| 摘要 |
Biaxially-oriented, heatset polyester film is heat relaxed at a uniform temperature and supported buy impingement with gas such as air, while subjecting the film to low tension in its longitudinal dimension. Undesirable draw lines, as defined herein, are avoided by maintaining the longitudinal dimension of the film in an arcuate configuration composed of a single curve or serpentine succession of curves free of straight segments. Each such curve is characterized as having a radius of curvature in the range from about 1 inch to about 8 inches, subtending an arc of no less than 40 DEG . A serpentine configuration is preferred in which case the gas impinges upon alternate sides of the web. Temperatures of heat relaxation preferably are within the range from 30 to 100 centrigrade degrees higher than the polyester glass transition temperature.
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