Optimisation of steep carbonate coating formulations with ultra fine platy kaolin

摘要

Maintaining high paper gloss without compromising light scattering potential in steep particle-size-distribution carbonate coating recipes is non-trivial. While the use of fine blocky kaolin is accepted practice for gloss generation with standard carbonates, there is doubt over its compatibility with steeper pigment blends. This is because the enhanced light scattering potential of such coating systems is a result of large, clearly defined pores. As these become larger, there is a chance that the fine kaolin will partially fill them, thereby reducing the system's light scattering potential. Additionally, the partial filling of these pores would further increase the ink setting rate of the system. It is proposed that the use of ultra fine, but platy, kaolin may overcome these shortcomings. This assumes that the aspect ratio of the kaolin plates can be engineered to be sufficiently fine to aid gloss development, but concurrently have a large enough plate diameter to stop it from filling the voids created by the steep partner carbonate. The performance of coatings formulated with such a kaolin, a new product development, is reported here for the first time and is contrasted against that obtained from a fine blocky kaolin.