New Laboratory Test to Characterize the Immobilization and the Dewatering of Paper Coating Colors, 1998 Coating Conference Proceedings

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A novel laboratory test to characterize the immobilization and water retention of paper coating colors is presented. A modified commercial rheometer is used to characterize the immobilization kinetics by measuring the transient viscosity during dewatering. Additionally, a fiberoptical reflection NIR spectroscopy device is integrated into the rheometer gap to determine the loss of water in a thin layer at the paper/coating color interface. With this technique the dewatering of coating colors is characterized under conditions closer to the manufacturing process than with previously used laboratory tests. A thin coating color layer is used, a shear stress as well as a pressure gradient is applied and the color dewaters directly into the basepaper. Examples are presented where the runnability and the loss of water of the coating colors during processing are predicted better with the new technique than with other laboratory tests. The instrument is easy to handle and can be adapted to many commercial rotational rheometers, as far as the immobilization measurements are concerned. Therefore, it can be used for the optimization of coating color formulations and quality control purposes. The optional optical part is more sophisticated and is recommended for fundamental studies on dewatering mechanisms and processes at the current stage of development.