Rubber composition

Abstract

The present invention relates to a rubber composition exhibiting an improved compromise between fatigue strength and stiffness performance, which is based on an elastomeric matrix comprising at least one polyisoprene and at least one copolymer comprising ethylene and diene units, a paraffin oil having a glass transition temperature below -75°C, a reinforcing filler comprising carbon black, and a crosslinking system, wherein the at least one polyisoprene and at least one copolymer comprising ethylene and diene units represents more than 40% by mass of the elastomeric matrix.

Description

[Technical field]

[0001] The field of the invention is that of rubber compositions reinforced with carbon black and comprising highly saturated diene elastomers, particularly those intended for use in tires, and more particularly in tire sidewalls. [Background technology]

[0002] A tire usually comprises two beads intended to come into contact with the rim, a crown consisting of at least one crown reinforcement and a tread, and two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. The sidewall is an elastomeric layer situated between the crown and the bead, external to the carcass reinforcement with respect to the internal cavity of the tire, so as to completely or partially cover the area of ​​the carcass reinforcement extending from the crown to the bead. In the conventional manufacture of tires, the various components of the crown, carcass reinforcement, beads and sidewalls are assembled to form a pneumatic tire. The assembly step is followed by a tire forming step that gives the assembly a toroidal shape, followed by an impress vulcanization step. Tires, and especially sidewalls, are subjected to many mechanical stresses that are repeated periodically during running. These stresses, in the form of bending deformation and compressive stresses, test the durability of the tire and contribute to shortening its service life. One method for improving the durability of tires is to increase the fatigue resistance of the rubber composition that constitutes the tire. For example, a tire is typically subjected to a fatigue test of 125 m. 2 / g, and 100m 2 The use of silica having a small specific surface area, much smaller than 1 / g, in rubber compositions is described in EP 722977 B1 and EP 547344 B1, respectively, as being advantageous for fatigue resistance. Additionally, tire sidewalls are also exposed to the action of ozone. The deformation cycles combined with the action of ozone can cause cracks or tears to develop in the sidewalls, preventing the use of the tire regardless of tread wear. Thus, for example, highly cohesive rubber compositions are required to construct tire sidewalls due to their ability to undergo large deformations without failure, even when crack initiation is present. In order to minimize the effect of ozone on rubber compositions, it is known to use copolymers with a relatively low sensitivity to oxidation, such as highly saturated diene elastomers that contain ethylene units at a molar content of more than 50 mol% of the monomer units of the elastomer. For example, mention may be made of copolymers of ethylene and 1,3-diene, in particular copolymers of ethylene and 1,3-butadiene, that contain more than 50 mol% of ethylene. The use of such copolymers of ethylene and 1,3-butadiene in tire treads is described, for example, in WO 2014 / 114607 A1, and has the effect of providing tires with good wear resistance and rolling resistance. The use of copolymers of ethylene and 1,3-diene in compositions for sidewalls is also described in EP 2 682 423 A1, for example to increase ozone resistance. However, it is still advantageous to further improve fatigue resistance without reducing other properties of the composition, in particular stiffness and rolling resistance. Summary of the Invention

[0003] Continuing their research, the applicants have discovered that the use of certain plasticizers in rubber compositions comprising highly saturated copolymers based on ethylene units and diene units allows for an improvement in the fatigue resistance of the rubber composition without compromising stiffness or even rolling resistance.

[0004] The first subject of the invention is therefore an elastomeric matrix comprising at least one polyisoprene and at least one copolymer comprising ethylene units and diene units, - a paraffin oil having a glass transition temperature, Tg, of less than -75°C; a reinforcing filler comprising carbon black; - Cross-linked systems wherein the at least one polyisoprene and the at least one copolymer comprising ethylene units and diene units represent more than 40% by mass of the elastomeric matrix. Another subject of the invention is a tire comprising a composition according to the invention.

[0005] I - Definition The expression "composition based on" means a composition comprising a mixture and / or product of in situ reaction of the various components used, some of which may react and / or are intended to at least partially react with one another during various stages of the preparation of the composition; it is to be understood that the composition may thereby be fully or partially crosslinked or non-crosslinked. The expression "phr" is understood within the context of the present invention to mean parts by weight per 100 parts by weight of elastomer. In this specification, all percentages (%) are weight percentages (%) unless otherwise specified.

[0006] Furthermore, any value interval indicated by the expression "between a and b" denotes a range of values ​​greater than a and less than b (i.e., the limits a and b are excluded), whereas any value interval indicated by the expression "from a to b" means a range of values ​​from a to b (i.e., including the strict limits a and b). In this specification, when a value interval is indicated by the expression "from a to b", the interval indicated by the expression "between a and b" is also preferentially indicated. As used herein, the expressions "all of the monomeric units of an elastomer" or "total amount of monomeric units of an elastomer" refer to all constituent repeat units of an elastomer resulting from the insertion of monomers into the elastomer chain by polymerization. Unless otherwise specified, the content of monomeric or repeat units in highly saturated diene elastomers is given as a mole percentage calculated based on the total monomeric units of the elastomer.

[0007] When referring to a "major" compound, this is understood in the present invention to mean that this compound is predominant among the compounds of the same type in the composition, i.e. that it represents the largest mass among the compounds of the same type. Thus, for example, the main elastomer is the elastomer that represents the largest mass relative to the total mass of elastomers in the composition. Similarly, a "major" filler is the filler that represents the largest mass among the fillers of the composition. By way of example, in a system that contains only one elastomer, the latter is, in the present invention, the main, and in a system that contains two elastomers, the main elastomer represents the majority of 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, the term "major" is understood to mean that it is present in more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferentially the "major" compound represents 100%. The carbon-containing compounds referred to herein may be of fossil or bio-based origin. In the latter case, they may be partially or completely derived from biomass or may be obtained from renewable starting materials derived from biomass. Polymers, plasticizers, fillers, etc. are of particular relevance.

[0008] All values ​​for the glass transition temperature "Tg" stated herein are measured in known manner according to DSC (Differential Scanning Calorimetry) in accordance with standard ASTM D3418 (1999). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] II - Description of the Invention II-1 Elastomer matrix According to the invention, the elastomeric matrix comprises more than 40% by weight of at least one polyisoprene and at least one copolymer comprising ethylene units and diene units (hereinafter referred to as "copolymer"). The term "elastomeric matrix" is intended to mean all of the elastomers of the composition.

[0010] The term "copolymer comprising ethylene units and diene units" is intended to mean any copolymer that comprises in its structure at least ethylene units and diene units. The copolymer may therefore comprise monomer units other than ethylene units and 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 from 3 to 6 carbon atoms. For example, the alpha-olefin units may be selected from the group consisting of propylene, butene, pentene, hexene or mixtures thereof. In a known manner, the expression "ethylene unit" refers to a -(CH2-CH2)- unit resulting from the insertion of ethylene into the elastomeric chain.

[0011] The term "diene unit" is intended to mean a monomer unit which contains a carbon-carbon double bond and originates from the insertion of a monomer subunit resulting from the polymerization of a conjugated or non-conjugated diene monomer. Preferably, the diene unit is selected from the group consisting of butadiene units, isoprene units and mixtures of these diene units. In particular, the diene units of the copolymer may be 1,3-diene units having 4 to 12 carbon atoms, such as 1,3-butadiene or 2-methyl-1,3-butadiene units. More preferably, the diene units are mainly, or even preferentially exclusively, 1,3-butadiene units. In the copolymer, the ethylene units advantageously represent between 50 mol% and 95 mol% of the monomer units of the copolymer, i.e. between 50 mol% and 95 mol% of the monomer units of the copolymer. Advantageously, the ethylene units in the copolymer represent more than 60 mol%, preferably more than 70 mol%, of the monomer units of the copolymer. Also advantageously, in the copolymer, the ethylene units represent at most 90 mol%, preferably at most 85 mol%, of the monomer units of the copolymer. Advantageously, the copolymer (i.e. for the sake of completeness, at least one copolymer comprising ethylene units and diene units) is a copolymer of ethylene and 1,3-diene (preferably 1,3-butadiene), i.e. according to the invention a copolymer consisting exclusively of ethylene and 1,3-diene (preferably 1,3-butadiene) units, more preferentially a random copolymer of ethylene and 1,3-diene (preferably 1,3-butadiene). When the copolymer is a copolymer of ethylene and a 1,3-diene, said copolymer advantageously comprises units of formula (I) and / or (II). The presence of the saturated six-membered ring unit 1,2-cyclohexanediyl of formula (I) as a monomer unit in the copolymer may result from a very specific sequence of insertions of ethylene and 1,3-butadiene in the polymer chain as it grows.

[0012] [ka] -CH2-CH(CH=CH2)- (II) For example, a copolymer of ethylene and a 1,3-diene may lack units of formula (I), in which case it preferably comprises units of formula (II).

[0013] When the copolymer of ethylene and 1,3-diene comprises units of formula (I) or units of formula (II), or else units of formula (I) and units of formula (II), the mole percentages o and p, respectively, of units of formula (I) and units of formula (II) in the highly saturated diene elastomer, calculated based on the total monomer units of the highly saturated diene elastomer, preferably satisfy the following formula (eq.1) and more preferentially satisfy the following formula (eq.2): 0 <o+p≦25 (eq.1) 0 <o+p<20 (eq.2) According to the invention, the copolymer, preferably a copolymer of ethylene and of a 1,3-diene (preferably of 1,3-butadiene), is a random copolymer. Advantageously, the number average mass (Mn) of the copolymer, preferably of ethylene and of 1,3-diene (preferably of 1,3-butadiene), is in the range from 100 000 to 300 000 g / mol, preferably from 150 000 to 250 000 g / mol. The Mn of the copolymers is determined in known manner by size exclusion chromatography (SEC), as described below.

[0014] The SEC (Size Exclusion Chromatography) technique allows the separation of macromolecules by size by passing them in solution through a column packed with a porous gel. The macromolecules are separated according to their hydrodynamic volume, the bulkiest being eluted first. Although not an absolute method, SEC allows the understanding of the molar mass distribution of the polymers. The various number-average molar masses (Mn) and mass-average molar masses (Mw) can be determined from commercially available standards, and the polydispersity index (PI=Mw / Mn) can be calculated by "Moore" calibration. There is no special treatment of the polymer samples before the analysis. The latter is simply calculated as a solution of approximately 1 g.l -1The compound is dissolved in the elution solvent at a concentration of 0.45 μm. The solution is then filtered through a filter with a pore size of 0.45 μm before injection. The instruments used are Waters Acquity or Waters Alliance chromatography lines. The elution solvent is tetrahydrofuran containing 250 ppm BHT (butylated hydroxytoluene) antioxidant, and the flow rate is 1 ml.min. -1 The temperature of the column is 35°C and the analysis time is 40 min. The columns used are three Agilent columns with the trade name InfinityLab PolyPore. The volume of the sample solution injected is 100 μl. The detector is an Acquity or Waters 2410 differential refractometer and the software for utilizing the chromatographic data is the Waters Empower system. The calculated average molar mass is compared to a calibration curve made with polystyrene standards.

[0015] The copolymers can be obtained by various synthesis methods known to those skilled in the art, in particular as a function of the target microstructure of the highly saturated diene elastomer. In general, they can be prepared by copolymerization of at least a diene, preferably a 1,3-diene, more preferably 1,3-butadiene, and ethylene, according to known synthesis methods, in particular in the presence of a catalyst system comprising a metallocene complex. In this respect, mention can be made of catalyst systems based on metallocene complexes, which are described in the name of the applicant in EP 1092731, WO 2004035639, WO 2007054223 and WO 2007054224. The copolymers, including the random cases, can also be prepared by processes using preformed types of catalyst systems, such as those described in WO 2017093654 A1, WO 2018020122 A1 and WO 2018020123 A1.

[0016] The copolymers may consist of a mixture of copolymers containing ethylene and diene units which differ from each other by their microstructure and / or by their macroscopic structure. As indicated above, the elastomeric matrix of the composition according to the invention also comprises polyisoprene, which may be any microstructural elastomer. Advantageously, the polyisoprene, preferably the polyisoprene having a mass content of 1,4-cis bonds of at least 90% of the mass of the polyisoprene, is natural rubber, synthetic polyisoprene or a mixture thereof.More preferably, the polyisoprene, preferably the polyisoprene having a mass content of cis-1,4 bonds of at least 90% of the mass of the polyisoprene, is natural rubber.

[0017] The content of copolymer, preferably of ethylene and 1,3-diene, preferably 1,3-butadiene, in the composition may be less than 50 phr, preferably in the range from 15 to less than 45 phr, more preferably in the range from 20 to 40 phr. Further, the content of polyisoprene, preferably natural rubber, in the composition may be greater than 50 phr, preferably in the range of from greater than 55 phr to 80 phr, more preferably in the range of from 60 to 80 phr. According to the invention, the elastomeric matrix can contain at least one other elastomer that is not a polyisoprene or a copolymer comprising ethylene units and diene units, but this is not necessary.Preferentially, therefore, the at least one polyisoprene and the at least one copolymer comprising ethylene units and diene units represent more than 50% by weight, preferably more than 60% by weight, preferably more than 70% by weight, preferably more than 80% by weight, preferably more than 90% by weight of the elastomeric matrix.Advantageously, the at least one polyisoprene and the at least one copolymer comprising ethylene units and diene units represent the only elastomer of the composition, i.e. 100% by weight of the elastomeric matrix.

[0018] When the elastomeric matrix comprises at least one other elastomer that is not polyisoprene or a copolymer comprising ethylene and diene units, the at least one other elastomer can represent less than 50% by weight of the elastomeric matrix, preferably less than 40% by weight, preferably less than 30% by weight, preferably less than 20% by weight, preferably less than 10% by weight. The other elastomer may be any diene elastomer known to those skilled in the art that is not polyisoprene or a copolymer comprising ethylene and diene units.

[0019] II-2 Liquid plasticizers According to the invention, the rubber composition is based on at least a paraffin oil having a glass transition temperature (Tg) below -75°C. The paraffin oil may be any paraffin oil known to those skilled in the art, provided that this oil has a Tg below -75° C. It may also be a mixture of several paraffin oils having a Tg below -75° C. Paraffin oil is a plasticizer that is liquid at 20°C, called a "low Tg plasticizer", and is known for its plasticizing properties with respect to elastomers. At room temperature (20°C), low Tg plasticizers are somewhat viscous but liquid (i.e., substances that have the ability to eventually take the shape of their container, just to be clear), unlike high Tg hydrocarbon resins, which are essentially solids at room temperature. Paraffin "oil" should also not be confused with paraffin "wax", which is not liquid at room temperature. Advantageously, the Tg of the paraffin oil is in the range of -78°C to -150°C, preferably -80°C to -120°C.

[0020] Furthermore, the paraffin oil that can be used according to the invention can be defined according to its crystallinity. Advantageously, the paraffin oil has a crystallinity of less than 20%, preferably less than 10%, more preferably less than 5%, measured by differential scanning calorimetry at a temperature of 20° C. Standard ISO 1-1357-3 (2013) is used to determine the temperature and enthalpy of melting and crystallization of polymers used by Differential Scanning Calorimetry (DSC). The reference enthalpy of polyethylene is 277.1 J / g (Handbook of Polymer, 4th Edition, J. Brandrup, EH Immergut and EA Grulke, 1999). In the present invention, the content of paraffin oil is within the range of 5 to 60 phr, preferably 10 to 45 phr. As examples of commercially available paraffin oils with a Tg below -75°C, mention may be made of Extensoil 51 oil from Repsol or Tudalen 1968 oil from Hansen & Rosenthal. The composition according to the invention may contain plasticizers other than paraffin oils having a Tg below -75°C that are liquid at 20°C (hereinafter referred to as "other liquid plasticizers"), however this is neither essential nor preferred.

[0021] Preferably, the total content of plasticizers that are liquid at 20° C. in the composition ranges from 5 to 60 phr, preferably from 10 to 45 phr. Furthermore, the composition according to the invention advantageously does not contain or contains less than 15 phr of plasticizers other than paraffin oil that are liquid at 20° C., preferably less than 10 phr of them, preferably less than 5 phr of them. Particularly preferably, paraffin oil having a Tg below -75°C is the only plasticizer of the composition according to the invention that is liquid at 20°C.

[0022] II-3 Reinforcing fillers The rubber composition according to the present invention also has the essential feature of including a reinforcing filler which includes carbon black. The rubber composition may contain other types of "reinforcing" fillers known for their ability to reinforce rubber compositions that can be used in the manufacture of tires, such as organic fillers other than carbon black, reinforcing inorganic fillers such as silica, combined in a known manner with coupling agents. Such reinforcing fillers typically consist of nanoparticles, the average size of which (by mass) is less than a micrometer, generally less than 500 nm, most often between 20 and 200 nm, and more particularly and more preferentially between 20 and 150 nm. The content of reinforcing fillers is adjusted by those skilled in the art depending on the use of the rubber composition. Advantageously, the content of reinforcing fillers in the composition according to the invention is in the range of 20 to 80 phr, preferably 25 phr to 65 phr, preferably 25 to 49 phr.

[0023] All carbon blacks, especially those conventionally used in tires or their treads, are suitable as carbon blacks. Among the latter, mention may be made, inter alia, of the reinforcing carbon blacks of the 100, 200 and 300 series, or of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as N115, N134, N234, N326, N330, N339, N347, N375, N550, N683 and N772 carbon blacks. These carbon blacks can be used alone as they are commercially available, or in other forms, for example as support for some of the rubber additives used. Carbon blacks can, for example, already be incorporated in diene elastomers, especially isoprene elastomers, in the form of masterbatches (see, for example, WO 97 / 36724 A2, WO 99 / 16600 A1).

[0024] Advantageously, the carbon black has a molecular weight of 30 to 100 m 2 / g, preferably 33 to 70m 2 / g, more preferably 35 to 50m 2 / g. The BET specific surface area can be measured according to standard ASTM D6556-09 [multipoint method (5 points) - gas: nitrogen - relative pressure range P / P0: 0.05-0.30]. Advantageously, the reinforcing filler mainly, preferably exclusively, comprises carbon black. In particular, the reinforcing filler preferably consists of at least 80% by weight, preferably at least 90% by weight, of carbon black. Particularly preferably, the reinforcing filler exclusively comprises carbon black, i.e. 100% by weight of carbon black.

[0025] The carbon black content in the composition according to the invention is preferentially in the range from 20 to 80 phr, preferably from 25 phr to 65 phr, preferably from 25 to 49 phr. The carbon black may also be a mixture of various carbon blacks, in which case the carbon black content is relative to the total carbon black. If a reinforcing inorganic filler is used, this may be the case, in particular of the siliceous type, preferentially silica (SiO2), or of the aluminous type, in particular alumina (Al2O3). The silica used may be any reinforcing silica known to the skilled artisan, in particular having a BET specific surface area and a CTAB specific surface area of ​​at least 450 m 2 / g, preferably 30 to 400m 2 / g, especially 60-300m 2 The silica may be any precipitated or fumed silica having a silica content in the range of 0.1 to 1.0 μm / g.

[0026] In the present disclosure, 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), more specifically according to the method derived from standard NF ISO 5794-1, Appendix E, June 2010 [multipoint (5-point) volumetric method - gas: nitrogen - degassing under vacuum: 1 hour at 160°C - relative pressure p / po range: 0.05 to 0.17]. For inorganic fillers such as silica, for example, CTAB specific surface area values ​​were determined according to standard NF ISO 5794-1, Annex G, June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) onto the "external" surface of the reinforcing filler.

[0027] The term "reinforcing inorganic filler" is here to be understood as meaning any inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also known as "white filler", "transparent filler" or even "non-black filler", in contrast to carbon black, which is capable of reinforcing by itself, without any other means than intermediate coupling agents, the rubber composition intended for the manufacture of tires. In a known manner, some reinforcing inorganic fillers can be characterized in particular by the presence of hydroxyl (-OH) groups on their surface. Any type of precipitated silica can be used, in particular highly disperse precipitated silica (called "HDS" for "highly disperse" or "highly disperse silica"). These highly disperse or non-highly disperse precipitated silicas are well known to those skilled in the art. Mention may be made, for example, of the silicas described in WO 03 / 016215 A1 and WO 03 / 016387 A1. In particular, among the commercially available HDS silicas, the Ultrasil® 5000GR and Ultrasil® 7000GR silicas from Evonik, or the Zeosil® 1085GR, Zeosil® 1115 MP, Zeosil® 1165MP, Zeosil® Premium 200MP and Zeosil® HRS 1200 MP silicas from Solvay can be used. As non-HDS silicas the following commercially available silicas can be used: Ultrasil® VN2GR and Ultrasil® VN3GR silicas from Evonik, Zeosil® 175GR silica from Solvay or Hi-Sil EZ120G(-D), Hi-Sil EZ160G(-D), Hi-Sil EZ200G(-D), Hi-Sil 243LD, Hi-Sil 210 and Hi-Sil HDP 320G silicas from PPG.

[0028] The reinforcing inorganic filler may be a mixture of various reinforcing inorganic fillers, in which case the proportion of the reinforcing inorganic fillers in the reinforcing filler is relative to all of the reinforcing inorganic fillers. In a known manner, at least difunctional coupling agents (or bonding agents) of chemical and / or physical nature intended to provide a satisfactory link between the inorganic filler (the surface of its particles) and the diene elastomer can be used to couple the reinforcing inorganic filler to the diene elastomer. In particular, at least difunctional organosilanes or polyorganosiloxanes are used. The term "difunctional" is understood to 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 difunctional compound can contain a first functional group containing a silicon atom, capable of interacting with the hydroxyl groups of the inorganic filler, and a second functional group containing a sulfur atom, capable of interacting with the diene elastomer.

[0029] Preferably, the organosilane is selected from the group consisting of organosilane polysulfides (symmetrical or asymmetrical), for example polyorganosiloxanes, mercaptosilanes, block mercaptosilanes, such as bis(3-triethoxysilylpropyl)tetrasulfide (abbreviated as TESPT) sold under the name Si69 by Evonik, or bis(triethoxysilylpropyl)disulfide (abbreviated as TESPD) sold under the name Si75 by Evonik, S-(3-(triethoxysilyl)propyl)octanethioate sold under the name NXT Silane by the company Momentive. More preferentially, the organosilane is an organosilane polysulfide. Of course, mixtures of the above listed coupling agents may also be used. When a reinforcing inorganic filler is used, a person skilled in the art can easily adjust the content of the coupling agent in the composition of the present invention, which typically corresponds to 0.5% to 15% by weight relative to the amount of the reinforcing inorganic filler.

[0030] II-4 Crosslinked system The crosslinking system may be any type of system known to those skilled in the art in the field of rubber compositions for tires. It may in particular be based on sulfur and / or peroxides and / or bismaleimides. Preferentially, the crosslinking system is based on sulfur, in which case it is called a vulcanization system. Sulfur can be contributed in any form, in particular in the form of molecular sulfur or sulfur donors. At least one vulcanization accelerator is also preferentially present, optionally and preferentially present, and various known vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, for example stearates, and salts of transition metals, guanidine derivatives (in particular diphenylguanidine), or also known vulcanization retarders can be used.

[0031] Sulphur is used in a preferred content between 0.3 and 10 phr, more preferentially between 0.3 and 5 phr. Primary vulcanization accelerators are used in a preferred content between 0.5 and 10 phr, more preferentially between 0.5 and 5 phr.

[0032] As accelerators, any compound capable of acting as an accelerator of the vulcanization of diene elastomers in the presence of sulfur can be used, in particular accelerators of the thiazole type, and also their derivatives, or accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type. As examples of such accelerators, the following compounds can be mentioned in particular: 2-mercaptobenzothiazyl disulfide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazole sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazole sulfenamide ("DCBS"), N-(tert-butyl)-2-benzothiazole sulfenamide ("TBBS"), N-(tert-butyl)-2-benzothiazole sulfenimide ("TBSI"), tetrabenzyl thiuram disulfide ("TBZTD"), zinc dibenzyl dithiocarbamate ("ZBEC") and mixtures of these compounds.

[0033] II-5 Possible Additives The rubber composition according to the invention may also contain all or some of the conventional additives usually used in elastomeric compositions for tires, such as plasticizers (e.g. plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical antiozonants, antioxidants, anti-fatigue agents, reinforcing resins (e.g. those described in WO 02 / 10269). However, in a particularly advantageous manner, the composition according to the invention does not contain any plasticizers other than those listed above, or contains less than 20 phr thereof, preferably less than 10 phr thereof, preferably less than 5 phr thereof. Advantageously, the composition according to the invention does not contain a plasticizing hydrocarbon resin.

[0034] II-6 Preparation of Rubber Composition The composition according to the invention can be prepared using two successive preparation steps, which are well known to those skilled in the art: - a first stage ("non-productive" stage) of thermomechanical work or kneading, which can be carried out in a single thermomechanical step, in which all the necessary components other than the crosslinking system, in particular the elastomer matrix, the reinforcing fillers and any other various additives, are introduced into a suitable mixer, such as a standard internal mixer (for example of the "Banbury" type). The incorporation of any fillers into the elastomer can be carried out in one or more runs by thermomechanical kneading. It is a directly kneaded masterbatch, if the fillers are already fully or partially incorporated in the elastomer in the form of a masterbatch, as described for example in WO 97 / 36724 and WO 99 / 16600, incorporating, where appropriate, other elastomers or fillers present in the composition not in the form of a masterbatch and also any other various additives other than the crosslinking system; the non-productive stage can be carried out at elevated temperatures up to a maximum temperature of between 110°C and 200°C, preferably between 130°C and 185°C, for a period generally between 2 and 10 minutes; - a second stage of mechanical work ("productive" stage) carried out in an external mixer such as an open mill, after cooling the mixture obtained in the first non-productive stage to a low temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated and the combined mixture is then mixed for a few minutes, for example between 5 and 15 minutes.

[0035] Such steps are described, for example, in EP 0501227, EP 0735088, EP 0810258, WO 00 / 05300 or WO 00 / 05301. The final compositions thus obtained are then calendered, for example in the form of sheets or slabs, in particular for laboratory characterization, or else extruded (or coextruded with other rubber compositions) in the form of semi-finished (or profiled) elements of rubber that can be used, for example, as tire sidewalls. These products can then be used for the construction of tires according to techniques known to those skilled in the art. The composition may be in the uncured state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization) and may be a semi-finished product that can be used in a tire. Crosslinking (or curing), where appropriate vulcanization, is carried out in a known manner at temperatures generally between 130° C. and 200° C. for a sufficient period of time which may vary, for example, between 5 and 90 minutes, depending in particular on the curing temperature, on the crosslinking system employed and on the crosslinking kinetics of the composition in question.

[0036] II-7 Tires A subject of the invention is also a tire comprising a rubber composition according to the invention. Preferably, the composition according to the invention is present at least in the sidewall of the tire according to the invention. Advantageously, the composition according to the invention is present exclusively in the sidewall of the tire. The tyre according to the invention may be intended to equip passenger-type motor vehicles, SUVs ("sports utility vehicles"), or two-wheeled vehicles (in particular motorcycles), or aircraft, or also industrial vehicles selected from vans, heavy vehicles - i.e. metro trains, buses, heavy road transport vehicles (large trucks, tractors, trailers) or off-road vehicles, such as large agricultural vehicles or earth-moving equipment.

[0037] III - Preferred Embodiments In light of the above, preferred embodiments of the present invention are described as follows: A. - an elastomeric matrix comprising at least one polyisoprene and at least one copolymer comprising ethylene units and diene units, - a paraffin oil having a glass transition temperature, Tg, of less than -75°C; a reinforcing filler comprising carbon black; - Cross-linked systems wherein the at least one polyisoprene and the at least one copolymer comprising ethylene units and diene units represent more than 40% by mass of the elastomeric matrix. B. The rubber composition of embodiment A, wherein the copolymer comprising ethylene units and diene units is a copolymer of ethylene and a 1,3-diene. C. The rubber composition of embodiment B, wherein the ethylene units in the copolymer represent between 50 mol % and 95 mol % of the monomer units of the copolymer. D. The rubber composition of embodiment B or C, wherein the 1,3-diene is 1,3-butadiene. E. The rubber composition of any one of embodiments B through D, wherein the copolymer comprises units of formula (I) or units of formula (II), or alternatively, units of formula (I) and units of formula (II).

[0038] [ka] -CH2-CH(CH=CH2)- (II) F. The rubber composition according to embodiment E, wherein the mole percentages of units of formula (I) and units of formula (II), respectively o and p, in the copolymer satisfy the following formula (eq.1), and preferentially satisfy the following formula (eq.2), where o and p are calculated based on the total monomer units of the copolymer: 0 <o+p≦25 (eq.1) 0 <o+p<20 (eq.2) G. The rubber composition of any one of embodiments A through F, wherein the copolymer is a random copolymer. H. The rubber composition of any one of embodiments A to G, wherein the copolymer has a number average mass, Mn, in the range of 100000 to 300000 g / mol, preferably 150000 to 250000 g / mol. I. The rubber composition according to any one of embodiments A to H, wherein the content of copolymer comprising ethylene units and diene units is less than 50 phr, preferably in the range of 15 to less than 45 phr, more preferably in the range of 20 to 40 phr. J. The rubber composition of any one of embodiments A-I, wherein the polyisoprene contains a mass content of cis-1,4-bonds of at least 90%, based on the mass of the polyisoprene. K. The rubber composition of any one of embodiments A-J, wherein the polyisoprene is natural rubber, synthetic polyisoprene, or a mixture thereof, preferably natural rubber. L. The rubber composition according to any one of embodiments A to K, having a natural rubber content of greater than 50 phr, preferably in the range of from greater than 55 phr to 80 phr, and more preferably in the range of from 60 to 80 pce. M. The rubber composition according to any one of embodiments A to L, wherein the at least one polyisoprene and the at least one copolymer comprising ethylene units and diene units represent more than 70% by weight, preferably more than 90% by weight, of the elastomeric matrix. N. The rubber composition according to any one of embodiments A to M, wherein the at least one polyisoprene and the at least one copolymer comprising ethylene units and diene units represent 100% by weight of the elastomeric matrix. O. The rubber composition according to any one of embodiments A to N, wherein the paraffin oil has a Tg within the range of -78°C to -150°C, preferably -80°C to -120°C. P. The rubber composition according to any one of embodiments A to O, wherein the paraffin oil has a crystallinity of less than 20%, preferably less than 10%, more preferably less than 5%, as measured at a temperature of 20° C. by differential scanning calorimetry according to standard ISO 11357-3-2013. Q. The rubber composition of any one of embodiments A to P, wherein the paraffin oil content is in the range of 5 to 60 phr, preferably 10 to 45 phr. The rubber composition according to any one of embodiments A to Q, wherein the total content of plasticizers that are liquid at R. 20° C. is in the range of 5 to 60 phr, preferably 10 to 45 phr. S. The rubber composition of any one of embodiments A-R, comprising no plasticizers other than paraffin oil that are liquid at 20° C. or less than 15 phr thereof, preferably less than 10 phr thereof. T. The rubber composition of any one of embodiments A through S, wherein the rubber composition does not include a plasticizing hydrocarbon resin. U. The rubber composition of any one of embodiments A through T, wherein the reinforcing filler comprises primarily, and preferably exclusively, carbon black. V. Carbon black is 30~100m 2 / g, preferably 33 to 70m 2 / g, more preferably 35 to 50m 2 The rubber composition according to any one of embodiments A to U, having a BET specific surface area in the range of 1 / g. W. The rubber composition according to any one of embodiments A to V, wherein the carbon black content is in the range of 25 phr to 65 phr, preferably 25 to 49 phr. X. The rubber composition according to any one of embodiments A to W, wherein the total reinforcing filler content is in the range of 25 phr to 65 phr, preferably 25 to 49 phr. Y. The rubber composition according to any one of embodiments A to X, wherein the crosslinking system is a vulcanization system. Z. A tire comprising the rubber composition defined in any one of embodiments A-Y. AA. The tire of embodiment Z, wherein the rubber composition defined in any one of embodiments A-Y is present in at least one sidewall of the tire. EXAMPLES

[0039] IV - Working Examples IV-1 Measurements and tests used Fatigue Testing The fatigue strength, expressed as the number of cycles or in relative units (ru), is measured in a known manner on 12 test specimens which have been subjected to repeated low-frequency tensile deformation up to an elongation of 75% at 60° C. using a Monsanto (MFTR) machine until the specimen breaks according to standards ASTM D4482-85 and ISO 6943. The results are expressed in relative units (ru): values ​​greater than that of the control, arbitrarily set at 100, represent improved results, i.e. better fatigue strength of the rubber samples.

[0040] Dynamic Properties The dynamic properties, tan(δ)max, are measured with a viscosity analyzer (Metravib V A4000) according to standard ASTM D5992-96. Samples of the vulcanized compositions (cylindrical specimens, thickness 4 mm and cross-sectional area 400 mm 2 ) are subjected to a sinusoidal load of simple alternating shear stress at a frequency of 10 Hz according to standard ASTM D 1349-99 at a temperature of 60° C. 2 ) response is recorded. A peak-to-peak strain amplitude sweep is performed from 0.1 to 50% (forward cycle) and then from 50% to 1% (return cycle). The result is used as the loss factor (tan δ). The maximum value of tan δ observed for the return cycle (tan(δ)max) is reported. The response of a sample of the vulcanized composition subjected to a simple alternating sinusoidal shear stress during a temperature sweep and subjected to an applied sinusoidal stress of 0.7 MPa at a temperature of 60°C at a frequency of 10 Hz was also recorded and the complex dynamic shear modulus (G * ) is measured. For ease of reading, the results are presented on a scale of 100 (percent), with the control assigned a value of 100. A result above 100 indicates an improvement in the performance in question. For "tan(δ)max," a result above 100 indicates reduced hysteresis and therefore better rolling resistance. * ", and results exceeding 100 indicate that the complex dynamic shear modulus G * This represents a decrease in stiffness, which means less stiffness and therefore an improvement when used in tire sidewalls.

[0041] IV-2 Preparation of Composition In the following examples, rubber compositions were produced as described above in section II-6. In particular, a "non-productive" stage was carried out in a 0.4 liter mixer for 6 minutes at an average blade speed of 50 revolutions per minute until a maximum drop temperature of 160° C. was reached. A "productive" stage was carried out in an open mill for 10 minutes at 23° C. Crosslinking of the composition was carried out at temperatures between 130°C and 200°C under pressure. IV-3 Rubber Test The purpose of the examples presented below is to compare the performance compromise between fatigue resistance and rolling resistance of a composition according to the invention (C1) against two control compositions (T1 and T2). The compositions (phr) tested as well as the results obtained are presented in Table 1.

[0042] The performance results are expressed as a percentage, based on 100, relative to a control composition T1, which corresponds to a conventional sidewall composition. [Table 1] (1) Natural rubber (2) An elastomer containing 79 mol% ethylene units, 7 mol% 1,2-cyclohexanediyl units, 8 mol% 1,2 butadiene units, and 6 mol% 1,4 butadiene units. (3) Carbon black of grade N330 according to standard ASTM D-1765 (4) "Lubrirob Tod 1880" glycerol trioleate (sunflower oil containing 85% by weight oleic acid) from Novance (Tg=-90°C) (5) Trioctyl phosphate (tri-2-ethylhexyl phosphate), “Disflamoll TOF” from Lanxess (Tg=-110°C) (6) "Extensoil 51" paraffin oil (Tg=-80°C) from Repsol (7) N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine, Santoflex 6-PPD from Flexsys (8) "Pilnox TMQ" 2,2,4-trimethyl-1,2-dihydroquinoline from Nocil (9) N-Cyclohexyl-2-benzothiazole sulfenamide, "Santocure CBS" from Flexsys

[0043] The results presented in Table 1 above show that, compared to the control composition T1, the control composition T2 allows for an improvement in fatigue resistance, but at the expense of the stiffness of the composition. On the other hand, the fatigue resistance of the composition according to the invention is greatly improved compared to the control composition, without compromising the stiffness of the composition. It was also observed that the hysteresis of the composition according to the invention is not impaired compared to the control composition T1 (data not shown).

Claims

1. an elastomeric matrix comprising at least one polyisoprene and at least one copolymer comprising ethylene units and diene units, a paraffin oil having a glass transition temperature, Tg, of less than -75°C; a reinforcing filler comprising carbon black; - Crosslinked systems wherein the at least one polyisoprene and the at least one copolymer comprising ethylene units and diene units represent more than 40% by mass of the elastomer matrix.

2. The rubber composition of claim 1, wherein the copolymer comprising ethylene units and diene units is a copolymer of ethylene and a 1,3-diene.

3. The rubber composition of claim 2, wherein the 1,3-diene is 1,3-butadiene.

4. The rubber composition according to any one of claims 1 to 3, wherein the content of the copolymer containing ethylene units and diene units is in the range of less than 50 phr.

5. The rubber composition according to any one of claims 1 to 4, wherein the content of natural rubber is greater than 50 phr.

6. The rubber composition according to any one of claims 1 to 5, wherein the paraffin oil has a Tg within the range of -78°C to -150°C.

7. 7. The rubber composition according to claim 1, wherein the paraffin oil has a crystallinity of less than 20%, measured at a temperature of 20° C. by differential scanning calorimetry according to standard ISO 11357-3-2013.

8. The rubber composition according to any one of claims 1 to 7, wherein the content of the paraffin oil is within a range of 5 to 60 phr.

9. The rubber composition according to any one of claims 1 to 8, wherein the total content of the reinforcing fillers is in the range of 25 phr to 65 phr.

10. A tire comprising the rubber composition according to any one of claims 1 to 9.

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