Aqueous primer paint composition for automobile exterior component, and automobile exterior component

Abstract

The purpose of the present invention is to provide an aqueous primer paint composition for an automobile exterior component, the aqueous primer paint composition having adhesion properties superior to those of conventional primer paint compositions and having paint physical properties, such as coating workability and stability, equivalent to those of conventional primer paint compositions. This aqueous primer composition for an automobile exterior component has a resin makeup composed of a chlorinated polyolefin (A), a urethane dispersion (B), an alkyd dispersion (C), an epoxy dispersion (D), and an acrylic resin (E) and further contains carbon black (F) as a conductive material, the composition being characterized in that: the chlorinated polyolefin (A) has a weight-average molecular weight of 90,000-110,000 and a melting point of 72-80ºC; and 45.0-60.0 mass% of the chlorinated polyolefin (A) in terms of solid content is contained with respect to 100 mass% of the total amount of resin solid contents of the chlorinated polyolefin (A), the urethane dispersion (B), the alkyd dispersion (C), the epoxy dispersion (D), and the acrylic resin (E).

Description

Water-based primer coating composition for automobile exterior parts, and automobile exterior parts

[0001] The present invention relates to an aqueous primer coating composition for automotive exterior parts, and to an automotive exterior part.

[0002] Examples of components used in automobiles include steel sheets that form the body and plastic materials that form the bumpers. Examples of paint systems for steel sheets such as the body include a four-layer paint system consisting of a primer coat, an intermediate coat, a base coat, and a clear coat, using a substrate that has been subjected to a chemical conversion treatment. Examples of paint systems for plastic materials include a three-layer paint system consisting of a primer coat, a base coat, and a clear coat.

[0003] Conventionally, these two components have large differences in thermal strength and expansion coefficient, so it has been common to paint them using paint compositions suited to each component. However, from the perspective of matching color tones and simplifying management, there has been a demand for using base paint compositions and clear paints with as similar compositions as possible for the body and bumper.

[0004] On the other hand, since coating systems for plastic materials require baking and curing at lower temperatures than coating systems for steel sheets, it was necessary to change the general-purpose base coating composition and clear coating for automobile bodies to a composition that can be cured at low temperatures. However, such base coating compositions and clear coatings had the problem of not having sufficient adhesion to plastic materials.

[0005] To solve the above problems, methods have been studied for improving the adhesion of the entire multi-layer coating film by imparting even higher adhesion to the primer coating. For example, Patent Documents 1 to 3 describe primer coating compositions containing a relatively high amount of chlorinated polyolefin. However, increasing the amount of chlorinated polyolefin is expected to result in a decrease in coating properties such as paint workability and stability, and coating film properties such as water resistance and flexibility, which are derived from other resins. In addition, since the color is limited to white, its use is limited to paint colors with high brightness. There is also the problem that applying a low-brightness coating color on top of a white primer requires a high-concealment design or a thick coating film, which increases costs.

[0006] JP 2004-75735 A JP 2004-307684 A International Publication No. 2004 / 078861

[0007] In view of the above-mentioned current situation, an object of the present invention is to provide an aqueous primer coating composition for automotive exterior parts which has superior adhesion compared to conventional primer coating compositions and has coating properties such as ease of application and stability equivalent to those of conventional primer coating compositions.

[0008] The present invention relates to an aqueous primer composition for automobile exterior parts, which has a resin composition consisting of a chlorinated polyolefin (A), a urethane dispersion (B), an alkyd dispersion (C), an epoxy dispersion (D), and an acrylic resin (E), and further contains carbon black (F) as a conductive material, wherein the chlorinated polyolefin (A) has a weight-average molecular weight of 90,000 to 110,000 and a melting point of 72 to 80°C, and the aqueous primer composition contains 45.0 to 60.0 mass% of the chlorinated polyolefin (A) in terms of solid content, relative to 100 mass% of the total resin solid content of the chlorinated polyolefin (A), the urethane dispersion (B), the alkyd dispersion (C), the epoxy dispersion (D), and the acrylic resin (E).

[0009] The aqueous primer composition for automotive exterior parts preferably contains the carbon black (F) in an amount of 6.4 to 7.2% by mass relative to 100% by mass of the total resin solids. The aqueous primer composition for automotive exterior parts preferably contains the alkyd dispersion (C) in an amount of 10.0 to 20.0% by mass in terms of solids relative to 100% by mass of the total resin solids of the chlorinated polyolefin (A), the urethane dispersion (B), the alkyd dispersion (C), the epoxy dispersion (D), and the acrylic resin (E), and 9.5 to 10.5% by mass in terms of resin solids.

[0010] The present invention relates to an automotive exterior part having a plastic molded body and a multilayer paint film, wherein the multilayer paint film comprises a primer paint film obtained from the above-mentioned aqueous primer paint composition for automotive exterior parts, a base paint film, and a clear paint film. The plastic molded body is preferably made of polypropylene and / or polycarbonate ABS resin. The automotive exterior part is preferably an automotive bumper. The automotive exterior part may also be a spoiler, garnish, or the like. The base paint film in the multilayer paint film is preferably obtained by applying a base paint for automotive bodies. The clear paint film in the multilayer paint film is preferably obtained by applying a clear paint for automotive bodies containing a curing accelerator and a low-molecular-weight isocyanate compound.

[0011] The aqueous primer coating composition for automotive exterior parts of the present invention (hereinafter referred to as "aqueous primer coating composition") is a primer coating composition that, by incorporating a high amount of chlorinated polyolefin, can obtain a primer coating film that has high adhesion, excellent pigment dispersibility, paint workability, stability, etc., and also has excellent coating film properties such as water resistance and weather resistance. Because it is possible to form such a primer coating film, base coating compositions and clear coatings for automobile bodies can also be suitably used as topcoats.

[0012] The present invention will be described in detail below. The aqueous primer coating composition for automotive exterior parts of the present invention has a resin composition consisting of a chlorinated polyolefin (A), a urethane dispersion (B), an alkyd dispersion (C), an epoxy dispersion (D), and an acrylic resin (E), and is characterized in that the chlorinated polyolefin (A) is contained in an amount of 45.0 mass% or more in terms of solid content relative to 100 mass% of the total resin solid content of the components (A) to (E).

[0013] Although blending a chlorinated polyolefin (A) to improve adhesion is a known technique, a primer coating composition containing 45.0% by mass or more of a chlorinated polyolefin relative to 100% by mass of the total resin solids has not been investigated to date. Furthermore, by limiting the resin composition other than the chlorinated polyolefin to a specific constitution, it is possible to obtain a primer coating film that is excellent in coating film properties such as water resistance and flexibility without any deterioration in coating properties such as paintability and stability.

[0014] Chlorinated Polyolefin (A) The aqueous primer coating composition of the present invention contains 45.0 to 60.0 mass% of chlorinated polyolefin (A) in terms of solids, based on 100 mass% of the total resin solids. If the solids content is less than 45.0 mass%, it is difficult to obtain better adhesion. If the solids content exceeds 60.0 mass%, it is difficult to prepare a coating, which is not preferable. The content of the chlorinated polyolefin (A) is preferably 47.5 to 52.5 mass%.

[0015] The chlorinated polyolefin (A) is a chlorinated product of a polyolefin, and examples of the polyolefin to be chlorinated include one or more polymers selected from olefins such as ethylene, propylene, butene, and methylbutene, as well as radical copolymers of these olefins with vinyl acetate, butadiene, acrylic esters, methacrylic esters, and the like.

[0016] Among these, chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, and chlorinated ethylene-vinyl acetate copolymer are particularly preferred. The chlorinated polyolefin (A) also includes those obtained by graft-polymerizing the above-mentioned chlorinated polyolefins with polymerizable monomers. Examples of the polymerizable monomers include alkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, glycidyl (meth)acrylate, adducts of glycidyl (meth)acrylate and monocarboxylic acids, hydroxyalkyl (meth)acrylates, acrylic acid, and methacrylic acid.

[0017] The chlorinated polyolefin (A) does not necessarily have to be water-dispersible; however, it can be water-dispersed by the polyurethane dispersion (B) or a surfactant. However, from the viewpoints of the storage stability of the primer coating composition and the water resistance of the resulting coating film, it is preferable that the chlorinated polyolefin (A) itself has water-dispersibility.

[0018] The chlorinated polyolefin (A) can be imparted with water dispersibility, for example, by graft polymerizing a polymerizable unsaturated dicarboxylic acid or its anhydride by a known method. The polymerizable unsaturated dicarboxylic acid or its anhydride is a compound having one polymerizable unsaturated bond and two or more carboxyl groups or their anhydride groups per molecule. Examples include maleic acid and its anhydride, itaconic acid and its anhydride, and citraconic acid and its anhydride. One or more selected from these can be suitably used. The amount of these monomers used is preferably 90 to 10% by weight, particularly 80 to 30% by weight, based on the total amount of the chlorinated polyolefin.

[0019] In order to make the chlorinated polyolefin obtained above water-soluble or water-dispersible, it is preferable to neutralize some or all of the carboxyl groups contained in the molecule with an amine compound.

[0020] Examples of the amine compound include triethylamine, tributylamine, dimethylethanolamine, triethanolamine, dimethylamine, dibutylamine, and diethanolamine.

[0021] The chlorinated polyolefin (A) preferably has a chlorination rate of 50% by weight or less, particularly about 12 to 35% by weight, and a weight-average molecular weight of 1,000 to 150,000, particularly about 30,000 to 120,000, from the viewpoints of storage stability of the primer coating composition and appearance of the coating film.

[0022] The chlorinated polyolefin (A) preferably has a weight-average molecular weight of 90,000 to 110,000. If the weight-average molecular weight is outside the above range, a decrease in cohesive strength (decreased adhesiveness) and a decrease in compatibility occur, which is undesirable. The lower limit of the weight-average molecular weight is more preferably 95,000, and the upper limit is more preferably 105,000. In this specification, the weight-average molecular weight is the weight-average molecular weight in terms of polystyrene measured by GPC (gel permeation chromatography).

[0023] Furthermore, the chlorinated polyolefin (A) preferably has a melting point of 72 to 80°C. If the melting point is less than 72°C, the water resistance of the resulting coating film may be insufficient. If the melting point is more than 80°C, this is undesirable because it may have an adverse effect on the substrate, especially when the substrate is made of a plastic material. The lower limit of the melting point is more preferably 73°C, and the upper limit is more preferably 77°C. In the present invention, the melting point can be measured, for example, by differential scanning calorimetry (DSC).

[0024] The primer coating composition of the present invention further contains a urethane dispersion (B). By adding the urethane dispersion, high recoatability and adhesion to polycarbonate ABS can be achieved.

[0025] Polyurethane dispersions are preferably prepared by reacting a polyol, such as polyester polyol or polyether polyol, with a polyisocyanate, and then chain-extending the polyurethane, optionally in the presence of a chain extender, which is a low-molecular-weight compound having two or more active hydrogen atoms, such as a diol or diamine, to prepare a stable dispersion or solution in water. A wide variety of conventional polyurethane dispersions can be used. Examples of methods for stably dispersing or dissolving a polyurethane resin in water include the following: (1) A method in which an anionic group, such as a carboxyl group, or a cationic group, such as an amino group, is introduced into the side chain or terminal of a polyurethane polymer, and the ionic groups are partially or completely neutralized to impart hydrophilicity, resulting in dispersion or dissolution in water by self-emulsification. (2) A method in which a hydrophilic polyol, such as polyethylene glycol, is used as the main raw material for the polyurethane to produce a water-soluble polyurethane, which is then dispersed or dissolved in water. (3) A method in which a polymer in which the reaction has been completed or a polymer in which the terminal isocyanate groups have been blocked with a blocking agent such as oxime, alcohol, phenol, mercaptan, amine, or sodium bisulfite is forcibly dispersed in water using a nonionic and / or cationic emulsifier and mechanical shearing force, and a method in which a urethane prepolymer having terminal isocyanate groups is mixed with water / emulsifier / chain extender and mechanical shearing force is used to simultaneously disperse and polymerize the polymer.

[0026] The method for producing the polyurethane resin is not limited to a single method, and a mixture obtained by each method can also be used. Specifically, as disclosed in, for example, Japanese Patent Laid-Open Publication No. 5-245427, a urethane prepolymer is synthesized by polymerizing (i) an aliphatic and / or alicyclic diisocyanate, (ii) a polyether diol or polyester diol or a mixture thereof having a number average molecular weight of 500 to 5,000, (iii) a low-molecular-weight polyhydroxyl compound, and (iv) a dimethylolalkanoic acid in an NCO / OH equivalent ratio of 1.1 to 1.9 in the presence or absence of a hydrophilic organic solvent not containing an active hydrogen group in the molecule, by a one-shot or multi-stage method; the prepolymer is then mixed with water after or while being neutralized with an amine, thereby carrying out a water-extension reaction and simultaneously emulsifying and dispersing the prepolymer in water; and, if necessary, the organic solvent is distilled off, thereby obtaining a polyurethane dispersion having an average particle size of about 0.001 to 1.0 μm and excellent production stability and storage stability.

[0027] As the urethane dispersion (B), commercially available products can also be used. The commercially available urethane dispersion is not particularly limited, and examples thereof include Urethane Dispersion VPLS2952 (manufactured by Sumika Bayer Urethane Co., Ltd.), Urethane Dispersion HUX561 (manufactured by Asahi Denka Kogyo Co., Ltd.), and NeoRez R9603 (manufactured by Kusumoto Chemicals Co., Ltd.).

[0028] The primer coating composition of the present invention further contains an alkyd dispersion (C). The alkyd dispersion (C) allows a primer coating composition with excellent pigment dispersibility to be obtained. It also imparts flexibility to the resulting coating film. The alkyd dispersion (C) is preferably an aqueous alkyd resin stably dispersed or dissolved in water, and a wide variety of conventionally known dispersions can be used.

[0029] The alkyd resin is a polyester reaction product of a polyhydric alcohol and a polyfunctional carboxylic acid, part of whose acid component may be a long-chain fatty acid of vegetable oil. Examples of polyhydric alcohols include glycerol, trimethylolethane, trimethylolpropane, diethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 1,2-propanediol, ethylene glycol, butylene glycol, dipropylene glycol, and pentaerythritol.

[0030] Examples of polyfunctional carboxylic acids include phthalic anhydride, adipic acid, maleic anhydride, isophthalic acid, sebacic acid, azelaic acid, terephthalic acid, trimellitic anhydride, linoleic acid, linolenic acid, benzoic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, and fumaric acid.

[0031] Examples of oils that can be used to modify the alkyd resin include tung oil, linseed oil, soybean oil, safflower oil, castor oil, corn oil, cottonseed oil, pelara oil, sesame oil, coconut oil, dehydrated castor oil, tall oil, etc. The aqueous alkyd resin used in the present invention preferably has an acid value of 5 to 100 on a resin solids basis, more preferably 10 to 40. An acid value of less than 5 on a resin solids basis is undesirable because the dispersibility of the alkyd resin in water is insufficient and a stable water-soluble resin cannot be obtained, while an acid value of more than 100 is undesirable because the water resistance and weather resistance of the primer coating film (film) are reduced.

[0032] Specific examples of the aqueous alkyd resin used in the present invention include S118, S126, S346, and S212 of the Watersol series manufactured by Dainippon Ink Co., Ltd., and 376, 580, 585, 5, and 27 of the Arolon series manufactured by Nippon Shokubai Co., Ltd.

[0033] The content of the alkyd dispersion (C) is preferably 10.0 to 20.0 mass% in solids relative to 100 mass% of the total resin solids of the chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D), and acrylic resin (E). If the content is less than 10.0 mass%, pigment dispersibility may be insufficient. If the content exceeds 20.0 mass%, adhesion may decrease, which is undesirable. The lower limit of the content is more preferably 11.0 mass%, and even more preferably 12.0 mass%. The upper limit is more preferably 19.0 mass%, and even more preferably 18.0 mass%.

[0034] The primer coating composition of the present invention further contains an epoxy dispersion (D). The epoxy dispersion (D) is a component that imparts water resistance and adhesion to the coating film. The epoxy dispersion is preferably one in which an aqueous epoxy resin is stably dispersed or dissolved in water, and a wide variety of conventionally known epoxy dispersions can be used.

[0035] The epoxy resin is not particularly limited as long as it has one or more epoxy groups in one molecule, and conventional epoxy resins used in paints can be used. Specific examples include bisphenol-type epoxy resins obtained by adding epichlorohydrin to bisphenol, novolac-type epoxy resins obtained by adding epichlorohydrin to phenol novolac resin, and those obtained by adding epichlorohydrin to polyols such as pentaerythritol, sorbitol, and glycerin.

[0036] These resins can be made aqueous by forced emulsification using an emulsifier, or by carboxyl-modifying the resin and then neutralizing it with a basic substance. Commercially available aqueous epoxy resins include bisphenol-type epoxy resins such as Epilez 3510W60, 3515W60, 3522W60, 3540Wy55, and 880SAW-65 manufactured by Shell Chemical Co., Ltd.; novolac-type epoxy resins such as Denacol EM150 manufactured by Nagase Chemtech Co., Ltd., Epilez 6006W70 and 5003W55 manufactured by Shell Chemical Co., Ltd., and WEX-5100 manufactured by Tohto Kasei Co., Ltd.; and polyols having epichlorohydrin added thereto such as Denacol EX611, EX614, EX411, and EX313 manufactured by Nagase Chemtech Co., Ltd.

[0037] The content of the epoxy dispersion (D) is preferably 9.5 to 10.5 mass% in solids relative to 100 mass% of the total resin solids of the chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D), and acrylic resin (E). If the content is less than 9.5 mass%, water resistance, adhesion, etc. may be insufficient. If the content exceeds 10.5 mass%, the amount of other resins with adhesive properties decreases, resulting in a relative decrease in adhesion, which is undesirable. The lower limit of the content is more preferably 9.75 mass%, and the upper limit is more preferably 10.25 mass%.

[0038] The primer coating composition of the present invention further contains an acrylic resin (E). The acrylic resin (E) is a component that functions as a pigment dispersing resin and is preferably a water-soluble acrylic resin. Examples of the water-soluble acrylic resin include water-soluble acrylic resins containing structural units derived from hydrophilic (meth)acrylic monomers. Examples of the hydrophilic (meth)acrylic monomer include carboxyl group-containing (meth)acrylic monomers such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid; hydroxyl group-containing (meth)acrylic monomers such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and ring-opening adducts of these (meth)acrylates with caprolactone or ethylene oxide; amino group-containing (meth)acrylic monomers such as dimethylaminoethyl (meth)acrylate; and acrylamide monomers such as acrylamide and N-methoxymethylacrylamide. These may be used alone or in combination of two or more.

[0039] The water-soluble acrylic resin may contain, in addition to the structural units derived from the hydrophilic (meth)acrylic monomer, structural units derived from other (meth)acrylic monomers or styrene-based monomers, as appropriate.

[0040] The water-soluble acrylic resin can be obtained by polymerizing a hydrophilic (meth)acrylic monomer, but may also be obtained by copolymerizing it with the above-mentioned other (meth)acrylic monomers or styrene-based monomers, or by making it water-soluble with an acid or alkali, as necessary. For example, when the hydrophilic (meth)acrylic monomer is a carboxyl group-containing (meth)acrylic monomer, it can be made water-soluble by neutralizing it with an amine or ammonia, and when it is an amino group-containing (meth)acrylic monomer, it can be made water-soluble by neutralizing it with an organic acid or the like.

[0041] The primer coating composition of the present invention provides electrical conductivity to a plastic molded article to be coated, and contains carbon black (F) as a conductive material. Commercially available carbon blacks include, for example, Toka Black #4300, #4400, #4500, #5500 (furnace blacks manufactured by Tokai Carbon Co., Ltd.), Printex L (furnace blacks manufactured by Degussa Co., Ltd.), Raven 7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, Conductex SC ULTRA, Conductex 975ULTRA, and PUER BLACK 100, 115, 205, etc. (manufactured by Columbian Co., Ltd., furnace black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B, etc. (manufactured by Mitsubishi Chemical Corporation, furnace black), MONARCH 1400, 1300, 900, Vulcan XC-72R, BlackPearls 2000, etc. (manufactured by Cabot Corporation, furnace black), Examples of the black pigment include Ensaco Black, Ensaco 250G, Ensaco 260G, Ensaco 350G, Super P-Li (manufactured by TIMCAL Corporation), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo Corporation), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black), but are not limited to these, and two or more types may be used in combination.

[0042] The content of the carbon black (F) is preferably 6.4 to 7.2% by mass relative to 100% by mass of the total resin solid content. By being in this range, suitable conductivity can be imparted to the plastic molded article to be coated.

[0043] The primer coating composition may optionally contain a white pigment. Conventional white pigments may be used, such as titanium oxide, zinc white, white lead, and zinc sulfide. These may be used alone or in combination. The average particle size of the white pigment is not particularly limited, but is preferably 0.2 to 0.3 μm from the viewpoints of dispersibility, smoothness of the coating film, and adhesion.

[0044] The primer coating composition used in the present invention may contain known auxiliary compounding agents such as inorganic fillers, organic modifiers, stabilizers, plasticizers, and additives, as required.

[0045] The proportion of water in the primer coating composition is preferably 45 to 90% by mass, more preferably 50 to 80% by mass, based on the total primer coating composition. If the proportion of water is less than 45% by mass, the viscosity increases, resulting in reduced storage stability and coating workability. On the other hand, if the proportion of water exceeds 90% by mass, the proportion of nonvolatile matter decreases, coating efficiency deteriorates, and appearance defects such as sagging and popping become more likely to occur. The primer coating composition may further contain an organic solvent, the proportion of which is typically 40% by mass or less relative to the water contained.

[0046] esters such as ethyl acetate, n-butyl acetate, isobutyl acetate, and amyl acetate; ethers such as n-butyl ether and isobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, isopropanol, n-butanol, 2-butanol, n-propylene glycol, and isopropylene glycol; cellosolves such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoethyl ether acetate; carbitols such as diethylene glycol monoethyl ether; propylene glycol alkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether; and other solvents such as dioxane, N-methylpyrrolidone, dimethylformamide, and diacetone alcohol.

[0047] The present invention also relates to an automobile exterior part having a plastic molded body and a multilayer coating film, wherein the multilayer coating film comprises a primer coating film obtained using the primer coating composition of the present invention, a base coating film, and a clear coating film.

[0048] The plastic molded article is not particularly limited, and examples thereof include automobile exterior parts such as bumpers, spoilers, grilles, fenders, etc. The material thereof is also not particularly limited, and examples thereof include polyolefins such as polyethylene and polypropylene, polystyrene, ABS, vinyl chloride, polycarbonate, polyacetal, polyester, polyamide, polyurethane, PPO, polymethyl methacrylate, epoxy resin, phenolic resin, melamine resin, etc.

[0049] The primer coating film is a primer coating film obtained using the primer coating composition of the present invention. The method for applying the primer coating composition to the surface of a plastic molded body is not particularly limited, and can be, for example, spray coating or bell coating. Industrially, examples of methods that can be used include an air electrostatic spray coating machine commonly known as a "react gun" or a rotary atomization electrostatic coating machine commonly known as a "micro-micro bell," "micro bell," "metallic bell," etc. Furthermore, the plastic molded body may be washed and degreased as necessary.

[0050] The primer coating preferably has a dry film thickness of 10 to 30 μm. If it is less than 10 μm, the hiding power will be insufficient, and if it exceeds 30 μm, popping and dripping will be likely to occur. It is preferably 15 to 20 μm. The dry film thickness can be measured using an SDM-miniR manufactured by SANKO Corporation.

[0051] The primer coating is preferably dried before the base coating composition is applied. The drying temperature may be set as appropriate, but is preferably 40 to 110°C, more preferably 50 to 100°C. There are no particular restrictions on the drying method, and known methods such as hot air drying and infrared drying may be used.

[0052] The base coating film is typically obtained from a base coating composition containing a color pigment, a film-forming resin, a curing agent, and, if necessary, additives. Examples of color pigments contained in the base coating composition include conventionally known color pigments, such as organic azo lake pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments, as well as inorganic pigments such as yellow lead, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. Furthermore, flat pigments such as aluminum powder and graphite powder may be added. Extender pigments such as calcium carbonate, barium sulfate, clay, and talc may also be added. Furthermore, if necessary, lustrous materials such as interference mica pigments and aluminum pigments may also be added.

[0053] The film-forming resin and curing agent for the base coating composition may be, for example, a film-forming resin such as an acrylic resin, polyester resin, alkyd resin, or fluorine-based resin, and a curing agent such as an amino resin and / or a blocked polyisocyanate compound.

[0054] The total pigment concentration (PWC) in the base coating composition is preferably 3% by mass at the lower limit and 70% by mass at the upper limit. If it exceeds 70% by mass, the coating film appearance deteriorates. The lower limit is more preferably 4% by mass, and even more preferably 5% by mass. The upper limit is more preferably 65% ​​by mass, and even more preferably 60% by mass.

[0055] The base coating composition is preferably a solution type, and if it is a solution type, it may be an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), or a non-aqueous dispersion type.

[0056] In the automotive exterior part of the present invention, the base coating film may be obtained by applying an automotive body base paint composition, which is preferable because the application of the automotive body base paint has advantages such as matching the color tones of the automotive body and the exterior part and simplifying maintenance.

[0057] The thickness of the coating film when applied using the above base coating composition varies depending on the desired application, but in many cases a thickness of 10 to 30 μm is useful. If it is less than 10 μm, the base may not be concealed and film breakage may occur, and if it exceeds 30 μm, the image clarity may decrease and problems such as unevenness and running may occur during application. The dry film thickness of the base coating film is usually 10 to 30 μm. If it is less than 10 μm, the concealing properties will be poor, and if it exceeds 30 μm, it will be uneconomical.

[0058] The method for applying the base coating composition is not particularly limited, and examples thereof include spray coating and electrostatic coating.

[0059] The base coating film formed by the above-mentioned base coating composition may be coated with the next clear coating composition without being dried by heat, or may be dried at a temperature of 40°C to 110°C. In particular, in the case of an aqueous-based coating, if the drying temperature is below 40°C, the coating may not blend with the clear coating, resulting in a deterioration in the appearance of the coating. If the temperature is too high, peeling may occur between the base coating film and the clear coating film.

[0060] The above-mentioned clear coating composition is a coating used to form the top layer (uppermost layer) of a three-layer coating film by applying it over an uncured base film, and it imparts excellent physical properties such as weather resistance and solvent resistance to the cured coating film.

[0061] The clear coating composition is not particularly limited, and any conventionally known composition may be used, but for example, a two-component clear coating (e.g., a two-component curing urethane coating) using a hydroxyl group-containing polyol resin as the main component and an isocyanate curing agent is preferred. This is because the resulting clear coating film has a good appearance and excellent acid resistance. The polyol resin used as the main component is not particularly limited, but examples of usable polyols include polyester polyols, acrylic polyols, polycarbonate polyols, and polyurethane polyols.

[0062] Examples of the isocyanate used as the curing agent include non-yellowing compounds having two or more isocyanate groups in the molecule (e.g., adducts such as hexamethylene diisocyanate and isophorone diisocyanate, nurates, biurets, etc.). Commercially available curing agents include Dismodur 3600 and Sumidur 3300 manufactured by Sumika Bayer, Coronate HX manufactured by Nippon Polyurethane Co., Ltd., Takenate D-140NL and D-170N manufactured by Mitsui Takeda Chemical Co., Ltd., and Duranate 24A-90PX and THA-100 manufactured by Asahi Kasei Corporation. Examples of commercially available clear coatings include R2500-1 manufactured by Nippon Bee Chemical Co., Ltd., which is a two-component curing urethane coating.

[0063] Furthermore, conventionally known additives such as curing accelerators, antifoaming agents, rheology control agents, lubricants, UV absorbers, and organic solvents may be used as needed.

[0064] In the automobile exterior part of the present invention, the clear coating film may be obtained by applying an automobile body clear paint composition, which is preferable because the application of the automobile body clear paint has advantages such as matching the color tone of the automobile body and the exterior part and simplifying maintenance.

[0065] The clear coating composition for automobile bodies is not particularly limited, but preferably contains a curing accelerator. By containing the curing accelerator, curing at low temperatures can be carried out without problems even when targeting plastic molded bodies. Examples of the curing accelerator include ZCAT (dibutyltin dilaurate).

[0066] The clear coating composition for automobile bodies preferably further contains a low molecular weight isocyanate compound as a curing agent, which easily penetrates into the lower layer. The low molecular weight isocyanate compound penetrates into the base coating film or primer coating film and cures, thereby improving the adhesion and strength of the multi-layer coating film. Examples of the curing agent include Desmodur N3900 and Desmodur N3400.

[0067] The method for applying the clear coating composition is not particularly limited, and for example, air spray coating, airless spray coating, bell coating, etc. can be used.

[0068] As described above, the primer coating composition, base coating composition, and clear coating composition are applied in this order to the surface of the plastic molded body to form a three-layer uncured film consisting of each coating component, and the next baking step is carried out. When selecting each coating composition, it is necessary to select a coating that can be sufficiently cured and dried in the baking step. If drying is insufficient and water or solvent remains inside the cured coating film, the performance of the cured coating film, such as water resistance and solvent resistance, is likely to deteriorate.

[0069] The dry film thickness of the clear coating is preferably 20 to 50 μm. If it is outside this range, there is a risk of poor appearance such as roughness on the surface and poor workability such as sagging and popping.

[0070] The baking step is a step in which the above three uncured film layers are simultaneously baked to form a cured coating film consisting of three layers: the primer coating film, the base coating film, and the clear coating film.

[0071] The baking temperature is preferably, for example, 70 to 130°C, in order to strike a balance between rapid curing and preventing deformation of the plastic molded body. It is preferably 80 to 110°C. The baking time is usually 10 to 60 minutes, preferably 15 to 50 minutes, and more preferably 20 to 40 minutes. Baking times of less than 10 minutes result in insufficient curing of the coating film, and the cured coating film's properties, such as water resistance and solvent resistance, are reduced. On the other hand, baking times of more than 60 minutes result in excessive curing, resulting in reduced adhesion during recoating, longer overall coating process times, and higher energy costs. Note that this baking time refers to the time during which the substrate surface actually maintains the target baking temperature; more specifically, it refers to the time during which the target temperature is maintained after it is reached, regardless of the time it takes to reach the target baking temperature.

[0072] Examples of heating devices used to simultaneously bake the uncured coating film include drying ovens that use heat sources such as hot air, electricity, gas, and infrared rays. It is also preferable to use a drying oven that uses two or more of these heat sources in combination, as this shortens the drying time.

[0073] The present invention will be described below with reference to examples. In the examples, "%" and "parts" used in the formulations mean "% by mass" and "parts by mass" unless otherwise specified. The present invention is not limited to the examples described below.

[0074] (Example 1) (Production Example) Production of Water-Based Primer Paint 3.9 parts by mass of water-soluble acrylic resin (manufactured by Nippon Paint, solids concentration 30% by mass, hydroxyl value 71 KOHmg / g), 13.2 parts by mass of alkyd dispersion resin (manufactured by DIC, solids concentration 35% by mass), 2.5 parts by mass (43.1% by mass) of conductive carbon black, 30.1 parts by mass of titanium oxide, 2.5 parts by mass of extender pigment, 2.7 parts by mass of pigment wetting agent, 1.4 parts by mass of surface conditioner, 0.6 parts by mass of antifoaming agent, and 43.1 parts by mass of pure water were premixed, and then a pigment paste was produced using a Dyno-Mill. 37.6 parts by mass of this pigment paste was further mixed with 24 parts by mass of polyolefin emulsion (1) (weight average molecular weight 100,000, melting point 75°C), 10.3 parts by mass of urethane dispersion resin (manufactured by Dai-ichi Kogyo Seiyaku, solid content concentration 35% by mass), 2.1 parts by mass of epoxy dispersion resin (manufactured by Hexion, solid content concentration 65% by mass), 5 parts by mass of propylene glycol monomethyl ether, 2.2 parts by mass of thickener, 1.4 parts by mass of surface conditioner, 0.3 parts by mass of antifoaming agent, 0.1 part by mass of pH adjuster, and 17 parts by mass of pure water to prepare an aqueous primer.

[0075] (Formation of Coated Product) The resulting aqueous primer was spray-coated onto the surface of a PP material or PC-ABS material (aqueous primer coating thickness of 7 to 11 μm), and after drying at 80°C for 3 minutes, Base 1 (AR-700 or AR-3100: Nippon Paint) or Base 2 (AR-3100: Nippon Paint) was coated to a dry film thickness of 2.5 to 10 μm, and again dried for 3 minutes at 80°C. A clear coat (R-2590: Nippon Paint) was coated onto this coated plate to a dry film thickness of 30 to 35 μm, and kept dried at 90°C for 20 minutes to obtain a coated product.

[0076] The resulting multilayer coating film was evaluated as follows. (Adhesion after water resistance test) The resulting coated product was immersed in warm water at 40°C for 10 days, removed from the warm water, and dried at room temperature for 1 hour. 100 squares were made on the surface of the test piece at 2m intervals using a single-edged razor, and cellophane adhesive tape (JIS Z 1522) was firmly pressed onto the surface and quickly peeled off in a 90° direction, and the peeling state of the coating film was evaluated by the number of squares remaining. 5: 100 squares remain intact 4: Peeling area is less than 5% and no complete peeling of the grids 3: Peeling area is less than 15% and no complete peeling of the grids 2: Peeling area is less than 35% and complete peeling of the grids occurs 1: Peeling area is 35% or more

[0077] (Appearance after high-temperature water resistance test) The coated product was immersed in 80°C water for 5 hours, removed from the water, and visually evaluated for appearance. The effective surface was examined for blistering, peeling, cracking, whitening, and wrinkles. The blistering was compared with No. 9-MD specified in ASTM D 714. 5: No blistering (better than ASTM D 714 No. 9-MD), peeling, cracking, whitening, or wrinkles. 4: No blistering (bigger than ASTM D 714 No. 9-MD), peeling, cracking, whitening, or wrinkles. 3: Any of blistering (bigger than ASTM D 714 No. 9-MD), peeling, cracking, whitening, or wrinkles is present. 2: Three of blistering (bigger than ASTM D 714 No. 9-MD), peeling, cracking, whitening, and wrinkles are present. 1: All of blistering (bigger than ASTM D 714 No. 9-MD), peeling, cracking, whitening, and wrinkles are present.

[0078] (Adhesion after high-temperature water resistance test) The coated samples were immersed in the above-mentioned 80°C warm water for 5 hours, pulled out, and then dried at room temperature for 1 hour, and then evaluated in the same manner as for adhesion after the above-mentioned water resistance test. 5: 100 pieces remain intact 4: Peeled area is less than 5% and there is no complete peeling of the grid 3: Peeled area is less than 15% and there is no complete peeling of the grid 2: Peeled area is less than 35% and there is complete peeling of the grid 1: Peeled area is 35% or more

[0079] Examples 2 to 6 and Comparative Examples 1 to 8 Coated articles were obtained in the same manner as in Example 1, except that the formulation of the coating composition was changed to that shown in Table 1.

[0080]

[0081] It was shown that the aqueous primer coating compositions obtained in the examples can produce multi-layer coating films with excellent adhesion and water resistance. It was also shown that the base coating composition for automobile bodies and the clear coating composition for automobile bodies can be used without any problems.

[0082] According to the present invention, it is possible to obtain an aqueous primer coating composition for automotive exterior parts that has superior adhesion compared to conventional primer coating compositions and has coating properties such as ease of application and stability equivalent to those of conventional primer coating compositions. Furthermore, since it is possible to laminate a commonly used base coating for automobile bodies or a clear coating for automobile bodies, it is possible to obtain effects such as matching the color tones of the automobile body and the automobile exterior parts and reducing the number of paint management processes.

Claims

1. An aqueous primer composition for automotive exterior parts, comprising a resin composition consisting of chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D) and acrylic resin (E), and further containing carbon black (F) as a conductive material, wherein the chlorinated polyolefin (A) has a weight average molecular weight of 90,000 to 110,000 and a melting point of 72 to 80 °C, and contains chlorinated polyolefin (A) in a solid content of 45.0 to 60.0% by mass based on 100% by mass of the total resin solid content of chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D) and acrylic resin (E).

2. The aqueous primer composition for automotive exterior parts according to claim 1, which contains carbon black (F) in the range of 6.4 to 7.2% by mass based on 100% by mass of the total resin solid content.

3. The aqueous primer composition for automotive exterior parts according to claim 1 or 2, wherein the alkyd dispersion (C) is contained in a solid content of 10.0 to 20.0% by mass based on 100% by mass of the total resin solid content of chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D) and acrylic resin (E), and the epoxy dispersion (D) is contained in a solid content of 9.5 to 10.5% by mass.

4. An automotive exterior part having a plastic molded body and a multilayer coating film, wherein the multilayer coating film has a primer coating film, a base coating film, and a clear coating film obtained by the aqueous primer coating composition for automotive exterior parts according to claim 1 or 2.

5. The automotive exterior part according to claim 4, wherein the plastic molded body is made of polypropylene and / or polycarbonate / ABS resin.

6. The automotive exterior part according to claim 4, which is an automotive bumper.

7. The automotive exterior part according to claim 4, wherein the base coating film is obtained by applying a base paint composition for automotive body.

8. The automotive exterior part according to claim 4, wherein the clear coating film is obtained by applying a clear paint composition for automotive body containing a curing accelerator and a low molecular weight isocyanate compound.

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