Patent ID: 8575261

Claim:
A process of preparing a rubber composition which comprises, based upon parts by weight per 100 parts by weight rubber (phr): (A) a sequential phase mixing process which comprises: (1) a first mixing phase comprised of forming a first rubber composition comprised of EPDM rubber containing a dispersion of a particulate filler reinforcement therein, followed by: (2) a second mixing phase comprised of forming a second rubber composition by blending said first rubber composition with at least one conjugated diene-based rubber wherein said conjugated diene-based rubber includes a cis 1,4-polyisoprene rubber, followed by: (3) blending sulfur curative comprised of elemental sulfur with said second rubber composition, or (B) a parallel phase mixing process which comprises: (1) a first mixing phase comprised of forming a first rubber composition by blending EPDM rubber, particulate rubber reinforcing filler and sulfur curative comprised of elemental sulfur; (2) a second mixing phase comprised of forming a second rubber composition of: (a) cis 1,4-polyisoprene rubber, or (b) cis 1,4-polyisoprene rubber and cis 1,4-polybutadiene rubber; wherein said second rubber composition optionally also contains at least one of styrene/butadiene rubber, butyl rubber, halogenated butyl rubber, and brominated copolymer of paramethylstyrene and isobutylene, followed by (3) blending said first rubber composition with said second rubber composition; wherein, for said sequential and parallel phase mixing processes, said EPDM rubber is provided as: (4) an EPDM rubber as an ethylene/propylene/non-conjugated diene terpolymer having an ethylene content in a range of from about 40 to about 90 weight percent and a non-conjugated diene content in a range of about 1 to about 15 weight percent, or (5) a combination of EPDM elastomers as ethylene/propylene/non-conjugated diene terpolymers composed of: (a) a first EPDM rubber having an ethylene content of from about 40 to about 70 weight percent, and a non-conjugated diene content in a range of about 1 to about 15 weight percent, and (b) a second EPDM rubber having an ethylene content of from about 60 to about 90 weight percent, and a non-conjugated diene content in a range of about 1 to about 15 weight percent, wherein the ethylene content of said second EPDM rubber is at least 10 percentage units higher than the ethylene content of said first EPDM rubber, and wherein the weight ratio of said first EPDM rubber to said second EPDM rubber is in a range of from about 10/90 to about 90/10, wherein said first rubber composition for said first mixing phase contains: (6) particulate reinforcing filler comprised of: (a) precipitated silica in an amount of up to about 80 phr, (b) optionally exfoliated clay platelets in an amount of up to 10 phr, (c) rubber reinforcing carbon black in an amount of up to 100 phr, and wherein additional low unsaturation polymers are included with the EPDM rubber in the first mixing phase consisting of at least one of polyethylene and polypropylene.