Tire tread reinforced with a silica of low specific surface area
A tire tread incorporating an elastomeric composition reinforced by an inorganic filler, based on at least: (i) a diene elastomer; (ii) as reinforcing inorganic filler, more than 80 phr of a silica of low specific surface area having the following characteristics: (a) a BET specific surface area of less than 130 m 2 /g; (b) an average particle size, d w , of between 30 and 300 nm; (iii) a coupling agent providing the bond between the reinforcing inorganic filler and the diene elastomer; (iv) a vulcanization system comprising sulfur, a vulcanization accelerator and between 0.5 and 1.5 phr of zinc as vulcanization activator. Preferably, this silica furthermore has a disagglomeration rate α greater than 5×10 3 μm −1 /min (measured in the ultrasound disagglomeration test). Compared with a conventional tread for “Green Tires” which is reinforced with a silica of higher specific surface area, the tread of the invention has an improved compromise of (wear resistance/rolling resistance/grip on wet ground) performances. The use of a very small amount of zinc makes it possible to overcome an increase in the induction delays during the vulcanization, when such a silica of low specific surface area is used.
1. A tire having a tread incorporating an elastomeric composition reinforced with an inorganic filler, said composition comprising:
(i) a diene elastomer;
(ii) as reinforcing inorganic filler, more than 80 phr of a silica having the following features:
(a) a BET specific surface area of more than 70 and less than 130 m 2 /g;
(b) an average particle size, d w , of between 30 and 300 nm;
(iii) a coupling agent; and
(iv) a vulcanization system comprising sulfur, a vulcanization accelerator and between 0.5 and 1.5 phr of zinc as vulcanization activator.
2. The tire according to claim 1 , wherein the diene elastomer comprises at least 50 phr of a butadiene elastomer.
3. The tire according to claim 2 , wherein the butadiene elastomer is selected from the group consisting of polybutadienes, styrene-butadiene copolymers and mixtures of these elastomers.
4. The tire according to claim 1 , wherein the amount of silica is greater than 90 phr.
5. The tire according to claim 4 , wherein the amount of silica is between 90 and 150 phr.
6. The tire according to claim 1 , wherein the vulcanization accelerator is a sulfenamide accelerator and wherein the overall amount of sulfur and sulfenamide accelerator is between 1.25 and 2.75 phr.
7. The tire according to claim 6 , wherein the overall amount of sulfur and sulfenamide accelerator is within a range from 1.5 to 2.5 phr.
8. The tire according to claim 1 , wherein the vulcanization accelerator is a sulfenamide accelerator and the vulcanization system further comprises a guanidine derivative, and wherein the overall amount of sulfur, sulfenamide and guanidine derivative is within a range from 1.75 to 4.25 phr.
9. The tire according to claim 8 , wherein the guanidine derivative is DPG (diphenylguanidine).
10. The tire according to claim 1 , wherein zinc is supplied in the form of zinc oxide.
11. The tire according to claim 10 , wherein zinc is supplied in the presence of a fatty acid.
12. The tire according to claim 11 , wherein the fatty acid is stearic acid.
13. The tire according to claim 12 , wherein the amount of stearic acid is of 0.5 to 3 phr.
14. The tire according to claim 1 , wherein the quantity of zinc is within a range from 0.7 to 1.3 phr.
15. The tire according to claim 1 , wherein the coupling agent is selected from the group consisting of polyfunctional silanes and polysiloxanes.
16. The tire according to claim 15 , wherein the coupling agent is a polysulfurised alkoxysilane.
17. The tire according to claim 16 , wherein the quantity of polysulfurised silane is less than 6 phr.
18. The tire according to claim 1 , wherein the composition further comprises carbon black.
19. The tire according to claim 18 , wherein the amount of carbon black is between 2 and 20 phr.
20. The tire according to claim 1 , wherein the silica has the following features:
a BET surface area of between 70 and 130 m 2 /g;
a particle size d W of between 50 and 200 nm;
a disagglomeration rate α greater than 5×10 −3 μm −1 /min.
21. The tread according to claim 20 , wherein the silica has the following features:
a BET surface area within a range from 100 to 125 m 2 /g;
a particle size d W within a range from 100 to 150 nm.
22. The tire according to claim 21 , wherein the silica has the following feature:
a disagglomeration rate α greater than 1×10 −2 μm −1 /min.