WO2014082963A1

WO2014082963A1 - Tyre for a vehicle, having a tread comprising a heat-expandable rubber composition

Info

Publication number: WO2014082963A1
Application number: PCT/EP2013/074617
Authority: WO
Inventors: Chika OCHIAI; Salvatore Pagano
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2012-11-29
Filing date: 2013-11-25
Publication date: 2014-06-05
Also published as: FR2998509A1; EP2925537A1

Abstract

The invention relates to a tyre for a vehicle, in particular a winter tyre, the tread of which comprises a rubber composition that is heat expandable in the unvulcanised state and expanded in the vulcanised state. In the unvulcanised state, the composition comprises at least one diene elastomer, such as natural rubber and/or a polybutadiene, more than 50 phr of a reinforcing filler, such as silica or carbon black, 2 to 60 phr of microparticles of a metal oxide such as an aluminosilicate, 2 to 25 phr of a blowing agent such as sodium or potassium (hydrogen)carbonate and 2 to 25 phr of a hot-melt compound having a melting point of 60° to 220°C, such as citric acid, the total content of the blowing agent and the hot-melt compound being higher than 10 phr. The combined use of these different compounds, at the recommended rates, enables a very high grip to be obtained on both dry ice and melting ice.

Description

VEHICLE BANDAGE WITH TREAD BAND COMPRISING THERMO-EXPANDABLE RUBBER COMPOSITION

1. DOMAIN OF THE INVENTION

The invention relates to rubber compositions used as tire treads, pneumatic or non-pneumatic, for vehicles, in particular "winter" tires able to roll on floors covered with ice or ice without being provided with nails (also called "studless" bandages).

It relates more particularly to vehicle tires, especially winter tires, the tread of which is specifically adapted for driving under conditions called "dry ice" or "cold ice" corresponding to a temperature range typically below -5. ° C., while also satisfying the so-called "melting ice" conditions encountered in a temperature range of between -5 ° C. and 0 ° C., a range in which, in a known manner, the pressure of the tires at the passage of the vehicle causes a melting superficial ice which is covered with a thin film of water harmful to the adhesion of these bandages.

2. STATE OF THE ART To avoid the harmful effects of nails, in particular their strong abrasive action on the floor covering itself and a markedly degraded road behavior on dry ground, the bandage manufacturers have proposed various solutions of modifying the formulation. rubber compositions themselves. 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 it wears, 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, consisting in particular of incorporating hydrosoluble powders (ie, which can dissolve in water) in the constitutive composition of the tread. Such powders solubilize more or less on contact with the snow or melted ice, which allows on the one hand the creation on the surface of the tread porosities may improve the attachment of the tread on the ground and on the other hand the creation of grooves playing the role of evacuation channels of the liquid film created between the bandage and the ground. Examples of such water-soluble powders include, for example, the use of cellulose powder, PVA (polyvinyl alcohol) or starch, powders of guar gum or xanthan gum, or powder magnesium or potassium sulphate (see, for example, patent applications JP 3-159803, JP 2002-211203, WO 2008/080750, WO 2008/080751, WO 2010/009850, WO 2011/073188, WO 2011/086061, WO 2012/052331, WO 2012/085063).

Other solutions have also been proposed, consisting in using hollow microparticles of metal oxide capable of generating, after expulsion of the rubber matrix, a surface microroughness effective for adherence on melting ice, without penalizing the reinforcing properties and hysteresis. As examples of such hollow microparticles, there may be mentioned in particular aluminosilicate microparticles as described for example in the applications WO 2011/073186, WO 2011/086061, WO 2011/113731.

These water-soluble powders or hollow metal oxide microparticles, however, are not sufficiently effective for dry ice running conditions (non-melting).

3. BRIEF DESCRIPTION OF THE INVENTION

In the course of their research, the Applicants have discovered a specific rubber composition that provides excellent adhesion to bandages on both dry ice and melting ice.

Consequently, the present invention relates to a tire whose tread comprises, in the unvulcanized state, a heat-expandable rubber composition comprising at least one diene elastomer, more than 50 phr of a reinforcing filler, between 2 and 60 phr of microparticles of at least one metal oxide, between 2 and 25 phr of an expansion agent and between 2 and 25 phr of a hot-melt compound whose melting point is between 60 ° C. and 220 ° C. , the total content of blowing agent and hot melt compound being greater than 10 phr.

The invention also relates to a bandage in the vulcanized state obtained after firing (vulcanization) of the green tire according to the invention as described above.

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 (in particular motorcycles) as industrial vehicles chosen in particular from vans and" heavy goods vehicles "(ie, metros, buses, road transport vehicles such as trucks, tractors). that its advantages will be easily understood in the light of the description and examples of embodiment which follow.

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 term "from a to b" means the range of values from "a" to "b" (i.e. including the strict limits a and b). The bandage of the invention therefore has the essential characteristic that its tread, in the uncured state, comprises a heat-expandable rubber composition (at least for the upper part of the tread which comes into direct contact with the tread). the surface of the road) comprising at least: - a (at least one) diene elastomer;

- more than 50 phr of a (at least one) reinforcing filler;

between 2 and 60 phr of microparticles of one (at least one) metal oxide;

between 2 and 25 phr of one (at least one) blowing agent;

between 2 and 25 phr of a (at least one) hot melt compound whose melting temperature is between 60 ° C and 220 ° C;

the total content of blowing agent and hot melt compound being greater than 10 phr.

The various components above are described in detail below.

4.1. Diene elastomer

By elastomer (or rubber, the two terms being synonymous) of the "diene" type, it should be recalled that an elastomer derived at least in part (ie a homopolymer or a copolymer) of monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or otherwise).

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, and for example copolymers of dienes and alpha-olefins of the EPDM type, fall into the category of essentially saturated diene elastomers, having a level of diene origin units which is low or very low, always less than 15% (mole%). By contrast, essentially unsaturated diene elastomer is understood to mean a diene elastomer derived at least in part from conjugated diene monomers having a proportion 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 content of units of diene origin (conjugated dienes) which is greater than 50%.

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. The elastomers can be for example block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or starred or functionalized with a coupling agent and / or starring or functionalization. For coupling with carbon black, there may be mentioned for example functional groups comprising a C-Sn bond or amino functional groups such as benzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may be made, for example, of silanol or polysiloxane functional groups having a silanol end (as described, for example, in 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% and those having a cis-1,4 content of greater than 80%, the polyisoprenes and the copolymers, are preferably suitable. of butadiene-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-link content of - 1,4 between 20%> and 80%>, butadiene-isoprene copolymers and in particular 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, 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 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%, are especially suitable. and 60%> by weight and more particularly between 20%> and 50%>, a butadiene content of between 5%> and 50%> by weight and more particularly between 20%> and 40%>, a content in units -1.2 of the butadiene part of between 4%> and 85%>, a content of trans-1,4 units of the butadiene part of between 6%> and 80%>, a content of -1,2 units more -3,4 of the isoprene part of between 5%> and 70%> and a trans-1,4 content of the isoprene part of between 10%> and 50%>, and more generally any butadiene-styrene copolymer; isoprene having a Tg between -20 ° C and -70 ° C. 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 greater than 90%, butadiene-styrene copolymers 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 synthetic polyisoprene, said synthetic rubber or synthetic polyisoprene 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 greater than 90%, said polybutadiene being able to be used in particular in cutting with not more than 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. Charge Any known filler for its ability to reinforce a rubber composition is usable, for example an organic filler such as carbon black, or an inorganic filler such as silica to which is associated in a known manner a coupling agent.

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

Preferably, the content of total reinforcing filler (in particular silica or carbon black or a mixture of silica and carbon black) is between 50 and 150 phr. A content equal to or greater than 50 phr is favorable for good mechanical strength; beyond 150 phr, there is a risk of excessive rigidity of the rubber layer. For these reasons, the total reinforcing filler content is more preferably within a range of 70 to 120 phr.

Suitable carbon blacks are, for example, all carbon blacks which are conventionally used in tires (so-called pneumatic grade blacks) such as blacks of the series 100, 200, 300 (ASTM grades), such as, for example, NI 15 blacks, N134, N234, N326, N330, N339, N347, N375. The carbon blacks could for example already be incorporated into the diene elastomer, in particular isoprenic elastomer, in the form of a masterbatch (see, for example, applications WO 97/36724 or WO 99/16600).

As examples of organic fillers other than carbon blacks, mention may be made of functionalized polyvinyl organic fillers as described in applications WO-A-2006/069792 and WO-A-2006/069793, WO-A-2008/003434. and WO-A-2008/003435. "Reinforcing inorganic filler" means any inorganic or mineral filler, irrespective of its color and origin (natural or synthetic), also called "white" filler, "clear" filler or even "non-black filler" "As opposed to carbon black, capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition for the manufacture of bandages, in other words able to replace, in its function of 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 mineral fillers of the siliceous type, in particular silica (SiO ₂ ). The silica used can be any silica reinforcer known to those skilled in the art, especially 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. As highly dispersible precipitated silicas (called "HDS"), mention may be made, for example, of the "Ultrasil" 7000 and "Ultrasil" silicones 7005 from the Evonik company, the "Zeosil" 1165MP, 1135MP and 1115MP silicas from the Rhodia company, the silica "Hi-Sil" EZ150G from the company PPG, the silicas "Zeopol" 8715, 8745 and 8755 of the Huber Company.

According to another particularly preferred embodiment, the majority filler used is a reinforcing inorganic filler, in particular silica, at a level within a range of 70 to 120 phr, reinforcing inorganic filler to which advantageously black of carbon at a minority rate at most equal to 15 phr, in particular in a range of 1 to 10 phr.

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

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

In particular, polysulphide silanes having the following general formula (I) are not suitable for the following definition:

(I) Z - A - S _x - A - Z, wherein:

x is an integer of 2 to 8 (preferably 2 to 5);

the symbols A, which are identical or different, represent a divalent hydrocarbon radical (preferably a C 1 -C 18 alkylene group or a C ₆ -C ₁₂ arylene group, more particularly a C ₁ -C ₁₀ , especially C ₁ -C ₄ , alkylene, in particular propylene);

the symbols Z, identical or different, correspond to one of the three formulas below:

-

in which:

the radicals R ¹ , which may be substituted or unsubstituted, which are identical to or different from one another, represent a Ci-C18 alkyl, C ₅ -C ₈ cycloalkyl or C ₆ -C ₁₈ aryl group (preferably C ₁ -C ₈ alkyl groups); C ₆ , cyclohexyl or phenyl, especially C ₁ -C ₄ alkyl groups, more particularly methyl and / or ethyl).

- the radicals R ^2, substituted or unsubstituted, identical or different, represent an alkoxy group or Ci-Ci ₈ cycloalkoxy, C ₅ -C ₈ (preferably a group selected from alkoxyls Cg and C cycloalkoxyls ₅ -C ₈ , more preferably still a group selected from C ₁ -C ₄ alkoxyls, in particular methoxyl and ethoxyl).

In the case of a mixture of polysulfurized alkoxysilanes corresponding to formula (I) above, in particular common commercially available mixtures, the average value of "x" is a fractional number preferably of between 2 and 5, more preferably close to 4. But the invention can also be advantageously implemented for example with disulfide alkoxysilanes (x = 2).

As examples of silane polysulfides, are more particularly the bis (mono, trisulfide or tetrasulfide) of bis (alkoxyl (Ci-C ₄₎ alkyl (Ci-C ₄₎ alkyl silyl (Ci-C ₄ )), such as polysulfides of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl). Among these compounds, bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, of formula [(C ₂ H ₅ O) ₃ Si (CH ₂ ) ₃ S ₂ ] ₂ or bis-disulfide ( triethoxysilylpropyl), abbreviated TESPD, of formula [(C ₂ H ₅ O) ₃ Si (CH ₂ ) ₃ S] ₂ . Mention may also be made, by way of preferred examples, of polysulfides (in particular disulfides, trisulphides or tetrasulfides) of bis- (monoalkoxyl (Ci-C ₄ ) -dialkyl (Ci-C ₄ ) silylpropyl), more particularly bis-monoethoxydimethylsilylpropyl tetrasulfide. as described in the aforementioned patent application WO 02/083782 (or US Pat. No. 7,217,751).

By way of example of coupling agents other than a polysulphurized alkoxysilane, mention may be made in particular of bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulfides (R ² = OH in formula I above) as described by US Pat. for example in patent applications WO 02/30939 (or US Pat. No. 6,774,255), WO 02/31041 (or US 2004/051210), and WO 2007/061550, or else silanes or POS bearing functional azo-dicarbonyl groups, as described for example in patent applications WO 2006/125532, WO 2006/125533, WO 2006/125534.

As examples of other sulphurized silanes, mention may be made, for example, of silanes carrying at least one thiol function (-SH) (called mercaptosilanes) and / or of at least one blocked thiol function, as described for example in patents or patent applications US 6,849,754, WO 99/09036, WO 2006/023815, WO 2007/098080. Of course, it would also be possible to use mixtures of the coupling agents described above, as described in particular in the aforementioned application WO 2006/125534. When they are reinforced with an inorganic filler such as silica, the rubber compositions preferably comprise between 2 and 15 phr, more preferably between 3 and 12 phr of coupling agent.

4.3. Metal oxide microparticles

Another essential feature of the rubber composition of the tread of the tire of the invention is that it comprises between 2 and 60 phr of microparticles of at least one metal oxide, preferably in powder form. By microparticles is meant by definition and generally particles whose size (ie, diameter or greater dimension in the case of anisometric particles) is micrometric, that is to say, whose median size (expressed in weight) is between 1 μιη and 1 mm. Preferably, the median size is between 2 μιη and 800 μιη, more preferably between 3 and 600 μιη.

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 may be various disadvantages: a possible loss of aesthetics (particles too visible on the surface of the tread) and a risk of loosening, when rolling, relatively large tread elements, it was found that the performance of adhesion on ice melting could be degraded.

For all these reasons, it is preferred that the microparticles have a median size of between 5 and 500 μιη, in particular in a range of 5 to 200 μιη. 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 reasons identical to those set out above, the level of microparticles is preferably between 5 and 50 phr, more preferably in a range of 10 to 40 phr.

According to another preferred embodiment, the microparticles are hollow microparticles. According to another preferred embodiment, combined or not with the above, the metal of the metal oxide is selected from the group consisting of uminium, silicon, transition metals (in particular zirconium and titanium) and mixtures of such metals . More preferably, 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, this metal oxide is an aluminosilicate. It is more particularly possible to use hollow microparticles of aluminosilicate such as have been described in the above-mentioned applications WO 2011/073186, WO 2011/086061, WO 2011/113731.

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, in a simple and preferential manner, to use particle size analysis 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 μιη, etc.); 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 size (or median diameter) is finally calculated in a known manner from the histogram of the particle size distribution.

4.4. Expansion agent and associated hot-melt compound In known manner, a blowing agent ("blowing agent" in English) is a thermally decomposable compound, intended to release during a thermal activation, for example during the vulcanization of the bandage, a large amount of gas (for example nitrogen or carbon dioxide) and thus lead to the formation of bubbles. The release of gas in the rubber composition therefore comes from this thermal decomposition of the blowing agent.

There are physical or chemical expansion agents, of the endothermic or exothermic type. It is preferable to use chemical expansion agents, more preferably exothermic chemical expansion agents, for example diazo, dinitroso, hydrazide, carbazide, semi-carbazide or tetrazole compounds. carbonates, citrates, as described in particular in the aforementioned application WO 2011/064128.

The blowing agent preferably used is a carbonate or hydrogencarbonate, in particular a carbonate or hydrogencarbonate (also called bicarbonate) of sodium (Na), potassium (K) or ammonium (NH ₄ ).

More preferably, it is a carbonate selected from the group consisting of sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, and mixtures of such carbonates (including, of course, their hydrated forms) . Such an expansion agent has the advantage of only releasing carbon dioxide and water during its decomposition; it is therefore particularly favorable to the environment. Hydrogen carbonate or sodium bicarbonate (NaHCO 3) is particularly used. Preferably, the content of this blowing agent is between 5 and 25 phr, more preferably between 8 and 20 phr.

An essential characteristic of the invention is to add to the previously described blowing agent a hot-melt compound whose melting temperature is between 60 ° C and 220 ° C, preferably between 100 ° C and 200 ° C, more preferably between 120 ° C and 180 ° C. The content of this hot-melt compound is between 2 and 25 phr, preferably between 2 and 20 phr, especially between 2 and 15 phr. Its function is to turn into a liquid in the specific temperature range indicated above, before or at the moment when the blowing agent thermally decomposes and releases gas bubbles.

Any compound having a melting temperature in the areas indicated above is likely to be suitable. In particular, the rubber additives known to those skilled in the art may be used as being compatible, both in their form (for example in powder form) and by their chemical nature, with conventional rubber compositions for bandages.

By way of examples, there may be mentioned in particular thermoplastic polymers such as polyethylene or polypropylene; thermoplastic hydrocarbon plasticizing resins with a high glass transition temperature (Tg), whose melting temperature (or what is considered equivalent here, the softening temperature measured for example according to the known "Ring and Bail" method - ISO 4625 standard ) is included in the above fields; urea or a thermofusible derivative of urea; such compounds have been described in more detail in the aforementioned application WO 2011/064128. Melting temperature is a well-known basic physical constant (available for example in "Handbook of Chemistry and Physics") of hot melt compounds, organic or inorganic; it can be controlled by any known method, for example by the Thiele method, the Kofler bench method or by DSC analysis.

The hot melt compound preferably used is a carboxylic acid. Any carboxylic acid having a melting temperature between 60 ° C and 220 ° C (so solid at 23 ° C), preferably between 100 ° C and 200 ° C, in particular between 120 ° C and 180 ° C, is likely to agree.

By dispersing homogeneously in the composition, during its melting in the specific temperature range indicated above, this carboxylic acid has the function of chemically activating (ie, by chemical reaction) the blowing agent which, during its thermal decomposition, will release much more gas bubbles (C0 ₂ and H ₂ 0) than if it was used alone.

The carboxylic acids may be monoacids, diacids or triacids, they may be aliphatic or aromatic; they may also comprise additional functional groups (other than COOH) such as hydroxyl groups (OH), ketone groups (C = O) or groups bearing ethylenic unsaturation.

According to a preferred embodiment, the pKa (Ka acid constant) of the carboxylic acid is greater than 1, more preferably between 2.5 and 12, in particular between 3 and 10.

According to another preferred embodiment, combined or otherwise with the preceding, the carboxylic acid comprises, along its hydrocarbon chain, from 2 to 22 carbon atoms, preferably from 4 to 20 carbon atoms. The aliphatic monoacids preferably comprise, along their hydrocarbon chain, at least 16 carbon atoms; mention may be made, for example, of palmitic acid (Cl 6), stearic acid (Cl 8), nonadecanoic acid (Cl 9), behenic acid (C 20) and their various mixtures. The aliphatic diacids preferably comprise, along their hydrocarbon chain, from 2 to 10 carbon atoms; mention may be made, for example, of oxalic acid (C2), malonic acid (C3), succinic acid (C4), glutaric acid (C5), adipic acid (C6), pimellic acid (C7), suberic acid (C8), azelaic acid (C9), sebacic acid (C10) and their various mixtures. As aromatic monoacid, there may be mentioned for example benzoic acid. The acids having functional groups may be monoacids, diacids or triacids, of the aliphatic type as aromatic; we can quote Examples include tartaric acid, malic acid, maleic acid, glycolic acid, α-ketoglutaric acid, salicylic acid, phthalic acid or citric acid.

Preferably, the carboxylic acid is chosen from the group consisting of palmitic acid, stearic acid, nonadecanoic acid, behenic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimellic acid, suberic acid, azelaic acid, sebacic acid, benzoic acid, tartaric acid, malic acid, maleic acid, glycolic acid, α-ketoglutaric acid, salicylic acid, phthalic acid, citric acid and mixtures of these acids.

More particularly, the carboxylic acid is selected from the group consisting of malic acid, α-ketoglutaric acid, citric acid, stearic acid and mixtures thereof. More preferably still, citric acid, stearic acid or a mixture of these two acids is used.

In order to obtain optimum adhesion of the tread on ice, the total amount of expansion agent (in particular of carbonate or hydrogencarbonate) and of hot-melt compound (in particular of carboxylic acid) is greater than 10 phr, preferably between 10 and 40 phr. This total amount is more preferably greater than 15 phr, in particular between 15 and 40 phr.

4.5. Various additives

The heat-expandable rubber composition may also comprise all or part of the usual additives normally used in tread rubber compositions, such as, for example, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants , plasticizing agents, reinforcing resins, a crosslinking system based on either sulfur, or sulfur and / or peroxide and / or bismaleimide donors, vulcanization accelerators, vulcanization activators.

According to a preferred embodiment, the thermo-expandable rubber composition also comprises a liquid plasticizer (at 20 ° C) whose function is to soften the matrix by diluting the diene elastomer and the reinforcing filler; its Tg (glass transition temperature) is by definition less than -20 ° C, preferably less than -40 ° C.

More preferably, for optimum performance of the tread of the bandage of the invention, this liquid plasticizer is used at a relatively low level, such that the weight ratio reinforcing filler on liquid plasticizer is greater than 2.0, more preferably greater than 2.5, especially greater than 3.0. Any extender oil, whether aromatic or non-aromatic, any liquid plasticizer known for its plasticizing properties vis-à-vis 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.

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 DAE (Distillate Aromatic Extracts), Treated Distillate Aromatic Extracts (TDAE) oils, Residual Aromatic Extract oils (RAE), Treated Residual Aromatic Extract (TREE) oils, Residual Aromatic Extract oils (SRAE), mineral oils, vegetable oils, plasticisers ethers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures of these compounds. According to a more preferred embodiment, the liquid plasticizer is selected from the group consisting of MES oils, TDAE oils, naphthenic oils, vegetable oils and mixtures of these oils.

As phosphate plasticizers, for example, mention may be made of those containing from 12 to 30 carbon atoms, for example trioctyl phosphate. As examples of ester plasticizers, mention may be made in particular of compounds selected from the group consisting of trimellitates, pyromellitates, phthalates, 1,2-cyclohexane dicarboxylates, adipates, azelates, sebacates, glycerol and mixtures of these compounds. Among triesters above, there may be mentioned include glycerol triesters, preferably consisting predominantly (for more than 50%, more preferably more than 80% by weight) of an unsaturated fatty acid Ci ₈ is 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 triesters (trioleates) with high oleic acid content are well known, they have been described for example in the application WO 02/088238, as plasticizers in bandage treads. According to another preferred embodiment, the rubber composition according to the invention may also comprise, as a solid plasticizer (at 23 ° C.), a plasticizing hydrocarbon resin having a Tg greater than + 20 ° C., preferably greater than + 30 ° C, as described for example in the applications WO 2005/087859, WO 2006/061064 or 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". ". They may be aliphatic, aromatic or aliphatic / aromatic type that is to say based on aliphatic and / or aromatic monomers. They may be natural or synthetic, whether or not based on petroleum (if so, 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).

The Tg of this resin is measured in a known manner by DSC (Differential Scanning Calorimetry), according to the ASTM D3418 standard. The macrostructure (Mw, Mn and Ip) of the hydrocarbon resin is determined by steric exclusion chromatography (SEC): tetrahydroiurane solvent; temperature 35 ° C; concentration 1 g / 1; flow rate 1 ml / min; filtered solution on 0.45 μιη porosity filter before injection; Moore calibration with polystyrene standards; set of 3 "WATERS" columns in series ("STYRAGEL" HR4E, HR1 and HR0.5); differential refractometer detection ("WATERS 2410") and its associated operating software ("WATERS EMPOWER").

According to a particularly preferred embodiment, the plasticizing hydrocarbon resin is chosen 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, homopolymer or C9 cut copolymer resins, alpha-methyl-styrene homopolymer or copolymer resins and mixtures thereof. resins. Among the above copolymer resins are more preferably used those selected from the group consisting of (D) CPD / vinylaromatic copolymer resins, (D) CPD / terpene copolymer resins, copolymer resins (D) CPD / 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 is in a known manner in the form of three possible isomers: L-limonene (laevorotatory enantiomer), D-limonene (dextrorotatory enantiomer), or the dipentene, racemic of the dextrorotatory and levorotatory enantiomers. . Suitable vinylaromatic monomers are, for example, styrene, alpha-methylstyrene, ortho-, meta-, para-methylstyrene, vinyltoluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes, vinylmesitylene, and the like. , divinylbenzene, vinylnaphthalene, any vinylaromatic monomer from a C ₉ cut (or more generally from a C ₈ to C ₁₀ cut). Preferably, the vinyl-aromatic compound is styrene or a vinylaromatic monomer derived from a C ₉ cut (or more generally from a C ₈ to C ₁₀ 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.

In the case where it is desired to increase the rigidity of the tread once expanded, without reducing the content of liquid plasticizer above, it will be advantageous to incorporate reinforcing resins (eg acceptors and donors of methylene) such as described for example in WO 02/10269 or US 7,199,175.

The heat-expandable rubber composition may also contain coupling enhancers when a coupling agent is used, inorganic filler recovery agents when an inorganic filler is used, or more generally, bleaching agents. implementation (processability) likely in a known manner, through an improvement of the dispersion of the load in the rubber matrix and a lowering of the viscosity of the compositions, to improve their processability in the green state; these agents are for example hydroxysilanes or hydrolysable silanes such as alkyl-alkoxysilanes, polyols, polyethers, amines, hydroxylated or hydrolysable polyorganosiloxanes.

4.6. Manufacture of the Compositions The rubber compositions are manufactured in appropriate mixers, for example using three successive preparation phases according to a general procedure known to a person skilled in the art: a first thermomechanical working or mixing phase (sometimes referred to as a "no" phase). -productive ") 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 (non-productive) at lower temperature (preferably below 100 ° C) during of which is incorporated the blowing agent, finally a third phase of mechanical work (sometimes called "productive" phase) at low temperature, typically less than 120 ° C, for example between 60 ° C and 100 ° C, phase finish during which is incorporated the crosslinking system or vulcanization.

A method that can be used for the manufacture of such rubber compositions comprises, for example, and preferably the following steps: incorporating into a mixer, at least one of the elastomer or mixture of elastomers, at least the reinforcing filler, the metal oxide microparticles, the hot-melt compound, the optional other optional additives, by thermomechanically kneading the whole, in one or more times, until reaching a maximum temperature of between 130 ° C and 200 ° C;

cool the assembly to a temperature below 100 ° C;

then incorporating the blowing agent into the mixture thus obtained and cooled, kneading thermomechanically all until a maximum temperature below 100 C;

then incorporate a crosslinking system;

mix everything up to a maximum temperature below 120 ° C; extruding or calendering the resulting rubber composition.

By way of example, during the first non-productive phase, all the necessary constituents, any additional coating or processing agents and other various additives, are introduced into a suitable mixer such as a conventional internal mixer. with the exception of the blowing agent and the crosslinking system. After thermomechanical work, falling and cooling of the mixture thus obtained, a second (non-productive) phase of thermomechanical work is then conducted in the same internal mixer, during which phase the blowing agent is incorporated at a more moderate temperature. (eg 60 ° C), to reach a maximum temperature of fall below 100 ° C. The low temperature crosslinking system is then incorporated, usually 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 5 phr, that of the primary accelerator is preferably between 0.5 and 8 phr. It is possible to use as accelerator (primary or secondary) any compound capable of acting as accelerator for vulcanization of diene elastomers in the presence of sulfur, in particular thiazole-type accelerators and their derivatives, accelerators of the thiuram type, zinc dithiocarbamates. These accelerators are for example selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), tetrabenzylthiuram disulfide ("TBZTD"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N, N dicyclohexyl-2-benzothiazylsulfenamide ("DCBS"), N-tert-butyl-2-benzothiazylsulfenamide ("TBBS"), N-tert-butyl-2-benzothiazylsulfenamide ("TBSI"), zinc dibenzyldithiocarbamate (" ZBEC ") and mixtures of these compounds.

If a carboxylic acid is used as a hot-melt compound, the latter having the effect of reducing the induction time (that is to say the time required for the beginning of the vulcanization reaction) during the baking of the composition it is advantageous to use a vulcanization retarder to counteract this phenomenon, and thus to provide the rubber composition with the time necessary for complete expansion prior to vulcanization. The level of this vulcanization retarder is preferably between 0.5 and 10 phr, more preferably between 1 and 5 phr, in particular between 1 and 3 phr. Vulcanization retarders are well known to those skilled in the art. Mention may be made, for example, of N-cyclohexylthiophthalimide sold under the name "Vulkalent G" by the company Lanxess, N- (trichloromethylthio) benzenesulfonamide sold under the name "Vulkalent E / C" by Lanxess, or else marketed phthalic anhydride. under the name "Vulkalent B / C" by Lanxess. Preferably, N-cyclohexylthiophthalimide (abbreviated as "CTP") is used.

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 calendered or extruded in the form of a heat-expandable tread.

In the green state (ie, uncured) and therefore unexpanded, the density or density denoted Di of the heat-expandable rubber composition is preferably between 1, 100 and 1, 400 g / cm ³ , more preferably in a range from 1.50 to 1. 350 g / cm ³ . The vulcanization (or cooking) is conducted in a known manner at a temperature generally between 130 ° C and 200 ° C, for a sufficient time which may vary for example between 5 and 90 min depending in particular on the cooking temperature, the system of vulcanization adopted and the kinetics of vulcanization of the composition under consideration. It is during this vulcanization step that the blowing agent will release a significant amount of gas, lead to bubble formation in the foam rubber composition and eventually expand.

In the fired (ie, vulcanized) state, the density denoted D ₂ of the rubber composition once expanded (ie, in the state of foam rubber) is preferably between 0.700 to 1.000 g / cm ³ , more preferably within a range of 0.750 to 0.950 g / cm ³ .

Its volume expansion rate T _E (expressed in%) is preferably between 25% and 75%, more preferably in a range of 30 to 60%>, this expansion rate T _E being calculated in a known manner to from densities Di and D ₂ above, as follows:

T _E = [(D 1 / D ₂ ) - 1] x 100.

The rubber composition thus formulated offers the bandages of the invention a very good adhesion on ice, both on dry ice and on melting ice.

Claims

1. Tread whose tread comprises, in the uncured state, a heat-expandable rubber composition comprising at least one diene elastomer, more than 50 phr of a reinforcing filler, between 2 and 60 phr of microparticles. at least one metal oxide, between 2 and 25 phr of an expansion agent and between 2 and 25 phr of a hot-melt compound whose melting point is between 60 ° C. and 220 ° C., the total content of agent expansion and heat fusible compound being greater than 10 phr.

The tire 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.

The tire of claim 2, wherein said rubber composition comprises 50 to 100 phr of natural rubber or synthetic polyisoprene.

4. A bandage according to claim 2, wherein said composition comprises 50 to 100 phr of a polybutadiene having a cis-1,4 bond ratio greater than 90%.

5. Bandage according to any one of claims 1 to 4, wherein the reinforcing filler content is between 50 and 150 phr, preferably within a range of 70 to 120 phr.

The tire of any one of claims 1 to 5, wherein the reinforcing filler is an inorganic filler, preferably silica.

7. Bandage according to any one of claims 1 to 6, wherein the level of microparticles is between 5 and 50 phr, preferably in a range of 10 to 40 phr.

8. Bandage according to any one of claims 1 to 7, wherein the median weight size of the microparticles is between 2 and 800 μιη, preferably between 3 and 600 μιη.

Bandage according to any one of claims 1 to 8, wherein the microparticles are hollow microparticles.

The tire of any one of claims 1 to 9, wherein the metal oxide metal is selected from the group consisting of aluminum, silicon, transition metals and mixtures of such metals.

The tire of claim 10, 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 tire of claim 11, wherein the metal oxide is an aluminosilicate.

A tire as claimed in any one of claims 1 to 12, wherein the blowing agent is a carbonate or hydrogencarbonate, preferably a sodium, potassium or ammonium carbonate or hydrogencarbonate.

The tire of claim 13, wherein the blowing agent is selected from the group consisting of sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, and mixtures of such carbonates.

15. A bandage according to any one of claims 1 to 14, wherein the content of blowing agent is between 5 and 25 phr, preferably between 8 and 20 phr.

Bandage according to any one of claims 1 to 15, wherein the melting temperature of the hot-melt compound is between 100 ° C and 200 ° C, preferably between

120 and 180 ° C.

Bandage according to any one of claims 1 to 16, wherein the hot melt compound is a carboxylic acid.

The bandage of claim 17, wherein the carboxylic acid is selected from the group consisting of malic acid, α-ketoglutaric acid, citric acid, stearic acid and mixtures of these acids.

19. Bandage according to any one of claims 1 to 18, wherein the level of heat fusible compound is between 2 and 20 phr, preferably between 2 and 15 phr.

20. Bandage according to any one of claims 1 to 19, wherein the total content of blowing agent and heat-fusible compound is greater than 15 phr.

A bandage according to any one of claims 1 to 20, wherein the heat-expandable rubber composition further comprises a liquid plasticizer at 20 ° C, preferably at a rate such as a weight ratio of reinforcing filler to plasticizer. liquid is greater than 2.0, preferably greater than 2.5.

A bandage according to any one of claims 17 to 21, wherein the heat-expandable rubber composition further comprises a vulcanization retarder, preferably at a level of between 0.5 and 10 phr.

A bandage according to any one of claims 1 to 22, wherein the density of the heat-expandable rubber composition is between 1,100 and 1,400 g / cm ³ , preferably in the range of 1,150 to 1,350 g / cm ^3. .

24. A vulcanized tire obtained after baking a tire according to any one of claims 1 to 23.