| 摘要 |
1,236,432. Vacuum forming sheets of polyethylene terephthalate. ALGEMENE KUNSTIZJDE UNIE. N.V. 6 Sept., 1968 [8 Sept., 1967], No. 42582/68. Heading B5A. Shaped articles of polyethylene terephthalate are made by heating a sheet or film of amorphous polyethylene terephthalate and vacuum forming the hot sheet or film, the part or parts of the sheet or film which are to be subjected to the greatest deformation in the vacuum forming step being subjected to an additional heat treatment to increase the crystallinity of the polymer. The sheet may be heated by infra-rod radiators to 90-120‹ C. with the particular parts thereof being additionally heated to 110-140‹ C. The shaped article formed may be heated at a temperature higher than that used at the beginning of the shaping operation so as to further increase the crystallinity of the polymer. The term polyethylene terephthalate includes copolymers containing not more than 10% of other units. |
