BR112019011307B1 - PNEUMATIC COMPRISING A RUBBER COMPOSITION BASED ON EPOXIDIZED POLYISOPRENE - Google Patents

Abstract

Tire comprising a rubber composition which improves the compromise between the rigidity in the cured state and the hysteresis of the composition, which composition comprises: - from more than 50 to 100 pcs of polyisoprene which contains an epoxidized polyisoprene which has a molar rate of epoxidation ranging from 5% to less than 50%, - a carbon black, - a cross-linking system, the epoxidized polyisoprene being an epoxidized natural rubber or an epoxidized synthetic polyisoprene having a 1,4-cis binding molar ratio of at least 90% before epoxidation or mixing thereof, with the proviso that if the epoxidized polyisoprene is an epoxidized polyisoprene having a molar epoxidation rate of 5% to 25%, the rubber composition contains more than 50 pcs of polyisoprene epoxidized, said composition being free of silica.

Description

[001] The field of the present invention is that of rubber compositions reinforced by a reinforcing charge that can be used for the manufacture of tires for vehicles.

[002] During running-in, a tire tread is subjected to mechanical stress and aggression resulting from direct contact with the ground. In the case of a tire mounted on a vehicle carrying heavy loads, the mechanical stresses and aggressions suffered by the tire are amplified under the effect of the weight carried by the tire.

[003] Minas tires are subjected to great demands, at the same time: - at the local level: running-in on the macro penetrators represented by the pebbles that make up the tracks (crushed rock) - at the global level: important torque transfer because the inclinations of the lanes to leave the mine are of the order of 10%, and great demands on the tires during the U-turns for loading and unloading manoeuvres.

[004] This has the consequence that the beginnings of cracks that are created in the tread under the effect of these requests and these aggressions, tend to propagate more on the surface or inside the tread. The propagation of cracks in the tread can lead to damage to the tread and therefore reduce the service life of the tread or the tyre. A tire that runs on stony ground is very exposed to the beginnings of cracks. The very aggressive nature of stony ground exacerbates not only this type of aggression on the tread, but also its consequences on the tread.

[005] This is especially true for the tires that equip the civil engineering vehicles that usually evolve in mines. This is also true for tires that are fitted to agricultural vehicles because of the stony soil of arable land. The tires fitted to heavy construction site vehicles that travel on both stony and bituminous soils are also subject to these same attacks. Due to the two aggravating factors that are the weight carried by the tire and the aggressive nature of the tread surface, the resistance to crack propagation of a tread of a tire for a civil engineering vehicle, an agricultural vehicle or a heavy vehicle construction site proves to be crucial to minimize the impact of the aggressions suffered by the tread.

[006] It is therefore important to have tires for vehicles, notably those that carry heavy loads, of which the tread has a resistance to crack propagation large enough to minimize the effect of a crack initiation on the lifetime of the tread. To solve this problem, it is known by the professional that, for example, natural rubber in the treads allows to obtain high properties of resistance to the propagation of cracks.

[007] On the other hand, it remains interesting that the proposed solutions to solve this problem do not harm the other properties of the rubber composition, notably hysteresis. In fact, the use of a hysteretic composition in a tire can be manifested by an increase in the internal temperature of the tire, which can lead to a decrease in the durability (in English "durability") of the tire.

[008] Given the foregoing, there is an ongoing objective to provide rubber compositions that have an improved compromise between resistance to crack propagation and hysteresis.

[009] Surprisingly, Applicants have found that total suppression of silica in a rubber composition notably comprising (i) more than 50 to 100 pce of polyisoprene which contains an epoxidized polyisoprene which has a molar rate of epoxidation ranging from 55 to less than 50%, (ii) as a filler a carbon black, it makes it possible to further reduce hysteresis and improve resistance to cracking propagation.

[0010] Thus, the present application describes a rubber composition comprising: - from more than 50 to 100 pcs of polyisoprene containing an epoxidized polyisoprene having a molar epoxidation rate ranging from 5% to less than 50%, - a carbon black, - a crosslinking system, the epoxidized polyisoprene being an epoxidized natural rubber or an epoxidized synthetic polyisoprene having a 1,4-cis binding molar ratio of at least 90% prior to epoxidation or mixing of the same, with the proviso that if the epoxidized polyisoprene is an epoxidized polyisoprene having a molar epoxidation rate of 5% to 25%, the rubber composition contains more than 50 pcs of epoxidized polyisoprene, the composition being silica-free.

[0011] The invention relates in particular to a tire comprising the rubber composition according to the invention.

[0012] Also described in the present application is a process for manufacturing the rubber composition usable within the scope of the present invention.

I. DEFINITIONS

[0013] By the expression “part and weight per hundred parts by weight of elastomer” (or pce), it is necessary to understand in the sense of the present invention, the part by mass to one hundred parts by mass of elastomer or rubber.

[0014] In this application, unless otherwise expressly stated, all percentages (%) indicated are percentages (%) by mass.

[0015] On the other hand, every range of values designated by the expression “between a and b” represents the range of values that goes from more than a to less than b (that is to say limits a and b excluded) while every range of values designated by the expression “from a to b” means the range of values from a to b (meaning it includes the strict limits a and b). In the present application, when a range of values is designated by the expression "from a to b", the range represented by the expression "between a and b" is also designated and preferably.

[0016] In the present application, the expression composition “based on”, means a composition comprising the mixture and/or the reaction product of the different constituents used, some of these basic constituents being capable of, or destined to, react with each other, at least in part, during the different stages of manufacture of the composition, in particular during its reticulation or vulcanization. By way of example, a composition based on an elastomeric matrix and sulfur comprises the elastomeric matrix and sulfur before cooking, while after cooking the sulfur is no longer detectable since the latter has reacted with the elastomeric matrix, thus forming sulfur bridges ( polysulfides, disulfides, monosulfides).

[0017] When reference is made to a “majority” compound, it is understood in the sense of the present invention, that this compound is the majority among the compounds of the same type in the composition, that is to say that it is the one that represents the largest amount by mass among compounds of the same type, for example more than 50%, 60%, 70%, 80%, 90%, and even 100% by weight with respect to the total weight of the type of compound. Thus, for example, a major reinforcing charge is the reinforcing charge that represents the greatest mass relative to the total mass of the reinforcing fillers in the composition. In contrast, a “minority” compound is a compound that does not represent the largest mass fraction among compounds of the same type.

[0018] Within the scope of the invention, the carbonaceous products mentioned in the description may be of fossil or biological origin. In the latter case, they can be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Particularly concerned are polymers, plasticizers, fillers, etc.

II. DETAILED DESCRIPTION OF THE INVENTION II.1 1 Polyisoprene

[0019] Polyisoprene is understood to mean the set of polyisoprenes and epoxidized polyisoprenes present in the rubber composition.

[0020] Polyisoprene is understood to be a polyisoprene that is not epoxidized. The polyisoprene can be natural rubber, a synthetic polyisoprene that has a 1,4-cis binding molar ratio of at least 90%, or even a mixture of these.

[0021] Epoxidized polyisoprene is understood to mean a natural rubber or epoxidized synthetic polyisoprene that has a 1,4-cis binding molar ratio of at least 90% before epoxidation or mixing thereof.

[0022] The epoxidized polyisoprene that constitutes all or part of the polyisoprene is an elastomer and should not be confused with an epoxidized polyisoprene of low molar mass generally used as a plasticizer that is not an elastomer considering its low molar mass. An epoxidized polyisoprene elastomer generally has a high raw Mooney viscosity. The Mooney viscosity (ML 1+4) at 100°C of the epoxidized polyisoprene used within the scope of the present invention is preferably greater than 20, more preferably 30, even more preferably 40. It is also generally less than or equal to 150. By way of indication, the Mooney viscosities (ML 1+4) at 100°C of natural rubbers epoxidized at 25 mole % can be of the order of 40 to 150. The Mooney viscosity ranges of epoxidized polyisoprene are preferably from 30 to 150, more preferably from 40 to 150, even more preferably from 50 to 140. These Mooney viscosity values apply to any of the embodiments of the invention.

[0023] Mooney viscosity is measured using an oscillating consistometer as described in ASTM D1646 (1999). The measurement is made according to the following principle: the sample analyzed in the raw state (i.e., before cooking) is molded (formed) inside a cylindrical enclosure heated to a given temperature (for example 100°C). After 1 minute of preheating, the rotor rotates inside the specimen at 2 revolutions/minute and the useful torque to maintain this movement is measured after 4 minutes of rotation. Mooney viscosity (ML 1+4) is expressed in “Mooney units” (MU, with 1 MU = 0.83 Newton.meter).

[0024] Epoxidized polyisoprene, whether an epoxidized natural rubber or an epoxidized synthetic polyisoprene, can be obtained in a known manner by epoxidating polyisoprene, for example by processes based on chlorohydrin or bromohydrin or processes based on hydrogen peroxides , alkyl or peracid hydroperoxides (such as peracetic acid or performance steel). Epoxidized polyisoprenes are commercially available. The molar epoxidation rate, which is a supplier data, corresponds to the ratio of the number of moles of epoxidized isoprene units to the number of moles of an isoprene unit in the polyisoprene before epoxidation.

[0025] According to the present invention, the term "an epoxidized polyisoprene" should be understood as one or more epoxidized polyisoprenes that can be distinguished either by their microstructure, their macrostructure or their epoxidation rate. In the case where the polyisoprene comprises several epoxidized polyisoprenes, the reference to the amount of epoxidized polyisoprene of the polyisoprene applies to the total mass of the epoxidized polyisoprenes of the polyisoprene. For example, the feature according to which epoxidized polyisoprene is present in the rubber composition at a rate greater than 50 pce means that in case of mixing epoxidized polyisoprenes, the total mass of epoxidized polyisoprenes is greater than 50 pce.

[0026] In the case where the epoxidized polyisoprene is a mixture of epoxidized polyisoprenes that can be distinguished from each other by their molar rate of epoxidation, the reference to a molar rate of epoxidation, whether preferred or not, applies to each of the epoxidized polyisoprenes in the mixture.

[0027] In the case where the epoxidized polyisoprene is an epoxidized polyisoprene having a molar epoxidation rate of 5% to 25%, the rubber composition contains more than 50 pcs of epoxidized polyisoprene. In other words, considering the above definitions, when the polyisoprene does not contain another epoxidized polyisoprene other than an epoxidized polyisoprene having a molar epoxidation rate of 5 to 25% or a mixture of epoxidized polyisoprenes each having a molar rate of 5 to 25% epoxidation, the rubber composition contains more than 50 pcs of such epoxidized polyisoprene or blend of epoxidized polyisoprenes. A minimum rate of more than 50 pcs of such epoxidized polyisoprene in the rubber composition makes it possible to improve the property compromise between stiffness, shear modulus at 100% elongation and hysteresis of the composition in the baked state.

[0028] According to a preferred embodiment of the invention, the epoxidized polyisoprene comprises mainly, and even preferably exclusively, an epoxidized natural rubber.

[0029] According to a special embodiment of the invention, the polyisoprene contains a polyisoprene which has a molar ratio of 1,4-cis binding of at least 90%. According to this special embodiment of the invention, the polyisoprene is preferably constituted by a mixture of a polyisoprene having a 1,4-cis binding molar ratio of at least 90% and epoxidized polyisoprene. According to this special embodiment, in its preferred form or not, the polyisoprene having a 1,4-cis binding molar ratio of at least 90% is a natural rubber.

[0030] Epoxidized polyisoprene, whether it comes from the epoxidation of synthetic polyisoprene or natural rubber, has a molar epoxidation rate ranging from 5% to less than 50%. When the molar rate of epoxidation is less than or equal to 5%, the intended technical effect is considered insufficient while at a rate equal to or greater than 50%, the composition becomes too rigid. The molar epoxidation rate is preferably 5 to 40%, more preferably 10 to 35%. Thus, according to the composition described in the present application, the epoxidized polyisoprene comprises mainly, and even preferably exclusively, an epoxidized polyisoprene which has a molar epoxidation rate of 5 to 40%, more preferably of 10 to 35%.

[0031] According to a more particularly preferred embodiment of the invention, the epoxidized polyisoprene is an epoxidized polyisoprene which has a molar epoxidation rate of from 5 to 35%, more preferably from 5 to 30%, even more preferably from 5 to 25%. Thus, according to the composition described in the present application, the epoxidized polyisoprene comprises mainly, and even preferably exclusively, an epoxidized polyisoprene which has a molar epoxidation rate of from 5 to 35%, more preferably from 5 to 30%. preferably from 5 to 25%.

[0032] The rate of polyisoprene in rubber composition is more than 50pce to 100pce. The rate of polyisoprene in the rubber composition is preferably greater than 80 pcs, more preferably equal to 100 pcs. These preferred embodiments are notably advantageous for the use of the rubber composition as a component made of rubber in a tire, for example as a tread of a tire for a vehicle intended to carry heavy loads, in particular from the point of view of the durability of the tire. pneumatic.

[0033] According to the embodiment in which the epoxidized polyisoprene is an epoxidized polyisoprene having a molar epoxidation rate of 5 to 35%, preferably 5 to 30%, more preferably 5% to 25% , the amount of epoxidized polyisoprene is preferably greater than 80 pce, more preferably equal to 100 pce.

II.2 2 Complementary elastomer

[0034] Optionally, when the polyisoprene content is less than 100 pce, the rubber composition according to the invention comprises a complementary, preferably diene, elastomer.

[0035] A “diene” elastomer (or indistinctly rubber) means, in a known manner, one (or several) elastomers consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers carrying two bonds carbon-carbon double bonds, conjugated or not).

[0036] These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. It is understood in general by "essentially unsaturated", a diene elastomer derived at least in part from conjugated diene monomers, which have a rate of motifs or units of dienic origin (conjugated dienes) that is greater than 15% (% in moles); this is why diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall under the preceding definition and can be classified notably as “essentially saturated” diene elastomers (low or very high rate of motifs of dienic origin). low, always less than 15% in mole percentage). In the category of "essentially unsaturated" diene elastomers, "heavily unsaturated" diene elastomer is understood in particular to mean a diene elastomer which has a rate of motifs of diene origin (conjugated dienes) which is greater than 50%.

[0037] These definitions being given, it is understood more especially by diene elastomer susceptible of being used in the compositions according to the invention: (a) a ternary copolymer obtained by copolymerization of ethylene, of an α-olefin that has from 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, such as, for example, elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the type mentioned, such as notably hexadiene-1,4 , ethylidene norbornene, dicyclopentadiene; (b) a copolymer of isobutene and isoprene (butyl rubber), as well as halogenated, in particular chlorinated or brominated, versions of this type of copolymer. (c) a ternary copolymer obtained by copolymerizing ethylene, an α-olefin having from 3 to 6 carbon atoms with an unconjugated diene monomer having from 6 to 12 carbon atoms, such as elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the type mentioned, such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene; (d) a copolymer of isobutene and isoprene (butyl rubber), as well as halogenated, in particular chlorinated or brominated, versions of this type of copolymer.

[0038] Although it applies to any type of diene elastomer, the pneumatic professional will understand that the present invention is preferably executed with essentially unsaturated diene elastomers, especially of type (a) or (b) above.

[0039] In the case of copolymers of type (b), the latter contain from 20 to 99% by weight of diene units and from 1 to 80% by weight of vinylaromatic units.

[0040] As conjugated dienes, notably 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C1-C5 alkyl)-1,3-butadienes, such as example 2,3-dimethyl-1,3-butadiene, 2,4-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl -1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene.

[0041] As vinylaromatic compounds, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial mixture “vinyl-toluene”, para-tertiarybutylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene , vinylnaphthalene.

[0042] When the polyisoprene content is less than 100 pce, the rubber composition according to the invention may also comprise an essentially unsaturated complementary diene elastomer chosen from the group consisting of polybutadienes, butadiene copolymers, isoprene copolymers and mixtures thereof. The amount of this essentially unsaturated complementary diene elastomer in the rubber composition is advantageously less than 20 pce (that is to say from 0 to less than 20 pce), preferably it is comprised in the range from 0 to 10 pce, preferably from 0 to 5pc. Advantageously, the rubber composition according to the invention does not contain an essentially unsaturated complementary diene elastomer chosen from the group consisting of polybutadienes, butadiene copolymers, isoprene copolymers and mixtures thereof.

[0043] The rubber composition according to the invention optionally contains from 0 to less than 20 pcs of a butyl rubber. By butyl rubber is understood to be copolymers of isoprene and isobutylene, in particular those halogenated. According to any one of the embodiments of the invention, the amount of butyl rubber in the rubber composition is preferably from 0 to 10 pce, more preferably from 0 to 5 pce. Advantageously, the rubber composition according to the invention is devoid of butyl rubber.

II.3 3 Load

[0044] The rubber composition has the essential characteristic of comprising a carbon black.

[0045] As carbon blacks, all carbon blacks are suitable, notably the blacks conventionally used in tires or their treads (so-called pneumatic grade blacks). Among the latter, mention will be made more particularly of carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM grades), such as, for example, blacks N115, N134, N234, N326, N330 , N339, N347, N375, N550, N683, N772). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a support for some of the rubber manufacturing additives used. Among the latter, the 100, 200, 300 series (ASTM grade) reinforcing carbon blacks, such as, for example, N115, N134, N234, N375, will be cited more particularly.

[0046] According to a preferred embodiment of the invention, the carbon black has a BET specific surface of at least 90 m2/g, preferably at least 100 m2/g. The BET specific surface of carbon blacks is measured according to the D6556-10 standard [multipoint method (minimum 5 points) - gas - nitrogen - relative pressure range P/PO: 0.01 to 0.5].

[0047] The amount of carbon black in the composition described in the present invention is 30 to 90 pcs, preferably 30 to 70 pcs, more preferably 35 to 60 pcs.

[0048] The composition described in the present invention has the essential characteristic of being free of silica. In other terms, the composition described in the present invention comprises 0 pc of silica.

[0049] The silica used can be any silica known to the professional, capable of reinforcing alone, without any means other than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic belts, in other words suitable for replacing, in its reinforcing function, a conventional pneumatic grade carbon black.

[0050] The silica used may be precipitated or fumed silica that has a BET surface as well as a CTAB specific surface, both of which are less than 450 m2/g, preferably from 30 to 400 m2/g, notably between 60 and 300 m2/g . As an example of silica useful for the needs of the invention, the silica “Ultrasil VN3” marketed by the company Evonik can be cited. As highly dispersible precipitated silicas (so-called "HDS"), for example, the silicas "Ultrasil 7000" and "Ultrasil 7005" from the company Degussa, the silica "Zeosil" 1165MP, 1135MP, and 1115MP from the company Rhodia, the silica “Hi-Sil EZ150G” from the company PPG, the silicas “Zeopol” 8715, 8745 and 8755 from the company Huber, the high specific surface silicas as described in the application WO 03/16837.

[0051] The physical state in which the silica is presented is indifferent, whether it is in the form of powder, microbeads, granules, or even spheres. Naturally, mixtures of different silicas are also understood by silica.

[0052] Advantageously, the composition described in the present invention is free of reinforcing inorganic filler, preferably inorganic filler, other than silica, or contains less than 10 pce thereof, preferably less than 5 pce. Preferably the composition described in the present invention is free of reinforcing inorganic filler, preferably of inorganic filler.

[0053] By “inorganic filler” should be understood here any inorganic or mineral filler, whatever its color and origin (natural or synthetic), also called “white” filler, “clear” filler or even “not black” as opposed to carbon black. Such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface. An inorganic filler is said to be “reinforcing” when it is capable of reinforcing by itself, with no other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic belts. In other words, without a coupling agent, the inorganic filler does not reinforce, or not sufficiently, the composition and is therefore not included in the definition of “reinforcing inorganic filler”.

[0054] As inorganic fillers, siliceous mineral fillers can be cited, preferably silica (SiO2). It is also possible to cite mineral fillers of the aluminous type as inorganic fillers, especially alumina (Al2O3) or aluminum (oxides) hydroxides, or even reinforcing titanium oxides, for example described in US 6,610,261 and US 6,747,087.

[0055] The professional will understand that as a filler equivalent to the silica described in the present invention, a reinforcing filler of another nature, notably organic, could be used, provided that this reinforcing filler is covered by a layer of silica.

[0056] Advantageously, the rubber composition does not contain a coupling agent, which is the same as saying that the coupling agent rate is equal to 0 pce.

[0057] The professional can find examples of coupling agent in the following documents: WO 02/083782, WO 02/30939, WO 02/31041. WO 2007/061550, WO 2006/125532, WO 2006/125533, WO 2006/125534, US 6 849 754, WO 99/09036, WO 2006/023815, WO 2007/098080, WO 2010/072685 and WO 2008/055986.

[0058] Alkoxysilane-polysulfide compounds may be cited, in particular bis-(trialkoxysilylpropyl) polysulfides, more especially bis-3-triethoxysilylpropyl disulfide (abbreviated "TESPD") and bis-3-triethoxysilylpropyl tetrasulfide (in abbreviated “TESPT”). It is recalled that TESPD, with the formula [(C2H5O)3Si(CH2)3S]2, is notably marketed by the company Degussa under the names Si266 or Si75 (in the second case, in the form of a disulfide mixture (75% in weight) and polysulphides). TESPT of the formula [(C2H5O)3Si(CH2)3S2]2 is notably marketed by the company Degussa under the name Si69 (or X50S when it is maintained at 50% by weight on carbon black), in the form of a commercial mixture of Sx polysulfides, with an average value for x that is close to 4.

[0059] On the other hand, the composition described in the present invention advantageously does not comprise a coating agent or comprises less than 0.5 pcs thereof, such as hydroxysilane or hydrolysable silanes such as hydroxysilane (see for example WO 2009/062733), alkylalkoxysilanes, in particular alkyltriethoxysilanes such as, for example, 1-octyltriethoxysilane, polyols (for example, diols or thiols), polyethers (for example, polyethylene glycols), primary, secondary or tertiary amines (for example, trialkanolamines), a guanidine possibly substituted, notably diphenylguanidine, hydroxylated or hydrolysable polyorganosiloxanes (for example a,w-dihydroxypolyorganosilanes (especially a,w-dihydroxypolydimethylsiloxanes)) (see for example EP 0 784 072), fatty acids such as for example stearic acid. In particular, the composition described in the present invention advantageously does not comprise polyethylene glycols or comprises less than 0.5 pcs thereof.

[0060] Advantageously, the composition described in the present invention does not comprise nanocarbon, in particular nanocarbon as described in WO 2014/020374.

II.4 4 Reticulation system

[0061] The crosslinking system can be based on sulfur, sulfur donors, peroxide, bismaleimides or mixtures thereof.

[0062] According to any one of the embodiments of the invention, the crosslinking system is preferably a vulcanization system, that is to say a system based on sulfur (or a sulfur-donor agent) and a primary vulcanization accelerator . To this base vulcanization system can be added, incorporated during the first non-productive phase and/or during the productive phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid or compounds equivalents, quantum derivatives (in particular diphenylguanidine), or known vulcanization retarders.

[0063] When sulfur is used, it is used at a preferred rate of between 0.5 and 12 pce, in particular between 1 and 10 pce. The primary vulcanization accelerator is used at a preferred rate comprised between 0.5 and 10 pce, more preferably comprised between 0.5 and 5.0 pce.

[0064] It is possible to use as an accelerator (primary or secondary) any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur, notably thiazole-type accelerators as well as their derivatives, sulfenamide-type accelerators, thiurams, dithiocarbamates, dithiophosphates , thioureas and xanthates. As an example of such accelerators, the following compounds may be cited in particular: 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2 -benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds.

II.5 5 Miscellaneous additives

[0065] The rubber composition according to the invention may also comprise all or part of the usual additives commonly used in rubber compositions intended to constitute mixtures of finished articles made of rubber such as tires, such as plasticizers (hydrocarbon resins or extension oils), pigments, protective agents such as antiozone waxes, chemical antiozonants, antioxidants, antifatigue agents.

[0066] According to any one of the embodiments of the invention, the amount of plasticizer, notably extension oil or other liquid plasticizer at 23°C, is preferably less than 10 pcs (that is to say from 0 to less than 10 pcs) , more preferably less than 5 pcs (that is to say from 0 to less than 5 pcs). This plasticizer can be a solid hydrocarbon resin (or plasticizer resin), an extension oil (or plasticizer oil), or a mixture of the two.

[0067] Preferably, extension oil or other liquid plasticizer at 23°C (of which the composition described in the present invention is devoid of or contains less than 10 pce, preferably less than 2 pce) is chosen from the group consisting of naphthenic oils (low or high viscosity, notably hydrogenated or not), paraffinic oils, MES oils (Medium Extracted Solvates), TDAE oils (Treated Distillate Aromatic Extracts), mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these compounds.

[0068] Preferably, the thermoplastic hydrocarbon resin (of which the composition described in the present invention is devoid of or contains less than 10 pce, preferably less than 5 pce) is chosen from the group consisting of naphthenic oils (low or high viscosity , notably hydrogenated or not) is chosen from the group consisting of aliphatic or aromatic resins or even of the aliphatic/aromatic type, that is to say based on aliphatic and/or aromatic monomers. These resins can be natural or synthetic, based on petroleum or not (if applicable, also known as petroleum resins).

II.6 6 Tire and tire tread

[0069] The composition described in the present invention is especially well adapted to tire treads. Thus, there is described in the present invention a tread comprising a composition described in the present invention.

[0070] The composition described in the present invention can be present in the entire tread described in the present invention.

[0071] According to the invention the composition described in the present invention is present in a radially inner portion of the tread described in the present invention. Preferably, in the case in question, a radially outer portion of the tread is constituted by a composition different from that of the present invention. The tread can also comprise two positions different from each other but both according to the present invention, one being present in a radially outer portion of the tread, the other in a radially inner portion.

[0072] A tire comprising a composition described in the present invention or a tread described in the present invention is described in the present invention.

[0073] A tire having a geometry of revolution with respect to an axis of rotation, its geometry is usually described in a meridian plane that contains the axis of rotation of the tire. For a given meridian plane, the radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to the meridian plane. By convention, the expressions "radially inward, respectively radially outward" mean "closest, respectively farthest from the axis of rotation of the tyre". By "axially inner, respectively axially outer", it is understood "nearest, respectively furthest from the equatorial plane of the tyre", the equatorial plane of the tire being the plane passing through the middle of the tread surface of the tire and which is perpendicular to the axis tire rotation.

[0074] The pneumatic is preferably carried out before vulcanization (or baking). The vulcanization is then carried out classically.

[0075] According to a particularly advantageous embodiment, the tyre, preferably a tire for civil engineering vehicles or heavy vehicles, can comprise a tread: - which has an axial width L and which is constituted by an overlap radially of a first portion and of a second portion radially exterior to the first portion, - the first portion being constituted by a radial superimposition of N layers C1i, i ranging from 1 to N, - each layer C1i having a radial thickness E1i, measured in an equatorial plane of the tyre, substantially constant over at least 80% of the axial width L of the tread, and consisting of a polymeric material M1i having a dynamic shear modulus G1i, measured at a frequency equal to 10 Hz, a deformation equal to 50% of the crest-to-crest deformation amplitude and a temperature equal to 60°C, - the second portion being constituted by a single layer C2, - the layer C2 having a radial thickness E2, measured in the equatorial plane of the tyre, substantially constant over at least 80% of the axial width L of the tread, and consisting of a polymeric material M2 having a dynamic shear modulus G2, measured at a frequency equal to 10 Hz, a deformation equal to 50% of the amplitude of crest-to-crest deformation and a temperature of 60°C, - the following relations being checked simultaneously: a. 1/(Ei/Gi + E2/G2) > Go/(Ei + E2), with Ei =( ∑f=1E1i/G1i) with Eii, Ei, E2 in mm, Gii, Gi, G2 in MPa and with 1 MPa < Go < 1.8 MPa b. Gi < Go c. Ei > Eimin = 25 mm d. G2 > G0 > G1 e. E2 < E2max = 70 mm f. 1/ (∑ji=iEu/Gii) < 1/(∑=j+1£lf/Glf) for 1 < j < N-1 - any or all of the materials M1i being constituted by a composition described in the present invention .

[0076] The dynamic shear modulus is measured on a Metravib VA4000 type viscosity analyzer, in accordance with ASTM D 5992-96. The response of a sample of vulcanized polymeric material, which is in the form of a specimen of 4 mm thick and 400 mm2 in section, subjected to a sinusoidal request in alternating simple shear, at a frequency of 10 Hz, with a sweep in strain amplitude from 0.1% to 45% (outward cycle), and then from 45% to 0.1% (backward cycle), and at a temperature of 60°C. The dynamic shear modulus is thus measured for a frequency equal to 10 Hz, a strain equal to 50% of the crystalline strain amplitude and a temperature equal to 60°C.

[0077] Advantageously, in the tire tread described above, i = 1. Thus, preferably, the tire tread described in the present invention: - has an axial width L and is constituted by a radial superimposition of a first portion and a second portion radially exterior to the first portion, - the first portion being constituted by a single layer C1, - the layer C1 having a radial thickness E1, measured in an equatorial plane (XZ) of the tire, substantially constant in at least 80% of the axial width L of the tread, and consisting of a polymeric material M1 having a dynamic shear modulus G1, measured at a frequency equal to 10 Hz, a deformation equal to 50% of the crest-to-ridge deformation amplitude and a temperature equal to 60°C, - the second portion being constituted by a single layer C2, - the layer C2 having a radial thickness E2, measured in the equatorial plane (XZ) of the tyre, substantially constant over at least 80% of the width axial L of the tread, and consisting of a polymeric material M2 having a dynamic shear modulus G2, measured at a frequency equal to 10 Hz, a deformation equal to 50% of the crest-to-crest deformation amplitude and a temperature equal to at 60°C, - the following relations being checked simultaneously: a. 1/(E1/G1+E2/G2) > G0/(E1+E2), with E1, E2 in mm, G1, G2 in MPa and with 1 MPa < Go < 1.8 MPa b. G1 < G0 c. Ei > Eimin = 25 mm d. G2 > Go > G1 e. E2 < E2max = 70 mm - the material Mi being constituted by a composition described in the present invention.

[0078] In figure i, a meridian section of the top of the tire i for heavy vehicle of civil engineering type according to the invention is represented, which comprises a tread 2, intended to come into contact with a soil. The directions XX', YY' and ZZ' are respectively the circumferential, axial and radial directions of the tire. The XZ plane is the equatorial plane of the tire. The tread, which has an axial width L, is constituted by a radial superimposition of a first portion 2i and a second portion 22 radially external to the first portion 2i.

[0079] The first portion 2i consists of a radial superimposition of N layers Cii, i ranging from i to N, each layer Cii having a radial thickness Eii, measured in an equatorial plane XZ of the tire, substantially constant in at least 8o% of the axial width L of the tread 2, and being constituted by a polymeric material Mii that has a dynamic shear modulus Gii, measured for a frequency equal to 1 Hz, a deformation equal to 50% of the crest-to-crest deformation amplitude and a temperature equal to 60°C. The first multilayer portion 2i can be likened to a single-layer portion whose equivalent radial thickness Ei is equal to the sum of the respective radial thicknesses Eii of the layers Cii and whose equivalent flexibility Ei/Gi of the first portion is equal to the sum of the respective flexibilities E1i/G1i of the C1i layers.

[0080] The second portion consists of a single layer C2, layer C2 having a radial thickness E2, measured in the equatorial plane XZ of the tyre, substantially constant over at least 80% of the axial width L of the tread 2, and being consisting of a polymeric material M2 having a dynamic shear modulus G2, measured at a frequency equal to 10 Hz, a strain equal to 50% of the crest-to-crest strain amplitude and a temperature equal to 60°C.

[0081] Radially within the first radially inner portion 21, the top reinforcement 3 is depicted, comprising two top layers comprising metal reinforcements. Radially within the top reinforcement 3, carcass reinforcement 4 is shown comprising a carcass layer comprising metallic reinforcements.

[0082] In figure 2, a meridian section of the top of the tire 1 for heavy vehicle of civil engineering type is shown according to a preferred mode of the invention, which comprises a tread 2, intended to come into contact with a soil . According to this preferred embodiment, the first portion 21 is constituted by a single layer C1. In this special case, the tread is constituted by the radial superimposition of two layers, the first and second portions being monolayers: the tread is called bilayer.

[0083] A radial layer thickness is a distance measured, according to the radial direction, between the respectively radially inner and radially outer faces of the layer. This thickness is measured in the equatorial plane of the tire, passing through the middle of the tread and perpendicular to the axis of rotation of the tire. This thickness is measured on a new tire, meaning that it has not been rotated and, therefore, is not worn out. By substantially constant radial thickness, it is understood a thickness comprised within a range of + or - 5% with respect to an average thickness and at least 80% of the axial width l of the tread band.

[0084] A dynamic shear modulus is measured on a Metravib VA4000 type viscosity analyzer, in accordance with ASTM D 5992-96. The response of a sample of vulcanized polymeric material, which is in the form of a specimen of 4 mm thick and 400 mm2 in section, subjected to a sinusoidal request in alternating simple shear, at a frequency of 10 Hz, with a sweep in strain amplitude from 0.1% to 45% (outward cycle), and then from 45% to 0.1% (backward cycle), and at a temperature of 60°C. The dynamic shear modulus is thus measured for a frequency equal to 10 Hz, a strain equal to 50% of the crystalline strain amplitude and a temperature equal to 60°C.

[0085] Advantageously, six inequalities that combine the radial thicknesses and/or the dynamic shear modulus of the constitutive layers of the first and second portions of the tread band must be verified.

[0086] The first inequality 1/(EI/GI+E2/G2) > GO/(EI+E2), with E1 = ∑i=1Eli, G1i = E1i/(∑i=1E1i /G1i) with Eii, Ei , E2 in mm, Gii, Gi, G2 in MPa and with 1 MPa < GO < 1.8 MPa, means that the stiffness of a tread according to the invention, constituted by a first portion, itself constituted by the radial superimposition of N layers Cii, which have respective radial thicknesses Eii and which are constituted by polymeric materials Mii which have respective shear modulus Gii, and a second outer radial portion, constituted by a single layer C2 which has a radial thickness E2 and which is constituted by a polymeric material M2 which has a respective shear modulus G2, must be greater than the stiffness of a tread band of the state of the art, constituted by a single equivalent layer, which has a radial thickness equal to the sum of the radial thicknesses of all the constituent layers respectively of the first and second portions, said equivalent layer being constituted by a polymeric material having a dynamic shear modulus G0. The G0 reference dynamic shear modulus, in the range of tires for heavy vehicles of the civil engineering type, is usually at least equal to i MPa and at most equal to i.8 MPa.

[0087] To simplify the writing of the inequality, the equivalent radial thickness E1 and the equivalent dynamic shear modulus G1 of the first portion assimilated to a single equivalent layer C1 are introduced. By definition, the equivalent radial thickness E1 of the first portion is equal to the sum of the respective radial thicknesses E1i of the layers C1i. Also by definition, the equivalent flexibility E1/G1 of the first portion, which is the inverse of the equivalent stiffness G1/E1, is equal to the sum of the respective flexibilities E1i/G1i of layers C1i, hence the expression of the equivalent dynamic shear modulus G1 of first portion.

[0088] This first inequality expresses that, in the new tyre, that is to say at the beginning of its life, when it is mounted on the front axle of the vehicle, the multilayer tread of a tire according to the invention must be more rigid than the monolayer tread of a state-of-the-art tire. In fact, the tread of a new tyre, at the beginning of its life on the front axle, wears out in a preponderant way under the imposed effort. Now, locally, the effort applied to the tread is the product of the stiffness of the tread by the local slip rate to which wear is proportional. Consequently, with imposed effort, when the tread stiffness increases, the local slip rate, and therefore wear, decreases. Thus, in early life, the more rigid multilayer tread of the invention will wear out less quickly than the prior art monolayer tread.

[0089] The second inequality G1 < G0 means that the equivalent dynamic shear modulus G1 of the first portion must be less than the dynamic shear modulus G0 of the single polymeric material, constituting the tread of a tire of the state of the art, measured in the same conditions. If the residual radial thickness of the tread is called Er, at the end of the life of the tire on the rear axle, measured from the top reinforcement, the second inequality can also be written G1Er < G0/Er. For the tire of the invention, Er corresponds to the residual radial thickness of the first radially inner portion of the partially worn tread, a part of the layers C1i which are the most radially outer having been completely worn. This new relationship expresses that the rigidity of the multilayer tread of the invention at the end of life G1/Er must be lower than that of the tread of the state of the art G0/Er. The tread of a worn tire, at the end of its life on a rear axle, is predominantly worn under imposed deformation. Now, the local slip rate is the ratio of the local effort, applied on the tread, by the stiffness of the tread. Thus, when the tread stiffness decreases, the local effort decreases. Wear being an increasing function of local effort, when the tread stiffness decreases, wear, which varies in the same direction as local effort, decreases. As a result, the tread of the invention, which is less rigid, will wear out less quickly than the tread of the state of the art.

[0090] Thus, the first two inequalities express that the wear of a tread of a tire according to the invention is less rapid than that of a tire of the state of the art, at the beginning of life as at the end of life, whether say over the life of the tyre.

[0091] The third inequality Ei > Eimin = 25 mm means that the equivalent radial thickness E1 of the first radially interior portion must at least be equal to a minimum value Eimin, equal to 25 mm and which corresponds to the depth of influence of the indenters that cover usually the carriageways. In other words, the first radially inner portion must be thick enough to be able to have sufficient flexibility to guarantee a cushioning effect that allows it to surround the indenter.

[0092] The fourth inequality G2 > G0 > Gi means that the dynamic shear modulus G2 of the second portion must be at the same time greater than the reference dynamic shear modulus G0 and the equivalent dynamic shear modulus Gi of the first portion, that is that there must be a decreasing gradient of dynamic shear modulus there when passing from the second portion to the first portion.

[0093] The fifth inequality E2 < E2max = 70 mm means that the radial thickness E2 of the single layer C2 of the second radially outer portion must at most be equal to a maximum value E2max, equal to 70 mm and which corresponds to the radial thickness limit for beyond which the running of the tire over the penetrators no longer impacts the deformations of the radially inner layers of the first portion. In other words, the radially outer second portion must not be too thick to allow the cushion effect of the radially inner first portion and to ensure sufficient rigidity of that radially outer second portion intended to come into contact with the indenters.

[0094] The sixth inequality 1 / (∑j=1E1i /G1i') <1 / (∑i=j+1E1i / G1i), for 1 < j <N-1, means that within the first portion, the stiffness of the The set made up of the j layers C1j which are the most radially interior must be less than the stiffness of the set made up of the (N-j-1) layers which are the most radially outside. There is thus a decreasing stiffness gradient for the layers of the first portion when going from the layers that are the most radially outer to the layers that are the most radially inner. Thus the layers that are the most radially interior, the least rigid and therefore the most flexible, ensure a cushioning role in relation to the layers that are the most radially exterior.

[0095] The present invention can be applied to any type of tire. The tire according to the invention can be used to equip tourism-type motor vehicles, SUVs ("Sport Utility Vehicles"), or two-wheelers (notably motorcycles), or airplanes, or even industrial vehicles chosen from pickup trucks, "Heavy Vehicles". ” - meaning metro, buses, road transport equipment (trucks, tractors, trailers), off-road vehicles such as agricultural or civil engineering equipment -, and others.

[0096] A tire notably comprises a tread of which the tread surface is provided with a sculpture formed by a plurality of grooves that delimit elements in relief (blocks, ribs) in order to generate scraps of matter as well as voids. These grooves represent an indented volume which, adapted to the total volume of the tread (which includes both the volume of embossed elements and that of all the grooves) is expressed by a percentage designated in the present application as “volumic void rate ”. A zero volumetric void rate indicates a tread without groove or void.

[0097] The present invention is especially well adapted to tires intended for civil engineering, agricultural vehicles and heavy vehicles, more especially for civil engineering or agricultural vehicles whose tires are subjected to very specific stresses, notably stony soils on which they run. Thus, advantageously, the tire according to the invention is a tire for civil engineering, agricultural or heavy vehicles, preferably civil engineering vehicles.

[0098] The tread described in the present invention may have one or more grooves, the average depth of which ranges from 15 to 120 mm, preferably from 65 to 120 mm.

[0099] The tire according to the invention may have a diameter ranging from 20 to 63 inches, preferably from 35 to 63 inches.

[00100] On the other hand, the average rate of volumetric void in the tread assembly described in the present invention can be comprised in a range ranging from 5 to 40%, preferably from 5 to 25%.

II.7 Manufacturing process

[00101] The rubber composition can be manufactured in appropriate mixers, using two successive preparation phases well known to the professional: a first working phase or thermomechanical kneading (so-called “non-productive phase”) at high temperature, up to a temperature maximum between 110°C and 200°C, followed by a second mechanical working phase (so-called “productive” phase) to a lower temperature, typically below 110°C, for example between 40°C and 100°C, finishing phase during which the reticulation system is incorporated.

[00102] As an example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, any coating agents, are introduced into an appropriate mixer such as a usual internal mixer or complementary execution and other various additives, with the exception of the vulcanization system. The total mixing time, in this non-productive phase, is preferably between 2 and 10 minutes. After cooling the mixture thus obtained during the first non-productive phase, the low temperature vulcanization system is then incorporated, generally in an external mixer such as a cylinder mixer; everything is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

[00103] The first kneading step is generally carried out by incorporating the reinforcing load into the elastomer once or several times by kneading thermomechanically. In the case where the reinforcing filler, in particular carbon black, is already incorporated in whole or in part in the elastomer in the form of a masterbatch as described for example in WO 97/36724 or WO 99/1660, it is the master mix which is directly kneaded and, if applicable, other elastomers or reinforcing fillers present in the composition that are not in the form of a master mix, as well as additives which are not the crosslinking system.

[00104] The process for preparing the rubber composition according to the invention may comprise the following steps: - add, during a first so-called non-productive step, to polyisoprene, carbon black, kneading for this thermomechanically until reaching a maximum temperature between 110 and 200°C, - cool the whole to a temperature below 110°C, - then incorporate the reticulation system, - knead everything to a maximum temperature below 110°C to obtain a mixture.

[00105] The process may also include the following step: - calendering or extruding the mixture obtained.

[00106] After incorporating all the ingredients of the rubber composition, the final composition thus obtained is then calendered, for example in the form of a sheet or a plate, notably for characterization in the laboratory, or even extruded, for to form, for example, a rubber profile used as a rubber component for making tires. The rubber composition according to the invention can be used in the form of calendering in a tire.

[00107] Thus, according to a special embodiment of the invention, the rubber composition according to the invention, which can be either in the raw state (before crosslinking or vulcanization) or in the baked state (after crosslinking or vulcanization), is in a tyre, for example in a tire tread.

[00108] The tire, another object of the invention, which contains the rubber composition according to the invention, can be either in the raw state (before crosslinking or vulcanization), or in the baked state (after crosslinking or vulcanization) which composition may be in the form of a calender or an extrudate to form a tire rubber component.

[00109] The characteristics of the present invention, as well as others, will be better understood by reading the following description of several examples of implementation of the invention, given by way of illustration and not limitation.

111. EXAMPLES OF CARRYING OUT THE INVENTION 111.1- Measurements and tests used: Dynamic properties:

[00110] The dynamic properties are measured in a viscosity analyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of the vulcanized composition (cylindrical specimen of 4 mm thickness and 400 mm2 section) is recorded, submitted to a sinusoidal request in alternating simple shear, at a frequency of 10 Hz, at 80°C and 100°C. A sweep is carried out in strain amplitude from 0.1% to 100% (outward cycle), and then from 100% to 0.1% (return cycle). The results explored are the complex dynamic shear modulus G* and the loss factor tan(δ). In the return cycle, the value of G* at 50% of deformation is registered as well as the loss factor, annotated tan(δ)max.

[00111] The results of tan(δ)max at 100°C are expressed in base 100, the value 100 being assigned to the reference. A result of less than 100 indicates that the composition of the example considered is less hysteretic at 100°C, reflecting a lower rolling resistance of the tread comprising such a composition.

Tensile tests:

[00112] They are carried out in accordance with the French standard NF T 46-002 of September 1988. The calculated nominal secant modulus is measured in the second elongation (that is, after settling) by returning to the initial section of the specimen ( or apparent stress, in MPa) at 10% and 100% of annotated elongation MAS10 and MAS100 respectively. All these traction measurements are carried out under normal conditions of temperature (23 ± 2°C) and hygrometry (50 ± 5% relative humidity), in accordance with the French standard NF T 40-102 (December 1079).

[00113] The results are expressed in base 100, the value 100 being assigned to the reference. A result of less than 100 indicates that the composition of the example considered has less rigidity, which is especially advantageous for compositions used in a radially inner portion of the tread of a tire, in particular tires designed to carry heavy loads, in particular that roll over stony ground just like a tire for a civil engineering vehicle.

Cracking tests:

[00114] The dynamic cracking test allows evaluating the resistance of mixtures to the propagation of a crack in a specimen.

[00115] The measurement comprises 3 parts: (i) Accommodation of the specimen at 27% at a frequency of 10Hertz, (ii) Energy characterization of the unnotched specimen to determine the law G = f (deformation) in which the energy restitution rate G represents the crack loading criterion at the bottom of the notch, (iii) Crack measurement on a specimen notched under air at 80°C, 10 Hertz, at an energy restitution rate G of 300 J/m2 after notching the specimen.

[00116] The measurement of the propagated lengths is carried out after the stoppage of the request. The crack propagation velocity Vp represents the crack length propagated per load cycle. Due to the dimensions of the specimen, it is expressed in nanometers per cycle.

[00117] The Vp results are expressed in base 100, the value 100 being assigned to the reference. A result of less than 100 indicates that the composition of the example considered has better resistance to crack propagation.

111.2- Preparation of rubber compositions:

(1) borracha natural (2) borracha natural epoxidada a 25 % (3) sílica “Ultrasil VN3” da empresa Evonik (4) N115 da empresa Cabot (5) N-1,3-dimetilbutil-N-fenilparafenilenodiamina, “Santoflex 6-PPD” da empresa Flexsys (6) polietileno glicol “CARBOWAX 8000” da empresa Dow Corning (7) N-cicloexil-2-benzotiazol-sulfenamida (“Santocure CBS” da empresa Flexsys)[00118] The details of the formulations of composition C1 and T1 to T7 are described in table I. They were prepared according to the process described above and then calendered, or in the form of plates (with a thickness ranging from 2 to 3 mm) or thin rubber sheets, for measuring their physical or mechanical properties, or in the form of directly usable profiles, after cutting and/or joining to the desired dimensions. Table I

(1) natural rubber (2) 25% epoxidized natural rubber (3) silica “Ultrasil VN3” from Evonik company (4) N115 from Cabot company (5) N-1,3-dimethylbutyl-N-phenylparaphenylenediamine, “Santoflex 6 -PPD” by Flexsys company (6) polyethylene glycol “CARBOWAX 8000” by Dow Corning company (7) N-cyclohexyl-2-benzothiazolesulfenamide (“Santocure CBS” by Flexsys company)

[00119] The T1 composition is a reference composition that is conventionally used in a tread of a tire for a vehicle designed to carry heavy loads, in particular that runs on stony soils such as a tire for a civil engineering vehicle. Composition C1 is in accordance with the invention. The reference compositions T2 to T7 differ from the compositions according to the present invention in that they comprise silica, either in addition to carbon black, or replacing an equivalent amount of carbon black, and this in the presence or absence coating agent.

111.3- Properties of rubber compositions:

Tabela III

[00120] The results of the dynamic properties and tensile tests on the one hand, and those of the cracking tests appear respectively in table II and III. Table II

Table III

[00121] All compositions based on epoxidized natural rubber have a tan(δ)max value at 100°C significantly lower than composition T1, which demonstrates a particularly advantageous reduction in hysteresis. However, the composition C1 according to the invention presents a value of tan(δ)max at 100°C among the lowest of those of the reference compositions based on epoxidized natural rubber, which demonstrates a decrease in hysteresis and a better rolling resistance.

[00122] On the other hand, the values of G* 50% and of the MAS10 and MAS100 modules of the C1 composition are at an acceptable level for use in tires. Composition C1 is, in comparison with the reference compositions, less rigid, which is especially advantageous when the composition is used in a radially inner portion of a tire tread, in particular of tires intended to carry heavy loads, in particular that roll over stony ground just like a civil engineering tire.

[00123] Finally, the C1 composition according to the present invention presents a particularly remarkable resistance to the propagation of cracks in relation to the compositions classically conventionally used in a tread of a tire for a vehicle intended to carry heavy loads.

Claims (14)

1. Tire characterized in that it comprises a tread comprising a rubber composition present in a radially inner portion of the tread, said composition comprising: - from more than 50 to 100 phr of polyisoprene containing an epoxidized polyisoprene having a molar ratio of epoxidation ranging from 5% to less than 50%, - a carbon black, - a cross-linking system, the epoxidized polyisoprene being an epoxidized natural rubber or an epoxidized synthetic polyisoprene having a molar ratio of 1,4-cis binding of at least 90% before epoxidation or mixing thereof, with the proviso that if the epoxidized polyisoprene is an epoxidized polyisoprene having a molar epoxidation rate of 5% to 25%, the rubber composition contains more than 50 phr of polyisoprene epoxidized, the composition being silica-free, said tire being a tire for civil engineering vehicles. 2. Tire according to claim 1, characterized in that the level of carbon black in the rubber composition is from 30 to 90 phr, preferably from 30 to 70 phr, more preferably from 35 to 60 phr. 3. Tire according to claim 1 or 2, characterized in that the carbon black has a BET specific surface of at least 90 m2/g, preferably at least 100 m2/g. 4. Tire according to any one of claims 1 to 3, characterized in that the epoxidized polyisoprene comprises mostly an epoxidized natural rubber. 5. Tire according to any one of claims 1 to 4, characterized in that the epoxidized polyisoprene comprises mostly an epoxidized polyisoprene having a molar epoxidation rate of 5% to 40%. 6. Tire according to any one of claims 1 to 4, characterized in that the epoxidized polyisoprene comprises a majority of epoxidized polyisoprene having a molar epoxidation rate of 5% to 35%, preferably 5 to 30%. 7. Tire according to any one of claims 1 to 4, characterized in that the epoxidized polyisoprene comprises mostly an epoxidized polyisoprene having a molar epoxidation rate of 10% to 35%. 8. Tire according to any one of claims 1 to 7, characterized by the fact that the polyisoprene rate in the rubber composition is greater than 80 phr. 9. Tire according to claim 6 or 7, characterized by the fact that the rate of epoxidized polyisoprene in the rubber composition is greater than 80 phr. 10. Tire according to any one of claims 1 to 9, characterized in that the polyisoprene contains a polyisoprene having a 1,4-cis binding molar ratio of at least 90%. 11. Tire according to claim 10, characterized in that the polyisoprene consists of a mixture of polyisoprene having a molar ratio of 1,4-cis binding of at least 90% and epoxidized polyisoprene. 12. Tire according to any one of claims 1 to 11, characterized in that the rate of polyisoprene in the rubber composition is equal to 100 phr. 13. Tire according to any one of claims 1 to 9, characterized in that the rate of epoxidized polyisoprene in the rubber composition is equal to 100 phr. 14. Pneumatic according to any one of claims 1 to 13, characterized in that the composition is free of inorganic filler.

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