Effect of curvature of coating die edges on the pinning of contact line

Coating die edges are not mathematical corners, they are rounded. Contact lines do not actually pin. The effects of the radius of curvature of the downstream edge of slot dies on contact line location, effective contact angle, and low-flow limit-air-fingers penetrating from downstream and breaking apart the coating-bead-are examined by solving the Navier-Stokes system for Newtonian flow. The geometry of the die surface is represented by two straight lines and an arc of circle connecting them. The local contact angle is treated as a specified equilibrium value. The system of equations is solved by Galerkin's method and finite element basisfunctions. The results show how the edge rounding affects the contact line position and stability of the flow, and indicate the minimum radius of curvature necessary to apparently pin the contact line. 0 2005 American Institute of Chemical Engineers AIChE J, 52: 447-455, 2006