A multi-layer forming nozzle includes a valve member which can open and close a flow passage of molten resin which forms an intermediate layer of a multi-layer molded product by injection molding. The valve member is operated in response to resin pressure differentials at the front and back of the valve...http://www.google.co.uk/patents/US5030077?utm_source=gb-gplus-sharePatent US5030077 - Multi-layer molding nozzle
