Rubber composition based on highly saturated diene elastomer and an imidazole derivative

Abstract

The invention relates to a rubber composition having improved mechanical properties. The rubber composition is based on at least one elastomer matrix comprising at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50 and 95 mol% of the monomer units of the copolymer; a reinforcing filler; a crosslinking system; and from 0.1 to 10 phr of at least one particular imidazole. The invention also relates to a tyre comprising this composition, in particular in its tread.

Description

[0001] RUBBER COMPOSITION BASED ON A HIGHLY SATURATED DIENE ELASTOMER AND AN IMID AZOLE DERIVATIVE

[0002] The present invention relates to rubber compositions intended in particular for the manufacture of tires or semi-finished products for tires.

[0003] A tire must meet a large number of technical requirements, often contradictory, including low rolling resistance, high wear resistance, and high grip on both dry and wet roads.

[0004] Among these properties, rolling resistance and wear resistance are the most important from an environmental point of view, as they help to reduce fuel consumption and extend the life of the tires, respectively.

[0005] The diene rubber compositions traditionally used in tires are rubber compositions reinforced with highly unsaturated diene elastomers such as polybutadienes, polyisoprenes, butadiene and styrene copolymers. It has been proposed, in particular in document WO 2014 / 114607 A1, to use copolymers of ethylene and 1,3-butadiene in rubber compositions for tires. The rubber compositions reinforced with copolymer of ethylene and 1,3-butadiene are particularly described for improving the performance compromise of a tire, namely wear resistance and rolling resistance.

[0006] However, it remains of interest to tire manufacturers to improve the overall performance compromise, taking into account in particular the mechanical properties of the tire's constituent compositions which reflect the ability of these compositions to withstand the stresses to which they are subjected.

[0007] Thus, there is a need to improve the trade-off between stiffness and mechanical properties, for example by improving the mechanical properties of rubber composition without excessively penalizing their stiffness.

[0008] Continuing its research, the Applicant unexpectedly discovered that the use of a particular imidazole in rubber compositions comprising a highly saturated dimethyl elastomer makes it possible to improve the properties without excessively penalizing their rigidity.

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

[0010] - an elastomer matrix comprising at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer,

[0011] - a reinforcing charge,

[0012] - a crosslinking system, s an imidazole of formula (I): in which,

[0013] ° Ra represents a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted,

[0014] ° Rb represents a hydrocarbon group,

[0015] ° Rc and Rd represent, independently of one another, a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted, or Rc and Rd form together with the carbon atoms of the imidazole ring to which they are attached, a ring optionally interrupted by one or more heteroatoms and / or substituted

[0016] It also relates to a tire comprising a composition according to the invention.

[0017] I- DEFINITIONS

[0018] 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. The term "elastomer matrix" means all the elastomers in the composition, including the copolymer defined below.

[0019] 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.

[0020] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts of elastomer present in the rubber composition considered.

[0021] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0022] 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.

[0023] 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.

[0024] 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).

[0025] II- DESCRIPTION OF THE INVENTION

[0026] II- 1 Elastomer matrix According to the invention, the elastomer matrix comprises at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer represent between 50% and 95% by mole of the monomer units of the copolymer (hereinafter referred to as “the copolymer”).

[0027] The term "copolymer containing ethylene units and 1,3-diene units" means any copolymer comprising, within its structure, at least ethylene units and 1,3-diene units. The copolymer may thus comprise monomer units other than the ethylene units and the 1,3-diene units. For example, the copolymer may also comprise alpha-olefin units, in particular alpha-olefin units having from 3 to 18 carbon atoms, advantageously having 3 to 6 carbon atoms. For example, the alpha-olefin units may be chosen from the group consisting of propylene, butene, pentene, hexene or mixtures thereof.

[0028] As is well known, the expression "ethylene unit" refers to the -(CH2-CH2)- motif resulting from the insertion of ethylene into the elastomer chain.

[0029] As is known, the expression "1,3-diene unit" refers to the units resulting from the insertion of 1,3-diene by a 1,4 addition, a 1,2 addition or a 3,4 addition in the case of a substituted diene such as isoprene for example.

[0030] Preferably, the 1,3-diene units are chosen from the group consisting of butadiene units, isoprene units and mixtures of these 1,3-diene units. In particular, the 1,3-diene units of the copolymer may be 1,3-diene units having 4 to 12 carbon atoms, for example 1,3-butadiene, 2-methyl-1,3-butadiene (or isoprene) units. More preferably, the 1,3-diene units are for more than 50%, by mole, or even preferably exclusively, 1,3-butadiene units.

[0031] In the copolymer, the ethylene units represent between 50% and 95% by mole of the monomer units of the copolymer. Advantageously, the ethylene units in the copolymer represent between 55% and 90%, preferably from 60% to 90%, preferably from 70% to 85%, by mole of the monomer units of the copolymer.

[0032] Advantageously, the copolymer is a copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene), that is to say, according to the invention, a copolymer consisting exclusively of ethylene units and 1,3-diene units (preferably 1,3-butadiene). When the copolymer is a copolymer of ethylene and a 1,3-diene, it advantageously contains units of formula (IV) and / or (V). The presence of a saturated 6-membered cyclic unit, 1,2-cyclohexanediyl, of formula (IV) as a monomer unit in the copolymer may result from a series of very specific insertions of the polymeric ethylene during its growth.

[0033] -CH2-CH(CH=CH2)- (V)

[0034] For example, the copolymer of ethylene and a 1,3-diene may be devoid of units of formula (IV). In this case, it preferably contains units of formula (V).

[0035] When the copolymer of ethylene and a 1,3-diene comprises units of formula (IV) or units of formula (V) or units of formula (IV) and units of formula (V), the molar percentages of the units of formula (IV) and units of formula (V) in the copolymer, respectively o and p, preferably satisfy the following equation (eq. 1), more preferably equation (eq. 2), o and p being calculated on the basis of all the monomer units of the copolymer.

[0036] 0 < o+p < 25 (eq. 1)

[0037] 0 < o+p < 20 (eq. 2)

[0038] According to the invention, the copolymer, preferably the copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene), is a random copolymer.

[0039] Advantageously, the number-average mass (Mn) of the copolymer, preferably of the copolymer of ethylene and a 1,3-diene (preferably 1,3-butadiene) is within a range from 100,000 to 300,000 g / mol, preferably from 150,000 to 250,000 g / mol.

[0040] The Mn of the copolymer is determined in a known manner, by size exclusion chromatography (SEC) as described in point IV-1 below.

[0041] The copolymer can be obtained according to different synthesis methods known to those skilled in the art, in particular depending on the targeted microstructure of the copolymer. Generally, it can be prepared by copolymerization of at least one diene, preferably a 1,3-diene, more preferably 1,3-butadiene, and ethylene and according to known synthesis methods, in particular in the presence of a catalytic system comprising a metallocene complex. Mention may be made in this respect of catalytic systems based on metallocene complexes, which catalytic systems are described in documents EP 1 092 731, WO 2004035639, WO 2007054223 and WO 2007054224 in the name of the Applicant. The copolymer, including when it is random, can also be prepared by a process using a preformed type catalytic system such as those described in documents WO 2017093654 Al, WO 2018020122 Al and WO 2018020123 Al.

[0042] The copolymer may consist of a mixture of copolymers containing ethylene units and 1,3-diene units which differ from each other in their microstructures and / or in their macrostructures.

[0043] According to the invention, the elastomer matrix may comprise at least one other diene elastomer, which is not the copolymer as defined above, but this is not necessary. Preferably, the content of the at least one copolymer is within a range from more than 50 to 100 phr, preferably from 60 to 100 phr, preferably from 80 to 100 phr. Advantageously, the at least one copolymer containing ethylene units and 1,3-diene units is the only elastomer in the composition, i.e. it represents 100% by mass of the elastomer matrix.

[0044] By "diene" elastomer (or indistinctly rubber), whether natural or synthetic, is meant an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers bearing two carbon-carbon double bonds, conjugated or not). This definition includes the copolymer containing ethylene units and 1,3-diene units.

[0045] When the elastomer matrix comprises at least one other diene elastomer, which is not the copolymer containing ethylene units and 1,3-diene units, the at least one other elastomer may be, for example, chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. The butadiene copolymers are particularly chosen from the group consisting of butadiene-styrene copolymers (SBR). II-2 Reinforcing filler

[0046] The composition according to the invention advantageously comprises a reinforcing filler, known for its ability to reinforce a rubber composition usable for the manufacture of tires. Such a reinforcing filler typically consists of particles whose average size (by mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

[0047] The reinforcing filler may comprise carbon black, silica or a mixture thereof. Advantageously, the reinforcing filler of the composition according to the invention comprises more than 50% by mass, preferably more than 80% by mass, of silica.

[0048] Any type of precipitated silica may be suitable, in particular highly dispersible precipitated silicas (known as "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas, whether highly dispersible or not, are well known to those skilled in the art. Examples include the silicas described in applications WO03 / 016215-A1 and WO03 / 016387-A1. Among the commercial HDS silicas, we can notably use the silicas “Ultrasil ® 5000GR”, “Ultrasil ® 7000GR” from the company Evonik, the silicas “Zeosil ® 1085GR”, “Zeosil® 1115 MP”, “Zeosil® 1165MP”, “Zeosil® Premium 200MP”, “Zeosil® HRS 1200 MP” from the company Solvay.As non-HDS silica, the following commercial silicas can be used: silicas “Ultrasil ® VN2GR”, “Ultrasil ® VN3GR” from Evonik, silica “Zeosil® 175GR” from Solvay, silicas “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(-D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” from PPG.

[0049] To couple the silica to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner to ensure a sufficient connection, of a chemical and / or physical nature, between the inorganic filler (surface of its particles) and the diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. By "bifunctional", we mean a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound may comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the diene elastomer.Preferably, the organosilanes are chosen from the group consisting of polysulfurized organosilanes (symmetrical or asymmetrical) such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, marketed under the name “Si69” by the company Evonik or bis-(triethoxysilylpropyl) disulfide, abbreviated to TESPD, marketed under the name “Si75” by the company Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl) octanethioate marketed by the company Momentive under the name “NXT Silane”. More preferably, the organosilane is a polysulfurized organosilane.

[0050] The coupling agent content can easily be adjusted by a person skilled in the art. Typically and preferably, the coupling agent level represents from 0.5% to 15% by weight relative to the quantity of silica.

[0051] The level of reinforcing filler can easily be adjusted by a person skilled in the art depending on the use of the rubber composition. Advantageously, the level of reinforcing filler, in the composition according to the invention, is within a range from 20 to less than 200 phr, preferably from 25 to 150 phr, preferably from 30 to 100 phr.

[0052] Preferably, the silica content in the composition according to the invention is within a range from 20 to less than 200 phr, preferably from 25 to 150 phr, preferably from 30 to 100 phr, and the composition comprises from 0.5 to 10 phr, preferably less than 1 to 5 phr of carbon black.

[0053] The blacks that can be used in the context of the present invention can be any black conventionally used in tires or their treads (so-called tire-grade blacks). Among the latter, mention will be made more particularly of reinforcing carbon blacks of the 100, 200, 300 series, or blacks of the 500, 600 or 700 series (ASTM 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 support for certain of the rubber additives used. Carbon blacks could, for example, already be incorporated into the diene elastomer, in particular isoprene, in the form of a masterbatch (see, for example, applications WO 97 / 36724 or WO 99 / 16600). II-3 Imidazole

[0054] The composition according to the invention comprises from 0.1 to 10 pce of at least one imidazole of general formula (I): in which,

[0055] - Ra represents a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted, the hydrocarbon group optionally interrupted by one or more heteroatoms and / or substituted not containing a dipole containing at least one nitrogen atom,

[0056] - Rb represents a hydrocarbon group,

[0057] - Rc and Ra represent, independently of each other, a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted,

[0058] - or Rc and Ra form together with the carbon atoms of the imidazole ring to which they are attached, a ring possibly interrupted by one or more heteroatoms and / or substituted.

[0059] By the expression "optionally interrupted by one or more heteroatoms and / or substituted", it is meant that the groups Ra, Rc and Ra may, independently and when they represent a hydrocarbon group, be interrupted by a heteroatom (i.e. in other words that a heteroatom is intercalated in the hydrocarbon chain), preferentially chosen from nitrogen, oxygen and sulfur, and / or substituted by a functional group. By functional group, is meant a group comprising a heteroatom, preferentially chosen from amino, alkylamine, alkoxyl and hydroxyl groups, preferentially chosen from hydroxyl and amino groups.

[0060] An amino group means a group of the formula -NH2. A hydroxyl group means a group of the formula -OH.

[0061] According to the invention Ra does not hold a dipole containing at least one nitrogen atom. In particular Ra does not contain a nitrile oxide, nitrile imine and nitrone dipole. Preferably, the imidazole of general formula (I) does not contain a dipole containing at least one nitrogen atom. As examples of a dipole containing at least one nitrogen atom, mention may be made of nitrile oxide, nitrile imine and nitrone dipoles.

[0062] Preferably, the imidazole of general formula (I) has groups such as:

[0063] - Ra is selected from the group consisting of a hydrogen atom, alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms, aralkyl groups having from 7 to 25 carbon atoms, optionally substituted, it being understood that Ra does not contain a dipole containing at least one nitrogen atom

[0064] - Rb is selected from the group consisting of alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms and aralkyl groups having from 7 to 25 carbon atoms,

[0065] - Rc and Ra are independently selected from the group consisting of a hydrogen atom, alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms and aralkyl groups having from 7 to 25 carbon atoms; optionally substituted, or Rc and Ra form together with the carbon atoms of the imidazole ring to which they are attached, a ring selected from aromatic, heteroaromatic or aliphatic rings, comprising from 5 to 12 carbon atoms, preferably 5 or 6 carbon atoms.

[0066] Preferably, Ra is chosen from the group consisting of alkyl groups having from 2 to 12 carbon atoms and aralkyl groups having from 7 to 13 carbon atoms, optionally substituted, it being understood that Ra does not contain a dipole containing at least one nitrogen atom. More preferably, Ra is chosen from the group consisting of aralkyl groups having from 7 to 13 carbon atoms, optionally substituted and Rb is chosen from the group consisting of alkyl groups having from 1 to 12 carbon atoms. It is understood that Ra does not contain a dipole containing at least one nitrogen atom. Even more preferably, Ra is chosen from the group consisting of aralkyl groups having from 7 to 11 carbon atoms, optionally substituted and Rb is chosen from the group consisting of alkyl groups having from 1 to 4 carbon atoms. It is well understood that Ra does not contain a dipole containing at least one nitrogen atom.

[0067] Preferably, Rc and Ra are independently selected from the group consisting of a hydrogen atom and alkyl groups having from 1 to 12 carbon atoms, cycloalkyl groups having from 5 to 8 carbon atoms, aryl groups having from 6 to 24 carbon atoms and aralkyl groups having from 7 to 13 carbon atoms. Alternatively and also preferably, Rc and Ra form with the carbon atoms of the imidazole ring to which they are attached, a phenyl or cyclohexene ring.

[0068] Very preferably, Rc and Ra represent the hydrogen atom, Ra and Rb being chosen as described previously.

[0069] Ra may be a naphthylalkyl group comprising from 11 to 13 carbon atoms, optionally substituted by at least one hydroxyl group, Rb is an alkyl group having from 1 to 4 carbon atoms, Rc and Ra are independently selected from the group consisting of a hydrogen atom and alkyl groups having from 1 to 12 carbon atoms. By naphthylalkyl group is meant a group of general formula (II), where n represents an integer between 1 and 3:

[0070] Ra may be a naphthylalkyl group comprising from 11 to 13 carbon atoms substituted by at least one hydroxyl group, Rb is an alkyl group having from 1 to 3 carbon atoms, Rc and Ra are a hydrogen atom. For example, Ra is a 2-naphthol-l-methyl group, Rb is a methyl group, Rc and Ra are the hydrogen atom, the compound (I) then corresponding to the formula (III):

[0071] Preferably, the imidazole of formula (I) is selected from the group consisting of 1-benzyl-2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-propylimidazole, 2-benzylimidazole, 2-phenylimidazole, 2-phenyl-4-methyl imidazole, 2-Heptadecylimidazole, 2-Phenyl-4,5-dihydroxymethylimidazole, 1,2-Dimethyl-1H-benzimidazole and mixtures thereof. More preferably, the imidazole of formula (I) is selected from the group consisting of 1-benzyl-2-methylimidazole, 2-ethylimidazole and mixtures thereof. The rubber composition according to the invention preferably comprises from 0.5 to 8 pce, preferably from 0.5 to 5 pce, of imidazole of general formula (I).

[0072] The imidazoles useful for the purposes of the invention are either commercially available or easily prepared by those skilled in the art according to well-known techniques such as described for example in documents JP2012211122, JP2007269658 or in Science of Synthesis 2002, 72, 325-528.

[0073] For example, as commercially available imidazoles useful for the purposes of the invention, mention may be made of 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-propylimidazole, 2-benzylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-Heptadecylimidazole, 2-Phenyl-4,5-dihydroxymethylimidazole, 1,2-dimethylimidazole, 1-decyl-2-methylimidazole, 1-benzyl-2-methylimidazole or 1-((2-Methyl-1H-Imidazol-1-yl)Methyl)Naphthalen-2-ol commercially available under the name "Aradur 3123" from Huntsman.

[0074] II-4 Crosslinking system

[0075] The crosslinking system may be any type of system known to those skilled in the art in the field of tire rubber compositions. It may in particular be based on sulfur, and / or peroxide and / or bismaleimides.

[0076] Preferably, the crosslinking system is sulfur-based, in which case it is referred to as a vulcanization system. Advantageously, the vulcanization system comprises molecular sulfur and / or at least one sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferably, various known vulcanization activators may be used, such as zinc oxide, stearic acid or equivalent compounds such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders.

[0077] Sulphur is used at a preferential rate of between 0.5 and 12 pce, in particular between 1 and 10 pce. The vulcanisation accelerator is used at a preferential rate of between 0.5 and 10 pce, more preferably between 0.5 and 5.0 pce.

[0078] 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 ("TB SI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds.

[0079] Particularly advantageously, the crosslinking system comprises sulfur and a vulcanization accelerator, and the mass ratio of the sulfur content to the vulcanization accelerator content is within a range from 0.4 to 1.5, preferably from 0.7 to 1.5, more preferably from 0.9 to 1.1.

[0080] II-5 Possible additives

[0081] 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, fillers (reinforcing or non-reinforcing / other than those mentioned above), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants.

[0082] The composition according to the invention may comprise a 1,3-dipolar compound corresponding to the formula (VI):

[0083] QAB (VI) in which:

[0084] - Q comprises a dipole containing at least one nitrogen atom,

[0085] - A, preferably divalent, is an atom or group of atoms linking Q to B,

[0086] - B comprises an imidazole ring corresponding to the formula (VII): in which:

[0087] ° 3 of the 4 symbols Z, Y, R and R', identical or different, each represent an atom or a group of atoms, Z and Y being able to form together with the carbon atoms to which they are attached a cycle, and

[0088] ° the fourth symbol Z, Y, R or R' denotes a direct connection to A. Such compounds are described in application WO2015059274A1.

[0089] Furthermore, the rubber composition advantageously does not comprise epoxy resin, preferably no reinforcing resin, or comprises less than 1 pce, preferably less than 0.5 pce. Furthermore, it advantageously does not comprise guanidine derivative or comprises less than 0.5 pce, preferably less than 0.4 pce, more preferably less than 0.3 pce.

[0090] II-6 Preparation of rubber compositions

[0091] The compositions in accordance with the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

[0092] - 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, the epoxy resin, any other various additives, with the exception of the crosslinking system, the amine hardener and any condensation accelerator. 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.

[0093] - a second mechanical working phase (so-called "productive" phase), which can be carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min. Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0094] The final composition thus obtained is then calendered, for example, in the form of a sheet or plate, in particular for characterization in the laboratory, or else extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber usable, for example, as an internal layer of a tire. These products can then be used for the manufacture of tires, according to techniques known to those skilled in the art.

[0095] 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.

[0096] 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.

[0097] II-7 Rubber article

[0098] 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.

[0099] 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.

[0100] More particularly, the invention also relates to a tire provided with a tread comprising a composition according to the invention. The composition according to the invention may constitute part or all of the tread of the tire.

[0101] The tire according to the invention can be intended to equip any type of vehicle, in particular motor vehicles, without any particular limitation.

[0102] III- PREFERRED EMBODIMENTS

[0103] In view of the foregoing, preferred embodiments of the invention are described below:

[0104] 1. Rubber composition based on at least:

[0105] - an elastomer matrix comprising at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer,

[0106] - a reinforcing charge,

[0107] - a crosslinking system,

[0108] - from 0.1 to 10 pce of at least one imidazole of formula (I): in which,

[0109] ° Ra represents a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted, the hydrocarbon group optionally interrupted by one or more heteroatoms and / or substituted not containing a dipole containing at least one nitrogen atom,

[0110] ° Rb represents a hydrocarbon group,

[0111] ° Rc and Rd represent, independently of each other, a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted,

[0112] ° or Rc and Rd form together with the carbon atoms of the imidazole ring to which they are attached, a ring possibly interrupted by one or more heteroatoms and / or substituted.

[0113] 2. Rubber composition according to embodiment 1, in which the ethylene units in the copolymer represent between 55% and 90% by mole of the monomer units of the copolymer.

[0114] 3. A rubber composition according to any one of the preceding embodiments, wherein the copolymer containing ethylene units and 1,3-diene units is a copolymer of ethylene and 1,3-diene.

[0115] 4. A rubber composition according to any one of the preceding embodiments, wherein the 1,3-diene is 1,3-butadiene.

[0116] 5. Rubber composition according to any one of the preceding embodiments, in which the copolymer contains units of formula (IV) or units of formula (V) or units of formula (IV) and of formula (V):

[0117] -CH2-CH(CH=CH2)- (V)

[0118] 6. Rubber composition according to any one of embodiment 5, in which the molar percentages of the units of formula (IV) and the units of formula (V) in the copolymer, respectively o and p, satisfy the following equation (eq. 1), preferentially to equation (eq. 2), o and p being calculated on the basis of all the monomer units of the copolymer.

[0119] 0 < o+p < 25 (eq. 1)

[0120] 0 < o+p < 20 (eq. 2)

[0121] 7. A rubber composition according to any preceding embodiment, wherein the copolymer containing ethylene units and 1,3-diene units is a random copolymer.

[0122] 8. Rubber composition according to any one of the preceding embodiments, in which the content of the at least one copolymer containing ethylene units and 1,3-diene units is within a range from 50 to 100 pce, preferably from 80 to 100 pce.

[0123] 9. Rubber composition according to any one of the preceding embodiments, in which the imidazole of general formula (I) does not contain a dipole containing at least one nitrogen atom.

[0124] 10. Rubber composition according to any one of the preceding embodiments, in which, in the imidazole of formula (I):

[0125] - Ra is selected from the group consisting of a hydrogen atom, alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms, aralkyl groups having from 7 to 25 carbon atoms, optionally substituted,

[0126] - Rb is selected from the group consisting of alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms and aralkyl groups having from 7 to 25 carbon atoms,

[0127] - Rc and Ra are independently selected from the group consisting of a hydrogen atom, alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms and aralkyl groups having from 7 to 25 carbon atoms, optionally substituted, or Rc and Ra form together with the carbon atoms of the imidazole ring to which they are attached, a ring selected from aromatic, heteroaromatic or aliphatic rings, comprising from 5 to 12 carbon atoms, preferably 5 or 6 carbon atoms.

[0128] 11. Rubber composition according to any one of the preceding embodiments, in which, in the imidazole of formula (I), Ra is chosen from the group consisting of alkyl groups having from 2 to 12 carbon atoms and aralkyl groups having from 7 to 13 carbon atoms, optionally substituted.

[0129] 12. A rubber composition according to any one of the preceding embodiments, wherein, in the imidazole of formula (I), Ra is selected from the group consisting of aralkyl groups having from 7 to 13 optionally substituted carbon atoms and Rb is selected from the group consisting of alkyl groups having from 1 to 12 carbon atoms.

[0130] 13. A rubber composition according to any one of the preceding embodiments, wherein, in the imidazole of formula (I), Ra is selected from the group consisting of aralkyl groups having from 7 to 11 optionally substituted carbon atoms and Rb is selected from the group consisting of alkyl groups having from 1 to 4 carbon atoms.

[0131] 14. A rubber composition according to any one of the preceding embodiments, wherein, in the imidazole of formula (I), Rc and Ra are independently selected from the group consisting of a hydrogen atom and alkyl groups having from 1 to 12 carbon atoms, cycloalkyl groups having from 5 to 8 carbon atoms, aryl groups having from 6 to 24 carbon atoms and aralkyl groups having from 7 to 13 carbon atoms, Rc and Ra being very preferably the hydrogen atom.

[0132] 15. Rubber composition according to any one of embodiments 1 to 13, in which, in the imidazole of formula (I), Rc and Ra form with the carbon atoms of the imidazole ring to which they are attached, a phenyl or cyclohexene ring.

[0133] 16. Rubber composition according to any one of the preceding embodiments, in which the imidazole content of formula (I) is within a range from 0.5 to 8 pce, preferably from 0.5 to 5 pce.

[0134] 17. Rubber composition according to any one of the preceding embodiments, the composition not comprising a guanidine derivative or comprising less than 0.5 phr, preferably less than 0.4 phr, more preferably less than 0.3 phr. 18. Rubber composition according to any one of the preceding embodiments, in which the reinforcing filler comprises carbon black, silica or a mixture thereof.

[0135] 19. Rubber composition according to any one of the preceding embodiments, in which the reinforcing filler comprises more than 50% by weight, preferably more than 80% by weight of silica.

[0136] 20. Rubber composition according to any one of the preceding embodiments, in which the level of the reinforcing filler is within a range from 20 to less than 200 pce, preferably from 30 to 100 pce.

[0137] 21. Rubber composition according to any one of the preceding embodiments, in which the crosslinking system is a vulcanization system based on molecular sulfur and / or based on a sulfur donor agent.

[0138] 22. Rubber composition according to any one of the preceding embodiments, comprising sulfur and a vulcanization accelerator, the mass ratio of the sulfur content to the vulcanization accelerator content being within a range from 0.4 to 1.5, preferably from 0.7 to 1.5, more preferably from 0.9 to 1.1.

[0139] 23. Rubber composition according to any one of the preceding embodiments, the composition not comprising epoxy resin, preferably reinforcing resin, or comprising less than 1 pce, preferably less than 0.5 pce.

[0140] 24. Rubber article comprising a composition as defined in any one of embodiments 1 to 23.

[0141] 25. Pneumatic or non-pneumatic comprising a composition as defined in any one of embodiments 1 to 23.

[0142] 26. Pneumatic or non-pneumatic according to embodiment 25, in which the composition defined in any one of embodiments 1 to 23 is present in the tread of the pneumatic tire.

[0143] IV- EXAMPLES

[0144] IV- 1 Measurements and tests used

[0145] Mechanical properties (after curing): Tensile test

[0146] These tensile tests are used to determine the yield stresses and the properties at break. Unless otherwise indicated, they are carried out in accordance with French standard NF T 46-002 of September 1988. Processing of the tensile records also allows the modulus curve to be plotted as a function of elongation. The modulus used here is the nominal (or apparent) secant modulus measured at first elongation, calculated by referring to the initial section of the specimen. The nominal secant modulus (or apparent stresses, in MPa) at 100% elongation, denoted MS Al 00, is measured at first elongation. The stiffness MS Al 00 is expressed on a base of 100 relative to the control composition Tl for compositions Cl and C2 or relative to composition T2 for composition C3. A value greater than 100 indicates an improvement in the reinforcement of the composition considered compared to the control composition.

[0147] The elongation at break (AR%) and breaking stress (CR) tests are based on the NF ISO 37 standard of December 2005 on a type H2 dumbbell specimen and are measured at a tensile speed of 500 mm / min. The elongation at break is expressed as a % elongation. The breaking stress is expressed in MPa. These values ​​are expressed on a base of 100 relative to the control composition Tl for compositions Cl and C2 or relative to composition T2 for composition C3. A value greater than 100 indicates an improvement in the mechanical properties of the composition considered compared to the control composition.

[0148] All these traction measurements are carried out under normal temperature (23±2°C) and hygrometry (50+5% relative humidity) conditions, according to the French standard NF T 40-101 (December 1979).

[0149] Determination of the microstructure of elastomers by nuclear magnetic resonance (NMR):

[0150] Ethylene and 1,3-butadiene copolymers are characterized by NMR spectrometry 1 H, 13 C. NMR spectra are recorded on a Brüker Avance III 500 MHz Spectrometer equipped with a BBIz-grad 5 mm “broadband” cryoprobe. The quantitative 'H NMR experiment uses a single 30° pulse sequence and a 5 second repetition delay between each acquisition. 64 to 256 accumulations are performed. The NMR experiment 13 Quantitative C uses a 30° single-pulse sequence with proton decoupling and a 10-second repetition delay between each acquisition. 1024 to 10240 accumulations are performed. Two-dimensional experiments are used for the purpose of determining the structure of polymers. The determination of the microstructure of copolymers is defined in the literature, according to the article by Llauro et al., Macromolecules 2001, 34, 6304-6311.

[0151] NMR measurements are carried out at 25°C. The copolymers are dissolved in a deuterated solvent (approximately 25 mg of elastomer in 1 ml), generally deuterated chloroform (CDCL).

[0152] Determination of the macrostructure of polymers by size exclusion chromatography (SEC): Size exclusion chromatography (SEC) allows the fractionation of polymer chains in a solvent according to their hydrodynamic volume. Like any chromatographic system, the technique is based on the elution of a solute (the polymer) through a column containing a stationary phase. The system is composed in this order: a solvent reservoir, a pumping system, an injector, a set of columns and detectors. The measuring chain is equipped with a Waters Alliance e2695 module and a Waters fRJ410 refractometer.

[0153] The mobile phase is eluted with a flow rate of 1 mL / min. The polymer is solubilized in THF in the presence of 1% wt of diisopropylamine and 1% wt of triethylamine at a concentration of 1 g / L. A volume of 100 pL is injected through a set of 3 AGILENT size exclusion chromatography columns (MIXED B LS). The columns are thermostated in an oven at 35°C. The stationary phase of the columns is based on a polystyrene divinylbenzene gel with controlled porosity. The polymer chains are separated according to the hydrodynamic volume they occupy when solubilized in the solvent. The larger the volume they occupy, the less accessible the pores of the columns are and the shorter their elution time. Detection is ensured by a refractometer (RI) thermostated at 35°C. Each elution volume is associated with a mass via Moore calibration (certified standard passage: standard polystyrenes from Polymer Standard Service (Mainz).The WATERS: EMPOWER software is used for data acquisition and analysis. It is then possible to determine the number-average molar masses (Mn), the mass-average molar masses (Mw) as well as the polydispersity (Ip = Mw / Mn).

[0154] Mooney ML 1+4

[0155] For polymers and rubber compounds, Mooney viscosities ML(l+4) at 100°C are measured using an oscillating consistometer according to ASTM D-1646 (1999). The Mooney plasticity measurement is carried out according to the following principle: the raw compound (i.e. before curing) is molded in a cylindrical chamber heated to 100°C. After one minute of preheating, the rotor rotates within the specimen at 2 revolutions / minute and the torque needed to maintain this movement after 4 minutes of rotation is measured. The Mooney plasticity ML(l+4) is expressed in "Mooney units" (MU, with 1 MU = 0.83 Nm).

[0156] IV-2 Synthesis of copolymer El:

[0157] In polymer synthesis, all reagents are obtained commercially except for metallocenes. Butyloctylmagnesium BOMAG (20% in heptane, C = 0.88 mol.L 1 ) comes from Chemtura and is stored in a Schlenk tube under an inert atmosphere. Ethylene, grade N35, comes from Air Liquide and is used without prior purification.

[0158] The copolymer of ethylene and 1,3-butadiene: elastomer E1 (in accordance with the invention) is synthesized according to the procedure described below.

[0159] The polymerization of ethylene (grade N35, from the company Air Liquide, used without prior purification) and 1,3-butadiene is carried out according to a continuous process in solution in methylcyclohexane at 80°C under 11.5 bar in the presence of a catalytic system (94 pmoles Nd per 100 g of monomers), the mass concentration of monomer feed in the reactor being 6%, the mass ratio 1,3-butadiene / ethylene being 0.53, the molar ratio active Mg / Nd being 3.7. At the desired conversion (73%, 120 minutes) to reach an Mn of approximately 139 Kg / mol, the polymerization is stopped at the line outlet using a solution of antioxidants in methylcyclohexane (0.6 pce of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 0.7 pce of 2,2'-methylene-bis(4-methyl-6-tertbutylphenol, pce: part by weight per hundred parts of elastomer).The copolymer is recovered by a steam distillation process called “stripping” well known to those skilled in the art, then dried on a screw machine equipped with a single screw.

[0160] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] at 0.0065 mol / L, a co-catalyst, butyloctylmagnesium (BOMAG) whose BOMAG / Nd molar ratio is equal to 2.2, and a preformed monomer, 1,3-butadiene whose 1,3-butadiene / Nd molar ratio is equal to 90. The medium is heated to 80°C for a period of 5 hours. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 AL

[0161] The microstructure of copolymer El and its properties are shown in Tables 1 and 2. For the microstructure, Table 1 indicates the molar ratios of ethylene units (Eth), 1,3-butadiene units, 1,2-cyclohexanediyl units (cycle).

[0162] [Table 1]

[0163] [Table 2]

[0164] IV-3 Preparation of compositions

[0165] 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 60 revolutions per minute until a maximum drop temperature of 165°C was reached. The “productive” phase was carried out in a cylinder tool at 40°C for 5 minutes.

[0166] The crosslinking of the composition was carried out at a temperature of 150°C, under pressure.

[0167] IV-4 Rubber composition tests

[0168] The examples presented below aim to compare the compromise of performance, mechanical properties (elongation at break and breaking stress) and rigidity of three compositions in accordance with the present invention (C1 to C3) with two control compositions (T1 and T2).

[0169] Table 3 presents the tested compositions (in pce), as well as the results obtained.

[0170] Compositions Cl and C2 differ from the control composition Tl, and composition C3 from composition T2, only by the presence of an imidazole. Control compositions T2 and C3 allow us to study the impact of the mass ratio of the sulfur content on the content of the vulcanization accelerator compared to compositions Tl and CL.

[0171] The results of compositions C1 and C2 are expressed as a percentage base 100 relative to the control composition T1 and the results of composition C3 are expressed as a percentage base 100 relative to the control composition T2.

[0172] [Table 3]

[0173] (1) Elastomer El obtained by the process described in point IV-2 above

[0174] (2) Silica “Zeosil 1165MP” from Solvay

[0175] (3) Liquid silane triethoxysilylpropyltetrasulfide (TESPT) “Si69” from Evonik

[0176] (4) l-benzyl-2-methylimidazole (BMI) CAS: 13750-62-4 from Aldrich (5) 2-ethylimidazole CAS 1072-62-4 from Aldrich

[0177] (6) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine “Santoflex 6-PPD” from Flexsys

[0178] (7) Anti-ozone wax “VARAZON 4959” from the company Sasol Wax

[0179] (8) Stearic acid “Pristerene 4931” from Uniqema

[0180] (9) Industrial grade zinc oxide from Umicore (10) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from Flexsys

[0181] The results presented in Table 3 above show that the combination of a copolymer according to the invention and an imidazole according to the invention makes it possible to improve both the elongation at break and the breaking strength of the composition without excessively impacting the rigidity of the composition. This effect is particularly marked for compositions having a mass ratio of the sulfur content to the vulcanization accelerator content greater than 0.5.

Claims

Claims 1. Rubber composition based on at least: - an elastomer matrix comprising at least one copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer, - a reinforcing charge, - a crosslinking system, - from 0.1 to 10 pce of at least one imidazole of formula (I): in which, o Ra represents a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted, the hydrocarbon group optionally interrupted by one or more heteroatoms and / or substituted not containing a dipole containing at least one nitrogen atom, o Rb represents a hydrocarbon group, o Rc and Rd represent, independently of one another, a hydrogen atom or a hydrocarbon group, optionally interrupted by one or more heteroatoms and / or substituted, or Rc and Rd form together with the carbon atoms of the imidazole ring to which they are attached, a ring optionally interrupted by one or more heteroatoms and / or substituted.

2. A rubber composition according to claim 1, wherein the copolymer containing ethylene units and 1,3-diene units is a copolymer of ethylene and 1,3-diene, the 1,3-diene preferably being 1,3-butadiene.

3. Rubber composition according to any one of the preceding claims, in which the content of the at least one copolymer containing ethylene units and 1,3-diene units is within a range from 50 to 100 phr, preferably from 80 to 100 phr.

4. A rubber composition according to any one of the preceding claims, wherein, in the imidazole of formula (I): - Ra is selected from the group consisting of a hydrogen atom, alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms, aralkyl groups having from 7 to 25 carbon atoms, optionally substituted, it being understood that Ra does not contain a dipole containing at least one nitrogen atom, - Rb is selected from the group consisting of alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms and aralkyl groups having from 7 to 25 carbon atoms, - Rc and Ra are independently selected from the group consisting of a hydrogen atom, alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 5 to 24 carbon atoms, aryl groups having from 6 to 30 carbon atoms and aralkyl groups having from 7 to 25 carbon atoms, optionally substituted, or Rc and Ra form together with the carbon atoms of the imidazole ring to which they are attached, a ring selected from aromatic, heteroaromatic or aliphatic rings, comprising from 5 to 12 carbon atoms, preferably 5 or 6 carbon atoms.

5. Rubber composition according to any one of the preceding claims, wherein, in the imidazole of formula (I), Ra is selected from the group consisting of alkyl groups having from 2 to 12 carbon atoms and aralkyl groups having from 7 to 13 carbon atoms, optionally substituted, it being understood that Ra does not contain a dipole containing at least one nitrogen atom.

6. A rubber composition according to any preceding claim, wherein in the imidazole of formula (I), Ra is selected from the group consisting of by aralkyl groups having from 7 to 13 carbon atoms optionally substituted and Rb is chosen from the group consisting of alkyl groups having from 1 to 12 carbon atoms, it being understood that Ra does not contain a dipole containing at least one nitrogen atom.

7. A rubber composition according to any one of the preceding claims, wherein, in the imidazole of formula (I), Ra is selected from the group consisting of aralkyl groups having from 7 to 11 optionally substituted carbon atoms and Rb is selected from the group consisting of alkyl groups having from 1 to 4 carbon atoms, it being understood that Ra does not contain a dipole containing at least one nitrogen atom.

8. A rubber composition according to any one of the preceding claims, wherein, in the imidazole of formula (I), Rc and Ra are independently selected from the group consisting of a hydrogen atom and alkyl groups having from 1 to 12 carbon atoms, cycloalkyl groups having from 5 to 8 carbon atoms, aryl groups having from 6 to 24 carbon atoms and aralkyl groups having from 7 to 13 carbon atoms, Rc and Ra being very preferably the hydrogen atom.

9. A rubber composition according to any one of claims 1 to 7, wherein, in the imidazole of formula (I), Rc and Ra form, with the carbon atoms of the imidazole ring to which they are attached, a phenyl or cyclohexene ring.

10. Rubber composition according to any one of the preceding claims, in which the level of imidazole of formula (I) is within a range from 0.5 to 8 phr, preferably from 0.5 to 5 phr.

11. Rubber composition according to any one of the preceding claims, the composition not comprising a guanidine derivative or comprising less than 0.5 phr, preferably less than 0.4 phr, more preferably less than 0.3 phr.

12. A rubber composition according to any preceding claim, wherein the reinforcing filler comprises more than 50% by weight, preferably more than 80% by weight of silica.

13. Rubber composition according to any one of the preceding claims, in which the level of the reinforcing filler is within a range from 20 to less than 200 phr, preferably from 30 to 100 phr.

14. Rubber composition according to any one of the preceding claims, comprising sulfur and a vulcanization accelerator, the mass ratio of the sulfur content to the vulcanization accelerator content being within a range from 0.4 to 1.5, preferably from 0.7 to 1.5, more preferably from 0.9 to 1.

1.

15. A tire comprising a composition as defined in any one of claims 1 to 14, wherein the composition is preferably present in the tread of the tire.

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