Rubber composition comprising a highly saturated diene elastomer

Abstract

The present invention relates to a rubber composition based on at least one elastomer matrix predominantly comprising a highly saturated diene elastomer, a reinforcing filler, a vulcanisation system and a liquid butadiene polymer functionalised at the chain end by an alkoxysilyl function, optionally partially or completely hydrolysed, having a number-average molar mass (Mn) of 1000 g / mol or greater. The highly saturated diene elastomer is a copolymer of ethylene and of a 1,3-diene in which the ethylene units represent at least 50 mol% of the monomer units of the copolymer.

Description

[0001] Rubber composition comprising a highly saturated diene elastomer

[0002] Technical field

[0003] 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.

[0004] Prior art

[0005] The use of highly saturated diene elastomer is known in the manufacture of tires. For example, the Applicant has described copolymers of ethylene and 1,3-butadiene and their application in a tire tread in document WO2014114607A1. This document indicates that the use of these copolymers in the tread has the effect of conferring good wear resistance and rolling resistance properties to the tire.

[0006] Tire manufacturers are always looking for ways to improve tire performance. This research involves continuously improving the properties of the rubber compounds used to make tires. Tire compounds generally respond to compromises between performance properties that are difficult to reconcile simultaneously (namely, stiffness, which must be high, and rolling resistance, which must be low to minimize fuel consumption). Therefore, it is a constant goal for tire manufacturers to find formulas that improve the balance between all these performance properties.

[0007] In the above-discussed field of tires comprising a highly saturated diene elastomer in the tread, there is a need, particularly under certain heavy load transport conditions, for rubber compositions which give the tire increased stiffness to improve road handling, as well as improved hysteretic properties to minimize rolling resistance.

[0008] It is known to improve the stiffness of a rubber compound for a tire by increasing the reinforcing filler content or by incorporating certain reinforcing resins. However, experience shows that such stiffening penalizes, in a known manner, most often in a prohibitive manner, the rolling resistance properties, accompanied by a significant increase in the hysteretic losses of the rubber compound. Improving stiffness performance while maintaining low rolling resistance is therefore a constant concern for tire designers.

[0009] Statement of the invention

[0010] Continuing its efforts, the Applicant has found a rubber composition that makes it possible to meet this need in the field of application of highly saturated diene elastomers to rubber compositions for tires, and in particular for the tread. In particular, the Applicant has found, against all expectations, a rubber composition that combines the use of a highly saturated diene elastomer with the use of a functionalized liquid butadiene polymer that makes it possible to increase the rigidity while significantly reducing the hysteresis of the composition, whereas a composition using a non-functional liquid polybutadiene degrades these two properties. These improved properties promise to give the tire good rolling resistance properties and improved road behavior, particularly when transporting heavy loads.

[0011] Thus, a first object of the invention is a rubber composition based on at least

[0012] - an elastomer matrix mainly comprising a highly saturated diene elastomer,

[0013] - a reinforcing charge,

[0014] - a vulcanization system and

[0015] - a liquid butadiene polymer functionalized at the end of the chain by an alkoxysilyl function, optionally partially or totally hydrolyzed.

[0016] 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.

[0017] Summary of the invention

[0018] The invention, described in more detail below, relates to at least one of the embodiments listed in the following points:

[0019] 1. Rubber composition based on at least

[0020] - an elastomer matrix comprising mainly a highly saturated diene elastomer, which highly saturated diene elastomer is 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,

[0021] - a reinforcing charge,

[0022] - a vulcanization system and

[0023] - a liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed, having a number-average molar mass (Mn) greater than or equal to 1,000 g / mol.

[0024] 2. Rubber composition according to embodiment 1, in which the ethylene units represent from 50% to 95% by mole of the monomer units of the highly saturated diene copolymer.

[0025] 3. Rubber composition according to any one of the preceding embodiments, in which the ethylene units represent at least 60 mol% of the monomer units of the highly saturated diene copolymer, preferably from 65% to 90 mol% of the monomer units of the highly saturated diene copolymer.

[0026] 4. A rubber composition according to any one of the preceding embodiments, wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene or P-famesene, or a mixture of myrcene and P-famesene, preferably 1,3-butadiene.

[0027] 5. A rubber composition according to any one of the preceding embodiments, wherein the copolymer of ethylene and a 1,3-diene is a copolymer of ethylene and 1,3-butadiene. 6. A rubber composition according to any one of the preceding embodiments, wherein the copolymer is random.

[0028] 7. Rubber composition according to any one of the preceding embodiments, in which the content of the highly saturated diene elastomer varies in a range from 60 to 100 pce, preferably from 80 to 100 pce and very preferably from 90 to 100 pce.

[0029] 8. Composition according to any one of the preceding embodiments in which the liquid butadiene polymer is a liquid polybutadiene functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed.

[0030] 9. Composition according to any one of the preceding embodiments in which the alkoxysilyl functions are functions corresponding to the formula - Si(OR) nR'3-n, wherein each R, independently of the others, denotes a hydrogen atom or a C1-C4 alkyl, each R, independently of the others, denotes a C1-C10 alkyl, preferably a C1-C4 alkyl, and n is an integer from 1 to 3, preferably 3.

[0031] 10. Composition according to any one of the preceding embodiments in which the alkoxysilyl functions are functions corresponding to the formula Si(OR)s, in which each R, independently of the others, denotes a hydrogen atom or a C1-C10 alkyl, preferably a C1-C4 alkyl, preferably a C1-C4 alkyl.

[0032] 11. Composition according to any one of the preceding embodiments in which the alkoxysilyl functions are trimethoxysilyl or triethoxysilyl functions, optionally partially or totally hydrolyzed.

[0033] 12. Composition according to any one of the preceding embodiments in which the functionalized liquid butadiene polymer is functionalized at each end of the main chain by an alkoxysilyl function, optionally partially or totally hydrolyzed.

[0034] 13. Composition according to any one of the preceding embodiments in which the functionalized liquid butadiene polymer is a liquid polybutadiene functionalized at each end of the main chain by an alkoxysilyl function, optionally partially or totally hydrolyzed.

[0035] 14. Composition according to any one of the preceding embodiments in which the rate of liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed, is within a range from 0.5 to 25 pce, preferably from 5 to 15 pce.

[0036] 15. Composition according to any one of the preceding embodiments in which the liquid butadiene polymer has a Tg comprised in a range from -60°C to -100°C, more preferably from -80°C to -100°C.

[0037] 16. Composition according to any one of the preceding embodiments in which the liquid butadiene polymer has a number-average molar mass greater than or equal to 1000 g / mol and less than or equal to 50000 g / mol, preferably less than or equal to 10000 g / mol, even more preferably less than or equal to 5000 g / mol.

[0038] 17. Composition according to any one of the preceding embodiments in which the reinforcing filler comprises at least one silica, one carbon black or a mixture of silica and carbon black.

[0039] 18. Composition according to any one of the preceding embodiments in which the reinforcing filler comprises a silica as the majority reinforcing filler.

[0040] 19. Composition according to any one of the preceding embodiments in which the level of reinforcing filler is within a range from 5 to 150 pce.

[0041] 20. Composition according to any one of the preceding embodiments in which the silica content is within a range from 20 to 60 pce.

[0042] 21. Pneumatic or non-pneumatic tire comprising a composition according to any one of the preceding embodiments.

[0043] 22. Pneumatic or non-pneumatic tire according to the preceding embodiment comprising a composition according to any one of embodiments 1 to 20 in all or part of its tread.

[0044] Definitions

[0045] 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.

[0046] 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.

[0047] 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 designated.

[0048] In the present application, the term "all the monomer units of the elastomer" or "the totality of 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.

[0049] 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 a mass proportion of more than 50%; when the compound represents 100% by mass, it is also referred to as "majority".

[0050] 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, fillers, etc.

[0051] Detailed description of the invention

[0052] 1- Elastomer matrix

[0053] By "elastomer matrix" we mean all the elastomers in the composition.

[0054] According to the invention, the elastomer matrix mainly comprises at least one highly saturated diene elastomer, namely a copolymer containing ethylene units and 1,3-diene units (hereinafter referred to as "the copolymer").

[0055] The highly saturated diene elastomer useful for the purposes of the invention is a copolymer, preferably a statistical copolymer. The term "statistical copolymer" is understood in a known manner to mean a copolymer in which the sequential distribution of the monomer units obeys a known statistical law.

[0056] The highly saturated diene elastomer useful for the purposes of the invention is a copolymer which comprises ethylene units resulting from the polymerization of ethylene. As is known, the expression "ethylene unit" refers to the unit

[0057] -(CH2-CH2)- 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 mol% of all the monomer units of the elastomer. The maximum proportion of ethylene units is fixed by the elastomeric nature of the polymer, this proportion is preferably at most 95 mol%, more preferably at most 90 mol%, even more preferably at most 85 mol%. Thus, preferably, the highly saturated diene elastomer comprises from 50% to 95 mol% of ethylene units, molar percentage calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0058] Preferably, the highly saturated diene elastomer comprises at least 60 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 at least 70 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.

[0059] The highly saturated diene elastomer according to the invention being a copolymer of ethylene and a 1,3-diene, it 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.

[0060] 1,3-diene units are those for example of a 1,3-diene having 4 to 24 carbon atoms.

[0061] Suitable 1,3-dienes include butadiene, isoprene, 2,3-di(C1-C5 alkyl)-1,3-butadiene such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene or 2-methyl-3-isopropyl-1,3-butadiene, aryl-

[0062] 1,3-butadiene such as phenyl-1,3-butadiene, 1,3-pentadiene. Also suitable as 1,3-diene is a 1,3-diene of formula CH2=CR-CH=CH2, in which R represents a hydrocarbon chain having 3 to 20 carbon atoms, such as for example a linear monoterpene (CIOHIÔ), such as myrcene, a linear sesquiterpene (C15H24), such as P-famesene etc....

[0063] The highly saturated diene elastomer is preferably a copolymer of ethylene and a

[0064] 1,3-diene among 1,3-butadiene, isoprene, myrcene, P-famesene and a mixture of myrcene and P-famesene.

[0065] Preferably, the 1,3-diene is 1,3-butadiene or isoprene, more preferably 1,3-butadiene, in which case the highly saturated diene elastomer is a copolymer of ethylene and 1,3-butadiene, preferably random.

[0066] According to the invention, in particular when the first 1,3-diene is 1,3-butadiene or a mixture of 1,3-butadiene and at least one other 1,3-diene, the highly saturated diene elastomer may additionally contain 1,2-cyclohexanediyl units. The presence of these cyclic structures in the copolymer results from a very particular insertion of ethylene and 1,3-butadiene during the polymerization. The content of 1,2-cyclohexanediyl units in the copolymer varies according to the respective contents of ethylene and 1,3-butadiene in the copolymer. The copolymer preferably contains less than 15 mol% of 1,2-cyclohexanediyl unit units.

[0067] 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 1 092 731, WO 2004035639, WO 2007054223 and

[0068] WO 2007054224, as well as WO2020070442, WO2020070443 and WO2020074804 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. The highly saturated diene elastomer is random according to one embodiment of the invention. The highly saturated diene elastomer useful for the purposes of the invention can consist of a mixture of highly saturated diene elastomers which differ from each other by their microstructures or by their macrostructures.

[0069] According to the invention, the level of the highly saturated diene elastomer in the rubber composition is preferably at least 50 parts by weight per hundred parts of elastomer of the rubber composition (phr). More preferably, the level of the highly saturated diene elastomer in the rubber composition varies in a range from 60 to 100 phr, preferably 80 to 100 phr. More preferably, it varies in a range from 90 to 100 phr.

[0070] Additionally, the elastomer matrix of the composition of the invention may comprise at least one other elastomer, in a minority. Particularly noteworthy are the diene elastomers known to those skilled in the art for their use in the field of tires, such as a polybutadiene (abbreviated as "BR"), a synthetic polyisoprene (IR), natural rubber (NR), a butadiene copolymer such as a butadiene-styrene copolymer (SBR), an isoprene copolymer and mixtures of these elastomers.

[0071] 2- Liquid butadiene polymer

[0072] The composition of the invention comprises a liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed, having a number-average molar mass (Mn) greater than or equal to 1,000 g / mol.

[0073] According to the invention, the term "liquid butadiene polymer" means a more or less viscous butadiene polymer which is liquid at room temperature (approximately 23°C below latm), that is to say, as a reminder, having the capacity to eventually take the shape of its container.

[0074] "Butadiene polymer" means a homopolymer or copolymer of butadiene, in other words a diene polymer selected from the group consisting of polybutadienes, different butadiene copolymers and mixtures of these polymers. Among the butadiene copolymers, mention will be made in particular of copolymers of butadiene and a vinylaromatic monomer, preferably styrene.

[0075] Preferably, the liquid butadiene polymer is a liquid polybutadiene.

[0076] According to the invention, the liquid butadiene polymer is functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed. By "chain-end functionalized polymer" is meant a polymer comprising an alkoxysilyl functional group at at least one chain end, i.e. at one end of the main chain of the polymer or at each of the two ends of the main chain of the polymer. Preferably, the liquid butadiene polymer is functionalized by an alkoxysilyl function at each end of the main chain of the polymer, i.e. at both ends of the chain.

[0077] By "alkoxysilyl function, optionally partially or totally hydrolyzed" is meant a function corresponding to the formula - Si(OR) nR'3-n, each R, independently of the others, represents a hydrogen atom or a C1-C10 alkyl radical, preferably C1-C4, or C6-C10 aryl, each R, independently of the others, denotes a C1-C10 alkyl, preferably C1-C4, or C6-C10 aryl, and n is an integer from 1 to 3, preferably 3. Preferably, the alkoxysilyl function is a function corresponding to the formula - Si(OR)s, R being as defined above, preferably a C1-C10 alkyl, more preferably C1-C4. Even more preferably, the alkoxysilyl function is a trimethoxysilyl or triethoxysilyl function, optionally partially or totally hydrolyzed. According to the invention, the alkoxysilyl function, optionally partially or totally hydrolyzed, is linked to the butadiene polymer by a covalent bond or by a group which may comprise one or more heteroatoms chosen from N and O.

[0078] All the preferential and advantageous aspects concerning the functionalized liquid butadiene polymer are combinable according to the invention. Thus, advantageously, the liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function is a functionalized liquid polybutadiene carrying at each end of the main chain a trialkoxysilyl function, preferably trimethoxysilyl or triethoxysilyl, the alkoxysilyl functions optionally being partially or totally hydrolyzed.

[0079] According to the invention, the liquid butadiene polymer functionalized at the end of the chain has a number-average molar mass (Mn) greater than or equal to 1000 g / mol and preferably less than or equal to 50000 g / mol, preferably less than or equal to 10000 g / mol, even more preferably less than or equal to 5000 g / mol. Thus, according to a preferred embodiment, the liquid butadiene polymer functionalized at the end of the chain has a number-average molar mass (Mn) varying from 1000 g / mol to 5000 g / mol.

[0080] Preferably, the liquid butadiene polymer functionalized at the chain end according to the invention also has a Tg in a range from -60°C to -100°C, more preferably from -80°C to -100°C.

[0081] According to the invention, the various preferential characteristics above of the liquid butadiene polymer functionalized at the chain end can be combined with each other.

[0082] The liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function can be obtained in a simple and known manner by functionalization of a liquid telechelic butadiene polymer carrying -OH functions at the chain ends, obtained by radical polymerization, with a functionalization agent of alkoxysilane type capable of reacting with the -OH functions of the polymer. Mention may be made of alkoxysilane compounds carrying an isocyanate function as functionalization agent. Such polymers useful for the purposes of the invention and their synthesis are for example described in document WO2016180649A1.

[0083] The Tg of the liquid polymer is measured by DSC according to ASTM D3418 (1999). The macrostructure (Mw, Mn and IP) of the liquid polymer is determined by size exclusion chromatography (SEC): tetrahydrofuran solvent; temperature 35°C; concentration 1 g / l; flow rate 1 ml / min; solution filtered through a 0.45 pm porosity filter before injection; Moore calibration with polystyrene standards; set of 3 "WATERS" columns in series ("STYRAGEL" HR4E, HR1 and HR0.5); detection by differential refractometer ("WATERS 2410") and its associated operating software ("WATERS EMPOWER").

[0084] Liquid butadiene polymers useful for the purposes of the invention can be found commercially under the names, for example, "POLYVEST EP ST-E 60" and "POLYVEST EP ST-E 100" marketed by the company EVONIK.

[0085] According to any one of the embodiments of the invention, the level of liquid butadiene polymer functionalized at each chain end by an alkoxysilyl function is advantageously greater than or equal to 0.5 phr, preferably within a range from 0.5 phr to 25 phr, preferably from 1 to 20 phr, more preferably from 5 phr to 15 phr. The liquid butadiene polymer functionalized at each chain end by an alkoxysilyl function may be a mixture of several liquid butadiene polymers functionalized at each chain end by an alkoxysilyl function as described above.

[0086] According to one embodiment of the invention, the liquid butadiene polymer functionalized at the chain end by alkoxysilyl functions, optionally partially or totally hydrolyzed, is the only plasticizer in the rubber composition. In other words, the rubber composition does not comprise any other plasticizer than the liquid butadiene polymer functionalized at the chain end by alkoxysilyl functions, optionally partially or totally hydrolyzed.

[0087] 3- Reinforcing charge

[0088] The composition according to the invention comprises a reinforcing filler. Any type of reinforcing filler known for its ability to reinforce a rubber composition suitable for the manufacture of tires may be used, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica, alumina, or a blend of these two types of filler. More particularly, the reinforcing filler comprises at least one silica, one carbon black or a mixture of silica and carbon black.

[0089] Suitable carbon blacks are all carbon blacks, in particular so-called pneumatic grade blacks. Among the latter, we will mention in particular the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as blacks NI 15, N134, N234, N326, N330, N339, N347, N375, or, depending on the intended applications, blacks of higher series (for example N660, N683, N772). The carbon blacks could, for example, already be incorporated into an isoprene elastomer in the form of a masterbatch (see for example applications WO 97 / 36724 or WO 99 / 16600).

[0090] Examples of organic fillers other than carbon blacks include functionalized polyvinyl organic fillers as described in applications WO-A-2006 / 069792, WO-A-2006 / 069793, WO-A-2008 / 003434 and WO-A-2008 / 003435.

[0091] The composition may contain one type of silica or a blend of several silicas. The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area and a CTAB specific surface area both less than 450 m 2 / g, preferably 30 to 400 m 2 / g. As highly dispersible precipitated silicas (called "HDS"), mention may be made, for example, of the silicas "Ultrasil 7000" and "Ultrasil 7005" from the company Degussa, the silicas "Zeosil" 1165MP, 1135MP and 1115MP from the company Solvay, the silica "Hi-Sil EZ150G" from the company PPG, the silicas "Zeopol" 8715, 8745 and 8755 from the company Huber, treated precipitated silicas such as, for example, the silicas "doped" with aluminium described in application EP-A-0735088 or the silicas with a high specific surface area as described in application WO 03 / 16837.

[0092] According to one embodiment of the invention, the reinforcing filler is predominantly an inorganic reinforcing filler (preferably silica), i.e. it comprises more than 50% (>50%) by weight of an inorganic reinforcing filler such as silica relative to the total weight of the reinforcing filler. Optionally, according to this variant, the reinforcing filler also comprises carbon black. According to this option, 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 carbon black rate may be in a range from 0.5 to 20 phr, in particular from 1 to 10 phr). In the indicated ranges, the coloring (black pigmenting agent) and anti-UV properties of carbon blacks are benefited from, without otherwise penalizing the typical performances provided by the reinforcing inorganic filler.

[0093] In this presentation, 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 the standard NF ISO 5794-1, annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - vacuum degassing: one hour at 160°C - relative pressure range p / po: 0.05 to 0.2],

[0094] For inorganic fillers such as silica, for example, the CTAB specific surface area values ​​were determined according to standard NF ISO 5794-1, annex G of June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the reinforcing filler.

[0095] A person skilled in the art will understand that, as a filler equivalent to silica, a reinforcing filler of another nature, in particular organic, could be used, provided that this reinforcing filler is covered with a layer of silica, or else comprises functional sites on its surface, in particular hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer.

[0096] The physical state in which the reinforcing filler is presented is indifferent, whether in the form of powder, microbeads, granules, balls or any other suitable densified form.

[0097] For the purposes of the invention, the total reinforcing filler content (carbon black and / or reinforcing inorganic filler such as silica) is from 5 to 150 phr, more preferably from 20 to 65 phr. Below 5 phr of filler, the composition may not be sufficiently reinforced, while above 150 phr of filler, the composition may be less effective in rolling resistance.

[0098] Preferably, silica is used as the majority filler. Silica preferably represents more than 50% by mass of the reinforcing filler. In other words, the proportion of silica in the reinforcing filler is greater than 50% by weight of the total weight of the reinforcing filler. More preferably, silica represents more than 85% by mass of the reinforcing filler. According to certain preferred embodiments, the silica content varies from 20 phr to 60 phr.

[0099] Carbon black, when present, is then used in a minor manner, preferably at a rate in the range from 0.1 to 10 pce, more preferably from 0.5 to 10 pce, in particular from 1 to 5 pce.

[0100] To couple the reinforcing inorganic filler to the diene elastomer, it is possible to use, in a well-known manner, an at least bifunctional coupling agent (or bonding agent) intended to ensure a sufficient connection, of a chemical and / or physical nature, between the inorganic filler (surface of its particles) and the diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. By "bifunctional", we mean a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer.For example, such a bifunctional compound may comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the diene elastomer. Preferably, the organosilanes are chosen from the group consisting of polysulfurized organosilanes (symmetrical or asymmetrical) such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, marketed under the name "Si69" by the company Evonik or bis-(triethoxysilylpropyl) disulfide, abbreviated to TESPD, marketed under the name "Si75" by the company Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as "NXT-Silane" or "NXT-Z45 Silane" marketed by the company Momentive.Of course, mixtures of these coupling agents could also be used.

[0101] Those skilled in the art will understand that the coupling agent content is dependent on the amount of reinforcing inorganic filler to be coupled to the elastomer. Typically, the coupling agent content represents from 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler, in particular silica.

[0102] The composition according to the invention may optionally also contain coupling activators, agents for covering inorganic fillers or more generally processing aids capable, in a known manner, thanks to an improvement in the dispersion of the filler in the rubber matrix and a reduction in the viscosity of the composition, of improving its processability in the raw state, these agents being known elsewhere.

[0103] 4- Crosslinking system

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] The rubber composition according to the invention may optionally also comprise all or part of the usual additives usually used in elastomer compositions for tires, pigments, protective agents such as anti-ozone waxes, chemical antiozonants, antioxidants, plasticizers, anti-fatigue agents, reinforcing resins (as described for example in application WO 02 / 10269).

[0109] It goes without saying that the invention relates to the rubber compositions previously described both in the so-called "raw" or non-crosslinked state (i.e., before curing) and in the so-called "cured" or crosslinked, or even vulcanized state (i.e., after crosslinking or vulcanization).

[0110] 6- Preparation of the rubber composition

[0111] The composition in accordance with the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:

[0112] - a first thermomechanical working or mixing phase (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 elastomer matrix, the liquid polybutadiene polymer, 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 the applications

[0113] 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 masterbatch are incorporated, as well as any other various additives other than the crosslinking system.

[0114] - a second phase of mechanical work (so-called "productive" phase), which is carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C.

[0115] Such phases are well known to those skilled in the art.

[0116] 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 else extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber usable in a tire, for example as a tread. These products can then be used for the manufacture of tires, according to techniques known to those skilled in the art.

[0117] 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.

[0118] Crosslinking (or curing), and 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. 7 Pneumatic

[0119] The present invention also relates to a pneumatic or non-pneumatic tire comprising a rubber composition according to the invention.

[0120] 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.

[0121] EXAMPLES OF CARRYING OUT THE INVENTION

[0122] 1- Tests and measurements:

[0123] 1-1. Determination of the microstructure of elastomers:

[0124] The microstructure of elastomers is determined by NMR analysis 1 H, supplemented by NMR analysis 13 C when the resolution of the NMR spectra of the X H does not allow the attribution and quantification of all species. Measurements are carried out using a BRUKER 500MHz NMR spectrometer at frequencies of 500.43 MHz for proton observation and 125.83 MHz for carbon observation.

[0125] 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.

[0126] For measurements on soluble elastomers, a liquid NMR probe is used to observe the proton and carbon in proton-decoupled mode.

[0127] The preparation of insoluble samples is carried out in rotors filled with the analyzed material and a deuterated solvent allowing swelling, generally deuterated chloroform (CDCL). 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.

[0128] Soluble samples are dissolved in a deuterated solvent (approximately 25 mg of elastomer in 1 ml), generally deuterated chloroform (CDCL). The solvent or solvent blend used must always be deuterated and its chemical nature can be adapted by those skilled in the art.

[0129] In both cases (soluble sample or swollen sample):

[0130] For proton NMR, a single 30° pulse sequence is used. 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 time between each pulse is adapted to obtain a quantitative measurement.

[0131] 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.

[0132] NMR measurements are carried out at 25°C. 1-2, Determination of the Tg of elastomers

[0133] Glass transition temperature (Tg) values ​​are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999).

[0134] 1-3, Measurement of dynamic properties:

[0135] The dynamic properties G*(25%) and tanômax (25%) at 60°C are measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of crosslinked composition (cylindrical specimen 4 mm thick and 400 mm2 in cross-section) is recorded, subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under the defined temperature conditions, for example at 60°C according to the ASTM D 1349-99 standard. A strain amplitude sweep is carried out from 0.1 to 100% (forward cycle), then from 100% to 0.1% (return cycle). The results used are the complex dynamic shear modulus G* and the loss factor tan(ô). For the return cycle, the value of tan(ô) max at 25% deformation observed at 60°C is indicated, noted tanômax (25%), as well as the complex dynamic shear modulus G* at 25% deformation, at 60°C.

[0136] The tanômax (25%) measurement is a descriptor of hysteresis and therefore an indication of the rolling resistance property of the tire. The value in base 100 is calculated according to the operation: (tanômax (25%) value at 60°C of the control / tanômax (25%) value at 60°C of the sample) * 100. In this way, a lower value than the control represents a decrease in hysteresis performance (i.e. an increase in hysteresis) while a higher value represents a better hysteresis performance (i.e. a lower hysteresis).

[0137] The G* (25%) measurement is a descriptor of stiffness and therefore an indication of the wear resistance property of the tire. The value in base 100 is calculated according to the operation: (G* (25%) value at 60°C of the sample / G* (25%) value at 60°C of the control) * 100. In this way, a lower value than the control represents a decrease in stiffness, while a higher value represents a higher stiffness.

[0138] 2- Preparation of rubber compositions:

[0139] The rubber compositions, the formulation details of which are given in Table 1, were prepared as follows:

[0140] The elastomer is introduced into an internal mixer (final filling rate: approximately 70% by volume), whose initial tank temperature is approximately 90°C. When the temperature reaches 100°C, the liquid butadiene polymer, silica, carbon black and coupling agent are introduced, as well as the various other ingredients except for the sulfur and vulcanization accelerators. Thermomechanical work (non-productive phase) is then carried out in one step, lasting a total of approximately 3 to 4 minutes, until a maximum "drop" temperature of 160°C is reached. The resulting mixture is recovered, cooled and then the sulfur and vulcanization accelerators are incorporated on a cylinder tool at 25°C, mixing everything (productive phase) for an appropriate time (e.g., 5 minutes).

[0141] 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. Crosslinking was then carried out at a temperature of 150°C, under pressure. Preparation of the elastomer

[0142] Elastomer El is a highly saturated diene elastomer, a copolymer of ethylene and 1,3-butadiene prepared according to the following procedure:

[0143] In a 70 L reactor containing methylcyclohexane (64 L), ethylene (5600 g) and 1,3-butadiene (2948 g), butyloctylmagnesium (BOMAG) dissolved in methylcyclohexane and the catalytic system is added. The Mg / Nd ratio is 6.2. The volume of the solution of the catalytic system introduced is 840 mL, the concentration of the catalytic system solution in Nd being 0.0065 M. The reaction temperature is regulated at a temperature of 80 ° C and the polymerization reaction starts. The polymerization reaction proceeds at a constant pressure of 8.3 bar. The reactor is supplied throughout the polymerization with ethylene and 1,3-butadiene in the molar proportions 73 / 27. 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 after steam stripping and drying to constant mass.The polymerization time is 225 minutes. The weighted mass (6.206 kg) allows the average catalytic activity of the catalytic system to be determined, expressed in kilograms of synthesized polymer per mole of neodymium metal per hour (kg / mol.h). The copolymer has an ML value of 62.

[0144] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] at 0.0065 mol / L, a co-catalyst, butyloctylmagnesium (BOMAG) whose BOMAG / Nd molar ratio is equal to 2.2, and a preformed monomer, 1,3-butadiene whose 1,3-butadiene / Nd molar ratio is equal to 90. The medium is heated to 80°C for a period of 5 hours. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 AL

[0145] [Table 1]

[0146] (1) Copolymer of ethylene and 1,3-butadiene containing 74 mol% of ethylene unit, 19 mol% of butadiene unit in the form of 1,2 and 1,4 units and 7 mol% of 1,2-cyclohexanediyl unit, Tg -44°C

[0147] (2) “Zeosil 1165 MP” from Solvay-Rhodia in the form of microbeads

[0148] (3) Carbon black grade N234 according to ASTM Dl 765, from Cabot Company

[0149] (4) Silane Mercapto - Thiocarboxylate Oligomer (“NXT-Z45”) - CAS 922519-17-3 - Momentive company

[0150] (5) LBR-307, Kuraray company (non-functional liquid polybutadiene, Tg -95°C and Mn 8000 g / mol)

[0151] (6) POLYVEST ST E 100 from Evonik (functional liquid polybutadiene with triethoxysilyl at each end of the chain, Tg -80°C and Mn 3300 g / mol)

[0152] (7) Diphenylguanidine “Perkacit DPG” from Flexsys

[0153] (8) Anti-ozone wax “VARAZON 4959” from the company Sasol Wax

[0154] (9) N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine “Santoflex 6PPD” from Flexys

[0155] (10) Stearic acid “Pristerene 4931” from Uniqema

[0156] (11) Industrial grade Zinc Oxide from Umicore

[0157] (12) N-cyclohexyl-2-benzothiazol-sulfenamide “Santocure CBS” from Flexsys

[0158] 3- Results:

[0159] Composition T1 is the control without liquid butadiene polymer to evaluate the effect of the nature of the liquid butadiene polymer used in compositions C1 and C2. Composition C2 is in accordance with the invention.

[0160] The results show that the composition according to the invention, with an elastomer matrix based on an EBR and a liquid polybutadiene functionalized at each chain end by an alkoxysilyl function, makes it possible to significantly improve both the hysteresis performance (reduction in hysteresis) and the rigidity compared with a composition not comprising liquid polybutadiene. This effect is observed against all expectations since the joint use of an EBR and a non-functionalized liquid polybutadiene degrades these two properties. The joint improvement in hysteresis performance and rigidity predicts, for a tire comprising such a composition, a reduction in rolling resistance and improved road holding.

Claims

Claims 1. Rubber composition comprising at least - an elastomer matrix comprising mainly a highly saturated diene elastomer, which highly saturated diene elastomer is 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, - a reinforcing charge, - a vulcanization system and - a liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed, having a number-average molar mass (Mn) greater than or equal to 1,000 g / mol.

2. Rubber composition according to claim 1, in which the ethylene units represent at least 50% and at most 95% by mole of the monomer units of the copolymer, preferably from 65% to 90%.

3. A rubber composition according to any preceding claim, wherein the copolymer of ethylene and a 1,3-diene is a copolymer of ethylene and 1,3-butadiene.

4. Rubber composition according to any one of the preceding claims, in which the level of highly saturated diene elastomer varies in a range from 60 to 100 phr, preferably from 80 to 100 phr, very preferably from 90 to 100 phr.

5. Rubber composition according to any one of the preceding claims in which the functionalized liquid butadiene polymer is a liquid polybutadiene functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed.

6. Rubber composition according to any one of the preceding claims in which the functionalized liquid butadiene polymer is functionalized at each end of the main chain by an alkoxysilyl function, optionally partially or totally hydrolyzed.

7. Rubber composition according to any one of the preceding claims in which the alkoxysilyl function, optionally partially or totally hydrolyzed, corresponds to the formula Si(OR)3, in which each R, independently of the others, denotes a hydrogen atom or a C1-C10 alkyl, preferably C1-C4.

8. Rubber composition according to any one of the preceding claims in which the alkoxysilyl function is a trialkoxysilyl function, preferably trimethoxysilyl or triethoxysilyl, optionally partially or totally hydrolyzed.

9. Rubber composition according to any one of the preceding claims in which the functionalized liquid butadiene polymer is a liquid polybutadiene functionalized at each end of the main chain by a trialkoxysilyl function, preferably trimethoxysilyl or triethoxysilyl, optionally partially or totally hydrolyzed.

10. Rubber composition according to any one of the preceding claims in which the level of liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed, is within a range from 0.5 to 25 phr, preferably from 1 to 20 phr, more preferably from 5 to 15 phr.

11. Rubber composition according to any one of the preceding claims in which the liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed, has a Tg within a range from -60°C to -100°C.

12. Rubber composition according to any one of the preceding claims in which the liquid butadiene polymer functionalized at the chain end by an alkoxysilyl function, optionally partially or totally hydrolyzed, has a number-average molar mass in a range from 1000 g / mol to 5000 g / mol.

13. Rubber composition according to any one of the preceding claims in which the reinforcing filler comprises a silica as the majority reinforcing filler.

14. Rubber composition according to any one of the preceding claims in which the silica content is within a range of 20 to 60 pce.

15. A pneumatic or non-pneumatic tire comprising a rubber composition according to any one of the preceding claims.

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