A MATHEMATICAL-MODEL OF ROLL-TO-WEB KISS COATING

A mathematical model is presented for equilibrium flow in the coating bead of a roll-to-web kiss coater, operating in reverse mode with the web, tension T, wrapped over the applicator roll at a small angle, bet a. The lubrication approximation is introduced and predictions present ed for the him thicknesses on both the web and applicator roll, which move with peripheral speeds U-1 and U-2 respectively, the gap thicknes s commensurate with the position of the applicator roll centre, the fl uid pressure as a function of the web-to-roll speed ratio, S = U-1/U-2 , capillary number, Ca, and applied load, T beta, for the case S < 1. In particular, the ratio of web film thickness to applicator roll radi us is found to be directly proportional to Ca and (1 - S)(2) and inver sely proportional to T beta. A comparison with experimental data confi rms that this ratio is proportional to Ca, that the pressure maximum l ies downstream of the applicator rolls central position, and that a su b-ambient loop exists close to the downstream meniscus.