JP2014201652A - Water-based coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based coating composition with which the metallic feeling of a coating film obtained by coating is excellent, and in which the generation of a hydrogen gas caused by reaction between an aluminum pigment and water is suppressed upon storage, and having an excellent metallic feeling even if being coated after storage.SOLUTION: Provided is a water-based coating composition comprising: a zinc oxide pigment; a flaky aluminum pigment; and a coating film forming resin, and also provided is a method for forming a coating film in which the surface of a coating film obtained by coating the object to be coated with the water-based coating composition is further coated with a clear coating.

Description

The present invention relates to an aqueous coating composition excellent in finish and storage stability of a coating film obtained by coating.

In some cases, a paint containing scaly aluminum flake pigment is applied for the purpose of imparting design properties to an automobile body outer plate or an industrial product. Until now, organic solvent-based paints with excellent finish and storage stability have been used.

  In recent years, in order to reduce the environmental load, the conversion from organic solvent-based paints to water-based paints is progressing. Water-based paints containing scaly aluminum pigments have the problem that aluminum and water react with each other to generate hydrogen gas, resulting in a decrease in storability, and the surface of the scaly aluminum pigments is modified to reduce the finish. Was.

Patent Document 1 relates to a water-based coating composition that is excellent in metallization of a coating film obtained by coating, and suppresses the generation of hydrogen gas due to the reaction between an aluminum pigment and water during storage. An aqueous paint composition containing at least one rust preventive pigment selected from a rust preventive pigment, a phosphite rust preventive pigment and a condensed phosphate rust preventive pigment, a scaly aluminum pigment, and a resin composition Things are listed. Although the water-based coating composition described in Patent Document 1 is excellent in storability, depending on the dispersion state of the rust preventive pigment in the coating, the metallic feeling of the coating film obtained by coating becomes insufficient. There was a problem that there was a possibility.
There was a problem.

JP 2008-248073 A

  An object of the present invention is to provide an aqueous coating composition that is excellent in metallization of a coating film obtained by coating and in which hydrogen gas generation due to the reaction between an aluminum pigment and water during storage is suppressed.

The present invention
1. An aqueous coating composition containing a zinc oxide pigment, a scaly aluminum pigment, and a film-forming resin;
2. Furthermore, the aqueous coating composition of 1 containing phosphoric acid containing resin,
3. Item 3. The aqueous coating composition according to Item 1 or 2, wherein the primary average particle size of the zinc oxide pigment is in the range of 10 to 250 nm.
4). 4. The water-based paint according to any one of 1 to 3, wherein the content of the zinc oxide pigment is within a range of 0.01 to 3 parts by mass as a solid part by mass with respect to 100 parts by mass of the solid content of the coating film-forming resin. Composition,
5. It is related with the coating-film formation method which coats a clear coating on the coating film obtained by apply | coating the water-based coating composition of any one of 1-4 to a to-be-coated article.

The aqueous coating composition of the present invention does not generate hydrogen gas due to the reaction between aluminum and water during storage, and is excellent in the metallic feeling of the coating film obtained by coating.

The aqueous coating composition of the present invention contains a scaly aluminum pigment for the purpose of imparting a metallic feeling to a coating film obtained by painting.

  The scaly aluminum pigment is generally produced by pulverizing and grinding aluminum in a ball mill or attritor mill using a grinding aid in the presence of a grinding fluid, and usually has an average particle size (D50) for coating. Those having a thickness of about 1 to 50 μm, particularly about 5 to 25 μm, and having a thickness in the range of 0.01 μm to 10 μm, particularly 0.1 μm to 5 μm, are suitable for stability in the paint and the coating film to be formed. Used from the point of finishing. The average particle diameter means a long diameter. As the grinding aid, aliphatic amines, aliphatic amides and aliphatic alcohols are used in addition to higher fatty acids such as oleic acid, stearic acid, isostearic acid, lauric acid, palmitic acid and myristic acid. Aliphatic hydrocarbons such as mineral spirits are used as the grinding fluid.

  The scaly aluminum flake pigments can be roughly classified into a leafing type and a non-leafing type depending on the type of grinding aid. The leafing type is an arrangement (leafing) on the surface of the coating film obtained by painting when blended into a paint composition, giving a strong finish with a metallic feel, heat reflection, and rust prevention Therefore, it is often used for various building materials such as tanks, ducts, piping and roof roofing. In the water-based coating composition of the present invention, it is preferable to use a non-leafing type scaly aluminum pigment from the viewpoint of the metal feeling and finish of the coating film obtained by coating.

  In the aqueous coating composition of the present invention, the amount of the scaly aluminum pigment is based on 100 parts by mass of the solid content of the resin composition to be described later, from the viewpoint of the metallic feeling and the finished appearance of the coating film obtained by coating. The content is preferably in the range of 0.1 to 50 parts by mass, and more preferably in the range of 0.5 to 40 parts by mass.

  The aqueous coating composition of the present invention contains a zinc oxide pigment for the purpose of suppressing the generation of hydrogen caused by the surface of the scaly aluminum pigment reacting with water in the coating composition.

  Zinc oxide pigments are white powder pigments, which can be industrially produced by heating and vaporizing metallic zinc and burning it with air, or by burning zinc sulfate or zinc nitrate. In the aqueous coating composition of the present invention. Furthermore, from the point of improving the weather resistance, those surface-treated with oxides or hydroxides such as silica, alumina and zirconia, organic silicon compounds such as polydimethylsiloxane, and stearic acid. Higher fatty acids and those surface-treated with an organic titanium compound such as isopropyl triisostearoyl titanate can be used.

  As the zinc oxide pigment in the aqueous coating composition of the present invention, it is preferable to use a pigment having a primary average particle size in the range of 5 nm to 800 nm, and more preferably a primary average particle size in the range of 10 nm to 250 nm. . Particularly preferably, the primary average particle diameter is in the range of 15 nm to 150 nm. Here, the primary average particle diameter of a zinc oxide pigment shall be defined as a primary average particle diameter measured by observing the coating film containing a zinc oxide pigment with an electron microscope.

  The content of the zinc oxide pigment in the aqueous coating composition of the present invention is 100 parts by mass of the solid content of the resin composition described in terms of the storage stability of the aqueous coating composition and the finish of the coating film obtained by coating. On the other hand, it is preferably within a range of 0.01 to 35 parts by mass, more preferably within a range of 0.1 to 20 parts by mass, and particularly preferably within a range of 0.3 to 3 parts by mass.

  The aqueous coating composition of the present invention contains a film-forming resin. As the film-forming resin, a thermosetting resin composition is preferable. Specifically, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, or a urethane resin having a crosslinkable functional group such as a hydroxyl group is used as a melamine resin. , Urea resins, polyisocyanate compounds (including block bodies) and the like are also used in combination, and these can be used by dissolving or dispersing in water. A combination of an acrylic resin, a polyester resin, and a melamine resin as a crosslinking agent is particularly preferred from the viewpoints of finish and coating film performance.

  The water-based coating composition of the present invention may contain a phosphoric acid-containing resin from the viewpoint of the smoothness and water resistance of a coating film obtained by coating.

  The phosphate group-containing resin can be produced, for example, by copolymerizing a phosphate group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers by a known method such as a solution polymerization method. Examples of the phosphoric acid group-containing polymerizable unsaturated monomer include acid phosphooxyethyl (meth) acrylate, acid phosphooxypropyl (meth) acrylate, a reaction product of glycidyl (meth) acrylate and alkyl phosphoric acid, and the like. . These can be used alone or in combination of two or more.

  In the phosphoric acid group-containing resin, the use ratio when copolymerizing the phosphoric acid group-containing polymerizable unsaturated monomer and the other polymerizable unsaturated monomer is 1/99 to 40 / About 60 is preferable, about 5/95 to 35/65 is more preferable, and about 10/90 to 30/70 is more preferable.

  The blending amount of the phosphate group-containing resin in the aqueous coating composition of the present invention is usually preferably about 0.5 to 15 parts by mass, and preferably 0.75 to 10 parts by mass with respect to 100 parts by mass of the coating film-forming resin solid content. The degree is more preferable.

  Moreover, a color pigment can be mix | blended with the water-based coating composition of this invention as needed. As the color pigment, conventionally known pigments for ink and paint can be used alone or in combination of two or more. Specific examples of color pigments include metal oxide pigments such as titanium oxide and iron oxide, composite metal oxide pigments such as titanium yellow, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, and perinone pigments. Examples thereof include pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, indanthrene pigments, dioxazine pigments, and indigo pigments.

  The preferable content of these color pigments in the aqueous coating composition of the present invention is 50 parts by mass or less with respect to 100 parts by mass of the solid content of the coating film-forming resin from the viewpoint of the color tone and finish of the coating film obtained by coating. It is preferable that it is in the range of 1 to 30 parts by mass.

  The water-based coating composition of the present invention can contain a luster pigment in addition to the scale-like aluminum flake pigment. Examples of the glitter pigment include a scale-like metal pigment having a surface coated with a metal oxide, a scale-like metal pigment having a surface adsorbed with a colored pigment, and a metal oxide layer by causing an oxidation-reduction reaction on the surface. Scale-like metal pigments, aluminum solid solution iron oxide pigments, glass flake pigments, glass flake pigments coated with metal oxide on the surface, glass flake pigments with colored pigments chemically adsorbed on the surface, titanium dioxide on the surface Interference mica pigment coated with, reduced mica pigment reduced from interference mica pigment, colored mica pigment chemically adsorbed on the surface, coated with iron oxide on the surface, graphite pigment coated with titanium dioxide on the surface, surface Silica flake and alumina flake pigment coated with titanium dioxide, plate-like iron oxide pigment, hologram pigment, synthetic mica pigment, spiral Cholesteric liquid crystal polymer pigments having granulation, and the like oxy bismuth pigments chloride. Various glitter pigments can be appropriately used depending on the glitter feeling for which one or more of these are desired.

  When using a luster pigment other than the flaky aluminum pigment, the blending amount thereof is a coating film obtained by coating with respect to 100 parts by mass of the coating film forming resin solid content as a total amount with the flaky aluminum pigment. From the standpoint of glitter and finish, it is preferably 50 parts by mass or less, more preferably in the range of 1 to 30 parts by mass.

  The water-based coating composition of the present invention further includes various kinds of water or organic solvents, rheology control agents, pigment dispersants, antisettling agents, curing catalysts, antifoaming agents, antioxidants, ultraviolet absorbers, and the like as necessary. Additives, extender pigments and the like can be appropriately blended.

  The aqueous coating composition of the present invention can be prepared by mixing and dispersing the aforementioned components. The zinc oxide pigment can be mixed with the resin component and water in advance to prepare a pigment dispersion, and the pigment dispersion can be mixed with the above-described components and blended in the aqueous coating composition.

  The pigment dispersion will be described. When a pigment is blended in the coating composition, it is necessary to stably exist in a good dispersion state in the coating composition. Therefore, the pigment may be blended into the coating composition as a powder and then dispersed, but a pigment dispersion containing a high concentration of the pigment and maintaining a good dispersion state is prepared in advance. And can be blended into the coating composition as a pigment dispersion.

  When preparing the pigment dispersion of the zinc oxide pigment for blending in the aqueous coating composition of the present invention, for example, it can be carried out as follows. The film-forming resin and the zinc oxide pigment in the aqueous coating composition of the present invention are mixed. The blending ratio at this time is such that the zinc oxide pigment is in the range of 100 to 1000 parts by mass with respect to 100 parts by mass of the solid content of the coating film-forming resin from the viewpoint of the dispersion state in the pigment dispersion. preferable. Furthermore, water is added and it adjusts so that solid content may be in the range of 30-80 mass%. The obtained zinc oxide pigment, resin and water mixture are used in combination with grinding media such as glass beads and ceramic beads, and dispersed using a disperser such as a bead mill or paint conditioner, so that the zinc oxide pigment has a high concentration. The pigment dispersion contained in the can be adjusted. Further, the pigment dispersion may contain a commercially available pigment dispersant for the purpose of maintaining a good dispersion state of the pigment.

  In the coating composition of the present invention, the zinc oxide pigment may be blended as a powder without preparing a pigment dispersion in advance from the viewpoint of reducing the man-hour for preparing the coating.

  The aqueous coating composition of the present invention is obtained by mixing the above-described scaly aluminum pigment, zinc oxide pigment, coating film-forming resin composition and, if necessary, a bright pigment other than a color pigment or scaly aluminum pigment, It is preferable to adjust the pH within the range of 6 to 10 by adding the basic neutralizing agent composition in order to enhance the effect of suppressing gas generation during storage.

  Examples of the basic neutralizer composition include aliphatic tertiary amines, and specifically include triethylamine, N, N-dimethylaminoethanol, 2-amino-2-methylpropanol, diethanolamine, triethanolamine, and the like. Ethanolamine or the like can be used.

  Next, the manufacturing method of the water-based coating composition of this invention is demonstrated. A high-concentration scaly aluminum pigment solution containing a scaly aluminum pigment and an organic solvent is prepared in advance. Next, the high-concentration scaly aluminum pigment solution is added to the mixture of the film-forming resin in the aqueous coating composition and mixed with stirring. When a bright pigment other than the scale-like aluminum pigment is blended, a high-concentration bright pigment liquid containing the bright pigment and, for example, ethylene glycol monobutyl ether is prepared in advance and added. When a coloring pigment is blended, the coloring pigment dispersion can be prepared and added in the same manner as the above-described zinc oxide pigment dispersion is prepared. Next, the aforementioned zinc oxide pigment is added and further stirred and mixed, and then the basic neutralizer composition is added to adjust the pH of the aqueous coating composition. Thereafter, an additive or water can be added as necessary to produce an aqueous coating composition having a viscosity suitable for coating.

  The organic solvent used for the high-concentration scaly aluminum liquid is not particularly limited. For example, glycol ether solvents such as ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, hexyl cellosolve, acetic acid. Ethylene glycol monomethyl ether, methyl methoxy butanol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monopropyl and propylene glycol monobutyl ether, ether ester solvent methoxybutyl acetate, alcohol solvent methyl alcohol, ethyl alcohol , Isopropyl alcohol, 2-ethylhexyl alcohol and n-butyl alcohol , It can be used n- methylpyrrolidone, and mixtures thereof.

  The coating film forming method of the present invention relates to a method of further applying a clear paint on a coating film obtained by coating the above-mentioned aqueous coating composition on an article to be coated.

  In the coating film forming method of the present invention, the object to be coated includes metals such as iron, zinc, and aluminum, alloys containing these, and molded products plated or vapor-deposited with these metals, and building materials such as concrete and slate. In addition, a molded article made of glass, plastic, foam, or the like can be given. Depending on these materials, it can be appropriately subjected to degreasing treatment or surface treatment to obtain an article to be coated. Furthermore, it is also possible to form an undercoating film or an intermediate coating film on the above-mentioned material or a material that has been subjected to various treatments to form an article to be coated, and these are particularly preferable.

  The undercoat film is formed to conceal the surface of the material or impart anticorrosion and rustproofness to the material, and can be obtained by applying an undercoat paint, drying and curing. it can. The type of the undercoat paint is not particularly limited, and examples thereof include an electrodeposition paint and a solvent-type primer.

  The intermediate coating film is formed to conceal the undercoat film or impart adhesion, chipping resistance, etc., and is a dry-cured undercoat film or an uncured undercoat film. It can be obtained by applying an intermediate coating on top, drying and curing. The type of intermediate coating is not particularly limited, and known ones can be used. For example, an organic solvent-based or water-based intermediate coating containing a thermosetting resin composition and a color pigment as essential components can be preferably used. .

  In the case where an undercoating film or an intermediate coating film is used as the object to be coated, the undercoating film or the intermediate coating film is heated, and the coating composition of the present invention is applied after crosslinking and curing. be able to. Alternatively, the undercoating film and / or the intermediate coating film can be applied in an uncured state.

  In the coating film forming method of the present invention, a clear coating is further applied on the coating obtained by applying the aqueous coating composition to the object to be coated to form a clear coating. .

  The clear paint in the method for forming a coating film of the present invention is a liquid paint which forms a colorless or colored transparent coating film comprising a resin component and a solvent as main components, and further blending other additives for paint as required. It is.

  As the clear paint in the method of the present invention, conventionally known clear paints can be used without limitation. For example, a liquid or powdery coating composition containing a base resin and a crosslinking agent can be applied. Examples of the base resin include acrylic resin, polyester resin, alkyd resin, fluororesin, urethane resin, and silicon-containing resin containing a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a silanol group, and an epoxy group. Examples of the crosslinking agent include melamine resin, urea resin, polyisocyanate compound, block polyisocyanate compound, epoxy compound or resin, carboxyl group-containing compound or resin, acid anhydride, alkoxy which can react with the functional group of the base resin. Examples include silane group-containing compounds or resins. Further, if necessary, additives such as a solvent such as water and an organic solvent, a curing catalyst, an antifoaming agent, an ultraviolet absorber, a rheology control agent, an antioxidant, and a surface conditioner can be appropriately blended.

  In the clear paint, a color pigment and a dye can be blended in a timely manner within a range not impairing transparency. As the color pigments and dyes, conventionally known pigments and dyes for inks and paints can be used alone or in combination of two or more. The amount of addition may be determined as appropriate, but is 30 parts by mass or less, preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the resin solid content in the clear coating film.

  The clear coating can be applied by a method such as electrostatic coating, air spraying, airless spraying, and the film thickness is preferably in the range of 5 to 40 μm based on the cured coating film. The clear coating film itself can be crosslinked and cured at a temperature of about 70-150 ° C.

  The coating film forming method of the present invention is a so-called 2C2B process in which the aqueous coating composition of the present invention is applied, heated, dried and cured, and then the clear coating is applied on the coated film, heated, and dried and cured. However, a multi-layer coating film can also be obtained by a so-called 2C1B process in which a clear coating is applied in an uncured state after the aqueous coating composition is applied, and then heated to cure them simultaneously.

  Next, an Example is given and this invention is demonstrated more concretely.

Production Example 1
(Manufacture of acrylic resin emulsion)
In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device, 130 parts by mass of deionized water, Aqualon KH-10 (trade name, surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) The components were charged, stirred and mixed in a nitrogen stream, and heated to 80 ° C. Next, 1% of the total amount of the following monomer emulsion (1) and 5.3 parts by mass of 6% ammonium persulfate aqueous solution were introduced into the reaction vessel and maintained at 80 ° C. for 15 minutes. Then, the remaining monomer emulsion (1) was dripped in the reaction container hold | maintained at the same temperature over 3 hours, and it age | cure | ripened for 1 hour after completion | finish of dripping. Thereafter, the following monomer emulsion (2) was added dropwise over 1 hour, and after aging for 1 hour, the mixture was cooled to 30 ° C while gradually adding 40 parts by mass of a 5% dimethylethanolamine aqueous solution to the reaction vessel, It was discharged while being filtered through nylon cloth, and the average particle size was 100 nm (submicron particle size distribution measuring device “COULTER N4 type” (manufactured by Beckman Coulter, Inc.) and diluted with deionized water and measured at 20 ° C.). An acrylic resin emulsion having a solid content concentration of 30% was obtained. The obtained acrylic resin had an acid value of 33 mgKOH / g and a hydroxyl value of 25 mgKOH / g.

  Monomer emulsion (1): 42 parts by weight of deionized water, 0.72 parts by weight of Aqualon KH-10, 2.1 parts by weight of methylenebisacrylamide, 2.8 parts by weight of styrene, 16.1 parts by weight of methyl methacrylate, ethyl acrylate Monomer emulsion (1) obtained by mixing and stirring 28 parts by mass and 21 parts by mass of n-butyl acrylate.

  Monomer emulsion (2): 18 parts by weight of deionized water, 0.31 parts by weight of Aqualon KH-10, 0.03 parts by weight of ammonium persulfate, 5.1 parts by weight of methacrylic acid, 5.1 parts by weight of 2-hydroxyethyl acrylate Monomer emulsion (2) obtained by mixing and stirring 3 parts by mass of styrene, 6 parts by mass of methyl methacrylate, 1.8 parts by mass of ethyl acrylate and 9 parts by mass of n-butyl acrylate.

Production Example 2
(Manufacture of polyester resin)
In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator, 109 parts by weight of trimethylolpropane, 141 parts by weight of 1,6-hexanediol, 126 parts by weight of hexahydrophthalic anhydride and 120 parts of adipic acid A mass part was charged, and the temperature until reaching 160 ° C. to 160 ° C. was raised to 3 hours, followed by a condensation reaction at 230 ° C. for 4 hours. Subsequently, in order to add a carboxyl group to the obtained condensation reaction product, 38.3 parts by mass of trimellitic anhydride was further added and reacted at 170 ° C. for 30 minutes, and then 2-ethyl-1-hexanol (20 The polyester resin solution having a solid content concentration of 70% was obtained by diluting with a mass dissolved in 100 g of water at 0.1 ° C. at 0.1 ° C. The obtained polyester resin had an acid value of 46 mgKOH / g, a hydroxyl value of 150 mgKOH / g, and a weight average molecular weight of 6,400. Here, the weight average molecular weight means that measured by gel permeation chromatography (GPC) using a standard polystyrene calibration curve.
Production Example 3 Production of Phosphate Group-Containing Resin Solution A mixed solvent of 27.5 parts of methoxypropanol and 27.5 parts of isobutanol was placed in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device. After being heated to 110 ° C., while maintaining at 110 ° C., 25 parts of styrene, 27.5 parts of n-butyl methacrylate, 20 parts of branched higher alkyl acrylate (trade name “Isostearyl Acrylate”, manufactured by Osaka Organic Chemical Industry Co., Ltd.) , 7.5 parts of 4-hydroxybutyl acrylate, 15 parts of the following phosphoric acid group-containing polymerizable monomer, 12.5 parts of 2-methacryloyloxyethyl acid phosphate, 10 parts of isobutanol and 4 parts of tert-butyl peroxyoctanoate 121.5 parts of the resulting mixture was added dropwise to the above mixed solvent over 4 hours, and tert- Chill peroxyoctanoate mixture consisting of 0.5 parts of isopropanol 20 parts was added dropwise for 1 hour. Thereafter, the mixture was aged and stirred for 1 hour to obtain a phosphate group-containing resin solution having a solid content of 50%. The phosphate group-containing resin had an acid value of 83 mgKOH / g, a hydroxyl value of 29 mgKOH / g, and a weight average molecular weight of 10,000.
Phosphoric acid group-containing polymerizable monomer: 57.5 parts of monobutyl phosphoric acid and 41 parts of isobutanol were placed in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device, and the temperature was raised to 90 ° C. Thereafter, 42.5 parts of glycidyl methacrylate was added dropwise over 2 hours, followed by further stirring and aging for 1 hour. Subsequently, 59 parts of isopropanol was added to obtain a phosphate group-containing polymerizable monomer solution having a solid content of 50%. The acid value of the obtained monomer was 285 mgKOH / g.

Example 1
In a stainless steel beaker, TAPPA METALLUX 3560 (trade name, scaly aluminum pigment, solid content 65% by mass, D50 = 13 μm, manufactured by Ecart Co., non-leafing type) 15.4 parts (solid content 10 parts), phosphate group 8 parts of resin solution (4 parts of solid content), 36.6 parts of 2-ethyl-1-hexanol (mass dissolved in 100 g of water at 20 ° C .: 0.1 g), and 0.2 part of 2- (dimethylamino) ethanol. 5 parts were mixed uniformly to obtain a high concentration aluminum pigment liquid.

  100 parts by mass of the acrylic resin emulsion obtained in Production Example 1, 57 parts by mass of the polyester resin solution obtained in Production Example 2, 60.6 parts by mass of the above high-concentration scaly aluminum pigment liquid (1), NANOBYK-3820 (product) Name, dispersion of zinc oxide nanoparticles, primary average particle size 20 nm, manufactured by BYK) 0.22 part (solid content 0.1 part) and Cymel 325 (trade name, manufactured by Nippon Cytec Industries, Inc., melamine resin, solid content 80%) 37.5 parts by mass are mixed uniformly, and further, Primal ASE-60 (trade name, manufactured by Rohm and Haas, polyacrylic acid thickener), 2- (dimethylamino) ethanol and deionized water. Ford Cup No. at pH 8.0, paint solids content 25%, 20 ° C. An aqueous coating composition (1) having a viscosity of 40 seconds according to 4 was prepared.

Examples 2-13, Comparative Examples 1-7
The water-based paint shown in Table 1 was prepared in the same manner as in Example 1.

(Creation of test plate)
"Electron GT-10HT" (trade name: manufactured by Kansai Paint Co., Ltd., epoxy resin polyamine-based cationic resin, block poly as a hardener on a degreased and zinc phosphate-treated steel plate (JISG 3141, size 400 x 300 x 0.8 mm) An electrodeposition coating film was obtained by electrodeposition coating using an isocyanate compound) to a film thickness of 20 μm based on the cured coating film, followed by heating at 170 ° C. for 20 minutes for crosslinking and curing.

  On the obtained electrodeposition coating film, an intermediate coating “Lugabake Intermediate Coating Gray” (trade name: manufactured by Kansai Paint Co., Ltd., polyester resin / melamine resin type, organic solvent type) is based on the cured coating film by air spray. Then, the coating plate was coated so that the film thickness was 30 μm, heated at 140 ° C. for 30 minutes to be crosslinked and cured, and an intermediate coating film was formed.

The water-based coating composition was applied onto a substrate by air spraying so as to have a thickness of 15 μm based on the cured coating film, allowed to stand for 15 minutes, and heated at 80 ° C. for 10 minutes to evaporate water. Next, a clear paint (Lugabake Clear, manufactured by Kansai Paint, trade name, acrylic resin / amino resin type, organic solvent type) is applied to these uncured surfaces using a minibell rotary electrostatic coating machine, and a booth temperature of 25 The cured coating film was coated to a thickness of 35 μm under the conditions of ° C. and humidity of 75%. After coating, the sample was allowed to stand at room temperature for 15 minutes, and then heated in a hot-air circulating drying oven at 140 ° C. for 30 minutes to simultaneously dry and cure the multilayer coating film to obtain a test plate.
(Colorimetry)
The obtained test plate was measured with ALCOPE LMR-200 (trade name, laser-type metallic feeling measuring device, manufactured by Kansai Paint Co., Ltd.). The results of the displayed IV (intensity, the brighter the value is) are shown in Table 1.
(Gas generation measurement)
After preparing the aqueous coating composition and leaving it to stand for 1 day, 200 g of the coating material is put into a dedicated glass container (internal volume 500 ml), and the container is immersed in a constant temperature bath at 40 ° C. without being stoppered, and left for 1 hour. The instrument was plugged in and started (0 hour), the amount of accumulated gas generated for 7 days was measured, and the results are shown in Table 1.
(Paint test after storage)
500 g of the above-mentioned aqueous coating composition is put into a 1 L inner surface coated iron container and left in a constant temperature room at 40 ° C. for 7 days. Table 1 shows the results.

The water-based coating composition of the present invention can be applied to various industrial products, particularly to the outer plate of an automobile body.

Claims (5)

An aqueous coating composition containing a zinc oxide pigment, a scaly aluminum pigment, and a film-forming resin. Furthermore, the water-based coating composition of Claim 1 containing phosphoric acid containing resin. The aqueous coating composition according to claim 1 or 2, wherein the primary average particle diameter of the zinc oxide pigment is in the range of 10 to 250 nm. The aqueous solution according to any one of claims 1 to 3, wherein the content of the zinc oxide pigment is in the range of 0.01 to 3 parts by mass as the solid part by mass with respect to 100 parts by mass of the solid content of the coating film-forming resin. Paint composition. The coating-film formation method which coats a clear coating on the coating film obtained by apply | coating the water-based coating composition of any one of Claims 1-4 to to-be-coated material.