From Theory to Practice- Use of Classical Theory to Design a Pigment with Improved Optical Properties, 1996 Coating Conference Proceedings

For thirty years ground calcium carbonate (GCC) has been used as a coating pigment for paper. The technical and economic advantages of GCC are now well known. These include the ability to coat at higher solids, increased brightness, reduced binder demand, improved coater runnability and excellent printability. The advantage of high brightness coating pigments leads often to reduced opacity. Therefore, in some cases, additive pigments with high scattering coefficients must be used to reach opacity targets. This is also true of hydrous clays, which have scattering coefficients similar to that of GCC. The theories of Kubelka-Munk, Mie and Weber can be used to explain this phenomenon. Pigments with the high brightness, broad particle size distribution and average particle size of the GCC’s presently used to coat glossy papers are not optimum for opacity. We have used light scattering theories to design a GCC pigment which would optimize opacity, but found that in doing so many of the advantages of the present pigments would be reduced. There would be significant negative influence on runnability, binder demand and solids content of the coatings using the “ideal opacifying GCC”. Therefore a compromise was decided upon by which, as much as possible, the present advantages of GCC would be retained in the new...