JP2005199151A - Multi-layer coating film formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer coating film formation method useful for coating of a large size object. <P>SOLUTION: In the multi-layer coating film formation method, an object to be coated is immersed in an electro-deposition bath and is subjected to electro-deposition coating and after cured, a top coat coating composition is directly coated and cured without applying middle coat. In the multi-layer coating film formation method, the object to be coated is not a completed product but respective constitution parts and the electro-deposition bath is constituted by a plurality of baths. The respective baths are constituted by the electro-deposition coating having different color. After the constitution parts subjected to electro-deposition coating in the respective electro-deposition baths is assembled to the completed product, the top coat is applied. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a multilayer coating film forming method and a coating system useful for painting a large object such as an automobile.

  On the surface of a substrate such as an automobile, a plurality of coating films having various roles are formed to protect the substrate and at the same time give a beautiful appearance. In general, an automobile body or the like is subjected to electrodeposition coating on an object to be coated which is a conductive substrate, followed by intermediate coating and top coating.

  However, in recent years, in order to save energy and reduce costs, a method of omitting a part of the coating process is being adopted. As one aspect of this simplification, there is a method of omitting intermediate coating.

  The electrodeposition coating film obtained by electrodeposition coating is generally achromatic such as black or gray. When the intermediate coating is omitted and the white or chromatic top coating composition is applied directly on the electrodeposition coating, the concealment of the top coating is insufficient and the electrodeposition coating below May be affected by color. In this case, even if the top coating composition is applied, a multilayer coating film having the desired color cannot be obtained.

  In order to avoid such inconveniences, Japanese Patent Application Laid-Open No. 2002-35691 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-79172 (Patent Document 2) apply a chromatic color electrodeposition paint to form a coating film. A coating formation method is described by forming and then applying a topcoat composition similar in color to the coating. It is described that this method improves the base concealment of the top coat and makes it possible to omit the intermediate coating step.

  By the way, a painting system for an automobile body that is generally performed at present has a form in which a plurality of painting steps are arranged along a conveying device. On the other hand, automobiles that are currently on the market are required to have a wide variety of colors that meet the needs of consumers. For this reason, when the above-described method using an electrodeposition paint having a color similar to that of the top coating composition is used in the current electrodeposition coating process, a coating system for electrodeposition coating having a color similar to the required color In addition, it is necessary to newly install a painting bath according to the number of colors required. This requires enormous space and a large amount of money and is difficult to do in practice.

JP 2002-35691 A JP 2002-79172 A

  An object of the present invention is to provide a method for forming a multilayer coating film useful for painting a large object such as an automobile, which can effectively coat a large object without performing an intermediate coating process.

  The present invention is a method for forming a multi-layer coating film in which an object to be coated is immersed in an electrodeposition bath, electrodeposited, cured, and then directly coated with an overcoating composition without being coated with an intermediate coating. The object to be coated is not a finished product but each component, and this electrodeposition bath is composed of a plurality of baths, each of which is composed of electrodeposition paints of different colors. The present invention provides a method for forming a multi-layer coating film, characterized by applying a top coat after assembling painted components into a finished product.

  In the method of the present invention, it is preferable that the electrodeposition coating film obtained by electrodeposition coating and the top coating film obtained by the topcoating have similar colors.

  Furthermore, the present invention provides an electrodeposition coating booth in which components are immersed in a bath of one color selected from a plurality of electrodeposition baths each forming a coating film of a different color, and electrodeposition coating booth is cured by electrodeposition coating. Provided is a coating system having an assembly booth for assembling components into a finished product and a topcoat coating booth for applying and curing a topcoat composition to the assembled finished product. Here, “booth” means “compartment”. The “electrodeposition coating booth” is a section where electrodeposition coating and curing thereof are performed in the coating system, and the “assembly booth” is a section where components are assembled into finished products. The “painting booth” is a section where top coating is performed in the coating system. The “intermediate coating booth” described in the present application is a section where the intermediate coating is performed on the cured electrodeposition coating film after the electrodeposition coating and the curing thereof are performed in a normal process. Say.

  In the method of the present invention, by using an electrodeposition coating composition that can obtain an electrodeposition coating of the same color as that of the top coat as the electrodeposition coating composition, it is possible to conceal the top coat even if the intermediate coating step is omitted. Sex is not impaired. In the method of the present invention, electrodeposition coating is performed in the state of components, not the finished product. Therefore, the amount of the colored electrodeposition coating composition used in the present invention can be made much smaller than the amount of coating used in general electrodeposition coating.

  Furthermore, in the method of the present invention, only the portion of the electrodeposition bath can be replaced with a plurality of small electrodeposition baths with respect to the existing coating system. For this reason, it can respond to the coating needs with respect to the various colors in the coating of a large-sized object at low cost. Therefore, the method of the present invention can reduce the coating cost in addition to omitting the intermediate coating step.

  The present invention will be described with reference to schematic process drawings. A schematic process in the method of the present invention is shown in FIG. In the present invention, electrodeposition coating is performed at the stage of component parts before assembling an object whose finished product is an automobile body or the like as an object to be coated. For example, when the object (finished product) to be coated is an automobile body, examples of such components include parts such as a vehicle door and a bonnet, and an automobile body frame.

  FIG. 2 shows a schematic diagram of electrodeposition coating that is generally performed at present. When electrodeposition coating of a finished automobile body is performed, the electrodeposition bath used for the electrodeposition coating needs to be large enough to immerse the automobile body. For example, a bath having a size of about 300 t is used as such an electrodeposition bath.

  FIG. 3 is a schematic explanatory diagram of the method of the present invention. In the coating method according to the present invention, the electrodeposition layer used for electrodeposition coating may be of a size sufficient to immerse the components of the automobile body. In the case of replacing the electrodeposition bath part for the method according to the present invention with respect to the coating system for forming a multi-layer coating film having an electrodeposition bath of about 300 tons, for example, an electrode for parts such as a vehicle door and a bonnet is used. It can be replaced with an electrodeposition bath of about 50 t as a bathing bath, and an electrodeposition bath of about 100 t as an electrodeposition bath for an automobile body frame. The form of these electrodeposition baths can be changed according to the form and size of each part. The electrodeposition bath in the method of the present invention is considerably smaller than the electrodeposition bath in the existing coating system, that is, the system for coating the finished product. For example, the volume of the electrodeposition bath used in the present invention is the same as the electrodeposition bath in the finished product. The volume is about 1/5 to 1/2 when painting. Therefore, a plurality of electrodeposition baths can be installed in place of one electrodeposition bath included in one existing coating system. The plurality of electrodeposition baths can correspond to the colored electrodeposition coating composition used. For example, in place of an existing electrodeposition bath, a plurality of color electrodeposition baths such as red, blue, green and gray electrodeposition baths can be provided. By using an electrodeposition bath with a small volume, it is possible to reduce the amount of paint composition used in the painting process and to respond more flexibly to painting needs for various colors. Usability is improved. As an electrodeposition bath that can be installed in place of an existing electrodeposition bath, it is preferable to install an electrodeposition bath of about 1 to 5 colors in consideration of equipment space, installation cost, the number of colors of the corresponding top coating composition, etc. It is more preferable to install an electrodeposition bath of about 2 to 5 colors. And 1-5 electrodeposition baths can be installed, more preferably 2-5 electrodeposition baths can be installed.

  In addition, by using an electrodeposition coating composition that yields an electrodeposition coating of the same color as the topcoat as the electrodeposition coating composition, the concealability of the topcoat is impaired even if the intermediate coating step is omitted. I can't. Examples of the “similar colors” mentioned here include a color gamut where process concealment of the top coat film is established. This process hiding means the hiding power of the top coating composition on the electrodeposition coating film. In the present invention, those having a color difference ΔE of 0.5 or less between the portion where the coating film of the top coating composition is formed on the electrodeposition coating film and the complete hiding plate (black and white hiding film thickness + 3 μm) are preferably used, Those having ΔE of 0.1 to 0.3 are more preferably used. The film thickness of the top coat film is a film thickness formed in a normal process, and is, for example, about 10 to 20 μm for the base coat paint, 30 to 40 μm for the clear paint, and 30 to 40 μm for the mono coat paint. Here, the monocoat paint refers to a one-coat topcoat paint (a coating film obtained by applying this paint), and examples thereof include a white solid and a black solid. The film thickness when the top coating composition (base coat paint) used is a solvent type is generally about 15 μm, and the film thickness when the top coating composition (base coat paint) is an aqueous type is generally about 13 μm. This measurement is performed according to JIS K 5600 4-1, and JIS K 5600 4-2, and the color difference is measured using a spectrophotometer. By expanding the color gamut width of the electrodeposition coating film, the pigment concentration of the top coating composition can be reduced, and the film thickness of the top coating film can be reduced.

  As an advantage of using a colored electrodeposition coating composition, it is not necessary to increase the pigment concentration in the top coating composition in order to increase the concealment of the top coating film by a coating process in which the intermediate coating is not performed. And disadvantages caused by increasing the pigment concentration, such as reduction of chipping property, can be eliminated.

  Furthermore, the electrodeposition coating composition generally used contains inorganic pigments such as extender pigments. Such inorganic pigments generally have a high specific gravity and are likely to settle in the electrodeposition coating composition. In addition, sedimentation is likely to occur during electrodeposition coating, and sediment settled during coating may fall on the horizontal upper surface of the object to be coated, resulting in a coating film having rough skin, uneven coating, and the like. . In the case of painting a large article such as an automobile body and having a large horizontal area, these are particularly serious problems. On the other hand, in the coating method according to the present invention, the electrodeposition coating on the object to be coated is performed in units of smaller components. Therefore, in the electrodeposition coating, the component parts can be easily directed in an arbitrary direction. For example, it can arrange | position so that the largest area part of a component may become the orthogonal | vertical direction with respect to the water surface of an electrodeposition coating composition, and it can reduce that a sediment falls on the horizontal surface of a to-be-coated article.

  Hereinafter, the coating process and the coating composition that can be used in the method according to the present invention will be described.

Electrodeposition Paint Composition The electrodeposition paint composition used in the method of the present invention contains a cationic epoxy resin, a curing agent, and a pigment including a color pigment.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an amine-modified epoxy resin. The cationic epoxy resin may be a known resin described in JP-A Nos. 54-4978 and 56-34186.

  Cationic epoxy resins typically open all of the epoxy rings of a bisphenol-type epoxy resin with an active hydrogen compound capable of introducing a cationic group, or some epoxy rings with other active hydrogen compounds. It is produced by opening the ring and opening the remaining epoxy ring with an active hydrogen compound capable of introducing a cationic group.

  A typical example of the bisphenol type epoxy resin is bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, there are Epicoat 828 (manufactured by Yuka Shell Epoxy Co., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3000-4000), etc. Examples of the latter commercially available product include Epicoat 807 (same as above, epoxy equivalent 170).

  The following formula described in JP-A-5-306327

[Wherein R represents a residue excluding the glycidyloxy group of the diglycidyl epoxy compound, R ′ represents a residue excluding the isocyanate group of the diisocyanate compound, and n represents a positive integer. An oxazolidone ring-containing epoxy resin represented by the above formula may be used as the cationic epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

  As a method for introducing an oxazolidone ring into an epoxy resin, for example, a block polyisocyanate curing agent blocked with a lower alcohol such as methanol and a polyepoxide are heated and kept in the presence of a basic catalyst, and a by-product lower alcohol is used as a system. It is obtained by distilling from the inside.

  Particularly preferred epoxy resins are oxazolidone ring-containing epoxy resins. This is because a coating film having excellent heat resistance and corrosion resistance and further excellent impact resistance can be obtained.

  It is known that an epoxy resin containing an oxazolidone ring can be obtained by reacting a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie, bisurethane). Specific examples and production methods of the oxazolidone ring-containing epoxy resin are described in, for example, paragraphs 0012 to 0047 of JP-A No. 2000-128959 and are publicly known.

  These epoxy resins may be modified with suitable resins such as polyester polyols, polyether polyols, and monofunctional alkylphenols. In addition, the epoxy resin can be chain-extended using a reaction between an epoxy group and a diol or dicarboxylic acid.

  These epoxy resins are ring-opened with an active hydrogen compound so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening, and more preferably 5 to 50% of them are occupied by primary amino groups. It is desirable to do.

  Active hydrogen compounds that can introduce a cationic group include primary amines, secondary amines, tertiary amine acid salts, sulfides and acid mixtures. In order to prepare a primary, secondary or / and tertiary amino group-containing epoxy resin, an acid salt of a primary amine, secondary amine or tertiary amine is used as an active hydrogen compound capable of introducing a cationic group.

  Specific examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. A plurality of amines may be used in combination.

Curing Agent The curing agent used in the present invention is preferably a blocked polyisocyanate obtained by blocking polyisocyanate with a blocking agent. Here, the polyisocyanate means a compound having two or more isocyanate groups in one molecule. The polyisocyanate may be, for example, any of aliphatic, alicyclic, aromatic and aromatic-aliphatic.

  Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4- C3-C12 aliphatic diisocyanates such as trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI) Methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3-diisocyanatomethyl cyclohexyl Carbon such as xane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate). Aliphatic diisocyanates having a number of 5 to 18; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethyl xylylene diisocyanate (TMXDI); Uretdione, uretoimine, burette and / or isocyanurate modified product); and the like. These may be used alone or in combination of two or more.

  Adducts or prepolymers obtained by reacting polyisocyanates with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at an NCO / OH ratio of 2 or more may also be used as curing agents.

  The polyisocyanate is preferably an aliphatic polyisocyanate or an alicyclic polyisocyanate, and more preferably an aliphatic polyisocyanate. This is because the formed coating film is excellent in weather resistance.

  Preferred specific examples of the aliphatic polyisocyanate or alicyclic polyisocyanate include hexamethylene diisocyanate, hydrogenated TDI, hydrogenated MDI, hydrogenated XDI, IPDI, norbornane diisocyanate, dimer (biuret) and trimer thereof. (Isocyanurate) etc. are mentioned.

  The blocking agent is added to a polyisocyanate group and is stable at ordinary temperature, but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature.

  As a blocking agent, when low temperature curing (160 ° C. or lower) is desired, lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam and β-propiolactam, and formaldoxime, acetoald It is preferable to use an oxime blocking agent such as oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, and cyclohexane oxime.

  The binder containing the cationic epoxy resin and the curing agent is generally contained in the electrodeposition coating composition in an amount that occupies 25 to 85 mass%, preferably 60 to 85 mass% of the total solid content of the electrodeposition coating composition. The

Pigment The electrodeposition coating composition used in the present invention contains a colored pigment as a pigment, and further contains an extender pigment as necessary. As a coloring pigment,
White system: titanium dioxide, zinc oxide, phosphoric acid (Zn, Al), molybdic acid (Zn, Ca),
Black: Carbon black, graphite (iron), iron black (iron black),
Blue: inorganic, bitumen, ultramarine, cobalt blue, organic: copper phthalocyanine blue, indanthrone blue,
Yellow: inorganic yellow, synthetic yellow iron oxide, transparent brown (yellow), bismuth vanadate, titanium yellow, zinc yellow (zinc yellow), strontium chromate, organic, monoazo yellow, monoazo yellow, disazo, monoazo yellow, Isoindolinone yellow, metal complex salt azo yellow, quinophthalone yellow, isoindoline yellow, benzimidazolone yellow,
Red; inorganic, red bean, transparent red, red, organic: monoazo red, monoazo red, unsubstituted quinacridone red, azo lake (Mn salt), quinacridone magenta, ansanthrone orange, dianthraquinonyl red, perylene Maroon, quinacridone magenta, perylene red, diketopyrrolopyrrole chrome vermilion,
Green: inorganic, chromium oxide, organic, chlorinated phthalocyanine green, brominated phthalocyanine green,
Others: pyrazolone orange, benzimidazolone orange, dioxazine violet, perylene violet and the like. In addition, carbon black or the like may be used together with the color pigment from the aspect of hiding the substrate of the object to be coated. In addition, aluminum powder, aluminum flakes, pearl mica, and the like can be added to form a metallic or pearly electrodeposition coating film.

  As the extender pigment, those commonly used in the coating field, for example, aluminum silicate, barium sulfate and the like can be used.

  A pigment is mix | blended with an electrodeposition coating composition in the quantity which occupies 5-25 mass% of the total solid of an electrodeposition coating composition.

  When a pigment is used as a component of an electrodeposition paint, generally, the pigment is dispersed in an aqueous medium at a high concentration together with a resin called a pigment dispersion resin to make a paste. This is because the pigment is in a powder form, and it is difficult to disperse in a single step in a low concentration uniform state used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste. In the present invention, the curing catalyst is dispersed in advance using a pigment dispersion resin and made into a paste, and then added to the mixture of the pigment and the pigment dispersion resin to further disperse the tin catalyst uniformly in the paint. Make it.

  As the pigment-dispersed resin varnish, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion-exchanged water or water containing a small amount of alcohol is used. In general, the pigment-dispersed resin varnish is used in a solid content of 20 to 40 parts by mass, and the pigment and catalyst are used in a ratio of 60 to 80 parts by mass.

Catalyst In addition to the above components, the electrodeposition coating composition used in the present invention is composed of organotin compounds such as dibutyltin laurate, dibutyltin oxide and dioctyltin oxide, amines such as N-methylmorpholine, strontium, cobalt, A metal salt such as copper may be included as a catalyst. These can act as a catalyst for the dissociation of the blocking agent of the curing agent. The concentration of the catalyst is preferably 0.1 to 6 parts by mass with respect to 100 parts by mass of the total of the cationic epoxy resin and the curing agent in the electrodeposition coating composition.

Preparation and coating of electrodeposition coating composition The electrodeposition coating composition used in the present invention comprises a cationic epoxy resin and a curing agent dispersed in an aqueous medium, a pigment dispersion paste, and deionized water in a predetermined ratio. Prepared by mixing with. Further, the aqueous medium usually contains a neutralizing agent in order to improve the dispersibility of the cationic epoxy resin. Neutralizing agents are inorganic or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid. The amount is that which achieves a neutralization rate of at least 20%, preferably 30-60%.

  The amount of curing agent is sufficient to react with active hydrogen-containing functional groups such as primary, secondary or / and tertiary amino groups and hydroxyl groups in the cationic epoxy resin during curing to give a good cured coating film. Generally, the weight ratio of the cationic epoxy resin to the curing agent is generally in the range of 90/10 to 50/50, preferably 80/20 to 65/35.

  The electrodeposition paint can contain conventional paint additives such as water-miscible organic solvents, surfactants, antioxidants, and UV absorbers. Moreover, an acrylic resin etc. can also be included other than the said resin component, for example.

  The electrodeposition coating composition is electrodeposited on the component parts of the object that is the object to be coated to form a cured coating film. The object to be coated when electrodeposition coating is performed using this electrodeposition coating composition is preferably a conductor that has been subjected to surface treatment such as zinc phosphate treatment in advance by dipping, spraying, etc. The surface treatment may not be performed. The conductor is not particularly limited as long as it can be a cathode in performing electrodeposition coating, and a metal substrate is preferable.

The conditions under which electrodeposition is performed are generally the same as those used for other types of electrodeposition coating. The applied voltage may vary greatly and may range from 1 volt to several hundred volts. The current density is usually about 10 amperes / m ^{2 to} 160 amperes / m ² and tends to decrease during electrodeposition.

  After electrodeposition coating, the coating film is baked in a conventional manner, for example, in a baking oven, in an oven or with an infrared heat lamp at an elevated temperature. The baking temperature may vary but is usually about 140 ° C to 180 ° C.

Assembling the components Next, the electrodeposited components are assembled into a finished product. Here, you may use the apparatus normally used for assembly operation of components. The top coating composition is applied to the finished product thus assembled.

Top coating composition and coating As the top coating composition that can be used in the method of the present invention, a top coating composition generally used in the coating field can be used. As the top coating composition, for example, a top coating composition containing a vehicle, a bright pigment and / or a coloring pigment, an extender pigment, various additives and a solvent can be used. As the color pigment used here, a color pigment that can be used in an electrodeposition coating composition can be used.

  The top coating composition is applied on the obtained electrodeposition coating film. Examples of the method for applying the top coating composition include a spray method and a roll coater method.

  A coating film formed by applying the top coating composition can be baked at, for example, 120 to 160 ° C. for a predetermined time to form a multilayer coating film. In this way, a painted finished product is obtained.

It is a figure which shows the schematic process in the method of this invention. It is the schematic of general electrodeposition coating. It is a schematic explanatory drawing of the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrodeposition bath, 2 ... To-be-coated object, 3 ... Component part.

Claims (9)

  A method for forming a multi-layer coating film comprising: dipping an object to be coated in an electrodeposition bath, electrodeposition-coating, curing, and directly coating and curing an overcoating composition without applying an intermediate coating, comprising: Is a component, not a finished product, the electrodeposition bath is composed of a plurality of baths, each bath is composed of electrodeposition paints of different colors, and each electrodeposition bath is electrodeposition-coated A method of forming a multi-layer coating film, wherein a top coat is applied after assembling parts into a finished product.   The method for forming a multilayer coating film according to claim 1, wherein the electrodeposition coating film obtained by the electrodeposition coating and the top coating film obtained by the top coating are of the same color.   3. The multilayer according to claim 2, wherein the color difference ΔE between the portion where the coating film is formed by the top coating composition on the electrodeposition coating film obtained by the electrodeposition coating and the complete hiding plate is 0.5 or less. Coating film forming method.   The method for forming a multilayer coating film according to claim 1, wherein the volume of the electrodeposition bath is 1/5 to 1/2 of that in the case of electrodeposition coating a finished product.   Electrodeposition coating booths in which components are immersed in one color bath selected from multiple electrodeposition baths that form coatings of different colors, electrodeposition coating and curing, and electrodeposition-coated components are finished products A painting system comprising: an assembly booth for assembling; and a topcoat painting booth for coating and curing the topcoat composition on the assembled finished product.   6. The coating system according to claim 5, wherein after the electrodeposition coating is cured, the top coating composition is applied without going through the intermediate coating booth.   6. The coating system according to claim 5, wherein the electrodeposition coating film obtained by the electrodeposition coating and the top coating film obtained by the top coating are of a similar color.   The coating system according to claim 7, wherein a color difference ΔE between a portion where a coating film is formed by a top coating composition on an electrodeposition coating film obtained by the electrodeposition coating and a complete hiding plate is 0.5 or less. . The coating system according to claim 5, wherein the volume of the electrodeposition bath is 1/5 to 1/2 of that in the case of electrodeposition coating a finished product.

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