A tire tread that comprises a rubber composition based on an elastomer matrix that comprises more than 50% by weight of at least one butyl rubber, on a reinforcing filler and on a plasticizing system that comprises at least one polybutene oil having a glass transition temperature below −75° C. A tire comprising such a tread has a good compromise between the wet grip performance and the rolling resistance performance.
1. A tire tread that comprises a rubber composition based:
on an elastomer matrix that comprises more than 50% by weight of at least one butyl rubber,
on a reinforcing filler,
and on a plasticizing system that comprises at least one polybutene oil having a glass transition temperature below −75° C.
2. The tread according to claim 1 , wherein the at least one polybutene oil has a glass transition temperature below −85° C.
3. The tread according to claim 1 , wherein the at least one butyl rubber represents more than 70% by weight of the elastomer matrix.
4. The tread according to claim 3 , wherein the at least one butyl rubber represents 100% by weight of the elastomer matrix.
5. The tread according to claim 1 , wherein the at least one butyl rubber is a copolymer of isobutylene and a C 4 to C 6 diene.
6. The tread according to claim 5 , wherein the at least one butyl rubber is a halogenated butyl rubber.
7. The tread according to claim 1 , wherein the at least one butyl rubber is a terpolymer of isobutylene, para-methylstyrene and halogenated para-methylstyrene.
8. The tread according to claim 1 , wherein the number-average molar mass of the at least one polybutene oil is between 400 g/mol and 10 000 g/mol.
9. The tread according to claim 1 , wherein the content of the at least one polybutene oil varies within a range extending from 10 to 80 phr.
10. The tread according to claim 1 , wherein the at least one polybutene oil is a homopolymer or copolymer of C 4 fraction raffinate.
11. The tread according to claim 1 , wherein the at least one polybutene oil is a homopolymer of isobutylene.
12. The tread according to claim 1 , wherein the at least one polybutene oil is a copolymer of isobutylene and 1-butene or a copolymer of isobutylene and 2-butene.
13. The tread according to claim 1 , wherein the at least one polybutene oil is a terpolymer of isobutylene, 1-butene and 2-butene.
14. The tread according to claim 1 , wherein the plasticizing system comprises between 0 and 30 phr of at least a second plasticizer.
15. The tread according to claim 1 , wherein the plasticizing system consists of the at least one polybutene oil.
16. The tread according to claim 1 , wherein the mass content of the plasticizing system P expressed relative to the mass of the at least one butyl rubber and the glass transition temperature Tg P of the plasticizing system expressed in kelvin satisfy the following equation:
P ×(208− Tg P )÷ Tg P ≧0.025.
17. The tread according to claim 1 , wherein the content of reinforcing filler is between 40 and 150 phr.
18. The tread according to claim 1 , wherein the reinforcing filler comprises a reinforcing organic filler.
19. The tread according to claim 1 , wherein the reinforcing filler comprises a reinforcing inorganic filler.
20. The tread according to claim 19 , wherein the composition additionally comprises a coupling agent.
21. The tread according to claim 20 , wherein the at least one butyl rubber is a halogenated butyl rubber and the coupling agent is an aminoalkylalkoxysilane or a mixture of aminoalkylalkoxysilane and alkylalkoxysilane polysulphide.
22. The tread according to claim 20 , wherein the reinforcing inorganic filler represents more than 50% by weight of the reinforcing filler.
23. The tread according to claim 22 , wherein the content of carbon black in the rubber composition is less than 20 phr.
24. A process for preparing a tire tread according to claim 1 , which process comprises:
thermomechanically kneading the elastomer matrix that comprises more than 50% by weight of the at least one butyl rubber, the reinforcing filler and the plasticizing system until a maximum temperature of between 110° C. and 190° C. is reached;
cooling the combined mixture to a temperature below 100° C.;
subsequently incorporating a crosslinking system;
kneading everything up to a maximum temperature below 110° C. in order to obtain a rubber composition;
extruding or calendering the rubber composition thus obtained.
25. A tire comprising a tread according to claim 1 .
26. A rubber composition as defined in claim 22 .
27. A process for manufacturing the rubber composition according to claim 26 , which process comprises:
thermomechanically kneading the elastomer matrix that comprises more than 50% by weight of the at least one butyl rubber, the reinforcing filler, the coupling agent and the plasticizing system until a maximum temperature of between 110° C. and 190° C. is reached;
cooling the combined mixture to a temperature below 100° C.;
subsequently incorporating a crosslinking system;
kneading everything up to a maximum temperature below 110° C. in order to obtain a rubber composition.