Patent Application
20130341837
The invention relates to the injection molding of fiber reinforced polymeric articles and more particularly to the use of an electric field to produce a preferred alignment of the reinforcing fibers as they arrive in the mold cavity.
The use of fibers having a high aspect ratio to reinforce molded polymeric (plastic) articles is well known. The reinforcing fibers may be glass or polymeric and are often the product of a “chopping” process which can produce a distribution of fiber lengths. The fibers are mixed into the polymer while in a molten state and thereafter the mix is caused to flow into a die or mold cavity without significant attention being paid to the alignment or orientation of the reinforcing the fibers in the article. This can result in significant variations in the physical properties of the molded articles.
According to the present invention, the orientation or “alignment” of reinforcing fibers such as glass or other fibers in an injection molded polymeric article is controlled while introducing the fibers and polymer medium into the mold cavity. This is achieved by applying a high voltage electric field to at least one or more portions of a mold apparatus such as the mold cavity defining the article during the injection step or an inflow channel connected to the cavity. The field is maintained and for a short setup time immediately following the fill or “packing” of the mold cavity. The field is thereafter removed, the mold cavity opened and the article recovered.
In an illustrative embodiment hereinafter described in detail, the reinforcing fibers are glass with a length between about 4 and 7 mm and the electric field is between about 1 and 5 kV per mm of electrode length. For a typical article, the packing time is on the order of 30 sec. to 2 or 3 min
Other advantages, features and characteristics of the present invention, as well as methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, the latter being briefly described hereinafter.
The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views and wherein:
Referring to
As shown in
Referring to
In step 32, glass reinforcing fibers of between about 4 and 7 mm in length are mixed into suitable injectable polymer such as polyethylene, polypropylene or other thermoplastic. In step 34, a high voltage DC field of between about 1 and 5 kV per mm of electrode length, depending on the size of the mold cavity, the type and size of the fibers, and viscosity of the molten polymer matrix, is applied to at least portions of the mold cavity by way of electrodes arranged around the cavity essentially as represented by the example of
After a setup time of between 30 sec. and 2-3 min, during which the field is continuously applied, the field is related as shown in step 38. In step 40, the mold is opened in
The selection of fiber lengths and the distribution of those fiber lengths can be optimized through the use of the method described in the co-pending application, Attorney Docket No. TEMA-127-A, filed concurrently herewith and the disclosure of that application is incorporated herein by reference.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.
