Multi-layer coating film formation method

Abstract

To provide a multitiered paint film forming method that can form a multitiered paint film having metallic luster with high transparency onto which a scenery can be photographed.SOLUTION: The multitiered paint film forming method includes: a step of painting a photoluminescent paint composition (Y) containing photoluminescent pigment (y1) onto an object to be painted to form a photoluminescent paint film; a step of painting a color clear paint composition (Z) containing coloring pigment (z1) onto the photoluminescent paint film to form a color clear paint film; and a step of heating the photoluminescent paint film and the color clear paint film to cure the paint films, where entire light transmittance in a region with wavelengths of 400 nm-700 nm of the color clear paint film is in a range of 10-60%, the formed multitiered paint film has a 20-degree specular glossiness of 90 or more, and the 20-degree specular glossiness / brightness L*(45°) which is a value determined by dividing the 20-degree specular glossiness by the brightness L*(45°) in a L*a*b* colorimetric system is 4 or more.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] The main purpose of applying paint is to protect the material and to add a beautiful appearance. For industrial products, aesthetics, especially "texture," are important in terms of enhancing their appeal. Consumers desire a wide variety of textures for industrial products, but in recent years, there has been a demand for a metallic luster (hereinafter referred to as "metallic luster") in areas such as automobile exterior panels, automobile parts, and home appliances.

[0003] Metallic gloss is a texture that has no grainy surface like a mirror, and is characterized by a large difference in brightness between the highlight and shade areas, which appear shiny when viewed nearly perpendicular to the painted board (highlights) and dark when viewed diagonally from above the painted board (shades).

[0004] More recently, designs with a highly transparent metallic sheen that allows the scenery to be reflected have become popular as they exude a sense of luxury.

[0005] Techniques for imparting such metallic luster to the surface of industrial products include metal plating and metal vapor deposition (see, for example, Patent Document 1), but if metallic luster could be imparted by painting, it would be advantageous from the standpoints of simplicity and cost.

[0006] Patent Document 2 describes that a metallic paint can achieve a good metallic appearance by diluting a metallic paint base containing a lustrous material, non-volatile solids including resin, and a solvent with a diluent consisting of a high-boiling point solvent and a low-boiling point solvent at a dilution ratio of 150 to 500%, and adding 5 to 10 parts by weight of a viscous resin for every 100 parts by weight of the resin content in the metallic paint base.

[0007] However, the appearance formed by the metallic paint described above does not have sufficient metallic luster, and does not have a design that allows the scenery to be reflected. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 63-272544 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-313500 Summary of the Invention [Problem to be solved by the invention]

[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 a highly transparent metallic luster in which the scenery is reflected. [Means for solving the problem]

[0010] The present invention encompasses the subject matter described in the following paragraphs.

[0011] Item 1. The following steps (1) to (3): Step (1): A step of applying a glitter coating composition (Y) containing a glitter pigment (y1) onto a substrate to form a glitter coating film; Step (2): A step of applying a color clear coating composition (Z) containing a color pigment (z1) onto the glossy coating film obtained in Step (1) to form a color clear coating film; Step (3): A method for forming a multilayer coating film, comprising a step of heating the glossy coating film and the color clear coating film formed in steps (1) and (2) separately or simultaneously to cure them, The total light transmittance of the color clear coating film in the wavelength range of 400 nm to 700 nm is within the range of 10 to 60%, The multi-layer coating film formed is The 20-degree specular gloss is 90 or more, and 20 degree specular gloss, L* a * b * Lightness L in the color system * (45°) 20° specular gloss / brightness L * (45°) is 4 or more.

[0012] Item 2. The method for forming a multilayer coating film according to Item 1, wherein the bright pigment (y1) contains indium particles.

[0013] Item 3. The method for forming a multilayer coating film according to Item 1 or 2, wherein the color pigment (z1) includes a black pigment. [Effects of the Invention]

[0014] According to the method for forming a multilayer coating film of the present invention, it is possible to form a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected. DETAILED DESCRIPTION OF THE INVENTION

[0015] The method for forming a multilayer coating film of the present invention comprises the following steps (1) to (3): Step (1): A step of applying a glitter coating composition (Y) containing a glitter pigment (y1) onto a substrate to form a glitter coating film; Step (2): A step of applying a color clear coating composition (Z) containing a color pigment (z1) onto the glossy coating film obtained in Step (1) to form a color clear coating film; Step (3): A method for forming a multilayer coating film, comprising a step of heating the glossy coating film and the color clear coating film formed in steps (1) and (2) separately or simultaneously to cure them, The total light transmittance of the color clear coating film in the wavelength range of 400 nm to 700 nm is within the range of 10 to 60%, The multi-layer coating film formed is The 20-degree specular gloss is 90 or more, and 20 degree specular gloss, L * a * b * Lightness L in the color system *(45°) 20° specular gloss / brightness L * (45°) is 4 or more.

[0016] Process (1) According to the method for forming a multilayer coating film of the present invention, first, a glittering coating composition (Y) containing a glittering pigment (y1) is applied to an object to be coated, thereby forming a glittering coating film.

[0017] Object to be coated The substrate to which the bright coating composition (Y) is applied is not particularly limited. Examples of the substrate include outer panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts such as bumpers; and outer panels of household electrical appliances such as mobile phones and audio equipment. Among these, outer panels of automobile bodies and automobile parts are preferred.

[0018] The material of these substrates is not particularly limited. Examples include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.)-plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, and epoxy resin; plastic materials such as various FRPs; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth. Among these, metal materials and plastic materials are preferred.

[0019] Furthermore, the surface of the object to which the multilayer coating film is applied may be a metal surface such as an outer panel of an automobile body, an automobile part, a household electrical appliance, or a metal substrate such as the steel plate that constitutes these, which has been subjected to a surface treatment such as phosphate treatment, chromate treatment, or composite oxide treatment.

[0020] A coating film may be further formed on an object that may or may not have been surface-treated. For example, a substrate to be coated may be subjected to a surface treatment as needed, and a primer coating film and / or intermediate coating film may be formed thereon. For example, when the substrate to be coated is an automobile body, the primer coating film and / or intermediate coating film may be formed using a known primer and / or intermediate coating composition that is commonly used in painting automobile bodies.

[0021] The undercoat paint composition for forming the undercoat paint film can be, for example, an electrodeposition paint, preferably a cationic electrodeposition paint. The intermediate paint composition for forming the intermediate paint film can be a paint prepared by mixing a base resin having a crosslinkable functional group such as a carboxyl group, a hydroxyl group, or the like, such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, or an epoxy resin, with a crosslinking agent such as an amino resin such as a melamine resin or a urea resin, or an optionally blocked polyisocyanate compound, together with a pigment, a thickener, and optionally other components.

[0022] Bright paint composition (Y) The glittering coating composition (Y) contains a glittering pigment (y1).

[0023] The glittering coating composition (Y) preferably contains a glittering pigment (y1), and further contains a surface conditioner, and water and / or an organic solvent.

[0024] Examples of the bright pigment (y1) include indium particles, vapor-deposited aluminum flake pigments, vapor-deposited chrome flake pigments, aluminum flake pigments, and optical interference pigments. Among these, indium particles are preferred from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster that reflects the scenery. One or more of these pigments can be appropriately selected and used.

[0025] Indium particles The indium particles are flaky particles, which are also called scale-like particles, plate-like particles, flake-like particles, etc.

[0026] In the present invention, the term "flaky particles" refers to particles having a substantially flat surface and a substantially uniform thickness in the direction perpendicular to the substantially flat surface. The term "flaky particles" also refers to particles having a shape in which the thickness is very thin and the length of the substantially flat surface is very long. 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 depending on the purpose, and examples thereof include polygons such as substantially rectangular, substantially square, substantially circular, substantially oval, substantially triangular, substantially square, substantially pentagonal, substantially hexagonal, substantially heptagonal, and substantially octagonal, and random, indeterminate shapes. Among these, a substantially circular shape is preferable.

[0028] The indium particles may be a single layer or may be a primary particle formed by stacking two or more layers, or may be a secondary particle formed by agglomeration of the primary particles of the indium particles.

[0029] The indium particles are made of indium with a purity of 95% or more and may contain trace amounts of impurities, but do not include alloys with other metals.

[0030] The indium particles can be produced by carrying out a release layer forming step, a vacuum deposition step, a release step, and, if necessary, other steps.

[0031] <Release layer formation process> The release layer forming step is a step of providing a release layer on a substrate.

[0032] The substrate is not particularly limited as long as it has a smooth surface, and various types can be used. Among these, resin films, metal foils, and composite films of metal foils and resin films that have flexibility, heat resistance, solvent resistance, and dimensional stability can be appropriately used. Examples of resin films include polyester films, polyethylene films, polypropylene films, polystyrene films, and polyimide films. Examples of metal foils include copper foils, aluminum foils, nickel foils, iron foils, and alloy foils. Examples of composite films of metal foils and resin films include those obtained by laminating the above-mentioned resin films and metal foils.

[0033] The release layer can be made of various organic materials that can be dissolved in the subsequent peeling step. In addition, if the organic material constituting the release layer is appropriately selected, the organic material that is attached and remains on the attachment surface of the island-structure film can function as a protective layer for the indium particles, which is preferable.

[0034] The protective layer has a function of suppressing aggregation, oxidation, elution into a solvent, etc. of indium particles. In particular, by using the organic material used in the release layer as the protective layer, it is preferable because it eliminates the need for a separate surface treatment step.

[0035] Examples of organic materials constituting a release 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 acid copolymers, modified nylon resins, polyvinylpyrrolidone, urethane resins, polyester resins, polyether resins, and alkyd resins. These may be used alone or in combination of two or more. Among these, cellulose acetate butyrate (CAB) is preferred because of its high functionality as a protective layer.

[0036] The method for forming the release layer is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include inkjet method, blade coating method, gravure coating method, gravure offset coating method, bar 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, microgravure 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 may 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 onto the release layer.

[0038] The average deposition thickness of the metal layer containing indium particles is preferably 60 nm or less, more preferably 55 nm or less, even more preferably 50 nm or less, and particularly preferably 45 nm or less, and is the same as the average thickness of the indium particles.

[0039] When the average deposition thickness of the metal layer is 60 nm or less, the surface roughness Ra of the coating film is reduced, which has the advantage of enabling the development of an excellent metallic luster. The average deposition thickness is determined, for example, by observing the cross section of the metal layer using a scanning electron microscope (SEM) and measuring the thickness of the metal layer at 5 to 10 points, and averaging the results.

[0040] The metal layer is preferably an island-structured film. The island-structured film can be formed by various methods, such as vacuum deposition, sputtering, plating, etc. Among these, vacuum deposition is preferred.

[0041] Vacuum deposition is preferable to plating because it can form films on resin substrates and does not produce waste liquid, and is preferable to sputtering because it can achieve a high degree of vacuum and has a high film formation rate (evaporation rate).

[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 peeling step is a step of peeling off the metal layer by dissolving the release layer. The solvent capable of dissolving the release layer is not particularly limited as long as it is a solvent capable of dissolving the release layer, and can be appropriately selected depending on the purpose, but it is preferable that the solvent can be used as it is as a solvent for the glittering coating composition (Y).

[0044] Examples of solvents capable of dissolving the release layer include alcohol-based solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, and propylene glycol; ether-based solvents such as tetrahydrone; ketone-based solvents such as acetone, methyl ethyl ketone, and acetylacetone; ester-based 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 monomethyl ether. Examples of suitable solvents include glycol ether solvents such as ethylene 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; 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, trimesine, nitrobenzene, aniline, methoxybenzene, and trimesine; aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, and dichlorobenzene; sulfur-containing compound solvents such as dimethyl sulfoxide; and nitrogen-containing compound solvents such as dimethylformamide, dimethylacetamide, acetonitrile, propionitrile, and benzonitrile. These may be used alone or in combination of two or more.

[0045] By dissolving the release layer, the island-structure film is peeled off from the substrate, the island structure is split, and each island becomes an indium particle. As a result, an indium particle dispersion liquid can be obtained without a particular pulverization step, but pulverization and classification may be performed as needed. Furthermore, if the primary particles of the indium particles are aggregated, they may be crushed as needed.

[0046] Furthermore, various treatments may be performed as necessary to recover the indium particles or adjust their physical properties. For example, the particle size of the indium particles may be adjusted by classification, or the indium particles may be recovered by methods such as centrifugation or suction filtration, or the solid content concentration of the dispersion may be adjusted. In addition, solvent substitution may be performed, or viscosity adjustment may be performed using an additive.

[0047] <Other processes> Other steps include, for example, a step of extracting the peeled metal layer as a dispersion liquid, and a step of recovering the island-shaped metal layer as indium particles from the dispersion liquid.

[0048] The cumulative 50% volume particle diameter D50 of the indium particles obtained by performing the above-mentioned release layer formation process, vacuum deposition process, peeling process, and further other processes as necessary is preferably 0.70 μm or less, more preferably 0.60 μm or less, even more preferably 0.50 μm or less, and particularly preferably 0.40 μm or less, from the viewpoint of forming a multilayer coating film having excellent metallic luster.

[0049] The indium particles may be commercially available, such as "Leaf Powder 49CJ-1120," "Leaf Powder 49CJ-1150," "Leaf Powder 49BJ-1120," and "Leaf Powder 49BJ-1150" (all manufactured by Oike Kogyo Co., Ltd.).

[0050] When the glittering coating composition (Y) of the present invention contains indium particles as the glittering pigment (y1), the content thereof 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 glittering coating composition (Y), from the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected. The upper limit is preferably 99.9 parts by mass or less, and may be 99 parts by mass or less. It is more preferably within the range of 90 to 99.9 parts by mass, and particularly preferably within the range of 95 to 99.9 parts by mass.

[0051] Examples of the surface conditioner include silicone-based surface conditioners, acrylic-based surface conditioners, vinyl-based surface conditioners, and fluorine-based surface conditioners, and among these, it is preferable to use a fluorine-based surface conditioner from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster that reflects the scenery. The above surface conditioners can be used alone or in appropriate combination of two or more.

[0052] Examples of the fluorine-based surface conditioner include a fluorine-based polymer and a fluorine-based oligomer having a perfluoroalkyl group and a polyalkylene oxide group, and a fluorine-based polymer and a fluorine-based oligomer having a perfluoroalkyl ether group and a polyalkylene oxide group.

[0053] Commercially available examples of the fluorine-based surface conditioner include "LE-604" and "LE-605" (both manufactured by Kyoeisha Chemical Co., Ltd.), "F-444" and "F-554" (both manufactured by DIC Corporation).

[0054] When the glittering coating composition (Y) of the present invention contains a surface conditioner, the content thereof is preferably 0.001 to 1.5 parts by mass, more preferably 0.003 to 1 part by mass, and even more preferably 0.005 to 0.5 parts by mass, based on 100 parts by mass of the solid content of the glittering coating composition (Y), from the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected.

[0055] As the organic solvent, those usually used in paints can be used. Specifically, for example, alcohol-based solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, propylene glycol, etc.; ether-based solvents such as tetrahydron; ketone-based solvents such as acetone, methyl ethyl ketone, acetylacetone, etc.; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, phenyl acetate, etc.; 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 Examples of suitable solvents include glycol ether solvents such as ethylene 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; 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, trimesine, nitrobenzene, aniline, methoxybenzene, and trimesine; aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, and dichlorobenzene; sulfur-containing compound solvents such as dimethyl sulfoxide; and nitrogen-containing compound solvents such as dimethylformamide, dimethylacetamide, acetonitrile, propionitrile, and benzonitrile. These may be used alone or in combination of two or more.

[0056] From the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected, the organic solvent preferably contains at least one solvent selected from glycol ether-based organic solvents and alcohol-based organic solvents, and more preferably contains a glycol ether-based organic solvent.

[0057] When the glittering coating composition (Y) of the present invention contains an organic solvent, the content thereof is preferably within the range of 85 to 99.9 parts by mass, more preferably within the range of 90 to 99.5 parts by mass, and even more preferably within the range of 95 to 99 parts by mass, relative to 100 parts by mass of the total of all components of the glittering coating composition (Y), from the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected.

[0058] Other ingredients The glittering coating composition (Y) may further contain, as necessary, pigments other than the glittering pigment (y1), viscosity adjusters, binder resins, crosslinkable components, pigment dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, and the like.

[0059] Examples of pigments other than the bright pigment (y1) include color pigments and extender pigments. These pigments can be used alone or in combination. Examples of color pigments include titanium oxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, perylene pigments, dioxazine pigments, and diketopyrrolopyrrole pigments. Examples of extender pigments include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white.

[0060] When the glittering coating composition (Y) of the present invention contains a pigment other than the glittering pigment (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 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 glittering coating composition (Y), from the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected.

[0061] Examples of the viscosity modifier include silica-based fine powder, mineral-based viscosity modifier, barium sulfate fine powder, polyamide-based viscosity modifier, organic resin fine particle viscosity modifier, diurea-based viscosity modifier, urethane association-type viscosity modifier, acrylic swelling-type polyacrylic acid-based viscosity modifier, and cellulose-based viscosity modifier.

[0062] Examples of the binder resin include acrylic resin, polyester resin, alkyd resin, and urethane resin.

[0063] Examples of the crosslinkable component include melamine resins, melamine resin derivatives, urea resins, (meth)acrylamides, polyaziridines, polycarbodiimides, and polyisocyanate compounds which may or may not be blocked.

[0064] The application of the glittering coating composition (Y) can be carried out according to a conventional method, such as air spray coating, airless spray coating, rotary atomization coating, etc. When applying the glittering coating composition (Y), electrostatic force may be applied if necessary. Among these, electrostatic coating using a rotary atomization method and electrostatic coating using an air spray method are preferred, and electrostatic coating using a rotary atomization method is particularly preferred.

[0065] Furthermore, when air spray coating, airless spray coating or rotary atomization coating is carried out, the glittering coating composition (Y) is preferably adjusted to a solids content and viscosity suitable for coating by appropriately adding water and / or an organic solvent and, if necessary, additives such as an antifoaming agent.

[0066] The solid content of the glittering coating composition (Y) of the present invention is preferably 0.1 to 15 mass %, more preferably 0.5 to 10 mass %, and even more preferably 1 to 5 mass %, from the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected.

[0067] Furthermore, the viscosity of the glittering coating composition (Y) is preferably within the range of about 8 to 30 seconds, particularly about 10 to 25 seconds, at 20°C as measured with a Ford Cup No. 3 viscometer, from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster in which the scenery is reflected.

[0068] Furthermore, the cured film thickness of the glitter 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, from the viewpoint of obtaining a multi-layer coating film with a highly transparent metallic luster that reflects the scenery.

[0069] Process (2) According to the method for forming a multilayer coating film of the present invention, a color clear coating composition (Z) containing a color pigment (z1) is then applied onto the glossy coating film obtained in step (1), thereby forming a color clear coating film.

[0070] The total light transmittance of the color clear coating film in the wavelength range of 400 nm to 700 nm is within the range of 10 to 60%. When the light transmittance is 10% or more, a multilayer coating film with a highly transparent metallic luster can be obtained, and when it is 60% or less, a multilayer coating film with excellent scenery reflection can be obtained. In particular, the total light transmittance of the color clear coating film in the wavelength range of 400 nm to 700 nm is preferably within the range of 12 to 55%, and more preferably within the range of 15 to 50%, from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster that reflects scenery.

[0071] Here, the total light transmittance of the color clear coating film in the wavelength range of 400 nm to 700 nm can be measured by the following method.

[0072] First, the color clear coating composition (Z) is applied to a polypropylene plate and cured. Next, the cured coating film is peeled off and collected, and the total light transmittance in the wavelength range of 400 nm to 700 nm is measured using a spectrophotometer. In the present invention, "total light transmittance in the wavelength range of 400 nm to 700 nm" means the average value of the total light transmittance in the wavelength range of 400 nm to 700 nm. As the spectrophotometer, for example, "UV-2700" (trade name, manufactured by Shimadzu Corporation) or the like can be used.

[0073] As the color pigment (z1), for example, pigments conventionally known for use in inks, paints, and plastic coloring can be used, and among these, it is preferable to include a black pigment from the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected.

[0074] Examples of the black pigment include composite metal oxide pigments, black iron oxide pigments, black titanium oxide pigments, perylene black pigments, and carbon black pigments. Of these, it is preferable to include carbon black pigments from the viewpoint of obtaining a multilayer coating film having a highly transparent metallic luster in which the scenery is reflected.

[0075] The content of the color pigment (z1) in the color clear paint composition (Z) is adjusted appropriately so that the total light transmittance of the color clear coating film in the wavelength region of 400 nm to 700 nm is within the range of 10 to 60%. Specifically, for example, based on 100 parts by mass of the resin solid content of the color clear paint composition (Z), the content is preferably within the range of 0.01 to 10 parts by mass, more preferably within the range of 0.05 to 5 parts by mass, and even more preferably within the range of 0.1 to 3 parts by mass.

[0076] When the color clear coating composition (Z) contains a black pigment as the color pigment (z1), the content thereof is preferably in the range of 0.15 to 0.9 parts by mass, more preferably in the range of 0.2 to 0.8 parts by mass, and even more preferably in the range of 0.3 to 0.7 parts by mass, based on 100 parts by mass of the resin solids content of the color clear coating composition (Z), from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster in which the scenery is reflected.

[0077] Furthermore, when the color clear coating composition (Z) contains a black pigment as the color pigment (z1), the content ratio is preferably within the range of 50 to 100 mass%, more preferably within the range of 70 to 100 mass%, and even more preferably within the range of 90 to 100 mass%, based on the total solid content of the color pigment (z1), from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster in which the scenery is reflected.

[0078] Any known thermosetting coating composition can be used as the color clear coating composition (Z), including, for example, an organic solvent-based thermosetting coating composition containing a base resin having a crosslinkable functional group and a curing agent, an aqueous thermosetting coating composition, and a powder thermosetting coating composition.

[0079] Examples of crosslinkable functional groups possessed by the base resin include carboxyl groups, hydroxyl groups, epoxy groups, silanol groups, etc. Types of base resins include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, fluororesins, etc. Examples of curing agents include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

[0080] Preferred combinations of base resin / curing agent for the color clear coating composition (Z) include carboxyl group-containing resin / epoxy group-containing resin, hydroxyl group-containing resin / polyisocyanate compound, hydroxyl group-containing resin / blocked polyisocyanate compound, and hydroxyl group-containing resin / melamine resin.

[0081] The color clear coating composition (Z) may be a one-component coating, or may be a multi-component coating such as a two-component coating.

[0082] Of these, the color clear coating composition (Z) is preferably a two-component clear coating containing the following hydroxyl group-containing resin (z1) and polyisocyanate compound (z2) from the viewpoint of adhesion of the resulting coating film.

[0083] Hydroxyl group-containing resin (z1) The hydroxyl-containing resin (z1) is a resin having at least one hydroxyl group per molecule. Examples of the hydroxyl-containing resin (z1) include hydroxyl-containing resins such as acrylic resins, polyester resins, polyurethane resins, polyolefin resins, polyether resins, polycarbonate resins, epoxy resins, and alkyd resins. These resins can be used alone or in combination of two or more.

[0084] As the hydroxyl group-containing resin (z1), it is preferable to use a hydroxyl group-containing acrylic resin (z11) from the viewpoint of the adhesion of the multi-layer coating film to be formed.

[0085] Hydroxyl-containing acrylic resin (z11) The hydroxyl group-containing acrylic resin (z11) can be produced, for example, by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer by a method known per se, such as a solution polymerization method in an organic solvent or an emulsion polymerization method in water.

[0086] The hydroxyl group-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds per molecule. Examples of the hydroxyl group-containing polymerizable unsaturated monomer include monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid with dihydric alcohols 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 terminal. However, in the present invention, a monomer corresponding to the polymerizable unsaturated monomer having an ultraviolet-absorbing functional group (xvii) described below should be defined as another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, and is excluded from the hydroxyl group-containing polymerizable unsaturated monomer. The hydroxyl group-containing polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0087] As other polymerizable unsaturated monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomers, for example, the following monomers (i) to (xx) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more. (i) Alkyl or cycloalkyl (meth)acrylates: for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and the like. (ii) Polymerizable unsaturated monomers having an isobornyl group: isobornyl (meth)acrylate, etc. (iii) Polymerizable unsaturated monomers having an adamantyl group: adamantyl (meth)acrylate, etc. (iv) Polymerizable unsaturated monomers having a tricyclodecenyl group: tricyclodecenyl (meth)acrylate, etc. (v) Aromatic ring-containing polymerizable unsaturated monomers: benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, and the like. (vi) Polymerizable unsaturated monomers having an alkoxysilyl group: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, etc. (vii) Polymerizable unsaturated monomers having a fluorinated alkyl group: perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; fluoroolefins, and the like. (viii) Polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group. (ix) Vinyl compounds: N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, etc. (x) Carboxyl group-containing polymerizable unsaturated monomers: (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl (meth)acrylate, etc. (xi) Nitrogen-containing polymerizable unsaturated monomers: (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, methylenebis(meth)acrylamide, ethylenebis(meth)acrylamide, adducts of glycidyl (meth)acrylate with amine compounds, and the like. (xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, etc. (xiii) Epoxy group-containing polymerizable unsaturated monomers: glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, etc. (xiv) (meth)acrylates having a polyoxyethylene chain with an alkoxy group at the molecular terminal. (xv) Polymerizable unsaturated monomers having a sulfonic acid group: 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allylsulfonic acid, 4-styrenesulfonic acid, etc.; sodium salts and ammonium salts of these sulfonic acids, etc. (xvi) Polymerizable unsaturated monomers having a phosphoric acid group: acid phosphooxyethyl (meth)acrylate, acid phosphooxypropyl (meth)acrylate, acid phosphooxypoly(oxyethylene)glycol (meth)acrylate, acid phosphooxypoly(oxypropylene)glycol (meth)acrylate, etc. (xvii) Polymerizable unsaturated monomers having an ultraviolet-absorbing functional group: 2-hydroxy-4(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, and the like. (xviii) Light-stable polymerizable unsaturated monomers: 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, etc. (xix) Polymerizable unsaturated monomers having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), etc. (xx) Polymerizable unsaturated monomers having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride, etc.

[0088] In this specification, the term "polymerizable unsaturated group" refers to an unsaturated group that can undergo radical polymerization. Examples of such polymerizable unsaturated groups include vinyl groups and (meth)acryloyl groups.

[0089] 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.

[0090] In the production of the hydroxyl group-containing acrylic resin (z11), the amount of the hydroxyl group-containing polymerizable unsaturated monomer used is preferably within the range of 15 to 50 mass %, and more preferably 20 to 40 mass %, based on the total amount of copolymerizable monomer components, from the viewpoints of adhesion, chipping resistance, finished appearance, etc. of the multilayer coating film to be formed.

[0091] The hydroxyl value of the hydroxyl-containing acrylic resin (z11) is preferably within the range of 50 to 210 mgKOH / g, particularly 80 to 200 mgKOH / g, and more particularly 100 to 170 mgKOH / g, from the viewpoints of adhesion, chipping resistance, and finished appearance of the multilayer coating film to be formed.

[0092] The weight average molecular weight of the hydroxyl group-containing acrylic resin (z11) is preferably within the range of 2,000 to 50,000, particularly 3,000 to 30,000, and even more particularly 4,000 to 10,000, from the viewpoints of adhesion, chipping resistance, and finished appearance of the multilayer coating film to be formed.

[0093] The acid value of the hydroxyl group-containing acrylic resin (z11) is preferably 30 mgKOH / g or less, particularly in the range of 1 to 20 mgKOH / g, from the viewpoints of the finished appearance of the multilayer coating film formed, adhesion, and the pot life of the color clear coating composition (Z).

[0094] The glass transition temperature of the hydroxyl group-containing acrylic resin (z11) is preferably within the range of -50 to 60°C, particularly 10 to 50°C, and more particularly 20 to 45°C, from the viewpoints of adhesion, chipping resistance, and finished appearance of the multilayer coating film to be formed.

[0095] In this specification, the glass transition temperature (°C) of the acrylic resin was calculated by the following formula.

[0096] 1 / Tg(K)=(W1 / T1)+(W2 / T2)+ (1) Tg(℃)=Tg(K)-273 (2) In each formula, W1, W2, and... represent the mass fractions of the monomers used in the copolymerization, and T1, T2, and... represent the Tg (K) of the homopolymer of each monomer. Note that T1, T2, and... are values ​​taken from Polymer Handbook (Second Edition, edited by J. Brandup and E. H. Immergut) pp. 139-179. When the Tg of the homopolymer of a monomer is unclear, the glass transition temperature (°C) is taken as the static glass transition temperature. For example, using a differential scanning calorimeter "DSC-220U" (Seiko Instruments Inc.), a sample is placed in a measuring cup, and the solvent is completely removed by vacuum suction. Then, the heat change is measured in the range of -20°C to +200°C at a heating rate of 3°C / min. The first change point in the baseline on the low-temperature side is taken as the static glass transition temperature.

[0097] As a copolymerization method for obtaining the hydroxyl group-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.

[0098] Examples of organic solvents used in the solution polymerization method include alcohol-based solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, and propylene glycol; ether-based solvents such as tetrahydrone; ketone-based solvents such as acetone, methyl ethyl ketone, and acetylacetone; ester-based 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, and diethylene glycol monomethyl ether. Examples of suitable solvents include glycol ether solvents such as ethylene 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; 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, trimesine, nitrobenzene, aniline, methoxybenzene, and trimesine; and aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, and dichlorobenzene.

[0099] Examples of the polymerization initiator that can be used in copolymerizing the hydroxyl group-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).

[0100] The above hydroxyl group-containing acrylic resins (z11) can be used alone or in combination of two or more kinds.

[0101] From the viewpoint of the water resistance and finished appearance of the coating film formed, the content of the hydroxyl group-containing acrylic resin (z11) in the color clear coating composition (Z) is preferably within a range of 20 to 80 parts by mass, more preferably 25 to 75 parts by mass, and even more preferably 30 to 70 parts by mass, based on 100 parts by mass of the resin solid content of the color clear coating composition (Z).

[0102] 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, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of the polyisocyanates.

[0103] 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, methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate), aliphatic diisocyanates such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0104] 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, Alicyclic diisocyanates such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), and norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2-isocyanatopropyl ,5-Di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-bicyclo(2.2.1)heptane Examples of such alicyclic triisocyanates include alicyclic triisocyanates such as 2-isocyanatoethyl-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.

[0105] Examples of the araliphatic polyisocyanate include araliphatic diisocyanates such as methylenebis(4,1-phenylene)diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof; and araliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0106] 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.

[0107] Furthermore, examples of the derivatives of the polyisocyanates include dimers, trimers, biurets, allophanates, uretdione, uretoimine, isocyanurates, oxadiazinetrione, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), and crude TDI of the above-mentioned polyisocyanates.

[0108] The above polyisocyanates and derivatives thereof may be used alone or in combination of two or more kinds.

[0109] Among aliphatic diisocyanates, hexamethylene diisocyanate compounds and among alicyclic diisocyanates, 4,4'-methylenebis(cyclohexyl isocyanate) can be preferably used. Among these, derivatives of hexamethylene diisocyanate are particularly suitable from the viewpoints of adhesion, compatibility, etc.

[0110] The polyisocyanate compound (z2) may be a prepolymer obtained by reacting the polyisocyanate or a derivative thereof with a compound having an active hydrogen group, such as a hydroxyl group or an amino group, which is reactive with the polyisocyanate under conditions of an excess of isocyanate groups. Examples of the compound reactive with the polyisocyanate include polyhydric alcohols, low-molecular-weight polyester resins, amines, and water.

[0111] Furthermore, as the polyisocyanate compound (z2), a blocked polyisocyanate compound, which is a compound in which the isocyanate group in the above polyisocyanates and derivatives thereof is blocked with a blocking agent, can also be used.

[0112] Examples of the blocking agent include phenol-based agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam-based agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohol-based agents such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ether-based agents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl ... Alcohol-based compounds such as methyloxyethyl methacrylate; oxime-based compounds such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, and methylthiophenol mercaptans such as ethylthiophenol; acid amides such as acetanilide, acetanisidide, acetotoluide, acrylamide, methacrylamide, acetic amide, stearic acid amide, and benzamide; imides such as succinimide, phthalic acid imide, and maleic acid imide; amines such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole;Examples of suitable azole compounds include urea-based compounds such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamate ester-based compounds such as N-phenylphenylcarbamate; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; and azole-based compounds. Examples of suitable azole-based 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.

[0113] When blocking (reacting with a blocking agent), a solvent may be added as needed.

[0114] The polyisocyanate compounds (z2) can be used either alone or in combination of two or more.

[0115] In the color clear coating composition (Z), the equivalent ratio (NCO / OH) of the hydroxyl groups of the hydroxyl-containing resin (z1) to the isocyanate groups of the polyisocyanate compound (z2) is preferably within the range of 0.5 to 2.0, more preferably 0.8 to 1.5.

[0116] The color clear coating composition (Z) may contain, as needed, water, solvents such as organic solvents, curing catalysts, antifoaming agents, ultraviolet absorbers, rheology control agents, anti-settling agents and other coating additives.

[0117] The color clear coating composition (Z) can be applied by methods such as electrostatic coating, air spraying, and airless spraying, and the thickness of the clear coating film is about 10 to 60 μm, more preferably about 15 to 50 μm, and even more preferably about 20 to 40 μm, based on the cured coating film.

[0118] The solid content of the color clear coating composition (Z) is within the range of 10 to 65% by mass, preferably 15 to 55% by mass, and more preferably 20 to 50% by mass. It is also preferable to appropriately adjust the viscosity of the clear coating composition (Z) using water and / or an organic solvent so that it is within a range suitable for coating, typically within the range of about 15 to 60 seconds, particularly about 20 to 50 seconds, at 20°C using a Ford Cup No. 4 viscometer.

[0119] Process (3) According to the method for forming a multilayer coating film of the present invention, the glossy coating film and the clear coating film formed in the steps (1) and (2) are then cured by heating separately or simultaneously.

[0120] Heating can be performed by, for example, hot air heating, infrared heating, high-frequency heating, etc. The heating temperature is preferably 80 to 160°C, more preferably 100 to 140°C. The heating time is preferably 10 to 60 minutes, more preferably 15 to 40 minutes. If necessary, before the heat curing, the composition may be directly or indirectly heated by preheating, air blowing, etc. at a temperature of about 50 to about 110°C, preferably about 60 to about 90°C, for about 1 to 60 minutes.

[0121] Multi-layer coating formation According to the method of the present invention, the following steps (1) to (3): Step (1): A step of applying a glitter coating composition (Y) containing a glitter pigment (y1) onto a substrate to form a glitter coating film; Step (2): A step of applying a color clear coating composition (Z) containing a color pigment (z1) onto the glossy coating film obtained in Step (1) to form a color clear coating film; Step (3): A step of curing the glossy coating film and the color clear coating film formed in steps (1) and (2) by heating them separately or simultaneously to form a multi-layer coating film; The total light transmittance of the color clear coating film in the wavelength range of 400 nm to 700 nm is within the range of 10 to 60%, The multi-layer coating film formed is The 20-degree specular gloss is 90 or more, and 20 degree specular gloss, L * a * b * Lightness L in the color system * (45°) 20° specular gloss / brightness L * By setting the angle (45°) to 4 or more, it is possible to form a multi-layer coating film with a highly transparent metallic luster that reflects the scenery.

[0122] When the 20-degree specular gloss of the multilayer coating film formed is 90 or more, the multilayer coating film has excellent metallic gloss, and in particular, the 20-degree specular gloss of the multilayer coating film is preferably 91 or more, more preferably 92 or more, and particularly preferably 100 or more.

[0123] In addition, the L of the multi-layer coating film formed * a * b * Lightness L in the color system * (45°) is preferably 18 or less, and more preferably 15 or less, from the viewpoint of forming a multi-layer coating film that has a highly transparent metallic luster that reflects the scenery and exudes a sense of luxury.

[0124] where L * a * b * Lightness L in the color system * (45°) is the brightness L measured when the measurement light is irradiated at an angle of 45° to the axis perpendicular to the measurement surface and received at an angle of 45° from the specular reflection angle to the direction of the measurement light. *and is defined as a value of brightness calculated from spectral reflectance using a multi-angle spectrophotometer (manufactured by X-rite, product name "MA-68II").

[0125] The 20-degree specular gloss of the multi-layer coating film formed is L * a * b * Lightness L in the color system * (45°) 20° specular gloss / brightness L * (45°) is 4 or more, it becomes a multi-layer coating film with high transparency, so that the scenery is reflected, and in particular, the 20 degree specular gloss / brightness L * (45°) is preferably 10 or more, and more preferably 15 or more. [Example]

[0126] 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. Note that "parts" and "%" are all based on mass.

[0127] [1] Preparation of substrate A degreased and zinc phosphate-treated steel plate (JIS G3141, size 400 mm x 300 mm x 0.8 mm) was electrodeposited with the cationic electrodeposition paint "Elecron GT-10" (product name: manufactured by Kansai Paint Co., Ltd., an epoxy resin polyamine-based cationic resin using a blocked polyisocyanate compound as a curing agent) to a film thickness of 20 μm based on the cured coating, and heated at 170°C for 20 minutes to crosslink and cure, forming an electrodeposition coating.

[0128] On the electrodeposited surface of the steel plate obtained, "TP-65-2" (trade name, manufactured by Kansai Paint Co., Ltd., polyester resin and amino resin organic solvent-based intermediate coating composition) was electrostatically coated using a rotary atomizing electrostatic coater to a cured film thickness of 35 μm, and the coating was cured by heating at 140°C for 30 minutes to form an intermediate coating film, thereby preparing the coated object.

[0129] [2] Preparation of paint Manufacture of bright coating composition (Y) Manufacturing Example 1 To a stirring and mixing vessel was added 100 parts (solids content 20 parts) of "Leaf Powder 49CJ-1120" (trade name, manufactured by Oike Kogyo Co., Ltd., indium particles, solids content 20%, dispersed in propylene glycol monomethyl ether), 0.28 parts (solids content 0.08 parts) of "LE-605" (trade name, manufactured by Kyoeisha Chemical Co., Ltd., fluorine-based surface conditioner, solids content 30%), and 1,610 parts of propylene glycol monomethyl ether, and the mixture was stirred and mixed to produce a lustrous coating composition (Y-1) with a solids content of 1.2% by mass.

[0130] Manufacturing Examples 2 to 5 Glittering coating compositions (Y-2) to (Y-5) were obtained in the same manner as in Production Example 1, except that the formulations and solid contents shown in Table 1 were used.

[0131] [Table 1]

[0132] Manufacture of color clear paint composition (Z) Manufacturing Example 6 "EMPEROR 3000" (product name, special carbon black manufactured by CABOT) was added to "KINO-6510" (product name, manufactured by Kansai Paint Co., Ltd., a two-component organic solvent-based paint based on hydroxyl group / isocyanate group curing acrylic resin and urethane resin), and the content of "EMPEROR 3000" was adjusted to 0.2 parts by mass based on 100 parts by mass of resin solids, and the mixture was stirred to produce color clear paint composition (Z-1).

[0133] Manufacturing Examples 7-12 Color clear coating compositions (Z-2) to (Z-7) were obtained in the same manner as in Production Example 6, except that the content of "EMPEROR 3000" was as shown in Table 2 below.

[0134] Evaluation of color clear coatings Using the color clear coating compositions (Z-1) to (Z-7) obtained above, free films of the color clear coating were evaluated using a "UV-2700" (trade name, manufactured by Shimadzu Corporation) to determine total light transmittance in the wavelength range of 400 nm to 700 nm. Free films of the color clear coating were prepared by applying one of the color clear coating compositions (Z-1) to (Z-7) to a polypropylene plate using a mini-bell-type rotary electrostatic applicator at a booth temperature of 23°C and humidity of 68% to a film thickness of 40 μm. The free films were then left at room temperature for 7 minutes, heated at 140°C for 30 minutes in a hot air circulating drying oven, and then peeled off. The evaluation results are also shown in Table 2.

[0135] [Table 2]

[0136] [3] Creating a test panel Creating test panels Example 1 The glossy coating composition (Y-1) produced in [2] above was applied onto the substrate prepared in [1] above using a mini-bell type rotary electrostatic coating machine under conditions of a booth temperature of 23°C and humidity of 63% so as to give a cured coating film with a thickness of 0.05 μm. After leaving it at room temperature for 15 minutes, it was heated in a hot air circulation drying oven at 140°C for 30 minutes to dry and cure, thereby obtaining a glossy coating film.

[0137] Next, the color clear coating composition (Z-3) prepared in [2] above was applied onto the glossy coating film using a mini-bell type rotary electrostatic coating machine at a booth temperature of 23°C and humidity of 68% so that the cured coating film would be 40 μm thick. After leaving it at room temperature for 7 minutes, it was heated in a hot air circulation drying oven at 140°C for 30 minutes to dry and cure, and the test panel of Example 1 was prepared.

[0138] Here, the thickness of the dry coating film of the glitter coating film was calculated from the following formula: The same applies to the following examples. x=sc / sg / S*10000 x: Film thickness [μm] sc: Painted solid content [g] sg: Paint film specific gravity [g / cm 3 ] S: Evaluation area of ​​coating solids [cm 2 ] Examples 2 to 4, 6 to 11, and Comparative Examples 1 and 2 Test panels were obtained in the same manner as in Example 1, except that the paints and film thicknesses shown in Table 3 were used.

[0139] Example 5 The glossy coating composition (Y-2) produced in [2] above was applied to the substrate prepared in [1] above using a mini-bell type rotary electrostatic coating machine at a booth temperature of 23°C and humidity of 63% so as to give a cured coating film with a thickness of 0.1 μm. The coating was then left at room temperature for 15 minutes, and then preheated in a hot air circulation drying oven at 80°C for 3 minutes to give an uncured glossy coating film.

[0140] Next, the color clear coating composition (Z-3) prepared in [2] above was applied onto the uncured glossy coating film using a mini-bell type rotary electrostatic coating machine at a booth temperature of 23°C and humidity of 68% so that the cured coating film would be 35 μm thick. After leaving it at room temperature for 7 minutes, it was heated in a hot air circulation drying oven at 140°C for 30 minutes, and the glossy coating film and clear coating film were simultaneously dried and cured to produce the test panel of Example 5.

[0141] Coating evaluation The coating film of each test plate obtained as described above was evaluated by the following method, and the results are shown in Table 3.

[0142] 20° specular gloss: The 20° gloss value was measured using a gloss meter (micro-TRI-gloss, manufactured by BYK-Gardner).

[0143] L * a * b * Lightness L in the color system * (45°): "MA-68II" (product name, manufactured by X-Rite) is used. * a * b *Lightness L in the color system * (45°) was measured.

[0144] 20 degree specular gloss / brightness L * (45°): 20° specular gloss, L * a * b * Lightness L in the color system * The calculation was made by dividing by (45°).

[0145] [Table 3]

[0146] [Table 4]

[0147] Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical concept of the present invention are possible.

[0148] For example, the configurations, methods, processes, shapes, materials, and numerical values ​​given in the above-described embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values ​​may be used as necessary.

[0149] Furthermore, the configurations, methods, steps, shapes, materials, and numerical values ​​of the above-described embodiments can be combined with one another without departing from the spirit of the present invention.

Claims

1. The following steps (1) to (3): Step (1): A step of applying a glitter coating composition (Y) containing a glitter pigment (y1) onto a substrate to form a glitter coating film; Step (2): A step of applying a color clear coating composition (Z) containing a color pigment (z1) onto the glossy coating film obtained in step (1) to form a color clear coating film; Step (3): A method for forming a multilayer coating film, comprising a step of heating the glossy coating film and the color clear coating film formed in steps (1) and (2) separately or simultaneously to cure them, the total light transmittance of the color clear coating film in the wavelength region of 400 nm to 700 nm is within the range of 10 to 60%, The multi-layer coating film formed is The 20-degree specular gloss is 90 or more, and The 20-degree specular gloss is ＊ a ＊ b ＊ Lightness L in the color system ＊ (45 °), which is the value obtained by dividing the 20-degree specular gloss / brightness L ＊ (45°) is 4 or more.

2. 2. The method for forming a multilayer coating film according to claim 1, wherein the bright pigment (y1) contains indium particles.

3. The method for forming a multilayer coating film according to claim 1 or 2, wherein the color pigment (z1) includes a black pigment.

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