Tire with improved durability

Abstract

The invention relates to a tyre (1) with a radial carcass reinforcement, said tyre (1) comprising two working crown plies (41, 42). According to the invention, the rubber mixture constituting the layer C comprises a composition comprising 50 phr to 70 phr of a reinforcing filler, at least 20 phr of which is pyrolytic carbon black.

Description

Technical Field

[0001] The present invention relates to a tire having a radial carcass reinforcement, and more particularly to a tire intended to be mounted on a vehicle (such as, for example, a truck, a tractor, a trailer or a bus) that carries heavy loads and travels at a constant speed. Background Art

[0002] Generally, in tires for heavy-duty vehicles, the carcass reinforcement is anchored in the two bead areas on both sides and is covered radially by a crown reinforcement composed of at least two superimposed layers formed by filaments or cords, the filaments or cords being parallel within each layer and crossing from one layer to another, forming an angle between 10° and 45° with the circumferential direction. The working layer forming the working reinforcement may also be covered by at least one layer called a protection layer, the protection layer being formed by reinforcing elements (called elastic reinforcing elements) that are advantageously metallic and extensible. It may also include a layer of metallic filaments or cords having low extensibility, the metallic filaments or cords forming an angle between 45° and 90° with the circumferential direction, and this ply is called a chafer ply and is located radially between the carcass reinforcement and the first crown ply (called the working ply), the carcass reinforcement and the first crown ply being formed by parallel filaments or cords with an absolute value of the angle of at most 45°. The chafer ply and at least the working ply together form a chafer reinforcement, the chafer reinforcement having little or no deformation under the various stresses it undergoes, and the chafer ply being substantially used to absorb the lateral compressive forces applied to all the reinforcing elements in the crown area of the tire.

[0003] When a cord shows a relative elongation of at most 0.2% under a tensile force equal to 10% of the breaking force, the cord is called inextensible.

[0004] When a cord shows a relative elongation of at least 3% and a maximum tangent modulus of less than 150 GPa under a tensile force equal to the breaking load, the cord is called elastic.

[0005] A circumferential reinforcing element is a reinforcing element that forms an angle within the range of +2.5° to -2.5° (relative to 0°) with the circumferential direction.

[0006] The circumferential direction or longitudinal direction of a tire is the direction that is tangent to the outer circumference of the tire and is defined by the traveling direction of the tire.

[0007] The lateral direction or axial direction of a tire is parallel to the axis of rotation of the tire.

[0008] The radial direction is the direction that intersects and is perpendicular to the axis of rotation of the tire.

[0009] The axis of rotation of a tyre is the axis about which the tyre rotates during normal use.

[0010] A radial plane or a meridian plane is a plane containing the axis of rotation of the tyre.

[0011] The circumferential mid-plane or the equatorial plane is a plane perpendicular to the axis of rotation of the tyre and dividing the tyre into two halves.

[0012] The "modulus of elasticity" of a rubber compound shall be understood as the secant modulus of elongation at 10% elongation and ambient temperature.

[0013] For a rubber composition, the secant modulus of elasticity at 10% elongation is the modulus of elasticity measured on the compound at an elongation value of 0.1 (i.e. 10% elongation, expressed as a percentage) during a uniaxial tensile test. A uniaxial tension is applied to the specimen at a constant rate, and the elongation and the force are measured. The measurement is carried out using an INSTRON-type tensile testing machine at a temperature of 23 °C and a relative humidity of 50% (ISO 23529 standard). The conditions for measuring and using the results to determine the elongation and the stress are as described in NF ISO 37 standard: 2012-03. The stress at 0.1 elongation is determined, and the secant modulus of elasticity at 10% elongation is calculated by determining the ratio of this stress value to the elongation value. A person skilled in the art will know how to select and adjust the dimensions of the specimen according to the amount of compound available and usable, especially in the case where the specimen is taken from a finished product such as a tyre.

[0014] Due to the improvement of road networks and the expansion of the global highway network, some tyres today called "road tyres" are designed to travel longer distances at higher speeds. As the wear on the tyres is reduced, this combination of driving conditions will undoubtedly enable an increase in the number of kilometres travelled; on the other hand, the durability of such tyres, especially the durability of the crown reinforcement, will be adversely affected.

[0015] This is because there are stresses in the crown reinforcement, more specifically shear stresses between the crown layers, and these stresses, combined with a non-negligible increase in the operating temperature at the ends of the axially shortest crown layers, result in the appearance of cracks in the rubber and their propagation at said ends.

[0016] In order to improve the durability of the crown reinforcement of tyres of the type under study, solutions have been proposed relating to the structure and quality of rubber compound layers and / or shaping elements arranged between and / or around the ends of the ply layers (more specifically the ends of the axially shortest ply layers).

[0017] It is a well-known practice to introduce a layer of rubber compound between the ends of the working ply in order to create a decoupling between said ends and thus limit the shear stress. However, this decoupling layer needs to have very good cohesion. For example, such a rubber compound layer is described in patent application WO 2004 / 076204.

[0018] To improve the resistance to degradation of the rubber compound located near the edge of the crown reinforcement, patent FR 1 389 428 proposes using a rubber forming element in combination with a low hysteresis tread, said rubber forming element covering at least the sides and the edge of the crown reinforcement and being made of a rubber compound with low hysteresis.

[0019] To avoid separation between the plies of the crown reinforcement, patent FR 2 222 232 teaches covering the ends of the reinforcement with a rubber pad, the Shore A hardness of said rubber pad being different from the Shore A hardness of the tread covering said reinforcement and being greater than the Shore A hardness of the forming element of the rubber compound arranged between the edge of the carcass reinforcement and the plies of the crown reinforcement.

[0020] The tires thus produced can effectively improve the performance, particularly in terms of durability.

[0021] Furthermore, the use of the tires on heavy-duty vehicles of the "site supply" type means that the tires are subjected to impact loads when driving over stony ground. These impact loads will of course have an adverse effect on the performance in terms of durability.

[0022] For a person skilled in the art, it is also a known practice to increase the number of plies constituting the crown reinforcement, thus improving the durability of the tire with respect to these impact loads.

[0023] The presence of one or more additional reinforcement element layers results in a greater tire mass and a higher tire manufacturing cost.

[0024] The inventors have particularly found that when driving on a ground that exerts great stress on the tire, the durability performance of such a tire may decrease (particularly at the shoulders of the tire), for example under particularly severe driving conditions combining vehicle speed, the load borne by the tire and the nature of the ground. In fact, for example, when driving at a relatively high speed on a ground of the "site supply" type that is very demanding on the tire, a decrease in durability performance can be observed. Summary of the Invention

[0025] Therefore, the inventors have set themselves the task of providing tires for "heavy-duty" vehicles (such as vehicles of the "site supply" type) that have improved durability performance with respect to the impact loads to which the tread is subjected, regardless of the nature of the ground and the driving conditions.

[0026] According to the present invention, this object is achieved by a tire comprising a radial carcass reinforcement, said tire comprising a crown reinforcement including two working crown plies, each working crown ply being formed by reinforcing elements interposed between two surface layers of rubber compound, crossing from one layer to the other and forming an angle between 10° and 45° with the circumferential direction, said angle being oriented on both sides of the circumferential direction, a rubber compound layer C being arranged between at least the ends of said at least two working crown plies, said crown reinforcement being radially covered by a tread which is connected to two beads via two sidewalls, the composition of the rubber compound constituting layer C comprising from 50 phr to 70 phr of reinforcing filler, said reinforcing filler including at least 20 phr of pyrolytic carbon black.

[0027] The expression "parts by weight per hundred parts by weight of elastomer" (or phr) is to be understood as meaning parts by mass per hundred parts by mass of elastomer or rubber (the two terms being synonymous).

[0028] In certain embodiments, the composition comprises from 50 phr to 70 phr of reinforcing filler, said reinforcing filler being pyrolytic carbon black. Thus, it should be understood that the composition comprises pyrolytic carbon black as the sole reinforcing filler (thus, the composition does not contain any inorganic reinforcing filler and other organic reinforcing fillers).

[0029] The reinforcing filler can be as described below.

[0030] Within the meaning of the present invention, the term "pyrolytic carbon black" is understood to mean carbon black produced by the pyrolysis process (for example in the case of the recovery of such a material) of a material comprising at least one carbon-based polymer and carbon black (hereinafter called the material to be pyrolyzed). Whatever its form, whether in the form of powder, granules, strips or any other form, and whether in a crosslinked state or not, the physical state of the material to be pyrolyzed provided is not important.

[0031] Preferably, the material to be pyrolyzed can be recovered from finished products or products produced during their manufacture / production (such as by-products or waste); these finished products can be selected from pneumatic tires, non-pneumatic tires, industrial conveyor belts, conveyor belts, rubber gaskets, rubber hoses, shoe soles and windshield wipers. Even more preferably, the pyrolytic carbon black usable within the scope of the present invention is carbon black obtained by the pyrolysis process of a material to be pyrolyzed originating from finished products selected from pneumatic tires and non-pneumatic tires.

[0032] Within the scope of the present invention, pyrolysis means any type of thermal decomposition carried out under anaerobic conditions, and the raw material thereof is the material to be pyrolyzed as defined above. Therefore, pyrolytic carbon black is different from so-called industrial carbon black and / or ASTM grade carbon black in that the carbon-based raw material used for pyrolysis is a material containing at least carbon-based polymers and carbon black, rather than a material derived from petroleum fractions or oils from coal or natural sources.

[0033] The pyrolytic carbon black that can be used within the scope of the present invention is particularly different from known carbon blacks (such as industrial carbon black, especially "furnace black") in that the ash content is higher than that of the said "furnace black". Relative to the total weight of the "furnace black", the ash content of the "furnace black" is less than 1% by weight.

[0034] Preferably, relative to the total weight of the pyrolytic carbon black, the ash content of the pyrolytic carbon black that can be used within the scope of the present invention ranges from 5% by weight to 30% by weight, more preferably less than 25% by weight, and even more preferably less than 22% by weight.

[0035] Preferably, relative to the total weight of the pyrolytic carbon black, the sulfur content of the pyrolytic carbon black that can be used within the scope of the present invention is greater than 1.5% by weight, preferably greater than 2% by weight, and more preferably ranges from 2.5% by weight to 5% by weight.

[0036] Relative to the total weight of the "furnace black", the sulfur content of the "furnace black" is less than 1.2% by weight.

[0037] Preferably, relative to the total weight of the pyrolytic carbon black, the zinc content of the pyrolytic carbon black that can be used within the scope of the present invention is greater than or equal to 2% by weight, preferably ranges from 2.5% by weight to 8% by weight.

[0038] Relative to the total weight of the "furnace black", the zinc content of the "furnace black" is substantially zero and particularly less than 0.5% by weight.

[0039] Preferably, the STSA specific surface area of the pyrolytic carbon black that can be used within the scope of the present invention measured according to standard ASTM D6556-2021 is within 20 m 2 / g to 200 m 2 / g, and more preferably within the range of 30 m 2 / g to 90 m 2 / g.

[0040] Preferably, the void volume of the pyrolytic carbon black that can be used within the scope of the present invention measured at a pressure of 50 MPa according to standard ASTM D7854 (2018) is within 30 ml / 100 g to 60 ml / 100 g, and more preferably within the range of 35 ml / 100 g to 55 ml / 100 g.

[0041] The ash content was determined by calcination in a platinum dish in a muffle furnace at 825 °C according to the following protocol. Prior to each series of measurements, the platinum dish was pre-determined and the tare weight of the platinum dish was weighed to an accuracy within 0.1 mg, and the mass was designated as P0. A 5 g sample of pyrolytic carbon black weighed accurately to within 0.1 mg was placed into the platinum dish; this mass was designated as P1. The platinum dish and its contents were pre-calcined using a Bunsen burner until smoke appeared and the product ignited. After the combustion of the product was complete, the platinum dish and its contents were placed into a muffle furnace heated to 825 °C for 1 h. After 1 h, the platinum dish was removed from the furnace and immediately placed into a desiccator at ambient temperature. When the platinum dish and the ash had returned to ambient temperature, the platinum dish was weighed again to obtain the mass P2. Finally, the ash content (ash %) could be obtained using the following formula:

[0042]

[0043] After the sample was calcined, the ash was absorbed in an acidic medium and the zinc content in the pyrolytic carbon black was determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) analysis. The ash was obtained by performing the above protocol. Approximately 100 mg of ash (test sample) was taken and placed into a PFA (Perfluoroalkoxy) tube for a HotBlock hotplate. Then 8 ml of 37% concentrated hydrochloric acid, 3 ml of 65% concentrated nitric acid and 0.5 ml of 40% hydrofluoric acid were added. The tube was closed with a tube stopper and heated at 130 °C for 2 h. After cooling, the contents were then transferred to a 100 ml PTFE (Polytetrafluoroethylene) volumetric flask that already contained 2 g of boric acid (for neutralizing hydrofluoric acid) using ultrapure water. Ultrapure water was added up to the calibration mark. The solution obtained was diluted 100-fold by taking 1 ml of the solution and placing it into a 100 ml PFTE volumetric flask that already contained 8 ml of 37% concentrated hydrochloric acid, 3 ml of 65% concentrated nitric acid, 0.5 ml of 40% hydrofluoric acid and 2 g of boric acid. Then, prior to analysis by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), the diluted solution was filtered through a 0.45 μm GHP syringe filter. Prior to analyzing the diluted solution, at least 5 calibration standards with zinc concentrations of 0 mg / l, 0.5 mg / l, 1 mg / l, 2 mg / l and 5 mg / l were analyzed by ICP-AES. These calibration standards were prepared by diluting a commercially available solution with a certified zinc concentration of 1 g / l in a 100 ml volumetric flask.

[0044] These volumetric flasks already contain 8 ml of 37% concentrated hydrochloric acid, 3 ml of 65% concentrated nitric acid, 0.5 ml of 40% hydrofluoric acid and 2 g of boric acid. The standard solution is analyzed by ICP-AES at a wavelength of λZn = 202.613 nm. For each standard concentration (c), the intensity IZn of the zinc signal is plotted on the IZn = f(c) curve, which corresponds to a calibration line (type y = ax + b). Then, the sample solution of unknown concentration (diluted solution) is measured under the same conditions as the standard sample. The measured intensity is related to the concentration using the previously obtained calibration line. Since the sample and volume are pre-recorded, the concentration [c] is directly obtained by software. 灰分 (in mass %). The zinc concentration [c] in the pyrolytic carbon black is obtained by the following equation 炭黑 (in mass %):

[0045] [c] 炭黑 = [c] 灰分 * 100 * ash content %

[0046] The sulfur content in the pyrolytic carbon black is determined by a LECO furnace. The LECO sulfur analyzer is designed to measure the sulfur content in organic materials and / or inorganic materials, especially by combustion and non-dispersive infrared detection. Before measuring the sulfur content in the sample, the boat is cleaned and the furnace is calibrated. The boat used for the LECO furnace is pre-cleaned: this involves analyzing an empty boat under the same conditions as the sample. A calibration curve is prepared based on a commercial standard sample called "BBOT" (whose purity is greater than 99.99%, and the contents of carbon (C), hydrogen (H), nitrogen (N), oxygen (O) and sulfur (S) are ensured). These contents are as follows: C% 72.52; H% 6.09; N% 6.51; O% 7.43 and S% 7.44. Weigh approximately 10 ± 3 mg, 20 ± 3 mg and 40 ± 3 mg of BBOT on the boat. The standard sample / boat assembly is placed into the combustion furnace and adjusted to 1350 °C under pure oxygen. The combination of the furnace temperature and the analysis flow rate causes the combustion of the sample and releases sulfur and / or carbon in the form of SO2(g). After 20 s, oxygen starts to flow through the lance, thus accelerating the combustion of difficult-to-burn materials. Sulfur and / or carbon in the form of SO2(g) are entrained by the oxygen flow through the infrared detection unit. The software of the instrument plots a straight line that relates the mass of the introduced standard sample to the response (area) observed on the detector. Thus, the calibration line is obtained. After thoroughly cleaning the sampling equipment, weigh approximately 80 ± 5 mg of pyrolytic carbon black and place it into the boat used for the LECO furnace.

[0047] The area of the observed SO2 peak is related to the concentration through the calibration line. The software of the instrument then calculates the weight % of sulfur in the sample based on the weight of the sample placed into the boat.

[0048] Pyrolytic carbon black is sold, for example, by BlackBear under the reference number "BBCT30" or by Scandinavian EnviroSystems under the reference number "P550".

[0049] The angle (expressed in degrees) of the working crown ply is measured in the cross-section of the tire. According to the invention, the angle is measured at the circumferential mid-plane. These measurements can also be carried out by radiography.

[0050] The rubber compound layer C can decouple the working crown ply, so that the shear stress is distributed over a greater thickness.

[0051] Within the meaning of the present invention, the working crown ply is said to be coupled if the distance by which the corresponding reinforcing elements of each ply are radially separated is less than the average diameter of the circle circumscribing the reinforcing elements, the rubber thickness being measured radially between the corresponding upper and lower radial generatrices of the reinforcing elements.

[0052] The average diameter of the circle circumscribing the reinforcing elements is defined as the average diameter of the circle circumscribing the reinforcing elements of each working crown ply.

[0053] According to a preferred embodiment of the invention, the rubber compound layer C is an elastomeric compound based on natural rubber or on synthetic polyisoprene having mainly cis-1,4 bonds and optionally based on at least one other diene elastomer, natural rubber or synthetic polyisoprene being present in a major amount relative to the content of one or more other diene elastomers used in the blend.

[0054] Among the diene elastomers that can be used in blend with natural rubber or synthetic polyisoprene having mainly cis-1,4 bonds, mention may be made preferably of polybutadiene (BR) having mainly cis-1,4 bonds, styrene-butadiene copolymer (SBR) in solution or emulsion, butadiene-isoprene copolymer (BIR) or styrene-butadiene-isoprene terpolymer (SBIR). These elastomers can be elastomers modified during or after polymerization by a branching agent (such as divinylbenzene) or a star branching agent (such as a carbonate, a tin halide or a silicon halide), or elastomers modified by a functionalizing agent such that an oxycarbonyl or carboxyl functional group or an amine functional group is grafted to the chain or the chain ends, for example by the action of dimethylaminobenzophenone or diethylaminobenzophenone. In the case of a blend of natural rubber or synthetic polyisoprene having mainly cis-1,4 bonds with one or more of the above-mentioned diene elastomers, natural rubber or synthetic polyisoprene is preferably used in a major amount, more preferably in an amount greater than 70 phr.

[0055] Also preferably, in addition to pyrolytic carbon black, the rubber compound layer C further comprises a reinforcing filler consisting of:

[0056] a) carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0057] b) or white fillers of the silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, said white fillers being selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0058] c) or a blend of the carbon black described in (a) and the white filler described in (b), wherein the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

[0059] The BET specific surface area is measured by the Brunauer, Emmet and Teller method described in “The Journal of the American Chemical Society” (Volume 60, page 309, February 1938), which corresponds to the NFT 45007 standard of November 1987.

[0060] If a transparent filler or a white filler is used, a coupling agent and / or a covering agent selected from reagents known to those skilled in the art must be used. As an example of a preferred coupling agent, alkoxysilane sulfides of the bis(3-trialkoxysilylpropyl) polysulfide type can be mentioned, in particular bis(3-triethoxysilylpropyl) tetrasulfide sold by Degussa under the name Si69 (pure liquid product) and under the name X50S (solid product (blended with N330 carbon black at 50 / 50 by weight)). As an example of a covering agent, fatty alcohols, alkylalkoxysilanes (such as hexadecyltrimethoxysilane or hexadecyltriethoxysilane sold by Degussa under the names Si116 and Si216 respectively), diphenylguanidine, polyethylene glycol or silicone oils optionally modified by OH or alkoxy functional groups can be mentioned. The covering agent and / or the coupling agent are used in a weight ratio of ≥1 / 100 and ≤20 / 100 relative to the filler, preferably between 2 / 100 and 15 / 100 when the transparent filler constitutes all of the reinforcing filler, and between 1 / 100 and 20 / 100 when the reinforcing filler consists of a blend of carbon black and a transparent filler.

[0061] As further examples of reinforcing fillers having the above morphology and SiOH and / or AlOH surface functional groups of silica and / or alumina type materials and which can be used as partial or total substitutes for these materials according to the invention, mention may be made of carbon blacks which are modified during the synthesis by adding a compound of silicon and / or aluminium to the feedstock oil of the furnace or after synthesis by adding an acid to an aqueous suspension of the carbon black in a sodium silicate and / or sodium aluminate solution, so as to cover at least partially the surface of the carbon black with SiOH and / or AlOH functional groups. As non-limiting examples of carbon-based fillers of this type having SiOH and / or AlOH functional groups on the surface, mention may be made of the fillers of the CSDP type described in document No. 24 of the ACS Rubber Division Meeting (Anaheim, California, 6-9 May 1997), and those in patent application EP-A-0799 854.

[0062] When using a transparent filler as the only reinforcing filler, hysteresis properties and cohesion properties are obtained by using precipitated silica or pyrogenic silica or precipitated alumina or aluminosilicate having a BET specific surface area between 30 m 2 / g and 260 m 2 / g. As non-limiting examples of fillers of this type, mention may be made of silica KS404 from Akzo, Ultrasil VN2 or VN3 and BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or Zeosil 1165MP from Rhodia, HI-SIL 2000 from PPG, etc.

[0063] The results obtained with the tyres according to the invention have effectively demonstrated that, regardless of the nature of the ground and the driving conditions, the performance in terms of durability can be improved. In particular, the durability performance of the tyre crown has been improved with respect to the impact loads at the edge of the tread (in particular at the shoulders of the tyre), regardless of the nature of the ground and the driving conditions.

[0064] The inventors believe that these results can be explained by the presence of pyrogenic carbon black used as a filler in layer C. The inventors have been able to demonstrate that the presence of pyrogenic carbon black in the rubber compound constituting layer C gives a higher elongation at break value for said layer C than for more common compounds. Generally, if the impact load is the same as that observed when driving over a stony ground, more specifically impacting the shoulders of the tyre, the breakage of the reinforcing elements (if such breakage occurs) is found in the innermost radial layer, more specifically at its ends. These observations seem to indicate that the presence of pyrogenic carbon black in the rubber compound constituting layer C can improve the durability performance of the tyre in the face of this type of attack.

[0065] Preferably, the thickness of the rubber compound layer C measured at the end of the narrowest working tread layer among the two working tread layers under consideration is preferably between 30% and 80% of the total thickness of the rubber compound between the cord generatrices of each of the two working tread layers: a thickness less than 30% does not yield conclusive results, and a thickness greater than 80% is useless for improving the separation between the resistance layers and is also disadvantageous in terms of cost.

[0066] Also preferably, the axial width D of the rubber compound layer C between the axially innermost end of the rubber compound layer C and the end of the axially narrowest working tread layer satisfies:

[0067] 3.φ2 ≤ D ≤ 25.φ2

[0068] where φ2 is the diameter of the reinforcing element of the axially narrowest working tread layer. This relationship defines the joint area between the rubber compound layer C and the axially narrowest working tread layer. Such a joint less than three times the diameter of the reinforcing element of the axially narrowest working layer may not be sufficient to obtain the decoupling of the working tread layer, especially to obtain a reduction in stress at the end of the axially narrowest working tread layer. A value of such a joint greater than twenty times the diameter of the reinforcing element of the axially narrowest working layer may lead to an excessive reduction in the camber stiffness of the tire crown reinforcement.

[0069] Preferably, the axial width D of the rubber compound layer C between the axially innermost end of the rubber compound layer C and the end of the axially narrowest working tread layer is greater than 5 mm.

[0070] The invention also preferably provides a rubber compound layer C at the axially outer end of the axially narrowest working tread layer, and the thickness of the rubber compound layer C satisfies that the radial distance d between the two working tread layers separated by the rubber compound layer C satisfies the following relationship:

[0071] 3 / 5.φ2 < d < 5.φ2

[0072] where φ2 is the diameter of the reinforcing element of the axially narrowest working tread ply.

[0073] The distance d is measured from cord to cord (i.e., between the cords of the first working layer and the cords of the second working layer). In other words, the distance d includes the thickness of the rubber compound layer C and the corresponding thicknesses of the rubber surface compound located radially outside the cords of the radially inner working layer and radially inside the cords of the radially outer working layer.

[0074] Various thickness measurements are made on the meridian cross-section of the tire, so the tire is in an uninflated state.

[0075] According to an advantageous embodiment of the invention, the axially widest working tread layer is located radially inside another working tread layer.

[0076] According to a variant of an embodiment of the invention, at least one surface layer of at least one working tread ply is made of a rubber compound, the composition of which comprises 50 phr to 70 phr of reinforcing filler, the reinforcing filler including at least 20 phr of pyrolytic carbon black.

[0077] According to a preferred embodiment of this variant of the invention, the rubber compound of the surface layers of the two working tread plies has a composition comprising 50 phr to 70 phr of reinforcing filler, the reinforcing filler including at least 20 phr of pyrolytic carbon black.

[0078] Thus, the inventors have observed that the combination of the pyrolytic-carbon-black-based rubber compound of the calendered surface layer of the working tread ply in this variant of the embodiment of the invention with the compound of layer C according to the invention enables the durability performance of the tyre to be maintained, or even improved, and even more significantly improved.

[0079] According to a preferred embodiment of this variant of the invention, the at least one surface layer of at least one working tread ply is an elastomer compound based on natural rubber, or on synthetic polyisoprene mainly having cis-1,4 bonds, and optionally based on at least one other diene elastomer, the content of natural rubber or synthetic polyisoprene being present in a major amount relative to the one or more other diene elastomers used in the blend.

[0080] Also preferably, in addition to pyrolytic carbon black, the at least one surface layer of at least one working tread ply further comprises a reinforcing filler consisting of:

[0081] a) carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0082] b) or a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, the white filler being selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0083] c) or a blend of the carbon black described in (a) and the white filler described in (b), wherein the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

[0084] According to an embodiment of the invention, the elastomeric compound of the at least one surface layer constituting at least one working crown ply is the same as the elastomeric compound of layer C arranged between at least the ends of the two working crown plies.

[0085] The metal element is preferably a steel cord.

[0086] According to a preferred embodiment of the invention, the reinforcing element of the working crown ply is an inextensible metal cord.

[0087] A preferred embodiment of the invention also supplements the radially outer side of the crown reinforcement by at least one additional layer (referred to as a protective layer) having a so-called elastic reinforcing element, the elastic reinforcing element being oriented at an angle between 10° and 45° with respect to the circumferential direction, and the direction of the angle being the same as the angle formed by the inextensible elements of the working layer radially adjacent thereto.

[0088] According to any of the above embodiments of the invention, the radially inner side of the crown reinforcement between the carcass reinforcement and the radially inner working layer closest to the carcass reinforcement can also be supplemented by a triangular layer having inextensible metal reinforcing elements, the inextensible metal reinforcing elements being made of steel, forming an angle greater than 60° with the circumferential direction, and the direction of the angle being the same as the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement layer. Description of the Drawings

[0089] Other details and advantageous features of the invention will become apparent hereinafter from the description of the exemplary embodiments of the invention given with reference to the drawings, which show a meridional view of a tire design according to an embodiment of the invention.

[0090] For easier understanding, the drawings are not drawn to scale. The drawings show only a half view of the tire, which extends symmetrically about an axis XX', which represents the circumferential median plane or equatorial plane of the tire. Detailed Description

[0091] In the drawings, the tire 1 has a size of 295 / 80R 22.5. The tire 1 includes a radial carcass reinforcement 2 anchored in two beads (not shown in the figures). The carcass reinforcement is formed of a single layer of metal cord. The carcass reinforcement 2 is hoop-shaped by a crown reinforcement 4, which is formed radially from the inside out by:

[0092] - a triangular layer 45 formed of non-wound inextensible 9.28 metal cords oriented at an angle equal to 65°,

[0093] - A first working layer 41 formed by non - wound inextensible 11.35 metal cords, the non - wound inextensible 11.35 metal cords being continuous over the entire width of the carcass ply and oriented at an angle equal to 26°,

[0094] - A second working layer 42 formed by non - wound inextensible 11.35 metal cords, the non - wound inextensible 11.35 metal cords being continuous over the entire width of the carcass ply, oriented at an angle equal to 18°, and crossing the metal cords of the first working layer,

[0095] - A protective layer 44 formed by non - wound elastic 6.35 metal cords, the non - wound elastic 6.35 metal cords being continuous over the entire width of the carcass ply and oriented at an angle equal to 18° in the same direction as the metal cords of the second working layer.

[0096] The crown reinforcement itself is covered by a tread 5.

[0097] The tire is inflated to a pressure of 8.5 bar.

[0098] The axial width L of the first working layer 41 41 is equal to 221 mm.

[0099] The axial width L of the second working layer 42 42 is equal to 202 mm.

[0100] The axial width L5 of the tread is equal to 242 mm.

[0101] The maximum axial width L is equal to 300 mm.

[0102] According to the invention, a first rubber compound layer C provides decoupling of the ends of the working crown layers 41 and 42.

[0103] The layer C is defined in the joining region between the two working crown layers 41 and 42 by its thickness, or more precisely by the radial distance d between the ends of layer 42 and layer 41 and the axial width D of layer C between the axial inner end of said layer C and the end of the radially outer working crown layer 42. The radial distance d is equal to 2.8 mm, i.e., approximately 2.1 times the diameter φ2 of the reinforcing element of the working crown layer 42, the diameter φ2 being equal to 1.35 mm. The radial distance D is equal to 19 mm, i.e., approximately 14 times the diameter φ2 of the reinforcing element of the working crown layer 42.

[0104] According to the invention, layer C is made of an elastomeric compound containing pyrolytic carbon black.

[0105] Various tires according to the invention were compared with reference tires of the same size.

[0106] The first tire I1 according to the invention has a layer C made of a compound 1 and a surface layer made of a compound R1.

[0107] The second tire I2 according to the invention has a layer C made of a compound 1 and a surface layer.

[0108] The reference tire T1 differs from the tire I1 according to the invention in the properties of the compound for the layer C, which layers C are made of a compound R1.

[0109] The various compounds used are listed below, and each compound shows the secant modulus of elasticity and the elongation at break at 10% elongation.

[0110] Compound R1 Compound 1 NR 100 100 Carbon black N347 52 Carbon black RCB 60 Antioxidant (6PPD) 1.5 1.5 Stearic acid 0.65 0.9 Zinc oxide 9.3 7.5 Cobalt salt (AcacCo) 1.12 1.12 Sulfur 6.1 4.5 Accelerator DCBS 0.93 0.8 CTP blocker (PVI) 0.25 0.15 <![CDATA[MA 10 (MPa)]]> 10.4 6.1 Elongation at break (%) 280 444

[0111] The values of the components are expressed in phr (parts by weight per hundred parts of elastomer).

[0112] The pyrolysis carbon black (carbon black RCB) contains 20% ash, 1.8% sulfur and 4.5% zinc.

[0113] The carbon black N347 contains 0.5% ash, 1% sulfur and 0% zinc.

[0114] The contents of the various components in the compound I1 other than the carbon black are adjusted according to the knowledge of those skilled in the art so as to obtain similar temperature and curing time conditions for the various tires and to enable comparison of the properties of the tires.

[0115] A first (especially heat - required) durability test is carried out on a testing machine, and each tire rolls in a straight line at a speed equal to the maximum speed rating (or speed index) specified for the tire under an initial load of 4000 kg. In order to shorten the duration of the test, the initial load is gradually increased.

[0116] Other (especially mechanically - required) durability tests are carried out on a testing machine, and a lateral force and a dynamic over - load are applied to the tire in a cyclic manner. The tires according to the invention are tested under the same conditions as those applied to the reference tire.

[0117] The tests thus carried out show that the distances covered by the tires according to the invention and the reference tire are substantially the same in each of these tests.

[0118] Tests were also carried out to characterize the breaking strength of the tire crown reinforcement subjected to impact loads. These tests consisted of running a tire inflated to the recommended pressure and subjected to the recommended load over a cylindrical obstacle or indentor tool, the diameter of which was equal to 1.5 inches (i.e., 38.1 mm), having a hemispherical head and a given height. The trajectory of the tire was adjusted so that the axis of the obstacle corresponded to the position of one of the axially outermost ribs of the tread. The breaking strength was characterized by the critical height of the indentor tool, i.e., the maximum height at which the indentor tool caused complete breakage of the crown reinforcement (i.e., breakage of all crown plies). These values represent the energy required to break the crown blocks. These values are expressed relative to a base number 100 (which corresponds to the value measured for the reference tire T1).

[0119] I1 125 I2 130 Reference T1 100

[0120] These results show that the breaking energy of tires I1 and I2 according to the invention is higher than that of tire T1 in the case of the tread surface being subjected to impact loads.

[0121] Final durability tests were carried out to reproduce driving conditions combining vehicle speed and particularly adverse ground. Thus, these tests reproduced the extreme conditions especially for "heavy-duty load" vehicles of the "site supply" type.

[0122] These final tests included: a phase of driving on a test track at 100 km / h for 2 hours under the load and pressure conditions indicated on the tire, and then a phase of driving on a stony road at 35 km / h for 12 minutes, repeated 25 times.

[0123] The purpose of the phase of driving at low speed on the stony road was to have an adverse effect on durability due to the tread being repeatedly subjected to impact loads.

[0124] The purpose of the phase of driving at high speed on the test track was to raise the temperature of the tire. This makes the tire more sensitive to the effects of repeated impact loads on the tread and promotes the propagation of cracks initiated during the phase of driving on the stony road.

[0125] At the end of the run, the tires were inspected using shearography and peeled so that any damage could be analyzed. This is a visual analysis, allowing a comparison between any cracks and crack propagation. The tires were scored and compared with each other. A score greater than 100 corresponds to a tire with less damage. The most severely damaged tire received a score of 100.

[0126] Fraction I1 110 I2 130 Reference T1 100

[0127] At the end of the run, tires I1 and I2 according to the invention showed a lower degree of damage than the reference tire T1.

[0128] During these final endurance tests, after driving for 2 hours at 100 km / h on a circuit in the first stage, the temperature of the tire at the end of the tread block portion is measured.

[0129] Temperature I1 93℃ I2 90℃ Reference T1 97℃

[0130] These results show that the temperature exhibited by the tire according to the present invention is not actually as high as that of the reference tire.

[0131] It is clearly seen from these tests that the tire according to the present invention can improve the performance in terms of impact load resistance in a satisfactory manner while exhibiting satisfactory durability performance.

Claims

1. A tire (1) comprising a radial carcass reinforcement (2), said tire comprising a crown reinforcement (4), said crown reinforcement (4) comprising two working crown layers (41, 42) having reinforcing elements, said reinforcing elements being inserted between two surface layers of a rubber compound, crossing from one layer to the other, and forming an angle between 10° and 45° with the circumferential direction, said angle being oriented on both sides of the circumferential direction, a rubber compound layer C being arranged between at least the ends of said two working crown layers, said crown reinforcement (4) being radially covered by a tread (5), said tread being connected to two beads (3) via two sidewalls, characterized in that, The rubber compound constituting the layer C contains a composition comprising 50 phr to 70 phr of reinforcing filler, and the reinforcing filler includes at least 20 phr of pyrolytic carbon black.

2. The tire according to claim 1, characterized in that, Relative to the total weight of the pyrolytic carbon black, the ash content of the pyrolytic carbon black ranges from 5 wt% to 30 wt%, preferably less than 25 wt%, more preferably less than 22 wt%, and the ash content is determined by calcination in a platinum dish in a muffle furnace at 825 °C according to the method described in the specification.

3. The tire according to claim 1 or 2, characterized in that, Relative to the total weight of the pyrolytic carbon black, the sulfur content of the pyrolytic carbon black is greater than 1.5 wt%, preferably greater than 2 wt%, and the preferred range is 2.5 wt% to 5 wt%. The sulfur content in the pyrolytic carbon black is determined by a LECO furnace according to the method described in the specification.

4. The tire (1) according to any one of claims 1 to 3, characterized in that, Relative to the total weight of the pyrolytic carbon black, the zinc content of the pyrolytic carbon black is greater than or equal to 2 wt%, and the preferred range is 2.5 wt% to 8 wt%. The zinc content is determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) analysis after calcining the sample and then absorbing the ash in an acidic medium according to the method described in the specification.

5. The tire according to any one of the preceding claims, characterized in that, The layer C is an elastomeric compound, and the elastomeric compound is based on natural rubber or on synthetic polyisoprene mainly having cis-1,4 bonds, and optionally based on at least one other diene elastomer. In the case of a blend, the content of natural rubber or synthetic polyisoprene is present in a major amount relative to the content of one or more other diene elastomers used.

6. The tire (1) according to any one of the preceding claims, characterized in that, In addition to the pyrolytic carbon black, the rubber compound layer C further contains a reinforcing filler composed of: a) Carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr, b) or a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and used in a content between 20 phr and 50 phr, preferably between 30 phr and 40 phr, c) Or a blend of the carbon black described in (a) and the white filler described in (b), where the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

7. The tire (1) according to any one of the preceding claims, characterized in that, At least one surface layer of at least one working tread layer is made of a rubber compound, and the composition of the rubber compound contains 50 phr to 70 phr of reinforcing filler, and the reinforcing filler includes at least 20 phr of pyrolytic carbon black.

8. The tire (1) according to claim 7, characterized in that, The at least one surface layer of at least one working tread layer (41, 42) is an elastomeric compound, and the elastomeric compound is based on natural rubber or on synthetic polyisoprene mainly having cis-1,4 bonds, and optionally based on at least one other diene elastomer. In the case of a blend, the content of natural rubber or synthetic polyisoprene is present in a major amount relative to the content of one or more other diene elastomers used.

9. The tire (1) according to any one of claims 7 and 8, characterized in that, In addition to the pyrolytic carbon black, the at least one surface layer of at least one working tread layer further contains a reinforcing filler composed of: a) Carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr, b) or a white filler of silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and used in a content between 20 phr and 50 phr, preferably between 30 phr and 40 phr, c) Or a blend of the carbon black described in (a) and the white filler described in (b), where the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

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