PRODUCTION METHOD OF HOLLOW PREPRODUCTS - BY INJECTION FROM THERMOPLASTIC MATERIAL

1450108 Injection-blow moulding UNILEVER Ltd 13 Dec 1973 [14 Dec 1972] 57722/73 Heading B5A A hollow thermoplastic preform to be blowmoulded is formed by injection moulding in a mould having a core formed by a mandrel having a blowing channel communicating with the outside surface of the mandrel wherein a pressure drop from the outside to the inside of the preform is established before release of the injection pressure, e.g. by applying a vacuum via the blowing channel. The pressure drop may be maintained from the commencement of injection or before preferably until the preform has completely set. As shown, the mandrel comprises a sleeve 5 and a relatively movable tip 6, part 6a of which is mounted on blowing tube 11. When the tip 6 is raised, groove 15 between tip 6 and sleeve 5 communicates with tube 11 via radial passages 13. The mandrel also includes a tube 21 forming passages 22a, b for coolant. The two-part injection-mould 3, 4 may also contain coolant passages. The tube 11 is communicable with a vacuum source 16 operated by control means 19 in the tip-closed, injection position. The mandrel is preferably mounted on a turret for rotation to the blowmoulding position.