JP2015187195A - Water-based coating composition and method for forming bilayer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition from which a bilayer coating film with superior brightness can be formed even when the coating composition is a water-based coating composition having a high resin solid concentration.SOLUTION: The water-based coating composition comprises a resin for forming a coating film, a curing agent, a scaly pigment, and an amphiphilic compound. The amphiphilic compound includes at least one hydrophobic moiety (A) as a repeating unit and at least one hydrophilic moiety (B) as a repeating unit: the hydrophobic moiety (A) has at least one group selected from a set consisting of a propylene oxide group, butylene oxide group, linear or branched 4-40C saturated hydrocarbon group, linear or branched 4-40C unsaturated hydrocarbon group, 6-40C aromatic ring-containing group having an aromatic ring, and hydrophobic polymer segment; and the hydrophilic moiety (B) has at least one group selected from a set consisting of an ethylene oxide group and an acid group. The amphiphilic compound has a number average molecular weight of 1500 to 100000. When the water-based composition is controlled to have a viscosity of 780 to 820 mPa s at 20°C and 60 rpm measured by a B-type viscometer as a coating viscosity, the resin solid concentration in the coating composition is 25 to 40 mass%.

Description

  The present invention relates to an aqueous coating composition, a method for forming a multilayer coating film using the aqueous coating composition, and a multilayer coating film obtained by this method.

  A plurality of coating films having various roles are sequentially formed on the surface of an object such as an automobile body to protect the object to be coated and at the same time impart a beautiful appearance and an excellent design. As a method for forming such a plurality of coating films, an undercoat film such as an electrodeposition coating film is formed on an object having excellent conductivity, and an intermediate coating film as required, and A method of sequentially forming a top coat film is common. Among these coating films, the top coating film composed of a base coating film and a clear coating film particularly greatly affects the appearance and design of the coating film. In particular, in automobiles, the appearance and design of a top coating film comprising a base coating film and a clear coating film formed on a vehicle body are extremely important.

  The base coating film can be broadly classified into a coating film containing no scaly pigment, which is called a so-called solid color, and a coating film containing scaly pigment having a glittering feeling. In recent years, consumers tend to prefer coating films containing scaly pigments that have a glittering feeling. The scaly pigment contained in the base coating film having a glittering feeling reflects light or produces interference light, which gives the coating film a glittering feeling.

  Since the scaly pigment is oriented in a state along the surface shape of the object to be coated, good light reflection or interference light is brought about. Therefore, when using a coating composition containing a scaly pigment, a cured coating is used. It is necessary to control the orientation of the scaly pigment contained in the film. For example, Japanese Patent Application Laid-Open No. 11-80620 (Patent Document 1) describes a coating composition containing a scaly pigment that is a metal piece. Such a coating composition contains a large amount of water and an organic solvent, whereby the scaly pigment is oriented in a state along the surface shape of the object to be coated in the formed coating film. FIG. 1 is a schematic diagram showing the orientation mechanism of scaly pigments in the process of applying and curing a conventional aqueous paint composition containing scaly pigments. Here, FIG. 1 (a) shows an uncured coating film before heating formed by applying a conventional aqueous coating composition, and FIG. 1 (b) shows an uncured coating film of (a). The cured coating film obtained by heating is shown. In an uncured coating film formed by applying a conventional aqueous coating composition, as shown in (a), the orientation of the scaly pigment is in a random state. Next, by heating, the thickness of the coating film becomes thinner as the solvent contained in the uncured coating film gradually evaporates. As the coating film becomes thinner, the slope of the scaly pigment becomes gentler, and as a result, the scaly pigment is oriented in a state along the surface shape of the object to be coated. That is, in the conventional coating composition, the scale-like pigment is oriented with respect to the surface of the object to be coated due to the volume shrinkage of the uncured coating film after coating.

  Thus, in the conventional water-based paint composition, in order to orient the scaly pigment in a state along the surface shape of the object to be coated, it is necessary to increase the volume shrinkage that occurs when the uncured coating film is heated. was there. That is, in the conventional aqueous coating composition, it is necessary to contain a large amount of solvent in order to increase the volume shrinkage of the uncured coating film.

On the other hand, in recent years, due to further demands for environmental load reduction such as energy saving and CO ₂ emission reduction, the volume of paint necessary for painting a desired dry film thickness is reduced, and the manufacture, transportation and painting of paint are reduced. It is demanded to reduce the environmental load during the subsequent heat curing. In order to realize this, it is necessary to reduce the amount of the solvent contained in the coating composition. However, when the amount of the solvent contained in the coating composition is reduced, the volume shrinkage that causes the orientation of the scaly pigment relative to the surface of the object to be coated is reduced. Therefore, there has been a problem that good orientation of the scaly pigment cannot be obtained and an excellent coating film appearance cannot be obtained.

  JP-T-2013-535311 (Patent Document 2) discloses a three-coat one-bake multi-layer coating using a water-based colored paint (A), a glitter pigment-containing water-based paint (B), and a clear coat paint (C). In the forming method, it describes a method capable of forming a multilayer coating film having excellent smoothness, sharpness and water resistance even if the preheating step after the application of the water-based colored paint (A) is omitted. Yes. Patent Document 2 discloses a coating film having a good appearance by coating a bright pigment-containing water-based paint (B) containing a large amount of a bright pigment with a thin film thickness such as a dry film thickness of 7 to 13 μm. ([0156] paragraph etc.). As described above, in the method described in Patent Document 2, the orientation of the glitter pigment is adjusted by controlling the pigment concentration of the coating composition and the coating film thickness. However, the dry film thickness of the coating film containing the glitter pigment is limited to a thin range such as 7 to 13 μm, and the content of the glitter pigment is in a large range such as 15 to 30 parts by mass. By being limited, there exists a subject that the design design range of the multilayer coating film obtained will be restrict | limited.

  JP-A-2011-131134 (Patent Document 3) discloses that all three hydroxyl groups of (a) acrylic resin emulsion, (b) water-soluble acrylic resin, (c) melamine resin, and (d) glycerin are alkylene. A method for forming a multilayer coating using an aqueous base paint comprising a polyether polyol etherified with an oxide is described. It is described that the coating film obtained by this method has a high flip-flop property and a uniform coating. On the other hand, the polyether polyol (d) described in Patent Document 3 and the amphiphilic compound in the present invention are clearly different in structure.

  JP 2007-39616 A (Patent Document 4) includes an acrylic resin emulsion obtained by two-stage emulsion polymerization, a curing agent, a bright pigment, and a nonionic pigment dispersant having an alkyl chain having 14 or more carbon atoms. A water-based metallic paint is described. And this patent document 4 uses a specific acrylic resin emulsion obtained by two-stage emulsion polymerization, uses a specific hydrophobic melamine resin aqueous dispersion as a curing agent, and uses a specific amount of pigment dispersant. The orientation of the glittering pigment in the two-coat / one-bake coating method is maintained while maintaining the excellent characteristics of the water-based metallic paint (for example, color developability, recoat adhesion, chipping, and water-resistant adhesion). It is described that a metallic coating film that is less disturbed after coating, has a fine feeling and a flip-flop property, and has a good appearance can be obtained (paragraph [0011]). On the other hand, in this patent document 4, it is not described at all about raising the solid content concentration of the paint in the aqueous metallic paint.

Japanese Patent Laid-Open No. 11-80620 Special table 2013-535311 gazette JP 2011-131134 A JP 2007-39616 A

  The present invention solves the above-mentioned conventional problems, and its object is to form a multilayer coating film having excellent glitter even in an aqueous coating composition having a high resin solid content concentration. It is in providing the coating composition which can be performed.

In order to solve the above problems, the present invention provides the following aspects.
[1]
An aqueous coating composition comprising a coating film-forming resin, a curing agent, a scaly pigment, and an amphiphilic compound,
The amphiphilic compound is a compound having at least one hydrophobic part (A) as a repeating unit and at least one hydrophilic part (B) as a repeating unit, wherein
The hydrophobic part (A) is a propylene oxide group, a butylene oxide group, a linear or branched saturated hydrocarbon group having 4 to 40 carbon atoms, a linear or branched non-carbon group having 4 to 40 carbon atoms. Having at least one group selected from the group consisting of a saturated hydrocarbon group, an aromatic ring-containing group having 6 to 40 carbon atoms having an aromatic ring, and a hydrophobic polymer segment;
The hydrophilic part (B) has at least one group selected from the group consisting of an ethylene oxide group and an acid group, and the amphiphilic compound has a number average molecular weight of 1500 to 100,000.
When the water-based coating composition is adjusted such that the viscosity by a B-type viscometer is 780 to 820 mPa · s at 20 ° C. and 60 rpm, the resin solid content concentration contained in the coating composition is 25 to 25. 40% by weight,
Water-based paint composition.
[2]
The aqueous coating composition in which the hydrophobic part (A) of the amphiphilic compound has a C6-C40 aromatic ring-containing group having an aromatic ring.
[3]
The water-based coating composition whose hydrophobic part (A) of the said amphiphilic compound is a C12-C40 aromatic ring-containing group having 2 to 4 aromatic rings.
[4]
The coating film-forming resin is an aqueous coating composition containing an acrylic resin emulsion.
[5]
The aqueous coating composition whose mass ratio (PWC) of the scale-like pigment with respect to resin solid content contained in the said aqueous coating composition is 5 to 30%.
[6]
A process of coating a water-based base coating composition on an object to be coated to form an uncured base coating;
The step of coating the clear coating composition on the resulting uncured base coating to form an uncured clear coating, and heating the resulting uncured base coating and clear coating simultaneously. Curing process,
A method for forming a multilayer coating film, comprising:
The aqueous base coating composition is any one of the above aqueous coating compositions,
A method for forming a multilayer coating film.
[7]
The multilayer coating film formation method whose dry film thickness of the base coating film formed by the said method is 3-50 micrometers.
[8]
A multilayer coating film obtained by the multilayer coating film forming method.

Even if the aqueous coating composition of the present invention is a so-called high resin solid content coating composition having a resin solid content concentration of 25 to 40% by mass, that is, a coating composition that gives a coating film with a small volume shrinkage, It is possible to form a multi-layer coating film having excellent luster and well oriented in a state along the surface shape of the object to be coated. Since the aqueous coating composition of the present invention has a high resin solid content concentration, the amount of the solvent contained in the composition is small as compared with a general aqueous coating composition. Therefore, the volume of the paint required for coating can be reduced by using the aqueous paint composition of the present invention. By using the water-based coating composition of the present invention, the energy required during the production, transportation, and heat-curing after coating can be reduced, and the amount of CO ₂ emission can be reduced.

It is a schematic diagram which shows the orientation mechanism of a scale-like pigment in the process in which the conventional water-based coating composition containing a scale-like pigment is applied and cured. It is a schematic diagram which shows the orientation mechanism of a scale-like pigment in the process in which the water-based coating composition of this invention is applied and hardened.

Aqueous paint composition The aqueous paint composition of the present invention comprises a film-forming resin, a curing agent, a scaly pigment, and an amphiphilic compound. The aqueous coating composition of the present invention is a coating composition having a resin solid content concentration of 25 to 40% by mass contained in the coating composition at the time of coating, ie, a so-called high resin solid content concentration. There is an advantage that the scaly pigment contained therein is well oriented with respect to the surface shape of the article to be coated, and a coating film having a good coating film appearance can be obtained.
Hereafter, each component contained in the water-based coating composition of this invention is demonstrated sequentially.

Film Forming Resin The aqueous coating composition of the present invention contains a film forming resin. A conventionally well-known thing can be used as coating-film formation resin. Specific examples of the coating film-forming resin include acrylic resin, polyester resin, alkyd resin, polyether resin, polyolefin resin, and urethane resin. Such a film-forming resin may be water-soluble, water-dispersible, or emulsion. Among the coating film forming resins, acrylic resins and / or polyester resins are preferably used from the viewpoint of coating film performance such as weather resistance and water resistance. These coating film forming resins may be used alone or in combination of two or more.

  One particularly preferred example of the film-forming resin is an acrylic resin emulsion. The acrylic resin emulsion can be obtained, for example, by emulsion polymerization of an α, β-ethylenically unsaturated monomer mixture. Preferred α, β-ethylenically unsaturated monomers used for the preparation of the acrylic resin emulsion include, for example, (meth) acrylic acid esters having 1 or 2 carbon atoms in the ester moiety, α, β-ethylenically unsaturated monomers having acid groups. Examples include saturated monomers and α, β-ethylenically unsaturated monomers having a hydroxyl group.

  Examples of the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion include methyl (meth) acrylate and ethyl (meth) acrylate. In addition, in this specification, (meth) acrylic acid ester shall mean both acrylic acid ester and methacrylic acid ester.

  Examples of the α, β-ethylenically unsaturated monomer having an acid group include acrylic acid, methacrylic acid, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, and ω-carboxy-polycaprolactone mono (meta). ) Acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl) oxy) poly (oxy (1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, vinylphosphine, 2-acryloyloxyethyl acid phosphate, 3-chloro-2-acid phosphooxypropyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid, p-hydroxy Styrene, 2,4-dihydroxy-4 ' -Vinyl benzophenone etc. can be mentioned.

  Examples of the α, β-ethylenically unsaturated monomer having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methallyl alcohol, and these Examples include adducts with ε-caprolactone. Among these, preferred are hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyethyl (meth) acrylate, and addition of these with ε-caprolactone. It is a thing.

  The α, β-ethylenically unsaturated monomer mixture may further use other α, β-ethylenically unsaturated monomers. Other α, β-ethylenically unsaturated monomers include (meth) acrylic acid esters having 3 or more carbon atoms in the ester moiety (for example, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) T-butyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, phenyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, t- (meth) acrylic acid Butylcyclohexyl, (meth) acrylate dicyclopentadienyl, (meth) acrylate dihydrodicyclopentadienyl, etc.), polymerizable amide compounds (for example, (meth) acrylamide, N-methylol (meth) acrylamide, N- Butoxymethyl (meth) acrylamide, N, N-dimethyl (meth) acrylic Amide, N, N-dibutyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide 2,4-dihydroxy-4′-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, etc.), polymerizable aromatic compounds (for example, styrene, vinyltoluene, α-methylstyrene, divinylbenzene, t-butylstyrene, para Chlorostyrene, vinylnaphthalene, 2-vinylpyridine, 4-vinylpyridine, etc.), polymerizable nitriles (eg, acrylonitrile, methacrylonitrile, etc.), polymerizable alkylene oxide compounds (eg, (meth) acrylic acid (poly) oxyethylene) , (Me T) acrylic acid (poly) propylene glycol, etc.), polyfunctional vinyl compounds (for example, (meth) acrylic acid allyl, (poly) oxyethylene di (meth) acrylate, trimethylolpropane tri (meth) acrylate, etc.), polymerizable Amine compounds (eg, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, etc.), α-olefins (eg, ethylene, propylene, etc.), vinyl esters (eg, vinyl acetate, vinyl propionate, persamic acid) Vinyl), dienes (eg, butadiene, isoprene, etc.), halogenated vinyls (eg, vinyl chloride, vinylidene chloride, etc.), polymerizable carbonyl compounds (eg, acrolein, diacetone (meth) acrylamide, formylstyrene, vinyl) Methyl ketone, vinyl ethyl ketone, vinyl isobutyl ketone, acryloxyalkylpropanals, methacryloxyalkylpropanals, diacetone acrylate, diacetone methacrylate, acetonyl acrylate, 2-hydroxypropyl acrylate acetyl acetate, butanediol acrylate acetyl acetate, etc. ), Polymerizable acetoacetoxy compounds (for example, acetoacetoxyethyl (meth) acrylate, acetoacetoxyethyl (meth) acrylate, etc.), polymerizable alkoxysilyl compounds (for example, γ- (meth) acryloxypropyltrimethoxysilane, γ- (Meth) acryloxypropylmethyldimethoxysilane, γ- (meth) acryloxypropyldimethylmethoxysilane, γ- (meth) acryl Xylpropyltriethoxysilane, γ- (meth) acryloxypropylmethyldiethoxysilane, γ- (meth) acryloxypropyldimethylethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxy Silane, trimethoxysilyl styrene, dimethoxymethylsilyl styrene, triethoxysilyl styrene, diethoxymethyl silyl styrene, etc.) and other polymerizable compounds (for example, vinyl pyrrolidone, diphenyl vinyl phosphine, etc.). The α, β-ethylenically unsaturated monomer can be variously selected according to the purpose.

  The acrylic resin emulsion can be prepared by emulsion polymerization of the α, β-ethylenically unsaturated monomer mixture. The emulsion polymerization is not particularly limited, and can be performed using a usual method. Specifically, for example, an emulsifier is dissolved in water or an aqueous medium containing an organic solvent such as alcohol, ether (for example, dipropylene glycol methyl ether, propylene glycol methyl ether) as necessary, and heated. It can carry out by dripping the said (alpha), (beta) -ethylenically unsaturated monomer mixture and a polymerization initiator under stirring. An α, β-ethylenically unsaturated monomer mixture emulsified in advance using an emulsifier and water may be similarly added dropwise.

  As the polymerization initiator, those usually used by those skilled in the art can be used. As the polymerization initiator, for example, an azo compound (for example, 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis (N- (2-carboxyethyl) -2-methylpropionamidine), Azobisisobutyronitrile, 2,2′-azobis-2,4′-dimethylvaleric nitrile, etc.), peroxides (t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroper Oxides, cumene hydroperoxide, dibenzoyl peroxide, di-t-butyl peroxide, t-butylperoxyneodecanoate, potassium persulfate, ammonium persulfate, etc.), redox initiators (eg, hydrogen peroxide and chloride) A combination of iron (II), a combination of ammonium persulfate and ammonium bisulfite, and the like. The polymerization initiator may be neutralized with a base as necessary, and can be used at a pH of 1 to 10, for example.

  As the emulsifier, those usually used by those skilled in the art can be used. As an emulsifier, for example, Antox MS-2N (manufactured by Nippon Emulsifier Co., Ltd., 2-sodium sulfoethyl methacrylate), New Coal 706 (manufactured by Nippon Emulsifier Co., Ltd., polyoxyethylene polycyclic phenyl ether), Adecalia Soap NE 10 (manufactured by Asahi Denka Co., Ltd., α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene), Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether), Laterum PD-104 (manufactured by Kao Corporation, polyoxyalkylene alkenyl ether ammonium sulfate), Aqualon HS-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., polyoxyethylene alkylpropenyl phenyl ether ammonium sulfate) and the like can be suitably used.

  In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

  The reaction temperature is determined by the initiator, and is usually 20 to 95 ° C., for a redox initiator, for example, 20 to 50 ° C., and for an azo system, for example, 40 to 95 ° C. Further, the inside of the reaction vessel may be pressurized to carry out the polymerization, and in that case, the polymerization may be carried out at a temperature of 95 ° C. or higher. In general, the reaction time is 1 to 8 hours. The amount of the initiator relative to the total amount of the α, β-ethylenically unsaturated monomer mixture is generally 0.05 to 5% by mass, preferably 0.1 to 3% by mass.

  The acrylic resin emulsion that can be prepared in this way preferably has an average particle size in the range of 0.01 to 1.0 μm. If the average particle size is less than 0.01 μm, the viscosity may be significantly increased and it may be difficult to increase the resin solid content concentration, and if it exceeds 1.0 μm, the appearance of the resulting coating film may be deteriorated. . More preferably, it is 0.05-0.5 micrometer. This average particle size can be adjusted, for example, by adjusting the monomer composition or emulsion polymerization conditions. In addition, the said average particle diameter is displayed with the volume average particle diameter measured by the laser light scattering method.

  The acrylic resin emulsion may be neutralized with a base as necessary, and can be used at a pH of 1 to 10, for example. This is because the stability in this pH region is high. This neutralization involves adding a basic compound such as ammonia, sodium hydroxide, potassium hydroxide, monoethanolamine, monomethylethanolamine, dimethylethanolamine, diethylethanolamine or triethylamine to the system before or after emulsion polymerization. Can be performed.

  The acrylic resin emulsion preferably has a number average molecular weight of 3000 at the lower limit. If it is less than 3000, workability and curability may be insufficient. An upper limit in particular is not restrict | limited, For example, it can also be set as a crosslinked emulsion using polyfunctional (meth) acrylate etc. The lower limit is more preferably 4000. In the present specification, the number average molecular weight is a value determined by a GPC method using polystyrene as a standard.

  The acrylic resin emulsion preferably has a hydroxyl value having a lower limit of 20 mgKOH / g and an upper limit of 180 mgKOH / g. There exists a possibility that the sclerosis | hardenability of a coating film may fall that it is less than 20 mgKOH / g. If it exceeds 180 mgKOH / g, the water resistance of the coating film may decrease. The lower limit is more preferably 30 mgKOH / g, and the upper limit is more preferably 160 mgKOH / g.

  The acrylic resin emulsion preferably has an acid value of a lower limit of 1 mgKOH / g and an upper limit of 80 mgKOH / g. If it is less than 1 mgKOH / g, the stability of the paint may be reduced. When it exceeds 80 mgKOH / g, the water resistance of the coating film may be lowered. The lower limit is more preferably 3 mgKOH / g, and the upper limit is more preferably 70 mgKOH / g.

  The aqueous coating composition of the present invention may contain other film-forming resin as necessary. Other film-forming resins are not particularly limited, and film-forming resins such as water-soluble acrylic resins, polyester resins, alkyd resins, epoxy resins, and urethane resins can be used.

Curing Agent The water-based coating composition of the present invention contains a curing agent that appropriately corresponds to the type of curable functional group possessed by the coating film-forming resin. A conventionally well-known thing can be used as a hardening | curing agent, Specifically, an amino resin, block isocyanate resin, an epoxy compound, an aziridine compound, a carbodiimide compound, an oxazoline compound etc. can be mentioned as a preferable thing. Among these, amino resins and / or blocked isocyanate resins are generally used. The said hardening | curing agent may be used independently and may use 2 or more types together.

  The amino resin is not particularly limited, and a water-soluble melamine resin and / or a water-insoluble melamine resin can be used.

  The blocked isocyanate resin can be prepared by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and isophorone diisocyanate. In such a blocked isocyanate resin, the blocking agent is dissociated by heating to generate an isocyanate group, which is cured by reacting with the functional group in the resin component.

  The blending amount of the curing agent is preferably a lower limit of 5 parts by mass and an upper limit of 120 parts by mass with respect to 100 parts by mass of the solid content of the coating film-forming resin. If it is less than 5 parts by mass, the curability may be insufficient. If it exceeds 120 parts by mass, the cured film may be too hard and brittle. As for the compounding quantity of a hardening | curing agent, it is more preferable that it is 10-100 mass parts with respect to 100 mass parts of solid content of the said coating-film formation resin.

Scale-like pigment The aqueous coating composition of the present invention contains a scale-like pigment. As the scaly pigment, for example, those having an average particle diameter (D50) of 2 to 50 μm and a thickness of 0.1 to 5 μm are preferable. Those having an average particle size in the range of 5 to 35 μm are excellent in glitter and are more preferably used. Specific examples of the scaly pigment include metallic scaly pigments such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, or metal oxides, and mixtures thereof. In addition, interference mica pigments, white mica pigments, graphite pigments, and the like are included in this. These scaly pigments may be colored as necessary.

  In this specification, the average particle diameter of the scaly pigment means the median diameter of the volume-based particle size distribution measured by a laser diffraction scattering method. Further, the thickness of the scaly pigment is obtained by observing a cross section of the coating film containing the scaly pigment with a microscope, measuring the thickness of the scaly pigment using image processing software, and measuring 100 or more measured values. It shall be defined as an average value.

  In the aqueous coating composition of this invention, it is preferable that the mass ratio (PWC) of the scale-like pigment with respect to the resin solid content contained in a coating composition is 5 to 30%. When the mass ratio of the scaly pigment is in the above range, a coating film having excellent glitter can be formed. Here, the “resin solid content” means the total amount of the film-forming resin and the curing agent contained in the aqueous coating composition.

  The water-based paint composition of the present invention may contain other pigments in addition to the scale-like pigment. Other pigments include colored pigments and extender pigments. Examples of the color pigment include, for example, organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylenes. Pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments and the like, and inorganic pigments such as yellow iron oxide, nickel titanium yellow, bengara, carbon black, and titanium dioxide. Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc.

  The total pigment concentration (PWC) in the aqueous coating composition of the present invention is preferably 5 to 50% by mass. The total pigment concentration (PWC) is more preferably 5 to 40%, further preferably 5 to 35%. When the total pigment concentration (PWC) exceeds 50%, the coating film appearance may be deteriorated.

Amphiphilic Compound The aqueous coating composition of the present invention contains an amphiphilic compound. The amphiphilic compound in the present specification is a compound having at least one hydrophobic part (A) as a repeating unit and at least one hydrophilic part (B) as a repeating unit. In the amphiphilic compound of the present invention, the hydrophobic part (A) and the hydrophilic part (B) are each provided as segments. That is, a random copolymer obtained by polymerizing a monomer mixture containing an α, β-ethylenically unsaturated monomer having a hydrophilic group and an α, β-ethylenically unsaturated monomer having a hydrophobic group by a classical radical polymerization method Etc. are not included in the amphiphilic compound in the present invention.

The hydrophobic part (A) in the amphiphilic compound is a propylene oxide group, a butylene oxide group, a linear or branched saturated hydrocarbon group having 4 to 40 carbon atoms, a linear or branched carbon number. It has at least one group selected from the group consisting of an unsaturated hydrocarbon group having 4 to 40 carbon atoms, an aromatic ring-containing group having 6 to 40 carbon atoms having an aromatic ring, and a hydrophobic polymer segment.
Examples of the propylene oxide group include propylene oxide groups having 2 to 1700 repeats.
Examples of the butylene oxide group include butylene oxide groups having 2 to 1400 repeats.
Examples of the linear or branched saturated hydrocarbon group having 4 to 40 carbon atoms include, for example, butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, Octadecane, Nonadecane, Icosan, Eicosan, Henicosan, Henicosan, Docosan, Tricosan, Tetracosan, Pentacosan, Hexacosan, Heptacosan, Octacosan, Nonacosan, Triacontan, Hentriakontan, Dotriacontan, Tritriacontan, Tetriacontan, Pentatriacontan And straight-chain saturated hydrocarbon groups such as hexatriacontane and tetracontane, and branched saturated hydrocarbon groups in which the straight-chain saturated hydrocarbon group has a branched chain.
Examples of the linear or branched unsaturated hydrocarbon group having 4 to 40 carbon atoms include, for example, a linear unsaturated hydrocarbon group having a carbon-carbon double bond in the linear saturated hydrocarbon group, And a branched unsaturated hydrocarbon group in which these linear unsaturated hydrocarbon groups have a branched chain.
Examples of the aromatic ring-containing group having 6 to 40 carbon atoms having an aromatic ring may include a phenyl group which may have a substituent, a naphthyl group which may have a substituent, and a substituent. A benzyl group, an optionally substituted pentarenyl group, an optionally substituted indenyl group, an optionally substituted azulenyl group, an optionally substituted heptalenyl group, and a substituent; Examples thereof include an octaenyl group which may have, an acenaphthyl group which may have a substituent, an indacenyl group which may have a substituent, and an anthracenyl group which may have a substituent. Here, as a substituent, for example, an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, an aldehyde group having 2 to 30 carbon atoms, an ester group having 2 to 30 carbon atoms, or an alkyl group having 1 to 30 carbon atoms. Examples include an alkoxy group, an aromatic oxy group having 6 to 30 carbon atoms, an aromatic alkyl group having 7 to 30 carbon atoms, and a group having an aromatic ring having 4 to 30 carbon atoms.
Examples of the hydrophobic polymer segment include a hydrophobic polymer segment having one or more of the above groups.
The hydrophobic part (A) preferably has an aromatic ring-containing group having 6 to 40 carbon atoms having an aromatic ring.

  The hydrophobic part (A) is more preferably an aromatic ring-containing group having 12 to 40 carbon atoms and having 2 to 4 aromatic rings. As such a hydrophobic part (A), for example, a phenyl group having a group having an aromatic ring having 4 to 30 carbon atoms as a substituent, and a benzyl having a group having an aromatic ring having 4 to 30 carbon atoms as a substituent Group, a naphthyl group which may have a substituent, a naphthyl group which may have a substituent, a phenoxyphenyl group which may have a substituent, a diphenylmethyl group which may have a substituent, a substituent And an indacenyl group which may have an anthracenyl group which may have a substituent. Specific examples of the group having an aromatic ring having 4 to 30 carbon atoms, which is an example of the substituent, include, for example, benzyl group, tolyl group, xylyl group, phenethyl group, trimethylphenyl group, cumenyl group, cumyl group, phenylpropylene. Group, diphenylmethyl group, styryl group, indenyl group, pyridyl group, thiophenyl group, furanyl group, pyrrolyl group, indolyl group, imidazolyl group, thiazolyl group, quinolinyl group, benzoimidazolinyl group and the like. As a more preferable embodiment in the case where the hydrophobic part (A) is an aromatic ring-containing group having 12 to 40 carbon atoms and having 2 to 4 aromatic rings, the substituent is an aromatic alkyl group having 7 to 30 carbon atoms. And a benzyl group having 1 to 3 substituents which are aromatic alkyl groups having 7 to 30 carbon atoms.

  The hydrophilic part (B) in the amphiphilic compound has at least one group selected from the group consisting of an ethylene oxide group and an acid group. Examples of the ethylene oxide group include ethylene oxide groups having 2 to 2200 repeats. Examples of the acid group include a carboxylic acid group, a phosphoric acid group, a sulfonic acid group, and a phenolic hydroxyl group.

  Examples of the hydrophilic part (B) of the amphiphilic compound having an acid group include, for example, an acrylic resin segment obtained by chain polymerization of the hydrophilic part (B), a polyester resin segment obtained by polycondensation, and a urethane obtained by addition polymerization. Examples include resin segments. When the hydrophilic part (B) is an acrylic resin segment, the acrylic resin is obtained by copolymerizing an α, β-ethylenically unsaturated monomer having an acid group and an arbitrary α, β-ethylenically unsaturated monomer. Segments can be prepared. Specific examples of the α, β-ethylenically unsaturated monomer having an acid group include the aforementioned α, β-ethylenically unsaturated monomer having an acid group. Specific examples of arbitrary α, β-ethylenically unsaturated monomers include the above-mentioned (meth) acrylic acid esters, α, β-ethylenically unsaturated monomers having a hydroxyl group, and other α, β-ethylenically unsaturated monomers. Can be mentioned.

  When the hydrophilic part (B) is a polyester resin segment, the polyester resin segment can be prepared, for example, by polycondensation of a polybasic acid and a polyol compound. Such a polybasic acid is not particularly limited, and examples thereof include linear dibasic acids such as oxalic acid, succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid; phthalic acid, phthalic anhydride, isophthalic acid , Aromatic fatty acids such as terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, tetrabromophthalic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride; maleic acid, Examples thereof include unsaturated dibasic acids such as maleic anhydride, fumaric acid and itaconic acid. Such a polyol compound is not particularly limited as long as it contains two or more hydroxyl groups. For example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, Polyhydric alcohols such as methylolpropane and glycerin, polyether polyols such as polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol, dicarboxylic acids such as adipic acid, sebacic acid, itaconic acid, maleic anhydride, phthalic acid and isophthalic acid Polyester polyols obtained from glycols such as ethylene glycol, triethylene glycol, propylene glycol, butylene glycol, tripropylene glycol, neopentyl glycol, polycaprola Ton polyols, polybutadiene polyols, polycarbonate polyols, such as polythioether polyols. The polyol compounds may be used alone or in combination of two or more. In addition, a compound having an acid group and a hydroxyl group, such as dimethylolpropionic acid and dimethylolbutyric acid, can also be used.

  When the hydrophilic part (B) is a polyurethane resin segment, for example, addition using a polyol compound, a compound having an active hydrogen group and a hydrophilic group in the molecule, an organic polyisocyanate, and optionally a chain extender and a polymerization terminator A urethane resin segment can be prepared by polymerization. The polyol compound is not particularly limited as long as it contains two or more hydroxyl groups. For example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, glycerin. Polyhydric alcohol such as polyethylene glycol, polypropylene glycol, polyether polyol such as polytetramethylene ether glycol, dicarboxylic acid such as adipic acid, sebacic acid, itaconic acid, maleic anhydride, phthalic acid, isophthalic acid and ethylene glycol, Polyester polyols obtained from glycols such as ethylene glycol, propylene glycol, butylene glycol, tripropylene glycol and neopentyl glycol, polycaprolactone polyol , Polybutadiene polyols, polycarbonate polyols, such as polythioether polyols. The polyol compounds may be used alone or in combination of two or more. The compound having an active hydrogen group and a hydrophilic group in the molecule includes an active hydrogen and an anion group {an anion group or an anion-forming group (which reacts with a base to form an anion group. In this case, a urethanization reaction A compound containing a known compound (for example, described in JP-B-42-24192 and JP-B-55-41607) , Specific examples include dimethylolpropionic acid, dimethylolbutyric acid, and the like, compounds known as compounds having active hydrogen and a cationic group in the molecule (for example, those described in JP-B-43-9076) and intramolecular Known as compounds having active hydrogen and nonionic hydrophilic groups (for example, see JP-B-48-41718). Ones, specifically, polyethylene glycol, alkyl alcohol alkylene oxide adduct) and the like. The organic polyisocyanate is not particularly limited as long as it has two or more isocyanate groups in the molecule. For example, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4- Trimethylhexamethylene diisocyanate, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate, dicyclohexylmethane-4,4′-diisocyanate, methylcyclohexyl-2,4-diisocyanate, methylcyclohexyl-2,6-diisocyanate, xylylene diene Isocyanate, 1,3-bis (isocyanate) methylcyclohexane, tetramethylxylylene diisocyanate, transcyclohexane-1,4-diisocyanate, lysine diisocyanate Any aliphatic diisocyanates, 2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, diphenylmethane-4,4′-diisocyanate, 1,5′-naphthene diisocyanate, tolidine diisocyanate, diphenylmethylmethane diisocyanate, tetraalkyldiphenylmethane Aromatic diisocyanates such as diisocyanate, 4,4′-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, lysine ester triisocyanate, triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate -4,4-isocyanatomethyloctane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate Such as birds isocyanates, and the like. Moreover, you may use with the dimer and trimer (isocyanurate coupling | bonding) of these polyisocyanate compounds, and you may make it react with an amine and use it as a biuret. Further, polyisocyanates having urethane bonds obtained by reacting these polyisocyanate compounds with polyols can also be used.

  When the hydrophilic part (B) has an acid group, the acid group is more preferably in a neutralized state. Examples of neutralizing agents that can be used for neutralizing the acid group of the hydrophilic part (B) include alkali metal salts such as sodium hydroxide, potassium hydroxide, lithium hydroxide; ammonia, triethylamine, triethanolamine, diethanolamine Organic base compounds such as monoethanolamine, dimethylethanolamine, monomethylethanolamine, diethylethanolamine, dimethylamine, trimethylamine, diisopropylamine, 2-amino-2-methyl-1-propanol;

  As the hydrophilic portion (B), an embodiment in which the ethylene oxide group having 2 to 2200 repetitions is more preferable.

  The amphiphilic compound has a number average molecular weight of 1500 to 100,000. When the number average molecular weight of the amphiphilic compound is less than 1500, a sufficient coating film appearance improving effect cannot be obtained. On the other hand, when the number average molecular weight exceeds 100,000, the viscosity is remarkably increased and it may be difficult to increase the resin solid content concentration.

  The amphiphilic compound may be prepared by a method such as a block copolymerization method using an α, β-ethylenically unsaturated monomer. In the block copolymerization method, in general, a multistage polymerization method in which a monomer is added in two or more stages is preferably used. When prepared by the block copolymerization method, as the α, β-ethylenically unsaturated monomer constituting the hydrophobic part (A), for example, the above-mentioned (meth) acrylic acid ester, α, β-ethylenically unsaturated group having a hydroxyl group Any monomer selected from monomers and other α, β-ethylenically unsaturated monomers can be used. As the α, β-ethylenically unsaturated monomer constituting the hydrophilic part (B), the α, β-ethylenically unsaturated monomer having the above acid group and / or the α, β-ethylenically unsaturated monomer having an ethylene oxide group Using (meth) acrylic acid ester, α, β-ethylenically unsaturated monomer having a hydroxyl group, and other α, β-ethylenically unsaturated monomer as an essential component (for example, methoxypolyethylene glycol monomethacrylate) Can be used. The block copolymerization method using an α, β-ethylenically unsaturated monomer is not particularly limited, and examples thereof include an atom transfer radical polymerization method (ATRP), a reversible addition-cleavage chain transfer polymerization method (RAFT), and a nitroxide. And controlled radical polymerization (NMP) and reversible transfer catalytic polymerization (RTCP).

  As a block copolymerization method using an α, β-ethylenically unsaturated monomer, for example, it can be prepared by a copolymerization method by a reversible chain transfer catalyzed polymerization (RTCP). The reversible transfer catalytic polymerization method is a living radical polymerization method using a polymer growth terminal control agent such as an organic iodine compound, a radical supply agent such as an azo compound, and a polymer growth terminal reactivation agent such as a phenol compound. It is a polymerization method capable of synthesizing a block copolymer having two or more segment structures by multistage polymerization. Examples of the organic iodine compound include alkyl iodides such as 2-iodo-1-phenylethane and 1-iodo-1-phenylethane, 2-cyano-2-iodopropane, 2-cyano-2-iodobutane, and 1-cyano. Examples include cyano group-containing iodides such as -1-iodocyclohexane and 2-cyano-2-iodovaleronitrile. Examples of the azo compound include azo compounds such as azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile). Examples of the phenolic compound include phenolic compounds such as phenol, hydroquinone, methoxyhydroquinone, t-butylphenol, catechol, and di-t-butylhydroxytoluene. This reversible transfer catalytic polymerization method can be carried out under known reaction conditions described in, for example, JP2013-75795A.

  Commercial products may be used as the amphiphilic compound. Examples of commercially available products include Neugen EA-197D, Neugen EA-207D, Neugen XL-400D, Neugen XL-400, Neugen XL-1000, Epan 450, Epan 485, Epan 680, Epan 720, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Examples include Epan 750, Epan 785, Epan U-108, Emulgen A-500, Emanon 3299V manufactured by Kao Corporation, New Coal 719, New Coal 723, New Coal 740, New Coal 2344 manufactured by Nippon Emulsifier Co., Ltd.

  The said amphiphilic compound may be used individually by 1 type, and may use 2 or more types together.

  The amphiphilic compound is preferably contained in the range of 0.01 to 15% by mass, more preferably in the range of 0.05 to 10% by mass with respect to the solid content of the aqueous coating composition. More preferably, it is contained in the range of 0.1 to 10% by mass. When the amount of the amphiphilic compound is less than the above range, the effect of improving the orientation of the scaly pigment by adding the amphiphilic compound may not be achieved. On the other hand, when the amount of the amphiphilic compound exceeds the above range, the obtained multilayer coating film may have poor coating performance such as water resistance.

Other components In addition to the above-mentioned components, the water-based coating composition of the present invention includes additives usually used by those skilled in the art, for example, surface conditioners, viscosity control agents, thickeners, antioxidants, UV inhibitors, extinction agents. A foaming agent or the like may be included. For example, by using a viscosity control agent, thixotropy can be imparted and coating workability can be adjusted. Viscosity control agents include, for example, crosslinked or non-crosslinked resin particles, fatty acid amide swelling dispersions, amide fatty acids, polyamides such as long chain polyaminoamide phosphates, colloidal swelling dispersions of polyethylene oxide, etc. Examples thereof include polyethylene-based ones, organic acid smectite clays, organic bentonite-based ones such as montmorillonite, and inorganic pigments such as aluminum silicate and barium sulfate. When these additives are used, they can be used in an amount usually used by those skilled in the art.

Preparation of aqueous coating composition The method for preparing the aqueous coating composition of the present invention is not particularly limited, and the coating film-forming resin, curing agent, scaly pigment, amphiphilic compound, and additives as necessary Can be prepared by a method commonly used by those skilled in the art, such as kneading and dispersing using a disper, a homogenizer, a kneader or the like.

  In the aqueous coating composition of the present invention, the resin solid content concentration contained in the coating composition is 25 to 40% by mass. Here, the “resin solid content concentration” means the concentration (mass%) of the total amount of the film-forming resin and the curing agent contained in the aqueous coating composition. The resin solid content concentration of the aqueous coating composition can be calculated from the amount of each component used in the preparation of the aqueous coating composition.

  The aqueous coating composition of the present invention has a higher resin solid content concentration than a conventional aqueous coating composition containing a scaly pigment (for example, a metallic base coating composition). The aqueous coating composition of the present invention is characterized in that a multi-layer coating film having excellent glitter can be formed even if it is a high solid content coating composition having a high solid content concentration. In the conventional water-based metallic base coating composition, in order to orient the scaly pigment in a state along the surface shape of the object to be coated, it is necessary to increase the volume shrinkage that occurs when heating the uncured coating film. It was. That is, in the conventional aqueous coating composition, it is necessary to contain a large amount of solvent in order to increase the volume shrinkage of the uncured coating film. FIG. 1 is a schematic diagram showing the orientation mechanism of scaly pigments in the process of applying a conventional aqueous coating composition containing scaly pigments and then curing. As schematically shown in FIG. 1, in the conventional aqueous coating composition, the regular orientation of the scaly pigment is increased by increasing the volume shrinkage from the uncured coating film to the cured coating film. I was getting.

  On the other hand, in order to reduce the volume of paint required to paint the desired dry film thickness, and to reduce the environmental load during the production, transportation and heat curing after painting, It is desirable that the amount of solvent contained in the product is as small as possible. However, when the amount of the solvent contained in the coating composition is reduced, the volume shrinkage that causes the orientation of the scaly pigment relative to the surface of the object to be coated is reduced. Therefore, there has been a problem that good orientation of the scaly pigment cannot be obtained and an excellent coating film appearance cannot be obtained.

  The water-based coating composition of the present invention contains a specific amphiphilic compound, so that even when it is applied by a normal coating method, the scaly pigment is coated as compared with the conventional coating composition. It will be oriented in a state along the surface shape. FIG. 2 is a schematic view showing the orientation mechanism of scaly pigments in the process of applying and curing the aqueous coating composition of the present invention. As schematically shown in FIG. 2, the scaly pigment is oriented better even in an uncured base coating film before heat-curing by coating with the aqueous coating composition of the present invention. It becomes. Therefore, even when the volume shrinkage from the uncured coating film to the cured coating film is small as compared with the conventional aqueous coating composition, regular orientation of the scaly pigment can be obtained. Thereby, there exists an advantage that the coating film excellent in the glitteriness can be formed.

  The aqueous coating composition of the present invention can be suitably used as an aqueous base coating composition that can be used for coating, for example, automobile bodies. On the other hand, the aqueous coating composition of the present invention is not limited to the aqueous base coating composition, and can be suitably used as, for example, an intermediate coating composition or a primer coating composition.

Multilayer coating film forming method The present invention also provides a multilayer coating film forming method obtained by coating the aqueous coating composition as an aqueous base coating composition. As such,
A process of coating a water-based base coating composition on an object to be coated to form an uncured base coating;
The step of applying a clear coating composition on the uncured base coating film to form an uncured clear coating film, and simultaneously heating the resulting uncured base coating film and clear coating film. Curing process,
The method of including is mentioned.

The article to be coated that can be used in the present invention is not particularly limited, and examples thereof include a metal substrate, a plastic substrate, and a foam thereof.

  Examples of the metal substrate include metals such as iron, steel, copper, aluminum, tin, and zinc, and alloys containing these metals. Specific examples of the metal substrate include automobile bodies such as passenger cars, trucks, motorcycles, and buses, and parts for automobile bodies. As for such a metal base material, it is more preferable that the electrodeposition coating film is previously formed. Moreover, chemical conversion treatment (for example, zinc phosphate chemical conversion treatment, zirconium chemical conversion treatment, etc.) as necessary may be performed before the electrodeposition coating film is formed.

  Examples of the plastic substrate include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. Specific examples of the plastic substrate include automobile parts such as spoilers, bumpers, mirror covers, grills, and door knobs. These plastic substrates are preferably washed with pure water and / or a neutral detergent. Moreover, the primer coating for enabling electrostatic coating may be given.

  An intermediate coating film as required may be further formed on the object to be coated. An intermediate coating composition is used for forming the intermediate coating film. In general, the intermediate coating composition contains a film-forming resin, a curing agent, and various pigments (for example, colored pigments, extender pigments, etc.). The film-forming resin and the curing agent are not particularly limited, and for example, a film-forming resin and a curing agent that can be used in the aqueous coating composition of the present invention can be used.

Coating method First, an uncured base coating film is formed by coating the water-based coating composition on an object to be coated.
As coating methods usually used in the coating of water-based paint compositions, multi-stage coating or one-stage coating by air electrostatic spray coating, or air electrostatic spray coating and rotary atomizing electrostatic coating called metallic bell. Examples of methods generally used in the field of automobile body painting, such as a painting method in combination with a machine. These coating methods have the advantage that the coating film obtained has a good coating film appearance.

  In the present specification, the “coating viscosity” means the viscosity at the time when the coating composition is prepared to be used for coating. In the conventional application of a water-based paint composition, it is common that the paint is diluted with water and an organic solvent as necessary before the paint is applied and the paint solid content concentration is lowered. On the other hand, the water-based paint composition used in the present invention has a feature that scale-like pigments are well arranged even when applied in a state of a high paint solid content.

  More specifically, the aqueous coating composition of the present invention is contained in the coating composition when the coating viscosity is adjusted to be 780 to 820 mPa · s at 20 ° C. and 60 rpm as measured by a B-type viscometer. The resin solid content concentration is 25 to 40% by mass. A coating composition having a viscosity of 780 to 820 mPa · s under the above conditions has a viscosity that can be applied suitably in the above-described coating method in a coating line, for example. Adjustment of the coating viscosity to the above range can be performed by diluting the coating composition with water and an organic solvent as necessary (collectively, these are “solvents”).

  In this specification, the coating viscosity of the aqueous coating composition is measured at a coating temperature of 20 ° C. at 60 rpm with a single cylindrical rotary viscometer. Examples of the single cylindrical rotary viscometer include a measuring instrument called a B-type viscometer such as a model TVB10 manufactured by Toki Sangyo Co., Ltd.

  In the method of the present invention, the dry film thickness of the base coating film to be formed is more preferably 3 to 50 μm. The aqueous coating composition used in the method of the present invention is a high resin solids coating composition. Therefore, even when the dry film thickness of the base film thickness is designed to be, for example, 15 to 50 μm, which is thicker than the conventional film thickness, there is an advantage that problems such as sagging during coating hardly occur. The dry film thickness of the formed base coating film is more preferably 5 to 30 μm.

  One of the characteristics of the aqueous coating composition of the present invention is that it is a high solid content coating composition having a resin solids concentration higher than that of a general aqueous coating composition. One of the advantages of the aqueous coating composition of the present invention being a high solid content coating composition is that it is possible to apply a desired film thickness with a smaller number of coatings when forming a coating film. Can be mentioned. Since a general water-based paint composition contains a larger amount of solvent, it is necessary to divide into several layers in order to obtain a desired film thickness in order to prevent the occurrence of problems such as sagging. Sometimes. In contrast, the aqueous coating composition of the present invention is a high solid content coating composition and has a low solvent content. Therefore, there is an advantage that a desired film thickness can be obtained with a smaller number of layers than a general aqueous coating composition.

  More specifically, in the method of the present invention, the solid content concentration in the uncured base coating film formed by applying the aqueous coating composition is more preferably 30 to 70%. Since the aqueous coating composition used in the method of the present invention contains a small amount of solvent, the solid content concentration in the uncured base coating film is in the high concentration range of 30 to 70%. For this reason, there also exists an advantage that it becomes easy to obtain the coating film excellent in the external appearance etc., without causing malfunctions, such as a sagging at the time of thick film coating.

  The solid content concentration in the uncured base coating film can be calculated by the following formula.

Solid content concentration (%) = {(Wc−Wa) / (Wb−Wa)} × 100
Wb: The total mass of the aluminum foil and the uncured base coating film in a state where the aqueous coating composition is coated on the aluminum foil.
Wc: An aluminum foil and a cured base coating in a state where an aqueous coating composition is applied onto aluminum foil, and the resulting uncured base coating is heated at 140 ° C. for 30 minutes and allowed to cool to room temperature in a desiccator. The total mass of
Wa: Mass of aluminum foil.

  An uncured clear coating film may be formed by coating a clear coating composition on an uncured base coating film obtained by applying an aqueous base coating composition. In the method for forming a multilayer coating film according to the present invention, the base coating film obtained by applying this water-based base coating may be baked, and then the clear coating composition may be applied thereon. Further, by applying a clear coating composition on the surface to form a clear coating film, the baking and drying step of the base coating film can be omitted, which is preferable from the viewpoint of economy and environment. In order to obtain a good finished coating film, it is more preferable to heat the uncured base coating film at 40 to 100 ° C. for 2 to 10 minutes before applying the clear coating composition.

  The clear coating composition used in the multilayer coating film forming method of the present invention is not particularly limited, and a clear coating composition containing a coating film forming resin and a curing agent as required can be used. Furthermore, a coloring component can be contained as long as it does not interfere with the design of the base. Examples of the form of the clear coating composition include solvent type, aqueous type and powder type.

  Preferred examples of the solvent-type clear coating composition include a combination of an acrylic resin and / or a polyester resin, an amino resin and / or an isocyanate, or a carboxylic acid / epoxy curing system in terms of transparency or acid etching resistance. An acrylic resin and / or a polyester resin are mentioned.

  Examples of the water-based clear coating composition include those containing a resin obtained by neutralizing a coating film-forming resin contained in the solvent-type clear coating composition described above as an example with a base to make it water-based. This neutralization can be carried out by adding tertiary amines such as dimethylethanolamine and triethylamine before or after polymerization.

  As the powder-type clear coating composition, commonly used powder coatings such as thermoplastic and thermosetting powder coatings can be used. A thermosetting powder coating is preferred because a coating film having good physical properties can be obtained. Specific examples of thermosetting powder coatings include epoxy-based, acrylic-based and polyester-based powder clear coating compositions, but acrylic-based powder clear coating compositions with good weather resistance are particularly preferred. preferable.

  The clear coating composition may contain a viscosity control agent. As a viscosity control agent, what was mentioned by the description about the above-mentioned aqueous coating composition can be used, for example. The clear coating composition may further contain a curing catalyst, a surface conditioner and the like as required.

  In the method for forming a multilayer coating film of the present invention, a base coating film formed by coating the above-mentioned aqueous coating composition containing a coloring component used as a water-based base coating on an object to be coated is aesthetically pleasing to the object to be coated. , Imparts designability.

  The clear coating composition can be applied by a commonly used method according to the form of the coating composition. As a specific example of the method of applying the clear coating composition to the base coating film, for example, a coating method using a rotary atomizing electrostatic coating machine called a microbell can be mentioned.

  The dry film thickness of the clear coating film formed by applying the clear coating composition is generally preferably about 10 to 80 μm, and more preferably about 20 to 60 μm. When the dry film thickness is less than 10 μm, the unevenness of the base cannot be concealed, and when it exceeds 80 μm, there is a possibility that problems such as peeling or sagging may occur during coating.

  The clear coating film thus formed is preferably formed by so-called two-coat one-bake, which is baked together with an uncured base coating film as described above. The baking temperature is preferably set to 80 to 180 ° C., more preferably 120 to 160 ° C., from the viewpoint of the crosslinking density and the properties of the obtained multilayer coating film. The baking time can be arbitrarily set according to the baking temperature, but it is appropriate that the baking time is 120 to 160 ° C. and the baking time is 10 to 40 minutes.

  The film thickness of the multilayer coating film formed by the multilayer coating film forming method of the present invention is generally 20 to 300 μm, and preferably 30 to 250 μm. When the film thickness is less than 20 μm, the strength of the film itself decreases, and when it exceeds 300 μm, film physical properties such as a cooling / heating cycle may decrease.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on mass unless otherwise specified.

Production Example 1 Production of Acrylic Resin Emulsion (Coating Film Forming Resin) 330 g of deionized water was added to a reaction vessel, and the temperature was raised to 80 ° C. while mixing and stirring in a nitrogen stream. Then 11.25 parts acrylic acid, 139 parts n-butyl acrylate, 75 parts methyl methacrylate, 187 parts n-butyl methacrylate, 75 parts 2-ethylhexyl methacrylate, 150 parts 2-hydroxyethyl methacrylate, styrene 112 Parts, thiocalcol 20 (n-dodecyl mercaptan, Kao Corporation, active ingredient 100%) 11.2 parts, latemul PD-104 (emulsifier, Kao Corporation, active ingredient 20%) 74.3 parts, and deionized water 3% of the monomer emulsion consisting of 300 parts and 2.63 parts of ammonium persulfate and 30% of the initiator solution consisting of 90 parts of deionized water were dropped into the reaction vessel in parallel over 15 minutes. After completion of the dropping, aging was performed at the same temperature for 15 minutes.

  Further, the remaining monomer emulsion and the initiator solution were dropped into the reaction vessel in parallel over 180 minutes. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Next, the mixture was cooled to 40 ° C. and filtered through a 200 mesh filter to obtain an acrylic resin emulsion having an average particle size of 200 nm, a nonvolatile content of 49%, a solid content acid value of 15 mgKOH / g, and a hydroxyl value of 85 mgKOH / g.

Production Example 2: Production of phosphoric acid group-containing acrylic resin (dispersant) 40 parts of ethoxypropanol was charged into a 1 liter reaction vessel equipped with a stirrer, a temperature controller, and a cooling tube, and 4 parts of styrene and n-butyl acrylate were added thereto. 35.96 parts, 18.45 parts of ethylhexyl methacrylate, 13.92 parts of 2-hydroxyethyl methacrylate, 7.67 parts of methacrylic acid, 20 parts of ethoxypropanol, phosmer PP (acid phosphooxyhexa (oxypropylene produced by Unichemical) ) Monomethacrylate) 40 parts of a solution in which 20 parts were dissolved and 121.7 parts of a monomer solution consisting of 1.7 parts of azobisisobutyronitrile were added dropwise at 120 ° C. for 3 hours, and stirring was further continued for 1 hour. The obtained resin was an acrylic acid varnish having an acid value of 105 mgKOH / g, of which an acid value of 55 mgKOH / g based on a phosphoric acid group, a hydroxyl value of 60 mgKOH / g and a number average molecular weight of 6000, and a nonvolatile content of 63%.
In this example, the number average molecular weight was measured using “HLC8220GPC” (trade name, manufactured by Tosoh Corporation) as a GPC apparatus, “Shodex KF-606M” and “Shodex KF-603” (both Showa Denko) as columns. The product was manufactured under the conditions of mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow rate: 0.6 cc / min, detector: RI.

Production Example 3: Production of block copolymer 1 (amphiphilic compound) In a reaction vessel, 23.9 parts of tripropylene glycol methyl ether, 16.1 parts of propylene glycol methyl ether, 3 parts of 2-iodo-2-cyanopropane and 0.25 part of dibutylhydroxytoluene was added, and the temperature was raised to 80 ° C. while mixing and stirring in a nitrogen stream. Next, a monomer mixture containing 10 parts of methyl methacrylate, 34.2 parts of ethyl acrylate and 5.8 parts of 2-hydroxyethyl methacrylate was prepared, 50 parts of the monomer mixture, 5 parts of tripropylene glycol methyl ether and 2, An initiator solution consisting of 1 part of 2′-azobis (2,4-dimethylvaleronitrile) was dropped into the reaction vessel in parallel over 90 minutes, and after completion of the dropping, maintained at the same temperature for 0.5 hour, the first stage Aged.
When the molecular weight was measured by GPC after sampling the polymer after the first stage of aging, an approximately unimodal GPC elution curve was obtained, and the number average molecular weight was 6,500 and the weight average molecular weight was 11,500. It was.
A monomer solution comprising 3.1 parts of methyl methacrylate, 34.2 parts of ethyl acrylate, 5.8 parts of 2-hydroxyethyl methacrylate and 6.9 parts of methacrylic acid at the same temperature in the mixture after the first stage aging And an initiator solution consisting of 10.0 parts of tripropylene glycol methyl ether and 2 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) are dropped into the reaction vessel in parallel over 150 minutes. , Kept at the same temperature for 0.5 hours, and the second stage of aging was performed.
When the polymer after the second stage aging was sampled and the molecular weight was measured by GPC, an approximately unimodal GPC elution curve was obtained, and the number average molecular weight was 10,500 and the weight average molecular weight was 20,000. . Compared with the first stage, the GPC curve was shifted to the high molecular weight side while maintaining a unimodality, so the monomer added in the second stage to the end of the polymer chain formed after the aging of the first stage. It is considered that an acrylic resin having a block structure was obtained by adding a polymer chain to extend.
After the second stage of aging, 23.1 parts of the solvent was distilled off at 110 ° C. under reduced pressure (70 torr) with a solvent removal apparatus, and then 180 parts of deionized water and 7.1 parts of dimethylaminoethanol were added to form a non-volatile solution. A block copolymer 1 having a content of 29%, a solid content acid value of 37 mgKOH / g, and a hydroxyl value of 50 mgKOH / g was obtained.

Production Example 4: Production of Block Copolymer 2 (Amphiphilic Compound) The monomer mixture to be added before aging in the first stage is a mixture comprising 25 parts of methyl methacrylate and 25 parts of n-butyl methacrylate, and the second stage. The same procedure as in Production Example 3 except that the monomer mixture to be added before aging was 10 parts of methyl methacrylate and 40 parts of Blemmer PME-400 (manufactured by NOF Corporation, methoxypolyethylene glycol monomethacrylate, 100% active ingredient). After aging in the second stage, 16.1 parts of the solvent was distilled off at 110 ° C. under reduced pressure (70 torr) using a solvent removal apparatus, and 190 parts of deionized water was added to obtain a number average molecular weight of 11, Block copolymer 2 having a weight average molecular weight of 20,500 and a nonvolatile content of 30% was obtained.

Comparative Production Example 1: Production of Copolymer 3 23.9 parts of tripropylene glycol methyl ether and 16.1 parts of propylene glycol methyl ether were added to a reaction vessel, and the mixture was heated to 105 ° C. with mixing and stirring in a nitrogen stream. Next, a monomer mixture containing 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate and 6.9 parts of methacrylic acid was prepared. An initiator solution consisting of 10.0 parts of propylene glycol methyl ether and 1.8 parts of tertiary butyl peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of the dropwise addition, the mixture was kept at the same temperature for 0.5 hours for aging.
Further, an initiator solution consisting of 5.0 parts of tripropylene glycol methyl ether and 0.5 part of tertiary butyl peroxy 2-ethylhexanoate was dropped into the reaction vessel over 0.5 hours. After completion of the dropping, the mixture was kept at the same temperature for 2 hours for aging.
After removing 16.1 parts of solvent at 110 ° C. under reduced pressure (70 torr) using a solvent removal apparatus, 204 parts of deionized water and 7.1 parts of dimethylaminoethanol were added to obtain a non-volatile content of 30%, a number average molecular weight of 10, 500, a weight average molecular weight of 28,500, a solid content acid value of 40 mgKOH / g, and a hydroxyl group value of 50 mgKOH / g were obtained.

Comparative production example 2: Production of copolymer 4 A monomer mixture of 35 parts of methyl methacrylate, 25 parts of n-butyl methacrylate, Blenmer PME-400 (manufactured by NOF Corporation, methoxypolyethylene glycol monomethacrylate, active ingredient 100%) 40 The reaction was carried out in the same procedure as in Comparative Production Example 1 except that the solvent was aging, and after aging, 16.1 parts of the solvent was distilled off at 110 ° C. under reduced pressure (70 torr) using a solvent removal apparatus. In addition, a copolymer 4 having a nonvolatile content of 30%, a number average molecular weight of 10,000 and a weight average molecular weight of 27,000 was obtained.

Example 1
Production of aqueous coating composition 130 parts of acrylic resin emulsion of Production Example 1, 1.8 parts of dimethylaminoethanol, 40 parts of Cymel 327 (mixed alkylated melamine resin, manufactured by Mitsui Cytec Co., Ltd., solid content 90%), flat pigment As an aluminum paste MH-8801 (aluminum flat pigment, manufactured by Asahi Kasei Chemicals Corporation, active ingredient 65%) 22 parts, phosphate group-containing acrylic resin of Production Example 2 5 parts, lauryl acid phosphate 0.4 parts, butyl cellosolve 50 parts , Neugen EA-207D (Amphiphilic compound, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4200, solid content 55%) 5.5 parts (3 parts in terms of solid content) are uniformly dispersed and diluted with deionized water The measured value of the B-type viscometer at a coating temperature of 20 ° C. and 60 rpm is 806 mPa · s, and the resin solid content concentration is 33% by mass. A water-based paint composition was obtained.
In addition, the resin solid content concentration of the water-based paint composition described in the table was calculated and calculated from each component used for the production of the water-based paint composition and the amount of deionized water used for dilution.

Double-layer coating formation Zinc phosphate treated thickness 0.8mm, length 30cm, width 40cm dull steel plate, cationic electrodeposition paint "Power Top U-50" (manufactured by Nippon Paint Co., Ltd.), dry film thickness 20μm In the coating plate that was electrodeposited so as to be baked at 160 ° C. for 30 minutes, a gray intermediate coating paint “Olga OP-30 previously diluted in 25 seconds (using a No. 4 Ford cup and measured at 20 ° C.) was used. (Polyester / melamine paint manufactured by Nippon Paint Co., Ltd.) was air sprayed using an air spray gun W-101-132G manufactured by ANEST IWATA to a dry film thickness of 35 μm, and baked at 140 ° C. for 30 minutes.
After cooling, the aqueous metallic base paint of the previous production example was applied by air spray so as to have a dry film thickness of 15 μm under conditions of room temperature of 23 ° C. and humidity of 68%. After setting for 4 minutes, preheating was performed at 80 ° C. for 5 minutes.
After preheating, the coated plate was allowed to cool to room temperature, and it was coated with Macflow-O-1810 (solvent type clear paint manufactured by Nippon Paint Co., Ltd.) as a clear paint and air sprayed to a dry film thickness of 35 μm and set for 7 minutes. Next, the coated plate was baked at 140 ° C. for 30 minutes with a dryer to obtain a coated test plate having a multilayer coating film.

  The following table shows the structure of the amphiphilic compound contained in the aqueous coating composition (the structure of the hydrophobic part (A) and the hydrophilic part (B), the structure constituted by the hydrophobic part (A) and the hydrophilic part (B). , And the number average molecular weight of the amphiphilic compound). The number average molecular weight is a value measured by a GPC method using polystyrene as a standard, using HLC-8220 manufactured by Tosoh Corporation.

  The coating viscosity of the aqueous coating composition shown in the table below is measured at 60 rpm and a coating temperature of 20 ° C. using a B-type viscometer (single cylinder rotary viscometer) of model TVB10 manufactured by Toki Sangyo Co., Ltd. Measurements were made.

Examples 2 to 15 and Comparative Examples 2 to 12
The type of amphiphilic compound was changed to that shown in the table below, and the same procedure as in Example 1 was conducted except that the amount of amphiphilic compound was 3 parts in terms of solid content. A water-based coating composition was prepared. Using the obtained aqueous coating composition, a multilayer coating film was formed in the same manner as in Example 1.

Example 16
An aqueous coating composition was prepared in the same manner as in Example 1 except that the amount of Neugen EA-207D was changed to 0.9 parts (0.5 parts in terms of solid content). Using the obtained aqueous coating composition, a multilayer coating film was formed in the same manner as in Example 1.

Example 17
An aqueous coating composition was prepared in the same manner as in Example 1 except that the amount of Neugen EA-207D was changed to 18.3 parts (10 parts in terms of solid content). Using the obtained aqueous coating composition, a multilayer coating film was formed in the same manner as in Example 1.

Comparative Example 1
An aqueous coating composition was prepared in the same manner as in Example 1 except that no amphiphilic compound was used. Using the obtained aqueous coating composition, a multilayer coating film was formed in the same manner as in Example 1.

  About the coating film obtained by the said Example and comparative example, it evaluated as follows. The results obtained are shown in the table below.

Flip-flop evaluation (FF characteristics)
The FF value measured using a laser-type metallic feeling measuring device (trade name: Alcorp LMR-200, manufactured by Kansai Paint Co., Ltd.) was used as an index of flip-flop properties. It shows that flip-flop property is so strong that FF value is large. The flip-flop evaluation is 1.41 or more according to the following criteria.
○: Flip-flop value 1.51 or more Δ: Flip-flop value 1.41 or more and less than 1.51 ×: Flip-flop value less than 1.41

  In the present invention, "strong flip-flop" means that the metallic coating film is visually observed, white from the front direction (perpendicular to the coating surface), and excellent in glitter as glitter, From the diagonal direction, there is little glitter and the hue is clearly visible, which means that the brightness difference between the two is large. That is, a metallic coating film whose metallic feeling changes remarkably depending on the viewing angle is referred to as “strong flip-flop” and has excellent design.

In the table above,
Oleic acid (manufactured by Kishida Chemical),
New Coal 719 (Nippon Emulsifier Co., Ltd.),
Emulgen 104P, Emulgen 409PV, Emulgen 109P, Emulgen 123P, Emulgen 2025G, Emulgen A-500, Emanon 3299V (all manufactured by Kao Corporation),
Neugen EA-137, Neugen EA-167, Neugen XL-100, Neugen EA-207D, Neugen EA-197D, Neugen XL-400D, Neugen XL-1000, DKS NL-600F, Epan 485, Epan 720, Epan 750, Epan 785, Epan U-108 (all made by Daiichi Kogyo Seiyaku Co., Ltd.),
It is.
*: The molecular weight of oleic acid was calculated according to the chemical structural formula.

As shown in the above table, the multilayer coating film obtained using the aqueous coating composition of the example has high FF properties, excellent glitter, and a good coating film appearance. It was confirmed that
In Comparative Example 1 and Comparative Examples 2 to 12 that do not contain an amphiphilic compound in the present invention, it was confirmed that the FF value was small and the glitter of the coating film was poor. On the other hand, when a multilayer coating film is formed using the aqueous coating composition of the present invention, even if it is applied at the same high resin solid content concentration as that of the comparative example, the FF value is large, and the coating film has a glittering feeling. It was confirmed to be excellent.

Even if the aqueous coating composition of the present invention is a high resin solid content coating composition, the multi-layer coating having excellent glitter properties in which the scaly pigment is well oriented in a state along the surface shape of the coating object. A film can be formed. In the aqueous coating composition of the present invention, the amount of the solvent contained in the composition is small as compared with a general aqueous coating composition. Therefore, by using the water-based paint composition of the present invention, the volume of the paint necessary for painting the desired dry film thickness is reduced, and the environmental burden during the production, transportation, and heat curing after painting is reduced. Can be reduced. By using the water-based coating composition of the present invention, the energy required during the production, transportation, and heat-curing after coating can be reduced, and the amount of CO ₂ emission can be reduced. Furthermore, since the water-based coating composition of the present invention requires a smaller amount of coating composition per unit coating area than the conventional coating composition, the manufacturing cost, transportation cost, storage cost and coating cost of the coating composition There is an advantage that can be reduced.

Claims (8)

An aqueous coating composition comprising a coating film-forming resin, a curing agent, a scaly pigment, and an amphiphilic compound,
The amphiphilic compound is a compound having at least one hydrophobic part (A) as a repeating unit and at least one hydrophilic part (B) as a repeating unit, wherein
The hydrophobic part (A) includes a propylene oxide group, a butylene oxide group, a linear or branched saturated hydrocarbon group having 4 to 40 carbon atoms, a linear or branched non-carbon group having 4 to 40 carbon atoms. Having at least one group selected from the group consisting of a saturated hydrocarbon group, an aromatic ring-containing group having 6 to 40 carbon atoms having an aromatic ring, and a hydrophobic polymer segment;
The hydrophilic part (B) has at least one group selected from the group consisting of an ethylene oxide group and an acid group, and the amphiphilic compound has a number average molecular weight of 1500 to 100,000.
When the water-based coating composition is adjusted so that the viscosity by a B-type viscometer is 780 to 820 mPa · s at 20 ° C. and 60 rpm, the resin solid content concentration contained in the coating composition is 25 to 25. 40% by weight,
Water-based paint composition.   The aqueous coating composition according to claim 1, wherein the hydrophobic part (A) of the amphiphilic compound has an aromatic ring-containing group having 6 to 40 carbon atoms and having an aromatic ring.   The aqueous coating composition according to claim 1 or 2, wherein the hydrophobic part (A) of the amphiphilic compound is an aromatic ring-containing group having 12 to 40 carbon atoms and having 2 to 4 aromatic rings.   The aqueous coating composition according to claim 1, wherein the coating film-forming resin includes an acrylic resin emulsion.   The water-based coating composition in any one of Claims 1-4 whose mass ratio (PWC) of the scale-like pigment with respect to the resin solid content contained in the said water-based coating composition is 5 to 30%. A process of coating a water-based base coating composition on an object to be coated to form an uncured base coating;
The step of coating the clear coating composition on the resulting uncured base coating to form an uncured clear coating, and heating the resulting uncured base coating and clear coating simultaneously. Curing process,
A method for forming a multilayer coating film, comprising:
The water-based paint composition is the water-based paint composition according to any one of claims 1 to 5.
A method for forming a multilayer coating film.   The method for forming a multilayer coating film according to claim 6, wherein the dry film thickness of the base coating film formed by the method is 3 to 50 μm.   A multilayer coating film obtained by the multilayer coating film forming method according to claim 6 or 7.

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