Gravure printing: Liquid transfer from cells and grooves

DIEGO M. CAMPANA; MARCIO S. CARVALHO

Minneapolis

Workshop; Industrial Partnership for Research in Iterfacial and Material Engineering IPRIME 2013; 2013

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. Dodds et al. (2009, 2011) studied the stretching of a liquid bridge as a model to the liquid transfer process from a single axisymmetric cavity. The volume of liquid transferred to the substrate was determined as a function of the wetting properties and operating conditions. We extend Dodds´ analyses by comparing the liquid transfer process from an axisymmetric cell (printing of a single dot) and from a 2D planar groove (printing of a line) and examining the effect of roll radius and cell width in the 2D planar flow. In this work, the plate moves relative to the cavity with a velocity obtained from a complete kinematics analysis of a roll-to-roll system, which include not only stretching, but also shearing and rotation. The free surface fluid flow is modeled by solving the Navier-Stokes equations coupled with the appropriate boundary conditions. We use the finite element method to discretize the differential equations while the free surface evolution is described by a pseudo-solid mesh deforming algorithm. We introduce several improvements in the numerical method used in previous works, such as the use of unstructured meshes, that is more appropriate to describe the large deformation experienced by the liquid interface, and a more flexible method to enforce non-linear boundary conditions. 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.