WO2015052131A1

WO2015052131A1 - Tire tread rubber composition containing polynitrone

Info

Publication number: WO2015052131A1
Application number: PCT/EP2014/071340
Authority: WO
Inventors: Etienne Fleury
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2013-10-08
Filing date: 2014-10-06
Publication date: 2015-04-16
Also published as: FR3011551A1; FR3011551B1

Abstract

The invention relates to a tire tread containing a rubber composition made of one or more diene elastomers, one or more reinforcing fillers, and a cross-linking system. The cross-linking system contains one or more polynitrone compounds selected from among the Formula (I) compounds.

Description

Tread rubber composition comprising a polynitrone

The present invention relates to a tread for a tire comprising a rubber composition based on a diene elastomer, a reinforcing filler and a crosslinking system based on a polynitrone compound.

It has been known and customary for many years to use tires and rubber compositions whose elastomeric matrix is crosslinked with sulfur, this crosslinking being then called vulcanization.

The conventional vulcanization system combines sulfur and at least one vulcanization accelerator.

However, it is known that such a system penalizes the implementation of the composition before cooking by the roasting phenomenon. The roasting phenomenon rapidly leads, during the preparation of the rubber compositions, to premature vulcanizations, to very high viscosities in the green state, and therefore to rubber compositions that are practically impossible to work and to implement industrially. .

In order to overcome these disadvantages, the vulcanization systems have been progressively improved, together with the methods for preparing rubber compositions.

Thus, in order to vulcanize the diene elastomers, a relatively complex vulcanization system is used which, in addition to sulfur or a sulfur-donor agent, is a primary vulcanization accelerator, such as benzothiazole ring sulfenamides, various secondary accelerators or activators. vulcanization, especially zinc derivatives such as zinc oxide (ZnO) alone or used with fatty acids, as well as possibly vulcanization retarders. There is therefore a need to simplify the rubber compositions and their preparation, and to have cross-linking systems that perform as well as vulcanization, in particular crosslinking systems which make it possible to limit or even avoid the roasting phenomenon and which lead to rheological and dynamic properties acceptable and equivalent to those obtained for compositions based on vulcanization systems.

Applicants have discovered that polynitrone compounds can be used as a crosslinking agent to replace vulcanization systems for the manufacture of tire tread rubber compositions.

The object of the invention is therefore a tire tread comprising a rubber composition based on one or more diene elastomers, one or more reinforcing fillers and a crosslinking system, characterized in that the system crosslinking agent comprises one or more polynitrone compounds chosen from compounds of formula

or

R 1 is a C 1 -C 25 aliphatic or C 6 -C 25 aromatic, preferably aromatic, C 6 -C 25 aliphatic hydrocarbon group, R 1 being optionally interrupted by one or more heteroatoms,

R2 is a C 1 - C 25 or aromatic C 6 - C 25 aliphatic hydrocarbon group, preferably C 6 -C 25 aromatic, R2 being optionally interrupted by one or more heteroatoms,

n is an integer greater than or equal to 2,

the crosslinking system being free of molecular sulfur or containing less than 0.1 phr. By molecular sulfur is meant any molecule consisting solely of sulfur. For example cyclooctasulfur S ₈ may be mentioned.

By the term "composition-based" is meant a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of or intended to react with one another, less in part, during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization.

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).

As explained above, the rubber composition of the tread according to the invention is based on one or more diene elastomers.

By diene elastomer, it is to be understood in a known manner (is meant one or more) elastomer derived at least in part (ie, a homopolymer or a copolymer) of monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or not ). More particularly, diene elastomer is any homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 12 carbon atoms, or 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. In the case of copolymers, these contain from 20% to 99% by weight of diene units, and from 1 to 80% by weight of vinylaromatic units.

As conjugated dienes that can be used in the process according to the invention, 1,3-butadiene, 2-methyl-1,3-butadiene and 2,3-di (C ₁ -C ₅ ) alkyl-1 are especially suitable. 3-butadiene such for example 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl 1,3-butadiene, phenyl-1,3-butadiene, 1,3-pentadiene and 2,4-hexadiene, etc.

As vinylaromatic compounds are especially suitable styrene, ortho-, meta, para-methylstyrene, the commercial mixture "vinylto luene", para-tert-butylstyrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene, etc.

The diene elastomer of the composition in accordance with the invention is preferably chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR) and butadiene copolymers. , in particular copolymers of butadiene and a vinyl aromatic monomer, isoprene copolymers and mixtures of these elastomers.

Polybutadienes and butadiene copolymers are particularly preferred. Such copolymers are more particularly butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), copolymers of isoprene-styrene (SIR) and copolymers of isoprene-butadiene-styrene (SBIR). .

Among these copolymers, butadiene-styrene copolymers (SBR) are particularly preferred.

The rubber composition of the tread according to the invention comprises, in addition to at least one elastomeric matrix as described above, at least one reinforcing filler.

It is possible to use any type of reinforcing filler known for its ability to reinforce a rubber composition that can be used for manufacturing tire treads, for example carbon black, a reinforcing inorganic filler such as silica with which it is associated with known manner a coupling agent, or a mixture of these two types of load.

Suitable carbon blacks are all carbon blacks, used individually or in the form of mixtures, especially blacks of the HAF, ISAF, SAF type conventionally used in treads of tires (so-called pneumatic grade blacks). Among the latter, mention will be made more particularly of reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), for example blacks NI 15, N 134, N 234, N 326, N 30 O, N 339, N 347, N 375. The carbon blacks could for example be already incorporated into the isoprene elastomer in the form of a masterbatch (see for example WO 97/36724 or WO 99/16600).

As reinforcing inorganic filler, is meant by the present application, by definition, any inorganic or inorganic filler whatever its color and its origin (natural or synthetic), capable of reinforcing on its own, without any other means than an agent intermediate coupling, a rubber composition for the manufacture of tires; 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, in particular of silica (SiO 2), or of the aluminous type, in particular alumina (Al 2 O 3). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or 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 m2 / g. Mention may also be made of mineral fillers of the aluminous type, in particular alumina (Al 2 O 3) or aluminum (oxide) hydroxides, or reinforcing titanium oxides, for example described in US 6,610,261 and US 6,747. 087. Reinforcing fillers of another nature, in particular carbon black, are also suitable as reinforcing fillers, provided that these reinforcing fillers are covered with a siliceous layer, or else comprise on their surface functional sites, in particular hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. By way of example, mention may be made, for example, of carbon blacks for pneumatics as described for example in WO 96/37547, WO 99/28380.

The physical state in which the reinforcing inorganic filler is present is indifferent whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing fillers, in particular highly dispersible siliceous fillers as described above.

Preferably, the level of total reinforcing filler

(carbon black and / or other reinforcing filler such as silica) is between 10 and 200 phr, more preferably between 30 and 150 phr, and even more preferably between 50 and 130 phr, the optimum being in a known manner different according to the particular applications targeted.

According to a variant of the invention, the reinforcing filler is predominantly other than carbon black, that is to say it comprises more than 50% by weight of the total weight of the filler, of one or more fillers other than carbon black, especially a reinforcing inorganic filler such as silica, or it consists exclusively of such a filler.

According to this variant, when carbon black is also present, it may be used at a level of less than 20 phr, more preferably less than 10 phr (for example between 0.5 and 20 phr, in particular from 1 to 10 phr).

According to another variant of the invention, a reinforcing filler comprising predominantly carbon black and optionally silica or other inorganic filler is used.

When the reinforcing filler comprises a filler requiring the use of a coupling agent to establish the bond between the filler and the elastomer, the rubber composition of the tread according to the invention further comprises, in a conventional manner, an agent capable of effectively providing this link. When the silica is present in the composition as a reinforcing filler, may be used as coupling agents organosilanes, including polysulfurized alkoxysilanes or mercaptosilanes, or at least bifunctional polyorganosiloxanes.

In the composition of the tread according to the invention, the level of coupling agent is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Its rate is preferably between 0, 5 and 12 phr. The presence of the coupling agent depends on that of the reinforcing inorganic filler. Its rate is easily adjusted by the skilled person according to the rate of this charge; it is typically in the range of 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler other than carbon black.

The rubber composition of the tread according to the invention may also contain, in addition to the coupling agents, coupling activators, charge-recovery agents or, more generally, processing aid agents capable of in a known manner, by improving the dispersion of the filler in the rubber matrix and by lowering the viscosity of the composition, to improve its ability to use in the green state, these agents being for example hydrolysable silanes such as alkylalkoxysilanes, polyols, polyethers, primary, secondary or tertiary amines, hydroxylated or hydrolysable polyorganosiloxanes.

The rubber composition of the tread according to the invention may also contain reinforcing organic fillers which may replace all or part of the carbon blacks or other reinforcing inorganic fillers described above. Examples of reinforcing organic fillers that may be mentioned are functionalized polyvinyl organic fillers as described in applications WO-A-2006/069792, WO-A-2006/069793, WO-A-2008/003434 and WO-A- 2008/003435.

As explained above, the tread rubber composition of the invention comprises a crosslinking system. By crosslinking system is meant the chemical agent (s) introduced during the so-called "productive" phase of the preparation of the compositions as described later, which allow the elastomeric chains to bond together forming a three-dimensional network. This is the crosslinking phenomenon.

The crosslinking system used according to the invention comprises one or more polynitrone compounds chosen from compounds of formula

or

R1 is a C1-C25 aliphatic or C6-C25 aromatic, preferably aromatic, C6-C25 hydrocarbon group, R1 being optionally interrupted by one or more heteroatoms,

R2 is a C1-C25 or aromatic C6-C25 aliphatic hydrocarbon group, preferably C6-C25 aromatic, R2 being optionally interrupted by one or more heteroatoms,

n is an integer greater than or equal to 2.

Preferably, R 1 is a polyvalent radical chosen from linear, branched or cyclic alk-poly-yl radicals, aralk-poly-yl radicals and ar-poly-yl radicals.

By alk-poly-yl radical is meant a polyvalent radical with n valences, from the removal of n hydrogen atoms on n carbon atoms different from a saturated hydrocarbon, n being as defined above.

By ar-poly-yl radical is meant a polyvalent radical with n valences, from the removal of n hydrogen atoms on n carbon atoms different from an aromatic hydrocarbon, n being as defined above. By aralk-poly-yl radical is meant a polyvalent radical with n valences, resulting from the removal of n hydrogen atoms on n carbon atoms different from a hydrocarbon composed of one or more aromatic nuclei and a or more saturated hydrocarbon, n being as defined above.

Preferably, R ₂ is selected from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups.

Preferably, n is 2 or 3 and more preferably 2.

When n is 2, R 1 is then an alkylene, aralkylene or arylene radical. When n is 3, R 1 is then an alk-tri-yl, aralk-tri-yl or ar-tri-yl radical.

A particularly preferred polynitrone compound is le, Ν'- [benzene-1,3-diyldimethylidene] bis (N-phenylamine oxide). The preparation of this compound is described in the document Makromol.Chem. 1967, 108, 292-5.

The at least one polynitrone compound represents from 0.1 to 20 phr, preferably from 0.1 to 10 phr, more preferably from 0.1 to 5 phr, more preferably from 0.2 to 5 phr (parts by weight per hundred diene elastomer).

Nitrones in general and their synthesis are described in Torsesell, K. B. G. "Nitrile Oxides, Nitrones and Nitronates in Organic Synthesis", New York: VCH Publications, 1988.

Polynitrones in particular and their synthesis are described in WO2009136920.

According to the invention, the crosslinking system is devoid of molecular sulfur or contains less than 0.1 phr.

In addition to the molecular sulfur of the crosslinking system, a quantity of sulfur, molecular or otherwise, not part of the crosslinking system, is potentially present in the composition of the tread according to the invention. This sulfur can come from other ingredients of the composition, introduced in the so-called "non-organic" phase. the preparation as described later. For example, it may be carbon black or the coupling agent as described above. In the composition of the tread of the invention, the level of sulfur in the composition is preferably less than 2 phr.

The crosslinking system used in the composition of the tread according to the invention makes it possible to simplify the formulation of the composition, in particular by avoiding the drawbacks related to the presence of molecular weight sulfur in conventional vulcanization systems.

Preferably, the crosslinking system of the rubber composition of the tread according to the invention is free of molecular sulfur or comprises less than 0.05 phr.

Preferably, the system for crosslinking the composition of the tread according to the invention does not comprise a primary or secondary vulcanization accelerator or vulcanization activator system.

The rubber composition used according to the invention may also comprise all or part of the usual additives normally used in elastomer compositions intended for the production of treads, for example plasticizers or extension oils, which the latter are of aromatic or non-aromatic nature, pigments, protective agents such as anti-ozone waxes (such as C32 ST Ozone wax), chemical antiozonants, anti-oxidants (such as 6-paraphenylenediamine), anti-fatigue agents, reinforcing resins, acceptors (for example phenolic resin novo lacquer) or methylene donors (for example HMT or H3M) as described for example in application WO 02/10269.

Preferably, the composition according to the invention comprises, as preferential non-aromatic or very weakly aromatic plasticizing agent, at least one compound chosen from the group consisting of naphthenic, paraffinic, MES, TDAE, and ester oils. especially trio leates) of glycerol, plasticizing resins hydrocarbon compounds having a high Tg preferably greater than 30 ° C, and mixtures of such compounds.

The composition used according to the invention may also contain, in addition to the coupling agents, activators for coupling the reinforcing inorganic filler or, more generally, processing aid agents that are capable in a known manner, by means of an improvement of the dispersion of the inorganic filler in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green state, these agents being, for example, hydrolysable silanes such as alkylalkoxysilanes; (In particular alkyltriethoxysilanes), polyols, polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialkano-amines), hydroxylated or hydrolyzable POSs, for example α, ω-dihydroxy polyorganosiloxanes (in particular α, ω-dihydroxy-polydimethylsiloxanes), fatty acids such as, for example, stearic acid.

The rubber composition used according to the invention is manufactured in appropriate mixers, generally using two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or thermo-mechanical mixing (sometimes qualified of "nonproductive" phase) at a high temperature, up to a maximum temperature of between 1 10 ° C and 190 ° C, preferably between 1 15 ° C and 170 ° C and still more preferably between 1 15 ° C and 160 ° C, followed by a second phase of mechanical work (sometimes referred to as a "productive" phase) at a lower temperature, typically below 1 10 ° C, for example between 30 ° C and 100 ° C, finishing phase at during which the crosslinking system can be incorporated.

The invention therefore also relates to a method for preparing a rubber composition for the production of a tread according to the invention, comprising the following steps: - Incorporating into said diene elastomers or, in a first step, the reinforcing fillers or by thermomechanically kneading the whole, in one or more times, to reach a maximum temperature between 1 1 0 ° C and 190 ° C;

- Then incorporate, in a second step, the crosslinking system and knead the whole to a maximum temperature of less than 1 10 ° C, preferably less than 80 ° C.

According to a preferred embodiment of the invention, all the basic constituents of the composition used according to the invention, with the exception of the crosslinking system, namely the reinforcing fillers or the coupling agent, the case optionally, are intimately incorporated, by kneading, the diene elastomer or the diene elastomers during the first so-called non-productive phase, that is to say that is introduced into the mixer and that the at least one of these basic constituents is kneaded thermomechanically, in one or more steps, until the maximum temperature is reached between 1 ° C. and 190 ° C., preferably between 1 ° C. and 170 ° C. and more preferably still between 1 ° C and 160 ° C.

The two phases can be carried out consecutively on the same mixer or be separated by a cooling step at a temperature below 100 ° C, the last step then being performed on a second mixer.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step in the course of which all the necessary constituents, the possible stabilizing agents, are introduced into a suitable mixer such as a conventional internal mixer. implementation complementary and other various additives, with the exception of the crosslinking system. The total mixing time in this non-productive phase is preferably between 1 and 15 minutes. After cooling the mixture thus obtained during the first non-productive phase, the low temperature crosslinking system is then incorporated, generally in an external mixer such as a roll mixer; the whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 min.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded in the form of a rubber profile that can be used as a tire tread for passenger car or truck.

Finally, the invention is obj and a tire comprising a tread as defined above.

The invention is illustrated by the following examples.

Examples Measurements and tests used

Traction tests

These tensile 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 second elongation is measured (i.e., after a cycle of accommo dation at the extension rate provided for the measurement itself. same) the nominal secant modulus (or apparent stress, in MPa) at 100% elongation (denoted MA 100) and at 300% elongation (denoted MA300).

The breaking stresses (in MPa) and the elongations at break (in%) are measured at 23 ° C ± 2 ° C, and under normal hygrometry conditions (50 ± 5% relative humidity).

Dynamic Properties

The dynamic properties G * and tan (δ) max are measured on a viscoanalyzer (Metravib VA4000) according to the ASTM D 5992 standard. 96. The response of a sample of vulcanized composition (cylindrical specimen with a thickness of 2 mm and a section thickness of 79 mm ² ) is recorded, subjected to a sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, under the conditions normal temperature (40 ° C) according to ASTM D 1349-99. A strain amplitude sweep is carried out from 0.1% to 100% peak-to-peak (forward cycle), then from 100% to 0.1% peak-to-peak (return cycle). The results exploited are the complex dynamic shear modulus (G *) and the loss factor tan (δ). For the return cycle, the maximum value of tan (δ) observed, denoted tan (δ) max, as well as the complex modulus difference (AG *) between the values at 0.1% and at 100% deformation are indicated. (Payne effect).

This value is representative of the hysteresis of the material and in this case of the rolling resistance: the lower the value of tan (δ) max, the lower the rolling resistance. The values of G * measured at 40 ° C. are representative of the stiffness, that is to say of the resistance to deformation: the higher the value of G *, the greater the rigidity of the material, and therefore the strength high wear. Preparation of compositions

The following tests are carried out in the following manner: the diene elastomer (s), the reinforcing filler or fillers, are introduced into an internal 70% filled mixer whose initial tank temperature is approximately 90 ° C. the optional coupling agent and then, after one to two minutes of mixing, the various other ingredients with the exception of the crosslinking system (polynitrone compound) or the vulcanization system (sulfur and sulfenamide accelerator). Thermomechanical work (non-productive phase) is then carried out in one step (total mixing time equal to about 5 minutes), until a maximum "falling" temperature of about 160 ° C. is reached. The mixture thus obtained is recovered, it is cooled and then the crosslinking system (polynitrone compound) or the vulcanization system (sulfur and accelerator are added sulfenamide) on an external mixer (homo-finisher) at 70 ° C, mixing the whole (productive phase) for about 5 to 6 min.

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties, or in the form of profiles that can be used directly, after cutting and / or or assembly to the desired dimensions, for example as semi-finished products for tires, in particular as treads of tires.

Example 1

The object of this example is to compare the properties of a rubber composition comprising a dinitrone crosslinking system (composition A), usable for the manufacture of a tire tread, with the properties of compositions. comparative rubber compounds comprising a sulfur, accelerator, zinc oxide and stearic acid vulcanization system (compositions C-1 and C-2).

The formulations of the compositions are given in Table 1. The amounts are expressed in parts per 100 parts by weight of elastomer (phr).

Table 1

Composition C-1 to C-2

SBR (1) 100.00 100.00 100.00

Silica (2) 70,00 70,00 70,00

Silane (3) 7.00 7.00 7.00

ZnO (4) 1, 50 - 1, 50

Stearic acid (5) 2.00 - 2.00

Antioxidant (6) 2.00 - 2.00 Dinitrone (7) - 0.92

Sulfur 1,00 - 1,20

Accelerator (8) 1.58 - 1.90

(1) SBR prepared by anionic polymerization (containing 25% by weight of styrene and 58% by weight of 1,2-butadiene unit);

(2) silica "ZEOSIL 1165 MP" from Rhodia in the form of microbeads (BET and CTAB: about 150-160 m2 / g);

(3) TESPT ("SI69" from Degussa);

(4) zinc oxide (industrial grade - Umicore company);

(5) stearin ("Pristerene 4931" - Uniqema company);

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

(7) N, N '- [benzene-1,3-diyldimethylidene] bis (N-phenylamine oxide); CAS RN: 15351-52-7

(8) CBS: N-cyclohexyl-2-benzothiazyl sulfenamide ("Santocure CBS" from Flexsys);

The extensometry properties at 23 ° C in the crosslinked state are given in Table 2.

Table 2

NM: not measurable Composition A according to the invention, crosslinked with a dinitrone compound, has properties similar to those of comparative vulcanized compositions C-1 and C-2, while having a greatly simplified formula.

Example 2

The objective of this example is to compare the properties of rubber compositions comprising a dinitrone-based crosslinking system (composition B-1 and B-2), usable for the manufacture of a tire tread, with the properties of comparative rubber compositions comprising a sulfur, accelerator, zinc oxide and stearic acid vulcanization system (compositions C-3 and C-4).

The formulations of the compositions are given in Table 3. The amounts are expressed in parts per 100 parts by weight of elastomer (phr).

Table 3

Composition C-3 C-4 B-1 B-2

S B R (1) 100.00 100.00 100.00 1 00.00

Carbon black

54.00 54.00 54.00 54.00

(2)

ZnO (3) 2.00 2.00

Stearic acid

2.70 2.70

(4)

Accelerator (5) 0.60 0, 80

Sulfur 0.60 O. N / A

Dinitrone (6) 1, 00 2, 00 (1) SBR prepared by anionic polymerization (containing 26.5% by weight of styrene and 24% by weight of 1,2-butadiene unit);

(2) Carbon black N234;

(3) zinc oxide (industrial grade - Umicore company);

(4) stearin ("Pristerene 4931" - Uniqema company);

(5) CBS: N-cyclohexyl-2-benzothiazyl sulfenamide ("Santocure CBS" from Flexsys)

(6) N, N '- [benzene-1,3-diyldimethylidene] bis (N-phenylamine oxide); CAS RN: 15351-52-7

The rheological and dynamic properties at 23 ° C in the crosslinked state are given in Table 4.

Table 4

The compositions B-1 and B-2 according to the invention, crosslinked with a dinitrone compound, have properties similar to those of the comparative vulcanized compositions C-1, C-2 and C-3 while having a greatly simplified formula. In addition, the compositions B-1 and B-2 according to the invention have a reduced hysteresis level compared to the comparative compositions.

Claims

1. Tire tread comprising a rubber composition based on one or more diene elastomers, one or more reinforcing fillers and a crosslinking system, characterized in that the crosslinking system comprises one or more selected polynitrone compounds among the compounds of formula

or

n is an integer greater than or equal to 2,

the crosslinking system being free of molecular sulfur or containing less than 0.1 phr.

2. A tread according to claim 1, characterized in that R 1 is a polyvalent radical chosen from linear, branched or cyclic alk-poly-l radicals, aralk-poly-yl radicals, and ar-poly-radicals. yl.

3. A tread according to claim 1 or 2, characterized in that R2 is selected from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups.

4. Tread according to any one of the preceding claims, characterized in that the polynitrone compound is N, N'- [benzene-1,3-diyldi (Z) methylylidene] bis (N-phenylamine oxide).

5. Tread according to any one of the preceding claims, characterized in that said polynitrone compound (s) represent from 0.1 to 20 phr, preferably from 0.1 to 10 phr, more preferably from 0.1 to 10 phr. 5 phr, more preferably 0.2 to 5 phr (parts by weight per cent of diene elastomer).

6. Tread according to any one of the preceding claims, characterized in that the crosslinking system is free of molecular sulfur or comprises less than 0.05 phr.

7. Tread according to any one of the preceding claims, characterized in that the diene elastomer or elastomers are selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, copolymers d isoprene and mixtures of these elastomers.

8. tread according to any one of the preceding claims, characterized in that the reinforcing fillers or fillers are selected from silica, carbon black and mixtures thereof, preferably carbon black.

9. tread according to any one of the preceding claims, characterized in that the reinforcing fillers or fillers are present at a rate between 10 and 200 phr, preferably between 30 and 150 phr, more preferably between 50 and 130 phr.

10. A tire characterized in that it comprises a tread as defined in any one of the preceding claims.

1 1. Process for preparing a rubber composition for the manufacture of a tread as defined in any one of the preceding claims, characterized in that it comprises the following steps: - Incorporating into said diene elastomers or, in a first step, the reinforcing fillers or by thermomechanically kneading the whole, in one or more times, to reach a maximum temperature between 1 1 0 ° C and 190 ° C;

- Then incorporate, in a second step, the crosslinking system as defined in any one of claims 1 to 6 and knead the whole to a maximum temperature of less than 1 10 ° C, preferably less than 80 ° C.