Numerical solution of the liquid transfer between a cavity and a moving surface. Application to models of roto-gravure printing systems

DIEGO M. CAMPANA; SEBASTIÁN UBAL; MARÍA D. GIAVEDONI; FERNANDO A. SAITA; MARCIO S. CARVALHO

Tandil

Congreso; XIII Reunión sobre Recientes Avances en Física de Fluidos y sus Aplicaciones (FLUIDOS 2014); 2014

Instituto de Física "Arroyo Seco", Universidad Nacional del Centro de la Provincia de Buenos Aires

In this work we propose a model for the liquid transfer between a cavity and a moving substrate, which represents a simplification of the fluid dynamics problem taking place in a roll-to-roll gravure printing system. The full 3D model is solved numerically using the finite elements method; and a robust fully coupled Arbitrary-Lagrangian-Eulerian technique is used to simultaneously calculate the unknown three-dimensional flow domain, and the flow variables. The relative motion between the cavity and the substrate mimics this of a roll-to-roll system, featuring stretching, shearing and rotation. This kinematics promotes different curvatures between the front and rear parts of the 3D meniscus. The results suggest that the liquid fraction extracted from the cavity strongly depends on the Capillary number (Ca). At high Ca, the contact lines are pinned, resulting in relatively small liquid fractions being transferred, but also good registration of the printed pattern. At moderate Ca the contact lines have more mobility and the size of the drop attached to the substrate is smaller, and this results in a reduction of the liquid fraction. By contrast, at small values of Ca the contact lines have high mobility and the surface motion promotes a spreading of the liquid outside the cavity. The liquid filament is now formed between two flat surfaces and, after the filament breakup, approximately half of the liquid volume can be transferred to the substrate. While the liquid fraction is considerably increased at low Ca, the high mobility of the contact lines could result in severe loss of fidelity of the printed pattern.