FR2955328A1 - RUBBER COMPOSITION FOR WINTER PNEUMATIC BEARING BAND - Google Patents

Abstract

A rubber composition that can be used in particular as a tread of a winter tire, with a high adhesion on melting ice, comprising at least one diene elastomer such as natural rubber and / or 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, between 2 and 50 phr of water-soluble microparticles such as microparticles of magnesium sulphate and between 2 and 50 phr of hollow microparticles of at least one oxide metal such as an aluminosilicate. The invention also relates to winter tires whose tread comprises such a composition.

Description

1. DOMAIN OF THE INVENTION

The invention relates to rubber compositions that can be used as tire treads for vehicles, in particular "winter" tires capable of rolling on floors covered with ice or ice without being provided with nails (also called pneumatic "studless"). .

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

2. STATE OF THE ART

In order to avoid the harmful effects of nails, in particular their abrasive action on the floor covering itself and a markedly degraded road behavior on dry ground, the tire manufacturers have proposed various solutions consisting of modifying the formulation of the constituent rubber compositions. of their treads.

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

Other solutions have therefore been proposed, including incorporating water-soluble powders (i.e., which can dissolve in water) in the constitutive tread composition. Such powders solubilize more or less in contact with 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 on the other hand the creation of grooves acting as channels for evacuating the liquid film created between -1- P10-2401 2955328 -2-

pneumatic and soil. Examples of such water-soluble powders include, for example, the use of cellulose powder, PVA (polyvinyl alcohol) or starch, or powders of guar gum or xanthan gum (see for example, patent application 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 tread. If the powder is not soluble under the conditions of use of the tire, the aforementioned functions (creation of microporosities and water discharge channels) are not fulfilled 10 and the adhesion is not improved.

3. BRIEF DESCRIPTION OF THE INVENTION

Continuing their research, the Applicants have discovered a novel rubber composition capable of generating an effective surface micro-roughness and which makes it possible to greatly improve the ice adhesion of the treads and tires comprising them, under conditions of melting ice. .

Consequently, the present invention relates to a rubber composition that can be used in particular as a tread of a winter tire, comprising at least one diene elastomer, more than 30 phr of a liquid plasticizer, and between 50 and 150 phr of a filler. reinforcer, characterized in that it further comprises between 2 and 50 phr of water-soluble microparticles and between 2 and 50 phr of hollow microparticles of at least one metal oxide. At first, these different microparticles, protruding on the surface of the tread, fulfill the claw function previously described without the disadvantage of being highly abrasive vis-à-vis the asphalt used as a road surface. Then, in a second step, after progressive expulsion of the rubbery matrix, on the one hand by at least partial hydrosolubilization of the water-soluble microparticles, on the other hand by breaking the hollow structure of the metal oxide microparticles, all these microparticles release microcavities that act as a storage volume and drainage channel of the water film on the surface of the ice; under these conditions, the contact between the tread surface and the ice is no longer lubricated and the coefficient of friction is thus improved.

The tires of the invention are particularly intended for equipping tourism-type motor vehicles, including 4x4 vehicles (four-wheel drive) and SUV vehicles ("Sport Utility Vehicles"), two-wheeled vehicles (especially motorcycles) as vehicles. P10-2401 -3-

industrial vehicles chosen in particular from vans and "heavy goods vehicles" (ie, metro, buses, road transport equipment such as trucks, tractors).

The invention and its advantages will be readily understood in the light of the following description and embodiments.

4. DETAILED DESCRIPTION OF THE INVENTION

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

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

The rubber composition of the invention is based on at least one diene elastomer, a plasticizer system, a reinforcing filler, water-soluble microparticles and hollow metal oxide microparticles, components which are described in detail below.

4.1 - Diene elastomer

By elastomer (or rubber, the two terms being synonymous) of the "diene" type, it is recalled that an elastomer derived from at least a part (ie a homopolymer or a copolymer) of diene monomers (monomers carrying two double bonds) must be understood. carbon-carbon, conjugated or not).

The diene elastomers can be classified in known manner into two categories: those known as "essentially unsaturated" and those known as "essentially saturated". Butyl rubbers, such as, for example, copolymers of dienes and alpha-olefins of the EPDM type, fall into the category of essentially saturated diene elastomers, with a level of units of diene origin which is low or very low, always less than 15. % (mole%). In contrast, by essentially unsaturated diene elastomer is meant 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% (mol%). ). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer is particularly understood to mean a diene elastomer having a degree of diene origin units (conjugated dienes 40) which is greater than 50%. P10-2401 -4-

It is preferred to use at least one diene elastomer of the highly unsaturated type, in particular a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), polybutadienes (BR) and butadiene copolymers, copolymers of isoprene and mixtures of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-copolymers of butadiene-styrene (SBIR) and mixtures of such copolymers. to elastomers can be for example block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or starred or functionalized with a coupling agent and / or starring or functionalization. For coupling to carbon black, there may be mentioned, for example, functional groups comprising a C-Sn bond or amino functional groups such as benzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may be made, for example, of silanol or polysiloxane functional groups having a silanol end (as described, for example, in US Pat. No. 6,013,718), alkoxysilane groups (as described, for example, in US 5,977,238), carboxylic groups (as described, for example, in US 6,815,473 or US 2006/0089445) or polyether groups (as described for example in US 6,503,973). By way of other examples of such functionalized elastomers, mention may also be made of elastomers (such as SBR, BR, NR or IR) of the epoxidized type.

Polybutadienes, and in particular those having a content of 1,2-units of between 4% and 80%, or those having a cis-1,4 content of greater than 80%, polyisoprenes and butadiene copolymers, are particularly suitable. styrene and in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a 1,2-butadiene content of the butadiene part of between 4% and 65%, a trans-1,4-linkage content of between 20% and 80%, butadiene-isoprene copolymers and especially those having an isoprene content of between 5% and 90% by weight and a glass transition temperature ("Tg measured according to ASTM D3418-82) from -40 ° C. to -80 ° C., the isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg of between -25 ° C. C and -50 ° C.

In the case of butadiene-styrene-isoprene copolymers, those having a styrene content of between 5% and 50% by weight and more particularly of between 10% and 40% and an isoprene content of between 15% and 60% are particularly suitable. % by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of -1,2 units of the butadiene part. between 4% and 85%, a trans-1,4 content of part P10-2401 5 -5-

butadiene content between 6% and 80%, a content of -1,2 units plus -3,4 of the isoprenic part of between 5% and 70% and a trans-1,4 content of the isoprene part of between 10% and % and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg of between -20 ° C and -70 ° C. According to a particularly preferred embodiment of the invention, the diene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and polybutadienes having a cis-1,4 bond ratio of greater than 90%, copolymers of butadiene-styrene and mixtures of these elastomers. According to a more particular and preferred embodiment, the heat-expandable rubber composition comprises 50 to 100 phr of natural rubber or of synthetic polyisoprene, said natural rubber or synthetic polyisoprene which can be used in particular in blending (mixing) with at most 50 phr of a polybutadiene having a cis-1,4 bond ratio greater than 90%.

According to another particular and preferred embodiment, the heat-expandable rubber composition comprises 50 to 100 phr of a polybutadiene having a cis-1,4 bond ratio of greater than 90%, said polybutadiene being able to be used in particular in blending with at most 20 to 50 phr of natural rubber or synthetic polyisoprene.

To the diene elastomers of the treads according to the invention could be associated, in a minor amount, synthetic elastomers other than diene, or even polymers other than elastomers, for example thermoplastic polymers. 4.2 - Plasticizer system

Another essential feature of the rubber composition of the invention is that it comprises 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; its Tg is by definition less than -20 ° C, preferably less than -40 ° C.

Any extender oil, whether of aromatic or non-aromatic nature, any liquid plasticizer known for its plasticizing properties with respect to diene elastomers, is usable. At ambient temperature (20 ° C.), these plasticizers or these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the capacity to eventually take on the shape of their container) , in contrast to, in particular, hydrocarbon plasticizing resins which are inherently solid at room temperature. P10-2401 -6-

Particularly suitable liquid plasticizers selected from the group consisting of naphthenic oils (low or high viscosity, including hydrogenated or not), paraffinic oils, oils MES (Medium Extracted Solvates), oils TDAE (Treated Distillate Aromatic Extracts), mineral oils, vegetable oils, ethers plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures of these compounds.

As phosphate plasticizers, for example, mention may be made of those containing from 12 to 30 carbon atoms, for example trioctyl phosphate. By way of examples of plasticizer-esters, mention may be made especially of the compounds chosen from the group consisting of trimellitates, pyromellitates, phthalates, 1,2-cyclohexane dicarboxylates, adipates, azela- lates, sebacates and triesters. glycerol and mixtures of these compounds. Among the triesters above, mention may be made in particular of glycerol triesters, preferably consisting predominantly (for more than 50%, more preferably for more than 80% by weight) of a C18 unsaturated fatty acid; 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 vegetable oils of sunflower or rapeseed), the fatty acid used is more than 50% by weight, more preferably still more than 80% by weight. % by weight of oleic acid. Such high oleic acid esters (trioleates) are well known and have been described, for example, in WO 02/088238, as plasticizers in tire treads.

The level of liquid plasticizer in the composition of the invention is preferably greater than 40 phr, more preferably in a range of 50 to 100 phr.

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

Hydrocarbon resins are polymers that are well known to those skilled in the art, essentially based on carbon and hydrogen, and therefore inherently miscible in diene (s) elastomer compositions when they are further qualified as "plasticisers". ". 35 These have been described, for example, in the book "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), of which Chapter 5 is dedicated to their applications, in particular in rubberized rubber (5.5 Rubber Tires and Mechanical Goods) They may be aliphatic, aromatic or aliphatic / aromatic, that is to say based on aliphatic and / or aromatic monomers. They may be natural or synthetic, whether or not based on petroleum (if it is P10-2401 -7-

the case, also known as petroleum resins). They are preferably exclusively hydrocarbon-based, that is to say they contain only carbon and hydrogen atoms.

Preferably, the plasticizing hydrocarbon resin has at least one, more preferably all, of the following characteristics:

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

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

According to a particularly preferred embodiment, the plasticizing hydrocarbon resin is selected from the group consisting of cyclopentadiene homopolymer or copolymer resins (abbreviated to CPD), dicyclopentadiene homopolymer or copolymer resins (abbreviated to DCPD), terpene homopolymer or copolymer resins, homopolymer or C5 cut copolymer resins, C9 homopolymer or cut copolymer resins, and mixtures of these resins. Among the above copolymer resins are more preferably those selected from the group consisting of (D) CPD / vinylaromatic copolymer resins, (D) CPD / terpene copolymer resins, (D) CPD copolymer resins / C5 cut, (D) CPD / C9 cut copolymer resins, terpene / vinylaromatic copolymer resins, terpene / phenol copolymer resins, C5 / vinylaromatic cut copolymer resins, C9 / vinylaromatic cut copolymer resins, and mixtures of these resins. The term "terpene" here combines in a known manner the alpha-pinene, beta-pinene and limonene monomers; preferably a limonene monomer is used, which compound is known in the form of three possible isomers: L-limonene (laevorotatory enantiomer), D-limonene (dextrorotatory enantiomer), or the dipentene, racemic of the 40 enantiomers dextrorotatory and levorotatory. As a vinylaromatic monomer, they are suitable for P10-2401.

styrene, alpha-methylstyrene, ortho-, meta-, para-methylstyrene, vinyl-toluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, any vinylaromatic monomer resulting from a C9 cut (or more generally from a C8 to Cm cut). Preferably, the vinyl-aromatic compound is styrene or a vinylaromatic monomer resulting from a C9 cut (or more generally from a C8 to Cm cut). Preferably, the vinylaromatic compound is the minor monomer, expressed as a mole fraction, in the copolymer under consideration.

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

The level of total plasticizer (i.e., liquid plasticizer plus, if appropriate, solid hydrocarbon resin) is preferably between 40 and 100 phr, more preferably in a range of 50 to 80 phr.

4.3 - Charge

Any type of reinforcing filler known for its ability to reinforce a rubber composition which can be used for the manufacture of tires, for example an organic filler such as carbon black, or a reinforcing inorganic filler such as which is associated in a known manner a coupling agent.

Such a reinforcing filler preferably consists of nanoparticles whose average (mass) size is less than 500 nm, most often between 20 and 200 nm, in particular and preferably between 20 and 150 nm.

Suitable carbon blacks are all carbon blacks, especially blacks conventionally used in tires or tire treads (so-called pneumatic grade blacks). Among the latter, there will be mentioned more particularly the reinforcing carbon blacks of the series 100, 200 or 300 (ASTM grades), such as, for example, the blacks N115, N134, N234, N326, N330, N339, N347 and N375. The carbon blacks could for example already be incorporated into the isoprene elastomer in the form of a masterbatch (see for example WO 97/36724 or WO 99/16600). Examples of organic fillers other than carbon blacks include functionalized polyvinyl organic fillers as described in WO-A-2006/069792, WO-A-2006/069793, WO-A-2008 / 003434 and WO-A-2008/003435. P10-2401 -9-

"Reinforcing inorganic filler" means any inorganic or mineral filler whatever its color and origin (natural or synthetic), still called "white" filler, "clear" filler or even "non-filler" black "as opposed to carbon black, 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 able to replace, in its function reinforcement, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (OH) on its surface.

Suitable reinforcing inorganic fillers are, in particular, mineral fillers of the siliceous type, in particular silica (SiO 2 or aluminous type, in particular alumina (Al 2 O 3). The silica used may be any reinforcing silica known to man. of the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m 2 / g, preferably from 30 to 400 m 2 / g, especially between 60 and 300 m 2 / g. highly dispersible precipitated silica titers (called "HDS"), there may be mentioned, for example, the silicas "Ultrasil" 7000 and "Ultrasil" 7005 from Degussa, the silicas "Zeosil" 1165MP, 1135MP and 1115MP from Rhodia, silica "Hi-Sil" EZ150G from PPG, the "Zeopol" silicas 8715, 8745 and 8755 from Huber As examples of reinforcing aluminas, mention may be made of "Baikalox" "Al25" or "CR125" aluminas from Ba'ikowski company, "APA-100RDX "Condea," Degussa's Aluminoxid C "or" AKP-G015 "from Sumitomo Chemicals.

Preferably, the total reinforcing filler content (carbon black and / or reinforcing inorganic filler) is between 60 and 120 phr, in particular between 70 and 100 phr. According to a particular embodiment, the filler comprises silica, carbon black or a mixture of carbon black and silica. According to another particular embodiment, the reinforcing filler comprises predominantly carbon black; in such a case, the carbon black is present at a level preferably greater than 60 phr, associated or not with a reinforcing inorganic filler such as silica in a minority amount. According to another particular embodiment, the reinforcing filler comprises an inorganic filler, 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 phr, associated or not with carbon black in a minor amount; the carbon black, when present, is preferably used at a level of less than 20 phr, more preferably less than 10 phr (for example between 0.1 and 10 phr). 40 P10-2401 -10-

Independently of the first aspect of the invention, namely the search for an optimized adhesion on melting ice, the majority use of a reinforcing inorganic filler such as silica is also advantageous from the point of view of adhesion. on wet or snowy ground.

According to another possible embodiment of the invention, the reinforcing filler comprises a blend of carbon black and reinforcing inorganic filler such as silica in similar amounts; in such a case, the level of inorganic filler, in particular silica, and the level of carbon black are preferably each between 25 and 75 phr, more particularly each comprised between 30 and 50 phr.

In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is well known in order to provide a sufficient chemical and / or physical connection between the feedstock and the feedstock. inorganic (surface of its particles) and the diene elastomer. In particular, organosilanes or bifunctional polyorganosiloxanes are used.

Polysulphurized silanes, called "symmetrical" or "asymmetrical" silanes according to their particular structure, are especially used, as described for example in the applications WO03 / 002648 (or US 2005/016651) and WO03 / 002649 (or US 2005/016650). .

Particularly suitable, without the following definition being limiting, so-called "symmetrical" polysulfide silanes having 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 C 1 -C 18 alkylene groups or C 6 -C 12 arylene groups, more particularly C 1 -C 10 alkylenes, especially C 1 -C 4 alkylenes, in particular propylene); Z is one of the following formulas:

Wherein: R 1, substituted or unsubstituted, which are identical to or different from each other, represent a C 1 -C 18 alkyl, C 5 -C 18 cycloalkyl or C 6 -C 18 aryl group (from P 10); -2401 -11-

preferably C 1 -C 6 alkyl, cyclohexyl or phenyl, especially C 1 -C 4 alkyl groups, more particularly methyl and / or ethyl). the radicals R2, substituted or unsubstituted, which are identical to or different from one another, represent a C1-C18 alkoxyl or a C5-C18 cycloalkoxyl group (preferably a group chosen from C1-C8 alkoxyls and C5-C8 cycloalkoxyls, plus still more preferably a group chosen from C1-C4 alkoxyls, in particular methoxyl and ethoxyl).

As examples of polysulfurized silanes, mention may be made more particularly of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) polysulfides. Among these compounds, bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated as TESPT, or bis (triethoxysilylpropyl) disulfide, abbreviated as TESPD, is especially used. Mention may also be made, by way of preferred examples, of polysulfides (in particular disulphides, trisulphides or tetrasulfides) of bis (monoalkoxyl (C 1 -C 4) -dialkyl (C 1 -C 4) silylpropyl), more particularly bis-monoethoxydimethylsilylpropyl tetrasulfide, as described above. in the patent application WO 02/083782 (or US 2004/132880).

As coupling agent other than polysulfurized alkoxysilane, there may be mentioned in particular bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulfides (R2 = OH in formula (I) above) as described in the WO 02/30939 (or US Pat. No. 6,774,255) and WO 02/31041 (or US 2004/051210), or else silanes or POS bearing azo-dicarbonyl functional groups, as described for example in the patent applications WO 2006 / 125532, WO 2006/125533, WO 2006/125534.

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

Those skilled in the art will understand that, as the equivalent filler of the reinforcing inorganic filler described in this paragraph, it would be possible to use a reinforcing filler of another nature, in particular an organic filler, since this reinforcing filler would be covered with a filler. inorganic layer such as silica, or would comprise on its surface functional sites, especially hydroxyl, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. 4.4 - Water-soluble microparticles and hollow microparticles of metal oxide

The essential characteristics of the rubber compositions of the invention are that they comprise between 2 and 50 phr of water-soluble microparticles and between 2 and 50 phr of hollow microparticles (or microspheres) of at least one metal oxide, the term oxide including, of course, the hydroxides. P10-2401 -12-

These microparticles may be, for example, in the form of powder, microbeads, granules, beads or any other suitable densified form. A presentation in powder form is preferred.

By microparticles is meant by definition and generally size particles (ie, larger dimension in the case of anisometric particles) micrometer, that is to say, whose average size or median size (both expressed in weight) are between 1 μm and 1 mm. Preferably, the median size is between 2 μm and 800 μm, more preferably in a range of 5 to 200 μm.

Below the minima indicated above, the intended technical effect (namely the creation of a suitable micro-roughness) may be insufficient, whereas beyond the maximum values indicated, there are various disadvantages, especially when the rubber composition is used as a tread: in addition to a possible loss of aesthetics (particles too visible on the surface of the tread) and a risk of loosening, during rolling, relatively large tread elements it was found that the melting ice adhesion performance could be degraded.

For all these reasons, it is preferred that the microparticles have a median size of between 2 μm and 500 μm, more preferably still in the range of 5 to 200 μm. This area of particularly preferred size seems to correspond to an optimized compromise between on the one hand the desired surface roughness and on the other hand a good contact between the rubber composition and the ice.

On the other hand, for the same reasons as those set out above, the level of each type of microparticles (water-soluble microparticles on the one hand and metal oxide hollow microparticles on the other hand) is preferably between 5 and 40.degree. pce, more preferably between 10 and 35 phr.

According to a preferred embodiment, the water-soluble microparticles are microparticles of metal salts, these salts being chosen more preferentially from the group consisting of chlorides, carbonates (including in particular hydroxycarbonates, bicarbonates), sulphates and mixtures of such salts. Even more preferentially, the salt chosen is a sulphate.

According to another preferred embodiment, which can be combined in particular with the preceding one, the metal of the metal salt is an alkaline or alkaline-earth metal. It will be recalled here simply that the group of alkali metals is that of the univalent chemical elements located in the first column of the Periodic Table and not including hydrogen (H); in the order of P10-2401 40 -13-

increasing atomic number, the alkali metals are lithium, sodium, potassium, rubidium, cesium and francium. The group of alkaline earth metals is that of the chemical elements of group 2 (or IIa) of the periodic table; in order of increasing atomic number, the alkaline earth metals are beryllium, magnesium, calcium, strontium, barium and radium.

Preferably, the metal of the water-soluble metal salt is selected from the group consisting of Na (sodium), K (potassium), Mg (magnesium), Ca (calcium) and mixtures of such metals. More preferably still, the metal is magnesium.

According to a preferred embodiment, the metal of the metal oxide is selected from the group consisting of aluminum, silicon, zirconium, transition metals and mixtures of such metals. By transition metal is meant more particularly the metals of the fourth period ranging from scandium to zinc, preferably titanium and zinc.

Aluminum, silicon, titanium, zirconium and zinc are even more preferable.

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

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

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

4.5 - Miscellaneous additives P10-2401 -14-

The rubber compositions of the invention also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tire treads, in particular for winter tires, such as, for example, protective agents such as waxes. anti-ozone, chemical antiozonants, anti-oxidants, reinforcing resins, acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M), a crosslinking system based on either sulfur or of sulfur and / or peroxide and / or bismaleimide donors, vulcanization accelerators, vulcanization activators.

These compositions may also contain coupling activators when a coupling agent is used, inorganic filler recovery agents or, more generally, processing aids which can be used in a known manner, by means of an improvement. the dispersion of the filler in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green state; these agents are for example hydrolysable silanes such as alkyl-alkoxysilanes, polyols, polyethers, amines, hydroxylated or hydrolysable polyorganosiloxanes.

4.6 - Manufacture of rubber compositions and treads

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

A process which can be used for the manufacture of such compositions comprises, for example, and preferably the following steps:

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, between 2 and 50 phr of water-soluble microparticles and between 2 and 50 phr of microparticles. hollow of at least one metal oxide, thermomechanically kneading the whole, in one or more times, until a maximum temperature of between 130 ° C and 200 ° C; - cool all at a temperature below 100 ° C; - then incorporate a crosslinking system; P10-2401 -15-

- mix everything up to a maximum temperature below 120 ° C; - Extrude or calender the rubber composition thus obtained, especially in the form of a tire tread.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, the possible coating agents, are introduced into a suitable mixer such as a conventional internal mixer. or of complementary implementation and other various additives, with the exception of the crosslinking system. After cooling the mixture thus obtained during the first non-productive phase, the low temperature crosslinking system is then incorporated, generally in an external mixer such as a roll mill; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The actual crosslinking system is preferably based on sulfur and a primary vulcanization accelerator, in particular a sulfenamide type accelerator. To this vulcanization 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. 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.

As accelerator (primary or secondary) can be used any compound capable of acting as an accelerator of vulcanization of diene elastomers in the presence of sulfur, in particular thiazole-type accelerators and their derivatives, accelerators of thiuram type, zinc dithiocarbamates. These accelerators are more preferably selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated "CBS"), N, N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazylsulfenamide ("TBBS"), N-tert-butyl-2-benzothiazylsulfenimide ("TBSI"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures thereof. these compounds.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded in the form of a rubber profile that can be used directly as a tread of a tire. winter.

The vulcanization (or baking) is conducted in a known manner at a temperature generally between 130 ° C and 200 ° C, for a sufficient time which may vary for example between P10-2401 -16- and 90 min depending in particular on the temperature cooking, the vulcanization system adopted and the kinetics of vulcanization of the composition in question.

The rubber compositions according to the invention may constitute all or only a part of the tread according to the invention, in the case of a composite type tread formed of several rubber compositions of different formulations.

The invention relates to the rubber and tire compositions previously described in both green (i.e., pre-firing) and fired (i.e., crosslinking or vulcanization) conditions.

EXAMPLES OF THE EMBODIMENT OF THE INVENTION 5.1 Preparation of Rubber Compositions

In these tests, two compositions (denoted C-1 and C-2) based on diene elastomers (NR and BR cleavage with cis-1,4 bond ratios greater than 95%) are compared, reinforced by a silica blend. and carbon black which are associated or not, on the one hand 15 pce of 20 microparticles magnesium sulfate and on the other hand pce hollow microparticles aluminosilicate. Table 1 gives the formulation of the two compositions (rate of the different products expressed in phr).

For the manufacture of these compositions, the following procedure was carried out: the reinforcing filler (carbon black, silica and its agent) was introduced successively into an internal mixer, the initial batch temperature of which was approximately 60 ° C. associated coupling), the liquid plasticizer, the magnesium sulfate microparticles, the hollow aluminosilicate microparticles, the diene elastomer (or diene elastomer cutting) and the various other ingredients with the exception of the vulcanization system; the mixer is thus filled to about 70% (% by volume). Theromechanical work (non-productive phase) is then carried out in one step, which lasts a total of about 3 to 4 minutes, until a maximum temperature of "fall" of 165 ° C is reached. The mixture thus obtained is recovered, cooled, and sulfur and a sulfenamide type accelerator are incorporated on an external mixer (homo-finisher) at 30 ° C, mixing the whole (productive phase) for a suitable time (for example between 5 and 12 minutes).

5.2 - Friction tests on ice

These two compositions are then subjected to a laboratory test consisting of measuring their coefficient of friction on ice. P10-2401 25 -17-

The principle is based on a rubber composition slider sliding at a given speed (for example 5 km / h) on an ice track with an imposed load (for example equal to 3 kg / cm 2). Prior to the test, the surface of the test pad is lapped by planing to a thickness of 0.5 mm, followed by a series of repeated sliding friction on real dry soil (asphalt) under the said imposed load (for example 3 kg / cm2). The forces generated in the direction of advance (Fx) of the pad and perpendicular to the advance (Fz) are measured. The ratio Fx / Fz determines the coefficient of friction of the specimen 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, patent applications EP 1052270 and EP 1505112) makes it possible to evaluate, under representative conditions, the adhesion on melting ice that would be obtained after a rolling test on vehicle equipped with tires whose tread is made of the same rubber compositions.

The results are expressed in Table 2; a value greater than that of the control (composition C-1), arbitrarily set at 100, indicates an improved result, that is to say an aptitude at a shorter braking distance. It is found that the composition of the invention C-2 shows a significant improvement (gain of 10%) in the coefficient of friction on ice, compared to the control composition C-1.

In conclusion, the compositions according to the invention offer the tires and their treads an adhesion on melting ice which is improved. Table 1 Composition No. C-1 C-2 BR (1) 60 60 NR (2) 40 40 silica (3) 80 80 coupling agent (4) 6.5 6.5 carbon black (5) 4 4 water-soluble microparticles (6) - 15 hollow microparticles (7) - 15 non-aromatic oil (8) 65 65 DPG (9) 1.5 1.5 ZnO 1.2 1.2 stearic acid 1 1 anti-ozone wax 1.5 1.5 antioxidant (10) 2 2 sulfur 2 2 accelerator (11) 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) ASTM grade N234 (Cabot Company); (6) magnesium sulfate (Aldrich company, median particle size: about 100 μm); (7) aluminosilicate ("Fillite 200/7" from Japan Fillite) (median particle size: about 90 μm); (8) MES oil ("Catenex SNR" from Shell); (9) diphenylguanidine (Perkacit DPG from Flexsys); (10) N-1,3-dimethylbutyl-N-phenylparaphenylenediamine (Santoflex 6-PPD from Flexsys); (11) N-dicyclohexyl-2-benzothiazol sulfenamide ("Santocure CBS" from Flexsys). Table 2 Rubber composition: C-1 C-2 Ice friction test (-2 ° C): 100 110 P10-2401 15 25

Claims (21)

REVENDICATIONS1. A rubber composition that can be used in particular as a tread of a winter tire, comprising at least one diene elastomer, more than 30 phr of a liquid plasticizer, and between 50 and 150 phr of a reinforcing filler, characterized in that it comprises in addition, between 2 and 50 phr of water-soluble microparticles and between 2 and 50 phr of hollow microparticles of at least one metal oxide. The composition of claim 1, wherein the diene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers. 3. Composition according to claim 2, comprising 50 to 100 phr of natural rubber or synthetic polyisoprene. 4. The composition according to claim 3, wherein the synthetic rubber or the synthetic polyisoprene is used in a blend with at most 50 phr of a polybutadiene having a cis-1,4 bond ratio greater than 90%. 5. Composition according to claim 2, comprising 50 to 100 phr of a polybutadiene having a cis-1,4 bond ratio greater than 90%. 6. Composition according to claim 5, wherein the polybutadiene is used in a blend with at most 50 phr of natural rubber or synthetic polyisoprene. 7. Composition according to any one of claims 1 to 6, wherein the level of liquid plasticizer is greater than 40 phr, preferably within a range of 50 to 100 phr. 8. A composition according to any one of claims 1 to 7, wherein the liquid plasticizer is selected from the group consisting of naphthenic oils, paraffinic oils, MES oils, TDAE oils, mineral oils, vegetable oils. , ethers plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures of these compounds. P10-2401 25 - 20 - 9. Composition according to any one of claims 1 to 8, wherein the reinforcing filler comprises predominantly carbon black, the carbon black content is preferably greater than 60 phr. 10. Composition according to any one of claims 1 to 6, wherein the reinforcing filler comprises predominantly a reinforcing inorganic filler, the level of reinforcing inorganic filler preferably being greater than 70 phr. 11. Composition according to any one of claims 1 to 10, wherein the total reinforcing filler content is between 60 and 120, preferably between 70 and 100 phr. 12. Composition according to any one of claims 1 to 11, wherein the water-soluble microparticles are microparticles of metal salts. 15 The composition of claim 12, wherein the metal salts are selected from the group consisting of chlorides, carbonates, sulfates and mixtures of such salts. 14. A composition according to claim 12 or 13, wherein the metal of the metal salt is an alkali or alkaline earth metal, preferably selected from Na, K, Mg, Ca and mixtures of such metals. The composition of claim 14, wherein the water-soluble microparticles are magnesium sulfate microparticles. 16. Composition according to any one of claims 1 to 15, wherein the water-soluble microparticles have a median size (by weight) of between 2 and 500 microns. 17. A composition according to any one of claims 1 to 16 wherein in which the metal oxide metal is selected from the group consisting of aluminum, silicon, zirconium, transition metals and mixtures such metals. 18. The composition according to claim 17, wherein the metal oxide is selected from the group consisting of aluminum oxides and / or hydroxides, silicon oxides and / or hydroxides, aluminum oxides and / or hydroxides. and silicon, and mixtures of such oxides and / or hydroxides. The composition of any one of claims 1 to 18, wherein the metal oxide is an aluminosilicate. P10-2401 5-21- 20. Composition according to any one of claims 1 to 19, wherein the hollow microparticles of metal oxide have a median size (by weight) of between 2 and 500 microns. 21. Winter tire whose tread comprises a rubber composition according to any one of claims 1 to 20. P10-2401