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
1999-03-08
2001-06-05
Niland, Patrick D. (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...
C152S151000, C152S450000, C152S565000, C152S905000, C524S323000, C524S342000, C524S437000, C524S444000, C524S490000, C524S491000, C524S492000, C524S493000, C524S496000, C524S502000
Reexamination Certificate
active
06242523
ABSTRACT:
FIELD
The invention relates to a rubber composition composed of high Tg diene-based elastomers and which contains a high Tg liquid polymer of high vinyl polybutadiene and to such a composition being sulfur cured. The invention also relates to a tire having a tread of such rubber composition.
BACKGROUND
High performance tires have rubber treads which typically have a relatively high aromatic oil content in order to increase their traction on dry road surfaces.
In particular, while increasing the oil content of a tread rubber composition conventionally increases its dry traction, it also conventionally reduces its durability as evidenced by a reduction of one or more of 300% modulus, breaking strength, Energy to Break and DIN abrasion resistance physical properties.
For example, a tire with a tread rubber composition that is too soft may exhibit good traction but its surface may have insufficient resistance to abrasion and may blister or otherwise physically degrade under long running conditions. On the other hand, a tire tread that is too hard may exhibit good abrasion resistance and associated physical wear characteristics but will likely tend to skid during vehicular cornering. It is believed that such phenomenon is well known to those having skill in such rubber compounding art.
Therefore, a means of providing a high performance tire tread with a combination of both good, dry traction accompanied with good durability, including abrasion resistance, is desired in order to provide a tire with sufficient dry traction so that it can travel at relatively high speeds and sufficient durability so that it can travel over an extended period of time at relatively high speeds.
Accordingly, this invention relates to providing a tire tread rubber composition with a combination of good, dry traction and durability by use of high Tg diene-based elastomers together with a minor amount of a high Tg liquid high vinyl polybutadiene polymer in place of at least a portion of an aromatic rubber processing oil.
In one aspect, while it is believed to be well known to those having skill in such art that while use of higher Tg polymers typically increases hysteresis of a rubber composition and consequently its traction, it is believed that it would normally be expected to reduce its durability, including a resistance to abrasion property, as hereinbefore discussed.
It is similarly believed to be well known to those having skill in such art that while use of higher molecular weight polymers typically improves durability of a rubber composition, it is believed that it would normally be expected to decrease its traction insofar as a tire tread is concerned.
It is a significant aspect of this invention that benefits of the aforesaid desirable abrasion resistance and durability physical properties have been observed to be obtained via the use of a liquid polymer that has both a higher Tg and molecular weight than the rubber processing oil which it, at least partially, replaces in a rubber composition for a tire tread.
In practice, rubber processing oil, particularly aromatic processing oil, is sometimes blended with relatively high viscosity (Mooney viscosity) elastomers in order to reduce their viscosity so that the unvulcanized elastomer may be more easily processed in conventional rubber processing equipment, including internal rubber mixers and various rubber extruders. Such oil extended elastomers may be used, for example, for rubber compositions as components of tires such as tire treads. The use of viscosity-reducing aromatic processing oil in relatively high viscosity elastomers for such purpose is well known to those having skill in such art.
Sometimes, it has been proposed to use various liquid polymers which contain carbon-to-carbon double bond unsaturation to replace at least a portion of such rubber processing oil. The philosophy has been for the liquid polymer to help in reducing the viscosity of the elastomer and to later co-vulcanize with the elastomer upon curing the rubber composition.
Such use of rubber processing oil and proposed use of unsaturated liquid polymers is well known to those having skill in such art.
Indeed, while rubber processing oils have been used to improve the processability of various high viscosity elastomers, the inclusion of processing oils in such rubbers often results in a decrease in its modulus of elasticity. Accordingly, the inclusion of substantial amounts of processing oils in rubber compounds is frequently not always a good option for attaining good processability.
Alternatively, high performance rubber composition requirements, particularly for tire treads, have traditionally necessitated using elastomers of relatively high viscosity and associated very poor processability characteristics. As hereinbefore pointed out, it has been known to add a liquid polymer which is co-vulcanizable with such an elastomer.
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 elastomer”. In the description of this invention, the terms “rubber” and “elastomer” can be used interchangeably, unless otherwise distinguished. The terms “rubber composition”, “compounded rubber” and “rubber compound” can be used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and the terms “cure” and “vulcanize” may also be used interchangeably herein, unless otherwise noted and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
PRACTICE AND SUMMARY OF THE INVENTION
This invention relates to the use in a rubber composition of a liquid high Tg, high vinyl polybutadiene polymers which contain a vinyl unsaturation in a range of about 40 to about 95, preferably about 60 to about 90, percent and having a molecular weight (number average) in a range of about 1,000 to about 20,000, alternatively about 3,000 to about 14,000. It is desirable that the polymer is liquid and can be pourable at a temperature in a range of about 20° C. to about 25° C., and preferably administered within such temperature, although it might be used at a temperature above or below such temperature range.
In accordance with this invention, a rubber composition is provided which is comprised of, based upon its rubber component, (A) 100 parts by weight (phr) of at least one solid diene-based elastomer selected from homopolymers and copolymers of conjugated diene and copolymers of at least one conjugated diene with a vinyl aromatic compound selected from styrene and alpha-methylstyrene; wherein said elastomers have a Tg of lower than +10° C., alternatively lower than −10° C. and at least 50, preferably at least 70, and alternatively 100 weight percent of said elastomers have a Tg above −40° C., (B) from about 5 to about 50, alternatively about 10 to about 30, phr of a liquid polymer of high vinyl polybutadiene having a vinyl (1,2-) content in a range of about 40 to about 95, preferably about 60 to about 90, percent and a Tg in a range of about −5° C. to about −40° C. preferably about −15° C. to about −25° C.
In practice, it may also be desired for the rubber composition to include a hydrocarbon-based tackifying resin having a softening point in a range of about 30° C. to about 200° C. (ASTM test method E2858T), in an amount of about 5 to about 60, alternatively about 10 to about 30, phr, in order to provide increased traction for a tire tread of such rubber composition. Representative classes of such resins are, for example, aliphatic resins, aliphatic/aromatic resins, aromatic resins, terpene resins and phenolic resins.
Representative of aliphatic resins are, for example, terpolymers of piperylene/2-methyl-2-butene/dicyclopentadiene such as, for example, WINGTACK® 115 from The Goodyear Tire & Rubber Company.
Representative of aliphatic/aromatic resins are, for example, coumarone-indene resins such as, for example, Cumar R-13 from Neville Chemical.
Representative of aromatic resins are, for example
Blok Edward John
Futamura Shingo
Kralevich, Jr. Mark Leslie
Sandstrom Paul Harry
Niland Patrick D.
The Goodyear Tire & Rubber Company
Young Jr Henry C
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