Origin of the bubble defect in the extrusion coating process

During the extrusion coating process, a polymer film is extruded through a flat die, stretched in air, then coated on a substrate (steel sheet in our case) in a laminator consisting of a chill roll and a flexible pressure roll. The nip, i.e., the area formed by the contact between the pressure and the chill rolls, constitutes the very heart of the extrusion coating process. Indeed, in this region, some of the most critical properties, such as adhesion, barrier properties, optical properties, are achieved. The thermomechanical analysis of Sollogoub et al., Polym. Eng. Sci., 48, 1634 (2008), was used to study the origin of the bubble defect appearing during the extrusion coating process. First, we investigate the influence of process parameters on the bubble defect. Then, we compute the thermomechanical parameters of the process, and finally, we derive a realistic bubble defect appearance criterion. POLYM. ENG. SCI., 00:000–000, 2010. a 2010 Society of Plastics Engineers