Effect of blade-tip shape on the doctoring step in gravure printing processes

Abstract

A fundamental limit to the gravure printing process is in the doctoring step, in which a residual film defines the lower bound on allowable feature size. The resolution of finer features requires thin residual films, but these thin films increase the likelihood of wearing the doctor blades. A computational model was used to study the effect of blade-tip shape on residual film thickness while also minimizing the likelihood of wear. The blade-tip shape is altered by varying the bevel angles and the predicted film thickness is computed under various wiping speeds, configurations, and applied forces. In all cases studied, a slower wiping speed resulted in a thinner residual film, which is due to the doctoring step being governed by elastohydrodynamic lubrication. In some cases, a reversal of the wiping configuration created a thinner film, but it had no impact on the likelihood of wearing. Higher applied force leads to thinner residual film but the blade shape can have a more significant influence, indicating that lubrication forces dominate at this scale. Lastly, the likelihood of blade wear was predicted to vary within a small range for a fixed blade-tip shape over all conditions studied, which suggests that tip shape is the primary factor to consider when minimizing blade wear.