Liquid transfer between a cavity and a rotating roll

DIEGO M. CAMPANA; MARCIO S. CARVALHO

Minneapolis

Workshop; Industrial Partnership for Research in Iterfacial and Material Engineering IPRIME 2014; 2014

Printing technologies have gained much attention due to their potential applicability in the production of flexible electronics. Among the many available options, gravure printing is attractive because it allows printing of small patterns (in the order of 10 microns) with liquids of medium to high viscosity (up to 1000 cP) at high substrate speeds, when a roll-to-roll configuration is used. In gravure printing, one of the rolls is engraved with small cavities or grooves that are filled with liquid, which is then transferred to the substrate. The characteristic of the printed pattern is directly related to the dynamics of the liquid transfer process. The model developed in this work considers the complete kinematics of a roll-to-roll system. The results show that as the roll radius is reduced and the shear and rotation of the top plate relative to the cavity becomes more pronounced, a larger volume of liquid is removed from the cavity. However, due to lateral displacement of the liquid bridge, special care must be taken in the wettability properties of the substrate to avoid errors in the pattern fidelity. When the roll radius and cavity geometry are fixed, the predictions show a strong non-linear behavior of the liquid fraction extracted from the cavity as a function of the capillary number. The model was extended to 3D flow, which required a robust fully coupled Arbitrary-Lagrangian-Eulerian finite element method to calculate the unknown three-dimensional flow domain, simultaneously with the flow variables. The results show that at moderate values of Ca the contact line pins markedly on the cavity but slips easily on the moving plate, thus reducing the size of the drops left over it after the filament breakup. However, at low values of Ca, the contact lines have higher mobility and the pressure difference created by the non-symmetric meniscus drains completely the liquid outside the cavity. At that situation, half of the liquid volume can be transferred to the substrate. High speed visualization of liquid transfer process from cavities engraved in a glass surface to a rotating roll are under way to validate the model