Functionalized sulfur compounds as replacement agents for guanidines in rubber

Abstract

The present invention relates to a rubber composition comprising at least one sulfur compound, in particular as a replacement agent for a guanidine compound. The present invention also relates to a process for vulcanizing such a rubber composition, as well as articles comprising said vulcanized composition, including tires. Finally, the present invention relates to the use of a sulfur compound as a replacement agent for a guanidine compound.

Description

[0001] SULFUR COMPOUNDS FUNCTIONALIZED AS REPLACEMENTS FOR GUANIDINES IN RUBBER

[0002] FIELD OF INVENTION

[0003] The present invention relates to the field of rubber. More particularly, the present invention relates to a rubber composition comprising at least one functionalized sulfur compound, notably as a replacement for a guanidine compound. The present invention also relates to a method for vulcanizing such a rubber composition, as well as articles comprising this vulcanized composition, particularly tires. Finally, the present invention relates to the use of a functionalized sulfur compound as a replacement for a guanidine compound.

[0004] TECHNICAL BACKGROUND

[0005] Tires used today are primarily made of natural and / or synthetic rubber. Given current environmental challenges, rubber must address complex issues that combine performance with environmental responsibility and durability. Tires, and in particular their treads, must therefore offer good wear resistance, traction, and low rolling resistance, while simultaneously minimizing their environmental impact.

[0006] One solution used by tire manufacturers involves rubber compounds with reduced rolling resistance, which lowers fuel consumption and improves grip for safer driving. They have also developed such rubber compounds by incorporating a reinforcing filler such as silica.

[0007] The formulation of these compositions may require the use of a coupling agent to bind the reinforcing filler to the elastomer. This coupling step is sometimes called "silanization" when the coupling agent is a silane. It precedes the steps of adding vulcanization accelerators and then shaping and vulcanizing the rubber. To promote efficient coupling and / or accelerate vulcanization, guanidine compounds are generally added to these rubber compositions, notably 1,3-diphenyl guanidine (DPG; CAS No. 102-06-7).

[0008] DPG offers numerous advantages. It accelerates the coupling step and partially neutralizes silica, thus limiting the adsorption of accelerators by the silica. It also accelerates the vulcanization step (acting as a secondary accelerator) while maintaining a suitable pre-vulcanization time. However, the use of guanidine compounds presents other problems during their implementation. Indeed, these compounds, and DPG in particular, are suspected of being reprotoxic and decompose within the temperature ranges at which the compositions are formulated. Their decomposition leads to the release of aniline, a compound toxic by ingestion, inhalation, and skin contact.

[0009] Therefore, there is a need for replacement agents for guanidine compounds in rubber. More specifically, there is a need for less harmful replacement agents, particularly those that do not generate aniline or nitrosamine. There is also a need for bio-based rather than petroleum-based replacement agents.

[0010] Thus, one objective of the present invention is to provide replacement agents for guanidine compounds, and more particularly for DPG, in rubber.

[0011] Another objective of the present invention is to provide replacement agents for guanidine compounds, and more particularly for DPG, in rubber that are less harmful, preferably bio-based, while preserving the properties of the rubber.

[0012] Another objective of the present invention is to provide replacement agents for guanidine compounds that are easily handled and suitable for rubber preparation and vulcanization processes.

[0013] SUMMARY OF THE INVENTION

[0014] The present invention meets, in whole or in part, the above objectives.

[0015] The inventors have made a surprising discovery: functionalized sulfur compounds of general formula (I) can be used as replacements for guanidine compounds in rubber. These sulfur compounds allow the production of rubbers with similar, or even improved, rheometric, mechanical, and / or dynamic properties compared to rubbers produced using guanidine compounds such as DPG. These properties are maintained even with smaller quantities of sulfur compound used compared to the amount of guanidine compound typically added. They can be used, in particular, as vulcanization accelerators, filler dispersion aids, and / or filler-elastomer coupling agents.

[0016] Sulfur compounds with the general formula (I) are also compatible with other vulcanization accelerators to form an effective crosslinking system. Therefore, they are particularly preferred in combination with thiurams. Another advantage of these sulfur compounds is that they can be obtained from bio-based raw materials. "Bio-based raw materials" refers to raw materials derived from biomass. "Biomass" includes, in particular, organic matter of plant, animal, bacterial, or fungal origin (usable as an energy source). Biomass can be considered a renewable raw material when its consumption is at least equal to its regeneration.

[0017] These compounds can also be easily formulated in pre-dispersed form as masterbatches. These formulations, generally presented as granules or strips, are easy for operators to handle, do not generate dust, mix quickly into rubbers, and do not require any changes to production lines, which is an advantage for manufacturers.

[0018] Thus, the present invention relates to a rubber composition comprising:

[0019] (a) at least one elastomer, preferably at least one diene elastomer,

[0020] (b) a reinforcing load,

[0021] (c) possibly a charge-elastomer coupling agent,

[0022] (d) at least one sulfur compound of the following general formula (I), or one of its salts:

[0023] R3-X-CH(NRiR2)-(CH2)n-(S)pZ (I) in which:

[0024] Z is a hydrogen atom or a -(CH2) group n -CH(NRiR2)-X-R3;

[0025] Ri and R2, identical or different, are chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or not, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s);

[0026] X is chosen from -C(=O)- , -CH2- or -CN;

[0027] Rest:

[0028] (i) is zero when X represents -CN,

[0029] (ii) be a hydrogen atom,

[0030] (iii) either -ORa, Ra being a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s);

[0031] (iv) either -NRbRc, Rb and Rc, identical or different, being chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); n is an integer equal to 1 or 2, preferably equal to 2; and p is an integer between 1 and 8; provided that if Z is a hydrogen atom, then p is equal to 1; and

[0032] (e) a crosslinking system; said composition comprising strictly less than 0.1 part per annum of guanidine compound. The present invention also relates to a method for vulcanizing a rubber composition such as that according to the invention, comprising the following steps:

[0033] 1) a coupling step comprising the mixing of:

[0034] (a) at least one elastomer, preferably at least one diene elastomer,

[0035] (b) a reinforcing load,

[0036] (c) possibly a charge-elastomer coupling agent, and

[0037] (f) possibly other additives;

[0038] 2) an acceleration step comprising the addition of the crosslinking system (e) to the mixture obtained at the end of step 1); and

[0039] 3) a vulcanization step of the mixture obtained at the end of step 2), in order to obtain a vulcanized rubber composition; wherein at least one sulfur compound of general formula (I) such as according to the invention is added during step 1) and / or during step 2).

[0040] The present invention relates to an article, preferably a tire, comprising a rubber composition such as according to the invention vulcanized, preferably by the vulcanization process according to the invention.

[0041] The present invention relates to the use of a sulfur compound of the following general formula (I), or one of its salts:

[0042] R3-X-CH(NRiR2)-(CH2)n-(S)pZ (I) in which:

[0043] Z is a hydrogen atom or a -(CH2) group n -CH(NRiR2)-X-R3;

[0044] Ri and R2, identical or different, are chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or not, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s);

[0045] X is chosen from -C(=O)- , -CH2- or -CN;

[0046] Rest:

[0047] (i) is zero when X represents -CN,

[0048] (ii) either a hydrogen atom, (iii) or -ORa, Ra being a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s);

[0049] (iv) either -NRbRc, Rb and Rc, identical or different, being chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); n is an integer equal to 1 or 2, preferably equal to 2; and p is an integer between 1 and 8; provided that if Z is a hydrogen atom, then p is equal to 1, as a replacement for a guanidic compound, especially in a rubber composition, preferably as defined below.

[0050] Preferably, the rubber composition includes:

[0051] (a) at least one elastomer, preferably a diene elastomer,

[0052] (b) silica as a reinforcing filler,

[0053] (c) possibly a silica-elastomer coupling agent,

[0054] (d) at least one sulfur compound of general formula (I) as defined below,

[0055] (e) a crosslinking system comprising a thiuram; and said composition comprising strictly less than 0.1 pc of guanidic compound.

[0056] More preferably, the rubber composition comprises:

[0057] (a) at least one elastomer, selected from the group consisting of polyisoprenes, natural rubbers (NR), butadiene rubbers (BR), styrene-butadiene rubbers (SBR) and mixtures thereof, preferably SBR / BR mixtures, preferably SSBR / BR mixtures,

[0058] (b) silica as a reinforcing filler,

[0059] (c) a silane, preferably a polysulfide silane, as a silica-elastomer coupling agent,

[0060] (d) at least one sulfur compound of general formula (I) as defined below,

[0061] (e) a crosslinking system comprising sulfur, a primary sulfur vulcanization accelerator and thiuram as a secondary accelerator; and said composition comprising strictly less than 0.1 pc of guanidic compound.

[0062] DETAILED DESCRIPTION

[0063] In this application, it is understood that "pc" corresponds to "part percent of elastomer": one pc corresponds to one part of an ingredient per hundred parts of elastomer, by mass. For example: a dosage of 10 pc of an ingredient is equivalent to 100 g of elastomer plus 10 g of the ingredient ("pc" corresponds to "phr" in English).

[0064] It is understood that the rubber compositions according to the invention correspond to the so-called "raw" or non-crosslinked or non-vulcanized state (Le., before curing), or to the so-called "cured" or crosslinked or vulcanized state (i.e., vulcanization is a crosslinking reaction). These include, in particular, vulcanizable or vulcanized rubber compositions.

[0065] Sulfur compounds such as those according to the invention allow, in particular, the replacement of guanidine compounds in rubber compositions while preserving the properties of the latter. Thus, the composition according to the invention comprises strictly less than 0.1 part per guanidine compound, preferably strictly less than 0.05 part per guanidine compound. Advantageously, said composition does not substantially comprise any guanidine compound (i.e., it may comprise a guanidine compound in trace amounts), or even does not comprise any guanidine compound at all.

[0066] Thus, the use of sulfur compounds as described in the invention, as a replacement for guanidine compounds, is also part of the invention. Preferably, these compounds are used as replacements for guanidine compounds as vulcanization accelerators, particularly as primary and / or secondary accelerators.

[0067] The term "guanidine compound" or "guanidine" refers to an organic compound bearing a guanidine chemical group (-HN-C(=NH)-NH-), such as those commonly used in the rubber industry, particularly as vulcanization accelerators. Examples include diphenylguanidine (DPG) and diorthotolylguanidine (CAS: 97-39-2, DOTG), especially DPG.

[0068] In particular, the composition according to the invention does not include an oxetane derivative, i.e. an organic compound comprising an oxetane (or 1,3-epoxypropane) ring.

[0069] The composition according to the invention can be used alone or in a mixture with any other suitable rubber composition for manufacturing articles, preferably for the manufacture of tires. The manufacture of tire treads or the retreading of worn tires is preferred. This rubber composition is particularly useful in the manufacture of articles such as tires, automotive hoses such as fluid transport hoses, engine mounts, bushings, drive belts, printing rollers, shoe heels and soles, floor tiles, swivel casters, seals and gaskets, conveyor belt covers, hard rubber battery cases, automotive floor mats, truck mud flaps, ball mill liners, and windshield wiper blades.Advantageously, the rubber compound is used in a tire as a component of all or some of the tire's parts. In particular, this compound is that of all or part of a layer of a tire, such as the tread, the tire belt plies, the carcass ply, the tire sidewalls, or any other layer, preferably the tread. The tire tread refers specifically to the entire rubber layer in contact with the ground (i.e., across its full thickness) or a portion thereof, particularly when it is composed of several layers.

[0070] The invention also relates to an article as mentioned above, preferably a tire, comprising the rubber composition according to the invention vulcanized. Said tire may comprise said rubber composition in all or part of one or more of its various layers, such as the tread, the tire belt plies, the carcass ply, the tire sidewall, or any other layer.

[0071] In particular, the tire according to the invention is chosen from tires intended to equip a two-wheeled vehicle, a passenger vehicle, or even a so-called "heavy goods vehicle" (i.e., metro, bus, off-road vehicles, road transport vehicles such as trucks, tractors, trailers), or even airplanes, civil engineering, agricultural, or handling equipment.

[0072] Sulphur compound(s) of general formula (I):

[0073] The composition according to the invention comprises at least one, preferably one, sulfur compound of the following general formula (I), or one of its salts:

[0074] R3-X-CH(NRiR2)-(CH2)n-(S)pZ (I) in which:

[0075] Z is a hydrogen atom or a -(CH2) group n -CH(NRiR2)-X-R3;

[0076] Ri and R2, identical or different, are chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or not, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s);

[0077] X is chosen from -C(=O)- , -CH2- or -CN;

[0078] R3 is:

[0079] (i) is zero when X represents -CN,

[0080] (ii) be a hydrogen atom,

[0081] (iii) either -ORa, Ra being a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and possibly comprising one or more heteroatom(s); (iv) or -NRbRc, Rb and Rc, identical or different, being chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and possibly comprising one or more heteroatom(s); n is an integer equal to 1 or 2, preferably equal to 2; and p is an integer between 1 and 8; provided that if Z is a hydrogen atom, then p is equal to 1.

[0082] When Z is a -(CH2)n-CH(NRiR2)-X-R3 group, it is understood that n and the different radicals X, Ri, R2 and R3 are respectively identical in the general formula (I): we obtain symmetrical sulfides, di- or polysulfides (cf for example cystine and homocystine).

[0083] Preferably, said sulfur compound has the following general formula (la): R3-X-CH(NRiR2)-(CH2) n -SH (la) in which Ri, R2, R3, X and n are as defined above.

[0084] Heteroatoms include, in particular, oxygen, nitrogen, and sulfur.

[0085] In particular, Ri and R2 are hydrogen atoms.

[0086] In particular, n is equal to 2.

[0087] In particular, p is an integer between 1 and 5, preferably p is equal to 1 or 2 or 3.

[0088] We particularly prefer compounds with the general formula (I) or (la), for which X is -C(=O)- and R3 is -OR a , with R a as defined above. R a is preferentially H.

[0089] Preferred compounds include: cysteine, with the formula HS-CH2-CH(NH2)-COOH (CAS 52-90-4 for the L form and CAS 921-01-7 for the D form); dicysteine ​​monosulfide, with the formula HOOC-CH(NH2)-CH2-S-CH2-CH(NH2)-COOH; cystine, with the formula HOOC-CH(NH2)-CH2-SS-CH2-CH(NH2)-COOH (CAS 56-89-3 for the L form and CAS 349-46-2 for the D form); homocysteine, with the formula HS-(CH2)2-CH(NH2)-COOH (CAS 6027-13-0 for the L form and CAS 6027-14-1 for the D form); dihomocysteine ​​monosulfide, with the formula HOOC-CH(NH2)-(CH2)2-S-(CH2)2-CH(NH2)-COOH; homocystin, with the formula HOOC-CH(NH2)-(CH2)2-SS-(CH2)2-CH(NH2)-COOH (CAS 626-72-2 for the L form and CAS 870-93-9 for the D form); dicysteine ​​trisulfide (HOOC-CH(NH2)-CH2-SSS-CH2-CH(NH2)-COOH), dicysteine ​​tetrasulfide, dicysteine ​​pentasulfide; and dihomocysteine ​​trisulfide (HOOC-CH(NH2)-(CH2)2-SSS-(CH2)2-CH(NH2)- COOH), dihomocysteine ​​tetrasulfide, dihomocysteine ​​pentasulfide.

[0090] The preferred sulfur compounds according to the invention are cysteine, dicysteine ​​monosulfide, cystine, homocysteine, dihomocysteine ​​monosulfide, homocystine, dicysteine ​​trisulfide, dicysteine ​​tetrasulfide, dihomocysteine ​​trisulfide, dihomocysteine ​​tetrasulfide, and one of their salts, preferably homocysteine.

[0091] A particularly preferred sulfur compound is homocysteine.

[0092] Homocysteine ​​and its derivatives (in particular sulfur compounds of general formula (I) for which n equals 2) are particularly well suited for formulation in a rubber composition: it disperses homogeneously and does not form crystals in vulcanized rubber.

[0093] When reference is made in this description to sulfur compounds of general formula (I), the salts of these compounds are included in that expression. When a salt of a sulfur compound of general formula (I) is used, it is preferably a basic salt. In particular, said salt is a metallic salt or a quaternary ammonium salt. Preferably, said salt is selected from alkali metal salts, alkaline earth metal salts, and quaternary ammonium salts.

[0094] The term "metals" used to obtain said metallic salt refers in particular to the metals in columns 1 to 5 (formerly IA to VA) of the periodic table of elements, as well as aluminum, tin, and lead. Specifically, said metal is chosen from the group consisting of: alkali metals, alkaline earth metals, scandium, titanium, zirconium, vanadium, niobium, aluminum, tin, and lead.

[0095] The term "alkali metals" refers to the metals corresponding to group 1 (1 ère column) of the periodic table of elements. Lithium, sodium, and potassium are particularly noteworthy examples. The term "alkaline earth metals" refers to the metals corresponding to group 2 (2 ème column) of the periodic table of elements. Magnesium, calcium, strontium and barium are particularly noteworthy.

[0096] By "quaternary ammoniums", we mean in particular ammoniums of the following general formula (III):

[0097] +N(R5R6R7R8) (III) in which the radicals R5, Re, R? and R8, identical or different, are chosen independently of each other from the group consisting of: the hydrogen atom, a (Ci-Cio)alkyl, a (C6-Cio)aryl, a (Ci-Cio)alkoxy, a polyalkylalkoxy, a (Ci-Cio)alcohol and a polyol; preferably from the hydrogen atom, a (Ci-Cio)alkyl and a (Ci-Cio)alcohol. The ammonium of monoethanolamine ( + NH3(CH2CH2OH)), diethanolamine, triethanolamine and methyldiethanolamine.

[0098] In particular, said basic salt is chosen from among the monoalkaline, dialkaline, alkaline-earth or quaternary ammonium salts of homocysteine, dihomocysteine ​​monosulfide, or homocystin, preferably from among the dialkaline or alkaline-earth salts of homocysteine, dihomocysteine ​​monosulfide or homocystin.

[0099] The basic salt in question is chosen from the following group: monosodium homocysteine, disodium homocysteine; monosodium cysteine, disodium cysteine, disodium cystine, disodium homocystine; monopotassium homocysteine, dipotassium homocysteine; monopotassium cysteine, dipotassium cysteine, dipotassium cystine, and dipotassium homocystine. Disodium homocysteine ​​and disodium homocystine are particularly preferred.

[0100] The sulfur compound may exist in any enantiomeric form, of type L, D, or in racemic form. The L form, which is found in nature, is particularly preferred. Free forms (i.e., unsalted forms of the sulfur compounds according to the invention) are also preferred.

[0101] The sulfur compound with general formula (I) is usually in solid form, particularly as a powder. For example, cysteine ​​may be commercially available (marketed, for example, by Wacker or Showa Denko).

[0102] In particular, the total quantity of sulfur compound(s) in the composition is between 0.10 and 10 pc, in particular between 0.10 and 5 pc, preferably between 0.25 and 3 pc, preferably again between 0.5 and 2 pc.

[0103] Masterbatches:

[0104] Vulcanizing additives such as the sulfur compounds according to the invention are conventionally used in relatively small doses compared to other ingredients. For optimal rubber properties, their distribution in the mixture to be vulcanized must be homogeneous. Therefore, it is advantageous to introduce them into the rubber composition as a masterbatch. Thus, the sulfur compound(s) can be in the form of a masterbatch.

[0105] These masterbatches are generally presented in the form of strips, wafers, or granules. These so-called pre-dispersed forms are easily handled, unlike powders or liquids. Furthermore, the physical presentation as a masterbatch improves the compatibility between the sulfur compound(s) of general formula (I) and the composition, and therefore improves their dispersion within the latter. In this application, the quantity of each ingredient in the masterbatch is expressed by mass, relative to the total mass of the masterbatch (mass %), and not by weight.

[0106] Any type of masterbatch known to a person skilled in the art can be used.

[0107] Masterbatches, preferably thermoplastic, include in particular:

[0108] - at least one support, which is an elastomer, for example as defined for the rubber composition according to the invention;

[0109] - at least one sulfur compound as per the invention;

[0110] - possibly a filler, for example such as defined for the rubber composition according to the invention;

[0111] - possibly a plasticizer; and

[0112] - possibly one or more additional additives.

[0113] Among the fillers, we can mention reinforcing or diluting fillers such as silica and / or carbon black or other mineral or organic fillers.

[0114] The plasticizer can be an oil (paraffinic, naphthenic, hydrogenated naphthenic, or of vegetable origin, i.e., derived from fatty acids), or a saturated or unsaturated phthalate plasticizer. Its purpose is to facilitate the incorporation of other additives and / or to adjust the viscosity.

[0115] Additional additives include desiccants, carbon nanotubes (CNTs), anti-sticking agents, and colorants.

[0116] The fillers are generally between 0 and 60% by mass each, more preferably between 0 and 50% by mass each, relative to the total mass of the masterbatch. Plasticizers are generally between 0 and 15% by mass, relative to the total mass of the masterbatch. Other additives may be between 0 and 10% by mass, more preferably between 0 and 2% by mass, relative to the total mass of the masterbatch.

[0117] Masterbatches may include any type of elastomer and in particular those mentioned for the composition of rubber according to the invention.

[0118] In particular, these masterbatches use at least one elastomer as a support, specifically a mixture of elastomers, chosen from: an isoprene rubber, such as NR natural rubber (for Natural

[0119] Rubber) or IR (synthetic polyisoprenes); HR butyl rubber (isobutylene-isoprene copolymers); EPDM (ethylene-propylene-diene monomer terpolymer); EPR (ethylene-propylene rubber); BR (butadiene rubber); SBR (styrene-butadiene rubber) such as SSBR (Solution-Styrene-Butadiene Rubber) and ESBR (Emulsion-Styrene-Butadiene Rubber); NBR (nitrile-butadiene rubber); a copolymer of ethylene and an alpha-olefin (as defined below); a copolymer of ethylene and an unsaturated carboxylic acid ester such as EVA (ethylene-vinyl acetate copolymer) (as defined below); a copolymer selected from ethylene / alkyl (meth)acrylate / maleic anhydride copolymers such as EMA (ethylene-methyl acrylate copolymer); a block copolymer such as styrene-butadiene-styrene (SBS), styrene-ethylene / butylene-styrene (SEBS) or styrene-isoprene-styrene (SIS), possibly grafted;and a POE (polyolefin elastomer).

[0120] Examples of alpha-olefins include: propylene, butene, hexene, and octene.

[0121] Examples of copolymers of ethylene and unsaturated carboxylic acid esters include alkyl (meth)acrylates, in which the alkyl group contains from 1 to 24 carbon atoms. Advantageously, examples of acrylates or methacrylates include methyl methylacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, and 2-ethylhexyl acrylate. These esters can be introduced by grafting (onto polyethylenes) or by direct copolymerization.

[0122] At least one copolymer of ethylene and an alpha-olefin and at least one copolymer of ethylene and an unsaturated carboxylic acid ester can also be used as an elastomer. Such elastomers are described in document WO 2008 / 074962.

[0123] An elastomer such as those mentioned above can also be used, substituted by one or more siloxy group(s), for example with the formula -Si(OR a ) ; with R a = H or an alkyl group, for example methyl or ethyl; one or more carboxymercaptan group(s), for example as defined in US application 2013 / 0281609.

[0124] Preferably, said elastomer is chosen from the group consisting of SBRs (styrene-butadiene rubbers) such as SSBR (Solution-Styrene-Butadiene Rubber) and ESBR (Emulsion-Styrene-Butadiene Rubber), EPDMs (ethylene-propylene-diene monomer terpolymers), BRs (butadiene rubbers), POEs (polyolefin elastomers), NR (natural rubber) and their mixtures such as SBR / BR.

[0125] Preferably, the masterbatch comprises an elastomer as defined above, at least one sulfur compound as according to the invention and a reinforcing filler, preferably silica.

[0126] More preferably, the masterbatch comprises: - at least one elastomer selected from the group consisting of SBR (styrene-butadiene rubbers), EPDM (ethylene-propylene-diene monomer terpolymers), BR (butadiene rubbers), POEs (polyolefin elastomers), NR (natural rubber) and their mixtures such as SBR / BR;

[0127] - at least one sulfur compound as described in the invention; and

[0128] - silica.

[0129] The total quantity of elastomer(s) can be from 20 to 80%, preferably from 20 to 50%, preferably still from 5 to 35% by mass, relative to the total mass of the master mixture.

[0130] The total quantity of sulfur compound(s) can be from 20 to 80%, preferably from 30 to 60% by mass, relative to the total mass of the master mixture.

[0131] Masterbatches may include all or part of the total amount of sulfur compound(s) to be incorporated into the rubber composition, preferably all of the sulfur compound(s).

[0132] The masterbatches of the invention can be manufactured using both rubber and thermoplastics industry techniques. Single or twin screw extruders, internal mixers, and possibly roller mixers can all be used.

[0133] Elastomer(s):

[0134] The compositions according to the invention may contain a single elastomer or a mixture of several elastomers. Elastomers are also commonly called "rubbers".

[0135] The elastomers used are primarily based on unsaturated materials such as natural and / or synthetic rubbers. Preferably, the elastomer(s) in question is / are a diene elastomer. A "diene elastomer" is understood to mean, in particular, an elastomer derived at least in part (Le., a homopolymer, or a copolymer) from diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or not).

[0136] Diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated".

[0137] Generally, a "mostly unsaturated" diene elastomer is defined as one derived at least in part from conjugated diene monomers, with a diene monomer content (conjugated dienes) greater than 15% by mole. Within the category of "mostly unsaturated" diene elastomers, a "highly unsaturated" diene elastomer is defined as one with a diene monomer content (conjugated dienes) greater than 50% by mole. Examples of "mostly saturated" diene elastomers (low or very low diene monomer content, less than 15% by mole) include butyl rubbers and diene-alpha-olefin copolymers such as EPDM.

[0138] The diene elastomers according to the invention can be essentially unsaturated or essentially saturated, preferably strongly unsaturated.

[0139] Examples of conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and mixtures thereof. Examples of copolymers of such conjugated dienes with monomers include styrene, alpha-methylstyrene, acetylene, vinylacetylene, acrylonitrile, methacrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate, and mixtures thereof.

[0140] Highly unsaturated elastomers include, in particular, natural rubber (NR), cis-polyisoprene, butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene copolymers, isoprene-butadiene copolymers, styrene-isoprene-butadiene terpolymers, polychloroprene, chloroisobutene-isoprene, nitrile-chloroprene, styrene-chloroprene, poly(acrylonitrile butadiene) and mixtures thereof; preferably butadiene rubber, styrene-butadiene rubber and mixtures thereof.

[0141] Furthermore, mixtures of two or more highly unsaturated diene elastomers with elastomers having less unsaturation such as EPDM, EPR, butyl or halogenated butyl rubbers are also covered by the invention.

[0142] In particular, the elastomer(s) is / are chosen from: an isoprene rubber, such as natural rubber NR (for Natural Rubber) or IR (synthetic polyisoprenes); a butyl HR rubber (isobutylene-isoprene copolymer); an EPDM (ethylene-propylene-diene monomer terpolymer); an EPR (ethylene-propylene rubber); a BR (butadiene rubber); an SBR (styrene-butadiene rubber) such as SSBR (Solution-Styrene-Butadiene Rubber) and ESBR (Emulsion-Styrene-Butadiene Rubber); an NBR (nitrile-butadiene rubber); a copolymer of ethylene and an alpha-olefin (as defined below); a copolymer of ethylene and an unsaturated carboxylic acid ester such as EVA (ethylene-vinyl acetate) (as defined below); a copolymer selected from ethylene / alkyl (meth)acrylate / maleic anhydride copolymers such as EMA (ethylene-methyl acrylate copolymer);a block copolymer such as styrene-butadiene-styrene (SBS), styrene-ethylene / butylene-styrene (SEBS) or styrene-isoprene-styrene (SIS), possibly grafted; a POE (polyolefin elastomer); and mixtures thereof.

[0143] Examples of alpha-olefins include: propylene, butene, hexene, and octene.

[0144] Examples of copolymers of ethylene and unsaturated carboxylic acid esters include alkyl (meth)acrylates, in which the alkyl group contains from 1 to 24 carbon atoms. Advantageously, examples of acrylates or methacrylates include methyl methylacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, and 2-ethylhexyl acrylate. These esters can be introduced by grafting (onto polyethylenes) or by direct copolymerization.

[0145] Alternatively, at least one copolymer of ethylene and an alpha-olefin and at least one copolymer of ethylene and an unsaturated carboxylic acid ester may be used as a support. Such supports are described in document WO 2008 / 074962.

[0146] An elastomer such as those mentioned above can also be used, substituted by:

[0147] - one or more siloxy group(s), for example with the formula -Si(OR a ) ; with R a = H or an alkyl group, for example methyl or ethyl;

[0148] - one or more carboxymercaptan group(s), for example as defined in US application 2013 / 0281609.

[0149] NR or partially epoxy-coated dienic rubbers can also be used.

[0150] Preferably, said elastomer is chosen from the group consisting of polyisoprenes, NR (natural rubbers), SBR (styrene-butadiene rubbers) such as SSBR (Solution-Styrene-Butadiene Rubber) and ESBR (Emulsion-Styrene-Butadiene Rubber), EPDM (ethylene-propylene-diene monomer terpolymer), BR (butadiene rubbers), POEs (polyolefin elastomers) and their mixtures such as SBR / BR and even more preferably SSBR / BR.

[0151] According to a preferred embodiment, the diene elastomer is chosen from the group consisting of polyisoprenes, natural rubbers (NR), butadiene rubbers (BR), styrene-butadiene rubbers (SBR) and their mixtures, preferably SBR / BR mixtures, preferably SSBR / BR mixtures.

[0152] Reinforcing charge:

[0153] The composition according to the invention comprises a reinforcing filler. Any type of reinforcing filler known to those skilled in the art may be used, and in particular silica, carbon black, or a mixture of silica and carbon black. Preferably, the reinforcing filler comprises predominantly an inorganic reinforcing filler, preferably silica (i.e., more than 50% by mass of inorganic filler, preferably silica, relative to the total mass of the reinforcing filler). More preferably, the reinforcing filler consists of silica.

[0154] Silica can be of any type known to be useful in strengthening rubber compositions. Examples of suitable silica fillers include, for example, silica, precipitated silica, amorphous silica, vitreous silica, fumed silica, fused silica, synthetic silicates such as aluminum silicates, alkaline earth metal silicates such as magnesium silicate and calcium silicate, natural silicates such as kaolin and other natural silicas, or silicas obtained by combustion of a natural element, such as silica obtained from the combustion of rice husks.

[0155] Highly dispersed silicas with, for example, BET surfaces of approximately 5 to approximately 1000 m² are also useful. 2 / g and preferably from about 20 to about 400 m 2 / g, preferably still between 60 and 300 m 2 / g, and primary particle diameters of about 5 to about 500 nm and preferably about 10 to about 400 nm. These highly dispersed silicas can be prepared, for example, by precipitation of silicate solutions or by flame hydrolysis of silicon halides.

[0156] Silicas can also be present in the form of mixed oxides with other metallic oxides such as, for example, oxides of Al, Mg, Ca, Ba, Zn, Zr, Ti and others. For example, silicas from the "Ultrasil®" range marketed by the company Evonik are used, such as ULTRASIL® 4000 GR, ULTRASIL® 5000 GR, ULTRASIL® 5500 GR, ULTRASIL® VN 2, ULTRASIL® VN 2 GR, ULTRASIL® 6100 GR, ULTRASIL® 7000 GR, ULTRASIL® VN 3, ULTRASIL® VN 3 GR, ULTRASIL® 7800 GR, ULTRASIL® 7500 GR, ULTRASIL® 9500 GR and ULTRASIL® 9100 GR.

[0157] Mixtures of two or more silica fillers can be used as reinforcing fillers.

[0158] Carbon black fillers can also be used. Suitable carbon black fillers include any of the commercially available carbon blacks known to those skilled in the art. Examples of carbon blacks include furnace black, channel black, and lamp black. Carbon blacks obtained by pyrolysis of organic plant derivatives or by pyrolysis of raw or vulcanized rubber parts can also be used.

[0159] In particular, so-called pneumatic grade blacks can be used. Among these, we will mention in particular the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as for example blacks N 115, N134, N234, N326, N330, N339, N347, N375, or, depending on the applications intended, blacks of higher series (for example N660, N683, N772).

[0160] The reinforcing filler is incorporated into the rubber composition in widely varying quantities.

[0161] Generally, the amount of inorganic reinforcing filler such as silica can vary from about 5 to about 150 parts per annum, preferably from about 10 to about 100 parts per annum, and more preferably from about 15 to about 90 parts per annum.

[0162] Carbon blacks, if any, are generally incorporated into the rubber composition in quantities ranging from about 1 to about 80 parts per annum and preferably from about 5 to about 60 parts per annum.

[0163] Charge-elastomer coupling agent:

[0164] The composition according to the invention optionally comprises a filler-elastomer coupling agent, which allows the filler to be covalently bound to the elastomer. The coupling agent acts as a connecting bridge between the filler and the elastomer, thus improving the reinforcing effect of the rubber due to the reinforcing filler. The coupling agent is different from the sulfur compound of general formula (I) when present.

[0165] Silanes, and more preferably polysulfide silanes, are preferred as coupling agents. Silanes are particularly useful when the reinforcing filler consists mainly of an inorganic filler, especially silica.

[0166] Examples of polysulfurized silanes include: polysulfides (in particular disulfides, trisulfides or tetrasulfides) of bis-(alkoxyl(Ci-C4)-alkyl(Ci-C4)silyl-(Ci-C4)alkyl), such as bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl) polysulfides. Among these compounds, bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, with the formula [(C2H5O)3Si(CH2)3S2]2, and bis-(triethoxysilylpropyl) disulfide, abbreviated TESPD, with the formula [(C2H5O)3Si(CH2)3S]2, are particularly used; and the polysulfides (in particular disulfides, trisulfides or tetrasulfides) of bis- (monoalkoxyl(Ci-C4)-dialkyl(Ci-C4)silylpropyl), more particularly the tetrasulfide of bis-monoethoxydimethylsilylpropyl as described in patent application WO 02 / 083782.

[0167] As coupling agents, we will also mention: bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulfides as described in patent application WO 02 / 030939, or silanes or POS bearing azo-dicarbonyl functional groups, as described for example in patent applications WO 2006 / 125532, WO 2006 / 125533 and WO 2006 / 125534, or silanes bearing thioester, mercapto-blocked groups such as S-(3- (triethoxysilyl)propyl)octanethioate, or silanes as described in document WO 2005 / 40264.

[0168] Preferably, the coupling agent is chosen from among the following polysulfide silanes: 3-mercaptopropyltrimethoxysilane; bis-(3-triethoxysilylpropyl)tetrasulfide; bis-(3-triethoxysilylpropyl)disulfide; 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide; trimethoxysilylpropylmercaptobenzothiazoltetrasulfide; triethoxysilylpropyl methacrylate monosulfide; and dimethoxymethylsilylpropyl-N,N-dimethyl-thiocarbamoyltetrasulfide.

[0169] For example, it is possible to use the following commercial silanes, marketed by Evonik: Si 69® (Bis(triethoxysilylpropyl)tetrasulfide), Si 75® and Si 266® (Bis(triethoxysilylpropyl)disulfide).

[0170] In particular, the quantity of the coupling agent is between 0.5 and 20 pc, preferably between 3 and 15 pc, preferably between 4 and 9 pc.

[0171] Crosslinking system:

[0172] The crosslinking system is, in particular, a vulcanization system. It may comprise various compounds that enable the crosslinking / vulcanization of the rubber. It includes, in particular, one or more vulcanization accelerators, preferably sulfur-containing. Specifically, the vulcanization accelerator(s) used in said crosslinking system is / are different from the sulfur-containing compound(s) of formula (I) according to the invention.

[0173] For example, the crosslinking system may include a sulfur donor, such as elemental sulfur, and at least one sulfur-containing vulcanization accelerator. Specifically, the crosslinking system includes a sulfur donor, such as elemental sulfur, at least one sulfur-containing primary vulcanization accelerator, and / or at least one sulfur-containing secondary vulcanization accelerator, such as thiuram. Preferably, the crosslinking system includes thiuram.

[0174] In particular, the sulfur donor is used in an amount between 0.5 and 10 pc, more preferably between 0.5 and 5.0 pc, for example between 0.5 and 3.5 pc.

[0175] Vulcanization accelerators may be present in quantities of 0.05 to 20 parts per kilogram, preferably 0.1 to 5 parts per kilogram, and even more preferably 0.15 to 3 parts per kilogram. Various known vulcanization activators may also be added, such as metal oxides like zinc oxide (preferably 0.5 to 10 parts per kilogram), stearic acid, or others (preferably 0.5 to 5 parts per kilogram each).

[0176] Any compound capable of acting as a vulcanization accelerator can be used as a sulfur vulcanization accelerator, particularly in the presence of a sulfur donor such as elemental sulfur.

[0177] Preferably, the sulfur-based vulcanizing accelerator is selected from the group consisting of thiazoles, sulfenamides, thiurams, dithiocarbamates, dithiophosphates, xanthates, dithiodiamines, thioureas, poly(phenol sulfides), their derivatives, and mixtures thereof. More specifically, a sulfenamide (such as CBS, DCBS, TBBS, or TBSI), a thiazole (such as MBTS or MBT), a thiuram (such as TBzTD), a dithiocarbamate (such as ZBEC), or mixtures thereof may be used as a sulfur-based vulcanizing accelerator.

[0178] We prefer an accelerator chosen from the group consisting of ZBEC, CBS, DCBS, TBBS, TBSI, MBTS, MBT, TBzTD and their mixtures.

[0179] CBS, TBBS, and mixtures thereof are particularly preferred as sulfur-based vulcanization accelerators, and even more so as primary vulcanization accelerators. TBBS is especially preferred as a primary vulcanization accelerator.

[0180] Thiurams, and in particular TBzTD, are particularly preferred as a sulfur-based vulcanization accelerator, and more preferentially as a secondary vulcanization accelerator.

[0181] Examples of thiazoles include 2-mercaptobenzothiazole (known as MBT, CAS No. 149-30-4), 2,2'-dithiobis(benzothiazole) (known as MBTS, CAS No. 120-78-5) and mixtures thereof.

[0182] Among the sulfenamides, we can mention N-Cyclohexyl-2-benzothiazole sulfenamide (called CBS, CAS No. 95-33-0), N-tert-Butyl-2-benzothiazole sulfenamide (called TBBS, CAS No. 95-31-8), N-Benzothiazol-2-ylsulfanyl-N-tert-butyl-benzothiazole-2-sulfenamide (called TBSI, CAS No. 3741-80-8), N,N-dicyclohexylbenzothiazole-2-sulfenamide (called DCBS, CAS No. 4979-32-2) and their mixtures.

[0183] Thiurams are notably chosen from among the sulfides, disulfides and polysulfides of thiurams.

[0184] The thiurame can be chosen from the group consisting of:

[0185] - tetramethylthiuram sulfide (TMTM, CAS No. 97-74-5),

[0186] - tetrabenzylthiuram disulfide (TBzTD, CAS No.: 10591-85-2),

[0187] - tetramethylthiuram disulfide (TMTD, CAS No.: 97-74-5),

[0188] - tetraethylthiuram disulfide (TETD, CAS No.: 97-77-8), - tetrabutylthiuram disulfide (TBTD, CAS No.: 1634-02-2),

[0189] - tetrakis(2-ethylhexyl)thiuram disulfide (TOTD, CAS No.: 37437-21-1),

[0190] - tetraisobutylthiuram disulfide (TiBTD, CAS No.: 3064-73-1),

[0191] - dimethyldiphenyl thiurame disulfide (TMPTD, CAS No. 10591-84-1),

[0192] - of dipentamethylenethiuram hexasulfide (DPTT, CAS No. 971-15-3) and their mixtures.

[0193] In particular, thiurame disulfide is chosen from the group consisting of:

[0194] - tetrabenzylthiuram disulfide (TBzTD),

[0195] - tetrakis(2-ethylhexyl)thiuram disulfide (TOTD),

[0196] - tetraisobutylthiuram disulfide (TiBTD), and mixtures thereof.

[0197] Preferably, the thiuram disulfide is tetrabenzylthiuram disulfide (TBzTD), with the following formula:

[0198] Among the dithiocarbamates, the dithiocarbamate salts of zinc, copper, or sodium are of particular concern. Examples include: zinc dibenzyldithiocarbamate (ZBEC, CAS No. 14726-36-4), zinc diethyldithiocarbamate (ZDEC, CAS No. 14324-55-1), zinc dibutyldithiocarbamate (ZDBC, CAS No. 136-23-2), copper dibutyldithiocarbamate (ODBC, CAS No. 13927-71-4), sodium dibenzyldithiocarbamate (NaBEC, CAS No. 55310-46-8), and mixtures thereof.

[0199] Dithiophosphates are in particular selected from di- and polysulfides of dithiophosphates and their salts such as their zinc salts. Among the dithiophosphates are: phosphorodithioic acid, mixed esters 0,0-bis (2-ethylhexyl and iso-Bu), zinc salts (ZDTP, CAS No. 68442-22-8), phosphorodithioic acid, mixed esters 0,0-bis (2-ethylhexyl, iso-Bu and iso-Pr), zinc salts (CAS No. 85940-28-9), isodecyl zinc phosphorodithioate (CAS No. 25103-54-2) and mixtures thereof.

[0200] Xanthates are selected from (C1-C20) alkyl esters of xanthate and di- or polysulfides of (C1-C20) alkyl esters of xanthogen, or their metal salts (e.g., their alkaline earth or zinc salts). Xanthates may be selected from the group consisting of zinc isopropyl xanthate (ZIX), sodium isopropyl xanthate (SIX), zinc butyl xanthate (ZBX), dibutyl xanthogen disulfide, diisopropyl xanthogen disulfide, diisobutyl xanthogen disulfide, and mixtures thereof.

[0201] Dithiodiamines include dithiodimorpholine (DTDM, CAS No. 103-34-4) and caprolactam disulfide (CLD, CAS No. 23847-08-7).

[0202] Most of these products are marketed by Arkema under the EKALAND™ and Mixland+® brands. Examples include: MIXLAND+® S, MIXLAND+® CBS, MIXLAND+® TBBS, MIXLAND+® MBT, MIXLAND+® MBTS, EKALAND™ TBzTD, MIXLAND+® TBzTD, EKALAND™ ZBEC C, MIXLAND+® ZBEC, MIXLAND+® ZDTP, MIXLAND+® ZnO, and MIXLAND+® DTDM. Preferably, MIXLAND+® S, MIXLAND+® CBS, MIXLAND+® TBBS, EKALAND™ TBzTD, MIXLAND+® TBzTD, and MIXLAND+® ZnO are recommended.

[0203] Poly(phenol sulfide) refers in particular to oligomers or polymers as described in application WO 2015 / 001234. Poly(phenol sulfides) are marketed in particular by the company Arkema under the generic name Vultac®, among which are Vultac® 2, Vultac® 3, Vultac® 5, Vultac® TB7, Vultac® 710 and Vultac® TB710, MIXLAND +® TBP 75.

[0204] The rubber composition according to the invention may also include one or more other additives such as:

[0205] - crosslinking retardants, allowing in particular to increase the toasting time, or "scorch time" such as MIXLAND +® CTPI (CAS No. 17796-82-6);

[0206] - compounds that improve resistance to reversal of the composition thanks to their ability to reform crosslinking bridges in use (such as PERKALINK 900 or HTS or VULCUREN);

[0207] - antioxidants;

[0208] - antiozonants;

[0209] - anti-fatigue additives;

[0210] - plasticizers such as oils or waxes;

[0211] - fillers other than silica and carbon black such as organic fillers to lighten the composition;

[0212] - reinforcing pigments; and

[0213] - reinforcing and / or plasticizing and / or tackifying resins.

[0214] Vulcanization process for the rubber composition according to the invention

[0215] The present invention also relates to a method for vulcanizing a rubber composition as described in the invention, comprising the following steps: 11

[0216] 1) a coupling step comprising the mixing of:

[0217] (a) at least one elastomer, preferably at least one diene elastomer, as defined above,

[0218] (b) a reinforcing load as defined above,

[0219] (c) possibly a charge-elastomer coupling agent as defined above, and

[0220] (f) possibly other additives;

[0221] 2) an acceleration step comprising the addition of a crosslinking system (e) as defined above to the mixture obtained at the end of step 1); and

[0222] 3) a vulcanization step of the mixture obtained at the end of step 2), in order to obtain a vulcanized rubber composition; wherein at least one sulfur compound of general formula (I) as defined above is added during step 1) and / or during step 2), preferably during step 1).

[0223] The three stages of coupling, acceleration, and vulcanization are known to those skilled in the art and can be carried out under conventional conditions. Stages 1) and 2) are generally performed in an internal or roller mixer, preferably agitated.

[0224] Coupling step

[0225] The coupling step allows the reinforcing filler to be coupled to the elastomer. A coupling agent may be required for this. Preferably, the coupling agent used is a silane: in this case, the coupling step is called the silanization step.

[0226] The elastomer, reinforcing filler, optionally the coupling agent, optionally the sulfur compound(s), and optionally other additives can be mixed in this way. The temperature can be increased to between 50 and 150 °C, preferably between 60 and 140 °C (this temperature increase is called a "pass"). This temperature increase can be achieved through self-heating generated by the mixing of the constituents added at this stage, or by heating the mixer, or both. The mixture can then be left to cool. In one embodiment, the reinforcing filler can be added to the mixture in two passes ranging from 100 to 180 °C, preferably from 120 to 165 °C each. The resulting cooled mixture is then said to be "coupled" (or "silanized" if a silane is used).

[0227] 2) Acceleration stage

[0228] The acceleration step involves adding the crosslinking system to the coupled mixture. This addition can be carried out at a temperature between 20 and 140 °C, preferably between 30 and 100 °C. At the end of this acceleration step, a so-called "raw" rubber is obtained. It must then be shaped and vulcanized. 3) Shaping / Vulcanization Step

[0229] During this stage, the rubber compound can be shaped using methods known to those skilled in the art, and then transferred to a final shaping element, such as a mold, which is heated to a temperature between 100 and 200°C, preferably between 140 and 180°C. This stage can last between 5 and 90 minutes. At the end of this stage, a "cured" rubber is obtained, which can be used to manufacture various articles, such as tires.

[0230] The examples below are given for illustrative purposes only and are not limiting to the present invention.

[0231] EXAMPLES

[0232] A-Preparation and Vulcanization Protocol for Rubber Compositions The following preparation protocol is carried out in a HAAKE™ PolyLab™ QC mixer.

[0233] A-1) Coupling step:

[0234] 1 ère pass :

[0235] The mixer is heated to 70°C and the agitation is increased to 60 rpm.

[0236] The SSBR (Solution-Styrene Butadiene Rubber) and BR (Butadiene Rubber) elastomers are introduced. Then, the mixture is prepared for 1 minute.

[0237] Half of the total planned quantity of silica, silane, ZnO, stearic acid and DPG (comparative) or a sulfur compound according to the invention is added, and then mixed for 2 min.

[0238] Next, the other half of the silica, the antioxidant, the wax, and a manufacturing aid are added. Then, the mixture is stirred for 1 minute.

[0239] We lift and clean the mixer piston for 1 minute, then lower the piston.

[0240] The mixer temperature is increased to 130°C. When 130°C is reached, the stirring is stopped.

[0241] The mixture is left to rest and cool for 45 minutes.

[0242] 2 ême pass :

[0243] The mixer is heated to 100°C and the agitation is increased to 60 rpm.

[0244] Then, the cooled mixture obtained after the first pass, having been previously chopped, is introduced. It is mixed for 2 minutes. Then, the mixer temperature is increased to 160°C.

[0245] When 160°C is reached, the stirring is stopped.

[0246] The mixture is left to rest and cool for 45 minutes.

[0247] A-2) Acceleration stage:

[0248] The mixer is heated to 50°C and the agitation is increased to 30 rpm.

[0249] The cooled mixture obtained at the end of the coupling step is introduced, after being cut.

[0250] Mix for 2 minutes.

[0251] Next, accelerators are added: sulfur, sulfenamide and possibly thiuram.

[0252] Mix for 2 minutes, then stop stirring.

[0253] Samples of this raw rubber are taken in order to perform rheometry tests.

[0254] A-3) Shaping / vulcanization stage:

[0255] The mixture is passed over an external mixer (cylinders) to form a plate.

[0256] The mixture is placed in a vulcanizing press. It is vulcanized at 160 °C for a time corresponding to t90 (in minutes), determined by rheometric analysis: a cured rubber is obtained.

[0257] B-Protocols for the analysis of rubber compositions

[0258] B-1) Rheometry:

[0259] These tests are carried out on the "raw" rubber parts obtained according to the previous steps A-1 and A-2. They are performed using an MDR Pioneer rheometer according to the standard: NF ISO 6502-2:2018 "Rubber - Measurement of vulcanization characteristics using rheometers - Part 2: Oscillating disc rheometer".

[0260] In particular, we determine:

[0261] Ts2 (min):

[0262] Time required for the rubber to begin to vulcanize (time from which the vulcanizing torque reaches a value slightly above that of the minimum torque - usually 2 units above).

[0263] Values ​​are given as a base of 100 relative to the reference. A Ts2 value equal to or greater than 100 indicates a pre-vulcanization time equal to or greater than the reference. This is preferable to ensure a safety margin before the start of vulcanization. t90 (min) (or 90% curing time):

[0264] Time required to achieve 90% complete vulcanization of the rubber.

[0265] The values ​​are given as a base of 100 relative to the reference. A t90 value equal to or less than 100 indicates a vulcanization time equal to or shorter than the reference.

[0266] Delta C (dN.m):

[0267] This parameter is used to measure the increase in vulcanizing torque. More precisely, it represents the difference between the maximum torque reached during vulcanization and the initial minimum torque. It indicates the extent of rubber cross-linking.

[0268] A high Delta C means that the rubber has undergone significant vulcanization, which generally results in better mechanical properties, such as increased strength.

[0269] The values ​​are given as a base of 100 relative to the reference. A Delta C value equal to or close to 100 indicates a crosslinking density similar to the reference.

[0270] CRI (cure rate index) corresponds to the vulcanization speed index. The CRI is calculated using the following formula: CRI = 100 / (t90 - ts2).

[0271] B-2) Analysis on a tensile test bench:

[0272] The analyses are carried out on a HOUNSFIELD H5KS apparatus using rubber parts vulcanized according to step A-3 above.

[0273] Five test specimens of vulcanized rubber, without defects, are cut in the calendering direction, according to ISO 23529:2016 "Rubber — General procedures for the preparation and conditioning of test specimens for physical test methods".

[0274] Tensile strength (MPa):

[0275] This value characterizes the force that must be applied to the rubber sample for it to break. Values ​​are expressed as a base of 100 relative to the reference. A tensile strength value equal to or greater than 100 indicates improved mechanical properties.

[0276] B-3) DMA Analysis (Dynamic Mechanical Analysis)

[0277] DMA analysis is performed on a Mettler Toledo DMA1 apparatus according to the standard "ISO 4664-1:2022 Vulcanized or thermoplastic rubber — Determination of dynamic properties" on a small-sized test apparatus. The vulcanized rubber sample is clamped between two jaws and pre-tensioned to 1%. It is then subjected to tensile stress following an oscillatory deformation of "± A" pm in frequency and over a temperature range. "A" should correspond to the linearity zone of the sample.

[0278] We thus obtain the values ​​of conservation modulus (=elastic modulus E'), loss modulus E” (viscous modulus) and the damping factor tan 5 = E” / E' as a function of temperature.

[0279] The tests are carried out in tension, the distance between supports holding the rubber part is equal to 20mm, the width 2mm and the thickness 2mm.

[0280] The temperature sweep tests are carried out under the following conditions:

[0281] - Tensile test with a pre-deformation of 1%,

[0282] - Oscillation of amplitude A = 20 pm around the pre-tension position,

[0283] - Oscillation frequency: 10Hz,

[0284] - Conditioning: 30 minutes at 80°C,

[0285] - Temperature range: -80°C to +120°C

[0286] - Temperature rise rate 1 K / min. tan 5(40°C):

[0287] The value tan 5(40°C) corresponds to an indication of the rolling resistance phenomenon in the case where the rubber part is used to constitute the tread of a tire.

[0288] The results are expressed as a base of 100. This means that a value equal to, close to, or lower than the reference value indicates an equal, close, or lower rolling resistance. An equal or lower rolling resistance is desirable for higher-performance tires.

[0289] C - Rubber composition tests

[0290] Four compositions are prepared according to steps A-1) and A-2) mentioned above (coupling and acceleration): the first composition comprises DPG, the second homocysteine ​​at a concentration of 1 part, the third homocysteine ​​at a concentration of 0.5 parts, and the fourth homocystin at a concentration of 2 parts. C-1) Preparation of the rubber compositions

[0291] The ingredients of the four rubber compositions are as follows:

[0292] [Table 1]

[0293] Quantities are in pieces.

[0294] C-2) Properties of the raw rubbers obtained

[0295] The rheometric properties of the rubbers obtained are determined using an MDR Pioneer rheometer.

[0296] The results are as follows:

[0297] [Table 2]

[0298] The sulfur compounds according to the invention make it possible to obtain a Delta C, a t90 and a CRI similar to those obtained with DPG.

[0299] Furthermore, the sulfur compounds according to the invention make it possible to obtain a higher ts2: the safety time for handling the rubber before crosslinking is longer.

[0300] The sulfur compounds according to the invention therefore make it possible to maintain the rheometric properties of raw rubbers, in the absence of DPG and even with a smaller quantity of compound (1 or 0.5 pc for homocysteine ​​vs. 2 pc for DPG).

[0301] C-3) Properties of the cured rubbers obtained

[0302] The tested rubbers are vulcanized according to step A-3) and their mechanical properties are determined.

[0303] A HOUNSFIELD H5KS tensile testing machine is used for the tensile tests. The tan(Δ40°C) is determined using a DMA1 dynamic mechanical analyzer.

[0304] Mettler Toledo.

[0305] The results are as follows:

[0306] [Table 3]

[0307] It is noted that the tensile strength and the Tan(delta 40°C) are similar to those obtained with DPG. The sulfur compounds according to the invention therefore make it possible to maintain the properties of the cured rubbers, in the absence of DPG and even with a smaller quantity of compound (1 or 0.5 parts per liter for homocysteine ​​vs. 2 parts per liter for DPG).

[0308] D-Process for preparing the sulfur compound as a masterbatch. Preparation of the masterbatch on a POE / EVA support.

[0309] A masterbatch is prepared based on L-homocysteine.

[0310] In the HAAKE mixer, the following conditions are observed:

[0311] - Filling coefficient: 0.6 to 0.95, preferably 0.85;

[0312] - Initial mixer temperature: 20-80°C, preferably 50°C.

[0313] Thus, the mixing chamber is heated to 50°C and the rotors are rotated at 60 revolutions per minute.

[0314] 7g of poly(ethylene-1-butene) (CAS No. 25087-34-7), 3g of ethylene-vinyl acetate copolymer (melting point 53°C), 15g of oil (CAS No. 64742-55-8), are introduced into the mixing chamber, as well as 75g of L-homocysteine.

[0315] The mixing torque increases until it reaches a maximum. Once the maximum is reached, mixing continues for 2 minutes. Then the rotors are stopped and the white master mixture is recovered by draining the mixing chamber.

[0316] The mixture is then analyzed using a Mooney viscometer: Final viscosity at 80 °C = ML(1+4) = 22 MU

Claims

DEMANDS 1. Rubber composition comprising: (a) at least one elastomer, preferably at least one diene elastomer, (b) a reinforcing load, (c) possibly a charge-elastomer coupling agent, (d) at least one sulfur compound of the following general formula (I), or one of its salts: R3-X-CH(NRiR2)-(CH2)n-(S)pZ (I) in which: Z is a hydrogen atom or a -(CH2) group n -CH(NRiR2)-X-R3; Ri and R2, identical or different, are chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or not, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); X is chosen from -C(=O)- , -CH2- or -CN; Rest: (i) is zero when X represents -CN, (ii) be a hydrogen atom, (iii) either -ORa, Ra being a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); (iv) either -NRbRc, Rb and Rc, identical or different, being chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); n is an integer equal to 1 or 2, preferably equal to 2; and p is an integer between 1 and 8; provided that if Z is a hydrogen atom, then p is equal to 1; and (e) a crosslinking system; said composition comprising strictly less than 0.1 pc of guanidic compound.

2. Rubber composition according to claim 1, wherein said sulfur compound has the following general formula, or one of its salts: R3-X-CH(NRiR2)-(CH2)n-SH (la) in which Ri, R2, R3, X and n are as defined in claim 1.

3. Rubber composition according to claim 1, wherein said sulfur compound is selected from the group consisting of: cysteine, dicysteine ​​monosulfide, cystine, homocysteine, dihomocysteine ​​monosulfide, homocystine, dicysteine ​​trisulfide, dicysteine ​​tetrasulfide, dicysteine ​​pentasulfide, dihomocysteine ​​trisulfide, dihomocysteine ​​tetrasulfide, dihomocysteine ​​pentasulfide, and one of their salts, preferably homocysteine.

4. Rubber composition according to any one of the preceding claims, wherein the total quantity of the sulfur compound(s) is between 0.10 and 10 pc, preferably between 0.10 and 5 pc.

5. Rubber composition according to any one of the preceding claims, said composition not comprising any guanidic compound.

6. Rubber composition according to any one of the preceding claims, wherein the elastomer(s) is / are selected from the group consisting of polyisoprenes, natural rubbers (NR), styrene-butadiene rubbers (SBR) such as SSBR (Solution Rubber-Styrene Butadiene) and ESBR (Emulsion Rubber-Styrene Butadiene), ethylene-propylene-diene monomer terpolymers (EPDM), butadiene rubbers (BR), polyolefin elastomers (POEs) and mixtures thereof such as SBR / BR and even more preferably SSBR / BR.

7. Rubber composition according to any one of the preceding claims, wherein the reinforcing filler comprises predominantly silica.

8. Rubber composition according to any one of the preceding claims, wherein the crosslinking system comprises a sulfur donor, such as elemental sulfur, and at least one sulfur vulcanization accelerator.

9. Rubber composition according to claim 8, wherein said sulfur-containing vulcanization accelerator is selected from the group consisting of thiazoles, sulfenamides, thiurams, dithiocarbamates, dithiophosphates, xanthates, dithiodiamines, thioureas, poly(phenol sulfides), their derivatives and mixtures, preferably among the thiurams.

10. Rubber composition according to any one of the preceding claims, wherein the sulfur compound(s) is / are in the form of a masterbatch.

11. A method for vulcanizing a rubber composition as described in any one of claims 1 to 10, comprising the following steps: 1) a coupling step comprising the mixing of: (a) at least one elastomer, preferably at least one diene elastomer, (b) a reinforcing load, (c) possibly a charge-elastomer coupling agent, and (f) possibly other additives; 2) an acceleration step comprising the addition of the crosslinking system (e) to the mixture obtained at the end of step 1); and 3) a vulcanization step of the mixture obtained at the end of step 2), in order to obtain a vulcanized rubber composition; wherein at least one sulfur compound of general formula (I) as defined in any one of claims 1 to 3 is added during step 1) and / or during step 2).

12. Article, preferably a tire, comprising a rubber composition as defined in any one of claims 1 to 10 vulcanized.

13. Use of a sulfur compound of the following general formula (I), or one of its salts: R3-X-CH(NRiR2)-(CH2)n-(S) P -Z (I) in which: Z is a hydrogen atom or a group -(CH2)n-CH(NRiR2)-X-R3; Ri and R2, identical or different, are chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or not, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); X is chosen from -C(=O)- , -CH2- or -CN; Rest: (i) is zero when X represents -CN, (ii) be a hydrogen atom, (iii) either -ORa, Ra being a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); (iv) either -NRbRc, Rb and Rc, identical or different, being chosen from: a hydrogen atom or a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, aromatic or non-aromatic, of 1 to 20 carbon atom(s) and which may include one or more heteroatom(s); - n is an integer equal to 1 or 2, preferably equal to 2; and p is an integer between 1 and 8; provided that if Z is a hydrogen atom, then p is equal to 1; in place of a guanidic compound.

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