WO2022019199A1 - Multi-layer coated film and multi-layer coated film forming method - Google Patents

Abstract

A method for forming a multi-layer coated film according to the present invention comprises a first step for coating an aqueous base coating material composition onto a coating target so as to form a base coated film (I), a second step for coating an aqueous clear coating material composition onto the base coated film (I) so as to form a clear coated film (II), and a step for simultaneously drying the base coated film and the clear coated film, wherein at least the aqueous base coating material composition contains a metal compound containing at least one metal selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum, and molybdenum.

Description

Multi-layer coating film and method for forming multi-layer coating film

The present invention relates to a multi-layer coating film and a method for forming a multi-layer coating film.

Conventionally, organic solvent-type acrylic lacquer paints and two-component urethane paints have been used as repair paints in the field of automobile repair paints in terms of quick-drying, adhesion, water resistance, polishing workability, and the like. .. However, in recent years, from the viewpoint of environmental protection, the conversion from organic solvent-based paints to water-based paints has been promoted in the automobile repair paint industry, and various water-based coloring base paints and clear paints have been proposed.
Further, in order to improve workability at a painting site, there is a demand for drying at a lower temperature and in a short time, for example, drying at 60 ° C. for 20 minutes for polishing. Also, in a multi-layer coating film forming method such as wet-on-wet coating of clear paint on a base coat and drying at the same time, such as 2-coat / 1-bak coating of water-based paint, the level is as high as that of a solvent. At the same time, it is required to have finishability and coating film performance.

As a method for improving the drying property at a low temperature and in a short time, for example, in Patent Document 1, the applicant applies a hydroxyl group-containing resin emulsion component, a first component containing a molybdenum compound and water, and a polyisocyanate component and an organic solvent. A water-based two-component polyurethane coating composition containing the second component containing the above and a coating method thereof have been proposed. According to this aqueous two-component polyurethane coating composition, it is possible to form a coating film in which the drying time required to reach the desired coating film hardness is short.

However, as described above, in recent years, further improvement in workability and shortening of the process are required, and the coating composition of Patent Document 1 is coated on a water-based base coating film by wet-on-wet coating and clear coating. When the film was coated to form a multi-layer coating film, the drying property, water resistance and coating film hardness may be insufficient. Even under conditions where the drying temperature cannot be raised, it is required to achieve finishability, coating film hardness and drying property (particularly polishability) in the multi-layer coating film.
As one means of improving the dryness, it is conceivable to increase the content of the curing catalyst in the clear coating composition, but in such a case, the usable time (also referred to as pot life) is significantly reduced and the finish is affected. In some cases, the physical characteristics of the coating film, particularly the hardness and water resistance of the coating film in the multi-layer coating film may be deteriorated, which hinders the drying time and shortening of the process.

JP-A-2019-142999

The present invention has been made in view of the above circumstances, and the finishability is also good in a method for forming a multi-layer coating film using an aqueous coating composition as a coating film for forming a base coating film and a clear coating film. It is an object of the present invention to provide a multi-layer coating film having excellent drying property, water resistance and coating film hardness, and a method for forming such a multi-layer coating film having excellent drying property at a lower temperature and in a short time. And.

The present inventors intentionally added a metal catalyst into the base coating film to try to form a multi-layer coating film. As a result, it was found that the presence of the metal compound in the base coating film improved the physical characteristics of the coating film, particularly the hardness and water resistance of the coating film in the multi-layer coating film, and led to the present invention.

That is, the method for forming the multi-layer coating film of the present invention is the first step of applying the water-based base coating composition to the object to be coated to form the base coating film (I), and the base coating film (I). A method for forming a multi-layer coating film, which comprises a second step of applying a water-based clear coating composition to form a clear coating film (II) and a step of simultaneously drying the base coating film and the clear coating film. At least the aqueous base coating composition comprises a metal compound containing at least one metal selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum.

The content concentration of the metal compound in the water-based base coating composition is preferably equal to or higher than the content concentration of the metal compound in the clear coating composition.

The metal is derived from a metal catalyst, and the content of the metal catalyst in the aqueous base coating composition is 0.01 part by mass or more with respect to 100 parts by mass of the total resin solid content in the aqueous base coating composition. It is preferably 5 parts by mass or less.

The water solubility of the metal compound is preferably 1 × 10 ^-3 mg / 1000 g or more and 5 × 10 ⁵ mg / 1000 g or less.

The water-based base coating composition contains a first film-forming resin, and the first film-forming resin is a water-dispersible acrylic resin (a1), a water-dispersible polyurethane resin (a2), and a water-soluble acrylic resin (a3). At least one is preferable.

The water-based clear coating composition contains a second film-forming resin, the second film-forming resin contains a hydroxyl group-containing resin and a polyisocyanate compound (b), and the polyisocyanate compound (b) contains 3 isocyanate groups. It is preferable to contain a polyisocyanate compound (b1) having more than one and having a molecular weight of 350 or less.

The water-based clear coating composition preferably contains a second film-forming resin, and the second film-forming resin preferably contains a dispersion-type acrylic resin (a4).

The object to be coated is preferably an old coating film or a damaged part of the coated body.

The object to be coated is preferably industrial machinery, construction machinery, railroad vehicles, large vehicles, hulls, buildings or structures, or parts thereof.

The multi-layer coating film of the present invention is a clear coating film (II) of a water-based clear coating film composition on a base coating film (I) layer of a water-based base coating composition and a base coating film (I) layer on an object to be coated. ) A multi-layer coating film having a layer, having a Martens hardness value of 7 N / mm ² or more.

Further, in the other multi-layer coating film of the present invention, a cured base coating film layer obtained by coating and curing a water-based base coating composition and a water-based clear coating composition are coated and cured on an object to be coated. A multi-layer coating having a cured clear coating layer, wherein the cured clear coating is composed of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum. It contains at least one metal compound selected from the above, and the concentration of metal elements in the cured clear coating film is 20 ppm or more.

According to the method for forming a multi-layer coating film of the present invention, a multi-layer coating film having excellent drying properties, finishability, water resistance, and coating film hardness at a low temperature in a short time can be obtained.
Further, the multi-layer coating film of the present invention is excellent in finishability, drying property, water resistance and coating film hardness.

Hereinafter, a method for forming a multi-layer coating film of the present invention will be described.
In the present specification, "the resin contains a monomer as a raw material thereof" means that the resin is a (co) polymer of a raw material monomer containing the monomer, unless the contradictory contents are specified separately. do. Further, in the present specification, the (co) polymer means a polymer or a copolymer.

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

[Method for forming a multi-layer coating film]
The method for forming a multi-layer coating film of the present invention is a first step of applying a water-based base coating composition to an object to be coated to form a base coating film (I), and on the base coating film (I). A method for forming a multi-layer coating film, which comprises a second step of applying a water-based clear coating composition to form a clear coating film (II), and a step of simultaneously drying the base coating film and the clear coating film. , At least the aqueous base coating composition comprises a metal compound containing at least one metal selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum.
In the present invention, the cured coating film is a cured and dried state defined in JIS K 5600-1-1, that is, the center of the coated surface is strongly sandwiched between the thumb and the index finger, and the coated surface is not dented by fingerprints. The coating film is in a state where the movement of the coating film is not felt and the center of the coated surface is rapidly and repeatedly rubbed with the fingertips so that no scratch marks are left on the coated surface. On the other hand, the uncured coating film is a state in which the coating film has not reached the cured and dried state, and also includes a touch-dried state and a semi-cured and dried state specified in JIS K 5600-1-1.
When the water-based base coating composition does not contain a curing agent, for example, the base coating film immediately after the water-based base coating composition is applied is in an uncured state because it does not undergo a cross-linking reaction. Due to the penetration of the curing agent component from the clear, it becomes semi-cured or cured.
The cured and dried state can be easily confirmed by the above method, but it can also be confirmed by infrared spectroscopy (IR) analysis or the like whether the hardness of the coating film of the multi-layer coating film is constant.

<First step>
The first step is a step of applying the water-based base coating composition to the object to be coated to form the base coating film (I).

(Applied material)
In the present invention, the object to be coated to which the water-based base coating composition is applied is not particularly limited. Specific examples thereof include automobiles such as automobiles and motorcycles or parts thereof, industrial machines, construction machines, railroad cars, large vehicles, hulls, buildings or structures, and parts thereof.

The base material of the object to be coated to which the water-based base coating composition is applied is not particularly limited, and specifically, for example, metals such as aluminum, iron, stainless steel, zinc, copper, and tin; glass, concrete, and slate plates. Inorganic materials such as plastics, organic materials such as vinyl chloride; wood; objects to be coated with a coating film on these base materials and the like. The object to be coated may be a molded product containing the above-mentioned base material.

The coating film of the object to be coated includes an undercoat coating film in which a surface-treated substrate is coated with an undercoat coating composition, a cured or uncured colored base coating film, and a coated body. Examples thereof include a surface-treated coating film in which a primer surfacer is applied to a damaged portion, a known coating film such as a new automobile coating film or a repair coating film, or a known polished coating film.

The method for forming a multi-layer coating film of the present invention is particularly suitable for repair coating of an automobile body, and is applied to an object to be coated such as a primer surfacer-coated surface-treated coating film, a known coating film, or a polished known coating film. Effective for painting.

(Aqueous base paint composition)
The water-based coating composition in the present invention contains a first film-forming resin. Examples of the first film-forming resin include, but are not limited to, acrylic resin, polyester resin, alkyd resin, urethane resin, fluororesin, epoxy resin, silicone resin, and polyether resin. Further, it is preferable to contain at least one resin having a crosslinkable functional group such as a hydroxyl group, a carbonyl group and an amino group, and it is particularly preferable to contain a resin containing a hydroxyl group. This is because a part of the polyisocyanate compound (b) in the aqueous clear coating composition described later permeates to the base coating film and undergoes a cross-linking reaction to improve the curability and water resistance of the multi-layer coating film. Is.
The film-forming resin may be used alone or in combination of two or more. When two or more types of film-forming resin are used, the hydroxyl value of the film-forming resin as a whole contained in the water-based base coating composition is in the range of 1 to 200 mgKOH / g from the viewpoint of improving dryness, finish and water resistance. Of these, it is preferably adjusted to the range of 5 to 100 mgKOH / g.
The film-forming resin contained in the water-based base coating composition shall include at least one of a water-dispersible acrylic resin (a1), a water-dispersible polyurethane resin (a2), and a water-soluble acrylic resin (a3). Is preferable.

-Water-dispersible acrylic resin (a1)-
The water-dispersed acrylic resin (a1) is preferably a hydroxyl group-containing acrylic resin emulsion which is an aqueous dispersion of a hydroxyl group-containing acrylic resin because the hardness of the formed coating film is excellent.

As the water-dispersible acrylic resin (a1), a (meth) acryloyl group-containing polymerizable unsaturated monomer is an essential component, and a copolymer obtained by copolymerizing other polymerizable unsaturated monomers as necessary is dispersed in water. It will be. For example, those obtained by emulsion polymerization in one step or in multiple steps using the above-mentioned polymerizable unsaturated monomer component and a polymerization initiator in the presence of water and a dispersion stabilizer are preferably mentioned.

The average particle size of the water-dispersed acrylic resin (a1) is preferably 0.02 μm or more and 1.0 μm or less, and more preferably 0.05 μm or more and 0.3 μm or less.

In the present specification, the average particle size of the water-dispersed resin is the value of the volume average particle size measured by the Coulter counter method at a measurement temperature of 20 ° C. The measurement by the Coulter counter method can be performed using, for example, "COOLTER N4 type" (manufactured by Beckman Coulter, trade name).

The water-dispersed acrylic resin (a1) may be a single-layer type or a multi-layer type such as a core / shell type, but the single-layer type is preferable from the viewpoint of recoatability and the like.

Examples of the polymerizable unsaturated monomer that can be a copolymerization component of the water-dispersible acrylic resin (a1) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl. Linear or branched alkyl (meth) acrylates such as (meth) acrylates, pentyl (meth) acrylates, hexyl (meth) acrylates, 2-ethylhexyl (meth) acrylates, lauryl (meth) acrylates, stearyl (meth) acrylates; cyclohexyl Alicyclic alkyl (meth) acrylates such as (meth) acrylates and isobornyl (meth) acrylates; aralkyl (meth) acrylates such as benzyl (meth) acrylates; 2-methoxyethyl (meth) acrylates, 2-ethoxyethyl (meth) Alkoxyalkyl (meth) acrylates such as acrylates; perfluoroalkyl (meth) acrylates; N, N-dialkylaminoalkyl (meth) acrylates such as N, N-diethylaminoethyl (meth) acrylates; (meth) acrylamides; (meth) acrylamides. ) Acrylonitrile; Vinyl ester compounds such as vinyl acetate and vinyl propionate; Vinyl aromatic compounds such as styrene and α-methylstyrene; Allyl (meth) acrylate, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate , Tetraethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,4-butanediol di (meth) acrylate, neopentyl glycol di (meth) Acrylate, 1,6-hexanediol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol di (meth) acrylate, 1,1,1-trishydroxymethylethanji (meth) ) Acrylate, 1,1,1-Trishydroxymethylethanetri (meth) acrylate, 1,1,1-Trishydroxymethylpropanetri (meth) acrylate, triallyl isocyanurate, diallyl terephthalate, divinylbenzene, etc. Polyvinyl compound having at least two polymerizable unsaturated groups; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-Hydroxypropyl (meth) acrylate, hydroxyalkyl (meth) acrylate such as hydroxybutyl (meth) acrylate, allyl alcohol, ε-caprolactone modified form of the above hydroxyalkyl (meth) acrylate, polyoxyethylene having a hydroxyl group at the molecular end. Hydroxyl group-containing polymerizable unsaturated monomer such as chain-containing (meth) acrylate; carboxyl group-containing polymerizable unsaturated monomer such as (meth) acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate; (meth) achlorine, formyl Stylol, vinyl alkyl ketone having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone, etc.), carbonyl such as acetoacetoxyethyl (meth) acrylate, acetoacetoxyallyl ester, diacetone (meth) acrylamide, etc. Group-containing polymerizable unsaturated monomer; glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate, 3,4 -Epoxy group-containing polymerizable unsaturated monomers such as epoxycyclohexylpropyl (meth) acrylate and allylglycidyl ether; isocyanato group-containing polymerizable monomers such as isocyanatoethyl (meth) acrylate, m-isopropenyl-α, and α-dimethylbenzyl isocyanate. Unsaturated monomer; alkoxysilyl group-containing polymerizable unsaturated monomer such as vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane; epoxy group-containing polymerizable unsaturated monomer Oxidation and curing of a reaction product of a monomer or a hydroxyl group-containing polymerizable unsaturated monomer and an unsaturated fatty acid, dicyclopentenyloxyethyl (meth) acrylate, dicyclopentenyloxypropyl (meth) acrylate, dicyclopentenyl (meth) acrylate, etc. Examples thereof include a sex group-containing polymerizable unsaturated monomer, and these can be used alone or in combination of two or more.

The dispersion stabilizer used for emulsion polymerization of the water-dispersible acrylic resin (a1) is not particularly limited, but for example, sodium dialkylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and poly. Anionic emulsifiers such as sodium oxyethylene alkylphenyl ether sulfate and sodium alkyldiphenyl ether disulfonate, nonionic emulsifiers such as polyoxyethylene higher alcohol ethers and polyoxyethylene alkylphenyl ethers, and anionic or cations with radically polymerizable double bonds. Sexual reactive emulsifiers can be mentioned.

The reactive emulsifier is an emulsifier having both a nonionic group, an anionic group and one or more cationic groups and a polymerizable unsaturated group in the molecule. Specific examples of the polymerizable unsaturated group include a (meth) allyl group, a (meth) acryloyl group, a propenyl group, a butenyl group and the like. Commercially available products of reactive emulsifiers include "Latemuru" (trade name, manufactured by Kao Co., Ltd.), "Eleminor" (trade name, manufactured by Sanyo Kasei Co., Ltd.), and "Aqualon" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). ), "Adecaria Soap" (trade name, manufactured by Asahi Denka Co., Ltd.), "ANTOX" (trade name, manufactured by Nippon Emulsifier Co., Ltd.) and the like.

As the polymerization initiator, conventionally known ones can be used without limitation, and examples thereof include peroxide-based polymerization initiators and azo-based polymerization initiators.

In the present invention, as the water-dispersible acrylic resin (a1), a polyvinyl chloride compound having at least two polymerizable unsaturated groups in one molecule is contained as a copolymerization component in the water resistance of the coloring base coating film. Suitable from the viewpoint of sharpness and coating hardness.
Examples of the polyvinyl compound having at least two polymerizable unsaturated groups in the above-mentioned molecule include the above-exemplified compounds, which can be used alone or in combination of two or more, and the copolymerization amount thereof may be used. , 0.1% by mass or more and 10% by mass or less, preferably 0.5% by mass or more and 5% by mass or less, based on the mass of the totally polymerizable unsaturated monomer used for producing the water-dispersible acrylic resin (a1). It is more preferable to have.

The water-dispersed acrylic resin (a1) preferably has a solid acid value of 5 mgKOH / g or less, and more preferably 4 mgKOH / g or less, from the viewpoint of water resistance and recoating compatibility of the water-based base coating film. preferable.

As a method of water dispersion of the resin, a part or all of anionic groups such as a carboxyl group contained in the acrylic resin are neutralized with a basic compound and dispersed in water, or an aqueous solution containing the basic compound is used. It is also possible to add and disperse the acrylic resin in the medium. The basic compound that serves as a neutralizing agent for the hydroxyl group-containing acrylic resin is not particularly limited, but specifically, for example, an inorganic base such as sodium hydroxide or potassium hydroxide, trimethylamine, dimethylaminoethanol, or 2-methyl. Examples thereof include organic amines such as 2-amino-1-propanol, triethylamine, and ammonia. Of these, organic amine compounds are preferable, and tertiary amines such as triethylamine, tributylamine, dimethylethanolamine, and diethylenetriamine are particularly preferable.

Here, as the resin solid content in the present specification, about 2.0 g of a sample is collected in an aluminum foil cup having a diameter of about 5 cm, and the residue (g) after heating at 110 ° C. for 1 hour is measured as a non-volatile content. It is a calculated value.

-Water-dispersible polyurethane resin (a2)-
As the water-dispersible polyurethane resin (a2), those known in the art can be used without limitation. For example, a urethane prepolymer obtained by reacting a polyisocyanate, a polyol and a carboxyl group-containing diol is dispersed in water. The polyurethane resin emulsion or the polyurethane resin dispersion obtained thereby can be mentioned.

The average particle size of the water-dispersed polyurethane resin (a2) may be 0.01 μm or more and 1.0 μm or less, and in particular, 0.1 μm or more and 0.5 μm or less.

Polyisocyanate compounds as constituents include aliphatic diisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimerate diisocyanate, and lysine diisocyanate; burette type adducts and isocyanurate ring adducts of these diisocyanate compounds; isophorone. Diisocyanate, 4,4'-methylenebis (cyclohexylisocyanate), methylcyclohexane-2,4- (or -2,6-) diisocyanate, 1,3- (or 1,4-) di (isocyanatomethyl) cyclohexane, 1, , 4-Cyclohexanediisocyanate, 1,3-Cyclopentane diisocyanate, 1,2-Cyclohexanediisocyanate and other alicyclic diisocyanates; Buret-type adducts of these diisocyanates, isocyanurate ring adducts; Range isocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalenedi isocyanate, 1,4-naphthalenedi isocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether isocyanate , (M- or p-) phenylenediisocyanate, 4,4'-biphenylenediocyanate, 3,3'-dimethyl-4,4'-biphenylenediisocyanate, bis (4-isocyanatophenyl) sulfate, isopropylidenebis (4-) Aromatic diisocyanate compounds such as phenylisocyanate); burette-type adducts of these diisocyanate compounds, isocyanurate ring adducts; triphenylmethane-4,4', 4'-triisocyanate, 1,3,5-triisocyanate Polys having 3 or more isocyanate groups in one molecule such as isocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4'-dimethyldiphenylmethane-2,2', 5,5'-tetraisocyanate, etc. Isocyanate compounds; burette-type adducts of these polyisocyanate compounds, isocyanurate ring adducts; ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylol propionic acid, polyalkylene glycol, trimethylolpropane, hexanetriol, etc. Isocyanate on the hydroxyl group of the polyol Urethane adducts formed by reacting polyisocyanate compounds at a ratio of an excess amount of groups; burette-type adducts of these urethanization adducts, isocyanurate ring adducts, and the like can be mentioned.

Examples of the polyol include polyether polyols such as polyethylene glycol, polypropylene glycol, polyethylene-propylene (block or random) glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, and polyoctamethylene ether glycol; dicarboxylic acid (adipic acid). , Succinic acid, sebacic acid, glutaric acid, maleic acid, fumaric acid, phthalic acid, etc.) and glycols (ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5 -Polycols condensed and polymerized with (pentanediol, neopentylglycol, bishydroxymethylcyclohexane, etc.), such as polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polyneopentyl adipate, poly-3-methylpentyl adipate, polyethylene / Polyester polyols such as butylene adipate, polyneopentyl / hexyl adipate; polycaprolactone polyol, poly-3-methylvalerolactone polyol; polycarbonate polyol; ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4- Butanediol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, octanediol, tricyclodecanedimethylol, hydrogenated bisphenol A, cyclohexanedimethanol, low molecular weight glycols such as 1,6-hexanediol; and the like. , Can be used alone or in combination of two or more.

Examples of the carboxyl group-containing diol include dimethylol acetic acid, trimethylol propionic acid, and trimethylol butyric acid.

The urethane prepolymer can be produced based on a conventionally known method.

The water-dispersed polyurethane resin (a2) may be neutralized with a neutralizing agent. The neutralizing agent is not particularly limited as long as it can neutralize the carboxyl group, and the neutralizing agent mentioned in the section of the basic compound of the water-dispersible acrylic resin (a1) can be used.

Since the water-dispersible polyurethane resin (a2) has good medium sharpening property of the coloring base coating film, it is preferable that the water-dispersible polyurethane resin (a2) has a cyclic structure in the molecule. More preferably, the polyisocyanate constituting the water-dispersible polyurethane resin (a2) contains a compound derived from an alicyclic diisocyanate compound as a part of its components.
Further, the water-dispersible polyurethane resin (a2) preferably has a solid acid value of 20 mgKOH / g or less and 5 gKOH / g or more and 18 mgKOH / g from the viewpoint of water resistance and recoating compatibility of the coloring base coating film. The following is more preferable.

-Water-soluble acrylic resin (a3)-
The water-soluble acrylic resin is a resin obtained by polymerizing a polymerizable unsaturated monomer having a hydrophilic functional group and another polymerizable unsaturated monomer with a polymerization initiator in the presence of a hydrophilic organic solvent. Since it can be in a dissolved state (transparent) in an aqueous medium, it is clearly distinguished from the dispersion type acrylic resin which is in a dispersed state in an aqueous medium, which will be described later.

The hydrophilic functional group-containing polymerizable unsaturated monomer is a compound having at least one hydrophilic functional group and one or more polymerizable unsaturated bonds in one molecule, and the hydrophilic functional group is, for example, a phosphate group or a sulfonic acid. Examples thereof include a group, a carboxyl group, an amino group, an amide group, and a polyoxyalkylene chain.

Specific examples thereof include N-substituted (meth) acrylamide, polyoxyalkylene chain-containing (meth) acrylate, dialkylaminoalkyl (meth) acrylate, acid group-containing (meth) acrylate, etc., which may be used alone or. Two or more types can be used in combination.

Among them, an acid group-containing polymerizable unsaturated monomer is preferable from the viewpoint of drying property, water resistance and weather resistance, and (meth) acrylic acid, maleic acid, a phosphoric acid group-containing polymerizable unsaturated monomer and a sulfonic acid-containing polymerizable monomer are preferable. Unsaturated monomers are more preferred.

Examples of the phosphate group-containing polymerizable unsaturated monomer include 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate, 2-methacryloyloxypropyl acid phosphate and the like.

Examples of the sulfonic acid group-containing polymerizable unsaturated monomer include 2-acrylamide-2-methylpropanesulfonic acid, allylsulfonic acid, styrenesulfonic acid sodium salt, sulfoethylmethacrylate, and sulfonic acid group-containing polymerization such as sodium salt and ammonium salt thereof. Examples include sex unsaturated monomers.

In particular, the water-soluble acrylic resin in which a carboxyl group-containing polymerizable unsaturated monomer and a phosphoric acid group-containing polymerizable unsaturated monomer are used in combination as the acid group-containing polymerizable unsaturated monomer is coated when the composition of the present invention is repeatedly applied. It is preferable because it has the effect of improving the layer compatibility.

As the hydroxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers that can be copolymerized with the hydrophilic functional group-containing polymerizable unsaturated monomer, the above-mentioned ones can be preferably used.

Further, it is desirable that the phosphoric acid group-containing water-soluble acrylic resin neutralizes the acid group with a neutralizing agent. The neutralizing agent is not particularly limited as long as it can neutralize the carboxyl group. For example, an inorganic base such as sodium hydroxide or potassium hydroxide, trimethylamine, dimethylaminoethanol, or 2-methyl 2 is used. -Amino-1-propanol, triethylamine, ammonia and other organic amines can be mentioned.

The hydrophilic organic solvent used for the polymerization is not strictly distinguished, but for example, an organic solvent that dissolves at least 20 g in 100 g of water at 20 ° C. can be used, and an alcohol-based organic solvent; an ether-based organic solvent; Examples thereof include ethylene glycol ether-based organic solvent; diethylene glycol ether-based organic solvent; propylene glycol ether-based organic solvent; dipropylene glycol ether-based organic solvent; ester-based organic solvent, and the like. These can be used alone or in combination of two or more.

The hydroxyl value of the water-soluble acrylic resin (a3) is not particularly limited, but is preferably 1 mgKOH / g or more and 200 mgKOH / g or less, and 5 mgKOH / g or more and 100 mgKOH / g or less from the viewpoint of dryness and finish. Is particularly preferred.

The acid value of the water-soluble acrylic resin (a3) is preferably 1 mgKOH / g or more and less than 100 mgKOH / g, particularly 5 mgKOH / g, from the viewpoint of achieving both storage stability and drying property of the paint and water resistance of the coating film. It is preferably 60 mgKOH / g or less.

The weight average molecular weight of the water-soluble acrylic resin (a3) is preferably 1,000 or more and 500,000 or less, more preferably 1,500 or more and 150,000 or less, and 2,000 or more and 70,000 or less. Is particularly preferable.

The amount of the water-soluble acrylic resin (a3) contained in the water-based base coating composition is 0.5% by mass with respect to the total resin solid content contained in the water-based base coating composition from the viewpoint of weather resistance and drying property. It is preferably 20% by mass or less, and more preferably 1% by mass or more and 15% by mass or less.
<Resin component>
As the resin component in the water-based base coating composition used in the present invention, at least one of the above-mentioned water-dispersed acrylic resin (a1), water-dispersed polyurethane resin (a2) and water-soluble acrylic resin (a3) is used as a main component. It is preferable to contain the water-dispersible polyurethane resin (a2) from the viewpoint of medium sharpening property. In particular, from the viewpoint of water resistance and coating hardness of the multi-layer coating film, the resin (a1) and the resin (a2) based on the total solid content of the resin (a1), the resin (a2) and the resin (a3). It is suitable that the total solid content is 80% by mass or more, preferably 90% by mass or more.
When the proportion of the water-dispersible resin is within the above range, the multi-layer coating film has good recoating compatibility when the water-based base coating composition is reapplied, has excellent coating film hardness, and has a high-finished appearance. May be obtained, which is particularly preferable.

-Other resins-
Further, as other resins, acrylic resin other than resin (a1) and resin (a3), silicone resin, urethane resin other than resin (a2), fluororesin, epoxy resin, polyester resin, alkyd resin and the like, or a mixture thereof. Examples thereof include a resin or a modified resin, for example, an acrylic modified polyester resin, an acrylic silicone resin, an acrylic modified epoxy resin, an epoxy ester resin, and the like. In addition, these may be used alone or in combination of two or more.

Other resins may be used as long as they do not affect the storability, coating performance, and weather resistance of the paint, but from the viewpoint of weather resistance and storability of the paint, all the resins in the water-based base paint composition. It is preferably 20% by mass or less, more preferably less than 5% by mass, based on the solid content.

The usage ratio of the water-dispersed acrylic resin (a1) and the water-dispersed polyurethane resin (a2) is 99 in terms of the mass ratio of the water-dispersed acrylic resin (a1) / water-dispersed polyurethane tree (a2) resin solid content. It is suitable that the color is in the range of 1/1 to 1/99, preferably 80/20 to 20/80, from the viewpoint of the substrate adhesion and water resistance of the colored base coating film.

-Metal compound-
The water-based base coating composition comprises a metal compound. The metal of the metal compound is preferably derived from a metal catalyst. Examples of the metal compound include metal compounds containing at least one metal selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum. The metal compound is preferably water-soluble or water-dispersible. Examples of such metal compounds may be carbonates, phosphates, nitrates, sulfates, acetates, fluoroacids and salts thereof, organic acid salts such as carboxylic acids, oxides, alkali salts and the like. These metal compounds may be anhydrous or hydrated.

As the metal compound, zinc octylate, manganese octylate, tin octylate, cobalt octylate, titanium octylate, aluminum octylate, zirconium octylate, bismuth octylate are available because of their excellent catalytic activity and easy industrial availability. , Or a carboxylic acid metal salt compound such as lead octylate, an alkali molybdic acid salt such as sodium molybdenate, sodium phosphate molybdenum, calcium molybdenate, ammonium molybdenate; molybdenum oxide such as molybdenum trioxide; Can be done.

A water-dispersible or water-soluble metal compound is particularly preferable, and a water-soluble metal compound is particularly preferable, and a specific example is particularly preferable, from the viewpoint of transferability to a clear coating film and improvement of coating film hardness of a multi-layer coating film. , The following (chemical formula, water solubility: unit mg / 1000 g [measurement temperature]).
Specific examples include molybdenum trioxide (MoO ₃ , 1.34 × 10 ³ [20 ° C]), sodium molybdate (Na ₂ MoO ₄ , 3.94 × 10 ⁵ [25 ° C]), and calcium molybdate (CaMoO _4). , 50 [25 ° C]), molybdic acid (H ₂ MoO ₄ , 1.33 × 10 ³ [18 ° C]). Diammonium molybdate and phosphomolybdic acid are soluble in water. As the metal compound as the metal catalyst, a commercially available product can be used.
The above water solubility is based on Sidney L. Phillips (1997): Properties of Inorganic Compounds: Version 2.0, Boca Raton, CRC Press.

From the viewpoint of water resistance, the metal compound is not soluble in water, or the water solubility of the metal compound ^{is preferably 1 × 10 -3} mg / 1000 g or more, and more preferably 0.05 mg / 1000 g or more. It is preferably 0.1 mg / 1000 g or more, and more preferably 0.1 mg / 1000 g or more. The water solubility of the metal compound ^{is preferably 5 × 10 5} mg / 1000 g or less.

Here, it is preferable that the metal compound of the present application itself is a colorless (white) powder or a light-colored powder, and it is preferable that the metal compound has almost no effect on coloring when it is used as a coating film. Therefore, the metal compound of the present application is different from the coloring pigment described later.

It is particularly preferable that the metal compound has a small particle size from the viewpoint of water dispersibility and easy migration from the base coating film. Specifically, the average primary particle size is preferably 1 nm or more and 1000 nm or less, more preferably 2 nm or more and 200 nm or less, and further preferably 3 nm or more and 150 nm or less.
It is convenient and desirable to mix the metal compound in the paint by stirring with shear dispersion, for example, a disper.

The content concentration of the metal compound in the water-based base coating composition is preferably equal to or higher than the content concentration of the metal compound in the water-based clear coating composition described later. When the content concentration of the metal compound in the water-based clear paint composition is equal to or higher than the content concentration of the metal compound in the water-based clear paint composition, the water-based clear paint composition does not contain a metal catalyst. However, sufficient curability can be obtained, and the hardness of the coating film can be improved as a multi-layer coating film.
This is because when a water-based clear paint is applied on a water-based base coating film wet-on-wet, both coating films are aqueous media, so that the metal compound in the base coating film becomes a clear coating film during the drying process. By migrating. As a result, even when drying under low temperature and short time conditions, a sufficient amount of metal catalyst can be obtained when both coating films are dried at the same time.
Therefore, this method has the effect of improving the hardness, water resistance, and drying property of the multi-layer coating film without impairing the finish.
Further, even when an aqueous clear coating composition containing a metal catalyst is used in this method, the finishability and the hardness of the coating film can be improved. It is considered that this is because when the water-based base coating film is wet-on-wet coated, the metal catalyst is also prevented from being transferred from the clear coating film to the base coating film during the drying process to some extent.

Furthermore, in the method of the present invention, it is not necessary to add a large amount of a metal catalyst or the like that affects the pot life to the aqueous clear paint composition as in the conventional case. When a metal catalyst is added, the concentration of the metal compound in the aqueous base coating film may be adjusted to be equal to or higher than the concentration of the metal compound in the clear coating film. The multi-layer coating film obtained by the method of the present invention has the effects of excellent workability such as drying property and excellent water resistance.

The content of the metal compound in the water-based base coating composition is preferably in the range of 0.01 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the total resin solid content in the water-based base coating composition. It is more preferably in the range of 0.03 parts by mass or more and 3.0 parts by mass or less, and further preferably in the range of 0.05 parts by mass or more and 1.5 parts by mass or less. When the content is in the above range, the hardness and workability of the multi-layer coating film after curing are particularly improved.
Here, 100 parts by mass of the total resin solid content used as a reference for the content of the metal compound in the water-based base coating composition is the water-dispersible acrylic resin (a1) blended in the water-based base coating composition. Based on the total mass of 100 parts by mass of the resin solid content, the resin solid content of the water-dispersible polyurethane resin (a2), and the resin solid content of the water-soluble acrylic resin (a3).
The solid content concentration of the metal compound in the water-based base coating composition shall be 0.01% by mass or more and 4.0% by mass or less based on the total solid content in the water-based base coating composition. Is more preferable, 0.02% by mass or more and 2.0% by mass or less is more preferable, and 0.03% by mass or more and 1.0% by mass or less is further preferable.
In this case, the total solid content includes the above resin (a1), resin (a2), and resin (a3), as well as other resins, coloring pigments, and other additive components, which are blended as necessary. Is their total solid content.

-Coloring pigment-
The water-based base coating composition may contain a color pigment. As the coloring pigment, conventionally known pigments can be used without particular limitation. Specific examples thereof include metal oxide pigments such as titanium oxide and iron oxide, composite metal oxide pigments such as titanium yellow, carbon black, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, and perinone. Color pigments such as pigments, benzimidazolone pigments, isoindolin pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, indanslon pigments, dioxane pigments, indigo pigments; aluminum (vapor deposition) (Including aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, aluminum oxide coated with titanium oxide or iron oxide, mica coated with titanium oxide or iron oxide, glass flakes, hologram pigments, etc. Pigments; and the like, which can be used alone or in combination of two or more depending on the desired color and coating performance.

When an aluminum pigment is contained as the coloring pigment, it is preferable to use a surface-treated aluminum pigment, and an inorganic phosphoric acid treatment, a resin coating, a method of further treating the resin coating with a phosphoric acid compound, and a titanium-based treatment agent are used. Processed ones and the like can be used. In particular, from the viewpoint of improving the hardness and water resistance of the multi-layer coating film, it is preferable to use at least one selected from silica-treated aluminum pigments, aluminum pigments treated with titanium-based treatment agents, and molybdate-treated aluminum pigments. In particular, it is preferable to use an aluminum pigment treated with molybdic acid.

The content of the coloring pigment varies depending on the type of the coloring pigment, but is preferably 0.1 part by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the resin solid content contained in the aqueous base coating composition. It is more preferably 0.5 parts by mass or more and 200 parts by mass or less.

When a surface-treated aluminum pigment is blended as a coloring pigment in the water-based base paint composition used in this method, the blending ratio thereof is the water-based base paint composition from the viewpoint of paint stability, coating film hardness and weather resistance. The resin solid content contained in the product is preferably 1 part by mass or more and 100 parts by mass or less, and more preferably 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the resin solid content.
When the water-based base coating composition contains a coloring pigment, it may be referred to as a water-based coloring base coating composition.

-Other ingredients-
The water-based paint composition according to the present invention includes a resin emulsion or a water-soluble resin other than the water-dispersible acrylic resin (a1), the water-dispersible urethane resin (a2) and the water-soluble acrylic resin (a3), a neutralizing agent, and the like. Leology control agent (viscosity adjuster), polymer fine particles, surface conditioner, defoamer, hard ultraviolet absorber, light stabilizer, dispersion aid, preservative, silane coupling agent, defoamer, other than the above metal compounds The curing catalyst and / or paint additives usually used in the preparation of water-based paints such as rust-preventive pigments, neutralizers, and organic solvents can be blended as needed.

The aqueous base coating composition in the present invention may contain a curing agent and / or a diluent. When a curing agent and / or a diluent is contained, it is preferable to mix them immediately before painting. A water-based base coating composition containing no curing agent is called a one-component type. It is particularly preferable that the water-based base coating composition is a one-component coating composition from the viewpoint of shortening the process and from the viewpoint of hardness and drying property of the multi-layer coating film.
When a diluent is added to the aqueous base coating composition, the mass ratio of the main ingredient and the diluent can be appropriately adjusted depending on the coating environment and the like. Generally, from the viewpoint of the appearance of the base coating film and the physical characteristics of the coating film, it is preferable that the diluent component is 30 parts by mass or more and 300 parts by mass or less, and 40 parts by mass or more and 250 parts by mass or less, based on 100 parts by mass of the main component. It is more preferable to have.

Further, examples of the curing agent when the aqueous base coating composition contains a curing agent include a polyisocyanate curing agent, a blocked isocyanate curing agent, a melamine curing agent, an oxazoline curing agent, and a carbodiimide curing agent. The curing agent may be contained in either the main component or the diluent component, or may be mixed and used as a separate component immediately before painting.

The viscosity of the aqueous base coating composition is not particularly limited, but the viscosity when no curing agent or diluent is added is 100 mPa · sec or more and 3000 mPa · sec or less from the viewpoint of storage stability. It is preferably 600 mPa · sec or more and 2000 mPa · sec or less.
In the present specification, the viscosity is a value measured at a rotation speed of 60 rpm using a viscometer digital bismetron viscometer VDA type (manufactured by Shibaura System Co., Ltd.) within 10 minutes after preparing the sample at 25 ° C. do.

The solid content of the aqueous base coating composition is not particularly limited, but the solid content concentration is 5% by mass or more and 60% by mass or less from the viewpoint of the finishability of the formed coating film. Is preferable, and it is particularly preferable that it is 10% by mass or more and 50% by mass or less.
In addition, in this specification, a solid content (or may be described as a solid content concentration) means a non-volatile content, and means a residue obtained by removing volatile components such as water and an organic solvent from a sample. Then, it can be calculated by multiplying the mass of the sample by the solid content concentration. Specifically, it can be measured by dividing the mass of the residue (nonvolatile substance) obtained by drying about 3 grams of a sample at 105 ° C. for 3 hours by the mass before drying. It may be expressed in parts per hundred. The residue may be solid or liquid at room temperature.

(Painting of water-based base paint composition)
Examples of the method for applying the water-based base coating composition include air spray, airless spray, rotary atomization, brush, roller, hand gun, universal gun, immersion, roll coater, curtain flow coater, roller curtain coater, die coater and the like. It can be appropriately selected depending on the intended use of the object to be coated. In addition, the water-based base coating composition may be applied a plurality of times using these methods.

After coating the water-based base coating composition, it is preferable to perform the second step in a state where the base coating film (I) is undried, but the step of drying the base coating film (I) before performing the second step. Can also be included. Examples of the drying step include normal temperature drying or forced drying, and in the case of normal temperature drying, specifically, 10 minutes or more (preferably 1 hour or more, more preferably 1 hour or more) at room temperature (for example, less than 10 to 40 ° C.). Can be left to stand (for 2 hours or more), or in the case of forced drying, it can be heated at 40 to 120 ° C. for 1 to 120 minutes (preferably 5 to 60 minutes). In the case of forced drying, from the viewpoint of finishability, it can be set (standing) at room temperature for 1 to 120 minutes (preferably 5 to 60 minutes) in advance before heat curing. For drying, for example, a blower or the like may be used.

The film thickness of the base coating film (I) can be appropriately adjusted according to the condition of the surface to be coated, but in general, the dry film thickness is preferably 5 μm or more and 60 μm or less, and particularly preferably 10 μm or more and 40 μm or less.

<Second step>
The second step is a step of coating the water-based clear coating composition on the base coating film (I) to form the clear coating film (II).

(Aqueous clear paint composition)
The aqueous clear coating composition used in the present invention preferably contains a second film-forming resin, and the second film-forming resin preferably contains a dispersion-type acrylic resin (a4).
The water-based clear paint composition has two liquids, a first liquid containing a dispersion type acrylic resin (a4) and water, and a second liquid containing a polyisocyanate compound (b), and the two liquids are mixed immediately before painting. It is preferable that the composition is an aqueous two-component coating composition that is appropriately diluted and used. The first liquid functions as a main agent and the second liquid functions as a curing agent.

In the water-based clear coating composition, the ratio of the first liquid to the second liquid is preferably 5 parts by mass or more and 100 parts by mass or less based on 100 parts by mass of the first liquid, and particularly 30 parts by mass. It is more preferable that the amount is 70 parts by mass or more.

The water-based clear coating composition may contain components other than the first liquid and the second liquid, if necessary. Specific examples of the components other than the first liquid and the second liquid include a rheology control agent, a diluent component containing water, a siloxane bond forming component such as an organic silane compound, and a catalyst component thereof, and coating thereof. When the first liquid and the second liquid are mixed immediately before, they can be mixed and used together.
Hereinafter, the details of the first liquid and the second liquid will be described.

(1) First Liquid The first liquid of the water-based clear paint composition contains a hydroxyl group-containing resin as the second film-forming resin, and the hydroxyl group-containing resin contains a dispersion-type acrylic resin (a4) and water. Is preferable.
Since the hydroxyl group-containing resin is applied to water-based paints, it is either a water-soluble resin or a water-dispersible resin. Here, in the present specification, the "water-soluble" resin can take a state in which the resin is dissolved or semi-dissolved in water when the resin is mixed with water, and is "water-dispersible". It has a different form from resin. The water-dispersible resin is further divided into an emulsion type and a colloidal dispersion type. In the present specification, the emulsion type is a form obtained by emulsion polymerization or the like in the presence of an emulsifier using water as a solvent, or a form obtained by mechanically forcibly dispersing a resin completely insoluble in water in water. Called a mold.
On the other hand, the polymerization reaction of the above-mentioned monomer mixture is carried out in the presence of no solvent or a suitable organic solvent, and the mixture is added dropwise and mixed in water, and if necessary, the excess organic solvent is removed to disperse the mixture, or it is necessary after the polymerization reaction. A form in which water is added and dispersed after removing an excess organic solvent is called a dispersion type.
The first liquid of the water-based clear coating composition preferably has a solid content concentration of 20% by mass or more and 60% by mass or less, and 30% by mass or more and 50% by mass or less, from the viewpoint of pot life and finishability of the formed coating film. Is particularly preferable.
The dispersion type acrylic resin (a4) will be described below.

-Dispersion type acrylic resin (a4)-
The dispersion type acrylic resin (a4) is preferably contained in an amount of 50% by mass or more based on the total resin solid content contained in the first liquid. The content of the dispersion type acrylic resin (a4) is the total resin solid content contained in the first liquid from the viewpoints of dryness of the obtained multi-layer coating film, finish such as glossiness, weather resistance and water resistance. On the other hand, it can be 60% by mass or more, more than 70% by mass, and 75% by mass or more, and the upper limit is more preferably 99.5% by mass or less and 98% by mass or less.

Here, the total resin solid content contained in the first liquid includes the resin solid content of the dispersion type acrylic resin (a4), the polyether polyol (a5) blended as necessary, and the dispersion type acrylic resin. When a hydroxyl group-containing resin other than (a4) is contained, it refers to the total mass of those resin solids.

The dispersion type acrylic resin (a4) is, for example, a copolymer of a hydroxyl group-containing polymerizable unsaturated monomer (a4-1) and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer. be able to.

The hydroxyl group-containing polymerizable unsaturated monomer (a4-1) is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in one molecule, and specifically, for example, 2-hydroxyethyl (meth). A monoesterified product of (meth) acrylic acid such as acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and a dihydric alcohol having 2 to 8 carbon atoms. Ε-caprolactone modified product of monoesteride of the (meth) acrylic acid and a dihydric alcohol having 2 to 8 carbon atoms; N-hydroxymethyl (meth) acrylamide; allyl alcohol, and poly having a hydroxyl group at the molecular end. Examples thereof include (meth) acrylate having an oxyethylene chain. Of these, 2-hydroxyethyl methacrylate and / or 2-hydroxypropyl methacrylate are preferable from the viewpoint of drying property and reactivity with a curing agent described later.

Examples of other monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer (a4-1) include carboxyl group-containing unsaturated monomers such as acrylic acid and methacrylic acid; methyl (meth) acrylate and ethyl (meth) acrylate. , N-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate Alkyl with acrylic acid or methacrylic acid such as isooctyl (meth) acrylate, lauryl (meth) acrylate, isomyristyl (meth) acrylate, stearyl (meth) acrylate, isostearyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name). Ester compound (linear or branched alkyl (meth) acrylate); alicyclic alkyl (meth) acrylate such as cyclohexyl (meth) acrylate and isobornyl (meth) acrylate; polymerizable organic siloxane such as polysiloxane mono (meth) acrylate Aralkyl (meth) acrylates such as benzyl (meth) acrylates; aromatic ring-containing polymerizable unsaturated monomers such as styrene and vinyltoluene; alkoxyalkyl (meth) acrylates such as 2-methoxyethyl (meth) acrylates; (meth) acrylonitrile , (Meta) acrylamide, diacetone (meth) acrylamide and other nitrogen-containing polymerizable unsaturated monomers; allyl (meth) acrylate, ethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, pentaerythritol. Polymerizable unsaturated monomer having at least two polymerizable unsaturated groups in one molecule such as di (meth) acrylate, 1,1,1-trishydroxymethylpropantri (meth) acrylate; vinyl monomer such as vinyl acetate An epoxy group-containing polymerizable unsaturated monomer such as glycidyl (meth) acrylate and allyl glycidyl ether, 3,4-epoxycyclohexylmethyl (meth) acrylate; an alkoxysilyl group-containing non-polymerizable monomer such as 3-methacryloyloxypropyltrimethoxysilane. Saturated monomers; Examples thereof include oxidatively curable group-containing polymerizable unsaturated monomers such as dicyclopentenyloxyethyl (meth) acrylate. These can be used alone or in combination of two or more.

As a method for preparing the dispersion type acrylic resin (a4), the monomer is polymerized by a conventionally known method such as solution polymerization in the presence of no solvent or an organic solvent, and then dispersed in water as needed. There is a method of obtaining by. As a method of water dispersion, a conventionally known method can be used. For example, a method of neutralizing a part or all of anionic groups such as a carboxyl group contained in the above resin with a basic compound such as amine and ionizing them to disperse them in water, or an aqueous medium containing the basic compound. It is possible to use a method such as adding the resin to the inside and dispersing it.

In the present invention, the dispersion-type acrylic resin (a4) is obtained by copolymerizing the polymerizable unsaturated monomer components having different compositions in multiple stages, which is excellent in the storage stability of the main agent (I). More preferred from.

The dispersion type acrylic resin (a4) is superior in water resistance and weather resistance because it does not use an emulsifier as compared with the emulsion type acrylic resin. Since the dispersion type acrylic resin (a4) is not manufactured from an aqueous medium, it is easy to obtain fine particles having a relatively low molecular weight and a small particle size and a good balance. It is extremely excellent in handling workability of paints such as properties, and is also excellent in dryness and glossiness. Further, the dispersion type acrylic resin (a4) can obtain an extremely excellent coating film appearance even though it is a water-based paint, and has excellent reactivity with the polyisocyanate compound (b), so that the coating film has extremely excellent weather resistance. A membrane can be obtained.

The hydroxyl value of the dispersion type acrylic resin (a4) is not particularly limited, but is 30 mgKOH / g from the viewpoint of the balance between drying property, finish property, weather resistance, and paint handling workability such as pot life and hand stirring property. It is preferably 200 mgKOH / g or less, and particularly preferably 50 mgKOH / g or more and 170 mgKOH / g or less.

The acid value of the dispersion-type acrylic resin (a4) is preferably less than 40 mgKOH / g, and particularly preferably 5 mgKOH / g or more and 35 mgKOH / g or less, from the viewpoint of achieving both storage stability and drying property of the paint. preferable.

In addition, in this specification, the acid value and the hydroxyl value are both values in terms of solid content, and are values measured by a method based on JIS K0070.

The weight average molecular weight of the dispersion type acrylic resin (a4) is preferably 1,000 or more and 100,000 or less, and particularly preferably 2,000 or more and 70,000 or less.
As used herein, the weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

The glass transition temperature (hereinafter sometimes abbreviated as Tg) of the dispersion type acrylic resin (a4) is 40 ° C. or higher from the viewpoint of improving the drying property in a short time, particularly from the viewpoint of being able to polish and repair in a shorter time. Is preferable, 42 ° C. or higher and 70 ° C. or lower is more preferable, and 45 ° C. or higher and 65 ° C. or lower is particularly preferable.
In order to obtain such a dispersion type acrylic resin (a4) having a relatively high glass transition temperature, it is preferable that the homopolymer contains a monomer having a glass transition temperature of 30 ° C. or higher as a part of the component thereof, and the glass transition temperature is preferably contained. It is more preferable to include a monomer having a temperature of 40 ° C. or higher and 130 ° C. or lower as a part of the copolymerization component thereof.

Specific examples of the monomer having a glass transition temperature of 30 ° C. or higher of the homopolymer include styrene, methyl methacrylate, ethyl methacrylate, and methacrylate having a branched alkyl group having 3 to 4 carbon atoms, for example, i-propyl methacrylate. (Meta) acrylate having a cyclic alkyl structure such as cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, etc., cetyl acrylate (also known as hexadecyl acrylate), benzyl methacrylate, etc., such as i-butyl methacrylate and tert-butyl methacrylate. In addition, isostearyl acrylate, stearyl methacrylate and the like can be mentioned, and from the viewpoint of adhesion to the object to be coated and coating film hardness, particularly from styrene, methyl methacrylate, and methacrylate having a branched alkyl group having 3 to 4 carbon atoms. It is particularly preferred to use at least one selected monomer. In addition, these monomers can be used alone or in combination.

When a monomer having a glass transition temperature of 30 ° C. or higher is used, the amount used is preferably 50% by mass or more and 100% by mass or less in other polymerizable unsaturated monomers from the viewpoint of coating film hardness. , 70% by mass or more and 95% by mass or less is more preferable.

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

The dispersion type acrylic resin (a4) preferably has an average particle size of 50 nm or more and 500 nm or less, preferably 80 nm or more and 300 nm or less, from the viewpoint of water resistance, weather resistance, and finish such as gloss (smoothness). It is more preferable to have. In the present specification, the average particle size is a Coulter counter N4 (trade name, manufactured by Beckman Coulter Co., Ltd., particle size distribution measuring device), and the sample is diluted with deionized water to a concentration suitable for measurement. The value is measured at room temperature (about 20 ° C).

The solid content concentration of the dispersion-type acrylic resin (a4) after production is preferably about 35% by mass or more and 65% by mass or less from the viewpoint of dispersion stability of the dispersion-type acrylic resin (a4) in water. ..

As the dispersion type acrylic resin (a4), a commercially available product can also be used. The commercial products are not particularly limited, and are, for example, MACRYNAL series (manufactured by allnex) such as MACRYNAL SM 6825w / 37WA, MACRYNAL SM 6810w / 42WA, MACRYNAL VSM6299 / 42WA, Bihydrol A145, Bihydrol A2470, Bihydrol A2472, Bihydrol A2472. Bihydrol series such as Bihydrol A2646 (manufactured by Sumika Cobestro Urethane), Barnock series such as Barnock WD-551 (manufactured by DIC), NeoCryl series such as NeoCryl XK-555 (manufactured by DSM), etc. Can be done.

The solid content concentration of the dispersion-type acrylic resin (a4) in the water-based clear coating composition is preferably about 20% by mass or more and 70% by mass or less with respect to the total solid content of the water-based clear coating composition. It is more preferably about 35% by mass or more and 65% by mass or less.

The first liquid of the water-based clear paint composition includes a water-dispersible resin or a water-soluble resin other than the dispersion type acrylic resin (a4), a pigment component, a neutralizing agent, a rheology control agent, a surface conditioner, a defoaming agent, and the like. Other components such as a curing catalyst, an ultraviolet absorber, a light stabilizer, and an organic solvent can be blended as needed.
The solid content concentration when other components are blended is preferably 30% by mass or less, more preferably 20% by mass or less, and 10% by mass with respect to the total solid content of the aqueous clear coating composition. % Or less is more preferable.

Among these, the rhology control agent includes, for example, a polyamide-based leology control agent such as fatty acid amide, polyamide, acrylic amide, long-chain polyaminoamide, aminoamide and salts thereof (for example, phosphate); polyether polyol urethane prepolymer. , Urethane-based rehology control agents such as urethane-modified polyether-type viscosity modifiers; Cellulose-based reology control agents such as hydroxypropyl cellulose; Inorganic layered compound-based relogy control agents such as montmorillonite, bentonite, clay; Aminoplast-based reology control agents such as hydrophobically modified ethoxylate aminoplast, polyethylene, polypropylene, polyethylene oxide, oxidation. Examples thereof include polyolefin waxes such as polypropylene, ethylene vinyl acetate, polyethylene chloride, and chlorinated polypropylene, and only one kind may be used, or a mixture of two or more kinds may be used.

Commercially available rheology control agents include polyamide rheology control agents such as "Disparon AQ-600" and "Disparon AQH-800" (trade name, manufactured by Kusumoto Kasei Co., Ltd.); Aminoplast rheology control agents such as "REOBYK H600" and "RHEOBYK H600VF" (manufactured by BYK Chemie); "ACRYSOL ASE60" (manufactured by Dow Chemical), "Biscalex HV-30" (manufactured by BASF), " Polycarboxylic acid-based such as "SN Sickener 613", "SN Sickener 617", "SN Sickener 618", "SN Sickener 630", "SN Sickener 634", "SN Sickener 636", (the above product name is manufactured by Sannopco). Rheology control agent; "Adecanol UH-814N", "UH-752", "UH-750", "UH-462" (trade name, manufactured by ADEKA), "SN Sickener 621N", "SN Sickener 623N" ( Urethane-based rheology control agents such as "Reolate 244" and "Leolate 278" (trade name, manufactured by Elementis Japan); "HEC Daicel SP600N" (trade name, manufactured by Daicel Chemical Co., Ltd.). Cellular rheology control agents such as (manufactured by Kogyo Co., Ltd.); Inorganic layered compound rheology control agents such as "BENTONE HD" (trade name, manufactured by Elementis Japan); BYK Chemie AQUACER series, Nippon Paper Group supermarket Polyolefi elementis Japan such as Kron series, Arrow base series manufactured by Unitika, Chemipearl series manufactured by Mitsui Kagaku, etc., can be used alone or in combination of two or more.

In the present invention, it is suitable to use a polycarboxylic acid-based rheology control agent and / or a nonionic rheology control agent as the rheology control agent from the viewpoint of sagging resistance of the formed coating film.

Examples of the nonionic rheology control agent include urethane-based rheology control agents, cellulosic-based rheology control agents, layered compound-based rheology control agents, and aminoplast-based rheology control agents.

The rheology control agent contains the active ingredient of the rheology control agent in an amount of 0.01 part by mass or more and 1.0 part by mass or less based on 100 parts by mass of the resin solid content of the dispersion type acrylic resin (a4). Is preferable, and it is particularly preferable that the content is 0.1 part by mass or more and 0.5 part by mass or less.

-Polyester polyol (a5)-
In the present invention, the polyether polyol (a5) may be contained as a part of the second film-forming resin from the viewpoint of obtaining a coating film having an excellent finished appearance. The polyether polyol (a5) is preferably contained in the first liquid.

Examples of the polyether polyol (a5) include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyoxyalkylene glyceryl ether and the like, which may be used alone or in combination of two or more. Among these, it is preferable to contain polyoxyalkylene glyceryl ether from the viewpoint of improving the finish of the coating film.
The polyoxyalkylene structure in the polyoxyalkylene glyceryl ether can be any one selected from polyoxyethylene, polyoxypropylene, and polyoxybutylene, and polyoxypropylene is preferable.

As the above-mentioned polyether polyol (a5), the number average molecular weight is in the range of 400 or more and 5000 or less, particularly in the range of 500 or more and 1500 or less, and the hydroxyl value is in the range of 30 mgKOH / g or more and 400 mgKOH / g or less, particularly 100 mgKOH / g or more and 350 mgKOH / g or less. It is preferable to use the one in.
Commercially available products of the polyether polyol (a5) include Sannicks PP-1000, PP-2000, PP-3000, GP-600, GP-1000, GP-3000, GL-300, FA-103, FA-703 ( (Manufactured by Sanyo Kasei Kogyo Co., Ltd.), Exenol EL-1020, EL-2020, EL-3020, EL-510, EL-540, EL-3030, EL-5030, EL-823, EL-828, EL-830, EL-837, EL-840, EL-850, EL-851B (above, Asahi Glass Urethane Co., Ltd.), Preminol PML-3005, PML-3012, PML-4002, PML-5001, PML-7001 (above, Asahi Glass Urethane Co., Ltd.) Made) and the like.

When the first liquid contains a polyether polyol (a5), the content thereof is based on the total resin solid content contained in the first liquid from the viewpoint of the balance between finishability and curability and the hardness of the obtained coating film. It is preferably 0.05% by mass or more, more preferably 1% by mass or more, further preferably 2% by mass or more, preferably 40% by mass or less, and 25% by mass or less. Is more preferable, and it is further preferable that it is 15% by mass or less.

The first liquid component includes a resin (a4), a hydroxyl group-containing resin other than the component (a5), another resin emulsion or a water-soluble resin, a pigment component, a neutralizing agent, a rheology control agent, a surface conditioner, a defoaming agent, and the like. A curing catalyst, an ultraviolet absorber, a light stabilizer, an organic solvent and the like may be blended as necessary.
When the curing catalyst is contained in the first liquid component, the content thereof is the mass of the active component of the curing catalyst based on 100 parts by mass of the solid content of the hydroxyl group-containing resin from the viewpoint of water resistance and maintenance of catalytic ability. It is preferably 0.001 part by mass or more, more preferably 0.005 part by mass or more, more preferably 1.0 part by mass or less, and more preferably 0.5 part by mass or less. It is preferably 0.1 part by mass or less, and more preferably 0.1 part by mass or less.

(2) Second Liquid The second liquid of the aqueous clear coating composition according to the present invention preferably contains the polyisocyanate compound (b) as a curing agent component.

-Polyisocyanate compound (b)-
The polyisocyanate compound (b) is a compound having two or more free isocyanate groups in one molecule, and those conventionally used for producing polyurethane can be used. In particular, it is preferable that the isocyanate group content is within a specific range. Specifically, from the viewpoint of water adhesion resistance, the isocyanate group content is preferably 10% by mass or more, more preferably 12% by mass or more, particularly 18% by mass or more, and 60% by mass or less, further 55% by mass or less. It is preferable to have.

Here, in the present specification, the isocyanate group content is expressed as a mass fraction of the amount of isocyanate groups contained in the polyisocyanate compound (b). The amount of isocyanate group can be measured in accordance with JIS K 1603-1 (2007).

The polyisocyanate compound (b) is a hydrophilized polyisocyanate compound in which a hydrophilic group is introduced into the polyisocyanate compound, or an aqueous dispersible poly in which the polyisocyanate compound can be dispersed in water by using a surfactant. It is preferable to use a polyisocyanate compound for water-based paints such as an isocyanate compound. Examples of the hydrophilic group include an anionic group such as an acid group and a nonionic group containing a polyoxyalkylene (polyether chain) unit. Examples of the acid group include a carboxyl group, a phosphoric acid group, a sulfonic acid group and the like.

Further, it is also possible to include a hydrophobic polyisocyanate compound in combination with the curing agent in addition to the polyisocyanate compound for water-based paint. As the hydrophobic polyisocyanate compound, those usually used in solvent-based coating compositions can be used.

As the polyisocyanate compound for water-based paint or the polyisocyanate compound contained in the hydrophobic polyisocyanate compound, those conventionally used for producing polyurethane can be used. For example, aliphatic diisocyanates such as tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; alicyclic diisocyanates such as 4,4'-methylenebis (cyclohexyl isocyanate) and isophorone diisocyanate; xylylene diisocyanate. , Aromatic diisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polyphenylmethane diisocyanate (hereinafter referred to as Polymeric MDI); and similar compounds such as these isocyanurates and burettes, which are one or more mixed. Can be used.
Among these, it is particularly preferable to contain a polyisocyanate compound (b1) having three or more isocyanate groups and a molecular weight of 350 or less from the viewpoint of drying property in a shorter time.

-Polyisocyanate compound (b1) with a molecular weight of 350 or less-
Examples of the polyisocyanate compound (b1) having three or more isocyanate groups and a molecular weight of 350 or less include 1,8-diisocyanato-4-isocyanatomethyloctane and (2S) -2,6-diisocyanatohexanoic acid 2-. Aliphatic triisocyanate compounds such as isocyanatoethyl (common name: lysine triisocyanate), 2,6-diisocyanatohexanoate 2-isocyanatoethyl, 1,6,11-triisocyanatoundecane, 1,3,5 -Alicyclic triisocyanate compounds such as triisocyanatocyclohexane and 1,3,5-trimethylisocyanatocyclohexane, aromatics such as 1,3,5-triisocyanatobenzene and 2,4,6-triisocyanatotoluene Examples thereof include triisocyanates, which can be used alone or in combination of two or more.

The polyisocyanate compound (b1) having three or more isocyanate groups and having a molecular weight of 350 or less is preferably an aliphatic triisocyanate compound from the viewpoint of pot life and finishability of the formed coating film, and among them, 1,8-. Diisocyanato-4-isocyanatomethyloctane, (2S) -2,6-diisocyanatohexanoic acid 2-isocyanatoethyl (common name: lysine triisocyanate) is more preferable, and 1,8-diisocyanato-4-isocyanate is particularly preferable. Methyloctane is preferred.

The polyisocyanate compound (b1) having three or more isocyanate groups and having a molecular weight of 350 or less in the present invention may have a molecular weight in the range of 200 to 300 from the viewpoint of coating workability and finishability of the formed coating film. It is more preferably in the range of 230 to 280.

The polyisocyanate compound (b1) having three or more isocyanate groups and a molecular weight of 350 or less in the present invention has a viscosity at 23 ° C. of 1 mPa · s or more and 50 mPa · s or less from the viewpoint of coating workability and finishability of the formed coating film. It is preferably 1 mPa · s or more and 30 mPa · s or less.

As for the amount of the polyisocyanate compound (b) in the second liquid, it is preferable that the polyisocyanate compound (b) is 20 parts by mass or more and 100 parts by mass or less in 100 parts by mass of the entire second liquid. It is more preferable that the amount is equal to or more than 80 parts by mass and not more than 80 parts by mass.
When the polyisocyanate compound (b1) is contained in the second liquid, the total solid of the polyisocyanate compound (b) is obtained from the viewpoints of coating workability, finishability of the formed coating film, quick-drying property, and coating film hardness. Based on the amount, it is preferably 5% by mass or more and 100% by mass or less, more preferably 10% by mass or more and 90% by mass or less, and further preferably 10% by mass or more and 60% by mass or less.

These polyisocyanate compounds (b) can be used alone or in combination of two or more. When two or more kinds of polyisocyanate compounds (b) are used in the second liquid, the isocyanate group content in the second liquid is 5% by mass or more on average, and further, from the viewpoint of storage stability and weather resistance. It is more preferable that the blending amount is adjusted to be 8% by mass or more, 55% by mass or less, and further preferably 50% by mass or less.

The content of the polyisocyanate compound (b) in the aqueous clear coating composition is generally an equivalent ratio (NCO / OH) of the isocyanate group of the polyisocyanate compound to the hydroxyl group of the dispersion type acrylic resin (a4). The amount can be appropriately adjusted to be 0.5 or more and 5.0 or less, but from the viewpoint of curability and weather resistance, 1.1 or more and 3.0 or less are preferable, and 1.2 or more and 2.0. It is more preferable that the amount is as follows. When the equivalent ratio (NCO / OH) is within the above preferable range, there is an advantage that the curing reactivity of the aqueous clear coating composition can be ensured in a good range. The above equivalent ratios are all converted into solid content.

-Other ingredients-
The second liquid of the aqueous clear coating composition according to the present invention contains a resin containing no crosslinkable reactive group such as a hydroxyl group, a film forming aid, a pigment component, a neutralizing agent, a rheology control agent, a surface adjusting agent, and an erasing agent. A foaming agent, a curing catalyst, an ultraviolet absorber, a light stabilizer, a dehydrating agent and the like can be blended as needed.

The second liquid of the water-based clear paint composition preferably contains an organic solvent from the viewpoint of coating workability and finishability of the obtained coating film.

The organic solvent is preferably a compound having no hydroxyl group, and specifically, for example, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol divinyl ether, diethylene glycol ethyl methyl ether, and diethylene glycol. Isopropylmethyl ether, diethylene glycol butylmethyl ether, triethylene glycol dimethyl ether, triethylene glycol divinyl ether, tetraethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol diisopropyl ether, propylene Glycoldi-n-butyl ether, propylene glycol diisobutyl ether, propylene glycol diallyl ether, propylene glycol diphenyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol diisobutyl ether, dipropylene glycol Allyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol diisobutyl ether, tripropylene glycol diallyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether, butylene glycol di-n- Glycol ether-based organic solvents such as butyl ether, 2-butoxyethyl diethoxyethyl ether, 2-butoxyethyl triethoxy ether, 2-butoxyethyl tetraethoxyethyl ether; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol Acetate-based organic solvents such as mono-n-butyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate; acetone, methyl ethyl ketone, methyl amyl ketone, methyl isobutyl ketone. Etc. Ethyl-based organic solvents; ester-based organic solvents such as ethyl acetate, butyl acetate, isobutyl acetate, methyl benzoate, ethyl ethoxypropionate, ethyl propionate, methyl propionate, etc.; These can be used alone or in combination of two or more. Above all, from the viewpoint of the finishability of the formed coating film, the organic solvent preferably contains an organic solvent having a boiling point higher than that of water, particularly a compound having a boiling point of 150 to 250 ° C., and in addition, it is a hydrophilic solvent. preferable.

As for the amount of the organic solvent in the second liquid, the mass of the organic solvent is 10% by mass based on 100 parts by mass of the polyisocyanate compound (b) from the viewpoint of compatibility with the polyisocyanate compound (b), that is, finishability. It is preferably 3 parts or more and 300 parts by mass or less, and particularly preferably 30 parts by mass or more and 250 parts by mass or less.

The aqueous clear coating composition used in this method is a mixture obtained by mixing the first component containing the hydroxyl group-containing resin and the second component containing the polyisocyanate component and an organic solvent immediately before use. Can be appropriately diluted with a diluent or the like before coating. As the ratio of the first component and the second component to be used, it is suitable that the second component is 20 to 100 parts by mass, particularly 30 to 70 parts by mass, based on 100 parts by mass of the first component.
At that time, as the third component, a film forming aid, a pigment component, a neutralizing agent, a rheology control agent, a surface adjusting agent, a defoaming agent, a curing catalyst, an ultraviolet absorber, a light stabilizer, a dehydrating agent, etc. The paint additive can be added later if necessary.

In this method, sufficient curability can be obtained even if the aqueous clear coating composition does not contain a curing catalyst, but when the curing catalyst is contained, the content thereof is the hydroxyl group-containing resin contained in the first component. The mass of the active ingredient of the curing catalyst is preferably 0.001 part by mass or more, more preferably 0.005 part by mass or more, and 1.0 mass by mass, based on 100 parts by mass of the solid content of the above. The amount is preferably parts or less, particularly preferably 0.5 parts by mass or less, and more preferably 0.1 parts by mass or less.
As the curing catalyst, for example, a conventionally known urethane curing catalyst can be used. Examples of the urethane curing catalyst include amine compounds such as triethylamine, organic tin compounds such as dibutyltin dilaurate, dibutyltin diacetate, dioctyltin diacetate, and tin dioctylate, and zinc octylate (2-ethyl). Examples thereof include organic metal compounds such as zinc hexane). From the viewpoint of water resistance, those different from those listed in the section of metal compounds of the above base coating composition can be used.

(Painting of water-based clear paint composition)
Examples of the method for applying the water-based clear coating composition applied to the present invention include air spray, airless spray, rotary atomization, brush, roller, hand gun, universal gun, immersion, roll coater, curtain flow coater, and roller curtain coater. , Die coater and the like, which can be appropriately selected depending on the intended use of the object to be coated, and may be applied a plurality of times.

The drying conditions of the base coating film and the clear coating film in the method for forming the multi-layer coating film of the present invention are not particularly limited, and room temperature drying, forced drying, baking drying, etc. may be performed depending on the object to be coated and the working environment. You can choose. Forced drying or baking drying is preferable from the viewpoint of polishability, finishability, and water resistance, and forced drying is particularly preferable from the viewpoint of selectivity of the object to be coated and energy reduction.
In the case of forced drying, it can be heated for 10 to 120 minutes under mild temperature conditions of 40 to 120 ° C, preferably 40 to 70 ° C, and left at room temperature (5 to 45 ° C) to volatilize the solvent (setting). Time) may be provided as needed. If necessary, air drying (ventilation) may be used in combination.
The setting can usually be performed by leaving the painted object to be coated in a dust-free atmosphere at room temperature for 30 seconds to 60 minutes. The relative humidity (hereinafter sometimes abbreviated as RH) at the time of setting is preferably 80% or less, and particularly preferably 70% or less.
An IR furnace, an electric hot air dryer, or the like can be used for drying.

The dry film thickness of the clear coating film is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 100 μm or less, and particularly preferably 15 μm or more and 60 μm or less from the viewpoint of ensuring a film thickness that can be polished and repaired.

The method for forming a multi-layer coating film of the present invention is particularly suitable for repair coating of automobiles and the like. Since a coating film having excellent hardness can be obtained in a short drying time, the surface can be polished at an early stage after the coating film is formed.

Examples of the polishing method include a method in which a clear coating film is watered with a water-resistant polishing paper, and then the sharpened surface is sequentially polished with a compound for rough polishing and a compound for finish polishing. As a result, it is possible to obtain a clear coating film having excellent glossiness and gloss and having an inconspicuous difference in appearance from the unrepaired portion.

Further, since the paint composition used in this method is wet-on-wet coated on the water-based base coating film, there is no step of baking the water-based base paint, which saves energy and shortens the process, and the base composition and the clear composition. Since both of them are water-based, it is an environment-friendly coating film forming method. In addition, since this method does not require the addition of a large amount of metal catalyst to the water-based clear paint composition, the pot life of the water-based clear paint composition is improved, and the finish and water resistance are maintained. , The multi-layer coating film has an extremely excellent effect in that sufficient coating film hardness can be obtained. In addition, this method can be applied wet-on-wet, and has the effect of improving workability in terms of improving pot life.

According to the method for forming a multi-layer coating film of the present invention, the catalyst-derived metal compound in the uncured base coating film is contained in the uncured clear coating film by containing the metal compound in the aqueous base coating composition. Therefore, the reactivity in the clear coating film is improved, and the low temperature curing can be completed in a short time.

[Multi-layer coating film]
In the multi-layer coating film of the present invention, a water-based base coating composition is applied to an object to be coated, and a water-based clear coating composition is applied onto the base coating film (I) and the base coating film (I) to clear coat. It has a film (II) layer, and the Martens hardness value of the multi-layer coating film is 7 N / mm ² or more.
Martens hardness value of the multilayer coating film, from the viewpoint of polishing properties, 7N / mm ² or more preferably, 10 N / mm ² or more is more preferable. It can be said that the upper limit is a cured and dried state when the Martens hardness becomes a constant value, but as a guide, 120 N / mm ² or less is preferable, and 80 N / mm ² or less is more preferable.

Specifically, depending on the film thickness and drying time of the multi-layer coating film, for example, the uncured base coating film layer (I) is 5 μm or more and 60 μm or less, and the uncured clear coating film layer (II) is 5 μm or more and 500 μm. The drying time after coating of the multi-layer coating film (evaluation test coating plate: drying time 60 ° C. 20 minutes) obtained from the following multi-layer coating film was set to 60 ° C. and 20 minutes, and the film was taken out from the drying furnace and had a relative humidity of 50% and 20 minutes. The Martens hardness value of the coated plate after being left in an environment of ℃ for 1 hour is in this range. The state of the multi-layer coating film at this drying time and temperature is a semi-cured state, but even if the multi-layer coating film of the present invention is in a semi-cured state, the Martens hardness value of the multi-layer coating film within the above range is high. Workability is good because it exceeds the above lower limit and can be polished and repaired.
When the curing progresses further from this state and the cured and dried state is reached, the Martens hardness value becomes a constant value at a value exceeding ^{120 N / mm 2.}

The multi-layer coating film of the present invention is a curing base coating film obtained by coating and curing a water-based base coating composition on an object to be coated, and a cured clear coating film formed by coating and curing an aqueous clear coating composition. A multi-layer coating having , The metal element concentration of the metal compound is 20 ppm or more.
The metal element concentration of the metal compound in the coating film can be measured by scraping a predetermined amount of the transparent clear coating film layer of the cured and dried multi-layer coating film and performing elemental analysis or the like.

In the multi-layer coating film of the present invention, the metal compound derived from the catalyst in the uncured base coating film is transferred to the uncured clear coating film by containing the metal compound in the aqueous base coating composition. The reactivity in the clear coating film is improved, low temperature curing is completed in a short time, and the hardness and water resistance of the multi-layer coating film are higher than those in the case where the water-based base coating composition does not contain a metal compound. Is also improving.

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

[Example 1]
(Aqueous base paint composition)
First, the acrylic resin emulsion and the pigment contained in the aqueous base coating composition were synthesized by the following procedure.

-Acrylic resin emulsion (a1)-
100 parts of deionized water in a reaction vessel equipped with a thermometer, thermostat, agitator, reflux cooler, nitrogen introduction tube and dropping device, "Newcol 707SF" (trade name, manufactured by Nippon Ester Co., Ltd., polyoxyethylene polycyclic phenyl) 2.5 parts of ether sulfate ester salt) and one part of the monomer mixture (9 parts of styrene, 40 parts of n-butyl acrylate, 40 parts of 2-ethylhexyl acrylate, 10 parts of 2-hydroxyethyl acrylate, 1 part of allyl methacrylate). In addition, the mixture was stirred and mixed with a nitrogen stream, and 3 parts of a 3% ammonium persulfate aqueous solution was added at 60 ° C. Then, the temperature was raised to 80 ° C., and a pre-emulsion consisting of the remaining 99 parts of the monomer mixture, 2.5 parts of "Neucol 707SF", 4 parts of 3% ammonium persulfate and 100 parts of deionized water was pumped over 4 hours. Was added to the reaction vessel and aged for 1 hour after the addition was completed. Then, 33 parts of deionized water was added, and the pH was adjusted to 7.5 with dimethylethanolamine to obtain an aqueous dispersion solution of acrylic resin (a1) having an average particle size of 100 nm and a solid content of 30%.

-Urethane resin emulsion (a2)-
115.5 parts of polybutylene adipate with a number average molecular weight of 2000 and 115.5 parts of polycaprolactone diol with a number average molecular weight of 2000 in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen introduction tube and dropping device. , 15.2 parts of dimethylolpropionic acid, 14.5 parts of 1,4-butanediol and 120.1 parts of isophorone diisocyanate are charged and reacted with stirring in a nitrogen stream at 85 ° C. for 7 hours to have an NCO content of 4. 0% prepolymer was obtained. Next, the prepolymer was cooled to 50 ° C., 165 parts of acetone was added and uniformly dissolved, then 15.7 parts of triethylamine was added under stirring, and 600 parts of deionized water was added while keeping the temperature below 50 ° C. to obtain the obtained product. After holding the aqueous dispersion at 50 ° C. for 2 hours to complete the water elongation reaction, acetone was distilled off at 70 ° C. or lower under reduced pressure, the pH was adjusted to 8.0 with triethylamine and deionized water, and the solid content was 30. %, An aqueous dispersion solution of urethane resin (a2) having an average particle diameter of 150 nm was obtained.

-Water-soluble acrylic resin (a3)-
A mixed solvent of 27.5 parts of methoxypropanol and 27.5 parts of isobutanol was put in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux cooler, a nitrogen introduction tube and a dropping device, heated to 110 ° C., and styrene. 25 parts, n-butyl methacrylate 27.5 parts, "isostearyl acrylate" (manufactured by Osaka Organic Chemical Co., Ltd.) 20 parts, hydroxybutyl acrylate 7.5 parts, phosphate group-containing polymerizable monomer solution (Note 1) 15 parts (Note 1) Solid content), 12.5 parts of 2-methacryloyloxyethyl acid phosphate, 10 parts of isobutanol, and 4 parts of t-butylperoxyoctanoate, 121.5 parts of the mixture was added to the above mixed solvent in 4 hours, and further. A mixture consisting of 0.5 part of t-butylperoxyoctanoate and 20 parts of isopropanol was added dropwise in 1 hour. Then, it was stirred and aged for 1 hour to obtain a water-soluble acrylic resin (a3) solution having a solid content of 50%.
(Note 1) Phosphoric acid group-containing polymerizable monomer solution: 57.5 parts of monobutyl phosphate and 41.1 parts of isobutanol are put in a flask, and 42.5 parts of glycidyl methacrylate is added dropwise in 2 hours under air aeration, and then further. It was aged with stirring for 1 hour. Then, 5.9 parts of isopropanol was added to obtain a phosphoric acid group-containing polymerizable monomer solution having a solid content of 50%.

-Synthesis of pigments-
Preparation of Pigment Paste P1 Aluminum pigment paste "Hydrolan2156" (manufactured by Ekart, silica-coated aluminum flakes, pigment content 60%), a water-soluble acrylic resin (a3) solution having a solid content of 50%, and methoxy in a stirring and mixing container. The propanol and propanol were stirred and mixed at a mass ratio of 50/20 (inner resin solid content 10 parts by mass) / 30 to obtain an aluminum pigment paste (P1).

Preparation of Pigment Paste P2 Aluminum pigment paste "Alpaste WL-7640" (manufactured by Toyo Aluminum Co., Ltd., molybdic acid-coated aluminum flakes, pigment content 59%), the water-soluble acrylic resin (a3), and methoxy in a stirring and mixing container. 35 parts of propanol and 50/20 (inner resin solid content 10 parts by mass) / 30 stirring and mixing were mixed to obtain an aluminum pigment paste (P2).

-Preparation of Aqueous Base Paint Composition (X-1)-
Acrylic resin emulsion (a1) 150 parts (resin solid content 45 parts) and urethane resin emulsion (a2) 150 parts (resin solid content 45 parts) are mixed and "Primal ASE60" (trade name, manufactured by Roam and Haas). 17.8 parts of polyacrylic acid-based thickener, acid value 270 mgKOH / g, active ingredient 28%, "BYK-024" (trade name, BYK-CHEMIE, polyether-modified silicone compound, active ingredient 100% ) Is added, and then stirring is continued for 1 hour. 100 parts of the above aluminum pigment paste (P1) is added to the stirring mixing container, the pH is adjusted with dimethylethanolamine, and then deionized water is added to add the solid content. A 20% first solution was obtained.
To another stirring and mixing container, 995 parts of water and 5 parts of "Laponite RD" (trade name, manufactured by Rochwood Adaptives Limited, an inorganic thickener, synthetic hectorite) were added, and the mixture was stirred and mixed to obtain a diluent component. Both were mixed with 100 parts of the first liquid with a disper so that the diluent component was 100 parts, and an aqueous base coating composition was obtained.
To this, as a metal compound, K-KAT XK614 (trade name, manufactured by KING INDUSTRIES, zinc compound, zinc compound content 65%) was added to 100 parts by mass of the resin solid content of the base coating composition. It was added and mixed so as to be 3 parts by mass, and mixed with a disper to obtain an aqueous base coating composition (X-1).

(Aqueous clear paint composition)
-Dispersion type acrylic resin-
400 parts of propylene glycol monopropyl ether was placed in a four-necked glass flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet, and the temperature was raised to 120 ° C. under a nitrogen stream while stirring. When the temperature reached 120 ° C., a mixed solution 1 in which the following first-stage monomer formulation and a polymerization initiator (12 parts of t-butylperoxy-2-ethylhexanoate) were mixed in advance was added dropwise over 4 hours. After the completion of the dropping, the mixture was kept at a temperature of 120 ° C. for 1 hour.
A mixed solution in which the following second-stage monomer formulation and a polymerization initiator (2.4 parts of t-butylperoxy-2-ethylhexanoate) are previously mixed in the flask while maintaining the temperature of 120 ° C. 2 was added dropwise over 1 hour, and after the addition was completed, the solution was kept at 120 ° C. for 1.5 hours to obtain an acrylic resin solution.
The resin solid content of the obtained acrylic resin solution was 66.7%, the hydroxyl value was 120 mgKOH / g, the glass transition temperature was 53 ° C., the weight average molecular weight was 14,000, and the average particle size was 170 nm.
Subsequently, propylene glycol monopropyl ether was distilled off from the obtained acrylic resin solution under reduced pressure until the solid content became 85%. This was cooled to 95 ° C., the pH was adjusted to 8.0 with dimethylethanolamine, and the mixture was stirred for 30 minutes. Further, while stirring, deionized water was added dropwise over 2 hours so that the resin solid content became 50% to obtain an aqueous dispersion of acrylic resin (a4), colloidal dispersion.

(1st stage monomer compounding)
Styrene 96 parts Methyl methacrylate 104 parts Isobutyl methacrylate 152 parts n-Butyl methacrylate 108 parts n-Butyl acrylate 32 parts 2-Hydroxyethyl methacrylate 192 parts Glycidyl methacrylate 8 parts

(Combining the second stage monomer)
Styrene 8 parts Methyl methacrylate 8 parts Isobutyl methacrylate 12 parts n-Butyl methacrylate 16 parts n-Butyl acrylate 8 parts 2-Hydroxyethyl methacrylate 32 parts Acrylic acid 24 parts

-Manufacturing of clear paint composition (Y-1)-
(1) Liquid 1 Dispersion type acrylic resin (a4) with a resin solid content of 50% 65 parts (resin solid content 32.5 parts), Sanniks GP-600 (Note 2) 2 parts, "BYK-348" ( Note 3) 0.5 copies, "BYK-015" (Note 4) 1 copy, "TINUVIN 384-2" (Note 5) 1 copy, "TINUVIN 292" (Note 6) 0.5 copies, "SN thickener 621N" ( Note 7) 0.5 part and 29.5 parts of deionized water were mixed, and dimethylethanolamine was added dropwise at room temperature until the pH reached 7.6 to prepare the first solution.

(Note 2) "Sanniks GP-600": Trade name, manufactured by Sanyo Chemical Industries, Ltd., polyoxypropylene glyceryl ether, number average molecular weight 600, hydroxyl value 280 mgKOH / g, non-volatile content 100%
(Note 3) "BYK-348": Product name, manufactured by Big Chemie Japan, polyether-modified siloxane, weight average molecular weight 1,500, non-volatile content 100%
(Note 4) "BYK-015": Product name, manufactured by Big Chemie Japan, polyether-modified siloxane, weight average molecular weight 2,200, non-volatile content 100%
(Note 5) "TINUVIN 384-2": Trade name, manufactured by BASF, benzotriazole-based ultraviolet absorber, non-volatile content 95%, 1-methoxy-2-propyl acetate 5%
(Note 6) "TINUVIN 292": Product name, manufactured by BASF, hindered amine-based light stabilizer, 100% non-volatile content
(Note 7) "SN Thickener 621N": Product name, manufactured by San Nopco Ltd., nonionic rheology control agent, non-volatile content 30%

(2) Second liquid In a separate container from the first liquid, 25 parts of the polyisocyanate compound "Baihijour XP2655" (Note 8), 15 parts of dipropylene glycol dimethyl ether, 5 parts of ethylene glycol monobutyl ether acetate, and diethylene glycol monoethyl ether acetate. Five parts were mixed and mixed until uniform to prepare a second solution.

(Note 8) "Baihijour XP2655": Trade name, manufactured by Sumika Cobestrourethane, hexamethylene diisocyanate polyisocyanate having a sulfonic acid group, NCO content 21%, non-volatile content 100%

(3) Preparation of Clear Paint Composition (Y-1) Immediately before painting, the equivalent ratio of the hydroxyl value in the main agent to the isocyanate group (NCO) in the curing agent is determined between the first liquid and the second liquid. The blending amount is adjusted so that NCO / OH = 1.6, and after manual stirring with a spatula, 21.7 parts of deionized water is added to the main agent and further manual stirring is performed to obtain a metal catalyst. An aqueous clear paint composition (Y-1) not contained was prepared. The pot life was 2 hours and the workability was good.

(Preparation of object to be coated for evaluation test)
A coating plate having a primer surfacer coated on an electrodeposition coating plate coated with an epoxy resin-based electrodeposition paint is polished with # 240 paper, and a commercially available water-based primer is placed on the coating plate with a partially exposed steel plate. The surfacer "Retan WB Eco Plasaf" (trade name, Kansai Paint Co., Ltd., a two-component water-based urethane primer surfacer for automobile repair) is spray-painted to a dry film thickness of 60 μm, dried at 60 ° C for 30 minutes, and then # Water polished with 400 paper. The undercoat film coated with this primer surfacer was designated as the object to be coated S.

(Formation of multi-layer coating film)
The object to be coated S is placed horizontally, and the water-based base coating composition (X-1) is spray-coated under the conditions of 25 ° C. and a relative humidity of 40% until the glossiness of the base coating film becomes 25 or less. Air blow was performed. This spray coating and air blowing were performed two more times to obtain a colored base coating film having a dry film thickness of 15 μm.
Next, the water-based clear coating composition (Y-1) is wet-on-wet (sometimes referred to as W / W in the table) on the uncured colored base coating film to have a dry film thickness of 40 μm. After air spray coating so that the coating plate is horizontally maintained at room temperature for 20 minutes, it is dried at 60 ° C. for 20 minutes using an electric hot air dryer and cooled to room temperature to obtain a multi-layer coating film (XY-). 1) was formed.

[Examples 2 to 23, Comparative Examples 1 to 4]
In Example 1, the multi-layer coating films (XY-2) to (XY-26) are the same as in Example 1 except that the base coating composition and the clear coating composition are those shown in Tables 1 to 3. ) Was formed.
In addition, each base paint composition and clear paint composition were manufactured as follows.

-Manufacturing of water-based base coating compositions (X-2) to (X-18)-
The water-based base paint composition is the same as that of the water-based base paint composition (X-1), except that the types and contents of the metal compounds in the water-based base paint composition and the combinations of the pigment pastes are as shown in Tables 1 to 3. Compounds (X-2) to (X-18) were prepared, and each aqueous base coating composition was prepared.

-Manufacturing of solvent-based base coating composition (X-19)-
Sodium molybdate is added so that the solid content of Retan PGHB Ecobase 202 Sun Metallic (trade name, solvent-based metallic base paint composition for automobile repair manufactured by Kansai Paint Co., Ltd.) is 0.30 parts by mass with respect to 100 parts by mass. The solvent-based base coating composition (X-19) was prepared by mixing with a disperser.

-Manufacturing of clear paint composition (Y-2)-
In the production of the clear coating composition (Y-1), 12.5 parts of the polyisocyanate compound "Baihijour XP2655" (Note 8) and 12.5 parts of 1,8-diisocyanato-4-isocyanatomethyloctane are used. The same preparation was performed except for the above, to obtain an aqueous clear coating composition (Y-2) containing no metal catalyst. The pot life was 2 hours and the workability was good.

-Manufacturing of clear paint composition (Y-3)-
A metal catalyst of sodium molybdate so as to be 0.01 part by mass with respect to 100 parts by mass of the resin solid content in the clear paint composition in the first liquid (1) of the production of the clear paint composition (Y-1). The mixture was prepared in the same manner except that it was added as an aqueous clear coating composition (Y-3). The pot life was 2 hours and the workability was good.

-Manufacturing of clear paint composition (Y-4)-
0.03 parts by mass of sodium molybdate was added as a metal catalyst to 100 parts by mass of the resin solid content in the clear paint composition in the first liquid (1) of the production of the clear paint composition (Y-1). A water-based clear paint composition (Y-4) was obtained in the same manner except for the above. The pot life was 2 hours and the workability was good.

-Manufacturing of clear paint composition (Y-5)-
0.10 parts by mass of sodium molybdate was added as a metal catalyst to 100 parts by mass of the resin solid content in the clear paint composition in the first liquid (1) of the production of the clear paint composition (Y-1). A water-based clear paint composition (Y-5) was obtained by preparing in the same manner except for the above. The pot life was one hour and the workability was slightly inferior.

-Manufacturing of clear paint composition (Y-6)-
As a top clear paint composition, "Retan PG Multi HX (Q) Clear" and its curing agent (organic solvent type urethane curable paint composition manufactured by Kansai Paint Co., Ltd.) are abbreviated as the main agent curing agent weight ratio (main hardness ratio). The clear paint composition (Y-6) was obtained by mixing 2: 1 with (there is) immediately before painting. The pot life was one hour and the workability was slightly inferior.

-Manufacturing of clear paint composition (Y-7)-
0.30 parts by mass of sodium molybdate was added as a metal catalyst to 100 parts by mass of the resin solid content in the clear paint composition in the first liquid (1) of the production of the clear paint composition (Y-1). A water-based clear paint composition (Y-7) was obtained by preparing in the same manner except for the above. The pot life was extremely short, less than 30 minutes, and painting had to be done in a short time, resulting in poor workability.

-Manufacturing of clear paint composition (Y-8)-
Dioctyltin diacetate (urethane curing catalyst) is uniformly added to the clear coating composition (Y-1) in an amount of 0.05 parts by mass based on 100 parts by mass of the hydroxyl group-containing resin solid content contained in the clear coating composition. The mixture was mixed until a clear paint composition (Y-8) was obtained. The pot life was 2 hours and the workability was good.

-Manufacturing of clear paint composition (Y-9)-
Dioctyltin diacetate (urethane curing catalyst) is uniformly added to the clear paint composition (Y-3) in an amount of 0.05 part by mass with respect to 100 parts by mass of the hydroxyl group-containing resin solid content contained in the clear paint composition. The mixture was mixed until it became a water-based clear paint composition (Y-9). The pot life was 2 hours and the workability was good.

[evaluation]
The following evaluations were performed on the multi-layer coating films obtained in the above Examples and Comparative Examples. The test results are shown in Tables 1 to 3.

[Drying (polishing)]
The multi-layer coating film (evaluation test coating plate) of Examples and Comparative Examples has a drying time of 30 minutes by an electric hot air dryer, and in addition, a drying time of 20 minutes, 30 minutes, and 40 minutes by an electric hot air dryer. A multi-layer coating film (drying property evaluation test coating plate) was also prepared. Each of the multi-layer coating films (evaluation test coating plate) having different drying times by an electric hot air dryer was polished and repaired by the following polishing repair method.
(Polished repair method)
After each test coating plate is water-polished with # 2000 water-resistant abrasive paper, it is polished with a rough-polishing buff for 60 seconds using a rough-polishing compound to remove paper scratches caused by the water-resistant abrasive paper, and further for finishing. The buff was polished with a finishing compound for 60 seconds to remove buffing scratches.

From the above-mentioned polishing and repairing, a coating film in a good coating film condition with no residual paper scratches or deterioration of gloss was selected. It was evaluated according to the following evaluation criteria. As for the evaluation, A, B, and C pass, and D fails.
A: Polishing repair is possible with a test coating board with a drying time of 20 minutes or more B: Polishing repair is possible with a test coating plate with a drying time of 30 minutes or more C: Polishing repair is possible with a test coating plate with a drying time of 40 minutes or more D: Polishing and repair is impossible with a test coating board with a drying time of 40 minutes.

[Finishness]
With respect to the multi-layer coating film (evaluation test coating plate) obtained in Examples and Comparative Examples, the appearance of the coating film was visually observed and evaluated for problems such as unevenness, armpits, blemishes, smoothness, and glossiness. As for the evaluation, A, B, and C pass, and D fails.
A: The appearance of the coating film is very good. B: No unevenness, armpits, or chijimi are observed, and the smoothness and glossiness are good. C: Deterioration of smoothness and slight glossiness are observed, but unevenness is observed. , Armpits and chijimi are hardly recognized, and there is no problem in practical use. D: Unevenness, armpits, chijimi and glossiness occur remarkably, and there is a clear problem.

[Coating film hardness]
A multi-layer coating film having a dry film thickness 15 μm base coating film layer and a clear coating film layer having a dry film thickness of 40 μm obtained in Examples and Comparative Examples (evaluation test coating plate: drying time 60 ° C. 30 minutes and 60 ° C. 20 minutes). Was taken out of the drying oven and left to stand in an environment of 50% relative humidity and 20 ° C. for 1 hour, and then the coated plate was used as a test plate. When the multi-layer coating film was measured by IR (infrared spectroscopy), a peak of isocyanate groups was confirmed in each case, and it was confirmed that the coating film was in a semi-cured state.
Using a Fisherscope HM2000 (FISCHER), the coating film surface indenter was pushed in, and the Martens hardness value obtained from the pushing depth and the pushing force at that time was measured. The measurement conditions were: 5 mN × 4 μm / 20 seconds. The measured Martens hardness was evaluated according to the following evaluation criteria.
A: Martens hardness value is 7 N / mm ² or more B: Martens hardness value is 5 N / mm ² or more and less than 7 N / mm ² C: Martens hardness value is 3 N / mm ² or more and 5 N Less than / mm ² D: Martens hardness value is less than ^{3 N / mm 2.}

[water resistant]
The multi-layer coating film (evaluation test coating plate) obtained in Examples and Comparative Examples was immersed in a constant temperature water bath at 40 ° C. for 10 days, taken out, and then visually observed for the state of the coating film after being left for 1 hour. , Blister and other coating film abnormalities were evaluated according to the following evaluation criteria.
A: No abnormality B: Very small amount, at least one abnormality of gloss, crack, and blister is observed C: Partially, at least one abnormality of gloss, crack, and blister is observed D: Partial or coated At least one abnormality of gloss, cracks, and blisters is prominently observed on the entire surface of the film.

[Environmental support]
In the paint composition, the harmful volatile organic compound (VOC) contained in the paint composition immediately before painting is 420 g / L or less and the water content in the solvent is 50% or more. Those in which the main solvent is almost an organic solvent or those which do not meet the above criteria are marked with x.

(Measurement of metal concentration)
As a typical example, the multi-layer coating film shown in Table 4 below was completely cured at 80 ° C. for 30 minutes, and only the clear coating film (transparent portion) was scraped off with a cutter to collect 0.2 g. This sample was dissolved in a strong acid solution and elemental analysis was performed. An ICPS-8100 manufactured by Shimadzu Corporation was used as the measuring device. Table 4 shows the results of calculating the amount of increase in the metal element concentration in the clear coating film.

As shown in Tables 1 to 4, in the examples in which at least the water-based base coating composition contains the metal compound among the water-based base coating composition and the water-based clear coating composition, the comparison in which the water-based base coating composition does not contain the metal compound. It can be seen that the multi-layer coating material is superior in terms of dryness, finishability, hardness, and water resistance as compared with Example 1 and Comparative Example 4 in which the metal compound is contained only in the clear coating composition.
Further, according to the method for forming a multi-layer coating film of the present invention, the harmful volatile organic compound (VOC) contained in the coating composition immediately before coating is 420 g / L or less, and the water content in the solvent is 50. Since it is composed of% or more, it is possible to obtain an environment-friendly multi-layer coating film.

Claims (12)

The first step of applying the water-based base coating composition to the object to be coated to form the base coating film (I), and
A second step of coating the water-based clear coating film composition on the base coating film (I) to form the clear coating film (II), and a step of simultaneously drying the base coating film and the clear coating film. It is a method for forming a multi-layer coating film to have.
The aqueous base coating composition contains a metal compound containing at least one metal selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum. Forming method. The method for forming a multi-layer coating film according to claim 1, wherein the content concentration of the metal compound in the water-based base coating composition is equal to or higher than the content concentration of the metal compound in the clear coating composition. The metal is derived from a metal catalyst and
Claim 1 that the content of the metal catalyst in the aqueous base coating composition is 0.01 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the total resin solid content in the aqueous base coating composition. The method for forming a multi-layer coating film according to 2. The method for forming a multilayer coating film according to any one of claims 1 to 3, wherein the water solubility of the metal compound is 1 × 10 ^-3 mg / 1000 g or more and 5 × 10 ^{5 mg / 1000 g or less.} The water-based base coating composition comprises a first film-forming resin.
The first item according to any one of claims 1 to 4, wherein the first film-forming resin is at least one of a water-dispersible acrylic resin (a1), a water-dispersible polyurethane resin (a2), and a water-soluble acrylic resin (a3). Method of forming a multi-layer coating film. The method for forming a multilayer coating film according to any one of claims 1 to 5, wherein the aqueous clear coating composition contains a urethane curing catalyst. The water-based clear coating composition contains a second film-forming resin and contains.
The second film-forming resin contains a hydroxyl group-containing resin and a polyisocyanate compound (b), and the polyisocyanate compound (b) has a polyisocyanate compound (b1) having three or more isocyanate groups and a molecular weight of 350 or less. The method for forming a multilayer coating film according to any one of claims 1 to 6, which comprises. The water-based clear coating composition contains a second film-forming resin and contains.
The method for forming a multi-layer coating film according to any one of claims 1 to 7, wherein the second film-forming resin contains a dispersion type acrylic resin (a4). The method for forming a multi-layer coating film according to any one of claims 1 to 8, wherein the object to be coated is an old coating film or a damaged portion of a coated body. The formation of the multi-layer coating film according to any one of claims 1 to 9, wherein the object to be coated is an industrial machine, a construction machine, a railroad vehicle, a large vehicle, a hull, a building or a building, or a part thereof. Method. On the object to be coated, the base coating film (I) layer of the aqueous base coating composition,
A multi-layer coating film having a clear coating film (II) layer of an aqueous clear coating composition on the base coating film (I) layer.
A multi-layer coating film having a Martens hardness value of 7 N / mm ^{2 or more.} A composite having a cured base coating film layer obtained by coating and curing the water-based base coating composition and a cured clear coating film layer formed by coating and curing the water-based clear coating composition on the object to be coated. It is a layer coating film
The cured clear coating comprises at least one metal compound selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum.
A multi-layer coating film having a metal element concentration of 20 ppm or more in the cured clear coating film.