Hydrodynamics of reverse metering flows

A two-roller system, consisting of an image bearing roll and a biased metering roll, is a common design for liquid ink electrophotography. To stabilize toned images, the development system is required to minimize the liquid content of the toned images. The reverse metering roll, moving in a direction opposite to the process direction, provides a mechanical shearing that reduces the liquid film thickness of the toned image. In this report, a discussion of the hydrodynamic metering mechanism is presented based on the study of modeling results as well as experiments. Formulation of computational models, based on the Navier-Stokes equations for free surface flows, is given followed by the description of experimental apparatus and methods. The critical parameters identified through this study include process parameters as well as geometrical and material properties (roller and gap sizes, process and metering speeds, viscosity, surface tension, etc.). The impact ofthe fluid flow characteristics on the final toned image attributes, such as the background cleanliness and the potential image degradation due to viscous shearing, is then discussed. Such issues can be made more apparent by examining the calculated fluid flow details.