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
2000-07-28
2002-03-12
Cain, Edward J. (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...
C524S493000, C524S495000, C524S496000
Reexamination Certificate
active
06355719
ABSTRACT:
BACKGROUND OF THE INVENTION
There has recently developed trends in some tire markets for silica-based tread markets. With this trend, increasing levels of silica have been used with concomitant reductions in the levels of carbon black. As one increases the level of silica in a rubber with decreasing levels of carbon black, the electrical resistivity of the rubber increases. This is undesirable when the rubber is used in a tire due to the potential building of static electricity in the vehicle on which the tires are mounted. While it is described in some instances to use silica fillers, it is also desirable to avoid the potential problems when the carbon black levels are decreased.
SUMMARY OF THE INVENTION
The present invention relates to heterogeneous silica/carbon black-filled rubber compounds and a process for making such compounds.
DETAILED DESCRIPTION OF THE INVENTION
There is disclosed a process for the production of a heterogeneous silica/carbon black-filled rubber compound comprising
(a) intimately dispersing from 30 to 60 phr of a silica filler and 5 to 80 phr of a carbon black in a first rubber to form a first nonproductive compound;
(b) intimately dispersing curatives in said first nonproductive compound to form a first productive compound;
(c) separately intimately dispersing from 20 to 100 phr of a silica filler in a second rubber, which is different from said first rubber, to form a second nonproductive compound;
(d) intimately dispersing curatives in said second nonproductive compound to form a second productive compound; and
(e) mixing said first productive compound with said second productive compound to form a heterogeneous silica/carbon black-filled rubber compound.
There is also disclosed a heterogenous silica black-filled rubber compound prepared by a process comprising
(a) intimately dispersing from 30 to 60 phr of a silica filler and 5 to 80 phr of a carbon black in a first rubber to form a first nonproductive compound;
(b) intimately dispersing curatives in said first nonproductive compound to form a first productive compound;
(c) separately intimately dispersing from 20 to 100 phr of a silica filler in a second rubber, which is different from said first rubber, to form a second nonproductive compound;
(d) intimately dispersing curatives in said second nonproductive compound to form a second productive compound; and
(e) mixing said first productive compound with said second productive compound to form a heterogeneous silica/carbon black-filled rubber compound.
The present invention relates to heterogeneous silica/carbon black-filled rubber compound. Heterogeneous as used herein means containing dissimilar ingredients and/or levels of ingredients. More specifically, the term means a rubber compound containing the selective dispersion of silica and carbon black in a first rubber and silica in a second rubber. Thereafter, upon adding curatives to each rubber compound and the subsequent mixing of the two productives, there is a higher concentration of the carbon in one phase, resulting in improved conductivity of the overall rubber compound and more optimum curing of each of the two phases.
One critical aspect of the present invention is that the first rubber and second rubber are different. Even though the two rubbers are different, each of the two rubbers may be selected from the same group of rubbers. The first rubber and second rubber may be selected from the group consisting of emulsion polymerized styrene/butadiene copolymers, solution polymerized styrene/butadiene copolymers, natural rubber, cis 1,4-polybutadiene, synthetic cis 1,4-polyisoprene, styrene/isoprene copolymers, 3,4-polyisoprene, isoprene/butadiene copolymers, medium vinyl polybutadiene (20 percent to 60 percent by weight of vinyl units), styrene/isoprene/butadiene terpolymers, butyl rubber, polychloroprene, acrylonitrile/butadiene copolymers and ethylene/propylene/diene terpolymers and mixtures thereof.
In accordance with a preferred embodiment of the present invention, the first rubber (used to make the first nonproductive) and the second rubber (used to make the second nonproductive) have different glass transition temperatures (Tg). The term “Tg” refers to the glass transition temperature of the identified rubber and is suitably determined by a differential scanning calorimeter at a rate of 10° C. per minute. In a particularly preferred embodiment, the Tg of the first rubber is higher than the Tg of the second rubber. For example, the Tg of the first rubber may range from −50° C. to 0° C. (high Tg rubber) and the Tg of the second rubber may range from −100° C. to −51° C. (low Tg rubber). In accordance with this embodiment, the difference between the Tg of the first and second rubber generally ranges from about 60° C. to 0° C.
Representative examples of high Tg rubbers include 3,4 polyisoprene which typically contains about 65 weight percent 3,4-isoprene units and has a Tg of about −16° C. Another example of a high Tg rubber is a solution-polymerized styrene/butadiene copolymer rubber containing 12 weight percent styrene, a vinyl content of about 40 weight percent, a Tg of −45° C. and a Mooney viscosity (ML 1+4) at 100° C. of 90. Another high Tg rubber is a styrene/isoprene/butadiene terpolymer rubber containing 20 weight percent styrene, 40 weight percent isoprene and 40 percent butadiene, a Tg of −42° C. and a Mooney viscosity at 100° C. of 90. Yet another high Tg rubber is a high cis 1,4-polybutadiene rubber characterized by the weight percent of 1,4-bonds of at least 9 percent. Another high Tg rubber is a solution-polymerized medium cis 1,4-polybutadiene 40 to 60 weight percent of the units of a vinyl 1,2-structure and 35 to 45 weight percent of its units of a cis 1,4-structure. Such solution-polymerized polybutadiene has a Tg of −65° C and Mooney viscosity (ML 1+4) at 100° C. of about 44. Additional examples of high Tg rubbers are emulsion-polymerized styrene/butadiene copolymer rubber characterized by a weight percent of from 23.5 to 40 weight percent styrene. For example, an emulsion-polymerized styrene/butadiene copolymer rubber having 23.5 weight percent styrene typically has a Tg of about −55° C. An emulsion-polymerized styrene/butadiene copolymer rubber having 40 weight percent styrene typically has a Tg of about −32° C. to −35° C. The preferred high Tg rubber will depend on the application of the rubber compound of the present invention.
Representative examples of the low Tg rubber include polybutadiene rubber having 95 weight percent or more cis 1,4-structure, a Tg of from −95° C. to −105° C. and a Mooney viscosity (ML 1+4) at 100° C. of 5 from 30 to 100. Another example of a low Tg rubber is an isoprene/butadiene copolymer rubber prepared by neodymium catalysis and characterized by having an isoprene content of about 20 weight percent, a Tg of about −90° C. and a Mooney viscosity (ML 1+4) at 100° C. of 82. Yet another example is an isoprene/butadiene copolymer rubber prepared by neodymium catalysis and characterized by having an isoprene content of about 10 weight percent, a Tg of about −98° C. and a Mooney viscosity (ML 1+4) at 100° C. of 82. Other examples of suitable rubbers are solution-polymerized styrene/butadiene copolymer rubbers containing up to 10 weight percent of styrene. Such styrene/butadiene copolymers exhibit a Tg of from −93° C. to −80° C. and Mooney viscosities (ML 1+4) at 100° C. from 30 to 100. The preferred low Tg rubber will depend on the application of the rubber compound of the present invention.
Another example is cis 1,4-polyisoprene. The cis 1,4-polyisoprene rubber includes both natural and synthetic rubbers. The cis 1,4-polyisoprene rubber, natural or synthetic, typically has a cis 1,4-content of about 96 to about 99 weight percent. Synthetic cis 1,4-polyisoprene generally has a Tg of about −65° C. Natural rubber typically has a Tg of about −65° C. Typical Mooney viscosities (ML 1+4) at 100° C. for synth
Agostini Giorgio
Corvasce Filomeno Gennaro
Dauvister Pierre Marie Jean
Cain Edward J.
Hendricks Bruce J.
The Goodyear Tire & Rubber Company
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