Rubber composition comprising emulsion-polymerized conjugated diene polymer and silica suspension, and method for producing same

The invention provides a rubber composition (a silica master batch) that contains silica in a highly dispersed state, which is prepared by mixing a suspension with an emulsion of an emulsion-polymerized conjugated diene polymer and then coagulating the resultant mixture, wherein the suspension is prepared by highly dispersing wet silica, which does not undergo secondary coagulation yet, or silica, which is prepared by mechanically dissociating secondary coagulation masses of silica, in water and the emulsion-polymerized conjugated diene polymer contains a functional group that is reactive with silica or has high affinity for silica; and a method for producing the rubber composition. A clam (a small mass of a rubber) which contains silica in a highly dispersed state is hardly dried. Therefore, the clam is dried in an apparatus which is composed of a drying apparatus composed of a dehydrator and a hot-air drier and a heating roll for drying purposes provided to the drying apparatus, whereby a rubber composition in which silica is highly dispersed and which has high reinforcing performance can be produced. As a method for mixing the emulsion of the emulsion-polymerized conjugated diene copolymer with the silica suspension, a mere agitating/mixing procedure can be employed, and a process of mixing the components homogenously while applying a stimulus such as heat or pressure to the mixture of the components using a steam ejector to cause the coagulation of the components can also be employed desirably.