Tire comprising a tread formed by multiple elastomer blends

Abstract

A tire with a radial carcass reinforcement, having a crown reinforcement, itself capped radially by a tread connected to two beads by two sidewalls, the tread having 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. 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 of at least two axially outer parts formed of a second blended elastomeric compound, the first blended elastomeric compound having a macro dispersion Z-value higher than 65 and a maximum tan(δ) value, denoted tan(δ)max, lower than 0.120, and the complex dynamic shear modulus G* 1% at 100° C. of the second blended elastomeric compound having a value at least 10% higher than that of the complex dynamic shear modulus G* 1% at 100° C. of the first blended elastomeric compound.

Claims

1. A tire with a radial carcass reinforcement, comprising: a crown reinforcement, a tread radially capping the crown reinforcement and 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 a central part than at 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 of 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 and a maximum tan(δ) value, denoted tan(δ)max, lower than 0.120 at 100° C., and wherein the complex dynamic shear modulus G* 1% at 100° C. of the second blended elastomeric compound has a value in MPa of at least 10% higher than that of the complex dynamic shear modulus G* 1% at 100° C. of the first blended elastomeric compound.

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 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.

4. 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.

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

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

7. The tire according claim 1, wherein the first layer of blended elastomeric compound, made up of a first blended elastomeric compound forming a part that extends at least into the region of the equatorial plane and of at least two axially outer parts formed of a second blended elastomeric compound, forms the radially outer layer of the tread.

8. The tire according to claim 7, wherein the at least two layers of blended elastomeric compounds includes a radially inner second layer in contact with the first layer, the radially inner second layer having a value of the complex dynamic shear modulus G* 1% at 100° C. at least 10% higher than that of the complex dynamic shear modulus G* 1% at 100° C. of the first blended elastomeric compound of the first layer.

9. The tire according to claim 1, wherein the at least two layers of blended elastomeric compounds includes a radially outer second layer in contact with the first layer, forming the radially outer layer of the tread, the radially outer second layer having a macro dispersion Z-value higher than 55 and a maximum tan(δ) value, denoted tan(δ)max, lower than 0.120 at 100° C.

10. The tire according to claim 9, wherein the tread comprises a radially inner third layer in contact with the first layer, and wherein the blended elastomeric compound that makes up the third layer has a value of the complex dynamic shear modulus G* 1% at 100° C. at least 10% higher than that of the complex dynamic shear modulus G* 1% at 100° C. of the first blended elastomeric compound of the first layer.

11. The tire according to claim 9, 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 10% 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.

12. The tire according to claim 11, wherein the tread further comprises a radially inner third layer in contact with the first layer, 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 third layer of blended elastomeric compound is greater than 25% 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.

13. The tire according to claim 1, wherein the tire 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(δ) value, denoted tan(δ)max, lower than 0.100 at 100° C.

14. The tire according to claim 5, wherein the complex dynamic shear modulus G* 1% at 100° C. of the second blended compound is 2.4 or lower.

15. The tire according to claim 6, wherein the complex dynamic shear modulus G* 1% at 100° C. of the first blended compound is 2 or lower.

16. The tire according to claim 10, 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 10% 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.

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 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 40.00R57, 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 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.

(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 33%.

(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(δ)max value of 0.087.

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

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

(13) 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 according to the invention by at least 10%.

(14) The tread 6 comprises a radially outer second layer 62 that comes into contact with the ground and is made up of the compound M1.

(15) The tread 6 further comprises a radially inner third layer 63 in contact with the first layer 61 made up of the blended compound M2.

(16) The tread 6 also comprises a radially innermost additional layer 64 made up of a blended elastomeric compound M3 with a tan(δ)max value of 0.060.

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

(18) TABLE-US-00001 Compound M1 Compound M2 Compound M3 NR 100 100 100 Black N134 35 Black N234 35 Black N347 34 Silica 170G 10 10 10 Anti-ozone wax 1 1 C32 ST Antioxidant (6PPD) 1.5 2.5 1 Silane on black 1 2 PEG (6000-20000) 1.67 Stearic acid 1 2 2 Accelerant CBS 1.7 1.4 1.35 Sulphur sol 2H 1.2 1.25 1.45 Zinc oxide 2.7 3 4.5 Z value 58 43 40 MSA300/MSA100 1.33 1.25 1.25 G*1% return 1.59 2.1 2 tan(δ).sub.max 0.087 0.098 0.060

(19) The thickness d.sub.61 of the first layer 61 is 32 mm.

(20) The thickness d.sub.62 of the second layer 62 is 46 mm.

(21) The thickness d.sub.63 of the third layer 63 is 14 mm.

(22) The thickness d.sub.64 of the additional layer 64 is 22 mm.

(23) 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 140% and therefore higher than 10%.

(24) The ratio of the thickness d.sub.63 of the third layer 63 to the thickness d.sub.61 of the first layer 61 is 45% and therefore higher than 25%.

(25) The ratio of the thickness d.sub.64 of the additional layer 64 to the total thickness of the tread, namely the sum of the thicknesses (d.sub.61+d.sub.62+d.sub.63+d.sub.64) is 19% and therefore between 15 and 25%.

(26) 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.

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

(28) 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 64.5 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.

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

(30) 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.

(31) 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.

(32) The thickness of the radially outer layer made up of the material A1 is 92 mm and the thickness of the radially inner layer made up of the material A2 is 22 mm.

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

(34) TABLE-US-00002 Compound A1 Compound A2 NR 100 100 Black N234 35 Black N347 34 Silica 170G 10 10 Anti-ozone wax 1 C32 ST Antioxidant (6PPD) 2.5 1 Silane on black 1 2 Stearic acid 2 2 Accelerant CBS 1.4 1.35 Sulphur sol 2H 1.25 1.45 Zinc oxide 3 4.5 Z value 43 40 MSA300/MSA100 1.25 1.25 G*1% return 2.1 2 tan(δ).sub.max 0.098 0.060

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

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

(37) The latter testing involved running the vehicles along a looped 500-meter 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.

(38) The tires P1 according to the invention of size 40.00R57 are inflated to 7 bar and subjected to a load of 54 tonnes.

(39) 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.

(40) 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 respectively fitted to the same vehicles.

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

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