Investigation of Film Transfer in Metered Size Presses as Related to Base Paper and Coating Color Properties, 1998 Metered Size Press Forum II Proceedings

The maximum coat weight and paper quality achievable with the film coating technique is limited by the film splitting effect and misting of color occurring at high speeds. It is common knowledge that color dewatering during dwell time plays an important role in the film splitting process. In this paper, the influence of the absorption potential of the base paper was investigated with typical coating colors and two different speed levels. The film transfer rate was measured as a function of dwell time, base paper absorption potential and pigment type.

The filtration model for the color transfer was proved by the results obtained with different dwell times and color pigments, which have a slow and a fast dewatering behaviour (Clay and Calcium Carbonate). It was also found that the base paper absorption potential, determined with the dynamic penetration measurement (EMCO-method) has a significant influence on the film transfer rate in metered size presses. There is a maximum and a minimum amount of wet film thickness, which can be transferred under stable conditions. Based on these limits, a film coating application diagram was developed, which allows to chose the optimum color solids content for any coat weight to be applied. Experience from running machines proves the reliability of the application diagram.