Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1997-11-18
2003-02-04
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S445000, C524S449000, C524S451000, C524S476000, C524S482000, C524S526000
Reexamination Certificate
active
06515059
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of recycling scrap EPDM rubber. More particularly, the method of recycling includes incorporating devulcanized EPDM into a rubber composition for forming a rubber sheet material for roofing. The present invention also relates to a rubber sheet material formed from a composition having devulcanized EPDM therein.
BACKGROUND OF THE INVENTION
It is common in the art to employ rubber sheet material to cover rooftops. Typically, these rubber sheet materials are comprised of EPDM rubber, which is a terpolymer of ethylene, propylene and a diene monomer. Also included within such rubber sheet materials is a curative that effects the crosslinking of the EPDM terpolymer and thereby creates a durable protective membrane layer on top of the roof. The EPDM terpolymers have fully saturated backbones, giving excellent resistance to ozone and oxidation.
These protective membranes must be able to withstand severe environmental conditions without the membrane failing. Depending on the geographic location, the EPDM terpolymer membranes must be able to withstand temperatures that can reach up to as high as about 90° C. for prolonged periods of time. Further, these membranes must be able to withstand long exposure to UV light without undergoing chemical degradation. Still further, these membranes must be able to withstand long exposure to ozone without undergoing chemical degradation. In addition to the severe environmental conditions that a membrane must withstand, EPDM membranes must have superior physical durability to withstand the many stresses and strains that are imparted upon a membrane due to the natural shifting of buildings and the like.
Although such EPDM membranes have been found to be advantageous over asphalt based roofing membranes, the life of such membranes typically will not exceed thirty years of use, especially in harsh environmental conditions. The replacement of such EPDM membranes is preferably accomplished by removing the existing membrane from the roof by cutting the membrane in sections, followed by backing out any deck screws and removing the batten cover strips and flashings. If the membrane is on a ballast roof system, the gravel, e.g., river washed stones, must first be removed before cutting the membranes into sections. Further, before the roofing membrane is replaced, wet or degraded insulation boards are typically also replaced.
Because thousands of square feet of EPDM based membranes are used to cover roofs, disposal of scrap EPDM membranes is a problem. It is common to use these scrap rubber membranes as a source of fuel.
Attempts are also made to recycle the material. These recycling techniques include ambiently or cryogenically grinding the cured scrap membrane into finely ground particles and incorporating such particles into new roofing membranes or flashing formulations such as described in U.S. Pat. No. 4,732,925.
It is also known that the sulfur crosslinks formed between EPDM polymer chains can be broken by chemical processes that include the use of peptizing agents or devulcanizing agents, such as Delink® devulcanization process. The sulfur crosslinks can also be broken by mechanical processes such as ultrasonic or microwave treatment.
Although devulcanized EPDM has some “rubber-like” characteristics, and is typically more useful than ambiently or cryogenically ground EPDM, there are several reasons why devulcanized EPDM cannot be used to replace virgin EPDM in all applications. For example, recycled rubber is generally not suitable for use in applications where dynamic performance is needed, such as in tires. Accordingly, attempts thus far to employ devulcanized EPDM have included applications where dynamic properties are not essential, and where minimal reliability is demanded. These applications have included rubber moldings and weather stripping for use in automobile trim, as well as applications including spark plug boot covers, automotive floor mats, splash guards, mud flaps, and head lamp liners.
Although many uses of recycled rubber, especially EPDM, have been found, the supply of scrap rubber is still great because the largest use of rubber is in applications where dynamic performance is highly essential. There is, therefore, a need to find uses for recycled rubber that will not deleteriously impact the product in which devulcanized scrap rubber is incorporated.
SUMMARY OF INVENTION
It is therefore, an object of the present invention to provide a method of recycling used or scrap EPDM membrane.
It is another object of the present invention to provide a roofing membrane that incorporates devulcanized EPDM rubber as part of the overall polymer content present in the EPDM formulation.
It is yet another object of the present invention to provide a novel use for devulcanized EPDM rubber.
At least one or more of the foregoing objects, together with the advantages thereof over the known art relating to roofing membranes, which shall become apparent from the specification that follows, are accomplished by the invention as hereinafter described and claimed.
In general the present invention provides a method of recycling EPDM rubber including the steps of devulcanizing previously cured EPDM rubber, and adding the devulcanized EPDM rubber to a composition for forming an elastomeric membrane for roofing, the composition including a rubber mixture including from about 50 to about 95 parts by weight virgin EPDM rubber, and from about 5 to about 50 parts by weight of the devulcanized EPDM rubber, to total one hundred parts by weight rubber, from about 75 to about 300 parts by weight phr of a filler, from about 35 to about 135 parts by weight phr of a processing oil, and a cure package.
The present invention further includes a method of recycling EPDM rubber comprising the steps of devulcanizing EPDM rubber, and incorporating the devulcanized EPDM rubber into a composition for forming a rubber sheet material for roofing.
The present invention also includes a roof membrane comprising a rubber mixture including from about 50 to about 95 parts by weight virgin EPDM rubber, and from about 5 to about 50 parts by weight of a devulcanized EPDM rubber, to total 100 parts by weight rubber, from about 75 to about 300 parts by weight phr of a filler, from about 35 to about 135 parts by weight phr of a processing oil, and a cure package.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
The present invention relates to a method of recycling EPDM by incorporating devulcanized EPDM into a composition for forming a rubber sheet material for roofing. Recovered EPDM polymer is devulcanized and used as a curable replacement for virgin EPDM polymer in EPDM-based formulations. The rubber sheet material that is formed has many of the same physical characteristics as similar rubber sheet materials that employ one hundred percent virgin EPDM.
Devulcanized EPDM, or recovered scrap EPDM as it may be referred to, is recycled by adding the rubber to a composition in order to form a rubber sheet material. This rubber sheet material can be employed in such uses such as roofing membranes and flashing, pipe boot flashing, recovery boards, and walkway pads and runners.
In a preferred embodiment of the present invention, devulcanized EPDM is recycled by adding devulcanized rubber to a composition comprising an EPDM rubber component, a filler, a processing oil, and a sulfur/accelerator cure package. More specifically, the composition comprises of an EPDM rubber component, from about 60 to about 300 parts by weight filler per hundred parts by weight rubber (phr), from about 35 to about 125 parts by weight processing oil phr, and a cure package. Preferably, the composition comprises an EPDM rubber component, from about 75 to about 200 parts by weight filler, from about 50 to about 100 parts by weight processing oil, and a cure package. Still more preferably, the composition comprises an EPDM rubber component, from about 90 to about 175 parts by weight filler phr, from about 65 to about 90 parts by weight processing oil phr, and a cure package.
Davis James A.
Fannin Brenda J.
McKamie J. Arvis
BFS Diversified Products LLC
Mulcahy Peter D.
Palmer Meredith E.
Skoglund Rodney L.
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