| 摘要 |
The process of the parent Specification (wherein an oriented polymeric linear terephthalate ester film, which has been stretched in two mutually perpendicular directions by a factor of at least 2.5 at 80-120 DEG C. and heat-set at 150-205 DEG C., is stretched in one of the directions by a factor of 1.4-2.0 at 80-205 DEG C. and thereafter heat-set under tension in one direction of stretch at 150-235 DEG C.) is modified in that a polymeric linear terephthalate ester film, which has been biaxially oriented by elongating it in two mutually perpendicular directions at an elevated temperature and then heat-set at a temperature of from 5 DEG C. above the elevated temperature to 149 DEG C., is stretched at an elevated temperature in one direction by a factor of at least 1.05. In one embodiment of the invention which is particularly adapted for relatively thick films and continuous operation, a polymeric linear terephthalate ester film which has been uniformly oriented by stretching in both directions by a factor of 2.5-5.0, preferably about 3.0, at about 80-120 DEG C. and heat-set at about 85-149 DEG C., is stretched in one direction by a factor of at least 1.05 to a point less than the breaking-point of the film, and preferably by a factor of from 1.4 to about 4.0, especially by a factor of from 1.4 to about 2.0, at a temperature of 80-205 DEG C. and is then heat-set at about 150-235 DEG C. under a tension sufficient to prevent shrinking in the direction of stretch. The film is preferably composed of polyethylene terephthalate, but may alternatively be composed of any polymeric linear terephthalate ester formed by reacting a glycol selected from the group having the formula HO(CH2)nOH, where n is an integer from 2 to 10 inclusive, with terephthalic acid or an ester-forming derivative thereof or a low molecular weight alkyl ester thereof, such as the dimethyl or diethyl ester, and up to 20% by weight of a second acid or ester thereof, the second acid being a dicarboxylic acid such as iso-phthalic acid, diphenic acid, sebacic acid, hexahydroterephthalic acid, adipic acid, azelaic acid, naphthalic acid, 2,5-dimethyl terephthalic acid or bis-p-carboxyphenoxyethane. The treatment of the invention improves the tear resistance of the film in both directions Specification 786,176 also is referred to. |
