Modelling reflectance factor for special pigment coatings

Abstract

A numerical model to calculate goniometric refectance factor for effect coatings with interference flakes was developed and analysed here. The model incorporates three parts of the light scattering events; from the front surface of the coating, from pigments inside the coating, and from the coating substrate. In order to validate the model, refectance spectra were measured at an incident angle of 45º and at refected angles of −60º, −30º, −20º, 0º, 30º and 65º using a commercial multi-angle spectrometer. Metal lustre coating was used for testing the model. It contains Iriodin 4504 pigment, an interference mica-based pigment coated with iron (III) oxide from Merck. This coating includes all spectral characteristics involved in the model. The thickness of the interference layer on the pigments was adjusted to obtain good matches of interference features between modelled and measured refectance factor. The infuence of surface coverage by pigments and of the pigment orientation distribution on the resulting spectra was analysed. The first parameter represents the fraction of surface area covered with pigments and the second how well the pigments inside the coatings are oriented.