Vessel of thermoplastic material with increased resistance against gas permeance

1442958 Portable containers CONTINENTAL CAN CO Inc 12 Feb 1975 [13 May 1974] 5961/75 Heading B8D [Also in Divisions B4- B5] A thermoplastics container, closed at one end and having an internal flange 47 at the other, has its body 32 of greater stiffness and of lower gas permeability than that of the flange whereby a metal end closure, not shown, may be double seamed to the flange. The container is formed from a composite billet 10 comprised of an outer peripheral area 12 of a mouldable thermoplastics resin of relatively low stiffness and gas permeability and a core 11 of the thermoplastics resin modified by a material which provides the greater stiffness and permeability. The billet is heated and pressed between dies 35, 36 causing the outer portion of the billet to flow radially outwards into a groove in a mould chamber 37 to provide the container flange and, by moving the dies downwardly into the mould chamber, causing the core material of the billet to be extruded into the form of the container body. The resulting container is ejected by raising the dies. The outer area of the billet may be polyethylene, polypropylene or polystyrene and material added to the core may be nylon, vinylidene chloride polymers or acrylonitrile copolymers having an acrylonitrile content of at least 60% by weight. Alternatively the material added may include fillers such as wood flour, mica, asbestos fibre, CaCO 3 and TiO 2 . The billet core may comprise a laminate of a sheet of the first thermoplastics resin and a sheet of a second resin having low gas permeability.