Sheet Coating by Drawdown Of Extruded Polymer

By Fan Ding, A. Jeffrey Giacomin, John C. Slattery

An approximate analytic solution for coating a highly viscous Newtonian fluid onto a substrate is developed (low Poiseuille number and high capillary number). Two particular extrusion angles are considered: parallel and perpendicular to the mov-ing substrate. We obtain expressions for the curtain shape, coating thickness, contact length, contact pressure, drawing force, apparent contact angle, and contact convexity.

In this paper, we identify a process indeterminacy that arises in the curtain coating employing a parallel slit. We show that, by orienting the extrusion slit perpendicular to the moving substrate, this indeterminacy vanishes. Thus, a unique solution for the contact length is always obtained. The extension to a viscoelastic fluid is also briefly considered.