Dienrubber composition with microsilica

Description

[0001] The field of the present invention is that of diene rubber compositions reinforced with silica and intended for use in a tire, more particularly in a tire tread.

[0002] A tire tread must, in a known way, meet a large number of technical requirements, often contradictory, including low rolling resistance, high wear resistance, and high grip on both dry and wet roads.

[0003] This compromise of properties, particularly from the point of view of rolling resistance and wear resistance, has been improved in recent years on low energy consumption "Green Tires", intended in particular for passenger vehicles, thanks in particular to the use of new low hysteretic rubber compositions which are characterized by being reinforced mainly with specific inorganic fillers described as reinforcing, in particular highly dispersible silicas known as "HDS" ("Highly Dispersible Silica"), capable of competing, from the point of view of reinforcing power, with conventional carbon blacks of tire grade.

[0004] Improving grip properties, particularly on wet surfaces, remains a constant concern for tire designers. One way to give tires high wet grip is to use a rubber compound in the tread that exhibits high hysteresis potential.

[0005] The highly dispersible silicas traditionally used in rubber tread compounds are generally precipitation or pyrolysis silicas, also known as reinforcing silicas. See, for example, the publication in the Encyclopedia of Polymer Science and Technology, John Wiley and Sohns, Inc., Vol. 11, p. 612 (2004).

[0006] The use of silica fume, also known as microsilica, is widespread in the concrete industry. Its use in tire rubber compounds is much less common, and when it is used, it is at much lower levels than the silica traditionally used. Patent application JP2006241297 proposed replacing precipitated silica with microsilica in a diene rubber compound reinforced with carbon black to improve its processability. Document EP2072284 also proposed adding microsilica to a tire inner rubber compound comprising butyl rubber and carbon black as a reinforcing filler to improve the inner rubber's impermeability.It was also proposed in document EP2336231A1 to introduce into a diene rubber composition for a tire tread comprising, as a reinforcing filler, highly structured precipitated silica, microsilica at a rate much lower than that of the precipitated silica to improve the tire's rolling resistance performance. Document JP2008031244A discloses a tire tread composition comprising a diene elastomer, precipitated silica, microsilica, a silane coupling agent, and a crosslinking system.

[0007] The Applicant discovered that the introduction, in a diene rubber composition comprising a reinforcing silica, of microsilica at a higher rate than the reinforcing silica makes it possible to increase the hysteretic potential of the rubber composition and thus improve the wet grip performance of a tread of a tire containing such a rubber composition.

[0008] Thus, a first object of the invention is a rubber composition comprising a diene elastomer, a first silica which is a precipitation or pyrogenation silica and which has a specific surface area BET greater than 100 m² / g as a reinforcing filler, a second silica which is a microsilica with a specific surface area BET less than 50 m² / g, a silane coupling agent and a crosslinking system, in which the rates of the first silica and the second silica being expressed in part by weight per percent parts of elastomer, pce, and noted respectively T1 and T2 T1 is greater than 15 pce and is less than T2 and the sum of T1 and T2 is greater than 75 pce.

[0009] Another object of the invention is a tire which comprises a rubber composition according to the invention, preferably in its tread. Description

[0010] Any range of values ​​designated by the expression "between a and b" represents the range of values ​​greater than "a" and less than "b" (i.e., bounds "a" and "b" excluded) while any range of values ​​designated by the expression "from a to b" means the range of values ​​from "a" to "b" (i.e., including the strict bounds "a" and "b").

[0011] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is to be understood in the sense of the present invention, the part, by mass per hundred parts by mass of elastomer.

[0012] The compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they may be partially or entirely derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of previously used materials; that is, they may be partially or entirely produced through a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0013] In the present invention, the term "pneumatic" (in English, "tire") refers to a pneumatic or non-pneumatic tire. A pneumatic tire typically comprises two beads for contact with a rim, a crown consisting of at least one crown reinforcement and a tread, and two sidewalls. The tire is reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic tire, on the other hand, typically comprises a base, designed, for example, for mounting on a rigid rim, a crown reinforcement connecting to a tread, and a deformable structure, such as spokes, ribs, or dimples, this structure being arranged between the base and the crown. Such non-pneumatic tires do not necessarily include sidewalls. Non-pneumatic tires are described, for example, in documents WO 03 / 018332 and FR2898077.According to any one of the embodiments of the invention, the tire according to the invention is preferably a pneumatic tire.

[0014] Microsilica, also known as silica fume, should not be confused with fumed silica, also called pyrogenated silica. The production process, particle morphology, and applications of microsilica differ from those of fumed silica. Microsilica is traditionally obtained in the manufacturing processes of silicon or ferrosilicon alloys. During an electrometallurgical process involving the carboreduction of quartz in the production of silicon and Fe-Si alloys, a byproduct, a gas with the formula SiO₂, is formed. This gas is recovered by oxidizing it in contact with oxygen to form SiO₂, which condenses into spherical particles of silica fume. Silica fume, or microsilica, is an amorphous, non-crystalline, and polymorphic form of SiO₂. Microsilica is essentially made up of spherical particles of nanometric size.The most important application of microsilica is as a pozzolanic material for high-performance concrete.

[0015] By "dienic" elastomer (or indistinctly rubber), whether natural or synthetic, should be understood in a known way as an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers bearing two carbon-carbon double bonds, conjugated or not).

[0016] The term diene elastomer specifically refers to a type of elastomer suitable for use in compositions according to the invention: (a) - any homopolymer of a diene monomer, conjugated or not, having from 4 to 24 carbon atoms; (b) - any copolymer of a diene, conjugated or not, having from 4 to 24 carbon atoms and at least one other monomer.

[0017] A copolymer of a diene, conjugated or not, having from 4 to 24 carbon atoms and at least one other monomer, is understood to be a copolymer of a diene and one or more other monomers. Examples of other monomers include ethylene, an olefin, and a diene, conjugated or not, different from the first diene.

[0018] Suitable conjugated dienes are those with 4 to 24 carbon atoms, particularly 1,3-dienes with 4 to 12 carbon atoms, such as 1,3-butadiene and isoprene, or a 1,3-diene with the formula CH₂=CR-CH=CH₂, where R represents a hydrocarbon chain with 3 to 20 carbon atoms, such as a linear monoterpene (C₁₀H₁₆), like myrcene, or a linear sesquiterpene (C₁₅H₂₄), like farnesene, etc. In particular, 1,3-butadiene, isoprene, myrcene, and farnesene are suitable conjugated dienes.

[0019] Suitable as unconjugated dienes are unconjugated dienes having 6 to 12 carbon atoms, such as 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene.

[0020] Suitable olefins include vinylaromatic compounds with 8 to 20 carbon atoms and aliphatic α-monoolefins with 3 to 12 carbon atoms.

[0021] Examples of suitable vinylaromatic compounds include styrene, ortho-, meta-, para-methylstyrene, the commercial mixture "vinyl-toluene", and para-tert-butylstyrene.

[0022] As suitable aliphatic α-monoolefins, acyclic aliphatic α-monoolefins having from 3 to 18 carbon atoms are particularly suitable.

[0023] More specifically, diene elastomer is: (a')- any homopolymer of a conjugated diene monomer, in particular any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms; (b')- any copolymer obtained by copolymerization of one or more dienes conjugated with each other or with one or more vinylaromatic compounds having from 8 to 20 carbon atoms; (c') - a copolymer of isobutene and isoprene (butyl rubber), as well as halogenated versions, in particular chlorinated or brominated, of this type of copolymer; (d') - any copolymer obtained by copolymerization of one or more dienes, conjugated or not, with ethylene, an α-monoolefin or their mixture such as for example elastomers obtained from ethylene, propylene with an unconjugated diene monomer of the aforementioned type, or elastomers obtained from ethylene and one or more 1,3-dienes of the aforementioned type.

[0024] When the diene elastomer is a copolymer, it is preferentially a statistical copolymer.

[0025] Diene elastomers can be modified, for example, coupled, star-shaped, or functionalized. Among the functionalized elastomers are those bearing one or more functional groups including a heteroatom such as Si, N, and O.

[0026] The diene elastomer useful for the purposes of the invention is preferably a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene, or a mixture thereof. The 1,3-diene is preferably 1,3-butadiene or a mixture of 1,3-dienes, one of which is 1,3-butadiene. When the diene elastomer is a copolymer of a 1,3-diene, it is preferably a random copolymer.

[0027] According to a first embodiment of the invention, the diene elastomer is selected from the group of highly unsaturated elastomers, that is, diene elastomers containing at least 50 mole percent diene units. A diene unit is understood to be a unit resulting from the polymerization of a diene and containing a carbon-carbon double bond. Examples of highly unsaturated diene elastomers include polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.

[0028] According to a second embodiment of the invention, the diene elastomer is a copolymer of ethylene and a 1,3-diene and contains more than 50 mole percent ethylene units. Due to its predominant ethylene unit content, it is described as a highly saturated elastomer. It is preferentially statistical. The term "ethylene unit" is known to refer to the -(CH₂-CH₂)- motif resulting from the insertion of ethylene into the elastomeric chain.

[0029] Unless otherwise indicated, the rates of units resulting from the insertion of a monomer into a copolymer such as the copolymer useful to the invention are expressed as a molar percentage relative to the total monomer units of the copolymer.

[0030] Preferably, the highly saturated diene elastomer comprises at least 55 mol% ethylene units, preferably at least 60 mol% ethylene units, and more preferably at least 65 mol% ethylene units. In other words, the ethylene units in the highly saturated diene elastomer preferably represent at least 55 mol% of all the monomer units in the highly saturated diene elastomer, and more preferably at least 60 mol% of all the monomer units in the highly saturated diene elastomer. Even more preferably, the ethylene units represent at least 65 mol% of all the monomer units in the highly saturated diene elastomer.

[0031] Preferably, the ethylene units in the highly saturated diene elastomer represent at most 90 mole percent of all the monomer units in the highly saturated diene elastomer. More preferably, the ethylene units represent at most 85 mole percent of all the monomer units in the highly saturated diene elastomer. Even more preferably, the ethylene units represent at most 80 mole percent of all the monomer units in the highly saturated diene elastomer.

[0032] According to an advantageous embodiment, the highly saturated diene elastomer comprises from 55% to 90 mol% ethylene units, particularly from 55% to 85 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer. More advantageously, the highly saturated diene elastomer comprises from 55% to 80 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0033] According to another advantageous embodiment, the highly saturated diene elastomer comprises 60% to 90 mol% ethylene units, particularly 60% to 85 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer. More advantageously, the highly saturated diene elastomer comprises 60% to 80 mol% ethylene units, the mol% being calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0034] According to yet another advantageous embodiment, the highly saturated diene elastomer comprises from 65% to 90 mol% ethylene units, particularly from 65% to 85 mol% ethylene units, the mol% calculated on the basis of all the monomer units of the highly saturated diene elastomer. More advantageously, the highly saturated diene elastomer comprises from 65% to 80 mol% ethylene units, the mol% calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0035] The highly saturated diene elastomer, being a copolymer of ethylene and a 1,3-diene, also includes 1,3-diene units resulting from the polymerization of a 1,3-diene. The term "1,3-diene unit" or "diene unit" is known to refer to units resulting from the insertion of 1,3-diene by a 1,4-addition, a 1,2-addition, or a 3,4-addition, as in the case of isoprene, for example. Preferably, the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes, one of which is 1,3-butadiene. More preferably, the 1,3-diene is 1,3-butadiene, in which case the highly saturated diene elastomer is a copolymer of ethylene and 1,3-butadiene, preferably statistically.

[0036] Highly saturated diene elastomer can be obtained by various synthetic methods known to those skilled in the art, depending in particular on the desired microstructure of the highly saturated diene elastomer. Generally, it can be prepared by copolymerization of at least one 1,3-diene, preferably 1,3-butadiene, and ethylene, using known synthetic methods, particularly in the presence of a catalytic system comprising a metallocene complex. Examples include catalytic systems based on metallocene complexes, which are described in documents EP 1 092 731, WO 2004035639, WO 2007054223, and WO 2007054224 on behalf of the Applicant. Highly saturated diene elastomer, including when statistical, can also be prepared by a process using a preformed type catalytic system such as those described in documents WO 2017093654 A1, WO 2018020122 A1 and WO 2018020123 A1.Advantageously, the highly saturated diene elastomer is statistical and is preferably prepared by a semi-continuous or continuous process as described in documents WO 2017103543 A1, WO 201713544 A1, WO 2018193193 and WO 2018193194.

[0037] The highly saturated diene elastomer preferably contains units of formula (I) or units of formula (II). -CH 2 -CH(CH=CH 2 )- (II)

[0038] The presence of the saturated 6-membered cyclic motif, 1,2-cyclohexane, of formula (I) in the copolymer can result from a series of very specific insertions of ethylene and 1,3-butadiene into the polymer chain during its growth. When the highly saturated diene elastomer comprises units of formula (I) or units of formula (II), the molar percentages of units of formula (I) and units of formula (II) in the highly saturated diene elastomer, respectively o and p, preferably satisfy the following equation (eq. 1) or equation (eq. 2), o and p being calculated on the basis of all the monomer units of the highly saturated diene elastomer. 0 < o + p ≤ 30 0 < o + p < 25

[0039] Preferably, the highly saturated diene elastomer comprises units of formula (I) in a molar proportion greater than 0% and less than 15%, more preferably less than 10% molar, molar proportion calculated on the basis of all the monomer units of the highly saturated diene elastomer.

[0040] Preferably, the content of the highly saturated diene elastomer in the rubber composition is at least 50 parts by weight per hundred parts of elastomer in the rubber composition (wtw). More preferably, the content of the highly saturated diene elastomer in the rubber composition ranges from 80 to 100 wtw. Even more preferably, it ranges from 90 to 100 wtw. Advantageously, it is 100 wtw. The highly saturated diene elastomer may be a single highly saturated diene elastomer or a mixture of several highly saturated diene elastomers that differ from one another in their microstructures or macrostructures.In the case where the rubber composition contains several highly saturated diene elastomers that differ from one another by their microstructures or by their macrostructures, the rate of the highly saturated diene elastomer in the rubber composition refers to the mixture of highly saturated diene elastomers.

[0041] Embodiments of the invention in which the rubber composition comprises at least 50 parts per annum of a highly saturated diene elastomer are particularly advantageous for the use of the rubber composition in a tire tread, since the tread combines both good wet grip performance and good wear resistance performance.

[0042] The rubber composition of the invention may contain a single diene elastomer or a mixture of several diene elastomers, whether highly saturated or not. According to any one embodiment of the invention, the elastomers that make up the diene rubber composition according to the invention are preferably all diene elastomers.

[0043] The rubber composition according to the invention has another essential characteristic: it comprises, as a reinforcing filler, a silica having a specific surface area greater than 100 m² / g, referred to as the first silica. The first silica used as a reinforcing filler is a precipitated silica or a pyrogenated silica, preferably a precipitated silica, also known as precipitated silica.

[0044] Any type of precipitated silica can be used, including highly dispersible precipitated silicas (known as "HDS" for "highly dispersible" or "highly dispersible silica") provided they have a specific surface area (BET) greater than 100 m² / g. These precipitated silicas, whether highly dispersible or not, are well known to those skilled in the art. Examples include the silicas described in applications WO03 / 016215-A1 and WO03 / 016387-A1. Among the commercial HDS silicas, one can notably use the silicas “Ulsil ®< 5000GR”, “Ulsil ®< 7000GR” from the company Evonik, the silicas “Zeosil ®< 1115 MP”, “Zeosil ®< 1165MP”, “Zeosil ®< Premium 200MP”, “Zeosil ®< HRS 1200 MP” from the Solvay Company.As non-HDS silica, the following commercial silicas may be used: “Ultrasil ®< VN2GR”, “Ultrasil ®< VN3GR” silicas from Evonik, “Zeosil ®< 175GR” silica from Solvay, “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(-D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” silicas from PPG.

[0045] Of course, the first silica can be a mixture of silicas, in particular precipitated silicas such as those described above.

[0046] The physical state in which the first silica is presented is irrelevant, whether in the form of powder, microbeads, granules, or even balls or any other suitable densified form.

[0047] The first silica has a specific surface area BET preferentially less than 200 m² / g, more preferably less than 180 m² / g.

[0048] In this presentation, the specific surface area BET is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), and more specifically according to a method adapted from the standard NF ISO 5794-1, Annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160°C - relative pressure range w / in: 0.05 to 0.17].

[0049] The rubber compound may also include carbon black. All carbon blacks are suitable as carbon blacks, including those conventionally used in tires or their treads. Among these, particularly noteworthy examples include reinforcing carbon blacks of the 100, 200, and 300 series, or blacks of the 500, 600, or 700 series (ASTM D-1765-2017 grades), for example, N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, and N772. These carbon blacks may be used on their own, as commercially available, or in other forms, for example, as a carrier for certain rubber compound additives. When carbon black is used in the composition of rubber, it is preferably used at a rate less than or equal to 10 parts per cent (for example, the rate of carbon black may be in a range of 1 to 10 parts per cent).Advantageously, the carbon black content in the rubber composition is less than or equal to 5 parts per cubic centimeter. Within the specified ranges, the coloring (black pigmenting agent) and UV-resistant properties of carbon black are benefited without compromising the typical performance provided by silica.

[0050] Another essential characteristic of the rubber composition is that it includes microsilica with a specific surface area (BET) of less than 50 m² / g, preferably greater than 10 m² / g and less than 40 m² / g, and even more preferably greater than or equal to 15 m² / g and less than or equal to 30 m² / g. Microsilicas are commercially available products, for example, under the trade names "Sidistar" and "Microfume" from the respective companies Elkem and Ferropem.

[0051] The proportions of the first silica and the second silica in the rubber composition, denoted T1 and T2 respectively and expressed in parts per cubic meter (ppm), are such that T1 is greater than 15 ppm and less than T2, and the sum of T1 and T2, i.e., T1 + T2, is greater than 75 ppm. Typically, the sum of T1 and T2 is between 75 ppm and 180 ppm.

[0052] Preferably, the sum of T1 and T2 is less than 140%. Advantageously, the sum of T1 and T2 is greater than 90% and less than 140%.

[0053] According to a particularly preferred embodiment of the invention, the T1 and T2 rates are related by the following equation (1). This particularly preferred embodiment is advantageous for the application of the rubber compound in a tire tread, because the rubber compound contributes to hysteresis in the rolling resistance zone, which is reduced, while having a high hysteresis potential in the wet grip performance zone. T 2 ≥ 1.73 x T 1 + T 2 − 125

[0054] When this particularly preferred embodiment is combined with the embodiment in which the rubber composition contains more than 50 parts per annum of a highly saturated diene elastomer as defined above, the rubber composition has the property of giving a tire tread good performance in terms of grip, rolling resistance and wear resistance.

[0055] A coupling agent (or bonding agent), a silane, is commonly used to ensure sufficient chemical and / or physical connection between the silicas in the rubber compound (the surface of their particles) and the diene elastomer. Organosilanes or polyorganosiloxanes, at least bifunctional ones, are particularly used. "Bifunctional" means a compound possessing a first functional group capable of interacting with the silicas and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound might include a first functional group comprising a silicon atom, which is capable of interacting with the hydroxyl groups of a silica, for example, the first silica, and a second functional group comprising a sulfur atom, which is capable of interacting with the diene elastomer.

[0056] In particular, polysulfide silanes are used, described as "symmetric" or "asymmetric" depending on their particular structure, as described for example in applications WO03 / 002648 (or US 2005 / 016651) and WO03 / 002649 (or US 2005 / 016650).

[0057] In particular, without limitation, polysulfide silanes corresponding to the following general formula (I) are suitable: (I) ZAS x -AZ, in which: x is an integer from 2 to 8 (preferably from 2 to 5); the symbols A, identical or different, represent a divalent hydrocarbon radical (preferably a C1-C18 alkylene group or a C6-C12 arylene group, more particularly a C1-C10 alkylene, especially C1-C4, in particular propylene); the symbols Z, identical or different, correspond to one of the three formulas below: in which: the radicals R 1< , substituted or unsubstituted, identical or different from each other, represent a C 1 -C 18 alkyl group, a C 5 -C 18 cycloalkyl group or a C 6 -C 18 aryl group (preferably C 1 -C 6 alkyl, cyclohexyl or phenyl groups, in particular C 1 -C 4 alkyl groups, more particularly methyl and / or ethyl); the radicals R 2< , substituted or unsubstituted, identical or different from each other, represent a C 1 -C 18 alkoxyl group or a C 5 -C 18 cycloalkoxyl group (preferably a group chosen from C 1 -C 8 alkoxyls and C 5 -C 8 cycloalkoxyls, more preferably a group chosen from C 1 -C 4 alkoxyls, in particular methoxyl and ethoxyl).

[0058] In the case of a mixture of polysulfurized alkoxysilanes corresponding to formula (I) above, in particular common mixtures available commercially, the average value of "x" is a fractional number preferably between 2 and 5, more preferably close to 4. But the invention can also be advantageously implemented, for example, with disulfurized alkoxysilanes (x = 2).

[0059] Examples of polysulfurized silanes include polysulfides (especially disulfides, trisulfides or tetrasulfides) of bis-(alkoxyl(C1-C4)-alkyl(C1-C4)silyl-alkyl(C1-C4)), such as bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl) polysulfides. Among these compounds, in particular, the tetrasulfide of bis(3-triethoxysilylpropyl), abbreviated TESPT, with the formula [(C 2 H 5 O) 3 Si(CH 2 ) 3 S 2 ] 2 or the disulfide of bis-(triethoxysilylpropyl), abbreviated TESPD, with the formula [(C 2 H 5 O) 3 Si(CH 2 ) 3 S] 2, is used. We will also cite as preferential examples the polysulfides (in particular disulfides, trisulfides or tetrasulfides) of bis-(monoalkoxyl(C1-C4)-dialkyl(C1-C4)silylpropyl), more particularly the tetrasulfide of bis-monoethoxydimethylsilylpropyl as described in the aforementioned patent application WO 02 / 083782 (or US 7,217,751).

[0060] Examples of coupling agents other than a polysulfurized alkoxysilane include bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulfides (R 2< = OH in formula I above) as described, for example, in patent applications WO 02 / 30939 (or US 6 774 255), WO 02 / 31041 (or US 2004 / 051210), and WO2007 / 061550, or silanes or POS bearing azo-dicarbonyl functional groups, as described, for example, in patent applications WO 2006 / 125532, WO 2006 / 125533, WO 2006 / 125534.

[0061] Examples of other sulfide silanes include silanes with at least one thiol function (-SH) (called mercaptosilanes) and / or at least one blocked thiol function, as described for example in US patents or patent applications 6 849 754, WO 99 / 09036, WO 2006 / 023815, WO 2007 / 098080.

[0062] Of course, mixtures of the coupling agents previously described could also be used, as described in particular in the aforementioned application WO 2006 / 125534.

[0063] In the rubber composition according to the invention, the proportion of the silane coupling agent is adjusted by a person skilled in the art according to the chemical structure of the coupling agent and the total specific surface area developed by the first and second silicas in the rubber composition. It is preferably in the range of 1 to 15 parts per cubic centimeter, preferably from 1.5 to 10 parts per cubic centimeter, and even more preferably from 2 to 5 parts per cubic centimeter.

[0064] The rubber composition according to the invention has another essential characteristic: it contains a crosslinking system, preferably a vulcanization system, i.e., a sulfur-based crosslinking system. The sulfur is typically supplied in the form of molecular sulfur or a sulfur-donating agent, preferably in molecular form. Molecular sulfur is also referred to as molecular sulfur. A sulfur donor is defined as any compound that releases sulfur atoms, whether or not combined in a polysulfide chain, capable of inserting themselves into the polysulfide chains formed during vulcanization and bridging the elastomeric chains.In addition to the vulcanization system, various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), etc., are incorporated during the first non-productive phase and / or during the productive phase. The sulfur content is preferably between 0.5 and 4 parts per million (ppm), and that of the primary accelerator is preferably between 0.5 and 5 ppm. These preferred levels can be applied to any of the embodiments of the invention.

[0065] Any compound capable of accelerating the vulcanization of diene elastomers in the presence of sulfur can be used as a vulcanization accelerator (primary or secondary). Examples include thiazole-type accelerators and their derivatives, sulfenamide-type accelerators for primary accelerators, and thiurams, dithiocarbamates, dithiophosphates, thioureas, and xanthates for secondary accelerators. Examples of primary accelerators include sulfenamide compounds such as N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-ter-butyl-2-benzothiazyl sulfenamide ("TBBS"), and mixtures of these compounds. The primary accelerator is preferably a sulfenamide, more preferably N-cyclohexyl-2-benzothiazyl sulfenamide.Examples of secondary accelerators include thiuram disulfides such as tetraethylthiuram disulfide, tetrabutylthiuram disulfide ("TBTD"), tetrabenzylthiuram disulfide ("TBZTD"), and mixtures of these compounds. The secondary accelerator is preferably a thiuram disulfide, and more preferably tetrabenzylthiuram disulfide.

[0066] Vulcanization is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the cooking temperature, the vulcanization system adopted and the vulcanization kinetics of the composition considered.

[0067] The rubber composition according to the invention may also include all or part of the usual additives commonly used in elastomer compositions for the manufacture of tires, including pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, and plasticizers such as plasticizing oils or resins.

[0068] The rubber composition, prior to vulcanization, can be manufactured in suitable mixers, using two successive preparation phases according to a procedure well known to those skilled in the art: a first thermo-mechanical working or mixing phase (sometimes referred to as the "non-productive" phase) at high temperature, up to a maximum temperature between 110°C and 190°C, preferably between 130°C and 180°C, followed by a second mechanical working phase (sometimes referred to as the "productive" phase) at a lower temperature, typically below 110°C, for example between 40°C and 100°C, a finishing phase during which the sulfur or sulfur donor and the vulcanization accelerator are incorporated.

[0069] As an example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary components, any additional processing agents, and other miscellaneous additives, with the exception of the vulcanizing system, are introduced into a suitable mixer, such as a standard internal mixer. The total mixing time in this non-productive phase is preferably between 1 and 15 minutes. After the mixture obtained in the first non-productive phase has cooled, the low-temperature vulcanizing system is then incorporated, generally in an external mixer such as a roller mixer. The mixture is then blended (productive phase) for a few minutes, for example, between 2 and 15 minutes.

[0070] The rubber compound can be calendered or extruded into a sheet or plate, particularly for laboratory characterization, or into a semi-finished (or profiled) rubber product for use in a tire. The compound can be in its raw state (before curing or vulcanization) or in its cured state (after vulcanization). It can constitute all or part of a semi-finished article, especially one intended for use in a pneumatic or non-pneumatic tire with a tread, particularly within the tire's tread itself.

[0071] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration and not limitation. Examples

[0072] Microstructure of elastomers by magnetic resonance analysis nuclear (NMR):

[0073] The microstructure of elastomers is determined by 1<H NMR analysis, supplemented by 13<C NMR analysis when the resolution of the 1<H NMR spectra does not allow for the identification and quantification of all species. Measurements are performed using a BRUKER 500 MHz NMR spectrometer at frequencies of 500.43 MHz for proton observation and 125.83 MHz for carbon observation.

[0074] For insoluble elastomers that swell in a solvent, a 4mm HRMAS z-grad probe is used to observe the proton and carbon in proton-decoupled mode. Spectra are acquired at rotation speeds of 4000 Hz to 5000 Hz.

[0075] For measurements on soluble elastomers, a liquid NMR probe is used, allowing observation of the proton and carbon in proton-decoupled mode.

[0076] The preparation of insoluble samples is carried out in rotors filled with the material to be analyzed and a deuterated solvent that induces swelling, generally deuterated chloroform (CDCl3). The solvent used must always be deuterated, and its chemical composition can be adapted by those skilled in the art. The quantities of material used are adjusted to obtain spectra with sufficient sensitivity and resolution.

[0077] Soluble samples are dissolved in a deuterated solvent (approximately 25 mg of elastomer in 1 mL), generally deuterated chloroform (CDCI3). The solvent or solvent cutting agent used must always be deuterated, and its chemical composition can be adapted by a person skilled in the art.

[0078] In both cases (soluble sample or swollen sample): For proton NMR, a single 30° pulse sequence is used. The spectral window is adjusted to observe all the resonance lines belonging to the analyzed molecules. The accumulation number is set to obtain a signal-to-noise ratio sufficient for quantifying each motif. The recycle time between each pulse is adjusted to obtain a quantitative measurement.

[0079] For carbon NMR, a simple 30° pulse sequence is used with proton decoupling only during acquisition to avoid Nuclear Overhauser Effects (NOE) and maintain quantitative accuracy. The spectral window is adjusted to observe all resonance lines belonging to the analyzed molecules. The accumulation number is set to obtain a signal-to-noise ratio sufficient for quantifying each motif. The recycle time between each pulse is optimized for quantitative measurement.

[0080] NMR measurements are performed at 25°C. Glass transition temperature of polymers :

[0081] The glass transition temperature (Tg) is measured using a Differential Scanning Calorimeter according to ASTM D3418 (1999). Mooney viscosity:

[0082] Mooney viscosity is measured using an oscillating consistometer as described in ASTM D1646 (1999). The measurement is performed according to the following principle: the sample being analyzed in its raw state (i.e., before cooking) is molded (shaped) in a cylindrical chamber heated to a given temperature (100°C). After 1 minute of preheating, the rotor rotates inside the specimen at 2 revolutions per minute, and the torque required to maintain this rotation is measured after 4 minutes of rotation. Mooney viscosity (ML) is expressed in "Mooney units" (MU, with 1 MU = 0.83 Newton-meters). Dynamic properties :

[0083] Dynamic properties are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96.

[0084] We record the response of a sample of vulcanized composition (cylindrical specimen of 4 mm thickness and of 400 mm² cross-section), subjected to a sinusoidal loading in simple alternating shear, at the frequency of 10Hz, during a temperature sweep, under a fixed stress of 0.7 MPa, we record the value of tanδ observed at 0°C (tanδ at 0°C).

[0085] To measure tan delta max at 23°C, a deformation amplitude sweep is performed at 23°C from 0 to 50% (forward cycle), then from 50% to 0% (return cycle). For the return cycle, the maximum observed value of tanδ, tanδ(max), is measured.

[0086] The results are expressed as a base of 100 relative to a control. A value greater than that of the control, arbitrarily set at 100, indicates a measured quantity greater than that of the control.

[0087] For tanδ at 0°C, a value greater than 100 indicates a higher hysteretic potential than the control in the wet grip performance zone, i.e., improved wet grip performance.

[0088] For tanδ(max) at 23°C, a value less than 100 indicates lower hysteresis properties than the control in the rolling resistance performance area, i.e., improved rolling resistance performance. Preparation of rubber compositions :

[0089] Four rubber compounds, C1 to C4, are prepared. The manufacturing process for these compounds is as follows: The elastomer, then the precipitating silica, and, if applicable, the microsilica, the silane coupling agent, and various other ingredients (excluding the vulcanizing system) are introduced into an internal mixer (final fill level: approximately 70% by volume) with an initial tank temperature of approximately 80°C. A single-stage thermomechanical process (non-productive phase) is then carried out, lasting approximately 5 to 6 minutes, until a maximum "drop" temperature of 160°C is reached.

[0090] The mixture thus obtained is collected, cooled, then sulfur and a sulfenamide-type accelerator are incorporated on a mixer (homo-finisher) at approximately 60°C, mixing everything (productive phase) for an appropriate time (for example between 5 and 12 min).

[0091] The detailed formulations of the compositions are shown in Table 1. The silane and DPG content is indexed to the total surface area developed by the silicas. The total sulfur content, which originates from molecular sulfur (S8) and polysulfide silane, is identical in all compositions. Compositions C2, C3, and C4 are compositions according to the invention. They differ from composition C1 by the presence of microsilica. In the compositions according to the invention, microsilica is used at a higher rate than precipitated silica, partially replacing it compared to composition C1.The compositions thus obtained are then calendered, either in the form of plates (with a thickness ranging from 2 to 3 mm) or thin sheets of rubber, for the measurement of their physical or mechanical properties after vulcanization at 150°C (cured state), or in the form of profiles directly usable, after cutting and / or assembly to the desired dimensions, for example as semi-finished products for tires.

[0092] The ethylene-1,3-butadiene copolymer, elastomer E1, is synthesized according to the procedure described below. All reagents are commercially available except for metallocene, which can be prepared according to the procedure described in document WO 2007054224. Butylloctylmagnesium BOMAG (20% in heptane, C = 0.88 mol.L⁻¹) is obtained from Chemtura and is transferred and then stored in a Schlenk tube under an inert atmosphere. The ethylene, of N35 grade, is obtained from Air Liquide and is used without prior purification.

[0093] In a 90 L reactor containing 64 L of methylcyclohexane, ethylene (Et), and butadiene (Bd) at a molar ratio of 80% ethylene to 20% butadiene, 13.6 mmol of a 0.01 mol / L butylclotylmagnesium (BOMAG) solution is added to the methylcyclohexane. A portion of this solution is used to neutralize impurities in the reactor. Following this, 745 mL of a catalytic system solution (see Table 2) is added. The [active Mg] / [Nd] ratio is 4.8. At this point, the reaction temperature is regulated to 80°C, and the polymerization reaction begins. The polymerization reaction proceeds at a constant pressure of 8 bar. The reactor is fed throughout the polymerization process with ethylene and butadiene (Bd) at a molar ratio of 80% ethylene and 20% butadiene. After 6500 g of polymer has formed, the polymerization reaction is stopped by cooling, degassing the reactor, and adding ethanol. An antioxidant is then added to the polymer solution.The copolymer is recovered by a steam stripping process, well known to those skilled in the art, and then dried to a volatile matter content of less than 0.8% by mass. The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me₂SiFlu₂Nd(µ-BH₄)₂Li(THF)], a cocatalyst, butylmagnesium (BOMAG), and a preforming monomer, 1,3-butadiene, in the amounts indicated in Table 2. It is prepared according to a preparation method conforming to paragraph II.1 of patent application WO 2017 / 093654 A1.

[0094] The microstructure of the E1 copolymer and its properties are shown in Tables 3 and 4. For the microstructure, Table 3 shows the molar rates of ethylene (Et) units, 1,3-butadiene units, and 1,2-cyclohexanediyl (ring) motifs.

[0095] Since the tanδ value at 0°C of compositions C2, C3, and C4 is higher than that of composition C1, the C2 to C4 rubber compositions possess a greater hysteresis potential in the wet grip performance range than composition C1. This result is obtained even though the precipitate silica content traditionally used in tire rubber compositions is much lower than the precipitate silica content of composition C1, which is representative of conventional tire tread rubber compositions.

[0096] From the comparison of compositions C2 to C4 with composition C1, it is surprisingly observed that the addition in a rubber composition comprising a precipitated silica of a microsilica at a higher rate than the precipitated silica to partially replace it increases the hysteretic potential of the rubber composition in the wet grip performance zone.

[0097] Compositions C2 and C4 in which the silica levels satisfy relation (1) are the compositions which also present the best compromise of performance between wet grip and rolling resistance, since they also each have a value of tandelta max at 23°C which turns out to be among the lowest. Table 1 Composition C1 C2 C3 C4 E1 Elastomer 100 100 100 100 Carbon black (1) 3 3 3 3 Precipitation silica (2) 76 37.5 37.5 19 Microsilica (3) 0 76 123 114 Silane coupling agent (4) 6.1 3.9 4.5 2.9 DPG (5) 1.5 1.0 1.1 0.7 Liquid plasticizing agent (6) 22 22 22 22 Plasticizing resin (7) 50 50 50 50 Anti-ozonating wax (8) 1.6 1.6 1.6 1.6 Antioxidant (9) 2 2 2 2 ZnO (10) 0.9 0.9 0.9 0.9 Stearic acid (11) 2 2 2 2 Sulfur 1.0 1.2 1.2 1.3 CBS (12) 2 2 2 Tanδ 0°C 100 106 112 110 Tanδ max 23°C 100 100 117 88 (1) N234 (2) "Zeosil 1165 MP" from Solvay-Rhodia in microbead form, BET of 160 m² / g (3) "Microfume Concrete Premium" (92 to 96% SiO₂) from Ferropem-Montricher, BET of 24 m² / g (4) TESPT ("Si69" from Evonik) (5) Diphenylguanidine (6) MES / HPD (Catenex SNR from Shell) (7) C9 / Dicyclopentadiene hydrocarbon resin "Escorez 5600" from Exxon (Tg = 55°C) (8) "Redezon 500" ozone-reducing wax from Repsol (9) N-1,3-dimethylbutyl-N-phenyl-para-phenyldiamine ("Santoflex 6-PPD" from Flexsys) (10) Industrial-grade zinc oxide Umicore (11) Stearine “Pristerene 4931” from Uniquema (12) N-cyclohexyl-2-benzothiazol-sulfenamide (“Santocure CBS” from Flexsys) Table 2 Synthesis of the catalytic system Metallocene concentration (mmol / L) 6.5 Alkylating agent concentration (mmol / L) 14 butadiene / Nd metal molar ratio 90 Table 3 Elastomer E1 Ethylene (%mol) 77 Butadiene 1.3 (%mol) 15 1,2-cyclohexanediyl (%mol) 8 Table 4 Elastomer E1 Tg (°C) -40°C Mn (g / mol) 142000 Mooney (ML (1+4)) at 100°C 85 ± 8

Claims

1. Rubber composition which comprises a diene elastomer, a first silica which is a precipitated or pyrogenic silica and which has a BET specific surface of greater than 100 m2 / g as reinforcing filler, a second silica which is a microsilica with a BET specific surface of less than 50 m2 / g, the BET specific surface being determined according to the method described in the specification, a silane coupling agent and a crosslinking system, in which: the contents of the first silica and of the second silica being expressed as part by weight per hundred parts of elastomer, phr, and respectively denoted T1 and T2: T1 is greater than 15 phr and is less than T2, and the sum of T1 and of T2 is greater than 75 phr.

2. Rubber composition according to Claim 1, in which the second silica has a BET specific surface of greater than 10 m2 / g and of less than 40 m2 / g.

3. Rubber composition according to Claim 1 or 2, in which the first silica has a BET specific surface of less than 200 m2 / g, preferentially of less than 180 m2 / g.

4. Rubber composition according to any one of Claims 1 to 3, in which the diene elastomer is a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene or their mixture.

5. Rubber composition according to any one of Claims 1 to 4, in which the diene elastomer is a copolymer of ethylene and of a 1,3-diene and contains more than 50 mol% of ethylene units.

6. Rubber composition according to Claim 4 or 5, in which the 1,3-diene is 1,3-butadiene or a mixture of 1,3-dienes, one of which is 1,3-butadiene.

7. Rubber composition according to any one of Claims 1 to 6, in which the sum of T1 and of T2 is less than 140 phr.

8. Rubber composition according to any one of Claims 1 to 7, in which the sum of T1 and of T2 is greater than 90 phr and less than 140 phr.

9. Rubber composition according to any one of Claims 1 to 8, in which T1 and T2 satisfy the following relationship (1): T 2 ≥ 1.73 x T 1 + T 2 − 12510. Rubber composition according to any one of Claims 1 to 9, in which the crosslinking system is a vulcanization system.

11. Tyre which comprises a rubber composition according to any one of Claims 1 to 10.

12. Tyre which comprises a tread comprising a rubber composition according to any one of Claims 1 to 10.