Method for forming multilayer coating film

Abstract

A method for forming a multilayer coating film, comprising the following steps (1)-(3): step (1): a step for forming a bright coating film by coating an object to be coated with a bright coating composition (Y) containing indium particles (y1); step (2): a step for forming a clear coating film by applying a clear coating composition (Z) containing a hydroxyl group-containing acrylic resin (z1) and a polyisocyanate compound (z2) onto the bright coating film obtained in step (1); and a step (3) of curing the bright coating film formed in the step (1) and the clear coating film formed in the step (2) by heating the bright coating film formed in the step (1) and the clear coating film formed in the step (2) separately or simultaneously, the hydroxyl value of the hydroxyl group-containing acrylic resin (z1) being in the range of 10 mgKOH / g to 75 mgKOH / g.

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 power. 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. Prior art literature Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 63-272544 Patent Document 2: Japanese Patent Application Publication No. 2003-313500 Summary of the invention Problem that the invention aims to solve

[0009] 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 high coating film performance. Technical Solution

[0010] The present invention includes the subject matters described in the following items.

[0011] 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) containing indium particles (y1) 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 acrylic resin (z1) and a polyisocyanate compound (z2) on the bright coating film obtained in step (1) to form a clear coating film; and Step (3): a step of curing the bright coating film formed in the step (1) and the clear coating film formed in the step (2) by heating them separately or simultaneously. The hydroxyl value of the hydroxyl-containing acrylic resin (z1) is in the range of 10 mgKOH / g to 75 mgKOH / g.

[0012] Item 2. The method for forming a multilayer coating film according to Item 1, wherein the bright coating composition (Y) further contains a hydroxyl group-containing resin (y2).

[0013] Item 3. The method for forming a multilayer coating film according to Item 1 or 2, wherein the bright coating composition (Y) further contains a melamine resin (y3).

[0014] Item 4. A multilayer coating film forming method according to any one of Items 1 to 3, wherein in the clear coating composition (Z), the equivalent ratio (NCO / OH) of the total number of moles of isocyanate groups of the polyisocyanate compound (z2) to the total number of moles of hydroxyl groups of the hydroxyl-containing acrylic resin (z1) is in the range of 0.7 to 1.5. Beneficial Effects

[0015] According to the method for forming a multilayer coating film of the present invention, a multilayer coating film having excellent metallic gloss and exhibiting excellent coating film properties such as adhesion can be formed. DETAILED DESCRIPTION

[0016] The multilayer coating film forming method of the present invention comprises the following steps (1) to (3): Step (1): a step of applying a bright coating composition (Y) containing indium particles (y1) 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 acrylic resin (z1) and a polyisocyanate compound (z2) on the bright coating film obtained in step (1) to form a clear coating film; and Step (3): a step of curing the bright coating film formed in the step (1) and the clear coating film formed in the step (2) by heating them separately or simultaneously. The hydroxyl value of the hydroxyl-containing acrylic resin (z1) is in the range of 10 mgKOH / g to 75 mgKOH / g.

[0017] Process (1) According to the method for forming a multilayer coating film of the present invention, first, a bright coating composition (Y) containing indium particles (y1) is applied to a coating object to form a bright coating film.

[0018] Painted object The coating material to which the bright coating composition (Y) is applied is not particularly limited. Examples of the coating material include: outer panels of automobile bodies such as cars, trucks, motorcycles, and buses; automobile parts such as bumpers; and outer panels of home appliances such as mobile phones and audio equipment. Among them, outer panels of automobile bodies and automobile parts are preferred.

[0019] 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.) electroplated 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, etc., plastic materials such as various FRP (fiber reinforced polymer), inorganic materials such as glass, cement, concrete, wood, fiber materials such as paper, cloth, etc. Among them, metal materials and plastic materials are preferred.

[0020] The surface to be coated with the multilayer coating may be automobile body panels, automobile parts, home appliances, or metal substrates such as steel sheets that constitute them, which have been subjected to surface treatments such as phosphate treatment, chromate treatment, and composite oxide treatment.

[0021] A coating film may be further formed on an object that has been subjected to or has not been subjected to a surface treatment. For example, a coated object as a substrate may be subjected to a surface treatment to form a primer coating film and / or a mid-coat coating film thereon. For example, when the coated object is a car body, the primer coating film and / or the mid-coat coating film may be formed using a coating composition for a primer and / or a mid-coat that is known per se and is commonly used in the coating of a car body.

[0022] 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. 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.

[0023] Bright coating composition (Y) The bright coating composition (Y) is a bright coating composition containing indium particles (y1).

[0024] The bright coating composition (Y) is preferably a coating composition containing indium particles (y1), a surface conditioner, and water and / or an organic solvent.

[0025] Indium particles (y1) The indium particles (y1) are flaky particles, which may also be referred to as flaky particles, plate-like particles, or sheet-like particles.

[0026] In the present invention, the flaky particles refer to particles having a substantially flat surface and a substantially uniform thickness in a direction perpendicular to the substantially flat surface. 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] <Peeling Layer Forming Step> The release layer forming step is a step of providing a release layer on the substrate.

[0032] As the substrate, there is no particular limitation 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 having 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. As metal foils, copper foils, aluminum foils, nickel foils, iron foils, alloy foils, etc. can be listed. 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.

[0033] As the peeling layer, various organic substances that can be dissolved in the subsequent peeling process can be used. 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.

[0034] 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.

[0035] 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, 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 because it has a high function as a protective layer.

[0036] There is no particular limitation on the method for forming the release layer, and it 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.

[0037] <Vacuum deposition process> The vacuum deposition step is a step of vacuum-depositing a metal layer containing indium particles (y1) on the release layer.

[0038] 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).

[0039] If the average vapor deposition thickness of the metal layer is 60 nm or less, the surface roughness Ra of the coating film is reduced, and excellent metallic gloss can be achieved. The average vapor deposition 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).

[0040] 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.

[0041] 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 preferred over the sputtering method in that the vacuum degree can be increased and the film formation speed (deposition rate) is high.

[0042] 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.

[0043] <Peeling process> The stripping step is a step of stripping the metal layer from the substrate by dissolving the stripping layer. The solvent capable of dissolving the stripping layer is not particularly limited as long as it is a solvent capable of dissolving 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).

[0044] 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. They can be used alone or in combination of two or more.

[0045] By dissolving the peeling layer, the island structure film is peeled off from the substrate, the island structure 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 the primary particles of the indium particles (y1) can be pulverized and classified as needed. In addition, when the primary particles of the indium particles (y1) are agglomerated, they can also be broken as needed.

[0046] 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.

[0047] <Other Processes> 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.

[0048] 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.

[0049] 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.).

[0050] 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 50 parts by mass or more, more preferably 70 parts by mass or more, further preferably in the range of 80 to 99.9 parts by mass, particularly preferably in the range of 90 to 99.9 parts by mass, based on 100 parts by mass of the solid content of the bright coating composition (Y).

[0051] As the surface conditioning agent, for example, silicone surface conditioning agents, acrylic surface conditioning agents, vinyl surface conditioning agents, fluorine surface conditioning agents, acetylene glycol surface conditioning agents and the like can be cited, wherein from the viewpoint of obtaining a coating film with excellent metallic luster, a fluorine surface conditioning agent is preferably included. The above surface conditioning agents can be used alone or in combination of two or more.

[0052] 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.

[0053] 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).

[0054] When the bright coating composition (Y) of the present invention contains a surface conditioner, the content of the surface conditioner is preferably 0.01 to 2.0 parts by mass, more preferably 0.05 to 1.5 parts by mass, and even more preferably 0.1 to 1.0 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.

[0055] As the organic solvent, 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 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 solvents can be used alone or in combination of two or more.

[0056] From the viewpoint of obtaining a coating film having excellent metallic gloss, the organic solvent preferably contains at least one solvent selected from glycol ether organic solvents and alcohol organic solvents, and more preferably contains a glycol ether organic solvent.

[0057] When the bright coating composition (Y) of the present invention contains an organic solvent, the content of the organic solvent 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 even more preferably in the range of 95 to 99 parts by mass, based on 100 parts by mass of the total of all components of the bright coating composition (Y), from the viewpoint of obtaining a coating film having excellent metallic gloss.

[0058] Other Ingredients The bright coating composition (Y) may further contain, as appropriate, 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.

[0059] 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.

[0060] When the bright coating composition (Y) of the present invention contains a pigment other than the indium particles (y1), the content of the pigment other than the indium particles (y1) 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 even more 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.

[0061] Examples of the viscosity adjuster include silica-based fine powder, mineral-based viscosity adjusters, barium sulfate micronized powder, polyamide-based viscosity adjusters, organic resin microparticle viscosity adjusters, diurea-based viscosity adjusters, urethane-associated viscosity adjusters, acrylic acid-swellable polyacrylic acid-based viscosity adjusters, and cellulose-based viscosity adjusters.

[0062] As said binder resin, a hydroxyl group-containing resin (y2) is mentioned, for example.

[0063] The above-mentioned hydroxyl-containing resin (y2) is a resin having at least one hydroxyl group in one molecule. As the hydroxyl-containing resin (y2), well-known resins can be widely used, for example, there can be listed: acrylic resins having hydroxyl groups, polyester resins having hydroxyl groups, acrylic modified polyester resins having hydroxyl groups, polyether resins having hydroxyl groups, polycarbonate resins having hydroxyl groups, polyurethane resins having hydroxyl groups, epoxy resins having hydroxyl groups, alkyd resins having hydroxyl groups and other resins. They can be used alone or in combination of two or more. Among them, from the viewpoints of adhesion of the formed coating film, the hydroxyl-containing resin (y2) preferably includes a hydroxyl-containing acrylic resin (y2-1).

[0064] The hydroxyl-containing acrylic resin (y2-1) can be obtained by, for example, copolymerizing a hydroxyl-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer (a polymerizable unsaturated monomer other than the hydroxyl-containing polymerizable unsaturated monomer).

[0065] 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 a diol 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 a diol having 2 to 8 carbon atoms; adducts of (meth)acrylic acid and epoxy-containing compounds (e.g., "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals, glycidyl neodecanoate); N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular end.

[0066] As other polymerizable unsaturated monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer, for example, monomers shown in the following (1) to (6) etc. can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0067] (1) Acid group-containing polymerizable unsaturated monomers A polymerizable unsaturated monomer containing an acid group is a compound having one or more acid groups and one or more polymerizable unsaturated bonds in one molecule. Examples of such monomers include: carboxyl-containing monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, and maleic anhydride; sulfonic acid-containing monomers such as vinyl sulfonic acid and 2-sulfoethyl (meth)acrylate; acidic phosphate ester monomers such as 2-(meth)acryloyloxyethyl phosphate, 2-(meth)acryloyloxypropyl phosphate, 2-(meth)acryloyloxy-3-chloropropyl phosphate, and 2-methacryloyloxyethylphenyl phosphate. These monomers may be used alone or in combination.

[0068] (2) Esterification products of acrylic acid or methacrylic acid and monohydric alcohol having 1 to 20 carbon atoms Specifically, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isotetradecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and the like are listed.

[0069] (3) Aromatic vinyl monomers Specific examples thereof include styrene, α-methylstyrene, and vinyltoluene.

[0070] By using an aromatic vinyl monomer as a constituent component, the glass transition temperature of the obtained resin increases, and a coating film having a high refractive index and being hydrophobic can be obtained, so that the gloss of the coating film is improved, thereby achieving an effect of improving the finished appearance.

[0071] When an aromatic vinyl monomer is used as a constituent component, the blending ratio thereof is preferably in the range of 3% by mass to 50% by mass, particularly preferably in the range of 5% by mass to 40% by mass, based on the total amount of the monomer components.

[0072] (4) Glycidyl-containing polymerizable unsaturated monomers The glycidyl group-containing polymerizable unsaturated monomer is a compound having one or more glycidyl groups and one or more polymerizable unsaturated bonds in one molecule, and specific examples thereof include glycidyl acrylate and glycidyl methacrylate.

[0073] (5) Nitrogen-containing compounds containing polymerizable unsaturated bonds For example, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-[3-(dimethylamino)propyl](meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetone(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylate, vinylpyridine, vinylimidazole, acrylonitrile, methacrylonitrile, and the like can be mentioned.

[0074] (6) Other vinyl compounds Examples thereof include vinyl acetate, vinyl propionate, vinyl chloride, vinyl versatate, etc. Examples of vinyl versatate include commercially available products such as "VEOVA 9" and "VEOVA 10" (these are trade names, manufactured by HEXION).

[0075] As other polymerizable unsaturated monomers, one or two or more monomers shown in (1) to (6) above may be used.

[0076] In the present invention, a polymerizable unsaturated monomer refers to a monomer having one or more (e.g., 1 to 4) polymerizable unsaturated groups. A polymerizable unsaturated group refers to an unsaturated group that can undergo free radical polymerization. Examples of the polymerizable unsaturated group include vinyl, (meth)acryloyl, (meth)acrylamide, vinyl ether, allyl, propenyl, isopropenyl, and maleimide.

[0077] 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.

[0078] From the viewpoint of curability and water resistance, the hydroxyl value of the hydroxyl-containing acrylic resin (y2-1) is preferably 30 mgKOH / g to 200 mgKOH / g, more preferably 40 mgKOH / g to 180 mgKOH / g, and particularly preferably 50 mgKOH / g to 150 mgKOH / g.

[0079] From the viewpoint of curability and water resistance, the acid value of the hydroxyl-containing acrylic resin (y2-1) is preferably 0.5 mgKOH / g to 15 mgKOH / g, more preferably 1 mgKOH / g to 12 mgKOH / g, and particularly preferably 2 mgKOH / g to 10 mgKOH / g.

[0080] From the viewpoint of the finished appearance and curability of the coating film, the weight average molecular weight of the hydroxyl-containing acrylic resin (y2-1) is preferably in the range of 2,000 to 50,000, more preferably in the range of 3,000 to 45,000, and further preferably in the range of 5,000 to 40,000.

[0081] It should be noted that in this specification, the average molecular weight is a value calculated based on the molecular weight of standard polystyrene according to the chromatogram measured by gel permeation chromatography. The gel permeation chromatograph uses "HLC8120GPC" (manufactured by Tosoh Co., Ltd.). As chromatographic columns, four columns "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (all manufactured by Tosoh Co., Ltd., are trade names) are used, and the analysis is carried out under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1cc / min, detector: RI.

[0082] From the viewpoint of the hardness of the coating film and the finished product appearance, the glass transition temperature of the hydroxyl-containing acrylic resin (y2-1) is preferably -50°C to 60°C, more preferably -20°C to 50°C, and particularly preferably in the range of 0°C to 45°C.

[0083] In this specification, the glass transition temperature (° C.) of the acrylic resin is calculated according to the following formula.

[0084] 1 / Tg(K)=(W1 / T1)+(W2 / T2)+……(1) Tg(℃)=Tg(K)-273(2) In each formula, W1, W2, ... represent the mass fractions of the monomers used for copolymerization, and T1, T2, ... represent the Tg (K) of the homopolymer of each monomer. It should be noted that T1, T2, ... are values ​​from pages III-139 to 179 of Polymer Hand Book (Second Edition, edited by J. Brandup·EH Immergut). In addition, the glass transition temperature (°C) of the homopolymer of the monomer when Tg is unclear is set as the static glass transition temperature. For example, a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instruments Co., Ltd.) is used to take the sample into a measuring cup, vacuum aspirate to completely remove the solvent, and then measure the heat change in the range of -20°C to +200°C at a heating rate of 3°C / min, and the initial baseline change point on the low temperature side is set as the static glass transition temperature.

[0085] The copolymerization method for copolymerizing the above-mentioned monomer mixture to obtain the hydroxyl-containing acrylic resin (y2-1) is not particularly limited, and a known copolymerization method can be used. Among them, 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.

[0086] Examples of the organic solvent used in the solution polymerization method include aromatic solvents such as toluene, xylene, and Swazol 1000 (a trade name of a high-boiling-point petroleum solvent manufactured by COSMO PETROLEUM CO., LTD.); ester solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, and propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; and alcohol solvents such as isopropyl alcohol, n-butanol, isobutyl alcohol, and 2-ethylhexanol.

[0087] These organic solvents can be used alone or in combination of two or more. From the perspective of the solubility of the acrylic resin, ester solvents and ketone solvents are preferably used. In addition, aromatic solvents can be preferably combined with these organic solvents for use.

[0088] Examples of the polymerization initiator that can be used in the copolymerization of the hydroxyl-containing acrylic resin (y2-1) include known free radical polymerization initiators such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, di-tert-amyl peroxide, tert-butyl peroctoate, 2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile).

[0089] When the bright coating composition (Y) of the present invention contains a hydroxyl-containing acrylic resin (y2-1) as the hydroxyl-containing resin (y2), the content of the hydroxyl-containing acrylic resin (y2-1) is preferably in the range of 50% by mass to 100% by mass, more preferably in the range of 55% by mass to 100% by mass, and further preferably in the range of 60% by mass to 100% by mass, based on the solid content of the hydroxyl-containing resin (y2), from the viewpoint of forming a multilayer coating film having excellent metallic gloss and exhibiting excellent coating film properties such as adhesion.

[0090] When the bright coating composition (Y) of the present invention contains a hydroxyl-containing resin (y2), the content of the hydroxyl-containing resin (y2) is preferably in the range of 0.1 to 15 parts by mass, more preferably in the range of 0.5 to 12 parts by mass, and even more preferably in the range of 1 to 10 parts by mass, based on 100 parts by mass of the solid content of the bright coating composition (Y), from the viewpoint of forming a multilayer coating film having excellent metallic gloss and exhibiting excellent coating film properties such as adhesion.

[0091] Examples of the crosslinking component include melamine resin (y3), melamine resin derivatives, urea resins, (meth)acrylamide, polyaziridine, polycarbodiimide, blocked or unblocked polyisocyanate compounds, and the like. Among them, from the viewpoint of adhesion of the formed coating film, it is preferred to contain melamine resin (y3).

[0092] As the melamine resin (y3), a partially methylolated melamine resin or a completely methylolated melamine resin obtained by a reaction between a melamine component and an aldehyde component can be used. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

[0093] In addition, as the melamine resin (y3), the methylol groups of the above-mentioned methylolated melamine resin may be partially or completely etherified with a suitable alcohol. Examples of the alcohol used for etherification include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, 2-ethyl-1-butanol, and 2-ethyl-1-hexanol.

[0094] As the melamine resin (y3), preferred are methyl-etherified melamine resins obtained by partially or completely etherifying the methylol groups of a partially or completely methylolated melamine resin with methanol, butyl-etherified melamine resins obtained by partially or completely etherifying the methylol groups of a partially or completely methylolated melamine resin with butanol, and methyl-butyl mixed etherified melamine resins obtained by partially or completely etherifying the methylol groups of a partially or completely methylolated melamine resin with methanol and butanol. More preferred is a methyl-butyl mixed etherified melamine resin.

[0095] The weight average molecular weight of the melamine resin (y3) is preferably 400 to 6,000, more preferably 500 to 4,000, and even more preferably 600 to 3,000.

[0096] As the melamine resin (y3), a commercially available product can be used. Examples of the trade names of commercially available products include: “CYMEL 202,” “CYMEL 203,” “CYMEL 204,” “CYMEL 211,” “CYMEL 212,” “CYMEL 238,” “CYMEL 251,” “CYMEL 253,” “CYMEL 254,” “CYMEL 303,” “CYMEL 323,” “CYMEL 324,” “CYMEL 325,” “CYMEL 327,” “CYMEL 350,” “CYMEL 370,” “CYMEL 380,” “CYMEL 385,” “CYMEL 1156,” “CYMEL 1158,” “CYMEL 1116,” and “CYMEL 1130” (all manufactured by Allnex Japan Co., Ltd.); 746", "Resimene 747" (all manufactured by MONSANTO); "U-VAN 120", "U-VAN 20HS", "U-VAN 20SE", "U-VAN 2021", "U-VAN 2028", "U-VAN 28-60" (all manufactured by Mitsui Chemicals, Inc.); and "Sumimal M55", "Sumimal M30W", "Sumimal M50W" (all manufactured by Sumitomo Chemical Co., Ltd.), etc.

[0097] When the bright coating composition (Y) of the present invention contains a melamine resin (y3), the content of the melamine resin (y3) is preferably in the range of 0.1 to 10 parts by mass, more preferably in the range of 0.3 to 8 parts by mass, and further preferably in the range of 0.5 to 5 parts by mass, based on 100 parts by mass of the solid content of the bright coating composition (Y), from the viewpoint of forming a multilayer coating film having excellent metallic gloss and exhibiting excellent coating film properties such as adhesion.

[0098] 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 application may be optionally performed, among which electrostatic coating by rotary atomization and electrostatic coating by air spray are preferred, and electrostatic coating by rotary atomization is particularly preferred.

[0099] 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 optionally an additive such as a defoaming agent to adjust the solid content and viscosity suitable for coating.

[0100] From the viewpoint of forming a multilayer coating film having excellent metallic gloss and exhibiting excellent coating film properties such as adhesion, the solid content of the bright coating composition (Y) of the present invention is preferably in the range of 0.1% by mass to 15% by mass, more preferably in the range of 0.5% by mass to 10% by mass, and more preferably in the range of 1% by mass to 5% by mass.

[0101] From the viewpoint of forming a multilayer coating film having excellent metallic gloss and exhibiting excellent coating film properties such as adhesion, the viscosity of the bright coating composition (Y) is preferably about 8 seconds to 30 seconds, particularly preferably about 10 seconds to 25 seconds, measured in a No. 3 Ford cup viscometer at 20°C.

[0102] From the viewpoint of forming a multilayer coating having excellent metallic gloss and exhibiting excellent coating properties such as adhesion, the cured film thickness of the bright coating is preferably about 0.01 μm to 2 μm, more preferably 0.025 μm to 1 μm, and even more preferably about 0.05 μm to 0.5 μm.

[0103] Process (2) According to the multilayer coating film forming method of the present invention, a clear coating film is formed by coating the bright coating film obtained in step (1) with a clear coating composition (Z) containing a hydroxyl-containing acrylic resin (z1) and a polyisocyanate compound (z2).

[0104] Hydroxyl-containing acrylic resin (z1) The hydroxyl-containing acrylic resin (z1) is an acrylic resin having at least one hydroxyl group in one molecule, and the hydroxyl value is in the range of 10 mgKOH / g to 75 mgKOH / g. If the hydroxyl-containing acrylic resin (z1) is less than 10 mgKOH / g, the adhesion of the formed multilayer coating is poor. If the hydroxyl-containing acrylic resin (z1) exceeds 75 mgKOH / g, the adhesion of the formed multilayer coating is poor. Among them, from the viewpoints of the adhesion of the formed multilayer coating and the compatibility with the polyisocyanate compound (z2), the hydroxyl value of the hydroxyl-containing acrylic resin (z1) is preferably in the range of 12 mgKOH / g to 70 mgKOH / g, and more preferably in the range of 15 mgKOH / g to 65 mgKOH / g.

[0105] The hydroxyl-containing acrylic resin (z1) can be produced, for example, by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers (polymerizable unsaturated monomers other than the hydroxyl-containing polymerizable unsaturated monomer) by a method known per se, such as a solution polymerization method in an organic solvent, an emulsion polymerization method in water, or the like.

[0106] As the hydroxyl-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers, the compounds described in the description column of the hydroxyl-containing acrylic resin (y2-1) can be used.

[0107] From the viewpoint of adhesion of the formed multilayer coating film, the weight average molecular weight of the hydroxyl-containing acrylic resin (z1) is preferably in the range of 2,000 to 50,000, more preferably in the range of 3,000 to 45,000, and further preferably in the range of 5,000 to 40,000.

[0108] 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 (z1) is preferably below 30 mgKOH / g, particularly preferably in the range of 1 mgKOH / g to 20 mgKOH / g.

[0109] From the viewpoints of adhesion, chipping resistance, finished product appearance, etc. of the formed multilayer coating film, the glass transition temperature of the hydroxyl-containing acrylic resin (z1) is preferably in the range of -50°C to 60°C, more preferably in the range of -30°C to 50°C, and particularly preferably in the range of -10°C to 45°C.

[0110] As a copolymerization method for obtaining the hydroxyl-containing acrylic resin (z1) by copolymerizing the above-mentioned polymerizable unsaturated monomer mixture, a solution polymerization method in which polymerization is performed in an organic solvent in the presence of a polymerization initiator can be preferably used.

[0111] 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.

[0112] Examples of the polymerization initiator that can be used in the copolymerization of the hydroxyl-containing acrylic resin (z1) 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).

[0113] The above-mentioned hydroxyl-containing acrylic resin (z1) can be used alone or in combination of two or more.

[0114] Polyisocyanate compound (z2) 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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-toluene diisocyanate (common name: 2,4-TDI) or 2,6-toluene diisocyanate (common name: 2,6-TDI) or a mixture thereof, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene; aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate, and the like.

[0119] 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.

[0120] The above-mentioned polyisocyanate and its derivatives may be used alone or in combination of two or more.

[0121] Among aliphatic diisocyanates, hexamethylene diisocyanate compounds can also 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.

[0122] As the polyisocyanate compound (z2), a prepolymer can be used: a prepolymer obtained by reacting the 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.

[0123] Furthermore, as the polyisocyanate compound (z2), a compound obtained by blocking the isocyanate groups in the above-mentioned polyisocyanates and derivatives thereof with a blocking agent, that is, a blocked polyisocyanate compound can also be used.

[0124] 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 monobutyl ether. Ether series 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, 2-hydroxyethyl methacrylate and other alcohol series; oxime series such as formamide oxime, acetamide oxime, acetone oxime, methyl ethyl ketone oxime, diacetyl monooxime, benzophenone oxime and cyclohexane oxime; dimethyl malonate, diethyl malonate, acetoethyl ester, Active methylene series such as ethyl acetate, methyl acetoacetate and acetylacetone; thiol series such as butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methyl thiophenol, ethyl thiophenol; amide series such as acetanilide, acetoanisidine, acetyltoluidine, acrylamide, methacrylamide, acetamide, stearamide, benzamide; imide series such as succinimide, phthalimide, maleimide; diphenylamine, phenylnaphthylamine, xylene Amine series such as amine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylaniline; imidazole series such as imidazole, 2-ethylimidazole; urea series such as urea, thiourea, ethyleneurea, ethylenethiourea, diphenylurea; carbamate series such as N-phenylcarbamate; imine series such as ethyleneimine, propyleneimine; sulfite series such as sodium bisulfite, 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.

[0125] When performing the terminal blocking (reacting the terminal blocking agent), a solvent may be optionally added.

[0126] The polyisocyanate compounds (z2) can be used alone or in combination of two or more.

[0127] From the viewpoint of forming a multilayer coating film exhibiting excellent coating film properties such as adhesion, in the clear coating composition (Z), the equivalent ratio (NCO / OH) of the total number of moles of isocyanate groups of the polyisocyanate compound (z2) to the total number of moles of hydroxyl groups of the hydroxyl-containing acrylic resin (z1) is preferably in the range of 0.70 to 1.50, more preferably in the range of 0.75 to 1.40, and further preferably in the range of 0.8 to 1.20.

[0128] The clear coating composition (Z) may optionally contain appropriate solvents such as water and organic solvents, resins other than the hydroxyl-containing acrylic resin (z1), curing agents other than the polyisocyanate compound (z2), curing catalysts, defoaming agents, ultraviolet absorbers, rheology control agents, anti-settling agents and other coating additives.

[0129] In the clear coating composition (Z), coloring pigments can 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 can be used alone or in combination as ink or coating. The amount thereof varies depending on the type of coloring pigment used, but can generally be set within the range of 30% by mass or less, preferably 0.05% by mass to 20% by mass, and more preferably 0.1% by mass to 10% by mass relative to the total solid content of the resin component of the clear coating composition (Z).

[0130] 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 about 10 to 60 μm, more preferably 15 to 50 μm, and even more preferably about 20 to 40 μm based on the cured coating film.

[0131] The solid content of the clear coating composition (Z) is in the range of 10% to 65% by mass, preferably 15% to 55% by mass, and more preferably 20% to 50% by mass. The viscosity of the clear coating composition (Z) is appropriately adjusted 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. using a No. 4 Ford cup viscometer.

[0132] Process (3) According to the multilayer coating film forming method of the present invention, the bright coating film formed in the step (1) and the clear coating film formed in the step (2) are then cured by heating them separately or simultaneously.

[0133] 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. The heating time is preferably 10 minutes to 60 minutes, more preferably 15 minutes to 40 minutes. Optionally, 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.

[0134] The present invention also includes the following embodiments. 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) containing indium particles (y1) 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 acrylic resin (z1) and a polyisocyanate compound (z2) on the bright coating film obtained in step (1) to form a clear coating film; and Step (3): a step of curing the bright coating film formed in the step (1) and the clear coating film formed in the step (2) by heating them separately or simultaneously. The hydroxyl value of the hydroxyl-containing acrylic resin (z1) is in the range of 10 mgKOH / g to 75 mgKOH / g. Item 2. The method for forming a multilayer coating film according to Item 1, wherein the bright coating composition (Y) further contains a hydroxyl-containing resin (y2). Item 3. The method for forming a multilayer coating film according to item 1 or 2, wherein the bright coating composition (Y) further contains a melamine resin (y3). Item 4. A multilayer coating film forming method according to any one of items 1 to 3, wherein in the clear coating composition (Z), the equivalent ratio (NCO / OH) of the total number of moles of isocyanate groups of the polyisocyanate compound (z2) to the total number of moles of hydroxyl groups of the hydroxyl-containing acrylic resin (z1) is in the range of 0.7 to 1.5. Item 5. The method for forming a multilayer coating film according to any one of items 1 to 4, wherein the content of the indium particles (y1) in the glittering coating composition (Y) is 50 parts by mass or more based on 100 parts by mass of the solid content of the glittering coating composition (Y). Item 6. The method for forming a multilayer coating film according to any one of items 1 to 5, wherein the content of the hydroxyl-containing resin (y2) is 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). Item 7. The method for forming a multilayer coating film according to Item 6, wherein the hydroxyl-containing resin (y2) contains a hydroxyl-containing acrylic resin (y2-1). Item 8. The method for forming a multilayer coating film according to item 3, wherein the content of the melamine resin (y3) is in the range of 0.1 to 10 parts by mass based on 100 parts by mass of the solid content of the bright coating composition (Y). Item 9. The method for forming a multilayer coating film according to any one of Items 1 to 8, wherein the bright coating composition (Y) further contains a surface conditioner. Item 10. The method for forming a multilayer coating film according to Item 9, wherein the surface conditioner contains a fluorine-based surface conditioner. Item 11. The method for forming a multilayer coating film according to item 9 or 10, wherein the content of the surface conditioning agent is in the range of 0.01 to 0.2 parts by mass based on 100 parts by mass of the solid content of the bright coating composition (Y). Item 12. The method for forming a multilayer coating film according to any one of Items 1 to 11, wherein the bright coating composition (Y) further contains an organic solvent. Item 13. The method for forming a multilayer coating film according to Item 12, wherein the content of the organic solvent is within a range of 85 to 99.9 parts by mass based on 100 parts by mass of the solid content of the bright coating composition (Y). Item 14. The method for forming a multilayer coating film according to any one of Items 1 to 13, wherein the solid content of the bright coating film is 0.1% by mass to 15% by mass. Item 15. The method for forming a multilayer coating film according to any one of items 1 to 14, wherein the cured film thickness of the bright coating film is 0.01 μm to 2 μm. Item 16. The method for forming a multilayer coating film according to any one of Items 1 to 15, wherein the object to be coated includes an outer panel of an automobile body and an automobile part. Example

[0135] 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.

[0136] 1. Preparation of substrate 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 obtained by using a blocked polyisocyanate compound 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 heated at 170° C. for 20 minutes to allow it to cross-link and cure, thereby forming an electrodeposition coating film.

[0137] 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 heated at 140°C for 30 minutes to cure it to form a mid-coat coating film, thereby preparing a coated object.

[0138] 2. Preparation of coating Production of hydroxyl-containing acrylic resin (y2-1) Production Example 1 Into a reaction container equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet tube and a dropping device, 22 parts of "Swazol 1000" (trade name, manufactured by Maruzen Petrochemical Co., Ltd., an aromatic petroleum-based solvent) and 10 parts of butyl acetate were charged, and after the temperature was raised to 125° C., a monomer mixture consisting of 17 parts of 2-hydroxyethyl acrylate, 25 parts of styrene, 8 parts of n-butyl acrylate, 34.35 parts of isobutyl methacrylate, 15 parts of 2-ethylhexyl acrylate, 0.65 parts of acrylic acid, 1 part of di-tert-amyl peroxide (polymerization initiator) and 20 parts of "Swasol 1000" was added dropwise at the same temperature over 3 hours, and after completion of the dropping, the mixture was aged for two hours. Next, as an additional catalyst, a mixed solution consisting of 0.5 parts of di-tert-amyl peroxide and 8 parts of "Swasol 1000" was dripped over 1 hour, and after the dripping was completed, it was kept at 125°C for 1 hour to obtain a hydroxyl-containing acrylic resin solution (y2-1) with a solid content of 60%. The obtained hydroxyl-containing acrylic resin (y2-1-1) had a hydroxyl value of 82 mgKOH / g, an acid value of 5 mgKOH / g, a weight average molecular weight of 28,000, and a glass transition temperature of 17°C.

[0139] Production of bright coating composition (Y) Production Example 2 In a stirring and 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), 0.27 parts (solid content: 0.08 parts) of "LE-605" (trade name, manufactured by Kyoeisha Chemical Co., Ltd., fluorine-based surface conditioner, solid content: 30%), 2.3 parts (solid content: 1.4 parts) of a hydroxyl-containing acrylic resin (y2-1-1), 0.66 parts (solid content: 0.59 parts) of "CYMEL 327" (trade name, manufactured by Allnex Corporation, imino group-containing melamine resin, solid content: 90%) and 1,701 parts of propylene glycol monomethyl ether were added and stirred and mixed to prepare a bright coating composition (Y-1) having a solid content of 1.2% by mass.

[0140] Production Examples 3 to 9 Except for setting the formulation and solid content as shown in Table 1, the same procedure as in Production Example 2 was carried out to obtain bright coating compositions (Y-2) to (Y-8).

[0141] [Table 1] The values ​​in Table 1 () are solid content

[0142] [Table 2] Table 1 (Continued) The values ​​in () are solid content

[0143] (*1) “METALURE L-71011AE”: trade name, manufactured by Eckart, vapor-deposited aluminum flake pigment, solid content 10%, dispersed in ethyl acetate.

[0144] Production of hydroxyl-containing acrylic resin (z1) Production Example 10 27 parts of "Swazol 1000" (trade name, manufactured by COSMO PETROLEUM CO., LTD., aromatic organic solvent) and 5 parts of propylene glycol monomethyl ether acetate were placed in a reaction container equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet tube and a dropping device. While blowing nitrogen into the reaction container, the charged liquid was stirred at 150° C., and a monomer mixture consisting of 20 parts of styrene, 10.5 parts of n-butyl acrylate, 3.5 parts of 2-hydroxyethyl methacrylate, 50 parts of isobutyl methacrylate, 15 parts of 2-ethylhexyl acrylate, 1.0 part of acrylic acid and 1.5 parts of di-tert-amyl peroxide (polymerization initiator) was dropped therein at a uniform rate over 4 hours. Then, after aging at 150° C. for 1 hour, the mixture was cooled, and 21 parts of isobutyl acetate was added for dilution to obtain a hydroxyl-containing acrylic resin (z1-1) solution having a solid content concentration of 65% by mass. The obtained hydroxyl-containing acrylic resin (z1-1) had a hydroxyl value of 15 mgKOH / g, an acid value of 8 mgKOH / g, a weight average molecular weight of 30,000, and a glass transition temperature of 24°C.

[0145] Production Examples 11 to 15 In Production Example 10, except that the blending composition was set as shown in Table 2, a hydroxyl-containing acrylic resin (z1-2) to (z1-6) solution having a solid content concentration of 65% by mass was obtained in the same manner as in Production Example 10. The acid value, hydroxyl value, weight average molecular weight and glass transition temperature of each hydroxyl-containing acrylic resin are collectively shown in Table 2.

[0146] [Table 3] Table 2

[0147] [Table 4] Table 2 (continued)

[0148] Preparation of clear coating composition (Z-1) Production Example 16 Immediately before coating, a main agent obtained by uniformly mixing 144.9 parts (94.2 parts solid content) of the hydroxyl-containing acrylic resin (z1-1) solution obtained in Production Example 10 and 0.4 parts (0.2 parts solid content) of "BYK-300" (trade name, manufactured by BYK Chemie, surface conditioner, active ingredient 52%) and 5.8 parts (5.8 parts solid content) of "Sumidur N3300" (trade name, manufactured by Sumika Covestro Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate, solid content 100%) were uniformly mixed, and butyl acetate was further added to adjust the viscosity to 30 seconds using a No. 4 Ford cup at 20°C to obtain a clear coating composition (Z-1).

[0149] Production Examples 17 to 23 Except for using the formulations described in Table 3, clear coating compositions (Z-2) to (Z-8) were obtained in the same manner as in Production Example 16.

[0150] [Table 5] Table 3

[0151] [Table 6] Table 3 (continued)

[0152] 3. Preparation of test board Preparation of test board Example 1 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 chamber temperature of 23°C and a humidity of 63% in such a manner that the cured coating film had a film thickness of 0.05 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.

[0153] Next, the transparent coating composition (Z-2) 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.

[0154] Here, the film thickness of the dried coating film of the bright coating film was calculated according to the following formula. The same applies to the following examples. x=sc / sg / S*10000 x: film thickness [μm]. sc: coating solid content [g]. sg: coating specific gravity [g / cm 3 ]. S: Evaluation area of ​​coated solid content [cm 2 ].

[0155] Examples 2 to 7, 9 to 13 and Comparative Examples 1 to 3 Except for using the coating material and film thickness described in Table 4, a test plate was obtained in the same manner as in Example 1.

[0156] Example 8 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 mini bell-shaped 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.

[0157] Next, the clear coating composition (Z-2) 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 8.

[0158] Coating evaluation The coating films of the test plates obtained as described above were evaluated by the following methods. Table 4 shows the results.

[0159] Initial water resistance The test plate was immersed in warm water at 40°C for 240 hours, and the water drops / stains were wiped off with a cloth after being pulled up. Within 10 minutes at room temperature of 23°C, the multilayer coating of the test plate was cut into a grid shape with a cutter in a manner that reached the base, and 100 checkerboards of 2mm×2mm in size were made. Then, a transparent tape was attached to the surface, and the residual state of the checkerboard coating after the tape was quickly peeled off was checked, and the water-resistant adhesion was evaluated according to the following criteria. A and B were qualified. A: 100 checkered patterns of the coating film remain, and no small edge defects of the coating film occur at the cut edge of the cutter. B: 100 checkered coating films remained, but small edge defects of the coating film occurred at the cut edge of the cutter, and the number of coating films remaining with edge defects was less than 10. C: 100 cross-sectional coating films remained, but small edge defects of the coating film occurred at the cut edge of the cutter, and 10 or more coating films with edge defects remained. D: 90 to 99 checkerboard-shaped coating films remain. E: The number of remaining cross-section coating films was 89 or less.

[0160] Improves water-resistant adhesion after weathering tests In the accelerated weathering test, Super Xenon Weather Meter (trade name, manufactured by Suga Test Instruments Co., Ltd.) specified in JIS B 7754 was used, and 1 hour and 42 minutes of irradiation with a xenon arc lamp and 18 minutes of irradiation with the lamp under rain conditions were used as a total of two hours as one cycle. After 2000 hours, the same operation as the above-mentioned water-resistant adhesion test was performed. A, B, and C were qualified.

[0161] 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.

[0162] [Table 7] Table 4

[0163] [Table 8] Table 4 (continued)

[0164] As mentioned above, although embodiment and Example of this invention were specifically described, this invention is not limited to the said embodiment, Various deformation|transformation based on the technical idea of ​​this invention is possible.

[0165] For example, the configurations, methods, processes, shapes, materials, and numerical values ​​listed in the above-mentioned embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values ​​may be used.

[0166] Furthermore, the configurations, methods, steps, shapes, materials, numerical values, and the like of the above-described embodiments may be combined with one another as long as they do not depart from the gist of the present invention.

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 (Y) containing indium particles (y1) 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 acrylic resin (z1) and a polyisocyanate compound (z2) on the bright coating film obtained in step (1) to form a clear coating film; and Step (3): a step of curing the bright coating film formed in the step (1) and the clear coating film formed in the step (2) by heating them separately or simultaneously. in, The hydroxyl value of the hydroxyl-containing acrylic resin (z1) is in the range of 10 mgKOH / g to 75 mgKOH / g.

2. The method for forming a multilayer coating film according to claim 1, wherein: The bright coating composition (Y) further contains a hydroxyl-containing resin (y2).

3. The method for forming a multilayer coating film according to claim 1 or 2, wherein: The bright coating composition (Y) further contains a melamine resin (y3).

4. The method for forming a multilayer coating film according to any one of claims 1 to 3, wherein: In the clear coating composition (Z), the equivalent ratio NCO / OH of the total molar number of isocyanate groups of the polyisocyanate compound (z2) to the total molar number of hydroxyl groups of the hydroxyl-containing acrylic resin (z1) is in the range of 0.7 to 1.5.

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