Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-02-10
2001-12-25
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...
C523S335000, C524S210000, C524S251000
Reexamination Certificate
active
06333373
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the recovery of elastomers. More particularly, the present invention relates to co-grinding an elastomer and an additive in a slurry to produce ground elastomer particles.
2. Description of the Related Art
In recycling and reusing rubber materials, it is generally known to decrease the size of such rubber materials to small ground rubber particles (i.e., particles of irregular outline that pass through a minus 80 mesh or through a minus 50-mesh or finer). Such particles can be chemically more reactive and mechanically easier to dissolve into various mixes.
A variety of rubber products (e.g., natural rubber, synthetic rubber, vulcanized rubber, automotive tire scrap, etc.) may be reduced to ground rubber particles. Known methods for producing rubber of a decreased size include cryogenic cracking of the rubber. Other known methods include the milling of the rubber between horizontal grinding stones in a horizontal grinding mill. Such milling techniques have been developed in the flour, paper pulp industry and the paint pigment compounding industries. Such milling techniques include grinding the rubber between opposed milling wheels, such that one wheel is fixed and the other wheel rotates relative to the fixed wheel. Such known milling techniques include pressing the two wheels against a rubber slurry, such that the rubber is ground to a fine state (i.e., powder) in a single pass. However, such known milling methods have the disadvantage of creating friction and introducing energy to the slurry, which may increase the temperature of the slurry. Increased slurry temperatures may cause “flash over” in which the slurry becomes a largely dry rubber mass that inhibits grinding. Such known milling methods further have the disadvantage of not producing a uniformly fine rubber powder that passes through a minus 50-mesh.
Accordingly, it would be advantageous to have a method for converting an elastomer to a ground particle. It would also be advantageous to have a method to convert an elastomer to a decreased size that decreases soak time of the elastomer. It would also be advantageous to have a method to convert an elastomer to a decreased size that decreases grinding time of the elastomer. It would also be advantageous to have a method that converts an elastomer to a decreased size carried out at a relatively low temperature of an elastomer slurry. It would also be advantages to have an elastomer that chemically combines with an additive to modify the physical properties of the elastomer.
SUMMARY OF THE INVENTION
In accordance with the present invention is provided a method for converting an elastomer to a decreased size in a grinding apparatus. The method includes optionally soaking the elastomer in a first additive. The method further includes reducing the size of the elastomer to form at least one elastomer particle of a first size. The method also includes optionally removing impurities from the elastomer. Further, the method includes adding a carrier to the elastomer particle to form an elastomer slurry. Also, the method includes providing a second additive to the slurry. In addition, the method includes converting the elastomer particle to a second size, the second size being less than the first size. The method also includes recovering the elastomer particle of the second size.
In accordance with the present invention is also provided a ground particle. The ground particle includes an elastomer and an additive. The ground particle is preferably capable of passing through a minus 50-mesh or through a minus 80-mesh.
Additional objects, features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects, features and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The size of an elastomer (e.g., natural rubber, synthetic rubber, recycled rubbers containing polyethylene and/or polypropylene, vulcanized rubber, carbon black, waste from tire production, various polymers, various plastics, thermoplastic elastomers, thermoplastic vulcanates, polyethylene plastics, etc.) may be decreased using a variety of mechanisms. According to an exemplary embodiment, the elastomer is soaked in a fluid. According to a preferred embodiment, the fluid is soapy water and/or an aromatic oil. Soaking the elastomer, among other things, causes the elastomer to swell, removes oils a from the elastomer and dissolves adhesives in the elastomer.
According to an exemplary embodiment, a variety of water-soluble additives may be added to the soaking fluid. The additive, when used during soaking of the elastomer, decreases the swelling time of the elastomer as compared to elastomers soaked in the absence of the additive. According to an alternative embodiment, the additive may be a chemical that swells the rubber, but is not a tackifier, such as tetrahydrofuran (THF) or dimethyl formamide (DMF). According to other alternative embodiments, a variety of additives (as described below) may be used when soaking the elastomer. According to a preferred embodiment the additive used when soaking the elastomer is a fatty amine, such as DELAMIN™ commercially available from Hercules, Inc.
The size of the soaked elastomer may be decreased in a grinding apparatus, such as a set of milling stones. According to an alternative embodiment, the size of the soaked elastomer may be decreased by freezing the elastomer and cracking or hammering the elastomer into small sized particles. According to other alternative embodiments, the soaked elastomer is shredded by a series of blades or an Archimedes screw apparatus. According to still other alternative embodiments, the size of a soaked or non-soaked elastomer may be decreased by brute force (i.e., by two counteracting surfaces). According to a preferred embodiment, grinding of the soaked elastomer material is achieved using the grinding apparatus as disclosed in U.S. Pat. No. 5,238,194 issued Aug. 24, 1993 to Rouse et al. for “METHOD OF PRODUCING FINE ELASTOMERIC PARTICLES” and incorporated herein by reference. The grinding apparatus expediently includes a horizontal grinding machine providing a fixed stator and a rotating rotor, on which disc-shaped grinding stones having hollow centers can be mounted. The grinding stones provide flat, opposing abrasive surfaces (i.e., flat annulus surface), and each grinding stone is opposed to the other. The abrasive surfaces provide periodically spaced openings in the annulus for introducing the elastomers to be ground between the closed, cooperating abrading surfaces.
Impurities (e.g., metals, cords, reinforcing materials, etc.) may be removed from the ground elastomer. According to an alternative embodiment, a magnet may be used to remove certain metallic impurities from the ground elastomer. According to a preferred embodiment, the impurities can be removed by passing the ground elastomer through a screen that allows ¼-inch to ⅝-inch particles to pass through.
An elastomer slurry may be formed by adding a carrier to the ground elastomer. According to an alternative embodiment, the carrier may be a gas (e.g., air) that may carry a wet or dry stream of elastomer particles. According to other alternative embodiments, the carrier is a fluid (e.g., water). According to other alternative embodiments, the carrier may be provided through the grinding apparatus before the slurry is provided through the grinding apparatus. According to any alternative or preferred embodiment, a uniform set point fluid flow rate through a properly spaced set of grinding stones is determined as disclosed in U.S. Pat. No. 5,238,194 issued Aug. 24, 1993 to Rouse et al. for “METHOD OF PRODUCING FINE ELASTOMERIC PARTICLES” and incorporated herein by reference.
According to an exemplary embodi
Deeb Victor M.
Rouse Michael W.
Cain Edward J.
Heller Ehrman White McAuliffe LL
R&D Technology, Inc.
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