Investigation on topology of platelet-like effect-pigments in automotive surface-coatings

To investigate the interrelation between the orientation of platelet-like effect pigments in surface coatings and their coloristic properties, two metallic basecoat systems (Al, Al-blue mixture) have been deliberately blended with a colorless organic extender (nearly spherical), that allows for a systematic disturbance of the alignment of the pigment particles. As methods of investigation, goniospectrophotometry, confocal Laser-scanning microscopy, and microscopic image analysis of basecoat cross-cuts have been employed. From the reflection-indicatrix, the variation of colorimetrical quantities with deorientation agent content have been derived in a direct way. Moreover, the phase-function of the Al-pigments has been determined from fitting the equation of radiative transfer to the experimental reflection surfaces. The phase-function provides information about the distribution function sf polar angles of the pigment particles in 3-dimensional space. The distribution function of the orientation angle alpha of Al-pigments in cross-cuts of basecoats as obtained from microscopic image analysis can be satisfactorily explained within a simulation model, that allows for a calculation of the distribution function for a when assuming the individual distribution functions for polar- and azimuthal-angle of the surface normal of the pigment particles, taking fully into account induced axes of anisotropy. (C) 1997 Elsevier Science S.A.