Multilayer coating film and method for forming a multilayer coating film

Abstract

The object of the present invention is to provide a multi-layer coating film that can suppress deterioration of appearance such as sagging and undercoating while maintaining color development. [Solution] A multilayer coating comprising a metallic base coating and a light-transmitting colored coating on the metallic base coating, wherein the metallic base coating is a cured coating of a metallic base paint composition, and the metallic base paint composition comprises a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME), and the light-transmitting colored coating is a cured coating of a colored paint composition, and the colored paint composition comprises a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE), wherein the acrylic resin fine particles (MD and CD) have a core-shell structure.

Description

Technical Field

[0006] , , ,

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

Background Art

[0002] In the coating film of an automobile, it is known to adjust the color tone by adding an aluminum flake pigment to a metallic base coating film.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As disclosed in Patent Document 1, in an aqueous base coating film, the color tone of a metallic base coating film is adjusted with an aluminum flake pigment, but it is difficult to adjust the color tone in a solvent base coating film. In particular, when a light-transmissive colored coating film is laminated as a multilayer coating film, it is very difficult to maintain the color development property.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a multilayer coating film that can suppress the deterioration of appearance such as sagging and running while maintaining the color development property in a multilayer coating film including a metallic base coating film and a light-transmissive colored coating film.

Means for Solving the Problems

[0006] To solve the above problems, the present invention provides the following aspects. [1] A metallic base coating film, A light-transmissive colored coating film on the metallic base coating film, A multilayer coating film comprising: The aforementioned metallic base coating is a cured coating of a metallic base paint composition. The metallic base coating composition comprises a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME). The light-transmitting colored coating film is a cured coating film of a colored paint composition. The aforementioned colored paint composition comprises a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE). The acrylic resin microparticles (MD) and the acrylic resin microparticles (CD) are both multilayer coatings having a core-shell structure. This makes it possible to provide a multilayer coating that can suppress deterioration of appearance such as sagging and undercoating while maintaining color development. [2] In one embodiment, the solid content mass ratio (MC) / (MD) of aluminum flake pigment (MC) and acrylic resin fine particles (MD) contained in the metallic base coating composition is in the range of 0.3 to 3. [3] In one embodiment, both the acrylic resin fine particles (MD) and the acrylic resin fine particles (CD) have a glass transition temperature in the range of 60 to 150°C and an average particle diameter in the range of 50 to 500 nm. [4] In one embodiment, both the acrylic resin fine particles (MD) and the acrylic resin fine particles (CD) have a core glass transition temperature in the range of 80 to 140°C. [5] In one embodiment, both the hydroxyl group-containing acrylic resin (MA) and the hydroxyl group-containing acrylic resin (CA) have a weight-average molecular weight of 10,000 or more and 60,000 or less, a glass transition temperature in the range of -30 to 40°C, and a hydroxyl value of 10 mg KOH / g or more and 50 mg KOH / g or less. [6] In one embodiment, the content of the organic solvent (CE) is in the range of 40 to 80% by mass relative to the total mass of the colored paint composition. [7] In one embodiment, the thickness of the metallic base coating is in the range of 12 to 26 μm. The thickness of the light-transmitting colored coating is in the range of 8 to 24 μm. [8] Metallic base coating and A light-transmitting colored coating film is formed on the aforementioned metallic base coating film, A method for forming a multilayer coating film comprising, The above method involves the following steps: Step (1) prepares a metallic base paint composition comprising a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME). Step (2) prepares a colored paint composition comprising a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE), Step (3) involves applying the metallic base coating composition onto the object to be coated to form an uncured metallic base coating film, The steps include (4) applying the colored paint composition onto the uncured metallic base coating to form an uncured light-transmitting colored coating, A method for forming a multilayer coating film, comprising the step (5) of baking and curing the uncured metallic base coating film and the uncured light-transmitting colored coating film to form the metallic base coating film and the light-transmitting colored coating film. This makes it possible to produce a multilayer coating film that can maintain color development while suppressing deterioration of appearance such as sagging and undercoating. [9] Metallic base coating and A light-transmitting colored coating film is formed on the metallic base coating film, A clear coating is formed on the light-transmitting colored coating, A method for forming a multilayer coating film comprising, The method includes the following steps: Step (1) of preparing a metallic base paint composition containing a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME); Step (2) of preparing a colored paint composition containing a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE); Step (6) of preparing a clear paint composition; Step (3) of coating the metallic base paint composition on an object to be coated to form an uncured metallic base paint film; Step (4) of coating the colored paint composition on the uncured metallic base paint film to form an uncured light-transmissive colored paint film; Step (7) of coating the clear paint composition on the uncured light-transmissive colored paint film to form an uncured clear paint film; Step (8) of baking and curing the uncured metallic base paint film, the uncured light-transmissive colored paint film, and the uncured clear paint film to form the metallic base paint film, the light-transmissive colored paint film, and the clear paint film. By this method, a multi-layer paint film can be manufactured that can suppress appearance deterioration such as sagging and running while maintaining color development properties.

Effects of the Invention

[0007] According to the present invention, a multi-layer paint film can be provided that can suppress appearance deterioration such as sagging and running while maintaining color development properties.

Modes for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described. These descriptions are for the purpose of exemplifying the present invention and do not limit the present invention in any way.

[0009] In the present invention, two or more embodiments can be arbitrarily combined.

[0010] The materials, components, compounds, resins, monomers, polymers, pigments, and solvents described in this specification may each be used alone or in combination of two or more thereof, unless otherwise specified.

[0011] In the present invention, the paint and the paint composition can be used interchangeably.

[0012] In the present invention, the term "solid content" is a concept including the solid content and the non-volatile content. Also, the solid content may be referred to as NV.

[0013] In this specification, numerical ranges are intended to include the upper and lower limits of the range, unless otherwise specified. For example, 60 to 150 °C means 60 °C or higher and 150 °C or lower.

[0014] In this specification, the hydroxyl group-containing acrylic resin (MA), isocyanate compound (MB), aluminum flake pigment (MC), acrylic resin fine particles (MD), organic solvent (ME), hydroxyl group-containing acrylic resin (CA), isocyanate compound (CB), blue pigment (CC), acrylic resin fine particles (CD), and organic solvent (CE) may be referred to as MA component, MB component, MC component, MD component, ME component, CA component, CB component, CC component, CD component, and CE component, respectively.

[0015] [[ID= ]]In this specification, (meth)acrylic means one or more selected from the group consisting of acrylic and methacrylic.

[0016] In the present invention, for the convenience of explanation of each step, the steps are numbered and represented as step (1) etc., but this is a number for specifying or distinguishing each step and does not mean the order of the steps.

[0017] (Multi-layer coating film) The multi-layer coating film according to the present invention comprises a metallic base coating film and a light-transmissive colored coating film on the metallic base coating film, and A multilayer coating film comprising, The aforementioned metallic base coating is a cured coating of a metallic base paint composition. The metallic base coating composition comprises a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME). The light-transmitting colored coating film is a cured coating film of a colored paint composition. The aforementioned colored paint composition comprises a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE). Both the acrylic resin microparticles (MD) and the acrylic resin microparticles (CD) are multilayer coating films having a core-shell structure.

[0018] The following describes metallic base coating compositions that form a metallic base coating film and colored coating compositions that form a light-transmitting colored coating film.

[0019] • Metallic base paint composition The metallic base paint composition comprises a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME), wherein the acrylic resin fine particles (MD) have a core-shell structure.

[0020] Hydroxyl group-containing acrylic resin (MA) The MA component is a polymer of one or more monomers, including a hydroxyl group-containing monomer.

[0021] MA components are obtained by polymerizing one or more monomers, including a hydroxyl group-containing monomer, according to conventional methods.

[0022] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, allyl alcohol, and methacrylic alcohol. Monoester compounds of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms are also examples.

[0023] The MA component may be a homopolymer of hydroxyl group-containing monomers, or a copolymer of a hydroxyl group-containing monomer and another monomer.

[0024] When the MA component is a copolymer, it is obtained by copolymerizing a hydroxyl group-containing monomer with another monomer. The amount of the hydroxyl group-containing monomer is, for example, 5 to 20% by mass relative to the total mass of the hydroxyl group-containing monomer and the other monomer.

[0025] Other monomers include, for example, acid group-containing monomers, (meth)acrylic acid esters, polymerizable aromatic compounds, polymerizable nitriles, α-olefins, vinyl esters, and dienes.

[0026] Examples of acid group-containing monomers include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, itaconic acid, 3-vinyl salicylic acid, 3-vinylacetylsalicylic acid, 2-acryloyloxyethyl acid phosphate, and 2-acrylamido-2-methylpropanesulfonic acid.

[0027] Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth)acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, dihydrodicyclopentadienyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0028] Examples of polymerizable aromatic compounds include styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, and vinylnaphthalene.

[0029] Examples of polymerizable nitriles include acrylonitrile and methacrylonitrile.

[0030] Examples of α-olefins include ethylene and propylene.

[0031] Examples of vinyl esters include vinyl acetate and vinyl propionate.

[0032] Examples of dienes include butadiene and isoprene.

[0033] As for other monomers, styrene is preferable from the viewpoint of improving water resistance.

[0034] In one embodiment, the MA component is one or more selected from the group consisting of homopolymers and copolymers. In another embodiment, the MA component is a copolymer.

[0035] The Mw of the MA component is, for example, 10,000 or more. In one embodiment, the Mw of the MA component is 10,000 to 60,000. In another embodiment, the Mw of the MA component is 10,000 or more, 20,000 or more, 30,000 or more, 40,000 or more, or 50,000 or more. In yet another embodiment, the Mw of the MA component is 60,000 or less, 50,000 or less, 40,000 or less, 30,000 or less, or 20,000 or less. The Mw may be determined, for example, by gel permeation chromatography (GPC) using polystyrene as a standard.

[0036] The Tg of the MA component is, for example, -30°C or higher. In one embodiment, the Tg of the MA component is -30°C or higher and 40°C or lower. In another embodiment, the Tg of the MA component is -30°C or higher, -20°C or higher, -10°C or higher, 0°C or higher, 10°C or higher, 20°C or higher, or 30°C or higher. In yet another embodiment, the Tg of the MA component is 40°C or lower, 30°C or lower, 20°C or lower, 10°C or lower, 0°C or lower, -10°C or lower, or -20°C or lower. The Tg of the MA component may be measured or calculated by known methods. For example, the Tg may be measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

[0037] The hydroxyl value of the MA component is, for example, 10 mg KOH / g or more. In one embodiment, the hydroxyl value of the MA component is 10 to 50 mg KOH / g. In another embodiment, the hydroxyl value of the MA component is 10 mg KOH / g or more, 20 mg KOH / g or more, 30 mg KOH / g or more, or 40 mg KOH / g or more. In yet another embodiment, the hydroxyl value of the MA component is 50 mg KOH / g or less, 40 mg KOH / g or less, 30 mg KOH / g or less, or 20 mg KOH / g or less.

[0038] In one embodiment, the MA component has an Mw of 10,000 to 60,000, a Tg in the range of -30 to 40°C, and a hydroxyl value of 10 mg KOH / g to 50 mg KOH / g.

[0039] The acid value of the MA component is, for example, 0.2 mg KOH / g or higher. In one embodiment, the acid value of the MA component is 0.2 to 20 mg KOH / g. In another embodiment, the acid value of the MA component is 0.2 mg KOH / g or higher, 0.5 mg KOH / g or higher, 1.0 mg KOH / g or higher, 5.0 mg KOH / g or higher, 10.0 mg KOH / g or higher, or 15.0 mg KOH / g or higher. In yet another embodiment, the acid value of the MA component is 20.0 mg KOH / g or less, 15.0 mg KOH / g or less, 10.0 mg KOH / g or less, 5.0 mg KOH / g or less, 1.0 mg KOH / g or less, or 0.5 mg KOH / g or less.

[0040] The hydroxyl value and acid value may be measured or calculated using known methods. For example, the hydroxyl value and acid value may be measured in accordance with JIS K 0070:1992.

[0041] The content of MA component in the metallic base coating composition is not particularly limited, and may be, for example, 30 to 98% by mass relative to the total mass of resin solids in the metallic base coating composition. In one embodiment, the content of MA component is 30% or more by mass, 35% or more by mass, 40% or more by mass, 45% or more by mass, 50% or more by mass, 55% or more by mass, 60% or more by mass, 65% or more by mass, 70% or more by mass, 75% or more by mass, 80% or more by mass, 85% or more by mass, 90% or more by mass, or 95% or more by mass, relative to the total mass of resin solids in the metallic base coating composition. In another embodiment, the MA component content is 98% by mass or less, 95% by mass or less, 90% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, or 35% by mass or less, based on the total mass of the resin solids of the metallic base coating composition.

[0042] Isocyanate compounds (MB) By using MB components together with MA components, the adhesion between the substrate, intermediate coating, or primer coating and the metallic base coating can be improved. Furthermore, the crosslinking of the metallic base coating improves the coating's physical properties and enhances its water resistance.

[0043] The MB component may be a polyisocyanate or a blocked isocyanate obtained by blocking the polyisocyanate.

[0044] Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimers), pentamethylene diisocyanate, tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate); aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate; and modified products of these diisocyanates (urethanes, carbodiimides, uretdiones, uretonimines, biuret and / or isocyanurate modified products, etc.).

[0045] Examples of blocking agents include monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenolcarbinol, and methylphenylcarbinol; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type terminal diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycolphenol; polyester-type terminal polyols obtained from diols such as ethylene glycol, propylene glycol, and 1,4-butanediol, and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenols such as para-t-butylphenol and cresol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam.

[0046] As blocking agents, active hydrogen compounds such as methyl diketones, methyl ketoesters, and methyl diester compounds, such as alkyl esters including acetylacetone, ethyl acetoate, and diethyl malonate, may be used. Blocking isocyanates made from imidazole compounds or pyrazole compounds may also be used.

[0047] A blocking rate of 100% for the blocked isocyanate is preferable. This results in better storage stability for the metallic base coating composition.

[0048] The content of MB components in the metallic base coating composition is not particularly limited; for example, it may be 10 to 20% by mass relative to the total mass of resin solids in the metallic base coating composition.

[0049] When using a blocked isocyanate as the MB component, from the viewpoint of more appropriately promoting the curing reaction, the number of moles of isocyanate groups of the blocked isocyanate per mole of hydroxyl groups of the MA component may be, for example, 0.2 to 0.6, and preferably 0.3 to 0.5. In one embodiment, the number of moles of isocyanate groups of the blocked isocyanate per mole of hydroxyl groups of the MA component is 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. In another embodiment, the number of moles of isocyanate groups of the blocked isocyanate per mole of hydroxyl groups of the MA component is 0.6 or less, 0.5 or less, 0.4 or less, or 0.3 or less.

[0050] The metallic base paint composition may also contain other curing agents besides the MB component, such as melamine resin, guanamine resin, urea resin, and other amino resins.

[0051] If the metallic base coating composition contains curing agents other than the MB component, the amount of the other curing agents is, for example, 10 to 30 parts by mass per 100 parts by mass of the resin solids content of the metallic base coating composition.

[0052] Aluminum flake pigment (MC) As the MC component, known flake-shaped aluminum pigments can be used. Examples of MC components include leafing, semi-leafing, or non-leafing aluminum flakes prepared by a conventional method of grinding aluminum flakes together with fatty acids such as stearic acid in a ball mill.

[0053] The average particle size of the MC component may be, for example, 15 to 25 μm.

[0054] The average particle thickness of the MC component may be, for example, 0.5 to 1.5 μm.

[0055] The MC component may, for example, be one with particle properties such that the gradient n in the Rosin-Rammler diagram is 2.5 or greater.

[0056] The average particle size of the MC component is the 50th percentile value of the particle size distribution measured by a laser diffraction particle size distribution analyzer. The average particle thickness (μm) is a value obtained by the formula "4000 / water surface coverage area (cm2 / g)", and the measurement method is described, for example, on page 1243 of the "Aluminum Handbook" (9th edition, published April 15, 1972, Japan Light Metals Association; Asakura Shoten).

[0057] The rosin-Rammler diagram for the MC component refers to a particle size distribution diagram that follows the formula "R = 100 exp(-bDn)" (where R is the cumulative weight percentage from the maximum particle size to particle size D, D is the particle size, and b and n are constants). The gradient n refers to the value of n in the rosin-Rammler equation, which is represented by the straight line connecting the cumulative weight percentage from the maximum particle size to particle size D in the particle size diagram. A preferred gradient n in the rosin-Rammler diagram is 2.7 to 3.5.

[0058] The specific measurement method involves determining the particle size distribution using a laser diffraction particle size distribution analyzer, plotting the resulting cumulative distribution for each particle size on a rosin-Rammler diagram, and then shifting the resulting line to draw an extrapolation line from the pole (Pol P) to determine n.

[0059] The MC component can be obtained, for example, by wet grinding atomized aluminum spherical powder, whose particle size has been pre-selected by primary classification, in a grinding medium consisting of a grinding aid and an aliphatic or aromatic hydrocarbon solvent, followed by sieving classification in the wet state and then solid-liquid separation using a filter press or the like. The particle shape is macroscopically circular or rounded and flattened, with very few uneven fracture surfaces present at the flake edges.

[0060] The MC component content in the metallic base coating composition is, for example, 1 to 15 parts by mass per 100 parts by mass of the vehicle's solid content. In one embodiment, the MC component content in the metallic base coating composition is 1 part by mass or more, 5 parts by mass or more, or 10 parts by mass or more per 100 parts by mass of the vehicle's solid content. In another embodiment, the MC component content in the metallic base coating composition is 15 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less per 100 parts by mass of the vehicle's solid content.

[0061] Furthermore, as aluminum flake pigments, for example, those described in Japanese Patent Publication No. 2011-251252, Japanese Patent Publication No. 2009-291713, Japanese Patent Publication No. 2006-212478, and Japanese Patent Publication No. 2005-270896 may be used.

[0062] Acrylic resin microparticles (MD) The MD component consists of acrylic resin particles having a core-shell structure.

[0063] In the MD component, the resin particles are preferably prepared as non-crosslinked resin particles. Furthermore, the monomer copolymerized in the presence of a dispersion-stable resin to obtain non-crosslinked resin particles is not particularly limited as long as it is a radically polymerizable unsaturated monomer.

[0064] In the synthesis of dispersion-stable resins and MD components, it is preferable to use polymerizable monomers having functional groups. This is because MD components having functional groups can react with MB components together with dispersion-stable resins containing functional groups to form a three-dimensionally crosslinked coating film.

[0065] The dispersion-stable resin is not particularly limited as long as it can stably synthesize the MD component in an organic solvent. Specifically, it is preferable to use acrylic resin, polyester resin, polyether resin, polycarbonate resin, or polyurethane resin as the dispersion-stable resin.

[0066] The hydroxyl value (solids content) of the dispersion-stable resin is, for example, 10 to 250 mgKOH / g, preferably 20 to 180 mgKOH / g.

[0067] The acid value (solid content) of the dispersion-stable resin is, for example, 0 to 100 mg KOH / g, preferably 0 to 50 mg KOH / g.

[0068] The number-average molecular weight (Mn) of the dispersion-stable resin is, for example, 800 to 100,000, preferably 1,000 to 20,000.

[0069] The method for synthesizing the dispersion-stable resin is not particularly limited, but methods such as obtaining it by radical polymerization in the presence of a radical polymerization initiator, or by condensation or addition reactions are preferred.

[0070] The monomer used to obtain a dispersion-stable resin can be appropriately selected according to the properties of the resin, but it is preferable to use a monomer having a functional group such as a hydroxyl group or an acid group, and if necessary, monomers having a functional group such as a glycidyl group or an isocyanate group may also be used.

[0071] The MD component can be obtained by polymerizing a polymerizable monomer in the presence of a dispersion-stable resin. A radically polymerizable monomer can be used as the polymerizable monomer.

[0072] For the synthesis of MD components, it is preferable to use polymerizable monomers that have functional groups such as hydroxyl groups, acidic groups, glycidyl groups, and isocyanate groups.

[0073] Examples of polymerizable monomers having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxymethyl methacrylate, allyl alcohol, and adducts of hydroxyethyl (meth)methacrylate and ε-caprolactone.

[0074] Examples of acidic groups include carboxyl groups and sulfonic acid groups.

[0075] Examples of polymerizable monomers containing a carboxyl group include (meth)acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, and fumaric acid.

[0076] Examples of polymerizable monomers having a sulfonic acid group include t-butylacrylamidesulfonic acid.

[0077] When using polymerizable monomers having acidic groups, it is preferable that some of the acidic groups are carboxyl groups.

[0078] Examples of polymerizable monomers having a glycidyl group include glycidyl (meth)acrylate.

[0079] Examples of polymerizable monomers having an isocyanate group include m-isopropenyl-α,α-dimethylbenzyl isocyanate and isocyanatoethyl acrylate.

[0080] Other polymerizable monomers include, for example, alkyl esters of (meth)acrylate such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and tridecyl methacrylate; addition reaction products of oil fatty acids and acrylic acid or methacrylate ester monomers having an oxirane structure (for example, addition reaction products of stearic acid and glycidyl methacrylate); and oxirane compounds containing alkyl groups with 3 or more carbon atoms and acrylic acid Alternatively, addition reaction products with methacrylic acid, styrene, α-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, pt-butylstyrene, benzyl (meth)acrylate, itaconic acid esters (such as dimethyl itaconic acid), maleic acid esters (such as dimethyl maleate), fumaric acid esters (such as dimethyl fumaric acid), and others include acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, vinyl acetate, beova monomer (manufactured by Shell Chemical Co., Ltd., trade name), vinyl propionate, vinyl pivalate, ethylene, propylene, butadiene, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, acrylamide, vinylpyridine, etc.

[0081] In the preparation of MD components, the composition ratio of dispersion-stable resin and polymerizable monomer can be arbitrarily selected depending on the purpose. For example, for a total of 100% by mass of dispersion-stable resin and polymerizable monomer, it is preferable that the dispersion-stable resin be 3 to 80% by mass, particularly 5 to 60% by mass, and the polymerizable monomer be 97 to 20% by mass, particularly 95 to 40% by mass.

[0082] The total concentration of the dispersion-stable resin and polymerizable monomer in the organic solvent is preferably 30 to 80% by mass, and particularly preferably 40 to 60% by mass, based on the total mass.

[0083] The polymerization reaction to obtain the MD component is preferably carried out in the presence of a radical polymerization initiator.

[0084] Examples of radical polymerization initiators include azo-based initiators such as 2,2'-azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile), as well as benzoyl peroxide, lauryl peroxide, and t-butyl peroctoate.

[0085] The amount of radical polymerization initiator is, for example, 0.2 to 10 parts by mass, preferably 0.5 to 5 parts by mass, per 100 parts by mass of the total polymerizable monomers.

[0086] The polymerization reaction temperature can be, for example, 60 to 160°C.

[0087] The polymerization reaction time can be, for example, about 1 to 15 hours.

[0088] The hydroxyl value (solids content) of the MD component is, for example, 50 to 400, preferably 100 to 300. In one embodiment, the hydroxyl value (solids content) of the MD component is 50 or more, 100 or more, 150 or more, 200 or more, 250 or more, 300 or more, or 350 or more. In another embodiment, the hydroxyl value (solids content) of the MD component is 400 or less, 350 or less, 300 or less, 250 or less, 200 or less, 150 or less, or 100 or less.

[0089] The acid value (solid content) of the MD component is, for example, 0 to 200 mg KOH / g, preferably 0 to 50 mg KOH / g. In one embodiment, the acid value (solid content) of the MD component is 0 mg KOH / g or more, 50 mg KOH / g or more, 100 mg KOH / g or more, or 150 mg KOH / g or more. In another embodiment, the acid value (solid content) of the MD component is 200 mg KOH / g or less, 150 mg KOH / g or less, 100 mg KOH / g or less, or 50 mg KOH / g or less.

[0090] In one embodiment, the Tg of the MD component is 60 to 150°C. In another embodiment, the Tg of the MD component is 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, or 140°C or higher. In yet another embodiment, the Tg of the MD component is 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, 90°C or lower, 80°C or lower, or 70°C or lower.

[0091] In one embodiment, the Tg of the core portion of the MD component is 80 to 140°C. In another embodiment, the Tg of the core portion of the MD component is 80°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, 120°C or higher, or 130°C or higher. In yet another embodiment, the Tg of the core portion of the MD component is 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, 90°C or lower, 80°C or lower, or 70°C or lower.

[0092] In one embodiment, the Tg of the shell portion of the MD component is 10 to 60°C. In another embodiment, the Tg of the shell portion of the MD component is 10°C or higher, 20°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher. In yet another embodiment, the Tg of the shell portion of the MD component is 60°C or lower, 50°C or lower, 40°C or lower, 30°C or lower, or 20°C or lower.

[0093] The Tg of the MD component and the CD component described later may be calculated taking into account the type and amount of raw material monomers. Specifically, the Tg of a copolymer made from n types of monomers can be determined by the following FOX formula (Equation (1)). 1 / Tg=W1 / Tg1+W2 / Tg2+ +Wn / Tgn Formula (1) In formula (1), Tgn is the glass transition temperature (°C) of the homopolymer of each monomer. Wn is the mass fraction of each monomer, and W1 + W2 + ... + Wn = 1.

[0094] Therefore, the Tg of the core of a certain MD component can be determined by applying the glass transition temperature of the monomer homopolymer used to form the core and the mass fraction of that monomer to equation (1). Similarly, the Tg of the entire core-shell of a certain MD component can be determined by applying the glass transition temperature of the monomer homopolymer used and the mass fraction of that monomer in the entire core-shell of the MD component to equation (1).

[0095] The average particle size of the MD component is, for example, 50 to 10,000 nm, preferably 50 to 500 nm. In one embodiment, the average particle size of the MD component is 50 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, or 450 nm or more. In another embodiment, the average particle size of the MD component is 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, 150 nm or less, or 100 nm or less. Light scattering can be used as a method for measuring the average particle size.

[0096] In one embodiment, the MD component has a Tg of 60 to 150°C and an average particle diameter of 50 to 500 nm.

[0097] The MD component is particulate in the metallic base paint composition, but does not necessarily have to form a particulate structure in the metallic base coating film.

[0098] In a metallic base coating composition, the content of the MD component is, for example, 2 to 15% by mass relative to the total mass of the resin solids in the metallic base coating composition. In one embodiment, the content of the MD component is 2% or more by mass, 5% or more by mass, or 10% or more by mass relative to the total mass of the resin solids in the metallic base coating composition. In another embodiment, the content of the MD component is 15% or less by mass, 10% or less by mass, or 5% or less by mass relative to the total mass of the resin solids in the metallic base coating composition.

[0099] In one embodiment, the solid content mass ratio (MC) / (MD) of the MC component and MD component contained in the metallic base coating composition is 0.3 to 3.0, 0.4 to 2.0, 0.5 to 1.7, or 0.6 to 1.6. In another embodiment, the solid content mass ratio (MC) / (MD) of the MC component and MD component contained in the metallic base coating composition is 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.5 or more, 2.0 or more, or 2.5 or more. In yet another embodiment, the solid content mass ratio (MC) / (MD) of the MC component and MD component contained in the metallic base coating composition is 3.0 or less, 2.5 or less, 2.0 or less, 1.5 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.4 or less.

[0100] Organic solvents (ME) The metallic base paint composition contains an organic solvent (ME) and is a solvent-type paint composition.

[0101] Examples of organic solvents include ester-based solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ether-based solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, methyl methoxybutanol, ethoxypropanol, ethylene glycol isopropyl ether, ethylene glycol-t-butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methoxybutanol, and propylene glycol monobutyl ether; alcohol-based solvents such as methanol, ethanol, butanol, and propyl alcohol; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon-based solvents such as Swarzol, Shellzol, and mineral spirits; and aromatic solvents such as xylene, toluene, Solvesso-100 (S-100), and Solvesso-150 (S-150).

[0102] In one embodiment, the ME component is one or more selected from the group consisting of ester solvents, ketone solvents, and aromatic solvents. In another embodiment, the ME component is one or more selected from the group consisting of butyl acetate, methyl isobutyl ketone, xylene, and toluene.

[0103] Other ingredients The metallic base paint composition may optionally contain coloring pigments, extender pigments, gloss pigments, curing catalysts, viscosity modifiers, defoaming agents, ultraviolet absorbers, light stabilizers, antioxidants, surface modifiers, film-forming aids, rust inhibitors, etc.

[0104] The method for preparing the metallic base coating composition is not particularly limited. For example, it can be prepared by stirring, kneading, or dispersing the MA-ME components using a disperser, homogenizer, roll, sand grind mill, or kneader.

[0105] The solid content of the metallic base coating composition is, for example, 25-40% of the total mass of the metallic base coating composition. In one embodiment, the solid content of the metallic base coating composition is 25% or more, 30% or more, or 35% or more of the total mass of the metallic base coating composition. In another embodiment, the solid content of the metallic base coating composition is 40% or less, 35% or less, or 30% or less of the total mass of the metallic base coating composition.

[0106] ·Colored paint composition The colored paint composition comprises a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE), wherein the acrylic resin fine particles (CD) have a core-shell structure.

[0107] Hydroxyl group-containing acrylic resin (CA) The CA component is a polymer of one or more monomers, including a hydroxyl group-containing monomer. The types and materials of the CA component are the same as those of the MA component.

[0108] The CA component may be the same as or different from the MA component in terms of type and characteristics.

[0109] In one embodiment, the CA component is one or more selected from the group consisting of homopolymers and copolymers. In another embodiment, the CA component is a copolymer.

[0110] In one embodiment, the CA component is one or more selected from the group consisting of homopolymers and copolymers. In another embodiment, the CA component is a copolymer.

[0111] The Mw of the CA component is, for example, 10,000 or more. In one embodiment, the Mw of the CA component is 10,000 to 60,000. In one embodiment, the Mw of the CA component is 10,000 or more, 20,000 or more, 30,000 or more, 40,000 or more, or 50,000 or more. In another embodiment, the Mw of the CA component is 60,000 or less, 50,000 or less, 40,000 or less, 30,000 or less, or 20,000 or less.

[0112] The Tg of the CA component is, for example, -30°C or higher. In one embodiment, the Tg of the CA component is -30°C or higher and 40°C or lower. In one embodiment, the Tg of the CA component is -30°C or higher, -20°C or higher, -10°C or higher, 0°C or higher, 10°C or higher, 20°C or higher, or 30°C or higher. In another embodiment, the Tg of the CA component is 40°C or lower, 30°C or lower, 20°C or lower, 10°C or lower, 0°C or lower, -10°C or lower, or -20°C or lower.

[0113] The hydroxyl value of the CA component is, for example, 10 mg KOH / g or more. In one embodiment, the hydroxyl value of the CA component is 10 to 50 mg KOH / g. In another embodiment, the hydroxyl value of the CA component is 10 mg KOH / g or more, 20 mg KOH / g or more, 30 mg KOH / g or more, or 40 mg KOH / g or more. In yet another embodiment, the hydroxyl value of the CA component is 50 mg KOH / g or less, 40 mg KOH / g or less, 30 mg KOH / g or less, or 20 mg KOH / g or less.

[0114] In one embodiment, the CA component has an Mw of 10,000 to 60,000, a Tg in the range of -30 to 40°C, and a hydroxyl value of 10 mg KOH / g to 50 mg KOH / g.

[0115] In one embodiment, both the MA component and the CA component have an Mw of 10,000 to 60,000, a Tg in the range of -30 to 40°C, and a hydroxyl value of 10 mg KOH / g to 50 mg KOH / g.

[0116] The acid value of the CA component is, for example, 0.2 mg KOH / g or higher. In one embodiment, the acid value of the CA component is 0.2 to 20 mg KOH / g. In another embodiment, the acid value of the CA component is 0.2 mg KOH / g or higher, 0.5 mg KOH / g or higher, 1.0 mg KOH / g or higher, 5.0 mg KOH / g or higher, 10.0 mg KOH / g or higher, or 15.0 mg KOH / g or higher. In yet another embodiment, the acid value of the CA component is 20.0 mg KOH / g or less, 15.0 mg KOH / g or less, 10.0 mg KOH / g or less, 5.0 mg KOH / g or less, 1.0 mg KOH / g or less, or 0.5 mg KOH / g or less.

[0117] The content of the CA component in the colored paint composition is not particularly limited, and may be, for example, 40 to 87% by mass of the resin solids content of the colored paint composition. In one embodiment, the content of the CA component is 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, or 85% by mass or more, based on the total mass of the resin solids content of the colored paint composition. In another embodiment, the content of the CA component is 87% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, or 45% by mass or less, based on the total mass of the resin solids content of the colored paint composition.

[0118] Isocyanate compounds (CB) The CB component may be a polyisocyanate or a blocked isocyanate obtained by blocking the polyisocyanate.

[0119] The CB component may be the same as or different from the MB component.

[0120] The content of CB component in the colored paint composition is not particularly limited; for example, it may be 10 to 20% by mass of the resin solids content of the colored paint composition.

[0121] When using a blocked isocyanate as the CB component, from the viewpoint of more appropriately promoting the curing reaction, the number of moles of isocyanate groups of the blocked isocyanate per mole of hydroxyl groups of the CA component may be, for example, 0.2 to 0.6, and preferably 0.3 to 0.5. In one embodiment, the number of moles of isocyanate groups of the blocked isocyanate per mole of hydroxyl groups of the CA component is 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. In another embodiment, the number of moles of isocyanate groups of the blocked isocyanate per mole of hydroxyl groups of the CA component is 0.6 or less, 0.5 or less, 0.4 or less, or 0.3 or less.

[0122] The colored paint composition may also contain other curing agents besides the CB component, such as melamine resin, guanamine resin, urea resin, and other amino resins.

[0123] If the colored paint composition contains curing agents other than the CB component, the amount of the other curing agents is, for example, 10 to 30 parts by mass per 100 parts by mass of the resin solids content of the colored paint composition.

[0124] Blue pigment (CC) A known blue pigment can be used as the CC component. The CC component is different from the MC component.

[0125] Examples of blue pigments include phthalocyanine-based pigments and slub-based pigments.

[0126] Other blue pigments that can be used include Green 10405 (manufactured by CERDEC), FASTONGN SUPER BLUE 6070S Indanthrone (manufactured by DIC), FASTONGN BLUE RSK Phthalocyanine α (manufactured by DIC), FASTONGN BLUE 5380 Phthalocyanine β (manufactured by DIC), FASTONGN GREEN MY Halogenated Phthalocyanine (manufactured by DIC), and Blue 10336 (manufactured by CERDEC).

[0127] The content of CC component in the colored paint composition is not particularly limited, and may be, for example, 0.1 to 25 parts by mass per 100 parts by mass of the total solid content of the colored paint composition. In one embodiment, the content of CC component in the colored paint composition is 0.1 parts by mass or more, 1.0 part by mass or more, 2.0 parts by mass or more, 5.0 parts by mass or more, 10.0 parts by mass or more, 15.0 parts by mass or more, or 20.0 parts by mass or more, per 100 parts by mass of the total solid content of the colored paint composition. In another embodiment, the content of CC component in the colored paint composition is 25.0 parts by mass or less, 20.0 parts by mass or less, 15.0 parts by mass or less, 10.0 parts by mass or less, or 5.0 parts by mass or less, per 100 parts by mass of the total solid content of the colored paint composition.

[0128] Acrylic resin microparticles (CD) The CD component consists of acrylic resin particles with a core-shell structure. The type and material of the CD component are the same as those of the MD component.

[0129] The CD components may be the same as or different from the MD components.

[0130] The hydroxyl value (solid content) of the CD component is, for example, 50 to 400 mg KOH / g, preferably 100 to 300 mg KOH / g. In one embodiment, the hydroxyl value of the CD component is 50 mg KOH / g or more, 100 mg KOH / g or more, 150 mg KOH / g or more, 200 mg KOH / g or more, or 250 mg KOH / g or more. In another embodiment, the hydroxyl value of the CD component is 300 mg KOH / g or less, 250 mg KOH / g or less, 200 mg KOH / g or less, or 150 mg KOH / g or less.

[0131] The acid value (solid content) of the CD component is, for example, 0 to 200 mgKOH / g, preferably 0 to 50 mgKOH / g. In one embodiment, the acid value of the CD component is 0 mgKOH / g or more, 50 mgKOH / g or more, 100 mgKOH / g or more, or 150 mgKOH / g or more. In another embodiment, the acid value of the CD component is 200 mgKOH / g or less, 150 mgKOH / g or less, 100 mgKOH / g or less, or 50 mgKOH / g or less.

[0132] In one embodiment, the Tg of the CD component is 60 to 150°C. In another embodiment, the Tg of the CD component is 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, or 140°C or higher. In yet another embodiment, the Tg of the CD component is 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, 90°C or lower, 80°C or lower, or 70°C or lower.

[0133] In one embodiment, the Tg of the core portion of the CD component is 80 to 140°C. In another embodiment, the Tg of the core portion of the CD component is 80°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, 120°C or higher, or 130°C or higher. In yet another embodiment, the Tg of the core portion of the CD component is 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, or 90°C or lower.

[0134] In one embodiment, the Tg of the shell portion of the CD component is 10 to 60°C. In another embodiment, the Tg of the shell portion of the CD component is 10°C or higher, 20°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher. In yet another embodiment, the Tg of the shell portion of the CD component is 60°C or lower, 50°C or lower, 40°C or lower, 30°C or lower, or 20°C or lower.

[0135] In one embodiment, both the MD component and the CD component have a core Tg in the range of 80 to 140°C.

[0136] In one embodiment, the Tg of the shell portion of the CD component is 20 to 50°C.

[0137] The average particle diameter of the CD component is, for example, 50 to 10000 nm, preferably 50 to 500 nm. In one embodiment, the average particle diameter of the CD component is 50 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, or 450 nm or more. In another embodiment, the average particle diameter of the CD component is 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, 150 nm or less, or 100 nm or less.

[0138] In one embodiment, the CD component has a Tg of 60 to 150°C and an average particle diameter of 50 to 500 nm.

[0139] In one embodiment, both the MD component and the CD component have a Tg in the range of 60 to 150°C and an average particle diameter in the range of 50 to 500 nm.

[0140] The CD component is particulate in the colored paint composition, but does not necessarily have to form a particulate structure in the colored paint film.

[0141] The CD component content in the colored paint composition is, for example, 2 to 15% by mass relative to the total mass of the resin solids in the colored paint composition. In one embodiment, the CD component content is 2% or more by mass, 5% or more by mass, or 10% or more by mass relative to the total mass of the resin solids in the colored paint composition. In another embodiment, the CD component content is 15% or less by mass, 10% or less by mass, or 5% or less by mass relative to the total mass of the resin solids in the colored paint composition.

[0142] Organic solvents (CE) The colored paint composition contains an organic solvent (CE) and is a solvent-type paint composition.

[0143] Examples of organic solvents include ester-based solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ether-based solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, methyl methoxybutanol, ethoxypropanol, ethylene glycol isopropyl ether, ethylene glycol-t-butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methoxybutanol, and propylene glycol monobutyl ether; alcohol-based solvents such as methanol, ethanol, butanol, and propyl alcohol; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon-based solvents such as Swarzol, Shellzol, and mineral spirits; and aromatic solvents such as xylene, toluene, Solvesso-100 (S-100), and Solvesso-150 (S-150).

[0144] In one embodiment, the CE component is one or more selected from the group consisting of ester solvents, ketone solvents, and aromatic solvents. In another embodiment, the CE component is one or more selected from the group consisting of butyl acetate, methyl isobutyl ketone, xylene, and toluene.

[0145] The CE component may be the same as or different from the ME component.

[0146] In one embodiment, the content of the CE component is 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, based on the total mass of the colored paint composition. In another embodiment, the content of the CE component is 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total mass of the colored paint composition.

[0147] Other ingredients The colored paint composition may optionally contain coloring pigments, extender pigments, gloss pigments, curing catalysts, viscosity modifiers, defoaming agents, ultraviolet absorbers, light stabilizers, antioxidants, surface modifiers, film-forming aids, rust inhibitors, etc.

[0148] The method for preparing the colored paint composition is not particularly limited and can be prepared in the same way as the metallic base paint composition.

[0149] The solid content of the colored paint composition is, for example, 20 to 60% of the total mass of the colored paint composition. In one embodiment, the solid content of the colored paint composition is 20% or more by mass, 30% or more by mass, 40% or more by mass, or 50% or more by mass, based on the total mass of the colored paint composition. In another embodiment, the solid content of the colored paint composition is 60% or less by mass, 50% or less by mass, 40% or less by mass, or 30% or less by mass, based on the total mass of the colored paint composition.

[0150] In one embodiment, the multilayer coating of the present invention comprises a metallic base coating and a light-transmitting colored coating on the metallic base coating. In other words, the multilayer coating of the present invention comprises a metallic base coating and a light-transmitting colored coating adjacent to each other in order.

[0151] In another embodiment, the multilayer coating of the present invention comprises a metallic base coating, a light-transmitting colored coating on the metallic base coating, and a clear coating on the light-transmitting colored coating. In other words, the multilayer coating of the present invention comprises, in order and adjacent to each other, a metallic base coating, a light-transmitting colored coating, and a clear coating.

[0152] The substrate to which the multilayer coating film of the present invention is applied is not particularly limited, and examples include metal substrates, plastic substrates and their foams.

[0153] Examples of metal substrates include metals such as iron, steel, copper, aluminum, tin, and zinc, as well as alloys containing these metals. Specifically, examples of metal substrates include automobile bodies such as passenger cars, trucks, motorcycles, and buses, and parts for automobile bodies. It is preferable that such metal substrates have an electrodeposited coating film formed on them beforehand. Furthermore, the metal substrates may be subjected to chemical conversion treatment (e.g., zinc phosphate conversion treatment, zirconium conversion treatment, etc.) as needed before the formation of the electrodeposited coating film.

[0154] Examples of plastic substrates include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. Specific examples of plastic substrates include automotive parts such as spoilers, bumpers, mirror covers, grilles, and door handles.

[0155] When the object to be coated is a metal substrate, an intermediate coating film may be provided on the metal substrate on which the electrodeposited coating has been formed. The intermediate coating film is not particularly limited and may be formed using, for example, an intermediate coating paint composition containing a coating-forming resin and, if necessary, a curing agent.

[0156] If the object to be coated is a plastic substrate, a primer coating may be provided on the plastic substrate. The primer coating is not particularly limited and may be formed using, for example, a primer coating composition containing a coating resin and, if necessary, a curing agent.

[0157] In other words, the object to be coated may be an object having an electrodeposited coating film and an intermediate coating film, or it may be an object having a primer coating film.

[0158] The thickness of the metallic base coating can be adjusted as appropriate, for example, 10 to 30 μm. In one embodiment, the thickness of the metallic base coating is 12 to 26 μm.

[0159] The thickness of the light-transmitting colored coating can be adjusted as appropriate, for example, from 5 to 30 μm. In one embodiment, the thickness of the light-transmitting colored coating is from 8 μm to 24 μm.

[0160] In one embodiment, the thickness of the metallic base coating is 12 to 26 μm, and the thickness of the light-transmitting colored coating is 8 μm to 24 μm.

[0161] The method for forming the multilayer coating is not particularly limited, and known methods for forming multilayer coatings can be used. For example, a multilayer coating can be formed by preparing a workpiece and a coating composition, forming 1, 2, or 3 uncured coating films on the workpiece in a predetermined order, and then baking and curing the uncured coating films to form the coating films.

[0162] In one embodiment, a multilayer coating is formed by a method comprising the steps of: (1) preparing the metallic base coating composition described above; (2) preparing the colored coating composition described above; (3) applying the metallic base coating composition to a workpiece to form an uncured metallic base coating film; (4) applying the colored coating composition to the uncured metallic base coating film to form an uncured light-transmitting colored coating film; and (5) baking and curing the uncured metallic base coating film and the uncured light-transmitting colored coating film to form a metallic base coating film and a light-transmitting colored coating film. This results in a multilayer coating having the configuration of workpiece / metallic base coating film / light-transmitting colored coating film.

[0163] In another embodiment, a multilayer coating is formed by a method comprising the steps of: (1) preparing the metallic base coating composition described above; (2) preparing the colored coating composition described above; (6) preparing the clear coating composition; (3) applying the metallic base coating composition to the workpiece to form an uncured metallic base coating film; (4) applying the colored coating composition onto the uncured metallic base coating film to form an uncured light-transmitting colored coating film; (7) applying the clear coating composition onto the uncured light-transmitting colored coating film to form an uncured clear coating film; and (8) baking and curing the uncured metallic base coating film, the uncured light-transmitting colored coating film, and the uncured clear coating film to form a metallic base coating film, a light-transmitting colored coating film, and a clear coating film. This results in a multilayer coating having the configuration of workpiece / metallic base coating film / light-transmitting colored coating film / clear coating film.

[0164] In the present invention, "applying a metallic base coating composition to a workpiece" includes both cases where the metallic base coating composition is applied directly to the workpiece and cases where the metallic base coating composition is applied via another coating film (e.g., an intermediate coating film).

[0165] In the present invention, "applying a colored paint composition onto a metallic base coating" includes cases where the colored paint composition is applied directly onto the metallic base coating, and cases where the colored paint composition is applied via another coating (for example, another base coating).

[0166] The method for applying the metallic base coating composition, the colored coating composition, and the clear coating composition is not particularly limited, and known coating methods can be used. For example, the coating composition can be applied using an air electrostatic spray, a rotary atomizing electrostatic coating machine, or the like.

[0167] The amount applied can be adjusted as appropriate depending on the type and application of the paint composition used.

[0168] After each uncured coating film is formed, a time interval called a setting may be introduced. This interval allows the solvents contained in the coating film to evaporate, improving the appearance of the multi-layer coating. The interval may be, for example, 10 seconds to 15 minutes.

[0169] Furthermore, preheating (drying) may be performed during the interval period. This preheating allows for the efficient evaporation of solvents contained in the uncured coating film. This preheating does not actively cure the coating film.

[0170] Preheating conditions include, for example, heating at room temperature to 100°C for 1 to 10 minutes.

[0171] Preheating can be performed using, for example, a hot air heater or an infrared heater.

[0172] The curing in step (5) or step (8) can be carried out using a conventional heating furnace (e.g., a gas furnace, electric furnace, IR furnace, induction furnace, etc.).

[0173] The heat curing temperature can be set appropriately depending on the paint composition used, for example, 60 to 160°C, and the heat curing time is for example, 10 to 30 minutes.

[0174] The clear coating composition is not particularly limited, and known clear coating compositions used in multi-layer coatings can be used. Examples of clear coating compositions include those described in Japanese Patent Publication No. 2022-060947 and Japanese Patent Publication No. 2012-031440.

[0175] The thickness of the clear coating is not particularly limited, but is, for example, 20 to 40 μm.

[0176] Applications of the multilayer coating film of the present invention include, for example, automobile bodies and automobile parts. [Examples]

[0177] The present invention will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and do not limit the present invention in any way.

[0178] The materials used in the example are as follows: Hydroxyl group-containing acrylic resin (MA component, CA component): Manufactured according to Manufacturing Example 1 described below. Isocyanate compound (MB component, CB component): 1,6-Hexamethylene diisocyanate, manufactured by Asahi Kasei Corporation, product name "Duranate 24A-100" Aluminum flake pigment (MC component): Manufactured by Asahi Kasei Corporation, product name "Aluminum Paste" Acrylic resin fine particles 1 (MD component): Having a core-shell structure, manufactured according to manufacturing example 2 described below. Acrylic resin microparticles 2 (for comparison): Having a single-layer structure, manufactured according to manufacturing example 3 described below. Coloring pigment: Product name "CYANINE BLUE G314R" manufactured by Sanyo Shikiso Co., Ltd. Extender pigment: Product name "Talc TP-A25" manufactured by Fuji Talc Industrial Co., Ltd. Mica pigment: CQV Corporation product name "ATM CHAOS SPLENDOR BLUE AC-781K-SP" Organic solvent (ME component, CE component): A mixed solvent consisting of toluene, xylene, methyl isobutyl ketone, and butyl acetate in a mass ratio of 1:1:1:1.

[0179] The materials for the clear coating composition are as follows: Surface conditioning agent: ALTANA Corporation, product name "BYK310" Light stabilizer 1: BASF product name "Tinuvin 290" Light stabilizer 2: BASF product name "Tinuvin 384-2"

[0180] A polyester resin having amphoteric groups was produced according to Reference Example 1 of Japanese Patent Publication No. 2022-060947. The acid value of the polyester resin was 59, the hydroxyl value was 90, and the Mn content was 1054. This polyester resin was used in the following Production Examples 2 and 3.

[0181] Manufacturing Example 1: Production of hydroxyl group-containing acrylic resin (MA component and CA component) A reaction apparatus equipped with a stirring blade, thermometer, dropping device, temperature control device, nitrogen gas inlet, and condenser was prepared. 57 parts by mass of butyl acetate was charged into the reaction apparatus, and the temperature was raised to 120°C while stirring and introducing nitrogen gas. Next, a mixture consisting of 7.6 parts by mass of methyl methacrylate, 52.3 parts by mass of n-butyl acrylate, 15.9 parts by mass of n-butyl methacrylate, 1.0 part by mass of methacrylic acid, and 23.2 parts by mass of 2-hydroxyethyl methacrylate was prepared. A solution of 1.0 part by mass of t-butyl peroxy-2-ethylhexanoate dissolved in 5 parts by mass of butyl acetate was also prepared. These mixtures and solutions were added dropwise to the reaction system over 3 hours. After the addition was complete, the reaction mixture was allowed to mature for 1 hour. Then, a solution of 0.1 parts by mass of t-butyl peroxy-2-ethylhexanoate dissolved in 5 parts by mass of butyl acetate was prepared. This solution was added dropwise to the reaction system over 1 hour. Next, the reaction system was aged for 2 hours while maintaining the temperature at 120°C to obtain a hydroxyl group-containing resin. The characteristics of the obtained hydroxyl group-containing resin are as follows. Non-volatile content: 60% Mw: 49000 Tg: -14℃ Hydroxyl value: 30 mg KOH / g

[0182] Manufacturing Example 2: Manufacturing of Core-Shell Structured Acrylic Resin Microparticles (MD Component) A 1 L reaction vessel equipped with a stirrer, condenser, and temperature control device was prepared. 232 parts by mass of deionized water, 10 parts by mass of polyester resin, and 0.75 parts by mass of dimethylethanolamine were charged into the reaction vessel. The mixture was then stirred while maintaining the temperature at 80°C to dissolve the substances. A solution was also prepared by dissolving 1.0 part by mass of 4,4'-azobis(4-cyanopentanoic acid) in 20 parts by mass of deionized water and 0.260 parts by mass of dimethylethanolamine. This solution was added to the reaction mixture. Next, a mixed solution consisting of 108 parts by mass of methyl methacrylate and 27 parts by mass of ethylene glycol dimethacrylate was prepared. This mixed solution was added dropwise to the reaction system over 60 minutes. The reaction system was then maintained at 80°C for 60 minutes to complete the first stage of the reaction. A solution was also prepared by dissolving 0.5 parts by mass of 4,4'-azobis(4-cyanopentanoic acid) in 25 parts by mass of deionized water and 0.3 parts by mass of dimethylethanolamine. The solution was added to the mixture obtained in the first reaction. Next, a mixed solution consisting of 9.5 parts by mass of styrene, 20 parts by mass of methyl methacrylate, 14 parts by mass of n-butyl acrylate, and 6 parts by mass of ethylene glycol dimethacrylate was prepared. This mixed solution was added dropwise to the reaction system over 60 minutes. Next, a solution was prepared by dissolving 1.5 parts by mass of 4,4'-azobis(4-cyanopentanoic acid) in 15 parts by mass of deionized water and 1.4 parts by mass of dimethylethanolamine. This solution was added to the reaction system and stirred at 80°C for 60 minutes to complete the second reaction and obtain an emulsion. The emulsion had a non-volatile content of 45%, pH 7.2, viscosity of 105 cps (25°C), and particle size of 0.2 μm. The obtained emulsion was solvent-substituted with xylene to obtain a dispersion. The characteristics of the obtained dispersion and acrylic resin fine particles having a core-shell structure are as follows. Content of core-shell acrylic resin fine particles in the dispersion: 40% by mass Particle size of core-shell acrylic resin microparticles in dispersion: 0.25 μm Tg (overall core and shell) of core-shell acrylic resin microparticles: 85℃ Core-shell acrylic resin microparticles: Tg of the core portion: 105℃ Tg of the shell portion of core-shell acrylic resin microparticles: 40℃

[0183] Manufacturing Example 3: Manufacturing of single-layer acrylic resin microparticles A 1 L reaction vessel equipped with a stirrer, condenser, and temperature control device was prepared. 281 parts by mass of deionized water, 30 parts by mass of polyester resin, and 3 parts by mass of dimethylethanolamine were charged into the reaction vessel. The mixture was then stirred while maintaining the temperature at 80°C to dissolve the components. A solution was also prepared by dissolving 1.0 part by mass of 4,4'-azobis(4-cyanopentanoic acid) in 45 parts by mass of deionized water and 0.9 parts by mass of dimethylethanolamine. This solution was added to the reaction mixture. Next, a mixed solution consisting of 30 parts by mass of n-butyl acrylate, 70 parts by mass of styrene, and 60 parts by mass of ethylene glycol dimethacrylate was prepared. This mixed solution was added dropwise to the reaction system over 60 minutes. Next, a solution was prepared by dissolving 0.5 parts by mass of 4,4'-azobis(4-cyanopentanoic acid) in 15 parts by mass of deionized water and 0.4 parts by mass of dimethylethanolamine. The solution was added to the reaction system and stirred at 80°C for a further 2 hours to obtain an emulsion with 40% non-volatile content and a particle size of 0.12 μm. This emulsion was spray-dried to obtain polymer crosslinked fine particles. These polymer crosslinked fine particles were heated in a mixed solvent of methyl amyl ketone and xylene (mass ratio 1:1) using an ultrasonic disperser to adjust the residue to 40% to obtain a dispersion solution of stable acrylic resin fine particles (single-layer structure). The Tg of the acrylic resin fine particles was 58°C.

[0184] Manufacturing of metallic base paint compositions Metallic base paint compositions 1 to 7 were obtained by blending each component according to the compositions listed in Table 1 and stirring. Metallic base paint compositions 5 to 7 correspond to comparative examples. The compositions other than the organic solvent in the table are expressed in terms of solid content (parts by mass). In addition, since metallic base paint compositions 3 and 4 are two-component paint compositions, the MB component was added immediately before painting.

[0185] [Table 1]

[0186] Manufacturing of colored paint compositions Colored paint compositions 1 to 5 were obtained by blending each component according to the compositions listed in Table 2 and stirring. Colored paint composition 5 corresponds to a comparative example. The compositions other than the organic solvent in the table are expressed in terms of solid content (parts by mass). In addition, since colored paint compositions 3 and 4 are two-component paint compositions, the CB component was added immediately before painting.

[0187] [Table 2]

[0188] Manufacturing of two-component clear coating compositions The first liquid was prepared by mixing 0.15 parts by mass of surface modifier, 2 parts by mass of light stabilizer 1, and 1 part by mass of light stabilizer 2 with 100 parts by mass of acrylic polyol resin on a solid content basis. The second liquid was prepared by mixing a nurate compound of hexamethylene diisocyanate. In the second liquid, the ratio of the number of moles of NCO groups in the nurate compound to the number of moles of OH groups in the acrylic polyol resin of the first liquid was adjusted to 1. In the two-component clear coating composition, the non-volatile content was set to 50% using a solvent prepared by mixing butyl acetate and Solvesso 100 in a mass ratio of 7:3.

[0189] Example 1 The surface of the ABS resin substrate to be coated was wiped with isopropyl alcohol. At 25°C / 70%RH, metallic base coating composition 1 (MB1) and colored coating composition 1 (C1) were applied to the surface of the substrate in two stages using RoboBell 951, adjusting the discharge rate so that the dry film thicknesses were 15 μm for the metallic base coating and 15 μm for the light-transmitting colored coating. The coatings were then applied sequentially under the following conditions and set at room temperature for 5 minutes. Painting conditions: Gun distance: 150mm Pitch width: 65mm Gun speed: Standard painting conditions are 700 mm / s. Rotation speed: 25,000 rpm Shaping air pressure: 0.2 MPa

[0190] On an uncured light-transmitting colored coating, a two-component clear coating composition was applied in one stage using RoboBell 951 under the following conditions to achieve a dry film thickness of 25 μm, and then set for 10 minutes. Next, it was dried at 80°C for 30 minutes to obtain a coated article having the following configuration: substrate / metallic base coating / light-transmitting colored coating / clear coating. Painting conditions: Gun distance: 200mm Gun speed: 700mm / s Rotation speed: 25,000 rpm Shaping air pressure: 0.07 MPa

[0191] Examples 2-4 and Comparative Examples 1-4 Painting was carried out in the same manner as in Example 1, except that the metallic base paint composition and the colored paint composition were changed as shown in Table 3, to obtain a painted article having the following configuration: substrate / metallic base coating / light-transmitting colored coating / clear coating.

[0192] The obtained painted items were evaluated for the following color development and appearance. In all evaluations, a rating of A is considered acceptable.

[0193] (Color development evaluation) The color development of the painted items was visually evaluated according to the following criteria. A: The color is uniform, and the hue, saturation, and brightness are all good. B: Non-uniformity is visible in one or more of the following items: hue, saturation, and brightness. C: Hue, saturation, or brightness is insufficient or excessive, resulting in poor color development as a multi-layer coating.

[0194] (Appearance evaluation) The appearance of the painted items (including the presence or absence of drips or undercoats) was visually evaluated according to the following criteria. A: The surface finish is smooth and free from uneven coloring and gloss. B: Unevenness is observed in the appearance of the coating. C: The paint film shows noticeable unevenness in appearance, indicating poor quality. There is a significant discrepancy in the surface texture and gloss.

[0195] [Table 3]

[0196] According to the present invention, it is possible to provide a multi-layer coating film that can suppress deterioration of appearance such as sagging and undercoating while maintaining color development. [Industrial applicability]

[0197] According to the present invention, it is possible to provide a multi-layer coating film that can suppress deterioration of appearance such as sagging and undercoating while maintaining color development.

Claims

1. Metallic base coating and The light-transmitting colored coating on the metallic base coating, A multilayer coating film comprising, The metallic base coating is a cured coating of a metallic base paint composition. The metallic base coating composition comprises a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME). The light-transmitting colored coating film is a cured coating film of a colored paint composition. The aforementioned colored paint composition comprises a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE). The acrylic resin fine particles (MD) and the acrylic resin fine particles (CD) are both multilayer coating films having a core-shell structure.

2. The multilayer coating film according to claim 1, wherein the solid content mass ratio (MC) / (MD) of aluminum flake pigment (MC) and acrylic resin fine particles (MD) contained in the metallic base coating composition is in the range of 0.3 to 3.

3. The multilayer coating film according to claim 1, wherein both the acrylic resin fine particles (MD) and the acrylic resin fine particles (CD) have a glass transition temperature in the range of 60 to 150°C and an average particle diameter in the range of 50 to 500 nm.

4. The multilayer coating film according to claim 1, wherein both the acrylic resin fine particles (MD) and the acrylic resin fine particles (CD) have a core portion glass transition temperature in the range of 80 to 140°C.

5. The multilayer coating film according to claim 1, wherein the hydroxyl group-containing acrylic resin (MA) and the hydroxyl group-containing acrylic resin (CA) each have a weight-average molecular weight of 10,000 or more and 60,000 or less, a glass transition temperature in the range of -30 to 40°C, and a hydroxyl value of 10 mg KOH / g or more and 50 mg KOH / g or less.

6. The multilayer coating film according to claim 1, wherein the content of the organic solvent (CE) is in the range of 40 to 80% by mass with respect to the total mass of the colored coating composition.

7. The thickness of the metallic base coating is in the range of 12 to 26 μm. The multilayer coating according to claim 1, wherein the thickness of the light-transmitting colored coating is in the range of 8 to 24 μm.

8. Metallic base coating and A light-transmitting colored coating film is formed on the aforementioned metallic base coating film, A method for forming a multilayer coating film comprising, The above method involves the following steps: Step (1) prepares a metallic base paint composition comprising a hydroxyl group-containing acrylic resin (MA), an isocyanate compound (MB), an aluminum flake pigment (MC), acrylic resin fine particles (MD), and an organic solvent (ME), Step (2) is to prepare a colored paint composition comprising a hydroxyl group-containing acrylic resin (CA), an isocyanate compound (CB), a blue pigment (CC), acrylic resin fine particles (CD), and an organic solvent (CE), Step (3) involves applying the metallic base coating composition onto the object to be coated to form an uncured metallic base coating film, Step (4) involves applying the colored paint composition onto the uncured metallic base coating to form an uncured light-transmitting colored coating, A method for forming a multilayer coating film, comprising the step (5) of baking and curing the uncured metallic base coating film and the uncured light-transmitting colored coating film to form the metallic base coating film and the light-transmitting colored coating film.

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