Tire tread

Abstract

1. A tire having a rubber tread with a first, radially inner layer C1 and a second, radially outer layer C2, the first and second layers being intended to come into contact with the ground during running in a new or worn state, the rubber composition of the first layer C1 comprising more than 50 phr of a copolymer of ethylene and a 1,3-diene, a reinforcing filler, and a plasticizing system, the 1,3-diene being 1,3-butadiene or isoprene, and the ethylene units in the copolymer representing more than 50 mol % of all monomer units of said copolymer.

Description

[Technical field]

[0001] The subject of the invention is a vehicle tire, in particular a tread for a vehicle tire. [Background technology]

[0002] Since tires have a geometry that exhibits rotational symmetry about their axis of rotation, the geometry of the tire is generally described in a meridian plane that contains the tire's axis of rotation. For a given meridian plane, the terms radial, axial, and circumferential refer to directions perpendicular to the tire's axis of rotation, parallel to the tire's axis of rotation, and perpendicular to the meridian plane, respectively. The terms "radially", "axially" and "circumferentially" mean "radially", "axially" and "circumferentially", respectively. "Radially inner" and "radially outer" mean "closer" and "farther" respectively from the tire's axis of rotation. "Axially inner" and "Axially outer" mean "closer" and "farther" respectively from the tire's equatorial plane, which is the plane that passes through the center of the tire's tread surface and is perpendicular to the tire's axis of rotation. The tread is that part of the tire intended to come into contact with the ground through its tread surface, extending radially from the bottom surface to the tread surface, axially from a first tread edge to a second tread edge that defines the axial width of the tread, and circumferentially around the entire circumference of the tire. The tread is provided with a tread pattern including in particular pattern elements or element blocks separated by various main grooves, longitudinal or circumferential grooves, lateral or diagonal grooves, the element blocks may also include various finer slits or sipes, regardless of whether the tire is intended to be fitted to a passenger car or a heavy vehicle. The grooves form channels for drainage when driving on wet ground. A radial type tire comprises, radially inside the tread, a reinforcement consisting of a crown reinforcement and, radially inside the crown reinforcement, a radial carcass reinforcement. The crown reinforcement comprises at least one crown layer consisting of parallel reinforcing elements or reinforcements covered with a rubber mixture. The radial carcass reinforcement comprises at least one carcass layer consisting of parallel, substantially radially oriented (i.e. at an angle between 85° and 95° with the circumferential direction) reinforcements covered with a rubber mixture.

[0003] The rubber composition of a tire tread is specialized for its performance with respect to contact with the ground on which it travels, which meets tire wear regulations. The tread of a tire is responsible for the majority of the rolling resistance of the tire. This contribution can, of course, vary widely depending on the tire design, but can be of the order of about 50%. Typically, the material closest to the ply of crown reinforcement of the tire is adjusted, for example by introducing a low hysteresis underlayer, particularly to minimize rolling resistance, with care being taken that the underlayer does not come into contact with the ground on which the tire is traveling during the specified life of the tire. The tread material can also be further specialised. There can be two rubber compositions in the thickness direction of the tread. EP 0 869 016 A2 shows a tread having a first radially inner layer and a second radially outer layer, in which the first radially inner layer comes into progressively greater contact with the running ground during wear of the tread. In this example, the rubber composition of the first layer has a higher grip performance than the second layer. The performance compromise between rolling resistance and wear resistance of the tread can be improved by introducing a copolymer of ethylene and 1,3-butadiene containing more than 50 mol% of ethylene units into the rubber composition. See, for example, WO2014114607A1. However, such a composition does not provide the tread with optimal grip performance, especially in passenger cars. It is known that the grip performance of a tire can be improved by increasing the contact surface of the tread on the running ground. One solution is the use of a highly deformable rubber composition that constitutes the tread, and in particular the surface of the tread that is intended to contact the running surface. The use of a very soft rubber composition, although still favorable for grip, can lead to a deterioration of the road holding of the tire. It is known that to improve road holding, an increase in the stiffness of the tread is desirable, which can be obtained, for example, by increasing the content of reinforcing fillers or by incorporating specific reinforcing resins into the rubber compositions which constitute these treads, but generally these solutions are not always satisfactory, since they may be accompanied by a decrease in rolling resistance.

[0004] One solution to meet the two conflicting requirements of road holding and grip also involves creating a stiffness gradient by the phenomenon of accommodation of the rubber composition of the tread, as described in WO 02 / 10269 and WO 2012084599. This accommodation phenomenon can lead to a decrease in the stiffness of the rubber composition at the surface of the tread under the effect of the deformations that the tread undergoes during the rotation of the tire. This decrease in stiffness at the surface of the tread does not or hardly occurs at the inside of the tread, which consequently maintains a higher level of stiffness than at the surface of the tread. The above technical solutions for improving grip, road holding and rolling resistance performance are generally described with respect to highly unsaturated diene elastomers characterized by a molar diene content significantly greater than 50%. JP 2013-185048 A describes that the processability of a rubber composition containing a copolymer of ethylene and 1,3-butadiene is improved by introducing 5 to 10 phr of a plasticizing resin. Not only is the molar content of ethylene in the copolymer significantly below 50%, but grip performance is also not addressed. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a benefit to using conjugated diene copolymers in tire treads having a molar ethylene content of greater than 50% in the rubber composition, and there is also a need for improved tread grip performance. [Means for solving the problem]

[0006] The applicant has continued to work and found that the combination of a highly saturated diene elastomer and a specific plasticizing system in a rubber composition for a tire tread can improve the grip performance of the tire. Certain embodiments of the present invention even have the effect of improving the performance compromise between grip and rolling resistance. Other specific embodiments of the present invention also allow for an improvement in the performance compromise between grip and road holding.

[0007] One subject of the invention is a tire having an axis of rotation and comprising a crown extended by two sidewalls and two beads, a carcass reinforcement fixed in the two beads, a crown reinforcement and a rubber tread radially external from said crown reinforcement, said tread comprising a first radially internal layer C1 and a second radially external layer C2, said first and second layers intended to come into contact with the ground during running in new or worn condition, characterized in that the rubber composition of the first layer C1 comprises more than 50 phr of a copolymer of ethylene and 1,3-diene, a reinforcing filler and a plasticizing system, the 1,3-diene being 1,3-butadiene or isoprene, and the ethylene units in the copolymer represent more than 50 mol % of the total monomer units of the copolymer. A mass content or content of the copolymer of ethylene and 1,3-diene in the layer C1 of more than 50 phr means that this copolymer of ethylene and 1,3-diene is the elastomer that constitutes the majority of the rubber composition of the first layer C1 of the tread. The predominant content of ethylene and 1,3-diene copolymer contributes to good road holding of the tire, which may also contribute to improved rolling resistance performance of the tire.

[0008] According to a first alternative of the invention, the rubber composition of the layer C1 comprises a second elastomer, preferably a diene elastomer, i.e. an elastomer comprising diene monomer units. According to one embodiment of the first alternative of the invention, the content of the second elastomer is preferably less than 30 phr, very preferentially less than 10 phr. The second elastomer may be a highly unsaturated diene elastomer selected from the group consisting of polybutadiene, polyisoprene, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. According to a second alternative of the invention, the copolymer of ethylene and of 1,3-diene is the only elastomer of the rubber composition of the first layer C1. According to one alternative embodiment of the tyre according to the invention, the rubber composition of the second layer C2 comprises less than 50 phr of a copolymer of ethylene and of a 1,3-diene. Preferentially, the ratio K between the dynamic shear modulus of the rubber composition of the first layer C1 and the dynamic shear modulus of the rubber composition of the second layer C2 is greater than 1.1, preferably greater than 1.2, the dynamic shear modulus being measured at 60°C during a temperature sweep at an applied stress of 0.7 MPa and a frequency of 10 Hz. The ratio of the moduli between the two layers C1 and C2 of the tread allows the layer C1 to stiffen the tread and the crown of the tire, which improves the tire's road holding. Preferentially, K is less than 2.5, preferably less than or equal to 1.5. Advantageously, the rubber composition of the first layer C1 has a dynamic shear modulus between 1 and 2.5 MPa, the dynamic shear modulus being measured at 60° C. during a temperature sweep, at an applied stress of 0.7 MPa and a frequency of 10 Hz. If such ratio or such dynamic modulus value is exceeded, the grip performance of the tire may decrease when the layer C1 comes into contact with the ground on which it is traveling.

[0009] According to another subject of the invention, the tread comprises ribs separated by grooves having a base, the limit of use of the tire being determined by a minimum radial height h of these ribs relative to the base, VC1 and VC2 being the volumes of materials C1 and C2 located in the tread at radial heights greater than said minimum radial height h, the VC1 / VC2 ratio being greater than 15%, preferentially greater than 25% and even more preferentially greater than 35%. If it is less than 15%, the improvement in rolling resistance and stiffness of the tread will be insufficient. Preferentially, the VC1 / VC2 ratio is less than 75%. If the ratio exceeds 75%, the grip performance of the tire will decrease when the tread surface is mainly made up of the layer C1.

[0010] The features of the present invention will be better understood with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0011]

Figure 1

[0012] Figure 1 (not drawn to scale for ease of understanding) shows a partial section in a meridian plane of the crown of a tyre 1 according to the invention. This tyre 1 comprises, in particular from radially inside to outside, a carcass reinforcement 2, a crown reinforcement 3 and a tread 4 extended laterally by a sidewall 5. The tread 4 comprises a first layer C1 and a second layer C2. The tread 4 also comprises a circumferential groove 6. In a new state, the radially outer surface of the layer C2 constitutes the tread surface of the tyre on the running ground. On the other hand, as the tread wears, the layer C1 gradually comes into contact with the running ground. FIG. 1 also shows the median plane EP and the axis of rotation YY'. The circumferential grooves 6 contain protrusions or wear indicators intended to illustrate the maximum legally permissible wear of the tread. The axially outer circumferential grooves 6 show such protrusions 61. When the tread surface contacts the ground on which the tire is running at the level of the wear indicators, the tire is worn and must be replaced. The legal minimum height is 1.6 mm, and the wear indicators usually have a height h slightly higher than that. This height is measured from the bottom 62 of the circumferential groove 6. The line L corresponds to the intersection between the toric surface S of the overall shape of the tread surface of the tread and the offset of height h radially outward relative to the bottom of the circumferential groove. The volume V of the tread corresponds to its "usable" volume. This volume is equal to the sum of the volume VC1 of the layer C1 and the volume VC2 of the layer C2, both arranged radially outward relative to the surface S. The intersection of these volumes with the meridian plane of FIG. 1 corresponds to the surfaces SC1 and SC2. In FIG. 1, the surface SC1 is colored slightly grey to differentiate it within the layer C1, and the surface SC2 is also represented by a dot pattern to differentiate it within the layer C2. In the example shown in FIG. 1, the ratio of the two volumes in the new state is about 40%. Figure 1 clearly shows the effect of stiffening the tread and crown of the tire when the ratio of the dynamic modulus between the two rubber blends of layers C1 and C2 is greater than 1.1, preferentially greater than 1.2. It is preferred that the ratio does not exceed 2.5, very preferentially not exceeding 1.5, so as not to reduce the grip of the tire when the tread surface is the majority of layer C1.

[0013] In the following, any interval of values ​​indicated by the expression "between a and b" denotes a range of values ​​greater than "a" and less than "b" (i.e. excluding the limits a and b), whereas any interval of values ​​indicated by the expression "from a to b" means a range of values ​​from "a" to "b" (i.e. including the precise limits a and b). The abbreviation "phr" means parts by weight per 100 parts by weight of elastomer (or of the total of the elastomers, if several elastomers are present). In this application, "all of the monomeric units of an elastomer" or "total amount of monomeric units of an elastomer" means all of the constituent repeat units of an elastomer resulting from the insertion of monomers into the elastomer chain by polymerization. Unless otherwise specified, the monomeric units or repeat units in highly saturated diene elastomers are given as mole percentages calculated based on the monomeric units of the copolymer, i.e., calculated based on the total monomeric units of the elastomer.

[0014] The compounds described in the present invention may be of fossil or bio-based origin. In the latter case, they may be derived, in part or in whole, from biomass or from renewable raw materials derived from biomass. In particular, elastomers, plasticizers, fillers, etc. are concerned. The copolymer of ethylene and 1,3-diene useful for the purpose of the present invention is preferably a random elastomer comprising ethylene units resulting from the polymerization of ethylene. As is known, the expression "ethylene units" refers to -(CH2-CH2)- units resulting from the insertion of ethylene into the elastomer chain. In the copolymer of ethylene and 1,3-diene, the ethylene units account for more than 50 mol% of the monomer units of the copolymer. Preferably, the ethylene units in the copolymer account for more than 60 mol%, advantageously more than 70 mol% of the monomer units of the copolymer. According to any one of the embodiments of the present invention, including the preferential alternative form variants, the highly saturated diene elastomer preferentially accounts for at most 90 mol% of the ethylene units. The copolymers useful for the purposes of the present invention, hereinafter also referred to as "highly saturated diene elastomers", also contain 1,3-diene units resulting from the polymerization of 1,3-dienes, said 1,3-dienes being 1,3-butadiene or isoprene. As is known, the term "1,3-diene units" refers to units resulting from the insertion of 1,3-diene by 1,4-addition, 1,2-addition or 3,4-addition in the case of isoprene. Preferably, the 1,3-diene is 1,3-butadiene.

[0015] According to the first embodiment of the present invention, the copolymer of ethylene and 1,3-diene contains units of formula (I). The presence of the saturated six-membered ring unit as a monomer unit of the copolymer and 1,2-cyclohexanediyl of formula (I) can result from a series of very special insertions of ethylene and 1,3-butadiene during the growth of the polymer chain.

Chemical formula

Chemical formula

[0016] Preferably, the highly saturated diene elastomer contains units obtained from 1,3-diene insertion by 1,4-addition, that is, the unit of -CH2-CH=CH-CH2- when the 1,3-diene is 1,3-butadiene, or the unit of -CH2-CMe=C-CH2- when the 1,3-diene is isoprene. The highly saturated diene elastomer contains units of formula (I) or units of formula (II-1), or alternatively contains units of formula (I) and units of formula (II-1). The molar percentages (o and p respectively) of the units of formula (I) and the units of formula (II-1) in the highly saturated diene elastomer preferably satisfy the following mathematical formula (Formula 1), more preferably satisfy the mathematical formula (Formula 2). o and p are calculated based on all monomer units of the highly saturated diene elastomer. 0 < o + p ≦ 25 (Formula 1) 0 < o + p < 20 (Formula 2) According to the first embodiment, the second embodiment, the third embodiment and the fourth embodiment of the invention, and preferential alternatives thereof, the highly saturated diene elastomer is preferentially a random copolymer.

[0017] Highly saturated diene elastomers, in particular according to the first, second, third and fourth embodiments, can be obtained by various synthesis methods known to those skilled in the art, in particular depending on the intended microstructure of the highly saturated diene elastomer. In general, said elastomers may be prepared by copolymerization of at least 1,3-diene, preferably 1,3-butadiene, with ethylene, according to known synthesis methods, in particular in the presence of a catalyst system comprising a metallocene complex. With regard to catalyst systems based on metallocene complexes, said catalyst systems are described in EP 1092731, WO 2004035639, WO 2007054223 and WO 2007054224 in the name of the applicant. Highly saturated diene elastomers may be prepared, including randomly, by methods using preformed catalyst systems such as those described in WO2017093654A1, WO2018020122A1 and WO2018020123A1. The highly saturated diene elastomer may consist of a mixture of copolymers of ethylene and 1,3-diene which differ from one another in their microstructure or macrostructure. According to the first embodiment of the invention, the second embodiment of the invention, the third embodiment and the fourth embodiment, the highly saturated diene elastomer is preferably a copolymer of ethylene and 1,3-butadiene, more preferentially a random copolymer of ethylene and 1,3-butadiene.

[0018] According to one particular embodiment of the invention, the copolymer of ethylene and 1,3-diene has at the chain end a functional group F1 which is a silanol or alkoxysilane function, this embodiment also favouring the improvement of rolling resistance. According to this embodiment, the silanol or alkoxysilane functionality is located at the end of the chain of the highly saturated diene elastomer. In the present application, the alkoxysilane or silanol functionality at one of the ends is referred to as functional group F1 in the present application. Preferably, the functional group is directly bonded to the terminal unit of the highly saturated diene elastomer by a covalent bond, which means that the silicon atom of the functional group is directly bonded to the carbon atom of the terminal unit of the highly saturated diene elastomer by a covalent bond. The terminal unit to which the functional group F1 is directly bonded preferably consists of a methylene bonded to an ethylene unit or a 1,2-cyclohexanediyl unit of formula (I), the Si atom of which is bonded to the methylene. The terminal unit is understood to mean the last unit inserted into the copolymer chain by copolymerization, the unit being preceded by the penultimate unit and the unit being preceded by the penultimate unit.

[0019] According to a first alternative of this embodiment, the functional group F1 is of formula (III-a) [ka] -R1 symbols, which may be the same or different, represent alkyl; -R 2 The symbols may be the same or different and represent hydrogen atoms, hydrocarbon-based chains or chemical functional groups F 2 represents a hydrocarbon-based chain substituted with; -f is an integer ranging from 0 to 2. In formula (III-a), R 1 The symbol is preferentially alkyl having at most 6 carbon atoms, more preferentially methyl or ethyl, more preferentially still methyl.

[0020] If 3-f is greater than 1, then R 1 The symbols are advantageously identical and are in particular methyl or ethyl, more particularly methyl. According to a second alternative of this embodiment, the functional group F 1 is of formula (III-b), [ka] -R 2 The symbols may be the same or different and represent hydrogen atoms, hydrocarbon-based chains or chemical functions F 2 represents a hydrocarbon-based chain substituted with The hydrocarbon-based chains represented by the R2 symbol in formulae (III-a) and (III-b) include alkyl, especially those having 1 to 6 carbon atoms, preferentially methyl or ethyl, more preferentially methyl. As hydrocarbon-based chains substituted with a chemical functionality F2, represented by the R2 symbol in formulae (III-a) and (III-b), mention may be made of alkanediyl chains, in particular those having at most 6 carbon atoms, very particularly the 1,3-propanediyl group, which has a substituent chemical functionality F2, i.e. one valence of the alkanediyl chain is linked to the functionality F2 and the other valence is linked to the silicon atom of a silanol or alkoxysilane function. In formulae (III-a) and (III-b), the chemical function F2 is understood to mean a group different from a saturated hydrocarbon-based group and capable of participating in a chemical reaction. Chemical functions that may be suitable include ether functions, thioether functions, primary, secondary or tertiary amine functions, thiol functions, silyl functions. The primary or secondary amine or thiol functions may be protected or unprotected. Protective groups for amine and thiol functions are, for example, silyl groups, in particular trimethylsilyl or tert-butyldimethylsilyl groups. Preferably, the chemical function F2 is a primary, secondary or tertiary amine function or a thiol function, and the primary or secondary amine or thiol functions are protected or unprotected with a protective group. Preferably, the R2 symbols, which may be the same or different, represent an alkyl chain having at most 6 carbon atoms or an alkanediyl chain having at most 6 carbon atoms, substituted with the chemical functionality F2 of formulae (III-a) and (III-b).

[0021] Examples of the functional group F1 include a dimethoxymethylsilyl group, a dimethoxyethylsilyl group, a diethoxymethylsilyl group, a diethoxyethylsilyl group, a 3-(N,N-dimethylamino)propyldimethoxysilyl group, a 3-(N,N-dimethylamino)propyldiethoxysilyl group, a 3-aminopropyldimethoxysilyl group, a 3-aminopropyldiethoxysilyl group, a 3-thiopropyldimethoxysilyl group, a 3-thiopropyldiethoxysilyl group, a methoxydimethylsilyl group, a methoxydiethylsilyl group, an ethoxydimethylsilyl group, an ethoxydiethyl ... Examples of such silyl groups include a 3-(N,N-dimethylamino)propyl methoxymethylsilyl group, a 3-(N,N-dimethylamino)propyl methoxyethylsilyl group, a 3-(N,N-dimethylamino)propyl ethoxymethylsilyl group, a 3-(N,N-dimethylamino)propyl ethoxyethylsilyl group, a 3-aminopropyl methoxymethylsilyl group, a 3-aminopropyl methoxyethylsilyl group, a 3-aminopropyl ethoxymethylsilyl group, a 3-aminopropyl ethoxyethylsilyl group, a 3-thiopropyl methoxymethylsilyl group, a 3-thiopropyl ethoxymethylsilyl group, a 3-thiopropyl methoxyethylsilyl group, and a 3-thiopropyl ethoxyethylsilyl group. The functional group F1 includes the silanol forms of the above functional groups that contain only one ethoxy or methoxy function, which can be obtained by hydrolysis of the ethoxy or methoxy function. In this regard, the dimethylsilanol group, the diethylsilanol group, the 3-(N,N-dimethylamino)propylmethylsilanol group, the 3-(N,N-dimethylamino)propylethylsilanol group, the 3-aminopropylmethylsilanol group, the 3-aminopropylethylsilanol group, the 3-thiopropylethylsilanol group and the 3-thiopropylmethylsilanol group are preferred. As functional groups F1, mention may be made of those mentioned above, whether the functional groups are in alkoxy or silanol form, and also those containing amine or thiol functions in form protected by silyl groups, in particular trimethylsilyl or tert-butyldimethylsilyl groups. Preferably, the functional group F1 is of formula (III-a), where f is equal to 1. In relation to this preferred alternative, groups in which R1 is methyl or ethyl are very particularly preferred, such as the dimethoxymethylsilyl, dimethoxyethylsilyl, diethoxymethylsilyl, diethoxyethylsilyl, 3-(N,N-dimethylamino)propyldimethoxysilyl, 3-(N,N-dimethylamino)propyldiethoxysilyl, 3-aminopropyldimethoxysilyl, 3-aminopropyldiethoxysilyl, 3-thiopropyldimethoxysilyl and 3-thiopropyldiethoxysilyl groups. Protected forms of amine or thiol functions with at least four functional groups according to the above list, protected with silyl groups, in particular trimethylsilyl or tert-butyldimethylsilyl groups, are also preferred. More preferably, the functional group F1 is of formula (III-a), where f is equal to 1 and R1 is methyl. In this more preferred alternative, the dimethoxymethylsilyl, dimethoxyethylsilyl, 3-(N,N-dimethylamino)propyldimethoxysilyl, 3-aminopropyldimethoxysilyl and 3-thiopropyldimethoxysilyl groups, as well as the amine or thiol functions in protected form of 3-aminopropyldimethoxysilyl or 3-thiopropyldimethoxysilyl protected with trimethylsilyl or tert-butyldimethylsilyl, are also very particularly suitable.

[0022] The copolymers of ethylene and 1,3-diene having functional groups F1 (silanol or alkoxysilane functions) at the chain ends can be prepared by the method described in the patent application filed under number PCT / FR2018 / 051305 or the patent application filed under number PCT / FR2018 / 051306, which method comprises the following steps (a) and (b) and, optionally, (c): (a) copolymerization of a monomer mixture in the presence of a catalyst system comprising an organomagnesium compound and a metallocene; (b) reacting the polymer obtained in step (a) with a functionalizing agent; (c) If necessary, a hydrolysis reaction. Step (a) is common to the copolymerization step carried out to prepare the non-functionalized copolymers described above, the only difference being that the copolymerization reaction is followed by step (b), which is a reaction for functionalization of the copolymer. Step (b) comprises the reaction of the copolymer obtained in step (a) with a functionalizing agent to functionalize the copolymer at the chain ends. The functionalizing agent is a compound of formula (IV): [ka] - Fc1 symbols, which may be the same or different, represent an alkoxy group or a halogen atom; - Rc2 symbols may be the same or different and represent a hydrogen atom, a hydrocarbon-based chain or a hydrocarbon-based chain substituted with a chemical functional group Fc2; -g is an integer ranging from 0 to 2. When the Fc1 symbol represents an alkoxy group, the alkoxy group is preferably methoxy or ethoxy.When the Fc1 symbol represents a halogen atom, the halogen atom is preferably chlorine.

[0023] The functionalizing agent may be of formula (IV-1), formula (IV-2), formula (IV-3), or formula (IV-4): [ka] in which the Fc1 and Rc2 symbols are defined in formula (IV); In formulae (IV-1) and (IV-2), g is an integer ranging from 0 to 2; In formula (IV-3), g is an integer ranging from 0 to 1. The hydrocarbon-based chain represented by the R symbol in formulae (III), (IV-1), (IV-2), (IV-3) and (IV-4) is alkyl, preferably having at most 6 carbon atoms, more preferentially methyl or ethyl, and even more preferably methyl. The hydrocarbon-based chains substituted with the chemical function Fc2, represented by the Rc2 symbol in formulae (IV), (IV-1), (IV-2), (IV-3) and (IV-4), include alkanediyl chains, preferably containing at most 6 carbon atoms, more preferentially 1,3-propanediyl groups, which carry a substituent chemical function F2, i.e. one valence of the alkanediyl chain is linked to the function F2 and the other valence is linked to the silicon atom of a silanol or alkoxysilane function. In formulae (IV), (IV-1), (IV-2), (IV-3) and (IV-4), chemical functionality is understood to mean a group that is different from a saturated hydrocarbon-based group and can participate in a chemical reaction. The skilled person will understand that chemical functionality Fc2 is a group that is chemically inert with respect to the chemical species present in the polymerization medium. Chemical functionality Fc2 may be in protected form, for example, as in the case of primary amine, secondary amine or thiol functionality. Chemical functionality Fc2 includes ether, thioether, protected primary amine, protected secondary amine, tertiary amine, protected thiol and silyl functionality. Preferably, chemical functionality Fc2 is a protected primary amine functionality, a protected secondary amine functionality, a tertiary amine functionality or a protected thiol functionality. Protective groups for primary amine, secondary amine and thiol functionality include silyl groups, for example trimethylsilyl and tert-butyldimethylsilyl groups. g is preferably other than 0, which means that the functionalizing agent contains at least one Si-Rc2 bond.

[0024] As functionalizing agents, dimethoxydimethylsilane, diethoxydimethylsilane, dimethoxydiethylsilane, diethoxydiethylsilane, (N,N-dimethyl-3-aminopropyl)methyldimethoxysilane, (N,N-dimethyl-3-aminopropyl)methyldiethoxysilane, (N,N-dimethyl-3-aminopropyl)ethyldimethoxysilane, (N,N-dimethyl-3-aminopropyl)ethyldiethoxysilane, 3-methoxy-3,8,8,9,9-pentamethyl-2-oxa-7-thia-3,8-di Siladecane, trimethoxymethylsilane, triethoxymethylsilane, trimethoxyethylsilane, triethoxyethylsilane, (N,N-dimethylaminopropyl)trimethoxysilane, (N,N-dimethylaminopropyl)triethoxysilane, (N-(3-trimethoxysilyl)propyl)-N-(trimethylsilyl)silaneamine, (N-(3-triethoxysilyl)propyl)-N-(trimethylsilyl)silaneamine, and 3,3-dimethoxy-8,8,9,9-tetramethyl-2-oxa-7- Thia-3,8-disiladecane, preferably dimethoxydimethylsilane, dimethoxydiethylsilane, (N,N-dimethyl-3-aminopropyl)methyldimethoxysilane, (N,N-dimethyl-3-aminopropyl)ethyldimethoxysilane, 3-methoxy-3,8,8,9,9-pentamethyl-2-oxa-7-thia-3,8-disiladecane trimethoxymethylsilane, trimethoxyethylsilane, (N,N-dimethylaminopropyl)trimethoxysilane, (N-(3-trimethoxysilyl)propyl) -N-(trimethylsilyl)silaneamine, and 3,3-dimethoxy-8,8,9,9-tetramethyl-2-oxa-7-thia-3,8-disiladecane, more preferentially trimethoxymethylsilane, trimethoxyethylsilane, (N,N-dimethylaminopropyl)trimethoxysilane, (N-(3-trimethoxysilyl)propyl)-N-(trimethylsilyl)silaneamine, and 3,3-dimethoxy-8,8,9,9-tetramethyl-2-oxa-7-thia-3,8-disiladecane. The functionalizing agent is typically added to the polymerization medium resulting from step (a). The functionalizing agent is typically added to the polymerization medium at a degree of monomer conversion selected by the skilled artisan depending on the desired macrostructure of the elastomer. Step (a) is generally carried out under ethylene pressure, and degassing of the polymerization reactor may be carried out prior to the addition of the functionalizing agent. The functionalizing agent is added to the polymerization medium under inert and anhydrous conditions and maintained at the polymerization temperature. Typically, 0.25 to 10 moles of functionalizing agent per mole of cocatalyst, preferably 2 to 4 moles of functionalizing agent per mole of cocatalyst, are used. The functionalizing agent is contacted with the polymerization medium for a time sufficient to allow the functionalization reaction. This contact time is judiciously selected by those skilled in the art depending on the concentration of the reaction medium and the temperature of the reaction medium. Typically, the functionalization reaction is carried out under stirring at a temperature ranging from 17°C to 80°C for 0.01 to 24 hours.

[0025] Once functionalized, the elastomers can be recovered, in particular by isolating them from the reaction medium. The techniques for separating the elastomers from the reaction medium are well known to those skilled in the art and are chosen by them depending on the amount of elastomer to be separated, its macrostructure and the tools available to them. Examples include the coagulation of the elastomer in a solvent such as methanol, and the evaporation of the solvent and residual monomers of the reaction medium, for example under reduced pressure. When the functionalizing agent is of formula (IV), (IV-1) or (IV-2) and g is equal to 2, step (b) may be followed by a hydrolysis reaction to form an elastomer having silanol functions at the chain ends. The hydrolysis may be carried out in a manner known to those skilled in the art by removing the solution containing the elastomer at the end of step (b). When the functionalizing agent is of formula (IV), (IV-1), (IV-2), (IV-3) or (IV-4), when g is other than 0 and when Rc2 represents a hydrocarbon-based chain substituted with the function Fc2 in protected form, step (b) may also be followed by hydrolysis to deprotect the function at the end of the elastomer chain. The hydrolysis reaction is a step of deprotecting a function and is generally carried out in an acidic or basic medium, depending on the chemical nature of the function to be deprotected. For example, silyl groups, especially trimethylsilyl or tert-butyldimethylsilyl groups, protecting amine or thiol functions can be hydrolyzed in an acidic or basic medium in a manner known to those skilled in the art. The choice of deprotection conditions is judiciously made by those skilled in the art, taking into account the chemical structure of the substrate to be deprotected.

[0026] Step (c) is an optional step depending on whether it is desired to convert functional groups into silanol functions or whether it is desired to deprotect protected functionalities. Preferentially, step (c) is carried out before separating the elastomer from the reaction medium at the end of step (b) or simultaneously with this separation step. The content of ethylene and 1,3-diene copolymers, whether or not they have silanol or alkoxysilane functionality, is greater than 50 phr, preferentially greater than 70 phr. The remainder, up to 100 phr, can be any diene elastomer, such as 1,3-butadiene homopolymer or copolymer, or isoprene homopolymer or copolymer. Advantageously, the content of ethylene and 1,3-diene copolymer is 100 phr. A high content of copolymers in the rubber composition is more favorable for a performance compromise between rolling resistance, wear resistance and grip. Another essential feature of the rubber composition of layer C1 is that it comprises a reinforcing filler and a plasticizing system, which is preferably hydrocarbon-based.

[0027] Advantageously, the reinforcing filler comprises silica. The reinforcing fillers typically consist of nanoparticles having an average (mass-average) particle size of less than 1 micrometer, generally less than 500 nm, usually between 20 and 200 nm, in particular and more preferentially between 20 and 150 nm. The content of reinforcing filler in the rubber composition of layer C1 is advantageously ≧35 phr and ≦100 phr, preferably ≧50 phr and ≦100 phr. Preferably, silica represents more than 50% by mass of the reinforcing filler. More preferentially, silica represents more than 85% by mass of the reinforcing filler. Optionally, the reinforcing filler of the rubber composition of layer C1 comprises 35 to 100 phr of a reinforcing filler comprising silica. The silica used may be any reinforcing silica known to those skilled in the art, in particular one having a BET specific surface area and a CTAB specific surface area of ​​450 m 2 / g, preferably 30 to 400m 2 / g range, especially 60-300m 2 It can be any precipitated or fumed silica with a specific surface area of ​​0.1 μm / g. In this document, the BET specific surface area is determined by gas adsorption using the method of Brunauer-Emmett-Teller described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), more specifically according to a method adapted from NF ISO standard 5794-1, Appendix E, as of June 2010 [multipoint (5-point) volumetric method - gas: nitrogen - degassing under vacuum: 160°C for 1 hour - relative pressure p / p0 range: 0.05 to 0.17]. CTAB specific surface area values ​​were determined according to NF ISO standard 5794-1, Appendix G, June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the reinforcing filler. Any type of precipitated silica can be used, in particular highly dispersible precipitated silica (called "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas may be highly dispersible or not and are well known to those skilled in the art. Examples include the silicas described in WO 03 / 016215 A1 and WO 03 / 016387 A1. Among the commercially available HDS silicas, in particular the Ultrasil® 5000GR and Ultrasil® 7000GR silicas from Evonik or Zeosil® 1085GR, Zeosil® 1115MP, Zeosil® 1165MP, Zeosil® Premium 200MP and Zeosil® HRS 1200 from Solvay. MP silicas can be used. As non-HDS silicas, the following commercially available silicas may be used: Ultrasil® VN2GR and Ultrasil® VN3GR silicas from Evonik, Zeosil® 175GR silica from Solvay, or Hi-Sil EZ120G(-D), Hi-Sil EZ160G(-D), Hi-Sil EZ200G(-D), Hi-Sil 243LD, Hi-Sil 210 and Hi-Sil HDP 320G silicas from PPG.

[0028] The reinforcing filler may comprise any type of "reinforcing" filler other than silica, such as carbon black, known for its ability to reinforcing rubber compositions that can be used in particular in the manufacture of tires. All carbon blacks, particularly those conventionally used in tires or tire treads, are suitable as carbon blacks. The latter more particularly include reinforcing carbon blacks of the 100, 200 and 300 series, or blacks of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as N115, N134, N234, N326, N330, N339, N347, N375, N550, N683 and N772 blacks. These carbon blacks can be used in isolated form, as commercially available, or in any other form, such as, for example, as a carrier for part of the rubber additive used. Preferably, carbon black is used in a content of less than or equal to 20 phr, more preferentially less than or equal to 10 phr (for example, the carbon black content may range from 0.5 to 20 phr, in particular from 1 to 10 phr). Advantageously, the carbon black content in the rubber composition is less than or equal to 5 phr. Within the above ranges, the coloring properties (black colorant) and UV stabilizing properties of carbon black are beneficial and do not adversely affect the typical performance qualities contributed by silica.

[0029] To couple the reinforcing inorganic filler (silica in this case) to the elastomer, it is possible to use in a known manner at least difunctional coupling agents (or bonding agents) intended to ensure a sufficient link of chemical and / or physical nature between the inorganic filler (the surface of its particles) and the elastomer, in which case the rubber composition of layer C1 comprises a coupling agent for bonding the silica to the elastomer. In particular, at least difunctional organosilanes or polyorganosiloxanes are used. The term "difunctional" is understood to mean a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the elastomer. Silane polysulfides, which are called "symmetrical" or "asymmetrical" depending on their specific structure, as described in WO 03 / 002648 A1 (or US 2005 / 016651 A1) and WO 03 / 002649 A1 (or US 2005 / 016650 A1), are particularly used. Without being limited to the following definition, particularly preferred are silane polysulfides corresponding to the following general formula (V): [ka] During the ceremony: -x is an integer from 2 to 8 (preferably from 2 to 5); The -A symbols may be the same or different and are divalent hydrocarbon radicals (preferably C1-C 18 Alkylene group or C6-C 12 Arylene groups, more specifically C1-C 10 alkylene, particularly C1-C4 alkylene, in particular propylene); The -Z symbols, which may be the same or different, correspond to the following three formulae: [ka] During the ceremony: The -Ra radicals are substituted or unsubstituted, may be the same or different, and may be C1 to C 18 Alkyl groups, C5-C 18 Cycloalkyl group or C6-C 18 an aryl group (preferably a C1-C6 alkyl, cyclohexyl or phenyl group, in particular a C1-C4 alkyl group, more particularly methyl and / or ethyl); The -Rb radicals are substituted or unsubstituted, may be the same or different, and are C1 to C 18 Alkoxy group or C5-C 18 a cycloalkoxyl group (preferably a group selected from C1-C8 alkoxyl and C5-C8 cycloalkoxyl, even more preferentially a group selected from C1-C4 alkoxyl, in particular methoxyl and ethoxyl), or a hydroxyl group, or the two Rb radicals are C3-C18 Represents a dialkoxy group. In the case of mixtures of alkoxysilane polysulfides corresponding to formula (V) above, in particular the usual commercial mixtures, the average value of the "x" index is preferably within the range of 2 to 5, more preferentially a fractional number of about 4.

[0030] More specifically, examples of silane polysulfides include bis((C1-C4)alkoxyl(C1-C4)alkylsilyl(C1-C4)alkyl)polysulfides (especially disulfides, trisulfides or tetrasulfides), such as bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl) polysulfides. Among the abovementioned compounds, in particular used is bis(3-triethoxysilylpropyl)tetrasulfide (abbreviated TESPT) of the formula [(C2H5O)3Si(CH2)3S2]2 sold under the name Si69 by Evonik, or bis(triethoxysilylpropyl)disulfide (abbreviated TESPD) of the formula [(C2H5O)3Si(CH2)3S]2 sold under the name Si75 by Evonik. Preferred examples include bis(mono(C1-C4)alkoxydi(C1-C4)alkylsilylpropyl)polysulfides (particularly disulfides, trisulfides or tetrasulfides), more specifically bis(monoethoxydimethylsilylpropyl)tetrasulfide, such as those described in the above-mentioned patent application WO 02 / 083782 (A1) (or U.S. Pat. No. 7,217,751 specification (B2)). Of course, mixtures of the above coupling agents may also be used. The content of coupling agent in the rubber composition of the C1 layer is advantageously less than or equal to 25 phr, it being understood that it is generally desirable to use as little as possible. Typically, the content of coupling agent is between 0.5 and 15% by mass relative to the reinforcing inorganic filler. The content of coupling agent is preferentially in the range of 0.5 to 20 phr, more preferentially in the range of 3 to 15 phr. This content is easily adjusted by the skilled person according to the content of the reinforcing inorganic filler used in the layer C1 composition of the tread of the tire of the invention.

[0031] Another essential feature of the rubber composition of layer C1 is that it comprises a plasticizing system, advantageously understood to comprise a plasticizing hydrocarbon-based resin and a liquid hydrocarbon-based plasticizer, the total content of which is greater than 10 phr and not more than 80 phr, preferably greater than 30 phr and not more than 80 phr. Hydrocarbon-based resins, also known as hydrocarbon-based plasticizing resins, are polymers well known to those skilled in the art, essentially based on carbon and hydrogen, but which may contain other types of atoms, such as oxygen, and which can be used in polymer matrices, in particular as plasticizers or tackifiers. The resins are essentially at least partially miscible (i.e. compatible) in the content used with the intended polymer composition, and act as true diluents. Hydrocarbon resins are described, for example, in the book entitled "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), the fifth chapter of which is devoted, inter alia, to applications in the tire rubber field (5.5. "Rubber Tires and Mechanical Goods"). As is well known, these hydrocarbon-based resins can also be described as thermoplastic resins, in the sense that the resins soften and can be molded when heated. The softening point of the hydrocarbon-based resins is measured according to ISO standard 4625 (the "ring and ball" method). The Tg is measured according to ASTM standard D3418 (1999). The macrostructure (Mw, Mn and PI) of the hydrocarbon-based resins is determined by size exclusion chromatography (SEC); solvent tetrahydrofuran; temperature 35°C; concentration 1 g / L; flow rate 1 mL / min; the solution is filtered through a 0.45 μm porosity filter before injection; Moore calibration with polystyrene standards; set of three Waters columns in series (Styragel HR4E, HR1 and HR0.5); detection by a differential refractometer (Waters 2410) and associated operating software (Waters Empower). The hydrocarbon-based resins may be aliphatic or aromatic, or of the aliphatic / aromatic type, i.e. based on aliphatic and / or aromatic monomers. They may be natural or synthetic, and may or may not be petroleum-based (in which case they are also known as petroleum resins). Preferably, the hydrocarbon-based plasticizing resins have a glass transition temperature higher than 20°C. Advantageously, the hydrocarbon-based plasticizing resin has at least one, and more preferentially all, of the following properties: Tg greater than -30°C; - number average molecular weight (Mn) between 300 and 2000 g / mol, more preferentially between 400 and 1500 g / mol; A polydispersity index (PI) less than -3, more preferentially less than 2 (note: PI=Mw / Mn, Mw being the weight average molecular weight). Preferably, the hydrocarbon-based plasticizing resin is selected from the group consisting of cyclopentadiene homopolymer resins, cyclopentadiene copolymer resins, dicyclopentadiene homopolymer resins, dicyclopentadiene copolymer resins, terpene homopolymer resins, terpene copolymer resins, C5 fraction homopolymer resins, C5 fraction copolymer resins, C9 fraction homopolymer resins, C9 fraction copolymer resins, hydrogenated cyclopentadiene homopolymer resins and hydrogenated cyclopentadiene copolymer resins. More preferentially, the hydrocarbon-based plasticizing resin is a C9 fraction copolymer resin or a dicyclopentadiene copolymer resin, hydrogenated or non-hydrogenated. Examples include, most particularly, C9 fraction copolymer resin and hydrogenated dicyclopentadiene copolymer resin.

[0032] Hydrocarbon-based liquid plasticizers are known to soften rubber compositions by diluting their elastomers and reinforcing fillers. The Tg of the plasticizer is typically below -20°C, preferentially below -40°C. Any hydrocarbon-based extender oil or any hydrocarbon-based liquid plasticizer known for its plasticizing properties towards diene elastomers can be used. At ambient temperature (23°C), these plasticizers or these oils are more or less viscous and liquid (i.e., if we may note, a substance that has the ability to eventually take the shape of its container) in contrast to hydrocarbon-based plasticizing resins, which are essentially solids at ambient temperature. Hydrocarbon-based liquid plasticizers include liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE oils, MES (medium extraction solvates) oils, TDAE (treated distillate aromatic extract) oils, RAE (residual aromatic extract) oils, TRAE (treated residual aromatic extract) oils and SRAE (safe residual aromatic extract) oils, mineral oils, and mixtures of these compounds. Preferably, the hydrocarbon-based liquid plasticizer is selected from the group consisting of liquid diene polymers, aliphatic polyolefin oils, paraffinic oils, MES oils, TDAE oils, TRAE oils, SRAE oils, mineral oils, and mixtures thereof. More preferentially, the hydrocarbon-based liquid plasticizer is a liquid diene polymer, aliphatic polyolefin oil, paraffinic oil, MES oil, or mixtures thereof.

[0033] According to one particular embodiment of the invention, the mass ratio between the content of the hydrocarbon-based plasticizing resin and the total content of the hydrocarbon-based plasticizing resin and the hydrocarbon-based liquid plasticizer is greater than 0.4. This particular embodiment is also favorable for improving the road holding of tires whose treads comprise such a rubber composition. The plasticizing system may contain other plasticizers, generally in small amounts, than the hydrocarbon-based plasticizing resins and the hydrocarbon-based liquid plasticizers, useful for the needs of the present invention, as long as the desired performance compromise is not adversely altered. These other plasticizers may be, for example, processing aids conventionally used in small amounts to promote the dispersion of silica. According to any one of the embodiments of the present invention, the hydrocarbon-based plasticizing resins and the hydrocarbon-based liquid plasticizers advantageously constitute a substantial major part of the plasticizing system, i.e. the ratio of the content of the hydrocarbon-based plasticizing resins and the hydrocarbon-based liquid plasticizers to the content of the total plasticizing system in the rubber composition of the layer C1, expressed in phr, is advantageously greater than 0.8, and very advantageously greater than 0.9.

[0034] According to an advantageous feature of the layer C1 rubber composition, the mass ratio between the content of reinforcing fillers and the total content of hydrocarbon-based plasticizing resins and hydrocarbon-based liquid plasticizers is greater than or equal to 1.1, the content being expressed in phr. The layer C1 according to this particular embodiment provides a stiffening in the tread, which allows to improve the road holding of the tire, the tread having a high grip surface due to the use of a highly deformable rubber composition intended to come into contact with the ground. The rubber composition of layer C1 may also comprise all or part of the useful additives customarily used in elastomeric compositions for the manufacture of tires, in particular pigments, protective agents, anti-ozone waxes, chemical antiozonants, antioxidants, crosslinking systems which may be based either on sulfur or sulfur donors and / or on peroxides and / or bismaleimides, vulcanization accelerators or retarders, or vulcanization activators. The actual crosslinking system is preferentially based on the vulcanization system, i.e., sulfur and a primary vulcanization accelerator. Sulfur is typically provided in the form of molecular sulfur or sulfur donor, preferably in molecular form. Sulfur in molecular form is also referred to by the term "molecular sulfur". The term "sulfur donor" means any compound that releases sulfur atoms, optionally combined in the form of polysulfide chains, which can be inserted into the polysulfide chains formed during vulcanization and crosslinking of the elastomer chains. Various known secondary vulcanization accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (especially diphenylguanidine), etc., are added to the vulcanization system and incorporated during the first non-productive and / or productive phases. The content of sulfur is preferably between 0.5 and 3.0 phr, and the content of the primary accelerator is preferably between 0.5 and 5.0 phr. These preferred contents may apply to any one of the embodiments of the present invention.

[0035] As vulcanization accelerators (primary or secondary), any compound capable of acting as an accelerator of the vulcanization of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and its derivatives, accelerators of the sulfenamide type for the primary accelerators, or thiurams, dithiocarbamates for the secondary accelerators. Accelerators of the dithiophosphate, thiourea and xanthate type may also be used. Examples of primary accelerators include in particular sulfenamide compounds such as N-cyclohexyl-2-benzothiazylsulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazylsulfenamide ("DCBS"), N-(tert-butyl)-2-benzothiazylsulfenamide ("TBBS"), and mixtures of these compounds. The primary accelerators are preferentially sulfenamides, more preferentially N-cyclohexyl-2-benzothiazylsulfenamide. Examples of secondary accelerators include thiuram disulfides such as tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide ("TBTD"), tetrabenzyl thiuram disulfide ("TBZTD") and mixtures of these compounds. The secondary accelerator is preferentially a thiuram disulfide, more preferentially tetrabenzyl thiuram disulfide.

[0036] Crosslinking (i.e. curing), optionally vulcanization, is carried out in a known manner, typically at temperatures between 130°C and 200°C, for a sufficient time, which may vary, for example, between 5 and 90 minutes, depending, inter alia, on the curing temperature, the crosslinking system used and the crosslinking rate of the composition under consideration. The rubber composition may be prepared, prior to crosslinking, in a suitable mixer using two successive preparation stages well known to those skilled in the art: a first stage (sometimes called the "non-productive" stage) of thermomechanical processing or kneading at high temperatures up to a maximum temperature of between 110°C and 190°C, preferably between 130°C and 180°C, followed by a second stage (sometimes called the "productive" stage) of mechanical processing at lower temperatures, typically below 110°C, for example between 40°C and 100°C, during which finishing stage the sulfur or sulfur donors and crosslinking accelerators are incorporated. For example, the first (non-productive) stage is carried out in a single thermomechanical step during which all the necessary ingredients and any additional processing agents and various other additives, except the crosslinking system, are introduced into a suitable mixer, such as a standard internal mixer. The total mixing time in this non-productive stage is preferably between 1 and 15 minutes. After cooling the mixture thus obtained in the first non-productive stage, it is mixed at low temperature. The crosslinked system They are then combined, typically in an external mixer such as an open mill; and then everything is mixed for a few minutes, for example between 2 and 15 minutes (production stage). The rubber composition can be calendered or extruded, for example, in the form of sheets or slabs, especially for laboratory characterization, and in the form of rubber semi-finished products (or profiled elements) that can be used for tires. The composition can be either in the raw state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization), and can be a semi-finished product that can be used for tires.

[0037] Determination of the microstructure of elastomers: The microstructure of the elastomer is 1 As determined by H NMR analysis, 1When the resolution of a H NMR spectrum does not allow the assignment and quantification of all chemical species 13 Correction is made by C NMR analysis. Measurements are performed using a Bruker 500 MHz NMR spectrometer at frequencies of 500.43 MHz for proton observation and 125.83 MHz for carbon observation. For elastomers that are insoluble in solvents but have the ability to swell, a 4 mm z-grad HRMAS probe is used to observe protons and carbons in proton decoupling mode. Spectra are acquired at spinning rates of 4000 Hz to 5000 Hz. In the measurement of soluble elastomers, a liquid NMR probe is used to observe protons and carbons in proton decoupling mode. The preparation of the insoluble samples is carried out in a rotor filled with the analyte and a deuterated solvent that allows swelling, typically deuterated chloroform (CDCl3). The solvent used must necessarily be deuterated and its chemistry can be adapted by the skilled artisan. The amount of material used is adjusted to obtain a spectrum with sufficient sensitivity and resolution. Soluble samples are dissolved in a deuterated solvent (approximately 25 mg of elastomer in approximately 1 ml), typically deuterated chloroform (CDCl3). The solvent or solvent blend used must necessarily be deuterated, and its chemistry can be adapted by one skilled in the art. In either case (soluble or swollen samples): For proton NMR, a 30° single pulse sequence is used. The spectral window is adjusted to observe all resonance lines belonging to the molecule being analyzed. The number of integrations is adjusted to obtain a signal-to-noise ratio sufficient for quantification of each subunit. The waiting time between each pulse is adapted to obtain a quantitative measurement. For carbon NMR, a 30° single pulse sequence is used, with proton decoupling only during acquisition to avoid the "Nuclear Overhauser Effect" (NOE) and maintain quantitative conditions. The spectral window is adjusted to observe all resonance lines belonging to the molecule being analyzed. The number of integrations is adjusted to obtain a signal-to-noise ratio sufficient for quantification of each subunit. The waiting time between each pulse is adapted to obtain a quantitative measurement. The NMR measurements are carried out at 25°C.

[0038] Determination of Mooney Viscosity: Mooney viscosity is measured according to ASTM standard D-1646 (1999). The measurement is carried out according to the following principle: the sample is analyzed in the uncured state (i.e. before curing) and cast (molded) in a cylindrical chamber heated to a given temperature (100 °C). After 1 minute of preheating, a rotor is rotated in the test specimen at 2 revolutions per minute and the working torque required to maintain this movement after 4 minutes of rotation is measured. Mooney viscosity is expressed in "Mooney units" (MU, where 1 MU = 0.83 Newton meters).

[0039] The stiffness of a rubber composition is determined by the dynamic shear modulus G * The vulcanized composition samples were subjected to an applied stress of 0.7 MPa and alternating sinusoidal shear stress at a frequency of 10 Hz during a temperature sweep from a minimum temperature below the Tg of the elastomer of the composition to a maximum temperature above 100° C., and the response was recorded; * The value was taken at a temperature of 60°C.

[0040] Six rubber compositions T1 and M1 to M5 (the details of the formulations are shown in Table 1) were prepared as follows: The elastomer, the reinforcing filler and the various other components, except for the sulfur and the vulcanization accelerator, are continuously introduced into an internal mixer (final degree of filling: about 70% by volume), the initial container temperature of which is about 80°C. Then the thermomechanical processing (non-productive phase) is carried out in one step, which lasts about 3-4 minutes in total, until the maximum "dropping" temperature of 165°C is reached. The mixture thus obtained is recovered and cooled, then the sulfur and the vulcanization accelerator are added in a mixer (homofinisher) at 30°C, and everything is kneaded for an appropriate time (for example, about 10 minutes) (productive phase). The composition thus obtained is then either calendered into rubber plates (2-3 mm thick) or in the form of thin sheets for measuring the physical or mechanical properties, or extruded into the form of profile elements, for example for tires. The five rubber compositions M1 to M5 all contain a copolymer of ethylene and 1,3-butadiene, the content of ethylene units being greater than 50%. In composition M5, the copolymer has silanol or alkoxysilane functions at the chain ends.

[0041] The ethylene and 1,3-butadiene copolymers (EBR) used in compositions M1 to M4 are prepared according to the following procedure. As a cocatalyst, butyloctylmagnesium (BOMAG) (0.00021 mol / L) was added to the reactor containing methylcyclohexane, followed by the metallocene [{Me2SiFlu2Nd(μ-BH4)2Li(THF)}2] (0.07 mol / L). 13 H8 groups. The alkylation time is 10 minutes and the reaction temperature is 20°C. The monomers are then added continuously in the form of a gaseous mixture of ethylene / 1,3-butadiene with a molar composition of 80 / 20. The polymerization is carried out under conditions of constant temperature and pressure of 80°C and 8 bar. 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 an oven under vacuum to constant weight. In the EBR copolymer, the molar content of ethylene units is 79%, the molar content of 1,4 units is 6%, the molar content of 1,2 units is 8% and the molar content of 1,2-cyclohexanediyl units is 7%. The Mooney viscosity is 85.

[0042] For the EBR-F copolymer used in rubber composition M5, the copolymer is prepared according to the same procedure as for the EBR copolymer, with one difference: When the desired monomer conversion is achieved, the reactor contents are degassed and then the functionalizing agent (N,N-dimethyl-3-aminopropyl)methyldimethoxysilane is introduced by overpressure under an inert atmosphere. The reaction medium is stirred for a time of 15 minutes and at a temperature of 80° C. After the reaction, the medium is degassed and then precipitated from methanol. The polymer can be redissolved in toluene and then precipitated from methanol to remove the ungrafted "silane" molecules, improving the quality of the spectral signals for the quantification of the amount of functional group content and the integration of the various signals. The polymer is treated with an antioxidant and then vacuum dried at 60° C. until constant mass. In the EBR-F copolymer, the molar content of ethylene units is 76%, the molar content of 1,4 units is 6%, the molar content of 1,2 units is 9%, and the molar content of 1,2-cyclohexanediyl units is 9%. The Mooney viscosity is 84.

[0043] [Table 1] (1) SBR-27% styrene; 5% 1,2-butadiene; 15% 1,4-cis; 80% 1,4-trans; Tg-48°C; (2) copolymers of ethylene and non-functional 1,3-butadiene (EBR); (3) copolymers of ethylene and functionalized 1,3-butadiene (EBR-F); (4) N234 according to ASTM standard D-1765; (5) Zeosil 1165 MP, Solvay-Rhodia, in the form of microbeads; (6) Flexon 630 TDAE oil, manufactured by Shell; (7) Escorez 2173 resin, manufactured by Exxon; (8)MES / HPD (Shell Catenex SNR); (9) Escorez 5600 C9 / dicyclopentadiene hydrocarbon-based resin from Exxon (Tg=55°C); (10) N-1,3-dimethylbutyl-N-phenyl-paraphenylenediamine (Santoflex 6-PPD from Flexsys); (11) TESPT (Si69 manufactured by Evonik); (12) Pristerene 4931 stearin, manufactured by Uniqema; (13) Zinc oxide, technical grade, manufactured by Umicore; (14) Diphenylguanidine; (15) N-cyclohexyl-2-benzothiazole sulfenamide (Santocure CBS from Flexsys); (16) Tetrabenzyl thiuram disulfide (Perkacit TBzTD, manufactured by Flexsys)

[0044] Table 2 below shows the ratio values ​​between the filler content and the plasticizing system content. [Table 2]

[0045] Table 3 below shows the stiffness properties of the six indicated mixes. [Table 3]

[0046] Table 1 above also shows the rubber composition T1 shown in WO 2016 / 202702, which was used as a mixture for the second tread layer, and five compositions according to the invention for mixtures that can constitute the first tread layer. Rubber composition T1 contains 100 phr SBR and has a dynamic shear modulus of 0.9 MPa, which makes it particularly suitable for providing tires with excellent grip due to a large contact area, especially on rough ground. The first four compositions C1 to C4 according to the invention for the first tread layer contain 100 phr of said EBR diene elastomer, composition C5 contains 100 phr of said EBR-F diene elastomer. These five compositions have a dynamic shear modulus between 1.2 MPa and 2.3 MPa, making them suitable for stiffening the tread and thereby improving the road holding of the tire, while allowing for use in contact with the ground during running when the tread is in a worn state. It should be noted that the ratio of filler content / plasticizer content varies between 1.1 and 2 (Table 2). Finally, the filler content of these compositions is much lower than composition T1, which allows a significant reduction in its hysteresis. Another aspect of the present invention may be as follows. [1] A tire comprising a crown having a rotation axis, extended by two sidewalls and two beads, a carcass reinforcement fixed to the two beads, a crown reinforcement, and a rubber tread radially outside the crown reinforcement, wherein the tread comprises a first radially inner layer C1 and a second radially outer layer C2, and the first layer and the second layer are intended to contact the ground during running in a new or worn state, and the rubber composition of the first layer C1 contains more than 50 phr of a copolymer of ethylene and 1,3-diene, a reinforcing filler, and a plasticizing system, the 1,3-diene is 1,3-butadiene or isoprene, and the ethylene units in the copolymer account for more than 50 mol% of all monomer units of the copolymer, characterized in that the tire (1). [2] The tire (1) according to [1], wherein the 1,3-diene is 1,3-butadiene. [3] The copolymer comprises units of formula (I) or units of formula (II-1) as follows, or units of formula (I) and units of formula (II-1): [ka] The tire (1) according to [1] or [2] above, which contains. [4] The molar percentages o and p of the units of formula (I) and the units of formula (II-1) in the copolymer respectively satisfy the following mathematical formula (Formula 1), more preferably mathematical formula (Formula 2), and o and p are calculated based on all monomer units of the copolymer: 0 < o + p ≤ 25 (Formula 1) 0 < o + p < 20 (Formula 2) The tire (1) according to [3] above, which is. [5] The copolymer of ethylene and 1,3-diene has a functional group F which is silanol or alkoxysilane functional at the chain ends 1 The tire according to any one of [1] to [4] above, which has. [6] The reinforcing filler of the rubber composition of the layer C1 contains 35 to 100 phr of a reinforcing filler containing silica, and the tire according to any one of [1] to [5] above. [7] The plasticizing system of the rubber composition of the layer C1 contains a hydrocarbon-based plasticizing resin and a hydrocarbon-based liquid plasticizer, and the total content of the hydrocarbon-based plasticizing resin and the hydrocarbon-based liquid plasticizer exceeds 10 phr and is 80 phr or less, and the tire according to any one of [1] to [7] above. [8] The tire according to any one of the above [1] to [7], wherein the hydrocarbon-based plasticized resin has a glass transition temperature higher than 20°C. [9] The tire according to any one of the above [1] to [8], wherein the mass ratio between the reinforcing filler content and the plasticizing system content is 1.1 or more.

[10] The tire (1) according to any one of the above [1] to [9], wherein the copolymer of ethylene and 1,3-diene is the only elastomer in the rubber composition of the first layer C1.

[11] The tire (1) according to any one of the above [1] to [9], wherein the rubber composition of the first layer C1 contains a second elastomer, preferably a highly unsaturated diene elastomer.

[12] The tire (1) according to any one of the above [1] to

[11] , wherein the rubber composition of the second layer C2 contains less than 50 phr of the copolymer of ethylene and 1,3-diene according to any one of the above [1] to

[10] .

[13] The tire (1) according to any one of the above [1] to

[12] , wherein the dynamic shear modulus of the rubber composition of the first layer C1 is between 1 MPa and 2.5 MPa, and the dynamic shear modulus is measured at 60°C during a temperature sweep at an applied stress of 0.7 MPa and a frequency of 10 Hz.

[14] The tire (1) according to any one of the above [1] to

[13] , wherein the ratio K between the dynamic shear modulus of the rubber composition of the first layer C1 and the dynamic shear modulus of the rubber composition of the second layer C2 is greater than 1.1, preferably greater than 1.2, and the dynamic shear modulus is measured at 60°C during a temperature sweep at an applied stress of 0.7 MPa and a frequency of 10 Hz.

[15] A tire according to any one of the above [1] to

[14] , wherein the tread comprises ribs separated by grooves having bottoms, the limit of use of the tire being defined by a minimum radial height h of the ribs relative to the bottoms, VC1 and VC2 being the volumes of materials C1 and C2 located in the tread at radial heights greater than the minimum radial height h, and the VC1 / VC2 ratio being greater than 15%, preferentially greater than 25%, and even more preferentially greater than 35%.

Claims

1. A tire having an axis of rotation and comprising a crown extended by two sidewalls and two beads, a carcass reinforcement fixed to the two beads, a crown reinforcement, and a rubber tread radially outward from the crown reinforcement, said tread comprising a first, radially inner layer C1 and a second, radially outer layer C2, said first and second layers being intended in a new or worn condition to come into contact with the ground during running, The rubber composition of the first layer C1 comprises at least one elastomer, a reinforcing filler, and a plasticization system, the at least one elastomer comprises more than 50 phr of a copolymer of ethylene and 1,3-diene, the 1,3-diene being 1,3-butadiene or isoprene, and the ethylene units in the copolymer account for more than 50 mol % of the total monomer units of the copolymer; The rubber composition of the second layer C2 includes an elastomer, the content of a copolymer of ethylene and 1,3-diene in the rubber composition of the second layer C2 is less than 50 phr, the 1,3-diene is 1,3-butadiene or isoprene, and ethylene units in the copolymer account for more than 50 mol % of the total monomer units of the copolymer; phr means parts by weight per 100 parts by weight of the total elastomer; A tire, wherein the dynamic shear modulus of the rubber composition of the first layer C1 is between 1 MPa and 2.5 MPa, and a ratio K of the dynamic shear modulus of the rubber composition of the first layer C1 to the dynamic shear modulus of the rubber composition of the second layer C2 is greater than 1.1 and less than 2.5, and the dynamic shear modulus is measured at 60° C. during a temperature sweep at an applied stress of 0.7 MPa and a frequency of 10 Hz.

2. The tire according to claim 1, wherein the 1,3-diene contained in the at least one elastomer of the rubber composition of the first layer C1 is 1,3-butadiene.

3. The copolymer contained in the at least one elastomer of the rubber composition of the first layer C1 has a unit of formula (I) or a unit of formula (II-1) as shown below, or a unit of formula (I) and a unit of formula (II-1): 【Chemistry 1】 3. The tire of claim 1 or 2, comprising:

4. The molar percentages o and p of the units of formula (I) and the units of formula (II-1) in the copolymer contained in the at least one elastomer of the rubber composition of the first layer C1 satisfy the following mathematical formula (Formula 1), where o and p are calculated based on all monomer units of the copolymer: 0<o+p≦25 (Formula 1) 4. The tire of claim 3,

5. The copolymer contained in at least one of the elastomers of the rubber composition of the first layer C1 has a functional group F, which is a silanol or alkoxysilane functional group, at the chain end. 1 The tire according to any one of claims 1 to 4, having

6. 6. The tire according to claim 1, wherein the plasticization system of the rubber composition of the first layer C1 comprises a hydrocarbon-based plasticizing resin and a hydrocarbon-based liquid plasticizer, and the total content of the hydrocarbon-based plasticizing resin and the hydrocarbon-based liquid plasticizer is more than 10 phr and not more than 80 phr.

7. 7. The tire of claim 6, wherein said hydrocarbon-based plasticizing resin has a glass transition temperature greater than 20°C.

8. 8. Tire according to claim 6 or 7, wherein the mass ratio of the reinforcing filler content to the total content of the plasticization system comprising the hydrocarbon-based plasticizing resin and the hydrocarbon-based liquid plasticizer is greater than or equal to 1.

1.

9. Tire according to any one of the preceding claims, wherein the ratio K is greater than 1.2 and less than 2.5.

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