Laminated coating film formation method and laminated coating film structure

Abstract

To provide a laminated coating film structure and a method for forming a laminated coating film in which the color of a base intermediate coating film is not seen through when a black coating film is formed on a white intermediate coating film in an inner-plate portion of a vehicle body.SOLUTION: A method for forming a laminated coating film on a to-be-coated object W in which an inner-plate portion 1 forming an inner side of a vehicle body and an outer-plate portion 2 forming an outer side of the vehicle body are joined to each other, includes: a step of forming an electrodeposition film 10 on the to-be-coated object; a step of forming an intermediate coating film 11 having a reflectivity of 83% or less on the electrodeposition film; and a step of forming a black-based high-concentration color-development coating film on at least the intermediate coating film formed on the inner-plate portion. In the step of forming the black-based high-concentration color-development coating film on the intermediate coating film formed on at least the inner-plate portion, a concentration of dispersed pigments contained in the black-based high-concentration color-development coating film is 2 wt% or more and 25 wt% or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for forming a laminated coating film and a laminated coating film structure, and more particularly to a method for forming a laminated coating film and a laminated coating film structure in which the base color cannot be seen through when, for example, the inner plate portion such as the door opening of a vehicle body is to be painted black.

Background Art

[0002] As generally shown in the schematic cross-sectional view of FIG. 6, an automotive coating film is formed by sequentially laminating an electrodeposition film 51 formed by electrodeposition coating mainly for rust prevention, a primer coating film 52, and a topcoat coating film 60 on an object to be coated 50. The topcoat coating film 60 is composed of a color coating film 53 containing a pigment for color development and a clear coating film 54 thereon. In addition to the purpose of color development, the color coating film 53 aims to improve the adhesion and smoothness between the primer coating film 52 and the clear coating film 54.

[0003] In addition to the purpose of improving the adhesion and smoothness between the electrodeposition film 51 and the topcoat coating film 60, the primer coating film 52 aims to enhance light resistance deterioration resistance, chipping resistance, and color development. In particular, when the electrodeposition film 51 formed by an epoxy-based cationic electrodeposition paint is irradiated with a large amount of ultraviolet rays, the surface layer portion thereof deteriorates and the upper coating film peels off. Therefore, the electrodeposition film 51 is protected from ultraviolet rays by the primer coating film 52 to enhance light resistance deterioration resistance.

[0004] When color-matching different colors for each predetermined region such as a two-tone color, as shown in FIG. 7, for example, a first-color paint is applied to a part of the region on the primer coating film 52 applied to the electrodeposition film 51 to form a color coating film 53a, and after appropriately applying masking thereon, a second-color paint is applied to the region adjacent to the color coating film 53a to form a color coating film 53b (see Patent Document 1). Incidentally, when a large area of the outer panel portion exposed on the vehicle body surface is a white body color, the primer coating film formed on the entire vehicle body is generally white, which is the same color as the colored coating film. For example, when the first paint applied to the vehicle body roof is black and the second paint applied to the other outer panel portions is a white two-tone color, a white paint is used to form the primer coating film, and this is formed on the entire object to be painted.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as described above, for example, when the first paint applied to the vehicle body roof is black and the second paint applied to the other outer panel portions is a white two-tone color, and further, when it is desired to apply the first black color to the uneven portions such as the inner panel portion (usually a portion not exposed on the front side) of the vehicle body door opening, in the uneven portions, the thickness of the paint tends to be uneven and a portion with a thin film thickness is generated. As a result, in such a portion where the colored coating film is thin, the white paint of the primer coating film as the base is revealed, and there is a problem that a beautiful black color cannot be painted.

[0007] Also, in the uneven portions of the inner panel portion, not only the colored coating film but also the primer coating film below it has a portion with a thin film thickness in the same manner. Therefore, in a portion where the inner panel portion is easily irradiated with ultraviolet rays, if the film thickness of the colored coating film and the primer coating film is thin, ultraviolet rays reach the electrodeposition film, and there is a problem that the rust prevention performance deteriorates due to the deterioration of the electrodeposition film.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide a laminated coating film structure and a laminated coating film forming method in which the color of the underlying primer coating film does not show through when a black coating film is formed on a white primer coating film in the inner panel portion of a vehicle body.

Means for Solving the Problem

[0009] In order to solve the above-described problems, a method for forming a laminated coating film according to the present invention is a method for forming a laminated coating film on an object to be coated in which an inner panel portion not exposed on the front side of the vehicle body and an outer panel portion exposed on the front side of the vehicle body are joined, the method comprising: a step of forming an electrodeposition film on the object to be coated; a step of forming an intermediate coating film having a reflectance of 83% or less on the electrodeposition film; and a step of forming a black-based high-concentration color-developing coating film on the intermediate coating film formed on the inner panel portion, wherein in the step of forming the black-based high-concentration color-developing coating film on the intermediate coating film formed on the inner panel portion, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 2 wt% or more and 25 wt% or less.

[0010] In addition, when the reflectance of the intermediate coating film is greater than 60%, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 7 wt% or more; when the reflectance of the intermediate coating film is greater than 40% and 60% or less, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 5 wt% or more; when the reflectance of the intermediate coating film is greater than 30% and 40% or less, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 2.9 wt% or more; and when the reflectance of the intermediate coating film is 30% or less, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is preferably 2.0 wt% or more.

[0011] Further, after the step of forming the black-based high-concentration color-developing coating film on the intermediate coating film formed on the inner panel portion, it is desirable to perform a step of laminating a black-based low-concentration color-developing coating film having a concentration of the dispersed pigment equal to or less than the concentration of the dispersed pigment in the black-based high-concentration color-developing coating film at a location where light hits the black-based high-concentration color-developing coating film.

[0012] According to such a method, for example, even if the surface shape of the inner panel portion of an object to be coated coated with a white-based intermediate coating film is uneven, and thus the black-based high-concentration color-developing coating film applied on the intermediate coating film is thinly formed, since the amount of the dispersed pigment in the black-based high-concentration color-developing coating film is high-concentration, it is possible to prevent the white color of the underlying intermediate coating film from being seen through. Also, even in the inner panel portion where light hits and is irradiated with ultraviolet rays, by forming a black-based low-concentration color-developing coating film on top of the black-based high-concentration color-developing coating film in the portion where the ultraviolet rays are irradiated, not only can the prevention of base material transparency be achieved, but also the transmission of ultraviolet rays can be suppressed.

[0013] Also, in order to solve the above-described problems, a laminated coating film structure according to the present invention is a laminated coating film structure in which a laminated coating film is formed on an object to be coated obtained by joining an inner panel portion that is not exposed on the front side of the vehicle body and an outer panel portion that is exposed on the front side of the vehicle body, and includes an electrodeposition film formed on the object to be coated, a primer coating film having a reflectance of 83% or less formed on the electrodeposition film, and a black-based high-concentration color-developing coating film formed on the primer coating film formed on the inner panel portion, and is characterized in that the concentration of the dispersion pigment contained in the black-based high-concentration color-developing coating film is 2 wt% or more and 25 wt% or less.

[0014] In addition, when the reflectance of the primer coating film is greater than 60%, the concentration of the dispersion pigment contained in the black-based high-concentration color-developing coating film is 7 wt% or more, when the reflectance of the primer coating film is greater than 40% and 60% or less, the concentration of the dispersion pigment contained in the black-based high-concentration color-developing coating film is 5 wt% or more, when the reflectance of the primer coating film is greater than 30% and 40% or less, the concentration of the dispersion pigment contained in the black-based high-concentration color-developing coating film is 2.9 wt% or more, and when the reflectance of the primer coating film is 30% or less, it is desirable that the concentration of the dispersion pigment contained in the black-based high-concentration color-developing coating film is 2.0 wt% or more.

[0015] Also, after the step of forming a black-based high-concentration color-developing coating film on the primer coating film formed on the inner panel portion, it is desirable to perform a step of laminating a black-based low-concentration color-developing coating film having a dispersion pigment concentration equal to or lower than the dispersion pigment concentration of the black-based high-concentration color-developing coating film at the location where light hits the black-based high-concentration color-developing coating film.

[0016] According to such a configuration, the surface shape of the inner panel portion of the object to be coated with the white primer coating film is uneven. Therefore, even if the black high-concentration color-developing coating film applied on the primer coating film is formed thinly, since the amount of the dispersed pigment in the black high-concentration color-developing coating film is high, it is possible to prevent the white color of the primer coating film as the base from showing through. Also, even in the inner panel portion, in a portion where light hits and can be irradiated with ultraviolet rays, by laminating and forming a black low-concentration color-developing coating film on the black high-concentration color-developing coating film, it is possible to suppress not only the prevention of base showing through but also the transmission of ultraviolet rays.

Effects of the Invention

[0017] According to the present invention, when forming a black coating film on a white primer coating film in the inner panel portion of a vehicle body, it is possible to provide a laminated coating film structure and a method for forming a laminated coating film in which the color of the base primer coating film does not show through.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the laminated coating film forming method and the laminated coating film structure according to the present invention will be described with reference to the drawings. Note that the following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its applications, or its uses.

[0020] FIG. 1 is a perspective view showing an example of a vehicle body part to which the laminated coating film forming method according to an embodiment of the present invention is applied. The laminated coating film forming method of the present invention is suitable for, for example, painting in the door opening 20 of the vehicle body (coated object W) shown in FIG. 1, that is, painting of a portion including an uneven shape. The coated object W is formed by joining an outer plate portion exposed on the front side of the vehicle body and an inner plate portion not exposed on the front side of the vehicle body.

[0021] FIG. 2 is a cross-sectional view schematically showing the laminated coating film structure of the present invention, and includes a part of the door opening 20, the roof 21, and other vehicle body surfaces 22. The door opening 20 is formed by an inner plate portion 1 having an uneven shape (the unevenness is not shown). In the door opening 20 formed by the inner plate portion 1, a portion where external light hits from a gap such as a door is called a boundary portion 3.

[0022] In the following description, as an example, a case where the roof 21 is black, other vehicle body surfaces 22 are white (pearl mica) two-tone color, and the door opening 20 is painted black will be described.

[0023] As shown in FIG. 2, an electrodeposition film 10 is formed on the entire surface of the coated object W. The coated object W is made of an iron plate, a steel plate, aluminum, stainless steel, etc., and is, for example, an iron plate constituting a vehicle body of an automobile. The electrodeposition film 10 is formed by immersing the coated object W in a cationic electrodeposition paint, using the coated object W as the cathode and the electrode plate in the electrodeposition tank as the anode, and passing a direct current therebetween to deposit and form on the coated object W side. The thickness of this electrodeposition film 10 is formed to be, for example, 20 μm.

[0024] On the electrodeposited film 10, as an intermediate coat film, for example, a white base intermediate coat film 11 (white-based intermediate coat film) is formed. The white base intermediate coat film 11 is formed from an oil-based (solvent-based) intermediate coat paint to which a white pigment is added as a colorant. The oil-based intermediate coat paint is, for example, a melamine-curing type oil-based paint containing a polyester resin, a melamine resin, and a coloring pigment. The film thickness of the white base intermediate coat film 11 is formed to be 5 μm or more and 40 μm or less.

[0025] Also, on the white base intermediate coat film 11 at the door opening 20, a high-concentration black clear coat film 12 (black-based high-concentration color-developing coat film) is formed. This high-concentration black clear coat film 12 has an increased amount of dispersed pigment of the contained black pigment. Specifically, when the reflectance of the white base intermediate coat film 11 (intermediate coat film) is 83% or less, the concentration of the dispersed pigment is 7 wt% or more and 25 wt% or less. In the present invention, the intermediate coat film is not limited to white-based. When it is not white-based, the reflectance becomes lower, and the concentration of the dispersed pigment can also be made lower. For example, when the reflectance of the intermediate coat film is 60% or less, the concentration of the dispersed pigment is 5 wt% or more and 25 wt% or less. Also, when the reflectance of the intermediate coat film is 40% or less, the concentration of the dispersed pigment is 2.9 wt% or more and 25 wt% or less. Further, when the reflectance of the intermediate coat film is 30% or less, the concentration of the dispersed pigment is 2.0 wt% or more and 25 wt% or less.

[0026] By increasing the concentration of the black pigment in this way, even if the thickness of the high-concentration black clear coat film 12 in the inner panel portion 1 is thin (for example, 10 μm), the underlying white base intermediate coat film 11 cannot be seen through. Note that when the concentration of the dispersed pigment amount is high, there is a risk of discoloration due to ultraviolet irradiation. However, since the high-concentration black clear coat film 12 is formed in the inner panel portion 1 where ultraviolet rays are not constantly irradiated, its discoloration can be prevented.

[0027] Also, in the door opening 20, a normal black clear coating film 13 (black-based low-concentration color-developing coating film) is formed on the high-concentration black clear coating film 12 at the boundary portion 3. The black clear coating film 13 may have the same composition as the high-concentration black clear coating film 12, except that the amount of dispersed pigment is less than that of the high-concentration black clear coating film. The film thickness of the black clear coating film 13 is formed, for example, to be 25 μm. When the reflectance of the white base intermediate coating film 11 (intermediate coating film) is, for example, 83%, the concentration of the dispersed pigment in the black clear coating film 13 is 2.9 wt% or more and 4.5 wt% or less, which is made lower than the concentration of the dispersed pigment in the high-concentration black clear coating film 12.

[0028] Thus, in the boundary portion 3 of the door opening 20, although there is more ultraviolet irradiation than the inner panel portion 1 on the more vehicle body inner side, by forming a black clear coating film 13 with a thickness of, for example, 25 μm on the high-concentration black clear coating film 12 at the boundary portion 3, not only can the prevention of base penetration be achieved, but also the effect of suppressing the transmission of ultraviolet rays can be obtained.

[0029] Also, in the roof 21, a black clear coating film 13 is formed on the white base intermediate coating film 11. The film thickness of the black clear coating film 13 is formed, for example, to be 25 μm. In the roof 21, since the film thickness of the black clear coating film 13 is formed thick, for example, to be 25 μm, it does not transmit ultraviolet rays, and since the concentration of the dispersed pigment is not too high, discoloration due to ultraviolet irradiation can be suppressed.

[0030] Also, on the vehicle body surface 22 other than the roof 21, a pearl mica coating film 14 is formed on the white base intermediate coating film 11. The pearl mica coating film 14 is formed by forming a film from an aqueous base paint or a solvent base paint containing various micas and uniformly dispersed therein. A known mica-containing paint is applied, and a coating layer 25 of the mica-containing paint for forming the concealment layer 15 is laminated. As this mica-containing paint, a paint containing a film-forming resin component compatible with the second color paint, a curing agent, a solvent, various additive components, etc., and containing various micas and uniformly dispersed therein can be used.

[0031] Furthermore, a clear coating film 15 is formed on the white pearl mica coating film 14. The resin for forming the clear coating film 15 is not particularly limited, but it is formed by a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid-epoxy curing system, etc. The film thickness of the clear coating film 15 is, for example, formed to be 30 μm.

[0032] According to the laminated coating film structure configured in this way, even when the high-concentration black clear coating film 12 applied to the inner plate portion 1 is in a thin state such as a thickness of 10 μm, (when the reflectance of the white base intermediate coating film 11 is, for example, 83%), since the concentration of the dispersed pigment is 7 wt% or more and 25 wt% or less, the white color of the white base intermediate coating film 11 which is the base layer does not leak through. Also, in a place where ultraviolet rays are irradiated more than other inner plate portions 1, such as the boundary portion 3 where external light hits from a gap such as a door which is a part (end portion) of the inner plate portion 1, by laminating and forming the black clear coating film 13 on the high-concentration black clear coating film 12, not only can the prevention of base layer leakage be achieved, but also the effect of suppressing the transmission of ultraviolet rays can be obtained.

[0033] Subsequently, the method for forming the laminated coating film of the present invention will be described based on FIGS. 3 to 5. (Formation of the electrodeposition film 10) The object to be coated W is, for example, an iron plate, a steel plate, aluminum, stainless steel, etc. as described above. When the object to be coated W is an iron plate of an automobile or the like, the electrodeposition film 10 may be formed in advance on the iron plate. The electrodeposition film 10 is a film of paint or resin formed on the surface of the vehicle body by electrodeposition coating, and has a role of ensuring corrosion resistance and adhesion to the intermediate coating film. This electrodeposition film 10 is deposited and formed on the surface of the object to be coated W as shown in FIG. 3(a) by immersing the object to be coated W in a cationic electrodeposition paint, making the object to be coated W the cathode and the electrode plate in the electrodeposition tank the anode, and flowing a direct current between them. The film thickness of this electrodeposition film 10 is, for example, formed to be 20 μm.

[0034] The cationic electrodeposition paint contains a cationic epoxy resin, a curing agent, and a pigment and additives. Cationic epoxy resins include epoxy resins modified with amines. As the epoxy resin, those modified with resins such as polyester polyol, polyether polyol, and alkylphenol, and those with an extended chain length of the epoxy resin can be used.

[0035] Compounds capable of introducing a cationic group include primary amines, acid salts of secondary amines and tertiary amines, sulfides, and acid mixtures. Examples include primary amines blocked secondary amines such as butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N,N-dimethylethanolamine acetate, diethyldisulfide-acetic acid mixture, ketimine of aminoethylethanolamine, and diketimine of diethylenetriamine.

[0036] As the curing agent, blocked polyisocyanates obtained by blocking polyisocyanates with blocking agents can be used. The polyisocyanate may be any of aliphatic, alicyclic, aromatic-aliphatic, etc.

[0037] Among polyisocyanates, examples of aromatic isocyanates include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), etc. Examples of aliphatic isocyanates include hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, etc. Examples of alicyclic isocyanates include 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4´-dicyclohexylmethane diisocyanate (hydrogenated MDI), 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, and norbornane diisocyanate, etc. Examples of aromatic-aliphatic isocyanates include xylylene diisocyanate (XDI), and tetramethylxylylene diisocyanate (TMXDI), etc. Also, urethanized products, biuret, and isocyanurate-modified products, etc., which are modified products of these isocyanates, are included. These can be used alone or in combination of two or more.

[0038] Examples of blocking agents include lactam-based blocking agents such as ε-caprolactam, and oxime-based blocking agents such as formaldehyde oxime. The amount of the curing agent is generally in the range of 80 / 20 to 50 / 50 in terms of the solid content weight ratio to the curing agent of the cationic epoxy resin, and the amounts of the cationic epoxy resin and the curing agent are generally in the range of 30 to 80% by weight of the total solid content of the electrodeposition coating composition.

[0039] Electrodeposition coatings generally contain pigments as colorants. Examples of coloring pigments include titanium oxide, carbon black, and iron oxide. Examples of extender pigments include kaolin, talc, aluminum silicate, calcium carbonate, mica, and clay. Examples of rust preventive pigments include zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, and calcium molybdate, etc. The amount of the pigment can be in the range of 10 to 30% by weight of the total solid content of the electrodeposition coating composition.

[0040] (Formation of white base intermediate coat film 11) Next, as shown in Fig. 3(b), on the electrodeposited film 10 of the object to be coated W, for example, by air spray coating, airless spray coating, rotary atomization coating, curtain coating, etc., a white base intermediate coat film 11 (white intermediate coat film) is formed so that the dry film thickness (state where the solvent has completely volatilized) is 5 μm or more and 40 μm or less. During coating, electrostatic application may be performed. When the dry film thickness of the white base intermediate coat film 11 is less than 5 μm, the strength becomes insufficient, which is not preferable.

[0041] Here, the white base intermediate coat film 11 can be formed by coating an oil-based (solvent-based) intermediate coat paint. As the oil-based (solvent-based) intermediate coat paint, for example, a melamine-curing type oil paint containing a polyester resin, a melamine resin, a coloring pigment, a extender pigment, talc, a surface conditioner, a dispersant, etc. can be used.

[0042] As the solvent, for example, a hydrocarbon solvent, an ester solvent, a ketone solvent, an alcohol solvent, an ether solvent, an aromatic petroleum solvent, etc. are used, and according to the coating work environment, the evaporation rate of the solvent is adjusted so that the initial fluidity when applying the oil-based color paint is high.

[0043] In addition, a pigment is added as a colorant to the oil-based color paint. Examples of the pigment include, for example, a coloring pigment, an extender pigment, a bright pigment, etc. Examples of the coloring pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, etc., and inorganics include lead yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide, etc. Furthermore, as the extender pigment, calcium carbonate, barium sulfate, clay, talc, etc. may be used in combination.

[0044] (Formation of high-concentration black clear coat film 12) Next, as shown in FIG. 3(c), in the door opening 20, a high-concentration black clear coating film 12 (black-based high-concentration color-developing coating film) is applied on the white base intermediate coating film 11. This coating is formed, for example, by air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, etc., so that the dry film thickness (state where the solvent has completely volatilized) is, for example, 10 μm. Electrostatic application may be performed during coating.

[0045] As described above, the black paint of the high-concentration black clear coating film 12 is prepared by blending a film-forming matrix resin, a black pigment, and, if necessary, a cross-linking agent, a solvent, and other additive components. As the black pigment to be blended in the black paint, various black pigments for paints can be used, and either organic pigments or inorganic pigments may be used. Examples of such black pigments include carbon black, acetylene black, lamp black, bone black, graphite, black iron oxide (magnetite), black titanium oxide, copper manganese black, copper chromium black, cobalt black, cyanine black, aniline black, etc. These can be used alone or in combination of two or more. Here, when the reflectance of the white base intermediate coating film 11 (intermediate coating film) is 83% or less, the concentration of the dispersed pigment is made high at 7 wt% or more and 25 wt% or less.

[0046] As the matrix resin of the black paint, various resins used as matrix resins for paints can be used. For example, an acrylic resin, a vinyl resin, a polyester resin, an alkyd resin, a urethane resin, etc. having one or more functional groups selected from a hydroxyl group, a carboxyl group, a silicon-containing group, an epoxy group, an isocyanate group that may be blocked, etc. can be mentioned.

[0047] Examples of the cross-linking agent include one or more mixtures selected from a melamine resin, a urea resin, a polyisocyanate compound that may be blocked, a carboxyl group-containing compound, an epoxy group-containing compound, etc. that react with the above-described functional groups.

[0048] Examples of organic solvents used for diluting the paint include aromatic solvents such as toluene, xylene, "Swazol 1000" (trade name, a high-boiling petroleum-based solvent manufactured by Cosmo Oil Co., Ltd.); aliphatic solvents such as mineral spirit; ester solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, and propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; and alcohol solvents such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol.

[0049] When the black paint is aqueous, as the base resin, those containing a sufficient amount of hydrophilic groups, such as carboxyl group, hydroxyl group, methylol group, amino group, sulfonic acid group, polyoxyethylene bond, etc., for solubilizing or water-dispersing the resin may be used, and the base resin may be solubilized or water-dispersed by neutralizing this hydrophilic group to form an alkali salt.

[0050] Various additives that can be added to the paint as necessary, such as tackifiers, flow regulators, light stabilizers, ultraviolet absorbers, extender pigments, pigment dispersants, etc., can be incorporated into the black paint.

[0051] (Formation of black clear coating film 13) Next, as shown in Fig. 4(a), a black clear coating film 13 (a black-based low-concentration color-developing coating film) is applied onto the white base intermediate coating film 11 of the roof 21 and onto the high-concentration black clear coating film 12 at the boundary portion 3. This application is performed, for example, by air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, etc., so as to form a dry film thickness (in a state where the solvent has completely volatilized) of, for example, 25 μm. Electrostatic application may be performed during the application. The composition of the black clear coating film 13 may be the same as that of the high-concentration black clear coating film 12 except for the concentration of the dispersed pigment. The concentration of the dispersed pigment is lower than that of the high-concentration black clear coating film 12. Specifically, when the reflectance of the white base intermediate coating film 11 (intermediate coating film) is, for example, 83%, it is set to be 2.9 wt% or more and 4.5 wt% or less.

[0052] (Heat curing of the white base intermediate coating film 11, high-concentration black clear coating film 12, and black clear coating film 13) After applying the high-concentration black clear coating film 12 on the uncured white base intermediate coating film 11 and further forming the black clear coating film 13, the uncured white base intermediate coating film 11, high-concentration black clear coating film 12, and black clear coating film 13 are heat-cured at once, thereby forming a laminated coating film including the cured white base intermediate coating film 11, high-concentration black clear coating film 12, and black clear coating film 13. The baking temperature and baking time for heat curing can be set as appropriate.

[0053] (Formation of the pearl mica coating film 14) Next, as shown in FIG. 4(b), after masking 16 is applied to the door opening 20 and the roof 21, on the vehicle body surface 22 other than the roof 21, a white pearl mica coating film 14 is painted on the white base intermediate coating film 11. This painting is formed, for example, by air spray painting, airless spray painting, rotary atomization painting, curtain coat painting, etc., so that the dry film thickness (in a state where the solvent has completely volatilized) is 10 μm or more and 20 μm or less. During painting, electrostatic application may be performed.

[0054] Next, on the vehicle body surface 22 other than the roof 21, a pearl mica coating film 14 is formed on the white base intermediate coating film 11. The pearl mica coating film 14 is formed by uniformly dispersing various micas in an aqueous-based paint or a solvent-based paint. A known mica-containing paint is applied, and a coating layer 25 of the mica-containing paint for forming the concealment layer 15 is laminated. As this mica-containing paint, those containing a resin component having film-forming properties compatible with the second color paint, a curing agent, a solvent, various additive components, etc., and using known paints containing various micas and uniformly dispersed therein are applicable.

[0055] As the solvent, for example, hydrocarbon solvents, ester solvents, ketone solvents, alcohol solvents, ether solvents, aromatic petroleum solvents, etc. are used, and depending on the painting work environment, the evaporation rate of the solvent is adjusted to make the initial fluidity high when applying the oil-based color paint.

[0056] In addition, a pigment is added as a colorant to the water-based color paint. Examples of the pigment include, for example, coloring pigments, extender pigments, pearlescent pigments, etc. Examples of the coloring pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, etc., and in the case of inorganic ones, lead yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide, etc. are included. Furthermore, as the extender pigment, calcium carbonate, barium sulfate, clay, talc, etc. may be used in combination.

[0057] (Formation of Clear Coating Film 15) Next, as shown in Fig. 5(a), a clear paint is applied onto the white pearl mica coating film 14 by an airless spray, an air spray, a rotary atomization painting machine, etc. Electrostatic application may be performed during the painting. After painting so that the dry film thickness becomes 35 to 40 μm, it is heated at 140 degrees for 20 minutes to be cured.

[0058] The resin for forming the clear coating film 15 is not particularly limited, and examples include combinations of acrylic resins and / or polyester resins with amino resins, or acrylic resins and / or polyester resins having a carboxylic acid-epoxy curing system, etc.

[0059] For example, a two-component urethane clear paint contains a hydroxyl group-containing acrylic resin and a polyisocyanate compound. Examples of the hydroxyl group-containing acrylic resin include a hydroxyl group-containing polymerizable unsaturated monomer, or other polymerizable unsaturated monomers. Examples of the hydroxyl group-containing polymerizable unsaturated monomer include a monoesterified product of a polyhydric alcohol and acrylic acid or methacrylic acid, a compound obtained by ring-opening polymerization of ε-caprolactone with the monoesterified product of the polyhydric alcohol and acrylic acid or methacrylic acid, etc. Examples of other polymerizable unsaturated monomers include alkyl esters of acrylic acid or methacrylic acid, carboxyl group-containing polymerizable unsaturated monomers, aminoalkyl acrylates, aminoalkyl methacrylates, acrylamide, methacrylamide or its derivatives, quaternary ammonium base-containing monomers, polyvinyl compounds, ultraviolet-absorbing or ultraviolet-stable polymerizable unsaturated monomers, etc.

[0060] Examples of the polyisocyanate compound include aliphatic diisocyanates, cycloaliphatic diisocyanates, aromatic diisocyanates, organic polyisocyanates themselves, cyclized polymers of organic polyisocyanates with each other, isocyanate biuret bodies, etc. Examples of the organic solvent include hydrocarbon solvents, ester solvents, ketone solvents, alcohol solvents, ether solvents, aromatic petroleum solvents, etc.

[0061] The clear paint can appropriately contain pigments, non-aqueous dispersion resins, polymer fine particles, curing catalysts, ultraviolet absorbers, light stabilizers, coating surface conditioners, antioxidants, fluidity modifiers, waxes, etc. as required. Examples of the curing catalyst include organic tin compounds, triethylamine, diethanolamine, etc. Examples of the ultraviolet absorber include compounds such as benzophenone-based, benzotriazole-based, cyanoacrylate-based, salicylate-based, oxalic acid anilide-based compounds, and ultraviolet stabilizers such as hindered amine-based compounds.

[0062] (Heat curing of the white pearl mica coating film 14 and the clear coating film 15) A clear coating film 15 is applied onto the uncured white pearl mica coating film 14, and by curing the uncured white pearl mica coating film 14 and the clear coating film 15 together by heating, a laminated coating film including the cured white pearl mica coating film 14 and the clear coating film 15 can be formed. The baking temperature and baking time for heat curing can be set as appropriate.

[0063] As described above, according to the embodiment of the present invention, the surface shape of the inner plate portion 1 of the object to be coated W coated with the intermediate coating film (white base intermediate coating film 11) is uneven. Therefore, even if the color-developing coating film applied on the intermediate coating film is thinly formed, by making the amount of the dispersed pigment in the color-developing coating film (high-concentration black clear coating film 12) high-concentration, it is possible to prevent the white system of the underlying intermediate coating film from showing through. Further, when the amount of the dispersed pigment in the high-concentration black clear coating film 12 is high-concentration, discoloration of the high-concentration black clear coating film 12 due to ultraviolet rays is likely to occur. However, in the roof 21 where there is a lot of ultraviolet irradiation, by forming the black clear coating film 13 thick and not making the amount of its dispersed pigment high-concentration, discoloration of the color clear coating film can be suppressed. Also, in a place like the boundary portion 3 where light hits and ultraviolet rays are irradiated when the door is opened, by laminating and forming the black clear coating film 13 on the high-concentration black clear coating film 12, not only can the prevention of underlying showing-through be achieved, but also the effect of suppressing the transmission of ultraviolet rays can be obtained.

[0064] In the above embodiment, the white base intermediate coating film 11 (white-based intermediate coating film) is white. However, in the present invention, it is not limited to this and may be a white system or a color other than the white system. The white system may not only be pure white but also have a chroma. Also, the lightness is not limited. Also, the high-concentration black clear coating film 12 (black-based high-concentration color-developing coating film) and the black clear coating film 13 (black-based low-concentration color-developing coating film) are black. However, in the present invention, it is not limited to this and each may be a black system as long as it is a black system. The black system may not only be pure black but also have a chroma. Also, the lightness is not limited.

Example

[0065] The method for forming a laminated coating film and the laminated coating film structure according to the present invention will be further described based on examples.

[0066] (Example 1) In Example 1, on the inner plate portion (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and a white (reflectivity 83%) intermediate coating film were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 7 wt% was formed on the intermediate coating film. For the black color clear coating film, a base resin in which an acrylic resin having a carboxyl group and an acrylic resin having an epoxy group were crosslinked was used for the resin of the paint, and carbon black was used for the black pigment. As evaluation items, color tone (such as no base penetration), appearance (such as no sagging), and weather resistance (ultraviolet light transmittance) were provided. For the color tone, the concave-convex shaped object was painted and the color tone was visually confirmed. Also, for the appearance (sagging), the concave-convex shaped object was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 100 MJ of ultraviolet light was irradiated, and the change in color tone was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with any of the color tone, appearance, and weather resistance.

[0067] (Comparative Example 1) In Comparative Example 1, on the inner plate portion (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and a white (reflectivity 83%) intermediate coating film were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 25 μm and a concentration of 3 wt% was formed on the intermediate coating film. As evaluation items, color tone (such as no base penetration), appearance (such as no sagging), and weather resistance (ultraviolet light transmittance) were provided. For the color tone, the concave-convex shaped object was painted and the color tone was visually confirmed. Also, for the appearance (sagging), the concave-convex shaped object was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 100 MJ of ultraviolet light was irradiated, and the change in color tone was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with the color tone and weather resistance, but sagging occurred due to the thick film.

[0068] (Comparative Example 2) In Comparative Example 2, on the inner panel part (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and an intermediate coating film of white (reflectivity 83%) were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 3 wt% was formed on the intermediate coating film. As evaluation items, color tone (such as no base color bleeding), appearance (such as no sagging), and weather resistance (ultraviolet transmittance) were set. For the color tone, the concave-convex shaped object was painted and the color tone was visually confirmed. Also, for the appearance (sagging), the concave-convex shaped object was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 100 MJ of ultraviolet rays were irradiated and the change in color tone was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with the appearance and weather resistance, but since the color clear film was thin, there were parts where the underlying white color could be seen through.

[0069] (Comparative Example 3) In Comparative Example 3, on the inner panel part (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and an intermediate coating film of white (reflectivity 83%) were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 5 wt% was formed on the intermediate coating film. As evaluation items, color tone (such as no base color bleeding), appearance (such as no sagging), and weather resistance (ultraviolet transmittance) were set. For the color tone, the concave-convex shaped object was painted and the color tone was visually confirmed. Also, for the appearance (sagging), the concave-convex shaped object was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 100 MJ of ultraviolet rays were irradiated and the change in color tone was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with the appearance and weather resistance, but since the concentration of the high-concentration color clear was low, the base color was seen through.

[0070] (Example 2) In Example 2, on the inner panel part (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and an intermediate coating film of white (reflectivity 60%) were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 5 wt% was formed on the intermediate coating film. As evaluation items, tone (such as no undercoat bleeding), appearance (such as no sagging), and weather resistance (UV transmittance) were set. For the tone, the uneven-shaped object was painted and the tone was visually confirmed. Also, for the appearance (sagging), the uneven-shaped object was painted and the presence or absence of sagging was confirmed. For weather resistance, a xenon weather meter was used to irradiate 100 MJ of UV rays and the change in its tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, there were no problems with any of the tone, appearance, and weather resistance.

[0071] (Comparative Example 4) In Comparative Example 4, on the inner panel part (uneven shape) of the door opening of the vehicle body, an electrodeposition film and a white (reflectivity 60%) intermediate coat film were formed on the object to be painted, and further, a black color clear coat film with a film thickness of 10 μm and a concentration of 4 wt% was formed on the intermediate coat film. As evaluation items, tone (such as no undercoat bleeding), appearance (such as no sagging), and weather resistance (UV transmittance) were set. For the tone, the uneven-shaped object was painted and the tone was visually confirmed. Also, for the appearance (sagging), the uneven-shaped object was painted and the presence or absence of sagging was confirmed. For weather resistance, a xenon weather meter was used to irradiate 100 MJ of UV rays and the change in its tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, there were no problems with the appearance and weather resistance, but since the color clear film was thin, there were parts where the underlying white color was visible through.

[0072] (Example 3) In Example 3, on the inner panel part (uneven shape) of the door opening of the vehicle body, an electrodeposition film and a light gray (reflectivity 40%) intermediate coat film were formed on the object to be painted, and further, a black color clear coat film with a film thickness of 10 μm and a concentration of 3 wt% was formed on the intermediate coat film. As evaluation items, tone (such as no undercoat bleeding), appearance (such as no sagging), and weather resistance (UV transmittance) were set. For the tone, the uneven-shaped object was painted and the tone was visually confirmed. Also, for the appearance (sagging), the uneven-shaped object was painted and the presence or absence of sagging was confirmed. For weather resistance, a xenon weather meter was used to irradiate 100 MJ of UV rays and the change in its tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, there were no problems with color tone, appearance, or weather resistance.

[0073] (Comparative Example 5) In Comparative Example 5, on the inner panel part (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and a primer coating film of light gray color (reflectance 40%) were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 2 wt% was formed on the primer coating film. As evaluation items, color tone (such as no substrate bleeding), appearance (such as no sagging), and weather resistance (ultraviolet transmittance) were set. For the color tone, the concave-convex shaped object was painted and the color tone was visually confirmed. Also, for the appearance (sagging), the concave-convex shaped object was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 100 MJ of ultraviolet rays were irradiated, and the color tone change was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with appearance and weather resistance, but due to the thin color clear coating film, there were parts where the underlying white color was visible through.

[0074] (Example 4) In Example 4, on the inner panel part (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and a primer coating film of gray color (reflectance 30%) were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 2 wt% was formed on the primer coating film. As evaluation items, color tone (such as no substrate bleeding), appearance (such as no sagging), and weather resistance (ultraviolet transmittance) were set. For the color tone, the concave-convex shaped object was painted and the color tone was visually confirmed. Also, for the appearance (sagging), the concave-convex shaped object was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 100 MJ of ultraviolet rays were irradiated, and the color tone change was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with color tone, appearance, or weather resistance.

[0075] (Comparative Example 6) In Comparative Example 6, on the inner panel part (concave-convex shape) of the door opening of the vehicle body, an electrodeposited film and a primer coating film of white color (reflectance 83%) were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 30 wt% was formed on the primer coating film. As evaluation items, tone (such as no substrate transparency), appearance (such as no sagging), and weather resistance (UV transmittance) were provided. For the tone, the uneven-shaped object was painted, and the tone was visually confirmed. Also, for the appearance (sagging), the uneven-shaped object was painted, and the presence or absence of sagging was confirmed. For the weather resistance, using a xenon weather meter, 100 MJ of UV rays were irradiated, and the change in tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, color mottling occurred due to poor pigment dispersion.

[0076] (Example 5) In Example 5, on the outer panel part of the vehicle body, an electrodeposition film and a white (reflectivity 83%) intermediate coating film were formed on the object to be painted, and further, a black color clear coating film with a film thickness of 25 μm and a concentration of 3 wt% was formed on the intermediate coating film. As evaluation items, tone (such as no substrate transparency), appearance (such as no sagging), and weather resistance (UV transmittance) were provided. For the tone, the flat-shaped steel plate was painted, and the tone was visually confirmed. Also, for the appearance (sagging), with the flat-shaped steel plate standing vertically, the steel plate was painted, and the presence or absence of sagging was confirmed. For the weather resistance, using a xenon weather meter, 1500 MJ of UV rays were irradiated, and the change in tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, there were no problems with any of the tone, appearance, and weather resistance.

[0077] (Example 6) In Example 6, on the outer panel part of the vehicle body, an electrodeposition film and a gray (reflectivity 30%) intermediate coating film were formed on the object to be painted, and further, a black color clear coating film with a film thickness of 25 μm and a concentration of 3 wt% was formed on the intermediate coating film. As evaluation items, tone (such as no substrate transparency), appearance (such as no sagging), and weather resistance (UV transmittance) were provided. For the tone, the flat-shaped steel plate was painted, and the tone was visually confirmed. Also, for the appearance (sagging), with the flat-shaped steel plate standing vertically, the steel plate was painted, and the presence or absence of sagging was confirmed. For the weather resistance, using a xenon weather meter, 1500 MJ of UV rays were irradiated, and the change in tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, there were no problems with any of the tone, appearance, and weather resistance.

[0078] (Example 7) In Example 7, on the outer panel part of the vehicle body, an electrodeposited film and a white (reflectivity 83%) intermediate coating film were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 25 μm and a concentration of 4 wt% was formed on the intermediate coating film. As evaluation items, color tone (such as no base penetration), appearance (such as no sagging), and weather resistance (ultraviolet transmittance) were set. For the color tone, a flat steel plate was painted and the color tone was visually confirmed. Also, for the appearance (sagging), with the flat steel plate standing vertically, the steel plate was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 1500 MJ of ultraviolet rays were irradiated, and the change in color tone was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with any of the color tone, appearance, and weather resistance.

[0079] (Comparative Example 7) In Comparative Example 7, on the outer panel part of the vehicle body, an electrodeposited film and a white (reflectivity 83%) intermediate coating film were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 25 μm and a concentration of 7 wt% was formed on the intermediate coating film. As evaluation items, color tone (such as no base penetration), appearance (such as no sagging), and weather resistance (ultraviolet transmittance) were set. For the color tone, an uneven-shaped object was painted and the color tone was visually confirmed. Also, for the appearance (sagging), the uneven-shaped object was painted and the presence or absence of sagging was confirmed. Also, for the weather resistance, using a xenon weather meter, 1500 MJ of ultraviolet rays were irradiated, and the change in color tone was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with the color tone and appearance, but discoloration with a color difference ΔE exceeding 3 occurred in terms of weather resistance.

[0080] (Comparative Example 8) In Comparative Example 8, on the outer panel part of the vehicle body, an electrodeposited film and a white (reflectivity 83%) intermediate coating film were formed on the object to be coated, and further, a black color clear coating film with a film thickness of 25 μm and a concentration of 5 wt% was formed on the intermediate coating film. As evaluation items, tone (such as no base penetration), appearance (such as no sagging), and weather resistance (UV transmittance) were provided. For the tone, the uneven-shaped object was painted and the tone was visually confirmed. Also, for the appearance (sagging), the uneven-shaped object was painted and the presence or absence of sagging was confirmed. Further, for the weather resistance, a xenon weather meter was used to irradiate 1500 MJ of UV rays and the change in its tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, there were no problems with the tone and appearance, but discoloration with a color difference ΔE exceeding 3 occurred in terms of weather resistance.

[0081] (Example 8) In Example 8, on the outer panel near the inner panel of the door opening of the vehicle body, an electrodeposition film and a white (reflectance 83%) intermediate coating film were formed on the object to be coated. Further, a black color clear coating film with a film thickness of 10 μm and a concentration of 7 wt% was formed on the intermediate coating film, and further, a black color clear coating film with a film thickness of 25 μm and a concentration of 3 wt% was formed thereon. As evaluation items, tone (such as no base penetration), appearance (such as no sagging), and weather resistance (UV transmittance) were provided. For the tone, a flat-shaped steel plate was painted and the tone was visually confirmed. Also, for the appearance (sagging), with the flat-shaped steel plate standing vertically, the steel plate was painted and the presence or absence of sagging was confirmed. Further, for the weather resistance, a xenon weather meter was used to irradiate 1500 MJ of UV rays and the change in its tone was measured. A color difference ΔE within 3 was considered a pass. As a result of the experiment, there were no problems with all of the tone, appearance, and weather resistance.

[0082] (Comparative Example 9) In Comparative Example 9, on the outer panel near the inner panel of the door opening of the vehicle body, an electrodeposition film and a white (reflectance 83%) intermediate coating film were formed on the object to be coated. Further, a black color clear coating film with a film thickness of 25 μm and a concentration of 3 wt% was formed on the intermediate coating film, and further, a black color clear coating film with a film thickness of 10 μm and a concentration of 7 wt% was formed thereon. As evaluation items, tone (such as no base transparency), appearance (such as no sagging), and weather resistance (ultraviolet transmittance) were set. For the tone, a steel plate with a planar shape was painted, and the tone was visually confirmed. Also, for the appearance (sagging), with the steel plate having a planar shape standing vertically, the steel plate was painted, and the presence or absence of sagging was confirmed. Moreover, for the weather resistance, using a xenon weather meter, 1500 MJ of ultraviolet rays were irradiated, and the change in its tone was measured. A color difference ΔE within 3 was considered qualified. As a result of the experiment, there were no problems with the tone and appearance, but discoloration with a color difference ΔE exceeding 3 occurred in terms of weather resistance.

Explanation of symbols

[0083] W Object to be painted 1 Inner panel part 2 Outer panel part 3 Boundary part 10 Electrodeposition film 11 White base intermediate coating film (white-based intermediate coating film) 12 High-concentration black clear coating film (black-based high-concentration color-developing coating film) 13 Black clear coating film (black-based low-concentration color-developing coating film) 14 White pearl mica coating film 15 Clear coating film 20 Door opening 21 Roof 22 Vehicle body surface other than the roof

Claims

1. A method for forming a laminated coating film on an object to be coated in which an inner plate portion not exposed on the front side of the vehicle body and an outer plate portion exposed on the front side of the vehicle body are joined, comprising a step of forming an electrodeposited film on the object to be coated, a step of forming an intermediate coating film having a reflectance of 83% or less on the electrodeposited film, and a step of forming a black-based high-concentration color-developing coating film on the intermediate coating film formed on the inner plate portion, In the step of forming a black-based high-concentration color-developing coating film on the intermediate coating film formed on the inner plate portion, a laminated coating film forming method, characterized in that the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 2 wt% or more and 25 wt% or less.

2. When the reflectance of the intermediate coating film is greater than 60%, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 7 wt% or more, When the reflectance of the intermediate coating film is greater than 40% and 60% or less, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 5 wt% or more, When the reflectance of the intermediate coating film is 30% or less, the concentration of the dispersed pigment contained in the black-based high-concentration color-developing coating film is 2.0 wt% or more, A laminated coating film forming method according to claim 1, characterized in that it is so.

3. After the step of forming a black-based high-concentration color-developing coating film on the intermediate coating film formed on the inner plate portion, at a location where light hits the black-based high-concentration color-developing coating film, a black-based low-concentration color-developing coating film having a concentration of the dispersed pigment equal to or lower than the concentration of the dispersed pigment in the black-based high-concentration color-developing coating film is laminated. A laminated coating film forming method according to any one of claims 1 or 2, characterized in that the step is performed.

4. A laminated coating film structure in which a laminated coating film is formed on an object to be coated in which an inner plate portion not exposed on the front side of the vehicle body and an outer plate portion exposed on the front side of the vehicle body are joined, an electrodeposited film formed on the object to be coated, an intermediate coating film having a reflectance of 83% or less formed on the electrodeposited film, A black high-concentration color-developing coating film formed on the intermediate coating film formed on the inner plate portion, and A laminated coating film structure, wherein the concentration of the dispersed pigment contained in the black high-concentration color-developing coating film is 2 wt% or more and 25 wt% or less.

5. When the reflectance of the intermediate coating film is greater than 60%, the concentration of the dispersed pigment contained in the black high-concentration color-developing coating film is 7 wt% or more, When the reflectance of the intermediate coating film is greater than 40% and 60% or less, the concentration of the dispersed pigment contained in the black high-concentration color-developing coating film is 5 wt% or more, When the reflectance of the intermediate coating film is 30% or less, the concentration of the dispersed pigment contained in the black high-concentration color-developing coating film is 2 wt% or more, The laminated coating film structure according to claim 4, characterized in that it is so.

6. The laminated coating film structure according to any one of claims 4 or 5, characterized in that a black low-concentration color-developing coating film having a concentration of the dispersed pigment equal to or lower than that of the dispersed pigment in the black high-concentration color-developing coating film is laminated on a portion of the black high-concentration color-developing coating film where light hits.

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