JP5004015B2 - MULTILAYER COATING FORMATION METHOD AND COATED ARTICLE - Google Patents

Description

  The present invention relates to a method for forming a multilayer coating film and a coated article, and more specifically, a metal material such as a magnesium alloy, an aluminum alloy, and stainless steel in a household appliance, an OA device, a mobile device, an automobile part, etc. In addition, the present invention relates to a method for forming a multilayer coating film and a coated article that can form a multilayer coating film having glitter, high hardness, and excellent adhesion.

  As a method of painting magnesium alloy molded products, after chemical conversion treatment, apply a primer coat of a two-component urethane paint containing a glittering material, then apply an intermediate paint of a two-component urethane paint containing a glittering material, and finally A method of applying a UV curable resin coating as a top coating is known (for example, see Patent Document 1).

  However, in this method, a two-component urethane paint is used for the undercoat and the intermediate coat, and there are restrictions on the two-component preparation and working life, and a baking process is included in each step of the undercoat and the intermediate coat. Has a drawback in that it requires a UV irradiation step and is difficult to shorten.

  In addition, as a metallic coating excellent in color developability using magnesium or a magnesium alloy as an object to be coated, a two-coat two-bake (labeled “2C2B”) in which a clear coat having a color pigment is applied on a base coat containing light-reflective flakes. The type of metallic coating is known (for example, see Patent Document 2). In this Patent Document 2, acrylic resins, polyester resins, alkyl resins, fluororesins, etc. are exemplified as resins used for the base coat, and these resins are used by mixing with crosslinking agents such as amino resins and block polyisocyanate compounds. Is disclosed (see paragraph No. 0019 of Patent Document 2). Further, this Patent Document 2 discloses at least one kind of heat selected from an acrylic resin, a polyester resin, an alkyd resin, a fluororesin, a polycarbonate resin, and a modified resin thereof as a resin used for a paint for forming a clear coat layer. A mixture of a curable resin and a crosslinking agent such as an amino resin and / or a polyisocyanate compound is disclosed (see paragraph No. 0023 of Patent Document 2). In Patent Document 2, a paint including a resin containing a modified epoxy resin and a modified urethane is disclosed as a base coat in the examples, and a paint including an acrylic resin, a melamine resin, and an epoxy resin is used as a clear coat. It is disclosed (see the Example column of Patent Document 2). The metallic coating described in Patent Document 2 aims at coating with excellent color developability (see Example column and Paragraph number 0047 column of Patent Document 2).

  However, this method requires setting and baking processes (also referred to as drying processes) in the base coat and clear coat processes, making it difficult to shorten the process, and depending on variations in each baking condition, the base coat and clear coat processes are difficult. There is concern about poor adhesion between coats.

  Further, as a method for coating a metal material surface, a method is known in which, after chemical conversion treatment, an acrylic resin powder coating is used as a primer, a colored solvent paint is used as a base coat, and an acrylic resin powder clear coating paint is used as a top coat. (For example, refer to Patent Document 3).

  However, in this method, since powder coating is used for undercoating and topcoating, it is difficult to shorten the process by entering a baking process in each coating process, and depending on the variation in each baking condition, interlayer adhesion between the intermediate coating and the topcoat In addition, the use of acrylic resin-based powder clear coat paint as the top coat has the disadvantages that the primer and the top coat have to be thick to some extent in order to obtain the required smoothness. It was.

  Furthermore, although it is a vehicle wheel, as a coating method to obtain a plating-like appearance, an aluminum alloy, a magnesium alloy or the like is used as a base material, and after coating a powder coating that can form a glossy coating film, The intermediate coating composition containing an ultra-thin scaly aluminum having a thickness of 0.01 to 0.1 μm and a diameter of 1 to 60 μm is subjected to intermediate coating so that the film thickness after drying is 0.1 to 3 μm. A method of overcoating a colored or non-colored powder clear coat paint is known (see, for example, Patent Document 4).

  However, in this method, since powder coating is used for undercoating and topcoating, it is difficult to shorten the process by entering a baking process in each coating process, and depending on the variation in each baking condition, interlayer adhesion between the intermediate coating and the topcoat There was a drawback that there was concern about defects.

  Moreover, as a coating method to a plastic molded product, (a) polyester resin, (b) glass transition temperature 20-90 degreeC obtained by copolymerizing the monomer mixture containing 30-80 weight% of methyl methacrylate, a weight average A one-component base coat paint (A) containing an acrylic resin having a molecular weight of 5,000 to 50,000 and a hydroxyl value of 30 to 150 mgKOH / g, and (c) a block polyisocyanate in a specific ratio was applied, and then (D) a glass transition temperature of 20 to 90 ° C. obtained by copolymerizing a monomer mixture containing 15 to 50% by weight of methyl methacrylate, a weight average molecular weight of 3,000 to 20,000, and a hydroxyl value of 30 to 150 mgKOH / a two-component clear coat paint (B) containing an acrylic resin (g) and (e) a polyisocyanate It is known to paint (for example, see Patent Document 5). However, with this method, the use time is limited due to the use of a two-pack type topcoat clear, and a high-hardness coating film with a pencil hardness of 3H or higher is expected because it is formed by urethane bonding. There was a disadvantage that it was not possible.

  Furthermore, as a method for forming a top coat film by a 2-coat 1-bake method, as a base coat paint, a specific (d) vinyl copolymer 40 to 80% by weight, (e) an alkyl etherified melamine resin 10 to 50% by weight, (f A clear polyisocyanate comprising 0 to 40% by weight of a polyisocyanate, (g) a cellulose resin of 0 to 20% by weight, and (h) an organic crosslinked fine particle of 0 to 30% by weight. 40) 90% by weight of a copolymer of vinyl monomers containing 20% by weight or more of cycloalkyl ester of acrylic acid, (b) 5-50% by weight of alkyl etherified melamine resin, (c) blocked polyisocyanate It is known to use 5 to 50% by weight (see, for example, Patent Document 6).

  However, this method has a drawback that a high-hardness coating film having a pencil hardness of 3H or more cannot be expected because the topcoat clear has rubber elasticity based on a urethane bond.

JP 2006-150261 A JP 2001-191020 A Japanese Patent Laid-Open No. 10-024524 JP 2000-140748 A JP 2004-154625 A JP-A-6-142598

  An object of the present invention is to use a metallic paint that is formed on a metal material, in particular, a magnesium alloy, an aluminum alloy, or a stainless steel material, has a glittering property, has a high hardness, and is excellent in adhesion. It is providing the coating article formed by forming a coating film by the multilayer coating-film formation method and the multilayer coating-film formation method.

As means for solving the above problems,
Claim 1
“(1) (a) a melamine resin, a hydroxyl value of 50 to 100 mg KOH / g, and a hydroxyl group-containing acrylic resin having a glass transition temperature (Tg) of 50 to 100 ° C., a cellulose resin and / or a microgel; , Containing luster pigments,
(b) The ratio of the hydroxyl group-containing acrylic resin to the melamine resin is 50:50 to 90:10 in terms of solid content, and the ratio of the cellulose-based resin and / or the microgel is the hydroxyl group-containing acrylic resin and melamine. the total solid content of the resin, Ri 20% by mass in solid content, a base coat paint which has been diluted by a solvent, on the surface of the metal material, the step of painting,
(2) (a) containing a melamine resin and a hydroxyl group-containing acrylic resin having a hydroxyl value of 50 to 100 mgKOH / g and a glass transition temperature (Tg) of 70 to 100 ° C.
(b) a step of applying a clear coat paint in which the ratio of the hydroxyl group-containing acrylic resin to the melamine resin is 50:50 to 90:10 in terms of solid mass ratio;
(3) a step of simultaneously baking the base coat paint and the clear coat paint;
A method for forming a multilayer coating film characterized by comprising:
Claim 2
“The surface of the metal material is subjected to a chemical conversion treatment and then coated with a primer,” according to claim 1.
Claim 3
“Coated article obtained by the multilayer coating film forming method according to claim 1 or 2”.

  According to the present invention, a multi-layer coating film capable of forming a metallic coating film with high hardness and excellent glossiness on the surface of a metal material, in particular, on the surface of a magnesium alloy, an aluminum alloy, or stainless steel with good adhesion. A forming method can be provided.

  According to the present invention, for the base coat paint, the solid content ratio of the hydroxyl group-containing acrylic resin and the melamine resin is limited to a specific range, and the solid content ratio of the cellulosic resin and / or the microgel is limited to a specific range. Therefore, it is possible to provide a method for forming a multilayer coating film that has a separation property between an excellent base coat layer and a clear coat layer, and can obtain a coating film appearance excellent in aluminum orientation and clear smoothness.

According to the present invention, for the clear coat paint, since the solid content ratio of the hydroxyl group-containing acrylic resin and the melamine resin is limited to a specific range, the adhesion between the base coat layer and the clear coat layer when recoating is excellent. And the multilayer coating-film formation method which can form the coating film which has sufficient hardness can be provided.
According to the present invention, since the surface of the metal material is subjected to the chemical conversion treatment and the primer treatment, the adhesion between the surface of the metal material and the multilayer coating film can be further improved.
ADVANTAGE OF THE INVENTION According to this invention, the coated article which has the metallic coating film which was formed with the multilayer coating-film formation method which concerns on this invention, and had the high brightness and the outstanding brightness can be provided.

  The hydroxyl value of the hydroxyl group-containing acrylic resin contained in the base coat paint used in the method for forming a multilayer coating film of the present invention is 50 to 100 mgKOH / g, preferably 70 to 90 mgKOH / g. When the hydroxyl value is less than 50 mgKOH / g, a base coat layer having sufficient hardness cannot be obtained, and when the hydroxyl value exceeds 100 mgKOH / g, the base coat layer becomes brittle.

  Moreover, the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin contained in the base coat paint is 50 to 100 ° C., more preferably 55 to 90 ° C., and particularly preferably 60 to 90 ° C. When the glass transition temperature of the hydroxyl group-containing acrylic resin is less than 50 ° C., the coating film hardness is insufficient, and when it exceeds 100 ° C., the coating film becomes brittle.

Here, the glass transition temperature is a numerical value calculated from the formula shown below.
1 / Tg = Σ (mi / Tgi)
Tg: Glass transition temperature of hydroxyl group-containing acrylic resin mi: Molar fraction of monomer i component Tgi: Glass transition temperature (K) of homopolymer obtained by homopolymerizing monomer i component
Moreover, the weight average molecular weight of the hydroxyl group-containing acrylic resin contained in the base coat paint is preferably 7,000 to 20,000, more preferably 9,000 to 15,000. When the weight-average molecular weight of the hydroxyl group-containing acrylic resin is less than 7,000, the uneven orientation of the glittering pigment tends to occur, and when it exceeds 20,000, atomization at the time of atomization coating is deteriorated, and the smoothness of the obtained coating film is improved. Since it falls, it is not preferable.

  The hydroxyl group-containing acrylic resin contained in the base coat paint used in the method for forming a multilayer coating film of the present invention can be obtained using a known method such as a radical polymerization method.

  Specific examples of the copolymerizable radical polymerizable monomer having a hydroxyl group include, for example, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and methacrylic acid. 2-hydroxyethyl acid, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, allyl alcohol, an adduct of acrylic acid and versatic acid glycidyl ester, methacrylic acid and versatic acid glycidyl ester Adducts: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxy methacrylate Propyl, 3-hydroxypropyl methacrylate, (meth) ethylene oxide acrylate hydroxyalkyl esters and / or propylene oxide adducts of methacrylic acid 4-hydroxy butyl. The radically polymerizable monomer having a hydroxyl group can be used alone or in combination of two or more.

  Specific examples of other copolymerizable radical polymerizable monomers include, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, acrylic acid sec-butyl, hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, methacrylic acid n-butyl, isobutyl methacrylate, sec-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, lauryl methacrylate, methacrylic acid Allyl, styrene, acrylonitrile, methacrylonitrile and the like. These monomers may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the radical polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, 4,4′-azobis-4-cyanovaleric acid, -Azo compounds such as azobis-1-cyclohexanecarbonitrile and dimethyl-2,2'-azobisisobutyrate; methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,5,5-trimethylhexanone peroxide, 1,1-bis (t- Butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) -cyclohexane, 2,2-bis (t-butylperoxy) octane, t-butylhydroperoxide, diisopropylbenzene Hydroperoxide, dicumyl peroxide, t-butylcumyl peroxide, isobuty Ruperoxide, lauroyl peroxide, benzoyl peroxide, diisopropyl peroxydicarbonate, t-butylperoxy 2-ethylhexanoate, t-butylperoxyneodecanate, t-butylperoxylaurate, t-butylperoxybenzoate, t-butylperoxy Examples thereof include organic peroxides such as isopropyl carbonate and t-butyl peroxyacetate. These radical polymerization initiators may be used alone or in combination of two or more.

  The blending amount of the radical polymerization initiator is not particularly limited, but is preferably 0.01 to 20% by mass with respect to the total amount of the radical polymerizable monomer. Moreover, although radical polymerization temperature changes with kinds of radical polymerization initiator, it is preferable to carry out on the conditions of 50-200 degreeC, and it is more preferable to carry out on the conditions of 80-160 degreeC.

  Examples of the organic solvent used in the production of the hydroxyl group-containing acrylic resin include cycloaliphatic hydrocarbons such as cyclohexane and ethylcyclohexane, aromatic hydrocarbon solvents such as toluene, xylene, ethylbenzene and aromatic naphtha, acetone, methyl ethyl ketone, Ketone solvents such as methyl isobutyl ketone, cyclohexanone and isophorone, ethyl acetate, n-butyl acetate, methoxypropyl acetate, isobutyl acetate, 3-methoxybutyl acetate, ester solvents such as bis (2-ethylhexyl) adipate, dibutyl ether , Ether solvents such as tetrahydrofuran, 1,4-dioxane, 1,3,5-trioxane, nitrogen-containing solvents such as acetonitrile, valeronitrile, N, N-dimethylformamide, N, N-diethylformamide, and the like. . The organic solvent may be one kind alone or may be two or more kinds of mixed solvents. At this time, the solid content concentration of the hydroxyl group-containing acrylic resin can be arbitrarily selected as long as the dispersion stability of the resin is not impaired, but is usually 10 to 70% by mass in terms of solid content concentration.

  As the melamine resin contained in the base coat paint used in the method for forming a multilayer coating film of the present invention, conventionally known ones can be used, and examples thereof include butyl etherified melamine resin, methyl etherified melamine resin, and butylmethyl mixed etherified melamine resin. It is done.

Examples of commercially available butyl etherified melamine resins include Uban 21R (trade name, manufactured by Mitsui Chemicals, Inc.), Super Becamine G-821-60 (trade name, manufactured by Dainippon Ink and Chemicals, Inc.), and the like. Examples of commercially available methyl aleylated melamine resins and butyl methyl etherified melamine resins include Cymel 327 (trade name, manufactured by Nippon Cytec Industries Co., Ltd.), Nicarak MS-11 (trade name, Co., Ltd.) Sanwa Chemical Co., Ltd.).
The mixing ratio of the hydroxyl group-containing acrylic resin and melamine resin used in the base coat paint is 50/50 to 90/10 (hydroxyl group-containing acrylic resin / melamine resin) in terms of resin solid content ratio (mass ratio), preferably 70/30. ~ 90/10. If the amount of the melamine resin in the total solid content exceeds 50% by mass, the adhesion to the clear coat layer as a base during recoating becomes insufficient, and if it is less than 10% by mass, sufficient adhesion to the primer layer is obtained. Absent. Here, recoating refers to a coating operation in which a base coat paint is further applied on the clear coat layer to form a base coat layer. This recoating has an appearance on the surface of the final coating, such as a poor appearance due to foreign matter adhering to the coating, a poor appearance due to aggregates contained in the coating, and a poor appearance due to the repelling of the clear coat coating on the surface of the base coating. It may be performed when a product that has been evaluated as a defective product due to a defect is repainted to be a non-defective product.

  Further, the cellulose resin and / or the microgel contained in the base coat paint used in the method for forming a multilayer coating film of the present invention is used for the purpose of easily performing the 2-coat 1-bake coating method. Here, the 2-coat 1-bake coating method is also referred to as a wet-on-wet coating method, which is formed by applying a base coat paint and is still applied to the surface of the paint layer which is still uncured. Method of forming a paint layer by applying paint and forming a multi-layer coating film comprising a base coat layer and a clear coat layer by simultaneously baking a paint layer by a base coat paint and a paint layer by a clear coat paint Can be mentioned.

  Examples of the cellulose-based resin include thermoplastics based on a natural polymer fiber, particularly a carboxylic acid-modified cellulose resin obtained by modifying cellulose with carboxylic acid, such as cellulose acetate propionate. Resin (CAP), cellulose acetate butyrate (CAB) and the like can be mentioned as preferred examples. For example, CAB-381-0.5, 381-2, 531-1, 551-0.5 (trade names) Commercially available cellulose acetate butyrate resin such as Eastman Kodak Co.) can be suitably employed.

The microgel in the present invention includes, for example, a micron unit or less contained in a polymer non-aqueous dispersion produced by emulsion polymerization of a polyfunctional monomer and an acrylic or vinyl monomer copolymerizable therewith. Polymer fine particles having a particle size of
When emulsion polymerization is performed, polymerization initiators such as inorganic persulfates, water-soluble organic peroxides, and azo compounds, and anionic, cationic, and amphoteric emulsifiers are used. Polyfunctional (crosslinkable) monomers include glycol diacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, trimethylolpropane triacrylate, neopentyl glycol Examples include diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, and divinylbenzene. Examples of acrylic or vinyl monomers include methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, and styrene. Typical copolymer compositions include styrene / divinylbenzene copolymer, alkyl acrylate / divinylbenzene copolymer, alkyl acrylate / ethylene glycol / dimethacrylate copolymer.
Suitable microgels in the present invention include polymer fine particles contained in a polymer non-aqueous dispersion produced by the method described in JP-A-1-279902.
A polymer non-aqueous dispersion containing this suitable microgel is described in JP-A-1-279902,
(1) The following components
(a) a hydroxyl group-containing α, β-ethylenically unsaturated monomer,
(b) a polyfunctional α, β-ethylenically unsaturated monomer, and
(c) Emulsion polymerization of α, β-ethylenically unsaturated monomers other than (a) and (b) using a water-soluble polymerization initiator in the presence of a soap-free or ester group-containing surfactant After adding an organic solvent to the resulting polymer aqueous dispersion, a basic compound catalyst or an acidic compound catalyst is added, and the ester group-containing surfactant and the water-soluble compound are maintained at 95 ° C. or lower in a suspended state. A step of completely hydrolyzing the polymerization initiator;
(2) An acidic compound or a basic compound is added to the suspension to neutralize the basic compound catalyst or the acidic compound catalyst, and then a dispersion stabilizing resin is added, and then an organic acid amine salt is added to the suspension. And then separating the system into two layers, an organic layer and an aqueous layer, removing the aqueous layer, adding water to wash the organic layer, adding an organic acid amine salt, and allowing to stand to separate and remove the aqueous layer. Process,
(3) removing residual moisture in the organic layer;
Can be manufactured.

  The blending amount of the cellulose resin and / or the microgel is 1 to 20% by mass, preferably 5 to 15% by mass with respect to 100 parts by mass of the total resin solid content of the hydroxyl group-containing acrylic resin and melamine resin.

  When the blending amount of the cellulosic resin and / or the microgel is less than 1% by mass, the drying property of the base coat is not sufficient, and the separation property with the clear coat film is not good. If it exceeds 20% by mass, the interlayer adhesion between the base coat film and the clear coat film is not good. Here, the separation property means that the coating is applied when the clear coat paint is applied to the surface of the base coat film formed by applying the base coat paint on the surface of the metal material before the base coat paint is dried. This refers to the property that the paint component in the base coat film is difficult to diffuse into the clear coat paint. Therefore, if the clear coat film has a good separation property, when the clear coat paint is applied to the base coat layer, it becomes difficult for the components forming the clear coat film to penetrate into the base coat film. Transparency and high glossiness can be realized. However, generally speaking, when the separation property of the base coat layer and the clear coat layer is improved, the base coat layer and the clear coat layer are easily peeled off.In the present invention, the good separation property and good adhesion are obtained. It is possible to form a multilayer coating film having

  Furthermore, the base coat paint used in the method for forming a multilayer coating film of the present invention contains a glitter pigment.

  The glitter pigment includes metal powder pigment and / or pearl pigment, and the metal powder pigment includes aluminum powder, bronze powder, copper powder, tin powder, lead powder, zinc powder, iron phosphide, pearl metal coating Examples thereof include mica powder and mica-like iron oxide.

  The base coat paint contains pigments such as coloring pigments and extender pigments in addition to the glitter pigment, and an ultraviolet absorber, a light stabilizer, an antioxidant, a surface conditioner, a pigment dispersant, and a curing agent as necessary. It may contain paint additives such as catalysts and anti-settling agents.

  Examples of the color pigment include white pigments such as titanium oxide, black pigments such as carbon black, acetylene black, lamp black, bone black, graphite, iron black, and aniline black, yellow iron oxide, titanium yellow, monoazo yellow, and condensed azo yellow. , Azomethine yellow, bismuth vanadate, benzimidazolone, isoindolinone, isoindoline, quinophthalone, benzidine yellow, permanent yellow, and other yellow pigments, permanent orange and other orange pigments, red iron oxide, naphthol AS azo red, ansanthrone, Red pigments such as anthraquinonyl red, perylene maroon, quinacridone red pigment, diketopyrrolopyrrole, watching red, permanent red, cobalt purple, quinacridone violet, dioxazine Violet pigments such as Oretto, cobalt blue, phthalocyanine blue, blue pigments such as threne blue and green pigment such as phthalocyanine green and the like.

  The extender pigment is used for the purpose of reinforcing and increasing the coating film. In the present invention, a pigment known as an extender can be appropriately contained in the base coat paint. Examples of the extender pigment include barita powder, precipitated barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, alumina white, gloss white, mica powder, and the like.

  In the multilayer coating film forming method of the present invention, a clear coat paint is used. The hydroxyl value of the hydroxyl group-containing acrylic resin used for the clear coat paint is 50 to 100 mgKOH / g, preferably 70 to 90 mgKOH / g. When the hydroxyl value of the hydroxyl group-containing acrylic resin is less than 50 mgKOH / g, the glossiness is insufficient and the appearance of the coating film is deteriorated. When the hydroxyl value exceeds 100 mgKOH / g, the adhesion of the basecoat film to the clearcoat layer during recoating is insufficient. This is not preferable.

  Further, in order to obtain a composite film with high hardness, the clear coat layer forming the outermost layer film is required to be the hardest coat layer among the respective coat layers. Therefore, the glass transition temperature of the hydroxyl group-containing acrylic resin contained in the clear coat paint used for forming the clear coat layer is in a higher range than the glass transition temperature of the hydroxyl group-containing acrylic resin contained in the base coat paint. It is preferable. Specifically, the glass transition temperature of the hydroxyl group-containing acrylic resin contained in the base coat paint is preferably 50-100 ° C., whereas the glass transition temperature of the hydroxyl group-containing acrylic resin contained in the clear coat paint is 70- 100 degreeC is preferable, More preferably, it is 70-90 degreeC.

  If the glass transition temperature of the hydroxyl group-containing acrylic resin contained in the clear coat paint is less than 70 ° C., the coating film hardness becomes insufficient, and if it exceeds 100 ° C., the coating film becomes brittle.

  The weight average molecular weight of the hydroxyl group-containing acrylic resin contained in the clear coat paint is preferably 7,000 to 15,000, more preferably 9,000 to 15,000. When the weight average molecular weight of the hydroxyl group-containing acrylic resin is less than 7,000, the moisture resistance of the coating film is insufficient, and when it exceeds 15,000, the smoothness of the coating film is lowered, which is not preferable.

  The acid value of the hydroxyl group-containing acrylic resin is preferably in the range of 5 to 15 mgKOH / g. If the acid value is less than 5 mgKOH / g, the coating film hardness is insufficient, and if it exceeds 15 mgKOH / g, the adhesion during recoating is not preferred.

  As the melamine resin contained in the clear coat paint, a conventionally known melamine resin can be used, and it may be the same as the melamine resin used as the above-mentioned base coat paint.

  The mixing ratio of the hydroxyl group-containing acrylic resin and melamine resin in the clear coat paint used in the method for forming a multilayer coating film of the present invention is 50/50 in terms of resin solid content ratio (hydroxyl group-containing acrylic resin / melamine resin mass ratio). It is -90/10, More preferably, it is 60 / 40-80 / 20.

  If the amount of melamine resin in the total solid content of the hydroxyl group-containing acrylic resin and melamine resin exceeds 50% by mass, adhesion during recoating cannot be obtained, and if it is less than 10% by mass, sufficient coating film hardness cannot be obtained.

  The clear coat paint can contain coloring pigments, aluminum, pearl pigments and the like to the extent that transparency is not hindered, and can also contain silica, resin beads, etc. as a matting agent. Further, paint additives such as ultraviolet absorbers, light stabilizers, antioxidants, surface conditioners, and curing catalysts can be contained.

In the multilayer coating film forming method of the present invention, the base coat paint may be applied directly to the surface of the metal material, but the object is to improve the adhesion of the base coat layer to the surface of the metal material. Then, it is preferable to perform a chemical conversion treatment on the surface of the metal material, and further perform a primer treatment for applying a primer to the surface of the metal material subjected to the chemical conversion treatment.
As the primer used in the method for forming a multilayer coating film of the present invention, various primers can be adopted as long as the adhesion between the surface of the metal material and the base coat layer can be improved, and among them, an epoxy resin and a curing agent are contained. Primers are preferred.

  The epoxy resin contained in the primer preferably has two or more epoxy groups in one molecule, and conventionally known epoxy resins such as liquid epoxy resins and solid epoxy resins can be used without particular limitation. In the present invention, the epoxy resin includes a modified epoxy resin modified with a modifier. Examples of the modifier include, for example, a monocarboxylic acid having a linear or branched unsaturated hydrocarbon chain or saturated hydrocarbon chain having 1 to 18 carbon atoms, succinic acid and its anhydride, maleic acid and its anhydride. Dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, and dimer acid, trimellitic anhydride And a polycarboxylic acid such as pyromellitic anhydride, a carboxyl group-containing compound such as a carboxyl group-containing vinyl copolymer, an isocyanate group-containing compound, and a cyclic ester compound such as caprolactone. When a solid epoxy resin is used, the solid epoxy resin can be used by dissolving or dispersing it in an organic solvent that can be dissolved or dispersed.

Examples of commercially available epoxy resins that can be used in the present invention include JER1001, 1002 on the left, 1003 on the left, 1055 on the left, 1004 on the left, 1007 on the left (above, manufactured by Japan Epoxy Resins Co., Ltd.) Epototo YD-134, 011 012, left 013, left 014, left 017, left 7011R, left 907, (totokasei Co., Ltd.) E. Examples of modified epoxy resins such as bisphenol / epichlorohydrin type epoxy resins such as R662E, 663UE, 664U, 667E (above, manufactured by Dow Chemical Co., Ltd.) include Epicron P-439, H-305-45 (above, Dainippon). Ink Chemical Industry Co., Ltd.), Arakid 9201N, Same as left 9203N, Same as left 9208, (Arakawa Chemical Industries, Ltd.).
Preferred examples of the curing agent contained in the primer include at least one selected from melamine resins and blocked polyisocyanate compounds, polyamide resins, amine compounds, and the like. When the curing agent is a melamine resin and a blocked polyisocyanate compound, the primer is handled as a one-component paint, and when the curing agent is a polyamide resin or an amine compound, it is treated as a two-component paint. .

  The melamine resin as a curing agent contained in the primer may be the same as the melamine resin used as a base coat paint or a clear coat paint.

  Examples of the blocked polyisocyanate compound contained in the primer as a curing agent include compounds in which a non-yellowing polyisocyanate compound is blocked with a blocking agent. Specific examples include hexamethylene diisocyanate and trimethyl. Polyisocyanate compounds such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated difermethane diisocyanate, and hydrogenated xylylene diisocyanate, and their adducts, for example, addition reaction products formed by the addition reaction of the above various isocyanate compounds with hydroxyl group-containing compounds Products, burettes such as addition reaction products having bonds obtained by the addition reaction of urea bonds with isocyanate groups, and dimers (uretidiones) or trimers (isomers) of these. Anurelate) such as phenols such as phenol, m-cresol, xylenol, alcohols such as methanol, ethanol, butanol, 2-ethylhexanol, cyclohexanol, caprolactam, methyl ethyl ketone oxime, ethyl acetoacetate, Examples include those blocked with an active hydrogen-containing compound such as diethyl malonate.

  The polyamide resin as a curing agent contained in the primer is usually a resin having amino groups at both ends obtained by reacting a fatty acid dimer (dimer acid) with a diamine, and the molar ratio of dimer acid to amine. To adjust the molecular weight.

  As the amine compound contained in the primer as a curing agent, polyamine, amide polyamine, cyclic amine, aromatic amine and the like are used.

  The content ratio of the epoxy resin and the curing agent contained in the primer of the present invention is preferably 60/40 to 90/10 in terms of solid content ratio (epoxy resin / curing agent), and preferably 75/25 to 85/15. Is particularly preferred.

  When the content of the curing agent contained in the primer is less than 10% by mass in terms of solid content, the adhesion to the material may be insufficient, and when it exceeds 40% by mass, the base coat coating is applied. Adhesion of the film may be insufficient.

  The primer can contain a rust preventive pigment for the purpose of improving the corrosion resistance of the coating film. As the rust-preventing pigment, pigments that are usually used for undercoating can be used.

  Specific examples of rust preventive pigments include chromium-based pigments such as zinc chromate and strontium chromate, and non-polluting rust-preventing pigments that do not contain chromium. Rust pigments are preferred.

  Examples of pollution-free rust preventive pigments include (1) zinc phosphate rust preventive pigment, magnesium phosphate rust preventive pigment, aluminum phosphate rust preventive pigment, calcium phosphate rust preventive pigment, zinc phosphite rust preventive pigment, Magnesium phosphite rust preventive pigment, calcium phosphite rust preventive pigment, and condensed phosphate rust preventive pigments such as aluminum phosphite rust preventive pigment, (2) Treat the surface of particles made of condensed phosphate with a metal compound And (3) zinc molybdate rust preventive pigment, cyanamide zinc rust preventive pigment, zinc rust preventive pigment such as cyanamide zinc calcium rust preventive pigment, and (4) silica. These can be used alone or in combination of two or more.

  In the primer, pigments conventionally used for paints such as inorganic pigments, organic pigments, processed pigments other than rust preventive pigments are contained as necessary. Examples of the organic pigment include azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and the like. Examples of inorganic pigments include yellow iron oxide, red pepper, titanium dioxide, and carbon black.

In the present invention, the shape of the metal material as the object to be coated may be plate-shaped or molded. Examples of the metal material include magnesium alloy, aluminum alloy, and stainless steel, and magnesium alloy is particularly preferable. The magnesium alloy here includes JIS standard AZ91D, the aluminum alloy includes JIS standard ADC12, and the stainless steel includes JIS standard SUS304.
Examples of the coated article produced by the multilayer coating film forming method of the present invention include a mobile phone, a digital camera, an AV device, an electronic component, a vehicle interior / exterior part, a cosmetic container, and the like.

For the purpose of improving the adhesion of the base coat layer to the metal surface, these metal materials are preferably subjected to chemical conversion treatment according to the type of metal prior to primer coating.
The magnesium alloy is preferably subjected to a chemical conversion treatment such as a chromic acid type, a manganese phosphate type, or an organic adsorption type through a degreasing treatment using a solvent, an alkali, an emulsion, or the like, and a pickling treatment.
For aluminum and aluminum alloys, chemical conversion treatment of alkali-chromate, chromate, phosphate phosphate, and zinc phosphate is performed after degreasing treatment, washing treatment, and surface adjustment process. Is preferred.

  Further, for stainless steel, it is preferable to perform chromate treatment, polishing, shot blasting, pickling, etc. after degreasing treatment and water washing treatment. Furthermore, you may perform powder primer coating etc. to each chemical conversion processed metal raw material as needed.

  In the multilayer coating film forming method of the present invention, a base coat is applied to the surface of the primer layer formed by further applying a primer to the surface of the metal material, preferably the surface of the metal material subjected to chemical conversion treatment, and baking it. Without applying the paint and baking and hardening the base coat paint, the clear coat paint is applied by a wet-on-wet method, and the base coat paint and the clear coat paint are baked simultaneously.

  Examples of the method for applying the primer, base coat paint, and clear coat paint include air spray coating, airless spray coating, electrostatic coating, and immersion coating. Of these, spray coating is preferable. Examples of the dilution solvent for the paint used for spray coating include conventionally known solvents such as aromatic solvents, ester solvents, ketone solvents, and alcohol solvents.

  The preferred viscosity of the liquid primer is Iwata Cup NK2 (20 ° C.), preferably 10 to 30 seconds, and the dry coating thickness of the primer is preferably 10 to 50 μm, more preferably 10 to 30 μm.

  The preferred viscosity of the base coat paint is Iwata Cup NK2 (20 ° C.), preferably 7 to 20 seconds, and the dry coating thickness is preferably 5 to 40 μm, more preferably 10 to 30 μm.

  The suitable viscosity of the clear coat paint is preferably Iwatata Cup NK2 (20 ° C.) and adjusted to 10 to 30 seconds, and the dry coating thickness is preferably 10 to 50 μm, more preferably 10 to 40 μm.

When the base coat paint and the clear coat paint are applied wet-on-wet, it is preferable that the base coat paint is applied and then left at room temperature for several minutes before the clear coat paint is applied on the base coat paint.
When both the base coat and clear coating are cured at the same time, after applying the clear coat paint, set at room temperature for 5 to 30 minutes and then at a temperature of 100 to 180 ° C. for 10 to 120 minutes, preferably 150. It is preferable to heat at ˜170 ° C. for 15 to 30 minutes.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. Unless otherwise specified, “part” and “%” mean “part by mass” and “% by mass”, respectively.

<Manufacture of acrylic resin B-1 for base coat paint>
In a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a dropping funnel, 66.3 parts of xylene, 4 parts of Solvesso # 100 (trade name, manufactured by Esso Chemical Co., Ltd., aromatic naphtha), n -Charge 20 parts of butanol. The contents contained in the four-neck flask were heated to 140 ° C. Next, in this four-necked flask, a mixture of 71.4 parts of methyl methacrylate, 6.5 parts of butyl acrylate, 21 parts of 2-hydroxypropyl methacrylate, 1.1 parts of acrylic acid and 1.1 parts of acrylic acid monomer. And 2.3 parts of t-butylperoxy-2-ethylhexanoate as an initiator were dropped at a constant rate from a dropping funnel over 2 hours. After completion of the dropping, the contents of the four-necked flask were kept at the reflux temperature for 1 hour, and then the contents were cooled to 105 ° C. After cooling to 105 ° C., a mixed solution consisting of 0.4 parts of t-butylperoxy-2-ethylhexanoate and 7 parts of xylene is added to the contents of the cooled four-necked flask over 30 minutes. It was dropped at a constant speed. Then, the polymerization reaction was terminated when the contents of the four-necked flask were kept at 105 ° C. for 3 hours. From the obtained polymerization reaction product liquid, an acrylic resin B-1 for base coat paint having a solid content of 50% by mass, a hydroxyl value of 82, an acid value of 9, a glass transition temperature of 82 ° C., and a weight average molecular weight of 12,000 was obtained.

<Manufacture of acrylic resin B-2 to 6 for base coat paint>
Except having replaced with the monomer (polymerizable monomer) of the kind shown in Table 1, it manufactured similarly to B-1, and obtained acrylic resin B-2 to B6 for base coat paints. The characteristic values of the obtained resin are shown in Table 1.

  In the table, “Placcel FM-1D” is an unsaturated fatty acid hydroxyalkyl ester modified ε-caprolactone manufactured by Daicel Chemical Industries, Ltd. under the trade name.

<Production of microgel (polymer non-aqueous dispersion)>
A polymer aqueous dispersion A1 was prepared as follows by the production method described as “Production Example A1” in the lower left column and the lower right column of page 12 of JP-A-1-279902.
That is, in a flask equipped with a stirrer, a reflux condenser, two dropping funnels, a nitrogen introducing tube and a thermometer, 380 parts of deionized water and Lapisol B90 (manufactured by NOF Corporation, di-2-ethylhexyl) A surfactant aqueous solution that is a mixture with 7.4 parts of a trade name of sodium sulfosuccinate, 90% effective content) is charged, heated to 80 ° C. under a nitrogen stream, and an aqueous polymerization initiator solution (to 10 parts of deionized water). An aqueous solution obtained by dissolving 0.25 part of sodium persulfate) was added. After reaching 80 ° C. again, the particle-forming α, β-ethylenically unsaturated monomer mixture (1.2 parts of 2-hydroxyethyl methacrylate and ethylene glycol was maintained while maintaining the temperature of the mixture in the flask at 80 ± 2 ° C. A mixture of 3 parts of dimethacrylate, 15 parts of styrene and 80.8 parts of n-butyl methacrylate) was added dropwise over 3 hours. During the dropping of the monomer mixture, an aqueous polymerization initiator solution (a) (an aqueous solution in which 0.25 part of sodium persulfate was dissolved in 10 parts of deionized water) was added dropwise over 2 hours after 1 hour from the start of dropping. . After completion of dropping of the particle-forming α, β-ethylenically unsaturated monomer and the polymerization initiator aqueous solution (a), a polymer aqueous dispersion A1 was prepared by further heating to 80 ° C. for 2 hours for polymerization.
Subsequently, a microgel was produced as follows by the method of “Production Example B1” described on pages 18 to 19 of “JP-A-1-279902”.

  In a flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, 100 parts of the polymer aqueous dispersion A1, 400 parts of methylpentyl ketone and 45.3 parts of 3N aqueous sodium hydroxide solution were charged. The contents of the flask were heated to 85 ° C. and subjected to a hydrolysis reaction at 85 ± 2 ° C. for 3 hours. Next, the temperature is lowered to 80 ° C., 45.3 parts of 3N hydrochloric acid aqueous solution is added to the contents of the flask to neutralize, and then 143 parts of acrylic resin A solution is added to the contents of the flask as a particle dispersion stabilizing resin. After stirring for 10 minutes, 50 parts of a 20% aqueous solution of triethylamine acetate was added and the stirring was immediately stopped and the mixture was allowed to stand. The organic layer in which the polymer particles were dispersed was separated into the upper layer, and the aqueous layer was separated into the lower layer. The aqueous layer was removed. 400 parts of deionized water is added to the organic layer in which the remaining polymer particles are dispersed, and the temperature is raised to 70 ° C. with stirring. When the temperature reaches 70 ° C., 25 parts of a 20% aqueous solution of triethylamine acetate is added and immediately stirred. Stopped and left to stand. Again, since the organic layer in which the polymer particles were dispersed was separated into an upper layer and an aqueous layer was separated into a lower layer, the lower aqueous layer was removed. In the remaining organic layer, 2.6% by mass of water remained by a Karl Fischer moisture meter. Next, the temperature of the organic layer was cooled to 50 ° C., and 114 parts of methyl orthoformate were dropped from the dropping funnel over 30 minutes, and the reaction was continued at 50 ° C. for 30 minutes. Thereafter, 200 parts of xylene was added, a Dean-Stark trap was newly installed between the reflux condenser and the flask, the upper part of the reflux condenser and the aspirator were combined, and the flask was heated and stirred to reduce the pressure to 300 ± 100 mmHg, 80 Under conditions of ± 10 ° C., 504 parts of the solvent was distilled off to obtain a microgel (polymer non-aqueous dispersion). The heating residue of the obtained microgel was 50.2%, the viscosity by a Brookfield viscometer at 20 ° C. and 60 rpm was 543 cps, the average particle size by “Autosizer (trade name)” manufactured by Malvern was 83 nm, and the Karl Fischer moisture meter The moisture content due to was 0.1%.

The acrylic resin A was prepared as follows. That is, 42 parts of xylene was charged into a reactor equipped with a stirrer, a reflux condenser, a dropping funnel, a nitrogen introduction tube and a thermometer. The contents in the reactor were heated while stirring while introducing nitrogen gas into the reactor. When the temperature of the contents reached 140 ° C., 36.4 parts of n-butyl methacrylate and 2-ethylhexyl were added. Mixture of monomer mixture consisting of 11.7 parts of methacrylate, 11.1 parts of 2-hydroxyethyl methacrylate and 0.8 part of acrylic acid and 3.0 parts of t-butylperoxybenzoate which is a polymerization initiator 0 parts were dropped into the reactor at a constant rate over 2 hours with a dropping funnel while maintaining the contents of the reactor at 140 ° C. After dropping, the temperature was maintained at 140 ° C. for 2 hours, and then cooled, and the contents in the reactor were taken out. Acrylic resin A was separated from this content. The heating residue of this acrylic resin A was 60%, and the number average molecular weight was 6500.
<Manufacture of acrylic resin C-1 for clear paint>
Except having replaced with the raw material shown in Table 2, it manufactured similarly to B-1, and obtained acrylic resin C-1 to C-6 for clear coat paints. The characteristic values of the obtained resin are shown in Table 2.

<Preparation of base coat paint BC-1>
9 parts of an aluminum pigment (aluminum paste 6340NS; trade name, manufactured by Toyo Aluminum Co., Ltd.) made into a paste by being wetted with 15 parts of an organic solvent was stirred into 48.6 parts of base coat paint acrylic resin B-1. While adding gradually, a homogeneous mixture was prepared. Next, 8 parts of melamine resin (Cymel 325; trade name, manufactured by Nippon Cytec Co., Ltd.) and 2.2 parts of a 60% solution of epoxy resin (Epicoat 1001P; trade name, manufactured by Japan Epoxy Resin Co., Ltd.) 14 parts of a 20% solution of CAB (CAB531-1; trade name, manufactured by Eastman Kodak), 0.2 part of BYK-410 (trade name, manufactured by BYK Chemie) as an anti-settling agent, and azitol XL480 as a surface conditioner A base coat paint BC-1 was prepared by sequentially mixing 3 parts of a 10% solution (trade name, manufactured by Cytec Surface Specialty) and stirring uniformly.

<Creation of base coat paints BC-2 to BC-11>
Except having replaced with the raw material shown in Table 3, it manufactured similarly to BC-1, and obtained base coat paint BC-2-BC-11.

<Creation of clear paints CC-1 to CC-8>
The raw materials shown in Table 4 were sequentially mixed and stirred uniformly to prepare clear coat paints CC-1 to CC-8.

Notes in Tables 3 and 4) Melamine resin: “Cymel 325”, manufactured by Nippon Cytec Co., Ltd., trade name, solid content 80%
2) Epoxy resin solution: 60% xylene solution of trade name “Epicoat 1001P” manufactured by Japan Epoxy Resin Co., Ltd. 3) Cellulose: Cellulose Acetate Butyrate (CAB), manufactured by Eastman Kodak Company, trade name “CAB531-1” 20) Ethyl acetate solution of 4) Microgel: Organic crosslinked fine particle polymer non-aqueous dispersion prepared from Table 5 Production Example B1 of JP-A-1-279902, heating residue 50%
5) Aluminum pigment: “Aluminum paste 6340NS”, manufactured by Toyo Aluminum Co., Ltd., trade name, heating residue 70% by mass
6) Anti-settling agent: “BYK-410”, manufactured by BYK-Chemie Co., Ltd., trade name 7) Surface conditioner: Nihon Cytec Industries, Ltd., trade name “Azitol XL480”, 10% xylene solution 8) Diluting solvent: xylene / Butyl acetate = 70/30 mixed solution <Coating film test method>
(1) Base coat finger dryness After applying the base coat paint and leaving it to stand at room temperature for 3 minutes, the surface of the coating film is contacted with a finger and the drying property of the coating film surface is evaluated.
○: The surface is dry and the finger is not sticky. X: The surface is not sufficiently dried and the finger remains sticky. (2) Appearance (aluminum orientation)
The evaluation was performed based on flip-flop property (FF value), which is an index representing the brightness difference that changes depending on the visual direction. As a measuring apparatus, a commercially available metallic feeling evaluation apparatus (ALCOP LMR100, manufactured by Fuji Kogyo Co., Ltd.) was used.
○: FF value 1.7 or more ×: FF value less than 1.7 (3) Appearance (clear smoothness)
The smoothness of the surface of the overall coating film was judged visually.
○: Remarkably smooth (coating irregularities are hardly seen)
Δ: Decreased smoothness (coating irregularities are seen)
X: A considerable decrease in smoothness (the unevenness of the coating film is remarkable)
(4) Adhesion Cut lines with a cutter to reach the substrate on the coating surface, make 100 squares of 1.0mm in length and 1.0mm in width, stick adhesive cellophane tape on the surface, 20 The number of residual coatings in the squares after peeling them off rapidly at ℃ is examined. This adhesion evaluates the adhesion between the primer-coating layer, the base coat layer, and the clear coat layer.
○: All 100 pieces remain Δ: 99-95 pieces remain x: 94 pieces or less remain (5) Pencil hardness Mitsubishi Uni Co., Ltd., certified by the Japan Paint Inspection Association with 3H pencil hardness indication on the coating surface Is kept at 45 degrees and is pushed forward by about 10 mm with a load of about 1 kg, and the occurrence of peeling, cracking and scratching of the coating film is examined.
○: There is no occurrence of peeling, cracking and scratching of the coating film after 5 repetitions. ×: There is at least one occurrence of peeling, cracking and scratching of the coating film after 5 repetitions. ) Recoatability The test plate prepared as described in Example 1 was allowed to stand at room temperature for 1 day, and the same base coat as that used for the test plate without sanding on the clear coat paint film. The paint and the clear coat paint are applied wet-on-wet under the same conditions as the test plate, and baked to obtain a test plate for the recoatability test. This test plate is allowed to stand at room temperature for 3 days and then subjected to the above-described adhesion test. The evaluation criteria are the same as in the adhesion test. This recoatability test is a test method mainly for examining the adhesion between the clearcoat layer and the basecoat layer applied thereon.

Example 1
On the surface of a commercially available magnesium alloy (Mg—Al—Zn alloy, equivalent to JIS AZ91D) subjected to chemical conversion treatment with a manganese phosphate chemical conversion treatment agent (Mugbond P10: trade name, manufactured by Parker Processing Co., Ltd.) Fine primer no. A primer coating film was formed by applying 5000 (trade name, manufactured by BASF Coatings Japan Co., Ltd., epoxy resin / melamine cross-linking primer) with air spray so that the dry coating thickness was 20 μm. This primer coating was baked at 160 ° C. for 20 minutes. Next, the viscosity of the base coat paint BC-1 was adjusted to 12 seconds (20 ° C.) with Iwata Cup NK2 by adding and mixing a diluting solvent (xylene / butyl acetate = 50/50 mixed solution). Viscosity-adjusted base coat paint BC-1 was applied to the surface of the primer layer by air spray so that the dry film thickness was 15 μm. After setting the base coat paint film at room temperature for 3 minutes, the viscosity of the clear coat paint CC-1 is set on the uncured base coat paint film by using a diluent solvent (xylene / butyl acetate = 50/50). By adding and mixing the mixed solution), the clear coat paint CC-1 adjusted to 16 seconds (20 ° C.) with Iwata Cup NK2 was applied by air spray so that the dry film thickness was 25 μm. . The base coat paint film and the clear coat paint film formed on the paint film were baked at 160 ° C. for 20 minutes to obtain a test plate. The coating test results are shown in Table 5.

注：表５において、ＢＣはベースコート層を示し、ＣＣはクリヤーコート層を示し、ＡＣはアクリル樹脂を示し、ＭＦはメラミン樹脂を示す。

Note: In Table 5, BC represents a base coat layer, CC represents a clear coat layer, AC represents an acrylic resin, and MF represents a melamine resin.

(Examples 2-5, Comparative Examples 1-14)
A test plate was prepared in the same manner as in Example 1 except that the base coat paint and the clear coat paint shown in Tables 5 to 7 were used. The test results are shown in Tables 5 to 7 (Example 6).
Example 1 except that the material was changed to a commercially available aluminum alloy (Al—Si—Cu alloy, equivalent to JIS ADC12), and the chemical conversion treatment was changed to an organometallic salt (Palcoat 3753: trade name, manufactured by Nippon Parkerizing Co., Ltd.) A test plate was prepared in the same manner as described above. The coating test results are shown in Table 5 (Example 7)
The material is commercially available stainless steel (austenite type, equivalent to JIS SUS304), the chemical conversion treatment is chromate type (Palchrome R282: trade name, manufactured by Nihon Parkerizing Co., Ltd.), and the primer is epoxy resin / amide polyamine crosslinked type (Bell Fine Primer No. 2000: A test plate was prepared in the same manner as in Example 1 except that the trade name was changed to a trade name, manufactured by BASF Coatings Japan Co., Ltd. The coating test results are shown in Table 5.

注：表６及び表７において、ＢＣはベースコート層を示し、ＣＣはクリヤーコート層を示し、ＡＣはアクリル樹脂を示し、ＭＦはメラミン樹脂を示す。
＜まとめ＞
表５〜表７に示す結果から明らかなように、本発明に従う実施例１〜７は、塗膜外観、付着性、リコート性において、優れていることがわかる。

Note: In Tables 6 and 7, BC represents a base coat layer, CC represents a clear coat layer, AC represents an acrylic resin, and MF represents a melamine resin.
<Summary>
As is apparent from the results shown in Tables 5 to 7, it can be seen that Examples 1 to 7 according to the present invention are excellent in coating film appearance, adhesion, and recoatability.

  In Comparative Example 1, the hydroxyl value of the hydroxyl group-containing acrylic resin used for the base coat paint is less than 50 mgKOH / g and inferior in adhesion, pencil hardness, and recoatability. In Comparative Example 2, the hydroxyl value of the hydroxyl group-containing acrylic resin is 100 mgKOH / g. g was exceeded, and adhesion and recoatability were inferior. In Comparative Example 3, since the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin used for the base coat paint was less than 50 ° C., the pencil hardness was inferior, and in Comparative Example 4, the recoatability was inferior because it was 100 ° C. or higher. Further, in Comparative Example 5, since the blending amount of the cellulose-based resin in the base coat paint is less than 1% by mass with respect to 100 parts by mass of the total resin solid content of the hydroxyl group-containing acrylic resin and melamine resin, the touch after the base coat paint is applied It was inferior to dryness, and in Comparative Example 6 which is 25 mass% or more, it was inferior to interlayer adhesion and recoatability. Furthermore, Comparative Example 7 is inferior in adhesion and pencil hardness when the amount of melamine resin in the total solid content of the hydroxyl group-containing acrylic resin and melamine resin used in the base coat paint is less than 10% by mass, and Comparative Example 8 is the amount of melamine resin. Was over 50% by mass, and the recoatability was poor. In Comparative Example 9, the amount of melamine resin in the total solid content of the acrylic resin and melamine resin used for the clear coat paint exceeds 50% by mass, the smoothness and recoatability are inferior, and the amount of melamine resin is less than 10% by mass. In certain Comparative Example 10, sufficient coating film hardness was not obtained. In Comparative Example 11, the hydroxyl value of the hydroxyl group-containing acrylic resin used in the clear coat paint is less than 50 mgKOH / g, and the pencil hardness and recoatability are inferior. In Comparative Example 12, the hydroxyl value of the hydroxyl group-containing acrylic resin exceeds 100 mgKOH / g. The film appearance was poor and the recoatability was poor. In Comparative Example 13, since the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin used for the clear coat paint is less than 70 ° C., the pencil hardness is inferior, and in Comparative Example 14, the recoating property is inferior because it is 100 ° C. or higher. .

Claims (3)

(1) (a) a hydroxyl group-containing acrylic resin having a melamine resin and a hydroxyl value of 50 to 100 mgKOH / g and a glass transition temperature (Tg) of 50 to 100 ° C., a cellulose resin and / or a microgel, Containing a luster pigment,
(b) The ratio of the hydroxyl group-containing acrylic resin to the melamine resin is 50:50 to 90:10 in terms of solid content, and the ratio of the cellulose-based resin and / or the microgel is the hydroxyl group-containing acrylic resin and melamine. the total solid content of the resin, Ri 20% by mass in solid content, a base coat paint which has been diluted by a solvent, on the surface of the metal material, the step of painting,
(2) (a) containing a melamine resin and a hydroxyl group-containing acrylic resin having a hydroxyl value of 50 to 100 mgKOH / g and a glass transition temperature (Tg) of 70 to 100 ° C.
(b) a step of applying a clear coat paint in which the ratio of the hydroxyl group-containing acrylic resin to the melamine resin is 50:50 to 90:10 in terms of solid mass ratio;
(3) a step of simultaneously baking the base coat paint and the clear coat paint;
A method for forming a multilayer coating film, comprising:   The method for forming a multilayer coating film according to claim 1, wherein the surface of the metal material is subjected to chemical conversion treatment and then coated with a primer.   The coated article obtained by the multilayer coating-film formation method of the said Claim 1 or 2.