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

Abstract

To provide an aqueous primer coating composition for an automobile exterior component, the composition having more excellent adhesion than a conventional primer coating composition, and having coating properties such as coating work efficiency and stability equivalent to a conventional primer coating composition.SOLUTION: An aqueous primer coating composition for an automobile exterior component is provided, having a resin composition composed of chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D) and an 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 45.0 to 60.0 mass% of the chlorinated polyolefin (A) in a 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), and the epoxy dispersion (D) and the acrylic resin (E).SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Examples of members used in automobiles include steel plates that make up the body and plastic materials that make up bumpers. Examples of the coating system for steel plates such as the body include a coating system consisting of four layers: undercoat painting - intermediate coat painting - base coat painting - clear coat painting, using a substrate subjected to chemical conversion treatment. Examples of the coating system for plastic materials include a coating system consisting of three layers: primer painting - base coat painting - clear coat painting.

[0003] Conventionally, since there is a large difference in strength against heat and expansion rate between these two members, it has been common to perform painting using paint compositions suitable for each member. However, from the viewpoints of matching the color tone and simplifying management, there has been a desire to use base paint compositions and clear paints having as similar a composition as possible between the body and the bumper.

[0004] On the other hand, in the coating system for plastic materials, baking and curing at a lower temperature than that of the coating system for steel plates is essential. Therefore, it has been necessary to change general-purpose base paint compositions and clear paints for automotive bodies to compositions that can be cured at a low temperature. However, there has been a problem that such base paint compositions and clear paints do not have sufficient adhesion to plastic materials.

[0005] In order to solve the above problems, a method of enhancing the adhesion of the entire multilayer coating film by imparting higher adhesion to the primer paint has been studied. For example, Patent Documents 1 to 3 describe primer paint compositions with a relatively high content of chlorinated polyolefin. However, increasing the content of chlorinated polyolefin is expected to reduce the paint physical properties such as paint workability and stability derived from other resins, and the coating film physical properties such as water resistance and flexibility. In addition, since it is limited to white, the application is limited to paint colors with high lightness. There is also a problem that when a low lightness paint color is applied on top of a white primer, it is necessary to perform a high hiding design or increase the coating film thickness, resulting in increased costs.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] In view of the above situation, an object of the present invention is to provide an aqueous primer paint composition for automotive exterior parts that has better adhesion than conventional primer paint compositions and has paint physical properties such as paint workability and stability equivalent to those of conventional primer paint compositions.

Means for Solving the Problems

[0008] The present invention is an aqueous primer composition for automotive exterior parts having a resin composition comprising 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 above chlorinated polyolefin (A) has a weight average molecular weight of 90,000 to 110,000 and a melting point of 72 to 80 °C. The present invention relates to an aqueous primer composition for automotive exterior parts, which contains chlorinated polyolefin (A) in an amount of 45.0 to 60.0% by mass in terms of solid content based on 100% by mass of the total amount of resin solids of chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D) and acrylic resin (E).

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

[0010] The present invention relates to 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 from the above aqueous primer coating composition for automotive exterior parts. The above plastic molded body is preferably made of polypropylene and / or polycarbonate / acrylonitrile-butadiene-styrene (PC / ABS) resin. The above automotive exterior part is preferably an automotive bumper. Further, the above automotive exterior part may be a spoiler, a garnish, etc. The base coating film in the above multilayer coating film is preferably obtained by applying an automotive body base paint. The clear coating film in the above multilayer coating film is preferably obtained by applying an automotive body clear paint containing a curing accelerator and a low molecular weight isocyanate compound. [[Effect of the Invention]]

[0011] The aqueous primer paint composition for automotive exterior parts of the present invention (hereinafter referred to as "aqueous primer paint composition") has high adhesiveness by highly compounding chlorinated polyolefin, as well as excellent pigment dispersibility, paint workability, stability, etc., and can obtain a primer coating film excellent in coating film physical properties such as water resistance and weather resistance. Since such a primer coating film can be formed, a base paint composition for automotive bodies and a clear paint can also be suitably used as topcoat paints.

Embodiments for Carrying Out the Invention

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

[0013] Although it is a known method to blend chlorinated polyolefin (A) to enhance adhesiveness, a primer paint composition in which chlorinated polyolefin is blended in an amount of 45.0% by mass or more based on the total amount of 100% by mass of the resin solid content has not been studied so far. In addition, by limiting the resin composition other than chlorinated polyolefin to a specific configuration, a decrease in paint physical properties such as paint workability and stability is not observed, and a primer coating film excellent in coating film physical properties such as water resistance and flexibility can be obtained.

[0014] Chlorinated polyolefin (A) The aqueous primer paint composition of the present invention contains chlorinated polyolefin (A) in an amount of 45.0 to 60.0% by mass in terms of solid content based on 100% by mass of the total amount of resin solids. If it is less than 45.0% by mass, it is difficult to obtain better adhesion. On the other hand, if it exceeds 60.0% by mass, it is not preferable because it is difficult to form a paint. The content of the above chlorinated polyolefin (A) is preferably 47.5 to 52.5% by mass.

[0015] The above chlorinated polyolefin (A) is a chlorinated product of polyolefin. As the polyolefin to be chlorinated, there are mentioned one or more polymers selected from olefins such as ethylene, propylene, butene, and methylbutene, and further radical copolymers of these olefins with vinyl acetate, butadiene, acrylic ester, methacrylic ester, etc.

[0016] Among these, in particular, chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, and chlorinated ethylene-vinyl acetate copolymer are mentioned as suitable ones. Further, the chlorinated polyolefin (A) includes those obtained by graft polymerizing a polymerizable monomer to the above chlorinated polyolefin. Examples of the polymerizable monomer include alkyl esters of (meth)acrylic acid, alkoxyalkyl (meth)acrylates, glycidyl (meth)acrylate, adducts of glycidyl (meth)acrylate and monocarboxylic acid, hydroxyalkyl (meth)acrylate, acrylic acid, methacrylic acid, etc.

[0017] Although the chlorinated polyolefin (A) can be dispersed in water by a polyurethane dispersion (B) or a surfactant even if it does not necessarily have water dispersibility, from the viewpoints of the storage stability of the primer paint composition and the water resistance of the obtained coating film, it is preferable that the chlorinated polyolefin (A) itself has water dispersibility.

[0018] As a method for imparting water dispersibility to the chlorinated polyolefin (A), for example, it can be obtained 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 its anhydride group in one molecule. For example, maleic acid and its anhydride, itaconic acid and its anhydride, citraconic acid and its anhydride, etc. can be mentioned, and one or more selected from these can be preferably used. The usage amount of these monomers is preferably 90 to 10% by weight, particularly 80 to 30% by weight based on the total amount with the chlorinated polyolefin.

[0019] The chlorinated polyolefin obtained above is preferably neutralized with an amine compound for a part or all of the carboxyl groups contained in its molecule for solubilization or water dispersion.

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

[0021] The chlorinated polyolefin (A) has a chlorine content 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, which is suitable from the viewpoints of the storage stability of the primer paint composition and the appearance of the coating film.

[0022] The above chlorinated polyolefin (A) preferably has a weight average molecular weight of 90,000 to 110,000. If the above weight average molecular weight is outside the above range, it is not preferable because the cohesive force decreases (the adhesiveness decreases) and the compatibility decreases. The lower limit of the above 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 it exceeds 80°C, it is not preferable because it has an adverse effect when the substrate is 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 by, for example, differential scanning calorimetry (DSC).

[0024] The primer paint composition of the present invention further contains a urethane dispersion (B). By adding the urethane dispersion, it is possible to have high recoatability and adhesiveness to polycarbonate / acrylonitrile-butadiene-styrene copolymer (PC / ABS).

[0025] The polyurethane dispersion is preferably obtained by reacting a polyurethane obtained by reacting a polyol such as a polyester polyol or a polyether polyol with a polyisocyanate in the presence of a chain extender which is a low molecular weight compound having two or more active hydrogens such as a diol or a diamine, and then chain-extending it and stably dispersing or dissolving it in water. Conventionally known ones can be widely used. As a method for stably dispersing or dissolving the polyurethane resin in water, for example, the following methods can be used. (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 the polyurethane polymer, and a part or all of the ionic groups are neutralized to impart hydrophilicity and dispersed or dissolved in water by self-emulsification. (2) A method in which a hydrophilic polyol such as polyethylene glycol is used as the polyol of the main raw material of the polyurethane to form a water-soluble polyurethane and dispersed or dissolved in water. (3) A method of forcibly dispersing a polymer in which the reaction is completed or a polymer in which terminal isocyanate groups are blocked with a blocking agent such as oxime, alcohol, phenol, mercaptan, amine, sodium bisulfite, etc. into water using a nonionic and / or cationic emulsifier and mechanical shear force. Further, a method of mixing a urethane prepolymer having terminal isocyanate groups with water / emulsifier / chain extender and performing dispersion and high molecular weightization simultaneously using mechanical shear force.

[0026] The method for producing the polyurethane resin is not limited to a single method, and mixtures obtained by each method can also be used. Specifically, for example, as disclosed in JP-A-5-245427, in the presence or absence of a hydrophilic organic solvent containing no active hydrogen group in the molecule, (i) an aliphatic and / or alicyclic diisocyanate, (ii) a polyether diol or polyester diol having a number average molecular weight of 500 to 5,000 or a mixture thereof, (iii) a low molecular weight polyhydroxyl compound, and (iv) dimethylolalkanoic acid are polymerized in a one-shot or multi-step method at a ratio within the range of an NCO / OH equivalent ratio of 1.1 to 1.9 to synthesize a urethane prepolymer. Then, after neutralizing the prepolymer with an amine or while neutralizing it, it is mixed with water to cause a water elongation reaction and at the same time emulsified and dispersed in water, and then, if necessary, the above organic solvent is distilled off to obtain a polyurethane dispersion having an average particle diameter of about 0.001 to 1.0 μm and excellent production stability and storage stability.

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

[0028] The primer paint composition of the present invention further contains an alkyd dispersion (C). By using the above alkyd dispersion (C), a primer paint composition excellent in pigment dispersibility can be obtained. In addition, flexibility can be imparted to the resulting coating film. As the above alkyd dispersion (C), an aqueous alkyd resin stably dispersed or dissolved in water can be preferably used, and conventionally known ones can be widely used.

[0029] The above alkyd resin is a polyesterification reaction product of a polyhydric alcohol and a polyfunctional carboxylic acid, a part of the acid component of which may be a long-chain fatty acid of vegetable oil. Examples of the polyhydric alcohol 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 the polyfunctional carboxylic acid 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] Oils that can be used to modify alkyd resins include tung oil, linseed oil, soybean oil, safflower oil, castor oil, corn oil, cottonseed oil, perilla oil, sesame oil, coconut oil, dehydrated castor oil, tall oil, and the like. The aqueous alkyd resin used in the present invention preferably has a resin solid acid value of 5 to 100, more preferably 10 to 40. If the resin solid acid value is less than 5, the dispersibility of the alkyd resin in water is insufficient and a stable water-soluble resin cannot be obtained, which is not preferable. If it exceeds 100, the water resistance and weather resistance of the primer coating film (coating) will decrease, which is not preferable.

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

[0033] The content of the above alkyd dispersion (C) is preferably 10.0 to 20.0% by mass in terms of solid content 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). If the above content is less than 10.0% by mass, the pigment dispersibility may be insufficient. If the above content exceeds 20.0% by mass, the adhesion may decrease, which is not preferable. The lower limit of the above content is more preferably 11.0% by mass, and even more preferably 12.0% by mass. The upper limit is more preferably 19.0% by mass, and even more preferably 18.0% by mass.

[0034] The primer coating composition of the present invention further contains an epoxy dispersion (D). The above epoxy dispersion (D) is a component that imparts water resistance and adhesion to the coating film. The above epoxy dispersion is preferably a stable dispersion or solution of an aqueous epoxy resin in water, and conventionally known ones can be widely used.

[0035] The above 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. Specifically, bisphenol type epoxy resins obtained by adding epichlorohydrin to bisphenol, novolac type epoxy resins obtained by adding epichlorohydrin to phenol novolac resins, and those obtained by adding epichlorohydrin to polyols such as pentaerythritol, sorbitol, and glycerin are available.

[0036] These are made water-based by forced emulsification using an emulsifier, or by carboxyl modification followed by neutralization with a basic substance. Commercially available water-based products include, for bisphenol type epoxy resins, Epirez 3510W60, 3515W60, 3522W60, 3540Wy55, 880SAW-65, etc. manufactured by Shell Chemical Co., Ltd.; for novolac type epoxy resins, Denacol EM150 manufactured by Nagase ChemteX Corporation, Epirez 6006W70, 5003W55 manufactured by Shell Chemical Co., Ltd., WEX-5100 manufactured by Tohto Kasei Co., Ltd., etc.; for the type obtained by adding epichlorohydrin to polyols, Denacol EX611, EX614, EX411, EX313, etc. manufactured by Nagase ChemteX Corporation.

[0037] The content of the above epoxy dispersion (D) is preferably 9.5 to 10.5% by mass in terms of solid content 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). If the above content is less than 9.5% by mass, there is a risk that water resistance, adhesion, etc. will be insufficient. If the above content exceeds 10.5% by mass, the amount of resin with other adhesion performance decreases, and the adhesion force relatively decreases, which is not preferable. The lower limit of the above content is more preferably 9.75% by mass, and the upper limit is more preferably 10.25% by mass.

[0038] The primer paint composition of the present invention further contains an acrylic resin (E). The acrylic resin (E) is a component that acts as a pigment dispersion 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 monomers 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 obtained by reacting 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] In addition to the structural units derived from the hydrophilic (meth)acrylic monomers, the water-soluble acrylic resin may appropriately contain structural units derived from other (meth)acrylic monomers or styrene-based monomers.

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

[0041] The primer paint composition of the present invention imparts conductivity to a plastic molded article as an object to be coated, and contains carbon black (F) as a conductive material. Examples of commercially available carbon blacks include, for example, Tokablack #4300, #4400, #4500, #5500, etc. (manufactured by Tokai Carbon Co., Ltd., furnace black), Printex L, etc. (manufactured by Degussa Co., Ltd., furnace black), Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., PUER BLACK100, 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), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, etc. (manufactured by Cabot Co., Ltd., furnace black), Ensaco250G, Ensaco260G, Ensaco350G, SuperP-Li (manufactured by TIMCAL Co., Ltd.), Ketjenblack EC-300J, EC-600JD (manufactured by Akzo Co., Ltd.), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black), etc. However, the present invention is not limited thereto, and two or more of them may be used in combination.

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

[0043] The primer paint composition may be blended with a white pigment as required. As the white pigment, conventionally known ones can be used. For example, titanium oxide, zinc white, lead white, zinc sulfide, etc. may be mentioned, and only one kind or two or more kinds may be used in combination. The average particle size of the white pigment is not particularly limited, but from the viewpoints of dispersibility, smoothness of the coating film, ensuring adhesion, etc., it is preferably 0.2 to 0.3 μm.

[0044] In the primer paint composition used in the present invention, known auxiliary compounding agents such as inorganic fillers, organic modifiers, stabilizers, plasticizers, additives, etc. can be contained as necessary.

[0045] The blending ratio of water in the above primer paint composition is preferably 45 to 90% by mass, more preferably 50 to 80% by mass, based on the entire primer paint composition. When the blending ratio of water is less than 45% by mass, the viscosity increases, and the storage stability and painting workability decrease. On the other hand, when the blending ratio of water exceeds 90% by mass, the ratio of the non-volatile component decreases, the painting efficiency deteriorates, and appearance abnormalities such as sagging and running are likely to occur. The above primer paint composition may further contain an organic solvent, and the blending ratio thereof is usually 40% by mass or less with respect to the water contained.

[0046] Examples of the above organic solvents include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane, heptane, and octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and cyclopentane; 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 relates to 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 from the primer coating composition of the present invention.

[0048] The plastic molded body is not particularly limited, and examples thereof include automotive exterior parts such as bumpers, spoilers, grills, and fenders. Also, the material thereof is not particularly limited, and examples 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, and the like.

[0049] The above primer coating film is a primer coating film obtained from the primer coating composition of the present invention. The method of applying the primer coating composition to the surface of the plastic molded body is not particularly limited, and for example, it can be applied by methods such as spray coating or bell coating. Industrially, for example, methods using an air electrostatic spray coating machine commonly called "react gun" or a rotary atomization type electrostatic coating machine commonly called "micromicro bell", "micro bell", "metallic bell", etc. can be mentioned. Also, the above plastic molded body may be washed and degreased as necessary.

[0050] The above primer coating film 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, sagging and running are likely to occur. Preferably, it is 15 to 20 μm. The above dry film thickness can be measured using SDM-miniR manufactured by SANKO.

[0051] The above primer coating film is preferably dried before applying the base paint composition. 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 method and infrared drying method may be adopted, for example.

[0052] The above base coating film is usually obtained from a base paint composition containing a coloring pigment, a film-forming resin, a curing agent, and additives as required. Examples of the coloring pigment contained in the above base paint composition include conventionally known coloring 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, metal complex pigments, etc., and inorganic lead yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide, etc. Furthermore, flat pigments such as aluminum powder and graphite powder may be added. Also, extender pigments such as calcium carbonate, barium sulfate, clay, and talc may be contained. Furthermore, depending on the need, a brightening material such as an interference mica pigment or an aluminum pigment may be contained.

[0053] Examples of the film-forming resin and curing agent of the above base paint composition include film-forming resins such as acrylic resin, polyester resin, alkyd resin, and fluorine-based resin, and curing agents such as amino resin and / or blocked polyisocyanate compound.

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

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

[0056] In the automotive exterior parts of the present invention, the above base coating film may be obtained by applying a base paint composition for an automotive body. By being able to apply the base paint for an automotive body, there are advantages such as matching the color tones of the automotive body and the exterior parts and simplifying management, so it is preferable.

[0057] The film thickness of the coating film during painting with the above base paint composition varies depending on the desired application, but in many cases, 10 to 30 μm is useful. If it is less than 10 μm, the base may not be concealed and film breakage may occur. If it exceeds 30 μm, the distinctness of image may decrease, or defects such as unevenness and running may occur during painting. Also, the dry film thickness of the base coating film is usually 10 to 30 μm. If it is less than 10 μm, the hiding power is poor, and if it exceeds 30 μm, it lacks economic efficiency.

[0058] The method of applying the above base paint composition is not particularly limited, and examples thereof include a spray painting method and an electrostatic painting method.

[0059] The base coating film formed by the above base paint composition may be painted with the next clear paint composition as it is without being dried by heat, or may be dried at a temperature of 40°C to 110°C. Particularly in the case of an aqueous base paint, if the drying temperature is 40°C or lower, compatibility with the clear paint may occur and the appearance of the coating film may deteriorate. If the temperature is too high, whitening may occur between the base coating film and the clear coating film.

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

[0061] The above clear coating composition is not particularly limited, and conventionally known ones may be used. For example, a two-component clear coating (for example, a two-component curable urethane coating) using a polyol resin containing a hydroxyl group as the main agent and an isocyanate as the curing agent is preferable. This is because the resulting clear coating film has a good appearance and excellent acid resistance. The polyol resin used as the above main agent is not particularly limited, and for example, polyester polyol, acrylic polyol, polycarbonate polyol, polyurethane polyol, etc. can be used.

[0062] Examples of the isocyanate used as the above curing agent include non-yellowing type compounds having two or more isocyanate groups in the molecule (for example, adducts such as hexamethylene diisocyanate and isophorone diisocyanate, nurate bodies, burette bodies, etc.). Examples of commercially available curing agents include Desmodur 3600 and Sumidur 3300 manufactured by Sumitomo Bayer Urethane Co., Ltd., Coronate HX manufactured by Nippon Polyurethane Industry Co., Ltd., Takenate D-140NL and D-170N manufactured by Mitsui Takeda Chemical Industries, Ltd., Duranate 24A-90PX and THA-100 manufactured by Asahi Kasei Corporation, etc. Examples of commercially available clear coatings include R2500-1 manufactured by Nippon BEE Chemical Co., Ltd., which is a two-component curable urethane coating.

[0063] Furthermore, conventionally known additives such as curing accelerators, defoamers, rheology control agents, lubricants, UV absorbers, etc. and organic solvents are used as necessary.

[0064] In addition, in the automotive exterior parts of the present invention, the above clear coating film may be obtained by applying a clear coating composition for automotive body. Applying the clear coating for automotive body has advantages such as matching the color tones of the automotive body and exterior parts and simplifying management, so it is preferable.

[0065] The clear paint composition for automobile bodies is not particularly limited, but preferably contains a curing accelerator. By including the above-mentioned curing accelerator, curing at a low temperature for a plastic molded body can be carried out without problems. Examples of the above-mentioned curing accelerator include ZCAT (dibutyltin dilaurate) and the like.

[0066] The clear paint composition for automobile bodies preferably further contains a low molecular weight isocyanate compound that easily penetrates into the lower layer as a curing agent. By curing in a state where the low molecular weight isocyanate compound penetrates into the base coating film or the primer coating film, the adhesiveness and strength of the multi-layer coating film can be enhanced. Examples of the above-mentioned curing agent include Desmodur N3900, Desmodur N3400 and the like.

[0067] The method of applying the clear paint composition is not particularly limited, and for example, air spray coating, airless spray coating, bell coating or the like can be employed.

[0068] As described above, a primer paint composition, a base paint composition and a clear paint composition are sequentially applied on the surface of the plastic molded body to form an uncured film of three layers composed of each paint component, and then the following baking process is carried out. When selecting each paint composition, it is necessary to select a paint that can be sufficiently cured and dried in the baking process. If drying is insufficient and water or solvent remains inside the cured coating film, the performance such as water resistance and solvent resistance in the cured coating film is likely to deteriorate.

[0069] The dry film thickness of the clear coating film is preferably 20 to 50 μm. If it is outside the above range, there is a risk of appearance deterioration such as rough texture and poor workability such as sagging and running.

[0070] The baking process is a process of simultaneously baking the uncured film of the above three layers to form a cured coating film composed of three layers of a primer coating film, a base coating film and a clear coating film.

[0071] From the balance between rapid curing and prevention of deformation of the plastic molded body, the baking temperature is preferably, for example, 70 to 130°C, 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. If the baking time is less than 10 minutes, the curing of the coating film is insufficient, and the performance such as water resistance and solvent resistance of the cured coating film deteriorates. On the other hand, if the baking time exceeds 60 minutes, over-curing occurs, resulting in a decrease in adhesion in recoating, an increase in the total time of the coating process, and an increase in energy cost. Note that this baking time means the time during which the surface of the substrate actually continues to maintain the target baking temperature. More specifically, it does not consider the time until the target baking temperature is reached, but means the time when the target temperature is reached and then maintained.

[0072] Examples of the heating device used to simultaneously bake the uncured film of the paint include, for example, a drying oven that uses a heat source such as hot air, electricity, gas, or infrared rays. Also, using a drying oven that combines two or more of these heat sources is preferable because it shortens the drying time.

Example

[0073] Hereinafter, the present invention will be described with reference to examples. In the examples, “%” and “parts” in the mixing ratio mean “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 an aqueous primer paint 3.9 parts by mass of a water-soluble acrylic resin (manufactured by Nippon Paint, solid content concentration 30% by mass, hydroxyl value 71 mg KOH / g), 13.2 parts by mass of an alkyd dispersion resin (manufactured by DIC, solid content 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 prepared using a dyno mill. To 37.6 parts by mass of this pigment paste, 24 parts by mass of a polyolefin emulsion (1) (weight average molecular weight 100,000, melting point 75°C), 10.3 parts by mass of a urethane dispersion resin (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., solid content concentration 35% by mass), 2.1 parts by mass of an 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 parts by mass of pH adjuster, and 17 parts by mass of pure water were further mixed to prepare an aqueous primer.

[0075] (Formation of Coated Product) The obtained aqueous primer was spray-coated on the surface of a PP material or a PC-ABS material (the thickness of the aqueous primer coating film was 7 - 11 μm), dried at 80°C for 3 minutes, and then Base 1 (AR-700 or AR-3100: manufactured by Nippon Paint) and Base 2 (AR-3100: manufactured by Nippon Paint) were each coated to a dry film thickness of 2.5 - 10 μm and dried again at 80°C for 3 minutes. Clear (R-2590: manufactured by Nippon Paint) was coated on this coated plate to a dry film thickness of 30 - 35 μm and dried at 90°C for 20 minutes under Keep to obtain a coated product.

[0076] The following evaluations were performed on the obtained multi-layer coating film. (Adhesion after Water Resistance Test) The obtained coated product was immersed in warm water at 40°C for 10 days, pulled out from the warm water, and dried at room temperature for 1 hour. 100 base marks were made on the surface of the test piece at 2 m intervals with a single-edge razor, and cellophane adhesive tape (JIS Z 1522) was sufficiently pressure-bonded thereon and quickly peeled off in the 90° direction, and the peeling state of the coating film was evaluated by the number of base marks of the remaining coating film. 5: When 100 pieces remain as they are 4: When the peeling area is less than 5% and there is no complete peeling in a grid pattern 3: When the peeling area is less than 15% and there is no complete peeling in a grid pattern 2: When the peeling area is less than 35% and there is complete peeling in a grid pattern 1: When the peeling area is 35% or more

[0077] (Appearance after high-temperature water resistance test) The obtained painted product was immersed in warm water at 80 °C for 5 hours, pulled out from the warm water, and the appearance was visually evaluated. Examine the state of swelling, peeling, cracking, whitening, and wrinkling of the effective surface. Swelling is compared with No. 9-MD specified in ASTM D 714 5: When there is no swelling (superior to ASTM D 714 No. 9-MD), peeling, cracking, whitening, and wrinkling 4: When there is swelling (greater swelling than ASTM D 714 No. 9-MD), peeling, cracking, whitening, and wrinkling 3: When there is swelling (greater swelling than ASTM D 714 No. 9-MD) and any of peeling, cracking, whitening, and wrinkling 2: When there is swelling (greater swelling than ASTM D 714 No. 9-MD), and three of peeling, cracking, whitening, and wrinkling 1: When there is swelling (greater swelling than ASTM D 714 No. 9-MD), peeling, cracking, whitening, and all of wrinkling

[0078] (Adhesion after high-temperature water resistance test) The painted product immersed in warm water at 80 °C for 5 hours and then pulled out was further dried at room temperature for 1 hour, and then evaluated in the same manner as the adhesion after the above water resistance test 5: When 100 pieces remain as they are 4: When the peeling area is less than 5% and there is no complete peeling in a grid pattern 3: When the peeling area is less than 15% and there is no complete peeling in a grid pattern 2: When the peeling area is less than 35% and there is a complete peeling of the grid pattern 1: When the peeling area is 35% or more

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

[0080]

Table 1

[0081] It was shown that a multi-layer coating film having excellent adhesion and water resistance can be obtained by the aqueous primer paint composition obtained in the examples. It was also shown that the base paint composition for automobile bodies and the clear paint composition for automobile bodies can be used without problems.

Industrial Applicability

[0082] According to the present invention, an aqueous primer paint composition for automobile exterior parts having better adhesion than conventional primer paint compositions and paint physical properties such as coating workability and stability equivalent to those of conventional primer paint compositions can be obtained. In addition, since a base paint for automobile bodies and a clear paint for automobile bodies that are usually used can be laminated, effects such as matching the color tones of automobile bodies and automobile exterior parts and reducing the paint management process can also be obtained.

Claims

1. A resin composition comprising chlorinated polyolefin (A), urethane dispersion (B), alkyd dispersion (C), epoxy dispersion (D) and acrylic resin (E), furthermore, an aqueous primer composition for automotive exterior parts 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, An aqueous primer composition for automotive exterior parts, characterized in that the chlorinated polyolefin (A) is contained in a solid content of 45.0 to 60.0% by mass based on the total amount of 100% by mass of the resin solids of the 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, wherein carbon black (F) is contained in the range of 6.4 to 7.2% by mass based on the total amount of 100% by mass of the resin solids.

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

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

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