Consolidation of particulate suspension - model study with plastic pigments

The microscopic mechanisms and parameters controlling consolidation and leveling of particulate suspension coatings on paper were studied.  A simplified model system consisting of a model suspension of plastic pigment and impermeable substrates with well defined topog. was used.  The suspension contains spherical carboxylated polystyrene plastic pigment in water and the substrates were a photocopier transparency and an ink jet printer transparency.  A math. model based on a dynamic simulation technique was used to clarify the mechanisms influencing leveling of suspensions.  High initial solids content resulted in smooth surfaces, high opacity, and high light scattering efficiency of the coated samples.  The compression of electrostatic potential through addn. of electrolyte resulted in high packing d. of the coating layer.  The leveling movement of the particulate suspension was limited by build-​up of a dense layer of particles at the coating-​air interface, and by flocculation of the suspension.  The difference in immobilization and initial solids content controlled the final surface roughness of the coatings.