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
1997-09-16
2002-08-06
Mulcahy, Peter D. (Department: 1713)
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...
C524S526000, C152S450000
Reexamination Certificate
active
06429245
ABSTRACT:
FIELD
This invention relates to a tire having a rubber tread which is composed of at least two defined elastomers with spaced-apart Tg's. The tread rubber may be reinforced with either carbon black or a combination of silica and carbon black reinforcing fillers, together with a coupling agent for the silica.
BACKGROUND
Pneumatic rubber tires are conventionally prepared with a rubber tread which can be a blend of various rubbers which is typically reinforced with carbon black.
In one aspect, rubbers are evaluated, selected and blended for a purpose of achieving desired tire tread properties and particularly a balance of tire tread characteristic properties, mainly, traction, rolling resistance, and wear.
Typically, the tread rubber is reinforced with carbon black or a combination of carbon black and silica fillers. Often, the silica is used with a silica coupler to couple the silica to the elastomers for rubber reinforcement purposes. Such use of carbon black and silica, including use of silica couplers, is well known to those having skill in such art.
Historically, it is recognized that tires have heretofore been suggested and/or have been prepared with treads of rubber compositions which are based on (i) blends of elastomers having similar Tg's or (ii) blends of elastomers with widely spaced apart Tg's by at least 30° C.
For example, tires with treads composed of a blend of elastomers with glass transition temperatures (Tg's) differing by at least 30° C. might be prepared with styrene/butadiene copolymer rubbers having a Tg in a range of about −35° C. to about −50° C. blended with natural rubber having a Tg of about −60 to about −65° C. and/or cis 1,4-polybutadiene rubber having a Tg of about −85 to about −105° C. to obtain tire tread compositions with acceptable traction on wet road surfaces and on sometimes icy road surfaces.
Also, a tire with tread composed of emulsion polymerization prepared styrene/butadiene copolymer rubber with a Tg in a range of about −35 to about −50° C. with natural cis 1,4-polyisoprene rubber having a Tg of about −65° C. might be used for winter performance, such as traction on icy road surfaces and/or might reduce the tread's traction on a wet road surface.
Here, it is desired to provide a tire tread composed of elastomers with substantially spaced apart and defined Tg's, to the exclusion of elastomers of specified intermediate Tg's, to enhance traction and/or treadwear.
In the description of this invention, 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”.
The terms such as “compounded rubber”, “rubber compound” and “rubber composition” relate generally to “rubber which has been mixed with various rubber compounding ingredients”. Such terms are well known to those skilled in the rubber mixing art, especially for tires.
The terms “vulcanized”, “vulcanize”, “cured” and “cure”, if used herein, are used interchangeably to refer to the “vulcanization of rubber” and such terms are well known to those having a skill in the rubber vulcanization art.
The term “Tg”, as used herein, refers to the “glass transition temperature of a particular elastomer”. Glass transition temperatures are well known characterizations of elastomers. They may, for example, be suitably determined by a DSC instrument with a heating rate of 20° C. per minute.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, a pneumatic tire is provided having a tread of a rubber composition comprised of, based on 100 parts by weight rubber, and exclusive of elastomers having a Tg between −30° C. and −85° C.;
(A) about 20 to about 50, alternatively about 30 to about 40, phr of at least one synthetic elastomer having a Tg in a range of −30° C. to about +10° C. selected from high vinyl polybutadiene with a vinyl 1,2-content in a range of about 75 to about 95 percent; isoprene/butadiene copolymer containing about 10 to about 90 percent units derived from isoprene; 3,4-polyisoprene having a 3,4-microstructure content of at least 60 percent; emulsion polymerization prepared styrene/butadiene copolymer having from about 45 to about 65 percent units derived from styrene and a vinyl 1,2-content based on the butadiene component thereof in a range of about 8 to about 15 percent; and solution polymerization prepared styrene/butadiene copolymer having from about 15 to about 40 percent units derived from styrene and a vinyl 1,2-content based on the butadiene component thereof in a range of about 15 to about 60 percent; and
(B) about 50 to about 80, alternatively about 60 to about 70 phr of at least one synthetic elastomer having a Tg in a range of −85° C. to about −110° selected from isoprene/butadiene copolymer having about 10 to about 30 percent units derived from isoprene; cis 1,4-polybutadiene rubber having about 90 to about 98 percent cis 1,4-microstructure, and a vinyl 1,2-content in a range of about 2 to about 10 percent with the remainder being primarily of a trans 1,4-microstructure;
(C) about 40 to about 100, alternatively about 60 to about 90, phr of particulate reinforcing filler selected from (1) carbon black or (2) carbon black and silica, preferably precipitated silica, with a weight ratio of carbon black to silica in a range of about 1/20 to about 20/1, alternatively about 1/5 to about 5/1;
(D) at least one silica coupler for the silica, if silica is used, having a moiety reactive with the surface of said silica and another, sulfur based, moiety interactive with said elastomer.
Typically, the silica coupler has a silane moiety reactive with the surface of the silica such as, for example, silanol groups thereon, and another, polysulfide based, moiety interactive with the elastomers, typically in a weight ratio of silica to coupler of about 7/1 to about 15/1. For example, the coupler may be a bis-(trialkoxysilylalkyl)polysulfide having from 2 to about 8 sulfur atoms in its polysulfidic bridge. Exemplary of such a coupler may be a bis-(3-triethoxysilylpropyl)polysulfide having an average of about 2 to about 5 sulfur atoms in its polysulfidic bridge.
Significantly, the tread rubber composition is required to contain an appreciable content of elastomer(s) having a relatively high Tg in a range of −30 to about +10° C. A purpose of utilizing such high Tg elastomers is to enhance traction, particularly wet traction.
Also, significantly, the tread rubber composition is required to contain an appreciable content of elastomer(s) having a relatively low Tg in a range of about −85 to about −110° C. A purpose of utilizing such low Tg elastomer(s) is to reduce treadwear.
It is further significant, for the purposes of this invention, that elastomers having a Tg within a range of −35 to −85° C. are intended to be excluded. This is because such elastomers are considered herein as not being suitable, or entirely significant contributors to traction and/or, as the case may be, reduced treadwear. Representative examples of such elastomers desired to be excluded are those such as, for example, cis 1,4-polyisoprene whether natural or synthetic, and emulsion polymerization prepared styrene/butadiene elastomers (SBR's) containing less than 45 percent units derived from styrene.
While the mechanism may not be completely understood, it is believed that it is the prescribed combination of high and low spatially defined Tg elastomers which acts to promote the aforesaid more optimized traction and treadwear aspects of the tire tread rubber composition.
The various polybutadiene rubbers for use in this invention can be prepared by organic solution polymerization processes for 1,3-butadiene monomer well known to those having skill in such art.
The organic solution polymerization prepared isoprene/butadiene copolymer elastomer can be suitably prepared by copolymerization of isoprene and 1,3-butadiene in an organic solvent solution in the presenc
Blok Edward John
Francik William Paul
Halasa Adel Farhan
Sandstrom Paul Harry
Verthe John Joseph Andre
Mulcahy Peter D.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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