RUBBER COMPOSITION WITH A HIGHLY SATURATED DIENE ELASTOMER

Abstract

The invention relates to a rubber composition having improved tear strength. Said composition is based on 20 to 50 phr of copolymer containing ethylene units and units of a 1,3-diene of formula CH2=CR-CH=CH2, where R represents a hydrocarbon chain having 3 to 20 carbon atoms, the ethylene units in the copolymer representing between 50% and 95 mol% of the monomer units of the copolymer; 50 to 80 phr of polyisoprene having a percentage by weight of 1,4-cis bonds of at least 90% of the weight of the polyisoprene; comprising more than 50% by weight of carbon black relative to the total weight of reinforcing filler; an aliphatic diacid dialkyl ester plasticizer; and a vulcanization system. The invention also relates to rubber articles comprising a composition according to the invention, in particular pneumatic tires, at least one sidewall of which comprises a composition according to the invention.

Description

[0001] Rubber composition comprising a highly saturated diene elastomer

[0002] The field of the present invention is that of rubber compositions comprising a highly saturated diene elastomer, in particular compositions intended for use in a tire, more particularly in a tire sidewall.

[0003] The sidewalls of a tire are exposed to both the action of ozone and deformation cycles such as flexing during tire rolling. Deformation cycles combined with the action of ozone can cause cracks or fissures to appear in the sidewall, preventing the use of the tire regardless of tread wear. Therefore, rubber compositions are sought that are highly cohesive to form, for example, tire sidewalls due to their ability to withstand large deformations without breaking, even in the presence of incipient cracks.

[0004] To minimize the action of ozone on rubber compositions, it is known to use copolymers having less sensitivity to oxidation, such as for example highly saturated diene elastomers, elastomers comprising ethylene units at a molar content greater than 50% of the monomer units of the elastomer. The use of copolymers of ethylene and 1,3-diene in a sidewall composition is also for example described in document EP 2 682 423 A1 to increase the resistance to ozone. However, there appears to be a decline in the cohesion properties of the rubber composition when the molar content of ethylene in the copolymer is greater than 50%.

[0005] Furthermore, diene rubber compositions comprising copolymers of ethylene and 1,3-butadiene, once crosslinked, can exhibit a much higher rigidity than the diene rubber compositions traditionally used as is apparent from document WO 2014 / 114607 AL. However, this increased rigidity, although favorable to improved wear resistance for use in treads, can sometimes prove unsuitable for certain applications.

[0006] It has therefore been sought to reduce the cured stiffness of such compositions comprising an ethylene-based diene rubber. To do this, it is known to reduce the bridge density of the rubber composition. However, this solution is accompanied by an increase in the hysteresis of the rubber composition, which is detrimental to rolling resistance. Document WO 2021 / 053296 A1 provided a solution for reducing the cured stiffness of compositions comprising an ethylene-based diene rubber without penalizing the hysteresis by using rubber compositions which comprise a copolymer of ethylene and a 1,3-diene of formula CH2=CR-CH=CH2, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms.

[0007] It would therefore be of interest to tire manufacturers to have rubber compositions, usable in particular in sidewalls, offering improved resistance to crack propagation, preferably also reducing rigidity, without penalizing hysteresis, or even improving it.

[0008] Continuing its research, the Applicant unexpectedly discovered that the use of a specific liquid plasticizer in a composition based on a specific copolymer containing ethylene units and a 1,3-diene makes it possible to solve the aforementioned technical problem.

[0009] Thus, the invention relates to a rubber composition based on at least:

[0010] - 20 to 50 pce of copolymer containing ethylene units and units of a 1,3-diene of formula (I), the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer,

[0011] CH2=CR-CH=CH2(I) the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms;

[0012] - 50 to 80 pce of polyisoprene comprising a mass rate of 1,4-cis bonds of at least 90% of the mass of the polyisoprene;

[0013] - a reinforcing filler comprising more than 50% by mass of carbon black relative to the total mass of reinforcing filler;

[0014] - an aliphatic diacid dialkyl ester plasticizer; and

[0015] - a vulcanization system.

[0016] The invention also relates to a rubber article comprising a composition according to the invention, in particular a pneumatic tire of which at least one sidewall comprises a composition according to the invention.

[0017] I- DEFINITIONS

[0018] The expression "based on" used to define the constituents of a catalytic system means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0019] 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.

[0020] By “elastomer matrix” is meant all the elastomers in the composition, including the copolymer defined below.

[0021] 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.

[0022] 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 by mass of the elastomer matrix.

[0023] On the other hand, 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 the 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.

[0024] 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%.

[0025] 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.

[0026] 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).

[0027] II- DESCRIPTION OF THE INVENTION

[0028] II- 1 Elastomer matrix

[0029] The composition according to the invention is based on at least:

[0030] - 20 to 50 pce of at least one copolymer containing ethylene units and units of a 1,3-diene of formula (I), the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer,

[0031] CH2=CR-CH=CH2(I) the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms;

[0032] - 50 to 80 pce of polyisoprene comprising a mass rate of 1,4-cis bonds of at least 90% of the mass of the polyisoprene.

[0033] In this document, unless otherwise indicated, the expression "the copolymer" means "the at least one copolymer containing ethylene units and units of a 1,3-diene of formula (I), the ethylene units in the copolymer representing between 50% and 95% by mole of the units, CH2=CR-CH=CH2 (I), the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms" for the sake of simplification of drafting.

[0034] 1,3-Diene of formula (I) is a substituted 1,3-diene, which can give rise to units of 1,2-configuration represented by formula (1), 3,4-configuration represented by formula (2) and 1,4-configuration whose trans form is represented below by formula (3).

[0035] (1) (2) (3) As is also well known, the ethylene unit is a “-(CH2- CH2)-” motif unit.

[0036] The copolymer useful for the purposes of the invention is a copolymer containing ethylene units and 1,3-diene of formula (I), which implies that monomer units of the copolymer are units resulting from the polymerization of ethylene and 1,3-diene of formula (I). The copolymer therefore comprises ethylene units and units of 1,3-diene of formula (I). According to the invention, the 1,3-diene may be a single compound, i.e. a single (in English "one") 1,3-diene of formula (I) or be a mixture of 1,3-dienes of formula (I), the 1,3-dienes of the mixture being differentiated from each other by the group represented by the symbol R.

[0037] The copolymer useful for the purposes of the invention is advantageously a random copolymer according to any one of the embodiments of the invention. Very advantageously, the copolymer is an atactic polymer according to any one of the embodiments of the invention.

[0038] In formula (I) of 1,3-diene, the hydrocarbon chain represented by the symbol R is an unsaturated chain of 3 to 20 carbon atoms. Preferably, the symbol R represents a hydrocarbon chain having 6 to 16 carbon atoms.

[0039] The hydrocarbon chain represented by the symbol R may be a saturated or unsaturated chain. Preferably, the symbol R represents an aliphatic chain, in which case in formula (I) of 1,3-diene, the hydrocarbon chain represented by the symbol R is an aliphatic hydrocarbon chain. It may be a straight or branched chain, in which case the symbol R represents a straight or branched chain. Preferably, the hydrocarbon chain is acyclic, in which case the symbol R represents an acyclic chain. More preferably, the symbol R represents an unsaturated and branched acyclic hydrocarbon chain. Thus, the hydrocarbon chain represented by the symbol R is advantageously an unsaturated and branched acyclic chain containing from 3 to 20 carbon atoms, in particular from 6 to 16 carbon atoms. Very advantageously, the 1,3-diene is myrcene, P-famesene or a mixture of myrcene and P-farnesene.Even more advantageously, the 1,3-diene is myrcene.

[0040] Advantageously, the copolymer contains 1,3-diene units of formula (I) which represent between 10% and 40%, preferably between 15% and 30%, by mole of the monomer units of the copolymer. Also advantageously, the copolymer contains ethylene units which represent from 60% to 90% by mole of the monomer units of the copolymer, i.e. from 60% to 90% by mole of the ethylene units and the 1,3-diene units. Very preferably, the copolymer contains ethylene units which represent from 70% to 85% by mole of the monomer units of the copolymer.

[0041] The copolymer may comprise a second 1,3-diene chosen from 1,3-butadiene, isoprene or a mixture thereof. In this case, the copolymer is a copolymer of ethylene, a 1,3-diene of formula (I) and a second 1,3-diene chosen from 1,3-butadiene, isoprene or a mixture thereof, the monomer units of the copolymer are units resulting from the polymerization of ethylene, the 1,3-diene of formula (I) and the second 1,3-diene. The copolymer may thus comprise ethylene units, units of the 1,3-diene of formula (I) and units of the second 1,3-diene. Advantageously, the second 1,3-diene of the copolymer is 1,3-butadiene.

[0042] When the copolymer contains units of the second 1,3-diene, these advantageously represent between 1% and 49%, preferably between 4% and 29%, preferably between 4% and 25%, in moles of the monomer units of the copolymer.

[0043] According to one embodiment of the invention, the copolymer contains more than 60% to 90% by mole of ethylene units and at most 20% by mole, preferably at most 15% by mole of units of the 1,3-diene of formula (I). According to this embodiment of the invention, the copolymer preferably contains less than 30% by mole of units of the second 1,3-diene or preferably contains less than 20% by mole of units of the second 1,3-diene.

[0044] When the second 1,3-diene is 1,3-butadiene or a mixture of 1,3-butadiene and isoprene, the copolymer may additionally contain 1,2-cyclohexanediyl unit units. The presence of these cyclic structures in the copolymer results from a very specific insertion of ethylene and 1,3-butadiene during polymerization. The content of 1,2-cyclohexanediyl unit units in the copolymer varies depending on the respective contents of ethylene and 1,3-butadiene in the copolymer. The copolymer preferably contains less than 15 mol% of 1,2-cyclohexanediyl unit units.

[0045] Preferably, the copolymer has a glass transition temperature of less than -35°C, preferably between -90°C and -35°C, more preferably between -70°C and The copolymer can be prepared by a process which comprises the copolymerization of ethylene, 1,3-diene of formula (I) and the optional second 1,3-diene, in the presence of a catalytic system based at least on one metallocene of formula (II) and one organomagnesium compound of formula (III)

[0046] P(Cp 1 CP 2 ) Nd(BH4) w Nx (H)

[0047] MgRW (III) in which:

[0048] - Cp 1 and Cp 2 , identical or different, being chosen from the group consisting of the cyclopentadienyl group of formula C5H4, the unsubstituted fluorenyl group of formula C13IL and the substituted fluorenyl groups,

[0049] - P being a group bridging the two Cp groups 1 and Cp 2and representing a ZR group 3 R 4 , Z representing a silicon or carbon atom, R 3 and R 4 , identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl,

[0050] - y, integer, being equal to or greater than 0,

[0051] - x, whole number or not, being equal to or greater than 0,

[0052] - L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium,

[0053] - N representing a molecule of an ether, preferably diethyl ether or tetrahydrofuran,

[0054] - R 1 and R 2 , identical or different, representing a carbon group.

[0055] Substituted fluorenyl groups include those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms. The choice of radicals is also guided by the accessibility of the corresponding molecules, which are substituted fluorenes, because the latter are commercially available or easily synthesized.

[0056] As substituted fluorenyl groups, mention may be made more particularly of the 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl groups. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the rings as shown in the diagram below, position 9 corresponding to the carbon atom to which the P bridge is attached.

[0057] The catalytic system can be prepared in a traditional manner by a process similar to that described in patent application WO 2007054224 or WO 2007054223. For example, the organomagnesium compound and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature ranging from 20 to 80°C for a period of between 5 and 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene. Generally, after its synthesis, the catalytic system is used as is in the process for synthesizing the copolymer in accordance with the invention.

[0058] Alternatively, the catalytic system may be prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1. According to this alternative, the catalytic system further contains a preformation monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene, in which case the catalytic system is based at least on the metallocene, the organomagnesium compound and the preformation monomer. For example, the organomagnesium compound and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature of 20 to 80°C for 10 to 20 minutes to obtain a first reaction product, then with this first reaction product, the preformation monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene is reacted at a temperature ranging from 40 to 90°C for 1 to 12 hours.The conjugated diene as pre-formation monomer is preferably a 1,3-diene such as 1,3-butadiene, isoprene or a 1,3-diene of formula (I), in particular myrcene or P-famesene. The catalytic system thus obtained can be used immediately in the process according to the invention or can be stored under an inert atmosphere before its use in the process according to the invention.

[0059] The metallocene used to prepare the catalytic system may be in the form of a crystallized or non-crystalline powder, or in the form of single crystals. The metallocene may be in a monomeric or dimeric form, these forms depending on the method of preparation of the metallocene, as for example described in patent application WO 2007054224 or WO 2007054223. The metallocene may be prepared in a conventional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth borohydride in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent.The metallocene is finally dried and isolated in solid form.

[0060] Like any synthesis carried out in the presence of organometallic compounds, the synthesis of the metallocene and that of the catalytic system take place under anhydrous conditions under an inert atmosphere. Typically, the reactions are carried out from solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0061] The organomagnesium useful for the purposes of the invention has the formula MgR'R. 2 in which R 1 and R 2 , identical or different, represent a carbon group. A carbon group is understood to mean a group which contains one or more carbon atoms. Preferably, R 1 and R 2 contain 2 to 10 carbon atoms. More preferably, R 1 and R 2each represent an alkyl. The organomagnesium is advantageously a dialkylmagnesium, better butylethylmagnesium or butyloctylmagnesium, even better butyloctylmagnesium.

[0062] According to any one of the embodiments of the invention, the molar ratio of the organomagnesium to the Nd metal constituting the metallocene is preferably within a range from 1 to 100, more preferably is greater than or equal to 1 and less than 10. The range of values ​​from 1 to less than 10 is in particular more favorable for obtaining copolymers with high molar masses.

[0063] When the copolymer useful for the purposes of the invention is a copolymer which has a microstructure as defined according to the first variant of the invention, it is prepared according to the process mentioned in the present application using a metallocene of formula (II) in which Cp 1 and Cp 2, identical or different, are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula CBHS. For this variant, the following metallocenes are particularly suitable, in which the symbol Flu has the fluorenyl group of formula C13H8: [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2]; [Me2SiFlu2Nd(p-BH4)2Li(THF)]; [Me2SiFlu2Nd(p- BH4)(THF)]; [{Me2SiFlu2Nd(p-BH4)(THF)}2]; [Me2SiFlu2Nd(p-BH4)]. A person skilled in the art also knows how to adapt the polymerization conditions and the concentrations of each of the reactants (constituents of the catalytic system, monomers) according to the equipment (tools, reactors) used to carry out the polymerization and the various chemical reactions. As is known to those skilled in the art, the copolymerization as well as the handling of the monomers, the catalytic system and the polymerization solvent(s) are carried out under anhydrous conditions and under an inert atmosphere.Polymerization solvents are typically hydrocarbon solvents, either aliphatic or aromatic.

[0064] The polymerization is preferably carried out in solution, continuously or batchwise. The polymerization solvent may be a hydrocarbon, aromatic or aliphatic solvent. Examples of polymerization solvents include toluene and methylcyclohexane. The monomers may be introduced into the reactor containing the polymerization solvent and the catalytic system or, conversely, the catalytic system may be introduced into the reactor containing the polymerization solvent and the monomers. The copolymerization is typically carried out under anhydrous conditions and in the absence of oxygen, in the optional presence of an inert gas. The polymerization temperature generally varies within a range from 30 to 150°C, preferably from 30 to 120°C. Preferably, the copolymerization is carried out at constant ethylene pressure.

[0065] During the polymerization of ethylene, 1,3-diene of formula (I) and the optional second 1,3-diene, in a polymerization reactor, a continuous addition of ethylene and 1,3-diene of formula (I) and the optional second 1,3-diene, can be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for the synthesis of random copolymer.

[0066] The polymerization can be stopped by cooling the polymerization medium. The polymer can be recovered using conventional techniques known to those skilled in the art, such as precipitation, evaporation of the solvent under reduced pressure or stripping with water vapor.

[0067] The content of the copolymer is advantageously within a range from 20 to 45 phr, preferably from 31 to 45 phr. It is understood that the copolymer may be constituted by a mixture of copolymers which differ by their microstructure or by their macrostructure. Furthermore, the content of polyisoprene comprising a mass content of 1,4-cis bonds of at least 90% of the mass of the polyisoprene is advantageously within a range from 55 to 80 phr, preferably from 55 to 69 phr. Advantageously, the polyisoprene comprises a mass content of 1,4-cis bonds of at least 98% of the mass of the polyisoprene.

[0068] Preferably, the polyisoprene is selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR) and mixtures thereof. More preferably, the polyisoprene is a natural rubber.

[0069] In a particularly preferred manner, the total content of the copolymer and the polyisoprene is within a range from 90 to 100 phr, preferably from 95 to 100 phr. Preferably the total content of the copolymer and the polyisoprene is 100 phr, that is to say that the copolymer and the polyisoprene are the only elastomers in the composition.

[0070] II-2 Reinforcing charge

[0071] The composition according to the invention is based on at least one reinforcing filler comprising more than 50% by mass of carbon black relative to the total mass of reinforcing filler. 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.

[0072] Advantageously, the reinforcing filler of the composition according to the invention comprises more than 80% by mass of carbon black. More preferably, the reinforcing filler consists exclusively of carbon black, that is to say that the carbon black represents 100% by mass of the reinforcing filler.

[0073] Suitable carbon blacks are all carbon blacks, including those conventionally used in tires or their treads. Among the latter, we will particularly mention the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as for example blacks NI 15, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772. These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used. Carbon blacks could, for example, already be incorporated into the diene elastomer, in particular isoprene elastomer, in the form of a masterbatch (see, for example, applications WO97 / 36724-A2 or WO99 / 16600-A1). Among the aforementioned carbon blacks, those having a BET specific surface area in a range from 21 to 69 m2 / g, preferably 33 to 60 m 2 / g, preferably 40 to 49 m 2 / g, are particularly preferred.

[0074] Thus, preferably, the reinforcing filler comprises more than 50% by weight, preferably more than 80% by weight, of at least one carbon black having a BET specific surface area within a range of 21 to 69 m 2 / g, preferably 33 to 60 m 2 / g, preferably 40 to 49 m 2 / g. The BET specific surface area of ​​carbon blacks is measured according to ASTM D6556-10 [multi-point method (minimum 5 points) - gas: nitrogen - relative pressure range P / P0: 0.1 to 0.3],

[0075] The composition according to the invention may comprise fillers other than carbon black but this is not obligatory or preferable. This may in particular be an inorganic filler such as silica.

[0076] 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 15 to 80 phr, preferably from 20 to 55 phr, more preferably from 25 to 45 phr.

[0077] Preferably, the carbon black content in the composition according to the invention is within a range from 15 to 80 phr, preferably from 20 to 55 phr, more preferably from 25 to 45 phr, and the composition does not comprise any filler other than carbon black or comprises less than 10 phr, preferably less than 5 phr, more preferably the composition does not comprise any filler other than carbon black.

[0078] II-3 Plasticizing system

[0079] The rubber composition according to the invention is based on at least one aliphatic diacid dialkyl ester plasticizer. This plasticizer is by nature a liquid plasticizer. By definition, a liquid plasticizer is liquid at room temperature (20°C, 1 atm).

[0080] Preferably, the aliphatic diacid dialkyl ester plasticizer is a compound of formula ROOC-(CH2) n-COOR in which R is a linear or branched alkyl and n represents an integer from 4 to 20. Preferably, the radical R is an alkyl comprising from 4 to 20 carbon atoms, preferably from 6 to 12 carbon atoms and more preferably from 6 to 10 carbon atoms. Preferably, the radical R is a branched alkyl, and very preferably, R is a 2-ethylhexyl radical. Preferably for the purposes of the invention, n represents an integer from 4 to 12, and preferably an integer from 6 to 10. Very preferably, n is equal to 8. Very preferably, the aliphatic diacid dialkyl ester plasticizer is di-2-ethylhexyl sebacate [Chem 1] below.

[0081] [Chem 1]

[0082] Di-2-ethylexyl sebacate sebacate, CAS number 122-62-3, has a glass transition temperature of -104°C and is, for example, marketed under the name “Plasthall DOS” by the company Hallstar.

[0083] Of course, the aliphatic diacid dialkyl ester plasticizer can be a mixture of several aliphatic diacid dialkyl ester plasticizers.

[0084] Preferably for the purposes of the invention, the level of aliphatic diacid dialkylester plasticizer in the composition is within a range from 5 to 50 phr, preferably from 7 to 40 phr and more preferably from 8 to 30 phr.

[0085] According to the invention, the composition may comprise a liquid plasticizer other than the aliphatic diacid dialkyl ester plasticizer, but this is neither mandatory nor preferred.

[0086] When the composition comprises another liquid plasticizer, the total level of liquid plasticizer is preferably within a range of 5 to 150 phr, preferably 10 to 100 phr.

[0087] Preferably, the composition does not comprise a liquid plasticizer other than the aliphatic diacid dialkyl ester plasticizer or comprises less than 30 phr, preferably less than 15 phr, preferably less than 10 phr. More preferably, the composition does not comprise a liquid plasticizer other than the aliphatic diacid dialkyl ester plasticizer.

[0088] II-4 Crosslinking system

[0089] The crosslinking system of the composition according to the invention is a vulcanization system, that is to say a sulfur-based crosslinking system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or a sulfur-donating agent. Those skilled in the art know how to adapt the quantity of sulfur-donating agent to obtain the desired quantity of sulfur in the composition. Preferably, the sulfur is provided in the form of molecular sulfur.

[0090] At least one vulcanization accelerator is also present and, optionally and preferably, various known vulcanization activators may be used such as zinc oxide, stearic acid or equivalent compound such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders.

[0091] The sulfur is used at a preferred rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferred rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr. More preferably, the composition comprises from 0.6 to 2 phr, preferably from 0.7 to 1.8 phr of sulfur and from 0.6 to 1 phr, preferably from 0.6 to 0.9 phr of at least one vulcanization accelerator.

[0092] The mass ratio of sulfur to vulcanization accelerator may be in a range from 0.75 to 3.00, preferably from 1.00 to 2.75, more preferably from 1.30 to 2.33.

[0093] 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 ("ZBEC") and mixtures of these compounds.

[0094] Advantageously, the vulcanization accelerator is chosen from sulfenamide type accelerators and their mixtures, preferably chosen from the group consisting of CBS, TBBS, DCBS and their mixtures. Particularly advantageously, the vulcanization accelerator is CBS. Advantageously, also, the composition does not comprise any vulcanization accelerator other than sulfenamide type accelerators, preferably other than CBS. II-5 Possible additives

[0095] 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, etc.

[0096] II-6 Preparation of rubber compositions

[0097] The compositions usable within the framework of the present invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

[0098] - 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 are introduced into a suitable mixer such as a conventional internal mixer (for example of the "Banbury" type), in particular the elastomeric matrix, the reinforcing filler, any other various additives, with the exception of the crosslinking system. The incorporation of the possible 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.

[0099] - a second phase of mechanical work (so-called "productive" phase), which can be carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and everything is then mixed for a few minutes, for example between 5 and 15 min.

[0100] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301. The final composition thus obtained is then calendered for example in the form of a sheet or a plate, in particular for laboratory characterization, or extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber usable for example as a tire sidewall. These products can then be used for the manufacture of tires, according to techniques known to those skilled in the art.

[0101] 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.

[0102] 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.

[0103] II-7 Rubber article

[0104] The present invention also relates to a rubber article comprising at least one composition according to the invention. Preferably, the rubber article is a tire.

[0105] 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.

[0106] More particularly, the invention also relates to a tire comprising a rubber composition according to the invention, the composition being present in at least one sidewall of the tire. The composition according to the invention may constitute part or all of the sidewall of the tire. The tire according to the invention may be intended to equip any type of vehicle, in particular motor vehicles, without any particular limitation.

[0107] III- EXAMPLES

[0108] III- 1 Measurements and tests used

[0109] III- 1.1 Determination of the microstructure of Ethylene-Myrcene copolymers (Elastomer El):

[0110] Spectral characterization and microstructure measurements of Ethylene-Myrcene copolymers are performed by Nuclear Magnetic Resonance (NMR) spectroscopy.

[0111] Spectrometer: For these measurements, a Bruker Avance III HD 400 MHz spectrometer is used, equipped with a Bruker cryo-BBFO z-grad 5 mm probe.

[0112] Experiments: 1H experiments are recorded using a radiofrequency pulse with a flip angle of 30°, the number of repetitions is 128 with a recycle delay of 5 seconds. 1H-13C HSQC (Heteronuclear Single Quantum Coherence) and HMBC (Heteronuclear Multiple-Bond Correlation) NMR correlation experiments are recorded with a number of repetitions of 128 and a number of increments of 128. The experiments are carried out at 25°C.

[0113] Sample preparation: 25 mg of sample is solubilized in 1 mL of deuterated chloroform (CDCh).

[0114] Sample calibration: The chemical shift axes 'H and 13 C are calibrated against the protonated solvent impurity (CHCl3) at ôin = 7.2 ppm (for the most deshielded signal) and 813c = 77 ppm (for the least deshielded signal).

[0115] Spectral assignment for ethylene and 1,3-myrcene copolymers: In representations A, B, C below, the symbols Ri and R2 represent the attachment points of the unit to the polymer chain. The signals of the insertion forms of 1,3-diene A, B and C were observed on the different recorded spectra. According to S. Georges et al., (Polymer 55 (2014) 3869-3878), the signal of the -CH= group n°8” characteristic of form C shows chemical shifts 'H and 13C identical to the group - CH= n°3. The chemical shifts of the characteristic signals of motifs A, B and C are presented in Table 1. Motifs A, B and C correspond respectively to the 3,4-configuration, 1,2-configuration and 1,4-trans-configuration units. Quantifications were carried out from the integration of the 1D 'H NMR spectra using Topspin software. The integrated signals for the quantification of the different motifs are: Ethylene: signal at 1.2 ppm corresponding to 4 protons

[0116] Total myrcene: signal no. 1 (1.59 ppm) corresponding to 6 protons

[0117] Form A: signal no. 7 (4.67 ppm) corresponding to 2 protons

[0118] Form B: signal n°8' (5.54 ppm) corresponding to 1 proton The quantification of the microstructure is carried out in molar percentage (molar %) as follows: molar % of a motif = 1H integral of a motif * 100 / X (1H integrals of each motif).

[0119] [Table 1]

[0120] III- 1.2 Determination of the macrostructure of polymers by size exclusion chromatography (SEC): a) Principle of measurement:

[0121] Size exclusion chromatography (SEC) separates macromolecules in solution according to their size using columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first. Combined with 3 detectors (3D), a refractometer, a viscometer and a 90° light scattering detector, SEC can be used to assess the absolute molar mass distribution of a polymer. The various number-average (Mn), weight-average (Mw) absolute molar masses and the polydispersity index (Ip = Mw / Mn) can also be calculated. b) Polymer preparation:

[0122] Each sample is solubilized in tetrahydrofuran at a concentration of approximately 1 g / L. The solution is then filtered through a 0.45 pm porosity filter before injection. c) 3D SEC analysis:

[0123] To determine the number-average molar mass (Mn), and where appropriate the weight-average molar mass (Mw) and the polydispersity index (Ip) of polymers, the method below is used.

[0124] The number-average molar mass (Mn), weight-average molar mass (Mw) and polydispersity index of the polymer (hereinafter referred to as sample) are determined absolutely by triple detection size exclusion chromatography (SEC). Triple detection size exclusion chromatography has the advantage of measuring average molar masses directly without calibration.

[0125] The refractive index increment dn / dc value of the sample solution is measured online using the peak area detected by the refractometer (RI) of the liquid chromatography equipment. To apply this method, it must be ensured that 100% of the sample mass is injected and eluted through the column. The RI peak area depends on the sample concentration, the RI detector constant and the dn / dc value.

[0126] To determine the average molar masses, the previously prepared and filtered lg / l solution is used and injected into the chromatographic system. The equipment used is a "WATERS alliance" chromatographic chain. The elution solvent is tetrahydrofuran containing 250 ppm of BHT (2,6-diter-butyl 4-hydroxy toluene), the flow rate is 1 mL.min' 1, the system temperature of 35°C and the analysis time of 60 min. The columns used are a set of three AGILENT columns with the trade name “PL GEL MIXED B LS”. The injected volume of the sample solution is 100 pL. The detection system is composed of a Wyatt differential viscometer with the trade name “VISCOSTAR II”, a Wyatt differential refractometer with the trade name “OPTILAB T-REX” with a wavelength of 658 nm, a Wyatt multi-angle static light scattering detector with a wavelength of 658 nm and the trade name “DAWN HELEOS 8+”.

[0127] For the calculation of the number-average molar masses and the polydispersity index, the value of the refractive index increment dn / dc of the sample solution obtained above is integrated. The software for processing the chromatographic data is the “ASTRA de Wyatt” system.

[0128] Ill- 1.3 Dynamic Properties

[0129] The dynamic properties G'(10%) and G” max are measured at a temperature of 23°C on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of crosslinked composition (cylindrical specimen 4 mm thick and 400 mm 2 of section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under the defined temperature conditions, for example at 23°C according to standard ASTM D 1349-99. A strain amplitude sweep is carried out from 0.1 to 50% (forward cycle), then from 50% to 0.1% (return cycle). The results used are the dynamic shear modulus G' and the viscous modulus G”. For the return cycle, the maximum value of G” observed, noted G”max, is indicated, as well as the dynamic shear modulus G'(10%) at 10% strain, at 23 °C.

[0130] It is recalled that, in a manner well known to those skilled in the art, the value of G' (10%) at 23°C is representative of the rigidity of the material. The performance results G'(10%) at 23°C are expressed on a base of 100, the value 100 being assigned to the control. For G' (10%) at 23°C a result greater than 100 indicates that the composition of the example considered is less rigid, reflecting, for a tire sidewall undergoing an imposed deformation, better endurance.

[0131] It is also recalled that, in a manner well known to those skilled in the art, the value of G”max at 23°C is representative of the hysteresis of the material. The G”max performance results at 23°C are expressed on a base of 100, the value 100 being assigned to the control. For G”max at 23°C, a result greater than 100 indicates that the composition of the example considered is less hysteretic, reflecting, for a tire sidewall undergoing an imposed deformation, lower rolling resistance.

[0132] III- 1.4 Tearability

[0133] The tearability indices are measured at 60°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.

[0134] III-2 Synthesis of polymers:

[0135] In polymer synthesis, all reagents are obtained commercially except for metallocenes. BOMAG butylloctylmagnesium (20% in heptane, C = 0.88 mol.L' ') is obtained from Chemtura and is stored in a Schlenk tube under an inert atmosphere. Ethylene, grade N35, is obtained from Air Liquide and is used without prior purification. Myrcene (purity > 95%) is obtained from Sigma-Aldrich.

[0136] The ethylene and myrcene copolymer: elastomer El was synthesized according to the procedure described below: In a reactor containing methylcyclohexane at 80°C, as well as ethylene (Et) and myrcene (Myr) in the proportions indicated in Table 3, butyloctylmagnesium (BOMAG) is added to neutralize the impurities in the reactor, then the catalytic system (see Table 2). At this time, the reaction temperature is regulated at 80°C and the polymerization reaction starts. The polymerization reaction takes place at a constant pressure of 8 bars. The reactor is supplied throughout the polymerization with ethylene and myrcene (Myr) in the proportions defined in Table 3. The polymerization reaction is stopped by cooling, degassing the reactor and adding ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven until constant mass.The catalyst system is a preformed catalyst system. It is prepared in methylcyclohexane from a metallocene, [Me2SiFlu2Nd(p-BH4)2Li(THF)], a cocatalyst, butyloctylmagnesium (BOMAG), and a preforming monomer, 1,3-butadiene, in the contents indicated in Table 2. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017 / 093654 AL.

[0137] The microstructure of Telastomer El and its properties are shown in Table 3. For the microstructure, Table 3 shows the molar ratios of ethylene (Eth) units and myrcene units. Also shown is the molar ratio of myrcene units according to whether they are 1,4-configured, 1,2-configured, and 3,4-configured.

[0138] [Table 2]

[0139] [Table 3]

[0140] III-3 Preparation of compositions

[0141] In the following examples, the rubber compositions were produced as described in point II-6 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. The crosslinking of the composition was carried out at a temperature of 150°C, under pressure, for a period of 15 minutes.

[0142] III-3 Rubber composition tests

[0143] The examples presented below are intended to compare the tearability, rigidity and hysteresis performances of a composition in accordance with the invention (Cl) with a control composition (Tl).

[0144] Table 4 presents the tested compositions (in pce), as well as the results obtained.

[0145] [Table 4] (1) Natural rubber

[0146] (2) Elastomer El prepared according to the process described in point III-2 above

[0147] (3) Carbon black grade N550 according to ASTM D-1765

[0148] (4) “Tudalen 1968” paraffinic oil from the company Klaus Dahleke (5) “Plasthall DOS” oil from the company Hallstar (Tg = -104°C)

[0149] (6) 2,2,4-trimethyl-l,2-dihydroquinoline “Pilnox TMQ” from Nocil

[0150] (7) Anti-ozone wax “VARAZON 4959” from the company Sasol Wax

[0151] (8) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine “Santoflex 6-PPD” from Flexsys

[0152] (9) Industrial grade zinc oxide from Umicore (10) Stearic acid “Pristerene 4931” from Uniqema

[0153] (11) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from Flexsys

[0154] The results presented in Table 4 above show that the use of the specific plasticizer makes it possible to improve both the tear resistance, endurance and rolling resistance of rubber composition based on a highly saturated diene elastomer.

Claims

Claims: Rubber composition based on at least: - 20 to 50 pieces of copolymer containing ethylene units and units of a 1,3-diene of formula (I), the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer, CH2=CR-CH=CH2(I) the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms; - 50 to 80 pieces of polyisoprene comprising a mass percentage of 1,4-cis bonds of at least 90% of the mass of the polyisoprene; - a reinforcing filler comprising more than 50% by mass of carbon black relative to the total mass of reinforcing filler; - a dialkyl ester plasticizer of aliphatic diacid; and - a vulcanizing system. Rubber composition according to claim 1, wherein the copolymer contains ethylene units representing from 60% to 90%, preferably from 70% to 85%, by moles, of the monomer units of the copolymer. Rubber composition according to any one of the preceding claims, wherein the 1,3-diene of formula (I) is myrcene, p-farnesene, or a mixture of myrcene and p-farnesene, preferably myrcene. Rubber composition according to any one of the preceding claims, wherein the copolymer contains units of 1,3-diene of formula (I) representing from 10% to 40%, preferably from 15% to 30%, by moles, of the monomer units of the copolymer. Rubber composition according to any one of the preceding claims, wherein the percentage of the copolymer is in the range of 20% to 45%. A rubber composition according to any one of the preceding claims, wherein the polyisoprene is present in a proportion ranging from 55 to 80 parts per million (ppm), and wherein the polyisoprene is present in a proportion ranging from 55 to 80 ppm. A rubber composition according to any one of the preceding claims, wherein the polyisoprene is selected from the group consisting of natural rubber, synthetic polyisoprenes, and mixtures thereof, preferably the polyisoprene being a natural rubber. A rubber composition according to any one of the preceding claims, wherein the proportion of reinforcing filler is in a proportion ranging from 15 to 80 ppm, preferably from 20 to 55 ppm, and preferably from 25 to 45 ppm. A rubber composition according to any one of the preceding claims, wherein the proportion of the aliphatic diacid dialkyl ester plasticizer is in a proportion ranging from 5 to 50 ppm, preferably from 7 to 40 ppm, and more preferably from 8 to 30 ppm.Rubber composition according to any one of the preceding claims, wherein the aliphatic diacid dialkyl ester plasticizer is a compound of formula ROOC-(CH2). n -COOR wherein R is a linear or branched alkyl and n represents an integer from 4 to 20. Rubber composition according to claim 9, wherein the radical R is an alkyl comprising from 4 to 20 carbon atoms, preferably from 6 to 12 carbon atoms and more preferably from 6 to 10 carbon atoms, and n represents an integer from 4 to 12, preferably an integer from 6 to 10, and more preferably n is equal to 8. Rubber composition according to any one of the preceding claims, wherein the aliphatic diacid dialkyl ester plasticizer is di-2-ethylexyl sebacate. A rubber composition according to any one of the preceding claims, the rubber composition not containing any liquid plasticizer other than aliphatic diacid dialkyl ester plasticizer, or containing less than 30 parts per liter, preferably less than 15 parts per liter, preferably less than 10 parts per liter. A rubber composition according to any one of the preceding claims, the rubber composition not comprising any liquid plasticizer other than aliphatic diacid dialkyl ester plasticizer. A rubber article comprising a rubber composition defined in any one of claims 1 to 13. A tire comprising a rubber composition defined in any one of claims 1 to 13, the composition being present in at least one sidewall of the tire.