Patent ID: 7122586

Claim:
A process of preparing a silica reinforced rubber composition comprises a series of sequential mixing steps conducted in at least one internal rubber mixer; (A) wherein said mixing steps are comprised of at least two sequential non-productive mixing steps followed by a productive mixing step; (B) wherein said non-productive mixing steps are comprised of at least one preliminary non-productive mixing step followed by a subsequent, final non-productive mixing step and wherein the maximum mixing temperature for said final non-productive mixing step is at least 20° C. lower than the maximum mixing temperature for said preliminary non-productive mixing step(s); (C) wherein at least one diene-based elastomer, amorphous precipitated silica having hydroxyl groups on its surface and coupling agent are added in at least one of said preliminary non-productive mixing steps to the exclusion of addition thereof in said final non-productive mixing step and said productive mixing step and wherein said coupling agent is comprised of a bis(3-trialkoxysilylalkyl) polysulfide where said polysulfide contains an average of from 2 to about 4, alternately from about 2 to 2.6 or from 3.5 to 4, connecting sulfur atoms in its polysulfidic bridge; (D) wherein free sulfur and sulfur vulcanization accelerator(s) are added in said productive mixing step to the exclusion of such addition in said non-productive mixing steps; (E) wherein said preliminary non-productive mixing step(s) are individually conducted to a maximum mixing temperature in a range of from about 150° C. to about 180° C.; (F) wherein said final non-productive mixing step is conducted to maximum mixing temperature in a range of from about 90° C. to about 130° C. and at least 20° C. lower than said maximum temperature for said preliminary non-productive mixing step(s); (G) wherein said productive mixing step is conducted to a maximum mixing temperature in a range of from about 90° C. to about 120° C.; and (H) wherein the rubber composition is removed from its respective internal rubber mixer at the conclusion of each mixing step and cooled to a temperature below 40° C.; wherein said rubber composition is comprised of: (1) at least one diene-based elastomer; and (2) reinforcing filler consisting of rubber reinforcing carbon black and said synthetic amorphous precipitated silica aggregates, and, optionally, additional reinforcement material selected from the group consisting of at least one of short fibers and exfoliated clay particles, and (3) said coupling agent.