Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1998-12-18
2001-08-07
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S328800, C264S328140, C264S334000, C425S130000
Reexamination Certificate
active
06270711
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to multi-cavity injection molding apparatus for three layer molding and more particularly to such apparatus wherein an elongated pin extending through a central melt channel in each heated nozzle has a central melt bore extending rearwardly from its front end.
Multi-cavity injection molding apparatus for making three layer protective containers for food or preforms or parisons for beverage bottles are known. One layer of a barrier material such as ethylene vinyl alcohol copolymer (EVOH) or nylon is molded between two layers of a polyethylene terephthalate (PET) type material. In some multi-cavity apparatus the two different melts are distributed through a single melt distribution manifold having two melt passages, but preferably for materials such as these having different injection temperatures of about 400° F. and 565° F. respectively, the two melts are distributed through two different melt distribution manifolds. In some cases, the two melts are injected sequentially, while in other cases both coinjection and sequential injection are utilized. The two melts are both injected through a heated nozzle having a central melt channel and an annular melt channel extending around the central melt channel to a gate leading to the cavity.
As seen in U.S. Pat. No. 4,717,324 to Schad et al. which issued Jan. 5, 1988, valve gated apparatus has been used for three layer molding. However, that apparatus has the disadvantage that it does not disclose sprue gating apparatus and also that the valve gated apparatus does not teach simultaneous or coinjection of the two melts.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to at least partially overcome the disadvantages of the prior art by providing multi-cavity injection molding apparatus for three layer molding which allows sprue gating with fixed pins and simultaneous or coinjection by valve gating.
To this end, in one of its aspects, the invention provides multi-cavity injection molding apparatus for three layer molding having one or more melt distribution manifolds with a front face and a plurality of heated nozzles mounted in a mold. Each heated nozzle has a rear end abutting against the melt distribution manifold and a front end adjacent a gate leading to a cavity in the mold. Each heated nozzle has a central melt channel extending therethrough from the rear end to the front end and one annular melt channel extending around the central melt channel to the front end. An elongated pin having a rear end, a front end and an outer surface extends in the central melt channel in each heated nozzle in alignment with a gate leading to a cavity in the mold.
A melt passage from melt source branches in the melt distribution manifold and extends through the one annular melt channel in each heated nozzle to the gate. Another melt passage from another melt source branches in the melt distribution manifold and extends along the elongated pin in the central melt channel in each heated nozzle to the gate. Each elongated pin has a central melt bore and one or more lateral melt bores. The central melt bore extends a predetermined distance rearwardly from the front end of the elongated pin to a rear end of the central melt bore. The lateral melt bore extends outwardly from the rear end of the central melt bore to the outer surface of the elongated pin.
In another of its aspects, the invention further provides a method of continuously injection molding three layer products in a multi-cavity injection molding apparatus having a front melt distribution manifold spaced from a rear distribution manifold with a plurality of heated nozzles mounted in a mold. Each heated nozzle has a rear end abutting against the front melt distribution manifold and a front end adjacent a gate leading to a cavity in the mold. Each heated nozzle also has a central melt channel extending therethrough from the rear end to the front end and one annular melt channel extending around the central melt channel to the front end. An elongated pin having a rear end, a front end and an outer surface extends in the central melt channel in each heated nozzle in alignment with a gate leading to a cavity in the mold. The method comprises the steps of injecting a first molten material from a first melt source into the cavities through a first melt passage which branches in the front melt distribution manifold and extends through the annular melt channel in each heated nozzle through the aligned gate. After a predetermined quantity of the first molten material has been injected into the cavities, simultaneously injecting a second molten material from a second melt source into the cavities through a second melt passage which branches in the rear melt distribution manifold and extends along the elongated pin through a bore through the front melt distribution manifold and the aligned central melt channel through each of the heated nozzles and the aligned gates. This forms an inner layer of the second material between two outer layers of the first material in each of the cavities. When the cavities are nearly full, the injection of the second material through the second melt passage is discontinued, while the injection of the first material through the first melt passage is continued until the cavities are full. After a cooling period, the mold is opened and the molded products are ejected. Finally, the mold is closed after ejection of the molded products.
In another of its aspects, the invention further provides a multi-cavity hot runner injection molding apparatus for three layer molding having a front melt distribution manifold and a rear melt distribution manifold mounted in a mold extending substantially parallel to each other with an insulative air space between them. It includes a number of heated nozzles, each having a rear end, a front end, a central melt channel extending therethrough and an annular melt channel extending around the central melt channel to the front end, one or more melt bores extending from the rear end of the heated nozzle to the annular melt channel. The heated nozzles are mounted in the mold with the rear end of each heated nozzle abutting against the front melt distribution manifold. An elongated pin having a rear end, a front end and an outer surface extends in the central melt channel in each heated nozzle in alignment with a gate leading to a cavity in the mold. A number of melt transfer and dividing bushings each having a rear end and a front end and are mounted in openings through the front melt distribution manifold with their rear ends abutting against the rear melt distribution manifold and the front end of each melt transfer and dividing bushing abutting against the rear end of one of the heated nozzles. Each elongated pin has a central melt bore and one or more lateral melt bores. The central melt bore extends a predetermined distance rearwardly from the front end of the elongated pin to a rear end of the central melt bore. The lateral melt bore extending outwardly from the rear end of the central melt bore to the outer surface of the elongated pin. Thus, a first melt passage from a first melt source branches in the rear melt distribution manifold and extends through each melt transfer and dividing bushing and the annular melt channel in each heated nozzle to a gate adjacent the front end of the heated nozzle leading to a cavity in the mold. A second melt passage from a second melt source branches in the front melt distribution manifold and extends through the melt transfer and dividing bushing and along the elongated pin in the central melt channel in each heated nozzle to the gate.
Further objects and advantages of the invention will appear from the following description taken together with the accompanying drawings.
REFERENCES:
patent: 4717324 (1988-01-01), Schad et al.
patent: 4789318 (1988-12-01), Ehritt
patent: 4808101 (1989-02-01), Schad et al.
patent: 4957682 (1990-09-01), Kobayashi et al.
patent: 4990301 (1991-02-01), Krishnakumar et al.
patent: 5374178 (199
Babin Denis L.
Gellert Jobst Ulrich
Foley & Lardner
McDowell Suzanne E.
Mold-Masters Limited
Silbaugh Jan H.
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