JP2007056161A - Water-based metallic coating and method for forming multi-layered coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based coating composition which maintains the excellent characteristics of a water-based metallic coating and can simultaneously give coating films capable of holding an excellent flip-flop property by a two-coat, one base coating method. <P>SOLUTION: This water-based coating composition comprising a coating film-forming resin, a curing agent and a bright pigment is characterized in that the coating film-forming resin comprises an acrylic resin emulsion obtained by a two step emulsion polymerization method using a monomer mixture containing a two or more unsaturated double bond-having unsaturated monomer in an amount of 0.05 to 30.0 mass% based on the solid content of the coating film-forming resin, and having an acid value of 1 to 30 mgKOH/g, a hydroxyl group value of 10 to 150, and a particle diameter of 20 to 140 nm; the curing agent is a hydrophobic melamine resin aqueous dispersion having a particle diameter of 20 to 140 nm; and a specific urethane-based compound is contained in an amount of 0.01 to 20 mass% based on a resin content in the coating composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water-based metallic paint, a multilayer coating film forming method using the same, and a multilayer coating film obtained by the forming method.

  As water-based paints used in automobile coatings, paints containing resins such as acrylic resins having functional groups such as carboxyl groups and hydroxyl groups and melamine resins as crosslinking agents are used. As a cross-linking agent, a hydrophobic melamine resin is often used despite being used in an aqueous medium.

  When a hydrophobic melamine resin is used as a crosslinking agent in the water-based paint, there is a problem that water dispersibility is poor. As techniques for solving such problems, Patent Documents 1 (Japanese Patent Laid-Open No. 53-99232) and 2 (Japanese Patent Laid-Open No. 2004-315623) describe a hydrophobic melamine resin, a specific acid value, and a hydroxyl value. It has been proposed to use an aqueous resin dispersion obtained by reacting with an acrylic resin having a molecular weight, an alkyd resin, or the like as a crosslinking agent, but the water dispersibility is not satisfactory.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-308993) includes an acrylic resin (A) having a weight average molecular weight of 5,000 to 100,000, an acid value of 10 to 100 mgKOH / g, and a hydroxyl value of 20 to 200 mgKOH / g, and a hydrophobic melamine resin (B). And a reaction product obtained by heating the polyester resin (C), and an aqueous resin dispersion having a viscosity increase rate of 20 to 200% before and after the heating treatment is disclosed. This is intended to improve performance such as water dispersibility by modifying a hydrophobic melamine resin using a high acid value acrylic resin or the like.

  On the other hand, Patent Documents 4 (Japanese Patent Laid-Open No. 63-193968) and 5 (Japanese Patent Laid-Open No. 07-041729) disclose a hydrophobic melamine resin, a specific acid value, a hydroxyl value, and a molecular weight in an aqueous metallic paint. It has been proposed to use an aqueous resin dispersion obtained by dispersing with a graft resin, acrylic resin, alkyd resin or the like as a crosslinking agent, but water dispersibility is not satisfactory.

The present inventors also filed several patents and proposed water-based colored paints mainly composed of acrylic resins using hydrophobic melamine resins (Japanese Patent Application No. 2004-332110; Patent Document 6 and Japanese Patent Application No. 2004-2004). 349019; Patent Document 7).
The techniques of Patent Documents 6 and 7 can improve the dispersibility of the hydrophobic melamine resin and provide a coating film having excellent color developability, recoat adhesion, chipping properties, and water-resistant adhesion.

However, using the above-mentioned water-based colored paint as a metallic base paint, after applying the metallic base paint, apply the clear paint without curing the metallic base paint, and apply both the metallic base paint and the clear paint once. When it is used for the production of metallic composite coatings that are heat-cured (so-called two-coat / one-bake), the metallic feeling obtained with a metallic base single layer and the multilayer after forming a clear coating on the metallic coating There may be a difference in appearance between the metallic feeling of the coating film. When painting a metallic coating and a clear coating by the two-coat / one-bake method, as shown in Fig. 1, before moving from the metallic coating to the clear coating, it is dried at a low temperature for a short time (for example, at 80 ° C for about 5 minutes). Apply the clear paint after the preheating process. However, preheating alone is not enough to fix the glitter pigment, and when clear paint is applied on an uncured metallic coating, clear coating (often solvent-based coating) affects the metallic coating, This is because the orientation of the glitter pigment is disturbed. As shown in FIG. 2, the orientation of the glitter pigment is ideally arranged in parallel. However, as schematically shown in FIG. Orientation is disturbed when clear paint is applied.
JP-A-53-99232 JP 2004-315623 A JP 2002-308993 A JP-A-63-193968 Japanese Patent Application Laid-Open No. 07-041729 Japanese Patent Application No. 2004-332110 Japanese Patent Application No. 2004-349019

  The present invention maintains the excellent properties of the above-described water-based metallic paints of the present inventors, such as color development, recoat adhesion, chipping property, water adhesion resistance, etc., and orientation of glitter pigments in a two-coat one-bake coating method. Is a water-based metallic paint composition that provides a coating film that is not disturbed before and after the application of clear paint and does not change in flip-flop properties and can maintain excellent flip-flop properties, and a two-coat one-bake coating method using the same, and further An object of the present invention is to provide a multilayer coating film having excellent flip-flop properties obtained therefrom.

（式中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４及びＲ^５は、互いに同一でも異なってもよい炭化水素基を表し、Ｒ^１は、ウレタン結合を有していてもよい炭化水素基を表し、Ｒ^３は分岐鎖又は２級の炭化水素基を表し、ｎは２以上の自然数であり、ｊは一般式（１）においては１以上、一般式（２）においては２以上の自然数であり、ｋ及びｍは１〜５００の範囲内の自然数である。）で表されるウレタン系化合物を塗料組成物中の樹脂固形分に対して、０．０１〜２０質量％の量で含有し、かつずり速度１０^４／ｓにおける塗料粘度が１５ｍＰａ・ｓ以下であることを特徴とする水性メタリック塗料組成物を提供する。 That is, the present invention is a water-based metallic paint containing a film-forming resin, a curing agent and a glitter pigment,
The film-forming resin is a two-stage emulsification using a monomer mixture containing 0.05 to 30.0% by mass of an unsaturated monomer having two or more unsaturated double bonds based on the solid content of the film-forming resin. It contains an acrylic resin emulsion obtained by polymerization and having an acid value of 1 to 30 mg KOH / g, a hydroxyl value of 10 to 150, and a particle size of 20 to 140 nm.
The curing agent is a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm, and is further represented by the general formula (1) or (2)

(In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ represent a hydrocarbon group which may be the same or different from each other, and R ¹ represents a hydrocarbon group which may have a urethane bond. R ³ represents a branched chain or a secondary hydrocarbon group, n is a natural number of 2 or more, j is a natural number of 1 or more in the general formula (1), and 2 or more in the general formula (2). And k and m are natural numbers in the range of 1 to 500.) The urethane compound represented by the formula (1) is contained in an amount of 0.01 to 20% by mass relative to the resin solid content in the coating composition. Also provided is an aqueous metallic coating composition characterized by having a coating viscosity of 15 mPa · s or less at a shear rate of 10 ⁴ / s.

  The unsaturated monomer having two or more unsaturated double bonds of the present invention includes ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth). It is selected from the group consisting of acrylate, glycerin di (meth) acrylate, and allyl (meth) acrylate.

The present invention also includes a step (I) of forming a metallic base coating film by applying a water-based metallic base coating material on an object to be coated, and applying a clear coating on the metallic base coating film without curing it. A method for forming a multilayer coating film comprising a step (II) of forming a coating film, and a step (III) of simultaneously heating the metallic base coating film and the clear coating film,
Provided is a method for forming a multilayer coating film, wherein the water-based metallic base paint is as described above.
The present invention further provides a multilayer coating film obtained by the multilayer coating film forming method.

  In the water-based metallic paint of the present invention, the emulsion particles of the acrylic resin emulsion which is a film-forming resin are three-dimensionalized due to the presence of unsaturated monomers having two or more unsaturated double bonds in one molecule. Even when the clear paint is applied, it is possible to effectively prevent the orientation of the glittering pigment from being disturbed by the influence of the clear paint (particularly, an organic solvent type clear paint). Moreover, since the water-based metallic coating composition of the present invention contains the urethane compound represented by the general formulas (1) and (2), the coating viscosity at the time of coating is low and coating is easy. Furthermore, since it shows a high viscosity after coating, the retainability of the orientation of the glitter pigment becomes higher.

  The aqueous metallic paint of the present invention can basically provide a coating film having excellent color developability. Moreover, when it uses for the multilayer coating-film formation method, the multilayer coating film which has the outstanding recoat adhesiveness, chipping property, water-resistant adhesion, and coloring property can be obtained.

Hereinafter, the present invention will be described in detail.
Aqueous metallic paint The aqueous metallic paint of the present invention comprises a film-forming resin, a curing agent and a glitter pigment, and the above-mentioned film-forming resin contains two or more unsaturated double coatings. Obtained by two-stage emulsion polymerization using a monomer mixture containing 0.05 to 30.0% by mass of an unsaturated monomer having a bond with respect to the solid content of the film-forming resin, an acid value of 1 to 30 mg KOH / g, and a hydroxyl value of 10 -150 and an acrylic resin emulsion having a particle size of 20 to 140 nm, and the curing agent contains a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm.

In the present invention, as described above, when forming an acrylic resin emulsion that is a film-forming resin, an unsaturated monomer having two or more unsaturated double bonds may be contained as a component of the acrylic monomer. is necessary. When an unsaturated monomer having two or more unsaturated double bonds is used in forming an acrylic resin emulsion, a crosslinking reaction occurs in the acrylic resin emulsion, and a three-dimensional acrylic resin emulsion is obtained.

  The present inventors presume that the use of the three-dimensional acrylic resin emulsion can prevent the disorder of the orientation of the glitter pigment due to the following reasons. The disorder of the orientation of the glittering pigment that occurs when the metallic base paint of the present invention is applied and then the clear paint is applied. The clear paint solvent penetrates into the metallic base coating film when the clear paint is applied. It is thought to occur by swelling the emulsion particles. Therefore, it is assumed that the use of a three-dimensional acrylic resin emulsion can prevent swelling caused by the solvent of such a clear paint, and can effectively prevent disorder of the orientation of the glitter pigment.

  Moreover, in this invention, the urethane type compound represented by General formula (1) or (2) is contained. This urethane compound is thought to contribute to the control of the viscosity of the paint, and the viscosity decreases under the shearing force applied when painting with a paint gun, and the viscosity rises when applied on the substrate. It is considered that the film functions to maintain the orientation of the glitter pigment.

  Further, in the formation of a multilayer coating film in automobile coating, when the above-mentioned aqueous metallic paint is used, it is formed using a paint containing the hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm together with the acrylic resin emulsion. Therefore, a multilayer coating film excellent in recoat adhesion, chipping resistance, and water adhesion resistance can be obtained.

Coating film-forming resin The coating film-forming resin comprises a monomer mixture containing 0.05 to 30.0% by mass of an unsaturated monomer having two or more unsaturated double bonds based on the solid content of the coating film-forming resin. It is an acrylic resin emulsion obtained by the two-stage emulsion polymerization used, having an acid value of 1 to 30 mg KOH / g, a hydroxyl value of 10 to 150, and a particle size of 20 to 140 nm.

Acrylic resin emulsion The acrylic resin emulsion has an acid value of 1 to 30 mgKOH / g. If it is less than 1 mgKOH / g, the stability of the emulsion may be lowered. If it exceeds 30 mgKOH / g, the water resistance of the resulting coating film may be reduced. It is preferable that it is 3-25 mgKOH / g.

  The acrylic resin emulsion has a hydroxyl value of 10 to 150. If it is less than 10, the physical properties of the coating film may be lowered. When it exceeds 150, there exists a possibility that the water resistance of the coating film obtained may fall. It is preferable that it is 15-120. In addition, the acid value of the said acrylic resin emulsion is a measured value, and a hydroxyl value is the value calculated | required by calculation from the compounding quantity of the various unsaturated monomers used for the synthesis | combination.

  The particle diameter of the acrylic resin emulsion is in the range of 20 to 140 nm. When the particle diameter is less than 20 nm, there is a risk that the coating solid content (NV) is significantly reduced. When exceeding 140 nm, there exists a possibility that the coloring property of the coating film obtained may fall.

The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions. More preferably, it is 30-120 nm, and still more preferably 50-100 nm. In addition, the particle size of the acrylic resin emulsion and the hydrophobic melamine resin dispersion according to the present invention is ELS-800 (manufactured by Otsuka Electronics Co., Ltd.), which is a particle size measuring device using a dynamic light scattering method, and It is an average dispersed particle size value measured according to the above conditions.
Sample; infinite dilution with ion-exchanged water Measurement temperature: 25 ° C

  In the present invention, the acrylic resin emulsion has an unsaturated monomer having two or more unsaturated double bonds as an essential monomer, and other raw materials such as a carboxylic acid group-containing unsaturated monomer and a hydroxyl group-containing unsaturated monomer. And those emulsified by emulsion polymerization. The acrylic resin emulsion used in the present invention is preferably a so-called core-shell type acrylic resin emulsion having a core part and a shell part by two-stage emulsion polymerization.

  When the coating film-forming resin contains a core-shell type acrylic resin emulsion, the core part is a core monomer mixture containing a carboxylic acid group-containing unsaturated monomer having an acid value of 0 to 100 mgKOH / g. It is preferable that it is obtained by emulsion polymerization. If it exceeds 100 mgKOH / g, the water resistance of the resulting coating film may be reduced. More preferably, it is 0-50 mgKOH / g. In addition, the acid value of the said core part is an acid value of the acrylic resin emulsion obtained by emulsion polymerization of the 1st step.

  The shell part is preferably obtained by emulsion polymerization of a shell monomer mixture containing a carboxylic acid group-containing unsaturated monomer having an acid value of 25 to 200 mgKOH / g. When the acid value is less than 25 mgKOH / g, the stability of the emulsion may be lowered, and the coating workability may be insufficient. If it exceeds 200 mgKOH / g, the water resistance of the resulting coating film may be reduced. Preferably it is 30-180 mgKOH / g.

  The monomer mixture for the core and / or the monomer mixture for the shell needs to contain an unsaturated monomer having two or more unsaturated double bonds as an essential monomer. It is necessary for unsaturated monomers having two or more unsaturated double bonds to form a crosslinked structure in the emulsion particles and not be affected by the clear paint applied to the upper layer. Unsaturated monomers having two or more unsaturated double bonds may be included in either the core monomer mixture or the shell monomer mixture or both, but are included in both the core monomer mixture and the shell monomer mixture It is preferable to minimize the influence from the clear paint. The use amount of the unsaturated monomer having two or more unsaturated double bonds is 0.05 to 30.0% by mass, preferably 0.5 to 10.0% by mass, based on the solid content of the film-forming resin. More preferably, it is 1.0-5.0 mass%. If it is less than 0.05% by mass, the effect of adding this monomer cannot be obtained. When it exceeds 30.0 mass%, it will become difficult to synthesize an acrylic resin emulsion. As used herein, the resin for forming a coating film refers to an acrylic resin emulsion obtained by two-stage emulsion polymerization.

  The core monomer mixture and / or the shell monomer mixture may have a hydroxyl group. The hydroxyl value is 10 to 150, preferably 15 to 120. If the hydroxyl value is less than 10, sufficient curability may not be obtained. If it exceeds 150, various performances of the resulting coating film may be deteriorated.

  Further, the core monomer mixture and / or the shell monomer mixture may contain the other ethylenically unsaturated monomers. Moreover, it is preferable that the glass transition temperature (calculated value from monomer mixing | blending) of the said core-shell type acrylic resin emulsion is -20-80 degreeC from a viewpoint of the physical property of the coating film obtained.

  The unsaturated monomer having two or more unsaturated double bonds is not particularly limited as long as it is a vinyl monomer having two or more unsaturated groups capable of radical polymerization in the molecule. Specifically, for example, vinyl compounds such as divinylbenzene and divinylsulfone; (meth) allyl (meth) acrylate (hereinafter, both allyl and methallyl are expressed as (meth) allyl), diallyl or dimethallyl phthalate, (Meth) allyl compounds such as di (meth) allyl (meth) acrylamide, tri (meth) allyl cyanurate or isocyanurate, tri (meth) allyl trimellitate, bis ((meth) allylnadiimide); mono or polyethylene Mono- or polyoxyalkylene glycol di (meth) acrylate such as glycol di (meth) acrylate, mono- or polypropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythrin Ritorutori (meth) acrylate, glycerol tri (meth) acrylate of (meth) acrylate compounds. In addition, allyloxy polyethylene glycol polypropylene glycol monoacrylate (Blenmer AKEP manufactured by NOF Corporation), dicyclomentenyl acrylate (FANCRYL FA-511A manufactured by Hitachi Chemical Co., Ltd.), dicyclomentenyloxyethyl acrylate (FANCRYL FA- manufactured by Hitachi Chemical Co., Ltd.) 512A), dicyclomentenyloxyethyl methacrylate (FANCRYL FA-512M manufactured by Hitachi Chemical Co., Ltd.), dihydrodicyclopentadienyl acrylate (commercial product from BASF), 3-cyclohexenylmethyl methacrylate (commercial product from Daicel) ), 3-cyclohexenylmethyl acrylate (commercial product from Daicel), butanediol-1,4-divinyl ether (commercial product from BASF), triallyl isocyanurate (TAIC manufactured by Nippon Kasei Co., Ltd.) It is available. In the present invention, among these, allyl methacrylate or ethylene glycol di (meth) acrylate is preferable. Particularly preferably, an unsaturated monomer having two or more unsaturated double bonds of 4 atoms or less, preferably 3 atoms or less, when the distance between the unsaturated double bonds is expressed by the number of atoms, Specific examples include allyl methacrylate. In addition, the unsaturated monomer which has two or more unsaturated double bonds can be used individually or in mixture of 2 or more types.

  The carboxylic acid group-containing unsaturated monomer is not particularly limited. For example, acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, 2-acryloyl Oxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid, ω-carboxy-polycaprolactone mono (meth) 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 and the like can be mentioned.

  Examples of the hydroxyl group-containing unsaturated monomer include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacrylic alcohol, and ε- of hydroxyethyl (meth) acrylate. A caprolactone adduct can be mentioned. Among these, preferred are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and ε-caprolactone adduct of hydroxyethyl (meth) acrylate.

  Examples of the other ethylenically unsaturated monomers include, for example, (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion [methyl (meth) acrylate or ethyl (meth) acrylate]; carbon number in the ester portion. 3 or more (meth) acrylic acid esters [for example, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl methacrylate, Phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, dihydrodicyclopentadienyl (meth) acrylate, etc.] Polymerizable amide compounds [for example, (meth) acrylamide, N-methylol (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, 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, α-methylstyrene , Vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.]; polymerizable nitriles (eg, acrylonitrile, methacrylonitrile, etc.); α-olefins (eg, ethylene, propylene, etc.); vinyl esters (eg, vinyl acetate) , Propionic acid Alkylsulfonyl and the like] and the like.

  The monomer mass ratio of the core monomer mixture / shell monomer mixture [core portion / shell portion] is preferably 50/50 to 98/2, and more preferably 65/35 to 95/5. . When the shell ratio is larger than 50/50, the stability of the emulsion is lowered, and when the shell ratio is smaller than 98/2, the water resistance of the resulting coating film may be lowered.

  The emulsion polymerization for obtaining the acrylic resin emulsion can be carried out using a generally well-known method. Specifically, the emulsifier is dissolved in water or an aqueous medium containing an organic solvent such as alcohol as necessary, and the monomer mixture for core or the monomer mixture for shell and the polymerization initiator are heated and stirred. This can be done by dripping. A core monomer mixture or a shell monomer mixture emulsified in advance using an emulsifier and water may be similarly dropped.

  Examples of the polymerization initiator include azo oily compounds (for example, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvalero). Nitrile) etc.) and aqueous compounds (eg, anionic 4,4′-azobis (4-cyanovaleric acid), cationic 2,2′-azobis (2-methylpropionamidine)); and redox Oily peroxides (for example, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, etc.) and aqueous peroxides (for example, potassium persulfate, ammonium peroxide, etc.) are preferred.

  Examples of the emulsifier include those often used by those skilled in the art. In particular, reactive emulsifiers such as Antox MS-60 (trade name, manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS- 2 (trade name, manufactured by Sanyo Kasei Kogyo Co., Ltd.), Adekaria soap NE-20 (trade name, manufactured by Asahi Denka Co., Ltd.), Aqualon HS-10 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and the like are preferable.

  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 polymerization initiator, and for example, it is preferably 60 to 90 ° C. for an azo initiator and 30 to 70 ° C. for a redox initiator. In general, the reaction time is 1 to 8 hours. The content of the polymerization initiator based on the total mass of the core monomer mixture and the shell monomer mixture is generally 0.1 to 5% by mass, and preferably 0.2 to 2% by mass.

  The acrylic resin emulsion can be used at a pH of 3 to 10 by neutralizing with a base as necessary. This is because the stability in this pH region is high. This neutralization is preferably performed by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

  The content of the acrylic resin emulsion in the aqueous metallic paint is preferably 5 to 95% by mass, more preferably 10 to 85% by mass in the solid content of the paint, and 20 to 70% by mass. More preferably. When the said content is outside the said range, there exists a possibility that coating workability | operativity and the external appearance of the coating film obtained may fall.

Curing Agent The curing agent used in the production method of the present invention is a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm. The hydrophobic melamine resin aqueous dispersion is a dispersion of resin particles having a particle diameter of 20 to 140 nm obtained by reacting a specific acrylic resin and a hydrophobic melamine resin in water. Since such a hydrophobic melamine resin aqueous dispersion is used, a coating film having excellent color developability can be obtained.

  Moreover, when the said hydrophobic melamine resin aqueous dispersion is used, the multilayer coating film which has the outstanding recoat adhesiveness, chipping resistance, and water-resistant adhesion property can be obtained. If it is less than 20 nm, a significant reduction in the solid content of the paint occurs. If the thickness exceeds 140 nm, the water dispersibility is lowered, and the adhesion and surface smoothness of the formed coating film may be lowered. It is preferable that it is 30-120 nm, and it is more preferable that it is 50-100 nm. In addition, the said particle diameter is the value measured by the method similar to the particle diameter of the acrylic resin emulsion mentioned above.

  As the hydrophobic melamine resin aqueous dispersion, an acrylic resin having an acid value of 20 to 100 mgKOH / g, a hydroxyl value of 10 to 100, and a number average molecular weight of 5000 to 15000 and a hydrophobic melamine resin are 5/95 to 50/50. It is preferable to be obtained by a production method including a step (1) of mixing and reacting at a mass ratio and a step (2) of dispersing the reaction product obtained in the above step (1) in water. As a result, the hydrophobic melamine can be present uniformly and stably in the coating film, so that the aggregation caused by the contact of the glitter pigment and / or the coloring pigment with the hydrophobic melamine can be suppressed. Therefore, good color developability can be imparted to the resulting coating film. At the same time, the coating film obtained can be provided with good recoat adhesion, chipping resistance, and water adhesion resistance.

  In the step (1), first, an acrylic resin having an acid value of 20 to 100 mgKOH / g, a hydroxyl value of 10 to 100, and a number average molecular weight of 5000 to 15000 and a hydrophobic melamine resin are in a mass ratio of 5/95 to 50/50. The process of mixing and reacting is performed. By performing the step (1), a reaction product of the acrylic resin and the hydrophobic melamine resin can be obtained.

  The acrylic resin has an acid value of 20 to 100 mgKOH / g. When it exceeds 100 mgKOH / g, reaction control becomes extremely difficult. If the acid value is less than 20 mgKOH / g, the particle size may exceed 140 nm. It is preferable that it is 40-80 mgKOH / g.

  The acrylic resin has a hydroxyl value of 10-100. If it is less than 10, the particle size may exceed 140 nm. If it exceeds 100, the reaction control may be extremely difficult. It is preferable that it is 40-80.

  The acrylic resin has a number average molecular weight of 5000 to 15000. If it is less than 5000, the particle size may exceed 140 nm. If it exceeds 15,000, reaction control may be extremely difficult. It is preferable that it is 7000-11000. The number average molecular weight of the acrylic resin is a value measured with a polystyrene standard by the GPC method.

  A conventionally known hydrophobic melamine resin can be used, but the solubility parameter δ (SP) is preferably in the range of 9.0 ≦ SP ≦ 11.5. If it is less than 9.0, the particle size may exceed 140 nm. When it exceeds 11.5, the particle size exceeds 140 nm, and when it is formed into a coating film, the performance such as water resistance may be deteriorated. It is more preferable that 9.5 ≦ SP ≦ 11.0.

  The solubility parameter δ is generally called SP (solubility parameter) among those skilled in the art, and is a scale indicating the degree of hydrophilicity or hydrophobicity of the resin, and the compatibility between the resins. It is also an important measure for judging. The solubility parameter can be numerically quantified based on, for example, a turbidity measurement method (reference document: kW Suh, DH Clarke J. Polymer. Sci., A-1, 5). , 1671 (1967).). The solubility parameter δ in the present specification is a parameter determined by a turbidity measurement method. The solubility parameter by the turbidity measurement method is, for example, dissolving a resin solid content (predetermined mass) to be measured in a certain amount of good solvent (acetone, etc.) and then dropping a poor solvent such as water or hexane. From the respective titration amounts until the resin is insolubilized and turbidity is generated in the solution, it can be determined by a known calculation method described in the above-mentioned reference or the like.

  In the step (1), the mixing ratio of the acrylic resin and the hydrophobic melamine resin is preferably 5/95 to 50/50 (mass ratio, acrylic resin / hydrophobic melamine resin). If the blending amount of the acrylic resin is less than 5/95, the particle size may exceed 140 nm. When the blending amount of the acrylic resin is larger than 50/50, there is a possibility that the NV (solid content concentration) of the coating material may be remarkably lowered or reaction control may be extremely difficult. More preferably, it is 10 / 90-40 / 60. In addition, the mixing method of an acrylic resin and hydrophobic melamine resin can be performed by a conventionally well-known method.

  In the present invention, in the above step (1), since the blending amount of the acrylic resin with respect to the hydrophobic melamine resin is small, when the obtained hydrophobic melamine resin aqueous dispersion is used as the curing agent, the function as the curing agent is lowered. There are few things. And although there are few compounding quantities of an acrylic resin, the particle size after water dispersion is 20-140 nm. For this reason, the hydrophobic melamine resin aqueous dispersion obtained by this invention can be used suitably as a hardening | curing agent of water-based metallic paint. In the step (1), in addition to the acrylic resin and the hydrophobic melamine resin, other resins such as a polyester resin may be included within the range not excluding the effect of the present invention.

  In the step (1), the reaction temperature between the acrylic resin and the hydrophobic melamine resin is preferably 70 to 100 ° C., more preferably 75 to 90 ° C. Moreover, it is preferable that reaction time is 1 to 10 hours, and it is more preferable that it is 1 to 5 hours. If it is less than the lower limit, the particle size may exceed 140 nm. If the upper limit is exceeded, reaction control may be extremely difficult.

  In the said process (2), the process obtained by carrying out the water dispersion of the reaction product obtained by performing the said process (1) obtains the hydrophobic melamine resin aqueous dispersion with a particle size of 20-140 nm. . By performing the step (2), an aqueous dispersion (aqueous dispersion) in which resin particles having a particle diameter of 20 to 140 nm are dispersed in water can be obtained.

  In the step (2), the method for water-dispersing the reaction product obtained in the step (1) is not particularly limited, and an ordinary resin water-dispersing method can be used. After cooling to a temperature of 50 ° C. or lower, it is preferable to disperse in water by diluting with water. Thereby, a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm can be suitably obtained. If it is not cooled to 50 ° C. or lower, it may not be possible to obtain a particle size of 20 to 140 nm. It is more preferable to disperse in water by cooling to 30 to 40 ° C. and then diluting with water.

  In the said process (2), pH can be used at 6.5-10 by neutralizing with a base as needed. This is because the stability in this pH region is high. This neutralization is preferably performed by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after the reaction between the acrylic resin and the hydrophobic melamine resin. In particular, after the reaction between the acrylic resin and the hydrophobic melamine resin, a tertiary amine is added, and then the reaction product is cooled to a temperature of 50 ° C. or lower and then diluted with water to disperse the water. It is particularly preferable to do this. Thereby, a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm can be suitably obtained.

Specific urethane compound The urethane compound contained in the aqueous metallic paint composition of the present invention is represented by the general formula (1) or (2).

(In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ represent a hydrocarbon group which may be the same or different from each other, and R ¹ represents a hydrocarbon group which may have a urethane bond. R ³ represents a branched chain or a secondary hydrocarbon group, n is a natural number of 2 or more, j is a natural number of 1 or more in the general formula (1), and 2 or more in the general formula (2), k and m are natural numbers within the range of 1 to 500.)

Examples of the urethane compound represented by the general formula (1) include one or more mono- or polyisocyanates represented by R ^1- (NCO) j and HO- (R ² -O) k. It can be obtained by reacting as a raw material one or more polyether monoalcohols represented by —R ³ . In this case, R ^{1 to} R ³ in the formula are determined by the above R ^1- (NCO) j and HO- (R ² -O) k-R ³ .

The mono- or polyisocyanate represented by R ^1- (NCO) j is not particularly limited as long as it has one or more isocyanate groups in one molecule. For example, methyl isocyanate, ethyl isocyanate, butyl isocyanate, propyl Aliphatic monoisocyanates such as isocyanate, hexyl isocyanate, octyl isocyanate, lauryl isocyanate, octadecyl isocyanate; aromatic monoisocyanates such as phenyl isocyanate and tolylene isocyanate; alicyclic monoisocyanates such as cyclohexyl isocyanate; methylene diisocyanate and dimethylene Diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diiso Anate, dipropyl ether diisocyanate, 2,2-dimethylpentane diisocyanate, 3-methoxyhexane diisocyanate, octamethylene diisocyanate, 2,2,4-trimethylpentane diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate, 3-butoxyhexane diisocyanate, 1 , 4-Butylene glycol dipropyl ether diisocyanate, thiodihexyl diisocyanate, metaxylylene diisocyanate, paraxylylene diisocyanate, tetramethylxylylene diisocyanate, and the like; metaphenylene diisocyanate, paraphenylene diisocyanate, 2,4-tolylene diisocyanate 2,6-tolylene diisocyanate, dimethyl Aromatic diisocyanates such as rubenzene diisocyanate, ethylbenzene diisocyanate, isopropylbenzene diisocyanate, tolidine diisocyanate, 1,4-naphthalene diisocyanate, 1,5-naphthalene diisocyanate, 2,6-naphthalene diisocyanate, 2,7-naphthalene diisocyanate; Alicyclic diisocyanates such as diisocyanate and isophorone diisocyanate; biphenyl diisocyanates such as 3,3′-dimethylbiphenyl diisocyanate and 3,3′-dimethoxybiphenyl diisocyanate; diphenylmethane-4,4′-diisocyanate and 2,2′-dimethyldiphenylmethane -4,4'-diisocyanate, diphenyldimethylmethane-4,4'-diisocyanate, 2,5 2 ′, 5′-tetramethyldiphenylmethane-4,4′-diisocyanate, cyclohexylbis (4-isocyanatophenyl) methane, 3,3′-dimethoxydiphenylmethane-4,4′-diisocyanate, 4,4′-dimethoxydiphenylmethane -3,3'-diisocyanate, 4,4'-diethoxydiphenylmethane-3,3'-diisocyanate, 2,2'-dimethyl-5,5'-dimethoxydiphenylmethane-4,4'-diisocyanate, 3,3 ' -Diisocyanates of phenylmethane such as dichlorodiphenyldimethylmethane-4,4'-diisocyanate, benzophenone-3,3'-diisocyanate; 1-methylbenzene-2,4,6-triisocyanate, 1,3,5-trimethylbenzene -2,4,6-triisocyanate, 1,3, -Naphthalene triisocyanate, biphenyl-2,4,4'-triisocyanate, diphenylmethane-2,4,4'-triisocyanate, 3-methyldiphenylmethane-4,6,4'-triisocyanate, triphenylmethane-4, 4 ′, 4 ″ -triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate, tris ( Triisocyanate such as (isocyanatophenyl) thiophosphate, tetraisocyanate and the like.

The polyether monoalcohol represented by HO— (R ² —O) k—R ³ is not particularly limited as long as it is a branched chain or secondary monohydric alcohol polyether. Such a compound can be obtained by addition polymerization of alkylene oxide or styrene oxide or the like to a branched chain or secondary monohydric alcohol. The branched chain or secondary monohydric alcohol referred to here is the general formula (3) or (4).

(Wherein R ^{6 to} R ¹⁰ are hydrocarbon groups, for example, alkyl groups, alkenyl groups, alkylaryl groups, cycloalkyl groups, cycloalkenyl groups, etc.). Therefore, R2 is a group obtained by removing the hydroxyl group in the general formula (4) or (5). From the viewpoint of water resistance of the resulting coating film, R ³ is preferably an alkyl group, and the total number of carbon atoms is preferably 8 to 36, more preferably 12 to 24.

Moreover, the alkylene oxide, styrene oxide, etc. to be added may be obtained by homopolymerization, two or more kinds of random polymerization or block polymerization. The degree of polymerization k is preferably 1 to 500, and more preferably 10 to 200, from the viewpoint of the appearance of the resulting coating film. The ratio of ethylene to total ^{R 2,} from the viewpoint of the appearance of the resulting coating film is preferably from 50 to 100 wt% of the total ^{R 2,} and more preferably 65 to 100 wt%.

As a method for obtaining the urethane compound represented by the general formula (1), for example, mono- or polyisocyanate represented by R ^1- (NCO) j and HO- (R ² -O) k-R ³ Are mixed so that the ratio of the hydroxyl value to the isocyanate value from each compound is 1.05 / 1 to 1.4 / 1. Similar to the reaction, for example, a method of reacting by heating at 80 to 90 ° C. for 1 to 3 hours can be mentioned.

The urethane-based compound represented by the general formula (2) is, for example, a compound of the mono- or polyisocyanate represented by R ^1- (NCO) j that is a raw material for obtaining the general formula (1). Two or more polyisocyanates, a polyether monoalcohol represented by HO— (R ² —O) k—R ³ , and further represented by R ⁴ — [(O—R ⁵ ) m—OH] n. One or two or more polyether polyols can be reacted as raw materials. In this case, R ^{1 to} R ⁵ in the formula are represented by R ⁴ -[(O—R ⁵ ) m—OH] n, R ¹ — (NCO) j, HO— (R ² —O) k—R ³ . It is determined.

Among the mono- or polyisocyanates represented by R ^1- (NCO) j, polyisocyanate wherein j is 2 or more has two or more isocyanate groups in one molecule. Specifically, Mention may be made, for example, of polyisocyanates represented by R ^1- (NCO) j (where j is 2 or more) described in the general formula (1). The polyether monoalcohol represented by HO— (R ² —O) k—R ³ is not particularly limited as long as it is a branched chain or secondary monohydric alcohol polyether. Specifically, Those mentioned in the above general formula (1) can be mentioned.

Examples of the polyether polyol represented by R ⁴ -[(O—R ⁵ ) m—OH] n include those described for the polyether polyol described later. Here, R ⁵ is determined by the alkylene oxide, styrene oxide, or the like to be added, and is preferably an alkylene oxide or styrene oxide having 2 to 4 carbon atoms from the viewpoint of easy industrial availability. Alkylene oxide, styrene oxide, etc. to be added may be homopolymerized, two or more kinds of polymers or block polymerized ones. The degree of polymerization m is preferably 1 to 500, more preferably 1 to 200, and still more preferably 10 to 200. Moreover, it is preferable that the ratio of the ethylene group which occupies for R5 is 50-100 mass% of the whole R5 from a viewpoint of the external appearance of the coating film obtained, and it is still more preferable that it is 65-100 mass%. The molecular weight of such a polyether polyol is preferably 500 to 50000, and more preferably 1000 to 20000.

As a method for obtaining the urethane compound represented by the general formula (2), for example, one or two or more polyisocyanates represented by the above R ^1- (NCO) j and HO— (R ² —O). ) and one or more polyether monoalcohols represented by ^{k-R 3, R 4 -} [(O-R 5) m-OH] 1 , two or more polyether represented by n The polyol is blended so that the ratio of the hydroxyl value to the isocyanate value from each compound is 1.05 / 1 to 1.4 / 1, and in the same manner as the reaction between a normal polyether and an isocyanate, for example, The method of making it react for 1 to 3 hours at 80-90 degreeC can be mentioned.

  Content with respect to the resin solid content of the water-based base coating material of the urethane compound represented by the general formula (1) or (2) is 0.01 to 20% by mass, and is 0.1 to 10% by mass. Is preferred. When the content is less than 0.01% by mass, improvement in the appearance of the resulting coating film is insufficient, or when the water-based paint contains a glittering material as a coloring component described later, the resulting coating film flip-flop If the property is insufficiently improved or exceeds 20% by mass, various performances of the resulting coating film may be deteriorated.

Bright pigment As the bright pigment contained in the aqueous metallic paint of the present invention, for example, a non-colored or colored metal bright agent such as a metal or alloy such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide And mixtures thereof. When the luster pigment is a flat pigment, those having an average particle diameter (D50) of 2 to 50 μm and a thickness of 0.1 to 5 μm are preferable. Further, any of the above-mentioned glitter pigments having an average particle diameter in the range of 10 to 35 μm is excellent in glitter feeling and is more preferably used. Other bright pigments include interference mica pigments, white mica pigments, graphite pigments, and the like.

  On the other hand, a coloring pigment can be contained if necessary. Examples of the colored pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, indigo pigments, perinone pigments, and perylene pigments. Pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and the like. Examples of inorganic pigments include chrome lead, yellow iron oxide, bengara, barium sulfate, carbon black, and titanium dioxide.

  Further, the pigment concentration (PWC) of the glitter pigment is generally preferably 18.0% or less. When the upper limit is exceeded, the coating film appearance may be deteriorated. More preferably, it is 0.01 to 15.0%, and particularly preferably 0.01 to 13.0%. The total pigment concentration (PWC) in the water-based metallic paint is preferably 0.1 to 50%. More preferably, it is 0.5 to 40%, and particularly preferably 1.0 to 30%. When the upper limit is exceeded, the coating film appearance may be deteriorated.

  The water-based metallic paint may contain other film-forming resin as necessary. Other film-forming resins are not particularly limited, and film-forming resins such as acrylic resins other than the acrylic resin emulsion, polyester resins, alkyd resins, epoxy resins, and urethane resins can be used.

  The other film-forming resin has a number average molecular weight of 3,000 to 50,000, preferably 6,000 to 30,000. When it is less than 3000, workability and curability are not sufficient, and when it exceeds 50000, the non-volatile content at the time of coating becomes too low, and workability may be deteriorated.

  The other film-forming resin preferably has an acid value of 10 to 100 mgKOH / g, more preferably 20 to 80 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, Water dispersibility may be reduced. Moreover, it is preferable to have a hydroxyl value of 20 to 180, and further 30 to 160. If the upper limit is exceeded, the water resistance of the coating film is lowered, and if it is less than the lower limit, the curability of the coating film may be lowered.

  The blending ratio of the acrylic resin emulsion and the other film-forming resin in the water-based metallic paint is 5 to 95% by mass, preferably 10 to 85% by mass based on the total amount of the resin solid content. %, More preferably 20 to 70% by mass, and other film-forming resin is 95 to 5% by mass, preferably 90 to 15% by mass, and more preferably 80 to 30% by mass. When the ratio of the acrylic resin emulsion is less than 5% by mass, workability is lowered, and when it is more than 95% by mass, the film forming property may be deteriorated.

  As said other film forming resin, it is preferable to use a water-soluble acrylic resin from a compatible point with the said acrylic resin emulsion. The water-soluble acrylic resin can be obtained by using the above-mentioned carboxylic acid group-containing unsaturated monomer as an essential component and performing solution polymerization together with other ethylenically unsaturated monomers.

  The water-soluble acrylic resin is usually neutralized with a basic compound, for example, an organic amine such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, and dimethylethanolamine, and added to water. Although used by dissolving, this neutralization may be performed on the water-soluble acrylic resin itself or at the time of production of the water-based metallic paint.

Moreover, the said water-based metallic coating material can contain polyether polyol. By including the polyether polyol, the coating film performance can be further improved.
As the polyether polyol, one having at least one primary hydroxyl group in one molecule, a number average molecular weight of 300 to 3000, a hydroxyl value of 30 to 700, and a water tolerance of 2.0 or more is used. It is preferable. If the above conditions are not satisfied, the water resistance may not be lowered or the target appearance may not be improved.

  As such a polyether polyol, a compound obtained by adding an alkylene oxide such as propylene oxide to an active hydrogen-containing compound such as a polyhydric alcohol, a polyhydric phenol, or a polyvalent carboxylic acid can be used. Specific examples include commercially available products such as Prime Pole PX-1000, Sanix SP-750 (trade names, all manufactured by Sanyo Chemical Industries, Ltd.), and PTMG-650 (trade names, manufactured by Mitsubishi Chemical Corporation). Can do. The polyether polyol is preferably contained in an amount of 1 to 40% by mass, more preferably 3 to 30% by mass in the solid content of the coating resin.

  The said water-based metallic coating material can contain another hardening | curing agent in the range which does not inhibit the hardening of this invention. As said other hardening | curing agent, what is generally used for coating materials other than the hydrophobic melamine resin aqueous dispersion mentioned above can be used together. For example, blocked isocyanate, epoxy compound, aziridine compound, carbodiimide compound, oxazoline compound, hydrophilic melamine resin, metal ion and the like can be mentioned.

  The above-mentioned blocked isocyanate can be obtained by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. Examples include those that dissociate and generate isocyanate groups.

  When these hardening | curing agents are contained, it is preferable that the content is 10-100 mass parts with respect to 100 mass parts of resin solid content in an aqueous metallic coating material. Outside the above range, curability may be insufficient.

  Furthermore, the above-mentioned water-based metallic paint containing the urethane compound of formula (1) or (2) as a viscosity agent may contain other viscosity control agents in order to prevent the compatibility with the top coating film and to ensure the coating workability. Can be added. As other viscosity control agents, those generally showing thixotropy can be used, for example, polyamides such as cross-linked or non-cross-linked resin particles, swelling dispersions of fatty acid amides, amide fatty acids, and long chain polyaminoamide phosphates. And polyethylene pigments such as colloidal swelling dispersion of polyethylene oxide, organic bentonite materials such as organic acid smectite clay and montmorillonite, and inorganic pigments such as aluminum silicate and barium sulfate.

  In addition to the above-described components, the water-based metallic paint may contain additives that are usually added to the paint, such as surface conditioners, thickeners, antioxidants, UV inhibitors, and antifoaming agents. These compounding amounts are within the range known to those skilled in the art.

  The method for producing the water-based metallic paint is not particularly limited, including those described later, and is well known to those skilled in the art such as kneading and dispersing a composition such as a pigment using an SG mill, a Glen mill, a kneader, or a roll. All methods can be used.

Multilayer coating film forming method The aqueous metallic paint can be suitably used as an aqueous metallic base paint for automobiles. For this reason, it can apply to the multilayer coating-film formation method applied to a motor vehicle body, components, etc. Examples of the method for forming a multilayer coating film include, for example, the step (I) of forming the metallic base coating film by applying the above-described aqueous metallic paint to an object to be coated, without curing the metallic base coating film. Examples thereof include a step (II) of forming a clear coating film by applying a clear coating thereon and a step (III) of simultaneously heating the metallic base coating film and the clear coating film.

  The object to be coated used in the method for forming a multilayer coating film can be used for various substrates such as metal molded products, plastic molded products, foams, etc. It is preferable to apply to this.

  Examples of the metal molded product include, for example, plates and molded products made of iron, copper, aluminum, tin, zinc, etc. and alloys containing these metals. Specifically, passenger cars, trucks, motorcycles, buses, etc. Car bodies and parts. These metals are preferably subjected to chemical conversion treatment with phosphate, chromate or the like in advance.

  An electrodeposition coating film may be formed on the metal molded article subjected to the chemical conversion treatment. As such an electrodeposition paint, a cation type and an anion type can be used, but a cationic electrodeposition paint composition is preferable from the viewpoint of corrosion resistance.

  Examples of the plastic molded product include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, and the like, and specifically, spoilers. Automobile parts such as bumpers, mirror covers, grills, door knobs, and the like. Further, these plastic molded products are preferably those washed with steam or neutral detergent with trichloroethane. Furthermore, primer coating for enabling electrostatic coating may be applied.

If necessary, an intermediate coating film may be formed on the object to be coated. An intermediate coating is used to form the intermediate coating film. The intermediate coating contains a film-forming resin, a curing agent, various organic and inorganic coloring components, extender pigments, and the like. The coating film-forming resin and the curing agent are not particularly limited, and specifically, the coating film-forming resin and the curing agent mentioned in the previous water-based metallic paint can be used and used in combination. It is what From the viewpoint of various performances and costs of the obtained intermediate coating film, an acrylic resin and / or a polyester resin, an amino resin and / or an isocyanate are used in combination.
Examples of the coloring component contained in the intermediate coating material include those described in the previous aqueous metallic coating material. In general, it is preferable to use a so-called color intermediate coating composition that combines a gray-based intermediate coating composition mainly composed of carbon black and titanium dioxide, a set gray that combines the hues of the top coating, and various coloring components. Further, flat pigments such as aluminum powder and mica powder may be added.

  In the intermediate coating material, in addition to the above components, additives usually added to the coating material, for example, a surface conditioner, an antioxidant, an antifoaming agent, and the like may be blended.

  As a method of applying the above-mentioned water-based metallic paint to the object to be coated, from the viewpoint of improving the appearance, multi-stage painting by air electrostatic spray painting, preferably two-stage painting, or air electrostatic spray painting is applied. And a coating method combining a rotary atomizing electrostatic coating machine called a metallic bell.

  Although the film thickness of the coating film at the time of application | coating by the said water-based metallic paint changes with desired uses, generally it is preferable that it is 10-30 micrometers by a dry film thickness. If the dry film thickness is less than 10 μm, the substrate cannot be concealed and the film breaks. If it exceeds 30 μm, the sharpness may be deteriorated, or defects such as unevenness or sagging may occur during coating. is there. In order to obtain a multilayer coating film having a good appearance, it is preferable to heat the obtained base coating film at 40 to 100 ° C. for 2 to 10 minutes before applying the clear paint.

The aqueous metallic coating composition of the present invention is required to have a coating viscosity of 15 mPa · s or less at a shear rate of 10 ⁴ / s. The shear rate of 10 ⁴ / s corresponds to the shear rate of the coating machine, in which case the paint viscosity is 15 mPa · s or less, preferably 10 mPa · s or less. That is, the viscosity of the paint is reduced under a high shearing force applied at the time of coating the paint, the atomized particle diameter of the paint can be further reduced, and high FF properties are exhibited in the resulting coating film. When it exceeds 15 mPa · s, the FF property of the metallic coating film decreases. The viscosity of the paint is measured with a CAP2000 Viscometer manufactured by Brookfield Engineering Laboratories, using No. 1 cone, and the viscosity at a shear rate of 25000 / sec (measurement temperature: 25 ° C.) is measured.

  In the multilayer coating film forming method, a clear coating film is formed by applying the clear coating material on the base coating film obtained by applying the water-based metallic coating material without heating and curing. The clear coating film smoothes and protects unevenness, flickering, and the like caused by the base coating film, and further gives an aesthetic appearance.

  The clear paint is not particularly limited, and a clear paint containing a film-forming resin and a curing agent 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 paint include a solvent type, an aqueous type and a powder type.

  Preferred examples of the solvent-type clear paint 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 from the viewpoint of transparency or acid etching resistance. An acrylic resin and / or a polyester resin etc. can be mentioned.

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

  Furthermore, it is preferable that a viscosity control agent is added to the clear paint in order to ensure the coating workability. As the viscosity control agent, those generally showing thixotropy can be used. As such a thing, a conventionally well-known thing can be used, for example. Moreover, a curing catalyst, a surface conditioner, etc. can be included if necessary.

  In addition, as a clear paint used in the said multilayer coating-film formation method, from a viewpoint of the influence which it has on the environment by content of an organic solvent, Ford Cup No. 20 in 20 degreeC. 4 is preferably a solvent-type clear paint, a water-based clear paint, or a powder-type clear paint having a clear paint solid content of 50% by mass or more when diluted to a viscosity of 20 to 50 seconds.

  Specific examples of the method for applying the above clear paint to the base coating film include a micro-microbell and a coating method using a rotary atomizing electrostatic coater called a microbell.

  On the other hand, as the powder type clear paint, a normal powder paint such as a thermoplastic and thermosetting powder paint can be used. A thermosetting powder coating is preferred because a coating film having good physical properties can be obtained. Specific examples of the thermosetting powder coating material include epoxy-based, acrylic-based, and polyester-based powder clear coating materials, and acrylic-based powder clear coating materials having good weather resistance are particularly preferable.

  The dry film thickness of the clear coating film formed by applying the clear paint is generally preferably 10 to 80 μm, and more preferably 20 to 60 μm. When the dry film thickness is less than 10 μm, the unevenness of the foundation 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 forms a cured coating film by being heated simultaneously with the previously formed base coating film. The heat curing temperature is preferably set to 80 to 180 ° C, and more preferably 120 to 160 ° C, from the viewpoints of curability and physical properties of the resulting multilayer coating film. Although the heat curing time can be arbitrarily set according to the above temperature, it is appropriate that the heat curing temperature is 120 ° C. to 160 ° C. and the time is 10 to 30 minutes.

  The film thickness of the multilayer coating film thus obtained is generally 30 to 300 μm and preferably 50 to 250 μm. When the film thickness is less than 30 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 multilayer coating film thus obtained is also one aspect of the present invention.

  The coated product having a multilayer coating film obtained by the above-mentioned multilayer coating film forming method has a multilayer coating film having extremely high glitter and color development, recoat adhesion, chipping resistance, and water adhesion resistance on the surface thereof. Is.

  The water-based metallic paint of the present invention is obtained by water-dispersing a reaction product obtained by mixing and reacting a film-forming resin containing a specific acrylic resin emulsion, a specific acrylic resin and a hydrophobic melamine resin in a specific composition. Since it contains the hardening | curing agent containing the hydrophobic melamine resin aqueous dispersion with a particle size of 20-140 nm, a specific urethane type compound, and a pigment, the coating film which has the outstanding coloring property can be obtained. Further, in the method for forming a multilayer coating film in automobile coating, when the water-based metallic paint is used as an aqueous base paint, a multilayer coating film having excellent recoat adhesion, chipping property, and water-resistant adhesion can be obtained. Therefore, the water-based metallic paint can be suitably used as a water-based base paint.

  EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail, this invention is not limited only to these Examples. In the examples, “parts” and “%” mean “parts by mass” and “% by mass” unless otherwise specified.

Production Example 1 Production of Acrylic Resin Emulsion Em-1 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added and heated to 80 ° C. with mixing and stirring in a nitrogen stream. Next, 20 parts of styrene, 35.03 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 5.7 parts of 2-hydroxyethyl methacrylate, 0.7 part of allyl methacrylate, 0.5 part of Aqualon HS-10, 1st stage ethylenically unsaturated monomer mixture consisting of 0.5 part of Adeka Soap NE-20 and 49.7 parts of ion-exchanged water, 0.21 part of ammonium persulfate and 8.6 parts of ion-exchanged water The initiator solution was added dropwise to the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Further, in this reaction vessel, 25.75 parts of butyl methacrylate, 2.4 parts of 2-hydroxyethyl methacrylate, 1.55 parts of methacrylic acid, 0.3 part of allyl methacrylate, 0.3 part of Aqualon HS-10 and A second-stage ethylenically unsaturated monomer mixture consisting of 24.7 parts of ion-exchanged water and an initiator solution consisting of 0.08 parts of ammonium persulfate and 7.4 parts of ion-exchanged water were mixed at 0.5 ° C at 80 ° C. Dripping in parallel over time. After completion of the dropping, aging was performed at the same temperature for 2 hours.

  Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion exchange water and 0.24 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-1 having an acid value of 10 mgKOH / g and a hydroxyl value of 35 was obtained.

Production Examples 2 to 4 Production of Acrylic Resin Emulsions Em-2 to 4 Acrylic resin emulsions Em-2 to 4 were formed in the same manner as in Production Example 1 using the monomer composition shown in Table 1 below. The particle diameters of the obtained emulsion particles are also shown in Table 1.

ＡＭＡ＝アリルメタクリレート
ＥＧＤＭ＝エチレングリコールジメタクリレート
ＤＭＥＡ＝ジメチルエタノールアミン

AMA = allyl methacrylate EGDM = ethylene glycol dimethacrylate DMEA = dimethylethanolamine

Production Example 5 Production of acrylic resin emulsion Em-5 226.5 parts of ion-exchanged water was added to a reaction vessel, and the temperature was raised to 80 ° C. while mixing and stirring in a nitrogen stream. Next, 20 parts of styrene, 35.03 parts of methyl acrylate, 8.57 parts of butyl acrylate, 5.7 parts of 2-hydroxyethyl methacrylate, 0.7 part of allyl methacrylate, Aqualon HS-10 (trade name, polyoxy Ethylene alkyl propenyl phenyl ether sulfate ester (Daiichi Kogyo Seiyaku Co., Ltd.) 0.5 part, Adekaria soap NE-20 (α- [1-[(allyloxy) methyl] -2-nonylphenoxy] ethyl) -ω-hydroxy Oxyethylene (manufactured by Asahi Denka Co., Ltd., 80% aqueous solution) from the first stage ethylenically unsaturated monomer mixture comprising 0.5 parts and ion exchange water 80 parts, ammonium persulfate 0.24 parts and ion exchange water 10 parts The resulting initiator solution was added dropwise to the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Further, in this reaction vessel, 22.7 parts of butyl acrylate, 2.4 parts of 2-hydroxyethyl methacrylate, 4.6 parts of methacrylic acid, 0.3 part of allyl methacrylate, 0.2 part of Aqualon HS-10 and A second-stage ethylenically unsaturated monomer mixture consisting of 10 parts of ion-exchanged water and an initiator solution consisting of 0.06 parts of ammonium persulfate and 10 parts of ion-exchanged water were mixed in parallel at 80 ° C. for 0.5 hour. And dripped. After completion of the dropping, aging was performed at the same temperature for 2 hours.

  Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 87.1 parts of ion exchange water and 0.32 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 300 nm, a non-volatile content of 30%, An emulsion resin Em-5 having an acid value of 30 mgKOH / g and a hydroxyl value of 35 was obtained.

  The monomer composition and the particle size of the emulsion are summarized in Table 2 as in Table 1.

  Among the acrylic resin emulsions, Em-4 and Em-5 are both comparative examples, and Em-4 does not use an unsaturated monomer having two or more unsaturated double bonds. -5 has a particle size of 300 nm larger than the specified value.

Production of Acrylic Ac-1 for Dispersion 23.9 parts of dipropylene glycol methyl ether and 16.1 parts of propylene glycol methyl ether were added to the reaction vessel, and the mixture was heated to 120 ° C. while mixing and stirring in a nitrogen stream. Next, 12.5 parts of methyl methacrylate, 54.5 parts of ethyl acrylate, 14.5 parts of 2-hydroxyethyl acrylate, 8.5 parts of methacrylic acid, 10.0 parts of styrene, and dipropylene glycol methyl ether 10. An initiator solution consisting of 0 parts and 2.0 parts of t-butylperoxy 2-ethylhexanoate was added dropwise to the reaction vessel in parallel over 3 hours. After completion of dropping, aging was carried out at the same temperature for 0.5 hour.

  Next, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 part of t-butylperoxy 2-ethylhexanoate was dropped into the reaction vessel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Furthermore, using a solvent removal apparatus, 16.1 parts of the solvent was distilled off under reduced pressure (9332 Pa) at 80 ° C. to obtain a nonvolatile content of 72%, an acid value of 55 mgKOH / g, a hydroxyl value of 70, and a number average molecular weight (Mn) = 9000 acrylic resins were obtained.

Production of Hydrophobic Melamine Resin Water Dispersion MFD-1 282.4 parts of the above-mentioned acrylic Ac-1 resin was added to Cymel 251 (trade name, methyl / butylated melamine resin, manufactured by Mitsui Cytec Co., Ltd., non-volatile content 80%, SP = 10. .8) Mix with 750 parts and stir at 80 ° C. for 8 hours. Thereafter, 17.6 parts of dimethylethanolamine was added and dispersed uniformly. After cooling to 50 ° C., 1200.0 parts of ion-exchanged water was added dropwise over 1 hour to obtain a hydrophobic melamine resin aqueous dispersion. The particle size of the resin particles in this aqueous dispersion was 80 nm. The nonvolatile content (NV) was 35% by mass.

Production of Hydrophobic Melamine Resin Water Dispersion MFD-2 282.4 parts of the above-mentioned acrylic Ac-1 resin was replaced with Uban 20SB (trade name, butylated melamine resin, manufactured by Mitsui Chemicals, non-volatile content 75%, SP = 9.6. ) It was mixed with 800.0 parts and stirred at 80 ° C. for 10 hours. Thereafter, 17.6 parts of dimethylethanolamine was added and dispersed uniformly. After cooling to 50 ° C., 1200.0 parts of ion-exchanged water was added dropwise over 1 hour to obtain a hydrophobic melamine resin aqueous dispersion. The particle size of the resin particles in this aqueous dispersion was 90 nm. The nonvolatile content (NV) was 35% by mass.

Production Acrylic Ac-2 for Dispersion 50.0 parts of dipropylene glycol methyl ether was added to a reaction vessel, and the temperature was raised to 130 ° C. while stirring in a nitrogen stream. Next, 14.8 parts of acrylic acid, 32.5 parts of 2-hydroxyethyl methacrylate, 47.8 parts of butyl acrylate, 5.0 parts of α-methylstyrene dimer, 10.0 parts of dipropylene glycol methyl ether and t -An initiator solution consisting of 13.0 parts of butyl peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of dropping, aging was carried out at the same temperature for 0.5 hour.
Next, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 part of t-butylperoxy 2-ethylhexanoate was dropped into the reaction vessel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Furthermore, 16.1 parts of the solvent was distilled off at 80 ° C. under reduced pressure (9332 Pa) using a solvent removal apparatus to obtain a nonvolatile content of 72%, an acid value of 110 mg KOH / g, a hydroxyl value of 140, and a number average molecular weight (Mn) = 3000 acrylic resins were obtained.

Production of Hydrophobic Melamine Resin Water Dispersion MFD-3 357.0 parts of the above-mentioned acrylic Ac-2 resin was replaced with Uban 20SB (trade name, butylated melamine resin, manufactured by Mitsui Chemicals, Inc., non-volatile content 75%, SP = 9.6. ) It was mixed with 800.0 parts and stirred at 80 ° C. for 2 hours. Thereafter, 36.6 parts of dimethylethanolamine was added and dispersed uniformly, cooled to 40 ° C., and then 1200.0 parts of ion-exchanged water was added dropwise over 1 hour to obtain a hydrophobic melamine resin aqueous dispersion. The particle size of the resin particles in this aqueous dispersion was 60 nm. The nonvolatile content (NV) was 35% by mass.

Method for Producing Dispersion Acrylic Ac-3 6.28 parts of diethanolamine was added to 100 parts of the acrylic Ac-1 resin and mixed and stirred. While continuing stirring, 133.72 parts of deionized water was added dropwise to this over 30 minutes. Stirring was further continued for 10 minutes to obtain a dispersion acrylic Ac-3 in which Ac-1 was water-solubilized. The nonvolatile content (NV) was 30% by mass.

Production of Hydrophobic Melamine Resin Water Dispersion MFD-4 To 666.7 parts of the above water-soluble acrylic Ac-3 resin, Yuban 20SB (trade name, butylated melamine resin, manufactured by Mitsui Chemicals, non-volatile content 75%, SP = 9 .6) The mixture was stirred with 800.0 parts, and then 1200 parts of ion-exchanged water was added dropwise over 1 hour to obtain a hydrophobic melamine resin aqueous dispersion. The particle size of the solid content = 30% resin particles in this aqueous dispersion was 230 nm.

Table 3 shows the acid value, hydroxyl value and molecular weight of the acrylic resin for dispersion (Ac-1 and Ac-2).
Table 4 shows the raw acrylic resin of the hydrophobic melamine resin aqueous dispersion, the type of melamine, the mass ratio of acrylic resin / melamine resin, and the particle size.

サイメル２５１：日本サイテック（株）社から市販の疎水性メラミン樹脂、商品名。
ユーバン２０ＳＢ：三井化学（株）社から市販の疎水性メラミン樹脂、商品名。

Cymel 251: Hydrophobic melamine resin commercially available from Nippon Cytec Co., Ltd., trade name.
Euban 20SB: Hydrophobic melamine resin commercially available from Mitsui Chemicals, Inc., trade name.

シャニンブルーＧ３１４:山陽色素社製、フタロシアニンブルー顔料、商品名。
ＥＦＫＡ４５５０：エフカ社製、ノニオン系顔料分散剤、商品名。 Creating colored pigment paste

Shannin Blue G314: Sanyo Dye, phthalocyanine blue pigment, trade name.
EFKA4550: manufactured by EFKA Corporation, nonionic pigment dispersant, trade name.

  To the formulation shown in Table 5, 68.3 g of 0.5 mm diameter zircon beads were added as a dispersion medium. This was stirred for 5 hours at 3000 rpm using an SG mill. Zircon beads were separated by filtration to obtain a Shanin blue G314 pigment paste.

Example 1
166.7 parts of the acrylic resin emulsion Em-1 obtained in Production Example 1 and 7 parts of a 10% by mass dimethylaminoethanol aqueous solution, 114.3 parts of MFD-1 obtained in Production Example 8, and Prime Pol PX-1000 (Brand name, Sanyo Chemical Industries, Ltd. bifunctional polyether polyol, number average molecular weight 1000, hydroxyl value 278, water tolerance infinity) 10 parts, aluminum paste MH8801 (Asahi Kasei aluminum pigment) 29.2 parts as a bright pigment , 13 parts of the Shannin Blue G314 pigment paste obtained above and 3.3 parts of urethane compound Adecanol SDX-1014 (trade name, Urethane compound (active ingredient 30% by mass) manufactured by Asahi Denka Co., Ltd.) are mixed and stirred. % Aqueous solution of dimethylaminoethanol to adjust the pH to 8.5, and uniformly disperse the aqueous base paint. It was. Furthermore, the viscosity of the paint is 20 ° C. Ion exchange water was added and diluted so as to be 60 seconds in a 4 Ford cup to obtain an aqueous base paint (Example 1) used for coating.

Examples 2-4 and Comparative Examples 1-5
Aqueous base paints (Examples 2 to 4 and Comparative Examples 1 to 5) were obtained in the same manner as in Example 1 except that the type of emulsion resin was changed as shown in Tables 6 and 7.

アデカノールＳＤＸ−１０１４：旭電化社製ウレタン系化合物（有効成分３０質量％）、商品名。
アデカノールＵＨ−４２０：旭電化社製ウレタン系化合物（有効成分３０質量％）、商品名。

Adecanol SDX-1014: Urethane compound (active ingredient 30% by mass) manufactured by Asahi Denka Co., Ltd., trade name.
Adecanol UH-420: Urethane compound (active ingredient 30% by mass) manufactured by Asahi Denka Co., Ltd., trade name.

Formation of multi-layer paint film Cathodic electrodeposition paint “Power Top V-20” and polyester melamine gray intermediate paint “Orga H-870 (both trade names)” manufactured by Nippon Paint Co., Ltd. A water-based base paint (Examples 1 to 4 and Comparative Example 1) obtained as described above was applied to a test plate that had been coated and heat-cured to have a dry film thickness of 25 μm and 40 μm. The product was applied at an atomization pressure of 5 kg / cm ^{2 according} to the product name (manufactured by Lansburg Co.), preheated at 80 ° C. for 5 minutes, and then wet-on-wet on top of “Mac Flow O-1810” (product of Nippon Paint) Name, acid epoxy curable acrylic resin clear paint) by spraying, setting for about 7 minutes, baking at 140 ° C for 30 minutes and drying Coated test piece of two-coat one-bake (2C1B) were prepared respectively as. In addition, the cured coating film by a base coating material and a clear coating material was apply | coated so that the dry film thickness might be 15 micrometers and 40 micrometers, respectively.

  About the coating film obtained by apply | coating a clear coating on the water-based base coating film of Examples 1-4 and Comparative Examples 1-5, FF value, denseness, coloring property, water resistance, CP property, NSR, and nonuniformity The results are shown in Tables 6 and 7 as determined by the following evaluation method.

Evaluation methods
Measurement method of high shear viscosity Measured with Brookfield Engineering Laboratories CAP2000 Viscometer (No. 1 cone use, viscosity at shear rate = 25000 / sec (measurement temperature: 25 ° C.))

It was performed denseness <br/> visually evaluated. The evaluation criteria are as follows.
○: The glitter pigment is oriented closely and the coating film has no particle feeling of the glitter pigment.
(Triangle | delta): The orientation of a luster pigment is a little sparse, and the particle | grain feeling of the luster pigment is somewhat felt in a coating film.
X: The orientation of the glitter pigment is sparse, and the particle feeling of the glitter pigment is felt on the coating film.

Flip flop (FF)
Using a “Minolta color change colorimeter CM512-M2” manufactured by Minolta, flip-flop properties were evaluated from the L values of the respective coating films at 15 degrees and 110 degrees with respect to incident light. Note that the flip-flop property was obtained by (L value at 15 degrees) / (L value at 110 degrees).

Color development Visual evaluation was performed. The evaluation criteria are as follows.
(White blur)
○: There is no white blur △: There is a slight white blur ×: There is a white blur (blueness)
◎: Strong blueness ○: Slightly blueness △: Slightly blueness ×: Low blueness

Cationic electrodeposition paint Power Top V-20 manufactured by Nippon Paint Co., Ltd. and polyester / melamine gray intermediate coating paint Olga H-870 (both trade names) are applied to water-resistant phosphoric acid-treated steel sheets to a dry film thickness of 25 μm and 40 μm, respectively. The base paint obtained in Examples 1 to 3 and Comparative Examples 1 to 6 was applied to the test plate that had been coated and heat-cured using an electrostatic coating machine AutoREA (trade name, manufactured by Lansburg Co.). / Cm ² , set for about 7 minutes, and preheated at 60 ° C. for 7 minutes to obtain an uncured base coating film. On top of that, “Mac Flow O-1810 (trade name, acid epoxy curable acrylic resin clear paint)” manufactured by Nippon Paint Co., Ltd. was applied by spray, set for about 7 minutes, and then set at 140 ° C. for 30 minutes. After baking and drying, a test plate having a multilayer coating film was prepared by 2 coats 1 bake (2C1B) as a coating method, and the coated surface after the test plate was immersed in warm water at 40 ° C. for 10 days was visually observed. The visual results were represented by the following ○ to ×.

○: No occurrence of blisters, etc .: Δ: Some occurrence of blisters, etc .: x: Many occurrences of blisters, etc. are observed

Chipping resistance (CP)
About the coating test board obtained by formation of the said multilayer coating film, evaluation of chipping resistance was performed as follows. Using a gravel tester tester (manufactured by Suga Test Instruments Co., Ltd.), 100 g of No. 7 crushed stone was made to collide with the coating film at an angle of 30 degrees with an air pressure of 2.94 × 10 ⁵ N / m ² from a distance of 35 cm. . After washing and drying, a peel test was performed using an industrial gum tape manufactured by Nichiban Co., Ltd., and then the degree of peeling of the coating film was visually observed and evaluated.

Criterion 5: No peeling at all.
4: The peeling area is small and the frequency is low.
3: The peeled area is small, but the frequency is slightly high.
2: The peeled area is large, but the frequency is low.
1: The peeling area is large and the frequency is high.

Initial recoat adhesion (NSR)
Apply the same base paint as the first coat on the above-mentioned coating test board, followed by the same clear paint as the first coat, and baked and dried at 140 ° C. for 30 minutes, 2 coats 1 bake (2C1B) 2 A coating test plate for each coat was prepared.

  The initial recoat adhesion of the obtained multilayer coating film was evaluated by the following evaluation method. A 2mm bun that reaches the substrate by holding the cutting blade of the cutter (NT cutter (trade name) S type, A type or equivalent) at about 30 degrees with respect to the initial cured coating surface. Eyes were formed, and an adhesive tape (adhesive tape manufactured by Nichiban Co., Ltd.) was evenly crimped with a fingertip so as not to leave bubbles. Immediately after holding one end of the adhesive tape, the adhesive tape was peeled off from the test piece by pulling it perpendicularly to the coated surface. The initial recoat adhesion was evaluated by visually measuring [number of cells not peeled off] / [number of cells of goblet cells = 100].

Unevenness (finished appearance)
The obtained coating film test piece was visually evaluated according to the following criteria.
There is no unevenness in the orientation of the aluminum pigment: ○ Good Some unevenness in the orientation of the aluminum pigment is observed: Δ Slightly poor Unevenness in the orientation of the aluminum pigment is noticeable: × Poor

  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. In other words, in the measurement value obtained by the Minolta color change colorimeter CM512-M2, the larger the value of (L value at 15 degrees) / (L value at 110 degrees), the more "designed flip-flops" and the better the design characteristics. .

  As is clear from the results in Tables 6 and 7 above, the coating films of the examples had higher FF values after clear coating than the comparative examples, and other coating film performances (denseness, color developability, water resistance, CP In terms of performance, initial recoatability and unevenness, the performance of the coating film of the example is higher and superior to that of the comparative example. In Example 4, the acrylic resin for dispersion of the hydrophobic melamine resin MFD-3 is Ac-2, which has an acid value of 110 mg KOH / g, a hydroxyl value of 140, and a number average molecular weight of 3000 as shown in Table 3. Therefore, it is an example that deviates slightly from the preferred ranges of the hydroxyl value and the number average molecular weight, and the FF value is slightly lower.

  The aqueous metallic paint of the present invention can be suitably used as an aqueous metallic paint in automobile painting.

It is a figure which shows typically the process and cross section from metallic base coating to clear coating. It is a figure which shows typically orientation of the luster pigment of an ideal metallic base coating film.

Claims (4)

A water-based metallic paint containing a film-forming resin, a curing agent and a glitter pigment,
The film-forming resin is a two-stage emulsification using a monomer mixture containing 0.05 to 30.0% by mass of an unsaturated monomer having two or more unsaturated double bonds based on the solid content of the film-forming resin. It contains an acrylic resin emulsion obtained by polymerization and having an acid value of 1 to 30 mg KOH / g, a hydroxyl value of 10 to 150, and a particle size of 20 to 140 nm.
The curing agent is a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm, and is further represented by the general formula (1) or (2)

(In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ represent a hydrocarbon group which may be the same or different from each other, and R ¹ represents a hydrocarbon group which may have a urethane bond. R ³ represents a branched chain or a secondary hydrocarbon group, n is a natural number of 2 or more, j is a natural number of 1 or more in the general formula (1), and 2 or more in the general formula (2). And k and m are natural numbers in the range of 1 to 500.) The urethane compound represented by the formula (1) is contained in an amount of 0.01 to 20% by mass relative to the resin solid content in the coating composition. A water-based metallic paint composition having a paint viscosity of 15 mPa · s or less at a shear rate of 10 ⁴ / s.   The unsaturated monomer having two or more unsaturated double bonds is ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, The water-based metallic paint according to claim 1, which is one or more monomers selected from the group consisting of glycerin di (meth) acrylate and allyl (meth) acrylate. Step (I) of forming a metallic base coating film by applying a water-based metallic base coating on an object to be coated, and forming a clear coating by applying a clear coating on the metallic base coating without curing the metallic base coating. A method for forming a multilayer coating film comprising the step (II) and the step (III) of simultaneously heating the metallic base coating film and the clear coating film,
The method for forming a multilayer coating film according to claim 1, wherein the water-based metallic base paint is the water-based metallic paint according to claim 1.   A multilayer coating film formed by the multilayer coating film forming method according to claim 3.

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