Rubber composition

Abstract

The invention relates to a rubber composition which comprises: more than 90 phr of a highly saturated diene elastomer which is a copolymer of ethylene and 1,3-butadiene and contains more than 50 mol% of ethylene units; between 30 phr and 55 phr of a reinforcing filler which comprises more than 90 wt.% of a carbon black; a vulcanisation system; and a content of less than 3 phr of a polyalkylene glycol bearing a hydroxy function at each polymer chain end, the polyalkylene glycol being a homopolymer of ethylene glycol or propylene glycol or a copolymer of ethylene glycol and propylene glycol. The composition has improved properties of resistance to crack propagation.

Description

Rubber composition

[0001] The field of the present invention is that of rubber compositions reinforced with carbon black and rich in a highly saturated diene elastomer. These rubber compositions are particularly intended for use in a tire.

[0002] It is known to use in tire rubber compositions copolymers having a lower sensitivity to oxidation, such as for example highly saturated diene elastomers that are copolymers of ethylene and 1,3-butadiene which contain more than 50 mol% of ethylene units. The use of these copolymers of ethylene and 1,3-butadiene in a tire tread is for example described in document WO 2014114607 A1 and has the effect of giving the tire an improved performance compromise between rolling resistance and wear resistance. It is also known to use such copolymers in aircraft tire treads to increase wear resistance at high speed, as is for example described in document WO 2016012259 A1.

[0003] It is also important to have rubber compositions that exhibit good cohesion, including good resistance to crack propagation. During rolling, a tire tread is subjected to mechanical stresses and attacks resulting from direct contact with the ground. This results in the formation of cracks. As they propagate on the surface or inside the tread, the crack incipients can damage the material that makes up the tread. This damage to the tread reduces the tire's tread life.Since the mechanical stresses and the attacks suffered by the tire are amplified under the effect of the weight carried by the tire, good cohesion is particularly sought for a composition intended to be used as a tread of a tire mounted on a vehicle carrying heavy loads, such as a tire for a heavy goods vehicle or civil engineering vehicle. To increase the resistance to crack propagation of a rubber composition reinforced with a carbon black and containing such a highly saturated diene elastomer, the Applicant has described in document WO 2020053520 A1 the use in the rubber composition of low sulfur levels, in particular less than 1 pce.

[0004] Continuing its efforts, the Applicant has developed a new rubber composition rich in a highly saturated diene elastomer and reinforced mainly with carbon black which also has good crack propagation resistance properties.

[0005] Thus, a first subject of the invention is a rubber composition which comprises more than 90 phr of a highly saturated diene elastomer which is a copolymer of ethylene and 1,3-butadiene and which contains more than 50% by mole of ethylene units, between 30 phr and 55 phr of a reinforcing filler which comprises more than 90% by mass of a carbon black, a vulcanization system and at a rate of less than 3 phr a polyalkylene glycol carrying at each end of the polymer chain a hydroxy function, the polyalkylene glycol being a homopolymer of ethylene glycol or propylene glycol or a copolymer of ethylene glycol and propylene glycol.

[0006] Another subject of the invention is a tire which comprises a tread, the portion of which intended to be in contact with the rolling ground is made up entirely or in part of a rubber composition in accordance with the invention. Description

[0007] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​greater than "a" and less than "b" (i.e., excluding the limits 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" (i.e., including the strict limits a and b).

[0008] The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if more than one elastomer is present).

[0009] 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, 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.

[0010] 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.

[0011] Unless otherwise indicated, the rates of units resulting from the insertion of a monomer into a copolymer such as the highly saturated diene elastomer useful for the purposes of the invention are expressed as a molar percentage relative to the total monomer units of the copolymer.

[0012] The highly saturated diene elastomer useful for the purposes of the invention is a copolymer of ethylene and 1,3-butadiene, preferably a random copolymer. The monomer units of the copolymer are those resulting from the copolymerization of ethylene and 1,3-butadiene. The copolymer therefore contains ethylene units and butadiene units. In a known manner, an ethylene unit is a monomer unit of the unit -(CH2-CH2)-. Also in a known manner, a butadiene unit is a monomer unit of the unit -CH2-CH(CH=CH2)- (1,2 unit) or -CH2-CH=CH-CH2- (1,4 unit). The highly saturated diene elastomer contains more than 50 mol% of ethylene units.

[0013] The highly saturated diene elastomer preferably comprises at least 60 mol% of ethylene units, more preferably at least 65 mol% of ethylene units. In other words, the ethylene units preferably represent at least 60 mol% of all the monomer units of the highly saturated diene elastomer, more preferably at least 65 mol% of all the monomer units of the highly saturated diene elastomer. Preferably, the ethylene units represent at most 80 mol% of all the monomer units of the highly saturated diene elastomer. More preferably, the ethylene units represent at most 75 mol% of all the monomer units of the highly saturated diene elastomer.Advantageously, the highly saturated diene elastomer comprises from 60% to 80% by mole of ethylene units, particularly from 60% to 75% by mole of ethylene units, more particularly from 65% to 75% by mole of ethylene units, molar percentage calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0014] The highly saturated diene elastomer can be obtained according to different synthesis methods known to those skilled in the art, in particular depending on the targeted microstructure of the highly saturated diene elastomer. Generally, it can be prepared by copolymerization of 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 patent applications EP 1 092731, WO 2004035639, WO 2007054223 and WO 2007054224 in the name of the Applicant. The highly saturated diene elastomer, including when it is random, can also be prepared by a process using a preformed type catalytic system such as those described in patent applications WO 2017093654 A1, WO 2018020122 A1 and WO 2018020123 A1.Advantageously, the highly saturated diene elastomer is random and is preferably prepared according to a semi-continuous or continuous process as described in patent applications WO 2017103543 A1, WO 201713544 A1, WO 2018193193 and WO 2018193194.

[0015] The highly saturated diene elastomer preferably contains units of formula (I) or units of formula (II), unit 1,2. -CH2-CH(CH=CH2)- (II)

[0016] The presence of saturated 6-membered cyclic unit, 1,2-cyclohexane unit, of formula (I) 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. When the highly saturated diene elastomer comprises units of formula (I) or units of formula (II), the molar percentages of the units of formula (I) and the units of formula (II) in the highly saturated diene elastomer, respectively o and p, preferably satisfy the following equation (eq. 1) or equation (eq. 2), where o and p are calculated on the basis of all the monomer units of the highly saturated diene elastomer. 0 < o+p < 30 (eq. 1) 0 < o+p < 25 (eq. 2)

[0017] Preferably, the highly saturated diene elastomer comprises units of formula (I) in a molar ratio greater than 0% and less than 15%, more preferably less than 10% mol, molar percentage calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0018] According to a particularly preferred embodiment, the highly saturated diene elastomer contains 1,4-units of trans configuration (1,4-trans units). When the diene elastomer contains 1,4-trans units, the 1,4-trans units represent more than 50 mol% of the 1,4-units of the highly saturated diene elastomer, preferably more than 80 mol% of the 1,4-units of the highly saturated diene elastomer.

[0019] The highly saturated diene elastomer can consist of a mixture of highly saturated diene elastomers which differ from each other in their microstructures or in their macrostructures.

[0020] The content of the highly saturated diene elastomer in the rubber composition is greater than 90 parts by weight per hundred parts of elastomer of the rubber composition (pce). In the case where the highly saturated diene elastomer consists of a mixture of highly saturated diene elastomers which differ from each other in their microstructures or in their macrostructures, the content of the highly saturated diene elastomer in the rubber composition relates to the mixture of highly saturated diene elastomers.

[0021] The rubber composition may contain, in addition to the highly saturated diene elastomer, a second diene elastomer at a mass content of less than 10 phr. A diene elastomer is understood to mean an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers bearing two carbon-carbon double bonds, conjugated or not). The second elastomer may be chosen from the group of highly unsaturated diene elastomers consisting of polymers containing 1,3-butadiene units or isoprene units such as polybutadienes, butadiene copolymers, isoprene copolymers. A highly unsaturated diene elastomer is an elastomer which contains more than 50 mol% of diene units.

[0022] The rate of highly saturated diene elastomer in the rubber composition is preferably greater than 95 pce, advantageously equal to 100 pce.

[0023] The rubber composition comprises any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition, in particular usable for the manufacture of a tire tread. Such a reinforcing filler typically consists of nanoparticles 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. The rate of the reinforcing filler is between 30 pce and 55 pce, preferably varies from 35 pce to 50 pce, more preferably varies from 35 pce to 45 pce.

[0024] The reinforcing filler has the essential characteristic of containing more than 90% by mass of a carbon black, mass percentage calculated relative to the mass of the reinforcing filler in the rubber composition. Preferably, the mass content of carbon black is greater than 95% of the mass of the reinforcing filler. When the mass content of carbon black in the rubber composition is less than 100% of the mass of the reinforcing filler, the reinforcing filler may therefore comprise any type of filler other than carbon black which is also known for its ability to reinforce a rubber composition usable for the manufacture of tires, for example a reinforcing inorganic filler such as silica with which a coupling agent is associated in a known manner. Advantageously, the mass content of carbon black is equal to 100% of the mass of the reinforcing filler.When carbon black is the only reinforcing filler in the rubber composition, the desired technical effect is greater.

[0025] Suitable carbon blacks are all reinforcing carbon blacks, in particular the blacks conventionally used in tires or their treads (so-called tire-grade blacks). Among the latter, we will mention in particular the reinforcing carbon blacks of the 100, 200, 300 series, or the 500, 600 or 700 series blacks (ASTM grades), such as for example blacks N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772). The carbon black can also be a mixture of carbon blacks, in which case the mass content of carbon black is relates to the mixture of carbon blacks. When the rubber composition according to the invention is used in a tread, the carbon black is preferably a carbon black of the 100 or 200 series.

[0026] Preferably, the carbon black has a BET specific surface area greater than 90 m 2 / g. more preferably, the BET specific surface area of ​​carbon black is greater than 100 m 2 / g. Preferably, the carbon black has a BET specific surface area of ​​less than 145 m 2 / g. Carbon black more preferably has a BET specific surface area of ​​less than 130 m 2 / g.

[0027] The BET specific surface area is typically measured according to ASTM D6556-09 [multipoint method (5 points) - gas: nitrogen - relative pressure range P / PO: 0.05 to 0.30],

[0028] Another essential characteristic of the rubber composition is to contain at a rate of less than 3 pce a polyalkylene glycol, the polyalkylene glycol being a homopolymer of ethylene glycol or propylene glycol or a copolymer of ethylene glycol and propylene glycol. As is well known, a polyalkylene glycol is an oxyalkylene polymer which carries at each end of the polymer chain a hydroxyl (OH) function. Preferably, the polyalkylene glycol is a polyethylene glycol, a homopolymer of ethylene oxide which carries at each end of the polymer chain a hydroxyl (OH) function.

[0029] The level of polyalkylene glycol in the rubber composition is less than 3 phr, preferably less than 2 phr. A higher level of polyalkylene glycol does not provide an additional gain in the crack propagation resistance property. Therefore, a level of less than 2 phr is advantageous from the point of view of the compromise between the properties of the rubber composition and its cost. Preferably, the level of polyalkylene glycol in the rubber composition is greater than 0.2 phr. Advantageously, the level of polyalkylene glycol in the rubber composition is greater than 0.2 phr and less than 2 phr.

[0030] The polyalkylene glycol useful for the purposes of the invention preferably has a weight-average molar mass of between 2000 and 20000 g / mol, preferably between 5000 and 10000 g / mol. The polyalkylene glycol useful for the purposes of the invention is generally a commercially available product, such as “Carbowax” PEG 8000 from Dow Corning.

[0031] The rubber composition may also include all or part of the usual additives normally used in elastomer compositions intended to constitute treads, such as, for example, crosslinking agents, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants.

[0032] The rubber composition contains a vulcanization system. The vulcanization system typically includes sulfur and a vulcanization accelerator.

[0033] Sulfur is typically provided in the form of molecular sulfur or a sulfur donor agent, preferably in molecular form. Sulfur in molecular form is also referred to as molecular sulfur. A sulfur donor is any compound that releases sulfur atoms, combined or not in the form of a polysulfide chain, capable of being inserted into the polysulfide chains formed during vulcanization and bridging the elastomer chains. The sulfur content in the rubber composition is preferably less than 2 phr, preferably between 0.3 and 1.5 phr. According to any one of the embodiments of the invention, the sulfur content is advantageously less than 1 phr.

[0034] Any compound capable of acting as a vulcanization accelerator (primary or secondary) that can act as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide type for primary accelerators, and accelerators of the guanidine, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type for secondary accelerators. Guanidine is understood to mean any compound that contains the divalent radical -HN-C(=NH)-NH-. Guanidine is preferably diphenylguanidine. The vulcanization accelerator is used at a preferential rate of between 0.3 and 5 phr, more preferably between 0.5 and 2.5 phr. According to any one of the embodiments of the invention, the rate of the vulcanization accelerator is advantageously less than 1 phr.

[0035] Examples of primary accelerators include sulfenamide compounds such as N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), and mixtures of these compounds. The primary accelerator is preferably a sulfenamide, more preferably N-cyclohexyl-2-benzothiazyl sulfenamide.

[0036] Examples of secondary accelerators include thiuram polysulfides, preferably thiuram disulfides such as tetraethylthiuram disulfide, tetrabutylthiuram disulfide ("TBTD"), tetrabenzylthiuram disulfide ("TBZTD") and mixtures of these compounds. The secondary accelerator is preferably a thiuram disulfide, more preferably tetrabenzylthiuram disulfide.

[0037] The vulcanization accelerator is preferably a sulfenamide. When the vulcanization accelerator is a sulfenamide, it is preferably N-cyclohexyl-2-benzothiazyl sulfenamide.

[0038] As is well known, the vulcanization system may also comprise vulcanization activators such as metal oxides such as zinc oxide or fatty acids such as stearic acid.

[0039] The rubber composition can be manufactured in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first working phase or thermo-mechanical mixing (sometimes referred to as the "non-productive" phase) at high temperature, up to a maximum temperature of between 110°C and 190°C, preferably between 130°C and 180°C, followed by a second phase of mechanical working (sometimes referred to as the "productive" phase) at a lower temperature, typically below 110°C, for example between 40°C and 100°C, finishing phase during which the sulfur or sulfur donor and the vulcanization accelerator are incorporated. For example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, any additional processing agents and other various additives, with the exception of the sulfur and the vulcanization accelerator, are introduced into a suitable mixer such as a conventional internal mixer. The total mixing time in this non-productive phase is preferably between 1 and 15 min. After cooling the mixture thus obtained during the first non-productive phase, the sulfur and the vulcanization accelerator are then incorporated at low temperature, generally in an external mixer such as a roller mixer, and the whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 min.

[0040] Preferably, the rubber composition is extruded to form all or part of a profile of a tread of a tire. Then during the assembly of a tire usually comprising, radially from the outside to the inside, a tread, a crown reinforcement and a carcass reinforcement, the tread is laid radially outside the crown reinforcement. Radially means in a known manner in a radial direction relative to the axis of rotation of the tire.

[0041] The tire may be in the raw state (i.e. before the tire curing step) or in the cured state (i.e. after the tire curing step). The tire is preferably a tire for a vehicle carrying heavy loads, in particular a tire for a heavy goods vehicle or a tire for a civil engineering vehicle, preferably a tire for a heavy goods vehicle.

[0042] In summary, the invention may be implemented according to any of the following embodiments 1 to 19:

[0043] Mode 1: Rubber composition which comprises more than 90 pce of a highly saturated diene elastomer which is a copolymer of ethylene and 1,3-butadiene and which contains more than 50% by mole of ethylene units, between 30 pce and 55 pce of a reinforcing filler which comprises more than 90% by mass of a carbon black, a vulcanization system and at a rate of less than 3 pce a polyalkylene glycol carrying at each end of the polymer chain a hydroxy function, the polyalkylene glycol being a homopolymer of ethylene glycol or propylene glycol or a copolymer of ethylene glycol and propylene glycol.

[0044] Mode 2: Rubber composition according to mode 1 in which the highly saturated diene elastomer comprises at least 60 mol% of ethylene units.

[0045] Mode 3: Rubber composition according to mode 1 or 2 in which the highly saturated diene elastomer comprises at least 65 mol% of ethylene units.

[0046] Mode 4: Rubber composition according to any one of modes 1 to 3 in which the highly saturated diene elastomer comprises at most 80 mol% of ethylene units.

[0047] Mode 5: Rubber composition according to any one of modes 1 to 4 in which the highly saturated diene elastomer comprises at most 75 mol% of ethylene units.

[0048] Mode 6: Rubber composition according to any one of modes 1 to 5 in which the highly saturated diene elastomer contains units of formula (I), preferably at a molar rate greater than 0% and less than 15%.

[0049] Mode 7: A rubber composition according to any one of modes 1 to 6 in which the highly saturated diene elastomer is a random copolymer.

[0050] Mode 8: Rubber composition according to any one of modes 1 to 7 in which the level of polyalkylene glycol is less than 2 pce.

[0051] Mode 9 Rubber composition according to any one of modes 1 to 8 in which the level of polyalkylene glycol is greater than 0.2 pce.

[0052] Mode 10: Rubber composition according to any one of modes 1 to 9 in which the polyalkylene glycol is a polyethylene glycol.

[0053] Mode 11: Rubber composition according to any one of modes 1 to 10 in which the rate of the reinforcing filler varies from 35 pce to 50 pce.

[0054] Mode 12: Rubber composition according to any one of modes 1 to 11 in the rate of the reinforcing charge varies from 35 pce to 45 pce.

[0055] Mode 13: Rubber composition according to any one of modes 1 to 12 in which the carbon black represents more than 95% by mass of the reinforcing filler.

[0056] Mode 14: Rubber composition according to any one of modes 1 to 13 in which the carbon black represents 100% by mass of the reinforcing filler.

[0057] Mode 15: Rubber composition according to any one of modes 1 to 14 in which the polyethylene glycol has a weight average molar mass of between 2000 and 20000 g / mol.

[0058] Mode 16: Rubber composition according to any one of modes 1 to 15 wherein the polyalkylene glycol has a weight average molar mass of between 5000 and 10000 g / mol.

[0059] Mode 17: Rubber composition according to any one of modes 1 to 16 in which the rate of highly saturated diene elastomer is greater than 95 pce.

[0060] Mode 18: Rubber composition according to any one of modes 1 to 17 in which the rate of the highly saturated diene elastomer is equal to 100 pce.

[0061] Mode 19: Tire which comprises a tread, the portion of which intended to be in contact with the rolling ground consists entirely or partly of a rubber composition defined according to any one of modes 1 to 18.

[0062] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative purposes. Examples

[0063] Determination of the microstructure of elastomers by nuclear magnetic resonance (NMR): Ethylene and 1,3-butadiene copolymers are characterized by NMR spectrometry 1 H, 13 C. NMR spectra are recorded on a Brüker Avance III 500 MHz Spectrometer equipped with a BBIz-grad 5 mm “broadband” cryoprobe. The NMR experiment 1 Quantitative H, 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 1 H / 13C 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. 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 (CDCI3).

[0064] Glass transition temperature of polymers: The glass transition temperature (Tg) is measured using a differential scanning calorimeter according to ASTM D3418 (1999).

[0065] Mooney Viscosity: Mooney viscosity is measured using an oscillating consistometer as described in ASTM D1646 (1999). The measurement is carried out according to the following principle: the sample analyzed in the raw state (i.e., before curing) is molded (shaped) in a cylindrical enclosure heated to a given temperature (100°C). After 1 minute of preheating, the rotor rotates within the test piece at 2 revolutions / minute and the torque useful to maintain this movement after 4 minutes of rotation. The Mooney viscosity (ML) is expressed in "Mooney units" (MU, with 1 MU = 0.83 Newton meters).

[0066] Size exclusion chromatography (SEC / RI): 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. The mobile phase is eluted with a flow rate of 1 mL / min. The polymer is solubilized in THF 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 dispersity (D = Mw / Mn).

[0067] Mechanical resistance in the presence of crack initiation (tearability): The force and tear deformation are measured on a specimen stretched at 375 mm / min to cause the specimen to break. The tensile specimen consists of a parallelepiped-shaped rubber plate, 2.5 mm thick, 84 mm long and 10 mm wide. 3 very fine notches, 3 mm long, are made using a razor blade, halfway along and aligned in the width direction of the specimen, before starting the test. The force (N / mm) to be exerted to achieve rupture is determined and the elongation at break is measured. The Energy to cause rupture ("Tearability") of the specimen can be determined, which is the product of the force and the elongation at break. The test was conducted in air at a temperature of 100°C. High values ​​indicate good cohesion of the rubber composition although there are signs of cracking.

[0068] Reinforcing properties: Tensile tests are used to determine yield stresses and fracture properties. Unless otherwise stated, they are based on the French standard NFT 46-002. A processing of the traction recordings allows the modulus curve to be plotted in function of elongation. The modulus used here is the nominal (or apparent) secant modulus measured at first elongation, calculated by referring to the initial section of the specimen. The nominal secant moduli (or apparent stresses, in MPa) at 100% and 300% elongation, noted MSA100 and MSA300 respectively, are measured at first elongation. The reinforcement index is the ratio of the MSA300 modulus to the MSA100 modulus. Tensile measurements are carried out at a temperature of 60°C ± 2°C, and under normal humidity conditions (50 ± 5% relative humidity).

[0069] Preparation of rubber compositions: It is introduced into an internal mixer of volume: 3300 cm 3 (final filling rate: approximately 70% by volume), whose initial tank temperature is approximately 50°C, successively the elastomer, the reinforcing filler, if applicable the plasticizing hydrocarbon resin, the secondary accelerators as well as the various other ingredients with the exception of the sulfur and the primary accelerator. A thermomechanical work is then carried out (non-productive phase) in one step, which lasts a total of approximately 3 to 4 minutes, until a maximum "fall" temperature of 160°C is reached. The mixture thus obtained is recovered, cooled and then the sulfur and the primary accelerator are incorporated on an external mixer (roll mixer) at 30°C, mixing everything (productive phase) for 10 minutes.

[0070] The details of the formulations of the compositions are shown in Table 1.

[0071] The compositions thus obtained are then calendered, either in the form of plates (with a thickness ranging from 2 to 3 mm) or thin sheets of rubber, for the measurement of their physical or mechanical properties after vulcanization at 140°C (cooked state), or in the form of profiles which can be used directly, after cutting and / or assembly to the desired dimensions, for example as semi-finished products for tires.

[0072] The copolymer of ethylene and 1,3-butadiene, elastomer El, is synthesized according to the procedure described below in the presence of a catalytic system containing a neodymium metallocene and an organomagnesium according to a Mg / Nd molar ratio of 2.2. The polymerization being carried out with a Mg / Nd molar ratio greater than 2.2, BOMAG is added to the polymerization medium. All reagents are obtained commercially except for the metallocene which can be prepared according to the procedure described in WO 2007054224. Butyloctylmagnesium BOMAG (20% in heptane, C = 0.88 mol.L -1 ) comes from Chemtura and is transferred and stored in a Schlenk tube under an inert atmosphere. The ethylene, N35 grade, comes from Air Liquide and is used without prior purification. The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(p-BH4)2Li(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 11.1 of patent application WO 2017093654 A1. The polymerization of ethylene and 1,3-butadiene is carried out according to a continuous process in solution in methylcyclohexane at 80°C under 10 bar in the presence of a catalytic system (81 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 0.5, the molar ratio active Mg / Nd being 4. At the desired conversion (71%) to reach an Mn of approximately 160,000 g / mol, the polymerization is stopped at the line outlet using a solution of antioxidants in methylcyclohexane (1 pce of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 0.9 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 worm machine equipped with a single screw. The copolymer contains 74% ethylene units, 7% 1,2-unit, 12% 1,4-unit (of which more than 80% 1,4-trans) and 7% cyclic unit (1,2-cyclohexane unit), the percentages being molar). Its transition temperature is - 44°C (AT of 7°C, the AT being the temperature difference between the beginning of the glass transition and its end), its Mn of 154516 g / mol (Ip 1.70), its ML (1+4) at 100°C of 65.

[0073] Results : The results are shown in Table 2. The results are expressed on a base of 100 relative to a control ([value of the composition considered / value of the control composition]xl00). A value greater than 100 indicates a value higher than that of the control.

[0074] Compositions C1 to C3 which contain a highly saturated diene elastomer, a carbon black and a polyalkylene glycol, in this case a polyethylene glycol, are all in accordance with the invention. Composition C0 which differs from compositions C1 to C3 in that it does not contain a polyalkylene glycol is a control composition of C1 to C3.

[0075] Table 2 shows that the addition of polyalkylene glycol to a rubber composition reinforced with carbon black and containing a highly saturated diene elastomer significantly increases the tear resistance performance. Moreover, these gains are obtained with a reinforcement level of the same order of magnitude as that of the control composition C0. The best results are obtained for rubber compositions in which the polyalkylene glycol content is greater than 0.2 pce.

[0076] Table 1 (1) Elastomer El (2) Carbon black N234 (BET 120 m 2 / g) (3) Anti-ozone wax “VARAZON 4959” from the company Sasol Wax (4) N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine “Santoflex 6PPD” from Flexys (5) Stearin “Pristerene 4931” from Uniqema company (6) Industrial grade zinc oxide from Umicore (7) Polyethylene glycol “CARBOWAX 8000” from Dow Corning (8) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from Flexys

[0077] Table 2

Claims

Claims 1. A rubber composition which comprises more than 90 phr of a highly saturated diene elastomer which is a copolymer of ethylene and 1,3-butadiene and which contains more than 50 mol% of ethylene units, between 30 phr and 55 phr of a reinforcing filler which comprises more than 90% by mass of a carbon black, a vulcanization system and at a level of less than 3 phr a polyalkylene glycol carrying at each polymer chain end a hydroxyl function, the polyalkylene glycol being a homopolymer of ethylene glycol or propylene glycol or a copolymer of ethylene glycol and propylene glycol.

2. Rubber composition according to claim 1 in which the highly saturated diene elastomer comprises at least 60 mol% of ethylene units, preferably at least 65 mol% of ethylene units.

3. Rubber composition according to claim 1 or 2 in which the highly saturated diene elastomer comprises at most 80 mol% of ethylene units, preferably at most 75 mol% of ethylene units.

4. A rubber composition according to any one of claims 1 to 3 wherein the highly saturated diene elastomer is a random copolymer.

5. Rubber composition according to any one of claims 1 to 4 in which the level of polyalkylene glycol is less than 2 pce.

6. Rubber composition according to any one of claims 1 to 5 in which the level of polyalkylene glycol is greater than 0.2 pce.

7. A rubber composition according to any one of claims 1 to 6 wherein the polyalkylene glycol is a polyethylene glycol.

8. Rubber composition according to any one of claims 1 to 7 in which the level of the reinforcing filler varies from 35 pce to 50 pce, preferably from 35 pce to 45 pce.

9. Rubber composition according to any one of claims 1 to 8 in which the carbon black represents more than 95% by mass of the reinforcing filler.

10. Rubber composition according to any one of claims 1 to 9 in which the carbon black represents 100% by mass of the reinforcing filler.

11. Rubber composition according to any one of claims 1 to 10 in which the polyethylene glycol has a weight average molar mass of between 2000 and 20000 g / mol.

12. A rubber composition according to any one of claims 1 to 11 wherein the polyalkylene glycol has a weight average molar mass of between 5,000 and 10,000 g / mol.

13. Rubber composition according to any one of claims 1 to 12 in which the level of highly saturated diene elastomer is greater than 95 pce.

14. Rubber composition according to any one of claims 1 to 13 in which the level of highly saturated diene elastomer is equal to 100 pce.

5. A tire which comprises a tread, the portion of which intended to be in contact with the rolling ground is made up entirely or in part of a rubber composition defined according to any one of claims 1 to 14.

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