Patent ID: 6350401
Filing Date: 2002-02-26
Classification: B29C

Abstract:
A method of continuously injection molding multi-layer products in a multi-cavity injection molding apparatus having a plurality of melt distribution manifolds and a plurality of heated nozzles mounted in a mold, each heated nozzle having a rear end abutting against one of the melt distribution manifolds and a front end adjacent a gate leading to a cavity in the mold, each heated nozzle having first, second and third melt channels extending therethrough from the rear end to the front end, a sprue bushing extending to said one of the melt distribution manifolds with the first and third melt passages extending through the sprue bushing, and valve means in the sprue bushing with actuating means to actuate the valve means between open and closed positions for controlling melt flow through the first melt channel in each heated nozzle, a first melt passage for conveying melt from a first source branching in said one of the melt distribution manifolds and extending through the first melt channel in each heated nozzle to the gate, a second melt passage for conveying melt from a second melt source branching in another of the melt distribution manifolds and extending through the second melt channel in each heated nozzle to the gate, and a third melt passage for conveying melt from the first melt source branching in said one of the melt distribution manifolds and extending through the third melt channel in each heated nozzle to the gate, comprising the steps of;(a) with the valve means in the sprue bushing in the closed position, injecting a first molten material from the first melt source through the third melt passage, whereby the first molten material flows in the third melt passage through the third annular channel in each heated nozzle and the aligned gate into the cavities, (b) after a predetermined quantity of the first molten material has been injected into the cavities, simultaneously injecting a second molten material from the second melt source into the cavities through the second melt passage, whereby the second molten material flows through the second melt channel in each heated nozzle and the aligned gate and splits the first molten material flowing from the third channel in each heated nozzle to form two outer layers of the first material in each of the cavities, (c) after flow of the second molten material into the cavities has been established, actuating the valve means in the sprue bushing to the open position to simultaneously inject first molten material from the first melt source into the cavities through the first melt passage, whereby the first molten material flows through the first melt channel in each heated nozzle and the aligned gate and splits the second molten material flowing from the second melt channel in each heated nozzle to form a central layer of the first material between two intermediate layers of the second material in each of the cavities, (d) the cavities are full and after a cooling period, opening the mold and ejecting the molded products, and (e) closing the mold after ejection of the molded products.