A TIRE COMPRISING A TREAD

Abstract

A tire has a tread comprising at least three radially superposed portions which comprise a radially external portion being made of a first rubber composition (FC), a radially intermediate portion being made of a second rubber composition (SC) and a radially internal portion being made of a third rubber composition (TC); wherein each of the rubber compositions is based on at least an elastomer matrix and a reinforcing filler; wherein the first rubber composition (FC) and the third rubber composition (TC) are such that the reinforcing filler predominately comprises a reinforcing inorganic filler, and wherein the second rubber composition (SC) is such that the reinforcing filler predominately comprises carbon black.

Claims

1.-23. (canceled)

24. A tire having a tread comprising at least three radially superposed portions which comprise a radially external portion being made of a first rubber composition, a radially intermediate portion being made of a second rubber composition, and a radially internal portion being made of a third rubber composition, wherein each of the rubber compositions is based on at least: an elastomer matrix; and a reinforcing filler, wherein the reinforcing filler in the first rubber composition and the third rubber composition predominately comprises a reinforcing inorganic filler, and wherein the reinforcing filler in the second rubber composition predominately comprises carbon black.

25. The tire according to claim 24, wherein the carbon black exhibits a BET surface area of less than 110 m.sup.2/g.

26. The tire according to claim 24, wherein the carbon black exhibits an oil absorption number of compressed Sample of less than 90 ml/100 g.

27. The tire according to claim 24, wherein the reinforcing inorganic filler predominately comprises silica.

28. The tire according to claim 24, wherein an amount of the reinforcing filler in the first rubber composition is 60 to 200 phr, wherein an amount of the reinforcing filler in the second rubber composition is between 0 and 120 phr, and wherein an amount of the reinforcing filler in the third rubber composition is 20 to 200 phr.

29. The tire according to claim 24, wherein an amount in phr of the reinforcing filler in the first rubber composition is higher than an amount in phr of the reinforcing filler in the second rubber composition, and wherein the amount in phr of the reinforcing filler in the second rubber composition is lower than an amount in phr of the reinforcing filler in the third rubber composition.

30. The tire according to claim 29, wherein the amount of the reinforcing filler in the second rubber composition is less than 60 phr.

31. The tire according to claim 24, wherein each of the rubber compositions is further based on a crosslinking system based on sulfur and a vulcanization accelerator.

32. The tire according to claim 31, wherein an amount in phr of the vulcanization accelerator in the first rubber composition is lower than an amount in phr of the vulcanization accelerator in the second rubber composition, and wherein the amount in phr of the vulcanization accelerator in the second rubber composition is higher than an amount in phr of the vulcanization accelerator in the third rubber composition.

33. The tire according to claim 32, wherein the amount of the vulcanization accelerator in the second rubber composition is more than 2 phr.

34. The tire according to claim 31, wherein a total amount in phr of sulfur and vulcanization accelerator in the first rubber composition is lower than a total amount in phr of sulfur and vulcanization accelerator in the second rubber composition, and wherein the total amount in phr of sulfur and vulcanization accelerator in the second rubber composition is higher than a total amount in phr of sulfur and vulcanization accelerator in the third rubber composition.

35. The tire according to claim 34, wherein the total amount in phr of sulfur and vulcanization accelerator in the second rubber composition is more than 4 phr.

36. The tire according to claim 31, wherein the vulcanization accelerator is selected from the group consisting of sulfenamide type vulcanization accelerators, thiuram type accelerators, zinc dithiocarbamate type vulcanization accelerators and mixtures thereof.

37. The tire according to claim 36, wherein the vulcanization accelerator predominately comprises a sulfenamide type vulcanization accelerator.

38. The tire according to claim 24, wherein the elastomer matrix comprises at least a diene elastomer selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures thereof.

39. The tire according to claim 24, wherein the third rubber composition is further based on a plasticizing agent comprising a liquid plasticizer exhibiting a glass transition temperature of less than −70° C.

40. The tire according to claim 39, wherein an amount of the liquid plasticizer is 5 to 100 phr.

41. The tire according to claim 24, wherein the radially external portion made of the first rubber composition is adjacent to the radially intermediate portion made of the second rubber composition, and wherein the radially intermediate portion made of the second rubber composition is adjacent to the radially internal portion made of the third rubber composition.

42. The tire according to claim 24, wherein the radially external portion, the radially intermediate portion and the radially internal portion are intended to come into contact with the ground during a service life of the tire.

43. The tire according to claim 24, wherein the tire is a snow tire.

Description

EXAMPLE

[0142] In the test, three rubber compositions (C-1, C-2 and C-3) were used. The three rubber compositions are based on a diene elastomer (SBR/BR or NR) reinforced with a blend of silica (as a reinforcing inorganic filler) and carbon black or reinforced with carbon black only. The formulations of the three rubber compositions are given at Table 1 with the content of the various products expressed in phr.

[0143] Each rubber composition was produced as follows: The reinforcing filler, the elastomer matrix and the various other ingredients, with the exception of sulphur and a sulphenamide type vulcanization accelerator (as a vulcanization accelerator) in a crosslinking system, were successively introduced into an internal mixer having an initial vessel temperature of approximately 60° C.; the mixer was thus approximately 70% full (% by volume). Thermomechanical working (non-productive phase) was then carried out in one stage, which lasts in total approximately 3 to 4 minutes, until a maximum “dropping” temperature of 165° C. was reached. The mixture thus obtained was recovered and cooled and then sulphur and the sulphenamide type vulcanization accelerator were incorporated on an external mixer (homofinisher) at 20 to 30° C., everything being mixed (productive phase) for an appropriate time (for example, between 5 and 12 min).

[0144] The rubber compositions thus obtained were subsequently calendered, either in the form of sheets (thickness of 2 to 3 mm) or of fine sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of profiled elements which could be used directly, after cutting and/or assembling to the desired dimensions, for example as tire semi-finished products, in particular as tire treads.

[0145] In order to confirm the effect of the invention, two tires (T-1: a reference, and T-2: an example according to the invention) having treads comprising the radially external portion, the radially intermediate portion and the radially internal portion produced by superposition of the sheets of the rubber compositions (C-1, C-2 and C-3), as shown in Table 2, are compared.

[0146] These tires, as snow tire having treads comprising grooves circumferentially and/or axially extending, were conventionally manufactured and in all respects identical apart from the rubber compositions of treads. These tires are radial carcass passenger vehicle tires and the size of them is 205/55R16.

[0147] As snow braking test, a 1,400 cc passenger car provided on all of the four wheels with the same kind of these tires (in the new state) under 220 kPa of tire inflation pressure mounted onto 6.5 J×16 rim was run on a snow covered road at a temperature of −10° C., the deceleration from 50 to 5 km/h during sudden longitudinal braking while anti-lock braking system (ABS) activated was measured. The above snow tests were conducted on a hard pack snow with a CTI penetrometer reading of about 90 in accordance with Standard ASTM F1805.

[0148] Furthermore, all of the tires were fitted to the front and rear axles of motor vehicles, under nominal tire inflation pressure, and were subjected to rolling on a circuit in order to reproduce the tires in the worn state. Then, the above snow braking test was done with the worn tires. Each of the worn tires was still in the service life, and in each of them, each radially internal portion made of each third rubber composition at least partially appeared on each tread surface and could at least partially contact with the ground.

[0149] The results of the braking tests on snow road are reported in Table 2, in relative units, the base 100 being selected for the reference tire T-1 (it should be remembered that a value of greater than 100 indicates an improved performance).

[0150] The results from Table 2 demonstrate that the test tire T-2 according to the invention has certainly higher values of the grip performance on snow than that of the reference T-1 in the worn state, and while improving the grip performance in the new state.

[0151] In conclusion, the treads of the tires in accordance with the invention allow an improvement braking performance on snow in the worn state while improving or maintaining the grip performance in the new state.

TABLE-US-00001 TABLE 1 Rubber composition(s) C-1 C-2 C-3 BR (1) 25 SBR (2) 75 NR (3) 100 100 Carbon black 1 (4) 4 Carbon black 2 (5) 30 5 Silica 1 (6) 120 Silica 2 (7) 60 Coupling agent (8) 9.6 12 Liquid plasticizer 1 (9) 25 Liquid plasticizer 2 (10) 30 Hydrocarbon resin (11) 55 Antioxidant (12) 2.8 Antiozone wax 1.9 1.5 DPG (13) 2.1 1.8 Stearic acid 3.0 2.0 Zinc oxide 1.5 3.0 3.0 Sulphur 1.4 2.0 2.0 CBS (14) 1.6 4.0 1.7 (1) BR: BR with 0.3% of 1,2 vinyl; 2.7% of trans; 97% of cis-1,4 (Tg.sub.DSC = −105° C.); (2) SBR: Solution SBR with 16% of styrene unit (Tg.sub.DSC = −65° C.); (3) NR: Natural rubber (peptised); (4) Carbon black 1: Carbon black (ASTM grade N234 from Cabot, BET (in accordance with ASTM D6556-10): 116 m.sup.2/g, COAN: 101 ml/100 g); (5) Carbon black 2: Carbon black (ASTM grade N774 from Cabot, BET (in accordance with ASTM D6556-10): 32 m.sup.2/g, COAN: 65 ml/100 g); (6) Silica 1: Silica (“Zeosil 1165MP” from Rhodia (CTAB: 160 m.sup.2/g, BET (in accordance with the French standard NF ISO 9277 of December 1996): about 160 m.sup.2/g)); (7) Silica 2: Silica (“Zeosil Premium 200MP” from Rhodia (CTAB: 200 m.sup.2/g, BET (in accordance with the French standard NF ISO 9277 of December 1996): 215 m.sup.2/g)); (8) Coupling agent TESPT (“Si69” from Evonik); (9) Oleic sunflower oil (“Agripure 80” from Cargill, Weight percent oleic acid: 100%); (10) Tris(2-ethylhexyl)phosphate (“Disflamoll TOF” from Lanxess, Tg.sub.DSC = −105° C.); (11) Hydrocarbon resin C.sub.5/C.sub.9 type (“Escorez ECR-373” from Exxon, Tg.sub.DSC = 44° C.). (12) Mixture of N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (“Santoflex 6-PPD” from Flexsys); (13) Diphenylguanidine (“Perkacit DPG” from Flexsys); (14) N-dicyclohexyl-2-benzothiazolesulphenamide (“Santocure CBS” from Flexsys).

TABLE-US-00002 TABLE 2 T-1 T-2 First rubber composition (FC) C-1 C-1 Second rubber composition (SC) C-1 C-2 Third rubber composition (TC) C-1 C-3 Snow braking in the new state 100 111 Snow braking in the worn state 100 132