Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1995-09-12
1998-02-17
Krass, Fredrick
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C08L 9500
Patent
active
057192154
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to the treatment of vulcanate rubber, particularly scrap rubber from automobile tires as well as from other sources, to effect partial or high levels of dissociation of the rubber vulcanate network and the incorporation of such treated rubber into stable bituminous compositions.
BACKGROUND TO THE INVENTION
Motor vehicle tires represent a significant disposal problem and attempts have been made to recycle the same, for example, by incorporation of recycled ground rubber formed from such tires into various products, including asphalt compositions for roadway pavements. Such ground rubber is often identified by the term "rubber crumb" and that expression is employed herein.
Recycled rubber crumb generally contains a variety of rubber polymers, including styrene-butadiene rubber, natural rubber and its synthetic analog (cis-polyisoprene), cis-polybutadiene, butyl rubber and EPDM rubber. Often such recycled rubber crumb comprises predominantly styrene-butadiene rubber.
A search of the prior art in the facilities of the United States Patent and Trademark Office has located the following United States patents related to the reclaiming of rubber from vulcanized rubber waste, including automobile tires:
______________________________________ 1,168,230 1,133,952
1,981,811 2,645,817
3,880,807 3,896,059
4,161,464 4,146,508
4,469,817 5,095,040
______________________________________
mechanical and chemical procedures.
Crumb rubber generally is recycled rubber that has been reduced to ground or particulate form by mechanical shearing or grinding. A variety of procedures have been used to reclaim materials from ground scrap rubber, one of the most common being an alkali process in which ground rubber is treated in aqueous sodium hydroxide solution at elevated temperature. Other reclaiming processes involve treatment of ground rubber in processing oils using various combinations of high temperature and excessive shear for the purpose of producing liquified materials which may be incorporated into the manufacture of new tires or used directly as fuel oil.
In addition, it has been proposed that scrap crumb rubber be incorporated into asphalt paving materials. In general, crumb rubber may be incorporated into asphalt paving materials by one of two processes, namely a wet process or a dry process.
In the wet process, the crumb rubber is blended into the asphalt cement, by batch blending in which batches of crumb rubber and asphalt are mixed in production, by continuous blending with a continuous production system, or by terminal blending. An asphalt cement binder that has been modified with crumb rubber is termed asphalt rubber. In the dry process, the rubber crumb is added to heated aggregate, not the asphalt cement, or hot mix asphalt mixture during production of the mix.
In one such wet procedure, hot asphalt (about 190.degree. to 220.degree. C.) is mixed with approximately 25 to 30 wt % crumb and the mixture then is diluted with kerosene. A variation of this procedure uses about 22 wt % crumb with dilution being effected using extender oil. It is thought that blending the crumb rubber and asphalt at elevated temperature may promote limited chemical bonding of the components. However, these compositions exhibit only short-term stability and, therefore, must be employed shortly after formation.
A recent variation of the wet process is contained in U.S. Pat. No. 4,992,492. The process involves a mixture of asphalt or sulfur-treated asphalt (81 to 86%), crumb rubber (8 to 10%), extender oil (4 to 6%) and a high molecular weight (>100,000) olefinically-unsaturated synthetic rubber (2 to 3%) which is blended together at 175.degree. to 180.degree. C. for about two hours.
As claimed, this process differs from the present invention in a number of important facets. In the referenced process the ground crumb rubber is dispersed in the bitumen, however, the vulcanate network undergoes limited, if any, chemical disassociation. Such crumb rubber compositions would b
REFERENCES:
patent: 4166049 (1979-08-01), Huff
patent: 4412864 (1983-11-01), Kurashige et al.
patent: 5114648 (1992-05-01), Kuc, Sr.
patent: 5304576 (1994-04-01), Martinez
patent: 5380773 (1995-01-01), Bellio et al.
Liang Zhi-Zhong
Woodhams Raymond T.
Krass Fredrick
Polyphalt L.L.C.
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