Study of Coating Water Loss and Immobilization Under Dynamic Conditions, 1993 Coating Conference Proceedings

T. S. Young

D. E. Pivonka

L. G. Weyer

B. Ching

A computer-interfaced noncontact reflection detector was used with a CLC laboratory coater to study coating water loss and immobilization under conditions typical of high speed short dwell type blade coaters. The coating gloss data were related to surface moisture content by simultaneous gloss and moisture measurements on a coated glass plate. The observed gloss decay and immobilization solids data show that water retention on a short dwell type coater depends not only on the coating water viscosity, but also the capability of the coating to form a high solids cake barrier at the coating-paper interface. For clay-based rotogravure coatings that contain clay- adsorbing cellulosic thickeners, the cake formation mechanism seems to play a major role in water retention. The clay-adsorbing thickeners were found to give a higher degree of solids flocculation and a lower immobilization solids, as well as better coverage, smoothness, and rotogravure printability than thickeners with low clay affinity. The relative dewatering rates determined from low speed or static tests did not correlate with dewatering rates observed on the CLC coater, possibly indicating a failure to simulate the cake formation process.