Abstract
Theoretical prediction of coatability can often involve uncertainties, such as the assumption of boundary conditions or the constraints of theoretical model, when it is compared with experimental observations. In order to predict the low coating flow limit in slot coating process it is important to understand the major mechanism of maintaining a stable coating bead. In this study a theoretical
method is applied to analyze the feeding slot pressure upon the coating bead and correlate the prediction to the experimental slot coating at low capillary number (< 0.3). The theoretical analysis and experiments were carried out with Newtonian fluids. The computational calculation was performed using Nekton, a commercial finite element fluid dynamics software. The analysis indicates that the pressure drop of the feeding slot acts against the capillary pressure of the bead meniscus and provides the stability for the coating process. The pressure drop decreases as the coating thickness decreases until it reaches a certain minimum value. At this value the pressure drop is overcome by the capillary pressure and a stable process turns into a unstable process. The phenomenon has been correlated with the minimum wet coating thickness observed in the experiments. The correlation established in the study shows that the pressure drop of the feeding slot provides the major stability for the coating process at low capillary number.