Advanced Coating Technology Experience, 1999 Coating Conference Proceedings

Dr. Peter Fisera

Sappi Fine Paper Europe

Dr. Bob Vyse, Salim Ladak & Jahan Ghofraniha

Honeywell-Measurex Devron Inc.

Advanced Coating Technology (ACT) is a new on-line system that integrates measurement and modelling to predict the location of the gel point, which is used as a quantitative representation of print quality in the coating process. As part of ACT, a machine direction (MD) drying model has been developed recently as a co-operative project by Honeywell-Measurex and Sappi, Gratkorn. This model was installed at the Sappi, Gratkorn mill on two coating machines producing woodfree coated (WFC) paper and measuring respectively 6.4 m and 8.5 m wide. An overview of the modelling scheme and initial results from the mill installation are presented.

The MD drying model is based on energy and mass balances, with emphasis on the modelling of ambient and boundary air conditions. The gas consumption and scanner measurements at the beginning of each coater are used as model input values. The computed web values are compared with the scanner measurements at the end of each coating station. Several additional on-line temperature measurement sensors have been installed to compare the measured and computed values at the measurement locations. The results show a good correlation between model prediction and actual measurements.

The model computes temperature, moisture and partial pressure MD profiles for both the base sheet and the coating layer. These profiles, and especially the position of a given coat moisture gel point and the evaporation rate in its surroundings, are correlated with the printability mottle number of coated paper. The model is tuned if the computed evaporation and temperature correspond to the measurements for different drying conditions. The MD drying model result is the run-time conditional probability of the mottling number and is representative of the drying process performance.