Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-10-11
2003-06-24
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S905000
Reexamination Certificate
active
06581659
ABSTRACT:
FIELD
This invention relates to a tire having a tread of a cap/base construction wherein the tread cap is composed of trans 1,4-polybutadiene, solution polymerization prepared styrene/butadiene copolymer rubber, cis 1,4-polyisoprene and defined amounts of carbon black and amorphous silica reinforcement.
BACKGROUND
Tires are often prepared with a tread of a cap/base construction where the outer tread cap is designed to be road contacting and the underlying base is designed to support the tread cap and is not designed to be road contacting.
For various purposes, it is sometimes desired to provide a tire tread cap with a rubber composition which has a relatively high degree of durability and which has good, relatively low, rolling resistance, good, relatively high, traction and good, relatively low, treadwear.
For such purposes, it is believed to be rather commonplace to often use cis 1,4-polybutadiene rubber in a tread cap rubber composition to enhance its treadwear.
It is also sometimes desirable to provide a tire tread cap rubber composition with various amounts of amorphous silica reinforcement and carbon black for various purposes.
In particular, where it is desired to provide a tire tread cap with enhanced balance of traction and treadwear properties, cis 1,4-polybutadiene rubber and silica reinforcement may be included in its formulation.
However, for various purposes, it is also sometimes desired to provide a tire tread cap with an enhanced durability in a sense of resistance to tear initiation and propagation, particularly where a tire might be used in off-the-road service conditions environment, yet still have an enhanced balance of traction and treadwear.
Historically, trans 1,4-polybutadiene have been used in various tire components, including a tire sidewall (U.S. Pat. Nos. 5,626,697 and 5,386,865), a tire tread base of a cap/base construction (U.S. Pat. No. 5,229,195) as well as a tread with a portion intended to be road contacting as Japanese publications 60-133; 60-101,504; and 60-143,453 and U.S. Pat. Nos. 4,510,291 and 5,025,059. Also, see U.S. Pat. Nos. 5,174,838, 5,386,865, 5,229,459 and 5,885,389.
It is important to appreciate that trans 1,4-polybutadiene may be similar to a thermoplastic polymer which becomes elastomeric upon being sulfur vulcanized. As an elastomer, trans 1,4-polybutadiene, unlike most elastomers, may tend to strain crystallize under low strain (low elongation) conditions so that it, therefore, may provide modulus strength enhancement during the dynamic operation of a tire tread. This phenomenon may provide improved tear resistance, particularly resistance to irregular wear of a tire tread's road-contacting surface under service conditions.
A preparation of a trans 1,4-polybutadiene resin and its characterization may readily be found in U.S. Pat. No. 5,089,574.
In the description of this invention, the terms “rubber” and “elastomer” if used herein, may be used interchangeably, unless otherwise prescribed. The terms “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 such terms are well known to those having skill in the rubber mixing or rubber compounding art.
The term “phr” if used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer” which in this invention is intended to include the aforesaid trans 1,4-polybutadiene resin.
A reference to an elastomer's Tg refers to a “glass transition temperature” which can conveniently be determined by a differential-scanning calorimeter at a heating rate of 10° C. per minute.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, a tire is provided having a tread of a cap/base construction, where the tread cap is intended to be ground-contacting rubber; wherein the tread cap is of a rubber composition which comprises, based on 100 parts by weight (phr) of rubber (A) 100 phr of rubber comprising, and preferably consisting essentially of, (1) about 5 to about 50, alternatively, about 10 to about 30, phr of trans 1,4-polybutadiene polymer having a trans 1,4 content in a range of about 80 to about 90 percent, (2) about 30 to about 70, alternatively, about 40 to about 60, phr of organic solution polymerization prepared styrene/butadiene copolymer rubber containing about 5 to about 40, alternatively about 5 to about 15, weight percent units styrene, and (3) about 5 to about 50, alternatively about 20 to about 40, phr of cis 1,4-polyisoprene rubber (B) about 40 to about 95 phr reinforcing filler as carbon black and amorphous silica; wherein said filler contains (i)about 35 to about 75 phr of carbon black and about 5 to about 20 phr of said amorphous silica or (ii) about 5 to about 30 phr of carbon black and about 35 to about 90 phr of said amorphous silica and (C) at least one silica coupling agent having a moiety reactive with hydroxyl (e.g. silanol groups) on the surface of the said silica and an additional moiety interactive with the said elastomer(s).
A significant aspect of this invention is the utilization of the trans 1,4-polybutadiene to replace a significant portion of commonly used cis 1,4-polyisoprene rubber in the tire tread rubber composition in a circumstance where the tire tread rubber contains defined amounts of amorphous silica reinforcement where, insofar as the carbon black and silica are concerned, (i) silica is in a minority or (ii) silica is in the majority.
In one aspect, it may be desired for the silica to be in a minority insofar as the carbon black and silica reinforcement is concerned in order to maximize wear resistance of the tread rubber composition.
In another aspect, it may be desired for the silica to be in a majority insofar as the carbon black and silica reinforcement is concerned in order to maximize a reduction of rolling resistance for the tire itself.
For the replacement of a portion of the otherwise used cis 1,4-polyisoprene rubber in the tread cap rubber composition, it is considered herein that the trans 1,4-polybutadiene has a particular advantage in that, for example, it tends to strain crystallize under low strain (low elongation such as, for example, about 5 to 20 percent elongation) conditions in a cured rubber conditions in contrast to the more commonly used cis 1,4-polyisoprene which would be expected to tend to strain crystallize at somewhat higher such low strains, or elongations, of about 25 percent or higher. This is important where low strain stiffness for a rubber composition is desired such as, for example, in tire tread for treadwear resistance and handling.
Accordingly, this phenomenon may provide improved tread wear and tire handling properties for a tread rubber which contains a trans 1,4-polybutadiene polymer.
The inclusion of the trans 1,4-polybutadiene in the tire tread cap rubber composition is, therefore, considered herein to be of a significant benefit, as compared to a more commonly used cis 1,4-polyisoprene rubber in that the trans 1,4-polybutadiene structure is observed to improve resistance to abrasion, or wear, promotes higher rebound values with predictive lower rolling resistance for a tire with tread of such rubber composition, for the rubber composition.
Another significant aspect of this invention is the use of a solution polymerization derived styrene/butadiene copolymer elastomer (S-SBR) in combination with the trans 1,4-polybutadiene. This is considered herein to be significant because the presence of the S-SBR in the rubber composition considered herein to promote a reduction in rolling resistance and increase in traction and handling for a tire having a tread of such rubber composition.
The use of a relatively low to conventional styrene content in a range of about 5 to about 15 weight percent in the S-SBR is considered as being significant because a relatively low styrene content for the S-SBR is considered herein to promote a reduction in rolling resistance for a tire
Blok Edward John
Holtzapple Gregory Martin
Verthe John Joseph Andre
LandOfFree
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