Plastic and nonmetallic article shaping or treating: processes – Orienting or aligning solid particles in fluent matrix material
Reexamination Certificate
1999-08-17
2001-07-17
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Orienting or aligning solid particles in fluent matrix material
C264S142000, C264S323000, C264S328180
Reexamination Certificate
active
06261495
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an improved injection molding machine and method of using the machine to form parts. More specifically, the present invention relates to a plunger molding machine for reinforced polymer compositions, particularly, polymers loaded with thermally conductive media, such as carbon and aluminum in the form of fibers and flakes.
In the molding industry, it has been well known to injection mold plastics into various articles of commerce. In particular, it has become well known to load such plastics or polymer-based compositions with other media to form a reinforced polymer composition. Reinforcing a polymer composition with other media is done for many different purposes. For example, reinforced polymer may be employed to provide a thermally conductive plastic where the reinforcing media is highly thermally conductive, such as carbon fiber or aluminum flakes. Another example, is where the polymer is loaded with copper fiber to provide an electrically conductive polymer composition. Still further, aluminum flakes may be loaded in the polymer composition to provide a composition with EMI shielding. Also, glass, carbon or other fiber may be employed to add strength and/or stiffness.
In general, the loading of polymer, with a reinforcing media, raises many concerns as to the ability to successfully injection mold such a mixture because of the presence of the additional reinforcing media. For example, the loading of long carbon fiber into a polymer composition raises concerns as to strand and/or filament breakage during the melting and molding process. There is present the competing issues of the concern of thorough mixing of the loaded composition with the concern of excessive breakage of the delicate reinforcing media. Prior art molding machines typically create high turbulence and/or grinding of the polymer for the purposes of mixing the composition. These prior art machines commonly included a torpedo-shaped member or spreader to increase the level of turbulence to improve turbulence. However, such turbulence and grinding under pressure results in greatly reduced reinforcement media length.
However, these known processes are incompatible with the examples above, particularly the thermally conductive composition with carbon fiber, where it is critical that the breakage or damage to the reinforcing media be kept to a minimum to ensure that the desired properties of the composition are maintained. In the above example, if the lengths of the carbon fibers loaded within the polymer composition are ground up into much shorted lengths, it is clear that the overall thermal conductivity of the composition will be degraded as a result.
To address these problems, compression molding has been attempted where there is a manual lay-up of material and the reinforcing media thereon. As can be understood, such manual assembly is expensive and is far too slow for mass production. Thus, compression molding is inadequate and impractical for molding reinforced material and suffers from economic and geometry-related limitations.
In addition to the problems associated with the reduction of the length of reinforcing media, the alignment of such media is also a concern. In the examples above, a highly aligned and oriented loading of reinforcing media along the path of conductivity is preferred to obtain higher performance of the molded composition. For example, a highly oriented array of carbon fiber within a polymer base would yield higher thermal conductivities than a composition that included randomly oriented fibers because the number of transitions from carbon to polymer to carbon within the composition would be greatly reduced. Further, packing densities are higher when the fibers or filaments are well-aligned. The foregoing alignment and breakage problems become even more important where the aspect ratio of the reinforcing media becomes larger and larger.
In view of the foregoing, there is a demand for an improved injection molding machine and method that is well suited for accommodating polymer compositions loaded with reinforcing media having aspect ratios greater than 1:1. There is a demand for a molding machine that is capable of greatly decreasing the amount of breakage of reinforcing media during the molding process. There is also a demand for a molding machine and method of using the machine that can better align reinforcing media along the line of melt flow to provide a better oriented reinforced composition.
SUMMARY OF THE INVENTION
The present invention preserves the advantages of prior art molding machines and methods for molding reinforced plastic. In addition, it provides new advantages not found in currently known machines and methods and overcomes many disadvantages of such currently available machines and methods.
The invention is generally directed to the novel and unique molding machine and method of using the same to molding reinforced polymer into articles. The molding machine and method of using the machine of the present invention enables reinforced polymer to be molded with minimal damage to the reinforcing particles loaded in the polymer molding composition.
The plunger machine of the present invention has particular application in molding polymer that is reinforced with particles having an aspect ratio greater than 1:1. The plunger machine includes a barrel housing with a smooth barrel bore that defines a main melt chamber. A plunger housing, having a plunger bore, defines an initial melt chamber that is in communication with the main melt chamber. A plunger resides in the plunger bore and is reciprocatable therein. The barrel bore is continuously inwardly to provide a smooth transition and alignment of reinforcing members in the polymer mixture during the melt process. The smooth bore ensures substantial alignment of the reinforcement members with the longitudinal axis of the bore to avoid excessive breakage of the reinforcing particles and prepare the polymer mixture for extrusion into a mold assembly. Compression is minimized to avoid unwanted breakage of the reinforcement members which is deleterious to the integrity of the reinforcing media.
In accordance with the method of the present invention, a mixture of polymer, reinforcing particles, such as carbon fibers of an aspect ration greater than 1:1, are fed into a feed port with the assistance of an auger through a hopper. The mixture is gently fed into an initial melt chamber where the mixture is melt and then urged by a plunger into a main melt chamber. The walls of the main melt chamber are heated by heater bands, or the like, and gradually and inwardly tapered to gradually and gently melt the mixture and to gradually align the reinforcing particles with the polymer base without causing excessive breakage to the reinforcing particles. At the exit port of the main melt chamber, the reinforcing members are substantially aligned lengthwise along the direction of flow of the melt within the chamber so as to provide a highly oriented melt mixture for subsequent injection into a mold for an article. The surface area of the bore is minimized versus the volume of the bore to reduce friction within the bore.
It is therefore an object of the present invention to provide a molding machine and method of molding that is suitable for molding reinforced polymer compositions.
It is an object of the present invention to provide a molding machine and method of molding that can mold reinforced polymer compositions while substantially decreasing the amount of breakage of the reinforcing media.
It is a further object of the present invention to provide a molding machine that aligns reinforcing media in a polymer composition with the melt flow for optimal results during injection molding.
Another object of the present invention is to provide a molding machine that can directly injection feed a mold or produce highly oriented reinforced polymer pellets for later use in an injection molding process.
It is a further object of the present invention to provide an injection mo
McCullough Kevin A.
Miller James D.
Barlow Josephs & Holmes, Ltd.
Chip Coolers, Inc.
Tentoni Leo B.
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