GB839108A - Process for making oriented films - Google Patents

Abstract

Oriented films having balanced properties are made from unoriented films of orientable crystallizable linear organic polymers by successively stretching the unoriented films laterally and longitudinally at 70-120 DEG C. while preventing significant contraction in the other direction, subjecting the oriented film to a modifying treatment at 20-150 DEG C. for 0.01-5 mins. while maintaining tension in both directions so that the film remains substantially unaltered in dimensions, and heat-setting the resulting film at 150-230 DEG C. under conditions such that no substantial shrinkage occurs. The film may be made of a polyester, preferably polyethylene terephthalate, and longitudinal stretching preferably precedes lateral stretching. Preferred conditions for the modifying treatment comprise 0.01-3 mins. at 70-95 DEG C. After heat-setting, the film may be heat-relaxed at 90-150 DEG C. while under slight tension. A water-permeable colloid layer (e.g. gelatin) may be applied to the heat-set film, preferably prior to heat-relaxing. The process may be applied to films having a thin layer of a hydrophobic polymer (e.g. a vinylidene chloride copolymer) on one or both surfaces. Both base film and copolymer layer (if present) may be tinted (e.g. for use as X-ray photographic film base) and may contain an autostatic material. Specifications 578,079, 603,827, 718,422, 746,386, 772,148, 779,645, 786,176, and U.S.A. Specification 2,071,250 are referred to.