Method for forming multilayer coating film

Abstract

This method for forming a multilayer coating film includes steps (1) to (3). Step (1) is a step for coating an aqueous coating material composition (X) on an object to be coated to form a first coating film. Step (2) is a step for coating a photoluminescent coating material composition (Y) on the first coating film formed in step (1) to form a second coating film. Step (3) is a step for separately or simultaneously baking and curing the first coating film formed in step (1) and the second coating film formed in step (2). The photoluminescent coating material composition (Y) is coated while the complex viscosity of the first coating film, as measured at a frequency of 0.1 Hz and a temperature of 25°C, falls within the range 100,000-1,500,000 Pa·s. The photoluminescent coating material composition (Y) contains indium particles (y1).

Description

Method for forming a multilayer coating film

[0001] The present invention relates to a method for forming a multilayer coating film.

[0002] The purpose of painting is mainly to protect the material and impart aesthetics. In industrial products, aesthetics, especially "texture", is important from the perspective of enhancing the product's competitiveness. The textures required by consumers for industrial products are diverse, but in recent years, in fields such as automotive exterior panels, automotive parts, and home appliances, an excellent gloss is required.

[0003] Technologies for imparting an excellent gloss to the surface of industrial products include metal plating and metal vapor deposition (for example, see Patent Document 1). However, if an excellent gloss can be imparted by painting, it is advantageous from the viewpoints of simplicity and cost.

[0004] Patent Document 2 describes that a metallic paint base containing a brightening material, a non-volatile solid content containing a resin, and a solvent is diluted at a dilution ratio of 150 to 500% using a diluent composed of a high-boiling solvent and a low-boiling solvent, and 5 to 10 parts by weight of a viscous resin is added to 100 parts by weight of the resin content in the above metallic paint base. According to the metallic paint, a good metallic appearance can be achieved. However, the appearance formed by the above metallic paint has insufficient gloss.

[0005] In recent years, for automotive collision prevention support, the application of a millimeter-wave radar using radio waves in the millimeter-wave band has been attempted. However, in a coating film formed from a conventional metallic paint using an aluminum pigment as a brightening material, the millimeter-wave radar may be blocked by the aluminum pigment in the coating film.

[0006] Japanese Patent Application Laid-Open No. 63-272544, Japanese Patent Application Laid-Open No. 2003-313500

[0007] An object of the present invention is to provide a method for forming a multilayer coating film that can form a coating film having an excellent gloss and high millimeter-wave transparency.

[0008] The present invention encompasses the subject matter described in the following sections.

[0009] Item 1. A method for forming a multilayer coating film, comprising the following steps (1) to (3): Step (1): A step of applying an aqueous coating composition (X) onto an object to be coated to form a first coating film; Step (2): A step of applying a glossy coating composition (Y) onto the first coating film formed in Step (1) to form a second coating film; and Step (3): A step of baking and curing the first coating film formed in Step (1) and the second coating film formed in Step (2) separately or simultaneously, wherein the glossy coating composition (Y) is applied while the complex viscosity of the first coating film is in the range of 100,000 to 1,500,000 Pa·s when measured under conditions of a frequency of 0.1 Hz and a temperature of 25°C, and the glossy coating composition (Y) contains indium particles (y1).

[0010] Item 2. The method for forming a multilayer coating film according to Item 1, wherein the glossy coating composition (Y) further contains a surface modifier (y2), a pigment dispersant (y3), a viscosity modifier (y4), and water (y5), and has a solid content of 0.1 to 15% by mass.

[0011] Item 3. The multilayer coating method according to Item 2, wherein the surface modifier (y2) includes a silicone-based surface modifier.

[0012] Item 4. The method for forming a multilayer coating film according to Item 2, wherein the pigment dispersant (y3) contains a phosphate group-containing compound.

[0013] Item 5. The method for forming a multilayer coating according to Item 2, wherein the viscosity modifier (y4) includes an aggregate viscosity modifier.

[0014] Item 6. The method for forming a multilayer coating according to Item 2, wherein the water (y5) content is in the range of 45 to 95 parts by mass per 100 parts by mass of the total components of the glossy coating composition (Y).

[0015] According to the multi-layer coating film formation method of the present invention, it is possible to form a coating film that has excellent gloss and high millimeter-wave transmittance.

[0016] The present invention provides a method for forming a multilayer coating film, comprising the following steps (1) to (3): step (1): applying an aqueous coating composition (X) to an object to be coated to form a first coating film; step (2): applying a glossy coating composition (Y) to the first coating film formed in step (1) to form a second coating film; and step (3): baking and curing the first coating film formed in step (1) and the second coating film formed in step (2) separately or simultaneously. The method is characterized in that the glossy coating composition (Y) is applied while the complex viscosity of the first coating film is measured under conditions of a frequency of 0.1 Hz and a temperature of 25°C and is in the range of 100,000 to 1,500,000 Pa·s, and the glossy coating composition (Y) contains indium particles (y1).

[0017] Step (1) According to the multilayer coating film forming method of the present invention, first, an aqueous coating composition (X) is applied to the object to be coated, and a first coating film is formed.

[0018] The substrate to which the aqueous coating composition (X) is applied is not particularly limited. Examples of such substrates include the exterior panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts such as bumpers; and the exterior panels of household electrical appliances such as mobile phones and audio equipment. Of these, the exterior panels of automobile bodies and automobile parts are preferred.

[0019] The materials of these objects to be coated are not particularly limited. Examples include metallic materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized 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, epoxy resin, and various FRP plastic materials; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth. Of these, metallic and plastic materials are preferred.

[0020] The surfaces to which the multi-layer coating is applied may include metal surfaces such as the exterior panels of automobile bodies, automobile parts, household electrical appliances, and metal substrates such as steel plates that make up these, which may have been subjected to surface treatments such as phosphate treatment, chromate treatment, or composite oxide treatment.

[0021] A coating film may be formed on an object that has been surface-treated or not. For example, the substrate (the object to be coated) may be surface-treated as needed, and then a primer coating film may be formed on it. If the object to be coated is an automobile body, for example, this primer coating film can be formed using a known primer paint composition that is commonly used in the painting of automobile bodies.

[0022] As the primer paint composition for forming the above-mentioned primer film, for example, an electrodeposition paint, preferably a cationic electrodeposition paint, can be used.

[0023] Water-based paint composition (X) Any known water-based thermosetting paint composition can be used as the above-mentioned water-based paint composition (X). The water-based paint composition (X) may be a one-component paint composition or a multi-component paint composition such as a two-component paint composition. Among these, a one-component water-based paint composition is preferred from the viewpoint of ease of handling during painting.

[0024] The above-mentioned aqueous paint composition (X) preferably contains a binder resin (x1) and a crosslinking component (x2).

[0025] Binder resin (x1) Examples of the binder resin (x1) include acrylic resin (x11), polyester resin (x12), polyurethane resin (x13), epoxy resin (x14), etc. In the present invention, acrylic resin (x11), polyester resin (x12), or polyurethane resin (x13) can be suitably used.

[0026] The above binder resin (x1) can be used alone or in combination of two or more types.

[0027] Acrylic resin (x11) As the above acrylic resin (x11), a water-soluble or water-dispersible acrylic resin that has been conventionally used in water-based paints and is known on its own can be used.

[0028] The acrylic resin (x11) described above preferably has a crosslinkable functional group that can react with the crosslinkable component (x2). Examples of such crosslinkable functional groups include hydroxyl groups, carboxyl groups, alkoxysilyl groups, and the like.

[0029] The above-mentioned acrylic resin (x11) can be produced, for example, by copolymerizing polymerizable unsaturated monomers using methods that are known themselves, such as solution polymerization in an organic solvent or emulsion polymerization in water.

[0030] Examples of polymerizable unsaturated monomers that can be used include the monomers listed below (i) to (xxi). These polymerizable unsaturated monomers can be used individually or in combination of two or more.

[0031] (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, etc.

[0032] (ii) Polymerizable unsaturated monomers having an isobornyl group: isobornyl (meth)acrylate, etc.

[0033] (iii) Polymerizable unsaturated monomers having an adamantyl group: adamantyl (meth)acrylate, etc.

[0034] (iv) Polymerizable unsaturated monomers having a tricyclodecenyl group: tricyclodecenyl (meth)acrylate, etc.

[0035] (v) Polymerizable unsaturated monomers containing aromatic rings: benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, etc.

[0036] (vi) Polymerizable unsaturated monomers having an alkoxysilyl group: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, etc.

[0037] (vii) Polymerizable unsaturated monomers having a fluorinated alkyl group: perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; fluoroolefins, etc.

[0038] (viiii) A polymerizable unsaturated monomer having a photopolymerizable functional group such as a maleimide group.

[0039] (ix) Vinyl compounds: N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, etc.

[0040] (x) Carboxylate-containing polymerizable unsaturated monomers: (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl (meth)acrylate, etc.

[0041] (xi) Nitrogen-containing polymerizable unsaturated monomers: (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, methylenebis(meth)acrylamide, ethylenebis(meth)acrylamide, adducts of glycidyl (meth)acrylate with amine compounds, etc.

[0042] (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.

[0043] (xiii) Epoxy group-containing polymerizable unsaturated monomers: glycidyl (meth)acrylate, β-methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, etc.

[0044] (xiv) Polymerizable unsaturated monomers having a polyoxyethylene chain with an alkoxy group at the molecular end: methoxypolyethylene glycol mono(meth)acrylate, methoxypolypropylene glycol mono(meth)acrylate, etc.

[0045] (xv) Polymerizable unsaturated monomers having a sulfonic acid group: 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allyl sulfonic acid, 4-styrenesulfonic acid, etc.; sodium salts and ammonium salts of these sulfonic acids, etc.

[0046] (xvi) Polymerizable unsaturated monomers having a phosphoric acid group: acid phosphoxyethyl (meth)acrylate, acid phosphoxypropyl (meth)acrylate, acid phosphoxypoly(oxyethylene) glycol (meth)acrylate, acid phosphoxypoly(oxypropylene) glycol (meth)acrylate, 2-(meth)acryloyloxyethyl acid phosphate, etc.

[0047] (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.

[0048] (xviii) Light-stable polymerizable unsaturated monomers: 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, etc.

[0049] (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.

[0050] (xx) Polymerizable unsaturated monomers having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride, etc.

[0051] (xxi) Hydroxyl group-containing polymerizable unsaturated monomers: Monoesters of (meth)acrylic acid and 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 forms of the monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having polyoxyethylene chains with hydroxyl groups at the molecular ends. However, monomers that fall under "(xvii) Polymerizable unsaturated monomers having ultraviolet-absorbing functional groups" are excluded from the above "Hydroxy group-containing polymerizable unsaturated monomers," even if they contain hydroxyl groups.

[0052] In this specification, an unsaturated group means an unsaturated group that can undergo radical polymerization. Examples of such unsaturated groups include vinyl groups and (meth)acryloyl groups.

[0053] 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.

[0054] From the viewpoint of reactivity with the crosslinkable component, the acrylic resin (x11) preferably has a hydroxyl value in the range of 1 to 200 mg KOH / g, more preferably in the range of 2 to 180 mg KOH / g, and even more preferably in the range of 5 to 150 mg KOH / g.

[0055] From the viewpoint of the complex viscosity of the first coating film formed in step (1), the acrylic resin (x11) described above preferably has a hydroxyl value in the range of 1 to 170 mgKOH / g, more preferably in the range of 2 to 160 mgKOH / g, and even more preferably in the range of 5 to 150 mgKOH / g.

[0056] The above acrylic resin (x11) is preferably in the range of 1 to 170 mg KOH / g, more preferably in the range of 3 to 160 mg KOH / g, and even more preferably in the range of 5 to 150 mg KOH / g, from the viewpoint of water solubility or water dispersibility.

[0057] In the case where step (3) described below is a step in which the first coating film formed in step (1) and the second coating film formed in step (2) are simultaneously baked and cured, the above-mentioned acrylic resin (x11) preferably has a glass transition temperature in the range of 20 to 100°C, more preferably in the range of 35 to 100°C, and even more preferably in the range of 50 to 100°C, from the viewpoint of suppressing the mixing of layers between the first and second coating films.

[0058] In this specification, the glass transition temperature Tg (°C) of the acrylic resin was calculated using the following formula.

[0059] 1 / Tg(K) = (W1 / T1) + (W2 / T2) + ... (1) Tg(°C) = Tg(K) - 273 (2) In each formula, W1, W2, ... are the respective mass fractions of the monomers used in copolymerization, and T1, T2, ... are the Tg(K) of the homopolymer of each monomer. Note that T1, T2, ... are values ​​from Polymer Hand Book (Second Edition, edited by J. Brandup and E.H. Immergut), III-139 to 179. When the Tg of the monomer homopolymer is not clearly defined, the glass transition temperature (°C) is defined as the static glass transition temperature. For example, using a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instruments Inc.), the sample is placed in a measuring cup, the solvent is completely removed by vacuum suction, and the change in calorific value is measured in the range of -20°C to +200°C at a heating rate of 3°C / min. The point of change at the first baseline on the lower temperature side is defined as the static glass transition temperature.

[0060] When the above-mentioned acrylic resin (x11) is obtained by a water-soluble type and / or by a solution polymerization method in an organic solvent, and when step (3) described below is a step of simultaneously baking and curing the first coating film and the second coating film formed in steps (1) and (2), respectively, from the viewpoint of suppressing the mixing of layers between the first coating film and the second coating film, it is preferable that it includes a weight-average molecular weight in the range of 2,000 to 80,000, more preferably in the range of 3,000 to 70,000, and even more preferably in the range of 4,000 to 60,000.

[0061] In this specification, the weight-average molecular weight is the value calculated from the chromatogram measured by gel permeation chromatography, based on the molecular weight of standard polystyrene. The gel permeation chromatograph used was "HLC8120GPC" (manufactured by Tosoh Corporation). Four columns were used: "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (all product names manufactured by Tosoh Corporation). The measurements were performed under the following conditions: mobile phase; tetrahydrofuran, measurement temperature; 40°C, flow rate; 1 cc / min, detector; RI.

[0062] When the aqueous paint composition (X) contains an acrylic resin obtained by a solution polymerization method in the water-soluble type and / or in an organic solvent, the content of the acrylic resin is preferably in the range of 2 to 70 parts by mass, more preferably in the range of 5 to 60 parts by mass, and even more preferably in the range of 10 to 50 parts by mass, based on 100 parts by mass of resin solids in the aqueous paint composition (X), when step (3) below is a step in which the first coating film formed in step (1) and the second coating film formed in step (2) are simultaneously baked and cured.

[0063] The above-mentioned acrylic resin (x11) can be used alone or in combination of two or more types.

[0064] Polyester resin (x12) The polyester resin (x12) can be a water-soluble or water-dispersible polyester resin that has been conventionally used in water-based paints and is known for itself. Preferably, the polyester resin (x12) has a crosslinkable functional group that can react with the crosslinkable component (x2). Examples of such crosslinkable functional groups include hydroxyl groups and carboxyl groups.

[0065] The above-mentioned polyester resin (x12) can usually be produced by an esterification reaction or transesterification reaction between an acid component and an alcohol component.

[0066] As the above-mentioned acid component, compounds commonly used as acid components in the manufacture of polyester resins can be used. Examples of such acid components include aliphatic polybasic acids, alicyclic polybasic acids, aromatic polybasic acids, and the like.

[0067] Examples of the above-mentioned aliphatic polybasic acids include aliphatic compounds having two or more carboxyl groups in one molecule, acid anhydrides of the aliphatic compounds, and esters of the aliphatic compounds. Examples of aliphatic polybasic acids include aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanediic acid, dodecanediic acid, brassic acid, octadecanediic acid, citric acid, and butanetetracarboxylic acid; anhydrides of the aliphatic polycarboxylic acids; and esters of the aliphatic polycarboxylic acids of lower alkyl groups having approximately 1 to 4 carbon atoms. The aliphatic polybasic acids can be used alone or in combination of two or more types.

[0068] Examples of the alicyclic polybasic acid include compounds having one or more alicyclic structures and two or more carboxyl groups in one molecule, acid anhydrides of the compound, and esters of the compound. The alicyclic structure is mainly a 4- to 6-membered ring structure. Examples of alicyclic polybasic acids include alicyclic polycarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; anhydrides of the alicyclic polycarboxylic acid; and esters of lower alkyl groups having about 1 to 4 carbon atoms of the alicyclic polycarboxylic acid. The alicyclic polybasic acid can be used alone or in combination of two or more types.

[0069] The aforementioned aromatic polybasic acid generally refers to an aromatic compound having two or more carboxyl groups in one molecule, an acid anhydride of the aromatic compound, and an ester of the aromatic compound, such as aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of the aromatic polycarboxylic acid; and esters of lower alkyl groups having about 1 to 4 carbon atoms of the aromatic polycarboxylic acid. The aromatic polybasic acid can be used alone or in combination of two or more types.

[0070] Acid components other than the aforementioned aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids can also be used. Such acid components are not particularly limited and include, for example, fatty acids such as coconut oil fatty acid, cottonseed oil fatty acid, hemp seed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, and safflower oil fatty acid; monocarboxylic acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid, and 10-phenyloctadecanoic acid; and hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethoxybenzoic acid. These acid components can be used individually or in combination of two or more.

[0071] As the alcohol component, polyhydric alcohols having two or more hydroxyl groups in one molecule can be suitably used. Examples of such polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, and 1,5-butyl-2-ethyl-1,3-propanediol. Pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricyclodecanediethanol Examples include dihydric alcohols such as neopentyl glycol hydroxypivalate, hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; polylactone diols obtained by adding lactone compounds such as ε-caprolactone to these dihydric alcohols; ester diol compounds such as bis(hydroxyethyl) terephthalate; polyether diol compounds such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, polybutylene glycol, and polytetramethylene ether glycol; trihydric or higher alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris(2-hydroxyethyl)isocyanuric acid, sorbitol, and mannitol; polylactone polyol compounds obtained by adding lactone compounds such as ε-caprolactone to these trihydric or higher alcohols; and fatty acid esters of glycerin.

[0072] Other alcohol components besides the polyhydric alcohols mentioned above can also be used. Such alcohol components are not particularly limited and include, for example, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; and alcohol compounds obtained by reacting monoepoxy compounds such as propylene oxide, butylene oxide, and "Cardura E10P" (trade name, manufactured by HEXION, a glycidyl ester of a synthetic highly branched saturated fatty acid) with an acid.

[0073] The method for producing the polyester resin (x12) is not particularly limited and can be carried out according to conventional methods. For example, the polyester resin (x12) can be produced by heating the acid component and the alcohol component in a nitrogen stream at a temperature of about 150 to 250°C for about 5 to 10 hours to carry out an esterification reaction or transesterification reaction between the acid component and the alcohol component.

[0074] When carrying out the esterification or transesterification reaction of the above acid and alcohol components, they may be added to the reaction vessel all at once, or one or both may be added in several stages. First, a hydroxyl group-containing polyester resin may be synthesized, and then the obtained hydroxyl group-containing polyester resin may be reacted with an acid anhydride to perform half-esterification to obtain a carboxyl group-containing polyester resin. Alternatively, a carboxyl group-containing polyester resin may be synthesized first, and then the above alcohol component may be added to obtain a hydroxyl group-containing polyester resin.

[0075] In the above esterification or transesterification reactions, known catalysts such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, and tetraisopropyl titanate can be used as catalysts to accelerate the reaction.

[0076] When the aqueous paint composition (X) contains the polyester resin (x12), the amount of polyester resin (x12) is preferably in the range of 2 to 70 parts by mass, more preferably in the range of 5 to 65 parts by mass, and even more preferably in the range of 10 to 60 parts by mass, based on 100 parts by mass of resin solids in the aqueous paint composition (X), when step (3) described below is a step in which the first paint film formed in step (1) and the second paint film formed in step (2) are simultaneously baked and cured.

[0077] The polyester resin (x12) described above can be modified with an acrylic resin, a polyisocyanate compound, or the like during or after the preparation of the resin, and it is preferable that it contains an acrylic-modified polyester resin (x121) that has been modified with an acrylic resin.

[0078] Acrylic Modified Polyester Resin (x121) As a method for producing the above acrylic modified polyester resin (x121), known methods can be used, for example, radical polymerization of a radically polymerizable unsaturated group-containing polyester resin and a polymerizable unsaturated monomer, or esterification reaction of a polyester resin and an acrylic resin, and among these, it is preferable to produce it by radical polymerization of a radically polymerizable unsaturated group-containing polyester resin and a polymerizable unsaturated monomer.

[0079] The radical polymerization described above is a method of graft polymerization in which polymerizable unsaturated monomers are polymerized using radically polymerizable unsaturated groups in a polyester resin as graft sites. The polyester resin containing radically polymerizable unsaturated groups is not particularly limited and can be obtained, for example, by an esterification or transesterification reaction between an acid component containing a polybasic acid having polymerizable unsaturated groups and an alcohol component.

[0080] Examples of acid components containing polybasic acids having the polymerizable unsaturated group mentioned above include maleic anhydride, itaconic anhydride, fumaric anhydride, citraconic anhydride, mesaconic anhydride, tetrahydrophthalic anhydride, 2-pentenioic anhydride, methylenesuccinic anhydride, allylmalonic anhydride, isopropylidenesuccinic anhydride, 2,4-hexadiene dioanhydride, acetylenedicarboxylic anhydride, and 4-cyclohexene-1,2-dicarboxylic anhydride, among other unsaturated dicarboxylic acid anhydrides.

[0081] In addition to acid components containing polybasic acids having polymerizable unsaturated groups, the above-mentioned acid components may also include, for example, aliphatic polybasic acids, alicyclic polybasic acids, aromatic polybasic acids, and the like.

[0082] The aliphatic polybasic acid, alicyclic polybasic acid, and aromatic polybasic acid mentioned above can be the compounds described in the section on polyester resin (x12).

[0083] The alcohol component can be one of the compounds described in the description section for polyester resin (x12).

[0084] The esterification or transesterification reaction can be carried out by the method described in the description section for polyester resin (x12).

[0085] As the polymerizable unsaturated monomer, the monomer described in the description section for acrylic resin (x11) can be used.

[0086] Acrylic-modified polyester resin (x121) can be obtained, for example, by copolymerizing a radically polymerizable unsaturated group-containing polyester resin and a polymerizable unsaturated monomer using a known method.

[0087] From the viewpoint of reactivity with the crosslinkable component, the above-mentioned acrylic-modified polyester resin (x121) is preferably in the range of 1 to 250 mg KOH / g, more preferably in the range of 2 to 200 mg KOH / g, and even more preferably in the range of 5 to 180 mg KOH / g.

[0088] From the viewpoint of water dispersibility, the above-mentioned acrylic-modified polyester resin (x121) preferably has an acid value in the range of 1 to 150 mg KOH / g, more preferably in the range of 2 to 200 mg KOH / g, and even more preferably in the range of 5 to 180 mg KOH / g.

[0089] The above-mentioned acrylic-modified polyester resin (x121) preferably has a glass transition temperature in the range of -60 to 30°C, and more preferably in the range of -50 to 30°C.

[0090] In the case where step (3) described below is a step in which the first coating film formed in step (1) and the second coating film formed in step (2) are simultaneously baked and cured, the weight-average molecular weight of the above-mentioned acrylic-modified polyester resin (x121) is preferably in the range of 500 to 50,000, more preferably in the range of 800 to 30,000, and even more preferably in the range of 1,000 to 10,000.

[0091] When the aqueous paint composition (X) contains the acrylic-modified polyester resin (x121), the content of the acrylic-modified polyester resin (x121) is preferably in the range of 2 to 70 parts by mass, more preferably in the range of 5 to 65 parts by mass, and even more preferably in the range of 10 to 60 parts by mass, based on 100 parts by mass of the resin solids in the aqueous paint composition (X), when step (3) described below is a step in which the first coating film formed in step (1) and the second coating film formed in step (2) are simultaneously baked and cured.

[0092] Polyurethane resin (x13) The polyurethane resin (x13) is preferably a water-soluble or water-dispersible resin having urethane bonds in its molecule, and may take any of the following forms in an aqueous medium: water-soluble type, colloidal dispersion type, emulsion type, or slurry type.

[0093] As the polyurethane resin (x13) mentioned above, any known polyurethane resin can be used. For example, a polyurethane obtained by reacting a polyol such as polyester polyol, polycarbonate polyol, or polyether polyol with a polyisocyanate can be further obtained by extending the chain in the presence of a chain extender, which is a low molecular weight compound having at least two active hydrogens in one molecule, such as a diol or diamine, if necessary. This can then be used after being stably dispersed or dissolved in an aqueous medium.

[0094] Examples of polyester polyols used in the production of the polyurethane resin (x13) include polyester diols obtained by reacting aliphatic diols such as 1,4-butanediol and 1,6-hexanediol with aliphatic dicarboxylic acids such as adipic acid and sebacic acid; and polyester diols obtained by reacting the aliphatic diol with aromatic dicarboxylic acids such as terephthalic acid.

[0095] Examples of the polycarbonate polyols include polycarbonate diols obtained by reacting diols such as 1,6-hexanediol and 3-methyl-1,5-pentanediol with carbonate compounds such as dimethyl carbonate.

[0096] Examples of the aforementioned polyether polyols include polyalkylene glycols obtained by ring-opening polymerization of ethylene oxide, propylene oxide, and the like.

[0097] Examples of the polyisocyanates include aliphatic and alicyclic diisocyanates such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and hydrogenated xylylene diisocyanate, as well as isocyanurate ring adducts thereof.

[0098] Furthermore, examples of diols used as chain extenders include ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and cyclohexanediol, while examples of diamines include ethylenediamine, propylenediamine, and xylylenediamine.

[0099] As a method for stably dispersing or dissolving the polyurethane resin (x13) in water, for example, the following method can be used.

[0100] (1) A method for introducing carboxyl groups into polyurethane by using carboxyl group-containing diols such as dimethylolpropionic acid and dimethylolbutanoic acid as raw materials for the manufacture of polyurethane, thereby imparting hydrophilicity to the polyurethane by neutralizing some or all of the carboxyl groups, and dispersing or dissolving in water by self-emulsification.

[0101] (2) A method for producing water-soluble polyurethane using a hydrophilic polyol such as polyethylene glycol as a polyol, which is a raw material for the production of polyurethane, and dispersing or dissolving it in water.

[0102] (3) A method for forcibly dispersing polyurethane in which the reaction has been completed or polyurethane in which terminal isocyanate groups have been blocked with a blocking agent such as oxime, alcohol, phenol, mercaptan, amine, or sodium bisulfite in water using a nonionic and / or cationic emulsifier and mechanical shear force.

[0103] (4) A method for simultaneously dispersing and increasing the molecular weight of a urethane prepolymer having terminal isocyanate groups by mixing it with water / emulsifier / chain extender and using mechanical shear force.

[0104] The polyurethane resin (x13) is not limited to one obtained by a single manufacturing method, and mixtures of polyurethanes obtained by each method can also be used.

[0105] When the aqueous paint composition (X) contains the polyurethane resin (x13), the amount of the polyurethane resin (x13) is preferably in the range of 2 to 70 parts by mass, more preferably in the range of 5 to 60 parts by mass, and even more preferably in the range of 10 to 50 parts by mass, based on the total resin solids content in the aqueous paint composition (X), when step (3) described below is a step in which the first coating film formed in step (1) and the second coating film formed in step (2) are simultaneously baked and cured.

[0106] Crosslinkable component (x2) The above crosslinkable component (x2) can be a known crosslinkable component, specifically, for example, amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, carbodiimide compounds, polyhydrazide compounds, polysemicarbazide compounds, oxazoline group-containing compounds, epoxy compounds, polycarboxylic acids, etc. The crosslinkable component (x2) can be used alone or in combination of two or more types.

[0107] The above crosslinkable component (x2) preferably includes at least one crosslinking agent selected from amino resins, blocked polyisocyanate compounds, and carbodiimide compounds, and more preferably includes amino resins and blocked polyisocyanate compounds.

[0108] As the above-mentioned amino resin, a partially methylolated amino resin or a fully methylolated amino resin obtained by the reaction of an amino component and an aldehyde component can be used. Examples of amino components include melamine, urea, benzoguanamine, acetoganaamine, steroguanamine, spiloganamine, and dicyandiamide. Examples of aldehyde components include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

[0109] A methylolated amino resin can also be used in which the methylol group has been partially or completely etherified with a suitable alcohol. Examples of alcohols that can be used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethyl-1-butanol, and 2-ethyl-1-hexanol.

[0110] Melamine resin is preferred as the above amino resin. In particular, methyl etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol, butyl etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with butyl alcohol, and methyl-butyl mixed etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol and butyl alcohol, are preferred, and methyl-butyl mixed etherified melamine resin is more preferred.

[0111] The weight-average molecular weight of the melamine resin is preferably in the range of 450 to 6000, more preferably in the range of 500 to 4000, and particularly preferably in the range of 550 to 3000.

[0112] Commercially available melamine resins can be used. Examples of commercially available product names include "Cymel 202", "Cymel 203", "Cymel 211", "Cymel 238", "Cymel 251", "Cymel 254", "Cymel 303", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 370", "Cymel 385", "Cymel 1156", "Cymel 1158", and "Cymel 1130" (all manufactured by Ornex Japan Co., Ltd.); "Uban 20SE60" and "Uban 28-60" (both manufactured by Mitsui Chemicals, Inc.); and others.

[0113] When the above-mentioned melamine resin is used as the crosslinkable component (x2), a sulfonic acid such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, or dinonylnaphthalenesulfonic acid; a neutralized salt of the sulfonic acid and an amine; or a neutralized salt of a phosphate ester compound and an amine can be used as the curing catalyst.

[0114] When the aqueous paint composition (X) contains the above-mentioned melamine resin, the amount of melamine resin is preferably in the range of 5 to 55 parts by mass, more preferably in the range of 10 to 50 parts by mass, and even more preferably in the range of 15 to 45 parts by mass, based on 100 parts by mass of resin solids in the aqueous paint composition (X), from the viewpoint of curability.

[0115] The aforementioned blocked polyisocyanate compound is a compound in which the isocyanate group of a polyisocyanate compound is blocked with a blocking agent.

[0116] The above polyisocyanate compounds are compounds having two or more isocyanate groups in one molecule.

[0117] The above-mentioned polyisocyanate compounds include, for example, aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of said polyisocyanates.

[0118] Examples of the above aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer diisocyanate, and 2,6-methyl diisocyanatohexanoate (common name: lysine). Examples include aliphatic diisocyanates such as diisocyanates; 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.

[0119] Examples of the alicyclic polyisocyanates include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), methyl-2,4-cyclohexane diisocyanate, 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), and 2-methyl-1,3- Alicyclic diisocyanates such as cyclohexylene diisocyanate, methylenebis(4,1-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI), methyl-2,6-cyclohexanediisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or mixtures thereof, norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane Rohexane, 2-(3-isocyanatopropyl)-2,5-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)he Examples include alicyclic triisocyanates such as butane, 6-(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.

[0120] Examples of the aforementioned aromatic aliphatic polyisocyanates include aromatic aliphatic diisocyanates such as methylenebis(4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0121] Examples of the aromatic polyisocyanates include aromatic diisocyanates such as m-phenylenediisocyanate, p-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, 1,5-naphthalenediisocyanate, 2,4'- or 4,4'-diphenylmethanediisocyanate or mixtures thereof, 2,4- or 2,6-tolylenediisocyanate or mixtures thereof, 4,4'-toluidinediisocyanate, and 4,4'-diphenyletherdiisocyanate; 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.

[0122] Examples of the polyisocyanate derivatives include dimers, trimers, biuretes, allophanates, uretodiones, uretoimines, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like.

[0123] Examples of the blocking agents include phenolic blocking agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohol blocking agents such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ether blocking 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, and butyrolactamic acid. Alcohol-based blocking agents such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; oxime-based blocking agents such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based blocking agents such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; mercaptan-based blocking agents such as butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol; acid amide-based blocking agents such as acetanilide, acetanisidide, acetoluid, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide; imide-based blocking agents such as succinimide, phthalimide, and maleimide;Examples of blockers include amine-based blockers such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazole-based blockers such as imidazole and 2-ethylimidazole; urea-based blockers such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamic acid ester-based blockers such as phenyl N-phenylcarbamate; imine-based blockers such as ethyleneimine and propyleneimine; sulfite-based blockers such as sodium bisulfite and potassium bisulfite; and azole-based blockers. Examples of the above-mentioned azole-based blocking agents include pyrazoles or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazoles or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

[0124] Among the blocking agents, oxime-based blocking agents, active methylene-based blocking agents, pyrazoles, or pyrazole derivatives are particularly preferred.

[0125] As the blocking agent, a hydroxycarboxylic acid having one or more hydroxyl groups and one or more carboxyl groups, such as hydroxypivalic acid or dimethylolpropionic acid, can also be used.

[0126] When the above-mentioned blocked polyisocyanate compound is used as the crosslinkable component (x2), organometallic compounds, acid compounds, basic compounds, etc., can be used as the curing catalyst.

[0127] When the aqueous paint composition (X) contains the blocked polyisocyanate compound, the content of the blocked polyisocyanate compound is preferably in the range of 1 to 55 parts by mass, more preferably in the range of 2 to 50 parts by mass, and even more preferably in the range of 3 to 45 parts by mass, based on 100 parts by mass of resin solids in the aqueous paint composition (X), when step (3) described below is a step in which the first paint film formed in step (1) and the second paint film formed in step (2) are simultaneously baked and cured.

[0128] As the carbodiimide compound, a compound having at least two carbodiimide groups in one molecule can be suitably used. For example, a compound obtained by decarbonizing the isocyanate groups of an isocyanate group-containing compound can be used.

[0129] As the above-mentioned carbodiimide compound, it is preferable to use a water-soluble or water-dispersible carbodiimide compound from the viewpoint of the storage stability of the resulting aqueous coating composition. The water-soluble or water-dispersible carbodiimide compound can be used without particular limitations, as long as it is a carbodiimide compound that can be stably dissolved or dispersed in an aqueous medium.

[0130] Specifically, examples of the above water-soluble carbodiimide compounds include "Carbodilite SV-02," "Carbodilite V-02," "Carbodilite V-02-L2," and "Carbodilite V-04" (all manufactured by Nisshinbo Inc., trade names). As for the above water-dispersible carbodiimide compounds, examples of "Carbodilite E-01," "Carbodilite E-02," and "Carbodilite E-05" (all manufactured by Nisshinbo Inc., trade names) can be used.

[0131] When the aqueous paint composition (X) contains the above-mentioned carbodiimide compound, the content of the carbodiimide compound is preferably in the range of 0.1 to 30 parts by mass, more preferably in the range of 0.5 to 27 parts by mass, and even more preferably in the range of 1 to 25 parts by mass, based on 100 parts by mass of resin solids in the aqueous paint composition (X), when step (3) described below is a step in which the first paint film formed in step (1) and the second paint film formed in step (2) are simultaneously baked and cured.

[0132] When the aqueous paint composition (X) contains the above-mentioned crosslinkable component (x2), the content of the above-mentioned crosslinkable component (x2) is preferably in the range of 1 to 55 parts by mass, more preferably in the range of 2 to 50 parts by mass, and even more preferably in the range of 3 to 45 parts by mass, based on 100 parts by mass of resin solids in the aqueous paint composition (X), when step (3) described below is a step in which the first and second paint films formed in steps (1) and (2) are simultaneously baked and cured.

[0133] Other components: The aqueous paint composition (X) may further contain, as needed, pigments, pigment dispersants, viscosity modifiers, anti-settling agents, organic solvents, defoamers, ultraviolet absorbers, light stabilizers, surface modifiers, etc.

[0134] Suitable pigments include, for example, coloring pigments such as titanium dioxide, zinc oxide, carbon black, phthalocyanine blue, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, slene pigments, and perylene pigments; extender pigments such as talc, clay, kaolin, barita, barium sulfate, barium carbonate, calcium carbonate, silica, and alumina white; and luminous pigments such as aluminum powder, mica powder, and mica powder coated with titanium dioxide. Among these, the inclusion of barium sulfate is particularly preferable.

[0135] If the aqueous paint composition (X) contains the above-mentioned pigment, the pigment may be a pigment dispersion liquid that has been pre-dispersed using a resin, water or an organic solvent, and the pigment.

[0136] If the aqueous paint composition (X) contains the above-mentioned pigment, the amount thereof is preferably in the range of 0.01 to 250 parts by mass, and more preferably in the range of 3 to 150 parts by mass, based on 100 parts by mass of the resin solids content of the aqueous paint composition (X).

[0137] As the pigment dispersant, for example, any compound of anionic, cationic, or nonionic type can be used. In particular, when step (3) described below is a step in which the first coating film formed in step (1) and the second coating film formed in step (2) are simultaneously baked and cured, it is preferable to use an anionic compound from the viewpoint of suppressing the mixing of layers between the first and second coating films and forming a coating film with excellent gloss. The pigment dispersants can be used individually or in appropriate combinations of two or more types.

[0138] As anionic compounds, compounds having functional groups such as phosphate groups, carboxyl groups, sulfonic acid groups, and sulfate ester groups can be used. In particular, when step (3) described below is a step in which the first coating film formed in step (1) and the second coating film formed in step (2) are simultaneously baked and cured, it is preferable to include a phosphate group-containing compound from the viewpoint of suppressing the formation of a mixed layer between the first and second coating films and forming a coating film with excellent gloss.

[0139] The above anionic compounds can also be used after neutralization with a neutralizing agent. Examples of neutralizing agents 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.

[0140] Examples of the phosphate group-containing compounds mentioned above include polyoxyethylene alkyl ether phosphates, polyoxyethylene phenyl ether phosphates, alkyl phosphate esters, and alkyl phosphate ester salts.

[0141] If the aqueous paint composition (X) contains a pigment dispersant, the amount of the dispersant is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 27 parts by mass, and even more preferably 1 to 25 parts by mass, based on 100 parts by mass of the resin solids content of the aqueous paint composition (X), from the viewpoint of forming a paint film with excellent gloss.

[0142] The aqueous coating composition (X) can be applied by adding water, an organic solvent, etc., to adjust the viscosity to a level suitable for coating, and then applying it as needed using known methods such as rotary atomization, air spraying, airless spraying, or a bar coater. The film thickness can be applied to a range of preferably 10 to 40 μm, more preferably 15 to 35 μm, and even more preferably 20 to 30 μm, based on the cured film thickness.

[0143] The first coating film is subjected to the formation of the second coating film in the next step (2), and in step (3) described later, it is heat-cured separately or simultaneously with the first coating film, the second coating film, and optionally the clear coat coating film described later, which are formed in steps (1) and (2), respectively. In particular, it is preferable to subject the first coating film to the formation of the second coating film in the next step (2) while it is still uncured, and in step (3) described later, it is heat-cured simultaneously with the first coating film, the second coating film, and optionally the clear coat coating film described later, which are formed in steps (1) and (2).

[0144] If necessary, before performing the next step (2), which is the formation of the second coating film, the obtained uncured first coating film may be dried to the extent that it is not substantially cured, or the solid content may be adjusted to the extent that it is not dried, by means of preheating, air blowing, etc. The above preheating can be performed by known heating means, and for example, a drying oven such as a hot air furnace, electric furnace, or infrared induction heating furnace can be used.

[0145] The above preheating can usually be performed by directly or indirectly heating the workpiece coated with the aqueous paint composition (X) in a drying oven at a temperature of 40 to 110°C, preferably 50 to 110°C, more preferably 60 to 110°C, and most preferably 75 to 105°C for 30 seconds to 20 minutes, preferably 1 to 15 minutes, more preferably 2 to 10 minutes, and most preferably 2 to 4 minutes. The above air blowing can usually be performed by blowing air heated to room temperature or about 25°C to about 80°C onto the painted surface of the workpiece for about 30 seconds to 15 minutes.

[0146] In this specification, "solids" refers to the non-volatile components, such as resins, crosslinking components, and pigments, contained in the paint composition that remain after drying the paint composition at 110°C for one hour. For example, the total solids of a paint composition can be calculated by weighing the paint composition into a heat-resistant container such as an aluminum foil cup, spreading the paint composition on the bottom surface of the container, drying it at 110°C for one hour, weighing the mass of the components remaining in the paint composition after drying, and determining the ratio of the mass of the components remaining after drying to the total mass of the paint composition before drying.

[0147] In this specification, "resin solids" can be calculated by summing the solids of the binder resin and the solids of the crosslinkable components.

[0148] The first coating film is formed by applying the aqueous paint composition (X). The complex viscosity of the first coating film is measured under conditions of a frequency of 0.1 Hz and a temperature of 25°C, and while it is within the range of 100,000 to 1,500,000 Pa·s, the glossy paint composition (Y) described below is applied.

[0149] From the viewpoint of forming a coating film that has excellent gloss and high millimeter-wave transmittance, the complex viscosity of the first coating film described above is preferably in the range of 110,000 to 1,400,000 Pa·s, more preferably in the range of 120,000 to 800,000 Pa·s, and particularly preferably in the range of 120,000 to 500,000 Pa·s.

[0150] The complex viscosity of the first coating film described above is specifically evaluated by the following method.

[0151] First, the aqueous coating composition (X) is applied to the object to be coated to obtain a first coating film. If necessary, preheating is performed, and immediately before applying the glossy coating composition (Y), the first coating film on the object to be coated is scraped off with a spatula and collected in a sample bottle, which is then immediately sealed to obtain the sample. The obtained sample can be subjected to dynamic viscoelasticity measurement (temperature 25°C, frequency 1 Hz, strain 0.1%, jig: parallel plate (Φ=8 mm), gap: 0.5 mm) using a rotary rheometer (ARES-G2 manufactured by T.A. Instruments Co., Ltd.) to measure its complex viscosity.

[0152] The complex viscosity of the first coating film can be adjusted mainly by adjusting the type and / or amount of the binder resin (x1), but is not limited thereto.

[0153] Step (2) According to the multilayer coating film forming method of the present invention, a glossy coating composition (Y) containing indium particles (y1) is then applied to the first coating film formed in step (1) to form a second coating film.

[0154] The glossy paint composition (Y) contains indium particles (y1).

[0155] The above-mentioned glossy coating composition (Y) further contains a surface modifier (y2), a pigment dispersant (y3), a viscosity modifier (y4), and water (y5), and preferably has a solid content of 0.1 to 15% by mass.

[0156] Indium particles (y1) The above indium particles (y1) are flaky particles. These flaky particles are sometimes also referred to as scale-like particles, plate-like particles, or flake-like particles.

[0157] In the present invention, "flaky particles" means particles having a substantially flat surface and a substantially uniform thickness in the direction perpendicular to the substantially flat surface. The flaky particles are defined as particles with a very thin thickness and a very long substantially flat surface. 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 particle.

[0158] There are no particular restrictions on the shape of the approximately flat surface, and it can be appropriately selected depending on the purpose. Examples include polygons such as approximately rectangles, approximately squares, approximately circles, approximately ellipses, approximately triangles, approximately quadrilaterals, approximately pentagons, approximately hexagons, approximately heptagons, approximately octagons, and other polygons, as well as random irregular shapes. Among these, approximately circular is preferred.

[0159] The indium particles (y1) may be a single layer, or two or more layers may be stacked to form primary particles. The primary particles of indium particles (y1) may aggregate to form secondary particles.

[0160] The indium particles (y1) described above consist of indium with a purity of 95% or higher, and may contain trace amounts of impurities, but are not alloys with other metals.

[0161] The above-mentioned indium particles (y1) can be manufactured by performing a delamination layer formation step, a vacuum deposition step, a delamination step, and other steps as necessary.

[0162] <Release Layer Formation Process> The release layer formation process is the process of forming a release layer on the substrate.

[0163] The above-mentioned 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 foil and resin film that have flexibility, heat resistance, solvent resistance, and dimensional stability can be used as appropriate. Examples of resin films include polyester film, polyethylene film, polypropylene film, polystyrene film, and polyimide film. Examples of metal foils include copper foil, aluminum foil, nickel foil, iron foil, and alloy foil. Examples of composite films of metal foil and resin film include those made by laminating the above-mentioned resin film and metal foil.

[0164] Various organic materials that can be dissolved in a later peeling process can be used as the peeling layer. By appropriately selecting the organic material constituting the peeling layer, the organic material adhering to and remaining on the adhesion surface of the island-like structure film can function as a protective layer for the indium particles (y1), which is preferable.

[0165] The protective layer has the function of suppressing aggregation, oxidation, and elution into the solvent of indium particles (y1). In particular, it is preferable to use the organic material used in the release layer as the protective layer, as this eliminates the need for a separate surface treatment process.

[0166] Examples of organic materials that can be used as a protective layer to constitute the release layer include cellulose acetate butyrate (CAB), other cellulose derivatives, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polyacrylic acid, polyacrylamide, polyvinyl butyral, acrylic acid copolymer, modified nylon resin, polyvinylpyrrolidone, urethane resin, polyester resin, polyether resin, and alkyd resin. These may be used individually or in combination of two or more. Among these, cellulose acetate butyrate (CAB) is preferred due to its high functionality as a protective layer.

[0167] There are no particular restrictions on the method for forming the above-mentioned release layer, and it can be appropriately selected according to the purpose. Examples include the 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, and die coating method. These may be used individually or in combination of two or more methods.

[0168] <Vacuum deposition process> The above vacuum deposition process is a process of vacuum deposition of a metal layer containing indium particles (y1) onto the peel layer.

[0169] The average deposition thickness of the metal layer containing indium particles (y1) 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 deposition thickness of the metal layer containing indium particles (y1) is the same as the average thickness of the indium particles (y1).

[0170] When the average deposition thickness of the above-mentioned metal layer is 60 nm or less, the surface roughness Ra of the coating film decreases, which has the advantage of producing excellent gloss. The average deposition thickness is calculated, for example, by observing the cross-section of the metal layer using a scanning electron microscope (SEM), measuring the thickness of the metal layer at 5 to 10 locations, and taking the average value.

[0171] The metal layer is preferably an island-like structure film. The island-like structure film can be formed by various methods, such as vacuum deposition, sputtering, and plating. Among these, vacuum deposition is preferred.

[0172] Vacuum deposition is preferable to plating in that it can form films on resin substrates and does not produce waste liquid, and is preferable to sputtering in that it can achieve a high degree of vacuum and has a high film deposition rate (deposition rate).

[0173] In the vacuum deposition method, the deposition rate is preferably 10 nm / sec or higher, and more preferably 10 nm / sec or higher and 80 nm / sec or lower.

[0174] <Peeling Process> The above peeling process is a process of peeling off the metal layer by dissolving the peeling layer. There are no particular restrictions on the solvent that can dissolve the peeling layer, and any solvent that can dissolve the peeling layer can be appropriately selected according to the purpose, but it is preferable to use a solvent that can be used as is as a solvent for the glossy paint composition (Y).

[0175] Solvents capable of dissolving the above-mentioned peeling layer include, for example, alcohol-based solvents such as methanol, ethanol, propanol, isopropanol, butanol, octanol, dodecanol, ethylene glycol, and propylene glycol; ether-based solvents such as tetrahydrone; ketone-based solvents such as acetone, methyl ethyl ketone, and acetylacetone; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, and phenyl acetate; ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethyl glycol monomethyl ether, triethyl Examples include glycol ether solvents such as ethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and diethylene glycol monomethyl ether acetate; phenolic solvents such as phenol and cresol; aliphatic or aromatic hydrocarbon solvents such as pentane, hexane, heptane, octane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, octadecane, octadecene, benzene, toluene, xylene, trimesin, nitrobenzene, aniline, methoxybenzene, and trimesin; 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 individually or in combination of two or more.

[0176] By dissolving the exfoliation layer, the island-like structure film is detached from the substrate, and the island-like structure breaks apart, with each island becoming an indium particle (y1). This allows for the acquisition of an indium particle (y1) dispersion without any grinding process, although grinding and classification may be performed as needed. If the primary particles of the indium particle (y1) are aggregated, they may be crushed as needed.

[0177] Furthermore, various treatments may be performed as needed to recover the indium particles (y1) or adjust their physical properties. For example, the particle size of the indium particles (y1) may be adjusted by classification, or the indium particles (y1) may be recovered by methods such as centrifugation or suction filtration, or the solid content concentration of the dispersion may be adjusted. Solvent replacement may be performed, or viscosity adjustment may be performed using additives.

[0178] <Other processes> Other processes include, for example, a process of extracting the peeled metal layer as a dispersion, and a process of recovering the island-shaped metal layer from the dispersion as indium particles (y1).

[0179] The cumulative 50% volume average particle diameter D50 of the indium particles (y1) obtained by performing the above-mentioned peeling layer formation step, vacuum deposition step, peeling step, and other steps 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 with excellent gloss.

[0180] Commercially available products can be used as the indium particles (y1) mentioned above. Examples of such commercially available products include "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.).

[0181] In the glossy coating composition (Y), the content of indium particles (y1) 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 95 parts by mass, and particularly preferably in the range of 65 to 90 parts by mass, based on 100 parts by mass of solid content of the glossy coating composition (Y), from the viewpoint of forming a coating film with excellent gloss.

[0182] Surface modifier (y2) Examples of the surface modifier (y2) include silicone-based surface modifiers, acrylic-based surface modifiers, vinyl-based surface modifiers, fluorine-based surface modifiers, and acetylenediol-based surface modifiers. Among these, it is preferable to include a silicone-based surface modifier from the viewpoint of obtaining a coating film with excellent gloss. Each of the surface modifiers (y2) can be used individually or in appropriate combinations of two or more types.

[0183] As the silicone-based surface modifiers mentioned above, polydimethylsiloxane or modified silicones derived from it are used. Examples of modified silicones include polyether-modified silicone, acrylic-modified silicone, and polyester-modified silicone.

[0184] When the glossy coating composition (Y) contains a surface modifier (y2), the amount of y2 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 solids of the glossy coating composition (Y), from the viewpoint of forming a coating film that has excellent gloss and high millimeter-wave transmittance.

[0185] Pigment dispersant (y3) As the above pigment dispersant (y3), for example, the pigment dispersant of the aqueous coating composition (X) described above can be used. Any anionic, cationic, or nonionic compound can be used, and among them, it is preferable to use an anionic compound from the viewpoint of forming a coating film with excellent gloss. The pigment dispersant (y3) can be used individually or in appropriate combinations of two or more types.

[0186] As anionic compounds, compounds having functional groups such as phosphate groups, carboxyl groups, sulfonic acid groups, and sulfate ester groups can be used, and among these, it is preferable to include a compound containing a phosphate group from the viewpoint of forming a coating film that has excellent gloss and high millimeter-wave transmittance.

[0187] The above-mentioned anionic compounds can also be used after being neutralized with a neutralizing agent. As a neutralizing agent, for example, the aforementioned neutralizing agent can be used as a pigment dispersant in the aqueous paint composition (X).

[0188] Examples of the phosphate group-containing compounds mentioned above include polyoxyethylene alkyl ether phosphates, polyoxyethylene phenyl ether phosphates, alkyl phosphate esters, and alkyl phosphate ester salts.

[0189] If the glossy coating composition (Y) contains a pigment dispersant (y3), the amount of the dispersant 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 solids of the glossy coating composition (Y), from the viewpoint of forming a coating film with excellent gloss.

[0190] Viscosity modifier (y4) Examples of the viscosity modifier (y4) include association-type viscosity modifiers, inorganic viscosity modifiers, polyacrylic acid-based viscosity modifiers, cellulose derivative-based viscosity modifiers, protein-based viscosity modifiers, alginic acid-based viscosity modifiers, polyvinyl-based viscosity modifiers, polyether-based viscosity modifiers, maleic anhydride copolymer-based viscosity modifiers, and polyamide-based viscosity modifiers. Among these, association-type viscosity modifiers are preferred, and acrylic association-type viscosity modifiers, described later, are particularly preferred.

[0191] Examples of the above-mentioned associated viscosity modifiers include acrylic associated viscosity modifiers, which are acrylic resins having a hydrophilic acrylic main chain and hydrophobic side chains; and urethane associated viscosity modifiers, which have a hydrophobic portion, a urethane bond, and a polyether chain in one molecule, and which exhibit an effective thickening effect by the association of the hydrophobic portions in an aqueous medium.

[0192] Examples of the inorganic viscosity modifiers include silicates, metal silicates, montmorillonite, organic montmorillonite, and colloidal alumina.

[0193] Examples of the polyacrylic acid-based viscosity modifiers include sodium polyacrylate and polyacrylic acid-(meth)acrylic acid ester copolymers.

[0194] Examples of the aforementioned cellulose derivative-based viscosity modifiers include carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, and cellulose nanofibers.

[0195] Examples of the protein-based viscosity modifiers include casein, sodium caseinate, and ammonium caseinate.

[0196] Examples of the aforementioned alginate-based viscosity modifiers include sodium alginate.

[0197] Examples of the polyvinyl-based viscosity modifiers include polyvinyl alcohol, polyvinylpyrrolidone, and polyvinylbenzyl ether copolymer.

[0198] Examples of the polyether-based viscosity modifiers include polyether dialkyl esters, polyether dialkyl ethers, and polyether epoxy modified products.

[0199] Examples of the maleic anhydride copolymer-based viscosity modifier include partial esters of vinyl methyl ether-maleic anhydride copolymers.

[0200] Examples of the aforementioned polyamide-based viscosity modifiers include polyamide amine salts.

[0201] These viscosity modifiers (y4) can be used individually or in combination of two or more types.

[0202] When the glossy coating composition (Y) contains a viscosity modifier (y4), the amount of the y4 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 solids of the glossy coating composition (Y), from the viewpoint of forming a coating film that has excellent gloss and high millimeter wave transmittance.

[0203] When the glossy coating composition (Y) contains water (y5), the amount of water (y5) is preferably in the range of 45 to 95 parts by mass, more preferably in the range of 55 to 93 parts by mass, and even more preferably in the range of 65 to 90 parts by mass, based on 100 parts by mass of the total components of the glossy coating composition (Y), from the viewpoint of forming a coating film with excellent gloss.

[0204] The solid content of the glossy coating composition (Y) is preferably in the range of 0.1 to 15% by mass, more preferably in the range of 0.5 to 13.5% by mass, and even more preferably in the range of 1.5 to 12% by mass, from the viewpoint of forming a coating film that has excellent gloss and high millimeter wave transmittance.

[0205] The other component luminous paint composition (Y) may further contain, as needed, an organic solvent, a pigment other than the indium particles (y1), a binder resin, a crosslinking component, an ultraviolet absorber, and a light stabilizer.

[0206] As the above organic solvents, those commonly used in paints can be used. Specifically, for example, 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 Examples include glycol ether solvents such as 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, trimesin, nitrobenzene, aniline, methoxybenzene, and trimesin; 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 individually or in combination of two or more.

[0207] Other pigments besides the indium particles (y1) mentioned above include coloring pigments, luminous pigments other than indium particles (y1), extender pigments, etc. These pigments can be used alone or in combination of two or more. Examples of coloring pigments include titanium dioxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, surene pigments, perylene pigments, dioxazine pigments, and diketopyrrolopyrrole pigments. Examples of luminous pigments other than indium particles (y1) include vapor-deposited metal flake pigments other than indium particles (y1), aluminum flake pigments, and light-interfering pigments. Examples of extender pigments include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white.

[0208] If the glossy coating composition (Y) contains pigments other than indium particles (y1), the amount of these pigments 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 solids of the glossy coating composition (Y), from the viewpoint of forming a coating film that has excellent gloss and high millimeter wave transmittance.

[0209] Examples of the binder resin include acrylic resin, polyester resin, polyether resin, polycarbonate resin, polyurethane resin, epoxy resin, and alkyd resin. Among these, it is preferable that the binder resin contains acrylic resin, more preferably water-soluble or water-dispersible acrylic resin, and even more preferably water-soluble acrylic resin. These can be used individually or in combination of two or more.

[0210] If the glossy coating composition (Y) contains a binder resin, the amount of the binder resin 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 solids of the glossy coating composition (Y), from the viewpoint of having excellent gloss.

[0211] Examples of the crosslinkable component include melamine resin, melamine resin derivatives, urea resin, (meth)acrylamide, polyaziridine, polycarbodiimide, and polyisocyanate compounds, which may or may not be blocked.

[0212] If the glossy coating composition (Y) contains the above-mentioned crosslinkable component, the amount 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 solids of the glossy coating composition (Y), from the viewpoint of forming a coating film with excellent gloss and high millimeter-wave transmittance.

[0213] The glossy coating composition (Y) can be applied according to conventional methods, such as bar coating, air spray coating, airless spray coating, and rotary atomization coating. When applying the glossy coating composition (Y), additional coatings may be applied as needed, with bar coating, rotary atomization electrostatic coating and air spray electrostatic coating being preferred, and bar coating and rotary atomization electrostatic coating being particularly preferred.

[0214] When performing air spray painting, airless spray painting, or rotary atomization painting, it is preferable that the glossy paint composition (Y) is adjusted to a viscosity suitable for painting by appropriately containing water and / or an organic solvent and, if necessary, an additive such as an antifoaming agent.

[0215] From the viewpoint of forming a coating film that has excellent gloss and high millimeter-wave transmittance, the viscosity of the glossy coating composition (Y) is preferably in the range of 8 to 30 seconds, particularly 10 to 25 seconds, at 20°C using a Ford Cup No. 3 viscometer.

[0216] Before applying the glossy paint composition (Y), it is preferable to perform ultrasonic dispersion treatment on the glossy paint composition (Y) from the viewpoint of forming a coating film that has excellent gloss and high millimeter-wave transmittance. As a disperser, for example, "UH-50" (product name, manufactured by MST Corporation) can be used.

[0217] From the viewpoint of forming a coating film that has excellent gloss and high millimeter-wave transmittance, the cured film thickness of the glossy coating film is preferably about 0.01 to 2 μm, more preferably about 0.025 to 1 μm, and even more preferably about 0.05 to 0.5 μm.

[0218] Step (3) According to the multilayer coating film forming method of the present invention, the first coating film formed in step (1) and the second coating film formed in step (2) are then cured by baking them separately or simultaneously.

[0219] From the viewpoint of shortening the process, it is preferable that the first and second coating films be heat-cured simultaneously.

[0220] The heating method can be carried out by means of, for example, hot air heating, infrared heating, or high-frequency heating. The heating temperature is preferably 80 to 160°C, and more preferably 100 to 140°C. The heating time is preferably 10 to 60 minutes, and more preferably 15 to 40 minutes. If necessary, before the heat curing, preheating, air blowing, etc., may be performed directly or indirectly for about 1 to 60 minutes at a temperature of about 40 to about 110°C, preferably about 60 to about 100°C.

[0221] Other steps: In the multilayer coating method of the present invention, a clear coating composition (Z) may be applied to the second coating obtained in step (2) to form a clear coating. From the viewpoint of durability of the multilayer coating, it is preferable to apply the clear coating composition (Z) to form a clear coating.

[0222] In particular, from the viewpoint of shortening the process and saving energy, it is preferable to apply the clear coating composition (Z) on the second coating obtained in step (2) while the second coating is still uncured, and then heat-cur the first coating, the second coating, and the clear coating simultaneously.

[0223] Any known thermosetting paint composition can be used as the clear coating composition (Z). Examples of such thermosetting paint compositions include organic solvent-type thermosetting paint compositions containing a binder resin having a crosslinkable functional group and a crosslinkable component, aqueous thermosetting paint compositions, powder thermosetting paint compositions, and the like.

[0224] Examples of crosslinkable functional groups in the above-mentioned binder resin include carboxyl groups, hydroxyl groups, epoxy groups, and silanol groups. Examples of types of binder resin include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, and fluororesins. Examples of crosslinkable components 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.

[0225] Preferred binder resin / crosslinkable component combinations 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.

[0226] The clear coating composition (Z) described above may be a one-component coating or a multi-component coating such as a two-component coating.

[0227] In particular, the clear coating composition (Z) is preferably a two-component clear coating containing the following hydroxyl group-containing resin (z1) and polyisocyanate compound (z2) from the viewpoint of the adhesion of the resulting coating film.

[0228] Hydroxyl group-containing resin (z1) The above hydroxyl group-containing resin (z1) is a resin having at least one hydroxyl group in one molecule. Examples of the hydroxyl group-containing resin (z1) include acrylic resins, polyester resins, polyurethane resins, polyolefin resins, polyether resins, polycarbonate resins, epoxy resins, alkyd resins, and other resins that have hydroxyl groups. These can be used individually or in combination of two or more types.

[0229] As the hydroxyl group-containing resin (z1), it is preferable to use a hydroxyl group-containing acrylic resin (z11) from the viewpoint of adhesion of the formed multilayer coating film.

[0230] Hydroxyl group-containing acrylic resin (z11) The above hydroxyl group-containing acrylic resin (z11) can be produced, for example, by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer by a method known in itself, such as solution polymerization in an organic solvent or emulsion polymerization in water.

[0231] The above-mentioned hydroxyl group-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in one molecule. As the hydroxyl group-containing polymerizable unsaturated monomer, for example, the hydroxyl group-containing polymerizable unsaturated monomer (xxi) mentioned above can be used in the acrylic resin (x11) of the aqueous paint composition (X). The above-mentioned hydroxyl group-containing polymerizable unsaturated monomer can be used alone or in combination of two or more types.

[0232] Other polymerizable unsaturated monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomers include, for example, the polymerizable unsaturated monomers (i) to (xx) mentioned above in the acrylic resin (x11) of the aqueous paint composition (X).

[0233] These polymerizable unsaturated monomers can be used individually or in combination of two or more.

[0234] In the production of the hydroxyl group-containing acrylic resin (z11), the amount of the hydroxyl group-containing polymerizable unsaturated monomer used is preferably in the range of 15 to 50% by mass, and more preferably in the range of 20 to 40% by mass, relative to the total amount of copolymer monomer components, from the viewpoint of adhesion, chipping resistance, and finished appearance of the formed multilayer coating film.

[0235] The hydroxyl value of the above-mentioned hydroxyl group-containing acrylic resin (z11) is preferably in the range of 50 to 210 mg KOH / g, more preferably in the range of 80 to 200 mg KOH / g, and even more preferably in the range of 100 to 170 mg KOH / g, from the viewpoint of adhesion, chipping resistance, and finished appearance of the formed multilayer coating film.

[0236] The weight-average molecular weight of the hydroxyl group-containing acrylic resin (z11) is preferably in the range of 2,000 to 50,000, more preferably in the range of 3,000 to 30,000, and even more preferably in the range of 4,000 to 10,000, from the viewpoint of adhesion, chipping resistance, and finished appearance of the formed multilayer coating film.

[0237] The acid value of the hydroxyl group-containing acrylic resin (z11) is preferably 30 mg KOH / g or less, and more preferably in the range of 1 to 20 mg KOH / g, from the viewpoint of the finished appearance of the multilayer coating film formed, adhesion, and the pot life of the clear coating composition (Z).

[0238] The glass transition temperature of the hydroxyl group-containing acrylic resin (z11) is preferably -50 to 60°C, more preferably 10 to 50°C, and even more preferably in the range of 20 to 45°C, from the viewpoint of adhesion, chipping resistance, and finished appearance of the formed multilayer coating film.

[0239] As a copolymerization method for obtaining a hydroxyl group-containing acrylic resin (z11) by copolymerizing the above 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.

[0240] Organic solvents used in the above solution polymerization method include, for example, 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, and diethylene glycol monomethyl ether. Examples of solvents include glycol ether solvents such as ethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and diethylene glycol monomethyl ether acetate; phenolic solvents such as phenol and cresol; aliphatic or aromatic hydrocarbon solvents such as pentane, hexane, heptane, octane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, octadecane, octadecene, benzene, toluene, xylene, trimesin, nitrobenzene, aniline, methoxybenzene, and trimesin; and aliphatic or aromatic chlorinated hydrocarbon solvents such as dichloromethane, chloroform, trichloroethane, chlorobenzene, and dichlorobenzene.

[0241] Examples of polymerization initiators that can be used in copolymerization of 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).

[0242] The above-mentioned hydroxyl group-containing acrylic resin (z11) can be used alone or in combination of two or more types.

[0243] Polyisocyanate compound (z2) The polyisocyanate compound (z2) is a compound having at least two isocyanate groups in one molecule, and the polyisocyanate compounds and their derivatives described in the description section of the blocked polyisocyanate compound of the crosslinkable component (x2) can be used.

[0244] The above-mentioned polyisocyanates and their derivatives may be used individually or in combination of two or more types.

[0245] From the viewpoint of adhesion, compatibility, and other factors, the above-mentioned polyisocyanates and their derivatives preferably include derivatives of hexamethylene diisocyanate.

[0246] As the polyisocyanate compound (z2), a prepolymer may be used, which is obtained by reacting the polyisocyanate and its derivatives with a compound having an active hydrogen group, such as a hydroxyl group or an amino group, that can react with the polyisocyanate, under conditions of excess isocyanate groups. Examples of compounds that can react with the polyisocyanate include polyhydric alcohols, low molecular weight polyester resins, amines, and water.

[0247] As the polyisocyanate compound (z2), a blocked polyisocyanate compound may also be used, which is a compound obtained by blocking the isocyanate groups in the above-mentioned polyisocyanate and its derivatives with a blocking agent. As the blocked polyisocyanate compound, the blocked polyisocyanate compound described in the description section of the blocked polyisocyanate compound of the crosslinkable component (x2) may be used.

[0248] The polyisocyanate compounds (z2) can be used individually or in combination of two or more.

[0249] The equivalent ratio (NCO / OH) of the hydroxyl group of the hydroxyl group-containing resin (z1) and the isocyanate group of the polyisocyanate compound (z2) in the clear coating composition (Z) is preferably in the range of 0.5 to 2.0, and more preferably in the range of 0.8 to 1.5.

[0250] The clear coating composition (Z) may optionally contain solvents such as water and organic solvents, curing catalysts, defoamers, ultraviolet absorbers, viscosity modifiers, and anti-settlement agents.

[0251] In the clear coating composition (Z), coloring pigments may be used as appropriate, within a range that does not impair the transparency of the coating film. As coloring pigments, pigments that are known for use in inks or paints can be used individually or in combination of two or more types. The amount of coloring pigment used will vary depending on the type of coloring pigment used, but it can usually be within the range of 30% by mass or less, preferably 0.05 to 20% by mass, and more preferably 0.1 to 10% by mass, relative to the total solid content of the resin component of the clear coating composition (Z).

[0252] The clear coating composition (Z) can be applied by methods such as electrostatic coating, air spraying, or airless spraying, and the thickness of the clear coating film is approximately 10 to 60 μm, more preferably 15 to 50 μm, and even more preferably 20 to 40 μm, based on the cured coating film.

[0253] The solid content of the clear coating composition (Z) is in the range of 10 to 65% by mass, preferably 15 to 55% by mass, and more preferably 20 to 50% by mass. It is preferable to adjust the viscosity of the clear coating composition (Z) using water and / or an organic solvent to a range suitable for painting, usually in the range of 15 to 60 seconds at 20°C, particularly 20 to 50 seconds, using a Ford Cup No. 4 viscometer.

[0254] The present invention will be described more specifically 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.

[0255] [1] Preparation of paints Production of acrylic resin Production example 1 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube and dropping device was charged with 35 parts of propylene glycol monopropyl ether and heated to 85°C. A mixture of 30 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, 29 parts n-butyl acrylate, 15 parts 2-hydroxyethyl acrylate, 6 parts acrylic acid, 20 parts propylene glycol monopropyl ether and 2.3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise over 4 hours, and the mixture was allowed to mature for 1 hour after the dropwise addition was complete. Then, a mixture of 16 parts propylene glycol monopropyl ether and 1 part of 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise over 1 hour, and the mixture was allowed to mature for 1 hour after the dropwise addition was complete. Finally, 7.4 parts of diethanolamine were added to obtain an acrylic resin solution (x11-1) with a solid content of 55% by mass. The obtained acrylic resin had an acid value of 47 mg KOH / g, a hydroxyl value of 72 mg KOH / g, and a weight-average molecular weight of 58,000.

[0256] Production Example 2 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with a mixed solvent of 27.5 parts methoxypropanol and 27.5 parts isobutanol. After raising the temperature to 110°C, a mixture of 25 parts styrene, 27.5 parts n-butyl methacrylate, 20 parts isostearyl acrylate (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd., branched higher alkyl acrylate), 7.5 parts 4-hydroxybutyl acrylate, 15 parts of the following phosphate group-containing polymerizable monomer, 12.5 parts 2-methacryloyloxyethyl acid phosphate, 10 parts isobutanol, and 4 parts t-butyl peroxyoctanoate was added dropwise over 4 hours. A mixture of 23 parts isopropanol and 0.5 parts t-butyl peroxyoctanoate was then added dropwise over 1 hour. After the dropwise addition was complete, the mixture was aged for 1 hour to obtain an acrylic resin solution (x11-2) with a solid content of 50% by mass. The resulting hydroxyl group-containing acrylic resin had an acid value of 83 mg KOH / g due to the phosphate group, a hydroxyl value of 29 mg KOH / g, and a weight-average molecular weight of 10,000.

[0257] Phosphate-containing polymerizable monomer: In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper, 57.5 parts monobutyl phosphate and 41 parts isobutanol were charged and the temperature was raised to 90°C. Then, 42.5 parts glycidyl methacrylate was added dropwise over 2 hours, and the mixture was aged for 1 hour after the completion of the dropwise addition. Subsequently, 59 parts isopropanol was added to obtain a phosphate-containing polymerizable monomer solution with a solid content of 50% by mass. The acid value due to the phosphate group of the obtained monomer was 285 mg KOH / g.

[0258] Manufacturing Example 3: 180 parts (100 parts solids) of the acrylic resin solution (x11-1) obtained in Manufacturing Example 1, 360 parts of deionized water, 6 parts (3 parts solids) of "Surfinol 104A" (trade name, manufactured by EVONIK, antifoaming agent, solids content 50% by mass), and 250 parts of "Varifine BF-20" (trade name, manufactured by Sakai Chemical Industry Co., Ltd., barium sulfate powder, average particle size 0.03 μm) were mixed and dispersed in a paint shaker for 1 hour to obtain an extender pigment dispersion.

[0259] Manufacturing Example 4 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, dropping device, and simple solvent removal trap was charged with 360 parts of "Sumijoule N-3300" (product name, manufactured by Sumika Covestro Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate, solids content 100%, isocyanate group content: 21.8%), 60 parts of "Uniox M-550" (product name, manufactured by NOF Corporation, polyethylene glycol monomethyl ether, average molecular weight: approximately 550), and 0.2 parts of 2,6-di-tert-butyl-4-methylphenol. The mixture was thoroughly mixed and heated at 130°C for 3 hours under a nitrogen stream. Next, 110 parts of ethyl acetate and 252 parts of diisopropyl malonate were charged, and while stirring under a nitrogen stream, 3 parts of a 28% methanol solution of sodium methoxide were added and stirred at 65°C for 8 hours. The amount of isocyanate in the obtained resin solution was 0.12 mol / kg. 683 parts of 4-methyl-2-pentanol were added to this, and the solvent was removed by distillation under reduced pressure for 3 hours while maintaining the system temperature at 80-85°C to obtain 1010 parts of the blocked polyisocyanate compound (x2-1) solution. The simple solvent removal trap contained 95 parts of isopropanol. The solid content of the obtained blocked polyisocyanate compound (x2-1) solution was approximately 60% by mass.

[0260] In manufacturing example 5, 454.5 parts (100 parts resin solids) of "WP-523H" (product name, manufactured by Kansai Paint Co., Ltd., an aqueous intermediate coating paint composition containing acrylic emulsion (by emulsion polymerization in water), polyester resin, and melamine) were uniformly mixed with 36.4 parts (20 parts solids) of the acrylic resin (x11-1) solution obtained in manufacturing example 1 to obtain aqueous coating composition (X-1).

[0261] Production Examples 6-13 Each aqueous paint composition (X-2) to (X-9) was obtained in the same manner as in Production Example 5, except that the amount and composition of the mixtures were as shown in Table 1 below.

[0262]

[0263] (*1) "ETERNACOLL UW-1053D": Product name, manufactured by UBE Corporation, urethane resin aqueous dispersion, solid content 30% by mass.

[0264] (*2) "DAOTAN TW 6466 / 36WA": Product name, manufactured by Daicel Ornex Co., Ltd., polyester-based urethane resin aqueous dispersion, solid content 36% by mass.

[0265] (*3) "Baihydrol UH-2606": Product name, manufactured by Sumika Covestro Urethane Co., Ltd., aqueous dispersion of polycarbonate-based urethane resin, solid content 35% by mass.

[0266] (*4) "Yuliano W321": Product name, manufactured by Arakawa Chemical Industries, Ltd., water-soluble urethane resin, solid content 34.5% by mass.

[0267] (*5) "Carbodilite E-05": Product name, manufactured by Nisshinbo Chemical Co., Ltd., polyvalent carbodiimide, NCN equivalent: 310, solid content 41.3% by mass.

[0268] Preparation of viscosity modifier (y4) Preparation Example 14 A mixture consisting of 20 parts methacrylic acid, 19.5 parts acrylate of a 60-mol adduct of n-octadecyl alcohol ethylene oxide, 60 parts propyl acrylate, and 0.5 parts diacrylate of a 15-mol adduct of ethylene glycol ethylene oxide was added to 50 parts of a 1% methyl triglycol solution of 2,2'-azobisisobutyronitrile. These mixtures were added dropwise to 350 parts of methyl triglycol from a dropping funnel at a constant rate over 1.5 hours, while uniformly stirring to allow the reaction to proceed. The reaction temperature was maintained at 80-90°C. After the addition was complete, the mixture was kept at the same temperature for 3 hours and then cooled to 40°C to obtain a diluted acrylic aggregate type viscosity modifier (y4-1) with a solid content of 20% by mass.

[0269] Manufacturing Example 15 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and two dropping devices was charged with 15.4 parts (10 parts solids) of the following macromonomer solution, 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, in a reaction vessel maintained at the same temperature, a mixture consisting of 31.5 parts N,N-dimethylacrylamide, 31.5 parts N-isopropylacrylamide, 27 parts 2-hydroxyethyl acrylate, 10 parts ethylene glycol monobutyl ether, and 40 parts diethylene glycol monoethyl ether acetate, and a mixture consisting of 0.15 parts "Perbutyl O" (trade name, manufactured by Nippon Oil & Fats Co., Ltd., polymerization initiator, t-butyl peroxy-2-ethylhexanoate) and 20 parts ethylene glycol monobutyl ether were simultaneously added dropwise to the reaction vessel over 4 hours. After the dropwise addition was complete, the mixture was stirred at the same temperature for 2 hours to allow it to mature. Next, in a reaction vessel maintained at the same temperature, a mixture consisting of 0.3 parts 2,2'-azobis(2,4-dimethylvaleronitrile) and 15 parts ethylene glycol monobutyl ether was added dropwise over 1 hour. After the dropwise addition was complete, the mixture was stirred at the same temperature for 1 hour to allow it to mature. Next, ethylene glycol monobutyl ether was added while the mixture was cooled to 30°C to obtain a copolymer solution with a solid content of 35%. The weight-average molecular weight of the obtained copolymer was 310,000. 215 parts of deionized water were added to the obtained copolymer solution to obtain a diluted acrylic association type viscosity modifier solution (y4-2) with a solid content of 20%.

[0270] Macromonomer solution: In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device, 16 parts of ethylene glycol monobutyl ether and 3.5 parts of 2,4-diphenyl-4-methyl-1-pentene were charged. Nitrogen gas was passed through the gas phase, and the temperature was raised to 160°C while stirring. Once 160°C was reached, a mixture consisting of 30 parts n-butyl methacrylate, 40 parts 2-ethylhexyl methacrylate, 30 parts 2-hydroxyethyl methacrylate, and 7 parts 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 solid content of 65%. The obtained macromonomer had a hydroxyl value of 129 mg KOH / g and a number-average molecular weight of 2300.

[0271] Manufacturing Example 16 of a Luminous Paint Composition: "Leaf Powder 49CJ-1120" (product name, manufactured by Oike Metallic Design Co., Ltd., indium particles, volume average particle size) 100 parts (20 parts solids) of approximately 0.3 μm, 20% solids content, dispersed in propylene glycol monomethyl ether; 1.8 parts (1.8 parts solids) of BYK-348 (trade name, manufactured by BYK, silicone-based surface modifier, 100% solids content); 1.8 parts (1.8 parts solids) of "Prysurf A208F" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous solution of polyoxyethylene alkyl (C8) ether phosphate ester with 99% solids content); 9 parts (1.8 parts solids) of the acrylic association type viscosity modifier diluent (y4-1) obtained in Production Example 14; 51.9 parts of 1% dimethylethanolamine aqueous solution; and 340 parts of deionized water were added and stirred to produce a glossy coating composition (Y-1) with a solids content of 5.0% by mass.

[0272] Production Examples 17-23 Each aqueous paint composition (Y-2) to (Y-8) was obtained in the same manner as in Production Example 16, except that the amount and composition of the mixtures were as shown in Table 2 below.

[0273]

[0274] (*6) "Hydroshine WS-3001": Product name, water-based vapor-deposited aluminum flake pigment, manufactured by Eckart, solids content: 10%, internal solvent: isopropanol, average particle size D50: 13 μm, thickness: 0.05 μm.

[0275] (*7) "BYK-381": Product name, manufactured by BYK, acrylic surface modifier, solids content 52%, internal solvent: dipropylene glycol monomethyl ether.

[0276] (*8) "BYK-190": Product name, manufactured by BYK, styrene-based block copolymer, solids content 40%.

[0277] Preparation of Clear Coating Composition (Z) Clear coating composition (Z-1) "KINO-6510T" (product name, manufactured by Kansai Paint Co., Ltd., an acrylic resin-based organic solvent type clear coat paint containing a hydroxyl group-containing acrylic resin and a polyisocyanate compound) was used as the clear coating composition (Z-1).

[0278] [2] Preparation of Samples and Test Plates Preparation of samples for complex viscosity measurement and test plates for specular gloss (60° gloss) and millimeter wave transmittance measurement Example 1 Two sheets of black and white opacity test paper were prepared, and the aqueous paint composition (X-1) prepared in [1] above was applied to each sheet of black and white opacity test paper using a bar coater No. 18 to a cured film thickness of 20 μm. After being left at room temperature for 5 minutes, preheating was performed at 80°C for 3 minutes to obtain two test plates on which an uncured first coating film was formed on the black and white opacity test paper.

[0279] Then, for one of the two test plates obtained, the uncured first coating film formed on the test plate was scraped off with a spatula and collected in a sample bottle. The bottle was immediately sealed with a lid and used as a sample for measuring the complex viscosity of the first coating film.

[0280] Next, for the remaining test plate, the glossy coating composition (Y-1) prepared in [1] above was applied to the uncured first coating film formed on the test plate using a bar coater No. 7 to a cured coating film thickness of 0.8 μm, and immediately preheated at 80°C for 3 minutes to prepare a test plate for measuring specular gloss (60° gloss) and millimeter-wave transmittance.

[0281] Here, the film thickness of the dried glossy coating was calculated using the following formula. The same applies to the following examples.

[0282] Film thickness [μm] = sc / sg / S*10000 sc: Coating solid content [g] sg: Coating film specific gravity [g / cm ３ ] S: Evaluation area of ​​coated solid content [cm²] ２ The solid content sc in the formula was calculated by the following method: An aluminum foil was prepared, its mass was measured, and then all areas except the 21 cm x 37 cm area were masked. In the preparation of the test plate in [3] above, the object to be coated prepared in [1] above and the masked aluminum foil were placed side by side, and the aqueous glossy coating composition was applied to them. After that, the masking was removed, and the aluminum foil coated with the aqueous glossy coating composition was dried at 140°C for 30 minutes. After drying, the mass of the aluminum foil with the glossy coating film attached was weighed, and the solid content sc was calculated by subtracting the mass of the aluminum foil before coating.

[0283] The specific gravity sg of the coating film in the formula was calculated using the specific gravity of each raw material (resin, pigment, additive, etc.) used in the water-based glossy coating composition. The specific gravity of the raw material was determined by referring to the specific gravity of each compound. The "Paint Raw Materials Handbook, 9th Edition" (Japan Paint Manufacturers Association) was used as a reference, and if it was unclear, the literature value for the specific gravity of each compound was referred to, and the specific gravity of resins and organic additives was approximated to 1.

[0284] In the formula, the evaluation area S for the coated solid content is the area on the coated plate to which the glossy coating film is attached, and was calculated from the unmasked area of ​​the masked aluminum foil, which is 21 cm x 37 cm.

[0285] Example 2 Deionized water was added to the aqueous paint composition (X-1) prepared in [1] above, and the viscosity was adjusted so that the viscosity measured using a B-type viscometer at 20°C and a rotation speed of 60 rpm was approximately 1000 mPa·s. Next, two black and white opacity test papers were prepared attached to steel plates, and the aqueous paint composition (X-1) with the adjusted viscosity was electrostatically coated onto each black and white opacity test paper using a rotary atomizing electrostatic coating machine to a cured film thickness of 20 μm. After being left at room temperature for 10 minutes, preheating was performed at 80°C for 3 minutes to obtain two test plates on which an uncured first coating film was formed on the black and white opacity test papers attached to the steel plates.

[0286] Then, for one of the two test plates obtained, the uncured first coating film formed on the test plate was scraped off with a spatula and collected in a sample bottle. The bottle was immediately sealed with a lid and used as a sample for measuring the complex viscosity of the first coating film.

[0287] Next, for the remaining test plate, the glossy coating composition (Y-1) manufactured in [1] above was applied to the uncured first coating film formed on the test plate using a mini-bell type rotary electrostatic coating machine under booth temperature of 23°C and humidity of 68%, so that the cured coating film had a thickness of 0.1 μm. After being left at room temperature for 3 minutes, it was preheated at 80°C for 3 minutes. After that, the black and white opacity test paper was peeled off the steel plate, and the black and white opacity test paper was used as a test plate for measuring specular gloss (60° gloss) and millimeter-wave transmittance.

[0288] Examples 3 to 17 and Comparative Examples 1 to 2 were prepared in the same manner as in Example 1, except that the paint, coating method, preheating temperature, and preheating time were as described in Table 3, to obtain samples for complex viscosity measurement and test plates for specular gloss (60° gloss) and millimeter-wave transmittance measurement.

[0289] Example 18 Deionized water was added to the aqueous paint composition (X-1) prepared in [1] above, and the viscosity was adjusted so that the viscosity measured using a B-type viscometer at 20°C and a rotation speed of 60 rpm was approximately 1000 mPa·s. Next, two black and white opacity test papers were prepared attached to steel plates, and the aqueous paint composition (X-1) with the adjusted viscosity was electrostatically coated onto each black and white opacity test paper using a rotary atomizing electrostatic coating machine to a cured film thickness of 20 μm. After being left at room temperature for 10 minutes, preheating was performed at 80°C for 3 minutes to obtain two test plates on which an uncured first coating film was formed on the black and white opacity test papers attached to the steel plates.

[0290] Then, for one of the two test plates obtained, the uncured first coating film formed on the test plate was scraped off with a spatula and collected in a sample bottle. The bottle was immediately sealed with a lid and used as a sample for measuring the complex viscosity of the first coating film.

[0291] Next, for the remaining test plate, the glossy coating composition (Y-1) prepared in [1] above was applied to the uncured first coating film formed on the test plate using a mini-bell type rotary electrostatic coating machine under booth temperature of 23°C and humidity of 68% to a cured coating film thickness of 0.1 μm. After being left at room temperature for 3 minutes, preheating was performed at 80°C for 3 minutes to obtain an uncured glossy coating film.

[0292] Next, the clear coating composition (Z-1) prepared in [1] above was applied to the uncured glossy coating film using a mini-bell type rotary electrostatic coating machine under booth temperature of 23°C and humidity of 68% to a cured coating film thickness of 35 μm. After being left at room temperature for 7 minutes, it was heated in a hot air circulating drying oven at 140°C for 30 minutes to dry and cure. After that, the black and white opacity test paper was peeled off the steel plate and used as a test plate for measuring specular gloss (60° gloss) and millimeter wave transmittance.

[0293] Examples 19 and Comparative Example 3 were prepared in the same manner as in Example 18, except that the paint, preheating temperature, and preheating time were as described in Table 4, to obtain samples for complex viscosity measurement and test plates for specular gloss (60° gloss) and millimeter-wave transmittance measurement.

[0294] [3] Coating film evaluation The coating film of each sample and test plate obtained as described above was evaluated using the following method, and the results are shown in Tables 3 and 4.

[0295] A rotational rheometer (ARES-G2, manufactured by T.A. Instruments Co., Ltd.) was used to perform dynamic viscoelasticity measurements (temperature 25°C, frequency 1 Hz, strain 0.1%, jig: parallel plate (Φ=8 mm), gap: 0.5 mm) to measure the complex viscosity of the sample used for complex viscosity measurement.

[0296] Specular Gloss (60° Gloss) For the test plates, the 60° gloss value of the coating on the black surface of the black-and-white opacity test paper was measured using a gloss meter (micro-TRI-gloss, manufactured by BYK-Gardner). A higher 60° gloss value indicates better gloss. For multi-layer coatings without a clear coating shown in Table 3, a value of 230 or higher was considered acceptable, and for multi-layer coatings with a clear coating shown in Table 4, a value of 140 or higher was considered acceptable.

[0297] Millimeter-wave transmission: Using a "Vector Network Analyzer" (ME7838A, manufactured by Anritsu Corporation), electromagnetic waves with frequencies of 60 to 90 GHz were incident from an oscillator at an incidence angle of 0° at room temperature. The attenuation rate when only black and white opacity test paper was installed and the attenuation rate when a test plate for millimeter-wave transmission measurement was installed were measured, and the attenuation rate at 76 GHz was determined from the following formula (3).

[0298] Attenuation rate (dB) = (Attenuation rate when only black and white opacity test paper is installed) - (Attenuation rate when the test board for millimeter-wave transmittance measurement is installed) ... Equation (3) From the obtained attenuation rate, the millimeter-wave transmittance at 76 GHz was determined by the following equation (4). Millimeter-wave transmittance (%) = 10 - {(Attenuation rate) / 20} × 100 ... Equation (4)

[0299]

[0300]

[0301]

[0302] Although embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the embodiments described above, and various modifications based on the technical concept of the present invention are possible.

[0303] For example, the configurations, methods, processes, shapes, materials, and numerical values ​​mentioned in the above-described embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values ​​may be used as needed.

[0304] The configurations, methods, processes, shapes, materials, and numerical values ​​of the embodiments described above can be combined with each other 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): A step of applying an aqueous coating composition (X) onto a workpiece to form a first coating film; Step (2): A step of applying a glossy coating composition (Y) onto the first coating film formed in Step (1) to form a second coating film; and Step (3): A step of baking and curing the first coating film formed in Step (1) and the second coating film formed in Step (2) separately or simultaneously, wherein the glossy coating composition (Y) is applied while the complex viscosity of the first coating film is in the range of 100,000 to 1,500,000 Pa·s when measured under conditions of a frequency of 0.1 Hz and a temperature of 25°C, and the glossy coating composition (Y) contains indium particles (y1).

2. The method for forming a multilayer coating film according to claim 1, wherein the glossy coating composition (Y) further contains a surface modifier (y2), a pigment dispersant (y3), a viscosity modifier (y4), and water (y5), and has a solid content of 0.1 to 15% by mass.

3. The method for forming a multilayer coating according to claim 2, wherein the surface modifier (y2) includes a silicone-based surface modifier.

4. The method for forming a multilayer coating film according to claim 2, wherein the pigment dispersant (y3) contains a phosphate group-containing compound.

5. The method for forming a multilayer coating film according to claim 2, wherein the viscosity modifier (y4) includes an aggregate viscosity modifier.

6. The method for forming a multilayer coating film according to claim 2, wherein the water (y5) content is in the range of 45 to 95 parts by mass with respect to 100 parts by mass of the total components of the glossy coating composition (Y).

Images