Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-06-18
2002-06-11
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06403693
ABSTRACT:
FIELD
The invention relates to the preparation of a composite of an elastomer composition containing silica-based reinforcement created by a controlled alkoxysilane condensation reaction within the elastomer matrix. The invention also relates to such composite and to a tire having at least one component of such composite.
BACKGROUND
Elastomer compositions typically contain particulate filler reinforcement such as, for example, carbon black and/or silica.
Silica reinforcement for an elastomer composition may be provided by adding particulate silica such as, for example, precipitated silica, to a rubber composition.
Alternatively, silica reinforcement may be formed in-situ within an elastomer host by a condensation of an alkoxysilane to form, for example, a polysiloxane within the elastomer matrix.
It is a purpose of this invention to enhance such a formation of the alkoxysilane condensation reaction product within an elastomer host.
While it is known that various condensation reactions may be promoted or retarded by the presence of acidic or base materials, such phenomenon as applied to an alkoxysilane, particularly an alkoxysilane polysulfide, condensation within an elastomer host is believed to be novel and inventive.
In practice, particularly where a particulate silica-based filler is added to an elastomer composition as an elastomer reinforcement such as, for example, an aluminosilicate or silica-modified carbon black, a coupling agent is often used to aid in coupling the filler to one or more diene-based elastomers. The use of various coupling agents for such purpose is well known to those having skill in such art.
Such coupling agents may be, for example, an alkoxyorganosilane polysulfide which has a constituent component, or moiety, (the alkoxysilane portion) capable of reacting with, for example, silanol groups, on the silica surface of the silica-containing filler and, also, a constituent component, or moiety, (the polysulfide portion) usually capable of interacting with the rubber, particularly a diene-based, sulfur vulcanizable rubber which contains carbon-to-carbon double bonds, or unsaturation. In this manner, then, the coupler may act as a connecting bridge between the silica-containing filler and the rubber and, thereby, enhance its reinforcing effect for the rubber composition.
In particular, it is envisioned that the silane moiety of the coupler, particularly a trialkoxysilane moiety, is available for reacting with virtually any reactive hydroxyl groups it may encounter and particularly with silanol groups (—Si—OH) on the surface of the silica-based filler and also with alkoxy groups on the coupler itself to form siloxane units (—Si—O—Si—).
In practice, alkoxyorganosilane polysulfides sometimes used are bis-(3-trialkoxysilylalkyl) polysulfides which contain from about 2 to 8, with an average of from about 3.5 to 4.5, sulfur atoms in its polysulfidic bridge.
During a typical mixing (processing) of the elastomer composition in an internal rubber mixer under high shear conditions to temperatures in a range of 150° C. to 175° C., the silane portion reacts with the surface of a silica-based filler (e.g.: which may be hydroxyl groups on the surface of the silica which may be in a form of silanol groups).
A portion of the polysulfidic bridge of such organosilane polysulfide typically breaks during such mixing operation, resulting in an exposed sulfur on the coupling agent which is available to apparently interact with one or more of the elastomer(s) in the elastomer composition.
However, it is to be appreciated that such interaction of the sulfur with the elastomer(s) is typically accompanied by an increase in the viscosity (e.g.: Mooney viscosity) of the rubber composition itself as the sulfur interacts with the elastomer(s). Too high of an elastomer viscosity under such conditions makes the rubber composition more difficult to process, or mix, in a typical internal rubber mixer.
Therefore, a degree of adjustment of various formulation ingredients (formulation tuning) and enhancement of various physical properties is limited because of such typical higher viscosity related processing limitations imposed via use of such coupling agent.
Uniquely, however, organosilane polysulfide compounds in a form of organosilane disulfide compounds with predominately contained only about two sulfur atoms in the polysulfidic bridge (e.g. and an average of about 2 to about 2.6 sulfur atoms) do not ordinarily cause such excessive viscosity build-up of the rubber composition during its internal mixing operation.
Such phenomenon in the use of the organosilane disulfide compounds is apparently due to stronger sulfur-to-sulfur bonds for the polysulfidic bridge of the disulfide and their inherent resistance to breaking upon high shear mixing at the aforesaid elevated temperatures, thus, enabling only a very limited amount of sulfur atoms available to interact with diene-based elastomer(s) in the rubber composition during the mixing operation. This phenomenon is well known to those having skill in such art.
Accordingly, it is desired to more effectively utilize the aforesaid rubber processing advantages afforded via use of such organosilane disulfide compound, including a bis-(trialkoxyorganosilane) disulfide, compound as a coupling agent.
The term “phr” as used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer”.
In the description of this invention, the terms “rubber” and “elastomer” if used herein, may be used interchangeably, unless otherwise prescribed. The terms such as “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and “rubber compounding” or “compounding” may be used to refer to “the mixing of such materials”. Such terms are well known to those having skill in the rubber mixing or rubber compounding art.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, a process of preparing a composite of an elastomer composition which contains a silica-based reinforcement therein comprises the sequential steps of:
(A) thermomechanically mixing in at least one preparatory mixing step to a temperature of about 140° C. to about 190° C., alternatively to about 150° C. to about 185° C., (i) 100 parts by weight of at least one sulfur vulcanizable elastomer selected from homopolymers and copolymers of conjugated diene hydrocarbons copolymers of at least one conjugated diene hydrocarbon and vinyl aromatic compound, (ii) about 15 to about 100, alternatively about 30 to about 90, phr of particulate filler comprised of at least one silica-based filler which contains reactive hydroxyl groups on the surface thereof (e.g.: silanol groups), (iii) about 0.05 to about 20 parts by weight per part by weight of said particulate filler of at least one organosilane compound, preferably a polysulfide compound and, more preferably, a disulfide selected from at least one of Formula (I) and (II) their mixtures:
Z—R
1
—Sn—R
1
—Z (I)
Z—R
1
—X (II)
wherein n is an integer of from 2 to 8 with an average of from 3.5 to 4.5, or an integer of from 2 to 4 with an average of from 2 to 2.6;
wherein Z is selected from the group consisting of:
wherein Z is preferably (Z3);
wherein R
1
is selected from the group consisting of a substituted or unsubstituted alkylene group having a total of 1 to 18 carbon atoms and a substituted or unsubstituted arylene group having a total of 6 to 12 carbon atoms, preferably alklylenes having from 2 to 6 carbon atoms; wherein R
2
may be the same or different and is individually selected from the group consisting of alkyls having 1 to 4 carbons and phenyl; and R
3
may be the same or different and is individually selected from the group consisting of alkoxy groups having 1 to 4 carbon atoms, preferably from 1 to 2 carbon atoms; and
wherein X is selected from mercapto, thiocyanato, amino, vinyl, epoxide, acrylate and meth
Edme Materne Thierry Florent
Kayser Francois
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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