Tire comprising a tread formed by multiple elastomer blends

Abstract

A tire of which the tread contains at least two layers of blended elastomeric compounds that are radially superposed and has a voids ratio that is lower in the central part than at the axially outer parts thereof. A first layer of blended elastomeric compounds of the tread is made up of a first blended elastomeric compound forming a central part, and of two outer parts formed of a second blended compound, the first blended compound having a Z-value higher than 55, the first blended compound and the second blended compound having a tan()max value lower than 0.110, the modulus G* of the second blended elastomeric compound having a value at least 10% higher than that of the modulus G* of the first blended elastomeric compound, a second layer of the tread, radially the outermost, being made up of a third blended compound of which the modulus G* has a value at least 10% higher than that of the modulus G* of the first blended elastomeric compound and the elongation at break of the third blended compound having a value at least 10% higher than those of the elongations at break of the first and second blended compounds.

Claims

1. A tire with a radial carcass reinforcement, comprising: a crown reinforcement, a tread radially capping the crown reinforcement, connected to two beads by two sidewalls, the tread comprising at least two layers of blended elastomeric compounds that are radially superposed and have a voids ratio that is lower in the central part than at the axially outer parts, wherein a first layer of blended elastomeric compounds of the tread is made up of: a first blended elastomeric compound forming a part extending at least into the region of the equatorial plane, and at least two axially outer parts formed of a second blended elastomeric compound, wherein the first blended elastomeric compound has a macro dispersion Z-value higher than 55, wherein the first blended compound and the second blended compound have a maximum tan() value, denoted tan()max, at 100 C. of lower than 0.110, wherein the complex dynamic shear modulus G* 1% at 100 C. in MPa of the second blended elastomeric compound has a value at least 10% higher than that of the complex dynamic shear modulus G* 1% at 100 C. in MPa of the first blended elastomeric compound, wherein a second layer of the tread, radially on the outside of the said first layer, is made up of a third blended elastomeric compound of which the complex dynamic shear modulus G* 1% at 100 C. in MPa has a value at least 10% higher than that of the complex dynamic shear modulus G* 1% at 100 C. in MPa of the first blended elastomeric compound, and wherein the elongation at break of the third blended elastomeric compound in a tearability test at 100 C. has a value at least 10% higher than those of the elongations at break of the first and second blended elastomeric compounds in a tearability test at 100 C.

2. The tire according to claim 1, wherein a ratio MSA300/MSA100 of the first blended elastomeric compound has a value at least 5% higher than that of a ratio MSA300/MSA100 of the second blended elastomeric compound.

3. The tire according to claim 1, wherein the ratio MSA300/MSA100 of the first blended elastomeric compound has a value which differs by at most 5% from that of the ratio MSA300/MSA100 of the third blended elastomeric compound of the second layer.

4. The tire according to claim 1, wherein the first blended elastomeric compound contains, by way of reinforcing filler, at least carbon black used at a content of between 10 and 70 phr, and wherein the carbon black has a BET specific surface area higher than 100 m.sup.2/g.

5. The tire according to claim 1, wherein the first blended elastomeric compound contains, by way of a cut of carbon black, with a BET specific surface area higher than 100 m.sup.2/g, and of a white filler, wherein the reinforcing filler is used at a content of between 10 and 90 phr, and wherein the ratio of carbon black to white filler is higher than 2.7.

6. The tire according to claim 1, wherein the complex dynamic shear modulus G* 1% at 100 C. in MPa of the second blended compound is higher than 1.6.

7. The tire according to claim 1, wherein the complex dynamic shear modulus G* 1% at 100 C. in MPa of the first blended compound is higher than 1.4.

8. The tire according to claim 1, wherein the complex dynamic shear modulus G* 1% at 100 C. in MPa of the third blended compound is higher than 1.6.

9. The tire according to claim 1, wherein the thickness, measured in the radial direction at the end of what in a meridian section of the tire is the radially outermost working layer, of the second layer of blended elastomeric compound is greater than 15% of the thickness, measured in the radial direction at the end of what in a meridian section of the tire is the radially outermost working layer, of the first layer of blended elastomeric compound.

10. The tire according to claim 1, wherein the tire further comprises an additional layer of a blended elastomeric compound in a radially innermost position of the tread, and wherein the blended elastomeric compound of the additional layer has a maximum tan() value, denoted tan()max, at 100 C. of lower than 0.80.

11. The tire according to claim 6, wherein the complex dynamic shear modulus G* 1% at 100 C. in MPa of the second blended compound is 2.4 or lower.

12. The tire according to claim 7, wherein the complex dynamic shear modulus G* 1% at 100 C. in MPa of the first blended compound is 2 or lower.

13. The tire according to claim 8, wherein the complex dynamic shear modulus G* 1% at 100 C. in MPa of the third blended compound is 2.4 or lower.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Further details and advantageous features of the invention will become apparent hereinafter from the description of some embodiments of the invention given with reference to FIGS. 1 and 2 which depict:

(2) FIG. 1, a diagrammatic meridian section of a tire according to embodiments of the invention,

(3) FIG. 2, a diagrammatic meridian view of the tread of the tire of FIG. 1.

(4) For ease of understanding, the figures have not been drawn to scale.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(5) FIG. 1 schematically depicts a tire 1 intended to be used on vehicles of the dumper type. It comprises a radial carcass reinforcement 2 anchored in two beads 3 around bead wires 4. The carcass reinforcement 2 is formed of a layer of metal cords. The carcass reinforcement 2 is hooped by a crown reinforcement 5, itself capped by a tread 6. The tread 6 is, according to an embodiment of the invention, made up of a central part 7 extending at least into the region of the equatorial plane XX, and of two axially outer parts 8, 9.

(6) According to an embodiment of the invention, the central part 7 of the tread 6 has a voids ratio (the tread patterns are not depicted in the figures) which is lower than that of the axially outer parts 8 and 9.

(7) FIG. 2 very schematically illustrates the makeup of the tread 6 for a tire of size 53/80R63, the said tread 6 being, according to an embodiment of the invention, made up of at least two radially superposed layers of blended elastomeric compound, a first layer of blended elastomeric compound forming a radially inner layer of the tread being made up of a first blended elastomeric compound forming a part extending at least in the region of the equatorial plane and of at least two axially outer parts formed of a second blended elastomeric compound and the radially outer layer of the tread being made up of a third blended elastomeric compound.

(8) The voids ratio in the central part of the tread 6 is 3%. The voids ratio in the axially outer parts of the tread 6 is 29%.

(9) According to an embodiment of the invention, the tread 6 is made up of a first layer 61 formed of a first blended elastomeric compound M1 forming a part 61a extending at least into the region of the equatorial plane XX and of at least two axially outer parts 61b formed of a second blended elastomeric compound M2.

(10) The filled blended elastomeric compound M1 has a macro dispersion Z-value of 58 and a tan()max value of 0.087.

(11) The blended elastomeric compound M2 has a tan()max value of 0.098.

(12) The blended elastomeric compound M2 has a complex dynamic shear modulus G* 1% at 100 C. of 2.1.

(13) The blended elastomeric compound M1 has a complex dynamic shear modulus G* 1% at 100 C. of 1.59.

(14) The value of the complex dynamic shear modulus G* 1% at 100 C. of the blended elastomeric compound M2 is higher than that of the complex dynamic shear modulus G* 1% at 100 C. of the blended elastomeric compound M1 by 32% and therefore, in accordance with the invention, by at least 10%.

(15) The tread 6 comprises a radially outer second layer 62 that comes into contact with the ground and is made up of a third blended elastomeric compound M3.

(16) The blended elastomeric compound M3 has a complex dynamic shear modulus G* 1% at 100 C. of 2.13.

(17) The value of the complex dynamic shear modulus G* 1% at 100 C. of the blended elastomeric compound M3 is higher than that of the complex dynamic shear modulus G* 1% at 100 C. of the blended elastomeric compound M1 by 34% and, therefore, in accordance with the invention, by at least 10%.

(18) The elongation at break of the blended elastomeric compound M3 in a tearability test at 100 C. is 320%.

(19) The elongation at break of the blended elastomeric compound M1 in a tearability test at 100 C. is 275%.

(20) The elongation at break of the blended elastomeric compound M2 in a tearability test at 100 C. is 238%.

(21) The value of the elongation at break of the blended elastomeric compound M3 in a tearability test at 100 C. is higher than that of the elongation at break of the blended elastomeric compound M1 in a tearability test at 100 C. by 16% and, therefore, in accordance with the invention, by at least 10%.

(22) The value of the elongation at break of the blended elastomeric compound M3 in a tearability test at 100 C. is higher than that of the elongation at break of the blended elastomeric compound M2 in a tearability test at 100 C. by 34% and, therefore, in accordance with the invention, by at least 10%.

(23) The tread 6 also comprises a radially innermost additional layer 63 made up of a blended elastomeric compound M4 with a tan()max value of 0.060.

(24) The compounds M1, M2, M3 and M4 are described in the table below, together with a number of their properties.

(25) TABLE-US-00001 Com- Com- Com- Com- pound M1 pound M2 pound M3 pound M4 NR 100 100 100 100 Black N134 35 40 Black N234 35 Black N347 34 Silica 170G 10 10 15 10 Anti-ozone wax C32 ST 1 1 1 Antioxidant (6PPD) 1.5 2.5 1.5 1 Silane on black 1 2 PEG (6000-20000) 1.67 2.5 Stearic acid 1 2 2 2 Accelerant CBS 1.7 1.4 1.7 1.35 Sulphur sol 2H 1.2 1.25 1.2 1.45 Zinc oxide 2.7 3 3 4.5 Z value 58 43 54 40 MSA300/MSA100 1.33 1.25 1.3 1.25 G*1% return 1.59 2.1 2.13 2 Elongation at break (% at 275 238 320 200 100 C.) tan().sub.max 0.087 0.098 0.122 0.060

(26) The thickness d.sub.61 of the first layer 61 is 64 mm.

(27) The thickness d.sub.62 of the second layer 62 is 14 mm.

(28) The thickness d.sub.63 of the third layer 63 is 22 mm.

(29) The ratio of the thickness d.sub.62 of the second layer 62 to the thickness d.sub.61 of the first layer 61 is 308% and therefore higher than 100%.

(30) The ratio of the thickness d.sub.63 of the additional layer 63 to the total thickness of the tread, namely the sum of the thicknesses (d.sub.61+d.sub.62+d.sub.63) is 17% and therefore between 15 and 25%.

(31) The thicknesses are measured on a meridian section of a tire in the new state, in the radial direction at the end of the radially outermost working layer.

(32) Tests were carried out using vehicles fitted with the tires according to the invention in order to evaluate the wearing properties thereof.

(33) These tests involve running tires fitted to the driven rear axle of a vehicle. The tires are inflated to a pressure of 7 bar and subjected to a load of 87.5 tonnes. The vehicles are driven along a track inclined at 14% successively uphill and downhill for a total duration of 1500 hours. The track is made up of stones ranging in size between 15 and 30 mm.

(34) These tests are carried out with tires according to the depiction of FIG. 2, denoted P1.

(35) These tires are compared against reference tires R1 which are the same size as the tires P1 and are fitted to the same vehicles. The tires R1 are tires which are known for this type of application.

(36) The treads of the reference tires R1 comprise two radially superposed layers, the radially outer layer being made up of a first material A1 and the radially inner layer being made up of a material A2.

(37) The thickness of the radially outer layer made up of the material A1 is 106 mm and the thickness of the radially inner layer made up of the material A2 is 22 mm.

(38) The makeup and properties of these materials are described in the table below.

(39) TABLE-US-00002 Compound A1 Compound A2 NR 100 100 Black N330 50 Black N347 34 Silica 170G 10 Anti-ozone wax C32 ST 1 Antioxidant (6PPD) 1.5 1 Silane on black 2 PEG (6000-20000) Stearic acid 2 2 Accelerant CBS 1.7 1.35 Sulphur sol 2H 0.6 1.45 Zinc oxide 2 4.5 Z value 48 40 MSA300/MSA100 1.28 1.25 G*1% return 2.01 2 Elongation at break (% at 230 200 100 C.) tan().sub.max 0.135 0.060

(40) The results obtained when running under the conditions described hereinabove demonstrated improvements in wear of between 15 and 20% with tires according to the invention as compared against the reference tires.

(41) Further testing was carried out using vehicles fitted with the tires according to the invention in order to evaluate their properties in terms of resistance to attack.

(42) The latter testing involved running the vehicles along a looped 500-metre track comprising a region 50 meters long made up of stones sized between 145 and 200 mm. The runs lasted for 500 hours at a speed of 15 km/h on the circuit outside of the stony region and 5 km/h over the said stony region.

(43) The tires P1 according to an embodiment of the invention of size 53/80R63 are inflated to 7 bar and subjected to a load of 74 tonnes.

(44) After running the tires are stripped and the number of cracks that reach the crown reinforcement counted. The number of cracks reaching the crown reinforcement is an indication of how well a tire resists attack.

(45) As in the case of the first tests, the tires according to an embodiment of the invention P1 are compared against the reference tires R1 described hereinabove and fitted to the same vehicles.

(46) The results obtained during these tests demonstrated improvements of the order of 20% in terms of resistance to attack of the tires according to embodiments of the invention as compared with the reference tires.

(47) The results of these two types of testing show that the tires according to embodiments of the invention lead to a compromise between better wear performance and better resistance to attack.