Experiments were made by using a pilot plant of successive biaxial stretching process for poly (ethylene terephthalate) (PET) films, whose molecular orientation (MO) and bowing behavior were investigated first during the whole tenter.The following results were obtained:(1) Higher temperatures in the latter of the transverse stretching zone can give rise to the bowing distortions.(2) At the center of film in the transverse direction (TD), the MO degree in the TD becomes high as the actual transverse stretching ratio increases, passing the plane random orientation point. That is, the MO of film tilts from the machine direction (MD) at the beginning of transverse stretching to the TD after stretching without rotation.(3) At the edge of film, the principal molecular orientation axis begins gradually to tilt from the MD to the TD with rotation at the point where the bowing distortion increases rapidly, and afterwards gradually changes further more to the TD with an increase of actual stretching ratio.
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