GB1281083A - Banded synthetic fibres formed by film fibrillation - Google Patents

Abstract

1281083 Banded fibres formed by film fibrillation SMITH & NEPHEW RESEARCH Ltd 3 Feb 1970 [5 Feb 1969] 6132/69 Heading B5B A longitudinal array of interconnected fibres, the individual longitudinal fibres of which are continuously bonded along their length by possessing successive regions of different crosssectional area, degree of orientation and morphology, may be formed by (a) taking a sheet or tape of synthetic polymeric thermoplastic material having on one or both sides or within its thickness a regular or irregular pattern or arrangement of regions of different morphology such that longitudinal sections along the sheet or tape show regular or irregular differences respectively in such morphology, and (b) stretching the sheet or tape longitudinally at a stretch ratio and temperature such as to produce a longitudinal array characterized in the manner described above. The expression "differences in morphology" is defined as meaning structural differences or the surface and/or within the thickness of the film, especially those relating to size, shape and arrangement of the polymer crystallites. The fibres in the array may possess alternate thick and thin portions or alternate solid portions and multistrand portions. In the example, the fibres of the array consist of polypropylene The array may be formed into a bundle of substantially separate fibres by application of a separating energy. The array may be twisted to form a yarn or may be chopped to form staple fibres. In the process of forming the array the differences in morphology may be caused by a random or a regular pattern of irradiation of the film, of differential cooling of an extruded melt forming the film, or of perforations in the film. The perforations may be flame perforations. The differences in morphology may correspond to differences in film thickness. The film may have on at least one surface a regular pattern of discrete raised embossments and the embossments may be hexagonally packed on the surface. The film may have on at least one surface a regular pattern of discrete depressions, or a regular pattern of two intersecting sets of parallel straight intersecting grooves, or on one surface a set of parallel grooves and on the other surface another set of parallel grooves, the two sets lying in intersecting directions. The film may have non-longitudinal grooves at an angle to the transverse direction. The film may be provided with a herringbone pattern or with generally longitudinal parallel wavy lines.