JP6859011B2 - Multi-layer coating film forming method - Google Patents

Description

The present invention relates to a method for forming a multi-layer coating film having excellent adhesion to the base material and cold heat load resistance on the base material.

Conventionally, for the purpose of imparting excellent appearance, performance, etc. on a base material, a coating composition is coated on the base material, and the formed wet coating film is cured to form a coating film. It has been done. The coating film is generally required to have high adhesion to the base material, and more recently, it is also required to have high cold and heat load resistance.

In Patent Document 1, a coating agent containing a specific polyester resin, epoxy resin and organic solvent, and the content ratio of the polyester resin to the epoxy resin is within a specific range, adheres to the base material and the metal vapor deposition layer. It is described that a coating film having high properties and having sufficient resistance even when subjected to cold shock treatment or hot water treatment can be formed. However, even with the coating agent, there is a problem that the adhesion to the substrate and the cold heat load resistance may be insufficient, especially when the coating film to be formed is relatively thick.

Japanese Unexamined Patent Publication No. 2011-74134

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for forming a multi-layer coating film having excellent adhesion to a base material and cold heat load resistance.

As a result of diligent studies to achieve the above object, the present inventors are a method for forming a multi-layer coating film in which two or more layers of coating film are formed on a base material, and a bisphenol skeleton is formed on the base material. A step of coating the undercoat coating composition (A) containing the polyol (a1) to form a coating film of the lowest layer, and a hydroxyl group-containing acrylic resin having a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C. According to the multi-layer coating film forming method including the step of coating the top coating composition (B) containing b1) and the polyisocyanate compound (b2) to form the uppermost coating film, the above object can be achieved. I found.

That is, the present invention includes the following aspects.

Item 1. A method for forming a multi-layer coating film in which two or more coating films are formed on a base material, wherein the undercoat coating composition (A) containing a polyol (a1) having a bisphenol skeleton is coated on the base material. A topcoat coating composition containing a hydroxyl group-containing acrylic resin (b1) and a polyisocyanate compound (b2) having a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C. A method for forming a multi-layer coating film, which comprises a step of coating B) to form an uppermost coating film.

Item 2. The method for forming a multi-layer coating film according to Item 1, wherein the polyol (a1) having a bisphenol skeleton is a polyol (a1') having a bisphenol A skeleton.

Item 3. The method for forming a multi-layer coating film according to Item 1 or 2, wherein the hydroxyl value of the polyol (a1) having a bisphenol skeleton is in the range of 50 to 600 mgKOH / g.

Item 4. The method for forming a multi-layer coating film according to any one of Items 1 to 3, wherein the undercoat coating composition (A) further contains a polyisocyanate compound (a2).

Item 5. The method for forming a multi-layer coating film according to any one of Items 1 to 4, wherein the coating film of the lowermost layer and the coating film of the uppermost layer are simultaneously heat-cured.

The method for forming a multi-layer coating film of the present invention can exhibit the effect of being able to form a multi-layer coating film having excellent adhesion to a base material and cold heat load resistance.

Hereinafter, the method for forming a multi-layer coating film of the present invention will be described in more detail.

The method for forming a multi-layer coating film of the present invention (hereinafter, may be abbreviated as "the present method") is
A method for forming a multi-layer coating film in which two or more layers of coating film are formed on a substrate, wherein the undercoat coating composition (A) containing a polyol (a1) having a bisphenol skeleton is coated on the substrate. The step of forming the coating film of the lower layer, and the topcoat coating composition (B) containing a hydroxyl group-containing acrylic resin (b1) and a polyisocyanate compound (b2) having a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C. It is characterized by including a step of painting to form a coating film on the uppermost layer.

The material of the substrate multilayer coating film forming method is applied in the substrate present invention is not particularly limited, inorganic materials, organic materials, or may be any of a hybrid material of organic and inorganic.

Examples of the inorganic material include metal materials such as iron, aluminum, brass, copper, tin, stainless steel, zinc-plated steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; glass; Examples include cement; concrete; polysiloxane, and the like.

The organic material is a material containing an organic resin, and examples of the organic resin include acrylic resins such as polymethylmethacrylate, polyethylene terephthalate, polyethylene naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, and polyethylene-1. Polyester resins such as 2-diphenoxyetane-4, 4'-dicarboxylate, polybutylene terephthalate, and epoxy resins represented by commercial products such as Epicoat (trade name: Yuka Shell Epoxy Co., Ltd.). Polycarbonate resin, polyimide resin, novolak resin, phenol resin, acrylonitrile-butadiene-styrene (ABS) resin, vinylidene chloride resin, polyurethane resin, cellulose ester (eg, triacetyl cellulose, diacetyl cellulose, propionyl cellulose, butyryl cellulose, acetyl propionyl) Cellulose, nitrocellulose), polyamide, polystyrene (eg, syndiotactic polystyrene), polyolefin (eg, polypropylene, polyethylene, polymethylpentene), polysulfone, polyethersulfone, polyarylate, polyetherimide, polyetherketone, etc. Be done.

Further, the organic material may contain pigments and / or fibers as a part of its components.

Examples of the pigment include calcium carbonate, silica, barium sulfate, barium carbonate, talc, clay, kaolin, aluminum hydroxide, magnesium oxide, aluminum oxide and the like.

Further, examples of the fiber include glass fiber, aramid fiber, carbon fiber, cellulose fiber and the like.

Therefore, various fiber reinforced plastic materials (Fiber Reinforced Plastics: hereinafter referred to as FRP material or simply FRP) are included in the above organic materials.

As the material of the base material, an organic material is preferable from the viewpoint of adhesion between the base material and the coating film formed on the base material.

Next, the undercoat coating composition (A) will be described.

Polypoly having a bisphenol skeleton (a1)
The polyol (a1) having a bisphenol skeleton is a compound having one or more bisphenol skeletons and two or more hydroxyl groups in one molecule.

Examples of the polyol (a1) having a bisphenol skeleton include a bisphenol compound (a11); a reaction product of a compound having a bisphenol skeleton and an epoxy group and a compound having a reactive group and a hydroxyl group with the epoxy group (a12). A reaction product (a13) of the compound having a bisphenol skeleton and an epoxy group and a compound having a reactive group that reacts with the epoxy group to generate a hydroxyl group and does not have a hydroxyl group can be used. Among them, from the viewpoint of adhesion to the base material, cold heat load resistance, etc., it is preferable to use the bisphenol compound (a11) and / or the reaction product (a12), and the reaction product (a12) is used. It is more preferable to use.

Examples of the bisphenol compound (a11) include the following general formula (I).

[In Formula I, R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ and R ¹⁰ are independently hydrogen atoms and 1 to 10 carbon atoms. Indicates an alkyl group or an aryl group]
A bisphenol compound represented by is used.

Specific examples of the bisphenol compound (a11) include 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A), 2,2'-, 2,4'-and 4, Mixture of 4'-methylenediphenol (common name: bisphenol F), 1,1-bis (4-hydroxyphenyl) -1-phenylethane (common name: bisphenol AP), 2,2-bis (4-hydroxyphenyl) ) Butane (common name: bisphenol B), 2,2-bis (3-methyl-4-hydroxyphenyl) propane (common name: bisphenol C), 1,1-bis (4-hydroxyphenyl) ethane (common name: Bisphenol E) and the like can be mentioned, and these can be used alone or in combination of two or more. Among them, as the bisphenol compound (a11), 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A) can be preferably used from the viewpoint of adhesion to the base material and the like. ..

Examples of the compound having a bisphenol skeleton and an epoxy group used in the production of the reaction product (a12) include a reaction product of the bisphenol compound (a11) and a diglycidyl ether compound; the bisphenol compound (a11). ) And epichlorohydrin (eg, epichlorohydrin, etc.) and the like can be used.

Examples of the diglycidyl ether compound include the following general formula (II).

[In Formula II, R ¹¹ and R ¹² each independently represent a hydrogen atom, a hydroxyl group or a methyl group, m represents an integer of 0 to 4, n represents an integer of 1 to 20, and n.

May be the same as each other or different from each other]
The compound represented by is preferably used.

Examples of the diglycidyl ether compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene (propylene) glycol diglycidyl ether, and polyethylene (propylene) glycol diglycidyl. Examples thereof include ether, neopentyl glycol diglycidyl ether, glycerin diglycidyl ether, and 1,6-hexanediol diglycidyl ether, which can be used alone or in combination of two or more. In addition, in this specification, "polyethylene (propylene) glycol" means a copolymer of ethylene glycol and propylene glycol, and includes both a block copolymer and a random copolymer.

As the diglycidyl ether compound, a commercially available product can be used. Commercially available product names include, for example, "Epolite 40E", "Epolite 100E", "Epolite 200E", "Epolite 400E", "Epolite 70P", "Epolite 200P", "Epolite 400P", "Epolite 1500NP", Examples thereof include "Epolite 1600" and "Epolite 80MF" (all manufactured by Kyoeisha Chemical Co., Ltd.).

Further, as the compound having a reactive group and a hydroxyl group with the epoxy group used in the production of the reaction product (a12), for example, a hydroxyl group-containing amine, a hydroxyl group-containing carboxylic acid and the like can be used.

As the hydroxyl group-containing amine, for example, monoalkanolamine, dialkanolamine and the like can be used. Specifically, for example, 2-aminoethanol (trivial name: monoethanolamine), 2- (2-hydroxyethylamino) ethanol (trivial name: diethanolamine) and the like can be used, and these can be used alone or 2 More than seeds can be used in combination.

Examples of the hydroxyl group-containing carboxylic acid include hydroxyetanoic acid (common name: glycolic acid), 2-hydroxypropionic acid (common name: lactic acid), and 3-hydroxy-2,2-dimethylpropionic acid (common name: hydroxypivalin). Acid), 2,3-dihydroxypropanoic acid (trivial name: glyceric acid), 2,2-bis (hydroxymethyl) propionic acid (trivial name: dimethylolpropionic acid), 2,2-bis (hydroxymethyl) butanoic acid (Trivial name: dimethylolbutanoic acid) and the like can be used, and these can be used alone or in combination of two or more.

Further, as a compound having a reactive group which reacts with the epoxy group to generate a hydroxyl group and which does not have a hydroxyl group, which is used in the production of the reaction product (a13), for example, an amine which does not have a hydroxyl group. Compounds, carboxylic acid compounds having no hydroxyl group, water and the like can be used.

Further, as the polyol (a1) having a bisphenol skeleton, a polyol (a1') having a bisphenol A skeleton can be preferably used from the viewpoint of adhesion to a base material and the like.

The polyol (a1') having a bisphenol A skeleton is, for example, a method using 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A) as the bisphenol compound (a11); the reaction generation. It can be obtained by a method or the like using a compound having a bisphenol A skeleton and an epoxy group as the compound having the bisphenol skeleton and an epoxy group which is a raw material of the substances (a12) and (a13).

The hydroxyl value of the polyol (a1) having a bisphenol skeleton is 50 to 600 mgKOH / g, preferably 70 to 500 mgKOH / g, and more preferably 100 to 100, from the viewpoint of adhesion to the substrate, water resistance of the coating film, and the like. It is preferably in the range of 500 mgKOH / g.

Further, the polyol (a1) having a bisphenol skeleton preferably has no epoxy group or has a small amount of epoxy group. Specifically, the epoxy equivalent of the polyol (a1) having the bisphenol skeleton is preferably larger than 2,000 g / eq, and more preferably larger than 2,500 g / eq. The larger the epoxy equivalent, the smaller the epoxy group amount.

The number average molecular weight of the polyol (a1) having a bisphenol skeleton is 180 to 20,000, preferably 300 to 15,000, and more preferably 400 to 7,000 from the viewpoint of adhesion to the substrate. It is preferable that it is within the range of.

In the present specification, the number average molecular weight and the weight average molecular weight are the retention times (retention capacity) measured by using a gel permeation chromatograph (GPC), and the retention time (retention) of standard polystyrene having a known molecular weight measured under the same conditions. It is a value obtained by converting the molecular weight of polystyrene by (capacity). Specifically, "HLC-8120GPC" (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph device, and "TSKgel G4000HXL", "TSKgel G3000HXL", "TSKgel G2500HXL" and "TSKgel" are used as columns. A total of 4 G2000HXL (trade name, all manufactured by Tosoh Corporation) are used, a differential refractometer is used as a detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow velocity: 1 mL / min. Can be measured below.

In the undercoat coating composition (A) according to the present invention, the content of the polyol (a1) having a bisphenol skeleton is the undercoat coating composition (A) from the viewpoint of adhesion to a substrate, cold heat load resistance, and the like. It is preferably in the range of 15 to 90% by mass, preferably 20 to 85% by mass, and more preferably 25 to 80% by mass, based on the total solid content of.

As used herein, the term "solid content" means a non-volatile component such as a resin, a curing agent, or a pigment contained in the composition, which remains after being dried at 110 ° C. for 1 hour. Therefore, for example, for the total solid content of the undercoat coating composition (A), the undercoat coating composition (A) is weighed in a heat-resistant container such as an aluminum foil cup, and the undercoat coating composition (A) is placed on the bottom surface of the container. After spreading, it is dried at 110 ° C. for 1 hour, and the mass of the components in the undercoat coating composition (A) remaining after drying is weighed, and the undercoat coating composition before drying is weighed. It can be calculated by obtaining the ratio of the mass of the component remaining after drying to the total mass of (A).

Further, the undercoat coating composition (A) preferably further contains the polyisocyanate compound (a2) from the viewpoint of adhesion to the base material, cold heat load resistance, and the like.

Polyisocyanate compound (a2)
The polyisocyanate compound (a2) is a compound having at least two isocyanate groups in one molecule, and is, for example, an aliphatic polyisocyanate, an alicyclic polyisocyanate, an aromatic aliphatic polyisocyanate, an aromatic polyisocyanate, or the like. Examples thereof include derivatives of polyisocyanates.

Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, and 1,3. An aliphatic diisocyanate such as −butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, diisocyanate dimerate, methyl 2,6-diisocyanatohexanate (common name: lysine diisocyanate); 2 , 6-Diisocyanatohexanoic acid 2-isocyanatoethyl, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1, , 8-Diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane and other aliphatic triisocyanates, etc. Can be mentioned.

Examples of the alicyclic polyisocyanate include 1,3-cyclopentenediisocyanate, 1,4-cyclohexanediisocyanate, 1,3-cyclohexanediisocyanate, and 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate (common name). : Isophorone diisocyanate), 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), 2-methyl-1,3-cyclohexylene diisocyanate, 1,3- or 1,4-bis (isocyanato) Alicyclic diisocyanates such as methyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis (4,1-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI), norbornan diisocyanate; 1,3,5 -Triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-Isocyanatopropyl) -2,6-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl)- Bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2) -Isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-Isocyanatopropyl) -bicyclo (2.2.1) -heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2) . 1) Examples of alicyclic triisocyanates such as heptane can be mentioned.

Examples of the aromatic aliphatic polyisocyanate include methylenebis (4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω'-diisocyanato-. Arophilic aliphatic diisocyanates such as 1,4-diethylbenzene, 1,3- or 1,4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof; 1,3 , 5-Triisosocyanatomethylbenzene and other aromatic aliphatic triisocyanates and the like can be mentioned.

Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylenedi isocyanate, 4,4'-diphenyldiisocyanate, 1,5-naphthalenediisocyanate, and 2,4-tolylene diisocyanate (common name: 2,4-tolylene diisocyanate). TDI) or 2,6-tolylene diisocyanate (common name: 2,6-TDI) or a mixture thereof, aromatic diisocyanates such as 4,4'-toluene diisocyanate and 4,4'-diphenyl ether diisocyanate; triphenylmethane-4 , 4', 4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene and other aromatic triisocyanates; 4,4'-diphenylmethane-2,2' , 5, 5'-Tetraisocyanate and other aromatic tetraisocyanates and the like.

Examples of the polyisocyanate derivative include the above-mentioned polyisocyanate dimer, trimmer, biuret, allophanate, uretdione, uretoimine, isocyanurate, oxadiazine trione, and polymethylene polyphenyl polyisocyanate (Crude MDI, Polymeric MDI). , Crude TDI and the like.

As the polyisocyanate compound (a2), the above-mentioned aliphatic diisocyanate, alicyclic diisocyanate and derivatives thereof can be preferably used from the viewpoint of adhesion to the base material, cold heat load resistance and the like.

Further, as the polyisocyanate compound (a2), a prepolymer obtained by reacting the polyisocyanate and its derivative with a compound capable of reacting with the polyisocyanate under the condition of excess isocyanate group may be used. Examples of the compound capable of reacting with the polyisocyanate include compounds having an active hydrogen group such as a hydroxyl group and an amino group. Specific examples thereof include polyhydric alcohols, low molecular weight polyester resins, amines and water. Can be used.

The polyisocyanate compound (a2) is a polymer of an isocyanate group-containing polymerizable unsaturated monomer, or a polymerizable unsaturated monomer other than the isocyanate group-containing polymerizable unsaturated monomer and the isocyanate group-containing polymerizable unsaturated monomer. A copolymer with a monomer may be used.

Further, the polyisocyanate compound (a2) may be a polyisocyanate compound in which the isocyanate group is blocked with a blocking agent, that is, a so-called blocked polyisocyanate compound.

Examples of the blocking agent include phenol-based agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; Oximes such as γ-butyrolactam and β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol and lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Ether systems such as butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, lactic acid. Alcohols such as butyl, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate; formamide oxime, acetoamide oxime, acetooxime, methyl ethyl ketooxime, diacetylmonooxime, benzophenone oxime, cyclohexane oxime, etc. Oxime-based; active methylene-based such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thio Mercaptans such as phenol, methylthiophenol, ethylthiophenol; acidamides such as acetoanilide, acetoaniside, acetotolide, acrylamide, methacrylicamide, acetateamide, stearate amide, benzamide; succinide imide, phthalateimide, maleateimide, etc. Imid-based; diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylphenylamine and other amine-based; imidazole, 2-ethylimidazole and other imidazole-based; urea, thiourea , Ethyleneurea, ethylenethiourea, diphenylurine Urea-based compounds such as elementary compounds; carbamic acid esters-based such as phenyl N-phenylcarbamic acid; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; azole-based compounds and the like can be mentioned. .. Examples of the azole compound include pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3, Pyrazole or pyrazole derivatives such as 5-dimethylpyrazole, 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole; 2-methylimidazoline , 2-Pyrazole imidazoline and other imidazoline derivatives and the like.

Among them, preferred blocking agents include oxime-based blocking agents, active methylene-based blocking agents, pyrazoles or pyrazole derivatives.

When blocking (reacting the blocking agent), a solvent can be added as needed. The solvent used for the blocking reaction may be one that is not reactive with the isocyanate group. For example, acetone, ketones such as methyl ethyl ketone, esters such as ethyl acetate, and N-methyl-2-pyrrolidone (NMP). Such solvents can be mentioned.

The polyisocyanate compound (a2) can be used alone or in combination of two or more.

When the undercoat coating composition (A) contains the above-mentioned polyisocyanate compound (a2), the blending ratio thereof is the isocyanate of the polyisocyanate compound (a2) from the viewpoint of adhesion to a base material, cold heat load resistance and the like. The equivalent ratio (NCO / OH) of the group (including the blocked isocyanate group) to the hydroxyl group of the polyol (a1) having a bisphenol skeleton is usually 0.5 to 2.0, particularly 0.6 to 1.5. It is preferable to use the ratio within the range.

Further, since the polyisocyanate compound (a2) can react with a hydroxyl group at a relatively low temperature to form a crosslinked coating film, it is particularly preferably used when the base material is a material that is easily thermally deformed such as an organic material. be able to.

When the undercoat coating composition (A) contains the polyisocyanate compound (a2), the undercoat coating composition (A) can contain a urethanization reaction catalyst.

Specific examples of the urethanization reaction catalyst include tin octylate, dibutyltin diacetate, dibutyltin di (2-ethylhexanoate), dibutyltin dilaurate, dioctyltin diacetate, and dioctyltindi (2). -Ethylhexanoate), dibutyltin oxide, dibutyltin sulfite, dioctyltin oxide, dibutyltin fatty acid salt, lead 2-ethylhexanoate, zinc octylate, zinc naphthenate, fatty acid zincs, bismuth octanate, 2- Organic metal compounds such as bismuth ethylhexanoate, bismuth oleate, bismuth neodecanoate, bismuth versaticate, bismuth naphthenate, cobalt naphthenate, calcium octylate, copper naphthenate, tetra (2-ethylhexyl) titanate; tertiary amine Etc., and these can be used individually or in combination of two or more.

When the above urethanization reaction catalyst is used, the amount of catalyst is 0.0001 to 0.5% by mass, particularly 0.0005 to 0.1, based on the total solid content of the undercoat coating composition (A). It is preferably in the range of mass%.

When the undercoat coating composition (A) contains the above-mentioned urethanization reaction catalyst, the undercoat coating composition (A) has acetic acid, propionic acid, butyric acid, isopentanoic acid, and hexanoic acid from the viewpoints of storage stability, curability, and the like. , 2-Ethylbutyric acid, naphthenic acid, octyl acid, nonanoic acid, decanoic acid, 2-ethylhexanoic acid, isooctanoic acid, isononanoic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, neodecanoic acid, versatic acid , Organic acids such as isobutyric anhydride, itaconic anhydride, acetic acid anhydride, citraconic anhydride, propionic anhydride, maleic anhydride, butyric anhydride, citric anhydride, trimellitic anhydride, pyromellitic anhydride, phthalic anhydride; hydrochloric acid, Inorganic acids such as phosphoric acid; metal coordinating compounds such as acetylacetone and imidazole compounds may be contained.

Further, the undercoat coating composition (A) preferably further contains an epoxy group-containing compound (a3) from the viewpoint of adhesion to the substrate and the like.

The epoxy group-containing compound (a3) is a compound having one or more epoxy groups in one molecule, and for example, an epoxy resin (a31), an epoxysilane compound (a32), or the like can be used.

As the epoxy resin (a31), for example, a reaction product of a polyphenol compound and epichlorohydrin (for example, epichlorohydrin or the like); a reaction product of a polyphenol compound and a diglycidyl ether compound, or the like can be used.

Examples of the polyphenol compound used for forming the epoxy resin (a31) include 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A), 2,2'-, 2,4. Mixtures of'-and 4,4'-methylenediphenol (common name: bisphenol F), 1,1-bis (4-hydroxyphenyl) -1-phenylethane (common name: bisphenol AP), 2,2-bis (4-Hydroxyphenyl) Butane (common name: bisphenol B), 2,2-bis (3-methyl-4-hydroxyphenyl) propane (common name: bisphenol C), 1,1-bis (4-hydroxyphenyl) Examples thereof include ethane (common name: bisphenol E), phenol novolac, cresol novolac and the like. Among them, from the viewpoint of adhesion to the base material and the like, it is preferable to use 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A) as the polyphenol compound.

Further, as the epoxy resin obtained by the reaction of the polyphenol compound with epihalohydrin, the resin of the following formula (III) derived from bisphenol A is particularly preferable.

Here, those represented by n = 0 to 8 are preferable.

Examples of commercially available products of the epoxy resin (a31) include "jER828EL", "jER1002", "jER1004", "jER1007", "jER834X90" (all manufactured by Mitsubishi Chemical Corporation) and the like.

The number average molecular weight of the epoxy resin (a31) is in the range of 300 or more, preferably 300 or more and less than 4,000, and more preferably 400 or more and less than 2,000 from the viewpoint of adhesion to the substrate. Is preferable.

The epoxy equivalent of the epoxy resin (a31) is 160 g / eq or more, preferably 180 to 2,500 g / eq, and more preferably 200 to 2,000 g / eq, from the viewpoint of adhesion to the substrate. It is preferably within the range.

When the undercoat coating composition (A) contains the epoxy resin (a31), the content of the epoxy resin (a31) is a solid of the undercoat coating composition (A) from the viewpoint of adhesion to the base material and the like. It is preferably in the range of 1 to 50% by mass, preferably 2 to 40% by mass, and more preferably 3 to 30% by mass with respect to the total amount.

The epoxysilane compound (a32) that can be used as the epoxy group-containing compound (a3) is a silane compound having one or more epoxy groups in one molecule, and is, for example, 2- (3,4-epoxycyclohexyl). ) Ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, etc. Can be done. Among them, 3-glycidoxypropyltrimethoxysilane can be preferably used from the viewpoint of adhesion to the base material and the like.

Examples of commercially available products of the epoxy silane compound (a32) include "KBM-303", "KBM-402", "KBM-403", "KBE-402", and "KBE-403" (above, Shin-Etsu). (Made by Chemical Industry Co., Ltd.) and the like.

The molecular weight of the epoxy silane compound (a32) is preferably in the range of 200 or more and less than 300, preferably 220 or more and less than 280, from the viewpoint of adhesion to the substrate and the like.

The epoxy equivalent of the epoxy silane compound (a32) is preferably in the range of 200 g / eq or more and less than 300 g / eq, preferably 220 g / eq or more and less than 280 g / eq, from the viewpoint of adhesion to the substrate and the like. Is.

When the undercoat coating composition (A) contains the epoxy silane compound (a32), the content of the epoxy silane compound (a32) is determined by the undercoat coating composition (a32) from the viewpoint of adhesion to the substrate and the like. It is preferably in the range of 0.1 to 10% by mass, preferably 0.2 to 7% by mass, and more preferably 0.3 to 5% by mass with respect to the total solid content of A).

The undercoat coating composition (A) contains a film-forming resin, a solvent, a pigment, a cross-linking agent, a catalyst, an ultraviolet absorber, a light stabilizer, an antioxidant, and a surface adjustment, as long as the effects of the present invention are not impaired. Other additive components usually used in the field of coating such as agents, defoamers, emulsifiers, surfactants, antifouling agents, wetting agents, thickeners, dyes, gloss adjusters and the like can be appropriately contained. ..

Examples of the type of the film-forming resin include acrylic resin, polyester resin, alkyd resin, polyurethane resin and the like. The film-forming resin preferably has a crosslinkable functional group such as a hydroxyl group, a carboxyl group, or an alkoxysilyl group. As the film-forming resin, a hydroxyl group-containing acrylic resin can be preferably used from the viewpoint of adhesion to the base material, cold heat load resistance, and the like.

The hydroxyl group-containing acrylic resin is, for example, a mixture containing a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, using a method known per se, for example. It can be produced by copolymerizing by a method such as a solution polymerization method in an organic solvent or an emulsion polymerization method in water.

The hydroxyl value of the hydroxyl group-containing acrylic resin is in the range of 20 to 170 mgKOH / g, preferably 35 to 150 mgKOH / g, and more preferably 50 to 140 mgKOH / g from the viewpoint of adhesion to the substrate and cold heat load resistance. It is preferable that it is inside.

The weight average molecular weight of the hydroxyl group-containing acrylic resin is 2,000 to 30,000, preferably 5,000 to 25,000, more preferably 5,000 to 25,000, from the viewpoint of adhesion to the substrate, cold heat load resistance, and the like. It is preferably in the range of 8,000 to 20,000.

The undercoat coating composition (A) may be in the form of a melt, a solution, a suspension, or an emulsion, but is in the form of a solution in which a polyol (a1) having a bisphenol skeleton is dissolved in a solvent. However, it is preferable from the viewpoint of productivity and workability. In this case, the undercoat coating composition (A) contains a polyol (a1) having a bisphenol skeleton and a solvent.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve, esters such as ethyl acetate and butyl acetate, and aromatic hydrocarbons such as toluene and xylene. , Alcohols such as methanol, ethanol, propanol and butanol, tetrahydrofuran, dimethylformamide, petroleum hydrocarbons and the like.

Examples of the pigment include bright pigments, coloring pigments, extender pigments and the like. The pigment can be used alone or in combination of two or more.

Examples of the brilliant pigment include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, glass flakes, aluminum oxide, mica, titanium oxide and / or aluminum oxide coated with iron oxide, titanium oxide and the like. / Or an iron oxide-coated mica or the like.

Examples of the coloring pigment include titanium oxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindolin pigment, slene pigment, and perylene. Examples thereof include based pigments, dioxazine based pigments, and diketopyrrolopyrrole based pigments.

Examples of the extender pigment include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, alumina white and the like.

When the undercoat coating composition (A) contains the above pigment, the content of the pigment is 1 to 70% by mass, preferably 5 to 60% by mass, based on the total solid content of the undercoat coating composition (A). %, More preferably in the range of 15 to 50% by mass.

In the method for forming a multi-layer coating film of the present invention, the undercoat coating composition (A) is coated on the base material to form a coating film of the lowest layer.

The coating method of the undercoat coating composition (A) is not particularly limited, and examples thereof include air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, and the like. Can be formed. Of these, methods such as air spray coating and rotary atomization coating are preferable. When painting, electrostatic electricity may be applied if necessary.

The coating film of the lowermost layer can be made into a cured coating film by heating or leaving at room temperature. Above all, from the viewpoint of production efficiency and the like, it is preferable to obtain a cured coating film by heating. The heating can be performed by a known heating means. Specifically, for example, it can be performed by hot air heating, infrared heating, high frequency heating, or the like.

When the undercoat coating composition (A) is applied to form a coating film of the bottom layer and then the coating film of the bottom layer is heat-cured, the heating temperature is high in productivity, workability and thermal stability of the base material. From the viewpoint of properties and the like, it is preferably in the range of 40 to 150 ° C., preferably 50 to 140 ° C., and more preferably 70 to 130 ° C. The heating time is preferably in the range of 15 minutes to 24 hours, preferably 30 to 120 minutes.

The coating film thickness of the lowermost coating film is preferably in the range of 5 to 70 μm, preferably 10 to 60 μm, and more preferably 15 to 50 μm as the cured film thickness.

The method for forming a multilayer coating film of the present invention further contains a hydroxyl group-containing acrylic resin (b1) and a polyisocyanate compound (b2) having a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C. after the above steps. The step of coating the topcoat coating composition (B) to form the uppermost coating film is included.

Hereinafter, the topcoat coating composition (B) will be described.

The topcoat coating composition (B) contains a hydroxyl group-containing acrylic resin (b1) and a polyisocyanate compound (b2).

Hydroxy group-containing acrylic resin (b1)
The hydroxyl group-containing acrylic resin (b1) is an acrylic resin having one or more hydroxyl groups in one molecule and having a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C. Among them, the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (b1) is preferably in the range of −15 ° C. or higher and lower than 50 ° C., preferably −10 ° C. or higher and lower than 40 ° C.

In the present specification, the glass transition temperature (Tg) of the acrylic resin is a value calculated by the following formula. 1 / Tg (K) = W ₁ / T ₁ + W ₂ / T ₂ + ... W _n / T _n
Tg (° C.) = Tg (K) -273
In the formula, W ₁ , W ₂ , ... W _n is the mass fraction of each monomer, and T ₁ , T ₂ ... T _n is the glass transition temperature Tg (K) of the homopolymer of each monomer. ..
The glass transition temperature of the homopolymer of each monomer is determined by POLYMER HANDBOOK Fourth Edition, J. Mol. Brandrup, E.I. h. Immunogut, E.I. A. The value according to Grulke (1999), and the glass transition temperature of a monomer not described in the document is static when a homopolymer of the monomer is synthesized so as to have a weight average molecular weight of about 50,000. Let it be the glass transition temperature.

The static glass transition temperature is set to 3 ° C. after taking a sample in a measuring cup using a differential scanning calorimeter "DSC-50Q type" (manufactured by Shimadzu Corporation, trade name) and sucking it in vacuum to completely remove the solvent. It was measured by measuring the change in calorific value in the range of −100 ° C. to 150 ° C. at a heating rate of / min and setting the first baseline change point on the low temperature side as the static glass transition temperature.

The hydroxyl group-containing acrylic resin (b1) can be obtained from, for example, a method known per se, for example, a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer. It can be produced by copolymerizing by a method such as a solution polymerization method in an organic solvent or an emulsion polymerization method in water.

The hydroxyl group-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in one molecule. Examples of the hydroxyl group-containing polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. Monoesterate of (meth) acrylic acid and divalent alcohol having 2 to 8 carbon atoms; ε-caprolactone modified product of monoesteride of (meth) acrylic acid and divalent alcohol having 2 to 8 carbon atoms; N -Hydroxymethyl (meth) acrylamide; allyl alcohol, (meth) acrylate having a polyoxyethylene chain having a hydroxyl group at the molecular end, and the like can be mentioned. These can be used alone or in combination of two or more.

As the other polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, for example, the following monomers (i) to (xx) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more.
(I) Alkyl or cycloalkyl (meth) acrylate: For example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl ( Meta) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (meth) Meta) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tricyclodecanyl (Meta) acrylate, etc.
(Ii) Polymerizable unsaturated monomer having an isobornyl group: isobornyl (meth) acrylate and the like.
(Iii) Polymerizable unsaturated monomer having an adamantyl group: adamantyl (meth) acrylate and the like.
(Iv) Polymerizable unsaturated monomer having a tricyclodecenyl group: tricyclodecenyl (meth) acrylate and the like.
(V) Aromatic ring-containing polymerizable unsaturated monomer: benzyl (meth) acrylate, styrene, α-methylstyrene, vinyltoluene and the like.
(Vi) Polymerizable unsaturated monomer having an alkoxysilyl group: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) Acryloyloxypropyltriethoxysilane, etc.
(Vii) Polymerizable unsaturated monomer having an alkyl fluorinated group: perfluoroalkyl (meth) acrylate such as perfluorobutylethyl (meth) acrylate and perfluorooctylethyl (meth) acrylate; fluoroolefin and the like.
(Viii) A polymerizable unsaturated monomer having a photopolymerizable functional group such as a maleimide group.
(Ix) Vinyl compound: N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate and the like.
(X) Carboxyl group-containing polymerizable unsaturated monomer: (meth) acrylic acid, maleic acid, crotonic acid, β-carboxyethyl (meth) acrylate and the like.
(Xi) Nitrogen-containing polymerizable unsaturated monomer: (meth) acrylonitrile, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylamino Additives of propyl (meth) acrylamide, methylenebis (meth) acrylamide, ethylenebis (meth) acrylamide, glycidyl (meth) acrylate and amine compounds, etc.
(Xii) Polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule: allyl (meth) acrylate, ethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, neo Pentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate and the like.
(Xiii) Epoxide group-containing polymerizable unsaturated monomer: glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate , 3,4-Epoxide cyclohexylpropyl (meth) acrylate, allyl glycidyl ether, etc.
(Xiv) A (meth) acrylate having a polyoxyethylene chain whose molecular end is an alkoxy group.
(Xv) Polymerizable unsaturated monomer having a sulfonic acid group: 2-acrylamide-2-methylpropanesulfonic acid, 2-sulfoethyl (meth) acrylate, allylsulfonic acid, 4-styrenesulfonic acid, etc .; sodium salts of these sulfonic acids And ammonium salts, etc.
(Xvi) Polymerizable unsaturated monomer having a phosphoric acid group: acid phosphooxyethyl (meth) acrylate, acid phosphooxypropyl (meth) acrylate, acid phosphooxypoly (oxyethylene) glycol (meth) acrylate, acid phosphooxypoly (Oxypropylene) glycol (meth) acrylate, etc.
(XVii) Polymerizable unsaturated monomer having UV-absorbing functional group: 2-hydroxy-4 (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2-hydroxy-4- (3-acryloyloxy-2-hydroxypropoxy) ) Benzophenone, 2,2'-dihydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2,2'-dihydroxy-4- (3-acryloyloxy-2-hydroxypropoxy) benzophenone, 2-( 2'-Hydroxy-5'-methacryloyloxyethylphenyl) -2H-benzotriazole and the like.
(Xviii) Photostable polymerizable unsaturated monomer: 4- (meth) acryloyloxy 1,2,2,6,6-pentamethylpiperidin, 4- (meth) acryloyloxy-2,2,6,6-tetra Methylpiperidin, 4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6- Tetramethylpiperidin, 1- (meth) acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidin, 4-crotonoyloxy-2,2,6,6-tetra Methylpiperidin, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine and the like.
(Xix) Polymerizable unsaturated monomer having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketone having 4 to 7 carbon atoms (eg, vinyl methyl ketone) , Vinyl ethyl ketone, vinyl butyl ketone), etc.
(Xx) Polymerizable unsaturated monomer having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride and the like.

As used herein, the polymerizable unsaturated group means an unsaturated group capable of radical polymerization. Examples of such polymerizable unsaturated group include an acryloyl group, a methacryloyl group, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a maleimide group, a vinyl ether group and the like.

Further, in the present specification, "(meth) acrylate" means acrylate or methacrylate. "(Meta) acrylic acid" means acrylic acid or methacrylic acid. In addition, "(meth) acryloyl" means acryloyl or methacryloyl. In addition, "(meth) acrylamide" means acrylamide or methacrylamide.

The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (b1) is adjusted, for example, by adjusting the type and compounding ratio of the polymerizable unsaturated monomer used in the synthesis of the hydroxyl group-containing acrylic resin (b1). can do.

Polyisocyanate compound (b2)
The polyisocyanate compound (b2) is a compound having at least two isocyanate groups in one molecule. Further, the polyisocyanate compound (b2) may be a polyisocyanate compound in which the isocyanate group is blocked with a blocking agent, that is, a so-called blocked polyisocyanate compound.

As the polyisocyanate compound (b2), the polyisocyanate compound described in the explanation column of the polyisocyanate compound (a2) can be used.

As the polyisocyanate compound (b2), aliphatic diisocyanates, alicyclic diisocyanates and derivatives thereof can be preferably used from the viewpoint of adhesion to a base material, cold heat load resistance and the like.

In the topcoat coating composition (B), the blending ratio of the hydroxyl group-containing acrylic resin (b1) and the polyisocyanate compound (b2) is the polyisocyanate compound from the viewpoint of adhesion to the substrate, cold heat load resistance, and the like. The equivalent ratio (NCO / OH) of the isocyanate group (including the blocked isocyanate group) of (b2) to the hydroxyl group of the hydroxyl group-containing acrylic resin (b1) is usually 0.5 to 2.0, particularly 0.6 to. It is preferable to use the ratio within the range of 1.5.

The topcoat coating composition (B) contains a catalyst, a solvent, a pigment, a cross-linking agent other than the polyisocyanate compound (b2), an ultraviolet absorber, a light stabilizer, and an antioxidant as long as the effects of the present invention are not impaired. , Surface conditioners, defoamers, emulsifiers, surfactants, antifouling agents, wetting agents, thickeners, dyes, gloss adjusters, and other additives normally used in the field of coating. be able to.

As the catalyst, for example, the urethanization catalyst described in the explanation column of the undercoat coating composition (A) can be used.

The topcoat coating composition (B) may be in the form of a melt, a solution, a suspension, or an emulsion, but the hydroxyl group-containing acrylic resin (b1) and the polyisocyanate compound (b2) are dissolved in the solvent. The solution form is preferable from the viewpoint of productivity and workability. In this case, the topcoat coating composition (B) contains a hydroxyl group-containing acrylic resin (b1) having a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C., a polyisocyanate compound (b2), and a solvent.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve, esters such as ethyl acetate and butyl acetate, and aromatic hydrocarbons such as toluene and xylene. , Alcohols such as methanol, ethanol, propanol and butanol, tetrahydrofuran, dimethylformamide, petroleum hydrocarbons and the like.

As the pigment, for example, the pigment described in the explanation column of the undercoat coating composition (A) can be used.

In the method for forming a multi-layer coating film of the present invention, the top coating composition (B) is coated on the lowermost coating film or the intermediate coating film described later to form the uppermost coating film. The lowermost coating film or intermediate coating film may be an uncured coating film or a cured coating film.

The coating method of the topcoat coating composition (B) is not particularly limited, and examples thereof include air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, and the like. Can be formed. Of these, methods such as air spray coating and rotary atomization coating are preferable. When painting, electrostatic electricity may be applied if necessary.

The coating film thickness of the uppermost coating film is preferably in the range of 5 to 70 μm, preferably 10 to 60 μm, and more preferably 15 to 50 μm as the cured film thickness.

The uppermost coating film can be made into a cured coating film by heating or standing at room temperature. Above all, from the viewpoint of production efficiency and the like, it is preferable to obtain a cured coating film by heating. The heating can be performed by a known heating means. Specifically, for example, it can be performed by hot air heating, infrared heating, high frequency heating, or the like.

When the top coat coating composition (B) is applied to form the top layer coating film and then the top layer coating film is heat-cured, the heating temperature is high in productivity, workability, and thermal stability of the base material. From the viewpoint of properties and the like, it is preferably in the range of 40 to 150 ° C., preferably 50 to 140 ° C., and more preferably 70 to 130 ° C. The heating time is preferably in the range of 15 minutes to 24 hours, preferably 30 to 120 minutes.

Further, in the method for forming a multi-layer coating film of the present invention, the coating film of the lowermost layer may be cured before the coating of the topcoat coating composition (B), and the coating film of the lowermost layer is uncured. In this state, the topcoat coating composition (B) may be applied to form an uppermost coating film, and then the lowermost coating film and the uppermost coating film may be cured at the same time. Above all, it is preferable to use the latter method from the viewpoint of energy saving and the like.

In the present invention, the cured coating film is a cured and dried state defined in JIS K 5600-1-1, that is, the center of the coated surface is strongly sandwiched between the thumb and the index finger, and the coated surface is dented by fingerprints. The coating film is in a state where it does not adhere, the movement of the coating film is not felt, and the center of the coated surface is rapidly and repeatedly rubbed with the fingertip to leave no scratches on the coated surface. On the other hand, the uncured coating film is a state in which the coating film has not reached the cured and dried state, and also includes a touch-dried state and a semi-cured and dried state defined in JIS K 5600-1-1.

Further, in the method for forming a multi-layer coating film of the present invention, an intermediate coating film layer different from these coating films may be formed between the coating film of the lowermost layer and the coating film of the uppermost layer. Further, the intermediate coating film layer may be a single layer or two or more layers.

When forming the intermediate coating film layer, each of the lowermost coating film, the intermediate coating film layer, and the uppermost coating film may be cured or may be cured at the same time. Above all, from the viewpoint of energy saving and the like, it is preferable to cure the lowermost coating film, the intermediate coating film layer and the uppermost coating film at the same time.

The intermediate coating film layer can be formed by coating the intermediate coating coating composition.

As the intermediate coating composition, a known coating composition can be used. Specifically, for example, a coating composition containing a substrate resin having a crosslinkable functional group and a crosslinking agent can be used. Above all, from the viewpoint of cold heat load resistance and the like, it is preferable to use a coating composition containing a hydroxyl group-containing acrylic resin and a polyisocyanate compound.

In addition, the intermediate coating composition includes catalysts, solvents, pigments, ultraviolet absorbers, light stabilizers, antioxidants, surface conditioners, defoamers, emulsifiers, surfactants, antifouling agents, wetting agents, and thickeners. Other additive components usually used in the field of coating such as thickeners, dyes and gloss adjusters can be appropriately contained.

When the lowermost coating film, the intermediate coating film layer formed as required, and the uppermost coating film are simultaneously heat-cured, the heating temperature determines the productivity, workability, and thermal stability of the base material. From the viewpoint of the above, it is preferably in the range of 40 to 150 ° C., preferably 50 to 140 ° C., and more preferably 70 to 130 ° C. The heating time is preferably in the range of 15 minutes to 24 hours, preferably 30 to 120 minutes.

Hereinafter, the present invention will be described in more detail with reference to Production Examples, Examples and Comparative Examples. However, the present invention is not limited thereto. In each example, "parts" and "%" are based on mass unless otherwise specified. The film thickness of the coating film is based on the cured coating film.

Production of polyol (a1) having a bisphenol skeleton Production Example 1
To the reaction vessel, add 230 parts of bisphenol A, 800 parts of "Epolite 200P" (trade name, manufactured by Kyoeisha Chemical Co., Ltd., tripropylene glycol diglycidyl ether, epoxy equivalent 200 g / eq, molecular weight 400), and 0.2 part of dimethylbenzylamine. The reaction was carried out at 160 ° C. until the epoxy equivalent reached 515 g / eq. Next, 210 parts of diethanolamine was added and reacted at 130 ° C. until the epoxy equivalent became 30,000 g / eq or more, and then ethylene glycol monobutyl ether was further added as a solvent, and a polyol having a bisphenol skeleton having a solid content of 80% (a1). -1) A solution was obtained. The obtained polyol (a1-1) having a bisphenol skeleton had a hydroxyl value of 340 mgKOH / g and a number average molecular weight of 1,300.

Production Examples 2-4
In Production Example 1, a bisphenol skeleton having a solid content of 80% was prepared in the same manner as in Production Example 1 except that the compounding composition, the epoxy equivalent when the hydroxyl group-containing amine was added, and the epoxy equivalent at the end of the reaction were shown in Table 1. Solutions of polyols (a1-2) to (a1-4) having were obtained. The hydroxyl value and number average molecular weight of the polyol having each bisphenol skeleton are also shown in Table 1.

(Note) in Table 1 means the following.

(Note 1) "Epolite 40E": trade name, manufactured by Kyoeisha Chemical Co., Ltd., ethylene glycol diglycidyl ether, epoxy equivalent 133 g / eq, molecular weight 265.

Production Example 5 of Production of Hydroxyl-Containing Acrylic Resin
45 parts of butyl acetate was placed in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen introduction tube and a dropping device, and the mixture was stirred at 115 ° C. while blowing nitrogen gas into the reaction vessel. A monomer mixture consisting of 28 parts of methacrylate, 30 parts of styrene, 35 parts of isobornyl acrylate, 7 parts of ethyl acrylate, 10 parts of butyl acetate and 4 parts of 2,2'-azobisisobutyronitrile was prepared at a uniform rate over 4 hours. The mixture was added dropwise and aged at the same temperature for 1 hour. After that, a mixture of 15 parts of butyl acetate and 1.0 part of 2,2'-azobisisobutyronitrile was added dropwise to the reaction vessel over 3 hours, and after completion of the addition, the mixture was aged for 1 hour and then diluted with butyl acetate. , A hydroxyl group-containing acrylic resin (Ac-1) solution having a solid content of 50% was obtained. The obtained hydroxyl group-containing acrylic resin (Ac-1) had a hydroxyl value of 121 mgKOH / g and a weight average molecular weight of 15,000.

Production Example 6 of Production of Undercoat Paint Composition (A)
53.8 parts (43 parts of solid content) and "CR-95" (trade name, manufactured by Ishihara Sangyo Co., Ltd., titanium oxide pigment, containing solid content) of the polyol (a1-1) solution having a bisphenol skeleton obtained in Production Example 1. 80 parts (rate 100%) was placed in a wide-mouthed glass bottle, glass beads were added and sealed, and the mixture was dispersed with a paint shaker for 30 minutes, and then the glass beads were removed to obtain a pigment-dispersed paste.
Next, the obtained pigment dispersion paste 133.8 parts (solid content 123 parts), "Sumijour N-3300" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanurate ring adduct of hexamethylene diisocyanate, solid content contained Rate 100%) 57 parts, dibutyltin diacetate 0.04 parts and "Disparon LF-1985-50" (trade name, manufactured by Kusumoto Kasei Co., Ltd., surface conditioner, solid content 50%) 0.1 parts (solid) (0.05 parts) was mixed uniformly, and the mixture was further diluted and stirred with butyl acetate so that the solid content became 30% to obtain an undercoat coating composition (A-1).

Production Examples 7 to 13
Undercoat coating compositions (A-2) to (A-8) having a solid content of 30% were obtained in the same manner as in Production Example 6 except that the compounding composition was as shown in Table 2 in Production Example 6. The compounding composition shown in Table 2 depends on the solid content mass of each component.

(Note 2) "jER 834X90": Product name, manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, solid content 90%.

(Note 3) "KBM-403": Trade name, manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane, solid content 100%.

Production Example 14 of Production of Hydroxyl Group-Containing Acrylic Resin (b1)
45 parts of butyl acetate was placed in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux cooler, a nitrogen introduction tube and a dropping device, and the mixture was stirred at 115 ° C. while blowing nitrogen gas into the reaction vessel. A monomer mixture consisting of 25 parts of acrylate, 28 parts of styrene, 47 parts of n-butyl acrylate, 10 parts of butyl acetate and 4 parts of 2,2′-azobisisobutyronitrile was added dropwise at a uniform rate over 4 hours, and the same was added. Aged at temperature for 1 hour. After that, a mixture of 15 parts of butyl acetate and 1.0 part of 2,2'-azobisisobutyronitrile was added dropwise to the reaction vessel over 3 hours, and after completion of the addition, the mixture was aged for 1 hour and then diluted with butyl acetate. , An acrylic resin (b1-1) solution having a hydroxyl group having a solid content of 50% was obtained. The obtained hydroxyl group-containing acrylic resin (b1-1) had a glass transition temperature of −14 ° C., a hydroxyl value of 121 mgKOH / g, and a weight average molecular weight of 15,000.

Production Examples 15 to 20
In Production Example 14, solutions of hydroxyl group-containing acrylic resins (b1-2) to (b1-7) having a solid content of 50% were obtained in the same manner as in Production Example 14, except that the monomer compounding composition was as shown in Table 3. It was. Table 3 also shows the glass transition temperature, hydroxyl value, and weight average molecular weight of each hydroxyl group-containing acrylic resin.

Production Example 21 of Production of Topcoat Coating Composition (B)
140 parts (70 parts solid content) of the hydroxyl group-containing acrylic resin (b1-1) solution obtained in Production Example 14, "Sumijour N-3300" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate) Ring adduct, solid content 100%) 30.4 parts, dibutyltin diacetate 0.02 part and "Disparon LF-1985-50" (trade name, manufactured by Kusumoto Kasei Co., Ltd., surface conditioner, solid content content 50%) 0.1 part (solid content 0.05 part) is uniformly mixed, and further diluted and stirred with butyl acetate so that the solid content becomes 30% to obtain a topcoat coating composition (B-1). It was.

Production Examples 22 to 27
In Production Example 21, topcoat coating compositions (B-2) to (B-7) having a solid content of 30% were obtained in the same manner as in Production Example 21 except that the compounding composition was as shown in Table 4. The compounding composition shown in Table 4 depends on the solid content mass of each component.

Production Example 28 of intermediate coating composition
140 parts (70 parts solid content) of the hydroxyl group-containing acrylic resin (Ac-1) solution obtained in Production Example 5, "Sumijour N-3300" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate) Ring adduct, solid content 100%) 30.4 parts, "GX-180A" (trade name, manufactured by Asahi Kasei Metals Co., Ltd., aluminum pigment paste, solid content 74%) 1 part (solid content 0.74 parts) ), 0.04 part of dibutyltin diacetate and 0.1 part of "Disparon LF-1985-50" (trade name, manufactured by Kusumoto Kasei Co., Ltd., surface conditioner, solid content 50%) 0.1 part (solid content 0.05 part) ) Was uniformly mixed, and the mixture was further diluted and stirred with butyl acetate so that the solid content became 30% to obtain an intermediate coating composition (M-1).

Preparation of test plate
Base material Base material (a): Acrylonitrile-butadiene-styrene (ABS) plate A 100 mm × 150 mm × 3.0 mm acrylonitrile-butadiene-styrene (ABS) plate is degreased with isopropyl alcohol to form a base material (a). did.

Base material (b): Polypropylene (PP) plate The surface of a 100 mm × 150 mm × 3.0 mm polypropylene (PP) plate was degreased with isopropyl alcohol to obtain a base material (b).

Base material (c): Fiber reinforced plastic (FRP) plate The surface of a 100 mm × 150 mm × 3.0 mm fiber reinforced plastic (FRP) plate was degreased with isopropyl alcohol to obtain a base material (c).

Example 1
The undercoat coating composition (A-1) obtained in Production Example 6 was coated on the base material (a) using an air spray so as to have a film thickness of 30 μm, and set at room temperature for 10 minutes. , An uncured undercoat coating was formed. Next, the topcoat coating composition (B-3) obtained in Production Example 23 was coated on the uncured undercoat coating film with an air spray so that the film thickness was 35 μm, and the film thickness was 35 μm, and the film thickness was 35 μm, and the film thickness was 35 μm. The setting was performed to form an uncured topcoat film. Then, the uncured undercoat film and the uncured topcoat film were heated at 90 ° C. for 1 hour to be cured to obtain a test plate. In this embodiment, the undercoat coating film corresponds to the lowest coating film, and the topcoat coating film corresponds to the uppermost coating film.

Examples 2 to 17, Comparative Examples 1 to 5
As the base material, the undercoat coating composition (A), the topcoat coating composition (B), and the intermediate coating composition, those shown in Table 5 are used, and the film thickness of each coating composition is as shown in Table 5. Each test plate was obtained in the same manner as in Example 1 except that the test plate was changed to.

Example 18
The undercoat coating composition (A-2) obtained in Production Example 7 was coated on the base material (a) using an air spray so as to have a film thickness of 30 μm, and set at room temperature for 10 minutes. , An uncured undercoat coating was formed. Next, the intermediate coating composition (M-1) obtained in Production Example 28 was coated on the uncured undercoat coating film with an air spray so as to have a film thickness of 15 μm, and 10 at room temperature. The setting was performed for a minute to form an uncured intermediate coating film. Next, the topcoat coating composition (B-3) obtained in Production Example 23 was coated on the uncured intermediate coating film with an air spray so as to have a film thickness of 35 μm, and 10 at room temperature. The setting was performed for a minute to form an uncured topcoat film. Then, the uncured undercoat film, the uncured intermediate coat film, and the uncured top coat film were heated at 90 ° C. for 1 hour to be cured to obtain a test plate. In this embodiment, the undercoat coating film corresponds to the lowest coating film, and the topcoat coating film corresponds to the uppermost coating film.

Evaluation test Each of the obtained test plates was evaluated by the following test method. The evaluation results are shown in Table 5.

Test method Water resistance: For each test plate, the adhesion to the substrate and the appearance after being immersed in warm water at 40 ° C. for 10 days or 30 days were evaluated according to the following criteria.

<Adhesion with base material [after water resistance test]>
Make 100 2 mm x 2 mm goban eyes on the coated surface of each test plate according to JIS K 5600-5-6 (1990), attach adhesive tape to the surface, peel off rapidly, and then apply goban eyes. The residual state of the film was examined, and the adhesion was evaluated according to the following criteria.

⊚: Remaining number / total number = 100 / 100, no edge chipping ○: Remaining number / total number = 100 / 100, with edge chipping Δ: Remaining number / total number = 99 to 90 / 100 pieces ×: remaining number / total number = 89 pieces or less / 100 pieces.

<Appearance [after water resistance test]>
⊚: No change in appearance with respect to the coating film before the test ○: Slight gloss, blistering or discoloration is observed with respect to the coating film before the test, but there is no problem when it is made into a product. Level Δ: Slight gloss, cracks, blister or discoloration is observed with respect to the coating film before the test, and the product is inferior. Or discoloration is seen.

Cold heat load resistance: For each test plate, a cold heat cycle test of 500 cycles was carried out with "-30 ° C 3 hours → cooling 3 hours → 70 ° C 90% RH 3 hours → cooling 3 hours" as one cycle, and the following The cold heat load resistance was evaluated according to the evaluation criteria.

<Appearance [after cold cycle test]>
⊚: No change in appearance with respect to the coating film before the test ○: Slight gloss, blistering or discoloration is observed with respect to the coating film before the test, but there is no problem when it is made into a product. Level Δ: Slight gloss, cracks, blister or discoloration is observed with respect to the coating film before the test, and the product is inferior. Or discoloration is seen.

Claims (5)

An undercoat coating composition which is a method for forming a multi-layer coating film of two or more layers on a base material which is an organic material and contains a polyol (a1) having a bisphenol skeleton on the base material which is an organic material. It contains a step of coating (A) to form a coating film of the lowest layer, and a hydroxyl group-containing acrylic resin (b1) and a polyisocyanate compound (b2) having a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C. A method for forming a multi-layer coating film, which comprises a step of coating the top coating composition (B) to form a coating film on the uppermost layer. The method for forming a multi-layer coating film according to claim 1, wherein the polyol (a1) having a bisphenol skeleton is a polyol (a1') having a bisphenol A skeleton. The method for forming a multilayer coating film according to claim 1 or 2, wherein the hydroxyl value of the polyol (a1) having a bisphenol skeleton is in the range of 50 to 600 mgKOH / g. The method for forming a multi-layer coating film according to any one of claims 1 to 3, wherein the undercoat coating composition (A) further contains a polyisocyanate compound (a2). The method for forming a multi-layer coating film according to any one of claims 1 to 4, wherein the coating film on the bottom layer and the coating film on the top layer are simultaneously heat-cured.