FR3088643A1 - TIRE TREAD RUBBER COMPOSITION - Google Patents

Abstract

The invention relates to a tire having an improved performance compromise, the tread comprising a rubber composition based on at least one elastomeric matrix, a reinforcing filler and a vulcanization system, in which the elastomeric matrix comprises from 35 to 95 parts by weight per hundred parts by weight of elastomer, pce, of a first diene elastomer, said first diene elastomer being a copolymer based on butadiene and styrene, which copolymer comprising within its structure at least one alkoxysilane group linked to the elastomer by the silicon atom, and at least one function comprising a nitrogen atom, and having a glass transition temperature below -70 ° C, from 5 to 40 phr of a second elastomer, said second diene elastomer being isoprene elastomer.

Description

Title of the invention: RUBBER COMPOSITION OF TIRE TRUCK The present invention relates to tires with a tread, in particular a snow, winter or all-season tread, capable of running on soils covered with snow (in English called "snow tires", "winter tires" or "all season"). In a known manner, these snow tires identified by an inscription M + S or MS or even M&S, marked on their sidewalls, are characterized by a design of the tread and a structure intended above all to ensure in mud and fresh snow or melting behavior better than that of road type tires (in English called "tire type road") designed to roll on snow-free ground.

Snowy soils, called white soils, have the characteristic of having a low coefficient of friction, which has led to the development of snow tires comprising treads based on diene rubber compositions having a low glass transition temperature. , Tg. However, the wet grip performance of these tires comprising such treads is generally lower than that of road tires, the treads of which are generally based on rubber compositions of different formulations, in particular at higher To respond to this problem, application WO 2012/069565 proposes a tread whose composition comprises a diene elastomer carrying at least one SiOR function, R being a hydrogen or a hydrocarbon radical in association with a high level of inorganic charge. reinforcing and a specific plasticizing system.

Furthermore, since fuel savings and the need to protect the environment have become a priority, it is desirable to use rubber compositions which can be used for the manufacture of various semifinished products used in the construction of envelopes. tires with reduced rolling resistance. However, the reduction in rolling resistance is often contradictory, both with improved grip on both wet and snow-covered surfaces.

In addition, since snow or winter treads are generally provided with more flexible treads and / or made of a softer rubber composition than the so-called "summer" treads, their abrasion resistance is proven to be this. often reduced. Also, it is important to keep as much as possible, or even improve, the abrasion resistance of snow or winter treads.

[0005] [0007] [0008] [0009] [0010] [0011] [0012]

Thus, manufacturers are always looking for solutions to further improve a compromise of properties such as rolling resistance, grip on snow, wet grip and abrasion resistance of tire tread intended for drive in particular on snowy ground.

Continuing its research, the Applicant has unexpectedly discovered that the combined use of certain functional diene elastomers with an isoprene elastomer makes it possible to further improve the aforementioned performance compromise.

Thus, the subject of the invention is a tire, the tread of which comprises a rubber composition based on at least one elastomeric matrix, a reinforcing filler and a vulcanization system, in which the elastomeric matrix comprises:

- from 35 to 95 parts by weight per hundred parts by weight of elastomer, pce, of a first diene elastomer, said first diene elastomer being a copolymer based on butadiene and styrene, which copolymer comprising within its structure at at least one alkoxy silane group linked to the elastomer by the silicon atom, and at least one function comprising a nitrogen atom, and having a glass transition temperature below -70 ° C.,

- from 5 to 40 phr of a second elastomer, said second diene elastomer being isoprene elastomer, and

- optionally from 0 to 40 phr of a third diene elastomer.

In the present document, unless otherwise indicated, the expressions “the composition” or “the composition in accordance with the invention” designate the composition of the tread according to the invention.

I- DEFINITIONS

By the expression composition based on, is meant a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially , during the various phases of manufacturing the composition; the composition thus being able to be in the fully or partially crosslinked state or in the non-crosslinked state.

By the expression part by weight per hundred parts by weight of elastomer (or phr), it is understood within the meaning of the present invention, the part, by mass per hundred parts by mass of elastomer.

In the present document, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass.

On the other hand, any range of values designated by the expression between a and b represents the range of values going from more than a to less than b (i.e. limits a and b excluded) while any range of values designated by the expression from a to b signifies the range of values going from a to b (that is to say including the strict limits a and b). In the present, when describing a range of values by the expression from a to b, the range represented by the expression between a and b is also and preferably described.

When referring to a majority compound, it is understood in the sense of the present invention, that this compound is predominant among the compounds of the same type in the composition, that is to say that it is the one which represents the largest amount by mass among compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the largest mass relative to the total mass of the elastomers in the composition. Likewise, a so-called majority charge is that representing the largest mass among the charges of the composition. For example, in a system comprising a single elastomer, the latter is predominant within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers. Preferably by majority, we mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

The compounds comprising carbon mentioned in the description can be of fossil origin or bio-based. In the latter case, they can be, partially or totally, from biomass or obtained from renewable raw materials from biomass. Are concerned in particular polymers, plasticizers, fillers, etc.

The glass transition temperatures (Tg) of the elastomers are determined using a differential scanning calorimeter, according to standard ASTM E1356-08 which dates from 2014.

II- DESCRIPTION OF THE INVENTION II-1 Elastomeric matrix [0017] According to the invention, the elastomeric matrix of the composition of the tread of the tire comprises:

- from 35 to 95 phr of a first diene elastomer, said first diene elastomer being a copolymer based on butadiene and styrene, which copolymer comprising within its structure at least one alkoxysilane group linked to the elastomer by the atom of silicon, and at least one function comprising a nitrogen atom, and having a glass transition temperature below -70 ° C.,

- from 5 to 40 phr of a second elastomer, said second diene elastomer being isoprene elastomer, and

- optionally from 0 to 40 phr of a third diene elastomer.

By diene elastomer (or indistinctly rubber), whether natural or synthetic, must be understood in known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of diene monomer units (carrier monomers of two carbon-carbon double bonds, conjugated or not).

The first diene elastomer is a copolymer based on butadiene and styrene.

For the purposes of the present invention, a copolymer based on styrene and butadiene is any copolymer obtained by copolymerization of one or more styrenic compounds with one or more butadiene (s). As styrene monomers suitable in particular are styrene, methylstyrenes, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes. As monomers butadienes are suitable in particular 1,3-butadiene, 2-methyl-l, 3-butadiene, 2,3-di (alkyl-C ₅₎ -l, 3-butadienes such as e.g. 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1 , 3-butadiene and an aryl-1,3-butadiene. These elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used. The elastomers can, for example, be block, statistical, sequenced, microsequenced.

Advantageously, the first diene elastomer is a butadienestyrene copolymer (SBR).

Note that the SBR can be prepared as an emulsion (ESBR) or in solution (SSBR). Whether ESBR or SSBR, the SBR can be of any microstructure compatible with a glass transition temperature below -70 ° C. In particular, the butadiene-styrene copolymer can have a styrene content of between 1% and 60% by weight and more particularly between 10% and 50%, a content (molar%) of -1.2 bonds of the butadiene part included. between 4% and 75%, a content (molar%) of trans-1,4 bonds between 10% and 80%.

Advantageously, the first diene elastomer has a glass transition temperature in a range from -105 ° C to -70 ° C, preferably from -100 ° C to -75 ° C, preferably from -95 ° C at -80 ° C.

Preferably, the first diene elastomer is a styrene-butadiene copolymer has any one, advantageously the combination of two or three, even more advantageously all, of the following characteristics:

- it is a styrene-butadiene copolymer prepared in solution (SSBR),

its mass content of styrene relative to the total weight of the styrene-butadiene copolymer is between 1 and 15%, preferably between 1 and 5%,

- its content of vinyl bonds in the butadiene part of between 4 and

25%, preferably between 10 and 15%.

The first diene elastomer comprises within its structure at least one alkoxysilane group bonded to the elastomer via the silicon atom, and a function comprising a nitrogen atom.

In the present description, the concept of alkoxysilane group located within the structure of the elastomer is understood to mean a group whose silicon atom is located in the skeleton of the polymer and directly connected to it. This positioning within the structure includes the ends of polymer chains. Thus, the terminal grouping is included in this notion. The alkoxysilane group is not a pendant group.

When the alkoxysilane group is at the end of the chain, it will then be said that the diene elastomer is functionalized at the end or end of the chain.

When the alkoxysilane group is located in the main elastomer chain, it will be said that the diene elastomer is coupled or even functionalized in the middle of the chain, as opposed to the position at the chain end and although the group is not located not precisely in the middle of the elastomer chain. The silicon atom of this function links the two branches of the main chain of the diene elastomer.

When the silicon atom is in the central position to which at least three elastomeric branches are linked forming a star structure of the elastomer, it will then be said that the diene elastomer is star-shaped. The silicon atom is thus substituted by at least three branches of the diene elastomer.

It should be noted that it is known to those skilled in the art that when an elastomer is modified by reaction of a functionalizing agent on the living elastomer resulting from an anionic polymerization step, a mixture of modified species of this elastomer, the composition of which depends on the conditions of the modification reaction and in particular on the proportion of reactive sites of the functionalizing agent relative to the number of living elastomer chains. This mixture comprises species functionalized at the end of the chain, coupled, star-shaped and / or non-functionalized.

Advantageously, the first diene elastomer comprises, as the majority species, the diene elastomer functionalized in the middle of the chain by an alkoxysilane group linked to the two branches of the diene elastomer via the silicon atom, the alkoxy radical being optionally partially or completely hydrolyzed to hydroxyl. More particularly still, the diene elastomer functionalized in the middle of the chain with an alkoxysilane group represents 70% by weight of the first diene elastomer.

The alkoxysilane group, the alkoxyl radical, optionally partially or completely hydrolyzed to hydroxyl, may comprise a C1-C10 or even C _r C ₈ , preferably C1-C4, alkyl radical, more preferably the alkoxyl radical is a methoxy or an ethoxy.

The first diene elastomer also comprises at least one function comprising a nitrogen atom.

This function comprising a nitrogen atom can be located at the chain end and be directly connected to the elastomer via a covalent bond or a hydrocarbon group.

This function comprising a nitrogen atom can also, and advantageously, be carried by the alkoxy silane group. The function comprising a nitrogen atom can be carried by the silicon of the alkoxy silane group, directly or through a spacer group. The spacer group may be an atom, in particular a heteroatom, or a group of atoms.

The spacer group may be a divalent hydrocarbon radical, linear or branched, aliphatic in Ci-Ci ₈ , saturated or not, cyclic or not, or a divalent aromatic hydrocarbon radical in C ₆ -Ci ₈ and may contain one or more aromatic radicals and / or one or more heteroatoms. The hydrocarbon radical can optionally be substituted.

[0037] Advantageously, the spacer group is a divalent hydrocarbon radical, linear or branched, aliphatic Ci-Ci _8, most preferably an aliphatic divalent hydrocarbon radical Ci-Cio, more preferably a divalent linear hydrocarbon radical in C ₂ or C ₃ .

The first diene elastomer can also include another function (that is to say a function different from those mentioned above) within Γ elastomer, but this is not preferable.

The first diene elastomer can also be a mixture of several first diene elastomers.

The alkoxysilane group can be represented by the formula:

(* -) _a If (OR ') _b R _c X in which,

- * - represents the bond to an elastomer chain;

- the radical R represents a substituted or unsubstituted alkyl radical, being in C 1 -C 10, even in C _r C ₈ , preferably an alkyl radical in C ₁ -C ₄ , more preferably methyl and ethyl;

- in the alkoxyl radicals of formula -OR ', optionally partially or totally hydrolyzed to hydroxyl, R' represents an alkyl radical, substituted or unsubstituted, being Ci-Cio, or even C _r C ₈ , preferably an alkyl radical in Ci-C ₄ , more preferably methyl and ethyl;

- X represents a group comprising the nitrogen function;

- a is worth lou 2, b is worth 1 or 2, and c is worth 0 or Is provided that a + b + c = 3.

Those skilled in the art will understand that the value of a is a function of the positioning of the alkoxy silane group within the structure of the elastomer. When a is 1, the group is located at the end of the chain. When a is 2, it is located in the middle of the chain.

As a function comprising a nitrogen atom, there may be mentioned the amine functions. Particularly suitable are primary amines, protected or not by a protective group, secondary, protected or not by a protective group, or tertiary.

Thus, as secondary or tertiary amine function, mention may be made of amines substituted by C _r C 10 alkyl radicals, preferably C ₁ -C ₄ alkyl radicals, more preferably a methyl or ethyl radical, or else the amines cyclic forming a heterocycle containing a nitrogen atom and at least one carbon atom, preferably from 2 to 6 carbon atoms. For example, the methylamino-, dimethylamino-, ethylamino-, diethylamino-, propylamino-, dipropylamino-, butylamino-, dibutylamino-, pentylamino-, dipentylamino-, hexylamino-, dihexylamino-, hexamethyleneamino- groups are suitable. - and dimethylamino-. Also suitable when the amine is cyclic the groups morpholine, piperazine, 2,6-dimethylmorpholme, 2,6-dimethylpiperazine, 1-ethylpiperazine, 2-methylpiperazine, 1-benzylpiperazine, piperidine, 3,3-dimethylpiperidme, 2,6- dimethylpiperidme, l-methyl-4- (methylamino) piperidme, 2,2,6,6-tetramethylpiperidine, pyrrolidine, 2,5-dimethylpyrrolidine, azetidine, hexamethyleneimine, heptamethyleneimine, 5-benzyloxyindole, 3-azaspiro [5,5] undecane , 3-aza-bicycle [3.2.2] nonane, carbazole, bistrimethylsilylamine, pyrrolidine and hexamethyleneamine, preferably the pyrrolidine and hexamethyleneamine groups.

Preferably, the amine function is a tertiary amine function, preferably diethylamine or dimethylamine.

Advantageously, at least two, preferably at least three, preferably at least four, more preferably all of the following characteristics are met:

the function comprising a nitrogen atom is a tertiary amine, more particularly a diethylamino- or dimethylamino- group,

the function comprising a nitrogen atom is carried by the alkoxy silane group by means of a spacer group defined as an aliphatic C ₁ -C ₁₀ hydrocarbon radical, more preferably still the linear C ₂ or C ₃ hydrocarbon radical,

the alkoxysilane group is a methoxysilane or an ethoxysilane, optionally partially or completely hydrolyzed to silanol,

the first diene elastomer is a butadiene-styrene copolymer,

the first diene elastomer is mainly functionalized in the middle of the chain by an alkoxysilane group linked to the two branches of the first diene elastomer by means of the silicon atom,

- The first diene elastomer has a glass transition temperature in a range from -105 ° C to -70 ° C.

In a particularly preferred manner, at least two, preferably at least three, preferably at least four, more preferably all of the following characteristics are met:

the function comprising a nitrogen atom is a tertiary amine, more particularly a diethylamino- or dimethylamino- group,

the function comprising a nitrogen atom is carried by the alkoxysilane group via a linear C ₃ aliphatic hydrocarbon radical,

the alkoxysilane group is methoxysilane or ethoxysilane, optionally partially or totally hydrolyzed to silanol,

the first diene elastomer is a butadiene-styrene copolymer,

the first diene elastomer is mainly functionalized in the middle of the chain by an alkoxysilane group linked to the two branches of the first diene elastomer by means of the silicon atom,

- The first diene elastomer has a glass transition temperature in a range from -95 ° C to -80 ° C.

The level of the first diene elastomer in the composition of the tread of the tire according to the invention can advantageously be included in a range from 40 to 80 phr.

The first diene elastomer can be obtained by a process as described below.

The first step in a process for preparing the first diene elastomer is the anionic polymerization of at least one conjugated diene monomer or the polymerization of at least one conjugated diene monomer and a vinylaromatic monomer, in the presence of an initiator polymerization. The monomers are as described above.

As the polymerization initiator, any known monofunctional anionic initiator can be used. However, an initiator containing an alkali metal such as lithium is preferably used.

Organolithium initiators are particularly suitable for those comprising a carbon-lithium bond. Representative compounds are the aliphatic organoliths such as ethyllithium, n-butyllithium (n-BuLi), isobutyllithium, etc.

According to the implementation of the invention according to which the other function is directly linked to the elastomer chain, the latter can be provided by the polymerization initiator. Such initiators are, for example, amine-functional polymerization initiators which lead to living chains having an amine group at the non-reactive end of the chain.

As amine-functional polymerization initiators, mention may preferably be made of lithium amides, products of the reaction of an organolithium compound, preferably an alkyllithian compound, and an acyclic or cyclic secondary amine, cyclical preference.

As secondary amine which can be used to prepare the initiators, mention may be made of dimethylamine, diethylamine, dipropylamine, di-n-butylamine, di-sec-butylamine, dipentylamine, dihexylamine, di-n-octylamine, di- ( 2-ethylhexyl) amine, di-cyclohexylamine, N-methylbenzylamine, diallylamine, morpholine, piperazine, 2,6-dimethylmorpholme, 2,6-dimethylpiperazine, 1-ethylpiperazine, 2-methylpiperazine, 1-benzylpiperazine, piperidine, 3,3- dimethylpiperidine, 2,6-dimethylpiperidine,

-methyl-4- (methylamino) piperidme, 2,2,6,6-tetramethylpiperidine, pyrrolidine, 2,5-dimethylpyrrolidine, azetidine, hexamethyleneimine, heptamethyleneimine, 5-benzyloxyindole, 3-azaspiro [5,5] undecane, 3- aza-bicycle [3.2.2] nonane, carbazole, bistrimethylsilylamme, pyrrolidine and hexamethyleneamine. The secondary amine, when it is cyclic, is preferably chosen from pyrrolidine and hexamethyleneamine.

The alkyllithian compound is preferably ethyllithium, n-butyllithium (n-BuLi), isobutyllithium, etc.

The polymerization is preferably carried out in the presence of an inert hydrocarbon solvent which can for example be an aliphatic or alicyclic hydrocarbon such as pentane, hexane, heptane, iso-octane, cyclohexane, methylcyclohexane or an aromatic hydrocarbon such as benzene, toluene, xylene.

The microstructure of the elastomer can be determined by the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used. Preferably, when the diene elastomer is based on a diene and a vinyl aromatic, a polar agent is used during the polymerization step in amounts such that it promotes the statistical distribution of the vinyl aromatic along the polymer chains. .

Advantageously, the living diene elastomer resulting from the polymerization is then functionalized by means of a functionalizing agent capable of introducing an alkoxy silane group within the polymer structure to prepare the first diene elastomer.

The modification reaction of the living diene elastomer, obtained at the end of the first step, can take place at a temperature between - 20 ° C and 100 C, by addition to the living polymer chains or vice versa. a non-polymerizable functionalizing agent capable of forming an alkoxysilane group, the silicon atom integrating within the elastomer chain, whether or not carrying a function comprising a nitrogen atom. It is in particular a functionalizing agent carrying reactive functions vis-à-vis the living elastomer, each of these functions being directly linked to the silicon atom.

The functionalization agent corresponds to the formula:

(OR ') _d Si (R) _c X in which, • in the alkoxylated radicals of formula -OR', optionally partially or completely hydrolyzable, R 'represents an alkyl radical, substituted or unsubstituted, in C _r Cio, or even in C _r -C ₈ alkyl preferably Ci-C _4, more preferably methyl and ethyl;

• R represents an alkyl radical, substituted or unsubstituted Ci-Cio, or _Ci-C8, preferably C1-C4, more preferably methyl and ethyl;

• X represents a group including a function comprising a nitrogen atom;

• d is 2 or 3, c is 0 or 1, provided that d + c = 3.

The function comprising a nitrogen atom is as defined above.

The function comprising a nitrogen atom can be a primary amine, protected or not, secondary, protected or not, or tertiary. The nitrogen atom can then be substituted by two groups, identical or different, which may be a trialkyl silyl radical, the alkyl group having 1 to 4 carbon atoms, or a C ₁ -C 10 alkyl radical, preferably C1-C alkyl -C4, more preferably a methyl or ethyl radical, or else the two nitrogen substituents form with the latter a heterocycle containing a nitrogen atom and at least one carbon atom, preferably from 2 to 6 carbon atoms Mention may be made, for example, as functionalizing agent, of (N, N-dialkylaminoalkyl) trialkoxysilanes, (N-alkylaminoalkyl) trialkoxysilanes, the secondary amine function of which is protected by a trialkyl silyl group and the (aminoalkyl) groups trialcoxysilanes whose primary amine function is protected by two trialkyl silyl groups, the divalent hydrocarbon group making it possible to link the amine function to the trialcoxysilane group is the spacer group as described above, preferably t aliphatic in C1-C10, more particularly linear in C ₂ or C ₃ .

The functionalizing agent can be chosen from 3- (N, N-dimethylaminopropyl) trimethoxysilane,

3- (N, N-dimethylaminopropyl) triethoxysilane, 3- (N, N-diethylaminopropyl) trimethoxysilane, 3- (N, N-diethylaminopropyl) triethoxysilane, 3- (N, N-dipropylaminopropyl) trimethoxysilane, 3- (N, N-dipropylaminopropyl) triethoxysilane, 3- (N, N-dibutylaminopropyl) trimethoxysilane, 3- (N, N-dibutylaminopropyl) triethoxysilane, 3- (N, N-dipentylaminopropyl) trimethoxysilane, 3- (N , N-dipentylaminopropyl) triethoxysilane, 3- (N, N-dihexylaminopropyl) trimethoxysilane, 3- (N, N-dihexylaminopropyl) triethoxysilane, 3- (hexamethyleneaminopropyl) trimethoxysilane, 3- (hexamethyleneaminopropyl) triethoxysane (morpholinopropyl) trimethoxysilane, 3- (morpholinopropyl) triethoxysilane, 3- (piperidinopropyl) trimethoxysilane, 3- (piperidinopropyl) triethoxysilane. More preferably, the functionalizing agent is 3- (N, N-dimethylaminopropyl) trimethoxysilane.

The functionalizing agent can be chosen from 3- (N, N-methyltrimethylsilylaminopropyl) trimethoxysilane, 3- (N, N-methyltrimethylsilylaminopropyl) triethoxysilane, 3- (N, N-ethyltrimethylsilylaminopropyl) trimethoxysilane, 3 - (N, N-ethyltrimethylsilylaminopropyl) triethoxysilane, 3- (N, N-propyltrimethylsilylaminopropyl) trimethoxysilane, 3- (N, N-propyltrimethylsilylaminopropyl) triethoxysilane. More preferably, the functionalizing agent is 3- (N, N-methyltrimethylsilylaminopropyl) trimethoxysilane.

The functionalizing agent can be chosen from 3- (N, N-bistrimethylsilylaminopropyl) trimethoxysilane and 3- (N, N-bistrimethylsilylaminopropyl) triethoxy silane. More preferably, the functionalizing agent is 3- (N, N-bistrimethylsilylaminopropyl) trimethoxysilane.

The functionalizing agent is advantageously chosen from (N, N-dialkylaminoalkyl) trialkoxysilanes; more particular then the functionalizing agent is 3- (N, N-dimethylaminopropyl) trimethoxysilane.

It should be noted that it is known to those skilled in the art that when an elastomer is modified by reaction of a functionalizing agent on the living elastomer resulting from an anionic polymerization step, a mixture of modified species of this elastomer, the composition of which depends in particular on the proportion of reactive sites of the functionalizing agent relative to the number of living elastomer chains. This mixture comprises species functionalized at the end of the chain, coupled, star-shaped and / or non-functionalized.

The molar ratio of the functionalizing agent to the metal of the polymerization initiator essentially depends on the type of first diene elastomer desired. Thus, with a ratio ranging from 0.40 to 0.75, or even from 0.45 to 0.65, or even from 0.45 to 0.55, the formation of coupled species within the elastomer is preferred. modified, the alkoxysilane group then being in the middle of the chain. In the same way, with a ratio going from 0.15 to 0.40, even from 0.20 to 0.35, or even from 0.30 to 0.35, we mainly form star species (3 branches) in within the modified elastomer. With a ratio greater than or equal to 0.75, or even greater than 1, the majority of functionalized species are formed at the end of the chain.

Advantageously, the molar ratio between the functionalizing agent and the polymerization initiator varies from 0.35 to 0.65, preferably from 0.40 to 0.60 and even more preferably from 0.45 to 0, 55.

Thus, the first diene elastomer can comprise, as the majority species, the diene elastomer functionalized in the middle of the chain by an alkoxysilane group linked to the two branches of the diene elastomer via the silicon atom. More particularly still, the diene elastomer functionalized in the middle of the chain with an alkoxysilane group represents 70% by weight of the first diene elastomer.

Advantageously, the alkoxysilane group advantageously comprises an alkoxy radical, optionally partially or totally hydrolyzed to hydroxyl.

Alternatively, the alkoxysilane group advantageously carries a function comprising a nitrogen atom as defined above. This function is preferably a tertiary amine function as defined above, in particular diethylamino- or dimethylamino-, bonded to the silicon atom preferably via a spacer as defined above, in particular a divalent hydrocarbon radical linear in C ₂ or C ₃ .

When the functionalization agent carries a protected function, the synthesis process can continue with a step of deprotection of this function. This step is implemented after the modification reaction and is well known to those skilled in the art.

The synthesis process can also include a step of hydrolyzing the hydrolysable alkoxy functions, by adding an acidic, basic or neutral compound as described in document EP 2 266 819 A1. The hydrolysable functions are then transformed into hydroxyl function.

The process for the synthesis of the first diene elastomer can be continued in a manner known per se by the stages of recovery of the first diene elastomer.

These steps may in particular include a stripping step in order to recover the elastomer from the previous steps. This stripping step can have the effect of hydrolyzing all or part of the hydrolyzable functions of the first diene elastomer. Advantageously, at least 50 to 70 mol% of these functions can thus be hydrolyzed.

As indicated above, the second diene elastomer is an isoprene elastomer.

By isoprene elastomer is understood in known manner to be a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, polyisoprenes are preferably used having a rate (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%.

Advantageously, the second elastomer is a polyisoprene comprising a mass ratio of 1,4-cis bonds of at least 90% of the mass of the polyisoprene. Preferably, the second elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and their mixtures. More preferably, the polyisoprene is a natural rubber.

The level of the second diene elastomer in the composition of the tread of the tire according to the invention is preferably within a range ranging from 10 to 35 phr, preferably from 10 to 30 phr.

The composition of the tread of the tire according to the invention can optionally comprise a third diene elastomer, for example at a rate comprised in a range ranging from 0 to 40 phr.

Of course, the third diene elastomer is different from the first and from the second diene elastomer described herein.

Advantageously, the third diene elastomer is chosen from the group consisting of polybutadienes (BR), butadiene copolymers and their mixtures.

The level of the third diene elastomer in the composition of the tread of the tire according to the invention is preferably within a range ranging from 5 to 35 phr, preferably from 10 to 30 phr.

The composition of the tread of the tire according to the invention may comprise yet another diene elastomer, but this is not preferable. Thus, advantageously, the total level of the first, second and third diene elastomer, in the composition of the tread of the tire according to the invention, is included in a range ranging from 80 to 100 phr, preferably from 90 to 100 pce, more preferably 100 pce.

Advantageously, the total level of the first and second diene elastomer, in the composition of the tread of the tire according to the invention, is included in a range ranging from 80 to 100 phr, preferably from 90 to 100 phr , more preferably 100 pce.

The composition of the tread of the tire according to the invention may also contain in a minority any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers. Preferably, the elastomeric matrix does not contain a synthetic elastomer other than diene or a polymer other than elastomers or contains less than 10 phr, preferably less than 5 phr.

II-2 Reinforcing filler The composition of the tread of the tire according to the invention also comprises a reinforcing filler, known for its capacity to reinforce a rubber composition which can be used for the manufacture of tires.

The reinforcing filler can comprise a carbon black, a reinforcing inorganic filler or one of their mixtures.

The blacks which can be used in the context of the present invention can be any black conventionally used in tires or their treads (so-called pneumatic grade blacks). Among the latter, there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM grades), such as, for example, the 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 some of the rubber additives used. The 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).

As examples of organic fillers other than carbon blacks, mention may be made of organic fillers of functionalized polyvinyl as described in applications WO 2006/069792, WO 2006/069793, WO 2008/003434 and WO 2008/003435.

The BET specific surface area of carbon blacks is measured according to standard D6556-10 [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range Ρ / Ρ0: 0.1 to 0.3].

The silicas which can be used in the context of the present invention can be any silica known to a person skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface both of which are less than 450 m2 / g , preferably from 30 to 400 m2 / g.

The BET specific surface area of the silica is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in The Journal of the American Chemical Society Vol. 60, page 309, February 1938, more precisely according to French standard NE ISO 9277 of December 1996 (multi-point volumetric method (5 points) - gas: nitrogen - degassing: 1 hour at 160 ° C - relative pressure range p / in: 0.05 to 0.17). The CTAB specific surface of silica is determined according to French standard NE T 45-007 of November 1987 (method B).

Preferably, the silica has a BET specific surface of less than 200 m ² / g and / or a CTAB specific surface is less than 220 m ² / g, preferably a BET specific surface included in a range from 125 to 200 m ² / g and / or a specific CTAB surface in a range from 140 to 170 m ² / g.

By way of silica which can be used in the context of the present invention, mention will be made for example of highly dispersible precipitated silica (known as HDS) "Ultrasil 7000" and "Ultrasil 7005" from the company Evonik, silica "Zeosil 1165MP, 1135MP and 1115MP ”from the company Rhodia, the silica“ Hi-Sil EZ150G ”from the company PPG, the silicas“ Zeopol 8715, 8745 and 8755 ”from the company Huber, the silicas with high specific surface as described in application WO 03 / 16837.

To couple the reinforcing silica to the diene elastomer, use is made in a well known manner of a coupling agent (or bonding agent) at least bifunctional intended to ensure a sufficient connection, of chemical and / or physical nature, between the silica (surface of its particles) and the diene elastomer. In particular organosilanes or polyorganosiloxanes at least bifunctional are used.

The skilled person can find examples of coupling agent in the following documents: WO 02/083782, WO 02/30939, WO 02/31041,

WO 2007/061550, WO 2006/125532, WO 2006/125533, WO 2006/125534, US 6,849,754, WO 99/09036, WO 2006/023815, WO 2007/098080, WO 2010/072685 and WO 2008/055986.

Mention may in particular be made of the alkoxysilane-polysulphide compounds, in particular the bis- (trialkoxylsilylpropyl) polysulphides, very particularly the bis 3-triethoxysilylpropyl disulphide (in abbreviation TESPD) and the bis 3-triethoxysilylpropyl tetrasulphide (in abbreviation TESPT ). It is recalled that the TESPD, of formula [(C ₂ H ₅ O) 3Si (CH2) 3S] 2, is in particular marketed by the company Degussa under the names Si266 or Si75 (in the second case, in the form of a mixture of disulfide (75% by weight) and polysulfides). TESPT, of formula [(C ₂ H ₅ O) 3Si (CH2) ₃ S] ₂ is marketed in particular by the company Degussa under the name Si69 (or X50S when it is supported at 50% by weight on carbon black ), in the form of a commercial mixture of polysulfides Sx with an average value for x which is close to 4.

Advantageously, the reinforcing filler mainly comprises a reinforcing inorganic filler, preferably a silica.

The rate of reinforcing inorganic filler, preferably of silica, in the composition of the tread of the tire according to the invention can be included in a range ranging from 90 to 200 phr, preferably from 95 to 180 phr, preferably from 100 to 150 pce.

Furthermore, the level of carbon black in the composition of the tread of the tire according to the invention can be included in a range ranging from 0 to 40 phr, preferably from 1 to 20 phr, preferably from 2 to 10 pce.

II-3 Vulcanization system [0106] The vulcanization system preferably comprises molecular sulfur and / or at least one sulfur donor. At least one vulcanization accelerator is also preferably present, and, optionally, also preferentially, various known vulcanization activators can be used such as zinc oxide, stearic acid or equivalent compound such as stearic acid salts and salts. of transition metals, guanidine derivatives (in particular diphenylguanidine), or also known vulcanization retardants.

Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr.

Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea type, can be used as accelerator. and xanthates. Examples of such accelerators include the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS), N-ter-butyl-2-benzothiazyl sulfenamide (TBBS), Nter-butyl-2-benzothiazyl sulfenimide (TBSI), tetrabenzylthiuram disulfide (TBZTD), zinc dibenzyldithiocarbamate (ZBEC) and mixtures of these compounds.

II-4 Plasticizer System [0110] The rubber composition of the tread of the tire according to the invention can also comprise a plasticizer system comprising a plasticizer resin having a glass transition temperature above 20 ° C, called "High Tg" (also called "plasticizing resin" in the present for the sake of simplification of writing ").

II-4.1 Plasticizing resin [0112] The name "resin" is reserved in the present application, by definition known to those skilled in the art, to a compound which is solid at room temperature (23 ° C), in contrast to a liquid plasticizing compound such as an oil.

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, which can be used in particular as plasticizing agents or tackifying agents in polymeric matrices. They are generally by nature miscible (i.e., compatible) at the levels used with the polymer compositions for which they are intended, so as to act as true diluents. They have been described for example in the work entitled Hydrocarbon Resins by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), Chapter 5 of which is devoted to their applications, especially in pneumatic rubber (5.5.). They can be aliphatic, cycloaliphatic, aromatic, hydrogenated aromatic, of the aliphatic / aromatic type, that is to say based on aliphatic and / or aromatic monomers. They can be natural or synthetic, based on petroleum or not (if this is the case, also known as petroleum resins). Their Tg is preferably greater than 20 ° C (most often between 30 ° C and 95 ° C).

In known manner, these plasticizing resins can also be qualified as thermoplastic resins in the sense that they soften by heating and can thus be molded. They can also be defined by a softening point or temperature. The softening temperature of a plasticizing resin is generally about 50 to 60 ° C higher than its Tg value. The softening point is measured according to ISO standard 4625 ("Ring and Ball" method). The macro structure (Mw, Mn and Ip) is determined by steric exclusion chromatography (SEC) as indicated below.

As a reminder, the SEC analysis, for example, consists in separating the macromolecules in solution according to their size through columns filled with a porous gel; the molecules are separated according to their hydrodynamic volume, the largest being eluted first. The sample to be analyzed is simply dissolved beforehand in an appropriate solvent, tetrahydrofuran at a concentration of 1 g / liter. The solution is then filtered on a filter with a porosity of 0.45 μm, before injection into the apparatus. The apparatus used is for example a Waters alliance chromatographic chain according to the following conditions:

- elution solvent is tetrahydrofuran;

- temperature 35 ° C;

- concentration 1 g / liter;

- flow rate: 1 ml / min;

- volume injected: 100 μΐ;

- Moore calibration with polystyrene standards;

- set of 3 Waters columns in series (Styragel HR4E, Styragel HR1 and Styragel HR 0.5);

- detection by differential refractometer (for example WATERS 2410) which can be equipped with operating software (for example Waters Millenium).

A Moore calibration is carried out with a series of commercial standards of low Ip polystyrene (less than 1.2), of known molar masses, covering the range of masses to be analyzed. We deduce from the recorded data (mass distribution curve of molar masses) the mass-average molar mass (Mw), the number-average molar mass (Mn), as well as the polymolecularity index (Ip = Mw / Mn).

All the molar mass values indicated in the present application therefore relate to calibration curves produced with polystyrene standards.

According to a preferred embodiment of the invention, the plasticizing resin has at least any one, preferably 2 or 3, more preferably all, of the following characteristics:

- A Tg greater than 25 ° C (in particular between 30 ° C and 100 ° C), more preferably greater than 30 ° C (in particular between 30 ° C and 95 ° C);

- a softening point above 50 ° C (in particular between 50 ° C and 150 ° C);

- a number-average molar mass (Mn) of between 300 and 2000 g / mol, preferably between 400 and 1500 g / mol;

- a polymolecularity index (Ip) of less than 3, preferably of 2 (reminder: Ip = Mw / Mn with Mw average molar mass by weight).

The above preferred high Tg plasticizing resins are well known to those skilled in the art and available commercially, for example sold with regard to:

- polylimonene resins: by the company DRT under the name Dercolyte L120 (Mn = 625 g / mol; Mw = 1010 g / mol; Ip = 1.6; Tg = 72 ° C) or by the company ARIZONA under the name Sylvagum TR7125C (Mn = 630 g / mol; Mw = 950 g / mol; Ip = 1.5, Tg = 70 ° C);

- C5 cut / vinyl aromatic copolymer resins, especially cut

C5 / styrene or cut C5 / cut C9: by Neville Chemical Company under the names Super Nevtac 78, Super Nevtac 85 or Super Nevtac 99, by Goodyear Chemicals under the name Wingtack Extra, by Kolon under names Hikorez T1095 and Hikorez T1100, by Exxon under names Escorez 2101 and Escorez 1273;

- limonene / styrene copolymer resins: by DRT under the name Dercolyte TS 105 from the company DRT, by ARIZONA Chemical Company under the names ZT115LT and ZT5100.

According to the invention, the plasticizing resin having a glass transition temperature above 20 ° C. can be chosen from the group comprising or consisting of homopolymer or copolymer resins of cyclopentadiene (abbreviated as CPD), resins of dicyclopentadiene homopolymer or copolymer (abbreviated as DCPD), terpene homopolymer or copolymer resins, C5 cut homopolymer or copolymer resins, C9 cut homopolymer or copolymer resins, homopolymer or copolymer resins of alpha-methyl-styrene and their mixtures. Preferably, the plasticizing resin is chosen from the group comprising or consisting of the copolymer (D) CPD / vinyl aromatic resins, the copolymer resins (D) CPD / terpene, the terpene phenol copolymer resins, the copolymer resins (D ) CPD / C5 cut, copolymer resins (D) CPD / C9 cut, terpene / vinyl aromatic copolymer resins, terpene / phenol copolymer resins, C5 / vinyl aromatic copolymer resins, and mixtures thereof.

The term terpene here groups together in a known manner the alpha-pinene, beta-pinene and limonene monomers; a limonene monomer is preferably used, a compound which is known in the form of three possible isomers: L-limonene (levorotatory enantiomer), D-limonene (dextrorotatory enantiomer), or else dipentene, racemic of dextrorotatory and levorotatory enantiomers . As vinyl aromatic monomer, for example, styrene, alpha-methylstyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, vinyl-toluene, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes are suitable. hydroxystyrenes, vinyl mesitylene, divinylbenzene, vinylnaphthalene, any vinyl aromatic monomer resulting from a C ₉ cut (or more generally from a C ₈ to Cio cut).

More particularly, there may be mentioned the plasticizing resins chosen from the group consisting of homopolymer resins (D) CPD, copolymer resins (D) CPD / styrene, polylimonene resins, limonene copolymer resins / styrene, limonene / D copolymer resins (CPD), C5 cut / styrene copolymer resins, C5 cut / C9 cut copolymer resins, and mixtures of these resins.

All of the above plasticizing resins are well known to those skilled in the art and commercially available, for example sold by the company DRT under the name Dercolyte with regard to the polylimonene resins, by the company Neville Chemical Company under name Super Nevtac, by Kolon under the name Hikorez or by the company Exxon Mobil under the name Escorez for the C ₅ cut resins / styrene or C ₅ cut resins / C ₉ cut, or by the company Struktol under the name 40 MS or 40 NS (mixtures of aromatic and / or aliphatic resins).

Advantageously, the level of plasticizing resin having a glass transition temperature greater than 20 ° C. in the composition of the tread according to the invention is included in a range ranging from 10 to 50 phr, preferably from 20 to 45 pce.

11-4.2 Liquid plasticizer at 23 ° C. [0126] Although this is not necessary for the implementation of the present invention, the plasticizer system for the rubber composition of the tread of the tire according to invention may include a plasticizer liquid at 23 ° C, called "low Tg", that is to say which by definition has a Tg less than -20 ° C, preferably less than -40 ° C. According to the invention, the composition can optionally comprise from 0 to 50 phr of a plasticizer liquid at 23 ° C.

When a plasticizer liquid at 23 ° C is used, its rate in the composition of the tread according to the invention can be within a range ranging from 10 to 45 phr, preferably from 15 to 30 phr.

Any plasticizer liquid at 23 ° C (or extension oil), whether of an aromatic or non-aromatic nature, known for its plasticizing properties with respect to diene elastomers, can be used. At room temperature (23 ° C), these more or less viscous plasticizers or oils are liquids (that is to say, substances having the capacity to take the form of their container in the long term) , as opposed in particular to plasticizing resins which are by nature solid at room temperature.

Particularly suitable are the plasticizers liquid at 23 ° C chosen from the group comprising or consisting of liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE oils, MES oils (Medium Extracted Solvates), TDAE oils (Treated Distillate Aromatic Extracts), RAE oils (Residual Aromatic Extract oils), TRAE oils (Treated Residual Aromatic Extract) and SRAE oils (Safety Residual Aromatic Extract oils), mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these plasticizers liquid at 23 ° C.

For example, the plasticizer liquid at 23 ° C can be a petroleum oil, preferably non-aromatic. A liquid plasticizer is qualified as non-aromatic when it has a content of polycyclic aromatic compounds, determined with the extract in DMSO according to the IP 346 method, of less than 3% by weight, relative to the total weight of the plasticizer. .

The plasticizer liquid at 23 ° C can also be a liquid polymer resulting from the polymerization of olefins or dienes, such as polybutenes, polydienes, in particular polybutadienes, polyisoprenes (also known under the name "LIR ”) Or copolymers of butadiene and isoprene, or alternatively copolymers of butadiene or isoprene and styrene or mixtures of these liquid polymers. The number-average molar mass of such liquid polymers is preferably within a range from 500 g / mol to 50,000 g / mol, preferably from 1,000 g / mol to 10,000 g / mol. By way of example, mention may be made of the "RICON" products from SARTOMER.

When the liquid plasticizer at 23 ° C is a vegetable oil, it may for example be an oil chosen from the group comprising or consisting of linseed, safflower, soybean, corn, cotton, shuttle oil, castor, abrasive, pine, sunflower, palm, olive, coconut, peanut, grape seed and mixtures of these oils. Vegetable oil is preferably rich in oleic acid, that is to say that the fatty acid (or all of the fatty acids if several are present) from which it is derived, comprises oleic acid according to a mass fraction. at least equal to 60%, even more preferably according to a mass fraction at least equal to 70%. As vegetable oil, a sunflower oil is advantageously used which is such that all of the fatty acids from which it is derived comprises oleic acid according to a mass fraction equal to or greater than 60%, preferably 70% and, according to a particularly advantageous embodiment of the invention, according to a mass fraction equal to or greater than 80%.

According to another particular embodiment of the invention, the liquid plasticizer is a triester chosen from the group consisting of triesters of carboxylic acid, phosphoric acid, sulfonic acid and mixtures of these triesters.

As an example of phosphate plasticizers, mention may be made of those which contain between 12 and 30 carbon atoms, for example trioctyl phosphate. Mention may in particular be made, as examples of plasticizers of esters of carboxylic acid, of the compounds chosen from the group consisting of trimellitates, pyromellitates, phthalates, 1,2-cyclohexane dicarboxylates, adipates, azelates, sebacates , glycerol triesters and mixtures of these compounds. Among the above triesters, mention may in particular be made of glycerol triesters, preferably consisting mainly (for more than 50%, more preferably for more than 80% by weight) of a Ci ₈ unsaturated fatty acid, it is ie chosen from the group consisting of oleic acid, linoleic acid, linolenic acid and mixtures of these acids. The glycerol triester is preferred. More preferably, whether it is of synthetic or natural origin (case for example of vegetable oils of sunflower or rapeseed), the fatty acid used consists [0135] [0136] [0137] [0138] [0139] [0141] for more than 50% by weight, more preferably still for more than 80% by weight of oleic acid. Such triesters (trioleates) with a high oleic acid content are well known, they have been described for example in application WO 02/088238, as plasticizers in tire treads.

When the liquid plasticizer at 23 ° C is an ether plasticizer, it may for example be polyethylene glycol or polypropylene glycol.

Preferably, the plasticizer liquid at 23 ° C is chosen from the group comprising or consisting of MES oils, TDAE oils, naphthenic oils, vegetable oils and mixtures of these mixtures of these plasticizers liquid at 23 ° C. More preferably, the plasticizer which is liquid at 23 ° C. is a vegetable oil, preferably a sunflower oil.

Advantageously, the composition of the tread according to the invention does not include a plasticizer at 23 ° C.

II-4.3 Viscous plasticizing resin at 20 ° C

Although this is not necessary for the implementation of the present invention, the plasticizer system of the rubber composition of the tread of the tire according to the invention may comprise a viscous plasticizer resin at 20 ° C, called "de low Tg ”, that is to say which by definition has a Tg comprised in a range from -40 ° C. to -20 ° C. According to the invention, the composition can optionally comprise, in addition to or in substitution for all or part of the liquid plasticizer at 23 ° C, from 0 to 140 phr of viscous plasticizing resin at 20 ° C.

Preferably, the viscous plasticizing resin at 20 ° C. exhibits at least any one, preferably 2 or 3, preferably all, of the following characteristics:

- A Tg of between -40 ° C and 0 ° C, more preferably between -30 ° C and 0 ° C and more preferably still between -20 ° C and 0 ° C;

- a number average molecular mass (Mn) of less than 800 g / mol, preferably less than 600 g / mol and more preferably less than 400 g / mol;

- A softening point in a range from 0 to 50 ° C, preferably from 0 to 40 ° C, more preferably from 10 to 40 ° C, preferably from 10 to 30 ° C;

- a polymolecularity index (Ip) less than 3, more preferably less than 2 (reminder: Ip = Mw / Mn with Mw average molecular weight by weight).

The preferred viscous plasticizing resins at 20 ° C above are well known to those skilled in the art and available commercially, for example sold with regard to:

[0142] [0143] [0144] [0145] [0146] [0147]

- aliphatic resin: by the company CRAY VALLEY under the name * Wingtack 10 "(Mn = 480 g / mol; Mw = 595 g / mol; Ip = 1.2; SP = 10 ° C; Tg = -28 ° C);

- indene coumarone resins: by the company Rutgers Chemicals under the name "Novares C30" (Mn = 295 g / mol; Mw = 378 g / mol; Ip = 1.28; SP = 25 ° C; Tg = -19 ° C);

- C9 cutting resins: by the company Rutgers Chemicals under the name "Novares TT30" (Mn = 329 g / mol; Mw = 434 g / mol; Ip = 1.32; SP = 25 ° C; Tg = -12 ° C) .

When a viscous plasticizing resin at 20 ° C is used, its content in the composition of the tread according to the invention can be included in a range ranging from 20 to 120 phr, preferably from 40 to 90 phr.

Very advantageously, the total level of liquid plasticizer at 23 ° C and viscous plasticizer resin at 20 ° C is within a range from 0 to 50 phr, preferably from 10 to 45 phr, preferably from 15 to 30 phr.

II-5 Other possible additives

The rubber compositions of the tread of the tire according to the invention can optionally also include all or part of the usual additives usually used in elastomer compositions for tires, such as for example plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical antiozonants, antioxidants, anti-fatigue agents, reinforcing resins (as described for example in application WO 02/10269).

II-6 Preparation of rubber compositions

The composition in accordance with the invention can be produced in suitable mixers, using two successive preparation phases well known to those skilled in the art:

- a first thermomechanical working phase or kneading (so-called “non-productive” phase), which can be carried out in a single thermomechanical step during which one introduces, into a suitable mixer such as a usual internal mixer (for example of 'Banbury' type), all the necessary constituents, in particular the elastomeric matrix, any fillers, any other miscellaneous additives, with the exception of the vulcanization system. The incorporation of the possible filler into the elastomer can be carried out once or several times by thermomechanically kneading. The non-productive phase can be carried out at high temperature, up to a maximum temperature between 110 ° C and 200 ° C, preferably between 130 ° C and 185 ° C, for a period generally between 2 and 10 minutes.

a second mechanical working phase (so-called “productive” phase), which is carried out in an external mixer such as a cylinder mixer, after the mixture obtained during the first non-productive phase has cooled to a lower temperature, typically below 120 ° C, for example between 40 ° C and 100 ° C. The vulcanization system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min.

[0148] Such phases have been described for example in applications EP-A-0501227, EPA-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

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

The composition can be either in the raw state (before vulcanization), or in the cooked state (after vulcanization), can be a semi-finished product which can be used in a tire.

The vulcanization of the composition can be carried out in a manner known to the skilled person, for example at a temperature between 130 ° C and 200 ° C, under pressure.

II-7 Tread and tire [0153] In known manner, the tread of a tire, whether it is intended to equip a passenger vehicle or other, comprises a tread surface intended to be in contact with the ground when the tire is rolling. The tread is provided with a tread comprising in particular tread elements or elementary blocks delimited by various main grooves, longitudinal or circumferential, transverse or even oblique, the elementary blocks being able moreover to have various incisions or finer lamellae. The grooves constitute channels intended to evacuate water during rolling on wet ground and the walls of these grooves define the leading and trailing edges of the tread elements, depending on the direction of the turn.

According to the invention, the tread can be made of a single composition. It can also, and advantageously, comprise several portions (or layers), for example two, superimposed in the radial direction. In other words, the portions (or layers) are parallel, at least substantially, to each other, as well as to the tangential (or longitudinal) plane, plane defined as being orthogonal to the radial direction.

Thus, the composition according to the invention can be present in the entire tread according to the invention.

Preferably, the tread comprises at least one radially inner portion and a radially outer portion, the composition according to the invention advantageously being present in a radially inner portion of the tread of the tire according to the invention. In this case, the radially outer portion of the tread is preferably made up of a composition different from that according to the present invention. The tread can also comprise two compositions which are different from each other but both conform to the present invention, one being present in a radially outer portion of the tread, the other in a radially inner portion.

A tire having a geometry of revolution relative to an axis of rotation, its geometry is usually described in a meridian plane containing the axis of rotation of the tire. For a given meridian plane, the radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to the meridian plane. By convention, the expressions “radially interior, respectively radially exterior” mean “closer, respectively farther from the axis of rotation of the tire”. By "axially interior, respectively axially exterior" is meant "closer, respectively farther from the equatorial plane of the tire", the equatorial plane of the tire being the plane passing through the middle of the tire rolling surface and perpendicular to the axis of rotation of the tire.

[0158] Preferably, the tread of the tire according to the invention:

- has an axial width L and being constituted by a radial superposition of a first portion and of a second portion radially external to the first portion,

the first portion being constituted by a single layer Ci,

the layer Ci having a radial thickness E _h measured in an equatorial plane (XZ) of the tire, substantially constant over at least 80% of the axial width L of the tread, and consisting of a composition in accordance with the invention ,

the second portion being constituted by a single layer C ₂ ,

the layer C ₂ having a radial thickness E ₂ , measured in the equatorial plane (XZ) of the tire, substantially constant over at least 80% of the axial width L of the tread, and consisting of a rubber composition C ₂ different from the composition according to the invention.

The radially inner portion of the tread does not, by definition, come into contact with the ground when the tire is new or when the radially outer portion of the tread is not sufficiently worn. On the other hand, the radially inner portion of the tread is intended to be in contact with the ground after wear of the radially outer portion of the tread. A person skilled in the art therefore clearly understands that the most radially outer part of the radially inner portion of the tread according to the invention is advantageously located above the wear indicator of the tread of the tire.

Advantageously, the thickness of the radial thickness E ₂ of the second portion of the tire is in a range from 4 to 8 mm, preferably from 4.5 to 7.5 mm.

Furthermore, the radial thickness thickness Ei of the first portion of the tire is in a range from 1 to 5 mm, preferably from 1.5 to 4.5 mm.

The invention particularly relates to tires intended to equip motor vehicles of the tourism and SUV (Sport Utility Vehicles) type.

The invention relates to tires both in the raw state (that is to say, before baking) and in the baked state (that is to say, after vulcanization).

III- BRIEF DESCRIPTION OF THE SINGLE FIGURE [0164] [fig.l]

On Ligure 1, a meridian section of the top of a tire is represented.

1, comprising a tread 2, intended to come into contact with a ground. The directions XX ’, YY’ and ZZ ’are the circumferential, axial and radial directions of the tire, respectively. The XZ plane is the equatorial plane of the tire. The tread, having an axial width L, is constituted by a radial superposition of a first portion 21 and of a second portion 22 radially external to the first portion 21.

The second portion 21 is constituted by a single layer Ci, the layer Ci having a radial thickness E _b measured in the equatorial plane XZ of the tire, substantially constant over at least 80% of the axial width L of the tread.

2, and being constituted by a polymeric material 1.

The second portion 22 consists of a single layer C ₂ , the layer C ₂ having a radial thickness E ₂ , measured in the equatorial plane XZ of the tire, substantially constant over at least 80% of the axial width L of the tread 2.

Radially inside the first radially inner portion 21, there is shown the crown block 3, comprising two crown layers comprising reinforcements, preferably textile. Radially inside the crown reinforcement 3 is shown the carcass reinforcement 4 comprising a carcass layer.

[0168] [0169] [0170] [0171] [0172] [0173] [0174]

IV- PREFERRED EMBODIMENTS

In view of the above, the preferred embodiments of the invention are described below:

A. A tire whose tread comprises a rubber composition based on at least one elastomeric matrix, a reinforcing filler and a vulcanization system, in which the elastomeric matrix comprises:

- from 35 to 95 parts by weight per hundred parts by weight of elastomer, pce, of a first diene elastomer, said first diene elastomer being a copolymer based on butadiene and styrene, which copolymer comprising within its structure at at least one alkoxysilane group linked to the elastomer by the silicon atom, and at least one function comprising a nitrogen atom, and having a glass transition temperature below -70 ° C.,

- from 5 to 40 phr of a second elastomer, said second diene elastomer being isoprene elastomer, and

- optionally from 0 to 40 phr of a third diene elastomer.

B. A tire according to embodiment A, in which the first diene elastomer is a butadiene-styrene copolymer.

C. A tire according to any one of the preceding embodiments, in which the alkoxysilane group comprises an alkoxylated radical, optionally partially or totally hydrolyzed in hydroxyl, in Ci-Cio, or even in Ci-C ₈ , preferably in C1-C4 , more preferably methoxy and ethoxy.

D. A tire according to any one of the preceding embodiments, in which the function comprising a nitrogen atom is located at the end of the chain and is directly connected to the elastomer via a covalent bond or a group hydrocarbon.

E. A tire according to any one of the preceding embodiments, in which the function comprising a nitrogen atom is carried by the silicon of the alkoxysilane group, directly or through a spacer group defined as being an atom or a divalent hydrocarbon radical, linear or branched, aliphatic in Ci-Cis, saturated or not, cyclic or not, or a divalent aromatic hydrocarbon radical in C ₆ -Ci ₈ , said spacer group optionally containing one or more aromatic radicals and / or a or more heteroatoms.

F. A tire according to any one of the preceding embodiments, in which the alkoxysilane group is represented by the formula (* -) _a Si (OR ') _b R _c X in which,

- * - represents the bond to an elastomer chain;

- the radical R represents a substituted or unsubstituted alkyl radical in C _r Cio, [0175] [0176] [0177] [0178] [0179] or even in C _r C ₈ , preferably a C ₁ -C ₄ alkyl radical ₄ , more preferably methyl and ethyl;

- in the alkoxylated radical (s) of formula -OR ', optionally partially or totally hydrolyzed to hydroxyl, R' represents an alkyl radical, substituted or unsubstituted, being C _r Cio, or even C _r C ₈ , preferably a radical alkyl-C _4, more preferably methyl and ethyl;

- X represents a group including the function comprising a nitrogen atom;

- a is 1 or 2, b is 1 or 2, and c is 0 or 1, provided that a + b + c = 3.

G. A tire according to any one of the preceding embodiments, in which the function comprising a nitrogen atom is chosen from primary amines, protected or not, secondary, protected or not, or tertiary, cyclic or not.

H. A tire according to any one of embodiments A to F, in which the function comprising a nitrogen atom is a tertiary amine function, preferably diethylamine or dimethylamine.

I. A tire according to any one of the preceding embodiments, in which the first diene elastomer is mainly functionalized in the middle of the chain by an alkoxysilane group, linked to the two branches of the first diene elastomer via the atom of silicon, the alkoxy radical being optionally partially or completely hydrolyzed to hydroxyl.

J. A tire according to any one of the preceding embodiments, in which the first diene elastomer has a glass transition temperature in a range from -105 ° C to -70 ° C, preferably from -100 ° C to -75 ° C, preferably from -95 ° C to -80 ° C.

K. A tire according to any one of the preceding embodiments, in which at least two, preferably at least three, preferably at least four, of the following characteristics are met:

the function comprising a nitrogen atom is a tertiary amine, more particularly a diethylamino- or dimethylamino- group,

the function comprising a nitrogen atom is carried by the alkoxysilane group via a spacer group defined as an aliphatic C _r Cio hydrocarbon radical, more preferably still the linear C ₂ or C ₃ hydrocarbon radical,

the alkoxysilane group is a methoxysilane or an ethoxysilane, optionally partially or completely hydrolyzed to silanol,

the first diene elastomer is a butadiene-styrene copolymer,

- The first diene elastomer is mainly functionalized in the middle of [0180] [0181] [0182] [0183] [0184] [0185] [0186] [0187] chain by an alkoxysilane group linked to the two branches of the first diene elastomer by l 'intermediary of the silicon atom,

- The first diene elastomer has a glass transition temperature in a range from -105 ° C to -70 ° C.

L. A tire according to any one of embodiments A to J, in which all of the following characteristics are met:

the function comprising a nitrogen atom is a tertiary amine, more particularly a diethylamino- or dimethylamino- group,

the function comprising a nitrogen atom is carried by the alkoxysilane group via a linear C ₃ aliphatic hydrocarbon radical,

the alkoxysilane group is methoxysilane or ethoxysilane, optionally partially or totally hydrolyzed to silanol,

the first diene elastomer is a butadiene-styrene copolymer,

the first diene elastomer is mainly functionalized in the middle of the chain by an alkoxysilane group linked to the two branches of the first diene elastomer by means of the silicon atom,

- The first diene elastomer has a glass transition temperature in a range from -95 ° C to -80 ° C.

M. Pneumatics according to any one of the preceding embodiments, in which the level of the first diene elastomer in the composition is in a range from 40 to 80 phr.

N. A tire according to any one of the preceding embodiments, in which the second elastomer is a polyisoprene comprising a mass rate of 1,4-cis bonds of at least 90% of the mass of the polyisoprene.

O. A tire according to embodiment N, in which the polyisoprene is chosen from the group consisting of natural rubber, synthetic polyisoprenes and their mixtures.

P. A tire according to embodiment N or M, in which the polyisoprene is a natural rubber.

Q. A tire according to any one of the preceding embodiments, in which the level of the second diene elastomer in the composition is in a range from 10 to 35 phr.

R. A tire according to any one of the preceding embodiments, in which the third diene elastomer is chosen from the group consisting of polybutadienes, butadiene copolymers and their mixtures.

S. A tire according to any one of the preceding embodiments, in which the level of the third diene elastomer in the composition is within a range going from 5 to 35 phr.

T. Pneumatic tire according to any one of the preceding embodiments, in which the total rate of the first, second and third diene elastomer, preferably the first and second diene elastomer, in the composition, is included in a range from 80 to 100 phr, preferably from 90 to 100 phr, more preferably from 100 phr.

[0189] U. A tire according to any one of the preceding embodiments, in which the reinforcing filler comprises a carbon black, a reinforcing inorganic filler or one of their mixtures.

V. A tire according to any one of the preceding embodiments, in which the reinforcing filler mainly comprises a reinforcing inorganic filler.

W. Pneumatic according to the embodiment U or V, in which the reinforcing inorganic filler is silica.

X. A tire according to any one of embodiments U to W, in which the rate of reinforcing inorganic filler in the composition is included in a range from 90 to 200 phr, preferably from 95 to 180 phr, preferably from 100 to 150 pce.

Y. A tire according to any one of embodiments U to X, in which the level of carbon black in the composition is within a range ranging from 0 to 40 phr, preferably from 1 to 20 phr, preferably from 2 to 10 pce.

Z. A tire according to any one of the preceding embodiments, in which the vulcanization system is based on sulfur or on a sulfur donor.

[0195] AA. Tire according to any one of the preceding embodiments, in which the composition further comprises at least one plasticizing resin having a glass transition temperature above 20 ° C.

BB. A tire according to embodiment AA, in which the plasticizing resin having a glass transition temperature above 20 ° C. is chosen from the group consisting of homopolymer or copolymer resins of cyclopentadiene, homopolymer resins or copolymer of dicyclopentadiene , terpene homopolymer or copolymer resins, C ₅ cut homopolymer or copolymer resins, C ₉ cut homopolymer or copolymer resins, alpha-methyl-styrene homopolymer or copolymer resins and their mixtures.

CC. Tire according to embodiment AA or BB, in which the level of plasticizing resin having a glass transition temperature greater than 20 ° C., in the composition is within a range ranging from 10 to 45 phr, preferably from 15 to 30 pce.

DD. A tire according to any one of the preceding embodiments, in which the composition also comprises optionally comprises from 0 to 50 phr of plasticizer liquid at 23 ° C.

EE. Tire according to embodiment DD, in which the plasticizer liquid at 23 ° C. is chosen from the group consisting of liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE oils, MES oils, TDAE oils, RAE oils, TRAE oils, SRAE oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures thereof.

[0200] FF. A tire according to any one of the preceding embodiments, in which the tread comprises at least one radially inner portion and a radially outer portion, the composition being present in a radially inner portion of the tread.

GG. A tire according to the embodiment FF, in which the radially outer portion has a radial thickness E ₂ lying in a range from 4 to 8 mm, preferably from 4.5 to 7.5 mm.

HH. A tire according to the embodiment FF or GG, in which the radially inner portion has a radial thickness Ei lying in a range from 1 to 5 mm, preferably from 1.5 to 4.5 mm.

H. A tire according to any one of embodiments FF to HH, in which the radially outer portion comprises a rubber composition different from the composition of the radially inner portion.

V- EXAMPLES [0204] V-l Measurements and tests used [0205] Dynamic properties:

The dynamic properties G * and tan (ô) Max are measured on a viscoanalyzer (Metravib VA4000), according to standard ASTM D5992-96. The response of a sample of vulcanized composition (2 mm thick cylindrical specimen and 79 mm ² cross section) is recorded, subjected to a sinusoidal stress in alternating single shear, at the frequency of 10 Hz, under normal conditions of temperature (23 ° C) or at 0 ° C according to ASTM D 1349-09 for tan (ô) Max measurements, or at 20 ° C for G * measurements. A deformation amplitude sweep is carried out from 0.1% to 50% (outward cycle), then from 50% to 0.1% (return cycle). For the return cycle, the maximum value of tan d observed (tan (d) max) is indicated, as well as the difference in complex modulus (DG *) between the values at 0.1% and 50% deformation (effect Payne).

The results used are the tan (ô) Max loss factors at 0 ° C and 23 ° C, as well as the complex dynamic shear modulus G * at -20 ° C.

The results of tan (ô) Max at 0 ° C are expressed in base 100, the value 100 being assigned to the control. A result greater than 100 indicates improved performance, that is to say that the composition of the example considered reflects better grip on wet ground of the tread comprising such a composition.

The results of tan (ô) Max at 23 ° C and G * at -20 ° C are expressed in base 100, the value 100 being assigned to the control. A result less than 100 indicates improved performance, that is to say that the composition of the example considered respectively reflects better rolling resistance and better grip on snow-covered ground of the tread comprising such a composition.

Abrasion resistance [0211] The abrasion resistance obtained by determining the volume loss by abrasion is measured according to standard NE ISO 4649 of November 2010 which consists in determining the volume loss of a sample after displacement of 40 linear meters on standardized abrasive paper.

More particularly, the determination of the loss of volume by abrasion is carried out according to the indications of standard NL ISO 4649 of November 2010 (method B), using an abrasimeter where the cylindrical specimen is subjected to the action of '' an abrasive cloth of grains P60 and fixed on the surface of a drum rotating under a contact pressure of 5 N (N = Newton) and for a stroke of 40 m. A loss in mass of the sample is measured and the loss in volume is calculated from the density (p) of the material constituting the test piece. The density (p) of the material constituting the test piece is conventionally obtained on the basis of the mass fractions of each constituent of the material and their respective density (p).

The results are shown in base 100. The arbitrary value 100 being assigned to the control composition makes it possible to compare the volume of loss of substance of the various compositions tested. The value expressed in base 100 for the composition tested is calculated according to the operation: (measured value of the volume of loss of substance of the control composition / measured value of the volume of loss of substance of the composition tested) X 100. In this way , a result greater than 100 will indicate a decrease in volume loss and therefore an improvement in abrasion resistance, which corresponds to an improvement in wear resistance performance. Conversely, a result of less than 100 will indicate an increase in volume loss and therefore a decrease in abrasion resistance, which corresponds to a decrease in wear resistance performance.

[0214] Raw tack (or tack):

[0215] Tack is the ability of an assembly of unvulcanized mixtures to resist tearing stress.

Is used for the measurement of raw tack (CAC or tack) a test device is inspired by the probe tack tester (ASTM D2979-95). An Instron traction machine is used comprising a fixed metal jaw and a movable metal jaw. A first test piece made of a 3mm thick mixing film is bonded to the fixed jaw. A second test piece made of a 3mm thick mixing film is bonded to the movable jaw. The mixing films are bonded to the surface of the metal jaws with a double-sided adhesive (Tesafix® 4970).

For the preparation of the mixing test pieces, the mixing films are obtained by calendering to a thickness of 3 mm. The test pieces are cut using a 1 cm diameter cookie cutter.

The principle of the measurement consists in bringing the two mixing films into contact for 5 seconds by applying a compression force of 40 N. After this contact phase, they are separated by driving the cross member of the traction machine . The speed of movement of the cross member in this tearing phase is lmm / s. The displacement of the cross-member and the force are measured continuously as a function of time during the contact and tear-off phases.

The result of raw tights (CAC) is the measurement of the maximum force (in Newton, N) reached during the tearing. A value of 9 N and above is desirable for the present invention.

The CAC results are expressed in base 100, the value 100 being assigned to the witness. A result greater than 100 indicates improved performance, that is to say better adhesion of the composition to its support.

V-2 Preparation of the compositions [0222] 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 speed of pallets of 50 revolutions per minute until reaching a maximum drop temperature of 160 °. vs. The "productive" phase was carried out in a cylinder tool at 23 ° C for 5 minutes.

V-3 Tests of rubber compositions [0224] The examples presented below are intended to compare the performance compromise between rolling resistance, grip on wet ground, grip on snowy ground, the abrasion resistance and raw tights of seven compositions in accordance with the present invention (C1 to C7) with five control compositions (T1 to T5).

The formulations tested all contain an elastomeric matrix the nature and contents of which are presented in Table 1 below, 120 phr of “Zeosil 1165 MP” silica from the company Rhodia of the “HDS” type, 9.6 phr of liquid silane TESPT (“Si69” from Degussa) as coupling agent for silica to elastomers, 4 phr of carbon black Grade ASTM N234 from Cabot, 19 phr of glycerol trioleate (sunflower oil 85% by weight of oleic acid) "Lubrirob Tod 1880" from the company Novance, 2 pce of anti-ozone wax ("VARAZON 4959" from the company Sasol

Wax), 3 pce of antioxidant (Nl, 3-dimethylbutyl-N-phenylparaphenylenediamine, "Santoflex 6-PPD" from Flexsys), 47 pce of plasticizing resin (C5 / C9 resin, "ECR-373 resin "From the company ExxonMobil), 3 pce of stearic acid (" Pristerene 4931 "from the company Uniqema), 2 pce of Diphenylguanidine" Perkacit DPG "from the company Flexsys, 1.4 pce of sulfur, 1.6 pce of N -cyclohexyl-2-benzothiazol-sulfenamide (“Santocure CBS” from the company Flexsys) as a vulcanization accelerator, and 1.5 phr of industrial grade zinc oxide (company Umicore). The properties of these formulations are also presented in Table 1 below.

The control compositions differ from composition C1 only by the nature of the copolymer based on butadiene and styrene.

Compositions C2 to C4 make it possible to study the impact of the respective levels of butadiene-styrene-based copolymer and of polyisoprene of the compositions in accordance with the invention on the abovementioned performance compromise.

The compositions C5 to C7 show the impact of the addition of polybutadiene in the compositions according to the invention.

[Tables 1]

Cl Tl T2 T3 T4 T5 C2 C3 C4 C5 C6 C7 NR (a) 25 25 25 25 25 25 5 40 15 25 15 25 SBR 1 (b) 75 - - - - - 95 60 85 45 75 50 SBR 2 (c) - 75 - SBR 3 (d) - - 75 - - - - - - - - - SBR 4 (e) - - - 75 - - - - - - - - SBR 5 (f) - - - - 75 - - - - - - - SBR 6 (g) - - - - - 75 - - - - - - BR (h) - - - - - - - - - 30 10 25 tan (ô) max to 23 ° C 100 107 103 118 143 129 98 102 98 105 99 106 tan (ô) max at 0 ° C 100 124 118 168 258 170 96 106 98 100 93 99 G * at -20 ° C 100 249 188 782 3990 850 91 115 93 77 66 71 Abrasion 100 65 55 8 -57 -27 98 96 120 100 100 100 CAC 100 104 125 108 103 157 80 128 112 136 120 139

at. Natural rubber

b. SBR 1: SBR with 3% of styrene unit and 13% of unit 1,2 of the butadiene part, and carrying an amino-alkoxysilane function in the middle of the elastomer chain (Tg -88C)

vs. SBR2: SBR (starred Sn) with 15.5% of styrene unit and 24% of unit 1,2 of the butadiene part, and carrying a silanol function at the end of the elastomer chain (Tg -65 ° C)

d. SBR 3: SBR with 25% of styrene unit and 24% of unit 1,2 of the butadiene part, and carrying an amino-alkoxysilane function in the middle of the elastomer chain (Tg -65C)

e. SBR 4: SBR (starred Sn) with 26% of styrene unit and 24% of unit 1,2 of the butadiene part, and carrying a silanol function at the end of the elastomer chain (Tg -48 ° C)

f. SBR 5: SBR (starred Sn) with 25% of styrene unit and 58% of unit 1,2 of the butadiene part, and carrying a silanol function at the end of the elastomer chain (Tg -24 ° C)

g. SBR 6: SBR (star 3-tris-ditertiobuty (phenyl phosphite) with 26.5% of styrene unit and 24% of unit 1,2 of the butadiene part, and not functionalized (Tg -48 ° C)

h. BR: Polybutadiene with 0.5% of 1,2 unit and 97% of 1,4-cis (Tg = -108 ° C) [0229] These results show that the substitution of the copolymer based on styrene and butadiene in accordance with the invention by a copolymer based on styrene and butadiene not in accordance with the invention, in a composition also comprising polyisoprene, systematically causes a loss of performance in abrasion resistance, adhesion on snow-covered ground and potentially in resistance to rolling. Furthermore, it has been found that when the compositions comprise 5 phr of polyisoprene, the raw tack properties are acceptable limits for a partially radially inner use of tread. In addition, at 40 phr of polyisoprene, the performance compromise is still observed but is no longer optimal. Finally, the experiments carried out have shown that the addition of polybutadiene in the compositions according to the invention makes it possible to further improve the aforementioned performance compromise, in particular from the point of view of grip on snow-covered ground and raw tights.

Claims (1)

Tire whose tread comprises a rubber composition based on at least one elastomeric matrix, a reinforcing filler and a vulcanization system, in which the elastomeric matrix comprises: - from 35 to 95 parts by weight per hundred parts by weight of elastomer, pce, of a first diene elastomer, said first diene elastomer being a copolymer based on butadiene and styrene, which copolymer comprising within its structure at at least one alkoxysilane group linked to the elastomer by the silicon atom, and at least one function comprising a nitrogen atom, and having a glass transition temperature below -70 ° C, - from 5 to 40 phr of a second elastomer, said second diene elastomer being isoprene elastomer, and - optionally from 0 to 40 phr of a third diene elastomer. A tire according to claim 1, in which at least two, preferably at least three, preferably at least four, of the following characteristics are met: the function comprising a nitrogen atom is a tertiary amine, more particularly a diethylamino or dimethylamino group, the function comprising a nitrogen atom is carried by the alkoxysilane group by means of a spacer group defined as an aliphatic C ₁ -C ₁₀ hydrocarbon radical, more preferably still the linear C ₂ or C ₃ hydrocarbon radical, the alkoxysilane group is a methoxysilane or an ethoxysilane, optionally partially or completely hydrolyzed to silanol, the first diene elastomer is a butadienestyrene copolymer, - the first diene elastomer is mainly functionalized in the middle of the chain by a linked alkoxysilane group to the two branches of the first diene elastomer via the silicon atom, - the first diene elastomer has a temperature of glass transition included in a range from -105 ° C to -70 ° C. [Claim 3] Tire according to any one of the preceding claims, in which the second elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and their mixtures. [Claim 4] Tire according to any one of the preceding claims, in which the third diene elastomer is chosen from the group consisting of polybutadienes, butadiene copolymers and their mixtures. [Claim 5] A tire according to any one of the preceding claims, in which the total level of the first, second and third diene elastomer, preferably the first and second diene elastomer, in the composition, is 100 phr. [Claim 6] Tire according to any one of the preceding claims, in which the reinforcing filler comprises a carbon black, an inorganic reinforcing filler or a mixture thereof. [Claim 7] A tire according to claim 6, in which the reinforcing filler mainly comprises a reinforcing inorganic filler. [Claim 8] A tire according to claim 6 or 7, in which the rate of reinforcing inorganic filler in the composition is within a range from 90 to 200 phr, preferably from 95 to 180 phr, preferably from 100 to 150 phr. [Claim 9] A tire according to any one of the preceding claims, in which the tread comprises at least one radially inner portion and a radially outer portion, the composition being present in a radially inner portion of the tread. [Claim 10] A tire according to claim 9, in which the radially outer portion comprises a rubber composition different from the composition of the radially inner portion. 1/1