Abstract
The fluid mechanics of narrow stripe coating for low viscosity Newtonian solutions was investigated. A narrow stripe could be produced either through a slot die with a shim to control the slot width or through a rectangular nozzle. A flow visualization technique was employed to observe the mechanism on how a narrow stripe breaks at high coating speeds. Two-dimensional and three-dimensional numerical simulations on coating flows were also carried out to examine the fluid motion. The coating solution was found to expand laterally after emanating from the slot die channel at low coating speeds. The stripe width contracts gradually with increasing coating speed until coating failures appear. The coating defect observed switches from ribbing to a periodic stable and break-up motion. The effects of various fluid properties, geometric and operating parameters on the variation of coating width and maximum coating speeds were examined. A universal correlation involving two dimensionless groups, Reynolds and Bond number, was established for the prediction of coating width. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.