FR3121145A1 - Composite comprising an elastomeric composition and a metallic reinforcing element - Google Patents

Abstract

The invention relates to a composite comprising at least one reinforcing element having a surface comprising an alloy of copper, zinc, and from 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum, said reinforcing element being embedded in an elastomeric composition based on at least one diene elastomer, a reinforcing filler and a sulfur crosslinking system, comprising an oxide metal, a stearic acid derivative and a vulcanization accelerator, the sulfur content being between 1 and 5 phr, and the metal oxide to stearic acid derivative mass ratio being less than 4.

Description

Composite comprising an elastomeric composition and a metallic reinforcing element

Technical field of the invention

The present invention relates to the field of reinforced rubber products, in particular intended for pneumatic or non-pneumatic tires, as well as articles comprising such reinforced products.

Prior art

The reinforcement plies of pneumatic tires or reinforced rubber articles usually comprise a rubber composition, called a calender, and metallic reinforcing cords. The calendering composition must meet numerous characteristics, such as good properties of adhesion to metal reinforcing cords, hysteretic properties giving the plies a low contribution to rolling resistance as well as good resistance to cracking and this , throughout the life of the tyre.

The adhesion between the metal cables and the surrounding rubber is one of the key properties for the effectiveness of the reinforcement plies of pneumatic tires or reinforced rubber articles. The calendering compositions, which comprise a diene elastomer, in particular natural rubber, a reinforcing filler, also generally comprise a specific vulcanization system and, as adhesion promoter, cobalt salts. This specific vulcanization system usually comprises a high sulfur content, a high zinc oxide to stearic acid mass ratio, a so-called slow vulcanization accelerator and a vulcanization retarder. In these systems, the adhesion between the calendering composition and the metal cable is created via the phenomenon of sulfurization of the brass-coated surface of the cable, the cobalt salts having an effect on the durability of the adhesion.

Many studies have been carried out by tire manufacturers to limit the sulfur, metal oxide and/or cobalt salt contents while maintaining one or more of the performances of the calendering compositions, as well as their durability. Thus, the documents WO2016/058942 and WO2016/0589431 propose sheathing the metal reinforcing elements, making it possible to lower the sulfur and zinc oxide levels in the compositions for calendering the reinforcements thus sheathed and to reduce, or even eliminate cobalt from the calendering composition. However, this approach requires sheathing the reinforcing elements.

Other research work has focused on the reformulation of the metal support, in particular by proposing reinforcement elements whose surface is coated with an alloy comprising cobalt. Mention may be made, for example, of US Patent 4,347,290 which teaches a composite comprising an elastomeric composition and a metal reinforcing element whose surface is coated with a Cu-Zn-Co alloy showing an improvement in adhesion, with however a ZnO ratio / relatively high stearic acid. This document does not address the aspect of the behavior of the properties over time.

Document EP 3 476 624 teaches a composite comprising an elastomeric composition and a reinforcing element whose surface comprises brass and from 1 to 10% by weight of one or more metals chosen from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum. The examples show that elastomeric compositions comprising an adhesion-promoting resin (resorcinol/HMMM system) and not comprising cobalt salts exhibit good adhesion properties over time.

Continuing her research, the applicant discovered that a composite comprising at least one reinforcing element having a surface comprising an alloy of copper, zinc, and 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum, said reinforcing element being embedded in an elastomeric composition based on at least one diene elastomer, a reinforcing filler and a crosslinking system with sulphur, comprising a metal oxide, a derivative of stearic acid and a vulcanization accelerator, the sulfur content being between 1 and 5 phr, and the ratio by mass of metal oxide to derivative of stearic acid being less than 4 , exhibited both good adhesion properties of the composition to the reinforcing element, while improving the durability of performance in terms, in particular, of adhesion strength, contribution to rolling resistance and resistance to the cracking.

Detailed description of the invention

The invention relates to a composite comprising at least one reinforcing element having a surface comprising an alloy of copper, zinc, and from 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum, said reinforcing element being embedded in an elastomeric composition based on at least one diene elastomer, a reinforcing filler and a sulfur crosslinking system, comprising an oxide metal, a stearic acid derivative and a vulcanization accelerator, the sulfur content being between 1 and 5 phr, and the metal oxide to stearic acid derivative mass ratio being less than 4.

Preferably, the invention relates to a composite in which the surface of the reinforcing element comprises an alloy of copper, zinc, and 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin manganese, iron and molybdenum, preferably chosen from cobalt and nickel.

Preferably, the invention relates to a composite in which the surface of the reinforcing element comprises an alloy of copper, zinc, and 2 to 8% by weight of at least one metal chosen from cobalt and nickel, preferably cobalt.

Preferably, the invention relates to a composite in which the surface of the reinforcing element comprises 55 to 75% copper by weight.

Preferably, the invention relates to a composite in which the elastomeric composition comprises at least 50 phr, preferably at least 70 phr, more preferably at least 90 phr of at least one isoprene elastomer.

Preferably, the invention relates to a composite in which the elastomeric composition comprises 100 phr of at least one isoprene elastomer.

Preferably, the invention relates to a composite in which the isoprene elastomer is chosen from the group consisting of synthetic polyisoprenes, natural rubber, isoprene copolymers and mixtures thereof, preferably chosen from the group consisting of natural rubber and polyisoprenes comprising a mass content of cis 1,4 bonds of at least 90%, more preferably of at least 98% relative to the mass of isoprene elastomer and mixtures thereof.

Preferably, the invention relates to a composite in which the elastomeric composition comprises from 1 to 4 phr of sulphur.

Preferably, the invention relates to a composite in which the sulfur/vulcanization accelerator mass ratio is less than or equal to 4.

Preferably, the invention relates to a composite in which the mass ratio of metal oxide to stearic acid derivative in the elastomeric composition is less than 3.

Preferably, the invention relates to a composite in which the metal oxide of the crosslinking system is zinc oxide.

Preferably, the invention relates to a composite in which the elastomeric composition does not comprise cobalt salts or comprises less than 1 phr, preferably less than 0.5 phr.

Preferably, in a preferred arrangement, the invention relates to a composite in which the reinforcing filler of the elastomeric composition mainly comprises carbon black.

Preferably, in another preferred arrangement, the invention relates to a composite in which the reinforcing filler of the elastomeric composition mainly comprises silica.

Preferably, in this preferred arrangement, the invention relates to a composite in which the elastomeric composition comprises a silica coupling agent, the coupling agent content being in a range ranging from 5 to 18% by weight relative to the amount of silica, preferably in a range ranging from 8 to 12% by weight relative to the quantity of silica.

Preferably, the invention relates to a composite in which the elastomeric composition does not comprise any reinforcing, tackifying or adhesion-promoting resin, or comprises less than 2 phr in total, preferably less than 1 phr.

The invention also relates to a finished or semi-finished article comprising a composite according to the invention.

The invention also relates to a pneumatic tire comprising a composite according to the invention.

Definitions

The compounds comprising carbon mentioned in the description can be of fossil origin or biobased. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This concerns in particular polymers, plasticizers, fillers, etc.

Composite

The invention relates to a composite comprising at least one reinforcing element having a surface comprising an alloy of copper, zinc, and from 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum, said reinforcing element being embedded in an elastomeric composition.

By the expression composite "comprising at least one reinforcing element, said reinforcement being embedded in an elastomeric composition", is meant 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 manufacture of the composite, in particular during the crosslinking of the composition or during the manufacture of the composite before crosslinking of the composition, said reinforcing element being completely covered with said composition.

Said reinforcing element is a wired element. It can be all or part metal. By wire element is meant 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.

Said reinforcement element comprises a metallic surface.

The metallic surface of the reinforcing element constitutes at least a part, and preferably the whole of the surface of said element and is intended to come into direct contact with the elastomeric composition. Preferably, the reinforcing element is metallic, that is to say made of a metallic material. Preferably, the reinforcing element is a steel reinforcing element coated with a metallic surface as defined herein.

The steel of the steel reinforcing element is preferably a carbon steel or a stainless steel. When the steel is a carbon steel, its carbon content, expressed in % by weight, is preferably between 0.01% and 1.2% or between 0.05% and 1.2%, or even 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% by weight of chromium and at least 50% by weight of iron.

The reinforcing element has a mechanical resistance ranging from 1000 MPa to 5000 MPa. Such mechanical strengths correspond to the steel grades commonly encountered in the field of tires, namely, NT (Normal Tensile), HT (High Tensile), ST (Super Tensile), SHT (Super High Tensile), UT ( Ultra Tensile), UHT (Ultra High Tensile) and MT (Mega Tensile), the use of high mechanical strength possibly allowing improved reinforcement of the elastomeric composition in which the reinforcing element is embedded, and a lightening of the elastomeric composition thus strengthened.

The elastomeric composition coats the entire reinforcement element, with the possible exception of the cutting planes of the composite.

The metallic surface of the reinforcing element comprises an alloy of copper, zinc, and 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum.

Preferably, the metal surface of the reinforcing element comprises an alloy of copper, zinc, and 2 to 8% by weight of at least one metal chosen from cobalt and nickel, preferably cobalt.

Preferably, the metallic surface of the reinforcing element comprises 55 to 75% by weight of copper.

Some metals being subject to oxidation in contact with ambient air, the metal may be partly oxidized.

According to a preferred embodiment, the composite is a reinforced product which comprises several reinforcing elements as defined above and an elastomeric calendering composition in which the reinforcing elements are embedded, the elastomeric calendering composition consisting of the elastomeric 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 reinforcement reinforcement for a tire.

The composite in accordance with the invention may be in the raw state (before crosslinking of the elastomeric composition) or in the cured state (after crosslinking of the elastomeric composition). The composite is cured after bringing the reinforcing element(s) into contact with the elastomeric composition described herein.

The composite can be made by a process that includes the following steps:

• Make two layers of the elastomeric composition of the composite according to the invention,
• Take the reinforcement element(s) sandwiched in the two layers by placing it (them) between the two layers,
• If necessary, fire the composite.

Alternatively, the composite can be manufactured 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 over its entire length or a part of its length.

The production of the layers can be done by calendering. During the curing of the composite, the elastomeric composition is crosslinked.

When the composite is intended for use as reinforcement in a tire, the curing of the composite generally takes place during the curing of the tire.

Diene elastomers

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

These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” generally means a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or units of diene origin (conjugated dienes) which is greater than 15% (% in moles); thus diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the above definition and may in particular be qualified as "essentially saturated" diene elastomers (rate of units of weak or very weak diene origin, always less than 15% (% in moles)). The diene elastomers included in the composition according to the invention are preferably essentially unsaturated.

By diene elastomer capable of being used in the compositions in accordance with the invention is meant in particular:

1. any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms;
2. any copolymer of a diene, conjugated or not, having 4 to 18 carbon atoms and at least one other monomer.

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

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

Suitable olefins are vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms.

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

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

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

The above diene elastomers can, for example, be block, random, sequenced, microsequenced, and be prepared in dispersion or in solution; they can be coupled and/or starred or further functionalized with a coupling and/or starring or functionalizing agent, for example epoxidized.

Preferably, the elastomeric 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. In a very preferred mode, the elastomeric composition of the composite according to the invention comprises 100 phr of at least one isoprene elastomer.

By "isoprene elastomer" is meant an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from the group consisting of natural rubber (NR) which can be plasticized or peptized, synthetic polyisoprenes (IR ), the various isoprene copolymers, in particular isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene (SBIR) copolymers, and mixtures of these elastomers.

Preferably, the isoprene elastomer is chosen from the group consisting of synthetic polyisoprenes, natural rubber, isoprene copolymers and mixtures thereof, preferably from the group consisting of natural rubber, polyisoprenes comprising a mass rate of cis 1,4 bonds of at least 90%, more preferentially of at least 98% with respect to the mass of isoprene elastomer and mixtures thereof. Very preferably, the isoprene elastomer is natural rubber.

Reinforcing charge

The elastomeric composition of the composite according to the invention comprises a reinforcing filler. It is possible to use any type of reinforcing filler known for its ability to reinforce an elastomeric composition that can be used for the manufacture of pneumatic tires, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica, or else a blending of these two types of filler, in particular a blending of carbon black and silica.

Suitable carbon blacks are all carbon blacks, in particular blacks of the HAF, ISAF, SAF type conventionally used in tires (so-called tire-grade blacks). Among the latter, mention will be made more particularly of the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as for example the blacks N115, N134, N234, N326, N330, N339, N347, N375, or again, according to intended applications, higher series blacks (e.g. 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 of carbon blacks is measured according to standard D6556-10 [multipoint method (at least 5 points) – gas: nitrogen – relative pressure range P/P0: 0.1 to 0.3].

By "reinforcing inorganic filler", must be understood in the present application, by definition, any inorganic or mineral filler (regardless of its color and its natural or synthetic origin), also called "white" filler, "clear" filler or even "non-black filler" as opposed to carbon black, capable of reinforcing on its own, with no 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) at its surface.

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 can be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface area as well as a CTAB specific surface area, both of which are less than 450 m ² /g, preferably from 30 to 400 m ² /g. As highly dispersible precipitated silicas (known as "HDS"), mention will be made, for example, of the "Ultrasil 7000" and "Ultrasil 7005" silicas from Degussa, the "Zeosil 1165MP", "1135MP" and "1115MP" silicas from the company Rhodia, the silica "Hi-Sil EZ150G" from the company PPG, the silicas "Zeopol 8715", "8745" and "8755" from the Company Huber, silicas with a high specific surface as described in application WO 03/ 16837.

The physical state in which the reinforcing inorganic filler is present is irrelevant, whether in the form of powder, microbeads, granules, beads or any other appropriate densified form. Of course, the term “reinforcing inorganic filler” also means mixtures of various reinforcing inorganic fillers, in particular of highly dispersible siliceous and/or aluminous fillers.

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.

Preferably, the elastomeric 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 vehicle tire tourism or utility vehicle such as heavy goods vehicle. In a preferred arrangement, the reinforcing filler mainly comprises carbon black, and preferably consists of carbon black.

Preferably, the elastomeric 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 mainly comprises silica and preferably consists of silica.

To couple the reinforcing inorganic filler to the elastomer, it is optionally possible to use, in known manner, an at least bifunctional coupling agent (or bonding agent) intended to ensure a sufficient connection, of a chemical and/or physical nature, between the inorganic filler (surface of its particles) and the elastomer, in particular organosilanes, or bifunctional polyorganosiloxanes.

It is possible in particular to use polysulphide silanes, called "symmetrical" or "asymmetrical" according to their particular structure, as described for example in applications WO03/002648 (or US 2005/016651) and WO03/002649 (or US 2005/016650) .

As examples of polysulphide silanes, mention will be made more particularly of the polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis-(alkoxyl(C1-C4)-alkyl(C1-C4)silyl-alkyl(C1-C4)), such as, for example, bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl) polysulphides. Among these compounds, use is made in particular of bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, of formula [(C2H5O)3Si(CH2)3S2]2 or bis-(triethoxysilylpropyl) disulfide, abbreviated TESPD, of formula [(C2H5O)3Si(CH2)3S]2. Mention will also be made, by way of preferred examples, of the polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis-(monoalkoxyl(C1-C4)-dialkyl(C1-C4)silylpropyl), more particularly bis-monoethoxydimethylsilylpropyl tetrasulphide as described in US patent application 2004/132880.

As coupling agent other than polysulphurized alkoxysilane, mention will be made in particular of bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulphides as described in patent applications WO 02/30939 and WO 02/31041, or even silanes or POS bearing azo-dicarbonyl functional groups, as described for example in patent applications WO 2006/125532, WO 2006/125533, WO 2006/125534.

In the elastomeric compositions in accordance with the invention, the content of coupling agent is preferably in a range ranging from 5 to 18% by weight relative to the amount of silica, preferably in a range ranging from 8 to 12% by weight per relative to the amount of silica.

Those skilled in the art will understand that, as an equivalent filler of 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 a inorganic layer such as silica, or would comprise functional sites, in particular hydroxyls, on its surface, making it possible to establish the bond between the filler and the elastomer in the presence or absence of a covering or coupling agent.

Cross-linking system

The elastomeric composition of the composite according to the invention comprises a sulfur-based crosslinking system comprising a metal oxide, a derivative of stearic acid and a vulcanization accelerator. We then speak of a vulcanization system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or of a sulfur-donating agent.

The sulfur is used at a rate of between 1 and 5 phr, in particular ranging from 1 to 4 phr. This rate, although low compared to the usual calendering compositions, is sufficient in the context of the invention to ensure both good crosslinking of the elastomeric composition and sufficient and lasting adhesion to the metal reinforcing element.

The vulcanization accelerator is used at a preferential rate such that the sulfur/vulcanization accelerator mass ratio is less than or equal to 4.

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 as well as their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type. As examples of such accelerators, mention may be made in particular of the following compounds: 2-mercaptobenzothiazyl disulphide (abbreviated as "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.

The metal oxide to stearic acid derivative mass ratio in the crosslinking system is less than 4, and preferably less than 3. The metal oxide is preferably zinc oxide.

The crosslinking system may also optionally include a vulcanization retarder.

Miscellaneous additives

The elastomeric 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.

Preferably, the elastomeric composition of the composite according to the invention does not comprise any reinforcing, tackifying or adhesion-promoting resin, or comprises in total less than 2 phr, preferably less than 1 phr and very preferably less than 0.2 pc. Indeed, the use of such resins is not necessary to obtain and maintain the good performance of the composite according to the invention, in particular the adhesion performance.

By reinforcing resin is meant a resin known to those skilled in the art for stiffening elastomeric compositions, stiffness measured for example by the Young's Modulus, according to the ASTM 412-98a standard, or the complex dynamic shear modulus G* according to the standard ASTM D 5992-96. By adhesion-promoting resin, is meant a resin known to those skilled in the art for improving adhesion on a reinforcing element, for example a resin of the formophenolic type or based on resorcinol, generally used at low rate, typically up to to 2 phr, this resin also being able to exhibit reinforcing properties when it is used at higher rates.

Preferably, the elastomeric composition of the composite according to the invention does not comprise any cobalt salts or comprises less than 1 phr, preferably less than 0.5 phr.

Thus, the specific characteristics of the elastomeric composition and of the metal surface of the composite according to the invention make it possible to achieve and maintain excellent performance, in particular in terms of adhesion, hysteretic losses and resistance to cracking.

Finished or semi-finished and pneumatic article

The invention also relates to a finished or semi-finished article comprising a composite according to the invention. The finished or semi-finished article can be any article comprising a composite. Mention may be made, for example and in a non-limiting manner, of conveyor belts, pneumatic or non-pneumatic tires.

The pneumatic tire, another object of the invention, has the essential characteristic of comprising the composite in accordance with the invention. The tire may be in the uncured state (before crosslinking of the elastomeric composition) or in the cured state (after crosslinking of the elastomeric composition). Generally, during the manufacture of the tire, the composite is deposited in the green state (that is to say before crosslinking of the elastomeric composition) in the structure of the tire before the step of curing the tire .

The invention relates particularly to pneumatic tires intended to be fitted to motor vehicles of the tourist type, SUV ("Sport Utility Vehicles"), or two wheels (in particular motorcycles), or airplanes, or even industrial vehicles chosen from vans, "Weight -heavy”, that is to say metro, bus, road transport vehicles (trucks, tractors, trailers), off-road vehicles such as agricultural or civil engineering machinery, and others.

Examples

Preparation of specimens

The following tests are carried out as follows: the elastomer diene, the reinforcing filler as well as the various other ingredients with the exception of the vulcanization system. Thermomechanical work is then carried out (non-productive phase) in one step, which lasts a total of about 3 to 4 min, until a maximum “falling” temperature of 165°C is reached.

The mixture thus obtained is recovered, cooled and then sulfur and an accelerator (sulfenamide) are incorporated on a mixer (homo-finisher) at 30°C, mixing the whole (productive phase) for an appropriate time (for example between 5 and 12 minutes).

The compositions thus obtained are then calendered in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber then are either subjected to a curing step at 150° C. for 15 min before measuring their physical properties or mechanical or used to make the measuring specimens for the adhesion tests, as described below.

Measurement methods

Membership test

The elastomeric compositions thus prepared are used to make a composite in the form of a test piece according to the protocol detailed below.

The metal/rubber composite used in this test is a block of elastomeric composition, consisting of two plates measuring 200 mm by 4.5 mm (millimeters) and 3.5 mm thick, applied one on the other before the cooking ; the thickness of the resulting block is then 7 mm. It is during the making of this block that the reinforcements, for example fifteen in number, are trapped between the two raw plates; only a determined length of reinforcement, for example 4.5 mm, is left free to come into contact with the elastomeric composition to which this length of reinforcement will bond during curing; the rest of the length of the reinforcements is isolated from the elastomeric composition (for example using a plastic or metal film) to prevent any adhesion outside the determined contact zone. Each reinforcement passes right through the block of rubber, at least one of its free ends being kept of sufficient length (at least 5 cm, for example between 5 and 10 cm) to allow the subsequent traction of the reinforcement.

Each metal reinforcement is made up of 2 steel wires with 0.7% carbon, 30/100th millimeters in diameter, twisted together. Two coatings are evaluated, namely a so-called “brass” coating comprising 63% copper and the remainder zinc, and a so-called “ternary” coating comprising 67% copper, 4% cobalt and the remainder zinc.

The block comprising the fifteen reinforcements is then placed in a suitable mold and then baked for 15 minutes at 150° C., under a pressure of approximately 15 bar.

After curing the block, the following accelerated aging conditions are applied, making it possible to determine the resistance of the samples to the combined action of heat and humidity: the rubber blocks are placed in an oven at a temperature of 55 °C, for 14 days and at a relative humidity of 95%.

Pull-out force measurement

At the end of the cooking and aging described above, the block is cut into test specimens serving as samples, each containing a reinforcement which is pulled out of the rubber block, using a traction according to the method described in standard ASTM D 2229-02; the pulling speed is 100 mm/min; adhesion is thus characterized by the force necessary to pull the reinforcement out of the specimen, at ambient temperature; the tearing force represents the average of the 15 measurements corresponding to the 15 reinforcements of the composite.

The higher the value of the force, the greater the adhesion between the cable and the elastomeric composition. The results are expressed in base 100 relative to the unaged control specimen of composition C01 for mixtures comprising only carbon black as reinforcing filler, and of composition C06 for mixtures comprising silica. A higher value than that of the unaged control specimen, arbitrarily set at 100, indicates an improved result, i.e. a higher pull-out force than that of the unaged control specimen.

Assessment of hysteretic losses

The rolling resistance induced by the composition tested is estimated by measuring the energy losses, at a temperature of 60° C., of the energy restored on the sixth rebound of a sample to which an initial energy has been imposed, such as described in the DIN 53-512 standard of April 2000. This measurement is calculated as follows: P60(%)=100x(E0-E1)/E0, where E0 represents the initial energy and E1 the restored energy. The specimens are tested after firing and after accelerated aging at 77°C for 14 days and 21 days in a ventilated enclosure.

The results are expressed in base 100 relative to the unaged control specimen of composition C01 for mixtures comprising only carbon black as reinforcing filler, and of composition C06 for mixtures comprising silica. A value higher than that of the unaged control specimen, arbitrarily set at 100, indicates a degraded result, i.e. a hysteretic loss (value of P60) greater than that of the unaged control specimen.

Crack propagation resistance test

The cracking rate was measured on specimens of elastomeric compositions C01 to C10, using a cyclic fatigue machine (“Elastomer Test System”) of type 381, from the company MTS, as explained below.

The resistance to cracking is measured using repeated tractions on a specimen initially accommodated (after a first cycle of traction), then notched. The tensile specimen consists of a rubber plate of parallelepipedic shape, for example of thickness between 0.5 and 1.5 mm, length between 60 and 100 mm and width between 4 and 8 mm, both the side edges each being covered lengthwise with a cylindrical rubber bead (diameter 5 mm) allowing anchoring in the jaws of the traction machine. The specimens thus prepared are tested after firing and after accelerated aging at 77°C for 14 days and 21 days in a ventilated enclosure. The test was carried out in air, at a temperature of 60°C. After accommodation, 4 very fine notches of length between 5 and 7 mm are made using a razor blade, at mid-width and aligned in the direction of the length of the specimen, one at each end and two located on either side of the center of the specimen, before the start of the test. At each tensile cycle, the rate of deformation of the specimen is automatically adjusted so as to maintain constant the rate of energy release (quantity of energy released as the crack progresses), at a value equal to approximately 1000 J/m2. The crack propagation rate is measured in nanometers per cycle.

The results are expressed in base 100 relative to the unaged control specimen of composition C01 for mixtures comprising only carbon black as reinforcing filler, and of composition C06 for mixtures comprising silica. A value greater than that of the unaged specimen, arbitrarily set at 100, indicates a degraded result, i.e. a crack propagation rate greater than that of the unaged control specimen. When the specimen breaks, the mention “nm” for “unmeasurable” is indicated. This mention testifies to a test specimen presenting a low resistance to the propagation of cracks.

Results

The tables below show the results of measurements carried out on mixtures C01 to C10. C01 to C05 blends only include carbon black as reinforcing filler. Blends C06 to C09 include only silica as reinforcing filler and blend C10 includes a blend of carbon black and silica.

These examples show that the mixtures in accordance with the invention have an excellent compromise of adhesion performance/hysteretic properties/resistance to the propagation of cracks and improved adhesion when the support is in accordance with the invention.

nm=not measurable

nm=not measurable

Claims (15)

Composite comprising at least one reinforcing element having a surface comprising an alloy of copper, zinc, and 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum, said reinforcing element being embedded in an elastomeric composition based on at least one diene elastomer, a reinforcing filler and a sulfur crosslinking system, comprising a metal oxide, a derivative of stearic acid and a vulcanization accelerator, the sulfur content being between 1 and 5 phr, and the mass ratio of metal oxide to stearic acid derivative being less than 4. Composite according to Claim 1, in which the surface of the reinforcing element comprises an alloy of copper, zinc, and from 1 to 10% by weight of at least one metal chosen from cobalt, nickel, tin, manganese , iron and molybdenum, preferably chosen from cobalt and nickel. Composite according to Claim 2, in which the surface of the reinforcing element comprises an alloy of copper, zinc, and 2 to 8% by weight of at least one metal chosen from cobalt and nickel, preferably cobalt. A composite according to any preceding claim wherein the surface of the reinforcing element comprises 55 to 75 wt% copper. Composite according to any one of the preceding claims, in which the elastomeric composition comprises at least 50 phr, preferably at least 70 phr, more preferably at least 90 phr of at least one isoprene elastomer. Composite according to the preceding claim, in which the elastomeric composition comprises 100 phr of at least one isoprene elastomer. Composite according to any one of the preceding claims, in which the elastomeric composition comprises from 1 to 4 phr of sulphur. Composite according to any one of the preceding claims, in which the sulfur/vulcanization accelerator mass ratio is less than or equal to 4. Composite according to any one of the preceding claims, in which the mass ratio of metal oxide to stearic acid derivative in the elastomeric composition is less than 3. Composite according to any one of the preceding claims, in which the elastomeric composition does not comprise cobalt salts or comprises less than 1 phr thereof, preferably less than 0.5 phr. Composite according to any one of the preceding claims, in which the reinforcing filler of the elastomeric composition mainly comprises carbon black. Composite according to any one of Claims 1 to 10, in which the reinforcing filler of the elastomeric composition mainly comprises silica. Composite according to any one of the preceding claims, in which the elastomeric composition does not comprise any reinforcing, tackifying or adhesion-promoting resin, or comprises less than 2 phr in total, preferably less than 1 phr. Finished or semi-finished article comprising a composite according to any one of the preceding claims. A pneumatic tire comprising a composite according to any one of claims 1 to 13.