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
1999-01-08
2001-08-14
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S232000, C525S194000, C525S198000, C525S089000, C525S099000
Reexamination Certificate
active
06274676
ABSTRACT:
TECHNICAL FIELD
This invention relates to improved rubber compositions. More particularly, this invention is directed toward rubber vulcanizates that demonstrate improved tear strength. Specifically, the rubber compositions and vulcanizates of this invention include at least one polyolefin copolymer as an additive to achieve the desired properties. The preferred embodiments of this invention are directed toward vulcanizable compositions of matter that are useful for fabricating tires.
BACKGROUND OF THE INVENTION
Off road or heavy truck tires are often subjected to rough road conditions that produce repetitive, localized high pressure pounding on the tire. These stresses can cause fatigue fracture and can lead to crack formation and growth. This degradation of the tire has also been referred to as chipping or chunking of the tread surface or base material.
In an attempt to prevent this degradation, it is known to add reinforcements such as carbon black, silicas, silica/silanes or short fibers to tire compositions. Silica has been found advantageous because of its ability to deflect and suppress cut prolongation, and silanes have been added to bind the silica to unsaturated elastomers. The fibers that have been added include nylon and aramid fibers.
It is also known that the addition of polyolefins to rubber compositions can provide several beneficial properties. For example, low molecular weight, high density polyethylene, and high molecular weight, low density polyethylene, are known to improve the tear strength of polybutadiene or natural rubber vulcanizates. In the tire art, it has also been found that polyethylene increases the green tear strength of carcass compounds and permits easy extrusion in calendering without scorch. Polypropylene likewise increases the green strength of butyl rubber. Polypropylene, has also been effective in raising the static and dynamic modulus of rubber, as well as the tear strength of the rubber.
Although the addition of polyolefins to rubber compositions is known to provide several beneficial effects, the addition of polyolefin to tire recipes has, heretofore, had a deleterious affect on the mechanical, wear, and hysteresis properties of tires, as well as handling and ride comfortability of the tires.
Accordingly, there remains a need in the art to improve the tear strength of rubber vulcanizates, especially those deriving from tire compositions, without sacrificing the other properties of vulcanizates, tire components, or tires.
SUMMARY OF INVENTION
It is therefore an object of the present invention to provide a tire component having increased tear strength, where the tire component is less susceptible to chipping and chunking, without substantially impacting the mechanical and wear properties of the tire component.
It is another object of the present invention to provide a tire component having increased tear strength, where the tire component is less susceptible to chipping or chunking, without substantially impacting the hysteresis properties of the tire component.
It is yet another object of the present invention to provide a vulcanizate having increased tear strength, where the vulcanizate is less susceptible to chipping and chunking, without substantially impacting the mechanical and wear properties of the vulcanizate.
It is still another object of the present invention to provide a vulcanizate having increased tear strength, where the vulcanizate is less susceptible to chipping or chunking, without substantially impacting the hysteresis properties of the vulcanizate.
It is also an object of the present invention to provide vulcanizable compositions of matter that will give rise to a cured product having increased tear strength, where the cured product is less susceptible to chipping and chunking, without substantially impacting the mechanical and wear properties of the cured product.
It is another object of the present invention to provide vulcanizable compositions of matter that will give rise to a cured product having increased tear strength, where the cured product is less susceptible to chipping or chunking, without substantially effecting the hysteresis properties of the cured product.
It is yet another object of the present invention to provide a tire having increased tear strength without substantially impacting the mechanical and wear properties of the tire at high temperatures.
It is still yet another object of the present invention to provide a vulcanizate having increased tear strength without substantially impacting the mechanical and wear properties of the vulcanizate after heat aging.
At least one or more of the foregoing objects, together with the advantages thereof over the known art relating to tire components and compositions for making the same, which shall become apparent from the specification that follows, are accomplished by the invention as hereinafter described and claimed.
In general the present invention provides a tire having improved tear strength including at least one component comprising a vulcanized elastomer; and up to about 35 parts by weight of polyolefin copolymer per one hundred parts by weight rubber.
The present invention also provides a vulcanizable composition of matter comprising an elastomer up to about 35 parts by weight of polyolefin copolymer per one hundred parts by weight rubber; and up to about 100 parts by weight.
The present invention further provides a vulcanizate prepared by a process comprising the steps of preparing a vulcanizable composition of matter that includes an elastomer and a polyolefin copolymer; and vulcanizing the composition of matter with at least one vulcanizing agent.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
It has now been found that the addition of polyolefin copolymers to vulcanizable compositions of matter that are useful for making tires provides for tires and tire components having increased tear strength without substantially affecting the mechanical, wear and hysteresis properties of the tire rubber. Notably, the mechanical properties of the tire components are not substantially degraded after heat aging by the addition of the polyolefin polymers. Accordingly, the present invention is directed toward vulcanizable compositions of matter, tire recipes, vulcanizates, tire components, and tires containing polyolefin copolymers. The practice of the present invention is especially useful in base stock recipes, but inasmuch as the increase in tear strength does not deleteriously impact the wear, mechanical, and hysteresis properties of the rubber, the practice of the present invention may also be applied to the tread and sidewall stocks of tires. Furthermore, it should be understood that the practice of the present invention is believed to be especially advantageous for off-road or heavy-duty truck tires, although it is believed that the practice of the present invention will improve other tires such as passenger tires.
The polyolefin copolymers that are useful in practicing this invention include random, block, and statistical copolymers of ethylene and propylene. For purposes of this specification, these copolymers of ethylene and propylene may simply be referred to as copolymers. Preferably, these copolymers will contain a major amount, i.e. more than 50% by weight, of polypropylene monomeric units. More preferably, the copolymers will contain from about 1 to 30 percent by weight polyethylene or ethylene monomeric units, with the remainder of the copolymer substantially including polypropylene or propylene monomeric units. Even more preferably, the copolymers will contain from about 5 to about 25 percent by weight ethylene monomeric units, and even more preferably from about 10 to about 20 percent by weight ethylene monomeric units, with the remainder of the copolymers substantially including propylene monomeric units. It should be understood that many of the commercially available copolymers that are useful in practicing this invention contain some amount of contamination or by-products of polymerization, and therefore the copolymers of this invent
Lin Chen-Chy
Tatsuro Hamada
Bridgestone Corporation
Burleson David G.
Choi Ling-Siu
Reginelli Arthur M.
Wu David W.
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