An investigation of the spatial and optical behavior of biaxially drawn PET film

Abstract

AbstractThe paper investigates the evolution of the spatial and optical properties of particle‐doped poly(ethylene terephthalate) PET film, as a function of the degree of biaxial extension. Mean surface roughness and peak particle concentration were the main spatial parameters studied. A sharp increase in the average asperity height has been recorded for early forward draw, followed by an abrupt decline that continues almost linearly through the remaining sideways draw. This behavior has been explained in terms of the unequal stress distribution and subsequent yielding in the polymer film surrounding the particles. The peak concentration drops initially due to stretching of the film surface, but remains constant through the transverse draw. The wide angle haze was found to be an exponential function of forward extension, similar to the stress/strain curve for PET. However, the surface haze followed the same trend as surface roughness, suggesting a probable correlation between the two. A consideration of the transversal particle migration suggests that the screw extrusion part of the process may be instrumental in the augmentation of the base surface roughness of the film leaving the slit die.