METHOD FOR PREDICTING DRY PAINT COLOR VALUE FROM LIQUID PAINT COLOR VALUE

Abstract

The present invention relates to a method for predicting a dry paint color value from a liquid paint color value, and, when producing a second liquid film having the same component as a first liquid film, a process for producing a second dry film by drying and curing the second liquid film can be skipped, and a reflection rate of the second dry film can be predicted according to the prediction method according to the present invention.

Claims

1. A method for predicting a dry paint color value from a liquid paint color value, comprising the steps of: (a) preparing 1.sup.st to n.sup.th first liquid coating films having the same components; (b) measuring liquid reflectance .sub.1stR.sub.wet for each of the 1.sup.st to n.sup.th first liquid coating films at wavelength r; (c) drying and curing each of the 1.sup.st to n.sup.th first liquid coating films to prepare 1.sup.st to n.sup.th first dry coating films; (d) measuring dry reflectance .sub.1stR.sub.Dry for each of the 1.sup.st to n.sup.th first dry coating films at wavelength r; (e) obtaining a weight value (Weight) and a bias value (Bias) for the first liquid coating films at wavelength r by the following equation: $\left[\begin{array}{c}{\mathrm{Weight}}_r\\ {\mathrm{Bias}}_r\end{array}\right]={\left({\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]\right)}^{-1}.Math.{\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{c}{}_{1\mathrm{st}}{R}_{{\mathrm{Dry}}_1}\\ .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{Dry}}_n}\end{array}\right],$ wherein, when $R=\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right],$ R.sup.T is a transposed matrix of matrix R, and R.sup.1 is an inverse matrix of matrix R; (f) preparing a second liquid coating film having the same components as the first liquid coating films; (g) measuring liquid reflectance .sub.2ndR.sub.wet for the second liquid coating film at wavelength r; and (h) applying the weight value (Weight) and the bias value (Bias) in step (e) and applying the .sub.2ndR.sub.wet in step (g) to the following equation: ${}_{2\mathrm{nd}}{R}_{{\mathrm{Dry}}_r}={\mathrm{Weight}}_r{}_{2\mathrm{nd}}{R}_{{\mathrm{wet}}_1}+{\mathrm{Bias}}_r,$ to obtain dry reflectance .sub.2ndR.sub.Dry for the second dry coating film at wavelength r.

2. The method for predicting a dry paint color value from a liquid paint color value according to claim 1, wherein step (a) comprises preparing each of 1.sup.st to n.sup.th first liquid paints with the same components, wherein n is an integer of 2 or more; and applying the 1.sup.st to n.sup.th first liquid paints to an object to be coated to prepare each of the 1.sup.st to n.sup.th first liquid coating films.

3. The method for predicting a dry paint color value from a liquid paint color value according to claim 2, wherein step (f) comprises preparing a second liquid paint having the same components as the first liquid paints; and applying the second liquid paint to an object to be coated to prepare the second liquid coating film.

4. The method for predicting a dry paint color value from a liquid paint color value according to claim 1, wherein the method further comprises (i) obtaining predicted values of CIE L*, a* and b* of the second dry coating film from the dry reflectance .sub.2ndR.sub.Dry of step (h).

5. The method for predicting a dry paint color value from a liquid paint color value according to claim 4, wherein a color difference (E*) between the predicted values of CIE L*, a* and b* of the second dry coating film obtained from the dry reflectance .sub.2ndR.sub.Dry and the measured values of CIE L*, a* and b* of the second dry coating film is 0.5 or less.

Description

MODE FOR INVENTION

[0012] Hereinafter, the present invention will be described in detail with reference to the following examples.

[0013] Korean Patent No. 10-2191784 (hereinafter referred to as Patent Document 1) discloses an electrodeposition coating system equipped with a liquid paint inspection kit, and also discloses a color measuring device configured to measure the color of a liquid paint through a viewing window. However, Patent Document 1 merely discloses the measurement of the color of a liquid paint, without teaching or suggesting the prediction of the color of a dry paint from the measurement.

[0014] The present invention provides a method for predicting a dry paint color value from a liquid paint color value.

[0015] According to the present invention, a first liquid coating film and a first dry coating film dried and cured therefrom are prepared. The reflectance at wavelength r is measured for the prepared first liquid coating film and first dry coating film. The measured reflectances of the first liquid coating film and first dry coating film are applied to the equation according to the present invention to obtain a weight value (Weight) and a bias value (Bias) applied to the relationship between the reflectance of the liquid coating film and the reflectance of the dry coating film.

[0016] Thereafter, a second liquid coating film having the same components as the first liquid coating film is prepared, and the weight value (Weight) and bias value (Bias) obtained by applying the reflectances of the first liquid coating film and the first dry coating film may be used to predict the reflectance of the second dry coating film.

[0017] Therefore, according to the method for predicting a dry paint color value from a liquid paint color value according to the present invention, when producing a second liquid paint coating film having the same components as the first liquid paint coating film, the process of drying and curing the second liquid paint coating film to prepare a second dry paint coating film can be omitted, and the reflectance of the second dry coating film can be predicted according to the prediction method according to the present invention.

[0018] The method for predicting a dry paint color value from a liquid paint color value according to the present invention may comprise the steps of (a) preparing 1.sup.st to n.sup.th first liquid coating films having the same components; (b) measuring liquid reflectance .sub.1stR.sub.wet for each of the 1.sup.st to n.sup.th first liquid coating films at wavelength r; (c) drying and curing each of the 1.sup.st to n.sup.th first liquid coating films to prepare 1.sup.st to n.sup.th first dry coating films; (d) measuring dry reflectance .sub.1stR.sub.Dry for each of the 1.sup.st to n.sup.th first dry coating films at wavelength r; (e) obtaining a weight value (Weight) and a bias value (Bias) for the first liquid coating films at wavelength r by the following equation:

[00003]$\left[\begin{array}{c}{\mathrm{Weight}}_r\\ {\mathrm{Bias}}_r\end{array}\right]={\left({\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]\right)}^{-1}.Math.{\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{c}{}_{1\mathrm{st}}{R}_{{\mathrm{Dry}}_1}\\ .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{Dry}}_n}\end{array}\right],$

wherein, when

[00004]$R=\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right],$

R.sup.T is a transposed matrix of matrix R, and R.sup.1 is an inverse matrix of matrix R; (f) preparing a second liquid coating film having the same components as the first liquid coating films; (g) measuring liquid reflectance .sub.2ndR.sub.wet for the second liquid coating film at wavelength r; and (h) applying the weight value (Weight) and the bias value (Bias) in step (e) and applying the .sub.2ndR.sub.wet in step (g) to the following equation: .sub.2ndR.sub.Dry.sub.r=Weight.sub.r.sub.2ndR.sub.wet.sub.r+Bias.sub.r, to obtain dry reflectance .sub.2ndR.sub.Dry for the second dry coating film at wavelength r.

[0019] In the present invention, the relationship between the liquid coating film and dry coating film dried and cured therefrom at wavelength r (nm) may be expressed by the following equation 1:

[00005]$\begin{array}{cc}{R}_{{\mathrm{Dry}}_r}={\mathrm{Weight}}_r{R}_{{\mathrm{Wet}}_r}+{\mathrm{Bias}}_r,& \left[\mathrm{Equation}1\right]\end{array}$ [0020] wherein [0021] R.sub.Dry.sub.r is the reflectance (%) of a dry film at wavelength r (nm), [0022] R.sub.Wet.sub.r is the reflectance (%) of a liquid film at wavelength r (nm), [0023] Weight.sub.r is the weight value, and [0024] Bias.sub.r is the bias value.

[0025] Therefore, liquid coating films having the same components may be prepared n times, and each of these liquid coating films may be dried and cured to prepare dry coating films, and the relationship between the liquid coating films and dry coating films may be expressed by the following equation 2:

[00006]$\begin{array}{cc}{R}_{{\mathrm{Dry}}_{n,r}}={\mathrm{Weight}}_r{R}_{{\mathrm{Wet}}_{n,r}}+{\mathrm{Bias}}_r,& \left[\mathrm{Equation}2\right]\end{array}$ [0026] wherein [0027] R.sub.Dry.sub.n,x is the reflectance (%) of the nth prepared dry coating film at wavelength r (nm), [0028] R.sub.wet.sub.n,r is the reflectance (%) of the nth prepared liquid coating film at wavelength r (nm), [0029] Weight.sub.r is the weight value, and [0030] Bias.sub.r is the bias value.

[0031] Equation 2 may be expressed as a determinant for each of the 1.sup.st to n.sup.th liquid coating films and dry coating films prepared by using the same components, as the following equation 3:

[00007]$\begin{array}{cc}\left[\begin{array}{c}{R}_{{\mathrm{wet}}_{1,r}}\\ .Math.\\ R_{{\mathrm{wet}}_{n,r}}\end{array}\right]=\left[\begin{array}{cc}{R}_{{\mathrm{wet}}_{1,r}}& 1\\ .Math.& .Math.\\ R_{{\mathrm{wet}}_{n,r}}& 1\end{array}\right]\left[\begin{array}{c}{\mathrm{Weight}}_r\\ {\mathrm{Bias}}_r\end{array}\right],& \left[\mathrm{Equation}3\right]\end{array}$ [0032] wherein [0033] R.sub.Dry.sub.i,r is the reflectance (%) of the 1st prepared dry coating film at wavelength r (nm), [0034] R.sub.Dry.sub.n,r is the reflectance (%) of the nth prepared dry coating film at wavelength r (nm), [0035] R.sub.wet.sub.i,r is the reflectance (%) of the 1st prepared liquid coating film at wavelength r (nm), [0036] R.sub.wet.sub.n,r is the reflectance (%) of the nth prepared liquid coating film at wavelength r (nm), [0037] Weight.sub.r is the weight value, and [0038] Bias.sub.r is the bias value.

[0039] By applying the least square method to Equation 3, Weight.sub.r and Bias.sub.r at wavelength r (nm) may be obtained from the following equation 4:

[00008]$\begin{array}{cc}\left[\begin{array}{c}{\mathrm{Weight}}_r\\ {\mathrm{Bias}}_r\end{array}\right]={\left({\left[\begin{array}{cc}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ R_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{cc}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ R_{{\mathrm{wet}}_n}& 1\end{array}\right]\right)}^{-1}.Math.{\left[\begin{array}{cc}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ R_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{c}{R}_{{\mathrm{Dry}}_1}\\ .Math.\\ R_{{\mathrm{Dry}}_n}\end{array}\right],& \left[\mathrm{Equation}4\right]\end{array}$$\mathrm{wherein}$$\mathrm{when}R=\left[\begin{array}{cc}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ R_{{\mathrm{wet}}_n}& 1\end{array}\right],$ [0040] RT is the transposed matrix of matrix R, and [0041] R1 is the inverse matrix of matrix R.

[0042] Accordingly, the reflectance may be measured at wavelength r (nm) for each of the 1st to nth first liquid coating films prepared by using the same components and the first dry coating films prepared therefrom, and the measured reflectance may be applied to Equation 4 to obtain a weight value (Weight) and a bias value (Bias) at wavelength r (nm).

[0043] Thereafter, second liquid coating film having the same components as the first liquid coating films may be prepared, the reflectance at wavelength r (nm) of the second liquid coating film may be measured, and the measured reflectance may be applied to Equation 2 to obtain the reflectance of the second dry coating film.

[0044] Meanwhile, the color values CIE L*, a* and b* of the second dry coating film may be obtained from the reflectance of the second dry coating film obtained from Equation 2.

[0045] A method for obtaining color values CIE L*, a* and b* from reflectance is known in the art, and is disclosed, for example, in Recipe Prediction of Colorant Proportion for Target Color Reproduction, J. of the Korean Oil Chemists' Soc., Vol. 25, No. 4, December, 2008. 438-445 (Non-patent Document 1).

[0046] For example, in the XYZ colorimetric system, the tristimulus value XYZ of the color of an object due to reflection may be obtained, for example, at a wavelength of from 380 nm to 780 nm, by using the following equations:

[00009]$\begin{array}{c}X=K{}_{380}^{780}S\left(\right)\stackrel{\_}{x}\left(\right)R\left(\right)d\\ Y=K{}_{380}^{780}S\left(\right)\stackrel{\_}{y}\left(\right)R\left(\right)d\\ Z=K{}_{380}^{780}S\left(\right)\stackrel{\_}{z}\left(\right)R\left(\right)d\\ K=\frac{100}{{}_{380}^{780}S\left(\right)\stackrel{\_}{y}\left(\right)R\left(\right)d}\end{array},$ [0047] wherein [0048] S() is the spectral distribution of the standard illuminant used to represent color, x(), y(), z() are the color matching functions in the XYZ colorimetric system, and R() is the spectral incidence angle reflectance.

[0049] Meanwhile, the CIE L*, a* and b* colorimetric systems may be obtained by using the tristimulus value XYZ, for example, as follows:

[00010]$\begin{array}{c}{L}^{*}=116{\left(Y//Y_n\right)}^{1/2}-16\\ a^{*}=500\left[{\left(X/X_n\right)}^{1/3}-{\left(Y/Y_n\right)}^{1/3}\right]Y/Y_n>0.008856\\ b^{*}=200\left[{\left(Y/Y_n\right)}^{1/3}-{\left(Z/Z_n\right)}^{1/3}\right]\\ L^{*}=903.29\left(Y/Y_n\right)\\ a^{*}=5007.787[X/X_n)-\left(Y/Y_n\right)]Y/Y_{n}0.008856\\ b^{*}=2007.787\left[\left(X/Y_n\right)-\left(Z/Z_n\right)\right]\end{array},$ [0050] wherein [0051] Xn, Yn and Zn are the tristimulus values of standard light.

[0052] Hereinafter, examples of the present invention will be described.

EXAMPLES

Example 1: Product Name FU2300-LGREY

[0053] For the product name FU2300-LGREY, 1.sup.st to 10.sup.th first liquid coating films were prepared. Specifically, 1.sup.st to 10.sup.th first liquid paints were prepared by using the same components applied to the preparation of the product name FU2300-LGREY Each of the prepared 1.sup.st to 10.sup.th first liquid paints was applied to a covering paper at a thickness of 25 m to prepare 1.sup.st to 10.sup.th first liquid coating films. For each of the prepared first liquid coating films, colorimetry was performed by using a non-contact colorimeter X RITE VS450 or VS3200 at 10 nm intervals at a wavelength of 400 nm to 700 nm within 1 minute, and the reflectance was measured at 10 nm intervals at a wavelength of 400 nm to 700 nm for each of the first liquid coating films.

[0054] Meanwhile, a thinner (TH0254(N)) was added to each of the prepared 1.sup.st to 10.sup.th first liquid paints to adjust the viscosity according to a coating viscosity (coating viscosity: 25 C., Ford Cup No. 4, 26 to 28 seconds). Thereafter, each of the first liquid paints was applied to an electrodeposited CR steel plate with 90200 mm by using an air sprayer 2 to 3 times in a reciprocating motion with a thickness of 353 m, left at room temperature (10 to 30 C.) for 5 to 10 minutes, followed by curing at 150 C. for 30 minutes. Thereafter, the reflectance was measured by using a colorimeter X RITE 17 or C17800 at 10 nm intervals at a wavelength of 400 nm to 700 nm for each of the first dry coating films.

[0055] From the measured reflectance of the first liquid paints and first dry paints, weight values (Weight) and bias values (Bias) were obtained at 10 nm intervals in a wavelength range of 400 nm to 700 nm.

Examples 2 to 5

[0056] The process of Example 1 was performed for each of the product names FU2300-WHITE PEARL BASE(D) (Example 2), FU2300-DGREY (Example 3), FU2300-Shimmering Silver (Example 4), and FU2300-Nocturne Gray (Example 5), to obtain the weight values (Weight) and bias values (Bias) at each wavelength.

[0057] The weight values (Weight) and bias values (Bias) at each wavelength are shown in Tables 1 to 3 below:

TABLE-US-00001 TABLE 1 Product Model name coefficient 400 410 420 430 440 450 460 470 480 490 FU2300- Bias 3.504 1.522 0.571 0.541 0.743 0.475 0.221 0.025 0.014 0.184 LGREY Weight 0.114 0.064 0.061 0.045 0.074 0.070 0.073 0.076 0.079 0.085 FU2300- Bias 5.103 1.179 3.455 3.232 3.385 4.127 5.158 6.122 0.136 8.511 WHITE Weight 0.206 0.067 0.044 0.051 0.051 0.042 0.033 0.023 0.114 0.006 PEARL BASE(D) FU2300- Bias 4.731 4.654 4.528 4.610 4.639 4.572 4.535 4.514 4.521 4.447 DGREY Weight 0.133 0.141 0.145 0.174 0.191 0.192 0.202 0.209 0.220 0.219 FU2300- Bias 4.279 4.276 4.057 4.081 4.110 4.085 4.034 4.048 4.078 4.085 Shimmering Weight 0.040 0.055 0.059 0.076 0.090 0.097 0.108 0.119 0.131 0.147 Silver FU2300- Bias 4.531 4.442 4.459 4.432 4.343 4.412 4.418 4.483 4.506 4.486 Nocturne Weight 0.009 0.003 0.038 0.050 0.030 0.076 0.098 0.139 0.163 0.178 Gray

TABLE-US-00002 TABLE 2 Product Model name coefficient 500 510 520 530 540 550 560 570 580 590 FU2300- Bias 0.385 0.387 0.580 0.524 0.562 0.426 0.627 0.639 0.725 1.080 LGREY Weight 0.090 0.092 0.087 0.089 0.089 0.093 0.090 0.090 0.093 0.087 FU2300- Bias 8.489 8.945 9.418 10.254 10.477 10.455 11.220 10.949 10.707 10.110 WHITE Weight 0.016 0.007 0.002 0.009 0.012 0.010 0.019 0.015 0.009 0.001 PEARL BASE (D) FU2300- Bias 4.479 4.478 4.504 4.486 4.477 4.497 4.491 4.480 4.512 4.449 DGREY Weight 0.237 0.244 0.253 0.253 0.255 0.265 0.270 0.271 0.281 0.271 FU2300- Bias 4.194 4.146 4.091 4.141 4.007 4.105 4.147 4.036 3.981 3.759 Shimmering Weight 0.166 0.170 0.170 0.179 0.172 0.183 0.192 0.184 0.181 0.167 Silver FU2300- Bias 4.455 4.522 4.498 4.462 4.485 4.469 4.437 4.432 4.419 4.448 Nocturne Weight 0.176 0.218 0.213 0.205 0.221 0.231 0.212 0.214 0.219 0.233 Gray

TABLE-US-00003 TABLE 3 Product Model name coefficient 600 610 620 630 640 650 660 670 680 690 700 FU2300- Bias 1.346 1.337 1.217 1.300 1.389 0.239 0.489 1.144 1.115 1.447 1.461 LGREY Weight 0.083 0.085 0.088 0.087 0.087 0.113 0.104 0.087 0.092 0.092 0.099 FU2300- Bias 10.281 10.098 9.500 9.590 9.608 9.730 9.132 8.648 8.340 8.485 8.566 WHITE Weight 0.002 0.001 0.009 0.009 0.011 0.010 0.019 0.021 0.027 0.030 0.035 PEARL BASE(D) FU2300- Bias 4.421 4.495 4.471 4.452 4.418 4.420 4.394 4.421 4.392 4.358 4.376 DGREY Weight 0.267 0.284 0.283 0.282 0.278 0.279 0.283 0.289 0.289 0.290 0.310 FU2300- Bias 3.714 3.775 3.736 3.746 3.677 3.652 3.727 3.708 3.683 3.638 3.677 Shimmering Weight 0.163 0.169 0.168 0.170 0.166 0.166 0.175 0.177 0.180 0.181 0.191 Silver FU2300- Bias 4.433 4.406 4.392 4.372 4.428 4.360 4.326 4.318 4.228 4.194 4.290 Nocturne Weight 0.233 0.217 0.220 0.220 0.255 0.231 0.212 0.204 0.168 0.152 0.203 Gray

Test Example: Comparison of Errors in Prepared Coating Films

[0058] The predicted and measured values of L*, a* and b* of Examples 1 to 5 are compared, and the error values are shown in Table 4 below:

TABLE-US-00004 TABLE 4 Error Product name Category L* a* b* E* L* a* b* FU2300-LGREY Predicted 73.12 1.99 4.57 0.31 0 0.12 0.29 value Measured 73.12 2.11 4.28 value FU2300-WHITE Predicted 84.54 1.77 2.86 0.39 0.22 0.25 0.2 PEARL BASE(D) value Measured 84.32 1.52 3.06 value FU2300-DGREY Predicted 34.31 0.12 3.29 0.21 0.16 0.11 0.09 value Measured 34.15 0.01 3.2 value FU2300-Shimmering Predicted 44.33 0.75 1.12 0.26 0.1 0.06 0.23 Silver value Measured 44.23 0.81 0.89 value FU2300-Nocturne Predicted 30.18 0.44 2.21 0.08 0.04 0.06 0.03 Gray value Measured 30.14 0.5 2.18 value

[0059] As shown in Table 4, according to the method for predicting a dry paint color value from a liquid paint color value according to the present invention, the range of the color difference between the predicted values and the measured values of CIE L*, a* and b* of the second dry coating films may be 0.5 or less, or 0.4 or less. That is, the color difference (E*) between the predicted values of CIE L*, a* and b* of the second dry coating films obtained from the dry reflectance .sub.2ndR.sub.Dry and the measured values of CIE L*, a* and b* of the second dry coating films prepared by drying and curing may be 0.5 or less, or 0.4 or less.

[0060] Hereinafter, various embodiments of the present invention will be described in detail.

[0061] (1) A method for predicting a dry paint color value from a liquid paint color value, comprising the steps of: (a) preparing 1.sup.st to n.sup.th first liquid coating films having the same components; (b) measuring liquid reflectance .sub.1stR.sub.wet for each of the 1.sup.st to n.sup.th first liquid coating films at wavelength r; (c) drying and curing each of the 1.sup.st to n.sup.th first liquid coating films to prepare 1.sup.st to n.sup.th first dry coating films; (d) measuring dry reflectance .sub.1stR.sub.Dry for each of the 1.sup.st to n.sup.th first dry coating films at wavelength r; (e) obtaining a weight value (Weight) and a bias value (Bias) for the first liquid coating films at wavelength r by the following equation:

[00011]$\left[\begin{array}{c}{\mathrm{Weight}}_r\\ {\mathrm{Bias}}_r\end{array}\right]={\left({\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]\right)}^{-1}.Math.{\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right]}^T.Math.\left[\begin{array}{c}{}_{1\mathrm{st}}{R}_{{\mathrm{Dry}}_1}\\ .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{Dry}}_n}\end{array}\right],$

wherein, when

[00012]$R=\left[\begin{array}{cc}{}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_1}& 1\\ .Math.& .Math.\\ {}_{1\mathrm{st}}{R}_{{\mathrm{wet}}_n}& 1\end{array}\right],$

R.sup.T is a transposed matrix of matrix R, and R.sup.1 is an inverse matrix of matrix R; (f) preparing a second liquid coating film having the same components as the first liquid coating films; (g) measuring liquid reflectance .sub.2ndR.sub.wet for the second liquid coating film at wavelength r; and (h) applying the weight value (Weight) and the bias value (Bias) in step (e) and applying the .sub.2ndR.sub.wet in step (g) to the following equation: .sub.2ndR.sub.Dry.sub.r=Weight.sub.r.sub.2ndR.sub.wet.sub.r+Bias.sub.r, to obtain dry reflectance .sub.2ndR.sub.Dry for the second dry coating film at wavelength r.

[0062] (2) The method for predicting a dry paint color value from a liquid paint color value, wherein step (a) comprises: preparing each of 1.sup.st to n.sup.th first liquid paints with the same components, wherein n is an integer of 2 or more; and applying the 1.sup.st to n.sup.th first liquid paints to an object to be coated to prepare each of the 1.sup.st to n.sup.th first liquid coating films.

[0063] (3) The method for predicting a dry paint color value from a liquid paint color value, wherein step (f) comprises: preparing a second liquid paint having the same components as the first liquid paints; and applying the second liquid paint to an object to be coated to prepare the second liquid coating film.

[0064] (4) The method for predicting a dry paint color value from a liquid paint color value, wherein the method further comprises (i) obtaining predicted values of CIE L*, a* and b* of the second dry coating film from the dry reflectance .sub.2ndR.sub.Dry of step (h).

[0065] (5) The method for predicting a dry paint color value from a liquid paint color value, wherein a color difference (E*) between the predicted values of CIE L*, a* and b* of the second dry coating film obtained from the dry reflectance .sub.2ndR.sub.Dry and the measured values of CIE L*, a* and b* of the second dry coating film is 0.5 or less.