Patent GB-1512727-A (GB)
Title: Welded polymer articles and process
IPC: B29C65/48
Filed: 1975-06-05
Abstract: 1512727 Seaming non-metallic sheet metal RAYCHEM CORP 5 June 1975 [6 June 1974] 24289/75 Heading B5K Abutting surfaces of polymeric material are joined by disposing between the surfaces insert means 1 formed of thermoplastic material having dispersed therein a heat-activatable cross-linking agent, the insert means having one or more gaps 10, 14, 18 therein, and heating the surfaces and insert means under compression, to cause the insert means to flow and the crosslinking agent to be activated, whereby the surfaces are joined by cross-linked weld material and the escape of gases from the weld area is facilitated by the gap(s). In one embodiment, Figs. 1 and 5, the insert means comprises a plurality of separate I-shape inserts with the gaps 10 being spaces between adjacent inserts. Two polymeric sheet segments 2, 3, e.g. opposite ends of a single sheet, are joined by the inserts 1 by the application of heat and pressure by platens 4, 5 which may be heated electrically or by steam and are cooled, before withdrawal, by the circulation of cooling water through passageways therein. Spaced cylinders 11 apply pressure to the plates 4 at the positions of the inserts so that the thermoplastic material flows to fill the spaces 10 which have allowed the escape of trapped air and gaseous by-products of the crosslinking reaction. The final bond is substantially free of voids, Fig. 6 (not shown). In other embodiments, the insert means comprises a single I-section member having either perforations 14, Fig. 7, in the flanges 15, 16 thereof or perforations 18, Fig. 8, through the upright portion 19 connecting flanges 20, 21. The insert means may have a foraminous reinforcing member 23, Fig. 10, e.g. a length of glass fibre cloth. Fig. 11 shows the cross-section of suitable insert means. Specified polymeric materials for the surfaces to be joined are saturated and unsaturated polyesters, polyvinyl halides, natural rubber, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, isoprene-isobutylene copolymers, polyisoprene, polybutadiene, polysulphides, polychloroprene, polysiloxanes, fluorocarbons, chlorosulphonated polyethylene, plasticized polyvinyl chloride, polybutene and, preferably, polyolefins, e.g. polyethylene, poly- (butene-1), various copolymers of ethylene, propylene and butene, ethylene/ethyl acrylate, ethylene/vinyl acetate, or ethylene/methyl acrylate copolymers in which repeat units derived from ethylene predominate, and blends of such copolymers with major proportions of polyethylene. Preferably, the surfaces to be joined are cross-linked from the outset. Preferably, the cross-linking agent is blended with the polymeric constituent of the insert means in the melt phase. Specified polymeric materials for the insert include, for the preferred polyethylenic materials for the surfaces, ethylene/vinyl acetate, ethylene/methyl acrylate, and ethylene/ethyl acrylate copolymers and blends of such copolymers with low density polyethylene or minor proportions of polyethylene. Examples of cross-linking agents are given, a peroxide cross-linking agent being preferred. Additionally, a "co-agent" may be combined in the insert material to maximize the number of cross-links formed through the agency of a given number of free radicals generated by the agent itself. Various co-agents, otherwise known as polyfunctional monomers, are specified. Also, the insert may contain fillers, e.g. carbon black or calcium carbonate, ultraviolet stabilizers, antioxidants and acid acceptors. Preferably, the modulus of the weld, at 150C and 100% elongation, is at least equal to that of the polymeric material joined thereby and at most twice or three times that of the polymeric material.