Rubber composition comprising a blocked mercaptosilane coupling agent

1. A rubber composition that is free of zinc or that contains less than 0.5 phr of zinc, and wherein zinc has not been replaced with another metal, which can be used for the manufacture of tires, based on at least:

one diene elastomer;

one sulphur-based crosslinking system;

one inorganic filler as reinforcing filler;

one blocked mercaptosilane of general formula I below:

(R 3 O)R 2 R 1 —Si—Z—S—C(═O)-A

wherein:

R 1 and R 2 , which are identical or different, represent a monovalent hydrocarbon-based group selected from the group consisting of alkyls, which are linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

R 3 represents a monovalent hydrocarbon-based group selected from the group consisting of linear or branched alkyls having from 1 to 4 carbon atoms;

A represents hydrogen or a monovalent hydrocarbon-based group chosen from alkyls, which are linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

Z represents a divalent bonding group comprising from 1 to 18 carbon atoms.

2. The composition according to claim 1 , wherein Z contains one or more heteroatoms chosen from O, S and N.

3. The composition according to claim 1 , wherein:

R 1 and R 2 are identical or different and are selected from the group consisting of methyl, ethyl, n-propyl and isopropyl;

R 3 is selected from the group consisting of methyl and ethyl;

A is selected from the group consisting of alkyls having from 1 to 18 carbon atoms and the phenyl radical;

Z is selected from the group consisting of C 1 -C 18 alkylenes and C 6 -C 12 arylenes.

4. The composition according to claim 3 , wherein Z is selected from the group consisting of C 1 -C 10 alkylenes.

5. The composition according to claim 4 , wherein Z is selected from the group consisting of C 1 -C 4 alkylenes.

6. The composition according to claim 3 , wherein R 1 and R 2 are each methyl.

7. The composition according to claim 3 , wherein A is selected from the group consisting of alkyls having from 1 to 7 carbon atoms and the phenyl radical.

8. The composition according to claim 3 , wherein R 1 and R 2 are each methyl, A is a heptyl, R 3 is ethyl and Z is a propylene.

9. The composition according to claim 1 , wherein the diene elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

10. The composition according to claim 1 , wherein the reinforcing inorganic filler is the predominant reinforcing filler.

11. The composition according to claim 1 , wherein the reinforcing inorganic filler is a siliceous or aluminous filler.

12. The composition according to claim 1 , wherein the reinforcing inorganic filler is present in an amount greater than 50 phr.

13. The composition according to claim 1 , wherein the blocked mercaptosilane is present in an amount between 2% and 20% by weight relative to the amount of reinforcing inorganic filler.

14. The composition according to claim 1 , wherein the blocked mercaptosilane is present in an amount between 2 and 15 phr.

15. A process for preparing a rubber composition that is free of zinc or that contains less than 0.5 phr of zinc, and wherein zinc has not been replaced with another metal, comprising, incorporating at least, by kneading, into at least (i) one diene elastomer, (ii) an inorganic filler as reinforcing filler, (iii) a blocked mercaptosilane of general formula I below:

(R 3 O)R 2 R 1 —Si—Z—S—C(═O)-A

in which:

R 1 and R 2 , which are identical or different, represent a monovalent hydrocarbon-based group chosen from alkyls, which are linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

R 3 represents a monovalent hydrocarbon-based group chosen from linear or branched alkyls having from 1 to 4 carbon atoms;

A represents hydrogen or a monovalent hydrocarbon-based group chosen from alkyls, which are linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

Z represents a divalent bonding group comprising from 1 to 18 carbon atoms, and (iv) a sulphur-based vulcanization system.

16. Process according to claim 15 , wherein it comprises the following steps:

in a first phase, incorporating into the diene elastomer, in a mixer, the reinforcing filler and the blocked mercaptosilane by thermomechanically kneading all the ingredients, one or more times, until a maximum temperature between 130° C. and 200° C. is reached;

cooling the mixture down to a temperature below 100° C.;

then, in a second phase, incorporating: the vulcanization system;

kneading everything up to a maximum temperature below 120° C.; and

extruding or calendering the rubber composition thus obtained.

17. Process according to claim 16 , in which a covering agent is introduced completely or partly during the first phase.

18. Process according to claim 16 , in which a covering agent is introduced completely or partly during the second phase.

19. Tire or semi-finished product comprising a rubber composition according to claim 1 .

20. Tire tread comprising a rubber composition according to claim 1 .

21. The composition according to claim 12 , wherein the reinforcing inorganic filler is present in an amount between 60 and 140 phr.

22. The composition according to claim 13 , wherein the blocked mercaptosilane is present in an amount between 2% and 15% by weight relative to the amount of reinforcing organic filler.

23. The composition according to claim 14 , wherein the blocked mercaptosilane is present in an amount between 4 and 12 phr.

24. The composition according to claim 3 , wherein R 1 and R 2 are identical or different and are selected from the group consisting of methyl and ethyl.