Among the recent trends in the paper coating industry are the increased use of calcium carbonate pigments with a narrow particle size distribution (NPSD) and an increased interest in using synthetic rheology modifiers. Conventional rheology modifiers, designed for optimum water retention in coating colours with conventional pigments, are generally less efficient in holding on to water in coating colours containing high amounts of NPSD calcium carbonate pigments. The objective of this study was to compare various laboratory techniques available to measure water retention in laboratory environment. The purpose was to use coating colours containing different types of co-binders, traditional thickeners and synthetic rheology modifiers (WRRM's). Both static and dynamic water retention methods were examined. Results indicate, for instance, that a rather poor correlation between the various methods exists. While the ultrasonic method showed rather poor reproducibility and trends, the Immobilisation Time method using the immobilisation cell method was acceptable. A better correlation between the static water retention and the dynamic water retention for co-binders that function as thickeners was found, compared to those that function as rheology modifiers. This discrepancy was attributed to the mechanism of how water retention is achieved in the coating, and the measurement technique.
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