Rubber composition comprising a highly saturated diene elastomer

Abstract

The invention relates to a rubber composition having a good performance compromise between elongation at break, tear strength and fatigue resistance. This composition is based on at least one elastomer matrix comprising from 85 to 98 phr of at least one copolymer containing ethylene units and 1,3-diene units, the molar fraction of ethylene units in the copolymer being within a range extending from more than 50% to 95%, and from 2 to 15 phr of a polyisoprene comprising a content by weight of cis-1,4 bonds of at least 90% of the weight of the polyisoprene, a reinforcing filler comprising carbon black having a BET specific surface area within a range extending from 50 to 160 m2 / g, and a crosslinking system. The invention also relates to a tyre comprising this composition.

Description

[0001] RUBBER COMPOSITION COMPRISING A HIGHLY SATURATED DIENE ELASTOMER

[0002] 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 goods vehicle tire.

[0003] Tires designed for vehicles carrying heavy loads have specific characteristics in terms of size, robustness and architecture that distinguish them from other tires, particularly tires for passenger vehicles. Their treads must meet a large number of technical requirements, often contradictory, such as low rolling resistance, high wear resistance, as well as good resistance to attack by foreign bodies present on the surface on which the tire rolls.

[0004] Indeed, the use of these tires on terrains with many stones and other bodies or potholes, generates aggressions of the tread. For machines carrying heavy loads, in particular heavy goods vehicles, it is known that the treads of the tires equipping these vehicles are subjected to repetitive impacts which can cause tearing of material from the tread. It is therefore necessary that the treads of the tires of these vehicles have good resistance to aggressions as well as a better elongation at break in order to limit the appearance of cracks in the rubber compositions which constitute these treads. The elongation at break corresponds to the capacity of these compositions to deform without breaking.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 repeated cyclically during the rolling of the tire) must also be taken into account. Improving elongation at break should preferably be done without excessively penalizing tear resistance and fatigue resistance, or even by improving them.

[0005] Thus, manufacturers are always looking for solutions to further improve the elongation at break properties while maintaining the tear resistance properties within acceptable limits. Continuing its research, the Applicant unexpectedly discovered that the addition of a specific quantity of a polyisoprene in a rubber composition comprising mainly a highly saturated diene elastomer, makes it possible to further improve the aforementioned performance compromise.

[0006] Thus, a first subject of the invention is a rubber composition based on at least one elastomer matrix comprising from 85 to 98 pce of at least one copolymer containing ethylene units and 1,3-diene units, the molar fraction of the ethylene units in the copolymer being within a range from more than 50% to 95%, and from 2 to 15 pce of a polyisoprene comprising a mass content 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 within a range from 50 to 160 m 2 / g and a crosslinking system.

[0007] A second subject of the invention is a heavy goods vehicle tire which comprises a rubber composition in accordance with the invention.

[0008] I- DEFINITIONS

[0009] 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 manufacture of the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0010] By “elastomer matrix” is meant all the elastomers in the composition, including the copolymer defined below.

[0011] 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.

[0012] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts of elastomer present in the rubber composition considered.

[0013] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass. Furthermore, any interval of values ​​designated by the expression "between a and b" represents the range of values ​​from more than a to less than b (i.e., excluding limits a and b), while any interval of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict limits a and b). In this document, 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 a "majority" compound is referred to, within the meaning of the present invention, this compound is the majority among the compounds of the same type in the composition, that is to say that it is the one which represents the largest quantity by mass among the compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the largest mass relative to the total mass of the elastomers in the composition. In the same way, a so-called majority filler is the one representing the largest mass among the fillers in the composition. For example, in a system comprising a single elastomer, this is the majority within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers. On the contrary, a "minority" compound is a compound which does not represent the largest mass fraction among the compounds of the same type.Preferably by majority, we mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

[0015] The compounds mentioned in the description may be of fossil or bio-sourced origin. 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, i.e. 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 stated, all glass transition temperature “Tg” values ​​described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999).

[0017] II- DESCRIPTION OF THE INVENTION

[0018] II- 1 Elastomer matrix

[0019] According to the invention, the elastomer matrix comprises from 85 to 98 pce of at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer represent between 50% and 95% by mole of the monomer units of the copolymer (hereinafter referred to as "the copolymer") and from 2 to 15 pce of a polyisoprene comprising a mass content of 1,4-cis bonds of at least 90% of the mass of the polyisoprene.

[0020] By "copolymer containing ethylene units and 1,3-diene units" is meant any copolymer comprising, within its structure, at least ethylene units and 1,3-diene units. The copolymer may thus comprise monomer units other than the ethylene units and the 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 3 to 6 carbon atoms. For example, the alpha-olefin units may be chosen from the group consisting of propylene, butene, pentene, hexene or mixtures thereof. However, the copolymer does not comprise a unit of a 1,3-diene of formula CH2=CR-CH=CH2, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms.

[0021] As is well known, the expression "ethylene unit" refers to the -(CH2-CH2)- motif resulting from the insertion of ethylene into the elastomer chain.

[0022] As is known, the expression "1,3-diene unit" refers to the 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.

[0023] Preferably, the 1,3-diene units are chosen 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. More preferably, the 1,3-diene units are predominantly, in moles, or even preferentially exclusively, 1,3-butadiene units.

[0024] 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.

[0025] 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). Preferably, the copolymer does not contain a 1,3-diene unit of formula CH2=CR- CH=CH2, in which R represents a hydrocarbon chain having 3 to 20 carbon atoms.

[0026] 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 the saturated 6-membered cyclic unit, 1,2-cyclohexanediyl, of formula (I) as a monomeric unit in the copolymer may result from a series of very specific insertions of ethylene and 1,3-butadiene into the polymer chain during its growth.

[0027] For example, the copolymer of ethylene and a 1,3-diene may be devoid of units of formula (I). In this case, it preferably contains units of formula (II).

[0028] 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 the units of formula (I) and the 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.

[0029] 0 < o+p < 25 (eq. 1)

[0030] 0 < o+p < 20 (eq. 2)

[0031] According to the invention, the copolymer, preferably the copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene), is a random copolymer.

[0032] Advantageously, the number-average mass (Mn) of the copolymer, preferably of the copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene) is within a range from 100,000 to 300,000 g / mol, preferably from 150,000 to 250,000 g / mol. The Mn of the copolymer is determined in a known manner, by size exclusion chromatography (SEC) as described in point III-1 below.

[0033] The copolymer can be obtained according to different synthesis methods known to those skilled in the art, in particular depending on the targeted microstructure of the copolymer. Generally, it can be prepared by copolymerization of at least one diene, preferably a 1,3-diene, more preferably 1,3-butadiene, and ethylene and according to known synthesis methods, in particular in the presence of a catalytic system comprising a metallocene complex. Mention may be made in this respect of catalytic systems based on metallocene complexes, which catalytic systems are described in documents EP 1 092 731, WO 2004035639, WO 2007054223 and WO 2007054224 in the name of the Applicant. The copolymer, including when it is statistical, can also be prepared by a process using a preformed type catalytic system such as those described in documents WO 2017093654 Al, WO 2018020122 Al and WO 2018020123 AL

[0034] The copolymer may consist of a mixture of copolymers containing ethylene units and 1,3-diene units which differ from each other in their microstructures and / or in their macrostructures.

[0035] Advantageously, the rate of at least one copolymer containing ethylene units and 1,3-diene units may be within a range from 88 to 97 pce, preferably more than 90 to 96 pce.

[0036] Advantageously, the polyisoprene having a mass content of 1,4-cis bond of at least 90% of the mass of the polyisoprene, is a natural rubber, a synthetic polyisoprene or a mixture thereof. More preferably, the polyisoprene, preferably having a mass content of 1,4-cis bond of at least 90% of the mass of the polyisoprene, is a natural rubber.

[0037] Advantageously, the level of polyisoprene in the composition according to the invention is preferably within a range from 3 to 12 pce, preferably from 4 to less than 10 pce.

[0038] II-2 Reinforcing charge

[0039] 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, in particular and more preferably between 20 and 150 nm.

[0040] According to the invention, the reinforcing filler comprising carbon black has a BET specific surface area in a range from 50 to 160 m 2 / g.

[0041] The reinforcing filler may also include a reinforcing filler other than carbon black, in particular silica, but this is not mandatory.

[0042] 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 the carbon black having a BET specific surface area in a range of from 50 to 160 m 2 / g. When the reinforcing filler comprises a mixture of carbon black and silica, the reinforcing filler advantageously 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.

[0043] The blacks that can be used in the context of the present invention can be any black conventionally used in tires or their treads (so-called tire-grade blacks). Among the latter, mention will be made more particularly of the reinforcing carbon blacks of the 100, 200, 300 series (ASTM grades), such as for example blacks NI 15, N134, N234, N326, N330, N339, N347, N375). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a support for some of the rubber additives used. The carbon blacks could for example already be incorporated into the diene elastomer, in particular isoprene in the form of a masterbatch (see for example applications WO 97 / 36724 or WO 99 / 16600).

[0044] Among the above-mentioned carbon blacks, those having a BET specific surface area in the range from 90 to 160 m 2 / g, and preferably 100 to 150 m2 / g, are particularly preferred.

[0045] The BET specific surface area of ​​carbon blacks is measured according to standard D6556-10 [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range P / P0: 0.1 to 0.3]. Any type of precipitated silica may be suitable as silicas, in particular highly dispersible precipitated silicas (called "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 W003 / 016215-A1 and W003 / 016387-A1. Among the commercial HDS silicas, we can notably use the silicas “Ultrasil ® 5000GR”, “Ultrasil ® 7000GR” from the company Evonik, the silicas “Zeosil ® 1085GR”, “Zeosil® 1115 MP”, “Zeosil® 1165MP”, “Zeosil® Premium 200MP”, “Zeosil® HRS 1200 MP” from the company Solvay.As non-HDS silica, the following commercial silicas can be used: silicas “Ultrasil ® VN2GR”, “Ultrasil ® VN3GR” from Evonik, silica “Zeosil® 175GR” from Solvay, silicas “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(-D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” from PPG.

[0046] In this presentation, the BET specific surface area 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 precisely according to a method adapted from the NF ISO 5794-1 standard, annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - vacuum degassing: one hour at 160°C - relative pressure range p / po: 0.05 to 0.17],

[0047] To couple the silica to the diene elastomer, it is possible to use, in a well-known manner, an at least bifunctional coupling agent (or bonding agent) intended to ensure a sufficient connection, of a chemical and / or physical nature, between the inorganic filler (surface of its particles) and the diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. By "bifunctional", we mean 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 filler and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the diene elastomer.

[0048] Preferably, when used, the organosilanes are chosen from the group consisting of polysulfurized organosilanes (symmetrical or asymmetrical) such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, marketed under the name “Si69” by the company Evonik or bis-(triethoxysilylpropyl) disulfide, abbreviated to TESPD, marketed under the name “Si75” by the company Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl) octanethioate marketed by the company Momentive under the name “NXT Silane”. More preferably, the organosilane is a polysulfurized organosilane.

[0049] When the reinforcing filler comprises silica, the coupling agent content can easily be adjusted by a person skilled in the art. Typically, the coupling agent content represents from 0.5% to 15% by weight relative to the quantity of silica.

[0050] The level of reinforcing filler can easily be adjusted by a person skilled in the art depending on the use of the rubber composition. Advantageously, the level of reinforcing filler, in the composition according to the invention, is within a range from 20 to 70 phr, preferably from 30 to 60 phr.

[0051] II-3 Crosslinking system

[0052] The crosslinking system may be any type of system known to those skilled in the art in the field of tire rubber compositions. It may in particular be based on sulfur, and / or peroxide and / or bismaleimides.

[0053] Preferably, the crosslinking system is sulfur-based, in which case it is 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, also preferably, various known vulcanization activators may be used, 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 retarders.

[0054] Sulphur is used at a preferential rate of between 0.5 and 2 pce, in particular between 0.6 and 1.5 pce. The vulcanisation accelerator is used at a preferential rate of between 0.5 and 2 pce, more preferably between 0.6 and 1.5 pce.

[0055] Any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur may 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, but are not limited to, the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZB EC") and mixtures of these compounds.

[0056] II-4 Possible additives

[0057] The rubber compositions according to the invention may optionally also comprise all or part of the usual additives usually used in elastomer compositions for tires, such as for example 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 (as described for example in application WO 02 / 10269).

[0058] The rubber composition preferably does not comprise rubber crumb. The term “rubber crumb” means a crosslinked composition based on at least one elastomer and a filler in the form of particles which have 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.

[0059] 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 formophenolic resin, preferably no reinforcing resin. Examples of such reinforcing resins can be found in chapter II.3 of application WO20198679A1.

[0060] Advantageously, the composition according to the invention does not comprise liquid plasticizer at 23°C or comprises less than 10 pce, preferably less than 5 pce. Preferably, the composition according to the invention does not comprise liquid plasticizer at 23°C.

[0061] II-5 Preparation of compositions

[0062] The rubber compositions in accordance with the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

[0063] - a first phase of working or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents, in particular the elastomeric matrix, the reinforcing filler, any other various additives, with the exception of the crosslinking system, are introduced into a suitable mixer such as a standard internal mixer (for example of the "Banbury" type). The incorporation of the filler into the elastomer can be carried out in one or more stages by thermomechanical mixing.In the case where the filler is already incorporated in whole or in part into the elastomer in the form of a masterbatch as described for example in applications WO 97 / 36724 or WO 99 / 16600, it is the masterbatch which is directly mixed and where appropriate the other elastomers or fillers present in the composition which are not in the form of a masterbatch are incorporated, as well as any other various additives other than the crosslinking system. The non-productive phase can be carried out at high temperature, up to a maximum temperature of between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally of between 2 and 10 minutes.

[0064] - a second phase of mechanical work (so-called "productive" phase), which can be carried out in an external mixer such as a cylinder 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 everything is then mixed for a few minutes, for example between 5 and 15 min.

[0065] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0066] The final composition thus obtained is then calendered, for example, in the form of a sheet or plate, in particular for characterization in the laboratory, or extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber product usable, for example, as a tire tread. These products can then be used for the manufacture of tires, according to techniques known to those skilled in the art.

[0067] 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 which can be used in a tire.

[0068] 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.

[0069] II-6 Rubber article

[0070] The present invention also relates to a rubber article comprising at least one composition according to the invention. The rubber article may be chosen from the group consisting of tires, tracks, conveyor belts, belts and anti-vibration articles. Preferably, the rubber article is chosen from the group consisting of tires and conveyor belts. More preferably, the rubber article is a tire.

[0071] In the present invention, the term "tyre" means a pneumatic or non-pneumatic tire. A pneumatic tire usually comprises two beads intended to come into contact with a rim, a crown composed of at least one crown reinforcement and a tread, two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic tire, for its part, usually comprises a base, designed for example for mounting on a rigid rim, a crown reinforcement, ensuring the connection with a tread and a deformable structure, such as spokes, ribs or cells, this structure being arranged between the base and the crown. Such non-pneumatic tires do not necessarily comprise 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 bandage.

[0072] The tire according to the invention may be intended to equip any type of vehicle, in particular motor vehicles, without any particular limitation. However, given the performance compromise of the composition according to the invention, it is particularly well suited to heavy goods vehicle tires, in particular to their tread. Thus, the invention also relates to a heavy goods vehicle tire comprising a composition according to the invention. Preferably, the composition according to the invention is present in the tread of the heavy goods vehicle tire. The composition according to the invention may constitute part or all of the tread of the tire.

[0073] The term "heavy goods vehicle tire" means a tire, in particular with a radial carcass reinforcement, for vehicles with a maximum permissible laden weight (MPW) of more than 3.5 tonnes. These vehicles are equipped with wheels whose rims have a nominal diameter greater than or equal to 19.5 inches. Thus, preferably, the diameter of the heavy goods vehicle tire according to the invention is within a range extending from 19.5 to 25 inches. III- EXAMPLES

[0074] III-l Measures and tests used

[0075] Fatigue test

[0076] 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 tractions up to an elongation of 75%, at 23°C, using a Monsanto device (type “MFTR”) until the specimen breaks, according to standards ASTM D4482-85 and ISO 6943.

[0077] The result is expressed on a base of 100 relative to a control composition. A value higher than that of the control, arbitrarily set at 100, indicates an improved result, i.e. better fatigue resistance of the rubber samples, and therefore better endurance.

[0078] Mechanical properties after curing: Tensile test

[0079] The elongation at break (AR%) and breaking stress (CR) tests are based on the NF ISO 37 standard 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. The elongation at break is expressed as a % elongation. The breaking stress is expressed in MPa. These values ​​are expressed on a base of 100 compared 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.

[0080] All these traction measurements are carried out under normal hygrometry conditions (50+5% relative humidity), according to the French standard NF T 40-101 (December 1979).

[0081] Tearability

[0082] Tearability indices are measured at 100°C. In particular, the force required to achieve rupture (FRD, in MPa (in N / mm 2 )) and the strain at break (DRD, in %) is measured on a specimen of dimensions 10 x 85 x 2.5 mm notched in the center of its length by 3 notches to a depth of 3 mm, to cause the specimen to break. Thus we can determine the Energy to cause the rupture (Rupture Energy) of the specimen which is the product of the FRD and the DRD.

[0083] The results of Energy at Break are expressed on a base of 100 compared to a control composition. A result above 100 indicates an improvement in tear resistance. Determination of the microstructure of elastomers by nuclear magnetic resonance (NMR):

[0084] Copolymers of ethylene and 1,3-butadiene are characterized by 1H NMR spectrometry, 13 C. NMR spectra are recorded on a Brüker Avance III 500 MHz Spectrometer equipped with a BBIz-grad 5 mm “broadband” cryoprobe. The quantitative 'H NMR experiment uses a single 30° pulse sequence and a 5 second repetition delay between each acquisition. 64 to 256 accumulations are performed. The NMR experiment 13 Quantitative C uses a 30° single-pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. Two-dimensional experiments are used for the purpose of determining the structure of polymers. 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.

[0085] NMR measurements are carried out at 25°C. The copolymers are dissolved in a deuterated solvent (approximately 25 mg of elastomer in 1 ml), generally deuterated chloroform (CDCh).

[0086] Determination of the macrostructure of polymers by size exclusion chromatography (SEC):

[0087] 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 is composed in this order: 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.

[0088] The mobile phase is eluted with a flow rate of 1 mL / min. The polymer is solubilized in THF in the presence of 1% wt of diisopropylamine and 1% wt of triethylamine at a concentration of 1 g / L. A volume of 100 pL is injected through a set of 3 AGILENT size exclusion chromatography columns (MIXED B LS). The columns are thermostated in an oven at 35°C. The stationary phase of the columns is based on a polystyrene divinylbenzene 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 pores of the columns are and the shorter their elution time. Detection is ensured by a refractometer (RI) thermostated at 35°C. Each elution volume is associated with a mass via Moore calibration (certified standard passage: standard polystyrenes from Polymer Standard Service (Mainz).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) as well as the polydispersity (Ip = Mw / Mn).

[0089] Mooney ML 1+4

[0090] For polymers and rubber compounds, 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 carried out according to the following principle: the raw compound (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 / minute and the torque needed to maintain this movement 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).

[0091] III-2 Synthesis of copolymer El:

[0092] In the synthesis of ethylene and 1,3-butadiene copolymers, all reagents are obtained commercially except for the metallocenes. Butyloctylmagnesium BOMAG (20% in Theptane, C = 0.88 mol.L 1 ) comes from Chemtura and is stored in a Schlenk tube under an inert atmosphere. Ethylene, grade N35, comes from Air Liquide and is used without prior purification.

[0093] The copolymer of ethylene and 1,3-butadiene: elastomer E1 (in accordance with the invention) is synthesized according to the procedure described below.

[0094] The polymerization of ethylene (grade N35, from the company Air Liquide, used without prior purification) and 1,3-butadiene is carried out according to a continuous process in solution in methylcyclohexane at 80°C under 11.5 bar in the presence of a catalytic system (94 pmoles Nd per 100 g of monomers), the mass concentration of monomer feed in 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 reach an Mn of approximately 139 Kg / mol, the polymerization is stopped at the line outlet using a solution of antioxidants in methylcyclohexane (0.6 pce of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 0.7 pce of 2,2'-methylene-bis(4-methyl-6-tertbutylphenol, pce: part by weight per hundred parts of elastomer).The copolymer is recovered by a steam distillation process called "stripping" well known to those skilled in the art, then dried on a screw machine equipped with a single screw. The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(p-BH4)2 i(THF)] at 0.0065 mol / L, a co-catalyst, butyloctylmagnesium (BOMAG) whose BOMAG / Nd molar ratio is equal to 2.2, and a preformed monomer, 1,3-butadiene whose 1,3-butadiene / Nd molar ratio is equal to 90. The medium is heated to 80°C for a period of 5 hours. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 AL.

[0095] The microstructure of copolymer El and its properties are shown in Tables 1 and 2. For the microstructure, Table 1 indicates the molar ratios of ethylene units (Eth), 1,3-butadiene units, 1,2-cyclohexanediyl units (cycle).

[0096] [Table 1]

[0097] [Table 2]

[0098] III-3 Preparation of compositions

[0099] In the following examples, the rubber compositions were produced as described in point II.5 above. In particular, the “non-productive” phase was carried out in a 0.4 liter mixer for 3.5 minutes, for 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 cylinder tool at 23°C for 5 minutes.

[0100] The crosslinking of the composition was carried out at a temperature between 130°C and 200°C, under pressure.

[0101] III-4 Rubber composition tests

[0102] The examples presented below are intended to compare the performance compromise between the elongation at break and the tear strength of compositions in accordance with the present invention (C1 to C3) with control compositions (T0 to T3). Table 3 presents the compositions tested (in pce), as well as the results obtained.

[0103] The control compositions differ from the compositions (Cl to C3) by the nature of the copolymer based on butadiene and styrene, by the nature of the natural rubber, by the rate of reinforcing filler.

[0104] The results of elongation at break at 60°C and tear resistance are expressed as a percentage base 100 compared to the control compound T0, corresponding to a usual tread compound for heavy goods vehicles. A decrease of less than 10 percent in tear resistance is considered acceptable given the high performance of the control compound T0.

[0105] [Table 3]

[0106] (1) Natural rubber (2) Polybutadiene Neodymium 98% 1,4-Cis, Tg = -108°C

[0107] (3) SBR solution functionalized tin with 15% styrene unit and 24% polybutadiene 1,2 units of the butadiene part (Tg = -65°C)

[0108] (4) Elastomer El prepared in point III-2 above (5) Carbon black grade N234 according to ASTM D-1765

[0109] (6) Silica “Zeosil 1165MP” from Solvay

[0110] (7) Silane Mercapto - Thiocarboxylate Oligomer “NXT-Z45” from Momentive

[0111] (8) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine “Santoflex 6-PPD” from Flexsys

[0112] (9) Polyethylene glycol “CARBOWAX 8000” from Dow Coming Company

[0113] (10) Stearic acid “Pristerene 4931” from Uniqema

[0114] (11) Industrial grade zinc oxide from Umicore

[0115] (12) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from Flexsys

[0116] (13) Diphenylguanidine “Perkacit DPG” from Flexsys

[0117] The results presented in Table 3 above show that the compositions comprising a copolymer containing ethylene units and 1,3-diene units in accordance with the invention exhibit better elongation at break without too much impact on tear resistance when these compositions comprise less than 20 phr of polyisoprene comprising a mass content of 1,4-cis bonds of at least 90%.

[0118] Furthermore, fatigue resistance tests were carried out on compositions Tl to T3 and Cl to C3 to compare the effect of the polyisoprene content on the endurance of two formulations (Table 4).

[0119] The fatigue resistance results are expressed as a percentage base 100 relative to the control composition Tl for compositions Cl, C2 and T2, and relative to composition T3 for composition C3.

[0120] [Table 4]

[0121] The results presented in Table 4 above show that the presence of polyisoprene at levels in accordance with the invention makes it possible to improve fatigue resistance.

[0122] Thus, the compositions in accordance with the invention exhibit a very good performance compromise between elongation at break, tear strength and fatigue resistance, and consequently better endurance or longevity.

Claims

Claims 1. Rubber composition based on at least: - an elastomer matrix comprising from 85 to 98 pce of at least one copolymer containing ethylene units and 1,3-diene units, the molar fraction of ethylene units in the copolymer being within a range from more than 50% to 95%, and from 2 to 15 pce of a polyisoprene comprising a mass content 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 the range from 50 to 160 m 2 / g, and - a crosslinking system.

2. A 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. A rubber composition according to any preceding claim, wherein the 1,3-diene units are 1,3-butadiene units.

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

5. Rubber composition according to any one of the preceding claims, in which the content of the at least one copolymer containing ethylene units and 1,3-diene units is within a range from 88 to 97 phr, preferably more than 90 to 96 phr.

6. A rubber composition according to any preceding claim, 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, in which the level of polyisoprene is within a range from 3 to 12 pce, preferably from 4 to less than 10 pce.

8. A rubber composition according to any preceding claim, wherein the carbon black has a BET specific surface area in the range of 90 to 160 m 2 / g, and preferably 100 to 150 m 2 / g.

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

10. A 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, in which the level of reinforcing filler is within a range from 20 to 70 phr, preferably from 30 to 60 phr.

12. A rubber composition according to any preceding claim, wherein the crosslinking system is a molecular sulfur-based and / or sulfur-donating agent-based vulcanization system.

13. A rubber composition according to any preceding claim, the rubber composition not comprising rubber crumb.

14. Rubber composition according to any one of the preceding claims, the rubber composition not comprising formophenolic resin, preferably not reinforcing resin.

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