Tire with tread for low temperature performance and wet traction
This invention relates to a tire with tread for promoting a combination of winter service at low temperatures and for promoting wet traction. The tread is of a rubber composition containing low Tg styrene/butadiene elastomer and cis 1,4-polybutadiene rubber, along with high Tg liquid styrene/butadiene polymer, traction resin and vegetable triglyceride oil.
1. A pneumatic tire having a circumferential rubber tread of a rubber composition comprised of, based on parts by weight per 100 parts by weight elastomer (phr):
(A) diene-based elastomers comprised of;
(1) about 40 to about 90 phr of a styrene/butadiene elastomer having a Tg in a range of from at least −50° C. to about −85° C.,
(2) about 10 to about 60 phr of high cis 1,4-polybutadiene rubber having a Tg in a range of from about −100° C. to about −105° C. and a cis 1,4-isometric content of at least about 95 percent, together with
(3) about 3 to about 50 phr of low molecular weight liquid styrene/butadiene polymer having a Tg in a range of from about −30° C. to about 0° C., and
(B) about 50 to about 250 phr of rubber reinforcing filler comprised of a combination of precipitated silica and rubber reinforcing carbon black in a ratio of precipitated silica to rubber reinforcing carbon black of at least 9/1, together with silica coupling agent having a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with said diene-based elastomers and polymer,
(C) about 5 to about 45 phr of resin comprised of styrene-alphamethylstyrene resin having a softening point (ASTM E28) in a range of from about 60° C. to about 125° C., and
(D) about 5 to about 50 phr of vegetable triglyceride oil.
2. The tire of claim 1 wherein the tread rubber composition further contains up to 25 phr of at least one additional low Tg diene based elastomer comprised of cis 1,4-polyisoprene.
3. The tire of claim 1 wherein said styrene/butadiene elastomer is a functionalized elastomer containing at least one of siloxane, amine and thiol functional groups reactive with hydroxyl groups on said precipitated silica.
4. The tire of claim 1 wherein said styrene/butadiene elastomer is tin coupled.
5. The tire of claim 3 wherein said functionalized styrene/butadiene elastomer is a tin coupled elastomer.
6. The tire of claim 1 wherein said tread rubber composition further contains up to 25 phr of at least one additional diene based elastomer comprised of at least one of cis 1,4-polyisoprene, isoprene/butadiene, and styrene/isoprene rubber.
7. The tire of claim 1 wherein said silica coupling agent is comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average of from about 1 to about 4 connecting sulfur atoms in its polysulfidic bridge or is comprised of an alkoxyorganomercaptosilane.
8. The tire of claim 1 wherein said precipitated silica and silica coupling agent are pre-reacted to form a composite thereof prior to their addition to the rubber composition.
9. The tire of claim 1 wherein said precipitated silica and silica coupling agent are added to the rubber composition and reacted together in situ within the rubber composition.
10. The tire of claim 1 wherein said styrene-alphamethylstyrene resin has a styrene content of from about 10 to about 30 percent.
11. The tire of claim 1 wherein said tread is provided as being sulfur cured.
12. The tire of claim 3 wherein said tread is provided as being sulfur cured.
13. The tire of claim 5 wherein said tread is provided as being sulfur cured.
14. The tire of claim 7 wherein said tread is provided as being sulfur cured.
15. The tire of claim 10 wherein said tread is provided as being sulfur cured.