Influence of Coating Compostion on Web Release In High Speed Film-Transfer Coating, 1996 Coating Conference Proceedings

In this study, the initial aim was to establish a base for further studies of the one-sided film-transfer coating process. This was done by determining the impact of rather simple coating color compositions, without any further coating color or coated paper optimization, on the runnability for both the paper web and the applied coating film at high machine speeds (1200 - 2000 m/min). Under the prevailing process conditions, the process was monitored by measuring the amount of premetered coating applied on the film transfer roll, the amount of coating transferred to the paper web and the point of web release at different machine speeds. The film transfer to the paper web was studied by applying different amounts of coating film on the roll before entering the pressure nip. Release of the paper web, or film splitting area, was studied by measuring the distance between the nip outlet and the point of web release. As the point of web release was changed, the release angle also changed in the same proportion. Our study was performed at a constant web tension at the pressure nip outlet. This allowed us to study the impact of process variations caused by changing coating color compositions. In this study we characterized and compared coating colors with different pigment packing abilities (Clay and CaCO3 ). This was done to reveal their influence on pressure dewatering and immobilization, thereby causing variations in the release point of the paper web from the film transfer roll. Within the studied pigment systems, the dewatering speed has been changed by adding different levels (0, 0.3 and 0.7 pph) of a water soluble polymer (CMC). The effect of coating color solids content has also been revealed in respect to web release.