WO2014131672A1

WO2014131672A1 - Tyre, the beads of which are provided with a protective compound that reduces road noise

Info

Publication number: WO2014131672A1
Application number: PCT/EP2014/053229
Authority: WO
Inventors: Boyong XUE; Bozena Voge; Salvatore Pagano
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2013-02-28
Filing date: 2014-02-19
Publication date: 2014-09-04
Also published as: FR3002540A1; FR3002540B1

Abstract

Motor vehicle tyre (1) comprising at least: a crown (2) comprising at least a tread (3), a crown reinforcement or belt (4) arranged circumferentially between the tread (3) and a carcass reinforcement (5); two beads (6), two sidewalls (7) connecting the beads (6) to the tread (3), the carcass reinforcement (5) running through the two sidewalls (7) and being anchored in each bead (6); the two beads (6) containing a layer of rubber composition (8) referred to as the "bead cushioning compound" which is intended to come into contact with a rim (9) on which the tyre is intended to be mounted, characterized in that this bead cushioning compound (8), able to reduce road noise, contains at least: 70 to 100 phr of butyl rubber; optionally 0 to 30 phr of another diene elastomer, - over 50 phr of a reinforcing filler; - over 30 phr of a hydrocarbon-containing plasticising resin with a glass transition temperature in excess of 20°C.

Description

BANDAGE IN WHICH THE BOURRELETS ARE PROVIDED WITH A PROTECTIVE MIXTURE REDUCING THE NOISE OF ROLLING 1. FIELD OF THE INVENTION

The invention relates to tires, pneumatic or non-pneumatic, for motor vehicles and architectures of the bead zones of these bandages, as well as rubber compositions usable for the manufacture of such bandages.

It relates more particularly to the rubber compositions used in the beads and capable of reducing the noise emitted by these tires during the running of these motor vehicles.

2. STATE OF THE ART

It is known that the noise emitted by a rolling tire is due, among other things, to the vibrations of its structure resulting from the contact of the tire with the unevenness of the road surface, 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 different manifestations is dependent on the band's own modes of vibration but also on the nature of the coating on which the vehicle is moving. The frequency range corresponding to the noise generated by the bandages 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 "noise noise" refers rather to the perceived overall level in the vehicle and in a frequency range up to 2000 Hz. The noise called "cavity noise" refers to the annoyance due to the resonance of the inflation cavity of the tire casing. With regard to the noise emitted outside the vehicle, the various interactions between the bandage and the road surface, the bandage and the air, which will cause discomfort to the residents of the vehicle when it is rolling 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 so-called "sculpture" noise due to the arrangement of the sculptural elements and 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 during their research a specific rubber composition which, used as a bead protector mixture, has improved sound barrier properties in a frequency range between 80 and 800 Hz, and which is therefore likely to help to reduce the noise emitted both inside and outside the vehicles when rolling tires.

Accordingly, a first object of the invention relates to a tire for a motor vehicle, comprising: an apex (2) comprising at least one tread (3), a crown reinforcement or belt (4) arranged circumferentially between the tread band, bearing (3) and a carcass reinforcement (5);

- two beads (6), two flanks (7) connecting the beads (6) to the tread

(3), the carcass reinforcement (5) passing through both flanks (7) and being anchored in each bead (6);

the two beads (6) comprising a layer of rubber composition (8) called "bead protective compound" intended to come into contact with a rim (9) on which the tire is intended to be mounted, characterized in that bead protector mixture (8) comprises at least:

70 to 100 phr of butyl rubber;

optionally 0 to 30 phr of another diene elastomer; - more than 50 phr of a reinforcing filler;

more than 30 phr of a hydrocarbon plasticizing resin having a glass transition temperature (Tg) which is greater than 20 ° C. The bandages 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 (including motorcycles) as vehicles. 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 bandages both in the green (i.e., before baking) and the baked (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 FIGS. 1 and 2 relating to these examples, which diagrammatically show, in radial cross-section, an example of a bandage conforming 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 indistinctly rubber, both terms being considered synonymous here), 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 bandage of the invention therefore has the essential characteristic of comprising two beads or beads whose at least the contact surface with the rim on which this tire may be mounted is formed by a layer of rubber composition so-called "bead protector mix" or "bead protector mix", of specific composition, which comprises at least: - 70 to 100 phr of a (at least one, that is to say one or several) butyl rubber; optionally 0 to 30 phr of a (at least one, that is to say one or more) other diene elastomer, different from a butyl rubber;

more than 50 phr of one (at least one, that is to say one or more) reinforcing filler;

- more than 30 phr of a (at least one, that is to say one or more) hydrocarbon plasticizing resin having a Tg greater than 20 ° C.

This specific formulation is described in detail below. 4.1. Butyl rubber

By elastomer (or "rubber", both of which are considered synonymous) of the "diene" type, must be understood, in known manner, an elastomer derived at least in part (ie, a homopolymer or a copolymer) from diene monomers (ie , monomers carrying two carbon-carbon double bonds, whether they are conjugated or not).

The protective bead protector according to the invention has the essential characteristic of comprising, as diene elastomer, 70 to 100 phr of butyl rubber. This butyl rubber can be used alone or in combination with one or more other diene elastomer (s).

By butyl rubber, is meant in known manner a copolymer of isobutylene and isoprene (abbreviated IIR), and the halogenated versions, preferably chlorinated (CIIR) or brominated (BIIR), of this type of copolymer.

A preferred embodiment of the invention consists in using from 80 to 100 phr, in particular from 90 to 100 phr of butyl rubber, the optional supplement (from 0 to 20 phr, in particular from 0 to 10 phr) consisting of at least one other diene elastomer, different from a butyl rubber, more preferably from another diene elastomer selected from the group consisting of natural rubber, synthetic polyisoprenes, styrene-butadiene copolymers and mixtures thereof.

The latter is preferentially chosen from the group of diene elastomers consisting of polybutadienes (BR), synthetic polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers (other than butyl) and mixtures of these elastomers. Such copolymers are for example selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-copolymers butadiene-styrene (SBIR) and mixtures of such copolymers. Butyl rubber is preferably associated with an isoprene elastomer, ie a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), polyisoprenes synthesis (IR), the various isoprene copolymers (by definition other than butyl) or a mixture of these elastomers. Among the isoprene copolymers, mention will be made in particular of isoprene-styrene copolymers (SIR), isoprene-butadiene copolymers (BIR) or isoprene-butadiene-styrene copolymers (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; of these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used. According to another preferred embodiment, the other diene elastomer may also be an SBR elastomer.

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

The physical state under which the reinforcing filler is present is indifferent whether in the form of powder, microbeads, granules, beads or any other suitable densified form. It consists preferentially of nanoparticles whose average size (in mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm.

Preferably, the level of reinforcing filler (in particular silica or carbon black or a mixture of silica and carbon black) is between 50 and 150 phr. A content greater than 50 phr, preferably greater than 60 phr, is favorable to good mechanical strength; above 150 phr, there is a risk of excessive stiffness of the rubber layer and increased hysteresis. For these reasons, the level of reinforcing filler is more preferably between 50 and 120 phr, in particular from 70 to 100 phr.

Suitable carbon blacks are all the carbon blacks conventionally used in bandages or their bead zones (so-called pneumatic grade blacks), such as, for example, reinforcing carbon blacks of the series (ASTM grades) 100, 200, 300, or more preferentially blacks of higher series, in particular 500, 600, 700 or 800 (as for example the blacks N550, N683, N774). The carbon blacks could for example already be incorporated into a diene elastomer, in particular isoprene in the form of a masterbatch (see for example applications WO 97/36724 or WO 99/16600). According to another preferred embodiment, the bead-protecting compound comprises between 50 and 100 phr of carbon black, in particular of a carbon black selected from the group consisting of series blacks (ASTM) 500, 600, 700, 800 and their mixtures. "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 bandages, in other words able to replace, in its function of reinforcement, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

Suitable reinforcing inorganic fillers are mineral fillers of the siliceous type, in particular silica (SiO ₂ ). The silica used 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. In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in 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.

Particularly suitable, without the following definition being limiting, polyisulfide 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);

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

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

in which:

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

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

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

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

In the bead protecting mixture, when it is reinforced with 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.

4.3. Hydrocarbon plasticizing resin The bead protective mixture also comprises, as solid plasticizer (at 23 ° C), a plasticizing hydrocarbon resin whose Tg is greater than 20 ° C.

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 based on petroleum or not (if so, also known as petroleum resins). They are preferably exclusively hydrocarbon-based, that is to say they contain only carbon and hydrogen atoms.

In a known manner, these hydrocarbon resins can also be described as thermoplastic resins in that they soften by heating and can thus be molded. They can also be defined by a point or softening point, the temperature at which the product, for example in the form of powder, agglutinates; this datum tends to replace the melting point, which is rather poorly defined, of resins in general. The softening temperature of a hydrocarbon resin is generally about 40 to 60 ° C. higher than the value of Tg. Preferably, the plasticizing hydrocarbon resin has at least one, more preferably all, of the following characteristics: a Tg greater than 30 ° C (more preferably between 40 and 100 ° C);

a softening point above 70 ° C, in particular between 80 ° C and 150 ° C;

a number-average molecular weight (Mn) of between 400 and 2000 g / mol (more preferentially between 500 and 1500 g / mol);

a polymolecularity index (Ip) of less than 3, more preferably less than 2 (booster: Ip = Mw / Mn with Mw weight average molecular weight). The Tg of the resin is measured by DSC (Differential Scanning Calorimetry) according to ASTM D3418. The softening point is measured according to ISO 4625 ("Ring and Bail" method). The macrostructure (Mw, Mn and Ip) 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 columns "WATERS" in series ("STYRAGEL" HR4E, HR1 and HR0.5); differential refractometer detection ("WATERS 2410") and its associated operating software ("WATERS EMPOWER").

According to a particularly preferred embodiment, the plasticizing hydrocarbon resin is chosen from the group consisting of cyclopentadiene homopolymer or copolymer resins (abbreviated to CPD), dicyclopentadiene homopolymer or copolymer resins (abbreviated to DCPD), terpene homopolymer or copolymer resins, homopolymer or C5 cut copolymer resins, homopolymer or C9 cut copolymer resins, alpha-methyl-styrene homopolymer or copolymer resins and mixtures thereof. resins.

Among the above copolymer resins are more preferably used those selected from the group consisting of (D) CPD / vinylaromatic copolymer resins, (D) CPD / terpene copolymer resins, copolymer resins (D) CPD / C5 cut, (D) CPD / C9 cut copolymer resins, terpene / vinylaromatic copolymer resins, terpene / phenol copolymer resins, C5 / vinylaromatic cut copolymer resins, C9 / vinylaromatic cut copolymer resins, and mixtures of these resins.

The term "terpene" here combines in a known manner the alpha-pinene, beta-pinene and limonene monomers; preferably, a limonene monomer is used which is in a known manner in the form of three possible isomers: L-limonene (laevorotatory enantiomer), D-limonene (dextrorotatory enantiomer), or the dipentene, racemic of the dextrorotatory and levorotatory enantiomers. . Suitable vinylaromatic monomers are, for example, styrene, alpha-methylstyrene, ortho-, meta-, para-methylstyrene, vinyltoluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, any vinylaromatic monomer from a C ₉ cut (or more generally from a C ₈ to C ₁₀ cut). Preferably, the vinyl-aromatic compound is styrene or a vinylaromatic monomer derived from a C ₉ cut (or more generally from a C ₈ to C ₁₀ cut). Preferably, the vinylaromatic compound is the minor monomer, expressed as a mole fraction, in the copolymer under consideration.

All the resins above are well known and commercially available, for example sold by DRT under the name "Dercolyte" for polylimonene resins, by the company Neville Chemical Company under the name "Super Nevtac" or by Kolon under "Hikorez" name for C ₅ / styrene resins or C ₅ / C ₉ cut resins or ExxonMobil under the name "Escorez" (mixtures of aromatic and / or aliphatic resins). The amount of hydrocarbon resin in the bead protector mixture is preferably between 30 and 100 phr, more preferably between 35 and 70 phr.

4.4. Various additives

The bead protector mixture may also comprise all or part of the usual additives normally used in bandage rubber compositions, such as, for example, protective agents such as chemical antioxidants, anti-oxidants and plasticizing oils, which are of aromatic or nonaromatic nature, in particular very slightly aromatic or non-aromatic oils, for example naphthenic oils (at low or high viscosity, in particular hydrogenated or not), paraffinic oils, MES oils (Medium Extracted Solvates), DAE (Distillate Aromatic Extracts), Treated Distillate Aromatic Extracts (RAA), Residual Aromatic Extract (TREE), Residual Aromatic Extract oils (SRAE), mineral oils, vegetable oils, ethers, ester plasticizers , phosphates, sulfonates, reinforcing resins (such as resorcinol or bismaleimide), acceptors or donors of ethylene such as hexamethylenetetramine or hexamethoxymethylmelamine, a crosslinking system based on either sulfur, or sulfur and / or peroxide donors and / or bismaleimides, vulcanization accelerators, vulcanization activators.

The bead protector mixture may also contain coupling enhancers when a coupling agent is used, inorganic filler recovery agents when an inorganic filler is used, or more generally, filler assisting agents. in a known manner, by improving the dispersion of the filler in the rubber matrix and by lowering the viscosity of the compositions, to improve their processability in the green state; these agents are for example hydroxysilanes or hydrolysable silanes such as alkyl-alkoxysilanes, polyols, polyethers, amines, hydroxylated or hydrolysable polyorganosiloxanes. 4.5. Production of compositions

The rubber compositions forming the bead protecting mixture 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 "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 qualified "Productive" phase) at a lower temperature, typically below 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system or vulcanization. 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 5 phr, that of the primary accelerator is preferably between 0.5 and 8 phr. It is possible to use as accelerator (primary or secondary) any compound capable of acting as accelerator for vulcanization of diene elastomers in the presence of sulfur, in particular thiazole-type accelerators and their derivatives, accelerators of the thiuram type, zinc dithiocarbamates. These accelerators are 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"), tetrabenzylthiuram disulfide ("TBzTD"), and mixtures of 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 bead protector mixture. 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 bead protecting mixture has, in the vulcanized state (ie, after firing) a Shore A hardness of between 30 and 60; its secant modulus in extension (denoted E10) is preferably between 2 and 20 MPa, preferably between 4 and 15 MPa. Shore A hardness is measured at 23 ° C according to ASTM D2240-1986. The secant modulus in extension (E10) is the tensile modulus measured at 23 ° C in second elongation (ie, after an accommodation cycle) at 10% elongation (according to ASTM D412-1998, specimen "C"), this module being the secant modulus "true" that is to say, brought back to the actual section of the specimen (normal temperature and humidity conditions according to ASTM D1349-1999).

5. EXAMPLES OF CARRYING OUT THE INVENTION

The rubber composition described above is therefore used, in the beads of the tire of the invention, as a protective mixture between on the one hand the rim on which is intended to be mounted the tire of the invention, and on the other hand the rest of the bead, acting as a filter element for rolling noise.

The appended FIG. 1 represents in radial section, very schematically (in particular without respecting a specific scale), an example of a tire for a motor vehicle having a radial carcass reinforcement, according to the invention.

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

More specifically, a bandage belt generally consists of at least two superposed belt plies, sometimes called "working" or "crossed" plies, whose reinforcing elements or "reinforcements" are arranged substantially parallel to each other 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 bandage 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" plies responsible for protecting the rest of the belt from external aggressions, perforations, or so-called "hooping" 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 cords or textile cords. ") consisting of thin wires assembled together by wiring or twisting.

The carcass reinforcement (5) is here anchored in each bead (6) by winding around two rods (6a, 6b), the overturning (5a, 5b) of this armature (5) being for example arranged outwardly tire (1) which is shown here mounted on its rim (9). The carcass reinforcement (5) consists of at least one ply reinforced by radial textile cords, that is to say that these cords are arranged substantially parallel to each other and extend from a bead to the other so as to form an angle of between 80 ° and 90 ° to the median circumferential plane (plane perpendicular to the axis of rotation of the bandage which is situated halfway between the two beads (6) and passes through the middle of the crown reinforcement (4) Of course, this tire (1) also comprises, in a known manner, a layer (10) of inner rubber (commonly called "inner liner" or "inner liner") which defines the face radially. internal of the bandage and which is intended to protect the carcass ply from the diffusion of air from the interior space to the bandage.

The appended FIG. 2 simply reproduces by enlarging it a bead zone (6) of this exemplary bandage (1) according to the invention, of which at least the contact surface with the rim (9) is constituted by the protective mixture of bead (8) described in detail above.

Thanks to its specific formulation, this bead protector mixture is likely to contribute to significantly reduce the noise emitted both inside and outside the vehicles during the rolling of the tires, as demonstrated in the following tests. 5.1. Production of compositions

For the purposes of these tests, three rubber compositions (denoted C-0, C-1 and C-2) were prepared whose formulation is given in Table 1 (rate of the various products expressed in phr).

Composition C-0 is the control composition, it is a conventional composition for bead protector mix; it does not include butyl rubber or plasticizing hydrocarbon resin. Compositions C1 and C-2 are in accordance with the invention, they essentially comprise on the one hand a butyl rubber (75 or 95 phr), on the other hand another diene elastomer (NR, respectively 25 and 5 phr), more of 50 phr of a reinforcing filler (carbon black, respectively 65 and 90 phr), and finally more than 30 phr of a plasticizing hydrocarbon resin (respectively 40 and 50 phr) having a Tg greater than 20.degree. ° C and 52 ° C). Their Shore A hardness is between 40 and 45, their E10 modulus is between 4 and 15 MPa.

For the manufacture of these compositions, the following procedure was carried out: the reinforcing filler, the elastomers, the plasticizing resin for the plastics were successively introduced into an internal mixer, the initial batch temperature of which was approximately 60.degree. compositions Cl and C-2, as well as the various other ingredients with the exception of the vulcanization system and the blowing agent; the mixer was thus filled to about 70% (% by volume). Thermomechanical work (non-productive phase) was then carried out in a step of about 2 to 4 minutes, until a maximum "falling" temperature of about 150 ° C. was reached. The mixture thus obtained was recovered, cooled to about 50 ° C. and then the vulcanization system was incorporated on an external mixer (homo-finisher) at 30 ° C., mixing the whole (productive phase) for a few minutes. minutes. For compositions C-1 and C-2 comprising the non-halogenated butyl rubber, a second (ultra-accelerator) vulcanization accelerator was required simply to accelerate vulcanization.

The compositions C-0, C-1 and C-2 thus prepared were then extruded as a rubber profile used as a bead protector mix (8) in accordance with the schematic representation of Figures 1 and 2.

5.2. Bandage tests

To then characterize the noise reduction properties of the tires, a rolling test was conducted in which the sound level emitted by the tires was evaluated by measuring the sound pressure level, when the vehicle was traveling at a speed of 60 km / h, thanks to several microphones arranged inside the vehicle ("road noise"). The vehicle used was a "Subaru" brand vehicle ("RI" model); the road surface used for this test corresponds to a semi-rough asphalt; when passing through the measuring area, the sound pressure recording is triggered.

The results in Table 2 express the differences in recorded sound level between the bandages according to the invention denoted by P1 and P-2 (with compositions C1 and C-2, respectively) with respect to the control bandages marked P-0 (with composition C- 0), in a frequency range of 80 to 800 Hz. These differences are expressed in acoustic energy (dB (A)) which corresponds to the integration of the acoustic pressure as a function of the frequency on the Frequency domains considered, a negative value indicating a noise reduction with respect to the reference (composition C-0).

By reading Table 2, it can be seen that a noise reduction of 0.3 to 0.5 dB (A), which is therefore quite significant for those skilled in the art, is obtained thanks to the specific formulation of the two mixtures. bead protectors according to the invention; it is noted in particular that the best result is obtained with the highest rate of plasticizing resin.

Table 1

polybutadiene rubber with 0.3% of 1-2; 2.7% trans; 97% cis 1-4

(Tg = -104 ° C);

natural rubber (peptized);

non-halogenated butyl rubber (Tg = -65 ° C);

ASTM N774 grade (Cabot company);

aliphatic modified aromatic resin ("Escorez 2173"; ExxonMobil); aromatic modified cycloaliphatic resin ("Escorez 5600"; ExxonMobil);

N-dicyclohexyl-2-benzothiazol sulfenamide

("Santocure CBS" from the company Flexsys);

tetrabenzylthiuram disulfide ("Perkacit TBzTD", Flexsys).

Table 2

(*) Noise difference between the bandages according to the invention (P-1 and P-2)

and the control bandages (P-0) inside the vehicle.

Claims

1. A tire (1) for a motor vehicle, comprising at least one vertex (2) comprising at least one tread (3), a crown reinforcement or belt (4) arranged circumferentially between the tread (3) and a tread (3) carcass reinforcement (5);

- two beads (6), two flanks (7) connecting the beads (6) to the tread

the two beads (6) comprising a layer of rubber composition (8) called "bead protector mixture" intended to come into contact with a rim (9) on which the tire is intended to be mounted, characterized in that this bead protector mixture (8) comprises at least (pce meaning parts by weight per hundred parts of elastomer or rubber): - 70 to 100 phr of butyl rubber;

optionally 0 to 30 phr of another diene elastomer;

- more than 50 phr of a reinforcing filler;

more than 30 phr of a hydrocarbon plasticizing resin having a glass transition temperature (Tg) which is greater than 20 ° C.

The tire of claim 1, wherein the bead protector mixture comprises 80 to 100 phr of the butyl rubber and 0 to 20 phr of the other optional diene elastomer.

A tire according to any one of claims 1 to 2, wherein the other diene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

The tire of claim 3, wherein the other diene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes, styrene-butadiene copolymers, and mixtures thereof.

5. Bandage according to any one of claims 1 to 4, wherein the reinforcing filler content in the bead protection mixture is between 50 and 150 phr, preferably between 50 and 120 phr.

6. Bandage according to any one of claims 1 to 5, wherein the level of plasticizing hydrocarbon resin is between 30 and 100 phr, preferably between 35 and 70 phr.

7. Bandage according to any one of claims 1 to 6, wherein the Tg of the hydrocarbon plasticizing resin is greater than 30 ° C, preferably between 40 and 100 ° C.

The tire of any one of claims 1 to 7, wherein the reinforcing filler comprises silica or carbon black or a mixture of silica and carbon black.

Bandage according to any one of claims 1 to 8, the bead protector mixture comprising between 50 and 100 phr of carbon black.

The tire of claim 8 or 9, the carbon black being selected from the group consisting of standard carbon blacks (ASTM) 500, 600, 700, 800 and mixtures thereof.