RUBBER COMPOSITION COMPRISING A HIGHLY SATURATED DIENIC ELASTOMER

Abstract

The invention relates to a rubber composition exhibiting a good compromise in performance between elongation at break, tear resistance, and fatigue resistance. This composition is based on at least one elastomeric matrix comprising 85 to 98 parts per cent of at least one copolymer containing ethylene units and 1,3-diene units, the mole fraction of ethylene units in the copolymer being in the range of more than 50% to 95%, and 2 to 15 parts per cent of a polyisoprene having a mass fraction of 1,4-cis bonds of at least 90% of the mass of the polyisoprene, a reinforcing filler comprising carbon black having a specific surface area (BET) in the range of 50 to 160 m² / g, and a crosslinking system. The invention also relates to a tire comprising this composition.

Description

Title of the invention: RUBBER COMPOSITION COMPRISING A HIGHLY SATURATED DIENIC ELASTOMER

[0001] The present invention relates to rubber compositions comprising a highly saturated diene elastomer, the rubber compositions being particularly intended for use in a tread for a heavy-duty tire.

[0002] Tires intended for vehicles carrying heavy loads have specific characteristics in terms of dimensions, robustness, and design that distinguish them from other tires, particularly tires for passenger vehicles. Their treads must meet a large number of technical requirements, often conflicting, such as low rolling resistance, high wear resistance, and good resistance to foreign matter present on the surface on which the tire rolls.

[0003] Indeed, the use of these tires on terrain with numerous stones and other debris, or potholes, causes damage to the tread. For vehicles carrying heavy loads, particularly trucks, it is known that the treads of the tires fitted to these vehicles are subjected to repeated impacts that can cause material to tear from the tread. It is therefore necessary that the treads of the tires on these vehicles exhibit good resistance to damage as well as a high elongation at break in order to limit the appearance of cracks in the rubber compounds that make up these treads. Elongation at break corresponds to the ability of these compounds to deform without breaking.It is also necessary to consider tear resistance (the ability of the compounds to resist crack propagation) and fatigue resistance (the ability of the compounds to withstand the numerous mechanical stresses that are cyclically repeated during tire rolling). Improving elongation at break should preferably be done without significantly compromising tear resistance and fatigue resistance, or even by improving them.

[0004] Thus, manufacturers are always looking for solutions to further improve elongation at break properties while maintaining tear resistance properties within acceptable limits.

[0005] Continuing its research, the Applicant unexpectedly discovered that the addition of a specific amount of a polyisoprene to a ca composition Rubber, consisting mainly of a highly saturated diene elastomer, allows for further improvement of the aforementioned performance compromise.

[0006] Thus, a first object of the invention is a rubber composition based on at least one elastomeric matrix comprising 85 to 98 parts per cent of at least one copolymer containing ethylene units and 1,3-diene units, the mole fraction of ethylene units in the copolymer being in a range of more than 50% to 95%, and 2 to 15 parts per cent of a polyisoprene having a mass ratio of 1,4-cis bonds of at least 90% of the mass of the polyisoprene, a reinforcing filler comprising carbon black having a BET specific surface area in a range of 50 to 160 m2 / g and a crosslinking system.

[0007] A second object of the invention is a heavy-duty tire which comprises a rubber composition according to the invention. I- DEFINITIONS

[0008] The expression "composition based on" means a composition comprising the mixture and / or the in situ reaction product of the different constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the different phases of manufacturing the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0009] By "elastomer matrix" is meant all the elastomers of the composition, including the copolymer defined below.

[0010] Unless otherwise indicated, the rates of units resulting from the insertion of a monomer into a copolymer are expressed as a molar percentage relative to the total monomer units of the copolymer.

[0011] The expression "part by weight per hundred parts by weight of elastomer" (or pce) is to be understood in the context of the present invention as the part, by mass per hundred parts of elastomer present in the rubber composition considered.

[0012] In the present, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0013] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​from greater than a to less than b (that is, excluding the bounds a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (that is, including the strict bounds a and b). In the present case, when an interval of values ​​is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

[0014] When reference is made to a "major" compound, it is understood, for the purposes of the present invention, that this compound is the majority among compounds of the same type in the The composition is defined as the elastomer that represents the largest mass fraction among the compounds of the same type. For example, a major elastomer is the elastomer with the greatest mass relative to the total mass of the elastomers in the composition. Similarly, a major filler is the one with the greatest mass fraction among the fillers in the composition. For instance, in a system comprising a single elastomer, this elastomer is considered the major component within the meaning of the present invention; and in a system comprising two elastomers, the major elastomer represents more than half the mass of the elastomers. Conversely, a "minor" compound is a compound that does not represent the largest mass fraction among the compounds of the same type. Preferably, "major" means present at more than 50%, preferably more than 60%, 70%, 80%, or 90%, and most preferably, the "major" compound represents 100%.

[0015] The compounds mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already in use, that is to say, they may be partially or totally derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, polymers, plasticizers, fillers, etc.

[0016] Unless otherwise indicated, all glass transition temperature values ​​“Tg” described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999). II- DESCRIPTION OF THE INVENTION II-1 Elastomer Matrix

[0017] According to the invention, the elastomeric matrix comprises 85 to 98 parts per cent of at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer (hereinafter referred to as "the copolymer") and 2 to 15 parts per cent of a polyisoprene having a mass percentage of 1,4-cis bonds of at least 90% of the mass of the polyisoprene.

[0018] The term “copolymer containing ethylene units and 1,3-diene units” means any copolymer comprising, within its structure, at least ethylene units and 1,3-diene units. The copolymer may thus comprise monomer units other than ethylene units and 1,3-diene units. For example, the copolymer may also comprise alpha-olefin units, in particular alpha-olefin units having from 3 to 18 carbon atoms, advantageously having from 3 to 6 carbon atoms. For example, alpha-olefin units can be chosen from the group consisting of propylene, butene, pentene, hexene, or mixtures thereof. However, the copolymer does not include a unit of a 1,3-diene with the formula CH2=CR-CH=CH2, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms.

[0019] In a known manner, the expression "ethylene unit" refers to the -(CH2-CH2)- motif resulting from the insertion of ethylene into the elastomer chain.

[0020] In a known manner, the expression "1,3-diene unit" refers to units resulting from the insertion of 1,3-diene by a 1,4 addition, a 1,2 addition or a 3,4 addition in the case of a substituted diene such as isoprene for example.

[0021] Preferably, the 1,3-diene units are selected from the group consisting of butadiene units, isoprene units, and mixtures of these 1,3-diene units. In particular, the 1,3-diene units of the copolymer may be 1,3-diene units having 4 to 12 carbon atoms, for example, 1,3-butadiene, 2-methyl-1,3-butadiene (or isoprene) units. Even more preferably, the 1,3-diene units are predominantly, by mole, or even preferably exclusively, 1,3-butadiene units.

[0022] In the copolymer, the ethylene units represent between 50% and 95% by mole of the monomer units of the copolymer. Advantageously, the ethylene units in the copolymer represent between 55% and 90%, preferably from 60% to 90%, preferably from 60% to 80%, by mole of the monomer units of the copolymer.

[0023] Advantageously, the copolymer is a copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene), that is to say, according to the invention, a copolymer consisting exclusively of ethylene units and 1,3-diene units (preferably 1,3-butadiene).

[0024] Preferably, the copolymer does not contain a unit of a 1,3-diene of formula CH2=CR-CH=CH2 in which R represents a hydrocarbon chain having 3 to 20 carbon atoms.

[0025] When the copolymer is a copolymer of ethylene and a 1,3-diene, it advantageously contains units of formula (I) below and / or (II) below. The presence of a saturated 6-member cyclic motif, 1,2-cyclohexanediyl, of formula (I) as a monomer unit in the copolymer can result from a series of very specific insertions of ethylene and 1,3-butadiene into the polymer chain during its growth. -CH2-CH(CH=CH2)- (II)

[0026] For example, the copolymer of ethylene and a 1,3-diene may be devoid of formula units (I). In this case, it preferably contains formula units (II).

[0027] When the copolymer of ethylene and a 1,3-diene comprises units of formula (I) or units of formula (II) or units of formula (I) and units of formula (II), the molar percentages of units of formula (I) and units of formula (II) in the copolymer, respectively o and p, preferably satisfy the following equation (eq. 1), more preferably equation (eq. 2), o and p being calculated on the basis of all the monomer units of the copolymer. 0 < o+p < 25 (eq. 1) 0 < o+p < 20 (eq. 2)

[0028] According to the invention, the copolymer, preferably the copolymer of ethylene and a 1,3-diene (preferably of 1,3-butadiene), is a statistical copolymer.

[0029] Advantageously, the number-average mass (Mn) of the copolymer, preferably of the copolymer of ethylene and a 1,3-diene (preferably of 1,3-butadiene) is in the range of 100,000 to 300,000 g / mol, preferably of 150,000 to 250,000 g / mol.

[0030] The Mn of the copolymer is determined in a known manner, by size exclusion chromatography (SEC) as described in point III-1 below.

[0031] The copolymer can be obtained by various synthetic methods known to those skilled in the art, particularly depending on the desired microstructure of the copolymer. Generally, it can be prepared by copolymerization of at least one diene, preferably a 1,3-diene, preferably 1,3-butadiene, and ethylene, using known synthetic methods, particularly in the presence of a catalytic system comprising a metallocene complex. Examples include catalytic systems based on metallocene complexes, which are described in documents EP 1 092 731, WO 2004035639, WO 2007054223, and WO 2007054224 on behalf of the Applicant. The copolymer, including when statistical, can also be prepared by a process using a preformed catalytic system such as those described in documents WO 2017093654 Al, WO 2018020122 Al and WO 2018020123 AL

[0032] The copolymer may consist of a mixture of copolymers containing ethylene units and 1,3-diene units which differ from each other by their microstructures and / or by their macrostructures.

[0033] Advantageously, the proportion of at least one copolymer containing ethylene units and 1,3-diene units can be in the range of 88 to 97 pc, preferably more than 90 to 96 pc.

[0034] Advantageously, polyisoprene having a 1,4-cis bond mass ratio of at least 90% of the polyisoprene mass, is a natural rubber, a polyisoprene of synthesis or a mixture thereof. Preferably, the polyisoprene, preferably having a mass percentage of 1,4-cis bonding of at least 90% of the mass of the polyisoprene, is a natural rubber.

[0035] Advantageously, the rate of polyisoprene in the composition according to the invention is preferably in the range of 3 to 12 pc, preferably from 4 to less than 10 pc. II-2 Reinforcing Load

[0036] The composition according to the invention comprises a reinforcing filler, known for its ability to reinforce a rubber composition usable for the manufacture of tires. Such a reinforcing filler typically consists of particles whose average size (by mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, and in particular and more preferably between 20 and 150 nm.

[0037] According to the invention, the reinforcing filler comprising carbon black has a specific surface area BET in the range of 50 to 160 m2 / g.

[0038] The reinforcing filler may also include a reinforcing filler other than carbon black, in particular silica, but this is not mandatory.

[0039] For example, the reinforcing filler may comprise more than 50% by weight, preferably more than 90% by weight, preferably 100% by weight, of carbon black. In this case, the reinforcing filler preferably comprises more than 50% by weight, preferably more than 90% by weight, preferably 100% by weight of carbon black having a specific surface area BET in the range of 50 to 160 m² / g. When the reinforcing filler comprises a mixture of carbon black and silica, the reinforcing filler advantageously comprises 50% to 95% by weight, preferably 60% to 95% by weight of silica and 5% to 50% by weight, preferably 5% to 40% by weight, of carbon black.

[0040] The blacks usable within the scope of the present invention can be any black conventionally used in tires or their treads (so-called tire-grade blacks). Among these, special mention should be made of reinforcing carbon blacks of the 100, 200, and 300 series (ASTM grades), such as NI 15, N134, N234, N326, N330, N339, N347, and N375 blacks. These carbon blacks can be used in isolation, as commercially available, or in any other form, for example, as a carrier for certain rubber additives used. The carbon blacks could, for example, already be incorporated into the diene elastomer, particularly isoprene, in the form of a masterbatch (see, for example, applications WO 97 / 36724 or WO 99 / 16600).

[0041] Among the aforementioned carbon blacks, those having a BET specific surface area in the range of 90 to 160 m2 / g, and preferably 100 to 150 m2 / g, are particularly preferred.

[0042] The specific surface area BET of carbon blacks is measured according to standard D6556-10 [multipoint method (minimum 5 points) - gas: nitrogen - relative pressure range P / PO: 0.1 to 0.3].

[0043] Any type of precipitated silica may be suitable as a silica, in particular highly dispersible precipitated silica (known as "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas, whether highly dispersible or not, are well known to those skilled in the art. Examples include the silicas described in applications WO03 / 016215-A1 and WO03 / 016387-A1. Among the commercial HDS silicas, one can notably use the “Ulsil ® 5000GR”, “Ulsil ® 7000GR” silicas from the company Evonik, the “Zeosil ® 1085GR”, “Zeosil® 1115 MP”, “Zeosil® 1165MP”, “Zeosil® Premium 200MP”, “Zeosil® HRS 1200 MP” silicas from the Solvay Company.As non-HDS silica, the following commercial silicas may be used: “Ultrasil® VN2GR”, “Ultrasil® VN3GR” silicas from Evonik, “Zeosil® 175GR” silica from Solvay, “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(-D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” silicas from PPG.

[0044] In the present exposition, the specific surface area BET is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), and more specifically according to a method adapted from the standard NF ISO 5794-1, Annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160°C - relative pressure range w / in: 0.05 to 0.17].

[0045] To couple the silica to the diene elastomer, a coupling agent (or bonding agent) that is at least bifunctional can be used in a well-known manner to ensure sufficient chemical and / or physical connection between the inorganic filler (surface of its particles) and the diene elastomer. Organosilanes or polyorganosiloxanes that are at least bifunctional are used in particular. "Bifunctional" means a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer.For example, such a bifunctional compound may comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic charge, and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the diene elastomer.

[0046] Preferably, when used, organosilanes are chosen from the group consisting of polysulfide organosilanes (symmetric or asymmetric) such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT and marketed under The designation "Si69" by Evonik or bis-(triethoxysilylpropyl) disulfide, abbreviated TESPD and marketed under the name "Si75" by Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl octanethioate) marketed by Momentive under the name "NXT Silane". More preferably, the organosilane is a polysulfide organosilane.

[0047] When the reinforcing filler includes silica, the coupling agent content can easily be adjusted by a person skilled in the art. Typically, the coupling agent content ranges from 0.5% to 15% by weight relative to the amount of silica.

[0048] The reinforcing filler content can easily be adjusted by a person skilled in the art according to the intended use of the rubber compound. Advantageously, the reinforcing filler content in the compound according to the invention is within a range of 20 to 70 parts per annum, preferably from 30 to 60 parts per annum. II-3 Crosslinking System

[0049] The crosslinking system can be any type of system known to those skilled in the art in the field of tire rubber compounds. In particular, it can be sulfur-based, and / or peroxide-based, and / or bismaleimide-based.

[0050] Preferably, the crosslinking system is sulfur-based; this is then referred to as a vulcanization system. Advantageously, the vulcanization system comprises molecular sulfur and / or at least one sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally and also preferably, various known vulcanization activators such as zinc oxide, stearic acid, or equivalent compounds such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retardants may be used.

[0051] Sulfur is used at a preferential rate of between 0.5 and 2 parts per annum, in particular between 0.6 and 1.5 parts per annum. The vulcanization accelerator is used at a preferential rate of between 0.5 and 2 parts per annum, more preferably between 0.6 and 1.5 parts per annum.

[0052] Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used as an accelerator, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. Examples of such accelerators include the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-ter-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-ter-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC"), and mixtures thereof. compounds. II-4 Possible Additives

[0053] The rubber compositions according to the invention may optionally also include all or part of the usual additives commonly used in tire elastomer compositions, such as plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing resins (such as described for example in application WO 02 / 10269).

[0054] The rubber composition preferably does not include rubber powder. "Rubber powder" is understood to mean a cross-linked composition based on at least one elastomer and a filler in the form of particles having a size, namely their diameter in the case of spherical particles or their largest dimension in the case of anisometric particles, of a few tens or hundreds of microns.

[0055] The composition according to the invention does not require the use of reinforcing resins (or hardening resins) known to those skilled in the art for stiffening rubber compositions, in particular by increasing their Young's modulus or the dynamic shear complex G*. Advantageously, the rubber composition does not comprise a formophenolic resin, preferably no reinforcing resin. Examples of such reinforcing resins can be found in Chapter II.3 of application WO20198679A1.

[0056] Advantageously, the composition according to the invention does not include liquid plasticizer at 23°C or includes less than 10 parts per liter, preferably less than 5 parts per liter. Preferably, the composition according to the invention does not include liquid plasticizer at 23°C. II-5 Preparation of compositions

[0057] Rubber compositions according to the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: - a first thermomechanical working or mixing phase (the so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents, including the elastomeric matrix, the reinforcing filler, and any other miscellaneous additives, with the exception of the crosslinking system, are introduced into a suitable mixer such as a standard internal mixer (for example, a "Banbury" type mixer). The incorporation of the filler into the elastomer can be carried out in one or more stages by thermomechanical mixing. nimiste. In cases where the filler is already fully or partially incorporated into the elastomer as a masterbatch, as described, for example, in applications WO 97 / 36724 or WO 99 / 16600, the masterbatch is directly mixed, and where applicable, other elastomers or fillers present in the composition that are not in masterbatch form, as well as any other miscellaneous additives other than the crosslinking system, are incorporated. The non-productive phase can be carried out at high temperature, up to a maximum temperature between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally between 2 and 10 minutes. - a second mechanical working phase (the so-called "productive" phase), which can be carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min.

[0058] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0059] The final composition thus obtained is then calendered, for example, into a sheet or plate, particularly for laboratory characterization, or extruded (or co-extruded with another rubber composition) into a semi-finished (or profile) rubber product usable, for example, as a tire tread. These products can then be used for tire manufacturing, according to techniques known to those skilled in the art.

[0060] The composition can be either in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), can be a semi-finished product that can be used in a tire.

[0061] The crosslinking of the composition can be carried out in a manner known to those skilled in the art, for example at a temperature between 130°C and 200°C, under pressure. II-6 Rubber Article

[0062] The present invention also relates to a rubber article comprising at least one composition according to the invention. The rubber article may be selected from the group consisting of tires, tracks, conveyor belts, belts, and anti-vibration articles. Preferably, the rubber article is selected from the group consisting of tires and conveyor belts. Even more preferably, the rubber article is a tire.

[0063] In the present invention, the term "pneumatic" (in English, "tire") refers to a pneumatic or non-pneumatic tire. A pneumatic tire comprises A non-pneumatic tire typically comprises two beads for contact with a rim, a crown consisting of at least one crown reinforcement and a tread, and two sidewalls. The tire is reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic tire, on the other hand, typically comprises a base, designed, for example, for mounting on a rigid rim, a crown reinforcement connecting to a tread, and a deformable structure, such as spokes, ribs, or dimples, this structure being positioned between the base and the crown. Such non-pneumatic tires do not necessarily include a sidewall. Non-pneumatic tires are described, for example, in documents WO 03 / 018332 and FR2898077. According to any one of the embodiments of the invention, the tire according to the invention is preferably a pneumatic tire.

[0064] The tire according to the invention can be used to equip any type of vehicle, particularly motor vehicles, without any particular limitation. However, given the performance compromise of the compound according to the invention, it is particularly well-suited to heavy-duty tires, especially their tread. Thus, the invention also relates to a heavy-duty tire comprising a compound according to the invention. Preferably, the compound according to the invention is present in the tread of the heavy-duty tire. The compound according to the invention may constitute part or all of the tire's tread.

[0065] The term "heavy-duty tire" refers to a tire, particularly one with a radial carcass, for vehicles with a maximum authorized mass (MAM) exceeding 3.5 tonnes. These vehicles are equipped with wheels whose rims have a nominal diameter of 19.5 inches or more. Preferably, the diameter of the heavy-duty tire according to the invention falls within a range of 19.5 to 25 inches. III- EXAMPLES III-1 Measurements and tests used Fatigue test

[0066] Fatigue resistance, expressed in number of cycles or in relative unit (ur), is measured in a known manner on 12 specimens subjected to repeated low-frequency tensile stresses up to an elongation of 75%, at 23°C, using a Monsanto apparatus (type "MFTR") until the specimen breaks, according to ASTM D4482-85 and ISO 6943 standards.

[0067] The result is expressed as a base of 100 relative to a reference composition. A value greater than that of the reference, arbitrarily set at 100, indicates a result improved, that is to say, better resistance to fatigue of the rubber samples, and therefore better endurance.

[0068] Mechanical properties after baking: Tensile test

[0069] The elongation at break (AR%) and tensile strength (CR) tests are based on standard NF ISO 37 of December 2005 on a type H2 dumbbell specimen and are measured at a tensile speed of 500 mm / min at a temperature of 60°C. Elongation at break is expressed as a percentage of elongation. Tensile strength is expressed in MPa. These values ​​are expressed as a base of 100 relative to a control composition. A value greater than 100 indicates an improvement in the mechanical properties of the composition considered compared to the control composition.

[0070] All these tensile measurements are carried out under normal hygrometric conditions (50+5% relative humidity), according to the French standard NF T 40-101 (December 1979). Tearability

[0071] Tear resistance indices are measured at 100°C. Specifically, the force required to achieve failure (FRD, in MPa (in N / mm²)) is determined, and the strain at failure (DRD, in %) is measured on a specimen measuring 10 x 85 x 2.5 mm, notched along its length with three notches to a depth of 3 mm, to induce fracture. Thus, the energy required to cause fracture (Fracture Energy) of the specimen, which is the product of the FRD and the DRD, can be determined.

[0072] The Energy Breaking results are expressed as a base of 100 relative to a control composition. A result greater than 100 indicates an improvement in tear resistance.

[0073] Determination of the microstructure of elastomers by magnetic resonance nuclear (NMR):

[0074] Ethylene-1,3-butadiene copolymers are characterized by ¹H,¹³C NMR spectroscopy. The NMR spectra are recorded on a Brüker Avance III 500 MHz spectrometer equipped with a 5 mm BBIz-grad "broadband" cryo-probe. The quantitative ¹H NMR experiment uses a single 30° pulse sequence and a 5-second repetition delay between each acquisition. 64 to 256 accumulations are performed. The quantitative ¹³C NMR experiment uses a single 30° pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. The two-dimensional ¹H / ¹³C experiments are used to determine the polymer structure. The determination of the microstructure of copolymers is defined in the literature, according to the article by Llauro et al., Macromolecules 2001, 34, 6304-6311.

[0075] The NMR measurements are carried out at 25°C, the copolymers being in solution in a deuterated solvent (approximately 25mg of elastomer in ImL), usually deuterated chloroform (CDC13).

[0076] Determination of the macrostructure of polymers by size exclusion chromatography Steric (SEC):

[0077] Size exclusion chromatography (SEC) allows the fractionation of polymer chains in a solvent according to their hydrodynamic volume. Like any chromatographic system, the technique is based on the elution of a solute (the polymer) through a column containing a stationary phase. The system consists, in this order, of a solvent reservoir, a pumping system, an injector, a set of columns, and detectors. The measurement chain is equipped with a Waters Alliance e2695 module and a Waters fRI410 refractometer.

[0078] The mobile phase is eluted at a flow rate of 1 mL / min. The polymer is solubilized in THF in the presence of 1 wt% diisopropylamine and 1 wt% triethylamine at a concentration of 1 g / L. A volume of 100 pL is injected through a set of three A GELENT (MIXED B LS) size-exclusion chromatography columns. The columns are oven-heated at 35°C. The stationary phase of the columns is based on a divinylbenzene polystyrene gel with controlled porosity. The polymer chains are separated according to the hydrodynamic volume they occupy when solubilized in the solvent. The larger the volume they occupy, the less accessible the column pores are to them, and the shorter their elution time. Detection is performed using a refractometer (RI) thermostated at 35°C.Each elution volume is associated with a mass via Moore calibration (certified standard: Polymer Standard Service (Mainz) standard polystyrenes). The WATERS: EMPOWER software is used for data acquisition and analysis. It is then possible to determine the number-average molar masses (Mn), the mass-average molar masses (Mw), and the polydispersity (Ip = Mw / Mn). Mooney ML 1+4

[0079] For polymers and rubber compositions, the Mooney viscosities ML(l+4) at 100°C are measured using an oscillating consistometer according to ASTM D-1646 (1999). The Mooney plasticity measurement is performed according to the following principle: the composition in its raw state (i.e., before curing) is molded in a cylindrical chamber heated to 100°C. After one minute of preheating, the rotor rotates within the specimen at 2 revolutions per minute, and the torque required to maintain this rotation after 4 minutes of rotation is measured. The Mooney plasticity ML(l+4) is expressed in "Mooney units" (MU, with 1 MU = 0.83 Nm). III-2 Synthesis of the El copolymer:

[0080] In the synthesis of ethylene and 1,3-butadiene copolymers, all reagents are commercially available except for the metallocenes. The BOMAG butylmagnesium (20% in heptane, C = 0.88 mol.L*) is sourced from Chemtura and is stored in a Schlenk tube under an inert atmosphere. The N35 grade ethylene is sourced from Air Liquide and is used without prior purification.

[0081] The ethylene and 1,3-butadiene copolymer: El elastomer (according to the invention) is synthesized according to the procedure described below.

[0082] The polymerization of ethylene (N35 grade, from Air Liquide, used without prior purification) and 1,3-butadiene is carried out by a continuous process in solution in methylcyclohexane at 80°C under 11.5 bar in the presence of a catalytic system (94 pmoles Nd for 100 g of monomers), the mass concentration of monomer feed into the reactor being 6%, the mass ratio 1,3-butadiene / ethylene being 0.53, the molar ratio active Mg / Nd being 3.7. At the desired conversion (73%, 120 minutes) to achieve a Mn of approximately 139 kg / mol, polymerization is stopped at the line outlet using an antioxidant solution in methylcyclohexane (0.6 parts per cent of elastomer: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 0.7 parts per cent of 2,2'-methylene-bis(4-methyl-6-tert-butylphenol). The copolymer is recovered by a steam stripping process, well known to those skilled in the art, and then dried on a screw conveyor equipped with a single screw.

[0083] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(q-BH4)2Li(THF)] at 0.0065 mol / L, a co-catalyst, butylmagnesium (BOMAG) with a BOMAG / Nd molar ratio of 2.2, and a preforming monomer, 1,3-butadiene with a 1,3-butadiene / Nd molar ratio of 90. The medium is heated to 80°C for 5 hours. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 AL

[0084] The microstructure of the El copolymer and its properties are shown in Tables 1 and 2. For the microstructure, Table 1 shows the molar ratios of the ethylene (Eth) units, the 1,3-butadiene units, and the 1,2-cyclohexanediyl (ring) motifs.

[0085] [Tables 1] Elastomer Ethylene (%mol) 68.6 Butadiene 1.3 (%mol) 14.9 1,2-cyclohexanediyl (%mol) 8.5

[0086] [Tables2] Elastomer El Tg (°C) -43.4 Mn (g / mol) 157,700 Mooney (ML (1+4)) at 100°C 69.9 III-3 Preparation of compositions

[0087] In the following examples, the rubbery compositions were produced as described in section II.5 above. In particular, the "non-productive" phase was carried out in a 0.4-liter mixer for 3.5 minutes, at an average paddle speed of 50 revolutions per minute, until a maximum drop temperature of 160°C was reached. The "productive" phase was carried out in a roller tool at 23°C for 5 minutes.

[0088] The crosslinking of the composition was carried out at a temperature between 130°C and 200°C, under pressure. III-4 Tests of Rubber Compositions

[0089] The examples presented below are intended to compare the performance trade-off between elongation at break and tear resistance of compositions according to the present invention (Cl to C3) with control compositions (T0 to T3).

[0090] Table 3 presents the compositions tested (in pieces), as well as the results obtained.

[0091] The control compositions differ from the compositions (Cl to C3) by the nature of the butadiene and styrene based copolymer, by the nature of the natural rubber, by the rate of reinforcing filler.

[0092] The elongation at break at 60°C and tear resistance results are expressed as a percentage, base 100, relative to the control composition T0, corresponding to a typical heavy-duty tire tread compound. A decrease of less than 10 percent in tear resistance is considered acceptable given the high performance of the control composition T0.

[0093] [Tables3] Composition T0 Tl Cl C2 T2 T3 C3 NR(1) 60 - 2.5 5 20 - 5 BR (2) 20 - - - - - - SBR (3) 20 - - - - - - Elastomer El (4) - 100 97.5 95 80 100 95 Black (5) 55 40 40 40 40 12 12 Silica (6) - - - - - 24 24 Silane (7) - - - - - 2 2 Paraffin 1 1 1 1 1 1 1 Antioxidant (8) 2 2 2 2 2 2 2 Polyethylene Glycol (9) - 0.6 0.6 0.6 0.6 - - Stearic Acid (10) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 ZnO(ll) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Accelerator (12) 1 1 1 1 1 0.5 0.5 Sulfur 1 1 1 1 1 0.75 0.75 DPG(13) - - - - - 0.75 0.75 Properties Elongation Fracture (%) 100 121 115 110 74 121 130 Tearability 100 132 110 93 17 101 97

[0094] (1) Natural rubber (2) Neodymium Polybutadiene 98% 1,4-Cis, Tg = -108°C (3) SBR solution functionalized tin with 15% styrene motif and 24% polybutadiene motifs 1,2 of the butadiene part (Tg = -65°C) (4) Elastomer El prepared in point III-2 above (5) N234 grade carbon black according to ASTM D-1765 (6) Silica “Zeosil 1165MP” from the Solvay company (7) Silane Mercapto-Thiocarboxylate Oligomer “NXT-Z45” from Momentive (8) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine “Santaflex 6-PPD” from Flexsys (9) Polyethylene glycol “CARBOWAX 8000” from Dow Corning (10) Stearic acid “Pristerene 4931” from the company Uniqema (11) Industrial grade zinc oxide from Umicore (12) N-cyclohexyl-2-benzothiazyl sulfenamide “Santicure CBS” from Flexsys (13) Diphenylguanidine “Perkacit DPG” from the company Flexsys

[0095] The results presented in Table 3 above show that compositions comprising a copolymer containing ethylene units and 1,3-diene units according to the invention exhibit better elongation at break without significantly impacting tear resistance when these compositions comprise less than 20 pc of polyisoprene having a mass percentage of 1,4-cis bonds of at least 90%.

[0096] Furthermore, fatigue resistance tests were carried out on the Tl to T3 and Cl to C3 compositions to compare the effect of the polyisoprene content on the endurance of two formulations (Table 4).

[0097] The fatigue resistance results are expressed as a percentage based on 100 relative to the control composition Tl for compositions Cl, C2 and T2, and relative to composition T3 for composition C3.

[0098] [Tables4] Compositions Tl Cl C2 T2 T3 C3 Properties Fatigue (MFTR) Base 100 100 112 138 53 100 149

[0099] The results presented in Table 4 above show that the presence of polyisoprene at levels in accordance with the invention improves fatigue resistance.

[0100] Thus, the compositions according to the invention present a very good compromise of performance between elongation at break, resistance to tearing and resistance to fatigue, and consequently better endurance or longevity.

Claims

Demands

1. Rubber composition based on at least: - an elastomeric matrix comprising 85 to 98 parts per cent of at least one copolymer containing ethylene units and 1,3-diene units, the mole fraction of ethylene units in the copolymer being in the range of more than 50% to 95%, and 2 to 15 parts of a polyisoprene having a mass percentage of 1,4-cis bonds of at least 90% of the mass of the polyisoprene, - a reinforcing filler comprising carbon black having a specific surface area BET in the range of 50 to 160 m2 / g, and - a crosslinking system.

2. Rubber composition according to claim 1, wherein the copolymer containing ethylene units and 1,3-diene units is a copolymer of ethylene and 1,3-diene.

3. Rubber composition according to any one of the preceding claims, wherein the 1,3-diene units are 1,3-butadiene units.

4. Rubber composition according to any one of the preceding claims, wherein the copolymer does not contain a unit of a 1,3-diene of formula CH2=CR-CH=CH2 in which R represents a hydrocarbon chain having 3 to 20 carbon atoms.

5. Rubber composition according to any one of the preceding claims, wherein the proportion of at least one copolymer containing ethylene units and 1,3-diene units is in the range of 88 to 97 pc, preferably more than 90 to 96 pc.

6. Rubber composition according to any one of the preceding claims, wherein the polyisoprene is selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof, preferably the polyisoprene is natural rubber.

7. Rubber composition according to any one of the preceding claims, wherein the polyisoprene content is in the range of 3 to 12 pc, preferably from 4 to less than 10 pc.

8. Rubber composition according to any one of the claims previous, in which carbon black has a BET specific surface area in the range of 90 to 160 m2 / g, and preferably 100 to 150 m2 / g.

9. Rubber composition according to any one of the preceding claims, wherein the reinforcing filler comprises more than 50% by weight, preferably more than 90% by weight, of carbon black.

10. Rubber composition according to any one of claims 1 to 8, wherein the reinforcing filler comprises from 50% to 95% by weight, preferably from 60% to 95% by weight, of silica and from 5% to 50% by weight, preferably from 5% to 40% by weight, of carbon black.

11. Rubber composition according to any one of the preceding claims, wherein the reinforcing filler ratio is in the range of 20 to 70 pc, preferably 30 to 60 pc.

12. Rubber composition according to any one of the preceding claims, wherein the crosslinking system is a vulcanizing system based on molecular sulfur and / or a sulfur-donating agent.

13. Rubber composition according to any one of the preceding claims, the rubber composition not comprising rubber powder.

14. Rubber composition according to any one of the preceding claims, the rubber composition not comprising any formophenolic resin, preferably no reinforcing resin.

15. Heavy-duty tire comprising a composition according to any one of claims 1 to 14, the composition being present in the tread of the tire.