GB1262978A - Heat shrinkable components with meltable liner - Google Patents

Abstract

1,262,978. Laminate for heat-shrunk-packaging. ELECTRONIZED CHEMICALS CORP. 9 April, 1969, No. 18200/69. Heading B8C. [Also in Divisions F2 and H2] A polymer laminate, used for instance for skin tight packaging and as end caps for tubes and wires, comprises a hollow body 11 of flexible orientated thermoplastic having a heat actuable memory therein, said memory being activable at a temperature above room temperature (78‹ F.) to induce a major shrinkage in said body, and a non-heat shrinkable, unorientated, cross-linkable, thermoplastic, insert disposed within said body said insert having a portion 12 thereof adapted to melt in the presence of the deforming heat and having another portion 14 thereof cross-linked to substantially prevent the melting of said other portion at least at the heat deformable temperature used to activate the memory of said body. As shown, in an end cap 10 for covering and insulating the bared ends of spliced electrical wires the outer shell 11, of modified polyethylene having added thereto a flame retardant, an anti-oxidant, a vinyl stabilizer and an inert inorganic carrier, is extruded in tubular form and is moulded to form the closed end of the cap the shell 11, while being shaped, being treated by electron beam irradiation to provide dimensional stability at elevated temperatures by cross-linking. The cap 11 is then heated and expanded up to not more than 200% of its original diameter, by applying internal air pressure to expand the cap against an external mould, whereupon it is cooled to below, e.g. 275‹ F., so that it sets in its expanded condition. The inner meltable liner 12 is extruded, at the same time, from a thermoplastics material, e.g. a modified polyolefine, which melts at a temperature between room temperature, i.e. 78‹ F., and the shrinking temperature of the material 11. The material of the liner 12 is cross-linkable so that a portion, e.g. 14, Fig. 2, can be cross-linked by high energy ionizing radiation. In use, when the cap is placed over the bared ends of spliced wires, and heated to shrink the outer jacket 11, the portion of the liner 12 not irradiated melts and moulds itself around the wire ends, and the irradiated portion 14, which does not melt, collapses under the compressive force of the outer jacket 11 and forms a dam which prevents extrusion of any melted material out from the cap. The laminate may be in the form of an open ended tube in which case a portion of the inner liner 12 is irradiated at each end. Copolymers particularly suitable for use as the liner 12 are stated to be selected polyolefines, polyvinylhalides, polyacrylates, polysilastic rubbers, polybutadiene rubbers, ethylene ethyl acrylate. The liner may contain a small portion of non cross-linkable materials, e.g. atactic polypropylene. The materials of the tubular laminate may also include colours, anti-blocking agents &c. Other polymers mentioned for the outer jacket 11 are fluorinated ethylene propylene, and polyethylene terephthalate.