EP2694581A1

EP2694581A1 - Rubber tyre composition comprising an azo-silane coupling agent

Info

Publication number: EP2694581A1
Application number: EP12710754.8A
Authority: EP
Inventors: Christelle DARNAUD; José Carlos ARAUJO DA SILVA; Karine Longchambon; Anne Veyland
Original assignee: Michelin Recherche et Technique SA Switzerland; Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Current assignee: Michelin Recherche et Technique SA Switzerland; Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2011-04-01
Filing date: 2012-03-28
Publication date: 2014-02-12
Also published as: FR2973384A1; US20140371345A1; CN103459485A; JP2014514395A; WO2012130884A1; FR2973384B1

Abstract

The invention relates to a rubber composition for tyres, comprising at least a diene elastomer, an inorganic reinforcing filler, and a coupling agent linking the inorganic filler and the diene elastomer. The composition is characterised in that the coupling agent is an azo-silane compound having formula (I) (G¹)_3-a(G²)_aSi-Z-NH-C(O)-N=N-C(O)-NH-Z-Si(G¹)_3-a(G²)_a, wherein: - G¹, which may be identical or different, each represent a monovalent hydrocarbon group selected from among optionally substituted, linear or branched alkyls having between 1 and 18 carbon atoms, cycloalkyls or aryls, optionally substituted, having between 5 and 18 carbon atoms; - G², which may be identical or different, each represent a hydroxyl group or a monovalent group selected from among optionally substituted, linear or branched alkoxyls having between 1 and 18 carbon atoms, cycloalkoxyls, optionally substituted, having between 5 and 18 carbon atoms; - Z represents a divalent linking group comprising between 1 and 18 carbons; and - a is equal to 1, 2 or 3.

Description

PNEUMATIC RUBBER COMPOSITION COMPRISING AZOSILANE COUPLING AGENT

The present invention relates to compositions of diene elastomers reinforced with an inorganic filler such as silica, intended for the manufacture of tires or semi-finished products for tires, in particular to the treads of these tires.

It relates more particularly to coupling agents intended to ensure the connection in such compositions between these diene elastomers and these reinforcing inorganic fillers.

In order to reduce the fuel consumption and nuisances emitted by motor vehicles, significant efforts have been made by tire designers to obtain tires with both a very low rolling resistance, improved adhesion, and improved performance. on dry ground only on wet or snowy ground, as well as a good resistance to wear.

This has been made possible in particular by the development of new elastomer compositions reinforced with specific inorganic fillers described as "reinforcing", having a high dispersibility, capable of competing with the conventional carbon black from the reinforcing point of view, and also offering these compositions a reduced hysteresis synonymous with a lower rolling resistance for the tires comprising them. Such rubber compositions, comprising reinforcing inorganic fillers, for example of the silica or alumina type, have for example been described in patents or patent applications EP 501 227 or US Pat. No. 5,227,425, EP 735,088 or US Pat. No. 5,852,099. 810,258 or US 5,900,449, EP 881,252, WO99 / 02590, WO99 / 06480, WO00 / 05300, WO00 / 05301, WO02 / 10269. The implementation (or "processability") of the rubber compositions containing such fillers nevertheless remains more difficult than for conventional carbon-loaded rubber compositions. In particular, it is necessary to use a coupling agent, also called bonding agent, whose function is to ensure the connection between the surface of the inorganic filler particles and the elastomer, while facilitating the dispersion of this load inorganic within the elastomeric matrix.

By "coupling" agent (inorganic filler / elastomer), it is recalled here that must be understood, in known manner, an agent capable of establishing a sufficient connection, of a chemical and / or physical nature, between the inorganic filler and the elastomer diene. Such a coupling agent, at least bifunctional, has the simplified general formula "YW-X", in which: Y represents a functional group ("Y" function) which is capable of binding physically and / or chemically to the feedstock such a bond can be established, for example, between a silicon atom of the coupling agent and the hydroxyl groups (OH) surface of the inorganic filler (for example the surface silanols when it comes to silica);

X represents a functional group ("X" function) capable of binding physically and / or chemically to the diene elastomer, for example via a sulfur atom;

- W represents a divalent group making it possible to connect "Y" and "X". In particular, the coupling agents must not be confused with simple inorganic filler agents which, in a known manner, may comprise the active "Y" function with respect to the inorganic filler but are in any case without the function "X" active vis-à-vis the diene elastomer. Coupling agents, in particular (silica / diene elastomer), have been described in a large number of patent documents, the best known being bifunctional sulphide silanes, in particular alkoxysilanes, which are nowadays considered as products providing, for vulcanizates loaded with silica, the best compromise in terms of safety when roasting, ease of implementation and strengthening power. Among these sulphurized silanes, bis 3-triethoxysilylpropyl tetrasulfide (abbreviated to TESPT), a reference coupling agent in tires with low rolling resistance and called "green tires" for the energy saving offered, must be mentioned in particular. ("Energy-saving Green Tires" concept). It is still sought today to improve the performance of these coupling agents for inorganic filler such as silica.

The need is particularly present in the case of rubber matrices based on an isoprene elastomer such as those used in the treads of heavy-duty tires, in which, in known manner, an effective bond with the elastomer is much more difficult to obtain compared to the use of carbon black.

Pursuing their research, the Applicants have discovered a new coupling agent which, alone but also in combination with other types of coupling, makes it possible to very significantly improve the coupling performance on a diene elastomer, and in particular an isoprene elastomer.

The subject of the invention is thus a rubber composition for a tire based on at least one diene elastomer, an inorganic filler as reinforcing filler, a coupling agent ensuring the bond between the inorganic filler and the diene elastomer, characterized in that the coupling agent is an azosilane compound of the following formula (I):

in which :

- G ¹ , identical or different, each represent a monovalent hydrocarbon group selected from alkyls, linear or branched, substituted or unsubstituted, having from 1 to 18 carbon atoms, cycloalkyls or aryls, substituted or unsubstituted, having 5 to 18 carbon atoms,

G ² , which are identical or different, each represent a hydroxyl group or a monovalent group chosen from linear or branched, substituted or unsubstituted alkoxyls having from 1 to 18 carbon atoms, the substituted or unsubstituted cycloalkoxyls having from 5 to 18 carbon atoms,

Z represents a divalent linking group comprising from 1 to 18 carbon atoms; a is equal to 1, 2 or 3. Preferably, the diene elastomer is chosen from the group consisting of polybutadienes, synthetic polyisoprenes and rubber. butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

Preferably, the reinforcing inorganic filler is a siliceous or aluminous filler.

The invention also relates to a tire or semi-finished product comprising a rubber composition as described above, and further relates to a tire tread comprising such a rubber composition.

MEASUREMENTS AND TESTS USED

The rubber compositions are characterized, before and after firing, as indicated below. Traction tests

These tensile tests make it possible to determine the modulus of elasticity and the properties at break and are based on the standard F ISO 37 of December 2005.

The secant modulus (or apparent stress, in MPa, referred to strain, without unit) at 100 is measured as a second elongation (Le., After an accommodation cycle at the extension rate provided for the measurement itself). % elongation (noted MA100) and 300% elongation (noted MA300). The true stress at break (in MPa) and the elongation at break (in%) are also measured.

Dynamic Property The dynamic property tan (δ) _max is 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 according to the ASTM D standard. 1349 - 99. A strain amplitude sweep of 0.1 to 90% (forward cycle) and then 90% to 0.1% (return cycle) are performed. The result exploited is the loss factor (tan δ). For the return cycle, the maximum value of tan δ observed (tan (δ) max) is given between the values at 0, 1% and at 50% deformation (Payne effect).

DETAILED DESCRIPTION OF THE INVENTION

The compositions of the invention are therefore based on at least one diene elastomer, an inorganic filler as reinforcing filler and an azosilane compound of formula (I) as inorganic filler coupling agent. diene elastomer.

By the term "base-based" composition is meant in the present application a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents (for example the coupling agent). being capable of, or intended to react with each other, at least in part, during the different phases of manufacture of the compositions, in particular during their vulcanization (cooking).

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight. Diene elastomer

By elastomer or "diene" rubber, is generally meant an elastomer derived at least in part (i.e. a homopolymer or a copolymer) of monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or not).

The diene elastomers, in known manner, can be classified into two categories: those said to be "essentially unsaturated" and those termed "essentially saturated". By "essentially unsaturated" diene elastomer is meant 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, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within this definition and may instead be referred to 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 obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) - any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

(c) - a ternary copolymer obtained by copolymerization of ethylene, an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to

12 carbon atoms, for example elastomers obtained from ethylene, propylene with a nonconjugated 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, those skilled in the tire art will understand that the present invention is preferably implemented with essentially unsaturated diene elastomers, in particular of type (a) or (b) above.

By way of conjugated dienes, 1,3-butadiene, 2-methyl-1,3-butadiene and 2,3-di-(C 1 -C 5) -l-3-butadienes, such as for example 2-butadiene, are especially suitable. 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, ary 1-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methyl styrene, the commercial "vinyl-toluene" mixture, para-tertiobutyl styrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene.

The copolymers may contain from 99% to 20% by weight of diene units and from 1% to 80% by weight of vinyl aromatic units. The elastomers may have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the amounts of modifying and / or randomizing agent used. The elastomers can be for example block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or starred or functionalized with a coupling agent and / or starring or functionalization. For coupling with carbon black, there may be mentioned, for example, functional groups comprising a C-Sn bond or amino functional groups such as benzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may be made, for example, of silanol or polysiloxane functional groups having a silanol end (as described, for example, in FR 2,740,778 or US Pat. No. 6,013,718), alkoxysilane groups (such as as described for example in FR 2,765,882 or US 5,977,238), carboxylic groups (as described for example in WO 01/92402 or US 6,815,473, WO 2004/096865 or US 2006/0089445) or groups polyethers (as described for example in EP 1 127 909 or US Pat. No. 6,503,973). As other examples of functionalized elastomers, mention may also be made of elastomers (such as SBR, BR, R or IR) of the epoxidized type.

Polybutadienes, and in particular those having a content (mol%) in units -1.2 of between 4% and 80%, or those having a content (mol%) of cis-1,4 of greater than 80%, are suitable. polyisoprenes, copolymers of butadiene-styrene and in particular those having a Tg (glass transition temperature (Tg, measured according to ASTM D3418) of between 0 ° C. and -70 ° C. and more particularly between -10 ° C. and -60 ° C. C, a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (mol%) in -1,2 bonds of the butadiene part of between 4% and 75%, a content (mol%) in trans-1,4 bonds of between 10% and 80%), butadiene-isoprene copolymers and especially those having a content of in isoprene of between 5% and 90% by weight and a Tg of -40 ° C. to -80 ° C., the isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg between - 25 ° C and - 50 ° C. In the case of butadiene-styrene-isoprene copolymers are especially suitable those having a styrene content of between 5% and 50% by weight and more particularly of between 10% and 40%, an isoprene content of between 15% and 60%. by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content (mol%) in -1,2 units of the butadiene part between 4% and 85%), a content (mol%) in trans-1,4 units of the butadiene part of between 6%> and 80%), a content (mol%) in units -1,2 plus -3.4 of the isoprene part of between 5% and 70% and a content (mol%) in trans units of -1.4 of the isoprene part of between 10% and 50%, and more generally any butadiene-styrene copolymer isoprene having a Tg between -20 ° C and -70 ° C.

In summary, particularly preferably, the diene elastomer of the composition according to the invention is selected from the group of diene elastomers (highly unsaturated) consisting of polybutadienes (BR), synthetic polyisoprenes (TR), rubber natural (NR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-copolymers butadiene-styrene (SBIR) and mixtures of such copolymers.

According to a particular embodiment, the diene elastomer is predominantly (Le., For more than 50 phr) an SBR, whether it is an emulsion prepared SBR ("ESBR") or a prepared SBR in solution ("SSBR"), or a blend (mixture) SBR / BR, SBR / NR (or SBR / IR), BR / NR (or BR / IR), or SBR / BR / NR (or SBR / BR / IR). In the case of an SBR elastomer (ESBR or SSBR), an SBR having an average styrene content, for example between 20% and 35% by weight, or a high styrene content, for example 35 to 35% by weight, is used in particular. 45%, a vinyl ring content of the butadiene part of between 15% and 70%, a content (mol%) of trans-1,4 bonds of between 15% and 75% and a Tg of between -10 ° C. and - 55 ° C; such an SBR can be advantageously used in admixture with a BR preferably having more than 90% (mol%) of cis-1,4 bonds.

According to another particular embodiment, the diene elastomer is predominantly (for more than 50 phr) an isoprene elastomer. This is particularly the case when compositions of the invention are intended to constitute, in tires, the rubber matrices of certain treads (for example for industrial vehicles), crown reinforcing plies (for example of working plies, protective plies or hooping webs), carcass reinforcement plies, sidewalls, beads, guards, underlayments, rubber blocks and other internal gums providing the interface between the aforesaid areas of the tires.

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

According to another particular embodiment, especially when it is intended for a tire sidewall, a tubeless tire sealing inner liner (or other airtight element), the composition according to the invention may contain less than an essentially saturated diene elastomer, in particular at least one EPDM copolymer or a butyl rubber (optionally chlorinated or brominated), that these copolymers are used alone or in admixture with highly unsaturated diene elastomers as mentioned above, in particular NR or IR, BR or SBR.

According to another preferred embodiment of the invention, the rubber composition comprises a blend of one (or more) diene elastomers called "high Tg" having a Tg between -70 ° C and 0 ° C and d one (or more) diene elastomers known as "low Tg" between -110 ° C and -80 ° C, more preferably between -105 ° C and -90 ° C. The high Tg elastomer is preferably selected from the group consisting of S-SBR, E-SBR, natural rubber, synthetic polyisoprenes (having a (mol%) content of cis-1,4 linkages of preferably greater than 95%), BIRs, SIRs, SBIRs, and mixtures of these elastomers. The low Tg elastomer preferably comprises butadiene units at a level (mol%) of at least 70%); it consists preferably of a polybutadiene (BR) having a content (mol%) of cis-1,4 chains greater than 90%. According to another particular embodiment of the invention, the rubber composition comprises, for example, from 30 to 100 phr, in particular from 50 to 100 phr, of a high Tg elastomer in a blend with 0 to 70 phr, in particular from 0 to 50 phr, of a low Tg elastomer; according to another example, it comprises for all 100 pce one or more SBR prepared (s) in solution.

According to another particular embodiment of the invention, the diene elastomer of the composition according to the invention comprises a blend of a BR (as low elastomer Tg) having a rate (mol%) of cis chains -1.4 greater than 90%, with one or more S-SBR or E-SBR (as elastomer (s) high Tg).

The compositions of the invention may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer (s) may be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.

Reinforcing inorganic filler By "reinforcing inorganic filler" is meant here, in known manner, any inorganic or inorganic filler, regardless of its color and origin (natural or synthetic), also called "white" filler, "clear" filler "or" non-black filler "charge as opposed to carbon black, this inorganic filler being able to reinforce on its own, with no other means than an intermediate coupling agent, a rubber composition intended for the manufacture of a tread of tires, in other words able to replace, in its reinforcing function, a conventional carbon black pneumatic grade, in particular for tread; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

Preferably, the reinforcing inorganic filler is a filler of the siliceous or aluminous type, or a mixture of these two types of filler.

The silica (SiO ₂ ) used may be any reinforcing silica known to those skilled in the art, especially any precipitated or fumed silica having a BET surface and a CTAB specific surface area both less than 450 m 2 / g, preferably 30 at 400 m / g. Highly dispersible precipitated silicas (so-called "HDS") are preferred, in particular when the invention is used for the manufacture of tires having a low rolling resistance; examples of such silicas mention the "Ultrasil 7000" silicas from Degussa, the "Zeosil 1165 MP, 1135 MP and 1115 MP" silicas from Rhodia, the "Hi-Sil EZ150G" silica from PPG, the "Zeopol 8715, 8745" silicas or 8755 "of the Huber Society. The reinforcing alumina (Al 2 O 3) preferably used is a highly dispersible alumina having a BET surface area ranging from 30 to 400 m 2 / g, more preferably from 60 to 250 m 2 / g, an average particle size of at most 500 nm, more preferably at most equal to 200 nm. As non-limiting examples of such reinforcing aluminas, there may be mentioned the aluminas "Baikalox A125" or "CR125" (Baikowski company), "APA-100RDX" (Condea), "Aluminoxid C" (Degussa) or "AKP-G015" (Sumitomo Chemicals).

By way of other examples of inorganic filler suitable for use in the tread rubber compositions of the invention, mention may also be made of aluminum (oxide) hydroxides, aluminosilicates, titanium oxides, silicon carbides or nitrides, all of the reinforcing type as described for example in the applications WO 99/28376, WO 00/73372, WO 02/053634, WO 2004/003067, WO 2004/056915. When the treads of the invention are intended for tires with low rolling resistance, the reinforcing inorganic filler used, in particular if it is silica, preferably has a BET surface area of between 60 and 350 m 2 / boy Wut. An advantageous embodiment of the invention consists in using a reinforcing inorganic filler, in particular a silica, having a high BET specific surface area, in a range of 130 to 300 m ² / g, because of the high reinforcing power of such charges. According to another preferred embodiment of the invention, it is possible to use a reinforcing inorganic filler, in particular a silica, having a BET specific surface area of less than 130 m ² / g, preferably in such a case of between 60 and 130 m ^2. / g (see for example WO03 / 002648 and WO03 / 002649).

The physical state in which the reinforcing inorganic filler is present is indifferent whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers as described above.

Those skilled in the art will be able to adapt the degree of reinforcing inorganic filler according to the nature of the inorganic filler used and according to the type of tire concerned, by example tire for motorcycle, for passenger vehicle or for commercial vehicle such as van or truck. Preferably, this level of reinforcing inorganic filler will be chosen between 20 and 200 phr, more preferably between 30 and 150 phr, in particular greater than 50 phr, and more preferably still less than 140 phr.

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, more precisely according to the French standard F 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). Finally, one skilled in the art will understand that, as equivalent filler of the reinforcing inorganic filler described in this paragraph, it would be possible to use a reinforcing filler of another nature, in particular organic, since this reinforcing filler would be covered with an inorganic layer such as silica, or would comprise on its surface functional sites, in particular hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. Examples of such organic fillers include functionalized polyvinylaromatic organic fillers as described in WO 2006/069792 and WO 2006/069793. The reinforcing inorganic filler can be used also associated with an organic reinforcing filler, in particular carbon black, for example a black of the HAF, ISAF, SAF type, conventionally used in tires and particularly in the treads of tires (for example). black examples NI 15, N134, N234, N326, N330, N339, N347, N375, or, depending on the targeted applications, blacks of higher series, for example N660, 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 elastomer in the form of a masterbatch (see for example WO 97/36724 or WO 99/16600).

The amount of carbon black present in the total reinforcing filler can vary within wide limits, it is preferably lower than that of the reinforcing metal hydroxide. Advantageously, carbon black is used in a very small proportion, at a preferential rate of less than 10 phr. In the ranges indicated, the coloring properties (black pigmentation agent) and anti-UV properties of the carbon blacks, without also penalize the typical performances provided by the reinforcing inorganic filler. Of course, the composition of the invention may be completely devoid of carbon black. Coupling agent

The azosilane compound according to the invention, used as coupling agent has the formula:

in which :

Z represents a divalent linking group comprising from 1 to 18 carbon atoms; a is equal to 1, 2 or 3. In the formula (I) above, the person skilled in the art will immediately understand that the function (noted "X" in the introduction of the present application) intended to ensure the connection with the diene elastomer is provided by the central azodicarbamide group (NC (0) -N = NC (O) -N), while two functions (denoted " Y "in the introduction of the present application) intended to ensure the binding with the reinforcing inorganic filler are provided by the silyl groups which carry at least one hydroxyl group or hydrolysable attached to their silicon atom.

Advantageously, Z may contain one or more heteroatoms chosen from O, S, N and Si.

Preferably, a is 3.

Advantageously, Z is chosen from C ₁ -C 18 alkylenes and C ₆ -C ₁₂ arylenes, preferably from C ₁ -C ₁₀ alkylenes, more preferably Z is chosen from C ₁ -C ₄ alkylenes, and even more preferentially Z is a propylene. According to one embodiment, G ² is an ethoxyl.

Coupling agents which are suitable for the invention are: (EtO) ₃ Si-CH 2 -NH-CO-N = N-CO-NH-CH ₂ -Si (OEt) 3,

(EtO) ₃ Si-CH ₂ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -CH ₂ -Si (OEt) ₃ ,

(EtO) ₃ Si-CH ₂ -CH ₂ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -CH ₂ -CH ₂ -Si (OEt) ₃ ,

(EtO) ₃ Si-CH ₂ -CH ₂ -CH ₂ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -CH ₂ -CH ₂ -CH ₂ -Si (OEt) ₃ , (EtO ) ₃ Si- (CH ₂₎ n-NH-CO-N = N-CO-NH- (CH ₂₎ ₁₁ -Si (OEt) _3,

(EtO) ₃ Si- (CH ₂ ) i ₂ -NH-CO-N = N-CO-NH- (CH ₂ ) ₁₂ -Si (OEt) ₃ ,

(EtO) ₃ Si-CH ₂ CH (CH ₃ ) CH ₂ -NH-CO-N = N-CO-NH-CH ₂ CH (CH ₃ ) CH ₂ -Si (OEt) ₃ ,

(EtO) ₃ Si-CH ₂ -CH ₂ -C ₆ H ₄ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -C ₆ H ₄ -CH ₂ -CH ₂ -Si (OEt) ₃ , (EtO) ₃ Si-CH ₂ -CH ₂ -C ₆ H ₄ -NH-CO-N = N-CO-NH-C ₆ H ₄ -CH ₂ -CH ₂ -Si (OEt) ₃ ,

(MeO) ₃ Si-CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -Si (OMe) ₃ ,

(MeO) ₃ Si-CH ₂ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -CH ₂ -Si (OMe) ₃ ,

(MeO) ₃ Si-CH ₂ -CH ₂ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -CH ₂ -CH ₂ -Si (OMe) ₃ ,

(MeO) ₃ Si-CH ₂ -CH ₂ -CH ₂ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -CH ₂ -CH ₂ -CH ₂ -Si (OMe) ₃ , (MeO ) ₃ Si- (CH ₂₎ n-NH-CO-N = N-CO-NH- (CH ₂₎ ₁₁ -Si (OMe) _3,

(MeO) ₃ Si- (CH ₂ ) i ₂ -NH-CO-N = N-CO-NH- (CH ₂ ) ₁₂ -Si (OMe) ₃ ,

(MeO) ₃ Si-CH ₂ CH (CH ₃ ) CH ₂ -NH-CO-N = N-CO-NH-CH ₂ CH (CH ₃ ) CH ₂ -Si (OMe) ₃ ,

(MeO) ₃ Si-CH ₂ -CH ₂ -C ₆ H ₄ -CH ₂ -NH-CO-N = N-CO-NH-CH ₂ -C ₆ H ₄ -CH ₂ -CH ₂ -Si (OMe) ₃ , (MeO) ₃ Si-CH ₂ -CH ₂ -C ₆ H ₄ -NH-CO-N = N-CO-NH-C ₆ H ₄ -CH ₂ -CH ₂ -Si (OMe) ₃ , with Me = methyl, Et = ethyl and R = C ₁₃ H ₂₇ (OCH ₂ CH ₂ ) ₅ .

And more particularly the compound 1-2 azodicarboxylic acid, bis (3-aminopropyl triethoxysilane) amide is suitable for the invention, the following formula (Ia) °, in which a is equal to 3, G ² is an ethoxyl and Z is a propylene

(CH ₃ CH ₂ O) ₃ Si- (CH ₂ ) ₃ -NH-C (O) -N = NC (O) -NH- (CH ₂ ) ₃ -Si (OCH ₂ CH ₃ ) ₃ The azosilane compounds of formula (I) according to the invention may be prepared via an acylation reaction between an azobiscarboxy compound of formula (A):

G ⁴ -Z'-C (O) -N = NC (O) -Z'-G ⁴

and an aminosilane compound of formula (B):

(G ¹ ) 3-a (G ² ) _to Si-Z-NH ₂

in which

Z ', which may be identical or different, each represents an oxygen atom, an NH or NA ¹ radical, where A ¹ is a C ¹ -C 12 alkyl or aryl group, G ⁴ , which may be identical or different, each represents a hydrogen atom, a Cl-Cl 8 alkyl group, a benzyl group (-CH ₂ -C ₆ H ₅ ) or an alkyl group (CH ₂ -CH ₂ -O) _p - G ⁵ or (CH (CH ₃ ) -CH ₂ -O) _p -G ⁵ , where p is between 1 to 18 and G ⁵ , identical or different, represent a saturated or unsaturated, branched or unbranched, monovalent hydrocarbon chain, in C1-C32.

In particular, the reaction is preferably carried out in the presence of a solvent, in particular a non-alcoholic solvent, under an inert atmosphere atmosphere, at a temperature preferably of between -25 ° C. and 25 ° C.

According to one embodiment of the invention, the composition comprises a second coupling agent used in a blend with the azosilane compound of formula (I).

For this second coupling agent, the sulfurized silane compounds corresponding to formula (II) are particularly suitable: wherein: x is a number from 2 to 8, preferably from 2 to 5;

Z ¹ and Z ² , identical or different, each represent a divalent hydrocarbon radical having 1 to 18 carbon atoms;

Y ¹ and Y ² , identical or different, each respond to one of the formulas below:

in which :

the radicals R 1, which are substituted or unsubstituted, which are identical to or different from one another, represent a C 1 -C 18 alkyl or C ₅ -C ₅ cycloalkyl group;

IC8 or C ₆ -Ci8;

the radicals R 1, substituted or unsubstituted, which are identical to or different from each other, represent a hydroxyl, C 1 -C 18 alkoxyl or C 5 -C 18 cycloalkoxyl group. Preferably, Z ¹ and Z ² are chosen from the group consisting of C 1 -C 10 alkylenes, preferably C ¹ -C 4 alkylenes, and more preferably Z ¹ and Z ² represent propylene. According to one embodiment variant of the invention, the radicals R 1 are chosen from C 1 -C 4 alkyls, preferably methyl.

According to another variant embodiment of the invention, the radicals are chosen from the group consisting of hydroxyl and C 1 -C 4 alkoxyls, preferably from the group consisting of hydroxyl, methoxyl and ethoxyl.

Those skilled in the art will be able to adjust the organosilane content of formula (I) according to the particular embodiments of the invention, in particular the amount of reinforcing inorganic filler used, the preferential rate representing between 2% and 20% by weight relative to the amount of reinforcing inorganic filler; levels below 15% are more particularly preferred.

Thus, preferably, the overall level of coupling agent is between 2 and 15 phr, preferably between 2 and 12 phr. Various additives

The rubber compositions in accordance with the invention may also comprise all or part of the usual additives normally used in elastomer compositions intended for the manufacture of tires, in particular treads, such as, for example, plasticizers or lubricating oils. extension, whether these are aromatic or non-aromatic, pigments, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing resins, 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 crosslinking system based on either sulfur or sulfur donors and / or peroxide and / or bismaleimides, vulcanization accelerators, vulcanization activators.

Preferably, these compositions comprise, as preferred non-aromatic or very weakly aromatic plasticizing agent, at least one compound selected from the group consisting of naphthenic, paraffinic, MES, TDAE oils, esters (especially trioleate) oils. glycerol, the hydrocarbon plasticizing resins having a high Tg preferably greater than 30 ° C, and mixtures of such compounds. These compositions may also contain, in addition to the coupling agents, coupling activators, covering agents (comprising, for example, the only Y function) of the reinforcing inorganic filler or, more generally, processing aid agents capable of in a known manner, thanks to an improvement of the dispersion of the inorganic filler in the rubber matrix and to a lowering of the viscosity of the compositions, to improve their ability to use in the green state, these agents being for example hydroxylated or hydrolysable silanes such as alkylalkoxysilanes (especially alkyltriethoxysilanes), polyols, polyethers (for example polyethylene glycols), esters, primary, secondary or tertiary amines (for example trialkanol amines), hydroxylated POSs or hydrolyzable mixtures of such compounds, for example, ω-dihydroxy-polyorganosiloxanes (especially,-dihydroxy-pol ydimethylsiloxanes), fatty acids such as stearic acid. The reinforcing filler described above, that is to say the reinforcing inorganic filler plus carbon black, if appropriate, can also be added, depending on the intended application, inert (ie, non-reinforcing) fillers such as clay particles, bentonite, talc, chalk, kaolin, usable for example in colored tire sidewalls or treads.

Crosslinking system

The crosslinking system is preferably a vulcanization system, that is to say a system based on sulfur (or a sulfur-donor agent) and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the production phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide. , stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine)), or known vulcanization retarders.

Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The primary vulcanization accelerator is used at a preferred level of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr. It is possible to use as accelerator (primary or secondary) any compound capable of acting as accelerator for vulcanization of diene elastomers in the presence of sulfur, in particular thiazole-type accelerators and their derivatives, accelerators of the thiuram type, zinc dithiocarbamates. These accelerators are for example selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), tetrabenzylthiuram disulfide ("TBZTD"), N-cyclohexyl-2- benzothiazyl sulfenamide ("CBS"), N, N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide ("TBSI"), zinc dibenzyldithiocarbamate ("ZBEC"), 1-phenyl-2,4-dithiobiuret ("DTB"), zinc dibuthylphosphorodithioate ("ZBPD"), zinc 2-ethylhexylphosphorodithioate ("ZDT / S") ), bis-0,0-di (2-ethylhexyl) -thiophosphonyl disulfide ("DAPD"), dibutylthiourea ("DBTU"), zinc isopropyl-xanthate ("ZIX"), zinc dialkyl dithiophosphate, dilakyldithiophosphate, copper, dialkyl thiophosphoryl polysulfides, dialkyl dithiophosphoryl derivatives, dialkyl dithiophosphoryl derivatives (such as sine salts, cobalt salts, polysulfides, etc.) and mixtures of these compounds.

Manufacture of rubber compositions

The rubber compositions of the invention are manufactured in appropriate mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes called phase "non-productive") at a high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed by a second mechanical working phase (sometimes referred to as "Productive" phase) at lower temperature, typically below 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system or vulcanization.

According to a preferred embodiment of the invention, all the basic constituents of the compositions of the invention, with the exception of the vulcanization system, namely the reinforcing inorganic filler, the coupling agent of formula (I) and the carbon black are intimately incorporated, by kneading, with the diene elastomer during the first so-called non-productive phase, that is to say that it is introduced into the mixer and kneaded thermomechanically, in one or more steps, at least these various basic constituents until reaching the maximum temperature between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, the possible coating agents, are introduced into a suitable mixer such as a conventional internal mixer. or other complementary additives and other additives, with the exception of the vulcanization system. The total mixing time in this non-productive phase is preferably between 1 and 15 minutes. After cooling the mixture thus obtained during the first non-productive phase, the mixture is then incorporated. low temperature vulcanization system, generally in an external mixer such as a roll mill; the whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 min. Incorporation of the coating agent, if any, can be carried out entirely during the non-productive phase (Le., In the internal mixer), at the same time as the inorganic filler, or entirely during the phase productive (with the external mixer), or fractionated over the two successive phases. 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 in the form of a rubber profile that can be used, for example, as a tread. tire for passenger vehicle. The vulcanization (or cooking) is conducted in a known manner at a temperature generally between 130 ° C and 200 ° C, for a sufficient time which may vary for example between 5 and 90 min depending in particular on the cooking temperature, the system of vulcanization adopted and the kinetics of vulcanization of the composition under consideration.

The invention relates to the rubber compositions previously described both in the so-called "raw" state (Le., Before firing) and in the so-called "cooked" or vulcanized state (Le., After crosslinking or vulcanization). The compositions according to the invention can be used alone or in a blend (Le., In a mixture) with any other rubber composition that can be used for the manufacture of tires.

EXAMPLES OF CARRYING OUT THE INVENTION

Synthesis of silane A of formula (I-a)

Basic Ingredients:

- Diisopropyl azodicarboxylate (Jayhawk Chemicals) with a purity higher than 94%;

3-aminopropyl (triethoxy-silane) marketed by the company Evonik Degussa GmbH with a purity higher than 98%;

Pentane and isopropanol marketed by Aldrich, Acros and Merck-Schuchardt. 164.2 g (mmol 742) of 3-aminopropyl (triethoxy-silane) are used as the initial charge in 1000 g of pentane at 0 ° C. in a flask under an inert atmosphere, and the mixture is stirred. 75 g of diisopropyl azodicarboxylate (DIAD, 371 mmol) are added dropwise from -5 ° C. to 5 ° C., to the solution for a period of 30 minutes. Stirring is continued for an additional 30 minutes of -5 ° C. The cooling bath is then removed and the solution is stirred for 180 minutes, until the temperature of the mixture reaches room temperature, and all the volatile compounds (pentane, isopropanol) are then removed. a rotary evaporator at a pressure of up to 6 mbar The NMR studies show that the red oil obtained (194 g, yield greater than 99%) contains the target product with a purity greater than 85 mol%.

Synthesis of the Azosilane of Formula (III) The Azosilane of Formula (III)

is synthesized in two stages, according to the embodiment described in patent EP 1 893 681, as follows: by reaction of an isocyanate silane with an ethyl carbazate for forming a hydrazino precursor, according to the following reaction scheme:

then oxidation of the precursor above to obtain the compound Ethyl-N- (3-triethoxysilylpropyl) carbamoylazoformate.

- Synthesis of the precursor ingredient: a) fillers

b) operating protocol:

Ethyl carbazate and anhydrous toluene are charged at room temperature (23 ° C.) into the reactor which is placed under an argon atmosphere. The reactor is stirred at 300 rpm and the reaction mixture is then heated to 60 ° C. The reaction mixture becomes substantially homogeneous on heating. The 99.8 g of silane are then added in 60 min using an isobaric dropping funnel. The reaction mixture is stirred for 2 hours at 60 ° C. before returning to ambient temperature. The reaction mixture is left standing for a few hours at room temperature. A white solid crystallizes. It is then filtered, washed twice with 150 ml of isopropyl ether and then filtered under vacuum. The solid is finally dried in an oven at 60 ° C to constant weight equal to 131.5 g. The product is analyzed by NMR (molar purity> 99%). Yield = 97.4%.

Synthesis of the compound of formula III (final azosilane)

The azosilane of formula III is obtained in one step from the oxidation precursor of the azo-functional hydrazino function using an N-Bromosuccinimide (BS) and pyridine-based oxidant system added in stoichiometric amounts with respect to the precursor. a) charges

b) operating protocol:

The precursor, pyridine and dichloromethane are charged to a reactor which is placed under an argon atmosphere; the reaction medium is substantially colorless homogeneous. N-Bromosuccinimide is added in 30 minutes with a spatula. The temperature is kept below 25 ° C. From the first addition of NBS, the reaction medium becomes bright orange. The reaction medium is stirred at room temperature for 2 hours after the end of the addition of NBS. The reaction medium is concentrated under reduced pressure on a rotary evaporator. The residue, which is in the form of an orange paste, is taken up in 100 ml of a heptane / iPr ₂ mixture (1/1: vol / vol) and then filtered on a sintered glass (125 ml) of porosity. The filter cake is washed with an additional 4 x 25 ml of the above solvent mixture. The mother liquors are filtered a second time on the cake. The filtrate is concentrated under reduced pressure. An odorless bright orange liquid is obtained: m = 18.8 g.

This liquid is analyzed by NMR, its molar composition is as follows (mol%): azosilane of formula III: 94.5%;

precursor compound: 0.2%;

succinimide: 5%;

pyridine residues: 0.3%.

Preparation of rubber compositions

The following tests are carried out in the following manner: the diene elastomer, the silica supplemented with a small quantity, is introduced into an internal mixer filled to 70% and whose initial vessel temperature is approximately 90.degree. of carbon black, the coupling agent and then, after one to two minutes of mixing, the various other ingredients with the exception of the vulcanization system. Thermomechanical work (non-productive phase) is then carried out in one step (total mixing time equal to about 5 minutes), until a maximum temperature of "fall" of about 165 ° C. is reached. The mixture thus obtained is recovered, cooled and the coating agent (when the latter is present) and the vulcanization system (sulfur and sulfenamide accelerator) are added to an external mixer (homo-finisher) at 50 ° C. mixing the whole (productive phase) for about 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, or in the form of profiles that can be used directly, after cutting and / or or assembly to the desired dimensions, for example as semi-finished products for tires, in particular as treads of tires. Trial 1

This test is intended to demonstrate the improved properties of a rubber composition according to the invention comprising the novel coupling agent compared to a control composition using a coupling agent traditionally used in the rubber compositions for treads of tires having silica as a reinforcing filler.

Four compositions based on a diene elastomer (natural rubber, R) reinforced with a highly dispersible silica (HDS) are prepared for this purpose, these compositions essentially differing from the following technical characteristics:

the composition C1 is a first control composition containing the compound TESPT (trade name: "Si69") as coupling agent,

the composition C2 is a composition in accordance with the invention comprising the azosilane compound of formula (Ia) as a coupling agent with a number of moles identical to that of the TESPT of the first control composition (isomolar silicon content), the structure of the TESPT molecules having the same number of functions ensuring the bond with the charge as the coupling agent of formula (Ia) according to the invention,

composition C3 is a second control composition containing the azosilane compound of formula (III), see below, as coupling agent in which the amount of coupling agent has been adjusted so as to be at isomolar rate silicon with respect to the amount of coupling agent of formula (Ia) of the composition C2 according to the invention, in terms of functional group ensuring the binding to the inorganic filler (silicon isomolar rate).

The conventional coupling agent used in control composition Cl is TESPT. It is recalled that TESPT is bis (3-triethoxysilylpropyl) tetrasulfide having the structural formula (Et = ethyl):

The conventional coupling agent used in the control compositions C3 and C'3 is azosilane of structural formula (III) (Et = ethyl):

Tables 1 and 2 give the formulation of the various compositions (Table 1 - rate of the different products expressed in phr or parts by weight per hundred parts of elastomer) as well as their properties after firing (approximately 25 min at 150 ° C.); the vulcanization system is sulfur and sulfenamide.

Examination of the results in Table 2 shows firstly that the composition C2 according to the invention, comprising a coupling agent of formula (Ia), compared with the control composition C1 comprising the coupling agent TESTP, exhibits significantly improved properties concerning the reinforcement of the composition (MA300 / MA100) and also the hysteresis (values of tan (ô) _max significantly reduced), while maintaining properties that are almost similar in terms of properties at break (stress and elongation at breaking).

Furthermore, the comparison of the composition C3 not in accordance with the invention, comprising another coupling agent of formula with a rate corresponding to the composition C2 according to the invention, to an identical number of functions ensuring the connection. with the load, has both degraded elongation and degradation properties and degraded reinforcement (in particular the MA300 module is not measurable).

Trial 2

The object of this test is to demonstrate the improved properties of a rubber composition according to the invention comprising the novel coupling agent in a blend with another coupling agent conventionally used in tire tread rubber compositions having silica as a reinforcing filler, compared to a control composition comprising this coupling agent traditionally used alone as well as to a composition comprising a coupling of two coupling agents traditionally used.

the composition C l is identical to the composition C1 of the test 1 with the exception of the level of the coupling agent TESPT,

the composition C4 is a composition according to the invention comprising as coupling agent a blend consisting of 50% of TESPT compound relative to at the content of TESPT in composition C 1 and of azosilane compound of formula (Ia) with an isomolar silicon content relative to these 50% of TESPT, composition C5 is a second control composition comprising as coupling agent a cross-section consisting of 50% of TESPT compound relative to the level of TESPT in composition C 1 and an azosilane compound of formula (III) with an isomolar content relative to the amount of coupling agent of formula (I-a ) of the composition C4 according to the invention, in terms of functional group ensuring the binding to the inorganic filler (silicon isomolar rate). Tables 3 and 4 give the formulation of the various compositions (Table 3 - levels of the various products expressed in phr or parts by weight per hundred parts of elastomer) as well as their properties after curing (approximately 25 min at 150 ° C.); the vulcanization system is sulfur and sulfenamide. Table 4 shows that the composition C4 according to the invention, comprising as a coupling agent a coupling agent coupling of formula (Ia) and of TESPT compound, compared to the control composition C 1 comprising the agent TESTP coupling alone as well as composition C5 comprising a cleavage of azosilane compound of formula (III) and of TESPT compound, present:

significantly improved properties concerning the reinforcement of the composition (MA300 / MA100) with respect to the composition C 1 and of the same order of magnitude as for the composition C5,

significantly improved hysteresis properties (tan (δ) _max values significantly decreased) with respect to both compositions C 1 and C 5,

- And properties at break very close to those of the composition C 1, unlike the composition C5 which has properties at break (stress and elongation at break) degraded compared to the composition Cl.

It clearly appears that a composition in accordance with the invention comprising, as coupling agent, an azosilane compound of formula (I) alone or in a blend, in particular with another coupling agent conventionally used in tire compositions, makes it possible to obtain improved properties (strengthening, hysteresis) compared to the control compositions.

Claims

1) rubber composition for a tire based on at least one diene elastomer, an inorganic filler as a reinforcing filler, a coupling agent ensuring the bond between the inorganic filler and the diene elastomer, characterized in that the agent coupling agent is an azosilane compound of formula (I) below:

in which :

Z represents a divalent linking group comprising from 1 to 18 carbon atoms,

- a is equal to 1, 2 or 3.

2) A composition according to claim 1, wherein Z contains one or more heteroatoms selected from O, S, N and Si.

3) Composition according to any one of claims 1 or 2, wherein a is equal to 3. 4) Composition according to any one of claims 1 to 3, wherein Z is selected from alkylene Ci-Cis and C ₆ -C ₁₂ arylenes.

5) The composition of claim 4, wherein Z is selected from C1-C10 alkylenes, and preferably Z is selected from C1-C4 alkylene.

6) Composition according to claim 5, wherein Z is a propylene.

7) Composition according to any one of claims 1 to 6, wherein G ² is an ethoxyl. 8) Composition according to any one of the preceding claims, in which the diene elastomer is chosen from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and these elastomers.

9) Composition according to any one of the preceding claims, wherein the reinforcing inorganic filler is a siliceous or aluminous filler.

10) Composition according to any one of the preceding claims, wherein the amount of reinforcing inorganic filler is greater than 50 phr, preferably less than 140 phr.

11) Composition according to any one of claims 1 to 10, which comprises a second coupling agent.

12) Composition according to claim 11, wherein the second coupling agent consists of a sulphurized silane compound corresponding to formula (II): wherein: x is an integer of 2 to 8, preferably 2 to 5;

- The radicals R1, substituted or unsubstituted, identical or different from each other, represent a C ₁ -C 18 alkyl, C ₅ -C 18 cycloalkyl or C ₆ -C 18 aryl group; the radicals R 1, substituted or unsubstituted, which are identical to or different from each other, represent a hydroxyl, C 1 -C 18 alkoxyl or C 5 -C 18 cycloalkoxyl group. 13. The rubber composition according to claim 12, wherein Z ¹ and Z ² are selected from the group consisting of C 1 -C 10, preferably C 1 -C 4, alkylene.

14) A rubber composition according to claim 13, Z ¹ and Z ² representing propylene.

15) Composition according to any one of claims 12 to 14, the radicals R 1 being chosen from C 1 -C 4 alkyls, preferably representing methyl.

16) Composition according to any one of claims 12 to 15, the radicals R being chosen from the group consisting of hydroxyl and alkoxyls C1-C4, preferably from the group consisting of hydroxyl, methoxyl and ethoxyl.

17) Composition according to any one of the preceding claims, wherein the overall level of coupling agent is between 2% and 20% by weight relative to the amount of reinforcing inorganic filler; preferably this level is less than 15%.

18) Composition according to any one of the preceding claims, wherein the overall level of coupling agent is between 2 and 15 phr, preferably between 2 and 12 phr.

19) A rubber composition according to any one of the preceding claims, which comprises a covering agent selected from the group consisting of hydroxylated or hydrolyzable silanes, polyols, polyethers, esters, amines, hydroxylated or hydrolysable polysiloxanes, and mixtures of such compounds.

20. The composition of claim 19, wherein the coating agent is an α, )- (dihydroxy) -polyorganosiloxane oil. 21) Pneumatic or semi-finished product comprising a rubber composition according to any one of claims 1 to 20.

Tire tread comprising a rubber composition according to any one of claims 1 to 20.