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 containing 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 0.150, and the elongation at break in a tearability test of the second blended elastomeric compound at 100° C. having a value at least 10% higher than that of the elongation at break of the first blended elastomeric compound in a tearability test at 100° C.

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, wherein the tread comprises 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 65 and a maximum tan(δ) value, denoted tan(δ)max, lower than 0.150 at 100° C., and wherein the elongation at break in a tearability test of the second blended elastomeric compound at 100° C. has a value at least 10% higher than that of the elongation at break of the first blended elastomeric compound in a tearability test at 100° C.

2. The tire according to claim 1, wherein first blended elastomeric compound has a ratio MSA300/MSA100 of a value at least 15% higher than that of the 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 140 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 140 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 first blended elastomeric compound is higher than 2.10 MPa.

6. The tire according to 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.

7. The tire according to claim 6, wherein the at least two layers of blended elastomeric compounds include a radially inner second layer in contact with the first layer, the radially inner second layer having an elongation at break value in tearability testing at 100° C., that is at least 10% higher than that of the elongation at break of the first blended elastomeric compound of the said first layer in tearability testing at 100° C.

8. The tire according to claim 1, wherein the at least two layers of blended elastomeric compounds include a radially outer second layer in contact with the said first layer, forming the radially outer layer of the tread, the radially outer second layer having a macro dispersion Z-value higher than 65 and a maximum tan(δ) value, denoted tan(δ)max, lower than 0.150 at 100° C.

9. The tire according to claim 8, 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 an elongation at break value in tearability testing at 100° C., that is at least 10% higher than that of the elongation at break of the first blended elastomeric compound of the first layer in tearability testing at 100° C.

10. The tire according to claim 8, wherein the tire is of a dimension less than or equal to 57 inches, 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 50% 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.

11. The tire according to claim 9, wherein the tire is of a dimension less than or equal to 57 inches, 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.

12. The tire according to claim 8, wherein the tire is of a dimension strictly greater than 57 inches, 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.

13. The tire according to claim 9, wherein the tire is of a dimension strictly greater than 57 inches, 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 35% 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.

14. 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 said additional layer has a maximum tan(δ) value, denoted tan(δ)max, lower than 0.100 at 100° C.

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 to 3 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, according to a first embodiment of the invention,

(4) FIG. 3, a diagrammatic meridian view of the tread of the tire of FIG. 1, according to a second embodiment of the invention.

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

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(6) 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.

(7) 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.

(8) FIGS. 2 and 3 very schematically illustrate the makeup of the tread 6 for two tires of different sizes, 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.

(9) FIG. 2 schematically depicts the tread 6 of a tire of size 53/80R63.

(10) 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%.

(11) 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 61 a 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.

(12) The filled blended elastomeric compound M1 has a macro dispersion Z-value of 80 and a tan(δ)max value of 0.133.

(13) The blended elastomeric compound M2 has an elongation at break under tearability testing at 100° C. of 447%.

(14) The blended elastomeric compound M1 has an elongation at break under tearability testing at 100° C. of 316%.

(15) The value of elongation at break under tearability testing at 100° C. of the elastomeric compound M2 is greater than that of the elongation at break under tearability testing at 100° C. of the blended elastomeric compound M1 by 41% and therefore, in accordance with the invention, by at least 10% and preferably 30%.

(16) 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.

(17) 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.

(18) 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.

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

(20) TABLE-US-00001 Compound M1 Compound M2 Compound M3 NR 100 100 100 Black with BET 46 specific area 150 m.sup.2/g and structure OAN 135 ml/100 g Black N115 40 Black N347 34 Silica 170G 10 15 10 Anti-ozone wax 1 1 C32 ST Antioxidant (6PPD) 1.5 1.5 1 Silane on black 2 PEG (6000-20000) 1.67 2.5 Stearic acid 1 2 2 Accelerant CBS 1.7 1.4 1.35 Sulphur sol 2H 1.2 1.4 1.45 Zinc oxide 2.7 3 4.5 Z value 80 57 40 MSA300/MSA100 1.35 1.06 1.25 G*1% return 2.57 2.72 2 Elongation at break 316 447 200 (% at 100° C.) tan(δ).sub.max 0.133 0.142 0.060

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

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

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

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

(25) 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 22% and therefore higher than 10%.

(26) 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 44% and therefore higher than 35%.

(27) 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 17% and therefore between 15 and 25%.

(28) 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.

(29) FIG. 3 schematically depicts the tread 6 of a tire of size 40.00R57.

(30) 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%.

(31) According to an embodiment of the invention, the tread 26 is made up of a first layer 261 formed of a first blended elastomeric compound M21 forming a part 261a extending at least into the region of the equatorial plane XX′ and of at least two axially outer parts 261b formed of a second blended elastomeric compound M22.

(32) The tread 26 comprises a radially outer second layer 262 coming into contact with the ground and made up of the compound M21.

(33) The tread 26 also comprises a radially inner third layer 263 in contact with the first layer 261 made up of the compound M22.

(34) The tread 26 also comprises a radially innermost additional layer 264 made up of a blended elastomeric compound M23 a tan(δ)max value of 0.060.

(35) The compounds M21, M22 and M23 are identical to the compounds M1, M2 and M3 corresponding to FIG. 2.

(36) The thickness d.sub.261 of the first layer 261 is 32 mm.

(37) The thickness d.sub.262 of the second layer 262 is 46 mm.

(38) The thickness d.sub.263 of the third layer 263 is 14 mm.

(39) The thickness d.sub.264 of the additional layer 264 is 22 mm.

(40) The ratio of the thickness d.sub.262 of the second layer 262 to the thickness d.sub.261 of the first layer 261 is 140% and therefore higher than 50%.

(41) The ratio of the thickness of d.sub.263 of the third layer 263 to the thickness d.sub.261 of the first layer 261 is 44% and therefore higher than 25%.

(42) The ratio of the thickness d.sub.64 of the additional layer 264 to the total thickness of the tread, namely the sum of the thicknesses (d.sub.261+d.sub.262+d.sub.263+d.sub.264) is 19% and therefore between 15 and 25%.

(43) As with FIG. 2, the thickness measurements are taken in a meridian section of a tire in the new state, in the radial direction at the end of the radially outermost working layer.

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

(45) These tests involve running tires fitted to the driven rear axle of a vehicle. 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.

(46) These tests are carried out on the one hand with tires according to the depiction of FIG. 2, denoted P1 (size 53/80R63) and tires according to the depiction of FIG. 3, denoted P2 (size 40.00R57).

(47) The tires P1 of size 53/80R63 are inflated to a pressure of 7 bar and subjected to a load of 87.5 tonnes.

(48) The tires P2 of size 40.00R57 are inflated to a pressure of 7 bar and subjected to a load of 64.5 tonnes.

(49) These tires are respectively compared against reference tires R1 and R2 fitted respectively to the same vehicles. The tires R1 and R2 are tires which are known for this type of application.

(50) The tires R1 are the same size as the tires P1 and the tires R2 are the same size as the tires P2.

(51) The treads of the reference tires R1 and R2 are produced in identical ways and 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.

(52) In tire R1, 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.

(53) In tire R2, 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.

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

(55) TABLE-US-00002 Compound A1 Compound A2 NR 100 100 Black N115 40 Black N347 34 Silica 170G 15 10 Anti-ozone wax C32 ST 1 Antioxidant (6PPD) 1.5 1 Silane on black 2 PEG (6000-20000) 2.5 Stearic acid 2 2 Accelerant CBS 1.4 1.35 Sulphur sol 2H 1.4 1.45 Zinc oxide 3 4.5 Z value 57 40 MSA300/MSA100 1.06 1.25 G*1% return 2.72 2 Elongation at break 447 200 (% at 100° C.) tan(δ).sub.max 0.142 0.060

(56) 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.

(57) 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.

(58) 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.

(59) 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.

(60) The tires P2 according to an embodiment of the invention of size 40.00R57 are inflated to 7 bar and subjected to a load of 54 tonnes.

(61) 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.

(62) As in the case of the first tests, the tires according to the invention P1 and P2 are respectively compared against the reference tires R1 and R2 described hereinabove and respectively fitted to the same vehicles.

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

(64) 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.