New laboratory test to characterize immobilization and dewatering of papercoating colors

A novel laboratory test characterizes the immobilization and water retentio n of paper coating colors. A modified commercial rheometer measures the tra nsient viscosity during dewatering. A fiber optical reflection near infrare d spectroscopy device integrated into the rheometer gap determines the loss of water in a thin layer at the paper to coating color interface. With thi s technique, the characterization of dewatering of coating colors uses cond itions closer to the manufacturing process than previously used laboratory tests. Using a thin coating color layer and a shear stress and pressure gra dient, the color dewaters directly into the base paper. Examples show predi ction of runnability, and the loss of water of coating colors during proces sing are better with the new technique than with other laboratory tests. Th e instrument has easy handling and can adapt to many commercial rotational rheometers for the immobilization measurements. It is therefore useful for optimization of coating color formulations and quality control.