Romain Castellani

Abnormal Behaviors in the Capillary Rheometry of Plastisol Formulations

Abstract The rheology of plastisol formulations for flooring applications using knife-over-roll coating process is studied using both Couette and capillary rheometers. The behavior is similar in many aspects to the rheology of suspensions: Shear thinning behavior at low shear rate, then a Newtonian plateau at intermediate shear rates followed by a dilatancy peak. However several abnormal phenomena may be observed in capillary experiments. At very high shear rates, a second shear thinning behavior is observed which depends on the flow geometry. Due to the non-monotonous behavior of the plastisol viscosity, this is analysed using a dedicated numerical method. An apparent slip velocity has been determined. Otherwise capillary experiments point out the existence of important entrance pressure loss. These measures are interpreted using a modified Cogswell method as an important elongationnal viscosity, around hundred times the shear viscosity.

Modelling of the Plastisol Knife Over Roll Coating Process

Abstract The knife-over-roll coating process of plastisol formulations for flooring applications has been investigated. The coexistence of smooth spherical PVC particles and rough calcium carbonate aggregates in a Newtonian plasticizer makes this suspension a more complex system than those encountered in the literature. The shear viscosity has been measured with Couette and capillary devices in the wide range of shear rates encountered in the process, resulting in a non-monotonous viscosity curve. A numerical model based on the lubrication approximation theory allows accounting for this non-monotonous behavior. It predicts the deposited thickness, the pressure field between roll and knife and the separating force as a function of the plastisol rheology and the coating parameters.