A TIME DEPENDENT CHANGE IN COATING VISCOSITY: IMPROVED CONTROL OF VISCOSITY THROUGH SELECTION OF COATING COMPONENTS

摘要

A North American mill observed an irreversible increase in coating viscosity with time in the supply system of theirrnpaper machine coater. Coating viscosity was within target ranges following preparation. However, with time andrnrecirculation, increasing viscosity resulted in pumping pressure exceeding the limits of the equipment, resulting inrncosts associated with lost productivity and waste.rnData from large-scale experiments showed increasing coating viscosity with time and recirculation. Thesernexperiments, however, required production coating quantities and 24 to 72 hours to complete. A small-scalernlaboratory test was developed in which coating viscosity was measured continuously over time at an elevatedrntemperature. Results from this test simulated observations made in production and large scale experiments.rnA designed experiment was conducted using the lab test method to assess the relative contribution of the rawrnmaterials in the coating to the viscosity increases observed in process. Major contributing factors shown torninfluence coating viscosity from the designed experiment were insolubilizer, pigment “fines” fraction andrninsolubilizer/co-binder interactions. Formulation strategies based on these findings were implemented to controlrnviscosity build.