Patent ID: 6099780
Filing Date: 2000-08-08
Classification: B29C,B29K

Abstract:
A method of injection molding multi-layer products in a multi-cavity injection molding apparatus having a front melt distribution manifold spaced from a rear distribution manifold by melt transfer bushings with a plurality of heated nozzles each mounted in a mold, between the front melt distribution manifold and a gate leading to a cavity in the mold, each heated nozzle having a central channel extending therethrough and an annular me lt channel extending around the central channel, an elongated valve pin extending in the central channel in each heated nozzle in alignment with a gate leading to a cavity in the mold, and valve pin actuating mechanism to reciprocate each valve pin between a retracted fully open position and a forward partially open position wherein the front end of the valve pin is seated adjacent the aligned gate to block melt flow through the annular melt channel, comprising the steps of;(a) with the valve pins in the forward partially open position, injecting a first molten material from a first melt source into the cavities through a first melt passage which branches in the rear melt distribution manifold and extends through passages in the melt transfer bushings and along the valve pins through bores through the front melt distribution manifold and the central channels through the heated nozzles, and through the aligned gates into the cavities,(b) after a predetermined quantity of the first molten material has been injected into the cavities, retracting the valve pins to the fully open position and simultaneously coinjecting a second molten material from a second melt source into the cavities through a second melt passage which branches in the front melt distribution manifold and extends through the annular channel in each heated nozzle and through the aligned gates whereby the second molten material forms a middle layer between inner and outer layers of the first material in each of the cavities,(c) when the cavities are nearly full, returning the valve pins to the partially open position to discontinue the injection of the second material through the second melt passage, while continuing the injection of the first material through the first melt passage until the cavities are full,(d) after decompressing the first material and a cooling period, opening the mold and ejecting the molded products, and(e) closing the mold after ejection of the molded products.