Patent GB-1260837-A (GB)
Title: The manufacture of filaments, fibres and yarns
Inventor: VERNON BRIAN JAMES
IPC: B29C43/22
Filed: 1968-04-11
Abstract: 1,260,837. Film fibrillation. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 26 March, 1969 [11 April, 1968], No. 17522/68. Heading B5B. Artificial fibres are made by profiling a film web of a molecularly-orientable synthetic organic thermoplastic polymer by impressing into a surface thereof a plurality of longitudinally extending grooves disposed in close but spaced apart relationship and stretching the profiled film web to effect longitudinal orientation thereof at a stretch ratio sufficiently high to render the film web fibrillatable and subjecting the stretched film web to a fibrillation treatment, the grooves being formed by passing the film web at a temperature below the crystalline melting point of the polymer through the nip formed between two contra-rotating cylindrical elements having non-yielding surfaces, at least one of the cylindrical elements having a plurality of closely-spaced parallel surface ridges, each ridge having inwardly directed sides leading to peaks which are rounded off to a small radius. The pitch of the ridges may be within the range 0À003 to 0À05 inch and the depth of the troughs formed between adjacent ridges may be within the range 0À002 to 0À02 inch. Both surfaces of the film web may be impressed with the grooves by passage through the nip formed between two cylindrical elements each of which has ridges of identical profile and pitch, the cylindrical elements being positioned in such a manner that the peaks of the ridges of one element are opposite those of the other. The film web may be preheated prior to contacting the cylindrical elements and the preheated web may be formed by the blown-film technique in a preceding stage of the process. The fibrillation treatment may comprise an air blast treatment effected by passing the stretched web through an elongated passage of restricted cross-section through which a current of air flows at a high velocity in the direction of travel of the web. The web may consist of a laminate of two or more polymer films which differ in chemical and/or physical properties. The laminate may be formed by feeding two or more separate films in superimposed relationship to the nip. A heat transfer medium may be circulated through one or both elements to maintain them at a desired surface temperature. The cylindrical elements may be of steel. The filaments produced by fibrillation may be cut to form staple fibres which may be twisted into a yarn. The ridges may be divided lengthwise into two or more sections separated by short unridged portions of the peripheral surface of the elements, the unridged portions being in staggered relationship across the width thereof whereby the fibres resulting from the fibrillation step are incompletely separated from one another. The fibrillation step may comprise a twisting operation which yields the resulting fibres in the form of a yarn. The film webs used in the process of the invention may consist of polypropylene, high density polyethylene or a nylon. The term "polymer" is used in the Specification to include a polymer composition. The individual fibres of the invention may have a denier of, for example 5 to 90 and a tenacity of, for example, up to 7 grams per denier.