Base coating material composition and coated article

Abstract

To provide 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.SOLUTION: A solvent-type base coating material composition comprises: a pigment (A); a hydroxy group-containing acrylic resin (B1) having a weight average molecular weight of 10,000 or more and 20,000 or less; a hydroxy 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) that are insoluble and stably dispersed in a solution of the hydroxy group-containing acrylic resin (B1); an acid catalyst (F); and an amine compound (G).SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a base paint composition and a painted article.

Background Art

[0002] On an object to be painted such as a base material constituting an automobile, a base coating film and a clear coating film can be provided thereon for the purpose of imparting design, resistance, etc. The base paint composition for forming the base coating film can affect the design of the object to be painted. As such a base paint composition, Patent Document 1 describes a base paint composition containing a pigment, a hydroxyl group-containing acrylic resin, a blocked isocyanate compound, polymer crosslinked fine particles stably dispersed and insoluble in the hydroxyl group-containing acrylic resin solution, and an acrylic resin having a weight average molecular weight different from that of the hydroxyl group-containing acrylic resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, in a solvent-based base paint composition, it is necessary to dry the solvent in the paint composition and cure the coating film during coating film formation, which may increase the energy load and equipment load. On the other hand, if drying and coating film curing at a lower temperature are attempted, the storage stability may decrease.

[0005] In addition, the base paint composition is a very important paint that affects the appearance of the object to be painted, and moreover, high control is required to satisfy performance such as adhesion to the coating films existing above and below the base coating film.

[0006] From the perspective of environmental protection, further reduction of energy load is required, and there is room for improvement in the base paint composition described in Patent Document 1. For example, in the examples of Patent Document 1, although the painted article is dried at 80 °C for 30 minutes during production, further reduction in temperature is required, and shortening of the heating time is also required.

[0007] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a solvent-based base paint composition capable of reducing the energy load during film formation and achieving both storage stability while maintaining the appearance of the paint film.

Means for Solving the Problems

[0008] The present disclosure provides the following aspects. [1] 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), An amine compound (G), A solvent-based base paint composition containing wherein the solvent-based base paint composition has a solid content of 35% by mass or more, The solvent-based base paint composition uses a cone plate type viscometer to measure the viscosity V1 at a shear rate of 0.1 / sec at 23 °C, then changes the shear rate from 0.1 / sec to 25,000 / sec and shears for 30 seconds, Next, when the viscosity V2 after returning the shear rate to 0.1 / sec and 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 coloring pigments and flaky pigments, The hydroxyl group-containing acrylic resin (B1) is a polymer of one or more monomers containing a hydroxyl group-containing monomer (b), and 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, having a glass transition temperature of 10°C or higher and 40°C or lower, having a hydroxyl value of 10 mgKOH / g or higher and 90 mgKOH / g or lower, the melamine resin (E) contains a fully alkylated type melamine resin, the acid catalyst (F) is a catalyst having no counter ion, the amine compound (G) contains a secondary amine compound, a solvent-based base paint composition. [2] The acid catalyst (F) contains a sulfonic acid compound, and the solvent-based base paint composition according to [1]. [3] the amine compound (G) has a boiling point within the range of 70 to 115°C, 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, and the solvent-based base paint composition according to [1] or [2]. [4] the content of the melamine resin (E) is 3 parts by mass or more and 15 parts by mass or less based on 100 parts by mass in total of the resin solids in the base paint composition, and the solvent-based base paint composition according to any one of [1] to [3]. [5] the mass ratio of the contents of the blocked isocyanate compound (C) and the melamine resin (E) is within the range of blocked isocyanate compound (C):melamine resin (E) = 2:1 to 1:4, and the solvent-based base paint composition according to any one of [1] to [4]. [6] the equivalent ratio of the acid catalyst (F) and the amine compound (G) is within the range of acid catalyst (F):amine compound (G) = 3.5:1 to 1:2, and the solvent-based base paint composition according to any one of [1] to [5]. [7] The hydroxyl group-containing acrylic resin (B1) is a polymer of the hydroxyl group-containing monomer (b) and another monomer other than the hydroxyl group-containing monomer (b), The solvent-based base paint composition according to any one of [1] to [6], wherein the hydroxyl group-containing monomer (b) is 5% by mass or more and 20% by mass or less in the total of the hydroxyl group-containing monomer (b) and the other monomer. [8] The solvent-based base paint composition according to any one of [1] to [7], wherein the gel fraction after heating the solvent-based base paint composition at 75 ° C for 10 minutes is 40% or more. [9] A coated article having an object to be coated, and a base coating film formed from the solvent-based base paint composition according to any one of [1] to [8].

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

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

[10] , wherein the object to be coated includes a plastic resin substrate. [Effect of the Invention]

[0009] The present disclosure can provide a solvent-based base paint composition that maintains the appearance of the resulting coating film while reducing the energy load during coating film formation and having good storage stability. [Embodiments for Carrying Out the Invention]

[0010] The base paint composition of the present disclosure includes 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 cross-linked fine particles (D) that are insoluble and stably dispersed in the solution of the hydroxyl group-containing acrylic resin (B1), an acid catalyst (F) and an amine compound (G), a solvent-based base paint composition comprising wherein the base paint composition has a solid content of 35% by mass or more, wherein the base paint composition uses a cone plate viscometer, measures the viscosity V1 at a shear rate of 0.1 / sec at 23°C, then changes the shear rate from 0.1 / sec to 25,000 / sec and shears for 30 seconds, and then when 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, wherein the pigment (A) contains one or more selected from the group consisting of a coloring pigment and a flaky pigment, wherein the hydroxyl group-containing acrylic resin (B1) is a polymer of one or more monomers containing a hydroxyl group-containing monomer (b), and the hydroxyl group-containing monomer (b) is a lactone-modified product of a monoester compound of (meth)acrylic acid and a divalent alcohol having 2 to 8 carbon atoms, having a glass transition temperature of 10°C or more and 40°C or less, and having a hydroxyl value of 10 mgKOH / g or more and 90 mgKOH / g or less, wherein the melamine resin (E) contains a fully alkylated melamine resin, wherein the acid catalyst (F) is a catalyst having no counter ion, and wherein the amine compound (G) contains a secondary amine compound.

[0011] According to the solvent-based base paint composition of the present disclosure, it has been found that a solvent-based base paint composition having good reduction of energy load during film formation and storage stability while maintaining the appearance of the obtained coating film can be provided. The present disclosure should not be construed as being limited to a specific theory, but the reason why the solvent-based base paint composition of the present disclosure can exhibit such effects is considered as follows.

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

[0013] [Base Paint Composition] The base paint composition according to the embodiments of the present disclosure includes a pigment (A), a film-forming resin (B) (the film-forming resin (B) includes a hydroxyl group-containing acrylic resin (B1) and a hydroxyl group-containing acrylic resin (B2)), a blocked isocyanate compound (C), a melamine resin (E), polymer crosslinked fine particles (D) that are insoluble in the hydroxyl group-containing acrylic resin (B1) and are stably dispersed, an acid catalyst (F), and an amine compound (F). The hydroxyl group-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 group-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 one or more selected from the group consisting of a coloring pigment and a flaky pigment.

[0015] Examples of the coloring pigment 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, metal complex pigments, etc. Examples of the inorganic pigments include lead yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide, etc.

[0016] Examples of the flaky pigment include metal flakes, metal oxide flakes, pearl pigments, mica, etc. Examples of the metal flakes include aluminum, chromium, gold, silver, copper, brass, titanium, nickel, nickel chromium, stainless steel, etc. Examples of the metal oxide flakes include oxides of metal flakes, such as alumina, chromium oxide, etc. In an embodiment where the base paint composition contains a flaky pigment, a metallic luster can be imparted to the base coating film, and as described later, the color tone changes more significantly depending on the angle of observing the base coating film, that is, a base coating film with high flip-flop property (hereinafter sometimes referred to as "FF property") can be formed.

[0017] In order to easily prevent the reaction of metal flakes, metal oxide flakes, pearl pigments, etc. with water to generate gas, a metal coating, for example, a coating of a metal compound such as molybdic acid, chromic acid, yttrium, and rare earth metals, or an organic polymer coating, for example, an organic polymer coating obtained using a polymerizable monomer, etc. may be formed on the metal flakes, metal oxide flakes, and pearl pigments. For example, the metal flakes, metal oxide flakes, and pearl pigments may have a coating 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 a mixture or combination thereof. Incidentally, for example, when using chromium oxide or the like, the toxicity can be removed by using a chemically inactivated one.

[0018] The flaky pigment may include a vapor-deposited metal pigment. Such a flaky pigment is generally obtained by vapor-depositing a metal thin film (metal oxide thin film) on a base film, peeling off the base film, and then pulverizing the vapor-deposited metal film into metal flakes (metal oxide flakes). As the metal material to be vapor-deposited, for example, the materials described above for the metal flakes and metal oxide flakes can be used. In this embodiment, the flaky 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. Also for the vapor-deposited metal pigment, the above-described coating may be formed on its surface as necessary.

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

[0020] The content of the pigment (A) is not particularly limited. For example, the pigment concentration of the pigment (A), that is, the mass ratio of the pigment (A) to the resin solid content of the base paint composition may be 1% by mass or more and 20% by mass or less. The resin solid content of the base paint composition means the solid content of the film-forming resin (B), the blocked isocyanate compound (C), the melamine resin (E), and other curing agents that may be included. In the present disclosure, the solid content of a certain component may mean the heating residue when the component is heated at 110°C for 1 hour.

[0021] The base paint composition may contain an extender pigment. Examples of the extender pigment include calcium carbonate, barium sulfate, clay, talc, etc.

[0022] When using an extender pigment, one kind may be used alone, or two or more kinds may be used in combination. When the base paint composition contains an extender pigment, the content of the extender pigment, for example, the mass ratio of the extender pigment to the resin solid content of the base paint composition may be 0.1% by mass or more and 20% by mass or less.

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

[0024] By including the hydroxyl group-containing acrylic resin (B1), even when the solid content of the base paint composition is as high as 35% by mass or more, the coating viscosity does not become too high, so that unevenness of the coating film can be reduced. Further, when the base paint composition contains a flaky pigment, the orientation of the flaky pigment is less likely to be disturbed, so that excellent FF properties (flip-flop properties: properties in which the light and shade of the coating film surface change depending on the viewing angle) can be obtained. The upper limit of the solid content of the base paint composition is not particularly limited, and 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 product of a monoester compound of (meth)acrylic acid and a divalent alcohol having 2 to 8 carbon atoms, it has a long-chain structure having a hydroxyl group in the side chain. Thereby, the reactivity with the isocyanate compound (C) as a curing agent can be enhanced, and the adhesion between the object to be coated and the base coating film, or the adhesion between the intermediate coating film or primer coating film provided on the object to be coated and the base coating film can be enhanced. For example, when the object to be coated is made of plastic, the base paint composition according to the embodiment of the present disclosure can form a base coating film having good adhesion to the object to be coated without providing a primer coating film on the object to be coated.

[0026] The hydroxyl group-containing acrylic resin (B1) can be obtained by polymerizing one or more monomers containing a 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 monoester compounds of (meth) acrylic acid and a divalent alcohol having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate, with a lactone such as ε-caprolactone. In this specification, “(meth)acrylic” means both acrylic and methacrylic.

[0028] The above hydroxyl group-containing monomer (b) preferably includes a lactone-modified product of a monoester compound of (meth) acrylic acid and a divalent alcohol having 2 to 8 carbon atoms. In the above hydroxyl group-containing monomer (b), the content of the lactone-modified product of the monoester compound of (meth) acrylic acid and a divalent alcohol having 2 to 8 carbon atoms 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 still more preferably 95% by mass or more and 100% by mass or less in 100% by mass of the above hydroxyl group-containing monomer (b).

[0029] The hydroxyl group-containing acrylic resin (B1) may be a polymer of a hydroxyl group-containing monomer (b) and another monomer other than the hydroxyl group-containing monomer (b). In such an embodiment, the hydroxyl group-containing acrylic resin (B1) is obtained by polymerizing a monomer mixture of the hydroxyl group-containing monomer (b) and the above other monomer. In the above monomer mixture, the hydroxyl group-containing monomer (b) is preferably 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 still more preferably 10% by mass or more and 20% by mass or less in the total of the hydroxyl group-containing monomer (b) and the other monomer.

[0030] As monomers other than the hydroxyl group-containing monomer (b), for example, 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, 2-acrylamido-2-methylpropanesulfonic acid, etc. can be mentioned.

[0031] Also, as monomers other than the hydroxyl group-containing monomer (b), for example, (meth)acrylate 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, dicyclopentadienyl (meth)acrylate, dihydrodicyclopentadienyl (meth)acrylate, etc.), polymerizable aromatic compounds (e.g., styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, and vinyl naphthalene, etc.), polymerizable nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), α-olefins (e.g., ethylene, propylene, etc.), vinyl esters (e.g., vinyl acetate, vinyl propionate, etc.), dienes (e.g., butadiene, isoprene, etc.), etc. can be mentioned. From the viewpoint of enhancing water resistance, it is preferable to use styrene.

[0032] Furthermore, as monomers other than the hydroxyl group-containing monomer (b), for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, etc. can be mentioned.

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

[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) method using polystyrene as a standard.

[0035] The glass transition temperature of the hydroxyl group-containing acrylic resin (B1) may preferably be 10°C or higher and 40°C or lower, more preferably 10°C or higher and 35°C or lower, and still 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 group-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 still more preferably 20 mgKOH / g or more and 50 mgKOH / g or less. Further, the acid value of the hydroxyl group-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 the acid value are values in terms of solid content and may be measured or calculated by a known method. For example, the hydroxyl value and the acid value may be measured in accordance with JIS K 0070:1992.

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

[0038] [Acrylic resin (B2)] The base paint composition contains an acrylic resin (B2) having a weight average molecular weight of 3,000 or more and 7,500 or less. Thereby, the viscosity of the base paint composition can be adjusted more easily.

[0039] The acrylic resin (B2) can be obtained by polymerizing monomers. As the monomers, for example, the hydroxyl group-containing monomers (b) and other monomers described above for the hydroxyl group-containing acrylic resin (B1) may be used.

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

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

[0042] As the acrylic resin (B2), only one kind may be used, or two or more kinds may be used in combination. The content of the acrylic resin (B2) is not particularly limited. For example, it may be 10% by mass or more and 50% by mass or less in the resin solid content of the base paint composition. When the blending amount of the acrylic resin (B2) is large, the viscosity of the paint tends to be low. When the blending amount of the acrylic resin (B2) is within the above range, the viscosity of the paint is not too high, the adverse effects that may occur during painting are suppressed, the viscosity of the paint does not become too low, the physical properties of the paint film are good, and the adhesion and water resistance can be improved.

[0043] In the above base paint composition, the total content of the solid components 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, still more preferably 95% by mass or more and 100% by mass or less in 100% by mass of the total amount of the solid components of the film-forming resin (B).

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

[0045] [Block isocyanate compound (C)] By using the block isocyanate compound (C) together with the hydroxyl group-containing acrylic resin (B1), the adhesion between the object to be coated and the base coating film, or the adhesion between the intermediate coating film or primer coating film provided on the object to be coated and the base coating film can be enhanced. Further, when the base coating film crosslinks, the physical properties of the coating film are improved and the water resistance performance is improved.

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

[0047] Examples of the polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimers), pentamethylene diisocyanate, tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate); aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate; modified products of these diisocyanates (urethane compounds, carbodiimides, uretdiones, uretonimines, biurets and / or isocyanurate modified products, etc.).

[0048] As the blocking agent, for example, monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, methylphenyl carbinol, etc.; cellosolves such as ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, etc.; polyether type diols at both ends such as polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol phenol, etc.; polyester type polyols at both ends obtained from diols such as ethylene glycol, propylene glycol, 1,4-butanediol, etc. and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, sebacic acid, etc.; phenols such as para-t-butylphenol, cresol, etc.; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, cyclohexanone oxime, etc.; and lactams represented by ε-caprolactam, γ-butyrolactam are preferably used. As the blocking agent, alkyl esters which are active hydrogen compounds such as methyl diketone, methyl ketoester and methyl diester compounds, for example, acetylacetone, ethyl acetoacetate, diethyl malonate, etc. may be used. Also, blocked isocyanate using an imidazole compound or a pyrazole compound may be used.

[0049] The blocking rate of the blocked isocyanate compound (C) is preferably 100%. Thereby, there is an advantage that the storage stability of the base paint composition becomes better.

[0050] Two or more kinds of the blocked isocyanate compound (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 the isocyanate group of the blocked isocyanate compound (C) to the number of moles of the hydroxyl group of the hydroxyl group-containing acrylic resin (B1) may be 0.2 / 1.0 to 0.6 / 1.0, preferably 0.3 / 1.0 to 0.5 / 1.0.

[0051] [Melamine resin (E)] The above melamine resin (E) is a compound having two or more groups capable of reacting with the hydroxyl groups of the film-forming resin (B) (hydroxyl group-containing acrylic resin (B1) and hydroxyl group-containing acrylic resin (B2)) in one molecule, and can form a film by undergoing a crosslinking reaction with the above film-forming resin (B) (hydroxyl group-containing acrylic resin (B1) and hydroxyl group-containing acrylic resin (B2)). By including the melamine resin (E) in the base paint composition, the storage stability and various physical properties (processability, scratch resistance) of the resulting coating film can be improved.

[0052] 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 or its polycondensate as reactive functional groups in one molecule of the triazine nucleus. -NX1X2 [X1 and X2 each independently represent a hydrogen atom, a methylol group or -CH2-OR 1 . 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. When a plurality of -CH2-OR 1 are included in the same molecule, the plurality of R 1 may be the same or different.]

[0053] Examples of the melamine resin include a fully alkyl type containing only -N(CH2OR 1 )2 as a reactive functional group; a methylol group type containing -N(CH2OR 1 )(CH2OH) as a reactive functional group; an imino group type containing -N(CH2OR 1 )(H) as a reactive functional group; and a methylol / imino group type containing -N(CH2OR 1 )(CH2OH) and -N(CH2OR 1 )(H), or containing -N(CH2OH)(H). R 1is preferably an alkyl group having 1 to 4 carbon atoms, more 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 both represent a compound of -CH2-OR 1 or a fully alkylated melamine resin (E1) which is a polycondensate thereof. Examples of the fully alkylated melamine resin (E1) include methylated melamine resin, butylated melamine resin, isobutylated melamine resin and the like. By including the fully alkylated melamine resin (E), the resulting base paint composition has good storage stability and good reactivity with the film-forming resin (B) in the presence of high temperature and a catalyst.

[0055] The degree of polymerization of the above fully alkylated melamine resin (E1) is 1 or more, preferably 1.2 or more, more preferably 1.5 or more, preferably 10 or less, more preferably 5 or less, and still more preferably 3 or less.

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

[0057] As the above-mentioned fully alkylated melamine resin (E1), commercially available products can also be used. Examples of such commercially available products include Resimene 745, Resimine 751, Resimine 755, Resimine CE-6550, Resimine CE-7103, Resimine 747 (all from Prefere Resins), Cymel 303, Cymel 325, Cymel 350, Cymel 370, Mycote 715 (all methylated melamine resins, manufactured by Ornex Japan), Cymel 202, Cymel 235, Cymel 254, Cymel 1123, Cymel 1128, Cymel 1170, Mycote 212 (all methyl-butylated mixed melamine resins, manufactured by Ornex Japan), Sumimar M-40S (methylated melamine resin, manufactured by Sumitomo Chemical), Amidia J-820-60, Amidia L-127-60 (both butylated melamine resins, manufactured by DIC), and the like. These may be used alone or in combination of two or more.

[0058] The content of the fully alkylated melamine resin (E1) in the above-mentioned melamine resin (E) is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and the upper limit is 100% by mass.

[0059] As the above-mentioned melamine resin (E), only one kind may be used, or two or more kinds may be used in combination.

[0060] The ratio ((E) / (B)) of the content of the melamine resin (E) to the total solid content of the above-mentioned film-forming resin (B) is preferably 3 / 97, more preferably 5 / 95 or more, preferably 30 / 70 or less, and more preferably 20 / 80 or less on a mass basis. Being within the above range has the advantage that the processability and scratch resistance of the resulting coating film become good.

[0061] The mass ratio of the content of the above-mentioned blocked isocyanate compound (C) and melamine resin (E) is preferably in the range of blocked isocyanate compound (C):melamine resin (E) of 2:1 to 1:4, more preferably in the range of 2:1 to 1:3, and even more preferably in the range of 1:1 to 1:3.

[0062] The content of the above-mentioned 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, based on 100 parts by mass of the total resin solids in the base paint composition.

[0063] The base paint 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 melamine resin (E). When containing other curing agents other than the isocyanate compound (C) and melamine resin (E), the content of the other curing agent is, for example, 10 parts by mass or more and 30 parts by mass or less based on 100 parts by mass of the resin solids of the base paint composition.

[0064] [Acid catalyst (F)] The above-mentioned acid catalyst (F) can act as a catalyst for promoting the reaction between the above-mentioned hydroxyl group-containing acrylic resin (B1) and melamine resin (E). Therefore, there is an advantage that high reactivity can be imparted to the obtained base paint composition.

[0065] The above-mentioned 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 above-mentioned sulfonic acid compound include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. As the above-mentioned sulfonic acid compound, only one kind may be used, or two or more kinds may be used in combination.

[0066] The content rate of the sulfonic acid compound can preferably be 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, still more preferably 95% by mass or more and 100% by mass or less in 100% by mass of the acid catalyst (F).

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

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

[0069] [Amine compound (G)] The amine compound (G) has an action of neutralizing the acid catalyst (F), and by coexisting with the acid catalyst (F), there is an advantage that both the stability during storage of the base paint composition (for example, 15 to 50 °C) and the high reactivity during heating, drying, and curing after coating can be achieved. A part of the amine compound (G) may exist in the form of forming 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 contain a tertiary amine compound.

[0071] Further, the substituent of the nitrogen atom of the above 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 -CH2- contained in the saturated or unsaturated aliphatic hydrocarbon group may be replaced with -O-. Further, the substituents of the nitrogen atom of the above amine compound may be bonded to each other to form a ring containing the nitrogen atom.

[0072] Examples of the above 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, diallylamine; tertiary aliphatic amine compounds such as triethylamine, tributylamine, triallylamine, N,N-dimethylethanolamine, N-methyldiallylamine, N,N-dimethylallylamine; secondary cyclic amine compounds such as piperidine, 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,4-lupeptide, 2,6-lupeptide, 3,5-lupeptide, 3-piperidinemethanol; tertiary cyclic amine compounds such as N-methylpiperidine, N-methylpiperazine, N-methylmorpholine; and amine compounds which are aromatic compounds such as pyridine, 4-ethylpyridine.

[0073] The boiling point of the above amine compound (G) is 70°C or higher, preferably 80°C or higher, preferably 115°C or lower, more preferably 111°C or lower, and even more preferably 100°C or lower. When the boiling point of the amine compound (G) is within the above range, there is an advantage that the storage stability of the above base paint composition can be further enhanced.

[0074] The content of the above amine compound (G) is preferably in the range where the neutralization rate of the above sulfonic acid compound (G) by the above amine compound (G), that is, the neutralization rate in terms of moles determined by the following formula, is 50% or more and 350% or less, more preferably in the range of 80% or more and 300% or less, and even more preferably in the range of 150% or more and 250% or less. Neutralization rate (%) = [(basic valence number of amine compound (G) × number of moles of amine compound (G)) / (acid value number of acid catalyst (F) × number of moles of acid catalyst (F))] × 100

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

[0076] The content of the above amine compound (G) can be preferably 0.1 part by mass or more and 0.8 part by mass or less, more preferably 0.1 part by mass or more and 0.5 part by mass or less, and even more preferably 0.1 part by mass or more and 0.3 part by mass or less, based on 100 parts by mass of the total resin solids of the base paint composition (the total resin solid content of the above hydroxyl group-containing acrylic resin (B1), hydroxyl group-containing acrylic resin (B2), blocked isocyanate compound (C) and melamine resin (E)).

[0077] The above-mentioned fully alkylated melamine resin (E1) is known to have lower reactivity compared to melamine resins generally used as crosslinking agents such as imino group-containing melamine resins and methylol group-containing melamine resins. However, as a result of the studies by the present inventors, it has been found that the low reactivity of the above-mentioned fully alkylated melamine resin (E1) is in the case of low-temperature reactions (for example, 60 to 80 °C), and when the fully alkylated melamine resin (E1), the above-mentioned acid catalyst (F), and the above-mentioned amine compound (G) are used so as to achieve the above-mentioned neutralization rate, the reactivity at high temperatures is increased. By combining the above-mentioned fully alkylated melamine resin (E1), the above-mentioned acid catalyst (F), the above-mentioned amine compound (G), and the above-mentioned neutralization rate, a base paint composition having good storage stability and particularly suitable for high-temperature and short-time coating can be obtained. Furthermore, since the crosslinking density can be increased, there is an advantage that a coating film excellent in coating film processability (adhesion, crack resistance) can be obtained.

[0078] The above-mentioned acid catalyst (F) and the above-mentioned amine compound (G) may be directly used in the preparation of the base paint composition, or may be used in the preparation of the base paint composition as a mixture obtained by previously mixing these. At this time, in the above-mentioned mixture, a part or all of the above-mentioned acid catalyst (F) and the above-mentioned 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 an amino group contained in the amine compound (G)). After forming a salt of a part or all of the sulfonic acid compound (C) and the amine compound (G), it may be blended into the base paint composition. Examples of the salt of a part or all of the above-mentioned acid catalyst (F) and the above-mentioned amine compound (G) include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as dinonylnaphthalene disulfonic acid and dinonylnaphthalene sulfonic acid, and amine-blocked products thereof. As the salt of a part or all of the above-mentioned acid catalyst (F) and the above-mentioned amine compound (G), commercially available products can also be used.

[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, and the neutralization rate is preferably 100% or more and 1,300% or less, based on 100 parts by mass of the total resin solid content of the hydroxyl group-containing acrylic resin (B1), hydroxyl group-containing acrylic resin (B2), blocked isocyanate compound (C), and melamine resin (E); more preferably, the content of the acid catalyst (F) is 0.1 part by mass or more and 5 parts by mass or less, and the neutralization rate is 200% or more and 1,000% or less, based on 100 parts by mass of the total resin solid content; still more preferably, the content of the acid catalyst (F) is 2 parts by mass or more and 9 parts by mass or less, and the neutralization rate is 300% or more and 900% or less, based on 100 parts by mass of the total resin solid content. By having the acid catalyst (F), the amount of the amine compound (G), and the neutralization rate as described above, the base paint composition has high storage stability at low temperatures (storage temperature, for example, 15 to 30°C), higher reactivity at high temperatures, and better processability (adhesion, crack resistance) and scratch resistance of the resulting coating film.

[0080] [Polymer crosslinked fine particles (D)] The polymer crosslinked fine particles (D) can act as a viscosity modifier and contribute to the adjustment of the viscosity described later. Usually, since the paint is thinned by the shear force applied during painting, the viscosity immediately after coating is lower than the viscosity before painting. Therefore, if the viscosity after coating is low, the paint will drip downward, causing unevenness in the coating film. The base paint composition according to the embodiment of the present disclosure contains the polymer crosslinked fine particles (D), so that the viscosity thinned during painting can be quickly restored and increased, the base paint composition applied to the object to be coated can be prevented from dripping, and unevenness in the coating film can be reduced.

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

[0082] [Polymer crosslinked fine particles (D) by emulsion polymerization] The polymer crosslinked fine particles (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 form an emulsion containing crosslinked polymer fine particles, and then removing water by solvent substitution, azeotropy, centrifugation, filtration, drying, or the like. The emulsion polymerization may be carried out using a known emulsifier and / or dispersant, but it is preferable to use an emulsifier having an amphoteric ion group. When the polymer crosslinked fine particles (D) are added to the base paint composition, the structural viscosity varies depending on the particle size, so it is important to obtain a uniform particle size. However, the use of an emulsifier having an amphoteric ion group makes it easy to obtain polymer crosslinked fine particles with a uniform particle size.

[0083] Examples of the ethylenically unsaturated monomer used in the preparation of the polymer crosslinked 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, and other monomers having an ethylenically unsaturated bond copolymerizable 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 ethylenically unsaturated group-containing monomers each carrying a group capable of reacting with each other.

[0085] Examples of the monomer 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. Examples of these compounds are as follows.

[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 allyloxydimethacrylate, 1,1,1-tris(hydroxymethyl)ethane diacrylate, 1,1,1-tris(hydroxymethyl)ethane triacrylate, 1,1,1-tris(hydroxymethyl)ethane dimethacrylate, 1,1,1-tris(hydroxymethyl)ethane trimethacrylate, 1,1,1-tris(hydroxymethyl)propane diacrylate, 1,1,1-tris(hydroxymethyl)propane triacrylate, 1,1,1-tris(hydroxymethyl)propane dimethacrylate, 1,1,1-tris(hydroxymethyl)propane trimethacrylate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl terephthalate, diallyl phthalate and divinylbenzene.

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

[0088] The monomers constituting the polymer crosslinked fine particles (D) may contain monomers having functional groups capable of reacting with a crosslinking agent. 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, methacrylalcohol, and nitrogen-containing ones such as acrylamide and methacrylamide.

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

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

[0091] As other radically polymerizable unsaturated monomers other than the radically polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group contained in the above monomer mixture, for example, 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, 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, benzyl methacrylate; Aromatic vinyl monomers such as styrene, vinyltoluene, ethylvinylbenzene; Carboxyl group-containing monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, citraconic acid; Amide group- or substituted amide group-containing monomers such as acrylamide, methacrylamide, N,N-dimethylacrylamide, N-methylacrylamide, N-n-butoxymethylacrylamide; Hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, 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, N,N-diethylaminoethyl methacrylate; Epoxy group-containing monomers such as glycidyl methacrylate, glycidyl acrylate, glycidyl allyl ether, glycidyl methallyl ether, glycidyl vinyl ether; Mercapto group-containing monomers such as vinyl mercaptan, allyl mercaptan; 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, divinylbenzene; And the like.

[0092] Among the above other radically polymerizable unsaturated monomers, for example, 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.), Substituted amino group-containing monomers (preferably N,N-di-lower alkylamino-lower alkyl (meth)acrylates such as N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl methacrylate, etc.), It is preferably included one or more selected from the group consisting of.

[0093] The amount of the 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 or more and 30 parts by mass or less, more preferably in the range of 5 parts by mass or more and 15 parts by mass or less, based on 100 parts by mass of the total amount of the monomer mixture. Further, the total amount of the acrylate monomer and the methacrylate monomer, contained in the monomer mixture, is preferably in the range of 50 parts by mass or more and 90 parts by mass or less, based on 100 parts by mass of the total amount of the monomer mixture. Also, the amount of the carboxyl group-containing monomer, contained in the monomer mixture, is preferably in the range of 10 parts by mass or less. Furthermore, the amount of the substituted amino group-containing monomer, contained in the monomer mixture, is preferably in the range of 10 parts by mass or less. When the polymer crosslinked fine particles (D) of the present disclosure are prepared by multi-stage polymerization, the amount of the monomer contained in the monomer mixture is the total amount of the monomers used in each polymerization.

[0094] The polymerization conditions for preparing the polymer crosslinked fine particles (D) can be appropriately selected by those skilled in the art according to the types and amounts of the monomers used. For example, using an appropriate polymerization initiator and a chain transfer agent used as necessary, heating and reacting with stirring for several hours in a nitrogen stream or at the reflux temperature of an organic solvent, the monomer mixture is preferably polymerized so as to be within the range of the weight average molecular weight described below. The polymerization temperature is generally 30°C or higher and 180°C or lower, preferably 60°C or higher and 150°C or lower.

[0095] Examples of the organic solvent used in the polymerization include Aliphatic or alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, "Rouse", "Mineral Spirit EC", "Shellsol 71", "VM&P Naphtha", "Shell TS28 Solvent" (manufactured by Shell), "Isopar C", "Isopar E", "Isopar G", "Isopar H", "Isopar M", "Naphtha No. 3", "Naphtha No. 5", "Naphtha No. 6", "Solvent No. 7" (manufactured by Exxon Chemical), "IP Solvent 1016", "IP Solvent 1620", "IP Solvent 2028", "IP Solvent 2835" (manufactured by Idemitsu Kosan Co., Ltd.), "Whitezol" (manufactured by Japan Energy Corporation), "Mitsubishi Mineral Turpentine", "Diamond Solvent", "Pegazol AN-45", "Pegazol 3040" (manufactured by JXTG Energy Corporation), etc.; 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), "Solvesso 150" (manufactured by Exxon Chemical), etc.; Ketone organic solvents such as acetone, acetylacetone, methyl ethyl ketone, methyl i-butyl ketone, methyl amyl ketone, cyclohexanone, etc.; Ester organic solvents such as methyl acetate, ethyl acetate, n-butyl acetate, aluminum acetate, etc.; 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, benzyl cellosolve, etc.; Carbitol 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, benzyl carbitol, etc.; And the like can be mentioned.

[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; azo compounds such as 2,2'-azobis-i-butyl nitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile. These may be used alone or in combination of two or more. The amount of the polymerization initiator used is generally preferably 0.5 parts by mass or more and 15 parts by mass or less, more preferably 2 parts by mass or more and 8 parts by mass or less, based on 100 parts by mass of the total amount of the monomers. When the polymer crosslinked fine particles (D) of the present disclosure are prepared by multi-stage polymerization, the preferable range of the amount of the polymerization initiator used can be applied to each polymerization.

[0097] In the preparation of the polymer crosslinked fine particles (D), when the monomer mixture is subjected to two-stage polymerization, 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 polymer crosslinked fine 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 or more and 100,000 or less, 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 microparticles (D) have a dissolved portion and a particulate portion, the mass ratio of the dissolved portion to the particulate portion is preferably in the range of dissolved portion:particulate portion = 20:80 to 80:20, more preferably in the range of 30:70 to 70:30.

[0100] As another example of the preparation of the crosslinked polymer microparticles (D), there is an example in which a monomer mixture not containing a radically polymerizable unsaturated monomer having a pendant side chain containing a higher unsaturated aliphatic group is polymerized, and a pendant side chain containing a higher unsaturated aliphatic group is introduced into the obtained copolymer. Specifically, for example, a monomer mixture containing an alkylene group-containing monomer is polymerized, and then a pendant side chain containing a higher unsaturated aliphatic group can be introduced by reacting the carboxyl group of a higher unsaturated fatty acid with the alkylene group of the obtained copolymer.

[0101] The compounding amount of the crosslinked polymer microparticles (D) in the base paint composition is generally 5 to 40 parts by mass, preferably 10 to 30 parts by mass, per 100 parts by mass of the total solid content of the film-forming resin (B), the blocked isocyanate compound (C), and the melamine resin (E). If the compounding amount of the crosslinked polymer microparticles (D) is too small, the sagging property of the base paint composition and, in the case of wet-on-wet coating, the penetration into the lower layer paint composition becomes large and the initial purpose cannot be achieved. On the other hand, if the compounding amount is too large, the film performance deteriorates and the smoothness of the film is impaired, and a high-quality finish appearance cannot be obtained.

[0102] Examples of commercially available crosslinked polymer microparticles (D) include Setalux 1801, 1850, SA-50, and 53 (manufactured by Allnex).

[0103] In the solid content of the above base paint composition, the total content of the pigment (A), the film-forming resin (B), the blocked isocyanate compound (C), the crosslinked polymer microparticles (D), the melamine resin (E), the acid catalyst (F), and the amine compound (G) is, for example, preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and the upper limit is 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, aliphatic hydrocarbons, and the like.

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

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

[0107] The base paint composition of the present disclosure, when measuring the viscosity V1 at a shear rate of 0.1 / sec at 23°C using a cone and plate viscometer, then changing the shear rate from 0.1 / sec to 25,000 / sec and shearing for 30 seconds, and then returning to 0.1 / sec and shearing for 1 second and measuring the viscosity V2, 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 more preferable. The viscosity recovery rate represents the ratio of the viscosity at the weak shear point to the viscosity at the strong shear point, and a high viscosity recovery indicates that the viscosity recovers immediately even immediately after painting. The base paint composition of the present disclosure has a viscosity that recovers rapidly even immediately after painting. The above viscosity recovery rate V2 / V1 may preferably be 90% or more and 100% or less, more preferably 90% or more and 95% or less.

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

[0109] [Painted article] The painted article according to an embodiment of the present disclosure a substrate to be coated, and includes a base paint film formed from the solvent-based base paint composition according to an embodiment of the present disclosure.

[0110] The painted article according to an embodiment of the present disclosure may include a multi-layer paint film including an intermediate paint film or a primer paint film provided on the substrate to be coated, a base paint film provided on the intermediate paint film or the primer paint film, and a clear paint film provided on the base paint film.

[0111] In one aspect, the painted article according to the embodiment of the present disclosure may not have an intermediate coating film or a primer coating film, and a base coating film may be provided on the object to be painted. That is, in this aspect, the painted article according to the embodiment of the present disclosure may include a multi-layer coating film including a base coating film provided on the object to be painted and a clear coating film provided on the base coating film. For example, when the object to be painted is made of plastic, the base paint composition according to the embodiment of the present disclosure can form a base coating film having good adhesion to the object to be painted without providing a primer coating film on the object to be painted.

[0112] [Object to be painted] The object to be painted is not particularly limited, and examples include metal substrates, plastic substrates, and foams thereof.

[0113] Examples of the metal substrate include metals such as iron, steel, copper, aluminum, tin, zinc, and alloys containing these metals. Specifically, examples of the metal substrate include automobile bodies such as passenger cars, trucks, motorcycles, buses, and parts for automobile bodies. It is preferable that such a metal substrate has an electrodeposition coating film formed thereon in advance. Further, before forming the electrodeposition coating film, chemical conversion treatment (for example, zinc phosphate chemical conversion treatment, zirconium chemical conversion treatment, etc.) may be performed as necessary.

[0114] Examples of the plastic resin substrate include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, etc. Specifically, examples of the plastic substrate include automobile parts such as spoilers, bumpers, mirror covers, grills, door knobs, etc. It is preferable that these plastic substrates are 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 object to be coated is a metal substrate, an intermediate coating film may be provided on the metal substrate on which electrocoating is formed. Further, when the object to be coated 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 each 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 or the like.

[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 film-forming resin and, if necessary, a curing agent or the like. Further, the clear coating film may 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 the solvent-based clear coating composition include, from the viewpoints of transparency or acid etching resistance, etc., 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 film-forming resin. Further, a two-component clear coating with isocyanate as a crosslinking agent is more preferred. In particular, the isocyanate of the clear coating penetrates into the colored base coating layer and cures to form a multilayer coating film with excellent water resistance.

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

[0119] The clear coating composition may contain a viscosity control agent. Examples of the viscosity control agent include crosslinked or non-crosslinked resin particles, a swollen dispersion of a fatty acid amide, an amide-based fatty acid, polyamide-based ones such as a phosphate of a long-chain polyaminoamide, polyethylene-based ones such as a colloidal swollen dispersion of polyethylene oxide, organoacid smectite clay, organobentonite-based ones such as montmorillonite, and the like.

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

[0121] [Method for manufacturing a coated article] The base coating composition of the present disclosure is applied to an object to be coated by the same coating method as a normal base coating. The base coating composition is applied onto an object to be coated provided with an intermediate coat film or a primer coat film. Further, a clear coating is applied on the base coat film to form a clear coat film. The coating film forming method may be a generally used method, and it is applied using a spray coater to form a so-called wet-on-wet uncured coating film, and then 2 to 3 layers may be cured simultaneously.

[0122] The coating methods for the intermediate coating composition, the primer coating composition, the base aqueous coating composition, and the clear coating composition are not particularly limited. Depending on the type of the object to be coated, for example, multi-stage coating or one-stage coating by air spray coating, bell coating, air electrostatic spray coating, or a coating method combining air electrostatic spray coating and a rotary atomization type electrostatic coater called a metallic bell, or other coating methods generally used in the coating field may be used.

[0123] Examples of the heating device used for heat-curing the uncured coating film include a drying oven using a heat source such as hot air, electricity, gas, infrared rays, etc. Further, it is preferable to use a drying oven using two or more of these heat sources in combination because the drying time is shortened.

[0124] The painted article according to the embodiment of the present disclosure can also be manufactured by heat-curing the coating film each time each coating composition is applied and sequentially forming the upper-layer coating film. Further, the painted article according to the embodiment of the present disclosure can be manufactured in a mode that omits the steps of forming the intermediate coating film and the primer coating film and does not include the intermediate coating film and the primer coating film.

Example

[0125] The present disclosure will be described in more detail with the following 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 reaction apparatus equipped with a stirring blade, a thermometer, a dropping device, a temperature control device, a nitrogen gas inlet, and a cooling pipe, and the temperature was raised to 120° C. with stirring while introducing nitrogen gas. Next, a mixture consisting of 0.5 part 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 prepared by dissolving 2.0 parts of t-butylperoxy-2-ethylhexanoate in 5 parts of butyl acetate were dropped into the reaction apparatus over 3 hours. After the dropping was completed, the mixture was aged for 1 hour, and then a solution prepared by dissolving 0.2 part of t-butylperoxy-2-ethylhexanoate in 5 parts of butyl acetate was dropped into the reaction apparatus over 1 hour, and the reaction was aged for 2 hours while maintaining the temperature at 120° C. to complete the reaction. The nonvolatile content of the obtained hydroxyl group-containing resin was 60%, the weight average molecular weight was 13,400, the glass transition temperature was 20° C., and the hydroxyl value was 30 mgKOH / g. Table 1 shows the compounding monomer components, characteristic values, and the amounts of the first and second stages of the polymerization initiator (t-butylperoxy-2-ethylhexanoate).

[0127] (Production Examples 1-2 to 1-3) Production of Hydroxyl Group-Containing Acrylic Resins (B1-2 to B1-3) Using the same reaction apparatus as in Production Example B1-1 and with the formulations described in Table 1, hydroxyl group-containing acrylic resins of Production Examples B1-2 to B1-3 were obtained by the same operations. Table 1 also shows the characteristic values and the like of the obtained hydroxyl group-containing acrylic resins (B-2 to B-3).

[0128]

Table 1

[0129] (Production Example 2) Production of Hydroxyl Group-Containing Acrylic Resin (B2) Using the same reactor as in Production Example 1-1 and with the formulation described in Table 2, a hydroxyl group-containing acrylic resin (B2) was obtained by the same operation. The characteristic values (weight-average molecular weight, heating residue amount, polymerization initiator amounts in the first and second stages) are listed in Table 2.

[0130]

Table 2

[0131] Reference Example 1 Production Method of Polyester Resin Having Both Ionic Groups Into a 2 L Kolben equipped with a stirrer, nitrogen inlet tube, temperature controller, condenser, and decanter, 134 parts of bis(hydroxyethyl)taurine, 130 parts of neopentyl glycol, 236 parts of azelaic acid, 186 parts of phthalic anhydride, and 27 parts of xylene were charged and the temperature was raised. The water generated by the reaction was removed by azeotropic distillation with xylene. The temperature was raised to 190 °C over about 2 hours from the start of reflux, and stirring and dehydration were continued until the carboxylic acid equivalent oxidation reached 145, and then it was cooled to 140 °C. Next, while maintaining the temperature at 140 °C, 314 parts of "Cardura E10" (glycidyl ester of pertic acid manufactured by Shell) was added dropwise over 30 minutes, and then stirring was continued for 2 hours to complete the reaction. The obtained polyester resin had an acid value of 59, a hydroxyl value of 90, and a Mn of 1054.

[0132] (Production Example 3) Method for Producing Polymer Crosslinked Fine Particles (D) In a 1 L reaction vessel equipped with a stirrer, a cooler, and a temperature control device, 281 parts of deionized water, 30 parts of the polyester resin obtained in Reference Example 1 above, and 3 parts of dimethylethanolamine were charged, and the mixture was dissolved while maintaining the stirring temperature at 80°C. To this, a solution prepared by dissolving 1.0 part of azobiscyanovaleric acid in 45 parts of deionized water and 0.9 part of dimethylethanolamine was added. 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, 0.5 part of azobiscyanovaleric acid dissolved in 15 parts of deionized water and 0.4 part of dimethylethanolamine was added, and stirring was continued at 80°C for another 2 hours to obtain an emulsion with a non-volatile content of 40% and a particle size of 0.12 μm. This emulsion was spray-dried to obtain polymer crosslinked fine particles. The polymer crosslinked fine particles were mixed with a solvent prepared by mixing methyl amyl ketone and xylene in a weight ratio of 1:1, and using an ultrasonic disperser, the heating residue was adjusted to 40% to obtain a stable dispersion solution of polymer crosslinked particles.

[0133] Examples 1 to 9 and Comparative Examples 1 to 8 By blending the raw materials according to the compositions (colored base paint formulations) shown in Tables 3 and 4 below and stirring, the base paint compositions of Examples 1 to 9 and Comparative Examples 1 to 8 were obtained. The units of the compositions in the table are parts by mass, and are the amounts in terms of solid content excluding the organic solvent. The amount of the polymer crosslinked fine particles (D) represents the amount relative to a total of 100 parts by mass of the hydroxyl group-containing acrylic resin (B1), hydroxyl group-containing acrylic resin (B2), blocked isocyanate compound (C), and melamine resin (E).

[0134] Preparation of Coating Paint The base paint compositions of Examples 1 to 9 and Comparative Examples 1 to 8 were adjusted so that the viscosity of Ford Cup No. 4 was 13 seconds at a paint temperature of 20°C using methyl amyl ketone / Solvesso 100 = 1 / 1 (weight ratio) as the diluting thinner.

[0135] Production of Coated Articles On the surface of a substrate made of ABS resin (70 mm × 150 mm × 3 mm) wiped with isopropyl alcohol, in an environment of 25°C / 70% relative humidity (RH), the base paint composition of Example 1 was spray-coated (dry film thickness: 25 μm) using a spray gun "Wider - 71" (manufactured by Anest Iwata Corporation), and set at room temperature for 5 minutes. On top of that, using RoboBell 951, 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) under the conditions of (gun distance: 200 mm, gun speed: 700 mm / s, rotation speed: 25000 rpm, shaping air pressure: 0.07 MPa). Then, after setting for 10 minutes, it was dried at 70°C for 10 minutes to produce the coated article of Example 1.

[0136] Except for using the base paint compositions of Examples 2 to 9 and Comparative Examples 1 to 8 shown in Table 3 and Table 4, coated articles of Examples 2 to 9 and Comparative Examples 1 to 8 were obtained in the same manner as in Example 1.

[0137] Using the obtained base paint compositions and coated articles, the following evaluations were conducted. The evaluation results are shown in the following table.

[0138] (Viscosity recovery rate [%]) Using a cone - plate type viscometer "DHR - 3" manufactured by TA Instruments, at 23°C, after measuring the viscosity V1 at a shear rate of 0.1 / sec, the shear rate was changed from 0.1 / sec to 25000 / sec and sheared for 30 seconds, and then the viscosity V2 after returning to a shear rate of 0.1 / sec and shearing for 1 second was measured. From the obtained V1 and V2, the viscosity recovery rate V2 / V1 [%] was calculated. The evaluation criteria are as follows, with ○ indicating pass and × indicating fail. ○: Viscosity recovery rate is 90% or more ×: Viscosity recovery rate is less than 90%

[0139] (Coating viscosity evaluation) The base paint compositions of the examples and comparative examples were adjusted to have a non-volatile content of 35% using methyl amyl ketone / solvesso 100 = 1 / 1 (weight ratio) as a diluting thinner. The viscosity (seconds) of Ford cup No. 4 was measured at a paint temperature of 20 °C and evaluated according to the following criteria. When the coating viscosity is 18 seconds or less, the coating workability is suitable and a coating film with good appearance can be formed. Evaluation criteria 〇: The number of seconds of Ford cup No. 4 at a non-volatile content of 35% is 18 seconds or less. ×: The number of seconds of Ford cup No. 4 at a non-volatile content of 35% exceeds 18 seconds.

[0140] (Adhesion evaluation) Test panels were prepared using the base paint compositions of the examples and comparative examples according to the above coating article preparation procedure. For the coating films of the obtained test panels, a cross-cut tape (registered trademark) peel test was conducted in accordance with JIS K5600-5-6:1999. One hundred 2 mm squares of cross-cuts were prepared, and the cross-cut tape peel test was performed, and the number of non-peeled cross-cuts was counted. The evaluation criteria are as follows, with 〇 being qualified and × being unqualified. 〇: 0 / 100 (no peeling) ×: 1 / 100 to 100 / 100 (peeling present)

[0141] (Water resistance) Test panels were prepared using the base paint compositions of the examples and comparative examples according to the above coating article preparation procedure. The obtained test panels were immersed in a water resistance tank at 40 °C for 240 hours. After the immersion, for the coating films of the test pieces taken out from the water resistance tank, within 1 hour after taking out, a cross-cut tape (registered trademark) peel test and appearance observation were conducted in accordance with JIS K5600-5-6:1999. One hundred 2 mm squares of cross-cuts were prepared, and the cross-cut tape peel test was performed, and the number of non-peeled cross-cuts was counted. Also, the appearance was checked for any abnormalities such as blisters. The evaluation criteria are as follows, with 〇 being qualified and × being unqualified. 〇: 0 / 100 (no peeling), no appearance abnormalities △: 0 / 100 (no peeling), with appearance abnormality ×: 1 / 100 - 100 / 100 (with peeling), regardless of appearance abnormality

[0142] (Storage stability) After preparing the base paint compositions of the examples and comparative examples, they were left standing at 40°C for 10 days. Whether there were non-fluid lumps in the base paint compositions or the viscosity of the whole base paint composition was 50% or more compared to the initial viscosity was evaluated as "×", and otherwise as "〇".

[0143] (Low-temperature curability (gel fraction measurement)) After applying the base paint composition to a polypropylene plate with a bar coater to a dry film thickness of 20 μm, an intermediate coat film was formed by heating and curing at 70°C for 10 minutes. For the single coat film peeled from the polypropylene plate, the mass of the coat film before and after heating and refluxing acetone for 3 hours with a Soxhlet extractor was measured, and the gel fraction was determined by the following formula. Gel fraction (mass%) = (mass of coat film after extraction / mass of coat film before extraction) × 100 The low-temperature curability was evaluated according to the following criteria. In the following five-level evaluation, a B evaluation or above was considered qualified. A: Gel fraction is 50% or more B: Gel fraction is 40% or more and less than 50% C: Gel fraction is less than 40%

[0144]

Table 3

[0145]

Table 4

[0146] The raw materials in the above table (excluding those in the production examples) will be described. · Block isocyanate compound (C): manufactured by Asahi Kasei Chemicals 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, fully alkylated melamine resin, manufactured by Ornex Japan) E-4: C251 (Cymel 251, methylol melamine resin, manufactured by Ornex Japan) E-5: C327 (Cymel 327, imino melamine resin, manufactured by Ornex Japan) · Pigment (A): Aluminum pigment (scaly pigment), manufactured by Toyo Aluminum Co., Ltd., product 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)

[0147] Examples 1 to 10 are examples of the present disclosure, in which the adhesion and water resistance are good, the appearance of the obtained coating film is maintained, the low-temperature curability is good, the energy load during coating film formation can be reduced, and the storage stability of the coating composition is good.

[0148] Comparative Example 1 is an example without using a fully alkylated melamine resin, and the coating film appearance, storage stability of the coating composition, and low-temperature curability were not sufficiently satisfactory. Comparative Example 2 is an example without using a fully alkylated melamine resin, and the coating film appearance and storage stability of the coating composition were not sufficiently satisfactory. Comparative Example 3 is an example using an acid catalyst having a counter ion, and the coating film appearance and low-temperature curability were not sufficiently satisfactory. Comparative Example 4 is an example in which a secondary amine compound is not used as the amine compound, and the appearance of the coating film and the low-temperature curability were not sufficiently satisfactory. Comparative Example 5 is an example in which a secondary amine compound is not used as the amine compound, and the storage stability of the coating composition was not sufficiently satisfactory. Comparative Example 6 is an example in which no amine compound is used, and the storage stability of the coating composition was not sufficiently satisfactory. Comparative Example 7 is an example in which acrylic resin (B2) is not used, the coating viscosity was high, and the storage stability of the coating composition was not sufficiently satisfactory. Comparative Example 8 is an example in which no melamine resin is used, and the appearance of the coating film and the low-temperature curability were not sufficiently satisfactory.

Industrial Applicability

[0149] According to the solvent-based base coating composition of the present disclosure, it is possible to provide a solvent-based base coating composition with good reduction of energy load during film formation and storage stability while maintaining the appearance of the resulting coating film, and it can be preferably used for coating automobiles and the like.

Claims

1. 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 cross-linked fine particles (D) that are insoluble and stably dispersed in the solution of the hydroxyl group-containing acrylic resin (B1), An acid catalyst (F), An amine compound (G), A solvent-based base paint composition containing the above, The solvent-based base paint composition has a solid content of 35% by mass or more, For the solvent-based base paint composition, using a cone plate type viscometer, at 23 °C, after measuring the viscosity V1 at a shear rate of 0.1 / sec, the shear rate is changed from 0.1 / sec to 25,000 / sec and sheared for 30 seconds, Then, when the viscosity V2 after returning the shear rate to 0.1 / sec and 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), and the hydroxyl group-containing monomer (b) includes 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) includes a fully alkylated type melamine resin, The acid catalyst (F) is a catalyst having no counter ion, The amine compound (G) includes a secondary amine compound, A solvent-based base paint composition.

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

3. The amine compound (G) has a boiling point in the range of 70 to 115 °C, The content of the amine compound (G) is 0.1 part by mass or more and 0.8 part 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 Claim 1.

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 Claim 1.

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 claim 1.

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 claim 1.

7. The hydroxyl group-containing acrylic resin (B1) is a polymer of the hydroxyl group-containing monomer (b) and another monomer other than the hydroxyl group-containing monomer (b). In the total of the hydroxyl group-containing monomer (b) and the other monomer, 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 claim 1.

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 claim 1.

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

10. Having a solvent-based base coating film provided on the object to be coated on which an intermediate coating film or a primer coating film has been previously provided. The coated article according to claim 9.

11. The object to be coated contains a plastic resin substrate. The coated article according to claim 9.

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