Abstract
In this report the changes of structure and properties of biaxially stretched poly (ethylene terephthalate) films are described.
Sample films used in this study were the T-die extruded film with 140μ thickness. The biaxial stretching of the films was done using a film-stretcher for wet-process. Stretching of the unstretched film was carried out in a recirculating hot silicon-oil bath. The films were stretched by the following three methods, (1) uniaxially with the constant width, (2) biaxially with two-way successive stretching, (3) biaxially with simultaneous stretching. Some of the stretched films were heat-set.
Mechanical properties of the biaxially and successively stretched films were compared in both stretching directions as shown in Figure 6. The intersecting point of two curves (MD and TD) in Figure 6 shows the balance value. In the case of this experiment, the balance value is about MD×TD=4.0×2.0. On the other hand, good balance of properties of the biaxially simultaneously stretched films in all directions could be achieved, as shown in Figure 7. Results of X-ray diffraction diagram and polarized infrared spectra analysis support the balance of mechanical properties of biaxially stretched films.
Uniplanar-axial orientation is observed in the cases of uniaxial stretching under constant width and unbalanced successively biaxial stretching, while the orientation is uniplanar in the films simultaneously and balanced successively biaxially stretched.
The simultaneons biaxial stretching is a method perferable to the successive biaxial stretching, not only for polypropylene film but also for poly (ethyleneterephthalate) film.
