Elastomeric compositions with improved properties

Abstract

The invention relates to an elastomeric composition for heavy-duty tires based on at least one elastomeric matrix, fillers including graphite and a reinforcing filler and a vulcanization system, characterized in that: the elastomeric matrix comprises at least 50 parts per anthic elastomer selected from the group consisting of isoprene elastomers, butadien elastomers and mixtures of these dienic elastomers, the reinforcing filler comprises mainly carbon black, the graphite has a crystallite size Lc in the range of 80 to 500 nm, more preferably 90 to 400 nm, more preferably 100 to 300 nm, the total filler content is less than or equal to 65 parts per anthic.

Description

Title of the invention: Elastomeric compositions with improved properties technical field

[0001] The field of the present invention is that of reinforced elastomeric compositions used for the manufacture of tires carrying heavy loads, such as those intended to equip a heavy goods vehicle, a civil engineering vehicle, a tractor, a bus, an airplane etc.

[0002] TECHNOLOGICAL BACKGROUND

[0003] Tires intended for use on heavy-duty vehicles have treads that, compared to the treads of light-duty vehicle tires, particularly those of passenger cars or light trucks, have greater thicknesses of rubber material, notably to support the weight these vehicles carry. Typically, the wearing portion of the tread on a heavy-duty vehicle can have a thickness of at least 15 mm, while that of a construction vehicle can have a thickness of at least 30 mm, or even up to 120 mm. These tires may, in particular, have an axial width greater than 37 inches.

[0004] During driving, the elastomeric compositions, such as those of the tread, sidewalls, etc., of these tires are subjected to mechanical stresses and wear resulting in particular from contact with the ground. In the case of a tire mounted on a vehicle carrying heavy loads, the mechanical stresses and wear are amplified by the weight carried by the tire.

[0005] For example, the tires of mining vehicles are subjected to strong stresses, both i) at the local level, i.e., from driving on the macro-indenters represented by the pebbles that constitute the tracks (crushed rock) and ii) at the global level by the passage of significant torque due to the slopes of the tracks to exit the mine shaft (slope of the order of 10%) and by U-turns for loading and unloading maneuvers.

[0006] Furthermore, in the case of vehicles intended for mining or quarrying use for transporting loads, access difficulties and performance requirements lead manufacturers of these vehicles to increase their load capacity. It follows that the vehicles are becoming increasingly larger, and therefore increasingly heavier, and can carry an increasingly heavy load. The current masses of these vehicles can reach several hundred tons, and the same is true for the load to be transported; the total mass can reach up to 600 tonnes.

[0007] The tires of vehicles carrying heavy loads are therefore subjected to increasing stress. They must simultaneously exhibit good wear properties, be capable of transmitting the necessary torque, and withstand the stresses, particularly from the stones encountered on the roads.

[0008] These strong stresses are also encountered in particular for the treads of tires which are mounted on agricultural vehicles due to the stony soil of arable land.

[0009] The tires fitted to heavy construction vehicles which travel on both stony and bituminous surfaces also experience these same aggressions.

[0010] Due to the two aggravating factors of the weight carried by the tire and the aggressive nature of the road surface, the wear resistance and tear resistance of a tire for a civil engineering vehicle, an agricultural vehicle or a heavy goods vehicle is crucial to minimizing the impact of the aggressions suffered in particular by the tread.

[0011] It is therefore important to have elastomeric compositions for vehicle tires, particularly those carrying heavy loads, which contribute to wear resistance and resistance to damage. Thus, these elastomeric compositions must be sufficiently rigid and possess good deformation at break and tear resistance properties.

[0012] To solve this problem, it is known to those skilled in the art, for example, to use a large amount of reinforcing fillers in order to obtain good rigidity of the elastomeric composition for this type of tire or to use increasingly thinner reinforcing fillers.

[0013] However, the use of increasingly fine reinforcing fillers often requires increasing the proportion of plasticizers, such as oils or resins, to overcome the difficulties in processing and handling this type of reinforcing filler. However, the presence of plasticizers in elastomeric compositions causes a degradation of certain mechanical properties of these compositions, such as their deformation properties at break.

[0014] Increasing the rate of reinforcing loads also presents a drawback. It leads to significant internal heating problems in the reinforcing belt, which can result in tire degradation.

[0015] Indeed, the fact that tires for vehicles carrying heavy loads have, on the one hand, larger dimensions than tires for passenger vehicles and, on the other hand, that the elastomeric compositions are subjected to repeated and greater stresses and deformations due to the load The friction they carry generates heat. This heat, generated when the tire is in motion, is dissipated into the environment more or less rapidly depending on the thermal conductivity of each tire compound. When the thermal conductivity of an elastomeric compound is too low, heat accumulates and leads to the compound's phenolic resin formation. The tire then loses its elastic properties, which is detrimental to its use.

[0016] Thus, when manufacturers seek to improve the rigidity and / or resistance to aggression of elastomeric compositions for tires carrying heavy loads, this improvement is often carried out at the expense of other properties such as the hysteresis of the materials and therefore ultimately at the expense of the temperature of the tire in operation.

[0017] Document JP2005325308 proposes a solution for improving resistance to stress, elongation at break, and heat dissipation by combining a specific resin and 150 mesh natural graphite. However, no mention is made of improving the stiffness of these compositions.

[0018] There is therefore still an unmet need for elastomeric compositions for heavy load-bearing tires, particularly of the civil engineering type, which satisfy the compromise of resistance to aggression, rigidity, deformation at break and thermal conductivity properties; or even advantageously to improve this compromise compared to prior art compositions.

[0019] The purpose of the present invention is to meet this need.

[0020] Continuing this research, the Inventors unexpectedly discovered that, for tires carrying heavy loads, particularly those of the construction equipment type, the use of a specific graphite in an elastomeric composition made it possible to obtain a good compromise of properties in terms of resistance to damage, rigidity, deformation at break, and thermal conductivity, and even to improve this compromise of properties compared to prior art compositions. Advantageously, the amount of reinforcing fillers in the elastomeric composition can even be reduced; this is more economically and environmentally favorable given the scarcity of resources.

[0021] Thus, the invention relates to an elastomeric composition for heavy-duty tires based on at least one elastomeric matrix, fillers including graphite and a reinforcing filler, and a vulcanization system, characterized in that: - the elastomeric matrix comprises at least 50 parts of a diene elastomer chosen from the group consisting of isoprene elastomers, Butadiene elastomers and mixtures of these diene elastomers, - the reinforcing filler comprises mainly carbon black, - Graphite exhibits a crystallite size Le within a range ranging from 80 to 500 nm, more preferably from 90 to 400 nm, more preferably from 100 to 300 nm, - the total charge rate is less than or equal to 65%.

[0022] Another object of the invention relates to a heavy-duty tire comprising at least one composition as described above. Preferably, the tire is a construction tire or a heavy-duty tire. DETAILED DESCRIPTION OF THE INVENTION

[0023] Definitions

[0024] The expression "composition based on" means a composition comprising the mixture and / or the in situ reaction product of the different constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the different phases of manufacturing the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0025] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is to be understood in the context of the present invention as the part, by mass per hundred parts by mass of elastomer.

[0026] In the present, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0027] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​going from more than a to less than b (that is to say, bounds a and b excluded) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​going from a to b (that is to say, including the strict bounds a and b).

[0028] When referring to a "major" compound, for the purposes of this invention, it is understood that this compound is the major compound among the compounds of the same type in the composition, that is to say, it is the one that represents the greatest quantity by mass among the compounds of the same type. Thus, for example, a major elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. Similarly, a so-called major filler is the one representing the greatest mass among the fillers in the composition. By way of example, in a system comprising a single elastomer, this elastomer is the major compound for the purposes of this invention; and in a system comprising two elastomers, the major elastomer represents more than half the mass of the elastomers. Conversely, a "minor" compound is a compound that does not represent the largest mass fraction among compounds of the same type. Preferably, a major compound is understood to be a compound present at more than 50% by weight, preferably more than 60%, 70%, 80%, or 90% by weight, and most preferably, the "major" compound represents 100% by weight relative to the total weight of compounds of the same type.

[0029] The compounds mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Obviously, the compounds mentioned may also come from the recycling of materials already used, that is to say, they may be partially or totally derived from a recycling process, or even obtained from raw materials themselves derived from a recycling process. This includes, in particular, polymers, plasticizers, fillers, etc.

[0030] The term "heavy-duty vehicle tire" refers to tires, particularly radial tires, for heavy-duty vehicles such as, for example, trucks, aircraft, subways, construction equipment, tractors, trailers, or road buses, equipped with wheels whose rims have a nominal diameter of 19.5 inches or more. A heavy-duty vehicle is distinguished by the dimensions of its axle(s) and, in particular, by its maximum authorized weight, which is greater than or equal to 3.5 tonnes.

[0031] The term "tread" means the outer layer of the tire that is in direct contact with the rolling surface.

[0032] The term "diene" elastomer (or, indiscriminately, "rubber"), whether natural or synthetic, is to be understood in a known manner as an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers bearing two carbon-carbon double bonds, conjugated or not). In the present application, diene elastomers are by definition non-thermoplastic. Preferably, when diene elastomers are copolymers, they are statistical polymers. Diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated".The term "essentially unsaturated" generally refers to a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of diene motifs or units (conjugated dienes) greater than 15% (mol%); thus, diene elastomers such as butyl rubbers or EPDM-type diene and alpha-olefin copolymers do not fall under the previous definition and can be described in particular as "essentially saturated" diene elastomers (low or very low proportion of diene motifs, always less than 15% mol). The diene elastomers usable within the scope of the invention are essentially unsaturated diene elastomers. Butyl elastomers are therefore not usable within the scope of the present invention since they are essentially saturated diene elastomers.

[0033] All glass transition temperature values ​​“Tg” are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (2008).

[0034] Elastomer matrix

[0035] As indicated above, the elastomeric composition of the invention comprises an elastomeric matrix.

[0036] By definition, the elastomeric matrix refers to all the elastomers present in the composition. A polymer that does not exhibit elastic properties like those of natural rubber will therefore not be considered part of the elastomeric matrix and its percentage will not be taken into account in the calculation of the parts per unit area.

[0037] The elastomeric matrix of the elastomeric composition of the invention comprises at least 50 parts per annum of a diene elastomer selected from the group consisting of isoprene elastomers, butadien elastomers, and mixtures of these diene elastomers. For example, the elastomeric matrix may comprise an isoprene elastomer or a mixture of isoprene elastomers, a butadien elastomer or a mixture of butadien elastomers, or a mixture of isoprene and butadien elastomers. These diene elastomers have a proportion of diene motifs or units (conjugated dienes) greater than 15 mol%.Thus, the elastomeric matrix of the composition of the present invention comprises at least 50 parts per cent of a diene elastomer having a proportion of diene motifs or units (conjugated dienes) greater than 15 mol%; this elastomer being selected from the group consisting of isoprene elastomers, butadien elastomers, and mixtures of these diene elastomers. In addition to the aforementioned diene elastomers, the elastomeric matrix may also comprise thermoplastic elastomers.

[0038] The term "isoprene elastomer" is commonly understood to mean a homopolymer or copolymer of isoprene. Isoprene copolymers comprise at least one isoprene monomer and at least one other monomer distinct from isoprene, with the diene monomer content exceeding 15 mol%. Therefore, butyl rubber is excluded from the definition of an isoprene elastomer. The other monomer may be ethylene, an olefin, or a conjugated or unconjugated diene.

[0039] The term "butadiene elastomer" is understood to mean, in a known manner, a homopolymer or copolymer of butadiene. Butadiene copolymers comprise at least one butadiene monomer and another monomer different from butadiene monomer; the The diene monomer content is greater than 15% by mole. The other monomer may be ethylene, an olefin, or a conjugated or unconjugated diene.

[0040] Suitable conjugated dienes are conjugated dienes having 4 to 12 carbon atoms, in particular 1,3-dienes, such as 1,3-butadiene and isoprene.

[0041] Suitable as unconjugated dienes are unconjugated dienes having 6 to 12 carbon atoms, such as 1,4-hexadiene, ethylidene norbomene, dicyclo-pentadiene.

[0042] Suitable olefins include vinylaromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms. Suitable vinylaromatic compounds include, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, and para-tert-butylstyrene. Suitable aliphatic α-monoolefins include, in particular, acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms.

[0043] More specifically, the isoprene elastomer can be selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), various isoprene copolymers, and mixtures of these elastomers. Among the isoprene copolymers, isoprene-styrene (SIR) is a particular example. Isobutene-isoprene copolymers (butyl rubber - IIR) are not among the isoprene copolymers usable within the scope of the invention because they are essentially saturated copolymers, having a diene-derived motif content of less than 15% by mol.

[0044] This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene. Among these synthetic polyisoprenes, polyisoprenes with a molar percentage of cis-1,4 bonds greater than 90% are preferably used, and even more preferably greater than 98%.

[0045] More specifically, the butadiene elastomer can be selected from the group consisting of polybutadienes (BR), various butadiene copolymers, and mixtures of these elastomers. Among the butadiene copolymers, particular examples include ethylene-butadiene copolymers (EBR), butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), and isoprene-butadiene-styrene copolymers (SBIR). For clarity, isoprene-butadiene and isoprene-butadiene-styrene elastomers are classified as butadiene copolymers and not as isoprene copolymers.

[0046] Suitable are polybutadienes, and in particular those having a -1,2 unit content (molar %) between 4% and 80% or those having a cis-1,4 unit content (molar %) greater than 80%, polyisoprenes, butadiene-styrene copolymers, and in particular those having a glass transition temperature (Tg, measured according to ASTM D3418-99)) between 0°C and -90°C and more particularly between -10°C and -70°C, a styrene content between 1% and 60% by weight and more particularly between 20% and 50%, a -1,2 bond content (molar %) of the butadiene portion between 4% and 75%, a trans-1,4 bond content (molar %) between 10% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content between 5% and 90% by weight and a Tg of -40°C to -80°C, isoprene-styrene copolymers and in particular those having a styrene content between 5% and 50% by weight and a Tg between -5°C and - 50°C.In the case of butadiene-styrene-isoprene copolymers, those with a styrene content between 5% and 50% by weight, and more particularly between 10% and 40%, are particularly suitable; those with an isoprene content between 15% and 60% by weight, and more particularly between 20% and 50%, a butadiene content between 5% and 50% by weight, and more particularly between 20% and 40%, a butadiene fraction (molar %) in -1.2 units of between 4% and 85%, a trans-1.4 unit (molar %) of between 6% and 80%, an isoprene fraction (molar %) in between -1.2 and -3.4 units of between 5% and 70%, and a trans-1.4 unit (molar %) of between 5% and 70%. isoprene portion comprising between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg between -5°C and -70°C.

[0047] Advantageously, the diene elastomer can be selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), isoprene-styrene copolymer (SIR), polybutadienes (BR), ethylene-butadiene copolymers (EBR), butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-butadiene-styrene copolymers (SBIR) and mixtures of these elastomers.

[0048] Even more advantageously, the diene elastomer can be chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), polybutadienes (BR), ethylene-butadiene copolymers (EBR), butadiene-styrene copolymers (SBR) and mixtures of these elastomers.

[0049] Even more advantageously, the diene elastomer can be an isoprene elastomer; more preferably is chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR) and mixtures of these elastomers.

[0050] The aforementioned diene elastomers can be modified, i.e. either coupled and / or star-shaped, or functionalized, or coupled and / or star-shaped and simultaneously functionalized.

[0051] Thus, the aforementioned diene elastomers, particularly when synthetic, can be coupled and / or star-shaped, for example by means of a silicon atom or tin that binds the elastomer chains together.

[0052] The aforementioned diene elastomers can be simultaneously or alternatively functionalized and comprise at least one functional group. By functional group, we mean a group comprising at least one heteroatom selected from Si, N, S, O, P. Particularly suitable as functional groups are those comprising at least one function such as: silanol, an alkoxysilane, a primary, secondary or tertiary amine, cyclic or non-cyclic, a thiol, an epoxide.

[0053] Particularly advantageously, the elastomeric composition of the invention may comprise from 60 to 100 parts per annum, preferably from 70 to 100 parts per annum, preferably from 80 to 100 parts per annum, preferably from 90 to 100 parts per annum, of a diene elastomer selected from the group consisting of isoprene elastomers, butadiene elastomers and mixtures of these elastomers. According to one embodiment, the rubber composition may comprise from 60 to 99 parts per annum, preferably 70 to 99 parts per annum, for example from 80 to 98 parts per annum, for example from 90 to 97 parts per annum, of a diene elastomer selected from the group consisting of isoprene elastomers, butadiene elastomers and mixtures of these elastomers; the complement could be another different diene elastomer.

[0054] More particularly advantageously, the elastomeric composition of the invention may comprise from 60 to 100 parts per annum, preferably from 70 to 100 parts per annum, preferably from 80 to 100 parts per annum, preferably from 90 to 100 parts per annum, of an isoprene elastomer and mixtures of such elastomers. According to one embodiment, the rubber composition may comprise from 60 to 99 parts per annum, preferably from 70 to 99 parts per annum, for example from 80 to 98 parts per annum, for example from 90 to 97 parts per annum, of an isoprene elastomer; the remainder being another diene elastomer, preferably a butadiene elastomer as defined above.

[0055] Even more advantageously, the elastomeric composition of the invention may comprise from 60 to 100 parts per annum, preferably from 70 to 100 parts per annum, preferably from 80 to 100 parts per annum, preferably from 90 to 100 parts per annum, of a diene elastomer selected from the group consisting of natural rubber, synthetic polyisoprene and mixtures of these elastomers. According to one embodiment, the rubber composition may comprise from 60 to 99 parts per annum, preferably 70 to 99 parts per annum, for example from 80 to 98 parts per annum, for example from 90 to 97 parts per annum, of a diene elastomer selected from the group consisting of natural rubber, synthetic polyisoprene and mixtures of these elastomers; the complement may be another diene elastomer, preferably a butadien elastomer as defined above.

[0056] Charge

[0057] The elastomeric composition of the invention comprises fillers including a reinforcing filler and graphite.

[0058] The term "filler" here refers to any type of filler, whether reinforcing, non-reinforcing, or inert. As reinforcing fillers, carbon black or inorganic reinforcing fillers such as silica or alumina are known to those skilled in the art. As non-reinforcing or inert fillers, graphite, clay, talc, mica, etc., are known to those skilled in the art. In the context of the present invention, zinc oxide is not considered a non-reinforcing filler. It is an activator of the vulcanization system.

[0059] The total filler content (i.e., the sum of the reinforcing and non-reinforcing filler content) in the elastomeric composition of the present invention is less than or equal to 65 parts per annum (ppm), preferably less than or equal to 60 parts per annum, and preferably less than or equal to 55 parts per annum. More preferably, the total filler content is in the range of 20 to 65 parts per annum, more preferably in the range of 25 to 60 parts per annum, and even more preferably in the range of 25 to 55 parts per annum. At this total filler content, a good compromise is obtained in terms of resistance to damage, stiffness, deformation at break, and thermal conductivity.

[0060] Reinforcing charge

[0061] The elastomeric composition of the invention comprises a reinforcing filler, this reinforcing filler comprising predominantly carbon black. In addition to carbon black, which is the predominant reinforcing filler, the elastomeric composition of the invention may optionally also comprise a second reinforcing filler such as silica, for example.

[0062] The total reinforcing filler content, i.e., the carbon black content and the silica content when present, is less than or equal to 60%, more preferably less than or equal to 55%, more preferably less than or equal to 50%, more preferably less than or equal to 45%. This reinforcing filler content is advantageously greater than or equal to 20%, more preferably greater than or equal to 25%, more preferably greater than or equal to 30%. Preferably, the reinforcing filler content in the elastomeric composition is in the range of 20% to 60%, more preferably from 25% to 55%, more preferably from 30% to 45%.

[0063] Carbon black

[0064] Preferably, carbon black represents more than 55% by weight of the total weight of the reinforcing charge, more preferably more than 60% by weight, more preferably more than 80% by weight, more preferably still represents 100% by weight of the total weight of the reinforcing charge.

[0065] Thus, preferably the reinforcing charge ratio is less than or equal to 60%, more preferably less than or equal to 55%, more preferably less than or equal to 50%, more preferably still less than or equal to 45%, and the black of carbon represents more than 55% by weight of the total weight of the reinforcing load, more preferably more than 60% by weight, more preferably more than 80% by weight, more preferably still represents 100% by weight of the total weight of the reinforcing load.

[0066] More preferably, the rate of reinforcing fillers in the elastomeric composition is in the range of 20% to 60%, more preferably 25% to 55%, more preferably 30% to 45% and carbon black represents more than 55% by weight of the total weight of the reinforcing filler, more preferably more than 60% by weight, more preferably more than 80% by weight, more preferably still represents 100% by weight of the total weight of the reinforcing filler.

[0067] The reinforcing charges can be described below.

[0068] The reinforcing filler comprises mainly carbon black. The carbon black usable within the scope of the present invention is a finely divided, amorphous carbon black, well known to those skilled in the art of tire manufacturing. It is generally obtained by thermal decomposition or incomplete combustion of hydrocarbons using the heat produced by the complete combustion of a fuel by air. The process for obtaining carbon black is the furnace process. All carbon blacks are suitable, including those conventionally used in tires. Among these, we will mention in particular the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as NI 15, N134, N234, N326, N330, N339, N347, N375, N550 blacks.These carbon blacks can be used in isolation, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used. Carbon blacks could, for example, already be incorporated into the diene elastomer, in particular isoprene, in the form of a masterbatch (see, for example, applications WO97 / 36724-A2 or WO99 / 16600-A1).

[0069] The carbon black used in the elastomeric compositions of the invention is an ASTM grade carbon black that has little or no conductive properties. It therefore belongs neither to the category of acetylene carbon blacks, also called acetylene black, nor to the category of conductive carbon blacks. Carbon blacks are distinguished from conductive carbon blacks, in particular, by their structure, measurable by oil absorption index evaluated according to ASTM D2414. Preferably, the carbon black usable in the present invention has an oil absorption index measured according to ASTM D2414 (the "DBP index") in the range of 30 ml / 100g to 185 ml / 100g. Carbon blacks exhibiting conductive properties, also called conductive carbon black, have an oil absorption measured according to ASTM D2414 generally greater than 190 ml / lOOg.

[0070] Preferably, the elastomeric composition of the invention contains less than 2 parts per annum of conductive carbon black or less than 2 parts per annum of acetylene black. More preferably, the elastomeric composition of the invention is free of conductive carbon black or acetylene black.

[0071] Preferably, the carbon black usable within the framework of the elastomeric composition of the invention has an external STSA surface, measured according to ASTM D6556-17, within a range of 30 to 145 m2 / g, more preferably from 35 to 140 m2 / g, more preferably from 60 to 130 m2 / g, more preferably from 65 to 95 m2 / g.

[0072] Preferably, the carbon black usable within the framework of the elastomeric composition of the invention has a compressed oil absorption number CO AN, measured according to ASTM D3493-18, in the range of 50 to 130 ml / lOOg, preferably in the range of 65 to 125 ml / lOOg, more preferably in the range of 70 to 120 ml / lOOg, more preferably in the range of 75 to 120 ml / lOOg.

[0073] Preferably, the carbon black usable within the framework of the elastomeric composition of the invention has a specific surface area NSA, measured according to ASTM D6556-17, in the range of 25 to 160 m2 / g, preferably 35 to 150 m2 / g, more preferably 50 to 150 m2 / g, more preferably 70 to 140 m2 / g.

[0074] More preferably, the carbon black usable within the framework of the present invention has an external surface STSA, measured according to ASTM D6556-17, within a range of 30 to 145 m2 / g and a compressed oil absorption number COAN, measured according to ASTM D3493-18, within a range of 50 to 130 ml / lOOg.

[0075] More preferably, the carbon black usable within the framework of the present invention has an external surface STSA, measured according to ASTM D6556-17, within a range of 35 to 140 m2 / g and a compressed oil absorption number COAN, measured according to ASTM D3493-18, within a range of 65 to 125 ml / lOOg.

[0076] More preferably, the carbon black usable within the framework of the present invention has an external surface STSA, measured according to ASTM D6556-17, within a range of 60 to 130 m2 / g and a compressed oil absorption number COAN, measured according to ASTM D3493-18, within a range of 70 to 120 ml / lOOg.

[0077] More preferably still, carbon black usable within the framework of the The present invention has an external surface area STSA, measured according to ASTM D6556-17, within a range of 65 m2 / g to 95 m2 / g and a compressed oil absorption number COAN, measured according to ASTM D3493-18, within a range of 75 to 120 ml / 100g.

[0078] Silica

[0079] According to one embodiment of the invention, the elastomeric composition may, in addition to carbon black, comprise silica, in particular precipitated silica, as a reinforcing filler, and may further comprise a coupling agent for the silica to the diene elastomer of the elastomeric matrix. Silicas, in a known manner, may be characterized in particular by the presence of hydroxyl groups (-OH) on their surface.

[0080] The silica (SiO2) used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenated silica having a specific surface area BET and a specific surface area CTAB both less than 450 m2 / g, preferably within a range of 30 to 400 m2 / g, in particular 60 to 300 m2 / g.

[0081] Any type of precipitated silica can be used, in particular highly dispersible precipitated silicas (known as "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas, whether highly dispersible or not, are well known to those skilled in the art. Examples include the silicas described in applications WO03 / 016215-A1 and WO03 / 016387-A1. Among the commercial HDS silicas, one can notably use the “Ulsil ® 5000GR”, “Ulsil ® 7000GR” silicas from the company Evonik, the “Zeosil ® 1085GR”, “Zeosil® 1115 MP”, “Zeosil® 1165MP”, “Zeosil® Premium 200MP”, “Zeosil® HRS 1200 MP” silicas from the Solvay Company.As non-HDS silica, the following commercial silicas may be used: “Ultrasil® VN2GR”, “Ultrasil® VN3GR” from Evonik, “Zeosil® 175GR” from Solvay, “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(-D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” from PPG.

[0082] The physical state in which the reinforcing inorganic filler is presented is irrelevant, whether it is in the form of powder, microbeads, granules, or spheres, or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also includes mixtures of different reinforcing inorganic fillers, in particular silicas as described above.

[0083] The amount of silica used is always less than the amount of black used, since silica is a minor reinforcing inorganic filler in the elastomeric composition. Preferably, silica represents 45% by weight or less of the total weight of the reinforcing filler, more preferably 40% by weight or less, more preferably represents 20% by weight or less of the total weight of the reinforcing load.

[0084] The specific surface area BET of 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, Annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160°C - relative pressure range w / in: 0.05 to 0.17].

[0085] For inorganic fillers such as silica for example, the specific surface area values ​​CT AB were determined according to standard NF ISO 5794-1, Annex 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.

[0086] To couple silica to the diene elastomer, a coupling agent (or bonding agent) that is at least bifunctional can be used in a well-known manner to ensure sufficient chemical and / or physical connection between the silica (surface of its particles) and the diene elastomer. Organosilanes or polyorganosiloxanes that are at least bifunctional are used in particular. "Bifunctional" means 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 may comprise a first functional group including a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler, and a second functional group including a sulfur atom, said second functional group being capable of interacting with the diene elastomer.

[0087] Preferably, the organosilanes are chosen from the group consisting of polysulfide organosilanes (symmetric or asymmetric) such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT and marketed under the name "Si69" by Evonik, or bis-(triethoxysilylpropyl) disulfide, abbreviated TES PD and marketed under the name "Si75" by Evonik, polyorganosiloxanes, mercaptosilanes, and blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl octanethioate) marketed by Momentive under the name "NXT Silane". More preferably, the organosilane is a polysulfide organosilane.

[0088] Typically, the coupling agent content ranges from 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler. This percentage is easily adjusted by those skilled in the art according to the silica content used in the elastomeric composition of the invention.

[0089] The elastomeric compositions of the invention may also contain silica coating agents when such a filler is used, making it possible to improve their usability in the raw state. These recovery agents are well known (see for example patent applications WO2006 / 125533-A1, WO2007 / 017060-A1 and WO2007 / 003408-A1), examples include hydrolyzable silanes such as hydroxysilanes (see for example WO2009 / 062733-A2), alkylalkoxysilanes, polyols (for example diols or triols), polyethers (for example polyethylene glycols), primary, secondary or tertiary amines, hydroxylated or hydrolyzable polyorganosiloxanes (for example α, co-dihydroxy-polyorganosilanes (see for example EP0784072-A1).

[0090] Graphite

[0091] The composition of the invention comprises at least one graphite. The elastomeric composition of the invention may contain a single graphite as described below or a mixture of several graphites as described below.

[0092] Graphite is generally understood to mean a stack of graphene sheets, graphene being a sheet of atom-thickness in which the carbon atoms are arranged in an essentially hexagonal lattice. Unlike the aforementioned carbon blacks, graphite therefore has a crystalline structure.

[0093] Graphite can be natural or synthetic. When the graphite is synthetic, it can notably be obtained by a complex process of heating petroleum coke at very high temperature.

[0094] Graphite is not considered a reinforcing filler and is therefore not taken into account in the calculation of reinforcing fillers. Graphite is a filler and is therefore taken into consideration in the calculation of the total filler content.

[0095] The graphite usable within the framework of the present invention has a crystallite size, denoted Le, in the range of 80 to 500 nm, more preferably 90 to 400 nm, more preferably 100 to 300 nm. The measurement of the crystallite size is described in paragraph 1 of the Methods and Measurements section.

[0096] The graphite usable within the framework of the present invention may have a specific surface area BET in the range of 10 to 50 m2 / g; preferably from 15 to 40 m2 / g, more preferably from 20 to 30 m2 / g. The measurement of the specific surface area BET is described in paragraph 2 of the methods and measurements section.

[0097] The graphite usable within the framework of the present invention may have a particle size distribution D90 in the range of 50 to 150 pm, more preferably from 60 to 140 pm, and even more preferably from 70 to 130 pm. D90 corresponds to the 90th percentile of the particle size mass distribution, that is to say, 90% by mass of the particles have a size smaller than D90 and 10% by mass of the particles have a size greater than D90. H is expressed in pm. The measurement of D90 is described in paragraph 3 of the methods and measurements section.

[0098] Preferably the graphite usable within the framework of the present invention is expanded graphite.

[0099] Preferably, the rate of graphite in the elastomeric composition of the present invention is in the range of 1 to 12 pc, more preferably of 1 to 11 pc.

[0100] Preferably, the mass ratio of graphite to carbon black in the elastomeric composition is in the range of 0.05 to 0.5, preferably in the range of 0.06 to 0.4.

[0101] Graphites usable within the framework of the present invention are commercially available from suppliers such as Imerys for example.

[0102] Surprisingly, the inventors have identified that the use of the aforementioned graphite in an elastomeric composition for heavy-duty tires, particularly those of the construction equipment type, makes it possible to obtain a good compromise of resistance to damage, rigidity, deformation at break, and thermal conductivity, and even to improve this compromise of properties compared to prior art compositions. Advantageously, the amount of reinforcing fillers in the elastomeric composition can even be reduced.

[0103] Vulcanization system

[0104] The elastomeric composition of the invention includes a vulcanization system known to those skilled in the art in the field of elastomeric compositions for pneumatics.

[0105] Sulfur can be supplied in any form, including in the form of molecular sulfur, or a sulfur-donating agent.

[0106] At least one vulcanization accelerator is also preferably present, and, optionally and also preferably, various known vulcanization activators such as zinc oxide, stearic acid, or equivalent compounds such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders may be used. It should be noted that zinc oxide is considered a vulcanization activator and not a filler. Therefore, it is not taken into account in the calculation of the total filler content.

[0107] Sulfur is used at a preferential rate within a range of 0.5 to 10 pc, in particular from 1 to 5 pc.

[0108] The vulcanization accelerator is used at a preferential rate within a range of 0.5 to 10 pc, more preferably within a range of 0.5 to 5.0 pc.

[0109] Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used as an accelerator, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. Examples of such accelerators include the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-ter-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-ter-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds.

[0110] Plasticizers

[0111] The elastomeric composition of the invention may optionally include at least one plasticizer.

[0112] In a manner known to those skilled in the art of elastomeric tire compounds, this plasticizer is preferably selected from high glass transition temperature (Tg) hydrocarbon resins, low Tg hydrocarbon resins, plasticizing oils, and mixtures thereof. Preferably, the plasticizer is selected from high Tg hydrocarbon resins, plasticizing oils, and mixtures thereof.

[0113] A high Tg hydrocarbon resin is by definition a solid at ambient temperature and pressure (20°C, 1 atm), while a plasticizing oil is liquid at ambient temperature and a low Tg hydrocarbon resin is viscous at ambient temperature.

[0114] The total plasticizer content in the elastomeric composition of the invention can be in the range of 0 to 10 parts per annum, more preferably from 0 to 5 parts per annum.

[0115] Preferably, if the elastomeric composition includes a plasticizer, the plasticizer is a hydrocarbon resin having a Tg greater than 20°C.

[0116] Preferably, if the elastomeric composition includes a plasticizer, preferably a hydrocarbon resin having a Tg greater than 20°C, the plasticizer content is in the range of 1 to 10 pc, preferably 1 to 5 pc.

[0117] Preferably, the elastomeric composition is free of plasticizer.

[0118] Hydrocarbon resins, also called hydrocarbon plasticizing resins, are polymers well known to those skilled in the art, essentially based on carbon and hydrogen but which may contain other types of atoms, for example oxygen, and which are particularly useful as plasticizing or tackifying agents in polymer matrices. They are by nature at least partially miscible (i.e., compatible) at the rates used with the polymer compositions to which they These resins are designed to act as true diluents. They were described, for example, in the book "Hydrocarbon Resins" by R. Mildenberg, M. Zander, and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), Chapter 5 of which is devoted to their applications, particularly in pneumatic rubber (5.5. "Rubber Tires and Mechanical Goods"). It is well known that these hydrocarbon resins can also be classified as thermoplastic resins in that they soften upon heating and can thus be molded.

[0119] Hydrocarbon resins can be aliphatic, aromatic, or of the aliphatic / aromatic type, i.e., based on aliphatic and / or aromatic monomers. They can be natural or synthetic, petroleum-based or not (if so, also known as petroleum resins).

[0120] Plasticizers are commercially available from suppliers such as Arizona, Kraton, Exxon, etc.

[0121] Other additives

[0122] Elastomeric compositions according to the invention may also include all or part of the usual additives and processing agents known to those skilled in the art and commonly used in elastomeric compositions for tires such as fillers (reinforcing or non-reinforcing / other than those mentioned above), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing resins (such as described for example in application WO 02 / 10269).

[0123] Manufacture of elastomeric compositions

[0124] The elastomeric compositions according to the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: - a first thermomechanical working or mixing phase (the so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents, including the elastomer matrix, fillers (notably carbon black and graphite), and any other miscellaneous additives, with the exception of the crosslinking system, are introduced into a suitable mixer such as a standard internal mixer (for example, a Banbury type mixer). The incorporation of the filler into the elastomer can be carried out in one or more stages by thermomechanical mixing. In cases where the filler is already incorporated, in whole or in part, into the elastomer in the form of a masterbatch, as described, for example, in applications WO 97 / 36724 or WO 99 / 16600, the masterbatch is directly mixed, and, if necessary, the other elastomers or fillers present in the mixture are incorporated. position which are not in the form of masterbatch, as well as any other miscellaneous additives other than the crosslinking system.

[0125] The non-productive phase can be carried out at high temperature, up to a maximum temperature within a range of 110°C to 200°C, preferably from 130°C to 185°C, for a duration generally within a range of 2 to 10 minutes. - a second mechanical working phase (the so-called "productive" phase), which is carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example within a range of 40°C to 100°C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example within a range of 5 to 15 min.

[0126] The final composition thus obtained is then calendered, for example in the form of a sheet or plate, particularly for characterization in the laboratory, or extruded in the form of a semi-finished (or profile) elastomeric product usable for the manufacture of a tire.

[0127] The composition can be either in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), can be a semi-finished product that can be used in a tire.

[0128] The crosslinking of the composition can be carried out in a manner known to those skilled in the art, for example at a temperature in the range of 100°C to 200°C, under pressure.

[0129] Pneumatic

[0130] The present invention also relates to a tire comprising an elastomeric composition of the invention as described above.

[0131] Given the improved compromise of properties within the framework of the present invention, the tire is a tire for vehicles carrying heavy loads, advantageously chosen from the group consisting of heavy truck tires, civil engineering tires, mining tires, aircraft tires, bus tires, subway tires and agricultural tires.

[0132] The elastomeric composition of the invention can be used at any type of position of these different tires.

[0133] The tire according to the invention exhibits improved resistance to damage, improved rigidity, improved deformation at break, and improved thermal conductivity. It therefore offers greater durability and, given its good thermal conductivity, can travel faster safely.

[0134] METHODS AND MEASURES:

[0135] 1-Measurement of crystallite size by X-ray diffraction

[0136] The size of the crystallites Le is determined from the full width at half maximum of the peaks (commonly called FWHM) obtained by analysis of the X-ray diffraction profiles.

[0137] The contribution to the broadening of the diffraction peak is mainly related to the size of the crystallites, the presence of irregularities in the atomic packing, point, linear or planar defects, and finally to an instrumental component. For the graphitic powder, only the size of the crystallites is considered significant and will be measured using the Scherrer formula:

[0138] [Math.l] A' * To FUT / M * cos 0

[0139] with K the form factor (0.89), A the wavelength of Cu Ka (1.541874Â) and 0 the angle of the plane diffraction peak (002) (in rad).

[0140] The preparation and acquisition follow the method described in the AFNOR standards NF EN 13925-1, NF EN 13925-2, NF EN 13925-3 published in 2003.

[0141] The data are collected using an Empyrean diffractometer from Malvern PANalytical coupled to a PIXcel3D-Medipix3 detector. The diffractometer has the following characteristics shown in Table 1:

[0142] [Tables 1] Empyrean Instrument PIXcel3D-Medipix3 X-ray Detector, Bragg-Brentano Geometry, Cu-Ka X-ray Source, Generator Parameters: 45 kV - 40 mA, Scan Speed: 0.077s, Sample Spinning: 120 rpm

[0143] Table 1: Instrument data and measurement parameters

[0144] The data were analyzed using PANalytical X'Pert HighScore Plus software.

[0145] 2- Measurement of the specific surface area BET of graphite

[0146] The method is based on recording the nitrogen absorption isotherm Liquid in the range p / pO = 0.04–0.26 at 77 K. Following the procedure proposed by Brunauer, Emmet, and Teller (Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc., 1938, 60, 309–319), the monolayer capacity can be determined. Based on the nitrogen molecule cross-section, the monolayer capacity, and the sample weight, the specific surface area can then be calculated.

[0147] 3-Measurement of graphite particle size

[0148] The mass size distribution of graphite particles can be measured by laser granulometry using a Malverne Mastersizer 3000 instrument. The measurement is performed on liquid particles diluted in alcohol after a 1-minute ultrasonic treatment to ensure particle dispersion. The measurement is carried out in accordance with ISO 13320-1:2009 and allows, in particular, the determination of the D90, i.e., the average diameter below which 90% by mass of the total particle population is present.

[0149] 4-Thermal conductivity:

[0150] The thermal conductivity of a material is a physical quantity that characterizes a material's ability to allow heat transfer by conduction. It represents the amount of heat transferred per unit area and time, under a temperature gradient of 1 Kelvin and per meter. It is expressed in Wm⁻².K⁻¹. Thus, a thermal conductivity of 1 Wm⁻².K⁻¹ represents the amount of heat that propagates through a material by thermal conduction, through a surface area of ​​1 m², over a distance of 1 m.

[0151] Thermal conductivity is measured at room temperature (23°C) on a Hotdisk TPS 2500 thermal analyzer with a 5501 type probe, according to ISO 22007-2: 2015. The measuring specimen (constituting the baked composition to be analyzed) is circular in shape (diameter 5 cm, thickness 5 mm) and the measurement is carried out in the direction of the thickness.

[0152] The results are expressed on a scale of 100, with the arbitrary value 100 assigned to the control for calculating and comparing the thermal conductivity of the different samples tested. The value on a scale of 100 for the sample to be tested is calculated using the following formula: (thermal conductivity value of the sample to be tested / thermal conductivity value of the control) x 100. Thus, a result less than 100 indicates a decrease in thermal conductivity and therefore a decrease in heat transfer by conduction. Conversely, a result greater than 100 indicates an increase in thermal conductivity and therefore an improvement in heat transfer by conduction.

[0153] 5-Tensile tests:

[0154] These tensile tests allow the determination of the breaking properties. Unless otherwise specified, they are based on the French standard NF T46-002 of September 1988.

[0155] Processing the tensile recordings allows the modulus curve to be plotted as a function of elongation. The stresses at break (in MPa) and the elongations at break (in %) are recorded.

[0156] All these tensile measurements are carried out at a temperature of 60°C ± 2°C, and under normal humidity conditions (50 ±5% relative humidity) according to French standard NF T40-101 (December 1979).

[0157] Thus, we can determine the energy to cause the rupture (rupture energy) of the specimen which is the product of the stress at rupture and the elongation at rupture (rupture energy = stress at rupture * elongation at rupture).

[0158] The results are indicated on a scale of 100; the arbitrary value 100 being assigned to the reference value for tensile strength, elongation at break, and fracture energy, respectively. A result less than 100 for tensile strength, elongation at break, or fracture energy indicates a decrease in the value concerned, which corresponds to a decrease in the deformation at break property; conversely, a result greater than 100 indicates an increase in this value, which corresponds to an improvement in the deformation at break property.

[0159] 6-Mechanical resistance in the presence of crack initiation

[0160] Measurement of mechanical resistance in the presence of crack initiation (tearability): The tensile strength and strain at break are measured on a specimen stretched at 375 mm / min to induce fracture. The tensile specimen consists of a parallelepiped-shaped rubber plate, 2.5 mm thick, 84 mm long, and 10 mm wide. Three very fine notches, 3 mm long, are made with a razor blade at mid-length and aligned across the width of the specimen before the test begins. The force (N / mm) required to induce fracture is determined, and the elongation at break is measured. The energy required to fracture (tear energy) of the specimen, which is the product of the force and the elongation at break, can then be determined. The test was conducted in air at a temperature of 100°C. The results are shown in base 100, with the arbitrary value 100 being assigned to the control to calculate and compare the rupture energy of the different samples tested.High values ​​indicate good cohesion of the rubber composition, even with the presence of crack initiation points, which corresponds to improved tear resistance performance.

[0161] 7-Dynamic properties:

[0162] The dynamic property tan(φ)max is measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a vulcanized composition sample (cylindrical specimen 4 mm thick and 400 mm²) is recorded. (of section), subjected to sinusoidal alternating simple shear loading at a frequency of 10 Hz and a temperature of 100°C7 according to ASTM D 1349-99. A strain amplitude sweep is performed from 0.1 to 50% (forward cycle), then from 50% to 0.1% (return cycle). The result used is the complex dynamic shear modulus G*. On the return cycle, the value of G* is recorded at 35% strain.

[0163] The results are reported on a scale of 100, with the arbitrary value 100 assigned to the control for calculating and comparing the complex modulus G*35% of the different samples tested. The value on a scale of 100 for the sample to be tested is calculated using the following formula: (value of the complex modulus G*35% of the sample to be tested / value of the complex modulus G*35% of the control) x 100. Thus, a result less than 100 indicates a decrease in the complex modulus G*35% and therefore a decrease in the rigidity of the composition. Conversely, a result greater than 100 indicates an increase in the complex modulus G*35% and therefore an improvement in the rigidity of the composition.

[0164] 8- Microstructure of diene elastomers:

[0165] The microstructure of elastomers is characterized by the near-infrared (NIR) spectroscopy technique.

[0166] Near-infrared (NIR) spectroscopy is used to quantitatively determine the mass percentage of styrene in the elastomer as well as its microstructure (relative distribution of 1,2-, 1,4-trans, and 1,4-cis butadiene units). The principle of the method is based on the Beer-Lambert law generalized to a multicomponent system. Since the method is indirect, it uses multivariate calibration [Vilmin, F.; Dussap, C.; Coste, N. Applied Spectroscopy 2006, 60, 619-29] performed using standard elastomers whose composition was determined by 13C NMR. The styrene content and the microstructure are then calculated from the NIR spectrum of an elastomer film approximately 730 pm thick. Spectrum acquisition is carried out in transmission mode between 4000 and 6200 cm1 with a resolution of 2 cm1, using a Bruker Tensor 37 Fourier transform near-infrared spectrometer equipped with a Peltier-cooled InGaAs detector. EXAMPLES

[0167] Test no. 1:

[0168] This test aims to demonstrate that the elastomeric compositions of the invention present a better compromise of properties - resistance to aggression, rigidity, deformation at break and thermal conductivity - compared to a composition of the prior art.

[0169] For this purpose, 4 elastomeric compositions are prepared, notably intended for the fa manufacturing of tires carrying heavy loads, especially for a civil engineering tire. - TO is a control composition not containing graphite and which presents a good compromise of properties - resistance to aggression, rigidity, deformation at break and thermal conductivity; - Tl is a control composition including graphite; - Cl and C2 are compositions according to the invention comprising a specific graph.

[0170] Table 2 gives the formulation of the different compositions, the rates being expressed in pce (parts by weight per percent parts by weight of elastomers).

[0171] [Tables2] T0 Tl Cl C2 Diene elastomer (1) 100.00 100.00 100.00 100.00 Carbon black (2) 45.00 35.00 41.40 35.00 Graphite (3) (-) 10.00 (-) (-) Graphite (4) (-) (-) 3.60 10.00 Antioxidant (5) 1.00 1.00 1.00 1.00 Stearic acid (6) 1.50 1.50 1.50 1.50 ZnO 4.50 4.50 4.50 4.50 Accelerator (7) 1.33 1.33 1.33 1.33 DPG (8) 0.10 0.10 0.10 0.10 Sulfur 1.42 1.42 1.42 1.42 Total reinforcing charge rate 45.00 35.00 41.40 35.00 Total charge rate 45.00 45.00 45.00 45.00

[0172] (1) Natural rubber

[0173] (2) ASTM N347 grade carbon black having an STSA external surface measured according to ASTM D6556-17 equals 83 m2 / g, a CO AN measured according to ASTM D3493-18 equals 99 ml / lOOg, a specific NSA surface area measured according to ASTM D6556-17 equals 85 m2 / g.

[0174] (3) Natural 150 mesh graphite, exhibiting a Specific surface area BET = 0.5 m² / g, D90 = 150 pm, and Lc = 493 nm. This graphite is marketed by Imerys under the reference "Timrex 80*150". The specific surface area BET, D90, and crystallite size Le are measured according to the methods described above.

[0175] (4) Expanded graphite having a specific surface area BET = 25 m² / g, a D90 = 105 pm and an Lc=157 nm. This graphite is marketed by Imerys under the reference "Timex C-Term 001". The BET specific surface area, D90 and crystallite size Le are measured according to the methods described above.

[0176] (5) Nl,3-dimethylbutyl-N-phenyl-para-phenylenediamine marketed by Flexys under the reference "Santoflex 6-PPD"

[0177] (6) Stearine marketed by the company Uniquema under the name “Pristerene 4931)

[0178] (7) N-cyclohexyl-2-benzothiazyl-sulfenamide marketed by Flexys under the reference “Sancure CBS”

[0179] (8) diphenylguanidine marketed by Flexys under the reference “Perkacit”

[0180] The elastomeric compositions to be tested are prepared as follows: natural rubber, then the reinforcing filler, graphite, and finally the various other ingredients, with the exception of sulfur and the vulcanization accelerator, are introduced into an internal mixer filled to 70% and with an initial tank temperature of approximately 60°C. A thermomechanical process (non-productive phase) is then carried out in one or two stages (total mixing time of approximately 3 to 6 minutes, until a maximum "drop" temperature of approximately 160-165°C is reached). The resulting mixture is collected, cooled, and then sulfur and the vulcanization accelerator are added to an external mixer (homo-finisher) at 40°C, with the mixture being blended for 4 to 10 minutes (productive phase).

[0181] The compositions are then shaped for measurements of their physical or mechanical properties (for example in the form of test specimens) and if necessary baked (or vulcanized) for measurements of baked properties.

[0182] The properties measured after cooking at 120°C for 300 min are reported in Table 3.

[0183] [Tables3] Composition T0 Tl Cl C2 Thermal conductivity (base 100) 100 126 126 171 Elongation at break (base 100) 100 102 103 113 Energy of rupture (base 100) 100 88 104 117 Tear energy (base 100) 100 50 95 85 Stiffness (base 100) 100 84 97 93

[0184] Compared to the T0 elastomeric composition, the use of a natural graphite with a 150 mesh improves thermal conductivity and elongation at break but at the expense of stiffness, fracture energy and tear energy (therefore of resistance to aggression).

[0185] The use of graphite with a crystallite size of 157 nm (elastomeric composition according to the invention Cl) surprisingly yields the same thermal conductivity and elongation at break as the control composition Tl. However, it provides significantly higher fracture energy, tear energy, and stiffness properties than the control composition Tl, and comparable to those of the control composition T0. These effects are achieved with a significantly lower graphite content than that used in the elastomeric composition Tl.

[0186] Advantageously, the compromise of properties—resistance to attack, stiffness, deformation at break, and thermal conductivity—is always improved even when the graphite content is increased without increasing the filler content. The elastomeric composition according to the invention C2 exhibits overall better properties compared to the control compositions T0 and TL

[0187] Test #2:

[0188] This test aims to demonstrate that the elastomeric compositions of the invention present a better compromise of properties - resistance to aggression, rigidity, deformation at break and thermal conductivity - compared to a composition of the prior art.

[0189] For this purpose, 4 elastomeric compositions are prepared, notably intended for the manufacture of tires for heavy goods vehicles: - T2 is a control composition not containing graphite and which presents a good compromise of properties - resistance to aggression, rigidity, deformation at break and thermal conductivity; - T3 is a reference composition including graphite; - C3 and C4 are compositions according to the invention comprising a specific graphic.

[0190] Table 4 gives the formulation of the different compositions, the rates being expressed in pce (parts by weight per hundred parts by weight of elastomers).

[0191] [Tables4] T2 T3 C3 C4 Diene elastomer (1) 100.00 100.00 100.00 100.00 Carbon black (2) 36.50 26.50 31.80 26.50 Silica (9) 10.00 10.00 10.00 10.00 Coupling agent (10) 0.50 0.50 0.50 0.50 Graphite (3) (-) 10.00 (-) (-) Graphite (4) (-) (-) 4.70 10.00 PEG (11) 0.84 0.84 0.84 0.84 Antioxidant (5) 1.00 1.00 1.00 1.00 Stearic acid (6) 1.50 1.50 1.50 1.50 ZnO 4.50 4.50 4.50 4.50 Accelerator (7) 1.33 1.33 1.33 1.33 DPG (8) 0.10 0.10 0.10 0.10 Sulfur 1.42 1.42 1.42 1.42 Total Reinforcing Charge Rate 46.50 36.50 41.80 36.50 Total Charge Rate 46.50 46.50 46.50 46.50

[0192] Ingredients (1) to (8) are the same as those in the compositions in Table 2.

[0193] (9) Silica “Zeozil 1165 MP” type HDS marketed by the Solvay company, specific surface area CT AB equal to 160 m2 / g and specific surface area BET equal to 165 m2 / g.

[0194] (10) Coupling agent Bis[3-(triethoxysilyl)propyl] tetrasulfide silane (TESPT) marketed by Evonik under the reference "Si69"

[0195] (11) Polyethylene glycol marketed by Dow Corning under the reference "Carbowax 8000"

[0196] The elastomeric compositions are prepared as previously described. The silica, coupling agent, and PEG are added during the non-productive phase of the manufacturing process.

[0197] The compositions are then shaped for measurements of their physical or mechanical properties (for example in the form of 4 mm test pieces, etc.) and if necessary baked (or vulcanized) for measurements of baked properties.

[0198] The properties measured after cooking at 120°C for 300 min are reported in Table 5.

[0199] [Tables5] Composition T3 T4 C3 C4 Thermal conductivity (base 100) 100 123 123 153 Elongation at break (base 100) 100 96 101 100 Energy at break (base 100) 100 81 97 90 Energy at break (base 100) 100 20 67 44 Stiffness (base 100) 100 87 97 99

[0200] As with the previous compositions, the elastomeric compositions according to the invention C3 and C4 comprise the best compromise of properties - resistance to aggression, stiffness, deformation at break and thermal conductivity - compared to the control compositions T3 and T4.

Claims

Claims

1. Elastomeric composition for a tire carrying heavy loads based on at least one elastomer matrix, fillers including graphite and a reinforcing filler and a vulcanization system, characterized in that: - the elastomer matrix comprises at least 50 pce of a diene elastomer chosen from the group consisting of isoprene elastomers, butadiene elastomers and mixtures of these diene elastomers, - the reinforcing filler mainly comprises a carbon black, - the graphite has a crystallite size Le in a range from 80 to 500 nm, more preferably from 90 to 400 nm, more preferably from 100 to 300 nm, - the total filler content is less than or equal to 65 pce.

2. Elastomeric composition according to claim 1, in which the total rate of fillers is less than or equal to 60 pce, preferably less than or equal to 55 pce.

3. Elastomeric composition according to claim 1, in which the total rate of fillers is within a range from 20 to 65 phr, more preferably within a range from 25 to 60 phr, more preferably still from 25 to 55 phr.

4. Elastomeric composition according to any one of the preceding claims, in which the graphite has a BET specific surface area in a range from 10 to 50 m2 / g, preferably from 15 to 40 m2 / g, more preferably still from 20 to 30 m2 / g.

5. Elastomeric composition according to any one of the preceding claims, in which the graphite has a particle size distribution D90 comprised in a range from 50 to 150 pm, more preferably from 60 to 140 pm, even more preferably from 70 to 130 pm.

6. An elastomeric composition according to any preceding claim, wherein the graphite is expanded graphite.

7. Elastomeric composition according to any one of the claims preceding, wherein the reinforcing filler further comprises at least one precipitated silica and the composition further comprises an agent for coupling the silica to the diene elastomer of the elastomer matrix.

8. Elastomeric composition according to any one of the preceding claims, in which the graphite content is within a range from 1 to 12 pce, more preferably from 2 to 11 pce.

9. Elastomeric composition according to any one of the preceding claims, in which the level of the diene elastomer is within a range from 60 to 100 pce, preferably from 70 to 100 pce, preferably from 80 to 100 pce, preferably from 90 to 100 pce.

10. An elastomeric composition according to any one of the preceding claims, wherein the diene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprene, isoprene-styrene copolymers, polybutadienes, ethylene-butadiene copolymers, butadiene-styrene copolymers, isoprene-butadiene copolymers, isoprene-butadiene-styrene copolymers and blends of these diene elastomers, preferably selected from the group consisting of natural rubber, synthetic polyisoprene, polybutadienes, ethylene-butadiene copolymers, butadiene-styrene copolymers and blends of these diene elastomers, more preferably still is selected from the group consisting of natural rubber, synthetic polyisoprene and the blend of these diene elastomers.

11. Elastomeric composition according to any one of the preceding claims, in which the level of reinforcing fillers is less than or equal to 60 phr, more preferably less than or equal to 55 phr, more preferably less than or equal to 50 phr, more preferably less than or equal to 45 phr.

12. Elastomeric composition according to any one of the preceding claims, in which the carbon black has an external surface STSA, measured according to ASTM D6556-17, comprised in a range from 30 to 145 m2 / g, more preferably from 35 to 140 m2 / g, more preferably from 60 to 130 m2 / g, more preferably from 65 to 95 m2 / g.

13. An elastomeric composition according to any preceding claim, wherein the carbon black has a number compressed oil absorption CO AN, measured according to ASTM D3493-18, in a range from 50 to 130 ml / 100g, preferably from 65 to 125 ml / 100g, more preferably from 70 to 120 ml / 100g, even more preferably from 75 to 120 ml / 100g.

14. A heavy-duty tire comprising at least one composition according to any one of claims 1 to 13, preferably the tire is a civil engineering tire or a heavy-duty tire.