WO2018060631A1 - Tyre tread comprising a thermoplastic elastomer - Google Patents

Abstract

The invention relates to a tyre tread comprising a composition having the basis of at least one elastomer matrix comprising, between 50 and 100 phr of styrenic thermoplastic elastomer (TPS) comprising at least one rigid styrenic segment and at least one flexible diene segment comprising at least 20% by mass of conjugated diene units in relation to the mass of the flexible diene segment, the conjugated diene units being totally or partially hydrogenated, and between 0 and 50 phr of diene elastomer comprising more than 50% by mass of polyisoprene in relation to the mass of diene elastomer, said composition also having the basis of at least one reinforcing filler.

Description

 TIRE TREAD WITH PNEUMATIC COMPRISING AN ELASTOMER

 THERMOPLASTIC

The field of the present invention is that of treads for tires.

During rolling, a tire tread undergoes mechanical stresses and aggression resulting from the direct contact with the ground, which has the effect of creating cracking primers in the tread. These stresses and aggressions are exerted on the tread cyclically at each turn of the wheel. This periodicity has the consequence that the crack initiators which are created in the tread, tend to propagate on the surface or inside the tread. Crack propagation in the tread can result in damage to the tread and thus reduce the life of the tread or the tire. It is therefore important to have tires whose tread has a resistance to crack propagation sufficiently high to minimize the effect of a crack initiation on the life of the tread. To solve this problem, tire manufacturers, for example, use natural rubber in the treads because of the crack-growth resistance properties of natural rubber as mentioned in "Table 3.7 Comparison of elastomers properties" p. 162-163, Hofmann Rubber Technology Handbook, Hanser Publishers (1989).

Other solutions have been made to improve the resistance to crack propagation, in particular in the application WO 2015/091933 which proposes to add to the diene elastomeric matrix a minority content of thermoplastic styrene elastomer.

Nevertheless, there is still a need to further improve the crack propagation resistance of the tire treads, without penalizing, or even improving, the rolling resistance. These improvements should preferably not be made at the expense of other properties of the compositions, such as cooking properties.

Surprisingly, the Applicant has discovered that the selection of a specific diene elastomer in the presence of a high concentration of thermoplastic styrene elastomer in a tread of a tire makes it possible to improve further the resistance to propagation. crack, rolling resistance and rigidity, while improving the cooking properties of the compositions.

Thus a first object of the invention is a tire tread comprising a composition based on at least:

an elastomer matrix comprising between 50 and 100 phr of styrenic thermoplastic elastomer comprising at least one styrenic rigid segment and at least one diene flexible segment comprising at least 20% by weight of conjugated diene units relative to the weight of the diene flexible segment, the diene units conjugates which may be totally or partially hydrogenated,

 o between 0 and 50 phr of diene elastomer comprising more than 50% by weight of polyisoprene relative to the diene elastomer mass,

 a reinforcing filler. The invention also relates to a tire which comprises the tread according to the invention.

I-DEFINITIONS By the expression "part by weight per hundred parts by weight of elastomer" (or phr), is meant for the purposes of the present invention, the part, by weight per hundred parts by weight of elastomer, thermoplastics and non-thermoplastics combined. For the purposes of the present invention, thermoplastic styrene elastomers (TPS) are part of the elastomers. In the present, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass.

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). In the present invention, when a range of values is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also designated and preferentially. As used herein, "composition based on" is understood to mean a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of or intended to react between they, at least in part, during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization. By way of example, a composition based on an elastomeric and sulfur matrix comprises the elastomeric matrix and the sulfur before firing, whereas after firing the sulfur is no longer detectable because the latter has reacted with the elastomeric matrix in forming sulfur bridges (polysulfides, disulfides, mono-sulphide).

When reference is made to a "majority" compound, in the sense of the present invention, it is understood that this compound is predominant among the compounds of the same type in the composition, that is to say it is the one which represents the largest quantity by mass among the compounds of the same type, for example more than 50%, 60%, 70%, 80%, 90% or even 100% % by weight relative to the total weight of the type of compound. Thus, for example, a majority reinforcing filler is the reinforcing filler representing the largest mass relative to the total weight of the reinforcing fillers in the composition. In contrast, a "minor" compound is a compound that does not represent the largest mass fraction among compounds of the same type.

In the context of the invention, the carbonaceous products mentioned in the description may be of fossil origin or biobased. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. These include polymers, plasticizers, fillers, etc.

DETAILED DESCRIPTION OF THE INVENTION l-1 Elastomeric Matrix

 As indicated above, the elastomeric matrix (or elastomeric matrix) comprises:

 between 50 and 100 phr of styrenic thermoplastic elastomer comprising at least one styrenic rigid segment and at least one diene flexible segment comprising at least 20% by weight of conjugated diene units relative to the weight of the diene flexible segment, the diene units conjugates which may be totally or partially hydrogenated,

 o between 0 and 50 phr of diene elastomer comprising more than 50% by weight of polyisoprene relative to the diene elastomer mass. 11-l-a styrenic thermoplastic elastomer

 The styrenic thermoplastic elastomer comprises at least one styrenic rigid segment and at least one diene flexible segment comprising at least 20% by weight of conjugated diene units relative to the mass of the flexible segment, the conjugated diene units being able to be totally or partially hydrogenated . The rigid and flexible segments can be arranged linearly, star or connected.

A flexible segment refers to an elastomeric type polymer block, a rigid segment refers to a thermoplastic type polymer block.

The diene flexible comprises at least 20% by weight of conjugated diene monomer units (also called conjugated diene units). The diene flexible segment may be the homopolymer of a conjugated diene or the random or block copolymer of several conjugated dienes or the copolymer of one or more conjugated dienes and at least one other non-diene monomer such as styrenic monomer. The proportion of conjugated diene units which form the diene flexible segment is preferably at least 50%, more preferably at least 60%, even more preferably at least 70% by weight of the weight of the diene flexible segment. Advantageously, it is at least 80% by weight of the mass of the diene flexible segment. These rates, whether preferential or not, apply to any of the embodiments of the invention.

The conjugated diene units may be 1,3-butadiene units or / and isoprene units. Thus, the diene flexible segment may be a polybutadiene, a polyisoprene or a copolymer of 1,3-butadiene and isoprene. The copolymer of 1,3-butadiene and isoprene may be of a block or random nature.

The rigid styrenic segment advantageously has a glass transition temperature above 80 ° C. Preferably, the styrenic rigid is a polystyrene.

The styrenic rigid segment may be the homopolymer of a styrenic monomer or the block or random copolymer of several styrenic monomers or the copolymer of one or more styrenic monomers and of another non-styrenic monomer such as a 1,3 - diene.

By styrene monomer is to be understood in the present description styrene or substituted styrene. Examples of substituted styrenes which may be mentioned are methylstyrenes (for example Γ-methylstyrene, m-methylstyrene or p-methylstyrene, alpha-methylstyrene, alpha-2-dimethylstyrene, alpha-4-dimethylstyrene or diphenylethylene), para-tert-butylstyrene, chlorostyrenes (for example o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene or 2,4-dichlorostyrene). 6-trichlorostyrene), bromostyrenes (for example o-bromostyrene, m-bromostyrene, p-bromostyrene, 2,4-dibromostyrene, 2,6-dibromostyrene or 2,4,6-tribromostyrene) fluorostyrenes (for example Γο-fluorostyrene, m-fluorostyrene, p-fluorostyrene, 2,4-difluorostyrene, 2,6-difluorostyrene or 2,4,6-trifluorostyrene) or para-hydroxy- styrene.

The styrenic thermoplastic elastomer may comprise a diblock consisting of a single styrenic rigid segment connected to a single diene flexible segment.

The diblock consisting of a single rigid styrenic segment connected to a single diene flexible segment may be selected from the group consisting of or consisting of styrene / butadiene block copolymer (SB), styrene / isoprene (SI), styrene / butadiene / isoprene (SBI) and mixtures of these copolymers. In this designation the diene soft block is a random or block copolymer.

The styrenic thermoplastic elastomer preferably comprises or is preferably constituted by a styrenic thermoplastic elastomer comprising at least two rigid styrenic segments. More preferably, the styrenic thermoplastic elastomer comprises predominantly a styrenic thermoplastic elastomer having at least two rigid styrenic segments. When the styrenic thermoplastic elastomer comprises a styrenic thermoplastic elastomer having at least two styrenic rigid segments, generally at least two chain ends of the styrenic thermoplastic elastomer are each provided with a styrenic rigid segment and the rigid styrenic segments are connected by the styrenic thermoplastic elastomer. or the flexible diene segments. Preferably, the styrenic thermoplastic elastomer comprising at least two rigid styrenic segments is a triblock. The triblock then consists of two rigid styrenic segments and a flexible diene segment.

The triblock consisting of two rigid styrenic segments and a diene flexible segment may be selected from the group consisting of or consisting of styrene / butadiene / styrene block copolymer (SBS), styrene / isoprene / styrene (SIS), styrene / butadiene / isoprene / styrene (SBIS) and mixtures of these copolymers. In this designation the diene soft block can be a random or block copolymer. Preferably, the triblock consisting of two styrenic rigid segments and a diene flexible segment is selected from the group consisting of or consisting of a styrene / isoprene / styrene block copolymer (SIS), styrene / butadiene / isoprene / styrene (SBIS) and mixtures of these copolymers, more preferably the triblock consisting of two rigid styrenic segments and a diene flexible segment is a styrene / isoprene / styrene block copolymer (SIS).

In the case where the styrenic thermoplastic elastomer is a diblock, the denomination of "the at least one rigid segment" designates the rigid segment present in the styrenic thermoplastic elastomer. In the different cases of a diblock, for example in the case of a triblock, the name "the at least one rigid segment" designates the rigid segments present in the thermoplastic styrene elastomer. In the case where the thermoplastic styrene elastomer is a diblock or a triblock, the name of "the at least one flexible segment" designates the flexible segment present in the thermoplastic styrene elastomer. In cases where the styrenic thermoplastic elastomer is neither a diblock nor a triblock, the denomination of "the at least one flexible segment" designates the flexible segments present in the thermoplastic styrene elastomer. According to the invention, a fraction of the diene units of the diene flexible segment can be hydrogenated. Alternatively, all of the diene units of the diene flexible segment can be hydrogenated. It will be appreciated by those skilled in the art that it may equivalently use a styrenic thermoplastic elastomer whose double bonds of a fraction of the diene units of the diene soft segment will have been reduced in a single bond by a process other than hydrogenation. Among the methods which make it possible to reduce the double bonds of the diene units in single bond, mention may be made of reductions with aluminum hydride or with diimine, for example. When all of the diene units of the diene flexible segment of the thermoplastic elastomer is hydrogenated, the diblock consisting of a single styrenic rigid segment connected to a single diene flexible segment may be selected from the group comprising or consisting of the styrene block copolymer / ethylene / butylene (SEB), styrene / ethylene / propylene (SEP), styrene / ethylene / ethylene / propylene (SEEP) and mixtures of these copolymers. In this designation, the hydrogenated flexible diene block is a random or block copolymer.

When all the diene units of the diene flexible segment of the thermoplastic elastomer is hydrogenated, the triblock consisting of two rigid styrenic segments and a diene flexible segment may be selected from the group comprising or consisting of the styrene / ethylene / block copolymer. butylene / styrene (SEBS), styrene / ethylene / propylene / styrene (SEPS), styrene / ethylene / ethylene / propylene / styrene (SEEPS) and mixtures of these copolymers. In this designation, the hydrogenated flexible diene block is a random or block copolymer. Styrene thermoplastic elastomers are also suitable mixtures of a triblock copolymer and a diblock copolymer described herein. Indeed, the triblock copolymer may contain a minority weight fraction of diblock copolymer consisting of a rigid styrenic segment and a diene flexible segment, the rigid block and the flexible block being respectively of the same chemical nature, in particular of the same microstructure, as the rigid and flexible blocks of the triblock. The presence of diblock copolymer in the triblock copolymer generally results from the synthesis process of the triblock copolymer which can lead to the formation of a secondary product such as the diblock copolymer. Most often the percentage of diblock copolymer in the triblock copolymer does not exceed 40% by weight of triblock copolymer. Advantageously, the mass ratio of the styrenic rigid segment is between 5 and 40% of the mass of the thermoplastic styrene elastomer. Below the minimum indicated, the thermoplastic nature of the styrenic thermoplastic elastomer is likely to decrease significantly while above the maximum recommended, the elasticity of the composition can be affected. For these reasons, the mass ratio of the styrenic rigid segment in the styrenic thermoplastic elastomer is preferably in a range from 10 to 35%, more preferably from 10 to 20% of the mass of the thermoplastic styrene elastomer. These levels, whether preferential or not, apply to any of the embodiments of the invention, especially when the polystyrene forms the rigid styrenic segment of the thermoplastic styrene elastomer.

The number-average molar mass (denoted Mn) of the styrenic thermoplastic elastomer is preferably between 50,000 and 500,000 g / mol, more preferably between 60,000 and 450,000 g / mol, more preferably between 80,000 and 300,000 g / mol. Advantageously it is between 100,000 and 200,000 g / mol. These preferred ranges of average molar mass values apply regardless of the embodiment of the invention.

The molar mass is determined in a known manner by steric exclusion chromatography (SEC). The sample is first solubilized in tetrahydrofuran at a concentration of about 1 g / l; then the solution is filtered on 0.45 μιτι porosity filter before injection. The apparatus used is a chromatographic chain "WATE S alliance". The elution solvent is tetrahydrofuran, the flow rate 0.7 ml / min, the system temperature 35 ° C and the analysis time 90 min. A set of four WATERS columns in series, of trade names "STYRAGEL" ("HMW7", "HMW6E" and two "HT6E") is used. The injected volume of the solution of the polymer sample is 100 μΙ. The detector is a differential refractometer "WATERS 2410" and its associated software for the exploitation of chromatographic data is the "WATERS MILLENIUM" system. The calculated average molecular weights relate to a calibration curve made with polystyrene standards.

The styrenic thermoplastic elastomer is present in a mass proportion of between 50 and 100 phr, that is to say between 50% and 100% by weight of the mass of the elastomer matrix of the composition of the tread. Advantageously, the level of thermoplastic styrene elastomer in the tread composition according to the invention is between 55 and 100 phr, preferably between 60 and 95 phr, more preferably between 65 and 90 phr.

Of course, when the thermoplastic styrene elastomer is a mixture of styrenic thermoplastic elastomers according to the invention, the rates indicated apply to the mixture and not to each of the thermoplastic styrene elastomers.

According to the invention, the styrenic thermoplastic elastomer may have a glass transition temperature of less than -20 ° C. This glass transition temperature (Tg) is generally attributed to the glass temperature of the diene flexible segment of the thermoplastic styrene elastomer. The glass transition temperature is measured by means of a Differential Scanning Calorimeter according to ASTM D3418 (1999). Preferably, the styrenic thermoplastic elastomer has a Tg preferably less than -30 ° C, more preferably less than -40 ° C, even more preferably less than -50 ° C. ll-lb Diene Elastomer

 The composition of the tread according to the invention comprises between 0 and 50 phr of diene elastomer comprising predominantly at least one polyisoprene. Thus, the composition according to the invention may contain, as diene elastomer, a single polyisoprene or a mixture of a polyisoprene with one or more other diene elastomers, the diene elastomer being predominantly composed of polyisoprene.

By elastomer (or "rubber", the two terms being considered synonymous) of the "diene" type, it will be recalled here that it is to be understood in known manner that one or more elastomers derived from at least a part (Le. a homopolymer or copolymer) of diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or otherwise).

These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". The term "essentially unsaturated" is generally understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a level of units or units of diene origin (conjugated dienes) which is greater than 15% (mol%); Thus, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the above definition and may in particular be described as "essentially saturated" diene elastomers ( low or very low diene origin, always less than 15%). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer is particularly understood to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

Given these definitions, the term "diene elastomer" can be understood more particularly to be 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;

 (b) any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

(c) a ternary copolymer obtained by copolymerization of ethylene, an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, carbon, such as elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene;

 (d) a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated versions, in particular chlorinated or brominated, of this type of copolymer.

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

As conjugated dienes 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C ₁ -C ₅ alkyl) -1,3-butadienes, such as for example 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1 3-butadiene, aryl-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, vinylnaphthalene.

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, there may be mentioned, for example, 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, there may be mentioned, for example, silanol or polysiloxane functional groups having a silanol end (as described, for example, in F 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 still 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 SBR, BR, N R or IR) of the epoxidized type.

In summary, the diene elastomer of the composition can be chosen, for example, from the group of highly unsaturated diene elastomers constituted by natural rubber (NR), synthetic polyisoprenes (IR) and polybutadienes (abbreviated to "BR"). ), the copolymers of butadiene, isoprene copolymers 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), isoprene-copolymers butadiene-styrene (SBIR), butadiene-acrylonitrile copolymers (NBR), butadiene-styrene-acrylonitrile copolymers (NSBR) or a mixture of two or more of these compounds.

According to the invention, the diene elastomer comprises predominantly at least one polyisoprene. In other words, the diene elastomer comprises more than 50% by weight of polyisoprene relative to the diene elastomer mass. Preferably, the diene elastomer comprises from 60 to 100%, preferably from 70 to 100%, or more, by weight of polyisoprene relative to the diene elastomer mass.

By "polyisoprene" is meant in known manner a homopolymer or copolymer of isoprene, in other words a diene elastomer selected from the group consisting of natural rubber (NR) which can be plasticized or peptized, synthetic polyisoprenes (IR), the various isoprene copolymers and the mixtures of these elastomers. Among the isoprene copolymers, mention will in particular be made of copolymers of isobutene-isoprene (butyl rubber IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene ( SBIR).

The polyisoprene is preferably selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof. Preferably, the polyisoprene has a mass ratio of cis 1,4 units of at least 90%, more preferably at least 98% relative to the weight of the polyisoprene.

More preferably, the polyisoprene is natural rubber, a synthetic polyisoprene or a mixture thereof. More preferably, the polyisoprene is natural rubber.

The diene elastomer content is between 0 and 50 phr. Advantageously, the level of diene elastomer in the tread composition according to the invention is between 0 and 45, preferably between 5 and 40, more preferably between 10 and 35 phr.

Whether they contain a single polyisoprene or a mixture of at least polyisoprene and one or more diene elastomers, the compositions of the invention may be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers, it being understood that the elastomeric matrix (including the diene and synthetic elastomers and the abovementioned polymers) mainly comprises polyisoprene. However, advantageously, only the styrenic thermoplastic elastomer and the diene elastomer constitute the elastomer matrix, which means that the elastomer matrix does not contain other elastomers than the first diene elastomer and the thermoplastic styrene elastomer.

11-2 Reinforcing filler

The composition of the tire according to the invention advantageously comprises a reinforcing filler, known for its ability to reinforce a rubber composition that can be used for the manufacture of tires.

The reinforcing filler may comprise carbon black, an organic filler other than carbon black, an inorganic filler or a mixture of at least two of these filler. Preferably, the reinforcing filler comprises a carbon black, a reinforcing inorganic filler or a mixture thereof. More preferably still, the reinforcing filler mainly comprises carbon black and in a minor way an inorganic filler. Particularly advantageously, the reinforcing filler comprises from 50 to 100% by weight of carbon black, preferably from 55 to 90% by weight, preferably from 60 to 80% by weight.

Such a reinforcing filler typically consists of particles whose average size (in mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

According to the invention, the level of reinforcing filler, preferably the reinforcing filler predominantly comprising carbon black, may be in a range from 10 to 160 phr, preferably from 25 to 100 phr, preferably from 35 to 85 phr. preferably 45 to 65 phr.

The blacks that can be used in the context of the present invention may be all black conventionally used in tires or their treads (so-called pneumatic grade blacks). Among these, the reinforcing carbon blacks of the 100, 200, 300 series, or the 500, 600 or 700 series blacks (ASTM grades), for example the blacks NI 15, N134, N234, N326, are especially suitable. N330, N339, N347, N375, N550, N683, N772). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used. The carbon blacks could for example already be incorporated into the diene elastomer, in particular isoprene in the form of a masterbatch (see for example applications WO 97/36724 or WO 99/16600). The BET surface area of the carbon blacks is measured according to the D6556-10 standard [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range Ρ / Ρ0: 0.1 to 0.3]. As examples of organic fillers other than carbon blacks, mention may be made of functionalized polyvinyl organic fillers as described in applications WO 2006/069792, WO 2006/069793, WO 2008/003434 and WO 2008/003435. "Reinforcing inorganic filler" means any inorganic or mineral filler, irrespective of its color and origin (natural or synthetic), also called "white" filler, "clear" filler or even "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 intended for the manufacture of pneumatic tires, in other words able to replace, in its function of reinforcement, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface. In other words, without a coupling agent, the inorganic filler does not make it possible to reinforce or not sufficiently the composition and is therefore not included in the definition of "reinforcing inorganic filler".

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferentially silica (SiO ₂ ). 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, in particular between 60 and 300 m ² / g-A of highly dispersible precipitated silicas (called "HDS"), there may be mentioned for example the silicas "Ultrasil" 7000 and "Ultrasil" 7005 from the company Degussa, silicas "Zeosil" 1165MP, 1135MP and 1115MP from the company hodia, the silica "Hi-Sil" EZ150G from the company PPG, the "Zeopol" silicas 8715, 8745 and 8755 from the company Huber, the silicas with high specific surface area as described in WO 03/016387.

In the present description, with regard to silica, the BET surface area is determined in a known manner by gas adsorption using the method of Brunauer-Emmett-Teller described in "The Journal of the American Chemical Society" Flight . 60, page 309, February 1938, specifically according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: time at 160 ° C - relative pressure range p / po: 0.05 at 0.17). The CTAB specific surface is the external surface determined according to the French standard NF T 45-007 of November 1987 (method B).

Reinforcing inorganic fillers are also suitable for mineral fillers of the aluminous type, in particular alumina (Al ₂ O ₃ ) or aluminum (oxide) hydroxides, or reinforcing titanium oxides, for example described in US Pat. No. 6,610,261 and US Pat. US 6,747,087. 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 above.

Those skilled in the art will understand that, as the equivalent filler of the reinforcing inorganic filler described in this paragraph, it would be possible to use a reinforcing filler of another nature, in particular an organic filler, since this reinforcing filler would be covered with a filler. 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.

In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner 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 at least bifunctional polyorganosiloxanes are used. Those skilled in the art can find examples of coupling agent in the following documents: WO 02/083782, WO 02/30939, WO 02/31041, WO 2007/061550, WO 2006/125532, WO 2006/125533, WO 2006/125534, US 6,849,754, WO 99/09036, WO 2006/023815, WO 2007/098080, WO 2010/072685 and WO 2008/055986. The content of coupling agent is advantageously less than 10 phr, it being understood that it is generally desirable to use as little as possible. Typically when a reinforcing inorganic filler is present, the level of coupling agent is from 0.5% to 15% by weight based on the amount of inorganic filler. Its level is preferably in a range from 0.5 to 7.5 phr. This level is easily adjusted by those skilled in the art according to the level of inorganic filler used in the composition.

The rubber composition in accordance with the invention may also contain, in addition to the coupling agents, coupling activators, inorganic charge-covering agents or, more generally, processing aid agents which can be used in a known manner, by improving the dispersion of the filler in the rubber matrix and lowering 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 (especially 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 such as stearic acid.

11-3 Miscellaneous additives

The tread composition according to the invention may also comprise all or part of the usual additives usually used in elastomer compositions, for example plasticizers, pigments, protective agents such as anti-ozone waxes, chemical ozonants, anti-oxidants, anti-fatigue agents, a crosslinking system, vulcanization accelerators or retarders, vulcanization activators. According to the invention, the crosslinking system is preferably based on sulfur, but it may also be based on sulfur donors, peroxide, bismaleimides or their mixtures.

11-4 Tires

 The present invention can be applied to any type of tire. The tire according to the invention may be intended to equip motor vehicles of the tourism type, SUV ("Sport Utility Vehicles"), or two wheels (including motorcycles), or planes, or industrial vehicles chosen among vans, "Weight "heavy" - that is, metros, buses, road transport vehicles (trucks, tractors, trailers), off-the-road vehicles such as agricultural or civil engineering equipment, and others.

Thus, the present invention also relates to a tire comprising a tread according to the invention.

A tire includes a tread whose tread surface is provided with a tread formed by a plurality of grooves delimiting relief elements (blocks, ribs) so as to generate material edges and troughs. These grooves represent a void volume which, relative to the total tread volume (including both the volume of relief elements and that of all grooves) is expressed as a percentage herein referred to as "rate". of hollow volume ". A trough volume of zero indicates a tread without grooves or recesses.

The present invention is particularly well suited to tires for civil engineering vehicles and trucks, especially civil engineering vehicles whose tires are subject to specific constraints. Thus, advantageously, the tire according to the invention is a tire for civil engineering vehicles or heavy goods vehicles, preferably civil engineering vehicles.

The tread according to the invention may have one or more grooves with an average depth of 15 to 120 mm, preferably 65 to 120 mm. The tires according to the invention may have a diameter of from 20 to 63 inches, preferably from 35 to 63 inches.

Furthermore, the average rate of trough on the entire tread according to the invention can be in a range from 5 to 40%, preferably from 5 to 25%.

11-5 Preparation of rubber compositions

 The compositions used in the tires of the invention may be manufactured in appropriate mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first working phase or thermomechanical mixing ( sometimes referred to as a "non-productive" phase) at a high temperature, up to a maximum temperature of between 80 ° C and 140 ° C, preferably between 100 ° C and 125 ° C, followed by a second mechanical working phase (sometimes referred to as a "productive" phase) at a lower temperature, typically below 100 ° C., for example between 60 ° C. and 100 ° C., a finishing phase during which the chemical crosslinking agent is incorporated, in particular the crosslinking system.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents and other various additives are introduced into a suitable mixer such as a conventional internal mixer. the exception of the crosslinking system. The total mixing time, in this non-productive phase, is preferably between 2 and 10 min. After cooling the mixture thus obtained during the first non-productive phase, the low temperature crosslinking system is then incorporated, generally in an external mixer such as a roll mill; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The first kneading step is generally carried out by incorporating the reinforcing filler into the elastomeric matrix in one or more times by thermomechanically kneading. In the case where the reinforcing filler, in particular carbon black, is already incorporated in whole or in part into the elastomeric matrix in the form of a masterbatch as described for example in the applications WO 97/36724 or WO 99 / 16600, the masterbatch is directly kneaded and if necessary is incorporated other elastomers or reinforcing fillers present in the composition that are not in the form of masterbatch, as well as additives other than the crosslinking system.

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 in the form of a rubber profile that can be used, for example, as a tread. The invention relates to tires and tire treads previously described both in the green state (that is to say, before firing) and in the fired state (that is to say, after crosslinking or vulcanization). . The aforementioned features of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of illustration and not limitation.

III-EXAMPLES III-1 Measurements and Tests Used Heometry:

The measurements are carried out at 150 ° C. with an oscillating chamber rheometer according to DIN 53529 - Part 3 (June 1983). The evolution of the rheometric torque, ACouple, as a function of time describes the evolution of the stiffening of the composition as a result of the vulcanization reaction. The measurements are processed according to DIN 53529 - Part 2 (March 1983): T ₀ is the induction time (expressed in min), that is to say the time required for the beginning of the vulcanization reaction; T _a (for example T ₉₉ ) is the time required to reach a conversion of%, that is to say% (for example 99%) of the difference between the minimum and maximum couples. The conversion rate constant denoted by K (expressed in min ^-1 ), of order 1, calculated between 30% and 80% of conversion, which makes it possible to evaluate the kinetics of vulcanization, is also measured. 100. Resistance to crack propagation:

The cracking rate was measured on specimens of rubber compositions, using a 381 type "Elastomer Test System" of the MTS company, as explained hereinafter. Resistance to cracking is measured by repeated tractions on a specimen initially accommodated (after a first traction cycle) and then scored. The tensile test piece consists of a parallelepiped-shaped rubber plate, for example of thickness between 1 and 2 mm, of length between 130 and 170 mm and of width between 10 and 15 mm, the two lateral edges being each lengthwise covered with a cylindrical rubber bead (diameter 5 mm) allowing anchoring in the jaws of the traction machine. The test pieces thus prepared are tested in the new state. The test was conducted in air at a temperature of 20 ° C, 60 ° C or 80 ° C. After accommodation, 3 very fine cuts of between 15 and 20 mm in length are made using a razor blade, at half width and aligned along the length of the test piece, one at each end and one in the center of the latter, before starting the test. At each pulling cycle, the rate of deformation of the specimen is adjusted automatically so as to keep the rate of energy restitution (amount of energy released during the progression of the crack) constant, at a value of less than or equal to approximately 500 J / m ² . The crack propagation rate is measured in nanometers per cycle.

Resistance to crack propagation is expressed in relative units (u.r.) by dividing the speed of propagation of the control by that of the mixture, the speeds being measured at the same rate of energy release.

Dynamic properties (after cooking):

The dynamic properties G * (50%) and tan (5) max are measured on a viscoanalyzer (Metravib V A4000), according to the ASTM D 5992 - 96 standard. The response of a sample of vulcanized composition (cylindrical test specimen) is recorded. 4 mm thick and 400 mm 2 section), subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at 60 ° C. according to ASTM D 1349-99. A strain amplitude sweep is carried out. peak to peak of 0.1 to 50% (forward cycle), then 50% to 1% (return cycle). The results exploited are the complex dynamic shear modulus (G *) and the loss factor tan (5). For the return cycle, the maximum value of tan (5) observed (tan (δ) max) and the complex dynamic shear modulus G * at 50% deformation at 60 ° C are indicated. It is recalled that the value of G * 50% back to 60 ° C is representative of the stiffness of the material: the higher G * 50% return to 60 ° C, the stiffer the material. Moreover, the lower the value of tan (5) max at 60 ° C, the lower the composition will have a low hysteresis and thus improved rolling resistance. The results are presented in base 100.

111-2 Preparation of compositions

The following tests are carried out as follows: an internal mixer (final filling ratio: approximately 70% by volume) is introduced, the initial temperature of which is approximately 60 ° C., the elastomer diene, styrenic thermoplastic elastomer, reinforcing filler and various other ingredients with the exception of the vulcanization system. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of about 3 to 4 minutes, until a maximum temperature of "fall" of 165 ° C is reached.

The mixture thus obtained is recovered, cooled and then sulfur and a sulfenamide type accelerator are incorporated on a mixer (homo-finisher) at 30 ° C., mixing the whole (productive phase) for a suitable time (for example between 5 and 12 minutes).

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties, or extruded in the form of a profile. 111-3 Testing of rubber compositions

 The formulation of compositions C and T is described in Table I. These compositions were prepared according to the process described in point 111-2 above. Composition C is in accordance with the invention in that the elastomer matrix comprises natural rubber and more than 50 phr of a thermoplastic styrene elastomer.

Control composition T is not in accordance with the present invention because it contains exactly 50 phr of styrenic thermoplastic elastomer, which is outside the value page claimed for the styrene thermoplastic elastomer level.

The crack propagation resistance, stiffness and rolling resistance of these compositions were measured according to the protocols described in point III-1 above. The results are given in base 100 relative to the control composition T. For the induction time T ₀ and the conversion rate constant K, a value greater than that of the control indicates, respectively, a better safety at the early vulcanization of the formulation and a better cooking speed. For resistance to crack propagation and G * 50% deformation at 60 ° C, a value greater than that of the control indicates an improved result, that is to say, respectively a superior resistance to crack propagation and a superior rigidity. For the value of tan (5) max at 60 ° C, the lower the value, the lower the composition will have a low hysteresis and thus improved rolling resistance. The overall results are recorded in Table II.

Table I

 (1) natural rubber

 (2) SIS "D1161" marketed by Kraton

 (3) "Ultrasil VN3" marketed by Evonik

(4) N115 Mn 6000-20000 g / mol polyethylene glycol from Sasol Mari

 N-cyclohexyl-2-benzothiazol sulfenamide, "Santocure CBS", marketed by Flexsys

Table II

The results show a very strong improvement in the crack propagation resistance of the tread composition according to the invention compared with the control composition. This improvement is also accompanied by a gain in safety at the early vulcanization without degrading the cooking speed as well as a gain in rigidity and an improvement in rolling resistance. Thus, the present invention can significantly improve the life of tires, since these become much less sensitive to the crack propagation at their tread, while improving their baking properties, the resistance to rolling and stiffness.

Claims

A tire tread comprising a composition based on at least: an elastomeric matrix comprising  o between 50 and 100 phr of styrenic thermoplastic elastomer comprising at least one styrenic rigid segment (TPS) and at least one diene flexible segment comprising at least 20% by weight of conjugated diene units relative to the weight of the diene flexible segment, the conjugated diene units that can be totally or partially hydrogenated,  o between 0 and 50 phr of diene elastomer comprising more than 50% by weight of polyisoprene relative to the diene elastomer mass,  a reinforcing filler. A tread according to claim 1, wherein the diene elastomer comprises from 60 to 100%, preferably from 70 to 100%, by weight of polyisoprene relative to the diene elastomer mass. A tread according to claim 1 or 2, wherein the polyisoprene has a mass ratio of 1,4-cis units of at least 90% of the weight of the polyisoprene. A tread according to claim 3, wherein the polyisoprene is natural rubber, synthetic polyisoprene or a mixture thereof. A tread according to any one of claims 1 to 4, wherein the diene flexible segment of the TPS comprises at least 50% by weight, preferably at least 60% by weight, of conjugated diene units relative to the weight of the flexible diene segment of the TPS. A tread according to any one of claims 1 to 5, wherein the conjugated diene units of the flexible diene segment of TPS contain 1,3-butadiene units and / or isoprene units. A tread according to any one of claims 1 to 6, wherein the styrenic rigid segment of TPS has a glass transition temperature of greater than 80 ° C. A tread according to any one of claims 1 to 7, wherein the styrenic rigid segment of TPS is a polystyrene. A tread according to any one of claims 1 to 8, wherein the styrenic thermoplastic elastomer comprises a styrenic thermoplastic elastomer having at least two rigid styrenic segments. 10. Tread according to claim 9, wherein the styrenic thermoplastic elastomer comprises predominantly a styrenic thermoplastic elastomer having at least two rigid styrenic segments. 11. Tread according to claim 9 or 10, wherein the styrenic thermoplastic elastomer having at least two styrenic rigid segments is a triblock consisting of two rigid styrenic segments and a diene flexible segment. 12. A tread according to claim 11, wherein the triblock consisting of two styrenic rigid segments and a diene flexible segment is selected from the group consisting of styrene / butadiene / styrene block copolymer (SBS), styrene / isoprene styrene (SIS), styrene / butadiene / isoprene / styrene (SBIS) and mixtures of these copolymers. 13. A tread according to any one of claims 9 to 12, wherein the styrenic thermoplastic elastomer further comprises a diblock comprising a rigid styrenic segment connected to a diene flexible segment. 14. A tread according to claim 13, wherein the diblock comprising a styrenic rigid segment connected to a diene flexible segment is selected from the group consisting of styrene / butadiene block copolymer (SB), styrene / isoprene (SI), styrene / butadiene / isoprene (SBI) and mixtures of these copolymers. A tread according to any one of claims 1 to 14, wherein a fraction of the conjugated diene units of the diene flexible segment of the TPS is hydrogenated. A tread according to any one of claims 1 to 14, wherein all of the conjugated diene units of the flexible diene segment of the TPS are hydrogenated. 17. A tread according to claims 11 and 16, wherein the triblock consisting of two rigid styrenic segments and a diene flexible segment is selected from the group consisting of styrene / ethylene / butylene / styrene block copolymer (SEBS), styrene / ethylene / propylene / styrene (SEPS), styrene / ethylene / ethylene / propylene / styrene (SEEPS) and mixtures of these copolymers. A tread according to claims 13 and 16, wherein the diblock having a rigid styrenic segment and a diene flexible segment is selected from the group consisting of styrene / ethylene / butylene block copolymer (SEB), styrene / ethylene / propylene (SEP), styrene / ethylene / ethylene / propylene (SEEP) and blends of these copolymers. 19. Tread according to any one of claims 1 to 18, wherein the styrenic thermoplastic elastomer has a glass transition temperature below -20 ° C, preferably below -30 ° C. 20. Tread according to any one of claims 1 to 19, wherein the styrenic thermoplastic elastomer content is between 55 and 100 phr, preferably between 60 and 95 phr, more preferably between 65 and 90 phr. 21. A tread according to any one of claims 1 to 20, wherein the reinforcing filler comprises a carbon black, a reinforcing inorganic filler or a mixture thereof. The tread of claim 21, wherein the reinforcing inorganic filler is silica. 23. A tread according to claim 21 or 22, wherein the reinforcing filler comprises from 50 to 100% by weight of carbon black, preferably from 55 to 90% by weight, preferably from 60 to 80% by weight. 24. Tread according to any one of claims 1 to 23, wherein the level of reinforcing filler is in a range from 10 to 160 phr, preferably from 25 to 100 phr. 25. A tire comprising a tread according to any one of claims 1 to 24. Tire according to claim 25, wherein the tire is an off-road tire, preferably a civil engineering vehicle tire.