Multilayer coating film forming method

Abstract

A method for forming a multilayer coating film, comprising: step (1): applying a bright coating composition (Y) on a coated object to form a bright coating film; step (2): applying a clear coating composition (Z) containing (z1) a hydroxyl-containing resin and (z2) a polyisocyanate compound on the bright coating film obtained in step (1) to form a clear coating film; and step (3): curing the bright coating film and the clear coating film formed in steps (1) and (2) by heating them separately or simultaneously, wherein the bright coating composition (Y) contains indium particles (y1), a surface conditioner (y2) and an organic solvent (y3), and has a solid content of 0.1% to 15% by mass.

Description

Technical Field

[0001] The present invention relates to a method for forming a multi-layer coating film. Background Art

[0002] The purpose of coating is mainly to protect raw materials and give beauty. In industrial products, beauty, especially "texture", is important from the perspective of improving their product value. The texture of industrial products required by consumers is diverse. In recent years, in the fields of automobile outer panels, automobile parts, home appliances, etc., a metallic gloss (hereinafter referred to as "metallic gloss") is required.

[0003] Metallic gloss refers to a texture that has no graininess on the surface like a mirror, appears shiny when viewed nearly perpendicularly to the coated plate (highlight), and appears dark when viewed from an angle above the coated plate (shadow), that is, a texture characterized by a large difference in brightness between the highlight area and the shadow area.

[0004] Technologies for imparting the metallic gloss to the surface of industrial products include metal plating and metal vapor deposition (see, for example, Patent Document 1). If metallic gloss can be imparted by painting, it is advantageous from the standpoints of simplicity and cost.

[0005] Patent document 2 discloses that a good metallic appearance can be achieved according to the following metallic coating, which is characterized in that a metallic coating base material containing a glazing material, a non-volatile solid component containing a resin, and a solvent is diluted at a dilution rate of 150% to 500% using a diluent composed of a high-boiling point solvent and a low-boiling point solvent, and 5 to 10 parts by weight of a tackifying resin is added to 100 parts by weight of the resin component in the above-mentioned metallic coating base.

[0006] However, the metallic gloss of the appearance formed by the above-mentioned metallic paint is insufficient.

[0007] Furthermore, in painting, it is required to protect the raw materials while providing aesthetics, and excellent coating properties such as high adhesion are required.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 63-272544

[0011] Patent Document 2: Japanese Patent Application Publication No. 2003-313500 Summary of the invention

[0012] Problem that the invention aims to solve

[0013] An object of the present invention is to provide a method for forming a multilayer coating film which can form a multilayer coating film having excellent metallic gloss and exhibiting excellent coating film performance.

[0014] Technical Solution

[0015] The present invention includes the subject matters described in the following items.

[0016] Item 1. A method for forming a multilayer coating film, comprising the following steps (1) to (3): step (1): a step of applying a bright coating composition (Y) on a coated object to form a bright coating film; step (2): a step of applying a clear coating composition (Z) containing a hydroxyl-containing resin (z1) and a polyisocyanate compound (z2) on the bright coating film obtained in step (1) to form a clear coating film; step (3): a step of curing the bright coating film and the clear coating film formed in the steps (1) and (2) by heating them separately or simultaneously, wherein the bright coating composition (Y) contains indium particles (y1), a surface conditioner (y2) and an organic solvent (y3), and has a solid content of 0.1% to 15% by mass.

[0017] Item 2. The method for forming a multilayer coating film according to Item 1, wherein the indium particles (y1) are 70 parts by mass or more based on 100 parts by mass of the total solid content of the bright coating composition (Y).

[0018] Item 3. The method for forming a multilayer coating film according to Item 1 or 2, wherein the surface conditioner (y2) contains a fluorine-based surface conditioner.

[0019] Item 4. The method for forming a multilayer coating film according to any one of Items 1 to 3, wherein the organic solvent (y3) contains at least one solvent selected from the group consisting of alcohol solvents and glycol ether solvents.

[0020] Beneficial Effects

[0021] According to the method for forming a multilayer coating film of the present invention, a multilayer coating film having excellent metallic gloss and showing excellent coating film properties such as adhesion can be formed. DETAILED DESCRIPTION

[0022] The multilayer coating film forming method of the present invention is a multilayer coating film forming method comprising the following steps (1) to (3): step (1): a step of applying a bright coating composition (Y) on a coating object to form a bright coating film; step (2): a step of applying a clear coating composition (Z) containing a hydroxyl-containing resin (z1) and a polyisocyanate compound (z2) on the bright coating film obtained in step (1) to form a clear coating film; step (3): a step of curing the bright coating film and the clear coating film formed in the steps (1) and (2) by heating them separately or simultaneously, wherein the bright coating composition (Y) contains indium particles (y1), a surface conditioner (y2) and an organic solvent (y3), and has a solid content of 0.1% to 15% by mass.

[0023] Process (1)

[0024] According to the method for forming a multilayer coating film of the present invention, first, a bright coating composition (Y) is applied to an object to be coated to form a bright coating film.

[0025] Painted object

[0026] The coating object to which the bright coating composition (Y) is applied is not particularly limited. Examples of the coating object include: outer panels of automobile bodies such as cars, trucks, motorcycles, and buses; automobile parts such as bumpers; and outer panels of household appliances such as mobile phones and audio equipment. Among them, outer panels of automobile bodies and automobile parts are preferred.

[0027] The materials of these coated objects are not particularly limited. For example, metal materials such as iron, aluminum, brass, copper, tin plate, stainless steel, galvanized steel, zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) 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; plastic materials such as various FRP (fiber reinforced polymer); inorganic materials such as glass, cement, concrete; wood; fiber materials such as paper and cloth, etc. Among them, metal materials and plastic materials are preferred.

[0028] In addition, the surface to be coated with the multilayer coating may be a metal surface of a metal substrate such as an automobile body panel, automobile parts, home appliances, or steel plates constituting them, which may have been subjected to surface treatments such as phosphate treatment, chromate treatment, or composite oxide treatment.

[0029] A coating film may be further formed on the object to be coated with or without surface treatment. For example, the object to be coated as a substrate may be subjected to surface treatment as needed to form a primer coating film and / or a mid-coat coating film thereon. For example, in the case where the object to be coated is an automobile body, the primer coating film and / or the mid-coat coating film may be formed using a coating composition for primer and / or mid-coat that is known per se and is commonly used in the coating of automobile bodies.

[0030] As the primer coating composition for forming the above-mentioned primer film, for example, an electrodeposition coating can be used, preferably a cationic electrodeposition coating. In addition, as the mid-coat coating composition for forming the above-mentioned mid-coat coating film, a base resin such as an acrylic resin, polyester resin, alkyd resin, urethane resin, epoxy resin, etc. having crosslinking functional groups such as carboxyl and hydroxyl groups, an amino resin such as melamine resin and urea resin, a crosslinking agent such as an optionally blocked polyisocyanate compound, a pigment, a thickener, and optionally other components can be used.

[0031] Bright coating composition (Y)

[0032] The glittering coating composition (Y) is a glittering coating composition containing indium particles (y1), a surface conditioner (y2) and an organic solvent (y3), and having a solid content of 0.1% to 15% by mass.

[0033] Indium particles (y1)

[0034] The indium particles (y1) are flaky particles, which may also be referred to as flaky particles, plate-like particles, or sheet-like particles.

[0035] In the present invention, the flaky particles refer to particles having a substantially flat surface and having a substantially uniform thickness in a direction perpendicular to the substantially flat surface. In addition, the flaky particles refer to particles having a shape in which the thickness is very thin and the length of the substantially flat surface is very long. It should be noted that the length of the substantially flat surface is the diameter of a circle having the same projected area as the projected area of ​​the flaky particles.

[0036] The shape of the substantially flat surface is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include substantially rectangular, substantially square, substantially circular, substantially elliptical, substantially triangular, substantially quadrilateral, substantially pentagonal, substantially hexagonal, substantially heptagonal, substantially octagonal and other polygonal shapes, random indefinite shapes, etc. Among them, a substantially circular shape is preferred.

[0037] The indium particles (y1) may be formed in a single layer or in two or more layers to form primary particles. In addition, the primary particles of the indium particles (y1) may be aggregated to form secondary particles.

[0038] It should be noted that the indium particles (y1) are composed of indium with a purity of 95% or more and may contain a trace amount of impurities, but do not contain alloys with other metals.

[0039] The indium particles (y1) can be produced by performing a peeling layer forming step, a vacuum deposition step, a peeling step, and other steps as necessary.

[0040] <Peeling Layer Forming Step>

[0041] The release layer forming step is a step of providing a release layer on the substrate.

[0042] As the above-mentioned substrate, there is no particular restriction as long as it has a smooth surface, and various substrates can be used. Among them, resin films, metal foils, and composite films of metal foils and resin films with flexibility, heat resistance, solvent resistance and dimensional stability can be appropriately used. As resin films, for example, polyester films, polyethylene films, polypropylene films, polystyrene films, polyimide films, etc. can be listed. In addition, as metal foils, copper foils, aluminum foils, nickel foils, iron foils, alloy foils, etc. can be listed. In addition, as composite films of metal foils and resin films, composite films formed by laminating the above-mentioned resin films with metal foils can be listed.

[0043] As the peeling layer, various organic substances that can be dissolved in the subsequent peeling process can be used. In addition, if the organic material constituting the peeling layer is appropriately selected, the organic substance attached / remaining on the attachment surface of the island structure film can function as a protective layer for the indium particles (y1), which is preferred.

[0044] The protective layer has a function of suppressing aggregation, oxidation, elution of the indium particles (y1) into a solvent, etc. In particular, it is preferred to use an organic substance used for the release layer as the protective layer because it is not necessary to provide a separate surface treatment step.

[0045] Examples of organic substances constituting the peeling layer that can be used as a protective layer include cellulose acetate butyrate (CAB), other cellulose derivatives, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polyacrylic acid, polyacrylamide, polyvinyl butyral, acrylic copolymers, modified nylon resins, polyvinyl pyrrolidone, urethane resins, polyester resins, polyether resins, alkyd resins, etc. These may be used alone or in combination of two or more. Among them, cellulose acetate butyrate (CAB) is preferred in terms of its high function as a protective layer.

[0046] There is no particular limitation on the method for forming the release layer, and the method can be appropriately selected according to the purpose, and examples thereof include: inkjet method, blade coating method, gravure coating method, gravure offset coating method, rod coating method, roll coating method, knife coating method, air knife coating method, comma coating method, U-comma coating method, AKKU coating method, smoothing coating method, micro gravure coating method, reverse roll coating method, four-roll coating method, five-roll coating method, dip coating method, curtain coating method, slide coating method, die coating method, etc. These methods can be used alone or in combination of two or more.

[0047] <Vacuum deposition process>

[0048] The vacuum deposition step is a step of vacuum-depositing a metal layer containing indium particles (y1) on the release layer.

[0049] The average vapor-deposited thickness of the metal layer containing indium particles (y1) is preferably 60 nm or less, more preferably 55 nm or less, further preferably 50 nm or less, and particularly preferably 45 nm or less. It should be noted that the average vapor-deposited thickness of the metal layer containing indium particles (y1) is the same as the average thickness of the indium particles (y1).

[0050] If the average vapor-deposited thickness of the metal layer is 60 nm or less, the surface roughness Ra of the coating film is reduced, and an excellent metallic gloss can be exhibited. The average vapor-deposited thickness is, for example, an average value of the thickness of the metal layer measured at 5 to 10 locations by observing the cross section of the metal layer using a scanning electron microscope (SEM).

[0051] The metal layer is preferably an island structure film. The island structure film can be formed by various methods such as vacuum evaporation, sputtering, and plating. Among them, vacuum evaporation is preferred.

[0052] The vacuum deposition method is preferred over the plating method in that a film can be formed even on a resin substrate and no waste liquid is generated, and is more preferred in that the vacuum degree can be increased and the film formation speed (deposition rate) is high.

[0053] The deposition rate in the vacuum deposition method is preferably 10 nm / sec or more, and more preferably 10 nm / sec or more and 80 nm / sec or less.

[0054] <Peeling process>

[0055] The stripping step is a step of stripping the metal layer by dissolving the stripping layer. The solvent capable of dissolving the stripping layer is not particularly limited as long as it can dissolve the stripping layer, and can be appropriately selected according to the purpose, but is preferably a solvent that can be directly used as a solvent for the bright coating composition (Y).

[0056] Examples of the solvent capable of dissolving the peeling layer include: alcohol solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, and propylene glycol; ether solvents such as tetrahydrocannabinol; ketone solvents such as acetone, methyl ethyl ketone, and acetylacetone; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, and phenyl acetate; ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, and triethylene glycol monoethyl ether. ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, diethylene glycol monomethyl ether acetate and other glycol ether solvents; phenolic solvents such as phenol and cresol; aliphatic or aromatic hydrocarbon solvents such as pentane, hexane, heptane, octane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, octadecane, octadecene, benzene, toluene, xylene, mesitylene, nitrobenzene, aniline, methoxybenzene, mesitylene and other aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, dichlorobenzene and other aliphatic or aromatic chlorinated hydrocarbon solvents; sulfur-containing compound solvents such as dimethyl sulfoxide; nitrogen-containing compound solvents such as dimethylformamide, dimethylacetamide, acetonitrile, propionitrile, benzonitrile and the like. These solvents can be used alone or in combination of two or more.

[0057] By dissolving the peeling layer, the island structure film is peeled off from the substrate, and the island structure film is split and each island becomes an indium particle (y1). Thus, the indium particle (y1) dispersion can be obtained without a special pulverization step, but it can also be pulverized and classified as needed. In addition, in the case of primary particle aggregation of the indium particle (y1), it can also be broken as needed.

[0058] Furthermore, various treatments may be performed as needed to recover the indium particles (y1) and adjust the physical properties. For example, the particle size of the indium particles (y1) may be adjusted by classification, and the indium particles (y1) may be recovered by centrifugation, suction filtration, and the solid content concentration of the dispersion may be adjusted. In addition, solvent replacement may be performed, and viscosity adjustment may be performed using additives.

[0059] <Other Processes>

[0060] Examples of other steps include a step of taking out the peeled metal layer as a dispersion liquid, and a step of recovering the island-shaped metal layer as indium particles (y1) from the dispersion liquid.

[0061] From the viewpoint of forming a multilayer coating having excellent metallic gloss, the cumulative 50% volume particle size D50 of the indium particles (y1) obtained by performing the above-mentioned peeling layer forming step, vacuum evaporation step, peeling step, and other steps as required is preferably 0.70 μm or less, more preferably 0.60 μm or less, further preferably 0.50 μm or less, and particularly preferably 0.40 μm or less.

[0062] As the indium particles (y1), commercially available products may be used, such as “LEAFPOWDER 49CJ-1120”, “LEAFPOWDER 49CJ-1150”, “LEAFPOWDER 49BJ-1120”, and “LEAFPOWDER 49BJ-1150” (all manufactured by Oike Industries, Ltd.).

[0063] From the viewpoint of obtaining a coating film having excellent metallic gloss, the content of the indium particles (y1) in the bright coating composition (Y) of the present invention is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and preferably 90 parts by mass or more, based on 100 parts by mass of the solid content of the bright coating composition (Y). The upper limit is preferably 99.9 parts by mass or less, and may be 99 parts by mass or less. It is further preferably in the range of 90 to 99.9 parts by mass, and particularly preferably in the range of 95 to 99.9 parts by mass.

[0064] Surface conditioning agent (y2)

[0065] The surface conditioner (y2) is used to assist the indium particles (y1) to be uniformly oriented on the object to be coated when the bright coating composition (Y) is applied to the object to be coated.

[0066] As the surface conditioning agent (y2), for example, there can be listed: silicone-based surface conditioning agents, acrylic-based surface conditioning agents, vinyl-based surface conditioning agents, fluorine-based surface conditioning agents and the like, wherein, from the viewpoint of obtaining a coating film with excellent metallic luster, a fluorine-based surface conditioning agent is preferably included. The above-mentioned surface conditioning agents can be used alone or in appropriate combination of two or more.

[0067] Examples of the fluorine-based surface conditioning agent include fluorine-based polymers and fluorine-based oligomers having a perfluoroalkyl group and a polyoxyalkylene group, and fluorine-based polymers and fluorine-based oligomers having a perfluoroalkyl ether group and a polyoxyalkylene group.

[0068] Examples of commercially available products of the fluorine-based surface conditioner include: "LE-604", "LE-605" (both manufactured by Kyoeisha Chemical Co., Ltd.), "F-444", and "F-554" (both manufactured by DIC Corporation).

[0069] From the viewpoint of obtaining a coating film having excellent metallic gloss, the content of the surface conditioner (y2) in the bright coating composition (Y) of the present invention is preferably 0.001 to 1 part by mass, more preferably 0.003 to 0.5 parts by mass, and even more preferably 0.005 to 0.3 parts by mass, based on 100 parts by mass of the solid content of the bright coating composition (Y).

[0070] Organic solvent (y3)

[0071] As the organic solvent (y3) in the bright coating composition (Y) of the present invention, an organic solvent used in general coatings can be used. Specifically, for example, alcohol solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, and propylene glycol; ether solvents such as tetrahydrocannabinol; ketone solvents such as acetone, methyl ethyl ketone, and acetylacetone; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, and phenyl acetate; ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, Glycol ether solvents such as monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and diethylene glycol monomethyl ether acetate; phenolic solvents such as phenol and cresol; aliphatic or aromatic hydrocarbon solvents such as pentane, hexane, heptane, octane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, octadecane, octadecene, benzene, toluene, xylene, mesitylene, nitrobenzene, aniline, methoxybenzene, and mesitylene; aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, and dichlorobenzene; sulfur-containing compound solvents such as dimethyl sulfoxide; nitrogen-containing compound solvents such as dimethylformamide, dimethylacetamide, acetonitrile, propionitrile, and benzonitrile, etc. These can be used alone or in combination of two or more.

[0072] From the viewpoint of obtaining a coating film having excellent metallic gloss, the organic solvent (y3) preferably contains at least one solvent selected from the group consisting of glycol ether organic solvents and alcohol organic solvents, and more preferably contains a glycol ether organic solvent.

[0073] From the viewpoint of obtaining a coating film having excellent metallic gloss, the content of the organic solvent (y3) in the bright coating composition (Y) of the present invention is preferably in the range of 85 to 99.9 parts by mass, more preferably in the range of 90 to 99.5 parts by mass, and further preferably in the range of 95 to 99 parts by mass, based on 100 parts by mass of the total components of the bright coating composition (Y).

[0074] The solid content of the bright coating composition (Y) of the present invention is 0.1% to 15% by mass. In particular, from the viewpoint of obtaining a coating film having excellent metallic gloss, the solid content of the bright coating composition (Y) is preferably in the range of 0.5% to 10% by mass, and more preferably in the range of 1% to 5% by mass.

[0075] Other Ingredients

[0076] The bright coating composition (Y) may further contain, as necessary, a pigment other than the indium particles (y1), a viscosity adjuster, a binder resin, a crosslinking component, a pigment dispersant, an anti-settling agent, an ultraviolet absorber, a light stabilizer, and the like.

[0077] As pigments other than the above-mentioned indium particles (y1), there can be listed: coloring pigments, bright pigments other than indium particles (y1), extender pigments, etc. The pigments can be used alone or in combination of two or more. As the coloring pigments, for example, there can be listed: titanium oxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, threne pigments, perylene pigments, dioxazine pigments, pyrrolopyrrole diketopyrrole pigments, etc. As bright pigments other than the indium particles (y1), for example, there can be listed: vapor-deposited metal flake pigments other than indium particles (y1), aluminum flake pigments, optical interference pigments, etc. As the extender pigments, for example, there can be listed: clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, aluminum oxide white, etc.

[0078] When the bright coating composition (Y) of the present invention contains a pigment other than the indium particles (y1), the content thereof is preferably in the range of 0.01 to 30 parts by mass, more preferably in the range of 0.05 to 20 parts by mass, and further preferably in the range of 0.1 to 15 parts by mass, based on 100 parts by mass of the solid content of the bright coating composition (Y), from the viewpoint of obtaining a coating film having excellent metallic gloss.

[0079] Examples of the viscosity adjuster include silica powder, mineral viscosity adjusters, barium sulfate microparticle powder, polyamide viscosity adjusters, organic resin microparticle viscosity adjusters, diurea viscosity adjusters, urethane associative viscosity adjusters, acrylic acid-swellable polyacrylic acid viscosity adjusters, and cellulose viscosity adjusters.

[0080] Examples of the binder resin include acrylic resins, polyester resins, alkyd resins, and urethane resins.

[0081] Examples of the crosslinking component include melamine resins, melamine resin derivatives, urea resins, (meth)acrylamide, polyaziridine, polycarbodiimide, and blocked or unblocked polyisocyanate compounds.

[0082] The bright coating composition (Y) can be applied by a conventional method, for example, air spray coating, airless spray coating, rotary atomization coating, etc. When applying the bright coating composition (Y), electrostatic coating may be applied as needed. Among them, electrostatic coating by rotary atomization and electrostatic coating by air spray are preferred, and electrostatic coating by rotary atomization is particularly preferred.

[0083] When air spray coating, airless spray coating or rotary atomization coating is performed, the bright coating composition (Y) preferably contains water and / or an organic solvent and, if necessary, an additive such as a defoaming agent to adjust the solid content and viscosity suitable for coating.

[0084] Furthermore, from the viewpoint of obtaining a multilayer coating film exhibiting excellent metallic gloss, the viscosity of the bright coating composition (Y) is preferably about 8 seconds to 30 seconds, more preferably about 10 seconds to 25 seconds, measured in a Ford Cup No. 3 viscometer at 20°C.

[0085] Furthermore, from the viewpoint of obtaining a multilayer coating film exhibiting excellent metallic gloss, the cured film thickness of the bright coating film is preferably about 0.01 to 2 μm, more preferably about 0.025 to 1 μm, and even more preferably about 0.05 to 0.5 μm.

[0086] Process (2)

[0087] According to the multilayer coating film forming method of the present invention, a clear coating composition (Z) containing a hydroxyl group-containing resin (z1) and a polyisocyanate compound (z2) is then applied on the bright coating film obtained in step (1) to form a clear coating film.

[0088] The hydroxyl-containing resin (z1) is a resin having at least one hydroxyl group in one molecule. Examples of the hydroxyl-containing resin (z1) include acrylic resins having a hydroxyl group, polyester resins having a hydroxyl group, polyurethane resins having a hydroxyl group, polyolefin resins having a hydroxyl group, polyether resins having a hydroxyl group, polycarbonate resins having a hydroxyl group, epoxy resins having a hydroxyl group, alkyd resins having a hydroxyl group, and the like. These resins may be used alone or in combination of two or more.

[0089] From the viewpoint of adhesion of the formed multilayer coating film, etc., it is preferable to use a hydroxyl-containing acrylic resin (z11) as the hydroxyl-containing resin (z1).

[0090] Hydroxyl-containing acrylic resin (z11)

[0091] The hydroxyl-containing acrylic resin (z11) can be produced, for example, by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer with other polymerizable unsaturated monomers that can copolymerize with the hydroxyl-containing polymerizable unsaturated monomer by a method known per se, such as solution polymerization in an organic solvent, emulsion polymerization in water, or the like.

[0092] The above-mentioned hydroxyl-containing polymerizable unsaturated monomer 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 include: monoesters of (meth)acrylic acid and diols 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 diols having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol, and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular end. However, in the present invention, the monomer corresponding to the polymerizable unsaturated monomer having an ultraviolet absorbing functional group (xvii) described later should be defined as the above-mentioned other polymerizable unsaturated monomers that can be copolymerized with the hydroxyl-containing polymerizable unsaturated monomer, and are excluded from the hydroxyl-containing polymerizable unsaturated monomer. The above-mentioned hydroxyl group-containing polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0093] As other polymerizable unsaturated monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer, for example, the following monomers (i) to (xx) etc. can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0094] (i) Alkyl (meth)acrylate or cycloalkyl (meth)acrylate: 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, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, tricyclodecyl (meth)acrylate, etc.

[0095] (ii) Polymerizable unsaturated monomer having an isobornyl group: isobornyl (meth)acrylate, etc.

[0096] (iii) Polymerizable unsaturated monomer having an adamantyl group: adamantyl (meth)acrylate, etc.

[0097] (iv) Polymerizable unsaturated monomer having a tricyclodecenyl group: tricyclodecenyl (meth)acrylate, etc.

[0098] (v) Aromatic ring-containing polymerizable unsaturated monomers: benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, etc.

[0099] (vi) Polymerizable unsaturated monomers having an alkoxysilyl group: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, and the like.

[0100] (vii) Polymerizable unsaturated monomers having a fluoroalkyl group: perfluoroalkyl (meth)acrylates such as perfluorobutyl ethyl (meth)acrylate and perfluorooctyl ethyl (meth)acrylate; fluoroolefins, and the like.

[0101] (viii) A polymerizable unsaturated monomer having a photopolymerizable functional group such as a maleimide group.

[0102] (ix) Vinyl compounds: N-vinyl pyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, and the like.

[0103] (x) Carboxyl group-containing polymerizable unsaturated monomers: (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl (meth)acrylate, and the like.

[0104] (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, methylenebis(meth)acrylamide, ethylenebis(meth)acrylamide, adducts of glycidyl (meth)acrylate and amine compounds, etc.

[0105] (xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and the like.

[0106] (xiii) Epoxy-containing polymerizable unsaturated monomers: glycidyl (meth)acrylate, β-methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, and the like.

[0107] (xiv) (Meth)acrylates having a polyoxyethylene chain having an alkoxy group at the molecular terminal.

[0108] (xv) Polymerizable unsaturated monomers having a sulfonic acid group: 2-acrylamide-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allylsulfonic acid, 4-styrenesulfonic acid, etc.; sodium salts and ammonium salts of these sulfonic acids, etc.

[0109] (xvi) Polymerizable unsaturated monomers having a phosphoric acid group: acidic phosphonooxyethyl (meth)acrylate, acidic phosphonooxypropyl (meth)acrylate, acidic phosphonooxypoly (oxyethylene) glycol (meth)acrylate, acidic phosphonooxypoly (oxypropylene) glycol (meth)acrylate, etc.

[0110] (xvii) Polymerizable unsaturated monomers having ultraviolet absorbing functional groups: 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, etc.

[0111] (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-crotonyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonylamino-2,2,6,6-tetramethylpiperidine, 1-crotonyl-4-crotonyloxy-2,2,6,6-tetramethylpiperidine, and the like.

[0112] (xix) Polymerizable unsaturated monomers having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrene, vinyl alkyl ketones having 4 to 7 carbon atoms (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), etc.

[0113] (xx) Polymerizable unsaturated monomers having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride, and the like.

[0114] In the present specification, the polymerizable unsaturated group refers to an unsaturated group that can be radically polymerized. Examples of the polymerizable unsaturated group include a vinyl group and a (meth)acryloyl group.

[0115] In addition, 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.

[0116] From the viewpoints of water resistance of the formed coating film and finished product appearance, the content of the hydroxyl-containing acrylic resin (z11) in the clear coating composition (Z) is preferably in the range of 20 to 80 parts by mass, more preferably 25 to 75 parts by mass, and further preferably 30 to 70 parts by mass, based on 100 parts by mass of the resin solid content of the clear coating composition (Z).

[0117] In the manufacture of a hydroxyl-containing acrylic resin (z11), from the viewpoints of adhesion, stone chipping resistance, finished product appearance, etc. of the formed multilayer coating, the amount of the above-mentioned hydroxyl-containing polymerizable unsaturated monomer used is in the range of 15% to 50% by mass, preferably in the range of 20% to 40% by mass, relative to the total amount of the copolymerizable monomer components.

[0118] From the viewpoints of adhesion, stone chipping resistance, finished product appearance, etc. of the formed multilayer coating film, the hydroxyl value of the above-mentioned hydroxyl-containing acrylic resin (z11) is preferably in the range of 50 mgKOH / g to 210 mgKOH / g, more preferably in the range of 80 mgKOH / g to 200 mgKOH / g, and further preferably in the range of 100 mgKOH / g to 170 mgKOH / g.

[0119] In addition, from the viewpoints of adhesion, stone chipping resistance, finished product appearance, etc. of the formed multilayer coating film, the weight average molecular weight of the above-mentioned hydroxyl-containing acrylic resin (z11) is preferably in the range of 2000 to 50000, more preferably in the range of 3000 to 30000, and further preferably in the range of 4000 to 10000.

[0120] In addition, from the viewpoint of the finished appearance and adhesion of the formed multilayer coating film and the shelf life of the clear coating composition (Z), the acid value of the hydroxyl-containing acrylic resin (z11) is preferably in the range of 30 mgKOH / g or less, and more preferably in the range of 1 mgKOH / g to 20 mgKOH / g.

[0121] In addition, from the viewpoints of adhesion, stone chipping resistance, finished product appearance, etc. of the formed multilayer coating film, the glass transition temperature of the hydroxyl-containing acrylic resin (z11) is preferably in the range of -50°C to 60°C, more preferably in the range of 10°C to 50°C, and further preferably in the range of 20°C to 45°C.

[0122] In this specification, the glass transition temperature (° C.) of the acrylic resin is calculated according to the following formula.

[0123] 1 / Tg(K)=(W1 / T1)+(W2 / T2)+……(1)

[0124] Tg(℃)=Tg(K)-273(2)

[0125] In each formula, W1, W2, ... represent the mass fraction of each monomer used for copolymerization, and T1, T2, ... represent the Tg (K) of the homopolymer of each monomer. It should be noted that T1, T2, ... are the values ​​of pages III-139 to 179 of Polymer Hand Book (Second Edition, edited by J. Brandup·EH Immergut). In addition, the glass transition temperature (°C) when the Tg of the homopolymer of the monomer is unclear is set as the static glass transition temperature. For example, a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instrument) is used, and the sample is taken into a measuring cup, and after vacuum suction is performed to completely remove the solvent, the heat change is measured in the range of -20°C to +200°C at a heating rate of 3°C / min, and the initial change point of the baseline on the low temperature side is set as the static glass transition temperature.

[0126] As a copolymerization method for obtaining the hydroxyl-containing acrylic resin (z11) by copolymerizing the above-mentioned polymerizable unsaturated monomer mixture, a solution polymerization method in which polymerization is carried out in an organic solvent in the presence of a polymerization initiator can be preferably used.

[0127] Examples of the organic solvent used in the solution polymerization method include: alcohol solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, and propylene glycol; ether solvents such as tetrahydrocannabinol; ketone solvents such as acetone, methyl ethyl ketone, and acetylacetone; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, and phenyl acetate; ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and diethylene glycol di Glycol ether solvents such as methyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and diethylene glycol monomethyl ether acetate; phenol solvents such as phenol and cresol; aliphatic or aromatic hydrocarbon solvents such as pentane, hexane, heptane, octane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, octadecane, octadecane, octadecene, benzene, toluene, xylene, mesitylene, nitrobenzene, aniline, methoxybenzene, and mesitylene; aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, and dichlorobenzene, etc.

[0128] Examples of the polymerization initiator that can be used in the copolymerization of the hydroxyl-containing acrylic resin (z11) include known radical polymerization initiators such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, t-butyl peroctoate, 2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile).

[0129] The above-mentioned hydroxyl-containing acrylic resin (z11) can be used alone or in combination of two or more.

[0130] Polyisocyanate compound (z2)

[0131] The polyisocyanate compound (z2) is a compound having at least two isocyanate groups in one molecule, and examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates.

[0132] Examples of the aliphatic polyisocyanate 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, 2,6-diisocyanatohexanoic acid methyl ester (common name: aliphatic triisocyanates such as 2,6-diisocyanatohexanoic acid 2-isocyanatoethyl ester, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane, etc.

[0133] Examples of the alicyclic polyisocyanate 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, , 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated benzyl diisocyanate) or mixtures thereof, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), norbornane diisocyanate and other alicyclic diisocyanates; 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-bis(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-bis(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-( alicyclic triisocyanates such as 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.

[0134] Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as methylenebis(4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-phenylenediisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylphenylenediisocyanate) or a mixture thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatotoluene.

[0135] Examples of the aromatic polyisocyanate include: aromatic diisocyanates 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 a mixture thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0136] Examples of the polyisocyanate derivatives include dimers, trimers, biuret, allophanate, uretdione, uretimine, isocyanurate, oxadiazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), and crude TDI of the polyisocyanates.

[0137] The above-mentioned polyisocyanate and its derivatives may be used alone or in combination of two or more.

[0138] Among aliphatic diisocyanates, hexamethylene diisocyanate compounds can be preferably used, and among alicyclic diisocyanates, 4,4'-methylenebis(cyclohexyl isocyanate) can be preferably used. Among them, hexamethylene diisocyanate derivatives are particularly optimal from the viewpoints of adhesion and compatibility.

[0139] In addition, as the polyisocyanate compound (z2), a prepolymer can be used: a prepolymer obtained by reacting the above-mentioned polyisocyanate and its derivatives with a compound having an active hydrogen group such as a hydroxyl group or an amino group that can react with the polyisocyanate under the condition of an excess of isocyanate groups. Examples of the compound that can react with the polyisocyanate include polyols, low molecular weight polyester resins, amines, water, and the like.

[0140] Furthermore, as the polyisocyanate compound (z2), a blocked polyisocyanate compound obtained by blocking the isocyanate groups in the above-mentioned polyisocyanates and derivatives thereof with a blocking agent may be used.

[0141] Examples of the end-capping agent include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxybiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohols such as methanol, ethanol, propanol, butanol, amyl alcohol, and lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol monomethyl ether. Ethers such as monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; alcohols such as benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, hydroxymethyl urea, hydroxymethyl melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; oximes such as formamide oxime, acetamide oxime, acetone oxime, methyl ethyl ketone oxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; dimethyl malonate, diethyl malonate, ethyl acetoacetate Ester, methyl acetoacetate and acetylacetone and other active methylene series; butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol and other thiol series; acetanilide, acetoanisidine, acetyltoluidine, acrylamide, methacrylamide, acetamide, stearamide, benzamide and other amide series; succinimide, phthalimide, maleimide and other imide series; diphenylamine, phenylnaphthylamine, dimethylamino Amines such as aniline, N-phenyldimethylaniline, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylaniline, etc.; imidazoles such as imidazole and 2-ethylimidazole, ureas such as urea, thiourea, ethyleneurea, ethylenethiourea, diphenylurea, etc.; carbamates such as N-phenylcarbamate, etc.; imines such as ethyleneimine and propyleneimine, etc.; sulfites such as sodium bisulfite and potassium bisulfite, azole compounds, etc. 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.

[0142] When performing the terminal blocking (reacting the terminal blocking agent), a solvent may be added as necessary.

[0143] The polyisocyanate compounds (z2) can be used alone or in combination of two or more.

[0144] The equivalent ratio (NCO / OH) of the hydroxyl group of the hydroxyl-containing resin (z1) to the isocyanate group of the polyisocyanate compound (z2) in the clear coating composition (Z) is preferably in the range of 0.5 to 2.0, more preferably 0.8 to 1.5.

[0145] The clear coating composition (Z) may contain as needed a solvent such as water or an organic solvent, a curing catalyst, a defoaming agent, an ultraviolet absorber, a rheology control agent, an anti-settling agent or other coating additives.

[0146] In the clear coating composition (Z), coloring pigments may be used appropriately within the range that does not impair the transparency of the coating film. As coloring pigments, two or more pigments known per se may be used alone or in combination as ink or coating. The amount thereof varies depending on the type of coloring pigment used, but the total solid content of the resin component of the clear coating composition (Z) may preferably be 30% by mass or less, more preferably 0.05% by mass to 20% by mass, and further preferably 0.1% by mass to 10% by mass.

[0147] The clear coating composition (Z) can be applied by electrostatic coating, air spraying, airless spraying or the like, and the thickness of the clear coating film is preferably about 10 μm to 60 μm, more preferably 15 μm to 50 μm, and further preferably about 20 μm to 40 μm based on the cured coating film.

[0148] The solid content of the clear coating composition (Z) is preferably in the range of 10% to 65% by mass, more preferably in the range of 15% to 55% by mass, and further preferably in the range of 20% to 50% by mass. In addition, the viscosity of the clear coating composition (Z) is appropriately adjusted in advance to a range suitable for coating using water and / or an organic solvent, and is usually appropriately adjusted to preferably about 15 seconds to 60 seconds, more preferably about 20 seconds to 50 seconds, at 20°C in a Ford Cup No. 4 viscometer.

[0149] Process (3)

[0150] According to the multilayer coating film forming method of the present invention, the bright coating film and the clear coating film formed in the steps (1) and (2) are then cured by heating them separately or simultaneously.

[0151] The heating method can be carried out, for example, by hot air heating, infrared heating, high frequency heating, etc. The heating temperature is preferably 80°C to 160°C, more preferably 100°C to 140°C. In addition, the heating time is preferably 10 minutes to 60 minutes, more preferably 15 minutes to 40 minutes. If necessary, before the heat curing, heating can be carried out directly or indirectly for about 1 minute to 60 minutes by preheating, blowing, etc., preferably at a temperature of about 50°C to about 110°C, more preferably at a temperature of about 60°C to about 90°C.

[0152] The present invention may also adopt the following configurations.

[0153] Item 1. A method for forming a multilayer coating film, comprising the following steps (1) to (3): step (1): a step of applying a bright coating composition (Y) on a coated object to form a bright coating film; step (2): a step of applying a clear coating composition (Z) containing a hydroxyl-containing resin (z1) and a polyisocyanate compound (z2) on the bright coating film obtained in step (1) to form a clear coating film; step (3): a step of curing the bright coating film and the clear coating film formed in the steps (1) and (2) by heating them separately or simultaneously, wherein the bright coating composition (Y) contains indium particles (y1), a surface conditioner (y2) and an organic solvent (y3), and has a solid content of 0.1% to 15% by mass.

[0154] Item 2. The method for forming a multilayer coating film according to Item 1, wherein the indium particles (y1) are 70 parts by mass or more based on 100 parts by mass of the total solid content of the bright coating composition (Y).

[0155] Item 3. The method for forming a multilayer coating film according to Item 1, wherein the indium particles (y1) are present in an amount of 90 to 99.9 parts by mass based on 100 parts by mass of the total solid content of the glittering coating composition (Y).

[0156] Item 4. The method for forming a multilayer coating film according to any one of Items 1 to 3, wherein the surface conditioner (y2) contains a fluorine-based surface conditioner.

[0157] Item 5. The method for forming a multilayer coating film according to any one of Items 1 to 4, wherein the surface conditioner (y2) is 0.001 to 1 part by mass based on 100 parts by mass of the solid content of the bright coating composition (Y).

[0158] Item 6. The method for forming a multilayer coating film according to any one of Items 1 to 5, wherein the organic solvent (y3) contains at least one solvent selected from the group consisting of alcohol solvents and glycol ether solvents.

[0159] Item 7. The method for forming a multilayer coating film according to any one of Items 1 to 6, wherein the organic solvent (y3) is in a range of 85 to 99.9 parts by mass based on 100 parts by mass of all components of the bright coating composition (Y).

[0160] Item 8. The method for forming a multilayer coating film according to any one of Items 1 to 7, wherein the solid content of the bright coating composition (Y) is 0.5% by mass to 10% by mass.

[0161] Item 9. The method for forming a multilayer coating film according to any one of Items 1 to 7, wherein the solid content of the bright coating composition (Y) is 1% by mass to 5% by mass.

[0162] Item 10. The method for forming a multilayer coating film according to any one of Items 1 to 9, wherein the hydroxyl-containing resin (z1) includes a hydroxyl-containing acrylic resin (z11).

[0163] Item 11. The method for forming a multilayer coating film according to any one of Items 1 to 10, wherein the cured film thickness of the bright coating film is 0.01 μm to 2 μm.

[0164] Item 12. The method for forming a multilayer coating film according to any one of Items 1 to 11, wherein the cured film thickness of the clear coating film is 10 μm to 60 μm.

[0165] The present invention has been specifically described with reference to the above-mentioned embodiment and the following examples, but the present invention is not limited to the above-mentioned embodiment and the following examples, and various modifications based on the technical idea of ​​the present invention are possible.

[0166] For example, the structures, methods, processes, shapes, materials, and numerical values ​​listed in the above-mentioned embodiments and the following examples are merely examples, and different structures, methods, processes, shapes, materials, and numerical values ​​may be used as needed.

[0167] Furthermore, the configurations, methods, steps, shapes, materials, and numerical values ​​of the above-described embodiments and the following examples can be combined with each other as long as they do not depart from the gist of the present invention.

[0168] Example

[0169] The present invention will be described in more detail below with reference to Examples and Comparative Examples. However, the present invention is not limited to these Examples. It should be noted that "parts" and "%" are based on mass.

[0170] 1. Preparation of substrate

[0171] On a degreased and zinc phosphate treated steel plate (JIS G3141, size 400 mm × 300 mm × 0.8 mm), a cationic electrodeposition coating "Elecron GT-10" (trade name: manufactured by Kansai Paint Co., Ltd., a coating in which a blocked polyisocyanate compound is used as a curing agent in an epoxy resin polyamine-based cationic resin) was electroplated in a manner such that the film thickness was 20 μm based on the cured coating film, and then heated at 170°C for 20 minutes to allow it to cross-link and cure, thereby forming an electrodeposition coating film.

[0172] On the electrodeposition coated surface of the above-mentioned steel plate obtained, "TP-65-2" (trade name, manufactured by Kansai Paint Co., Ltd., a polyester resin and amino resin-based organic solvent-based mid-coat coating composition) was electrostatically coated using a rotary atomizing electrostatic coating machine in a manner such that the cured film thickness became 35 μm, and the mixture was heated at 140°C for 30 minutes to cure it, thereby forming a mid-coat coating film, thereby preparing a coated object.

[0173] 2. Preparation of coating

[0174] Acrylic resin production

[0175] Production Example 1

[0176] 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 50 parts of xylene and 20 parts of butyl acetate, and after the temperature was raised to 115° C., a mixture of 5 parts of styrene, 50 parts of methyl formate acrylate, 15.5 parts of n-butyl acrylate, 15 parts of 2-hydroxyethyl acrylate, 20 parts of “PLACCEL FM3X” (trade name, manufactured by Daicel Chemical Industries, Ltd., a xylene-diluted product of 3 mol of ε-caprolactone adduct of 2-hydroxyethyl methacrylate, solid content 80%), 1.5 parts of dimethylaminoethyl methacrylate, 1 part of acrylic acid, 15 parts of xylene, and 1.0 part of 2,2'-azobisisobutyronitrile was added dropwise over 3 hours, and the mixture was aged for 1 hour after the addition was completed. Then, a mixture of 5 parts of xylene 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 addition was completed. Further, 10 parts of xylene were added to obtain a hydroxyl-containing acrylic resin (R-1) solution having a solid content of 50%. The obtained hydroxyl-containing acrylic resin (R-1) had an acid value of 7.8 mgKOH / g, a hydroxyl value of 69.5 mgKOH / g, and a weight average molecular weight of 40,000.

[0177] Production of bright coating composition (Y)

[0178] Production Example 2

[0179] In a stirring mixing container, 100 parts (solid content 20 parts) of "LEAFPOWDER 49CJ-1120" (trade name, manufactured by Oike Industry Co., Ltd., indium particles, solid content 20%, dispersed in propylene glycol monomethyl ether), 0.28 parts (solid content 0.08 parts) of "LE-605" (trade name, manufactured by Kyoeisha Chemical Co., Ltd., fluorine-based surface conditioner, solid content 30%) and 1610 parts of propylene glycol monomethyl ether were added and stirred to produce a bright coating composition (Y-1) having a solid content of 1.2% by mass.

[0180] Production Examples 3 to 9

[0181] Except for setting the formulation and solid content as shown in Table 1, the same procedures as in Production Example 1 were carried out to obtain bright coating compositions (Y-2) to (Y-8).

[0182] [Table 1]

[0183] The values ​​in Table 1 () are solid content

[0184]

[0185] (*1) "METALURE L-71011AE": trade name, manufactured by Eckart, vapor-deposited aluminum flake pigment, solid content 10%, dispersed in ethyl acetate.

[0186] (*2) “R5000” (*2): Trade name, “RAVEN 5000 ULTRA III BEADS”, carbon black pigment, manufactured by COLUMBIAN CARBON CO.

[0187] Preparation of clear coating composition (Z)

[0188] Clear coating composition (Z-1)

[0189] "KINO-6510" (trade name, Kansai Paint Co., Ltd., containing components of a hydroxyl-containing resin and a polyisocyanate compound, a hydroxyl / isocyanate-curable acrylic resin / urethane resin two-component organic solvent-based paint) was used as the clear paint (Z-1).

[0190] Clear coating composition (Z-2)

[0191] "MAGICRON KINO-1210" (trade name, Kansai Paint Co., Ltd., acrylic resin-based acid / epoxy curing solvent-based paint) was used as the clear paint (Z-2).

[0192] 3. Preparation of test board

[0193] Preparation of test board

[0194] Example 1

[0195] The bright coating composition (Y-1) produced in the above "2. Preparation of coating" was applied to the substrate produced in the above "1. Preparation of substrate" using a minibell type rotary electrostatic coating machine under the conditions of a booth temperature of 23°C and a humidity of 63% in such a manner that the cured coating film had a film thickness of 0.05 μm. After being left at room temperature for 15 minutes, it was heated at 140°C in a hot air circulation drying furnace for 30 minutes to dry and cure it, thereby obtaining a bright coating film.

[0196] Next, the clear coating composition (Z-1) adjusted in the above-mentioned "2. Preparation of coating" was applied to the above-mentioned bright coating film using a mini bell-shaped rotary electrostatic coating machine at a chamber temperature of 23°C and a humidity of 68% so that the cured coating film became 35 μm. After being left at room temperature for 7 minutes, it was heated at 140°C in a hot air circulation drying oven for 30 minutes to dry and cure it, thereby producing a test plate of Example 1.

[0197] Here, the film thickness of the dried coating film of the bright coating film was calculated according to the following formula. The same also applies to the following examples.

[0198] x=sc / sg / S*10000

[0199] x: film thickness [μm].

[0200] sc: coating solid content [g].

[0201] sg: coating specific gravity [g / cm 3 ].

[0202] S: Evaluation area of ​​coated solid content [cm 2 ].

[0203] Examples 2, 4 to 7 and Comparative Examples 1 to 3

[0204] Except for using the coating material and film thickness described in Table 2, a test plate was obtained in the same manner as in Example 1.

[0205] Example 3

[0206] The bright coating composition (Y-2) produced in the above "2. Preparation of coating" was applied to the substrate produced in the above "1. Preparation of substrate" using a minibell type rotary electrostatic coating machine under the conditions of a chamber temperature of 23°C and a humidity of 63% in such a manner that the cured coating film had a film thickness of 0.1 μm. After being left at room temperature for 15 minutes, it was preheated at 80°C in a hot air circulation drying furnace for 3 minutes to obtain an uncured bright coating film.

[0207] Next, the clear coating composition (Z-1) adjusted in the above "2. Preparation of coating" was applied to the uncured glossy coating film using a mini bell-shaped rotary electrostatic coating machine at a chamber temperature of 23°C and a humidity of 68% so that the cured coating film became 35 μm. After being left at room temperature for 7 minutes, the clear coating composition was heated at 140°C in a hot air circulation drying oven for 30 minutes to simultaneously dry and cure the glossy coating film and the clear coating film, thereby producing a test plate of Example 3.

[0208] Coating evaluation

[0209] The coating films of the test plates obtained as described above were evaluated by the following methods. Table 2 shows the results.

[0210] Adhesion: Use a cutter to cut the multilayer coating of the test plate into a grid shape in a way that reaches the base, and make 100 squares of 2 mm × 2 mm in size. Then, stick a transparent tape on the surface, check the residual state of the square coating after the tape is quickly peeled off, and evaluate the adhesion according to the following criteria. Pass is qualified.

[0211] Pass: 100 square coatings remain.

[0212] Failure: The number of remaining checkered coating films is 99 or less.

[0213] Specular gloss (60° gloss): The 60° gloss value was measured using a gloss meter (micro-TRI-gloss, manufactured by BYK-Gardner). A larger value indicates excellent metallic gloss. A value of 280 or more was considered acceptable.

[0214] [Table 2]

[0215]

Claims

1. A method for forming a multilayer coating film, comprising the following steps (1) to (3): Step (1): a step of applying a bright coating composition to an object to be coated to form a bright coating film; Step (2): a step of applying a clear coating composition containing a hydroxyl-containing resin and a polyisocyanate compound on the bright coating film obtained in step (1) to form a clear coating film; Step (3): a step of curing the bright coating film and the clear coating film formed in the steps (1) and (2) by heating them separately or simultaneously. in, The bright coating composition contains indium particles as flaky particles, a surface conditioner, and an organic solvent, and has a solid content of 0.1% to 15% by mass.

2. The method for forming a multilayer coating film according to claim 1, wherein: The indium particles are contained in an amount of 70 parts by mass or more based on 100 parts by mass of the total solid content of the bright coating composition.

3. The method for forming a multilayer coating film according to claim 1 or 2, wherein: The surface conditioner includes a fluorine-based surface conditioner.

4. The method for forming a multilayer coating film according to claim 1 or 2, wherein: The organic solvent includes at least one solvent selected from the group consisting of alcohol solvents and glycol ether solvents.

5. The method for forming a multilayer coating film according to claim 3, wherein: The organic solvent includes at least one solvent selected from the group consisting of alcohol solvents and glycol ether solvents.

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