COMPOSITE CONTAINING SHORT FIBERS

Description

Technical field of the invention

[0001] The present invention relates to the field of composites, in particular composites allowing the reinforcement of rubber articles, for example for the reinforcement of pneumatic or non-pneumatic tires for vehicles. Prior art

[0002] Reinforcing plies for tires or rubber articles such as conveyor belts or belts usually consist of a rubber compound, called a calendering compound, and reinforcing cords, often metallic and surface-coated with brass.

[0003] The adhesion function generally imposes specific formulations on the calendering mixture, in particular the need for a high sulfur and zinc oxide content, a low amount of stearic acid, the presence of cobalt salt, the use of a long-delay accelerator. In addition, the calendering mixture is expected to have sufficient rigidity and induce as few hysteretic losses as possible in order to minimize rolling resistance or heating of the rubber articles. It is therefore clear that this complex mixture must fulfill several, sometimes contradictory, functions.

[0004] To increase the rigidity of calendering compositions, many avenues have been explored. For example, the amount of reinforcing filler can be increased, but this lever generally impacts the hysteresis of the compositions. It is also possible to increase the sulfur content, with the risk of sensitizing the compositions to aging phenomena, or to reduce the raw tack, i.e. before crosslinking of the composition, which can make calendering operations more complex ("processability" of the composition). Other levers are used, such as the incorporation of reinforcing resins such as formophenolic resins coupled with methylene-donating hardeners (typically hexamethylenetetramine (abbreviated as HMT), hexamethoxymethylmelamine (abbreviated as HMMM or H3M), or hexaethoxymethylmelamine).However, the combination of a methylene acceptor phenolic resin with HMT or H3M, a methylene donor, produces formaldehyde during crosslinking of the rubber composition. However, it is desirable to reduce or even eliminate formaldehyde from rubber compositions due to the potential environmental impact of these compounds.

[0005] Document JPH09279043 proposes to adjust the stiffness at low and high deformation of a rubber and / or polyolefin mixture by implementing a fiber cutting, with on the one hand short thermoplastic fibers of very small diameter (0.05 to 5 µm) comprising amide groups, a silane coupling agent or a formophenolic resin condensate allowing the adhesion of these fibers to the elastomeric matrix and on the other hand short organic or inorganic fibers. However, this document is silent as to the hysteretic properties of the mixtures obtained.

[0006] Continuing its research, the applicant discovered a composite based on at least one reinforcing element comprising a metal surface and a rubber composition comprising short fibers making it possible to significantly increase the rigidity of the compositions, without penalizing either their hysteresis or their processability. Detailed description of the invention Definitions

[0007] The carbon-containing compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This includes, in particular, polymers, plasticizers, fillers, etc. Composite

[0008] The invention relates to a composite based on at least one reinforcing element comprising a metal surface and a rubber composition.

[0009] The expression composite "based on at least one reinforcing element and one rubber composition" means a composite comprising the reinforcing element and said composition, the composition having been able to react with the surface of the reinforcing element during the various phases of manufacturing the composite, in particular during the crosslinking of the composition or during the making of the composite before crosslinking of the composition.

[0010] The said reinforcing element is a wire element. It may be entirely or partly metallic. A wire element is understood to mean an element having a length at least 10 times greater than the largest dimension of its section, regardless of the shape of the latter: circular, elliptical, oblong, polygonal, in particular rectangular or square or oval. In the case of a rectangular section, the wire element has the shape of a strip.

[0011] Said reinforcing element comprises a metallic surface.

[0012] The metallic surface of the reinforcing element constitutes at least a part, and preferably the entire surface of said element and is intended to come into direct contact with the rubber composition. Preferably, the reinforcing element is metallic, that is to say made of a metallic material.

[0013] The rubber composition coats at least part of the reinforcing element, preferably the entirety of said element.

[0014] According to a first variant of the invention, the metal surface of the reinforcing element is made of a material different from the rest of the reinforcing element. In other words, the reinforcing element is made of a material which is at least partly, preferably totally, covered by a metal layer which constitutes the metal surface. The material at least partly, preferably totally, covered by the metal surface is of a metallic or non-metallic nature, preferably metallic.

[0015] According to a second variant of the invention, the reinforcing element is made of the same material, in which case the reinforcing element is made of a metal which is identical to the metal of the metal surface.

[0016] The metal surface comprises a metal that may be selected from the group consisting of iron, copper, zinc, tin, aluminum, cobalt, nickel and alloys comprising at least one of these metals. The alloys may be, for example, binary or ternary alloys, such as steel, bronze and brass. Preferably, the metal surface comprises a metal selected from the group consisting of iron, copper, tin, zinc and an alloy comprising at least one of these metals. More preferably, the metal surface comprises a metal selected from the group consisting of steel, brass (Cu-Zn alloy), zinc and bronze (Cu-Sn alloy), and even more preferably from the group consisting of brass and steel. Very preferably, the metal surface is made of brass.

[0017] Some metals are subject to oxidation when in contact with ambient air, and the metal may be partially oxidized.

[0018] When the metal surface is made of steel, the steel is preferably a carbon steel or a stainless steel. When the steel is a carbon steel, its carbon content is preferably between 0.01% and 1.2% or between 0.05% and 1.2%, or between 0.2% and 1.2%, in particular between 0.4% and 1.1%. When the steel is stainless, it preferably comprises at least 11% chromium and at least 50% iron.

[0019] According to a preferred embodiment, the composite is a reinforced product which comprises several reinforcing elements as defined above and a calendering rubber in which the reinforcing elements are embedded, the calendering rubber consisting of the rubber composition of the composite according to the invention. According to this embodiment, the reinforcing elements are arranged generally side by side in a main direction. For an application envisaged in a tire, the composite can therefore constitute a reinforcing reinforcement for a tire.

[0020] The composite according to the invention may be in the raw state (before crosslinking of the rubber composition) or in the cured state (after crosslinking of the rubber composition). The composite is cured after bringing the reinforcing element(s) into contact with the rubber composition according to the invention.

[0021] The composite can be manufactured by a process that includes the following steps: Make two layers of the rubber composition of the composite according to the invention, Take the reinforcing element(s) sandwiched in the two layers by placing it(them) between the two layers, If necessary, cook the composite.

[0022] Alternatively, the composite may be made by depositing the reinforcing element on a portion of a layer, the layer is then folded back on itself to cover the reinforcing element which is thus sandwiched along its entire length or part of its length.

[0023] The layers can be made by calendering. During the curing of the composite, the rubber composition is crosslinked.

[0024] When the composite is intended for use as a reinforcing reinforcement in a tire, curing of the composite generally occurs during curing of the tire casing. Diene elastomers

[0025] The composite according to the invention comprises a rubber composition based on at least one diene elastomer. By diene elastomer, it is recalled that it should be understood that an elastomer is derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

[0026] These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". "Essentially unsaturated" generally means a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or patterns of diene origin (conjugated dienes) which is greater than 15% (mol %); thus, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins such as EPDM do not fall within the preceding definition and can in particular be described as "essentially saturated" diene elastomers (low or very low content of patterns of diene origin, always less than 15%). The diene elastomers included in the composition according to the invention are preferably essentially unsaturated.

[0027] The term diene elastomer capable of being used in the compositions in accordance with the invention is particularly understood to mean: (a) any homopolymer of a conjugated or unconjugated diene monomer having from 4 to 18 carbon atoms; (b) any copolymer of a conjugated or unconjugated diene having from 4 to 18 carbon atoms and at least one other monomer.

[0028] The other monomer can be ethylene, an olefin or a diene, conjugated or not.

[0029] Suitable conjugated dienes are conjugated dienes having 4 to 12 carbon atoms, in particular 1,3-dienes, such as 1,3-butadiene and isoprene.

[0030] Suitable olefins are vinylaromatic compounds with 8 to 20 carbon atoms and aliphatic α-monoolefins with 3 to 12 carbon atoms.

[0031] Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial mixture "vinyl-toluene", para-tert-butylstyrene.

[0032] Suitable aliphatic α-monoolefins are, in particular, acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms.

[0033] The diene elastomer is preferably a diene elastomer of the highly unsaturated type, in particular a diene elastomer selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), polybutadienes (BR), butadiene copolymers, isoprene copolymers and blends of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-butadiene-styrene copolymers (SBIR), ethylene-butadiene copolymers (EBR) and blends of such copolymers.

[0034] The above diene elastomers can be, for example, block, random, sequenced, microsequenced, and can be prepared in dispersion or in solution; they can be coupled and / or star-shaped or even functionalized with a coupling and / or star-shaping or functionalizing agent, for example epoxidized.

[0035] Preferably, the rubber composition of the composite according to the invention comprises at least 50 phr, preferably at least 70 phr, preferably at least 90 phr of at least one isoprene elastomer. Reinforcing charge

[0036] Any type of reinforcing filler known for its ability to reinforce a rubber composition suitable for the manufacture of tires may be used, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica, or a blend of these two types of filler, in particular a blend of carbon black and silica.

[0037] Suitable carbon blacks are all carbon blacks, in particular HAF, ISAF, SAF type blacks conventionally used in tires (so-called tire grade blacks). Among the latter, mention will be made more particularly of reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as for example blacks N115, N134, N234, N326, N330, N339, N347, N375, or even, depending on the intended applications, blacks of higher series (for example N660, N683, N772). The carbon blacks could for example already be incorporated into an isoprene elastomer in the form of a masterbatch (see for example applications WO 97 / 36724 or WO 99 / 16600). The BET specific surface area of ​​carbon blacks is measured according to standard D6556-10 [multi-point method (minimum 5 points) - gas: nitrogen - relative pressure range P / P0: 0.1 to 0.3].

[0038] By "reinforcing inorganic filler" is meant in the present application, by definition, any inorganic or mineral filler (whatever its color and its natural or synthetic origin), also called "white" filler, "light" filler or even "non-black filler" as opposed to carbon black, capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words capable of replacing, in its reinforcing function, a conventional tire-grade carbon black; such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface.

[0039] Suitable reinforcing inorganic fillers are, in particular, mineral fillers of the siliceous type, in particular silica (SiO 2 ), or of the aluminous type, in particular alumina (Al 2 O 3 ). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area and a CTAB specific surface area both of less than 450 m 2 < / g, preferably from 30 to 400 m 2 < / g. Examples of highly dispersible precipitated silicas (known as "HDS") include Ultrasil 7000 and Ultrasil 7005 silicas from Degussa, Zeosil 1165MP, 1135MP and 1115MP silicas from Rhodia, Hi-Sil EZ150G silica from PPG, Zeopol 8715, 8745 and 8755 silicas from Huber, and high specific surface area silicas as described in application WO 03 / 16837.

[0040] The physical state in which the reinforcing inorganic filler is present is irrelevant, whether in the form of powder, microbeads, granules, balls or any other suitable densified form. Of course, the term reinforcing inorganic filler also means mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers.

[0041] The reinforcing inorganic filler used, in particular if it is silica, preferably has a BET surface area of ​​between 45 and 400 m 2 < / g, more preferably between 60 and 300 m 2 < / g.

[0042] Preferably, the rubber composition of the composite according to the invention comprises from 10 to 100 phr, more preferably from 10 to 80 phr and more preferably from 10 to 60 phr of carbon black, the optimum being, in a known manner, different depending on the particular applications targeted: the level of reinforcement expected on a bicycle tire, for example, is of course lower than that required on a tire capable of rolling at high speed in a sustained manner, for example a motorcycle tire, a tire for a passenger vehicle or for a utility vehicle such as a heavy goods vehicle. In a preferred arrangement, the reinforcing filler consists of carbon black.

[0043] Preferably, the rubber composition of the composite according to the invention comprises from 10 to 150 phr, preferably from 10 to 100 phr of silica. In a preferred arrangement, the reinforcing filler consists of silica.

[0044] Preferably, the rubber composition of the composite according to the invention does not comprise coupling agents from the silane family or comprises less than 5 phr, preferably less than 3 phr, more preferably less than 2 phr, very preferably less than 1 phr, preferentially less than 0.5 phr. By composition not comprising a compound, it is understood that the composition does not comprise this compound voluntarily introduced into the composition and that this compound, if it is present, is present in the form of traces linked for example to the manufacturing process of the composition or the elements composing it.

[0045] A person skilled in the art will understand that, as a filler equivalent to the reinforcing inorganic filler described in this paragraph, a reinforcing filler of another nature, in particular organic, could be used, provided that this reinforcing filler is covered with an inorganic layer such as silica, or else comprises functional sites on its surface, in particular hydroxyls, making it possible to establish the bond between the filler and the elastomer in the presence or absence of a covering or coupling agent. System of crosslinking

[0046] The rubber composition of the composite according to the invention comprises a crosslinking system. Preferably, the crosslinking system is sulfur-based, in which case it is referred to as a vulcanization system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or a sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferably, various known vulcanization activators can be used, 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.

[0047] Preferably, the rubber composition of the composite according to the invention comprises at least 2 phr of zinc oxide, preferably at least 3 phr and more preferably at least 5 phr of zinc oxide.

[0048] Sulphur is used at a preferential rate of between 2.5 and 10 pce, in particular between 3 and 8 pce. The vulcanisation accelerator is used at a preferential rate in the range of 0.4 to 4 pce, preferably between 0.5 and 3.5 pce.

[0049] Any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur may 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, but are not limited to, the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds. Various additives

[0050] The rubber composition of the composite according to the invention may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of pneumatic tires, such as for example plasticizers or extender oils, whether the latter are of aromatic or non-aromatic nature, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing resins such as bismaleimides, acceptors (for example phenolic novolak resin) or methylene donors (for example HMT or H3M).

[0051] Preferably, the rubber composition of the composite according to the invention does not comprise reinforcing resin or comprises less than 10 pce, preferably less than 5 pce, preferably less than 2 pce, preferably less than 1 pce and very preferably less than 0.2 pce.

[0052] By reinforcing resin is meant a resin known to those skilled in the art for stiffening rubber compositions, stiffness measured for example by Young's Modulus, according to standard ASTM 412-98a, or the complex dynamic shear modulus G* according to standard ASTM D 5992-96. Fibers

[0053] The composite according to the invention comprises a rubber composition comprising fibers having a length of between 1 and 20 mm, preferably between 1 and 12 mm, and preferably between 5 and 10 mm and a diameter of between 10 µm and 100 µm, preferably between 10 and 50 µm.

[0054] Longer fibers reduce the processability of rubber compounds by increasing their raw Mooney viscosity, while fibers that are too short do not have the expected reinforcing effect. It has been shown that fibers with a length between 1 and 20 mm and a diameter between 10 µm and 100 µm can increase the rigidity of rubber compounds by maintaining or even lowering hysteresis, while preserving excellent processability. Fibers with a narrower diameter do not fully have the expected reinforcing effect, probably due to greater fiber fragility.

[0055] These fibers present in the rubber composition are preferably based on a material chosen from aramids, polyvinyl alcohols and their mixtures, preferably from para-aramids, polyvinyl alcohol and their mixtures. Very preferably, these fibers are based on polyvinyl alcohol.

[0056] Preferably, these fibers are based either on a material chosen from aramids, or on a material chosen from polyvinyl alcohols. In other words, according to this preference, these fibers are either based on an aramid material or on a material based on polyvinyl alcohol. That is to say that the composition according to this preference contains only one type of fiber and not a mixture of fibers based on an aramid material and fibers based on a material based on polyvinyl alcohol.

[0057] Preferably, the rubber composition of the composite according to the invention does not comprise fibers made of a material chosen from aramids, or comprises less than 1 pce.

[0058] Preferably, these fibers are coated with an adhesive composition making it possible to improve their adhesion to the rubber composition.

[0059] This adhesive composition may be a conventional Resorcinol-formaldehyde-latex glue, commonly abbreviated RFL glue, or an adhesive composition based on a phenol-aldehyde resin and a latex as described in documents WO 2013 / 017421, WO 2013 / 017422, WO 2013 / 017423, WO 2015 / 007641 and WO 2015 / 007642. The use of adhesive compositions based on a phenol-aldehyde resin and a latex is particularly advantageous due to the non-emission of formaldehyde.

[0060] Preferably, the rubber composition of the composite according to the invention comprises from 5 to 30 phr of said fibers, preferably from 5 to 20 phr of said fibers. These contents make it possible to ensure a good shift in the stiffness / hysteresis compromise while maintaining good processability of the raw compositions. Preferably, the composition according to the invention comprises from 5 to 30 phr of fibers in total, preferably from 5 to 20 phr of fibers in total. Very preferably, the composition according to the invention does not comprise any fibers other than said fibers.

[0061] Such fibers useful for the purposes of the invention may, for example, be the “Twaron” fibers marketed by the company Teijin, or the “Kuralon” fibers marketed by the company Kuraray. Finished article or semi-finished and pneumatic

[0062] The invention also relates to a finished or semi-finished article comprising a composite according to the invention. The finished or semi-finished article may be any article comprising a composite. Examples that may be mentioned, but are not limited to, conveyor belts, pneumatic or non-pneumatic tires.

[0063] The tire, another subject of the invention, has the essential characteristic of comprising the composite according to the invention. The tire may be in the raw state (before crosslinking of the rubber composition) or in the cured state (after crosslinking of the rubber composition). Generally, during the manufacture of the tire, the composite is deposited in the raw state (i.e. before crosslinking of the rubber composition) in the structure of the tire before the step of curing the tire.

[0064] The invention particularly relates to pneumatic tires intended to equip motor vehicles of the passenger car, SUV ("Sport Utility Vehicles"), or two-wheeled type (in particular motorcycles), or airplanes, or even industrial vehicles chosen from vans, "Heavy Goods Vehicles", i.e. metro, buses, road transport vehicles (trucks, tractors, trailers), off-road vehicles such as agricultural or civil engineering vehicles, and others. Examples Measurement methods

[0065] The Mooney plasticity measurement is carried out according to the following principle and in accordance with ASTM D-1646. The composition or elastomer, generally raw, is molded in a cylindrical chamber heated to a given temperature, usually 100°C. After one minute of preheating, an L-type rotor rotates within the specimen at 2 revolutions per minute and the torque needed to maintain this movement is measured after 4 minutes of rotation. The Mooney plasticity (ML 1+4) is expressed in "Mooney units" (MU, with 1 MU = 0.83 Newton.meters).

[0066] Tensile tests were carried out in accordance with French standard NF T 46-002 of September 1988. All tensile measurements were carried out under normal temperature (23±2°C) and hygrometry (50±5% relative humidity) conditions, according to French standard NF T 40-101 (December 1979).

[0067] The nominal secant modulus calculated by reducing it to the initial section of the test piece (or apparent stress, in MPa) at 10% elongation noted MA 10 was measured in second elongation (i.e. after accommodation), on samples cooked for 25 minutes at 150°C.

[0068] The dynamic properties tan(d)max at 60°C are measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of crosslinked composition (cylindrical specimen 4 mm thick and 400 mm 2< in section) is recorded, subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under the defined temperature conditions, for example at 40°C according to the ASTM D 1349-99 standard, or depending on the case at a different temperature. A strain amplitude sweep is carried out from 0.1 to 50% (forward cycle), then from 50% to 0.1% (return cycle). The results used are the loss factor tan(d). For the return cycle, the maximum value of tan(d) observed, noted tan(d)max, at 60°C is indicated. This value is expressed in base 100 taking the CO2 composition as a reference.

[0069] It is recalled that, in a manner well known to those skilled in the art, the value of tan(d)max at 60°C is representative of the hysteresis of the material, and therefore of the rolling resistance: the lower the tan(d)max at 60°C, the more the rolling resistance is reduced and therefore improved. Thus, a value lower than 100 will indicate reduced rolling resistance compared to the C02 composition and a value higher than 100 will indicate increased rolling resistance compared to C02. Preparation of the compositions

[0070] The following tests are carried out as follows: the diene elastomer, the reinforcing filler and the various other ingredients, including the fibres and, where appropriate, the formophenolic resins, with the exception of the vulcanisation system, are successively introduced into an internal mixer (final filling rate: approximately 70% by volume), whose initial tank temperature is approximately 60°C. Thermomechanical work (non-productive phase) is then carried out in one step, lasting a total of approximately 3 to 4 minutes, until a maximum "drop" temperature of 165°C is reached.

[0071] The mixture thus obtained is recovered, cooled and then sulfur and an accelerator (sulfenamide) are incorporated, and, if necessary, the formophenolic resin hardeners, on a mixer (homo-finisher) at 30°C, mixing everything (productive phase) for an appropriate time (for example between 5 and 12 min).

[0072] The compositions thus obtained are then calendered in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber and then subjected to a cooking step at 150°C for 25 min before measuring their physical or mechanical properties.

[0073] For each composition, the Mooney plasticity value expressed in UM (Mooney unit) is measured in the raw state, i.e. before vulcanization. The elastic modulus under tension at 10% elongation (MA 10 ) and the tan(d) max value are then measured in the cooked state, i.e. after vulcanization.

[0074] Tests were carried out with different rubber compositions presented in Table 1, based on natural rubber. Composition C01 corresponds to a conventional calendering composition. Composition C02 differs from composition C01 only in the lower carbon black content. This composition is therefore less hysteretic than the conventional composition C01. Composition FP1 is a composition similar to composition C01 whose rigidity has been increased in a manner known to those skilled in the art by adding a formophenolic resin. Compositions C03 to C08 comprise short fibers. [Table 1] C01 C02 FP1 C03 C04 C05 C06 C07 C08 Natural rubber (1) 100 100 100 100 100 100 100 100 100 Carbon black (2) 70 40 70 40 40 40 40 40 40 Zinc oxide (3) 8 8 8 8 8 8 8 8 8 Stearic acid (4) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 6PPD (5) 2 2 2 2 2 2 2 2 2 CTP (6) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Cobalt salt 1 1 1 1 1 1 1 1 1 Sulfur 5 5 5 5 5 5 5 5 5 TBBS (7) 0.7 0.7 1 0.7 0.7 0.7 0.7 0.7 0.7 Formophenolic resin (8) - - 10 - - - - - - Hardener (9) - - 8 - - - - - - Aramid fibers, length 6 mm (10) - - - 10 20 - - - - PVA fibers, length 6 mm (11) - - - - - 10 20 - - PVA fibers, length 10 mm (11) - - - - - - - 10 20 Raw properties Mooney Plasticity (1+4) (UM) 84 60 70 85 67 73 70 78 Properties to cook MA10 190 100 1310 1133 1743 1976 3164 2610 2560 Tan(delta)max return (60°C) 240 100 340 120 130 110 120 120 140 Stiffness / Hysteresis Tradeoff 0.6 - 5.0 51.7 54.8 187.6 153.2 125.5 61.5 Quantities expressed in pce (1) Natural rubber (peptized) (2) ASTM N326 grade (Cabot company) (3) Industrial grade zinc oxide (Umicore company) (4) Stearin “Pristerene 4931” (Uniqema company) (5) N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (Santoflex 6-PPD, Flexsys company) (6) N-(cyclohexylthio)phthalimide “Vulkalent G” (Lanxess company) or also “Duslin P” (Duslo company) (7) N-tert-butyl-2-benzothiazol-sulfenamide “Santocure” (Flexsys company) (8) Precondensed resin SRF 1524 (from Schenectady company; diluted to 75%) (9) Hexa-methylenetetramine (from Sigma-Aldrich; purity ≥ 99%) (10) Para-aramid fibers “Twaron 1080”, marketed by the Teijin company, length 6 mm and diameter 15 µm (11) Polyvinyl alcohol fibers “Kuralon” marketed by the Kuraray company, diameter 27 µm

[0075] From a processability point of view, it is observed that all compositions comprising fibers have Mooney viscosity values ​​close to or lower than those of the classic composition C01, which shows good processability of these compositions.

[0076] The rigid composition FP1 presents, as expected, a much higher rigidity than the compositions C01 and C02, with a hysteretic loss higher than the composition C01.

[0077] Surprisingly, we observe that compositions C03 to C08 have similar rigidities, or even higher than composition FP1, while presenting hysteretic losses close to the weakly loaded composition C02.

[0078] This shift in the stiffness / hysteresis trade-off is reflected by the eponymous indicator calculated as follows: Stiffness / hysteresis trade-off = (composition stiffness - reference stiffness) / reference stiffness / ((composition hysteresis - reference hysteresis) / reference hysteresis)

Claims

1. Composite based on at least one reinforcing element comprising a metallic surface and on a rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system and fibres having a length of between 1 and 20 mm and a diameter of between 10 µm and 100 µm.

2. Composite according to Claim 1, in which said fibres are based on a material selected from aramids, polyvinyl alcohols and mixtures thereof, preferentially from para-aramids, polyvinyl alcohol and mixtures thereof, and very preferentially polyvinyl alcohol.

3. Composite according to the preceding claim, in which said fibres are based on or else of a material selected from aramids, or else on or of a material selected from polyvinyl alcohols.

4. Composite according to any one of the preceding claims, in which said fibres have a length of between a and 12 mm and preferably between 5 and 10 mm.

5. Composite according to any one of the preceding claims, in which said fibres are coated with an adhesive composition.

6. Composite according to any one of the preceding claims, in which the rubber composition comprises from 5 to 30 phr of fibres, preferably from 5 to 20 phr of said fibres.

7. Composite according to any one of the preceding claims, in which the reinforcing filler of the rubber composition comprises carbon black, silica or a mixture of carbon black and silica.

8. Composite according to any one of the preceding claims, in which the rubber composition does not comprise coupling agents of the silane family, or comprises less than 5 phr, preferably less than 3 phr, preferably less than 2 phr, very preferably less than 1 phr, preferentially less than 0.5 phr, thereof.

9. Composite according to any one of the preceding claims, in which the rubber composition comprises at least 0.5 phr, preferentially at least 1 phr of cobalt salts.

10. Composite according to any one of the preceding claims, in which the rubber composition comprises a diene elastomer selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, ethylene / butadiene copolymers, and mixtures of these elastomers.

11. Composite according to any one of the preceding claims, in which the rubber composition comprises at least 50 phr, preferentially at least 70 phr, preferably at least 90 phr of a at least one isoprene elastomer.

12. Composite according to the preceding claim, in which the isoprene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes, isoprene copolymers and mixtures thereof.

13. Composite according to any one of the preceding claims, in which the metal of the metallic surface is iron, copper, tin, zinc or an alloy comprising at least one of these metals.

14. Rubber article comprising a composite according to any one of Claims 1 to 13.

15. Pneumatic tyre comprising a composite according to one of Claims 1 to 13.