Rheology in film processing (1) - high-order structural change of biaxially stretched films during Two-way successive stretching process

Abstract

Studies on high-order structures of poly(ethylene terephtalate) films prepared by uniaxial and biaxial stretching processes were done using Small-Angle Light Scattering(SALS). On uniaxial stretching, a butterfly shape was obtained in the Hv light scattering pattern, which indicated 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 showed good agreement with experimental ones. In the case of biaxially stretched films, the SALS patterns changed 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 was not easily destroyed by the second stretching. Further, it became obvious that a three step stretching system in which machine direction stretching was divided into two steps was effective in obtaining biaxially stretched films having 8 leaf SALS patterns including the butterfly shape. © 2005 The Society of Rheology, Japan.