Radial tires with reinforced tire carcasses.

Abstract

DEPCT68 This invention pertains to a tire (1) with a reinforced radial carcass which is composed of: Double-layer front tire operation (41,42) According to this invention, the rubber compound forming the C-layer consists of the following components: This consists of 50 to 70 phr of reinforcing filler, which includes at least 20 phr. Carbon black obtained from pyrolysis;

Description

TIRE WITH IMPROVED ENDURANCE PERFORMANCE

[0001] The present invention relates to a tire, with a radial carcass reinforcement and more particularly a tire intended to equip vehicles carrying heavy loads and traveling at high speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] Generally speaking, in heavy goods vehicle type tires, the carcass reinforcement is anchored on both sides in the bead area and is surmounted radially by a crown reinforcement consisting of at least two layers, superimposed and formed of parallel wires or cables in each layer and crossed from one layer to the next, making angles of between 10° and 45° with the circumferential direction. Said working layers, forming the working reinforcement, may also be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcement elements, called elastic.It may also comprise a layer of low-extensibility metal wires or cables forming an angle of between 45° and 90° with the circumferential direction, this ply, called the triangulation ply, being radially located between the carcass reinforcement and the first crown ply, called the working ply, formed of parallel wires or cables having angles at most equal to 45° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which, under the various stresses to which it is subjected, exhibits little deformation, the triangulation ply having the essential role of absorbing the transverse compression forces to which all the reinforcing elements are subjected in the area of ​​the crown of the tire.

[0003] Cables are said to be inextensible when said cables exhibit, under a tensile force equal to 10% of the breaking force, a relative elongation at most equal to

[0004] Cables are said to be elastic when said cables exhibit, under a tensile force equal to the breaking load, a relative elongation at least equal to 3% with a maximum tangent modulus less than 150 GPa.

[0005] Circumferential reinforcing elements are reinforcing elements which make angles with the circumferential direction in the range + 2.5°, - 2.5° around 0°.

[0006] The circumferential direction of the tire, or longitudinal direction, is the direction tangent to the periphery of the tire and defined by the rolling direction of the tire.

[0007] The transverse or axial direction of the tire is parallel to the tire's axis of rotation.

[0008] The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it.

[0009] The tire's axis of rotation is the axis around which it rotates during normal use.

[0010] A radial or meridian plane is a plane that contains the tire's axis of rotation.

[0011] The circumferential median plane, or equatorial plane, is a plane perpendicular to the tire's axis of rotation and which divides the tire into two halves.

[0012] The "modulus of elasticity" of a rubber compound is defined as the secant modulus of extension at 10% elongation and at room temperature.

[0013] For rubber compounds, the secant modulus of elasticity at 10% elongation is the elastic modulus of the compound measured in a uniaxial tensile experiment at an elongation value of 0.1 (i.e. 10% elongation, expressed as a percentage). A constant uniaxial tensile speed is imposed on the specimen, and its elongation and force are measured. The measurement is carried out using an INSTRON tensile testing machine at a temperature of 23°C and a relative humidity of 50% (ISO 23529 standard). The measurement conditions and The operating methods for the results to determine the elongation and the stress are as described in the standard NF ISO 37: 2012-03. The stress is determined for an elongation of 0.1 and the secant modulus of elasticity is calculated at 10% elongation by calculating the ratio of this stress value to the elongation value. A person skilled in the art will be able to choose and adapt the dimensions of the test piece according to the quantity of accessible and available mixture, particularly in the case of taking samples from a finished product such as a tire.

[0014] Some current tires, called "road tires", are designed to travel at high speeds and on increasingly long journeys, due to the improvement of the road network and the growth of the motorway network throughout the world. All the conditions under which such a tire is called upon to travel undoubtedly allow an increase in the number of kilometers traveled, the wear of the tire being less; on the other hand, the endurance of the latter and in particular of the crown reinforcement is penalized.

[0015] There are indeed constraints at the level of the crown reinforcement and more particularly shear constraints between the crown layers, combined with a significant increase in the operating temperature at the ends of the axially shortest crown layer, which result in the appearance and propagation of cracks in the rubber at the said ends.

[0016] In order to improve the endurance of the crown reinforcement of the type of tire studied, solutions relating to the structure and quality of the layers and / or profiles of rubber compounds which are arranged between and / or around the ends of the plies and more particularly the ends of the axially shortest ply have already been provided.

[0017] It is known in particular to introduce a layer of rubber mixture between the ends of the working layers to create a decoupling between said ends to limit shear stresses. Such decoupling layers must, however, have very good cohesion. Such layers of rubber mixtures are for example described in patent application WO 2004 / 076204.

[0018] Patent FR 1 389 428, to improve the resistance to degradation of rubber compounds located near the edges of the crown reinforcement, recommends the use, in combination with a low hysteresis tread, of a rubber profile covering at least the sides and marginal edges of the crown reinforcement and consisting of a low hysteresis rubber compound.

[0019] Patent FR 2 222 232, to avoid separations between crown reinforcement plies, teaches coating the ends of the reinforcement in a rubber mattress, the Shore A hardness of which is different from that of the tread surmounting said reinforcement, and greater than the Shore A hardness of the rubber mixture profile arranged between the edges of the crown reinforcement plies and the carcass reinforcement.

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

[0021] In addition, the use of tires on heavy-duty vehicles of the "site approach" type leads to the tires being subjected to shocks when driving on stony ground. These shocks are of course detrimental to performance in terms of endurance.

[0022] It is also known to those skilled in the art to increase the number of plies constituting the crown reinforcement to improve the endurance of the tire with regard to such impacts.

[0023] The presence of one or more layers of additional reinforcing elements leads to a greater mass of the tire and higher tire manufacturing costs.

[0024] The inventors have notably demonstrated that when driving on surfaces that are extremely demanding for tires, the endurance performance of such tires could be degraded, for example in driving conditions combining the speed of the vehicle, the load carried by the tire and the nature of the ground, which is particularly aggressive, particularly at the shoulders of the tire. It is indeed possible to observe a degradation of the endurance performance, for example, when driving at relatively high speed on construction site approach type surfaces that are very aggressive for the tire.

[0025] The inventors have thus set themselves the mission of providing tires for "Heavy Goods" vehicles, for example of the "construction site approach" type, whose endurance performance with regard to impacts suffered on the tread is improved whatever the nature of the ground and the driving conditions.

[0026] This object is achieved according to the invention by a tire comprising a radial carcass reinforcement, said tire comprising a crown reinforcement comprising two working crown layers, each formed of reinforcing elements inserted between two calendering layers of rubber mixture crossed from one layer to the other making angles of between 10° and 45° with the circumferential direction, said angles being oriented on either side of the circumferential direction, a layer C of rubber mixture being arranged between at least the ends of said at least two working crown layers, the crown reinforcement being radially capped with a tread, said tread being joined to two beads by means of two sidewalls, the rubber mixture constituting said layer C comprising a composition comprising 50 to 70 phr of reinforcing fillers, including at least 20 phr of pyrolysis carbon black.

[0027] The expression "part by weight per hundred parts by weight of elastomer" (or pce) means the part 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 to 70 phr of reinforcing fillers, the reinforcing fillers being pyrolysis carbon black. It must then be understood that the composition comprises pyrolysis carbon black as the only reinforcing fillers (the composition therefore does not comprise inorganic reinforcing fillers and other organic reinforcing fillers).

[0029] The reinforcing fillers may be as described below.

[0030] For the purposes of the present invention, the term "pyrolysis carbon black" means a carbon black resulting from a process of pyrolysis of a material comprising at least one carbon polymer and one carbon black, hereinafter the material to be pyrolyzed, for example in the context of recycling such a material. The physical state in which the material is present to be pyrolyzed is indifferent, whether in the form of powder, granules, strips, or any other form, in the crosslinked or non-crosslinked state.

[0031] Preferably, the material to be pyrolyzed may be recovered from manufactured articles or products generated during their manufacture / production (such as by-products or scraps); these manufactured articles may be chosen from the group consisting of tires, solid tires, industrial conveyor belts, transmission belts, rubber seals, rubber hoses, shoe soles and windshield wipers. Even more preferably, the pyrolysis carbon black that can be used in the context of the present invention is a carbon black obtained from a pyrolysis process in which the material to be pyrolyzed is derived from manufactured articles chosen from the group consisting of tires and solid tires.

[0032] Pyrolysis in the context of the present invention means any type of thermal decomposition in the absence of oxygen and whose raw material is the material to be pyrolyzed as defined above. Pyrolysis carbon blacks are therefore distinguished from so-called industrial and / or ASTM grade carbon blacks in that the carbon raw material used for pyrolysis is a material comprising at least one carbon polymer and one carbon black and not materials derived from petroleum fractions or from coal or from oils of natural origin.

[0033] The pyrolysis carbon blacks that can be used in the context of the present invention are distinguished from known carbon blacks such as industrial carbon blacks, in particular so-called “furnace” carbon blacks, in particular by a higher ash content than that of said so-called “furnace” carbon blacks. The ash content of so-called “furnace” carbon blacks is less than 1% by weight relative to the total weight of the so-called “furnace” carbon black.

[0034] Preferably, the pyrolysis carbon black usable in the context of the present invention has an ash content ranging from 5 to 30% by weight, more preferably less than 25% by weight, more preferably less than 22% by weight, relative to the total weight of the pyrolysis carbon black.

[0035] Preferably, the pyrolysis carbon black usable in the context of the present invention has a sulfur content greater than 1.5% by weight, preferably greater than 2% by weight, and more preferably ranging from 2.5 to 5% by weight, relative to the total weight of the pyrolysis carbon black.

[0036] The sulfur content of so-called “furnace” carbon blacks is less than 1.2% by weight relative to the total weight of the so-called “furnace” carbon black.

[0037] Preferably, the pyrolysis carbon black usable in the context of the present invention has a zinc content greater than or equal to 2% by weight, preferably ranging from 2.5 to 8% by weight, relative to the total weight of the pyrolysis carbon black.

[0038] The zinc content of so-called “furnace” carbon blacks is almost zero and a fortiori less than 0.5% by weight relative to the total weight of the so-called “furnace” carbon black.

[0039] Preferably, the pyrolysis carbon black usable in the context of the present invention has a specific surface area STSA measured according to the ASTM D 6556-2021 standard within a range from 20 to 200 m 2 / g, more preferably ranging from 30 to 90 m 2 / g.

[0040] Preferably, the pyrolysis carbon black usable in the context of the present invention has a void volume measured according to standard ASTM D7854 (2018) and at a pressure of 50 MPa within a range from 30 to 60 ml / 100g, more preferably from 35 to 55 ml / 100g.

[0041] The ash content is determined by calcination in platinum capsules in a muffle furnace at 825°C according to the following protocol. A capsule is previously identified before each series of measurements and is tared to the nearest 0.1 mg and the mass is noted PO. In the capsule, 5 g of pyrolysis carbon black sample are introduced and weighed precisely to the nearest 0.1 mg; this mass is noted PL The capsule and its contents are pre-calcined using a Bunsen burner until fumes appear and the product ignites. Once the product has completely burned, the capsule and its contents are introduced into a muffle furnace heated to 825°C for 1 h. After 1 h, the capsule is removed from the furnace and immediately placed in a desiccator at room temperature. When the capsule and the ash have returned to room temperature ambient temperature, the capsule is weighed again to obtain the mass P2. Finally, it is possible to obtain the ash content (% ash) using the formula below: % ash 100

[0042] The zinc content in the pyrolysis carbon black is determined after calcining the sample, then recovering the ash in an acid medium and assaying by ICP-AES (inductively coupled plasma atomic emission spectroscopy). The ash is obtained by carrying out the above protocol. Approximately 100 mg of ash (test sample) is taken and placed in a PFA (perfluoroalkoxy) tube for a HotBlock hot plate. 8 mL of 37% concentrated hydrochloric acid, 3 mL of 65% concentrated nitric acid and 0.5 mL of 40% hydrofluoric acid are then added. The tube is closed with its cap and heated at 130°C for 2 hours. After cooling, the contents are then transferred using ultrapure water into a 100 mL PTFE (polytetrafluoroethylene) volumetric flask already containing 2 g of boric acid (to neutralize the hydrofluoric acid). The volume is topped up with ultrapure water to the mark.The solution obtained is diluted by 100, by taking 1 mL in a 100 mL PFTE flask, previously containing 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. This diluted solution is then filtered through a 0.45 pm GHP syringe filter before being analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Before analyzing the diluted solution, at least 5 standards are analyzed by ICP-AES at zinc concentrations of 0, 0.5, 1, 2 and 5 mg / L. These standards were prepared in 100 mL volumetric flasks, by diluting a certified commercial solution to a zinc concentration of 1 g / L.

[0043] These volumetric flasks 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 solutions are analyzed by ICP-AES at a wavelength of XZn = 202.613 nm. For each standard concentration (c), the intensity of the zinc signal IZn is plotted on a graph IZn = f(c), which corresponds to the calibration line (of type y = ax + b). The sample solution (diluted solution) of unknown concentration is then measured under the same conditions as the standards. The measured intensity is related to the concentration using the calibration line obtained previously. We thus obtain the concentration [c] ce ndres in % by mass directly by the software, because the test portion and volume have been previously recorded. The zinc concentration in the pyrolysis black [c] no ir in mass % is obtained by the following equation: [c] œ ir = [c]œn* es ♦ 100 * % ash

[0044] The determination of the sulfur content in pyrolysis carbon blacks is carried out by LECO furnace. LECO sulfur analyzers are designed to measure, in particular, the sulfur content in organic and / or inorganic materials by combustion and non-dispersive infrared detection. Before measuring the sulfur content on the sample, the boats are cleaned and the furnace calibrated. The boats for LECO furnaces are previously cleaned: this involves analyzing the empty boat, under the same conditions as the samples. The preparation of the calibration curve is done from a commercial standard called "BBOT" whose purity is greater than 99.99% and whose carbon (C), hydrogen (H), nitrogen (N), oxygen (O) and sulfur (S) content is guaranteed. This content is as follows: C%: 72.52; H% 6.09; N% 6.51; 0% 7.43 and S% 7.44. Approximately 10 ± 3, 20 ± 3 and 40 ± 3 mg of BBOT are weighed exactly in a pod.The standard / boat assembly is introduced into the combustion furnace, regulated at 1350 C under pure oxygen. The combination of the furnace temperature and the analysis flow rate causes the combustion of the sample and the release of sulfur and / or carbon in the form of SO2(g). After a time of 20 s, oxygen begins to flow through the "lance" to accelerate the combustion of difficult-to-burn materials. The sulfur and / or carbon, in the form of SO2(g), are carried by an oxygen flow through the infrared detection cells. The instrument software plots a straight line connecting the mass of standard introduced and the observed response (area) on the detector. This gives a calibration straight line. After carefully cleaning the sampling equipment, approximately 80 ± 5 mg of pyrolysis carbon black is weighed and introduced into a LECO furnace boat.

[0045] The observed SO2 peak area is related to the concentration using the calibration line. The instrument software then calculates the mass % of sulfur in the sample using the mass of the sample introduced into the basket.

[0046] Pyrolysis carbon blacks are marketed, for example, by the company BlackBear under the reference “BBCT30” or by the company Scandinavian Enviro Systems under the reference “P550”.

[0047] The angles of the working crown layers, expressed in degrees, are measured on a section of the tire. According to the invention, the angle measurements are made at the circumferential median plane. These measurements can also be made by radiography.

[0048] The rubber compound layer C allows for decoupling of the said working crown layers in order to distribute the shear stresses over a greater thickness.

[0049] For the purposes of the invention, working crown layers are said to be coupled if the respective reinforcing elements of each of the layers are separated radially by a distance less than the average diameter of the circle circumscribed by the reinforcing elements, said rubber thickness being measured radially between the respectively radially upper and lower generatrices of said reinforcing elements.

[0050] The average diameter of the circle circumscribed by the reinforcing elements is defined as the average diameter of the circles circumscribed by the reinforcing elements of each of the working crown layers.

[0051] According to a preferred embodiment of the invention, the layer C of rubber mixture is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other diene elastomer(s) used.

[0052] Among the diene elastomers that can be used in blending with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 chains, we can cite a polybutadiene (BR) preferably with a majority of cis-1,4 chains, a styrene-butadiene copolymer (SBR) solution or emulsion, a butadiene-isoprene copolymer (BIR) or even a styrene-butadiene-isoprene terpolymer (SBIR). These Elastomers may be elastomers modified during polymerization or after polymerization by means of branching agents such as divinylbenzene or star-forming agents such as carbonates, halotins, halosilicones or even by means of functionalizing agents leading to grafting onto the chain or at the end of the chain of oxygenated carbonyl, carboxyl functions or even an amine function such as for example by the action of dimethyl or diethylamino benzophenone. In the case of blends of natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains with one or more of the diene elastomers mentioned above, the natural rubber or synthetic polyisoprene is preferably used at a majority rate and more preferably at a rate greater than 70 pce.

[0053] Also preferably, the layer C of rubber mixture, in addition to the pyrolysis carbon black, comprises a reinforcing filler consisting of: a) either carbon black used at a rate of between 20 and 50 phr, and preferably between 30 and 40 phr, b) or a white filler of silica and / or alumina type comprising SiOH and / or A1OH surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates or even carbon blacks modified during or after synthesis with a BET specific surface area of ​​between 30 and 260 m 2 / g used at a rate of between 20 and 50 pce, and preferably between 30 and 40 pce, c) or by a blend of carbon black described in (a) and a white filler described in (b), in which the overall filler rate is between 20 and 50 pce, and preferably between 30 and 40 pce.

[0054] The BET specific surface measurement is carried out according to the method of BR.UNAUER, EMMET and TELLER described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938, corresponding to the NFT 45007 standard of November 1987.

[0055] In the case of using a clear filler or white filler, it is necessary to use a coupling and / or covering agent chosen from agents known to those skilled in the art. Examples of preferred coupling agents include sulfurized alkoxy silanes of the bis-(3-trialkoxysilylpropyl) polysulfide type, and among these- in particular bis-(3-triethoxysilylpropyl) tetrasulfide marketed by DEGUSSA under the names Si69 for the pure liquid product and X50S for the solid product (50 / 50 blend by weight with black N330). Examples of covering agents include a fatty alcohol, an alkylalkoxysilane such as a hexadecyltrimethoxy or triethoxysilane respectively marketed by DEGUSSA under the names Sil 16 and Si216, diphenylguanidine, a polyethylene glycol, a silicone oil optionally modified by means of OH or alkoxy functions. The covering and / or coupling agent is used in a weight ratio relative to the filler of > 1 / 100 and < 20 / 100, and preferably between 2 / 100 and 15 / 100 when the light filler represents the entire reinforcing filler and between 1 / 100 and 20 / 100 when the reinforcing filler consists of a blend of carbon black and light filler.

[0056] As other examples of reinforcing fillers having the morphology and the SiOH and / or A1OH surface functions of the silica and / or alumina type materials previously described and which can be used according to the invention as a partial or total replacement for these, mention may be made of carbon blacks modified either during the synthesis by adding a silicon and / or aluminum compound to the furnace feed oil or after the synthesis by adding, to an aqueous suspension of carbon black in a sodium silicate and / or aluminate solution, an acid so as to at least partially cover the surface of the carbon black with SiOH and / or A1OH functions. As non-limiting examples of this type of carbon fillers with SiOH and / or A1OH functions on the surface, we can cite the CSDP type fillers described in Conference No. 24 of the ACS Meeting, Rubber Division, Anaheim, California, May 6-9, 1997 as well as those of patent application EP-A-0 799 854.

[0057] When a clear filler is used as the sole reinforcing filler, the hysteresis and cohesion properties are obtained by using a precipitated or pyrogenic silica, or a precipitated alumina or an aluminosilicate with a BET specific surface area of ​​between 30 and 260 m 2 / g. Non-limiting examples of this type of filler include silicas 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.

[0058] The results obtained with tires in accordance with the invention have effectively demonstrated that the performance in terms of endurance can be improved, whatever the nature of the ground and the driving conditions. The endurance properties of the crown of the tire, particularly with regard to impacts appearing on the edge of the tread, in particular at the shoulders of the tire, are improved whatever the nature of the ground and the driving conditions.

[0059] The inventors believe that these results can be interpreted by the presence of pyrolysis black used as a filler within layer C. The inventors were able to demonstrate that the presence of pyrolysis black in the rubber compound constituting layer C gives it higher elongation at break values ​​than with more usual compounds. Usually, during impacts comparable to those observed when driving on stony ground, more specifically impacting the shoulders of the tire, the rupture of reinforcing elements, if it occurs, is observed on the radially innermost layer and more specifically at its ends. These findings seem to indicate that in the face of this type of attack, the presence of pyrolysis black in the rubber compound constituting layer C makes it possible to improve the endurance performance of the tire.

[0060] Preferably, the thickness of the layer C of rubber mixture, measured at the end of the narrowest working crown layer of the two working crown layers considered, will preferably be between 30% and 80% of the overall thickness of the rubber mixture between the cable generators of the two working crown layers respectively: a thickness of less than 30% not allowing conclusive results to be obtained, and a thickness of more than 80% being useless with regard to improving the resistance to separation between layers and disadvantageous from a cost point of view.

[0061] More preferably, the axial width D of the rubber mixture layer C between the axially innermost end of said rubber mixture layer C and the axially narrowest end of the working crown layer is such that: 3.(|)2 < D < 25 ,(|)2 with (|)2, diameter of the reinforcing elements of the axially narrowest working crown layer. Such a relationship defines an engagement zone between the rubber compound layer C and the axially narrowest working crown layer. Such an engagement below a value equal to three times the diameter of the reinforcing elements of the axially narrowest working layer may not be sufficient to obtain decoupling of the working crown layers, in particular to obtain attenuation of the stresses at the end of the axially narrowest working crown layer. A value of this engagement greater than twenty times the diameter of the reinforcing elements of the axially narrowest working layer may lead to too great a reduction in the drift stiffness of the tire crown reinforcement.

[0062] Preferably, the axial width D of the rubber mixture layer C between the axially innermost end of said rubber mixture layer C and the axially narrowest end of the working crown layer is greater than 5 mm.

[0063] The invention also preferably provides that the thickness of the layer of rubber mixture C, at the axially outer end of the axially narrower working crown layer, has a thickness such that the radial distance d between the two working crown layers, separated by the layer of rubber mixture C, satisfies the relationship: 3 / 5.(|)2 < d < 5.(|)2 with (|)2, diameter of the reinforcing elements of the axially narrowest working crown layer.

[0064] The distance d is measured from cable to cable, i.e. between the cable of a first working layer and the cable of a second working layer. In other words, this distance d encompasses the thickness of the rubber compound layer C and the respective thicknesses of the calendering rubber compounds, radially outside the cables of the radially inner working layer and radially inside the cables of the radially outer working layer.

[0065] The various thickness measurements are taken on a meridian section of a tire, the tire therefore being in an uninflated state.

[0066] According to an advantageous embodiment of the invention, the axially widest working crown layer is radially inside the other working crown layers.

[0067] According to an alternative embodiment of the invention, at least one calendering layer of at least one working crown layer is made up of a rubber mixture comprising a composition comprising 50 to 70 phr of reinforcing fillers, including at least 20 phr of pyrolysis carbon black.

[0068] According to a preferred embodiment of this variant of the invention, the rubber mixture of the calendering layers of said two working crown layers comprises a composition comprising 50 to 70 phr of reinforcing fillers, including at least 20 phr of pyrolysis carbon black.

[0069] The inventors thus note that the rubber mixtures based on pyrolysis black from the calendering of the working crown layers associated with the mixtures of layer C, in accordance with the invention according to this variant embodiment of the invention, lead to a conservation, or even an improvement, of the endurance performance of the tire in an even more marked manner.

[0070] According to a preferred embodiment of this variant of the invention, said at least one calendering layer of at least one working crown layer is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other or other diene elastomers used.

[0071] Also preferably, said at least one calendering layer of at least one working crown layer, in addition to the pyrolysis carbon black, comprises a reinforcing filler consisting of: a) either carbon black used at a rate of between 20 and 50 pce, and preferably between 30 and 40 pce, b) either by a white filler of silica and / or alumina type comprising SiOH and / or A10H surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates or even carbon blacks modified during or after synthesis with a BET specific surface area of ​​between 30 and 260 m 2 / g used at a rate of between 20 and 50 pce, and preferably between 30 and 40 pce, c) or by a blend of carbon black described in (a) and a white filler described in (b), in which the overall filler rate is between 20 and 50 pce, and preferably between 30 and 40 pce.

[0072] According to one embodiment of the invention, the elastomeric mixture constituting said at least one calendering layer of at least one working crown layer is identical to the elastomeric mixture of layer C, arranged between at least the ends of said two working crown layers.

[0073] The metal elements are preferably steel cables.

[0074] According to a preferred embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metal cables.

[0075] A preferred embodiment of the invention also provides that the crown reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented relative to the circumferential direction with an angle of between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

[0076] According to any of the embodiments of the invention mentioned above, the crown reinforcement can also be completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 60° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0077] Other advantageous details and characteristics of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to the figure which represents a meridian view of a diagram of a tire according to an embodiment of the invention.

[0078] The figure is not drawn to scale to simplify understanding. The figure represents only a half-view of a tire that extends symmetrically about the XX' axis, which represents the circumferential median plane, or equatorial plane, of a tire.

[0079] In the figure, the tire 1 is of size 295 / 80 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads, not shown in the figure. The carcass reinforcement is formed of a single layer of metal cables. This carcass reinforcement 2 is hooped by a crown reinforcement 4, formed radially from the inside to the outside: of a triangulation layer 45 formed of inextensible metal cables 9.28 not hooped, oriented at an angle equal to 65°, of a first working layer 41 formed of inextensible metal cables 11.35 not hooped, continuous over the entire width of the ply, oriented at an angle equal to 26°, of a second working layer 42 formed of inextensible metal cables 11.35 not hooped, continuous over the entire width of the ply, oriented at an angle equal to 18° and crossed with the metal cables of the first working layer, of a protective layer 44 formed of elastic metal cables 6.35 unfretted, continuous over the entire width of the sheet, oriented at an angle equal to 18° in the same direction as the metal cables of the second working layer.

[0080] The crown frame itself is topped with a tread 5.

[0081] The tire is inflated to a pressure of 8.5 bars.

[0082] The axial width L 41 of the first working layer 41 is equal to 221 mm.

[0083] The axial width L 42 of the second working layer 42 is equal to 202 mm.

[0084] The axial width of the L5 tread is 242 mm.

[0085] The maximum axial width L is equal to 300 mm.

[0086] According to the invention, a first layer of rubber mixture C decouples the ends of the working crown layers 41 and 42.

[0087] The engagement zone of the layer C between the two working crown layers 41 and 42 is defined by its thickness or more precisely the radial distance d between the end of the layer 42 and the layer 41 and by the axial width D of the layer C between the axially 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 (|)2 of the reinforcing elements of the working crown layer 42, the diameter (|)2 being equal to 1.35 mm. The axial distance D is equal to 19 mm, i.e. approximately 14 times the diameter (|)2 of the reinforcing elements of the working crown layer 42.

[0088] According to the invention, layer C consists of an elastomeric mixture comprising a pyrolysis black.

[0089] Different tires according to the invention are compared with reference tires of the same size.

[0090] First tires II according to the invention comprise a layer C made up of the mixture 1 and calendering layers made up of the mixture RI.

[0091] Second tires 12 according to the invention comprise a layer C and calendering layers made of the mixture 1.

[0092] The reference tires T1 differ from the tires II according to the invention by the nature of the mixtures of layer C, these being made up of the mixture RI.

[0093] The different mixtures used are listed below, expressing for each the secant modulus of elasticity at 10% elongation, the elongation at break.

[0094] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0095] Pyrolysis carbon black, RCB black, contains 20% ash, 1.8% sulfur and 4.5% zinc.

[0096] Carbon black N347 contains 0.5% ash, 1% sulfur and 0% zinc.

[0097] The contents of the various constituents, other than carbon black, are adapted according to the knowledge of those skilled in the art in mixture II to obtain similar temperature and curing time conditions for the different tires and to be able to compare the properties of the tires.

[0098] Initial endurance tests, particularly thermally demanding, were carried out on a test machine requiring each of the tires to run in a straight line at a speed equal to the maximum speed index prescribed for the said tire (speed index) under an initial load of 4000 kg, gradually increased to reduce the duration of the test.

[0099] Other endurance tests, particularly demanding mechanically, were carried out on a test machine cyclically imposing a transverse force and a dynamic overload on the tires. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires.

[0100] The tests thus carried out showed that the distances covered during each of these tests are substantially identical for the tires according to the invention and the reference tires.

[0101] Tests to characterize the breaking strength of a tire crown reinforcement subjected to impacts were also carried out. These tests consist of rolling a tire, inflated to a recommended pressure and subjected to a recommended load, over a cylindrical obstacle or indenter with a diameter equal to 1.5 inches, or 38.1 mm, with a hemispherical head, and of a determined 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 on the tread. The breaking strength is characterized by the critical height of the indenter, that is to say the maximum height of the indenter resulting in a total rupture of the crown reinforcement, that is to say the rupture of all the crown layers. The values ​​express the energy necessary to obtain the rupture of the crown block.The values ​​are expressed from a base of 100 corresponding to the value measured for the TL reference tire.

[0102] These results show that the breaking energy during an impact on the surface of the tread of tires II and 12 according to the invention is greater than that of tire T1.

[0103] Final endurance tests aimed at reproducing driving conditions combining vehicle speed and particularly aggressive ground conditions have been carried out. carried out. These tests thus reproduce extreme conditions, particularly for “heavy goods vehicle” vehicles of the “site approach” type.

[0104] These latest tests consist of reproducing twenty-five times a 2-hour driving phase at 100 km / h on a circuit under the load and pressure conditions indicated on the tire followed by a 12-minute driving phase at 35 km / h on a stony track.

[0105] The low-speed rolling phase on a stony track is intended to penalize endurance following repeated impacts on the tread.

[0106] The purpose of running at high speed on a circuit is to increase the temperature of the tire. This makes the tire more sensitive to the effects of repeated impacts on the tread and promotes the propagation of cracks initiated during running on stony tracks.

[0107] At the end of the run, the tires are inspected using shearography and dissected to analyze any damage. This is a visual analysis that allows for comparison of any cracks and their propagation. The tires are rated and compared with each other. A score above 100 corresponds to a less damaged tire. A value of 100 is assigned to the most damaged tire.

[0108] At the end of the rolling, the tires according to the invention II and 12 present less extensive damage than the reference tires TL

[0109] During these last endurance tests, the temperature of the tires at the ends of the crown block was measured following the first phase of running for 2 hours at 100 km / h on the circuit.

[0110] These results show that the tires according to the invention actually have lower temperatures than the reference tires.

[0111] These tests show that the tires according to the invention make it possible to improve performance in terms of impact resistance in a satisfactory manner while presenting satisfactory endurance performance.

Claims

DEPCT681. A tire (1) which is incorporated with radial carcass reinforcement (2), such tire which is incorporated with tread reinforcement (4) which is composed of two working layers of reinforcement elements (41,42) which are inserted between two skim layers of rubber compound and cross from one layer to another forming an angle between 10 and 45 degrees to the circumferential direction, such angle which is directed on either side of the circumferential direction, layer C of rubber compound which is arranged between at least the ends of such two working layers, the tread reinforcement (4) is radially fitted over the tread (5), such tread which is connected to two inner rims of the outer tire (3) by two side walls, which is characterized by the rubber compound forming such layer C being composed of elements which contain 50 to 70 phr of reinforcement filler, including at least 20 phr of pyrolysis carbon black.The tires under claim 1 are characterized by pyrolysis-derived carbon black having an ash content ranging from 5 to 30% by weight of the preferred choice of less than 25% by weight, and a higher preferred choice of less than 22% by weight relative to the total weight of the pyrolysis-derived carbon black. The ash content was determined by calcination in a platinum dish in a muffle furnace at 825 °C according to the protocol referred to in Description 3. The tires under claim 1 or 2 are characterized by pyrolysis-derived carbon black having The sulfur content of the pyrolysis carbon black is greater than 1.5% by weight, the choice of which is greater than 2% by weight, and the choice of which may have a range from 2.5 to 5% by weight relative to the total weight of the pyrolysis carbon black. The sulfur content in the pyrolysis carbon black is determined by the LECO furnace according to the method described in this description.

4. Tires (1) According to one of the claims 1 through 3, which is characterized that the pyrolysis carbon black contains zinc greater than or equal to 2% by weight, the choice of which has a range from 2.5 to 5% by weight relative to the total weight of the pyrolysis carbon black.5 to 8% by weight relative to the total weight of carbon black obtained from pyrolysis; zinc content determined after calcination of this sample, followed by ash collection in an acidic medium and analysis by ICP-AES (Induced Coupled Plasma Emission Spectroscopy) according to the method referred to in Description 5. Tires, according to one of the preceding claims, characterized by the fact that such C-layer is an elastomer compound based on natural rubber or synthetic polyisoprene with a predominance of cis-1,4 bonds and, alternatively, at least one diene elastomer, natural rubber or synthetic polyisoprene in the case of a mixture, which appears in a predominantly dominant amount relative to the amount of other diene elastomers (multiple) used. 6.Tire (1) pursuant to one of the preceding claims, which is characterized that the C layer of the rubber compound, apart from pyrolysis carbon black, is composed of a reinforcing filler formed from a) carbon black which is used in a quantity between 20 and 50 phr and preferably between 30 and 40 phr; b) or white filler of the silica and / or alumina type with a surface functional group of SiOH and / or AlOH which is selected from the group formed by precipitated or aerosolized silica, alumina or aluminosilicate; or otherwise carbon black modified during or after synthesis with a specific surface area of ​​BET in the range of 30 and 260 m³ / g which is used in a quantity of between 20 and 50 phr and preferably between 30 and 40 phr; c) or of a mixture of carbon black described in (a) and the white filler described in (b) where the total fill quantity is between 20 and 50 phr and preferably between 30 and 40 phr;7.Tire(1) under one of the preceding claims, which is characterized that at least one skim layer of at least one working ply has been made of a rubber compound in which 50 to 70 phr of reinforcing fillers have been included, which include at least 20 phr of pyrolysis carbon black.

8. Tire(1) under claim 7, which is characterized that at least one such skim layer of at least one working ply (41,42) is an elastomer compound based on natural rubber or synthetic polyisoprene in which cis-1,4 bonds are dominant and, alternatively, at least one diene elastomer of natural rubber or synthetic polyisoprene in the case of a mixture which is present in a quantity that is relative dominant to the quantity of other diene elastomers(s) that have been used.9.Tire (1) under any of the claims in clauses 7 and 8, which are characterized that at least one skim layer of at least one functional tread layer, other than pyrolysis carbon black, is incorporated with a reinforcing filler formed from a) carbon black which is used in an amount between 20 and 50 phr, and preferably between 30 and 40 phr, b) or a white filler of the silica and / or alumina type with surface functional groups of SiOH and / or AlOH which are selected from the group The filler is formed by precipitated or aerosolized silica alumina or aluminosilicate, or otherwise by carbon black modified during or after synthesis with a specific surface area of ​​BET in the range of 30 and 260 m³ / g, which is used at a concentration of between 20 and 50 phr and preferably between 30 and 40 phr), or of a mixture of carbon black described in (a) and the white filler described in (b), where the total filler concentration is between 20 and 50 phr and preferably between 30 and 40 phr;

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