MULTILAYERED COATING FILM AND COATED OBJECT

Abstract

A multilayer coating film includes a colored base layer 14 formed directly or indirectly on a surface of a coating target 11, and a luster material-containing layer 15 layered on the colored base layer 14 and containing flaked luster materials 22 and a colorant 23. With respect to the luster material-containing layer 15 in a state without the colorant, Y(10) of the XYZ color system is set to be 50 or more and 850 or less, and Y(20) is set to be equal to kY(10), where k is in a range of 0.2k0.6 and is determined according to the Y(10). The colorant concentration C of the luster material-containing layer is determined according to k. The surface reflectance R(%) of the colored base layer is determined according to the colorant concentration C of the luster material-containing layer and the Y(10).

Claims

1. A multilayer coating film, comprising a colored base layer containing a colorant and formed directly or indirectly on a surface of a coating target; and a luster material-containing layer containing flaked luster materials and a colorant and layered on the colored base layer, wherein a following equation is employed: Y(20)=kY(10), where k is a coefficient, Y represents a Y value according to an XYZ color system, which is calibrated by a standard white plate, of the luster material-containing layer in a state without the colorant, Y(10) represents a Y value of reflected light measured at a receiving angle of 10 (an angle toward a light source from a specular reflection angle), and Y(20) represents a Y value of reflected light measured at the receiving angle of 20, and a colorant concentration C of the luster material-containing layer is expressed in percent by mass, the Y(10), the coefficient k, and the colorant concentration C are three variables, and satisfy, when x-, y-, and z-coordinate axes of a three-dimensional orthogonal coordinate space represent the three variables, that coordinates (Y(10), k, C) are in a range defined by a octahedron consisting of eight planes expressed by equations A to H, shown below, in which the planes expressed by the equations C and F form an inwardly protruding ridge and the planes expressed by the equations D and G form an outwardly protruding ridge:
3000y120z+3000=0;Equation A
3000y120z=0;Equation B
5x3750y2000=0;Equation C
5x3750y+1000=0;Equation D
15000y9000=0;Equation E
5x1250y3000=0;Equation F
5x1250y=0; andEquation G
15000y3000=0, andEquation H a surface reflectance R(%) of visible light of the colored base layer satisfies a condition represented by a following expression using the Y(10) of and the colorant concentration C of the luster material-containing layer:
R0.6C+0.04Y(10)+4.

2. The multilayer coating film of claim 1, wherein the luster materials are aluminum flakes with a thickness of 25 nm or more and 200 nm or less.

3. The multilayer coating film of claim 2, wherein the aluminum flakes are oriented at an angle of 3 degrees or less with respect to a surface of the luster material-containing layer.

4. The multilayer coating film of claim 1, wherein the colorants of the colored base layer and the luster material-containing layer are deep in color.

5. The multilayer coating film of claim 4, wherein the colorants of the colored base layer and the luster material-containing layer are in similar colors.

6. The multilayer coating film of claim 5, wherein the colorants of the colored base layer and the luster material-containing layer are in a blackish color.

7. The multilayer coating film of claim 1, wherein a transparent clear layer is layered directly on the luster material-containing layer.

8. A coated object including the multilayered coating film of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is a diagram schematically illustrating a cross-sectional view of a multilayered coating film.

[0038] FIG. 2 is a diagram schematically illustrating a cross-sectional view of a known multilayer coating film to show how light is scattered by luster materials and is diffused on a base layer.

[0039] FIG. 3 schematically shows the control of scattered light by a laminated coating film according to the present invention.

[0040] FIG. 4 is a diagram illustrating reflected light for explaining how to calculate an FI value.

[0041] FIG. 5 is a graph showing an example angle dependence of Y(10) with respect to a luster material-containing layer in a state without a colorant.

[0042] FIG. 6 illustrates how a value Y is measured.

[0043] FIG. 7 is a graph showing a preferred range of Y(10) and colorant concentration C at coefficient k=0.4.

[0044] FIG. 8 is a graph showing a preferred range of Y(10) and colorant concentration C at coefficient k=0.2.

[0045] FIG. 9 is a graph showing a preferred range of Y(10) and colorant concentration C at coefficient k=0.6.

[0046] FIG. 10 is a graph showing a critical line of a surface reflectance R of a colored base layer.

[0047] FIG. 11 is a graph showing a relationship between the Y(10) and the coefficient k.

[0048] FIG. 12 is a graph showing a relationship between the coefficient k and the colorant concentration C.

[0049] FIG. 13 is a graph showing ranges of the Y(10), the coefficient k, and the colorant concentration C when an FI value is 30 or more.

[0050] FIG. 14 is a graph showing ranges of the Y(10), the coefficient k, and the colorant concentration C when an FI value is 35 or more.

DESCRIPTION OF EMBODIMENTS

[0051] Hereinafter, embodiments of the present invention will now be described with reference to the accompanying drawings. The following description of the preferred embodiments is only an example in nature, and is not intended to limit the scope, applications, or use of the present invention.

[0052] <Example Configuration of Multilayered Coating Film>

[0053] As illustrated in FIG. 1, a multilayer coating film 12 provided on a surface of an automobile body (steel plate) 11 according to the present embodiment contains a colored base layer 14, a luster material-containing layer 15, and a transparent clear layer 16 which are sequentially stacked one upon the other. An electrodeposition coating film (undercoat) 13 is formed on the surface of the automobile body 11 by cationic electrodeposition. The multilayer coating film 12 is provided on top of the electrodeposition coating film 13. In the multilayer coating film 12, the colored base layer 14 corresponds to an intermediate coat, and the luster material-containing layer 15 and the transparent clear layer 16 correspond to a topcoat.

[0054] A deep color pigment 21 is dispersed in the colored base layer 14. Flaked luster materials 22 and a deep color pigment 23 in a color similar to that of a pigment 21 of the colored base layer 14 are dispersed in the luster material-containing layer 15. Pigments of various hues including, for example, a black pigment (e.g., carbon black, perylene black, and aniline black) or a red pigment (e.g., perylene red) may be employed as the pigments 21 and 23. It is particularly preferable to employ as the pigment 21 carbon black having a particle size distribution with a peak at a particle size of 300 nm or more and 500 nm or less, and employ as pigment 23 carbon black having a particle size distribution with a peak at a particle size of 200 nm or less.

[0055] The surface smoothness of the colored base layer 14 is 8 or less in a measurement value Wd (wavelength of 3 to 10 mm) measured by WaveScan DOI (trade name) manufactured by BYK-Gardner, and the thickness of the luster material-containing layer 15 is 1.5 m or more and 6 m or less.

[0056] The luster material 22 of the luster material-containing layer 15 has a thickness of 25 nm or more and 200 nm or less, and is oriented approximately parallel to the surface of the luster material-containing layer 15. Specifically, the luster material 22 is oriented at an angle of 3 degrees or less with respect to the surface of the luster material-containing layer 15. After having applied a coating, which includes the luster material 22 and the pigment 23, on top of the colored base layer 14, a solvent included in the coating film is vaporized by stoving. As a result, the coating film shrinks in volume and becomes thin, and the luster material 22 is arranged at the orientation angle of 3 degrees or less (preferably 2 degree or less).

[0057] The colored base layer 14 contains a resin component which may be, e.g., a polyester-based resin. The luster material-containing layer 15 contains a resin component which may be, e.g., an acrylic-based resin. The colored base layer 16 contains a resin component which may be, e.g., an acid/epoxy-based cured acrylic resin.

[0058] <Control of Scattered Light, etc.>

[0059] As illustrated in FIG. 2, if a large number of luster materials 22 are dispersed in the luster material-containing layer 30, light is reflected multiple times by the plurality of luster materials 22. The FI value is low if a large portion of the light undergoes multiple reflections and comes out of the luster material-containing layer 30 as scattered light at angles diverging from the specular reflection angle. That is, reducing the scattered light is important to increase the FI value. In addition, the light reaching a base layer 31 after the multiple reflections is diffused by the base layer 31 (i.e., diffuse reflection). The FI value is low if the diffuse reflection is strong. Thus, reducing the diffuse reflection by the base layer 31 is important to increase the FI value.

[0060] As illustrated in FIG. 3, the pigments 23 contained in the luster material-containing layer 15 contribute to increasing the FI value by absorbing the scattered light. The multiple reflections increase the optical path length. Due to the increased optical path length, light is more likely to be absorbed by the pigments 23. A greater FI value is obtained as a result. The broken-line arrows show that the pigments 23 reduce the intensity of the scattered light. Further, the scattered light which has reached the colored base layer 14 is absorbed by the colored base layer 14. That means the diffuse reflection is reduced. A greater FI value is obtained as a result.

[0061] A small area occupancy of the luster materials 22 reduces specular reflection of light by the luster materials 22, which affects adversely in increasing the FI value. On the other hand, a large area occupancy of the bight materials 22 increases the number of multiple reflections by the bight materials 22, which results in an increase in the scattered light and affects adversely in increasing the FI value.

[0062] As illustrated in FIG. 4, the FI value is obtained from the equation shown below, wherein L*45 is a lightness index of reflected light (45 reflected light) that is angled 45 degrees from a specular reflection angle toward an angle of incident light, which is incident on a surface of the multilayer coating film 12 at a 45-degree angle from a normal to the surface, L*15 is a lightness index of reflected light (15 reflected light) that is angled 15 degrees from the specular reflection angle toward the angle of incident light, and L*110 is a lightness index of reflected light (110 reflected light) that is angled 110 degrees from the specular reflection angle toward the angle of incident light.

FI=2.69(L*15L*110).sup.1.11/L*45.sup.0.86

[0063] <Bright Material-Containing Layer>

[0064] FIG. 5 illustrates example angle dependence of a Y value according to the XYZ color system, which is calibrated by a standard white plate, of the luster material-containing layer in a state without a colorant. FIG. 6 illustrates how to measure Y values. Light from a light source 41 is incident on the luster material-containing layer 15 at an angle of 45. The receiving angle of a sensor 42 is defined such that the specular reflection angle is 0. A three-dimensional gonio-spectrophotometric color measurement system GCMS-4 from Murakami Color Research Laboratory was used to measure the values. In the example illustrated in FIG. 5, Y(10) is equal to 510 and Y(20) is equal to 200, wherein Y(10) represents a Y value of reflected light measured at a receiving angle of 10 (i.e., an angle toward the light source from the specular reflection angle), and Y(20) represents a Y value of the reflected light measured at a receiving angle of 20.

[0065] According to the present invention, the following expressions are used in order that the coated object has a surface shining effect in a relatively wide area of its surface and significant FF properties: 50Y(10)850 and Y(20)=kY(10), wherein Y(10), k, and a colorant concentration C (% by mass) of the luster material-containing layer satisfy a predetermined condition. Herein, k is a coefficient and satisfies 0.2k0.6. Details will be described below.

[0066] <Determination of Preferable Y(10), Coefficient k, Colorant Concentration C, and Surface Reflectance R>

[0067] The FI value of each multilayer coating film of the samples 1-42 shown in Tables 1-3 was obtained. The multilayer coating film (its base is an electrodeposition coating film) has the luster material-containing layer and the colored base layer. The samples 1-42 are examples of the multilayer coating film that was colored gray. The extender pigment of the colored base layer was barium sulfate. The thickness of each colored base layer was 10 m. After having employed a wet-on-wet method to apply coatings for the colored base layer and the luster material-containing layer, onto a steel product, the layers were stoved (heated at 140 C. for 20 minutes).

TABLE-US-00001 TABLE 1 SAMPLE 1 2 3 4 5 6 7 BRIGHT ACRYLIC RESIN (% by mass) 27.7 27.7 29.1 29.1 27.5 27.5 34.8 MATERIAL CARBON (% by mass) 34 11 29 16 36 9 34 CONTAINING MELAMINE RESIN (% by mass) 10.8 10.8 11.3 11.3 10.7 10.7 13.6 LAYER ALUMINUM (% by mass) 14.8 14.8 12.9 12.9 15.1 15.1 4.9 CHIPPING RESISTANCE AGENT 4.5 3.6 4.3 3.8 4.6 3.5 4.5 (% by mass) ADDITIVE (% by mass) 8.2 32.1 13.4 26.9 6.1 34.2 8.2 ALUMINUM PERTICLE SIZE (m) 10 10 10 10 10 10 10 ALUMINUM THICKNESS (nm) 100 100 100 100 100 100 100 ALUMINUM SURFACE ROUGHNESS 0.09 0.09 0.06 0.06 0.11 0.11 0.02 Ra (m) CARBON SIZE (nm) 100 100 100 100 100 100 100 LAYER THICKNESS (m) 3 3 3 3 3 3 3 Y(10) 109 112 222 218 89 95 695 Y(20) = Y(10) 0.4 44 45 89 87 36 38 278 COLORED ACRYLIC RESIN (% by mass) 65.8 65.8 65.8 65.8 65.8 65.8 65.8 BASE CARBON (% by mass) 4.1 9.1 9.1 9.1 9.1 9.1 9.1 LAYER MELAMINE RESIN (% by mass) 15.4 15.4 15.4 15.4 15.4 15.4 15.4 EXTENDER PIGMENT (% by mass) 5.6 5.6 5.6 5.6 5.6 5.6 5.6 ADDITIVE (% by mass) 9.1 4.1 4.1 4.1 4.1 4.1 4.1 LAYER THICKNESS (m) 10 10 10 10 10 10 10 SURFACE SMOOTHNESS Wd 8 or 8 or 8 or 8 or 8 or 8 or 8 or less less less less less less less SURFACE REFLECTANCE R(%) 28.1 13.6 13.6 13.6 13.6 13.6 13.6 FI 30.8 31.2 36.8 35.7 29.5 29.4 30.5 SAMPLE 8 9 10 11 12 13 14 BRIGHT ACRYLIC RESIN (% by mass) 34.8 33.5 33.5 35.1 35.1 30.1 32.5 MATERIAL CARBON (% by mass) 11 29 16 36 9 22.5 22.5 CONTAINING MELAMINE RESIN (% by mass) 13.6 13 13 13.6 13.6 11.7 12.6 LAYER ALUMINUM (% by mass) 4.9 6.8 6.8 4.6 4.6 11.6 8.1 CHIPPING RESISTANCE AGENT 3.6 4.3 3.8 4.6 3.5 4.1 4.1 (% by mass) ADDITIVE (% by mass) 32.1 13.4 26.9 6.1 34.2 20.1 20.1 ALUMINUM PERTICLE SIZE (m) 10 10 10 10 10 10 10 ALUMINUM THICKNESS (nm) 100 100 100 100 100 100 100 ALUMINUM SURFACE ROUGHNESS 0.02 0.03 0.03 0.01 0.01 0.05 0.04 Ra (m) CARBON SIZE (nm) 100 100 100 100 100 100 100 LAYER THICKNESS (m) 3 3 3 3 3 3 3 Y(10) 691 575 589 701 713 311 503 Y(20) = Y(10) 0.4 277 230 236 280 285 124 201 COLORED ACRYLIC RESIN (% by mass) 65.8 65.8 65.8 65.8 65.8 65.8 65.8 BASE CARBON (% by mass) 9.1 9.1 9.1 9.1 9.1 9.1 9.1 LAYER MELAMINE RESIN (% by mass) 15.4 15.4 15.4 15.4 15.4 15.4 15.4 EXTENDER PIGMENT (% by mass) 5.6 5.6 5.6 5.6 5.6 5.6 5.6 ADDITIVE (% by mass) 4.1 4.1 4.1 4.1 4.1 4.1 4.1 LAYER THICKNESS (m) 10 10 10 10 10 10 10 SURFACE SMOOTHNESS Wd 8 or 8 or 8 or 8 or 8 or 8 or 8 or less less less less less less less SURFACE REFLECTANCE R(%) 13.6 13.6 13.6 13.6 13.6 13.6 13.6 FI 31.8 36.2 36.8 28.5 29.3 40.2 41.1

TABLE-US-00002 TABLE 2 SAMPLE 15 16 17 18 19 20 21 22 BRIGHT ACRYLIC RESIN (% by mass) 27.1 27.1 28.5 28.5 26.9 26.9 34.2 34.2 MATERIAL CARBON (% by mass) 29 6 23 12 31 4 29 6 CONTAINING MELAMINE RESIN (% by mass) 10.5 10.5 11.1 11.1 10.4 10.4 13.3 13.3 LAYER ALUMINUM (% by mass) 15.7 15.7 13.8 13.8 16 16 5.8 5.8 CHIPPING RESISTANCE AGENT 4.3 3.4 4.1 3.7 4.4 3.4 4.3 3.4 (% by mass) ADDITIVE (% by mass) 13.4 37.3 19.6 31 11.3 39.3 13.4 37.3 ALUMINUM PERTICLE SIZE (m) 9 9 9 9 9 9 9 9 ALUMINUM THICKNESS (nm) 90 90 90 90 90 90 90 90 ALUMINUM SURFACE ROUGHNESS 0.09 0.09 0.06 0.06 0.11 0.11 0.02 0.02 Ra (m) CARBON SIZE (nm) 80 80 80 80 80 80 80 80 LAYER THICKNESS (m) 3 3 3 3 3 3 3 3 Y(10) 58 54 172 166 42 45 639 643 Y(20) = Y(10) 0.2 12 11 34 33 8 9 128 129 COLORED ACRYLIC RESIN (% by mass) 65.8 65.8 65.8 65.8 65.8 65.8 65.8 65.8 BASE CARBON (% by mass) 6.5 11 11 11 11 11 11 11 LAYER MELAMINE RESIN (% by mass) 15.4 15.4 15.4 15.4 15.4 15.4 15.4 15.4 EXTENDER PIGMENT (% by mass) 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 ADDITIVE (% by mass) 6.7 2.2 2.2 2.2 2.2 2.2 2.2 2.2 LAYER THICKNESS (m) 10 10 10 10 10 10 10 10 SURFACE SMOOTHNESS Wd 8 or 8 or 8 or 8 or 8 or 8 or 8 or 8 or less less less less less less less less SURFACE REFLECTANCE R(%) 21.3 8.2 8.2 8.2 8.2 8.2 8.2 8.2 FI 31.2 30.5 36 35.4 27.8 28.1 30.6 32 SAMPLE 23 24 25 26 27 28 BRIGHT ACRYLIC RESIN (% by mass) 33 33 34.5 34.5 29.4 31.9 MATERIAL CARBON (% by mass) 23 12 31 4 17.5 17.5 CONTAINING MELAMINE RESIN (% by mass) 12.8 12.8 13.4 1.34 11.4 12.4 LAYER ALUMINUM (% by mass) 7.5 7.5 5.4 5.4 12.4 9 CHIPPING RESISTANCE AGENT 4.1 3.7 4.4 3.4 3.9 3.9 (% by mass) ADDITIVE (% by mass) 19.6 31 11.3 39.3 25.3 25.3 ALUMINUM PERTICLE SIZE (m) 9 9 9 9 9 9 ALUMINUM THICKNESS (nm) 90 90 90 90 90 90 ALUMINUM SURFACE ROUGHNESS 0.03 0.03 0.01 0.01 0.05 0.04 Ra (m) CARBON SIZE (nm) 80 80 80 80 80 80 LAYER THICKNESS (m) 3 3 3 3 3 3 Y(10) 545 534 665 660 252 458 Y(20) = Y(10) 0.2 109 107 133 132 50 92 COLORED ACRYLIC RESIN (% by mass) 65.8 65.8 65.8 65.8 65.8 65.8 BASE CARBON (% by mass) 11 1 11 11 11 11 LAYER MELAMINE RESIN (% by mass) 15.4 15.4 15.4 15.4 15.4 15.4 EXTENDER PIGMENT (% by mass) 5.6 5.6 5.6 5.6 5.6 5.6 ADDITIVE (% by mass) 2.2 2.2 2.2 2.2 2.2 2.2 LAYER THICKNESS (m) 10 10 10 10 10 10 SURFACE SMOOTHNESS Wd 8 or 8 or 8 or 8 or 8 or 8 or less less less less less less SURFACE REFLECTANCE R(%) 8.2 8.2 8.2 8.2 8.2 8.2 FI 36.5 36.1 28.1 28.6 37.2 38.4

TABLE-US-00003 TABLE 3 SAMPLE 29 30 31 32 33 34 35 BRIGHT ACRYLIC RESIN (% by mass) 29.6 29.6 30.9 30.9 29.3 29.3 36.7 MATERIAL CARBON (% by mass) 39 16 33 22 41 14 39 CONTAINING MELAMINE RESIN (% by mass) 11.5 11.5 12 12 11.4 11.4 14.3 LAYER ALUMINUM (% by mass) 12.2 12.2 10.4 10.4 12.6 12.6 2.3 CHIPPING RESISTANCE AGENT 4.7 3.8 4.5 4 4.8 3.7 4.7 (% by mass) ADDITIVE (% by mass) 3 26.9 9.2 20.7 0.9 29 3 ALUMINUM PERTICLE SIZE (m) 12 12 12 12 12 12 12 ALUMINUM THICKNESS (nm) 120 120 120 120 120 120 120 ALUMINUM SURFACE ROUGHNESS 0.09 0.09 0.06 0.06 0.11 0.11 0.02 Ra(m) CARBON SIZE (nm) 150 150 150 150 150 150 150 LAYER THICKNESS (m) 3 3 3 3 3 3 3 Y(10) 262 259 378 370 243 238 840 Y(20) = Y(10) 0.6 157 155 227 222 146 143 504 COLORED ACRYLIC RESIN (% by mass) 65.8 65.8 65.8 65.8 65.8 65.8 65.8 BASE CARBON (% by mass) 1 6.1 6.1 6.1 6.1 6.1 6.1 LAYER MELAMINE RESIN (% by mass) 15.4 15.4 15.4 15.4 15.4 15.4 15.4 EXTENDER PIGMENT (% by mass) 5.6 5.6 5.6 5.6 5.6 5.6 5.6 ADDITIVE (% by mass) 12.2 7.1 7.1 7.1 7.1 7.1 7.1 LAYER THICKNESS (m) 10 10 10 10 10 10 10 SURFACE SMOOTHNESS Wd 8 or 8 or 8 or 8 or 8 or 8 or 8 or less less less less less less less SURFACE REFLECTANCE R(%) 37.1 22.5 22.5 22.5 22.5 22.5 22.5 FI 31.5 30.9 35.5 36.1 28.6 29.1 31.4 SAMPLE 36 37 38 39 40 41 42 BRIGHT ACRYLIC RESIN (% by mass) 36.7 35.3 35.3 36.9 36.9 31.9 34.4 MATERIAL CARBON (% by mass) 16 33 22 41 14 27.5 27.5 CONTAINING MELAMINE RESIN (% by mass) 14.3 13.7 13.7 14.4 14.4 12.4 13.4 LAYER ALUMINUM (% by mass) 2.3 4.2 4.2 2 2 9 5.6 CHIPPING RESISTANCE AGENT 3.8 4.5 4 4.8 3.7 4.2 4.2 (% by mass) ADDITIVE (% by mass) 26.9 9.2 20.7 0.9 29 15 15 ALUMINUM PERTICLE SIZE (m) 12 12 12 12 12 12 12 ALUMINUM THICKNESS (nm) 120 120 120 120 120 120 120 ALUMINUM SURFACE ROUGHNESS 0.02 0.03 0.03 0.01 0.01 0.05 0.04 Ra(m) CARBON SIZE (nm) 150 150 150 150 150 150 150 LAYER THICKNESS (m) 3 3 3 3 3 3 3 Y(10) 838 731 728 855 866 451 653 Y(20) = Y(10) 0.6 503 439 437 513 520 271 392 COLORED ACRYLIC RESIN (% by mass) 65.8 65.8 65.8 65.8 65.8 65.8 65.8 BASE CARBON (% by mass) 6.1 6.1 6.1 6.1 6.1 6.1 6.1 LAYER MELAMINE RESIN (% by mass) 15.4 15.4 15.4 15.4 15.4 15.4 15.4 EXTENDER PIGMENT (% by mass) 5.6 5.6 5.6 5.6 5.6 5.6 5.6 ADDITIVE (% by mass) 7.1 7.1 7.1 7.1 7.1 7.1 7.1 LAYER THICKNESS (m) 10 10 10 10 10 10 10 SURFACE SMOOTHNESS Wd 8 or 8 or 8 or 8 or 8 or 8 or 8 or less less less less less less less SURFACE REFLECTANCE R(%) 22.5 22.5 22.5 22.5 22.5 22.5 22.5 FI 30.2 35.6 35.1 29.3 28.7 37.1 36.8

[0068] Analysis results are shown in FIGS. 7 to 9. In the figures, the plots with circled numbers indicate the sample numbers in Tables 1-3.

[0069] As illustrated in FIG. 7, regarding the luster material-containing layer, if k is 0.4, the FI value is 30 or more when Y(10) and C satisfy 100Y(10)700 and 10C35. The FI value is 35 or more when Y(10) and C satisfy 200Y(10)600 and 15C30. In FIG. 7, the coordinates (x, y, z) given to the vertexes a to h of figures showing suitable ranges (the range in which the FI is 30 or more and the range in which the FI is 35 or more) indicate the coordinates of a three-dimensional orthogonal coordinate space whose x-, y- and z-coordinate axes represent three variables Y(10), k and C, respectively. Regarding this coordinate, the coordinates (x, y, z) given to the vertexes a to h, a to h of the figure showing the preferred range of FIGS. 8 and 9 (the range in which the FI is 30 or more and the range in which the FI is 35 or more) are also the same.

[0070] Similarly, as illustrated in FIG. 8, if k is 0.2, the FI value is 30 or more when Y(10) and C satisfy 50Y(10)650 and 5C30. The FI value is 35 or more when Y(10) and C satisfy 150Y(10)550 and 10C25.

[0071] Similarly, as illustrated in FIG. 9, if k is 0.6, the FI value is 30 or more when Y(10) and C satisfy 250Y(10)850 and 15C40. The FI value is 35 or more when Y(10) and C satisfy 350Y(10)750 and 20C35.

[0072] Next, regarding the surface reflectance R of the colored base layer, with a decrease in the colorant concentration C of the luster material-containing layer, or with a decrease in Y(10), more light reaches the colored base layer. In FIG. 7 where k=0.4, when the luster material-containing layer has a configuration corresponding to the vertex b, the amount of light reaching the colored underlying layer is largest. Based on samples 1 and 2 arranged along the ab line connecting the vertexes a and b of FIG. 7, the surface reflectance R of the colored base layer required to obtain FI=30 will be discussed.

[0073] As shown in Table 1, the surface reflectance R of sample 1 is 28.1%, and the surface reflectance R of sample 2 is 13.6%. Table 4 shows the FI values of the multilayer coating films of samples 1 and 2 in which the surface reflectance R is increased by changing the blending of the coloring base layer with respect to samples 1 and 2. Samples 1 and 2 are respectively the same as samples 1 and 2 except the blending ratio of the colored base layer. In each of samples 1 and 2, the surface reflectance R becomes less than 30 due to the increased surface reflectance R.

TABLE-US-00004 TABLE 4 SAMPLE 1 2 1 2 15 16 15 16 29 30 29 30 COLORED ACRYLIC RESIN (% by mass) 65.8 65.8 65.8 65.8 65.8 65.8 65.8 65.8 65.8 65.8 65.8 65.8 BASE CARBON (% by mass) 4.1 9.1 3.6 8.5 6.5 11 5.3 10.1 1 6.1 0.2 5.6 LAYER MELAMINE RESIN (% by mass) 15.4 15.4 15.4 15.4 15.4 15.4 15.4 15.4 15.4 15.4 15.4 15.4 EXTENDER PIGMENT (% by mass) 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 ADDITIVE (% by mass) 9.1 4.1 9.6 4.7 6.7 2.2 7.9 3.1 12.2 7.1 13 7.6 LAYER THICKNESS (m) 10 10 10 10 10 10 10 10 10 10 10 10 SURFACE SMOOTHNESS Wd 8 or 8 or 8 or 8 or 8 or 8 or 8 or 8 or 8 or 8 or 8 or 8 or less less less less less less less less less less less less SURFACE REFLECTANCE R (%) 28.1 13.6 29.7 15.5 21.3 8.2 24.8 10.9 37.1 22.5 39.4 23.9 FI 30.8 31.2 28.5 28.9 31.2 30.5 28.2 28.4 31.5 30.9 29.2 29.1

[0074] Table 4 shows that the surface reflectance R of the colored base layer affects the FI value of the multilayer coating film.

[0075] If samples 1, 2, 1 and 2 are plotted in the two-dimensional orthogonal coordinate system whose coordinate axes represent two variables, i.e., the colorant concentration C and the surface reflectance R, the plotted result is as shown in FIG. 10. The line Lab in the figure is a critical line of the surface reflectance R of the colored base layer, which is expected to have an FI value of 30 or more in the ab line, which is determined based on the surface reflectance R and the FI value of samples 1, 2, 1 and 2.

[0076] Likewise, regarding the ab line of FIG. 8 where k=0.2 and the ab line of FIG. 9 where k=0.6, samples 15, 16, 15, and 16 and samples 29, 30, 29, and 30 shown in Table 4 and arranged along the lines are plotted in FIG. 10, and critical lines Lab and Lab of the surface reflectance R in which the FI value is expected to be equal to or greater than 30 are determined based on the surface reflectances R and the FI values of the samples.

[0077] According to FIG. 10, the inclination of the critical lines Lab, Lab, and Lab of the surface reflectance R with respect to the colorant concentration C is 0.6. On the other hand, the intercept, which differs among these lines, depends on the difference of Y(10) among these lines. Therefore, if R=0.6C+Y(10)+, and the R value and Y(10) when C=0 are substituted, =0.04 and =2 are obtained.

[0078] Therefore, when the surface reflectance R satisfies the condition represented by the following expression, it is possible to obtain the FI value that is equal to or greater than 30.

R0.6C+0.4Y(10)+4

Here, the critical lines Lab, Lab, and Lab shown in FIG. 10 correspond to the lines ab, ab, and ab in FIGS. 7 to 9. The lines ab, ab, and ab are the Y(10) line with the largest amount of light reaching the colored base layer. When the Y(10) becomes larger than the respective lines of ab, ab and ab, less light reaches, so that the upper limit value of the surface reflectance R that can obtain the FI value of 30 or more is higher than that of each critical line shown in FIG. 10.

[0079] For example, when the Y(10) is 500, the critical line R.sub.500 of the surface reflectance R is as follows: R.sub.500=0.6C+0.04500+4=0.6C+24 When the Y(10) is 500, if the surface reflectance does not exceed the critical line R.sub.500, the FI value of 30 or more is obtained.

[0080] FIG. 11 illustrates a two-dimensional orthogonal coordinate system whose coordinate axes represent two variables, i.e., Y(10) and the coefficient k. The vertexes a to h, a to h, and a to h shown in FIGS. 7 to 9 are plotted to see the relationship between Y(10) and the coefficient k. A suitable range of the coefficient k differs depending on Y(10) as shown in the figure.

[0081] FIG. 12 illustrates a two-dimensional orthogonal coordinate system whose coordinate axes represent two variables, i.e., the coefficient k and the colorant concentration C. The vertexes a to h, a to h, and a to h are plotted to see the relationship between the coefficient k and the colorant concentration C. A suitable range of the colorant concentration C differs depending on the coefficient k as shown in the figure.

[0082] Thus, as illustrated in FIG. 13, ranges of Y(10), the coefficient k, and the colorant concentration C at which the FI value is 30 or more can be expressed by the three-dimensional orthogonal coordinate space whose x-, y-, and z-coordinate axes represent the three variables Y(10), k and C.

[0083] Specifically, the polyhedron shown in FIG. 13 is formed by the vertexes a to d, a to d, and a to d plotted in the three-dimensional orthogonal coordinate space. The polyhedron consists of ten planes A to J in total, each including four vertexes shown in Table 1.

[0084] A plane expressed by the coordinates (x, y, z) of the three-dimensional orthogonal coordinate space can be expressed by the equation x+y+z+=0. The ten planes are expressed by the equations shown in Table 5.

TABLE-US-00005 Table 5 Plane Vertexes Equation for Plane A (a, c, a, c) A: 3000y 120z + 3000 = 0 B (b, d, b, d) B: 3000y 120z = 0 C (c, d, c, d) C: 5x 3750y 2000 = 0 D (a, b, a, b) D: 5x 3750y + 1000 = 0 E (a, c, b, d) E: 15000y 9000 = 0 F (c, d, c, d) F: 5x 1250y 3000 = 0 G (a, b, a, b) G: 5x 1250y = 0 H (a, c, b, d) H: 15000y 3000 = 0 I (a, c, a, c) A: 3000y 120z + 3000 = 0 J (b, d, b, d) B: 3000y 120z = 0

[0085] The planes A and I are expressed by the same equation, which means that these planes are the same plane. The planes B and J are expressed by the same equation, which means that these planes are the same plane. Thus, the polyhedron shown in FIG. 13 can be said to be an octahedron consisting of the eight planes A to H. The C and F planes of this octahedron form an inwardly protruding ridge, and the D and G planes form an outwardly protruding ridge.

[0086] Specifically, the polyhedron shown in FIG. 13 is an octahedron which consists of the eight planes expressed by the equations A to H listed in Table 1, wherein the planes expressed by the equations C and F form an inwardly protruding ridge, and the planes expressed by the equations D and G form an outwardly protruding ridge. The FI value is 30 or more if Y(10), the coefficient k, and the colorant concentration C satisfy that the coordinates (Y(10), k, C) are in the range defined by the octahedron.

[0087] Similarly, as illustrated in FIG. 14, ranges of Y(10), the coefficient k, and the colorant concentration C at which the FI value is 35 or more can be expressed by the three-dimensional orthogonal coordinate space whose x-, y-, and z-coordinate axes represent the three variables Y(10), k and C. Specifically, this polyhedron is formed by the vertexes e to h, e to h, and e to h plotted in the three-dimensional orthogonal coordinate space, and consists of ten planes A to J in total, each including four vertexes shown in Table 2. The ten planes are expressed by the equations shown in Table 6.

TABLE-US-00006 Table 6 Plane Vertexes Equation for Plane A (e, g, e, g) A: 2000y 80z + 1600 = 0 B (f, h, f, h) B: 2000y 80z + 400 = 0 C (g, h, g, h) C: 3x 2250y 900 = 0 D (e, f, e, f) D: 3x 2250y + 300 = 0 E (e, g, f, h) E: 6000y 3600 = 0 F (g, h, g, h) F: 3x 750y 1500 = 0 G (e, f, e, f) G: 3x 750y 300 = 0 H (e, g, f, h) H: 6000y 1200 = 0 I (e, g, e, g) A: 2000y 80z + 1600 = 0 J (f, h, f, h) B: 2000y 80z + 400 = 0

[0088] The planes A and I are expressed by the same equation, which means that these planes are the same plane. The planes B and J are expressed by the same equation, which means that these planes are the same plane. Thus, the polyhedron shown in FIG. 14 can be said to be an octahedron consisting of the eight planes A to H. The C and F planes of this octahedron form an inwardly protruding ridge, and the D and G planes form an outwardly protruding ridge.

[0089] Specifically, the polyhedron shown in FIG. 14 is an octahedron which consists of the eight planes expressed by the equations A to H listed in Table 2, wherein the planes expressed by the equations C and F form an inwardly protruding ridge, and the planes expressed by the equations D and G form an outwardly protruding ridge. The FI value is 35 or more if Y(10), the coefficient k, and the colorant concentration C satisfy that the coordinates (Y(10), k, C) are in the range defined by the octahedron.

[0090] If the Y(10), the coefficient k, and the colorant concentration C are determined such that the FI value is 30 or more, the luster material-containing layer containing a colorant has the Y(10) of about 50 to 200, both inclusive, and the coefficient k(=Y(20)/Y(10) of about 0.1 to 0.4, both inclusive.

DESCRIPTION OF REFERENCE CHARACTERS

11 Automobile Body (Steel Plate)

12 Multilayer Coating Film

13 Electrodeposition Coating Film

14 Colored Base Layer

15 Bright Material-Containing Layer

16 Transparent Clear Layer

21 Pigment (Colorant)

22 Bright Material

23 Pigment (Colorant)