Water dispersion for metallic paint and water-based metallic paint

Abstract

To provide a water dispersion for metallic paint from which a cured coating film excellent in coating film appearance and lifting resistance is obtained, and aqueous metallic paint containing the same.SOLUTION: A water dispersion for metallic paint has an acrylic polymer (A) dispersed in an aqueous medium (B), the acrylic polymer (A) being produced from fumaric acid as an essential raw material. The acrylic polymer (A) has an acid number of 40-100 mg KOH / g. Particles made of the acrylic polymer (A) have an average particle diameter of 60 nm or less. The water dispersion for metallic paint has a water tolerance of 100% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous dispersion for a metallic paint and an aqueous metallic paint. [Background technology]

[0002] Traditionally, metallic coatings have been used to improve the quality and design of automobiles. Solvent-based paints with excellent drying properties have been the mainstream for these metallic paints, but in recent years, water-based metallic paints have been in demand due to environmental considerations. However, water-based metallic paints have a problem with the orientation of metallic pigments because the water dries slowly, which means that the required high brilliance cannot be obtained.

[0003] Under these circumstances, a glittering coating composition containing an acrylic resin, a curing agent, a glittering pigment, and a solvent in a specific ratio has been proposed (see, for example, Patent Document 1). However, the glittering coating composition has a problem in that it has insufficient lifting resistance.

[0004] Therefore, there has been a demand for a water-based material for metallic paints that is excellent in coating appearance and lifting resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-169416 A Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide an aqueous dispersion for a metallic paint which can give a cured coating film excellent in coating film appearance and lifting resistance, and an aqueous metallic paint containing the same. [Means for solving the problem]

[0007] As a result of intensive research aimed at solving the above problems, the present inventors have found that an aqueous dispersion for a metallic paint, in which a specific acrylic polymer containing fumaric acid as an essential raw material is dispersed in an aqueous medium, gives a cured coating film that is excellent in appearance and lifting resistance, and have completed the present invention.

[0008] That is, the present invention relates to an aqueous dispersion for a metallic paint, in which an acrylic polymer (A) containing fumaric acid as an essential raw material is dispersed in an aqueous medium (B), the aqueous dispersion being characterized in that the acrylic polymer (A) has an acid value of 40 to 100 mgKOH / g, the average particle size of particles formed by the acrylic polymer (A) is 60 nm or less, and the water tolerance is 100% or more. Effect of the Invention

[0009] The aqueous dispersion for a metallic paint of the present invention can be suitably used for various industrial water-based paints including those for vehicles, building exteriors, bridges, industrial machinery, gas tanks, construction machinery, ships, and plastics, because the aqueous dispersion for a metallic paint of the present invention gives a coating film excellent in appearance and lifting resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The aqueous dispersion for a metallic paint of the present invention is an aqueous dispersion for a metallic paint in which an acrylic polymer (A) containing fumaric acid as an essential raw material is dispersed in an aqueous medium (B), wherein the acrylic polymer (A) has an acid value of 40 to 100 mgKOH / g, the average particle size of particles formed by the acrylic polymer (A) is 60 nm or less, and the water tolerance is 100% or more.

[0011] The acrylic polymer (A) containing fumaric acid as an essential raw material is obtained by copolymerizing fumaric acid with other unsaturated monomers.

[0012] Examples of the other unsaturated monomers include styrene and / or styrene derivatives such as styrene, tert-butylstyrene, α-methylstyrene, and vinyltoluene; alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, poly(meth)acrylate, tert-butyl (meth)acrylate, and tert-butyl (meth)acrylate; Examples of the monomers include acrylic monomers having a hydroxyl group such as triethylene glycol mono(meth)acrylate, acrylic monomers having a glycidyl group such as glycidyl (meth)acrylate, vinyl esters of saturated aliphatic carboxylic acids such as vinyl acetate and vinyl propionate, acrylic monomers having a nitrogen atom such as (meth)acrylamide, N-methylol acrylamide, and N-methoxybutyl acrylamide, ethylenically unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid, ethylenically unsaturated dicarboxylic acids other than fumaric acid such as maleic acid, and further, acid anhydrides such as maleic acid, and monoesters of these acid anhydrides. These monomers can be used alone or in combination of two or more.

[0013] In the present invention, "(meth)acrylic acid" refers to either or both of methacrylic acid and acrylic acid, "(meth)acrylate" refers to either or both of methacrylate and acrylate, and "(meth)acrylamide" refers to either or both of methacrylamide and acrylamide.

[0014] The content of fumaric acid in the unsaturated monomer raw material of the acrylic polymer (A) is preferably from 4 to 12 mass %, more preferably from 7 to 12 mass %, since this further improves the coating film appearance and lifting resistance.

[0015] By using fumaric acid as an essential raw material for the acrylic polymer (A), a cured coating film having excellent appearance and lifting resistance can be obtained. Since this further improves lifting resistance, it is preferable that the unsaturated monomer raw material contains styrene, and the amount of styrene in the unsaturated monomer raw material is preferably 20 to 50 mass %.

[0016] By using fumaric acid as an essential raw material for the acrylic polymer (A), a cured coating film having excellent appearance and lifting resistance can be obtained. In order to further improve lifting resistance, it is preferable that the unsaturated monomer raw material contains an alkyl (meth)acrylate, and the alkyl (meth)acrylate in the unsaturated monomer raw material is preferably 20 to 70 mass %.

[0017] When the acrylic polymer (A) is cured by reacting it with a curing component such as isocyanate, it is preferable to use an acrylic monomer having a hydroxyl group.

[0018] The content of the hydroxyl-containing acrylic monomer in the unsaturated monomer raw material of the acrylic polymer (A) is preferably 2 to 10 mass %, more preferably 4 to 8 mass %, since this further improves the coating film appearance and lifting resistance.

[0019] The acid value of the acrylic polymer (A) is 40 to 100 mgKOH / g, and is preferably 60 to 100 mgKOH / g, as this further improves the storage stability of the aqueous dispersion and the appearance and lifting resistance of the resulting coating film.

[0020] The hydroxyl value of the acrylic polymer (A) is preferably from 10 to 50 mgKOH / g, more preferably from 20 to 40 mgKOH / g, since this further improves the appearance and lifting resistance of the resulting coating film.

[0021] The weight average molecular weight of the acrylic polymer (A) is preferably from 5,000 to 100,000, and more preferably from 10,000 to 50,000, since this further improves the coating film appearance and lifting resistance.

[0022] The average molecular weight in the present invention is a value calculated in terms of polystyrene based on gel permeation chromatography (hereinafter abbreviated as "GPC").

[0023] The acrylic polymer (A) can be produced by various methods, including, for example, a method in which an unsaturated monomer raw material is polymerized in an organic solvent using a polymerization initiator.

[0024] Examples of the organic solvent include aromatic hydrocarbon compounds such as toluene and xylene; alicyclic hydrocarbon compounds such as cyclohexane, methylcyclohexane, and ethylcyclohexane; ketone compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester compounds such as ethyl acetate, n-butyl acetate, isobutyl acetate, and propylene glycol monomethyl ether acetate; alcohol compounds such as n-butanol, isopropyl alcohol, and cyclohexanol; glycol compounds such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and diethylene glycol dimethyl ether; and aliphatic hydrocarbon compounds such as heptane, hexane, octane, and mineral turpentine. Among these, it is preferable to use a water-miscible organic solvent because it can be used as the aqueous medium (B) as it is. These organic solvents can be used alone or in combination of two or more.

[0025] Examples of the polymerization initiator include ketone peroxide compounds such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, and 2,2-bis(4,4-ditert-butylperoxycyclohexyl)propane. Peroxyketal compounds such as 2,2-bis(4,4-ditert-amylperoxycyclohexyl)propane, 2,2-bis(4,4-ditert-hexylperoxycyclohexyl)propane, 2,2-bis(4,4-ditert-octylperoxycyclohexyl)propane, and 2,2-bis(4,4-dicumylperoxycyclohexyl)propane; hydroperoxide compounds such as cumene hydroperoxide and 2,5-dimethylhexane-2,5-dihydroperoxide; 1,3-bis(tert -butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene peroxide, tert-butylcumyl peroxide, di-tert-butyl peroxide and other dialkyl peroxide compounds; decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and other diacyl peroxide compounds; bis(tert-butylcyclohexyl)peroxydicarbonyl peroxycarbonate compounds such as tert-butylperoxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, tert-butylperoxybenzoate, peroxyester compounds such as 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methyl)butyronitrile, and 1,1'-azobis(cyclohexane-1-carbonitrile). These polymerization initiators can be used alone or in combination of two or more kinds.

[0026] The aqueous medium (B) may be water, a hydrophilic organic solvent, or a mixture thereof. As the hydrophilic organic solvent, a water-miscible organic solvent that is miscible with water without being separated is preferred, and among them, an organic solvent having a solubility in water (the number of grams of the organic solvent that dissolves in 100 g of water) of 3 g or more at 25° C. is preferred. Examples of these water-miscible organic solvents include alcohol-based solvents such as methanol, ethanol, propanol, butanol, 1,3-butylene glycol-3-monomethyl ether (general name: 3-methoxybutanol), and 3-methyl-3-methoxybutanol (product name: Solfit, manufactured by Kuraray Co., Ltd.); ketone-based solvents such as acetone and methyl ethyl ketone; and glycol ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol dimethyl ether. These aqueous media (B) can be used alone or in combination of two or more kinds.

[0027] The aqueous medium (B) preferably contains water, and the content of water in the aqueous dispersion for a metallic paint is preferably from 10 to 50% by mass, more preferably from 15 to 40% by mass.

[0028] The aqueous dispersion for a metallic paint of the present invention is one in which the acrylic polymer (A) is dispersed in the aqueous medium (B). Examples of a method for dispersing the acrylic polymer (A) in the aqueous medium (B) include a phase inversion emulsification method.

[0029] The phase inversion emulsification method can be exemplified by a method in which a basic compound is added to the acrylic polymer (A) to neutralize some or all of the acid groups in the acrylic polymer (A), and then water is added to disperse the acrylic polymer in water.

[0030] Examples of the basic compound include organic amines such as monoalkanolamines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, butylamine, dibutylamine, tributylamine, N,N-dimethylethanolamine, and 2-aminoethanol, diethanolamine, diisopropanolamine, and dibutanolamine; inorganic basic compounds such as ammonia, sodium hydroxide, and potassium hydroxide; and quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetra-n-butylammonium hydroxide, and trimethylbenzylammonium hydroxide. Among these, it is preferable to use organic amines and ammonia (which may be aqueous ammonia). These basic compounds can be used alone or in combination of two or more kinds.

[0031] The amount of the basic compound used is preferably an amount that results in a neutralization rate of the acid groups in the acrylic polymer (A) in the range of 50 to 100%, since this further improves the dispersibility and storage stability of the aqueous dispersion. By setting the neutralization rate high, the average particle size of the particles formed by the acrylic polymer (A) can be controlled to be small.

[0032] The average particle size of the particles formed by the acrylic polymer (A) in the aqueous dispersion for metallic paint of the present invention is 60 nm or less, and is preferably 5 to 50 nm because this further improves the coating appearance and lifting properties. Here, the average particle size in the present invention refers to a value measured by a method for determining particle size distribution based on the measurement principle of detecting dynamic scattered light of particles.

[0033] The water tolerance of the aqueous dispersion for a metallic paint of the present invention is 100% or more, but is preferably 150% or more, and more preferably 300% or more, since this further improves the coating film appearance and lifting resistance.

[0034] A curing agent can be added to the metallic paint aqueous dispersion of the present invention when the paint is mixed. Examples of the curing agent include polyisocyanate compounds, amino resins, epoxy compounds, oxazoline compounds, carbodiimide compounds, etc., but polyisocyanate compounds are preferred because they improve the appearance of the resulting coating film. These curing agents can be used alone or in combination of two or more.

[0035] Examples of the polyisocyanate compound include aromatic diisocyanate compounds such as tolylene diisocyanate, diphenylmethane diisocyanate, m-xylylene diisocyanate, and m-phenylene bis(dimethylmethylene) diisocyanate; and aliphatic or alicyclic diisocyanate compounds such as hexamethylene diisocyanate, lysine diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 2-methyl-1,3-diisocyanatocyclohexane, 2-methyl-1,5-diisocyanatocyclohexane, 4,4'-dicyclohexylmethane diisocyanate, and isophorone diisocyanate.

[0036] Further, as the polyisocyanate compound, a prepolymer having an isocyanate group obtained by subjecting the above diisocyanate compound to an addition reaction with a polyhydric alcohol; a compound having an isocyanurate ring obtained by cyclizing and trimerizing the above diisocyanate compound; a polyisocyanate compound having a urea bond or a biuret bond obtained by reacting the above diisocyanate compound with water; a homopolymer of an acrylic monomer having an isocyanate group, such as 2-isocyanatoethyl (meth)acrylate, 3-isopropenyl-α,α-dimethylbenzyl isocyanate, or (meth)acryloyl isocyanate; or a copolymer having an isocyanate group obtained by copolymerizing the above acrylic monomer having an isocyanate group with a monomer such as another acrylic monomer, a vinyl ester compound, a vinyl ether compound, an aromatic vinyl monomer, or a fluoroolefin.

[0037] The polyisocyanate compound is preferably a water-dispersible polyisocyanate obtained by modifying the above-mentioned polyisocyanate compound, since it has excellent stability and curability and has a high degree of freedom in terms of pot life when blended with the aqueous dispersion for a metallic paint of the present invention.

[0038] The polyisocyanate compounds can be used alone or in combination of two or more kinds.

[0039] The amount of the polyisocyanate compound blended is preferably in the range of 0.5 to 2.0, more preferably 0.8 to 1.5, in terms of the equivalent ratio (isocyanate group / hydroxyl group) of the isocyanate group in the polyisocyanate compound to the hydroxyl group in the acrylic polymer (A), in order to obtain a coating film with high strength.

[0040] The urethanization reaction can be carried out in the presence of a urethanization catalyst to promote the progress of the reaction. Examples of the urethanization catalyst include amine compounds such as triethylamine, organic tin compounds such as dibutyltin dioctate, dibutyltin dilaurate, dioctyltin dilaurate, octyltin trilaurate, dioctyltin dineodecane, dibutyltin diacetate, dioctyltin diacetate, and tin dioctylate, and organic metal compounds such as zinc octylate (zinc 2-ethylhexanoate).

[0041] The water-based metallic paint of the present invention contains an aqueous dispersion for metallic paint and a metallic pigment. Examples of the metallic pigment include scaly aluminum, evaporated aluminum, aluminum oxide, mica, titanium oxide-coated mica, iron oxide-coated mica, and micaceous iron oxide.

[0042] The content of the metallic pigment in the solid content of the water-based metallic paint is preferably from 1 to 30% by mass, and more preferably from 5 to 25% by mass, since this further improves the appearance of the coating film.

[0043] The water-based metallic paint of the present invention may contain additives other than those mentioned above, such as defoamers, viscosity modifiers, light stabilizers, weather stabilizers, heat stabilizers, ultraviolet absorbers, antioxidants, leveling agents, pigment dispersants, thickeners, etc. Pigments other than the metallic pigments may also be used.

[0044] Examples of methods for applying the water-based metallic paint of the present invention include methods using a spray, an applicator, a bar coater, a gravure coater, a roll coater, a comma coater, a knife coater, an air knife coater, a curtain coater, a kiss coater, a shower coater, a wheeler coater, a spin coater, dipping, screen printing, etc. In addition, methods for forming a coating film after application include a method of drying at room temperature to 120°C. EXAMPLES

[0045] The present invention will be described in more detail below with reference to specific examples. The acid value of the acrylic polymer is measured in accordance with JIS test method K 0070-1992. The average particle size is measured using Nanotrac UPA-EX150 manufactured by Nikkiso Co., Ltd. The average molecular weight is measured under the following GPC measurement conditions.

[0046] [GPC measurement conditions] Measurement equipment: High-speed GPC equipment (Tosoh Corporation "HLC-8220GPC") Column: The following columns manufactured by Tosoh Corporation were used, connected in series. "TSKgel G5000" (7.8mm I.D. x 30cm) x 1 "TSKgel G4000" (7.8mm I.D. x 30cm) x 1 "TSKgel G3000" (7.8mm I.D. x 30cm) x 1 "TSKgel G2000" (7.8mmI.D. x 30cm) x 1 Detector: RI (differential refractometer) Column temperature: 40℃ Eluent: tetrahydrofuran (THF) Flow rate: 1.0mL / min Injection volume: 100 μL (sample concentration 4 mg / mL in tetrahydrofuran solution) Standard sample: A calibration curve was prepared using the following monodisperse polystyrene.

[0047] (monodisperse polystyrene) "TSKgel Standard Polystyrene A-500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-1000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-2500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-5000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-1" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-2" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-4" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-10" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-20" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-40" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-80" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-128" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-288" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-550" manufactured by Tosoh Corporation

[0048] (Example 1: Production of metallic paint aqueous dispersion (1)) 180 parts by mass of styrene (hereinafter St), 151 parts by mass of butyl acrylate (hereinafter BA), 104 parts by mass of n-butyl methacrylate (hereinafter n-BMA), 30 parts by mass of hydroxyethyl acrylate (hereinafter HEA), and 75 parts by mass of propylene glycol methyl ether (hereinafter PGM) were mixed to obtain a monomer mixture. Also, 17.5 parts by mass of perbutyl O (hereinafter PO) and 17.5 parts by mass of PGM were mixed to obtain an initiator solution. 11.7 parts by mass of fumaric acid (hereinafter FuA) and 150 parts by mass of PGM were charged into a 2-liter reaction vessel equipped with a stirrer, a thermometer, and a cooler, and the inside of the reaction vessel was heated to 100°C while stirring while feeding in nitrogen gas. After the temperature was raised, 33% by mass of the monomer mixture and 33% by mass of the initiator solution were dropped into the reaction vessel over 80 minutes. After 11.7 parts by mass of FuA was charged into the vessel, 33% by mass of the monomer mixture and 33% by mass of the initiator solution were dropped into the reaction vessel over 80 minutes. After 11.6 parts by mass of FuA was added into the reaction vessel, the remaining monomer mixture and initiator solution were dropped into the reaction vessel. During the dropping reaction, the temperature inside the reaction vessel was kept at 100°C while stirring was continued, and after the dropping was completed, stirring was continued for 30 minutes and then cooled to 70°C. After cooling, 44 parts by mass of 2-dimethylaminoethanol (hereinafter DMEA) was added into the reaction vessel while stirring, and 750 parts by mass of ion-exchanged water was dropped over 1 hour. After the dropping was completed, stirring was continued for 30 minutes to obtain a metallic paint water dispersion (1).

[0049] (Example 2: Production of metallic paint aqueous dispersion (2)) 180 parts by mass of St, 165 parts by mass of BA, 75 parts by mass of n-BMA, 30 parts by mass of HEA, and 75 parts by mass of PGM were mixed to obtain a monomer mixture. Also, 17.5 parts by mass of PO and 17.5 parts by mass of PGM were mixed to obtain an initiator solution. 17 parts by mass of FuA and 150 parts by mass of PGM were charged into a 2-liter reaction vessel equipped with a stirrer, a thermometer, and a cooler, and the reaction vessel was heated to 100° C. while stirring while feeding nitrogen gas. After the temperature was raised, 33% by mass of the monomer mixture and 33% by mass of the initiator solution were dropped into the reaction vessel over 80 minutes. After 17 parts by mass of FuA were charged into the vessel, 33% by mass of the monomer mixture and 33% by mass of the initiator solution were dropped into the reaction vessel over 80 minutes. After adding 17 parts by mass of FuA to the reaction vessel, the remaining monomer mixture and initiator solution were added dropwise to the reaction vessel. During the dropping reaction, the temperature inside the reaction vessel was kept at 100°C while stirring was continued, and after the dropping was completed, stirring was continued for 30 minutes and then cooled to 70°C. After cooling, 63 parts by mass of DMEA was added to the reaction vessel while stirring, and 750 parts by mass of ion-exchanged water was added dropwise over 1 hour. After the dropping was completed, stirring was continued for 30 minutes to obtain an aqueous dispersion (2) for metallic paint.

[0050] (Example 3: Production of metallic paint aqueous dispersion (3)) 180 parts by mass of St, 151 parts by mass of BA, 102 parts by mass of n-BMA, 30 parts by mass of HEA, and 75 parts by mass of PGM were mixed to obtain a monomer mixture. Also, 17.5 parts by mass of PO and 17.5 parts by mass of PGM were mixed to obtain an initiator solution. 7 parts by mass of ITA, 6 parts by mass of FuA, and 150 parts by mass of PGM were charged into a 2-liter reaction vessel equipped with a stirrer, a thermometer, and a cooler, and the reaction vessel was heated to 100° C. while stirring while feeding nitrogen gas. After the temperature increase, 33% by mass of the monomer mixture and 33% by mass of the initiator solution were dropped into the reaction vessel over 80 minutes. 7 parts by mass of ITA and 6 parts by mass of FuA were charged into the vessel, and then 33% by mass of the monomer mixture and 33% by mass of the initiator solution were dropped into the reaction vessel over 80 minutes. After 6 parts by mass of ITA and 6 parts by mass of FuA were added to the reaction vessel, the remaining monomer mixture and initiator solution were added dropwise to the reaction vessel. During the dropping reaction, the temperature inside the reaction vessel was kept at 100°C while stirring was continued, and after the dropping was completed, the stirring was continued for 30 minutes, and then the mixture was cooled to 70°C. After cooling, 44 parts by mass of DMEA was added to the reaction vessel while stirring, and 750 parts by mass of ion-exchanged water was added dropwise over 1 hour. After the dropping was completed, stirring was continued for 30 minutes to obtain an aqueous dispersion (3) for metallic paint.

[0051] (Comparative Example 1: Production of metallic paint aqueous dispersion (R1)) St 180 parts by mass, BA 151 parts by mass, n-BMA 104 parts by mass, HEA 30 parts by mass, FuA 35 parts by mass, and PGM 75 parts by mass were mixed to obtain a monomer mixture. Also, PO 17.5 parts by mass and PGM 17.5 parts by mass were mixed to obtain an initiator solution. In a 2-liter reaction vessel equipped with a stirrer, a thermometer, and a cooler, and PGM 150 parts by mass were charged, and the reaction vessel was heated to 100 ° C. while stirring and feeding nitrogen gas. After the temperature was raised, the monomer mixture and the initiator solution were dropped into the reaction vessel over 4 hours. During the drop reaction, stirring was continued while maintaining the temperature in the reaction vessel at 100 ° C., and after the drop was completed, stirring was continued for 30 minutes and then cooled to 70 ° C. After cooling, DMEA 44 parts by mass was added to the reaction vessel while stirring, and ion-exchanged water 750 parts by mass was dropped over 1 hour. After the dropwise addition was completed, stirring was continued for 30 minutes to obtain an aqueous dispersion for metallic paint (R1).

[0052] (Comparative Example 2: Production of metallic paint aqueous dispersion (R2)) 180 parts by mass of St, 145 parts by mass of BA, 101 parts by mass of n-BMA, 30 parts by mass of HEA, 45 parts by mass of acrylic acid (hereinafter referred to as AA) and 75 parts by mass of PGM were mixed to obtain a monomer mixture. 150 parts by mass of PGM was charged into a 2-liter reaction vessel equipped with a stirrer, a thermometer and a cooler, and the temperature inside the reaction vessel was raised to 100°C while stirring and feeding nitrogen gas. After the temperature was raised, the monomer mixture, 17.5 parts by mass of PO and 17.5 parts by mass of PGM were mixed and dropped into the reaction vessel over 4 hours. During the drop reaction, stirring was continued while maintaining the temperature inside the reaction vessel at 100°C, and stirring was continued for 30 minutes after the end of the drop, and then cooled to 70°C. After cooling, 33 parts by mass of DMEA was added to the reaction vessel while stirring, and 750 parts by mass of ion-exchanged water was dropped over 1 hour. After the dropwise addition was completed, stirring was continued for 30 minutes to obtain an aqueous dispersion for metallic paint (R2).

[0053] [Water tolerance measurement] 1g of dilution water was added to 10g of the metallic paint water dispersion obtained above, and the mixture was stirred until it was uniform. After stirring, newspaper was placed under the container containing the solution, and it was confirmed whether the letters could be read. Dilution water was added until the letters could no longer be read, and the water tolerance was calculated using the amount of dilution water just before the letters could no longer be read, using the formula below. Water tolerance (%) = 100 x amount of dilution water (g) / amount of metallic paint water dispersion (g)

[0054] [Preparation of water-based metallic paint] 20 parts by mass of butyl cellosolve and 20 parts by mass of 50% by mass aluminum paste ("Alpaste WXM-5660" manufactured by Toyo Aluminum K.K.; a scaly aluminum pigment) were mixed to obtain 40 parts by mass of a butyl cellosolve mixed solution of aluminum paste. Next, 100 parts by mass of the aqueous dispersion for metallic paint obtained above was stirred with a disperser, and 9 parts by mass of diethylene glycol dibutyl ether was added, followed by 1 part by mass of a surface conditioner (BYK-346 manufactured by BYK-Chemie Co., Ltd.) and 2 parts by mass of a surface conditioner (Surfynol 104BC manufactured by Evonik Corporation). After that, 31.5 parts by mass of the butyl cellosolve mixture of the aluminum paste and 27 parts by mass of a thickener (Rheovis AS-1130 manufactured by BASF Ltd., diluted with water to a concentration of 3% by mass), and the mixture was stirred for 15 minutes to obtain the main component of the aqueous metallic paint. Next, 100 parts by mass of the base material of the water-based metallic paint obtained above was mixed with 4 parts by mass of an isocyanate curing agent (DIC Corporation's "Burnoc DNW-5500"), and the viscosity was adjusted to 40 seconds (Ford cup #4 / 20°C) with deionized water to obtain a water-based metallic paint. The equivalent ratio (isocyanate group / hydroxyl group) was set to 1.

[0055] [Preparation of 1-coat coating test plate] The water-based metallic paint obtained above was sprayed onto a plastic ABS plate to a film thickness of 15 μm, and after setting for 5 minutes, it was dried at 80°C for 30 minutes using a hot air dryer to obtain a one-coat coating test plate with a dried coating film formed.

[0056] [Adjustment of clear paint for 2 coats] A dilution thinner was obtained by mixing 50 parts by mass of xylene, 30 parts by mass of butyl acetate, 10 parts by mass of propylene glycol monomethyl ether acetate, and 10 parts by mass of ethyl-3-ethoxypropionate. 23 parts by mass of the dilution thinner was mixed with 30 parts by mass of acrylic resin (DIC Corporation's "Acrydic A-859-B"), 13 parts by mass of isocyanate curing agent (Covestro's "Desmodur N-3300"), and a surface conditioner (BYK-Chemie Corporation's "BYK-331") to obtain a two-coat clear paint.

[0057] [Preparation of two-coat coating test panels] The water-based metallic paint obtained above was sprayed onto an ABS plastic plate to a film thickness of 15 μm, and after setting for 5 minutes, the two-coat clear paint obtained above was applied to a film thickness of 30 μm, and after setting for 5 minutes, the plate was dried at 80°C for 30 minutes using a hot air dryer to obtain a two-coat coating test plate with a dried coating film formed.

[0058] [Evaluation of coating appearance] The coating surface of the one-coat coating test plate obtained above was visually observed, and the coating appearance was evaluated according to the following criteria. ◯: No metallic unevenness at all, good brightness. △: There is some metallic unevenness and the brightness is slightly reduced. ×: Metallic unevenness is noticeable and there is no sense of brightness.

[0059] [Evaluation of lifting resistance] The surfaces of the one-coat coating film test plates and the two-coat coating film test plates obtained above were visually compared and observed, and the lifting resistance was evaluated according to the following criteria. Good: No difference in color or appearance of the coating film, and good lifting resistance. △: Differences were observed in the color and appearance of the coating film, and lifting resistance was slightly poor. ×: A significant difference was observed in the color and appearance of the coating film, and lifting resistance was poor.

[0060] Table 1 shows the compositions and evaluation results of the metallic paint aqueous dispersions (1) to (3) and (R1) to (R2) obtained above.

[0061] [Table 1]

[0062] It was confirmed that the coating films obtained from the metallic paint aqueous dispersions of Examples 1 to 3 were excellent in coating film appearance and lifting resistance.

[0063] Comparative Example 1 is an example in which the water tolerance is smaller than the lower limit of the present invention, but it was confirmed that the coating appearance and lifting resistance were insufficient.

[0064] Comparative Example 2 is an example in which fumaric acid, which is an essential component of the present invention, was not used, and it was confirmed that the coating appearance and lifting resistance were insufficient.

Claims

1. The aqueous dispersion for a metallic paint is characterized in that an acrylic polymer (A) containing fumaric acid as an essential raw material is dispersed in an aqueous medium (B), the acid value of the acrylic polymer (A) is 40 to 100 mgKOH / g, the average particle size of particles formed by the acrylic polymer (A) is 60 nm or less, and the water tolerance is 100% or more.

2. 2. The aqueous dispersion for a metallic paint according to claim 1, wherein the content of fumaric acid in the unsaturated monomer raw material for the acrylic polymer (A) is 4 to 12 mass %.

3. 3. The aqueous dispersion for a metallic paint according to claim 1, wherein the acrylic polymer (A) has a hydroxyl group.

4. 4. A water-based metallic paint comprising the aqueous dispersion for metallic paint according to claim 1 and a metallic pigment.

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