Method for matching a colour formulation

• US 5,929,998 A
• Filed: 08/21/1997
• Issued: 07/27/1999
• Est. Priority Date: 09/10/1996
• Status: Expired due to Term

• Current Assignee: Axalta Coating Systems Ip Co Llc (Axalta Coating Systems Ltd.)
• Original Assignee: Herbert GmbH
• Inventors: Tacke, Albert, Kettler, Wilhelm, Kolb, Matthias
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US08/915,781
• Time in Patent Office: 705 Days
• Field of Search: 356/402, 356/405, 356/406, 356/425
• US Class Current: 356/405
• CPC Class Codes: G01J 3/46 Measurement of colour; Colour measuring devices, e.g. colorimeters measuring colour temperature G01J5/60
• CPC Class Codes: G01J 3/463 Colour matching
• CPC Class Codes: G01J 3/465 taking into account the colour perception of the eye; using tristimulus detection
• CPC Class Codes: G01J 3/504 Goniometric colour measurements, for example measurements of metallic or flake based paints

Abstract

This invention relates to a method for matching a color formulation to a color shade model in the field of a color- and/or effect-imparting surface coating. The reflecting surface of a color shade, which is to be rematched, of a colored surface coating is determined metrologically over the visible spectral region using a goniometric spectral photometer with variation of the angle of measurement. The associated standard tristimulus values and/or the vectors in the CIELAB color solid which are derived therefrom are calculated from the measured reflection factors or spectral energy factors. Those formulations and/or color shades which exhibit reflection properties or properties derived therefrom which are the most similar to the measured color shade model are subsequently identified from a formulation database by means of the reflection spectra or the calorimetric dimensional numbers derived therefrom. By means of a computer-generated effect matrix, the metrologically determined, angle-dependent color difference between the desired color shade, i.e. the color shade to be rematched, and the actual color shade, i.e. the color shade corresponding to the nearest formulation from the formulation database, is minimized by means of a computer algorithm for function minimization taking into consideration secondary conditions in the sense of the L₂ standard, and a corrected formulation is produced.

Claims

1. A method for matching a colour shade formulation to a colour shade model in the field of a colour- and/or effect-imparting surface coating, comprising

i) determining metrologically one or more reflectance spectra of a reflectance surface of a colour shade of a coloured surface coating wherein the reflectance spectra are determined over a required spectral region using a goniometric spectral photometer with variation of the angle of measurement,

ii) calculating a set of associated standard tristimulus values and/or vectors in the CIELAB colour solid from the reflectance spectra,

iii) identifying those colour shade formulations from a formulation database, which exhibit reflection properties or reflection derived properties which are the most similar to the reflectance spectra of the measured colour shade,

iv) minimizing, with the aid of a computer-generated colour effect matrix, the metrologically determined, angle-dependent colour difference between the desired colour shade to be rematched, and the actual colour shade corresponding to the nearest formulation from the formulation database, wherein a computer algorithm for function minimisation, taking into consideration secondary conditions based upon an L₂ norm, is used with the colour effect matrix to produce a corrected formulation, and wherein the colour effect matrix is established by

a) experimentally determining, by means of a calibration table and using a goniometric spectral photometer, the reflection surfaces for each pigment which forms the basis of the formulations from the formulation database at a plurality of angles within the required spectral region,

b) determining the optical material parameter for each pigment forming the basis of the formulations from the formulation database by adapting a radiation transfer equation to the experimentally determined reflection surfaces, and

c) determining by a computer using the radiation transfer equation, the colour effect matrix, which describes the angular dependency of the colouristic effect in the reflection solid or the colour solid when the pigment concentrations are varied, for the entire formulation content of the formulation database, and storage of the colour effect matrix in the database.

2. A method according to claim 1, wherein a lacquer and/or a surface coating is produced corresponding to the corrected formulation as a reference model and the method according to claim 1 is repeated using the reference model as the actual colour shade.

3. A method according to claim 2, wherein the method is reiterated repeatedly, and the reference model of the method operation is used each time as the actual colour shade of the following method operation.