It may happen if the temperature of equipment is too or glue of high adhesion is applied to fairly thin flim. (The solution is to increase the speed or decrease the temperature.) The adhesion of glue is too high because it's too thick, or the base material is not good, or the stress is too strong when drying the film.(Solution: using the inlet air to press the film from the right side to make it flat and ensure the glue won't fall off.) And if the film you use is composite membrane, when the composite membrane is not composited compeletly, the same problem may occur too. I don't know your coating process, thus all above are the possible reasons that I suppose.
