Melt-processible, wear resistant polyethylene

This application claims the benefit of U.S. provisional application 60/251,395 filed Dec. 6, 2000, the entire disclosure of which is hereby incorporated by reference.

This invention relates to melt-processible, wear resistant polyethylene, compositions thereof, articles formed therefrom, and methods for making the same.

Ultrahigh molecular weight polyethylene (“UHMW PE”) is well-known for, among other properties, its chemical resistance, low friction coefficient, high toughness and in particular its excellent resistance against wear. As a result, it has found numerous applications in environments where abrasion and friction may occur, such as in the chemical industry, mining, mechanical engineering, the field of biomedical implants and the textile industry. Equally well-known, however, is the intractability of this polymer, which is due to the fact that UHMW PE, above its crystalline melting temperature, does not form a fluid phase that is of a viscosity that permits melt-processing techniques used with many thermoplastic polymers. Commonly, the viscosity of UHMW PE is above 10⁶ Pa·s at 180° C. Due to this high viscosity, UHMW PE is processed into shapes and objects with techniques that are dissimilar to melt-processing methods. Rods, sheets, blocks, slabs and profiles of UHMW PE are produced by cumbersome methods such as, for example, ram-extrusion, pre-forming and sintering of compressed powder, optionally followed by machining or skiving, high isostatic pressure processing, and the like. Unfortunately, these methods generally are less economical than common melt-processing, and, in addition, severely limit the types and characteristics of objects and products that can be manufactured with this polymer.

The above drawback of UHMW PE has long been recognized and techniques have been developed to circumvent the intractability of this material by, for example, adding solvents, lubricants, plasticizers, processing aids, as well as certain polyethylenes of lower molecular weight. See, e.g., U.S. Pat. Nos. 5,658,992 and 5,422,061. The aforementioned additions of lubricants, plasticizers, and processing aids or lower molecular weight polyethylenes, however, do not yield melt-processible PE compositions with a desired combination of properties.

Objectives of the invention include providing melt-processible polyethylenes that possess one or more of the beneficial properties associated with UHMW PE.

Accordingly, one of the objectives of the present invention is to provide melt-processible polyethylenes having good wear resistance.

Additionally, it is an object of the present invention to provide a method to melt-process polyethylene compositions into useful shapes and articles of high resistance against wear.

Still another object of the present invention is to provide useful shapes and articles of high resistance against wear that are manufactured by melt-processing of polyethylene compositions.

Yet another object of this invention is to provide novel useful shapes and articles of high resistance against wear that comprise polyethylene.

The present invention provides a melt-processible ethylene having high resistance against wear, and compositions and articles comprising at least in part a continuous polymeric phase comprising a melt-processible polyethylene having high resistance against wear.

The present invention also provides a method for producing an article comprising melt-processing a composition comprising a melt-processible polyethylene, wherein said polyethylene has a high resistance against wear.

Additional objects, advantages and features of the present invention are set forth in this specification, and in part will become apparent to those skilled in the art on examination of the following, or may be learned by practice of the invention. The inventions disclosed in this application are not limited to any particular set of or combination of objects, advantages and features. It is contemplated that various combinations of the stated objects, advantages and features make up the inventions disclosed in this application.

Definition: “Monomeric units” refers herein to a portion of a polymer that corresponds to the monomer reactant used to form the polymer. For example, —CH₂CH₂— represents a monomeric unit derived from the monomer reactant ethylene.