GB1420948A - Injection moulding process - Google Patents

Abstract

1420948 Injection moulding IMPERIAL CHEMICAL INDUSTRIES Ltd 27 Sept 1973 [26 Oct 1972] 49464/72 Heading B5A In a process of making articles having a skin of a synthetic polymer composition enclosing a core of a dissimilar synthetic polymer composition, the skin and core materials are plasticized in separate barrels 3 and 1 respectively and, prior to injection, plasticized skin material is fed to the outlet end of the core material barrel 1 to build up a plug of skin material therein and then when the desired amounts of skin material S and core material C have been built up in the barrel 1 both materials are injected through a sprue channel 8 into the mould cavity 9. The barrels 1 and 3 may contain plasticizing screw 2 and 4 respectively which may be axially reciprocable. Plasticizing of the core material may take place before, during, or after feeding of the skin material to the barrel 1. A multiway tap 5, in the position shown in Fig. 2 connects the two barrels and isolates both from the sprue channel 8. In another position (Figs. 3, 4, not shown) both barrels are connected to the sprue channel. Alternatively, in a second position the tap may connect one barrel to the sprue channel, the other being isolated. A further quantity of skin material may be injected after the core material. This may be done by switching back to the skin material barrel after injection of the core material. Alternatively, no switching is necessary if the tap 5 is as seen in Fig. 4 (not shown). The core material may be foamable. Numerous examples of suitable injection moulding materials are given.