Misting and the effect of rheological properties of the coating fluid

A laboratory device that was designed to simulate film splitting in a high-speed coating machine was utilized to study the relationship between coating fluid properties and misting, with the objective of identifying preferable fluid properties and constituents. The device quickly stretches a fluid filament at a constant rate of acceleration, as occurs in film splitting, and breakup of the filament is observed with a high-speed camera. Two coating fluids consisting of pigment and a latex binder were prepared with different thickeners, carboxy methyl cellulose (CMC) and alkali soluble thickener (AST). They were prepared such that they had the same flow curves, i.e., same values of viscosity versus shear rate. The two fluids were tested in the laboratory simulator and the one with AST, which was more elastic in extension, produced the larger volume of droplets on breakup. This finding suggests that elasticity can cause greater misting in a coating machine, consistent with earlier results on a pilot coater.