Compounding process for achieving uniform, fine particle...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

Reexamination Certificate

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C524S113000

Reexamination Certificate

active

06194485

ABSTRACT:

FIELD OF INVENTION
The present invention relates to compounding of quinoid curing agents. More specifically, the present invention relates to predissolving the curing agent in an organic polar solvent with subsequent mixing and precipitation of the curing agent within a dry rubber blend. The resulting blend is an “A” component for various applications. A preferred application is a sealant for tubeless pneumatic tires to seal punctures resulting from road debris such as nails.
BACKGROUND OF THE INVENTION
While there are many patents on sealant compositions for pneumatic tires, three patents: U.S. Pat. Nos. 4,116,895; 4,426,468; and 4,616,048 provide basic information on the field. An often used curative for the sealant compositions is a quinoid type system, which generally comprises a quinoid and a crosslinking activator. The quinoids and their activators are set forth in U.S. Pat. No. 4,426,468 ('468 column 5, line 28, through column 6, line 5). In U.S. Pat. No. 4,616,048 ('048) the crosslinking activator of the '468 patent is described as a cocuring agent “B” and the concept of a optional polar solvent accelerator is introduced (column 5, line 33, through column 6, line 8). The '468 patent in column 5, lines 28-29, explains the quinoid cure system depends on crosslinking through nitroso groups.
In U.S. Pat. No. 4,116,895 ('895) column 6, lines 4-13, the author explains that if the amount of crosslinking is too low the sealing properties at high temperature are ineffective while a crosslink density that is too high also prevents the sealant from functioning.
In the '468 patent column 2, line 32, through column 3, line 18, the author explains that tire sealants benefit from the optimization of three properties: tensile strength, elongation, and crosslink density. The examples of the '468 patent illustrate how the three properties can be correlated with various aspects of tire sealant performance. In the '468 patent the quinoid is diluted in cyclohexanone and then added to a butyl rubber and Piccotac component which have been premixed in hexane at about 50 wt. % solids.
The '048 patent teaches a method of dispersing quinoid curing agents in a rubber composition that results in a uniform fine dispersion of the quinoid. In the examples of the '048 patent (column 7, line 49, through column 8, line 20) the quinoid was made up as a 5 wt. % solution with surfactants in tetrahydrofuran, which was then mixed with a majority of the rubbers predissolved in hexane. This is consistent with the Detailed Description (column 4, line 31, through column 5, line 6) where the addition of the quinoid as a dissolved solution during mixing of the rubber in solvent results in the precipitation of the quinoid curative as a fine dispersion. Column 5, lines 39-42, specify that the solvent for the quinoid not only has to be a reasonably good solvent for the quinoid but it must be compatible with the masterbatch solvents in the rubber cement. Table II of the '048 patent illustrates the “solution method” increases the maximum torque of samples over samples prepared by the “conventional mixing” and decreases the time to reach maximum torque. These results imply the quinoid is more effective as a curative when finely dispersed. In Table IIIA the “solution method” results in lower swell ratios and higher solvent clarity which implicates more effective and uniform crosslinking. In Table IIIB the “solution method” resulted in enhanced solvent clarity and less microgel indicating more uniform crosslinking.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the present invention to provide an improved method of dispersing quinoid curing agents in a rubber composition, which method eliminates the use of nonpolar organic solvents to dissolve the rubbers. The elimination of nonpolar organic solvents eliminates the costly step of removing the nonpolar organic solvents from the final product. Further, the improved method only uses and recovers a single polar organic solvent while the method of the U.S. Pat. No. 4,616,048 recovered a blend of polar and nonpolar solvents which was difficult to separate and recycle.
It is yet another aspect of the present invention to disperse quinoid curing agents in a rubber composition, as above, whereby a uniform fine distribution is obtained.
It is a still further aspect of the present invention to disperse quinoid curing agents in a rubber composition, as above, so that a balanced combination of properties including tackiness, resiliency, compliance and cohesive strength essential for maximum sealing effectiveness is achieved.
These and other aspects of the present invention will become apparent from the following specification, which describes in detail the invention.
In general, the process for solution compounding a quinoid curing agent for a sealant composition, comprises the steps of:
(a) adding at least one quinoid curing agent to a solubilizing organic polar solvent and forming a solution,
(b) adding said quinoid curing agent solution to a rubber blend, and mixing and precipitating said curing agent in said blend forming a mixture so that a uniform fine dispersion of said curing agent is formed, and
(c) removing said organic polar solvent of said mixture to form a dry sealant component wherein the number average particle size of said dispersed quinoid curing agent is less than 10 microns and said rubber blend includes less than 10 wt. % of nonpolar solvents when said quinoid curing agent is added.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, quinoid curing agents are 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 as it achieves a uniform dispersion of small quinoid particles without the use of nonpolar organic solvents previously used to reduce the viscosity of the rubbers. Moreover, the present invention also relates to the use of peroxide cocuratives typically in the “B” component. The addition 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 thereafter the crosslink density will not significantly increase or decrease even though exposed to air and/or elevated temperatures.
The rubber or the sealant rubber compounds of the present invention generally contains at least one high molecular weight elastomer(s) as well as at least one liquid elastomeric type tackifiers. 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 said high molecular weight elastomer is at least about 50,000 and desirably at least about 100,000. The terms elastomer and rubber will be used interchangeably in this specification. This is especially true when specifying other components based on 100 parts by weight of rubber (phr).
The tackifiers utilized in the present invention are rubbery polymers of relatively low molecular weight, for example, those having a number average molecular weight of about 500 to about 5,000 and which often are liquids at room temperature (that is about 20° C. to about 25° C.). These will be considered as a rubber along with the high molecular weight elastomer.
Many structural types of low molecular weight polymers in liquid form are useful including ethylene-propylene copolymer (EP), ethylene-propylene-diene terpolymer (EPDM), polybutadiene (PBD), hydrogenated PBD, butyl rubber (BR), polypropylene (e.g. atactic), acrylonitrile-butadiene copolymer (ANB), styrene-butadiene copolymer (SBR), synthetic po

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