GB1339445A - Production of laminar articles - Google Patents

Abstract

1339445 Injection moulding IMPERIAL CHEMICAL INDUSTRIES Ltd 22 Nov 1971 [30 Nov 1970] 48712/71 Heading B5A In a process for producing articles having a skin of plastics material enclosing a core of dissimilar plastics material, the total amount of skin material injected into the mould cavity during an injection cycle is in an excess of that required in the moulded article, an amount of skin material equal to the excess thus being forced out of the mould cavity through one or more of the sprue channels through which only skin material was injected during the extension of the skin material within the cavity. Skin material may be injected through one sprue channel and core material through one or more other sprue channels. Additional skin material may then be injected through the same sprue channel(s) as the core material, e.g. to reduce surface exposure of core material at sprue areas or through yet another sprue channel. Moulds having two sprue channels are described in this Specification (Figs. 1-5) and in Specification 1,339,443 and moulds having three and five sprue channels are described in Specification 1,339,444. The injection of skin material may continue during or after core injection. Excess skin material may be expelled by the injection of the core material or by the subsequent foaming thereof. The excess skin material may be expelled before the cavity is full and, where the skin material is injected through more than one channel, may be expelled before or during injection of core material. Where skin material follows core material through the same sprue channel or where core material follows skin material through one or more channels, or where skin material is injected through more than one channel at no one time need there be an excess of skin material actually in the mould since a given volume of skin material already present may be displaced by the same volume of skin material which is subsequently injected. Some core material may be expelled with the excess of skin material. The excess material may be returned to its original injection chamber or diverted via a multi-way tap into another receptacle. The expulsion may be assisted by the suction provided by the retracting injection ram or screw or by a plunger in the receptacle. To permit a foamed core either less than a filling amount of material may be injected or the mould may be enlarged after injection and/or the excess skin material allowed to escape. The mould may be enlarged either by retraction of a mould member by an external force or by reducing the clamping pressure in a vertical flash mould. The excess skin material may be expelled during or after any mould enlargement. Examples of plastics materials, articles produced and the various combinations of skin and core materials are as disclosed in Specification 1,339,443.