Rubber compositions comprising a specific combination of a coupling agent and a hydrocarbon-based resin

Abstract

A rubber composition is based on at least: a diene elastomer; a reinforcing inorganic filler; an agent for coupling the reinforcing inorganic filler with the diene elastomer, said coupling agent being a blocked mercaptosilane of formula (I), as described in the claims; a hydrocarbon-based resin predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures thereof, and a crosslinking system. A semi-finished article and a tire may comprise at least one such rubber composition.

Claims

1. A rubber composition based on at least: a diene elastomer; a reinforcing inorganic filler; a coupling agent for coupling the reinforcing inorganic filler with the diene elastomer, the coupling agent being a blocked mercaptosilane of general formula (I):
(R.sup.4O).sub.dR.sup.3.sub.(3-d)—Si—Z—S—C(═O)—R.sup.5  (I) in which: the radical R.sup.3 is selected from the group consisting of linear or branched C.sub.1-C.sub.10 alkyls, the radical R.sup.4 is selected from the group consisting of a hydrogen atom or linear or branched C.sub.1-C.sub.10 alkyls, the radical R.sup.5 is selected from the group consisting of a hydrogen atom or linear or branched C.sub.1-C.sub.10 alkyls, Z is a divalent bonding group containing a linear or branched C.sub.1-C.sub.8 alkylene; and d is an integer equal to 1, 2 or 3; a hydrocarbon-based resin predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures thereof; and a crosslinking system, wherein the coupling agent has a content ranging from 3 to 20 phr, and wherein the reinforcing inorganic filler has a content ranging from 40 to 200 phr.

2. The rubber composition according to claim 1, wherein d is equal to 3.

3. The rubber composition according to claim 1, wherein the hydrocarbon-based resin has a number-average molecular mass Mn that is within a range extending from 200 to 2000 g/mol.

4. The rubber composition according to claim 1, wherein the hydrocarbon-based resin has a polydispersity index of less than or equal to 2.

5. The rubber composition according to claim 1, wherein the hydrocarbon-based resin is further composed, in a minor amount, of aromatic monomers.

6. The rubber composition according to claim 5, wherein a content of aromatic protons of the hydrocarbon-based resin is within a range extending from 1% to 20%.

7. The rubber composition according to claim 1, wherein a content of hydrocarbon-based resin is within a range extending from 15 to 150 phr.

8. The rubber composition according to claim 1, wherein the reinforcing inorganic filler comprises at least one silica.

9. The rubber composition according to claim 1 further comprising carbon black.

10. The rubber composition according to claim 1, wherein the diene elastomer is selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures thereof.

11. The rubber composition according to claim 10, wherein the diene elastomer is selected from the group consisting of polybutadienes, butadiene-styrene copolymers, isoprene-butadiene copolymers, isoprene-styrene copolymers, isoprene-butadiene-styrene copolymers, and mixtures thereof.

12. The rubber composition according to claim 1, wherein the diene elastomer is a functionalized elastomer.

13. The rubber composition according to claim 12, wherein the functionalized elastomer has a glass transition temperature Tg of less than or equal to −40° C.

14. A semi-finished article for a tire comprising at least one rubber composition according to claim 1.

15. A tire comprising at least one rubber composition according to claim 1.

Description

2—DETAILED DESCRIPTION OF THE INVENTION

(1) The invention and the advantages thereof will be readily understood in the light of the description and the implementation examples.

(2) A first subject of the present invention relates to a rubber composition based on at least: a diene elastomer; a reinforcing inorganic filler; an agent for coupling the reinforcing inorganic filler with the diene elastomer, said coupling agent being a blocked mercaptosilane of general formula (I):
(R.sup.4O).sub.dR.sup.3.sub.(3-d)—Si—Z—S—C(═O)—R.sup.5  (I) in which: the radical R.sup.3 is chosen from linear or branched C.sub.1-C.sub.18 alkyls, C.sub.3-C.sub.8 cycloalkyls and C.sub.6-C.sub.10 aryls; the radical R.sup.4 is chosen from a hydrogen atom, linear or branched C.sub.1-C.sub.18 alkyls, C.sub.3-C.sub.8 cycloalkyls or C.sub.6-C.sub.10 aryls; the radical R.sup.5 is chosen from a hydrogen atom, linear or branched C.sub.1-C.sub.18 alkyls, C.sub.3-C.sub.8 cycloalkyls, C.sub.6-C.sub.10 aryls and linear or branched C.sub.2-C.sub.8 alkoxyalkyls; the symbol Z represents a divalent bonding group containing from 1 to 18 carbon atoms; d is an integer equal to 1, 2 or 3; a hydrocarbon-based resin predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures thereof, and a crosslinking system.

(3) The term “composition based on” should be understood as meaning a composition including the mixture and/or the in situ reaction product of the various constituents used, some of these constituents being capable of reacting and/or being intended to react with each other, at least in part, during the various phases of manufacture of the composition.

(4) In the present description, unless expressly indicated otherwise, all the percentages (%) shown are mass percentages.

(5) Furthermore, any range of values denoted by the expression “between a and b” represents the range of values extending from more than “a” to less than “b” (i.e. limits a and b excluded), while any range of values denoted by the expression “from a to b” means the range of values extending from “a” up to “b” (i.e. including the strict limits a and b).

(6) In the present patent application, the term “phr” means parts by weight of a constituent per hundred parts by weight of elastomer.

(7) In the context of the invention, the carbon-based products mentioned in the description may be of fossil or biosourced origin. In the latter case, they may be partially or totally derived from biomass or may be obtained from renewable starting materials derived from biomass. Polymers, plasticizers, fillers and the like are notably concerned.

2.1—Constituents of the Rubber Composition

Diene Elastomer

(8) As mentioned previously, the compositions in accordance with the invention comprise at least one diene elastomer.

(9) It is recalled here that the term “elastomer” (or “rubber”, the two terms being regarded as synonymous) of the “diene” type should be understood, in a known manner, as meaning an (one or more is understood) elastomer at least partly derived (i.e., a homopolymer or a copolymer) from diene monomer(s) (i.e. monomer(s) bearing two conjugated or non-conjugated carbon-carbon double bonds).

(10) Diene elastomers may be classified in two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” generally refers to a diene elastomer resulting at least in part from conjugated diene monomers having a molar content of units of diene origin (conjugated dienes) which is greater than 15% (mol %); thus, diene elastomers such as butyl rubbers or copolymers of dienes and of α-olefins of EPDM type do not fall under the preceding definition and may notably be termed “essentially saturated” diene elastomers (low or very low molar content, always less than 15% (mol %), of units of diene origin). In the category of “essentially unsaturated” diene elastomers, the term “highly unsaturated” diene elastomer in particular refers to a diene elastomer having a molar content of units of diene origin (conjugated dienes) which is greater than 50% (mol %).

(11) Given these definitions, the term “diene elastomer that is capable of being used in the rubber compositions in accordance with the invention” more particularly refers to: (a) any homopolymer obtained by polymerization of a conjugated diene monomer containing from 4 to 12 carbon atoms; (b) any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more vinylaromatic compounds containing from 8 to 20 carbon atoms; (c) a ternary copolymer obtained by copolymerization of ethylene and of an α-olefin containing from 3 to 6 carbon atoms with a non-conjugated diene monomer containing from 6 to 12 carbon atoms, for instance the elastomers obtained from ethylene and propylene with a non-conjugated diene monomer of the abovementioned type, notably such as 1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene; (d) a copolymer of isobutene and of isoprene (butyl rubber) and also the halogenated versions, in particular chlorinated or brominated versions, of this type of copolymer.

(12) Although it applies to any type of elastomer, notably diene elastomer, a person skilled in the art will understand that the present invention is preferably performed with essentially unsaturated diene elastomers, in particular of the type (a) or (b) above.

(13) In the case of copolymers (b), they may contain from 20% to 99% by weight of diene units and from 1% to 80% by weight of vinylaromatic units.

(14) The following are notably suitable as conjugated dienes: 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C.sub.1-C.sub.5 alkyl)-1,3-butadienes, for instance 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene.

(15) The following, for example, are suitable as vinylaromatic compounds: styrene, ortho-, meta- or para-methylstyrene, the “vinyltoluene” commercial mixture, para-(tert-butyl)styrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene or vinylnaphthalene.

(16) Preferentially, the diene elastomer(s) of the composition according to the invention may be chosen from the group of diene elastomers consisting of polybutadienes (abbreviated to BRs), synthetic polyisoprenes (abbreviated to IRs), natural rubber (abbreviated to NR), butadiene copolymers, isoprene copolymers and the mixtures of these elastomers.

(17) Such copolymers are more preferentially chosen from the group consisting of butadiene/styrene copolymers (abbreviated to SBRs), whether the latter are prepared by emulsion polymerization (ESBR) or solution polymerization (SSBR), isoprene/butadiene copolymers (abbreviated to BIRs), isoprene/styrene copolymers (abbreviated to SIRs) and isoprene/butadiene/styrene copolymers (abbreviated to SBIRs).

(18) More preferentially, the diene elastomer(s) of the composition according to the invention may be chosen from the group of diene elastomers consisting of polybutadienes, butadiene-styrene copolymers, isoprene-butadiene copolymers, isoprene-styrene copolymers, isoprene-butadiene-styrene copolymers, and mixtures of these elastomers.

(19) The elastomers may have any microstructure, which depends on the polymerization conditions used, notably on the presence or absence of a modifying and/or randomizing agent and on the amounts of modifying and/or randomizing agent used. These elastomers may, for example, be block, random, sequential or microsequential elastomers and may be prepared in dispersion or in solution; they may be coupled and/or star-branched or else functionalized with a coupling and/or star-branching or functionalization agent.

(20) According to a preferred embodiment, the elastomer is a functionalized diene elastomer.

(21) Preferably, the functionalized diene elastomer is chosen from the group of diene elastomers consisting of polybutadienes, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. Even more preferentially, the functionalized elastomer is a butadiene-styrene copolymer.

(22) Preferably, the functionalized diene elastomer has a glass transition temperature Tg of less than or equal to −40° C., preferably within a range extending from −110° C. to −40° C., more preferentially from −110° C. to −60° C., even more preferentially from −110° C. to −80° C.

(23) The term “functionalized diene elastomer” refers to a synthetic diene elastomer which includes at least one chemical group comprising one or more heteroatoms, for instance a sulfur atom S, a nitrogen atom N, an oxygen atom O, a silicon atom Si or a tin atom Sn. In the context of the present description, this chemical group is also referred to as “function”. The two terms are used without distinction.

(24) This chemical group may be located at the chain end, that is to say at one end of the linear main elastomer chain. It will then be said that the diene elastomer is functionalized “at the chain end”. It is generally an elastomer obtained by reaction of a living elastomer with a functionalization agent, that is to say any at least monofunctional molecule, the function being any type of chemical group known to those skilled in the art to react with a living chain end.

(25) This chemical group may be located in the linear main elastomer chain. It will then be said that the diene elastomer is coupled or else functionalized “in the middle of the chain”, as opposed to the position “at the chain end” and although the group is not located precisely at the middle of the elastomer chain. It is generally an elastomer obtained by reaction of two chains of the living elastomer with a coupling agent, that is to say any at least difunctional molecule, the function being any type of chemical group known to those skilled in the art to react with a living chain end.

(26) This group may be central, to which n elastomer chains (n>2) are bonded, forming a star-branched structure of the elastomer. It will then be said that the diene elastomer is star-branched. It is generally an elastomer obtained by reaction of n chains of the living elastomer with a star-branching agent, that is to say any polyfunctional molecule, the function being any type of chemical group known to those skilled in the art to react with a living chain end.

(27) A person skilled in the art will understand that a functionalization reaction with an agent comprising more than one function which is reactive with regard to the living elastomer results in a mixture of species functionalized at the chain end and in the middle of the chain, constituting the linear chains of the functionalized diene elastomer, and also, where appropriate, star-branched species. Depending on the operating conditions, mainly the mole ratio of the functionalization agent to the living chains, certain species are predominant in the mixture.

(28) Preferentially, the functionalized diene elastomer comprises at least one polar function comprising at least one oxygen atom.

(29) Preferentially, the polar function may be chosen from the group consisting of silanol, alkoxysilanes, alkoxysilanes bearing an amine group, epoxide, ethers, esters, carboxylic acids and hydroxyl. The polar function notably improves the interaction between the reinforcing inorganic filler and the elastomer. Such functionalized elastomers are known per se and are described notably in the following documents: FR2740778, U.S. Pat. No. 6,013,718, WO2008/141702, FR2765882, WO01/92402, WO2004/09686, EP1127909, U.S. Pat. No. 6,503,973, WO2009/000750 and WO 2009/000752.

(30) In a preferred embodiment, the functionalized diene elastomer is a diene elastomer including a polar function that is a silanol.

(31) Preferably, the functionalized diene elastomer comprises, at one end of its main chain, a silanol function or a polysiloxane group bearing a silanol end of formula —(SiR.sub.1R.sub.2—O—).sub.mH with m representing an integer ranging from 3 to 8, preferably 3, R.sub.1 and R.sub.2, which may be identical or different, represent an alkyl radical of 1 to 10 carbon atoms, preferably an alkyl radical containing 1 to 4 carbon atoms.

(32) This type of elastomer may be obtained according to the processes described in EP 0778311 and more particularly according to the process consisting, after a step of anionic polymerization, in functionalizing the living elastomer with a functionalization agent of cyclic polysiloxane type, as long as the reaction medium does not allow the polymerization of the cyclopolysiloxane. Cyclic polysiloxanes that may be mentioned include those corresponding to formula (III):

(33) ##STR00001##
where m represents an integer ranging from 3 to 8, preferably 3, and R.sub.1 and R.sub.2, which may be identical or different, represent an alkyl radical of 1 to 10 carbon atoms, preferably an alkyl radical containing 1 to 4 carbon atoms. Among these compounds, mention may be made of hexamethylcyclotrisiloxane.

(34) In another preferred embodiment of the invention, the functionalized diene elastomer includes a polar function which is an alkoxysilane optionally bearing another function (or bearing another chemical group, these expressions being synonymous).

(35) Preferably, this functionalized diene elastomer comprises in its main chain at least one alkoxysilane group bonded to the elastomer chain via the silicon atom, and optionally bearing at least one other function.

(36) According to certain preferred variants, the alkoxysilane group (optionally bearing another function) is located at one end of the main chain of the elastomer.

(37) According to other preferred variants, the alkoxysilane group (optionally bearing another function) is located in the main elastomer chain. The silicon atom of this function bonds the two branches of the main chain of the diene elastomer.

(38) The alkoxysilane group (optionally bearing another function) comprises a C.sub.1-C.sub.10 alkoxy radical, optionally partially or totally hydrolysed to hydroxyl, or even a C.sub.1-C.sub.8, preferably C.sub.1-C.sub.4 alkoxy radical, and is more preferentially methoxy and ethoxy.

(39) The other function is preferably borne by the silicon of the alkoxysilane group, directly or via a spacer group, defined as being a saturated or unsaturated, cyclic or non-cyclic, divalent, linear or branched, aliphatic C.sub.1-C.sub.18 hydrocarbon-based radical, or a divalent aromatic C.sub.6-C.sub.18 hydrocarbon-based radical.

(40) The other function is preferably a function comprising at least one heteroatom chosen from N, S, O or P. Mention may be made, by way of example, among these functions, of cyclic or non-cyclic primary, secondary or tertiary amines, isocyanates, imines, cyanos, thiols, carboxylates, epoxides or primary, secondary or tertiary phosphines.

(41) Mention may thus be made, as secondary or tertiary amine function, of amines substituted with C.sub.1-C.sub.10 alkyl, preferably C.sub.1-C.sub.4 alkyl, radicals, more preferentially a methyl or ethyl radical, or else of cyclic amines forming a heterocycle containing a nitrogen atom and at least one carbon atom, preferably from 2 to 6 carbon atoms. For example, methylamino-, dimethylamino-, ethylamino-, diethylamino-, propylamino-, dipropylamino-, butylamino-, dibutylamino-, pentylamino-, dipentylamino-, hexylamino-, dihexylamino- or hexamethyleneamino-groups, preferably diethylamino- and dimethylamino-groups, are suitable.

(42) Mention may be made, as imine function, of ketimines. For example, (1,3-dimethylbutylidene)amino-, (ethylidene)amino-, (1-methylpropylidene)amino-, (4-N,N-dimethylaminobenzylidene)amino-, (cyclohexylidene)amino-, dihydroimidazole and imidazole groups are suitable.

(43) Mention may thus be made, as carboxylate function, of acrylates or methacrylates. Such a function is preferably a methacrylate.

(44) Mention may be made, as epoxide function, of epoxy or glycidyloxy groups.

(45) Mention may be made, as secondary or tertiary phosphine function, of phosphines substituted with C.sub.1-C.sub.10 alkyl, preferably C.sub.1-C.sub.4 alkyl, radicals, more preferentially a methyl or ethyl radical, or else diphenylphosphine. For example, methylphosphino-, dimethylphosphino-, ethylphosphino-, diethylphosphino, ethylmethylphosphino- and diphenylphosphino-groups are suitable.

(46) Preferentially, the other function is preferably a tertiary amine, more preferentially a diethylamino- or dimethylamino-group.

(47) Preferentially, the functionalized diene elastomer (notably an SBR) may comprise a polar function which is an alkoxysilane optionally bearing an amine group.

(48) Preferably, this functionalized diene elastomer comprises in its main chain at least one alkoxysilane group bonded to the elastomer chain via the silicon atom, and optionally bearing an amine group.

(49) Preferably, this alkoxysilane group may be represented by formula (IV):
(*-).sub.aSi(OR′).sub.bR.sub.cX  (IV)
in which: *- represents the bond to an elastomer chain; the radical R represents a substituted or unsubstituted C.sub.1-C.sub.10, or even C.sub.1-C.sub.8, alkyl radical, preferably a C.sub.1-C.sub.4 alkyl radical, more preferentially methyl and ethyl; in the alkoxy radical(s) of formula —OR′, which are optionally partially or totally hydrolysed to hydroxyl, R′ represents a substituted or unsubstituted C.sub.1-C.sub.10, or even C.sub.1-C.sub.8, alkyl radical, preferably a C.sub.1-C.sub.4 alkyl radical, more preferentially methyl and ethyl; X represents a group including the other function; a is equal to 1 or 2, b is equal to 1 or 2, and c is equal to 0 or 1, with the proviso that a+b+c=3.

(50) More preferentially, the functionalized diene elastomer is a diene elastomer (notably an SBR) comprises, within the main chain thereof, at least one alkoxysilane group of formula (IV) in which: *- represents the bond to an elastomer chain; the radical R represents a substituted or unsubstituted C.sub.1-C.sub.4 alkyl radical, more preferentially methyl and ethyl; in the alkoxy radical(s) of formula —OR′, which are optionally partially or totally hydrolysed to hydroxyl, R′ represents a substituted or unsubstituted C.sub.1-C.sub.4 alkyl radical, more preferentially methyl and ethyl; X represents a group including the other function; preferably a tertiary amine; a is equal to 1 or 2, b is equal to 1 or 2, and c is equal to 0 or 1, with the proviso that a+b+c=3.

(51) This type of elastomer is mainly obtained by functionalization of a living elastomer derived from an anionic polymerization. It should be pointed out that it is known to those skilled in the art that when an elastomer is modified by reaction of a functionalization agent with the living elastomer derived from a step of anionic polymerization, a mixture of modified species of this elastomer is obtained, the composition of which depends on the modification reaction conditions and notably on the proportion of reactive sites of the functionalization agent relative to the number of living elastomer chains. This mixture comprises species which are functionalized at the chain end, coupled, star-branched and/or non-functionalized.

(52) According to a particularly preferred variant, the modified diene elastomer comprises, as predominant species, the diene elastomer functionalized in the middle of the chain with an alkoxysilane group bonded to the two branches of the diene elastomer via the silicon atom. Even more particularly, the diene elastomer functionalized in the middle of the chain with an alkoxysilane group represents 70% by weight of the modified diene elastomer. Preferably, this functionalized diene elastomer has a glass transition temperature Tg of less than or equal to −40° C., preferably within a range extending from −110° C. to −40° C., more preferentially from −110° C. to −60° C., even more preferentially from −110° C. to −80° C.

(53) Whether or not they are functionalized, the diene elastomers may be used blended (mixed) with each other. Thus, the rubber compositions in accordance with the invention may contain just one diene elastomer, functionalized or non-functionalized, or else a mixture of several diene elastomers, functionalized or non-functionalized, it being possible for this (these) diene elastomer(s) to be used in combination with any type of synthetic elastomer other than a diene elastomer, or even with polymers other than elastomers, for example thermoplastic polymers.

Reinforcing Filler

(54) The rubber compositions in accordance with the invention comprise at least one reinforcing inorganic filler.

(55) In the present patent application, the term “reinforcing inorganic filler” should be understood, by definition, as meaning any inorganic or mineral filler (regardless of its colour and its origin, natural or synthetic), also known as “white filler”, “clear filler” or even “non-black filler”, as opposed to carbon black, which is capable of reinforcing by itself alone, without means other than an intermediate coupling agent, a rubber composition intended for the manufacture of tyres, in other words capable of replacing, in its reinforcing role, a conventional tyre-grade carbon black; such a filler is generally characterized, in a known manner, by the presence of hydroxyl (—OH) groups at its surface.

(56) The physical state in which the reinforcing inorganic filler is provided is not important, whether it be in the form of a powder, of micropearls, of granules, of beads or any other appropriate densified form. Needless to say, the term “reinforcing inorganic filler” also means mixtures of different reinforcing inorganic fillers, in particular of highly dispersible siliceous and/or aluminous fillers as described below.

(57) Mineral fillers of the siliceous type, in particular silica (SiO.sub.2), or of the aluminous type, in particular alumina (Al.sub.2O.sub.3), are notably suitable for use as reinforcing inorganic fillers. The silica used may be any reinforcing silica known to those skilled in the art, notably any precipitated or fumed silica with a BET specific surface area and also a CTAB specific surface area both of less than 450 m.sup.2/g, preferably from 30 to 400 m.sup.2/g. Mention will be made, as highly dispersible precipitated silicas (“HDSs”), for example, of the Ultrasil 7000 and Ultrasil 7005 silicas from the company Evonik, the Zeosil 1165MP, 1135MP and 1115MP silicas from the company Solvay, the Hi-Sil EZ150G silica from the company PPG, the Zeopol 8715, 8745 and 8755 silicas from the company Huber or the silicas with a high specific surface area as described in patent application WO 03/016387.

(58) Preferably, the reinforcing inorganic filler comprises at least one silica, and more preferentially consists of silica.

(59) Preferably, the reinforcing inorganic filler used, in particular if it is silica, has a BET specific surface area of between 45 and 400 m.sup.2/g, more preferentially of between 60 and 300 m.sup.2/g. The BET and CTAB specific surface areas are determined according to the measuring methods described previously.

(60) A person skilled in the art will understand that use might be made, as filler equivalent to the reinforcing inorganic filler described in the present section, of a reinforcing filler of another nature, notably organic nature, provided that this reinforcing filler is covered with an inorganic layer, such as silica, or else includes, at its surface, functional sites, notably hydroxyl sites, requiring the use of a coupling agent in order to establish the bond between the filler and the elastomer.

(61) Preferably, the content of reinforcing inorganic filler in the rubber compositions in accordance with the invention is within a range extending from 5 to 200 phr, more preferentially from 40 to 160 phr.

(62) In a preferred embodiment, the rubber composition in accordance with the invention also comprises an organic reinforcing filler, preferably carbon black.

(63) Organic reinforcing fillers that are notably suitable include carbon blacks or functionalized polyvinyl organic fillers, as described in patent applications WO-A-2006/069792, WO-A-2006/069793, WO-A-2008/003434 and WO-A-2008/003435.

(64) In this embodiment, the organic reinforcing filler is carbon black. All carbon blacks, notably “tyre-grade” blacks, are suitable as carbon blacks. Mention will more particularly be made, among the latter, of the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), for instance the N115, N134, N234, N326, N330, N339, N347 or N375 blacks, or else, depending on the applications targeted, the blacks of higher series (for example N660, N683 or N772). The carbon blacks may, for example, be already incorporated in an isoprene elastomer in the form of a masterbatch (see, for example, patent application WO 97/36724 or WO 99/16600).

(65) When it is present, the carbon black is preferentially used in a content within a range extending from 0.1 to 10 phr, more preferentially from 0.5 to 10 phr, notably from 1 to 4 phr.

Coupling Agent

(66) As mentioned previously, the rubber composition in accordance with the invention comprises at least one agent for coupling the reinforcing inorganic filler with the elastomer, said coupling agent being a blocked mercaptosilane of general formula (I):
(R.sup.4O).sub.dR.sup.3.sub.(3-d)—Si—Z—S—C(═O)—R.sup.5  (I)
in which: the radical R.sup.3 is chosen from linear or branched C.sub.1-C.sub.18 alkyls, C.sub.3-C.sub.8 cycloalkyls and C.sub.6-C.sub.10 aryls; the radical R.sup.4 is chosen from a hydrogen atom, linear or branched C.sub.1-C.sub.18 alkyls, C.sub.3-C.sub.8 cycloalkyls or C.sub.6-C.sub.10 aryls; the radical R.sup.5 is chosen from a hydrogen atom, linear or branched C.sub.1-C.sub.18 alkyls, C.sub.3-C.sub.8 cycloalkyls, C.sub.6-C.sub.10 aryls and linear or branched C.sub.2-C.sub.8 alkoxyalkyls; the symbol Z represents a divalent bonding group containing from 1 to 18 carbon atoms;

(67) Preferentially, in the general formula (I), the radical R.sup.3 is a linear or branched C1-C10 alkyl.

(68) More preferentially, in the general formula (I), the radical R.sup.3 is chosen from methyl, ethyl, propyl and isobutyl.

(69) Preferentially, in the general formula (I), the radical R.sup.4 is chosen from a hydrogen atom and linear or branched C1-C18 alkyls.

(70) More preferentially, in the general formula (I), the radical R.sup.4 is chosen from a hydrogen atom and linear or branched C1-C10 alkyls.

(71) Even more preferentially, in the general formula (I), the radical R.sup.4 is chosen from a hydrogen atom, methyl, ethyl, propyl and isobutyl.

(72) The group Z representing a divalent bonding group may be a hydrocarbon-based chain optionally interrupted with one or more heteroatoms chosen in particular from sulfur, nitrogen and oxygen; this chain containing from 1 to 18 carbon atoms.

(73) Preferentially, the group Z is chosen from the group consisting of a linear or branched C1-C18 alkylene, a saturated C3-C8 cycloalkylene and a C6-C12 arylene.

(74) More preferentially, the group Z is a linear or branched C1-C8 alkylene.

(75) Even more preferentially, the group Z is a linear C1-C4 alkylene.

(76) Even more preferentially, the group Z is chosen from methylene —CH.sub.2—, ethylene —CH.sub.2CH.sub.2—, propylene —CH.sub.2CH.sub.2CH.sub.2—; more preferentially, the group Z is propylene.

(77) Preferentially, the radical R.sup.5 is chosen from a hydrogen atom and linear or branched C1-C18 alkyls.

(78) Preferentially, the radical R.sup.5 is a linear or branched C1-C10 alkyl, even more preferentially a linear C6-C8 alkyl.

(79) Preferably, the radical R.sup.5 is chosen from the group consisting of hexyl, heptyl and octyl; more preferentially, the radical R.sup.5 is heptyl (C.sub.7H.sub.15—).

(80) Preferably, D is an integer equal to 3.

(81) In a preferred embodiment, the compound of formula (I) has the following characteristics: the radical R.sup.3 is chosen from linear or branched C1-C18 alkyls, C3-C8 cycloalkyls and C6-C10 aryls; the radical R.sup.4 is chosen from a hydrogen atom, linear or branched C1-C18 alkyls, C3-C8 cycloalkyls or C6-C10 aryls; the group Z is a linear or branched C1-C8 and preferably C1-C4 alkylene, the radical R.sup.5 is a linear or branched C1-C10 alkyl; even more preferentially, a linear C6-C8 alkyl, and d is an integer equal to 1, 2 or 3.

(82) In another preferred embodiment, the compound of formula (I) has the following characteristics: the radical R.sup.3 is a linear or branched C1-C10 alkyl, the radical R.sup.4 is chosen from a hydrogen atom and linear or branched C1-C10 alkyls, the group Z is chosen from the group consisting of a linear or branched C1-C18, preferably C1-C8 alkylene; more preferentially, Z is chosen from methylene, ethylene and propylene; even more preferentially, the group Z is propylene, the radical R.sup.5 is chosen from the group consisting of a hydrogen atom and linear or branched C1-C18 alkyls; preferably, R.sup.5 is a linear or branched C1-C10 alkyl, even more preferentially a linear C6-C8 alkyl, and d is an integer equal to 1, 2 or 3.

(83) In another preferred embodiment, the compound of formula (I) has the following characteristics: the radical R.sup.3 is chosen from methyl, ethyl, propyl and isobutyl, the radical R.sup.4 is chosen from a hydrogen atom, methyl, ethyl, propyl and isobutyl, the group Z is chosen from methylene —CH.sub.2—, ethylene —CH.sub.2CH.sub.2—, propylene —CH.sub.2CH.sub.2CH.sub.2—; more preferentially, the group Z is propylene, the radical R.sup.5 is a linear C6-C8 alkyl, and d is an integer equal to 1, 2 or 3; preferably, d is equal to 3.

(84) In another preferred embodiment, the compound of formula (I) has the following characteristics: the radical R.sup.3 is chosen from methyl, ethyl, propyl and isobutyl, the radical R.sup.4 is chosen from methyl, ethyl, propyl and isobutyl, the group Z is chosen from methylene —CH.sub.2—, ethylene —CH.sub.2CH.sub.2—, propylene —CH.sub.2CH.sub.2CH.sub.2—; more preferentially, the group Z is propylene, R.sup.5 is chosen from the group consisting of hexyl, heptyl and octyl; preferably, it is heptyl, and d is an integer equal to 1, 2 or 3; preferably, d is equal to 3.

(85) The blocked mercaptosilane coupling agents used in the compositions in accordance with the invention have been described, along with their syntheses, in WO 99/09036, WO 2010/072682, WO 2010/072683 and WO 203/087693.

(86) As a preferential example of a blocked mercaptosilane corresponding to formula (I), mention will be made most particularly of the compound having the particular formula (II) below:

(87) ##STR00002##

(88) The coupling agent of formula (II) is commercially available from Momentive. Inc. under the commercial reference NXT.

(89) In one variant of the invention, the coupling agent that may be used in the compositions of the invention may predominantly comprise a blocked mercaptosilane of formula (I), including these preferred embodiments, as described above and a second coupling agent, of chemical structure different from this blocked mercaptosilane of formula (I). This second coupling agent may be, for example, a polysulfide silane.

(90) Preferentially, in this embodiment, the coupling agent that may be used in the compositions of the invention comprises at least 70% by weight of a blocked mercaptosilane of formula (I), including these preferred embodiments, as described above relative to the total weight of the coupling agents used and a second coupling agent of chemical structure different from this blocked mercaptosilane of formula (I); this second coupling agent notably being present in a content of not more than 30% by weight relative to the total weight of the coupling agents used. This second coupling agent may be, for example, a polysulfide silane.

(91) Polysulfide silanes are well known to those skilled in the art and are used as agent for coupling a reinforcing inorganic filler with elastomers in rubber compositions.

(92) The polysulfide silanes may be “symmetrical” or “asymmetrical” depending on their particular structure. Such compounds are described, for example, in patent applications WO 03/002648 (or US 2005/016651) and WO 03/002649 (or US 2005/016650).

(93) Agents that are suitable in particular, without the definition below being limiting, are “symmetrical” polysulfide silanes, corresponding to general formula (V) below:
T-D-Sx-D-T  (V)
in which: x is an integer from 2 to 8 (preferably from 2 to 5); the symbols D, which may be identical or different, represent a divalent hydrocarbon-based radical (preferably C.sub.1-C.sub.18 alkylene groups or C.sub.6-C.sub.12 arylene groups, more particularly C.sub.1-C.sub.10 and notably C.sub.1-C.sub.4 alkylenes, in particular propylene); the symbols T, which may be identical or different, correspond to one of the formulae below:

(94) ##STR00003##
in which: the radicals R.sup.a, which may be substituted or unsubstituted and identical to or different from each other, represent a C.sub.1-C.sub.18 alkyl, a C.sub.5-C.sub.18 cycloalkyl or a C.sub.6-C.sub.18 aryl (preferably a C.sub.1-C.sub.6 alkyl, a cyclohexyl or a phenyl, notably a C.sub.1-C.sub.4 alkyl, more particularly methyl and/or ethyl), the radicals R.sup.b, which may be substituted or unsubstituted and identical to or different from each other, represent a C.sub.1-C.sub.18 alkoxyl or a C.sub.5-C.sub.18 cycloalkoxyl group (preferably a group selected from C.sub.1-C.sub.8 alkoxyls and C.sub.5-C.sub.8 cycloalkoxyls, even more preferentially a group chosen from C.sub.1-C.sub.4 alkoxyls, in particular methoxyl and ethoxyl).

(95) In the case of a mixture of polysulfide alkoxysilanes corresponding to the above formula (V), notably normal commercially available mixtures, the mean value of the “x” indices is a fractional number preferably between 2 and 5, more preferentially close to 4. However, the invention may also be advantageously performed, for example, with alkoxysilane disulfides (x=2).

(96) As examples of polysulfide silanes, mention will be made more particularly of bis((C.sub.1-C.sub.4)alkoxyl(C.sub.1-C.sub.4)alkylsilyl(C.sub.1-C.sub.4)alkyl) polysulfides (notably disulfides, trisulfides or tetrasulfides), for instance bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl) polysulfides. Among these compounds, use is made in particular of bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, of formula [(C.sub.2H.sub.5O).sub.3Si(CH.sub.2).sub.3S.sub.2].sub.2, or bis(3-triethoxysilylpropyl) disulfide, abbreviated to TESPD, of formula [(C.sub.2H.sub.5O).sub.3Si(CH.sub.2).sub.3S].sub.2. Preferential examples that will also be mentioned include bis(mono(C.sub.1-C.sub.4)alkoxyldi(C.sub.1-C.sub.4)alkylsilylpropyl) polysulfides (notably disulfides, trisulfides or tetrasulfides), more particularly bis(monoethoxydimethylsilylpropyl) tetrasulfide, as described in patent application WO 02/083782 (or US 2004/132880).

(97) Preferentially, the coupling agent used in the compositions of the invention consists of a blocked mercaptosilane of formula (I), including these preferred embodiments, as described above or a mixture of a blocked mercaptosilane of formula (I), including these preferred embodiments, as described above.

(98) In the rubber compositions in accordance with the invention, the content of coupling agent is preferentially within a range extending from 1 to 20 phr, from 1 to 15 phr and more preferentially from 3 to 14 phr.

(99) These rubber compositions of the invention may also optionally contain, in addition to the abovementioned coupling agents, coupling activators, agents for covering the inorganic fillers or more generally processing aids that are capable, in a known manner, by means of improving the dispersion of the filler in the rubber matrix and of lowering the viscosity of the compositions, of improving their ability to be processed in the raw state, these agents being, for example, hydrolysable silanes such as alkylalkoxysilanes, polyols, fatty acids, polyethers, primary, secondary or tertiary amines, or hydroxylated or hydrolysable polyorganosiloxanes.

Hydrocarbon-Based Resin

(100) The compositions of the invention comprise at least one specific hydrocarbon-based resin.

(101) This hydrocarbon-based resin is predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene, and mixtures of these monomers. This resin may optionally be hydrogenated.

(102) The hydrocarbon-based resin is preferably a plasticizing hydrocarbon-based resin.

(103) In a manner known to those skilled in the art, the term “plasticizing resin” is reserved in the present patent application, by definition, for a compound which is, on the one hand, solid at room temperature (23° C.) (as opposed to a liquid plasticizing compound such as an oil) and, on the other hand, compatible (that is to say miscible at the content used, typically of greater than 5 phr) with the rubber composition for which it is intended, so as to act as a true diluent.

(104) Hydrocarbon-based resins are polymers that are well known to those skilled in the art, which are miscible by nature in diene elastomer compositions, when they are also described as “plasticizing”. They have been described, for example, in the book entitled “Hydrocarbon Resins” by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), Chapter 5 of which is devoted to their applications, notably in the tyre rubber field (5.5. “Rubber Tires and Mechanical Goods”). They may be aliphatic, aromatic or of the aliphatic/aromatic type, i.e. based on aliphatic and/or aromatic monomers. They may be natural or synthetic and may or may not be petroleum-based (if such is the case, they are also known under as petroleum resins). They are preferentially exclusively hydrocarbon-based, i.e. they include only carbon and hydrogen atoms.

(105) The Applicant has discovered that, among plasticized hydrocarbon-based resins, resins predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures of these monomers used in combination with the organofunctional silane coupling agent as described previously make it possible, surprisingly, to obtain rubber compositions whose rolling resistance is improved without the wet grip being penalized. These compositions also have the advantage of having improved grip on snow-covered ground.

(106) When reference is made to a “predominant monomer” in a hydrocarbon-based resin, this is understood to mean, within the meaning of the present invention, that this monomer is predominant among the monomers forming the resin, that is to say that it is the one which represents the largest mass fraction among the monomers forming the resin. Thus, for example, a hydrocarbon-based resin predominantly composed of cyclopentadiene monomers is a resin in which the cyclopentadiene monomers represent the largest amount by mass among all the monomers making up this hydrocarbon-based resin. Similarly, a hydrocarbon-based resin predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures of these monomers is a hydrocarbon-based resin in which the sum of the monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures of these monomers represents the largest amount by mass among all the monomers making up said resin. In other words, a “predominant monomer” is a monomer which represents the largest mass fraction in the resin. On the contrary, a “minor monomer” is a monomer which does not represent the largest mass fraction in the resin.

(107) Preferentially, the optionally hydrogenated hydrocarbon-based resin comprises at least 50% by mass (>50% by mass) of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene, and mixtures of these monomers, relative to the total mass of all of the monomers of which said resin is constituted.

(108) Preferably, the optionally hydrogenated hydrocarbon-based resin may also comprise, in minor amount, aromatic monomers and/or aliphatic monomers.

(109) Preferentially, the optionally hydrogenated hydrocarbon-based resin comprises not more than 50% by mass (<50% by mass) of aromatic monomers and/or aliphatic monomers relative to the total mass of all of the monomers of which said resin is constituted, and more preferentially comprises not more than 40% by mass (<40% by mass) of aromatic monomers and/or aliphatic monomers.

(110) Examples of aromatic monomers that may be mentioned include monomers chosen from the group consisting of styrene, α-methylstyrene, ortho-, meta- or para-methylstyrene, vinyltoluene, para-(tert-butyl)styrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, indene, or any vinylaromatic monomer derived from a C9 fraction (or more generally from a C8, C9 or C10 fraction). Preferably, the vinylaromatic monomer is styrene or a vinylaromatic monomer derived from a C9 fraction.

(111) Examples of aliphatic monomers that may be mentioned include monomers chosen from the group consisting of isoprene, piperylene and amylene.

(112) According to a preferred embodiment, the optionally hydrogenated hydrocarbon-based resin is chosen from the group consisting of cyclopentadiene homopolymer resins, dicyclopentadiene homopolymer resins, methylcyclopentadiene homopolymer resins, and mixtures of these abovementioned homopolymer resins.

(113) Also in a preferred embodiment, the optionally hydrogenated hydrocarbon-based resin may be a mixture of abovementioned homopolymer resins and abovementioned copolymer resins.

(114) According to another embodiment which is also very preferential, the optionally hydrogenated hydrocarbon-based resin is chosen from the group consisting of resins predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixtures of these monomers and in minor amount composed of aromatic monomers.

(115) The optionally hydrogenated hydrocarbon-based resins that may be used in the compositions of the invention are often called CPD resins or DCPD resins.

(116) The optionally hydrogenated hydrocarbon-based resins are obtained via processes that are well known to those skilled in the art, for instance by thermal polymerization (i.e. without a polymerization catalyst).

(117) Preferably, the optionally hydrogenated hydrocarbon-based resin has a number-average molecular mass Mn within a range extending from 200 to 2000 g/mol, preferably from 200 to 600 g/mol.

(118) Preferably, the optionally hydrogenated hydrocarbon-based resin has a polydispersity index PI of less than or equal to 2, preferably less than or equal to 1.8, preferably less than 1.7.

(119) Preferably, the optionally hydrogenated hydrocarbon-based resin has a glass transition temperature Tg of greater than or equal to 30° C., preferably within a range extending from 30° C. to 80° C.

(120) Preferably, the optionally hydrogenated hydrocarbon-based resin is also composed in minor amount of aromatic monomers.

(121) Preferably, the content of aromatic protons in the optionally hydrogenated hydrocarbon-based resin is within a range extending from 1% to 20%, preferably from 2% to 15% and even more preferentially from 2% to 10%.

(122) Preferably, the optionally hydrogenated hydrocarbon-based resin has a number-average molecular mass Mn within a range extending from 200 to 600 g/mol and a polydispersity index PI of less than or equal to 2, preferably less than or equal to 1.8, preferably less than 1.7.

(123) Preferentially, the content of optionally hydrogenated hydrocarbon-based resin is within a range extending from 15 phr to 150 phr, preferentially from 25 to 120 phr and more preferentially from 30 to 115 phr. This is because, below 15 phr of the hydrocarbon-based resin that is of use for the purposes of the invention, the effect of the resin would be insufficient and the composition might present grip problems, while, above 150 phr, the composition might exhibit a difficulty in manufacturing in order to readily incorporate all of said resin into the composition.

(124) The glass transition temperature, the softening point, the macrostructure (Mn, Mw, PI) and the content of aromatic protons of the optionally hydrogenated hydrocarbon-based resin are determined according to the methods described above.

(125) The optionally hydrogenated hydrocarbon-based resins, predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene, and mixtures of these monomers, are commercially available from suppliers such as ExxonMobil, notably under the references Escorez E5600, Escorez E5415, Escorez E5320 and PR-383.

Crosslinking System

(126) In the compositions of the invention, use may be made of any type of crosslinking system known to those skilled in the art for rubber compositions.

(127) Preferably, the crosslinking system is a vulcanization system, i.e. a system based on sulfur (or on a sulfur-donating agent) and on a primary vulcanization accelerator. Various known secondary vulcanization accelerators or vulcanization activators, such as zinc oxide, stearic acid or equivalent compounds, or guanidine derivatives (in particular diphenylguanidine), are added to this base vulcanization system, being incorporated during the non-productive first phase and/or during the productive phase, as described subsequently.

(128) The sulfur is used in a preferential content within a range extending from 0.3 to 10 phr, more preferentially from 0.3 to 5 phr, in particular from 0.3 to 3 phr.

(129) The vulcanization system of the compositions of the invention may also comprise one or more additional accelerators, for example compounds of the thiuram, zinc dithiocarbamate, sulfenamide, guanidine or thiophosphate family. Use may be made in particular of any compound that is capable of acting as accelerator of the vulcanization of diene elastomers in the presence of sulfur, notably accelerators of the thiazole type and derivatives thereof, and accelerators of thiuram or zinc dithiocarbamate type. These accelerators are more preferentially chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated to “MBTS”), N-cyclohexyl-2-benzothiazolesulfenamide (abbreviated to “CBS”), N,N-dicyclohexyl-2-benzothiazolesulfenamide (abbreviated to “DCBS”), N-(tert-butyl)-2-benzothiazolesulfenamide (abbreviated to “TBBS”), N-(tert-butyl)-2-benzothiazolesulfenimide (abbreviated to “TBSI”), zinc dibenzyldithiocarbamate (abbreviated to “ZBEC”), tetrabenzylthiuram disulfide (TBzTD), and mixtures of these compounds. Preferably, use is made of a primary accelerator of the sulfenamide type.

Other Possible Additives

(130) The rubber compositions according to the invention as described previously make it possible, by themselves alone, to address the posed technical problem; in particular, they make it possible to have excellent rolling resistance properties without penalizing the wet grip. However, they may optionally also include all or some of the customary additives usually used in elastomer compositions intended notably for the manufacture of semi-finished products for tyres or of rubber articles, for instance pigments, protective agents such as antiozone waxes, chemical antiozonants, antioxidants, plasticizers other than those described previously, anti-fatigue agents, reinforcing resins, methylene acceptors (for example novolac phenolic resin) or methylene donors (for example HMT or H3M).

(131) The composition according to the invention may also include a plasticizing system. This plasticizing system may be composed of a hydrocarbon-based resin with a Tg of greater than 20° C. other than a DCDP resin, in addition to the specific hydrocarbon-based resin described previously, and/or a plasticizing oil.

(132) Needless to say, the compositions in accordance with the invention may be used alone or as a blend (i.e., as a mixture) with any other rubber composition that may be used for the manufacture of rubber articles, notably of semi-finished articles for tyres, or of tyres.

(133) It goes without saying that the invention relates to the rubber compositions described previously both in the “raw” or non-crosslinked state (i.e., before curing) and in the “cured” or crosslinked, or also vulcanized, state (i.e., after crosslinking or vulcanization).

2.2—Preparation of the Rubber Compositions

(134) The rubber compositions in accordance with the invention are manufactured in suitable mixers, using two successive preparation phases that are well known to those skilled in the art: a first phase of thermomechanical working or kneading (sometimes termed the “non-productive” phase) at high temperature, up to a maximum temperature of between 110° C. and 200° C., preferably between 130° C. and 180° C., followed by a second phase of mechanical working (sometimes termed the “productive” phase) at a lower temperature, typically of less than 110° C., for example between 60° C. and 100° C., during which finishing phase the crosslinking or vulcanization system is incorporated. Such phases have been described, for example, in patent applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00/05300 or WO00/05301.

(135) The first (non-productive) phase is preferentially performed in several thermomechanical steps. During a first step, the elastomers, the reinforcing fillers, notably the reinforcing inorganic filler, the organofunctional silane coupling agent as described above, the specific hydrocarbon-based resin as described above (and optionally the other ingredients with the exception of the crosslinking system) are introduced into a suitable mixer, such as a customary internal mixer, at a temperature between 20° C. and 100° C. and preferably between 25° C. and 100° C. After a few minutes, preferentially from 0.5 to 2 min, and a rise in the temperature to 90° C. or to 100° C., the other ingredients (i.e. those which remain, if not all were put in at the start) are added all at once or in portions, with the exception of the crosslinking system, during a mixing ranging from 20 seconds to a few minutes. The total duration of the kneading, in this non-productive phase, is preferably between 2 and 10 minutes at a temperature of less than or equal to 180° C. and preferentially of less than or equal to 170° C.

(136) After cooling of the mixture thus obtained, the crosslinking system is then incorporated at low temperature (typically less than 100° C.), generally in an external mixer, such as an open mill; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

(137) The final composition thus obtained is subsequently calendered, for example in the form of a sheet or of a plaque, notably for laboratory characterization, or else extruded, in order to form, for example, a rubber profile used in the manufacture of semi-finished products for tyres. These products may then be used for the manufacture of tyres, according to techniques known to those skilled in the art.

(138) The crosslinking (or curing) is performed in a known manner at a temperature generally of between 130° C. and 200° C., under pressure, for a sufficient time which may range, for example, between 5 and 90 min, as a function notably of the curing temperature, of the vulcanization system adopted, of the kinetics of crosslinking of the composition under consideration or else of the size of the tyre.

2.3—Semi-Finished Products for a Tyre and Tyre

(139) Another subject of the present invention relates to a semi-finished article for a tyre, comprising at least one rubber composition in accordance with the invention and as defined above. The semi-finished articles of the present invention have improved rolling resistance properties without the wet grip being penalized. Advantageously, they also have improved grip on snow-covered ground.

(140) The semi-finished article may be any article of use for the manufacture of a finished rubber article such as a tyre.

(141) Preferentially, the semi-finished article for a tyre may be chosen from underlayers, bonding rubbers between rubbers of different natures or calendering rubbers for metal or textile reinforcers, sidewall rubbers and treads. More preferentially, the semi-finished article for a tyre is a tread. The semi-finished articles are obtained via methods that are well known to those skilled in the art.

(142) Another subject of the present invention relates to a tyre comprising at least one rubber composition in accordance with the invention and as described above or comprising at least one semi-finished article for a tyre as described above. The tyres of the present invention have improved rolling resistance properties without the wet grip being penalized. Advantageously, they also have grip on snow-covered ground. The tyres of the invention may notably be intended to equip motor vehicles of the passenger vehicle, SUV (“Sports Utility Vehicles”), two-wheel vehicle (notably motorcycle) or aircraft type, such as industrial vehicles chosen from vans, heavy-duty vehicles, i.e. underground trains, buses, heavy road transport vehicles (lorries, tractors, trailers) or off-road vehicles such as heavy agricultural or construction plant vehicles, and other transportation or handling vehicles. The tyres of the invention are obtained via methods that are well known to those skilled in the art.

3—EXAMPLES

(143) The examples that follow illustrate the invention without, however, limiting it.

3.1—Manufacture of the Rubber Compositions

(144) For the following tests, the compositions are prepared in the following way: the diene elastomers, the reinforcing inorganic filler (silica), the carbon black, the coupling agent to be tested and then, after kneading for one to two minutes, the various other ingredients, including the resin to be tested, with the exception of the vulcanization system, are introduced into an internal mixer which is 70% filled and which has an initial vessel temperature of about 50° C. Thermomechanical working (non-productive phase) is then performed in one step (total kneading time equal to about 5 min), until a maximum “dropping” temperature of about 165° C. is reached.

(145) The mixture thus obtained is recovered and cooled and the vulcanization system (sulfur and accelerator) is then added on an external mixer (homofinisher) at 70° C., the whole being mixed (productive phase) for about 5 to 6 min.

(146) The compositions thus obtained are then calendered, either in the form of plaques (thickness of 2 to 3 mm) or of thin sheets of rubber for measurement of their physical or mechanical properties after curing.

3.2—Test A

(147) The aim of this test is to demonstrate the improved rolling resistance properties of a rubber composition in accordance with the invention when compared with rubber compositions not in accordance using plasticizing resins other than hydrocarbon-based resins predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene, and mixtures of these monomers, and using a coupling agent other than the blocked mercaptosilane of formula (I).

(148) In the rest of the description, for the sake of simplicity, the hydrocarbon-based resins predominantly composed of monomers chosen from the group consisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadiene, and mixtures of these monomers, will be referred to as DCDP resins. The coupling agent, the blocked mercaptosilane of formula (I) will be called the blocked mercaptosilane coupling agent.

(149) Eight rubber compositions based on diene elastomer reinforced with silica are compared, these compositions differing from each other essentially in the characteristics that follow: composition CP1 is a non-conforming rubber composition comprising a C5 fraction/C9 fraction resin and a polysulfide silane coupling agent; composition CP2 is a non-conforming rubber composition comprising a C5 fraction/C9 fraction resin and the blocked mercaptosilane coupling agent; composition CP3 is a non-conforming rubber composition comprising a resin based on terpenes (β-pinene) and a polysulfide silane coupling agent; composition CP4 is a non-conforming rubber composition comprising a resin based on terpenes (β-pinene) and the blocked mercaptosilane coupling agent; composition CP5 is a non-conforming rubber composition comprising an aromatic resin based on coumarone-indene and a polysulfide silane coupling agent; composition CP6 is a non-conforming rubber composition comprising a resin based on coumarone-indene and the blocked mercaptosilane coupling agent; composition CP7 is a non-conforming rubber composition comprising a DCPD resin and a polysulfide silane coupling agent, composition CP8 is a conforming rubber composition comprising a DCPD resin and the blocked mercaptosilane coupling agent.

(150) Table I presents the formulations of the rubber compositions CP1 to CP8. The content of the various ingredients is expressed in phr. The amounts of coupling agent (3) and (4) are adjusted so that all the compositions comprise the same molar content of silicon atom.

(151) TABLE-US-00002 TABLE I CP1 CP2 CP3 CP4 CP5 CP6 CP7 CP8 Elastomer (1) 100 100 100 100 100 100 100 100 Reinforcing 130 130 130 130 130 130 130 130 inorganic filler (2) Coupling 13 (—) 13 (—) 13 (—) 13 (—) agent (3) Coupling (—) 17.5 (—) 17.5 (—) 17.5 (—) 17.5 agent (4) Resin 1 (5) 88 88 (—) (—) (—) (—) (—) (—) Resin 2 (5) (—) (—) 88 88 (—) (—) (—) (—) Resin 3 (5) (—) (—) (—) (—) 88 88 (—) (—) Resin 4 (5) (—) (—) (—) (—) (—) (—) 88 88 Carbon 4 4 4 4 4 4 4 4 black (6) Antioxidant 6 6 6 6 6 6 6 6 (7) Anti-ozone 2.85 2.85 2.85 2.85 2.85 2.85 2.85 2.85 wax DPG (8) 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 Stearic acid 3 3 3 3 3 3 3 3 (9) ZnO (10) 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Accelerator 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 (11) Soluble sulfur 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 (1) Styrene-butadiene copolymer, aminoalkoxysilane-functional in the middle of the chain, with a glass transition temperature equal to −88° C., the microstructure of this copolymer is determined via the NIR method. The content of 1,2- units is 12.7% relative to the butadiene units. The mass content of styrene is 2.1%; this copolymer is synthesized according to the process described in WO 2017/060395; (2) Zeosil 1165 MP silica from the company Solvay, of HDS type; its BET specific surface area is 160 m.sup.2/g ; (3) bis(triethoxysilylpropyl)tetrasulfide polysulfide silane coupling agent sold under the reference Si69 from the company Evonik-Degussa; (4) Blocked mercapto silane coupling agent S-(3-(triethoxysilyl)propyl)octanethioate sold under the reference NXT by Momentive Inc.; (5) Resins 1 to 4: see table II below; (6) ASTM N234 grade carbon black sold by Cabot; (7) N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (Santoflex 6-PPD) from the company Flexsys and 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ); (8) Diphenylguanidine, Perkacit DPG from the company Flexsys; (9) Pristerene 4931 stearin from the company Uniqema; (10) Zinc oxide, industrial grade - from Umicore; (11) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from the company Flexsys).

(152) The resins used in compositions CP1 to CP8 are presented in Table 2 below.

(153) TABLE-US-00003 TABLE II Content of Commercial Resin Chemical Softening Tg Mn Mw aromatic Resin name manufacturer nature point (° C.) (° C.) g/mol g/mol PI protons (%) Resin Escorez ExxonMobil cut C5/cut C9 90 44 941 1575 1.67 12 1 ECR-373 Resin Piccolyte Pinova Terpenes (β- 135 87 1245 2368 1.9 4 2 S135 pinene) Resin Neopolymer Nisseki Coumarone- 98 48 735 1164 1.72 38 3 L-90 indene aromatic Resin PR-383 ExxonMobil DCDP 100 51 490 805 1.65 10 4

(154) The resins were analysed via the methods described in paragraph 1 “Measuring methods used”.

(155) Table III gives the properties after curing, about 40 min at 150° C. of compositions CP1 to CP8.

(156) TABLE-US-00004 TABLE III CP1 CP2 CP3 CP4 CP5 CP6 CP7 CP8 Tan (δ).sub.max 100 88 156 134 140 120 101 71 at 23° C. (base 100) Tan(δ).sub.−20° C. 100 107 36 45 57 74 94 127 (base 100)

(157) Examination of table III shows all the compositions comprising a polysulfide silane coupling agent (compositions CP3, CP5, CP7 not in accordance with the invention) do not make it possible to improve both the rolling resistance and the wet grip when compared with the control composition CP1, irrespective of the plasticizing resin used.

(158) When the polysulfide silane coupling agent is replaced with a blocked mercaptosilane coupling agent (compositions CP2, CP4, CP6 and CP8), it is observed that only composition CP2 not in accordance with the invention and composition CP8 allow an improvement in both the rolling resistance and the wet grip when compared with the control composition CP1.

(159) It is also noted that only the composition CP8 in accordance with the invention makes it possible to obtain a significant improvement both in the rolling resistance and in the wet grip when compared with the non-compliant composition CP2.

(160) Furthermore, surprisingly, it is found that composition CP8 in accordance with the invention combining the presence of the blocked mercaptosilane coupling agent and the DCPD resin shows an improvement in the rolling resistance performance (improvement of −29) and in the grip on wet ground (improvement of +27) which is greater than the addition of the effects of the rolling resistance and of the grip effect on snow-covered ground of composition CP2 relative to composition CP1 (rolling resistance: −12 and grip on wet ground: +7) and that of composition CP7 relative to CP1 (rolling resistance: +1 and grip on wet ground: −6). True synergism is thus seen on the effect of the choice of the blocked mercaptosilane coupling agent and of the resin DCDP within the same composition for the two abovementioned properties.