Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-02-18
2001-10-16
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S194000, C525S232000, C525S236000, C525S237000, C525S240000, C525S241000
Reexamination Certificate
active
06303694
ABSTRACT:
FIELD OF INVENTION
The present invention relates to compounding of quinoid curing agents, dry rubber blends including the curing agent, and sealants useful for various applications including sealants for tubeless pneumatic rubber tires to minimize loss of air due to punctures resulting from road debris such as nails.
BACKGROUND OF THE INVENTION
A frequently used curative for pneumatic tire sealant compositions is a quinoid type system, which generally comprises a quinoid and an activator. The activator, often described as a cocuring agent or “B” component, is used to achieve crosslinking in association with the dormant quinoid uniformly distributed as a curing agent into the elastomer or rubber (such blend being called an “A” component). The terms “elastomer” and “rubber” will be used interchangeably in this specification.
Traditionally, the quinoid rubber curing agent is solution compounded into the elastomer to form component A. This solution compounding usually achieves a uniform distribution of the curing agent in the elastomer. The quinoid curing agent is initially solubilized in an organic, polar solvent and then mixed with a rubber “masterbatch” (high molecular weight elastomer; low molecular weight tackifier; reinforcing agent; solvent). The various solvents are then removed to yield a uniform fine distribution of curing agent in elastomer (“component A”) to form a dry blend for later crosslinking the elastomer once the curing agent and the co-curing agent come together.
While many solvent processes in rubber compounding are acceptable for current manufacturing techniques, the use of organic, polar solvents in rubber compounding presents the expected issues of solvent purchasing and storage costs before manufacture, solvent removal costs during manufacture, solvent capture costs as a byproduct of manufacture, and other manufacturing costs involved with the use of solvents. Moreover, most rubber vulcanization processes begin with Banbury-type mixing techniques which is a dry, solid mixing process. Thus, the presence of solvents to intimately mix various ingredients is temporary.
SUMMARY OF THE INVENTION
The present invention solves a problem of solvent-blended processing of quinoid curing systems by minimizing the use of solvents for such curing systems.
The present invention advantageously provides a generally solvent free component A before mixing of component A with co-curing agent B. One aspect of the invention is a method of dispersing quinoid curing agents into an elastomer. Advantageously, the method preferably does not require either the use of polar, organic solvents to solubilize the quinoid before introduction into a rubber masterbatch or the use nonpolar organic solvents to dissolve the elastomer or other components of the rubber masterbatch. The general avoidance of these solvents from the production process eliminates the costly step of removing the solvents from the final product and produces a product having more consistent cure times.
Another aspect of the present invention is a generally solvent free rubber masterbatch for sealant compositions.
Another aspect of the present invention is a use of a quinoid curing agent in a solvent-less process to make elastomeric sealant compositions.
Another aspect of the present invention is a solvent-free elastomeric sealant composition.
These and other aspects of the present invention will become apparent from the following specification, which describes in detail the invention. In general, the present inventive process is directed to compounding a quinoid curing agent for a sealant composition by mixing an elastomer, optionally and preferably, in the substantial absence of an organic solvent. A quinoid curing agent is separately dispersed in a polymer having a molecular weight below about 5,000 to form a curing agent concentrate. The curing agent concentrate is then combined with the elastomer to form the sealant composition.
Alternatively, the curing agent may be added without first dispersing in a polymer but in the absence of an organic solvent.
Preferably, the elastomer comprises at least one polymer having a molecular weight above about 50,000 and at least one polymer having a molecular weight below about 5,000. Typically, the curing agent has a particle size less than about 5 microns and comprises from about 0.2 to about 2.0 parts by weight per hundred parts of elastomer/rubber (phr) of the sealant composition.
As stated above, in the present process, the curing agent concentrate and the elastomer constituent are advantageously substantially free of organic solvent. Moreover, each includes less than about 10.0 weight percent of organic solvent.
A feature of the present invention is the compounding of the sealant composition in a generally solvent free environment, which minimizes the introduction and removal of solvent in middle steps of a sealant composition manufacturing process.
An advantage of the present invention is the reduction of costs associated with including solvents in compounding and then removing those same solvents before sealant composition curing.
Another advantage is improved properties of the sealant composition resulting from a substantially solvent-free compounding process.
EMBODIMENTS OF THE INVENTION
According to the present invention, a quinoid curing agent is readily and uniformly dispersed in rubber compositions, especially the rubber mixtures typically called the “A” component. The method is an improvement over the prior art because it achieves a uniform dispersion of small quinoid particles without the use of polar, organic solvents to solubilize the curing agent. This advantage over the art can be further improved by avoiding the use of a nonpolar organic solvent, previously used to reduce the viscosity of the rubber component.
The present invention also includes within its scope the use of peroxide co-curing agents, typically called the “B” component. The combination of the A and B components results in a composition that will readily cure at temperatures from about 15° C. to about 150° C. and maintain their crosslink density even though exposed to air and/or elevated temperatures.
The sealant composition of the present invention generally contains at least one high molecular weight elastomer(s) as well as at least one elastomeric-type tackifier, all present in the rubber masterbatch.
Typically, the high molecular weight elastomer(s) which can be utilized in the present invention include ethylene-propylene-diene terpolymers (EPDM), polybutadiene, partially hydrogenated polybutadiene, butyl rubber, halo butyl rubber for example chloro- or bromo-, acrylonitrile-butadiene copolymer, styrene butadiene copolymer, natural rubber, or cis polyisoprene and the like. Mixtures of two or more of the above elastomers can also be used, as can various other conventional high molecular weight rubbers. The number average molecular weight of the high molecular weight elastomer is preferably at least about 50,000 and desirably at least about 100,000.
The elastomeric-type tackifiers utilized in the present invention are rubbery polymers of relatively low molecular weight. Generally, from about 55 to about 90 percent by weight of the sealant rubber compound of the present invention is the tackifier with from about 65 or 75 percent to about 90 percent being preferred. The amount of the high molecular weight rubber compounds accordingly is from about 10 percent to about 45 percent by weight with from about 10 percent to about 25 or 35 percent being preferred. The stated weights are based on the total weight of the high and low molecular weight rubbers. However, other components of the specified present invention system may be based on 100 parts by weight of rubber (phr).
According to the method of this invention, the high molecular weight elastomer(s) and the low molecular weight polymers do not need to be solubilized ir a nonpolar solvent before the quinoid curing agent is added. Accordingly, the invention is directed to situations where less than 10%, more preferably less than 1%, and most prefera
Hergenrother William L.
Hogan Terrence E.
Morehart Christine
Bridgestone Corporation
Burleson David G.
McCollister Scott A.
Nutter Nathan M.
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