Curtain Coating Technology
Introduction. Economies of scale occur when a coated product is manufactured wide, fast and in one pass. Substrates can be manufactured wide and multilayer coating can provide added functionality, but how to make a coated product faster? The first hurdle is curing (typically the bottleneck of the process). Once the oven is properly sized for the application, the fluid flow dynamics within the coating system need to be considered. As the fluid is coated faster and faster, the effects of film split, turbulence and air wreak havoc on the coated product and leave a trail of coating defects in the path. Some coating techniques, however, actually perform better under high-speed scenarios. One coating technique that should be considered for high-speed applications is curtain coating. Imagine taking a slot die, coating in close proximity, and raising it up in the air to allow the fluid to drop down onto the substrate. This rain shower of liquid can have some advantages, but the advantages can only be realized with higher speeds. Why is that? The fundamental equation behind the success of a falling curtain of fluid is the dimensionless Weber number.
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