Patent GB-941723-A (GB)
Title: Method for the production of a fibrous artificial organic polymeric material
IPC: D01D5/42
Filed: 1960-06-23
Abstract: 941,723. Non-woven network of artificial fibres. O. B. RASMUSSEN. June 23, 1960 [June 25, 1959], No. 22023/60. Heading B5B. A high molecular weight organic linear polymeric material is shaped into the form of a network of coherent fibres by stretching a film or band of the material unidirectionally, splitting the film or band in the stretching direction into fibres which, however, remain united to one another at intervals along their length so that they form a network by subjecting the stretched film or band to distortion, impact, supersonic vibration or lateral stretching, stretching the network transversely to cause the meshes of the network to expand laterally and subjecting the network to a fixing or setting treatment causing it to retain its dimensions and structure. The stretching and splitting may be carried out in the longitudinal direction or in a non-longitudinal direction as, for example, described in Specification 816,607. The transverse stretching is preferably effected in a direction at right angles to the direction of splitting of the film or band. The transverse stretching may be effected by means of a tentering device of known type in which the opposite borders of the advancing film or band are gripped by two rows of tenter clips travelling along diverging paths, but is preferably effected by clamping the split film or band between elastic bands which are stretched in the transverse direction. The clamping should be so slight that the individual fibres are able to slip between the bands during the spreading of the film or band, but the bands should have a surface providing a certain amount of friction to be overcome before the fibres slip, e.g. a surface layer of a foamed plastic, such as formed nylon. The fixing treatment may be effected by introducing the network of fibres between two supporting bands which exert sufficient pressure to keep the network in the spread state and passing the bands over a heater which raises the temperature of the network nearly to the melting point of the fibre material. The network remains in the distended state after being cooled and removed from the bands and can be twisted or rolled to form a coarse highly porous yarn. The network may be passed through the heated vapours of a swelling agent during the fixing heat treatment. The fixing treatment may consist in spraying a solution of a high polymer in a volatile solvent on to the network and thereafter evaporating off the solvent. The network may also be fixed by a chemical treatment which cross-links the fibre material, or the network may be subjected to ultra-violet rays, X- rays or radioactive irradiation. The network may be covered with a screen of material impervious to radiation and having a mesh of, for example, 1/10 mm. before exposing the network to irradiation. In an example, a 1 cm. wide band of polyethylene of specific gravity 0.96 is stretched at 115‹ C. to a stretch ratio of 14: 1 and then subjected to a longitudinal splitting treatment between rubber surfaces in known manner. The network of fibres thus produced is stretched to the original width of the band and then sandwiched between endless rubber bands which are stretched transversely so that the network is stretched to a width of 4 cm. This expanded network is then subjected at room temperature to radiation with accelerated electrons (#-particles) in a nitrogen atmosphere at a dose of 5 megarad. Immediately after being irradiated the network is passed through a bath of monomeric vinyl acetate and subsequently dried.