Composition for a tire tread and process for its preparation

A process for preparing a cross-linkable or cross-linked rubber composition that is usable to constitute a tread for a tire, that provides reduced hysteresis losses in the cross-linked state, that provides improved processing properties in the cross-linkable state, and that comprises a reinforcing inorganic filler and at least one diene elastomer having a molar ratio of units originating from conjugated dienes which is greater than 30% and comprising carboxylic acid functions along its chain, said process comprising:

• (a) preparing, in solution, said at least one diene elastomer comprising carboxylic acid functions along its chain by:
• (i) subjecting the initial diene elastomer in an inert hydrocarbon solvent to a hydroalumination or carboalumination reaction along its chain, by adding an agent derived from aluminum to said initial diene elastomer;
• (ii) adding to the product of said hydroalumination or carboalumination reaction at least one electrophilic agent, wherein said electrophilic agent reacts with said agent derived from aluminum;
• and
• (iii) stopping the reaction of said electrophilic agent and said agent derived from aluminum and recovering said at least one diene elastomer comprising carboxylic acid functions along its chain;
• (b) subjecting the constituents of said composition comprising said at least one diene elastomer comprising carboxylic acid functions along its chain and said reinforcing inorganic filler, with the exception of the cross-linking system, to a first phase of thermomechanical working, wherein the maximum temperature during the first phase of thermomechanical working is between 130° C. and 200° C.;
• and
• (c) subjecting the constituents of said composition comprising said at least one diene elastomer comprising carboxylic acid functions along its chain and said reinforcing inorganic filler to a second phase of mechanical working at a temperature that is less than the maximum temperature of said first phase of thermomechanical working, wherein a cross-linking system is added during the second phase of mechanical working.

A process for preparing a cross-linkable or cross-linked rubber composition that is usable to constitute a tread for a tire, that provides reduced hysteresis losses in the cross-linked state, that provides improved processing properties in the cross-linkable state, and that comprises a reinforcing inorganic filler and at least one diene elastomer having a molar ratio of units originating from conjugated dienes which is greater than 30% and comprising carboxylic acid functions along its chain, said process comprising:

• (a) preparing, in emulsion, said at least one diene elastomer comprising carboxylic acid functions along its chain by a copolymerization process including adding to an emulsifying solution a co-monomer comprising an unsaturated aliphatic carboxylic acid, such that said at least one diene elastomer comprises unsaturated aliphatic carboxylic acid functions along its chain;
• (b) subjecting the constituents of said composition comprising said at least one diene elastomer comprising carboxylic acid functions along its chain and said reinforcing inorganic filler, with the exception of the cross-linking system, to a first phase of thermomechanical working, wherein the maximum temperature during the first phase of thermomechanical working is between 130° C. and 200° C.;
• and
• (c) subjecting the constituents of said composition comprising said at least one diene elastomer comprising carboxylic acid functions along its chain and said reinforcing inorganic filler to a second phase of mechanical working at a temperature that is less than the maximum temperature of said first phase of thermomechanical working, wherein a cross-linking system is added during the second phase of mechanical working.