WO2020212184A1

WO2020212184A1 - Rubber composition

Info

Publication number: WO2020212184A1
Application number: PCT/EP2020/059778
Authority: WO
Inventors: Emma MORESO; Kahina MAMMERI
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2019-04-16
Filing date: 2020-04-06
Publication date: 2020-10-22
Also published as: CA3131172A1; FR3095208A1; FR3095208B1; EP3956156A1

Abstract

The invention relates to a rubber composition which comprises a diene elastomer, a reinforcing filler comprising more than 50% by weight of a silica, a crosslinking system, a modifying agent bearing an N-substituted imidazole function and a unit containing a group that is reactive with respect to the diene elastomer and if necessary a silane coupling agent to bond the diene elastomer to the silica, the total amount of modifying agent and silane coupling agent represents more than 5% by weight of the amount of silica, the ratio of the amount of modifying agent to the total amount of modifying agent and silane coupling agent is greater than 0.5, the amounts being expressed in phr.

Description

Rubber composition

The field of the present invention is that of diene rubber compositions predominantly comprising a silica and particularly intended for use in a tire.

In rubber compositions comprising a diene elastomer and predominantly a silica, it is known to use coupling agents to bind the diene elastomer to the silica. Coupling agents are compounds which typically have one group reactive towards the diene elastomer and another group reactive towards silica. The coupling agents traditionally used in diene rubber compositions for tires are silanes, in particular alkoxysilanes having as a group reactive with respect to the diene elastomer a polysulfide chain or a protected thiol function. With the use of silane coupling agents, the rubber compositions mainly comprising a silica can compete from the point of view of reinforcing properties with the compositions mainly comprising a carbon black. Since they also turn out to be less hysteretic than the compositions reinforced with carbon black, they therefore give the tire much better performance with respect to rolling resistance.

To further reduce the hysteretic properties of compositions comprising a diene elastomer and a silica, it is known to use compounds which exhibit a certain reactivity with silica while being devoid of reactive functions with respect to diene elastomers. These compounds are also known under the name of coating agent. The best known are the alkoxysilanes having an alkyl chain, such as triethoxyoctylsilane known under the trade name “Dynasylan Octeo”. The replacement of all or part of the silane coupling agent by a covering agent such as triethoxyoctylsilane results in a decrease in the hysteresis of the rubber composition with an increase in the elongations at break, but inevitably it is also observed a decrease in stiffness at medium deformations (50-100%).

However, it is also desirable to have low hysteretic rubber compositions which have not only high rigidity at medium deformations but also high elongation at break or high tensile stress. Now, those skilled in the art know that when they increase the rubber / filler bond density or the crosslinking density to increase the rigidity at medium deformation, a decrease in the elongation at break is observed. Conversely, a decrease in the rubber / filler bond density or in the crosslinking density is accompanied by an increase in the elongation at break, but also by a decrease in the stiffness at medium deformations. This is what happens when all or part of the coupling agent is replaced by a covering agent. The Applicant, continuing its efforts, has discovered a new composition which makes it possible both to reduce the amount of silane coupling agent, even to eliminate it, and to increase the rigidity at medium deformations without reducing the breaking properties.

Thus a first object of the invention is a rubber composition which comprises a diene elastomer, a reinforcing filler comprising more than 50% by mass of a silica, a crosslinking system, a modifying agent and, where appropriate, a conditioning agent. silane coupling to link the diene elastomer to silica, the modifying agent carrying an N-substituted imidazole function and a unit containing a group reactive with respect to the diene elastomer, characterized in that the total amount of the modifier and the silane coupling agent represents more than 5% by mass of the amount of silica, the ratio between the amount of the modifier and the total amount of the modifier and the silane coupling agent is greater than 0.5, the amounts being expressed in parts by weight per hundred parts of elastomer, phr.

The invention also relates to a semi-finished article which comprises a rubber composition according to the invention.

The invention also relates to a tire which comprises a rubber composition according to the invention or a semi-finished article according to the invention.

I. DETAILED DESCRIPTION OF THE INVENTION

Any interval of values designated by the expression "between a and b" represents the range of values greater than "a" and less than "b" (that is to say bounds a and b excluded) while any interval of values designated by the expression "from a to b" signify the range of values going from "a" to "b" (that is to say including the strict limits a and b).

The compounds mentioned in the description can be of fossil origin or biobased. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass.

An essential characteristic of the rubber composition in accordance with the invention is that it contains a diene elastomer. By elastomer (or indiscriminately rubber) "diene", should be understood in a known manner one (or more) elastomer constituted at least in part (ie, a homopolymer or a copolymer) of diene monomer units (monomers bearing two carbon double bonds -carbon, conjugated or not). The term "diene elastomer capable of being used in the compositions in accordance with the invention" particularly means any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms or any copolymer of a diene, conjugated or no, 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 18 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 vinyl aromatic compounds having from 8 to 20 carbon atoms and aliphatic α-monoolefins having from 3 to 12 carbon atoms.

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

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

Preferably, the diene elastomer useful for the purposes of the invention is a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene. More preferably, the diene elastomer useful for the purposes of the invention is a polybutadiene, a polyisoprene, a butadiene copolymer, an isoprene copolymer or a mixture of these elastomers.

An essential characteristic of the rubber composition according to the invention is to contain a modifying agent carrying an N-substituted imidazole function and a unit containing a group reactive with respect to the diene elastomer. By definition, the amount of the modifying agent in the rubber composition is greater than 0 phr, parts by weight per hundred parts of elastomer. The group reactive with the diene elastomer and constituting the modifying agent is typically a group which reacts with the carbon-carbon double bonds of the diene elastomer. The modifier is intended to modify the diene elastomer. Preferably, the group reactive with respect to the diene elastomer and constituting the modifying agent, hereinafter designated the group reactive with respect to the diene elastomer, is a dipole, in particular those containing a nitrogen atom. More preferably, the group reactive with respect to the diene elastomer is a nitrile oxide, a nitrone or a nitrile imine. The group reactive with respect to the diene elastomer is very preferably a nitrile oxide.

According to a particular embodiment of the invention, the modifying agent is a 1,3-dipolar compound which is an aromatic nitrile monooxide, compound comprising a benzene ring substituted by a nitrile oxide dipole and by a group containing the N-substituted imidazole function. The benzene nucleus of the aromatic nitrile monooxide is preferentially substituted ortho to the dipole.

According to a particularly preferred embodiment of the invention, the 1,3-dipolar compound contains a unit of formula (I) in which R 1 represents the dipole oxide of nitrile, one of the symbols R ₂ to R ₆ represents a saturated group having 1 to 6 carbon atoms and covalently bonded to one of the nitrogen atoms of the 5-membered ring of the imidazole function, the other symbols, identical or different, representing a hydrogen atom or a substituent. The substituent is preferably an alkyl having 1 to 3 carbon atoms. The saturated group is preferably an alkanediyl. Preferably, the saturated group contains 1 to 3 carbon atoms. Preferably, the saturated group is methanediyl.

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The imidazole function useful for the purposes of the invention is an N-substituted imidazole function, which implies that the imidazole function lacks an NH bond. Preferably, the N-substituted imidazole function useful for the purposes of the invention is a group of formula (II) in which the symbol Yi denotes an attachment to the group reactive with respect to the diene elastomer, the symbol Y ₂ represents a hydrogen atom or an alkyl having 1 to 6 carbon atoms, the symbols Y ₃ and Y ₄ are each a hydrogen atom.

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The alkyl represented by Y ₂ preferably contains 1 to B carbon atoms, very preferably a carbon atom in which case the alkyl represented by Y ₂ is methyl.

Another characteristic of the rubber composition in accordance with the invention is that it contains a reinforcing filler. The level of reinforcing filler in the rubber composition is preferably greater than or equal to 20 phr and less than or equal to 200 phr, very preferably greater than or equal to 25 phr and less than or equal to 160 phr. The reinforcing filler useful for the purposes of the invention comprises a silica. The silica represents more than 50% by mass of the reinforcing filler. Preferably, the silica represents more than 85% by weight of the reinforcing filler.

The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET specific surface area as well. a CTAB specific surface both less than 450 m ² / g, preferably within a range ranging from 30 to 400 m ² / g, in particular from 60 to 300 m ² / g. In the present disclosure, the BET specific 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 precisely according to a method adapted from standard NF ISO 5794-1, annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160 ° C - relative pressure range p / in: 0.05 to 0.17] The CTAB specific surface area 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 “outer” surface of the reinforcing filler.

Any type of precipitated silica can be used, in particular highly dispersible precipitated silicas (called “HDS” for “highly dispersible” or “highly dispersible silica”). These precipitated silicas, which may or may not be highly dispersible, are well known to those skilled in the art. Mention may be made, for example, of the silicas described in applications W003 / 016215-A1 and W003 / 016387-A1. Among the commercial HDS silicas, it is possible in particular to use the silicas "Ultrasil ^® 5000GR", "Ultrasil ^® 7000GR" from the company Evonik, the silicas "Zeosil ^® 1085GR", "Zeosil ^® 1115 MP", "Zeosil ^® 1165MP", " Zeosil ^® Premium 200MP, "" Zeosil HRS ^® 1200 MP "from the Solvay Company. As silica non HDS, the following commercial silicas can be used: silicas "Ultrasil ^® VN2GR", "Ultrasil ^® VN3GR" of Evonik, silica "Zeosil ^® 175gr""from Solvay, silicas" Hi -Sil EZ120G (- D) ”,“ Hi-Sil EZ160G (-D) ”,“ Hi-Sil EZ200G (-D) ”,“ Hi-Sil 243LD ”,“ Hi-Sil 210 ”,“ Hi-Sil HDP 320G ”from PPG.

The reinforcing filler may comprise any type of so-called reinforcing filler other than silica, known for its capacity to reinforce a rubber composition which can be used in particular for the manufacture of tires, for example a carbon black. Suitable carbon blacks are all carbon blacks, in particular the blacks conventionally used in tires or their treads. Among the latter, there will be mentioned more particularly the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (grades ASTM D-1765-2017), 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 available commercially, or in any other form, for example as a support for some of the rubber additives used.

Preferably, the carbon black is used at a rate less than or equal to 20 phr, more preferably less than or equal to 10 phr (for example the level of carbon black may be in a range ranging from 0.5 to 20 phr , in particular ranging from 1 to 10 pce). Advantageously, the level of carbon black in the rubber composition is less than or equal to 5 phr. In the intervals indicated, the properties coloring (black pigmentation agent) and anti-UV of carbon blacks, without furthermore penalizing the typical performances provided by silica.

To couple the silica to the diene elastomer, it is well known to use an at least bifunctional coupling agent (or binding agent) intended to ensure a sufficient connection, of a chemical and / or physical nature, between the silica (surface of its particles) and the elastomer, in which case the rubber composition comprises a coupling agent to bind the silica to the elastomer. The coupling agent is a silane. 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 silica and a second functional group capable of interacting with the elastomer.

Polysulfurized silanes are used in particular, called “symmetrical” or “asymmetrical” according to their particular structure, as described for example in applications W003 / 002648-A1 (or US2005 / 016651-A1) and W003 / 002649-A1 (or US2005 / 016650-A1). Polysulfurized silanes corresponding to the following general formula (III) are suitable in particular, without the definition below being limiting:

Z - A - S - A - Z (111) in which:

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

- the symbols A, which are identical or different, represent a divalent hydrocarbon radical (preferably a C 1 -C ₈ alkylene group or a C ₆ -Ci ₂ arylene group, more particularly a C ₁ -C ₀ alkylene, in particular an alkylene C ₁ -C ₄ , in particular propylene);

- the Z symbols, identical or different, correspond to one of the three formulas below:

in which :

- the R ^radicals, substituted or unsubstituted, identical or different, represent an alkyl group _Ci-8 cycloalkyl, C ₅ -C ₈ aryl or C ₆ -C ₈ (preferably C ₁ -C ₆ alkyl groups, cyclohexyl or phenyl, in particular C ₁ -C ₄ alkyl groups, more particularly methyl and / or ethyl).

- the radicals R ^b, substituted or unsubstituted, identical or different, represent an alkoxyl group Ci-Ci ₈ cycloalkoxy group or a C ₅ -C ₈ (preferably a group selected from alkoxyls -C ₈ and C ₅ -C ₈ cycloalkoxyls, plus more preferably a group chosen from C ₁ -C ₄ alkoxyls, in particular methoxyl and ethoxyl), or a hydroxyl group, or such that 2 Rb radicals represent a C ₃ -Ci ₈ dialkoxyl group.

In the case of a mixture of polysulfurized alkoxysilanes corresponding to formula (III) above, in particular of the usual mixtures available commercially, the average value of the “x” is a fractional number preferably included in a range ranging from 2 to 5, more preferably close to 4.

By way of examples of polysulphurized silanes, mention will be made more particularly of polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis- ((Ci-C ₄ ) -alkyl (Ci-C ₄ ) silyl-alkyl (Ci-C _4). )), such as, for example, bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) polysulfides. Among these compounds, use is made in particular of bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, of formula [(C ₂ H ₅ 0) ₃ Si (CH ₂ ) ₃ S ₂ ] ₂ marketed under the name "Si69" by the company Evonik or bis- (triethoxysilylpropyl) disulfide, abbreviated TESPD, of formula [(C ₂ H ₅ 0) ₃ Si (CH ₂ ) ₃ S] ₂ marketed under the name “Si75” by the company Evonik. As preferred examples, mention will also be made of bis- (monoalkoxyl (Ci-C ₄ ) -dialkyl (Ci-C ₄ ) silylpropyl) polysulfides (in particular disulfides, trisulfides or tetrasulfides), more particularly bis-monoethoxydimethylsilylpropyl tetrasulfide such as as described in the aforementioned patent application WO02 / 083782-A1 (or US7217751-B2).

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

According to one embodiment of the invention, the rubber composition contains a silane coupling agent, in which case the amount of the silane coupling agent in the rubber composition in accordance with the invention is greater than 0 phr. According to this embodiment of the invention, the amount of the coupling agent is such that the ratio between the amount of the modifying agent and the total amount of the modifying agent and of the silane coupling agent is greater than 0.5, the quantities being expressed in phr. The ratio is preferably greater than 0.6, more preferably greater than 0.75. The total amount of modifier and silane coupling agent corresponds to the sum of the amount of the coupling agent and the amount of the modifier in the rubber composition, the amounts being expressed in pce.

According to another embodiment of the invention, the rubber composition is devoid of a silane coupling agent, in which case the amount of the silane coupling agent in the rubber composition in accordance with the invention is equal to 0 phr. . It follows that the ratio between the amount of modifying agent and the total amount of modifying agent and silane coupling agent is equal to 1. Preferably, the ratio between the amount of modifier and the total amount of modifier and silane coupling agent is 1. In the rubber composition in accordance with the invention, the total amount of the modifying agent and of the silane coupling agent represents more than 5% by mass of the amount of silica, the amounts being expressed in phr. In other words, the ratio between the sum of the amount of the modifying agent expressed in phr and the amount of the silane coupling agent expressed in phr and the amount of silica expressed in phr is greater than 0.05. Preferably, the total amount of the modifying agent and of the silane coupling agent represents more than 8% by mass of the amount of silica, the amounts being expressed in phr, i.e. a ratio between the sum of the amount of the modifying agent expressed in phr and of the quantity of silane coupling agent expressed in phr and the quantity of silica expressed in phr greater than 0.08. According to any one of the embodiments of the invention, the total amount of the modifying agent and of the silane coupling agent preferably represents less than 50% by mass of the amount of silica, the amounts being expressed in pce.

Another essential characteristic of the rubber composition in accordance with the invention is that it contains a crosslinking system. The crosslinking system is preferably a vulcanization system, that is to say based on sulfur and on a primary vulcanization accelerator. The sulfur is typically supplied in the form of molecular sulfur or a sulfur donor agent, preferably in molecular form. Sulfur in molecular form is also referred to as molecular sulfur. The term “sulfur donor” is understood to mean any compound which releases sulfur atoms, combined or not in the form of a polysulphide chain, capable of being inserted into the polysulphide chains formed during vulcanization and bridging the elastomer chains. To the vulcanization system are added, incorporated during the first non-productive phase and / or during the productive phase, various secondary accelerators or known vulcanization activators such as zinc oxide, stearic acid, guanide derivatives ( in particular diphenylguanidine), etc. The sulfur content is preferably between 0.5 and 3.0 phr, that of the primary accelerator is preferably between 0.5 and 5.0 phr. These preferential rates can be applied to any of the embodiments of the invention.

It is possible to use as vulcanization accelerator (primary or secondary) any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type as well as their derivatives, accelerators of the sulfenamide type as regards primary accelerators, of the thiurams, dithiocarbamates, dithiophosphates, thioureas and xanthates type as regards the secondary accelerators. As examples of primary accelerators, mention may in particular be made of sulfenamide compounds such as N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N, N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS") , N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), and mixtures of these compounds. The primary accelerator is preferably a sulfenamide, more preferably N-cyclohexyl-2-benzothiazyl sulfenamide. As an example of secondary accelerators, we mention may in particular be made of thiuram disulfides such as tetraethylthiuram disulfide, tetrabutylthiuram disulfide (“TBTD”), tetrabenzylthiuram disulfide (“TBZTD”) and mixtures of these compounds. The secondary accelerator is preferably a thiuram disulfide, more preferably tetrabenzylthiuram disulfide.

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 may vary for example between 5 and 90 min depending in particular on the baking temperature, the crosslinking system adopted and the crosslinking kinetics of the composition considered.

The rubber composition in accordance with the invention may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tires, in particular pigments, protective agents such as anti-ozone waxes, anti- chemical ozonants, anti-oxidants.

The rubber composition, before crosslinking, can be manufactured in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first working phase or thermomechanical mixing (sometimes referred to as "non-productive" phase) at high temperature, up to a maximum temperature between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes qualified of "productive" phase) at a lower temperature, typically less than 110 ° C, for example between 40 ° C and 100 ° C, finishing phase during which the sulfur or the sulfur donor and the sulfur accelerator are incorporated. vulcanization.

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

According to a particularly preferred embodiment of the invention, the modifying agent is already grafted onto the diene elastomer. In other words, according to this mode, the modifying agent is grafted onto the diene elastomer prior to bringing the other constituents of the rubber composition into contact with the diene elastomer. According to a first variant of this particularly preferred embodiment, in the productive phase of the process for preparing the rubber composition, the modifying agent is incorporated into the diene elastomer by thermomechanical mixing before the introduction of the other constituents of rubber composition. The contact time between the diene elastomer and the thermomechanically mixed modifying agent is adjusted as a function of the conditions of the thermomechanical mixing, in particular as a function of the temperature. The higher the mixing temperature, the shorter this contact time. Typically it is 1 to 5 minutes for a temperature of 100 to 130 ° C.

According to a second variant of this particularly preferred embodiment, the non-productive phase of the process for preparing the rubber composition is preceded by a step during which the modifying agent is incorporated into the diene elastomer on a mixer. cylinder (called external mixer) to form a mixture which is homogenized for example by several passes over the cylinders. The mixture undergoes a heat treatment to graft the modifying agent onto the diene elastomer, for example under pressure at a temperature of at least 100 ° C, before being introduced into the internal mixer to proceed to the non-phase. productive with the incorporation of the other constituents of the rubber composition.

The rubber composition can be calendered or extruded in the form of a sheet or a plate, in particular for characterization in the laboratory, or else in the form of a semi-finished (or profile) of rubber which can be used in a tire. . The composition can be either in the uncured state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization). It can constitute all or part of a semi-finished article, in particular intended for use in a tire.

The aforementioned characteristics of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of illustration and not by way of limitation.

In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 19:

Mode 1: Rubber composition which comprises a diene elastomer, a reinforcing filler comprising more than 50% by mass of a silica, a crosslinking system, a modifying agent and optionally a silane coupling agent for binding the elastomer diene silica, the modifying agent bearing an N-substituted imidazole function and a unit containing a group reactive with respect to the diene elastomer, characterized in that the total amount of the modifying agent and the silane coupling agent represents more than 5% by mass of the amount of silica, the ratio between the amount of the modifier and the sum of the amount of the coupling agent and the amount of agent modification is greater than 0.5, the quantities being expressed in parts by weight per hundred parts of elastomer, phr.

Mode 2: Rubber composition according to mode 1 in which the total amount of the modifying agent and of the silane coupling agent represents more than 8% by mass of the amount of the silica.

Mode 3: Rubber composition according to mode 1 or 2 in which the ratio between the amount of the modifying agent and the total amount of the modifying agent and of the silane coupling agent is greater than 0.6, preferably equal to 1.

Mode 4: A rubber composition according to any one of modes 1 to 3 in which the group reactive with respect to the diene elastomer is a dipole, preferably a nitrile oxide, a nitrone or a nitrile imine.

Mode 5: A rubber composition according to any one of modes 1 to 4 wherein the modifying agent is a 1,3-dipolar compound which is an aromatic nitrile monooxide, a compound comprising a benzene ring substituted by a dipole oxide. nitrile and by a group containing the N-substituted imidazole function.

Mode 6: Rubber composition according to mode 5 in which the benzene ring is substituted ortho to the dipole.

Mode 7: Rubber composition according to any one of modes 5 to 6 in which the 1,3-dipolar compound contains a unit of formula (I) in which R 1 represents the nitrile oxide dipole, one of the symbols R ₂ to R ₆ represents a saturated group having 1 to 6 carbon atoms and covalently bonded to one of the nitrogen atoms of the 5-membered ring of the imidazole function, the other symbols, identical or different, representing a hydrogen atom or a substituent.

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Mode 8: Rubber composition according to mode 7 in which the saturated group contains 1 to 3 carbon atoms. Mode 9: A rubber composition according to any one of modes 7 to 8 in which the saturated group is an alkanediyl, preferably methanediyl.

Mode 10: A rubber composition according to any one of modes 7 to 9 in which the substituent is an alkyl having 1 to 3 carbon atoms.

Mode 11: A rubber composition according to any one of modes 1 to 10 in which the N-substituted imidazole function is a group of formula (II) in which the symbol Yi denotes an attachment to the group which is reactive with respect to l diene elastomer, the symbol Y ₂ represents a hydrogen atom or an alkyl having 1 to 6 carbon atoms, the symbols Y ₃ and Y ₄ are each a hydrogen atom.

Mode 12: A rubber composition according to mode 11 in which the alkyl represented by Y ₂ contains 1 to 3 carbon atoms, preferably is methyl.

Mode 13: Rubber composition according to any one of modes 1 to 12 in which the modifying agent is grafted onto the diene elastomer prior to bringing the other constituents of the rubber composition into contact with the diene elastomer.

Mode 14: A rubber composition according to any one of modes 1 to 13 in which the diene elastomer is a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene.

Mode 15: A rubber composition according to any one of modes 1 to 14 in which the diene elastomer is a polybutadiene, a polyisoprene, a butadiene copolymer, an isoprene copolymer or a mixture of these elastomers.

Mode 16: A rubber composition according to any one of modes 1 to 15 in which the crosslinking system is a vulcanization system.

Mode 17: A rubber composition according to any one of modes 1 to 16 in which the silane coupling agent is a bis- (a I koxy I (Ci-C ₄ ) -a I ky I (Ci-C) polysulfide ₄ ) if ly la I ky I (Ci- C ₄ )). Mode 18: A semi-finished article which comprises a rubber composition defined according to any one of modes 1 to 17.

Mode 19: A tire which comprises a rubber composition defined according to any one of modes 1 to 17 or a semi-finished article defined according to mode 18.

II. EXAMPLES OF EMBODIMENT OF THE INVENTION

1 Tensile tests:

The tensile tests make it possible to determine the elasticity stresses and the properties at break. Unless otherwise indicated, they are carried out in accordance with French standard NF T 46-002 of September 1988. Processing of the tensile records also makes it possible to plot the modulus curve as a function of the elongation. The modulus used here being the nominal (or apparent) secant modulus measured in first elongation, calculated by reducing to the initial section of the specimen. The nominal secant moduli (or apparent stresses, in MPa) at 100% elongation noted MSA100 are measured in first elongation. The breaking stresses (in MPa) and the elongation at break (in%) are measured at 23 ° C ± 2 ° C according to standard NF T 46-002.

The results are expressed in base 100 relative to a control. A value greater than that of the control, arbitrarily set at 100, indicates an improved result, that is to say a measured quantity greater than that of the control.

2 Preparation of rubber compositions:

The compound 2,4,6-trimethyl-3 - ((2-methyl-1H-imidazol-1-yl) methyl) benzonitrile oxide, the synthesis of which is described in patent application WO 2015059274, is used as modifying agent.

Silica is silica Zeosil 1165MP ^® marketed by Solvay; the silane coupling agent is TESPT (“Si69” from Degussa); the coating agent is triethoxyoctylsilane ("Dynasylan Octeo"); the antioxidant is Nl, 3-dimethylbutyl-N-phenyl-para-phenyldiamine (“Santoflex 6-PPD” from the company Flexsys); the stearic acid is stearin “Pristerene 4931” from the company Uniquema; the zinc oxide is of industrial grade from the company Umicore, the CBS accelerator is N-cyclohexyl-2-benzothiazylsulfenamide from the company Flexsys.

The procedure for the manufacture of these compositions is as follows:

Is introduced into an internal mixer (final filling rate: about 70% by volume), whose initial tank temperature is about 110 ° C, the elastomer, where appropriate the modifying agent which is mixed alone with the elastomer for approximately 2 minutes at 110 ° C., then the silica, optionally the silane coupling agent, as well as the various other ingredients with the exception of the vulcanization system. A thermomechanical work (non-productive phase) is then carried out in one step, which lasts approximately 5 min to 6 minutes, until a maximum “fall” temperature of 160 ° C. is reached. The mixture thus obtained is recovered, it is cooled and then sulfur and a sulfenamide type accelerator are incorporated on a mixer (homo-finisher) at 23 ° C., while mixing the whole (productive phase) for an appropriate time (for example between 5 and 12 min).

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

Example 1:

Six rubber compositions C1 to C6 are prepared. The formulations (in phr) of the rubber compositions C1 to C6 are described in Table 1 (Table 1).

The ratio between the amount of modifier and the sum of the amount of modifier and the amount of silane coupling agent is 0 for Cl; 0.56 for C2; 0.87 for C3; 1 for C4 and C5. Composition C1 not in accordance with the invention is a control composition, compositions C2 to C5 are in accordance with the invention, the ratio between the total amount of the modifying agent and of the silane coupling agent and the amount of the silica being greater than 0.05. Composition C6 is a composition which is not in accordance with the invention, because instead of the modifying agent, it contains triethoxyoctylsilane, covering agent, compound devoid of a group reactive with respect to diene elastomer.

The diene elastomer El is a copolymer of ethylene and of 1,3-butadiene containing 79.3% by mole of ethylene and 7% by mole of 1,2-cyclohexanediyl unit prepared in the presence of a catalytic system based on a metallocene [Me Si (Flu) Nd (p-BH ₄ ) Li (THF)] and a co-catalyst, butyloctylmagnesium, according to the following procedure:

In a reactor containing methylcyclohexane, the cocatalyst (0.36 mmol / L) is added, then the metallocene (0.07 mol / L). The alkylation time is 10 minutes, the reaction temperature is 20 ° C. Then, ethylene and 1,3-butadiene are added continuously in the respective molar amounts of 80% and 20% to the reactor. The polymerization is carried out at 80 ° C. under a pressure of 8 bars. The polymerization reaction is stopped by cooling, degassing the reactor and adding ethanol. An anti-oxidant is added to the polymer solution. The copolymer is recovered by drying in an oven under vacuum to constant mass. The Mooney viscosity of E1 is 87. The Mooney viscosity is measured using an oscillating consistometer as described in ASTM D1646 (1999). The measurement is carried out according to the following principle: the sample analyzed in the raw state (ie, before firing) is molded (shaped) in a cylindrical chamber heated to a given temperature (100 ° C.). After 1 minute of preheating, the rotor rotates within the specimen at 2 revolutions / minute and the torque useful to maintain this movement is measured after 4 minutes of rotation. Mooney viscosity (ML) is expressed in "Mooney unit" (MU, with 1 MU = 0.83 Newton.meter). Example 2:

Two rubber compositions C7 and C8 are prepared. The formulations (in phr) of the rubber compositions C7 to C8 are described in Table 2 (Table 2).

The ratio between the amount of modifier and the sum of the amount of modifier and the amount of silane coupling agent is 0 for C7; 1 for C8. Composition C7 is therefore not in accordance with the invention and is a control composition, composition C8 is in accordance with the invention, the ratio between the total amount of the modifying agent and of the silane coupling agent and the amount of silica being greater than 0.05. The diene elastomer E2 is a polyisoprene with a high rate of 1,4-cis bond (“IR 6596”, 98 mol% of 1,4-cis bond).

Example 3:

Two rubber compositions C9 and C10 are prepared. The formulations (in phr) of the C9 to C10 rubber compositions are described in Table 3 (Table 3).

The ratio between the amount of modifier and the sum of the amount of modifier and the amount of silane coupling agent is 0 for C9; 1 for CIO. Composition C9 is therefore not in accordance with the invention and is a control composition, the CIO composition is in accordance with the invention, the ratio between the total amount of the modifying agent and of the silane coupling agent and the amount of silica being greater than 0.05. The diene elastomer E3 is a copolymer of 1,3-butadiene and of styrene containing 26% by mass of styrene, the butadiene part of the copolymer containing 24% of unit 1,2.

3 Results:

The results are shown in Tables 1 to 3.

Compared with their respective control, the rubber compositions in accordance with the invention exhibit a much higher rigidity at medium deformation (100%), without the breaking properties being degraded. Even the rubber compositions devoid of silane coupling agent and in accordance with the invention not only see their rigidity greatly increased, but also their breaking property improved. The partial or total replacement of the silane coupling agent by the modifying agent makes it possible to increase the stiffness at medium deformation of the rubber compositions mainly comprising a silica without however reducing the elongations and the stresses at break. On the other hand, the partial replacement of the silane coupling agent by a covering agent does not make it possible to achieve such a compromise, since a decrease in rigidity at medium deformation is inevitably observed. Table 1

*: not measured

Table 2

Table 3

Claims

1. Rubber composition which comprises a diene elastomer, a reinforcing filler comprising more than 50% by mass of a silica, a crosslinking system, a modifier and optionally a silane coupling agent for binding the diene elastomer to silica, the modifying agent carrying an N-substituted imidazole function and a unit containing a group reactive with respect to the diene elastomer, characterized in that the total amount of the modifying agent and of the silane coupling agent represents more than 5% by mass of the amount of silica, the ratio between the amount of the modifier and the total amount of the modifier and the silane coupling agent is greater than 0.5, the quantities being expressed in parts by weight per hundred parts of elastomer, phr.

2. A rubber composition according to claim 1 wherein the total amount of the modifying agent and the silane coupling agent represents more than 8% by weight of the amount of silica.

B. A rubber composition according to claim 1 or 2 wherein the ratio between the amount of the modifying agent and the total amount of the modifying agent and the silane coupling agent is greater than 0.6, preferably equal. to 1.

4. A rubber composition according to any one of claims 1 to 3 wherein the reactive group with respect to the diene elastomer is a dipole, preferably a nitrile oxide, a nitrone or a nitrile imine.

5. A rubber composition according to any one of claims 1 to 4 wherein the modifying agent is a 1,3-dipolar compound which is an aromatic nitrile monooxide, compound comprising a benzene ring substituted with a nitrile oxide dipole. and by a group containing the N-substituted imidazole function.

6. The rubber composition of claim 5 wherein the benzene ring is substituted ortho to the dipole.

7. A rubber composition according to any one of claims 5 to 6 in which the 1,3-dipolar compound contains a unit of formula (I) in which R 1 represents the nitrile oxide dipole, one of the symbols R ₂ to R _6. represents a saturated group having 1 to 6 carbon atoms and covalently bonded to one of the nitrogen atoms of the 5-membered ring of the imidazole function, the other symbols, identical or different, representing a hydrogen atom or a substituent.

8. The rubber composition of claim 7 wherein the saturated group contains 1 to 3 carbon atoms.

9. A rubber composition according to any one of claims 7 to 8 wherein the saturated group is alkanediyl, preferably methanediyl.

10. A rubber composition according to any one of claims 7 to 9 wherein the substituent is an alkyl having 1 to 3 carbon atoms.

11. A rubber composition according to any one of claims 1 to 10 in which the N-substituted imidazole function is a group of formula (II) in which the symbol Yi denotes an attachment to the group which is reactive with respect to the. diene elastomer, the symbol Y represents a hydrogen atom or an alkyl having 1 to 6 carbon atoms, the symbols Y ₃ and Y ₄ are each a hydrogen atom.

pi)

12. A rubber composition according to claim 11 wherein the alkyl represented by 2 contains 1 to B carbon atoms, preferably is methyl.

13. The rubber composition according to any one of claims 1 to 12 wherein the modifying agent is grafted onto the diene elastomer prior to bringing the other constituents of the rubber composition into contact with the diene elastomer.

14. A semi-finished article which comprises a rubber composition as defined in any one of claims 1 to 13.

5. A tire which comprises a rubber composition defined according to any one of claims 1 to 13 or a semi-finished article defined according to claim 14.