Influences of pigments on runnability and qualify of LWC offset paper

Originally developed to replace the size press in high-speed applications, the filmpress has made a valuable contribution to modern trends towards pigmentizing at low application weights and on-line coating of paper and paperboard. On the other hand, the filmpress obviously has its limitations in terms of application weight film splitting, orange peel effect or misting and dusting. These phenomena turn out negative particularly in highspeed operation. Targeted development work will be needed to eliminate these problems. Apart from well-known influential factors, such as basepaper properties, viscoelasticity of the coating colour, solids content, type of doctor, rubber hardness etc. the pigments selected play a decisive role. This presentation outlines the implications of pigment combinations with native calcium carbonate and clays having different shape factors for an LWC offset grade at varied speeds. To this end, pilot coating tests were conducted at speeds of 750, 1000 and 7500 m/min for subsequent evaluation. The findings will help to identify the preferential pigment combinations giving optimum runnability, optical properties and printability.