Tire with rubber tread containing combination of resin blend and functionalized elastomer
This invention relates to a pneumatic tire with an outer, running surface containing, circumferential tread comprised of a styrene/butadiene (SBR) rich rubber composition containing two SBR's with spaced apart glass transition temperatures (Tg's), one of which is a functionalized SBR with a functional group reactive with hydroxyl groups on a precipitated silica, together with a combination of at least three resins with spaced apart softening points. The filler reinforcement is a combination of precipitated silica and specialized rubber reinforcing carbon black.
1. A pneumatic tire having an outer circumferential tread with a tread running surface where said tread is a sulfur-cured rubber composition comprised of, based on parts by weight per 100 parts by weight rubber (phr),
(A) conjugated diene-based elastomers comprised of:
(1) about 30 to about 70 phr of a solution polymerization derived styrene/butadiene elastomer (S-SBR) having a styrene content in a range of from about 35 to about 45 percent and vinyl content in a range of from about 20 to about 40 percent based upon
the polybutadiene portion of the elastomer, and a Tg in a range of from about −15° C. to about −22° C., and
(2) about 30 to about 70 phr of a functionalized solution polymerization derived styrene/butadiene elastomer (S-SBR-F) having a styrene content in a range of from about 35 to about 45 percent and a vinyl content in a range of from about 20 to about 40 percent based upon the polybutadiene portion of the elastomer, and a Tg in a range of from about −28° C. to about −40° C.;
wherein said Tg of said S-SBR and said S-SBR-F are spaced apart by at least 10° C.;
wherein said functionalized SBR-F contains functional group(s) consisting of siloxy groups reactive with hydroxyl groups contained on a precipitated silica filler rubber reinforcement;
(B) from about 8 to about 30 phr of at least three resins, each resin being present in an amount in a range of from about 0.5 to about 10 phr comprised of at least three resins selected from:
(1) polyester terephthalate resin, having a melting point in a range of from about 20° C. to about 26° C.,
(2) styrene/alphamethyl styrene resin, having a melting point in a range of from about 80° C. to about 90° C.,
(3) gum rosin, having a melting point in a range of from about 50° C. to about 70° C., and
(4) coumarone indene resin, having a melting point in a range of from about 90° C. to about 120° C.;
(C) about 70 to about 100 phr of rubber reinforcing filler consisting of a combination of rubber reinforcing carbon black and precipitated silica as:
(1) rubber reinforcing carbon black in a range of from about 20 to about 90 phr having a DBP (dibutyl phthalate) absorption value (ASTM D 2414) of at least 140 cc/100 g in combination with an Iodine value (ASTM D1510) of at least 200 g/kg, and
(2) precipitated silica in a range of from about 10 to about 50 phr,
wherein the weight ratio of said rubber reinforcing carbon black to said precipitated silica is at least 2/1, and
(D) silica coupling agent for said precipitated silica comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average of from about 2 to about 4 connecting sulfur atoms in its polysulfidic bridge.
2. Tire of claim 1 wherein said functionalized SBR-F is a methoxysilane functionalized styrene/butadiene elastomer.
3. The tire of claim 1 wherein said coupling agent is comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average of from about 2 to about 2.5 connecting sulfur atoms in its polysulfidic bridge.
4. Tire of claim 3 said functionalized SBR-F is comprised of a methoxysilane functionalized solution polymerization prepared styrene/butadiene elastomer.