound and/or its isocyanurate, and it is more preferable to use hexamethylene diisocyanate and/or its isocyanurate.

The blocked polyisocyanate compound that can be used as the curing agent (y4) is a compound in which the isocyanate group of the polyisocyanate compound is blocked with a blocking agent.

Examples of the blocking agents include phenol-based agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam-based agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohol-based agents such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and ethyl Ether-based compounds such as ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; alcohol-based compounds such as benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, and the like. oxime-based compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; active methylene-based compounds such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol; acid amide-based compounds such as acetanilide, acetanisidide, acetotoluide, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide; succinic acid amide, ... imide-based compounds such as maleic acid imide, phthalic acid imide, and maleic acid imide; amine-based compounds such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazole-based compounds such as imidazole and 2-ethylimidazole; urea-based compounds such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamate-based compounds such as N-phenylphenylcarbamate; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; and azole-based compounds. Examples of the azole compounds include pyrazole or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

Among them, preferred blocking agents include oxime-based blocking agents, active methylene-based blocking agents, pyrazole or pyrazole derivatives.

When blocking (reacting with a blocking agent), a solvent can be added as necessary. Solvents used in blocking reactions are preferably those that are not reactive with isocyanate groups, such as ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and N-methyl-2-pyrrolidone (NMP).

When the one-liquid type water-based colored coating composition (Y) contains the above-mentioned blocked polyisocyanate compound as the curing agent (y4), the content of the blocked polyisocyanate compound is preferably within the range of 5 to 60 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 25 to 45 parts by mass, based on the resin solid content in the one-liquid type water-based colored coating composition (Y), from the viewpoints of the cissing resistance of the coating film formed and the weather resistance of the coating film formed, etc.

As the amino resin that can be used as the curing agent (y4), a partially methylolated amino resin or a fully methylolated amino resin obtained by the reaction of an amino component with an aldehyde component can be used. Examples of the amino component include melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, and dicyandiamide. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

The methylolated amino resin may also be used in which the methylol groups are partially or completely etherified with a suitable alcohol. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, and 2-ethylhexanol.

As the amino resin, a melamine resin is preferred. As the melamine resin, for example, an alkyl etherified melamine resin in which the methylol groups of a partially or fully methylolated melamine resin are partially or completely etherified with the above-mentioned alcohol can be used.

As the alkyl etherified melamine resin, for example, methyl etherified melamine resin in which the methylol groups of a partially or fully methylolated melamine resin have been partially or completely etherified with methyl alcohol; butyl etherified melamine resin in which the methylol groups of a partially or fully methylolated melamine resin have been partially or completely etherified with butyl alcohol; methyl-butyl mixed etherified melamine resin in which the methylol groups of a partially or fully methylolated melamine resin have been partially or completely etherified with methyl alcohol and butyl alcohol can be suitably used.

The weight average molecular weight of the melamine resin is preferably in the range of 400 to 6000, more preferably 500 to 5000, and even more preferably 500 to 4000.

As the melamine resin, commercially available products can be used. Examples of the trade names of commercially available products include "Cymel 202", "Cymel 203", "Cymel 238", "Cymel 251", "Cymel 303", "Cymel 323", "Cymel 324", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 385", "Cymel 1156", "Cymel 1158", "Cymel 1116", and "Cymel 1130" (all manufactured by Allnex Japan Co., Ltd.), "U-Ban 120", "U-Ban 20HS", "U-Ban 20SE60", "U-Ban 2021", "U-Ban 2028", and "U-Ban 28-60" (all manufactured by Mitsui Chemicals, Inc.).

The above-mentioned melamine resins can be used alone or in combination of two or more.

When the one-liquid type water-based colored coating composition (Y) contains the above-mentioned amino resin as a curing agent (y4), the content is preferably within the range of 5 to 60 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 25 to 45 parts by mass, based on the resin solid content in the one-liquid type water-based colored coating composition (Y), from the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed.

The above curing agents (y4) can be used alone or in combination of two or more.

Color pigment (y5)
Examples of the color pigment (y5) include, but are not limited to, titanium oxide, zinc oxide, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, perylene pigments, dioxazine pigments, diketopyrrolopyrrole pigments, etc. From the viewpoint of the concealment of the base of the multilayer coating film formed, titanium oxide and carbon black can be preferably used.

The content of the color pigment (y5) in the one-component water-based colored coating composition (Y) is preferably within the range of 1 to 200 parts by mass, more preferably 2 to 100 parts by mass, and even more preferably 2 to 50 parts by mass, based on the resin solid content in the one-component water-based colored coating composition (Y), from the viewpoints of cissing resistance and weather resistance of the multilayer coating film formed.

The one-component water-based colored coating composition (Y) may further contain, as desired, resins other than the hydroxyl-containing acrylic resin emulsion (y1), the hydroxyl-containing polyester resin (y2), and the polyurethane resin (y3), extender pigments, luster pigments, UV absorbers, light stabilizers, defoamers, viscosity adjusters, surface adjusters, etc.

Resins other than the hydroxyl-containing acrylic resin emulsion (y1), the hydroxyl-containing polyester resin (y2), and the polyurethane resin (y3) include, for example, resins for dispersing pigments such as colored pigments (y5). Although known resins can be used as such pigment dispersion resins without particular restrictions, it is preferable to use water-soluble acrylic resins that are not emulsions. Examples of water-soluble acrylic resins that are not emulsions include acrylic resins containing hydroxyl groups, acrylic resins containing carboxyl groups, resins containing phosphate groups, tertiary amine-type acrylic resins, quaternary ammonium salt-type acrylic resins, and tertiary sulfonium salt-type acrylic resins. In particular, for colored pigments, from the standpoint of dispersion stability at high pigment concentrations, and further the gloss and water resistance of the resulting coating film, an acrylic copolymer obtained by copolymerizing a monomer mixture consisting of a polymerizable unsaturated monomer containing at least one functional group selected from a tertiary amino group, a quaternary ammonium base, a sulfo group, a carboxyl group, a phosphate group, etc., a nonionic polymerizable unsaturated monomer having a polyoxyalkylene chain, and other ethylenically unsaturated monomers in the presence of a radical polymerization initiator can be preferably used.

Examples of extender pigments include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white.

Examples of luster pigments include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, aluminum oxide coated with titanium oxide or iron oxide, mica coated with titanium oxide or iron oxide, glass flakes, etc., which can be used alone or in combination of two or more kinds.

The one-liquid type water-based colored coating composition (Y) is applied by inkjet. Various inkjet methods can be used, such as a method in which the one-liquid type water-based colored coating composition (Y) is used as ink and the ink is continuously sprayed and controlled by an electric field, a method in which the ink is intermittently sprayed using a piezoelectric element, and a method in which the ink is heated and the resulting foaming is used to spray it intermittently.

When painting, it is preferable that the one-component water-based colored coating composition (Y) contains a solvent such as water or an organic solvent, and if necessary, additives such as a viscosity adjuster and an antifoaming agent, so that the solid content and viscosity are adjusted to be suitable for painting.

The solid content of the one-component aqueous colored coating composition (Y) is preferably within the range of 10 to 60% by mass, more preferably 11 to 55% by mass, and even more preferably 12 to 50% by mass. In addition, it is preferable to appropriately adjust the viscosity of the one-component aqueous colored coating composition (Y) using water and/or an organic solvent so that the viscosity is within a range suitable for painting, usually within the range of 500 to 5000 mPa·s when measured at 20°C and 60 rpm using a B-type viscometer.

The cured film thickness of the colored coating film is preferably about 5.0 to 40 μm, more preferably about 6.0 to 35 μm, and even more preferably about 7.0 to 30 μm, from the viewpoint of the concealment property of the base of the multi-layer coating film to be formed.

The one-component aqueous colored coating composition (Y) may be maintained without heating after application by inkjet, but if necessary, it may be heated directly or indirectly before step (2) by preheating or the like at a temperature lower than that in step (3), for example, preferably at a temperature of about 50 to about 110°C, more preferably at a temperature of about 60 to about 90°C, for preferably about 1 to 60 minutes, more preferably about 1 to 30 minutes, and even more preferably about 1 to 10 minutes.

Step (2)
According to the method for forming a multilayer coating film of the present invention, a one-liquid type water-based clear coating composition (Z) containing a hydroxyl-containing acrylic resin emulsion (z1), a hydroxyl-containing polyester resin (z2), a polyurethane resin (z3), and a curing agent (z4) is then applied by inkjet coating onto the uncured colored coating film to form an uncured clear coating film. The uncured clear coating film is provided directly on the uncured colored coating film.

As the hydroxyl-containing acrylic resin emulsion (z1), the hydroxyl-containing acrylic resin emulsion described in relation to the hydroxyl-containing acrylic resin emulsion (y1) in step (1) can be used.

As the hydroxyl-containing polyester resin (z2), the hydroxyl-containing polyester resin described in relation to the hydroxyl-containing polyester resin (y2) in step (1) can be used.

As the polyurethane resin (z3), the polyurethane resin described for the polyurethane resin (y3) in step (1) can be used.

As the curing agent (z4), the curing agent described in relation to the curing agent (y4) in step (1) can be used.

The one-component water-based clear coating composition (Z) is a transparent composition with a different composition from the one-component water-based colored coating composition (Y), but the hydroxyl-containing acrylic resin emulsion (z1) is the same as the hydroxyl-containing acrylic resin emulsion (y1), the hydroxyl-containing polyester resin (z2) is the same as the hydroxyl-containing polyester resin (y2), the polyurethane resin (z3) is the same as the polyurethane resin (y3), and the curing agent (z4) is the same as the curing agent (y4). The resins being the same means that the structure of the resin as a component of the composition before being mixed with other components is the same. The curing agents being the same means that the structure of the curing agent as a component of the composition before being mixed with other components is the same.

The hydroxyl-containing acrylic resin emulsion (z1), hydroxyl-containing polyester resin (z2), polyurethane resin (z3), and curing agent (z4) in the one-component water-based clear coating composition (Z) are the same as the hydroxyl-containing acrylic resin emulsion (y1), hydroxyl-containing polyester resin (y2), polyurethane resin (y3), and curing agent (y4) in the one-component water-based colored coating composition (Y), so the multilayer coating film formed by curing the one-component water-based colored coating composition (Y) and the one-component water-based clear coating composition (Z) thereon has excellent cissing resistance. If one or more of the hydroxyl-containing acrylic resin emulsion (z1), hydroxyl-containing polyester resin (z2), polyurethane resin (z3), and curing agent (z4) in the one-component water-based clear coating composition (Z) are different from the hydroxyl-containing acrylic resin emulsion (y1), hydroxyl-containing polyester resin (y2), polyurethane resin (y3), and curing agent (y4) in the one-component water-based colored coating composition (Y), the cissing resistance is impaired in the multilayer coating film formed by curing the one-component water-based colored coating composition (Y) and the one-component water-based clear coating composition (Z) thereon.

Furthermore, since the hydroxyl-containing acrylic resin emulsion (z1), hydroxyl-containing polyester resin (z2), polyurethane resin (z3), and curing agent (z4) in the one-component water-based clear coating composition (Z) are the same as the hydroxyl-containing acrylic resin emulsion (y1), hydroxyl-containing polyester resin (y2), polyurethane resin (y3), and curing agent (y4) in the one-component water-based colored coating composition (Y), both steps (1) and (2) can be performed with one coating machine, which simplifies the coating process compared to using separate coating machines for steps (1) and (2).

The amounts of the hydroxyl-containing acrylic resin emulsion (z1), hydroxyl-containing polyester resin (z2), polyurethane resin (z3), and curing agent (z4) in the one-component water-based clear coating composition (Z) may be the same as or different from the amounts of the hydroxyl-containing acrylic resin emulsion (y1), hydroxyl-containing polyester resin (y2), polyurethane resin (y3), and curing agent (y4) in the one-component water-based colored coating composition (Y).

In a preferred embodiment, the absolute value of the difference between the contents of the hydroxyl-containing acrylic resin emulsion (y1), the hydroxyl-containing polyester resin (y2), the polyurethane resin (y3), and the curing agent (y4) in the one-component water-based colored coating composition (Y) based on the resin solid content in the one-component water-based colored coating composition (Y) and the contents of the hydroxyl-containing acrylic resin emulsion (z1), the hydroxyl-containing polyester resin (z2), the polyurethane resin (z3), and the curing agent (z4) in the one-component water-based clear coating composition (Z) based on the resin solid content in the one-component water-based clear coating composition (Z) is within 15% by mass. According to this configuration, the contents of the same components of the one-component water-based colored coating composition (Y) and the one-component water-based clear coating composition (Z) are close to each other, so that the multilayer coating film obtained using the multilayer coating film forming method of the present invention has even better cissing resistance. Furthermore, it is more suitable for carrying out steps (1) and (2) using a single coating machine.

The content of the hydroxyl-containing acrylic resin (z1) in the one-component water-based clear coating composition (Z) is preferably 2 to 70 mass%, more preferably 5 to 60 mass%, and even more preferably 10 to 55 mass%, based on the resin solid content in the one-component water-based clear coating composition (Z).

The content of the hydroxyl-containing polyester resin (z2) in the one-component water-based clear coating composition (Z) is preferably 2 to 70 mass%, more preferably 5 to 50 mass%, and even more preferably 10 to 40 mass%, based on the resin solid content in the one-component water-based clear coating composition (Z).

The content of polyurethane resin (z3) in one-component water-based clear coating composition (Z) is preferably 2 to 70 mass%, more preferably 5 to 50 mass%, and even more preferably 10 to 40 mass%, based on the resin solid content in one-component water-based clear coating composition (Z).

When the one-component water-based clear coating composition (Z) contains the above-mentioned blocked polyisocyanate compound as the curing agent (z4), the content of the blocked polyisocyanate compound is preferably within the range of 5 to 60 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 25 to 45 parts by mass, based on the resin solid content in the one-component water-based clear coating composition (Z), from the viewpoints of the cissing resistance of the coating film formed and the weather resistance of the coating film formed, etc.

When the one-component water-based clear coating composition (Z) contains the above amino resin as the curing agent (z4), from the viewpoints of its content, cissing resistance, weather resistance of the multilayer coating film formed, etc., the resin solid content in the one-component water-based clear coating composition (Z) is preferably within the range of 5 to 60 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 25 to 45 parts by mass.

The one-component water-based clear coating composition (Z) may contain, as necessary, appropriate additives such as water, a solvent such as an organic solvent, a resin other than the hydroxyl-containing acrylic resin emulsion (z1), the hydroxyl-containing polyester resin (z2) and the polyurethane resin (z3), a curing catalyst, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a viscosity adjuster, and an anti-settling agent.

The one-liquid water-based clear coating composition (Z) may not contain any coloring pigment, but may contain a coloring pigment as appropriate within the range that does not impair the transparency of the coating film. As the coloring pigment, a pigment known per se for inks or paints can be used alone or in combination of two or more kinds. The blending amount varies depending on the type of coloring pigment used, but can be preferably 30 mass % or less, more preferably 0.05 to 20 mass %, and even more preferably 0.1 to 10 mass % of the total solid content of the resin components in the one-liquid water-based clear coating composition (Z).

The one-component water-based clear coating composition (Z) is applied by inkjet. The inkjet method is as described in step (1). When applying the coating, it is preferable that the one-component water-based clear coating composition (Z) contains a solvent such as water or an organic solvent, and if necessary, additives such as a viscosity adjuster and an antifoaming agent, so as to have a solids content and viscosity suitable for application.

The solid content of the one-component water-based clear coating composition (Z) is preferably within the range of 10 to 60% by mass, preferably 11 to 55% by mass, and more preferably 22 to 50% by mass. In addition, it is preferable to appropriately adjust the viscosity of the one-component water-based clear coating composition (Z) using water and/or an organic solvent so that it is within a range suitable for coating, usually within the range of 200 to 5000 mPa·s when measured at 20°C and 60 rpm using a B-type viscometer.

From the viewpoint of weather resistance, the cured film thickness of the clear coating is preferably about 5.0 to 60 μm, more preferably about 6.0 to 50 μm, and even more preferably about 7.0 to 45 μm.

Step (3)
According to the method for forming a multilayer coating film of the present invention, the uncured colored coating film formed in step (1) and the uncured clear coating film formed in step (2) are then heated to 60 to 140°C, whereby they are cured simultaneously.

By heating the colored coating and the clear coating at the same time, the multi-layer coating containing these two coatings can be cured at once. In this case, one heat curing step can be omitted, improving energy conservation.

The heating method can be, for example, hot air heating, infrared heating, or high-frequency heating. The heating temperature is preferably 60 to 140°C, and more preferably 60 to 120°C. The heating time is preferably 10 to 60 minutes, and more preferably 15 to 40 minutes.

The present invention will be explained in more detail below with reference to manufacturing examples, working examples, and comparative examples. However, the present invention is not limited to these working examples. Note that "parts" and "%" are all based on mass. Furthermore, the thickness of the coating film is based on the cured coating film.

Production of Hydroxyl-Containing Acrylic Resin Emulsion (A1) Production Example 1
A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube, and a dropping device was charged with 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (product name, Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient 97%), and the mixture was stirred and mixed in a nitrogen stream and heated to 80°C. Next, 1% of the total amount of the monomer emulsion (1) described below and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80°C for 15 minutes. Thereafter, the remaining monomer emulsion (1) was added dropwise over 3 hours into the reaction vessel maintained at the same temperature, and after completion of the dropping, the mixture was aged for 1 hour. Thereafter, the following monomer emulsion (2) was added dropwise over 1 hour, and the mixture was aged for 1 hour, after which 40 parts of a 5% aqueous solution of dimethylethanolamine was gradually added to the reaction vessel while cooling to 30°C, and the mixture was discharged while filtering through a 100-mesh nylon cloth to obtain a hydroxyl-containing acrylic resin emulsion (A1-1) having a solids concentration of 30%. The obtained hydroxyl-containing acrylic resin emulsion (A1-1) had an acid value of 33 mgKOH/g and a hydroxyl value of 25 mgKOH/g.

Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2.1 parts of methylenebisacrylamide, 2.8 parts of styrene, 16.1 parts of methyl methacrylate, 28 parts of ethyl acrylate, and 21 parts of n-butyl acrylate were mixed and stirred to obtain monomer emulsion (1).

Monomer emulsion (2): 18 parts of deionized water, 0.31 parts of "Aqualon KH-10", 0.03 parts of ammonium persulfate, 5.1 parts of methacrylic acid, 5.1 parts of 2-hydroxyethyl acrylate, 3 parts of styrene, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate, and 9 parts of n-butyl acrylate were mixed and stirred to obtain monomer emulsion (2).

Production Example 2
A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube, and a dropping device was charged with 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (product name, Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient 97%), and the mixture was stirred and mixed in a nitrogen stream and heated to 80°C. Next, 1% of the total amount of the monomer emulsion (1) described below and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80°C for 15 minutes. Thereafter, the remaining monomer emulsion (1) was added dropwise over 3 hours into the reaction vessel maintained at the same temperature, and after completion of the dropping, the mixture was aged for 1 hour. Thereafter, the following monomer emulsion (2) was added dropwise over 1 hour, and the mixture was aged for 1 hour, after which 40 parts of a 5% aqueous solution of dimethylethanolamine was gradually added to the reaction vessel while cooling to 30°C, and the mixture was discharged while filtering through a 100-mesh nylon cloth to obtain a hydroxyl-containing acrylic resin emulsion (A1-2) having a solids concentration of 30%. The obtained hydroxyl-containing acrylic resin emulsion (A1-2) had an acid value of 33 mgKOH/g and a hydroxyl value of 25 mgKOH/g.

Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2.1 parts of methylenebisacrylamide, 1.4 parts of styrene, 8.0 parts of methyl methacrylate, 14 parts of ethyl acrylate, 34.5 parts of 2-ethylhexyl acrylate, and 10 parts of n-butyl acrylate were mixed and stirred to obtain monomer emulsion (1).

Monomer emulsion (2): 18 parts of deionized water, 0.31 parts of "Aqualon KH-10", 0.03 parts of ammonium persulfate, 5.1 parts of methacrylic acid, 5.1 parts of 2-hydroxyethyl acrylate, 1.5 parts of styrene, 3 parts of methyl methacrylate, 0.9 parts of ethyl acrylate, 9.9 parts of 2-ethylhexyl acrylate, and 4.5 parts of n-butyl acrylate were mixed and stirred to obtain monomer emulsion (2).

Production of Hydroxyl-Containing Acrylic Resin (A1') Production Example 3
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube and dropping device was charged with 35 parts of propylene glycol monopropyl ether and heated to 85 ° C., and then a mixture of 30 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 29 parts of n-butyl acrylate, 15 parts of 2-hydroxyethyl acrylate, 6 parts of acrylic acid, 15 parts of propylene glycol monopropyl ether and 2.3 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) was added dropwise over 4 hours, and the mixture was aged for 1 hour after the end of the dropwise addition. Then, a mixture of 10 parts of propylene glycol monopropyl ether and 1 part of 2,2'-azobis (2,4-dimethylvaleronitrile) was added dropwise over 1 hour, and the mixture was aged for 1 hour after the end of the dropwise addition. Further, 7.4 parts of diethanolamine and 13 parts of propylene glycol monopropyl ether were added to obtain a hydroxyl group-containing acrylic resin (A1'-1) solution with a solid content concentration of 55%. The resulting hydroxyl-containing acrylic resin (A1'-1) had an acid value of 47 mgKOH/g, a hydroxyl value of 72 mgKOH/g and a weight average molecular weight of 58,000.

Production of Hydroxyl-Containing Polyester Resin (A2) Production Example 4
A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a water separator was charged with 27 parts of trimethylolpropane, 31 parts of ethylene glycol, 35 parts of 3-methylpentanediol, 45 parts of succinic anhydride and 66 parts of adipic acid, and the temperature was raised between 160°C and 230°C over 3 hours, followed by condensation reaction at 230°C for 4 hours. Next, in order to add carboxyl groups to the obtained condensation reaction product, 7.7 parts of trimellitic anhydride were further added, and the mixture was reacted at 170°C for 30 minutes, followed by dilution with 2-ethyl-1-hexanol and deionized water to obtain an aqueous dispersion of hydroxyl-containing polyester resin (A2-1) having a solid content concentration of 40%. The obtained hydroxyl-containing polyester resin had an acid value of 26 mgKOH/g, a hydroxyl value of 108 mgKOH/g, a solid content concentration of 40%, and a weight average molecular weight of 1750.

Production Example 5
A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a water separator was charged with 27.3 parts of trimethylolpropane, 96 parts of 2-butyl-2-ethyl-1,3-propanediol, 21 parts of neopentyl glycol, 116.2 parts of isophthalic acid and 21.9 parts of adipic acid, and the temperature was raised between 160 ° C. and 230 ° C. over 3 hours, and then the condensation reaction was carried out for 4 hours at 230 ° C. Next, in order to add a carboxyl group to the obtained condensation reaction product, 10.6 parts of trimellitic anhydride was further added, and the reaction was carried out for 30 minutes at 170 ° C., and then diluted with 2-ethyl-1-hexanol and deionized water to obtain a hydroxyl group-containing polyester resin (A2-2) aqueous dispersion having a solid content concentration of 40%. The resulting hydroxyl-containing polyester resin had an acid value of 26 mgKOH/g, a hydroxyl value of 98 mgKOH/g, a solids concentration of 40%, and a weight average molecular weight of 1,600.

Production of Polyurethane Resin (A3) Production Example 6
A reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser was charged with 150.1 parts of polytetramethylene glycol (number average molecular weight 1000), 11.5 parts of 2,2-dimethylolpropionic acid, 14.4 parts of trimethylolpropane, 66.5 parts of isophorone diisocyanate, and 110.8 parts of methyl ethyl ketone, and the reaction system was purged with nitrogen gas, after which the mixture was reacted at 80°C with stirring to obtain an NCO-terminated urethane prepolymer with a free isocyanate group content of 10.3%. The resulting methyl ethyl ketone solution was cooled to 40°C, and 493.2 g of deionized water containing 8.1 parts of triethylamine was added to emulsify, after which 46.9 parts of a 5% aqueous solution of 2-(2-aminoethylamino)ethanol was added thereto and stirred for 60 minutes. The methyl ethyl ketone was then distilled off under reduced pressure and heating, and the concentration was adjusted with deionized water to obtain a polyurethane resin (A3-1) dispersion having a solid content of 35%, an acid value of 25 mgKOH/g, a hydroxyl value of 12 mgKOH/g, and an average particle size of 120 nm.

Production Example 7
A reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser was charged with 150.1 parts of polyethylene glycol (number average molecular weight 1000), 11.5 parts of 2,2-dimethylolpropionic acid, 14.4 parts of trimethylolpropane, 66.5 parts of isophorone diisocyanate, and 110.8 parts of methyl ethyl ketone, and the reaction system was purged with nitrogen gas, after which the mixture was reacted at 80°C with stirring to obtain an NCO-terminated urethane prepolymer with a free isocyanate group content of 10.3%. The obtained methyl ethyl ketone solution was cooled to 40°C, and 493.2 g of deionized water containing 8.1 parts of triethylamine was added to emulsify, and then 46.9 parts of a 5% aqueous solution of 2-(2-aminoethylamino)ethanol was added thereto and stirred for 60 minutes. After that, the methyl ethyl ketone was distilled off under reduced pressure and heating, and the concentration was adjusted with deionized water to obtain a polyurethane resin (A3-2) dispersion having a solid content of 35%, an acid value of 25 mgKOH/g, a hydroxyl value of 12 mgKOH/g, and an average particle size of 120 nm.

Production of Pigment Dispersion (P) Production Example 8
In a container equipped with a stirrer, 7.3 parts of the hydroxyl-containing acrylic resin (A1'-1) solution obtained in Production Example 3 (4 parts solids), 4 parts of "Carbon MA-100" (trade name, carbon black, manufactured by Mitsubishi Chemical Corporation), and 50 parts of deionized water were placed and mixed uniformly, and 2-(dimethylamino)ethanol was added to the mixed solution to adjust the pH to 7.5. The resulting mixed solution was then placed in a wide-mouth glass bottle, glass beads with a diameter of about 1.3 mm were added as a dispersion medium, and the bottle was sealed, and the mixture was dispersed for 4 hours using a paint shaker to obtain a pigment dispersion (P-1).

Preparation of one-liquid type water-based colored coating composition Production Example 9
Into a stirring mixing vessel were added 61.3 parts (8 parts solids) of the pigment dispersion (P-1) obtained in Production Example 8, 120 parts (36.0 parts solids) of the hydroxyl-containing acrylic resin emulsion (A1-1) obtained in Production Example 1, 40 parts (20 parts solids) of the hydroxyl-containing polyester resin (A2-1) solution obtained in Production Example 4, 28.6 parts (10 parts solids) of the polyurethane resin (A3-1) obtained in Production Example 6, and "Cymel 350" (trade name, manufactured by Allnex Japan, methyl ether). To the mixture, 30 parts (solids content: 30 parts) of esterified melamine resin (100% solids content) were uniformly mixed, and "Primal ASE-60" (product name, Rohm and Haas Company, polyacrylic acid-based thickener, solids content: 28%), 2-(dimethylamino)ethanol and deionized water were added to obtain one-component aqueous colored coating composition No. 1 having a pH of 8.0, a coating solids concentration of 20%, and a viscosity of 800 mPa·s after 1 minute at 60 rpm as measured with a B-type viscometer at a temperature of 20°C.

Production Examples 10 to 13
One-pack type water-based colored coating compositions No. 2 to No. 5 were obtained in the same manner as in Production Example 9, except that the blending compositions in Production Example 9 were as shown in Table 1.

One-liquid type water-based clear coating composition production example 14
In a stirring mixing vessel, 133.3 parts (40 parts solids) of the hydroxyl-containing acrylic resin emulsion (A1-1) obtained in Production Example 1, 40 parts (20 parts solids) of the hydroxyl-containing polyester resin (A2-1) solution obtained in Production Example 4, 28.6 parts (10 parts solids) of the polyurethane resin (A3-1) obtained in Production Example 6, and 30 parts (30 parts solids) of "Cymel 350" (trade name, manufactured by Ornex Japan Co., Ltd., methyl etherified melamine resin, 100% solids) were uniformly mixed, and "Primal ASE-60" (trade name, manufactured by Rohm and Haas Co., Ltd., polyacrylic acid-based thickener, 28% solids), 2-(dimethylamino)ethanol and deionized water were added to obtain a one-component water-based clear coating composition No. 1 having a pH of 8.0, a coating solids concentration of 20%, and a viscosity of 800 mPa·s after 1 minute at 60 rpm measured with a B-type viscometer at a temperature of 20 ° C. was obtained.

Production Examples 15 to 18
One-pack type water-based clear coating compositions No. 2 to No. 5 were obtained in the same manner as in Production Example 14, except that the blending compositions in Production Example 14 were as shown in Table 1.

Preparation of the object to be coated
Production Example 19
A cationic electrodeposition paint "ELECRON GT-10" (product name: manufactured by Kansai Paint Co., Ltd., using a blocked polyisocyanate compound as a curing agent for an epoxy resin polyamine-based cationic resin) was electrodeposited onto a degreased and zinc phosphate-treated steel plate (JIS G3141, size 400 mm x 300 mm x 0.8 mm) so that the film thickness based on the cured film was 20 μm, and the plate was heated at 170°C for 20 minutes to crosslink and cure, and then an undercoat paint "TP-65" (product name, manufactured by Kansai Paint Co., Ltd., polyester resin-based solvent undercoat paint) was electrostatically applied on top of the plate using a rotary atomizing bell-type coater so that the cured film thickness was 35 μm, and the plate was heated at 140°C for 30 minutes to crosslink and cure to obtain a coated substrate.

Preparation of coated panels for weather resistance test and anti-cracking test Example 1
Preparation of a coated plate for weather resistance test One-liquid type water-based colored coating composition No. 1 was filled into "X JET" (trade name, manufactured by SSI JAPAN, high viscosity micro-piezo jet dispenser, discharge port diameter 100 μm). Next, on the coated object prepared in Production Example 19, it was coated under the conditions of frequency 350 Hz, supply pressure 0.03 MPa, distance between discharge port and coated object 10 mm, 27 ° C, and relative humidity 50% so as to give a dry film thickness of 10 μm, and preheated at 80 ° C for 3 minutes to form an uncured colored coating film.

Next, one-component water-based clear coating composition No. 1 was filled into "X JET" (product name, manufactured by SSI JAPAN, high-viscosity micro-piezo jet dispenser, nozzle diameter 100 μm). Next, it was applied onto the uncured colored coating film under conditions of frequency 350 Hz, supply pressure 0.03 MPa, distance between nozzle and coated object 10 mm, 27°C, and relative humidity 50% so that the dry film thickness was 35 μm. After leaving it for 7 minutes, it was heated at 140°C for 30 minutes to cure the colored coating film and the clear coating film, and a coating plate for weather resistance test was prepared.

Preparation of coated plate for cissing resistance test One-liquid type water-based colored coating composition No. 1 was filled into "X JET" (trade name, manufactured by SSI JAPAN, high viscosity micro-piezo jet dispenser, discharge port diameter 100 μm). Next, on the substrate prepared in Production Example 19, it was coated under the conditions of frequency 350 Hz, supply pressure 0.03 MPa, distance between the discharge port and the substrate 10 mm, 27 ° C, and relative humidity 50% so as to give a dry film thickness of 10 μm, and preheated at 80 ° C for 3 minutes to form an uncured colored coating film.

Next, the one-component water-based clear coating composition No. 1 and the one-component water-based colored coating composition No. 1 were mixed so that the ratio of the one-component water-based clear coating composition/one-component water-based colored coating composition was 95/5, and filled into "X JET" (product name, manufactured by SSI JAPAN, high-viscosity micro-piezo jet dispenser, nozzle diameter 100 μm). Next, the uncured colored coating film was coated with the composition under the conditions of a frequency of 350 Hz, a supply pressure of 0.03 MPa, a distance between the nozzle and the coated object of 10 mm, 27°C, and a relative humidity of 50% so that the dry film thickness was 35 μm, and after leaving it for 7 minutes, it was heated at 140°C for 30 minutes to cure the colored coating film and the clear coating film, thereby preparing a coating plate for a cissing resistance test.

Examples 2 to 5, Comparative Examples 1 to 8
In Example 1, a weather resistance test coated plate and a cissing resistance test coated plate were prepared in the same manner as in Example 1, except that the combination of the one-component water-based colored coating composition and the one-component water-based clear coating composition was as shown in Table 1.

Comparative Example 9
One-liquid type water-based colored coating composition No. 1 was filled into "X JET" (trade name, manufactured by SSI JAPAN, high viscosity micro-piezo jet dispenser, discharge port diameter 100 μm). Next, on the coated object prepared in Production Example 19, the coating was applied under the conditions of a frequency of 350 Hz, a supply pressure of 0.03 MPa, a distance between the discharge port and the coated object of 10 mm, 27 ° C., and a relative humidity of 50% so as to give a dry film thickness of 10 μm, and then preheated at 80 ° C. for 3 minutes, and then heated at 140 ° C. for 30 minutes to cure the colored coating film, thereby preparing a coated plate for weather resistance test. In addition, for Comparative Example 9, a coated plate for cissing resistance test was not prepared.

Test method Weather resistance A cycle test combining irradiation and rainfall conditions was performed using a Superxenon weather meter (trade name, accelerated weather resistance tester, manufactured by Suga Test Instruments Co., Ltd.) under the test conditions described in JIS K5600-7-7 (Method 1). After a total cycle test time of 3000 hours, the multilayer coating film of the weather resistance test coated plate was cut into a grid shape with a cutter so as to reach the substrate, and 100 grids of 2 mm x 2 mm in size were made. Then, adhesive cellophane tape was attached to the surface, and the number of remaining grid coating films after the tape was rapidly peeled off at 20 ° C. was checked, and the weather resistance was evaluated according to the following evaluation criteria. ◎ and ◯ are pass. The evaluation results are shown in Table 1.
⊚: 100 grid-cut coating films remain, and no small edge chipping of the coating film occurs at the edges of the cutter cuts.
◯: 100 grid-patterned coating films remain, but small edge chipping of the coating film occurs at the edges of the cutter cuts.
△: The number of remaining grid-cut coating films is 99.
x: The number of remaining grid-cut coating films is 98 or less.

Crackling Resistance The coated plate for the crater resistance test obtained above was visually observed, and the crater resistance was evaluated according to the following evaluation criteria. ⊚ and ◯ are acceptable. The evaluation results are shown in Table 1.
◎: No dents or repelling on the painted surface.
〇: No repelling, but slight dents are visible.
△: Slight repelling is observed.
×: Numerous repellings are observed.

In addition, (Note 1) in the table has the following meaning:
(Note 1) "U-Ban 28-60": product name, manufactured by Mitsui Chemicals, Inc., butyl etherified melamine resin, manufactured by Mitsui Chemicals, Inc., solid content 60%.

Claims (1)

Step (1): A step of ink-jet coating a one-liquid type water-based colored coating composition (Y) containing a hydroxyl-containing acrylic resin emulsion (y1), a hydroxyl-containing polyester resin (y2), a polyurethane resin (y3), a curing agent (y4) and a color pigment (y5) on a substrate to form an uncured colored coating film;
Step (2): A step of ink-jet coating a one-liquid type water-based clear coating composition (Z) containing a hydroxyl-containing acrylic resin emulsion (z1), a hydroxyl-containing polyester resin (z2), a polyurethane resin (z3), and a curing agent (z4) on the uncured colored coating film to form an uncured clear coating film; and Step (3): A step of simultaneously curing the uncured colored coating film and the uncured clear coating film by heating them to 60 to 140°C.
A method for forming a multilayer coating film comprising the steps of:
the hydroxyl-containing acrylic resin emulsion (y1) and the hydroxyl-containing acrylic resin emulsion (z1) are the same hydroxyl-containing acrylic resin emulsion,
the hydroxyl-containing polyester resin (y2) and the hydroxyl-containing polyester resin (z2) are the same hydroxyl-containing polyester resin, and
The polyurethane resin (y3) and the polyurethane resin (z3) are the same polyurethane resin, and
The curing agent (y4) and the curing agent (z4) are the same curing agent.
A method for forming multi-layer coating films.