METHOD AND APPARATUS FOR MULTILAYER DIE COATING

摘要

A method and apparatus for simultaneously coating multiple thin layers of relatively viscous fluids, including pressure sensitive adhesives (PSAs), onto a moving substrate. The method of the present invention comprises the adjustment of the pressure gradients in the interface region between two confluent flows so as to avoid recirculation therein. In particular, the pressure gradient along the middle lip is regulated so as to not be excessively positive, in order to position the separating line between the top and bottom flows at a particular point on the die lips, thus enhancing stable flow. In the apparatus of the present invention, a step configuration is formed on the die lips so that the downstream lip steps away from the web in the direction of web travel. In another aspect of the invention, the pressure gradient at various locations in the bead is controlled by beveling the upstream and downstream lips. In yet a further aspect of the present invention, the viscosities of the two liquids being coated are matched at therelevant shear rates to promote good coating quality.