Patent ID: 8522847

Claim:
A method of preparation of a precipitated silica reinforced rubber composition for a tire tread which contains dual silica moieties comprised of an in situ hydrophobated precipitated silica and a hydrophilic precipitated silica comprised of at least two sequential preparatory non-productive mixing steps followed by a productive mixing step, which comprises, based upon parts by weight per 100 parts by weight rubber (phr): (A) blending a hydrophilic precipitated silica with a rubber composition comprised of at least one conjugated diene-based elastomer selected from cis 1,4-polyisoprene, cis 1,4-polybutadiene and styrene/butadiene copolymer to the exclusion of functionalized styrene/butadiene copolymer in at least one preparatory non-productive mixing step in an internal rubber mixer, and hydrophobating said hydrophilic precipitated silica with a hydrophobating agent in situ within said rubber composition in at least one of said non-productive mixing steps to thereby form a hydrophobated precipitated silica-containing rubber composition; (B) removing said hydrophobated precipitated silica-containing rubber composition from its internal rubber mixer, (C) blending a hydrophilic additional precipitated silica with said hydrophobated precipitated silica-containing rubber composition in at least one different and subsequent preparatory non-productive mixing step in an internal rubber mixer in the absence of additionally adding a silane based hydrophobation agent for said additional precipitated silica, to form a rubber composition which contains dual silica moieties in a form of a combination of said in situ hydrophobated precipitated silica and said hydrophilic additional precipitated silica; wherein said hydrophilic precipitated silica is hydrophobated in situ within the rubber composition by treatment with a hydrophobation agent comprised of an alkoxysilane wherein said alkoxysilane is of the general formula (I): Z n —Si—R 4-n (I) wherein R is a saturated alkyl radical having from one to 8 carbon atoms, n is a value of from 1 to 3 and Z is an alkoxy radical represented as (R 1 O)—, wherein R 1 is a saturated alkyl radical having from one to 3 carbon atoms.