AU2021253733A1 - Rubber composition comprising low-melting-point polyamide - Google Patents

Abstract

The invention relates to a rubber composition based on at least, a diene elastomer, from 10 to 60 phr of carbon black, from 5 to 30 phr of silica, a polyamide having a melting point below 170°C, and a crosslinking system, in which the carbon black represents from 50% to 95% by weight relative to the total weight of carbon black and silica. It also relates to a process for preparing the rubber composition and to a rubber article comprising the composition according to the invention.

Description

TITLE: RUBBER COMPOSITION COMPRISING LOW-MELTING-POINT POLYAMIDE DESCRIPTION

The present invention relates to rubber compositions exhibiting a good performance compromise between resistance to mechanical attack and hysteresis. It relates in particular to rubber articles such as pneumatic tyres, non-pneumatic tyres, caterpillar tracks, conveyor belts or any other rubber article for which the aforementioned performance compromise would be advantageous.

In particular, the rubber compositions of the invention are very advantageous when they are used in treads of pneumatic tyres for civil engineering vehicles. This is because these tyres have to have very different technical characteristics from the tyres intended for vehicles which run exclusively on roads (that is to say a bituminous surface), since the nature of the off-road surfaces on which they are mainly moving is very different and in particular much more aggressive, due to its stony nature. Furthermore, in contrast to passenger vehicle tyres, for example, tyres for large civil engineering vehicles have to be able to withstand a load which can be extremely heavy. Consequently, the solutions known for tyres running on a bituminous surface are not directly applicable to off-road tyres, such as tyres for civil engineering vehicles.

During running, a 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 to which the tyre is subjected are magnified under the effect of the weight bome by the tyre. Tyres for mining vehicles in particular are subjected to high stresses, both locally: running over the indenting macrobodies represented by the stones from which the tracks are formed (crushed rock), and also globally: high torque transmission since the slopes of the tracks for entering or leaving the "pits", or open-air minds, are about 10%, and high stresses on the tyres during U-turns performed by the vehicles for loading and unloading manoeuvres.

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The consequence of this is that the incipient cracks which are created in the tyre tread under the effect of these stresses and these attacks have a tendency to further propagate at the surface of or inside the tread, which can bring about localized or generalized tearing of the tread. These stresses can therefore result in damage to the tread and can thus reduce the lifetime of the tread and thus of the tyre. A tyre running over stony ground is highly exposed to attacks, and therefore to incipient cracks and cuts. 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 and quarries. 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 initiation and/or propagation in a tread of a tyre for a civil engineering vehicle, an agricultural vehicle or a construction site 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 intended to run on stony ground surfaces and bearing heavy loads, the tread of which exhibits a resistance to crack initiation and/or 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 those skilled in the art that, for example, natural rubber in treads makes it possible to obtain elevated properties of resistance to crack initiation and/or 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 reflecting the heat dissipation capacity of the composition. This is because the use of a composition that is too hysteretic 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.

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In the light of the above, it is an ongoing objective to provide rubber compositions which exhibit an improved compromise between the resistance to attacks and the hysteresis.

This performance compromise is also advantageous for rubber caterpillar tracks intended to be fitted to construction vehicles or agricultural vehicles for the same reasons as set out above. It is also advantageous for conveyor belts (or belt conveyors) which can receive large amounts of earth, ore, stones, rocks and which can dissipate huge amounts of energy via internal dissipation to the material constituting the belt during the punching of the belt between its load and the support driving it.

Solutions have been provided to improve this compromise. For example, application WO 2016/202970 Al which proposes using a specific composition, the elastomeric matrix of which comprises a diene elastomer selected from the group consisting of polybutadienes, butadiene copolymers and mixtures thereof, and a styrene thermoplastic elastomer comprising at least one rigid styrene segment and at least one flexible diene segment comprising at least 20% by weight of conjugated diene units.

However, manufacturers are always looking for solutions to further improve the performance compromise between resistance to attacks and hysteresis, preferably regardless of the nature of the elastomeric matrix.

Pursuing its research, the applicant has unexpectedly discovered that the use of polyamide having a melting point of less than 170°C in the presence of a specific blend of filler in a rubber composition makes it possible to improve the aforementioned performance compromise.

Thus a subject of the invention is a rubber composition based on at least a diene elastomer, from 10 to 60 phr of carbon black, from 5 to 30 phr of silica, a polyamide having a melting point of less than 170°C, and a crosslinking system, in which composition the carbon black represents from 55% to 95% by weight relative to the total weight of carbon black and silica.

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Another subject of the invention is a rubber article comprising a rubber composition according to the invention, and also a pneumatic or non-pneumatic tyre, the tread of which comprises a rubber composition according to the invention.

I- DEFINITIONS The expression "composition based on" should be understood as meaning a composition comprising the mixture and/or the product of the in situ reaction of the various constituents used, some of these constituents being able to react and/or being intended to react with one another, at least partially, during the various phases of manufacture of the composition; it thus being possible for the composition to be in the completely or partially crosslinked state or in the noncrosslinked state.

The expression "phr" should be understood as meaning, for the purposes of the present invention, the part by weight per hundred parts by weight of elastomer.

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

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 (i.e. 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 (i.e. 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.

When reference is made to a "predominant" compound, this is understood to mean, for the purposes 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 that which represents the greatest amount by weight among the compounds of the same type. Thus, for example, a predominant elastomer is the elastomer representing the greatest weight relative to the total weight of the elastomers in the composition. In the same way, a "predominant" filler is that representing the greatest weight among the fillers of the composition. By way of example, in a system

19035573_1 (GHMatters) P119923.AU comprising just one elastomer, the latter is predominant for the purposes of the present invention and, in a system comprising two elastomers, the predominant elastomer represents more than half of the weight of the elastomers. 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. Preferably, the term "predominant" is understood to mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferentially the "predominant" compound represents 100%.

The compounds comprising carbon mentioned in the description may be of fossil or biobased origin. In the latter case, they may be partially or totally derived from biomass or may be obtained from renewable starting materials derived from biomass. Polymers, plasticizers, fillers, etc. are notably concerned.

All the values for glass transition temperature "Tg" described in the present document are measured in a known manner by DSC (Differential Scanning Calorimetry) according to Standard ASTM D3418 (1999).

II- DESCRIPTION OF THE INVENTION II-A Composition II-A-I Elastomer matrix The composition according to the invention can contain just one diene elastomer or a mixture of several diene elastomers.

The term "diene" elastomer (or, without distinction, rubber), whether natural or synthetic, should be understood, in a known way, as meaning an elastomer 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 may be classified into two categories: "essentially unsaturated" or "essentially saturated". The term "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

19035573_1 (GHMatters) P119923.AU elastomers such as butyl rubbers or copolymers of dienes and of a-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). Advantageously, the diene elastomer is an essentially unsaturated diene elastomer.

The term "diene elastomer that can be used in the context of the present invention" particularly means: a) any homopolymer of a conjugated or non-conjugated diene monomer having from 4 to 18 carbon atoms, b) any copolymer of a conjugated or non-conjugated diene having from 4 to 18 carbon atoms and of at least one other monomer.

The other monomer can be ethylene, an olefin or a conjugated or non-conjugated diene.

Conjugated dienes that are suitable include conjugated dienes containing from 4 to 12 carbon atoms, in particular 1,3-dienes, notably such as 1,3-butadiene and isoprene.

Olefins that are suitable include vinylaromatic compounds containing from 8 to 20 carbon atoms and aliphatic a-monoolefins containing from 3 to 12 carbon atoms.

Vinylaromatic compounds that are suitable include, for example, styrene, ortho-, meta- or para methylstyrene, the "vinyltoluene" commercial mixture or para-(tert-butyl)styrene.

Aliphatic a-monoolefins that are suitable notably include acyclic aliphatic a-monoolefins containing from 3 to 18 carbon atoms.

Preferably, the diene elastomer is selected from the group consisting of polybutadienes (BRs), synthetic polyisoprenes (IRs), natural rubber (NR), butadiene copolymers, isoprene copolymers and mixtures thereof. Preferably selected from the group consisting of synthetic polyisoprenes, natural rubber and mixtures thereof.

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The butadiene copolymers are preferentially selected from the group consisting of butadiene/styrene copolymers (SBRs). It should be noted that the SBR can be prepared in emulsion (ESBR) or in solution (SSBR). Whether it is ESBR or SSBR. Mention may in particular be made, among copolymers based on styrene and on butadiene, in particular SBR, of those having a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (mol%) of 1,2- bonds of the butadiene part of between 4% and 75% and a content (mol%) of trans-1,4- bonds of between 10% and 80%. Advantageously, the butadiene/styrene copolymer is an SBR prepared in solution and has a styrene content of between 5% and 60%, preferably from 6% to 30%, by weight, relative to the total weight of the copolymer, and a content (mol%) of 1,2- bonds of the butadiene part of between 4% and 75%, preferably between 15% and 3 0 %.

Mention will in particular be made, among the isoprene copolymers, of isobutene/isoprene (butyl rubber - IIR), isoprene/styrene (SIR), isoprene/butadiene (BIR) or isoprene/butadiene/styrene (SBIR) copolymers.

Particularly advantageously, the diene elastomer mainly, preferably exclusively, comprises at least one polyisoprene. It may in particular be an epoxidized or non-epoxidized polyisoprene.

In the present text, the term "polyisoprene" means any polyisoprene whether it is epoxidized or not.

Advantageously, the diene elastomer is a non-epoxidized polyisoprene selected from the group consisting of natural rubber, a synthetic polyisoprene and a mixture thereof. Advantageously, the non-epoxidized polyisoprene has a molar content of 1,4-cis bonds of at least 90%.

Alternatively, the diene elastomer may be an epoxidized polyisoprene advantageously having a molar degree of epoxidation ranging from 1% to 85%.

The term "epoxidized polyisoprene" is intended to mean a polyisoprene which has undergone an epoxidation step. The epoxidized polyisoprene can be an epoxidized natural rubber, an

19035573_1 (GHMatters) P119923.AU epoxidized synthetic polyisoprene having a molar content of cis-1,4 bonds of at least 90% before epoxidation, or a mixture thereof.

The epoxidized polyisoprene used in the context of the present invention is an elastomer and is not to be confused with an epoxidized polyisoprene of low molar mass, 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. As an indication, the Mooney viscosities (ML 1+4) at 100°C of the epoxidized polyisoprenes that can be used in the context of the present invention are preferentially from 30 to 150, more preferentially from 40 to 150, even more preferentially from 50 to 140.

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 100C). 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. "Degree of epoxidation", expressed as molar percentage (mol%), is intended to mean the number of moles of epoxidized cis-1,4-polyisoprene units present in the rubber polymer per 100 mol of total monomer units in this same polymer. The degree of epoxidation may be measured especially by 1 H NMR analysis.

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As examples of commercially available epoxidized polyisoprenes, mention may be made of Epoxyprene 25 and Epoxyprene 50 from Guthrie or Ekoprena 25 and Ekoprena 50 from Felda.

According to the present invention, the expression "at least one epoxidized polyisoprene" should be understood as one or more epoxidized polyisoprenes which can differ in terms of either 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.

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.

According to the invention, the at least one epoxidized polyisoprene advantageously has a molar degree of epoxidation ranging from 1% to 85%, preferably from 5% to 55%, preferably from 10% to less than 49%, preferably from 15% to less than 40%.

The content of diene elastomer, preferably of polyisoprene, preferably of natural rubber, in the composition according to the invention, is within a range extending from 50 to 100 phr, preferably from 75 to 100 phr; it is more preferably 100 phr.

II-A-2 Fillers According to the invention, the composition is based on a filler comprising from 10 to 60 phr of carbon black and from 5 to 30 phr of silica, the carbon black representing from 50% to 95%, preferably from 55% to 95%, by weight relative to the total weight of carbon black and silica.

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The blacks that can be used in the context of the present invention can be any black conventionally used in pneumatic or non-pneumatic tyres or their treads ("tyre-grade" blacks). Among the latter, mention will be made more particularly of the reinforcing carbon blacks of the 100, 200 and 300 series, or the blacks of the 500, 600 or 700 series (ASTM grades), for instance 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 available commercially, or in any other form, for example as support for some of the rubber additives used. The carbon blacks might, for example, be already incorporated in the diene elastomer, in particular isoprene elastomer, in the form of a masterbatch (see, for example, applications WO 97/36724 or WO 99/16600). Mixtures of several carbon blacks can also be used in the prescribed amounts.

Mention may be made, as examples of organic fillers other than carbon blacks, of functionalized polyvinyl organic fillers, such as described in applications WO 2006/069792, WO 2006/069793, WO 2008/003434 and WO 2008/003435.

Advantageously, the BET specific surface area of the carbon black is at least90 m 2/g, preferably between 100 and 150 m 2/g. The BET specific surface area of the carbon blacks is measured according to Standard ASTM D6556-10 [multipoint (a minimum of 5 points) method - gas: nitrogen - relative pressure p/po range: 0.1 to 0.3].

The carbon black advantageously exhibits a COAN oil absorption number of greater than or equal to 90 ml/100 g. The COAN, orCompressed Oil Absorption Number, of the carbonblacks is measured according to Standard ASTM D3493-16.

Advantageously, the content of carbon black (whether there is one or more thereof) in the composition according to the invention is within a range extending from 15 to 55 phr, preferably from 30 to 50 phr.

The silicas that can be used in the context of the present invention can be any silica known to those skilled in the art, in particular any precipitated or fumed silica exhibiting a BET surface area and a CTAB specific surface area which are both less than 450 m 2/g, preferably from 30

19035573_1 (GHMatters) P119923.AU to 400 m2 /g. It can also be a mixture of several silicas, as long as they are used in the prescribed amounts.

The BET specific surface area of the silica is determined by gas adsorption using the Brunauer Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), and more specifically according to a method adapted from Standard NF ISO 5794-1, Appendix E, of June 2010 [multipoint (5 point) volumetric method - gas: nitrogen - degassing under vacuum: one hour at 160°C - relative pressure p/po range: 0.05 to 0.17].

The CTAB specific surface area values of the silica were determined according to Standard NF ISO 5794-1, Appendix G of June 2010. The process is based on the adsorption of CTAB (N hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the reinforcing filler.

The silicones that can be used in the context of the present invention advantageously have a BET specific surface area of less than 250 m /g and/or a CTAB specific surface area of less 2

than 220 m 2 /g, preferably a BET specific surface area within a range extending from 125 to 200 m /g and/or a CTAB specific surface area within a range extending from 140 to 170m 2/g. 2

Mention will be made, as silicas that can be used in the context of the present invention, for example, of the highly dispersible precipitated silicas (termed "HDSs") Ultrasil 7000 and Ultrasil 7005 from Evonik, 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 area as described in application WO 03/016387.

Advantageously, the content of silica (whether there is one or more thereof) in the composition according to the invention is within a range sending from 5 to 25 phr, preferably from 6 to 20 phr.

In order to couple the reinforcing silica to the diene elastomer, use may be made, in a well known way, of an at least bifunctional coupling agent (or bonding agent) intended to provide a

19035573_1 (GHMatters) P119923.AU satisfactory connection, of chemical and/or physical nature, between the silica (surface of its particles) and the diene elastomer (hereinafter simply referred to as "coupling agent"). Use is made in particular of organosilanes or polyorganosiloxanes which are at least bifunctional. The term "bifunctional" is understood to mean a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound can comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler, and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the diene elastomer.

Those 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.

However, it is advantageous in the context of the present invention not to use a coupling agent. Thus, preferentially, the content of coupling agent, in the composition according to the invention, is advantageously less than 6% by weight relative to the weight of silica, preferably less than 2%, preferably less than 1% by weight relative to the weight of silica. More preferably, the composition according to the invention does not comprise coupling agent.

Moreover, when the composition according to the invention comprises silica, the composition advantageously comprises a silica-covering agent. Among the covering agents for the silica, mention may be made, for example, of hydroxysilanes or hydrolysable silanes such as hydroxysilanes (see, for example, WO 2009/062733), alkylalkoxysilanes, especially alkyltriethoxysilanes such as, for example, 1-octyltriethoxysilane, polyols (for example diols or triols), polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialkanolamines), an optionally substituted guanidine, especially diphenylguanidine, hydroxylated or hydrolysable polyorganosiloxanes (for example a,o dihydroxypolyorganosilanes (especially a,o-dihydroxypolydimethylsiloxanes) (see, for example, EP 0 784 072), and fatty acids such as, for example, stearic acid. When a silica covering agent is used, it is used at a content of between 0 and 5 phr. Preferably, the silica

19035573_1 (GHMatters) P119923.AU covering agent is a polyethylene glycol. The content of silica-covering agent, preferably of polyethylene glycol, in the composition according to the invention is advantageously within a range extending from 1 to 6 phr, preferably from 1.5 to 4 phr.

Advantageously, the total content of carbon black and silica in the composition according to the invention is within a range extending from 15 to 90 phr and preferably from 20 to 70 phr.

Advantageously, the carbon black represents from 60% to 90% by weight, preferably from 65% to 80% by weight, relative to the total weight of carbon black and silica.

The composition according to the invention also has the essential characteristic of comprising a polyamide having a melting point of less than 170°C, hereinafter referred to as "the polyamide" for the sake of simplifying the wording. The melting point is measured in a well known manner by DSC according to Standard ASTM D3418 (2015).

Any polyamide the melting point of which is less than 170°C may be used.

The polyamides used in the context of the present invention may be homopolymers or copolymers, which may come from the condensation of lactams, optionally with lactones, and/or from the condensation of diacids and/or of amino acids with diamines. Preferably, the polyamides used in the context of the present invention are copolymers which come from the condensation of lactams, optionally with lactones, and/or from the condensation of diacids and/or of amino acids with diamines.

A copolymer is, in a manner well known to those skilled in the art, a polymer derived from the copolymerization of at least two types of monomer, which are chemically different, called comonomers.

Particularly advantageously, the polyamide the melting point of which is less than 170°C is a polyamide copolymer consisting of at least two different types of monomers selected from the group consisting of lactams, or of at least two different types of monomers selected from the

19035573_1 (GHMatters) P119923.AU group consisting of diacids and of at least two different types of monomers selected from the group consisting of diamines.

The lactams can for example have 3 to 12 carbon atoms on their main ring and can be substituted. Preferably, the lactams are selected from the group comprising or consisting of p,p dimethylpropriolactam, a,a-dimethylpropriolactam, amylolactam, caprolactam, capryllactam, oenantholactam, 2-pyrrolidone, lauryllactam and mixtures thereof. More preferably, the lactams are selected from the group comprising or consisting of caprolactam, lauryllactam and mixtures thereof.

The diacids (or dicarboxylic acids) can for example be acids having between 4 and 18 carbon atoms. Preferably, the diacids are selected from the group comprising or consisting of adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid, 1,4 cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulfoisophthalic acid, dodecanedioic acid and mixtures thereof. More preferably, the diacids are selected from the group comprising or consisting of adipic acid, dodecanedioic acid and mixtures thereof.

The diamines may for example be saturated aliphatic, aryl and/or cyclic diamines having 6 to 12 carbon atoms. Preferably, the diamines are selected from the group comprising or consisting of hexamethylenediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6 diaminohexane, polyol diamines, isophorone diamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), methaxylyenediamine, bis-p-aminocyclohexylmethane, trimethylhexamethylenediamine, phenylenediamine and mixtures thereof. More preferably, the diamines are selected from the group comprising or consisting of hexamethylenediamine, dodecamethylenediamine and mixtures thereof.

The amino acids may for example be alpha-omega amino acids. Preferably, the amino acids are selected from the group comprising or consisting of aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid, n-heptyl-11-aminoundecanoic acid, 12-aminododecanoic acid and

19035573_1 (GHMatters) P119923.AU mixtures thereof. Preferably, the amino acids are selected from the group comprising or consisting of aminocaproic acid, 12-aminododecanoic acid and mixtures thereof.

By way of example of a lactone, mention may be made of caprolactone, valerolactone and butyrolactone.

Moreover, the polyamide advantageously does not comprise a diene unit.

Regardless of the nature of the monomers of the polyamide that are usable in the context of the present invention, it is advantageous for the number-average molecular weight (Mn) to be within a range extending from 4000 to 1000 000 g/mol, preferably from 6000 to 500 000 g/mol.

The number-average molecular weight (Mn) of the thermoplastic polymers is determined, in a known manner, by size exclusion chromatography (SEC). For example, in the case of the polyamides, the sample is solubilized beforehand in hexafluoro-2-propanol to which has been added 0.02 M of sodium trifluoroacetate at a concentration of approximately 2 g/l. The equipment used is a "Waters Alliance" chromatographic system. The elution solvent is hexafluoro-2-propanol to which has been added 0.02 M of sodium trifluoroacetate, the flow rate is 0.5 ml/min and the system temperature is 35°C. A set of three Phenomenex columns is used in series, having the trade names "Phenogel" ("10 pm 105", "10pm 104"and "10m 103,". The injected volume of the solution of the polymer sample is 100 1. The detector is a "Waters 2410" differential refractometer and its associated software for exploiting the chromatographic data is the "Waters Millennium" system. The calculated average molar masses are relative to a standard curve produced with PMMA standards. The conditions can be adjusted by those skilled in the art.

Advantageously, the melting point of the polyamide the melting point of which is less than 170°C is less than 165°C, preferably less than 160°C, preferably between 100 and 160 °C, preferably between 120 and 160°C.

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The content of polyamide having a melting point of less than 170°C, in the composition according to the invention, can be within a range extending from 3 to 40 phr, preferably from 5 to 30 phr.

Advantageously, the total content of carbon black, silica and polyamide having a melting point of less than 170°C, in the composition according to the invention, is within a range extending from 20 to 90 phr, preferably from 30 to 80 phr.

Also advantageously, the volume fraction of the combination of carbon black, silica and polyamide having a melting point of less than 170°C, in the composition according to the invention, is within a range extending from 10% to 40%, preferably from 15% to 35%.

Advantageously, the total content of thermoplastic polymer, that is to say the sum of the thermoplastic polymers including the polyamide, in the composition according to the invention, is within a range extending from 3 to 40 phr, preferably from 5 to 30 phr. Particularly advantageously, the composition according to the invention does not comprise a thermoplastic polymer other than polyamide having a melting point of less than 170°C.

The polyamides that can be used in the context of the present invention can be synthesized in a manner well known to those skilled in the art, for example according to the processes described in documents DE 2324160, EP 0 627 454, EP 1 153 957 or else EP 1 153 957.

The polyamides that can be used in the context of the present invention are also commercially available. By way of example of a commercially available polyamide the melting point of which is less than 170°C, mention may be made of Orgasol 3401 or Orgasol 3402 from Arkema, or else the polyamides of the Elvamide (registered trademark) series from DuPont, such as Elvamides (registered trademark) 8061, 8063, 8066, and 8023R.

II-A-3 Crosslinking system The crosslinking system can be any type of system known to those skilled in the art in the field of rubber compositions for tyres. It may in particular be based on sulfur, and/or on peroxide and/or on bismaleimides.

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Preferentially, the crosslinking system is based on sulfur; it is then called a vulcanization system. The sulfur can be contributed in any form, in particular in the form of molecular sulfur and/or of a sulfur-donating agent. At least one vulcanization accelerator is also preferentially present, and, optionally, also preferentially, use may be made of various known vulcanization activators, such as zinc oxide, stearic acid or equivalent compound, such as stearic acid salts, and salts of transition metals, guanidine derivatives (in particular diphenylguanidine), or else known vulcanization retarders.

The sulfur is used at a preferential content of between 0.5 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferential content of between 0.5 and 10 phr, more preferentially of between 0.5 and 5.0 phr.

Use may be made, as 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 derivatives thereof, 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.

II-A-4 Possible additives The rubber compositions may optionally also comprise all or some of the usual additives customarily used in elastomer compositions for tyres, such as for example plasticizers (such as plasticizing oils and/or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing resins (as described for example in application WO 02/10269).

II-B Preparation process

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A subject of the present invention is also a process for preparing a composition for the manufacture of rubber compositions according to the invention, characterized in that it comprises the following steps: a) bringing at least a diene elastomer, a filler comprising carbon black and silica, the carbon black representing from 50% to 95%, preferably from 55% to 95%, by weight relative to the total weight of carbon black and silica, and a polyamide having a melting point of less than 170°C into contact and mixing, concomitantly or successively, on one or more occasions, by thermomechanically kneading the whole until a maximum temperature Ti greater than or equal to the melting point of the polyamide is reached, b) reducing the temperature of the mixture obtained in step (a) to a maximum temperature T2 lower than the melting point of the polyamide, then incorporating a crosslinking system into the mixture and kneading the entire resulting mixture.

The nature and the contents of diene elastomer, of carbon black, of silica, of optional coupling agent, of polyamide having a melting point of less than 170°C, and of crosslinking system are as defined in point II-A above in their general embodiments, and advantageously in their preferred embodiments.

The process according to the invention can be carried out using two successive phases of preparation according to a general procedure well known to those skilled in the art: step (a) thus constitutes a first phase of thermomechanical working or kneading (sometimes referred to as a "non-productive" phase) at high temperature, up to a maximum temperature of between 130°C and 190°C, preferably between 140°C and 180°C, followed by a second phase of mechanical working (sometimes referred to as a "productive" phase) (step (b) of the process according to the invention) at lower temperature, typically less than 110°C, for example between 60°C and 100°C, during which finishing phase the crosslinking system is incorporated. Such phases have been described, for example, in applications EP 0 501 227 A, EP 0 735 088 A, EP 0 810 258 A, WO 2000/05300 or WO 2000/05301.

The first (non-productive) phase can be preferentially performed in several thermomechanical steps. During a first step, at least one diene elastomer, at least one polyamide having a melting point of less than 170°C, carbon black and silica are introduced into an appropriate mixer, such

19035573_1 (GHMatters) P119923.AU as an ordinary internal mixer, at a temperature of between 20°C and 100°C and preferably between 25°C and 100°C. After a few minutes, preferably from 0.5 to 2 min, and a rise in the temperature to 90°C to 100°C, the other ingredients (that is to say, those which remain if not all were put in at the start) can be added all at once or portionwise, with the exception of the crosslinking system, during a compounding ranging from 20 seconds to a few minutes. The total duration of the kneading, in this non-productive phase, is preferably between 2 and 10 minutes at a temperature of less than or equal to 180°C and preferentially of less than or equal to 170°C.

After cooling the mixture thus obtained, the crosslinking system (preferably the vulcanization system) is then incorporated at low temperature (typically less than 100°C), generally in an external mixer, such as an open mill; the combined mixture is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The final composition thus obtained is subsequently calendered, for example in the form of a sheet or of a plaque, in particular for laboratory characterization, or also extruded, in order to form, for example, a rubber profiled element used in the manufacture of semi-finished products, in order to obtain products such as a tyre tread. These products can subsequently be used for the manufacture of tyres, according to techniques known to those skilled in the art.

The crosslinking (or curing) is performed in a known manner at a temperature generally of between 130°C and 200°C, under pressure, for a sufficient time which may range, for example, between 5 and 90 min, as a function notably of the curing temperature, of the vulcanization system adopted, of the kinetics of crosslinking of the composition under consideration.

The polyamide (the melting point of which is less than 170C) can be introduced in the solid state, as sold commercially, or in the liquid state. When the polyamide is introduced in liquid form, it is then necessary to carry out an additional step of heating the polyamide to a temperature above its melting point, before it is brought into contact with the other constituents of step (a). However, it is preferable to introduce the polyamide in the solid state.

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According to the invention, the maximum temperature Ti is preferably at least1°C, preferably 2°C, preferably 3C, preferably 4°C, preferably 5°C higher than the temperature of the polyamide. Preferably, the maximum temperature Tiis 1 to 20°C, preferably 5 to 20°C higher than the temperature of the polyamide.

According to the invention, the maximum temperature T2 is preferably less than 120°C, preferably less than 100°C, more preferably less than 90°C. Preferably, the maximum temperature T2 is within a range extending from 20 to 90°C.

II-C Composition obtainable by the process according to the invention and tyre A subject of the present invention is also a rubber composition obtainable by a process according to the invention.

II-D Rubber article A subject of the present invention is also a rubber article comprising a composition according to the invention or a composition obtainable by the process according to the invention.

Given the improved performance compromise within the context of the present invention, the rubber article is advantageously selected from the group consisting of pneumatic tyres, non pneumatic tyres, caterpillar tracks and conveyor belts.

More particularly, a subject of the invention is also a pneumatic or non-pneumatic tyre provided with a tread comprising a composition according to the invention or a composition obtainable by the process according to the invention.

The tread has a tread surface provided with a tread pattern formed by a plurality of grooves delimiting elements in relief (tread blocks, ribs) so as to generate edge corners of material and also voids. These grooves represent a volume of voids which, relative 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.

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The present invention is particularly well suited to treads of tyres intended to be fitted to civil engineering or agricultural vehicles and for heavy-duty vehicles, more particularly civil engineering vehicles, the tyres of which are subjected to highly specific stresses, in particular the stony ground surfaces on which they run. Thus, advantageously, the pneumatic or non pneumatic tyre provided with a tread comprising a composition according to the invention or a composition obtainable bythe process according to the invention is a tyre for a civil engineering vehicle, agricultural vehicle or heavy-duty vehicle, preferably a civil engineering vehicle. These tyres are provided with treads which have, in comparison with the thicknesses of the treads of the tyres for light vehicles, in particular for passenger vehicles or vans, great thicknesses of rubber material. Typically the wearing part of the tread of a tyre for heavy-duty vehicles has a thickness of at least 15 mm, that of a civil engineering vehicle at least 30 mm, or even up to 120 mm. Thus, the tread of the tyre according to the invention advantageously has one or more grooves of which the average depth ranges from 15 to 120 mm, preferably 65 to 120 mm.

The pneumatic tyres according to 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 of the tyre according to the invention can be within a range extending from 5% to 40%, preferably from 5% to 25%.

A subject of the invention is also a rubber caterpillar track comprising at least one rubber element comprising a composition according to the invention or a composition obtainable by the process according to the invention, the at least one rubber element being preferably an endless rubber belt or a plurality of rubber pads, and also a rubber conveyor belt comprising a composition according to the invention or a composition obtainable by the process according to the invention.

The invention relates to the tyres and semi-finished products for tyres described above, articles made of rubber, both in the raw state (that is to say, before curing) and in the cured state (that is to say, after crosslinking or vulcanization).

III- PREFERRED EMBODIMENTS

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In the light of the above, the preferred embodiments of the invention are described below: 1. Rubber composition based on at least a diene elastomer, from 10 to 60 phr of carbon black, from 5 to 30 phr of silica, a polyamide having a melting point of less than 170°C, and a crosslinking system, in which composition the carbon black represents from 50% to 95%, preferably from 55% to 95%, by weight relative to the total weight of carbon black and silica. 2. Composition according to embodiment 1, wherein the diene elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and the mixtures of these elastomers, preferably selected from the group consisting of synthetic polyisoprenes, natural rubber and mixtures thereof. 3. Composition according to embodiment 1, wherein the diene elastomer mainly, preferably exclusively, comprises at least one non-epoxidized polyisoprene selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof. 4. Composition according to embodiment 3, wherein the at least the non-epoxidized polyisoprene having a molar content of 1,4-cis bonds of at least 90%. 5. Composition according to embodiment 1, wherein the diene elastomer mainly, preferably exclusively, comprises at least one epoxidized polyisoprene having a molar degree of epoxidation ranging from 1% to 8 5 %. 6. Composition according to embodiment 5, wherein the at least one epoxidized polyisoprene has a molar degree of epoxidation ranging from 5% to 55%, preferably from 10% to less than 49%, preferably from 15% to less than 4 0 %. 7. Composition according to embodiment 5 or 6, wherein the epoxidized polyisoprene has a Mooney viscosity (ML 1+4) at 100°C, measured according to Standard ASTM D1646 (1999), within a range extending from 30 to 150, preferably from 40 to 150, more preferably from 50 to 140. 8. Composition according to any one of the preceding embodiments, wherein the content of carbon black is within a range extending from 15 to 55 phr, preferably from 20 to 50 phr. 9. Composition according to any one of the preceding embodiments, wherein the content of silica is within a range extending from 5 to 25 phr, preferably from 6 to 20 phr. 10. Composition according to any one of the preceding embodiments, not comprising a coupling agent, or comprising less than 6% by weight thereof relative to the weight of silica, preferably less than 2% by weight thereof relative to the weight of silica.

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11. Composition according to any one of the preceding embodiments, not comprising a coupling agent. 12. Composition according to any one of the preceding embodiments, wherein the total content of carbon black and silica is within a range extending from 15 to 90 phr, preferably from 20 to 70 phr. 13. Composition according to any one of the preceding embodiments, wherein the carbon black represents from 60% to 90% by weight, preferably from 65% to 80% by weight, relative to the total weight of carbon black and silica. 14. Composition according to any one of the preceding embodiments, wherein the polyamide the melting point of which is less than 170°C is a polyamide copolymer consisting of at least two different types of monomers selected from the group consisting of lactams, or of at least two different types of monomers selected from the group consisting of diacids and of at least two different types of monomers selected from the group consisting of diamines. 15. Composition according to embodiment 14, wherein the lactams are selected from the group consisting of p,p-dimethylpropriolactam, a,a-dimethylpropriolactam, amylolactam, caprolactam, capryllactam, oenantholactam, 2-pyrrolidone and lauryllactam and mixtures thereof. 16. Composition according to embodiment 14 or 15, wherein the diacids are selected from the group consisting of adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulfoisophthalic acid, dodecanedioic acid and mixtures thereof. 17. Composition according to any one of embodiments 14 to 16, wherein the diamines are selected from the group consisting of hexamethylenediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, polyol diamines, isophorone diamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), methaxylyenediamine, bis-p-aminocyclohexylmethane, trimethylhexamethylenediamine, phenylenediamine and mixtures thereof. 18. Composition according to any one of the preceding embodiments, wherein the melting point of the polyamide the melting point of which is less than 170°C is between 100 and 160°C, preferably between 120 and 160°C.

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19. Composition according to any one of the preceding embodiments, wherein the polyamide does not comprise a diene unit. 20. Composition according to any one of the preceding embodiments, wherein the content of the polyamide the melting point of which is less than 170°C is within a range extending from 3 to 40 phr, preferably from 5 to 30 phr. 21. Composition according to any one of the preceding embodiments, wherein the total content of carbon black, silica and the polyamide the melting point of which is less than 170°C is within a range extending from 20 to 90 phr, preferably from 30 to 80 phr. 22. Composition according to any one of the preceding embodiments, wherein the volume fraction of the combination of carbon black, silica and polyamide is within a range extending from 10% to 40%, preferably from 15% to 35%. 23. Composition according to any one of the preceding embodiments, wherein the total content of thermoplastic polymer is within a range extending from 3 to 40 phr, preferably from 5 to 30 phr. 24. Composition according to any one of the preceding embodiments, said composition not comprising a thermoplastic polymer other than polyamide having a melting point of less than 170 0 C. 25. Composition according to any one of the preceding embodiments, wherein the crosslinking system is based on molecular sulfur and/or sulfur-donating agent. 26. Process for preparing a composition according to any one of embodiments 1 to 25, characterized in that it comprises the following steps: a) bringing at least a diene elastomer, from 10 to 60 phr of carbon black, from 5 to 30 phr of silica, the carbon black representing from 50% to 95%, preferably from 55% to 95%, by weight relative to the total weight of carbon black and silica, and a polyamide having a melting point of less than 1700 C into contact and mixing, concomitantly or successively, on one or more occasions, by thermomechanically kneading the whole until a maximum temperature T I greater than or equal to the melting point of the polyamide is reached, b) reducing the temperature of the mixture obtained in step (a) to a maximum temperature T2 lower than the melting point of the polyamide, then incorporating a crosslinking system into the mixture and kneading the entire resulting mixture. 27. Process according to embodiment 26, wherein the polyamide is introduced in the solid state.

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28. Process according to embodiment 26 or 27, wherein the maximum temperature Ti is 1 to 20°C, preferably 5 to 20°C higher than the temperature of the polyamide. 29. Process according to any one of embodiments 26 to 28, wherein the maximum temperature T2 is less than 120°C, preferably less than 100°C. 30. Rubber composition obtainable by the process according to any one of embodiments 26 to 29. 31. Rubber article comprising a composition as defined in any one of embodiments 1 to 25 or 30. 32. Rubber article according to embodiment 31, said article being selected from the group consisting of pneumatic tyres, non-pneumatic tyres, caterpillar tracks and conveyor belts. 33. Pneumatic or non-pneumatic tyre provided with a tread comprising a composition as defined in any one of embodiments 1 to 25 or 31. 34. Tyre according to embodiment 33, which is a tyre for a civil engineering vehicle, agricultural vehicle or heavy-duty vehicle, preferably a civil engineering vehicle. 35. Tyre according to embodiment 33 or 34, the tread of which has one or more grooves, the average depth of which is within a range extending from 30 to 120 mm, preferably from 45 to 75 mm. 36. Tyre according to any one of the embodiments 33 to 35, having a mean volumetric void ratio over the entire tread within a range extending from 5% to 40%, preferably from 5% to 25%. 37. Tyre according to any one of embodiments 33 to 36, having a diameter within a range of from 20 to 63 inches, preferably from 35 to 63 inches. 38. Caterpillar track comprising at least one rubber element comprising a composition as defined in any one of embodiments I to 25 or 30. 39. Caterpillar track according to embodiment 38, wherein the at least one rubber element is an endless rubber belt or a plurality of rubber pads. 40. Rubber conveyor belt comprising a composition as defined in any one of embodiments 1 to 25 or 30.

IV- EXAMPLES IV-I Measurements and tests used Dynamic properties

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The dynamic properties G* and tan(6)max are measured on a viscosity analyser (Metravib VA4000) according to Standard ASTM D5992-96. The response of a sample of vulcanized composition (cylindrical test specimen with a thickness of 2 mm and a cross section of 79 mm2 ), subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, under standard temperature conditions (23°C) according to Standard ASTM D 1349-09, is recorded. A strain amplitude sweep is carried out from 0.1% to 50% (outward cycle) and then from 50% to 0.1% (return cycle). On the return cycle, the value of the loss factor, denoted tan(6)max, is recorded.

The hysteretic performance results (tan(6)max at 23°Ca) are expressed as a percentage base 100 relative to the control composition TI. A result greater than 100 indicates an improvement in hysteresis performance, or a decrease in hysteresis.

Caterpillartrack test This test is representative of resistance to attacks. It consists in running a metal caterpillar track mounted on a pneumatic tyre fitted on a wheel and vehicle, and inflated, on which rubber pads of a given composition are attached, on a track filled with stones, for a certain time. At the end of running, the pads are removed and the number of cuts visible to the naked eye on the surface are counted. The lower the number, the better the attack resistance performance.

To carry out this test, pads of different compositions were manufactured (see Table 1 below) according to the process described in point V-1 above. To obtain a pad, the non-crosslinked composition obtained in point V-i was calendered to a thickness of 5.5 mm, cut out from plates (2 of 260x120 mm, 2 of 25Ox100 mm and 2 of 235x90 mm) that are then stacked in a pyramid. This block of 6 plates was then inserted into a pyramid-shaped mould with a rectangular base of 260x120 mm and a flat top of 235x90 mm in area, and cured at a temperature of 120°C for 300 minutes at a pressure of 180 bar, thus allowing the crosslinking of the composition.

The pads were then mounted on two X-Trackl0 metal caterpillar tracks from the Caterpillar company, which were themselves mounted on two Michelin Xmine D2 12.00R24 tyres on the rear axle of a Scania R410 truck. The tyres were re-cut to support the caterpillar tracks. The tyres were inflated to a pressure of 7 bar and bore a load of 4250 kg per tyre.

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The truck ran on a flat track covered with 30/60 size porphyry stands obtained from Sonvoles Murcia, Spain, for 5 hours at a speed of 5 km/h. The density of stones on the track was around 1000 to 1500 stones per square metre.

At the end of the test, the cuts visible at the surface of the pads were counted. The result was averaged on the basis of 6 pads. The aggression performance results are expressed as a percentage base 100 relative to the control composition T1. A result greater than 100 indicates an improvement in the resistance to attacks.

IV-2 Preparation of the compositions In the examples which follow, the rubber compositions were produced as described in point II B above. In particular, the "non-productive" phase was carried out in a 0.4 litre mixer for 8 minutes, for a mean blade speed of 50 revolutions per minute, until a maximum dropping temperature of 165°C was reached. The "productive" phase was carried out in an open mill at 23°C for 5 minutes.

The crosslinking of the composition was carried out at a temperature of between 130°C and 200°C, under pressure.

IV-3 Tests on rubber compositions The examples presented below are intended to compare the performance compromise between the resistance to mechanical attacks and the hysteresis of four compositions in accordance with the present invention (C1 to C4) with two control compositions (Ti and T2).

The formulations tested all contain an elastomeric matrix and a filler system, the natures and contents of which are presented in Table 1 below, and also 1 phr of anti-ozone wax (Variazon 4959 from Sasol Wax), 1.5 phr of antioxidant (N-1,3-dimethylbutyl-N phenylparaphenylenediamine, Santoflex 6-PPD from Flexsys), 1 phr of stearic acid (Pristerene 4931 from Uniqema), 2.5 phr of industrial grade zinc oxide (Umicore), 1 phr of 2,2,4-trimethyl 1,2-dihydroquinoline (Pilnox TMQ from Nocil) and 2.5 phr of Carbowax 8000 polyethylene glycol from Dow Coming, 1.5 phr of sulfur, and 1.1 phr of N-cyclohexyl-2

19035573_1 (GHMatters) P119923.AU benzothiazolsulfenamide (Santocure CBS from Flexsys) as vulcanization accelerator. The properties of these formulations are also presented in Table 1 below.

The control TI is a composition conventionally used in treads of tyres for civil engineering vehicles.

The compositions Cl to C3 differ from the control T2 by the presence of polyamide having a melting point of less than 170°C, with different amounts of fillers. The composition C4 makes it additionally possible to study the impact of the nature of the diene elastomer on the aforementioned performance compromise.

[Table 1] TI T2 Cl C2 C3 C4 SBR(1 ) 100 - - - -

NR(2) - 100 100 100 100 ENR50) - - - - - 100 PA (- - 17 27 33 15 Carbon black(5 ) 60 40 46 34 22 18 Silica(6) 15 17 - 12 8 7

Tan(d) 60°C 100 176 136 188 231 231 Perfo caterpillar track 100 85 173 166 125 114 (1) Tin-functionalized solution SBR, with 5% of 1,2-polybutadiene units, 29% of styrene units - Tg = -52°C (2) Natural rubber (3) Epoxidized natural rubber at 50 mol% (Epoxyprene 50 from Guthrie) (4) Elvamide 8063 polyamide from DuPont (Mp = 158°C) (5) Carbon black of N115 grade according to Standard ASTM D-1765 (6) Ultrasil VN3 silica from Evonik

The results presented in Table 1 above show that the use of the filler system comprising a polyamide having a melting point of less than 170°C, carbon black and silica in accordance with the present invention makes it possible to greatly improve the resistance to attacks without penalizing the hysteresis, or even while improving it.

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Claims (15)

1. Rubber composition based on at least a diene elastomer, from 10 to 60 phr of carbon black, from 5 to 30 phr of silica, a polyamide having a melting point of less than 170°C, and a crosslinking system, in which composition the carbon black represents from 55% to 95% by weight relative to the total weight of carbon black and silica.

2. Composition according to Claim 1, wherein the diene elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and the mixtures of these elastomers, preferably selected from the group consisting of synthetic polyisoprenes, natural rubber and mixtures thereof.

3. Composition according to Claim 1, wherein the diene elastomer mainly, preferably exclusively, comprises at least one non-epoxidized polyisoprene selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof.

4. Composition according to any one of the preceding claims, wherein the content of carbon black is within a range extending from 15 to 55 phr, preferably from 20 to 50 phr.

5. Composition according to any one of the preceding claims, wherein the content of silica is within a range extending from 5 to 25 phr, preferably from 6 to 20 phr.

6. Composition according to any one of the preceding claims, not comprising a coupling agent, or comprising less than 6% by weight thereof relative to the weight of silica, preferably less than 2% by weight thereof relative to the weight of silica.

7. Composition according to any one of the preceding embodiments, wherein the carbon black represents from 60% to 90% by weight, preferably from 65% to 80% by weight, relative to the total weight of carbon black and silica.

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8. Composition according to any one of the preceding claims, wherein the polyamide the melting point of which is less than 170°C is a polyamide copolymer consisting of at least two different types of monomers selected from the group consisting of lactams, or of at least two different types of monomers selected from the group consisting of diacids and of at least two different types of monomers selected from the group consisting of diamines.

9. Composition according to any one of the preceding claims, wherein the melting point of the polyamide the melting point of which is less than 170°C is between 100 and 160°C, preferably between 120 and 160°C.

10. Composition according to any one of the preceding claims, wherein the content of the polyamide the melting point of which is less than 170°C is within a range extending from 3 to 40 phr, preferably from 5 to 30 phr.

11. Composition according to any one of the preceding claims, wherein the total content of carbon black, silica and the polyamide the melting point of which is less than 170°C is within a range extending from 20 to 90 phr, preferably from 30 to 80 phr.

12. Process for preparing a composition according to any one of Claims 1 to 11, characterized in that it comprises the following steps: a) bringing at least a diene elastomer, from 10 to 60 phr of carbon black, from 5 to 30 phr of silica, the carbon black representing from 50% to 95% by weight relative to the total weight of carbon black and silica, and a polyamide having a melting point of less than 170°C into contact and mixing, concomitantly or successively, on one or more occasions, by thermomechanically kneading the whole until a maximum temperature Ti greater than or equal to the melting point of the polyamide is reached, b) reducing the temperature of the mixture obtained in step (a) to a maximum temperature T2 lower than the melting point of the polyamide, then incorporating a crosslinking system into the mixture and kneading the entire resulting mixture.

13. Rubber composition obtainable by the process according to Claim 12.

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14. Rubber article comprising a composition as defined in any one of Claims I to 11 or 13.

15. Rubber article according to Claim 14, said article being selected from the group consisting of pneumatic tyres, non-pneumatic tyres, caterpillar tracks and conveyor belts.

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