Modelling reflectance factor for special effect pigment coatings

A numerical model to calculate goniometric reflectance 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, reflectance spectra were measured at an incident angle of 45 and at reflected angles of 60', 30, 20, 0, 30 and 65 using a commercial multi -angle spectrotneter..Metal lustre coating was used for testing die model. It contains Iriodin 4504 pigment, an interference mica-based pigment coated with iron (III) oxide (ruin Merck. This coating includes all spectral characteristics involved in the model. The thickness of the interference layer on the pigments WA S 'adjusted to obtain good matches of interference features between modelled and measured reflectance factor. The influence 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.