Plastic article or earthenware shaping or treating: apparatus – Distinct means to feed – support or manipulate preform stock... – And means to form or reshape preform
Reexamination Certificate
2001-10-05
2003-10-21
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Distinct means to feed, support or manipulate preform stock...
And means to form or reshape preform
C425S120000, C425S126100, C425S129100, C425S525000, C425S533000, C425S576000
Reexamination Certificate
active
06634877
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel injection mold, injection molding machine and an injection molding method for producing over-molded articles that can be made of one or more moldable materials. The invention is suitable for use with plastic resins, but can also be applied to glass, ceramics, powders or to combinations of them.
BACKGROUND OF THE INVENTION
Machines and molds for producing injection molded plastic articles of two or more layers of one or more different resins are well known. Such composite articles can be used in a wide variety of applications. Multi-materials can include materials with different molding properties, such as PET and PEN, the same material with various additives such as dyes, or combinations of these. For example, multi-layer multi-material articles which arc injection molded include the keys used in personal computer keyboards, wherein the indicia of the function assigned to the key is formed from a different colored material than the remainder of the key and components such as multi-colored lenses used for the stop and turn signal indicator lights in automobiles.
Another common use is in the manufacture of multi-layer, multi-material articles for the packaging of food wherein, for example, U.S. FDA regulations require that only virgin plastic materials be employed in locations which contact the food. Generally, it is desired to reduce the amount of virgin material which is employed in such packages for both environmental reasons (wherein it is preferred to use recycled materials) and for cost reasons (as virgin material is more expensive than recycled plastic materials). Accordingly, multi-layer multi-material packages have been produced which include a first, thin, layer of virgin plastic material which contacts the food and a second, thicker, layer of recycled or otherwise less expensive material which is laminated to the first layer during injection molding to provide strength to the package.
One area where such multi-layer packaging is employed is in bottles and other vessels manufactured from PET or other materials. PET bottles and vessels are commonly blow molded from “preforms” in a well known manner, the preforms having been manufactured by injection molding to form a thread on the neck portion of the bottle to receive a bottle closure. It is known to form a multi-layer preform of PET, the inner most layer of which is virgin plastic and at least some portion of the remainder of the preform being recycled plastic material. In such cases, when the bottle or vessel is blow molded from the preform, the virgin material forms a continuous inner layer within the vessel and the recycled or other material surrounds the outside of the inner layer to increase the overall strength of the vessel to an acceptable level.
In other circumstances, the layers employed in multi-layer articles can have properties other than, or in addition to, being different colors and virgin and recycled materials, for example layers can have different chemical properties, etc. Also, more than two layers can be employed, if desired. It is known, for example, to produce a multi-layer preform for blow molding PET bottles and vessels wherein a layer of barrier material is located between the inner layer of virgin material and the recycled material, the barrier layer inhibiting take-up of CO
2
gas from carbonated beverages stored in the blown bottle by the PET materials behind the barrier.
Various systems and techniques for molding multi-layer, multi-material plastic articles are known. Generally, such systems are based on either co-injection, over-molding and/or insert-molding systems. In all co-injection methods, the mold remains closed until the cavity is filled by the injection of two or more plastic materials into the cavity, either simultaneously or sequentially.
In sequential co-injection, a measured amount of a first material is injected into the cavity and an amount of a second material is then injected into the first material within the cavity. Due to a “skin” effect, the first material maintains its contact with the cavity walls and the second material pushes the first through the cavity, such that the materials fill the cavity with the second material sandwiched between inner and outer layers of the first.
In simultaneous co-injection, both materials are injected into the cavity at the same time, for at least part of the injection operation, and the differing viscosity, skin effects and other characteristics of the materials and the injection process result in the desired formation of layers of the materials within the cavity.
In the majority of co-injection methods, the article is made of maximum three different materials displaying different characteristics or/and functions. For example, one material can be a virgin resin, the second one can be a recycled version of same or different resin and the third can be a chemical barrier layer (such as EVOH, Nylon, MXD6) formed between them, or as a first layer. In common applications using two materials, an article can be formed having three or five layers (2M3L or 2M5L). If three materials are used, the article can have either three (3M3L) or five layers (3M5L).
Sequential co-injection systems for preforms are discussed in U.S. Pat. No. 4,781,954 to Krishnakumar et al. and U.S. Pat. No. 4,717,234 to Schad et al., the contents of each of which are incorporated herein by reference. A more recent co-injection system, shown in U.S. Pat. No. 5,582,788 to Collette et al., shows the use of a turret injection molding machine for co-injection which allows for improved cooling of molded articles.
Simultaneous co-injection systems for preforms are discussed in several U.S. Patents, such as those assigned to American National Can. Of interest in this regard is U.S. Pat. No. 5,523,045 to Kudert et al. which shows a multi-material co-injection nozzle design suitable for multi-layer preforms.
An innovative mold design capable of performing either simultaneous or sequential molding is described in U.S. patent application, Ser. No. 712,481 to Bertschi et al. and assigned to the assignee of the present invention (now U.S. Pat. No. 5,651,998). This application shows the first mold design wherein hot runner injection nozzles are located on the opposite sides of a cavity to inject two or more different resins. This approach simplifies the mold and allows for injecting into cavities which are arranged in a more compact, denser manner, as the nozzles for a single cavity are not on the same side of the mold.
While conventional co-injection methods offer some advantages as they use a single cavity and all the injection units are on one side of the injection molding machine, they also have several significant drawbacks. One of them is that it is difficult to obtain continuous and uniform layers of the different materials as they interact in a complete molten state and proper metering of the materials is often difficult. This is especially true when three materials are to injected. Further, the mold design and the hot runner design become very complicated as a single manifold or a single nozzle must be able to work with different materials having different processing parameters. These problems are further exacerbated for high cavitation molds, such as 48 or 96 cavity molds. Another difficulty is cooling, wherein thick articles require longer residence time in the mold close position, which affects the cycle time.
Some of the disadvantages of the co-injection systems are overcome by over-molding systems, where each injection operation is performed in a different mold cavity. Generally, the first injection operation is performed in a mold cavity to create the first layer of an article and the cavity is then changed to increase the volume and, commonly, to alter the geometry of the cavity space. Usually this is accomplished by changing the cavity and using the same core that holds the molded article. A second molding operation is then performed with the first layer of the article, which is retained by the core, being
Catoen Bruce
Hietkamp Doug
Mcginley Tom
Schad Robert
Sicilia Robert
Davis Robert
Del Sole Joseph S
Husky Injection Molding Systems Ltd.
Katten Muchin Zavis & Rosenman
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