CA2784412A1 - Winter tyre with improved grip on ice - Google Patents

Abstract

Winter tire with improved grip on melting ice, the tread of which comprises a composition comprising at least one diene elastomer such as natural rubber and / or a polybutadiene, more than 30 phr of a liquid plasticizer, between 50 and 150 phr of a reinforcing filler such as silica and / or carbon black, and 35 to 50 phr of hollow microparticles of at least one metal oxide such as an aluminosilicate, having a median size by weight of between 2 and 500 μm.

Description

WINTER PNEUMATIC WITH IMPROVED ICE ADHESION

1. DOMAIN OF THE INVENTION

The invention relates to the rubber compositions used as bands of tire bearings for vehicles, in particular tires winter able to ride on ice or ice covered ground without nails (also called pneumatic "studless").

It is more particularly related to the treads of winter tires that are specifically adapted for running under so-called "ice conditions"
melting "encountered in a temperature range typically between -5 C and 0 C.
recalls in effect that, in such a field, the pressure of the tires at the passage of a vehicle causes a superficial melting of the ice which is covered with a thin film of harmful water to the adhesion of these tires.

2. STATE OF THE ART

To avoid the harmful effects of nails, especially their strong action abrasive on the of the soil itself and significantly degraded road dry soil, manufacturers of tires proposed different solutions consisting of modify the formulation of the rubber compositions constituting their rolling.

Thus, it has been proposed first of all to incorporate solid particles into great hardness, such silicon carbide (see, for example, US Pat. No. 3,878,147), some flush the surface of the tread as and when the wear of this last, and thus come into contact with the ice. Such particles, able to act in definitive like micro-nails on hard ice, thanks to an effect of "claw" well known, remain relatively aggressive vis-à-vis the ground; they are not well adapted to the conditions rolling on a melting ice.

Other solutions have therefore been proposed, including incorporating powders water-soluble (ie, which can dissolve in water) in the composition constitutive of the tread. Such powders solubilize more or less on contact snow or melted ice, which allows on the one hand the creation on the surface of the tread of porosities likely to improve the attachment of the tread on the floor and other share the creation of throats playing the role of evacuation channels of the film liquid created between the pneumatic and soil. As examples of such water-soluble powders, can quote by example the use of cellulose powder, PVA (polyvinyl alcohol) or starch, or still powders of guar gum or xanthan gum (see for example requests JP 3-159803, JP 2002-211203, EP 940 435, WO 2008/080750, WO
2008/080751).
In all these examples, the solubility at very low temperature and in a very short time of the powder used is an essential factor for the proper functioning of the rolling. If the powder is not soluble in the conditions of use of the tire, the functions above mentioned (creation of microporosities and drainage channels) are not fulfilled and the adhesion is not improved. Another known disadvantage of these solutions is that they can strongly penalize the reinforcement of the rubber compositions (and so their resistance to wear) or their hysteresis (and therefore their resistance to rolling).

3. BRIEF DESCRIPTION OF THE INVENTION

Pursuing their research, the Claimants discovered a composition of rubber capable of generating an effective surface micro-roughness by means of microparticles specific, and which greatly improves the ice adhesion of treads and tires containing them, under conditions of melting ice, without penalize strengthening and hysteresis properties.

Accordingly, the present invention relates to a tire whose rolling comprises a rubber composition comprising at least one elastomer diene, more of 30 phr of a liquid plasticizer, between 50 and 150 phr of a filler reinforcing, characterized in said composition further comprises 35 to 50 phr of microparticles hollow of minus a metal oxide having a median size by weight of between 2 and 500 m.
At first, these hollow microparticles which are protruding at the surface of the tread, fulfill the previously described claw function without the inconvenience to be highly abrasive with respect to the asphalt used as a coating road. Then, in a second time, after crushing by breaking their hollow structure and expulsion of the rubbery matrix, said microparticles create microcavities that play the role of storage volume and drainage channel of the water film to the surface of the ice cream ; under these conditions, the contact between the surface of the rolling and ice no longer lubricated and the coefficient of friction is improved.

The tires of the invention are particularly intended for equipping vehicles to tourism-type engine, including 4x4 vehicles (four-wheel drive) and vehicles SUV ("Sport Utility Vehicles"), two-wheeled vehicles (including motorcycles) like the industrial vehicles chosen in particular from light trucks and heavy "(ie, subway, buses, road transport vehicles such as trucks, tractors).

The invention and its advantages will be easily understood in the light of the description and examples of embodiments that follow.

4. MEASUREMENTS AND TESTS USED

The treads and rubber compositions that make up these bands of rolling are characterized, before and after cooking, as indicated below.

4.1 - Mooney Plasticity An oscillating consistometer is used as described in the French standard (November 1980). The measure of Mooney plasticity is according to the principle next:
composition in the raw state (ie, before cooking) is molded in a chamber cylindrical heated at 100 C. After one minute of preheating, the rotor rotates within the test tube 2 revolutions / minute and we measure the useful torque to maintain this movement after 4 minutes of rotation. Mooney plasticity (ML 1 + 4) is expressed in "Mooney unit" (UM, with 1 UM =
0.83 Newton.meter).

4.2 - Timing time The measurements are carried out at 130 ° C., in accordance with the French standard NF T 43-005.
The evolution of the consistometric index as a function of time allows determine the time roasting of the rubber compositions, evaluated according to the standard aforementioned by the parameter T5 (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 UM) of 5 units above the minimum value measured for this index.

4.3 - 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 in time function describes the evolution of the stiffening of the composition as a result of reaction of vulcanization. Measurements are processed according to DIN 53529 - Part 2 (March 1983): Ti is the induction delay, that is the time required at the beginning of the reaction of vulcanization, T (eg Tgo) is the time required to achieve a conversion of a%, that is to say a% (for example 90%) of the difference between the minimum and maximum.

4.4 - Traction tests These tensile tests make it possible to determine the elasticity stresses and the properties at the break. Unless otherwise indicated, they shall be carried out in accordance with french standard NF T
46-002 of September 1988. We measure in second elongation (ie, after a cycle the rate of expansion provided for the measure itself).
secant modules Nominal (or apparent stresses, in MPa) at 10% elongation (denoted M10), 100%
of elongation (denoted M100) and 300% elongation (denoted M300). Constraints to the rupture (in MPa) and elongations at break (in%) are also measures. All of these tensile measurements are made under normal conditions of temperature (23 2 C) and hygrometry (50 5% relative humidity), according to the French standard NF T 40-101 (December 1979).

4.5 - Shore A Hardness The Shore A hardness of the compositions after firing is assessed in accordance with Standard ASTM D 2240-86.

4.6 - Properties d. picnics Dynamic properties are measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D5992-96. The response of a composition sample is recorded vulcanized (cylindrical specimen 4 mm thick and 400 mm2 in section), submitted to one sinusoidal stress in alternating simple shear, at the frequency of 10Hz, at a temperature of 0 C. A sweep in amplitude of deformation of 0.1% to 50%
(go cycle), then from 50% to 1% (return cycle). The exploited results are the loss factor tan (t); for the return cycle, we indicate the maximum value of tan (t) observed (noted tan (S) max) between the values at 0.15% and at 50% deformation (Payne effect).

5. DETAILED DESCRIPTION OF THE INVENTION

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

On the other hand, any range of values designated by the expression "between b "represents the value range greater than "a" and less than "b" (ie, terminals a and b excluded) while WO 2011/07318

6 PCT / EP2010 / 069621 that any interval of values designated by the expression "from a to b" means the area of values ranging from "a" to "b" (that is, including strict bounds a and b).

The rubber composition of the tread according to the invention, while at least for the portion (therefore carved) tread that is intended for enter contact with the road when driving the tire, is therefore based on minus one diene elastomer, a plasticizer system, a reinforcing filler and microparticles specific hollow components which are described in detail below.

5.1 - Diene elastomer By elastomer (or rubber, the two terms being synonymous) of the type "diene", one recalls that an elastomer derived at least in part (ie a homopolymer or a copolymer) of monomers dienes (monomers carrying two double carbon bonds carbon, conjugated or not).

The diene elastomers can be classified in known manner into two categories: those so-called "essentially unsaturated" and those termed "essentially saturated". The butyl rubbers, as for example copolymers of dienes and alpha-olefins type EPDM, enter the category of essentially saturated diene elastomers with a original reasons diene which is weak or very weak, always less than 15% (mol%).
On the contrary, essentially unsaturated diene elastomer means a diene elastomer from at least in part conjugated diene monomers having a rate of units or units of dienic origin (conjugated dienes) which is greater than 15% (mol%). In the category of elastomers Dienic "essentially unsaturated", in particular means elastomer diene "highly unsaturated" a diene elastomer having a level of origin diene (dienes conjugates) which is greater than 50%.

It is preferred to use at least one diene elastomer of the type strongly unsaturated, in particular a diene elastomer selected from the group consisting of rubber Natural Resources (NR), synthetic polyisoprenes (IRs), polybutadienes (BRs), copolymers of butadiene, the copolymers of isoprene and mixtures of these elastomers. Such copolymers are more preferentially selected from the group consisting of copolymers of butadiene-styrene (SBR), isoprene-butadiene copolymers (BIR), isoprene copolymers, styrene (SIR), isoprene-butadiene-styrene copolymers (SBIR) and such copolymers.

The elastomers can be for example blocks, statistics, sequenced, microsequenced, and be prepared in dispersion or in solution; they can be coupled and / or starred or even functionalized with a coupling agent and / or starring or functionalization. For a coupling with carbon black, there may be mentioned, for example, groups functional comprising a C-Sn bond or amino functional groups such as benzophenone by example; for coupling to a reinforcing inorganic filler such as silica, mention may be made for example, silanol or polysiloxane functional groups having a silanol end (such described, for example, in US 6,013,718), alkoxysilane groups (such as as described by US Pat. No. 5,977,238), carboxylic groups (as described by US Pat.
example in US 6,815,473 or US 2006/0089445) or else polyether groups (such as described by example in US 6,503,973). As other examples of such elastomers functionalized, we mention may also be made of elastomers (such as SBR, BR, NR or IR) of the type epoxides.
Polybutadienes, and in particular those having a content units -1.2 between 4% and 80% or those with a cis-1,4 content greater than 80%, polyisoprenes, butadiene-styrene copolymers and in particular those having a content styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, one 1,2-linkage content of the butadiene part of between 4% and 65%, a content in trans-1,4 bonds between 20% and 80%, the butadiene copolymers isoprene and especially those having an isoprene content of between 5% and 90% by weight and an glass transition temperature ("Tg" - measured according to ASTM D3418-82) of -40 C at -80 C, isoprene-styrene copolymers and especially those having a styrene content range between 5% and 50% by weight and a Tg between -25 C and -50 C.

In the case of butadiene-styrene-isoprene copolymers are suitable especially 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%
weight and more particularly between 20% and 50%, a butadiene content between 5% and 50%
by weight and more particularly between 20% and 40%, a content of units -1.2 from the butadiene part between 4% and 85%, a content of trans -1,4 units Of the game butadiene content between 6% and 80%, a content of -1,2 units plus -3,4 the part between 5% and 70% and a trans-1,4 content of the part isoprenic between 10% and 50%, and more generally any copolymer butadiene styrene-isoprene having a Tg between -20 C and -70 C.

According to a particularly preferred embodiment of the invention, the diene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes having a cis-1,4 bond ratio greater than 90%, the copolymers of butadiene-styrene and mixtures of these elastomers.

According to a more particular and preferential embodiment, the composition Rubber contains 50 to 100 phr of natural rubber or synthetic polyisoprene, said natural rubber or synthetic polyisoprene that can be used especially in cutting

-7-(mixture) with not more than 50 phr of a polybutadiene having a 1.4 greater than 90%.

According to another particular and preferred embodiment, the composition Rubber contains 50 to 100 phr of a polybutadiene having a cis-1,4 bond ratio greater than 90%, said polybutadiene can be used especially in a blend with at most 50 pce of natural rubber or synthetic polyisoprene.

To the diene elastomers of the treads according to the invention could to be associated, in a minor amount, synthetic elastomers other than diene, even polymers other than elastomers, for example thermoplastic polymers.

5.2 - Plasticizer system The rubber composition according to the invention has another characteristic essential of contain at least 30 phr of a liquid plasticizer (at 20 C) whose function is to soften the matrix by diluting the elastomer and the reinforcing filler; his Tg is by definition less than -20 C, preferably less than -40 C.

Any extension oil, whether aromatic or non-aromatic, any agent liquid plasticizer known for its plasticizing properties vis-à-vis of diene elastomers, is usable. At room temperature (20 ° C.), these plasticizers or these oils, more or less viscous liquids (ie, as a reminder, substances with the ability to eventually take the form of their container), as opposed to resins hydrocarbon plasticizers which are inherently temperature-stable room.

Particularly suitable liquid plasticizers selected from the group constituted by the naphthenic oils (low or high viscosity, in particular hydrogenated or no), the oils paraffinics, MES (Medium Extracted Solvates) oils, TDAE oils (Treated 3o Distillate Aromatic Extracts), mineral oils, vegetable oils, the plasticizers ethers, ester plasticizers, plasticizers phosphates, plasticisers sulfonates and mixtures of these compounds.

As phosphate plasticizers, for example, mention may be made of those contain between 12 and 30 carbon atoms, for example trioctyl phosphate. As examples of plasticizers esters, mention may be made in particular of the compounds chosen from the group consisting of by the trimellitates, pyromellitates, phthalates, 1,2-cyclohexane dicarboxylates, adipates, azelates, sebacates, triesters of glycerol and mixtures of these compounds. From triesters above, mention may be made in particular of triesters of glycerol, preferably constituted mainly (for more than 50%, more preferentially for more than 80%
by weight) of a

-8-unsaturated fatty acid at C8, that is to say selected from the group consisting of oleic acid, linoleic acid, linolenic acid and mixtures of these acids. More preferably, whether of synthetic or natural origin (for example, oils vegetable sunflower or rapeseed), the fatty acid used is more than 50% by weight, more preferentially for more than 80% by weight of oleic acid. Such tri (trioleates) with high oleic acid content are well known, they have been described for example in the WO 02/088238, as plasticizing agents in rolling for tires.

The level of liquid plasticizer in the composition according to the invention is higher preference at 40 phr, more preferably in a range of 50 to 100 phr.

According to another preferred embodiment, the compositions according to the invention also include, as a solid plasticizer (at 20 C), a resin hydrocarbon having a Tg greater than +20 C, preferably greater than +30 C, as described for example in WO 2005/087859, WO 2006/061064 and WO 2007/017060.

Hydrocarbon resins are polymers well known to humans job, essentially based on carbon and hydrogen, so miscible by nature in the diene (s) elastomer compositions (s) when further qualified of "plasticizers".
They have been described for example in the book entitled "Hydrocarbon Resins "from R.
Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9) whose Chapter 5 is devoted to their applications, especially in rubber pneumatic (5.5.
"Rubber Tires and Mechanical Goods." ~ They can be aliphatic, aromatic or still of the aliphatic / aromatic type that is to say based on monomers aliphatic and / or aromatics. They can be natural or synthetic, with or without oil (if that is the case, also known as petroleum resins). They are preferably exclusively hydrocarbon-based, that is to say that they contain only carbon atoms and hydrogen.
Preferably, the hydrocarbon plasticizing resin has at least one, more preferentially all, of the following characteristics:

a Tg greater than 20 C (more preferably between 40 and 100 C);
a number-average molecular mass (Mn) of between 400 and 2000 g / mol (more preferably between 500 and 1500 g / mol);
a polymolecularity index (Ip) of less than 3, more preferably less than 2 (recall: Ip = Mw / Mn with Mw weight average molecular weight).

-9 The Tg is measured in a known manner by DSC (Differential Scanning Calorimetry), according to the ASTM D3418 (1999). The macrostructure (Mw, Mn and Ip) of the resin hydrocarbon is determined by steric exclusion chromatography (SEC): solvent tetrahydrofuran, temperature 35 C; concentration 1 g / l; flow rate 1 ml / min; filtered solution on porosity filter 0.45 m before injection; Moore calibration with polystyrene standards ; set of 3 "WATERS" columns in series ("STYRAGEL" HR4E, HR1 and HRO.5); detection by differential refractometer ("WATERS 2410") and its operating system partner ("WATERS
Empower ").

According to a particularly preferred embodiment, the resin hydrocarbon plasticizer is selected from the group consisting of homopolymer resins or copolymer of cyclopentadiene (abbreviated as CPD), the homopolymer or copolymer resins of dicyclopentadiene (abbreviated to DCPD), homopolymer or copolymer resins terpene, C5 homopolymer or copolymer resins, homopolymer resins or C9 cutting copolymer, and mixtures of these resins. Among the resins of copolymers above are more preferably used those selected in the group constituted by the copolymer resins (D) CPD / vinylaromatic, copolymer resins (D) CPD / terpene, copolymer resins (D) CPD / C5 cut, copolymer resins (D) CPD /
C9 cut, terpene / vinylaromatic copolymer resins, copolymer resins terpene / phenol, C5 / vinylaromatic cut copolymer resins, copolymer resins chopped off C9 / vinylaromatic, and mixtures of these resins.

The term "terpene" here combines in a known manner the alpha-pinene monomers, beta-pinene and limonene; preferentially is used a limonene monomer, consisting of presenting known manner in the form of three possible isomers: L-limonene (enantiomer levorotatory), D-limonene (dextrorotatory enantiomer), or dipentene, racemic enantiomers dextrorotatory and levorotatory. As vinylaromatic monomer agree by styrene, alpha-methylstyrene, ortho-, meta-, para-methylstyrene, vinyl toluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, the hydroxystyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, any monomer vinylaromatic derived from a C9 cut (or more generally from a C8 cut to Cio). Of preferably, the vinyl aromatic compound is styrene or a monomer vinylaromatic from a Cg cut (or more generally from a C8 to C10 cut). Of preferably, the compound vinylaromatic is the minor monomer, expressed as a molar fraction, in the copolymer considered.

The content of hydrocarbon resin is preferably between 3 and 60 pce, more preferably between 3 and 40 phr, in particular between 5 and 30 phr.

-10-The level of total plasticizer (ie, more liquid plasticizer, the case appropriate, resin solid hydrocarbon) is preferably between 40 and 100 phr, more preferably included in a range of 50 to 80 phr.

5.3 - Charge Any type of reinforcing filler known for its ability to strengthen a rubber composition usable for the manufacture of tires, for example example a organic load such as carbon black, or a load reinforcing inorganic such as silica to which is associated in a known manner coupling.

Such a reinforcing filler typically consists of nanoparticles size average (by mass) is less than 500 nm, most often between 20 and 200 nm, in particularly and preferably between 20 and 150 nm.
Suitable carbon blacks are all carbon blacks, especially those black conventionally used in tires or treads of pneumatic (black called pneumatic grade). Among these, we will mention more especially blacks 100, 200 or 300 series of reinforcing carbon (ASTM grades), as example N115, N134, N234, N326, N330, N339, N347, N375. Carbon blacks could be for example already incorporated into the isoprene elastomer in the form of a masterbatch (see for example WO 97/36724 or WO 99/16600).

As examples of organic fillers other than carbon blacks, it is possible to quote organic functionalized polyvinyl fillers as described in WO-A-applications 2006/069792, WO-A-2006/069793, WO-A-2008/003434 and WO-A-2008/003435.

By "reinforcing inorganic filler" must be understood here any load inorganic or mineral, whatever its color and origin (natural or synthesis), again called "white" charge, "clear" charge or even "non-black" charge by opposition to black carbon, capable of reinforcing on its own, without any other means than a coupling intermediate, a rubber composition for the manufacture of pneumatic tires, other words capable of replacing, in its reinforcing function, a black of carbon conventional pneumatic grade; such a load is characterized generally, so known by the presence of hydroxyl groups (-OH) on its surface.

Inorganic reinforcing fillers are particularly suitable minerals from siliceous type, in particular silica (SiO 2, or aluminous type, in particular particular of alumina (Al 2 O 3). The silica used can be any reinforcing silica known to the man from especially any precipitated or fumed silica having a surface BET as well

-11-CTAB surface area both less than 450 m2 / g, preferably from 30 to 400 m2 / g, especially between 60 and 300 m2 / g. As precipitated silicas highly dispersible (say "HDS"), there are for example the silicas "Ultrasil" 7000 and "Ultrasil"
7005 of society Degussa, the silicas "Zeosil" 1 165MP, 1135MP and 11 15MP from Rhodia, silica "Hi Sil "EZ150G from PPG company, the silicas" Zeopol "8715, 8745 and 8755 of the Huber company.
As examples of reinforcing aluminas, mention may be made of "Baikalox" aluminas A125 or CR125 from Baikowski, "APA-100RDX" from Condea, "Aluminoxid C" from Degussa or "AKP-G015" from Sumitomo Chemicals.

Preferably, the total reinforcing filler content (black of carbon and / or load reinforcing inorganic substance) is between 60 and 120 phr, especially between 70 and 100 pce.
According to a particular embodiment, the feedstock comprises silica, carbon black or a mixture of carbon black and silica.
According to another particular embodiment, the reinforcing filler comprises black of carbon as a majority; in such a case, carbon black is present at a rate preferentially greater than 60 phr, associated or not with an inorganic filler reinforcing such as silica in a minority amount.
According to another particular embodiment, the reinforcing filler comprises a charge inorganic, in particular silica, as a majority; in such a case, the inorganic filler, in particular silica, is present at a rate preferably greater than 70 pce, associate or no to carbon black in minority quantity; carbon black, when present, is preferably used at a level of less than 20 phr, more preferably less than 10 phr (for example between 0.1 and 10 phr).

Regardless of the primary aspect of the invention, namely the search for a adherence optimized on melting ice, the use of a majority load reinforcing inorganic such as silica is also advantageous from the point of view of adhesion to wet soil or snowy.

According to another possible embodiment of the invention, the load reinforcement includes a cutting of carbon black and reinforcing inorganic filler such as silica in neighboring quantities; in such a case, the level of inorganic filler, in particular silica, and the rate carbon black are preferably each between 25 and 75 phr, more especially each between 30 and 50 phr.

To couple the reinforcing inorganic filler to the diene elastomer, uses so well known at least one bifunctional coupling agent (or linker) intended for

-12-ensure a sufficient chemical and / or physical connection between the charge inorganic (surface of its particles) and the diene elastomer. We use especially organosilanes or bifunctional polyorganosiloxanes.

In particular, polysulfurized silanes, called "symmetrical" or "asymmetrical" according to their particular structure, as described for example in the applications W003 / 002648 (or US 2005/01665 1) and W003 / 002649 (or US 2005/016650).

In particular, without the following definition being limiting, silanes so-called "symmetrical" polysulfides corresponding to the following general formula (I):

(I) Z - A - SX - A - Z, wherein:

x is an integer of 2 to 8 (preferably 2 to 5), - A is a divalent hydrocarbon radical (preferably groups alkylene C18 or C6-C12 arylene groups, more particularly alkylene in C1-C1o, especially C1-C4, in particular propylene);
Z is one of the following formulas:

Ri Ri R2 -Si-R1; -Si-R2; -Si-R2 in which:
the radicals R1, substituted or unsubstituted, identical or different between them, are C 1 -C 18 alkyl, C 5 -C 18 cycloalkyl or C 6 -C 6 aryl C18 (from preferably C 1 -C 6 alkyl, cyclohexyl or phenyl groups, especially C1-C4 alkyl groups, more particularly methyl and / or ethyl).
the radicals R2, substituted or unsubstituted, identical or different between them, represent a C1-C18 alkoxyl or C5-C18 cycloalkoxyl group (from preferably a group selected from C 1 -C 8 alkoxyls and C 5 -C 8 cycloalkoxyls, plus preferably still a group chosen from C 1 -C 4 alkoxyls, in particular methoxyl and ethoxyl).

As examples of polysulphide silanes, mention will be made more particularly the polysulfides of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl). Among these compounds, we use in particular bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, or disulfide bis- (triethoxysilylpropyl), abbreviated as TESPD. We will also mention examples polysulfides (especially disulfides, trisulphides or tetrasulfides)

-13-(C 1 -C 4 -alkyl) -dialkyl (C 1 -C 4) silylpropyl), more particularly the bis-tetrasulfide monoethoxydimethylsilylpropyl as described in the patent application WO
02/083782 (or US 2004/132880).

As a coupling agent other than polysulfurized alkoxysilane, mention may be made including POS
bifunctional polyorganosiloxanes or polysulfides of hydroxysilane (R2 = OH
in formula (I) above) as described in the patent applications WO
02/30939 (or US 6,774,255) and WO 02/31041 (or US 2004/051210), or else silanes or POS
carriers of azo-dicarbonyl functional groups, as described by example in patent applications WO 2006/125532, WO 2006/125533, WO 2006/125534.

In the rubber compositions according to the invention, the content of coupling is preferably between 2 and 12 phr, more preferably between 3 and 8 pce.

Those skilled in the art will understand that as an equivalent load load inorganic reinforcement described in this paragraph could be used reinforcing filler of another nature, particularly organic, since this reinforcing would be covered with an inorganic layer such as silica, or its surface of functional sites, in particular hydroxyls, requiring the use of an agent coupling for establish the connection between the load and the elastomer.

5.4 - Hollow microparticles of metal oxide The rubber composition according to the invention has the characteristic essential of have 35 to 50 phr of hollow microparticles (or microspheres) of at least an oxide metal, the term oxide including of course hydroxides; these microparticles have a median size by weight between 2 and 500 m.

By microparticles, definition and, in general, particle size micrometric, that is, whose average size or median size (both expressed by weight) are between 1 m and 1 mm.

Below the minima indicated above, the intended technical effect (ie the creation of a adapted micro-roughness) may be insufficient when beyond indicated, exposed to various disadvantages, in particular when the composition of rubber is used as tread: in addition to a loss of aesthetics (too much particles visible on the surface of the tread) and a risk of decohesion, when driving, of relatively large carving elements, it has been found that the performance adhesion on melting ice could be degraded.

-14-For all these reasons, it is preferred that the hollow microparticles have a median size (in weight) in a range of 5 to 200 m. This size domain particularly preferential seems to correspond to an optimized compromise between on the one hand the roughness of surface area and on the other hand a good contact between the composition of rubber and the ice cream.

According to a preferred embodiment, the metal of the metal oxide is chosen in the group consisting of aluminum, silicon, zirconium, transition and mixtures of such metals. Transition metal means more especially metals of the fourth period from scandium to zinc, preferentially titanium and zinc.
More preferably still more suitable are aluminum, silicon, titanium, zirconium and zinc.

According to a more preferred embodiment, the metal oxide is chosen in the group consisting of oxides and / or hydroxides of aluminum, oxides and / or hydroxides of silicon, oxides and / or hydroxides of aluminum and silicon, and mixtures such oxides and / or hydroxides. More preferably still, the metal oxide used is a aluminosilicate.

For the analysis of particle size and the calculation of the median size of microparticles (or median diameter for supposedly spherical microparticles), different known methods are applicable, for example by laser diffraction (see standard example ISO-8130-13 or JIS standard K5600-9-3).

It is also possible to use, in a simple and preferential manner, a analysis of the particle size by mechanical sieving; the operation consists of sifting a defined quantity sample (for example 200 g) on a vibrating table for 30 minutes with diameters of different sieves (for example, with a progression ratio of 1.26, with stitches 1000, 800, 630, 500, 400, ... 100, 80, 63 m); the refusals collected on each sieves are weighed on a precision scale; we deduce the% of refusal for each mesh diameter relative to the total weight of the product; the median size (or median diameter) or average (or average diameter) is finally calculated in a known manner from the histogram of the particle size distribution.

5.5 - Miscellaneous additives The rubber compositions according to the invention also comprise all or part of usual additives usually used in elastomer compositions intended for manufacture of treads for tires, in particular for winter tires, such as protective agents such as anti-ozone waxes, anti-antiozonants

-15-chemicals, antioxidants, reinforcing resins, acceptors (eg example resin phenolic novolak) or methylene donors (eg HMT or H3M), a crosslinking system based on either sulfur or sulfur donors and / or peroxide and / or bismaleimides, vulcanization accelerators, activators of vulcanization.
These compositions may also contain coupling activators when an agent coupling is used, inorganic filler or more generally, implementation support agents who are likely to known, thanks to improving the dispersion of the filler in the rubber matrix and a lowering the viscosity of the compositions, to improve their ability to the raw state; these agents are, for example, hydrolysable silanes such as alkoxysilanes, polyols, polyethers, amines, hydroxylated polyorganosiloxanes or hydrolysable.

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

- to incorporate in the diene elastomer, in a mixer, more than 30 phr of a liquid plasticizer, between 50 and 150 phr of a reinforcing filler, 35 to 50 phr of hollow microparticles of a metal oxide having a median size of weight between 2 and 500 m, by thermomechanically mixing the whole, in one or several times until a maximum temperature of 130 VS
and 200 C;
- cool all at a temperature below 100 C;
- Then incorporate a crosslinking system;
- mix everything up to a maximum temperature below 120 C;
extrude or calendering the rubber composition thus obtained, in particular in the form of a tire tread.

-16-For example, the first (non-productive) phase is conducted in one single step Thermomechanical during which is introduced, in a suitable mixer such as usual internal mixer, all the necessary constituents, the possible agents of additional recovery or implementation and other miscellaneous additives, the exception of crosslinking system. After cooling the mixture thus obtained course of the first non-productive phase, the crosslinking system is then incorporated into low temperature, usually in an external mixer such as a blender.
cylinders; all is then mixed (productive phase) for a few minutes, for example between 5 and min.
The actual crosslinking system is preferably based on sulfur and a primary vulcanization accelerator, in particular an accelerator sulfenamide type. AT
this vulcanization system are added, incorporated during the first phase productive and / or during the productive phase, various accelerators secondary or known vulcanization activators such as zinc oxide, stearic acid, guanidic derivatives (especially diphenylguanidine), etc. The sulfur content is preferably between 0.5 and 3.0 phr, that of the primary accelerator is preferably between 0.5 and 5.0 phr.

It is possible to use as accelerator (primary or secondary) any compound likely to act as a vulcanization accelerator for diene elastomers in the presence of sulfur, including thiazole accelerators and their derivatives, accelerators thiuram types, zinc dithiocarbamates. These accelerators are more preferably selected from the group consisting of 2-mercaptobenzothiazyl disulfide (in abstract "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated "CBS"), N, N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-ter-butyl-2-benzothiazyl sulfenimide ("TBSI"), dibenzyldithiocarbamate zinc ("ZBEC") and mixtures of these compounds.

The final composition thus obtained is then calendered, for example under the form of a leaf or plate, in particular for laboratory characterization, or again extruded in the form of a rubber profile directly usable as Band winter tire bearing.

The vulcanization (or cooking) is conducted in a known manner at a temperature usually between 130 C and 200 C, for a sufficient time which may vary by example between 5 and 90 min depending in particular on the cooking temperature, the heating system vulcanization adopted and the kinetics of vulcanization of the composition under consideration.

In the case of a composite type tread formed of several compositions of rubber of different formulations, the rubber compositions according to the invention

-17-previously described may constitute only part of the rolling according to the invention, at least for the portion (therefore carved) of the band bearing intended to come into contact with the road during the pneumatic.

The invention relates to the tires previously described both in the raw state (ie, before baked) (ie, after crosslinking or vulcanization).

6. EXAMPLES OF CARRYING OUT THE INVENTION
6.1 - Preparation of rubber compositions For the manufacture of these compositions, the following procedure was carried out:
we introduce in an internal mixer, whose initial tank temperature is about 60 C, successively the reinforcing filler (carbon black, silica and its coupling associated), liquid plasticizer, hollow oxide microparticles metallic, the elastomer diene (or diene elastomer blending) as well as the various other ingredients to the exception of the vulcanization system; the mixer is thus filled to about 70% (%
volume). We then conduct a thermomechanical work (non-productive phase) in a step, which lasts in total about 3 to 4 minutes, until reaching a temperature maximum of "fallen" of 165 C. The resulting mixture is recovered, cooled and then we incorporate sulfur and a sulfenamide type accelerator on an external mixer (homo-finisher) at 30 C, by mixing the whole (productive phase) for a suitable time (by example between 5 and 12 min).
6.2 - Rubber and friction tests on 0 ace In these tests, two compositions (denoted C-1 and C-2) based on elastomer dienes (NR and BR cleavage at cis-1,4 bond ratios greater than 95%), reinforced by cutting of silica and carbon black, with or without 40 pce of hollow microparticles of aluminosilicate.

Tables 1 and 2 give the formulation of the two compositions (Table 1 -rate of different products expressed in pce), their properties before and after cooking (30 min at 150 ° C);
the vulcanization system is sulfur and sulfenamide.

First of all, the examination of the different results in Table 2 reveals no degradation notable rubber properties for the composition according to the invention (C-2) despite the presence of a high level of metal oxide microparticles, which already constitutes a unexpected result for the skilled person:

-18-the processability in the raw state (Mooney plasticity) is certainly increased, but weakly;
the rheometric properties (cooking) are not modified in a manner sensitive;
after cooking, the modules in extension remain close; so surprisingly, the Shore hardness is slightly increased with respect to the amount of microparticles used;
- finally, the hysteresis (tan (S) max) is not increased.

Both compositions are then subjected to a laboratory test consisting of measure their coefficient of friction on ice. The principle is based on a skate of rubber composition sliding at a given speed (for example 5 km / h) on an ice track with a charge imposed (for example equal to 3 kg / cm 2). Prior to the test, the surface of the skate to test is lapped by planing to a thickness of 0.5 mm, followed by a series of friction by repeated sliding on real dry ground (asphalt) under the said imposed load (for example 3 kg / cm 2). The forces generated in the direction of advancement (Fx) of the pad and perpendicular to the advancement (Fz) are measured. The ratio Fx / Fz determines the coefficient of friction of the test tube on the ice. The temperature during the measurement is set at -2 ° C.

This test, the principle of which is well known to those skilled in the art (see for example requests for patent EP 1052270 and EP 1505112) makes it possible to evaluate under conditions representative the melting ice adhesion that would be obtained after a rolling test on equipped vehicle tires whose tread consists of the same compositions of rubber.

The results are shown in Table 3. A value greater than that witness (composition C-1), arbitrarily set at 100, indicates an improved result that is to say, a ability to a shorter braking distance. We see that the composition C-2 according to the invention shows a very sharp increase (23%) in the coefficient of ice friction, by relative to the control composition C-1 devoid of microparticles aluminosilicate.

In conclusion, the compositions according to the invention offer tires and to their bands rolling a grip on melting ice that is noticeably improved.

-19-Table 1 Composition N: C-1 C-2 BR (1) 60 60 NR (2) 40 40 silica (3) 80 80 coupling agent (4) 6.5 6.5 hollow microparticles (5) - 40 carbon black (6) 5 5 non-aromatic oil (7) 55 55 DPG (8) 1.5 1.5 ZnO 1.2 1.2 stearic acid 1 1 anti-ozone wax 1.5 1.5 antioxidant (9) 2 2 sulfur 2 2 accelerator (10) 1.7 1.7 (1) BR with 4.3% of 1-2; 2.7% trans; 97% cis 1-4 (Tg = -104 C);
(2) Natural rubber (peptized);
(3) "Zeosil 1115MP" silica from Rhodia, type "HDS"
(BET and CTAB: approximately 120 m2 / g);
(4) coupling agent TESPT ("Si69" from Degussa);
(5) aluminosilicate ("Fillite 200/7" from Japan Fillite) (median particle size: about 90 m);
(6) ASTM grade N234 (Cabot Company);
(7) MES oil ("Catenex SNR" from Shell);
(8) diphenylguanidine ("Perkacit DPG" from Flexsys);
(9) N-1,3-dimethylbutyl-N-phenylparaphenylenediamine ("Santoflex 6-PPD" from Flexsys);
(10) N-dicyclohexyl-2-benzothiazol sulfenamide ("Santocure CBS" from the company Flexsys).

-20-Table 2 Composition N: C-1 C-2 Properties before cooking:
Mooney (UM) 50 56 T5 (min) 12 13 Ti (min) 4 5 Tgo (min) 9.5 10 Properties after cooking:
Shore A 59 65 M10 (MPa) 3.0 3.5 M100 (MPa) 1.5 1.5 M300 (MPa) 1.5 1.3 tan (8) m. (0 C) 0.25 0.25 Table 3 Rubber composition: C-1 C-2 Friction on ice (-2 C) 100 123

Claims (15)

1. A tire whose tread comprises a composition of rubber comprising at least one diene elastomer, more than 30 phr of a plasticizer liquid, between 50 and 150 phr of a reinforcing filler, characterized in that said composition has in in addition to 35 to 50 phr of hollow microparticles of at least one metal oxide having a size median weight between 2 and 500 microns. 2. The tire according to claim 1, wherein the diene elastomer is chosen in the group consisting of natural rubber, synthetic polyisoprenes, the polybutadienes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers. 3. A tire according to claim 2, said composition comprising 50 to 100 pce of natural rubber or synthetic polyisoprene. 4. A tire according to claim 3, the natural rubber or the polyisoprene synthesis being used in a blend with at most 50 phr of a polybutadiene having a rate of cis-1,4 bonds greater than 90%. 5. A tire according to claim 2, said composition comprising 50 to 100 pce of a polybutadiene having a cis-1,4 bond ratio greater than 90%. 6. A tire according to claim 5, the polybutadiene being used in cutting with at plus 50 phr of natural rubber or synthetic polyisoprene. Pneumatic tire according to any one of claims 1 to 6, wherein rate liquid plasticizer is greater than 40 phr, preferably included in a area from 50 to 100 pce. 8. A tire according to any one of claims 1 to 7, wherein plasticizer liquid is selected from the group consisting of naphthenic oils, paraffinic oils, MES oils, TDAE oils, mineral oils, vegetable oils, plasticizers ethers, ester plasticizers, phosphate plasticizers, plasticisers sulphonates and mixtures of these compounds. 9. A tire according to any one of claims 1 to 8, wherein charge reinforcing agent includes a majority of carbon black, the rate of black carbon being preferably greater than 60 phr. 10. A tire according to any one of claims 1 to 8, wherein load reinforcement mainly comprises a reinforcing inorganic filler, the charge rate reinforcing inorganic being preferably greater than 70 phr. A tire according to any one of claims 1 to 10, wherein the rate of total reinforcing filler is between 60 and 120, preferably between 70 and 100 pce. Pneumatic tire according to any one of claims 1 to 11, wherein the metal of the metal oxide is selected from the group consisting of aluminum, silicon, zirconium, transition metals and mixtures of such metals. The tire of claim 12, wherein the metal oxide is chosen in the group consisting of oxides and / or hydroxides of aluminum, oxides and / or hydroxides of silicon, oxides and / or hydroxides of aluminum and silicon, and mixtures of such oxides and / or hydroxides. The tire of claim 13, wherein the metal oxide is a aluminosilicate. 15. A tire according to any one of claims 1 to 14, wherein the Hollow microparticles of metal oxide have a median size included in a domain from 5 to 200 μm.