| 摘要 |
A rubber composition of (i) 100 parts by weight of a starting rubber of (A) 40 to 120 parts of SBR and carbon black (CB) having an N2SA of at least 70 m2/g, (B) 40 to 120 parts by weight of an NR-CB rubber composition of NR and CB having an N2SA of at least 70 m2/g, and (C) BR and/or SBR having a Tg higher by at least 10° C. than that of the SBR in the SBR-CB rubber composition (A), wherein the rubber composition has a ratio of the average value FMB of the concentration of CB to the amount of rubber in the CB-containing rubber compositions (A) and (B) and the concentration FCOM of CB to the amount of rubber in the rubber composition of 1.2 to 3.0. In addition a rubber composition containing a CB-containing natural rubber master batch obtained by mixing a natural rubber (NR) starting latex and carbon black (CB) in a water-based medium and coagulating and drying it, an additional starting rubber having a glass transition temperature (Tg) of -50° C. to -20° C. and silica in an internal mixer.
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