Troubleshooting Rheology Problems in Metered Size Press, 1996 Metered Size Press Forum Proceedings

N. G. Triantafillopoulos, D. M. Lee

GenCorp Inc.

Metering size presses have gained popularity due to the development of film presses which allow the application of high-solids pigmented coatings at high speeds. The process has the advantage of separating premetered film formation from transfer and absorbency on to paper. The mechanical elements utilized for film metering, i.e., roll, blade, wire wound rod, or smooth rod, and dewatering properties of the coating define the operational window of the process with respect to attainable coat weights within a range of coating solids, viscosities and coater speed. Misting at the film split and orange peel patterns are the limiting factors. The dynamics of all metered size presses fall under the category of premetered thin-film coating flows, hence they share common coatability guidelines. This paper focuses on operational issues of conventional and metered size presses, with particular emphasis on rheological effects and their influence on film split. Factors which control film splitting, filamentation, and the formation of misting and orange peel are discussed with reference to both fluid continua and pigmented coatings. Key coating variables are pressure dewatering, water phase viscosity, elasticity, thixotropic breakdown, and elongational viscosity.