JPH0476745B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of painting an outer panel of an automobile formed by assembling a metal member and a plastic member. Automobile exterior panels, such as bumpers, facias, fenders, door panels, panel hoods, panel roofs, and panel trunk lids, which were previously mostly composed of metal materials, have recently been partially or fully replaced with plastic materials. It is being done. For example, bumpers and facias are made of plastics such as polyurethane, polypropylene, and polycarbonate instead of metal, and there are also cases where only the lower parts of fenders, door panels, etc. are made of plastic. In the future, it is inevitable that the range of plastics used in automobile exterior panels will further increase, and this trend is actually being observed in panel roofs, panel trunk lids, and the like. This is because the use of plastic can reduce vehicle weight and fuel consumption, is easy to process and can be molded into any shape, and improves the corrosion resistance and impact resistance of the vehicle body. This is because the effects are recognized. However, despite this current situation, there is still no established method for painting automobile exterior panels, which are made up of metal and plastic parts. After applying different paints suited to each part on separate painting lines, both parts were assembled onto the exterior of the car. According to this method, since the paints used for both parts (particularly colored base coats) are different, it is extremely difficult to make the color tone of both parts the same when assembled and integrated. This has the disadvantage that the assembly process of parts is complicated. Furthermore, in the field of automotive coatings, emphasis is being placed on the durability of coating films, particularly the reduction in corrosion resistance of coating films due to impact peeling and the progress of corrosion of steel materials. In particular, in cold regions of Europe and the United States, gravel mixed with a large amount of relatively coarsely crushed rock salt is often laid to prevent road surfaces from freezing in the winter.
When a car runs on this type of road, rock salt particles and pebbles thrown up by the wheels collide with the coating on the outside of the vehicle, and the shock peels off the coating locally from the car body. This often causes what is called "chipping." As a result of this phenomenon, the metal surface of the impacted portion of the outer surface of the vehicle body is exposed, and rust immediately develops and corrosion progresses. Paint peeling due to chipping usually occurs on the bottom of the car body and around the suspension, but it is also known to occur on the hood and roof, and localized corrosion becomes quite noticeable after about six months to a year. . In order to prevent this chipping and the progression of corrosion caused by it, various studies have been made on chemical conversion treatments on the surface of the external metal base of the car body, as well as electrodeposition primers, intermediate coats, and top coats, but there are no practical solutions. We have not yet come up with a solution. Therefore, in view of this situation, the inventors of the present invention
We are conducting extensive research into a method that allows the exterior panels of automobiles, which are made by assembling metal and plastic components, to be finished in the same color using a simplified process, while also forming a coating film with excellent chipping resistance. It was summer. As a result, after assembling and combining a metal part and a plastic part, a barrier coat having a specific composition and properties is applied to both parts, and then an intermediate coat and a top coat are applied. The above-mentioned defects can be eliminated, and the object of the present invention has been achieved. That is, the present invention is a method for painting an automobile exterior panel formed by combining a metal member and a plastic member. After forming the outer panel, a barrier coat mainly composed of a modified polyolefin resin whose static glass transition temperature is -30 to -60°C is applied to the outer panel, followed by an intermediate coat and a top coat. The present invention relates to a method for painting an automobile exterior panel, which is characterized by applying paint. A feature of the present invention is that when applying an intermediate coat paint and a top coat paint to an automobile exterior panel formed by assembling and combining metal members and plastic members, the paints are coated with specific compositions and properties before being applied. A barrier coat is applied to the outer panel. As a result, it has become possible to paint the metal and plastic parts of automobile exterior panels with a single intermediate coat and top coat, thereby eliminating the inconsistency in color tone between the two parts. Moreover, the chipping resistance, corrosion resistance, and physical performance of the formed coating film were also significantly improved. That is, the static glass transition temperature is −30 to −60℃.
Barrier coat coating film adjusted to
It is more flexible than intermediate and top coats for automobile exterior panels, and has unique viscoelasticity due to the modified polyolefin resin. Therefore, if a coating film with such physical properties is applied in advance to the entire surface of the metal and plastic parts of an automobile exterior panel, physical differences such as thermal elasticity and flexibility between the two parts will be eliminated. Most or all of the "distortion" that occurs between the intermediate coat film and the top coat film is absorbed into the barrier coat film, so the "distortion" etc. occurs between the intermediate coat film and the top coat film. Most of the damage could have been prevented from spreading. As a result, it has become possible to apply intermediate and top coat paints of a single composition to both parts of an automobile exterior panel, and it has become possible to finish both parts in the same color tone. Furthermore, even if a strong impact force is applied by rock salt, pebbles, etc. to the surface of the coating film consisting of the intermediate coating and top coating formed through the barrier coating film, most or all of the impact energy is absorbed by the barrier coating film. Because it is absorbed into the paint film, there is almost no impact peeling of the paint film, and most physical damage to the top coat film has been eliminated, so it is easy to prevent peeling of both the top coat and intermediate coat due to chipping, as well as metal parts. Rust and corrosion could be prevented. The coating method of the present invention will be specifically explained below. First, in the present invention, the automobile outer panel is an outer panel formed by assembling and combining a metal member and a plastic member. For example, the parts may be a bumper, a facia, a fender, a door panel, a panel hood, a panel roof, a panel trunk lid, or a combination of two or more of these parts. In other words, the individual parts themselves may be made up of a plastic part and a metal part, or the parts made of a metal part and a part made of a plastic part may be combined and integrated. Further, the metal part is mainly made of iron, copper, aluminum, zinc, or an alloy containing these, and the plastic part is made of, for example, polyurethane, polypropylene, polycarbonate, or the like. In the present invention, the term "automobile" in the outer panel of the automobile is not limited to so-called passenger cars, but should be understood to include motorcycles, trucks, safari cars, and the like. Of the above two parts, metal parts should be pretreated with a chemical conversion treatment using zinc phosphate, iron phosphate, chromate, etc. according to a conventional method, if necessary, and then painted with a cationic electrodeposition paint. is preferred. For the cationic electrodeposition coating, known electrodeposition paints can be used for coating the above-mentioned metal members. The cationic electrodeposition paint contains a basic water-dispersed resin that is neutralized with an organic or inorganic acid;
For example, water-based paints that use resins such as epoxy, acrylic, and polybutadiene that have a large number of amino groups in their resin skeletons (resins are not limited to these), and the resins contain neutralizing agents, pigments (coloring), etc. pigments, extender pigments, anti-rust pigments, etc.), hydrophilic solvents,
Water and, if necessary, a curing agent, a crosslinking agent, additives, etc. are blended to form a paint by a conventional method. The above basic water-dispersible resin (usually used by dissolving it in a hydrophilic solvent)
Neutralizing agents for neutralizing and dissolving (dispersing) in water include organic acids such as acetic acid, hydroxyl acetic acid, propionic acid, butyric acid, lactic acid, glycine, sulfuric acid, hydrochloric acid,
Inorganic acids such as phosphoric acid can be used. The appropriate amount of the neutralizing agent is within the range of about 0.1 to 0.4 neutralization equivalent relative to the base number (about 50 to 200) of the resin. The solid content is diluted with deionized water to a concentration of about 5 to 40% by weight, the pH is maintained within the range of 5.5 to 8.0, and the steel plate is electrodeposited using a conventional method. The thickness of the electrodeposition coating film is not particularly limited, but it is 10 to 10% based on the cured coating film.
40μ is preferred, and the coating is cured by heating to about 140-210°C. On the other hand, the plastic parts are treated with solvent vapor degreasing, polishing,
It is preferable to perform surface treatment by acid treatment, corona discharge, etc. In the present invention, after the electrodeposited metal member and plastic member are assembled to form an integrated automobile exterior panel, a barrier coat is applied over the entire surface of both parts. The barrier coat has a static glass transition temperature of -30 to -60°C (preferably -40 to -55°C).
This is a paint whose main component is a modified polyolefin resin. That is, as a modified polyolefin resin, for example, a propylene-ethylene copolymer (preferably a molar ratio of 40 to 80:60 to 20%) and a chlorinated polyolefin (chlorination rate of about 1 to 60%) are mixed. 50 parts by weight, preferably 10 to 20 parts by weight (both per 100 parts by weight of the copolymer), or 0.1 part by weight of maleic acid or maleic anhydride per 100 parts by weight of the above propylene-ethylene copolymer. -50 parts by weight, preferably 0.3 to 20 parts by weight of graft-polymerized resins.
In the present invention, if these modified polyolefin resins themselves have a static glass transition temperature within the above range, they can be used as a barrier coat by themselves; If it is desired to change the static glass transition temperature, a viscosity imparting agent can be added as necessary. The viscosity imparting agent includes, for example, rosin, petroleum resin (coumaron), ester gum, polybutadiene, epoxy-modified polybutadiene, low molecular weight aliphatic epoxy resin, low molecular weight aliphatic bisphenol, which has good compatibility with the modified polyolefin resin. Examples include type epoxy resin, polyoxytetramethylene glycol, vinyl acetate-modified polyethylene, etc., and the blending amount thereof is preferably 1 to 50 parts by weight per 100 parts by weight of the above-mentioned modified polyolefin resin. In addition, in order to improve the coating properties of the barrier coat, it is preferable to dissolve or disperse the above components in an organic solvent. Examples of organic solvents include aromatic hydrocarbons such as benzene, toluene, and xylene, hexane, heptane,
Examples include aliphatic hydrocarbons such as octane and decane, and chlorinated hydrocarbons such as trichlorethylene, perchlorethylene, dichloroethylene, dichloroethane, and dichlorobenzene. In the present invention, it is essential that the static glass transition temperature of the coating film forming the barrier coat is within the above range, and furthermore, the tensile strength elongation at break of the coating film must be within the -20°C atmosphere. 200～
Preferably it is 1000%. Furthermore, if the static glass transition temperature of the formed coating film is higher than -30°C, the above object of the present invention cannot be achieved, and if it is higher than -60°C, the performance of the coating film, particularly water resistance, adhesion, etc., decreases. So I don't like it. In particular, for the purpose of improving electrostatic coating on plastic parts, conductive substances are added to the barrier coat to reduce the volume resistivity of the coating film to 10 ⁷ Ωcm or less, especially
It is preferable to adjust it to 10 ³ to ^{10 5} Ωcm. Examples of the conductive substance include conductive carbon,
Examples include powders such as silver, nickel, aluminum, zinc oxide, tin dioxide, and tungsten oxide.
The content of these components may be within a range that does not cause deterioration of the physical performance of the barrier coating film, and specifically, 100 parts by weight of the modified polyolefin resin.
Parts by weight or less are preferred. Furthermore, extender pigments, coloring pigments (excluding anticorrosive pigments), etc. may be added to the barrier coat. The blending amount of these pigments is preferably 10 to 100 parts by weight per 100 parts by weight of the modified polyolefin resin. In the present invention, these barrier coats are applied to the surfaces of metal and plastic parts coated with cationic electrodeposition, but the coating method is not limited, and examples include spray coating, brush coating, dipping coating, melt coating, and static coating. Electrocoating and the like are available, and the coating film thickness is preferably 1 to 20 μm, particularly 5 to 10 μm, depending on the coating film formed. The static glass transition temperature of the formed coating film of the barrier coat used in the present invention is a value measured with a differential scanning calorimeter (Model DSC-10 manufactured by Daini Seikosha).
The tensile strength elongation at break is a value measured using a universal tensile testing machine with a constant temperature bath (Shimadzu Autograph S-D model), the sample length was 20 mm, and the tensile speed was
The samples used for these measurements, carried out at 20 mm/min, were
Painted on a tin plate to a thickness of 25μ and heated at 120℃ for 30μ
After being separately baked, it was isolated by the mercury amalgam method and used. When applying the following intermediate coating paint to the barrier coat coating surface, it is preferable to bake the barrier coat in advance, but it is also possible to apply the intermediate coating paint wet-on-wet without baking. The baking temperature may be within a range that does not deform or deform the plastic member, for example,
60-140℃, especially 80-120℃ is suitable. Intermediate paint: A paint to be applied to the above-mentioned barrier coated surface, and any known intermediate paint with excellent adhesion, smoothness, sharpness, overbake resistance, weather resistance, etc. can be used. Specifically, examples include organic solution type thermosetting intermediate coatings whose main components are short oils with an oil length of 30% or less, oil-free alkyd resins, or oil-free polyester resins, and amino resins. These alkyd resins and polyester resins have a hydroxyl value
60 to 140, acid value 5 to 20, and unsaturated oil (or unsaturated fatty acid) as the modified oil is preferable, and the amino resin is an alkyl (carbon number 1 to 5) etherified melamine resin or urea resin. , benzoguanamine resin, etc. are suitable.
The blending ratio of these may be 65 to 85%, especially 70 to 80%, for alkyd resin and/or oil-free polyester resin, and 35 to 15%, especially 30 to 20% for amino resin, based on the solid weight. preferable. Furthermore, the above amino resin can be replaced with a polyisocyanate compound or a blocked polyisocyanate compound. The form of the intermediate coating is most preferably an organic solution type, but it may also be a non-aqueous dispersion using the above vehicle component, a high solids type, an aqueous solution type, or an aqueous dispersion type. In the present invention, the hardness (pencil hardness) of the intermediate coating film is preferably in the range of 3B to 2H. Furthermore, extender pigments, coloring pigments, other paint additives, and the like can be added to the intermediate paint as necessary. In the present invention, the intermediate coating paint can be applied to the barrier coat surface by the same method as the barrier coat, and the coating film thickness is in the range of 10 to 50μ, particularly 20 to 30μ, based on the cured coating. is preferable, and the coating film is baked and hardened according to its composition, but conditions should be adopted that do not deform or alter the plastic member to be coated.
℃) for 10 to 40 minutes. Top coat: A paint applied to the intermediate coated surface, which imparts cosmetic properties to the object to be coated. Specifically, the finished appearance (sharpness, smoothness, gloss, etc.), weather resistance (gloss retention, color retention, etc.)
chalk resistance, etc.), chemical resistance, water resistance, moisture resistance,
Known paints that form coating films with excellent curability can be used; for example, paints whose main vehicle components are amino-acrylic resins, amino-alkyd resins, amino-polyester resins, etc. can give. The form of these paints is not particularly limited, and organic solution type, non-aqueous dispersion type, aqueous (dispersion) liquid type, powder type, high solid type, etc. can be used. The formation of the coating film is
This is carried out by drying at room temperature, drying by heating, irradiation with active energy rays, etc. In the present invention, the coating film formed by these top coats has a pencil hardness of 2B.
It is desirable that it be within the range of ~3H. The top coat used in the present invention is a metallic paint or a solid color finishing paint, which is a paint using the above vehicle main component mixed with a metallic pigment and/or a colored pigment, and a clear paint (color clear paint) that does not contain any or almost all of these pigments. (including paints). and,
A method of forming a top coat film using these paints includes, for example, applying a metallic paint containing a metallic pigment, a colored pigment if necessary, or a solid color paint containing a colored pigment, and curing by heating. (Metallic or litho color finish using 1-coat, 1-bake method). After applying metallic paint or solid color paint and curing with heat, apply clear paint and heat harden again (metallic or solid color finish using 2-coat, 2-bake method). After applying metallic paint or solid color paint, and then applying clear paint, heat both coats and cure them at the same time (2 coats 1 coat).
Metallic or solid color finish by baking method). These top coats are preferably applied by spray painting, electrostatic painting, etc. Also, the coating film thickness is 25 to 40μ in 1 above, based on the dry coating film.
In 2 and 3 above, metallic paints and solid color paints are 10 to 30μ, and clear paints are 25 to 30μ.
50μ each is preferred. The heating conditions can be arbitrarily selected depending on the vehicle components and the plastic material to be coated, but heating conditions of 60 to 140℃, especially 80 to 140℃ are recommended.
Preferably 10 to 40 minutes. The coating film formed by applying a barrier coat, intermediate coat paint, and top coat paint to the outer panel of the automobile, which is assembled by assembling metal parts and plastic parts coated with cationic electrodeposition paint as described above, is as follows:
The color matching between the metal part and the plastic part was good, and chipping resistance, corrosion resistance, and physical performance were also significantly improved. Next, examples and comparative examples related to the present invention will be described. Sample (1) Metal parts: Galvanized steel plate (size 300 x 90 x 0.8 mm) chemically treated with Bonderite #3030 (manufactured by Nihon Parkerizing Co., Ltd., zinc phosphate type) (2) Plastic parts: treated with trichloroethane Steam-degreased polyamide resin board (size 300 x 90 x
0.8mm) (3) Cationic electrodeposition paint: Elekron #9200 (manufactured by Kansai Paint Co., Ltd., epoxy polyamide cationic electrodeposition paint, gray color) (4) Barrier coat (A): Propylene-ethylene copolymer Printex L-6 (manufactured by Degussa, conductive carbon) is a resin in which maleic acid is grafted onto the resin.
(per 100 parts by weight of the graft polymer resin) dispersed in an organic liquid (static glass transition temperature -43°C, tensile strength elongation at -20°C 410%, volume resistivity)
2.3×10 ³ Ωcm). (B): 10 rosin per 100 parts by weight of the resin (A) above
Organic liquid of resin mixed with 10 parts by weight and Printex L-6 (static glass transition temperature -52℃, tensile strength elongation at -20℃ 700%, volume resistivity 4.5×10 ⁴ Ω)
cm). (C): Organic liquid (static glass transition temperature +5℃, volume specific Resistance value 5.2×10 ³ Ω
cm). (5): Intermediate paint Amirakku N-2 Sealer (manufactured by Kansai Paint Co., Ltd., amino polyester resin intermediate paint) (6) Topcoat paint (A): Amirakku White (manufactured by Kansai Paint Co., Ltd.,
Amino alkyd resin topcoat paint, 1 coat 1 bake white paint, pencil hardness HB) (B): Magikron Silver (manufactured by Kansai Paint Co., Ltd.,
Aminoacrylic resin topcoat paint, 2-coat, 1-bake silver metallic paint, pencil hardness H) (C): Magiklon Clear (manufactured by Kansai Paint Co., Ltd.,
Aminoacrylic resin topcoat, 2-coat, 1-bake clear paint, pencil hardness H) Examples and Comparative Examples The above metal parts were coated with cationic electrodeposition paint Elekron #9200 by the usual method, and heated to 30°C at 170°C. It was cured by heating for 20 minutes (cured coating thickness: 20 μm). Next, a barrier coat is applied by air spray, and an intermediate coat and a top coat are applied by electrostatic coating to the object to be coated, which is a combination of the metal member coated with the cationic electrodeposition paint and the plastic member. It was painted as shown in Table 1.

【table】

[Table] In Table 1, (1) All thick films are based on dry cured coatings. (2) The top coats of Examples 2, 3, and 5 and Comparative Examples 2 and 5 were all wet-on-wet two-coat one-bake systems, and after applying top coat (B) or (E), the top coat was applied at room temperature.
After leaving it for 15 minutes, I painted the top coat (C) or (F) and baked it. (3) In Comparative Example 4, (D): Soflex #2500 Primer (manufactured by Kansai Paint Co., Ltd., undercoat paint for plastics, polyolefin-urethane system) (E): Soflex #1400 Silver Metallic (manufactured by Kansai Paint Co., Ltd.) (F): Soflex #500 Clear (manufactured by Kansai Paint Co., Ltd., clear paint for plastic, urethane acrylic) (4) In Examples 1 to 5 and Comparative Examples 1 to 3. , a single barrier coat, an intermediate coat, and a top coat were applied to both sides of the metal member and the plastic member, and in Comparative Example 4, the metal member was coated with a cationic electrodeposition paint, an intermediate coat, and a top coat (B), (C). )
and paint (D) and (E) on the plastic parts.
In addition, (F) was painted. Comparative Example 5 Painting and baking were carried out in the same manner as in Example 1, except that an organic solvent solution of unmodified propylene-ethylene copolymer (static glass transition temperature of about -45°C) was used as the barrier coat. Performance Test Results A coating film performance test was conducted using the coated plates coated in the above Examples and Comparative Examples. The results are shown in Table 2.

【table】

【table】

【table】

Claims (1)

[Claims] 1. A method for painting an automobile exterior panel consisting of a metal member and a plastic component, which involves assembling a metal component and a plastic component coated with a cationic electrodeposition paint in advance to form an automobile exterior panel, and applying the steps to both components. Apply a barrier coat whose main component is a modified polyolefin resin made by graft polymerizing maleic acid or maleic anhydride to a propylene-ethylene copolymer and whose static glass transition temperature is -30 to -60°C. A method for painting an exterior panel of an automobile, which comprises applying an intermediate coat and a top coat.