Effect of Particle Shape and Latex Particle Size Distributions on Dewatering and Filter Cake Permeability

摘要

Excess dewatering of the coating is one of the most cited sources for runnability problems during the coating process. As the water penetrates the base sheet of the paper, the solids content of the coating increases. As this occurs, the solids fraction begins to climb towards the immobilization solids concentration. Once that concentration of particles is reached or very close to it, flow will cease and the possibilities for defects and runnability issues will amplify. Particle shape, size distribution and packing ability will affect the water retention properties of the coating. The influence of particle shape and latex particle size distribution was analyzed using a gravimetric water retention device. Two latexes, one with a monomodal particle size and the other with a mixture of particle sizes was used along with two pigments with varying particle shape. The permeability coefficient of the filtercake was determined using a combination of the filtration of suspensions equations and Darcy's Law. The effect of the coating formulation variables was evident in the amount of water removed from the samples during testing. The more spherical morphology of the pigment; the greater amount of dewatering occurred. The inclusion of a latex with a mixture of particle sizes increased the water holding capacity of the coating. The permeability constant was affected by the particle size distribution.