| 초록 |
Typically, the slot coating process is designed for a single liquid layer. However, many products demand coatings consisting of two or more layers. To avoid multiple passes through the oven, all the different layers are coated before the solidification process starts. One possibility is to coat the layers simultaneously, in the same station, using a the dual slot coating. The uniformity of the surface that separates the two liquids, the interlayer, plays a crucial role on the final product quality. The interlayer initiates at a point located in the mid-lip, usually called the interlayer separation point. In order to minimize cross-web thickness variation and mixing of the two layer, the separation point should be located at the downstream corner of the mid-lip. As it moves upstream, the top layer invades the mid-gap region and dangerous turnaround flow and microvortices may appear. This phenomenon is called mid-gap invasion. We confirm the existence of the mid-gap invasion by visualization of the coating flow, reveal "invasion" mechanisms from Navier Stokes theory, and provide a simple criteria from examining a onset of critical flow state. |
