Thermomechanical Analysis of Heat Sealing Parts on Plastic Films

Abstract

In order to clarify the optimal conditions for heat sealing of a plastic film, the expansion and contraction properties in the thickness direction of a film were examined with thermomechanical analysis (TMA). Specimens consisting of a biaxially oriented polypropylene (OPP) film and a cast polypropylene (CPP) film were made from laminated films used abundantly for packing. The heat sealing temperature was varied while the films were sealed at constant pressure by an impulse type heat sealer. TMA revealed that the compression behavior in the thickness direction of the heat-sealed laminated film was influenced by the relaxation of the orientation properties of the OPP layer. The compression TMA curves and DSC curves agreed well. Furthermore, the results of TMA and DSC indicated the existence of an oriented state of the film after heat sealing. It was suggested that relaxation of the molecule orientation in biaxially oriented OPP films led to the phenomenon of decreased tensile strength under 160°C heat sealing temperatures.