Practical operations for intermittent dual-layer slot coating processes

Transient behaviors of dual-layered patches for Newtonian liquids were numerically investigated in dual-layer slot coating processes for the first time using step-changed inlet flows. To further tune the leading and trailing edges in a patch cycle, startup and end lag times between the top and bottom layers were proposed, considering the flow state of a bottom-layer liquid in a coating bead region. Carefully chosen lag times significantly reduced the defects in the leading and trailing edges of a dual-layered patch. It was also found that a greater coating layer viscosity results in a greater amount of residue left on the die lips, which affects the next patch cycle.