EP2445958A1

EP2445958A1 - Tyre rubber composition comprising an acetylacetonate compound

Info

Publication number: EP2445958A1
Application number: EP10726070A
Authority: EP
Inventors: Kazumi Makiuchi; Salvatore Pagano
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2009-06-24
Filing date: 2010-06-18
Publication date: 2012-05-02
Also published as: US20120165446A1; FR2947274B1; JP5587407B2; CN102822258A; FR2947274A1; WO2010149580A1; JP2012530825A

Abstract

The invention relates to a rubber composition suitable for being used in particular for manufacturing tyres, comprising at least one diene elastomer, a reinforcing filler, a cross-linking system, 0.2 to 10 pce of an antioxidant such as a substituted paraphenylenediamine and 0.2 to 10 pce of chromium acetylacetonate (III). Said acetylacetonate compound is advantageously suitable for reducing antioxidant consumption during the thermal oxidative ageing of the composition. The invention also relates to a metal/rubber composite comprising such a composition and at least one metal reinforcement, as well as to a tyre comprising such a composition or such a composite.

Description

PNEUMATIC RUBBER COMPOSITION COMPRISING AN ACETYLACETONATE COMPOUND 1. FIELD OF THE INVENTION

The field of the present invention is that of rubber compositions that can be used in particular for the manufacture of semi-finished articles or products made of rubber such as, for example, pneumatic tires.

The present invention is more particularly related to antidegradant systems and agents for protecting these rubber compositions against aging due to oxidation.

2. STATE OF THE ART

As is known, the vulcanizates of diene rubbers which are essentially unsaturated, natural or synthetic, because of the presence of double bonds on their molecular chains, are likely to deteriorate more or less rapidly after prolonged exposure to the atmosphere. they are not protected because of known oxidation mechanisms. These complex mechanisms have been recalled for example in patent documents WO 99/02590 and WO 99/06480. They result, due to breaks in these double bonds and the oxidation of sulfur bridges, a stiffening and embrittlement of vulcanizates, degradation which is further accelerated under the combined action of heat by "thermo-oxidation", or that of light by "photo-oxidation".

These oxidation phenomena could be gradually inhibited by the development and marketing of various antioxidants, including derivatives of p-phenylenediamine ("PPD" or "PPDA") such as for example N-isopropyl -N'-phenyl-p-phenylenediamine ("I-PPD") or N, 3-dimethylbutyl-N'-phenyl-p-phenylenediamine ("6- PPD"), quinoline derivatives ("TMQ"), both excellent antioxidants and antiozonants (see, for example, patent applications WO 2004/033548, WO 2005/063510, WO 2005/133666). These antioxidants are today used systematically in diene rubber compositions, in particular in tire compositions, in order to combat aging and premature wear of these.

The well-known disadvantage of these antioxidants is that their concentration in the rubber compositions naturally decreases over time due to their very chemical function, that they also have a strong natural propensity to migrate from more concentrated areas to less areas. concentrated in antioxidant, so much so that the man of the The business is made to use relatively large quantities of product, which is relatively expensive and otherwise detrimental to the appearance of finished products due to the high tackiness of a large number of antioxidants, especially p-phenylenediamine.

To overcome the above disadvantages and thus further improve the protection and aging resistance of pneumatic tires, it has been proposed in particular to incorporate in these bandages additional layers of rubber, high concentration of antioxidant, functioning in a way as antioxidant reservoirs capable of delivering the antioxidant over time, by migration, depending on the degree of depletion of the adjacent zones (see, for example, the patent documents WO 2009/029114, EP 1 319 527 or US Pat. No. 7,082,976); .

The use of such antioxidant tanks, although effective, however, has the disadvantage of having to modify the internal structure of tires and therefore make their manufacture more complex and more expensive.

Also, designers of diene rubber articles, including manufacturers of pneumatic tires, are looking today for simple new solutions that can overcome, at least in part, the aforementioned drawbacks.

3. BRIEF DESCRIPTION OF THE INVENTION

During their research, the Applicants have discovered a new rubber composition which, during its aging, has the particularity of consuming less antioxidant and which therefore makes it possible to meet the above objective.

Accordingly, a first object of the invention relates to a rubber composition, usable in particular for the manufacture of a tire, comprising at least one diene elastomer, a reinforcing filler, a crosslinking system, between 0.2 and 10 phr. an antioxidant and between 0.2 and 10 phr of chromium (III) acetylacetonate.

Due to the presence of the above specific acetylacetonate, there has been unexpectedly a significant reduction in antioxidant consumption in rubber compositions during aging of the latter.

The longevity of rubber vulcanizates can thus be improved, in particular that of pneumatic tires which can be subjected in known manner to particularly severe driving conditions, in particular in a humid and corrosive atmosphere. The present invention also relates to the use of a composition according to the invention for the manufacture of articles or semi-finished products made of rubber, particularly pneumatic tires, in particular those intended for equipping tourism-type motor vehicles, SUVs. {"Sport Utility Vehicles"), two wheels (including bicycles, motorcycles), aircraft, such as industrial vehicles chosen from light trucks, "heavy vehicles" - that is to say, subway, bus, road transport equipment (trucks tractors, trailers), off-the-road vehicles such as agricultural or civil engineering -, other transport or handling vehicles.

The invention also relates per se to any article or semi-finished product of rubber, in particular a tire, comprising a composition according to the invention.

The invention also relates to the use of a composition according to the invention for the manufacture of a metal / rubber composite comprising a rubber composition and at least one metal reinforcement capable of adhering to said rubber composition.

The invention also relates to a metal / rubber composite comprising a diene rubber composition according to the invention and at least one metal reinforcement capable of adhering to said rubber composition.

The invention as well as its advantages will be readily understood in the light of the description and the following exemplary embodiments, as well as the single FIGURE relating to these examples which schematizes in radial section, a radial carcass reinforcement pneumatic tire conforming to FIG. the invention, incorporating a composition according to the invention.

4. MEASUREMENTS AND TESTS USED

The rubber compositions according to the invention are characterized, before and after cooking, as indicated below.

A) Mooney plasticity

An oscillating consistometer is used as described in the French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the uncured state (ie, before firing) is molded in a cylindrical chamber heated to 100 ^° C. After one minute of preheating, the rotor rotates within the test piece at 2 rpm and the useful torque is measured to maintain this movement after 4 minutes of rotation. The Mooney plasticity (ML 1 + 4) is expressed in "Mooney unit" (UM, with 1 UM = 0.83 Nm).

B) Toasting time

The measurements are carried out at 130 ^° C. in accordance with the French standard NF T 43-005 (1991). The evolution of the consistometric index as a function of time makes it possible to determine the toasting time of the rubber compositions, evaluated according to the above-mentioned standard by the parameter T5 (case of a large rotor), expressed in minutes, and defined as being the time required to obtain an increase in the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.

C) Rheometry

The measurements are carried out at 150 ^° C. with an oscillating chamber rheometer according to DIN 53529 - Part 3 (June 1983). The evolution of the rheometric torque as a function of time describes the evolution of the stiffening of the composition as a result of the vulcanization reaction. The measurements are processed according to DIN 53529 - Part 2 (March 1983): T _α (for example T ₉₅ ) is the time required to reach a conversion of α%, that is to say α% (for example 95 %) of the difference between the minimum and maximum couples.

D) Traction tests

These tests make it possible to determine the elastic stress and the properties at break. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. The modulus measurements were carried out in tension, unless otherwise expressly indicated according to the ASTM D 412 standard of 1998 (test-tube "C"); in second elongation (ie, after an accommodation cycle) the true secant moduli, that is to say, brought back to the actual section of the specimen at 10%, 100% and 300% elongation, noted respectively ElO, E100 and E300 and expressed in MPa (normal temperature and humidity conditions according to ASTM D 1349 of 1999). The breaking stresses (in MPa) and the elongations at break (in%) are also measured. All these tensile measurements are carried out under normal conditions of temperature (23 ± 2 ° C.) and hygrometry (50 ± 5% relative humidity), according to the French standard NF T 40-101 (December 1979). 5. DETAILED DESCRIPTION OF THE INVENTION

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

On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b).

The composition of the invention is a rubber-based composition (ie, comprising the mixture or the reaction product) of at least one diene elastomer, a reinforcing filler, a crosslinking system, between 0.2 and 10 phr of water. an antioxidant; it furthermore has the novel and essential characteristic of having between 0.2 and 10 phr of an acetylacetonate of alkaline or alkaline-earth metal.

A) Diene elastomer

By "diene" elastomer (or indistinctly rubber) is meant in known manner an elastomer derived at least in part (ie, a homopolymer or a copolymer) from monomers dienes (monomers carrying two carbon-carbon double bonds, conjugated or not) .

The diene elastomers can be classified in known manner into two categories: those known as "essentially unsaturated" and those known as "essentially saturated". In general, the term "diene elastomer" is used herein to mean a diene elastomer derived at least in part from conjugated diene monomers having a level of units or units of diene origin (conjugated dienes) which is greater than 15% (%). in moles). Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins EPDM type do not fall within the above definition and may be particularly described as "substantially saturated diene elastomers" "(low or very low diene origin, always less than 15%). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer is particularly understood to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

Given these definitions, the term "diene elastomer" can more particularly be understood as being capable of being used in the compositions in accordance with the invention:

(a) - any homopolymer obtained by polymerization of a conjugated diene monomer, preferably having from 4 to 12 carbon atoms; (b) - any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more vinyl aromatic compounds preferably having from 8 to 20 carbon atoms;

(c) - a ternary copolymer obtained by copolymerization of ethylene, an α-olefin preferably having from 3 to 6 carbon atoms with a non-conjugated diene monomer preferably having from 6 to 12 carbon atoms, for example elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type, such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene;

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

Although it applies to any type of diene elastomer, one skilled in the art of the tire will understand that the present invention is first used with essentially unsaturated diene elastomers, in particular of the type (a) or ( b) above.

More preferably, the diene elastomer is selected from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), the latter being prepared by emulsion polymerization (ESBR) as in solution (SSBR), the isoprene-butadiene copolymers (BIR ), isoprene-styrene copolymers (SIR) and isoprene-butadiene-styrene copolymers (SBIR).

The elastomers can be for example block, statistical, sequence, microsequential, and be prepared in dispersion or in solution; they can be coupled and / or star or functionalized with a coupling agent and / or starring or functionalization. For coupling with carbon black, there may be mentioned for example functional groups comprising a C-Sn bond or amino functional groups such as benzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may be made, for example, of silanol or polysiloxane functional groups having a silanol end (as described, for example, in US Pat. No. 6,013,718), alkoxysilane groups (as described, for example, in US 5,977,238), carboxylic groups (as described, for example, in US 6,815,473 or US 2006/0089445) or polyether groups (as described for example in US 6,503,973). By way of other examples of such functionalized elastomers, mention may also be made of elastomers (such as SBR, BR, NR or IR) of the epoxidized type.

Polybutadienes and in particular those having a content (mol%) in units

1,2 between 4% and 80% or those having a content (mol%) of cis-1,4 greater than 80%, polyisoprenes, butadiene-styrene copolymers and in particular those having a Tg (glass transition temperature, measured according to ASTM D3418) between

0 ⁰ C and - 70 ⁰ C and more particularly between - 10 ⁰ C and - 60 ⁰ C, and / or a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (mol%) in -1,2 bonds of the butadiene part of between 4% and 75%, a content (mol%) of trans-1,4 bonds of between 10% and 80%, butadiene-isoprene copolymers and especially those having an isoprene content of between 5% and 90% by weight and a Tg of -40 ^° C. to -80 ^° C., the isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg between -25 ° C and -

50 ⁰ C. In the case of butadiene-styrene-isoprene copolymers, those having a styrene content of between 5% and 50% by weight and more particularly between 10% and 40%, an isoprene content of between 15 % and 60% by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content (mol%) in units -1 , 2 of the butadiene part of between 4% and 85%, a content (mol%) in trans-1,4 units of the butadiene part of between 6% and 80%, a content (mol%) in units -1, 2 plus -3.4 of the isoprenic part of between 5% and 70% and a content (mol%) in trans units -1.4 of the isoprenic part of between 10% and 50%, and more generally any butadiene-based copolymer. styrene-isoprene having a Tg of between -20 ^° C. and -70 ^° C.

According to a particular embodiment, the majority diene elastomer by weight (in particular for more than 50 phr) is an SBR, whether it is an emulsion prepared SBR ("ESBR") or an SBR prepared in solution ("SSBR"), or a blend (mixture) SBR / BR, SBR / NR (or SBR / IR), BR / NR (or BR / IR), or SBR / BR / NR (or SBR / BR / IR). This is particularly the case when the compositions of the invention are intended to constitute, in the tires, the rubber matrices of certain treads (for example for passenger vehicles). In the case of an SBR elastomer (ESBR or SSBR), an SBR having an average styrene content, for example between 20% and 35% by weight, or a high styrene content, for example 35 to 35% by weight, is used in particular. 45%, a vinyl content of the butadiene part of between 15% and 70%, a content (mol%) of trans-1,4 bonds of between 15% and 75% and a Tg of between -10 ^° C. and - 55 ° C; such an SBR can be advantageously used in admixture with a BR preferably having more than 90% (mol%) of cis-1,4 bonds.

According to another particular embodiment, the majority diene elastomer by weight (in particular for more than 50 phr) is an isoprene elastomer. This is the case in particular when the compositions of the invention are intended to constitute, in pneumatic tires, the rubber matrices of certain treads (for example for industrial vehicles), crown reinforcement plies (for example). example of working plies, protective plies or hooping plies), carcass reinforcement plies, sidewalls, beads, protectors, underlayments, rubber blocks and other internal gums providing the interface between the aforesaid areas of the tires.

By "isoprene elastomer" is meant in known manner a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene copolymers (butyl rubber-HR), isoprene-styrene copolymers (SIR), isoprene-butadiene copolymers (BIR) or isoprene-butadiene-styrene copolymers. (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; of these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used.

According to another particular embodiment, especially when it is intended for a tire sidewall, a tubeless tire ("inner liner") of tire without a chamber (or other element impervious to air), the composition complies with the invention may contain at least one essentially saturated diene elastomer, in particular at least one EPDM copolymer or a butyl rubber (optionally chlorinated or brominated), that these copolymers may be used alone or as a mixture with highly unsaturated diene elastomers as mentioned previously, especially NR or IR, BR or SBR.

According to another particular embodiment of the invention, the rubber composition comprises a blend of one (or more) diene elastomers called "high Tg" having a Tg between -70 ⁰ C and 0 ⁰ C and d one (one or more) diene elastomers called "at low Tg" between -110 ^° C. and -80 ^° C., more preferably between -105 ^° C. and -90 ^° C. The high-Tg elastomer is preferably chosen in the group consisting of S-SBR, E-SBR, natural rubber, synthetic polyisoprenes (having a content (% molar) of cis-1,4 chains preferably greater than 95%), BIR, SIRs, SBIRs, and mixtures of these elastomers. The low Tg elastomer preferably comprises butadiene units at a level (mol%) of at least 70%; it consists preferably of a polybutadiene (BR) having a content (mol%) of cis-1,4 chains greater than 90%.

In conclusion, the rubber composition of the invention may contain one or more diene elastomers, the latter or they may also be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.

B) Reinforcing filler The composition of the invention comprises any type of so-called reinforcing filler known for its ability to reinforce a rubber composition that can be used for the manufacture of tires, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica to which is associated in a known manner a coupling agent, or a mixture of these two types of filler.

Such a reinforcing filler typically consists of nanoparticles whose average size (in mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

Preferably, the content of total reinforcing filler (in particular silica or carbon black or a mixture of silica and carbon black) is between 30 and 150 phr. Above 150 phr, there is a risk of increasing the hysteresis and therefore the rolling resistance of the tires. For this reason, the total reinforcing filler content is more preferably within a range of 40 to 120 phr.

By way of a particularly preferred example, in particular for use in an internal rubber composition of the tire of the invention, 30 to 100 phr, in particular 40 to 80 phr of carbon black, of silica, are used. or a mixture of silica and carbon black.

As another particularly preferred example, especially for use in an external rubber composition of the tire of the invention, from 40 to 150 phr, in particular from 50 to 120 phr of carbon black, silica, or a mixture of silica and carbon black.

Carbon blacks are suitable for all carbon blacks, in particular blacks of the HAF, ISAF, SAF type conventionally used in tires or their treads (so-called pneumatic grade blacks). Among these, carbon blacks of the 100, 200, 300, 600 or 700 series (ASTM grades), for example blacks Nl 15, N134, N234, N326, N330, N339, N347, N375, are particularly suitable. N550, N683, N772. 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 WO 97/36724 or WO 99/16600).

As examples of organic fillers other than carbon blacks, mention may be made of functionalized polyvinyl organic fillers as described in applications WO-A-2006/069792 and WO-A-2006/069793, WO-A-2008/003434. and WO-A-2008/003435. "Reinforcing inorganic filler" means any inorganic or mineral filler, irrespective of its color and origin (natural or synthetic), also called "white" filler or sometimes "clear" 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 other words able to replace, in its reinforcing function, a conventional carbon black pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferentially silica (SiO 2). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m ² / g, preferably from 30 to 400 m ² / g, especially between 60 and 300 m ² / g. As highly dispersible precipitated silicas (referred to as "HDS"), mention may be made of, for example, the Ultrasil 7000 and Ultrasil 7005 silicas from Degussa, the Zeosil 1165MP, 1135MP and 1115MP silicas from Rhodia, the Hi-SiI silica EZ150G from the PPG company, the Zeopol 8715, 8745 and 8755 silicas of the Huber Company.

In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner to ensure a sufficient chemical and / or physical connection between the inorganic filler (surface of its particles) and the diene elastomer. In particular, organosilanes or at least bifunctional polyorganosiloxanes are used.

In particular, polysulfide silanes, called "symmetrical" or "asymmetrical" silanes according to their particular structure, are used, as described for example in the applications WO03 / 002648 (or US 2005/016651) and WO03 / 002649 (or US 2005/016650).

In particular, polysulphide silanes having the following general formula (I) are not suitable for the following definition:

(I) Z - A - S _x - A - Z, wherein:

x is an integer of 2 to 8 (preferably 2 to 5);

- the symbols A, which are identical or different, represent a divalent hydrocarbon group (preferably an alkylene Ci-Ci ₈ or an arylene group C _O -C _I2, more particularly alkylene Ci-Cio, including Ci-C ₄ , especially propylene); the symbols Z, identical or different, correspond to one of the three formulas below: -,

in which: - the radicals R ^1, substituted or unsubstituted, identical or different, represent an alkyl group _Ci-8 cycloalkyl, C5-C18 aryl or C ₆ -C ₈ (preferably alkyl Ci-C _6, cyclohexyl or phenyl, especially alkyl groups, C1-C4 alkyl, more particularly methyl and / or ethyl). the radicals R ² , substituted or unsubstituted, which are identical to or different from one another, represent a C ₁ -C 18 alkoxyl or C ₅ -C 18 cycloalkoxyl group (preferably a group chosen from C ₁ -C ₈ alkoxyls and C ₅ cycloalkoxyls); -C ₈ , more preferably still a group selected from C1-C4 alkoxyls, in particular methoxyl and ethoxyl).

In the case of a mixture of polysulfurized alkoxysilanes corresponding to formula (I) above, in particular common commercially available mixtures, the average value of "x" is a fractional number preferably of between 2 and 5, more preferably close to 4. But the invention can also be advantageously implemented for example with disulfide alkoxysilanes (x = 2).

As examples of silane polysulfides, are more particularly the bis (mono, trisulfide or tetrasulfide) of bis (alkoxyl (Ci-C4) alkyl (C 1 -C ₄₎ alkyl SiIyI- (Ci-C ₄ )), such as polysulfides of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl). Among these compounds, bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, of formula [(C ₂ H ₅ O) ₃ Si (CH ₂ ) 3 S 2] 2 or bis (triethoxysilylpropyl) disulfide, in abbreviated form, is especially used. TESPD, of formula [(C ₂ H ₅ O) SSi (CH ₂ ) SS] ₂ . Also preferred are polysulfides (especially disulfides, trisulphides or in the aforementioned patent application WO 02/083782 (or US 7,217,751).

By way of example of coupling agents other than a polysulphurized alkoxysilane, mention may be made in particular of bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulfides (R ² = OH in formula I above) as described by US Pat. for example in patent applications WO 02/30939 (or US Pat. No. 6,774,255), WO 02/31041 (or US 2004/051210), and WO2007 / 061550, or else silanes or POS bearing azo functional groups. dicarbonyl, as described for example in patent applications WO 2006/125532, WO 2006/125533, WO 2006/125534.

As examples of other sulphurized silanes, mention may be made, for example, of silanes carrying at least one thiol function (-SH) (called mercaptosilanes) and / or of at least one blocked thiol function, as described for example in patents or patent applications US 6,849,754, WO 99/09036, WO 2006/023815, WO 2007/098080.

Of course, it would also be possible to use mixtures of the coupling agents described above, as described in particular in the aforementioned application WO 2006/125534.

In the rubber compositions of the invention, when they are reinforced with an inorganic filler such as silica, the content of coupling agent is preferably between 2 and 15 phr, more preferably between 3 and 12 phr.

Those skilled in the art will understand that as an equivalent load of the reinforcing inorganic filler described in this paragraph, it would be possible to use a reinforcing filler of another nature, in particular an organic filler such as carbon black, since this filler reinforcing would be covered with an inorganic layer such as silica, or would comprise on its surface functional sites, including hydroxyl, requiring the use of a coupling agent to establish the connection between the filler and the elastomer. By way of example, mention may be made, for example, of carbon blacks for tires as described for example in documents WO 96/37547 and WO 99/28380.

C) Crosslinking system

The crosslinking system is preferably a vulcanization system, that is to say a system based on sulfur (or a sulfur-donor agent) and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the production phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide. stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine).

Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The primary vulcanization accelerator is used at a preferred level of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr.

Any compound that can act as an accelerator for vulcanizing diene elastomers in the presence of sulfur, especially accelerators, can be used as accelerator. thiazoles and their derivatives, thiuram type accelerators, zinc dithiocarbamates. These primary accelerators are more preferably selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated "CBS"), N, N-dicyclohexyl-2-benzothiazyl sulphenamide (abbreviated "DCBS"), N-tert-butyl-2-benzothiazyl sulphenamide (abbreviated "TBBS"), N-tert-butyl-2-benzothiazyl sulphenimide (abbreviated "TBSI") and mixtures of these compounds .

D) Antioxidant

The composition of the invention has the characteristic of comprising between 0.2 and 10 phr of an antioxidant, preferably between 0.3 and 6 phr, more preferably between 0.5 and 4 phr of such an antioxidant.

The antioxidant used in the composition of the invention is any antioxidant capable of delaying, in a known manner, the aging of rubber vulcanizates attributable to the action of oxygen.

Mention may in particular be made of para-phenylenediamine derivatives (abbreviated as "PPD" or "PPDA"), also known in the known manner as substituted para-phenylenediamines, such as, for example, N, 3-dimethylbutyl-N'-phenyl. p-phenylenediamine (more commonly known by the abbreviated term "6-PPD"), N-isopropyl-N'-phenyl-p-phenylenediamine (abbreviated as "I-PPD"), phenylcyclohexyl-p- phenylenediamine, N, N'-di (1,4-dimethylpentyl) -p-phenylenediamine, N, N'-diaryl-p-phenylenediamine ("DTPD"), diaryl-p- phenylenediamine ("DAPD"), 2,4,6-tris (N, 4-dimethylpentyl-p-phenylenediamino) -1,3,5-triazine, and mixtures of such diamines.

Mention may also be made of quinoline derivatives ("TMQ") such as, for example, 1,2-dihydro-2,2,4-trimethylquinoline and 6-ethoxy-1,2-dihydro-2,2,4- trimethyl-quinoline.

Diphenylamines or substituted triphenylamines may also be mentioned, as described for example in applications WO 2007/121936 and WO 2008/055683, in particular 4,4'-bis (isopropylamino) -triphenylamine, 4,4'-bis (1,3-dimethylbutylamino) triphenylamine, 4,4'-bis (1,4-dimethylpentylamino) triphenylamine.

Mention may also be made of dialkylthiodipropionates or else phenolic antioxidants, in particular of the family of 2,2'-methylenebis [4-alkyl (Ci-Cio) -6-alkyl (Ci-Cl ₂ ) phenols, as described above. especially in the aforementioned application WO 99/02590. Of course, in the present description, the term antioxidant may refer to both a single antioxidant compound or a mixture of several antioxidant compounds.

Preferably, the antioxidant is selected from the group consisting of substituted p-phenylenediamines, substituted diphenylamines, substituted triphenylamines, quinoline derivatives, and mixtures of such compounds; more preferably still, the antioxidant is selected from the group consisting of substituted p-phenylenediamines and mixtures of such diamines.

E) Acetylacetonate

An essential characteristic of the composition according to the invention is that it contains between 0.2 and 10 phr of chromium (III) acetylacetonate.

Below 0.2 phr, the technical effect is likely to be insufficient, whereas beyond 10 phr, there is an increase in costs and the risk of degrading certain mechanical properties of the compositions, the initial state as after aging. For these various reasons, said level of chromium acetylacetonate is preferably between 0.3 and 6 phr, more preferably within a range of 0.5 to 2.5 phr.

The previously described chromium (III) acetylacetonate or chromium trisacetylacetonate is well known, it has been essentially used until now as polymerization catalysts polymers, as well as many other metal acetylacetonates (see for example US 3 247,175, US 3,313,796, FR 2,087,786 or GB 1,338,133).

F) Other constituents

The rubber compositions in accordance with the invention may also comprise all or part of the additives normally used in rubber compositions intended for the manufacture of pneumatic tires, such as, for example, plasticizers or extension oils, which these are of a kind aromatic or non-aromatic, especially very low or non-aromatic oils (eg, paraffinic oils, hydrogenated naphthenic oils, MES or TDAE oils), vegetable oils, plasticizers ethers, ester plasticizers (for example glycerol trioleates), fillers other than those mentioned above, for example lamellar fillers, hydrocarbon plasticizing resins having a high Tg, preferably greater than 30 ^° C., as described for example in the applications WO 2005/087859, WO 2006/061064 and WO 2007 / 017060, and mixtures of such compounds, other anti-degradants or anti-aging agents such as For example, antiozonants, accelerators, vulcanization activators or retarders, anti-eversion agents such as for example sodium hexathiosulphonate or N, N'-m- phenylene biscitraconimide, methylene acceptors and donors (for example resorcinol, HMT or H3M) or other reinforcing resins, bismaleimides, other adhesion promoter systems with respect to metal reinforcements, in particular brasses, such as for example salts metal such as organic salts of cobalt or nickel. Those skilled in the art will be able to adjust the formulation of the composition according to their particular needs.

The rubber compositions of the invention may also contain coupling enhancers when a coupling agent is used, inorganic filler recovery agents when an inorganic filler is used, or more generally, bleaching agents. in a known manner, by improving the dispersion of the filler in the rubber matrix and by lowering the viscosity of the compositions, to improve their ability to implement in the green state. These covering agents are well known (see, for example, patent applications WO 2006/125533, WO 2007/017060 and WO 2007/003408), for example hydroxysilanes or hydrolysable silanes such as hydroxysilanes, alkylalkoxysilanes, in particular alkyltriethoxysilanes such as, for example, 1-octyl-tri-ethoxysilane, polyols (for example diols or triols), polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialkanol amines); hydroxylated or hydrolysable polyorganosiloxanes (for example α, α-dihydroxy-poly-organosilanes (in particular α, α-dihydroxy-polydimethylsiloxanes).

According to a preferred embodiment of the invention, in the case in particular where the composition of the invention is intended to constitute a calendering matrix of a metal reinforcement, the composition comprises, in association with the acetylacetonate compound described above, at at least one cobalt compound at a preferential content of between 0.1 and 10 phr, more preferably between 0.3 and 6 phr, in particular between 0.5 and 4 phr. It has been found that a certain synergy could indeed exist between the two compounds, which also results in an improvement of the adhesive performance under thermal and wet aging conditions.

This cobalt compound is preferably an organic cobalt compound, chosen more preferentially from the group consisting of abietates, acetates, acetylacetonates, benzoates, butyrates, formates, linoleates, maleates, oleates, propionates, tallates, naphthenates, resinates, stearates, and the like. mixtures (i.e., salts, complexes, or other mixed derivatives) of such compounds, in particular among abietates, acetylacetonates, tallates, naphthenates, resinates and mixtures of such compounds. Acetylacetonates, tallates and cobalt naphthenates are preferred in the majority of cases.

"Metal reinforcement" means any reinforcing element capable of reinforcing the rubber matrix, whether it is entirely metallic or not, of which at least the surface or outer part, intended to come into contact with the rubber, is metal. This reinforcement may be in various forms, preferably in the form of a unitary yarn (monofilament), a film (for example a strip or a ribbon) or an assembly of threads, that these threads are twisted together. (For example, in the form of a cable) or substantially parallel to each other (for example in the form of a packet of son, a continuous fiber or a set of short fibers).

In the composites and tires of the invention, this reinforcement is more preferably in the form of a unitary yarn or an assembly of yarns, for example a cable or a strand manufactured with devices and methods of cabling or stranding known to those skilled in the art, which are not described here for the simplicity of the presentation.

It is preferable to use a reinforcement made of steel, in particular carbon pearlitic (or ferritoclastic) steel known in the known manner as "carbon steel", or stainless steel as described, for example, in EP-A patent applications. -648 891 or WO98 / 41682. But it is of course possible to use other steels or other alloys. When a carbon steel is used, its carbon content is preferably between 0.1% and 1.2%, especially between 0.5% and 1.1% (% by weight of steel); it is more preferably between 0.6% and 1.0%, such a content representing a good compromise between the mechanical properties required for the tire and the feasibility of the son.

The metal reinforcements as well as the cobalt salts that may be used for a preferential use have, for example, been described in more detail in the patent application WO 2005/113666.

To further improve the performance of the composition of the invention, particularly when the latter constitutes a calendering matrix of a metal reinforcement, a particular embodiment consists in using a bismaleimide compound. This type of compound, usable without hardener, has a cooking kinetics well adapted to that of tires, it is likely to activate the kinetics of adhesion and further improve, in the compositions according to the invention, the endurance in wet aging conditions of adhesive interphases.

It is recalled that the bismaleimides respond, in known manner, to the following formula:

wherein R is a substituted or unsubstituted hydrocarbon, aromatic or aliphatic, cyclic or acyclic radical, such radical may include a heteroatom selected from O, N and S; this radical R preferably comprises from 2 to 24 carbon atoms.

More preferred is a bismaleimide selected from the group consisting of N, N'-ethylene-bismaleimides, N, N'-hexamethylene-bismaleimides, N, N '- (m-phenylene) -bismaleimides, N, N' - ( p-phenylene) -bismaleimides, N, N '- (p-tolylene) -bismaleimides, N ₅ N- (methylenedi-p-phenylene) -bismaleimides, N, N' - (oxydi-p-phenylene) -bismaleimides and mixtures of these compounds. Such bismaleimides are well known to those skilled in the art.

In the case where a reinforcing resin or a bismaleimide is used, it is present in the composition of the invention at a preferred level of between 0.1 and 20%, more preferably between 1 and 8% by weight of rubber composition. For levels above the maximum values indicated, there is a risk of excessive stiffening of the compositions, and thus of embrittlement of the compositions; for rates below the indicated minima, the intended technical effect may be insufficient.

G) Preparation of rubber compositions

The compositions are manufactured in appropriate mixers, using two successive preparation phases well known to those skilled in the art: a first phase of work or thermomechanical mixing (so-called "non-productive" phase) at high temperature, up to a maximum of maximum temperature between 110 ⁰ C and 190 ⁰ C, preferably between 130 ⁰ C and 180 ⁰ C, followed by a second phase of mechanical work (so-called "productive" phase) to a lower temperature, typically less than 110 ⁰ C, finishing phase during which is incorporated the crosslinking system.

For example, the nonproductive phase is conducted in a single thermomechanical step of a few minutes (for example between 2 and 10 min) during which is introduced, in a suitable mixer such as a conventional internal mixer, all the necessary basic constituents and other additives, with the exception of the crosslinking or vulcanization system. After cooling the mixture thus obtained, it is then incorporated in an external mixer such as a roll mill, maintained at low temperature (for example between 30 ⁰ C and 100 ⁰ C), the vulcanization system. The whole is then mixed (productive phase) for a few minutes (for example between 5 and 15 min).

Preferably, chromium acetylacetonate is introduced during the non-productive phase, along with the antioxidant. However, the invention also applies to the case where all or only a fraction of this acetylacetonate is introduced during the productive phase. The final composition thus obtained can then be calendered, for example in the form of a sheet, a plate or extruded, for example to form a rubber profile used for the manufacture of a composite or a semi product. -fini, such as for example webs, tapes, underlays, other rubber blocks reinforced or not with metal reinforcements, intended to form for example a portion of the structure of a tire.

The vulcanization (or firing) may then be carried out in a known manner at a temperature generally of between 130 ^° C. and 200 ^° C., preferably under pressure, for a sufficient time which may vary, for example, between 5 and 90 min, depending in particular on the firing temperature, the vulcanization system adopted and the vulcanization kinetics of the composition under consideration.

The invention relates to rubber compositions and composites both in the so-called "raw" state (i.e., prior to firing) and in the so-called "fired" or vulcanized state (i.e. after vulcanization).

6. EXAMPLES OF CARRYING OUT THE INVENTION

A) Use of the composition of the invention in a tire

The rubber composition of the invention described above can be used for the manufacture of any article or semi-finished product made of rubber, in particular in motor vehicle tires, whether this composition is external or internal with respect to the structure of the tire.

By "external" or "external" composition (or mixture) is meant here any rubber part of the tire which gives on the outside of the tire, in other words which is contact with air or a gas inflation; by way of preferred examples, mention may be made in particular of the tread, the sidewalls or the sealing layer of the tire.

By "internal" or "internal" composition (or mixture) is meant a contrario any rubber part of the tire which does not give on the outside of the tire, in other words which is not in contact with the tire. air or an inflation gas, which is therefore located inside the tire structure itself; examples that may be mentioned include calender mixtures present in the bead zone, the carcass reinforcement or the crown reinforcement of the tire. The rubber composition of the invention is also usable for the manufacture of a metal / rubber composite, whether or not this composite is intended to be incorporated in a tire. This composite may be in various forms, for example in the form of a sheet, a strip, strip or a rubber block in which is incorporated the metal reinforcement, or a coating of rubber coating the metal reinforcement, the latter being in direct contact with the rubber composition. The final adhesion between the metal and the rubber composition can be obtained at the end of the firing of the finished article comprising the composite; preferably, this cooking is operated under pressure. The composites according to the invention are preferably intended for tires, in particular for radial tires to form all or part of the crown reinforcement, of the carcass reinforcement or the reinforcement of the bead zone of such tires.

By way of example, the appended FIGURE very schematically represents a radial section of a tire 1 with a radial carcass reinforcement according to the invention, intended for example for a heavy-duty vehicle or a passenger vehicle in this representation. General.

This tire 1 comprises a crown 2, two sidewalls 3, two beads 4, a carcass reinforcement 7 extending from one bead to the other. The top 2, surmounted by a tread (not shown in this schematic figure, for simplification), is in a manner known per se reinforced by a crown reinforcement 6 constituted for example by at least two superimposed crossed vertex plies (plies so-called "working" top), optionally covered with at least one protective ply or with a zero degree hooping crown ply. The carcass reinforcement 7 is wound around the two rods 5 in each bead 4, the upturn 8 of this armature 7 being for example disposed towards the outside of the tire 1 which is shown here mounted on its rim 9. The armature of carcass 7 consists of at least one ply reinforced by so-called "radial" cables, that is to say that these cables are arranged substantially parallel to each other and extend from one bead to the other of to form an angle between 80 ° and 90 ° with the median circumferential plane (plane perpendicular to the axis of rotation of the tire which is located halfway between the two beads 4 and passes through the middle of the crown reinforcement 6).

Of course, this tire 1 also comprises, in a known manner, a rubber or elastomer layer 10, commonly known as a rubber or sealing layer, which defines the radially inner face of the tire and which is intended to protect the carcass ply from the diffusion air from the interior space to the tire. Advantageously, particularly in the case of a truck tire, it may further comprise an intermediate reinforcing elastomer layer (not shown in the figure) which is located between the carcass ply and the sealing layer. The tire according to the invention has the essential feature of comprising in its structure at least one composition according to the invention. This composition, in the case of a so-called interior composition, may for example be a part of the bead zone 4 comprising the bead wire 5, a cross-crown ply or a ply of protection of the crown reinforcement 6, a ply forming all or part of the carcass reinforcement 7. This composition, in the case of a so-called external composition, may be present for example in the tread, in the sidewalls 3 or in the sealing layer 10 of the tire. .

According to a particular embodiment of the invention, the rubber composition of the invention is advantageously usable as a calendering composition (thus as an internal mixture) in the crown reinforcement 6 of all types of pneumatic tires, for example for vehicles. , vans or heavy vehicles. Preferably, in such a case, the rubber composition of the invention has, in the vulcanized state (ie, after firing), an ElO modulus which is greater than 4 MPa, more preferably between 6 and 20 MPa, for example between 6 and 15 MPa.

But it can also have an equally advantageous use in a carcass reinforcement 7 of a pneumatic tire for an industrial vehicle such as heavyweight; preferably, in such a case, the rubber composition of the invention has, in the vulcanized state, an ElO modulus which is less than 9 MPa, more preferably between 4 and 9 MPa.

B) Aging tests

For the purposes of this test, two rubber compositions (hereinafter Ci and C-2) were prepared, the formulation of which is given in Table 1, the rate of the different products being expressed in phr (parts by weight per cent). parts of total elastomer, here consisting of 100 phr of NR).

The control composition (CI) essentially comprises, in addition to the elastomer and the reinforcing filler (carbon black), an antioxidant, zinc oxide, stearic acid, sulfur and a sulfenamide accelerator. reinforcing resin (phenolic resin plus methylene donor) and a cobalt salt as adhesion promoter with respect to a metal reinforcement (cobalt naphthenate, Fluka product at 10% by weight of cobalt metal equivalent) . These compositions are for example intended to constitute the calendering gum of a crown reinforcement of a tire.

The composition of the invention C-2 is distinguished only by the additional presence of 1.6 phr of chromium (III) acetylacetonate compound. For the manufacture of these compositions, the following procedure was carried out: the reinforcing filler (carbon black), the elastomer, were successively introduced into an internal mixer, the initial vessel temperature of which was approximately 60 ^° C. diene (NR), an antioxidant and optionally acetylacetonate, and the various other ingredients with the exception of the vulcanization system; the mixer was thus filled to about 70% (% by volume). Thermomechanical work (non-productive phase) was then carried out in a step of about 2 to 4 minutes, until a maximum temperature of "fall" of 165 ° C. was reached. The mixture thus obtained was recovered, cooled, and sulfur and a sulfenamide type accelerator were incorporated on an external mixer (homoformer) at 30 ^° C., mixing the whole (productive phase) for a few minutes.

The compositions thus obtained are then either calendered in the form of plates (thickness of 2 to 3 mm) for the measurement of their physical or mechanical properties on the one hand, for the conduct of aging tests on the other hand.

The mechanical properties of these compositions have been reported in the attached Table 2. It is noted that the two compositions have almost equivalent properties, apart from an elongation at break advantageously higher in the presence of chromium acetylacetonate (composition C-2 according to the invention).

After baking the compositions (25 min at 150 ^° C.), the rubber blocks are placed in an oven at a temperature of 55 ° C., under a relative humidity of 60%, for one to several weeks, in order to compare the kinetics reducing the antioxidant levels of the compositions during this accelerated aging. The antioxidant level was measured by a known technique of HPLC (high performance liquid chromatography), firstly in the initial state on unaged samples, that is to say directly at the baking outlet, and secondly after aging from one to six weeks.

The results obtained are reported in the attached Table 3. The level of antioxidant in the compositions is expressed in relative units, with the base 100 being selected for the control composition in the initial state (i.e., after baking out).

On reading this table 3, it is firstly noted that, unexpectedly, the presence of chromium acetylacetonate already makes it possible, immediately after cooking (initial state), to reduce significantly (about 5%) the loss of antioxidant present in the composition.

In addition, after accelerated thermal aging, it is noted that regardless of the duration of aging, the presence of chromium acetylacetonate significantly reduces the consumption of antioxidant over time, compared to the control composition. In conclusion, the above thermal aging tests clearly demonstrate that the addition of chromium acetylacetonate, thereby functioning as an anti-degradant, significantly reduces the antioxidant consumption in the rubber compositions, thus offering the vulcanizates and therefore also the pneumatic tires comprising them, a potentially improved durability due to better protection against aging due to oxidation.

(1) natural rubber;

(2) N326 (designation according to ASTM D-1765);

(3) N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine; ("Santoflex 6PPD" from Flexsys);

(4) resorcinol (Sumitomo company);

(5) HMT (hexamethylenetetramine - Degussa company);

(6) cobalt naphthenate (Fluka - Product No. 60830);

(7) The ₅ H _2I CrO ₆ XH ₂ O (Aldrich - Product # 21679-31-2);

(8) sodium hexamethylenethiosulfate ("Duralink HTS" from Flexsys);

(9) N-tert-butyl-2-benzothiazyl sulfenamide ("Santocure TBBS" from Flexsys).

Table 3

Claims

1. A rubber composition, usable especially for the manufacture of a tire, comprising at least one diene elastomer, a reinforcing filler, a crosslinking system, between 0.2 and 10 phr of an antioxidant and between 0.2 and 10 phr. 10 phr of chromium (III) acetylacetonate.

The composition of claim 1, wherein the diene elastomer is selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

The composition of claim 1 or 2, wherein the reinforcing filler is selected from the group consisting of carbon black, inorganic fillers and mixtures of such fillers.

4. Composition according to claim 3, wherein the reinforcing filler is selected from the group consisting of carbon black, silica and mixtures of such fillers.

5. Composition according to any one of claims 1 to 4, wherein the reinforcing filler content is between 30 and 150 phr.

6. Composition according to any one of claims 1 to 5, wherein the crosslinking system is based on sulfur and an accelerator.

7. Composition according to any one of claims 1 to 6, wherein the level of chromium acetylacetonate is between 0.3 and 6 phr.

8. The composition of claim 7, wherein the level of chromium acetylacetonate is in a range of 0.5 to 2.5 phr.

9. Composition according to any one of claims 1 to 8, further comprising a cobalt salt.

The composition of claim 9, wherein the cobalt salt is selected from the group consisting of abietates, acetylacetonates, tallates, naphthenates, resinates and mixtures thereof.

The composition of any one of claims 1 to 10, wherein the antioxidant is selected from the group consisting of substituted p-phenylene diamines, substituted diphenylamines, substituted triphenylamines, quinoline derivatives, and mixtures thereof. such compounds.

The composition of claim 11, wherein the antioxidant is selected from the group consisting of substituted p-phenylene diamines and mixtures of such diamines.

13. Use of a composition according to any one of claims 1 to 12 for the manufacture of an article or a semi-finished rubber product.

14. Use of a composition according to any one of claims 1 to 12 for the manufacture of a tire.

Pneumatic tire comprising a composition according to any one of claims 1 to 12.

16. A pneumatic tire according to claim 15, the composition being an external composition of the tire, that is to say which is in contact with air or an inflation gas.

A pneumatic tire as claimed in claim 15, the composition being an inner composition of the tire, i.e. not in contact with air or an inflation gas.

18. Use of a composition according to any one of claims 1 to 12 for the manufacture of a metal / rubber composite comprising a rubber composition and at least one metal reinforcement.

19. Metal / rubber composite comprising a rubber composition according to any one of claims 1 to 12 and at least one metal reinforcement.