Film Thickness and Film Thickness Uniformity

Abstract

AbstractOne of the attractive features of premetered coating methods is the fact that the nominal thickness of the coated film is pre-determined by the law of mass conservation. For a constant coating width, in particular, the thickness only depends on the flow rate/width and the coating speed. Interesting is the question about the uniformity of the nominal film thickness, both in the machine and cross-web direction. This chapter shows that the film thickness uniformity in the machine direction is controlled by the design of the pump as well as the uniformity of the motors that drive the pump and pull the substrate through the coating machine. Achieving a good film thickness uniformity in the cross-web direction is more complicated because it depends on the design and performance of the slot die. Therefore, a large portion of this chapter is devoted to die design. Specifically, theoretical models for designing the die-internal geometry are presented, the performance of such dies is analyzed, and ways for optimizing die design are proposed.