JP2017185480A - Multilayer coating film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer coating film forming method excellent in adhesion with a base material and resistance to cold heat load.SOLUTION: A multilayer coating film forming method which forms two or more coating films onto a base material includes: a step of coating a primer coating composition (A) containing an acrylic resin (a1) having a hydroxyl group and an epoxy group onto a base material to form a coating film of a lowermost layer; and a step of coating a topcoat coating composition (B) containing a hydroxyl group-containing acrylic resin (b1) having a glass transition temperature (Tg) of -20°C or higher and lower than 50°C and a polyisocyanate compound (b2) onto the coating film to form a coating film of an uppermost layer.SELECTED DRAWING: None

Description

  The present invention relates to a method for forming a multilayer coating film having excellent adhesion to a substrate and resistance to cold and heat load on the substrate.

  Conventionally, for the purpose of imparting excellent appearance and performance on a substrate, a coating composition is applied on the substrate, and the formed wet coating film is cured to form a coating film. It has been broken. In general, the coating film is required to have high adhesion to the substrate, and more recently, it is also required to have high resistance to cold heat.

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

JP 2011-74134 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for forming a multilayer coating film that is excellent in adhesion to a base material and resistance to cold load.

  As a result of intensive investigations to achieve the above object, the inventors of the present invention are a multilayer coating film forming method for forming a coating film of two or more layers on a substrate. A step of forming an undercoat paint composition (A) containing an acrylic resin having a group (a1) to form a lowermost coating film, and a hydroxyl group containing a glass transition temperature (Tg) of −20 ° C. or higher and lower than 50 ° C. According to the method for forming a multi-layer coating film comprising the step of coating the top coating composition (B) containing the acrylic resin (b1) and the polyisocyanate compound (b2) to form the uppermost coating film. I found that I can achieve.

  That is, the present invention includes the following aspects.

  Item 1, A multi-layer coating film forming method for forming a coating film of two or more layers on a base material, wherein the base coating composition comprises an acrylic resin (a1) having a hydroxyl group and an epoxy group on the base material (A ) To form a lowermost coating film, and a top 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 more and less than 50 ° C. A method of forming a multilayer coating film, comprising: coating the composition (B) to form an uppermost coating film.

  Item 2. The method for forming a multilayer coating film according to Item 1, wherein the hydroxyl value of the acrylic resin (a1) having a hydroxyl group and an epoxy group is in the range of 20 to 170 mgKOH / g.

  Item 3. The multilayer coating film forming method according to Item 1 or 2, wherein the acrylic group (a1) having a hydroxyl group and an epoxy group has an epoxy group concentration in the range of 0.3 to 5.0 mol / kg.

  Item 4, the acrylic resin (a1) having a hydroxyl group and an epoxy group contains an aromatic polymerizable unsaturated monomer and / or an alicyclic polymerizable unsaturated monomer as a copolymerizable monomer component, The total content of the saturated monomer and the alicyclic polymerizable unsaturated monomer is an acrylic resin having a hydroxyl group and an epoxy group obtained by polymerizing a mixture of 10 to 90% by mass with respect to the total amount of the monomer components. The multilayer coating film formation method of any one of 1-3.

  Item 5. The method for forming a multilayer coating film according to any one of Items 1 to 4, wherein the undercoat coating composition (A) further contains a polyisocyanate compound (a2).

  Item 6. The multilayer coating film forming method according to any one of Items 1 to 5, wherein the lowermost layer coating and the uppermost layer coating are simultaneously heat-cured.

  The method for forming a multilayer coating film of the present invention can produce an effect that a multilayer coating film having excellent adhesion to a base material and cold heat resistance can be formed.

  Hereinafter, the multilayer coating film forming method of the present invention will be described in more detail.

The multilayer coating film forming method of the present invention (hereinafter sometimes abbreviated as “the present method”)
A multi-layer coating film forming method for forming a coating film of two or more layers on a base material, wherein an undercoat paint composition (A) containing an acrylic resin (a1) having a hydroxyl group and an epoxy group is applied on the base material And a top 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. B) is applied to form the uppermost coating film.

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

  Examples of the inorganic material include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; glass; 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 polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, polyethylene-1, Epoxy resins represented by commercially available products such as 2-diphenoxyethane-4, 4′-dicarboxylate, polyester resins such as polybutylene terephthalate, and 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, Lopionylcellulose, butyrylcellulose, acetylpropionylcellulose, nitrocellulose), polyamide, polystyrene (eg, syndiotactic polystyrene), polyolefin (eg, polypropylene, polyethylene, polymethylpentene), polysulfone, polyethersulfone, polyarylate , Polyetherimide, polyether ketone and the like.

  Moreover, the said organic material may contain a pigment and / or a fiber as a part of the component.

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

  Moreover, as said fiber, glass fiber, an aramid fiber, carbon fiber, a cellulose fiber etc. are mentioned, for example.

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

  The material for the substrate is preferably an organic material from the viewpoint of adhesion between the substrate and a coating film formed on the substrate.

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

Acrylic resin having a hydroxyl group and an epoxy group (a1)
The acrylic resin (a1) having a hydroxyl group and an epoxy group is an acrylic resin having one or more hydroxyl groups and one or more epoxy groups in one molecule.

  The acrylic resin (a1) having a hydroxyl group and an epoxy group includes, for example, a hydroxyl group-containing polymerizable unsaturated monomer, an epoxy group-containing polymerizable unsaturated monomer, the hydroxyl group-containing polymerizable unsaturated monomer, and an epoxy group-containing polymerizable unsaturated monomer. Produced by copolymerizing a mixture containing other polymerizable unsaturated monomers capable of copolymerization by a method known per se, for example, a solution polymerization method in an organic solvent, an emulsion polymerization method in water, etc. can do.

  The hydroxyl group-containing polymerizable unsaturated monomer is a compound having at least one hydroxyl group and one polymerizable unsaturated bond 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, 4-hydroxybutyl (meth) acrylate, and the like. Monoesterified product of (meth) acrylic acid and C2-C8 dihydric alcohol; ε-caprolactone modified product of monoesterified product of (meth) acrylic acid and C2-C8 dihydric alcohol; N -Hydroxymethyl (meth) acrylamide; allyl alcohol, and (meth) acrylate having a polyoxyethylene chain whose molecular terminal is a hydroxyl group. These can be used alone or in combination of two or more.

  The use ratio of the hydroxyl group-containing polymerizable unsaturated monomer in the acrylic resin (a1) having the hydroxyl group and the epoxy group is based on the total amount of the copolymerizable monomer components from the viewpoint of adhesion to the base material and resistance to cold load. Is preferably in the range of 8 to 50% by mass, preferably 15 to 40% by mass, and more preferably 20 to 30% by mass.

  The epoxy group-containing polymerizable unsaturated monomer is a compound having at least one epoxy group and one polymerizable unsaturated bond in one molecule. Examples of the epoxy group-containing polymerizable unsaturated monomer include glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, and 3,4-epoxycyclohexylethyl (meta). ) Acrylate, 3,4-epoxycyclohexylpropyl (meth) acrylate, allyl glycidyl ether and the like.

  The proportion of the epoxy group-containing polymerizable unsaturated monomer used in the acrylic resin (a1) having the hydroxyl group and the epoxy group is determined based on the total amount of the copolymerization monomer component from the viewpoints of adhesion to the base material and resistance to cold load. As a reference, it is suitable to be in the range of 5 to 70% by mass, preferably 8 to 60% by mass, and more preferably 10 to 40% by mass.

As the other polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer and the epoxy group-containing polymerizable unsaturated monomer, for example, the following monomers (i) to (xix) 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 ( (Meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl ( (Meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) a Acrylate, cyclododecyl (meth) acrylate, tricyclodecanyl (meth) acrylate, and the like.
(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 monomers: 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 and the like.
(Vii) Polymerizable unsaturated monomer having a fluorinated alkyl 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-vinyl pyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate and the like.
(X) Carboxy 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 Propyl (meth) acrylamide, methylene bis (meth) acrylamide, ethylene bis (meth) acrylamide, an adduct of glycidyl (meth) acrylate and an amine compound.
(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) (meth) acrylate having a polyoxyethylene chain whose molecular end is an alkoxy group.
(Xiv) Polymerizable unsaturated monomer having a sulfonic acid group: 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth) acrylate, allylsulfonic acid, 4-styrenesulfonic acid, etc .; sodium salt of these sulfonic acids And ammonium salts.
(Xv) polymerizable unsaturated monomer having a phosphate group: acid phosphooxyethyl (meth) acrylate, acid phosphooxypropyl (meth) acrylate, acid phosphooxypoly (oxyethylene) glycol (meth) acrylate, acid phosphooxypoly (Oxypropylene) glycol (meth) acrylate and the like.
(Xvi) Polymerizable unsaturated monomer having an ultraviolet-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.
(Xvii) Light-stable polymerizable unsaturated monomer: 4- (meth) acryloyloxy 1,2,2,6,6-pentamethylpiperidine, 4- (meth) acryloyloxy-2,2,6,6-tetra Methylpiperidine, 4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6- Tetramethylpiperidine, 1- (meth) acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetra Methylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6- Tetramethylpiperidine and the like.
(Xviii) polymerizable unsaturated monomer having a carbonyl group: acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrol, vinyl alkyl ketone having 4 to 7 carbon atoms (for example, vinyl methyl ketone) , Vinyl ethyl ketone, vinyl butyl ketone) and the like.
(Xix) Polymerizable unsaturated monomer having an acid anhydride group: maleic anhydride, itaconic anhydride, citraconic anhydride and the like.

  In the present specification, the polymerizable unsaturated group means an unsaturated group capable of radical polymerization. Examples of the polymerizable unsaturated group include acryloyl group, methacryloyl group, vinyl group, allyl group, propenyl group, isopropenyl group, maleimide group, vinyl ether group and the like.

  In the present specification, “(meth) acrylate” means acrylate or methacrylate. “(Meth) acrylic acid” means acrylic acid or methacrylic acid. “(Meth) acryloyl” means acryloyl or methacryloyl. “(Meth) acrylamide” means acrylamide or methacrylamide.

  The hydroxyl value of the acrylic resin (a1) having a hydroxyl group and an epoxy group is from 20 to 170 mgKOH / g, preferably from 35 to 150 mgKOH / g, more preferably from the viewpoints of adhesion to the base material and resistance to cold load. It is preferable to be within the range of 50 to 140 mgKOH / g.

  Moreover, the epoxy group concentration of the acrylic resin (a1) having a hydroxyl group and an epoxy group is from 0.3 to 5.0 mol / kg, preferably from the viewpoint of adhesion to the base material and cold load resistance. It is suitable to be in the range of 5 to 4.0 mol / kg, more preferably 0.7 to 3.0 mol / kg.

  In the present specification, the epoxy group concentration of the acrylic resin (a1) having a hydroxyl group and an epoxy group is the number of epoxy groups per 1 kg of the acrylic resin (a1) and is present in the acrylic resin (a1). It is a value obtained by dividing the number of epoxy groups to be divided by the mass of the acrylic resin (a1) (mol / kg), and is a theoretical value calculated from the mass of the raw material used during the synthesis of the acrylic resin (a1). . For this reason, the epoxy group density | concentration of this acrylic resin (a1) can be adjusted by adjusting the compounding ratio of the epoxy-group-containing polymerizable unsaturated monomer in the said copolymerization monomer component, for example.

  The acrylic resin (a1) having a hydroxyl group and an epoxy group is an aromatic polymerizable unsaturated monomer and / or an alicyclic ring as a copolymerization monomer component from the viewpoints of adhesion to a base material and resistance to cold load. It is preferable to contain a group polymerizable unsaturated monomer.

  Examples of the aromatic polymerizable unsaturated monomer include benzyl (meth) acrylate, styrene, α-methylstyrene, vinyltoluene and the like, and preferable examples include styrene.

  Examples of the alicyclic polymerizable unsaturated monomer include cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tricyclodecanyl ( Examples include meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, and preferable examples include cyclohexyl (meth) acrylate and isobornyl (meth) acrylate.

  The aromatic polymerizable unsaturated monomer and the alicyclic polymerizable unsaturated monomer can be used alone or in combination of two or more.

  When the mixture for producing the acrylic resin (a1) having a hydroxyl group and an epoxy group contains the above aromatic polymerizable unsaturated monomer and / or alicyclic polymerizable unsaturated monomer as a copolymerization monomer component, The total content of the aromatic polymerizable unsaturated monomer and the alicyclic polymerizable unsaturated monomer is 10 to 90 mass with respect to the total amount of the monomer components from the viewpoints of adhesion to the substrate and resistance to cold load and the like. %, Preferably 20 to 85% by mass, more preferably 30 to 80% by mass.

  Moreover, the weight average molecular weight of the acrylic resin (a1) having a hydroxyl group and an epoxy group is from 2,000 to 30,000, preferably from 5,000, from the viewpoints of adhesion to the base material and resistance to cold load. It is suitable that it is in the range of 25,000, more preferably 8,000 to 20,000.

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

  In the undercoat coating composition (A) according to the present invention, the content of the acrylic resin (a1) having a hydroxyl group and an epoxy group is selected from the viewpoints of adhesion to the substrate, resistance to cold and heat, and the like. It is suitable that it is in the range of 15 to 90% by mass, preferably 20 to 85% by mass, more preferably 25 to 80% by mass, based on the total solid content of (A).

  In the present specification, the “solid content” means non-volatile components such as a resin, a curing agent and a pigment contained in the composition remaining after drying at 110 ° C. for 1 hour. For this reason, for example, the total solid content of the undercoat coating composition (A) is measured by weighing the undercoat coating composition (A) in a heat-resistant container such as an aluminum foil cup and placing the undercoat coating composition (A) on the bottom of the container. After spreading the coating, it is dried at 110 ° C. for 1 hour, and the weight of the components in the primer coating composition (A) remaining in the primer coating composition (A) remaining after drying is weighed to determine the primer coating composition before drying. It can calculate by calculating | requiring the ratio of the mass of the component which remains after drying with respect to the total mass of (A).

  Moreover, it is preferable that the said undercoat coating material composition (A) contains a polyisocyanate compound (a2) further from viewpoints, such as adhesiveness with a base material, and heat-resistant load resistance.

Polyisocyanate compound (a2)
The polyisocyanate compound (a2) is a compound having at least two isocyanate groups in one molecule, and examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, And polyisocyanate derivatives.

  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, 1,3. -Aliphatic diisocyanates such as butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate); 2 , 6-Diisocyanatohexanoic acid 2-isocyanatoethyl, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,6 1-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyl Examples thereof include aliphatic triisocyanates such as octane.

  Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (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) Methyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis (4,1-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI), alicyclic diisocyanate such as norbornane 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-isocyanate) Toethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3 An alicyclic triisocyanate such as -isocyanatopropyl) -bicyclo (2.2.1) heptane can be used.

  Examples of the araliphatic polyisocyanate include methylene bis (4,1-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω′-diisocyanato- Aromatic aliphatic diisocyanates such as 1,4-diethylbenzene, 1,3- or 1,4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; 1,3 And araliphatic triisocyanates such as 5-triisocyanatomethylbenzene.

  Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4- TDI), 2,6-tolylene diisocyanate (common name: 2,6-TDI) or mixtures thereof, aromatic diisocyanates such as 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate; triphenylmethane-4 , 4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene and the like; 4,4′-diphenylmethane-2,2 ′ , 5,5'-tetraisocyanate and other aromatics Mention may be made of the tiger isocyanate.

  Examples of the polyisocyanate derivatives include dimer, trimer, biuret, allophanate, uretdione, uretoimine, isocyanurate, oxadiazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI). And Crude TDI.

  As the polyisocyanate compound (a2), the above aliphatic diisocyanates, alicyclic diisocyanates, and derivatives thereof can be suitably used from the viewpoints of adhesion to a base material, resistance to cold heat load, and the like.

  Moreover, as said polyisocyanate compound (a2), you may use the prepolymer formed by making the said polyisocyanate and its derivative (s), and the compound which can react with this polyisocyanate react on conditions with excess isocyanate group. 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. Specifically, for example, polyhydric alcohol, low molecular weight polyester resin, amine, water, etc. Can be used.

  The polyisocyanate compound (a2) is a polymer of an isocyanate group-containing polymerizable unsaturated monomer, or a polymerizable unsaturated group 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.

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

  Examples of the blocking agent include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and hydroxybenzoic acid methyl; ε-caprolactam, δ-valerolactam, lactams such as γ-butyrolactam, β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene Ethers such as glycol monomethyl ether and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol Alcohols such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; oximes such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime; dimethyl malonate, diethyl malonate , Active methylenes such as ethyl acetoacetate, methyl acetoacetate, acetylacetone; butyl mercaptan, t-butyl mercapta , Hexyl mercaptans, t-dodecyl mercaptans, 2-mercaptobenzothiazoles, thiophenols, methylthiophenols, ethylthiophenols and other mercaptans; Acid amides; succinimides, phthalic imides, maleic imides and other imides; diphenylamines, phenylnaphthylamines, xylidines, N-phenylxylidines, carbazoles, anilines, naphthylamines, butylamines, dibutylamines, butylphenylamines, etc. System: Imidazoles such as imidazole and 2-ethylimidazole; urea, thiourea, ethylene urea, ethylene thiourea, diphenyl urea N- phenylcarbamate ester of carbamic acid such as phenyl; ethyleneimine, imine and propylene imine; urea in sodium bisulfite, sulfite, such as bisulfite potassium; compounds such azole systems. Examples of the azole compounds 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 and 3-methyl-5-phenylpyrazole; Imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole and 2-phenylimidazole; 2-methylimidazoline And imidazoline derivatives such as 2-phenylimidazoline.

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

  When blocking (reacting the blocking agent), a solvent can be added as necessary. As the solvent used for the blocking reaction, those not reactive to isocyanate groups are preferable. For example, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and N-methyl-2-pyrrolidone (NMP) Such solvents can be mentioned.

  The said polyisocyanate compound (a2) can be used individually or in combination of 2 types or more, respectively.

  When the undercoating composition (A) contains the polyisocyanate compound (a2), the blending ratio thereof is an isocyanate of the polyisocyanate compound (a2) from the viewpoints of adhesion to the substrate and resistance to cold and heat load. The equivalent ratio (NCO / OH) of the group (including the blocked isocyanate group) to the hydroxyl group of the acrylic resin (a1) having the hydroxyl group and epoxy group is usually 0.5 to 2.0, particularly 0.6 to 1 It is suitable to use it in the ratio which becomes in the range of .5.

  Moreover, since the said 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 substrate is a material that is easily thermally deformed such as an organic material. be able to.

  Moreover, when undercoat coating composition (A) contains the said polyisocyanate compound (a2), this undercoat coating composition (A) can contain a urethanization reaction catalyst.

  Specific examples of the urethanization reaction catalyst include, for example, tin octylate, dibutyltin diacetate, dibutyltin di (2-ethylhexanoate), dibutyltin dilaurate, dioctyltin diacetate, dioctyltin di (2 -Ethylhexanoate), dibutyltin oxide, dibutyltin sulfite, dioctyltin oxide, dibutyltin fatty acid salt, lead 2-ethylhexanoate, zinc octylate, zinc naphthenate, zinc fatty acids, bismuth octanoate, 2- Organometallic compounds such as bismuth ethylhexanoate, bismuth oleate, bismuth neodecanoate, bismuth versatate, bismuth naphthenate, cobalt naphthenate, calcium octylate, copper naphthenate, tetra (2-ethylhexyl) titanate; tertiary amines Etc., and these Either alone or 2 or more kinds in combination may be used.

  Moreover, when using the said urethanization reaction catalyst, as catalyst amount, it is 0.0001-0.5 mass% with respect to the solid content total amount of undercoat coating composition (A), Especially 0.0005-0.1. It is preferable to be within the range of mass%.

  When the undercoating composition (A) contains the urethanization reaction catalyst, the undercoating composition (A) is acetic acid, propionic acid, butyric acid, isopentanoic acid, hexanoic acid from the viewpoint of storage stability, curability and the like. 2-ethylbutyric acid, naphthenic acid, octylic 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 anhydride, citraconic anhydride, propionic anhydride, maleic anhydride, butyric anhydride, citric anhydride, trimellitic anhydride, pyromellitic anhydride, phthalic anhydride; hydrochloric acid, It may contain inorganic acids such as phosphoric acid; metal coordination compounds such as acetylacetone and imidazole compounds.

  In addition, the undercoat coating composition (A) may further contain an epoxy group-containing compound (a3) other than the acrylic resin (a1) having a hydroxyl group and an epoxy group from the viewpoint of adhesion to the base material and the like. preferable.

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

  Examples of the polyphenol compound used for the formation of the epoxy resin (a31) include 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A), 2,2′-, 2,4. A mixture 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 include ethane (common name: bisphenol E), phenol novolak, cresol novolak, and the like. Especially, it is preferable to use 2, 2-bis (4-hydroxyphenyl) propane (common name: bisphenol A) as said polyphenol compound from viewpoints, such as adhesiveness with a base material.

  Moreover, as an epoxy resin obtained by reaction of a polyphenol compound and an epihalohydrin, a resin represented by the following formula (I) derived from bisphenol A is particularly preferable.

  Here, what is shown by n = 0-8 is suitable.

  As a commercial item of this epoxy resin (a31), "jER828EL", "jER1002", "jER1004", "jER1007", "jER834X90" (above, Mitsubishi Chemical Corporation make) etc. are mentioned, for example.

  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 preferred.

  In addition, the epoxy equivalent of the epoxy resin (a31) is 160 g / eq or more, preferably 180 to 2,500 g / eq, more preferably 200 to 2,000 g / eq, from the viewpoint of adhesion to the base material and the like. It is preferable to be within the range.

  When the undercoat coating composition (A) contains the epoxy resin (a31), the content of the epoxy resin (a31) is determined from the viewpoint of adhesion to the substrate, etc. It is suitable for the total amount to be in the range of 1 to 50% by mass, preferably 2 to 40% by mass, and more preferably 3 to 30% by mass.

  Moreover, the epoxy silane 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, for example, 2- (3,4-epoxycyclohexyl). ) Ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, etc. Can do. Of these, 3-glycidoxypropyltrimethoxysilane can be preferably used from the viewpoint of adhesion to the substrate.

  Moreover, as a commercial item of the said epoxysilane compound (a32), "KBM-303", "KBM-402", "KBM-403", "KBE-402", "KBE-403" (above, Shin-Etsu) Chemical Industry Co., Ltd.).

  The molecular weight of the epoxysilane 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.

  The epoxy equivalent of the epoxysilane 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. It is.

  In addition, when the undercoat coating composition (A) contains the epoxysilane compound (a32), the content of the epoxysilane compound (a32) is determined from the viewpoint of adhesion to the substrate, etc. It is suitable that it is 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).

  Moreover, it is preferable that the said undercoat coating material composition (A) contains the polyol (a4) which has a bisphenol skeleton further from viewpoints, such as adhesiveness with a base material.

  The polyol (a4) 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 (a4) having the bisphenol skeleton include, for example, a reaction product (a42) of a bisphenol compound (a41); 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. A compound having a bisphenol skeleton and an epoxy group, a reaction product (a43) of a compound having a reactive group which reacts with the epoxy group to form a hydroxyl group and does not have a hydroxyl group, and the like can be used. Especially, it is preferable to use the said bisphenol compound (a41) and / or the said reaction product (a42) from viewpoints, such as adhesiveness with a base material, and a heat-resistant load, and the said reaction product (a42) is used. More preferably it is used.

  Examples of the bisphenol compound (a41) include the following general formula (II)

[In the formula II, R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ and R ¹⁰ are each independently a hydrogen atom, having 1 to 10 carbon atoms. Represents an alkyl group or an aryl group]
The bisphenol compound represented by these can be used.

  Specific examples of the bisphenol compound (a41) 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 these, as the bisphenol compound (a41), 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A) can be suitably 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 (a42) include a reaction product of the bisphenol compound (a41) and a diglycidyl ether compound; the bisphenol compound (a41). ) And epihalohydrin (for example, epichlorohydrin, etc.).

  Examples of the diglycidyl ether compound include the following general formula (III):

[In Formula III, 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,

May be the same as or different from each other]
The compound represented by these can be used conveniently.

  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. Ether, neopentyl glycol diglycidyl ether, glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether and the like can be mentioned, and these can be used alone or in combination of two or more. In the present specification, “polyethylene (propylene) glycol” means a copolymer of ethylene glycol and propylene glycol, and includes both a block copolymer and a random copolymer.

  Moreover, a commercial item can be used as said diglycidyl ether compound. Examples of commercially available product names include “Epolite 40E”, “Epolite 100E”, “Epolite 200E”, “Epolite 400E”, “Epolite 70P”, “Epolite 200P”, “Epolite 400P”, “Epolite 1500NP”, “Epolite 1600”, “Epolite 80MF” (manufactured by Kyoeisha Chemical Co., Ltd.) and the like.

  Moreover, as a compound which has a reactive group with the said epoxy group and a hydroxyl group used in manufacture of the said reaction product (a42), a hydroxyl group containing amine, a hydroxyl group containing carboxylic acid, etc. can be used, for example.

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

  Examples of the hydroxyl group-containing carboxylic acid include hydroxyethanoic acid (common name: glycolic acid), 2-hydroxypropanoic acid (common name: lactic acid), 3-hydroxy-2,2-dimethylpropanoic acid (common name: hydroxypivalin). Acid), 2,3-dihydroxypropanoic acid (common name: glyceric acid), 2,2-bis (hydroxymethyl) propanoic acid (common name: dimethylolpropionic acid), 2,2-bis (hydroxymethyl) butanoic acid (Common name: dimethylol butanoic acid) etc. can be used, and these can be used individually or in combination of 2 or more types.

  Moreover, as a compound which has a reactive group which reacts with the said epoxy group and produces | generates a hydroxyl group, and does not have a hydroxyl group used in manufacture of the said reaction product (a43), for example, an amine which does not have a hydroxyl group A compound, a carboxylic acid compound having no hydroxyl group, water and the like can be used.

  In addition, as the polyol (a4) having the bisphenol skeleton, a polyol (a4 ′) having a bisphenol A skeleton can be preferably used from the viewpoint of adhesion to the substrate and the like.

  The polyol (a4 ′) having the bisphenol A skeleton is, for example, a method using 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A) as the bisphenol compound (a41); The compound having a bisphenol skeleton and an epoxy group, which is a raw material of the products (a42) and (a43), can be obtained by a method using a compound having a bisphenol A skeleton and an epoxy group.

  The number average molecular weight of the polyol (a4) having the bisphenol skeleton is in the range of 300 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 to be within.

  Moreover, the hydroxyl value of the polyol (a4) having the bisphenol skeleton is 100 to 500 mgKOH / g, preferably 150 to 500 mgKOH / g, more preferably 200 to 500 mgKOH / g, from the viewpoint of adhesion to the base material and the like. It is preferable to be within the range.

  When the undercoating composition (A) contains the polyol (a4) having the bisphenol skeleton, the content of the polyol (a4) having the bisphenol skeleton is determined from the viewpoint of adhesion to the substrate, etc. It is suitable that it is 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 solid content of the product (A).

  In the undercoating composition (A), a solvent, a pigment, a crosslinking agent, a catalyst, an ultraviolet absorber, a light stabilizer, an antioxidant, a surface conditioner, and an antifoaming agent, as long as the effects of the present invention are not impaired. , Other additive components ordinarily used in the field of coating, such as emulsifiers, surfactants, antifouling agents, wetting agents, thickeners, dyes, gloss adjusting agents, and the like can be appropriately contained.

  The undercoating composition (A) may be in the form of a melt, solution, suspension, or emulsion, but in the form of a solution in which an acrylic resin (a1) having a hydroxyl group and an epoxy group is dissolved in a solvent. It is preferable from the viewpoint of productivity and workability. In this case, the undercoat paint composition (A) contains an acrylic resin (a1) having a hydroxyl group and an epoxy group 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. And alcohols such as methanol, ethanol, propanol and butanol, tetrahydrofuran, dimethylformamide, petroleum hydrocarbons and the like.

  Examples of the pigment include a luster pigment, a color pigment, and an extender pigment. The pigments can be used alone or in combination of two or more.

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

  Examples of the color pigment include titanium oxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, selenium pigment, and perylene. Pigments, dioxazine pigments, diketopyrrolopyrrole pigments and the like.

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

  When the undercoat paint 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 paint composition (A). %, More preferably in the range of 15 to 50% by weight.

  Moreover, the epoxy group concentration of the undercoat coating composition (A) is 0.05 to 3.5 mol / kg, preferably 0.1 to 3. mol. It is suitable to be in the range of 0 mol / kg, more preferably 0.2 to 2.5 mol / kg.

  In this specification, the epoxy group concentration of the undercoat coating composition (A) is the number of epoxy groups per 1 kg of the solid content of the undercoat coating composition (A) and is present in the undercoat coating composition (A). It is a value obtained by dividing the number of epoxy groups to be divided by the solid content mass of the undercoat coating composition (A) (mol / kg). In the present specification, the epoxy group concentration of the undercoat coating composition (A) is a theoretical value calculated from the mass of raw materials used during the production of the undercoat coating composition (A).

  In the multilayer coating film forming method of the present invention, the undercoat coating composition (A) is coated on the substrate to form the lowermost coating film.

  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 preferred. When applying, electrostatic application may be applied as necessary.

  The lowermost coating film can be formed into a cured coating film by heating or standing at room temperature. Especially, it is preferable to set it as a cured coating film by heating from viewpoints, such as production efficiency. The heating can be performed by a known heating means. Specifically, it can be performed by, for example, hot air heating, infrared heating, high frequency heating or the like.

  After applying the undercoat coating composition (A) to form the lowermost coating film, when the lowermost coating film is cured by heating, the heating temperature is productivity, workability, and thermal stability of the substrate. From the viewpoint of properties and the like, it is preferable that the temperature is in the range of 40 to 150 ° C, preferably 50 to 140 ° C, more preferably 70 to 130 ° C. In addition, the heating time is preferably within a range of 15 minutes to 24 hours, preferably 30 to 120 minutes.

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

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

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

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

Hydroxyl 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 more and less than 50 ° C. Especially, it is suitable for the glass transition temperature (Tg) of this hydroxyl-containing acrylic resin (b1) to be in the range of −15 ° C. or higher and lower than 50 ° C., preferably −10 ° C. or higher and lower than 40 ° C.

In this specification, the glass transition temperature (Tg) of an 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 are mass fractions of each monomer, and T ₁ , T _2, ... T _n are glass transition temperatures Tg (K) of homopolymers of each monomer. .
In addition, the glass transition temperature of the homopolymer of each monomer is POLYMER HANDBOOK Fourth Edition, J. MoI. Brandrup, E .; h. Immergut, E .; A. The glass transition temperature of a monomer not described in the document, which is a value according to Grulk (1999), is a static value when a homopolymer of the monomer is synthesized with a weight average molecular weight of about 50,000. The glass transition temperature is assumed.

  The static glass transition temperature is 3 ° C. after a sample is taken into a measuring cup using a differential scanning calorimeter “DSC-50Q type” (trade name, manufactured by Shimadzu Corporation), and the solvent is completely removed by vacuum suction. It was measured by measuring the change in calorie in the range of −100 ° C. to 150 ° C. at a rate of temperature rise / minute, 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) is prepared by, for example, a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer by a method known per se, for example, It can be produced by copolymerization by a method such as a solution polymerization method in an organic solvent or an emulsion polymerization method in water.

  As the hydroxyl group-containing polymerizable unsaturated monomer, the hydroxyl group-containing polymerizable unsaturated monomer described in the explanation column of the acrylic resin (a1) having a hydroxyl group and an epoxy group can be used.

  Moreover, as another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, the epoxy group-containing polymerizable unsaturated compound described in the explanation column of the acrylic resin (a1) having the hydroxyl group and the epoxy group is used. Monomers and polymerizable unsaturated monomers (i) to (xix) can be used.

  The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (b1) is adjusted, for example, by adjusting the type and blending ratio of the polymerizable unsaturated monomer used during 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. The polyisocyanate compound (b2) may be a polyisocyanate compound in which an isocyanate group is blocked with a blocking agent, a so-called blocked polyisocyanate compound.

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

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

  In the top coating composition (B), the blending ratio of the hydroxyl group-containing acrylic resin (b1) and the polyisocyanate compound (b2) is selected from the viewpoints of adhesion to the substrate, resistance to cold and heat, and the like. The equivalent ratio (NCO / OH) of the isocyanate group (including the blocked isocyanate group) of (b2) and 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 it in a ratio that falls within the range of 1.5.

  In the top coating composition (B), a catalyst, a solvent, a pigment, a crosslinking 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. , And other additives such as surface conditioners, antifoaming agents, emulsifiers, surfactants, antifouling agents, wetting agents, thickeners, dyes, gloss adjusting agents, and the like that are usually used in the field of coating. be able to.

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

  The top 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. A solution form is preferable from the viewpoint of productivity and workability. In this case, the top 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. And 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 multilayer coating film forming method of the present invention, the top coating composition (B) is applied onto 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 top 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 preferred. When applying, electrostatic application may be applied as necessary.

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

  The uppermost coating film can be formed into a cured coating film by heating or standing at room temperature. Especially, it is preferable to set it as a cured coating film by heating from viewpoints, such as production efficiency. The heating can be performed by a known heating means. Specifically, it can be performed by, for example, hot air heating, infrared heating, high frequency heating or the like.

  After the top coating composition (B) is applied to form the uppermost coating film, when the uppermost coating film is cured by heating, the heating temperature depends on the productivity, workability, and thermal stability of the substrate. From the viewpoint of properties and the like, it is preferable that the temperature is in the range of 40 to 150 ° C, preferably 50 to 140 ° C, more preferably 70 to 130 ° C. In addition, the heating time is preferably within a range of 15 minutes to 24 hours, preferably 30 to 120 minutes.

  In the multilayer coating film forming method of the present invention, the lowermost layer coating film may be cured before the application of the top coating composition (B), and the lowermost layer coating film is uncured. In the state, the top coating composition (B) may be applied to form the uppermost coating film, and then the lowermost coating film and the uppermost coating film may be simultaneously cured. Of these, the latter method is preferably used 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 coating surface is strongly sandwiched between the thumb and index finger, and the coating surface has a dent due to fingerprints. The coating film does not stick, the movement of the coating film is not felt, and the center of the coating surface is rapidly and repeatedly rubbed with a fingertip so that the coating surface is not rubbed. On the other hand, an uncured coating film is a state in which the coating film has not reached the above-mentioned cured and dried state, and includes a finger-touch dried state and a semi-cured dried state defined in JIS K 5600-1-1.

  In the multilayer coating film forming method of the present invention, an intermediate coating film layer different from these coating films may be formed between the lowermost coating film and the uppermost coating film. The intermediate coating layer may be a single layer or two or more layers.

  When forming the intermediate coating film layer, the lowermost coating film, the intermediate coating film layer, and the uppermost coating film may be cured, or may be cured simultaneously. Among these, from the viewpoint of energy saving, it is preferable to simultaneously cure the lowermost coating film, the intermediate coating film layer, and the uppermost coating film.

  The intermediate coating layer can be formed by applying an intermediate coating composition.

  A known coating composition can be used as the intermediate coating composition. Specifically, for example, a coating composition containing a base resin having a crosslinkable functional group and a crosslinking agent can be used. Especially, it is preferable to use the coating composition containing a hydroxyl-containing acrylic resin and a polyisocyanate compound from viewpoints, such as heat-resistant load resistance.

  The intermediate coating composition is composed of a catalyst, a solvent, a pigment, an ultraviolet absorber, a light stabilizer, an antioxidant, a surface conditioner, an antifoaming agent, an emulsifier, a surfactant, an antifouling agent, a wetting agent, Other additive components ordinarily used in the field of coating such as a sticking agent, a dye, and a gloss adjusting agent can be appropriately contained.

  When the lowermost coating film, the intermediate coating film layer formed as necessary, and the uppermost coating film are heated and cured at the same time, the heating temperature depends on the productivity, workability, and thermal stability of the substrate. From such a viewpoint, it is preferable that the temperature is in the range of 40 to 150 ° C, preferably 50 to 140 ° C, more preferably 70 to 130 ° C. In addition, the heating time is preferably within a range of 15 minutes to 24 hours, preferably 30 to 120 minutes.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. However, the present invention is not limited to these. In each example, “parts” and “%” are based on mass unless otherwise specified. Moreover, the film thickness of a coating film is based on a cured coating film.

Production and production example 1 of acrylic resin (a1) having a hydroxyl group and an epoxy group
Into a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube and dropping device, 45 parts of butyl acetate was charged and stirred at 115 ° C. while blowing nitrogen gas. From 9.3 parts of methacrylate, 15 parts of glycidyl methacrylate, 30 parts of styrene, 40.3 parts of isobornyl acrylate, 5.4 parts of ethyl acrylate, 10 parts of butyl acetate and 4 parts of 2,2′-azobisisobutyronitrile. The resulting monomer mixture was added dropwise at a uniform rate over 4 hours and further aged at the same temperature for 1 hour. Thereafter, 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. After completion of the addition, the mixture was aged for 1 hour and then diluted with butyl acetate. An acrylic resin (a1-1) solution having a hydroxyl group and an epoxy group with a solid content of 50% was obtained. The obtained acrylic resin (a1-1) having a hydroxyl group and an epoxy group has a hydroxyl value of 40 mgKOH / g, an epoxy group concentration of 1.1 mol / kg, a weight average molecular weight of 15,000, an aromatic polymerizable unsaturated monomer, and The total content of the alicyclic polymerizable unsaturated monomer was 70.3% by mass based on the total amount of the monomer components.

Production Examples 2-7
In Production Example 1, the monomer blend composition is as shown in Table 1, and the solid content is 50 in the same manner as in Production Example 1 except that the amount of polymerization initiator is appropriately adjusted to the weight average molecular weight shown in Table 1. Acrylic resin (a1-2) to (a1-7) solutions having% hydroxyl group and epoxy group were obtained. Table 1 shows the hydroxyl value, the epoxy group concentration, the weight average molecular weight, and the total content of the aromatic polymerizable unsaturated monomer and the alicyclic polymerizable unsaturated monomer of the acrylic resin having each hydroxyl group and epoxy group.

Production and production example 8 of a hydroxyl group-containing acrylic resin having no epoxy group
In Production Example 1, the monomer blend composition is as shown in Table 1, and the solid content is 50 in the same manner as in Production Example 1 except that the amount of polymerization initiator is appropriately adjusted to the weight average molecular weight shown in Table 1. % Hydroxyl group-containing acrylic resin (a1-8) solution was obtained. The hydroxyl value of the obtained hydroxyl group-containing acrylic resin (a1-8) is 121 mgKOH / g, the weight average molecular weight is 15,000, and the total content of the aromatic polymerizable unsaturated monomer and the alicyclic polymerizable unsaturated monomer is: It was 65 mass% with respect to the total amount of a monomer component.

Production Example 9 for Production of Polyol (a4) Having Bisphenol Skeleton 9
To a 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 continued 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 reached 30,000 g / eq or more. Then, ethylene glycol monobutyl ether was further added as a solvent, and a polyol having a bisphenol skeleton having a solid content of 80% (a4 -1) A solution was obtained. The obtained polyol (a4-1) having a bisphenol skeleton had a hydroxyl value of 340 mgKOH / g and a number average molecular weight of 1,300.

Production and production example 10 of undercoating composition (A)
140 parts of acrylic resin (a1-1) solution having a hydroxyl group and an epoxy group obtained in Production Example 1 (solid content: 70 parts) and “CR-95” (trade name, manufactured by Ishihara Sangyo Co., Ltd., titanium oxide pigment, solid content) 80 parts) was placed in a wide-mouth glass bottle, sealed by adding glass beads, dispersed with a paint shaker for 30 minutes, and then the glass beads were removed to obtain a pigment dispersion paste.
Next, 220 parts of the obtained pigment dispersion paste (150 parts of solid content), “Sumijour N-3300” (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanurate cycloadduct of hexamethylene diisocyanate, solid content 100 %) 10.1 part, dibutyltin diacetate 0.04 part and "Disparon LF-1985-50" (trade name, manufactured by Enomoto Kasei Co., Ltd., surface conditioner, solid content 50%) 0.1 part (solid 0.05 part) was uniformly mixed and further diluted and stirred with butyl acetate so that the solid content was 30% to obtain an undercoat coating composition (A-1).

Production Examples 11 to 20
In Production Example 10, undercoat compositions (A-2) to (A-11) having a solid content of 30% were obtained in the same manner as in Production Example 10 except that the composition was as shown in Table 2. In addition, the compounding composition shown in Table 2 is based on the solid content mass of each component.

  (Note 1) “jER 834X90”: trade name, manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, solid content 90%.

  (Note 2) “KBM-403”: trade name, manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane, solid content 100%.

Production and production example 21 of hydroxyl group-containing acrylic resin (b1)
Into a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube and dropping device, 45 parts of butyl acetate was charged and stirred at 115 ° C. while blowing nitrogen gas. A monomer mixture comprising 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. Aged for 1 hour at temperature. Thereafter, 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. 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 with 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 22 to 27
In Production Example 21, except that the monomer blending composition is as shown in Table 3, a solution containing hydroxyl-containing acrylic resins (b1-2) to (b1-7) having a solid content of 50% was obtained in the same manner as in Production Example 21. It was. Table 3 shows the glass transition temperature, hydroxyl value, and weight average molecular weight of each hydroxyl group-containing acrylic resin.

Production and production example 28 of top coating composition (B)
140 parts of hydroxyl group-containing acrylic resin (b1-1) solution obtained in Production Example 21 (solid content 70 parts), “Sumidule N-3300” (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate) Cycloadduct, solid content 100%) 30.4 parts, dibutyltin diacetate 0.02 parts and “Dispalon LF-1985-50” (trade name, manufactured by Enomoto Kasei Co., Ltd., surface conditioner, solid content 50%) 0.1 part (solid content 0.05 part) was mixed uniformly, and further diluted with butyl acetate so that the solid content was 30%, and the top coating composition (B-1) was obtained. It was.

Production Examples 29 to 34
In Production Example 28, the top coating compositions (B-2) to (B-7) having a solid content of 30% were obtained in the same manner as in Production Example 28 except that the composition was as shown in Table 4. In addition, the compounding composition shown in Table 4 is based on the solid content mass of each component.

Production and production example 35 of intermediate coating composition
140 parts of hydroxyl group-containing acrylic resin (a1-8) solution obtained in Production Example 8 (solid content 70 parts), “Sumidule N-3300” (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate) Cycloadduct, solid content 100%) 30.4 parts, "GX-180A" (trade name, manufactured by Asahi Kasei Metals, aluminum pigment paste, solid content 74%) 1 part (solid content 0.74 parts) ), 0.04 part of dibutyltin diacetate and "Disparon LF-1985-50" (trade name, manufactured by Enomoto Kasei Co., Ltd., surface conditioner, solid content 50%) 0.1 part (0.05 part solids) ) Were further mixed and further diluted and stirred with butyl acetate so that the solid content was 30% to obtain an intermediate coating composition (M-1).

Preparation of test plate
Base material base material (a): Acrylonitrile-butadiene-styrene (ABS) plate 100 mm × 150 mm × 3.0 mm The surface of an acrylonitrile-butadiene-styrene (ABS) plate was degreased with isopropyl alcohol to obtain 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).

Substrate (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 substrate (c).

Example 1
On the base material (a), the undercoat paint composition (A-1) obtained in Production Example 10 was applied using an air spray so that the film thickness was 30 μm, and setting was performed at room temperature for 10 minutes. An uncured undercoat film was formed. Next, on the uncured undercoat film, the topcoat composition (B-3) obtained in Production Example 30 was applied using an air spray so that the film thickness was 35 μm, and the room temperature was 10 minutes. Setting was performed to form an uncured topcoat film. Thereafter, the uncured undercoat film and the uncured topcoat film were cured by heating at 90 ° C. for 1 hour to obtain a test plate. In this example, the undercoat coating layer corresponds to the lowermost coating layer, and the top coating layer corresponds to the uppermost coating layer.

Examples 2-22, Comparative Examples 1-3
As a base material, undercoat paint composition (A), topcoat paint composition (B), and intermediate coat paint composition, those shown in Table 5 are used, and the film thickness of each paint composition is as shown in Table 5. Each test plate was obtained in the same manner as in Example 1 except that the test plates were changed.

Example 23
On the base material (a), the undercoat paint composition (A-2) obtained in Production Example 11 was applied using an air spray so that the film thickness was 30 μm, and setting was performed at room temperature for 10 minutes. An uncured undercoat film was formed. Next, on the uncured undercoat film, the intermediate coating composition (M-1) obtained in Production Example 35 was applied using an air spray so that the film thickness would be 15 μm. Setting for minutes was performed to form an uncured intermediate coating film. Next, on the uncured intermediate coating film, the top coating composition (B-3) obtained in Production Example 30 was applied using an air spray so that the film thickness became 35 μm, and the coating composition was 10 at room temperature. Setting for minutes was performed to form an uncured topcoat film. Thereafter, the uncured undercoat film, uncured intermediate coat film and uncured topcoat film were cured by heating at 90 ° C. for 1 hour to obtain a test plate. In this example, the undercoat coating layer corresponds to the lowermost coating layer, and the top coating layer corresponds to the uppermost coating layer.

Evaluation Test Each test plate obtained 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 and appearance with the substrate after being immersed in warm water at 40 ° C. for 10 days or 30 days were evaluated according to the following criteria.

<Adhesion with substrate [after water resistance test]>
Make 100 2mm x 2mm gobangs according to JIS K 5600-5-6 (1990) on the coated surface of each test plate, apply adhesive tape to the surface, and peel off rapidly before applying the gobang mesh The remaining 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, edge chipping Δ: Remaining number / total number = 99 to 90 / 100 pieces ×: remaining number / total number = 89 or less / 100 pieces.

<Appearance [after water resistance test]>
◎: No change in appearance with respect to the coating film before the test ○: Slightly blurred, blistering or discoloration is seen with respect to the coating film before the test, but there is no problem when it is used as a product Level △: Slightly glazed, cracked, blistered or discolored with respect to the coating film before the test, and inferior as a product ×: Remarkably glossy, cracked, bulged with respect to the coating film before the test Or discoloration is seen.

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

<Appearance [after cooling cycle test]>
◎: No change in appearance with respect to the coating film before the test ○: Slightly blurred, blistering or discoloration is seen with respect to the coating film before the test, but there is no problem when it is used as a product Level △: Slightly glazed, cracked, blistered or discolored with respect to the coating film before the test, and inferior as a product ×: Remarkably glossy, cracked, bulged with respect to the coating film before the test Or discoloration is seen.

Claims (6)

  A multi-layer coating film forming method for forming a coating film of two or more layers on a base material, wherein an undercoat paint composition (A) containing an acrylic resin (a1) having a hydroxyl group and an epoxy group is applied on the base material And a top 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 of forming a multilayer coating film comprising the step of coating B) to form the uppermost coating film.   The method for forming a multilayer coating film according to claim 1, wherein the hydroxyl value of the acrylic resin (a1) having a hydroxyl group and an epoxy group is in the range of 20 to 170 mgKOH / g.   The method for forming a multilayer coating film according to claim 1 or 2, wherein the acrylic group (a1) having a hydroxyl group and an epoxy group has an epoxy group concentration in the range of 0.3 to 5.0 mol / kg.   The acrylic resin (a1) having a hydroxyl group and an epoxy group contains an aromatic polymerizable unsaturated monomer and / or an alicyclic polymerizable unsaturated monomer as a copolymerization monomer component, and the aromatic polymerizable unsaturated monomer and The total content of the alicyclic polymerizable unsaturated monomer is an acrylic resin having a hydroxyl group and an epoxy group obtained by polymerizing a mixture of 10 to 90% by mass with respect to the total amount of the monomer components. 4. The method for forming a multilayer coating film according to any one of 3 above.   The method for forming a multilayer coating film according to any one of claims 1 to 4, wherein the undercoating composition (A) further contains a polyisocyanate compound (a2).   The method for forming a multilayer coating film according to any one of claims 1 to 5, wherein the lowermost coating film and the uppermost coating film are heated and cured simultaneously.