Scattering in paper coatings

Paper coatings are porous structures of pigments, binder and air. This research aims at developing a model for the prediction of the bulk optical properties of coating from its structure and material characteristics. Two theoretical approaches have been studied and compared. In both cases the coating is treated as a structured layer consisting of individual scatterers in a medium, and the pores are regarded as scatters. In the first approach they are assumed to be independent. The second approach takes into account that due to their close position the pores are in fact correlated scatterers. The approximation used limits the consideration to pair correlation only. Comparison of the theories to reflectance measurements on polystyrene pigment coatings have uniform pore sizes in the range from 0.13 to 0.95 micrometers showed that for pore size parameters less than 5 the dependent scattering model provides a good prediction for the reflectance, but for larger pore size parameters the reflection behavior approaches that predicted by the independent scattering theory.