Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2001-01-05
2003-02-25
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C423S449200
Reexamination Certificate
active
06525105
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for separating rubber components and filler components from a vulcanized rubber or an unvulcanized rubber by liquidifying the vulcanized rubber or the unvulcanized rubber at normal temperature and normal pressure; and a method for separating structural members from a rubber composite material.
This invention also relates to a reusable rubber and a reusable carbon black recovered by such separation method; and a rubber composition containing such rubber or such carbon black. More specifically, this invention relates to a recovered rubber having excellent physical properties which has been obtained by treating a waste rubber composition by a particular method; a rubber composition having such recovered rubber blended therein; a recovered carbon black having excellent physical properties which has been obtained by treating a waste rubber composition by a particular method, and a rubber composition having such recovered carbon black blended therein.
Furthermore, this invention relates to a method for producing a carbon black which, when blended in a vulcanized rubber; exhibits extremely low value of loss tangent (tan &dgr;) at 60° C. which is an index for low fuel cost of the tire; such carbon black; and a rubber composition and a vulcanized rubber containing such carbon black.
BACKGROUND ART
Disposal of industrial wastes has nowadays become a serious social problem, and in the case of tires, the amount discarded is enormous and not only use as a fuel by incineration but also recovery and reuse of the raw materials included in the tire, namely, the rubber and the rubber subsidiary materials has become an urgent agenda. A rubber, however, is quite stable once it has vulcanized due to its crosslinked structure, and the rubber has been insoluble at room temperature in ordinary solvents, and at most, swellable to some extent in such solvents.
One process known in the art for the recovery of the rubber, carbon black, and other rubber subsidiaries from vulcanized rubber wastes is recovery of the rubber as a gaseous or liquid hydrocarbon by thermal decomposition of the vulcanized rubber. For example, JP-A 60-40193 discloses recovery of the rubber as a liquid hydrocarbon by thermal decomposition of used tires, cable wastes, or other vulcanized rubber wastes together with wastes of polyethylene, polypropylene or the like at a temperature of 150 to 500° C. and a pressure of 20 to 800 bar, and in the presence of a solvent. JP-A 7-310076 discloses a method for obtaining a decomposed oil having a reduced sulfur content wherein a vulcanized rubber is thermally decomposed to obtain a hydrocarbon (a gaseous product) and a decomposed oil containing carbon black (slurry-like product) and wherein the thermal decomposition is conducted in the presence of a hydrogen-donating solvent such as tetralin.
Also proposed are a method wherein direct or indirect heating is conducted at a high temperature of, for example, at least 500° C.; a method wherein the thermal decomposition is conducted in the presence of a solvent, a catalyst and hydrogen (U.S. Pat. No. 3,704,108); a method wherein the thermal decomposition is conducted in the presence of a molten salt (European Patent No. 71789, U.S. Pat. No. 3,996,022), and the like.
Such recovery of the rubber materials and subsidiaries from vulcanized rubber products by the thermal decomposition requires an enormous cost for installation when such recovery is to be conducted in an industrial scale, since a high temperature, high pressure thermal decomposition apparatus is required for the thermal decomposition.
A method for plasticizing vulcanized rubber powder is disclosed in Journal of Japan Rubber Association 49 (1976) page 829. In this method, various types of sulfur-vulcanized rubbers in the form of a powder having a particle diameter of up to 2 mm are immersed in carbon tetrachloride or toluene in the presence of benzoyl peroxide at a rubber powder (mg)/toluene (ml) ratio of 500/7 to 500/2 to thereby promote decomposition in the liquid by air oxidation at a temperature of 70 to 100° C.
This method, however, was an attempt to regenerate the vulcanized rubber by plasticizing the vulcanized rubber under heating, and re-vulcanizing and adding the plasticized reaction product in the fresh rubber. The article of Journal of Japan Rubber Association also described that the vulcanized rubber containing no carbon black was more susceptible to oxidative decomposition than the vulcanized rubber containing carbon black. In view of the situation that carbon black is blended in most commercially available industrial rubbers, this method is not very useful. In addition, the vulcanized rubber regenerated from the reaction product of the oxidative decomposition reaction exhibited inferior physical properties when the ratio of the re-vulcanized rubber to the fresh rubber was high.
When the rubber materials and subsidiaries are recovered from the vulcanized rubber product by the thermal decomposition as described above, substantially all of the rubber components in the vulcanized rubber are converted into low molecular weight hydrocarbons (C
4
-benzene, C
4
-cyclohexane, etc.). Main use of the thus recovered hydrocarbon has been used as a light fuel at the furthest, and such hydrocarbon could not be reused as a starting material of the rubber composition since the starting rubber is required a certain high molecular weight.
The disposal of industrial wastes is not a problem restricted to vulcanized rubber products, and scraps produced in kneading and processing as well as other unvulcanized scrap rubbers inevitably generated in the production of the vulcanized rubber products have also become a serious problem. In view of such situation, recovery of rubber materials and subsidiaries, and efficient reuse of such materials are also an important issue.
In the typical production of a rubber product such as tire, the starting rubber is first masticated, and the thus softened rubber is then admixed with a filler, a softener, a vulcanizer, a vulcanization accelerator, an antiaging agent and the like. The mixture is then kneaded, molded in an extruder of the like, vulcanized, and formed into products by appropriate processing. As is well known, a large amount of unvulcanized scrap rubber is inevitably produced in the course of such steps. Exemplary such unvulcanized scrap rubbers include rubber scraps discarded in the steps of mastication and kneading due to early vulcanization or uneven vulcanization (burned spot or scorching), and defective rubbers discarded in the step of vulcanization due to the so called sagging, and there are various types of the scrap rubbers depending on their production process including the one wherein vulcanized and unvulcanized parts are intermingled, and the one wherein steel member or organic fiber member is attached.
The issue of industrial waste disposal has recently become a quite serious social problem, and with regard to the unvulcanized scrap rubbers discharged from factories, it has been conceived that, not only the incineration of the unvulcanized scrap rubbers as fuels, but also the recovery of the starting rubber and rubber subsidiary materials and their efficient reuse are important.
Therefore, in the disposal of such unvulcanized scrap rubbers, complicated preliminary steps of sorting the scrap rubbers by their types, and removing members comprising steel or organic fibers as well as vulcanized portions have been conducted, and the recovery of the rubber for reuse in other rubber products has been only limited and most scrap rubbers have been discarded.
In view of such situation, if a method capable of separating structural members by liquidifying the vulcanized rubber composition at room temperature or at a relatively low temperature under normal pressure, or a method wherein a vulcanized rubber composition can be separated into the rubber component and the filler component at room temperature or at a relatively low temperature under normal pressure were realized, installation such as thermal
Ashizawa Susumu
Udagawa Yoshitaka
Cain Edward J.
The Yokohama Rubber Co. Ltd.
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