FR3124512A1 - RUBBER COMPOSITION - Google Patents

Abstract

The present invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system, and a phenolic antioxidant of general formula [Chem 1] below, in which the radical R1 represents a hydrogen atom, an alkyl group comprising from 1 to 18 carbon atoms, or an alkoxy group comprising from 1 to 18 carbon atoms, and the radicals R2 to R7 each represent, independently of each other, a hydrogen atom or a hydrocarbon group comprising from 1 to 18 carbon atoms.

Description

RUBBER COMPOSITION

The field of the present invention is that of rubber compositions, the rubber compositions being particularly intended for use in rubber articles such as, for example, tires.

Rubber articles are sensitive to oxidation, especially during their aging and require protection systems against this oxidation. Certain antioxidants exist and are used by those skilled in the art.

Nevertheless, it is interesting today to look for antioxidants that can be of natural origin in order to limit the compounds of fossil origin in rubber articles, and in particular in tires.

Eugenol and its possible derivatives are known to be easily obtained from plants such as cloves. Eugenol is mainly used today in cosmetic and dental care applications.

Continuing its research, the Applicant has discovered that the use of eugenol or a derivative of eugenol in a rubber composition comprising a diene elastomer, a reinforcing filler and a crosslinking system, makes it possible to protect this composition against oxidation and thus to improve the properties of this composition after ageing.

Thus, a first object of the invention is a rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system and a phenolic antioxidant of general formula [Chem 1] below, in which the radical R1 represents a hydrogen atom, an alkyl group comprising from 1 to 18 carbon atoms, or an alkoxy group comprising from 1 to 18 carbon atoms, and the radicals R2 to R7 each represent, independently of each other, an atom hydrogen or a hydrocarbon group comprising from 1 to 18 carbon atoms.

Another object of the invention is a pneumatic or non-pneumatic tire comprising a composition according to the invention.

I- DEFINITIONS

The expression "composition based on" means a composition comprising the mixture and/or the in situ reaction product of the various constituents used, some of these constituents being able to react and/or being intended to react with one another, less partially, during the various phases of manufacture of the composition; the composition thus possibly being in the totally or partially crosslinked state or in the non-crosslinked state.

By the expression "part by weight per hundred parts by weight of elastomer" (or phr), is meant within the meaning of the present invention, the part, by mass per hundred parts by mass of elastomer.

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

On the other hand, any interval of values denoted by the expression "between a and b" represents the domain of values going from more than a to less than b (i.e. limits a and b excluded) while any interval of values denoted by the expression “from a to b” signifies the range of values going from a to b (that is to say including the strict limits a and b). In this document, when an interval of values is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

When reference is made to a "majority" compound, it is meant within the meaning of the present invention that this compound is in the majority among the compounds of the same type in the composition, that is to say that it is the one which represents the greatest amount by mass among compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. In the same way, a so-called majority filler is the one representing the greatest mass among the fillers of the composition. By way of example, in a system comprising a single elastomer, the latter is predominant within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers. On the contrary, a "minority" compound is a compound which does not represent the largest mass fraction among compounds of the same type. Preferably, by majority is meant present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

The compounds mentioned in the description can be of fossil origin or biosourced. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned can also come from the recycling of materials already used, that is to say they can be, partially or totally, from a recycling process, or obtained from materials raw materials themselves from a recycling process. This concerns in particular polymers, plasticizers, fillers, etc.

Unless otherwise indicated, the glass transition temperature “Tg” values described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to standard ASTM D3418 (1999).

II- DESCRIPTION OF THE INVENTION

II-1 Elastomeric matrix

By "diene" elastomer (or indistinctly rubber), whether natural or synthetic, must be understood in a known manner an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not).

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

(a) - any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms;

(b) - 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 15 carbon atoms, in particular 1,3-dienes, such as in particular 1,3-butadiene and isoprene.

Suitable non-conjugated dienes are non-conjugated dienes having 6 to 12 carbon atoms, such as 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene.

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

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

As aliphatic α-monoolefins suitable are in particular acyclic aliphatic α-monoolefins having from 3 to 18 carbon atoms.

More particularly, the diene elastomer is:

(a’) - any homopolymer of a conjugated diene monomer, in particular any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b’) - any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more vinylaromatic compounds having from 8 to 20 carbon atoms;

(c’) - a copolymer of isobutene and isoprene (butyl rubber), as well as halogenated, in particular chlorinated or brominated, versions of this type of copolymer.

(d') - any copolymer obtained by copolymerization of one or more dienes, conjugated or not, with ethylene, an α-monoolefin or their mixture such as for example the elastomers obtained from ethylene, propylene with a monomer unconjugated diene of the aforementioned type.

Preferably, the diene elastomer is chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. Butadiene copolymers are particularly chosen from the group consisting of butadiene-styrene (SBR) copolymers.

The diene elastomer can be modified, that is to say either coupled and/or star-shaped, or functionalized, or coupled and/or star-shaped and simultaneously functionalized.

Thus, the diene elastomer can be coupled and/or starred, for example by means of a silicon or tin atom which binds the elastomer chains together.

The diene elastomer can be simultaneously or alternatively functionalized and comprise at least one functional group. By functional group is meant a group comprising at least one heteroatom chosen 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 amine , secondary or tertiary, cyclic or not, a thiol, an epoxide.

The rubber composition of the invention may contain a single diene elastomer or a mixture of several diene elastomers.

II-2 Specific antioxidant

According to the invention, the rubber composition is based on at least one phenolic antioxidant of general formula [Chem 1] below,

in which :

- the radical R1 represents a hydrogen atom, an alkyl group comprising from 1 to 18 carbon atoms, or an alkoxy group comprising from 1 to 18 carbon atoms,

- the radicals R2 to R7 each independently represent a hydrogen atom or a hydrocarbon group comprising from 1 to 18 carbon atoms.

Preferably, the R1 group is a hydrogen atom, a methyl, ethyl, isopropyl, tert-butyl or methoxy group.

Also preferably, the radicals R2 to R7 each independently represent a hydrogen atom, an alkyl group comprising from 1 to 18 carbon atoms, or an aryl group comprising from 6 to 18 carbon atoms. More preferably, the radicals R2 to R7 each independently represent a hydrogen atom, a methyl, ethyl, isopropyl or tert-butyl group.

Very preferably, the phenolic antioxidant of general formula [Chem 1] is eugenol of formula [Chem 2] below.

Eugenol and its derivatives of general formula [Chem 1] above, have the advantage of being able to be biosourced since eugenol can be easily extracted from plants and in particular from cloves, and its derivatives can be obtained by simple chemical modifications within the reach of any chemist.

Preferably for the purposes of the invention, the phenolic antioxidant of general formula [Chem 1] is present in the composition at a rate comprised in a range ranging from 0.2 to 10 phr, preferably from 0.5 to 8 phr and more preferably from 0.8 to 5 phr.

II-3 Reinforcing filler

The rubber composition in accordance with the invention has the other essential characteristic of comprising a reinforcing filler.

It is possible to use any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition that can be used in particular for the manufacture of tires, for example an organic filler such as carbon black, an inorganic filler such as silica or else a mixture of these two types of fillers.

Suitable carbon blacks are all carbon blacks, in particular the blacks conventionally used in tires or their treads. Among the latter, mention will be made more particularly of 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 for example the blacks N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used. The 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 WO97/036724-A2 or WO99/016600-A1).

As an example of organic fillers other than carbon blacks, mention may be made of functionalized polyvinyl organic fillers as described in applications WO2006/069792-A1, WO2006/069793-A1, WO2008/003434-A1 and WO2008/003435-A1 .

By “reinforcing inorganic filler”, should be understood here any inorganic or mineral filler, whatever its color and its origin (natural or synthetic), 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 tires. In a known manner, certain reinforcing inorganic fillers can be characterized in particular by the presence of hydroxyl (OH) groups at their surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferably 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 specific surface area as well as a CTAB specific surface area, both of which are less than 450 m ² /g, preferably comprised in a range ranging from 30 to 400 m ² /g, in particular from 60 to 300 m ² /g.

It is possible to use any type of precipitated silica, in particular highly dispersible precipitated silicas (called “HDS” for “highly dispersible” or “highly dispersible silica”). These precipitated silicas, highly dispersible or not, are well known to those skilled in the art. Mention may be made, for example, of the silicas described in applications WO03/016215-A1 and WO03/016387-A1. Among the commercial HDS silicas, it is possible in particular to use the "Ultrasil ® 5000GR", "Ultrasil ® 7000GR" silicas from the company Evonik, the "Zeosil ® 1085GR", "Zeosil® 1115 MP", "Zeosil® 1165MP", " Zeosil® Premium 200MP”, “Zeosil® HRS 1200 MP” from Solvay. As non-HDS silica, the following commercial silicas can be used: "Ultrasil ® VN2GR" and "Ultrasil ® VN3GR" silicas from Evonik, "Zeosil® 175GR" silica 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.

As other examples of inorganic fillers capable of being used in the rubber compositions of the invention, mention may also be made of mineral fillers of the alumina type, in particular alumina (Al ₂ O ₃ ), oxides of aluminium, aluminum hydroxides, aluminosilicates, titanium oxides, silicon carbides or nitrides, all of the reinforcing type as described for example in applications WO99/28376-A2, WO00/73372-A1, WO02/ 053634-A1, WO2004/003067-A1, WO2004/056915-A2, US6610261-B1 and US6747087-B2. Mention may in particular be made of the aluminas “Baikalox A125” or “CR125” (Baïkowski company), “APA-100RDX” (Condéa), “Aluminoxid C” (Evonik) or “AKP-G015” (Sumitomo Chemicals).

The physical state in which the reinforcing inorganic filler is present is irrelevant, whether it be in the form of powder, microbeads, granules, or else beads or any other appropriate densified form. Of course, the term “reinforcing inorganic filler” also means mixtures of different reinforcing inorganic fillers, in particular of silicas as described above.

Those skilled in the art will understand that replacing the reinforcing inorganic filler described above, a reinforcing filler of another nature could be used, since this reinforcing filler of another nature would be covered with an inorganic layer. such as silica, or else would comprise functional sites, in particular hydroxyl sites, on its surface, requiring the use of a coupling agent to establish the bond between this reinforcing filler and the diene elastomer. By way of example, mention may be made of carbon blacks partially or completely covered with silica, or carbon blacks modified with silica, such as, without limitation, fillers of the "Ecoblack®" type of the series “CRX2000” or “CRX4000” series from Cabot Corporation.

Preferably for the invention, the reinforcing filler is chosen from the group consisting of carbon blacks, silicas and mixtures thereof.

A person skilled in the art will know how to adapt the total reinforcing filler content according to the use concerned, in particular, for example, according to the type of tire concerned, for example a tire for a motorcycle, for a passenger vehicle or even for a utility vehicle such as a van or heavy. Preferably, this content of total reinforcing filler is within a range ranging from 10 to 200 phr, more preferably from 30 to 180 phr, and even more preferably from 40 to 160 phr; the optimum being in a known manner different according to the particular applications targeted.

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

For inorganic fillers such as silica for example, the CTAB specific surface values were determined according to standard NF ISO 5794-1, appendix G of June 2010. The process is based on the adsorption of CTAB (N-bromide hexadecyl-N,N,N-trimethylammonium) on the "external" surface of the reinforcing filler.

To couple the reinforcing inorganic filler to the diene elastomer, it is possible to use, in a well-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 filler inorganic (surface of its particles) and diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. By "bifunctional" is meant 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 comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the diene elastomer.

Preferably, the organosilanes are chosen from the group consisting of polysulphide organosilanes (symmetrical or asymmetrical) such as tetrasulphide of
bis(3-triethoxysilylpropyl), abbreviated TESPT marketed under the name “Si69” by the company Evonik or bis-(triethoxysilylpropyl) disulphide, abbreviated TESPD marketed under the name “Si75” by the company Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl) octanethioate marketed by the company Momentive under the name “NXT Silane”. More preferably, the organosilane is a polysulphide organosilane.

Of course, mixtures of the coupling agents described above could also be used.

The content of coupling agent in the composition of the invention is advantageously less than or equal to 30 phr, it being understood that it is generally desirable to use as little as possible. Typically the rate of coupling agent represents from 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler. Its content is preferably within a range ranging from 0.5 to 20 phr, more preferably within a range ranging from 3 to 3 phr. This rate is easily adjusted by those skilled in the art according to the rate of reinforcing inorganic filler used in the composition of the invention.

II-4 Cross-linking system

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

Preferably, the crosslinking system is sulfur-based, in which case we 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. At least one vulcanization accelerator is also preferentially present, and, optionally, also preferentially, various known vulcanization activators such as zinc oxide, stearic acid or equivalent compound such as stearic acid salts and salts can be used. of transition metals, guanidine derivatives (in particular diphenylguanidine), or alternatively known vulcanization retarders.

The sulfur is used at a preferential rate of between 0.2 phr and 10 phr, more preferentially between 0.3 and 7 phr. The primary vulcanization accelerator is used at a preferential rate comprised between 0.5 and 10 phr, more preferentially comprised between 0.5 and 5 phr.

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.

II-5 Possible additives

The rubber compositions according to the invention may also optionally comprise all or part of the usual additives usually used in elastomer compositions for tires, such as, for example, pigments, protective agents such as anti-ozone waxes, anti-ozonants chemicals, antioxidants other than the phenolic antioxidant of general formula [Chem 1], anti-fatigue agents, or even reinforcing resins (as described for example in application WO 02/010269).

II-6 Preparation of rubber compositions

The compositions in accordance with the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

- a first work phase or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which, in a suitable mixer such as a usual internal mixer (for example 'Banbury' type), all the necessary constituents, in particular the elastomeric matrix, the reinforcing filler, any other miscellaneous additives, with the exception of the crosslinking system. The incorporation of the possible filler into the elastomer can be carried out in one or more stages by mixing thermomechanically. In the case where the filler is already incorporated in whole or in part into the elastomer in the form of a masterbatch (“masterbatch” in English) as described for example in applications WO 97/036724 or WO 99 /016600, it is the masterbatch which is mixed directly and, if necessary, the other elastomers or fillers present in the composition which are not in the form of the masterbatch, as well as any other various additives other than the cross-linking system. The non-productive phase can be carried out at high temperature, up to a maximum temperature of between 110° C. and 200° C., preferably between 130° C. and 185° C., for a duration generally of between 2 and 10 minutes.

- a second phase of mechanical work (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 between 40° C. and 100° C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min.

Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00/005300 or WO00/005301.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for characterization in the laboratory, or else extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber that can be used, for example, as a tire sidewall. These products can then be used for the manufacture of tires, according to the techniques known to those skilled in the art.

The composition can be either in the raw state (before crosslinking or vulcanization), or in the cured state (after crosslinking or vulcanization), can be a semi-finished product which can be used in a tire.

The crosslinking (or curing), where appropriate the vulcanization, is carried out in a known manner at a temperature generally between 130° C. and 200° C., for a sufficient time which can vary for example between 5 and 90 min depending in particular on the curing temperature, the crosslinking system adopted and the crosslinking kinetics of the composition considered.

II-7 Rubber articles

The present invention also relates to a rubber article comprising a rubber composition according to the invention.

Indeed, the interest presented by the properties of the rubber composition according to the invention makes it possible to envisage a use in the numerous fields involving rubber articles. Mention may in particular be made of a use in various articles preferably chosen from pipes, belts, conveyor belts, caterpillars, pneumatic objects (and in particular tires), shoe soles, or even surgical gloves.

Preferably, the invention relates to a tire comprising a composition according to the invention. The tire according to the invention can be intended to equip motor vehicles of the passenger car type, SUV ("Sport Utility Vehicles"), or two wheels (in particular motorcycles), or airplanes, or even industrial vehicles chosen from vans, "Weight -heavy” − i.e. subways, buses, road transport vehicles (trucks, tractors, trailers), off-road vehicles such as agricultural or civil engineering machinery −, and others.

III- EXAMPLES

III-1 Example 1

In a first example illustrating the advantage of the invention, the polymer alone is considered, to be protected against thermo-oxidation. T0 corresponds to the case where the polymer is completely devoid of antioxidant system. T1 is a control in which the polymer is protected by a known phenolic antioxidant: “Irganox 1520 L” marketed by BASF. Composition C1 illustrates the present invention and contains the polymer, protected against oxidation by eugenol, in an isomolar amount of 3.2 phr of “Irganox 1520 L”.

Resistance to oxidation, “OIT”

In order to compare the antioxidant activity of the invention in this particular case, the OIT method ("Oxidation Induction Time") which describes the oxidation delay measured by DSC caused by the presence of an anti- oxidizing at high temperature (170°C) when a gas stream in contact with the composition is changed from helium to pure oxygen. The result is expressed in minutes.

The details of the procedure followed for this determination are summarized in Table 1 below:

Table 2 presents the compositions tested (in phr), the results obtained.

(1) Natural Rubber

(2) “Irganox 1520 L” sold by BASF, MW=424.8 g/mol,

(3) 95% Eugenol from Sigma Aldrich, M _W = 164.2 g/mol

The results show that eugenol significantly improves OIT from 18 to 30 min.

III-2 Example 2

The purpose of Example 2 is to measure the aging resistance performance of the invention subjected to a thermo-oxidative treatment by comparing a composition in accordance with the invention (C2), respectively with two control compositions (T2 and T3).

The rubber compositions were produced as described in point II.6 above, using an internal mixer (non-productive phase) where most of the ingredients are incorporated. The so-called productive phase is carried out on an external tool and concerns the incorporation of the sulfur and the accelerator. The various compositions were shaped, vulcanized in sheet form and subjected to a thermo-oxidizing treatment at 77° C. for 0, 7, 14, 21 and 28 days. For each of these points, the properties at break are characterized by uniaxial tensile measurements (modulus, elongation).

Limit properties, modulus and elongation at break

Tensile tests make it possible to determine the elasticity stresses and the breaking properties; carried out on the cooked mixtures produced in accordance with the AFNOR-NF-T46-002 standard of September 1988.

The elongations at break (in %) are measured at 23°C, under normal hygrometric conditions (50% relative humidity), according to the French standard NF T 40-101 (December 1979), and the moduli at rupture (in MPa).

Table 3 presents the compositions tested (in phr), and Table 4 presents the results obtained, in base 100.

Composition T2 T3 C2 Natural rubber (1) 100 100 100 Irganox (2) - 3.2 - Eugenol (3) - - 1.2 Carbon black (4) 60 60 60 Stearic acid 1 1 1 Zinc oxide 8 8 8 Cobalt Salt (5) 1 1 1 Accelerator (6) 1 1 1 Sulfur 5 5 5

(1) Natural Rubber

(2) “Irganox 1520 L” sold by BASF, MW=424.8 g/mol,

(3) 95% Eugenol from Sigma Aldrich, MW = 164.2 g/mol

(4) Cabot Company's ASTM N375 Grade Carbon Black

(5) Cobalt acetylacetonate from Sigma Aldrich

(6) Tertiobutyl-benzothiazyl sulfenamide (“TBBS”) from the company Solutia

Measured property Aging time T2 T3 C2 Modulus (MPa) initial 26 25 25 7 days 20 23 20 14 days 15 19 17 21 days 17 19 17 28 days 18 19 19 Elongation at Break (%) initial 440 500 450 7 days 170 270 200 14 days 80 190 110 21 days 70 180 100 28 days 40 130 90

The results presented in Table 4 above show that the compositions according to the invention make it possible to preserve the mechanical properties over thermo-oxidative ageing. We can see the illustration of this in that the breaking properties of composition C2 according to the invention contract less quickly than that of composition T2 which does not contain any protective agent. The difference is even clearer and more significant after 14 days of thermo-oxidative ageing.

Claims (12)

Rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system and a phenolic antioxidant of general formula [Chem 1] below,

in which :
- the radical R1 represents a hydrogen atom, an alkyl group comprising from 1 to 18 carbon atoms, or an alkoxy group comprising from 1 to 18 carbon atoms,
- the radicals R2 to R7 each independently represent a hydrogen atom or a hydrocarbon group comprising from 1 to 18 carbon atoms. Rubber composition according to Claim 1, in which the diene elastomer is chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, copolymers of isoprene, and mixtures of these elastomers. Rubber composition according to any one of the preceding claims, in which the phenolic antioxidant of general formula [Chem 1] is such that the R1 group is a hydrogen atom, a methyl, ethyl, isopropyl, tertiobutyl group or a methoxy. Rubber composition according to any one of the preceding claims, in which the phenolic antioxidant of general formula [Chem 1] is such that the radicals R2 to R7 each independently represent a hydrogen atom, an alkyl group comprising from 1 to 18 carbon atoms, or an aryl group comprising from 6 to 18 carbon atoms. Rubber composition according to the preceding claim, in which the phenolic antioxidant of general formula [Chem 1] is such that the radicals R2 to R7 each independently represent a hydrogen atom, a methyl, ethyl, isopropyl, or tert-butyl. A rubber composition according to any preceding claim, wherein the phenolic antioxidant of general formula [Chem 1] is eugenol of formula [Chem 2].
Rubber composition according to any one of the preceding claims, in which the level of phenolic antioxidant of general formula [Chem 1] is included in a range going from 0.2 to 10 phr, preferably from 0.5 to 8 phr and more preferably from 0.8 to 5 phr. Rubber composition according to any one of the preceding claims, in which the reinforcing filler is chosen from the group consisting of carbon blacks, silicas and mixtures thereof. Rubber composition according to any one of the preceding claims, in which the content of total reinforcing filler is within a range ranging from 10 to 200 phr, preferentially from 30 to 180 phr, and more preferentially from 40 to 160 phr. A rubber article comprising a rubber composition defined in any one of claims 1 to 9. Rubber article according to the preceding claim, in which the article is chosen from pipes, belts, conveyor belts, caterpillars, pneumatic objects (and in particular tires), shoe soles or surgical gloves. A tire comprising a rubber composition defined in any one of claims 1 to 9.