WO2013068269A1

WO2013068269A1 - Rubber composition containing a high level of non-isoprene diene synthetic elastomer

Info

Publication number: WO2013068269A1
Application number: PCT/EP2012/071435
Authority: WO
Inventors: Stéphanie CAMBON; Anne Veyland
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2011-11-10
Filing date: 2012-10-30
Publication date: 2013-05-16
Also published as: FR2982613B1; FR2982613A1

Abstract

The invention relates to a rubber composition in particular intended for producing tyres, based on at least one non-isoprene diene synthetic elastomer at a level higher than or equal to 65 parts by weight per hundred parts (pce) by weight of elastomer, carbon black as the majority by weight of reinforcing filler, zinc at a level within a range from 0 to 1 pce, and a sulphur-based cross-linking system and an accelerator such that the ratio between the level of sulphur in pce and the level of accelerator in pce is greater than or equal to 2.

Description

RUBBER COMPOSITION WITH HIGH SYNTHETIC ELASTOMER RATE

NON-ISOPRENE DIENIC

The present invention relates to rubber compositions for use in the manufacture of various semi-finished products used in the construction of tires, such as for example treads, in particular for heavy goods vehicles, making it possible to obtain pneumatic tires having good wear resistance without degradation of endurance and tire resistance.

Indeed, the tires that equip, in particular, heavy vehicles are generally subjected to severe stresses such as shocks against the sidewalk, climbs and curbs, penalizing the endurance of the tire. These strong stresses result in very large deformations of the tire which cause a decrease in the resistance to aggression and / or the endurance of the tire, the damage being able to go from a crack until the tearing off of a part of the tire. the tread. In known manner, the use of one or more non-isoprenic synthetic diene elastomers (for example styrene-butadiene copolymers or polybutadienes) in the rubber compositions for example for tread leads to an improvement in the resistance to abrasion. wear of the material, but unfortunately can also be accompanied by a degradation of the properties at break of the compositions, which can result in a decrease in the resistance to severe aggression and endurance of the finished products comprising such compositions, by example of the treads.

Thus, particularly in heavy weight, the level of non-isoprene diene synthetic elastomer in the compositions usually used is most often less than or equal to 40 parts by weight per hundred parts of elastomer (pce) in vehicle tires. heavy weight, because of the severe stresses encountered by these tires, in particular in parking maneuver on asphalt or more generally on aggressive soil.

There is therefore an industrial need to find compositions that provide good wear resistance of products comprising such compositions, without degradation of the resistance to attack and endurance of these products. Continuing its research, the Applicant has surprisingly discovered a composition to meet this need by combining a high rate of synthetic elastomers, a low level of zinc and a so-called "conventional" vulcanization system.

Thus, the invention relates to a rubber composition based on at least one non-isoprene diene synthetic elastomer at a level greater than or equal to 65 parts by weight per hundred parts by weight of elastomer (phr), black carbon as majority reinforcing filler by weight, zinc at a rate ranging from 0 to 1 phr, and a sulfur-based crosslinking system and an accelerator such as the ratio between the sulfur content in pce and the accelerator rate in pce is greater than or equal to 2. [0008] Such a composition makes it possible to improve the resistance to wear without degrading the endurance and the resistance to attack. It also has the advantage of being substantially free of zinc or zinc derivative, which leads to a reduction in the cost of this rubber composition and a reduction in the known environmental impact of these compounds, especially vis-à-vis -vis water and aquatic organisms. [0009] Preferably, the invention relates to a composition as defined above in which the non-isoprene diene synthetic elastomer comprises at least one elastomer composed of units derived from diene monomers chosen from 1,3-butadiene, 2,3-di (C 1 -C 5) alkyl-1,3-butadienes, aryl-1,3-butadienes, 1,3-pentadiene and 2,4-hexadiene. [0010] Alternatively, the invention preferably relates to a composition as defined above in which the non-isoprenic diene synthetic elastomer comprises at least one copolymer composed of diene units chosen from 1,3-butadiene, 2,3-diisocyanates and di (C 1 -C 5) alkyl-1,3-butadienes, aryl-1,3-butadienes, 1,3-pentadiene, 2,4-hexadiene and vinylaromatic units. More particularly, the invention relates to a composition as defined above wherein Γ non-isoprene diene synthetic elastomer comprises a blend of two non-isoprenic synthetic diene elastomers; and preferably, the non-isoprene diene elastomer is a blend of butadiene-styrene copolymer and polybutadiene. Preferably, the invention relates to a composition as defined above which additionally contains an isoprene elastomer at a rate within a range of 1 to 35 phr.

Also preferably, the invention relates to a composition as defined above in which the carbon black content is in a range of more than 30 to 90 phr.

[0014] Preferably also, the invention relates to a composition as defined above in which the reinforcing filler is a blend of carbon black and silica.

Preferably, the invention relates to a composition as defined above in which the reinforcing filler comprises a CTAB specific surface carbon black greater than or equal to 90 m ² / g.

[0016] Preferably also, the invention relates to a composition as defined above in which the level of zinc is in a range of 0 to 0.7 phr; and more preferably the level of zinc is in a range from 0.1 to 0.5 phr. Preferably, the invention relates to a composition as defined above in which the ratio between the sulfur content in pce and the accelerator rate in pce is greater than or equal to 3.

The invention also relates to a tire tread consisting of a composition as defined above. I- Description of the invention

The object of the invention therefore relates to a rubber composition for use in the manufacture of tires, based on at least one non-isoprenic diene synthetic elastomer at a level greater than or equal to 65 parts by weight per hundred parts by weight. elastomer weight (phr), carbon black as majority reinforcing filler by weight, zinc at a level ranging from 0 to 1 phr, and a sulfur-based crosslinking system and a accelerator such as the ratio between the sulfur content in pce and the accelerator rate in pce is greater than or equal to 2. By the term "composition based on" is meant a composition comprising the mixture and / or the reaction product in situ of the various basic constituents used, some of these constituents being able to react and / or being intended to react. between them, at least partially, during the various phases of manufacture of the composition, or during the subsequent firing, modifying the composition as it was initially prepared. Thus, the compositions as implemented for the invention may be different in the uncrosslinked state and in the crosslinked state.

In an equivalent manner, the invention preferably relates to a composition as defined above, wherein the composition is in the uncrosslinked state or in the crosslinked state.

In the present description, unless otherwise expressly indicated, all the percentages (%) indicated are% by weight. On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b).

1-1 Elastomer or rubber

[0023] In the usual way, the terms "elastomer" and "rubber" are used interchangeably in the text. I-I-a Nonisoprenic Diene Synthetic Elastomers

By "non-isoprene diene synthetic elastomer" is meant within the meaning of the present invention an elastomer derived at least in part (ie, a homopolymer or a copolymer) from monomers dienes (monomers bearing two carbon-carbon double bonds). ) other than isoprene. Thus, the nonisoprenic synthetic diene elastomers within the meaning of the present definition also include copolymers comprising isoprene as co-monomer. Natural rubber and isoprenic homopolymers (ie consisting of functionalized or non-functionalized isoprenic monomers) are excluded from the present definition. These non-isoprenic diene elastomers are preferably "essentially unsaturated" that is to say having a level of units or units of nonisoprenic diene origin (conjugated dienes) which is greater than 15% (mol%). In the category of "substantially unsaturated" non-isoprenic diene elastomers, the term "non-isoprene diene elastomer" is particularly understood to mean a non-isoprene diene elastomer having a non-isoprenic diene origin ratio (conjugated dienes) which is greater than 50%.

These definitions being given, is meant more particularly by non-isoprene diene synthetic elastomer capable of being used in the compositions according to the invention:

(a) any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms; except for isoprene;

(b) any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more aromatic vinyl compounds having from 8 to 20 carbon atoms (c) any mixture of the elastomers (a) and (b) as described above.

As conjugated dienes 1,3-butadiene, 2,3-di (C 1 -C 5) alkyl-1,3-butadienes (for example 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 such as phenyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinylaromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the "vinyl-toluene" commercial mixture, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, viny lnaphthalene.

The copolymers may contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinylaromatic units. The elastomers may have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the amounts of modifying and / or randomizing agent used. The elastomers can be for example block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or starred or functionalized with a coupling agent and / or starring or functionalization. For coupling with carbon black, mention may for example be made of functional groups comprising a C-Sn bond or amine functional groups such as aminobenzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may be made, for example, of silanol or polysiloxane functional groups having a silanol end (as described for example in FR 2 740 778 or US Pat. No. 6,013,718 and WO 2008/141702) , alkoxysilane groups (as described for example in FR 2,765,882 or US 5,977,238), carboxylic groups (as described for example in WO 01/92402 or US 6,815,473, WO 2004/096865 or US 2006 / 0089445) or polyether groups (as described for example in EP 1 127 909 or US 6,503,973, WO 2009/000750 and WO 2009/000752). As other examples of functionalized elastomers, mention may also be made of elastomers (such as, for example, butadiene-styrene copolymers, or polybutadienes) of the epoxidized type.

In summary, the non-isoprenic synthetic diene elastomer (s) of the composition according to the invention are preferably chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (abbreviated as "BR"), butadiene copolymers, copolymers of isoprene and mixtures of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene-copolymers. butadiene-styrene (SBIR). According to a preferred embodiment, the non-isoprene diene synthetic elastomer is predominantly (ie, for more than half of the total non-isoprenic diene synthetic elastomer content expressed in phr), an SBR, whether an emulsion-prepared SBR ("ESBR") or a solution-prepared SBR ("SSBR"), or a SBR / BR blend (blend). In the case of an SBR elastomer (ESBR or SSBR), an SBR having an average styrene content, for example between 20% and 35% by weight, or a high styrene content, for example 35 to 35% by weight, is used in particular. 45%, a vinyl ring content of the butadiene part of between 15% and 70%, a content (mol%) of trans-1,4 bonds of between 15% and 75% and a Tg of between -10 ° C. and - 70 ° C; such an SBR can be advantageously used in admixture with a BR preferably having more than 90% (mol%) of cis-1,4 bonds.

According to another preferred embodiment of the invention, the rubber composition comprises a blend of one (or more) non-synthetic diene elastomers. isoprenic so-called "high Tg" having a Tg between -70 ° C and 0 ° C and a (one or more) non-isoprenic synthetic diene elastomer said "low Tg" between - 110 ° C and -80 ° C, more preferably between -105 ° C and -90 ° C. The high Tg elastomer is preferably selected from the group consisting of S-SBR, E-SBR, BIR, SIR, SBIR, and mixtures of these elastomers. The low Tg elastomer preferably comprises butadiene units at a level (mol%) of at least 70%; it consists preferably of a polybutadiene (BR) having a content (mol%) of cis-1,4 chains greater than 90%.

According to another particular embodiment of the invention, the non-isoprene diene synthetic elastomer of the composition according to the invention comprises a blend of a BR (as low elastomer Tg) having a rate (% molar) of cis-1,4 linkages greater than 90%>, with one or more S-SBR or E-SBR (as elastomer (s) high Tg).

The composition according to the invention may contain a single non-isoprene diene synthetic elastomer or a mixture of several non-isoprenic synthetic diene elastomers. The overall rate of non-isoprenic synthetic diene elastomers introduced into the rubber composition must be within a range from 65 phr to 100 phr, preferably from 65 to 99 phr, more preferably from 70 to 95 phr, more preferably from 75 to 100 phr. at 95 phr and very preferably from 80 to 90 phr. Below 65 phr, the use of such elastomers is less relevant to the rubber properties concerned.

I-l-b Other elastomers of the composition

When the rubber composition comprises a non-isoprenic diene synthetic elastomer level of less than 100 phr, the elastomeric matrix of the composition is then a blend of synthetic (s) elastomer (s) diene (s) is not isoprenic (s) ( s) with at least one (i.e. one or more) elastomer not belonging to the category of non-isoprenic synthetic diene elastomers. In other words, the composition may contain an elastomer content that is different from a non-isoprenic diene synthetic elastomer in a range of from 0 to 35 phr, preferably from 1 to 35 phr, more preferably from 5 to 30 phr, more preferably from 5 to 25 phr, and very preferably from 10 to 20 phr. For example, these elastomers cut with non-isoprenic synthetic diene elastomers may advantageously be isoprenic elastomers, that is to say homopolymers of isoprene (or 2-methyl-1,3-butadiene), such as only natural rubber (NR) or synthetic isoprene elastomer. The natural rubber can in a known manner be functionalized, for example epoxidized (ENR). The term "synthetic isoprene elastomer" is understood to mean a homopolymer of isoprene other than natural rubber (NR), called synthetic polyisoprene (IR). This isoprene elastomer is preferably a synthetic cis-1,4 polyisoprene; of these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used. In known manner, the synthetic polyisoprene may be unmodified or may have a chemical function along the polyisoprene chain. The isoprenic elastomers can also be present in a blending with each other, in compliance with the prescribed rates.

It is also possible to envisage other elastomers, for example thermoplastic elastomers, thermoplastic elastomer blends or thermoplastic elastomer blends with isoprenic elastomers, always in compliance with the prescribed minimum rate of 65 phr of elastomer. non-isoprene diene synthetic.

For example, and preferably, the elastomeric matrix of the composition according to the present invention will consist of a SBR / NR cut, SBR / IR, BR / NR, BR / IR, or more preferably SBR / BR / NR or SBR / BR / IR.

1-2 Reinforcing filler

Carbon black is used as the majority reinforcing filler by weight (that is to say that it represents the highest content in pce among the reinforcing fillers of the composition, and preferably, it represents more than 50% > of the reinforcing filler), known for its ability to reinforce a rubber composition that can be used for the manufacture of tires, alone or in combination with a reinforcing inorganic filler such as silica.

As carbon blacks are suitable for all carbon blacks, including black type HAF, ISAF, SAF conventionally used in tires (so-called pneumatic grade black). Among these, mention will be made more particularly of reinforcing carbon blacks such as "CRX1346" from Cabot, or blacks from the 100 or 200 series (ASTM grades), such as blacks NI 15, NI 34, N220, or N234, or according to targeted applications, blacks of higher series (for example N326, N330, N339, N347, N375, N660, N683, N772). The carbon blacks could for example already be incorporated into the elastomer in the form of a masterbatch (see for example WO 97/36724 or WO 99/16600). As carbon blacks are preferentially suitable reinforcing carbon blacks having a specific surface CTAB (determined according to the French standard NF T 45-007 of November 1987, method B) greater than or equal to 90 m ² / g, which corresponds to in particular to carbon blacks 100, 200 series (ASTM grades), as mentioned above. More preferably, the carbon blacks will have a specific surface area greater than 120 m ² / g, more preferably in a range from 120 m ² / g to 180 m 2 / g.

Other types of reinforcing filler may be used in cutting with carbon black, in particular other reinforcing organic fillers or reinforcing inorganic fillers. As examples of organic fillers other than carbon blacks, mention may be made of the organic functionalized polyvinylaromatic fillers as described in applications WO-A-2006/069792 and WO-A-2006/069793.

By "reinforcing inorganic filler" must be understood in the present application, by definition, any inorganic or mineral filler (regardless of its color and origin (natural or synthetic), also called "white" charge, charge "clear" or "non-black filler" as opposed to carbon black, capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition for manufacturing tire, in other words able to replace, in its reinforcing function, a conventional carbon black pneumatic grade, such a charge is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) at its area.

The physical state in which the reinforcing inorganic filler is present is indifferent, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers as described below. As reinforcing inorganic fillers are particularly suitable mineral fillers of the siliceous type, in particular of silica (SiO ₂ ), or of the aluminous type, in particular alumina (Al ₂ O ₃ ). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m ² / g, preferably from 30 to 400 m ² / g. As highly dispersible precipitated silicas (referred to as "HDS"), mention may be made, for example, of the silicas "Ultrasil 7000" and "Ultrasil 7005" from the company Degussa, the silicas "Zeosil 1165MP", "1135MP" and "1115MP" of the Rhodia company, the "Hi-Sil EZ150G" silica of the PPG company, the "Zeopol 8715", "8745" and "8755" silicas of the Huber Company, the high surface area silicas as described in the application WO 03 / 16837.

When present in the composition, it is possible to use, in known manner, at least one bifunctional coupling agent (or bonding agent) intended to ensure a sufficient chemical and / or physical connection between the inorganic filler. (surface of its particles) and the diene elastomer, in particular organosilanes or bifunctional polyorganosiloxanes.

In particular, polysulfide silanes, known as "symmetrical" or "asymmetrical" silanes, are used according to their particular structure, as described for example in the applications WO03 / 002648 (or US 2005/016651) and WO03 / 002649 (or US 2005 / 016650). By way of examples of polysulphurized silanes, mention may be made more particularly of the polysulfides (in particular disulphides, trisulphides or tetrasulfides) of bis- (C ₁ -C ₄ ) alkoxyl-C ₁ -C ₄ alkylsilyl-alkyl (C ₁ -C ₄ ) C4)), such as polysulfides of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl). Among these compounds, bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, of formula [(C ₂ H ₅ O) 3 Si (CH 2) 3 S 2] 2 or bis (triethoxysilylpropyl) disulfide, in abbreviated form, is especially used. abbreviated TESPD, of formula [(C ₂ H ₅ O) 3Si (CH 2) 3 S] 2. Mention may also be made, by way of preferred examples, of polysulfides (in particular disulphides, trisulphides or tetrasulfides) of bis (monoalkoxyl (Ci-C ₄ ) -dialkyl (Ci-C ₄ ) silylpropyl), more particularly bis-monoethoxydimethylsilylpropyl tetrasulfide, such as described in patent application WO 02/083782 (or US 2004/132880). As coupling agent other than polysulfurized alkoxysilane, there may be mentioned bifunctional POS (polyorganosiloxanes) or hydroxysilane polysulfides (R2 = OH in formula III above) as described in the applications WO 02/30939 (or US Pat. No. 6,774,255) and WO 02/31041 (or US 2004/051210), or alternatively silanes or POS bearing azo-dicarbonyl functional groups, as described, for example, in the patent applications WO 2006 / 125532, WO 2006/125533, WO 2006/125534.

When the rubber compositions in accordance with the invention contain coupling agents, in a known manner, their level is adjusted according to the level of silica, it is preferably in a range from 0.1 to 10 phr, more preferably from 0.2 to 8 and even more preferably from 0.5 to 5 phr.

Those skilled in the art understand that as an equivalent load of the reinforcing inorganic filler described in this paragraph, could be used a reinforcing filler of another nature, especially organic, since this reinforcing filler would be covered an inorganic layer such as silica, or would comprise on its surface functional sites, especially hydroxyl, requiring the use of a coupling agent to establish the bond between the filler and the elastomer.

The person skilled in the art knows how to adapt on the one hand to the specific surface of the reinforcing filler and on the other hand according to the particular applications targeted, the total total reinforcing filler rate (carbon black and reinforcing inorganic filler). such as silica). Indeed, the optimum is known in different ways depending on the specific applications targeted: the level of reinforcement expected on a bicycle tire, for example, is of course less than that required on a tire capable of driving at high speed in a sustained manner, for example a motorcycle tire, a tire for a passenger vehicle or for a commercial vehicle such as a truck. Preferably, this level is in a range from 30 to 90 phr, preferably from 30 to 70 phr, more preferably from 40 to 60 phr. For the purposes of the invention, the reinforcing filler mainly contains, by weight, carbon black, that is to say that it represents the highest content in phr of the reinforcing fillers of the composition, preferentially the carbon represents more than 50% of the reinforcing filler, for example at a level within a range of 30 to 90 phr, preferably 30 to 70 phr, more preferably 40 to 60 phr. 1-3 Crosslinking system

The crosslinking system is preferably a vulcanization system, that is to say a system based on sulfur (that is to say sulfur or a sulfur donor agent) and a vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the production phase as described later, various known vulcanization activators such as the zinc compounds defined below. stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine).

Among the sulfur donor agents include for example 2-mercaptobenzothiazyl (abbreviated "MBTS"), or tetrabenzylthiuram disulfide (TBZTD).

Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr, if a sulfur donor is used, its rate is adjusted so as to obtain such a sulfur content of vulcanization. The vulcanization accelerator is used at a preferential rate of between 0.2 and 10 phr, more preferably between 0.3 and 6.0 phr.

It is possible to use as accelerator any compound (or mixture of compounds) capable of acting as an accelerator for vulcanizing diene elastomers in the presence of sulfur, in particular thiazole type accelerators and their derivatives, type accelerators. thiurams, zinc dithiocarbamates. These accelerators are for example selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), tetrabenzylthiuram disulfide (TBZTD), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N, N-dicyclohexyl-2 benzothiazyl sulfenamide (DCBS), N-tert-butyl-2-benzothiazyl sulfenamide (TBBS), N-tert-butyl-2-benzothiazyl sulfenimide (TBSI), zinc dibenzyldithiocarbamate (ZBEC) and mixtures thereof. For the purposes of the present invention, the crosslinking system is such that the ratio between the sulfur content (that is to say the level of vulcanization sulfur) in phr and the accelerator rate in phr. (that is to say the sum of the accelerator rates if there are several) is greater than or equal to 2 (vulcanization system called "conventional"), preferably greater than or equal to 3. Also preferably, this ratio is in a range from 2 to 15, most preferably 3 to 12 and more preferably 3 to 10. 1-4 Zinc compounds

As vulcanization activators, zinc-based compounds may be used. Among these compounds, there are, for example, zinc oxide (ZnO), zinc carboxylates such as zinc ethyl hexanoate (ZEH), zinc acetate or salts of zinc fatty acids, for example , zinc laurate or zinc stearate. Such compounds are more fully described in WO 2008/080582 or K-10-2004-0105992.

Other zinc compounds such as zinc dithiocarbamates, for example zinc dibenzyldithiocarbamate (ZBEC), may also be present as vulcanization accelerators. For the purposes of the present invention, the level of zinc compounds introduced into the composition will be such that the total zinc level is less than 1 phr, preferably less than 0.7 phr, and most preferably within a range of 0.1 to 0.5 phr.

In the case where zinc oxide is used, it is well known to those skilled in the art that it is useful to add a fatty acid, such as stearic acid, at a specific rate. preferably between 0.1 and 3 phr.

1-5 Various additives

The rubber compositions in accordance with the invention may also comprise all or part of the usual additives normally used in elastomer compositions intended for the manufacture of tires, in particular treads, for example plasticizers or plasticizers. extension oils, whether aromatic or non-aromatic, pigments, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing resins, acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M) as described for example in the application WO 02/10269, vulcanization activators provided, of course, in the case of activators based on zinc to meet the maximum rate of zinc recommended.

Preferably, these compositions comprise, as preferential non-aromatic or very weakly aromatic plasticizing agent, at least one compound selected from the group. consisting of naphthenic, paraffinic oils, MES oils, TDAE oils, esters (in particular trioleates) of glycerol, hydrocarbon plasticizing resins having a high Tg preferably greater than 30 ° C, and mixtures of such compounds.

These compositions may also contain, in addition to the coupling agents, coupling activators, reinforcing inorganic filler recovery agents or, more generally, processing aid agents that are capable in a known manner, thanks to an improvement of the dispersion of the inorganic filler in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green state, these agents being, for example, hydrolysable silanes such as alkylalkoxysilanes (in particular alkyltriethoxysilanes), polyols, polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialkanol amines), hydroxylated or hydrolyzable POSs, for example α, ω -dihydroxy- polyorganosiloxanes (especially α, ω-dihydroxy-polydimethylsiloxanes), fatty acids, for example stearic acid. II- Preparation of compositions

The rubber compositions of the invention are manufactured in appropriate mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes referred to as "non-productive" phase) at high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed by a second phase of mechanical work (sometimes qualified "Productive" phase) at a lower temperature, typically below 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system or vulcanization. According to a preferred embodiment of the invention, all the basic constituents of the compositions of the invention, with the exception of the vulcanization system, namely the reinforcing filler, the coupling agent, if appropriate, are intimately incorporated, by kneading, with the diene elastomer during the so-called non-productive first phase, that is to say that is introduced into the mixer and which is thermomechanically kneaded, in a or several steps, at least these different basic constituents until reaching the maximum temperature between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C. For example, the first phase (non-productive) is conducted in a single thermomechanical step during which is introduced, in a suitable mixer such as a conventional internal mixer, all the necessary constituents, the possible additional coating or processing agents and other miscellaneous additives, with the exception of the vulcanisation system. The total mixing time in this non-productive phase is preferably between 1 and 15 minutes. After cooling the mixture thus obtained during the first non-productive phase, the vulcanization system is then incorporated at low temperature, generally in an external mixer such as a roller mixer; the whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 min.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or extruded, to form for example a rubber profile used for manufacturing semi-finished products such as treads. The crosslinking (or vulcanization or cooking) is conducted in a known manner at a temperature generally between 130 ° C and 200 ° C, under pressure, for a sufficient time which may vary for example between 5 and 90 minutes depending in particular the firing temperature, the crosslinking system adopted, the kinetics crosslinking of the composition in question or the size of the tire. The invention particularly relates to the use of a rubber composition according to the invention for the manufacture of tires or semi-finished rubber products for these tires, these semi-finished products being particularly chosen from the group constituted by the treads, the sub-layers intended for example to be placed under these treads, the crown plies, the sidewalls, the carcass plies, the heels, the protectors, the inner tubes and the waterproof inner tires for tire without a chamber.

The composition according to the invention is particularly suitable for the manufacture of treads of tires intended to equip passenger vehicles, vans, 4x4 vehicles (4-wheel drive), two wheels, "heavy vehicles" ( that is, metro, bus, road transport equipment (trucks, tractors, trailers), off-the-road vehicles), aircraft, civil engineering, agricultural, or handling equipment, these treads may be used in the manufacture of new tires or for the retreading of used tires.

The invention relates to these tires and treads both in the green state (i.e., before firing) and in the fired state (i.e., after crosslinking or vulcanization). The tread according to the invention is particularly suitable for tires intended to equip motor vehicles of the heavy truck type.

The invention as well as its advantages will be readily understood in light of the detailed description which follows.

III-Examples III-1 Characterization of rubber compositions III-1-a Fixing time (or roasting time)

The measurements are carried out at 130 ° C., in accordance with the French standard NF T 43-005. The evolution of the consistometric index as a function of time makes it possible to determine the toasting time of the rubber compositions, evaluated in accordance with the standard referred to by parameter T5 (case of a large rotor), expressed in minutes, and defined as the time required to obtain an increase in the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.

ΠΙ-1-b Traction tests

These tensile tests make it possible to determine the properties at break: elongation at break (in%). All these tensile measurements are carried out at 60 ° C, according to the French standard NF T 40-101 (December 1979).

III-l-c Dynamic properties in shear

The dynamic property G * is measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen 4 mm in height and 400 mm ² in section), subjected to a sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, at 60 ° C., is recorded. A strain amplitude sweep of 0.1% to 100% (forward cycle) is performed, followed by 100% to 0.1%) (return cycle). The result exploited is the complex dynamic shear modulus G *. For the forward cycle, the value of the complex 50%> peak-to-peak deformation module denoted G * 50% cc is given.

III-2 Examples of Compositions [0078] The examples presented below are prepared as indicated above, their composition is given in Table 1, in phr.

Table 1

(1) natural rubber (plasticized, peptized) (Tg = -65 ° C)

(2) polybutadiene with 2.5% 1,4-trans; 92.5% of 1,4-cis; 5.0% 1-2 (Tg = -105 ° C) (3) Tin functional SBR with broad polydispersity index: polystyrene butadiene with the following mass levels: 50% 1,4-trans BR; 26% 1,4-cis-BR; 24% of BR 1.2; 15.5% styrene (Tg = -65 ° C). The molecular weight Mn of this polymer, determined by the SEC technique, is 145,000 g.mol ^-1

(4) N234 for composition A0 and N134 for compositions A1 to A4 (5) N-1,3 dimethylbutyl N-phenylparaphenylenediamine (6-PPD) (6) N-cyclohexyl-2-benzothiazylsulfenamide (CBS)

The compositions A0, Al, A2, A3 and A4 differ from each other in particular by the type of elastomer cutting, the level of synthetic diene elastomers not isoprenic, the zinc oxide content, the sulfur content and the accelerator rate in Table 1.

The rubber composition A0 is the control, corresponding to the composition used in the usual manner in the treads of heavy weight. It contains 40 phr of non-isoprenic synthetic diene elastomer and standard levels of zinc oxide, sulfur and accelerator. It also contains 3 phr of an implementing agent, the "AFLUX 42" marketed by Rhein Chemie, which is necessary because of its cutting of elastomers and 0.5 phr of hardener and 0.25 phr of hardening resin. . The compositions Al, A2, A3 and A4 contain an NR / BR / SBR blend (15/10/75), ie 85 phr of synthetic diene elastomers and are distinguished from each other by the zinc oxide (ZnO) content, sulfur and accelerator.

The composition A4 is the composition according to the invention. The level of 0.5 phr of ZnO corresponds to a level of 0.4 phr of zinc in this composition, the molar mass of ZnO being 83 g / mol, including 65 g / mol for zinc. III-3 Properties of the compositions

The properties of the compositions presented above are presented in Table 2 below.

Table 2

The comparison between the compositions A0 and Al shows the expected fact that the modulus G * increases between A0 and Al, with the level of non-isoprene diene synthetic elastomer, which can result in an improvement in the resistance to wear. Moreover, the increase in the non-isoprenic diene synthetic elastomer content penalizes the breaking properties of the rubber composition and thus decreases the endurance of the tread. Indeed, there is a significant decrease in the elongation elongation of Al relative to A0.

The comparison between the compositions A0 and A2 demonstrates the fact that the reduction of the ZnO content from 3 phr to 0.5 phr, combined with the increase in the level of non-isoprenic synthetic diene elastomers, also penalizes the properties. at breaking of a rubber composition conventionally used, even if the elongation of fracture is slightly improved with respect to Al.

The comparison between the compositions A0 and A3 highlights the fact that the modification of the sulfur content and the CBS content, so that the sulfur / CBS ratio changes from 1 (Al) to 4 (A3), combined. the increase in the level of non-isoprenic synthetic diene elastomers does not make it possible to find as good a rupture property as that of the control A0, even if the elongation of rupture is slightly improved with respect to Al.

The comparison between the compositions A0 and A4 highlights the fact that the modification of the sulfur content and the CBS content, so that the sulfur / CBS ratio changes from 1 (Al) to 4 (A4) associated with the reduction of the ZnO level from 3 phr to 0.5 phr and combined with the increase in the level of nonisoprenic synthetic diene elastomers makes it possible to find similar values of elongation of rupture and even leads to a slight improvement over the witness A0. Moreover, it will be noted that the fixing time does not decrease with the decrease in the ZnO rate but increases slightly, keeping a value quite acceptable. It will also be noted that the modulus obtained for compositions A1 to A4 is of the same order of magnitude, which is not greatly affected by the modification of the vulcanization system.

Thus, these results show that it is possible to increase the level of nonisoprenic synthetic diene elastomers in the composition, and therefore a priori to improve the wear resistance without degrading the endurance, with a rubber composition which comprises a non-isoprenic synthetic diene elastomer level greater than 65 phr (85 phr in the A4 example), a low zinc level (0.4 in the A4 example) and a sulfur and accelerator content characterized in that the ratio between sulfur content in pce and accelerator rate in phr is greater than 1 (4 in example A4).

Claims

1. A rubber composition based on at least one non-isoprene diene synthetic elastomer at a level greater than or equal to 65 parts by weight per hundred parts by weight of elastomer (phr), carbon black as majority reinforcing filler by weight, zinc at a rate ranging from 0 to 1 phr, and a sulfur-based crosslinking system and an accelerator such as the ratio between the sulfur content in phr and the accelerator rate in phr is greater than or equal to 2.

2. The composition as claimed in claim 1, characterized in that the non-isoprene diene synthetic elastomer comprises at least one elastomer composed of units derived from diene monomers chosen from 1,3-butadiene and 2,3-di (C 1 -C 6 alkyl). C ₅ ) -1,3-butadienes, aryl-1,3-butadienes, 1,3-pentadiene and 2,4-hexadiene.

3. Composition according to claim 1 characterized in that Γ non-isoprene diene synthetic elastomer comprises at least one copolymer composed of diene units selected from 1,3-butadiene, 2,3-di (C 1 -C 5) alkyl - 1,3-butadienes, aryl-1,3-butadienes, 1,3-pentadiene, 2,4-hexadiene and vinylaromatic units.

4. Composition according to any one of claims 1, 2 or 3, characterized in that Γ non-isoprene diene synthetic elastomer comprises a blend of two non-isoprene synthetic diene elastomers.

5. Composition according to claim 4 characterized in that Γ non-isoprene diene elastomer is a blend of butadiene-styrene copolymer and polybutadiene.

6. Composition according to any one of claims 1 to 5 characterized in that it further contains an isoprene elastomer at a rate within a range of 1 to 35 phr.

7. Composition according to any one of claims 1 to 6 characterized in that the carbon black content is in a range of more than 30 to 90 phr.

8. Composition according to any one of claims 1 to 7 characterized in that the reinforcing filler is a blend of carbon black and silica.

9. Composition according to any one of claims 1 to 8 characterized in that the reinforcing filler comprises a carbon black surface specific CTAB greater than or equal to 90 m ² / g.

10. Composition according to any one of claims 1 to 9 characterized in that the level of zinc is in a range of 0 to 0.7 phr.

11. The composition of claim 10 characterized in that the zinc level is in a range of 0.1 to 0.5 phr.

12. Composition according to any one of claims 1 to 11 characterized in that the ratio between the sulfur content in pce and the accelerator rate in pce is greater than or equal to 3.

Tire tread characterized in that it consists of a composition according to any one of claims 1 to 12.