WO2019092377A2 - Rubber composition on the basis of a polyamide having a low melting point - Google Patents

Abstract

The invention relates to a tyre, the tread of which comprises a rubber composition on the basis of at least one diene elastomer, a reinforcing filler, a polyamide having a melting point of less than 170 °C, and a cross-linking system. The invention also relates to a method for preparing a tread composition for the manufacture of tyres and to the composition that can be obtained by this method.

Description

 RUBBER COMPOSITION BASED ON LOW TEMPERATURE POLYAMIDE

 FUSION

The present invention relates to tires for passenger vehicles. It relates more particularly to tires adapted to sporty driving.

The adhesion of the tires to the ground on which they roll is one of the most important characteristics from the point of view of the driver's safety of a vehicle equipped with tires. It is also decisive for the performance of the vehicle in sport driving: if its tires lose their steering power due to lack of grip, the vehicle is no longer steerable. In particular, during braking in severe (or sporting) driving conditions, the temperature of the tires is subject to a sharp increase in temperature that can exceed 100 ° C.

A known solution to date for improving the braking performance in severe conditions is the use of an elastomer or elastomer cut with high vinyl levels (US Pat. No. 4,925,894). Another solution is described in WO 2012/012133 and consists of a tread composition comprising predominantly a butadiene-styrene copolymer with 50% vinyl pattern, 20 to 60 phr of a plasticizer having a Tg between 30 and 120 ° C, 25 to 60 phr of a vegetable oil and 100 to 200 phr of silica.

Continuing its research, the Applicant has surprisingly discovered that the use of a low melting point polyamide in a tire tread composition makes it possible to improve the braking performance under severe conditions, without degrading the performance of the tire. rolling resistance.

Tread compositions comprising polyamides have already been described in some state-of-the-art documents. For example, US 2012/0220706 discloses a tread comprising particulate polyamide having a melting temperature greater than 210 ° C to improve rolling resistance. However, these compositions do not make it possible to improve the braking performance of the tires under severe conditions.

There is therefore a real need for tires having a dissipation at high temperatures to improve driving performance in severe conditions of use, especially during braking. Preferably, the improvement of the braking performance under severe conditions must not be carried out to the detriment of other performance of the tire, in particular the rolling resistance. Thus, the present invention particularly relates to a tire whose tread comprises a rubber composition based on at least:

 a diene elastomer,

 a reinforcing filler,

 a polyamide whose melting point is less than 170 ° C, and

 a crosslinking system.

It also relates to a process for preparing compositions for the manufacture of such tires, as well as compositions obtained by this method.

The invention particularly relates to tires intended for equipping tourism-type motor vehicles, SUVs ("Sport Utility Vehicles"), or two wheels (in particular motorcycles), in particular vehicles intended to ride in sports conditions, but also tires. intended to equip "heavyweight" vehicles and aircraft.

The tires and tire treads described above, the rubber articles, both in the green (i.e., before firing) and the fired (i.e. after crosslinking or vulcanization).

The invention as well as its advantages will be readily understood in the light of the description and the following exemplary embodiments.

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 mass per hundred parts by weight of elastomer or rubber.

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 that it is the one which represents the largest amount 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, for example less than 50%, 40%, 30%, 20%, 10% or less.

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.

Unless otherwise indicated, when the term "composition" or "rubber composition" is used, reference is made to the rubber composition of the tread of the tire according to the present invention.

The glass transition temperatures (Tg) described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999).

II- DESCRIPTION OF THE INVENTION

ll-A Pneumatics

II-A-1 Diene Elastomer The tread rubber compositions of the tire of the invention may contain a single diene elastomer or a mixture of several diene elastomers.

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 (ie, a homopolymer or copolymer) of diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or otherwise).

The 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%.

These definitions being given, the term "diene elastomer" can be understood more particularly to mean the rubber compositions of the tire 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, for example 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-tertiarybutylstyrene, 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, 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, US 6,013,718 and WO 2008/141702), groups alkoxysilane (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, US 6,503,973, WO 2009/000750 and WO 2009/000752).

In summary, the diene elastomer of the tread composition of the tire according to the invention is preferably chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (abbreviated "BR"), synthetic polyisoprenes (IR), natural rubber (NR), butadiene copolymers, 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 of butadiene-styrene (SBIR), butadiene-acrylonitrile copolymers (NBR), butadiene-styrene-acrylonitrile copolymers (NSBR) or a mixture of two or more of these compounds.

Advantageously, the diene elastomer is mainly composed of styrene-butadiene copolymer (abbreviated to SBR), this SBR possibly being an emulsion or ESBR (that is to say prepared by emulsion polymerization), an SBR solution or SSBR (c). that is, prepared by solution polymerization), or a mixture of both.

Amongst the copolymers based on styrene and butadiene, in particular SBR, mention may be made especially of those having a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (mol%). in -1,2-bonds of the butadiene part of between 4% and 75%, a content (mol%) of trans-1,4 bonds of between 10% and 80%. Preferably, the Tg of the copolymer based on styrene and butadiene, in particular SBR (ESBR or SSBR), is between 0 and -80 ° C., more particularly between 0 ° C. and -70 ° C .; according to a particular embodiment, the Tg is between -5 ° C and -60 ° C, especially in a range of -10 ° C to -50 ° C. The person skilled in the art knows how to modify the microstructure of a copolymer based on styrene and butadiene, in particular on an SBR, to increase and adjust its Tg, in particular by modifying the styrene contents in -1-bonds. 2 or in trans-1,4 bonds of the butadiene part.

To the above styrene-butadiene copolymer may optionally be associated at least a second diene elastomer, different from said copolymer, said second diene elastomer, optional, being present at a weight content which is therefore at most equal to 50 phr, preferably at most equal to 40 phr, in particular at most equal to 30 phr (as a reminder, pce signifying parts by weight per hundred parts of elastomer, that is to say of the total of the elastomers present in the tread). Preferably, when a second diene elastomer is used, its content in the composition of the tread of the tire according to the invention is in a range from 10 to 30 phr.

This second optional diene elastomer is preferably chosen from the group consisting of polybutadienes (BR), natural rubber (NR), polyisoprenes of synthesis (IR), butadiene copolymers (other than styrene-butadiene-based copolymers), isoprene copolymers and mixtures of these elastomers.

Advantageously, the second elastomer is an isoprene elastomer. By "isoprene elastomer" is meant in known manner a homopolymer or copolymer of isoprene, in other words an isoprene elastomer chosen from the group comprising or consisting of natural rubber (NR), which can be plasticized or peptized, the 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 isoprene elastomer is preferably selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof. Among these synthetic polyisoprenes, polyisoprenes having a level (mol%) of 1,4-cis bonds greater than 90%, more preferably still greater than 98%, are preferably used. More preferably, the diene elastomer is natural rubber.

Preferably, the level of diene elastomer, preferably of styrene butadiene copolymer, is 50 to 100 phr, more preferably 60 to 100 phr, more preferably 70 to 100 phr, more preferably 80 to 100 phr, and more preferably very preferentially from 90 to 100 phr. In particular, the level of diene elastomer, preferably of styrene butadiene copolymer, is very preferably 100 phr. II-A-2 Reinforcing Filler

 The tread composition of the tire according to the invention comprises a reinforcing filler known for its ability to reinforce a rubber composition. 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. Preferably, the level of reinforcing filler in the composition of the tread of the tire according to the invention is in a range from 5 to 150 phr, preferably from 10 to 80 phr, more preferably from 15 to 75 phr. .

The reinforcing filler advantageously comprises or consists of carbon black, a reinforcing inorganic filler or mixtures thereof. The reinforcing filler is advantageously mainly composed of carbon black. The reinforcing filler may comprise, for example, from 50 to 100% by weight of carbon black, preferably from 55 to 90% by weight, preferably from 60 to 80% by weight. Particularly advantageously, the reinforcing filler comprises exclusively carbon black. The reinforcing filler may also further comprise a reinforcing inorganic filler. Preferably, the reinforcing inorganic filler is silica. When the composition of the tread of the tire according to the invention comprises carbon black (predominantly or exclusively, as a reinforcing filler), the carbon black content in the tread composition of the tire according to the invention. the invention is preferably in a range from 10 to 80 phr, preferably from 15 to 75 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 the latter, there will be mentioned more particularly the reinforcing carbon blacks of the series 100, 200, 300, or the series blacks 500, 600 or 700 (ASTM grades), such as, for example, the blacks N115, N134, N234, N326, 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]. Preferably, the BET specific surface area of the carbon black is in a range from 70 to 150 m ² / g, preferably from 100 to 120 m ² / g.

"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 charge 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 Rhodia, the "Hi-Sil" EZ150G silica from PPG, the "Zeopol" 8715, 8745 and 8755 silicas from Huber, the high surface area silicas 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, more precisely according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: 1 hour at 160 ° C. - relative pressure range p / po: 0.05 to 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 have on its surface functional sites, in particular hydroxyl sites, 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 according to 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 known manner, thanks to to improve the dispersion of the filler in the rubber matrix and to lower the viscosity of the compositions, to improve their ability to use 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 such as stearic acid.

ll-A-3 Polyamide

The tread composition of the tire according to the invention also has the essential characteristic of being based on at least one polyamide whose melting temperature is below 170 ° C. The melting temperature is measured in a well-known manner by DSC according to ASTM D3418.

Any polyamide whose melting temperature is below 170 ° C can be used.

The polyamides used in the context of the present invention may be homopolymers or copolymers, possibly derived from the condensation of lactams, optionally with lactones, and / or the condensation of diacids and / or amino acids with diamines. . Preferably, the polyamides used in the context of the present invention are copolymers derived from the condensation of lactams, optionally with lactones, and / or the condensation of diacids and / or amino acids with diamines.

A copolymer is, as is well known to those skilled in the art, a polymer resulting from the copolymerization of at least two types of monomer, chemically different, called comonomers.

Particularly advantageously, the polyamide whose melting temperature is below 170 ° C. is a copolymer polyamide consisting of at least two different types of monomers chosen from the group consisting of lactams, or at least two different types of monomers selected from the group consisting of diacids and at least two different types of monomers selected from the group consisting of diamines. The lactams may for example have 3 to 12 carbon atoms on their main cycle and may be substituted. Preferably, the lactams are chosen from the group comprising or consisting of β, β-dimethylpropylactam, α, adimethylpropylactam, amylolactam, caprolactam, capryllactam, oenantholactam, 2-pyrrolidone, lauryllactam and mixtures thereof. . More preferably, the lactams are selected from the group consisting of or consisting of caprolactam, lauryllactam and mixtures thereof.

The diacids (or dicarboxylic acid) can be for example acids having between 4 18 carbon atoms. Preferably, the diacids are selected from the group consisting of or consisting of adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid, 1,4-acid. cyclohexyldicarboxylic acid, terephthalic acid, sodium or lithium salt of sulphoisophthalic acid, dodecanedioic acid and mixtures thereof. More preferably, the diacids are selected from the group consisting of or consisting of adipic acid, dodecanedioic acid and mixtures thereof. The diamines may be, for example, saturated aliphatic, aryl and / or cyclic diamines having 6 to 12 atoms. Preferably, the diamines are chosen from the group comprising or consisting of hexamethylenediamine, piperazine, tetramethylene diamine, octamethylene diamine, decamethylene diamine, dodecamethylenediamine, 1,5 diaminohexane, 2,2,4 trimethyl-1,6-diamino-hexane, diamine polyols, isophorone diamine (IPD), methyl pentamethylenediamine (MPDM), bis (aminocyclohexyl) methane (BACM), bis (3-methyl-4-aminocyclohexyl) methane (BMACM), methaxylyenediamine, bis-p-aminocyclohexylmethane, trimethylhexamethylenediamine, phenylenediamine and mixtures thereof. More preferably, the diamines are selected from the group consisting of or consisting of hexamethylenediamine, dodecamethylenediamine and mixtures thereof.

The amino acids may for example be alpha-omega amino acids. Preferably, the amino acids are selected from the group consisting of or consisting of aminocaproic acid, amino-7-heptanoic acid, amino-11-undecanoic acid, n-heptyl-11-aminoundecanoic acid, amino-12-dodecanoic acid and mixtures thereof. Preferably, the amino acids are selected from the group consisting of or consisting of aminocaproic acid, amino-12-dodecanoic acid and mixtures thereof.

As an example of a lactone, mention may be made of caprolactone, valerolactone and butyrolactone.

Whatever the nature of the monomers of the polyamide that can be used in the context of the present invention, it is advantageous for the number-average molecular weight (Mn) to be in a range from 4,000 to 1,000,000 g / mol, preferably from 6,000 to 500,000 g / mol.

The number average molecular weight (Mn) of the TP is determined in a known manner, by size exclusion chromatography (SEC). For example, in the case of polyamides, the sample is first solubilized in hexafluoro-2-propanol supplemented with 0.02M sodium trifluoroacetate at a concentration of approximately 2 g / l. The apparatus used is a "WATERS alliance" chromatographic chain. The elution solvent is hexafluoro-2-propanol supplemented with 0.02M sodium trifluoroacetate, the flow rate 0.5 ml / min, the system temperature 35 ° C. A set of three PHENOMENEX columns is used in series, with the trade names "Phenogel"("ΙΟμιη 10 ⁵ ", "ΙΟμιη 10 ⁴ " and "ΙΟμιη 10 ³ "). The injected volume of the solution of the polymer sample is 100 μΙ. The detector is a "WATERS 2410" differential refractometer and its associated software for the exploitation of chromatographic data is the "WATERS MILLENIUM" system. The average molar masses calculated are relating to a calibration curve made with PMMA standards. The conditions are adaptable by those skilled in the art.

Advantageously, the melting temperature of the polyamide whose melting temperature is below 170 ° C. is less than 165 ° C., preferably less than 160 ° C., preferably between 100 and 160 ° C., preferably between 120 and 160 ° C. ° C.

The polyamides that can be used in the context of the present invention can be synthesized in a manner well known to those skilled in the art, for example according to the processes described in the documents DE 2324160, EP 0 627 454, EP 1 153 957 or else EP 1 153 957.

The polyamides that can be used in the context of the present invention are also commercially available. By way of example of a polyamide whose melting point is less than 170 ° C. available commercially, mention may be made of Orgasol 3401 or Orgasol 3402 from Arkema, or the polyamides from the Elvamide series (brand filed) of DuPont, such as Elvamide (registered trademark) 8061, 8063, 8066, and 8023R.

The amount of polyamide whose melting temperature is lower than 170 ° C. in the composition of the tread of the tire according to the invention may be in a range from 10 to 100 phr. Preferably, the level of polyamide whose melting point is less than 170 ° C. in the composition is within a range of from 20 to 80 phr, preferably from 25 to 50 phr. ll-A-4 Crosslinking System

 The crosslinking system of the composition of the tread of the tire according to the invention may be based on molecular sulfur and / or sulfur and / or peroxide donors, which are well known to those skilled in the art. The crosslinking system is preferably a sulfur-based vulcanization system (molecular sulfur and / or sulfur donor agent).

Sulfur is used at a preferred level of between 1 and 10 phr, preferably between 1 and 5 phr, more preferably between 1 and 3 phr.

The composition of the tread of the tire according to the invention advantageously comprises a vulcanization accelerator, which is preferably selected from the group consisting of thiazole accelerators and their derivatives, sulfenamide, thiourea accelerators and their mixtures. Advantageously, the vulcanization accelerator is chosen from the group constituted by the disulphide of 2- mercaptobenzothiazyl (MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS), N-tert-butyl-2-benzothiazyl sulfenamide (TBBS), N -butyl-2-benzothiazylsulfenimide (TBSI), morpholine disulfide, N-morpholino-2-benzothiazylsulfenamide (MBS), dibutylthiourea (DBTU), and mixtures thereof.

The level of vulcanization accelerator is preferably in a range from 0.5 to 3 phr, preferably from 0.6 to 2.5 phr, more preferably from 0.7 to 2 phr. ll-A-5 Liquid plasticizer

 The tread composition of the tire according to the invention may optionally comprise from 0 to 80 phr of liquid plasticizer at 23 ° C. (or extension oil or plasticizing oil). Any plasticizer liquid at 23 ° C, whether aromatic or non-aromatic, known for its plasticizing properties vis-à-vis diene elastomers, is usable. At room temperature (23 ° C.), these plasticizers or these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the capacity to eventually take on the shape of their container) , in contrast in particular to hydrocarbon plasticizing resins which are inherently solid at room temperature.

Particularly suitable are liquid plasticizers at 23 ° C selected from the group consisting of or consisting of liquid diene polymers, polyolefinic oils, naphthenic oils, paraffinic oils, DAE oils, MES (Medium Extracted Solvates) oils, oils and the like. Treated Distillate Aromatic Extracts (TDAE), Residual Aromatic Extract oils (RAE), Treated Residual Aromatic Extract (TREE) oils, Residual Aromatic Extract oils (SRAE), mineral oils, vegetable oils, ethers plasticizers , ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures thereof.

Preferably, the plasticizer liquid at 23 ° C is selected from the group comprising or consisting of MES oils, TDAE oils, naphthenic oils, vegetable oils and mixtures of these mixtures of these plasticizers liquid at 23 ° C. More preferably, the liquid plasticizer at 23 ° C is a vegetable oil, preferably a sunflower oil.

Preferably, the level of plasticizer liquid at 23 ° C in the composition of the tread of the tire according to the invention is preferably in a range from 5 to 70 phr, preferably from 10 to 60 phr. ll-A-6 Plasticizing resin

The tread composition of the tire according to the invention may also optionally comprise from 0 to 90 phr of hydrocarbon resin (or plasticizing resin) having a glass transition temperature greater than 20 ° C.

The term "resin" is hereby reserved, by definition known to those skilled in the art, to a compound that is solid at room temperature (23 ° C), as opposed to a liquid plasticizer such as an oil.

Hydrocarbon resins are polymers well known to those skilled in the art, essentially based on carbon and hydrogen but may include other types of atoms, used in particular as plasticizers or tackifying agents in polymeric matrices. They are inherently miscible (i.e., compatible) with the levels used with the polymer compositions for which they are intended, so as to act as true diluents. They have been described, for example, in the book "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), chapter 5 of which is devoted their applications, in particular pneumatic rubber (5.5 "Rubber Tires and Mechanical Goods"). They can be aliphatic, cycloaliphatic, aromatic, hydrogenated aromatic, aliphatic / aromatic type that is to say based on aliphatic and / or aromatic monomers. They may be natural or synthetic, whether or not based on petroleum (if so, also known as petroleum resins). Their Tg is preferably greater than 20 ° C (most often between 30 ° C and 95 ° C).

In a known manner, these hydrocarbon resins can also be described as thermoplastic resins in that they soften by heating and can thus be molded. They can also be defined by a point or softening point (in English, "softening point"). The softening temperature of a hydrocarbon resin is generally about 50 to 60 ° C. higher than its Tg value. The softening point is measured according to ISO 4625 ("Ring and Bail" method).

According to the invention, the hydrocarbon resin may be chosen from the group consisting of or consisting of homopolymer or copolymer resins of cyclopentadiene (abbreviated to CPD), homopolymer or copolymer resins of dicyclopentadiene (abbreviated to DCPD), resins of terpene homopolymer or copolymer, C5 homopolymer or copolymer resins, homopolymer resins or C9 cutting copolymer, alpha-methyl-styrene homopolymer or copolymer resins and mixtures thereof. Preferably, the hydrocarbon resin is selected from the group consisting of or consisting of CPD / vinylaromatic (D) copolymer resins, (D) CPD / terpene copolymer resins, terpene phenol copolymer resins, copolymer resins (D) and the like. ) CPD / C5 cut, (D) CPD / C9 cut copolymer resins, terpene / vinylaromatic copolymer resins, terpene / phenol copolymer resins, C5 / vinylaromatic cut copolymer resins, and mixtures thereof.

The term "terpene" includes, in a known manner, the alpha-pinene, beta- pinene and limonene monomers; preferably, a limonene monomer is used which is present in a known manner in the form of three possible isomers: L-limonene (laevorotatory enantiomer), D-limonene (dextrorotatory enantiomer), or the dipentene, racemic of the dextrorotatory and levorotatory enantiomers. . Suitable vinylaromatic monomers are, for example, styrene, alpha-methylstyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, vinyl-toluene, para-tertiarybutylstyrene, methoxystyrenes, chlorostyrenes, hydroxysty reins, vinylmesitylene, divinylbenzene, vinylnaphthalene, any vinylaromatic monomer derived from a C ₉ (or more generally from a C ₈ to Ci _0). More particularly, mention may be made of hydrocarbon resins chosen from the group consisting of (D) CPD homopolymer resins, (D) CPD / styrene copolymer resins, polylimonene resins, limonene / styrene copolymer resins, Limonene / D (CPD) copolymer resins, C5 / styrene cut copolymer resins, C5 / C9 cut copolymer resins, and mixtures of these resins.

All the above hydrocarbon resins are well known to those skilled in the art and commercially available, for example sold by the company DRT under the name "Dercolyte" for polylimonene resins, by the company Neville Chemical Company under the name " Super Nevtac ", by Kolon under the name" Hikorez "or by the company Exxon Mobil under the name" Escorez "with regard to the C ₅ / styrene resins or C ₅ / C ₉ cut resin resins or by the Struktol company under denomination "40 MS" or "40 NS" (mixtures of aromatic and / or aliphatic resins).

Preferably, the level of hydrocarbon resin having a glass transition temperature of greater than 20 ° C. in the tread composition of the tire according to the invention is in a range from 10 to 85 phr, preferably from to 80 pce. ll-A-7 Miscellaneous Additives

 The rubber compositions of the tread of the tire according to the invention may also comprise all or part of the usual additives known to those skilled in the art and usually used in tire rubber compositions, in particular tire strips. tire bearings, such as, for example, fillers other than those mentioned above, pigments, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing resins (as described for example in the application WO 02/10269). ll-B Preparation process

 The present invention also relates to a method for preparing a tread composition for the manufacture of tires according to the invention, characterized in that it comprises the following steps:

 a) contacting and mixing, concomitantly or sequentially, in one or more times, at least one diene elastomer, one or more reinforcing fillers, and a polyamide (whose melting point is preferably less than 170 ° C.) by thermomechanically kneading the whole until a maximum temperature T 1 is reached that is greater than or equal to the melting temperature of the polyamide (the melting point of which is preferably less than 170 ° C.), b) decreasing the temperature of the mixture obtained at step (a) up to a maximum temperature T2 below the melting point of the polyamide (the melting point of which is preferably below 170 ° C.), then incorporating into the mixture a crosslinking system and kneading the whole.

The process according to the invention can be carried out using two successive preparation phases according to a general procedure well known to those skilled in the art: step (a) then constitutes a first phase of work or thermo-mechanical mixing (sometimes qualified of "non-productive" phase) at high temperature, up to a maximum temperature of between 130 ° C and 190 ° C, preferably between 140 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes described as "productive" phase) (step (b) of the process according to the invention) at a lower temperature, typically below 110 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system. Such phases have been described for example in the applications EP 0 501 227 A, EP 0 735 088 A, EP 0 810 258 A, WO 2000/05300 or WO 2000/05301.

The first (non-productive) phase can be carried out preferentially in several thermomechanical steps. In a first step, a diene elastomer, one or more, is introduced into a suitable mixer such as a conventional internal mixer. several reinforcing filler (s), a polyamide whose melting temperature is below 170 ° C, optionally plasticizers such as liquid plasticizers at 23 ° C and / or resins whose glass transition temperature is greater than 20 ° C (and optionally the coupling agents and / or other ingredients with the exception of the crosslinking system), at a temperature between 20 ° C and 100 ° C and preferably between 25 ° C and 100 ° C ° C. After a few minutes, preferably from 0.5 to 2 min and a rise in temperature to 90 ° C to 100 ° C, the other ingredients (ie, those that remain if all were not put initially) can be added at one time or in parts, except for the crosslinking system during mixing ranging from 20 seconds to a few minutes. The total mixing time in this non-productive phase is preferably between 2 and 10 minutes at a temperature of less than or equal to 180 ° C., and preferably less than or equal to 170 ° C.

After cooling the mixture thus obtained, then incorporating the crosslinking system, preferably the vulcanization system, at low temperature (typically below 100 ° C), 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 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 the manufacture of semi-finished products. finished in order to obtain products such as a tire tread. These products can then be used for the manufacture of tires, according to the techniques known to those skilled in the art.

The crosslinking (or baking) 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 min depending in particular on the cooking temperature of the crosslinking system adopted, the kinetics of crosslinking of the composition considered

The polyamide (whose melting temperature is preferably less than 170 ° C.) can be introduced in the solid state, as sold commercially, or in the liquid state. When the polyamide (whose melting temperature is preferably less than 170 ° C.) is introduced in liquid form, it is then necessary to carry out a complementary step of heating the polyamide to a temperature above its melting point, before be brought into contact with the other constituents of step (a). However, it is preferable to introduce the polyamide (the melting point of which is preferably less than 170 ° C.) in the solid state. According to the invention, the maximum temperature T1 is preferably at least 1 ° C, preferably 2 ° C, preferably 3 ° C, preferably 4 ° C, preferably 5 ° C higher than the temperature of the polyamide ( whose melting point is preferably below 170 ° C). Preferably, the maximum temperature T1 is 5 to 20 ° C higher than the temperature of polyamide (whose melting point is preferably less than 170 ° C).

According to the invention, the maximum temperature T 2 is preferably less than 120 ° C, preferably less than 100 ° C, more preferably less than 90 ° C. Preferably, the maximum temperature T2 is in a range from 20 to 90 ° C.

II-B-1 Diene Elastomer

 The diene elastomer of the process according to the invention is as defined above for the composition of the tread of the tire according to the invention.

Thus, preferably, the diene elastomer is preferably chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (abbreviated "BR"), synthetic polyisoprenes (IR), natural rubber (NR), 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.

Advantageously, the diene elastomer is mainly composed of styrene-butadiene copolymer (abbreviated to SBR), this SBR possibly being an emulsion or ESBR (that is to say prepared by emulsion polymerization), an SBR solution or SSBR (c). that is, prepared by solution polymerization), or a mixture of both.

Amongst the copolymers based on styrene and butadiene, in particular SBR, mention may be made especially of those having a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (mol%). in -1,2-bonds of the butadiene part of between 4% and 75%, a content (mol%) of trans-1,4 bonds of between 10% and 80%.

Preferably, the Tg of the copolymer based on styrene and butadiene, in particular SBR (ESBR or SSBR), is between 0 and -80 ° C., more particularly between 0 ° C. and 70 ° C; according to a particular embodiment, the Tg is between -5 ° C and -60 ° C, especially in a range of -10 ° C to -50 ° C. The person skilled in the art knows how to modify the microstructure of a copolymer based on styrene and butadiene, in particular on an SBR, to increase and adjust its Tg, in particular by modifying the styrene contents in -1-bonds. 2 or in trans-1,4 bonds of the butadiene part.

To the above styrene-butadiene copolymer may be optionally combined at least a second diene elastomer, different from said copolymer, said second diene elastomer, optional, being introduced during the process according to the invention at a weight ratio which is accordingly at most equal to 50 phr, preferably at most equal to 40 phr, in particular at most equal to 30 phr (as a reminder, pce signifying parts by weight per hundred parts of elastomer, that is to say of the total of elastomers present in the tread). Preferably, when a second diene elastomer is used, it is introduced during the process according to the invention at a rate in a range from 10 to 30 phr.

This second optional diene elastomer is preferably chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR) and butadiene copolymers (other than copolymers based on styrene and butadiene). ), isoprene copolymers and mixtures of these elastomers.

Advantageously, the second elastomer is an isoprene elastomer. By "isoprene elastomer" is meant in known manner a homopolymer or copolymer of isoprene, in other words an isoprene elastomer chosen from the group comprising or consisting of natural rubber (NR), which can be plasticized or peptized, the 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 NR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene ( SBIR).

The isoprene elastomer is preferably selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof. Among these synthetic polyisoprenes, polyisoprenes having a level (mol%) of 1,4-cis bonds greater than 90%, more preferably still greater than 98%, are preferably used. More preferably, the diene elastomer is natural rubber.

Preferably, the diene elastomer, the styrene-butadiene copolymer preference, is introduced during the process according to the invention at a level in a range from 50 to 100 phr, more preferably from 60 to 100 phr, more preferably preferably from 70 to 100 phr, more preferably still from 80 to 100 phr and very preferably from 90 to 100 phr. In particular, the diene elastomer, preferably the styrene-butadiene copolymer, is very preferably introduced during the process according to the invention at a level of 100 phr. ll-B-2 Reinforcing Filler

 The reinforcing filler of the process according to the invention is as defined above for the composition of the tread of the tire according to the invention. Thus, preferably, the reinforcing filler is introduced during the process according to the invention at a level in a range from 5 to 150 phr, preferably from 10 to 80 phr, more preferably from 15 to 75 phr.

The reinforcing filler advantageously comprises or consists of carbon black, a reinforcing inorganic filler or mixtures thereof.

The reinforcing filler is advantageously mainly composed of carbon black. The reinforcing filler may comprise, for example, from 50 to 100% by weight of carbon black, preferably from 55 to 90% by weight, preferably from 60 to 80% by weight. Particularly advantageously, the reinforcing filler comprises exclusively carbon black. The reinforcing filler may also further comprise a reinforcing inorganic filler. Preferably, the reinforcing inorganic filler is silica. When carbon black is used (predominantly or exclusively, as a reinforcing filler), the carbon black is preferably introduced during the process according to the invention at a rate in a range from 10 to 80 phr, preferably from 15 to 75 phr. Preferably, the BET specific surface area of the carbon black is in a range from 70 to 150 m ² / g, preferably from 100 to 120 m ² / g.

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 Rhodia, the silica "Hi-Sil" EZ150G from 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 03/016387.

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 according to 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 known manner, thanks to to improve the dispersion of the filler in the rubber matrix and to lower the viscosity of the compositions, to improve their ability to use 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 such as stearic acid. ll-B-3 Polyamide

The polyamide (whose melting point is preferably less than 170 ° C.) of the process according to the invention is advantageously as defined above for the composition of the tread of the tire according to the invention. Thus, any polyamide (whose melting point is preferably less than 170 ° C.) can be used.

The polyamides used in the context of the present invention may be homopolymers or copolymers which may come from the condensation of lactams, optionally with lactones, and / or condensation of diacids and / or amino acids with diamines. Preferably, the polyamides used in the context of the present invention are copolymers derived from the condensation of lactams, optionally with lactones, and / or the condensation of diacids and / or amino acids with diamines.

Particularly advantageously, the polyamide (whose melting temperature is preferably less than 170 ° C.) is a copolymer polyamide consisting of at least two different types of monomers chosen from the group consisting of lactams, or at least two different types of monomers selected from the group consisting of diacids and at least two different types of monomers selected from the group consisting of diamines.

The lactams may for example have 3 to 12 carbon atoms on their main cycle and may be substituted. Preferably, the lactams are chosen from the group comprising or consisting of β, β-dimethylpropylactam, α, adimethylpropylactam, amylolactam, caprolactam, capryllactam, oenantholactam, 2-pyrrolidone, lauryllactam and mixtures thereof. . More preferably, the lactams are selected from the group consisting of or consisting of caprolactam, lauryllactam and mixtures thereof.

The diacids (or dicarboxylic acid) can be for example acids having between 4 18 carbon atoms. Preferably, the diacids are selected from the group consisting of or consisting of adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid, 1,4-acid. cyclohexyldicarboxylic acid, terephthalic acid, sodium or lithium salt of sulphoisophthalic acid, dodecanedioic acid and mixtures thereof. More preferably, the diacids are selected from the group consisting of or consisting of adipic acid, dodecanedioic acid and mixtures thereof.

The diamines may be, for example, saturated aliphatic, aryl and / or cyclic diamines having 6 to 12 atoms. Preferably, the diamines are chosen from the group comprising or consisting of hexamethylenediamine, piperazine, tetramethylene diamine, octamethylene diamine, decamethylene diamine, dodecamethylenediamine, 1,5 diaminohexane, 2,2,4 -trimethyl-l, 6-diamino-hexane, diamine polyols, isophorone diamine (IPD), methyl pentamethylenediamine (MPDM), bis (aminocyclohexyl) methane (BACM), bis (3-methyl-4-aminocyclohexyl) methane (BMACM), methaxylyenediamine, bisphenol aminocyclohexylmethane, trimethylhexamethylenediamine, phenylenediamine and mixtures thereof. More preferably, the diamines are selected from the group consisting of or consisting of hexamethylenediamine, dodecamethylenediamine and mixtures thereof.

The amino acids may for example be alpha-omega amino acids. Preferably, the amino acids are selected from the group consisting of or consisting of aminocaproic acid, amino-7-heptanoic acid, amino-11-undecanoic acid, n-heptyl-11-aminoundecanoic acid, amino-12-dodecanoic acid and mixtures thereof. Preferably, the amino acids are selected from the group consisting of or consisting of aminocaproic acid, amino-12-dodecanoic acid and mixtures thereof. As an example of a lactone, mention may be made of caprolactone, valerolactone and butyrolactone.

Whatever the nature of the monomers of the polyamide that can be used in the context of the present invention, it is advantageous for the number-average molecular weight (Mn) to be in a range from 4,000 to 1,000,000 g / mol, preferably from 6,000 to 500,000 g / mol.

The number average molecular weight (Mn) of the TP is determined in a known manner, by size exclusion chromatography (SEC). For example, in the case of polyamides, the sample is first solubilized in hexafluoro-2-propanol supplemented with 0.02M sodium trifluoroacetate at a concentration of approximately 2 g / l. The apparatus used is a "WATERS alliance" chromatographic chain. The elution solvent is hexafluoro-2-propanol supplemented with 0.02M sodium trifluoroacetate, the flow rate 0.5 ml / min, the system temperature 35 ° C. A set of three PHENOMENEX columns is used in series, with the trade names "Phenogel"("ΙΟμιη 10 ⁵ ", "ΙΟμιη 10 ⁴ " and "ΙΟμιη 10 ³ "). The injected volume of the solution of the polymer sample is 100 μΙ. The detector is a "WATERS 2410" differential refractometer and its associated software for the exploitation of chromatographic data is the "WATERS MILLENIUM" system. The calculated average molar masses relate to a calibration curve made with PMMA standards. The conditions are adaptable by those skilled in the art.

Advantageously, the melting temperature of the polyamide (whose melting point is preferably less than 170 ° C.) is between 100 and 160 ° C., preferably between 120 and 160 ° C. The polyamide (whose melting temperature is preferably less than 170 ° C.) may be introduced during the process according to the invention at a level in the range from 10 to 100 phr. Preferably, the polyamide (whose melting temperature is preferably less than 170 ° C.) introduced during the process according to the invention at a level ranging from 20 to 80 phr, preferably from 25 to 50 phr.

II-B-4 Crosslinking system

 The crosslinking system of the process according to the invention is as defined above for the composition of the tread of the tire according to the invention.

Thus, the system for crosslinking the composition of the tread of the tire according to the invention may be based on molecular sulfur and / or sulfur and / or peroxide donors, which are well known to those skilled in the art.

The crosslinking system is preferably a sulfur-based vulcanization system (molecular sulfur and / or sulfur donor agent).

Sulfur is introduced during the process according to the invention at a preferred level of between 1 and 10 phr, preferably between 1 and 5 phr, more preferably between 1 and 3 phr.

The composition of the tread of the tire according to the invention advantageously comprises a vulcanization accelerator, which is preferably selected from the group consisting of thiazole accelerators and their derivatives, sulfenamide, thiourea accelerators and their mixtures. Advantageously, the vulcanization accelerator is selected from the group consisting of 2-mercaptobenzothiazyl disulfide (MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS). ), N-tert-butyl-2-benzothiazylsulfenamide (TBBS), N-tert-butyl-2-benzothiazylsulphenide (TBSI), morpholine disulfide, N-morpholino-2-benzothiazylsulphenamide (MBS), dibutylthiourea (DBTU), and mixtures thereof.

The vulcanization accelerator is preferably introduced during the process according to the invention at a level in the range of 0.5 to 3 phr, preferably 0.6 to 2.5 phr, more preferably 0, 7 to 2 pce.

II-B-5 Liquid plasticizer

The process according to the invention may comprise a step of incorporating liquid plasticizer at 23 ° C., but this is not mandatory. Thus, the method according to the invention can not include liquid plasticizer incorporation step at 23 ° C. If the process according to the invention comprises a step of incorporating liquid plasticizer at 23 ° C., the liquid plasticizer at 23 ° C. is introduced during the process according to the invention at a rate advantageously less than 80 phr, preferably included. in a range from 5 to 70 phr, preferably from 10 to 60 phr.

The plasticizer liquid at 23 ° C of the process according to the invention is as defined above for the composition of the tread of the tire according to the invention. Thus, any liquid plasticizer at 23 ° C, whether aromatic or non-aromatic, known for its plasticizing properties vis-à-vis diene elastomers, is usable. At room temperature (23 ° C.), these plasticizers or these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the capacity to eventually take on the shape of their container) , in contrast in particular to hydrocarbon plasticizing resins which are inherently solid at room temperature.

Particularly suitable are liquid plasticizers at 23 ° C selected from the group consisting of or consisting of liquid diene polymers, polyolefinic oils, naphthenic oils, paraffinic oils, DAE oils, MES (Medium Extracted Solvates) oils, oils and the like. Treated Distillate Aromatic Extracts (TDAE), Residual Aromatic Extract oils (RAE), Treated Residual Aromatic Extract (TREE) oils, Residual Aromatic Extract oils (SRAE), mineral oils, vegetable oils, ethers plasticizers , ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures thereof.

Preferably, the plasticizer liquid at 23 ° C is selected from the group comprising or consisting of MES oils, TDAE oils, naphthenic oils, vegetable oils and mixtures of these mixtures of these plasticizers liquid at 23 ° C. More preferably, the liquid plasticizer at 23 ° C is a vegetable oil, preferably a sunflower oil.

II-B-6 Plasticizing resin

The process according to the invention may comprise a step of incorporation of hydrocarbon resin having a glass transition temperature greater than 20 ° C but this is not mandatory. Thus, the process according to the invention may not comprise a stage of incorporation of hydrocarbon resin having a glass transition temperature greater than 20 ° C. If the process according to the invention comprises a step of incorporating hydrocarbon resin having a glass transition temperature greater than 20 ° C., the hydrocarbon resin having a glass transition temperature greater than 20 ° C. is incorporated during the process according to the invention. 'invention at a rate advantageously less than 90 phr, preferably within a range of from 10 to 85 phr, preferably from 15 to 80 phr.

The hydrocarbon resin having a glass transition temperature greater than 20 ° C of the process according to the invention is as defined above for the composition of the tread of the tire according to the invention.

Thus, the hydrocarbon resin may be chosen from the group comprising or consisting of cyclopentadiene homopolymer or copolymer resins (abbreviated to CPD), dicyclopentadiene homopolymer or copolymer resins (abbreviated to DCPD), homopolymer resins or terpene copolymer, homopolymer or C5 cut copolymer resins, homopolymer or C9 cut copolymer resins, alpha-methyl-styrene homopolymer or copolymer resins, and mixtures thereof. Preferably, the hydrocarbon resin is selected from the group consisting of or consisting of CPD / vinylaromatic (D) copolymer resins, (D) CPD / terpene copolymer resins, terpene phenol copolymer resins, copolymer resins (D) and the like. ) CPD / C5 cut, (D) CPD / C9 cut copolymer resins, terpene / vinylaromatic copolymer resins, terpene / phenol copolymer resins, C5 / vinylaromatic cut copolymer resins, and mixtures thereof.

More particularly, mention may be made of hydrocarbon resins chosen from the group consisting of (D) CPD homopolymer resins, (D) CPD / styrene copolymer resins, polylimonene resins, limonene / styrene copolymer resins, Limonene / D (CPD) copolymer resins, C5 / styrene cut copolymer resins, C5 / C9 cut copolymer resins, and mixtures of these resins.

II-B-7 Miscellaneous Additives

 The method according to the invention may comprise a step of incorporating usual additives usually used in tire elastomer compositions, such as, for example, fillers other than those mentioned above, pigments, protective agents such as anti-corrosion waxes, ozone, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing resins (as described for example in the application WO 02/10269). II-C Composition obtainable by the process according to the invention, tread for tires and tires

The present invention also relates to a rubber composition that can be obtained by a method according to the invention. Also described herein is a tire tread comprising a composition obtainable by the method of the invention.

It also relates to a tire whose tread comprises a composition that can be obtained by the method according to the invention.

III- EXAMPLES

l l l-l Measurements and tests used

Dynamic properties:

The dynamic properties G * are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized composition (ie cooked to a conversion of at least 90%) is recorded (cylindrical specimen 2 mm thick and 78.5 mm ² section) subjected to alternating single shear sinusoidal stress at the frequency of 10 Hz. A temperature sweep of -80 to 200 ° C is carried out at a constant temperature rise rate of + 1.5 ° C / min at shear stress. peak-peak imposed 0.7M Pa. The specimen is biased in sinusoidal shear at 10 Hz, symmetrically around its equilibrium position. The exploited results are high temperature dissipation and low temperature dissipation.

The exploited results are high temperature dissipation and low temperature dissipation.

The high temperature dissipation is represented by the area under the curve of TanD = f (temperature) from 120 ° C to 160 ° C at a stress of 0.7M Pa corrected by the stiffness G * at each point. Performance is improved when the value of this descriptor increases.

The low temperature dissipation is represented by the area under the curve of TanD = f (temperature) from 20 ° C to 80 ° C at a stress of 0.7M Pa corrected by the stiffness G * at each point. Performance is improved when the value of this descriptor decreases

The results of high and low temperature dissipation are expressed in base 100, the value 100 being attributed to the control. A result greater than 100 indicates improved performance. For the high temperature dissipation, a result greater than 100 implies that the composition of the example under consideration has an improvement in the braking performance under severe conditions. For the low temperature dissipation, a result greater than 100 implies that the composition of the example considered is less hysteretic, translating a lower rolling resistance of the tread comprising such a composition.

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 vessel temperature of which is approximately 140 ° C., in succession the elastomer diene, the reinforcing filler, the polyamide and the 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 is incorporated and the vulcanization accelerator, 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.

The samples thus produced were baked for 20 minutes at 170 ° C. in a bell press. The samples were analyzed after cooling for 24 hours at room temperature. 111-3 Rubber Testing

The examples presented in Table 1 are intended to compare the high and low temperature dissipations of compositions according to the invention (C1 to C4) with a control composition T1 which differs from the compositions according to the present invention in that it does not comprise polyamide, and a control composition T2 which differs from the compositions according to the present invention in that it comprises a polyamide whose melting point is greater than 170 ° C. Table 1

 (1) Styrene-butadiene copolymer with 15.5% styrene unit (Tg -65 ° C)

 (2) Natural rubber

 (3) Polyamide "Orgasol 3401" (Arkema company) - Tf = 140 ° C.

 (4) Polyamide "BMNO - PA11" (Arkema company) - Tf = 189 ° C.

 (5) ASTM N234 grade carbon black (Cabot company)

 (6) Zinc oxide (industrial grade - Umicore company)

 (7) Stearin 'Pristerene 4931' (Uniqema company)

 (8) "Santocure CBS" accelerator (Solutia company)

These results show that the compositions in accordance with the invention all make it possible to improve the dissipation at high temperature and at low temperature, at different incorporation levels of the polyamide and for different types of diene elastomer. The compositions according to the invention thus make it possible to improve both the braking properties in severe conditions and the rolling resistance of the tires. On the other hand, the use of a polyamide whose melting temperature is greater than 170 ° C. (T2 not in accordance with the invention) negatively impacts the high temperature dissipation.

Claims

Tire whose tread comprises a rubber composition based on at least:  a diene elastomer,  a reinforcing filler,  a polyamide whose melting point is less than 170 ° C., and a crosslinking system, wherein the diene elastomer is predominantly styrene butadiene copolymer. A tire according to any one of the preceding claims wherein the reinforcing filler comprises carbon black, a reinforcing inorganic filler or mixtures thereof. Tire according to any one of the preceding claims, in which the reinforcing filler predominantly consists of carbon black. Tire according to any one of the preceding claims, in which the level of reinforcing filler in the composition is in a range from 5 to 150 phr, preferably from 10 to 80 phr. Tire according to any one of the preceding claims, in which the level of polyamide whose melting temperature is less than 170 ° C. in the composition is in a range from 10 to 100 phr, preferably from 20 to 80 phr. A tire according to any one of the preceding claims wherein the polyamide having a melting point of less than 170 ° C is a copolymer polyamide of at least two different types of monomers selected from the group consisting of lactams, or d at least two different types of monomers selected from the group consisting of diacids and at least two different types of monomers selected from the group consisting of diamines. Tire according to Claim 6, in which the lactams are chosen from the group consisting of β, β-dimethylpropriolactam, α, adimethylpropylactam, amylolactam, caprolactam, capryllactam, oenantholactam, 2-pyrrolidone and lauryllactam. and their mixtures. A tire according to claim 6 or 7, wherein the diacids are selected from the group consisting of adipic acid, sebacic acid, azelaic acid, suberic acid, isophthalic acid, butanedioic acid. 1,4-cyclohexyldicarboxylic acid, terephthalic acid, sodium or lithium salt of sulphoisophthalic acid, dodecanedioic acid and mixtures thereof. A tire according to any of claims 6 to 8, wherein the diamines are selected from the group consisting of hexamethylenediamine, piperazine, tetramethylene diamine, octamethylene diamine, decamethylene diamine, dodecamethylene diamine, 1,5 diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, isophorone diamine (IPD), methyl pentamethylenediamine (MPDM), bis (aminocyclohexyl) methane (BACM) , bis (3-methyl-4-aminocyclohexyl) methane (BMACM), methaxylyenediamine, bis-p-aminocyclohexylmethane, trimethylhexamethylenediamine, phenylenediamine and mixtures thereof 10. A tire according to any one of the preceding claims, wherein the melting temperature of the polyamide whose melting temperature is less than 170 ° C is between 100 and 160 ° C, preferably between 120 and 160 ° C. 160 ° C. 11. A tire according to any one of the preceding claims, wherein the crosslinking system is based on molecular sulfur and / or sulfur donor agent. Tire according to any one of the preceding claims, wherein the composition of the tread optionally comprises 0 to 80 phr of liquid plasticizer at 23 ° C. 13. A tire according to claim 14, wherein the level of plasticizer liquid at 23 ° C in the composition is in a range from 5 to 70 phr, preferably from 10 to 60 phr. A tire according to claim 14 or 15, wherein the liquid plasticizer at 23 ° C is selected from the group consisting of liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE oils, oils, and the like. MES, TDAE oils, RAE oils, TREE oils, SRAE oils, mineral oils, vegetable oils, ethers plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures thereof. 15. A tire according to any one of the preceding claims, wherein the composition of the tread optionally comprises 0 to 90 phr of hydrocarbon resin having a glass transition temperature greater than 20 ° C. 16. A tire according to claim 15, wherein the content of hydrocarbon resin having a glass transition temperature greater than 20 ° C in the composition is in a range from 10 to 85 phr, preferably from 15 to 80 phr. A tire according to claim 15 or 16, wherein the hydrocarbon resin having a glass transition temperature of greater than 20 ° C is selected from the group consisting of cyclopentadiene homopolymer or copolymer resins, homopolymer or copolymer resins of dicyclopentadiene, terpene homopolymer or copolymer resins, C ₅ homopolymer or copolymer cut resins, C ₉ homopolymer or copolymer resins, alpha-methyl-homopolymer or copolymer resins, styrene and mixtures thereof 18. Process for the preparation of a tread composition for the manufacture of tires according to any one of the preceding claims, characterized in that it comprises the following steps:  a) contacting and mixing, concomitantly or sequentially, in one or more times, at least one diene elastomer, one or more reinforcing fillers, and a polyamide whose melting point is less than 170 ° C., by thermomechanically kneading the whole until reaching a maximum temperature Tl greater than or equal to the melting temperature of the polyamide whose melting temperature is less than 170 ° C, b) lowering the temperature of the mixture obtained in step (a) to a maximum temperature T2 lower than the melting temperature of the polyamide whose melting point is less than 170 ° C., and then incorporating into the mixture a system of crosslinking and kneading the whole, wherein the at least one diene elastomer is predominantly made of styrene butadiene copolymer. 19. The method of claim 18, wherein the polyamide whose melting temperature is less than 170 ° C introduced in the solid state. 20. The method of claim 18 or 19, wherein the maximum temperature T1 is 5 to 20 ° C higher than the temperature of polyamide whose melting temperature is less than 170 ° C. 21. A process according to any one of claims 18 to 20, wherein the maximum temperature T2 is less than 120 ° C, preferably less than 100 ° C. 22. A rubber composition obtainable by the process according to any one of claims 18 to 21.