Penetration of Blade-Applied Viscous Coatings into Yarns in a Woven Fabric

Abstract

We developed a model based on first principles — Darcy’s law and lubrication theory — that can be used to predict the intra-yarn penetration depth of a coating applied to a fabric using the knife-over-roll technique. We verified the model by studying the penetration of a polyurethane coating formulation onto a woven nylon substrate. The results show that the penetration depth was greatest, 41 µm, when the gap between the blade and the substrate was smallest; however, we varied application speed and coating viscosity as well as gap distance. The minimum penetration depth was 18 µm, or about one fiber diameter, as determined by analysis based on scanning electron micrographs. Although the calculated penetration depths were about three times less than the measured depths, at least in part because of the many approximations and assumptions required by our derivations that are based on first principles, we consider the agreement to be good. The work brought out another important result: neither viscosity nor coating speed affected penetration depth.