JP2007039615A - Water-based metallic coating material and method for forming multi-layer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based metallic coating composition having excellent flip-flop property and appearance while keeping excellent properties such as color development, recoat adhesiveness, chipping resistance and water-resistant adhesiveness, a method for forming a multi-layer coating film by using the composition and a multi-layer coating film produced by the method. <P>SOLUTION: The water-based metallic coating material comprises a film-forming resin, a curing agent and a glittering pigment. The film-forming resin is produced by using a specific acrylic resin emulsion derived from a monomer mixture containing a specific amount of a carbonyl-containing unsaturated monomer and a specific amount of a crosslinking agent, and the curing agent is an aqueous dispersion of a specific hydrophobic melamine resin. <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 the crosslinking agent, one using a hydrophobic melamine resin has been proposed.

  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 a technique for solving such a problem, Patent Document 1 or 2 discloses an aqueous resin obtained by reacting a hydrophobic melamine resin with an acrylic resin, alkyd resin, or the like having a specific acid value, hydroxyl value, and molecular weight. Although it has been proposed to use the dispersion as a crosslinking agent, the water dispersibility is not satisfactory.

  In Patent Document 3, acrylic resin (A), hydrophobic melamine resin (B) and polyester resin (C) 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 are heated. An aqueous resin dispersion containing a reaction product obtained by treatment and having a thickening ratio 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 Document 4 or 5 discloses an aqueous solution obtained by dispersing a hydrophobic melamine resin and a graft resin, acrylic resin, alkyd resin, etc. having a specific acid value, hydroxyl value, and molecular weight in an aqueous metallic paint. Although it has been proposed to use a resin dispersion as a crosslinking agent, the water dispersibility is not satisfactory.

  In addition, since the aqueous resin dispersion disclosed here is not a small dispersion particle size, when this aqueous resin dispersion is used as a crosslinking agent for an aqueous metallic paint, the color developability and recoating of the resulting coating film Performances such as adhesion, chipping and water adhesion may not be sufficient.

The present inventors also filed several patents and proposed water-based colored paints mainly composed of acrylic resins using hydrophobic melamine resins (Patent Documents 6 and 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 used for the production of a metallic composite coating film that is heat-cured (so-called two-coat, one-bake), between the metallic feeling obtained with a metallic base single film and the metallic feeling after forming a clear coating film, There was a problem that the appearance might be different.

This is because when a metallic base coating and a clear coating are applied by the two-coat one-bake method, as shown in FIG. 1, before moving from the glitter coating to the clear coating, it is performed at a low temperature for a short time (for example, at 80 ° C.). (Approx. 5 minutes) The clear paint is applied after the preheating process to dry, but preheating alone is not enough to fix the glitter pigment, and when the clear paint is applied on the uncured metallic base coating It is thought that clear paint (many solvent-based paints) affects the metallic base coating film and disturbs the orientation of the glitter pigment. That is, the orientation of the glitter pigment is ideally arranged in parallel as shown in FIG. 2, but the glitter pigment is oriented in parallel to some extent when painting the metallic base paint as schematically shown in FIG. However, the orientation is disturbed during clear paint application, and thus it is considered that a difference in metallic feeling occurs before and after the formation of the clear coating film as described above.
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 coating composition that provides a metallic coating film that is less disturbed after clear coating, has excellent flip-flop properties, and has an excellent appearance, and a multi-layer coating film forming method using the same, and further flip-flop properties obtained therefrom An object of the present invention is to provide a multilayer coating film excellent in the above.

  As a result of intensive studies to achieve the above object, the present inventors have determined that a specific amount of carbonyl is used as the film forming resin in the aqueous metallic paint containing the film forming resin, the curing agent, and the glitter pigment. By using a specific acrylic resin emulsion obtained from a monomer mixture containing a group-containing unsaturated monomer and a specific amount of a crosslinking agent, and using a specific hydrophobic melamine resin aqueous dispersion as the curing agent, an aqueous metallic paint While maintaining excellent properties such as color development, recoat adhesion, chipping, water resistance, etc., the orientation of the metallic pigment in the two-coat / one-bake coating method is less likely to be disturbed after clear coating, and the flip-flop properties are excellent. Water-based metallic coating composition providing a metallic coating with excellent quality and multilayer coating form using the same The method further provides a multilayer coating film excellent in the flip-flop effect obtained therefrom, the objects can be achieved.

That is, the present invention is an aqueous metallic paint containing a film-forming resin, a curing agent and a glitter pigment,
The film-forming resin comprises an acrylic resin emulsion;
The acrylic resin emulsion is obtained by two-stage emulsion polymerization using a monomer mixture, and has an acid value of 1 to 30 mgKOH / g, a hydroxyl value of 10 to 150 mgKOH / g, and a particle size of 20 to 140 nm.
The monomer mixture contains 0.5 to 10.0% by mass of a carbonyl group-containing unsaturated monomer based on the solid content of the film-forming resin,
The curing agent is a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm,
Further, the crosslinking agent contains one or more compounds selected from the group consisting of hydrazine compounds or semicarbazide compounds in an amount of 0.5 to 1.5 equivalents relative to the amount of the carbonyl group-containing unsaturated monomer. The present invention relates to a water-based metallic paint.

In order to suitably carry out the present invention,
The carbonyl group-containing unsaturated monomer is selected from the group consisting of diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone, acrolein, and formylstyrene. One or more selected monomers are preferred.

As another aspect of the present invention,
(I) a process of forming a metallic base coating film by coating a water-based metallic base paint on an object to be coated;
(II) a step of applying a clear coating thereon to form a clear coating without curing the metallic base coating, and (III) heating the metallic base coating and the clear coating simultaneously. A method for forming a multilayer coating film comprising a step,
There is a multilayer coating film forming method characterized in that the water-based metallic base coating material is the above-mentioned water-based metallic coating material, and a multilayer coating film formed by the method.

  Since the water-based metallic paint of the present invention has the above-described configuration, the brightness in the two-coat / one-bake coating method is maintained while maintaining the excellent characteristics of the water-based metallic paint, such as color development, recoat adhesion, chipping property, and water adhesion resistance. The orientation of the conductive pigment is less likely to be disturbed after the clear paint is applied, and the water-based metallic paint that provides a metallic coating film with excellent flip-flop properties, the method for forming a multilayer coating film using the same, and the composite film with excellent flip-flop properties obtained therefrom. A layer coating can be provided.

Hereinafter, the present invention will be described in detail.
[Water-based metallic paint]
The aqueous metallic paint of the present invention contains a film-forming resin, a curing agent and a glitter pigment,
The coating film-forming resin contains an acrylic resin emulsion,
The acrylic resin emulsion is obtained by two-stage emulsion polymerization using a monomer mixture, and has an acid value of 1 to 30 mgKOH / g and a hydroxyl value of 10 to 150 mgKOH / g, a particle size of 20 to 140 nm,
The monomer mixture contains 0.5 to 10.0% by mass of a carbonyl group-containing unsaturated monomer based on the solid content of the film-forming resin.
The curing agent is a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm,
Furthermore, 0.5 to 1.5 equivalents of one or more compounds selected from the group consisting of hydrazine compounds or semicarbazide compounds are contained as a crosslinking agent with respect to the amount of the carbonyl group-containing unsaturated monomer.

  In this invention, as mentioned above, when forming the acrylic resin emulsion which is a film-forming resin, it is necessary to contain the unsaturated monomer containing a carbonyl group as one component of an acrylic monomer. When an unsaturated monomer containing a carbonyl group is used during the formation of an acrylic resin emulsion, a curing reaction occurs with a crosslinking agent during preheating after coating, and a three-dimensional coating film is obtained.

  Although not limited to a specific theory, the present inventors understand that the use of the acrylic resin emulsion can prevent the disorder of the orientation of the glitter pigment for 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. Since it is thought to occur by swelling the emulsion particles, if the paint containing the acrylic resin emulsion and the crosslinking agent is used, the swelling caused by the solvent of the clear paint can be prevented, and the disorder of the orientation of the glitter pigment is also effective. I guess it can be prevented.

  In the present invention, it is important to use the hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm together with the acrylic resin emulsion. By using a paint containing these, a coating film having excellent color developability can be obtained. Obtainable. For this reason, the obtained coating film has little blurring feeling. Moreover, when the aqueous metallic paint contains, for example, a blue pigment, a coating film having a strong bluish sensation can be obtained, and when it contains a black pigment, a coating film having a jet black feeling can be obtained.

  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. Moreover, the coating film excellent in coloring property can also be obtained. For this reason, the said water-based metallic paint can be used suitably in the multilayer coating-film formation method in automobile painting.

(Coating film forming resin)
The film-forming resin used in the aqueous metallic paint of the present invention contains an acrylic resin emulsion, and the acrylic resin emulsion is obtained by two-stage emulsion polymerization, and has an acid value of 1 to 30 mgKOH / g, a hydroxyl value of 10 to 150 mgKOH / g and a particle size of 20-140 nm.

  The acrylic resin emulsion is required to have an acid value of 1 to 30 mgKOH / g, and preferably 3 to 25 mgKOH / g. If the acid value is less than 1 mgKOH / g, the stability of the emulsion may be reduced, and if it exceeds 30 mgKOH / g, the water resistance of the resulting coating film may be reduced.

  The acrylic resin emulsion is required to have a hydroxyl value of 10 to 150 mgKOH / g, and preferably 15 to 120 mgKOH / g. When the hydroxyl value is less than 10 mgKOH / g, the physical properties of the coating film may be reduced, and when it exceeds 150 mgKOH / g, the water resistance of the obtained coating film may be reduced. 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 acrylic resin emulsion is required to have a particle size of 20 to 140 nm, preferably 30 to 120 nm, and more preferably 50 to 100 nm. When the particle size is less than 20 nm, the coating solid content (NV) may be remarkably reduced, and when it exceeds 140 nm, the color developability of the resulting coating film may be reduced.

The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions. The particle diameters of the acrylic resin emulsion and the hydrophobic melamine resin dispersion according to the present invention are average dispersed particle diameter values measured using ELS-800 (manufactured by Otsuka Electronics Co., Ltd.) under the following conditions.
Sample; infinite dilution with ion-exchanged water Measurement temperature: 25 ° C

  In the present invention, the acrylic resin emulsion is an emulsion obtained by emulsion polymerization, which will be described later, using a carbonyl group-containing unsaturated monomer as an essential monomer and a carboxylic acid group-containing unsaturated monomer or a hydroxyl group-containing unsaturated monomer as a raw material. Can be mentioned. 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 has an acid value of 0 to 100 mgKOH / g, preferably 0 to 50 mgKOH / g, and contains a carboxylic acid group It is desirable that the monomer mixture (a) containing an unsaturated monomer is obtained by emulsion polymerization. When the acid value exceeds 100 mgKOH / g, the water resistance of the resulting coating film may be lowered. 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 has an acid value of 25 to 200 mgKOH / g, preferably 30 to 180 mgKOH / g, and is obtained by emulsion polymerization of a monomer mixture (b) containing a carboxylic acid group-containing unsaturated monomer. It is desirable. 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. When the acid value exceeds 200 mgKOH / g, the water resistance of the resulting coating film may be lowered. The acid value of the shell part is the acid value of the acrylic resin emulsion obtained by the second stage emulsion polymerization.

  The monomer mixture (a) and / or the monomer mixture (b) needs to contain a carbonyl group-containing unsaturated monomer as an essential monomer. It is necessary for the carbonyl group-containing unsaturated monomer to form a cross-link in the coating film together with the cross-linking agent during preheating after applying the base paint, so that it is not affected by the clear paint applied to the upper layer. . The carbonyl group-containing unsaturated monomer may be contained in either or both of the monomer mixture (a) and the monomer mixture (b), but the monomer mixture (a) and the monomer mixture (b) The inclusion in both is preferable in order to minimize the influence from the clear paint. The carbonyl group-containing unsaturated monomer is used in an amount of 0.5 to 10.0 mass%, preferably 0.75 to 7.0 mass%, more preferably 1. It is 0-5.0 mass%. If the amount of the carbonyl group-containing unsaturated monomer is less than 0.5% by mass, the effect of adding the unsaturated monomer cannot be obtained, and if it exceeds 10.0% by mass, it is difficult to synthesize an acrylic resin emulsion. Become.

  The monomer mixture (a) and / or the monomer mixture (b) has a hydroxyl group. The hydroxyl value is 10 to 150 mgKOH / g, preferably 15 to 120 mgKOH / g. When the hydroxyl value is less than 10 mgKOH / g, sufficient curability may not be obtained, and when it exceeds 150 mgKOH / g, various performances of the resulting coating film may be deteriorated.

  Further, the monomer mixture (a) and / or the monomer mixture (b) may contain the other ethylenically unsaturated monomers. Moreover, it is preferable that the glass transition temperature (Tg) 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 carbonyl group of the carbonyl group-containing unsaturated monomer means one having a structure in which carbon atoms are bonded to both ends of the carbonyl group. Examples of the carbonyl group-containing unsaturated monomer include diacetone acrylamide (DAAM), Examples thereof include diacetone methacrylamide, acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone, acrolein, and formylstyrene. Of these, diacetone acrylamide (DAAM) is preferred.

Examples of the crosslinking agent include one or more compounds selected from the group consisting of hydrazine compounds or semicarbazide compounds. The hydrazine compound is a compound having at least two hydrazide groups represented by —CO—NH—NH ₂ in one molecule. Specific examples thereof include oxalic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, Glucanic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, dicarboxylic acid dihydrazide such as itaconic acid dihydrazide, carbonic acid polyhydrazide such as carbonic acid dihydrazide, carbodihydrazide, thiocarbodihydrazide, 4,4'-oxybenzenesulfonylhydrazide, aromatic dicarboxylic acid Examples thereof include polymer hydrazides such as hydrazide and polyacrylic acid hydrazide. Among the above compounds, adipic acid dihydrazide is preferable.

Specific examples of the semicarbazide compound include compounds having at least two semicarbazide groups represented by —NH—CO—NH—NH ₂ in one molecule, and specific examples thereof include aliphatic, alicyclic, aromatic It can be obtained by excessive reaction of N, N-substituted hydrazines such as N, N-dimethylhydrazine and the above exemplified hydrazides with diisocyanates such as aromatic bissemicarbazide, hexamethylene diisocyanate and isophorone diisocyanate or polyisocyanate compounds derived therefrom. The above-exemplified dihydrazide is excessively reacted with the isocyanate group in the reaction product of the polyfunctional semicarbazide, the polyisocyanate compound and an active hydrogen compound containing a hydrophilic group such as polyether polyols and polyethylene glycol monoalkyl ethers. Water-based polyfunctional semicarbazide obtained as described above, or a mixture of the polyfunctional semicarbazide and water-based polyfunctional semicarbazide. Among the above compounds, polyfunctional semicarbaside and aqueous polyfunctional semicarbaside are preferable.

  The amount of the crosslinking agent for the carbonyl group-containing unsaturated monomer is 0.5 to 1.5 equivalents, preferably 0.7 to 1.3 equivalents, more preferably 0, based on the amount of the carbonyl group-containing unsaturated monomer. .8 to 1.2 equivalents. When the blending amount of the crosslinking agent is less than 0.5 equivalent, the flip-flop property cannot be maintained, and when it exceeds 1.5 equivalent, the storage stability is lowered.

  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 Mention may be made of [oxy (1-oxo-1,6-hexanediyl)], maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid and the like.

  Examples of the hydroxyl group-containing unsaturated monomer include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, and ε of hydroxyethyl (meth) acrylate. -Caprolactone adducts may 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]; diene [e.g., butadiene, isoprene, etc.] and the like.

  The monomer mass ratio of the monomer mixture (a) / monomer mixture (b) [core part / shell part] is preferably 50/50 to 98/2, and preferably 65/35 to 95/5. More preferred. 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, an emulsifier is dissolved in water or an aqueous medium containing an organic solvent such as alcohol as necessary, and the monomer mixture (a) or the monomer mixture (b) and a polymerization initiator are heated and stirred. It can be performed by dropping. The monomer mixture (a) or the monomer mixture (b) 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). Nitriles) 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. Particularly, reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (Sanyo) Kasei Kogyo Co., Ltd.), Adequaria Soap NE-20 (Asahi Denka Co., Ltd.), Aqualon HS-10 (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 system. In general, the reaction time is 1 to 8 hours. The content of the polymerization initiator relative to the total mass of the monomer mixture (a) and the monomer mixture (b) is generally 0.1 to 5% by mass, and preferably 0.2 to 2% by mass.

  The said acrylic resin emulsion can be used by pH = 3-10 by neutralizing with a base as needed. This is because the stability in this pH region is high. This neutralization is preferably carried out 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 hardening | curing agent used for the water-based metallic coating material of this invention is a hydrophobic melamine resin water dispersion with a particle size of 20-140 nm. The hydrophobic melamine resin aqueous dispersion is obtained by dispersing 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 105 to 200 mgKOH / g, a hydroxyl value of 100 to 200 mgKOH / g, and a number average molecular weight of 1000 to 5000 and a hydrophobic melamine resin are 5/95 to 50 /. It is preferably obtained by a production method comprising a step (1) of mixing and reacting at a mass ratio of 50 and a step (2) of dispersing the reaction product obtained in the above step (1) in water. Thereby, color development property, recoat adhesion, chipping resistance, and water adhesion resistance can be improved.

  In the step (1), first, an acrylic resin having an acid value of 105 to 200 mgKOH / g, a hydroxyl value of 100 to 200 mgKOH / g, and a number average molecular weight of 1000 to 5000, and a hydrophobic melamine resin is 5/95 to 50/50. The process of mixing and reacting at a mass ratio 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 105 to 200 mgKOH / g. If it is less than 105 mgKOH / g, the particle size may exceed 140 nm. If it exceeds 200 mgKOH / g, the reaction control may be extremely difficult. It is preferable that it is 105-180 mgKOH / g.

  The acrylic resin has a hydroxyl value of 100 to 200 mgKOH / g. If it is less than 100 mgKOH / g, the particle size may exceed 140 nm. If it exceeds 200 mgKOH / g, the reaction control may be extremely difficult. It is preferable that it is 120-180 mgKOH / g.

  The acrylic resin has a number average molecular weight of 1000 to 5000. If it is less than 1000, the particle size may exceed 140 nm. If it exceeds 5000, reaction control may be extremely difficult. It is preferable that it is 1500-4000. The number average molecular weight of the acrylic resin is a value measured with a polystyrene standard by the GPC method.

  The acrylic resin is, for example, a monomer composition containing a carboxylic acid group-containing unsaturated monomer, a hydroxyl group-containing unsaturated monomer, and, if necessary, other ethylenically unsaturated monomers in a water-soluble organic solvent, known as emulsion polymerization. The polymerization method can be used.

  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- Acryloyloxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid, ω-carboxy-polycaprolactone mono (meth) acrylate, isocrotonic acid, α-hydro-ω-[(1-oxo-2-propenyl) oxy And poly [oxy (1-oxo-1,6-hexanediyl)], maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, and the like.

  Examples of the hydroxyl group-containing unsaturated monomer include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, and ε of hydroxyethyl (meth) acrylate. -Caprolactone adducts may 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), Polymerizable amide compounds [for example, (meth) acrylamide, N-methylo Ru (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meta ) Acrylamide, 2,4-dihydroxy-4′-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, etc.]; polymerizable aromatic compounds [eg, styrene, α- Methyl styrene, vinyl ketone, t-butyl styrene, parachlorostyrene, vinyl naphthalene, etc.]; polymerizable nitriles (eg, acrylonitrile, methacrylonitrile, etc.); α-olefins (eg, ethylene, propylene, etc.); vinyl esters (eg, Vinyl acetate, propi Nsan vinyl etc.]; and the like.

  Conventionally known hydrophobic melamine resins can be used, but the solubility parameter δ (Sp) is in the range of 9.0 ≦ Sp ≦ 11.5, preferably 9.5 ≦ Sp ≦ 11.0. It is preferable that. If the Sp is less than 9.0, the particle size may exceed 140 nm. If it exceeds 11.5, the particle size exceeds 140 nm, and the performance such as water resistance decreases when the coating film is formed. There is a risk.

  The solubility parameter δ is generally called Sp (solubility parameter) among those skilled in the art, and is a measure indicating the degree of hydrophilicity or hydrophobicity of the resin. 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 aqueous dispersion of the hydrophobic melamine resin 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 a range that does not exclude 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), it can use by pH = 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.

(Bright pigment)
The glittering pigment contained in the water-based metallic paint of the present invention is not particularly limited in shape and may be colored. For example, the average particle diameter (D50) is 2 to 50 μm and the thickness is What is 0.1-5 micrometers is preferable. Those having an average particle diameter in the range of 10 to 35 μm are excellent in glitter and are more preferably used. Specific examples include non-colored or colored metallic brightening agents such as aluminum, copper, zinc, iron, nickel, tin, and aluminum oxide, and alloys, and mixtures thereof. In addition, interference mica pigments, white mica pigments, graphite pigments, and the like are included therein.

  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.

  In addition, the other film-forming resin has a number average molecular weight of 3,000 to 50,000, preferably 6,000 to 30,000. If it is less than 3,000, workability and curability are not sufficient, and if it exceeds 50,000, the non-volatile content at the time of coating becomes too low, and the 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. Further, it preferably has a hydroxyl value of 20 to 180 mgKOH / g, and more preferably 30 to 160 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases. There is a fear.

  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, the 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 commercial products such as Prime Pole PX-1000, Sanix SP-750 (all of which are manufactured by Sanyo Chemical Industries), and PTMG-650 (manufactured by Mitsubishi Chemical). 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. For example, a block isocyanate, an epoxy compound, an aziridine compound, a carbodiimide compound, an oxazoline compound, a hydrophilic melamine resin, a metal ion, and the like can be given. An amino resin and / or a blocked isocyanate resin is generally used in view of various performances and costs of the obtained coating film.

  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, other viscosity control agents can be added to the water-based metallic paint in order to prevent the compatibility with the top coat film and ensure the coating workability. As the viscosity control agent, those generally showing thixotropy can be used, for example, polyamide-based ones such as crosslinked or non-crosslinked resin particles, swelling dispersions of fatty acid amides, amide fatty acids, and long-chain polyaminoamide phosphates. Viscosity develops depending on the shape of polyethylene, such as colloidal swelling dispersion of polyethylene oxide, organic bentonite such as organic acid smectite clay, montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, etc. A flat pigment etc. can be mentioned.

  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.

(Multi-layer coating 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. As the method for forming a multilayer coating film, for example, a step (I) of forming the base coating film by applying the above-described aqueous metallic coating to an object to be coated, without curing the base coating film thereon A method comprising a step (II) of forming a clear coating film by applying a clear paint and a step (III) of simultaneously heating the base coating film and the clear coating film can be mentioned.

  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 of iron, copper, aluminum, tin, zinc, and the like, 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 from the viewpoint of corrosion resistance, a cation type electrodeposition paint composition is preferable.

  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 articles 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. Specifically, the coating film-forming resin and the curing agent mentioned in the previous aqueous metallic paint can be used, and used in combination. It is From the viewpoint of various performances and costs of the obtained intermediate coating film, an acrylic resin and / or polyester resin, and an amino resin and / or 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 underlying layer cannot be concealed, resulting in film breakage. If the film thickness exceeds 30 μm, sharpness may be deteriorated, or defects such as unevenness or sagging may occur during painting. There is a fear. In order to obtain a multilayer coating film having a good appearance, it is preferable to heat the obtained metallic base coating film at 40 to 100 ° C. for 2 to 10 minutes before applying the clear paint. The reaction between the carbonyl group-containing unsaturated monomer and the cross-linking agent proceeds to such an extent that the orientation of the glitter pigment is not disturbed by the application of the clear paint by this preheating.

  In the multilayer coating film forming method, the clear coating film is formed by coating the clear coating material on the metallic base coating film obtained by applying the water-based metallic coating composition without heating and curing. The clear coating film smoothes and protects irregularities, flickering, and the like caused by the metallic 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 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 have a viscosity of 20 to 50 seconds.

  Specific examples of a method for applying the above clear paint to the metallic 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, ordinary powder paints such as thermoplastic and thermosetting powder paints 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 is heated simultaneously with the previously formed metallic base coating film to form a cured coating film. The heat curing temperature is preferably set to 80 to 180 ° C., more preferably 120 to 160 ° C., from the viewpoints of curability and physical properties of the obtained 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-described 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 crosslinking agent, 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 metallic base paint, a multilayer coating film having excellent recoat adhesion, chipping property, and water-resistant adhesion property can be obtained. . Therefore, the water-based metallic paint can be suitably used as a water-based metallic base paint.

  EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, 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)
Add 135.4 parts of ion-exchanged water and 1.1 part of Aqualon HS-10 (polyoxyethylene alkylpropenyl phenyl ether sulfate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) to the reaction vessel, and mix and stir in a nitrogen stream at 80 ° C. The temperature was raised to. Next, 35.73 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 5.7 parts of 2-hydroxyethyl methacrylate, 20 parts of styrene, 0.5 part of Aqualon HS-10, Adekaria soap NE-20 ( α- [1-[(allyloxy) methyl] -2-nonylphenoxy] ethyl) -ω-hydroxyoxyethylene (manufactured by Asahi Denka Co., Ltd., 80% aqueous solution) 0.5 part and ion-exchanged water 49.7 parts A first-stage ethylenically unsaturated monomer mixture and an initiator solution consisting of 0.21 part of ammonium persulfate and 8.6 parts of ion-exchanged water were dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Further, 25.3 parts of butyl methacrylate, 2.4 parts of 2-hydroxyethyl methacrylate, 2.3 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water were added to this reaction vessel. A second stage ethylenically unsaturated monomer mixture and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.4 parts ion-exchanged water were added dropwise in parallel over 0.5 hours at 80 ° C. . After completion of the dropping, aging was performed at the same temperature for 2 hours.

  Next, after cooling to 40 ° C. and filtering with a 400 mesh filter, 2.14 parts of ion-exchanged 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 acrylic resin emulsion Em-1 having a solid content acid value of 15 and a hydroxyl value of 35 was obtained.

(Production Examples 2-3: Production of acrylic resin emulsion Em-2-3)
Em-2 to 3 were obtained in the same manner as Em-1 in Production Example 1 except that the monomer composition of the emulsion was changed as shown in Table 1 below.

ＤＡＡＭ：ダイアセトンアクリルアミド

DAAM: diacetone acrylamide

(Production Example 4 Production of water-soluble acrylic resin)
To the reaction vessel, 23.89 parts of dipropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether were added, and the temperature was raised to 105 ° C. while mixing and stirring in a nitrogen stream. Next, 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate, 6.9 parts of methacrylic acid, 10.0 parts of dipropylene glycol methyl ether and t-butyl An initiator solution consisting of 1 part of peroxy 2-ethylhexanoate was added dropwise to the reaction vessel in parallel over 3 hours. After completion of the dropping, aging was performed at the same temperature for 0.5 hours.

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

  Furthermore, 16.11 parts of the solvent was distilled off at 110 ° C. under reduced pressure (70 torr) using a solvent removal apparatus, and then 204 parts of ion-exchanged water and 714 parts of dimethylethanolamine were added to obtain a water-soluble acrylic resin. The obtained acrylic resin solution had a non-volatile content of 30.0%, a solid content acid value of 40 mgKOH / g, and a hydroxyl value of 50 mgKOH / g.

(Production Example 5 Production of Hydrophobic Melamine Resin Water Dispersion MFD-1)
50 parts of MFDG (methyl propylene diglycol, manufactured by Nippon Emulsifier Co., Ltd.) was added to the reaction vessel, and the temperature was raised to 130 ° C. while stirring in a nitrogen stream. Next, an ethylenic polymer consisting of 14.77 parts of acrylic acid, 32.48 parts of 2-hydroxyethyl methacrylate, 47.75 parts of butyl acrylate, and 5 parts of MSD-100 (α-methylstyrene dimer, Mitsui Chemicals). A saturated monomer mixture and an initiator solution consisting of 13 parts of Kayaester O (tert-butyl peroctanoate, manufactured by Kayaku Akzo) and 10 parts of MFDG were dropped into the reaction vessel in parallel over 3 hours. After the completion of dropping, an initiator solution consisting of 0.5 parts of Kayaester O and 5 parts of MFDG was added dropwise over 0.5 hours. After completion of the dropwise addition, aging was performed at the same temperature for 1 hour. Next, the mixture was cooled to 50 ° C. to obtain an acrylic resin Ac1 having a nonvolatile content of 60%, a solid content acid value of 110 mgKOH / g, a hydroxyl value of 140 mgKOH / g, and a number average molecular weight (Mn) = 3000.

  178.5 parts of the obtained acrylic resin Ac1 was mixed with 800 parts of Uban 20SB (fully butylated melamine resin, manufactured by Nippon Cytec Co., Ltd., non-volatile content 75%, Sp = 9.6) and stirred at 80 ° C. for 4 hours. . Thereafter, 18.3 parts of dimethylethanolamine was added and dispersed uniformly. After cooling to 40 ° C., 1003.2 parts of ion-exchanged water was added dropwise over 1 hour to obtain a hydrophobic melamine resin aqueous dispersion MFD-1. Obtained. The particle size of the resin particles in this aqueous dispersion was 80 nm.

Example 1
153.3 parts of the acrylic resin emulsion Em-1 obtained in Production Example 1 as a film-forming resin, 5 parts of a 10 mass% dimethylethanolamine aqueous solution, and 16.7 of the water-soluble acrylic resin obtained in Production Example 4 Part, Prime Pole PX-1000 (Sanyo Kasei Kogyo Co., Ltd. bifunctional polyether polyol, number average molecular weight 1000, hydroxyl value 278, water tolerance infinity) 100 parts, MFD-1 obtained in Production Example 5 100 parts, As a bright pigment, 19 parts of aluminum paste MH8801 (Asahi Kasei Aluminum pigment), 30 parts of ethylene glycol monohexyl ether and 2.53 parts of ADH aqueous solution (7%) shown in Table 2 below were mixed and stirred. A dimethylaminoethanol aqueous solution was added to adjust the pH to 8.5 and dispersed uniformly to obtain an aqueous base paint. The resulting aqueous base paint has a paint viscosity of 20 ° C. Ion-exchanged water was added and diluted so that it would be 60 seconds in a 4 Ford cup to obtain an aqueous base paint used for coating.

Formation of multi-layer coating film Cationic electrodeposition paint "Power Top V-20" and polyester-melamine gray intermediate coating "Orga H-870" (both trade names) made by Nippon Paint Co., Ltd. The aqueous base paint obtained as described above is atomized by an electrostatic coating machine AutoREA (trade name, manufactured by Lansburg) on a test plate that has been coated and heat-cured to have a dry film thickness of 25 μm and 40 μm. After applying at a pressure of 5 kg / cm2 and preheating at 80 ° C. for 5 minutes, it was wet-on-wet, and “Mach Flow O-1810” (trade name, acid epoxy curable acrylic resin-based clear paint by Nippon Paint Co., Ltd.) ) By spraying, setting for about 7 minutes, and baking and drying at 140 ° C. for 30 minutes. 2C1B) coating test plates were prepared. In addition, the cured coating film by a base coating material and a clear coating material was applied so that the dry film thickness might be 15 micrometers and 40 micrometers, respectively.

The flip-flop (FF) property of the base single film obtained by applying only the obtained aqueous base paint and drying was evaluated. The results are shown in Table 2. Moreover, FF property was similarly evaluated about the coating film obtained by apply | coating a clear coating material on a base coating film, and the result was shown in Table 2. Furthermore, color difference variation (%) between the FF value of the base single film and the FF value after clear coating:
[(FF value after clear coating / FF value of base single film) × 100]
Is shown in Table 2. The test method is as described later.

(Examples 2-5 and Comparative Examples 1-3)
An aqueous base paint and a coating test plate were obtained in the same manner as in Example 1 except that the type of the acrylic resin emulsion was changed as shown in Table 2 (Example) and Table 3 (Comparative Example). Their FF properties were evaluated in the same manner as in Example 1, and the results are shown in Tables 2 and 3. The test method is as follows.

(Test method)
Flip-Flop (FF) Property Using a “Minolta color change colorimeter CM512-M2” manufactured by Minolta, flip-flop property was evaluated from the L value of each coating film at 15 degrees and 110 degrees with respect to incident light. The flip-flop property was obtained by a ratio of (L value at 15 degrees) / (L value at 110 degrees). The larger the ratio value, the stronger the flip-flop property.

  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.

ＡＤＨ：アジピン酸ジヒドラジド

ADH: Adipic acid dihydrazide

  From the above results, it was found that the aqueous metallic paints of Examples 1 to 5 of the present invention had excellent flip-flop properties as compared with the conventional aqueous metallic paints of Comparative Examples 1 to 3. As is clear from the results in Tables 2 and 3, the FF value of the base single film and the value of the FF value after the clear coating are not affected by the clear coating and are excellent. It is better that the color difference variation is closer to 100%, and in all of Examples 1 to 5, it exceeds 90%, whereas the crosslinking agent for the carbonyl group-containing unsaturated monomer in the film-forming resin is used. In Comparative Examples 1 and 2 and Comparative Example 3 in which an excessive amount of a crosslinking agent is used, it is only about 81 to 82%, and the FF value of the base single film and the FF value after clear coating are It means that the change is great.

  The color difference variation of Examples 1 to 5 is small because the carbonyl group present in the acrylic resin emulsion and the crosslinking agent (ADH in this example) blended in the paint are preheated after application of the base paint ( Since the viscosity of the coating surface is increased by causing a crosslinking reaction at 80 ° C. for 5 minutes, the solvent swelling of the base coating film and the mixing of the resin between the layers that occur after clear coating are suppressed, and the glitter pigment It is considered that the color difference variation is reduced as a result.

  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 comprises an acrylic resin emulsion;
The acrylic resin emulsion is obtained by two-stage emulsion polymerization using a monomer mixture, and has an acid value of 1 to 30 mgKOH / g, a hydroxyl value of 10 to 150 mgKOH / g, and a particle size of 20 to 140 nm.
The monomer mixture contains 0.5 to 10.0% by mass of a carbonyl group-containing unsaturated monomer based on the solid content of the film-forming resin,
The curing agent is a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm,
Further, the crosslinking agent contains one or more compounds selected from the group consisting of hydrazine compounds or semicarbazide compounds in an amount of 0.5 to 1.5 equivalents relative to the amount of the carbonyl group-containing unsaturated monomer. Water-based metallic paint.   The carbonyl group-containing unsaturated monomer is selected from the group consisting of diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone, acrolein, and formylstyrene. The water-based metallic paint according to claim 1, wherein the water-based metallic paint is one or more selected monomers. 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, wherein the water-based metallic base paint is the water-based metallic paint according to claim 1 or 2. A multilayer coating film formed by the multilayer coating film forming method according to claim 3.

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