| 摘要 |
1,196,375. Polyethylene terephthalate films. KALLE A.G. 30 May, 1968 [1 June, 1967], No. 25956/68. Heading B5B. Dimensionally stable polyethylene terephthalate films capable of lying flat are made by stretching a film of amorphous polyethylene terephthalate having a mean molecular weight of less than 13,500 at a temperature of 85‹ to 95‹ C. with a force of not more than 0.5 kg./ mm.<SP>2</SP> to a draw ratio of at least 3 : 1 in orthogonal directions of the film plane and then heating the film for at least 5 seconds to a temperature of at least 200‹ C. while it is held under tension such that its dimensions remain constant. The film may be simultaneously stretched in both said directions to a draw ratio of at least 3 : 1 with a force of not more than 0À2 kg./mm.<SP>2</SP> In a preferred embodiment, the film is made by melting a polyester material of appropriate molecular weight in an extruder at 260‹ to 300‹ C., preferably 275‹ to 290‹ C., and producing a film which is then cooled on a roller at 20‹ to 60‹ C., preferably 20‹ to 30‹ C., stretching the film so made, especially at 90‹ or 91‹ C., in orthogonal directions of the film plane at a draw ratio of 3 : 1 to 4 : 1, and heatsetting it at 200‹ to 240‹ C., preferably between 220‹ and 230‹ C., while it is held under tension to prevent shrinkage, for 5 to 20 seconds. Examples are given. |
