Patent ID: 7351763

Claim:
A process of preparing a rubber composition is comprised of at least one mixing step comprised of, based upon parts by weight per 100 parts by weight rubber (phr) mixing a rubber composition in an internal rubber mixer, wherein said rubber composition is comprised of: (A) at least one diene-based elastomer, (B) about 10 to about 200 phr of reinforcing filler composed of: (1) about 15 to about 100 weight percent of said filler as a composite of silica-containing carbon black having silica domains on its surface wherein said silica domains contain hydroxyl groups on their surface; (2) from zero to about 85 weight percent of at least one additional reinforcing filler selected from synthetic precipitated silica, which contains hydroxyl groups on the surface thereof and non-silica containing rubber reinforcing carbon black, together, and (3) a coupling agent comprised of a bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 4 connecting sulfur atom in its polylsulfidic bridge; wherein said mixing step comprises: (a) mixing said rubber composition in said internal rubber mixer from a temperature of less than 40° C. to allow said rubber composition to autogeneously reach an elevated temperature within a range of about 140 to about 180° C., and: (b) after said rubber composition autogeneously reaches said elevated temperature, mixing said rubber composition in said internal rubber mixer at an extended mixing temperature within about 10° C. of said elevated temperature for a period of from about 0.5 to about 15 minutes to promote an extended coupling interaction of the coupling agent with the silica domains contained on the surface of the silica-containing carbon black and optional synthetic precipitated silica during the extended mixing of the ingredients; wherein said rubber composition is then removed from said internal rubber mixer after said mixing step and cooled to a temperature below 40° C.; wherein said rubber mixture is thereafter mixed in at least one additional, subsequent, sequential mixing step in an internal rubber mixer, without said extended mixing and where said rubber composition is removed from said internal rubber mixer and cooled to a temperature below about 40° C.; wherein said rubber mixture is thereafter mixed in an internal rubber mixer for a period of from about 1.5 to about 3 minutes to a temperature in a range of from about 100° C. to about 120° C. during which free sulfur and at least one sulfur vulcanization accelerator is added.