| 摘要 |
1,233,713. Polypropylene split-fibres; composite extrusion dies. MITSUBISHI RAYON CO. Ltd. 29 Nov., 1963 [11 Dec., 1967; 7 Feb., 1968], No. 56936/68. Heading B5B. A polypropylene film, which may be composite, is slit into tapes which are hot-drawn, e.g. in air or steam, at a ratio of 5-15, and the drawn tapes are mechanically fibrillated by passage over a rotating roll provided with splitting means, e.g. spirally disposed needles or sawtooth wire on its surface. The process is conducted within the limits defined by R= K 1 t+K 2 r and R=100 (S 2 -S 1 )¸S 1 where t is the thickness of the film in Á, r is the draw ratio, S 1 and S 2 are the delivery and withdrawal speeds respectively of the film to and from the roll, 0À065#K 1 #0À095 and -0À18# K 2 # - 0À22. The polypropylene may be blended with a minor proportion of another polymer, e.g. low density polyethylene. Other conventional additives, e.g. a pigment, may be present. The composite film may comprise two polypropylene layers having different heat shrinkabilities due to differing chemical and/or physical characteristics. The extrusion die of Fig. 3 makes composite films from a single polymer supply 17a. The polymer is split into two streams, one of which passes through extruder 17b before reaching the orifice 27. The two streams, which are kept apart at 22b until actual extrusion, lead to layers of differing heat-shrinkability. |
