Tyre having a crown reinforcement with enhanced durability

Abstract

The invention relates to a tyre (1) with a radial carcass reinforcement (2), the crown reinforcement (4) comprising two working crown layers (41, 42), a layer C being arranged between at least the ends of the working crown layers. According to the invention, the layer C is an elastomer mixture based on at least a diene elastomer, a reinforcing filler, a sulphur crosslinking system, and a phenol-aldehyde resin which is present in an amount of less than 4 phr.

Description

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] In general, 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, known as 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 that exhibits minimal deformation under the various stresses it is subjected to. The triangulation layer's essential role 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, under a tensile force equal to 10% of the breaking force, said cables exhibit a relative elongation of no more than 0.2%.

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

[0005] Circumferential reinforcement elements are reinforcement elements that make angles with the circumferential direction within the range of +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 direction of rolling of the tire.

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

[0008] Radial direction is a direction that intersects the axis of rotation of the tire and is 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] Regarding rubber compounds, the strain at break value in elongation is determined by a tensile test. Tensile tests allow the determination of elastic stresses and fracture properties. A constant uniaxial tensile speed is applied to the specimen, and its elongation and the force exerted are measured. The measurement is performed 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 data processing conditions for determining 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 be able to select and adapt the dimensions of the test tube depending on the amount of mixture accessible and available, particularly in the case of test tube 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. Crack resistance is measured by 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 secure it in the jaws of the tensile testing machine. The prepared specimens are tested after sampling and after oven aging.After accommodation, four very fine notches, 5 to 7 mm long, are made with a razor blade at mid-width and aligned lengthwise along the specimen: one at each end and two on either side of the center of the specimen, before the measurement begins. At each tensile cycle, the specimen's strain rate is automatically adjusted 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. Those 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 modern tires, known as "road" tires, are designed for high speeds and increasingly long journeys, due to improvements in road networks and the growth of highways worldwide. The overall conditions under which such a tire is expected to operate undoubtedly allow for an increase in mileage, as tire wear is reduced; however, the tire's durability, and particularly that of the tread, is compromised.

[0016] Indeed, there are constraints at the level of the top reinforcement, and more specifically shear stresses between the top layers, combined with a significant increase in operating temperature at the ends of the axially shortest top layer, which results in the appearance and propagation of cracks in the gum at said ends.

[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 plies have already been provided.

[0018] It is known to introduce a layer of rubbery compound between the ends of the working layers to create decoupling between said ends and thus limit shear stresses. Such layers of rubbery compounds 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 layers of top reinforcement and carcass reinforcement.

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

[0022] Furthermore, it is known for producing tires with very wide treads or for increasing the load-bearing capacity of tires of a given size by incorporating a layer of circumferential reinforcing elements. Patent application WO 99 / 24269, for example, describes 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 wire rope wound to form a spiral whose angle of laying 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 molecules of at least one aromatic polyphenol and at least one dialdehyde compound, high-performance liquid chromatography (HPLC) can be 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 is required to extract the free molecules contained in the mixture. The extraction solvent is a suitable cutting solvent such as, for example, cyclohexane / methanol (50 / 50 by volume). This cutting solvent 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 cutting solvent for a minimum of 3 hours under agitation.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, lOpL of solution are injected under the same conditions as the mixture extracts.

[0028] Phenolaldehyde resin content refers to the sum of the contents of each of the two raw materials: aromatic polyphenol and dialdehyde compound comprising two aldehyde functions.

[0029] 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.

[0030] The C layer of rubbery mixture allows for decoupling of the aforementioned 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 rubber thickness being measured radially between the respective radially upper and lower generatrices of said reinforcing elements.

[0032] The average diameter of the circle circumscribed about the reinforcement elements is defined as the average diameter of the circles circumscribed about the reinforcement elements of each of the top working layers, the diameter being measured along the principal direction of a reinforcement 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 blends of natural rubber or predominantly synthetic polyisoprene. cis-1,4 linkages with one or more of the diene elastomers mentioned above, natural rubber or synthetic polyisoprene is used preferably in a majority rate and more preferentially in a rate greater than 70%.

[0035] Preferably, the reinforcing filler of layer C is also composed of: a) either carbon black used at a rate of between 30 and 60 parts per cubic meter (ppm), and preferably between 30 and 50 ppm, b) or a white filler of the silica and / or alumina type having SiOH and / or Al₂H surface functionalities chosen from the group formed by precipitated or fumed silicas, aluminas or aluminosilicates, or even carbon blacks modified during or after synthesis with a specific surface area of ​​BET between 30 and 260 m 2 / g used at a rate of between 30 and 60 pc, and preferably between 30 and 50 pc, c) either by a cutting of carbon black described in (a) and a white filler described in (b), in which the overall filler rate 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 the 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 the DEGUSSA Company 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 Sil 16 and Si216, diphenylguanidine, polyethylene glycol, silicone oil possibly modified by means of OH or alkoxy functions.The recovery and / or coupling agent is used in a weight-to-ratio ratio. to the charge > 1 / 100 and < 20 / 100, and preferably between 2 / 100 and 15 / 100 when the clear charge represents the entirety of the reinforcing charge and between 1 / 100 and 20 / 100 when the reinforcing charge consists of a cut of carbon black and clear charge.

[0038] Other examples of reinforcing fillers having the morphology and SiOH and / or A10H surface functionalities of the silica and / or alumina-type materials described above, and which can be used according to the invention as a partial or total replacement thereof, include carbon blacks modified either during synthesis by adding a silicon and / or aluminum compound to the furnace feed oil, or after synthesis by adding an acid to an aqueous suspension of carbon black in a sodium silicate and / or aluminate solution so as to at least partially coat the surface of the carbon black with SiOH and / or A1OH functionalities. Non-limiting examples of this type of carbon-based filler with SiOH and / or A1OH functionalities on its surface include 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 described in patent application EP-A-0 799 854.

[0039] When a clear filler is used as the sole reinforcing filler, hysteresis and cohesion properties are obtained by using precipitated or fumed silica, precipitated alumina, or an aluminosilicate with a specific surface area BET between 30 and 260 m 2 / g. As non-limiting examples of this type of filler, we can cite KS404 silica 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...

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

[0041] Advantageously, according to the invention, the thickness of layer C of the rubber compound, measured at the end of the narrower of the two working top layers considered, will preferably be between 30% and 80% of the overall thickness of the rubber compound between the cable generators of the two working top layers respectively: a thickness less than 30% not allowing conclusive results to be obtained, and a thickness greater than 80% being unnecessary in terms of improving resistance to separation between layers and disadvantageous from a cost perspective.

[0042] Advantageously, the axial width D of the rubbery mixture layer C between the innermost axial end of said rubbery mixture layer C and the axially narrowest 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.([>2 < d < 5.C[>2 with (|)2, 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 taken on a meridional section of a tire, the tire therefore being in a deflated 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, according to the invention, said at least one aromatic polyphenol comprising at least one aromatic ring bearing at least two functions hydroxyl in meta position 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 is required to extract the free molecules contained in the mixture. The extraction solvent is a cyclohexane / methanol mixture (50 / 50 by volume). This mixture is chosen for its 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 pm 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 solubilization solvent is identical to the measurement solvent (cyclohexane / methanol cutting (50 / 50 by volume)); and for each concentration, 1 OpL 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. 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 shown 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 contents of the C layers according to the invention can be similar in the calendering layers of the top reinforcement working layers while maintaining satisfactory adhesion properties with the metal. The balance of species in the phenol-aldehyde resin... Since aldehyde exists due to similar levels, migration does not occur and the respective properties of the C layer and these calendering layers of the working layers are preserved.

[0056] Furthermore, since the cost of elastomeric mixtures including phenol-aldehyde resin is not negligible, lower concentrations still offer a relative advantage in terms of 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 still 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, 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 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 layers of the 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 W02002 / 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 a meta position relative to one another the other, the two ortho positions of at least one of the hydroxyl functions 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 with 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 functional groups is present with a content less than or equal to 2 parts per million and preferably even less than or equal to 1 part per million in the elastomeric mixture constituting said at least one layer and / or at least one mixture profile elastomeric material disposed in contact with and / or around one end of at least one of said at least two top working layers of reinforcing elements.

[0069] Preferably, 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, 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 allows for greater limitation of the compressive stresses on the carcass reinforcement elements 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 in order to limit the stresses on said reinforcing elements and prevent excessive fatigue.

[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 corresponds to a measured tension referred to the metal cross-section of the reinforcing element. The measurements are taken on cables extracted from the tire along a portion of the layer of circumferential reinforcing elements extending from one 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 prestress 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 element reinforcement is the section of a composite element made of metal and rubber, the latter having notably penetrated the reinforcement element during the curing phase of the tire.

[0081] According to this formulation relating to the overall section of the reinforcement element, the reinforcement elements of the axially external parts and of the central part of at least one layer of circumferential reinforcement elements are metallic reinforcement 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 preferably still 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-as-relative-elongation curve with low slopes for low elongations and a substantially constant and steep slope for higher elongations.

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

[0086] Reinforcing elements particularly suited to creating 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 with a diameter of 26 / 100 mm, and 6 wound wires with a diameter of 23 / 100 mm. Such a cable has a secant modulus at 0.7% of 45 GPa and a maximum tangent modulus of 98 GPa, measured on a tensile stress-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 21.23 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 a 21.28 assembly, whose construction is 3x(0.32+6x0.28) 5.6 / 9.3 SS. This cable exhibits a secant modulus at 0.7% of 56 GPa and a maximum tangent modulus of 102 GPa, measured on a tensile stress-strain 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-strain curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall cross-section of the reinforcing element, this 21.28 cable exhibits a secant modulus at 0.7% of 27 GPa and a maximum tangent modulus of 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 stiffness even after the shaping and baking stages in conventional manufacturing processes.

[0089] According to a second embodiment of the invention, the circumferential reinforcing elements can be formed from inextensible metallic elements cut 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 layer. additional 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 / X 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 produced 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 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.

[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, 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 that 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 components 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 advantageous details and features of the invention will become apparent from the description of examples of 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.

[0101] The figure is not drawn to scale for ease of understanding. The figure only represents half a view of a tire that extends in a way symmetric with respect to the XX' axis which represents the circumferential median plane, or equatorial plane, of a tire.

[0102] In the figure, the tire 1 is size 315 / 70 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two ribs, not shown in the figure. The carcass reinforcement is formed of a single layer of steel cables. This carcass reinforcement 2 is reinforced by a top reinforcement 4, formed radially from the inside out: a first working layer 41 formed of steel cables oriented at an angle of 18°, a layer of circumferential reinforcing elements 43 formed of 21x23 steel steel cables, a second working layer 42 formed of steel cables oriented at an angle of 30° and crossed with the steel 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 forming 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 L 41 of the first working layer 41 is equal to 252 mm.

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

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

[0109] The axial width of the tread is 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 its inner axial end and its outer radial end. The radial distance d is 2.8 mm, approximately 2.1 times the diameter c)2 of the reinforcing elements of the working top layer 42, where c)2 is 1.35 mm. The axial distance D is 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 "Initial Ar" value corresponds to the elongation at break measured in the unaged state, also known as the initial state, and the "Aged Ar" value 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 27 days of aging at 90°C under a nitrogen atmosphere. It is expressed as a percentage loss of elongation at break (%DAr) and is calculated using the following formula: %DAr = 100 - [(Ar initial- Ar aged) / Ar initial]xl00, With, 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 / m 2 It is expressed in base 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 speed after aging is measured in nm / cycle for an energy release of 1000 J / m 2 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 being assigned to the reference mixture R and a higher value corresponding to a decrease in the propagation speed.

[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 mixture 1 and calendering layers made up of mixture R as well as a coating mixture for the circumferential reinforcing elements made up of 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 mixture 1.

[0123] Reference T tires differ from II tires 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 demanding in terms of heat, 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 relative mileage of the tires before a crack appeared at the end of the crown reinforcement is noted, with a value of 100 being assigned to the reference tire T.

[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 relative mileage of the tires before a crack appeared is denoted by . end of the top reinforcement, a value of 100 being assigned to the reference tire T.

[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 as well as 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 force required to detach the reinforcement is denoted as a relative value, with a value of 100 assigned to the reference tire T. The higher the force value, the greater the adhesion between the cable and the rubber compound.

[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. However, they are satisfactory and totally acceptable.

Claims

- 27 - 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 sulfur crosslinking system, and a resin phenol-aldehyde 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 in that the phenol-aldehyde resin content is less than 4 pc and preferably less than 2 pc. 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 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 calendering 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 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 a meta position relative to one another the other, the two ortho positions of at least one of the hydroxyl functions 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. 5 - Pneumatic (1) according to any one of the preceding claims, said pneumatic comprising at least one layer and / or at least one profile of elastomeric compound disposed in contact with and / or around an end of at least one of said at least two working top 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: - 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 in that the phenol-aldehyde resin content is less than 4 pc and preferably less than 2 pc. 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 functions 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 terephthal al dehy de. 10 - Pneumatic (1) according to 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 coating 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: - 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 in that the phenol-aldehyde resin content is less than 4 pc and preferably less than 2 pc.

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