Tire with tread to promote wet traction and reduce rolling resistance
This invention relates to a tire with a tread of a rubber composition for promoting a combination of beneficial wet traction and reduced rolling resistance, while limiting any loss of winter traction at low temperatures. The tread rubber composition contains a combination of high and lower glass transition temperature (Tg) elastomers. Its reinforcing filler is primarily precipitated silica. The high Tg elastomer is comprised of synthetic high vinyl polybutadiene rubber and the lower Tg elastomer is comprised of at least one of natural and synthetic cis 1,4-polyisoprene rubber. The tread rubber composition may contain at least one of vegetable oil based rubber processing aid and traction promoting resin. The tread rubber composition is intended to be exclusive of styrene-containing elastomers.
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) 100 phr of conjugated diene-based elastomers, consisting of (1), (2) and (3)
(1) about 10 to about 75 phr of a high vinyl polybutadiene rubber having a Tg in a range of from about −40° C. to about −10° C. and an isomeric vinyl 1,2-content in a range of from about 60 to about 85 percent,
(2) about 90 to about 25 phr of cis 1,4-polyisoprene rubber having a Tg in a range of from about −65° C. to about −75° C. and an isomeric cis 1,4-content of at least 95 percent, and
(3) up to about 25 phr of at least one of low vinyl polybutadiene elastomer having a vinyl 1,2-content of less than 15 percent having a Tg in a range of −108° C. to about −90° C., and 3,4-polyisoprene;
(B) about 80 to about 200 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
(C) about 10 to about 60 phr of at least one additive comprised of at least one of
(1) traction promoting resin,
(2) petroleum based rubber processing oil, and
(3) vegetable triglyceride rubber processing oil selected from the group consisting of sunflower, soybean, canola and safflower oil;
wherein the rubber composition is exclusive of synthetic copolymer based elastomers.
2. The tire of claim 1 wherein said high vinyl polybutadiene is a functionalized high vinyl polybutadiene elastomer comprised of a high vinyl polybutadiene elastomer which contains at least one end-chain functional group reactive with hydroxyl groups on said precipitated silica comprised of at least one of amine, thiol, siloxy and silane-sulfur groups.
3. The tire of claim 1 wherein said precipitated silica and silica coupling agent are provided as a composite of precipitated silica pre-reacted with silica coupling agent.
4. 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.
5. The tire of claim 1 wherein said silica coupling agent is comprised of:
(A) bis(3-trialkoxysilylalkyl) polysulfide containing an average in range of from about 2 to about 4 connecting sulfur atoms in its polysulfidic bridge, or
(B) an organoalkoxymercaptosilane, or
(C) their combination.
6. The tire of claim 5 wherein said silica coupling agent is comprised of a bis(3-triethoxysilylpropyl) polysulfide.
7. The tire of claim 1 wherein said silica coupling agent is comprised of an organoalkoxymercaptosilane.
8. The tire of claim 1 wherein said traction promoting resin is comprised of a styrene/alphamethylstyrene resin having a styrene content in a range of from about 10 to about 90 percent and a softening point within a range of from about 60° C. to about 125° C.
9. The tire of claim 1 wherein said traction promoting resin is comprised of a coumarone-indene resin having a softening point within a range of from about 60° C. to about 150° C.
10. The tire of claim 1 wherein said traction promoting resin is comprised of a petroleum hydrocarbon resin.
11. The tire of claim 1 wherein said traction resin is comprised of a terpene resin.
12. The tire of claim 11 wherein said terpene resin is a polymer comprised of at least one of limonene, alpha pinene, beta pinene and delta-3-carene and having a softening point in a range of from about 60° C. to about 160° C.
13. The tire of claim 1 wherein said traction promoting resin is comprised of terpene-phenol resin.
14. The tire of claim 1 wherein said additive is a combination of traction promoting resin, petroleum based rubber processing oil and vegetable triglyceride oil.
15. The tire of claim 1 wherein said additive is a combination of traction promoting resin and vegetable triglyceride oil.
16. The tire of claim 1 wherein said additive is a combination of traction promoting resin and petroleum based rubber processing oil.
17. The tire of claim 1 wherein said rubber processing oil of said additive is a combination of petroleum based rubber processing oil and vegetable triglyceride oil.
18. The tire of claim 1 wherein said tread rubber composition is a sulfur cured rubber composition.