EFFECT OF COATING COLOR CHEMISTRY AND TEMPERATURE ON RUNNABILITY AND COATED PAPER PROPERTIES

The ionic nature of the components in coating colours is of great impo rtance for the presence or absence of interparticle interactions, whic h in turn largely govern suspension rheology, machine runnability and final paper properties such as coating coverage or coating bulk. The a im of this study was to generate different types of association betwee n coating colour components by using anionic or cationized starch, whi ch show clear differences in interaction with anionic clay pigment. An other objective was to evaluate the influence of temperature on the co ating colour properties with correlation to results from pilot-scale c oating trials. It was found that the anionic starch caused a stabiliza tion effect originating from the repulsive forces created between the starch and the anionic clay pigment. This colloidally stable system ca used no problems in levelling of the suspension on the paper but resul ted in a relatively dense coating layer Starch with substituted cation ic groups showed a strong electrostatic interaction with the clay pigm ent resulting in an aggregated suspension system and deteriorated runn ability. This was reflected in the final coating layer as blade streak s due to build-up of coating deposits on the blade during levelling. H owever the aggregated suspension system resulted in a bulky coating st ructure covering the paper surface.