PROCESS AND APPARATUS FOR PRODUCING COLORED CHEMICAL COATINGS

• US 3,601,589 A
• Filed: 09/19/1969
• Issued: 08/24/1971
• Est. Priority Date: 09/19/1969
• Status: Expired due to Term

• Current Assignee: William H. Mccarty
• Original Assignee: William H. Mccarty
• Inventors: McCarty, William H.
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Wise, Edward J.
• Application Number:
  US04/859,474
• Time in Patent Office: 704 Days
• Field of Search: 356/175 235/150
• US Class Current: 382/165
• CPC Class Codes: G01J 3/46 Measurement of colour; Colour measuring devices, e.g. colorimeters measuring colour temperature G01J5/60
• CPC Class Codes: G01J 3/462 Computing operations in or between colour spaces; Colour management systems
• CPC Class Codes: G01J 3/463 Colour matching
• CPC Class Codes: G01J 3/465 taking into account the colour perception of the eye; using tristimulus detection
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77

Abstract

A computer-aided color formulation process is provided wherein a color standard is matched by a blend of pigments from a library of pigments. Reflectance values of the standard color at a plurality of reflectance points are supplied to a computer programmed to select pigments from the library and to approximate concentrations of the selected pigments to give a match to the reflectance data of the standard. The computer is also programmed to generate the pigment composition from a group of those selected to match the color of the standard, and to determine the metameric index of the match. The color of a blend of library pigments prepared in response to the concentration values generated by the computer is measured by a colorimeter under daylight to insure that the difference in color coordinates between the blend and the standard is within tolerance. If the color coordinate difference is not within tolerance, the process provides for determining the amount of selected pigment addition necessary to shade the blend to provide a color coordinate difference within tolerance. The blend is then measured by the colorimeter under incandescent light to insure that the metameric index is within tolerance.

Claims

1. A process of selecting pigments from a pigment library having a standard pigment to color match a surface coating, wherein said library pigments are nonflakelike pigments which scatter light diffusely, comprising the steps of:

generating signals representative of the reflectance spectrum of the surface coating; and

controlling an automatic processing system in response to a stored program to perform the steps comprising;

a. generating signals representative of absorption constants (K) and scattering constants (S) of N library pigments, N>

1, b. in response to said reflectance spectrum signals and said absorption and scattering constant signals, generating signals representative of N-1 concentration ratios between N-1 nonstandard library pigments and the standard library pigment in accordance with;

where R'"'"''"'"' the corrected reflectance of the surface coating at a given wavelength, K1,S1 the absorption and scatter constants of the standard library pigment at a given wavelength, Ki,Si the absorption and scatter constants of the ith pigment in the library, at a given wavelength, N the number of pigments to be considered from the library, and Ci/C1 the concentration ratio of the ith pigment to the standard pigment, c. and generating, in response to the N-1 concentration ratio signals, signals representative of library pigments selected for use in matching the color of the surface coating.

2. The process of claim 1 wherein said stored program controls the automatic processing system to perform the additional step of:

refining the concentration ratio signals obtained in step (b) by nonlinear least square solution procedures based on the total differential of the dependent variable prior to performing step (c).

3. The process of claim 1 wherein the concentrations Ci and C1 are weight fractions and wherein step (c) comprises the steps of:

d. generating a signal representative of the weight fraction of the standard library pigment in accordance with; and

e. generating signals representative of the weight fractions of the nonstandard library pigments considered from the library in accordance with;

Ci (Ci/C1) (CL), i 2...N, where Ci weight fraction of the ith library pigment, C1 weight fraction of the standard library pigment, N the number of pigments considered from the library, and Ci/C1 the concentration ratio of the ith pigment to the standard library pigment.

4. The process of claim 3 wherein said stored program controls of the automatic processing system to perform the further steps of:

f. generating a signal representative of a predetermined weight fraction value, g. comparing the nonstandard weight fraction sIgnals with the predetermined weight fraction signal, and h. eliminating from further processing the compared weight fraction signals having a value less than the predetermined weight fraction signal.

5. The process of claim 4 wherein said stored program controls the automatic processing system to perform the further steps of:

i. repeating steps (a), (b) and (d) through (h) after eliminating from further processing the absorption and scattering constants of the nonstandard pigments having a weight fraction value less than the predetermined weight fraction value as determined in step (g) to thereby reduce n by the number of nonstandard pigments eliminated, and j. repeating step (i) until each of the remaining nonstandard pigments has a weight fraction signal with a value at least as great as the predetermined weight fraction signal.

6. The process of claim 1 wherein said reflectance spectrum signal generating step comprises generating signals representative of reflectance values of the surface coating at a plurality of wavelengths to provide the reflectance spectrum of the surface coating.

7. The process of claim 6, wherein the automatic processing system comprises storage means, and wherein said reflectance spectrum signal generating step comprises:

measuring the reflectance values of the surface coating by a spectrophotometer, and entering the reflectance values in the storage means to provide a source for generating said reflectance value signals.

8. The process of claim 1 wherein said reflectance spectrum signal generating step comprises generating signals representative of reflectance values of the surface coating at a plurality of wavelengths between 400 and 700 millimicrons to provide the reflectance spectrum of the surface coating.

9. The process of claim 8 wherein said reflectance wavelengths are at 10 millimicrons to provide 31 reflectance values.

10. The process of claim 1 wherein the automatic processing system comprises storage means, and wherein the standard library pigment absorption constant and scattering constant signals generated in step (a) are initially generated by the steps comprising:

d. measuring the reflectance at a plurality of wavelengths (1) of each of a plurality of panels each having the standard library pigment as a chemical coating at a different level of incomplete hiding, (2) of a panel having the standard library pigment as a chemical coating at a level of complete hiding, and (3) of the substrates;

e. storing signals representative of the measured reflectances in said storage means;

f. storing signals representative of the weight of the standard library pigment per unit area on each of the panels in said storage means; and

g. controlling said automatic processing system in response to another stored program to perform the steps comprising;

h. in response to the signals stored in steps (e) and (f), generating a signal representative of a scattering constant of the standard library pigment in accordance with;

where S scattering constant, R'"'"''"'"' the corrected reflectance at complete hiding at a given wavelength, R'"'"''"'"''"'"''"'"' the corrected reflectance at incomplete hiding at a given wavelength, Rg'"'"''"'"' the reflectance of the substrate at a given wavelength, and X the weight of the standard pigment per unit area, i. repeating step (h) at each wavelength at which the reflectance is measured in step (d), j. averaging the generated scattering constant signals in each substrate set to generate signals representative of the scattering constant of the standard library pigment at each wavelength averaged over all reflectance spectra at incomplete hiding, k. in response to the signals generated in steps (e) and (j), generating signals representative of absorption constants of the standard library pigment in Accordance with;

K S(1-R'"'"''"'"')2/2R'"'"''"'"' where K absorption constant of the standard pigment, S scattering constant of the standard pigment, and R'"'"''"'"' the corrected reflectance at complete hiding at a given wavelength, and (l) entering the standard library pigment scattering constants signals generated in step (j), and the standard library pigment absorption constants signals generated in step (k) in said storage means.

11. The process of claim 10 wherein the nonstandard library pigment absorption constant and scattering constant signals generated in step (a) are initially generated by the steps comprising:

m. measuring the reflectance at a plurality of wavelengths of each of a plurality of panels each having a chemical coating of a different concentration of a plurality of nonstandard library pigments and the standard library pigments;

n. entering signals representative of the reflectances measured in step (m) and of the concentration of the library pigments used in step (m) in said storage means; and

o. controlling said automatic processing system in response to still another stored program to perform the steps comprising;

p. in response to the scattering constant signals entered in said storage means in step (l) and the signals entered in said storage means in step (n), generating signals representative of estimates of the absorption and scattering constants of the nonstandard library pigments at each wavelength in accordance with;

where R'"'"''"'"' the corrected reflectance of the surface coating at a given wavelength, S1 the scattering constant of the standard library pigment at a given wavelength, Ki,Si the absorption and scatter constants of the ith pigment in the library, at a given wavelength, N the number of pigments to be considered from the library, Ci the concentration of the ith pigment, and C1 the concentration of the standard library pigment, q. in response to the estimated scattering and absorption constant signals, generating improved nonstandard pigment scattering and absorption constant signals at each wavelength by nonlinear least square solution procedures based on the total differential of the dependent variable, and r. entering the improved nonstandard pigment scattering and absorption constant signals generated in step (q) in said storage means.

12. The process of claim 10 wherein the nonstandard library pigment absorption constant and scattering constant signals generated in step (a) are initially generated by the steps comprising:

m. measuring the reflectance at a plurality of wavelengths of each of a plurality of panels each having a chemical coating of a different concentration of a plurality of nonstandard library pigments and the standard library pigment;

n. entering signals representative of the reflectances measured in step (m) and of the concentrations of the library pigments used in step (m) in said storage means; and

o. controlling said automatic processing system in response to still another stored program to perform the steps comprising;

p. in response to the scattering and absorption constant signals entered in said storage means in step (l) and the signals entered in said storage means in step (n), generating signals representative of estimates of the absorption and scattering constants of the nonstandard library pigments at each wavelength in accordance with;

where R'"'"''"'"' the corrected reflectance of the surface coating at a given wavelength, K1,S1 the absorption and scatter constants of the standard library pigment at a given wavelength, Ki,Si the absorPtion and scatter constants of the ith pigment in the library, at a given wavelength, N the number of pigments to be considered from the library, Ci the concentration of the ith pigment, and C1 the concentration of the standard library pigment, q. in response to the estimated scattering and absorption constant signals, generating improved nonstandard pigment scattering and absorption constant signals at each wavelength by nonlinear least square solution procedures based on the total differential of the dependent variable, and r. entering the improved nonstandard pigment scattering and absorption constant signals generated in step (q) in said storage means.

13. The process of claim 1 further comprising the steps of:

d. selecting a subset of the library pigments selected in step (c); and

e. controlling said automatic processing system in response to another program to perform the steps comprising;

f. repeating step (a) for the selected subset of library pigments to generate signals representative of an initial estimate of a composition of the subset to spectrally match the surface coating, g. in response to the subset composition signals generated in step (f), generating improved subset composition signals by nonlinear least square solution procedures, and h. generating a signal representative of the metameric index of the improved subset composition signals.

14. The process of claim 13 further comprising the steps of:

i. comparing the metameric index signal to a reference to determine whether the metameric index is within tolerance, j. when the metameric index is outside tolerance, repeat steps (d) through (i) with different subsets of the library pigments selected in step (c) until the generated metameric index signal is within tolerance.

15. The process of claim 14 further comprising the steps of:

k. when the metameric index signal is within tolerance, preparing a chemical coating composition in response to the improved subset composition signals, and l. determining the color coordinate difference between the surface coating and the prepared chemical coating composition.

16. The process of claim 15 further comprising the step of:

m. shading the prepared chemical coating composition with additional amounts of the subset of pigments when the color coordinate difference measured in step (l) is out of tolerance.

17. The process of claim 15 further comprising the step of:

m. measuring the metameric index of the prepared chemical coating composition.

18. The process of claim 17 further comprising the steps of:

n. repeating steps (d) through (m) with a different subset of the library pigments until the measured metameric index of the prepared chemical coating is within tolerance.

19. A system for selecting pigments from a pigment library having nonflakelike pigments which scatter light diffusely including a standard pigment to color match a colored surface coating comprising:

storage means for storing signals representative of the reflectance spectrum of the surface coating, and for storing signals representative of absorption constants (K) and scattering constants (S) of N library pigments, N>

1; and

processing means, programmed to operate on said reflectance spectrum signals and on said absorption constant and scattering constant signals in said storage means, for generating signals representative of N-1 concentration ratios between N-1 nonstandard library pigments and the standard library pigment in accordance with;

where R'"'"''"'"' the corrected reflectance of the surface coating at a given wavelength, K1,S1 the absorption and scatter constants of the standard library pigment at a given wavelength, Ki,Si the absorption and scatter constants Of the ith pigment in the library, at a given wavelength, N the number of pigments to be considered from the library, and Ci/C1 the concentration ratio of the ith pigment to the standard pigment, said processing means being further programmed to operate on the N-1 concentration ratio signals for generating signals representative of library pigments selected for use in matching the color of the surface coating.

20. The system of claim 19 wherein the concentrations Ci and C1 are weight fractions and wherein said processing means is programmed to operate on the N-1 concentration ratio signals by:

generating a signal representative of the weight fraction of the standard library pigment in accordance with; and

generating signals representative of the weight fractions of the nonstandard library pigments considered from the library in accordance with;

Ci (Ci/C1) (CL), i 2...N, where Ci weight fraction of the ith library pigment, C1 weight fraction of the standard library pigment, N the number of pigments considered from the library, and Ci/C1 the concentration ratio of the ith library pigment to the standard library pigment.

21. The system of claim 20 wherein said processing system is further programmed for generating a signal representative of a predetermined weight fraction value, for comparing the nonstandard weight fraction signals with the predetermined weight fraction signal, and for eliminating from further processing the compared weight fraction signals having a value less than the predetermined weight fraction signal.

22. The system of claim 19 further comprising:

means for measuring the reflectance at a plurality of wavelengths (1) of each of a plurality of panels each having a standard library pigment chemical coating at a different level of incomplete hiding, (2) of a panel having the standard chemical coating at a level of complete hiding, and (3) of the substrates;

means for storing signals representative of the measured reflectances, and for storing signals representative of the weight of the standard library pigment per unit area on each of the panels; and

said processing means being further programmed to;

a. operate on said measured reflectance signals and on said weight signals for generating signals representative of scattering constants of the standard library pigment in accordance with;

where S scattering constant, R'"'"''"'"' the corrected reflectance at complete hiding at a given wavelength, R'"'"''"'"''"'"''"'"' the corrected reflectance at incomplete hiding at a given wavelength, Rg'"'"''"'"' the reflectance of the substrate at a given wavelength, and X the weight of the standard pigment per unit area, b. average the generated scattering constant signals in each substrate set to thereby generate signals representative of the scattering constant at each wavelength averaged over all reflectance spectra at incomplete hiding, and c. operate on said measured reflectance signals and on said averaged scattering constant signals for generating signals representative of absorption constants of the standard library pigment in accordance with;

K S(1-R'"'"''"'"')2/2R'"'"''"'"' where K absorption constant of the standard pigment, S scattering constant of the standard pigment, and R'"'"''"'"' the corrected reflectance at complete hiding at a given wavelength.

23. The system of claim 22 further including:

means for storing signals representative of the rEflectance at a plurality of wavelengths of each of a plurality of panels each having a chemical coating of a different concentration of a plurality of nonstandard library pigments and the standard library pigment, and of the concentrations of the library pigments; and

said processing means being further programmed to;

d. operate on said signals representative of the reflectance at a plurality of wavelengths of each of a plurality of panels each having a chemical coating of a different concentration of a plurality of nonstandard library pigments and the standard library pigment, on said signals representative of the concentrations of the library pigments, and on said signals representative of averaged scattering constants for generating signals representative of estimates of the absorption and scattering constants of the nonstandard library pigments at each wavelength in accordance with;

where R'"'"''"'"' the corrected reflectance of the surface coating at a given wavelength, S1 the scattering constant of the standard library pigment at a given wavelength, Ki,Si the absorption and scatter constants of the ith pigment in the library, at a given wavelength, N the number of pigments to be considered from the library, Ci the concentration of the ith pigment, and C1 the concentration of the standard library pigment, and e. operate on the estimated scattering and absorption constant signals for generating improved nonstandard pigment scattering and absorption constant signals at each wavelength by nonlinear least square solution procedures, based on the total differential of the dependent variable.

24. The system of claim 22 further including:

means for storing signals representative of the reflectance at a plurality of wavelengths of each of a plurality of panels each having a chemical coating of a different concentration of a plurality of nonstandard library pigments and the standard library pigment, and of the concentrations of the library pigments; and

said processing means being further programmed to;

d. operate on said signals generated by (b) and (c), on said signals representative of the reflectance at a plurality of wavelengths of each of a plurality of panels each having a chemical coating of a different concentration of a plurality of nonstandard library pigments and the standard library pigment, and on signals representative of the concentrations of the library pigments for generating signals representative of estimates of the absorption and scattering constants of the nonstandard library pigments at each wavelength in accordance with;

where R'"'"''"'"' the corrected reflectance of the surface coating at a given wavelength, K1,S1 the absorption and scatter constants of the standard library pigment at a given wavelength, Ki,Si the absorption and scatter constants of the ith pigment in the library, at a given wavelength, N the number of pigments to be considered from the library, Ci the concentration of the ith pigment, and C1 the concentration of the standard library pigment, and e. operate on the estimated scattering and absorption constant signals for generating improved nonstandard pigment scattering and absorption constant signals at each wavelength by nonlinear least square solution procedures based on the total differential of the dependent variable.

25. A process of selecting pigments from a pigment library to color match a colored surface coating, wherein said library consists of nonflakelike pigments which scatter light diffusely, comprising the steps of:

generating signals representative of the reflectance spectrum of the sUrface coating; and

controlling an automatic processing system in response to a stored program to perform the steps comprising;

a. generating signals representative of absorption constants (K) and scattering constants (S) of N library pigments, N>

1, b. in response to said reflectance spectrum signals and said absorption and scattering constant signals, generating signals representative of N-1 concentration ratios between N-1 nonstandard library pigments and the standard library pigment in accordance with a form of the following equation which is linear in the concentration ratio;

where R'"'"''"'"' the corrected reflectance of the surface coating at a given wavelength, Ki,Si the absorption and scatter constants of the ith pigment in the library at a given wavelength, N the number of pigments to be considered from the library, and Ci the concentration of the ith pigment, c. and generating, in response to the N-1 concentration ratio signals, signals representative of library pigments selected for use in matching the color of the surface coating.