Process for producing a vulcanizable rubber composition including carbon black-based and silica-based reinforcing fillers

A process for producing a vulcanizable rubber composition including carbon black-based and silica-based reinforcing fillers, characterized in that comprises the steps of

• a) intimately mixing at a temperature of from 130° to 180° C.:
• i) at least a first cross-linkable unsaturated chain polymer;
• ii) a first carbon black-based reinforcing filler, and optionally
• iii) one or more non cross-linking ingredients to obtain a first rubber composition having a Mooney viscosity of from 70 to 140 Ms, wherein the first carbon black-based reinforcing filler Is dispersed in a substantially homogeneous manner;
• b) cooling the first rubber composition obtained from step a) to a temperature not exceeding 100° C.,
• c) intimately mixing at a temperature of from 130° to 180° C.:
• i) the first high-viscosity rubber composition obtained from step b),
• ii) at least a second cross-linkable unsaturated chain polymer,
• iii) a second silica-based reinforcing filler, and optionally
• iv) one or more non cross-linking ingredients to obtain a second rubber composition wherein the carbon black-based and silica-based reinforcing fillers are dispersed in a substantially homogeneous manner;
• d) intimately mixing the second rubber composition thus obtained with a suitable vulcanizing system at a temperature lower than the vulcanization temperature.