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
2001-10-31
2004-11-02
Wyrozebski, Katarzyna (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, C524S575000, C525S332400, C525S332600, C525S332500, C525S332900, C525S333100, C525S333300
Reexamination Certificate
active
06812277
ABSTRACT:
FIELD OF THE INVENTION
Pneumatic rubber tire having at least one component or a rubber composition comprised of a major portion of relatively low Tg high cis 1,4-polybutadiene elastomer (BR) and a minor portion of a relatively high Tg, styrene-rich, styrene/isoprene elastomer (SIR) wherein the Tg of said BR is at least 60° C. lower than the Tg of said SIR. Said SIR has a styrene content of at least 30 weight percent. The styrene based units of said SIR are present substantially without large blocks of styrene units. Said BR is a high cis 1,4-polybutadiene having a cis 1,4-content of at least 96 percent and preferably has a branched macrostructure. In one aspect of the invention, said tire component is a tire tread, particularly a circumferential tire tread.
BACKGROUND OF THE INVENTION
Pneumatic rubber tires are often prepared with a component of a rubber composition which is composed of a blend of elastomers.
For example, a rubber tread component is typically comprised of a blend of elastomers to promote desirable tire tread properties such as, for example, traction, reduction in tread wear and reduced rolling resistance.
Historically, passenger tire treads are commonly composed of rubber blends of a styrene/butadiene copolymer elastomer (SBR), which is usually used to promote traction characteristics for the tire tread, and cis 1,4-polybutadiene rubber which is usually used to promote reduction in tread wear and reduction in rolling resistance for the tire tread.
Such rubber blends are typically SBR-rich in that the SBR is conventionally used as the major elastomer component of the tread rubber composition because tread traction on the road surface is usually a significantly desirable feature for the tire and, also, the SBR in its uncured state is relatively easy to process. Contrarily, the cis 1,4-polybutadiene rubber is conventionally a minor component of the rubber composition because, in its uncured state, it is typically of a relatively high viscosity (high Mooney viscosity) and therefore more difficult to process in rubber processing equipment.
Such SBR-rich tire tread rubber compositions may also sometimes contain minor amounts of one or more other elastomers, in addition to said minor amount of cis 1,4-polybutadiene rubber, such as, for example, cis, 1,4-polyisoprene rubber (particularly natural rubber), isoprene/butadiene copolymer rubber and/or 3,4-polyisoprene rubber, and perhaps trans 1,4-butadiene.
For a tire, it is often desired to optimize one or more of a tire's treadwear, skid resistance, and rolling resistance by choice of a tire tread's rubber composition.
However, as it is known to those having skill in such art, an optimization in one of such tire properties by varying the tire tread rubber composition usually diminishes one or more of the other two properties.
Achieving an optimization of all of treadwear, wet skid resistance and rolling resistance by the rubber composition for the tire tread is therefore a challenge.
Accordingly, for high performance tires, an increase in the rate of wear of the tread might be acceptable where very good wet and dry traction of a tire tread is desired. Thus, rubber compositions intended to emphasize very good wet and dry traction for a tire tread may, however, often exhibit a relatively lower resistance to abrasion, higher rolling resistance and lower snow traction and higher brittle point. These formulations usually contain a higher concentration of SBR as a major component of rubber compositions for such tire treads.
A traction promoting elastomer, such as for example styrene/butadiene elastomer, might be used for tread rubber compositions may typically exhibit a relatively high Tg above −50° C. such as, for example, Tg within a range of about zero down to about −50° C.
However, high Tg polymers typically raise the brittle point of the rubber compositions and such rubber compositions are therefore more susceptible to cracking at cold temperatures. For example, rubber compositions for treads for all-season tires may desirably have a brittle point below −40° C.
In contrast to such high Tg styrene/butadiene rubber, an elastomer such as, for example cis 1,4-polybutadiene, used in a tread rubber composition, in combination with such styrene/butadiene rubber, to promote good (relatively low) treadwear might have a much lower Tg, for example, a Tg lower than −90° C.
In such rubber composition, the low Tg cis 1,4-polybutadiene rubber is usually used to promote tread wear for a tire tread. However the amount of cis 1,4-polybutadiene is usually limited to a relatively minor component of the elastomers for a tire tread (e.g. usually less than 35 weight percent thereof) because if the cis 1,4-polybutadiene elastomer is present as a major component (e.g. greater than 50 weight percent), the resulting rubber composition typically exhibits a relatively high and, generally unacceptable, mixing and processing viscosity (e.g. a high Mooney ML 1+4 viscosity) without blending a rubber processing oil with the cis 1,4-polybutadiene to reduce its processing viscosity. In addition, levels of cis 1,4-polybutadiene greater than 35 weight percent in treads usually result in unacceptable wet traction.
In such rubber composition, the styrene/butadiene rubber is usually used to promote traction for a tire tread and is typically present as a major component of the elastomers (e.g. greater than 50 weight percent). The styrene content of the styrene/butadiene rubber in commercial tire treads is conventionally in a range of about 10 to about 40 weight percent of the elastomer.
Styrene/butadiene rubber and cis 1,4-polybutadiene rubber are typically compatible and therefore a plot of Tan delta versus temperature for a blend of such elastomers may exhibit one only maximum peak. Therefore, for rubber compositions based upon such on such compatible rubber blends, low temperature physical properties are typically sacrificed for high temperature physical properties of the rubber composition. For example, a tire treadwear property may be typically compromised with an increase in wet traction property when such compatible rubber blend is used for a tire tread rubber composition. Furthermore, the cold brittle point temperature of the tire tread rubber composition may typically be raised with an increase in wet traction when a compatible blend of such elastomers is used for the tire tread rubber composition to render the tire tread less useful at very low operating temperatures.
For a description of this invention, terms such as “compounded rubber”, “rubber compound” and “compound”, if used herein, refer to rubber compositions composed of one or more elastomers blended with various ingredients, including curatives such as sulfur and cure accelerators. The terms “elastomer” and “rubber” might be used herein interchangeably. It is believed that all of such terms are well known to those having skill in such art.
A reference to glass transition temperature, or Tg, of an elastomer or elastomer composition, if referred to herein, represents the glass transition temperature(s) of the respective elastomer or elastomer composition in its uncured state or possibly a cured state in a case of an elastomer composition. A Tg can be suitably determined by a differential scanning calorimeter (DSC) at a temperature rate of increase of 10° C. per minute. (ASTM 3418).
A reference to a rubber composition's brittle point relates to a cold temperature property value according to ASTM D746 for the rubber composition and is a measure of a temperature when a rubber composition becomes brittle and therefore a measure of the usefulness of the rubber composition at very cold temperatures
DISCLOSURE AND PRACTICE OF THE INVENTION
In accordance with this invention, a pneumatic rubber tire is provided having a tire tread, (circumferential rubber tread) where said tread is a rubber composition comprised of, based on parts by weight per 100 parts by weight of the tread rubber elastomers (phr),
(A) elastomers comprised of
(1) about 5 to about 45, altern
Halasa Adel Farhan
Jasiunas Chad Aaron
Zanzig David John
The Goodyear Tire & Rubber Company
Wyrozebski Katarzyna
Young, Jr. Henry C.
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