EP1576044A1 - Rubber composition for tyres, comprising a polyorganosiloxane oligomer as coupling agent - Google Patents

Abstract

The invention relates to an elastomer composition which can be used to produce tyres and which is based on at least one diene elastomer, an inorganic reinforcing filler and a coupling agent (diene elastomer/inorganic filler). The inventive composition is characterised in that the aforementioned coupling agent is a linear alpha , omega -dihydroxy-polyorganosiloxane oligomer comprising between 2 and 15 silicon atoms and, along the length of the chain thereof, at least one silicon atom bearing a sulphur pendant functional group (function F), having formula (I), wherein group G represents SH or an episulfide radical and R<1 >represents a divalent linkage group. The invention also relates to tyres or semi-finished products, such as treads, which are intended for tyres, comprising the inventive elastomer composition.

Description

 RUBBER COMPOSITION FOR TIRE COMPRISING A

POLYORGANOSILOXANE OLIGOMER AS A COUPLING AGENT

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

It relates more particularly to coupling agents of the polyorganosiloxane type (abbreviated as "POS") capable of ensuring the connection between an inorganic filler and a diene elastomer, in such compositions.

In order to reduce fuel consumption and the nuisance emitted by motor vehicles, significant efforts have been made in recent years by tire designers in order to obtain tires having both very low rolling resistance. , improved grip on both dry and wet or snow-covered ground and very good wear resistance.

In particular, the development of new reinforcing inorganic fillers such as, in particular, so-called "HDS" ("Highly Dispersible Silica") silicas, has made it possible to achieve the above compromise in properties (for example, see patents or patent applications EP 501 227, EP 692 492, EP 692 493, EP 735 088, WO99 / 02590, WO99 / 02602, WO 00/05300, WO 00/05301, WO 01/96442).

The use of these reinforcing inorganic fillers has certainly reduced the difficulties of processing the rubber compositions containing them, but this processing remains however more difficult than for the previous compositions loaded with carbon black. Indeed, for reasons of reciprocal affinities, the particles of inorganic charge tend to agglomerate together in the elastomeric matrix. These interactions tend to increase the consistency in the raw state of the compositions and to reduce their ability to be used in the raw state ("processability"); they also have the consequence of limiting the dispersion of the filler and therefore the reinforcing properties to a level substantially lower than that which it would theoretically be possible to achieve if all the bonds (white filler / elastomer) capable of being created during thermo-mechanical mixing operations were effectively obtained.

It is necessary in particular to use a coupling agent, also called a bonding agent, which has the function of ensuring the connection or bonding between the surface of the particles of inorganic filler and the elastomer, while facilitating the dispersion of this morganic load within the elastomeric matrix.

Coupling agents, in particular (silica / diene elastomer), have been described in a very large number of documents, the best known being bifunctional alkoxysilanes. It was first proposed (see for example application FR-A-2 094 859) to use mercaptosilane coupling agents for the manufacture of tire treads. It was quickly revealed and it is now well known that mercaptosilanes are capable of providing excellent coupling properties but that the industrial use of these coupling agents is not possible due to the high reactivity of the -SH functions leading very rapidly, during the preparation of the rubber composition in an internal mixer, to premature vulcanizations also called "scorching", to very high Mooney plasticities, finally to rubber compositions almost impossible to work and implement industrially.

To remedy this drawback, it has then been proposed to replace these mercaptoalkoxysilanes with polysulphurized alkoxysilanes, in particular bis- (alkoxylsilylalkyl) polysulphides well known to those skilled in the art (see for example FR-A-2 149 339, FR -A-2 206 330, US-A-3 842 111, US-A-3 873 489, US-A-3 997 581).

Among all these polysulphides, mention must be made in particular of bis- (trialkoxylsilylpropyl) polysulphides, very particularly bis 3-triethoxysilylpropyl tetrasulphide (abbreviated to "TESPT"), of formula [(C ₂ H ₅ θ) ₃ Si (CH ₂ ) ₃ S ₂ ] ₂ , sold in particular by the company Degussa under the name "Si69".

This TESPT polysulphurized alkoxysilane is today the benchmark coupling agent, for those skilled in the art, in tires loaded with low rolling resistance silica, sometimes qualified as "Green Tires" for the energy savings offered (or "energy-saving Green Tires"), offering an excellent industrial compromise in terms of safety in roasting, hysteresis and reinforcing power.

The compositions based on a reinforcing morganic filler such as silica and TESPT, however, have the known drawback of exhibiting very significantly slowed down vulcanization kinetics, as a general factor of two to three, compared with compositions loaded with black. of carbon. The longer baking times which result therefrom penalize, as we know, the industrial use of tires or tire treads based on these reinforcing inorganic fillers.

An effective solution to the problem posed above was recently proposed in the application WO 02/083782 teaching the use, in place of TESPT, of a tetrasulfide of mono-ethoxydimethylsilylpropyl (in abbreviation "MESPT"), of formula [(C ₂ H ₅ O) (CH ₃ ) ₂ Si (CH ₂ ) ₃ S ₂ ] ₂ , monoethoxylated homolog of the above-mentioned TESPT.

This MESPT coupling agent, in addition to the fact that it makes it possible to very significantly reduce the cooking times of the rubber compositions comprising it, is also advantageous from the point of view of the environment because of a number of functions. reduced ethoxy (only one ethoxy function instead of three, per silicon atom) and consequently a lesser release of ethanol during the processing of the rubber compositions. Thanks to the use of this coupling agent, the problem of VOCs ("Volatile Organic Compounds") is certainly greatly reduced, but it is not completely resolved. However, the Applicants have discovered during their research that a specific coupling agent, of another nature than an alkoxysilane, not only makes it possible, as for the MESPT above, to reduce the cooking times very significantly. , at a level equivalent to that observed on compositions loaded with carbon black, but still to completely solve the problem of emission of VOCs (ethanol) mentioned above.

This important result is obtained, moreover, without penalty, or even with an improvement in the coupling and reinforcement properties, thus offering the tires and their treads a new and particularly advantageous compromise in properties.

Consequently, a first subject of the invention relates to an elastomeric composition which can be used for the manufacture of tires, based on at least (i) a diene elastomer, (ii) an inorganic filler as a reinforcing filler, (iii) a coupling agent (inorganic filler / diene elastomer), characterized in that this coupling agent is a linear α, ω-dihydroxy-polyorganosiloxane oligomer comprising from 2 to 15 silicon atoms, and, along its chain, at least one silicon atom carrying a sulfur functional group (function denoted "F"), of formula (I):

R ¹ - G

in which the group G represents SH or an episulphide radical and R ¹ represents a divalent linking group.

Applications WO99 / 02580 and WO99 / 02602 had certainly already described rubber compositions based on reinforcing inorganic filler and of a coupling agent of the POS type with thiol functions (-SH). The latter is however characterized by the presence, at the chain ends (in positions α, ω), of alkyl or alkoxy groups; it does not solve the above problems.

A subject of the invention is also 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 plies, the sides, the carcass plies, the heels, the protectors, the air chambers or the gums waterproof interior for tubeless tires.

The subject of the invention is also these tires and these semi-finished products themselves, when they comprise a rubber composition in accordance with the invention.

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 and a high resistance to wear. The composition in accordance with the invention is particularly suitable for the manufacture of tires or tire treads intended for equipping passenger vehicles, vans, 4x4 vehicles (with 4-wheel drive), two wheels, "Heavy vehicles" ( i.e. metro, bus, road transport equipment (trucks, tractors, trailers), off-road vehicles), airplanes, civil engineering, agricultural, or handling equipment, treads conforming to the invention can be used during the manufacture of new tires or for retreading used tires.

Reduced cooking times are particularly advantageous for treads intended for retreading, whether it is "cold" retreading (use of a precooked tread) or conventional "hot" retreading (use of 'a raw tread). In the latter case, a reduced cooking time, in addition to reducing production costs, limits the overcooking (or postcooking) imposed on the rest of the casing (carcass) of the used tire (already vulcanized); thanks to the invention, with identical baking time, the treads can also be baked at a lower temperature, which is another means of preserving the carcass from the problem of overcooking mentioned above.

The invention also relates to a process for obtaining a rubber composition with improved vulcanization kinetics, usable for the manufacture of tires, in which at least one diene elastomer is incorporated, at least one reinforcing inorganic filler and one coupling agent ensuring the connection between the reinforcing inorganic filler and the elastomer, this method being characterized in that said coupling agent consists of a POS oligomer as above, and in that the whole is thermomechanically kneaded, by one or more steps, until reaching a maximum temperature between 110 ° C and 190 ° C.

The invention also relates to the use as coupling agent (inorganic charge / diene elastomer), in a rubber composition comprising a diene elastomer and reinforced with an inorganic charge, of such a POS oligomer.

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 represent curves of variation of modulus according to the elongation for diene rubber compositions, whether or not in accordance with _. the invention.

I. MEASUREMENTS AND TESTS USED

The rubber compositions are characterized before and after curing, as indicated below. 1-1. rheometry:

The measurements are carried out at 150 ° C. with an oscillating chamber rheometer, according to standard DIN 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): T ₀ is the induction time, that is to say the time necessary for the start of the vulcanization reaction; T _α (for example T ₉₉ ) is the time necessary to reach a conversion of%, that is to say% (for example 99%) of the difference between the minimum and maximum couples. (T ₉ -T ₀ ) is therefore practically the measurement of the cooking time from the minimum torque. We also measure the conversion speed constant noted K (expressed in min ^-1 ), of order 1, calculated between 30% and 80% conversion, which makes it possible to assess the vulcanization kinetics (the higher K, the higher the kinetics are fast).

1-2. Tensile tests

These tests make it possible to determine the elasticity stresses and the breaking properties. Unless indicated otherwise, 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 10% (ie after an accommodation cycle) at 10% elongation (noted MA10), 100% elongation (MAI 00) and 300% elongation (MA300). The stresses at break (in MPa) and the elongations at break (in%) are also measured. All these traction measurements are carried out under normal temperature and hygrometry conditions according to French standard NF T 40-101 (December 1979).

A processing of the traction records also makes it possible to trace 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.

1-3. Dynamic properties

The dynamic properties ΔG * and tan _max (δ) are measured on a viscoanalyzer (Metravib VA4000), according to standard ASTM D 5992-96. The response of a sample of vulcanized composition is recorded (cylindrical specimen 4 mm thick and 400 mm ² in section), subjected to a sinusoidal stress in alternating single shear, at the frequency of 10 Hz, under normal conditions of temperature (23 ° C) according to standard ASTM D 1349-99. A deformation amplitude sweep is carried out from 0.1 to 50% (outward cycle), then from 50%> to 1% (return cycle). The exploited results are the complex dynamic shear modulus (G *) and the loss factor tan δ. For the return cycle, the maximum value of tan δ observed (tan (δ) _max ) is indicated, as well as the difference in complex modulus (ΔG *) between the values at 0.15 and 50% of deformation (Payne effect). II. CONDITIONS FOR CARRYING OUT THE INVENTION

The rubber compositions according to the invention are based on at least each of the following constituents: (i) one (at least one) diene elastomer, (ii) one (at least one) inorganic filler as reinforcing filler, and (iii) one (at least one) specific POS oligomer, as defined below, as 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 phases of manufacturing the composition, in particular during its vulcanization.

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

LT-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 preceding definition and can be qualified in particular as "essentially saturated diene elastomers". "(rate of motifs 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 tires 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.

As conjugated dienes, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C ₁ -C ₅ alkyl) -1,3-butadienes, such as for example, 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 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 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 star or functionalized with a coupling and / or star-forming or functionalizing agent.

Preferably, polybutadienes are suitable and in particular those having a content of -1,2 units (between 4% and 80%) or those having a cis-1,4 content 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%>, a content of trans-1,4 bonds of between 20% and 80% _> , butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a transition temperature vitreous (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 included between -25 ° C and -50 ° C. In the case of butadiene-styrene-isoprene copolymers are particularly suitable those having a styrene content of between 5% and 50%> by weight and more particularly 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 units - 1.2 of the butadiene part between 4% and 85%, a content of trans units -1.4 of the part butadiene between 6% and 80%), a content of -1.2 units plus -3.4 of the isoprene part between 5%> and 70% and a content of trans units -1.4 of the isoprene part included 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) , 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 tread for a tire, whether it is a new or used tire (in the case of retreading).

In the case of a passenger vehicle tire, 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 content of vinyl bonds in 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 utility vehicle, in particular for a heavy vehicle, the diene elastomer is in particular an isoprene elastomer; "Isoprene elastomer" means in a known manner an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, polyisoprenes are preferably used having a rate (mol%) of cis-1,4 bonds greater than 90%>, more preferably still greater than 98%. 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 tire sidewall, the composition according to the invention may contain at least one essentially saturated diene elastomer, in particular at least one EPDM copolymer, which 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.

π-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 morganic filler" means, 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 (SiO ₂ ) or alumina (Al ₂ O ₃ ) 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 or pyrogenic silica 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 a 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 nonlimiting examples of such preferential highly dispersible silicas, mention may be made of Perkasil KS 430 silica from the company A zo, the BV3380 silica from the company Degussa, the Zeosil 1165 MP and 1115 MP silicas from the company Rliodia, the silica Hi- Sil 2000 from the company PPG, the Zeopol 8741 or 8745 silicas from the Huber company, treated precipitated silicas 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, a 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 Baikowski.

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 various reinforcing inorganic fillers, in particular of highly dispersible silicas and / or aluminas 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 NI 15, N134, 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 phr (parts by weight per hundred parts of elastomer), more preferably comprised within a range of 5 to 15 phr. In the ranges indicated, we benefit from the coloring properties (black pigmentation agent) and anti-UV of carbon blacks, without, moreover, penalizing the typical performances provided by the reinforcing inorganic charge, 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 depending on the intended 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 French standard NF 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 NF T 45-007 of November 1987 (method B).

Finally, those skilled in the art will understand that, as an equivalent charge of the reinforcing inorganic filler described in this paragraph, a reinforcing organic filler could be used, in particular a carbon black, 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

It is recalled here that by "coupling agent" (inorganic filler / elastomer) is meant, in known manner, an agent capable of establishing a sufficient bond, 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 a very simplified general formula "Y-A-F", in which:

Y represents a functional group ("Y" function) 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 hydroxyl groups on the surface inorganic filler (for example surface silanols when it is silica);

F represents a functional group ("F" function) capable of binding physically and / or chemically to the diene elastomer, for example via a sulfur atom; - A represents a divalent group making it possible to connect Y and F.

Coupling agents should in particular not be confused with simple agents for recovering the inorganic charge which, in known manner, may comprise the "Y" function active with respect to the inorganic charge but are devoid of the function "F" activates with respect to the diene elastomer.

The coupling agent used in the compositions of the invention is a linear α, ω- dihydroxy-polyorganosiloxane oligomer comprising from 2 to 15 silicon atoms, and, along its chain, at least one silicon atom carrying a pendant functional sulfur group (function "F"), having the formula (I): - R ¹ - G

in which G represents SH or an episulfide radical (or epithio) and R ¹ represents a divalent linking group.

By α, ω-dihydroxy-polyorganosiloxane, is meant in the present application a POS of which the majority (that is to say more than 50 mol%) of the silicon atoms of the ends (positions called "α, ω") of the polysiloxane chain carry a hydroxyl function (OH).

Preferably, this POS oligomer verifies at least one, preferably the following two characteristics:

- More than 60%, more preferably at least 80 mol% of the silicon atoms of the ends of the polysiloxane chain carry a hydroxyl (OH) function; - apart from the two Si atoms forming the chain ends, it does not contain OH groups on the other Si atoms (that is to say those located inside the chain).

Even more preferably, at least 90%> by moles of the silicon atoms of the ends of the polysiloxane chain carry a hydroxyl function (OH).

The group R ¹ linking G and the silicon atom carrying the function F is preferably chosen from alkylene groups, linear or branched, comprising from 1 to 20 carbon atoms, these groups being able to be interrupted by hydrocarbon groups of a other nature, for example by cycloalkylene or arylene groups.

More preferably, R ¹ is chosen from the following groups:

- the alkylene groups denoted r ¹ having from 1 to 20 carbon atoms;

- the alkylene- (poly) cycloalkylene-alkylene groups denoted r ² , of which the alkylene parts, linear or branched, have 1 to 20 carbon atoms, and the cyclic part comprises from 5 to

10 carbon atoms;

- the alkylene-phenylene-alkylene groups denoted r ^{3 in} which the alkylene parts, linear or branched, have from 1 to 20 carbon atoms;

- with the possibility that r ^! , r ² and r ³ comprise at least one heteroatom, for example an oxygen atom.

POS oligomers which can be used in the compositions of the invention are for example POSs of average formula (II) which follows: RΌ ₁

in lacquer) on:

- the symbols R 'mainly represent hydrogen, a minority of them (that is to say less than 50%, preferably less than 40% in moles, more preferably still less than 20%) which can, depending on the specific conditions of synthesis of the oligomer, represent a Ci -C ₁₅ alkyl, preferably Cι-C in _6;

the symbols R, which are identical or different, each represent a monovalent hydrocarbon group chosen from linear or branched alkyls having from 1 to 6 carbon atoms;

- the symbols F have the abovementioned meanings (either: - R ¹ - G);

the symbols pF represent precursor groups of the groups F;

- m, n, x, y and z are whole numbers or f shareholders; - m + n = 2;

- (x + y + z) representing the total number of silicon atoms is in a range from 2 to 15, preferably from 2 to 10, more preferably still from 2 to 7;

- x is equal to or different from zero, preferably different from zero;

- y is different from zero; - z is equal to or different from zero.

In formula (H) above, it will be understood that the symbols R may be identical or different within the same siloxyl unit (when several of them are present on this same unit), or identical or different from one siloxyl motif to another. These symbols R are preferably chosen from methyl, ethyl, propyl and butyl; more preferably, R is methyl.

When the function F carries an episulphide radical G, it is advantageously chosen from those corresponding to one of the formulas (Ill-a) or (Ill-b) below:

in which R ³ is chosen from the groups r ¹ and r ² defined above, or

(III-b)

in which n is an integer ranging from 4 to 7, R ³ is chosen from alkylene r ¹ .

Preferably, the group G (thiol or episulphide) of the function F is carried by a carbon of aliphatic or cycloaliphatic nature, with the possibility that an adjacent carbon of aliphatic or cycloaliphatic nature is substituted by OH or by SH.

Thus, by way of preferred examples, the aforementioned function F is chosen from those of formulas (1) to (13) below:

in which, if applicable:

- n is an integer ranging from 1 to 12, preferably equal to 1, 2 or 3 (for formulas (3), (4), (5), (9), (10) and (11));

- R ⁴ , R ⁵ and R ⁶ , identical or different, represent H or a monovalent hydrocarbon radical, preferably chosen from linear or branched alkyls having from 1 to 6 carbon atoms, more preferably from methyl, ethyl, propyl and butyl .

The pF symbols of formula (H) are formed in particular:

- or of radicals of the r ¹ , r ² or r ^{3 type} comprising one or more double bonds located in the alkylene part and / or, if it is r ² or r ³ , in the ring;

- either of an epoxy group corresponding to the formula (BT-a) or (ϋl-b) in which S is replaced by O;

- or radicals denoted r ⁴ of the following formula in which R ¹ has the same meaning as above and X represents a halogen atom, preferably Cl:

R ¹ - X

These pF groups can be converted into F groups by an appropriate sulfurization reaction. The reaction can be more or less complete, so that z can be different from zero.

This sulfurization reaction can in particular be carried out in the presence of H ₂ S when the pF group is of the (D1) unsaturation or (D2) epoxide type or when it is a group episulphide "assimilated pF". When the pF group is of halogen (D3) type, the sulfurization employs an appropriate sulfurization agent such as H ₂ S, Na ₂ S ₄ , NaSH, thiourea.

Thus, the preferential groups F previously mentioned (formulas 1 to 13) can be obtained by sulfurization of the preferential precursor groups (pF) which follow:

precursor of group F (1)

precursor of group F (2)

(precursor of group F (3)

OR ⁴

(17) ^• (CH,) n - O - C- precursor of group F (4)

R ⁴

(18) (CH ₂ ) n - precursor of group F (5)

(19) precursor of group F (9)

(20) precursor of group F (10) (21) precursor of group F (11)

(22) precursor of groups F (12) and (6)

(23) (CH ₂ ) _n - Cl

(24) a mixture of

and of

and finally the episulfide groups (12) and (13) above.

Indeed, the episulfide groups are potentially precursors (called in the present application "assimilated pF") for other groups F, during a sulfurization reaction. Thus, group (13) is a precursor of group (8); the group (12) is a precursor of the group (7). When z is different from 0, the two types of groups, e.g. (13) and (8), respectively 12) and (7) are present on the molecule.

The particularly preferred oligomers of formula (II) are those in which all of the groups R are methyl groups.

As preferred examples, mention may be made of POS oligomers having the following average formula (IV):

in which m, n, x, y and z are as defined above for formula (II); the symbols R ', identical or different, each represent hydrogen or an alkyl group having from 1 to 3 carbon atoms, with the condition that at least 80%, more preferably at least 90% o, symbols R' represent hydrogen (% molar).

Synthesis of POS oligomers

The POS oligomers previously described can be prepared by methods involving in particular:

a hydrolysis and condensation reaction of dialkyldialkoxysilanes carrying identical or different pF and / or F functions, optionally in the presence of one or more dialkyldialkoxysilanes not carrying such a function; then sulfurization in the case where these are pF functions and possibly for the assimilated functions pF; a hydrolysis and condensation reaction of dialkyldihalosilanes carrying identical or different pF and / or F functions, optionally in the presence of one or more dialkyldihalogenosilanes not carrying such a function; then sulfurization in the case where these are pF functions and possibly for the assimilated functions pF; a sulfurization reaction on a polysiloxane oligomer carrying one or more pF functions and optionally for the assimilated pF functions; a redistribution reaction between a polysiloxane oligomer and a mono- or poly-dialkyldialkoxysilane carrying one or more pF and / or F functions; then sulfurization in the case where they are pF functions and possibly for the assimilated functions pF.

More precisely, it is possible, for example, to prepare the oligomers of formula (II) by a process comprising the following steps (in the following, the symbols have the same meanings as above):

A) Hydrolyze and condense in an aqueous medium alkoxysilanes of formula:

R

I

RO-Si-OR '(V)

I PF or formula: RI R'O-Si-OR '(VI)

F or a mixture of (V) and (VI),

possibly operating in the presence of organosilanes of formula:

R

RO-Si-OR '( ^VM )

I R

As an example, reference may be made to US-A-4,994,198.

If the starting product is of formula (V) or comprises it, the hydrolysis and condensation product is then subjected to sulphurization with H ₂ S, eg according to WO-A-9902580 when the pF group is of type (Dl ) unsaturated, according to US-A-4,163,832 when the pF group is an episulphide assimilated group and according to US-A-4,281,202 when the pF group is of (D2) epoxy type. When the pF group is Cl, the sulfurization can be carried out according to the technique described in EP-A-997 489 in the presence of Na ₂ S ₄ or NaSH, or of FR-A-2 055 229 and FR-A-1 356 552 in the presence of thiourea and NH or sodium alcoholate; one can also operate as described in US-A-5,107,009 in the presence of NaSH, or in FR-A-2,294,171 in the presence of H ₂ S and NH

B) Hydrolyze and condense in an aqueous medium halos enosilanes of formula (VIII):

R

I

X-Si-X

I PF

pF being of type (Dl) or (D3), X being a halogen atom, preferably Cl, operating optionally in the presence of halosilanes of formula (IX):

R

I

X-Si-X

I R where X is as above (the person skilled in the art can refer to FR-A-2 514 013, JP 11180713 or US-A-6 028 157).

The hydrolysis and condensation product is then subjected to sulphurization as described above under A) for the unsaturated groups and the chlorinated groups. C) Carry out a sulfurization reaction with H? S as described above under A), on an oligomer of formula (X):

this oligomer of formula (X) which can be obtained in various ways:

by hydrolysis of the corresponding alkoxysilanes or of the oligomers (see e.g. US-A-4

994,198); by redistribution of the silanes or oligomers with α, ω-hydroxylated silicone oils or of compounds of formula (XI) below, in the presence of an acid or basic catalyst; by hydrolysis of chlorosilanes (see e.g. JP 11180713 or US-A-6,028,157).

D) Carry out a redistribution reaction between an α, ω-hydroxylated silicone oil, or a cyclic compound of formula (XI) (where u is a number ranging from 3 to 8):

with an organosilane (or a compound resulting from its hydrolysis) of formula (XII)

R

I R'O-Si-OR '

I PF or of formula (XIII)

R

I

R'O-Si-OR '

I F or a mixture of (XiT) and (XHI),

formulas in which R 'has the same meaning as in (A), this reaction being carried out in the presence of water and optionally a suitable catalyst, basic or acid. This access route essentially uses pF groups of type (Dl) or (D3). If a starting product is of formula (XII) or comprises it, the hydrolysis and condensation product is then subjected to sulphurization as seen above under (B).

The compounds of formula (V) to (XIII) are accessible to a person skilled in the art. As an indication, it can be specified that compounds of formula (VI) are described in FR-A-1 356 552 and US-A-4401 826.

The POS oligomers described above have been found to be sufficiently effective on their own for coupling a diene elastomer and a reinforcing inorganic filler such as silica. Without this being limiting, ^they may advantageously constitute the sole coupling agent present in the rubber compositions of the invention.

The POS oligomer content is preferably greater than 0.5 pci, more preferably greater than 1 pci and less than 15 pci. Below the minima indicated, the effect is likely to be insufficient, while beyond the maximum rate indicated, there is generally no longer any improvement in the coupling, while the costs of the composition increase. For these reasons, this POS oligomer content is more preferably between 2 and 10 pci.

A person skilled in the art will know how to adjust the POS oligomer content according to the intended application, in particular the part of the tire for which the rubber composition of the invention is intended, the nature of the diene elastomer and the quantity of reinforcing inorganic filler used. 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 elastomer and the filler. The efficiency of the POS oligomer makes it possible to use the latter at a preferential rate of between 0.5%> and 20% by weight relative to the amount of reinforcing inorganic filler; rates below 15%> are more particularly preferred.

Those skilled in the art will finally understand that the POS oligomers described above could be grafted beforehand on the reinforcing inorganic fillers, in particular on silica, via their Y function, the fillers thus precoupled can then be linked to the elastomer through their free type F function.

II-4. 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, anti-oxidants, anti-fatigue agents, adhesion promoters, coupling activators as described for example in the aforementioned applications WO00 / 05300 and WO00 / 05301, resins reinforcing agents 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. A reinforcing inorganic filler can also be associated, if necessary, with a conventional white filler that is not very reinforcing or not, for example particles of clays, bentonite, talc, chalk, kaolin. The rubber compositions in accordance with the invention may also contain, in addition to the POS oligomers described above, agents for covering 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 chosen from the preferred group consisting of hydrolyzable silanes such as alkylalkoxysilanes (in particular alkyltriethoxysilanes), polyols, polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialcanol-amines), Hydroxylated or hydrolyzable POSs, for example α, ω-dihydroxy-polyorganosiloxanes (in particular α, ω- dihydroxy-polydimethylsiloxanes), and mixtures of these compounds.

As preferred examples of α, ω- (dihydroxy) polyorganosiloxane oil, mention will be made in particular of those of formula:

in which ra a value sufficient to give the oil a dynamic viscosity at 25 ° C of between 5 and 1000 mPa.s, preferably between 10 and 200 mPa.s; and the organic radicals R ⁹ , because of their availability in industrial products, are generally methyl, ethyl, propyl and / or phenyl radicals, preferably at least 80% by number of these radicals R ⁹ being methyl radicals.

As preferred examples of polyalkylene glycols, mention will be made in particular of those of formula:

wherein its a value sufficient to give the compound a number average molecular weight of between 100 and 30,000, preferably between 200 and 20,000; and the radicals R ¹⁰ , identical or different from each other, each represent an alkylene radical, linear or branched, having from 1 to 4 carbon atoms.

By way of preferred examples of hydrolyzable silanes, mention will be made in particular of those of formula: (R ⁿ ) _t Si (E) _4-t

where t is 1, 2 or 3; the symbols R ¹¹ each represent a linear or branched Cι-C ₈ alkyl (such as for example methyl, ethyl, propyls, butyls), a Cs-C ₈ cycloalkyl (such as for example cyclohexyl), a C ₆ -Cι aryl or aralkyl having a C ₆ -Cι ₂ aryl part and a C] -C alkyl part (such as, for example, phenyl, xylyl, benzyl, phenylethyl); the symbols E are hydrolyzable groups and each represent a C ₁ -C ₁₀ alkoxy group (such as, for example, methoxy, ethoxy, octyloxy), a C ₆ -C ₁ aryloxy group (such as, for example, phenyloxy), a C ₁ -C C alkoxy group ₁₃ (such as, for example, acetoxy), a Cι-C ₈ ketiminoxy group (such as ON = C (CH) (C ₂ H ₅ ), ON = C (CH ₃ ) ₂ ).

If an inorganic charge recovery agent is used, in particular an α, ω- dihydroxy-POS, it is preferably used at a rate of 0.1 to 10 parts by weight, more preferably from 0.5 to 5 parts, per 100 parts of reinforcing inorganic filler, the total amount of POS oligomer and of covering agent advantageously representing less than 10%, more preferably less than 8% by weight relative to the quantity of reinforcing inorganic filler.

TJ-5. 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 _max ) of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes referred to as 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 aforementioned documents EP 501227, EP 735088, WO00 / 05300, WO00 / 05301 or WO02 / 083782.

The manufacturing method according to the invention is characterized in that at least the reinforcing inorganic filler and the POS oligomer 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 steps, at least these different basic constituents until reaching a maximum temperature between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary basic constituents are introduced into a suitable mixer such as a conventional internal mixer. (diene elastomer, reinforcing inorganic filler and coupling agent), then in a second step, for example after one to two minutes of kneading, any additional covering or processing agents and other various additives, with the exception of vulcanization system; when the apparent density of the reinforcing inorganic filler is weak (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.), in order to subject the compositions to a complementary thermomechanical treatment, in particular to improve still 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, a plate or even extradited, 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, air chambers or waterproof inner liners for tubeless tires.

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 (ie, 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

πi-1. Synthesis of the POS coupling agent

A) Synthesis of the precursor: α, ω-hydroxylated silicone oil from the corresponding ethoxysilanes.

a) raw materials:

- dimethyldiethoxysilane (commercially available);

- 2-ethylcyclohexenediethoxymethylsilane, synthesized from commercial diethoxymethylhydrogenosilane, according to the scheme:

(OEt) ₂ MeSiH (OEt MeSi

and the following conditions:

- platinum catalyst (Karstedt): 17 ppm reaction mass;

- MeSi (OEt) ₂ H: 1 eq (equivalent); - vinylcyclhexene (VCH): 1.32 equivalent / silane;

- 70 ° C, pouring of the silane on a VCH foot, control of the exotherm by ice bath;

- TT conversion rate (SiH): 100%) after 15 hours of reaction;

- Vacuum removal of the VCH, then distillation of the final product.

b) hydrolysis:

EtO ₂ SïMe ₂ + EtO— + cyclic

This step was carried out without catalysis and by direct hydrolysis of the mixture of silanes, using the following reagents:

Me (VCH) SiOEt ₂ : 315.76 g (or 1309.8 mmol); cyclohexane: 1 liter;

Me ₂ SiOEt: 157.9 g (or 1066.9 mmol); demineralized water: 947.33 g (i.e. 52.6 moles; 22.13 eq. / silanes).

The ethanol formed during the reaction is removed by azeotropic entrainment with cyclohexane.

Procedure:

Silanes and 636.91 g of water are introduced into a 3-liter flask equipped with a temperature probe and mechanical stirring. 1 liter of cyclohexane is added to the medium, which makes the system biphasic. The reaction medium is stirred and heated at 70 ° C for 3 hours. The temperature of the reaction medium rose to 100 ° C. and the heating was continued for 3 h 30 min.

An intermediate analysis of the organic phase of the medium by 1 H NMR shows that the hydrolysis is incomplete at this stage. An addition of water is carried out (310.42 g) and the heating is continued for 3 hours at 100 ° C. The medium is cooled, then the organic part is recovered by decantation, then dried over MgSO4. The solvent is removed. A translucent fluid oil is obtained. 1 H NMR indicates that the ends of the oligomer obtained are of HOSi type.

A POS oligomer of formula (XIV) is thus obtained:

in which

m + n = 2;

96.5%) of R 'are H and 3.5% are ethyl groups (mol%).

B) Synthesis of the α, ω-hydroχylated POS oligomer functionalized by secondary thiol functions:

The reactions were carried out in a standard 2-liter autoclave with magnetic stirring (model ABC 02000 SS 04, Autoclave Engineers Europe), equipped with a stirring device and a HS gas supply device, and the interior volume was maintained under an atmosphere of dry nitrogen. Previously, there was prepared a mixture A of 3.25 g of free radical initiator available under the tradename VAZO 52 ^® by Dupont de Nemours, 550.3 g of toluene and 200.3 g of the precursor oil obtained in step previous.

509.7 g of toluene was loaded into the autoclave, and bubbling of H S continuously for 5 minutes, then, under a pressure of 13 bars, mixture A was introduced. The autoclave was then isolated and the temperature of the medium brought to 100 ° C. for 1 hour. At the end of the reaction, after removal of the excess H S, the reaction medium was recovered. After devolatilization (50 ° C, 2 mbar), the functionalized oil was recovered.

Silicon NMR results:

The transformation rate of unsaturations is 86%> molar. No sulfides are observed to the accuracy of the 1 H NMR detection.

A bifunctional POS oligomer of formula (XV) is thus obtained:

in which

m + n = 2;

96.5% of R 'are H and 3.5% of ethyl groups (% by mole); the viscosity is 2020 mPa.s.

IH-2. Preparation of rubber compositions

The following tests are carried out as follows: a diene elastomer (or mixture of diene elastomers) is introduced into an internal mixer, filled to 70% and whose initial tank temperature is approximately 90 ° C. , 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 is then carried out (non-productive phase) 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, and then the vulcanization system (sulfur and accelerator) is added. sulfenamide) 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 40 to 120 phr.

III-3. Characterization tests

The purpose of this test is to demonstrate the improved coupling performance (inorganic filler / diene elastomer) provided by the POS oligomer, compared to the conventional TESPT coupling agent.

Two compositions are prepared for this based on a SSBR / BR blend reinforced with silica, denoted C-1 and C-2, these two compositions differing essentially in the nature of the coupling agent used:

- composition C-1: conventional TESPT silane; - Composition C-2: POS oligomer of formula (XV).

The diene elastomer is an elastomer known to a person skilled in the art: SSBR comprising 25%) by mass of styrene, the polybutadiene units present being 58% of the polybutadiene-1,2 units and 23% of the polybutadiene-1 units, 4 trans, said SSBR being used in admixture with a polybutadiene having a high rate of cis 1-4 bonds.

The two coupling agents are used at an isomolar silicon content, that is to say that whatever the composition is used, the same number of moles of functions Y reactive with respect to silica and of its surface hydroxyl groups.

With the POS oligomer is associated a small amount of covering agent (1 pce) of the inorganic load (aid for implementation); it should be noted that the total quantity (POS coupling agent + POS covering agent) - ie 5 phr - advantageously remains lower than that of the conventional coupling agent TESPT alone (6.4 phr) in the control composition C- 1. Relative to the weight of reinforcing inorganic filler, the level of coupling agent and covering agent, in the composition of the invention C-2, represents less than 10% 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) as well as their rheometric properties, and properties after cooking (40 min at 150 ° C); the vulcanization system is made up of sulfur and sulfenamide. The appended figure reproduces the module curves (in MPa) as a function of the elongation (in%); these curves are denoted Cl and C2 and correspond respectively to compositions C-1 and C-2.

The examination of the different results in Table 2 shows, for the composition according to the invention C-2, compared to the control composition C-1:

significantly faster vulcanization kinetics, illustrated both by a constant K of higher conversion speed (multiplied by 2.5) and by a significantly reduced cooking time (T ₉₉ - To) (divided by 2.5);

- After baking, the composition according to the invention has the highest values of modulus under strong deformation (MA300) and of MA300 / MA100 ratio, clear indicators for those skilled in the art of better reinforcement provided by the inorganic filler and its POS oligomer coupling agent; - finally, hysteresis properties also improved, as illustrated by tan (δ) _max and ΔG values very significantly reduced, which is an indicator of reduced rolling resistance.

The appended figure clearly confirms the previous observations: the composition of the invention (curve C2) reveals a higher level of reinforcement (module) whatever the rate of elongation under great deformation (elongations of 100% and more); for such an elongation domain, this behavior demonstrates a high quality of the bond or coupling between the reinforcing inorganic filler and the diene elastomer.

Thus, unexpectedly for a person skilled in the art, the composition according to the invention comprising the oligomer α, ω-dihydroxy-mercaptopolyorganosiloxane reveals not only superior reinforcing properties, but also and above all improved cooking properties compared to to those offered by the conventional TESPT coupling agent.

The invention finds particularly advantageous applications in rubber compositions intended for the manufacture of tire treads, in particular when these treads are intended for tires for passenger vehicles, motorcycles or industrial vehicles of the HGV type.

Table 1

(1) SBR solution with 57% of 1-2 polybutadiene units; 25% styrene; Tg = -26 ° C; 75 pce dry SBR extended with 13.5 pce of aromatic oil (a total of 88.5 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) oil "Enerflex 65" from the company BP;

(5) TESPT ("Si69" from the company DEGUSSA);

(6) POS oligomer of formula (XV);

(7) silicone oil of type α, ω-di-OH ("Rhodorsil 48V50" from the company Rhodia);

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

(9) N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine ("Santoflex 6-PPD" from the company FLEXSYS);

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

Table 2

Claims

1. Elastomeric composition usable for the manufacture of tires, based on at least one diene elastomer, an inorganic filler as reinforcing filler and a coupling agent, characterized in that this coupling agent is an α, ω- oligomer linear dihydroxy-polyorganosiloxane comprising from 2 to 15 silicon atoms, and, along its chain, at least one silicon atom carrying a sulfur functional group (function denoted "F"), of formula (I):

R ¹ - G

in which the group G represents SH or an episulphide radical and R ¹ represents a divalent linking group.

2. Composition according to claim 1, R ¹ being chosen from linear or branched alkylene having from 1 to 20 carbon atoms.

3. Composition according to claim 2, R ¹ being chosen from:

- the alkylene groups denoted r ¹ having from 1 to 20 carbon atoms;

- the alkylene- (poly) cycloalkylene-alkylene groups denoted r ² , of which the alkylene parts, linear or branched, have 1 to 20 carbon atoms, and the cyclic part contains from 5 to 10 carbon atoms;

- the alkylene-phenylene-alkylene groups denoted r whose alkylene parts, linear or branched, have from 1 to 20 carbon atoms.

4. Composition according to any one of claims 1 to 3, the polyorganosiloxane oligomer corresponding to the average formula (fi):

RΌ _1/2 O _1/2 R '

m

in that:

- m, n, x, y and z are whole or fractional numbers;

the symbols R ′ mainly represent hydrogen, a minority (less than 50 mol%) of them being able to represent a C 1 -C 5, preferably C 1 -C _6, alkyl; - The symbols R, identical or different, each represent a monovalent hydrocarbon group chosen from linear or branched Cι-C ₆ alkyls;

the symbols pF represent precursor groups of the groups F;

- m + n = 2; - (x + y + z) is included in a range from 2 to 15;

- x is equal to or different from zero, preferably different from zero;

- y is different from zero;

- z is equal to or different from zero.

5. Composition according to any one of claims 1 to 4, the function F carrying a radical G episulfide and corresponding to one of the formulas (Iϋ-a) or (III-b):

(Ill-a) R ³ -

in which R ³ is chosen from:

- the alkylene groups denoted r ¹ , linear or branched, having from 1 to 20 carbon atoms;

- the alkylene- (poly) cycloalkylene-alkylene groups denoted r ^{2 in} which the alkylene parts, linear or branched, contain from 1 to 20 carbon atoms and the cyclic part contains from 5 to 10 carbon atoms;

or :

in which n is an integer ranging from 4 to 7 and R is chosen from alkylene r.

6. Composition according to any one of claims 1 to 5, the function F being chosen from those of formulas (1) to (13) below:

in which, if applicable:

- n is an integer ranging from 1 to 12, preferably equal to 1, 2 or 3;

- R ⁴ , R ⁵ and R ⁶ , identical or different, represent H or a monovalent hydrocarbon radical, preferably chosen from linear or branched alkyls having from 1 to 6 carbon atoms.

7. Composition according to any one of claims 4 to 6, the polyorganosiloxane oligomer corresponding to the average formula (IV):

in which :

- the symbols R ', identical or different, each represent hydrogen or an alkyl group having from 1 to 3 carbon atoms; - At least 80%>, preferably at least 90% of these radicals R 'are Hydrogen (%> molar);

- m, n, x, y and z are whole or fractional numbers;

- m + n = 2;

- (x + y + z) representing the total number of silicon atoms is in a range from 2 to 15, preferably from 2 to 10;

- x is equal to or different from zero, preferably different from zero;

- y is different from zero; •>

- z is equal to or different from zero.

8. Composition according to any one of claims 1 to 7, the diene elastomer being chosen from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

9. Composition according to any one of claims 1 to 8, the rate of reinforcing inorganic filler being between 10 and 200 phr and the rate of POS oligomer between 1 and 20 phr (parts by weight percent of elastomer).

10. Composition according to any one of claims 1 to 9, comprising a recovery agent for the inorganic filler.

11. Composition according to claim 10, the covering agent being chosen from the group consisting of hydrolyzable silanes, polyols, polyethers, amines, hydroxylated or hydrolyzable polyorganosiloxanes and mixtures of these compounds.

12. Composition according to claim 11, the covering agent being an α, ω-dihydroxy-polyorganosiloxane.

13. Process for preparing a rubber composition vulcanizable with sulfur and usable for the manufacture of tires, in which there is incorporated into at least one diene elastomer, at least one reinforcing inorganic filler and a coupling agent, characterized in that:

this coupling agent is a linear α, ω-dihydroxy-polyorganosiloxane oligomer comprising from 2 to 15 silicon atoms, and, along its chain, at least one silicon atom carrying a functional group (function denoted "F" ) sulfur of formula (I):

R ¹ - G

in which the group G represents SH or an episulphide radical and R ¹ represents a divalent linking group; and in that :

- thermomechanically kneading the whole, in one or more steps, until reaching a maximum temperature between 110 ° C and 190 ° C.

14. Use of a rubber composition in accordance with any one of claims 1 to 12, for the manufacture of tires or semi-finished products intended for tires, these semi-finished products preferably being chosen from the group consisting of the treads, the under-layers of these treads, the crown plies, the sidewalls, the carcass plies, the heels, the protectors, the air chambers and the inner gums sealed for tubeless tires.

15. A tire comprising a rubber composition according to any one of claims 1 to 12.

16. Semi-finished product for a tire, comprising a rubber composition according to any one of claims 1 to 12.

17. Semi-finished product according to claim 16, consisting of a tire tread.

18. Use, as coupling agent (inorganic filler / diene elastomer), in an elastomeric composition reinforced with an inorganic filler intended for a tire or for a semi-finished product for a tire, of an α, ol oligomer -dihydroxy- linear polyorganosiloxane comprising from 2 to 15 silicon atoms, and, along its chain, at least one silicon atom carrying a sulfur-containing functional group (function denoted "F") of formula (I): R ¹ - G

in which the group G represents SH or an episulphide radical and R ¹ represents a divalent linking group.