Important Drying Parameters for the Layout of a New Production, 1998 Coating Conference Proceedings

A long list of publications referring to the drying concept indicate the complexity of this step in the production of coated paper. The fact that different producers with different drying philosophies finally meet the same quality target, underlines what is stated above.

Since triple coating of freesheet is a relatively new approach to premium grades, even in Europe, we considered our in-depth studies regarding the layout of the drying strategy for the latest European production line for coated freesheet worthy of publication.

Experiences, when single blade coatings have been "upgraded" to double blade coatings, showed that with any additional step in the coating process the drying concept and the coating formulation design become more important as far as the final paper quality is concerned. With an increased number of coatings applied, the liquid movement predominantly in vertical direction takes place within smaller distances due to an improved coating holdout. As a consequence we found a smaller operating window at lower surface temperature.

With inadequate drying strategy surface temperatures in the last coating step below 65°C were observed, which led to insufficient synthetic binder curing and paper quality deterioration. In-going paper moisture and film forming temperature of the synthetic binder were identified as the main factors to influence paper properties such as sheet gloss, print gloss, pick resistance and mottle.