WO2013092340A1

WO2013092340A1 - Tyre with improved grip on ice

Info

Publication number: WO2013092340A1
Application number: PCT/EP2012/075219
Authority: WO
Inventors: Hiroko Fukasawa; Salvatore Pagano
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2011-12-22
Filing date: 2012-12-12
Publication date: 2013-06-27
Also published as: FR2984902A1; FR2984902B1

Abstract

A tyre whereof the tread comprises a rubber composition based on at least one diene elastomer such as natural rubber and/or polybutadiene, more than 30 pce of a liquid plasticising agent, between 50 and 150 pce of a non-black reinforcing filler such as silica, optionally carbon black at a level lower than 3 pce, between 5 and 50 pce of a photocrosslinkable liquid polymer resin such as a poly(butadiene-acrylate) or poly(butadiene-methacrylate) resin, and between 5 and 70 pce of microparticles of poly(vinyl alcohol). Such a rubber composition greatly improves the grip of the tyre on cold ice.

Description

PNEUMATIC IMPROVED ICE ADHESION

1. DOMAIN OF THE INVENTION

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

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

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 tire manufacturers have proposed different solutions of modifying the formulation of the rubber compositions constituting 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 it wears, and thus come into contact with the ice. Such particles, capable of acting finally as micro-nails on hard ice, thanks to a well known "claw" effect, however remain relatively aggressive vis-à-vis the ground, besides they are not not well adapted to driving conditions on melting ice.

Other solutions have therefore been proposed, including incorporating water-soluble powders (ie, which can dissolve in water) in the constitutive composition of the tread. 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 strip of bearing porosities may improve the attachment of the tread on the ground and on the other hand the creation of grooves acting as evacuation channels of the liquid film created between the tire and the ground. Examples of such water-soluble powders include, for example, the use of cellulose powder or starch, guar gum powders or xanthan gum, or magnesium sulphate powder (see below). for example, patent application JP 3-159803, JP 2002-211203, WO 2008/080750, WO 2008/080751, WO 2010/009850).

These solutions are however not effective for dry ice conditions (non-melting). Another known disadvantage is that they can furthermore strongly penalize, for some of them, the strengthening of the rubber compositions (and therefore their resistance to wear) or their hysteresis (and therefore their rolling resistance).

3. BRIEF DESCRIPTION OF THE INVENTION

Continuing their research, the Applicants have discovered a specific rubber composition which makes it possible to greatly improve tire adhesion to dry ice, without affecting or even improving the grip on wet surfaces and without penalizing the reinforcing properties.

Accordingly, the present invention relates to a tire whose tread comprises a rubber composition based on at least one diene elastomer, more than 30 phr of a liquid plasticizer, between 50 and 150 phr of a non-reinforcing filler. black, optionally carbon black at a rate of less than 3 phr, between 5 and 50 phr of a photocurable liquid polymer resin and between 5 and 70 phr of polyvinyl alcohol microparticles (abbreviated as "PVA").

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. industrial vehicles chosen in particular from vans and "heavy goods vehicles" (ie, metro, buses, road transport vehicles such as trucks, tractors). Of course, the invention is applicable in cases where the tire and said polymer resin are both in the green (i.e., uncrosslinked) state as in the crosslinked state (i.e., after crosslinking or vulcanization).

The invention as well as its advantages will be readily understood in the light of the description and the following exemplary embodiments. 4. DETAILED DESCRIPTION OF THE INVENTION

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are percentages by mass. The abbreviation "phr" means parts by weight per hundred parts of elastomer or rubber (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 rubber composition of the invention is therefore based on at least one (i.e. one or more) diene elastomer, a plasticizer system, at least one (i.e., one or more reinforcing inorganic filler, at least one (i.e., one or more) photocurable liquid polymer resin and PVA microparticles, components which are described in detail below.

By the expression "based on", it is of course understood a composition comprising the mixture of the various constituents used or, where appropriate, their reaction product, some of these basic constituents being in particular capable of or intended to react with each other. at least partly during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization. 4.1. Diene elastomer

By elastomer (or rubber, the two terms being synonymous) of the "diene" type, it is recalled that must be understood an elastomer derived at least in part (ie a homopolymer or a copolymer) of monomers dienes (monomers carrying two double bonds 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, 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, in particular diene elastomer "highly unsaturated" a diene elastomer having a diene origin ratio (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.

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%, the polyisoprenes, the copolymers 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-1,4-linkage content of between 20% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a 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 between - 25 ° C and -50 ° C.

In the case of butadiene-styrene-isoprene copolymers are especially suitable those having a styrene content of between 5% and 50% by weight and more particularly of between 10% and 40%, an isoprene content of between 15% and 60%. by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of -1,2 units of the butadiene part 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 plus -3,4 of the isoprenic part of between 5% and 70% % and a trans-1,4-unit content of the isoprene portion of between 10% 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 diene elastomer used is predominantly, and more preferably for more than 50 phr (for recall, "phr" or "phr" in English meaning parts by weight per hundred parts of elastomer or rubber ), natural rubber (NR) or synthetic polyisoprene (IR). More preferably still, said natural rubber or synthetic polyisoprene is then used in blending with a polybutadiene (BR) having a cis-1,4 bond ratio which is preferably greater than 90%.

According to another particular and preferred embodiment, the diene elastomer used is predominantly, and more preferably for more than 50 phr, a polybutadiene (BR) having a cis-1,4 bond ratio greater than 90%. More preferably still, said polybutadiene is then used in a blend with natural rubber or synthetic polyisoprene. According to another particular and preferred embodiment, the diene elastomer used is a binary (mixing) blend of NR (or IR) and BR, or a ternary blend of NR (or IR), BR and SBR. Preferably, in the case of such cuts, the composition comprises between 25 and 75 phr of NR (or IR) and between 75 and 25 phr of BR, to which may be associated or not a third elastomer (ternary cutting) at a lower rate. at 30 phr, especially less than 20 phr. This third elastomer is preferably an SBR elastomer, in particular an SBR solution (called "SBR"). More preferably still, in the case of such a blend, the composition comprises from 35 to 65 phr of NR (or IR) and from 65 to 35 phr of BR. The BR used is preferably a BR having a cis-1,4 bond ratio greater than 90%, more preferably greater than 95%.

The diene elastomers of the compositions of the invention could be associated, in a minor amount, with synthetic elastomers other than diene, or even polymers other than elastomers, for example thermoplastic polymers. 4.2. Liquid plasticizer

Another essential feature of the rubber composition of the invention is that it comprises more than less than 30 phr of a liquid plasticizer (at 23 ° C.) whose function is to soften the matrix by diluting the elastomer and the reinforcing filler; its Tg is preferably less than -20 ° C, more preferably less than -40 ° C.

Any extender oil, whether aromatic or non-aromatic, any liquid plasticizer known for its plasticizing properties vis-à-vis diene elastomers, is usable. At room temperature (23 ° C.), these plasticizers or these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the capacity of eventually take the form of their container), in contrast to in particular plasticizing hydrocarbon resins which are inherently solid at room temperature.

Particularly suitable liquid plasticizers selected from the group consisting of polyolefinic oils, naphthenic oils, paraffmic oils, oils DAE (Distillate Aromatic Extracts), oils MES (Medium Extracted Solvates), oils TDAE (Treated Distillate Aromatic Extracts) ), Residual Aromatic Extracts (RAE) oils, Treated Residual Aromatic Extracts (TREE) oils, Safety Residual Aromatic Extracts (SRAE) oils, mineral oils, vegetable oils, ethers plasticizers, 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. According to a preferred embodiment of the invention, the liquid plasticizer, in particular petroleum oil, is of the non-aromatic type. A liquid plasticizer is described as non-aromatic if it has a content of polycyclic aromatic compounds, determined with the extract in DMSO according to the IP 346 method, of less than 3% by weight, relative to the total weight of the plasticizer. . In this respect, it is preferable to use a liquid plasticizer chosen from the group consisting of MES oils, TDAE oils, naphthenic oils (at low or high viscosity, especially hydrogenated), paraffinic oils and mixtures of these oils. . Also suitable as petroleum oil are RAE oils, TRAE oils and SRAE oils or mixtures thereof, which contain low levels of polycyclic compounds.

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 the triesters above, mention may be made especially of glycerol triesters, preferably consisting mainly (for more than 50%, more preferably for more than 80% by weight) of a C ₁₈ 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 triesters (trioleates) are well known and have been described, for example, in application 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 within a range of 50 to 100 phr. According to another preferred embodiment, the compositions of the invention may also comprise, as solid plasticizer (at 23 ° C.), a hydrocarbon resin having a Tg greater than + 20 ° C., preferably greater than + 30 ° C. C, as described for example in applications 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". ". They have been described, for example, in the book "Hydwcarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), chapter 5 of which is devoted their applications, in particular pneumatic rubber (5.5 "Rubber Tires and Mechanical Goods"). 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 preferably 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): solvent tetrahydrofuran; 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 present 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, divinylbenzene, vinylnaphthalene, any vinyl aromatic monomer from a C 9 fraction (or more generally from a Cg to C _10). Preferably, the vinyl-aromatic compound is styrene or a vinylaromatic monomer resulting 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.

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

4.3. Non-black reinforcing filler

By "non-black reinforcing filler" must be understood here any inorganic or organic filler other than carbon black, regardless of its color (other than black) and its origin (natural or synthetic), sometimes called "mineral" filler ", charge" white "or "clear" charge as opposed to carbon black, this non-black charge being able to reinforce on its own, with no other means than an intermediate coupling agent, a rubber composition for the manufacture of a tread of pneumatic, in other words able to replace, in its reinforcing function, a conventional tire grade carbon black for tread; such a filler is generally characterized, in known manner, by the presence of functional groups, in particular hydroxyl groups, at its surface, thereby requiring the use of a coupling agent intended to ensure a stable chemical bond between the diene elastomer and said charge. Preferably, the non-black reinforcing filler is an inorganic filler, more particularly a filler of the siliceous or aluminous type, or a mixture of these two types of filler.

The silica (SiO ₂ ) used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface area both less than 450 m ² / g, preferably 30 to 400 m ² / g. Highly dispersible precipitated silicas (so-called "HDS") are preferred, in particular when the invention is used for the manufacture of tires having a low rolling resistance; examples of such silicas are the Ultrasil 7000 silicas from Evonik, the Zeosil 1165 MP, 1135 MP and 1115 MP silicas from Rhodia, the Hi-Sil EZ150G silica from PPG, the Zeopol 8715 silicas, 8745 or 8755 of the Huber Company, the silicas as described in the application WO 03/016387.

The reinforcing alumina (Al 2 O 3) preferably used is a highly dispersible alumina having a BET surface area ranging from 30 to 400 m ² / g, more preferably from 60 to 250 m ² / g, an average particle size of at most 500 nm. more preferably at most equal to 200 nm. As non-limiting examples of such reinforcing aluminas, there may be mentioned aluminas "Baikalox A125" or "CR125" (Baïkowski company), "APA-100RDX" (Condéa), "Aluminoxid C" (Degussa) or "AKP-G015" (Sumitomo Chemicals).

By way of other examples of inorganic filler suitable for use in the rubber compositions of the invention, mention may also be made of aluminum (oxide) hydroxides, aluminosilicates, titanium oxides, carbides or nitrides of silicon, all of the reinforcing type as described for example in the applications WO 99/28376, WO 00/73372, WO 02/053634, WO 2004/003067, WO 2004/056915.

When the treads of the invention are intended for tires with low rolling resistance, the non-black reinforcing filler used, in particular if it is a reinforcing inorganic filler such as silica, preferably has a BET surface area between 60 and 350 m2 / g. An advantageous embodiment of the invention consists of using a non-black filler, in particular a reinforcing inorganic filler such as silica, having a high BET specific surface area, in a range of 130 to 300 m ² / g, because of the recognized high reinforcing power of such fillers. According to another preferred embodiment of the invention, it is possible to use a non-black filler having a BET specific surface area of less than 130 m ² / g, preferably in such a case of between 60 and 130 m ⁷ g (see for example WO03 applications). / 002648 and WO03 / 002649 mentioned above).

The physical state in which the non-black (especially inorganic) reinforcing filler is present is indifferent whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, non-black reinforcing filler is also understood to mean mixtures of different non-black reinforcing fillers, in particular inorganic fillers such as highly dispersible siliceous and / or aluminous fillers as described above. Preferably, such a reinforcing inorganic filler consists of nanoparticles whose average mass size is less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 μιη. This average size can be measured in a well-known manner, after dispersion by ultrasonic deagglomeration of the load to be analyzed in water (or aqueous solution containing a surfactant), for example by means of a centrifugal sedimentometer with X-ray detection type "XDC" (X-rays Disk Centrifuge), marketed by Brookhaven Instruments, according to the following procedure: a suspension of 3.2 g of inorganic filler sample to be analyzed in 40 ml of water, by action for 8 minutes, at 60% power (60% of the maximum position of the "output control"), a 1500 W ultrasound probe (3/4 "Vibracell sonifilator marketed by Bioblock); after sonifcation, 15 ml of the suspension is introduced into the rotating disc; after sedimentation for 120 minutes, the mass distribution of the particle sizes and the mean mass size of the particles d _w are calculated by the software of the XDC sedimentometer. In the present disclosure, the BET surface area is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, specifically according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: time at 160 ° C - relative pressure range p / po: 0.05 at 0.17). The CTAB specific surface is the external surface determined according to the French standard NF T 45-007 of November 1987 (method B).

Finally, those skilled in the art will understand that, as an equivalent load of the non-black reinforcing filler described in this paragraph, carbon black could be used if it were covered with a non-black layer, especially inorganic such as silica, having on its surface functional sites (in particular hydroxyl) requiring in known manner the use of a coupling agent to establish the bond between the filler (the surface of its particles) and the diene elastomer.

Preferably, the non-black reinforcing filler is a reinforcing inorganic filler, more preferably silica.

Preferably, the level of non-black reinforcing filler, in particular of silica, is between 60 and 120 phr, in particular between 70 and 100 phr.

To couple the non-black reinforcing filler to the diene elastomer, it is possible to use, in a well-known manner, at least a bifunctional coupling agent (or binding agent) intended to ensure a sufficient chemical and / or physical connection between the charge (surface of its particles) and the diene elastomer. In particular, organosilanes or 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).

Particularly suitable, without the following definition being limiting, so-called "symmetrical" polysulfide silanes having the following general formula (I):

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

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

- A is a divalent hydrocarbon radical (preferably alkylene groups C ₁ -C ₁₈ or arylene groups C ₂ -C _6, particularly alkylene C ₁ -C _10, especially C ₁ -C 4, particularly propylene);

Z is one of the following formulas:

R1 R1 R2

- Si- R1; - Si- R2; - Si- R2,

R2 R2 f2 wherein

- R.1 radicals, substituted or unsubstituted, identical or different, represent an alkyl group Ci-Cig, C5-C18 aryl or C ₆ -Ci8 (preferably alkyl, Ci-C ₆ , cyclohexyl or phenyl, especially C ₁ -C ₄ alkyl groups, more particularly methyl and / or ethyl). the radicals R 1, which are substituted or unsubstituted, which are identical to or different from one another, represent a C 1 -C 18 alkoxyl or C 5 -C 18 cycloalkoxyl group (preferably a group chosen from C 1 -C 6 alkoxyls and C 6 -C 8 cycloalkoxyls, more preferably a group selected from alkoxyl C 1 -C _4, especially 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 (Ci-C ₄ ) -dialkyl (Ci-C ₄ ) silylpropyl), more particularly bis-monoethoxydimethylsilylpropyl tetrasulfide. as described in 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 (R ² = OH in the formula (I) above) as described in the applications WO 02/30939 (or US Pat. No. 6,774,255) and WO 02/31041 (or US 2004/051210), or alternatively 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.

The rubber composition of the tread of the tire of the invention is devoid of carbon black or has less than 3 phr, in order to prevent carbon black from playing, because of its anti-UV properties. known, an antagonistic role therefore undesirable compared to the photocrosslinking of the photocurable liquid polymer resin.

Preferentially, carbon black is used in a very small amount, between 0.05 and 2.0 phr, in particular between 0.05 and 1.5 phr, a narrow concentration range in which the black retains its function as a reducing agent. black coloration of the composition but no longer fills that of anti-UV agent.

Suitable carbon blacks are all carbon blacks capable of bringing a black color to the rubber compositions, in particular blacks of the HAF, ISAF and SAF type known to those skilled in the art and conventionally used in tires. Among these are the reinforcing carbon blacks of the series (grades ASTM) 100, 200 or 300 used in the treads of these tires (for example NI 15, N134, N234, N326, N330, N339, N347, N375), but also those of the non-reinforcing type (because less structured) higher series 400 to 700 (for example blacks N660, N683, N772). Black non-reinforcing blacks used as black pigments in printing inks and paints could also be used as examples.

The carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used.

4.4. Photocrosslinkable liquid polymer resin

An essential feature of the present invention is the use of a photocurable liquid polymer resin in the rubber composition forming at least the surface or extreme surface of the tread of the invention, i.e. portion of the tread which is intended to come into contact with the road during the rolling of the tire. This polymer may be an oligomer, a prepolymer, a homopolymer or a copolymer. Its essential characteristic is that it is on the one hand liquid (at ambient temperature, ie 23 ° C) in the non (photo) crosslinked state and on the other functionalized that is to say carrying one or several groups or functions crosslinkable (polymerizable) under the action of UV radiation. The consequence is a hardening of the rubber matrix comprising this type of polymer, when this matrix, at least its surface, is exposed to UV.

Preferably, this polymer is an oligomer, typically having 3 to 20 monomer units. In such a preferential case, the number of functions capable of reacting under the action of UV is preferably within a range of 1 to 4 per oligomeric hydrocarbon backbone. The crosslinkable function or functions are more preferably in the telechelic position, that is to say at the ends of said oligomeric hydrocarbon backbone.

According to a preferred embodiment, a photocrosslinkable resin of the radical type (radical polymerizing) or cationic (cationic polymerizing) type is used.

More preferably, the photocurable resin is selected from the group consisting of acrylate, methacrylate, epoxide, oxetane, unsaturated polyester, vinyl ether, vinyl ester resins, and mixtures thereof. Such denominations refer in a well-known manner to the nature of the photo-crosslinkable (or photo-polymerizable) functional groups carried by the polymer (or preferentially oligomeric) constituting the hydrocarbon backbone of these resins.

More preferably still, among those set out above, the photocrosslinkable resin used is an acrylate resin (for example, monoacrylate, diacrylate, triacrylate, epoxy-acrylate, epoxy-diacrylate, urethane-acrylate, urethane-diacrylate) or a methacrylate resin (for example: monomethacrylate, diamethacrylate, urethane-monomethacrylate, urethane-dimethacrylate).

However, other possible examples include fumarate resins (for example mono fumarate, difumarate), maleate (for example monomaleate, dimaleate), and mixtures of such resins.

According to another preferred embodiment, the liquid polymer or oligomer constituting the resin is a diene-type polymer; in particular, this diene polymer, by liquid definition, is a polybutadiene or polyisoprene bearing the photocrosslinkable functional group.

Thus, more preferably still, the photocurable liquid polymer resin is a poly (butadiene-acrylate) or a poly (butadiene-methacrylate) or a mixture of both.

The weight average mass (denoted Mw) of the liquid polymer described above, in particular when it is a liquid diene polymer, is preferably between 200 and 5000 g / mol. This size is well known to those skilled in the art, available especially from polymer suppliers, also measurable by conventional techniques such as GPC ("Gel Permeation Chromatography") or SEC ("Size Exclusion Chromatography").

As a reminder, the SEC analysis, for example, consists in separating the macromolecules in solution according to their size through columns filled with a porous gel; the molecules are separated according to their hydrodynamic volume, the larger ones being eluted first. The sample to be analyzed is simply solubilized beforehand in a suitable solvent, for example tetrahydrofuran at a concentration of 1 g / liter. Then the solution is filtered on a filter, for example porosity 0.45 μιη, before injection into the apparatus. The equipment used is for example a chromatographic chain "Waters alliance". The elution solvent is for example tetrahydrofuran, the flow rate is 0.7 ml / min, the system temperature is 35 ° C. For example, a set of 4 "Waters" columns in series (denominations "Styragel HMW7", "Styragel HMW6E", and two "Styragel HT6E") are used. The injected volume of the solution of the polymer sample is for example 100 μΐ. The detector is a differential refractometer (for example "Waters 2410") that can be equipped with associated data mining software (for example "Waters Millenium"). A calibration of Moore is conducted with a series of commercial polystyrene standards with low Ip (less than 1.2), known molar masses, covering the field of masses to be analyzed. The mass-averaged molecular weight (Mw), the number-average molecular weight (Mn) and the polymolecularity index (Ip = Mw / Mn) are deduced from the recorded data (mass distribution curve of the molar masses).

The rubber composition may also comprise, in combination with the photo-crosslinkable liquid polymer resin previously described, a photoinitiator intended to promote, accelerate the process of surface photocrosslinking of the tread when the latter is exposed to UV radiation. .

In a known manner, the photoinitiators (also called photoinitiators or photoactivators) are stable compounds able to release, when exposed to light of appropriate wavelength, radical or ionic species that will favor and accelerate photocrosslinking or photooxidation processes.

These usable photoinitiators are preferably of the radical or cationic type. Such compounds are commonly used in the fields of photopolymerization of multifunctional monomers, surface treatment of materials with protective coatings, graphic arts and electronics for the production of microcircuits. They have also been described (see patent application WO 2006/077059) in treads of photo-oxidizable tires having improved adhesion on a wet road. Examples of cationic photoinitiators that may be mentioned are onium salts, more particularly sulphonium salts such as triarylsulphonium salts or iodonium salts such as diaryliodonium salts.

A photoinitiator of the radical type, more preferentially chosen from aromatic ketones, is preferably used, in particular those chosen from the group consisting of benzal ketals (especially diketals), benzoins (in particular benzoin ethers) and α, α-dialkoxy. acetophenones, α-hydroxyalkylphenones, α-aminoaromatic ketones (or α-aminoalkylphenones), acylphosphine oxides, benzophenones or thioxanthones in combination with a hydrogen donor (eg, a tertiary amine), and mixtures of such compounds.

Those skilled in the art will know, if necessary, adjust the amount of photoinitiator according to the particular applications targeted. This amount is preferably between 0.1 and 10 phr, more preferably between 0.2 and 5 phr. The photoinitiators previously described may be used alone when exposed to UV radiation or, when exposed to visible light, in combination with photosensitizers capable of activating their own photooxidative action. Such photosensitizers are, for example, dyes such as phthalenes (eosin, erythrosine, ethyl eosin, phloxine, bengal rose) and thiazines (thionine and methylene blue). If they are used without photosensitizers, the photoinitiators will preferably be chosen in such a way that their UV absorption spectrum and the emission spectrum of the light source (whether natural or artificial) responsible for photooxidation. of the tread, have a recovery zone.

4.5. Microparticles of PVA.

According to another essential characteristic of the invention, the rubber composition of the tread of the tire of the invention comprises between 5 and 70 phr of PVA microparticles.

Below the minimum indicated, the desired technical effect is insufficient while beyond the maximum recommended, one exposes to the prohibitive problems of increase of the module, weakening of the composition, also to difficulties of dispersion of the load and processability. For all the reasons indicated above, a microparticle content preferably between 10 and 50 phr is used.

It will be recalled here that PVA or poly (vinyl alcohol), also called poly (vinyl alcohol) or polyvinyl alcohol, is well known a thermoplastic polymer that can be obtained by at least partial hydrolysis of poly (vinyl acetate) polymer. ) in the presence in particular of sodium hydroxide. Strictly speaking, when the hydrolysis is not complete, it is a (random) copolymer of polyvinyl alcohol and polyvinyl acetate also called polyvinyl alcohol-vinyl coacetate. Preferably, the degree of polymerization (DP) of the PVA, that is to say the total number (n + p) of units (n) monomer vinyl alcohol and units (p) monomer vinyl acetate, is included between 200 and 1500, more preferably between 300 and 1000, in particular between 400 and 800. The degree of hydrolysis of PVA, expressed in% of vinyl monomer vinyl units (also represented by the ratio n / n + p) is preferably between 60 and 90%, more preferably between 65 and 85%, in particular between 70 and 80%.

By microparticles is meant by definition and in general size particles (by size, we mean the largest dimension in the case of anisometric particles) micrometer, that is to say whose median size (expressed by weight) is between 1 μιη and 1 mm. 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.

The median size of the PVA microparticles is preferably between 50 and 1000 μιη, more preferably between 100 and 800 μιη.

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

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 reason for progression, with meshes (in μιη) of 75 , 105, 150, 180, 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.

4.6. Various additives

The rubber compositions used in the treads according to the invention may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of treads for tires, in particular for winter tires, for example protective agents such as anti-ozone waxes, 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 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 aid agents that are capable in a known manner, by means of an improvement of 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 _O

Alkoxysilanes, polyols, polyethers, amines, hydroxylated or hydrolysable polyorganosiloxanes.

4.7. Manufacture of rubber compositions and treads

The rubber compositions are manufactured in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes referred to as a "non-productive" phase) at high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed by a second phase of mechanical work (sometimes referred to as "productive" phase) to lower temperature, typically less than 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system or vulcanization. A method that can be used for the manufacture of such compositions, capable of exhibiting, after photooxidation of their surface, an improved adhesion on ice, comprises for example and preferably the following steps: to incorporate into the diene elastomer (or the mixture of diene elastomers), in a mixer, more than 30 phr of a liquid plasticizer, between 50 and 150 phr of a non-black reinforcing filler, optionally carbon black at a rate of less than 3 phr, between 5 and 50 a photocurable liquid polymer resin and between 5 and 70 phr of PVA microparticles, thermomechanically kneading the whole, in one or more times, until a maximum temperature of between 130 ° C and 200 ° C;

cool the assembly to a temperature below 100 ° C;

then incorporate a crosslinking system;

mix everything to a maximum temperature below 120 ° C. 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 other complementary additives and other 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. 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 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, for example in the form of a rubber profile that can be used directly as a strip of tire rolling. 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. As explained above and illustrated by the following exemplary embodiments, a final step of photo-oxidation of the surface of the tread gives the latter improved adhesion on dry ice as on melting ice. This complementary step may consist of a simple natural exposure to UV-visible radiation or preferably an accelerated artificial aging, for example using one or more lamp (s) emitting in the UV-visible (eg steam lamp mercury, xenon lamp, fluorescent lamp, metal halide lamps), or in an accelerated photoaging chamber which may comprise one or more of said lamps. The rubber composition described above may constitute all or only a part of the tread of the tire according to the invention, in the case of a tread of composite type which would be formed of several rubber compositions of different formulations, it being understood that, in this second case, the previously described composition based on the photocurable liquid polymer resin, is that constituting the surface or extreme surface of the tread portion intended to come into contact with the ground (ice) during the rolling of the tire, in new condition as during its subsequent use.

5. EXAMPLES OF CARRYING OUT THE INVENTION

5.1. Preparation of rubber compositions and treads In this test, two compositions (hereinafter referred to as Cl and C-2) based on diene elastomers (NR and BR blend with higher cis-1,4 bond ratio) are compared. at 95%), essentially reinforced with silica, in which is used or not a photocurable liquid polymer resin fraction associated with PVA microparticles whose median size is between 10 and 200 μιη.

The following tests are carried out in the following manner: the reinforcing inorganic filler (silica), its associated coupling agent, is introduced successively into an internal mixer, the initial vessel temperature of which is approximately 60 ° C. of carbon, the liquid plasticizer, the photocurable liquid polymer resin and the PVA (in solid powder form) in the case of the invention, the diene elastomer (or diene elastomer blending) 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 then sulfur and a sulfenamide-type accelerator are incorporated on an external mixer (homo-fmisseur) at 30 ° C., mixing the whole (productive phase) for a suitable time (for example between 5 and 12 minutes).

The compositions thus obtained are then calendered either in the form of thin sheets or sheets of rubber for the measurement of their physical or mechanical properties, or extruded in the form of treads of winter tires for passenger vehicles. 5.2. Rubber Testing

The rubber compositions thus prepared are then characterized, before and after firing, as indicated below: Mooney plasticity: using an oscillating consistometer as described in the French standard NF T 43-005 (November 1980). The Mooney plasticity measurement is carried out according to the following principle: the raw composition (i.e., before firing) is molded in a cylindrical chamber heated to 100 ° C. After one minute of preheating, the rotor rotates within the test tube at 2 revolutions / minute and the useful torque is measured to maintain this movement after 4 minutes of rotation. Mooney plasticity (ML 1 + 4) is expressed in "Mooney unit" (UM, with 1 UM = 0.83 Newton.meter);

tensile tests: they make it possible to determine the elastic stress and the properties at break. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. We measure in second elongation

(ie, after an accommodation cycle at the expected extension rate for the measurement itself) the nominal secant moduli (or apparent stresses, in MPa) at 10% elongation (denoted M 10) and 100% of elongation (denoted M 100). The breaking stresses (in MPa) and the elongations at break (in%) are also measured. All these tensile measurements are carried out under normal conditions of temperature (23 ± 2 ° C) and humidity (50 ± 5% relative humidity), according to the French standard NF T 40-101 (December 1979);

Shore A hardness: The Shore A hardness of the compositions after curing is assessed according to ASTM D 2240-86;

dynamic properties: they are measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen with a thickness of 4 mm and a section thickness of 400 mm ² ) is recorded, subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz; during a temperature sweep under a fixed stress of 0.7 MPa, the value of tan (δ) observed at 0 ° C. is recorded. It is recalled that, in a manner well known to those skilled in the art, this value of tan (δ) at 0 ° C is representative of the adhesion potential on wet ground (the higher it is, the better the adhesion).

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

The composition Cl is the reference composition, it comprises 80 phr of silica, 5 phr of carbon black and 60 phr of liquid plasticizer, conventionally used as tire tread of the "studless"type; it is devoid of photocurable liquid polymer resin.

The composition C-2 is the composition according to the invention. It differs from the control composition C-1 by the addition of 10 phr of photocurable liquid polymer resin (Mw equal to about 1000 g / mol) and 30 phr of PVA which, combined with a very low level of carbon black (1 phr), induce a high photo-crosslinking ability and a high surface polarity of the composition according to the invention, which is assumed a posteriori - this is at least what the rolling tests seem to show. following - as being particularly favorable for ice grip.

The level of liquid plasticizer was adjusted in the composition of the invention C-2 in order to maintain the rigidity at a level close to that of the control composition C-1 (Shore A hardness between 50 and 55): As is known, a similar stiffness is a desirable condition for a rigorous comparison of ice driving performance.

First, the examination of the different results in Table 2 reveals no degradation of rubber properties for the composition according to the invention (C-2) compared to the control composition (C-1), despite the presence of photocurable liquid resin and PVA powder: the processability in the raw state (Mooney plasticity) is even improved (decreased substantially);

after curing, Shore hardness, modulus in extension and properties at break are little modified;

finally, the value of tan (δ) at 0 ° C is increased, which illustrates an improved wet grip potential.

But it is in fact only during real tests of ice rolling, driven on tires, that reveals the most unexpected result brought by the invention, as is clearly attested by the following tests.

5.3. Tire rolling tests The compositions C-1 and C-2 previously tested are then used as treads for winter tire tires with a radial carcass, respectively denoted Pl (control tires) and P-2 (tires according to the invention). , 205/65 RI 5 conventionally manufactured and identical in all respects, except the rubber compositions constitutive of their tread. All tires are mounted at the front and rear of a motor vehicle, under rated inflation pressure, and are first run on a circuit (about 2000 km), on dry ground , for break-in and start of wear. The vehicle used is a "Honda Civic" vehicle equipped with anti-lock braking system (ABS) and traction control system (TCS system for Traction Control System).

The tires Pl and P-2 are then subjected to a UV treatment (natural exposure to ultraviolet radiation) of a duration of three days to stiffen the surface, at least the extreme surface, of their tread by photocrosslinking of the liquid polymer resin. For this UV treatment, the tires were exposed to the outside, in a static position, in a south orientation, these tires being rotated around their axis by 1/3 of a turn each day, so as to expose their tire strip. rolling in a homogeneous way. Then tires thus lapped and treated with UV are subjected to a test of braking on ice in which one measures the necessary distance to go from 20 to 5 km / h during a brutal longitudinal braking (activated ABS) on a track covered with cold ice (-12 ° C). A value greater than that of the control, arbitrarily set at 100, indicates an improved result, that is to say a shorter braking distance.

The results obtained are reported in Table 3, in relative units, the base 100 being selected for the control tire P1 (as a reminder, a value greater than 100 indicates improved performance). It is found that the tires according to the invention (P-2), whose tread comprises photocurable liquid polymer resin and PVA, show a remarkable and unexpected increase (45%) in braking performance on cold ice.

Table 1

BR with 0.3% of 1-2; 2.7% trans; 97% cis 1-4 (Tg = -104 ° C); natural rubber (peptized);

"Zeosil 1165MP" silica from Rhodia, type "HDS"

(BET and CTAB: approximately 160 m ² / g);

coupling agent TESPT ("Si69" from Evonik);

poly (butadiene-acrylate) ("Nisso PB TEA-1000" from Nippon Soda Co Ltd);

Poval ^® "PVA 505" from Kuraray (DP equal to about 500; degree of hydrolysis of about 75%);

ASTM N234 grade (Cabot company);

MES oil ("Catenex SNR" from Shell);

diphenylguanidine ("Perkacit DPG" from Flexsys);

N-1,3-dimethylbutyl-N-phenylparaphenylenediamine

("Santoflex 6-PPD" from Flexsys);

N-dicyclohexyl-2-benzothiazol sulfenamide

("Santocure CBS" from the company Flexsys). Table 2

Table 3

Pneumatic ⁰ : Pl P-2

Ice braking (-12 ° C) 100 145

Claims

1. A tire whose tread comprises a rubber composition based on at least one diene elastomer, more than 30 phr of a liquid plasticizer, between 50 and 150 phr of a non-black reinforcing filler, optionally black carbon at a content of less than 3 phr, between 5 and 50 phr of a photocrosslinkable liquid polymer resin and between 5 and 70 phr of polyvinyl alcohol microparticles (abbreviated as "PVA").

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.

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

4. A tire 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. A tire 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%.

6. A tire according to claim 5, wherein the polybutadiene is used in a blend with at most 50 phr of natural rubber or synthetic polyisoprene.

7. A tire 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 pce.

8. A tire according to any one of claims 1 to 7, wherein the liquid plasticizer is selected from the group consisting of polyolefinic oils, naphthenic oils, paraffinic oils, DAE oils, MES oils, TDAE oils, PvAE oils, TREE oils, SRAE oils, mineral oils, vegetable oils, ethers plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures of these compounds.

9. A tire according to any one of claims 1 to 8, wherein the carbon black content is less than 2 phr.

10. A tire according to any one of claims 1 to 9, wherein the non-black reinforcing filler content is between 60 and 120 phr, preferably between 70 and 120 phr.

100 pce.

A tire according to any one of claims 1 to 10, wherein the non-black reinforcing filler is an inorganic filler, preferably silica.

A tire according to any of claims 1 to 11, wherein the photocurable liquid polymer resin is selected from the group consisting of acrylate, methacrylate, epoxide, oxetane, unsaturated polyester, vinyl ether, vinylester and mixtures of such resins. .

The tire of claim 12, wherein the photocurable liquid polymer resin is an acrylate or methacrylate resin.

A tire according to any one of claims 1 to 13, wherein the photocurable liquid polymer resin is a diene polymer, preferably a polybutadiene or a polyisoprene.

15. A tire according to claim 14, wherein the photocurable liquid polymer resin is a poly (butadiene acrylate) or a poly (butadiene methacrylate).

16. A tire according to any one of claims 1 to 15, wherein the PVA microparticle content is between 10 and 50 phr.

17. Pneumatic tire according to any one of claims 1 to 16, wherein the median size of the PVA microparticles is between 50 and 1000 μιη, preferably between 100 and 800 μιη.