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 of the at least one inner liner layer constituting the at least one working crown ply 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) carrying heavy loads and traveling at a sustained 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 consisting of at least two superimposed layers formed of threads or cords, the threads 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 with at least one layer called a protection layer, which is formed by reinforcing elements (called elastic reinforcing elements) that are advantageously metallic and extensible. It may also include a layer of metallic threads or cords having low extensibility, which form 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 of parallel threads 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 triangular reinforcement, which hardly deforms under the various stresses it undergoes, and the chafer ply is basically used to absorb the transverse compressive forces applied to all the reinforcing elements in the tire crown area.

[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 direction of travel of the tire.

[0007] The transverse 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] The radial plane or the meridian plane is the plane containing the axis of rotation of the tyre.

[0011] The circumferential midplane or the equatorial plane is the 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 a tensile testing machine of the INSTRON type 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, the combined conditions of travel of such tyres undoubtedly enable an increase in the number of kilometres travelled; on the other hand, the durability of such tyres, in particular the durability of the crown reinforcement, is 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 working 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 layer 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 layer of rubber compound is described in patent application WO 2004 / 076204.

[0018] In order 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] In order to avoid the 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, especially in terms of durability.

[0021] In addition, the use of the tires on heavy-duty vehicles of the "job-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 those skilled in the art, it is also a known practice to increase the number of plies constituting the crown reinforcement, thereby improving the durability of the tire with respect to these impact loads.

[0023] The presence of one or more additional reinforcing 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 be reduced (especially at the shoulders of the tire), for example, it may be reduced under particularly severe driving conditions that combine 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 job-site supply type that is very harsh on the tire, a reduction 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 "job-site supply" type), the durability performance of which with respect to the impact loads suffered by the tread is improved regardless of the nature of the ground and the driving conditions.

[0026] According to the 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 calendered skins of rubber compound, crossing from one ply 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 via two sidewalls to two beads, the rubber compound of at least one calendered skin constituting at least one working crown ply comprising a composition containing from 50 phr to 70 phr of reinforcing filler, said reinforcing filler having 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 contains from 50 phr to 70 phr of reinforcing filler, said reinforcing filler being pyrolytic carbon black. Thus, it should be understood that the composition contains 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 recycling of such a material) of a material comprising at least one carbon-based polymer and carbon black (hereinafter called the material to be pyrolyzed). The physical state of the material to be pyrolyzed provided, whether in the form of powder, granules, strips or any other form, in a crosslinked state or uncrosslinked state, is not important.

[0031] Preferably, the material to be pyrolyzed can be recovered from manufactured articles or products (such as by-products or waste) produced during their manufacture / production; these manufactured articles 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 manufactured articles 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, the raw material of which is the material to be pyrolyzed as defined above. Thus, pyrolytic carbon black differs 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 derived from coal or natural sources.

[0033] The pyrolytic carbon black that can be used within the scope of the present invention differs particularly from known carbon blacks (such as industrial carbon black, especially "furnace black") in that its 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 still 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 in the range of 20 m 2 / g to 200 m 2 / g, more preferably in 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 according to standard ASTM D7854 (2018) at a pressure of 50 MPa is in the range of 30 ml / 100 g to 60 ml / 100 g, more preferably in 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. Before each series of measurements, the platinum dish was pre-determined and the tare weight of the platinum dish was weighed to an accuracy of within 0.1 mg, and the mass was designated as P0. A 5 g sample of pyrolytic carbon black, accurately weighed to within 0.1 mg, was placed in 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 in a muffle furnace heated to 825 °C for 1 h. After 1 h, the platinum dish was removed from the furnace and immediately placed in 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 in a PFA (Perfluoroalkoxy) tube for a HotBlock hot plate. 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 sealed 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 in 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, before analysis by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), the diluted solution was filtered through a 0.45 μm GHP syringe filter. Before analyzing the diluted solution, at least 5 calibration samples 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 samples were prepared by diluting a commercial 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 was analyzed by ICP - AES at a wavelength of λZn = 202.613 nm. For each standard concentration (c), the intensity of the zinc signal IZn was plotted on a curve of IZn = f(c), which corresponds to a calibration line (type y = ax + b). Then, the sample solution (diluted solution) of unknown concentration was measured under the same conditions as the standard sample. The measured intensity was related to the concentration using the previously obtained calibration line. Since the sample and volume were pre - recorded, the concentration [c] was directly obtained by software. 灰分 (in mass %). The zinc concentration [c] in the pyrolytic carbon black was 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 was 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 boats were cleaned and the furnace was calibrated. The boats used for the LECO furnace were pre - cleaned: this involved analyzing an empty boat under the same conditions as the sample. A calibration curve was prepared based on a commercial standard sample called "BBOT" (with a purity greater than 99.99% and ensuring the contents of carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S)). The contents were 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 boats. The standard sample / boat assembly was placed in the combustion furnace and adjusted to 1350 °C under pure oxygen. The combination of the furnace temperature and the analysis flow rate caused the combustion of the sample, and sulfur and / or carbon were released in the form of SO2(g). After 20 s, oxygen began to flow through the lance, thus accelerating the combustion of difficult - to - burn materials. Sulfur and / or carbon in the form of SO2(g) were entrained by the oxygen flow through the infrared detection unit. The software of the instrument plotted a straight line that related the mass of the introduced standard sample to the response (area) observed on the detector. Thus, the calibration line was obtained. After thoroughly cleaning the sampling equipment, approximately 80 ± 5 mg of pyrolytic carbon black was weighed and placed in the boat used for the LECO furnace.

[0047] The area of the SO2 peak observed was related to the concentration through the calibration line. The software of the instrument then calculated the weight % of sulfur in the sample based on the weight of the sample placed in 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 of the working crown ply (expressed in degrees) 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] According to a preferred embodiment of the invention, the rubber compound of the calendered surface layer of the two working crown plies has a composition comprising 50 phr to 70 phr of reinforcing filler, said reinforcing filler having at least 20 phr of pyrolytic carbon black.

[0051] According to a preferred embodiment of the invention, the at least one calendered surface layer of at least one working crown ply of the rubber compound is an elastomeric compound, said elastomeric compound being 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, natural rubber or synthetic polyisoprene being present in a major amount relative to the content of one or more other diene elastomers used.

[0052] Among the diene elastomers that can be used in blend with natural rubber or synthetic polyisoprene mainly having cis-1,4 bonds, mention may be made of preferably polybutadiene (BR) mainly having cis-1,4 bonds, styrene-butadiene copolymer (SBR) in solution or emulsion, butadiene-isoprene copolymer (BIR) and 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 carbonate, tin halide or silicon halide), or elastomers modified by a functionalizing agent such that, for example, by the action of dimethylaminobenzophenone or diethylaminobenzophenone, an oxycarbonyl or carboxyl functional group or an amine functional group is grafted onto the chain or the chain ends. In the case of a blend of natural rubber or synthetic polyisoprene mainly having cis-1,4 bonds with one or more of the above diene elastomers, natural rubber or synthetic polyisoprene is preferably used in a major amount, more preferably in an amount greater than 70 phr.

[0053] Also preferably, in addition to pyrolytic carbon black, the at least one calendered surface layer of at least one working crown ply further comprises a reinforcing filler consisting of:

[0054] a) carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0055] b) or a BET specific surface area of 30 m2 from 260 m² / g to 260 m² / g 2 a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functional groups between 260 m² / g to 260 m² / g, said white filler being selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and being used in a content between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

[0056] 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.

[0057] 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.

[0058] 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, mention may be made of alkoxysilane sulfides of the bis(3-trialkoxysilylpropyl) polysulfide type, in particular bis(3-triethoxysilylpropyl) tetrasulfide sold by Degussa under the name Si69 (pure liquid product) and under the name X50S (solid product (blended 50 / 50 by weight with N330 carbon black)). As an example of a covering agent, mention may be made of fatty alcohols, alkylalkoxysilanes (such as hexadecyltrimethoxysilane or hexadecyltriethoxysilane sold by Degussa under the names Si116 and Si216 respectively), diphenylguanidine, polyethylene glycol or silicone oil optionally modified by OH or alkoxy functional groups. 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 accounts for all of the reinforcing filler, and between 1 / 100 and 20 / 100 when the reinforcing filler consists of a blend of carbon black and transparent filler.

[0059] 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 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 at least partially cover 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 CSDP type fillers described in document No. 24 of the ACS Rubber Division Meeting (Anaheim, California, 6-9 May 1997), and those fillers in patent application EP-A-0799 854.

[0060] 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.

[0061] 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 edges of the tread (especially at the shoulders of the tyre), regardless of the nature of the ground and the driving conditions.

[0062] The inventors consider that these results can be explained by the presence of pyrolytic carbon black used as a filler in at least one calendered skin layer of at least one working crown layer. The inventors have been able to demonstrate that the presence of pyrolytic carbon black in the rubber compound constituting at least one calendered skin layer of at least one working crown layer gives the rubber compound a higher elongation at break value than more common compounds.

[0063] According to an advantageous embodiment of the invention, the axially widest working crown layer is located radially inside another working crown layer.

[0064] The metal element is preferably a steel cord.

[0065] According to a preferred embodiment of the present invention, the reinforcing elements of the working crown ply are inextensible metal cords.

[0066] A preferred embodiment of the present invention also supplements the radially outer side of the crown reinforcement by means of at least one additional layer (referred to as a protection layer) having so-called elastic reinforcing elements, said elastic reinforcing elements being oriented at an angle between 10° and 45° with respect to the circumferential direction, and the direction of said angle being the same as the angle formed by the inextensible elements of the working layer radially adjacent thereto.

[0067] According to any of the above embodiments of the present invention, the crown reinforcement can also be supplemented on the radially inner side between the carcass reinforcement and the radially innermost working layer adjacent to said carcass reinforcement by means of a triangular ply having inextensible metal reinforcing elements made of steel, forming an angle greater than 60° with the circumferential direction, and the direction of said 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

[0068] In the following, other details and advantageous features of the present invention will become apparent from the description of the embodiments of the present invention given with reference to the accompanying drawings, which show a meridional view of a tyre design according to an embodiment of the present invention.

[0069] For easier understanding, the drawings are not drawn to scale. The drawings show only a half view of the tyre, which extends symmetrically about an axis XX', which represents the circumferential median plane or equatorial plane of the tyre. Detailed Description

[0070] In the drawings, the tyre 1 has a size of 295 / 80R 22.5. The tyre 1 includes a radial carcass reinforcement 2 anchored in two beads (not shown in the figures). The carcass reinforcement is formed by a single layer of metal cords. This carcass reinforcement 2 is hoop-shaped by a crown reinforcement 4, which is formed radially from the inside out by:

[0071] - a triangular ply 45 formed by non-wound inextensible 9.28 metal cords oriented at an angle equal to 65°,

[0072] - a first working layer 41 formed by non-wound inextensible 11.35 metal cords, said non-wound inextensible 11.35 metal cords being continuous over the entire width of the ply and oriented at an angle equal to 26°,

[0073] - A second working layer 42 formed of non - wound inextensible 11.35 metal cords, the non - wound inextensible 11.35 metal cords being continuous across the entire width of the carcass ply, oriented at an angle equal to 18°, and crossing the metal cords of the first working layer.

[0074] - A protective layer 44 formed of non - wound elastic 6.35 metal cords, the non - wound elastic 6.35 metal cords being continuous across 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.

[0075] The crown reinforcement itself is covered by the tread 5.

[0076] The tire is inflated to a pressure of 8.5 bar.

[0077] The axial width L of the first working layer 41 41 is equal to 221 mm.

[0078] The axial width L of the second working layer 42 42 is equal to 202 mm.

[0079] The axial width L5 of the tread is equal to 242 mm.

[0080] The maximum axial width L is equal to 300 mm.

[0081] According to the invention, the calendered surface layers of the working crown layers 41, 42 are made of an elastomeric compound containing pyrolytic carbon black.

[0082] Various tires according to the invention were compared with reference tires of the same dimensions.

[0083] Tire I according to the invention has calendered surface layers of the working crown layers 41, 42 made of compound 1.

[0084] The reference tire T1 differs from tire I1 according to the invention in the properties of the compound used for the calendered surface layers of the working crown layers 41, 42, these calendered surface layers being made of compound R.

[0085] The various compounds used are listed below, each compound showing the secant modulus of elasticity and the elongation at break at 10% elongation.

[0086]

[0087]

[0088] The values of the components are expressed in phr (parts by weight per hundred parts of elastomer).

[0089] The pyrolysis carbon black (carbon black RCB) contains 20% ash, 1.8% sulfur, and 4.5% zinc.

[0090] The carbon black N347 contains 0.5% ash, 1% sulfur, and 0% zinc.

[0091] The contents of the various components other than carbon black in the blend I1 are adjusted according to the knowledge of those skilled in the art, so as to obtain similar temperature and curing time conditions for various tires, and the properties of the tires can be compared.

[0092] A first (especially heat - required) durability test is carried out on a testing machine. Each tire rolls straight 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.

[0093] Other (especially mechanically - required) durability tests are carried out on a testing machine, applying lateral forces and dynamic over - loads 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 tires.

[0094] The tests thus carried out show that the distances covered by the tires according to the invention and the reference tires are substantially the same in each of these tests.

[0095] Tests were also carried out to characterize the breaking strength of the tire crown reinforcement subjected to impact loads. These tests include making a tire inflated to the recommended pressure and subjected to the recommended load travel on a cylindrical obstacle or indentation tool, the diameter of the obstacle or indentation tool being equal to 1.5 inches (i.e., 38.1 mm), having a hemispherical head and a given height. The trajectory of the tire is adjusted so that the axis of the obstacle corresponds to the position of one of the axially outermost ribs of the tread. The breaking strength is characterized by the critical height of the indentation tool, which is the maximum height at which the indentation tool causes a complete break of the crown reinforcement (i.e., all crown layers are broken). These values represent the energy required to break the crown block. These values are expressed relative to a base number 100 (which corresponds to the value measured for the reference tire T1).

[0096] I 105 Reference T1 100

[0097] These results show that the breaking energy of the tire I according to the invention during the impact on the tread surface is higher than that of the tire T1.

[0098] Final durability tests were carried out to reproduce the driving conditions combining vehicle speed and particularly harsh ground. Therefore, these tests reproduce the extreme conditions especially for "heavy - duty load" vehicles of the "site - supply" type.

[0099] These final tests include a phase of driving for 2 hours on a circular track at 100 km / h under the load and pressure conditions indicated on the tyre, followed by a phase of driving for 12 minutes on a stony road at 35 km / h, repeated 25 times.

[0100] The purpose of the phase of driving at low speed on a stony road is to have an adverse effect on durability due to the repeated impact loads on the tread.

[0101] The purpose of the phase of driving at high speed on a circular track is to raise the temperature of the tyre. This makes the tyre 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 a stony road.

[0102] At the end of the run, the tyre is inspected using shearography and peeled so that any damage can be analysed. This is a visual analysis, allowing a comparison to be made between any cracks and crack propagation. The tyres are scored and compared with each other. A score greater than 100 corresponds to a tyre with less damage. The most severely damaged tyre receives a score of 100.

[0103] Fraction: I 120 Reference T1 100

[0104] At the end of the run, tyre I according to the invention exhibits a lower degree of damage than reference tyre T1.

[0105] During these final durability tests, after driving for 2 hours on a circular track at 100 km / h in the first phase, the temperature of the tyre is measured at the end of the crown block.

[0106] Temperature I 94℃ Reference T1 97℃

[0107] These results show that the temperature exhibited by the tyre according to the invention is not actually as high as that of the reference tyre.

[0108] It is clear from these tests that the tyre according to the invention is capable of improving 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 plies (41, 42) having reinforcing elements, said reinforcing elements being inserted between two calendered surface layers of rubber compound, crossing from one ply 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 plies, 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 of at least one calendered skin layer constituting at least one working tread layer contains a composition comprising 50 phr to 70 phr of reinforcing filler, and the reinforcing filler has 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 analyzing the ash absorbed in an acidic medium after calcining the sample and by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) according to the method described in the specification.

5. The tire according to any one of the preceding claims, characterized in that, The at least one skin layer of at least one working tread layer is an elastomer compound, the elastomer compound is based on natural rubber, or based 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, natural rubber or synthetic polyisoprene is present in a major content relative to the content of one or more other diene elastomers used.

6. The tyre (1) according to any one of the preceding claims, characterised in that In addition to the pyrolytic carbon black, the at least one calendered skin layer of at least one working tread layer of the rubber compound further comprises a reinforcing filler consisting 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), wherein the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

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