Dewatering of coating dispersions - Model experiments and analysis

The dewatering of coating colours is an important phenomenon that to a larg e extent governs the runnability of industrial coaters. In this work, the d ewatering behaviour of model coating dispersions was investigated under sta tic conditions in the laboratory. Using monodisperse spherical polystyrene particles at a 48% solids content initially: filtration experiments were pe rformed at a constant pressure of 50 kPa. The filtration process M ns monit ored non-invasively using a dynamic magnetic resonance imaging (MRI) techni que based upon a multi-shot spiral readout. it was demonstrated that there is a concentration gradient of particles in the formed filter cake, which i s nor accounted for in the traditional filtration theory used in coating te chnology The concentration of particles was highest at the filter membrane and was found to decrease almost linearly towards the top of the filter cak e. Good agreement was found between a literature model describing filtratio n with a compressible filter cake and the concentration gradients measured by MRI.