Measuring flake orientation for metallic coatings

Metallic and pearlescent coatings, very popular in automotive applications, contain flake shaped pigments. The orientation distribution of these flakes inside the effect coatings determines to a large extend the color and visual appearance of the coating. Unfortunately the measurement of flake orientation distributions is far from straightforward. The two main current techniques use analysis with light microscopy on cross cuts, and confocal microscopy. We used both techniques on a large set of samples. A set of 117 metallic coatings were analyzed, where we varied the concentration of metallic pigment, the concentration of so-called disorienting agent and the type and size of metallic pigment. Trends that for a long time have been assumed to be true were now unambiguously proven true, and can now be stated in a quantitative manner. For example, large flakes generally show better orientation than small flakes. For waterborne cornflake pigments, we measured an orientation width of 19.4 for flakes with a median diameter of 16 mu m, and only 7.2 for flakes with a median diameter of 35 mu m. Surprisingly we found only a small effect on flake orientation when disorienting agent was added to a color formula. (C) 2008 Elsevier B.V. All rights reserved.