Copolymer rubber composition with silica filler, tires having a base of said composition and method of preparing same

A tire tread, comprising a rubber composition formed by a process comprising the steps of

• (a) preparing a base from a copolymer of a conjugated diene and an vinyl aromatic compound prepared by solution polymerization in a hydrocarbon solvent, having a total content of aromatic vinyl compound of between 5% and 50% by weight and a glass transition temperature (Tg) of between 0.degree. C. and -80.degree. C., and
• (b) thermomechanically working the base with a filler, the majority portion of which is a silica having a BET surface area of between 100 and 250 m.sup.2 /g, a CTAB surface area of between 100 and 250 m.sup.2 g, an oil absorption measured in DBP of between 150 and 250 ml/100 g, and an average projected area of the aggregates greater than 8500 nm.sup.2 before working and between 7000 and 8400 nm.sup.2 in the tread wherein the silica is added in an amount of from 30 to 150 parts by weight per 100 parts by weight of copolymer, together with other additives conventionally employed additives, with the exception of the vulcanization system, said thermomechanical working including at least one thermal step reaching a maximum temperature of between 130.degree. C. and 180.degree. C. for a suitable period of time which is a function of the temperature selected for the thermomechanical working and of the nature and volume of the components subjected to said thermomechanical working, and which is between 10 seconds and 20 minutes, and a finishing step during which the vulcanization system is added by mechanical working at a temperature below the vulcanization temperature.

A tire having a sulfur-vulcanized tread comprising a rubber composition formed by a process comprising the steps of

• (a) preparing a base from a copolymer of a conjugated diene and an aromatic vinyl compound prepared by solution polymerization in a hydrocarbon solvent having a total content of aromatic vinyl compound of between 5% and 50% and a glass transition temperature (Tg) of between 0.degree. C. and -80.degree. C., and
• (b) mechanically working the base with a filler, the majority portion of which is of a silica having a BET surface area of between 100 and 250 m.sup.2 /g, a CTAB surface area of between 10 and 250 m.sup.2 g, an oil absorption measured in DBP of between 150 and 250 ml/100 g, and an average projected area of the aggregates greater than 8500 nm.sup.2 before working and between 7000 and 84000 nm.sup.2 in the tire, wherein the silica is added in an amount of from 30 to 150 parts by weight per 100 parts by weight of copolymer, together with other additives conventionally employed with the exception of the vulcanization system said thermomechanical working including at least one thermal step reaching a maximum temperature of between 130.degree. C. and 180.degree. C. for a suitable period of time which is a function of the temperature selected for the thermomechanical working and of the nature and volume of the components subjected to said thermomechanical working and which is between 10 seconds and 20 minutes, and a finishing step during which the vulcanization system is added by mechanical working at a temperature below the vulcanization temperature.

A method of preparing a sulfur-vulcanizable rubber composition having a base of a copolymer of conjugated diene and an aromatic vinyl compound containing silica as filler, comprising the steps of

• (a) preparing a base from a copolymer of a conjugated diene and an aromatic vinyl compound prepared by solution polymerization in a hydrocarbon solvent having a styrene content of between 5% and 50% and a glass transition temperature of between 0.degree. C. and -80.degree. C., along or in association with another diene elastomer, a silica having a BET surface area of between 100 and 250 m.sup.2 /g, a CTAB surface area of between 100 and 250 m.sup.2 /g, a CTAB surface area of between 100 and 250 m.sup.2 /g, an oil absorption measured in DBP of between 150 and 250 ml/100 g, and an average projected area of the aggregates greater than 8500 nm.sup.2 before and possibly another reinforcing filler present in a minority amount by weight referred to the silica, wherein the silica is added in an amount of from 30 to 150 parts by weight per 100 parts by weight of copolymer, together with other additives conventionally used with the exception of the vulcanization system in such a manner that said thermomechanical working including at least one thermal step reaching a maximum temperature of between 130.degree. C. and 180.degree. C. for a suitable period of time which is a function of the temperature selected for the thermomechanical working and of the nature and volume of the components subjected to said thermomechanical working, which decreases the average projected area of the silica aggregates so that it is between 7000 and 8400 nm.sup.2 after thermomechanical mixing, the said period of time being between 10 seconds and 20 minutes and that the vulcanization system is then incorporated in the resultant mixture by mechanical finishing work at a temperature below the vulcanization temperature.