Patent ID: 7019084

Claim:
A method of preparing a rubber composition which comprises, based upon 100 parts by weight (phr) of diene-based elastomers, blending (A) (1) about 20 to about 90 phr of high trans random SBR having a Tg in a range of from about −55° C. to about −85° C. wherein said high trans random SBR is produced by a process that comprises copolymerizing styrene and 1,3-butadiene in an organic solvent at a temperature that is within the range of about 40° C. to about 120° C. in the presence of a catalyst system that is comprised of (A) an organolithium compound, (B) a group IIa metal salt selected from the group consisting of group IIa metal salt of an amino glycol, and (C) an organometallic compound selected from the group consisting of organoaluminum compounds containing less than 13 carbon atoms and organomagnesium compounds; (2) about 20 to about 60 phr of cis 1,4-polybutadiene rubber having a Tg in a range of about −95° C. to about −110° C.; and (3) about 0 to about 20 phr of cis 1,4-polyisoprene elastomer having a Tg in a range of about −65° C. to about −75° C.; (B) about 40 to about 80 phr of carbon black and precipitated silica reinforcing filler comprised of about 20 to about 60 phr of precipitated silica and about 15 to about 60 phr of carbon black and (C) at least one silica coupling agent having a moiety reactive with silanol groups on the surface of the said silica and an additional moiety interactive with the said elastomers and (D) zero to about 10 phr of rubber processing oil; wherein said method comprises (1) blending said elastomers and carbon black, exclusive of said silica and of sulfur curative, in an internal rubber mixer in a first preparatory internal rubber mixing stage for a period of about one to about 10 minutes to a temperature in a range of about 150° C. to about 180° C., (2) blending said precipitated silica and silica coupling agent, exclusive of said carbon black and of sulfur curative, in at least one internal rubber mixer in an additional, subsequent preparatory internal rubber mixing stage for a period of about one to about 10 minutes to a temperature of about 150° C. to about 180° C.; wherein said oil, if used, may be added either with the carbon black and/or with the silica, and (3) blending sulfur curative(s) with in an internal rubber mixer in a final internal rubber mixing stage for a period of about one to about 4 minutes to a temperature in a range of about 80° C. to about 130° C.; wherein said rubber composition is removed from said internal rubber mixer at the conclusion of each mixing stage and cooled to a temperature below 40° C.