Modelling printing processes: A computational approach

In a variety of industrial printing processes, liquids must be transferred from one substrate to another in order to create a liquid pattern, the wet print. With the notable exception of inkjet printing, surprisingly to date there has been no serious attempt to model printing processes either theoretically or computationally. As industrial competition places increasingly stringent demands on print quality and operation speed, fundamental research into the underlying fluid mechanics of liquid printing - long overlooked - is now becoming essential. Two quite different numerical schemes, a Lagrangian finite element method and an Eulerian volume of fluid method, are reviewed and the relative merits of both methods are briefly discussed. Sample computations are then presented to illustrate how a numerical approach may be used to (a) simulate micro-scale liquid printing from a trapezoidal cavity to a moving substrate, and (b) model a 'pintool' in which a rod is used to deposit a small dot of liquid onto a substrate. Finally, the authors model two distinct printing-related phenomena that may lead to serious process instabilities.