METHOD OF AND APPARATUS FOR PRODUCING A STRETCHED FILM COMPRISING A THERMOPLASTIC MATERIAL

摘要

1513797 Stretched films HOECHST AG 27 June 1975 [29 June 1974] 27299/75 Headings B5N and B5B Two or more stretched films are produced by extruding a melt of a thermoplastic material, e.g. polyester or polypropylene, through a slot die, longitudinally dividing the thermoplastic material to form two or more films, superposing at least two of the films and stretching them transversely. The melt may be longitudinally divided in the die lip during extrusion or the cooled film may be divided using knives, inductively heated dividing devices or laser devices. The films may have a thickness of 2-100 Á. The transverse stretching may be preceded by longitudinal stretching which may be effected while the films are parallel to adjacent each other before superposing them. Heat-setting may be effected after transverse stretching and the films then cut to suitable widths. In Fig. 1 melt leaving extruder 1 through slot die 2 is divided into two streams 4, 41 by dividing wedge 18 and the melt streams after solidification on cooling roller 3 are passed over roller 20 to a longitudinal stretching device comprising rollers 5a to 5f driven at different speeds. The films are superposed in device 12 in which film 4 is guided over rollers 8 and 11 supported by bearings 13 and 15 and film 41 is deviated over rollers 9 and 10 supported by bearings 14 and 16. The superimposed films are guided over collecting roller 111 and clamped by clips 17 and 171 and stretched by the transverse stretching frame having heating chamber 19. The film web may be separated and longitudinally stretched and then wound separately, or simultaneously wound or directly subjected to further treatment, e.g. coating or printing.