The Influence of the Measuring/Viewing Angle on the Color of Injection-Molded Plastics

Abstract

A multi-angle spectrophotometer was used to measure the CIELab coordinates L∗, a∗ and b∗ in different angles relative to the incident light. The specimens used were acrylonitrile-butadiene-styrene injection-molded plaques in different colors and with different surface textures. Variations in the coordinates when changing the measuring angle depended on the color and the texture. In general, however, smooth (glossy) surfaces were measured to be darker and of higher chroma than textured surfaces and as the gloss of the surfaces decreased (due to texturing), the lightness of the surfaces increased and the absolute values of a∗ and b∗ decreased over the range of measuring angles (not too close to the specular reflection angle). A psychometric study involving a human test panel was used as a complement to the measurement. The agreement between the measurements and this study cannot be said to be satisfactory, unless the variation in the color coordinates was quite clear. Possible reasons are discussed.

Keywords:

• color measurement
• color perception
• gloss
• polymer
• surface texture
• viewing angle

The authors thank all the observers who generously agreed to collaborate in the psychometric evaluation. The Swedish Agency for Innovation Systems (Vinnova), Volvo Car Corporation and Chalmers University of Technology are gratefully acknowledged for the financial support of the project.

Notes

Note: The plaques Bl1 and Bl2 do not have exactly the same color. Note that the plaques always contained an area with a smooth texture (not stated explicitly in the table).