Base coating material composition and coated article

Abstract

The present invention addresses the problem of providing a solvent-type base coating material composition that can achieve both reduction in energy load and storage stability during formation of a coating film while maintaining the appearance of the coating film.　This solvent-type base coating material composition comprises: (A) a pigment containing one or more kinds selected from the group consisting of coloring pigments and flake pigments; (B1) a specific hydroxy group-containing acrylic resin having a weight average molecular weight of 10,000-20,000; (B2) a hydroxy group-containing acrylic resin having a weight average molecular weight of 3,000-7,500; (C) a blocked isocyanate compound; (E) a melamine resin containing a fully alkylated melamine resin; (D) polymer crosslinked fine particles insoluble and stably dispersed in a solution of the hydroxy group-containing acrylic resin (B1); (F) an acid catalyst having no counterion; and (G) an amine compound containing a secondary amine compound. The solid content is 35% by mass or more. When a viscosity V1 is measured at 23°C under a shear rate of 0.1 / sec using a cone-plate viscometer, followed by 30 seconds of shearing with the shear rate changed from 0.1 / sec to 25,000 / sec and then one second of shearing with the shear rate returned to 0.1 / sec, and a viscosity V2 is subsequently measured, the viscosity recovery rate V2 / V1, which is the ratio of V2 to V1, is 90% or more.

Description

Base coating composition and coated article

[0001] The present disclosure relates to base coating compositions and coated articles.

[0002] On substrates such as automobiles, a base coating film and a clear coating film thereon can be applied for the purpose of imparting design and durability. The base coating composition that forms the base coating film can affect the design of the substrate. Patent Document 1 describes such a base coating composition, which contains a pigment, a hydroxyl-containing acrylic resin, a blocked isocyanate compound, crosslinked polymer particles that are insoluble and stably dispersed in a solution of the hydroxyl-containing acrylic resin, and an acrylic resin having a weight-average molecular weight different from that of the hydroxyl-containing acrylic resin.

[0003] Japanese Patent Application Laid-Open No. 2022-060947

[0004] Generally, in the case of a solvent-based coating composition, it is necessary to dry the solvent in the coating composition and cure the coating when forming a coating film, which can increase the energy load and the equipment load. On the other hand, if an attempt is made to dry and cure the coating film at a lower temperature, the storage stability can be reduced.

[0005] In addition, the base coating composition is an extremely important coating that determines the appearance of the coated object, and high levels of control are required in order to satisfy performance requirements such as adhesion to the coating films above and below the base coating film.

[0006] From the viewpoint of environmental protection, further reduction in energy load is required, and there is room for improvement in the base coating composition described in Patent Document 1. For example, in the examples of Patent Document 1, the coated article is prepared by drying at 80°C for 30 minutes, but there is a need to further lower the temperature and also to shorten the heating time.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a solvent-based coating composition that can achieve both reduced energy load during coating film formation and storage stability while maintaining the appearance of the coating film.

[0008] The present disclosure provides the following aspects: [1] A solvent-based base coating composition comprising: a pigment (A), a hydroxyl-containing acrylic resin (B1) having a weight-average molecular weight of 10,000 or more and 20,000 or less, a hydroxyl-containing acrylic resin (B2) having a weight-average molecular weight of 3,000 or more and 7,500 or less, a blocked isocyanate compound (C), a melamine resin (E), crosslinked polymer particles (D) that are insoluble and stably dispersed in a solution of the hydroxyl-containing acrylic resin (B1), an acid catalyst (F), and an amine compound (G), wherein the solvent-based base coating composition has a solids content of 35% by mass or more, and the viscosity V1 of the solvent-based base coating composition is measured at 23°C using a cone-plate viscometer at a shear speed of 0.1 / sec, and then the shear speed is changed from 0.1 / sec to 25,000 / sec and sheared for 30 seconds, the hydroxyl group-containing acrylic resin (B1) is a polymer of one or more monomers including a hydroxyl group-containing monomer (b), and the hydroxyl group-containing monomer (b) comprises a lactone-modified monoester compound of (meth)acrylic acid and a dihydric alcohol having from 2 to 8 carbon atoms; the glass transition temperature is from 10°C to 40°C; the hydroxyl group value is from 10 mgKOH / g to 90 mgKOH / g; the melamine resin (E) comprises a full-alkyl melamine resin; the acid catalyst (F) is a catalyst having no counter ion; and the amine compound (G) comprises a secondary amine compound. [2] The solvent-borne base coating composition according to [1], wherein the acid catalyst (F) contains a sulfonic acid compound. [3] The solvent-borne base coating composition according to [1] or [2], wherein the amine compound (G) has a boiling point in the range of 70 to 115°C, and the content of the amine compound (G) is 0.1 parts by mass or more and 0.8 parts by mass or less per 100 parts by mass of the total resin solids in the base coating composition.[4] The solvent-borne base coating composition according to any one of [1] to [3], wherein the content of the melamine resin (E) is 3 to 15 parts by mass per 100 parts by mass of the total resin solids in the base coating composition. [5] The solvent-borne base coating composition according to any one of [1] to [4], wherein the mass ratio of the blocked isocyanate compound (C) to the melamine resin (E) is in the range of blocked isocyanate compound (C):melamine resin (E) = 2:1 to 1:4. [6] The solvent-borne base coating composition according to any one of [1] to [5], wherein the equivalent ratio of the acid catalyst (F) to the amine compound (G) is in the range of acid catalyst (F):amine compound (G) = 3.5:1 to 1:2. [7] The solvent-based base coating composition according to any one of [1] to [6], wherein the hydroxyl-containing acrylic resin (B1) is a polymer of the hydroxyl-containing monomer (b) and a monomer other than the hydroxyl-containing monomer (b), and the hydroxyl-containing monomer (b) accounts for 5% by mass or more and 20% by mass or less of the total of the hydroxyl-containing monomer (b) and the other monomer. [8] The solvent-based base coating composition according to any one of [1] to [7], wherein the solvent-based base coating composition has a gel fraction of 40% or more after heating at 75°C for 10 minutes. [9] A coated article comprising a substrate and a base coating film formed from the solvent-based base coating composition according to any one of [1] to [8].

[10] The coated article according to [9], wherein the solvent-based base coating film is formed on the substrate previously provided with an intermediate coating film or a primer coating film.

[11] The coated article according to [9] or

[10] , wherein the substrate comprises a plastic resin substrate.

[0009] The present disclosure can provide a solvent-based coating composition that reduces the energy load during coating film formation and has good storage stability while maintaining the appearance of the resulting coating film.

[0010] The base coating composition of the present disclosure is a solvent-borne base coating composition comprising: a pigment (A); a hydroxyl-containing acrylic resin (B1) having a weight-average molecular weight of 10,000 or more and 20,000 or less; a hydroxyl-containing acrylic resin (B2) having a weight-average molecular weight of 3,000 or more and 7,500 or less; a blocked isocyanate compound (C); a melamine resin (E); crosslinked polymer particles (D) that are insoluble and stably dispersed in a solution of the hydroxyl-containing acrylic resin (B1); an acid catalyst (F); and an amine compound (G), wherein the base coating composition has a solids content of 35% by mass or more; and the viscosity V1 of the base coating composition is measured at 23°C using a cone-plate viscometer at a shear of 0.1 / sec, and then the shear is changed from 0.1 / sec to 25,000 / sec and sheared for 30 seconds; the shear is then returned to 0.1 / sec and the viscosity V2 after 1 second of shearing is measured; and the viscosity recovery rate V2 / V1, which is the ratio of V2 to V1, is 90% or more; the pigment (A) comprises one or more species selected from the group consisting of colored pigments and scaly pigments; the hydroxyl group-containing acrylic resin (B1) is a polymer of one or more monomers including a hydroxyl group-containing monomer (b), and the hydroxyl group-containing monomer (b) is a lactone-modified monoester compound of (meth)acrylic acid and a dihydric alcohol having from 2 to 8 carbon atoms; the glass transition temperature is 10°C or more and 40°C or less; the hydroxyl group value is 10 mgKOH / g or more and 90 mgKOH / g or less; the melamine resin (E) comprises a full alkyl melamine resin; the acid catalyst (F) is a catalyst having no counter ion; and the amine compound (G) comprises a secondary amine compound.

[0011] It has been found that the solvent-based base paint composition of the present disclosure can provide a solvent-based base paint composition that reduces the energy load during film formation and has good storage stability while maintaining the appearance of the resulting paint film. Although the present disclosure should not be interpreted as being limited to a particular theory, the reason why the solvent-based base paint composition of the present disclosure can achieve such effects is thought to be as follows.

[0012] Hereinafter, the solvent-based base coating composition and the coated article according to the embodiment of the present disclosure will be described in detail. Hereinafter, the "solvent-based base coating composition" will also be simply referred to as the "base coating composition."

[0013] [Base Coating Composition] The base coating composition according to an embodiment of the present disclosure comprises a pigment (A), a film-forming resin (B) (the film-forming resin (B) comprises a hydroxyl-containing acrylic resin (B1) and a hydroxyl-containing acrylic resin (B2)), a blocked isocyanate compound (C), a melamine resin (E), crosslinked polymer particles (D) that are insoluble in and stably dispersed in the hydroxyl-containing acrylic resin (B1), an acid catalyst (F), and an amine compound (F), wherein the hydroxyl-containing acrylic resin (B1) contained in the film-forming resin (B) has a weight-average molecular weight of 10,000 or more and 20,000 or less, and the hydroxyl-containing acrylic resin (B2) has a weight-average molecular weight of 3,000 or more and 7,500 or less.

[0014] [Pigment (A)] The pigment (A) includes at least one pigment selected from the group consisting of color pigments and scaly pigments.

[0015] Examples of color pigments include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments; and inorganic pigments include yellow lead, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide.

[0016] Examples of flake pigments include metal flakes, metal oxide flakes, pearl pigments, mica, etc. Examples of metal flakes include aluminum, chromium, gold, silver, copper, brass, titanium, nickel, nickel chromium, stainless steel, etc. Examples of metal oxide flakes include oxides of metal flakes, such as alumina and chromium oxide. In an embodiment in which the base paint composition contains a flake pigment, it is possible to impart a metallic luster to the base paint film, and as described below, it is possible to form a base paint film whose color tone changes more significantly depending on the angle from which the base paint film is observed, i.e., a base paint film with high flip-flop properties (hereinafter sometimes referred to as "FF properties")

[0017] To easily prevent gas generation due to reaction of metal flakes, metal oxide flakes, pearlescent pigments, etc. with water, metal coatings, such as coatings of molybdic acid, chromic acid, metal compounds such as yttrium and rare earth metals, or organic polymer coatings, such as coatings of organic polymers obtained using polymerizable monomers, may be formed on the metal flakes, metal oxide flakes, and pearlescent pigments. For example, the metal flakes, metal oxide flakes, and pearlescent pigments may have coatings containing silicon dioxide, zirconium oxide, aluminum oxide, chromium oxide, polymerized synthetic resin, vanadium oxide, molybdenum oxide and / or molybdenum peroxide, phosphate, phosphite, borate, chromate, or mixtures or combinations thereof. For example, when using chromium oxide, etc., its toxicity can be eliminated by chemically deactivating it.

[0018] The scaly pigment may include a vapor-deposited metal pigment. Such a scaly pigment is generally obtained by vapor-depositing a thin metal film (a thin metal oxide film) on a base film, peeling off the base film, and then pulverizing the vapor-deposited metal film into metal flakes (metal oxide flakes). Examples of the metal material to be vapor-deposited include the materials described above for the metal flakes and metal oxide flakes. In this embodiment, the scaly pigment is preferably a vapor-deposited aluminum pigment, a vapor-deposited chromium pigment, a vapor-deposited alumina pigment, or a vapor-deposited chromium oxide pigment. The vapor-deposited metal pigment may also have the above-described coating formed on its surface, if necessary.

[0019] Examples of commercially available scaly pigments include the METALURE (registered trademark) series, SILVERSHINE (registered trademark) series, HYDROSHINE (registered trademark) series, Liquid Black (registered trademark), and PLISMATIC (registered trademark) series manufactured by Ecart, the FD series, GX series, and BS series manufactured by Asahi Kasei Chemicals Corporation, and the 46 series and 63 series manufactured by Toyo Aluminum K.K. Two or more types of pigments (A) may be used in combination.

[0020] The content of pigment (A) is not particularly limited, and for example, the pigment concentration of pigment (A), i.e., the mass ratio of pigment (A) to the resin solids of the base coating composition, may be 1 mass% or more and 20 mass% or less. The resin solids of the base coating composition refer to the solids of the film-forming resin (B), the blocked isocyanate compound (C), the melamine resin (E), and any other curing agents that may be included. Furthermore, in this disclosure, the solids of a certain component may refer to the heating residue when that component is heated at 110°C for 1 hour.

[0021] The base coating composition may contain an extender pigment, such as calcium carbonate, barium sulfate, clay, or talc.

[0022] When an extender pigment is used, one type may be used alone, or two or more types may be used in combination. When the base paint composition contains a body pigment, the content of the body pigment may be, for example, 0.1 mass % or more and 20 mass % or less, as the mass ratio of the body pigment to the resin solids of the base paint composition.

[0023] [Hydroxyl-containing acrylic resin (B1)] The hydroxyl-containing acrylic resin (B1) is a polymer of one or more monomers including a hydroxyl-containing monomer (b), which is a lactone-modified monoester compound of (meth)acrylic acid and a dihydric alcohol having from 2 to 8 carbon atoms. The hydroxyl-containing acrylic resin (B1) has a weight-average molecular weight of from 10,000 to 20,000, a glass transition temperature of from 10°C to 40°C, and a hydroxyl value of from 10 to 50 mgKOH / g.

[0024] By including the hydroxyl group-containing acrylic resin (B1), even if the solid content of the base coating composition is as high as 35% by mass or more, the coating viscosity does not become too high, thereby reducing unevenness of the coating film. Furthermore, when the base coating composition contains a scaly pigment, the orientation of the scaly pigment is less likely to be disturbed, resulting in excellent FF properties (flip-flop properties: the property in which the brightness of the coating surface changes depending on the viewing angle). The upper limit of the solid content of the base coating composition is not particularly limited, but may be, for example, 60% by mass.

[0025] Furthermore, since the hydroxyl group-containing acrylic resin (B1) is polymerized using a hydroxyl group-containing monomer (b), which is a lactone-modified monoester compound of (meth)acrylic acid and a dihydric alcohol having from 2 to 8 carbon atoms, it has a long-chain structure containing a hydroxyl group in its side chain. This increases the reactivity with the isocyanate compound (C), which is the curing agent, and improves the adhesion between the substrate and the base coating film, or between an intermediate coating film or primer coating film provided on the substrate and the base coating film. For example, when the substrate is made of plastic, the base coating composition according to an embodiment of the present disclosure can form a base coating film that has good adhesion to the substrate, even without providing a primer coating film on the substrate.

[0026] The hydroxyl group-containing acrylic resin (B1) can be obtained by polymerizing one or more monomers including the hydroxyl group-containing monomer (b) according to a conventional method.

[0027] Examples of the hydroxyl group-containing monomer (b) include lactone-modified products obtained by modifying a monoester of (meth)acrylic acid with a dihydric alcohol having from 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, or 4-hydroxybutyl (meth)acrylate, with a lactone, such as ε-caprolactone. In this specification, "(meth)acrylic" refers to both acrylic and methacrylic.

[0028] The hydroxyl group-containing monomer (b) preferably contains a lactone-modified monoester compound of (meth)acrylic acid and a dihydric alcohol having from 2 to 8 carbon atoms. The content of the lactone-modified monoester compound of (meth)acrylic acid and a dihydric alcohol having from 2 to 8 carbon atoms in the hydroxyl group-containing monomer (b) may be preferably from 80 to 100% by mass, more preferably from 90 to 100% by mass, and even more preferably from 95 to 100% by mass, based on 100% by mass of the hydroxyl group-containing monomer (b).

[0029] The hydroxyl-containing acrylic resin (B1) may be a polymer of the hydroxyl-containing monomer (b) and a monomer other than the hydroxyl-containing monomer (b). In this embodiment, the hydroxyl-containing acrylic resin (B1) is obtained by polymerizing a monomer mixture of the hydroxyl-containing monomer (b) and the other monomer. In the monomer mixture, the hydroxyl-containing monomer (b) preferably accounts for 5% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 25% by mass or less, and even more preferably 10% by mass or more and 20% by mass or less, of the total of the hydroxyl-containing monomer (b) and the other monomer.

[0030] Examples of other monomers besides the hydroxyl group-containing monomer (b) include acid group-containing monomers such as 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-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acryloyloxyethyl acid phosphate, and 2-acrylamido-2-methylpropanesulfonic acid.

[0031] Further, examples of other monomers besides the hydroxyl group-containing monomer (b) include (meth)acrylic acid esters (e.g., 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, methyl meth ... (t)dicyclopentadienyl acrylate, dihydrodicyclopentadienyl (meth)acrylate, etc.), polymerizable aromatic compounds (for example, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.), polymerizable nitriles (for example, acrylonitrile, methacrylonitrile, etc.), α-olefins (for example, ethylene, propylene, etc.), vinyl esters (for example, vinyl acetate, vinyl propionate, etc.), dienes (for example, butadiene, isoprene, etc.). From the viewpoint of improving water resistance, it is preferable to use styrene.

[0032] Furthermore, examples of other monomers besides the hydroxyl group-containing monomer (b) include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, and methacryl alcohol.

[0033] The hydroxyl group-containing monomer (b) may be used alone or in combination of two or more kinds. Furthermore, the monomer other than the hydroxyl group-containing monomer (b) may be used alone or in combination of two or more kinds.

[0034] The weight average molecular weight of the hydroxyl group-containing acrylic resin (B1) may be, for example, 10,000 or more and 20,000 or less. In the present disclosure, the weight average molecular weight may be determined, for example, by gel permeation chromatography (GPC) using polystyrene as a standard.

[0035] The glass transition temperature of the hydroxyl group-containing acrylic resin (B1) may be preferably 10° C. or higher and 40° C. or lower, more preferably 10° C. or higher and 35° C. or lower, and even more preferably 15° C. or higher and 30° C. or lower. The glass transition temperature may be measured or calculated by a known method. For example, the glass transition temperature may be measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

[0036] The hydroxyl value of the hydroxyl-containing acrylic resin (B1) may preferably be 10 mgKOH / g or more and 90 mgKOH / g or less, more preferably 20 mgKOH / g or more and 70 mgKOH / g or less, and even more preferably 20 mgKOH / g or more and 50 mgKOH / g or less. Furthermore, the acid value of the hydroxyl-containing acrylic resin (B1) may preferably be 0.2 mgKOH / g or more and 15 mgKOH / g or less, more preferably 2 mgKOH / g or more and 7 mgKOH / g or less. In the present disclosure, the hydroxyl value and acid value are solid content equivalent values, and may be measured or calculated by known methods. For example, the hydroxyl value and acid value may be measured in accordance with JIS K 0070:1992.

[0037] The hydroxyl-containing acrylic resin (B1) may be used alone or in combination of two or more. The content of the hydroxyl-containing acrylic resin (B1) in the base coating composition is not particularly limited, and may be, for example, 30% by mass or more and 70% by mass or less, or 40% by mass or more and 60% by mass or less, of the resin solid content of the base coating composition.

[0038] [Acrylic Resin (B2)] The base coating composition contains an acrylic resin (B2) having a weight-average molecular weight of 3,000 or more and 7,500 or less, which makes it easier to adjust the viscosity of the base coating composition.

[0039] The acrylic resin (B2) can be obtained by polymerizing a monomer, such as the hydroxyl group-containing monomer (b) described above for the hydroxyl group-containing acrylic resin (B1) or other monomers.

[0040] The weight average molecular weight of the acrylic resin (B2) is preferably 3,500 or more, more preferably 4,000 or more, and is preferably 6,500 or less, more preferably 5,500 or less.

[0041] The hydroxyl value of the acrylic resin (B2) may be, for example, 40 mgKOH / g or less, or may be 0.1 mgKOH / g or more and 20 mgKOH / g or less.

[0042] The acrylic resin (B2) may be used alone or in combination of two or more. The content of the acrylic resin (B2) is not particularly limited and may be, for example, 10% by mass or more and 50% by mass or less of the resin solid content of the base coating composition. If the blending amount of the acrylic resin (B2) is high, the viscosity of the coating tends to be low. By blending the amount of the acrylic resin (B2) within the above range, the viscosity of the coating is not too high, and adverse effects that may occur during coating are suppressed, and the viscosity of the coating is not too low, so that the coating film properties are good and adhesion and water resistance can be improved.

[0043] In the base coating composition, the total content of the solids of the hydroxyl group-containing acrylic resin (B1) and the acrylic resin (B2) is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on 100% by mass of the total solids of the coating film-forming resin (B).

[0044] The coating film-forming resin (B) may contain a resin other than the hydroxyl group-containing acrylic resin (B1) and the acrylic resin (B2).

[0045] [Blocked Isocyanate Compound (C)] The use of a blocked isocyanate compound (C) together with a hydroxyl group-containing acrylic resin (B1) can improve adhesion between the substrate and the base coating film, or between the base coating film and an intermediate coating film or primer coating film provided on the substrate. Furthermore, crosslinking of the base coating film improves the coating film properties and water resistance.

[0046] The blocked isocyanate compound (C) can be prepared by blocking a polyisocyanate with a blocking agent.

[0047] Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimer), 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 (e.g., urethane-modified products, carbodiimide, uretdione, uretonimine, biuret, and / or isocyanurate-modified products).

[0048] Preferred examples of blocking agents that can be used include monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, and methylphenyl carbinol; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type diols terminated at both ends such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol phenol; polyester-type polyols terminated at both ends 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. Examples of blocking agents that can be used include active hydrogen compounds such as methyl diketone, methyl ketoester, and methyl diester compounds, such as alkyl esters of acetylacetone, ethyl acetoacetate, and diethyl malonate. Also, blocked isocyanates using imidazole compounds and pyrazole compounds can be used.

[0049] The blocked isocyanate compound (C) preferably has a blocking rate of 100%, which has the advantage of improving the storage stability of the base coating composition.

[0050] Two or more types of blocked isocyanate compounds (C) may be used in combination. The content of the blocked isocyanate compound (C) is not particularly limited, but from the viewpoint of more appropriately promoting the curing reaction, the ratio (NCO / OH) of the number of moles of isocyanate groups in the blocked isocyanate compound (C) to the number of moles of hydroxyl groups in the hydroxyl group-containing acrylic resin (B1) may be 0.2 / 1.0 to 0.6 / 1.0, and preferably 0.3 / 1.0 to 0.5 / 1.0.

[0051] [Melamine Resin (E)] The melamine resin (E) is a compound having two or more groups per molecule that can react with the hydroxyl groups of the film-forming resins (B) (hydroxyl-containing acrylic resin (B1) and hydroxyl-containing acrylic resin (B2)), and is capable of crosslinking with the film-forming resins (B) (hydroxyl-containing acrylic resin (B1) and hydroxyl-containing acrylic resin (B2)) to form a coating film. The inclusion of melamine resin (E) in the base coating composition can improve storage stability and the physical properties (processability, scratch resistance) of the resulting coating film.

[0052] The melamine resin is a thermosetting resin synthesized from melamine and aldehyde, and is preferably a compound having three reactive functional groups represented by the following formula as reactive functional groups in one triazine nucleus molecule, or a polycondensate thereof: -NX １ X ２ [X １ , X ２ are each independently a hydrogen atom, a methylol group, or —CH ２ -OR １ Represents R １ represents an alkyl group having 1 to 8 carbon atoms, preferably a linear or branched alkyl group having 1 to 8 carbon atoms. ２ -OR １ If it contains multiple R １ may be the same or different.

[0053] The melamine resin has a reactive functional group of -N(CH ２ OR １ ) ２ a full alkyl type containing only -N(CH ２ OR １ ) (CH ２ methylol group type containing -N(CH ２ OR １ ) (H) as a reactive functional group; ２ OR １ ) (CH ２ -OH) and -N(CH ２ OR １ ) (H), or —N(CH ２ Four types of methylol / imino group types containing R １ is preferably an alkyl group having 1 to 4 carbon atoms, and is preferably a methyl group, an n-butyl group, or an isobutyl group.

[0054] In the present disclosure, among the above melamine resins, X １ and X ２ All of the above are -CH ２ -OR １ or a polycondensate thereof. Examples of the full-alkyl methamine resin (E1) include methylated melamine resin, butylated melamine resin, and isobutylated melamine resin. The inclusion of the full-alkyl melamine resin (E) has the advantages of improving the storage stability of the resulting base coating composition and improving the reactivity with the film-forming resin (B) at high temperatures and in the presence of a catalyst.

[0055] The degree of polymerization of the full alkyl melamine resin (E1) is 1 or more, preferably 1.2 or more, more preferably 1.5 or more, and is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less.

[0056] The number average molecular weight of the full alkyl melamine resin (E1) is preferably 300 or more, and preferably 2,000 or less, more preferably 1,300 or less, even more preferably 1,000 or less, and particularly preferably 800 or less. In the present disclosure, the number average molecular weight is a value measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0057] Commercially available products can also be used as the full alkyl melamine resin (E1). Examples of such commercially available products include Resimene 745, Resimine 751, Resimine 755, Resimine CE-6550, Resimine CE-7103, and Resimine 747 (all of which are available from Preferec). Resins), Cymel 303, Cymel 325, Cymel 350, Cymel 370, Mycoat 715 (all methylated melamine resins, manufactured by Allnex Japan Co., Ltd.), Cymel 202, Cymel 235, Cymel 254, Cymel 1123, Cymel 1128, Cymel 1170, Mycoat 212 (all methyl-butylated mixed melamine resins, manufactured by Allnex Japan Co., Ltd.), Sumimal M-40S (methylated melamine resin, manufactured by Sumitomo Chemical Co., Ltd.), Amidair J-820-60, Amidair L-127-60 (all butylated melamine resins, manufactured by DIC Corporation). These may be used alone or in combination of two or more.

[0058] The content of the full-alkyl melamine resin (E1) in the melamine resin (E) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, with the upper limit being 100% by mass.

[0059] The melamine resin (E) may be used alone or in combination of two or more.

[0060] The ratio of the content of melamine resin (E) to the total amount of solids of film-forming resin (B) ((E) / (B)) is, by mass, preferably 3 / 97, more preferably 5 / 95 or more, and preferably 30 / 70 or less, more preferably 20 / 80 or less. Having a ratio within this range has the advantage of improving the processability and scratch resistance of the resulting coating film.

[0061] The mass ratio of the contents of the blocked isocyanate compound (C) and the melamine resin (E), i.e., blocked isocyanate compound (C):melamine resin (E), is preferably within a range of 2:1 to 1:4, more preferably within a range of 2:1 to 1:3, and even more preferably within a range of 1:1 to 1:3.

[0062] The content of the melamine resin (E) is preferably 3 parts by mass or more and 15 parts by mass or less, more preferably 4 parts by mass or more and 15 parts by mass or less, and even more preferably 5 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the total resin solids in the base coating composition.

[0063] The base coating composition may contain other curing agents, such as amino resins such as guanamine resins and urea resins, as curing agents other than the isocyanate compound (C) and the melamine resin (E). When the base coating composition contains other curing agents other than the isocyanate compound (C) and the melamine resin (E), the content of the other curing agents is, for example, 10 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the resin solid content of the base coating composition.

[0064] [Acid catalyst (F)] The acid catalyst (F) can act as a catalyst to promote the reaction between the hydroxyl group-containing acrylic resin (B1) and the melamine resin (E), thereby imparting high reactivity to the resulting base coating composition.

[0065] The acid catalyst (F) is a catalyst having no counter ion and may typically contain a sulfonic acid compound. The sulfonic acid compound may be a monosulfonic acid compound or a polysulfonic acid compound. Examples of the sulfonic acid compound include aliphatic sulfonic acids such as methanesulfonic acid; and aromatic sulfonic acids such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. The sulfonic acid compound may be used alone or in combination of two or more.

[0066] The content of the sulfonic acid compound may be preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on 100% by mass of the acid catalyst (F).

[0067] The acid catalyst (F) may contain an acid other than a sulfonic acid compound.

[0068] The content of the acid catalyst (F) is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, relative to 100 parts by mass of the total resin solids content of the hydroxyl group-containing acrylic resin (B1), the hydroxyl group-containing acrylic resin (B2), the blocked isocyanate compound (C), and the melamine resin (E). When the content of the acid catalyst (F) is within the above range, a coating film having good processability (adhesion, crack resistance) and scratch resistance can be formed on the precoated steel sheet.

[0069] [Amine compound (G)] The amine compound (G) has the effect of neutralizing the acid catalyst (F), and its coexistence with the acid catalyst (F) has the advantage of achieving both stability during storage of the base coating composition (for example, 15 to 50°C) and high reactivity during heat drying and curing after application. A portion of the amine compound (G) may exist as a salt with the acid catalyst (F).

[0070] The amine compound (G) is a compound having one or more amino groups, and includes a secondary amine compound. The amine compound (G) may further include a tertiary amine compound.

[0071] The substituent on the nitrogen atom of the amine compound is preferably a saturated or unsaturated aliphatic hydrocarbon group, and the hydrogen atoms contained in the saturated or unsaturated aliphatic hydrocarbon group may each independently be substituted with —COOH, —OH, etc., and the —CH ２ The - may be replaced by -O-. In addition, the substituents on the nitrogen atom of the amine compound may be bonded to each other to form a ring containing the nitrogen atom.

[0072] Examples of the amine compound (G) include secondary aliphatic amine compounds such as diethylamine, di-n-propylamine, diisopropylamine, diisobutylamine, di-n-butylamine, di-sec-butylamine, diamylamine, N-ethyl-1,2-dimethylpropylamine, N-methylhexylamine, di-n-octylamine, and diallylamine; tertiary aliphatic amine compounds such as triethylamine, tributylamine, triallylamine, N,N-dimethylethanolamine, N-methyldiallylamine, and N,N-dimethylallylamine; secondary cyclic amine compounds such as piperidine, 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,4-lupetidine, 2,6-lupetidine, 3,5-lupetidine, and 3-piperidinemethanol; tertiary cyclic amine compounds such as N-methylpiperidine, N-methylpiperazine, and N-methylmorpholine; and aromatic amine compounds such as pyridine and 4-ethylpyridine.

[0073] The boiling point of the amine compound (G) is 70° C. or higher, preferably 80° C. or higher, and preferably 115° C. or lower, more preferably 111° C. or lower, and even more preferably 100° C. or lower. Having the boiling point of the amine compound (G) within the above range has the advantage of further improving the storage stability of the base coating composition.

[0074] The content of the amine compound (G) is such that the neutralization rate of the sulfonic acid compound (G) by the amine compound (G), i.e., the neutralization rate calculated by the following formula, is preferably in the range of 50% to 350%, more preferably in the range of 80% to 300%, and even more preferably in the range of 150% to 250%: Neutralization rate (%) = [(base valence of amine compound (G) × number of moles of amine compound (G)) / (acid valence of acid catalyst (F) × number of moles of acid catalyst (F)] × 100

[0075] The equivalent ratio of the acid catalyst (F) to the amine compound (G), acid catalyst (F):amine compound (G), is preferably within a range of 3.5:1 to 1:2, more preferably within a range of 2.5:1 to 1:1.5, and even more preferably within a range of 2.4:1 to 1:1.5.

[0076] The content of the amine compound (G) is preferably 0.1 parts by mass or more and 0.8 parts by mass or less, more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, and even more preferably 0.1 parts by mass or more and 0.3 parts by mass or less, relative to 100 parts by mass of the total resin solids of the base coating composition (the total resin solids amount of the hydroxyl group-containing acrylic resin (B1), the hydroxyl group-containing acrylic resin (B2), the blocked isocyanate compound (C), and the melamine resin (E)).

[0077] The full-alkyl melamine resin (E1) is known to have lower reactivity than melamine resins commonly used as crosslinkers, such as imino group-type melamine resins and methylol group-type melamine resins. However, as a result of studies by the present inventors, it was found that the low reactivity of the full-alkyl melamine resin (E1) occurs only in low-temperature reactions (e.g., 60 to 80°C), and that when the full-alkyl melamine resin (E1) is used with the acid catalyst (F) and the amine compound (G) at the above-mentioned neutralization ratios, the reactivity at high temperatures is increased. By combining the full-alkyl melamine resin (E1), the acid catalyst (F), the amine compound (G), and the above-mentioned neutralization ratio, a base coating composition can be obtained that has good storage stability and is particularly suitable for high-temperature, short-time application. Furthermore, the crosslink density can be increased, resulting in a coating film with excellent coating processability (adhesion and crack resistance).

[0078] The acid catalyst (F) and the amine compound (G) may be used directly in the preparation of the base coating composition, or may be mixed in advance and used as a mixture in the preparation of the base coating composition. In this case, in the mixture, the acid catalyst (F) and part or all of the amine compound (G) may form a salt (for example, a salt in which the sulfonic acid group contained in the acid catalyst (F) is blocked by the amino group contained in the amine compound (G)). Alternatively, a salt may be formed between the sulfonic acid compound (C) and part or all of the amine compound (G) and then incorporated into the base coating composition. Examples of the salt of the acid catalyst (F) and part or all of the amine compound (G) include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as dinonylnaphthalenedisulfonic acid and dinonylnaphthalenesulfonic acid, and amine-blocked versions thereof. Commercially available products may also be used as the salt of the acid catalyst (F) and part or all of the amine compound (G).

[0079] In one embodiment, the content of the acid catalyst (F) is preferably 1 part by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the total resin solid content of the hydroxyl group-containing acrylic resin (B1), the hydroxyl group-containing acrylic resin (B2), the blocked isocyanate compound (C), and the melamine resin (E), and the neutralization rate is preferably 100% or more and 1,300% or less; the content of the acid catalyst (F) is more preferably 0.1 part by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the total resin solid content, and the neutralization rate is preferably 200% or more and 1,000% or less; and the content of the acid catalyst (F) is even more preferably 2 parts by mass or more and 9 parts by mass or less, relative to 100 parts by mass of the total resin solid content, and the neutralization rate is preferably 300% or more and 900% or less. When the base coating composition has the above-mentioned amounts of acid catalyst (F) and amine compound (G) and neutralization rate, the storage stability at low temperatures (storage temperature, for example, 15 to 30°C) is high and the reactivity at high temperatures is increased, resulting in better processability (adhesion, crack resistance) and scratch resistance of the resulting coating film.

[0080] [Crosslinked polymer microparticles (D)] The crosslinked polymer microparticles (D) can act as a viscosity adjuster and contribute to adjusting the viscosity, which will be described later. Normally, paint viscosity is reduced by the shear force applied during application, so the viscosity immediately after application is lower than the viscosity before application. Therefore, if the viscosity after application is low, the paint will sag, causing unevenness in the paint film. By including the crosslinked polymer microparticles (D), the base paint composition according to an embodiment of the present disclosure can quickly recover and increase the viscosity that has decreased during application, thereby preventing the base paint composition applied to the substrate from sagging and reducing unevenness in the paint film.

[0081] The crosslinked polymer particles (D) can be prepared by polymerizing a monomer mixture. Any polymerization method can be used as long as it can produce crosslinked particles, and multi-stage polymerization may also be used. More specifically, emulsion polymerization is preferably used.

[0082] Crosslinked polymer microparticles (D) prepared by emulsion polymerization The crosslinked polymer microparticles (D) used in the present disclosure are obtained by emulsion polymerizing an ethylenically unsaturated monomer and a crosslinkable copolymerizable monomer in an aqueous medium by a known method to prepare an emulsion containing crosslinked polymer microparticles, and then removing the water by solvent substitution, azeotropy, centrifugation, filtration, drying, or the like. Emulsion polymerization may be carried out using a known emulsifier and / or dispersant, but it is preferable to use an emulsifier having an amphoteric ionic group. When the crosslinked polymer microparticles (D) are added to a base coating composition, the structural viscosity varies depending on the particle size, so it is important to obtain a uniform particle size. The use of an emulsifier having an amphoteric ionic group makes it easier to obtain crosslinked polymer microparticles of a uniform particle size.

[0083] Examples of ethylenically unsaturated monomers used in preparing the crosslinked polymer fine particles (D) include alkyl esters of acrylic acid or methacrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, as well as other monomers having an ethylenically unsaturated bond that can be copolymerized therewith, such as styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, ethylene, propylene, vinyl acetate, vinyl propionate, acrylonitrile, methacrylonitrile, and dimethylaminoethyl (meth)acrylate. Two or more of these monomers may be used.

[0084] The crosslinkable copolymerizable monomer includes a monomer having two or more radically polymerizable ethylenically unsaturated bonds in the molecule and / or two kinds of ethylenically unsaturated group-containing monomers each bearing a group capable of reacting with each other.

[0085] Examples of monomers having two or more radically polymerizable ethylenically unsaturated groups in the molecule include polymerizable unsaturated monocarboxylic acid esters of polyhydric alcohols, polymerizable unsaturated alcohol esters of polybasic acids, and aromatic compounds substituted with two or more vinyl groups, and examples of these include the following compounds:

[0086] Ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate, glycerol diacrylate, glycerol allyloxy dimethacrylate, 1,1,1-trishydroxymethylethane diacrylate, 1,1,1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylethane dimethacrylate, 1,1,1-trishydroxymethylethane trimethacrylate, 1,1,1-trishydroxymethylpropane diacrylate, 1,1,1-trishydroxymethylpropane triacrylate, 1,1,1-trishydroxymethylpropane dimethacrylate, 1,1,1-trishydroxymethylpropane trimethacrylate, triallyl cyanurate, triallyl isocyanurate, triallyl trimeridate, diallyl terephthalate, diallyl phthalate, and divinylbenzene.

[0087] Furthermore, as a crosslinking monomer, instead of, or if desired together with, a monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule, a monomer having two types of ethylenically unsaturated groups, each of which carries a group capable of reacting with each other, can be used. Examples include a glycidyl group-containing ethylenically unsaturated monomer such as glycidyl methacrylate or glycidyl acrylate, and a carboxyl group-containing ethylenically unsaturated monomer such as acrylic acid, methacrylic acid, or crotonic acid; a hydroxyl group-containing ethylenically unsaturated monomer such as 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, allyl alcohol, or methallyl alcohol, and an ethylenically unsaturated monomer having an isocyanate group, such as vinyl isocyanate or isopropenyl isocyanate. However, in addition to these, any combination of two types of ethylenically unsaturated monomers each carrying a group capable of reacting with each other can be used.

[0088] The monomer constituting the crosslinked polymer fine particles (D) may contain a monomer having a functional group capable of reacting with a crosslinking agent, and examples thereof include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid, hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, allyl alcohol, and methacrylic alcohol, and nitrogen-containing monomers such as acrylic acid amide and methacrylic acid amide.

[0089] Polymerizable crosslinked particles (D) by non-aqueous dispersion polymerization The monomer mixture used to prepare the crosslinked polymer particles (D) contains a radical polymerizable monomer. The monomer mixture may contain a radical polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group. By including a radical polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group in the monomer mixture, there is an advantage that the crosslinked polymer particles can be suitably prepared.

[0090] Examples of radically polymerizable unsaturated monomers having a pendant side chain containing a higher unsaturated aliphatic group include those obtained by reacting a higher unsaturated fatty acid with an ethylenically unsaturated glycidyl ester. Examples of the higher unsaturated fatty acid include myristoleic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, and ricinoleic acid. Other examples of the higher unsaturated fatty acid include drying oils and semi-drying oil fatty acids with non-conjugated double bonds, such as linseed oil fatty acids, safflower oil fatty acids, soybean oil fatty acids, rice bran oil fatty acids, sesame oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, perilla oil fatty acids, hempseed oil fatty acids, cottonseed oil fatty acids, and tall oil fatty acids. The drying oils and semi-drying oil fatty acids include unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, eleostearic acid, and ricinoleic acid. The average carbon number of the higher unsaturated aliphatic group is preferably 13 to 23. In addition, fatty acids having conjugated double bonds, such as tung oil fatty acids, may be used in combination in an amount of 30% by mass or less based on the total saturated fatty acids. The ethylenically unsaturated glycidyl ester may include glycidyl acrylate, glycidyl methacrylate, methyl glycidyl acrylate, methyl glycidyl methacrylate, allyl glycidyl ether, and methallyl glycidyl ether. Among these, particularly preferred are those obtained by reacting at least one selected from oleic acid, linoleic acid, linoleic acid, safflower oil fatty acid, soybean oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, and tall oil fatty acid with glycidyl acrylate and / or glycidyl methacrylate. The radically polymerizable unsaturated monomer preferably has an iodine value of 60 to 180, particularly 70 to 150.

[0091] Examples of other radically polymerizable unsaturated monomers other than the radically polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group, which are contained in the above monomer mixture, include acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, i-octyl acrylate, 2-ethylhexyl acrylate, i-nonyl acrylate, stearyl acrylate, cyclohexyl acrylate, and benzyl acrylate; Methacrylic acid ester monomers such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, i-octyl methacrylate, 2-ethylhexyl methacrylate, i-nonyl methacrylate, n-dodecyl methacrylate, i-dodecyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate; aromatic vinyl monomers such as styrene, vinyl toluene, and ethyl vinyl benzene; carboxyl group-containing monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, and citraconic acid; amide group- or substituted amide group-containing monomers such as acrylamide, methacrylamide, N,N-dimethylacrylamide, N-methylacrylamide, and N-n-butoxymethylacrylamide; Hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, and methallyl alcohol; amino group- or substituted amino group-containing monomers such as aminoethyl acrylate, N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, and N,N-diethylaminoethyl methacrylate; epoxy group-containing monomers such as glycidyl methacrylate, glycidyl acrylate, glycidyl allyl ether, glycidyl methallyl ether, and glycidyl vinyl ether;Mercapto group-containing monomers such as vinyl mercaptan and allyl mercaptan; and monomers having two or more radically polymerizable unsaturated groups in one molecule such as (poly)ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, and divinylbenzene;

[0092] Of the other radically polymerizable unsaturated monomers, it is preferable to include one or more selected from the group consisting of: acrylic acid ester monomers (preferably ethyl acrylate, n-butyl acrylate, etc.), methacrylic acid ester monomers (preferably methyl methacrylate, n-butyl methacrylate, etc.), carboxyl group-containing monomers (preferably acrylic acid, methacrylic acid, ω-carboxy-polycaprolactone monoacrylate, etc.), and substituted amino group-containing monomers (preferably N,N-di-lower alkylamino-lower alkyl (meth)acrylates such as N,N-dimethylaminoethyl acrylate and N,N-diethylaminoethyl methacrylate, etc.).

[0093] The amount of radically polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group contained in the monomer mixture is preferably in the range of 0.5 parts by mass to 30 parts by mass, more preferably in the range of 5 parts by mass to 15 parts by mass, per 100 parts by mass of the total amount of the monomer mixture. The total amount of acrylic acid ester monomer and methacrylic acid ester monomer contained in the monomer mixture is preferably in the range of 50 parts by mass to 90 parts by mass, per 100 parts by mass of the total amount of the monomer mixture. The amount of carboxyl group-containing monomer contained in the monomer mixture is preferably in the range of 10 parts by mass or less. The amount of substituted amino group-containing monomer contained in the monomer mixture is preferably in the range of 10 parts by mass or less. When the crosslinked polymer microparticles (D) of the present disclosure are prepared by multi-stage polymerization, the amount of monomer contained in the monomer mixture is the total amount of monomers used in each polymerization.

[0094] The polymerization conditions for preparing crosslinked polymer microparticles (D) can be selected by those skilled in the art according to the type and amount of monomer used.For example, preferably use suitable polymerization initiator and chain transfer agent as needed, and heat react under stirring in nitrogen gas flow or at the reflux temperature of organic solvent for several hours, so that the above-mentioned monomer mixture is polymerized to be within the range of weight-average molecular weight described below.The polymerization temperature is generally 30 ℃ or more and 180 ℃ or less, preferably 60 ℃ or more and 150 ℃ or less.

[0095] Examples of organic solvents used in the polymerization include aliphatic or alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, "Rous", "Mineral Spirits EC", "Shellsol 71", "VM&P Naphtha", and "Shell TS28 Solvent" (all manufactured by Shell), "Isopar C", "Isopar E", "Isopar G", "Isopar H", "Isopar M", "Naphtha No. 3", "Naphtha No. 5", "Naphtha No. 6", and "Solvent No. 7" (all manufactured by Exxon Chemical Company), "IP Solvent 1016", "IP Solvent 1620", "IP Solvent 2028", and "IP Solvent 2835" (all manufactured by Idemitsu Kosan Co., Ltd.), "Whitesol" (manufactured by Japan Energy Co., Ltd.), "Mitsubishi Mineral Turpen", "Diamond Solvent", "Pegasol AN-45", and "Pegasol 3040" (all manufactured by JXTG Nippon Oil & Energy Corporation); Aromatic hydrocarbon organic solvents such as benzene, toluene, ethylbenzene, propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, "Solvesso 100" (manufactured by Exxon Chemical Co.), and "Solvesso 150" (manufactured by Exxon Chemical Co.); ketone organic solvents such as acetone, acetylacetone, methyl ethyl ketone, methyl-i-butyl ketone, methyl amyl ketone, and cyclohexanone; ester organic solvents such as methyl acetate, ethyl acetate, n-butyl acetate, and aluminum acetate; cellosolve organic solvents such as methyl cellosolve, ethyl cellosolve, n-propyl cellosolve, i-propyl cellosolve, n-butyl cellosolve, i-butyl cellosolve, i-amyl cellosolve, phenyl cellosolve, and benzyl cellosolve; Carbitol-based organic solvents such as methyl carbitol, ethyl carbitol, n-propyl carbitol, i-propyl carbitol, n-butyl carbitol, i-butyl carbitol, i-amyl carbitol, phenyl carbitol, and benzyl carbitol; and the like.

[0096] Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and t-butyl peroxypivalate; and azo compounds such as 2,2'-azobis-i-butylnitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile. These may be used alone, or two or more may be used in combination. The amount of the polymerization initiator used is generally preferably 0.5 to 15 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of the total amount of monomers. Note that when the crosslinked polymer microparticles (D) of the present disclosure are prepared by multi-stage polymerization, the preferred range of the amount of the polymerization initiator used can be applied to each polymerization.

[0097] In preparing the polymer crosslinked fine particles (D), when a monomer mixture is polymerized in two stages, in the first polymerization stage, a monomer mixture containing a radically polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group is copolymerized to form a dissolved portion, and then a monomer mixture not containing a radically polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group or a monomer mixture containing a radically polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group may be copolymerized to form a particle portion.

[0098] When the crosslinked polymer particles (D) have, for example, a dissolved portion and a particle portion, the weight-average molecular weight of the dissolved portion may be 15,000 to 100,000, and the particle portion is preferably crosslinked with a monomer having two or more polymerizable unsaturated groups. The weight-average molecular weight may be determined, for example, by gel permeation chromatography (GPC) using polystyrene as a standard.

[0099] When the crosslinked polymer fine particles (D) have a dissolved portion and a particle portion, the mass ratio of the dissolved portion to the particle portion (dissolved portion:particle portion) is preferably within a range of 20:80 to 80:20, more preferably within a range of 30:70 to 70:30.

[0100] Another example of preparing crosslinked polymer microparticles (D) is to polymerize a monomer mixture that does not contain radical polymerizable unsaturated monomers having pendant side chains that contain higher unsaturated aliphatic groups, and then introduce pendant side chains that contain higher unsaturated aliphatic groups into the resulting copolymer.Specifically, for example, by polymerizing a monomer mixture that contains alkylene group-containing monomers, and then reacting the carboxyl group of higher unsaturated fatty acid with the alkylene group that the resulting copolymer has, the pendant side chains that contain higher unsaturated aliphatic groups can be introduced.

[0101] The amount of crosslinked polymer particles (D) blended into the base coating composition is generally 5 to 40 parts by mass, preferably 10 to 30 parts by mass, per 100 parts by mass of the total solids of the film-forming resin (B), blocked isocyanate compound (C), and melamine resin (E). If the amount of crosslinked polymer particles (D) blended is too small, the base coating composition will be prone to sagging, and in the case of wet-on-wet coating, penetration into the lower layer coating composition will be excessive, preventing the initial purpose from being achieved. On the other hand, if the amount blended is too large, the coating film performance will be reduced and the film will become less smooth, making it impossible to obtain a high-quality finished appearance.

[0102] Commercially available crosslinked polymer particles (D) include, for example, Setalux 1801, 1850, SA-50, and 53 (manufactured by Allnex).

[0103] The total content of the pigment (A), film-forming resin (B), blocked isocyanate compound (C), crosslinked polymer microparticles (D), melamine resin (E), acid catalyst (F), and amine compound (G) in the solids of the base coating composition is, for example, preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, with the upper limit being 100% by mass or less.

[0104] [Organic Solvent] The base coating composition may contain an organic solvent. Examples of such organic solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; esters such as ethyl acetate, butyl acetate, amyl acetate, methyl benzoate, ethyl ethoxypropionate, ethyl propionate, and methyl propionate; ethers such as tetrahydrofuran, dioxane, and dimethoxyethane; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; aromatic hydrocarbons; and aliphatic hydrocarbons.

[0105] [Other Additives] The base coating composition of the present disclosure may contain other additives other than the curing catalyst and the crosslinked polymer fine particles (D), such as a viscosity modifier, an antifoaming agent, an ultraviolet absorber, a light stabilizer (e.g., a hindered amine), an antioxidant, a surface conditioner, a film-forming aid, and a rust inhibitor.

[0106] The method for producing the base coating composition is not particularly limited, and any method known in the art can be used, such as stirring, kneading, or dispersing the above-mentioned materials using a disper, homogenizer, roll, sand grind mill, kneader, or the like.

[0107] The base coating composition of the present disclosure is measured using a cone-and-plate viscometer at 23°C with a shear speed of 0.1 / sec. The viscosity V1 is then measured after changing the shear speed from 0.1 / sec to 25,000 / sec for 30 seconds, and then returning to 0.1 / sec for 1 second. The viscosity recovery rate V2 / V1, which is the ratio of V2 to V1, is 90% or more. The higher the viscosity recovery rate V2 / V1, the better. The viscosity recovery rate represents the ratio of the viscosity at a weak shear speed to the viscosity at a strong shear speed, and a high viscosity recovery indicates that the viscosity recovers quickly even immediately after application. The base coating composition of the present disclosure rapidly recovers its viscosity even immediately after application. The viscosity recovery rate V2 / V1 is preferably 90% or more and 100% or less, more preferably 90% or more and 95% or less.

[0108] The gel fraction of the solvent-based base coating composition after heating at 70°C for 10 minutes is preferably 40% by mass or more, more preferably 40% by mass to 80% by mass, and even more preferably 40% by mass to 70% by mass. The gel fraction can be calculated based on the following formula using the mass of the film after heating the base coating composition at 75°C for 10 minutes (mass of coating film before extraction) and the mass of the film after further heating and refluxing in acetone for 3 hours (mass of coating film after extraction): Gel fraction (mass %) = (mass of coating film after extraction / mass of coating film before extraction) x 100

[0109] [Coated Article] A coated article according to an embodiment of the present disclosure comprises: an object to be coated; and a base coating film formed from a solvent-based base coating composition according to an embodiment of the present disclosure.

[0110] A coated article according to an embodiment of the present disclosure may include a multilayer coating film including an intermediate coating film or a primer coating film provided on an object to be coated, a base coating film provided on the intermediate coating film or the primer coating film, and a clear coating film provided on the base coating film.

[0111] In one aspect, a coated article according to an embodiment of the present disclosure may have a base coating film provided on the substrate without having an intermediate coating film or a primer coating film. That is, in this aspect, a coated article according to an embodiment of the present disclosure may have a multilayer coating film including a base coating film provided on the substrate and a clear coating film provided on the base coating film. For example, when the substrate is made of plastic, the base coating composition according to an embodiment of the present disclosure can form a base coating film that has good adhesion to the substrate, even without providing a primer coating film on the substrate.

[0112] [Substrate] The substrate is not particularly limited, and examples thereof include metal substrates, plastic substrates, and foams thereof.

[0113] Examples of metal substrates include metals such as iron, steel, copper, aluminum, tin, and zinc, and alloys containing these metals. Specific 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 electrodeposition coating film formed thereon in advance. Furthermore, prior to the formation of the electrodeposition coating film, chemical conversion treatments (e.g., zinc phosphate chemical conversion treatment, zirconium chemical conversion treatment, etc.) may be performed as necessary.

[0114] Examples of plastic resin substrates include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, etc. Specific examples of plastic substrates include automobile parts such as spoilers, bumpers, mirror covers, grilles, doorknobs, etc. These plastic substrates are preferably degreased with a solvent such as petroleum benzine or isopropanol, or washed with pure water and / or a neutral detergent.

[0115] (2) Intermediate Coating Film, Primer Coating Film When the substrate is a metal substrate, an intermediate coating film may be provided on the metal substrate on which the electrodeposition coating has been formed. When the substrate is a plastic substrate, a primer coating film may be provided on the plastic substrate. The intermediate coating film and the primer coating film are not particularly limited, and may be formed using, for example, an intermediate coating composition or a primer coating composition containing a film-forming resin and, if necessary, a curing agent, etc., respectively.

[0116] (3) Clear Coating Film A clear coating film may be provided on the base coating film. The clear coating film is not particularly limited, and may be formed using a clear coating composition containing a coating film-forming resin and, if necessary, a curing agent. The clear coating film may also contain a coloring component. The form of the clear coating composition is not particularly limited, but a solvent-based one is preferred.

[0117] Preferred examples of solvent-based clear coating compositions include, from the viewpoints of transparency or acid etching resistance, a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate, or a composition containing an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system as a coating film-forming resin. Furthermore, two-component clear coatings using an isocyanate as a crosslinking agent are more preferred. In particular, the isocyanate in the clear coating penetrates into the colored base coating layer and hardens to form a multi-layer coating film with excellent water resistance.

[0118] Examples of water-based clear coating compositions include those containing resins obtained by neutralizing the film-forming resins contained in the solvent-based clear coating compositions with a base to make them water-based. This neutralization can be carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine before or after polymerization.

[0119] The clear coating composition may contain a viscosity control agent, such as crosslinked or non-crosslinked resin particles, polyamide-based agents such as swollen dispersions of fatty acid amides, amide-based fatty acids, and phosphates of long-chain polyaminoamides, polyethylene-based agents such as colloidal swollen dispersions of polyethylene oxide, organic acid smectite clays, and organic bentonite-based agents such as montmorillonite.

[0120] The method for manufacturing the coated article is not particularly limited, and the coated article can be manufactured, for example, by the method for manufacturing a coated article according to an embodiment of the present disclosure described below.

[0121] [Method for manufacturing coated articles] The base coating composition of the present disclosure is applied to a substrate using the same coating method as for ordinary base coatings. The base coating composition is applied to a substrate that has been provided with an intermediate coating film or a primer coating film. A clear coating is then applied on top of the base coating film to form a clear coating film. The coating film formation method may be a commonly used method, and after application using a spray coater to form an uncured coating film, so-called wet-on-wet, two or three layers may be cured simultaneously.

[0122] There are no particular limitations on the application methods for the intermediate coating composition, primer coating composition, base water-based coating composition, and clear coating composition. Depending on the type of substrate, a coating method commonly used in the coating field may be used, such as air spray coating, bell coating, multi-stage coating or single-stage coating using air electrostatic spray coating, or a coating method combining air electrostatic spray coating with a rotary atomizing electrostatic coater known as a metallic bell.

[0123] Examples of heating devices used to heat-cure an uncured coating film include drying ovens that use heat sources such as hot air, electricity, gas, infrared rays, etc. It is also preferable to use a drying oven that uses two or more of these heat sources in combination, as this shortens the drying time.

[0124] The coated article according to the embodiment of the present disclosure can also be produced by heat-curing the coating film after each coating composition is applied, and then sequentially forming upper coating films. Also, the coated article according to the embodiment of the present disclosure can be produced in a form that does not include the intermediate coating film and the primer coating film by omitting the steps of forming the intermediate coating film and the primer coating film.

[0125] The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited thereto.

[0126] (Production Example 1-1) Production of Hydroxyl Group-Containing Acrylic Resin (B1-1) 57 parts of butyl acetate was charged into a reactor equipped with a stirring blade, thermometer, dropping device, temperature control device, nitrogen gas inlet, and cooling tube, and the temperature was raised to 120 ° C. while stirring and introducing nitrogen gas. Next, a mixture consisting of 0.5 parts of methacrylic acid, 56.6 parts of 2-ethylhexyl methacrylate, 16.7 parts of methyl methacrylate, 15.0 parts of styrene, 8.9 parts of lactone-modified 2-hydroxyethyl methacrylate, and 2.3 parts of 2-hydroxyethyl methacrylate and a solution obtained by dissolving 2.0 parts of t-butylperoxy-2-ethylhexanate in 5 parts of butyl acetate were added dropwise into the reactor over 3 hours. After completion of the dropwise addition, the mixture was aged for 1 hour, and then a solution obtained by dissolving 0.2 parts of t-butylperoxy-2-ethylhexanate in 5 parts of butyl acetate was added dropwise into the reactor over 1 hour, and the mixture was maintained at 120 ° C. for 2 hours while aging to complete the reaction. The resulting hydroxyl-containing resin had a non-volatile content of 60% and a weight-average molecular weight of 13,400. The glass transition temperature was 20°C and the hydroxyl value was 30 mgKOH / g. Table 1 shows the blended monomer components, characteristic values, and the amounts of the polymerization initiator (t-butylperoxy-2-ethylhexanate) in the first and second stages.

[0127] (Production Examples 1-2 to 1-3) Production of Hydroxyl-Containing Acrylic Resins (B1-2 to B1-3) The hydroxyl-containing acrylic resins of Production Examples B1-2 to B1-3 were obtained in the same reaction apparatus as in Production Example B1-1, using the formulations shown in Table 1 and following the same procedures. Table 1 also shows the property values ​​of the resulting hydroxyl-containing acrylic resins (B-2 to B-3).

[0128]

[0129] (Production Example 2) Production of Hydroxyl-Containing Acrylic Resin (B2) Hydroxyl-containing acrylic resin (B2) was obtained in the same reaction apparatus as in Production Example 1-1 above, using the same procedures and with the same formulation as shown in Table 2. The properties (weight average molecular weight, amount of heating residue, amount of first-stage and second-stage polymerization initiator) are also shown in Table 2.

[0130]

[0131] Reference Example 1: Method for producing a polyester resin having an amphoteric group. A 2Q flask equipped with a stirrer, nitrogen inlet tube, temperature control device, condenser, and decanter was charged with 134 parts of bishydroxyethyl taurine, 130 parts of neopentyl glycol, 236 parts of azelaic acid, 186 parts of phthalic anhydride, and 27 parts of xylene, and the temperature was increased. The water produced by the reaction was removed by azeotropy with the xylene. The temperature was raised to 190°C over approximately 2 hours after the start of reflux, and stirring and dehydration were continued until the carboxylic acid equivalent oxidation reached 145, followed by cooling to 140°C. The temperature was then maintained at 140°C, and 314 parts of "Cardura E10" (Persatic acid glycidyl ester manufactured by Shell) were added dropwise over 30 minutes. Stirring was then continued for 2 hours, and the reaction was completed. The resulting polyester resin had an acid value of 59, a hydroxyl value of 90, and an Mn of 1054.

[0132] (Production Example 3) Method for producing crosslinked polymer microparticles (D) 281 parts of deionized water, 30 parts of the polyester resin obtained in Reference Example 1 above, and 3 parts of dimethylethanolamine were charged into a 1 L reaction vessel equipped with a stirrer, a cooler, and a temperature control device, and dissolved while maintaining the temperature at 80 ° C. A solution of 1.0 parts of azobiscyanovaleric acid dissolved in 45 parts of deionized water and 0.9 parts of dimethylethanolamine was added to the mixture. Next, a mixed solution consisting of 30 parts of n-butyl acrylate, 70 parts of styrene, and 60 parts of ethylene glycol dimethacrylate was added dropwise over 60 minutes. After the dropwise addition, a solution of 0.5 parts of azobiscyanovaleric acid dissolved in 15 parts of deionized water and 0.4 parts of dimethylethanolamine was added and stirred for another 2 hours at 80 ° C. to obtain an emulsion with a nonvolatile content of 40% and a particle size of 0.12 μm. This emulsion was spray-dried to obtain crosslinked polymer microparticles. These crosslinked polymer particles were mixed in a solvent of methyl amyl ketone and xylene in a weight ratio of 1:1, and the heating residue was adjusted to 40% using an ultrasonic disperser to obtain a stable dispersion solution of crosslinked polymer particles.

[0133] Examples 1 to 9 and Comparative Examples 1 to 8 Base coating compositions of Examples 1 to 9 and Comparative Examples 1 to 8 were obtained by blending and stirring raw materials according to the compositions (colored base coating composition) shown in Tables 3 and 4 below. The units of composition in the tables are parts by mass, and are amounts converted to solids excluding organic solvents. The amount of polymer crosslinked fine particles (D) represents the amount per 100 parts by mass of the total of the hydroxyl group-containing acrylic resin (B1), the hydroxyl group-containing acrylic resin (B2), the blocked isocyanate compound (C), and the melamine resin (E).

[0134] Preparation of Paints The base paint compositions of Examples 1 to 9 and Comparative Examples 1 to 8 were diluted with methyl amyl ketone / Solvesso 100 = 1 / 1 (by weight) as a thinner to adjust the viscosity of the paint at a temperature of 20°C to 13 seconds using a Ford Cup No. 4.

[0135] Preparation of Coated Articles The base paint composition of Example 1 was spray-coated (dry film thickness 25 μm) onto the surface of an ABS resin substrate (70 mm × 150 mm × 3 mm) wiped with isopropyl alcohol under an environment of 25°C / 70% relative humidity (RH) using a spray gun "Wider-71" (manufactured by Anest Iwata Corporation) and allowed to set at room temperature for 5 minutes. A clear paint composition (a mixture of R-2640-201 and hardener H-2550 manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was spray-coated (dry film thickness 25 μm) onto the surface using a Robobel 951 under the following conditions: gun distance: 200 mm, gun speed: 700 mm / s, rotation speed: 25,000 rpm, shaping air pressure: 0.07 MPa. The resulting mixture was then allowed to set for 10 minutes and then dried at 70°C for 10 minutes to prepare the coated article of Example 1.

[0136] The coated articles of Examples 2 to 9 and Comparative Examples 1 to 8 were obtained in the same manner as in Example 1, except that the base coating compositions of Examples 2 to 9 and Comparative Examples 1 to 8 shown in Tables 3 and 4 were used.

[0137] The resulting base coating compositions and coated articles were subjected to the following evaluations, and the evaluation results are shown in the table below.

[0138] (Viscosity Recovery Rate [%]) Using a TA Instruments Corp. Co-plate viscometer "DHR-3," viscosity V1 was measured at 23°C at 0.1 / sec shear, then the shear was changed from 0.1 / sec shear to 25,000 / sec shear and sheared for 30 seconds, and then returned to 0.1 / sec shear and sheared for 1 second, after which viscosity V2 was measured. From the obtained V1 and V2, viscosity recovery rate V2 / V1 [%] was calculated. The evaluation criteria were as follows, with ◯ being a pass and × being a fail. ◯: Viscosity recovery rate of 90% or more ×: Viscosity recovery rate of less than 90%

[0139] (Painting Viscosity Evaluation) The base paint compositions of the Examples and Comparative Examples were diluted with methyl amyl ketone / Solvesso 100 = 1 / 1 (weight ratio) as a thinner to adjust the non-volatile content to 35%. The Ford Cup No. 4 viscosity (seconds) was measured at a paint temperature of 20°C and evaluated according to the following criteria. A paint viscosity of 18 seconds or less ensures favorable paint workability and enables the formation of a paint film with a good appearance. Evaluation Criteria ◯: Ford Cup No. 4 viscosity in seconds at 35% non-volatile content is 18 seconds or less; ×: Ford Cup No. 4 viscosity in seconds at 35% non-volatile content is more than 18 seconds.

[0140] (Adhesion Evaluation) Test panels were prepared using the base coating compositions of the Examples and Comparative Examples according to the procedure for preparing coated articles described above. The coating films on the obtained test panels were subjected to a cross-cut Cellophane tape peeling test in accordance with JIS K5600-5-6:1999. 100 2 mm square cross-cuts were prepared, and a Cellophane tape peeling test was performed, and the number of cross-cuts that did not peel was counted. The evaluation criteria were as follows, with ◯ being a pass and × being a fail. ◯: 0 / 100 (no peeling) ×: 1 / 100 to 100 / 100 (peeling).

[0141] (Water Resistance) Test panels were prepared using the base coating compositions of the Examples and Comparative Examples according to the above-described procedure for preparing coated articles. The obtained test panels were immersed in a water-resistant tank at 40°C for 240 hours. After immersion, the coating films on the test pieces were removed from the tank and, within one hour of removal, a cross-cut Cellophane tape peeling test and appearance observation were carried out in accordance with JIS K5600-5-6:1999. 100 2mm square cross-cuts were prepared and a Cellophane tape peeling test was carried out, and the number of cross-cuts that did not peel was counted. The appearance was also checked for any abnormalities such as blisters. The evaluation criteria were as follows, with ◯ being a pass and × being a fail. ◯: 0 / 100 (no peeling), no abnormalities in appearance Δ: 0 / 100 (no peeling), abnormalities in appearance ×: 1 / 100 to 100 / 100 (peeling), no relation to abnormalities in appearance

[0142] (Storage stability) After preparing the base coating compositions of the Examples and Comparative Examples, they were left to stand for 10 days at 40° C. If lumps without flowability were formed in the base coating composition or if the viscosity of the entire base coating composition was 50% or more of the initial viscosity, the composition was evaluated as "×", and if not, the composition was evaluated as "◯".

[0143] (Low-temperature curing property (gel fraction measurement)) The base coating composition was applied to a polypropylene plate using a bar coater so that the dry film thickness was 20 μm, and then the intermediate coating film was heated and cured at 70° C. for 10 minutes to form an intermediate coating film. This intermediate coating film was peeled off from the polypropylene plate, and the coating mass was measured for the single coating film using a Soxhlet extractor before and after heating and refluxing acetone for 3 hours, and the gel fraction was calculated using the following formula: Gel fraction (mass %) = (coating mass after extraction / coating mass before extraction) × 100 Low-temperature curing property was evaluated according to the following criteria. A rating of B or higher on the following 5-point scale was considered to be acceptable. A: Gel fraction of 50% or more B: Gel fraction of 40% or more but less than 50% C: Gel fraction of less than 40%

[0144]

[0145]

[0146] The raw materials in the above table (excluding those in the production examples) are explained below. Blocked isocyanate compound (C): manufactured by Asahi Kasei Chemical Corporation, trade name: Duranate MF-K60B Melamine resin (E) E-1: Resimine 751 (manufactured by Prefere Resins) E-2: Resimine 745 (manufactured by Prefere Resins) E-3: C303LF (Cymel 303LF, full alkyl type melamine resin, manufactured by Allnex Japan) E-4: C251 (Cymel 251, methylol type melamine resin, manufactured by Allnex Japan) E-5: C327 (Cymel 327, imino type melamine resin, manufactured by Allnex Japan) Pigment (A): aluminum pigment (flake pigment), manufactured by Toyo Aluminum K.K., trade name: Alpaste 07-0674 Amine compound (G) G-1: DNPA (di-n-propylamine, boiling point 109°C) G-2: DIPA (diisopropylamine, boiling point 84°C) G-3: isobutylamine (boiling point 63°C) G-4*: 2-(dimethylamino)ethanol (tertiary amine compound) Organic solvent: methyl amyl ketone, Solvesso 100 (manufactured by ExxonMobil Corporation)

[0147] Examples 1 to 10 are examples of the present disclosure, and the coating compositions exhibited good adhesion and water resistance, maintaining the appearance of the resulting coating film, good low-temperature curing properties, reducing the energy load during coating film formation, and good storage stability.

[0148] Comparative Example 1 is an example in which a full-alkyl melamine resin was not used, and the coating film appearance, storage stability, and low-temperature curing properties of the coating composition were not fully satisfactory. Comparative Example 2 is an example in which a full-alkyl melamine resin was not used, and the coating film appearance and storage stability of the coating composition were not fully satisfactory. Comparative Example 3 is an example in which an acid catalyst having a counter ion was used, and the coating film appearance and low-temperature curing properties were not fully satisfactory. Comparative Example 4 is an example in which a secondary amine compound was not used as the amine compound, and the coating film appearance and low-temperature curing properties were not fully satisfactory. Comparative Example 5 is an example in which a secondary amine compound was not used as the amine compound, and the coating composition storage stability was not fully satisfactory. Comparative Example 6 is an example in which an amine compound was not used, and the coating composition storage stability was not fully satisfactory. Comparative Example 7 is an example in which an acrylic resin (B2) was not used, and the coating viscosity was high, and the coating composition storage stability was not fully satisfactory. Comparative Example 8 is an example in which a melamine resin was not used, and the coating film appearance and low-temperature curing properties were not fully satisfactory.

[0149] According to the solvent-based paint composition of the present disclosure, it is possible to provide a solvent-based paint composition that reduces the energy load during paint film formation and has good storage stability while maintaining the appearance of the resulting paint film, and can be preferably used for painting automobiles, etc.

Claims

1. A solvent-based base paint composition comprising a pigment (A), a hydroxyl group-containing acrylic resin (B1) having a weight average molecular weight of 10,000 or more and 20,000 or less, a hydroxyl group-containing acrylic resin (B2) having a weight average molecular weight of 3,000 or more and 7,500 or less, a blocked isocyanate compound (C), a melamine resin (E), polymer crosslinked fine particles (D) stably dispersed and insoluble in the solution of the hydroxyl group-containing acrylic resin (B1), an acid catalyst (F), and an amine compound (G), wherein the solvent-based base paint composition has a solid content of 35% by mass or more, and when the viscosity V1 is measured at 23 °C at a shear rate of 0.1 / sec using a cone plate viscometer, then changed from 0.1 / sec to 25,000 / sec and sheared for 30 seconds, and then the shear rate is returned to 0.1 / sec and the viscosity V2 after shearing for 1 second is measured, the viscosity recovery rate V2 / V1, which is the ratio of V2 to V1, is 90% or more, the pigment (A) contains one or more selected from the group consisting of a coloring pigment and a flaky pigment, the hydroxyl group-containing acrylic resin (B1) is a polymer of one or more monomers containing a hydroxyl group-containing monomer (b), the hydroxyl group-containing monomer (b) contains a lactone-modified product of a monoester compound of (meth)acrylic acid and a divalent alcohol having 2 to 8 carbon atoms, the glass transition temperature is 10 °C or more and 40 °C or less, the hydroxyl value is 10 mgKOH / g or more and 90 mgKOH / g or less, the melamine resin (E) contains a fully alkylated melamine resin, the acid catalyst (F) is a catalyst having no counter ion, and the amine compound (G) contains a secondary amine compound.

2. The solvent-based base paint composition according to claim 1, wherein the acid catalyst (F) contains a sulfonic acid compound.

3. The solvent-based base paint composition according to claim 1 or 2, wherein the amine compound (G) has a boiling point in the range of 70 to 115 °C, and the content of the amine compound (G) is 0.1 part by mass or more and 0.8 part by mass or less based on 100 parts by mass in total of the resin solids in the base paint composition.

4. The content of the melamine resin (E) is 3 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass in total of the resin solids in the base paint composition. The solvent-based base paint composition according to any one of claims 1 to 3.

5. The mass ratio of the content of the blocked isocyanate compound (C) and the melamine resin (E) is in the range of blocked isocyanate compound (C): melamine resin (E) = 2:1 to 1:

4. The solvent-based base paint composition according to any one of claims 1 to 4.

6. The equivalent ratio of the acid catalyst (F) and the amine compound (G) is in the range of acid catalyst (F): amine compound (G) = 3.5:1 to 1:

2. The solvent-based base paint composition according to any one of claims 1 to 5.

7. The hydroxyl group-containing acrylic resin (B1) is a polymer of the hydroxyl group-containing monomer (b) and other monomers other than the hydroxyl group-containing monomer (b). Among the total of the hydroxyl group-containing monomer (b) and the other monomers, the hydroxyl group-containing monomer (b) is 5% by mass or more and 20% by mass or less. The solvent-based base paint composition according to any one of claims 1 to 5.

8. The gel fraction after heating the solvent-based base paint composition at 75 ° C for 10 minutes is 40% or more. The solvent-based base paint composition according to any one of claims 1 to 7.

9. A coated article having a substrate to be coated and a base coating film formed from the solvent-based base paint composition according to any one of claims 1 to 8.

10. A coated article according to claim 9, having a solvent-based base coating film provided on the substrate to be coated on which an intermediate coating film or a primer coating film has been previously provided.

11. The coated article according to claim 9 or 10, wherein the substrate to be coated contains a plastic resin substrate.

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