OPTIMIZING SOLIDS AND RHEOLOGY IN BLADE COATING USING PIGMENT BLENDS, PaperCon 2010 Conference

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The paper industry has long known the potential advantages of running the highest coating solids possible from both a quality and economic standpoint. The limiting factor has always been blade runnability and coat weight control. The excellent rheology of calcium carbonate (GCC) has traditionally been used to increase the maximum solids level, but even with high levels of this material, the coating solids becomes quite demanding when very/ultra fine types are used to produce glossy grades.

Work has been done using lab and pilot coater trials to evaluate the influence of pigment shape, size and particle size distribution on the upper solids limit of a coating formulation. The major impact of pigment packing once all other components in the formulation are optimized is theoretically characterized.

A numerical model has been developed to describe and better visualize the influence of GCC particle size on the maximum volume fraction of the dispersed pigments. A simple but effective concept of blending a suitable coarse GCC fraction into the matrix of the fine host pigment is described and practical results presented.