Patent GB-1311085-A (GB)
IPC: B29C48/18
Filed: 1969-04-25
Abstract: 1311085 Profiled films; crimped yarns and fibres SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ NV 23 April 1970 [25 April 1969] 21196/69 Heading B5B [Also in Division D1] A film assembly comprises a film web which is fibrillatable after having been stretched in the longitudinal direction, which consists of a synthetic organic thermoplastic polymeric material, and which is provided on one or both surfaces thereof with closely spaced parallel ridges extending along the length of the film web consisting of thermoplastic meterial which "differs" i.e. in stress-strain characteristics from the material of which the film web consists having cross-sections which are substantially constant along their length and being firmly and permanently bonded to the film. The assembly may be manufactured by continuously melt extruding the thermoplastic film forming material through an extrusion die provided with a linear or an annular extrusion slot to form a film web and simultaneously continuously melt extruding the ridge - forming thermoplastic material separately through a row of closely spaced extrusion holes adjoining the slot or being in closely spaced relationship therewith to form parallel ridges strongly and permanently bonded to the film web and extending along the length thereof. The film portion of the assembly may consist of homo- and copolymers of vinyl chloride vinylidene chloride, vinyl acetate, acrylonitrile, as well as polyesters and polyamides. Preferred film-forming materials are homo- and copolymers of ethylene and particularly those of propylene. The term "differs" is  further defined as meaning that the stress-strain relationship of the material of the film differs from that of the ridges at any temperature, both in the condition as present in the assembly in stretched or unstretched condition. The polymeric starting material for the ridges may or may not be different from the film-forming material. When using different polymers they must be selected so that the melt extruded ridges strongly adhere to the melt extruded film and that this strong adhesion is maintained on solidification followed by stretching. Very good adhesion is obtained when using polymers consisting of identical monomer units but differing from one another in average molecular weight, distribution of molecular weight, stereoconfiguration, crystallinity, and/or orientation. It is stated that such differences can be produced by dividing a stream of a molten thermoplastic polymer into branches and heating this to different temperatures and/or during unequal periods of time and/or at different shear rates so that the average molecular weights in the branches decrease to a different degree, and finally by extruding the material in one of the branches through the slot shaped extrusion orifice and the other through the row of holes adjoining or close to the slot. The dissimilarity in average molecular weight can also be achieved at an identical temperature and with an identical period of heating of the branches if these branches contain different concentrations of molecular weight stabilizing agents or if such an agent is present in only one of the branches. Differences in the crystallinity of the film and ridge portions of the film web assembly can also be effected by the use of substances which influence crystallization, e.g. nucleating agents. The film web assembly may optionally be slit longitudinally into strips if of suitable width, stretched and fibrillated as by using a pinned rotating cylinder. The fibrillate may be heated to develop its crimp. Figures, accompanying the provisional Specification, show various arrangements of slots and holes suitable for use in the extrusion dies, and cross-sections of profiled films obtained therefrom.