Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-04
2002-07-16
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C521S041000, C524S492000, C524S495000
Reexamination Certificate
active
06420457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates broadly to the treatment and recycle of rubber products and still more particularly to the use of recycled crumb rubber. The United States Government has rights to this invention pursuant to contract number DE-AC09-96-SR18500 between the U.S. Department of Energy and Westinghouse Savannah River Company.
2. Discussion of Background
Existing efforts to recycle used rubber, in particular used tires, into new rubber articles, especially tires, have met with only limited commercial success. In the United States alone, there are currently billions of tires stock-piled in long term storage with additional millions being added annually to such stock piles. Because of the large volume involved with tires, this discussion will be directed to tires although much of these comments are applicable to other new and used rubber products.
Because used rubber is usually processed in the form of crumb rubber, references herein will be to rubber in that form. A major limitation in the recycling of used tire material is that the used tire rubber can not be readily mixed in economical proportions to form new tire polymer mixes having acceptable properties.
During the vulcanization process of rubber, such as in the manufacture of new tires, accelerators, promoters, and/or initiators, are used and the formation of large numbers of sulfur crosslinks are established and are inherent in the cured rubber. It is generally believed in the art that the sulfur compounds which are present in used rubber, such as tire rubber, are deleterious in a subsequent curing process which uses used rubber as a component in a new polymer mixture. Formulations of tire rubber which use more than minor amounts of a used, previously vulcanized rubber result in a brittle cured end product unsuitable for many uses such as automobile or truck tires. Heretofore, efforts to reclaim scrap rubber have primarily included a physical sheering process which is suitable for a rubber which can be mixed with asphalt, forming asphalt rubber. Such use is taught in U.S. Pat. No. 5,304,576.
It is also known to take used rubber and depolymerize the vulcanized rubber in an organic solvent and then recover various polymerized fractions as taught in U.S. Pat. No. 5,438,078. Similarly, U.S. Pat. No. 5,264,640 teaches taking scrap rubber from used tires and regenerating the monomeric chemicals which are subsequently recovered. This method uses gaseous ozone to break down the crosslinked structure of the rubber followed by thermal depolymerization in a reaction chamber. U.S. Pat. No. 5,369,215 teaches a similar process in which used tire material may be depolymerized under elevated temperatures and at a reduced pressure to recover the monomeric compounds.
U.S. Pat. No. 5,891,926, which is incorporated herein by reference, is directed to a devulcanization process for used rubber in which elevated temperatures and pressures are used to partially devulcanize the rubber. Thereafter, a solvent 2-butanol is used to extract the devulcanized rubber from the non-rubber and/or solids component.
U.S. Pat. No. 4,104,205 teaches a method to devulcanize rubber from hose end trim and butyl tire bladders. While tire tread material was also treated, difficulties in exothermic reactions and physical properties of the microwaved materials were noted.
U.S. Pat. No. 4,341,667 teaches that the green strength of elastomers reclaimed through heat, microwave, chemical treatments, or physical shearing can be improved by the addition of butene polymers.
U.S. Pat. No. 4,469,817 teaches the microwave treatment of a vulcanized rubber. The treatment uses microwaves to raise the temperature of the rubber to a devulcanization temperature followed by rapid cooling with water.
U.S. Pat. No. 4,665,101 is an improvement to convectional heating of used rubber where microwave heating is additionally used. The combination of the heating methods is used to provide a more uniform heating profile and avoid extremes of localized temperatures within the treated material.
This application also relates to commonly assigned U.S. application having Ser. No. 09/542,392 having Attorney Docket No. WSR-14R, “Combination Biological and Microwave Treatments of Used Rubber Products”, filed on Apr. 4, 2000 and which is incorporated herein by reference. Additionally, commonly assigned application Ser. No. 09/542,744 having Attorney Docket No. WSR-15R, entitled “Microbial Processing of Used Rubber”, filed on Apr. 4, 2000, is incorporated herein by reference.
There remains a strong need for a practical, economical system for processing used tire parts such as tread rubber into a material which can be incorporated at a substantial loading level into new rubber compounding mixtures having good mechanical and chemical properties.
SUMMARY OF THE INVENTION
The present invention is a process and the resulting product of the process in which used rubber having relatively high surface reactivity has the reactive agents (as well as sulfur crosslinks) altered such that the resulting treated rubber may be incorporated into polymer mixes for high quality new rubber products, including tires, at much greater levels than used heretofore.
It is a further object of the present invention to provide a process and resulting product which permits the incorporation of large particle sizes of previously vulcanized rubber into polymer mixes for new rubber products.
In accordance with this invention, it has been demonstrated that particles of used crumb rubber can be treated with microwave energy which effectively alters the surface chemistry and reactivity of the so treated vulcanized crumb tire rubber. It has been found that the microwave treatment of the crumb rubber particle affects the surface reactivity of the crumb rubber particles to an extent that the rubber particles can be integrated into a new tire polymer mix at much higher levels than previously possible. The microwave treatment of the crumb rubber can be controlled so as to target only specific types of chemical bonds or agents by the selection of desired processing conditions, such as time and temperature, of the microwave bombardment. It has been found that the crumb rubber so treated is compatible with the new rubber polymer component of a tire mix.
The use of microwaves to target and modify select chemical species or bonds provides a process which can be carried out on an economical basis. The process is thought to be particularly useful in that the microwave treatment alters a wide variety of chemical additives used by tire manufacturers and which are present within the used rubber. The ability to target or alter these chemical constituents further enhances the usefulness and compatibility of the treated used rubber with virgin polymer.
In addition, the microwave treatment treats both the surface and interior bulk of the crumb rubber particle. While the surface treatment is believed necessary to bring about favorable co-compounding of used, previously vulcanized rubber with new tire rubber formulations, the microwave treatment is further believed to bring about favorable changes within the interior of the rubber particles. As used herein, the term “bulk treatment” means the treatment of solid rubber particle with microwaves such that interior heating of the rubber particle occurs. The combination of heat and microwave radiation is believed to favorably alter the interior of the crumb rubber particles by the alteration of certain chemical constituents. As a result, a more uniform feed stock is provided and results in a crumb rubber product which is “sterilized”.
The use of the microwave treatment provides the potential of yielding a process and product which can be obtained on an economical basis at a commercial scale and in an environmentally acceptable manner.
It is thus an object of this invention to provide a microwave treatment process which alters by an effective amount the reactivity of used crumb rubber such that an increased amount of used crumb rubber can be mixed with a
Clark David E.
Folz Diane C.
Schulz Rebecca L.
Wicks George G.
Cain Edward J.
Westinghouse Savannah River Company LLC
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