Platy kaolin can provide significant value in the coating of paper and paperboard. It can be used in multiple applications, and provide benefits such as TiO_2 extension, smoothness improvement, improved print gloss or ink set rates, calendering intensity reduction, and improved barrier properties. It is not a pigment that can be simply substituted for traditional hydrous kaolin without some adjustment to the coating formulation. These adjustments can be as simple as reducing solids but may require binder changes as well. The coater set up may need to be adjusted because of the unique rheological behaviors these pigments exhibit. The rheological characteristics of platy kaolin are explored here. This includes high shear and low shear viscosity, oscillatory measure of viscoelasticity and water retention measurements. An extensive analysis reveals some unique behaviors that need to be understood when utilizing these materials. The degree of shear thinning behaviors is investigated using the Ostwald de-Waele power law. The immobilization point was determined using the Dougherty-Krieger (1-4) equation and related to Weeks' (5) work on blade coater runnability. An indirect measure of particle shape and size synergy is also demonstrated using the Dougherty-Krieger equation parameters.
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