The present invention relates to a rubber composition, in which reaction efficiency of the silane coupling agent and various properties are improved.
In recent years, both fuel efficiency and improved wet grip performance are strongly desired in a tire and in order to satisfy such demands, silica is compounded in the tread. However, sufficient reinforcing properties cannot be obtained with only silica and a silane coupling agent is used together with silica. Usually, a silane coupling agent having an alkoxyl group is used for tires. However, reaction of the silane coupling agent cannot sufficiently be completed in the rubber kneading step and in order to obtain sufficient reinforcing properties, more of the silane coupling agent than necessary must be compounded. Furthermore, the silane coupling agent that could not finish reacting during kneading (hereinafter referred to as unreacted silane coupling agent) reacts in the extrusion step to generate alcohol (such as ethanol) and there is the problem that bubbles arise in the extruded unvlucanized tread.
As a method to solve such problems, JP-A-2001-247718 discloses compounding various sodium salts in a rubber composition. According to this method, reaction efficiency of the silane coupling agent is improved, but the improvement is insufficient. Thus, generation of bubbles in the extruded tread cannot be suppressed completely.