Visualization study of liquid surface stability for full reverse 3-roll coater with rigid gravure roll

Abstract

Roll coating systems are widely used to coat a thin liquid layer on a moving substrate, and many publications discussing forward roll coating systems and reverse gap control coating systems are available. Recently, thinner and more uniform layers are required for use with the high-performance solutions involved. Moreover, high line speed coating is also required in order to reduce manufacturing costs. A reverse gravure roll system can coat a thin layer film at high line speed more easily than a flat roll coating system because only the liquid that enters the gravure cell is transferred to the next roll or substrate. However, the existence of the gravure cell complicates the flow between the rolls. To our knowledge, no systematic study in the literature has explored this condition in depth. In the present study, the flow between a reverse deformable roll and a solid stainless steel gravure roll is visualized in order to determine how the uniformity of coating in the high roll speed region is affected by operating parameters, that is, the speed ratio between the rolls and the properties of the coating liquid. The range for coating uniformity is compared with the case of a gap control system. The results show that the stable region can be extended by using the reverse gravure roll system.