FR3124798A1 - RUBBER COMPOSITION - Google Patents

Abstract

The invention relates to a rubber composition based on at least one diene elastomer, at least one reinforcing filler comprising mainly by weight a reinforcing inorganic filler, at least one agent for coupling the reinforcing inorganic filler to the diene elastomer, of at least one processing agent and of a cross-linking system, characterized in that the rate of agent for coupling the reinforcing inorganic filler to the diene elastomer is within a range ranging from 12 % to 18% by weight relative to the weight of the reinforcing inorganic filler and in that the processing agent consists essentially of a mixture of at least one carboxylic acid comprising from 4 to 28 carbon atoms and at least one aliphatic polyol comprising from 2 to 22 carbon atoms. The invention also relates to a tread or a tire comprising such a rubber composition.

Description

RUBBER COMPOSITION

The present invention relates to a rubber composition, in particular intended for the manufacture of a tread, in particular a tread for a tire, in particular for a passenger vehicle.

The tread is the part of the tire intended to come into contact with the ground via a tread surface. This tread is responsible for a large part of the tire's rolling resistance and handling. These contributions are of course very variable depending on the design of the tire, but an order of magnitude of around 50% can be reached.

The tire tread must therefore comply with a large number of technical requirements, among which are in particular rolling resistance, grip on wet ground, good road behavior (associated with good rigidity of the cured compositions), at the same time to good green properties such as the viscosity of rubber compositions in the green state (associated with the ease of industrial implementation of the compositions, also called processability).

However, it is well known to those skilled in the art that the improvement in performance for tires is often obtained to the detriment of its other performance.

For example, one way to give the tire high grip on wet surfaces is to use a rubber composition for the tread that has good hysteresis potential. However, at the same time, this tread must contribute to the lowest possible rolling resistance in order to limit the energy losses associated with rolling; that is to say, it must be as less hysterical as possible.

The improvement in rolling resistance has been made possible thanks to the use of new rubber compositions reinforced with inorganic fillers, in particular specific silicas of the highly dispersible type, capable of competing from the reinforcing point of view with a carbon black conventional pneumatic grade. These specific silicas of the highly dispersible type typically have a BET specific surface comprised in a range ranging from 100 to 250 m²/g.

However, the use of reinforcing inorganic fillers, although having a positive effect on the hysteretic properties of a rubber composition, is not without drawbacks. Indeed, because of their reciprocal affinity between them, the particles of reinforcing inorganic fillers agglomerate between them in the rubber composition having the consequence of limiting their dispersion and on the other hand of increasing the consistency in the raw state. rubber compositions therefore to make their industrial implementation (processability) more difficult than in the presence of carbon black. It is known to use agents for coupling the reinforcing inorganic filler to the diene elastomer in order to promote the dispersion of the reinforcing inorganic filler within the rubber composition. These agents for coupling the inorganic filler to the diene elastomer are expensive compounds which increase the cost price of the rubber composition in which they are incorporated. In addition, in order not to risk influencing other interactions of the constituents of the rubber composition, those skilled in the art know that it is desirable to use just the right quantity of coupling agent, either known manner an amount at most equal to 8% by mass relative to the mass of the reinforcing inorganic filler. Despite the use of agents for coupling the reinforcing inorganic filler to the diene elastomer, it is still sometimes necessary to improve the processability of rubber compositions.

In order to improve the raw processability of rubber compositions reinforced with inorganic fillers, it is known to use processing agents or plasticizers. Processing aids, also called "processing aids", are of a very varied chemical nature and, as their name suggests, improve the processability of rubber compositions. These are, for example, mineral oils, resins of petroleum origin, derivatives of fatty acids such as fatty acid esters, metal salt soaps, etc.

However, the use of processing agents can lead to a softening of the rubber composition, therefore reduced rigidity being synonymous with poorer road behavior of the tyre.

Thus, improving grip properties, in particular on wet ground, without penalizing rolling resistance and rigidity while maintaining good processability of the rubber composition remains a constant problem for tire designers.

The object of the present invention is to respond to this problem.

Continuing his research, the applicant has developed a particular rubber composition, based on at least one diene elastomer, at least one reinforcing filler mainly comprising a reinforcing inorganic filler, at least one coupling agent of the inorganic filler reinforcing the diene elastomer, at least one processing agent and at least one crosslinking system; this composition having a high rate of agent for coupling the reinforcing inorganic filler to the diene elastomer in combination with a specific processing agent; this rubber composition having good processability and improved hysteretic properties while retaining very good rigidity and very good grip on wet ground. Thus, the rubber compositions of the invention have a performance compromise – wet grip/hysteretic properties/rigidity/processability– improved compared to the compositions of the prior art.

A subject of the invention is therefore a rubber composition based on at least one diene elastomer, at least one reinforcing filler comprising mainly by weight a reinforcing inorganic filler, at least one coupling agent for the reinforcing inorganic filler to the diene elastomer, of at least one processing agent and of at least one crosslinking system, characterized in that the rate of agent for coupling the reinforcing inorganic filler to the diene elastomer is included in a range ranging from 12% to 18% by weight relative to the weight of the reinforcing inorganic filler and in that the processing agent consists essentially of a mixture of at least one carboxylic acid comprising from 4 to 28 atoms of carbon and at least one aliphatic polyol containing from 2 to 22 carbon atoms.

The invention also relates to a tread comprising all or part of a composition defined above.

Another object of the present invention relates to a tire comprising such a rubber composition or such a tread.

Methods

Mooney Viscosity

An oscillating consistometer is used as described in the French standard ISO 289-1 (2015). The measurement of the Mooney index is done according to the following principle: the raw rubber composition (i.e., before curing) is molded in a cylindrical chamber heated to 100°C. After one minute of preheating, the rotor rotates within the specimen at 2 revolutions/minute and the useful torque to maintain this movement is measured after 4 minutes of rotation. The Mooney index (ML 1 +4) is expressed in “Mooney units” (UM, with 10.83 N.m (Newton.meter)).

The Mooney index results are expressed in terms of performance in base 100, i.e. the value 100 is arbitrarily assigned to the control, in order to consecutively compare the Mooney index of the different sample compositions tested (c i.e. their processability). The value in base 100 of the sample composition under test is calculated according to the operation: (value the Mooney index of the control / value the Mooney index of the sample) * 100. A result greater than 100 indicates improved performance , that is to say that the composition of the sample considered shows a decrease in its viscosity, corroborating better processability compared to the control composition.

Glass transition temperature

The glass transition temperatures (Tg) of elastomers and plasticizing resins are determined using a differential scanning calorimeter, according to standard ASTM D3418-99.

Microstructure analysis of elastomers

The microstructure of elastomers is characterized by the technique of near infrared spectroscopy (NIR).

Near-infrared (NIR) spectroscopy is used to quantitatively determine the mass content of styrene in the elastomer as well as its microstructure (relative distribution of 1,2, 1,4-trans and 1,4-cis butadiene units). The principle of the method is based on the Beer-Lambert law generalized to a multicomponent system. The method being indirect, it calls upon a multivariate calibration [Vilmin, F.; Dussap, C.; Coste, N. Applied Spectroscopy 2006, 60, 619-29] carried out using standard elastomers with a composition determined by 13C NMR. The styrene content and the microstructure are then calculated from the NIR spectrum of an elastomer film approximately 730 μm thick. The acquisition of the spectrum is carried out in transmission mode between 4000 and 6200 cm-1 with a resolution of 2 cm-1, using a near infrared spectrometer with Fourier transform Bruker Tensor 37 equipped with a cooled InGaAs detector by Peltier effect.

Dynamic properties:

The dynamic properties G* and tan(δ) are measured on a viscoanalyzer (Metravib VA4000), according to standard ASTM D5992-96. The response of a sample of vulcanized composition (cylindrical test piece 4 mm thick and 10 mm in diameter) subjected to a sinusoidal stress in simple alternating shear, at a frequency of 10 Hz, during a sweep is recorded. in temperature from -80°C to +100°C with a ramp of +1.5°C/min, under a maximum stress of 0.7 MPa. The value of the tangent of the loss angle (tan delta or tan(δ)) is then recorded at 0°. The value of the dynamic modulus G* is raised at 60°C. The results used are therefore the values of tan(δ) at 0°C and the complex dynamic shear modulus G* at 60°C obtained on the temperature scan at 0.7 MPa.

The results of tan(δ) at 0°C are expressed in terms of performance in base 100, i.e. the value 100 is arbitrarily assigned to the control, in order to consecutively compare the tan(δ) at 0° C (i.e. wet grip) of the various sample compositions tested. The value in base 100 of the sample composition tested is calculated according to the operation: (value of tan(δ) at 0°C of the sample / value tan(δ) at 0°C of the control) * 100. A result greater than 100 indicates improved performance, that is to say that the composition of the sample considered has better grip on wet ground compared to the control composition.

The results of G* at 60°C are expressed in terms of performance in base 100, i.e. the value 100 is arbitrarily assigned to the control, in order to consecutively compare the G* at 60°C (c' i.e. the stiffness and, therefore, the handling) of the different sample compositions tested. The value in base 100 of the sample composition tested is calculated according to the operation: (value of G* at 60°C of the control / value G* at 60°C of the sample) * 100. Therefore, a A score above 100 indicates improved performance, i.e. improved stiffness, corroborating improved handling performance.

The dynamic property tan(δ)max at 23° C. is measured on a viscoanalyzer (Metravib VA4000), according to standard ASTM D5992-96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm thick and 10 mm in diameter) subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under normal temperature conditions, is recorded. 23°C according to ASTM D 1349-09. A deformation amplitude scan is performed from 0.1% to 100% (go cycle), then from 100% to 0.1% (return cycle). The result used is the maximum of the tangent of the loss angle tan(δ) at 23°C on the return cycle, noted tan(δ)max at 23°C.

The results of tan(δ)max at 23°C are expressed in terms of performance in base 100, i.e. the value 100 is arbitrarily assigned to the control, in order to consecutively compare the tan(δ)max to 23°C (i.e. the hysteresis properties) of the various sample compositions tested. The value in base 100 for the sample is calculated according to the operation: (value of tan(δ)max at 23°C of the control / value tan(δ)max at 23°C of the sample) * 100. A A result greater than 100 indicates improved performance, that is to say that the composition of the sample under consideration exhibits improved hysteretic properties corroborating better rolling resistance: compared to the control rubber composition.

Definition

The expression "composition based on" means 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, less partially, during the various phases of manufacture of the composition; the composition thus possibly being in the totally or partially crosslinked state or in the non-crosslinked state.

By the expression “part by weight per hundred parts by weight of elastomer” (or pce), it is to be understood in the present description, the part, by mass per hundred parts by mass of elastomer.

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

On the other hand, any interval 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 interval of values denoted by the expression “from a to b” means the range of values going from a to b (that is to say including the strict limits a and b).

When reference is made to a "predominant" compound, it is meant in the present description 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 most large amount by mass among compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. In the same way, a so-called majority filler is the one representing the greatest mass among the fillers of the composition. By way of example, in a system comprising a single elastomer, this is predominant within the meaning of the present description; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers. Preferably, by majority is meant present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

The compounds mentioned in the description can be of fossil origin or biosourced. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. Obviously, the compounds mentioned can also come from the recycling of materials already used, that is to say that they can be, partially or totally, from a recycling process, or even obtained from raw materials themselves. even from a recycling process. This concerns in particular polymers, plasticizers, fillers, etc.

In the present description, the term “tire” is understood to mean a pneumatic tire or a non-pneumatic tire.

Description of the invention

An object of the present invention is a rubber composition based on at least one diene elastomer, at least one reinforcing filler comprising mainly by weight a reinforcing inorganic filler, at least one coupling agent for the reinforcing inorganic filler to the diene elastomer, of at least one processing agent and of at least one crosslinking system, characterized in that the rate of agent for coupling the reinforcing inorganic filler to the diene elastomer is included in a range ranging from 12% to 18% by weight relative to the weight of the reinforcing inorganic filler and in that the processing agent consists essentially of a mixture of at least one carboxylic acid comprising from 4 to 28 atoms of carbon and at least one aliphatic polyol containing from 2 to 22 carbon atoms.

diene elastomer

As indicated above, the rubber composition of the invention comprises at least one diene elastomer.

By “diene” elastomer (or rubber) without distinction, whether natural or synthetic, must be understood in a known manner an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not).

These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” generally means a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or units of diene origin (conjugated dienes) which is greater than 15% (% by moles); thus diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the above definition and may in particular be qualified as "essentially saturated" diene elastomers (rate of units of weak or very weak diene origin, always less than 15% in moles).

In the present application, the diene elastomers are by definition non-thermoplastic and are preferentially homopolymers or random copolymers.

By diene elastomer capable of being used in the compositions in accordance with the invention is meant in particular:

• any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms;
• any copolymer of a diene, conjugated or not, having 4 to 18 carbon atoms and at least one other monomer.

The other monomer can be an olefin or a diene, conjugated or not.

Suitable conjugated dienes are conjugated dienes having from 4 to 12 carbon atoms, in particular 1,3-dienes, such as in particular 1,3-butadiene and isoprene.

Suitable olefins are vinylaromatic compounds having 8 to 20 carbon atoms and aliphatic alpha-monoolefins having 3 to 12 carbon atoms.

Suitable vinylaromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial “vinyl-toluene” mixture, para-tert-butylstyrene.

As aliphatic alpha-monoolefins suitable are in particular acyclic aliphatic alpha-monoolefins having from 3 to 12 carbon atoms.

More particularly, the diene elastomer is:

• any homopolymer of a conjugated diene monomer, in particular any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;
• any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more vinylaromatic compounds having from 8 to 20 carbon atoms;
• a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated versions, in particular chlorinated or brominated, of this type of copolymer.
• any copolymer obtained by copolymerization of one or more dienes, conjugated or not, with an alpha-monoolefin.

Preferably, the diene elastomer is chosen from the group consisting of natural rubber (NR), synthetic isoprene elastomers, synthetic butadien elastomers and mixtures of these elastomers.

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

By “butadiene elastomer”, is meant in known manner a homopolymer or a copolymer of butadiene, in particular a diene elastomer chosen from the group consisting of polybutadienes (BR), the various copolymers of butadiene and mixtures of these elastomers. Among the butadiene copolymers, particular mention will be made of butadiene-styrene (SBR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene (SBIR) copolymers.

Preferably, the diene elastomer is a synthetic butadiene elastomer, more preferably still is a copolymer of styrene and butadiene.

Preferably, the synthetic butadiene elastomer, preferably the copolymer of styrene and butadiene, has a glass transition temperature measured according to standard ASTM D3418-99 of less than or equal to -50° C., preferably comprised in a range ranging from - 110°C to -50°C, more preferably still within a range ranging from -90°C to -50°C.

The diene elastomer can be modified, that is to say either coupled and/or star-shaped, or functionalized, or coupled and/or star-shaped and simultaneously functionalized.

Preferably, the diene elastomer, preferably the butadiene polymer, more preferably the copolymer of styrene and butadiene, can be functionalized and can comprise at least functional group. By functional group is meant a group comprising at least one heteroatom chosen from Si, N, S, O, P. Particularly suitable as functional groups are those comprising at least one polar function comprising at least one oxygen atom and being chosen the group consisting of silanol, alkoxysilanes whether or not bearing an amine group, epoxide, ethers, esters, carboxylic acids and hydroxyl.

Suitable functionalized elastomers are those prepared by the use of a functional initiator, in particular those bearing an amine function. Such functional elastomers and their methods of obtaining are known to those skilled in the art.

Also suitable as functionalized elastomers are those obtained by copolymerization of at least one diene monomer and one monomer bearing a function.

As functionalized elastomers, those obtained by post-polymerization modification by reaction with a functionalizing agent introducing at least one function within the structure of the elastomer are also suitable. Such functionalized elastomers and their methods of obtaining are known to those skilled in the art. Such a functionalization can thus be carried out conventionally by various reactions, for example by radical grafting on the diene elastomer, by 1,3-dipolar reaction on the diene elastomer, by reaction of the (pseudo) living diene elastomer obtained at the resulting from a polymerization, coordinative or anionic, with a functionalizing agent.

Preferably, the diene elastomer is a copolymer of butadiene and styrene, said copolymer comprising at least one alkoxysilane group bearing or not carrying another function.

This modified diene elastomer comprises within its structure at least one alkoxysilane group and at least one other function, the silicon atom of the alkoxysilane group being bonded to the elastomer chain or chains, the alkoxysilane group optionally being partially or totally hydrolyzed to silanol . In the present description, the notion of alkoxysilane group located within the structure of the elastomer is understood as a group whose silicon atom is located in the backbone of the polymer and directly connected to it. This positioning within the structure includes the ends of polymer chains. Thus, the terminal group is included in this notion. The alkoxysilane group is not a pendant group.

According to certain variants, the alkoxysilane group is mainly located at one end of the main chain of the elastomer.

According to other variants, the alkoxysilane group is mainly located in the main elastomer chain, it will then be said that the diene elastomer is coupled or even functionalized in the middle of the chain, as opposed to the position "at the end of the chain" and although the group is not located precisely in the middle of the elastomer chain. The silicon atom of this function connects the two branches of the main chain 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 whose composition 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 functionalized species at the end of the chain, coupled, starred and/or non-functionalized.

Advantageously, the first diene elastomer comprises, as 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 totally 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 comprises a C1-C10 alkoxyl radical, optionally partially or totally hydrolyzed to hydroxyl, or even C1-C8, preferably C1-C4, and is more preferably methoxy and ethoxy.

The other function is preferably carried by the silicon of the alkoxysilane group, directly or via a spacer group defined as being an atom or a group of atoms. Preferably, the spacer group is a linear or branched divalent hydrocarbon-based radical, C1-C18 aliphatic, saturated or not, cyclic or not, or a C6-C18 aromatic divalent hydrocarbon-based radical.

The other function is preferably a function comprising at least one heteroatom chosen from N, S, O, P. One can, by way of example, mention among these functions, primary, secondary or tertiary amines, cyclic or not, isocyanates, imines, cyanos, thiols, carboxylates, epoxides, primary, secondary or tertiary phosphines.

Thus, as secondary or tertiary amine function, mention may be made of amines substituted by C1-C10 alkyl radicals, preferably C1-C4 alkyl, more preferably a methyl or ethyl radical, or cyclic amines forming a heterocycle containing a nitrogen atom and at least one carbon atom, preferably 2 to 6 carbon atoms. For example, methylamino-, dimethylamino-, ethylamino-, diethylamino-, propylamino-, dipropylamino-, butylamino-, dibutylamino-, pentylamino-, dipentylamino-, hexylamino-, dihexylamino-, hexamethyleneamino- groups are suitable, preferably diethylamino groups. - and dimethylamino

By way of imine function, mention may be made of ketimines. For example, the groups (1,3-dimethylbutylidene)amino-, (ethylidene)amino-, (1-methylpropylidene)amino-, (4-N,N-dimethylaminobenzylidene)amino-, (cyclohexylidene)amino-, dihydroimidazole and imidazole.

Thus, as carboxylate function, mention may be made of acrylates or methacrylates. Such a function is preferably a methacrylate.

By way of epoxide function, mention may be made of epoxy or glycidyloxy groups.

As a secondary or tertiary phosphine function, mention may be made of phosphines substituted with C1-C10 alkyl radicals, preferably C1-C4 alkyl radicals, more preferably a methyl or ethyl radical, or else diphenylphosphine. For example, the methylphosphino-, dimethylphosphino-, ethylphosphino-, diethylphosphino, ethylmethylphosphino- and diphenylphosphino- groups are suitable.

The other function is preferably an amine, preferably a tertiary amine, more preferably a diethylamino- or dimethylamino- group. Thus, preferentially, the diene elastomer is a copolymer of butadiene and styrene, said copolymer comprising at least one alkoxysilane group bearing or not an amine function, preferentially bearing a secondary or tertiary amine function.

The alkoxysilane group can be represented by the formula (I)

(*—)aSi (OR’)bRcX (I)

in which :

• *— represents bonding to an elastomeric chain;
• the radical R represents a substituted or unsubstituted, C1-C10 or even C1-C8 alkyl radical, preferably a C1-C4 alkyl radical, more preferably methyl and ethyl;
• in the alkoxyl radical(s) of formula –OR', optionally partially or totally hydrolyzed to hydroxyl, R' represents an alkyl radical, substituted or unsubstituted, being C1-C10, or even C1-C8, preferably an alkyl radical in C1-C4, more preferably methyl and ethyl;
• X represents a group including the other function; preferably an amine, more preferably still a secondary or tertiary amine;
• a is 1 or 2, b is 1 or 2, and c is 0 or 1, 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 alkoxysilane 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.

Mention may be made, by way of function comprising a nitrogen atom, of 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 C1-C10 alkyl radicals, preferably C1-C4 alkyl, more preferably a methyl or ethyl radical, or cyclic amines forming a heterocycle containing a nitrogen atom and at least one carbon atom, preferably 2 to 6 carbon atoms. For example, methylamino-, dimethylamino-, ethylamino-, diethylamino-, propylamino-, dipropylamino-, butylamino-, dibutylamino-, pentylamino-, dipentylamino-, hexylamino-, dihexylamino-, hexamethyleneamino- groups are suitable, preferably diethylamino groups. - and dimethylamino-. Also suitable when the amine is cyclic are morpholine, piperazine, 2,6-dimethylmorpholine, 2,6-dimethylpiperazine, 1-ethylpiperazine, 2-methylpiperazine, 1-benzylpiperazine, piperidine, 3,3-dimethylpiperidine, 2,6- dimethylpiperidine, 1-methyl-4-(methylamino)piperidine, 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 pyrrolidine groups and hexamethyleneamine.

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

Advantageously, the functionalized butadiene elastomer that can be used in the context of the composition, preferably the copolymer of styrene and butadiene, has at least two, preferably at least three, preferably at least four, more preferably all of the following characteristics :

• the amine function is a tertiary amine, more particularly a diethylamino- or dimethylamino- group,
• the amine function is carried by the alkoxysilane group via a spacer group defined as an aliphatic C1-C10 hydrocarbon radical, more preferably still the linear C2 or C3 hydrocarbon radical,
• the alkoxysilane group is a methoxysilane or an ethoxysilane, optionally partially or totally hydrolyzed to silanol,
• said 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 silicon atom,
• said elastomer has a glass transition temperature of less than or equal to -50°C.

Particularly preferably, the functionalized butadiene elastomer which can be used in the context of the composition, preferably the copolymer of styrene and butadiene, has at least two, preferably at least three, preferably at least four, more preferably all of the following characteristics:

• 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 C3 linear aliphatic hydrocarbon radical,
• the alkoxysilane group is methoxysilane or ethoxysilane, optionally partially or totally hydrolyzed to silanol,
• said 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 silicon atom,
• said elastomer has a glass transition temperature comprised in a range ranging from -110°C to -50°C.

The functionalized diene elastomer, in particular the functionalized butadiene elastomer, more particularly the copolymer of butadiene and functionalized styrene, which can be used in the context of the present composition can be mainly obtained by functionalization of a living elastomer resulting from an anionic polymerization by a compound comprising an alkoxysilane group, chosen in particular from trialkoxysilane and dialkoxyalkylsilane compounds substituted by a group comprising another function linked directly or via a spacer group to the silicon atom, the function and the spacer group being such than defined above. 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 whose composition 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 functionalized species at the end of the chain, coupled, starred and/or non-functionalized. According to a particularly preferred variant, the modified diene elastomer comprises as majority species the diene elastomer functionalized in the middle of the chain by an alkoxysilane group whose silicon atom is the branching point of the two branches of the diene elastomer . More particularly still, the diene elastomer functionalized in the middle of the chain with an alkoxysilane group represents 70% by weight of the modified diene elastomer.

Preferably, the rubber composition of the invention may contain a single diene elastomer or a mixture of several diene elastomers.

Preferably, the content of the diene elastomer, preferably of the butadiene elastomer, more preferably of the copolymer of styrene and butadiene, in the rubber composition is included in a range ranging from 50 to 100 phr, preferably ranging from 55 at 100 pc.

Preferably, the rubber composition may comprise at least a first butadiene elastomer E1 and a second diene elastomer E2 which may be chosen from the group consisting of natural rubber, synthetic polyisoprenes and butadiene elastomers of a different chemical nature from the butadiene elastomer E1. Preferably, the butadiene elastomer E1 is a copolymer of styrene and butadiene, more preferably still a copolymer of styrene and functionalized butadiene as described above and a second diene elastomer E2 which can be chosen from the group consisting of rubber natural, synthetic polyisoprenes and butadiene elastomers of a chemical nature different from the butadiene elastomer E1. Preferably, the content of the second diene elastomer E2 is within a range ranging from 0 to 50 phr, preferably from 0 to 45 phr.

The rubber composition according to the invention may also contain, in a minority manner, any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.

Reinforcing charge

The rubber composition of the invention comprises at least one reinforcing filler comprising mainly by weight a reinforcing inorganic filler. A reinforcing filler is known for its ability to reinforce a rubber composition that can be used for the manufacture of tires.

The rubber composition of the invention may comprise one or more reinforcing fillers.

It is possible to use any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition which can be used in particular for the manufacture of tires, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica or again a mixture of these two types of fillers.

Suitable carbon blacks are all carbon blacks, in particular the blacks conventionally used in tires or their treads. Among the latter, mention will be made more particularly of the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as for example the blacks N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used. 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 WO97/36724-A2 or WO99/16600-A1).

By “reinforcing inorganic filler”, should be understood here any inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also called “white” filler, “clear” filler or even “non-black” filler. as opposed to carbon black, capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires. In a known manner, certain reinforcing inorganic fillers can be characterized in particular by the presence of hydroxyl (—OH) groups at their surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferably silica (SiO2) or of the aluminous type, in particular alumina (Al2O3). The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET specific surface area as well as a CTAB specific surface area, both of which are less than 450 m2/g, preferably comprised in a range ranging from from 30 to 400 m2/g, in particular from 60 to 300 m2/g.

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

As other examples of reinforcing inorganic fillers capable of being used in the rubber compositions of the invention, mention may also be made of mineral fillers of the alumina type, in particular alumina (Al2O3), aluminum oxides , aluminum hydroxides, aluminosilicates, titanium oxides, silicon carbides or nitrides, all of the reinforcing type as described for example in applications WO99/28376-A2, WO00/73372-A1, WO02/053634- A1, WO2004/003067-A1, WO2004/056915-A2, US6610261-B1 and US6747087-B2. Mention may in particular be made of the aluminas “Baikalox A125” or “CR125” (Baïkowski company), “APA-100RDX” (Condéa), “Aluminoxid C” (Evonik) or “AKP-G015” (Sumitomo Chemicals).

Preferably, the reinforcing inorganic filler in the rubber composition of the invention is a silica, preferably a precipitated silica.

The physical state in which the reinforcing inorganic filler is present is irrelevant, whether it be in the form of powder, microbeads, granules, or else beads or any other appropriate densified form. Of course, the term “reinforcing inorganic filler” also means mixtures of different reinforcing inorganic fillers, in particular of silicas as described above.

Those skilled in the art will understand that replacing the reinforcing inorganic filler described above, a reinforcing filler of another nature could be used, since this reinforcing filler of another nature would be covered with an inorganic layer. such as silica, or else would comprise functional sites, in particular hydroxyl sites, on its surface, requiring the use of a coupling agent to establish the bond between this reinforcing filler and the diene elastomer. By way of example, mention may be made of carbon blacks partially or completely covered with silica, or carbon blacks modified with silica, such as, without limitation, fillers of the "Ecoblack®" type of the series CRX2000” or Cabot Corporation’s “CRX4000” series.

A person skilled in the art will be able to adapt the total reinforcing filler content according to the use concerned, in particular according to the type of tire concerned, for example tire for a motorcycle, for a passenger vehicle or even for a utility vehicle such as a van or heavy goods vehicle. Preferably, this content of total reinforcing filler is within a range ranging from 10 to 200 phr, more preferably from 30 to 180 phr, and even more preferably from 50 to 160 phr; the optimum being in a known manner different according to the particular applications targeted.

Preferably, the content of the reinforcing inorganic filler is within the range from 10 to 120 phr, preferably from 30 to 120 phr, preferably from 50 to 90 phr.

The reinforcing filler is mainly an inorganic reinforcing filler (preferably silica), that is to say that the reinforcing filler comprises more than 50% (>50%) by weight of an inorganic reinforcing filler such as silica relative to the total weight of the reinforcing filler, preferably more than 55% by weight, more preferably more than 60% by weight. Preferably, the reinforcing inorganic reinforcing filler, in particular silica, more preferably precipitated silica, represents from 60% to 100% by weight of the total weight of the reinforcing filler, more preferably represents from 60% to 98% by weight of the total weight of the reinforcing filler.

The reinforcing filler may further comprise carbon black. According to this option, the carbon black is used at a rate less than or equal to 20 phr, more preferably less than or equal to 10 phr (for example the rate of carbon black can be comprised in a range ranging from 0.5 to 8 pce, in particular ranging from 0.5 to 4 pce). Within the ranges indicated, the coloring (black pigmentation agent) and anti-UV properties of the carbon blacks are benefited, without penalizing moreover the typical performance provided by the reinforcing inorganic filler.

More preferably still, the reinforcing filler essentially consists of a mixture of carbon black and a reinforcing inorganic filler, in particular a silica, in particular a precipitated silica, the reinforcing inorganic filler being the majority by weight, relative to the weight of carbon black. carbon.

In this disclosure, BET surface area is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938) , and more specifically according to a method adapted from standard NF ISO 5794-1, appendix E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - vacuum degassing: one hour at 160°C - relative pressure range p/in: 0.05 to 0.17].

For inorganic fillers such as silica for example, the CTAB specific surface values were determined according to standard NF ISO 5794-1, appendix G of June 2010. The process is based on the adsorption of CTAB (N-bromide hexadecyl-N,N,N-trimethylammonium) on the "external" surface of the reinforcing filler.

Coupling agent of the reinforcing inorganic filler to the diene elastomer

As indicated above, the rubber composition of the invention comprises at least one agent for coupling the reinforcing inorganic filler to the diene elastomer, the level of this agent for coupling the inorganic filler to the diene elastomer being comprised in a range ranging from 12% to 18% by weight relative to the weight of the reinforcing inorganic filler.

To couple the inorganic reinforcing filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner intended to ensure a sufficient connection, of a chemical and/or physical nature, between the inorganic filler (surface of its aggregates) and the diene elastomer. By "bifunctional" is meant a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound can comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler and a second functional group comprising a sulfur atom, said second group functional being capable of interacting with the diene elastomer.

Surprisingly, and contrary to the habits of using an amount of at most 8% by weight of the agent for coupling the reinforcing inorganic filler to the diene elastomer with respect to the weight of the inorganic reinforcing filler, the applicant s it was found that by significantly increasing the amount of coupling agent of the reinforcing inorganic filler to the diene elastomer in the presence of a specific processing agent in a rubber composition, a compromise of properties could be achieved unexpected and to obtain a rubber composition exhibiting both good processability and improved hysteretic properties while retaining very good rigidity and very good grip on wet ground.

Preferably, the rate of agent for coupling the reinforcing inorganic filler to the diene elastomer is within a range ranging from 13% to 17% by weight relative to the weight of the reinforcing inorganic filler. More preferably still, the rate of this inorganic filler coupling agent being included in a range ranging from 13% to 16% by weight, more preferably still from 13.5% to 15.5% by weight relative to the weight of the reinforcing inorganic filler.

Preferably, the agent for coupling the reinforcing inorganic filler to the diene elastomer is chosen from polysulphide silanes, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, mercaptosilane dimers, blocked mercaptosilane dimers, mercaptosilane oligomers , blocked mercaptosilane oligomers and mixtures thereof.

Even more preferably, the agent for coupling the reinforcing inorganic filler to the diene elastomer is a polysulphide silane.

More particularly, it is possible to use polysulphide silanes, called "symmetrical" or "asymmetrical" according to their particular structure, as described for example in applications WO03/002648 (or US 2005/016651) and WO03/002649 (or US 2005/ 016650).

Preferably, polysulphide silanes corresponding to the following general formula (II) are suitable in particular, without the definition below being limiting:

Z-A-Sx-A-Z(II),

in which:

• x is an integer from 2 to 8 (preferably from 2 to 5);
• the symbols A, which are identical or different, represent a divalent hydrocarbon radical (preferably a C1-C18 alkylene group or a C6-C12 arylene group, more particularly a C1-C10 alkylene, in particular a C1-C4 alkylene, in particular propylene);
• the symbols Z, identical or different, correspond to one of the three formulas below: [Chem 1]

in which:

• the radicals R ^a , substituted or unsubstituted, identical or different from each other, represent a C1-C18 alkyl group, a C5-C18 cycloalkyl group or a C6-C18 aryl group (preferably C1-C6 alkyl groups , cyclohexyl or phenyl, in particular C1-C4 alkyl groups, more particularly methyl and/or ethyl).
• the radicals R ^b , substituted or unsubstituted, identical or different from each other, represent a C1-C18 alkoxyl group or a C5-C18 cycloalkoxyl group (preferably a group chosen from C1-C8 alkoxyls and C5 cycloalkoxyls -C8, more preferably still a group chosen from C1-C4 alkoxyls, in particular methoxyl and ethoxyl), or a hydroxyl group, or such that 2 radicals R ^b represent a C3-C18 dialkoxyl group

In the case of a mixture of polysulphurized alkoxysilanes corresponding to formula (II) above, in particular the usual commercially available mixtures, the average value of the "x"s is a fractional number preferably between 2 and 5, more preferably close to 4. But the rubber composition can also advantageously be comprised, for example, with disulfurized alkoxysilanes (x=2).

As examples of polysulphide silanes, mention will be made more particularly of the polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis-(alkoxyl(C1-C4)-alkyl(C1-C4)silyl-alkyl(C1-C4)), such as, for example, bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl) polysulphides. Among these compounds, use is made in particular of bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, of formula [(C2H5O)3Si(CH2)3S2]2 or bis-(triethoxysilylpropyl) disulfide, abbreviated TESPD, of formula [(C2H5O)3Si(CH2)3S]2. Mention will also be made, by way of preferred examples, of the polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis-(monoalkoxyl(C1-C4)-dialkyl(C1-C4)silylpropyl), more particularly bis-monoethoxydimethylsilylpropyl tetrasulphide as described in the aforementioned patent application WO02/083782 (or US7217751).

Preferably, the agent for coupling the reinforcing inorganic filler to the diene elastomer corresponds to formula (II) with x is an integer from 2 to 8 (preferably from 2 to 5), the symbols A, which are identical or different, represent a C1-C10 alkylene group, preferably a C1-C4 alkylene group, more preferably propylene, the symbols Z, which are identical or different, correspond to the formula Si(R ^b ) ₃ with R ^b , which are identical or different from each other , representing a C1-C4 alkoxyl group, in particular methoxyl and ethoxyl.

Even more preferably, the agent for coupling the inorganic reinforcing filler to the diene elastomer is chosen from the group consisting of bis(triethoxysilylpropyl) tetrasulphide, bis(trimethoxysilylpropyl) tetrasulphide, bis-(triethoxysilylpropyl) disulphide and bis-(trimethoxysilylpropyl) disulfide, more preferably is selected from the group consisting of bis(triethoxysilylpropyl) tetrasulfide and bis(trimethoxysilylpropyl) tetrasulfide.

By way of example of coupling agents other than a polysulphide alkoxysilane, mention will be made in particular of bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulphides (Rb=OH in formula I above) as described for example in patent applications WO02/30939-A1 (or US6774255-B1), WO02/31041-A1 (or US2004/051210-A1), and WO2007/061550-A1, or even silanes or POS bearing azo-functional groups dicarbonyl, as described for example in patent applications WO2006/125532-A1, WO2006/125533-A1, WO2006/125534-A1.

As examples of other sulfurized silanes, mention will be made, for example, of silanes bearing at least one thiol function (-SH) (known as mercaptosilanes) and/or at least one blocked thiol function, such as for example "NXT-Silane" marketed by the company Momentive, the dimers or oligomers of these silanes, as described for example in patents or patent applications US6849754, WO99/09036, WO2006/023815, WO2007/098080, WO2007/98120, EP1994038 , EP2079793, WO2010/072685 and WO2008/055986.

Implementer

The rubber composition of the invention comprises at least one specific processing agent, said processing agent essentially consists of a mixture of at least one carboxylic acid comprising from 4 to 28 carbon atoms and of at least an aliphatic polyol comprising from 2 to 22 carbon atoms.

Surprisingly, the applicant has noticed that the use of a specific processing agent in the presence of a higher rate of agent for coupling the reinforcing inorganic filler to the diene elastomer than that usually used (rate usually used is less than or equal to 8% by weight relative to the weight of the inorganic filler) in a rubber composition, makes it possible to reach an unexpected compromise of properties and to obtain a rubber composition having both good processability and improved hysteresis properties while maintaining very good stiffness and very good wet grip.

By “processing agent”, is meant any compound capable of improving the Monney index, and therefore capable of improving the processability, of a rubber composition comprising a reinforcing filler. These compounds are also called “processing aids” in English.

By "consists essentially of" within the meaning of the present description, is meant the fact that the processing agent may contain, in addition to the carboxylic acid comprising from 4 to 28 carbon atoms and the aliphatic polyol comprising from 2 to 22 carbon atoms, other ingredients in proportions which do not affect the characteristics and the function of the processing agent, namely its ability to improve the processability of a rubber composition reinforced with at least one reinforcing filler. Other ingredients which may be present in the processing agent may be, for example, ethylene glycol, polyethylene glycol or dioxin. Preferably the other ingredients which may possibly be present in the implementing agent represent less than 10% by weight of the total weight of the implementing agent, more preferably represent less than 6% by weight of the total weight of the implementing agent.

The processing agent used in the compositions of the invention is therefore a mixture of two ingredients: a polyol as defined above and a carboxylic acid as defined above, these two ingredients representing more than 50% by weight of all the ingredients of the implementing agent, more preferably more than 84% by weight of all the ingredients of the implementing agent, more preferably still more than 90% by weight of all of the ingredients of the implementer. The carboxylic acid that can be used in the processing agent can be a mixture of carboxylic acids as defined in the present description.

Preferably, the aliphatic polyol of the processing agent contains from 2 to 15 carbon atoms, preferably from 2 to 10 carbon atoms.

Preferably, the aliphatic polyol of the implementation agent is chosen from the group consisting of 1,2-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-butyl-2-ethyl -1,3-propanediol, 2-sec-butyl-2-methyl-1,3-propanediol, trimethylolpropane, erythritol, xylitol, sorbitol, dulcitol, mannitol, inositol and mixtures thereof.

More preferably still, the aliphatic polyol of the implementing agent is chosen from the group consisting of 1,2-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-butyl-2 -ethyl-1,3-propanediol, 2-sec-butyl-2-methyl-1,3-propanediol, trimethylolpropane and mixtures thereof.

Even more preferably, the aliphatic polyol of the processing agent is trimethylolpropane.

Preferably, the carboxylic acid of the implementing agent comprises from 6 to 22 carbon atoms, preferably from 8 to 20 carbon atoms, even more preferably comprises from 14 to 20 carbon atoms.

Preferably, the carboxylic acid of the implementing agent is chosen from the group consisting of caprylic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid , linolenic acid and mixtures thereof.

Preferably, the carboxylic acid of the processing agent is a mixture of several carboxylic acids having 16 to 18 carbon atoms.

Preferably, the processing agent consists essentially of an aliphatic polyol chosen from the group consisting of 1,2-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-butyl-2 -ethyl-1,3-propanediol, 2-sec-butyl-2-methyl-1,3-propanediol, trimethylolpropane and a carboxylic acid comprising 14-20 carbon atoms, more preferably comprising 16 to 18 atoms of carbon.

Preferably, the processing agent essentially consists of trimethylolpropane and a carboxylic acid comprising from 16 to 18 carbon atoms.

Preferably, in the processing agent, the weight ratio between said aliphatic polyol and said carboxylic acid is within a range from 1: 20 to 10: 1, preferably is within a range from 1:10 to 5:1.

Preferably, in the rubber composition, the level of processing agent as described above is within a range ranging from 1 to 10 phr, preferably ranging from 1 to 5 phr.

Preferably, in the rubber composition, the level of processing agent as described above is within a range from 0.2% to 3% by weight relative to the total weight of the constituents of the rubber composition. rubber, more preferably ranging from 0.5% to 2% by total weight of the constituents of the rubber composition.

The processing agents that can be used in the context of the invention are known and marketed. By way of example, mention may be made of the executing agent marketed under the reference “Aflux 37”.

Plasticizers

The rubber composition of the invention may additionally comprise at least one plasticizer. This plasticizer is preferably chosen from hydrocarbon-based resins with a high glass transition temperature (Tg), low-Tg hydrocarbon-based resins, plasticizing oils, and mixtures thereof. Preferably, the plasticizer is chosen from high-Tg hydrocarbon-based resins, plasticizing oils, and mixtures thereof. More preferably still, the plasticizer is a high-Tg hydrocarbon-based resin.

The total level of plasticizer in the composition is greater than or equal to 10 phr, more preferably greater than or equal to 20 phr, preferably from 20 to 70 phr, in particular from 30 to 60 phr.

By definition, a high Tg hydrocarbon resin is by definition a solid at room temperature and pressure (20°C, 1 atm), while a plasticizing oil is liquid at room temperature and a low Tg hydrocarbon resin is viscous at room temperature.

In known manner, high-Tg hydrocarbon-based resins are thermoplastic hydrocarbon-based resins, the Tg of which is greater than 20°C.

Hydrocarbon resins, also called hydrocarbon 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, for example oxygen, which can be used in particular as plasticizing agents or tackifying agents in polymeric matrices. They are by nature at least partially miscible (i.e., compatible) at the rates used with the polymer compositions for which they are intended, so as to act as true diluting agents. 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) in which chapter 5 is devoted their applications, in particular in pneumatic rubber (5.5. “Rubber Tires and Mechanical Goods”). In a known manner, these hydrocarbon resins can also be qualified as thermoplastic resins in the sense that they soften on heating and can thus be molded.

The hydrocarbon resins can be aliphatic, or aromatic or even of the aliphatic/aromatic type, that is to say based on aliphatic and/or aromatic monomers. They can be natural or synthetic, petroleum-based or not (if so, also known as petroleum resins). Suitable aromatic monomers are, for example, styrene, alpha-methylstyrene, indene, ortho-, meta-, para-methylstyrene, vinyl-toluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, any vinylaromatic monomer derived from a C9 cut (or more generally from a C8 to C10 cut). Preferably, the vinylaromatic monomer is styrene or a vinylaromatic monomer derived from a C9 cut (or more generally from a C8 to C10 cut). Preferably, the vinylaromatic monomer is the minority monomer, expressed as a molar fraction, in the copolymer under consideration.

According to a particularly preferred embodiment, the hydrocarbon-based plasticizing resin is chosen from the group consisting of resins of homopolymers or copolymers of cyclopentadiene (abbreviated to CPD) or dicyclopentadiene (abbreviated to DCPD), resins of terpene homopolymers or copolymers, resins of homopolymers or copolymers of terpene phenol, resins of homopolymers or copolymers of C5 cut, resins of homopolymers or copolymers of C9 cut, resins of homopolymers and copolymers of alpha-methyl-styrene and mixtures of these resins.

The above preferred high Tg hydrocarbon resins are well known to those skilled in the art and commercially available, for example sold as regards:

• 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/vinylaromatic copolymer resins, in particular C5 cut/styrene or C5 cut/C9 cut: 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 the names "Hikorez T1095" and "Hikorez T1100", by Exxon under the 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”;
• hydrocarbon resins, optionally hydrogenated, mainly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures of these monomers are commercially available from suppliers such as Exxon Mobil, in particular under the references "Escorez E5600", " Escorate E5415", "Escorez E5320", "Oppera PR-383".

According to a particular embodiment of the invention, when it is included in the composition, the level of hydrocarbon plasticizing resin Tg greater than 20° C. is within a range ranging from 10 to 70 phr, preferably ranging from 20 to 70 phr, even more preferably from 30 to 60 phr.

The plasticizer may also contain an extender oil (or plasticizing oil) which is liquid at 20°C, said to be at "low Tg", that is to say which by definition has a Tg of less than -20°C, preferably below -40°C.

Any extender oil, whether of aromatic or non-aromatic nature known for its plasticizing properties with respect to elastomers, can be used. At room temperature (20°C), these oils, more or less viscous, are liquids (i.e., as a reminder, substances having the capacity to take the shape of their container in the long term), by difference in particular with high Tg hydrocarbon resins which are by nature solid at room temperature.

Particularly suitable are plasticizing oils chosen from the group consisting of naphthenic oils (low or high viscosity, in particular hydrogenated or not), paraffinic oils, MES (Medium Extracted Solvates) oils, TDAE (Treated Distillate Aromatic Extracts) oils, 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 compounds.

Other additives

The rubber compositions in accordance with the invention may also comprise all or part of the usual additives and processing agents, known to those skilled in the art and usually used in rubber compositions for tires, in particular strips of bearing, such as fillers (reinforcing or non-reinforcing / other than those mentioned above), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, anti-oxidants, anti-fatigue agents, resins reinforcing (as described for example in application WO 02/10269).

Cross-linking system

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

Preferably, the crosslinking system is sulfur-based, in which case we speak of a vulcanization system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or of a sulfur-donating agent. At least one vulcanization accelerator is also preferentially present, and, optionally, also preferentially, various known vulcanization activators can be used such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), or alternatively known vulcanization retarders.

The sulfur is used at a preferential rate of between 0.2 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferential rate comprised between 0.2 and 10 phr, more preferentially comprised between 0.2 and 5.0 phr.

Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used as an accelerator, in particular accelerators of the thiazole type as well as their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type. As examples of such accelerators, mention may be made in particular of the following compounds: 2-mercaptobenzothiazyl disulphide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl- 2-Benzothiazyl sulfenamide (“DCBS”), N-ter-butyl-2-benzothiazyl sulfenamide (“TBBS”), N-ter-butyl-2-benzothiazyl sulfenimide (“TBSI”), tetrabenzylthiuram disulfide (“TBZTD”) , zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds.

Preparation of rubber compositions

The rubber composition in accordance with the invention is manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

• a first working phase or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which, in a suitable mixer such as a usual internal mixer (for example of the "Banbury"), all the necessary constituents, in particular the diene elastomer(s), the reinforcing filler(s), including the reinforcing inorganic filler, the agent for coupling the reinforcing inorganic filler to the diene elastomer, the processing agent specific, any other miscellaneous additives, with the exception of the crosslinking system. The incorporation of the reinforcing filler into the elastomer can be carried out in one or more stages by mixing thermomechanically. In the case where the filler is already incorporated in whole or in part into the elastomer in the form of a masterbatch (“masterbatch” in English) as described for example in applications WO 97/36724 or WO 99 /16600, it is the masterbatch which is mixed directly and, if necessary, the other elastomers or fillers present in the composition which are not in the form of the masterbatch are incorporated, as well as any other various additives other than the cross-linking system.
• a second phase of mechanical work (so-called "productive" phase), which is carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature , typically less than 120° C., for example between 40° C. and 100° C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min.

The non-productive phase can be carried out at high temperature, up to a maximum temperature of between 110° C. and 200° C., preferably between 130° C. and 185° C., for a duration generally of between 2 and 10 minutes.

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 even extruded in the form of a semi-finished (or profiled) rubber. Preferably, the rubber composition according to the invention is calendered to form a tire tread.

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

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

Tread and tire

Another object of the present invention relates to a tire tread comprising a rubber composition as defined in the description above, including in its preferred embodiments.

In known manner, the tread of a tire, whether it is intended to equip a passenger vehicle or any other type of vehicle, comprises a running surface intended to be in contact with the ground when the tire is rolling. The tread is provided with a tread pattern comprising in particular tread pattern elements or elementary blocks delimited by various main, longitudinal or circumferential, transverse or even oblique grooves, the elementary blocks possibly also comprising various finer incisions or sipes. The grooves constitute channels intended to evacuate the water during rolling on wet ground and the walls of these grooves define the leading and trailing edges of the tread pattern elements, depending on the direction of the bend.

A tread may consist of one and the same rubber composition: or it may 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, a plane defined as being orthogonal to the radial direction.

Thus, the rubber composition in accordance with the invention may be present in the entire tread according to the invention.

According to another preferred embodiment, the tread comprises at least one radially inner portion and one radially outer portion, the rubber composition in accordance with the invention being advantageously 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 of a rubber composition different from that according to the present invention. The tread may 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 with respect 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 designate respectively 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 inner, respectively radially outer" mean "closer to, respectively further from the axis of rotation of the tire". By "axially inner, respectively axially outer", is meant "closer to, respectively further from the equatorial plane of the tire", the equatorial plane of the tire being the plane passing through the middle of the running surface of the tire and perpendicular to the axis of rotation of the tire.

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 tire tread wear indicator.

Another object of the present invention relates to a tire comprising a rubber composition as defined in the above description including in its preferred embodiments or comprising a tread as defined in the above description including in his favorite styles.

The tire of the invention is preferably intended to equip motor vehicles of the passenger car and SUV (“Sport Utility Vehicles”) type.

In the present application, the term “tyre” is understood to mean a pneumatic tire or a non-pneumatic tire.

By "pneumatic tire" is meant a tire intended to form a cavity by cooperating with a support element, for example a rim, this cavity being capable of being pressurized to a pressure greater than atmospheric pressure.

By contrast, a "non-pneumatic tire" is understood to mean a tire which is not capable of being pressurized.

Thus, a tire usually comprises two beads intended to come into contact with a rim, a crown composed of at least one crown reinforcement and a tread, two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. The pneumatic tires according to the invention are intended in particular to equip vehicles of any type such as passenger vehicles, two-wheeled vehicles, heavy goods vehicles, agricultural vehicles, civil engineering vehicles or aircraft or, more generally, on any rolling device.

A non-pneumatic tire is a toroidal body consisting of at least one polymeric material, intended to perform the function of a tire but without being subjected to inflation pressure. A non-pneumatic tire can be solid or hollow. A hollow non-pneumatic tire can contain air, but at atmospheric pressure, i.e. it has no pneumatic stiffness provided by an inflation gas at a pressure greater than atmospheric pressure. Thus, a non-pneumatic tire usually comprises a base, designed for example for mounting on a rigid rim, a crown reinforcement, ensuring the connection with a tread and a deformable structure, such as spokes, ribs or cells, this structure being arranged between the base and the top. Such non-pneumatic tires do not necessarily include a sidewall. Non-pneumatic bandages are described for example in documents WO 03/018332 and FR2898077. Non-pneumatic tires are intended to be fitted in particular to passenger vehicles or two-wheelers.

Preferably, the tire of the invention comprising at least one tread of the invention or at least one rubber composition according to the invention is a pneumatic tire, more preferably a pneumatic tire intended to be fitted to passenger vehicles. The invention relates to tires both in the raw state (that is to say, before curing) and in the cured state (that is to say, after vulcanization).

Preferred embodiments

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

1. Rubber composition based on at least one diene elastomer, at least one reinforcing filler comprising mainly by weight a reinforcing inorganic filler, at least one agent for coupling the reinforcing inorganic filler to the diene elastomer, at least one processing agent and at least one crosslinking system, characterized in that the rate of agent for coupling the reinforcing inorganic filler to the diene elastomer is within a range ranging from 12% to 18% by weight relative to the weight of the reinforcing inorganic filler and in that the processing agent consists essentially of a mixture of at least one carboxylic acid comprising from 4 to 28 carbon atoms and of at least an aliphatic polyol comprising from 2 to 22 carbon atoms.

2. Rubber composition according to embodiment 1, in which the rate of coupling agent of the reinforcing inorganic filler to the diene elastomer is within a range ranging from 13% to 17% by weight relative to the weight of the filler reinforcing inorganic filler, preferably in a range ranging from 13% to 16% by weight, more preferably still from 13.5% to 15.5% by weight relative to the weight of the reinforcing inorganic filler.

3.Rubber composition according to any one of the preceding embodiments, in which the agent for coupling the reinforcing inorganic filler to the diene elastomer is chosen from polysulphide silanes, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, dimers mercaptosilane, blocked mercaptosilane dimers, mercaptosilane oligomers, blocked mercaptosilane oligomers and mixtures thereof.

4. Rubber composition according to any one of the preceding embodiments, in which the agent for coupling the reinforcing inorganic filler to the diene elastomer is a polysulphide silane.

5. Rubber composition according to any one of the preceding embodiments, in which the agent for coupling the reinforcing inorganic filler to the diene elastomer is a polysulphide silane of the following formula (II):

Z-A-Sx-A-Z(II),

in which:

• x is an integer from 2 to 8 (preferably from 2 to 5);
• the symbols A, which are identical or different, represent a divalent hydrocarbon radical (preferably a C1-C18 alkylene group or a C6-C12 arylene group, more particularly a C1-C10 alkylene, in particular a C1-C4 alkylene, in particular propylene);
• the symbols Z, identical or different, correspond to one of the three formulas below: [Chem 2]

in which:

• the radicals Ra, substituted or unsubstituted, identical or different from each other, represent a C1-C18 alkyl group, a C5-C18 cycloalkyl group or a C6-C18 aryl group (preferably C1-C6 alkyl groups, cyclohexyl or phenyl, in particular C1-C4 alkyl groups, more particularly methyl and/or ethyl).
• the Rb radicals, substituted or unsubstituted, identical or different from each other, represent a C1-C18 alkoxyl group or a C5-C18 cycloalkoxyl group (preferably a group chosen from C1-C8 alkoxyls and C5- C8, more preferably still a group chosen from C1-C4 alkoxyls, in particular methoxyl and ethoxyl), or a hydroxyl group, or such that 2 Rb radicals represent a C3-C18 dialkoxyl group

6. Rubber composition according to embodiment 5, in which the agent for coupling the reinforcing inorganic filler to the diene elastomer corresponds to the formula (II) with x being an integer from 2 to 8 (preferably from 2 to 5 ), the symbols A, which are identical or different, represent a C1-C10 alkylene group, preferably a C1-C4 alkylene, more preferably propylene, the symbols Z, which are identical or different, correspond to the formula Si(Rb)3 with Rb, identical or different from each other, representing a C1-C4 alkoxyl group, in particular methoxyl and ethoxyl.

7. Rubber composition according to any one of the preceding embodiments, in which the agent for coupling the inorganic reinforcing filler to the diene elastomer is chosen from the group consisting of bis(triethoxysilylpropyl) tetrasulphide, bis tetrasulphide (trimethoxysilylpropyl), bis-(triethoxysilylpropyl) disulfide and bis-(trimethoxysilylpropyl) disulfide, more preferably is chosen from the group consisting of bis(triethoxysilylpropyl) tetrasulfide and bis(trimethoxysilylpropyl) tetrasulfide.

8. Rubber composition according to any one of the preceding embodiments, in which the aliphatic polyol of the processing agent comprises from 2 to 15 carbon atoms, preferably from 2 to 10 carbon atoms.

9. Rubber composition according to any one of the preceding embodiments, in which the aliphatic polyol of the processing agent is selected from the group consisting of 1,2-pentanediol, 2-methyl-2-propyl- 1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-sec-butyl-2-methyl-1,3-propanediol, trimethylolpropane, erythritol, xylitol, sorbitol , dulcitol, mannitol, inositol and mixtures thereof.

10. Rubber composition according to any one of the preceding embodiments, in which the aliphatic polyol of the processing agent is chosen from the group consisting of 1,2-pentanediol, 2-methyl-2-propyl- 1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-sec-butyl-2-methyl-1,3-propanediol, trimethylolpropane and mixtures thereof.

11. A rubber composition according to any of the preceding embodiments, wherein the aliphatic polyol of the processing agent is trimethylolpropane.

12. Rubber composition according to any one of the preceding embodiments, in which the carboxylic acid of the processing agent comprises from 6 to 22 carbon atoms, preferably from 8 to 20 carbon atoms, more preferably still from 14 to 20 carbon atoms.

13. Rubber composition according to any one of the preceding embodiments, in which the carboxylic acid of the processing agent is chosen from the group consisting of caprylic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid and mixtures thereof.

14. A rubber composition according to any one of the preceding embodiments, wherein the weight ratio in the processing agent between said aliphatic polyol and said carboxylic acid is within a range from 1:20 to 10:1, preferably is within a range of 1:10 to 5:1.

15. Rubber composition according to any one of the preceding embodiments, in which the level of processing agent is within a range ranging from 1 to 10 phr, preferably ranging from 1 to 5 phr.

16. Rubber composition according to any one of the preceding embodiments, in which the rate of processing agent is within a range from 0.2% to 3% by weight relative to the total weight of the constituents of the rubber composition, more preferably ranging from 0.5% to 2% by weight.

17. Rubber composition according to any one of the preceding embodiments, in which the diene elastomer is chosen from the group consisting of natural rubber, synthetic isoprene elastomers, synthetic butadiene elastomers and mixtures of these elastomers.

18. Rubber composition according to any one of the preceding embodiments, in which the diene elastomer is an elastomer functionalized by at least one polar function comprising at least one oxygen atom.

19. A rubber composition according to embodiment 17, wherein the diene elastomer is a synthetic butadiene elastomer.

20. A rubber composition according to embodiment 19, wherein the diene elastomer is a copolymer of styrene and butadiene.

21. Rubber composition according to embodiment 20, in which the diene elastomer is a copolymer of styrene and butadiene comprising at least one polar function comprising at least one oxygen atom and being chosen from the group consisting of silanol, alkoxysilanes carriers or not of an amine group, epoxide, ethers, esters, carboxylic acids and hydroxyl.

22. Rubber composition according to embodiment 21, in which the diene elastomer is a copolymer based on butadiene and styrene, said copolymer comprising at least one alkoxysilane group which may or may not bear an amine function.

23. Rubber composition according to any one of embodiments 19 to 22, in which the butadiene elastomer has a glass transition temperature measured according to standard ASTM D3418-99 of less than or equal to -50° C., preferably comprised in a range ranging from -110°C to -50°C, more preferably still comprised in a range ranging from -90°C to -50°C.

24. Rubber composition according to any one of embodiments 19 to 23, in which the content of the butadiene elastomer is within a range ranging from 50 to 100 phr, preferably ranging from 55 to 100 phr.

25. Rubber composition according to any one of the preceding embodiments, in which the rubber composition further comprises a second diene elastomer, said second diene elastomer being either natural rubber or a synthetic isoprene elastomer or a butadiene elastomer and the content of the second diene elastomer ranging from 0 to 50 phr, preferably from 0 to 45 phr.

26. Rubber composition according to any one of the preceding embodiments, in which the reinforcing inorganic filler is a silica, preferably a precipitated silica.

27. Rubber composition according to any one of the preceding embodiments, in which the content of the reinforcing inorganic filler is within the range from 10 to 120 phr, preferably from 30 to 120 phr, more preferably from 50 to 90 phr. .

28. Rubber composition according to any one of the preceding embodiments, in which the reinforcing filler further comprises carbon black.

29. Rubber composition according to embodiment 28, in which the content of carbon black is included in a range ranging from 0.5 to 8 phr, preferably from 0.5 to 4 phr.

30. Rubber composition according to any one of the preceding embodiments, in which the content of the total reinforcing filler is within a range ranging from 10 to 200 phr, preferably from 30 to 180 phr, and even more preferably from 50 to 160 pc.

31. Rubber composition according to any one of the preceding embodiments, in which the crosslinking system is a sulfur vulcanization system.

32. Rubber composition according to any one of the preceding embodiments further comprising a plasticizer.

33. Rubber composition according to embodiment 32, in which the level of plasticizer is greater than or equal to 10 phr, preferably is within a range ranging from 20 to 70 phr, preferably ranging from 30 to 60 phr.

34. Tire tread comprising a rubber composition defined according to any one of embodiments 1 to 33.

35. Tire comprising a rubber composition defined according to any one of embodiments 1 to 33 or comprising a tread according to embodiment 34.

EXAMPLES

The examples presented below are intended to compare the various properties of the rubber composition in accordance with the invention (composition C1) with a series of control rubber compositions T1 to T6 and with a rubber composition of the prior art. (composition T0).

Formulation of rubber compositions

The levels of the various constituents of the rubber compositions presented in Table 1 are expressed in phr, unless otherwise stated. All the compositions (T0 to C1) have an identical crosslinking system. Given that the amount of agent for coupling the reinforcing inorganic filler to the diene elastomer varies in the compositions and that this coupling agent chosen for the examples releases sulfur during the crosslinking reaction, the molecular sulfur content is adapted accordingly for the compositions T1, T2, T5, T6 and C1 so that the crosslinking takes place with a sulfur content identical to the rubber compositions T0, T3 and T4.

T0 T1 T2 T3 T4 T5 T6 C1 Elastomer (1) 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Load (2) 70.00 70.00 70.00 70.00 70.00 70.00 70.00 70.00 Load (3) 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Coupling agent (4) 5.60 7.00 10.50 5.60 5.60 7.00 10.50 10.50 Implementer (5) (-) (-) (-) 4.00 (-) 4.00 (-) 4.00 Implementer (6) (-) (-) (-) (-) 6.00 (-) 6.00 (-) Plasticizer (7) 39.00 39.00 39.00 39.00 39.00 39.00 39.00 39.00 Anti-oxidant (8) 2.75 2.75 2.75 2.75 2.75 2.75 2.75 2.75 DPG (9) 1.60 1.60 1.60 1.60 1.60 1.60 1.60 1.60 Antioxidant (10) 4.60 4.60 4.60 4.60 4.60 4.60 4.60 4.60 Wax (11) 1.85 1.85 1.85 1.85 1.85 1.85 1.85 1.85 Stearic acid (12) 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Zinc oxide (13) 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Vulcanization Accelerator 1 (14) 1.73 1.73 1.73 1.73 1.73 1.73 1.73 1.73 Vulcanization Accelerator 2 (15) 0.72 0.72 0.72 0.72 0.72 0.72 0.72 0.72 Sulfur (16) 1.00 0.86 0.53 1.00 1.00 0.86 0.53 0.53 Rate (**) 8% 10% 15% 8% 8% 10% 15% 15%

1. Diene elastomer: copolymer of styrene and butadiene solution functionalized amino-alkoxysilane middle of chain having a Tg = -65°C, comprising 16% by weight of styrene relative to the weight of the elastomer, 46% by weight of butadiene 1,4-trans based on the weight of the butadiene part, 24% by weight of 1,4-cis-butadiene based on the weight of the butadiene part and 30% by weight of 1,2-vinyl butadiene based on the weight of the butadiene part. This functionalized elastomer is obtained by anionic polymerization according to the process described in the description above.

2. Reinforcing inorganic filler: precipitated silica marketed by Solvay under the name “Zeosil 1165 MP” with BET specific surface area=160 m2/g and CTAB=155 m2/g, the surfaces being measured with the methods described in the description.

3.Carbon Black: N234 grade carbon black marketed by Cabot Corporation

4. Agent for coupling the reinforcing inorganic filler to the diene elastomer: Bis[3-(triethoxysilyl)propyl] tetrasulphide silane (TESPT) marketed by Evonik under the reference “Si69”;

5. Processing agent: mixture of 25% by weight of trimethylolpropane, 70% by weight of carboxylic acids having 16 to 18 carbon atoms and 5% by weight of other ingredients, product marketed by Rheinchemie under the reference “Influx 37”.

6. Processing agent: Zinc stearate marketed by PMC Biogenix under the reference “Lubrazinc W” with a stearate purity greater than 97% by weight, the remaining 3% by weight being octadecanoic acid

7. Plasticizer: DCPD resin marketed by Exxon Mobil under the reference “Oppera PR-383” having a Tg=51°C.

8. Antioxidant: TMQ, polymer of 1,2-dihydro-2,2,4-trimethylquinoline marketed by Nocil Limited under the name "Pilnox TDQ".

9.DPG: diphenylguanidine marketed by Flexys under the reference “Perkacit”.

10. Antioxidant: N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine marketed by Flexys under the reference “Santoflex 6-PPD”.

11. Wax: “redezon 500” wax marketed by Repsol quimica

12. Stearic acid: stearic acid marketed by the company Uniqema under the reference “Pristerene 4931”.

13. Zinc oxide: industrial grade zinc oxide marketed by Umicore.

14. Vulcanization accelerator 1: N-cyclohexyl-2-benzothiazyl-sulfenamide marketed by Flexys under the reference “Santocure CBS”

15. Vulcanization accelerator 2: 2-2'-Dithiobis (benzothiazole) marketed by Nocil Limited under the trade name "PILCURE MBTS"

16.Sulfur: molecular sulfur marketed by S.F. Sulfur Corporation

(**) Rate: rate of agent for coupling the reinforcing inorganic filler to the diene elastomer. This rate is expressed as a percentage by weight of the agent for coupling the reinforcing inorganic filler to the diene elastomer relative to the weight of the reinforcing inorganic filler.

The rubber composition T0 is representative of a rubber composition of the prior art in which the rate of coupling agent of the inorganic filler to the diene elastomer is 8% by weight relative to the weight of the inorganic filler reinforcing.

The control rubber compositions T1 and T2 differ from the composition T0 in that the rate of coupling agent of the reinforcing inorganic filler to the diene elastomer is respectively 10% and 15% by weight relative to the weight of the filler reinforcing inorganic.

The control rubber compositions T3 and T4 differ from the composition T0 in that they also include a processing agent of a different chemical nature.

The control rubber composition T5 differs from the composition T3 in that the rate of agent for coupling the reinforcing inorganic filler to the diene elastomer is 10% by weight relative to the weight of the reinforcing inorganic filler.

The control rubber composition T6 differs from the composition T4 in that the rate of coupling agent of the reinforcing inorganic filler to the diene elastomer is 15% by weight relative to the weight of the reinforcing inorganic filler.

The rubber composition according to the invention C1 differs from the composition T6 by the chemical nature of the processing agent.

Preparation of rubber compositions:

For the tests which follow, the preparation of the rubber compositions is carried out in the following manner: an internal mixer, filled to 70% by volume and whose initial tank temperature is approximately 50° C., is introduced into the elastomer filler, the reinforcing fillers, the agent for coupling the reinforcing inorganic filler to the diene elastomer, then, after one to two minutes of mixing, the various other ingredients including the processing agent with the exception of the vulcanization system. One then carries out a thermomechanical work (non-productive phase) in one stage (total duration of the mixing equal to approximately 5 min), until reaching a maximum temperature of “drop” of approximately 165°C.

The mixture thus obtained is recovered, cooled, then the vulcanization system (sulfur and accelerators) is added to an external mixer (homo-finisher) at 70°C, mixing everything (productive phase) for approximately 5 to 6 min.

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties after curing, or in the form of profiles which can be used directly, after cutting and/or assembly to the desired dimensions, for example as semi-finished products for tires, in particular as tire treads.

The crosslinking of the rubber compositions is carried out at 150°C for 40 min under pressure.

Properties of rubber compositions:

The properties of the compositions are shown in Table 2 below.

T0 T1 T2 T3 T4 T5 T6 C1 Mooney index (performance in base 100) 100 109 117 118 118 118 124 131 G* at 60°C (performance in base 100) 100 97 98 98 104 103 103 97 tan( δ ) at 0°C (performance in base 100) 100 101 102 112 115 112 102 107 tan( δ )max at 23°C (performance in base 100) 100 105 103 87 86 89 88 98

When the level of coupling agent of the reinforcing inorganic filler with the diene elastomer is increased (comparison of composition T0 with compositions T1 and T2), it is observed, at iso-rigidity (descriptor G* at 60°C) , a significant increase in the Monney index reflecting a decrease in the viscosity of the compositions T1 and T2 and therefore an improvement in their processability compared to the control composition T0. The values of tan(δ)max at 23°C compositions T1 and T2 are also increased compared to that of the control composition T0, representing an improvement in the hysteretic properties at 23° C., therefore a reduction in rolling resistance compared to that of the composition T0. The wet grip property of compositions T1 and T2 (descriptor tan(δ) at 0°C) is not significantly modified.

When a processing agent is added to the rubber composition T0 to respectively obtain the rubber composition T3 and the rubber composition T4, there is observed, at iso-rigidity, as expected, a significant improvement in the processability of the compositions T3 and T4 relative to that of composition T0. There is also a significant improvement in wet grip (tan (d) at 0°C increased significantly) but to the detriment of hysteretic properties at 23°C, and therefore to the detriment of rolling resistance. The rolling resistance of composition T0 is better than that of compositions T3 and T4. The two processing agents, although of different chemical nature, make it possible to obtain the same rubber properties for compositions T3 and T4 when these rubber compositions comprise 8% by weight of coupling agent for the reinforcing inorganic filler at the diene elastomer.

The increase in the rate of coupling agent of the reinforcing inorganic filler to the diene elastomer in the composition T3 to obtain the composition T5 does not improve any of the rubber properties measured. The processability and wet grip of composition T5, at iso-rigidity, are equivalent to those of composition T3. Like composition T3, composition T5 does not exhibit the desired hysteretic properties. Indeed, the rolling resistance of composition T5 is less good than that of composition T0.

The increase in the level of agent for coupling the reinforcing inorganic filler to the diene elastomer in the composition T4 to obtain the composition T6 allows for a gain in processability (comparison of composition T6 with respect to T4). On the other hand, the grip properties on wet ground and the hysteretic properties of composition T6, at iso-rigidity, are less than or equivalent to those of composition T4. As for composition T4, the hysteretic properties of composition T6 are significantly lower than those of composition T0, reflecting an unsatisfactory rolling resistance.

Completely unexpectedly, when implementing agent (6) is replaced by implementing agent (5) in composition T6 to obtain composition C1 according to the invention, a significant improvement in the processability which does not take place to the detriment of the hysteretic properties at 23° C. (comparison of composition C1 according to the invention with the control composition T6). Indeed, the composition C1 according to the invention has hysteretic properties at 23° C. equivalent to the control composition T0. In addition, compared to the control composition T0, the composition C1 according to the invention exhibits, at iso-rigidity, a significant improvement in wet grip (value of tan (d) at 0° C. significantly increased for the composition C1 compared to the control composition T0).

These examples show that a specific processing agent combined with a high level of agent for coupling the reinforcing inorganic filler to the diene elastomer in the composition in accordance with the invention makes it possible to improve, surprisingly, the performance compromise processability-wet grip-rolling resistance at iso-rigidity.

Claims (15)

Rubber composition based on at least one diene elastomer, at least one reinforcing filler comprising mainly by weight a reinforcing inorganic filler, at least one agent for coupling the reinforcing inorganic filler to the diene elastomer, at least one processing agent and at least one crosslinking system, characterized in that the rate of agent for coupling the reinforcing inorganic filler to the diene elastomer is within a range from 12% to 18 % by weight relative to the weight of the reinforcing inorganic filler and in that the processing agent consists essentially of a mixture of at least one carboxylic acid comprising from 4 to 28 carbon atoms and of at least one polyol aliphatic containing 2 to 22 carbon atoms. Rubber composition according to claim 1, in which the rate of coupling agent of the reinforcing inorganic filler to the diene elastomer is within a range ranging from 13% to 17% by weight relative to the weight of the reinforcing inorganic filler , preferably in a range ranging from 13% to 16% by weight, more preferably still from 13.5% to 15.5% by weight relative to the weight of the reinforcing inorganic filler. Rubber composition according to any one of the preceding claims, in which the agent for coupling the reinforcing inorganic filler to the diene elastomer is chosen from polysulphide silanes, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, mercaptosilane dimers , blocked mercaptosilane dimers, mercaptosilane oligomers, blocked mercaptosilane oligomers and mixtures thereof. A rubber composition according to any preceding claim, wherein the coupling agent of the reinforcing inorganic filler to the diene elastomer is a polysulphide silane. A rubber composition according to any preceding claim, wherein the processing agent aliphatic polyol has 2 to 15 carbon atoms, preferably 2 to 10 carbon atoms. A rubber composition according to any preceding claim, wherein the processing agent aliphatic polyol is selected from the group consisting of 1,2-pentanediol, 2-methyl-2-propyl-1, 3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-sec-butyl-2-methyl-1,3-propanediol, trimethylolpropane, erythritol, xylitol, sorbitol, dulcitol, mannitol, inositol and mixtures thereof. A rubber composition according to any preceding claim, wherein the processing agent aliphatic polyol is selected from the group consisting of 1,2-pentanediol, 2-methyl-2-propyl-1, 3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-sec-butyl-2-methyl-1,3-propanediol, trimethylolpropane and mixtures thereof. A rubber composition according to any preceding claim, wherein the carboxylic acid of the processing agent comprises from 6 to 22 carbon atoms, preferably from 8 to 20 carbon atoms, preferably from 14 to 20 carbon atoms. A rubber composition according to any preceding claim, wherein the diene elastomer is selected from the group consisting of natural rubber, synthetic isoprene elastomers, synthetic butadiene elastomers and mixtures of these elastomers. Rubber composition according to any one of the preceding claims, in which the diene elastomer is an elastomer functionalized by at least one polar function comprising at least one oxygen atom. A rubber composition according to any of the claims, wherein the diene elastomer is a synthetic butadiene elastomer. Rubber composition according to any one of the preceding claims, in which the reinforcing inorganic filler is a silica, preferably a precipitated silica. A rubber composition according to any preceding claim further comprising a plasticizer. A tire tread comprising a rubber composition defined according to any one of claims 1 to 13. A tire comprising a rubber composition defined according to any one of Claims 1 to 13 or comprising a tread according to Claim 14.