SMALL ANGLE LIGHT SCATTERING STUDIES ON BIAXIALLY STRETCHED POLY(ETHYLENE TEREPHTHALATE) FILMS OBTAINED BY TWO-WAY SUCCESSIVE STRETCHING PROCESS

摘要

This report is concerned with the studies on the stretching behaviors of poly(ethylene terephthalate) (PET) films obtained by the uniaxial and biaxial stretching methods. Studies are mainly concentrated on clarifying the high-order structure development and the structural change on stretching using Small-Angle Light Scattering (SALS) technique. On uniaxial stretching, a butterfly shape was obtained in the Hv light scattering pattern, which indicates the existence of a sheaflike crystalline high-order structure in the stretched films. Numerical calculations based on the sheaf array model were carried out for the interpretation of experimentally obtained SALS patterns. Results of the calculated patterns show good agreement with experimental ones. In the case of biaxially stretched films, the SALS patterns change remarkably depending on the stretching conditions and stretching systems. Higher stretching temperatures were found to be effective in the two-way successive stretching system since the high-order structure formed at the initial uniaxial stretching can't be easily destroyed by the second stretching. Further, it became obvious that a three step stretching system in which machine direction stretching is divided into two steps is effective in obtaining biaxially stretched films having 8 leaf SALS patterns including the butterfly shape.