Method for forming a coating on the exterior and interior panels of an automobile, and coating on the exterior and interior panels of an automobile

Abstract

To provide a method for forming a coating on the exterior and interior panels of an automobile that can reduce the discrepancy in hue between the coatings on the exterior and interior panels. [Solution] A method for forming a coating on the exterior and interior panels of an automobile, comprising the steps of: (A) preparing a coating set including a first base coating and a second base coating; (B) applying the first base coating to the exterior panel of an automobile to form an uncured first base coating film; (C) applying the second base coating on the uncured first base coating film to form an uncured second base coating film; (D) curing the uncured first and second base coating films to form first and second base coating films; and (E) applying the second base coating to the interior panel to form a base coating film (BI2), wherein the interior panel consists only of the base coating film (BI2), the discharge rate of the second base coating in step (E) is 150 to 320 cc / min, and the movement speed of the spray gun is 1000 to 1300 mm / min.

Description

Technical Field

[0001] The present invention relates to a method for forming a coating film on an outer panel and an inner panel of an automobile, and to the coating films of the outer panel and the inner panel of an automobile.

Background Art

[0002] A plurality of coating films are formed on the surface of an automobile. These plurality of coating films protect the vehicle body of the automobile and at the same time impart excellent design properties to the automobile.

[0003] Among the surfaces of an automobile, examples of the plurality of coating films on the outer panel on the outside of the vehicle body include, for example, a primer coating film, a midcoat coating film, and a topcoat coating film in order from the outer panel side. Among these coating films, the topcoat coating film, which is located on the surface closest to the observer, particularly greatly affects the design properties of the automobile. Further, the topcoat coating film may be composed of a base coating film and a clear coating film from the vehicle body surface side.

[0004] Furthermore, the base coating film may also be composed of a first base coating film and a second base coating film from the vehicle body surface side (see, for example, Patent Documents 1 and 2). Mainly, the first base coating film has a base hiding property that makes the color of the underlying coating film (for example, the midcoat coating film) less conspicuous, and the second base coating film has design properties.

[0005] In recent years, since consumers prefer automobiles having a shiny feeling, in many cases, a flaky shiny pigment that generates a shiny feeling is blended into the base coating film of the outer panel, particularly the second base coating film that is on the observer side and mainly bears the design properties.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

[0007] On the surface of an automobile, the inner panels inside the vehicle body may have a different coating structure than the outer panels. For example, unlike the outer panels, high chipping resistance (prevention of scratches from flying stones) is not essential for inner panels, so there may be no intermediate coating. Also, there may be cases where only one of the first and second base coatings is present.

[0008] Depending on the vehicle model, the base coat of the exterior panels may consist of two layers: a first base coat and a second base coat, while the base coat of the interior panels (for example, the interior panels of the doors, gas covers, the inside of the tailgate, and the inside of the hood) may consist of only the first base coat. However, in this case, the base coat of the exterior panels consists of two layers, and the second base coat, which is mainly responsible for aesthetics, is on the observer's side, whereas the base coat of the interior panels consists only of the first base coat, which is mainly responsible for concealing the substrate. Therefore, a discrepancy in hue may occur between the paint of the exterior panels and the paint of the interior panels.

[0009] If a color discrepancy occurred, a third paint was sometimes prepared and applied separately to the first base coat of the interior panel in order to match the hue of the interior panel's paint film to that of the exterior panel's paint film. However, preparing a third paint meant that a total of three types of paint were needed to paint the exterior and interior panels: the paint for the first base coat, the paint for the second base coat, and the third paint. This resulted in additional processes and costs for preparing the third paint, as well as the need for additional equipment such as a spray gun to apply the third paint.

[0010] In response to this, the inventor considered using only the second base coating on the inner panel instead of the first base coating. In that case, it was thought that the hue of the second base coating on the observer's side of the two-layer base coating on the outer panel would be closer to the hue of the second base coating on the inner panel, thus reducing the sense of color discrepancy. However, simply changing the base coating of the inner panel from the first base coating to the second base coating did not reduce the sense of color discrepancy.

[0011] Therefore, the present invention aims to provide a method for forming a coating on the exterior and interior panels of an automobile that can reduce the discrepancy in hue of the coating on the exterior and interior panels of the automobile.

[0012] Furthermore, the present invention aims to provide paint coatings for the exterior and interior panels of an automobile in which the discrepancy in hue between the paint coatings of the exterior and interior panels is reduced. [Means for solving the problem]

[0013] The coating film forming method according to the present invention is a method for forming a coating film on the outer and inner panels of an automobile, Step (A) involves preparing a paint composition set for forming a multi-layer coating on the surface side of the outer panel, The multi-layer coating includes, in order from the outer panel side, a first base coating and a second base coating, adjacent to each other. The paint composition set includes a first base paint composition for forming the first base coating film and a second base paint composition for forming the second base coating film. The first base coating composition comprises a resin component, a first flake-like luminous pigment, and a coloring pigment. The second base paint composition comprises a resin component, a second flake-like luminous pigment, and a coloring pigment. The total solid content (NV1) of the resin component, the first flake-like luminous pigment, and the coloring pigment of the first base coating composition, relative to the total mass of the first base coating composition, is 20-30%. The amount of the first flake-like luminous pigment is 5 to 15 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the first flake-like luminous pigment, and the coloring pigment of the first base coating composition. The total solid content (NV2) of the resin component, the second flake-like luminous pigment, and the coloring pigment of the second base coating composition, relative to the total mass of the second base coating composition, is 10-20%. The amount of the second flake-like luminous pigment is 14 to 40 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the second flake-like luminous pigment, and the coloring pigment of the second base coating composition. The above NV2 is smaller than the above NV1 in process (A), (B) A step of applying the first base coating composition to the surface side of the outer panel to form an uncured first base coating film, Step (C) involves applying the second base coating composition onto the uncured first base coating to form an uncured second base coating, Step (D) of curing the uncured first base coating and the uncured second base coating to form the first base coating and the second base coating, Step (E) involves applying the second base coating composition to the surface side of the inner plate using a spray gun to form a base coating film (BI2), The inner plate includes only the base coating (BI2) as the base coating, A method for forming a coating film on the exterior and interior panels of an automobile, comprising step (E), wherein the discharge rate of the second base coating composition when applying the second base coating composition is 150 to 320 cc / min, and the movement speed of the spray gun is 1000 to 1300 mm / min. This makes it possible to reduce the discrepancy in hue of the coating film on the exterior and interior panels of an automobile.

[0014] In one embodiment of the method for forming a coating film on the outer and inner panels of an automobile according to the present invention, the dry film thickness of the base coating film (BI2) is 5 to 11 μm.

[0015] In one embodiment of the method for forming a coating film on the outer and inner panels of an automobile according to the present invention, the dry film thickness of the second base coating film is 3 to 5 μm.

[0016] In one embodiment of the method for forming a coating film on the outer and inner panels of an automobile according to the present invention, the average particle size of the first flake-like luminous pigment is 10 to 30 μm, and the average particle size of the second flake-like luminous pigment is 10 to 30 μm.

[0017] In one embodiment of the method for forming a coating on the outer and inner panels of an automobile according to the present invention, the NV2 is 12 to 17%.

[0018] In one embodiment of the method for forming a coating film on the outer panel and the inner panel of an automobile according to the present invention, the amount of the second flaky bright pigment is 20 to 30 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the second flaky bright pigment, and the coloring pigment in the second base coating composition.

[0019] The coating film according to the present invention is a coating film for the outer panel and the inner panel of an automobile, The coating film for the outer panel includes a multilayer coating film formed by using the method for forming a coating film on the outer panel and the inner panel of an automobile according to any one of the above, The multilayer coating film includes a first base coating film and a second base coating film, which are adjacent to each other in order from the outer panel side, The coating film for the inner panel is a coating film for the outer panel and the inner panel of an automobile, which includes only the base coating film (BI2) formed by using the method for forming a coating film on the outer panel and the inner panel of an automobile according to any one of the above as the base coating film. Thereby, the sense of incongruity in the hues of the coating films for the outer panel and the inner panel is reduced, and the coating films for the outer panel and the inner panel have excellent design properties.

Effects of the Invention

[0020] According to the present invention, it is possible to provide a method for forming a coating film on the outer panel and the inner panel of an automobile, which can reduce the sense of incongruity in the hues of the coating films for the outer panel and the inner panel of an automobile. Further, according to the present invention, it is possible to provide a coating film for the outer panel and the inner panel of an automobile, in which the sense of incongruity in the hues of the coating films for the outer panel and the inner panel is reduced.

Brief Description of the Drawings

[0021] [Figure 1] FIG. 1 is a schematic view showing an example of the layer configuration of a multilayer coating film for an outer panel formed by step (B) of the coating film forming method of the present invention. [Figure 2] FIG. 2 is a schematic view showing an example of the layer configuration of a multilayer coating film for an outer panel formed by step (C) of the coating film forming method of the present invention. [Figure 3] FIG. 3 is a schematic view showing an example of the layer configuration of a multilayer coating film for an outer panel formed by step (D) of the coating film forming method of the present invention. [Figure 4] Figure 4 is a schematic diagram showing an example of the layer structure of the coating film on the inner plate formed by step (E) of the coating film forming method of the present invention. [Figure 5] Figure 5 is a schematic diagram showing an example of the layer structure of the coating film on the inner plate formed by step (E) of the coating film forming method of the present invention. [Modes for carrying out the invention]

[0022] The embodiments of the present invention will be described below. These descriptions are for illustrative purposes only and do not limit the present invention in any way.

[0023] In the present invention, two or more embodiments can be arbitrarily combined.

[0024] In the present invention, paints and paint compositions can be used interchangeably.

[0025] Unless otherwise specified, numerical ranges are intended to include both the upper and lower limits of that range. For example, 20-30% means a range of 20% to 30%.

[0026] In this specification, the first base coating, the second base coating, and the base coating (BI2) may be collectively referred to as "base coating." Furthermore, the paint used for the base coating may simply be referred to as "base paint."

[0027] In this specification, the amount (parts by mass) of the first flake-like lustrous pigment relative to 100 parts by mass of the total solids of the resin component, first flake-like lustrous pigment, and coloring pigment of the first base coating composition may be referred to as "pigment mass concentration" or "PWC". In this specification, the amount (parts by mass) of the second flake-like lustrous pigment relative to 100 parts by mass of the total solids of the resin component, second flake-like lustrous pigment, and coloring pigment of the second base coating composition may be referred to as "pigment mass concentration" or "PWC".

[0028] In this invention, the average particle size of the flake-like luminous pigment refers to the median diameter of the volume-based particle size distribution measured by laser diffraction scattering using Nikkiso's Microtrac particle size distribution analyzer (product name "MT3300").

[0029] In this invention, a paint composition in which the most abundant dispersion medium is water is called an aqueous paint composition. In this invention, a paint composition in which the most abundant dispersion medium is a solvent is called a solvent-based paint composition.

[0030] In this specification, non-volatile content may be referred to as "solid content."

[0031] The attached drawings are schematic diagrams prioritizing ease of understanding the present invention, and therefore the scale of each coating film shown in the drawings is not accurate.

[0032] In this invention, the symbols such as the first, second, (A), (B), (C), (D), and (E) are merely symbols used to distinguish one element from another, and the symbols themselves do not limit the position or order.

[0033] (Coating film formation method) The coating film forming method according to the present invention is a method for forming a coating film on the outer and inner panels of an automobile, Step (A) involves preparing a paint composition set for forming a multi-layer coating on the surface side of the outer panel, The multi-layer coating includes, in order from the outer panel side, a first base coating and a second base coating, adjacent to each other. The paint composition set includes a first base paint composition for forming the first base coating film and a second base paint composition for forming the second base coating film. The first base coating composition comprises a resin component, a first flake-like luminous pigment, and a coloring pigment. The second base paint composition comprises a resin component, a second flake-like luminous pigment, and a coloring pigment. The total solid content (NV1) of the resin component, the first flake-like luminous pigment, and the coloring pigment of the first base coating composition, relative to the total mass of the first base coating composition, is 20-30%. The amount of the first flake-like luminous pigment is 5 to 15 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the first flake-like luminous pigment, and the coloring pigment of the first base coating composition. The total solid content (NV2) of the resin component, the second flake-like luminous pigment, and the coloring pigment of the second base coating composition, relative to the total mass of the second base coating composition, is 10-20%. The amount of the second flake-like luminous pigment is 14 to 40 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the second flake-like luminous pigment, and the coloring pigment of the second base coating composition. The above NV2 is smaller than the above NV1 in process (A), (B) A step of applying the first base coating composition to the surface side of the outer panel to form an uncured first base coating film, Step (C) involves applying the second base coating composition onto the uncured first base coating to form an uncured second base coating, Step (D) of curing the uncured first base coating and the uncured second base coating to form the first base coating and the second base coating, Step (E) involves applying the second base coating composition to the surface side of the inner plate using a spray gun to form a base coating film (BI2), The inner plate includes only the base coating (BI2) as the base coating, A method for forming a coating film on the exterior and interior panels of an automobile, comprising step (E), wherein the discharge rate of the second base coating composition when applying the second base coating composition is 150 to 320 cc / min, and the movement speed of the spray gun is 1000 to 1300 mm / min.

[0034] Figure 1 is a schematic diagram showing an example of the layer structure of a multi-layer coating film on an outer panel formed by step (B) of the coating film forming method of the present invention. The outer panel 1 in Figure 1 has a primer coating film 2 and an intermediate coating film 3 on its surface side, and the uncured first base coating film 14 is formed on the intermediate coating film 3.

[0035] Figure 2 is a schematic diagram showing an example of the layer structure of a multilayer coating film on an outer panel formed by step (C) of the coating film forming method of the present invention. In Figure 2, the outer panel 1 has an uncured second base coating film 15 formed on an uncured first base coating film 14.

[0036] Figure 3 is a schematic diagram showing an example of the layer structure of a multi-layer coating film on an outer panel formed by step (D) of the coating film forming method of the present invention. In the outer panel 1 of Figure 3, the uncured first base coating film 14 and the uncured second base coating film 15 of Figure 2 have cured to form the first base coating film 4 and the second base coating film 5.

[0037] Figures 4 and 5 are schematic diagrams showing an example of the layer structure of the coating film on an inner plate formed by step (E) of the coating film forming method of the present invention. In Figure 4, the inner plate 6 has an undercoat coating film 2 and an intermediate coating film 3 on its surface side, and the uncured base coating film (BI2) 17 is formed on the intermediate coating film 3. In the inner plate 6 of Figure 5, the uncured base coating film (BI2) 17 from Figure 4 has hardened, and a base coating film (BI2) 7 has been formed.

[0038] In one embodiment, the coating on the outer panel consists of an undercoat, an intermediate coat, a first base coat, a second base coat, and a clear coat, arranged in adjacent order from the outer panel side, while the multi-layer coating consists of a first base coat and a second base coat.

[0039] The following describes steps (A) to (E), which are essential steps of the method for forming a coating on the exterior and interior panels of an automobile according to the present invention.

[0040] ·Process (A) In step (A), a set of paint compositions for forming a multi-layer coating on the surface side of the outer panel is prepared.

[0041] • Paint composition set The paint composition set includes a first base paint composition for forming a first base coating film and a second base paint composition for forming a second base coating film.

[0042] • First base coating composition The first base coating composition forms the first base coating film on the exterior panels. The first base coating composition comprises a resin component, a first flake-like lustrous pigment, and a coloring pigment. The total solid content (NV1) of the resin component, the first flake-like lustrous pigment, and the coloring pigment of the first base coating composition is 20-30% of the total mass of the first base coating composition, and the amount of the first flake-like lustrous pigment is 5-15 parts by mass per 100 parts by mass of the total solid content of the resin component, the first flake-like lustrous pigment, and the coloring pigment of the first base coating composition. The first base coating composition is not used on the interior panels.

[0043] The following describes the resin component, the first flake-like luminous pigment, and the coloring pigment, which are essential components of the first base coating composition.

[0044] • Resin components As the resin component, conventionally known resin components of base coatings can be used. Examples of resin components include acrylic resins, polyester resins, alkyd resins, fluororesins, epoxy resins, polyurethane resins, polyether resins, and polyolefin resins. Alternatively, as the resin component, film-forming resins such as acrylic emulsion resins, polyether polyols, and urethane emulsion resins described in Patent Document 1, or water-dispersible resins described in Patent Document 2 may be used.

[0045] The resin component may be used alone or in combination of two or more types. The resin component of the first base coating composition may be the same as or different from the resin component of the second base coating composition described later.

[0046] The amount of resin component in the first base coating composition can be appropriately adjusted so that the total solid content (NV1) of the resin component, first flake-like luminous pigment, and coloring pigment of the first base coating composition is 20-30% of the total mass of the first base coating composition. For example, it is 85-100 parts by mass, preferably 85-95 parts by mass, per 100 parts by mass of the total solid content of the resin component, first flake-like luminous pigment, and coloring pigment of the first base coating composition.

[0047] • First flaky bright pigment The first flake-like luminous pigment can be any conventionally known flake-like luminous pigment. Examples of flake-like luminous pigments include metals such as aluminum, copper, zinc, iron, nickel, tin, and aluminum oxide; alloys thereof; luminous pigments such as interference mica, white mica, graphite, glass flakes, and alumina flakes; and flake-like luminous pigments in which these metals, alloys, interference mica, white mica, graphite, glass flakes, or alumina flakes are coated with metal oxides (e.g., titanium oxide, titanium dioxide, iron oxide) or metals (e.g., gold, silver). Other examples include the alumina flake pigment (a) described in Japanese Patent Publication No. 2016-221473; flake-shaped luminous pigments in which a metal substrate or glass flake substrate is coated with a metal oxide or metal; flake-shaped luminous pigments in which a colored pigment is chemically adsorbed onto the surface of a metal substrate or glass flake substrate; aluminum pigments in which an aluminum oxide layer is formed on the surface of an aluminum substrate; aluminum solid solution plate-shaped iron oxide pigments; flake-shaped luminous pigments in which the surface of interference mica, graphite or silica flakes is coated with titanium dioxide; and plate-shaped iron oxide pigments. Preferred flake-shaped luminous pigments are flake-shaped luminous pigments in which a glass substrate is coated with a metal oxide, glass flakes, etc.

[0048] In one embodiment, the first flake-like luminous pigment has a glass substrate coated with a metal oxide.

[0049] The first flake-like luminous pigment may be colorless, colored, or a combination of both. Examples of colored pigments include black, red, yellow, green, blue, and purple.

[0050] The average particle size of the first flake-like luminous pigment is, for example, 10 μm to 30 μm. In one embodiment, the average particle size of the first flake-like luminous pigment is 10 μm or more, 15 μm or more, 20 μm or more, or 25 μm or more. In another embodiment, the average particle size of the first flake-like luminous pigment is 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less.

[0051] In one embodiment of the method for forming a coating film on the outer and inner panels of an automobile according to the present invention, the average particle size of the first flake-like luminous pigment is 10 to 30 μm, and the average particle size of the second flake-like luminous pigment is 10 to 30 μm.

[0052] The first flake-like luminous pigment may be a commercially available product. Examples of commercially available flake-like luminous pigments include the Metashine® series from Nippon Sheet Glass Co., Ltd. and the Alumina Flake series from Merck & Co., Ltd.

[0053] The first flake-like luminous pigment may be used alone or in combination of two or more types. The first flake-like luminous pigment may be the same as or different from the second flake-like luminous pigment described later.

[0054] The amount of the first flake-like lustrous pigment in the first base coating composition is 5 to 15 parts by mass per 100 parts by mass of the total solids content of the resin component, the first flake-like lustrous pigment, and the color pigment of the first base coating composition. The amount of the second flake-like lustrous pigment in the second base coating composition, as described later, is 14 to 40 parts by mass per 100 parts by mass of the total solids content of the resin component, the second flake-like lustrous pigment, and the color pigment of the second base coating composition. Even if the PWC of the second flake-like lustrous pigment is 14 to 40 parts by mass, if the PWC of the first flake-like lustrous pigment is less than 5 parts by mass, it results in low opacity and substrate transparency. If the PWC of the first flake-like lustrous pigment is greater than 15 parts by mass, it results in poor appearance.

[0055] In one embodiment, the PWC of the first flake-like luminous pigment is 5 parts by mass or more, 6 parts by mass or more, 7 parts by mass or more, 8 parts by mass or more, 9 parts by mass or more, 10 parts by mass or more, 11 parts by mass or more, 12 parts by mass or more, 13 parts by mass or more, or 14 parts by mass or more. In another embodiment, the PWC of the first flake-like luminous pigment is 15 parts by mass or less, 14 parts by mass or less, 13 parts by mass or less, 12 parts by mass or less, 11 parts by mass or less, 10 parts by mass or less, 9 parts by mass or less, 8 parts by mass or less, 7 parts by mass or less, or 6 parts by mass or less.

[0056] • Coloring pigments Coloring pigments serve to impart both opacity and aesthetic appeal to the base coating.

[0057] The coloring pigment is not particularly limited, and known coloring pigments of base paints can be used. Examples of coloring pigments include organic coloring pigments such as azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolon pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments; and inorganic coloring pigments such as lead yellow, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. Preferred coloring pigments include carbon black.

[0058] The coloring pigment may be used alone or in combination of two or more types. The coloring pigment of the first base paint composition may be the same as or different from the coloring pigment of the second base paint composition.

[0059] The amount of coloring pigment in the first base coating composition can be appropriately adjusted so that the total solid content (NV1) of the resin component, first flake-like luminous pigment, and coloring pigment of the first base coating composition is 20-30% of the total mass of the first base coating composition. For example, the amount is 1-5 parts by mass, preferably 2-4 parts by mass, per 100 parts by mass of the total solid content of the resin component, first flake-like luminous pigment, and coloring pigment of the first base coating composition.

[0060] Other ingredients The first base coating composition may contain, in addition to the resin component, the first flake-like glossy pigment, and the coloring pigment, known base coating components such as extender pigments, curing agents, water, organic solvents, corrosion inhibitors, surface modifiers, thickeners, antioxidants, UV inhibitors, and defoamers. Each of these other components may be used individually or in combination of two or more.

[0061] • Organic solvents Examples of organic solvents include alcohols such as methanol, ethanol, 2-propanol, and 1-butanol; esters such as ethyl acetate, butyl acetate, isobutyl acetate, ethyl propionate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ethers such as diethyl ether, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, dioxane, and tetrahydrofuran (THF); and ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol. Examples of organic solvents include glycols such as 1,3-butylene glycol, pentamethylene glycol, and 1,3-octylene glycol; amides such as formamide, N-methylformamide, dimethylformamide (DMF), dimethylacetamide, dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP); ketones such as acetone, methyl ethyl ketone (MEK), methyl propyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; aliphatic hydrocarbons such as mineral spirits and kerosene; aromatic hydrocarbons such as toluene, xylene, mesitylene, and dodecylbenzene; and halogenated solvents such as chloroform and dichloromethylene. Organic solvents may be used individually or in combination of two or more.

[0062] The first base coating composition may be either an aqueous coating composition or a solvent-based coating composition. In one embodiment, the first base coating composition and the second base coating composition are aqueous coating compositions.

[0063] The total solid content (NV1) of the resin component, first flake-like luminous pigment, and coloring pigment of the first base coating composition relative to the total mass of the first base coating composition is 20-30%, and NV1 is greater than NV2, which will be described later. If NV1 is less than 20%, the paint workability evaluation shows that atomization during painting is poor, resulting in problems such as metallic unevenness and dripping. If NV1 is greater than 30%, the discharge amount during painting is extremely small, resulting in problems such as hue fluctuations during paint workability. In one embodiment, NV1 is 20% or more, 21% or more, 22% or more, 23% or more, 24% or more, 25% or more, 26% or more, 27% or more, 28% or more, or 29% or more. In another embodiment, NV1 is 30% or less, 29% or less, 28% or less, 27% or less, 26% or less, 25% or less, 24% or less, 23% or less, 22% or less, or 21% or less.

[0064] • Method for preparing the first base coating composition The method for preparing the first base coating composition is not particularly limited as long as it includes the resin component, the first flake-like lustrous pigment, and the coloring pigment described above, and satisfies the predetermined range of NV1 and the predetermined range of PWC; conventionally known methods can be used. For example, the first base coating composition can be prepared by kneading and dispersing the resin component, the first flake-like lustrous pigment, and the coloring pigment using a kneader or roll.

[0065] (Second base coating composition) The second base coating composition forms the second base coating film (BI2) on the outer panel and the base coating film (BI2) on the inner panel. The second base coating composition comprises a resin component, a second flake-like lustrous pigment, and a coloring pigment. The total solid content (NV2) of the resin component, the second flake-like lustrous pigment, and the coloring pigment of the second base coating composition is 10-20% of the total mass of the second base coating composition, and the amount of the second flake-like lustrous pigment is 14-40 parts by mass per 100 parts by mass of the total solid content of the resin component, the second flake-like lustrous pigment, and the coloring pigment of the second base coating composition.

[0066] The following describes the resin component, the second flake-like luminous pigment, and the coloring pigment, which are essential components of the second base coating composition.

[0067] • Resin components As the resin component, conventionally known resin components of base coatings can be used. Examples of resin components are the same as those listed in the first base coating composition described above.

[0068] The resin components may be used individually or in combination of two or more types.

[0069] The amount of resin component in the second base coating composition can be appropriately adjusted so that the total solid content (NV2) of the resin component, second flake-like luminous pigment, and coloring pigment of the second base coating composition is 10-20% of the total mass of the second base coating composition. For example, it is 80-90 parts by mass, and preferably 82-88 parts by mass, per 100 parts by mass of the total solid content of the resin component, second flake-like luminous pigment, and coloring pigment of the second base coating composition.

[0070] • Second-order flake-like luminous pigment The second flake-like luminous pigment can be any conventionally known flake-like luminous pigment. The flake-like luminous pigment is the same as the first flake-like luminous pigment mentioned in the first base coating composition above.

[0071] The average particle size of the second flake-like luminous pigment is, for example, 10 μm to 30 μm. In one embodiment, the average particle size of the second flake-like luminous pigment is 10 μm or more, 15 μm or more, 20 μm or more, or 25 μm or more. In another embodiment, the average particle size of the second flake-like luminous pigment is 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less.

[0072] The second flake-like luminous pigment may be used alone or in combination of two or more types.

[0073] The amount of the second flake-like lustrous pigment in the second base coating composition is 14 to 40 parts by mass per 100 parts by mass of the total solid content of the resin component, the second flake-like lustrous pigment, and the color pigment of the second base coating composition. Even if the PWC of the first flake-like lustrous pigment is 5 to 15 parts by mass, if the PWC of the second flake-like lustrous pigment is less than 14 parts by mass, the amount of lustrous pigment will be insufficient, resulting in gaps and a low-quality design. If the PWC of the second flake-like lustrous pigment is greater than 40 parts by mass, the amount of lustrous pigment will be too much, causing the lustrous pigment to overlap and resulting in a low-quality design.

[0074] In one embodiment, the PWC of the second flake-like luminous pigment is 14 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, or 35 parts by mass or more. In another embodiment, the PWC of the second flake-like luminous pigment is 40 parts by mass or less, 35 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, or 20 parts by mass or less.

[0075] In one embodiment of the method for forming a coating film on the exterior and interior panels of an automobile according to the present invention, the amount of the second flake-like lustrous pigment is 20 to 30 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the second flake-like lustrous pigment, and the coloring pigment of the second base coating composition.

[0076] • Coloring pigments As the coloring pigment, conventionally known coloring pigments for base coatings can be used. Examples of coloring pigments are the same as those listed in the first base coating composition described above.

[0077] Coloring pigments may be used individually or in combination of two or more types.

[0078] The amount of coloring pigment in the second base coating composition can be appropriately adjusted so that the total solid content (NV2) of the resin component, second flake-like luminous pigment, and coloring pigment of the second base coating composition is 10-20% of the total mass of the second base coating composition. For example, it is 10-20 parts by mass, and preferably 12-18 parts by mass, per 100 parts by mass of the total solid content of the resin component, second flake-like luminous pigment, and coloring pigment of the second base coating composition.

[0079] Other ingredients The second base coating composition may contain, in addition to the resin component, the second flake-like glossy pigment, and the coloring pigment, known base coating components such as extender pigments, curing agents, water, organic solvents, corrosion inhibitors, surface modifiers, thickeners, antioxidants, UV inhibitors, and defoamers. Each of these other components may be used individually or in combination of two or more.

[0080] • Organic solvents Examples of organic solvents are the same as those listed in the first base coating composition above.

[0081] The second base coating composition may be either a water-based coating composition or a solvent-based coating composition.

[0082] The total solid content (NV2) of the resin component, second flake-like glossy pigment, and coloring pigment of the second base coating composition relative to the total mass of the second base coating composition is 10-20%, and NV2 is smaller than NV1. If NV2 is less than 10%, a large discharge volume will be required to ensure the specified film thickness, which may cause dripping. If NV2 is greater than 20%, the NV difference between NV1 and NV2 is small, which may result in poor 2-base orientation and a design defect called low flip-flop (FF) properties. In one embodiment, NV2 is 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, 18% or more, or 19% or more. In another embodiment, NV2 is 20% or less, 19% or less, 18% or less, 17% or less, 16% or less, 15% or less, 14% or less, 13% or less, 12% or less, or 11% or less.

[0083] In one embodiment of the method for forming a coating on the outer and inner panels of an automobile according to the present invention, the NV2 is 12 to 17%.

[0084] • Method for preparing the second base coating composition The method for preparing the second base coating composition is not particularly limited as long as it includes the resin component, the second flake-like lustrous pigment, and the coloring pigment described above, and satisfies the predetermined range of NV2 and the predetermined range of PWC; conventionally known methods can be used. For example, the second base coating composition can be prepared by kneading and dispersing the resin component, the second flake-like lustrous pigment, and the coloring pigment using a kneader or roll.

[0085] ·Process (B) In step (B), the first base paint composition is applied to the surface side of the outer panel to form an uncured first base coating film.

[0086] The layer configuration on the surface side of the exterior panel to which the first base paint composition is applied is not particularly limited, but typically, as shown in Figure 1, it has a primer film and an intermediate coat film from the exterior panel side. Therefore, the target of the exterior panel to which the first base paint composition is applied in step (B) is typically the intermediate coat film.

[0087] The undercoat and intermediate coat are not particularly limited and can be conventionally known undercoat and intermediate coats.

[0088] The method for applying the first base coating composition is not particularly limited, and conventionally known methods for applying base coatings to the exterior panels of automobiles can be used. Examples of methods for applying the first base coating composition include spray painting and rotary atomization electrostatic painting.

[0089] The thickness of the uncured first base coating is not particularly limited and can be adjusted as appropriate according to the desired dry film thickness.

[0090] ·Process (C) In step (C), a second base coating composition is applied to the uncured first base coating to form an uncured second base coating. See, for example, Figure 2.

[0091] The method for applying the second base coating composition is not particularly limited, and conventionally known methods for applying base coatings to the exterior panels of automobiles can be used. Examples of methods for applying the second base coating composition include spray painting and rotary atomization electrostatic painting. The method for applying the first base coating composition in step (B) and the method for applying the second base coating composition in step (C) may be the same or different.

[0092] The thickness of the uncured second base coating is not particularly limited and can be adjusted as appropriate according to the desired dry thickness.

[0093] ·Process (D) In step (D), the uncured first base coating and the uncured second base coating are cured to form the first base coating and the second base coating. See, for example, Figure 3.

[0094] One example of a curing method is heat curing. The conditions for heat curing can be, for example, a temperature of 120-160°C for 10-30 minutes.

[0095] The dry film thickness of the first base coating is, for example, 12 to 19 μm, preferably 13 to 17 μm.

[0096] The dry film thickness of the second base coating is, for example, 4 to 6 μm, preferably 3 to 5 μm.

[0097] In one embodiment of the method for forming a coating film on the outer and inner panels of an automobile according to the present invention, the dry film thickness of the second base coating film is 3 to 5 μm.

[0098] Step (D) involves curing the uncured first base coating and the uncured second base coating to form the first base coating and the second base coating. Although not shown in the diagram, for example, in addition to these two layers, an uncured clear coating formed on the uncured second base coating may also be cured together.

[0099] ·Process (E) In step (E), the second base coating composition is applied to the surface side of the inner panel using a spray gun to form a base coating film (BI2). The inner panel consists only of the base coating film (BI2). The discharge rate of the second base coating composition when applying it is 150-320 cc / min, and the movement speed of the spray gun is 1000-1300 mm / min.

[0100] The layer configuration on the surface side of the inner panel to which the second base coating composition is applied is not particularly limited. For example, as shown in Figure 4, there may be an undercoat and an intermediate coat from the inner panel side, or, although not shown, there may be an undercoat from the inner panel side. The undercoat and intermediate coat on the inner panel side are not particularly limited and can be conventionally known undercoat and intermediate coats. The undercoat on the outer panel side and the undercoat on the inner panel side may be the same or different. The intermediate coat on the outer panel side and the intermediate coat on the inner panel side may be the same or different.

[0101] As shown in Figure 4, the second base coating composition is applied to the surface side of the inner plate using a spray gun to form an uncured base coating film (BI2).

[0102] The spray gun is not particularly limited as long as it can dispense the second base paint composition at a discharge volume within a predetermined range and the movement speed of the spray gun is within a predetermined range; conventionally known spray guns for automotive painting can be used.

[0103] The discharge rate of the second base coating composition when applying it is 150 to 320 cc / min. If the discharge rate is less than 150 cc / min, there is a problem with the painting process due to insufficient discharge, and if the discharge rate exceeds 320 cc / min, there is a problem with the workability due to dripping or unevenness. In one embodiment, the discharge rate of the second base coating composition is 150 cc / min or more, 160 cc / min or more, 170 cc / min or more, 180 cc / min or more, 190 cc / min or more, 200 cc / min or more, 210 cc / min or more, 220 cc / min or more, 230 cc / min or more, 240 cc / min or more, 250 cc / min or more, 260 cc / min or more, 270 cc / min or more, 280 cc / min or more, 290 cc / min or more, 300 cc / min or more, or 310 cc / min or more. In another embodiment, the discharge rate of the second base coating composition is 320 cc / min or less, 310 cc / min or less, 300 cc / min or less, 290 cc / min or less, 280 cc / min or less, 270 cc / min or less, 260 cc / min or less, 250 cc / min or less, 240 cc / min or less, 230 cc / min or less, 220 cc / min or less, 210 cc / min or less, 200 cc / min or less, 190 cc / min or less, 180 cc / min or less, 170 cc / min or less, or 160 cc / min or less.

[0104] The spray gun's movement speed when applying the second base coating composition is 1000 to 1300 mm / min. If the movement speed is less than 1000 mm / min, the discrepancy in hue of the coating film on the exterior and interior panels of the automobile cannot be reduced, and if the movement speed exceeds 1300 mm / min, the film becomes thin and a problem called "skipping" occurs. In one embodiment, the spray gun's movement speed when applying the second base coating composition is 1000 mm / min or more, 1100 mm / min or more, or 1200 mm / min or more. In another embodiment, the spray gun's movement speed when applying the second base coating composition is 1300 mm / min or less, 1200 mm / min or less, or 1100 mm / min or less.

[0105] The thickness of the uncured base coating (BI2) is not particularly limited and can be adjusted as appropriate according to the desired dry film thickness.

[0106] One method for curing the uncured base coating (BI2) is heat curing. The conditions for heat curing can be, for example, a temperature of 120-160°C for 10-30 minutes.

[0107] The dry film thickness of the base coating (BI2) is, for example, 4 to 12 m, preferably 5 to 11 μm.

[0108] In one embodiment of the method for forming a coating film on the outer and inner panels of an automobile according to the present invention, the dry film thickness of the base coating film (BI2) is 5 to 11 μm.

[0109] In step (E), the second base coating composition is applied using a spray gun under predetermined conditions to form a base coating film (BI2). For example, an uncured clear coating film formed on the uncured base coating film (BI2) may be cured together with the base coating film (BI2).

[0110] The order of processes (B), (C), (D), and (E) is not particularly restricted, except that process (C) comes after process (B). For example, the order could be (E), (B), (C), and (D); or (B), (C), (D), and (E); or (B) and (E) could be performed simultaneously, followed by processes (C) and (D).

[0111] The present invention's method for forming a coating on the exterior and interior panels of an automobile may include, in addition to steps (A) to (E), other steps such as: applying a clear coating paint onto an uncured second base coating to form an uncured clear coating; curing the uncured clear coating to form a clear coating; and applying a clear coating paint onto an uncured base coating (BI2) to form an uncured clear coating.

[0112] (Coating film on the exterior and interior panels of automobiles) The coating film according to the present invention is a coating film for the outer and inner panels of an automobile, The coating on the outer panel includes a multilayer coating formed using the coating method for the outer and inner panels of an automobile described in any of the above descriptions. The multi-layer coating includes, in order from the outer panel side, a first base coating and a second base coating, adjacent to each other. The coating film on the inner panel is a coating film for the outer and inner panels of an automobile, comprising, as a base coating film, only a base coating film (BI2) formed using the coating film formation method for the outer and inner panels of an automobile described in any of the above.

[0113] The coating on the exterior panel includes a multi-layer coating formed using the coating method of the present invention. The multi-layer coating also includes a first base coating and a second base coating, adjacent to each other from the exterior panel side. In one embodiment, the coating on the exterior panel consists of a primer coating, an intermediate coating, a first base coating, a second base coating, and a clear coating, adjacent to each other from the exterior panel side, and the multi-layer coating consists of a first base coating and a second base coating.

[0114] The dry film thickness of the first base coating is, for example, 12 to 19 μm, preferably 13 to 17 μm.

[0115] The dry film thickness of the second base coating is, for example, 4 to 6 μm, preferably 3 to 5 μm.

[0116] The coating on the inner panel includes only the base coating (BI2) formed using the coating method of the present invention as the base coating. Therefore, the coating on the inner panel does not include the first base coating formed from the first base coating composition. Furthermore, the coating on the inner panel does not include the base coating formed from base coatings other than the second base coating composition.

[0117] The dry film thickness of the base coating (BI2) is, for example, 4 to 12 μm, preferably 5 to 11 μm.

[0118] The coating on the inner panel only needs to include a base coating (BI2) formed using the coating method of the present invention as the base coating, and other layers are not particularly limited. The coating on the inner panel may, for example, consist of an undercoat, an intermediate coating, a base coating (BI2), and a clear coating, in order adjacent to each other from the inner panel side (not shown); or as shown in Figure 5, consisting of an undercoat, an intermediate coating, and a base coating (BI2), in order adjacent to each other from the inner panel side (not shown); or consisting of an undercoat, a base coating (BI2), and a clear coating. [Examples]

[0119] The present invention will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and do not limit the present invention in any way.

[0120] The details of each component of the paint composition used in the examples are as follows. Resin component 1: Acrylic emulsion resin, average particle size 150 nm, non-volatile content 20%, solids acid value 20 mg KOH / g, hydroxyl value 40 mg KOH / g, prepared by the method of Production Example 6 in paragraph

[0123] of Japanese Patent Publication No. 2014-147918. Resin component 2: Water-soluble acrylic resin, non-volatile content 30.0%, solid content acid value 40 mg KOH / g, hydroxyl value 50 mg KOH / g, prepared by the method of Production Example 8 in paragraph

[0125] of Japanese Patent Publication No. 2014-147918. Resin component 3: "Primepol PX-1000" manufactured by Sanyo Chemical Industries, Ltd., bifunctional polyether polyol, number average molecular weight 400, hydroxyl value 278 mgKOH / g, primary / secondary hydroxyl value ratio = 63 / 37, non-volatile content 100% Resin component 4: Abyssia brand product name "NeoLets R-9603", polycarbonate-based urethane emulsion resin, non-volatile content 33% Tertiary amine (neutralizing agent): 10% by mass aqueous solution of dimethylethanolamine 06-0672N: Bright pigment, product name "Alpaste (registered trademark) 06-0672" manufactured by Toyo Aluminum Co., Ltd., silver color, 17 μm CP-315: Bright pigment, manufactured by Asahi Kasei Corporation under the product name "CP series", silver color, 15 μm WL-0685: Luminous pigment, manufactured by Toyo Aluminum Co., Ltd., product name "Alpaste", silver color, 18 μm WL-Z-440: Bright pigment, manufactured by Toyo Aluminum Co., Ltd. under the product name "Alpaste", silver color, 14 μm R-5000: Coloring pigment (non-glossy pigment), product name "Carbon Black R-5000" manufactured by Columbia Carbon, black color. CR-97: Coloring pigment (non-glossy pigment), manufactured by Ishihara Sangyo Co., Ltd. under the product name "Typake", white. G-314: Coloring pigment (non-glossy pigment), manufactured by Sanyo Shikiso Co., Ltd., product name "Cyanine Blue G-314", blue color. RL-NF: Coloring pigment (non-glossy pigment), Clariant brand name "Violet RL-NF", violet color Red 400RG: Coloring pigment (non-glossy pigment), DIC Corporation product name "Quinacridone pigment", red color. Coloring Pigment (Non-Glossy Pigment) TM RED 8270: Coloring pigment (non-glossy pigment), manufactured by Dainichi Seika Co., Ltd. under the product name "Dipyroxide Pigment", red color. Clear coating: Product name "Macflow O-1810 Clear" manufactured by Nippon Paint Automotive Coatings Co., Ltd., an acid epoxy curing acrylic resin-based paint.

[0121] Details of other materials and equipment used in the examples are as follows: Steel plate: Zinc phosphate treated SPCC-SD steel plate, dimensions 20cm x 30cm x 0.8cm thick Spectrophotometer: Konica Minolta product name "CM-512m3" Standard light source box: BYK brand product name "BicoSpectra Pro"

[0122] • Preparation of the first base coating composition In addition to the resin components, flake-like glossy pigments, and coloring pigments shown in Table 1 (parts by mass), the following amounts of curing agent, tertiary amine, and corrosion inhibitor were added and uniformly dispersed to obtain the first base coating composition. Hardener: 15.2 parts by mass (non-volatile content 15.2 parts by mass) Tertiary amine: 40 parts by mass (concentration 10% by mass) Corrosion inhibitor: 0.2 parts by mass (non-volatile content 0.1 parts by mass)

[0123] • Preparation of the second base coating composition In addition to the resin components (calculated in terms of non-volatile content), flake-like glossy pigments, and coloring pigments shown in Table 2 (parts by mass), the same amount of curing agent, tertiary amine, and corrosion inhibitor as the first base coating composition was added and uniformly dispersed to obtain second base coating compositions 1 to 9.

[0124] [Table 1] In Table 1, "PWC" represents the amount (parts by mass) of the first flake-like lustrous pigment or coloring pigment relative to 100 parts by mass of the total solids content of the resin component, first flake-like lustrous pigment, and coloring pigment of the first base coating composition.

[0125] [Table 2] In Table 2, "PWC" represents the amount (parts by mass) of the second flake-like lustrous pigment or coloring pigment relative to 100 parts by mass of the total solids content of the resin component, second flake-like lustrous pigment, and coloring pigment of the second base coating composition.

[0126] • Preparation of the outer panels Nineteen exterior panels were prepared by sequentially applying a cationic electrodeposition coating and an intermediate coating to zinc phosphate-treated steel sheets, which were intended to be used as exterior panels for automobiles, in the same manner as in Example 1 of Patent Document 1, thereby forming a primer and an intermediate coating.

[0127] • Preparation of the inner panel Nineteen interior panels were prepared by sequentially applying a cationic electrodeposition coating and an intermediate coating to zinc phosphate-treated steel sheets, which were intended for use as interior panels for automobiles, in the same manner as in Example 1 of Patent Document 1, thereby forming a primer coating and an intermediate coating.

[0128] (Examples 1-11 and Comparative Examples 1-8) Painting of the interior panels On the intermediate coating of each inner panel, the second base coating composition, numbered as shown in Tables 3 and 4, was applied using a spray gun under the discharge volume and spray gun movement speed conditions shown in Tables 3 and 4, to achieve the dry film thickness shown in Tables 3 and 4, thereby forming an uncured base coating (BI2).

[0129] • Painting of the exterior panels Next, the first base coating composition was applied to the intermediate coating film of each exterior panel under standard robotic coating conditions to a dry film thickness of 12 μm, forming an uncured first base coating film. Then, the second base coating compositions, numbered as shown in Tables 3 and 4, were applied to the uncured first base coating film under standard robotic coating conditions to a dry film thickness of 4 μm, forming an uncured second base coating film.

[0130] Next, the inner and outer panels were preheated at 80°C for 3 minutes. Then, clear paint was spray-applied to the inner panels using a spray gun, and finally, clear paint was applied to the outer panels using a robotic coating process. The coating was then baked at 140°C for 30 minutes to form the paint film.

[0131] (Evaluation of the color match between the exterior and interior panels) For each of the obtained examples and comparative examples, the color difference ΔE of 45° at a light receiving angle of 45° was measured for the coating films of the outer and inner panels using a spectrophotometer. The hue match between the outer and inner panels was then evaluated according to the following criteria. Evaluations A and B indicate little hue discrepancy and are considered acceptable, while evaluations C and D indicate significant hue discrepancy and are considered unacceptable. For details on the color difference ΔE, please refer to paragraph

[0044] of Japanese Patent Application Publication No. 2011-088132. Evaluation A: ΔE45° is less than 1.0 Evaluation B: ΔE45° is between 1.0 and 1.5. Evaluation C: ΔE45° is between 1.5 and 2.0. Evaluation D: ΔE45° is 2.0 or greater.

[0132] (Evaluation of the transparency of the coating on the inner panel) For each of the obtained examples and comparative examples, the coating film on the inner panel was evaluated using a standard light source box. The light source was D65, the inner panel coating was positioned at a 45-degree angle from the horizontal, and the distance between the inner panel coating and the observer's eye was approximately 50 cm. The transparency of the underlying undercoat coating was evaluated by applying a black and white check film and painting according to the following criteria. Grade A: Pass Grade B: Almost a pass Rating C: Slightly see-through Rating D: Completely transparent

[0133] [Table 3]

[0134] [Table 4]

[0135] As shown in Table 3, we have been able to provide a method for forming a coating on the exterior and interior panels of an automobile that can reduce the discrepancy in hue between the coatings on the exterior and interior panels of the automobile. Furthermore, we have been able to provide a coating on the exterior and interior panels of an automobile in which the discrepancy in hue between the coatings on the exterior and interior panels is reduced. [Industrial applicability]

[0136] According to the present invention, it is possible to provide a method for forming a coating on the exterior and interior panels of an automobile that can reduce the discrepancy in hue of the coating on the exterior and interior panels of the automobile. Furthermore, according to the present invention, it is possible to provide a coating on the exterior and interior panels of an automobile in which the discrepancy in hue of the coating on the exterior and interior panels is reduced. [Explanation of Symbols]

[0137] 1: Exterior panel 2: Primer coating 3: Intermediate coating 4: First base coating 5: Second base coating 6: Inner plate 7: Base coating (BI2) 14: Uncured first base coating 15: Uncured second base coating 17: Uncured base coating (BI2)

Claims

1. A method for forming a coating on the outer and inner panels of an automobile, Step (A) of preparing a paint composition set for forming a multi-layer coating on the surface side of the outer panel, The multilayer coating includes a first base coating and a second base coating, adjacent to each other in order from the outer panel side. The paint composition set includes a first base paint composition for forming the first base coating film and a second base paint composition for forming the second base coating film. The first base coating composition comprises a resin component, a first flake-like luminous pigment, and a coloring pigment. The second base coating composition comprises a resin component, a second flake-like luminous pigment, and a coloring pigment. The total solid content (NV1) of the resin component, the first flake-like luminous pigment, and the coloring pigment of the first base coating composition, relative to the total mass of the first base coating composition, is 20-30%. The amount of the first flake-like luminous pigment is 5 to 15 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the first flake-like luminous pigment, and the coloring pigment of the first base coating composition. The total solid content (NV2) of the resin component, the second flake-like luminous pigment, and the coloring pigment of the second base coating composition, relative to the total mass of the second base coating composition, is 10 to 20%. The amount of the second flake-like luminous pigment is 14 to 40 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the second flake-like luminous pigment, and the coloring pigment of the second base coating composition. The above NV2 is smaller than the above NV1, in process (A), Step (B) involves applying the first base coating composition to the surface side of the outer panel to form an uncured first base coating film, Step (C) involves applying the second base coating composition onto the uncured first base coating to form an uncured second base coating, Step (D) of curing the uncured first base coating and the uncured second base coating to form the first base coating and the second base coating, Step (E) involves applying the second base coating composition to the surface side of the inner plate using a spray gun to form a base coating film (BI2), The inner plate includes only the base coating (BI2) as the base coating, A method for forming a coating film on the exterior and interior panels of an automobile, comprising step (E), wherein the discharge rate of the second base coating composition when applying the second base coating composition is 150 to 320 cc / min, and the movement speed of the spray gun is 1000 to 1300 mm / min.

2. The method for forming a coating on the outer and inner panels of an automobile according to claim 1, wherein the dry film thickness of the base coating (BI2) is 5 to 11 μm.

3. The method for forming a coating on the outer and inner panels of an automobile according to claim 1 or 2, wherein the dry film thickness of the second base coating is 3 to 5 μm.

4. A method for forming a coating film on the outer and inner panels of an automobile according to any one of claims 1 to 3, wherein the average particle size of the first flake-like luminous pigment is 10 to 30 μm, and the average particle size of the second flake-like luminous pigment is 10 to 30 μm.

5. A method for forming a coating on the outer and inner panels of an automobile according to any one of claims 1 to 4, wherein the NV2 is 12 to 17%.

6. The method for forming a coating film on the exterior and interior panels of an automobile according to any one of claims 1 to 4, wherein the amount of the second flake-like lustrous pigment is 20 to 30 parts by mass with respect to 100 parts by mass of the total solid content of the resin component, the second flake-like lustrous pigment and the coloring pigment of the second base coating composition.

7. A coating film for the exterior and interior panels of an automobile, The coating on the outer panel includes a multilayer coating formed using the coating method for the outer and inner panels of an automobile described in any one of claims 1 to 6. The multilayer coating includes a first base coating and a second base coating, adjacent to each other in order from the outer panel side. The coating film on the inner panel comprises, as a base coating film, only a base coating film (BI2) formed using the coating film formation method for the outer and inner panels of an automobile described in any one of claims 1 to 6.

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