Optimization of Formulation Parameters to Reduce Misting and Orange Peel Formation on Metered Film Coaters, 1998 Metered Size Press Forum II Proceedings

There are several process, base paper, and formulation variables which need to be considered in optimizing the performance of metered film coaters. For most situations the base paper and coating equipment are predetermined and can only be modified with great difficulty. This leads one to consider formulation variables as the easiest means to improve the runnability and quality of film coating. The two dominant runnability and quality issues in film coating are misting and orange peel formation. These originate from the film splitting of coating color in the application nip. The generally accepted theory suggests that film splitting is determined by the thickness of the non-immobilized coating layer as well as the formation and breakup of filaments in the extensional flow field of the application nip. Immobilization rate (coating solids, dewatering rate and immobilization solids), coat weight, elasticity and viscosity have therefore been found to be important variables in the control of film splitting. Another key parameter is the coating speed. Through the appropriate choice of pigment, latex, thickener, and coating solids the degree of misting and orange peel formation can be reduced. This paper provides a review of our current understanding of the role of process and formulation variables on misting and orange peel performance. A suggested strategy for optimizing coating formulation is presented. The formulation strategy varies depending on the coat weight and speed of operation and is illustrated with examples from our pilot coater studies for both fine paper and LWC applications.