Influence of Base Paper Filler Content and Pre-calendering on Metered Film Press Coating - Part 1: A Coating Process Study, 1998 Metered Size Press Forum II Proceedings

In this paper, the influence of base sheet filler content (10, 15 and 20 %) and pre-calendering on a metered film press (MFP) process runnability and coating layer formation were studied at high machine speeds (1200 - 2000 m/mm). A dynamic water penetration device was used to evaluate the difference in water absorption between different base paper filler contents. The measurements showed a higher water penetration for base paper with a higher tiller content especially at higher application pressures. Coating color transfer to the base paper showed that a paper with a higher filler content demanded less premetered coating film to achieve the desired coated paper properties at a coat weight of 8.0 g/m’/side. The lower premetered film thickness can be explained by a higher water penetration into the base paper, although less solid phase color penetrated into the paper. A lower solid phase penetration kept the coating on the surface and prevented it from striking into the base paper, which resulted in a better fiber coverage. Pre-calendering of the base paper also gives a denser paper surface and keeps the color more effectively on the paper surface, especially at the highest filler content of 20 %. By preventing severe color penetration, the variation in coat weight distribution was reduced with a more even surface as a result. Thereby, the coated paper surface smoothness was also improved as a result of a more uniform coating layer. It was also found that at a coat weight of 8.0 g/m 2 /side and 1800 m/min, there was no runnability problems such as color mist.