(232b) The Emptying of Liquid From Gravure Cells

The transfer of liquid from one surface to another is important in a wide variety of both natural and industrial settings, including printing processes such as gravure, lithography, and microcontacting. In these processes it is desirable to maximize the amount of liquid transferred from the printing image to the final substrate in order to minimize fouling of the image surface, as well as to avoid waste of potentially valuable and/or toxic compounds. To accomplish this requires that the printing liquid dewets the image surface, leaving behind as little residual liquid as possible. Therefore, it is important to understand how the surface properties of both the image and the final substrate affect the dewetting process, and thus the liquid transfer.

As a first step in understanding liquid transfer in printing processes, we use the Galerkin/finite element method to study the stretching of a finite volume of Newtonian liquid confined between a stationary trapezoidal cavity, which represents a model gravure cell, and a moving flat plate. The contact lines are allowed to slip along both surfaces, and we evaluate the effect of gravure cell geometry, contact angle, and capillary number on the fraction of liquid transferred to the moving plate. As the gravure cell is made wider at a fixed capillary number, the fraction of liquid transferred is increased. However, liquid transfer is often limited by contact line pinning, which prevents the gravure cell from being completely emptied.

To complement this computational study, we have also used flow visualization to monitor the stretching of a liquid drop both from beneath and beside the drop. The side view is used to track the breakup of the drop during stretching, allowing us to quantify liquid transfer using image analysis. Viewing from beneath the drop allows us to track the motion of the contact line, making it possible to observe both contact line pinning events and non-axisymmetric modes of breakup. By performing both sets of visualizations, we can better understand how surface properties affect the motion of the contact line, as well as the liquid transfer.