Modelling Reflectance Spectra for Special Effect Pigment Coatings

摘要

A good calculation model for goniometric reflectance for effect coatings with interference flakes was developed and analysed here. For this purpose, reflectance spectra for coatings were applied with Iriodin 4504 from Merck, a metal lustre coating using interference mica-based pigments coated with iron (III) oxide. The numerical model used for computation incorporates three parts of the light scattering behaviour; scattering from the front surface of the coating, scattering from pigments inside the coating and scattering from the coating substrate. In order to validate the model, reflectance spectra were measured at an incident angle of 45º and at reflected angles of 60º, 30º, 20º, 0º, -20º and -65º using a commercial multi-angle spectrometer. The thickness of the interference coating applied on the flakes was adjusted to obtain good matches of interference features between modelled and measured reflectance. The influence of surface coverage by pigments and the pigment slope distribution on the resulting spectra was analysed. The first parameter represents the fraction of surface area covered with pigments and the second tells us how well the pigments inside the coatings are oriented.