JP7757232B2 - Multi-layer coating film formation method - Google Patents

Description

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

The primary purpose of applying paint is to protect the material and add a beautiful appearance. For industrial products, aesthetics, especially texture, are important in enhancing their appeal. Consumers desire a wide variety of textures for industrial products, but in recent years, a metallic sheen has become popular in areas such as automobile exterior panels, automobile parts, and home appliances (hereafter referred to as "metallic sheen").

Metallic luster is a texture that has no granular surface like a mirror, and is characterized by a large difference in brightness between the highlight and shade areas; when viewed nearly perpendicular to the painted surface (highlights), it appears shiny, and when viewed diagonally from above (shades), it appears dark.

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.

Technologies 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 a metallic luster could be imparted by painting, it would be advantageous from the standpoints of simplicity and cost.

Patent Document 2 describes how 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 resin in the metallic paint base.

However, the exterior created by the above metallic paint lacked metallic luster and did not have the effect of reflecting the scenery.

Japanese Unexamined Patent Publication No. 63-272544 Japanese Patent Application Laid-Open No. 2003-313500

The objective of the present invention is to provide a method for forming a multi-layer coating film that can produce a multi-layer coating film with a highly transparent metallic luster that reflects the scenery.

The present invention encompasses the subject matter described in the following sections.

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 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
A method for ^forming a multilayer coating film, in which the 20-degree specular gloss/lightness L ^* (45° ⁾ , which is the value obtained by dividing the 20-degree specular gloss by the lightness L ^* (45° ⁾ in the L*a*b* color system, is 4 or more.

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

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.

The multilayer coating film forming method of the present invention makes it possible to form a multilayer coating film with a highly transparent metallic luster that reflects the scenery.

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 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
This is a method for ^forming a ^multilayer coating film in which the 20-degree specular gloss/lightness L ^* (45° ⁾ , which is the value obtained by dividing the 20-degree specular gloss by the lightness L ^* (45°) in the L*a*b* color system, is 4 or more.

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.

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.

The materials of these substrates are 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. Of these, metal materials and plastic materials are preferred.

In addition, the surfaces of the objects to which the multi-layer coating film is applied may include metal surfaces such as the outer panels of automobile bodies, automobile parts, household electrical appliances, and the metal substrates such as the steel plates that make up these items, which have been subjected to surface treatments such as phosphate treatment, chromate treatment, and composite oxide treatment.

A coating film may be further formed on an object, which may or may not have been surface-treated. For example, the substrate to be coated may be surface-treated as needed, and then a primer coating film and/or intermediate coating film may be formed on top of that. For example, if the substrate 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.

The primer coating composition for forming the primer coating film can be, for example, an electrodeposition coating, preferably a cationic electrodeposition coating. The intermediate coating composition for forming the intermediate coating film can be a paint made from a base resin such as an acrylic resin, polyester resin, alkyd resin, urethane resin, or epoxy resin having a crosslinkable functional group such as a carboxyl group or a hydroxyl group, an amino resin such as a melamine resin or a urea resin, or a crosslinker such as an optionally blocked polyisocyanate compound, together with a pigment, a thickener, and other optional components.

Glitter paint composition (Y)
The glittering coating composition (Y) contains a glittering pigment (y1).

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

Examples of the luster 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 selected and used as appropriate.

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

In the present invention, flaky particles refer to particles that have a substantially flat surface and a substantially uniform thickness in the direction perpendicular to the substantially flat surface. Furthermore, the flaky particles refer to particles that are very thin and have a very long substantially flat surface. The length of the substantially flat surface is the diameter of a circle that has the same projected area as the projected area of the flaky particle.

The shape of the substantially flat surface is not particularly limited and can be selected appropriately depending on the purpose. Examples 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, as well as random, indeterminate shapes. Of these, a substantially circular shape is preferable.

The indium particles may be a single layer, or may be a primary particle formed by stacking two or more layers. Furthermore, the primary particles of indium particles may aggregate to form secondary particles.

Note that 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.

The above-mentioned indium particles can be produced by performing a release layer formation process, a vacuum deposition process, a release process, and other processes as necessary.

<Release layer forming step>
The release layer forming step is a step of providing a release layer on a substrate.

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

The release layer can be made from various organic materials that are dissolvable in the subsequent release process. Furthermore, by appropriately selecting the organic material that makes up the release layer, the organic material that adheres to and remains on the adhesion surface of the island-structure film can function as a protective layer for the indium particles, which is advantageous.

The protective layer has the function of suppressing aggregation, oxidation, and elution of indium particles into the solvent. It is particularly preferable to use the organic material used in the release layer as the protective layer, as this eliminates the need for a separate surface treatment process.

Examples of organic materials that can be used as a protective layer to form a release 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 due to its high functionality as a protective layer.

The method for forming the release layer is not particularly limited and can be selected appropriately depending on the purpose. Examples include inkjet coating, blade coating, gravure coating, gravure offset coating, bar coating, roll coating, knife coating, air knife coating, comma coating, U comma coating, AKKU coating, smoothing coating, microgravure coating, reverse roll coating, four-roll coating, five-roll coating, dip coating, curtain coating, slide coating, and die coating. These methods may be used alone or in combination of two or more.

<Vacuum deposition process>
The vacuum deposition step is a step of vacuum-depositing a metal layer containing indium particles onto the release layer.

The average vapor 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. The average vapor deposition thickness of the metal layer containing indium particles is the same as the average thickness of the indium particles.

When the average vapor deposition thickness of the metal layer is 60 nm or less, the surface roughness (Ra) of the coating film is reduced, resulting in the advantageous effect of achieving an excellent metallic luster. The average vapor 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 locations, and then averaging the measurements.

The metal layer is preferably an island-structured film. Island-structured films can be formed by various methods, such as vacuum deposition, sputtering, and plating. Among these, vacuum deposition is preferred.

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 allows for a high degree of vacuum and has a high film formation speed (evaporation rate).

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.

<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 it can be used as a solvent for the bright coating composition (Y) as it is.

Examples of solvents that can dissolve 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.

By dissolving the release layer, the island structure film peels off from the substrate, and the island structure breaks up, with each island becoming an indium particle. This allows an indium particle dispersion to be obtained without any special grinding process, but grinding and classification may be carried out as needed. Furthermore, if the primary particles of the indium particles are agglomerated, they may be crushed as needed.

Furthermore, if necessary, various processes may be performed 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 solids concentration of the dispersion may be adjusted. Furthermore, solvent substitution may be performed, or viscosity may be adjusted using additives.

<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.

From the viewpoint of forming a multilayer coating film with excellent metallic luster, the cumulative 50% volume particle diameter D50 of the indium particles obtained by performing the above-mentioned release layer formation process, vacuum deposition process, release 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.

Commercially available indium particles can be used. Examples of such products include "Leaf Powder 49CJ-1120," "Leaf Powder 49CJ-1150," "Leaf Powder 49BJ-1120," and "Leaf Powder 49BJ-1150" (all manufactured by Oike Kogyo Co., Ltd.).

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 solids content of the glittering coating composition (Y), from the viewpoint of obtaining a multilayer coating film with 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. A content within the range of 90 to 99.9 parts by mass is more preferable, and a content within the range of 95 to 99.9 parts by mass is particularly preferable.

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

Examples of the fluorine-based surface conditioner include fluorine-based polymers and fluorine-based oligomers having a perfluoroalkyl group and a polyalkylene oxide group, and fluorine-based polymers and fluorine-based oligomers having a perfluoroalkyl ether group and a polyalkylene oxide group.

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

When the glitter 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 solids content of the glitter coating composition (Y), from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster that reflects the scenery.

The organic solvent can be one that is commonly used in paints. Specific examples include alcohol-based solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, and propylene glycol; ether-based solvents such as tetrahydron; 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.

From the perspective of obtaining a multi-layer coating film with a highly transparent metallic luster that reflects the scenery, 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.

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, per 100 parts by mass of all components of the glittering coating composition (Y), from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster in which the scenery is reflected.

Other Components 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.

Pigments other than the above-mentioned luster pigment (y1) include color pigments and extender pigments. These pigments can be used alone or in combination of two or more. 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.

When the glittering coating composition (Y) of the present invention contains a pigment other than the glittering pigment (y1), the content of the pigment other than the glittering pigment (y1) is preferably within the range of 0.01 to 30 parts by mass, more preferably within the range of 0.05 to 20 parts by mass, and even more preferably within the range of 0.1 to 15 parts by mass, based on 100 parts by mass of the solids content of the glittering coating composition (Y), from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster in which the scenery is reflected.

Examples of viscosity modifiers include silica-based fine powders, mineral-based viscosity modifiers, finely divided barium sulfate powder, polyamide-based viscosity modifiers, organic resin fine particle viscosity modifiers, diurea-based viscosity modifiers, urethane association-type viscosity modifiers, acrylic swelling-type polyacrylic acid-based viscosity modifiers, and cellulose-based viscosity modifiers.

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

Examples of the crosslinkable component include melamine resin, melamine resin derivatives, urea resin, (meth)acrylamide, polyaziridine, polycarbodiimide, and polyisocyanate compounds that may or may not be blocked.

The application of the glitter coating composition (Y) can be carried out according to conventional methods, such as air spray coating, airless spray coating, and rotary atomization coating. When applying the glitter coating composition (Y), electrostatic force may be applied if necessary. Of these, electrostatic coating using a rotary atomization method and electrostatic coating using an air spray method are preferred, with electrostatic coating using a rotary atomization method being particularly preferred.

Furthermore, when air spray coating, airless spray coating, or rotary atomization coating is used, it is preferable that the glitter coating composition (Y) contains water and/or an organic solvent, and if necessary, additives such as an antifoaming agent, to be appropriately adjusted to a solids content and viscosity suitable for coating.

From the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster that reflects the scenery, the solids content of the glittering coating composition (Y) of the present invention is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass.

Furthermore, from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster that reflects the scenery, the viscosity of the glitter coating composition (Y) is preferably within the range of approximately 8 to 30 seconds, particularly approximately 10 to 25 seconds, at 20°C as measured using a Ford Cup No. 3 viscometer.

The cured film thickness of the glossy coating 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.

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.

The total light transmittance of the above-mentioned color clear coating film in the wavelength range of 400 nm to 700 nm is within the range of 10 to 60%. A light transmittance of 10% or more makes it possible to obtain a multilayer coating film with a highly transparent metallic luster, while a light transmittance of 60% or less makes it possible to obtain a multilayer coating film that excels in reflecting scenery. 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 even 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 allows scenery to be reflected.

Here, the total light transmittance of the above-mentioned color clear coating film in the wavelength range of 400 nm to 700 nm can be measured using the following method.

First, 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" refers to the average value of the total light transmittance in the wavelength range of 400 nm to 700 nm. For example, the "UV-2700" (trade name, manufactured by Shimadzu Corporation) can be used as the spectrophotometer.

The color pigment (z1) can be, for example, a pigment conventionally known for use in inks, paints, and plastic coloring. Among these, it is preferable to use a black pigment, from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster that reflects the scenery.

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, as this will result in a multilayer coating film with a highly transparent metallic luster that reflects the scenery.

The content of color pigment (z1) in color clear paint composition (Z) is adjusted appropriately so that 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%. Specifically, for example, based on 100 parts by mass of the resin solids content of 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.

When the color clear paint composition (Z) contains a black pigment as the color pigment (z1), the content is preferably within the range of 0.15 to 0.9 parts by mass, more preferably within the range of 0.2 to 0.8 parts by mass, and even more preferably within 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 paint composition (Z), from the viewpoint of obtaining a multilayer coating film with a highly transparent metallic luster in which the scenery is reflected.

Furthermore, when the color clear paint composition (Z) contains a black pigment as the color pigment (z1), the content 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 that reflects the scenery.

Any known thermosetting coating composition can be used as the color clear coating composition (Z). Examples of such thermosetting coating compositions include organic solvent-based thermosetting coating compositions containing a base resin with crosslinkable functional groups and a curing agent, water-based thermosetting coating compositions, and powder thermosetting coating compositions.

Examples of crosslinkable functional groups possessed by the base resin include carboxyl groups, hydroxyl groups, epoxy groups, and silanol groups. Examples of types of base resins include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, and fluororesins. 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.

Preferred combinations of base resin and curing agent for 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.

Furthermore, the above-mentioned color clear paint composition (Z) may be a one-component paint or a multi-component paint such as a two-component paint.

Among these, a preferred color clear paint composition (Z) is a two-component clear paint containing the following hydroxyl group-containing resin (z1) and polyisocyanate compound (z2), from the viewpoint of the adhesion of the resulting paint film.

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 may be used alone or in combination of two or more.

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

Hydroxyl group-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.

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 terminated in a hydroxyl group. However, in the present invention, monomers corresponding to the polymerizable unsaturated monomer having an ultraviolet-absorbing functional group (xvii) described below should be defined as other polymerizable unsaturated monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer, and are excluded from the hydroxyl group-containing polymerizable unsaturated monomer. The above-mentioned hydroxyl group-containing polymerizable unsaturated monomers can be used alone or in combination of two or more types.

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, etc.
(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 and amine compounds, and the like.
(xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, etc.
(xiii) Epoxy group-containing polymerizable unsaturated monomers: glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, and the like.
(xiv) (meth)acrylates having a polyoxyethylene chain with an alkoxy group at the molecular terminal.
(xv) Polymerizable unsaturated monomers having a sulfonic acid group: 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allylsulfonic acid, 4-styrenesulfonic acid, 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, etc.
(xviii) Light-stable polymerizable unsaturated monomers: 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, and the like.
(xix) Polymerizable unsaturated monomers having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), and the like.
(xx) Polymerizable unsaturated monomers having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride, etc.

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

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

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

From the viewpoint of the adhesion, chipping resistance, and finished appearance of the multilayer coating film formed, 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 even more particularly 100 to 170 mgKOH/g.

Furthermore, from the viewpoints of the adhesion, chipping resistance, and finished appearance of the multilayer coating film formed, 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.

Furthermore, 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), the acid value of the hydroxyl group-containing acrylic resin (z11) is preferably 30 mgKOH/g or less, particularly within the range of 1 to 20 mgKOH/g.

Furthermore, from the viewpoints of the adhesion, chipping resistance, and finished appearance of the multilayer coating film formed, 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 even more particularly 20 to 45°C.

In this specification, the glass transition temperature (°C) of acrylic resins was calculated using the following formula:

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 in the copolymerization, and T1, T2, ... represent the Tg (K) of the homopolymer of each monomer. Note that T1, T2, ... are values according to pages III-139 to 179 of "Polymer Hand Book" (Second Edition, edited by J. Brandup and E.H. Immergut). 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" (manufactured by Seiko Instruments Inc.), a sample is placed in a measuring cup, and the solvent is completely removed by vacuum suction. Then, the change in heat quantity is measured in the range of -20°C to +200°C at a heating rate of 3°C/min, and the first change point of the baseline on the low-temperature side is taken as the static glass transition temperature.

As a copolymerization method for copolymerizing the above polymerizable unsaturated monomer mixture to obtain the hydroxyl group-containing acrylic resin (z11), 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.

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.

Polymerization initiators 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).

The above hydroxyl group-containing acrylic resin (z11) can be used alone or in combination of two or more types.

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 paint composition (Z) is preferably within the 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 solids content of the color clear paint composition (Z).

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.

Examples of the aliphatic polyisocyanates 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 2,6-diisocyanatohexanoate (2-isocyanatoethyl 2,6-diisocyanatohexanoate), 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

Examples of the alicyclic polyisocyanate 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), and 2-methyl-1,3-cyclohexylene diisocyanate. alicyclic diisocyanates such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or mixtures thereof, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), and norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2-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-isocyanatopropyl)-bicyclo(2.2.1)heptane Examples include 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.

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 mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; and araliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

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), 2,6-tolylene diisocyanate (common name: 2,6-TDI), or mixtures 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.

Furthermore, examples of derivatives of the polyisocyanates include dimers, trimers, biurets, allophanates, uretdiones, uretimines, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like.

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

Among aliphatic diisocyanates, hexamethylene diisocyanate compounds and among alicyclic diisocyanates, 4,4'-methylenebis(cyclohexyl isocyanate) are suitable for use. Among these, derivatives of hexamethylene diisocyanate are particularly suitable from the standpoints of adhesion, compatibility, etc.

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

In addition, as the polyisocyanate compound (z2), a blocked polyisocyanate compound, which is a compound in which the isocyanate groups in the above polyisocyanates and their derivatives are blocked with a blocking agent, can also be used.

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

When blocking (reacting with a blocking agent), a solvent can be added if necessary.

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

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.

If necessary, the color clear paint composition (Z) may contain appropriate amounts of paint additives such as water, solvents such as organic solvents, curing catalysts, antifoaming agents, ultraviolet absorbers, rheology control agents, and anti-settling agents.

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

The solids content of the color clear paint 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. Furthermore, it is preferable to adjust the viscosity of the clear paint composition (Z) appropriately using water and/or an organic solvent so that it is within a range suitable for application, typically within the range of approximately 15 to 60 seconds, particularly approximately 20 to 50 seconds, at 20°C as measured using a Ford Cup No. 4 viscometer.

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.

Heating can be performed by, for example, hot air heating, infrared heating, or high-frequency heating. 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, prior to the heat curing, the composition may be directly or indirectly heated by preheating, air blowing, or the like at a temperature of about 50 to about 110°C, preferably about 60 to about 90°C, for about 1 to 60 minutes.

Formation of a multi-layer coating film 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 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
By setting the 20-degree specular gloss/lightness L ^* (45°), which is the value obtained by dividing the 20-degree specular gloss by the lightness L ^* (45°) in the L ^* a ^* b ^* color system, to 4 or more, it is possible to form a multilayer coating film with a highly transparent metallic luster that reflects the scenery.

When the 20-degree specular gloss of the multilayer coating film formed is 90 or more, the resulting multilayer coating film has excellent metallic gloss. 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.

Furthermore, the lightness L ^* (45°) in the L ^* a ^* b ^* color system of the multilayer coating film formed is preferably 18 or less, and more preferably 15 or less, from the viewpoint of forming a multilayer coating film that has a highly transparent metallic luster that reflects the scenery and exudes a sense of luxury.

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

When the 20 ^- degree specular gloss of the formed ^multilayer coating film/lightness L ^* (45° ⁾ , which is the value obtained by dividing the 20-degree specular gloss of the formed multilayer coating film by the lightness L ^* (45°) in the L*a*b* color system, is 4 or more, the multilayer coating film becomes highly transparent, as if the scenery is being reflected in it.In particular, the 20-degree specular gloss of the multilayer coating film/lightness L ^* (45°) is preferably 10 or more, and more preferably 15 or more.

The present invention will be explained 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.

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

The resulting electrodeposition-coated surface of the steel plate was electrostatically coated with "TP-65-2" (product name, manufactured by Kansai Paint Co., Ltd., polyester resin and amino resin organic solvent-based intermediate coating composition) using a rotary atomizer electrostatic coater to a cured film thickness of 35 μm. The coating was then heated at 140°C for 30 minutes to cure, forming an intermediate coating film, and the substrate was then prepared.

[2] Preparation of paint
Production of glitter coating composition (Y)
Production Example 1
To a stirring and mixing vessel were 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 glittering coating composition (Y-1) with a solids content of 1.2% by mass.

Production 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.

Preparation of Color Clear Coating Composition (Z) Preparation Example 6
"EMPEROR 3000" (product name, special carbon black manufactured by CABOT Corporation) was added to "KINO-6510" (product name, hydroxyl group/isocyanate group curing type acrylic resin/urethane resin based two-component organic solvent-based paint manufactured by Kansai Paint Co., Ltd.), and the content of "EMPEROR 3000" was adjusted to 0.2 parts by mass based on 100 parts by mass of resin solids, followed by stirring to obtain color clear paint composition (Z-1).

Production Examples 7 to 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.

Evaluation of Color Clear Coating Films Using the color clear coating compositions (Z-1) to (Z-7) obtained above, free films of the color clear coating films 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 films were prepared by applying one of the color clear coating compositions (Z-1) to (Z-7) to a polypropylene plate using a minibell-type rotary electrostatic applicator at a booth temperature of 23°C and humidity of 68% to a film thickness of 40 μm, leaving the coating at room temperature for 7 minutes, heating it in a hot air circulating drying oven at 140°C for 30 minutes, and then peeling off the resulting coating film. The evaluation results are also shown in Table 2.

[3] Preparation of test plates
Creating test panels
Example 1
The glitter coating composition (Y-1) produced in [2] above was applied onto the substrate prepared in [1] above using a minibell-type rotary electrostatic coater at a booth temperature of 23°C and a humidity of 63% so as to give a cured coating film with a thickness of 0.05 µm. The coating was left to stand at room temperature for 15 minutes, and then heated in a hot air circulation drying oven at 140°C for 30 minutes to dry and cure, thereby obtaining a glitter coating film.

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 was 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, thereby producing the test panel of Example 1.

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: Coating 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 paint and film thickness shown in Table 3 were used.

Example 5
The glitter coating composition (Y-2) produced in [2] above was applied onto the substrate prepared in [1] above using a minibell-type rotary electrostatic coater at a booth temperature of 23°C and a humidity of 63% so as to give a cured coating film with a thickness of 0.1 µm. The coating was then left to stand 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 glitter coating film.

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 was 35 μm thick. After leaving it at room temperature for 7 minutes, it was heated in a hot air circulating drying oven at 140°C for 30 minutes to simultaneously dry and cure the glossy coating film and clear coating film, thereby producing the test panel of Example 5.

Evaluation of Coating Film The coating film of each test plate obtained as described above was evaluated by the following method. The results are shown in Table 3.

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

Lightness L* (45°) in the L ^* a ^* b ^* color system: The lightness L ^* (45°) in the L ^* a ^* b ^* color system was measured using an "MA ^- 68II" (trade name, manufactured by X-rite).

20-degree specular gloss/lightness L ^* (45°): Calculated by dividing the 20-degree specular gloss by the lightness L ^* (45°) in the L ^* a ^* b ^* color system.

The above provides a detailed description of embodiments and examples of the present invention, but 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.

For example, the configurations, methods, processes, shapes, materials, and numerical values described 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.

Furthermore, the configurations, methods, processes, shapes, materials, and numerical values of the above-described embodiments may be combined with one another without departing from the spirit of the present invention.

Claims (3)

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
A method for ^forming a multilayer coating film, in which the 20-degree specular gloss/lightness L ^* (45° ⁾ , which is the value obtained by dividing the 20-degree specular gloss by the lightness L ^* (45° ⁾ in the L*a*b* color system, is 4 or more. The method for forming a multilayer coating film according to claim 1, wherein the luster pigment (y1) contains indium particles. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the color pigment (z1) includes a black pigment.