Evaluation of the Jet Fountain Applicator in Blade Coating Systems for LWC Retrogravure, 1999 Coating Conference Proceedings

A.G. Hiorns, L. Coggon, M. Windebank--The roll applicator has for many years been the standard coating blade system when medium and high coat weights are required. In the roll applicator, it is the application of the excess coating film to the paper by a relatively slow moving roll (~15-20% of machine speed) sitting in a pond of coating colour that is responsible for the speed limitation. At higher speeds, the pond becomes unstable and this can result in excessive splashing and uneven film application. The drive for better machine efficiency has initially led to wider paper machines and higher machine speeds. Given that the roll applicator cannot fulfil the role of a high speed coating system, an alternative has been developed.

In the jet fountain coater, a jet of coating colour is projected from a narrow slot onto the base, thus eliminating the coating colour pond altogether. The metering systems used with the jet fountain coater are the same as those available with the roll applicator, i.e. rod or blade.

This new type of coater is being installed on big new machines by several paper companies. An understanding of the parameters which control the runnability of this type of coater and evaluating how the final paper quality compares to that of the more traditional coating systems should allow optimised pigments and formulations to be developed.

This report details the results from initial coating trials on rotogravure papers. A comparison of the paper quality produced by the roll and jet applicators shows that there are some minor differences in base paper coverage which result in the jet applicator giving glossier and brighter coated paper but having an increased roughness and slightly worse printability.

It is possible to optimise the performance of the clays used in LWC rotogravure. Due to their high shape factor, coating colour solids and blade geometry variations can have significant effects of the final paper quality. A range of machine parameters in the jet applicator were varied to see if any further optimisation specific to the jet could be measured. No significant effects on paper quality were found due to these additional parameters.

The potential speed advantage for the jet applicator was demonstrated with runs of up to 2000 m/min with no blade runnability problems.