Experimental and numerical analysis of non-Newtonian effect on film thickness and ribbing instability in forward roll coating process

In this paper non-Newtonian effect on film thickness and ribbing wavelength of a coating fluid in forward roll coating process were investigated. Non-Newtonian behavior of the coating fluid was accounted by using power-law model with power index, n, ranging from 0.8 to 1.2. Effects of roll speed ratio (V₂/V₁) of applicator roll to pick-up roll and gap distance on the coating film thickness and ribbing wavelength were also investigated. Numerical results were in good agreement with those of experimental data within 5-12%. Results indicated that the film thickness ratios were functions of power-law index, roll speed ratio and ratio of gap distance to roll radius, and the ribbing wavelength-to-gap ratio was a function of power-law index, capillary number and ratio of gap distance to roll radius. The correlations are accurate within 15%.