Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common...
Reexamination Certificate
2000-03-15
2001-12-25
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
Reexamination Certificate
active
06332767
ABSTRACT:
Copies of microfiche appendixes A,B, and C which are on three (3) microfiche and contain 99 total frames, are part of and are on file with the original specification hereof in the United States Patent and Trademark Office.
FIELD OF THE INVENTION
The present invention is concerned with improved multi-layer injection molded and injection blow molded articles, apparatus to manufacture such articles and methods to produce them.
BACKGROUND OF THE INVENTION
Containers for packaging food require a combination of physical properties which is not economically available with rigid and semi-rigid containers made from any single polymeric material. Among the properties required are low oxygen and moisture permeability, compatibility with the temperatures and pressures encountered in conventional food processing and sterilization, and the impact resistance and rigidity required to withstand shipping, warehousing, and abuse. Multi-layer constructions comprised of more than one plastic material can offer such a combination of properties.
Multi-layer containers have been made commercially by thermoforming and extrusion blow molding processes. These processes, however, suffer from major disadvantages. The chief disadvantage is that only a portion of the multi-layer material formed goes into the actual container. The remainder of the material can sometimes be recovered and used either in other applications or in one of the layers of future containers made by the same process. This “recycle” use, however, recovers only a part of the value of the original material because the scrap is a mixture of the materials. Other disadvantages of these processes include limited options in terminal end geometry or “finish,” in shape, and in material distribution.
Injection molding and injection blow molding are often preferred for making single layer containers because they are scrapless and overcome many of the other limitations of thermoforming and extrusion blow molding. These processes have not been commercially adapted to multi-layer constructions because of difficulties in achieving the required control of the location and uniformity of the various layers, particularly on a multi-cavity basis. In fact, even on a single cavity basis, multi-layer injection molding has been limited to relatively thick parts in which a thin surface layer of plastic covers a relatively thick core layer of either foamed plastic or of some other aesthetically unattractive material such as scrap plastic.
To be successfully commercially adapted to food containers, multi-layer injection molding would require two major improvements over the processes which are now commercially practiced. Economical multi-layer food containers require very thin core layers comprised of relatively expensive barrier-resin such as a copolymer comprised of vinyl alcohol and ethylene monomer units. The location and continuity of these thin core layers are important and must be precisely controlled. U.S. patent applications, Ser. No. 059,375, now abandoned in favor of Continuation Ser. No. 324,824, and Ser. No. 059,374, each assigned to the assignee of this application and incorporated herein by reference, disclose multi-layer, injection molded and injection blow molded articles, parisons and containers having a thin continuous core layer substantially encapsulated within inner and outer structural layers, and methods and apparatus to make them. The disclosures in the aforementioned applications apply to both single and multi-cavity injection molding machines.
The second improvement over current commercial multi-layer injection molding processes is that the process must be capable of forming containers on a multi-cavity basis. Although the relatively large parts made by current commercial multi-layer processes can be economically practiced on a single cavity basis, food containers, which are relatively small, require a multi-cavity process to be economical. The extension from single cavity processes to an acceptable multi-cavity process presents many serious technical difficulties.
One way to extend from a single cavity to a multi-cavity process would be to replicate for each cavity the polymeric material melting and displacement and other flow distributing means used in a single cavity process. Such replication would realize some advantages over a unit cavity process. For example, a common clamp means could be used. However, it would not provide the maximum advantage because individual polymeric material melting and displacement means would still be necessary. Such a multiplicity of melting and pressurization means would not only be costly but would create severe geometrical and design problems of positioning a large number of separate flow streams in a balanced configuration, thereby increasing the required spacing between cavities, and limiting the number of cavities which would fit within the area of the clamped platens.
An alternate means of molding multi-layer articles on a multi-cavity basis would be to have a single multi-layer nozzle with its associated melting, displacement and distributing means communicate with a single channel or runner feeding multiple materials to multiple cavities. Such a runner system might be either of the cold runner type in which the plastic in the runner is cooled and removed with the injection molded article in each cycle, or of the hot runner type in which the plastic remaining in the runner after each shot is kept hot and is injected into the cavities during subsequent shots. The chief limitation of this single runner approach is that the single runner channel itself would contain multiple materials which would make it very difficult to control the flow of the individual materials into each cavity, particularly for a process having elements of both sequential and simultaneous flow such as that described in U.S. patent application Ser. No. 059,374. Controlling the flow of multiple materials in a single runner would be even more difficult in a case in which the runner is long, as in a multi-cavity system.
In the preferred embodiments of the apparatus and methods of this invention, a single displacement source is used for each material which is to form a layer of the article, but the materials are kept separate while each material is split into several streams each feeding a separate nozzle for each cavity. The individual materials are thereby combined into a multi-layer stream only at the individual nozzles, in their central channels, which feed directly into each cavity. Although this approach avoids many of the disadvantages of the previously described methods, it presents many problems which must be satisfactorily overcome for successful injection of articles in which thin core layers are properly distributed and located.
Several of these problems result from the length of the runner and the distribution system for a multi-coinjection nozzle machine. For economical reasons, it is desirable to have as many cavities as possible within the machine in order to provide as many articles as possible upon each injection cycle. It is possible to minimize the average runner length for a given number of cavities by having the channels run directly to the remotest nozzle, redirecting a part of the stream as it passes near each other nozzle. It has been found that such a channel geometry, while suitable for most single layer injection molding, has a major disadvantage for precise multi-layer injection in that a given impetus introduced at the displacement or pressurization source will have its effect more immediately in the more proximate nozzles than in the more remote ones. The time delay between the initiation of an impetus and its effect at a distance results from the compressibility of the plastic. Because of this compressibility, material must flow in the channel before a desired pressure change can be achieved at a remote location. It has been found that in order to achieve the same flow initiation and termination times and the same relative flow rates of various layers in each nozzle as well as to obtain articles fro
Kudert Frederick G.
Latreille Maurice G.
McHenry Robert J.
Nahill George F.
Pfutzenreuter, III Henry
Heitbrink Tim
McDermott & Will & Emery
Pechiney Emballage Flexible Europe
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