Rubber composition comprising silicone oil

1. A tread for a pneumatic tire comprising a rubber composition comprising at least:

a diene elastomer;

at least 60 phr of silica;

20 to 100 phr of a plasticizer comprising more than 4 phr of a mercapto-modified silicone oil; and

0.2 and 20 phr of carbon black,

wherein the diene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures thereof, and

wherein the plasticizer further comprises a compound selected from the group consisting of hydrocarbon resins, liquid plasticizers other than the mercapto-modified silicone oil, and mixtures thereof.

2. The tread for a pneumatic tire according to claim 1 , wherein the content of the mercapto-modified silicone oil is from 5 to 35 phr.

3. The tread for a pneumatic tire according to claim 1 , wherein the mercapto-modified silicone oil bears at least two mercapto functions per molecule.

4. The tread for a pneumatic tire according to claim 1 , wherein the functional type of the mercapto-modified silicone oil is a α, ω difunctional type.

5. The tread for a pneumatic tire according to claim 1 , wherein the content of the silica is more than 70 phr and less than 120 phr.

6. The tread for a pneumatic tire according to claim 1 , wherein the liquid plasticizers are selected from the group consisting of polyolefinic oils, naphthenic oils, paraffinic oils, Distillate Aromatic Extracts (DAE) oils, Medium Extracted Solvates (MES) oils, Treated Distillate Aromatic Extracts (TDAE) oils, Residual Aromatic Extracts (RAE) oils, Treated Residual Aromatic Extracts (TRAE) oils, Safety Residual Aromatic Extracts (SRAE) oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures thereof.

7. The tread for a pneumatic tire according to claim 1 , wherein the hydrocarbon resins are selected from the group consisting of cyclopentadiene homopolymer or copolymer resins, dicyclopentadiene homopolymer or copolymer resins, terpene homopolymer or copolymer resins, C5 fraction homopolymer or copolymer resins, C9 fraction homopolymer or copolymer resins, alpha-methyl styrene homopolymer or copolymer resins, and mixtures thereof.

8. The tread for a pneumatic tire according to claim 1 , wherein the content of the plasticizer is from 20 to 80 phr.

9. A process of manufacturing the tread for a pneumatic tire according to claim 1 comprising at least the steps of:

incorporating, into a mixer, at least the diene elastomer and at least 60 phr of silica, during a first stage, kneading thermomechanically until a maximum temperature of between 130° C. and 200° C. is reached to obtain a combined mixture;

cooling the combined mixture to a temperature of less than less than 100° C.;

subsequently incorporating, during a second stage, a crosslinking system;

kneading the combined mixture including the crosslinking system up to a maximum temperature of less than 120° C. to obtain a rubber composition; and

extruding or calendering the rubber composition,

wherein the plasticizer comprising the mercapto-modified silicone oil is incorporated either during the first stage or during the second stage, or during both of the first and second stages so that the total weight of the plasticizer is from 20 to 100 phr and the mercapto-modified silicone oil is more than 4 phr.

10. The process according to claim 9 , wherein the mercapto-modified silicone oil is incorporated partially or totally during the second stage.

11. The process according to claim 9 , wherein the crosslinking system comprises less than 2 phr of zinc oxide.

12. The process according to claim 11 , wherein the crosslinking system is devoid of zinc oxide.

13. A pneumatic tire comprising the tread according to claim 1 .