WO2003097734A1 - Rubber composition for tyre comprising a coupling agent with polythiobenzothiazyl function - Google Patents

Abstract

.The invention concerns a elastomer composition for use in making tyres, based on at least (i) one diene elastomer, (ii) one inorganic filler as reinforcing filler and (iii) as coupling agent (inorganic filler/diene elastomer), one organosilicon compound having at least two functions capable of being grafted on the elastomer by means of a sulphur-containing group with polybenzothiazyl function, of formula (I): ≡Si -Z-Sx-Bzt,(AA)y, wherein: Z is a linear or branched divalent binding group for binding the polybenzothiazyl group with a silicon atom of the organosilicon compound; x is a whole or fractional number from 2 to 4; Bzt represents the 2-benzothiazole group, optionally substituted; AA represents an oxygenated organic or mineral monoacid or a polyacid, whereof at least one of the acid functions exhibits constant ionization in water, pKa, at 25 °C, higher than 3; y is a whole or fractional number other than 0 and not greater than 3. The invention also concerns tyres and tyre running treads comprising such a composition.

Description

 RUBBER COMPOSITION FOR TIRE COMPRISING A COUPLING AGENT WITH POLYTHIOBENZOTHIAZYL FUNCTION

The present invention relates to diene elastomer compositions reinforced with a white or inorganic filler, intended in particular for the manufacture of tires or semi-finished products for tires, in particular treads for these tires.

It relates more particularly to the use, in such compositions, of binding agents for the coupling of reinforcing inorganic fillers and diene elastomers.

It is generally known that, in order to obtain the optimal reinforcement properties imparted by a filler, it is necessary that the latter is present in the elastomeric matrix in a final form which is both as finely divided as possible and distributed by as homogeneously as possible. However, such conditions can only be achieved insofar as the filler has a very good ability, on the one hand to be incorporated into the matrix during mixing with the elastomer and to disaggregate, on the other hand to disperse homogeneously in this matrix.

In a completely known manner, carbon black exhibits such aptitudes, which is generally not the case for inorganic fillers. Indeed, for reasons of reciprocal affinities, the particles of inorganic charge have an unfortunate tendency, in the elastomeric matrix, to agglomerate between them. These interactions have the harmful consequence of limiting the dispersion of the filler and therefore the reinforcing properties to a level substantially lower than that which would theoretically be possible to achieve if all the bonds (inorganic filler / elastomer) capable of being created. during the mixing operation, were actually obtained. These interactions also tend to increase the viscosity in the raw state of the rubber compositions and therefore to make their implementation ("processability") more difficult than in the presence of carbon black.

Since fuel economy and the need to protect the environment have become a priority, it has however become necessary to produce tires with reduced rolling resistance, without penalizing their wear resistance. This was made possible in particular thanks to the discovery of new rubber compositions reinforced with specific inorganic fillers qualified as "reinforcing", capable of competing from the reinforcing point of view with a conventional carbon black of pneumatic grade, while offering these compositions a lower hysteresis, synonymous with a lower rolling resistance for the tires comprising them, as well as high grip properties on wet, snowy or icy conditions.

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 5,227,425, EP 735,088 or US 5,852,099, EP 810 258 or US 5 900 449, EP 881 252, WO99 / 02590, WO99 / 06480, WOOO / 05300, WO00 / 05301, WO02 / 10269. ^' Mention will be made in particular of documents EP 501 227, EP 735 088 or EP 881 252 which disclose dielectric rubber compositions reinforced with precipitated silicas with high dispersibility, such compositions making it possible to manufacture treads having a markedly improved rolling resistance. , without affecting the other properties, in particular those of adhesion, endurance and resistance to wear. Such compositions having such a compromise of contradictory properties are also described in application EP 810 258, with, as reinforcing inorganic fillers, specific aluminas with high dispersibility.

The use of these specific, highly dispersible inorganic fillers has certainly reduced the difficulties of processing in the raw state the rubber compositions containing them, but this processing nevertheless remains more difficult than for the compositions loaded conventionally with black. of carbon.

In particular, it is necessary to use a coupling agent, also called a bonding agent, which has the function of ensuring the bond between the surface of the particles of inorganic filler and the elastomer, while facilitating the dispersion of this filler inorganic within the elastomeric matrix.

By "coupling" agent (inorganic filler / elastomer) is understood in known manner a compound capable of establishing a sufficient connection, of chemical and / or physical nature, between the inorganic filler and the diene elastomer; such a coupling agent, at least bifunctional, has for example as simplified general formula "Y-T-X", in which:

Y represents a functional group (“Y” function) which is capable of physically and / or chemically binding to the inorganic charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and the surface hydroxyl groups (OH) of the inorganic filler (for example surface silanols when it is 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;

T represents a divalent organic group making it possible to connect Y and X.

Coupling agents should in particular not be confused with simple inorganic charge covering agents which in known manner may comprise the active Y function with respect to the inorganic charge but are devoid of the active X function with respect to - screw of the diene elastomer.

Coupling agents, in particular (silica / diene elastomer), have been described in numerous documents, the best known being bifunctional organosilanes carrying three organoxysilyl functions (in particular alkoxysilyl) as function Y, and, as function X , at least one function capable of reacting with the diene elastomer such as in particular a sulfur functional group (Le., comprising sulfur). Thus, it has been proposed in patent applications FR 2 094 859 or GB 1 310 379 to use a mercaptoalkoxysilane coupling agent for the manufacture of tire treads. It was quickly revealed and it is now well known that mercaptoalkoxysilanes are capable of providing excellent silica / elastomer coupling properties, but that the industrial use of these coupling agents is not possible due to the very high reactivity of the sulfur functions of the thiol -SH type (“X” functions) leading very quickly during the preparation of the rubber compositions, in an internal mixer, to premature vulcanizations also called “grilling”, very high viscosities in the raw state, ultimately rubber compositions almost impossible to work and implement industrially. To illustrate this problem, mention may be made, for example, of documents FR 2 206 330, US 3 873 489, US 4 002 594.

To remedy this drawback, it has been proposed to replace these mercaptoalkoxysilanes with polysulphurized alkoxysilanes, in particular bis- (alkoxylsilylρropyle) polysulphides as described in numerous documents (see for example FR 2 149 339, FR 2 206 330, US 3,842,111, US 3,873,489, US 3,997,581). Among these polysulfides, mention should be made in particular of bis 3-triethoxysilylpropyl tetrasulfide (abbreviated to TESPT) or bis 3-triethoxysilylpropyl disulfide (abbreviated to TESPD).

These polysulphurized alkoxysilanes, in particular TESPT, are generally considered to be the products providing, for vulcanizates comprising a reinforcing inorganic filler, in particular silica, the best compromise in terms of safety in roasting, ease of implementation and reinforcing power. As such, they are the coupling agents most used today in rubber compositions for tires.

However, unexpectedly, the Applicant has discovered during its research that specific coupling agents can exhibit coupling performance superior to that of polysulphurized alkoxysilanes, in particular to that of TESPT, in rubber compositions for tires.

These coupling agents are organosilicon compounds which have the essential characteristic of being carriers, as function X, of a particular polythiobenzothiazyl functional group. They also do not pose the aforementioned problems of premature roasting and those of implementation linked to too high a viscosity of rubber compositions in the raw state, disadvantages posed in particular by mercaptosilanes.

Consequently, a first subject of the invention relates to an elastomeric composition usable for the manufacture of tires, comprising at least, as basic constituents, (i) a diene elastomer, (ii) an inorganic filler as a reinforcing filler and ( iii), as coupling agent (inorganic filler / diene elastomer), an at least bifunctional organosilicon compound graftable on the elastomer by means of a sulfur group with polythiobenzothiazyl function, of formula:

(I) = Si - Z - S _x - Bzt, (AA) _y

in which: Z is a divalent linking group, linear or branched, making it possible to link the polythiobenzothiazyl group to a silicon atom of the organosilicon compound; x is an integer or fractional number from 2 to 4;

Bzt represents the group 2-benzothiazole, optionally substituted;

AA represents an oxygenated monoacid or polyacid, organic or mineral, of which at least one of the acid functions has an ionization constant in water, pKa, at

25 ° C, greater than 3; y is an integer or fractional number different from 0 and at most equal to 3.

Another subject of the invention is the use of a rubber composition in accordance with the invention for the manufacture of tires or for the manufacture of semi-finished products intended for such tires, these semi-finished products being chosen in particular in the group formed by the treads, the sub-layers intended for example to be placed under these treads, the crown reinforcement plies, the sides, the carcass reinforcement plies, the heels, the protectors , air chambers and waterproof inner liners for tubeless tires.

The invention also relates to these tires and these semi-finished products themselves, when they comprise an elastomeric composition in accordance with the invention, these tires being intended to equip passenger vehicles, 4x4 vehicles (with 4 wheel drive), SUN ("Sport Utility Vehicles ^ιr ), two wheels (especially bicycles or motorcycles), as industrial vehicles chosen from vans," Heavy vehicles "- ie, metro, bus, road transport equipment (trucks, tractors, trailers), off-road vehicles -, agricultural or civil engineering machinery, airplanes, other transport or handling vehicles.

The invention relates in particular to tire treads, these treads being able to be used during the manufacture of new tires or for retreading used tires; thanks to the compositions of the invention, these treads have both a low rolling resistance, a very good grip and a high resistance to wear.

The invention also relates to a process for preparing a rubber composition which can be used for the manufacture of tires, such a process comprising the following steps:

. incorporating into a diene elastomer, in a mixer, at least: a reinforcing inorganic filler; as coupling agent (inorganic filler / diene elastomer), an at least bifunctional organosilicon compound graftable onto the elastomer by means of a sulfur group, by thermomechanically kneading the whole, in one or several times, up to reach a maximum temperature between 110 ° C and 190 ° C;

• cool the assembly to a temperature below 100 ° C;

• ^'then incorporating a crosslinking system; . knead everything up to a maximum temperature below 120 ° C, and being characterized in that said sulfur group corresponds to the above formula (I).

Another subject of the invention is the use as a coupling agent (inorganic filler / diene elastomer), in a composition based on diene elastomer reinforced with an inorganic filler intended for the manufacture of tires, of a compound organosilicon at least bifunctional, graftable onto the elastomer by means of a sulfur group, with polythiobenzothiazyl function, corresponding to the above formula (I).

The invention as well as its advantages will be easily understood in the light of the description and of the exemplary embodiments which follow, as well as of the single figure relating to these examples which represents curves of variation of module as a function of the elongation for diene rubber compositions, whether or not according to the invention.

I. MEASUREMENTS AND TESTS USED

The rubber compositions are characterized before and after curing, as indicated below.

1-1. Toasting time

The measurements are carried out at 130 ° C, in accordance with French standard NF T 43-005 (1991). The evolution of the consistometric index as a function of time makes it possible to determine the toasting time of the rubber compositions, assessed in accordance with the aforementioned standard by parameter T5 (in the case of a large rotor), expressed in minutes, and defined as being the time necessary to obtain an increase in the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.

1-2. rheometry

The measurements are carried out at 150 ° C., with an oscillating chamber rheometer, according to DIN standard 53529 - part 3 (June 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. The measurements are processed according to DIN 53529 - part 2 (March 1983): the minimum and maximum torques, measured in dN.m (deciNewton.meter), are respectively named C _m i _n and C _max ; the difference between C _ma χ and C _m i _n is measured which makes it possible to assess the vulcanization yield.

1-3. Tensile tests

These tests make it possible to determine the elasticity stresses and the breaking properties. Unless otherwise indicated, they are carried out in accordance with French standard NF T 46-002 of September 1988. The second secant modules (or apparent stresses, or apparent stresses, in MPa) are measured at 100% elongation (ie after an accommodation cycle) elongation (denoted M100) and 300% elongation (denoted M300). These traction measurements are carried out under normal temperature (23 ± 2 ° C) and hygrometry (50 ± 5% relative humidity) conditions, according to French standard NF T 40-101 (December 1979).

A processing of the traction records also makes it possible to plot the module curve as a function of the elongation (see attached figure), the module used here being the true secant module measured in first elongation, calculated by reducing to the real section of the 'test tube and not in the initial section as previously for the nominal modules.

1-4. Dynamic properties:

The dynamic properties are measured on a viscoanalyzer (Metravib NA4000), according to standard ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm thick and 400 mm ² in section) is recorded, subjected to a sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, at a temperature of 40 ° C. A sweep in deformation amplitude is carried out from 0.1 to 50% (outward cycle), then from 50% to 1% (return cycle); for the return cycle, the maximum value of the loss factor is recorded, noted tan (δ) _ma χ.

IT CONDITIONS FOR CARRYING OUT THE INVENTION

The rubber compositions according to the invention are based on at least each of the following constituents: (i) (at least) a diene elastomer, (ii) (at least) an inorganic filler as reinforcing filler, (iii) (at least) a specific organosilicon compound as a coupling agent (inorganic filler / diene elastomer).

Of course, by the expression composition "based on" is meant a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some of these base constituents being capable of, or intended to react between them, at least in part, during the various stages of manufacturing the composition, in particular during its vulcanization.

II- 1. Diene elastomer

By "diene" elastomer or rubber is meant in known manner an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

In general, the term “essentially unsaturated” diene elastomer is understood here to mean a diene elastomer derived at least in part from conjugated diene monomers, having a rate of units or units of diene origin (conjugated dienes) which is greater than 15% (% in moles).

Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not enter into the definition. above and can in particular be qualified as “essentially saturated” diene elastomers (rate of units of diene origin low or very low, always less than 15%).

In the category of “essentially unsaturated” diene elastomers, the expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

These definitions being given, the term “diene elastomer capable of being used in the compositions according to the invention” is more particularly understood:

(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 dienes conjugated together or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

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

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

Although it applies to any type of diene elastomer, a person skilled in the art of the tire will understand that the present invention, in particular when the rubber composition is intended for a tire tread, is first put implemented with essentially unsaturated diene elastomers, in particular of the type (a) or (b) above.

By way of 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, are suitable. 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 commercial "vinyl-toluene" mixture, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene. , vinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl-aromatic units. The elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used. The elastomers can for example be block, statistical, sequence, microsequenced, and be prepared in dispersion or in solution; they can be coupled and / or stars or functionalized with a coupling and / or star-forming or functionalizing agent. Preferably, polybutadienes and in particular those having a content of units -1,2 between 4% and 80% or those having a content of cis-1,4 greater than 80%, polyisoprenes, butadiene copolymers- styrene and in particular those having a styrene content of between 5% and 50%) by weight and more particularly between 20%) and 40%, a content of -1,2 bonds in the butadiene part of between 4% and 65% o, a content of trans-1,4 bonds of between 20%> and 80% o, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5%> and 90%) by weight and a temperature of glass transition (Tg, measured according to standard ASTM D3418-82) from -40 ° C to -80 ° C, 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, in particular 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 of -1 units, 2 of the butadiene part between 4% and 85%>, a content of trans units -1.4 of the butadiene part between 6%> and 80% o, a content of units -1.2 plus -3.4 of the isoprene part of between 5%> and 70% and a content of trans units -1.4 of the isoprene part of between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg of between -20 ° C and -70 ° C.

In summary, in a particularly preferred manner, the diene elastomer of the composition in accordance with the invention is chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (BR), polyisoprenes (IR), natural rubber (NR) , the. butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene copolymers butadiene-styrene (SBIR).

The composition according to the invention is particularly intended for a tire tread, whether it is a new or used tire (in the case of retreading).

In the case of a tire for a passenger vehicle, the diene elastomer is for example an SBR, whether it is an SBR prepared in emulsion ("ESBR") or an SBR prepared in solution ("SSBR "), or a cut (mix) SBR / BR, SBR / NR (or SBR / IR), or even BR / NR, (or BR / IR). In the case of an SBR elastomer, use is in particular of an SBR having a styrene content of between 20%) and 30% by weight, a vinyl bond content of the butadiene part of between 15%> and 65%), a content of trans-1,4 bonds between 15% and 75% and a Tg between -20 ° C and -55 ° C. Such an SBR copolymer, preferably prepared in solution (SSBR), is optionally used in admixture with a polybutadiene (BR) preferably having more than 90%> of cis-1,4 bonds.

In the case of a tire for a commercial vehicle, in particular for a heavy vehicle, the diene elastomer is in particular an isoprene elastomer; by "isoprene elastomer" is understood in known manner a homopolymer or a copolymer of isoprene, in other words terms a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, polyisoprenes are preferably used having a rate (%> molar) of cis-1,4 bonds greater than 90%>, more preferably still greater than 98%). For such a tire for a commercial vehicle, the diene elastomer may also consist, in whole or in part, of another highly unsaturated elastomer such as, for example, an SBR elastomer.

According to another advantageous embodiment of the invention, in particular when it is intended for a sidewall of a tire, the composition according to the invention may contain at least one essentially saturated diene elastomer, in particular at least one EPDM copolymer, that this copolymer is for example used or not in admixture with one or more of the highly unsaturated diene elastomers mentioned above.

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

II-2. Reinforcing filler

The white or inorganic filler used as reinforcing filler can constitute all or only part of the total reinforcing filler, in the latter case associated for example with carbon black.

Preferably, in the rubber compositions according to the invention, the reinforcing inorganic filler constitutes the majority, that is to say more than 50%> by weight of the total reinforcing filler, more preferably more than 80% by weight of this total reinforcing load.

In the present application, the term "reinforcing inorganic filler" is understood, in a known manner, an inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also called "white" filler or sometimes "clear" filler "in contrast to carbon black, this inorganic filler being capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words capable of replacing, in its reinforcing function, a conventional charge of pneumatic grade carbon black.

Preferably, the reinforcing inorganic filler is an inorganic filler of the silica (SiO2) or alumina (AI2O3) type, or a mixture of these two fillers. ' The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated silica or hindered pyro having a BET surface as well as a CTAB specific surface, both less than 450 m ² / g, preferably from 30 to 400 m ² / g. Highly dispersible precipitated silicas (called "HDS") are preferred, in particular when the invention is implemented for the manufacture of tires having low rolling resistance; the term “highly dispersible silica” is understood to mean, in known manner, any silica having a significant ability to disaggregate and to disperse in an elastomeric matrix, observable in known manner by electron or optical microscopy, on fine sections. As non-limiting examples of such preferred highly dispersible silicas, mention may be made of Perkasil KS 430 silica from Akzo, BN3380 silica from Degussa, Zeosil 1165 MP and 1115 MP silica from Rhodia, Hi-Silica 2000 from the company PPG, the silicas Zeopol 8741 or 8745 from the company Huber, precipitated silicas treated such as for example the silicas "doped" with aluminum described in application EP-A-0 735 088.

The reinforcing alumina preferably used is a highly dispersible alumina having a BET surface area ranging from 30 to 400 m ² / g, more preferably between 60 and 250 m ² / g, an average particle size at most equal to 500 nm, more preferably at most equal to 200 nm, as described in the above-mentioned application EP-A-0 810 258. As nonlimiting examples of such reinforcing aluminas, mention may be made in particular of "Baikalox""A125","CR125","D65CR" aluminas from the company Baïko ski.

The physical state in which the reinforcing inorganic filler is present is immaterial, whether in the form of powder, microbeads, granules, pellets, beads or any other densified form. Of course, the term reinforcing inorganic filler is also understood to mean mixtures of different reinforcing inorganic fillers, in particular of highly dispersible silicas and / or alumina as described above.

When the rubber compositions of the invention are used as tire treads, the reinforcing inorganic filler used, in particular if it is silica, preferably has a BET surface area of between 60 and 250 m ² / g, more preferably between 80 and 200 m ² / g.

The reinforcing inorganic filler can also be used in cutting (mixing) with carbon black. As carbon blacks, all carbon blacks are suitable, in particular blacks of the HAF, ISAF, SAF type, conventionally used in tires and particularly in tire treads. By way of nonlimiting examples of such blacks, mention may be made of blacks Νl 15, Ν134, N234, N339, N347, N375.

The quantity of carbon black present in the total reinforcing filler can vary within wide limits, this quantity of carbon black being preferably less than the quantity of inorganic reinforcing filler present in the rubber composition.

In the compositions in accordance with the invention, in particular in the treads incorporating such compositions, it is preferred to use, in small proportion, a carbon black in association with the reinforcing inorganic filler, at a preferential rate of between 2 and 20 pce, more preferably within a range of 5 to 15 pce. In the ranges indicated, we benefit from the coloring properties (black pigmentation agent) and anti-UN of carbon blacks, without, moreover, penalizing the typical performances provided by the reinforcing inorganic load, namely low hysteresis (reduced rolling resistance) and high grip on wet, snowy or icy ground.

Preferably, the rate of total reinforcing filler (reinforcing inorganic filler plus carbon black if applicable) is between 10 and 200 phr, more preferably between 20 and 150 phr, the optimum being different according to the targeted applications; in fact, the level of reinforcement expected on a bicycle tire, for example, is in known manner significantly lower than that required on a tire capable of traveling at high speed in a sustained manner, for example a motorcycle tire, a tire for a passenger vehicle or for a utility vehicle such as Truck.

For the treads of such tires capable of running at high speed, the quantity of reinforcing inorganic filler, in particular if it is silica, is preferably between 30 and 140 phr, more preferably within a range of 50 to 120 pce.

In the present description, the BET specific surface 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 ΝF ISO 9277 of December 1996 [multi-point volumetric method (5 points) - gas: nitrogen - degassing: hour at 160 ° C - relative pressure range p / in: 0.05 at 0.17]. The CTAB specific surface is the external surface determined according to French standard ΝF T 45-007 of November 1987 (method B).

Finally, a person skilled in the art will understand that as an equivalent charge of the reinforcing inorganic filler described in this paragraph, a reinforcing organic filler, in particular a carbon black, could be used, covered at least in part with an inorganic layer. , for example silica, requiring the use of a coupling agent to establish the connection with the elastomer.

II-3. Coupling agent (organosilicon compound)

As explained above, a coupling agent (inorganic filler / diene elastomer) is, in known manner, carrying at least two functions, denoted here "Y" and "X", allowing it to be able to graft, of a on the one hand on the reinforcing inorganic filler by means of the function Y, for example a hydroxyl group or a hydrolyzable group, on the other hand on the diene elastomer by means of the function X, for example a sulfur function.

An essential characteristic of the organosilicon compound used as coupling agent in the compositions in accordance with the invention is that this compound can be grafted onto the elastomer by means of a sulfur group with polythiobenzothiazyl function, of formula:

(I) s Si - Z - S _x - Bzt, (AA) _y in which:

Z is a divalent linking group, linear or branched, making it possible to link the polythiobenzothiazyl group to a silicon atom of the organosilicon compound; - x is a whole or fractional number from 2 to 4;

Bzt represents the group 2-benzothiazole, optionally substituted; AA represents a monoacid or polyacid, organic or mineral, oxygenated, of which at least one of the acid functions has an ionization constant in water, pKa, at 25 ° C, greater than 3; - y is an integer or fractional number different from 0 and at most equal to 3.

It is recalled here that by “organosilicon” (or “organosilicon”) compound must be understood, by definition, an organic compound containing at least one Carbon-Silicon bond.

In formula (I) above, in the case where the route of synthesis of the compound considered can give rise to only one kind of polysulfurized group, the number x is then an integer which is equal to 2, 3 or 4, preferably equal to 2 or 3. But those skilled in the art will readily understand that this number can be a fractional average number when the synthetic route gives rise to a mixture of polysulphurized groups each having a number of sulfur atoms different ; in such a case, the polythiobenzothiazyl group synthesized in fact consists of a distribution of polysulphides, ranging from disulphide S to heavier polysulphides, centered on an average value (in moles) of "x" (fractional number) between 2 and 4, more preferably between 2 and 3.

In the present description, the term “aliphatic hydrocarbon group” means a linear or branched group, preferably comprising from 1 to 25 carbon atoms, optionally substituted. Advantageously, said aliphatic hydrocarbon group comprises from 1 to 12 carbon atoms, better still from 1 to 8 carbon atoms, more preferably still from 1 to 6 carbon atoms.

As saturated aliphatic hydrocarbon group, mention may be made of alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl, 2-methylbutyl, 1-ethylpropyl, hexyl, isohexyl, neohexyl, 1-methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 1,3-diniethylbutyl, 2-ethylbutyl, 1-methyl-1-ethylpropyl, heptyl, 1-methylhexyl, 1-propylbutyl, 4,4-dimethylρentyl, octyl, 1-methylheptyl, 2-ethylhexyl, 5,5-dimethylhexyl, nonyl, decyl, 1-methylnonyl, 3,7-dimethyloctyl and 7,7-dimethyloctyl.

The unsaturated aliphatic hydrocarbon groups which can be used comprise one or more unsaturations, preferably one, two or three unsaturations of ethylenic type (double bond) or and acetylenic type (triple bond). Examples are the alkenyl or alkynyl groups derived from the alkyl groups defined above by the removal of two or more hydrogen atoms. Preferably, the unsaturated aliphatic hydrocarbon groups comprise a single unsaturation. By carbocyclic radical is meant a monocyclic or polycyclic radical, optionally substituted, preferably C ₃ -C ₅ o- Advantageously, it is a C ₃ -Cι ₈ radical preferably mono-, bi- or tricyclic. When the carbocyclic radical comprises more than one cyclic nucleus (in the case of polycyclic carbocycles), the cyclic nuclei are condensed two by two. Two condensed nuclei can be orthocondensed or pericondensed. The carbocyclic radical can comprise, unless otherwise indicated, a saturated part and / or an aromatic part and / or an unsaturated part.

Examples of saturated carbocyclic radicals are cycloalkyl groups. Preferably, the cycloalkyl groups are C ₃ -Cι ₈ , better still C ₅ -Cι ₀ . Mention may in particular be made of the cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, adamantyl or norbornyl radicals.

The unsaturated carbocycle or any unsaturated part of the carbocyclic type exhibits one or more ethylenic unsaturation, preferably one, two or three. It advantageously contains from 6 to 50 carbon atoms, better still from 6 to 20, for example from 6 to 18 carbon atoms.

Examples of unsaturated carbocycles are C ₆ -C ₁₀ cycloalkenyl groups. Examples of aromatic carbocyclic radicals are C ₆ -C ₈ aryl groups and in particular phenyl, naphthyl, anthryl and phenanthryl.

A group having both an aliphatic hydrocarbon part and a carbocyclic part as defined above is, for example, an arylalkyl group such as benzyl, or an alkylaryl group such as tolyl.

The substituents of the aliphatic hydrocarbon groups or parts and of the carbocyclic groups or parts are, for example, alkoxy groups in which the alkyl part is preferably as defined above.

The divalent group Z is preferably chosen from aliphatic, saturated or unsaturated hydrocarbon groups, carbocyclic, saturated, unsaturated and / and aromatic, monocyclic or polycyclic groups, and groups having an aliphatic, saturated or unsaturated hydrocarbon part and a carbocyclic part. as defined above.

This group Z preferably contains from 1 to 18 carbon atoms, it more preferably represents an alkylene chain, a saturated cycloalkylene group, an arylene group, or a divalent group consisting of a combination of at least two of these groups. It is more preferably chosen from C 1 -C ₈ alkylene and C ₆ -C ₂ arylene; it can be substituted or interrupted by one or more heteroatoms, chosen in particular from S, O and N.

According to a particularly preferred embodiment of the invention, group Z represents a Cι-C ₈ alkylene, more preferably still a Cι-C alkylene chain, in particular methylene, ethylene or propylene, more preferably still propylene. The Bzt group can be substituted or unsubstituted. If Bzt is substituted, it is preferably substituted by one or more radicals chosen from: a saturated aliphatic hydrocarbon group; a saturated and / or aromatic, monocyclic or polycyclic carbocyclic group; a group having a saturated aliphatic hydrocarbon part and a saturated and / or aromatic, monocyclic or polycyclic carbocyclic part.

The group - S _x - Bzt, (AA) _is therefore preferred for general formula:

in which

n is an integer equal to 0, 1, 2, 3 or 4; preferably equal to 0, 1 or 2;

AA represents a mineral or organic, oxygenated acid, as defined above; - y is a non-zero whole or fractional number at most equal to 3, preferably at most equal to 2, and better understood in a range from 0.2 to 1.2;

P represents a radical chosen from a saturated aliphatic hydrocarbon group, a saturated and / or aromatic, monocyclic or polycyclic carbocyclic group, or a group having both a saturated hydrocarbon aliphatic part and a saturated and / or aromatic carbocyclic part, monocyclic or polycyclic ; preferably

P represents a Cι-C ₈ alkyl, better still in Cι ~ C ₃ .

According to the invention, AA is a weak oxygenated acid having one or more acid functions, at least one of which has an ionization constant in water pKa, at 25 ° C, greater than 3 and preferably ranging from 4 to 10. By way of examples, mention may be made, among organic acids, of mono-carboxylic acids, belonging to the series of fatty acids. By fatty acid is meant, in the context of the invention, carboxylic acids with a heavy, saturated or unsaturated hydrocarbon chain, preferably C -C ₂₅ , more preferably C ₄ -C ₂₂ - Preferably, the fatty acid is a saturated mono carboxylic acid of the type of lauric, myristic, palmitic and stearic acid.

By hydrolysable monovalent group which has been mentioned above with regard to the Y function, is meant groups such as, for example: halogen atoms, in particular chlorine; the groups -OR ¹ and -O-CO-R ¹ where R ¹ is chosen from the group consisting of aliphatic, saturated or unsaturated hydrocarbon groups, carbocyclic, saturated, unsaturated and / or aromatic, monocyclic or polycyclic groups, groups having an aliphatic, saturated or unsaturated hydrocarbon part and a carbocyclic part as defined above, R ¹ possibly being halogenated and / or substituted by one or more alkoxyl groups; the groups -ON ^: = CR ² R ³ in which R ² and R ³ independently take any of the meanings given above for R ¹ , R ² and R ^{3 which} may be halogenated and / or optionally substituted by one or more alkoxyl groups; the groups - O-NR ² R ³ in which R ² and R ³ are as defined above. Advantageously, such a hydrolysable monovalent group is an alkoxyl radical, linear or branched, C _j -C ₈ optionally halogenated and / or optionally substituted by one or more (C _[ -C ₃ ) alkoxy; C ₂ -C ₉ acyloxy optionally halogenated or optionally substituted by one or more (C, -C ₈ ) alkoxy; C ₅ -C ₁₀ cycloalkyloxy; or C ₆ -C _l aryloxy. By way of example, the hydrolyzable group is methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, methoxymethoxy, ethoxyethoxy, methoxyethoxy, β-chloropropoxy or β-chloroethoxy or alternatively acetoxy.

According to a preferred embodiment of the invention, the polythiobenzothiazyl group corresponds to formula (I) in which at least one, preferably all of the following characteristics is verified:

Bzt represents the 2-benzothiazole group optionally substituted with 1 to 4 radicals chosen from the group consisting of Cι-C ₈ linear or branched alkyls, C ₅ -C ₁₀ cycloalkyls, C ₆ -Cι ₂ aryls , (C ₆ -Cι ₂ ) aryl- (Cι-C ₈ ) alkyls and mixtures of these radicals;

AA represents a monoacid or a polyacid, organic, oxygenated, of which at least one of the acid functions has an ionization constant in water, pKa, at 25 ° C, ranging from 4 to 10; y is at most equal to 2;

Z represents a Cι-Cι ₈ alkylene or a C ₆ -Cι ₂ arylene.

According to a more preferred embodiment of the invention, the polythiobenzothiazyl group corresponds to formula (I) in which is verified at least one, more preferably all of the following characteristics:

Bzt represents the 2-benzothiazole group substituted by 1 or 2 alkyl radicals, linear or branched, in Cι-C ₈ ; - AA representing a fatty carboxylic monoacid, saturated or unsaturated, having from 4 to 22 carbon atoms; is in the range from 0.2 to 1.2; Z represents a Cι-C ₈ alkylene chain.

According to an even more preferred embodiment of the invention, the polythiobenzothiazyl group corresponds to formula (I) in which is verified at least one, even more preferably all of the following characteristics:

Bzt represents the 2-benzothiazole group substituted by 1 or 2 radicals chosen from the group consisting of methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl and n-hexyl;

AA represents a fatty mono carboxylic acid chosen from the group consisting of lauric acid, myristic acid, palmitic acid and stearic acid;

Z is chosen from C ₁ -C ₄ alkylene. Thus, as a particularly preferred embodiment of the invention, a group of formula (I) is used in accordance with the invention in which:

Bzt represents the 2-benzothiazole group optionally substituted by a radical chosen from the group consisting of methyl, ethyl, propyl and isopropyl;

AA represents stearic acid; Z is chosen from methylene, ethylene and propylene.

A person skilled in the art will know how to adapt the nature of the function Y to the particular organosilicon compound considered on which is grafted, via the linking group Z, the polythiobenzothiazyl group, this function Y possibly being different, for example a hydroxyl group or hydrolyzable, depending on the type of organosilicon compound considered, in particular a polyfunctional silane or polysiloxane.

Those skilled in the art will understand that by the expression "polyfunctional silane" is meant a silane carrying on the one hand a function Y consisting of one, two or three hydroxyl group (s) or monovalent group (s) ( s) hydrolyzable (s) linked to a silicon atom, and on the other hand to a function X consisting of a polythiobenzothiazyl group of formula (I) which is linked to the silicon atom of the function Y by the divalent linking group Z. Those skilled in the art will also understand that, by the expression "polyfunctional polysiloxane", is meant a carrier polysiloxane, in the chain and / or at the chain end (s), as function Y , at least one siloxyl unit equipped with one, two or three OH group (s) or monovalent group (s) hydrolysable, and, as function X, at least one siloxyl unit equipped with a polythiobenzothiazyl group of formula (I).

Without this embodiment being limiting, the organosilicon compound of formula (I) is preferably a silane compound carrying, as function Y, one or more (maximum equal to 3) groups (OR) attached to an atom of Silicon, R representing hydrogen or a monovalent, linear or branched hydrocarbon group (in particular alkyl).

Thus, as an organosilicon compound which is particularly suitable for the invention, a silane-polythiobenzothiazyl corresponding to the general formula can be used:

(II) (R ⁵ O) _a R ⁴ _{(3. A)} Si - Z - S _x - Bzt, (AA) _y ,

in which:

R represents a monovalent hydrocarbon group;

R ⁵ represents hydrogen or a monovalent hydrocarbon group, identical to or different from R ⁴ ; a is an integer equal to 1, 2 or 3;

Z, x, Bzt, AA and y have the meanings given above.

Those skilled in the art will readily understand that such a bifunctional organosilicon compound of formula (II) has a (first) "Y" function [symbolized by the 1 to 3 group (s) (OR ⁵ ) attached to the silicon atom. ] linked, via the linking group Z, to the group functional polythiobenzothiazyle of formula (I) [(second) function "X" symbolized by - S _x - Bzt, (AA) _y ].

The radicals R ⁴ and R ⁵ , which may be identical or different, are in particular hydrocarbon groups chosen from aliphatic, saturated or unsaturated hydrocarbon groups, carbocyclic, saturated, unsaturated or / and aromatic, monocyclic or polycyclic groups, and groups having a portion aliphatic hydrocarbon, saturated or unsaturated, and a carbocyclic part as defined above, preferably comprising from 1 to 18 carbon atoms, these various groups being able to be substituted or unsubstituted.

The radicals R ⁴ , identical or different if there are more than one, preferably represent an alkyl, a cycloalkyl or an aryl. They are more preferably chosen from the group consisting of Cι-C ₈ alkyls, C ₅ -Cιo cycloalkyls (in particular cyclohexyl) and phenyl. Even more preferably, R is chosen from the group consisting of Cι-C ₆ alkyls (in particular methyl, ethyl, propyl, isopropyl).

The radicals R ⁵ , identical or different if there are more than one, preferably represent an alkyl, a cycloalkyl, an acyl or an aryl. They are more preferably chosen from the group consisting of Cι-C ₈ alkyls, optionally halogenated and / or optionally substituted by one or more (C ₂ -C ₈ ) alkoxy, C ₂ -C ₉ acyls, optionally halogenated and or optionally substituted with one or more (C ₂ -C ₈ ) alkoxy, C ₅ -C ₁₀ cycloalkyls and Cβ-Cis aryls. Even more preferably, R ⁵ is chosen from the group consisting of Cι-C ₈ alkyls (in particular methyl, ethyl, n-propyl, isopropyl, n-butyl, β-cloropropyl, β-cloroethyl), optionally substituted by one or several (C ₂ -C ₈ ) alkoxy (in particular methoxy, ethoxy, propoxy, isopropoxy), C5-C ₁₀ cycloalkyls and phenyl.

According to the best known embodiment, R ⁴ and R ⁵ , identical or different, are both chosen (if a ≠ 3) from Cι-C ₄ alkyls, in particular from methyl and ethyl.

As more preferred organosilicon compounds which can be used in the compositions of., The invention, mention will be made in particular of the silanes-polythiobenzothiazyl of formula (II) in which the group Z represents a C 1 -C ₄ alkylene, in particular methylene, ethylene or propylene (more preferably still propylene), the radicals R ⁴ and R ⁵ , identical or different, more preferably representing a Cι-C ₃ alkyl, in particular methyl or ethyl, and more particularly, among these compounds, silanes-polythiobenzothiazyle for which x is equal to 2.

Thus, among these more preferred compounds of formula (II), there may be mentioned more particularly the alkoxysilanes-polythiobenzothiazyl in which:

R ⁴ and R ⁵ are both chosen from the group consisting of C 1 -C ₆ alkyls;

Z is chosen from Cι-C alkylene;

Bzt represents the 2-benzothiazole group substituted by 1 or 2 radicals chosen from the group consisting of methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl and n-hexyl;

AA represents a fatty mono carboxylic acid chosen from the group consisting of lauric acid, myristic acid, palmitic acid and stearic acid; y is at most equal to 2.

Even more preferably, the alkoxysilanes-polythiobenzothiazyl of formula (II) will be mentioned in which:

R ⁴ and R ⁵ are both chosen from methyl, ethyl, propyl, isopropyl, Z is chosen from methylene, ethylene and propylene.

Bzt represents the 2-benzothiazole group optionally substituted by a radical chosen from the group consisting of methyl, ethyl, propyl and isopropyl; - A A represents stearic acid; is in the range of 0.2 to 1.2.

Thus, as a particularly preferred embodiment of the invention, an alkoxysilane-polythiobenzothiazyl of formula (II) is used in which:

R ⁴ and R ⁵ are chosen from methyl and ethyl;

Z is propylene;

Bzt represents the 2-benzothiazole group, optionally substituted by methyl and / or ethyl; - AA represents stearic acid; is included in the range from 0.2 to 1.2,

such as, for example, the silanes-dithiobenzothiazyl of formula (II-1) below:

(T2) _a (Tl) ₃ . _a If • [CH3- (CH ₂ ) i6-COOH] _y

where T is chosen from methyl and ethyl; T is chosen from methoxy and ethoxy; a represents 1, 2 or 3; and y is a whole or fractional number ranging from 0.2 to 1.2,

in particular the silane-dithiobenzothiazyl of particular formula (ïï-2) below:

(CH ₃ CH ₂ 0) ₃ Si -AΌ, [CH ₃ - (CH2) iδ-COOH] _y

The above polyfunctional coupling agents, carrying the polythiobenzothiazyl group described above, have shown very good reactivity with respect to the diene elastomers used in rubber compositions for tires, and have been found to be sufficiently effective on their own for the coupling of such elastomers and of a reinforcing inorganic filler such as silica. Without this being limiting, they can advantageously constitute the only coupling agent present in the rubber compositions of the invention. In order to take into account the differences in specific surface area and density of the reinforcing inorganic fillers that may be used, as well as the molar masses of the coupling agents specifically used, it is preferable to determine the optimal level of coupling agent in moles. per square meter of reinforcing inorganic filler, for each reinforcing inorganic filler used; this optimal rate is calculated from the weight ratio [coupling agent / inorganic-reinforcing filler], the BET surface area of the filler and the molar mass of the coupling agent (denoted M below), according to the relationship following known:

(moles / m ² inorganic charge) = [coupling agent / inorganic charge] (1 / BET) (MM)

Thus, preferably, the amount of coupling agent used in the compositions according to the invention is between 10 ^-7 and 10 ^{~ 5} moles per m ² of reinforcing inorganic filler. Even more preferably, the amount of coupling agent is between 5.10 " ⁷ and 5.10" ⁶ moles per square meter of total inorganic charge.

Taking into account the quantities expressed above, in general, the content of coupling agent will preferably be greater than 1 phr, more preferably between 2 and 20 phr. Below the minima indicated, the effect is likely to be insufficient, while beyond the recommended maximum, there is generally no longer any improvement in coupling, while the costs of the composition increase; for these various reasons, this content of coupling agent is even more preferably between 3 and 15 phr.

Those skilled in the art will be able to adjust this content of coupling agent as a function of the intended application, for example of the part of the tire for which the composition of the invention is intended, the nature of the diene elastomer, the amount of reinforcing inorganic filler used and the nature of the organosilicon compound considered.

Of course, in order to reduce the costs of the rubber compositions, it is desirable to use as little as possible, that is to say the amount necessary for sufficient coupling between the diene elastomer and the reinforcing inorganic filler. Its effectiveness makes it possible, in a large number of cases, to use the coupling agent at a preferential rate representing between 0.5% o and 20% o by weight relative to the amount of reinforcing inorganic filler; rates below 15%> are more particularly preferred.

Finally, it will be noted that the organosilicon compound described above could be grafted beforehand (via the "Y" function) onto the reinforcing inorganic filler, the filler thus "precoupled" possibly being subsequently linked to the diene elastomer, via the free function "X".

H-4. Synthesis of the coupling agent (organosilicon compound)

By way of example, organosilicon compounds as described above can be prepared according to the preferred synthetic routes indicated below. The polyfunctional silanes of formula (II) where x = 2 are simply obtained by bringing a compound of formula (III) into contact:

(R ⁵ O) _a (R ⁴ ) -a Si - Z - S - S - Bzt (III)

in which R ⁴ , R ⁵ , a, Z and Bzt are as defined above with AA fatty acid as defined above, the molar ratio of AA fatty acid to compound (III) corresponding to y (whole or fractional number different from zero and at most equal to 3).

The contacting is preferably carried out in the absence of solvent at a temperature ranging from 15 ° C to 35 ° C and, preferably, at room temperature (23 ° C). It can nevertheless take place in a solvent, which is then simply eliminated from the reaction medium by evaporation under reduced pressure.

Compound (III) can be prepared in a conventional manner as taught in particular in EP-A-683 203. Alternatively, it is possible to prepare compound (III) by reaction of a sulfenamide of formula (IV) :

Bzt- • S - NZ ² Z ³ (IV)

wherein Bzt is as defined above, Z 2 represents a hydrogen atom, a saturated aliphatic hydrocarbon group or a saturated carbocyclic group, and Z represents a saturated aliphatic hydrocarbon group or a saturated carbocyclic group, on a mercapto silane of formula (V) defined below:

(R ⁵ O) _a (R ⁴ ) ₃ - _a Si - Z - SH (V)

where R ⁴ , R ⁵ , a and Z are as defined above.

This reaction is advantageously carried out in a solvent such as for example chloroform, dichloromethane, carbon tetrachloride, hexane, heptane, cylohexane, xylene, benzene, dichloroethylene, trichlorethylene, dioxane , diisopropyl ether, tetrahydrofuran and toluene.

The reaction temperature can vary between 15 ° C and 140 ° C, preferably between 50 ° C and 90 ° C. The molar ratio of (IV) to (V) generally oscillates between 1: 5 and 5: 1, for example between 1: 3 and 3: 1, preferably between 1: 1 and 1: 2. This type of reaction is described in particular in EP-A-794 221 and US-A-5 663 358.

Another method of preparing the compounds of formula (III) consists in reacting a sulfenyl halide of formula (VI):

Bzt - S - Hal (VI)

in which Bzt is as defined above and Hal represents a halogen atom, with the appropriate mercaptosilane of formula (V), this compound being as defined above, in presence of an organic base. The bases which can be used are, for example, N-methylmorpholine, triethylamine, tributylamine, diisopropylethylamine, dicyclohexylamine, N-methylpiperidine, pyridine, 4- (1-pyrrolidinyl) pyridine, picoline, 4- ( N, N-dimethylamino) pyridine, 2,6-di-t-butyl-4-methylpyridine, quinoline, N, N-dimethylaniline, N, N-diethylaniline, l, 8-diazabicyclo [5.4.0 ] -undec-7-ene (DBU), 1,5-diazabicyclo [4.3.0] non-5-ene (DBN) and 1,4-diazabicyclo [2.2.2] -octane (DABCO or triethylenediamine).

This reaction is preferably carried out in a polar aprotic solvent such as in particular a halogenated aliphatic hydrocarbon (for example chloroform) and an optionally halogenated aromatic hydrocarbon (for example benzene or possibly halogenated toluene).

The reaction can be carried out at a temperature ranging from 15 ° C to 50 ° C, and preferably ranging from 20 ° C to 25 ° C. This reaction is stoichiometric. It will preferably be in the presence of 1 to 1.5 equivalents of compound (V) per mole of compound (VI). The amount of base will be greater than or equal to the amount of sulfenyl halide used.

II-5. Miscellaneous additives

Of course, the rubber compositions in accordance with the invention also comprise all or part of the additives usually used in diene rubber compositions intended for the manufacture of tires, such as for example plasticizers, extension oils, protective agents such as anti-ozone waxes, anti-ozone chemicals, antioxidants, anti-fatigue agents, adhesion promoters, coupling activators as described for example in applications WO00 / 05300 and WO00 / 05301, reinforcing resins as described in WO02 / 10269, a crosslinking system based either on sulfur or on sulfur and / or peroxide and / or bismaleimide donors, vulcanization accelerators, vulcanization activators, etc. The reinforcing inorganic filler can also be associated, if necessary, with a conventional white filler with little or no reinforcement, for example particles of clays, bentonite, talc, chalk, kaolin.

The rubber compositions in accordance with the invention may also contain, in addition to the organosilicon compounds described above, agents for recovering the reinforcing inorganic filler, comprising for example the only function Y, or more generally agents for assisting in setting implemented in known manner, thanks to an improvement in the dispersion of the inorganic filler in the rubber matrix and to a lowering of the viscosity of the compositions, of improving their ability to be used in the raw state, these agents being for example alkylalkoxysilanes (in particular alkyltriethoxysilanes), polyols, polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialcanol-amines), hydroxylated or hydrolyzable polyorganosiloxanes, for example α, ω-dihydroxy-polyorganosiloxanes (in particular α, ω-dihydroxy-polydimethylsiloxanes).

II-6. Preparation of rubber compositions The compositions are produced in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first working or thermo-mechanical kneading phase (sometimes called a "non-productive" phase) at high temperature, up to a maximum temperature (noted T _ma χ) of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes called the "productive" phase ) at a lower temperature, typically less than 110 ° C., for example between 60 ° C. and 100 ° C., finishing phase during which the crosslinking or vulcanization system is incorporated; such phases have been described for example in the applications EP 501 227, EP 735 088, EP 810 258, EP 881 252, WO00 / 05300, O00 / 05301 or WO02 / 10269 mentioned above.

The manufacturing process according to the invention is characterized in that at least the reinforcing inorganic filler and the organosilicon compound are incorporated by kneading with the diene elastomer, during the first so-called non-productive phase, that is to say -to say that one introduces into the mixer and that one thermomechanically kneads, in one or more stages, at least these different basic constituents until reaching a maximum temperature of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C.

For example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary basic components are introduced into a suitable mixer such as a conventional internal mixer. (diene elastomer, reinforcing inorganic filler and organosilicon compound), then in a second step, for example after one to two minutes of mixing, any additional covering or implementing agents and other various additives, with the exception of the system vulcanization; when the apparent density of the reinforcing inorganic filler is low (general case of silicas), it may be advantageous to split its introduction into two or more parts. A second thermomechanical working step can be added to this internal mixer, after the mixture has fallen and intermediate cooling (cooling temperature preferably less than 100 ° C.), with the aim of subjecting the compositions to a complementary thermomechanical treatment, in particular for, further improving the dispersion, in the elastomeric matrix, of the reinforcing inorganic filler and of its coupling agent. The total duration of the kneading, in this non-productive phase, is preferably between 2 and 10 minutes.

After the mixture thus obtained has cooled, the vulcanization system is then incorporated at low temperature, generally in an external mixer such as a cylinder mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and. 15 minutes.

The final composition thus obtained is then calendered, for example in the form of a sheet, of a. plate or even extruded, for example to form a rubber profile used for the manufacture of semi-finished products such as treads, crown reinforcement plies, sidewalls, carcass reinforcement plies, heels, protectors, inner tubes or waterproof inner liners for tubeless tires. In summary, the process according to the invention for preparing an elastomeric composition which can be used for the manufacture of semi-finished products for tires, comprises the following stages:

• incorporate into a diene elastomer, in a mixer, at least: a reinforcing inorganic filler; as coupling agent (inorganic filler / diene elastomer), an organosilicon compound at least bifunctional graftable on the elastomer by means of a sulfur group, by thermomechanically kneading the whole, in one or more times, until reaching a maximum temperature between 110 ° C and 190 ° C;

• cool the assembly to a temperature below 100 ° C;

• then incorporate a crosslinking or vulcanization system;

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

said sulfur group being a group with polythiobenzothiazyl function corresponding to the above formula (I), more particularly to formula (II) above.

The vulcanization (or baking) is carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, preferably under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the temperature curing, the vulcanization system adopted, the vulcanization kinetics of the composition considered or of the size of the tire.

The vulcanization system proper is preferably based on sulfur and a primary vulcanization accelerator, in particular an accelerator of the sulfenamide type. To this crosslinking system are added, incorporated during the first non-productive phase and / or during the productive phase, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid, guanidine derivatives ( especially diphenylguanidine), etc. Sulfur is used at a preferential rate of between 0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr, for example between 0.5 and 3.0 phr when the invention is applied to a strip. tire bearing. The primary vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr in particular when the invention applies to a tire tread.

The invention relates to the rubber compositions previously described both in the so-called "raw" state (ie, before curing) 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 as a blend (ie, as a mixture) with any other rubber composition which can be used for the manufacture of tires. III. EXAMPLES OF EMBODIMENT OF THE INVENTION

III- 1. Synthesis of coupling agents

The coupling agents which can preferably be used in the compositions of the invention are silanes-polythiobenzothiazyl, more preferably alkoxysilanes corresponding to one of the aforementioned specific formulas (II), the synthetic methods of which are described below, by way of nonlimiting examples.

The melting points (Pf) expressed in degrees Celsius (° C) are determined by projection on a KOFFLER bench, previously calibrated (ΔT = ± 2 ° C). The boiling points (Eb _pre ssio _n ) are given in millibars (mbar). The 250 MHz spectra of the proton ( ¹ H NMR) and of the carbon ( ¹³ C NMR) are recorded on a BRUCKER AC 250 spectrometer. The chemical shifts (δc and δh) are expressed in parts per million (ppm) relative to deuterochloroform ( CDC1). The coupling constants noted J are expressed in Hz. The following abbreviations are used: s, singlet; yes, broad singlet; d, doublet; t, triplet; q, quadruplet; m, multiplet.

All manipulations with organosilicon compounds comprising alkoxysilane residues are carried out under an inert atmosphere and under anhydrous conditions.

Example 1

This example describes the synthesis of 2-benzothiazole and 3-triethoxysilyl-propyl disulfide, stearic acid, where the molar ratio of stearic acid / silane disulfide is 1.

a - 2-Benzothiazole and 3-triethoxysilyl-propyl disulfide

A solution of 2,2'-bis benzothiazole disulfide (60.1 mmol or 20 g) in 500 ml of chloroform is cooled to 0 ° C. The corresponding sulfenyl chloride (Bzt-S-Cl) is obtained by passing chlorine gas until the reagent is completely dissolved. To this orange solution obtained is added a mixture of 3-mercaptopropyltriethoxysilane (120.2 mmol or 28.61 g) and triethylamine (120.2 mmol or 12.16 g) dissolved in 100 ml of chloroform. The reaction medium is stirred for 6 hours at room temperature and then concentrated under reduced pressure. The crude product is taken up in 300 ml of anhydrous ether and the triethylamine hydrochloride is filtered. The solvent is removed by distillation under low pressure to obtain the disulfide.

By spectral analysis, the formula of the compound obtained is determined (yield: 69%>; orange oil appearance):

NMR Η (CDC1 ₃ ) δ _H

0.75 (t, 2H, J = 8.1 Hz, Si-CH ₂ ); 1.21 (t, 9H, J = 7 Hz, CH ₃ -CH ₂ ); 1.89 (m, 2H, CH ₂ ); 2.97 (t, 2H, J = 7.2 Hz, S-CH ₂ ); 3.80 (q, 6H, J = 7.1 Hz, CH ₃ -CH ₂ 0); 7.33 (m, 1H aromatic); 7.41 (m, 1H aromatic); 7.79 (d, 1H aromatic, J = 7.8 Hz); 7.85 (d, 1H aromatic, J = 8 Hz). ¹³ C NMR (CDC) δ _c

9.5 (Si-CH ₂ ); 18.2 (CH ₃ -CH ₂ ); 22.8 (CH ₂ ); 42.3 (S-CH ₂ ); 58.4 (~ OCH ₂ ); 121.1 (aromatic CH); 122.0 (aromatic CH); 126.3 (aromatic CH); 127.1 (aromatic CH); 135.7 (Aromatic C); 155.0 (C); 173.5 (C).

b - 2-Benzothiazole and 3-τriethoxysilylpropyl disulfide, stearic acid.

Into a 250 ml reactor equipped with magnetic stirring are successively introduced and at room temperature (23 ° C): 30 g of the silane disulfide prepared in Example la (74.4 mmol), 21.2 g of acid stearic (74.5 mmol) and 100 g of toluene. The medium is homogenized at room temperature for 10 minutes, then the solvent is removed on a rotary evaporator (50 ° C, 3.1-0 ² Pa).

Example 2:

For the synthesis of 2-benzothiazole and 3-triethoxysilyl-propyl disulfide, stearic acid where the stearic acid / silane disulfide molar ratio is equal to 0.26, the title compound is obtained in the same way as for example lb) using the following loads:

silane disulfide prepared in Example 1a): 30 g (74.4 mmol), - stearic acid: 5.5 g (19.2 mmol).

III-2. Preparation of rubber compositions

The following tests are carried out as follows: the elastomer is introduced into an internal mixer, filled to 70% and whose initial tank temperature is approximately 90 ° C. diene (or mixture of diene elastomers, if applicable), the reinforcing filler, the coupling agent, then, after one to two minutes of kneading, the various other ingredients with the exception of the vulcanization system. Thermomechanical work (non-productive phase) is then carried out in two stages (total mixing time equal to approximately 7 min), until a maximum "fall" temperature of approximately 165 ° C is reached. The mixture thus obtained is recovered, cooled, then the vulcanization system (sulfur and sulfenamide accelerator) is added on an external mixer (homo-finisher) at 30 ° C, mixing everything (productive phase) for 3 to 4 minutes .

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or of thin sheets of rubber for the measurement of their physical or mechanical properties, or in the form of profiles which can be used directly, after cutting and / or assembly to the desired dimensions, for example as semi-finished products for tires, in particular as tire treads. In the following tests, the diene elastomer is an SBR / BR blend and the reinforcing inorganic filler (HDS silica) is used at a preferential rate comprised within a range of 50 to 120 phr.

III-3. Characterization of rubber compositions

The purpose of this test is to demonstrate the improved coupling performance (inorganic filler / diene elastomer) in a composition in accordance with the invention, compared to a composition of the prior art using a conventional coupling agent TESPT.

composition C-1: conventional TESPT silane; composition C-2: silane-dithiobenzothiazyl of formula (II-2) synthesized in Example 2.

Recall that the TESPT is bis (3-triethoxysilylpropyl) tetrasulfide, of formula [(C2HsO) ₃ Si (CH ₂ ) ₃ S2] 2; it is marketed for example by the company Degussa under the name Si69 (commercial mixture of polysulphides S _x with an average value for x which is close to 4).

The developed formula of TESPT is:

This formula is to be compared with that of the coupling agent of formula (II-2) previously synthesized (Example 2):

The two coupling agents are used here at an isomolar silicon content, that is to say that whatever the composition is used, the same number of moles of functions Y (here Y = Si (OEt) ₃ ) reactive towards silica and its surface hydroxyl groups.

Relative to the weight of reinforcing inorganic filler, the level of coupling agent is in both cases less than 12 phr, which represents less than 15% by weight relative to the amount of reinforcing inorganic filler.

Tables 1 and 2 give the formulation of the different compositions (Table 1 - rate of the different products expressed in pce), their properties before and after cooking (40 min at 150 ° C). The appended figure reproduces the modulus curves (in MPa) as a function of the elongation (in%>), these curves being denoted Cl and C2 and corresponding respectively to compositions Cl and C-2. The examination of the different results leads to the following observations.

First of all, the rheometric properties indicate that the composition according to the invention C-2, compared to the control composition, leads to a higher vulcanization yield, as illustrated by a difference (C _max -C _m i _n ) greater , with, in addition, an equivalent grill security (T5).

After curing, the composition according to the invention C-2 has the highest values of modulus with high deformation (M 100 and M300), indicators known to those skilled in the art of the quality of the vulcanization yield but also of the coupling between the elastomer and the white filler via its coupling agent. This result is confirmed by the curves C1 and C2 in the appended figure, with a curve C2 situated clearly beyond the curve C1, whatever the elongation rate considered between 100%) and 300%>. As for the hysteresis properties, illustrated by tan (δ) _max , they are equivalent.

In conclusion, the coupling agent selected for the compositions in accordance with the invention gives the latter high reinforcing properties, excellent processing properties in the raw state and very good vulcanizability, revealing an overall efficiency at least equal if not greater than that of TESPT, a coupling agent (inorganic filler / elastomer) of reference in diene rubber compositions reinforced with an inorganic filler such as a reinforcing silica.

The invention finds particularly advantageous applications in rubber compositions intended for the manufacture of tire treads having both a low rolling resistance and a high resistance to wear, in particular when these treads are intended tires for passenger vehicles, motorcycles or industrial vehicles of the Truck type.

Table 1

(1) SBR with 59.5% of polybutadiene 1-2 units; 26.5% styrene; Tg ≈ -29 ° C; 75 pce dry SBR extended with 28.1 pce of aromatic oil (a total of 103.1 pce);

(2) BR with 4.3% of 1-2; 2.7% trans; 93% cis 1-4 (Tg = -104 ° C);

(3) "HD" type silica - "Zeosil 1165MP" from the company RHODIA in the form of microbeads (BET and CTAB: approximately 150-160 m ² / g);

(4) TESPT ("Si69" from DEGUSSA);

(5) triethoxysilyl-propyl-dithiobenzothiazyl (see synthesis in III-1, example 2);

(6) diphenylguanidine ("Vulkacit D" from the company BAYER);

(7) N-cyclohexyl-2-benzothiazyl-sulfenamide ("Santocure CBS" from the company FLEXSYS).

Claims

1. Elastomeric composition usable for the manufacture of tires, based on at least (i) a diene elastomer, (ii) an inorganic filler as a reinforcing filler and (iii), as a coupling agent (inorganic filler / diene elastomer), an organosilicon compound at least bifunctional graftable on the elastomer by means of a sulfur group with polythiobenzothiazyl function, of formula:

(I) ≡ Si - Z - S _x - Bzt, (AA) _y

in which:

Z is a divalent linking group, linear or branched, making it possible to link the polythiobenzothiazyl group to a silicon atom of the organosilicon compound; x is an integer or fractional number from 2 to 4; Bzt represents the group 2-benzothiazole, optionally substituted; - AA represents a monoacid or polyacid, organic or mineral, oxygenated, of which at least one of the acid functions has an ionization constant in water, pKa, at 25 ° C, greater than 3; y is an integer or fractional number different from 0 and at most equal to 3.

2. Composition according to claim 1, the symbol Bzt representing the 2-benzothiazole group substituted by 1 to 4 radicals chosen from the group consisting of alkyl, linear or branched, C ₁ -C ₅ , C ₅ -C ₁₀ cycloalkyls, C ₆ -Cι ₂ aryls, the (C ₆ - Ci ₂ ) aryl- (Cι-C ₈ ) alkyls and mixtures of these radicals.

3. Composition according to claim 2, the symbol Bzt representing the 2-benzothiazole group substituted by 1 or 2 alkyl radicals, linear or branched, Cj-Cs, preferably chosen from the group consisting of methyl, ethyl, propyl and isopropyl.

4. Composition according to any one of claims 1 to 3, AA representing a monoacid or a polyacid, organic, oxygenated, of which at least one of the acid functions has an ionization constant in water, pKa, at 25 ° C, ranging from 4 to 10.

5. Composition according to claim 4, AA representing a fatty, saturated or unsaturated mono-carboxylic acid having from 4 to 22 carbon atoms, preferably chosen from the group consisting of lauric acid, myristic acid, palmitic acid and stearic acid.

6. Composition according to any one of claims 1 to 5, being there at most equal to 2, preferably lying in the range from 0.2 to 1.2.

7. Composition according to any one of claims 1 to 6, Z representing a hydrocarbon group comprising from 1 to 18 carbon atoms and optionally one or more heteroatoms.

8. Composition according to claim 7, Z being chosen from Cι-Cι ₈ alkylene and C ₆ -Cι arylene, preferably from Cι-C ₈ alkylene.

9. Composition according to claim 8, Z being chosen from methylene, ethylene and propylene.

10. Composition according to any one of claims 1 to 9, the diene elastomer being chosen from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

11. Composition according to any one of claims 1 to 10, the rate of reinforcing inorganic filler being between 10 and 200 phr (parts by weight percent of elastomer) and the rate of coupling agent between 1 and 20 phr .

12. Composition according to any one of claims 1 to 11, the organosilicon compound being a silane-polythiobenzothiazyl of formula:

(II) (R ⁵ 0) _a R ⁴ _{(3. A)} Si - Z - S _x - Bzt, (AA) _y

in which:

R ⁴ represents a monovalent hydrocarbon group; '- R ⁵ represents hydrogen or a monovalent hydrocarbon group, identical to or different from R ⁴ ; a is an integer equal to 1, 2 or 3.

13. Composition according to claim 12, the group Z representing a C 1 -C alkylene and the radicals R ⁴ and R ⁵ , identical or different, a C ₁ -C ₆ alkyl.

14. Composition according to claim 13, Z being propylene, R ⁴ and R ⁵ , identical or different, being chosen from methyl and ethyl.

15. Composition according to any one of claims 12 to 14, Bzt representing the 2-benzothiazole group substituted by 1 or 2 alkyl radicals, linear or branched, chosen from methyl, ethyl, propyl, isopropyl; AA representing stearic acid.

16. Composition according to any one of claims 1 to 15, x being a whole or fractional number from 2 to 3.

17. Composition according to claim 16, x being equal to 2.

18. Composition according to any one of claims 1 to 17, the amount of coupling agent representing between 0.5%> and 20% by weight relative to the amount of reinforcing inorganic filler.

19. Composition according to any one of claims 1 to 18, the reinforcing inorganic filler being predominantly silica.

20. A composition according ^'to claim 19, the reinforcing inorganic filler forming the entire load renforçante.-

21. Composition according to any one of claims 1 to 19, the reinforcing inorganic filler being used in admixture with carbon black.

22. Composition according to claim 21, the carbon black being present at a level of between 2 and 20 phr.

23. Composition according to any one of claims 10 to 22, the diene elastomer being a butadiene-styrene copolymer (SBR) having a styrene content of between 20% and 30% by weight, a content of vinyl bonds of the butadiene part of between 15%>65%>, a content of trans-1,4 bonds of between 20%) and 75% and a temperature of ^"glass transition between -20 ° C and -55 ° C.

24. Composition according to claim 23, the SBR being an SBR prepared in solution (SSBR), preferably used in admixture with a polybutadiene.

25. The composition of claim 24, the polybutadiene having more than 90%> of cis-1,4 bonds. -

26. Composition according to any one of claims 10 to 22, the diene elastomer being an isoprene elastomer, preferably natural rubber or a synthetic cis-1,4 polyisoprene.

27. Composition according to any one of claims 1 to 26, characterized in that it is in the vulcanized state.

28. A process for preparing an elastomeric composition usable for the manufacture of tires, comprising the following steps:

• incorporate into a diene elastomer, in a mixer, at least: a reinforcing inorganic filler; as coupling agent (inorganic filler / diene elastomer), an organosilicon compound at least bifunctional ή which can be grafted onto the elastomer by means of a sulfur group, by thermomechanically kneading the whole, in one or more stages, until reaching a maximum temperature between 110 ° C and 190 ° C; cool the assembly to a temperature below 100 ° C; . then incorporate a crosslinking system; knead everything up to a maximum temperature below 120 ° C,

characterized in that said sulfur group comprises a polythiobenzothiazyl function and corresponds to the formula: (I) ≡ Si - Z - S _x - Bzt, (AA) _y

in which:

Z is a divalent linking group, linear or branched, making it possible to link the polythiobenzothiazyl group to a silicon atom of the organosilicon compound; x is an integer or fractional number from 2 to 4; Bzt represents the optionally substituted 2-benzothiazole group; - AA represents a monoacid or polyacid, organic or mineral, oxygenated, of which at least one of the acid functions has an ionization constant in water, pKa, at 25 ° C, greater than 3; r y is an integer or fractional number different from 0 and at most equal to 3.

29. Use of a rubber composition according to any one of claims 1 to 27 for the manufacture of tires or semi-finished products intended for tires, these semi-finished products being chosen in particular from the group consisting of treads, underlayments, crown reinforcement plies, sidewalls, carcass reinforcement plies, heels, protectors, air chambers and internal rubber compounds for tubeless tires.

30. A tire comprising a rubber composition according to any one of claims 1 to 27.

31. Semi-finished product for a tire comprising a rubber composition according to any one of claims 1 to 27, this semi-finished product being chosen in particular from the group consisting of treads, underlays, crown reinforcement plies, sidewalls, carcass reinforcement plies, heels, protectors, inner tubes and waterproof inner liners for tubeless tires.

32. Semi-finished product according to claim 31, consisting of a tire tread.

33. Tire tread according to claim 32, comprising a rubber composition according to any one of claims 23 to 26.

34. A tire comprising a tread according to claim 33.

35. Use as coupling agent (inorganic filler / diene elastomer), in a composition based on diene elastomer reinforced by an inorganic filler intended for the manufacture of tires, of an at least bifunctional organosilicon compound graftable on the elastomer by means of a sulfur group, characterized in that said sulfur group comprises a polythiobenzothiazyl function and corresponds to the formula:

(I) ^' ≡ Si - Z - Sx - Bzt, (AA) _y

in which: Z is a divalent linking group, linear or branched, making it possible to link the polythiobenzothiazyl group to a silicon atom of the organosilicon compound; x is an integer or fractional number from 2 to 4;

Bzt represents the optionally substituted 2-benzothiazole group;

AA represents an oxygenated monoacid or polyacid, organic or mineral, of which at least one of the acid functions has an ionization constant in water, pKa, at

25 ° C, greater than 3; y is an integer or fractional number different from 0 and at most equal to 3.