(184c) Comparison of Different Gravure Cell Geometries Using a Potential Energy Framework

Gravure cell printing is emerging as a viable strategy for mass production of flexible electronics, for applications like medical devices and solar cells. A key variable for design of efficient printing processes is the geometry of the wells used for ink transfer. In this work we examine various geometries and assess their effect on ink transfer. Previous work in this area includes investigation of the effect of different inclinations of the gravure cell walls, the scaling of ink transfer with gravure cell volume, and the effect of different aspect ratios of square gravure cells. The majority of past work has been limited to studies in two dimensions, and a general framework to investigate the effects of different gravure cell sizes and shapes in three dimensions is missing.

At the analytical level, a simple potential energy framework is introduced to analyze ink transfer. For a variety of geometries (disks, domes, and cones) we calculate the reversible work needed to transfer a droplet from a gravure cell onto a substrate, and the results of these calculations are compared to those of three dimensional continuum mechanics simulations. At the numerical level, our simulations rely on the Volume Of Fluid approach with a Brackbill surface tension model and a Hoffman dynamic contact angle model. The ink is described as a Bird-Carreau fluid, and automated remeshing is been implemented to account for topological changes during the printing process.

Our results indicate that the optimal geometry for a gravure cell consists of a dome. For lower contact angles, ink transfer increases dramatically in lower and wider shaped cells. There is good agreement between our model predictions and continuum mechanics simulations. For disks and cones, the model also predicts better ink transfer for wider and lower shapes, but the agreement between the model and simulations is not as good. We attribute the discrepancy to residual ink getting trapped in narrow spaces and in corners. The fluid time scales are too slow compared to the printing time scale. Overall, we believe that a potential energy description of gravure cell printing provides a general and simple framework to describe ink transfer for different geometries, contact angles, surface tensions, and sizes of gravure cells, and can be a useful tool for optimization of gravure cell printing processes.