JP6654331B2 - Multilayer coating method - Google Patents

Description

  The present invention relates to a method for forming a multi-layer coating film capable of forming a multi-layer coating film that ensures water-resistant adhesion and has excellent metallic gloss.

  The purpose of applying the paint is mainly to protect the material and to impart aesthetic appearance. In the case of industrial products, aesthetics, especially, "texture" is important from the viewpoint of enhancing the product power. The texture of industrial products demanded by consumers is diverse, but in recent years, in the fields of automobile outer panels, automobile parts, home electric appliances and the like, glossiness such as metal or pearl has been demanded (hereinafter referred to as “metal”). Gloss).)

  Metallic luster means that there is no graininess on the surface like a mirror surface, and when viewed close to perpendicular to the coated plate (highlight), it shines brightly, and when viewed from diagonally above the coated plate (shade) ) Is a texture that looks dark, that is, the luminance difference between the highlight area and the shade area is large.

  Techniques for imparting such metallic luster to the surface of an industrial product include metal plating and metal vapor deposition (eg, Patent Document 1), but a clear coat paint is usually applied to protect the surface. Therefore, adhesion to the treated surface and durability are required.

  On the other hand, it is advantageous from the viewpoints of simplicity, cost, and the like if the metal plating treatment or the metal deposition treatment as described above can impart a metallic luster by painting. For example, Patent Document 2 proposes a method for forming a metallic coating film, which comprises applying a composition containing nonleafing aluminum flakes and an organic solvent to an uncured coating surface, and then applying a clear coating. ing. Patent Document 3 proposes a coating method using a vapor-deposited aluminum piece provided with a leafing property. However, vapor-deposited aluminum having a leafing property is present in a large amount near the interface because the surface tension of the aluminum pigment is low, thereby causing a decrease in adhesion and easily causing peeling between the clear coating film layer. There was a problem of becoming.

  In recent years, from the viewpoint of low environmental load and the like, water-based paints have been required in the field of metal-based paints. For example, Patent Document 4 discloses a brilliant pigment obtained by pulverizing a deposited metal film into metal pieces. An aqueous cellulose derivative having an acid value of 20 to 150 mgKOH / g (solid content), wherein the aqueous cellulose derivative is used as a main binder resin, and the content of the glitter pigment is 20 to 70% by mass in PWC. An aqueous base coating composition characterized by the following has been proposed.

  However, the coating film formed by the paint described in Patent Document 4 has a problem in water resistance and the like.

JP-A-63-272544 JP-A-11-90318 JP 2005-144338 A JP 2009-155537 A

  It is an object of the present invention to provide a method for forming a multilayer coating film capable of forming a multilayer coating film having excellent water gloss and excellent metallic gloss.

As a result of intensive studies, the present inventors crushed the water-dispersible acrylic polymer particles (A), the cellulose derivative (B), the curing agent (C), and the vapor-deposited metal film on the object to be coated. A brilliant pigment-containing aqueous base coat paint containing the brilliant pigment (D) is applied to form a base coat coating film, and a specific acrylic resin (E), a hydroxyl group-containing acrylic resin ( It has been found that the above object can be achieved by a multilayer coating film forming method of forming a clear coat coating film by applying a clear coat paint containing F) and a curing agent (G), thereby completing the present invention. .
Thus, the present invention provides a glitter pigment (pulverized water-dispersible acrylic polymer particles (A), a cellulose derivative (B), a curing agent (C), and a vapor-deposited metal film on a substrate to form a metal piece). An aqueous base coat paint containing a brilliant pigment containing D) is applied to form a base coat film, and N-substituted (meth) acrylamide (i) and a hydroxyl group-containing polymerizable unsaturated monomer are formed on the base coat film. (Ii) an acrylic resin (E) which is a copolymer of a carboxyl group-containing polymerizable unsaturated monomer (iii) and another polymerizable unsaturated monomer (iv) other than (i) to (iii) Forming a clear coat film by applying a clear coat paint containing a hydroxyl group-containing acrylic resin (F) other than the resin (E) and a curing agent (G). To provide.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to form a multi-layer coating film having excellent adhesion to water and excellent metallic luster.

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

Substrate:
The object to which the method of the present invention can be applied is not particularly limited. For example, an outer plate portion of an automobile body such as a passenger car, a truck, a motorcycle, a bus; an automobile part; An outer plate portion of an electric product and the like can be mentioned, and among them, an outer plate portion of an automobile body and an automobile part are preferable.

  The substrate constituting these objects to be coated is not particularly limited, and may be, for example, an iron plate, an aluminum plate, a brass plate, a copper plate, a stainless steel plate, a tin plate, a galvanized steel plate, an alloyed zinc (Zn-Al , Zn-Ni, Zn-Fe, etc.) Metal plates such as plated steel plates; polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy Resin such as resin and plastic materials such as various FRPs; inorganic materials such as glass, cement and concrete; wood; fiber materials (paper, cloth, etc.), among which metal plates or plastic materials are preferred. is there.

  The object to be coated may be an undercoat film or an undercoat film and an intermediate coat film formed on the above-described substrate. When the base material is made of metal, it is preferable that a chemical conversion treatment such as a phosphate treatment, a chromate treatment, a metal oxide treatment, or the like be performed before the undercoating film is formed.

  The undercoat film is formed for the purpose of imparting anticorrosion properties, rust prevention properties, adhesion to a substrate, concealment of irregularities on the substrate surface (sometimes referred to as "underground concealment"), and the like. The undercoat paint used to form the undercoat film may be a known undercoat paint, for example, for a conductive substrate such as a metal, a cationic electrodeposition paint And an anionic electrodeposition paint. It is preferable to use a chlorinated polyolefin resin paint for a low-polar base material such as polypropylene.

  After application, the undercoat paint may be cured by means such as heating or blowing, or may be dried to such an extent that it is not cured. When a cationic electrodeposition paint or an anion electrodeposition paint is used as the undercoat, an undercoat and a multilayer coating having excellent appearance are prevented by preventing a layer between the coatings formed subsequently on the undercoat. In order to form the undercoat, it is preferable that the undercoat is cured by heating after the application of the undercoat.

  In addition, the intermediate coating film has an adhesive property with the undercoat coating film, a hiding property of the undercoat coating color (sometimes referred to as “color hiding property”), a hiding property of irregularities on the surface of the undercoat coating film, and an anti-coating property. It is formed on the undercoat film for the purpose of imparting chipping properties and the like.

  The intermediate coating film can be formed by applying an intermediate coating material, and the film thickness of the cured film is preferably in the range of usually 10 to 50 μm, particularly preferably 15 to 30 μm.

  As the intermediate coating, a known coating can be used.For example, as a vehicle component, a base resin such as a hydroxyl group-containing polyester resin or a hydroxyl group-containing acrylic resin, and a melamine resin or a crosslinking agent such as a blocked polyisocyanate. And an intermediate coating composition comprising the same.

  Intermediate coatings can be cured or touch-dried by means of heating, air blowing, etc. after coating, so that mixing with the coating applied subsequently to the intermediate coating film is suppressed, resulting in a multi-layer coating with excellent appearance. It is preferable because a film can be formed.

  In the method of the present invention, a glittering pigment-containing aqueous basecoat paint is applied on the above-mentioned substrate.

Aqueous basecoat paint containing bright pigment:
The brilliant pigment-containing aqueous base coat paint comprises a brilliant pigment (D), which is obtained by pulverizing a water-dispersible acrylic polymer particle (A), a cellulose derivative (B), a curing agent (C), and a deposited metal film into a metal piece. contains.

Water-dispersible acrylic polymer particles (A):
The water-dispersible acrylic polymer particles (A) constitute at least a part of the base resin in the present coating composition, and are usually prepared by polymerizing the polymerizable unsaturated monomer in the presence of a dispersion stabilizer such as a surfactant. Which is obtained by emulsion polymerization using a radical polymerization initiator, and particularly includes a polymerization containing a polymerizable unsaturated monomer (M-1) having two or more polymerizable unsaturated groups in one molecule. Water-dispersible acrylic polymer particles obtained by emulsion polymerization of a mixture of polymerizable unsaturated monomers, the polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule (M- Water-dispersible acrylic polymer particles obtained by subjecting 1) to emulsion polymerization with one or more other polymerizable unsaturated monomers (M-2) can be suitably used.

  The polymerizable unsaturated monomer (M-1) having two or more polymerizable unsaturated groups in one molecule includes an amide group-containing polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule. A saturated monomer (M-1-1), and other polymerizable unsaturated monomers (M-1-2) having two or more polymerizable unsaturated groups in one molecule. In particular, an amide group-containing polymerizable unsaturated monomer (M-1-1) having two or more polymerizable unsaturated groups in one molecule can be suitably used.

  Examples of the amide group-containing polymerizable unsaturated monomer (M-1-1) having two or more polymerizable unsaturated groups in one molecule include, for example, N, N'-methylenebis (meth) C1-6 alkylenebis (meth) acrylamide such as acrylamide, N, N'-ethylenebis (meth) acrylamide, N, N'-tetramethylenebis (meth) acrylamide; N, N'-1,3-phenylenebisacrylamide N, N '-(oxymethylene) bisacrylamide and the like. Examples of the polymerizable unsaturated monomer (M-1-2) having two or more polymerizable unsaturated groups in one molecule other than the monomer (M-1-1) include, for example, allyl (meth) Acrylate and 1,6-hexanediol di (meth) acrylate can be exemplified.

  The other polymerizable unsaturated monomer (M-2) is not particularly limited as long as it copolymerizes with the amide group-containing polymerizable unsaturated monomer (M-1). , A carboxyl group-containing polymerizable unsaturated monomer (M-2-1), a hydroxyl group-containing polymerizable unsaturated monomer (M-2-2), and other polymerizable unsaturated monomers (M-2-1). 2-3) and the like.

  Examples of the carboxyl group-containing polymerizable unsaturated monomer (M-2-1) include unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid; and unsaturated monomers such as maleic acid, fumaric acid, and itaconic acid. Examples thereof include dicarboxylic acids and half-monoalkyl esterified products of these unsaturated dicarboxylic acids, and these can be used alone or in combination of two or more. Among these, (meth) acrylic acid is preferable from the viewpoint of the viscosity development of the paint and the performance of the coating film.

  Examples of the hydroxyl group-containing polymerizable unsaturated monomer (M-2-2) include 2-hydroxyethyl (meth) acrylate, 2- or 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth). And C2-10 hydroxyalkyl esters of (meth) acrylic acid such as acrylate). The hydroxyl group in the hydroxyl group-containing polymerizable unsaturated monomer (M-2-2) can function as a functional group that reacts with the curing agent (C). These hydroxyl group-containing polymerizable unsaturated monomers (M-2-2) can be used alone or in combination of two or more.

  Further, other polymerizable unsaturated monomers (M-2-3) other than the above polymerizable unsaturated monomers (M-2-1) and (M-2-2) may be used. Examples of such a polymerizable unsaturated monomer (M-2-4) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and i-propyl (meth). (Meth) such as acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, and lauryl (meth) acrylate C1-20 alkyl esters of acrylic acid; aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene; glycidyl (meth) acrylic Glycidyl group-containing vinyl compounds such as acetate and allyl glycidyl ether; nitrogen-containing alkyl (C1-20) (meth) acrylates such as dimethylaminoethyl (meth) acrylate; vinyl such as vinyl acetate, vinyl propionate and vinyl chloride Compounds: Nitrile compounds containing a polymerizable unsaturated bond such as acrylonitrile and methacrylonitrile; and diene compounds such as butadiene and isoprene.

  As the other polymerizable unsaturated monomers (M-2), the above-mentioned polymerizable unsaturated monomers (M-2-1) to (M-2-3) are used alone or in combination of two or more. Can be used.

  Examples of the water-dispersible acrylic polymer particles (A) include a polymerizable unsaturated monomer (M-1) having two or more polymerizable unsaturated groups in one molecule, and a carboxyl group-containing polymerizable unsaturated monomer. Those obtained by emulsion-polymerizing a polymerizable unsaturated monomer mixture containing a monomer (M-2-1) and a hydroxyl group-containing polymerizable unsaturated monomer (M-2-2) are preferable. Among them, those using methacrylic acid as the carboxyl group-containing polymerizable unsaturated monomer (M-2-1) are particularly preferable from the viewpoint of the water resistance of the coating film. The reason for this is that methacrylic acid has a lower degree of dissociation in water than acrylic acid, and the carboxyl group, which is a hydrophilic functional group, is more uniformly distributed inside the particles than acrylic acid. It is conceivable that the localization is difficult to occur.

  In addition, in this specification, "(meth) acrylate" means acrylate or methacrylate, and "(meth) acrylic acid" means acrylic acid or methacrylic acid. Further, “(meth) acryloyl” means acryloyl or methacryloyl, and “(meth) acrylamide” means “acrylamide or methacrylamide”.

  The compounding ratio of the polymerizable unsaturated monomer (M-1) having two or more polymerizable unsaturated groups in one molecule in the polymerizable unsaturated monomer mixture is determined by the finish of the coating film and the water dispersibility. From the viewpoint of storage stability of the acrylic polymer particles (A), generally 0.1 to 5% by mass, preferably 0.5 to 4% by mass, and more preferably, based on the total amount of the polymerizable unsaturated monomer. Can be in the range of 1 to 3.5% by mass.

  The mixing ratio of the carboxyl group-containing polymerizable unsaturated monomer (M-2-1) in the polymerizable unsaturated monomer mixture is generally 0.1 from the viewpoint of the appearance of the coating film and water resistance. To 20% by mass, preferably 0.5 to 15% by mass, more preferably 1 to 10% by mass, and further comprises a hydroxyl group-containing polymerizable unsaturated monomer (M-2-2). Is generally 0.1 to 20% by mass, preferably 1 to 15% by mass, and more preferably 2 to 10% by mass from the viewpoints of curability and water resistance of the coating film. it can. Among them, it is particularly preferable to use methacrylic acid as the carboxyl group-containing polymerizable unsaturated monomer (M-2-1) in the above mixing ratio.

  The water-dispersible acrylic polymer particles (A) are, in the presence of an emulsifier and in the presence of a radical polymerization initiator, a polymerizable unsaturated monomer (M- It can be obtained by emulsion polymerization of 1) together with another polymerizable unsaturated monomer (M-2).

  Examples of the emulsifier include anionic emulsifiers such as sodium dialkylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene alkylphenyl ether sulfate and sodium alkyldiphenyl ether disulfonate; lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium Cationic emulsifiers such as chloride and alkylbenzyldimethylammonium chloride; nonionic emulsifiers such as polyoxyethylene higher alcohol ether and polyoxyethylene alkylphenyl ether; and reactive emulsifiers having a polymerizable unsaturated group. Can be.

  As the emulsifier, it is preferable to use a reactive emulsifier, and from the viewpoint of the water resistance of the obtained coating film, it is particularly preferable to use an anionic reactive emulsifier.

  Examples of the anionic reactive emulsifier include a sodium salt and an ammonium salt of a sulfonic acid compound having a polymerizable unsaturated group such as a (meth) allyl group, a (meth) acryl group, a propenyl group, and a butenyl group. be able to. Among these, an ammonium salt of a sulfonic acid compound having a polymerizable unsaturated group is preferable because the obtained coating film has excellent water resistance. Examples of commercially available products of the ammonium salt of the sulfonic acid compound include Latemul S-180A (trade name, manufactured by Kao Corporation).

  Further, among the ammonium salts of the sulfonic acid compound having a polymerizable unsaturated group, an ammonium salt of a sulfonic acid compound having a polymerizable unsaturated group and a polyoxyalkylene group is more preferable. Commercially available ammonium salts of sulfonic acid compounds having a polymerizable unsaturated group and a polyoxyalkylene group include, for example, Aqualon KH-10 (Daiichi Kogyo Seiyaku Co., Ltd., trade name), SR-1025A (Asahi Denka Kogyo) Company name, trade name).

  The concentration of the emulsifier is preferably in the range of usually 0.1 to 10% by mass, particularly preferably 1 to 5% by mass, based on the total amount of the radical polymerizable unsaturated monomers used.

  The water-dispersible acrylic polymer particles (A) preferably have a multilayer structure synthesized by a multi-step reaction. Specifically, for example, a core / shell structure having a two-layer structure and a first core / second core / shell structure having a three-layer structure can be given. From the viewpoints of coating film performance, productivity of the water-dispersible acrylic polymer particles (A), and the like, those having a core / shell structure of a two-layer structure are preferable. Among them, those in which the core portion is crosslinked in the particle and the shell portion is substantially uncrosslinked are particularly preferable from the viewpoints of coating film performance and finishability of the coating film.

  The water-dispersible acrylic polymer particles (A) having a core / shell structure in which a core portion is cross-linked in a particle include, for example, a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule first. The polymerizable unsaturated monomer mixture (I) containing (M-1) is subjected to emulsion polymerization to form a core portion, and then the carboxyl group-containing polymerizable unsaturated monomer (M-2-1) is prepared. It can be obtained by adding the polymerizable unsaturated monomer mixture (II) contained therein and further performing emulsion polymerization to form a shell portion.

  The proportion of the carboxyl group-containing polymerizable unsaturated monomer (M-2-1) used in the water-dispersible acrylic polymer particles (A) having a core / shell structure in which the core portion is crosslinked in the particles is as follows: In the synthesis of the core portion, it is usually in the range of 0 to 10% by mass, particularly 0 to 5% by mass, more preferably 0 to 5% by mass, based on the mass of the polymerizable unsaturated monomer mixture (I) forming the core portion. ２2% by mass, and in the subsequent synthesis of the shell part, usually 5-30% by mass, especially 7-25% by mass, based on the mass of the polymerizable unsaturated monomer mixture forming the shell portion. In particular, it is preferable to be within the range of 10 to 20% by mass.

  Further, when the polymerizable unsaturated monomer mixture (I) contains a polymerizable unsaturated monomer (M-1) having two or more polymerizable unsaturated groups in one molecule, The unsaturated monomer mixture (II) is obtained by further adding an aromatic vinyl compound to the polymerizable unsaturated monomer forming a shell portion in addition to the carboxyl group-containing polymerizable unsaturated monomer (M-2-1). It is preferably contained in an amount of usually 2 to 30% by mass, particularly 5 to 20% by mass based on the mass of the monomer mixture (II).

  Examples of the aromatic vinyl compound include styrene, α-methylstyrene, vinyltoluene and the like, and among them, styrene is particularly preferable.

  Further, in particular, the water-dispersible acrylic polymer particles (A) having a core / shell structure in which the core portion is cross-linked in a particle first have a polymerizable unsaturated group having two or more polymerizable unsaturated groups in one molecule. The saturated monomer (M-1) is used in an amount of usually 0.1 to 5% by mass, preferably 0.5 to 4% by mass, based on the mass of the polymerizable unsaturated monomer mixture (I) forming the core portion. The polymerizable unsaturated monomer mixture (I) contained in the range of 0.7% to 3.5% by mass, more preferably 0.75 to 3.5% by mass, is emulsion-polymerized, and then the polymerizable unsaturated monomer mixture forming the shell portion is formed. The carboxyl group-containing polymerizable unsaturated monomer (M-2-1) is usually in the range of 3 to 30% by mass, preferably 6 to 25% by mass, based on the mass of the saturated monomer mixture (II). , More preferably in the range of 11 to 20% by mass, and styrene usually in the range of 2 to 30% by mass. Or a polymerizable unsaturated monomer mixture (II) forming a shell portion contained in the range of 5 to 20% by mass, more preferably in the range of 11 to 20% by mass, and further emulsion-polymerized. The water-dispersible acrylic polymer particles obtained by the above method are preferred.

  When the water-dispersible acrylic polymer particles (A) have a two-layer structure, the mass ratio of the core part / shell part is not strictly limited, but from the viewpoint of the appearance and water resistance of the coating film, It is generally in the range from 95/5 to 50/50, in particular from 85/15 to 60/40, more particularly in the range from 80/20 to 65/35, based on the weight of all radically polymerizable unsaturated monomers used. Is preferred.

  In addition, as a method of cross-linking the water-dispersible acrylic polymer particles in the particles, in addition to the polymerizable unsaturated monomer (M-1) having two or more polymerizable unsaturated groups in one molecule, for example, a carboxyl group A small amount of a polymerizable unsaturated monomer (M-2-1) having a glycidyl group and a polymerizable unsaturated monomer (M-2-1) having a glycidyl group; It is also possible to use a method in which 2) and a polymerizable unsaturated monomer having an isocyanate group are used in small amounts, respectively.

  Examples of the polymerization initiator include peroxides represented by, for example, ammonium persulfate, potassium persulfate, ammonium peroxide, and the like; reduction of these peroxides with sodium hydrogen sulfite, sodium thiosulfate, Rongalit, ascorbic acid, and the like. Redox initiators in combination with an agent; azo compounds such as 4,4′-azobis (4-cyanobutanoic acid); These polymerization initiators can be used usually in the range of 0.01 to 10% by mass, preferably 0.1 to 5% by mass, based on the total amount of the polymerizable unsaturated monomers used.

  The reaction temperature at the time of the emulsion polymerization varies depending on the polymerization initiator used, but can be usually in the range of about 60 to about 90 ° C., and the reaction time can be usually about 5 to 10 hours. .

  The water-dispersible acrylic polymer particles (A) generally have a hydroxyl group in the range of 1 to 70 mgKOH / g, particularly 2 to 60 mgKOH / g, and more preferably 5 to 50 mgKOH / g, from the viewpoint of water resistance of the obtained coating film. It preferably has a valency.

  Further, the water-dispersible acrylic polymer particles (A) are generally from 5 to 90 mgKOH / g, particularly from 10 to 70 mgKOH / g, more preferably from 15 to 50 mgKOH / g, from the viewpoints of storage stability and water resistance of the obtained coating film. It preferably has an acid value in the range of g.

  Further, the water-dispersible acrylic polymer particles (A) can have an average particle diameter of usually from 10 to 1000 nm, preferably from 20 to 500 nm, more preferably from 40 to 350 nm. The average particle size of the water-dispersible acrylic resin (A) in the present invention is a value measured by a Coulter counter method at a measurement temperature of 20 ° C. This measurement can be performed using, for example, “COULTER N4 type” (trade name, manufactured by Beckman Coulter, Inc.).

  The water-dispersible acrylic polymer particles (A) are preferably neutralized with a basic compound. The basic compound is preferably water-soluble, for example, ammonia; methylamine, ethylamine, propylamine, butylamine, dimethylamine, trimethylamine, triethylamine, ethylenediamine, morpholine, methylethanolamine, 2- (dimethylamino) ethanol , Diethanolamine, triethanolamine, diisopropanolamine, amines such as 2-amino-2-methylpropanol, and the like. These can be used alone or in combination of two or more. Among them, 2- (dimethyl) It is preferable to use alkanolamines such as amino) ethanol, diethanolamine and triethanolamine.

  The water-dispersible acrylic polymer particles (A) are usually 5 to 70 parts by mass, preferably 5 to 60 parts by mass, more preferably 10 to 10 parts by mass, based on 100 parts by mass of the resin solids in the aqueous base coat paint. It can be used within the range of ５０50 parts by mass.

Cellulose derivative (B):
The cellulose derivative (B) is preferably a carboxylated cellulose ester from the viewpoint of use in an aqueous paint, such as carboxymethylcellulose acetate butyrate, carboxymethylcellulose acetate, carboxymethylcellulose butyrate, and carboxymethylcellulose propionate. These can be used alone or in combination of two or more.

  The amount of the cellulose derivative (B) used is 5 to 40 parts by mass, preferably 5 to 30 parts by mass, more preferably 10 to 25 parts by mass, based on 100 parts by mass of the resin solids in the aqueous base coat paint. It is desirable that the amount be within the range of parts by mass in terms of improving the metallic appearance of the obtained multilayer coating film and water resistance.

Curing agent (C):
Examples of the curing agent (C) include an amino resin, a polyisocyanate compound, a blocked polyisocyanate compound, an epoxy group-containing compound, a carboxyl group-containing compound, a carbodiimide group-containing compound, a hydrazide group-containing compound, and a semicarbazide group-containing compound. Can be Of these, amino resins and blocked polyisocyanate compounds that can react with hydroxyl groups are preferred. The curing agents can be used alone or in combination of two or more.

  Examples of the amino resin include a partially or completely methylolated amino resin obtained by a reaction of an aldehyde with an amino component such as melamine, urea, benzoguanamine, acetoguanamine, steroganamin, spiroguanamine, dicyandiamide, and the like. Aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like. In addition, those obtained by partially or completely etherifying the methylol group of this methylolated amino resin with an appropriate alcohol may be used. Examples of the alcohol used for the etherification include methyl alcohol, ethyl alcohol, and n. -Propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like.

  As the amino resin, a melamine resin is particularly preferable, and among them, a methyletherified melamine resin in which a methylol group of a methylolated melamine resin is partially or completely etherified with methyl alcohol, or partially or completely etherified with butyl alcohol Preferred are alkylated melamine resins, such as butyletherified melamine resins that have been etherified and methyl-butyl mixed etherified melamine resins that have been partially or completely etherified with methyl alcohol and butyl alcohol.

  As the blocked polyisocyanate compound, for example, an isocyanate group of a polyisocyanate compound having at least two isocyanate groups in one molecule is blocked with a blocking agent such as active methylene, oxime, phenol, alcohol, lactam, mercaptan, and pyrazole. Things can be mentioned. Examples of the polyisocyanate compound include an aliphatic polyisocyanate, an alicyclic polyisocyanate, an araliphatic polyisocyanate, an aromatic polyisocyanate, and a derivative of the polyisocyanate.

  The curing agent (C) is usually 5 to 60 parts by mass, preferably 10 to 50 parts by mass, more preferably 15 to 45 parts by mass, based on 100 parts by mass of the resin solids in the aqueous base coat paint. Can be used within the range.

Bright pigment (D):
The glitter pigment (D) is not particularly limited as long as it is a glitter pigment obtained by pulverizing a vapor-deposited metal film into a metal piece.

  Such a brilliant pigment is generally obtained by depositing a metal film on a base film, peeling the base film, and then pulverizing the deposited metal film into metal pieces. The thickness of the deposited metal film at this time, that is, the thickness of the metal piece obtained by pulverization is typically preferably about 0.01 to 1 μm. If the thickness is less than 0.01 μm, the color of the underlayer is easily transmitted, and if it exceeds 1 μm, the metal piece may cause irregular reflection.

  In addition, since the glitter pigment is a glitter pigment obtained by pulverizing a vapor-deposited metal film into a metal piece, the thickness of the metal pigment is extremely small. As the degree of pulverization of the metal pieces, typically, the average particle diameter (D50) is preferably 1 to 50 μm, and more preferably 5 to 20 μm. The average particle diameter is a median diameter (D50) of a volume-based particle size distribution measured by a laser diffraction scattering method, and is a value measured using a Microtrac particle size distribution analyzer manufactured by Nikkiso Co., Ltd.

  Further, the material of the deposited metal film is not particularly limited, and examples thereof include metal films of aluminum, gold, silver, copper, chromium, nickel, and the like. From the viewpoint of corrosion, it is particularly preferable to use aluminum pieces as glitter pigments. The aluminum piece may be appropriately surface-treated.

  The pigment mass concentration (PWC) of the brilliant pigment (D) is preferably from 10 to 40%, particularly preferably from 10 to 35%, from the viewpoint of imparting a metallic gloss to the formed coating film.

  In the present specification, the pigment mass concentration (PWC) of the glitter pigment (D) is the mass ratio of the glitter pigment (D) to the solid content of the paint.

  The glitter pigment-containing aqueous base coat paint may further contain other resin components, if necessary.

  As other resin components, those commonly used in aqueous base coat paints, for example, acrylic resins, polyester resins, urethane resins, epoxy resins and the like other than the component (A) can be mentioned, among which the acrylic resins described below And polyester resins are preferred. These resins can be used alone or in combination of two or more.

  The acrylic resin that can be contained as necessary is not particularly limited, and examples thereof include an acrylic resin obtained by copolymerizing a polymerizable unsaturated monomer by a solution polymerization method according to a conventional method. . As the organic solvent that can be used for solution polymerization, for example, a hydrophilic organic solvent such as a propylene glycol-based or dipropylene glycol-based solvent is preferable. From the viewpoint of water dispersibility, the acrylic resin preferably has an acid group such as a carboxyl group.

  The polymerizable unsaturated monomer is not particularly limited. For example, the carboxyl group-containing polymerizable unsaturated monomer (M-2-1) described above with respect to the water-dispersible acrylic polymer particles (A) And polymerizable unsaturated monomers such as a hydroxyl group-containing polymerizable unsaturated monomer (M-2-2) and other polymerizable unsaturated monomers (M-2-3).

  The acrylic resin preferably has a weight average molecular weight in the range of generally 1,000 to 200,000, particularly 2,000 to 100,000. In addition, the acrylic resin generally has a hydroxyl value in the range of 10 to 250 mgKOH / g, particularly 30 to 150 mgKOH / g, and an acid value in the range of usually 10 to 100 mgKOH / g, particularly 20 to 60 mgKOH / g. Is preferred.

  In the present specification, the number average molecular weight and the weight average molecular weight are defined as a retention time (retention capacity) measured using a gel permeation chromatograph (GPC) and a retention time (standard polystyrene having a known molecular weight measured under the same conditions). (Retention capacity) in terms of the molecular weight of polystyrene. Specifically, “HLC8120GPC” (trade name, manufactured by Tosoh Corporation) was used as a gel permeation chromatograph, and “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, and “TSKgel G-2500HXL” were used as columns. And "TSKgel G-2000HXL" (trade names, all manufactured by Tosoh Corporation), using a differential refractometer as a detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow rate: It can be measured under the condition of 1 mL / min.

  When the above acrylic resin is blended, its content is usually in the range of 0 to 40% by mass, preferably 5 to 35% by mass, based on the total resin solids in the aqueous base coat paint. be able to.

  The polyester resin that can be contained as necessary is not particularly limited.For example, a polyester resin that can be synthesized by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction according to a conventional method. Can be mentioned.

  The polybasic acid is a compound having two or more carboxyl groups in one molecule, for example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydroacid Examples thereof include phthalic acid, heptic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid and anhydrides thereof, and the above polyhydric alcohol has two or more hydroxyl groups in one molecule. Compounds, for example, ethylene glycol, propylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and the like. .

  Further, as the polyester resin, the polyester resin obtained as described above, linseed oil fatty acid, coconut oil fatty acid, safflower oil fatty acid, soybean oil fatty acid, sesame oil fatty acid, eno oil fatty acid, hemp oil fatty acid, tall oil fatty acid, Fatty acid-modified polyester resins modified with (semi) dry oil fatty acids such as dehydrated castor oil fatty acids can also be used. In general, the amount of modification with these fatty acids is preferably 30% by mass or less in oil length. Further, it may be one obtained by partially reacting a monobasic acid such as benzoic acid. Further, in order to introduce an acid group into the polyester resin, after the esterification reaction of the polybasic acid and the polyhydric alcohol, for example, trimellitic acid, a polybasic acid such as trimellitic anhydride or an anhydride thereof is reacted. You can also.

  The polyester resin preferably has a weight average molecular weight in the range of generally 1,000 to 200,000, particularly 2,000 to 50,000. The polyester resin has a hydroxyl value within a range of usually 10 to 250 mgKOH / g, particularly 30 to 150 mgKOH / g, and an acid value within a range of usually 10 to 100 mgKOH / g, particularly 20 to 60 mgKOH / g. Is preferred.

  When the above polyester resin is blended, its content should be generally in the range of 0 to 40% by mass, preferably 5 to 35% by mass based on the total resin solids in the aqueous base coat paint. Can be.

  In addition to the glitter pigment (D), the aqueous base coat paint may further contain other glitter pigments and pigments such as coloring pigments and extenders, if necessary.

  In the aqueous base coat paint, if necessary, an ultraviolet absorber, a light stabilizer, a surface conditioner, a polymer fine particle, a basic neutralizer, a preservative, a rust inhibitor, a silane coupling agent, a pigment dispersant, a sediment Other paint additives commonly used in the preparation of aqueous paints such as an inhibitor, a thickener, an antifoaming agent, a curing catalyst, a deterioration inhibitor, a flow inhibitor, water and an organic solvent can be contained.

  The aqueous basecoat paint preferably has a paint solid content in the range of generally 2 to 20% by mass, particularly 2 to 15% by mass, from the viewpoint of the glitter of the coating film to be formed. The aqueous base coat paint preferably has a pH in the range of usually 7.5 to 9.0, particularly preferably 7.5 to 8.5.

  In the present specification, the solid content of the glittering pigment-containing aqueous base coat paint is the mass ratio of the nonvolatile content after drying the glittering pigment-containing aqueous base coat paint at 110 ° C. for 1 hour. Approximately 2 g of the pigment-containing aqueous basecoat paint is weighed into an aluminum foil cup having a diameter of about 5 cm, spread sufficiently on the bottom of the cup, and then dried at 110 ° C. for 1 hour. The paint mass before drying and the paint mass after drying Can be calculated from

  The method for applying the brilliant pigment-containing aqueous base coat paint is not particularly limited, and examples thereof include methods such as air spray coating, airless spray coating, and rotary atomization coating. A wet film can be formed. These coating methods may be applied with static electricity, if necessary. Among them, a rotary atomization type electrostatic coating and an air spray type electrostatic coating are preferable, and a rotary atomization type electrostatic coating is preferable. Particularly preferred.

  In the case of air spray coating, airless spray coating or rotary atomization coating, the viscosity of the aqueous base coat paint is adjusted to a viscosity range suitable for the coating, usually 15 to 60 at 20 ° C. in a Ford cup # 4 viscometer. It is preferable to adjust the viscosity using water and / or an organic solvent as appropriate so that the viscosity is in the range of about seconds.

  Curing of the formed wet coating film can be performed by heating. The heating can be performed by a heating means known per se, for example, using a drying furnace such as a hot blast furnace, an electric furnace, or an infrared induction heating furnace. The heating temperature is usually in the range of about 80 to about 180 ° C, preferably about 100 to about 160 ° C. The heating time is not particularly limited, but can be generally about 10 to 40 minutes.

  The film thickness of the aqueous base coat paint is generally in the range of 0.1 to 10 μm, preferably 0.1 to 7 μm as a cured film thickness.

  Further, an aqueous base coat paint is applied on the object to be coated, and a clear coat paint is applied thereon without curing the coat, and the coat of the aqueous base coat paint and the clear coat coat are simultaneously heated and cured. A multi-layer coating film can be formed by a one-coat baking method. If the surface to be coated is an uncured intermediate coating film surface, a three-coat one-bake method can be used.

  When a multi-layer coating film is formed by the two-coat one-bake method, from the viewpoint of preventing the occurrence of coating defects such as repelling and the like, after application of the water-based base coating material, preheating is performed at a temperature at which the coating film is not substantially cured. Is preferably performed. The preheating temperature can be generally about 50 to 100 ° C., and the preheating time can be about 30 seconds to 10 minutes, preferably about 1 to 5 minutes.

  On the cured or uncured base coat film obtained as described above, after applying the clear coat paint using a coating machine such as a rotary atomization type electrostatic coating machine, an airless spray coating machine, an air spray coating machine, By heating and curing at a temperature of usually about 100 to about 180 ° C., preferably about 120 to about 160 ° C. for about 10 to 40 minutes, a multilayer coating film having an excellent appearance can be formed.

  In the coating line of an automobile body, the coating quality is usually reduced by applying the same type of paint to each of the zones using the same type of paint, so that the scattered paint adheres to an object to be coated or to a coating film. For example, an automobile coating line is generally divided into an undercoating zone, an intermediate coating zone, a basecoat coating zone, and a clear coat coating zone.

  Further, in each coating zone, coating is usually divided into two or more times, and setting (standing) for about 30 seconds to 3 minutes is performed between each coating to prevent dripping of the coating and the like. Measures are taken to obtain coating quality, and each coating in the same zone is called a first stage, a second stage,... In order from the coating performed first.

  Such a coating method is generally called multi-stage coating. For example, when coating in the same zone is divided into two times, two-stage coating is performed, and when coating is performed in three times, it is called three-stage coating. When the aqueous basecoat paint is applied in the basecoat coating zone, it is preferable to perform the two-stage coating from the viewpoint of the appearance of the coating film and the coating efficiency.

  When the aqueous basecoat paint is applied by the two-stage coating, the aqueous basecoat paint applied in the first stage and the aqueous basecoat paint applied in the second stage may be the same or different from each other. Above all, different aqueous base coat paints are used in the first stage and the second stage, and in the first stage, an aqueous base coat paint (X1) having a paint solid content of 8 to 40% by mass is applied. Is applied as the aqueous base coat paint (X2) by adjusting the above-mentioned glitter pigment-containing aqueous base coat paint in the range of 2 to 5% by mass, particularly 2 to 4% by mass, to thereby obtain excellent glitter and coating performance. (Hereinafter, this coating method is referred to as “double base coat coating method”).

  In addition, from the end of the first stage coating in the double base coat coating method to the start of the second stage coating, from the viewpoint of energy saving and productivity improvement, preheating is not performed, and is performed for about 30 seconds to 3 minutes. It is preferable to set an interval of

  The aqueous base coat paint (X1) is not particularly limited, and any known aqueous base coat paint can be used. For example, the above-mentioned brilliant pigment in which the solid content of the paint is adjusted within the range of 8 to 20% by mass. The aqueous base coat paint containing the aqueous base coat paint (X1-1) or the glitter pigment other than the glitter pigment (D) is less than 15% PWC, and the solid content of the paint is adjusted to 15 to 40% by mass. Base coat paint (X1-2) or the like can be used.

  The dry thickness (T1-1) of the aqueous base coat paint (X1-1) is in the range of 2 to 5 μm, particularly 2 to 4 μm, and the dry thickness (T1-2) of the aqueous base coat paint (X1-2) is And the dry film thickness (T2) of the aqueous basecoat paint (X2) is generally in the range of 0.1 to 1 μm, especially 0.1 to 0.5 μm. Is preferred.

  When applying the clear coat paint on the base coat paint film formed by the above double base coat paint method, from the viewpoint of preventing the occurrence of paint defects such as repelling, the paint film is applied after the application of the aqueous base coat paint in the second stage. It is preferable to perform preheating at a temperature at which is not substantially cured. The preheating temperature can be generally in the range of about 50 to about 100 ° C, and the preheating time can be generally about 30 seconds to 10 minutes, preferably about 1 to 5 minutes.

  On the uncured brilliant pigment-containing base coat film obtained by performing the above preheating, the clear coat paint is applied using a rotary atomization type electrostatic coating machine, an airless spray coating machine, an air spray coating machine or the like. After coating at a temperature of about 100 to about 180 ° C., preferably about 120 to about 160 ° C. for about 10 to 40 minutes to simultaneously cure both coatings, an excellent appearance (brightness, smoothness) Etc.) can be obtained.

Clear coat paint:
The clear coat paint used in the method of the present invention comprises N-substituted (meth) acrylamide (i), a hydroxyl group-containing polymerizable unsaturated monomer (ii), a carboxyl group-containing polymerizable unsaturated monomer (iii) and ( Acrylic resin (E) which is a copolymer of other polymerizable unsaturated monomers (iv) other than i) to (iii), hydroxyl group-containing acrylic resin (F) other than the resin (E), and a curing agent ( G).

  The acrylic resin (E) is a component for improving the water resistance of the multilayer coating film, and includes N-substituted (meth) acrylamide (i), a hydroxyl group-containing polymerizable unsaturated monomer (ii), and a carboxyl group-containing monomer. It is a copolymer of a polymerizable unsaturated monomer (iii) and another polymerizable unsaturated monomer (iv) other than (i) to (iii).

  Examples of the N-substituted (meth) acrylamide (i) include N-methylacrylamide, N-methylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-ethoxymethylacrylamide, N-ethoxymethylmethacrylamide, N-propoxymethylacrylamide, N-propoxymethylmethacrylamide, N-butoxymethylacrylamide, N-butoxymethylmethacrylamide, N-phenoxymethylacrylamide, N-phenoxymethylmethacryl Amide, N-ethylacrylamide, N-ethylmethacrylamide, Nn-propylacrylamide, Nn-propylmethacrylamide, N-isopropyla Riruamido, N- isopropyl methacrylamide, N- cyclopropyl acrylamide, include N- cyclopropyl methacrylamide, etc., it can be used either alone or in combination of two or more.

  Among them, N-methylolacrylamide, N-methylolmethacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-ethoxymethylacrylamide, N-ethoxy Methyl methacrylamide, N-propoxymethyl acrylamide, N-propoxymethyl methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide can be suitably used.

  Examples of the hydroxyl group-containing polymerizable unsaturated monomer (ii) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth). ) Monoester of (meth) acrylic acid such as acrylate and dihydric alcohol having 2 to 8 carbon atoms; ε-caprolactone of monoester of (meth) acrylic acid and dihydric alcohol having 2 to 8 carbon atoms Modified form; allyl alcohol, etc., which can be used alone or in combination of two or more.

  Examples of the carboxyl group-containing polymerizable unsaturated monomer (iii) include: unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; And the like. These can be used alone or in combination of two or more.

  Other polymerizable unsaturated monomers (iv) are polymerizable unsaturated monomers other than the above (i) to (iii), and include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n- Propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) C1-20 alkyl esters of (meth) acrylic acid such as acrylate and lauryl (meth) acrylate; aromatic vinyl compounds such as styrene, α-methylstyrene and vinyl toluene; glycidyl such as glycidyl (meth) acrylate and allyl glycidyl ether Group-containing vinyl compounds; vinyl acetate, vinyl propionate, Vinyl compounds such as vinyl chloride; polymerizable unsaturated bond-containing nitrile compounds such as acrylonitrile and methacrylonitrile; diene compounds such as butadiene and isoprene; and the like, used alone or in combination of two or more. can do.

  The acrylic resin (E) contains N-substituted (meth) acrylamide (i) in an amount of 3 to 50% by mass, particularly 10 to 30% by mass, and a hydroxyl group-containing polymerizable unsaturated compound, based on the total solid content of the monomers used. 1 to 30% by mass, particularly 1 to 25% by mass of the monomer (ii), 1 to 15% by mass, particularly 1 to 10% by mass of the carboxyl group-containing polymerizable unsaturated monomer (iii), and other It is desirable that the polymerizable unsaturated monomer (iv) is a copolymer of 5 to 95% by mass, particularly 35 to 88% by mass, from the viewpoint of ensuring the water-resistant adhesion of the multilayer coating film.

  The method for producing the acrylic resin (E) is not particularly limited. For example, a solution of a polymerizable unsaturated monomer (i) to (iv) in an organic solvent in the presence of a polymerization initiator according to a conventional method is used. It is obtained by copolymerization by a polymerization method.

  The acrylic resin (E) preferably has a weight average molecular weight in the range of 5,000 to 100,000, particularly 10,000 to 70,000. The acrylic resin (E) generally has a hydroxyl value in the range of 5 to 150 mgKOH / g, particularly 10 to 100 mgKOH / g, and an acid value in the range of usually 10 to 100 mgKOH / g, particularly 10 to 60 mgKOH / g. It is preferable to have

  The acrylic resin (E) can be used in a range of usually 5 to 50 parts by mass, preferably 10 to 45 parts by mass as solids based on 100 parts by mass of the resin solids in the clear coat paint. .

  The hydroxyl group-containing acrylic resin (F) is an acrylic resin other than the resin (E), and is usually a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable with the hydroxyl group-containing polymerizable unsaturated monomer. The polymerizable unsaturated monomer can be produced by copolymerization by a method known per se, for example, a method such as a solution polymerization method in an organic solvent.

  The hydroxyl group-containing polymerizable unsaturated monomer and the other polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer are not particularly limited, and may be any of the hydroxyl groups described above with respect to the acrylic resin (E). The polymerizable unsaturated monomer (ii), the carboxyl group-containing polymerizable unsaturated monomer (iii) and the other polymerizable unsaturated monomer (iv) can be appropriately selected and used.

  The hydroxyl group-containing acrylic resin (F) has a hydroxyl value of 80 to 200 mgKOH / g, particularly 90 to 170 mgKOH / g, and particularly preferably 100 to 100 mgKOH / g, from the viewpoint of finished appearance such as smoothness and sharpness and coating performance such as weather resistance. The acid value is preferably in the range of 140 to 140 mg KOH / g, and more preferably in the range of 1 to 40 mg KOH / g, particularly 3 to 30 mg KOH / g, and particularly preferably 5 to 20 mg KOH / g. The hydroxyl group-containing acrylic resin (F) has a weight average molecular weight of 4,000 to 20,000, particularly 6,000 to 16,000, and more particularly 8,000 to 12,000, from the viewpoint of a finished appearance such as smoothness and sharpness and a coating property such as weather resistance. Is preferably within the range.

  The hydroxyl group-containing acrylic resin (F) is used in a solid content of usually 10 to 70 parts by mass, preferably 15 to 60 parts by mass, based on 100 parts by mass of the resin solids in the clear coat paint. Can be.

  The use ratio of the acrylic resin (E) and the hydroxyl group-containing acrylic resin (F) may be 10/90 to 70/30, particularly 15/85 to 60/40 based on the total solid content of both. It is desirable from the viewpoint of ensuring the water resistance of the layer coating film.

  Examples of the curing agent (G) include a polyisocyanate compound, a blocked polyisocyanate compound, a melamine resin, a urea resin, a carboxyl group-containing compound, a carboxyl group-containing resin, an epoxy group-containing resin, and an epoxy group-containing compound. Of these, polyisocyanate compounds and / or melamine resins are preferred.

  The polyisocyanate compound is a compound having at least two isocyanate groups in one molecule, and examples thereof include aliphatic polyisocyanate, alicyclic polyisocyanate, araliphatic polyisocyanate, aromatic polyisocyanate, and polyisocyanate. Derivatives and the like can be mentioned, and they may be used alone or in combination of two or more. Among the above polyisocyanate compounds, aliphatic diisocyanates and derivatives of aliphatic diisocyanates can be suitably used from the viewpoints of smoothness, sharpness, weather resistance and the like of the obtained coating film.

  When a polyisocyanate compound is used as the curing agent (G), the equivalent ratio (NCO / OH) of the hydroxyl group in the acrylic resin (E) and the hydroxyl group-containing acrylic resin (F) to the isocyanate group in the polyisocyanate compound is: It is suitable to be in the range of 0.5 to 2.0, preferably 0.8 to 1.5.

  Examples of the melamine resin include a known partially or completely methylolated melamine resin obtained by a reaction between melamine and an aldehyde. Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. In addition, those obtained by etherifying the methylolated melamine resin with alcohol can also be used. Examples of the alcohol used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like can be mentioned.

  In addition, the clear coat paint may contain, if necessary, a coloring pigment, a brilliant pigment, a dye, or the like to such an extent that transparency is not impaired. An absorber, a light stabilizer, an antifoaming agent, a thickener, a rust inhibitor, a surface conditioner, and the like can be appropriately contained.

  The thickness of the clear coat coating film is preferably from 15 to 60 μm, particularly preferably from 20 to 50 μm, in terms of dry film thickness, from the viewpoint of the appearance of the coating film and coating workability.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited to only these examples. Note that “parts” and “%” are based on mass.

Production example of water-dispersible acrylic polymer particles (A) Production example 1
A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a dropping device was charged with 100 parts of deionized water and 0.5 part of Aqualon KH-10 (Note 1), and stirred and mixed in a nitrogen stream. The temperature was raised to ° C. Next, 10.3 parts of a 1% and 3% aqueous solution of ammonium persulfate of the total amount of the following monomer emulsion (1) were introduced into the reaction vessel, and the mixture was kept at 80 ° C. for 15 minutes. Thereafter, the remaining monomer emulsion (1) was dropped into the reaction vessel over 3 hours, and aging was performed for 1 hour after completion of the dropping. Thereafter, the following monomer emulsion (2) was added dropwise over 2 hours, and after aging for 1 hour, the mixture was cooled to 30 ° C while gradually adding 42 parts of a 5% aqueous solution of 2- (dimethylamino) ethanol to a reaction vessel. The mixture is discharged while being filtered through a 100-mesh nylon cloth, diluted with deionized water using a submicron particle size distribution analyzer “COULTER N4 type” (trade name, manufactured by Beckman Coulter, Inc.) at 20 ° C. ), An aqueous dispersion of water-dispersible acrylic polymer particles (A1) having an acid value of 33 mgKOH / g, a hydroxyl value of 48 mgKOH / g, and a solid content of 30%.

  (Note 1) Aqualon KH-10: polyoxyethylene alkyl ether sulfate ester ammonium salt: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name, active ingredient: 97%.

  Monomer emulsion (1): 60 parts of deionized water, 1 part of Aqualon KH-10, 3 parts of methylenebisacrylamide, 4 parts of styrene, 13 parts of methyl methacrylate, 30 parts of ethyl acrylate and 20 parts of n-butyl acrylate are mixed and stirred. Thus, a monomer emulsion (1) was obtained.

  Monomer emulsion (2): 20 parts of deionized water, 1 part of AQUALON KH-10, 0.1 part of superacid ammonium, 3 parts of styrene, 6 parts of methyl methacrylate, 2 parts of ethyl acrylate, 4 parts of n-butyl acrylate, 10 parts of 2-hydroxyethyl acrylate and 5 parts of methacrylic acid were mixed and stirred to obtain a monomer emulsion (2).

Preparation and Production Example 2 of Cellulose Derivative Aqueous Liquid
Using carboxymethyl cellulose acetate butyrate (“Solus3050”, trade name, acid value 50 mgKOH / g, manufactured by Eastman Chemical Company), water, octanol, and dimethylethanolamine, a 20% solids aqueous solution of a cellulose derivative having a pH of 7 ( B1) was obtained.

Production example of polyester resin Production example 3
A reactor equipped with a stirrer, a reflux condenser, a water separator, and a thermometer was charged with 109 parts of trimethylolpropane, 142 parts of 1,6-hexanediol, 126 parts of hexahydrophthalic anhydride, and 120 parts of adipic acid. After raising the temperature between 〜230 ° C. over 3 hours, a condensation reaction was performed at 230 ° C. for 4 hours. Next, in order to add a carboxyl group to the obtained condensation reaction product, 46 parts of trimellitic anhydride was further added, reacted at 180 ° C. for 1 hour, diluted with octanol, acid value 49 mg KOH / g, hydroxyl group Polyester resin (1) having a value of 140 mgKOH / g, a solid content of 70% and a weight average molecular weight of 6,400 was obtained.

Production example 4 of aqueous base coat paint
In a stirring and mixing vessel, a vapor-deposited aluminum flake paste (“Hydroshine WS-3004”, manufactured by Eckart, solid content: 10%, internal solvent: isopropanol, average particle diameter D50: 13 μm, thickness: 0.05 μm, surface is silica) ) Is added to the mixture so as to have a solid content of 30 parts, and while stirring, the cellulose derivative aqueous liquid (B1) obtained in Production Example 2 is mixed with 20 parts by solids, and “Cymel 251” (Nippon Cytec) (Industry, trade name, melamine resin, solid content 80%) 25 parts by solid content, 20 parts by weight of polyester resin (1) obtained in Production Example 3 in solid content, and acrylic resin emulsion obtained in Production Example 1 (A1) was added to and mixed with 35 parts by solid content. "Primal ASE-60" (trade name, polyacrylic acid-based thickener, manufactured by Rohm and Haas Co.), 2- (dimethylamino) ethanol and deionized water were added to the obtained mixture to adjust the pH to 8.0. An aqueous base coat paint (1) having a paint solid content of 10% was obtained.

Production Example 5
In a stirring and mixing vessel, a vapor-deposited aluminum flake paste ("Hydroshine WS-3004", manufactured by Eckart, solid content: 10%, internal solvent: isopropanol, average particle diameter D50: 13 µm, thickness: 0.05 µm, surface is silica) ) Was added to the mixture so as to have a solid content of 50 parts, and while stirring, the cellulose derivative aqueous liquid (B1) obtained in Production Example 2 was mixed with 20 parts by solids, and “Cymel 251” (Nippon Cytec) (Industry, trade name, melamine resin, solid content 80%) 25 parts by solid content, 20 parts by weight of polyester resin (1) obtained in Production Example 3 in solid content, and acrylic resin emulsion obtained in Production Example 1 (A1) was added to and mixed with 35 parts by solid content. "Primal ASE-60" (trade name, polyacrylic acid-based thickener, manufactured by Rohm and Haas Co.), 2- (dimethylamino) ethanol and deionized water were added to the obtained mixture to adjust the pH to 8.0. An aqueous base coat paint (2) having a paint solid content of 2.5% was obtained.

Production example of acrylic resin (E) Production example 6
A glass four-necked flask equipped with a thermometer, a stirrer, a cooling pipe, and a water separator was charged with 60 parts of “Swazol 1000” (a hydrocarbon-based solvent manufactured by Cosmo Oil Co., Ltd.) and 30 parts of n-butanol, and stirred. After raising the temperature to 90 ° C., 19.7 parts of n-butyl acrylate, 15 parts of methyl methacrylate, 30 parts of styrene, 20 parts of N-butoxymethylacrylamide, 12 parts of 2-hydroxylethyl methacrylate, 3.3 parts of acrylic acid And a mixture of 4 parts of azobisisobutyronitrile was dropped at a constant rate over 4 hours using a dropping pump while maintaining the mixture at 90 ° C. After completion of the dropwise addition, the mixture was kept at 90 ° C. for 1 hour and stirring was continued. Thereafter, a solution prepared by dissolving 0.5 part of azobisisobutyronitrile in 10 parts of “Swazole 1000” was added dropwise at a constant rate over 1 hour, and further kept at 90 ° C. for 1 hour, and an acrylic resin having a solid content of 50% was added. A solution (E1) was obtained. The obtained acrylic resin had an acid value of 25 mgKOH / g, a hydroxyl value of 50 mgKOH / g, and a weight average molecular weight of 20,000.

Production Examples 7 to 15
Acrylic (E2) to (E10) were obtained in the same manner as in Production Example 6, except that the components shown in Table 1 below were used. The following Table 1 shows the solid content, the weight average molecular weight, the acid value and the hydroxyl value of the obtained acrylic resins (E1) to (E10) in combination with the acrylic resin (E1) obtained in Production Example 6.

Production example of hydroxyl group-containing acrylic resin (F) Production example 16
31 parts of ethoxyethyl propionate was charged into a four-necked flask equipped with a stirrer, a thermometer, a condenser, and a nitrogen gas inlet, and the temperature was raised to 155 ° C. under nitrogen gas flow. After the temperature reached 155 ° C., the ventilation of nitrogen gas was stopped, and 30 parts of styrene, 37.5 parts of n-butyl acrylate, 30 parts of 2-hydroxypropyl acrylate, 2.5 parts of acrylic acid, and ditertiary mill peroxide (polymerization started) Agent) A monomer mixture having a composition of 4 parts was added dropwise over 4 hours. After 30 minutes, a polymerization initiator solution obtained by dissolving 0.5 part of 2,2′-azobis (2,4-dimethylvaleronitrile) (polymerization initiator) in 3 parts of Swazol 1000 (hydrocarbon solvent) is added for 1 hour. It dripped over. Then, the mixture was aged for 2 hours at 155 ° C. while passing nitrogen gas, cooled to 100 ° C., and diluted with 29 parts of butyl acetate to obtain a hydroxyl group-containing acrylic resin (F1) having a solid content of 60%.
The obtained hydroxyl group-containing acrylic resin (F1) had a hydroxyl value of 129 mgKOH / g, an acid value of 19 mgKOH / g, and a weight average molecular weight of about 12,000.

Production Example 17
In Production Example 16, the composition was composed of 30 parts of styrene, 37.5 parts of n-butyl acrylate, 30 parts of 2-hydroxypropyl acrylate, 2.5 parts of acrylic acid, and 4 parts of ditertiary mill peroxide (polymerization initiator). A monomer having a composition comprising 30 parts of styrene, 40.5 parts of n-butyl acrylate, 27 parts of 2-hydroxyethyl acrylate, 2.5 parts of acrylic acid, and 4 parts of ditertiary mill peroxide (polymerization initiator) Except for changing to a mixture, the same procedure as in Production Example 16 was carried out to obtain a hydroxyl-containing acrylic resin (F2) having a solid content of 60%.
The obtained hydroxyl group-containing acrylic resin (F2) had a hydroxyl value of 129 mgKOH / g, an acid value of 19 mgKOH / g, and a weight average molecular weight of about 12,000.

Production example 18 of clear-coat paint
The hydroxyl-containing acrylic resin (F1) solution obtained in Production Example 16 was 40 parts by solid content, and the hydroxyl-containing acrylic resin (E1) solution obtained in Production Example 6 was 20 parts by solid content, "BYK-300" (trade name) 0.2 parts, "TINUVIN900" (trade name, manufactured by BASF, benzotriazole-based ultraviolet absorber, 100% active ingredient) 2 And 1.0 part of "TINUVIN 292" (trade name, manufactured by BASF, hindered amine light stabilizer, 100% active ingredient) were uniformly mixed and mixed with "Duranate TLA-100". (Trade name, manufactured by Asahi Kasei Chemicals Corporation, polyisocyanate compound, solid content 100%, NCO content 21.8%), and mixed. Oil Co., adding hydrocarbon solvent), Ford cup No. at 20 ° C. 4 gave a clear coat paint (1) having a viscosity of 25 seconds.

Production Examples 19 to 34
In the same manner as in Production Example 18, the Ford cup No. The clear coat paints (2) to (17) having a viscosity of 25 seconds according to No. 4 were obtained. In addition, the composition of each clear coat paint in Table 2 is a solid content composition.
(Note 1) Melamine resin: Cymel 238, trade name, manufactured by Nippon Cytec Industries, Inc., solid content 100%

Preparation of Test Coating Material I:
A dry film of “Electron GT-10” (trade name, manufactured by Kansai Paint Co., Ltd., thermosetting epoxy resin-based cationic electrodeposition paint) is applied to a cold-rolled steel sheet of 45 cm long × 30 cm wide × 0.8 mm thick that has been treated with zinc phosphate. Electrodeposition coating was performed so as to have a thickness of 20 μm, and the coating was heated at 170 ° C. for 30 minutes and cured to obtain a test object I for test.

Production Example 1 of Test Plate I
"WP-522H N-2.0" (trade name, manufactured by Kansai Paint Co., polyester resin-based water-based intermediate coating, L * value of obtained coating film: 20) was rotated on test test object I. Using an atomizing type bell-type coating machine, electrostatic coating was performed to a dry film thickness of 20 μm, left for 3 minutes, and preheated at 80 ° C. for 3 minutes. The base coat paint (1) is electrostatically coated to a dry film thickness of 3 μm by using a rotary atomization type bell-type coating machine “ABB cartridge bell coating machine” (trade name, manufactured by ABB) for 2 minutes. After standing, preheating was performed at 80 ° C. for 5 minutes. Next, the clear coat paint (1) obtained in Production Example 18 was applied on the uncured base coat coated surface so as to have a dry film thickness of 30 μm, left for 7 minutes, and then heated at 140 ° C. for 30 minutes. Test plate I was prepared by simultaneously curing both coating films.

Examples 2 to 12, Comparative Examples 1 to 5
Test plates I of Examples 2 to 12 and Comparative Examples 1 to 5 were operated in the same manner as in Example 1 except that the clear coat paint (1) in Example 1 was changed to the clear coat paint shown in Table 3 below. Was prepared. Each test plate I was evaluated by the following test method. Table 3 shows the results.

(Test method 1)
Flip-flop property: For each test plate, the L value (brightness) at a light receiving angle of 15 degrees and a light receiving angle of 110 degrees was measured using a multi-angle spectrophotometer MA-68 (trade name, manufactured by X-Rite). The FF value was determined by the following equation.

  FF value = L value at a light receiving angle of 15 degrees / L value at a light receiving angle of 110 degrees.

  The larger the FF value, the larger the change in the L value (brightness) depending on the observation angle (light receiving angle), indicating that the flip-flop property is excellent.

  Brightness: Each test plate was visually observed while changing the angle, and the brightness was evaluated according to the following criteria.

    ：: The change in the metallic feeling depending on the viewing angle is large, the flip-flop property is excellent, and a good glittering feeling is obtained.

    Δ: The change in the metallic feeling due to the visual angle is slightly small, the flip-flop property is slightly inferior, and the glitter is slightly inferior.

    X: The change in the metallic feeling due to the visual angle is small, the flip-flop property is inferior, and the glitter is inferior.

  Smoothness: The appearance of the test plate was visually evaluated.

    A: Very excellent smoothness.

    ：: Excellent smoothness.

    Δ: Smoothness is slightly inferior.

    X: Poor smoothness.

  Initial adhesion: Cut into the multi-layer coating film on each test plate with a cutter so as to reach the substrate, make 100 gobangs of size 2 mm x 2 mm, attach an adhesive tape to the surface, and apply 20 ° C In, the number of remaining paint films after the tape was abruptly peeled was examined.

    ◎: 100 pieces remained, and the edge of the cut by the cutter was smooth.

    ：: 100 pieces remained, but small peeling of the coating film occurred at the intersection of the cuts of the cutter.

    Δ: 99 to 80 pieces remained.

    X: 79 to 50 or less remained.

    XX: 50 or less remained.

  Water resistance: Each test plate was immersed in warm water at 80 ° C. for 1 day, pulled up, dried at room temperature for 12 hours, and then subjected to a goban test in the same manner as the initial adhesion test. The evaluation criteria are the same as in the case of the initial adhesion test.

Preparation of test object II:
A dry film of “Electron GT-10” (trade name, manufactured by Kansai Paint Co., Ltd., thermosetting epoxy resin-based cationic electrodeposition paint) is applied to a cold-rolled steel sheet of 45 cm long × 30 cm wide × 0.8 mm thick that has been treated with zinc phosphate. Electrodeposited to a thickness of 20 μm, cured by heating at 170 ° C. for 30 minutes, and then coated on top with an intermediate coating “Amirac TP-65-2” (trade name, manufactured by Kansai Paint Co., polyester resin. An amino resin-based, organic solvent type intermediate coating) was applied so as to have a dry film thickness of 40 μm, and was cured by heating at 140 ° C. for 30 minutes to obtain a test object.

Preparation Example 13 of Test Plate II
The aqueous base coat paint (1) obtained in Production Example 4 was applied onto the test object II using a rotary atomization type bell-type coating machine “ABB cartridge bell coating machine” (trade name, manufactured by ABB). Then, electrostatic coating was performed to a dry film thickness of 2 μm to form a first base coating film. After an interval of one minute, the aqueous base coat paint (2) obtained in Production Example 5 was applied on the first base coat so as to have a dry film thickness of 0.2 μm. Was formed. After an interval of 2 minutes, preheating was performed at 80 ° C. for 3 minutes to form an uncured base coat film, and the clear coat paint (1) obtained in Production Example 6 was dried thereon to a dry film thickness of 30 μm. After the coating was carried out as described above and left for 7 minutes, the coating film was heated at 140 ° C. for 30 minutes to simultaneously cure these coating films, thereby preparing Test Plate II.

Examples 14 to 24 and Comparative Examples 6 to 10
The same operation as in Example 13 was carried out except that the clear coat paint (1) in Example 13 was changed to the clear coat paint shown in Table 4 below, to thereby obtain Examples 14 to 24 and Comparative Examples 6 to 10. Test plate II was prepared. Each test plate II was evaluated by the test method described above. Table 4 shows the results.

Claims (3)

A glitter containing water-dispersible acrylic polymer particles (A), a cellulose derivative (B), a curing agent (C), and a glitter pigment (D) obtained by pulverizing a vapor-deposited metal film into metal pieces on an object to be coated. Apply a water-soluble pigment-containing aqueous base coat paint to form a base coat film, and on the base coat film,
N-substituted (meth) acrylamide (i) 3 to 50% by mass, hydroxyl group-containing polymerizable unsaturated monomer (ii) 1 to 30% by mass, carboxyl group-containing polymerizable unsaturated monomer An acrylic resin (E ) which is a copolymer of 1 to 15% by mass of a saturated monomer (iii) and 5 to 95% by mass of another polymerizable unsaturated monomer (iv) other than (i) to (iii) ), Forming a clear coat film by applying a clear coat paint containing a hydroxyl group-containing acrylic resin (F) other than the resin (E) and a curing agent (G). Method. The method for forming a multilayer coating film according to claim 1 , wherein the use ratio of the acrylic resin (E) and the hydroxyl group-containing acrylic resin (F) is 10/90 to 70/30 based on the total solid content of both. The method for forming a multilayer coating film according to claim 1 or 2 , wherein the curing agent (G) is a polyisocyanate compound and / or a melamine resin.