Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-01-13
2002-05-07
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S098000, C525S193000, C525S197000, C525S240000, C524S080000, C524S496000, C241S021000
Reexamination Certificate
active
06384145
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method of preparing blend thermoplastic compositions using particles of recycled vulcanized, or crosslinked, rubber and to the compositions made by the method and articles formed from these compositions. The thermoplastic compositions produced by the method may be formed into many products, including automotive and industrial components.
BACKGROUND AND SUMMARY OF THE INVENTION
Both manufacturers and the general public have placed an emphasis in recent years on recycling materials. Recycling materials is desirable from the standpoint of reducing waste that must be landfilled, burned, or otherwise discarded. It has become desirable for manufacturers to include recycled plastic or recycled rubber content in the manufacture of articles. In some instances, recycled materials may also offer a cost advantage over virgin materials.
Recycling of thermoset polymeric materials, however, has faced serious difficulties in the preparation of materials for recycling and in maintaining desired properties for the articles that incorporate recycled material. One avenue for recycling crosslinked rubbers has been the use of ground crosslinked rubber as a filler in new thermoset polymeric materials. Ground crosslinked rubber may be produced in mesh sizes of from 10 to over 300, with a typical range being about 40-80 mesh. The ground crosslinked rubber has commonly been recycled by adding it to uncrosslinked rubber and then vulcanizing the blend rubber. In general, it has been reported in literature that blends cannot include more than about 10% recycled rubber without suffering a significant decrease in properties, including surface roughness. Mixtures including up to 30% ground crosslinked rubber in new rubber have been reported to have somewhat lower tensile strength as compared to virgin rubber.
One solution to the problem of how to incorporate larger amounts of recycled rubber without a decrease in properties is to chemically treat the recycled rubber. Stosky reported in “Innovation in the Development and Use of Recycled Rubber,” Paper No. 42, Rubber Division, American Chemical Society (May 6-9, 1997) that chemically treated recycled rubber could be incorporated in amounts of up to 75% in a blend with virgin rubber, resulting in a material having equivalent or even superior performance as compared to virgin rubber. The chemical treatment appears to involve a surface treatment that allows for crosslinks between the ground crosslinked rubber and the virgin thermosetting material. Another method of recycling rubber involves de-vulcanizing the rubber by physical or chemical means. De-vulcanized rubber may be mixed with virgin material, re-molded, and then re-vulcanized along with the new material to produced a crosslinked blend. A process of treating ground crosslinked rubber with a caustic gas to allow bonding with other polymers has also been reported.
These methods, however, involve added reactions and manufacturing steps that make recycling of materials more expensive. Moreover, these methods are directed to thermoset materials only. Thus, the need remains for a relatively simple and effective means of recycling cured rubber scrap into new articles, particularly articles formed from thermoplastic compositions.
The present invention provides a method of recycling a cured EPDM terpolymer or EPR copolymer rubber, or mixtures including these rubbers, by blending the recycle rubber into a thermoplastic material such as a thermoplastic polyolefin or resin or an olefin or vulcanizate thermoplastic elastomer to form a blend composition. The blend compositions comprise ground crosslinked rubber having a particle size of about 80 mesh or smaller, preferably of about 120 mesh or smaller. (The mesh size is inversely proportional to the particle size.) The compositions prepared according to the methods of the invention may include a surprisingly high level of recycle rubber without adverse effect on physical or aesthetic properties. Thus, the blend thermoplastic materials produced may comprise up to about 70% by weight of the ground crosslinked rubber, based upon the total weight of the blend material. The thermoplastic blend materials of the invention may also comprise a compatibilizer.
DETAILED DESCRIPTION
The term “ground crosslinked rubber” as used in relation to the methods and compositions of the invention refers to at least partially crosslinked or vulcanized rubber that has been reduced to particles. Preferably, the rubber is fully crosslinked; i.e., the crosslinking has been carried to an extent that formation of further crosslinks, if possible, would not substantially improve the physical properties of the rubber. The particle size of the recycle ground crosslinked rubber of the invention is about 80 mesh or smaller, preferably about 120 mesh or smaller, and it is especially preferred that the particle size be about 200 mesh or smaller.
The ground crosslinked rubber particles may be prepared by a number of methods. In one method, the rubber is swelled with solvent and then ground to a fine particle size. The rubber may be ground cryogenically. In a preferred procedure, the recycled rubber particles are prepared according to the procedure in Rouse, U.S. Pat. No. 5,411,215, incorporated herein by reference. In this procedure, the rubber is ground as a 10% by weight slurry in water of 10 mesh particles in a series of grinding mills having progressively finer grinding stone.
The rubbers that may be recycled in the methods and compositions of the invention are ethylene propylene rubber (also known as EPM or EPR), ethylene propylene diene monomer rubber (EPDM), and mixtures and blends of these. The rubbers will be collectively referred to herein as EPDM. Mixtures and blends of EPDM with other rubbers may also be used, as well as elastomeric alloys that include these rubbers. The rubber compound, which includes the rubber and any additives, may also typically include up to about 50% additives, preferably up to about 15% additives, based upon the weight of the rubber compound. Example of useful additives include, without limitation, accelerators, oils, colorants and fillers, especially carbon black.
The ground crosslinked rubber is mixed with a thermoplastic component. The thermoplastic component is preferably a polyolefinic material. Among preferred materials are homopolymers of ethylene, propylene, and butylene, and copolymers that include one or more of these monomers. In a particularly preferred embodiment, the recycled ground crosslinked rubber is ethylene propylene diene monomer rubber and the thermoplastic component is selected from polyethylene, polypropylene, ethylene copolymers, propylene copolymers, poly(ethylene propylene) copolymers, and combinations of these. In a particularly preferred embodiment, the rubber particles comprise EPDM rubber that is at least partially cured, preferably fully cured, and the thermoplastic composition comprises polypropylene.
Alternatively, the thermoplastic component can be a thermoplastic elastomer such as an olefinic thermoplastic elastomer, i.e., a TPO, or an olefinic vulcanizate elastomer, i.e., a TPV.
The ground crosslinked rubber particles can be included in the thermoplastic composition in amounts of up to about 70% by weight, and preferably up to about 60% by weight, based upon the total weight of the blend thermoplastic composition. Preferably, at least about 5% by weight of the recycle ground crosslinked rubber is included. The amount of ground rubber that is included is determined based upon the particular application and can readily be determined by straightforward testing.
The compositions of the invention may also include a compatibilizer. Generally speaking, a compatibilizer is required where the thermoplastic component consists essentially of a polyolefinic material, but may not be required where the thermoplastic component is a TPO or a TPV. Useful compatibilizers are plasticizers and oils that are used to improve physical properties of the blend. It is particularly preferred to inc
Citarel Louis
Hollister Annette K.
Mertzel Elaine A.
Rodak Laurel A.
Sheets James P.
Cooper Technology Services LLC
Fay Sharpe Fagan Minnich & McKee LLP
Wu David W.
Zalukaeva Tanya
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