Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common...
Reexamination Certificate
1999-03-18
2003-12-02
Walker, W. L. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
C425S563000, C425S566000, C425S573000
Reexamination Certificate
active
06655945
ABSTRACT:
FIELD OF INVENTION
The present invention relates to multi-layer products, and an apparatus and method for the injection molding of same. More specifically, it relates to a three-layer bottle preform and closure, and an apparatus and method for injection molding of same.
BACKGROUND OF THE INVENTION
Multi-cavity injection molding apparatus for making multi-layer molded products, such as protective containers for food, preforms for beverage bottles, and closures, are well-known. One or more layers of one material are typically molded within, or together with, one or more layers of another material, to form the molded product. At least one of these layers is usually a barrier layer formed from a barrier material to protect the contents of the molded product. Since the barrier material is expensive, typically only a very thin barrier layer is used in the molded product. It is also generally desirable to have this thin barrier layer uniformly and evenly distributed (i.e., well-balanced) throughout the molded product to provide the proper protection for the contents of the molded product.
An example of an injection molding apparatus used to make three-layer preforms with thin barrier layers is disclosed in U.S. Pat. No. 4,990,301 to Krishnakumar et al. Krishnakumar et al. disclose an injection molding device having multiple and selective melt inlets, passages, channels, and gates, requiring different manifold configurations, for forming multiple layer preforms. In particular, Krishnakumar et al. disclose the use of one large central melt passage and three small annular melt passages flowing into a central channel that opens into a cavity for multi-layer preforms. Depending on the application, either the large central melt passage or one of the three small annular melt passages may be chosen for a barrier material. Krishnakumar et al. inject the barrier material from a selected passage into the cavity, either directly against a cooled portion of preform material previously disposed in the cavity, or after injecting a hot portion of preform material from another passage, in addition to the cooled portion, into the cavity.
There are several problems with the device disclosed by Krishnakumar et al. First, the injection molding device disclosed by Krishnakumar et al. uses multiple melt inlets, passages, channels, and gates that require several different configurations for the same manifold, depending on the application, to make multi-layer preforms. As a result, the injection molding device of Krishnakumar et al. is complex and expensive to both manufacture and operate. Second, injecting a barrier material directly against a cooled portion of preform material previously disposed in a cavity often results in an uneven, or interrupted, barrier layer that does not properly protect the contents of the molded preform. An altered and non-uniform barrier layer may also present problems with blowing out the preform. Third, injecting a barrier material only after injecting a hot portion of preform material, in addition to the cooled portion, into a cavity adds additional time to the injection cycle or production time for the preforms.
Finally, the injection molding device disclosed by Krishnakumar et al. uses large and small passages for the flow of barrier material. The large passage can be problematic, since it can retain too much barrier material at a high temperature, thereby causing the degradation of the barrier material. On the other hand, the small passages can cause high pressure drops for the barrier material as it enters the cavity, thereby damaging or washing out the preform material already in the cavity.
Other examples of injection molding apparatus used to make three-layer preforms with thin barrier layers are disclosed in U.S. Pat. No. 4,957,682 to Kobayashi and U.S. Pat. No. 4,743,479 to Nakamura et al. Kobayashi discloses a method to form a two material, three layer preform. In a first step, PET is injected through an annular nozzle melt channel into a mold cavity. In a second step, a barrier layer of EVOH is injected through a central melt channel of the same nozzle. Because the thin layer of EVOH is divided only inside the cavity into a core barrier layer within the PET layer, there is no control over the uniformity of the barrier layer in the cavity. Also, the injected barrier layer will most likely damage or washout the PET layer already located in the cavity. Kobayashi also does not provide any means to control the position of the barrier core layer within the preform.
Similarly, Nakamura et al. disclose a method to produce a two material, three layer preform, where PET is injected first through a central melt channel. In contrast, the barrier layer is injected later from a separate annular channel simultaneously with additional PET. The method disclosed by Nakamura et al., however, positions the thin layer of EVOH directly against the cooled portion of PET already in the cavity. As previously explained, this arrangement results in an uneven, non-uniform, and unbalanced barrier layer within the preform.
Accordingly, it would be desirable to have an apparatus and method for injection molding of three-layer preforms or closures that overcomes the problems associated with the prior art by not having multiple melt inlets, passages, channels, and gates, and by having a single configuration for each of its manifolds. An injection molding apparatus and method for injection molding of three-layer preforms or closures without multiple melt inlets, passages, channels, and gates would be relatively simpler and less expensive, both to manufacture and operate.
It would also be desirable to have an apparatus and method for injection molding of three-layer preforms or closures that does not inject a barrier material either directly against a cooled portion of preform material previously disposed in a cavity, or after injecting a hot portion of preform material, in addition to the cooled portion, into the cavity. Such an apparatus and method would provide three-layer preforms or closures with more evenly and uniformly distributed barrier layers, and thus, better protection for the contents of the preforms or closures, without increasing the cycle or production time for the preforms or closures. Moreover, it would also be desirable to have an apparatus and method for injection molding of three-layer preforms or closures that avoids the problems associated with large and/or small passages or channel for barrier material.
In addition, it would be desirable to have an apparatus and method for injection molding of three-layer preforms or closures that is capable of controlling the position of the layer of the barrier material within the preform or closure.
SUMMARY OF THE INVENTION
The present invention provides an injection molding apparatus for multi-layer molding comprising a central melt channel and an annular melt channel radially spaced from the central melt channel. The apparatus also comprises a melt passage having a first melt portion in communication with the central melt channel, and a second melt portion in communication with the annular melt channel.
In addition, the present invention provides an injection molding apparatus for multi-layer molding that comprises a central melt channel having a first portion for flow of a first material, a second portion for flow of the first material and a second material, and a flow extension connecting the first portion and the second portion. The flow extension also has a flow opening. The apparatus further comprises an annular ring channel surrounding the central melt channel for flow of the second material. The annular ring channel is also in communication with the flow opening of the flow extension.
Moreover, the present invention also provides an injection molding apparatus for multi-layer molding comprising a central melt channel for flow of a first material and a second material, and an annular melt channel radially spaced from the central melt channel for flow of the first material. The apparatus also comprises a cavity for receiving flow
Babin Denis L.
Gellert Jobst U.
Luk Emmanuel
McDonnell & Boehnen Hulbert & Berghoff
Mold Masters Limited
Walker W. L.
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