WO2016135195A1

WO2016135195A1 - Diene rubber composition based on a 1,3-dipolar compound bearing an imidazole function and on a blocked mercaptosilane

Info

Publication number: WO2016135195A1
Application number: PCT/EP2016/053868
Authority: WO
Inventors: Anne-Frédérique SALIT; Sophie GANDER
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2015-02-26
Filing date: 2016-02-24
Publication date: 2016-09-01
Also published as: EP3261853A1; FR3033170A1

Abstract

The present invention relates to a rubber composition based at least on a diene elastomer, a reinforcing filler comprising a reinforcing inorganic filler, a 1,3-dipolar compound bearing an imidazole function and a blocked mercaptosilane, the blocked mercaptosilane being a blocked thiol comprising an organooxysilyl or silanol group. Such a composition has improved processing without adversely affecting the dispersion of the reinforcing inorganic filler.

Description

A diene rubber composition based on a 1,3-dipolar compound bearing an imidazole function and a blocked mercaptosilane.

The field of the present invention is that of diene rubber compositions reinforced by an inorganic filler such as silica and used in particular for the manufacture of tires for vehicles. It relates more particularly to the treads of tires with low rolling resistance.

The use of an inorganic filler-reinforced diene rubber composition, in particular in its tread, makes it possible to reduce the rolling resistance of the tire. The inorganic filler-reinforced diene rubber compositions generally comprise a silane as a coupling agent, such as a blocked polysulfide or mercaptosilane, a silane with a protected thiol function. The silane makes it possible to create interactions between the diene elastomer and the inorganic filler and to promote the dispersion of the inorganic filler in the rubber composition. An inorganic filler-reinforced diene rubber composition may have a relatively high green viscosity for some inorganic filler levels. A high value of the green viscosity of a diene rubber composition can lead to difficulties in processability of the diene rubber composition, especially in the extrusion and calendering stages. and thus decrease productivity in the tire manufacturing line. Solutions have already been proposed to solve this problem. For example it is known to replace a polysulfide silane with a mercaptosilane blocked in a silica-reinforced diene rubber composition, the blocked mercaptosilane being known to decrease the green viscosity of the diene rubber composition and facilitate its implementation. artwork.

Nevertheless, there is still a need to further improve the implementation of inorganic filler-reinforced diene rubber compositions.

The Applicants pursuing their efforts have discovered that the joint use of a specific additive and a blocked mercaptosilane makes it possible to substantially further improve the use of the diene rubber compositions reinforced with an inorganic filler.

The present invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler comprising a reinforcing inorganic filler, a 1,3-dipolar compound corresponding to formula (I) and a blocked thiol having an organooxysilyl or silanol group, Q.-AB (I)

in which :

Q. comprises a dipole containing at least and preferably a nitrogen atom, A, preferably divalent, is an atom or a group of atoms connecting Q. to B,

B comprises an imidazole ring corresponding to formula (II):

in which :

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

and the fourth symbol Z, Y, R or R 'denotes a direct attachment to A,

The invention also relates to a process for preparing a rubber composition based on at least one diene elastomer, a 1,3-dipolar compound corresponding to formula (I) as defined above, of a reinforcing filler comprising a reinforcing inorganic filler, a blocked thiol having an organooxysilyl or silanol group and a vulcanization system, which process comprises the following steps:

during the first so-called non-productive step, adding to the diene elastomer the 1,3-dipolar compound, the reinforcing filler, the thiol blocked by thermomechanically kneading until a maximum temperature of between 130 and 200 ° is reached; VS,

- cool the assembly to a temperature below 100 ° C,

- then incorporate the vulcanization system,

- mix everything up to a maximum temperature below 120 ° C.

The invention also relates to a tread comprising the rubber composition according to the invention. The invention further relates to a tire comprising the rubber composition according to the invention, in particular in its tread. I. DETAILED DESCRIPTION OF THE INVENTION

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight. The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if several elastomers are present).

On the other hand, any range of values designated by the expression "between a and b" represents the range of values greater than "a" and less than "b" (i.e., terminals a and b excluded). while any range of values designated by the term "from a to b" means the range of values from "a" to "b" (i.e. including the strict limits a and b).

By the term "composition based", it is understood in the present description a composition comprising the mixture and / or the reaction product in situ of the various constituents used, some of these basic constituents (for example the elastomer , the filler or other additive conventionally used in a rubber composition intended for the manufacture of tire) being capable of, or intended to react with each other, at least in part, during the various phases of manufacture of the composition intended for the manufacture of pneumatic. An essential characteristic of the rubber composition according to the invention is to comprise a diene elastomer.

By "diene" elastomer (or indistinctly rubber), one or more elastomers consisting at least in part (ie, a homopolymer or a copolymer) of monomeric diene units (monomers carrying two carbon double bonds) must be understood in known manner. -carbon, conjugated or not).

These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". The term "essentially unsaturated" is generally understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a level of units or units of diene origin (conjugated dienes) which is greater than 15% (mol%); 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 described as "essentially saturated" diene elastomers ( low or very low diene origin, always less than 15%). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer is particularly understood to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%. Given these definitions, the term "diene elastomer" can be understood more particularly to be used in the compositions according to the invention:

(a) - any homopolymer of a conjugated diene monomer, especially any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) - any copolymer obtained by copolymerizing one or more conjugated dienes with one another or with one or more vinyl romatic compounds having from 8 to 20 carbon atoms;

(c) - a ternary copolymer obtained by copolymerization of ethylene, an α-olefin having from 3 to 6 carbon atoms with a non-conjugated diene monomer containing from 6 to 12 carbon atoms, for example elastomers obtained at from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene;

(d) - a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated versions, in particular chlorinated or brominated, of this type of copolymer.

Although it applies to any type of diene elastomer, the person skilled in the tire art will understand that the present invention is preferably implemented with essentially unsaturated diene elastomers, in particular of the type (a) or (b). ) above.

In the case of copolymers of type (b), these contain from 20 to 99% by weight of diene units and from 1 to 80% by weight of vinylaromatic units.

As conjugated dienes 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C ₁ -C ₅ alkyl) -1,3-butadienes, such as for example 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1 3-butadiene, aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene.

Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the "vinyl-toluene" commercial mixture, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene and divinylbenzene. vinylnaphthalene.

Preferably, the diene elastomer is a substantially unsaturated elastomer chosen from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. As diene elastomer is particularly suitable polybutadiene (BR), a copolymer of butadiene and styrene (SBR), a natural rubber (NR) or a synthetic polyisoprene (IR) preferably having a molar ratio of cis-1,4 bond greater than 90%. The rubber composition according to the invention comprises a 1,3-dipolar compound. The term 1,3-dipolar compound is included as defined by IUPAC.

The 1,3-dipolar compound corresponds to formula (I):

Q.-A-B (I)

in which :

Q. comprises a dipole containing at least and preferably a nitrogen atom,

A, preferably divalent, is an atom or a group of atoms connecting Q. to B,

B comprises an imidazole ring corresponding to formula (II):

in which :

3 of the 4 symbols Z, Y, R and R ', which are identical or different, each represent an atom or a group of atoms, Z and Y being able to form together with the carbon atoms to which they are attached a ring (of course when neither Z, neither Y denotes the ^4T symbol),

and the only fourth symbol designates a direct attachment to A.

According to a first variant of the invention, R denotes a direct connection to A, in which case R is the 4 ^th symbol.

According to this variant, R 'may be a hydrogen atom or a carbon group which may contain at least one heteroatom.

According to a preferred embodiment of this variant, R 'represents a carbon group containing from 1 to 20 carbon atoms, preferably an aliphatic group, more preferably an alkyl group which preferably contains from 1 to 12 carbon atoms.

According to a second variant of the invention, R 'denotes a direct connection to A, in which case R' is the ^4th symbol. According to the first or the second variant, Z and Y may each be a hydrogen atom. According to another embodiment of the first variant or the second variant, Z and Y together with the carbon atoms to which they are attached a cycle. The ring formed by Z, Y and the atoms to which Z and Y are attached may be substituted or unsubstituted and may include at least one heteroatom. Z and Y can form with the two carbon atoms to which they are attached an aromatic ring. In this case, the imidazole ring may be a substituted or unsubstituted benzimidazole.

According to a third variant of the invention, of course when Y and Z do not form together with the carbon atoms to which they are attached a ring, Y or Z denotes a direct attachment to A, in which case Y or Z is the fourth ^ring. symbol.

According to a particular embodiment of the second or third variant of the invention, R represents a hydrogen atom or a carbon group which may contain at least one heteroatom. According to this particular embodiment of the second variant or of the third variant of the invention, R may be a group of 1 to 20 carbon atoms, preferably an aliphatic group, more preferably an alkyl group preferably containing 1 to 12 carbon atoms, even more preferably methyl.

A may be a group containing up to 20 carbon atoms, which group may contain at least one heteroatom. A may be an aliphatic or aromatic group.

When A is an aliphatic group, A preferably contains from 1 to 20 carbon atoms, more preferably from 1 to 12 carbon atoms, even more preferably from 1 to 6 carbon atoms, more particularly from 1 to 3 carbon atoms. When A is an aromatic group, A preferably contains from 6 to 20 carbon atoms, more preferably from 6 to 12 carbon atoms. As divalent group A is particularly suitable an alkylene group containing from 1 to 20 carbon atoms, preferably from 1 to 12 carbon atoms, more preferably from 1 to 6 carbon atoms, even more preferably from 1 to 3 carbon atoms. As the divalent group A containing from 1 to 3 carbon atoms, the methylene group is suitable. As divalent group A may also be suitable an arylene group preferably containing from 6 to 20 carbon atoms, more preferably from 6 to 12 carbon atoms.

Particularly suitable 1,3-dipolar compounds are compounds selected from the group consisting of nitrile oxides, nitrile imines and nitrones, in which case Q. contains a -C≡N → O, -C≡N → moiety → N- or -C = N (→ 0) -.

According to the particular embodiment of the invention, wherein Q. comprises a -C≡N-> O, Q. preferably has, more preferably represents the unit corresponding to formula (III) in which four of the five symbols R1 to R5, which are identical or different, are

each atom or group of atoms and the fifth symbol denotes a direct attachment to A, wherein R1 and R5 are both different from H. The four of the five symbols R1 to R5 may be aliphatic or aromatic groups. The aliphatic groups may contain from 1 to 20 carbon atoms, preferably from 1 to 12 carbon atoms, more preferably from 1 to 6 carbon atoms, even more preferably from 1 to 3 carbon atoms. The aromatic groups may contain from 6 to 20 carbon atoms, preferably from 6 to 12 carbon atoms.

R 1, R 3 and R 5 are each preferably an alkyl group of 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, even more preferably a methyl or ethyl group. According to a variant of this particular embodiment of the invention, R1, R3 and R5 are identical. According to this variant in which they are identical, R 1, R 3 and R 5 are each preferably an alkyl group of 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, even more preferentially a methyl or ethyl group.

More preferably, the 1,3-dipolar compound is 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzonitrile oxide having the formula (N1a) or the compound 2,4,6-triethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzonitrile oxide having the formula (IIIb):

According to the particular embodiment of the invention wherein Q comprises a -C = N (-> O) -, Q preferably has, more preferably represents the unit of formula (IV) or (V )

Y _r HC; O

(IV)

Y ₂

Y ₂ -HC _; O

(V)

in which :

Y 1 is an aliphatic group, preferably an alkyl group preferably containing 1 to 12 carbon atoms, or an aromatic group containing from 6 to 20 carbon atoms, preferentially an alkylaryl group, more preferably a phenyl or tolyl group,

and Y ₂ , having a direct attachment to A, is an aliphatic group, preferentially an alkylene group preferably containing 1 to 12 carbon atoms, or an aromatic group preferably containing 6 to 20 carbon atoms and having on its benzene ring the direct attachment to A.

The direct attachment of the benzene ring of Y ₂ to A amounts to saying that A is a substituent of the benzene ring of Y ₂ .

According to this particular embodiment of the invention, the 1,3-dipolar compound is the compound of formula (IVa), (IVb), (Va) or (Vb)

(IVa)

The amount of 1,3-dipolar compound introduced into the rubber composition is expressed as molar equivalents of imidazole ring. For example, if the 1,3-dipolar compound contains a single imidazole ring of formula (II) as defined above, one mole of 1,3-dipolar compound corresponds to one mole of imidazole ring. If the 1,3-dipolar compound contains two imidazole rings of formula (II) as defined above, one mole of 1,3-dipolar compound corresponds to two moles of imidazole ring. In the latter case, the use of the 1,3-dipolar compound according to a molar equivalent of imidazole ring corresponds to a half-mole of 1,3-dipolar compound.

According to any embodiment of the invention, the amount of 1,3-dipolar compound in the rubber composition is preferably between 0 and 3 molar equivalents, more preferably between 0 and 2 molar equivalents, more preferably between 0 and 1 molar equivalent, or even more preferably between 0 and 0.7 molar equivalent of imidazole ring per 100 mol of monomeric units constituting the diene elastomer. These preferred ranges make it possible to optimize more finely the compromise between the stiffness at bake and the hysteresis of the rubber composition according to its application, in particular in a tire. For each of these preferred ranges, the lower limit is preferably at least 0.1 molar equivalents of 1,3-dipolar compound.

The rubber composition according to the invention comprises a reinforcing filler comprising a reinforcing inorganic filler.

By "reinforcing inorganic filler" is meant in this application, by definition, any inorganic or mineral filler (regardless of its color and origin (natural or synthetic), also called "white" filler, "clear" filler even "non black charge"("non-black fi Mer") as opposed to carbon black, capable of on its own, without any means other than an intermediate coupling agent, reinforcing a rubber composition intended for the manufacture of tires, in other words able to replace, in its reinforcing function, a conventional carbon black of pneumatic grade ; such a charge is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferentially silica (SiO ₂ ). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m ² / g, preferably from 30 to 400 m ² / g, in particular between 60 and 300 m ² / g-A of highly dispersible precipitated silicas (called "HDS"), there may be mentioned for example the silicas "Ultrasil" 7000 and "Ultrasil" 7005 from the company Degussa, silicas "Zeosil" 1165 MP, 1135MP and 1115MP from Rhodia, the "Hi-Sil" silica EZ150G from PPG, the "Zeopol" silicas 8715, 8745 and 8755 from Huber, high surface area silicas such as described in WO 03/016387.

In the present disclosure, the BET surface area is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, specifically according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: time at 160 ° C - relative pressure range p / po: 0.05 at 0.17). The CTAB specific surface is the external surface determined according to the French standard NF T 45-007 of November 1987 (method B).

The physical state under which the reinforcing inorganic filler is present is indifferent, whether in the form of powder, microbeads, granules or beads. Of course, reinforcing inorganic filler is also understood to mean mixtures of different reinforcing inorganic fillers, in particular of highly dispersible silicas as described above.

Those skilled in the art will understand that as an equivalent load of the reinforcing inorganic filler described in this paragraph, it would be possible to use a reinforcing filler of another nature, in particular an organic filler such as carbon black, since this filler reinforcing would be covered with an inorganic layer such as silica, or would comprise on its surface functional sites, including hydroxyl, requiring the use of a coupling agent to establish the connection between the filler and the elastomer. By way of example, mention may be made, for example, of carbon blacks for tires as described for example in documents WO 96/37547 and WO 99/28380. According to a preferred embodiment, the reinforcing filler consists mainly of a reinforcing inorganic filler, that is to say that the proportion of reinforcing inorganic filler is greater than 50% by weight of the total weight of the reinforcing filler.

It will be noted that the reinforcing filler may contain, in addition to the abovementioned reinforcing inorganic filler (s), at least one organic filler, such as carbon black. This reinforcing organic filler is then preferably present in a weight fraction of less than 50% relative to the total weight of the reinforcing filler.

Suitable carbon blacks are all carbon blacks, especially blacks conventionally used in tires. Among the latter, there will be mentioned more particularly the reinforcing carbon blacks of the series 100, 200, 300, or the series blacks 500, 600 or 700 (ASTM 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 black, when present, is preferably used at a level of less than 20 phr, more preferably less than 10 phr (for example between 0.5 and 20 phr, in particular between 2 and 10 phr). In the ranges indicated, it benefits from the coloring properties (black pigmentation agent) and anti-UV carbon blacks, without otherwise penalizing the typical performance provided by the reinforcing inorganic filler.

According to a particular embodiment of the invention, the reinforcing inorganic filler, preferably a silica, represents more than 50% by weight of the mass of the reinforcing filler of the rubber composition. It is said that the reinforcing inorganic filler is the majority.

The total reinforcing filler content is preferably between 30 and 160 phr, more preferably between 40 phr and 160 phr. Within 30 phr, the reinforcement of the rubber composition may be insufficient to provide an adequate level of cohesion or wear resistance of the rubber component of the tire comprising this composition. Even more preferably, the total reinforcing filler content is at least 50 phr. Beyond 160 phr, there is a risk of increasing the hysteresis and therefore the rolling resistance of the tires. For this reason, the total reinforcing filler content is preferably in a range from 50 to 140 phr, especially for use in a tread of pneumatic. Any of these total reinforcing charge ratio ranges can be applied to any of the embodiments of the invention.

In order to couple the reinforcing inorganic filler to the diene elastomer, a coupling agent is used in a well-known manner, in particular an at least bifunctional silane (or bonding agent) intended to ensure a sufficient connection, of a chemical and / or physical nature. , between the inorganic filler (surface of its particles) and the diene elastomer.

The rubber composition according to the invention comprises, as coupling agent, a blocked thiol comprising an organooxysilyl or silanol group, hereinafter referred to as blocked thiol.

By organooxysilyl group is meant an SiOR group ^c where R ^c denotes a carbon group in which one carbon atom is bonded to the oxygen atom.

According to any of the embodiments of the invention, the thiol function of the coupling agent is preferably protected by an acyl group, in particular - C (= O) - A ¹ , the symbol A ¹ representing a group monovalent hydrocarbon selected from linear or branched alkyls, cycloalkyls or aryls having from 1 to 18 carbon atoms.

According to a first variant of the invention, the coupling agent is a blocked thiol (blocked mercaptosilane) of formula (la '): (R ² O) ₃ - _a R'a Si - Z ¹ - S - C (= 0) - A ¹ (the ')

in which :

the symbols R ¹ , which are identical or different, each represent a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

the symbols R ² , which are identical or different, each represent a hydrogen or a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

the symbol A ¹ being as defined previously;

the symbol Z ¹ represents a divalent linking group comprising from 1 to 18 carbon atoms;

a is an integer equal to 0, 1 or 2 The coupling agents of formula (la ') are for example described in patent application WO 9909036, WO 0248256, WO 2010072682, WO 2013087693, WO2013087698, WO2010072685. According to any one of the embodiments of the first variant, R ¹ is preferably chosen from methyl, ethyl, n-propyl and isopropyl, more preferably from methyl and ethyl, even more preferably methyl.

According to one embodiment of the first variant of the invention, the symbols R ² , which are identical or different, each represent a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 18 atoms. carbon, a being 0, 1 or 2. According to this embodiment, R2 is preferably methyl or ethyl. The coupling agents that are suitable for this embodiment are qualified in the present application as monocarboxylic acid, diorganooxysilane or triorganooxysilane species. Such coupling agents, such as S-octanoylmercaptopropylethoxydimethylsilane, S-octanoylmercaptopropyldiethoxymethylsilane, S-octanoylmercaptopropyltriethoxysilane, S-octanoylmercaptopropylmethoxydimethylsilane, S-octanoylmercaptopropyldimethoxymethylsilane and S-octanoylmercaptopropyltrimethoxysilane, are described, for example, in US Pat. WO 99/09036, WO 02/48256.

According to another embodiment of the first variant of the invention, the symbols R ² each represent a hydrogen, a being equal to 1 or 2. The coupling agents that are suitable for this embodiment are qualified in the present application of monohydroxysilane or dihydroxysilane species. These coupling agents, such as S-octanoylmercaptopropyhydroxydimethylsilane and S-octanoylmercaptopropyldihydroxymethylsilane, are for example described in patent applications WO 2010072682 and WO 2013087693. According to any one of the embodiments of the first variant of the invention. A ¹ is preferably chosen from alkyls having 1 to 18 carbon atoms and the phenyl radical, more preferably from alkyls having 1 to 7 carbon atoms and the phenyl radical. According to any of the first alternative embodiments of the invention, Z ¹ is preferably selected from alkylene Ci-Ci ₈ and arylene C ₆ -C ₂ ,, more preferably among alkylenes C ₁ -C ₀ , even more preferred among C 1 -C 4 alkylenes. According to one embodiment of the first variant of the invention, a is equal to 0. Advantageously, the blocked mercaptosilane corresponds to the formula (Ma ')

According to another embodiment of the first variant of the invention, the coupling agent is an organooxysilane of formula (la ') partially hydrolysed, in other words two of the R ² groups are respectively a hydrogen and a hydrocarbon group as defined previously. This embodiment of course applies when a is equal to 0 or 1.

According to the first variant of the invention, the coupling agent may be a mixture of compounds of formula (la ') which differ from each other by the chemical nature of their groups. In particular, the coupling agent may be a mixture of coupling agents chosen from monoorganooxysilane, diorganooxysilane, triorganooxysilane, monohydroxysilane and dihydroxysilane species.

According to a second variant of the invention, the coupling agent is of formula (Ib ').

R ⁴ R ³ Si - Z ¹ - S - C (= O) - A ¹ (Ib ')

in which :

the symbol R ³ being R ¹ or OR ² as defined previously,

the symbol R ⁴ represents a divalent group -O (R ⁵ CR ⁶ ) _m O- which forms a cyclic structure with the silicon atom,

R ⁵ and R ⁶ , identical or different, are R ² ,

m is an integer ranging from 1 to 15,

the symbols A ¹ and Z ¹ being as defined previously.

The coupling agents of formula (Ib ') are for example described in patent applications WO2006023785, WO 2006023815. According to the second variant of the invention, the coupling agent can be a mixture of compounds of formula (Ib') which are differentiated from each other by the chemical nature of their groups. According to a third variant of the invention, the coupling agent can be a mixture of compounds of formula (Ia ') and of formula (Ib').

According to a fourth variant of the invention, the coupling agent is a partially self-condensed form of (la ') or (Ib'). These coupling agents are typically siloxanes, products of the condensation reaction of the silanol or organooxysilyl functions of the compounds of formula (Ia ') or (Ib'). They have the characteristic of containing both an Si-O-Si siloxane function and a silanol or organooxysilyl function. According to a fifth variant of the invention, the coupling agent may be a by-product of the synthesis of the compound of formula (Ib '). This by-product results from a secondary reaction occurring in the formation of the cyclic Si-R ⁴ bond in the synthesis process of (Ib '), for example by addition of a diol on two different molecules of a halosilane. While the formation of the cyclic bond results from an intramolecular reaction, the by-product is the result of an intermolecular reaction. Such coupling agents are for example described in patent applications WO2006023785, WO 2006023815.

The coupling agent may be a mixture of the coupling agents defined according to any one of the variants of the invention. As a mixture, there may be mentioned for example:

a mixture of a compound defined according to the second variant and of a compound defined according to the fifth variant;

a mixture of a compound defined according to the first or second variant and a compound defined according to the fourth variant.

Typically, the coexistence of these compounds in a mixture may result from the method of synthesis of the compounds of formula (Ia ') or (Ib').

The blocked thiol content is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Typically, the blocked thiol content represents from 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler. Its level is preferably between 0.5 and 12 phr, more preferably in a range from 3 to 10 phr. This level is easily adjusted by those skilled in the art according to the level of reinforcing inorganic filler used in the composition.

In addition to the blocked thiol described, the rubber composition may contain another coupling agent. This other coupling agent may be a mercaptosilane, in particular derived from a blocked mercaptosilane of formula (Ia ') or (Ib') after deprotection of the thiol function. This other coupling agent can also be an organosilane or an at least bifunctional polyorganosiloxane, in particular a polysulfurized silane, said "symmetrical" or "asymmetrical" according to its particular structure, as described for example in WO03 / 002648 (or US 2005/016651) and WO03 / 002649 (or US 2005/016650). The rubber composition in accordance with the invention may also contain, in addition, coupling activators, inorganic charge-covering agents or, more generally, processing aid agents that can be used in a known manner, by means of an improvement. the dispersion of the filler in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green state.

The rubber composition in accordance with the invention may also comprise all or part of the usual additives normally used in elastomer compositions intended to constitute external mixtures of finished articles of rubber such as tires, in particular treads, such as, for example, plasticizers or extension oils, whether the latter are of aromatic or non-aromatic nature, especially very low or non-aromatic oils (eg, paraffinic oils, hydrogenated naphthenic oils, MES or TDAE oils), vegetable oils , in particular glycerol esters such as glycerol trioleate, hydrocarbon plasticizing resins having a high Tg, preferably greater than 30 ° C, as described for example in the applications WO 2005/087859, WO 2006/061064 and WO 2007 / 017060, pigments, protective agents such as anti-ozone waxes, anti-ozonants chemicals, anti-oxidants, d anti-fatigue agents, reinforcing resins (such as resorcinol or bismaleimide), acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M) as described for example in the application WO 02/10269 , a vulcanization system, vulcanization accelerators or retarders, vulcanization activators. The vulcanization system is preferably based on sulfur, but it may also be based on sulfur donors.

The rubber composition according to the invention is manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first phase of work or thermomechanical mixing (so-called "non-productive" phase) to high temperature, up to a maximum temperature between 130 ° C and 200 ° C, followed by a second mechanical working phase (so-called "productive" phase) to a lower temperature, typically less than 110 ° C, for example between 40 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system. The process for preparing the rubber composition according to the invention further comprising a vulcanization system comprises the following steps:

- Adding during a first so-called non-productive step to the diene elastomer the 1,3-dipolar compound, the reinforcing filler, the blocked thiol, by mixing thermomechanically until a maximum temperature of between 130 and 200 ° C is reached ,

- cool the assembly to a temperature below 100 ° C,

- then incorporate the vulcanization system,

- mix everything up to a maximum temperature below 120 ° C.

The amount of 1,3-dipolar compound added is preferably between 0 and 3 molar equivalents, more preferably between 0 and 2 molar equivalents, more preferably between 0 and 1 molar equivalent, or even more preferably between 0 and 0.7 molar equivalent of imidazole ring per 100 moles of monomeric units constituting the diene elastomer. For each of these preferred ranges, the lower limit is preferably at least 0.1 molar equivalents of 1,3-dipolar compound.

According to a preferred embodiment of the invention, the 1,3-dipolar compound is mixed with the diene elastomer before the introduction of the other constituents of the rubber composition, in particular before the addition of the reinforcing filler and the thiol blocked. The contact time between the diene elastomer and the 1,3-dipolar compound which are intimately mixed, in particular thermomechanically kneaded, is adjusted according to the mixing conditions, in particular the thermomechanical kneading, in particular as a function of the temperature. . The higher the temperature, the shorter the contact time. Typically it is from 1 to 5 minutes for a temperature of 100 to 130 ° C.

According to this preferred embodiment of the invention, at least one antioxidant is preferably added to the diene elastomer before it is introduced into a mixer, in particular at the end of the synthesis of the diene elastomer as is conventionally done.

After the incorporation of all the ingredients of the rubber composition, the final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded, for for example forming a rubber profile used as a rubber component for the manufacture of the tire. Thus according to a particular embodiment of the invention, the rubber composition according to the invention, which can be either in the green state (before vulcanization), or in the fired state (after vulcanization), is in a tire , especially in a tire tread.

The aforementioned features of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given as non-limiting and non-limiting.

II. EXAMPLES OF EMBODIMENT OF THE INVENTION II.1-Measurements and Tests Used: NMR Analysis:

The structural analysis as well as the determination of the molar purities of the synthesis molecules are carried out by NMR analysis. The spectra are acquired on a BRUKER Avance 3 400 MHz spectrometer equipped with a 5 mm BBFO-zgrad "broadband" probe. Experience quantitative NMR ¹ H, uses a simple pulse sequence 30 ° and a repeating time of 3 seconds between each 64 acquisitions. The samples are solubilized in deuterated dimethyl sulfoxide (DMSO). This solvent is also used for the lock signal. Calibration is performed on the deuterated DMSO proton signal at 2.44ppm against a TMS reference at Oppm. The ¹ H NMR spectrum coupled to the HSOC ¹ H / 13C and HMBC ¹ H / ¹³ C 2D experiments allows the structural determination of the molecules (see allocation tables). The molar quantifications are made from the quantitative 1D ¹ NMR spectrum.

Rheometry:

The measurements are carried out at 150 ° C. with an oscillating chamber rheometer according to DIN 53529 - Part 3 (June 1983). The measurements are processed according to DIN 53529 - Part 2 (March 1983). The evolution of the rheometric torque as a function of time describes the evolution of the stiffening of the composition as a result of the vulcanization reaction and thus makes it possible to follow the progress of the vulcanization. The minimum torque value C min is measured for each composition. The Cmin is representative of the green viscosity (before vulcanization) of the rubber composition and makes it possible to apprehend the aptitude of the rubber composition to be implemented (in English "processability").

Dynamic properties: The dynamic properties tan (δ) max are measured on a viscoanalyzer (Metravib VA4000) according to ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm in thickness and 400 mm ² in section), subjected to a sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, is recorded under normal conditions. temperature (23 ° C) according to ASTM D 1349-99. A strain amplitude sweep is performed from 0.1% to 100% (forward cycle) and then from 100% to 0.1% (return cycle). The dynamic shear complex modulus (G *) and the modulus difference (AG *) are measured between the values at 0.1 and 100% deformation (Payne effect).

11.2-Synthesis of 1,3-dipolar 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzonitrile oxide

This compound can be prepared according to the following reaction scheme:

11.2-1-Synthesis of 2- (chloromethyl) -1,3,5-trimethylbenzene:

This compound can be obtained according to a procedure described in the following article: Zenkevich, IG; Makarov, AA; Russian Journal of General Chemistry; flight. 77; nb. 4; (2007); p. 611-619 (Zhurnal Obshchei Khimii, vol.77, no.4, (2007), pp. 653-662)

A mixture of mesitylene (100.0 g, 0.832 mol), paraformaldehyde (26.2 g, 0.874 mol) and hydrochloric acid (240 mL, 37%, 2.906 mol) in acetic acid (240 mL ) is stirred and heated very slowly (1.5 hours) to 37 ° C. After cooling to room temperature, the mixture is diluted with water (1.0 l) with CH ₂ Cl ₂ (200 ml), the product is extracted with CH ₂ Cl ₂ (4 times per 50 ml). The organic phases are combined and then washed with water (5 times per 100 ml) and evaporated to 11-12 mbar (bath temperature = 42 ° C.). A colorless oil (133.52 g, 95% yield) is obtained. After 15-18 hours at + 4 ° C, the oil has crystallized. The crystals are filtered, washed with petroleum ether cooled to -18 ° C (40 ml) and then dried for 3 to 5 hours under atmospheric pressure at room temperature. A white solid (95.9 g, 68% yield) melting point 39 ° C is obtained. The molar purity is greater than 96% (1H NMR).

11.2-2-Synthesis of 3- (chloromethyl) -2,4,6-trimethylbenzaldehyde:

This compound can be obtained according to a procedure described in the following article: Yakubov, A. P .; Tsyganov, D. V .; Belenkii, L. I .; Krayushkin, M. M .; Bulletin of the USSR Academy of Sciences, Division of Chemical Science; flight. 40; nb. 7.2;

(1991); p. 1427 - 1432 (Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7 (1991), pp. 1609 - 1615

To a solution of TiCl ₄ (90.0 g, 0.474 mol) in dichloromethane (200 ml) at 17 ^° C is added under argon for 10-12 minutes a solution of 2- (chloromethyl) -1,3,5 trimethylbenzene (20.0 g, 0.118 mol) and dichloromethyl methyl ether (27.26 g, 0.237 mol) in dichloromethane (200 mL). After stirring for 15-20 minutes at 17-20 ^° C, water (1000 ml) and ice (500 g) are added to the reaction medium. After 10-15 minutes of stirring, the organic phase is separated. The aqueous phase is extracted with CH ₂ Cl ₂ (3 times in 75 ml). The combined organic phases are washed with water (4 times per 100 ml) and evaporated under reduced pressure to yield a solid ( bath = 28 ^° C). The target product (22.74 g) is obtained with a yield of 97%. Its melting point is 58 ° C. The molar purity estimated by ¹ H NMR is 95 mol%.

11.2-3-Sy-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzaldehyde:

A mixture of 3- (chloromethyl) -2,4,6-trimethylbenzaldehyde (10.0 g, 0.051 mol) and imidazole (10.44 g, 0.127 mol) in DMF (10 ml) is stirred at 80 ^°. C for an hour. After returning to 40-50 ° C, the mixture is diluted with water (200ml) and stirred for 10 minutes. The precipitate obtained is filtered and washed on the filter with water (4 times per 25 ml) and then dried at room temperature. A white solid (7.92 g, 64% yield) with a melting point of 161 ° C. is obtained. The molar purity is 91% ( ^1- NMR).

11.2-4-Synthesis of 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzaldehyde oxime:

To a solution of 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzaldehyde (20.3 g, 0.084 mol) in EtOH (110 mL) at 40 ^° C is added an aqueous solution of hydroxylamine (809 g, 0.134 mol, 50% in water, Aldrich) in EtOH (10 ml). The reaction medium is stirred for 2.5 hours at a temperature of 50 to 55 ° C. After returning to 23 ° C., the precipitate obtained is filtered and washed twice on the filter with an EtOH / H ₂ O mixture (10 ml / 15 ml) and dried for 15 to 20 hours under atmospheric pressure at room temperature. A white solid (19.57 g, 91% yield) with a melting point of 247 ° C. is obtained. The molar purity is greater than 87% ( ¹ H NMR).

11.2-5-Synthesis of 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzonitrile oxide:

To a mixture of 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzaldehyde oxime (8.80 g, 0.034 mol) in CH ₂ Cl ₂ (280 ml) at 6 ° C is added dropwise an aqueous solution of NaOCI (4% active chlorine, Aldrich, 49 ml) for 5 minutes. The temperature of the reaction medium is maintained between 6 and 8 ° C. The reaction medium is then stirred for 2 hours at 8 ° C. to 21 ° C. The organic phase is separated. The organic phase is washed with water (3 times in 50 ml). After concentration under reduced pressure (bath temperature = 22-23 ° C, 220 mbar), petroleum ether (10 ml) is added, the solvent is evaporated to 8-10 ml, and the solution is maintained at -18 ° C for 10-15 hours to obtain a precipitate. The precipitate is filtered and washed on the filter by the mixture of CH ₂ Cl ₂ / petroleum ether (2 ml / 6 ml) and then with petroleum ether (2 times 10 ml) and finally dried for 10-15 hours under atmospheric pressure at room temperature. A white solid (5.31 g, 61% yield) with a melting point of 139 ° C. is obtained. The molar purity is greater than 95 mol% ( ¹ H NMR).

II.3-Preparation of the rubber compositions:

The 1,3-dipolar compound whose synthesis is described above is used.

The compositions are prepared in the following manner: an internal mixer (final filling ratio: about 70% by volume) is introduced, the initial vessel temperature of which is about 110 ° C., the elastomer, if necessary, the 1,3-dipolar compound which is kneaded alone with the elastomer for about 2 minutes at 110 ° C., then the silica, the coupling agent, as well as the various other ingredients with the exception of the vulcanization. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts about 5 minutes to 6 minutes, until a maximum "falling" temperature of 160 ° C. is reached. The mixture thus obtained is recovered, cooled, and sulfur and a sulfenamide type accelerator are incorporated on a mixer (homo-finisher) at 23 ° C., mixing the whole (productive phase) for a suitable time (for example between 5 hours). and 12 min). The compositions thus obtained are then calendered, either in the form of plates (with a thickness ranging from 2 to 3 mm) or thin rubber sheets, for the measurement of their physical or mechanical properties, or in the form of directly usable profiles, after cutting and / or assembly to the desired dimensions, for example as semi-finished products for tires, in particular for treads.

The crosslinking is carried out at 150 ° C. The crosslinking time applied, t ' _c (90), is the time required for the pair of the composition to reach 90% of the maximum torque of the composition. The torques of the com position are measured at 150 ° C with an oscillating chamber rheometer according to DIN 53529 - Part 3 (June 1983). t ' _c (90), is determined according to standard NF T 43-015 for each of the compositions. From one composition to another, it varies from 20 to 40 minutes.

The formulations (in phr) of the compositions T1, T2, T3, A and B are described in Table I. All compositions contain a reinforcing inorganic filler, a silica.

Tl contains neither blocked mercaptosilane of formula (Γ) nor 1,3-dipolar compound of formula (I). T2 and T3 contain a blocked mercaptosilane of formula (), but do not contain a 1,3-dipolar compound of formula (I). The compositions T1, T2 and T3 are not in accordance with the invention.

A and B contain both a 1,3-dipolar compound of formula (I) and a blocked mercaptosilane of formula (Γ). A and B are in accordance with the invention.

The results are shown in Table I I. Comparison of the results of the compositions T1 and T2 on the one hand, Tl and T3 on the other hand shows that the replacement of the polysulfide silane Si69 by a blocked mercaptosilane of formula (I) in a rubber composition is accompanied by a decrease Cmin of 16 and 30%. Comparing the compositions A and B respectively with the composition Tl, it is unexpectedly observed that the combined use of a blocked mercaptosilane of formula () and a 1,3-dipolar compound of formula (I) makes it possible to reduce The Cmin value is further devalued, which corresponds to a decrease of the Cmin values of at least 50% relative to the control composition Tl.

These results for A and B are obtained without detriment of the AG * values at 23 ° C, since the low AG * values at 23 ° C remain at a low level, even lower than the Tl, T2 and T3. These values reflect a good dispersion of the reinforcing inorganic filler. All of these results show unexpectedly that the combined use of a blocked mercaptosilane of formula () and a 1,3-dipolar compound of formula (I) in an inorganic filler-reinforced rubber composition, silica makes it possible to significantly improve the implementation of the rubber composition without penalizing the dispersion of the reinforcing inorganic filler.

Table I

(1) SBR: SBR with 26% styrene and 25% 1,2 of the butadiene moiety

(2) 1,3-dipolar compound, the synthesis of which is described above in section 11.2 (2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) ) benzonitrile oxide)

(3) "Zeosil 1165 MP" silica from Rhodia (type HDS)

(4) TESPT ("Si69" from Degussa)

(5) Silane NXT 'from GE Silicones

(6) "NXT * Z 45" of the Momentive Company

(7) N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, from Flexsys

(8) MES / HPD

(9) Resin C5 / C9

(10) N-cyclohexyl-2-benzothiazol sulfenamide ("Santocure CBS" from the company Flexsys

Table I I

Composition Tl T2 T3 A B

Cmin dNm 12.8 10.7 8.9 5.5 6.2

AG * (MPa) at 23 ° C 7.1 6.1 6.9 2.0 3.0

G * (MPa) at 23 ° C 2.8 2.8 3.1 2.8 3.1

Claims

claims

A rubber composition based on at least one diene elastomer, a reinforcing filler comprising a reinforcing inorganic filler, a 1,3-dipolar compound of formula (I) and a blocked thiol having an organooxysilyl or silanol group ,

Q.-A-B (I)

in which :

B comprises a ring of formula II)

in which :

and the fourth symbol Z, Y, R or R 'denotes a direct attachment to A.

The rubber composition of claim 1 wherein R 'denotes a direct attachment to A.

The rubber composition of claim 2 wherein Z and Y are each a hydrogen atom.

A rubber composition according to claim 2 wherein Z and Y together with the carbon atoms to which they are attached form a ring, preferably an aromatic ring.

A rubber composition according to any one of claims 2 to 4 wherein R represents a hydrogen atom or a carbon group which may contain at least one heteroatom and preferably containing from 1 to 20 carbon atoms.

The rubber composition of claim 5 wherein R is an aliphatic group, preferably an alkyl group which preferably contains 1 to 12 carbon atoms. The rubber composition of claim 6 wherein R is methyl.

A rubber composition according to any one of claims 1 to 7 wherein A is a group containing up to 20 carbon atoms and may contain at least one heteroatom.

9. A rubber composition according to claim 8 wherein A is an aliphatic group preferably containing from 1 to 20 carbon atoms, more preferably from 1 to 12 carbon atoms, even more preferably from 1 to 6 carbon atoms, or a group aromatic containing preferentially from 6 to 20 carbon atoms, more preferably from 6 to 12 carbon atoms.

10. A rubber composition according to claim 9 wherein A is an alkylene group containing 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms, even more preferably 1 to 6 carbon atoms. 3 carbon atoms, or an arylene group preferably containing from 6 to 20 carbon atoms, more preferably from 6 to 12 carbon atoms.

11. A rubber composition according to any of claims 1 to 10 wherein the 1,3-dipolar compound is selected from the group consisting of nitrile oxides, nitrile imines and nitrones.

The rubber composition of claim 11 wherein Q contains a -C≡N → O motif.

The rubber composition according to claim 12 wherein Q comprises, preferably represents the unit of formula (III):

in which four of the five symbols R1 to R5, which are identical or different, are each an atom or a group of atoms, preferably an aliphatic group or an aromatic group, and the fifth symbol denotes a direct attachment to A, given that R1 and R5 are all two different from H.

The rubber composition of claim 13 wherein R1, R3 and R5 are the same.

15. A rubber composition according to any one of claims 13 to 14 wherein RI, R3 and R5 are each an alkyl group of 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms.

16. The rubber composition of claim 15 wherein R1, R3 and R5 are each methyl or ethyl.

The rubber composition according to claim 16, wherein the 1,3-dipolar compound is 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzonitrile oxide or 2,4,6-triethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzonitrile oxide. 18. A rubber composition according to any one of claims 1 to 17 wherein the amount of 1,3-dipolar compound is between 0 and 3 molar equivalents, preferably between 0 and 2 molar equivalents, more preferably between 0 and 1 equivalent. molar, even more preferably between 0 and 0.7 molar equivalent of imidazole ring per 100 mol of monomeric units constituting the diene elastomer.

The rubber composition according to any one of claims 1 to 18 wherein the diene elastomer is a substantially unsaturated elastomer selected from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

20. A rubber composition according to any one of claims 1 to 19 wherein the blocked thiol is of formula (la ')

(R ² 0) ₃ - _a R'a Si - Z ¹ - S - C (= O) - A ¹ (la ') in which:

the symbols R ¹ , which are identical or different, each represent a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms; the symbols R ² , which are identical or different, each represent a hydrogen or a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

the symbol A ¹ represents a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms;

- a is an integer equal to 0, 1 or 2.

21. Composition according to any one of claims 1 to 20 wherein R ¹ is selected from methyl, ethyl, n-propyl and isopropyl, preferably from methyl and ethyl, more preferably methyl. 22. Composition according to any one of claims 1 to 21 wherein A ¹ is chosen from alkyls having 1 to 18 carbon atoms and the phenyl radical, preferably from alkyls having 1 to 7 carbon atoms and the phenyl radical.

23. Composition according to any one of claims 1 to 22 wherein. Z ¹ is selected from alkylene Ci-Ci ₈ and arylene C ₆ -C ₂ ,, preferably from alkylene Ci-Ci _0, more preferably from alkylene Ci-C _4.

24. Composition according to any one of claims 1 to 23, wherein a is equal to 0.

25. Composition according to any one of claims 1 to 24 wherein the blocked thiol has the formula (Ma ')

26. A rubber composition according to any one of claims 1 to 25 wherein the reinforcing inorganic filler is a silica.

27. A rubber composition according to any one of claims 1 to 26 wherein the reinforcing inorganic filler is more than 50% by weight of the reinforcing filler.

28. Composition according to any one of claims 1 to 27, wherein the amount of reinforcing filler is greater than 50 phr, preferably in a range from 50 to 140 phr. 29. Composition according to any one of claims 1 to 28, wherein the blocked thiol content represents from 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler.

30. Composition according to any one of claims 1 to 29, wherein the blocked thiol content is between 0.5 and 12 phr, preferably in a range from

3 to 10 pce.

31. A rubber composition according to any one of claims 1 to 30 wherein it comprises a vulcanization system.

The process for preparing a rubber composition defined in claim 31, which process comprises the following steps:

during the first so-called non-productive step, the 1,3-dipolar compound, the reinforcing filler and the thiol blocked by thermomechanically kneading until a maximum temperature between

130 and 200 ° C,

- cool the assembly to a temperature below 100 ° C,

- then incorporate the vulcanization system,

- mix everything up to a maximum temperature below 120 ° C,

which 1,3-dipolar compound is as defined in any one of claims 1 to 31.

33. The process of claim 32 wherein the diene elastomer and the 1,3-dipolar compound are mixed prior to the addition of the reinforcing filler and the blocked thiol.

34. A tread which comprises a rubber composition according to any one of claims 1 to 31.

35. A tire which comprises a rubber composition according to any one of claims 1 to 31, preferably in its tread.