Patent GB-1279299-A (GB)
Title: Production of films and multifilamentary yarns therefrom
Inventor: DOW JAMES
IPC: B29C48/05
Filed: 1969-06-27
Abstract: 1279299 Films; film fibrillation SMITH & NEPHEW POLYFABRIK Ltd 19 June 1970 [27 June 1969] 32758/69 Heading B5B Films consisting of a synthetic organic thermoplastic polymeric material which when in film form can be drawn without breaking at a temperature between its second order transition temperature and its melting point are produced by melt extruding the material through a slot die and feeding the molten film thereby formed through nip means between co-operating members at least one of which is a positively driven roller maintained at a temperature below the melting point of the polymer, the nip means being such as to produce shear in the film between the two film surfaces and including means for forming grooves on at least one surface of the film, particularly continuous longitudinal grooves. In the embodiment shown in Fig. 1, a molten film 1 of the polymer is melt extruded from the slot die 2 and passes through the nip between rollers 3 and 4 and thereafter through the nip between driven rollers 5 and 6. Roller 4 is a relatively cool roller maintained at a temperature below the melting point of the polymer, e.g. at 70 C., and is provided with closely spaced parallel circumferential annular grooves to form corresponding longitudinal parallel grooves on one surface of the film. Roller 3 is a smooth heated roller, e.g. at 170 C., and rollers 3 and 4 are driven at different peripheral speeds to produce shear between the two surfaces of the film, e.g. the peripheral speed of roller 3 may be 10% below that of roller 4. Rollers 5 and 6 are driven at the same peripheral speed which is preferably a considerable multiple of the speed of roller 4 so that the film is stretched longitudinally at a stretch ratio sufficiently high to cause it to fibrillate or to be readily fibrillatable by subsequent conventional fibrillation treatment. The grooved film may be longitudinally slit to form a number of grooved tapes by known means, especially while it is still in contact with the roller 4. In the embodiment shown in Fig. 2, the molten film 1 extruded from the slot die 2 passes through the nip between grooved roller 7 maintained at 90 C. and doctor blade 8 supported on backing plate 9. Blade 8 is a flexible strip of metal having a sharp edge where it contacts the film in a trailing disposition. The blade may be provided with heating or cooling means. In the embodiment shown in Fig. 3, the doctor blade 8 shown in Fig. 2 is replaced by a needle comb 11 having 100 needle 12 per inch and a length similar to that of roller 13. Roller 13 in this embodiment has a smooth peripheral surface. It is maintained at a temperature below the melting point of the polymer. In an example, the apparatus shown in Fig. 2 is used to produce a polypropylene film web 112 microns thick having a thickness of 10 microns at the grooves, the web is slit into tapes having 25 longitudinal grooves each and the tapes are stretched at a stretch ratio of 5:1 to 6:1 and fibrillated by passing the tapes through an air Venturi passage to form multi-filament yarns.