A Statistical Study of Process Variables to Optimize a High Speed Curtain Coater-Part II

In Part I of this work, we identified four important process, base sheet, and formulation variables that strongly influence the runnability of a curtain coater at high speed, using a Taguchi orthogonal array experimen-tal design approach. The effects identified are base sheet roughness, coating rheology, curtain height, and the amount of steam applied in the boundary layer air removal system (steam substitution system [SSS]). In the second phase of our study, we examine the contribution of these four variables on curtain coating stability in more depth using a D-optimal design of experiment. The results show the set-up of the boundary layer air removal system to be the most critical variable to maintaining the stability of the curtain. We found base sheet roughness, in combination with the parameters of the coating formulation, to also be very important. Coating coverage improved with the smoothness of the base sheet and excellent coating coverage was attainable at low coat weights. A shear thinning coating was found to provide the most favorable coating rheology for curtain stability at high speeds.