Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/34—Heterocyclic compounds having nitrogen in the ring
  • C08K5/3412—Heterocyclic compounds having nitrogen in the ring having one nitrogen atom in the ring
  • C08K5/3415—Five-membered rings

Definitions

• the present invention relates to rubber compositions intended in particular for the manufacture of tires or semi-finished products for tires, as well as to anti-reversion agents which can be used for the thermal protection of such compositions.
• the vulcanization with sulfur has the known drawback of leading to limited resistance of the vulcanizates obtained, due to thermal aging ("thermal aging") of the latter.
• thermal aging the vulcanizates of diene elastomers crosslinked from sulfur exhibit significant sensitivity to temperature when the latter reaches a value close to the initial curing or vulcanization temperature.
• This phenomenon known as reversion, is accompanied by a deterioration in the mechanical properties of vulcanizates.
• anti-reversion agents we have therefore tried to suppress, at least limit this phenomenon of reversion by using in rubber compositions specific additives, called anti-reversion agents, making it possible to thermally stabilize the vulcanizates.
• anti-reversion agents today constitute an important research center, particularly in the tire sector for which optimal thermal stability is sought.
• a widely described family of anti-reversion agents is constituted by maleimide compounds, more particularly by bismaleimides or biscitraconimides used alone or in combination with other compounds (see for example EP 191931 or US 4803250; EP 640114 or WO93 / 23467, EP 703943 or US 5872188, EP 709234 or US 5503940, EP 823453 or US 6079468, EP 988999, US 5328636, US 5616279, US 5623007, WO92 / 07904 or US 5426155, WO . 95/16738, request JP2001-226528).
• a first subject of the invention relates to a rubber composition which can be used for the manufacture of tires, based on at least (i) a diene elastomer, (ii) a reinforcing filler, (iii) a vulcanization system and (iv) a maleimide compound, characterized in that said maleimide compound is a citraconimidomaleimide of specific formula (R hydrocarbon radical): (I)
• the invention also relates to a process for preparing a rubber composition which can be used for the manufacture of tires and which has improved resistance to reversion, this composition being based on a diene elastomer, a reinforcing filler and a vulcanization system, said method comprising the following steps:
• the subject of the invention is also the use of a composition according to the invention for the manufacture of a finished article or of a semi-finished rubber product intended for any ground connection system of motor vehicles, such as tire, internal safety support for tire, wheel, rubber spring, elastomeric articulation, other suspension and anti-vibration element.
• the invention particularly relates to the use of a composition according to the invention for the manufacture of tires or semi-finished rubber products intended for these tires, these semi-finished products preferably being chosen from the group consisting by treads, crown reinforcement plies, sidewalls, carcass reinforcement plies, beads, protectors, underlays, rubber blocks and other internal gums, in particular decoupling gums , intended to provide the connection or the interface between the aforementioned areas of the tires.
• a subject of the invention is also the finished articles and semi-finished rubber products themselves, in particular tires and semi-finished products for tires, when they comprise an elastomeric composition in accordance with the invention.
• the tires in accordance with the invention are in particular intended for passenger vehicles as for industrial vehicles chosen from vans, "Heavy vehicles” - Le., Metro, bus, road transport equipment (trucks, tractors, trailers), off-road vehicles -the road - agricultural or civil engineering machinery, aircraft, other transport or handling vehicles.
• the rubber compositions are characterized, before and after curing, as indicated below.
• the measurements are made at 130 ° C, in accordance with 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, assessed in accordance with the aforementioned standard by parameter T5 (case of a large rotor), expressed in minutes, and defined as being the time necessary to obtain an increase in the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.
• the measurements are carried out at 150 ° C. with an oscillating chamber rheometer, according to standard 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): the minimum and maximum torques, measured in dN.m (deciNewton.meter), are respectively named C m i n and C max ; the difference noted ⁇ Couple (in dN.m) between C ma and C m j n is also measured, which makes it possible to assess the vulcanization yield.
• the mechanical properties indicated below are those measured at "optimum cooking", that is to say, in known manner, those obtained, for a determined cooking temperature, after the minimum cooking time to reach the maximum rheometric torque C m a ⁇ .
• the reversion can be analyzed according to different methods, the aim being to determine, in an indirect way, the evolution of the density of the sulfur bridges, between a so-called optimum cooking (corresponding to the maximum torque C max ) and a prolonged cooking. .
• the first approach consists in measuring the evolution (decrease) of the rheometric torque: the parameters ⁇ R 60 and ⁇ R 18 o represent the evolution in% of the torque between C max and the torque measured after 60 or 180 min of cooking, respectively, at a determined cooking temperature (for example 150 ° C.). The higher the parameters ⁇ R 60 and ⁇ R 180 , the greater the reversion phenomenon.
• the second approach consists in measuring the evolution (decrease) of the aforementioned MAI 00 or M A300 modules: the parameters ⁇ MA100 and ⁇ MA300 correspond to the evolution in% of the respective modules measured at the optimum cooking time (C max ) and after a 6 hour baking at a determined baking temperature (150 ° C).
• C max optimum cooking time
• 150 ° C determined baking temperature
• the rubber compositions of the invention are based on at least one (that is to say one or more) elastomer (s) diene (s), a (one or more) filler (s) reinforcing ( s), one (one or more) crosslinking system (s) and one (one or more) citraconimidomaleimide compound (s) of formula (I) above.
• composition based on
• a composition comprising the mixture and / or the reaction product of the various constituents used, some of these base constituents being capable of, or intended to react with each other , at least in part, during the various stages of manufacturing the composition, in particular during its vulcanization.
• iene elastomer or rubber in known manner an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).
• diene elastomers can be classified into two categories: "essentially unsaturated” or "essentially saturated”.
• the term "essentially unsaturated” means a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of units or units of diene origin (conjugated dienes) which is greater than 15% (mol%).
• diene elastomers such as butyl rubbers or copolymers of dienes and of alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular as “essentially saturated diene elastomers”. "(rate of motifs of diene origin low or very low, always less than 15%).
• the expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a rate of units of diene origin (conjugated dienes) which is greater than 50%.
• 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C 1 -C 5 alkyl) -1,3-butadienes such as for example, are suitable.
• Suitable vinyl-aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tertiobu ⁇ ylstyrene, ethoxy styrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene, vinylnaphthalene.
• the copolymers can contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl-aromatic units.
• the elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used.
• the elastomers can for example be block, statistical, sequence, microsequenced, and be prepared in dispersion or in solution; they can be coupled and / or stars or functionalized with a coupling and / or star-forming or functionalizing agent.
• Polybutadienes are suitable, in particular those having a content of -1,2 units of between 4% and 80% or those having a cis-1,4 content greater than 80%, polyisoprenes, butadiene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20%> and 40%, a content of -1,2 bonds of the butadiene part of between 4% and 65%, a content of trans-1,4 bonds between 20% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content between 5% and 90% by weight and a glass transition temperature (Tg, measured according to ASTM D3418 -82) from -40 ° C to -80 ° C, isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg of between -25 ° C and
• butadiene-styrene-isoprene copolymers especially 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% are suitable.
• the diene elastomer of the composition in accordance with the invention is preferably chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (BR), polyisoprenes (IR), natural rubber (NR), copolymers of butadiene, isoprene copolymers and mixtures of these elastomers.
• Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene copolymers- butadiene-styrene (SBIR).
• the diene elastomer is predominantly (that is to say for more than 50 phr) an SBR, whether it is an SBR prepared in emulsion ("ESBR") or an SBR prepared in solution (“S SBR”), or a cut (mixture) SBR / BR, SBR / NR (or SBR / IR), or even BR / NR (or BR / IR).
• SBR SBR prepared in emulsion
• S SBR SBR prepared in solution
• an SBR elastomer use is in particular of an SBR having a styrene content of between 20% and 30% by weight, a vinyl bond content of the butadiene part of between 15% and 65%, a bond content trans-1,4 between 15% and 75% and a Tg between -20 ° C and -55 ° C; such an SBR can advantageously be used in admixture with a BR preferably having more than 90% of cis-1,4 bonds.
• the diene elastomer is mainly (for more than 50 phr) an isoprene elastomer.
• the compositions of the invention are intended to constitute, in tires, the rubber matrices of certain treads (for example for industrial vehicles), crown reinforcement plies (for example working plies, protective plies or hooping plies), carcass reinforcement plies, sidewalls, beads, protectors, underlayers, rubber blocks and other internal gums which provide the interface between the above-mentioned areas of tires.
• compositions according to the invention are for example advantageously usable as "decoupling gums" in the zones of the tire (called “decoupling zones”) having the function of ensuring mechanical decoupling between two different parts of said tire, these zones being known manner exposed to the greatest risks of overheating, and therefore of reversion.
• They can also advantageously constitute the annular rubber profiles used to stiffen the sidewalls of tires designed for run on flat tires ("run-flat tires” - see for example US 5,427,166).
• isoprene elastomer is understood 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.
• NR natural rubber
• IR synthetic polyisoprenes
• isoprene copolymers mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers (SBIR).
• This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, polyisoprenes are preferably used having a rate (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%.
• the composition in accordance with invention may contain at least one essentially saturated diene elastomer, in particular at least one EPDM copolymer or butyl rubber (optionally chlorinated or bromine), whether these copolymers are used alone or in admixture with highly unsaturated diene elastomers as mentioned above, in particular NR or IR, BR or SBR.
• compositions of the invention may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer or elastomers being able to be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.
• reinforcing filler known for its capacity to reinforce a rubber composition which can be used for the manufacture of tires can be used, for example an organic filler such as carbon black, or an inorganic reinforcing filler such as silica to which in this second case, a coupling agent will be associated.
• carbon blacks all carbon blacks are suitable, in particular blacks of the HAF, ISAF, SAF type conventionally used in tires (so-called pneumatic grade blacks).
• HAF HAF
• ISAF SAF type conventionally used in tires
• pneumatic grade blacks there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as, for example, the blacks NI 15, NI 34, N234, N326, N330, N339, N347, N375, or else , depending on the intended applications, the blacks of higher series (for example N660, N683, N772).
• any inorganic or mineral filler whatever its color and its origin (natural or synthesis), also called “white” charge, “clear” charge or even “non-black filler” as opposed to carbon black, this inorganic charge being capable of reinforcing on its own, without other means that an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words capable of replacing, in its reinforcement function, a conventional carbon black of pneumatic grade; such a charge is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface.
• -OH hydroxyl groups
• inorganic fillers in particular mineral fillers of the siliceous type are suitable, in particular silica (Si) 2 ), or aluminous tyP e , in particular alumina (AI 2 O 3 ).
• the silica used can be any reinforcing silica known to a person skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface, both less than 450 m 2 / g, preferably from 30 to
• HDS highly dispersible precipitated silicas
• PPG, Zeopol 8715, 8745 and 8755 silicas from the Huber Company.
• reinforcing aluminas mention may be made of "Baikalox” "A125” or “CR125” aluminas from the company Baikowski, "APA-100RDX” from Condea, "Aluminoxid C” from Degussa) or "AKP- G015" from Sumitomo Chemicals.
• an at least bifunctional coupling agent intended to ensure a sufficient connection, of chemical and / or physical nature, between the inorganic filler will be used in a well known manner. (surface of its particles) and the diene elastomer, in particular organosilanes or bifunctional polyorganosiloxanes.
• the rate of total reinforcing filler is between 20 and 200 phr, more preferably between 30 and 150 phr (parts by weight per hundred parts of elastomer), the optimum being different depending on the intended applications: the level of reinforcement expected on a bicycle tire, for example, is in known manner significantly lower than that required on a tire capable of traveling at high speed in a sustained manner, for example a motorcycle tire, a passenger car or utility vehicle tire such as Heavy goods vehicle.
• inventive rubber compositions have the novel and inventive characteristic of using, as anti-reversion agent agent, a citraconimidomaleimide compound comprising both a maleimide function and a citraconimide function, corresponding to the following formula (I): (I)
• the radical R is any hydrocarbon radical, aromatic or aliphatic, cyclic or acyclic, substituted or unsubstituted, linear or branched. Preferably, it contains from 1 to 25 carbon atoms, and optionally one or more heteroatom (s) chosen from O, N and S.
• R is chosen from the group consisting of alkylene having from 1 to 20 carbon atoms, cycloalkylene having from 6 to 24 carbon atoms, arylene having from 6 to 18 carbon atoms and aralkylene having from 7 to 25 carbon atoms.
• citraconimidomaleimides meeting this definition include those belonging to the preferential group consisting of N- (citraconimido-ethyl) maleimide, N- (citraconimido-hexamethyl) maleimide, N- (citraconimido-dodecamethyl) maleimide, N- (citraconimido-oxy-dipropyl) maleimide, N- (citraconimido-1,3-cyclohexyl) maleimide, N- (citraconimido-1,4-cyclohexyl) maleimide, N- (citraconimido -3,3'-dimethyl-4,4'-biphenyl) maleimide, N- (citracommido-m-phenyl) maleimide, N- (citraconimido-p-phenyl) maleimide, N- (citraconimido-o-phenyl ) maleimide
• citraconimidomaleimide is more preferably chosen from the group consisting of N- (citraconimido-m-phenyl) maleimide, N- (citraconimido-p-phenyl) maleimide, N- (citraconimido-o-phenyl) maleimide, N- (3-citraconimido-4,6-dimethyl-phenyl) maleimide , N- (3-citraconimido-4-methyl-phenyl) maleimide, N- (3-citraconimido-6-methyl-phenyl) maleimide, N- (3-citraconimido-2-methyl-phenyl) maleimide, N- (-citraconimido-4,4'- ethylene-bi-phenyl) maleimide, N- [2- (methylene-citraconimido) -phenyl] -methylene-maleimide, N- [2- (methylene-citraconimi
• R is a phenylene group, the selected citraconimidomaleimide being even more preferably the N- (citraconimido-p-phenyl) maleimide.
• Citraconimidomaleimide is present in the composition according to the invention at a preferential rate of between 0.1 and 10 phr. Below the minimum indicated, the targeted technical effect may be insufficient whereas, beyond the maximum indicated, there is a double risk for the plasticizing compositions in the raw state and excessive stiffening when cooked state. For all these reasons, a rate more preferably included in a range of 0.2 to 5 phr is used. An amount in the range of 0.2 to 2.5 phr has been found to be particularly well suited to pneumatic application.
• the compounds of formula (I) described above can be prepared by double addition-elimination reaction of a diamine in the presence of maleic anhydride and citraconic anhydride, followed by a cyclization step.
• FIG. 1 illustrates a preferred synthetic route, comprising the following steps inspired by known methods (R having the above meanings):
• a cyclization step of product C is carried out, in the presence of an anhydrous organic solvent (for example toluene), a catalyst of the Lewis acid type (for example ZnCl) and a cyclization agent such as hexamethyldisilazane (HMD S) to generate the product of formula (I) targeted:
• an anhydrous organic solvent for example toluene
• a catalyst of the Lewis acid type for example ZnCl
• a cyclization agent such as hexamethyldisilazane (HMD S)
• the vulcanization system proper is based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator.
• sulfur or a sulfur-donating agent
• a primary vulcanization accelerator To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the productive phase as described later, various secondary accelerators or known 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 10 phr, more preferably between 1 and 8 phr, in particular between 1 and 6 phr when the composition of the invention is intended, according to a preferential method of invention, to constitute an internal tire rubber, in particular a decoupling rubber.
• the primary vulcanization accelerator is itself. used at a preferential rate of between 0.5 and 10 pce, - more preferably between 0.5 and 5.0 pce.
• such an accelerator must allow crosslinking of the rubber compositions in industrially acceptable times, while preserving a minimum safety period ("roasting time") during which the compositions can be shaped without risk of premature vulcanization (“roasting").
• Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used.
• R 1 represents a hydrogen atom, a 2-mercaptobenzothiazyl group of formula (III):
• R 2 and R 3 independently represent a hydrogen atom, a 2-mercaptobenzothiazyl group (formula III), a C 1 -C 4 alkyl group or a C 5 -C 8 cycloalkyl group, preferably comprising 6 links , said cycle possibly comprising at least one heteroatom such as S, O or N.
• Thiazole accelerators and preferred derivatives are chosen in particular from the group consisting of 2-mercaptobenzothiazole, 2-mercaptobenzothiazyl disulfide, N-cyclohexyl-2-benzothiazyl sulfenamide, N, N-dicyclohexyl-2-benzothiazyl sulfenamide, N - ter-butyl-2-benzothiazyle sulfenamide, N-cyclohexyl-2-benzothiazyle sulfenimide, N-ter-butyl-2-benzothiazyle sulfenimide and mixtures of these compounds.
• the compounds of the thiuram family (formula V) and the zinc dithiocarbamate derivatives (formula VI) are also suitable:
• R 4 , R 5 , R 6 and R 7 each independently represent an alkyl group comprising from 1 to 8 carbon atoms, a benzyl group, a combination between R 4 and R 5 and a combination between R and R to form a cyclic pentamethylene group or a methyl-pentamethylene cyclic group and in which R 4 and R 5 and R 6 and R 7 are linked together.
• Thiuram-type accelerators are chosen in particular from the preferential group consisting of tetramethyl-thiuram monosulfide, tetramethyl-thiuram disulfide, tetraethyl-thiuram disulfide, tetrabutyl-thiuram disulfide, tetra-isobutyl disulfide -thiuram, tetrabenzyl-thiuram disulfide and mixtures of these compounds. Among them, tetrabenzyl-thiuram disulfide is more preferably retained.
• the primary vulcanization accelerators used in the composition according to the invention are more preferably chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS”), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated “ CBS “), N, N-dicyclohexyl-2-benzothiazyle sulfenamide (abbreviated” DCBS “), N-ter-butyl-2-benzothiazyle sulfenamide (abbreviated” TBBS “), N-ter-butyl-2-benzothiazyl sulfenimide (abbreviated "TBSI”) and mixtures of these compounds.
• MBTS 2-mercaptobenzothiazyl disulfide
• CBS N-cyclohexyl-2-benzothiazyl sulfenamide
• DCBS N-dicyclohexyl-2-benzothiazyle
• the elastomeric compositions in accordance with the invention may also comprise all or part of the usual additives used in rubber compositions intended for the manufacture of tires, such as for example plasticizers or extension oils, whether the latter are of aromatic or non-aromatic in nature, pigments, agents with protective waxes such as anti-ozone, chemical antiozonants, antioxidants, anti-fatigue agents, adhesion promoters, coupling activators, reinforcing resins , methylene acceptors and / or donors, or even other anti-reversion agents, for example conventional bismaleimides or biscitraconimides.
• plasticizers or extension oils whether the latter are of aromatic or non-aromatic in nature
• protective waxes such as anti-ozone, chemical antiozonants, antioxidants, anti-fatigue agents, adhesion promoters, coupling activators, reinforcing resins , methylene acceptors and / or donors, or even other anti-reversion agents, for example conventional bismaleimides or biscitrac
• these compositions comprise, as preferred non-aromatic or very weakly aromatic plasticizing agent, at least one compound chosen from the group consisting of naphthenic, paraffinic oils, MES oils, TDAE oils, esters (in particular trioleates) glycerol, hydrocarbon plastic resins preferably having a high Tg value (preferably greater than 30 ° C), and mixtures of such compounds.
• the reinforcing filler used is an inorganic filler
• agents for recovering such an inorganic filler more generally agents for assisting in the implementation, capable in known manner, thanks to an improvement in the dispersion of the inorganic filler in the rubber matrix and a lowering of the viscosity of the compositions, improving their ability to be used in the raw state.
• compositions are produced in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first working phase or thermomechanical kneading (so-called “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 mechanical working phase (so-called “productive” phase) to a lower temperature, typically below 110 ° C, for example between 40 ° C and 100 ° C, finishing phase during which the vulcanization system is incorporated.
• a first working phase or thermomechanical kneading at high temperature, up to a maximum temperature between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C
• a second mechanical working phase “so-called “productive” phase
• the process according to the invention for preparing a rubber composition having improved resistance to reversion comprises the following steps:. incorporating into a diene elastomer, during a first so-called “non-productive” step, at least one reinforcing filler, by thermomechanically kneading the whole, in one or more stages, until reaching a maximum temperature of between 110 ° C. and 190 ° C; • cool the assembly to a temperature below 100 ° C; • then incorporate, during a second so-called "productive” step, the vulcanization system; knead everything up to a maximum temperature below 110 ° C,
• citraconimidomaleimide compound of the above-mentioned formula (I) is also incorporated during any of the process steps.
• the non-productive phase is carried out in a single thermomechanical step during which all the necessary basic components (diene elastomer) are introduced into a suitable mixer such as a conventional internal mixer. , reinforcing filler and coupling agent if necessary, optionally all or part of the citraconimidomaleimide compound), then in a second step, for example after one to two minutes of kneading, the other additives, possible additional covering or implementing agents, with the exception of the vulcanization system.
• the total duration of the kneading, in this non-productive phase is preferably between 1 and 15 min.
• an vulcanization system and the citraconimidomaleimide compound (all of which are incorporated in an external mixer, such as a cylinder mixer, maintained at low temperature (for example between 40 ° C. and 100 ° C.). or the remaining part, if applicable).
• the whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 minutes.
• the final composition thus obtained can then be calendered, for example in the form of a sheet, a plate or else extruded, for example to form a rubber profile used for the manufacture of a semi-finished product for tire, such as plies, strips, underlayers, various rubber blocks, whether or not reinforced with textile or metallic reinforcements, intended to form part of the structure of the tire.
• Vulcanization (or baking) can then be carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, preferably under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the baking temperature, the vulcanization system adopted and the vulcanization kinetics of the composition considered.
• the invention relates to the rubber compositions previously described both in the so-called “raw” state (i.e. before curing) and in the so-called “cooked” or vulcanized state (i.e. after vulcanization).
• N- (p-citraconimidophenyl) -maleimide is prepared by reacting 1,4-phenylenediamine with maleic anhydride and then citraconic anhydride; the diacid then generated is then cyclized, taking inspiration from a process for the synthesis of N-alkyl- and N-arylimide derivatives as described in J. Org. Chem., Vol. 62 No. 8, 2652-2654, 1997.
• 1,4-phenylenediamine (1) is added (22.70 g or 0.200 mol -
• N- (4-amino-phenyl) maleamic acid (2) (41.19 g or 0.190 mol - 1 eq) in 400 ml of THF is added in 45 min a solution of citraconic anhydride (22, 37 g or 0.190 mol - leq) in 200 mL of THF.
• the reaction mixture is stirred at room temperature for 16 hours and then cooled using an ice bath for 20 min.
• the precipitate obtained is filtered on sintered glass, rinsed with ethyl ether and then dried under vacuum.
• the diacid (3) (40 g or 0.126 mol - 1 eq) and 800 ml of anhydrous toluene are introduced into a 2 L two-necked flask fitted with a condenser and under an inert nitrogen atmosphere.
• the mixture formed is subjected to mechanical stirring for a few min, then ZnCl 2 (36 g or 0.264 mol - 2.1 eq) is sublimed beforehand.
• the reaction mixture is brought to 80 ° C for 10 min and then the HMDS is added slowly (80 mL or 0.378 mol - 3 eq).
• the mixture is left under stirring and heating for 44 hours, then it is evaporated to dryness using a rotary evaporator (water bath at 80 ° C under 1 mm Hg).
• a rotary evaporator water bath at 80 ° C under 1 mm Hg.
• 500 ml of dichloromethane are added and the mixture is refluxed for 15 min to dissolve the maximum amount of product, the beige precipitate collected corresponding to ZnCl 2 is filtered hot on a sintered glass.
• the isolated organic phase is then washed respectively with 10% hydrochloric acid, saturated NaHCO 3 , NaCl, then dried over MgSO 4 , filtered and then evaporated.
• Thermomechanical work (non-productive phase) is then carried out in one step (total duration of mixing equal to approximately 5 min), until a maximum "fall" temperature of approximately 160 ° C. is reached.
• the mixture thus obtained is recovered, it is cooled and then the vulcanization system is added and (if it is present in the composition) the anti-reversion agent on an external mixer (homo-fmisseur) at 40 ° C, mixing the whole (productive phase) for 3 to 4 minutes on this cylinder tool.
• compositions thus obtained are then calendered in the form of plates (thickness of 2 to 3 mm) or of thin sheets of rubber for the measurement of their physical or mechanical properties, or extruded to form profiles which can be used directly, after cutting and / or assembly to the desired dimensions, as a semi-finished product for tires.
• composition according to the invention is compared with three control compositions, whether or not comprising an anti-reversion agent, the four compositions tested being identical with the following differences: composition T-1: control without anti-reversion agent; composition T-2: control with conventional anti-reversion agent (bismaleimide); composition T-3: control with conventional anti-reversion agent (biscitraconimide); - Composition C-1: composition according to the invention (citraconimidomaléimide).
• the bismaleimide compound used in the control composition T-2 is meta-phenylene-bismaleimide (abbreviated "MPBM”), well known to those skilled in the art and corresponding to the following specific formula:
• MPBM meta-phenylene-bismaleimide
• the biscitraconimide of composition T-3 is 1,3-bis- (citraconimidomethyl) -benzene ("Perkalink 900”), also well known and corresponding to the following specific formula:
• citraconimidomaleimide used in the composition according to the invention C-1 corresponds to the specific formula which follows:
• the essential characteristic distinguishing the three above compounds, and therefore the composition according to the invention C-1 from the control compositions T-2 and T-3, is the presence on one and only one of the two maleimide groups of a methyl group (instead of hydrogen or methyl, respectively, depending on the witness considered).
• the three maleimide compounds are used at an isomolar rate.
• Tables 1 and 2 give the formulation of the different compositions (Table 1 - rate of the different products expressed in pce), the properties before and after cooking, the rheometric properties as well as different parameters measuring the reversion.
• the evolution of the rheometric torque is followed after 60 min and 180 min at 150 ° C.
• the thermal stability of the compositions is also appreciated. by the evolution of the nominal secant module at 100% and 300% elongation, between the measurement at optimum cooking and after prolonged cooking for 6 hours (temperature of 150 ° C).
• composition C-1 appears remarkable, clearly superior to that observed on the three controls T1, T-2 and T-3, this whatever the parameter used (in accordance with the indications given in paragraph 1-5) .

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