Polymer Engineering and Science, Vol.47, No.6, 841-851, 2007
Experimental study on tensioned-web slot coating
Tensioned-web slot coating (TWSC) technology was developed in the early 1980s and was considered an efficient method for thin liquid film coating. An experimental study was carried out to investigate the effects of several key parameters on the minimum wet thickness of TWSC. The experiment was performed on a pilot coater with dilute Newtonian poly(vinyl) alcohol (PVA) solutions as test fluids coating on polyethyleneterephthalate (PET) substrates. It was found that the minimum wet thickness for TWSC was between 0.5 and 1.5 mu m, which is much lower than that obtained using conventional slot die coating. The minimum wet thickness was proportional to the tension number T-N, which is defined as the ratio of fluid viscous force over web tension. Furthermore, on the basis of the experimental data, two additional dimensionless groups: dimensionless pressure P-N and dimensionless surface tension L-N were found to be relevant to the performance of TWSC. A universal correlation involving these dimensionless groups as well as the die geometry was used to predict the minimum wet thickness of TWSC.