AU2017371532B2 - Tyre comprising a rubber composition based on epoxidized polyisoprene - Google Patents

Abstract

The present invention relates to a tyre comprising a rubber composition which improves the compromise between the stiffness in the cured state and the hysteresis of the composition, which composition comprises: - from more than 50 to 100 phr of polyisoprene containing an epoxidized polyisoprene having a molar degree of epoxidation 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 molar content of cis-1,4 bonds of at least 90% before epoxidation, or a mixture thereof, with the proviso that, if the epoxidized polyisoprene is an epoxidized polyisoprene having a molar degree of epoxidation of from 5% to 25%, the rubber composition contains more than 50 phr of epoxidized polyisoprene, said composition being free of silica.

Description

TYRE COMPRISING A RUBBER COMPOSITION BASED ON EPOXIDIZED POLYSOPRENE

The field of the present invention is that of rubber compositions reinforced by a reinforcing filler which can be used in the manufacture of tyres for vehicles.

During running, a tyre tread is subjected to mechanical stresses and to attacks resulting from direct contact with the ground. In the case of a tyre fitted to a vehicle bearing heavy loads, the mechanical stresses and the attacks undergone by the tyre are magnified under the effect of the weight borne by the tyre.

Mining tyres are subjected to high stresses, both:

- locally: running over the indenting macrobodies represented by the stones from which the tracks are formed (crushed rock) - globally: high torque transmission as the slopes of the tracks for exiting from the pit are of the order of 10%, and high stresses of the tyres during half-turns for the loading and unloading manoeuvres.

The consequence of this is that the incipient cracks which are created in the tread under the effect of these stresses and these attacks have a tendency to further propagate at the surface of or inside the tread. Crack propagation in the tread can result in damage to the tread and can thus reduce the lifetime of the tread or of the tyre. A tyre running over a stony ground surface is highly exposed to incipient cracks. The actual aggressive nature of the stony ground surface exacerbates not only this type of attack on the tread but also its consequences with regard to the tread.

This is particularly true for the tyres equipping civil engineering vehicles which are moving about generally in mines. This is also true for the tyres which are fitted to agricultural vehicles, due to the stony ground surface of arable land. The tyres which equip worksite heavy-duty vehicles, which are moving both on stony ground surfaces and on bituminous ground surfaces, also experience these same attacks. Due to the two aggravating factors, which are the weight borne by the tyre and the aggressive nature of the running ground surface, the resistance to crack propagation of a tread of a tyre for a civil engineering vehicle, an agricultural vehicle or a worksite heavy-duty vehicle proves to be crucial in minimizing the impact of the attacks undergone by the tread.

It is thus important to have available tyres for vehicles, in particular those bearing heavy loads, the tread of which exhibits a resistance to crack propagation which is sufficiently strong to minimize the effect of an incipient crack on the lifetime of the tread. In order to solve this problem, it is known to a person skilled in the art that, for example, natural

20310163_1 (GHMatters) P45201AU00 rubber in treads makes it possible to obtain elevated properties of resistance to crack propagation.

Furthermore, it remains advantageous for the solutions provided in order to solve this problem not to be disadvantageous to the other properties of the rubber composition, in particular the hysteresis. This is because the use of a hysteretic composition in a tyre may be apparent by a rise in the internal temperature of the tyre, which may result in a reduction in the durability of the tyre.

In the light of the above, embodiments of the present invention seek to provide rubber compositions which exhibit an improved compromise between resistance to crack propagation and the hysteresis.

Surprisingly, the Applicant Company has discovered that the complete suppression of silica in a rubber composition comprising in particular (i) from more than 50 to 100 phr of polyisoprene containing an epoxidized polyisoprene having a molar degree of epoxidation ranging from 5% to less than 50%, (ii) as filler, a carbon black, makes it possible to further reduce the hysteresis and to improve the resistance to crack propagation.

Thus, a description is given, in the present document, of a rubber composition comprising: - from more than 50 to 100 phr of polyisoprene containing an epoxidized polyisoprene having a molar degree of epoxidation 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 molar content of cis-1,4 bonds of at least 90% before epoxidation, or their mixture, with the proviso that, if the epoxidized polyisoprene is an epoxidized polyisoprene having a molar degree of epoxidation of from 5% to 25%, the rubber composition contains more than 50 phr of epoxidized polyisoprene, the composition being devoid of silica.

In one embodiment, the invention relates in particular to a tyre which comprises the rubber composition in accordance with embodiments of the invention.

A process for manufacturing the rubber composition which can be used in the context of an embodiment of the present invention is also described in the present document.

20310163_1 (GHMatters) P45201AU00

In one aspect, the present invention provides a tyre which comprises a tread having an axial width and being formed by a radial superimposition of a first portion and a second portion, the first portion being a radially interior portion of the tread and the second portion being radially exterior to the first portion, a composition of the first portion comprising a rubber composition, the said rubber composition comprising: - from more than 50 to 100 phr of polyisoprene containing an epoxidized polyisoprene having a molar degree of epoxidation 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 molar content of cis-1,4 bonds of at least 90% before epoxidation, or their mixture, with the proviso that, if the epoxidized polyisoprene is an epoxidized polyisoprene having a molar degree of epoxidation of from 5% to 25%, the rubber composition contains more than 50 phr of epoxidized polyisoprene, the rubber composition being devoid of silica, the said tyre being a tyre for civil engineering vehicles, wherein a composition of the second portion is different from the composition of the first portion.

1. DEFINITIONS The expression "part by weight per hundred parts by weight of elastomer" (or phr) should be understood as meaning, within the meaning of embodiments of the present invention, the part by weight per hundred parts by weight of elastomer or rubber.

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

Furthermore, any interval of values denoted by the expression "between a and b" represents the range of values extending from more than a to less than b (that is to say, limits a and b excluded), whereas any interval of values denoted by the expression "from a to b" means the range of values extending from a up to b (that is to say, including the strict limits a and b). In the present document, when an interval of values is denoted by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferentially denoted.

In the present document, the expression composition "based on" is understood to mean a composition comprising the mixture and/or the reaction product of the various constituents used, some of these base constituents being capable of reacting or intended to react with one another, at least in part, during the various phases of manufacture of the

20310163_1 (GHMatters) P45201AU00 composition, in particular during the crosslinking or vulcanization thereof. By way of example, a composition based on an elastomeric matrix and on sulfur comprises the elastomeric matrix and the sulfur before curing, whereas, after curing, the sulfur is no longer detectable as the latter has reacted with the elastomeric matrix with the formation of sulfur polysulfidee, disulfide, monosulfide) bridges.

When reference is made to a "predominant" compound, this is understood to mean, within the meaning of embodiments of the present invention, that this compound is predominant among the compounds of the same type in the composition, that is to say that it is the one which represents the greatest amount by weight among the compounds of the same type, for example more than 50%, 60%, 70%, 80%, 90%, indeed even 100%, by weight, with respect to the total weight of the compound type. Thus, for example, a predominant reinforcing filler is the reinforcing filler representing the greatest weight with respect to the total weight of the reinforcing fillers in the composition. On the contrary, a "minor" compound is a compound which does not represent the greatest fraction by weight among the compounds of the same type.

Within the context of embodiments of the invention, the carbon products mentioned in the description may be of fossil or biosourced origin. In the latter case, they may partially or completely result from biomass or be obtained from renewable starting materials resulting from biomass. Polymers, plasticizers, fillers, and the like, are concerned in particular.

II. DETAILED DESCRIPTION OF THE INVENTION

11.1 Polyisoprene

"Polyisoprene" is understood to mean all of the polyisoprenes and epoxidized polyisoprenes present in the rubber composition.

"Polyisoprene" is understood to mean a polyisoprene which is not epoxidized. The polyisoprene can be natural rubber, a synthetic polyisoprene having a molar content of cis 1,4 bonds of at least 90%, or else their mixture.

"Epoxidized polyisoprene" is understood to mean an epoxidized natural rubber or an epoxidized synthetic polyisoprene having a molar content of cis-1,4 bonds of at least 90% before epoxidation, or their mixture.

The epoxidized polyisoprene which constitutes all or part of the polyisoprene is an elastomer and is not to be confused with an epoxidized polyisoprene of low molar mass,

20310163_1 (GHMatters) P45201AU00 generally used as plasticizer, which is not an elastomer due to its low molar mass. An epoxidized polyisoprene, as elastomer, generally has a high Mooney viscosity in the raw state. The Mooney viscosity (ML 1+4) at 100°C of the epoxidized polyisoprene used in the context of the present invention is greater preferably than 20, more preferably than 30 and more preferably still than 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 to 25 mol% may be of the order of 40 to 150. The ranges of the Mooney viscosity of epoxidized polyisoprene are preferably from 30 to 150, more preferably from 40 to 150 and more preferably still from 50 to 140. These preferential values for Mooney viscosity apply to any one of the embodiments of the invention.

The Mooney viscosity is measured using an oscillating consistometer as described in Standard ASTM D1646 (1999). The measurement is carried out according to the following principle: the sample, analysed in the raw state (i.e., before curing), is moulded (shaped) in a cylindrical chamber heated to a given temperature (for example 100°C). After preheating for 1 minute, the rotor rotates within the test specimen at 2 revolutions/minute and the working torque for maintaining this movement is measured after rotating for 4 minutes. The Mooney viscosity (ML 1+4) is expressed in "Mooney unit" (MU, with 1 MU = 0.83 newton.metre).

The epoxidized polyisoprene, whether it is an epoxidized natural rubber or an epoxidized synthetic polyisoprene, can be obtained in a known way by epoxidation of polyisoprene, for example by processes based on chlorohydrin or bromohydrin or processes based on hydrogen peroxides, alkyl hydroperoxides or peracids (such as peracetic acid or performic acid). Epoxidized polyisoprenes are commercially available. The molar degree of epoxidation, which is information provided by the suppliers, corresponds to the ratio of the number of epoxidized moles of isoprene unit to the number of moles of isoprene unit in the polyisoprene before epoxidation.

According to embodiments of the present invention, the term "an epoxidized polyisoprene" should be understood as one or more epoxidized polyisoprenes which can differ either in their microstructure, their macrostructure or their degree of epoxidation. 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 weight of the epoxidized polyisoprenes of the polyisoprene. For example, the characteristic according to which the epoxidized polyisoprene is present in the rubber composition at a content of greater than 50 phr means that, in the case of a mixture of epoxidized polyisoprenes, the total weight of epoxidized polyisoprenes is greater than 50 phr.

203101631 (GHMatters) P45201AU00

In the case where the epoxidized polyisoprene is a mixture of epoxidized polyisoprenes which can differ from one another in their molar degree of epoxidation, the reference to a molar degree of epoxidation, whether preferential or not, applies to each of the epoxidized polyisoprenes of the mixture.

In the case where the epoxidized polyisoprene is an epoxidized polyisoprene having a molar degree of epoxidation of 5% to 25%, the rubber composition contains more than 50 phr of epoxidized polyisoprene. In other words, given the above definitions, when the polyisoprene contains no other epoxidized polyisoprene than an epoxidized polyisoprene having a molar degree of epoxidation of 5% to 25% or than a mixture of epoxidized polyisoprenes which each have a molar degree of epoxidation of 5% to 25%, the rubber composition contains more than 50 phr of this epoxidized polyisoprene or of this mixture of epoxidized polyisoprenes. A minimum content of more than 50 phr of such an epoxidized polyisoprene in the rubber composition makes it possible to improve the compromise in properties between the stiffness, the shear modulus at 100% elongation and the hysteresis of the composition in the cured state.

According to a preferred embodiment of the invention, the epoxidized polyisoprene predominantly comprises, indeed even preferably exclusively comprises, an epoxidized natural rubber. According to a specific embodiment of the invention, the polyisoprene contains a polyisoprene having a molar content of cis-1,4 bonds of at least 90%. According to this specific embodiment of the invention, the polyisoprene is preferably formed of a mixture of a polyisoprene having a molar content of cis-1,4 bonds of at least 90% and of the epoxidized polyisoprene. According to this specific embodiment, in or not in its preferred form, the polyisoprene having a molar content of cis-1,4 bonds of at least 90% is a natural rubber.

The epoxidized polyisoprene, whether resulting from the epoxidation of a synthetic polyisoprene or of natural rubber, has a molar degree of epoxidation ranging from 5% to less than 50%. When the molar degree of epoxidation is less than 5%, the targeted technical effect is regarded as insufficient, whereas, at a degree equal to or greater than 50%, the composition becomes too stiff. The molar degree of epoxidation is preferably from 5% to 40%, more preferably from 10% to 35%. Thus, according to the composition described in the present document, the epoxidized polyisoprene predominantly comprises, indeed even preferably exclusively comprises, an epoxidized polyisoprene having a molar degree of epoxidation of 5% to 40%, more preferably of 10% to 35%.

According to a very particularly preferred embodiment of the invention, the epoxidized polyisoprene is an epoxidized polyisoprene having a molar degree of epoxidation of 5% to

20310163_1 (GHMatters) P45201AU00

35%, more preferably of 5% to 30% and more preferably still of 5% to 25%. Thus, according to the composition described in the present document, the epoxidized polyisoprene predominantly comprises, indeed even preferably exclusively comprises, an epoxidized polyisoprene having a molar degree of epoxidation of 5% to 35%, more preferably of 5% to 30% and more preferably still of 5% to 25%.

The content of polyisoprene in the rubber composition is from more than 50 phr to 100 phr. The content of polyisoprene in the rubber composition is preferably greater than 80 phr, more preferably equal to 100 phr. These preferred embodiments are in particular advantageous for the use of the rubber composition as rubber component in a tyre, for example as tread of a tyre for a vehicle intended to bear heavy loads, in particular from the perspective of the durability of the tyre.

According to the embodiment in which the epoxidized polyisoprene is an epoxidized polyisoprene having a molar degree of epoxidation of 5% to 35%, preferably of 5% to 30% and more preferably of 5% to 25%, the content of epoxidized polyisoprene is preferably greater than 80 phr, more preferably equal to 100 phr.

11.2 Supplementary elastomer

Optionally, when the content of polyisoprene is less than 100 phr, the rubber composition in accordance with an embodiment of the invention comprises a supplementary elastomer, preferably a diene elastomer.

A "diene" elastomer (or without distinction rubber) should be understood, in a known way, as meaning an elastomer (or several elastomers) composed, at least in part (i.e., a homopolymer or a copolymer), of diene monomer units (monomers bearing two conjugated or non-conjugated carbon-carbon double bonds).

These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". "Essentially unsaturated" is understood to mean generally a diene elastomer resulting at least in part from conjugated diene monomers having a content of units of diene origin (conjugated dienes) which is greater than 15% (mol%); thus it is that diene elastomers such as butyl rubbers or copolymers of dienes and ofa-olefins of EPDM type do not come within the preceding definition and can in particular be described as "essentially saturated" diene elastomers (low or very low content, always less than 15%, of units of diene origin). In the category of "essentially unsaturated" diene elastomers, a "highly unsaturated" diene elastomer is understood in particular to mean a diene

20310163_1 (GHMatters) P45201AU00 elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

Given these definitions, diene elastomer capable of being used in the compositions in accordance with an embodiment of the invention is understood more particularly to mean:

a) a ternary copolymer obtained by copolymerization of ethylene and of an a-olefin having from 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, such as, for example, the elastomers obtained from ethylene and propylene with a non-conjugated diene monomer of the abovementioned type, such as, in particular, 1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene; b) a copolymer of isobutene and of isoprene (butyl rubber) and also the halogenated versions, in particular chlorinated or brominated versions, of this type of copolymer; c) a ternary copolymer obtained by copolymerization of ethylene and of an a-olefin having from 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, such as, for example, the elastomers obtained from ethylene and propylene with a non-conjugated diene monomer of the abovementioned type, such as, in particular, 1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene; d) a copolymer of isobutene and of isoprene (butyl rubber) and also the halogenated versions, in particular chlorinated or brominated versions, of this type of copolymer.

Although it applies to any type of diene elastomer, a person skilled in the art of tyres will understand that in an embodiment, the present invention is preferably employed with essentially unsaturated diene elastomers, in particular of the above type (a) or (b).

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

The following are suitable in particular as conjugated dienes: 1,3-butadiene, 2-methyl-1,3 butadiene, 2,3-di(C-C 5 alkyl)-1,3-butadienes, such as, for example, 2,3-dimethyl-1,3 butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene or 2-methyl-3 isopropyl-1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene or 2,4-hexadiene.

The following, for example, are suitable as vinylaromatic compounds: styrene, ortho-, meta- or para-methylstyrene, the "vinyltoluene" commercial mixture, para-(tert

20310163_1 (GHMatters) P45201AU00 butyl)styrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene or vinylnaphthalene.

When the content of polyisoprene is less than 100 phr, the rubber composition in accordance with an embodiment of the invention can also comprise an essentially unsaturated supplementary diene elastomer selected from the group consisting of polybutadienes, butadiene copolymers, isoprene copolymers and their mixtures. The content of this essentially unsaturated supplementary diene elastomer in the rubber composition is advantageously less than 20 phr (that is to say, from 0 to less than 20 phr); preferably, it is within a range extending from 0 to 10 phr, preferably from 0 to 5 phr. Advantageously, the rubber composition in accordance with an embodiment of the invention is devoid of essentially unsaturated supplementary diene elastomer selected from the group consisting of polybutadienes, butadiene copolymers, isoprene copolymers and their mixtures.

The rubber composition in accordance with an embodiment of the invention optionally contains from 0 to less than 20 phr of a butyl rubber. Butyl rubber is understood to mean the copolymers of isoprene and of isobutylene, in particular those which are halogenated. According to any one of the embodiments of the invention, the content of butyl rubber in the rubber composition is preferably from 0 to 10 phr, more preferably from 0 to 5 phr. Advantageously, the rubber composition in accordance with an embodiment of the invention is devoid of butyl rubber.

11.3 Filler

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

All carbon blacks, in particular the blacks conventionally used in tyres or their treads ("tyre grade" blacks), are suitable as carbon blacks. Among the latter, mention will more particularly be made of the reinforcing carbon blacks of the 100, 200 and 300 series, or the blacks of the 500, 600 or 700 series (ASTM grades), such as, for example, the N115, N134, N234, N326, N330, N339, N347, N375, N550, N683 and N772 blacks. These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as support for some of the rubber additives used. Mention will more particularly be made, among the latter, of the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grade), such as, for example, the N115, N134, N234 or N375 blacks.

According to a preferred embodiment of the invention, the carbon black exhibits a BET specific surface of at least 90 m 2/g, preferably of at least 100m 2/g. The BET specific surface

20310163_1 (GHMatters) P45201AU00 of the carbon blacks is measured according to Standard D6556-10 [multipoint (a minimum of 5 points) method- gas: nitrogen - relative pressure p/po range: 0.01 to 0.5].

The content of carbon black in the composition described in the present document is from 30 to 90 phr, preferably from 30 to 70 phr and more preferably from 35 to 60 phr.

The composition described in the present document exhibits the essential characteristic of being devoid of silica. In other words, the composition described in the present document comprises 0 phr of silica.

The silica used can be any silica known to a person skilled in the art, capable of reinforcing, by itself alone, without means other than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tyres, in other words capable of replacing, in its reinforcing role, a conventional tyre-grade carbon black.

The silica used can be a precipitated or fumed silica exhibiting a BET specific surface and a CTAB specific surface both of less than 450 m2/g, preferably from 30 to 400 m 2/g, in particular between 60 and 300 m 2/g. Mention may be made, as example of silica of use for the requirements of an embodiment of the invention, of the Ultrasil VN3 silica sold by Evonik. Mention will be made, as highly dispersible precipitated silicas ("HDSs"), for example, of the Ultrasil 7000 and Ultrasil 7005 silicas from Degussa, the Zeosil 1165MP, 1135MP and 1115MP silicas from Rhodia, the Hi-Sil EZ150G silica from PPG, the Zeopol 8715, 8745 and 8755 silicas from Huber or the silicas with a high specific surface as described in Application WO 03/016387.

The physical state in which the silica is provided is not important, whether it is in the form of a powder, of microbeads, of granules or else of beads. Of course, "silica" is also understood to mean mixtures of different silicas.

Advantageously, the composition described in the present document is devoid of reinforcing inorganic filler, preferably of inorganic filler, other than silica, or contains less than 10 phr thereof, preferably less than 5 phr thereof. Preferably, the composition described in the present document is devoid of reinforcing inorganic filler, preferably of inorganic filler.

The term "inorganic filler" should be understood here as meaning any inorganic or mineral filler, regardless of its colour and its origin (natural or synthetic), also known as "white filler", "clear filler" or even "non-black filler", in contrast to carbon black. Such a filler is generally characterized, in a known way, by the presence of hydroxyl (-OH) groups at its surface. An inorganic filler is said to be "reinforcing" when it is capable of reinforcing, by

20310163_1 (GHMatters) P45201AU00 itself alone, without means other than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tyres. In other words, without a coupling agent, the inorganic filler does not make it possible to reinforce, or to sufficiently reinforce, the composition and consequently does not come within the definition of "reinforcing inorganic filler".

Mention may in particular be made, as inorganic fillers, of mineral fillers of the siliceous type, preferably silica (Si 2 ). Mention may also be made, as inorganic fillers, of mineral fillers of the aluminous type, in particular alumina (A1 2 0 3 ) or aluminium (oxide) hydroxides, or also of reinforcing titanium oxides, for example described in US 6 610 261 and US 6 747 087.

A person skilled in the art will understand that, as filler equivalent to the silica described in the present document, use might be made of a reinforcing filler of another nature, in particular organic nature, provided that this reinforcing filler is covered with a layer of silica.

Advantageously, the rubber composition does not contain a coupling agent, which amounts to saying that the content of the coupling agent is equal to 0 phr.

A person skilled in the art can find coupling agent examples 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.

Mention may in particular be made of alkoxysilane polysulfide compounds, especially bis(trialkoxysilylpropyl) polysulfides, very particularly bis(3-triethoxysilylpropyl) disulfide (abbreviated to "TESPD") and bis(3-triethoxysilylpropyl) tetrasulfide (abbreviated to "TESPT"). It should be remembered that TESPD, of formula [(C2H 5 0) 3 Si(CH 2 ) 3 S] 2 , is in particular sold by Degussa under the name Si266 or Si75 (in the second case, in the form of a mixture of disulfide (at 75% by weight) and of polysulfides). TESPT, of formula

[(C 2 H 5 0)3 Si(CH 2 )3S]4, is sold in particular by Degussa under the name Si69 (or X50S when it is supported at 50% by weight on carbon black), in the form of a commercial mixture of polysulfides Sx with a mean value for x which is approximately 4.

Furthermore, the composition described in the present document advantageously does not comprise a covering agent or comprises less than 0.5 phr thereof, such as hydroxysilanes or hydrolysable silanes, such as hydroxysilanes (see, for example, WO 2009/062733), alkylalkoxysilanes, in particular alkyltriethoxysilanes, such as, for example, 1-octyltriethoxysilane, polyols (for example, diols or triols), polyethers (for

20310163_1 (GHMatters) P45201AU00 example, polyethylene glycols), primary, secondary or tertiary amines (for example trialkanolamines), an optionally substituted guanidine, in particular diphenylguanidine, hydroxylated or hydrolysable polyorganosiloxanes (for example, a,w dihydroxypolyorganosilanes (in particular a,w-dihydroxypolydimethylsiloxanes) (see, for example, EP 0 784 072) or fatty acids, such as, for example, stearic acid. In particular, the composition described in the present document advantageously does not comprise polyethylene glycols or comprises less than 0.5 phr thereof.

Advantageously, the composition described in the present document does not comprise nanocarbon, in particular nanocarbon as described in Application WO 2014/020374.

11.4 Crosslinking system

The crosslinking system can be based on sulfur, on sulfur donors, on peroxide, on bismaleimides or on their mixtures.

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 on a sulfur donating agent) and on a primary vulcanization accelerator. Various known secondary vulcanization accelerators or vulcanization activators, such as zinc oxide, stearic acid or equivalent compounds, or guanidine derivatives (in particular diphenylguanidine), or else known vulcanization retarders, can be added to this base vulcanization system, being incorporated during the first non-productive phase and/or during the productive phase, as are described subsequently.

When sulfur is used, it is used at a preferred content of between 0.5 and 12 phr, in particular between 1 and 10 phr. The primary vulcanization accelerator is used at a preferred content of between 0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr.

Use may be made, as (primary or secondary) accelerator, of any compound capable of acting as accelerator of the vulcanization of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type, and also their derivatives, or accelerators of sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. Mention may in particular be made, as examples of such accelerators, of the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated to MBTS), N-cyclohexyl-2 benzothiazolesulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolesulfenamide (DCBS), N (tert-butyl)-2-benzothiazolesulfenamide (TBBS), N-(tert-butyl)-2-benzothiazolesulfenimide (TBSI), tetrabenzylthiuram disulfide (TBZTD), zinc dibenzyldithiocarbamate (ZBEC) and the mixtures of these compounds.

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11.5 Various additives

The rubber composition in accordance with an embodiment of the invention can also comprise all or part of the usual additives customarily used in rubber compositions intended to constitute mixtures of finished rubber articles, such as tyres, such as, for example, plasticizers (hydrocarbon resins or extender oils), pigments, protective agents, such as antiozone waxes, chemical antiozonants or antioxidants, or antifatigue agents.

According to any one of the embodiments of the invention, the amount of plasticizer, in particular extender oil or other plasticizer which is liquid at 23°C, is preferably less than 10 phr (that is to say, from 0 to less than 10 phr), more preferably less than 5 phr (that is to say, from 0 to less than 5 phr). This plasticizer can be a solid hydrocarbon resin (or plasticizing resin), an extender oil (or plasticizing oil) or a mixture of the two.

Preferably, the extender oil or other plasticizer which is liquid at 23°C (of which the composition described in the present document is devoid or contains less than 10 phr thereof, preferably less than 2 phr) is selected from the group consisting of naphthenic oils (low- or high-viscosity, in particular hydrogenated or non-hydrogenated), paraffinic oils, MES (Medium Extracted Solvates) oils, TDAE (Treated Distillate Aromatic Extracts) oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and the mixtures of these compounds.

Preferably, the thermoplastic hydrocarbon resin (of which the composition described in an embodiment of the present invention is devoid or contains less then 10 phr thereof, preferably less than 5 phr) is selected from the group consisting of naphthenic oils (low- or high-viscosity, in particular hydrogenated or non-hydrogenated) is selected from the group consisting of aliphatic or aromatic resins or also resins of the aliphatic/aromatic type, that is to say based on aliphatic and/or aromatic monomers. These resins be natural or synthetic and are or are not based on petroleum (if such is the case, they are also known under the name of petroleum resins).

11.6 Tyre tread and tyre

The composition described in the present document is particularly well suited to tyre treads. Thus, a description is given, in the present document, of a tread comprising a composition described in the present document.

The composition described in the present document can be present in the whole of the tread described in the present document.

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According to an embodiment of the invention, the composition described in the present document is present in a radially internal portion of the tread described in the present document. Preferably, in this scenario, a radially exterior portion of the tread is formed of a composition different from that of embodiments of the present invention. The tread can also comprise two compositions different from one another but both in accordance with embodiments of the present invention, one being present in a radially exterior portion of the tread and the other in a radially interior portion.

A description is given, in the present document, of a tyre comprising a composition described in the present document or a tread described in the present document.

Since a tyre has a geometry which exhibits symmetry of revolution about an axis of rotation, its geometry is usually described in a meridian plane containing the axis of rotation of the tyre. For a given meridian plane, the radial, axial and circumferential directions respectively denote the directions perpendicular to the axis of rotation of the tyre, parallel to the axis of rotation of the tyre and perpendicular to the meridian plane. By convention, the expressions "radially interior" and respectively "radially exterior" mean "closer to" and respectively "further from" the axis of rotation of the tyre. "Axially interior" and respectively "axially exterior" are understood to mean "closer to" and respectively "further from" the equatorial plane of the tyre, the equatorial plane of the tyre being the plane passing through the middle of the tread surface of the tyre and perpendicular to the axis of rotation of the tyre.

The tyre is preferably produced before vulcanization (or curing). The vulcanization is subsequently carried out conventionally.

According to a particularly advantageous embodiment, the tyre, preferably a tyre for civil engineering or heavy-duty vehicles, can comprise a tread: - having an axial width L and being formed by a radial superimposition of a first portion and of a second portion radially exterior to the first portion, - the first portion being formed by a radial superimposition of N layers Cli, i varying from 1 to N, - each layer Cli having a radial thickness E 1 i, measured in an equatorial plane of the tyre, which is substantially constant over at least 80% of the axial width L of the tread, and being formed of a polymeric material M1 i having a dynamic shear modulus G 1i, measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C, - the second portion being formed by a single layer C 2 ,

- the layer C 2 having a radial thickness E 2 , measured in the equatorial plane of the tyre, which is substantially constant over at least 80% of the axial width L of the

20310163_1 (GHMatters) P45201AU00 tread, and being formed of a polymeric material M 2 having a dynamic shear modulus G 2 , measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C, - the following relationships being simultaneously satisfied: a. 1/(E 1 /G 1 +E 2/G 2) > Go/(E 1 +E2), with E1 = X E1 i, G1 = E1/(> E1 i/Gli) with E 1i, E 1and E2 in mm, G 1i, G 1and G2 in MPa and with 1 MPa Go 1.8 MPa b. G 1 < Go c. E 1 > E 1min = 25 mm d. G2 > Go> G1 e. E2 E 2 max = 70 mm f. 1/(EN E 1 i /Gli) < 1/(N Q±E 1 i/Gli) for 1 j N-1 - any one or all of the materials M1 i being formed of a composition described in the present document.

The dynamic shear modulus is measured on a viscosity analyser of Metravib VA4000 type according to Standard ASTM D 5992-96. The response of a sample of vulcanized polymeric material, having the form of a cylindrical test specimen with a thickness of 4 mm and with a cross section of 400 mm 2, subjected to a simple alternating sinusoidal shear stress, at the frequency of 10 Hz, with a strain amplitude sweep from 0.1% to 45% (outward cycle) and then from 45% to 0.1% (return cycle), and at a temperature of 60°C, is recorded. The dynamic shear modulus is thus measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C.

Advantageously, in the tyre tread described above, i = 1. Thus, preferably, the tread of the tyre described in the present document: - has an axial width L and being formed by a radial superimposition of a first portion and of a second portion radially exterior to the first portion, - the first portion being formed by a single layer C1, - the layer C1 having a radial thickness E1 , measured in an equatorial plane (XZ) of the tyre, which is substantially constant over at least 80% of the axial width L of the tread, and being formed of a polymeric material M1 having a dynamic shear modulus G 1, measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C, - the second portion being formed by a single layer C 2 ,

- the layer C 2 having a radial thickness E 2, measured in the equatorial plane (XZ) of the tyre, which is substantially constant over at least 80% of the axial width L of the tread, and being formed of a polymeric material M 2 having a dynamic shear modulus G 2 , measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C, - the following relationships being simultaneously satisfied:

20310163_1 (GHMatters) P45201AU00 a. 1/(E 1/G 1+E 2/G 2 ) > Go/(E +E2),with 1 E and E 2 in mm, G and 1 G 2 in MPa and with 1 MPa Go 1.8 MPa b. G 1 < Go c. E 1 > E 1 min = 25 mm d. G 2 >Go>G 1 e. E 2 E2max = 70 mm - the material M 1 being formed of a composition described in the present document.

A meridian section of the crown of a tyre 1 for a heavy vehicle of civil engineering type according to an embodiment of the invention, comprising a tread 2, intended to come into contact with a ground surface, is represented in Figure 1. The directions XX', YY' and ZZ' are respectively the circumferential, axial and radial directions of the tyre. The plane XZ is the equatorial plane of the tyre. The tread, having an axial width L, is formed by a radial superimposition of a first portion 21 and of a second portion 22 radially exterior to the first portion 21.

The first portion 21 is formed by a radial superimposition of N layers Cli, i varying from 1 to N, each layer Cli having a radial thickness E1 i, measured in an equatorial plane XZ of the tyre, which is substantially constant over at least 80% of the axial width L of the tread 2, and being formed by a polymeric material M1 i having a dynamic shear modulus G1

, measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C. The multilayer first portion 21 can be likened to a monolayer portion, the equivalent radial thickness E 1 of which is equal to the sum of the respective radial thicknesses E1 i of the layers Cli and the equivalent flexibility E1 /G 1 of the first portion of which is equal to the sum of the respective flexibilities 1E i/G1 i of the layers Cii.

The second portion 22 is formed by a single layerC 2, thelayerC 2 having a radial thickness E 2 , measured in the equatorial plane XZ of the tyre, which is substantially constant over at least 80% of the axial width L of the tread 2, and being formed of a polymeric material M 2 having a dynamic shear modulus G 2 , measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C.

The crown reinforcement 3, comprising two crown layers comprising metal reinforcers, is represented radially inside the first radially interior portion 21. The carcass reinforcement 4, comprising a carcass layer comprising metal reinforcers, is represented radially inside the crown reinforcement 3.

A meridian section of the crown of a tyre 1 for a heavy vehicle of civil engineering type according to an embodiment of the invention, comprising a tread 2, intended to come into

20310163_1 (GHMatters) P45201AU00 contact with a ground surface, is represented in Figure 2. According to this preferred embodiment, the first portion 21 is formed by a single layer C1 . In this particular case, the tread is formed by the radial superimposition of two layers, the first and second portions being monolayers: the tread is a "bilayer".

A layer radial thickness is a distance measured, along the radial direction, between the respectively radially interior and radially exterior faces of the layer. This thickness is measured in the equatorial plane of the tyre, which passes through the middle of the tread and is perpendicular to the axis of rotation of the tyre. This thickness is measured on a new tyre, that is to say a tyre which has not run, and consequently an unworn tyre. The expression "radial thickness which is substantially constant" is understood to mean a thickness within an interval of + or - 5% with respect to a mean thickness and over at least 80% of the axial width L of the tread.

A dynamic shear modulus is measured on a viscosity analyser of Metravib VA4000 type according to Standard ASTM D 5992-96. The response of a sample of vulcanized polymeric material, having the form of a cylindrical test specimen with a thickness of 4 mm and with a cross section of 400 mm 2, subjected to a simple alternating sinusoidal shear stress, at the frequency of 10 Hz, with a strain amplitude sweep from 0.1% to 45% (outward cycle) and then from 45% to 0.1% (return cycle), and at a temperature of 60°C, is recorded. The dynamic shear modulus is thus measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C.

Advantageously, six inequalities combining the radial thicknesses and/or the dynamic shear moduli of the constituent layers of the first and second tread portions have to be satisfied.

The first inequality 1/(E/G+E 2/G 2) > Go/(E1 +E 2), with E 1 = E lE 1 , G 1 = E1/(Z> E1 i/Gli) with E 1i, E 1and E 2 in mm, G 1i, G 1and G 2 in MPa and with 1 MPa Go 1.8 MPa, means that the stiffness of a tread according to an embodiment of the invention, formed by a first portion, itself formed by the radial superimposition of N layers Cli, having respective radial thicknesses E 1i and being formed of polymeric materials M1 i having respective shear moduli G 1i, and a second exterior radial portion, formed by a single layer C 2 , having a radial thickness E 2 and being formed of a polymeric material M 2 having a respective shear modulus G 2, has to be greater than the stiffness of a tread of the state of the art, formed by an equivalent single layer, having a radial thickness equal to the sum of the radial thicknesses of all the constituent layers of the first and second portions respectively, the said equivalent layer being formed of a polymeric material having a dynamic shear modulus Go. The reference dynamic shear modulus Go, in the field of tyres for heavy

20310163_1 (GHMatters) P45201AU00 vehicles of the civil engineering type, is usually at least equal to 1 MPa and at most equal to 1.8 MPa.

In order to simplify the writing of the inequality, the equivalent radial thickness E 1 and the equivalent dynamic shear modulus G 1of the first portion, likened to a single equivalent layer C1, are introduced. By definition, the equivalent radial thickness E 1 of the first portion is equal to the sum of the respective radial thicknesses E1 i of the layers Cli. By definition also, the equivalent flexibility E /G 1 of the first portion, which is the inverse of the equivalent stiffness G 1/E ,1 is equal to the sum of the respective flexibilities E1 i/G 1 i of the layers Cli, which gives the expression for the equivalent dynamic shear modulus G 1 of the first portion.

This first inequality expresses the fact that, on the new tyre, that is to say at the start of its life, when it is fitted to the front axle of the vehicle, the multilayer tread of a tyre according to an embodiment of the invention has to be stiffer than the monolayer tread of a tyre of the state of the art. This is because the tread of a new tyre, at the start of life on a front axle, wears predominantly under the force imposed. In point of fact, locally, the force applied to the tread is the product of the stiffness of the tread and of the local rate of slip to which wear is proportional. Consequently, with an imposed force, when the stiffness of the tread increases, the local rate of slip, and thus the wear, decrease. Thus, at the start of life, the multilayer tread in accordance with an embodiment of the invention, which is stiffer, will wear less quickly than the monolayer tread of the state of the art.

The second inequality G 1 < Go means that the equivalent dynamic shear modulus G 1 of the first portion has to be lower than the dynamic shear modulus Go of the single polymeric material of which the tread of a tyre of the state of the art is formed, measured under the same conditions. If the residual radial thickness of the tread, at the end of life of the tyre on a rear axle, measured from the crown reinforcement, is termed Er, the second inequality can also be written G1/Er < Go/Er. For the tyre of embodiments of the invention, Er corresponds to the residual radial thickness of the radially interior first portion of the partially worn tread, part of the most radially exterior layers Cli having been completely worn away. This new relationship expresses the fact that the stiffness of the multilayer tread of an embodiment of the invention at the end of life G1/Er has to be lower than that of the tread of the state of the art Go/Er. The tread of a worn tyre, at the end of life on a rear axle, wears predominantly under the strain imposed. In point of fact, the local rate of slip is the ratio of the local force, applied to the tread, to the stiffness of the tread. Thus, when the stiffness of the tread decreases, the local force decreases. As the wear is an increasing function of the local force, when the stiffness of the tread decreases, the wear, which varies in the same direction as the local force, decreases. Consequently, the tread in

20310163_1 (GHMatters) P45201AU00 accordance with an embodiment of the invention, which is less stiff, will wear less rapidly than the tread ofthe state ofthe art.

Thus, the first two inequalities express the fact that the wear of a tread of a tyre according to an embodiment of the invention is less rapid than that of a tyre of the state of the art, at the start of life and at the end of life, that is to say throughout the life of the tyre.

The third inequality E1 > E1 min = 25 mm means that the equivalent radial thickness E1 of the radially interior first portion has at least to be equal to a minimum value E1 min, equal to 25 mm and corresponding to the depth of influence of the indenting bodies usually covering the tracks run on. In other words, the radially interior first portion has to be sufficiently thick to be able to have a sufficient flexibility guaranteeing a cushioning effect which makes it possible to envelop the indenting body.

The fourth inequality G 2 > Go> G 1 means that the dynamic shear modulus G 2 of the second portion has to be greater both than the reference dynamic shear modulus Go and than the equivalent dynamic shear modulus G 1 of the first portion, that is to say that there has to be a decreasing gradient of the dynamic shear moduli when passing from the second portion to the first portion.

The fifth inequality E 2 E2max = 70 mm means that the radial thickness E 2 of the single layer C 2 of the radially exterior second portion has at most to be equal to a maximum value E2max, equal to 70 mm and corresponding to the limiting radial thickness beyond which the running of the tyre over the indenting bodies no longer has an impact on the strains of the radially interior layers of the first portion. In other words, in order to make possible the cushioning effect of the radially interior first portion and in order to guarantee a sufficient stiffness of the radially exterior second portion intended to come into contact with the indenting bodies, this radially exterior second portion must not be too thick.

The sixth inequality 1/(X 1 E1 i /Gli) < 1/(ZE± 1 E 1i /Gli), for 1 j N-1, means that, within the first portion, the stiffness of the assembly formed by the j most radially interior layers Cj has to be less than the stiffness of the assembly formed by the (N-j-1) most radially exterior layers. There is thus a decreasing gradient of stiffnesses, for the layers of the first portion, when passing from the most radially exterior layers to the most radially interior layers. Thus, the layers radially the most radially interior, which are the least stiff and thus the most flexible, act as cushion with regard to the most radially exterior layers.

Embodiments of the present invention can be applied to any type of tyre. The tyre according to an embodiment of the invention can be intended to equip motor vehicles of passenger vehicle type, SUVs ("Sport Utility Vehicles"), or two-wheel vehicles (in particular

20310163_1 (GHMatters) P45201AU00 motorcycles), or aircraft, or also industrial vehicles chosen from vans, heavy-duty vehicles - that is to say, underground trains, buses, heavy road transport vehicles (lorries, tractors, trailers) or off-road vehicles, such as heavy agricultural vehicles or civil engineering vehicles -, and others.

A tyre comprises in particular a tread, the running surface of which is provided with a pattern formed by a plurality of grooves delimiting elements in relief (blocks, ribs) so as to generate edges of material and also voids. These grooves represent a volume of voids which, with respect to the total volume of the tread (including both the volume of elements in relief and that of all the grooves), is expressed by a percentage denoted, in the present document, by "volumetric void ratio". A volumetric void ratio equal to zero indicates a tread without grooves or voids.

Embodiments of the present invention are particularly well suited to tyres intended for civil engineering or agricultural vehicles and for heavy-duty vehicles, more particularly for civil engineering or agricultural vehicles, the tyres of which are subjected to highly specific stresses, in particular the stony ground surfaces on which they run. Thus, advantageously, the tyre according to an embodiment of the invention is a tyre for civil engineering, agricultural or heavy-duty vehicles, preferably civil engineering vehicles.

The tread described in the present document can have one or more grooves, the mean depth of which ranges from 15 to 120 mm, preferably 65 to 120 mm.

The tyres according to an embodiment of the invention can have a diameter ranging from 20 to 63 inches, preferably from 35 to 63 inches.

Moreover, the mean volumetric void ratio over the whole of the tread described in the present document can be within a range extending from 5% to 40%, preferably from 5% to 25%.

11.7 Manufacturing process

The rubber composition can be manufactured in appropriate mixers, using two successive phases of preparation well known to a person skilled in the art: a first phase of thermomechanical working or kneading ("non-productive" phase) at high temperature, up to a maximum temperature of between 110°C and 200°C, followed by a second phase of mechanical working ("productive" phase) down to a lower temperature, typically of less than 110°C, for example between 40°C and 100°C, during which finishing phase the crosslinking system is incorporated.

203101631 (GHMatters) P45201AU00

By way of example, the first (non-productive) phase is carried out in a single thermomechanical stage during which all the necessary constituents, the optional supplementary covering agents or processing aids and various other additives, with the exception of the vulcanization system, are introduced into an appropriate mixer, such as an ordinary internal mixer. The total duration of the kneading, in this non-productive phase, is preferably between 2 and 10 min. After cooling the mixture thus obtained during the first non-productive phase, the vulcanization system is then incorporated at low temperature, generally in an external mixer, such as an open mill; everything is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The first stage of kneading is generally carried out by incorporating the reinforcing filler in the elastomer, in one or more goes, while kneading thermomechanically. In the case where the reinforcing filler, in particular the carbon black, is already incorporated, in all or in part, in the elastomer in the form of a masterbatch, as is described, for example, in Applications WO 97/36724 and WO 99/16600, it is the masterbatch which is directly kneaded and, if appropriate, the other elastomers or reinforcing fillers present in the composition which are not in the masterbatch form, and also the additives other than the crosslinking system, are incorporated.

The process for preparing the rubber composition in accordance with an embodiment of the invention can comprise the following stages: - adding the carbon black to the polyisoprene during a first "non-productive" stage, kneading thermomechanically until a maximum temperature of between 110°C and 200°C is reached, - cooling the combined mixture to a temperature of less than 110°C, - subsequently incorporating the crosslinking system, - kneading everything up to a maximum temperature of less than 110°C in order to obtain a mixture.

The process can also comprise the following stage: - calendering or extruding the mixture obtained.

After the incorporation of all the ingredients of the rubber composition, the final composition thus obtained is subsequently calendered, for example in the form of a sheet or plaque, in particular for laboratory characterization, or else extruded, in order to form, for example, a rubber profiled element used as rubber component in the preparation of the tyre. The rubber composition in accordance with an embodiment of the invention can be used in the form of a calendered product in a tyre.

20310163_1 (GHMatters) P45201AU00

Thus, according to a specific embodiment of the invention, the rubber composition in accordance with embodiments of the invention, which can either be in the raw state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization), is in a tyre, for example in a tyre tread.

The tyre, other subject-matter in accordance with an embodiment of the invention, which contains the rubber composition in accordance with embodiments of the invention, can either be in the raw state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization), which composition can be in the form of a calendered product or of an extrudate in order to form a rubber component of the tyre.

A better understanding of the abovementioned characteristics of the present invention, and also others, will be obtained on reading the following description of several implementational examples of the invention, given by way of illustration and without limitation.

III. IMPLEMENTATIONAL EXAMPLES OF THE INVENTION

111.1 Measurements and tests used:

Dynamic properties: The dynamic properties are measured on a viscosity analyser (Metravib VA4000) according to Standard ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical test specimen with a height of 4 mm and with a cross section of 400mm 2 ), subjected to a simple alternating sinusoidal shear stress, at the frequency of 10 Hz, at 80°C and at 100°C, is recorded. A strain amplitude sweep is carried out from 0.1% to 100% (outward cycle) and then from 100% to 0.1% (return cycle). The results made use of are the complex dynamic shear modulus G* and the loss factor tan(6). The value of the G* at 50% strain and also the loss factor, denoted tan()max, are recorded on the return cycle.

The results of tan(6)max at 100°C are expressed in base 100, the value 100 being assigned to the control. A result of less than 100 indicates that the composition of the example under consideration has a lower hysteresis at 100°C, reflecting a lower rolling resistance of the tread comprising such a composition.

Tensile tests: They are carried out in accordance with French Standard NF T 46-002 of September 1988. At second elongation (that is to say, after accommodation), the nominal secant modulus, calculated by reducing to the initial cross section of the test specimen, (or apparent stress, in MPa) is measured at 10% and 100% elongation, denoted MAS10 and MAS100

20310163_1 (GHMatters) P45201AU00 respectively. All these tensile measurements are carried out under the standard conditions of temperature (23 ± 2°C) and hygrometry (50% ±5% relative humidity), according to French Standard NF T 40-101 (December 1979).

The results are expressed in base 100, the value 100 being assigned to the control. A result of less than 100 indicates that the composition of the example under consideration exhibits a lower stiffness, which is particularly for compositions used in a radially interior portion of a tread of a tyre, in particular a tyre intended to bear heavy loads, in particular running over stony ground surfaces, such as a civil engineering vehicle tyre.

Cracking tests: The dynamic cracking test makes it possible to evaluate the resistance of the mixtures to the propagation of a crack on a test specimen.

The measurement comprises 3 parts: (i) Accommodation of the test specimen at 27% at a frequency of 10 hertz, (ii) Energy characterization of the unnotched test specimen in order to determine the law G = f(strain) where the energy restitution level G represents the criterion of loading of the crack at the notch bottom (iii) Cracking measurement on a notched test specimen under air at 80°C, 10 hertz, at an energy restitution level G de 300 J/m 2 after notching the test specimen.

The lengths propagated are measured after halting the stressing. The crack propagation rate PR represents the length of crack propagated per stress cycle. Due to the dimensions of the test specimen, it is expressed in nanometres per cycle.

The PR results are expressed in base 100, the value 100 being assigned to the control. A result of less than 100 indicates that the composition of the example under consideration exhibits a better resistance to crack propagation.

111.2 Preparation of the rubber compositions:

The breakdown of the formulations of the compositions 11 and C1 to C7 is described in Table 1. They were prepared in accordance with the process described above but calendered, either in the form of plaques (with a thickness ranging from 2 to 3 mm) or thin sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of profiled elements which can be used directly, after cutting and/or assembling to the desired dimensions.

Table I Composition C1 11 C2 C3 C4 C5 C6 C7

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NR (1) 100.00 - - - - - -

ENR25 (2) - 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Silica (3) 15.00 - 5.00 15.00 5.00 15.00 15.00 5.00 Black (4) 40.00 40.00 40.00 40.00 35.00 25.00 40.00 35.00 Antioxidant (5) 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 Paraffin 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 PEG (6) 2.50 - - - - - 2.5 0.83 ZnO 2.70 2.70 2.70 2.70 2.70 2.70 2.70 2.70 Stearicacid 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Sulfur 1.70 1.70 1.70 1.70 1.70 1.70 1.70 1.70 Accelerator (7) 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 (1) natural rubber (2) natural rubber epoxidized to 25% (3) silica, Ultrasil VN3 from Evonik (4) N115 from Cabot (5) N-(1,3-dimethylbutyl)-N'-phenyl-para-phenylenediamine, Santoflex 6-PPD from Flexsys (6) polyethylene glycol, Carbowax 8000 from Dow Corning (7) N-cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from Flexsys)

The composition C1 is a control composition which is conventionally used in a tread of a tyre for a vehicle intended to bear heavy loads, in particular running over stony ground surfaces, such as a civil engineering vehicle tyre. The composition 11 is in accordance with embodiments of the invention. The control compositions C2 to C7 differ from the compositions in accordance with embodiments of the present invention in that they comprise silica, either in addition to the carbon black or as replacement for an equivalent amount of carbon black, this being the case in the presence or in the absence of covering agent.

111.3 Properties of the rubber compositions:

The results of the dynamic properties and of the tensile tests, on the one hand, and those of the cracking tests appear respectively in Table 11 and Table Ill.

Table 11 Composition C1 11 C2 C3 C4 C5 C6 C7 Tan(6)max at 100 68 73 86 69 71 90 70 100°C G*(50%) at 100°C 100 91 101 145 98 107 146 96 MAS10at23°C 100 87 110 168 103 109 140 91 MAS100at23°C 100 105 132 203 125 136 155 111

20310163_1 (GHMatters) P45201AU00

Table Ill Composition C1 11 PR 100 63

All the compositions based on epoxidized natural rubber exhibit a value of tan()max at 100°C which is markedly lower than the composition C1, which demonstrates a particularly advantageous decrease in the hysteresis. However, the composition 11 in accordance with an embodiment of the invention exhibits a value of tan()max at 100°C which is among the lowest of those of the control compositions based on epoxidized natural rubber, which demonstrates a decrease in the hysteresis and thus a better rolling resistance.

Furthermore, the values of G* 50% and of the MAS10 and MAS100 moduli of the composition 11 are at a level acceptable for use in tyres. The composition 11 is, in comparison with the control compositions, less stiff, which is particularly advantageous when the composition is used in a radially interior portion of a tread of a tyre, in particular a tyre intended to bear heavy loads, in particular running over stony ground surfaces, such as a civil engineering vehicle tyre.

Finally, the composition 11 in accordance with an embodiment of the present invention exhibits a resistance to the propagation of cracks which is particularly noteworthy in comparison with the compositions conventionally used in a tread of a tyre for a vehicle intended to bear heavy loads.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

20310163_1 (GHMatters) P45201AU00

Claims (19)

1. Tyre which comprises a tread having an axial width and being formed by a radial superimposition of a first portion and a second portion, the first portion being a radially interior portion of the tread and the second portion being radially exterior to the first portion, a composition of the first portion comprising a rubber composition, the said rubber composition comprising: - from more than 50 to 100 phr of polyisoprene containing an epoxidized polyisoprene having a molar degree of epoxidation ranging from 5% to less than50%, - a carbon black, - a crosslinking system, the epoxidized polyisoprene being an epoxidized natural rubber or an epoxidized synthetic polyisoprene having a molar content of cis-1,4 bonds of at least 90% before epoxidation, or their mixture, with the proviso that, if the epoxidized polyisoprene is an epoxidized polyisoprene having a molar degree of epoxidation of from 5% to 25%, the rubber composition contains more than 50 phr of epoxidized polyisoprene, the rubber composition being devoid of silica, the said tyre being a tyre for civil engineering vehicles, wherein a composition of the second portion is different from the composition of the first portion.

2. Tyre according to Claim 1, wherein the content of carbon black in the rubber composition is from 30 phr to 90 phr.

3. Tyre according to Claim 1 or 2, wherein the carbon black exhibits a BET specific surface of at least 90 m 2/g.

4. Tyre according to any one of Claims 1 to 3, wherein the epoxidized polyisoprene predominantly comprises an epoxidized natural rubber.

5. Tyre according to any one of Claims 1 to 4, wherein the epoxidized polyisoprene predominantly comprises an epoxidized polyisoprene having a molar degree of epoxidation of 5% to 40%.

6. Tyre according to any one of Claims 1 to 4, wherein the epoxidized polyisoprene predominantly comprises an epoxidized polyisoprene having a molar degree of epoxidation of 5% to 35%

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7. Tyre according to any one of Claims 1 to 4, wherein the epoxidized polyisoprene predominantly comprises an epoxidized polyisoprene having a molar degree of epoxidation of 10% to 35%.

8. Tyre according to any one of Claims 1 to 7, wherein the content of polyisoprene in the rubber composition is greater than 80 phr.

9. Tyre according to Claim 6 or Claim 7, wherein the content of epoxidized polyisoprene in the rubber composition is greater than 80 phr.

10. Tyre according to any one of Claims 1 to 9, wherein the polyisoprene contains a polyisoprene having a molar content of cis-1,4 bonds of at least 90%.

11. Tyre according to Claim 10, wherein the polyisoprene is formed of a mixture of the polyisoprene having a molar content of cis-1,4 bonds of at least 90% and of the epoxidized polyisoprene.

12. Tyre according to either one of Claims 10 and 11, wherein the polyisoprene having a molar content of cis-1,4 bonds of at least 90% is a natural rubber.

13. Tyre according to any one of Claims 1 to 12, wherein the rubber composition optionally comprises a butyl rubber at a content within a range extending from 0 to 20 phr.

14. Tyre according to any one of Claims 1 to 13, wherein the rubber composition does not comprise butyl rubber.

15. Tyre according to any one of Claims 1 to 14, wherein the content of polyisoprene in the rubber composition is equal to 100 phr.

16. Tyre according to any one of Claims 1 to 9, wherein the content of epoxidized polyisoprene in the rubber composition is equal to 100 phr.

17. Tyre according to any one of Claims 1 to 16, wherein the composition is devoid of inorganic filler.

18. Tyre according to any one of Claims 1 to 17, wherein the crosslinking system of the rubber composition is a vulcanization system.

19. Tyre according to any one of Claims 1 to 18, wherein:

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- the first portion is formed by a radial superimposition of N layers Cli, i varying from 1 to N, - each layer Cli has a radial thickness E1 i, measured in an equatorial plane of the tyre, which is substantially constant over at least 80% of the axial width L of the tread, and is formed of a polymeric material M1 i having a dynamic shear modulus G1 i, measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C, any one or all of the polymeric materials M 1i being formed of the rubber composition according to any one of Claims 1 to 18, - the second portion is formed by a single layer C 2

, - the layer C 2 has a radial thickness E 2 , measured in the equatorial plane of the tyre, which is substantially constant over at least 80% of the axial width L of the tread, and is formed of a polymeric material M 2 having a dynamic shear modulus G 2

, measured for a frequency equal to 10 Hz, a strain equal to 50% of the peak-to-peak strain amplitude and a temperature equal to 60°C, and - the following relationships are simultaneously satisfied: a. 1/(E 1 /G 1 +E2/G 2) > Go/(E 1+E2), with E1 = X E1 i, G1 = E1/(> E1 i/Gli) with E 1i, E 1and E2 in mm, G 1i, G 1and G2 in MPa and with 1 MPa Go 1.8 MPa b. G 1 < Go c. E 1 > E 1min = 25 mm d. G2 > Go> G1 e. E2 E2max = 70 mm f. 1/(EN E 1 i /G 1 i) < 1/(ZN 1 E1 i /G 1i) for 1 j N-1.

20310163_1 (GHMatters) P45201AU00