EP2582746A1 - Pneumatic tyre, the belt of which is provided with a coating rubber that reduces rolling noise - Google Patents

Abstract

Radial tyre (1) for a motor vehicle, comprising: o a crown (2) comprising at least one tread (3) and one crown reinforcement or belt (7); o two inextensible beads (4), two side walls (5) connecting the beads (4) to the tread (3), a carcass reinforcement (6) passing into the two side walls (5) and anchored in the beads (4); o the belt (7), positioned circumferentially between the tread (3) and the carcass reinforcement (6), comprising textile or metal reinforcements coated in a rubber composition (8) referred to as a "belt coating rubber", characterized in that this belt coating rubber, capable of reducing the rolling noise of the tyre, comprises at least one diene elastomer and, as a high-density filler, more than 50 phr of particles referred to as high-density particles having a density of greater than 4 g/cm³.

Description

 PNEUMATIC BANDAGE WHOSE BELT IS PROVIDED

 OF A COATING GUM REDUCING THE ROAD NOISE 1. FIELD OF THE INVENTION

The invention relates to tires for motor vehicles and reinforcements of the crown reinforcement, also called "belts", of these tires, as well as rubber compositions usable for the manufacture of such tires.

It is more particularly related to the rubber compositions used in the crown ("crown") of tires with radial carcass reinforcement, to reduce the noise emitted by these tires during rolling.

2. STATE OF THE ART

It is known that the noise emitted by a rolling tire originates, inter alia, from the vibrations of its structure consecutive to the contact of the tire with the irregularities of the roadway, also causing a generation of various acoustic waves. The whole thing finally comes in the form of noise, both inside and outside the vehicle. The amplitude of these various manifestations is dependent on the vibration modes of the tire itself but also on the nature of the coating on which the vehicle moves. The frequency range corresponding to the noise generated by the tires typically ranges from about 20 to about 4000 Hz.

With regard to the perceived noise inside the vehicle, two modes of sound propagation coexist: - the vibrations are transmitted by the wheel center, the suspension system, the transmission to finally generate noise in the passenger compartment; this is called solid-state transmission, which is generally dominant at low frequencies of the spectrum (up to about 400 Hz);

the acoustic waves emitted by the tire are directly propagated by air inside the vehicle, the latter acting as a filter; this is referred to as airborne transmission, which generally dominates in the high frequencies (about 600 Hz and beyond). The so-called "road noise" refers rather to the perceived overall level in the vehicle and in a frequency range up to 2000 Hz. The noise called "road noise" refers to the annoyance due to the resonance of the inflation cavity of the tire envelope.

With regard to the noise emitted outside the vehicle, the various interactions between the tire and the road surface, the tire and the air, which will cause discomfort to the residents of the vehicle when the latter is driving on a road, are relevant. floor. There are also in this case several sources of noise such as the so-called "indentation" noise due to the impact of roughness of the road in the contact area, the noise called "friction" essentially generated in the output of the 'contact area, the noise' says of sculpture 'due to the arrangement of the elements of sculpture and to the resonance in the various furrows. The frequency range concerned by these external noises here typically corresponds to a range of about 300 to 3 000 Hz.

3. BRIEF DESCRIPTION OF THE INVENTION

However, the Applicants have discovered in their research a specific rubber composition which, used as a coating rubber reinforcements (textile and / or metal) of the tire belt, has improved sound barrier properties in a range of frequency between 500 and 2000 Hz, and is therefore likely to contribute to reduce the noise emitted both inside and outside of vehicles when driving tires.

Accordingly, a first object of the invention relates to a radial tire for a motor vehicle, comprising: a top (2) comprising a tread (3) and a crown reinforcement (7);

 two non-extensible beads (4), two sidewalls (5) connecting the beads (4) to the tread (3), a carcass reinforcement (6) passing through the two sides (5) and anchored in the beads (4). );

o the crown reinforcement or belt (7) disposed circumferentially between the tread (3) and the carcass reinforcement (6), comprising textile or metal reinforcements embedded in a rubber composition called "coating gum characterized in that the belt-coating gum comprises at least one diene elastomer and, as a high-density filler, more than 50 phr of so-called high-density particles whose density is greater than 4 g / cm ³ . The tires of the invention are particularly intended to equip tourism-type motor vehicles, including 4x4 vehicles (four-wheel drive) and SUV vehicles ("Sport Utility Vehicles"), two-wheel vehicles (including motorcycles) as industrial vehicles chosen in particular from vans and "heavy goods vehicles" (ie, metro, buses, road transport vehicles such as trucks, tractors, trailers, off-the-road vehicles such as agricultural or civil engineering vehicles).

The invention relates to the above tires both in the green (i.e., before firing) and the fired (i.e., after crosslinking or vulcanization) state.

The invention as well as its advantages will be readily understood in the light of the description and the following exemplary embodiments, as well as the single FIGURE relating to these examples, which schematizes, in radial section, an example of a radial tire according to FIG. invention.

4. DETAILED DESCRIPTION OF THE INVENTION

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

The abbreviation "pce" (usually "phr" in English) 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 from more than a to 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 from a to b (i.e., including the strict limits a and b). The tire of the invention therefore has the essential characteristic of being provided with a belt or crown reinforcement whose reinforcements, textile and / or metal, are embedded in a specific elastomeric composition or gum coating (called coating gum of belt) which comprises at least one diene elastomer and, as high density filler, more than 50 phr of so-called high density particles whose density is greater than 4 g / cm ³ , optionally a reinforcing filler and other optional additives , components which will be described in detail below.

4.1 - Formulation of Belt Coating Gum 4.1.a. Diene elastomer

The diene elastomers can be classified in known manner into two categories: those known as "essentially unsaturated" and those known as "essentially saturated". For example, butyl rubbers, copolymers of dienes and alpha-olefins EPDM type fall into the category of essentially saturated diene elastomers, having a rate of diene origin units which is low or very low, always less than 15% (% in moles) 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 polybutadienes (BR) (in particular those having a cis-1,4 ratio greater than 90%), polyisoprenes (NR), natural rubber (NR), butadiene copolymers, isoprene copolymers (other than IIR) 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.

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

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 between 4%> and 65%>, a content of trans-1,4 bonds of between 20%> and 80%>, copolymers of butadiene-isoprene 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) of -80 ° C to -40 ° C, isoprene-styrene copolymers and especially those having a styrene content of between 5%> and 50% > by weight and a Tg between -50 ° C and -10 ° 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% are especially suitable, an isoprene content of between 15% and 50% by weight. %> 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 particular and preferred embodiment of the invention, the belt-coating gum comprises, as diene elastomer, 50 to 100 phr of natural rubber or of a synthetic polyisoprene, the latter being able to be combined or no to a second diene elastomer. This second diene elastomer is preferably chosen from the group consisting of polybutadienes, butadiene copolymers and mixtures of these elastomers, in particular from the SBR copolymers (SBR solution or emulsion) with more preferably a Tg greater than -40 ° C. ( in particular in a range of -30 ° C to + 30 ° C) or polybutadienes (BR) more preferably having a cis-1,4 bond ratio greater than 90%> (in particular greater than 95%>). According to another more particular and preferred embodiment, the belt coating gum comprises, as diene elastomer, from 50 to 80 phr of natural rubber or synthetic polyisoprene with 20 to 50 phr of an SBR copolymer having more preferably, a Tg greater than -40 ° C (in particular in a range of -30 ° C to + 30 ° C) or a polybutadiene (BR) more preferably having a cis-1,4 bond ratio greater than 90 %>, more preferably still greater than 95%. According to another particular and preferred embodiment, the diene elastomer used is a ternary mixture of NR (or IR), BR and SBR. Preferably, in the case of such cuts, the composition comprises from 40 to 80 phr of NR (or IR) and from 20 to 60 phr of BR and SBR.

The diene elastomers previously described could be associated, in a minor amount, with synthetic elastomers other than dienes, or even polymers other than elastomers, for example thermoplastic polymers. 4. I .B. High density charge

The belt wrapping rubber of the tire of the invention has the essential characteristic of comprising more than 50 phr, preferably between 50 and 600 phr, of a high density filler, the density or density of the particles of which is greater than at 4 g / cm ³ , preferably greater than 4.5 g / cm ³ , more preferably still greater than 5 g / cm ³ .

Such high density fillers are well known to those skilled in the tire industry, they have been used essentially until now in tire treads, as a replacement or complement to less dense conventional fillers such as silica or carbon black. in an attempt to improve some of their properties of use or compromise of properties such as, for example, rolling resistance, wear resistance or adhesion (see in particular US Pat. No. 6,734,245 and US Pat. No. 6,838,495).

The high density charge used may be in the form of isometric or anisometric particles. It is preferably of micrometric size, that is to say that it is in the form of "microparticles" whose size is by definition greater than one micrometer. Preferably, these microparticles have a median diameter (or a median size if the particles are not substantially spherical), denoted hereinafter "D", which is between 1 and 500 μιη; more preferably, the median diameter D of the particles is between 2 and 400 μιη, in particular between 2 and 200 μιη.

The high density charge is preferably in the form of a powder. According to another preferred embodiment (whether in powder form or not), it is in the form of solid particles, but particles or hollow beads with high density could also be used.

The high density charge rate is more preferably between 50 and 500 phr. Below the minimum indicated, the technical effect is insufficient, while beyond the maximum recommended, we risk exposing ourselves to problems of increase of the module, weakening of the composition, as well as difficulties of dispersion of the charge and processability, not to mention a significant penalty for hysteresis. For all these reasons, this rate is more particularly included in a range of 70 to 450 phr, especially in a range of 100 to 450 phr. The high density charge is preferably metallic (that is to say based on metal or a metal derivative); it is preferably constituted by metals such as alkaline-earth metals, transition metals or rare earths, or else by derivatives of such metals such as, for example, sulphates, carbonates, sulphides, oxides and / or hydroxides, particularly by oxides such metals.

In the case of alkaline earth metals, mention will be made in particular of barium and strontium. In the case of transition metals, iron, copper, tin, zinc, molybdenum, silver, niobium, tungsten, rhenium, tantalum, hafiiium, bismuth and manganese will be mentioned in particular. . Finally, in the case of rare earths, mention will in particular be made of lanthanum, neodymium, cerium or samarium.

More preferably, the metal of the high-density filler, whether it is in the form of a metal or of a metal derivative such as an oxide, is chosen from the group consisting of iron, copper, tin, nickel and the like. Zinc, Tungsten, Bismuth, Cerium, Neodymium and mixtures of these metals.

These metals and / or metal derivatives, particularly metal oxides, are preferably chosen from those whose density is greater than 5 g / cm ³ . By way of examples of particularly preferred metal oxides, mention may be made especially of those selected from the group consisting of Fe ₂ O ₃ (density 5.1 g / cm ³ ), ZnO (5.7 g / cm ³ ), CuO ( 6.3 / cm ³ ), Sn0 ₂ (7.0 g / cm ³ ), WO ₃ (7.2 g / cm ³ ), CeO ₂ (7.3 g / cm ³ ), Nd ₂ O ₃ (7 , 2 g / cm ³ ), Bi ₂ O ₃ (8.9 g / cm ³ ) and mixtures of such oxides.

These metal oxides are well known and commercially available, for example from Nakalai Tesque Inc., Toho Zinc Co, Nihon Kagaku Sangyo Co., Kanto Kagaku, Taiyo Koko Co., American Elements.

The introduction of the high density filler into the elastomeric composition can be carried out according to various known methods, for example by solution mixing, by mass mixing in an internal mixer, or by extrusion mixing.

For the analysis of the particle size and the calculation of the median diameter of the particles, in particular microparticles, of the high-density filler, various known methods are applicable, for example by laser diffraction (for example according to ISO-8130-13 or JIS K5600 standard). -9- 3); it is also easy to use a grain size analysis by sieving mechanical through sieves of different diameters. The median diameter (or median size) is finally calculated in a well-known manner from the histogram of the particle size distribution. 4.1. VS . Reinforcing charge

The belt coating rubber may also comprise any type of reinforcing filler known for its ability to reinforce a rubber composition that can be used for the manufacture of tires, for example an organic filler such as carbon black, a reinforcing inorganic filler such as only silica with which is associated in a known manner a coupling agent, or a mixture of these two types of filler.

Such a reinforcing filler 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.

The density of this reinforcing filler is generally less than 3 g / cm ³ , in particular less than 2.5 g / cm ³ .

Preferably, the content of total reinforcing filler (in particular silica or carbon black or a mixture of silica and carbon black) is greater than 20 phr, in particular between 20 and 100 phr. Above 100 phr, there is a risk of increasing the hysteresis and therefore the rolling resistance of the tires. For this reason, the total reinforcing filler content is more preferably within a range of 30 to 90 phr.

As carbon blacks are suitable all carbon blacks conventionally used in tires or their treads (so-called pneumatic grade black). Among the latter, the reinforcing carbon blacks of the 100, 200, 300 series, or 500, 600 or 700 series blacks (ASTM grades), for example blacks NI 15, N134, N234, N326, will be mentioned more particularly. N330, N339, N347, N375, N550, N683, N772. The carbon blacks could for example already be incorporated into the diene elastomer, in particular isoprene 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 sometimes "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 tires, 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 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 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" 7005 silicas of the Degussa company, the "Zeosil" 1165MP, 1135MP and 1115MP silicas of the Rhodia company. silica "Hi-Sil" EZ150G from the company PPG, the silicas "Zeopol" 8715, 8745 and 8755 of the Huber Company. 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 di-substituted 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 alkylene, especially a C ₁ -C ₄ alkylene radical; , 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₎ silyl alkyl (Ci-C ₄ )), such as polysulfides of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl). Among these compounds, bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, of formula [(C ₂ H ₅ O) 3 Si (CH ₂ ) ₃ S ₂ ] ₂ or bis (triethoxysilylpropyl) disulphide is especially used. ), 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 WO2007 / 061550, or else silanes or POS bearing azo functional groups. dicarbonyl, 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.

In the noise-reducing belt-coating gum, when it is reinforced by an inorganic filler such as silica, the content of coupling agent is preferably between 2 and 15 phr, more preferably between 3 and 12 phr.

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

4. I .D. Various additives The belt coating gum may also comprise all or part of the usual additives normally used in tire rubber compositions, such as, for example, protective agents such as chemical antioxidants, anti-oxidants, plasticizers or plasticizers. extension oils, whether the latter are of aromatic or non-aromatic nature, especially very weak or non-aromatic oils, for example of the naphthenic or paraffmic type, with high or preferably low viscosity, MES or TDAE oils, high Tg hydrocarbon plasticizing resins, agents facilitating processing (processability) of the compositions in the green state, tackifying resins, reinforcing resins (such as resorcinol or bismaleimide), methylene acceptors or donors such as hexamethylenetetramine or hexamethoxymethylmelamine, a crosslinking system based on either sulfur or donor s of sulfur and / or peroxide and / or bismaleimides, vulcanization accelerators, vulcanization activators, known adhesion promoter systems of the metal salt type, for example salts (eg acetylacetonates, abietates, naphthenates, tallates) cobalt, nickel or lanthanide such as neodymium. In particular, it has been found that hydrocarbon plasticizing resins with a high Tg, preferably greater than 20 ° C., more preferably greater than 30 ° C. (measured according to ASTM D3418-1999), are advantageously usable because they can make it possible to further improve the technical effect of "sound barrier" provided by the belt coating gum previously described.

Hydrocarbon resins (it is recalled that the term "resin" is reserved by definition for a solid compound at 23 ° C.) are polymers well known to those skilled in the art, which can be used in particular as plasticizers or tackifying agents in matrices. polymer. They have been described, for example, in the book "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), chapter 5 of which is devoted their applications, in particular pneumatic rubber (5.5 "Rubber Tires and Mechanical Goods"). They can be aliphatic, aromatic, aliphatic / aromatic type that is to say based on aliphatic and / or aromatic monomers, hydrogenated or not. 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, their number-average molecular weight (Mn) is between 400 and 2000 g / mol, in particular between 500 and 1500 g / mol; their polymolecularity index (Ip) is preferably less than 3, especially less than 2 (booster: Ip = Mw / Mn with Mw weight average molecular weight). 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").

By way of examples of above-mentioned hydrocarbon plasticizing resins, mention may be made in particular of homopolymer or copolymer resins of cyclopentadiene or dicyclopentadiene, resins of terpene homopolymers or copolymers (eg alphapinene, betapinene, dipentene or polylimonene), resins of homopolymers or copolymers of C5 or C9 cut, for example C5 / styrene cut copolymer or C5 cut / C9 cut copolymer.

The content of hydrocarbon resin is preferably between 5 and 60 phr, especially between 5 and 50 phr, more preferably still within a range of 10 to 40 phr. The belt coating gum 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 likely in 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 ability to 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. I .E. Production of compositions

The rubber compositions forming the belt coating rubber are manufactured in suitable mixers, for example using two successive preparation phases according to a general procedure well known to those skilled in the art: a first thermomechanical working or mixing phase ( sometimes referred to as a "non-productive" phase) at a 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 mechanical working phase (sometimes referred to as a "productive" phase) at a lower temperature, typically less than 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which the crosslinking or vulcanization system is incorporated.

A process which can be used for the manufacture of such rubber compositions comprises, for example, and preferably the following steps: - incorporating in a mixer, to the diene elastomer or to the mixture of diene elastomers, the high density filler and the possible other filler reinforcing, 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 up to a maximum temperature below 120 ° C; extruding or calendering the resulting rubber composition.

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; all 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.

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

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded in the form of a rubber profile that can be used directly as a coating gum ( or calendering) textile and / or metal reinforcements in one or more webs (s) belt.

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.

Preferably, the belt coating gum has, in the vulcanized state (ie, after curing), a density or density which is greater than 1.4 g / cm ³ , in particular between 1, 5 and 3. 0 g / cm ³ . Its secant modulus in extension (noted E10) is preferably less than 30 MPa, more preferably between 3 and 30 MPa, in particular in a range of 4 to 20 MPa. This secant modulus in extension (E10) is the tensile modulus measured in second elongation (ie, after an accommodation cycle) at 10% elongation (according to ASTM D412-1998, specimen "C"), this module being the module secant "true" that is to say, brought back to the actual section of the specimen (normal temperature and humidity conditions according to ASTM D 1349-1999).

5. EXEMPLARY EMBODIMENT OF THE INVENTION

The rubber composition described above is therefore used, in the radial tire of the invention, as a coating gum of the crown reinforcement or belt disposed between the tread and the carcass reinforcement.

It should therefore be understood that this belt-coating rubber can constitute all or part of the rubber matrices coating the textile and / or metal reinforcements present in the belt itself of the tire, for example as a coating or calendering rubber for frettage top plies, top protection plies or working top plies, all constituting said belt.

The thickness of this belt coating rubber is preferably between 0.1 and 2 mm, especially in a range of 0.2 to 1.5 mm. The single appended figure shows in radial section, very schematically (in particular without respecting a specific scale), an example of a pneumatic tire for a motor vehicle with radial carcass reinforcement, according to the invention.

In this figure, the tire (1) schematically comprises a vertex (2) surmounted by a tread (3) (for simplicity, including a very simple sculpture), two inextensible beads (4) in which is anchored a frame carcass (6). The top (2), joined to said beads (4) by two sidewalls (5), is known per se reinforced by a crown reinforcement or "belt" (7) at least partly textile and / or metallic and radially external relative to the carcass reinforcement (6).

More specifically, a tire belt generally consists of at least two superposed belt plies, sometimes called "working" plies or "crossed" plies, whose reinforcing elements or "reinforcements" are arranged substantially parallel to one another inside a ply, but crossed from one ply to the other, that is to say inclined, symmetrically or otherwise, with respect to the median circumferential plane, of an angle which is generally between 10 ° and 45 ° depending on the type of tire considered. Each of these two crossed plies is made of a rubber matrix sometimes called "calendering rubber" coating the reinforcements. In the belt, the crossed plies can be supplemented by various other plies with reinforcements; mention will be made, in particular, of so-called "protection" sheets designed to protect the rest of the belt from aggressions external, perforations, or so-called "shrink" plies comprising reinforcements oriented substantially in the circumferential direction (so-called "zero degree" plies), whether radially external or internal to the crossed plies. For reinforcement of the above belts, in particular of their crossed plies, protective plies or hooping plies, reinforcement is generally used in the form of steel cables (cords) or textile cords (textile cords). ") consisting of thin wires assembled together by wiring or twisting The carcass reinforcement (6) is here anchored in each bead (4) by winding around two rods (4a, 4b), the overturning (6a, 6b) this reinforcement (6) being for example disposed towards the outside of the tire (1) which is represented here mounted on its rim (9), the carcass reinforcement (6) consists of at least one ply reinforced by radial textile cables, that is to say that these cables are arranged substantially parallel to each other and extend from one bead to the other so as to form an angle of between 80 ° and 90 ° with the plane medial circumferential (plane perpendicular to the axis of rotation of the tire which is located halfway between the two beads 4 and passes through the middle of the crown reinforcement 7). Of course, this tire (1) further comprises, in known manner, a layer (10) of inner rubber (commonly called "inner liner" or "inner liner") which defines the radially inner face of the tire and which is intended to protect the tire. carcass ply of air diffusion from the interior space to the tire.

This tire example (1) of the attached figure is characterized in that the metal and / or textile reinforcements, for all or part of them, of the belt (7) are embedded, embedded in a rubber matrix (or calendering gum) constituted by the belt coating gum (8) which has been described in detail previously.

This belt-coating gum (8) may constitute all or part of the rubber matrix of one or more tissues constituting the belt of the tire of the invention, in particular a protective crown ply, a crown ply hooping or even and particularly working top plies. Thanks to its improved sound barrier properties, it is likely to help reduce the noise emitted both inside and outside of vehicles when driving tires.

Claims

Radial tire (1) for a motor vehicle, comprising: o a crown (2) comprising at least one tread (3) and a crown reinforcement (7);

 two non-extensible beads (4), two sidewalls (5) connecting the beads (4) to the tread (3), a carcass reinforcement (6) passing through the two sides (5) and anchored in the beads (4). );

o the belt (7) disposed circumferentially between the tread (3) and the carcass reinforcement (6), comprising textile or metal reinforcements embedded in a rubber composition called "belt coating rubber", characterized in that said belt coating gum comprises at least one diene elastomer and, as a high-density filler, more than 50 phr of so-called high density particles having a density of greater than 4 g / cm ³ .

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.

Tire according to claim 2, wherein the belt coating rubber comprises 50 to 100 phr of natural rubber or synthetic polyisoprene.

A tire according to any one of claims 1 to 3, wherein the belt coating gum comprises 0 to 50 phr of at least one second diene elastomer other than natural rubber or synthetic polyisoprene.

The tire of claim 4, wherein the second diene elastomer is selected from the group consisting of polybutadienes, butadiene copolymers and mixtures of these elastomers.

6. A tire according to claim 4 or 5, wherein the level of synthetic rubber or synthetic polyisoprene is in a range of 50 to 80 phr and the second diene elastomer level is in a range of 20 to 50 phr.

7. A tire according to any one of claims 1 to 6, wherein the density of the high density particles is greater than 4.5 g / cm ³ .

The tire of claim 7, wherein the density of the high density particles is greater than 5.0 g / cm ³ .

9. A tire according to any one of claims 1 to 8, wherein the high density particles are microparticles.

The tire of any one of claims 1 to 9, wherein the high density particles are metal particles or a metal derivative.

The tire of claim 10, wherein the metal is selected from the group consisting of Iron, Copper, Etam, Zinc, Tungsten, Bismuth, Cerium, Neodymium, and mixtures of these metals.

The tire of claim 10 or 11, wherein the high density particles are metal oxide particles.

Tire according to claim 12, wherein the metal oxide is selected from Fe ₂ O ₃ , ZnO, CuO, SnO ₂ , WO ₃ , CeO ₂ , Nd ₂ O ₃ , Bi ₂ O ₃ and mixtures of such oxides. .

14. A tire according to any one of claims 1 to 13, wherein the high density particles are in the form of powder.

15. A tire according to any one of claims 1 to 14, wherein the belt coating rubber further comprises a reinforcing filler.

16. A tire according to claim 15, wherein the reinforcing filler comprises silica or carbon black or a mixture of silica and carbon black.

17. A tire according to claim 15 or 16, wherein the reinforcing filler content in the belt coating rubber is between 20 and 100 phr.

A tire according to any one of claims 1 to 17, wherein the belt coating gum has, in the vulcanized state, a density which is greater than 1.4 g / cm ³ .

The tire of claim 18, wherein the belt coating gum has a vulcanized state density of 1.5 to 3.0 g / cm ³ .