Method for forming multilayer coating film

Abstract

This method for forming a multilayer coating film comprises the following steps (1) to (3). Step (1): forming a brilliant coating film by coating an object to be coated with a brilliant coating composition (Y) containing a brilliant pigment (y1). Step (2): forming a clear coating film by coating the brilliant coating film formed in Step (1) with a clear coating composition (Z). Step (3): baking and curing the brilliant coating film and the clear coating film formed in Steps (1) and (2) separately or simultaneously. The brilliant pigment (y1) contains indium particles treated with a silane coupling agent.

Description

Method for forming multi-layer coating film

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

[0002] The main purpose of applying paint is to protect the material and to add beauty. For industrial products, beauty, especially "texture," is important in order to enhance their commercial appeal. Consumers desire a wide variety of textures for industrial products, but in recent years, excellent gloss has become a requirement in areas such as automobile exterior panels, automobile parts, and home appliances.

[0003] Techniques for imparting an excellent gloss to the surface of an industrial product include metal plating and metal vapor deposition (see, for example, Patent Document 1), but if an excellent gloss could be imparted by painting, it would be advantageous from the standpoints of simplicity and cost.

[0004] 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 per 100 parts by weight of the resin content in the metallic paint base.

[0005] Meanwhile, in recent years, autonomous driving has been attracting attention as a key technology for next-generation automobiles. To make autonomous driving possible, various sensing technologies must be utilized, one of which is the use of millimeter-wave radio waves (frequency 30-300 GHz), such as millimeter-wave radar.

[0006] Japanese Patent Application Publication No. 63-272544 Japanese Patent Application Publication No. 2003-313500

[0007] However, when a clear coating composition is applied onto the glossy coating film formed by the above-mentioned metallic paint, the solvent and curing agent contained in the clear coating composition penetrate into the glossy coating film, resulting in a problem of a decrease in the gloss of the multilayer coating film.

[0008] Furthermore, when a large amount of a luster pigment such as aluminum is blended into a coating composition in order to impart a superior gloss, the resulting coating film can sometimes cause the problem of blocking millimeter wave radar.

[0009] An object of the present invention is to provide a method for forming a multilayer coating film, which is capable of forming a coating film having an excellent glossy appearance and high millimeter wave transmittance.

[0010] The present invention includes the following embodiments. Item 1. A method for forming a multilayer coating film, comprising the following steps (1) to (3): Step (1): applying a glittering coating composition (Y) containing a glittering pigment (y1) to a substrate to form a glittering coating film, Step (2): applying a clear coating composition (Z) to the glittering coating film formed in step (1) to form a clear coating film, and Step (3): baking and curing the glittering coating film and clear coating film formed in steps (1) and (2) separately or simultaneously, wherein the glittering pigment (y1) contains indium particles treated with a silane coupling agent. Item 2. The method for forming a multilayer coating film according to Item 1, wherein the silane coupling agent is at least one selected from the group consisting of an amino group-containing silane coupling agent, an epoxy group-containing silane coupling agent, and a methyl group-containing silane coupling agent. Item 3. Item 4. The method for forming a multilayer coating film according to Item 1, wherein the amount of the silane coupling agent is 0.1 to 10 parts by mass per 100 parts by mass of the solid content of untreated indium particles. Item 5. The method for forming a multilayer coating film according to Item 1, wherein the glittering coating composition (Y) further contains a surface conditioner (y2), a pigment dispersant (y3), a viscosity modifier (y4) and water (y5), and has a solid content of 0.1 to 15% by mass. Item 6. The method for forming a multilayer coating film according to Item 4, wherein the surface conditioner (y2) comprises a silicone-based surface conditioner. Item 7. The method for forming a multilayer coating film according to Item 4, wherein the pigment dispersant (y3) comprises a phosphate group-containing compound. Item 8. The method for forming a multilayer coating film according to Item 4, wherein the viscosity modifier (y4) comprises an associative viscosity modifier. Item 5. The method for forming a multilayer coating film according to Item 4, wherein the content of the water (y5) is in the range of 50 to 95 parts by mass relative to 100 parts by mass of the total of all components of the glittering coating composition (Y).Item 9. The method for forming a multilayer coating film according to Item 1, further comprising the steps of: producing an indium particle dispersion, the steps including adding a silane coupling agent and an aqueous medium to a solvent-based dispersion containing flaky indium particles and an organic solvent, and hydrolyzing the silane coupling agent to surface treat the indium particles; and providing a bright coating composition (Y) containing the indium particle dispersion, wherein the indium particles have a number average particle size of 0.1 to 1 μm and a number average thickness of 10 to 100 nm, the silane coupling agent is a compound represented by the following general formula (1), the amount of the silane coupling agent per 100 parts by mass of the indium particles is 0.1 to 10 parts by mass, and the amount of the aqueous medium per 100 parts by mass of the solvent-based dispersion is 5 to 30 parts by mass. (In the general formula (1), R represents a methyl group or an ethyl group, and X represents an alkyl group having 1 to 4 carbon atoms or a group represented by any one of the following general formulas (2) to (4)). (In the general formula (2), A represents an alkylene group having 1 to 10 carbon atoms. In the general formula (3), W represents an alkylene group having 2 to 4 carbon atoms. In the general formula (4), Y represents an alkylene group having 1 to 4 carbon atoms, and Z represents an alkylene group having 2 to 10 carbon atoms. In the general formulas (2) to (4), "*" indicates the bonding position with "Si" in the general formula (1).) Item 10. A method for forming a multi-layer coating film according to Item 9, wherein the organic solvent contains propylene glycol monomethyl ether. Item 11. A method for forming a multi-layer coating film according to Item 9, wherein in the producing step, the silane coupling agent and the aqueous medium are added to the solvent-based dispersion, and then the mixture is stirred for 5 hours or more to hydrolyze the silane coupling agent. Item 12. Item 13. A method for forming an indium particle dispersion, comprising the steps of adding a silane coupling agent and an aqueous medium to a solvent-based dispersion containing flaky indium particles and an organic solvent, and hydrolyzing the silane coupling agent to surface-treat the indium particles, wherein the indium particles have a number-average particle diameter of 0.1 to 1 μm and a number-average thickness of 10 to 100 nm, the silane coupling agent is a compound represented by the following general formula (1), the amount of the silane coupling agent is 0.1 to 10 parts by mass per 100 parts by mass of the indium particles, and the amount of the aqueous medium is 5 to 30 parts by mass per 100 parts by mass of the solvent-based dispersion: (In the general formula (1), R represents a methyl group or an ethyl group, and X represents an alkyl group having 1 to 4 carbon atoms or a group represented by any one of the following general formulas (2) to (4)). (In the general formula (2), A represents an alkylene group having 1 to 10 carbon atoms. In the general formula (3), W represents an alkylene group having 2 to 4 carbon atoms. In the general formula (4), Y represents an alkylene group having 1 to 4 carbon atoms, and Z represents an alkylene group having 2 to 10 carbon atoms. In the general formulas (2) to (4), "*" represents the bonding position with "Si" in the general formula (1).) Item 14. The method for producing an indium particle dispersion according to Item 13, wherein the organic solvent contains propylene glycol monomethyl ether. Item 15. The method for producing an indium particle dispersion according to Item 13, wherein the silane coupling agent and the aqueous medium are added to the solvent-based dispersion, and then the mixture is stirred for 5 hours or more to hydrolyze the silane coupling agent. Item 16. Item 16. A method for producing an indium particle dispersion according to Item 13, wherein the aqueous medium is water or a mixed solvent of water and alcohol, and the amount of the alcohol in the mixed solvent is 2.5 parts by mass or less per part by mass of the water. Item 17. A method for producing an aqueous paint using the indium particle dispersion produced by the production method according to any one of Items 13 to 16. Item 18. A method for producing an aqueous ink using the indium particle dispersion produced by the production method according to any one of Items 13 to 16. Item 19. A method for producing a laminate, comprising a step of applying the aqueous paint produced by the production method according to Item 17 onto a substrate to form a coating layer. Item 20. A method for producing a laminate according to Item 19, further comprising a step of forming a coating layer on the coating layer. Item 21. A method for producing a laminate, comprising a step of applying the aqueous ink produced by the production method according to Item 18 onto a substrate to form a printed layer. Item 22. A method for producing a laminate according to Item 21, further comprising a step of forming a coating layer on the printed layer.

[0011] According to the method for forming a multilayer coating film of the present disclosure, a multilayer coating film having an excellent gloss and high millimeter wave transmittance can be formed.

[0012] In this specification, the term "comprise" is a concept that encompasses "consist essentially only of" and "consist only of."

[0013] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. Furthermore, in this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the upper and lower limits.

[0014] Method for forming a multilayer coating film The method for forming a multilayer coating film of the present disclosure comprises the following steps (1) to (3): step (1): applying a glittering coating composition (Y) containing a glittering pigment (y1) to an object to be coated to form a glittering coating film, step (2): applying a clear coating composition (Z) onto the glittering coating film formed in step (1) to form a clear coating film, and step (3): baking and curing the glittering coating film and clear coating film formed in steps (1) and (2) separately or simultaneously, wherein the glittering pigment (y1) contains indium particles treated with a silane coupling agent.

[0015] Step (1) According to the method for forming a multilayer coating film of the present disclosure, first, a substrate is coated with a glittering coating composition (Y) containing a glittering pigment (y1), thereby forming a glittering coating film.

[0016] Substrate 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 substrate may be used interchangeably with the target object.

[0017] 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. Of these, metal materials and plastic materials are preferred.

[0018] 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.

[0019] A coating film may be further formed on the substrate, which may or may not have been surface-treated. For example, the substrate may be surface-treated as needed, and a primer coating film and / or intermediate coating film may be formed thereon. For example, when 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.

[0020] 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.

[0021] Brilliant Coating Composition (Y) The brilliant coating composition (Y) of the present disclosure contains a brilliant pigment (y1), and the brilliant pigment (y1) contains indium particles treated with a silane coupling agent.

[0022] The indium particles used in producing the indium particles treated with a silane coupling agent are flaky particles, which are also called scale-like particles, plate-like particles, flake-like particles, etc.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The indium particles are made of indium with a purity of 95% or more and may contain trace amounts of impurities, but do not contain alloys with other metals.

[0027] 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.

[0028] <Release Layer Forming Step> The release layer forming step is a step of providing a release layer on a substrate.

[0029] 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.

[0030] 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 to and remains on the attachment surface of the island-structure film can function as a protective layer for the indium particles, which is preferable.

[0031] 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.

[0032] 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, 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.

[0033] 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.

[0034] <Vacuum Deposition Step> The vacuum deposition step is a step of vacuum-depositing a metal layer containing indium particles onto the release layer.

[0035] 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.

[0036] 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, and an excellent glossiness can be exhibited. The average vapor deposition thickness is determined by, for example, 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 measured values.

[0037] The metal layer is preferably an island-structured film. The island-structured film can be formed by various methods, such as vacuum deposition, sputtering, and plating. Among these, vacuum deposition is preferred.

[0038] The vacuum deposition method is preferable to the plating method in that it can form a film on a resin substrate and does not produce waste liquid, and is preferable to the sputtering method in that it can achieve a high degree of vacuum and has a high film formation speed (evaporation rate).

[0039] 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.

[0040] <Peeling step> 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 glittering coating composition (Y) as it is.

[0041] 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 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, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monobutyl ether, triethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monobutyl ether, triethylene glycol monobutyl ether, triethylene glycol monobutyl ether, triethylene glycol monobutyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol monomethyl ... Examples of suitable solvents include glycol ether solvents such as 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, and methoxybenzene; 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.

[0042] By dissolving the release layer, the island-structure film is peeled off from the substrate, and the island structure is split into individual islands, which become indium particles. 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.

[0043] 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.

[0044] <Other Steps> Examples of other steps include a step of extracting the peeled metal layer as a dispersion liquid, and a step of recovering island-shaped metal layers as indium particles from the dispersion liquid.

[0045] The cumulative 50% volume average 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 gloss.

[0046] Returning to the explanation of the composition of the bright coating composition (Y), the indium particles can be commercially available products, such as "Leaf Powder 49CJ-1120," "Leaf Powder 49CJ-1150," "Leaf Powder 49BJ-1120," and "Leaf Powder 49BJ-1150" (all manufactured by Oike Metallic Design Co., Ltd.).

[0047] The indium particles treated with a silane coupling agent can be obtained by treating indium particles with a silane coupling agent. Methods for treating indium particles with a silane coupling agent are known.

[0048] The silane coupling agent is not particularly limited, but from the viewpoint of obtaining a multilayer coating film having excellent gloss and high millimeter wave transmittance, at least one selected from the group consisting of amino group-containing silane coupling agents, epoxy group-containing silane coupling agents, and methyl group-containing silane coupling agents is preferred.

[0049] From the viewpoint of obtaining a multilayer coating film having an excellent glossy appearance and high millimeter wave transmittance, the amount of the silane coupling agent relative to the indium particles is preferably 0.1 to 10 parts by mass, for example 0.1 to 5 parts by mass, relative to 100 parts by mass of the solid content of the untreated indium particles.

[0050] From the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, the content of the glittering pigment (y1) in the glittering coating composition (Y) of the present invention is preferably 50 parts by mass or more, more preferably 55 parts by mass or more, more preferably in the range of 60 to 110 parts by mass, even more preferably in the range of 65 to 105 parts by mass, and particularly preferably in the range of 65 to 100 parts by mass, based on 100 parts by mass of the solid content of the glittering coating composition (Y).

[0051] From the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, the content of indium particles treated with a silane coupling agent in the glittering coating composition (Y) of the present invention is preferably 50 parts by mass or more, more preferably 55 parts by mass or more, even more preferably in the range of 60 to 100 parts by mass, and particularly preferably in the range of 65 to 95 parts by mass, based on 100 parts by mass of the solid content of the glittering coating composition (Y).

[0052] The glittering coating composition (Y) may further contain a surface conditioner (y2), a pigment dispersant (y3), a viscosity modifier (y4), and water (y5). From the viewpoint of obtaining a coating film having an excellent gloss and high millimeter wave transmittance, the glittering coating composition (Y) preferably further contains a surface conditioner (y2), a pigment dispersant (y3), a viscosity modifier (y4), and water (y5), and has a solids content of 0.1 to 15 mass%.

[0053] Surface Conditioner (y2) Examples of the surface conditioner (y2) include silicone-based surface conditioners, acrylic-based surface conditioners, vinyl-based surface conditioners, fluorine-based surface conditioners, and acetylene diol-based surface conditioners. Among these, from the viewpoint of obtaining a coating film having excellent gloss and high millimeter wave transmittance, it is preferable to contain a silicone-based surface conditioner. The above surface conditioners can be used alone or in appropriate combination of two or more.

[0054] The silicone-based surface conditioner may be polydimethylsiloxane or a modified silicone obtained by modifying polydimethylsiloxane. Examples of the modified silicone include polyether-modified silicone, acrylic-modified silicone, and polyester-modified silicone.

[0055] From the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, the content of the surface conditioner (y2) in the glittering coating composition (Y) of the present disclosure is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 3 to 10 parts by mass, based on 100 parts by mass of the solids content of the glittering coating composition (Y).

[0056] Pigment dispersant (y3) As the pigment dispersant (y3), for example, any of anionic, cationic, and nonionic compounds can be used, and among them, from the viewpoint of forming a coating film having excellent gloss and high millimeter wave transmittance, it is preferable to use an anionic compound. One type of pigment dispersant (y3) may be used alone, or two or more types may be used in combination.

[0057] As the anionic compound, a compound having a functional group such as a phosphate group, a carboxyl group, a sulfonic acid group, or a sulfate ester group can be used. Among these, from the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, it is preferable to include a compound having a phosphate group, i.e., a phosphate group-containing compound.

[0058] The anionic compounds can also be used after neutralization with a neutralizing agent. Examples of the neutralizing agent include ammonia; primary monoamines such as ethylamine, propylamine, butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, 2-amino-2-methyl-1-propanol, and 3-aminopropanol; secondary monoamines such as diethylamine, diethanolamine, di-n- or di-iso-propanolamine, N-methylethanolamine, and N-ethylethanolamine; tertiary monoamines such as trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, and dimethylethanolamine; and polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, and methylaminopropylamine.

[0059] Examples of the phosphate group-containing compound include polyoxyethylene alkyl ether phosphate, polyoxyethylene phenyl ether phosphate, alkyl phosphate ester, and alkyl phosphate ester salt.

[0060] From the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, the content of the pigment dispersant (y3) in the glittering coating composition (Y) of the present disclosure is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 3 to 10 parts by mass, based on 100 parts by mass of the solid content of the glittering coating composition (Y).

[0061] Viscosity modifier (y4) Examples of the viscosity modifier (y4) include associative viscosity modifiers, inorganic viscosity modifiers, polyacrylic acid viscosity modifiers, cellulose derivative viscosity modifiers, protein viscosity modifiers, alginic acid viscosity modifiers, polyvinyl viscosity modifiers, polyether viscosity modifiers, maleic anhydride copolymer viscosity modifiers, polyamide viscosity modifiers, etc. Among these, from the viewpoint of obtaining a coating film having excellent gloss and high millimeter wave transmittance, it is preferable to use an associative viscosity modifier, and it is particularly preferable to use an acrylic associative viscosity modifier described below.

[0062] Examples of the associative viscosity modifier include an acrylic associative viscosity modifier, which is an acrylic resin having a hydrophilic acrylic main chain and a hydrophobic side chain; and a urethane associative viscosity modifier, which has a hydrophobic moiety, a urethane bond, and a polyether chain in one molecule and effectively exhibits a thickening effect in an aqueous solvent by the hydrophobic moieties associating with each other.

[0063] Examples of inorganic viscosity modifiers include silicates, metal silicates, montmorillonite, organic montmorillonite, and colloidal alumina.

[0064] Examples of polyacrylic acid viscosity modifiers include sodium polyacrylate and polyacrylic acid-(meth)acrylic acid ester copolymers.

[0065] Examples of the cellulose derivative viscosity adjuster include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and cellulose nanofiber.

[0066] Examples of protein-based viscosity adjusters include casein, sodium caseinate, and ammonium caseinate.

[0067] Examples of alginic acid-based viscosity adjusters include sodium alginate.

[0068] Examples of polyvinyl viscosity modifiers include polyvinyl alcohol, polyvinylpyrrolidone, and polyvinylbenzyl ether copolymers.

[0069] Examples of polyether viscosity modifiers include polyether dialkyl esters, polyether dialkyl ethers, and epoxy-modified polyethers.

[0070] Examples of maleic anhydride copolymer viscosity modifiers include partial esters of vinyl methyl ether-maleic anhydride copolymers.

[0071] Examples of polyamide viscosity modifiers include polyamide amine salts.

[0072] These viscosity modifiers (y4) can be used either alone or in combination of two or more.

[0073] From the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, the content of the viscosity modifier (y4) in the glittering coating composition (Y) of the present disclosure is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 3 to 10 parts by mass, based on 100 parts by mass of the solids content of the glittering coating composition (Y).

[0074] Water (y5) From the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, the content of water (y5) in the glittering coating composition (Y) of the present disclosure is preferably within the range of 50 to 95 parts by mass, more preferably within the range of 55 to 93 parts by mass, and even more preferably within the range of 65 to 90 parts by mass, relative to 100 parts by mass of the total of all components of the glittering coating composition (Y).

[0075] The solid content of the glittering coating composition (Y) is preferably in the range of 0.1 to 15 mass%, more preferably in the range of 0.5 to 13.5 mass%, and even more preferably in the range of 1.5 to 12 mass%, from the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance.

[0076] In this specification, "solid content" refers to non-volatile components such as resins, curing agents, and pigments contained in a paint composition that remain after the paint composition has been dried for 1 hour at 110° C. Therefore, for example, the total solid content of a paint composition can be calculated by weighing out the paint composition into a heat-resistant container such as an aluminum foil cup, spreading the paint composition on the bottom of the container, drying it for 1 hour at 110° C., weighing the mass of the components in the paint composition that remain after drying, and determining the ratio of the mass of the components that remain after drying to the total mass of the paint composition before drying.

[0077] Other Components The bright coating composition (Y) may further contain, as necessary, an organic solvent, a pigment other than the indium particles (y1), a binder resin, a crosslinkable component, an ultraviolet absorber, a light stabilizer, and the like.

[0078] As the organic solvent, those usually used in paints can be used. Specific examples thereof 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. Examples of suitable solvents include glycol ether solvents such as 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, and methoxybenzene; 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.

[0079] Examples of pigments other than the indium particles (y1) include color pigments, luster pigments other than the indium particles (y1), and extender pigments. The pigments other than the indium particles (y1) 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 luster pigments other than the indium particles include vapor-deposited metal flake pigments other than the indium particles (y1), aluminum flake pigments, and optical interference pigments. Examples of extender pigments include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white.

[0080] When the glittering coating composition (Y) of the present disclosure contains a pigment other than indium particles (y1), the content thereof is preferably in the range of 0.01 to 10 parts by mass, more preferably in the range of 0.05 to 8 parts by mass, and even more preferably in the range of 0.1 to 5 parts by mass, based on 100 parts by mass of the solid content of the glittering coating composition (Y), from the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance.

[0081] Examples of the binder resin include acrylic resin, polyester resin, polyether resin, polycarbonate resin, polyurethane resin, epoxy resin, and alkyd resin, and among these, it is preferable to include an acrylic resin, more preferably a water-soluble or water-dispersible acrylic resin, and even more preferably a water-soluble acrylic resin. These can be used alone or in combination of two or more kinds.

[0082] When the glittering coating composition (Y) of the present disclosure contains a binder resin, the content thereof is preferably in the range of 0.5 to 20 parts by mass, more preferably in the range of 1 to 15 parts by mass, and even more preferably in the range of 3 to 10 parts by mass, based on 100 parts by mass of the solid content of the glittering coating composition (Y), from the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance.

[0083] 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.

[0084] When the glittering coating composition (Y) of the present disclosure contains the above-mentioned crosslinkable component, the content thereof is preferably in the range of 0.5 to 20 parts by mass, more preferably in the range of 1 to 15 parts by mass, and even more preferably in the range of 3 to 10 parts by mass, based on 100 parts by mass of the solid content of the glittering coating composition (Y), from the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance.

[0085] Indium Particle Dispersion 1. Indium Particle Dispersion and Manufacturing Method Thereof In a preferred embodiment, the bright coating composition (Y) of the present disclosure comprises an indium particle dispersion manufactured by a manufacturing method for an indium particle dispersion, the manufacturing method comprising adding a silane coupling agent and an aqueous medium to a solvent-based dispersion containing flaky indium particles and an organic solvent, and hydrolyzing the silane coupling agent to surface treat the indium particles. In this manufacturing method for an indium particle dispersion, preferably, the indium particles have a number-average particle diameter of 0.1 to 1 μm and a number-average thickness of 10 to 100 nm, and the silane coupling agent is a compound represented by the following general formula (1). The amount of silane coupling agent per 100 parts by mass of the indium particles is 0.1 to 10 parts by mass, and the amount of aqueous medium per 100 parts by mass of the solvent-based dispersion is 5 to 30 parts by mass.

[0086] (In the general formula (1), R represents a methyl group or an ethyl group, and X represents an alkyl group having 1 to 4 carbon atoms or a group represented by any one of the following general formulas (2) to (4)).

[0087] (In the general formula (2), A represents an alkylene group having 1 to 10 carbon atoms. In the general formula (3), W represents an alkylene group having 2 to 4 carbon atoms. In the general formula (4), Y represents an alkylene group having 1 to 4 carbon atoms, and Z represents an alkylene group having 2 to 10 carbon atoms. In addition, in the general formulas (2) to (4), "*" indicates the bonding position with "Si" in the general formula (1)).

[0088] 2. Solvent-Based Dispersion The above-mentioned method for producing an indium particle dispersion uses a solvent-based dispersion containing flaky indium particles and an organic solvent (hereinafter also referred to simply as a "solvent-based dispersion"). This solvent-based dispersion can be prepared by dispersing flaky indium particles in an organic solvent. Note that, as described in, for example, JP 2020-132998 A, flaky indium particles can be produced by forming a vapor-deposited thin film of indium on a release agent-coated substrate film by vapor deposition, dissolving the release agent in an organic solvent, and peeling it from the substrate film. Typically, cellulose acetate butyrate (CAB) or the like is used as the release agent due to its high functionality. Furthermore, propylene glycol monomethyl ether (PM) or the like is used as the organic solvent for dissolving the release agent due to its close boiling point to water, drying properties, and the like. While a trace amount of release agent may remain on the indium particles, it is preferable to reduce it as much as possible because this may affect the dispersion stability of the indium particles.

[0089] In some embodiments, the number-average particle size of the indium particles is 0.1 to 1 μm, preferably 0.1 to 0.7 μm. The number-average thickness of the indium particles is 10 to 100 nm, preferably 20 to 70 nm. A commercially available product may be used as the solvent-based dispersion containing flaky indium particles and an organic solvent. An example of a commercially available solvent-based dispersion is "Leaf Powder 49CJ-1120" (manufactured by Oike Kogyo Co., Ltd.). This solvent-based dispersion (commercially available product) is a solvent-based dispersion in which flaky indium particles with a pure indium content of 20% by mass are dispersed in an organic solvent, and the number-average particle size of the indium particles is 0.3 to 0.4 μm and the number-average thickness is 30 to 60 nm. The number-average particle size of the indium particles can be measured and calculated using a laser diffraction particle size distribution analyzer. The number-average thickness of the indium particles can be calculated as the average value of 20 particles observed and measured using an electron microscope.

[0090] 3. Silane Coupling Agent In the above-described method for producing an indium particle dispersion, a predetermined silane coupling agent and an aqueous medium are added dropwise, for example, to a solvent-based dispersion containing flaky indium particles while stirring the dispersion. This hydrolyzes the silane coupling agent, and the hydrolyzed silane coupling agent is adsorbed onto the surfaces of the flaky indium particles, thereby surface-treating the indium particles and improving dispersion stability.

[0091] In general formula (1), R is preferably a methyl group. In general formula (2), A is preferably an alkylene group having 3 to 8 carbon atoms. In general formula (3), W is preferably an alkylene group having 3 carbon atoms (propylene group). In general formula (4), Y is preferably an alkylene group having 2 or 3 carbon atoms. In general formula (4), Z is preferably an alkylene group having 4 to 8 carbon atoms.

[0092] The silane coupling agent may be a commercially available product or one synthesized according to a conventional method. Silane coupling agents are commercially available from, for example, Dow Corning Toray Co., Ltd., JNC Corporation, Evonik Corporation, and Shin-Etsu Chemical Co., Ltd. Examples of silane coupling agents commercially available from Shin-Etsu Chemical Co., Ltd. include methyltrimethoxysilane (KBM-13), methyltriethoxysilane (KBE-13), 3-glycidoxypropylmethyldimethoxysilane (KBM-402), 3-glycidoxypropyltrimethoxysilane (KBM-403), 8-glycidoxyoctyltrimethoxysilane (KBM-4803), N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (KBM-6803), and 3-aminopropyltrimethoxysilane (KBM-903) (the names in parentheses are trade names).

[0093] In some embodiments, the amount of silane coupling agent per 100 parts by mass of indium particles in the solvent-based dispersion is 0.1 to 10 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 0.5 to 5 parts by mass. When the amount of silane coupling agent is 0.1 parts by mass or more per 100 parts by mass of indium particles, the treatment effect of the silane coupling agent is exerted. On the other hand, even when the amount of silane coupling agent is 10 parts by mass or less per 100 parts by mass of indium particles, the treatment effect is exerted.

[0094] 4. Aqueous Medium In the above-described method for producing an indium particle dispersion, the aqueous medium is water or a mixed solvent of water and alcohol. Examples of the alcohol that can be used include water-soluble alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and butanol. In the mixed solvent, the amount of alcohol per part by mass of water is preferably 2.5 parts by mass or less.

[0095] By adding an aqueous solvent to the solvent-based dispersion together with the silane coupling agent, the silane coupling agent can be hydrolyzed in the system. That is, water or a mixed solvent of water and alcohol is added to the solvent-based dispersion so that the amount of water necessary for hydrolysis of the silane coupling agent is present. Considering that the resulting indium particle dispersion will be used directly in the preparation of an aqueous paint or ink, it is effective to mix a certain amount of water in the dispersion to prevent the occurrence of solvent shock, etc. Specifically, the amount of aqueous medium per 100 parts by mass of the solvent-based dispersion is 5 to 30 parts by mass, preferably 5 to 20 parts by mass. If the amount of aqueous medium is more than 30 parts by mass per 100 parts by mass of the solvent-based dispersion, the indium particles tend to settle in the resulting indium particle dispersion. The aqueous medium may be added in portions at the initial stage of hydrolysis and at the post-hydrolysis stage.

[0096] 5. Other Components In the above-described method for producing an indium particle dispersion, when the indium particles are surface-treated, other components (additives) besides the silane coupling agent may be used in combination. Examples of the additives include water-soluble dyes, pigments, ultraviolet absorbers, light stabilizers, antioxidants, leveling agents, antifoaming agents, preservatives, antifungal agents, photopolymerization initiators, nonionic surfactants, polymers such as polyvinylpyrrolidone, and other pigment dispersants.

[0097] In addition, various resins may be used together with the silane coupling agent. Examples of resins include polyolefin resins, polyhalogenated olefin resins, polyester resins, polyamide resins, polyimide resins, polyether resins, polyvinyl resins, polystyrene resins, polyvinyl alcohol resins, acrylic resins such as polymethacrylate resins, polyurethane resins, polyepoxy resins, polyphenol resins, polyurea resins, and polyethersulfone resins. The indium particle dispersion may further contain each of the surface conditioner (y2), pigment dispersant (y3), viscosity adjuster (y4), and water (y5) described above in relation to the bright coating composition (Y).

[0098] The reaction rate of the hydrolysis of a silane coupling agent varies depending on the type of silane coupling agent. The hydrolysis of a silane coupling agent in water usually proceeds over a period of about 1 to 3 hours. In the production method of this embodiment, the silane coupling agent is hydrolyzed in an aqueous medium in which water and an organic solvent coexist, so the hydrolysis proceeds more slowly than in water. In the production method of this embodiment, the silane coupling agent and the aqueous medium are added to the solvent-based dispersion, and then the mixture is stirred, preferably for 5 hours or more, more preferably for 10 to 25 hours, to hydrolyze the silane coupling agent.

[0099] Coating of the glittering coating composition (Y) Coating of the glittering coating composition (Y) can be carried out according to a conventional method, for example, air spray coating, airless spray coating, rotary atomization coating, etc. When coating the glittering coating composition (Y), electrostatic force may be applied if necessary, and among these, rotary atomization electrostatic coating and air spray electrostatic coating are preferred, and rotary atomization electrostatic coating is particularly preferred.

[0100] When air spray coating, airless spray coating or rotary atomization coating is carried out, the glittering coating composition (Y) is preferably adjusted to a viscosity suitable for coating by appropriately adding water and / or an organic solvent and, if necessary, additives such as an antifoaming agent.

[0101] From the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance, 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.

[0102] Furthermore, before application of the glittering coating composition (Y), it is preferable to subject the glittering coating composition (Y) to ultrasonic dispersion treatment, from the viewpoint of forming a coating film having an excellent gloss and high millimeter wave transmittance. As a disperser, for example, "UH-50" (trade name, manufactured by MST Co., Ltd.) or the like can be used.

[0103] Furthermore, the cured film thickness of the glitter coating film is preferably about 0.01 to 2.0 μm, more preferably about 0.025 to 1.0 μm, and even more preferably about 0.05 to 0.5 μm, from the viewpoint of forming a coating film having an excellent glossy appearance and high millimeter wave transmittance.

[0104] Step (2) According to the method for forming a multilayer coating film of the present disclosure, a clear coating composition (Z) is then applied onto the glossy coating film formed in step (1) to form a clear coating film.

[0105] Any known thermosetting coating composition can be used as the clear coating composition (Z), such as 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, or a powder thermosetting coating composition.

[0106] 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.

[0107] Preferred combinations of base resin / curing agent for the 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.

[0108] The clear coating composition (Z) may be a one-component coating, or a multi-component coating such as a two-component coating. A two-component coating may be a coating consisting of a liquid containing a base resin and another liquid containing a curing agent.

[0109] Of these, the clear coating composition (Z) is preferably a two-component clear coating composition containing each of the following hydroxyl group-containing resin (z1) and polyisocyanate compound (z2), from the viewpoint of adhesion of the resulting coating film.

[0110] 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 can be used alone or in combination of two or more.

[0111] 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 multilayer coating film to be formed.

[0112] Hydroxyl-containing acrylic resin (z11) The hydroxyl-containing acrylic resin (z11) can be produced, for example, by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl-containing polymerizable unsaturated monomer by a method known per se, such as a solution polymerization method in an organic solvent or an emulsion polymerization method in water.

[0113] 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 disclosure, a monomer corresponding to the polymerizable unsaturated monomer having an ultraviolet-absorbing functional group (xvii) described later 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 monomer can be used alone or in combination of two or more kinds.

[0114] 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) Polymerizable unsaturated monomers containing an aromatic ring: 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, etc. (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, etc. (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-(meth)acryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-(meth)acryloyloxy-2-hydroxypropoxy)benzophenone, 2-[2-hydroxy-5-[2-((meth)acryloyloxy)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 (meth)acrylamide, acetoacetoxyethyl methacrylate, formylstyrene, vinyl alkyl ketones having 4 to 7 carbon atoms (e.g., 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.

[0115] 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.

[0116] 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.

[0117] In the production of the hydroxyl group-containing acrylic resin (z11), the amount of the hydroxyl group-containing polymerizable unsaturated monomer used is suitably within the range of 15 to 50% by mass, preferably 20 to 40% by mass, based on the total amount of the polymerizable unsaturated monomer components constituting the hydroxyl group-containing acrylic resin (z11), from the viewpoints of adhesion, chipping resistance, finished appearance, etc. of the multilayer coating film to be formed.

[0118] 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, finished appearance, etc. of the multilayer coating film to be formed.

[0119] The weight average molecular weight of the hydroxyl group-containing acrylic resin (z11) is preferably in the range of 2,000 to 50,000, particularly 3,000 to 30,000, and 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.

[0120] Furthermore, 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 clear coating composition (Z).

[0121] 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.

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

[0123] 1 / Tg(K)=(W1 / T1)+(W2 / T2)+... (1) Tg(°C)=Tg(K)-273 (2) In each formula, W1, W2,... represent the mass fraction of each monomer used in 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 the monomer is unclear, the glass transition temperature (°C) is taken as the static glass transition temperature. For example, a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instruments Inc.) is used. A sample is placed in a measuring cup, and the solvent is completely removed by vacuum suction. Then, the change in calorific value is measured in the range of -20°C to +200°C at a heating rate of 3°C / min, and the first change point in the baseline on the low temperature side is taken as the static glass transition temperature.

[0124] As a copolymerization method for obtaining the hydroxyl group-containing acrylic resin (z11) by copolymerizing the 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.

[0125] 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, and diethylene glycol dimethyl ether. Examples of the solvent include glycol ether solvents such as diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and diethylene glycol monomethyl ether acetate; 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, and methoxybenzene; and aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, and dichlorobenzene.

[0126] 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).

[0127] The hydroxyl group-containing acrylic resin (z11) can be used alone or in combination of two or more kinds.

[0128] 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.

[0129] 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), isocyanate); and aliphatic triisocyanates 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.

[0130] 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 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

[0033] Examples of such alicyclic triisocyanates 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.

[0131] 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.

[0132] 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 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.

[0133] Furthermore, examples of the derivatives of the polyisocyanates include dimers, trimers, biurets, allophanates, uretdione, uretimine, isocyanurates, oxadiazinetrione, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the above polyisocyanates.

[0134] The above polyisocyanates and derivatives thereof may be used alone or in combination of two or more kinds.

[0135] Among aliphatic diisocyanates, hexamethylene diisocyanate compounds and among alicyclic diisocyanates, methylenebis(4,1-cyclohexanediyl)diisocyanate can be preferably used. Among these, derivatives of hexamethylene diisocyanate are particularly suitable from the viewpoints of adhesion, compatibility, etc.

[0136] 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.

[0137] Furthermore, as the polyisocyanate compound (z2), a blocked polyisocyanate compound, which is a compound in which the isocyanate groups in the above polyisocyanates and derivatives thereof are blocked with a blocking agent, can also be used.

[0138] 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 ... alcohol-based solvents such as methyloxyethyl methacrylate; oxime-based solvents such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based solvents 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 the 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 the 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.

[0139] When blocking is carried out (reaction of the blocking agent), a solvent may be added as necessary.

[0140] The polyisocyanate compounds (z2) can be used either alone or in combination of two or more.

[0141] In the clear coating composition (Z), the equivalent ratio (NCO / OH) of the isocyanate groups of the polyisocyanate compound (z2) to the hydroxyl groups of the hydroxyl-containing resin (z1) is preferably within the range of 0.5 to 2.0, more preferably 0.8 to 1.5.

[0142] The clear coating composition (Z) may contain, as required, water, solvents such as organic solvents, curing catalysts, antifoaming agents, ultraviolet absorbers, rheology control agents, anti-settling agents and other coating additives.

[0143] A coloring pigment can also be used in the clear coating composition (Z) as appropriate, provided that the transparency of the coating film is not impaired. As the coloring pigment, pigments known per se for inks or coatings can be used alone or in combination of two or more. The blending amount varies depending on the type of coloring pigment used, but can usually be 30% by mass or less, preferably 0.05 to 20% by mass, and more preferably 0.1 to 10% by mass, based on the total solid content of the resin components of the clear coating composition (Z).

[0144] The 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.

[0145] The solids content of the clear coating composition (Z) is in the range of 10 to 65% by mass, preferably 15 to 55% by mass, and more preferably 20 to 50% by mass. Furthermore, it is preferable to appropriately adjust the viscosity of the clear coating composition (Z) using water and / or an organic solvent so that it is in a range suitable for coating, typically in the range of about 15 to 60 seconds, particularly about 20 to 50 seconds, at 20°C as measured using a Ford Cup No. 4 viscometer.

[0146] Step (3) According to the method for forming a multilayer coating film of an embodiment of the present disclosure, the glossy coating film and the clear coating film formed in steps (1) and (2), respectively, are then baked and cured separately or simultaneously.

[0147] From the viewpoint of shortening the process, it is preferable that the glossy coating film and the clear coating film are simultaneously heat-cured.

[0148] Examples of heating devices used to simultaneously bake the uncured coating films include drying ovens that use a heat source such as hot air, gas, infrared rays, or high frequency. The baking temperature is preferably 70 to 160°C, more preferably 100 to 140°C. The baking time is preferably 10 to 60 minutes, more preferably 10 to 40 minutes. By performing baking under these conditions, the multilayer coating film can be sufficiently cured.

[0149] In the present disclosure, the bake hardening time means the time during which the substrate surface actually maintains the target baking temperature, and more specifically, the time during which the target temperature is maintained after it has been reached, regardless of the time it takes to reach the target baking temperature.

[0150] The thickness of the multilayer coating film obtained by the method for forming a multilayer coating film of the present disclosure, which includes steps (1) to (3), may be, for example, in the range of 20 μm to 150 μm, preferably 30 μm to 140 μm, and more preferably 50 μm to 100 μm.

[0151] Method for producing aqueous paint and method for producing aqueous ink In one embodiment, the present disclosure provides a method for producing an aqueous paint using an indium particle dispersion produced by the production method described in the section "1. Indium particle dispersion and method for producing same." In another embodiment, the present disclosure provides a method for producing an aqueous ink using an indium particle dispersion produced by the above production method. The aqueous paint and the aqueous ink may be a glittering paint composition (Y). Both the aqueous paint and the aqueous ink can be produced by adding various components such as a resin to the indium particle dispersion.

[0152] The resin used in the water-based paint and water-based ink is appropriately selected depending on the purpose, etc. Examples of the resin include acrylic resin, urethane resin, acrylic silicone resin, polyester resin, and acrylic urethane resin. The water-based paint and water-based ink obtained by the manufacturing method of this embodiment are applied to various substrates by coating, printing, or other techniques, and are used to express the desired metallic appearance.

[0153]

[0010] In one embodiment, the present disclosure provides a method for producing a laminate, the method comprising applying the aqueous coating material produced by the aforementioned production method onto a substrate to form a coating layer. In another embodiment, the present disclosure provides a method for producing a laminate, the method comprising applying the aqueous ink produced by the aforementioned production method onto a substrate to form a print layer.

[0154] Various films, sheets, resin molded bodies, and the like can be used as the substrate. The 20° gloss value of the surface of the formed coating film layer or printed layer is preferably 200 to 500. Furthermore, the 60° gloss value of the surface of the formed coating film layer or printed layer is preferably 140 to 400, more preferably 150 to 400. It is preferable that the surface of the formed coating film layer or printed layer satisfy one or both of the 20° gloss value and the 60° gloss value ranges described above. By setting the lower limit of the gloss value to the above-mentioned numerical value, the desired metallic appearance can be expressed. On the other hand, by setting the upper limit of the gloss value to the above-mentioned numerical value, excessive reflection of sunlight or lighting can be suppressed when used, for example, as a vehicle paint, thereby reducing the burden on drivers of oncoming and following vehicles.

[0155] The method for producing a laminate preferably further includes a step of forming a coating layer on the paint film layer or the printed layer. The laminate preferably has a substrate, a paint film layer or the printed layer, and a coating layer laminated in this order. By providing the coating layer, it is possible to effectively prevent the paint film layer or the printed layer from peeling off from the substrate. The coating layer can be formed, for example, by applying a coating agent such as a lacquer containing various resins onto the paint film layer or the printed layer, followed by drying. Examples of resins used in coating agents such as lacquers include (meth)acrylate ester-(meth)acrylic acid copolymers, styrene-(meth)acrylate ester-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid copolymers, ethylene-vinyl acetate-(meth)acrylic acid copolymers, ethylene-(meth)acrylate ester-(meth)acrylic acid copolymers, ammonium salts and amine salts of these copolymers, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate phthalate, vinyl alcohol-vinyl acetate copolymers, vinyl alcohol-ethylene copolymers, hydrophilic polyurethanes, hydrophilic polyesters, and ethylene oxide-alkylene (C3, C4) oxide copolymers.

[0156] Examples of methods for applying the water-based paint, water-based ink, and coating agent to a predetermined location include known coating methods such as gravure printing, flexographic printing, brush coating, gravure coating, die coating, bar coating, spray coating, flow coating, dip coating, spin coating, and curtain coating.

[0157] Methods for drying the aqueous paint, aqueous ink, and coating agent applied to a predetermined location include, for example, vacuum drying, pressure drying, heat drying, and air drying. Heating may also be used during drying. The heating temperature is preferably 30 to 150°C, and more preferably 40 to 100°C.

[0158] Products The above-mentioned water-based paints and water-based inks are capable of forming coating layers and print layers with high gloss and excellent metallic tones, and are environmentally friendly because they are water-based. Therefore, taking advantage of these properties, the above-mentioned water-based paints and water-based inks can be suitably used as materials for painting vehicle parts such as car bodies, door handles, and bumpers. Furthermore, laminates manufactured using the above-mentioned water-based paints and water-based inks have excellent transmittance for millimeter waves such as LiDAR. Therefore, taking advantage of these properties, the above-mentioned laminates can be suitably used as materials for constructing smartphones, home appliances, automotive electronic components, and the like.

[0159] 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.

[0160] Test 1 [1] Preparation of substrate 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., which uses an epoxy resin polyamine-based cationic resin and a blocked polyisocyanate compound as a curing agent) to a film thickness of 20 μm based on the cured coating, and the coating was then heated at 170°C for 20 minutes to crosslink and cure, forming an electrodeposition coating.

[0161] Onto the electrodeposition coated surface of the steel plate obtained, "TP-65-2" (trade name, manufactured by Kansai Paint Co., Ltd., polyester resin and amino resin-based organic solvent-based intermediate coating composition) was electrostatically coated using a rotary atomizer electrostatic coater so as to give 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 a coated object.

[0162] [2] Preparation of Paints Preparation of Luster Pigment (y1) Preparation Example 1 100 parts (20 parts solids) of "Leaf Powder 49CJ-1120" (trade name, manufactured by Oike Metallic Design Co., Ltd., untreated indium particles, solids content 20% by mass, dispersed in propylene glycol monomethyl ether) were weighed into a beaker. This was stirred using a disperser. 0.5 parts (0.5 parts solids) of an amino group-containing silane coupling agent ("KBM-903", trade name, manufactured by Shin-Etsu Chemical Co., Ltd., 3-aminopropyltrimethoxysilane, solids content 100% by mass) was added to this, followed by the addition of 9 parts of a 1 / 1 water / methanol mixed solvent to initiate hydrolysis. Stirring was continued for 20 hours, after which an additional 9 parts of a 1 / 1 water / methanol mixed solvent was added, and stirring was continued for another hour. After one hour had passed, the stirring was stopped and the mixture was collected in a sample container to obtain a bright pigment (y1-1) having a solid content of 17.3% by mass as a sample for use in producing a paint.

[0163] Production Examples 2 to 6 Bright pigments (y1-2) to (y1-6) were obtained in the same manner as in Production Example 1, except that the formulations and solid contents shown in Table 1 were used.

[0164]

[0165] (*1) Amino group-containing silane coupling agent: "KBM-903" (trade name, manufactured by Shin-Etsu Chemical Co., Ltd., 3-aminopropyltrimethoxysilane, solid content 100% by mass). (*2) Epoxy group-containing silane coupling agent: "KBM-403" (trade name, manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane, solid content 100% by mass). (*3) Methyl group-containing silane coupling agent: "KBM-13" (trade name, manufactured by Shin-Etsu Chemical Co., Ltd., methyltrimethoxysilane, solid content 100% by mass).

[0166] Production of Viscosity Modifier (y4) Production Example 7 In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen gas inlet tube, and two dropping devices, a mixture consisting of 20 parts of methacrylic acid, 19.5 parts of the acrylate of n-octadecyl alcohol ethylene oxide 60 mole adduct, 60 parts of propyl acrylate, and 0.5 parts of the diacrylate of ethylene glycol ethylene oxide 15 mole adduct, and 50 parts of a 1% solution of 2,2'-azobisisobutyronitrile in methyl triglycol were added dropwise from the dropping funnel to 350 parts of methyl triglycol at a constant rate over 1.5 hours, while stirring uniformly to allow the reaction to proceed. The reaction temperature was maintained at 80-90 ° C. After the completion of the dropwise addition, the mixture was maintained at the same temperature for 3 hours and then cooled to 40 ° C. to obtain a diluted acrylic association thickener solution (y4-1) with a solids content of 20% by mass.

[0167] Production Example 8 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen gas inlet tube, and two dropping devices was charged with 15.4 parts of the following macromonomer solution (solid content: 10 parts), 20 parts of ethylene glycol monobutyl ether, and 30 parts of diethylene glycol monoethyl ether acetate, and the temperature was raised to 85°C while blowing nitrogen gas into the liquid. Next, into a reaction vessel maintained at the same temperature, a mixture consisting of 31.5 parts of N,N-dimethylacrylamide, 31.5 parts of N-isopropylacrylamide, 27 parts of 2-hydroxyethyl acrylate, 10 parts of ethylene glycol monobutyl ether, and 40 parts of diethylene glycol monoethyl ether acetate, and a mixture consisting of 0.15 parts of "Perbutyl O" (trade name, manufactured by NOF Corporation, polymerization initiator, tert-butylperoxy-2-ethylhexanoate) and 20 parts of ethylene glycol monobutyl ether were simultaneously added dropwise over 4 hours, and after completion of the addition, the mixture was stirred at the same temperature for 2 hours to perform aging. Next, into the reaction vessel maintained at the same temperature, a mixture consisting of 0.3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) and 15 parts of ethylene glycol monobutyl ether was added dropwise over 1 hour, and after completion of the addition, the mixture was stirred at the same temperature for 1 hour to perform aging. Next, the mixture was cooled to 30°C while adding ethylene glycol monobutyl ether, to obtain a copolymer solution having a solid content of 35% by mass. The weight average molecular weight of the obtained copolymer was 310,000. 215 parts of deionized water was added to the obtained copolymer solution to obtain a diluted acrylic associative thickener solution (y4-2) having a solid content of 20% by mass.

[0168] Macromonomer solution: A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen gas inlet tube, and dropping device was charged with 16 parts of ethylene glycol monobutyl ether and 3.5 parts of 2,4-diphenyl-4-methyl-1-pentene. Nitrogen gas was passed through the gas phase, and the temperature was raised to 160°C while stirring. Once the temperature reached 160°C, a mixed solution consisting of 30 parts of n-butyl methacrylate, 40 parts of 2-ethylhexyl methacrylate, 30 parts of 2-hydroxyethyl methacrylate, and 7 parts of di-tert-amyl peroxide was added dropwise over 3 hours, and the mixture was stirred at the same temperature for 2 hours. The mixture was then cooled to 30°C and diluted with ethylene glycol monobutyl ether to obtain a macromonomer solution with a solids content of 65% by mass. The hydroxyl value of the resulting macromonomer was 129 mgKOH / g, and the number average molecular weight was 2,300.

[0169] Production of Glittering Coating Composition (Y) Production Example 9 To a stirring and mixing vessel were added 115.6 parts (solids content 20 parts) of the glittering pigment (y1-1) obtained in Production Example 1, 1.8 parts (solids content 1.8 parts) of BYK-348 (trade name, manufactured by BYK Corporation, silicone-based surface conditioner, solids content 100% by mass), 1.8 parts (solids content 1.8 parts) of "Plysurf A208F" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., polyoxyethylene alkyl (C8) ether phosphate ester, aqueous solution with a solids content of 99% by mass), 9 parts (solids content 1.8 parts) of the acrylic associative thickener diluted solution (y4-1) obtained in Production Example 7, 51.9 parts of a 1% aqueous dimethylethanolamine solution, and 330 parts of distilled water, and the mixture was stirred and mixed to produce a glittering coating composition (Y-1) with a solids content of 5.0% by mass.

[0170] Production Examples 10 to 19 Brilliant coating compositions (Y-2) to (Y-11) were obtained in the same manner as in Production Example 9, except that the formulations shown in Table 2 were used.

[0171]

[0172] (*4) "BYK-381": Trade name, manufactured by BYK Corporation, acrylic surface conditioner, solid content 52% by mass, internal solvent: dipropylene glycol monomethyl ether. (*5) "BYK-190": Trade name, manufactured by BYK Corporation, styrene-based block copolymer, solid content 40% by mass.

[0173] Preparation of Clear Coating Composition (Z) Clear Coating Composition (Z-1) "KINO-6510" (trade name, Kansai Paint Co., Ltd., hydroxyl group / isocyanate group curing type acrylic resin / urethane resin based two-component organic solvent-based coating composition containing a hydroxyl group-containing resin and a polyisocyanate compound) was used as clear coating composition (Z-1).

[0174] [3] Preparation of test plate Example 1 Preparation of test plate for measuring specular gloss (60° gloss) The glitter coating composition (Y-1) produced in [2] above was stirred for 1 minute using an ultrasonic disperser "UH-50" (trade name, manufactured by MST Co., Ltd.).

[0175] Next, the glitter coating composition (Y-1) 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 68% so as to give a cured coating film with a thickness of 0.05 µm. The coating was then left to stand at room temperature for 3 minutes and then preheated at 80°C for 3 minutes to give an uncured glitter coating film.

[0176] Next, the clear coating composition (Z-1) prepared in [2] above was applied onto the uncured glitter coating film using a minibell-type rotary electrostatic coater at a booth temperature of 23°C and humidity of 68% so as to give a cured coating film of 35 μm, and 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 preparing a test plate for measuring the specular gloss (60° gloss) of Example 1. Here, the film thickness of the dried glitter coating film was calculated using the following formula. The same applies to the following examples. Film thickness [μm] = sc / sg / S * 10000 sc: coated solids [g] sg: coating specific gravity [g / cm ３ ] S: Evaluation area of ​​coating solids [cm ２ ]

[0177] Preparation of test plate for measuring millimeter wave transmittance In the above "Preparation of test plate for measuring specular gloss (60° gloss)", a test plate for measuring millimeter wave transmittance was prepared in the same manner as in "Preparation of test plate for measuring specular gloss (60° gloss)", except that an OHP sheet (manufactured by Fujifilm Business Innovation Japan Co., Ltd., "PPC / laser OHP film GAAA5224", polyethylene terephthalate (PET), thickness 100 μm) was used instead of the substrate prepared in [1] above.

[0178] Examples 2 to 10 and Comparative Example 1 Test plates for measuring specular gloss (60° gloss) and millimeter wave transmittance were obtained in the same manner as in Example 1, except that the paints, preheating temperatures, and preheating times shown in Table 3 were used.

[0179] Evaluation of Coating Film The coating film of each test plate obtained as described above was evaluated by the following method.

[0180] Specular gloss (60° gloss) The 60° gloss value was measured using a gloss meter (micro-TRI-gloss, manufactured by BYK-Gardner). A higher value indicates better gloss. A value of 140 or higher is considered acceptable.

[0181] Millimeter-wave transmittance Using a "Vector Network Analyzer" (ME7838A, manufactured by Anritsu Corporation), electromagnetic waves having a frequency of 60 to 90 GHz were incident from a transmitter at an incident angle of 0° at room temperature, and the "attenuation rate when only an OHP sheet was placed" and the "attenuation rate when a test plate for measuring millimeter-wave transmittance was placed" were measured, and the attenuation rate at 76 GHz was calculated using the following formula (3): Attenuation rate (dB) = (attenuation rate when only an OHP sheet was placed) - (attenuation rate when a test plate for measuring millimeter-wave transmittance was placed) Formula (3) From the obtained attenuation rate, the millimeter-wave transmittance at 76 GHz was calculated using the following formula (4): Millimeter-wave transmittance (%) = 10 - {(attenuation rate) / 20} x 100 Formula (4)

[0182] The results are shown in Table 3. In the multilayer coating films of Examples 1 to 10 formed using a bright coating composition containing surface-treated indium particles, the penetration of the components in the clear coating composition into the bright coating film was suppressed, thereby suppressing a decrease in the brightness of the multilayer coating film, and the specular gloss (60° gloss) of the multilayer coating film was higher than that of the multilayer coating film of Comparative Example 1 formed using a bright coating composition containing untreated indium particles.

[0183] Test 2 [1] Substrate: An aluminum plate was prepared. [2] Preparation of Coating: Preparation of Indium Particle Dispersion (Example 1A) 50 g of a solvent-based dispersion containing flaky indium particles and propylene glycol monobutyl ether (trade name "Leaf Powder 49CJ-1120", manufactured by Oike Kogyo Co., Ltd., solids content 20%) and a rotor were placed in a beaker, and the mixture was stirred using a magnetic stirrer. 0.5 g of methyltrimethoxysilane (trade name "KBM-13", manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise to the beaker, and then 2 g of water was added to initiate hydrolysis. After 20 hours, an additional 3 g of water was added and the mixture was stirred for 1 hour, yielding an indium particle dispersion containing surface-treated flaky indium particles.

[0184] Examples 2A and 3A Indium particle dispersions were obtained in the same manner as in Example 1A, except that the conditions shown in Table 4 were used.

[0185] Example 4A 50 g of a solvent-based dispersion containing flaky indium particles and propylene glycol monobutyl ether (trade name "Leaf Powder 49CJ-1120", manufactured by Oike Kogyo Co., Ltd., solids content 20%) and a rotor were placed in a beaker, and the mixture was stirred using a magnetic stirrer. 0.5 g of methyltrimethoxysilane (trade name "KBM-13", manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise to the beaker, and then 4 g of a 1:1 water / methanol mixed solvent was added to initiate hydrolysis. After 20 hours, an additional 5 g of a water / methanol mixed solvent was added and stirred for 1 hour, yielding an indium particle dispersion containing surface-treated flaky indium particles.

[0186] Examples 5A to 13A, 17A, 18A, Comparative Example 1A Indium particle dispersions were obtained in the same manner as in Example 4A, except that the conditions shown in Table 4 were used.

[0187] (Example 14A) 50 g of a solvent-based dispersion containing flaky indium particles and propylene glycol monobutyl ether (trade name "Leaf Powder 49CJ-1120", manufactured by Oike Kogyo Co., Ltd., solids content 20%) and a rotor were placed in a beaker, and the mixture was stirred using a magnetic stirrer. 0.5 g of methyltrimethoxysilane (trade name "KBM-13", manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise to the beaker, and then 4 g of a 1:1 water / methanol mixed solvent was added to initiate hydrolysis. After 20 hours, an additional 8.5 g of a water / methanol mixed solvent was added and stirred for 1 hour, yielding an indium particle dispersion containing surface-treated flaky indium particles.

[0188] Examples 15A and 16A Indium particle dispersions were obtained in the same manner as in Example 14A, except that the conditions shown in Table 4 were used.

[0189] The meanings of the abbreviations in Table 4 are as follows: CP-1: Methyltrimethoxysilane CP-2: 3-glycidoxypropyltrimethoxysilane CP-3: 3-aminopropyltrimethoxysilane CP-4: 8-glycidoxyoctyltrimethoxysilane CP-5: N-2-(aminoethyl)-8-aminooctyltrimethoxysilane CP-6: 3-methacryloxypropyltrimethoxysilane CP-7: Vinyltrimethoxysilane Water / Meth: Mixed solvent of water / methanol = 1 / 1 (mass ratio) Water / IPA: Mixed solvent of water / isopropyl alcohol = 1 / 1 (mass ratio)

[0190]

[0191] Preparation of Water-Based Paint <Preparation and Evaluation of Coated Panels> A resin solution was obtained by mixing 40 g of paint resin, 10 g of isopropyl alcohol, 20 g of water, and 30 g of propylene glycol monomethyl ether. An acrylic resin (trade name "Acryset ARL-453", manufactured by Nippon Shokubai Co., Ltd.) was used as the paint resin. 50 g of each of the indium particle dispersions of Examples 1A to 18A and Comparative Example 1A was placed in a beaker, and 10 g of the resin solution was added while stirring using a disperser. The mixture was stirred for 10 minutes to obtain a water-based paint. [3] Preparation of Test Panels Preparation of Test Panels The obtained paint was applied to an aluminum plate using a No. 10 bar coater and allowed to set for 10 minutes to form a coating layer.

[0192] An acrylic lacquer (manufactured by Isamu Paint Co., Ltd.) was diluted two-fold with a mixed solvent of toluene / ethyl acetate / butanol / methyl isobutyl ketone = 65 / 15 / 10 / 10 (mass ratio) to obtain a coating agent. The resulting coating agent was applied to the paint layer using a No. 6 bar coater. Air-dried for 1 hour to form a coating layer on the paint layer, obtaining a coated plate (laminate). Coating evaluation: The 20° gloss and 60° gloss values ​​of the paint layer surface of the resulting coated plate were measured using a Micro Trigloss gloss meter (BYK Corporation). The results are shown in Table 5.

[0193] In this test, a 20° gloss value of 200 or more, preferably 250 or more, is evaluated as being particularly excellent in expressing a metallic tone. Also, a 60° gloss value of 150 or more, preferably 200 or more, is evaluated as being particularly excellent in expressing a metallic tone.

[0194]

[0195] 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.

[0196] 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.

[0197] 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. A method for forming a multilayer coating film, comprising the following steps (1) to (3): step (1): applying a glittering coating composition (Y) containing a glittering pigment (y1) to an object to be coated to form a glittering coating film; step (2): applying a clear coating composition (Z) to the glittering coating film formed in step (1) to form a clear coating film; and step (3): baking and curing the glittering coating film and clear coating film formed in steps (1) and (2) separately or simultaneously, wherein the glittering pigment (y1) contains indium particles treated with a silane coupling agent.

2. A method for forming a multilayer coating film according to claim 1, wherein the silane coupling agent is at least one selected from the group consisting of amino group-containing silane coupling agents, epoxy group-containing silane coupling agents, and methyl group-containing silane coupling agents.

3. The method for forming a multilayer coating film according to claim 1, wherein the amount of the silane coupling agent is 0.1 to 10 parts by mass per 100 parts by mass of the solid content of the untreated indium particles.

4. A method for forming a multi-layer coating film according to claim 1, wherein the glittering coating composition (Y) further contains a surface conditioner (y2), a pigment dispersant (y3), a viscosity adjuster (y4) and water (y5), and has a solids content of 0.1 to 15 mass %.

5. The method for forming a multi-layer coating film according to claim 4, wherein the surface conditioner (y2) includes a silicone-based surface conditioner.

6. The method for forming a multi-layer coating film according to claim 4, wherein the pigment dispersant (y3) comprises a phosphate group-containing compound.

7. The method for forming a multi-layer coating film according to claim 4, wherein the viscosity modifier (y4) includes an associative viscosity modifier.

8. A method for forming a multilayer coating film according to claim 4, wherein the content of the water (y5) is within the range of 50 to 95 parts by mass per 100 parts by mass of the total of all components of the glittering coating composition (Y).

9. The method for forming a multilayer coating film according to claim 1, further comprising the steps of: producing an indium particle dispersion, the step comprising adding a silane coupling agent and an aqueous medium to a solvent-based dispersion containing flaky indium particles and an organic solvent, and hydrolyzing the silane coupling agent to surface treat the indium particles; and providing a bright coating composition (Y) containing the indium particle dispersion, wherein the indium particles have a number average particle diameter of 0.1 to 1 μm and a number average thickness of 10 to 100 nm, the silane coupling agent is a compound represented by the following general formula (1), the amount of the silane coupling agent per 100 parts by mass of the indium particles is 0.1 to 10 parts by mass, and the amount of the aqueous medium per 100 parts by mass of the solvent-based dispersion is 5 to 30 parts by mass. (In the general formula (1), R represents a methyl group or an ethyl group, and X represents an alkyl group having 1 to 4 carbon atoms or a group represented by any one of the following general formulas (2) to (4)). (In the general formula (2), A represents an alkylene group having 1 to 10 carbon atoms. In the general formula (3), W represents an alkylene group having 2 to 4 carbon atoms. In the general formula (4), Y represents an alkylene group having 1 to 4 carbon atoms, and Z represents an alkylene group having 2 to 10 carbon atoms. In addition, in the general formulas (2) to (4), "*" indicates the bonding position with "Si" in the general formula (1)).

10. The method for forming a multi-layer coating film according to claim 9, wherein the organic solvent contains propylene glycol monomethyl ether.

11. A method for forming a multilayer coating film as described in claim 9, wherein in the manufacturing process, the silane coupling agent and the aqueous medium are added to the solvent-based dispersion, and then the mixture is stirred for 5 hours or more to hydrolyze the silane coupling agent.

12. A method for forming a multilayer coating film as described in claim 9, wherein the aqueous medium is water or a mixed solvent of water and alcohol, and the amount of alcohol in the mixed solvent per 1 mass part of water is 2.5 mass parts or less.

13. A method for producing an indium particle dispersion, comprising the steps of adding a silane coupling agent and an aqueous medium to a solvent-based dispersion containing flaky indium particles and an organic solvent, and hydrolyzing the silane coupling agent to surface treat the indium particles, wherein the indium particles have a number average particle diameter of 0.1 to 1 μm and a number average thickness of 10 to 100 nm, the silane coupling agent is a compound represented by the following general formula (1), the amount of the silane coupling agent per 100 parts by mass of the indium particles is 0.1 to 10 parts by mass, and the amount of the aqueous medium per 100 parts by mass of the solvent-based dispersion is 5 to 30 parts by mass. (In the general formula (1), R represents a methyl group or an ethyl group, and X represents an alkyl group having 1 to 4 carbon atoms or a group represented by any one of the following general formulas (2) to (4)). (In the general formula (2), A represents an alkylene group having 1 to 10 carbon atoms. In the general formula (3), W represents an alkylene group having 2 to 4 carbon atoms. In the general formula (4), Y represents an alkylene group having 1 to 4 carbon atoms, and Z represents an alkylene group having 2 to 10 carbon atoms. In addition, in the general formulas (2) to (4), "*" indicates the bonding position with "Si" in the general formula (1)).

14. The method for producing an indium particle dispersion liquid according to claim 13, wherein the organic solvent includes propylene glycol monomethyl ether.

15. The method for producing an indium particle dispersion liquid according to claim 13, wherein the silane coupling agent and the aqueous medium are added to the solvent-based dispersion liquid, and then the mixture is stirred for 5 hours or more to hydrolyze the silane coupling agent.

16. The method for producing an indium particle dispersion liquid according to claim 13, wherein the aqueous medium is water or a mixed solvent of water and alcohol, and the amount of the alcohol in the mixed solvent is 2.5 parts by mass or less per part by mass of the water.

17. A method for producing an aqueous paint using an indium particle dispersion produced by the method according to any one of claims 13 to 16.

18. A method for producing a water-based ink using an indium particle dispersion produced by the method according to any one of claims 13 to 16.

19. A method for producing a laminate, comprising the step of applying the aqueous coating material produced by the method of claim 17 onto a substrate to form a coating layer.

20. The method for producing a laminate according to claim 19, further comprising the step of forming a coating layer on said paint film layer.

21. A method for producing a laminate, comprising the step of applying the water-based ink produced by the method of claim 18 onto a substrate to form a printed layer.

22. The method for producing a laminate according to claim 21, further comprising the step of forming a coating layer on the printed layer.

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