STUDIES ON THE BIAXIALLY STRETCHING OF FILMS

Abstract

The purpose of this series of study is to investigate the biaxially stretched polymer films. In this report the changes of the structure and properties in biaxial stretching are described on polypropylene film.Films used in this study are a T-die extruded (150μ thickness) and/or a hot-pressed (200μ thickness). The apparatus for biaxial stretching of polymer films was designed and constructed. The biaxial streching was performed both in the machine direction (M. D.) and transverse direction (T. D.) of films simultaneously or independently.The unstretched films were stretched in a recirculating hot-glycerin bath. The films were stretched, (1) uniaxially with the constant width, (2) biaxially with successive stretching, (3) biaxially with simultaneous stretching. The stretched films were sometimes heas-set.The orientation behaviour in these stretched films was studied by the stress-strain curve, X-ray diffractogram and infrared spectra.Mechanical properties of the biaxially and successively stretched films were compared in both stretching directions as shown in Fig.3. The balanced value, the intersecting point of two curves (M. D. and T. D.), was illustrated in Fig.3. A good balance of properties could be achieved in the biaxially simultaneously stretched film in all directions. X-ray and polarized infrared spectra analysis support the conclusion on the balance of mechanical properties of biaxially stretched films.The simultaneous biaxial stretching is preferable to the successive biaxial stretchihg for polypropylene film.