Paint toning method

Abstract

To provide a paint toning method which can suppress a visual defect due to dust through an inner plate coating.SOLUTION: A paint toning method comprises the steps of: measuring glossiness Gs(20°) of respective painted surfaces with a gloss meter (angle 20°) after an outer plate paint and an inner plate paint to be used are respectively applied; predicting a visual defect on the outer plate based on the measurement result of the glossiness Gs(20°) and a prescribed threshold value; measuring, when determining the visual defect occurs, glossiness Gs(60°) of respective painted surfaces with the gloss meter (angle 60°) to calculate ratio of the inner plate Gs(60°) to the outer plate Gs(60°); calculating an outer plate reflectance ratio based on luminosity of the painted surface through the outer plate coating; calculating an inner plate reflectance ratio based on the outer plate reflectance ratio and the above ratio; calculating an inner plate luminosity based on the inner plate reflectance ratio; and toning color tone of the inner plate coating to be the inner plate luminosity.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a paint color matching method for matching the color tone of an interior panel paint. [Background technology]

[0002] As shown in the schematic cross-sectional view of Figure 4, the paint film of an automobile is formed by successively laminating a primer coating (electrodeposition film) 2, which is mainly applied by electrodeposition coating for rust prevention, an intermediate coating film 3, and a topcoat coating film 4 on an object to be coated 1. The topcoat coating film 4 is composed of a base coating film (color coating film) 5, which contains a pigment for color development, and a clear coating film 6 on top of that.

[0003] In the coating film of an automobile constructed as described above, the intermediate coating film 3 has the purpose of improving the adhesion between the primer coating film 2 and the topcoat coating film 4, improving the smoothness, as well as enhancing the light deterioration resistance, chipping resistance, and color development. In particular, when the primer coating film 2 formed by an epoxy cationic electrodeposition paint is exposed to a large amount of ultraviolet light, the surface layer deteriorates and the coating film above it peels off. For this reason, it has been conventional to use the intermediate coating film 3 to protect the primer coating film 2 from ultraviolet light and to improve the light deterioration resistance.

[0004] For example, Patent Document 1 listed below discloses a coating method for forming an automobile coating film consisting of an electrocoating film, an intermediate coating film, and a solid color coating film (corresponding to a topcoat coating film), as an example of a method for forming a laminated coating film for an automobile in which a primer coating film, an intermediate coating film, and a topcoat coating film are laminated in that order.

[0005] Specifically, this painting method describes how an intermediate coating film is formed by applying an intermediate coating on an electrodeposition film, then an interior solid color paint is applied to the interior plate to form an interior solid color coating film (interior plate painting), and finally an exterior solid color paint is applied to the exterior plate to form an exterior solid color coating film (exterior plate painting).The following cited document 1 describes how this painting method causes paint splashes (dust) from the interior painting to be applied to the exterior plate, and further describes how the paint splashes cause uneven coating defects called haze or dullness to appear on the exterior plate.

[0006] In recent years, when a color coating film and a clear coating film are laminated on a primer coating film, for example, a method of forming a laminated coating film is implemented in which a primer coating film (electrodeposition film) is formed on the object to be coated (exterior and interior panels), then an intermediate coating film (exterior panel coating) is applied to the exterior panel to color it, an intermediate coating film (interior panel coating) is applied to the interior panel to color it the same color as the exterior panel coating, and then a clear coating is applied to the entire panel (exterior and interior panels). This allows the color coating film (intermediate coating film) to be formed without the paint ever drying during the intermediate coating process. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2006-95418 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the above-mentioned method for forming a laminated coating film in which coloring is performed by intermediate coating, in the intermediate coating process, an intermediate coating (external panel coating) is applied to the outer panel after electrocoating to color it, and further, an intermediate coating (inner panel coating) is applied to the inner panel to color it the same color as the outer panel coating, thereby forming an intermediate coating film on the inner panel and the outer panel.

[0009] However, when this method of forming a laminated coating film is implemented, dust from the interior panel painting (called interior panel dust) is applied to the exterior panel, and when a clear coat is applied to an exterior panel with the interior panel dust applied thereto, a poor appearance of a "mottled pattern" caused by the interior panel dust appears on the surface of the exterior panel after the laminated coating film is formed (after the car is painted).

[0010] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a paint color matching method that can suppress poor appearance that appears on the surface of an exterior panel when a clear coat is applied to an exterior panel that has dust applied thereto by interior panel painting. [Means for solving the problem]

[0011] The paint color matching method of the present invention is a paint color matching method for priorly matching the color tone of an interior intermediate coat paint in the painting of an automobile in which, after electrodeposition painting, an exterior plate is painted with an exterior intermediate coat paint to color it, an interior plate is painted with the interior intermediate coat paint to color it the same color as the exterior plate paint, and then the interior and exterior plates are clear-coated. Specifically, the method includes a first gloss measurement step of painting the automobile using the interior intermediate coat paint and the exterior intermediate coat paint to be used for painting the automobile, and measuring the gloss (Gs(20°)) of each painted surface at an angle of 20° using a gloss meter; an appearance defect prediction step of predicting whether an appearance defect will appear on the surface of the exterior plate after painting of the automobile based on the measurement results of Gs(20°) of each painted surface and a threshold value for predicting appearance defect previously determined from past performance; and When it is determined that an appearance defect will occur in the appearance defect prediction step, a second gloss measurement step is performed in which a gloss meter is used to measure the gloss (Gs(60°)) of each of the painted surfaces at an angle of 60°; a ratio calculation step is performed in which the ratio of the inner panel Gs(60°), which is the gloss of the painted surface by the inner panel intermediate paint, to the outer panel Gs(60°), which is the gloss of the painted surface by the outer panel intermediate paint, is calculated based on the measurement results of Gs(60°) of each of the painted surfaces; and a colorimeter is used to calculate the L of the painted surface by the outer panel intermediate paint. * a * b *The method includes an exterior panel reflectance calculation step of measuring a color space and calculating an exterior panel reflectance, which is the reflectance of the painted surface with the exterior panel intermediate coat paint, based on the exterior panel lightness, which is a lightness index obtained by this measurement; an interior panel reflectance calculation step of calculating an interior panel reflectance, which is a reflectance corrected to suppress appearance defects, based on the exterior panel reflectance and the ratio; an interior panel lightness calculation step of calculating the interior panel lightness, which is a lightness index corrected to suppress appearance defects, based on the interior panel reflectance; and a color matching step of matching the color tone of the interior panel intermediate coat paint to be used in painting the automobile to achieve the interior panel lightness.

[0012] The above-mentioned poor appearance is caused by dust, which is paint splashes from the interior panel painting.

[0013] Therefore, by carrying out the paint color matching method of the present invention, it is possible to suppress poor appearance caused by dust, which is paint splashes caused by painting the interior panels.

[0014] Furthermore, in the paint color matching method of the present invention, it is preferable to determine in advance, from past performance, the difference in Gs(20°) between the painted surfaces at which a defective appearance occurs as the threshold value, and in this case, in the defective appearance prediction step, it is predicted whether or not a defective appearance will occur based on the threshold value.

[0015] On the other hand, if it is determined in the appearance defect prediction process that no appearance defect will occur, the interior panel intermediate coat paint to be used for painting the automobile is not newly mixed in color, but the interior panel intermediate coat paint of the current color tone is used for painting the automobile. Effect of the Invention

[0016] According to the paint color matching method of the present invention, it is possible to suppress poor appearance caused by dust, which is paint splashes caused by painting the interior panels. [Brief description of the drawings]

[0017] [Figure 1]FIG. 1 is a diagram showing an example of an outer plate portion and an inner plate portion of an automobile. [Diagram 2] FIG. 2 is a diagram showing an example of an undercoat painting process. [Diagram 3] FIG. 3 is a flow chart showing an example of a paint color matching method according to the present invention. [Figure 4] FIG. 4 is a cross-sectional view that illustrates an example of a multilayer coating structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the paint color matching method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the specification and drawings of the present application, elements that can be similarly explained may be given the same reference numerals to avoid duplicate explanations.

[0019] An embodiment of the paint color matching method according to the present invention will be described in detail with reference to Figures 1 to 3. Note that the following description of the preferred embodiment is merely illustrative and is not intended to limit the present invention, its applications, or its uses.

[0020] <Laminated coating structure for automobiles> FIG. 1 is a diagram showing an example of the outer and inner panel parts of an automobile, where (a) shows the outer panel part 10, (b) shows a door inner as an example of the inner panel part 20, and (c) shows a door opening as an example of the inner panel part 20.

[0021] In the case of forming a laminated coating film on the outer plate portion 10 and the inner plate portion 20 shown in FIG. 1, in this embodiment, for example, a primer coating film (electrodeposition film) 2 is formed on the coated object 1 composed of the outer plate portion 10 and the inner plate portion 20, and then an intermediate coating film 3 (outer intermediate coating film 3a) is formed by applying an intermediate coating film (outer plate painting) to the outer plate portion 10 from above the primer coating film 2 and coloring it, and then an intermediate coating film 3 (inner plate intermediate coating film 3b) is formed by applying an intermediate coating film (inner plate painting) to the inner plate portion 20 from above the primer coating film 2 and coloring it the same color as the outer plate painting. Finally, a clear coating film 6 is formed by applying a clear coating using a paint for giving a gloss. An example of a laminated coating film structure formed by a laminated coating film forming method in which the primer coating film 2, the intermediate coating film 3 (outer plate intermediate coating film 3a, inner plate intermediate coating film 3b) and the clear coating film 6 are sequentially laminated is shown in FIG. 2.

[0022] In Fig. 2, the object 1 is an iron plate, a steel plate, an aluminum plate, a stainless steel plate, or the like, such as an iron plate constituting the body of an automobile. In this embodiment, a primer coating film 2, an intermediate coating film 3 (an outer intermediate coating film 3a, an inner intermediate coating film 3b), and a clear coating film 6 are laminated in this order on the object 1. Note that the object 1 shown in Fig. 2 shows, as an example, a portion where no joints or seams exist between overlapping plate-shaped steel plates. For example, in the portion where there are joints or seams, a sealer coating (not shown) is formed by applying a waterproof and dustproof sealer coating on the primer coating film 2.

[0023] The primer coating film 2 is formed by immersing the substrate 1 in a cationic electrocoating paint and passing a direct current between the substrate 1 as the cathode and the electrode plate in the electrocoating tank as the anode, thereby depositing the primer coating film 2 on the substrate 1. The thickness of the primer coating film 2 is preferably 10 μm or more and 30 μm or less, and is formed to, for example, 15 μm.

[0024] The intermediate coating film 3 (external intermediate coating film 3a, internal intermediate coating film 3b) is formed by an oil-based (solvent-based) intermediate coating paint to which a pigment is added as a coloring agent. The oil-based intermediate coating paint is, for example, a melamine-cured oil-based paint containing polyester resin, melamine resin, and coloring pigment. The external intermediate coating film 3a and the internal intermediate coating film 3b are each formed to a thickness of 8 μm to 50 μm. In this embodiment, the external intermediate coating paint (external paint) used to form the external intermediate coating film 3a and the internal intermediate coating paint (interior paint) used to form the internal intermediate coating film 3b have the same color but different gloss (gloss value: Gs). Specifically, the same pigment is used, but the resin components are adjusted because the required characteristics (for example, when a sealer coating film is formed on the internal panel 20) are different between the internal panel 20 and the external panel 10.

[0025] The resin forming the clear coating film 6 is not particularly limited, but it may be formed from a combination of acrylic resin and / or polyester resin with amino resin, or from an acrylic resin and / or polyester resin having a carboxylic acid-epoxy curing system, or a urethane curing system made of an acrylic resin having a hydroxyl group and isocyanate, etc. The clear coating film 6 is formed to a thickness of, for example, 30 μm.

[0026] <Paint color matching method> Next, the paint color matching method of this embodiment will be described in detail.

[0027] When forming a laminated coating film as shown in Figure 2 by the above-mentioned laminated coating film formation method, in this embodiment, for example, in the intermediate coating process, an intermediate coating (exterior panel painting) is applied to the exterior panel portion 10 over the primer coating film 2 and colored to form an exterior intermediate coating film 3a, and then an intermediate coating (interior panel painting) is applied to the interior panel portion 20 over the primer coating film 2 and colored the same color as the exterior panel paint to form an interior intermediate coating film 3b.

[0028] In addition, when the interior panel is painted, dust (interior panel dust) 7, which is paint droplets from the interior panel paint, is sprayed onto and adheres to the exterior panel 10. Therefore, conventionally, the subsequent clear coating of the interior panel 20 and exterior panel 10 (the entire panel) has been carried out while this interior panel dust 7 is still adhered (see Figure 2).

[0029] However, when a clear coat is applied to an exterior panel portion 10 having interior panel dust 7 applied thereto, a poor appearance such as a "mottled pattern" caused by the interior panel dust 7 may appear on the surface of the exterior panel portion 10 after the multilayer coating film is formed (after the automobile is painted).

[0030] Therefore, in this embodiment, before painting the body of the automobile, it is predicted (determined) whether or not the appearance defect of "mottled pattern" caused by interior panel dust 7 will occur, and if it is determined that the appearance defect will occur, the color of the interior panel paint is adjusted to suppress the appearance defect caused by the interior panel dust 7.

[0031] FIG. 3 is a flow chart showing an example of the paint color-matching method of this embodiment, in which each step for matching the color tone of the interior panel paint used for painting the interior panels is described.

[0032] In the paint color matching method of this embodiment, first, exterior and interior paints to be used for painting an automobile are used for painting, and then a gloss meter is used to measure the gloss value (Gs(20°)) of each painted surface at an angle of 20°, which is more likely to produce a large gloss difference, for high-gloss painted surfaces where the gloss value (Gs(60°)) of each painted surface is 75 or more at an angle of 60° (Step S1: first gloss measurement step). Hereinafter, the gloss value of the surface painted with the interior paint and the gloss value of the surface painted with the exterior paint are referred to as the interior Gs(20°) and the exterior Gs(20°), respectively.

[0033] Next, in the paint color matching method of this embodiment, based on the measurement results of the inner plate Gs(20°) and the outer plate Gs(20°) in the first gloss measurement step, it is predicted whether or not a defective appearance such as a "mottled pattern" caused by the inner plate dust 7 will appear on the surface of the outer plate portion 10 after the automobile has been painted (Step S2: defective appearance prediction step). In this defective appearance prediction step, for example, based on past performance, the difference between the inner plate Gs(20°) and the outer plate Gs(20°) when a defective appearance will appear is obtained in advance as a threshold value for predicting defective appearance, and based on this threshold value, it is predicted whether or not a defective appearance will appear on the surface of the outer plate portion 10.

[0034] In this embodiment, as an example, the threshold value for predicting appearance defects is set to "10", and when the difference A between the inner plate Gs(20°) and the outer plate Gs(20°) obtained in the first gloss measurement process is equal to or greater than the threshold value (=10) (step S2, Yes), it is determined that an appearance defect will appear in the inner plate dust 7 portion on the surface of the outer plate portion 10. Note that, in this embodiment, the threshold value for predicting appearance defects is set to "10" as an example, but is not limited to this, and an optimal value is set as appropriate depending on the characteristics, color tone, etc. of the paint used.

[0035] On the other hand, if the difference A between the inner panel Gs(20°) and the outer panel Gs(20°) obtained by the first gloss measurement process is less than the threshold value (=10) (step S2, No), it is determined that no appearance defect will occur, and the paint color matching method of this embodiment is terminated. In other words, the interior panel paint and the outer panel paint of the current color tone are used as they are for painting the automobile without newly mixing the interior panel paint.

[0036] For example, if it is determined that a visual defect will occur in the visual defect prediction step (step S2, Yes), the paint color matching method of this embodiment then uses a gloss meter to measure the gloss value (Gs(60°)) of each of the above-mentioned painted surfaces at an angle of 60°, which is closer to the relationship between the visual glossiness and the gloss value than the angle of 20° (step S3: second gloss measurement step). Then, based on the measurement result of Gs(60°) in the second gloss measurement step, the ratio X of Gs(60°) of the painted surface of the interior paint (referred to as the interior painted surface) to Gs(60°) of the painted surface of the exterior paint (referred to as the exterior painted surface) is calculated according to the following formula (1) (step S4: ratio calculation step). Hereinafter, Gs(60°) of the interior painted surface and Gs(60°) of the exterior painted surface are referred to as the interior Gs(60°) and exterior Gs(60°), respectively.

[0037]

number

[0038] Next, in the paint color matching method of this embodiment, a colorimeter is used to measure the L of the exterior paint surface. * a * b * The color space is measured and the lightness index L1 of the exterior paint surface is obtained. * (Outer panel brightness L1 * ) (see equation (2) below) to calculate the reflectance Y1 of the painted surface of the exterior plate (exterior plate reflectance Y1) (Step S5: exterior plate reflectance calculation step).

[0039]

number

[0040] Next, in the paint color matching method of this embodiment, the reflectance Y2 (inner panel reflectance Y2) of the inner panel painted surface corrected to suppress appearance defects is calculated according to formula (3) based on the outer panel reflectance Y1 calculated in the outer panel reflectance calculation step and the ratio X calculated in the ratio calculation step (step S6: inner panel reflectance calculation step). Hereinafter, the inner panel reflectance Y2 is referred to as the target reflectance Y2.

[0041]

number

[0042] Next, in the paint color matching method of this embodiment, based on the target reflectance Y2 calculated in the interior panel reflectance calculation step, the lightness index L2 of the interior panel painted surface corrected to suppress appearance defects according to formula (4) is calculated. * (Inner plate brightness L2 * ) is calculated (Step S7: Inner plate lightness calculation step). Hereinafter, the lightness index L2 * Target lightness L2 * That is, in the interior panel lightness calculation step, the lightness of the interior panel painted surface is changed so as to cancel out the difference in glossiness between the respective painted surfaces (exterior panel painted surface and interior panel painted surface).

[0043]

number

[0044] Finally, in the paint color matching method of this embodiment, the target lightness L2 obtained in the inner panel lightness calculation process is * The color tone of the interior paint to be used for painting the automobile is adjusted so as to satisfy the above condition (step S8: color adjustment step).

[0045] <Effects> As described above, according to the paint color matching method of this embodiment, even when a clear coat is applied to an exterior panel portion 10 to which interior panel dust 7 has been applied due to interior panel painting, poor appearance on the surface of the exterior panel portion 10 can be suppressed. EXAMPLES

[0046] The paint color matching method according to the present invention will now be described in further detail with reference to examples, although the present invention is not limited to the following examples.

[0047] <Example> Prepare the exterior and interior paints to be used for painting the automobile (exterior and interior panels), and use these paints to carry out the paint color matching method shown in Figure 3 to match the interior paint to the target lightness L2 * The color was adjusted to be as follows.

[0048] Specifically, first, the prepared interior and exterior paints were used to paint each of the panels, and then a gloss meter (Murakami Color Laboratory: Precision Gloss Meter GM-26PRO) was used to measure the Gs(20°) of each painted surface at an angle of 20° (first gloss measurement step). As a result, the interior Gs(20°) was 84, and the exterior Gs(20°) was 58.

[0049] Next, based on the inner plate Gs(20°) and outer plate Gs(20°) obtained in the first gloss measurement process and a threshold value for predicting appearance defects (in this embodiment, the threshold value was set to "10"), it was predicted whether or not an appearance defect of "mottled pattern" caused by inner plate dust would occur (appearance defect prediction process). In this embodiment, since the difference between the outer plate Gs(20°) and the inner plate Gs(20°) was 26 (84-58), which is greater than the threshold value (=10), it was determined that an appearance defect would occur.

[0050] Next, a gloss meter (Murakami Color Laboratory: Precision Gloss Meter GM-26PRO) was used to measure the inner plate Gs(60°) and the outer plate Gs(60°) at an angle of 60° (second gloss measurement step), and further, based on the measurement results of the inner plate Gs(60°) and the outer plate Gs(60°), the ratio X of the inner plate Gs(60°) and the outer plate Gs(60°) was calculated according to the above formula (1) (ratio calculation step). As a result, the inner plate Gs(60°) was 93, the outer plate Gs(60°) was 84, and the ratio X was 1.107 (the inner plate Gs(60°) was 1.107 times the outer plate Gs(60°)).

[0051] Next, a colorimeter (Murakami Color Laboratory: Spectrophotometer CMS-35SPS) was used to measure the L of the exterior paint surface. * a * b * The color space is measured and the lightness index L1 of the exterior paint surface is obtained. *The outer panel reflectance Y1 was calculated from the formula (see formula (2)) (outer panel reflectance calculation step). As a result, L * a * b * Color space is L1 * = 15.90, a * =-0.50, b * =-2.99, and the exterior panel reflectance Y1 was 2.202.

[0052] Next, the target reflectance Y2 was calculated according to formula (3) based on the outer plate reflectance Y1 and the ratio X (inner plate reflectance calculation step). As a result, the target reflectance Y2 was 1.989.

[0053] Next, based on the target reflectance Y2, the target brightness L2 is calculated according to equation (4). * was calculated (inner plate lightness calculation process). As a result, the target lightness L2 * was 14.20.

[0054] Next, target brightness L2 * The color tone of the prepared interior paint was adjusted so that the color tone was as follows (color-matching process). The color of the interior paint after color matching was measured with the above-mentioned colorimeter. * a * b * Color space is L2 * = 14.20, a * =-0.48, b * =-2.94.

[0055] Then, using the exterior paint prepared above and the interior paint after color matching, painting was carried out to actually form a multilayer coating film by the above-mentioned multilayer coating film formation method (see Figure 2). More specifically, in the undercoat painting process of the above-mentioned multilayer coating film formation method, a clear coat was applied to the exterior panel part to which the interior panel dust had been applied.

[0056] <Comparative Examples 1 to 8> The exterior paint prepared above and the above target lightness L2 * A different lightness index L X *Using the same method for forming a multilayer coating film as in the above-mentioned embodiment (see FIG. 2), a coating was actually carried out to form a multilayer coating film. X * = 15.85, and Comparative Example 2 is L X * = 15.45, and Comparative Example 3 is L X * = 15.05, and in Comparative Example 4, L X * = 14.80, and Comparative Example 5 is L X * = 14.55, and Comparative Example 6 is L X * = 13.80, and Comparative Example 7 is L X * = 13.20, and Comparative Example 8 is L X * =12.60.

[0057] <Evaluation> The exterior panel after the multilayer coating film was formed by the above-mentioned multilayer coating film forming method (see FIG. 2) was visually observed to check for the presence or absence of appearance defects such as "mottled patterns" caused by inner panel dust.

[0058] Table 1 shows the evaluation results of Examples and Comparative Examples 1 to 8. As a result of observing the exterior panels of the above Examples, no appearance defects such as "mottled patterns" were confirmed (evaluation result: ⊚). In other words, it was found that the paint color matching method of the present invention can suppress appearance defects appearing on the surface of the exterior panel.

[0059] Moreover, as a result of observing the exterior plate parts of Comparative Examples 5 and 6, a slight whitish "mottled pattern" was confirmed (evaluation result: ○). As a result of observing the exterior plate part of Comparative Example 4, although it was not conspicuous, more "mottled patterns" were confirmed than in Comparative Examples 5 and 6 (evaluation result: △). As a result of observing the exterior plate parts of Comparative Examples 1 to 3, 7, and 8, the "mottled patterns" were quite noticeable (evaluation result: ×). Furthermore, Comparative Examples 1 to 7 had a whitish "mottled pattern", but Comparative Example 8 had a blackish "mottled pattern". From these results, the lightness index L2 of the interior plate paints toned by the paint color-matching method of the present invention was 100%. *It was found that the greater the difference between the two, the more likely it was that "mottled patterns" would appear.

[0060] [Table 1] [Explanation of symbols]

[0061] 1 Object to be coated 2 Primer coating (electrodeposition coating) 3. Undercoat 3a Outer panel intermediate coating 3b Interior panel intermediate coating 4 Topcoat 5 Base coating (color coating) 6 Clear coating 7 Dust (inner panel dust) 10 Outer panel 20 Inner plate part

Claims

1. A paint color-matching method for automobile painting, in which an outer panel is painted with an intermediate paint for an outer panel after electrodeposition painting to color it, and an inner panel is painted with an intermediate paint for an inner panel to color it the same color as the outer panel paint, and then the inner panel and the outer panel are clear-coated, in advance to match the color of the intermediate paint for an inner panel, A first gloss measurement step of coating the vehicle with an outer intermediate coating paint and an inner intermediate coating paint to be used for painting the vehicle, and measuring the gloss (Gs(20°)) of each coated surface at an angle of 20° using a gloss meter; an appearance defect prediction step of predicting whether an appearance defect will appear on the surface of the outer plate of the automobile after painting based on the measurement results of Gs (20°) of each painted surface and a threshold value for predicting an appearance defect that has been obtained in advance from past performance; a second gloss measurement step of measuring the gloss (Gs(60°)) of each of the painted surfaces at an angle of 60° using a gloss meter when it is determined that a visual defect will occur in the visual defect prediction step; A ratio calculation step of calculating a ratio of the inner plate Gs (60 °) which is the gloss of the painted surface by the inner plate intermediate coating paint and the outer plate Gs (60 °) which is the gloss of the painted surface by the outer plate intermediate coating paint based on the measurement results of Gs (60 °) of each painted surface; Using a colorimeter, measure the L of the painted surface with the outer panel undercoat paint. ＊ a ＊ b ＊ an exterior panel reflectance calculation step of measuring the color space and calculating the exterior panel reflectance, which is the reflectance of the painted surface of the exterior panel intermediate coating paint, based on the exterior panel lightness, which is the lightness index obtained by this measurement; An inner plate reflectance calculation step of calculating an inner plate reflectance, which is a reflectance corrected so as to suppress appearance defects, based on the outer plate reflectance and the ratio; An inner panel brightness calculation step of calculating an inner panel brightness, which is a brightness index corrected so as to suppress appearance defects, based on the inner panel reflectance; A color matching process for matching the color of the interior panel intermediate coating paint to be used for painting the automobile so as to achieve the interior panel lightness; Including, A method for mixing paint colors.

2. The appearance defect is caused by dust, which is paint splashes from the interior panel painting.

2. The method for mixing paint according to claim 1.

3. The difference in Gs (20°) between the respective painted surfaces at which a defect in appearance occurs is previously obtained as the threshold value from past records, In the appearance defect prediction step, it is predicted whether or not an appearance defect will occur based on the threshold value.

3. The paint color matching method according to claim 1 or 2.

4. When it is determined that no appearance defect will occur in the appearance defect prediction step, the interior panel intermediate coating paint to be used for painting the automobile is not newly mixed, and the interior panel intermediate coating paint of the current color tone is used for painting the automobile.

4. The method for mixing paint according to claim 3.

Images