Method for injection molding a multi-layer preform for use in blow molding a plastic bottle

A method of injection molding a multi-layer plastic preform to be blow molded into a container comprising the steps of:

• forming an inner layer of a preform of a first plastic material having an open end, sidewalls, and a closed end, said closed end having a plurality of spaced channels on the exterior surface thereof extending from a central area on the closed end to the sidewalls.
• providing an overmolding mold cavity defined by sidewalls, an open end for accommodating a core rod, and a closed end with an injection gate therethrough, and a plurality of channels on the interior surface of the closed end communicating with the gate and extending from the gate to the sidewalls;
• inserting a core rod and the inner plastic layer of the preform into said overmolding mold cavity with respective channels of the inner plastic layer of the preform and the overmolding mold cavity substantially aligned;
• and
• overmolding a second layer of a second plastic material on the inner plastic layer of the preform to form an overmolded multi-layer perform in said overmolding mold cavity by flowing the second plastic material from the gate only through the respective channels to the sidewalls of the overmolding mold cavity thereby limiting the second material in the closed end of the multi-layer preform to regions of the channels, and wherein the first plastic has a higher resistance to stress cracking than the second plastic.