RUBBER COMPOSITION WITH A HIGHLY SATURATED DIENE ELASTOMER

Description

[0001] The field of the present invention is that of rubber compositions based on highly saturated diene elastomer intended for use in a tire, in particular in its tread.

[0002] The use of highly saturated diene elastomer is known in the prior art. For example, copolymers of ethylene and 1,3-butadiene and their application in a tire tread are described in WO 2014114607A1. This document indicates that the use of these copolymers has the effect of conferring good wear resistance and rolling resistance properties to the tire.

[0003] In parallel, the use of tall oil ester plasticizer is described in documents JP2008201933, JP2008201944 and JP2008201945 in various elastomeric matrices and not comprising highly saturated diene elastomer, with effects also varied and dependent on the elastomeric matrices in which this type of plasticizer is used.

[0004] In the above-discussed field of tires comprising a highly saturated diene elastomer in the tread, there continues to be a need for rubber compositions with an improved balance between the properties of the glass transition temperature of the mixture, important for optimizing the tire's grip on the road, and the stiffness.

[0005] It is known to those skilled in the art that tire grip is adjusted according to the operating temperature using the glass transition temperature of the mixture. Particularly in cold weather, the skilled person must reduce the glass transition of the mixture compared to the glass transition temperature of the mixture used in hot weather. In order to reduce the glass transition of the mixture, the skilled person can add an oil with a low glass transition temperature to the composition. However, the use of an oil causes dilution of the polymers and leads to a reduction in the rigidity of the mixture. Lowering the rigidity of the mixture penalizes the behavior of the tire and increases tread wear. The problem to be solved by the skilled person is to be able to reduce the glass transition of the mixture without excessively reducing the rigidity of this mixture.

[0006] The Applicant has found a rubber composition which makes it possible to meet this need in the field of application of highly saturated diene elastomers for tires and in particular for the tread.

[0007] Thus, a first subject of the invention is a rubber composition based on at least one elastomer matrix comprising mainly a highly saturated diene elastomer, carbon black, a tall oil ester plasticizer; the highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene in which the ethylene units represent at least 50 mol% of the monomer units of the copolymer.

[0008] Another subject of the invention is a pneumatic or non-pneumatic tire which comprises a rubber composition according to the invention, preferably in its tread. I- DEFINITIONS

[0009] The expression "composition based on" means a composition comprising the mixture and / or the in situ reaction product of the different constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the different phases of manufacture of the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0010] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts by mass of elastomer.

[0011] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0012] On the other hand, any interval 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., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict limits a and b). In this document, when an interval of values ​​is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

[0013] In the present application, the term "all the monomer units of the elastomer" or "all the monomer units of the elastomer" means all the repeating units constituting the elastomer which result from the insertion of the monomers into the elastomer chain by polymerization. Unless otherwise indicated, the contents of a monomer unit or repeating unit in the highly saturated diene elastomer are given as a molar percentage calculated on the basis of all the monomer units of the elastomer.

[0014] When a "majority" compound is referred to, within the meaning of the present invention, this compound is the majority among the compounds of the same type in the composition, that is to say that it is the one which represents the largest quantity by mass among the compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the largest mass relative to the total mass of the elastomers in the composition. In the same way, a so-called majority filler is the one representing the largest mass among the fillers in the composition. For example, in a system comprising a single elastomer, this is the majority within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers. On the contrary, a "minority" compound is a compound which does not represent the largest mass fraction among the compounds of the same type.Preferably by majority, we mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

[0015] The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already in use, i.e. they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, polymers, plasticizers, fillers, etc.

[0016] Unless otherwise indicated, as is the case in the examples presented below, the glass transition temperature values ​​"Tg" described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999). II- DESCRIPTION OF THE INVENTION II-1 Elastomeric matrix

[0017] By “elastomer matrix” we mean all the elastomers in the composition.

[0018] According to the invention, the elastomer matrix mainly comprises at least one highly saturated diene elastomer, namely a copolymer containing ethylene units and diene units (hereinafter referred to as “the copolymer”).

[0019] The highly saturated diene elastomer, useful for the purposes of the invention, is a copolymer, preferably a random copolymer, which comprises ethylene units resulting from the polymerization of ethylene. In a known manner, the expression "ethylene unit" refers to the -(CH2-CH2)- unit resulting from the insertion of ethylene into the elastomer chain. The highly saturated diene elastomer is rich in ethylene units, since the ethylene units represent at least 50% by mole of all the monomer units of the elastomer.

[0020] Preferably, the highly saturated diene elastomer comprises at least 65 mol% of ethylene units. In other words, the ethylene units preferably represent at least 65 mol% of all the monomer units of the highly saturated diene elastomer. More preferably, the highly saturated diene elastomer comprises from 65% to 90 mol% of ethylene units, molar percentage calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0021] The highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene also comprises 1,3-diene units resulting from the polymerization of a 1,3-diene. As is known, the expression "1,3-diene unit" refers to the units resulting from the insertion of the 1,3-diene by a 1,4-addition, a 1,2-addition or a 3,4-addition in the case of isoprene. The 1,3-diene units are those for example of a 1,3-diene having 4 to 12 carbon atoms, such as 1,3-butadiene, isoprene, 1,3-pentadiene, an aryl-1,3-butadiene. Preferably, the 1,3-diene is 1,3-butadiene, in which case the highly saturated diene elastomer is a copolymer of ethylene and 1,3-butadiene, preferably random.

[0022] The highly saturated diene elastomer useful for the purposes of the invention can be obtained according to different synthesis methods known to those skilled in the art, in particular depending on the targeted microstructure of the highly saturated diene elastomer. Generally, it can be prepared by copolymerization of at least one 1,3-diene, preferably 1,3-butadiene, and ethylene and according to known synthesis methods, in particular in the presence of a catalytic system comprising a metallocene complex. Mention may be made, in this respect, of catalytic systems based on metallocene complexes, which catalytic systems are described in documents EP 1092 731, WO 2004035639, WO 2007054223 and WO 2007054224 in the name of the Applicant.The highly saturated diene elastomer, including when it is random, can also be prepared by a process using a preformed type catalytic system such as those described in documents WO 2017093654 A1, WO 2018020122 A1 and WO 2018020123 A1.

[0023] The highly saturated diene elastomer in the composition of the invention preferably contains units of formula (I) [Chem 1] or units of formula (II) [Chem 2].

[0024] The presence of saturated 6-membered cyclic unit, 1,2-cyclohexanediyl, of formula (I) in the copolymer may result from a series of very specific insertions of ethylene and 1,3-butadiene into the polymer chain during its growth. When the highly saturated diene elastomer comprises units of formula (I) or units of formula (II), the molar percentages of the units of formula (I) and the units of formula (II) in the highly saturated diene elastomer, respectively o and p, preferably satisfy the following equation (eq. 1) Math 1, more preferably equation (eq. 2) Math 2, and more preferably equation (eq. 3) Math 3, where o and p are calculated on the basis of all the monomer units of the highly saturated diene elastomer. Math 1 0 < o + p ≤ 35 Math 2 0 < o + p ≤ 25 Math 3 0 < o + p < 20

[0025] The highly saturated diene elastomer useful for the purposes of the invention may consist of a mixture of highly saturated diene elastomers which differ from each other by their microstructures or by their macrostructures.

[0026] According to the invention, the level of the highly saturated diene elastomer in the rubber composition is at least 50 parts by weight per hundred parts of elastomer of the rubber composition (phr). Preferably, the level of the highly saturated diene elastomer in the rubber composition varies in a range from 80 to 100 phr. More preferably, it varies in a range from 90 to 100 phr.

[0027] Additionally, the elastomer matrix of the composition of the invention may comprise any type of elastomer, in a minority capacity. Particularly noteworthy are the diene elastomers known to those skilled in the art for their use in the field of tires. II-2 Specific plasticizer

[0028] According to the invention, the rubber composition is based on at least one tall oil ester plasticizer (also called “tallate”).

[0029] Preferably for the purposes of the invention, the tall oil ester plasticizer is present in the composition at a level within a range of 5 to 50 phr, preferably 7 to 40 phr and more preferably 8 to 30 phr. Very preferably, the level of tall oil ester plasticizer is within a range of 8 to 15 phr.

[0030] Preferably, the tall oil ester plasticizer is a compound of formula TI(OR)3 in which R is a linear or branched alkyl and TI represents tall oil (or tallate).

[0031] Preferably, R is an alkyl comprising from 4 to 20 carbon atoms, preferably from 6 to 12 carbon atoms and more preferably from 6 to 10 carbon atoms.

[0032] Preferably, R is a branched alkyl, and very preferably, R is an isooctyl radical.

[0033] Most preferably, the tall oil ester plasticizer is the compound isooctyl tallate, [Chem 3] below.

[0034] Isooctyl tallate, CAS number 68333-78-8, has a glass transition temperature of -110°C and is, for example, marketed under the name “Plasthall 100” by the company Hallstar.

[0035] Furthermore, the composition according to the invention advantageously does not comprise any plasticizer other than the specific plasticizer above, or contains less than 15 phr, preferably less than 10 phr, preferably less than 5 phr. II-3 Reinforcing charge

[0036] The rubber composition in accordance with the invention has the other essential characteristic of comprising a reinforcing filler comprising carbon black.

[0037] A reinforcing filler typically consists of nanoparticles whose average size (by mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

[0038] Suitable carbon blacks are all carbon blacks, in particular the blacks conventionally used in tires or their treads (so-called tire-grade blacks). Among the latter, mention will be made more particularly of reinforcing carbon blacks of the 100, 200, 300 series, or blacks of the 500, 600 or 700 series (ASTM grades), such as for example blacks N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772). When the rubber composition in accordance with the invention is used in a tread, the carbon black is preferably a carbon black of the 100 or 200 series.

[0039] The carbon black content can vary to a large extent and is adjusted by a person skilled in the art according to the intended application of the rubber composition, in particular in the field of tires. For an application of the rubber composition in a tread, in particular for vehicles intended to carry heavy loads, the carbon black content in the rubber composition is preferably between 15 and 65 phr. For such an application in the field of heavy goods vehicles, the rubber composition may have an insufficient level of reinforcement below 15 phr and may have excessive hysteresis above 65 phr. Preferably, the carbon black content in the rubber composition is within a range of 20 to 45 phr. II-4 Crosslinking system

[0040] The crosslinking system may be any type of system known to those skilled in the art in the field of tire rubber compositions. It may in particular be based on sulfur, and / or peroxide and / or bismaleimides.

[0041] Preferably, the crosslinking system is sulfur-based, in which case it is referred to as a vulcanization system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or a sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferably, various known vulcanization activators can be used, such as zinc oxide, stearic acid or equivalent compounds such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders.

[0042] Sulphur is used at a preferential rate of between 0.2 pce and 10 pce, more preferably between 0.3 and 5 pce. The vulcanisation accelerator or accelerator mixture is used at a preferential rate of between 0.5 and 10 pce, more preferably between 0.5 and 5 pce.

[0043] Any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur may be used as an accelerator, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. Examples of such accelerators include, but are not limited to, the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds. II-5 Possible additives

[0044] The rubber compositions according to the invention may optionally also comprise all or part of the usual additives usually used in elastomer compositions for tires, such as for example plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing resins (as described for example in application WO 02 / 10269).

[0045] However, in a particularly advantageous manner, the composition according to the invention does not comprise any plasticizer other than those mentioned above or comprises less than 20 phr, preferably less than 10 phr, preferably less than 5 phr.

[0046] Advantageously, the composition according to the invention does not comprise any hydrocarbon plasticizing resin. II-6 Preparation of rubber compositions

[0047] The compositions in accordance with the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first phase of working or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents are introduced into a suitable mixer such as a conventional internal mixer (for example of the 'Banbury' type), in particular the elastomeric matrix, the reinforcing filler, any other various additives, with the exception of the crosslinking system. The incorporation of the possible filler into the elastomer can be carried out in one or more stages by thermomechanical mixing.In the case where the filler is already incorporated in whole or in part into the elastomer in the form of a masterbatch as described for example in applications WO 97 / 36724 or WO 99 / 16600, it is the masterbatch which is directly mixed and where appropriate the other elastomers or fillers present in the composition which are not in the form of a masterbatch are incorporated, as well as any other various additives other than the crosslinking system. The non-productive phase can be carried out at high temperature, up to a maximum temperature of between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally of between 2 and 10 minutes.a second phase of mechanical work (so-called "productive" phase), which is carried out in an external mixer such as a cylinder mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and everything is then mixed for a few minutes, for example between 5 and 15 min.

[0048] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0049] The final composition thus obtained is then calendered, for example, in the form of a sheet or plate, in particular for characterization in the laboratory, or extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber product usable, for example, as a tire tread. These products can then be used for the manufacture of tires, according to techniques known to those skilled in the art.

[0050] The composition can be either in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), can be a semi-finished product which can be used in a tire.

[0051] Crosslinking (or curing), where appropriate 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 curing temperature, the crosslinking system adopted and the crosslinking kinetics of the composition considered. II-7 Pneumatics

[0052] The present invention also relates to a tire comprising a rubber composition according to the invention.

[0053] Preferably, the composition according to the invention is present at least in the tread of the tire according to the invention.

[0054] The tire according to the invention may be intended to equip motor vehicles of the passenger car, SUV ("Sport Utility Vehicles"), or two-wheeled vehicles (particularly motorcycles), or airplanes, or even industrial vehicles chosen from vans, "Heavy Goods Vehicles" - that is to say metro, buses, road transport vehicles (trucks, tractors, trailers), off-road vehicles such as agricultural or civil engineering vehicles -, and others.

[0055] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative and non-limiting purposes. III. EXAMPLES OF CARRYING OUT THE INVENTION III.1 Tests and measurements: III.1-1 Determination of the microstructure of elastomers :

[0056] The microstructure of the elastomers is determined by 1H NMR analysis, supplemented by 13C NMR analysis when the resolution of 1H NMR spectra does not allow the attribution and quantification of all species. The measurements are carried out using a BRUKER 500MHz NMR spectrometer at frequencies of 500.43 MHz for proton observation and 125.83MHz for carbon observation.

[0057] For non-soluble elastomers that have the ability to swell in a solvent, a 4mm z-grad HRMAS probe is used to observe the proton and carbon in proton-decoupled mode. Spectra are acquired at rotation speeds of 4000Hz to 5000Hz.

[0058] For measurements on soluble elastomers, a liquid NMR probe is used to observe the proton and carbon in proton-decoupled mode.

[0059] The preparation of insoluble samples is carried out in rotors filled with the analyzed material and a deuterated solvent allowing swelling, generally deuterated chloroform (CDCl3). The solvent used must always be deuterated and its chemical nature can be adapted by the person skilled in the art. The quantities of material used are adjusted so as to obtain spectra with sufficient sensitivity and resolution.

[0060] Soluble samples are dissolved in a deuterated solvent (approximately 25 mg of elastomer in 1 mL), generally deuterated chloroform (CDCl3). The solvent or solvent blend used must always be deuterated and its chemical nature can be adapted by those skilled in the art.

[0061] In both cases (soluble sample or swollen sample): For proton NMR, a single 30° pulse sequence is used. The spectral window is adjusted to observe all the resonance lines belonging to the molecules analyzed. The accumulation number is adjusted to obtain a sufficient signal-to-noise ratio for the quantification of each pattern. The recycling time between each pulse is adapted to obtain a quantitative measurement.

[0062] For carbon NMR, a single 30° pulse sequence is used with proton decoupling only during acquisition to avoid “Nuclear Overhauser” (NOE) effects and to remain quantitative. The spectral window is adjusted to observe all the resonance lines belonging to the analyzed molecules. The accumulation number is adjusted to obtain a sufficient signal-to-noise ratio for the quantification of each pattern. The recycling delay between each pulse is adapted to obtain a quantitative measurement.

[0063] NMR measurements are performed at 25°C. III.1-2 Measurement of dynamic properties : Dynamic properties

[0064] The dynamic properties are measured on a viscoanalyzer (Metravib V A4000), according to the ASTM D5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen 4 mm thick and 400 mm2 in cross-section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz according to the ASTM D 1349-99 standard, is recorded.

[0065] The following results are from measurements using temperature scans under a given stress and strain scans at a stress frequency of 10Hz.

[0066] Stiffness: Stiffness is determined at 50% return strain during a strain sweep at 60°C from 0.1% to 100% peak-peak strain.

[0067] Glass transition temperature: The glass transition is determined as the temperature at which the mixture exhibits a maximum G" value during shear measurement tests at an imposed stress of 0.7 MPa. III.2 Preparation of rubber compositions:

[0068] The rubber compositions, the formulation details of which are given in Table 1, were prepared as follows: The elastomer, the reinforcing filler and the various other ingredients, with the exception of the sulfur and the vulcanization accelerators, are successively introduced into an internal mixer (final filling rate: approximately 70% by volume), whose initial tank temperature is approximately 90°C. The oils are introduced at 115°C. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of approximately 3 to 4 minutes, until a maximum "fall" temperature of 160°C is reached. The mixture thus obtained is recovered, cooled and then the sulfur and the vulcanization accelerators are incorporated on a mixer (homo-finisher) at 30°C, mixing everything (productive phase) for an appropriate time (for example, approximately ten minutes).

[0069] The compositions thus obtained are then calendered either in the form of plates (thickness 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties, or extruded in the form of a tire tread.

[0070] The elastomer (EBR) is prepared according to the following procedure: 30 mg of metallocene [{Me2SiFlu2Nd(µ-BH4)2Li(THF)}2, the symbol Flu representing the fluorenyl group of formula C13H8] are introduced into a first Steinie bottle in a glove box. The co-catalyst, butyloctylmagnesium previously dissolved in 300 ml of methylcyclohexane in a second Steinie bottle, is introduced into the first Steinie bottle containing the metallocene in the following proportions: 0.00007 mol / L of metallocene, 0.0004 mol / L of co-catalyst. After 10 minutes of contact at room temperature, a catalytic solution is obtained. The catalytic solution is then introduced into the polymerization reactor. The temperature in the reactor is then increased to 80°C. When this temperature is reached, the reaction starts by injecting a gaseous mixture of ethylene and 1,3-butadiene (80 / 20 mol%) into the reactor.The polymerization reaction takes place at a pressure of 8 bar. The proportions of metallocene and co-catalyst are 0.00007 mol / L and 0.0004 mol / L respectively. The polymerization reaction is stopped by cooling, degassing the reactor and adding ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven. In a reactor containing methylcyclohexane, ethylene and butadiene at 80°C in the proportions (80 / 20 mol% Ethylene / butadiene), butyloctylmagnesium (BOMAG) is added to neutralize the impurities in the reactor, then the catalytic system. At this time, the reaction temperature is regulated at 80°C and the polymerization reaction starts. The polymerization reaction takes place at a constant pressure of 8 bar. The reactor is supplied throughout the polymerization with ethylene and butadiene in the proportions 80 / 20% mol (Ethylene / Butadiene).The polymerization reaction is stopped by cooling, degassing the reactor, and adding ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven to constant mass.

[0071] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(µ-BH4)2Li(THF)], a co-catalyst, butyloctylmagnesium (BOMAG), and a pre-forming monomer, 1,3-butadiene, in the following contents: metallocene: 0.00007 mol / L, co-catalyst: 0.00036 mol / L. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 A1.

[0072] Rubber composition C3 is in accordance with the invention. Rubber compositions C1 and C2 are not in accordance with the invention, since they do not comprise the specific plasticizer necessary for the invention. Table 1 Components C1 C2 C3 EBR (1) 100 100 100 Carbon black (2) 42 42 42 Oil 1 (3) - 11 - Oil 2 (4) - - 11 Wax (5) 1 1 1 Antioxidant (6) 2 2 2 Stearic Acid 1,5 1,5 1,5 ZnO 2,5 2,5 2,5 Diphenylguanidine 0,5 0,5 0,5 Accelerators (7) 0,8 0,8 0,8 Sulfur 0,4 0,4 0,4 (1) EBR mooney 85, ethylene content: 77%, (2) Carbon black ASTM N234 from Cabot, (3) Paraffinic oil “Extensiol 51” from Repsol, (4) Oil “Plasthall 100” from Hallstar, (5) Ozone wax C32 ST, (6) Santoflex 6PPD from Flexsys, (7) Accelerators: cyclohexyl-benzothiazyl sulfenamide CBS and tetrabenzylthiuram disulfide TBzTD from Akrochem. III.3 Results:

[0073] The results are shown in Table 2. Table 2 MDC measures C1 C2 C3 Rigidity at 60°C (G*50% return) 1,25 0,92 1,07 Glass transition (TG" max) -39,45 -43,47 -47,08

[0074] The results show that the composition according to the invention simultaneously allows the glass transition of the mixture to be lowered, while maintaining high levels of rigidity, suitable for use in tire treads. The lowering of the glass transition temperature of the mixture allows this formulation to be used at lower temperatures and the slightest reduction in rigidity allows good tire behavior to be maintained as well as acceptable wear of the composition in the tread.

Claims

1. Rubber composition based on at least an elastomer matrix predominantly comprising a highly saturated diene elastomer, carbon black and a tall oil ester plasticizer; the highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene in which the ethylene units represent at least 50 mol% of the monomer units of the copolymer.

2. Rubber composition according to Claim 1, in which the ethylene units represent between 50 mol% and 95 mol% of the monomer units of the copolymer.

3. Rubber composition according to either of the preceding claims, in which the ethylene units represent at least 65 mol% of the monomer units of the copolymer, preferably from 65 mol% to 90 mol% of the monomer units of the copolymer.

4. Rubber composition according to any one of the preceding claims, in which the 1,3-diene is 1,3-butadiene.

5. Rubber composition according to any one of the preceding claims, in which the copolymer is a random copolymer.

6. Rubber composition according to any one of the preceding Claims, in which the content of highly saturated diene elastomer in the rubber composition varies within a range from 80 to 100 phr, preferably from 90 to 100 phr.

7. Rubber composition according to any one of the preceding claims, in which the content of tall oil ester plasticizer is within a range from 5 to 50 phr, preferably from 7 to 40 phr and more preferentially from 8 to 30 phr.

8. Rubber composition according to any one of the preceding claims, in which the aliphatic tall oil ester plasticizer is a compound of formula Tl(OR)3 in which R is a linear or branched alkyl and Tl represents tall oil.

9. Rubber composition according to the preceding claim, in which R is an alkyl comprising from 4 to 20 carbon atoms, preferably from 6 to 12 carbon atoms and more preferentially from 6 to 10 carbon atoms.

10. Rubber composition according to either of Claims 8 and 9, in which the radical R is a branched alkyl, and more preferentially R is an isooctyl radical.

11. Rubber composition according to any one of the preceding claims, in which the tall oil ester plasticizer is the compound isooctyl tallate.

12. Rubber composition according to any one of the preceding claims, in which the carbon black content is between 15 and 65 phr, preferably in the range from 20 to 45 phr.

13. Pneumatic or non-pneumatic tyre casing which comprises a rubber composition defined in any one of Claims 1 to 12, preferably in its tread.