Rubber composition comprising highly saturated diene elastomer

Abstract

The invention relates to a rubber composition based on at least one elastomer matrix mainly comprising a highly saturated diene elastomer, a reinforcing filler, a vulcanization system and a liquid butadiene polymer functionalized at the chain ends by alkoxysilyl functions, the liquid butadiene polymer has a number average molar mass (Mn) of 1000 g / mol or more, and the alkoxysilyl functional groups are optionally partially or completely hydrolyzed. The highly saturated diene elastomer is a copolymer of ethylene and a 1, 3-diene wherein the ethylene units comprise at least 50 mol% of the monomer units of the copolymer.

Description

Field of the Invention

[0001] The field of the invention is that of rubber compositions based on highly saturated diene elastomers intended for use in tyres, in particular their treads. Background of the Invention

[0002] The use of highly saturated diene elastomers is known in the manufacture of tyres. For example, the applicant has described in document WO2014 / 114607 A1 copolymers of ethylene and 1,3-butadiene and their use in tyre treads. This document shows that the use of these copolymers in the tread gives the tyre good abrasion resistance and rolling resistance properties.

[0003] Tyre manufacturers are constantly looking for solutions to improve tyre performance. This research involves continuously improving the properties of the rubber compositions used to manufacture tyres. The compositions that make up tyres generally satisfy a compromise between performance properties that are difficult to reconcile simultaneously, namely stiffness (which should be high) and rolling resistance (which should be low) in order to minimize fuel consumption. Thus, a constant goal of tyre manufacturers is to find formulations that can improve the balance between all these performance properties.

[0004] In the field of tyres incorporating highly saturated diene elastomers in their treads, in particular under certain conditions of transporting heavy loads, there is a need for a rubber composition that confers on the tyre increased stiffness (thus improving road handling) and improved hysteresis properties (thus minimizing rolling resistance).

[0005] It is known practice to increase the stiffness of rubber compositions for tyres by increasing the content of reinforcing fillers or by introducing certain reinforcing resins. However, experience has shown that such reinforcement has a known and generally unacceptable adverse effect on the rolling resistance properties, while the hysteresis losses of the rubber composition increase significantly. Thus, improving stiffness performance while maintaining low rolling resistance is a constant concern for tyre designers. Summary of the Invention

[0006] As a result of continuous efforts, the applicant has found a rubber composition that is capable of meeting this need in the field of rubber compositions incorporating highly saturated diene elastomers for use in tyres, in particular for their treads. Very particularly, the applicant has unexpectedly found a rubber composition that combines the use of highly saturated diene elastomers with the use of functionalized liquid butadiene polymers and is capable of increasing stiffness while significantly reducing the hysteresis of the composition, while compositions using non-functional liquid polybutadiene make these two properties worse. These improved properties are expected to confer on the tyre good rolling resistance properties and improved road handling, particularly when transporting heavy loads.

[0007] Thus, a first subject of the present invention is a rubber composition which is based at least on:

[0008] - an elastomeric matrix which mainly comprises a highly saturated diene elastomer;

[0009] - a reinforcing filler,

[0010] - a vulcanization system, and

[0011] - a liquid butadiene polymer functionalized at the chain ends by alkoxysilyl groups, the alkoxysilyl groups being optionally partially or completely hydrolyzed.

[0012] Another subject of the present invention is a pneumatic or non-pneumatic tire which comprises the rubber composition according to the present invention, preferably comprising the rubber composition according to the present invention in its tread.

[0013] Summary of the Invention

[0014] The present invention will be described in more detail below, the subject of which at least includes one of the embodiments listed in the following points:

[0015] 1. A rubber composition which is based at least on

[0016] - an elastomeric matrix which mainly comprises a highly saturated diene elastomer which is a copolymer of ethylene and a 1,3-diene, wherein the ethylene units account for at least 50 mol% of the monomer units of the copolymer,

[0017] - a reinforcing filler,

[0018] - a vulcanization system, and

[0019] - a liquid butadiene polymer functionalized at the chain ends by alkoxysilyl groups, the liquid butadiene polymer having a number-average molar mass (Mn) of greater than or equal to 1000 g / mol, the alkoxysilyl groups being optionally partially or completely hydrolyzed.

[0020] 2. The rubber composition according to embodiment 1, wherein the ethylene units account for 50 mol% to 95 mol% of the monomer units of the highly saturated diene copolymer.

[0021] 3. The rubber composition according to any one of the preceding embodiments, wherein the ethylene units account for at least 60 mol% of the monomer units of the highly saturated diene copolymer, preferably 65 mol% to 90 mol% of the monomer units of the highly saturated diene copolymer.

[0022] 4. The rubber composition according to any one of the foregoing embodiments, wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene or β-farnesene, or a mixture of myrcene and β-farnesene, preferably 1,3-butadiene.

[0023] 5. The rubber composition according to any one of the foregoing embodiments, wherein the copolymer of ethylene and 1,3-diene is a copolymer of ethylene and 1,3-butadiene.

[0024] 6. The rubber composition according to any one of the foregoing embodiments, wherein the copolymer is a random copolymer.

[0025] 7. The rubber composition according to any one of the foregoing embodiments, wherein the content of the highly saturated diene elastomer varies in the range of 60 phr to 100 phr, preferably 80 phr to 100 phr, and very preferably 90 phr to 100 phr.

[0026] 8. The composition according to any one of the foregoing embodiments, wherein the liquid butadiene polymer is a liquid polybutadiene functionalized with an alkoxysilyl group at the chain end, and the alkoxysilyl group is optionally partially or completely hydrolyzed.

[0027] 9. The composition according to any one of the foregoing embodiments, wherein the alkoxysilyl group has the formula -Si(OR) n R’ 3-n where each R independently represents a hydrogen atom or a C1-C4 alkyl group, each R’ independently represents a C1-C 10 alkyl group, preferably a C1-C4 alkyl group, and n is an integer from 1 to 3, preferably 3.

[0028] 10. The composition according to any one of the foregoing embodiments, wherein the alkoxysilyl group is a functional group corresponding to the formula Si(OR)3, where each R independently represents a hydrogen atom or a C1-C 10 alkyl group, preferably a C1-C4 alkyl group, preferably a C1-C4 alkyl group.

[0029] 11. The composition according to any one of the foregoing embodiments, wherein the alkoxysilyl group is a trimethoxysilyl group or a triethoxysilyl group, which is optionally partially or completely hydrolyzed.

[0030] 12. The composition according to any one of the foregoing embodiments, wherein the functionalized liquid butadiene polymer is functionalized with an alkoxysilyl group at each end of the main chain, and the alkoxysilyl group is optionally partially or completely hydrolyzed.

[0031] 13. A composition according to any one of the foregoing embodiments, wherein the functionalized liquid butadiene polymer is a liquid polybutadiene functionalized with alkoxysilyl groups at each end of the main chain, and the alkoxysilyl groups are optionally partially or completely hydrolyzed.

[0032] 14. A composition according to any one of the foregoing embodiments, wherein the content of the liquid butadiene polymer functionalized with alkoxysilyl groups (which are optionally partially or completely hydrolyzed) at the chain ends is in the range of 0.5 phr to 25 phr, preferably 5 phr to 15 phr.

[0033] 15. A composition according to any one of the foregoing embodiments, wherein the Tg of the liquid butadiene polymer is in the range of -60 °C to -100 °C, more preferably -80 °C to -100 °C.

[0034] 16. A composition according to any one of the foregoing embodiments, wherein the number-average molar mass of the liquid butadiene polymer is 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, and even more preferably less than or equal to 5000 g / mol.

[0035] 17. A composition according to any one of the foregoing embodiments, wherein the reinforcing filler at least comprises silica, carbon black, or a mixture of silica and carbon black.

[0036] 18. A composition according to any one of the foregoing embodiments, wherein the reinforcing filler comprises silica as the main reinforcing filler.

[0037] 19. A composition according to any one of the foregoing embodiments, wherein the content of the reinforcing filler is in the range of 5 phr to 150 phr.

[0038] 20. A composition according to any one of the foregoing embodiments, wherein the content of silica is in the range of 20 phr to 60 phr.

[0039] 21. A pneumatic tire or a non-pneumatic tire, the pneumatic tire or non-pneumatic tire comprising a composition according to any one of the foregoing embodiments.

[0040] 22. A pneumatic tire or a non-pneumatic tire according to the previous embodiment, the pneumatic tire or non-pneumatic tire comprising a composition according to any one of Embodiments 1 to 20 in all or part of its tread.

[0041] Definitions

[0042] The expression "the composition is based on" should be understood to mean that the composition comprises a mixture of the various components used and / or in-situ reaction products, some of which are capable of reacting and / or are intended to react at least in part with each other during the various stages of the manufacture of the composition; thus, the composition can be in a fully or partially crosslinked state, or in an uncrosslinked state.

[0043] For the purposes of the present invention, the expression "parts by weight / per hundred parts by weight of elastomer" (or phr) should be understood to mean parts by mass / per hundred parts by mass of elastomer.

[0044] Furthermore, any numerical interval expressed by the expression "between a and b" represents a numerical range extending from greater than a to less than b (i.e., the limits a and b are not included), while any numerical interval expressed by the expression "a to b" means a numerical range extending from a up to b (i.e., the strict limits a and b are included). In the present context, when a numerical interval is expressed by the expression "a to b", the interval expressed by the expression "between a and b" is also meant.

[0045] In the present application, the expression "all monomer units of the elastomer" or "total amount of monomer units of the elastomer" means all the constitutive repeating units of the elastomer resulting from the insertion of monomers into the elastomer chains by polymerization. Unless otherwise stated, the content of monomer units or repeating units in a highly saturated diene elastomer is given as a mole percentage calculated on the basis of all the monomer units of the elastomer.

[0046] When referring to a "major" compound, for the purposes of the present invention, it is understood to mean that among the compounds of the same type in the composition, this compound is the major one, i.e., the compound that is present in the largest amount by weight among the compounds of the same type. Thus, for example, the major elastomer is the elastomer that represents the largest weight relative to the total weight of the elastomers in the composition. In the same way, the "major" filler is the filler that represents the largest weight among the fillers of the composition. By way of example, in a system comprising only one elastomer, for the purposes of the present invention, said elastomer is major, and in a system comprising two elastomers, the major elastomer represents more than half of the weight of the elastomers. Conversely, a "minor" compound is a compound that does not represent the largest weight fraction among the compounds of the same type. Preferably, "major" is understood to mean a weight proportion greater than 50%; when the compound represents 100% by weight, it is also referred to as "major".

[0047] The compounds mentioned in the description can be compounds of fossil origin or can be biobased compounds. In the case where the compounds are biobased compounds, they can be partially or completely derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned can also be derived from the recycling of pre-used materials, i.e., they can be partially or completely derived from recycling processes or partially or completely obtained through starting materials that themselves are derived from recycling processes. They are in particular polymers, fillers, etc.

[0048] Detailed description of the invention

[0049] 1 - Elastomeric matrix

[0050] The term "elastomeric matrix" means all the elastomers of the composition.

[0051] According to the invention, the elastomeric matrix mainly comprises at least one highly saturated diene elastomer, i.e., a copolymer comprising ethylene units and 1,3-diene units (hereinafter referred to as "copolymer").

[0052] The highly saturated diene elastomers useful for the purposes of the present invention are copolymers, preferably random copolymers. In a known manner, the term "random copolymer" is understood to mean a copolymer in which the sequential distribution of the monomer units follows known statistical laws.

[0053] The highly saturated diene elastomers useful for the purposes of the present invention are copolymers comprising ethylene units resulting from the polymerization of ethylene. In a known manner, the term "ethylene unit" refers to the -(CH2-CH2)- unit obtained by inserting ethylene into the elastomeric chain. Since the ethylene units account for at least 50 mol% of all the monomer units of the elastomer, the highly saturated diene elastomers are rich in ethylene units. The maximum proportion of ethylene units is set by the elastomeric properties of the polymer; this proportion is preferably at most 95 mol%, more preferably at most 90 mol%, still more preferably at most 85 mol%. Thus, preferably, the highly saturated diene elastomer comprises 50 mol% to 95 mol% of ethylene units, the mole percentages being calculated based on all the monomer units of the highly saturated diene elastomer.

[0054] Preferably, the highly saturated diene elastomer comprises at least 60 mol% of ethylene units. In other words, the ethylene units preferably account for 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 65 mol% to 90 mol% of ethylene units, the mole percentages being calculated based on all the monomer units of the highly saturated diene elastomer.

[0055] Since the highly saturated diene elastomer according to the invention is a copolymer of ethylene and a 1,3-diene, it also contains 1,3-diene units resulting from the polymerization of the 1,3-diene. In a known manner, the expression "1,3-diene unit" means the unit resulting from the insertion of a 1,3-diene.

[0056] The 1,3-diene units are, for example, 1,3-diene units of a 1,3-diene containing 4 to 24 carbon atoms.

[0057] The following are particularly suitable as 1,3-dienes: butadiene, isoprene, 2,3-di(C1-C5 alkyl)-1,3-butadienes (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-1,3-butadienes (such as, for example, phenyl-1,3-butadiene) or 1,3-pentadiene. The following are also suitable as 1,3-dienes: 1,3-dienes of the formula CH2=CR-CH=CH2 (wherein R represents a hydrocarbon chain containing 3 to 20 carbon atoms), such as, for example, linear monoterpenes (C 10 H 16 )(such as, for example, myrcene), linear sesquiterpenes (C 15 H 24 )(such as, for example, β-farnesene), etc.

[0058] The highly saturated diene elastomer is preferably a copolymer of ethylene and a 1,3-diene selected from 1,3-butadiene, isoprene, myrcene and β-farnesene and mixtures of myrcene and β-farnesene.

[0059] 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 a random copolymer.

[0060] According to the invention, especially 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 can also contain 1,2-cyclohexanediyl units. The presence of these cyclic structures in the copolymer is caused by a very specific insertion of ethylene and 1,3-butadiene during the polymerization process. 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 units.

[0061] Highly saturated diene elastomers useful for the purposes of the present invention can be obtained according to various synthesis methods known to those skilled in the art, in particular according to the target microstructure of the highly saturated diene elastomer. Generally, it can be prepared, in particular, by copolymerization of at least one 1,3-diene (preferably 1,3-butadiene) and ethylene according to known synthesis methods in the presence of a catalytic system comprising a metallocene complex. In this regard, mention may be made of catalytic systems based on metallocene complexes, which are described in the documents EP 1092731, WO 2004 / 035639, WO 2007 / 054223 and WO 2007 / 054224 as well as WO 2020 / 070442, WO 2020 / 070443 and WO 2020 / 074804 in the name of the applicant. The highly saturated diene elastomer can also be prepared by using a preformed type of catalytic system (such as the catalytic systems described in the documents WO 2017 / 093654 A1, WO 2018 / 020122A1 and WO2018 / 020123 A1). According to one embodiment of the present invention, the highly saturated diene elastomer is random.

[0062] The highly saturated diene elastomer useful for the purposes of the present invention can consist of a mixture of highly saturated diene elastomers with different microstructures or macrostructures from each other.

[0063] According to the present invention, the content of the highly saturated diene elastomer in the rubber composition is preferably at least 50 parts by weight per 100 parts by weight of elastomer of the rubber composition (phr). More preferably, the content of the highly saturated diene elastomer in the rubber composition varies in the range of 60 phr to 100 phr, preferably 80 phr to 100 phr. More preferably, it varies in the range of 90 phr to 100 phr.

[0064] In addition, the elastomer matrix of the composition of the present invention can contain a small amount of at least one other elastomer. In particular, diene elastomers known to those skilled in the art for use in the tire field, such as polybutadiene (abbreviated as "BR"), synthetic polyisoprene (IR), natural rubber (NR), butadiene copolymers (such as butadiene-styrene copolymer (SBR)), isoprene copolymers, and mixtures of these elastomers.

[0065] 2 - Liquid butadiene polymer

[0066] The composition of the present invention contains a liquid butadiene polymer functionalized with an alkoxysilyl group at the chain end, the liquid butadiene polymer having a number average molar mass (Mn) greater than or equal to 1000 g / mol, and the alkoxysilyl group is optionally partially or completely hydrolyzed.

[0067] The "liquid butadiene polymer" according to the present invention is understood to mean a relatively viscous butadiene polymer that is liquid at ambient temperature (about 23 °C, 1 atm), i.e., as a reminder, it has the ability to ultimately assume the shape of its container.

[0068] "Butadiene polymer" is understood to mean a butadiene homopolymer or copolymer, in other words, a diene polymer selected from polybutadiene, various butadiene copolymers, and mixtures of these polymers. Among the butadiene copolymers, mention will be made in particular of copolymers of butadiene and vinyl aromatic monomers (preferably styrene).

[0069] Preferably, the liquid butadiene polymer is liquid polybutadiene.

[0070] According to the present invention, the liquid butadiene polymer is functionalized at the chain ends with alkoxysilyl groups, which are optionally partially or completely hydrolyzed. The expression "polymer functionalized at the chain ends" is understood to mean a polymer that contains alkoxysilyl groups at at least one chain end (i.e., at one end of the polymer backbone or at each of the two ends of the polymer backbone). Preferably, the liquid butadiene polymer is functionalized at each end of the polymer backbone (i.e., at the two ends of the chain) with alkoxysilyl groups.

[0071] "Optionally partially or completely hydrolyzed alkoxysilyl group" is understood to mean a functional group corresponding to the formula -Si(OR) n R’ 3-n where each R independently represents a hydrogen atom or a C1-C 10 alkyl group, preferably a C1-C4 alkyl group or a C6-C 10 aryl group, each R’ independently represents a C1-C 10 alkyl group, preferably a C1-C4 alkyl group or a C6-C 10 aryl group, and n is an integer from 1 to 3, preferably 3. Preferably, the alkoxysilyl group is a functional group corresponding to the formula -Si(OR)3, where R is as defined above, preferably a C1-C 10 alkyl group, more preferably a C1-C4 alkyl group. Even more preferably, the alkoxysilyl group is a trimethoxysilyl group or a triethoxysilyl group, which is optionally partially or completely hydrolyzed.

[0072] According to the present invention, the alkoxysilyl group (which is optionally partially or completely hydrolyzed) is bonded to the butadiene polymer by a covalent bond or by a group that may contain one or more heteroatoms selected from N and O.

[0073] According to the present invention, all preferred and advantageous aspects regarding the functionalized liquid butadiene polymers can be combined. Thus, advantageously, the liquid butadiene polymer functionalized at the chain ends with alkoxysilyl groups is a functionalized liquid polybutadiene having trialkoxysilyl groups (preferably trimethoxysilyl groups or triethoxysilyl groups) at each end of the main chain, and the alkoxysilyl groups can be optionally partially or completely hydrolyzed.

[0074] According to the present invention, the number average molar mass (Mn) of the liquid butadiene polymer functionalized at the chain ends is 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, and still more preferably less than or equal to 5000 g / mol. Thus, according to a preferred embodiment, the number average molar mass (Mn) of the liquid butadiene polymer functionalized at the chain ends ranges from 1000 g / mol to 5000 g / mol.

[0075] Preferably, the liquid butadiene polymer functionalized at the chain ends according to the present invention also has a Tg in the range of -60 °C to -100 °C, more preferably -80 °C to -100 °C.

[0076] According to the present invention, the various above-mentioned preferred features of the liquid butadiene polymer functionalized at the chain ends can be combined with each other.

[0077] The liquid butadiene polymer functionalized at the chain ends with alkoxysilyl groups can be obtained in a simple and known manner by functionalizing a telechelic liquid butadiene polymer having -OH groups at the chain ends obtained by radical polymerization with a functionalizing agent of the alkoxysilane type capable of reacting with the -OH groups of the polymer. As the functionalizing agent, alkoxysilane compounds bearing isocyanate groups can be mentioned. Such polymers and their synthesis for the purposes of the present invention are described, for example, in the document WO2016180649A1.

[0078] The Tg of the liquid polymer is measured by DSC according to standard ASTM D3418 (1999). The macrostructure (Mw, Mn and IP) of the liquid polymer is determined by size exclusion chromatography (SEC); the solvent is tetrahydrofuran; the temperature is 35 °C; the concentration is 1 g / l; the flow rate is 1 ml / min; before injection, the solution is filtered through a filter with a porosity of 0.45 μm; molar calibration is carried out using polystyrene standards; a set of 3 Waters columns in series (Styragel HR4E, HR1 and HR0.5); detection is carried out by a differential refractometer (Waters 2410) and its associated operating software (Waters Empower).

[0079] Liquid butadiene polymers useful for the purposes of the present invention are commercially available, for example sold by Evonik under the names "POLYVEST EP ST-E 60" and "POLYVEST EP ST-E 100".

[0080] According to any one of the embodiments of the present invention, the content of the liquid butadiene polymer functionalized with alkoxysilyl groups at each chain end is advantageously greater than or equal to 0.5 phr, preferably in the range of 0.5 phr to 25 phr, more preferably 1 phr to 20 phr, and even more preferably 5 phr to 15 phr.

[0081] The liquid butadiene polymer functionalized with alkoxysilyl groups at each chain end can be a mixture of various liquid butadiene polymers functionalized with alkoxysilyl groups at each chain end as described above.

[0082] According to one embodiment of the present invention, the liquid butadiene polymer functionalized at the chain ends with alkoxysilyl groups (which are optionally partially or fully hydrolyzed) is the sole plasticizer of the rubber composition. In other words, the rubber composition does not contain any plasticizer other than the liquid butadiene polymer functionalized at the chain ends with alkoxysilyl groups (which are optionally partially or fully hydrolyzed).

[0083] 3 - Reinforcing filler

[0084] The composition according to the present invention comprises a reinforcing filler. Any type of reinforcing filler known to be capable of reinforcing rubber compositions useful for the manufacture of tires can be used, such as organic fillers (e.g., carbon black), reinforcing inorganic fillers (e.g., silica or alumina), or blends of fillers of these two types. More specifically, the reinforcing filler comprises at least silica, carbon black, or a mixture of silica and carbon black.

[0085] All carbon blacks (especially "tire grade" carbon blacks) are suitable as carbon black. Among the "tire grade" carbon blacks, reinforcing carbon blacks of the 100, 200, or 300 series (ASTM grade) will be more particularly mentioned (e.g., N115, N134, N234, N326, N330, N339, N347, or N375 carbon black), or higher series carbon blacks depending on the target application (e.g., N660, N683, or N772). The carbon black can, for example, already have been introduced into an isoprene elastomer in masterbatch form (see, for example, applications WO 97 / 36724 and WO 99 / 16600).

[0086] As an example of an organic filler other than carbon black, mention may be made of functionalized vinyl organic fillers, such as those described in applications WO-A-2006 / 069792, WO-A-2006 / 069793, WO-A-2008 / 003434 and WO-A-2008 / 003435.

[0087] The composition may comprise 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 silica or pyrogenic silica having a BET specific surface area and a CTAB specific surface area both less than 450 m 2 / g, preferably from 30 m 2 / g to 400 m 2 / g. As highly dispersible precipitated silica (“HDS”), mention may be made, for example, of Ultrasil 7000 and Ultrasil 7005 silica from Degussa, Zeosil 1165MP, 1135MP and 1115MP silica from Solvay, Hi-Sil EZ150G silica from PPG, Zeopol 8715, 8745 and 8755 silica from Huber, treated precipitated silica (such as, for example, silica “doped” with aluminium as described in application EP-A-0735088) or silica having a high specific surface area as described in application WO 03 / 16837.

[0088] According to one embodiment of the invention, the reinforcing filler is mainly an inorganic reinforcing filler (preferably silica); that is to say, relative to the total weight of the reinforcing filler, the reinforcing filler comprises more than 50% by weight (> 50% by weight) of inorganic reinforcing filler (such as silica). Optionally, according to this variant, the reinforcing filler also comprises carbon black. According to this choice, the carbon black is used in an amount less than or equal to 20 phr, more preferably less than or equal to 10 phr (for example, the carbon black content may be in the range from 0.5 phr to 20 phr, in particular from 1 phr to 10 phr). Within the indicated ranges, the coloring properties (black colorant) and the anti-ultraviolet properties of the carbon black are exploited without impairing the typical properties provided by the reinforcing inorganic filler.

[0089] In the present application, 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), more specifically according to the method from Annex E of the standard NF ISO 5794-1 from June 2010 [multi-point (5 points) volume method - gas: nitrogen - vacuum degassing: 1 hour at 160 °C - relative pressure p / p0 range: 0.05 to 0.2].

[0090] For inorganic fillers (such as silica), the CTAB specific surface value is determined, for example, according to Annex G of the standard NF ISO 5794-1 from June 2010. The method is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the “outer” surface of the filler.

[0091] Those skilled in the art will understand that as a filler equivalent to silica, a reinforcing filler of another nature (especially of organic nature) can be used, provided that the reinforcing filler is covered with a silica layer or contains functional sites (especially hydroxyl sites) on its surface for which a coupling agent is required to establish a bond between the filler and the elastomer.

[0092] It is not important in what physical state the reinforcing filler is provided, whether in the form of powder, microbeads, granules, beads or any other suitable densified form.

[0093] For the purposes of the present invention, the total content of the reinforcing filler (carbon black and / or reinforcing inorganic filler (such as silica)) is from 5 phr to 150 phr, more preferably from 20 phr to 65 phr. When the filler is less than 5 phr, the composition may not be sufficiently reinforced, while when the filler is greater than 150 phr, the composition may be less effective in terms of rolling resistance.

[0094] Preferably, silica is used as the main filler. Silica preferably represents more than 50% by weight 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 weight of the reinforcing filler. According to certain preferred embodiments, the silica content varies from 20 phr to 60 phr.

[0095] When carbon black is present, it is used in a smaller amount, preferably in the range from 0.1 phr to 10 phr, more preferably from 0.5 phr to 10 phr, especially from 1 phr to 5 phr.

[0096] In order to couple reinforcing inorganic fillers to a diene elastomer, at least a bifunctional coupling agent (or binder) designed to provide a satisfactory chemical and / or physical bond between the inorganic filler (on the surface of its particles) and the diene elastomer can be used in a known manner. In particular, at least bifunctional silanes or polyorganosiloxanes are used. The term "bifunctional" refers to 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 can contain a first functional group containing a silicon atom and a second functional group containing a sulfur atom, the first functional group being capable of interacting with the hydroxyl groups of the inorganic filler and the second functional group being capable of interacting with the diene elastomer.

[0097] Preferably, the silane is selected from (symmetric or asymmetric) organosilane polysulfides (such as bis(3-triethoxysilylpropyl)tetrasulfide (abbreviated as TESPT) sold by Evonik under the name Si69, or bis(triethoxysilylpropyl)disulfide (abbreviated as TESPD) sold by Evonik under the name Si75), polyorganosiloxanes, mercapto silanes and capped mercapto silanes (e.g., NXT-Silane or NXT-Z45Silane sold by Momentive). Of course, mixtures of these coupling agents can also be used.

[0098] Those skilled in the art will understand that the content of the coupling agent depends on the amount of reinforcing inorganic filler to be coupled to the elastomer. Generally, the content of the coupling agent is from 0.5% to 15% by weight relative to the amount of the reinforcing inorganic filler (especially silica).

[0099] The composition according to the invention may also optionally contain a coupling activator, a reagent for covering the inorganic filler or more generally a processing aid, which is capable of reducing the viscosity of the composition by improving the dispersion of the filler in the rubber matrix in a known manner and improving its ability to be processed in the uncured state. Moreover, these reagents are known.

[0100] 4 - Crosslinking system

[0101] The crosslinking system can be of any type known to those skilled in the art in the field of rubber compositions for tires. The crosslinking system can be particularly based on sulfur and / or peroxides and / or bismaleimides.

[0102] Preferably, the crosslinking system is based on sulfur; it is then called a vulcanization system. Sulfur can be provided in any form (in particular in the form of elemental sulfur or sulfur donors). It is also preferred to have at least one vulcanization accelerator, and optionally, various known vulcanization activators or known vulcanization retarders can also be used, such as zinc oxide, stearic acid or equivalent compounds (such as stearates) and transition metal salts, guanidine derivatives (in particular diphenylguanidine).

[0103] Sulfur is used in a content preferably between 0.2 phr and 10 phr, more preferably between 0.3 phr and 5 phr. A vulcanization accelerator or a mixture of vulcanization accelerators is used in a content preferably between 0.5 phr and 10 phr, more preferably between 0.5 phr and 5 phr.

[0104] As the accelerator, any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used, in particular accelerators of the thiazole type and their derivatives, or sulfenamides, thiurams, dithiocarbamates, dithiophosphates, thioureas and xanthates. As examples of such accelerators, the following compounds can be particularly mentioned: 2-mercaptobenzothiazole disulfide (abbreviated as MBTS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazole sulfenamide (DCBS), N-(tert-butyl)-2-benzothiazole sulfenamide (TBBS), N-(tert-butyl)-2-benzothiazole sulfimide (TBSI), tetrabenzylthiuram disulfide (TBZTD), zinc dibenzyldithiocarbamate (ZBEC) and mixtures of these compounds.

[0105] 5 - Additive

[0106] The rubber composition according to the invention may also optionally contain all or part of the common additives usually used in elastomeric compositions for tires: pigments, protective agents (such as antiozonant waxes, chemical antiozonants, antioxidants), plasticizers, antifatigue agents, reinforcing resins (as described, for example, in application WO 02 / 10269).

[0107] The present invention obviously relates to the aforementioned rubber composition in the "uncured" or uncrosslinked state (i.e., before curing) and in the "cured" or crosslinked (or vulcanized) state (i.e., after crosslinking or vulcanization).

[0108] 6 - Preparation of rubber composition

[0109] The composition according to the invention can be manufactured in two successive preparation stages known to those skilled in the art in a suitable mixer:

[0110] - The first stage of thermomechanical processing or kneading (referred to as the "non-production" stage), which can be carried out in a single thermomechanical step, during which all the necessary components (especially the elastomeric matrix, polybutadiene liquid polymer, reinforcing fillers, and various other optional additives other than the crosslinking system) are introduced into a suitable mixer (such as a standard enclosed mixer (such as a "Banbury" type)). Optional fillers can be introduced into the elastomer either all at once or in batches during thermomechanical kneading. In the case where the fillers have been introduced wholly or partly into the elastomer in the form of a masterbatch (for example, as described in patent applications WO 97 / 36724 or WO 99 / 16600), what is introduced is the directly kneaded masterbatch, other elastomers or fillers (where appropriate) present in the composition that are not in the form of a masterbatch, and various other optional additives other than the crosslinking system.

[0111] - After cooling the mixture obtained during the first non-production stage to a lower temperature (usually below 120 °C), the second stage of mechanical processing ("production" stage) is carried out in an open mixer (such as a mill).

[0112] These stages are well known to those skilled in the art.

[0113] The final composition thus obtained is then calendered into the form of, for example, a film or sheet (especially for laboratory characterization), or extruded (or co-extruded with another rubber composition) into the form of a rubber semi-finished product (or molded element) that can be used for a tire (such as for use as a tread). Subsequently, tires can be manufactured using these products according to techniques known to those skilled in the art.

[0114] The composition can be in an uncured state (before crosslinking or vulcanization) or a cured state (after crosslinking or vulcanization), or can be a semi-finished product that can be used for a tire.

[0115] Crosslinking (or curing) (vulcanization where appropriate) is generally carried out in a known manner at a temperature between 130 °C and 200 °C for a sufficient time, which can vary, for example, between 5 minutes and 90 minutes, and depends in particular on the curing temperature, the crosslinking system employed, and the crosslinking kinetics of the composition under consideration.

[0116] 7 - Tire

[0117] Another subject of the present invention is a pneumatic tire or non-pneumatic tire that comprises a rubber composition according to the present invention. Detailed Description

[0118] The above and other features of the present invention will be better understood by reading the following description of multiple exemplary embodiments of the present invention given as non - limiting illustrations.

[0119] Exemplary embodiments of the present invention

[0120] 1 - Testing and measurement:

[0121] 1 - 1. Determination of elastomeric microstructure:

[0122] By 1 1H NMR analysis, the microstructure of the elastomer is determined. When 1 the resolution of the 1H NMR spectrum cannot achieve the identification and quantification of all species, then it is replaced by 13 13C NMR analysis. Measurements are carried out using a Bruker 500 MHz NMR spectrometer at a frequency of 500.43 MHz for observing protons and 125.83 MHz for observing carbon.

[0123] For elastomers that are insoluble in solvents but have the ability to swell, a 4 mm z - level HRMAS probe is used to observe protons and carbon in proton - decoupling mode. Spectra are acquired at a spinning speed of 4000 Hz to 5000 Hz.

[0124] For the measurement of soluble elastomers, a liquid NMR probe is used to observe protons and carbon in proton - decoupling mode.

[0125] Insoluble samples are prepared in a rotor filled with the analyzed material and a deuterated solvent that enables swelling (usually deuterated chloroform (CDCl3)). The solvent used must always be deuterated, and its chemical properties can be adjusted by those skilled in the art. The amount of the material used is adjusted to obtain a spectrum with sufficient sensitivity and resolution.

[0126] Soluble samples are dissolved in a deuterated solvent (usually deuterated chloroform (CDCl3)) (about 25 mg of elastomer in 1 ml). The solvent or solvent blend used must always be deuterated, and its chemical properties can be adjusted by those skilled in the art.

[0127] In both cases (soluble samples or swollen samples):

[0128] For proton NMR, a 30° single - pulse sequence is used. The spectral window is adjusted to observe all resonance lines belonging to the analyzed molecule. The number of accumulations is adjusted to obtain a sufficient signal - to - noise ratio for quantifying each unit. The recycle delay between each pulse is adjusted to obtain a quantitative measurement.

[0129] For carbon NMR, a 30° single pulse sequence was used and proton decoupling was carried out only during acquisition to avoid the nuclear Overhauser effect (NOE) and maintain quantification. The spectral window was adjusted to observe all resonance lines belonging to the molecule being analyzed. The number of accumulations was adjusted to obtain a sufficient signal-to-noise ratio to quantify each unit. The recycle delay between each pulse was adjusted to obtain quantitative measurements.

[0130] NMR measurements were carried out at 25 °C.

[0131] 1 - 2. Determination of Tg of elastomer

[0132] The value of the glass transition temperature (Tg) was measured by DSC (differential scanning calorimetry) in a known manner according to standard ASTM D3418 (1999).

[0133] 1 - 3. Measurement of dynamic properties:

[0134] The dynamic properties G*(25%) and tan δ at 60 °C were measured on a viscometer (Metravib VA4000) according to standard ASTM D 5992-96. max (25%). According to standard ASTM D 1349-99, the response of a crosslinked composition sample (cylindrical specimen with a thickness of 4 mm and a cross-section of 400 mm 2 subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz under defined temperature conditions (e.g., at 60 °C)) was recorded. A strain amplitude sweep was carried out from 0.1% to 100% (outward cycle) and then from 100% to 0.1% (return cycle). The results utilized were the complex dynamic shear modulus G* and the loss factor tan(δ). For the return cycle, the value of tan(δ) at 25% strain observed at 60 °C max was shown (denoted as tanδ max (25%)) and the complex dynamic shear modulus G* at 25% strain at 60 °C.

[0135] tanδ max (25%) measured values are descriptors of hysteresis and thus are indicators of the rolling resistance properties of tires. The value in base 100 was calculated according to the following operation: (control tanδ max (25%) value at 60 °C / sample tanδ max (25%) value at 60 °C) * 100. In this way, values less than the control indicate a reduction in hysteresis performance (i.e., an increase in hysteresis), while higher values indicate better hysteresis performance (i.e., lower hysteresis).

[0136] The G*(25%) measurement is a descriptor of stiffness and thus an indication of the abrasion resistance properties of the tire. The value in base 100 is calculated according to the following operation: (G*(25%) value of the sample at 60 °C / G*(25%) value of the control at 60 °C) * 100. In this way, a value less than that of the control indicates a reduction in stiffness, while a higher value indicates greater stiffness.

[0137] 2 - Preparation of rubber composition:

[0138] A rubber composition is prepared in the following manner, and Table 1 gives the details of its formulation:

[0139] The elastomer is introduced into a closed mixer with an initial vessel temperature of approximately 90 °C (final filling degree: approximately 70% by volume). When the temperature reaches 100 °C, the butadiene liquid polymer, silica, carbon black, and coupling agent, as well as various other components except sulfur and vulcanization accelerators, are introduced. Then, thermomechanical processing (non-production stage) is carried out in one step, which lasts for approximately 3 to 4 minutes in total until a maximum "discharge" temperature of 160 °C is reached. The mixture thus obtained is recovered and cooled, and then sulfur and vulcanization accelerators are introduced into a two-roll mill at 25 °C, and all the substances are mixed for an appropriate time (e.g., 5 minutes) (production stage).

[0140] Subsequently, the composition thus obtained is calendered into the form of a rubber sheet (thickness 2 mm to 3 mm) or a rubber film for measuring their physical or mechanical properties. Then, crosslinking is carried out under pressure at a temperature of 150 °C.

[0141] Preparation of elastomer

[0142] The elastomer E1 is a highly saturated diene elastomer (copolymer of ethylene and 1,3-butadiene) prepared according to the following steps:

[0143] The butyloctylmagnesium (BOMAG) and the catalyst system in methylcyclohexane solution were added to a 70 l reactor containing methylcyclohexane (64 l), ethylene (5600 g) and 1,3-butadiene (2948 g). The Mg / Nd ratio was 6.2. The volume of the introduced catalyst system solution was 840 ml, and the concentration of Nd in the catalyst system solution was 0.0065 M. The reaction temperature was adjusted to 80 °C, and the polymerization reaction began. The polymerization reaction was carried out at a constant pressure of 8.3 bar. Throughout the polymerization process, ethylene and 1,3-butadiene with a molar ratio of 73 / 27 were fed into the reactor. The polymerization reaction was terminated by cooling, degassing the reactor and adding ethanol. An antioxidant was added to the polymer solution. After steam stripping and drying to a constant mass, the copolymer was recovered. The polymerization time was 225 minutes. The weighed mass (6.206 kg) was used to determine the average catalytic activity of the catalyst system (expressed in kg of polymer synthesized per mole of neodymium metal per hour (kg / mol·h)). The ML value of the copolymer was equal to 62.

[0144] The catalyst system was a preformed catalyst system. The catalyst system was prepared from metallocene [Me2Si(Flu)2Nd(μ-BH4)2Li(THF)] at a concentration of 0.0065 mol / l, the cocatalyst butyloctylmagnesium (BOMAG) (the BOMAG / Nd molar ratio was equal to 2.2), and the preformed monomer 1,3-butadiene (the 1,3-butadiene / Nd molar ratio was equal to 90) in methylcyclohexane. The medium was heated at 80 °C for 5 h. It was prepared according to the preparation method in Section II.1 of Patent Application WO 2017 / 093654 A1.

[0145] [Table 1]

[0146]

[0147] (1) Copolymer of ethylene and 1,3-butadiene, containing 74 mol% of ethylene units, 19 mol% of 1,2 units and butadiene units in the form of 1,4 units, and 7 mol% of 1,2-cyclohexanediyl units, with a Tg of -44 °C

[0148] (2) Zeosil 1165MP in the form of microbeads from Solvay-Rhodia

[0149] (3) N234 grade carbon black from Cabot according to standard ASTM D-1765

[0150] (4) Mercapto silane - thio carboxylic acid ester oligomer (NXT-Z45) - CAS 922519-17-3 - Momentive

[0151] (5) LBR-307, Kuraray (non-functional liquid polybutadiene with a Tg of -95 °C and an Mn of 8000 g / mol)

[0152] (6) POLYVEST ST E 100 from Evonik (functional liquid polybutadiene with a Tg of -80 °C and an Mn of 3300 g / mol, having triethoxysilyl functional groups at each chain end)

[0153] (7) Perkacit DPG diphenylguanidine from Flexsys

[0154] (8) Anti-ozone wax, Varazon 4959 from Sasol Wax

[0155] (9) N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, Santoflex 6PPD from Flexsys

[0156] (10) Stearic acid, Pristerene 4931 from Uniqema

[0157] (11) Technical grade zinc oxide from Umicore

[0158] (12) N-cyclohexyl-2-benzothiazolesulfenamide, Santocure CBS from Flexsys

[0159] 3 - Results:

[0160] Composition T1 is a control without a liquid butadiene polymer to evaluate the effect of the properties of the liquid butadiene polymers used in Compositions C1 and C2. Composition C2 conforms to the present invention.

[0161] The results show that, compared to compositions that do not contain liquid polybutadiene, the compositions according to the present invention (having an elastomeric matrix based on EBR and a liquid polybutadiene functionalized at each chain end by alkoxysilyl functional groups) can significantly improve hysteresis performance (reduction of hysteresis) and stiffness. This effect was observed quite unexpectedly because the combined use of EBR and non-functionalized liquid polybutadiene made these two properties worse. For tires containing such compositions, the combined improvement of hysteresis and stiffness properties is expected to reduce rolling resistance and improve road handling.

Claims

1. A rubber composition, said rubber composition comprising at least - an elastomeric matrix, said elastomeric matrix mainly comprising a highly saturated diene elastomer, said highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene, wherein the ethylene units account for at least 50 mol% of the monomer units of the copolymer, - a reinforcing filler, - a vulcanization system, and - a liquid butadiene polymer functionalized at the chain ends by alkoxysilyl groups, said liquid butadiene polymer having a number-average molar mass (Mn) greater than or equal to 1000 g / mol, and said alkoxysilyl groups being optionally partially or completely hydrolyzed.

2. The rubber composition according to claim 1, wherein, The ethylene units account for at least 50 mol% and at most 95 mol% of the monomer units of the copolymer, preferably 65 mol% to 90 mol%.

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

4. The rubber composition according to any one of the preceding claims, wherein, The content of the highly saturated diene elastomer varies in the range of 60 phr to 100 phr, preferably 80 phr to 100 phr, very preferably 90 phr to 100 phr.

5. The rubber composition according to any one of the preceding claims, wherein, The functionalized liquid butadiene polymer is a liquid polybutadiene functionalized at the chain ends by alkoxysilyl groups, said alkoxysilyl groups being optionally partially or completely hydrolyzed.

6. The rubber composition according to any one of the preceding claims, wherein, The functionalized liquid butadiene polymer is functionalized at each end of the main chain by alkoxysilyl groups, said alkoxysilyl groups being optionally partially or completely hydrolyzed.

7. The rubber composition according to any one of the preceding claims, wherein, The alkoxysilyl functional group corresponds to the formula Si(OR)3, where each R independently represents a hydrogen atom or a C1-C 10 alkyl group, preferably a C1-C4 alkyl group, and the alkoxysilyl functional group is optionally partially or completely hydrolyzed.

8. The rubber composition according to any one of the preceding claims, wherein, The alkoxysilyl groups are trialkoxysilyl groups, preferably trimethoxysilyl groups or triethoxysilyl groups, which are optionally partially or completely hydrolyzed.

9. The rubber composition according to any one of the preceding claims, wherein, The functionalized liquid butadiene polymer is a liquid polybutadiene functionalized at each end of the main chain by trialkoxysilyl groups, preferably trimethoxysilyl groups or triethoxysilyl groups, said trialkoxysilyl groups being optionally partially or completely hydrolyzed.

10. The rubber composition according to any one of the preceding claims, wherein, The content of the liquid butadiene polymer functionalized at the chain ends by alkoxysilyl groups is in the range of 0.5 phr to 25 phr, preferably 1 phr to 20 phr, more preferably 5 phr to 15 phr, and said alkoxysilyl groups are optionally partially or completely hydrolyzed.

11. The rubber composition according to any one of the preceding claims, wherein, The Tg of the liquid butadiene polymer functionalized at the chain ends by alkoxysilyl groups is in the range of -60 °C to -100 °C, and said alkoxysilyl groups are optionally partially or completely hydrolyzed.

12. The rubber composition according to any one of the preceding claims, wherein, The number-average molar mass of the liquid butadiene polymer functionalized at the chain ends by alkoxysilyl groups is in the range of 1000 g / mol to 5000 g / mol, and said alkoxysilyl groups are optionally partially or completely hydrolyzed.

13. The rubber composition according to any one of the preceding claims, wherein, The reinforcing filler includes silica as the main reinforcing filler.

14. The rubber composition according to any one of the preceding claims, wherein, The content of silica is in the range of 20 phr to 60 phr.

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

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