Vortex-free Coating Device For Traveling Webs

Abstract

Coating devices for application of coating material to the surface of a web or a flexible substrate utilizing the study of flow patterns in blade coating to develop high-speed coaters, wherein the coater may be modified to provide an air layer between the coating liquid and any lower boundary. The coater devices of the described embodiments provide two inlet channels and an outlet channel. The first inlet channel carries the coating liquid, and the second channel can be used to pump the carrier fluid, e.g. air, into the coating head to pressurize the chamber and to keep the contact wetting line at the upstream section attached to the substrate. The air layer serves as a carrier fluid removing the wall shear stress on the coating liquid in the channel, and thus the coating flow for the operation of the device may proceed without flow separation from the wall (i.e., in a vortex-free mode) at relatively low flow rates appropriate for commercial applications. The excess coating liquid and all of the air leave the coater head at the outlet channel. A coating composition application chamber receives the liquid flow of the liquid coating composition from the upstream direction to the downstream direction. The coating composition application chamber is adapted for receiving a liquid flow of a carrier fluid introduced at the upstream side of the application chamber in the direction of the travel of the web positioning the liquid flow of the liquid coating composition between the carrier fluid and the web.