Characterizing start and end edges in intermittent slot coating processes via coating bead flow dynamics

The relationship between the coating bead flow dynamics and the profiles of patch coating films in intermittent slot coating processes was investigated using two-dimensional numerical simulations. In the continuous production of discrete coating patches, the start (rising) and end (falling) edges in the flow direction must be precisely analyzed, considering the liquid’s rheological properties and the residual liquid remaining in the coating bead region between on–off flow control stages. The residual volume, which significantly affects both the start and end edges for Newtonian and non-Newtonian liquids, was found to remain in the coating bead region only above a certain capillary number (Ca) of 0.1, with an increasing trend as Ca increases. The growth of the start edge height of coating patches was greatly influenced by the residual volume. In contrast, the end edge length was inversely proportional to the residual volume concerning Ca. Furthermore, for shear-thinning liquids with various power-law indices (n), a certain Ca value, similar to that for the Newtonian case, was confirmed to induce the occurrence of residual volume. Graphical abstract: (Figure presented.)