| Abstract
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A laboratory device has been designed and built to simulate film splitting in roll coating, which occurs through filament stretching and breakup. At high speeds and for some coatings, the breakup leads to unwanted misting. In our simulator, a fluid sample is initially held between two closely-spaced small disks, and then the top disk is pulled upward at a high, constant rate of acceleration to mimic coating machine conditions. Formation and breakup of the resulting filament are observed using a high-speed video camera, and the images are analyzed by software to obtain the number and size of droplets. Tests with various Newtonian fluids, at a Weber number of 30, show that one droplet forms at low Ohnesorge numbers, and that more and smaller droplets form at Oh numbers above 0.1. Associative polymer solutions, prepared to be weakly-elastic fluids like coating liquids, produced even more and smaller droplets, but only for Ohnesorge numbers in the range of 0.01 to 0.1. Simplified coating formulations, which were both shear thinning and elastic, generated smaller but more droplets than those of equivalent Newtonian fluids and than those of associative polymer solutions which were less elastic. The effects of acceleration, initial film thickness and surface tension, as well as solids content of formulations, are studied as well.
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