TIRE FEATURING A REINFORCED ENDURANCE TOP REINFORCEMENT

Abstract

The invention relates to a tire (1) with a radial carcass reinforcement (2), the crown reinforcement (4) comprising two working crown layers (41, 42), a layer C being disposed between at least the ends of said working crown layers. According to the invention, the layer C is an elastomeric mixture based on at least one diene elastomer, a reinforcing filler, a sulfur crosslinking system, and a phenol-aldehyde resin having a content of less than 4 parts per liter. Figure for the abstract: Fig 1

Description

Title of the invention: TIRE FEATURING A REINFORCED ENDURANCE TOP REINFORCEMENT

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

[0002] Generally, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted by a crown reinforcement consisting of at least two superimposed layers formed of parallel wires or cables in each layer and crossed from one layer to the next at angles between 10° and 45° with the circumferential direction. These working layers, forming the working reinforcement, may be further covered by at least one protective layer formed of advantageously metallic and extensible reinforcing elements, known as elastic elements.It may also include a layer of low-extensibility wires or cables forming an angle of between 45° and 90° with the circumferential direction. This layer, called the triangulation layer, is radially positioned between the carcass reinforcement and the first crown layer, known as the working layer, which is formed of parallel wires or cables having angles of no more than 45° in absolute value. The triangulation layer, together with at least the aforementioned working layer, forms a triangulated reinforcement which exhibits little deformation under the various stresses it is subjected to. The essential role of the triangulation layer is to resist the transverse compression forces exerted on all the reinforcing elements in the crown area 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 of at most equal to 0.2%.

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

[0005] Circumferential reinforcing elements are reinforcing elements which make angles with the circumferential direction within 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 axis of rotation of the tire.

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

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

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

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

[0012] The "modulus of elasticity" of a rubbery mixture is understood to be a secant modulus of extension at 10% elongation and at room temperature.

[0013] With regard to rubber compositions, the strain at break value in elongation is determined by a tensile test. Tensile tests make it possible to determine the elastic stresses and the fracture properties. A constant uniaxial tensile speed is applied to the specimen, and its elongation and the force are measured. The measurement is carried out using an INSTRON-type tensile testing machine, at a temperature of 100°C and a relative humidity of 50% (ISO 23529 standard). The measurement and results processing conditions for determining the elongation and stress are as described in standard NF ISO 37:2012-03. The stress is determined for an elongation of 0.1, and the secant modulus of elasticity at 10% elongation is calculated by dividing this stress value by the elongation value.A person skilled in the art will know how to choose and adapt the dimensions of the test specimen according to the quantity of mixture accessible and available, particularly in the case of specimen sampling from a finished product such as a tire.

[0014] The cracking rate is measured using a cyclic fatigue testing machine (“Elastomer Test System”) type 381, from MTS. The cracking resistance is measured using repeated tensile tests on a specimen that is initially prepared (after a first tensile cycle) and then notched. The tensile specimen consists of a parallelepiped-shaped rubber sample, for example, with a thickness between 0.5 and 1.5 mm, a length between 60 and 100 mm, and a width between 4 and 8 mm. Both lateral edges are covered lengthwise with a cylindrical rubber bead (5 mm diameter) to allow anchoring in the jaws of the tensile testing machine. The specimens thus prepared are tested after sampling and after oven aging.After accommodation, 4 very fine notches of length between 5 and 7 mm are made using a razor blade, at mid-width and aligned along the length of the specimen, one at each end and two located on either side of the center of the specimen, . Before the measurement begins, the strain rate of the specimen is automatically adjusted at each tensile cycle to maintain a constant energy release rate (the amount of energy released during crack propagation) of approximately 1000 J / m². The crack propagation speed is measured in nanometers per cycle. A person skilled in the art will be able to select and adapt the specimen dimensions according to the amount of accessible and available compound, particularly when taking samples from a finished product such as a tire.

[0015] Some current tires, known as "road" tires, are designed for high-speed driving and increasingly long journeys, due to improvements in the road network and the growth of the motorway network worldwide. The overall conditions under which such a tire is expected to operate undoubtedly allow for an increase in the number of kilometers traveled, as tire wear is reduced; however, the tire's durability, and in particular that of the tread, is compromised.

[0016] There are indeed constraints at the level of the top reinforcement and more particularly shear stresses between the top layers, combined with a non-negligible rise in operating temperature at the end of the axially shortest top layer, which result in the appearance and propagation of cracks in the rubber at said end.

[0017] 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 plies and more particularly the ends of the axially shortest ply have already been provided.

[0018] It is particularly known to introduce a layer of rubbery mixture between the ends of the working layers to create a decoupling between said ends in order to limit shear stresses. Such layers of rubbery mixtures are described, for example, in patent application WO 2004 / 076204.

[0019] French patent FR 1 389 428, to improve the resistance to degradation of rubber compounds located in the vicinity of the edges of the top 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 top reinforcement and made of a low hysteresis rubber compound.

[0020] French patent FR 2 222 232, to avoid separations between layers of top reinforcement, teaches to encase the ends of the reinforcement in a rubber mat, 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 rubbery mixture profile disposed between the edges of the top reinforcement layers and the carcass reinforcement.

[0021] The tires thus produced effectively improve performance, particularly in terms of endurance.

[0022] Furthermore, it is known that for producing tires with very wide treads, or for giving tires of a given size greater load capacities, a layer of circumferential reinforcing elements is introduced. Patent application WO 99 / 24269 describes, for example, the presence of such a layer of circumferential reinforcing elements.

[0023] The layer of circumferential reinforcing elements is usually made up of at least one metal cable wound to form a spiral whose angle of placement with respect to the circumferential direction is less than 2.5°.

[0024] Furthermore, document WO2022 / 207998 describes elastomeric mixtures comprising a phenol-aldehyde resin based on at least one aromatic polyphenol and at least one dialdehyde compound to improve the adhesion of elastomeric mixtures to metal in particular for making working reinforcement layers in which it is desired to eliminate the presence of cobalt for environmental reasons.

[0025] The inventors have set themselves the task of further improving the endurance of tires and in particular the endurance of elastomeric materials subjected to shear stresses between the top layers.

[0026] This objective is achieved according to the invention by a tire comprising a radial carcass reinforcement, said tire comprising a crown reinforcement, comprising at least two working crown layers of reinforcing elements inserted between two calendered layers of rubber compound, crossed from one layer to the other at angles between 10° and 45° with the circumferential direction, said angles being oriented on either side of the circumferential direction, a layer C of rubber compound being disposed between at least the ends of said 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, said layer C being an elastomeric compound based on at least one diene elastomer, a reinforcing filler, a sulfur crosslinking system, and a phenol-aldehyde resin based on: - of at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl groups in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl groups being unsubstituted, and - of at least one dialdehyde compound comprising two aldehyde functions, the phenol-aldehyde resin content is less than 4 pc and preferably less than 2 pc.

[0027] To detect the presence of the molecules of said at least one aromatic polyphenol and said at least one dialdehyde compound, a high-performance liquid chromatography (HPLC) method can be used. The chromatography apparatus consists of a degassing chamber, a pump, an injector, a column oven, and a UV detector. Prior to the HPLC analysis, a first step of extracting the free molecules contained in the mixture is necessary. The extraction solvent is a suitable solvent blend such as, for example: Cyclohexane / Methanol (50 / 50 by volume). This blend is chosen for the good solubility of the two products to be detected (at least 10 g / L). A sample of approximately 500 mg of the mixture extracted from the tire is contacted with 10 mL of the chosen solvent blend for a minimum of 3 hours under stirring.The resulting solution contains a mixture of compounds, including molecules of at least one aromatic polyphenol and at least one dialdehyde compound, which must therefore be separated and identified. This solution is injected (1 OpL) into a chromatography system equipped with a Macherey-Nagel Nucleosil C18 Nautilus 150 mm x 4.6 mm x 5 pm column (stationary phase) or similar. The column temperature is set at 40°C. UV detection is performed at a wavelength suitable for the constituents of interest, at an acquisition rate of 10 points per minute. The mobile phase is injected at a flow rate of 1 µL / min with an elution gradient that a person skilled in the art can adjust. Quantification of at least one aromatic polyphenol and at least one dialdehyde compound is performed based on an external calibration using the constituents of interest of known purity. An independent calibration curve is prepared for each molecule.The solubilization solvent is identical to the measurement solvent (well-chosen solvent cut); and for each concentration, 1 OpL of solution are injected under the same conditions as the mixture extracts.

[0028] By phenol-aldehyde resin content, we mean the sum of the contents of each of the two raw materials aromatic polyphenol and dialdehyde compound comprising two aldehyde functions.

[0029] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is necessary to understand the part, by mass per hundred parts by mass of elastomer or rubber, the two terms being synonymous.

[0030] The C layer of rubbery mixture allows for decoupling of said at least two working top layers in order to distribute the shear stresses over a greater thickness.

[0031] For the purposes of the invention, top working 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 about the reinforcing elements, said thickness of rubber being measured radially between the respectively radially upper and lower generatrices of said reinforcing elements.

[0032] The average diameter of the circle circumscribed about the reinforcing elements is defined as the average diameter of the circles circumscribed about the reinforcing elements of each of the top working layers, the diameter being measured along the principal direction of a reinforcing element extracted from a tire.

[0033] According to a preferred embodiment of the invention, the rubbery mixture layer C 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 synthetic polyisoprene in the case of cutting being present at a majority rate compared to the rate of the other or other diene elastomers used.

[0034] Among the diene elastomers that can be used in cutting with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 chains, we can mention 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 can be modified elastomers during polymerization or after polymerization by means of branching agents such as divinylbenzene or star-forming agents such as carbonates, halotins, halosilicons or by means of functionalizing agents leading to grafting onto the chain or at the end of the chain of oxygenated carbonyl, carboxyl functions or of an amine function such as for example by the action of dimethyl or diethylaminobenzophenone.In the case of natural rubber or synthetic polyisoprene blends with a majority of cis-1,4 chains and one or more of the diene elastomers mentioned above, natural rubber or synthetic polyisoprene is preferably used in a majority proportion and more preferably in a proportion greater than 70%.

[0035] Preferably, the reinforcing filler of layer C is also made up of: - a) either carbon black used at a rate of between 30 and 60 parts per liter, and preferably between 30 and 50 parts per liter, - b) or a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functions chosen from the group formed by precipitated or pyrogenated silicas, aluminas or aluminosilicates or even carbon blacks modified during or after the synthesis of specific surface area BET between 30 and 260 m2 / g used at a rate between 30 and 60 parts per cent, and preferably between 30 and 50 parts per cent, - c) either by a carbon black cutting described in (a) and a white filler described in (b), in which the overall filler ratio is between 30 and 60 pc, and preferably between 30 and 50 pc.

[0036] The measurement of specific surface area BET is carried out according to the method of BRUNAUER, EMMET and TELLER described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938, corresponding to standard NFT 45007 of November 1987.

[0037] In the case of using clear or white filler, it is necessary to use a coupling and / or coating agent chosen from those known to those skilled in the art. Examples of preferred coupling agents include sulfide alkoxysilanes of the bis-(3-triethoxysilylpropyl) 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 by weight cut with N330 black). Examples of covering agents include fatty alcohol, alkylalkoxysilane such as hexadecyltrimethoxy or triethoxysilane respectively marketed by the DEGUSSA Company under the names Sill6 and Si216, diphenylguanidine, polyethylene glycol, silicone oil possibly modified by means of OH or alkoxy functions.The coating and / or coupling agent is used in a weight ratio to the filler > 1 / 100 and < 20 / 100, and preferably between 2 / 100 and 15 / 100 when the clear filler represents the entire reinforcing filler and between 1 / 100 and 20 / 100 when the reinforcing filler consists of a cut of carbon black and clear filler.

[0038] As other examples of reinforcing fillers having the morphology and surface functions SiOH and / or A1OH of the silica and / or alumina type materials previously described and which can be used according to the invention in partial or total replacement of them, one can cite carbon blacks modified either during synthesis by adding to the furnace feed oil a compound of silicon and / or aluminum or after synthesis by adding, to an aqueous suspension of carbon black in a solution of sodium silicate and / or aluminate, an acid so as to cover at least partially the surface of the carbon black with SiOH and / or A1OH functions. As non-limiting examples of this type of carbon-based 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.

[0039] When a clear filler is used as the sole reinforcing filler, the hysteresis and cohesion properties are obtained by using precipitated or fumed silica, or precipitated alumina, or an aluminosilicate with a specific surface area (BET) between 30 and 260 m² / g. Non-limiting examples of this type of filler include KS404 silica from Akzo, Ultrasil VN2 or VN3 and BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or Zeosil 1165MP from Rhodia, HLSIL 2000 from PPG, etc.

[0040] In the case of using carbon black, it may be an industrial carbon black and / or ASTM grade carbon black.

[0041] Advantageously according to the invention, the thickness of the C layer of rubbery mixture, measured at the end of the narrower working top layer of the two working top layers considered, will preferably be between 30% and 80% of the overall thickness of rubbery mixture between cable generators respectively of the two working top layers: a thickness less than 30% not allowing to obtain conclusive results, and a thickness greater than 80% being useless with regard to the improvement in resistance to separation between layers and disadvantageous from a cost point of view.

[0042] Advantageously still, the axial width D of the rubbery mixture layer C between the innermost axial end of said rubbery mixture layer C and the least axially wide end of the top working layer is greater than 5 mm.

[0043] The invention further advantageously provides that the thickness of the rubbery mixture layer C, at the axially outer end of the axially narrowest working top layer, has a thickness such that the radial distance d between the two working top layers, separated by the rubbery mixture layer C, satisfies the relation: 3 / 5.02 < d < 5.02 with 02, diameter of the reinforcement elements of the axially least wide working top sheet.

[0044] The distance d is measured from cable to cable, that is, 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 calendered rubber compounds, radially outside the cables of the radially inner working layer and radially inside the cables of the radially outer working layer.

[0045] The different thickness measurements are carried out on a meridional section of a tire, the tire therefore being in an uninflated state.

[0046] Preferably according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, is present with a content less than or equal to 1 pc and preferably even less than or equal to 0.5 pc.

[0047] Preferably also according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted is phloroglucinol.

[0048] Preferably also according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is present with a content less than or equal to 2 pc and preferably even less than or equal to 1 pc.

[0049] Preferably according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is terephthalaldehyde.

[0050] To detect the presence of phloroglucinol and terephthalaldehyde molecules, high-performance liquid chromatography (HPLC) is used. The chromatography apparatus consists of a degassing chamber, a pump, an injector, a column oven, and a UV detector. Prior to HPLC analysis, a first step of extracting the free molecules contained in the mixture is necessary. The extraction solvent is a cyclohexane / methanol mixture (50 / 50 by volume). This mixture is chosen for the good solubility of the two products to be detected (at least 10 g / L). A sample of approximately 500 mg of the mixture extracted from the tire is contacted with 10 mL of the cyclohexane / methanol mixture for a minimum of 3 hours under stirring. The resulting solution contains a mixture of compounds, including phloroglucinol and terephthalaldehyde molecules, which must therefore be separated and identified.This solution is injected (1 OpL) into the chromatography system equipped with a Macherey-Nagel Nucleosil C18 Nautilus 150 mm x 4.6 mm x 5 µm column (stationary phase) or similar. The column temperature is set at 40°C. UV detection is performed at 266 nm at an acquisition rate of 10 points per minute. The mobile phase is injected at a flow rate of 1 µL / min with an elution gradient that a person skilled in the art can adjust. The quantifications of phloroglucinol and terephtaldehyde are performed based on an external calibration using phloroglucinol and terephtaldehyde of known purity (e.g., Acros Organics phloroglucinol Ref 241760250, 98.47% purity, and Acros Organics terephtaldehyde Ref 137891000, 99.0% purity). An independent calibration curve is performed for each molecule. Calibration curves from 0 to 0.5% wt% are performed at 5 concentration points, allowing the peak area to be determined as a function of concentration.The solubilizing solvent is . identical to that of measurement (cyclohexane / methanol cutting (50 / 50 by volume); and for each concentration, lOpL of solution are injected under the same conditions as the extracts of mixtures.

[0051] According to a preferred embodiment of the invention, the mass content of said at least one dialdehyde compound is greater than the mass content of said at least one aromatic polyphenol. More preferably, the mass content of said at least one dialdehyde compound is greater than 1.5 times the mass content of said at least one aromatic polyphenol.

[0052] Advantageously according to the invention, the sulfur content of the elastomeric mixture constituting layer C is greater than or equal to 4 pc.

[0053] The results obtained with tires conforming to the invention have indeed highlighted that performance in terms of endurance can be improved.

[0054] The inventors have demonstrated that the presence of a phenol-aldehyde resin, as defined according to the invention, in the rubbery mixture constituting layer C gives it higher elongation at break values ​​and lower crack propagation rates than with more conventional mixtures. The inventors believe they interpret this increase in elongation at break values ​​and this decrease in crack propagation rates as giving layer C greater resistance to the shear stresses to which it is subjected.

[0055] The inventors have further demonstrated another advantage of the C layer according to the invention with regard to the choice of producing top reinforcement working layers with calendered layers conforming to the teachings of document WO2022 / 207998. Indeed, the inventors have demonstrated that the presence of the C layer according to the invention allows for lower phenol-aldehyde resin contents than that recommended by document WO2022 / 207998 while maintaining very good adhesion of the calendered working layers to the metal constituting the reinforcing elements. In fact, the contents specified in document WO2022 / 207998 anticipate migration of the species into the surrounding mixtures and are thus designed with a sufficient content to maintain adequate adhesion to the metal after migration.The inventors have shown that the phenol-aldehyde resin content of the C layers according to the invention can be similar in the calendered layers of the top reinforcement working layers while maintaining satisfactory adhesion properties with the metal. Since the equilibrium of phenol-aldehyde resin species exists due to similar concentrations, migration does not occur, and the respective properties of the C layer and these calendered layers of the working layers are preserved.

[0056] Moreover, since the cost of an elastomeric mixture comprising a phenol-aldehyde resin is not negligible, lower contents still offer an advantage relative to the cost of manufacturing a tire.

[0057] Thus, according to an advantageous embodiment of the invention, at least one calendering layer of at least one of said at least two top working layers of reinforcing elements is made up of an elastomeric mixture based on at least one diene elastomer, a reinforcing filler, a sulfur crosslinking system, and a phenol-aldehyde resin based on: - of at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl groups in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl groups being unsubstituted, and - of at least one dialdehyde compound comprising two aldehyde functions, the phenol-aldehyde resin content being less than 4 parts per annum and preferably less than 2 parts per annum.

[0058] According to a preferred embodiment of the invention, said at least one calendering layer of at least one of said at least two top working layers of reinforcing elements is an elastomeric mixture similar or identical to the elastomeric mixture constituting layer C.

[0059] Preferably according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, is present with a content less than or equal to 1 pc and preferably even less than or equal to 0.5 pc in the elastomeric mixture constituting said at least one calendering layer of at least one working top layer.

[0060] Preferably also according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, is phloroglucinol in the elastomeric mixture constituting said at least one calendering layer of at least one working top layer.

[0061] Preferably also according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is present with a content less than or equal to 2 pc and preferably even less than or equal to 1 pc in the elastomeric mixture constituting said at least one calendering layer of at least one working top layer.

[0062] Preferably also according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is terephthalaldehyde in the elastomeric mixture constituting said at least one calendering layer of at least one working top layer.

[0063] The calendered layers of the top working layers of the top reinforcement, as defined according to the invention, allow for long-lasting adhesion to the reinforcing elements of the working layers with a cobalt content of zero or very low levels, thus best meeting environmental requirements. Compared to previous recommendations, particularly those of document WO2002 / 207998, the calendered layers can be produced at a reduced cost.

[0064] According to an advantageous embodiment of the invention, the tire comprising at least one layer and / or at least one profile of an elastomeric compound disposed in contact with and / or around an end of at least one of said at least two working apex layers of reinforcing elements, said at least one layer and / or at least one profile is an elastomeric compound based on at least one diene elastomer, a reinforcing filler, a sulfur crosslinking system, and a phenol-aldehyde resin based on: - of at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl groups in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl groups being unsubstituted, and - of at least one dialdehyde compound comprising two aldehyde functions, and the phenol-aldehyde resin content is less than 4 parts per annum and preferably less than 2 parts per annum.

[0065] According to a preferred embodiment of the invention, said at least one layer and / or at least one profile of elastomeric mixture, disposed in contact and / or around an end of at least one of said at least two top working layers of reinforcing elements, is an elastomeric mixture similar or identical to the elastomeric mixture constituting layer C.

[0066] Preferably according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, is present with a content less than or equal to 1 pc and preferably even less than or equal to 0.5 pc in the elastomeric mixture constituting said at least one layer and / or at least one profile of elastomeric mixture disposed in contact with and / or around an end of at least one of said at least two working top layers of reinforcing elements.

[0067] Preferably also according to the invention, said at least one aromatic polyphenol comprising at least one aromatic nucleus bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted is phloroglucinol in the elastomeric mixture constituting said at least one layer and / or at least one profile of elastomeric mixture disposed in contact and / or around an end of at least one of said at least two working top layers of reinforcing elements.

[0068] Preferably also according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is present with a content less than or equal to 2 pc and preferably even less than or equal to 1 pc in the elastomeric mixture constituting said at least one layer and / or at least one profile of elastomeric mixture disposed in contact and / or around an end of at least one of said at least two top working layers of reinforcing elements.

[0069] Preferably also according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is terephthalaldehyde in the elastomeric mixture constituting said at least one layer and / or at least one profile of elastomeric mixture disposed in contact and / or around an end of at least one of said at least two top working layers of reinforcing elements.

[0070] According to an advantageous embodiment of the invention, the crown reinforcement of the tire comprises at least one layer of circumferential reinforcing elements. The presence of such a layer of circumferential reinforcing elements further contributes to improving the tire's durability performance, and in particular that of the crown reinforcement.

[0071] Advantageously, in an embodiment of the invention, the layer of circumferential reinforcing elements has an axial width greater than 0.5 times the maximum axial width of the tire when it is mounted on its service rim and inflated to its recommended pressure.

[0072] The axial widths of the layers of reinforcing elements are measured on a cross-section of a tire, the tire therefore being in an uninflated state.

[0073] According to a preferred embodiment of the invention, the layer of circumferential reinforcing elements is radially arranged between two working top layers.

[0074] According to this embodiment of the invention, the layer of circumferential reinforcing elements makes it possible to limit the compression stresses on the reinforcement elements of the carcass reinforcement more significantly than a similar layer placed radially outside the working layers. It is preferably radially separated from the carcass reinforcement by at least one working layer so as to limit the stresses on said reinforcing elements and not to fatigue them too much.

[0075] Advantageously, according to the invention, the axial widths of the radially adjacent working top layers to said at least one layer of circumferential reinforcing elements are greater than the axial width of said at least one layer of circumferential reinforcing elements and preferably, said working top layers adjacent to said at least one layer of circumferential reinforcing elements are on either side of the equatorial plane and in the immediate axial extension of said at least one layer of circumferential reinforcing elements coupled over an axial width, to then be decoupled by said layer C of rubber mixture at least over the remainder of the width common to said two working layers.

[0076] According to an advantageous embodiment of the invention, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation between 10 and 120 GPa and a maximum tangent modulus less than 150 GPa.

[0077] According to a preferred embodiment, the secant modulus of the 0.7% elongation reinforcement elements is less than 100 GPa and greater than 20 GPa, preferably between 30 and 90 GPa and preferably still less than 80 GPa.

[0078] Preferably also, the maximum tangent modulus of the reinforcing elements is less than 130 GPa and preferably even less than 120 GPa.

[0079] The moduli expressed above are measured on a tensile stress-elongation curve determined with a preload of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal cross-section of the reinforcing element. The measurements are carried out on cables extracted from the tire on a portion of the layer of circumferential reinforcing elements extending from an axial end of said layer over an axial width of 50 mm towards the interior of said layer.

[0080] The moduli of the same reinforcing elements can be measured on a tensile stress-elongation curve determined with a preload of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall cross-section of the reinforcing element. The overall cross-section of the reinforcing element is the cross-section of a composite element made of metal and rubber, the latter having notably penetrated the reinforcing element during the curing phase of the tire.

[0081] According to this formulation relating to the overall section of the reinforcing element, the reinforcing elements of the axially external parts and of the central part of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation between 5 and 60 GPa and a maximum tangent modulus less than 75 GPa.

[0082] According to a preferred embodiment, the secant modulus of the 0.7% elongation reinforcement elements is less than 50 GPa and greater than 10 GPa, preferably between 15 and 45 GPa and even more preferably less than 40 GPa.

[0083] Preferably also, the maximum tangent modulus of the reinforcing elements is less than 65 GPa and preferably even less than 60 GPa.

[0084] According to a preferred embodiment, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a tensile stress curve as a function of relative elongation having low slopes for low elongations and a substantially constant and high slope for higher elongations.

[0085] The different characteristics of the reinforcement elements stated above are measured on reinforcement elements taken from tires.

[0086] Reinforcement elements more particularly suited to the realization of at least one layer of circumferential reinforcement elements according to the invention are, for example, assemblies of formula 21.23, whose construction is 3x(0.26+6x0.23) 4.8 / 7.5 SS; this stranded cable consists of 21 elementary wires of formula 3 x (1+6), with 3 strands twisted together each consisting of 7 wires, one wire forming a central core of diameter equal to 26 / 100 mm and 6 wound wires of diameter equal to 23 / 100 mm. Such a cable has a secant modulus at 0.7% equal to 45 GPa and a maximum tangent modulus equal to 98 GPa, measured on a tensile stress versus elongation curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal section of the reinforcing element.On a tensile stress versus elongation curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall section of the reinforcing element, this cable of formula 21.23 has a secant modulus at 0.7% equal to 23 GPa and a maximum tangent modulus equal to 49 GPa.

[0087] Similarly, another example of a reinforcing element is an assembly of formula 21.28, whose construction is 3x(0.32+6x0.28) 5.6 / 9.3 SS. This cable has a secant modulus at 0.7% equal to 56 GPa and a maximum tangent modulus equal to 102 GPa, measured on a tensile stress versus elongation curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal cross-section of the reinforcing element. On a tensile stress curve as a function of elongation determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall section of the reinforcing element, this cable of formula 21.28 has a secant modulus at 0.7% equal to 27 GPa and a maximum tangent modulus equal to 49 GPa.

[0088] The use of such reinforcing elements in at least one layer of circumferential reinforcing elements makes it possible in particular to maintain satisfactory layer stiffnesses even after the shaping and baking steps in conventional manufacturing processes.

[0089] According to a second embodiment of the invention, the circumferential reinforcing elements can be formed from inextensible metallic elements and cut so as to form sections of length much shorter than the circumference of the shortest layer, but preferably longer than 0.1 times said circumference, the cuts between sections being axially offset from one another. Even more preferably, the tensile modulus of elasticity per unit width of the additional layer is lower than the tensile modulus of elasticity, measured under the same conditions, of the most extensible top working layer.Such an embodiment makes it possible to give, in a simple way, to the layer of circumferential reinforcing elements a modulus that can easily be adjusted (by choosing the intervals between sections of the same row), but, in all cases, lower than the modulus of the layer made up of the same metallic elements but continuous, the modulus of the additional layer being measured on a vulcanized layer of cut elements, taken from the tire.

[0090] According to a third embodiment of the invention, the circumferential reinforcing elements are corrugated metallic elements, the ratio a / / of the wave amplitude to the wavelength being at most equal to 0.09. Preferably, the tensile modulus of elasticity per unit width of the additional layer is less than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working top layer.

[0091] The layer of circumferential reinforcing elements is advantageously formed by winding reinforcing elements in a substantially circumferential direction to form a helix. The circumferential reinforcing elements are usually coated with an elastomeric compound prior to or during winding.

[0092] Advantageously, according to the invention, the tire comprises at least one layer of circumferential reinforcing elements coated with a layer of elastomeric compound, the elastomeric compound of the layer coating the circumferential reinforcing elements being an elastomeric compound based on at least one diene elastomer, a reinforcing filler, a sulfur crosslinking system, and a phenol-aldehyde resin based on: - of at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl groups in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl groups being unsubstituted, and - of at least one dialdehyde compound comprising two aldehyde functions, and the phenol-aldehyde resin content is less than 4 parts per annum and preferably less than 2 parts per annum.

[0093] According to a preferred embodiment of the invention, the elastomeric mixture of the layer that encases the circumferential reinforcing elements is an elastomeric mixture similar or identical to the elastomeric mixture constituting layer C.

[0094] Preferably according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, is present with a content less than or equal to 1 pc and preferably even less than or equal to 0.5 pc in the elastomeric mixture constituting said elastomeric mixture of the layer which coats the circumferential reinforcing elements.

[0095] Preferably also according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted is phloroglucinol in said elastomeric mixture of the layer which coats the circumferential reinforcing elements.

[0096] Preferably also according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is present with a content less than or equal to 2 pc and preferably even less than or equal to 1 pc in said elastomeric mixture of the layer which coats the circumferential reinforcing elements.

[0097] Preferably, according to the invention, said at least one dialdehyde compound comprising two aldehyde functions is terephthalaldehyde in said elastomeric mixture of the layer which coats the circumferential reinforcing elements.

[0098] The metallic elements are preferably steel cables.

[0099] According to a preferred embodiment of the invention, the reinforcement elements of the top working layers are inextensible metal cables.

[0100] Other details and advantageous features of the invention will become apparent from the description of the exemplary embodiments of the invention with reference to [Fig. 1], which represents a meridian view of a diagram of a tire according to an embodiment of the invention.

[0101] [Fig. 1] is not shown to scale for ease of understanding. [Fig. 1] represents only a half-view of a tire which extends symmetrically with respect to the axis XX' which represents the circumferential median plane, or equatorial plane, of a tire.

[0102] In [Fig. 1], the tire 1 is size 315 / 70 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two flanges, not shown in [Fig. 1]. The carcass reinforcement is formed of a single layer of metal cords. This carcass reinforcement 2 is bound by a vertex reinforcement 4, formed radially from the inside out: - a first working layer 41 formed of metal cables oriented at an angle of 18°, - a layer of circumferential reinforcing elements 43 formed of 21x23 steel wire cables, - of a second working layer 42 formed of metal cables oriented at an angle equal to 30° and crossed with the metal cables of layer 41, the cables of each of the working layers 41, 42 being oriented on either side of the circumferential direction.

[0103] The metal cables constituting the reinforcement elements of the two working layers are cables of formula 9.35 (2+7x0.35). They are distributed in each of the working layers with a distance between the reinforcement elements, measured along the normal to the direction of the mean line of the cable equal to 2.2 mm.

[0104] The top reinforcement is itself capped with a tread 5.

[0105] The tire is inflated to a pressure of 9 bars.

[0106] The axial width L4i of the first working layer 41 is equal to 252 mm.

[0107] The axial width L4 2 of the second working layer 42 is equal to 232 mm.

[0108] The axial width L4 3 of the layer of circumferential reinforcing elements 43 is equal to 194 mm.

[0109] The axial width of the tread is equal to 266 mm.

[0110] The maximum axial width is equal to 315.9 mm.

[0111] According to the invention, a first layer of rubbery mixture C decouples the ends of the top working layers 41 and 42.

[0112] The engagement zone of layer C between the two working top layers 41 and 42 is defined by its thickness, or more precisely the radial distance d between the end of layer 42 and layer 41, and by the axial width D of layer C between the inner axial end of said layer C and the outer radial end of the working top layer 42. The radial distance d is equal to 2.8 mm, or approximately 2.1 times the diameter 02 of the reinforcement elements of the top working layer 42, the diameter 02 being equal to 1.35 mm. The axial distance D is equal to 19 mm.

[0113] Different tires according to the invention are compared to a reference tire of the same size.

[0114] The different mixtures used are listed below, expressing for each the elongation at break, the loss of elongation at break, the crack propagation rate and the crack propagation rate after aging.

[0115] The elongation at break is measured at 100°C and is expressed as a percentage. The value "Ar initial" corresponds to the elongation at break measured in the unaged state, referred to as the initial state, and the value "Ar aged" corresponds to the elongation at break measured in the aged state after aging for 27 days at 90°C under a nitrogen atmosphere.

[0116] The loss of elongation at break is measured after aging for 27 days at 90°C under a nitrogen atmosphere. It is expressed as a percentage loss of elongation at break (%DAr) and is calculated according to the formula: %DAr = 100 - [(Initial Ar - Aged Ar) / Initial Ar] x 100, where Ar = elongation at break.

[0117] Thus the higher the value, the less the elongation at break is degraded after aging for 27 days at 90°C under a nitrogen atmosphere.

[0118] The crack propagation speed is measured in nm / cycle for an energy release of 1000 J / m2. It is expressed as a base of 100, a value of 100 being assigned to the reference mixture R and a higher value corresponding to a decrease in the propagation speed.

[0119] The crack propagation rate after aging is measured in nm / cycle for an energy release of 1000 J / m² after aging for 27 days at 90°C under a nitrogen atmosphere. It is expressed as a base of 100, with a value of 100 assigned to the reference mixture R and a higher value corresponding to a decrease in the propagation rate. à-'Uùasgfi K MàSsægs i NK les ■30 47 47 i .5 .feâesttesqas. O &6 & zimc 'v- T 5 (Acs-ÆW ■ii - 4 5 •O DŒ O Ô.SC TP FVJJ S 1 > 015 i - i As 4®) îs 460 *4 &• v&ffî .2? jass»s. . N2 {Oàagesssssâ 34^ 54 zïDàj Vinsse & à ICS iz5. Speed ​​-âe spses vi-ei^ ISà 145

[0120] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0121] The first type II tires according to the invention comprise a layer C made up of the mixture 1 and calendering layers made up of the mixture R as well as a coating mixture for the circumferential reinforcing elements made up of the mixture R.

[0122] Second tires 12 according to the invention comprise a layer C, calendering layers and the coating mixture of the circumferential reinforcing elements made up of the mixture 1.

[0123] Reference tires T differ from tires II according to the invention by the nature of the compounds of layer C, these being made up of compound R.

[0124] Initial endurance tests, particularly thermally demanding, were carried out on a test machine imposing on each of the tires a straight line run at a speed equal to the maximum speed index prescribed for said tire (speed index) under an initial load of 4230 Kg progressively increased to reduce the duration of the test.

[0125] The results are presented in the following table. The mileage travelled by the tires before a crack appeared at the end of the apex reinforcement is noted as a relative value, with a value of 100 being assigned to the reference tire T. T II 12 100 105 108

[0126] Other endurance tests, particularly demanding mechanically, were carried out on a test machine that cyclically applied a transverse force and a dynamic overload to the tires. The tests were performed on the tires according to the invention under conditions identical to those applied to the reference tires.

[0127] The results are presented in the following table. The mileage travelled by the tires before a crack appeared at the end of the apex reinforcement is noted as a relative value, with a value of 100 being assigned to the reference tire T. T II 12 100 110 110

[0128] Pull-off tests were also carried out to confirm sufficient adhesion between the reinforcing elements of the working layers and the calendering layers made with the elastomeric mixture according to the invention.

[0129] Specimens of suitable dimensions are taken from tire 12 and from tire T. Each reinforcement is pulled out of the rubber block using a tensile testing machine according to the method described in ASTM D 2229-02; the tensile speed is 100 mm / min; the adhesion is thus characterized by the force required to pull the reinforcement out of the specimen at a temperature of 60°C; the pull-out force represents the average of the 15 measurements corresponding to the 15 reinforcements of the composite.

[0130] The results are presented in the following table. The relative force required to detach the reinforcement is denoted by , with a value of 100 being assigned to the reference tire T. The higher the force value, the greater the adhesion between the cable and the rubber compound. T 12 100 95

[0131] These results show that the calendered layers of the working layers of the crown reinforcement of the tires 12 according to the invention exhibit slightly inferior adhesion properties on the metal to those obtained with more common calendered layer mixtures of the T tire. They are however satisfactory and totally acceptable.

Claims

Demands

1. A tire (1) comprising a radial carcass reinforcement (2), said tire comprising a crown reinforcement (4), comprising at least two working crown layers (41, 42) of reinforcing elements inserted between two calendered layers of rubber compound, crossed from one layer to the other at angles between 10° and 45° to the circumferential direction, said angles being oriented on either side of the circumferential direction, a layer C of rubber compound being disposed between at least the ends of said two working crown layers, the crown reinforcement (4) being radially capped by a tread (5), said tread being joined to two beads by means of two sidewalls, characterized in that said layer C is an elastomeric compound based on at least one diene elastomer, a reinforcing filler, a system of sulfur crosslinking,and a phenol-aldehyde resin based on: - at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl groups in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl groups being unsubstituted, and - at least one dialdehyde compound comprising two aldehyde groups, and in that the phenol-aldehyde resin content is less than 4 parts per million and preferably less than 2 parts per million.

2. Pneumatic (1) according to claim 1, characterized in that the mass content of said at least one dialdehyde compound is greater than the mass content of said at least one aromatic polyphenol.

3. Pneumatic (1) according to any one of claims 1 or 2, characterized in that the sulfur content is greater than or equal to 4 pc.

4. Pneumatic (1) according to any one of the preceding claims, characterized in that at least one calendered layer of at least one of said at least two working top layers (41, 42) of reinforcing elements is an elastomeric mixture based on at least one diene elastomer, a filler strengthening, a sulfur crosslinking system, and a phenol-aldehyde resin based on: - at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, and - at least one dialdehyde compound comprising two aldehyde functions, the phenol-aldehyde resin content being less than 4 pc and preferably less than 2 pc.

5. A tire (1) according to any one of the preceding claims, said tire comprising at least one layer and / or at least one profile of an elastomeric compound disposed in contact with and / or around an end of at least one of said at least two working apex layers (41, 42) of reinforcing elements, characterized in that said at least one layer and / or at least one profile is an elastomeric compound based on at least one diene elastomer, a reinforcing filler, a sulfur crosslinking system, and a phenol-aldehyde resin based on: - at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl groups in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl groups being unsubstituted, and - at least one dialdehyde compound comprising two aldehyde groups,and in that the phenol-aldehyde resin content is less than 4 parts per annum and preferably less than 2 parts per annum.

6. Pneumatic (1) according to any one of the preceding claims, characterized in that said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, is present with a content less than or equal to 1 pc and preferably less than or equal to 0.5 pc.

7. Pneumatic (1) according to any one of the preceding claims, characterized in that said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl groups in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted is phloroglucinol.

8. Pneumatic (1) according to any one of the preceding claims, characterized in that said at least one dialdehyde compound comprising two aldehyde functions is present with a content less than or equal to 2 pc and preferably less than or equal to 1 pc.

9. Pneumatic (1) according to any one of the preceding claims, characterized in that said at least one dialdehyde compound comprising two aldehyde functions is terephthalaldehyde.

10. Pneumatic (1) according to any one of the preceding claims, characterized in that the top reinforcement (4) comprises a layer of circumferential reinforcing elements (43).

11. Pneumatic (1) according to claim 10, characterized in that the reinforcing elements of said at least one layer of circumferential reinforcing elements (43) are metallic reinforcing elements having a secant modulus at 0.7% elongation of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa.

12. Pneumatic (1) according to claim 10 or 11, the reinforcing elements of said at least one layer of circumferential reinforcing elements (43) being coated with a layer of elastomeric mixture characterized in that the elastomeric mixture of the layer which coats the circumferential reinforcing elements (43) is an elastomeric mixture based on at least one diene elastomer, a reinforcing filler, a sulfur crosslinking system, and a phenol-aldehyde resin based on: - at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two hydroxyl functions in meta positions relative to each other, the two ortho positions of at least one of the hydroxyl functions being unsubstituted, and - at least one dialdehyde compound comprising two aldehyde functions, and in that the phenol-aldehyde resin content is less than 4 pc and preferably less than 2 pc.

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