Rubber composition for the thread cap of a pneumatic tyre

Translation of description of equivalent WO 2004013221 A1

rubber composition for tire tread:

The present invention relates to a crosslinkable or crosslinked rubber composition which is usable for constituting a tire tread having improved wear resistance, such a tread and a tire incorporating this tread. The invention applies in particular to tourism type of tire covers.

Since fuel economies and the need to preserve the environment have become a priority, it is desirable to produce mixtures having good mechanical properties and as low a hysteresis as possible in order to implement them as compositions of rubber used for making various semi-finished products used in the composition of tires, such as treads, and to obtain tires having reduced rolling resistance.

Among the many proposed solutions to reduce the hysteresis of tread compositions and therefore the rolling resistance of tires comprising such compositions can be made, for example compositions described in patent US-A-4 550 142, US-A-5001196, EP-A-299 074 or EP-A-447 066.

It has also sought to improve the grip of the tires using tread rubber compositions incorporating specific plasticizers. The European patent EP-A-1028130 describes a rubber composition for a tire tread which is intended to improve the adhesion of incorporating tire. This rubber composition comprises a polymer resin obtained by copolymerization of dicyclopentadiene and limonene. The units resulting from the polymerization of limonene may be present either in minority or majority amount in this resin, as shown by the embodiments of this document in which the resins were obtained with mass fractions of 32% limonene to 68% dicyclopentadiene (examples 1-9) or 67% limonene to 33% dicyclopentadiene (example 10).

European patent EP-A-1063246, EP-A-1029873, EP-A-990 669 and EP Al 077 223 also disclose rubber compositions for a tire tread which is intended to improve Tyre adhesion to incorporating them. These rubber compositions each comprise a polymer resin obtained by copolymerization of four monomers consisting of dicyclopentadiene or dimethyl dicyclopentadiene, limonene, a polycyclic aromatic hydrocarbon (indene) and a monocyclic aromatic hydrocarbon (alkyl styrene or vinyl toluene) . In all Embodiments of each of these documents, the respective mass fractions of the four aforementioned monomers are either 25%, 25%, 25%, 25%, or 12.5%, 37.5%, 25%, 25%.

In addition to the rolling resistance reduction and the improvement of adhesion, it is also desirable to improve the wear resistance of tire treads and therefore to increase the life of recent (this resistance has also improved wear to reduce over time the ground debris due to tire rolling and the amount of waste tires that are destined for recycling, which helps to preserve the environment).

Relatively few solutions have been proposed to date to improve the wear resistance. One can for example quote the compositions described in patent documents JP-A-61 238501, EP-A-502 728 or EP-A-501227.

Now it is well known to the skilled person that improvement of performance for tires is often achieved at the expense of other performance. By way of example, mention may be made using polymers in amorphous or semi-crystalline tread compositions having a glass transition temperature (Tg) or melting temperature and a reduced molecular weight, use has the effect of improve grip on dry or damp corresponding tire but also penalize their wear resistance.

The object of the present invention is to provide a crosslinkable or crosslinked rubber composition which is usable for constituting a tire tread having improved wear resistance, and it is achieved in that the Applicants just discover surprisingly that a plasticizing resin of average molecular weight ranging from 400 to 2000 g / mol and a glass transition temperature above 50 ° C and below 120 ° C which comprises, in a mass fraction ranging from 70% to 100%, units derived from the polymerization of a monocyclic or bicyclic unsaturated teφène, gives a tire whose tread is formed of a rubber composition incorporating this resin, a resistance improved wear compared to that of known tires whose tread comprises process oil as plasticizer, while giving the casing of the invention a rolling resistance and grip on dry and wet soil that is near those of its known envelopes. Note that the plasticizing resin of the invention serves to confer improved endurance to the tire casing in its incoφorant the tread, to the extent that it improves the resistance of the tire to the separation of the plies of triangulation it has in its crown reinforcement.

Preferably, said resin has an average molecular weight ranging from 500 to 1000 g / mol and even more preferably, of from 550 to 700 g / mol.

Also preferably, said resin has a glass transition temperature ranging from 60 ° C to 100 ° C and, for still more preferably, from 65 ° C to 90 ° C. According to another preferred feature of the invention, said resin has a polydispersity index of less than 2.

According to another preferred feature of the invention, said resin comprises said units resulting from the polymerization of a monocyclic or bicyclic unsaturated teφène in a mass fraction ranging from 90% to 100%.

According to a first embodiment of the invention, said unsaturated teφène which is mostly or completely after the resin is an unsaturated monocyclic teφène, preferably a limonene (ie 1-methyl-4-isopropenyl cyclohexene) such as d-limonene (Enantiomer dextrorotatory) or dipentene (racemic enantiomers of Veer and Back limonene). In accordance with this first embodiment, the resin of the invention preferably has a glass transition temperature Tg ranging from 60 to 80 ° C and, for still more preferably, from 65 to 75 ° C.

According to a first exemplary embodiment according to the invention of this first embodiment, said resin further comprises one or more units derived from at least one hydrocarbon monomer or not is not a monocyclic unsaturated teφène and which may advantageously be a teφène unsaturated bicyclic such as α-pinene (ie 2,6,6-trimethylbicyclo [3.1.1] hept-2-ene), a monocyclic or polycyclic aromatic hydrocarbon such as styrene or an alkyl styrene, a cyclic diene such as dicyclopentadiene, a conjugated diene such as isoprene, acrylonitrile or methyl methacrylate.

Examples of such resins according to this first example include those sold by DRT under the name "Dercolyte L120" and by Arizona under the names "Sylvares TR7125" and "Sylvagum TR7125C" which include all units resulting from the polymerization of d-limonene or dipentene in a mass fraction of between 90% and

100%. In a second embodiment of the invention of this first embodiment, said resin is comprised of said units resulting from the homopolymerization of said unsaturated mono- teφène. Can advantageously be used a resin resulting in all of the homopolymerization of d-limonene or dipentene, preferably an average molecular weight of resin of from 550 g / mol to 650 g / mol and a glass transition temperature ranging from 60 ° C to 80 ° C.

Note that d-limonene is a natural extract (found naturally in the skin of oranges) and that, therefore, the plasticizing resin after the homopolymerization of this d-limonene is exclusively original natural, which helps to reduce pollution of the environment during rolling of tires whose treads incoφorent this resin.

According to a second embodiment of the invention, said unsaturated teφène which is mostly or completely after the resin is an unsaturated bicyclic teφène, preferably a α- pinene. According to this second embodiment, the resin of the invention preferably has a glass transition temperature Tg ranging from 80 to 100 ° C. According to a first exemplary embodiment according to the invention of this second embodiment, said resin further comprises a or more units derived from at least one hydrocarbon monomer or not which is not an unsaturated teφène bicyclic and which may advantageously be a monocyclic unsaturated teφène such as limonene or dipentene, or a monocyclic or polycyclic aromatic hydrocarbon such as styrene or an alkyl styrene. In a second embodiment of the invention of this second embodiment, said resin is comprised of said units resulting from the polymerization of said bicyclic unsaturated teφène.

According to a preferred feature of the invention, said rubber composition is based on one or more diene elastomers produced from each of at least one conjugated diene monomer having a molar ratio of units derived from conjugated dienes which is greater than 50%, and this composition comprises said resin in a mass fraction ranging from 5 to 45 phr, and in even more preferably in an amount ranging from 15 to 30 phr (phr: parts by weight per hundred parts of elastomer (s) diene ( s)).

According to an exemplary embodiment of the invention, said rubber composition comprises: - in an amount greater than 40 phr and up to 100 phr, one or more diene elastomers each having a glass transition temperature between -65 ° C and -10 ° C, and

- In an amount less than 60 phr and down to 0 phr, one or more diene elastomers each having a glass transition temperature between -110 ° C and -80 ° C. Said one or more diene elastomers, the glass transition temperature is between -65 ° C and -10 ° C belong to the group consisting of styrene-butadiene copolymers prepared in solution, of styrene and butadiene copolymers prepared in emulsion, natural polyisoprenes, synthetic polyisoprenes having a cis-1,4 linkage content greater than 95%, copolymers of butadiene and isoprene (BIR), styrene isoprene copolymers (SIR), of teφolymères styrene, butadiene, isoprene copolymers (SBIR) and a mixture of these elastomers.

Said at least one diene elastomer having a glass transition temperature is between -110 ° C and -80 ° C (preferably between -105 ° C and -90 ° C) comprises butadiene units in an amount equal or greater than 70% and is preferably made of a polybutadiene having a cis-1,4 linkage content greater than 90%.

According to a preferred embodiment of the invention, said rubber composition comprises as elastomer (s) diene (s) whose glass transition temperature is between -65 ° C and -10 ° C, at least a copolymer of styrene and butadiene prepared in solution having a glass transition temperature between -50 ° C and -15 ° C, or a copolymer of styrene and butadiene prepared in emulsion having a glass transition temperature of -65 ° C. and -30 ° C.

According to an exemplary embodiment of the invention, said rubber composition comprises said glass transition temperature of diene elastomers comprised between -65 ° C and - 10 ° C in an amount of 100 phr, for example a blend of several copolymers of styrene and butadiene prepared in solution.

According to an alternative embodiment of the invention, said rubber composition comprises a blend said elastomer glass transition temperature of the diene of between -65 ° C and -10 ° C with said one or more diene elastomers comprised of glass transition temperature between -110 ° C and -80 ° C.

According to a first embodiment of the invention of this embodiment, said composition comprises a blend of at least one of said polybutadienes having a cis-1,4 linkage content greater than 90% with at least one of said copolymers of styrene and butadiene prepared in solution. According to a second embodiment of the invention of this embodiment, said composition comprises a blend of at least one of said polybutadienes having a cis-1,4 linkage content greater than 90% with at least one of said copolymers of styrene and butadiene prepared in emulsion. According to a third embodiment according to the invention of this embodiment, said composition comprises a blend of at least one of said polybutadienes having a cis-1,4 linkage content greater than 90% with at least one of said polyisoprenes natural or synthetic.

As a copolymer of styrene and butadiene prepared in emulsion, can be advantageously used copolymers having an amount varying substantially emulsifier 1 pc to 3.5 pc, such as E-SBR copolymers comprising 1.7 pc respectively 1.2 pc emulsifier both of which are described in European patent EP-A-1173338 (see paragraph I. exemplary embodiments contained in the description of this application).

According to another characteristic of the invention, said rubber composition further comprises at least one plasticizing oil extracted paraffinic-type oil, aromatic or naphthenic in an amount of from 0 phr to 30 phr and preferably from 0 phr to 15 phr.

Advantageously, said rubber composition may be completely devoid of said plasticizing oil extracted from petroleum. Note that the improvement of the wear resistance conferred by the resin of the invention to the tire implies a reduction in the time of compression by compaction which is subject when driving the tread according to the invention and therefore, a reduction in the time of the loss in driving the plasticizing oil extracted from petroleum, such as aromatic oil. This results in even greater pollution of the environment during travel, which pollution is further minimized by the reduced amount or no oil that is initially present in the tread composition according to the invention.

According to an advantageous embodiment of the invention, said rubber composition further comprises, in an amount ranging from 10 pc to 40 pc, at least one plasticizing compound not extracted from natural or synthetic type of oil, which comprises at least one triester of glycerol fatty acid, so that the assembly constituted by said at least one fatty acid comprises oleic acid as a mass fraction equal to or greater than 60%.

This compound plasticizer of said glycerol fatty acid triester minimizes in the band of the tire tread incoφorant the one hand, the rolling exudation compression of the total plasticizer (including said resin and optionally said oil plasticizing extracted oil) and, on the other hand, migration of said plasticizer towards mixes adjacent to the tread, which results in compaction and curing also minimized for the tread and, therefore, by a conservation in time of the adhesion performance.

The composition according to the invention also comprises a reinforcing filler in an amount ranging from 50 to 150 phr.

According to another preferred feature of the invention, said reinforcing filler comprises a reinforcing inorganic filler in a weight fraction greater than 50%.

In this application, the term "reinforcing inorganic filler", in known manner, an inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also known as "white" filler or sometimes "clear filler "in contrast to carbon black, this inorganic filler being capable, on its own, without any other means than an intermediate coupling agent, a rubber composition for the manufacture of tires, in other words capable of replacing, in its reinforcing function, a conventional filler of carbon black tire-grade. Advantageously, the reinforcing inorganic filler is wholly or at least predominantly, silica (SiO 2). The silica used may be any reinforcing silica known to the skilled person, in particular any precipitated or pyrogenic silica having a BET surface and a CTAB specific surface both of less than 450 m²/ G, even if highly dispersible precipitated silicas are preferred. Preferably used a silica having specific CTAB BETOU surfaces which are both from 80 m²/ G to 260 m²/ G.

In the present specification, the BET specific surface is determined in known manner, according to the Brunauer-Emmet-Teller described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938 and corresponding to the standard AFNOR-NFT-45007 (November 1987); the CTAB specific surface is the external surface determined according to the same standard AFNOR-NFT-45007 of November 1987.

Highly dispersible silica is understood any silica having a very substantial ability to de-agglomeration and dispersion in an elastomeric matrix, observable manner known by electronic or optical microscopy on thin sections. Non-limiting examples of such preferred highly dispersible silicas include the silicas Ultrasil 7000 and Ultrasil 7005 from Degussa, the Zeosil 1165MP silicas, 1135MP and 1115MP from Rhodia, the silica Hi-Sil EZ150G from PPG, silicas Zeopol 8715, 8745 and 8755 from Huber, and treated precipitated silicas such as, for example, the silicas "doped" with aluminum described in the aforementioned application EP-A-0735088. The physical state in which the reinforcing inorganic filler is immaterial, whether in the form of a powder, microbeads, granules or balls. Of course it also means reinforcing inorganic filler mixtures of different reinforcing inorganic fillers, in particular of highly dispersible silicas such as described above. The reinforcing filler according to the invention advantageously comprises a blend of said reinforcing inorganic filler with carbon black, the weight fraction of carbon black in said reinforcing filler is preferably chosen less than or equal to 30%.

For example, blends black / silica or blacks partially or entirely covered with silica are suitable to form the reinforcing filler. Also suitable are reinforcing inorganic fillers comprising carbon blacks modified by silica such as, without limitation, the fillers sold by CABOT under the name "CRX

2000 ", which are described in International Patent WO-A-96/37547.

As reinforcing inorganic filler may also be used, without limitation,

- Aluminas (of formula A1₂0₃), Such as aluminas of high dispersibility which are described in European patent EP-A-810 258, or

- Aluminum hydroxides, such as those described in International Patent WO-A-99/28376.

The rubber composition according to the invention further comprises in conventional manner, a linker reinforcing inorganic filler / elastomer matrix (also called coupling agent), which has the function of ensuring a connection (or coupling) sufficient, such chemical and / or physical connection between said inorganic filler and the matrix, while facilitating the dispersion of this inorganic filler within said matrix.

By coupling agent is more precisely meant an agent capable of establishing a sufficient connection, of chemical and / or physical connection between the filler and the elastomer, while facilitating the dispersion of this filler within the elastomeric matrix. Such a coupling agent, at least bifunctional, has, for example, the simplified general formula "YTX" in which:

- Y represents a functional group ( "Y") which is capable of bonding physically and / or chemically with the inorganic filler, such a bond possibly being established, for example, between a silicon atom of the coupling agent and hydroxyl

(OH) surface of the inorganic filler (for example, surface silanols when it is silica);

- X represents a functional group ( "X") capable of bonding physically and / or chemically with the elastomer, for example via a sulfur atom; - T represents a group that links Y and X.

The coupling agents should in particular not be confused with simple agents for covering the filler in question which, in known manner, may comprise the Y function active vis-à-vis the filler but are devoid of the X function active living -to-vis the elastomer.

Such coupling agents, of variable effectiveness, have been described in a very large number of documents and are well known in the art. We can actually use any coupling agent known to or likely to ensure, in the diene rubber compositions usable for the manufacture of tires, the connection or coupling between a reinforcing inorganic filler such as silica and a diene elastomer such as organosilanes, in particular alkoxysilane polysulphides or mercaptosilanes, or polyorganosiloxanes bearing the functions X and Y above.

Coupling agents Silica / elastomer, especially, have been described in numerous documents, the best known being bifunctional alkoxysilanes, such as alkoxysilane polysulphides.

Particular uses alkoxysilane polysulphides, called "symmetrical" or "asymmetrical" depending on their specific structure, as described for example in patents US-3,842,111, US Patent 3,873,489, US-A-3 978 103, US Patent 3,997,581, US Patent 4,002,594, US Patent 4,072,701, US Patent 4,129,585, or in more recent US-A-5580919, US -A-5,583,245, US Patent 5,650,457, US Patent 5,663,358, US Patent 5,663,395, US Patent 5,663,396, US Patent 5,674,932, US 5,675,014, US Patent 5,684,171, US Patent 5,684,172, US Patent 5,696,197, US Patent 5,708,053, US Patent 5,892,085, EP-A-1 043,357 which set out in detail such known compounds.

Particularly suitable for the implementation of the invention, without the definition below being limiting, are symmetrical alkoxysilane polysulphides corresponding to the general formula (I):

(I) Z - A - S_not - A - Z wherein:

- N is an integer from 2 to 8 (preferably 2 to 5); - A is a divalent hydrocarbon radical (preferably alkylene groups

C cI8 or arylene groups C₆-C_I2More particularly alkylene C_rCι₀, Including CC₄ in particular propylene);

- Z corresponds to one of the formulas below: R1 R1 R2

-Yes- ; - Si-R2; - Si-R2

R2 R2 fc where:

- R * radicals, substituted or unsubstituted, identical or different, represent alkyl CpCig cycloalkyl C₅-Cι₈ aryl or C₆-Cι₈ (Preferably alkyl CC₆, Cyclohexyl or phenyl, in particular alkyl groups CC, more particularly methyl and / or ethyl).

- The R radicals, substituted or unsubstituted, identical or different, represent an alkoxy group or cycloalkoxy C Cιs C₅-Cι₈ (Preferably alkoxyl groups C

C₈ cycloalkoxy or C₅-C₈, More preferably alkoxyl groups CC, particularly methoxy and / or ethoxy).

In the case of a mixture of alkoxysilane polysulphides corresponding to the formula (I) above, in particular conventional commercially available mixtures, it is understood that the average value of "n" is a fractional number, preferably within a range 2 to 5. As alkoxysilane polysulphides, are more particularly of the polysulphides

(Including disulfide, trisulfide or tetrasulfide) of bis (alkoxyl (Cι-C) alkyl (CC) silylalkyl (CC)), such as the polysulphide bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) . Among these compounds, using the bis (3- triethoxysilylpropyl), abbreviated TESPT, of the formula [(C₂H5θ)₃Si (CH₂)₃S₂]₂ or disulfide, bis (triethoxysilylpropyl), abbreviated TESPD the formula [(CzHsO ^ S ^ Cl ^ SJZ. TESPD is marketed for example by Degussa under the names Si266 or Si75 (in the latter case, the form of a mixture of disulphide (75% by weight) and of polysulphides) or by Witco under the name Silquest A1589. TESPT is sold, for example, by Degussa under the name Si69 (or X50S when supported to 50% by weight on carbon black), or by Osi Specialties under the name Silquest A1289 (in both cases, a commercial mixture of polysulphides with an average value for n close to 4). also suitable are monoalkoxysilanes tetrasulfides such as monoethoxydimethylsilylpropyl tetrasulphide (abbreviated MESPT), which are the subject of international patent application PCT / EP02 / 03774 in the name of the plaintiffs. The compositions according to the invention also comprise, in addition to the diene elastomers, said plasticizing resin, said plasticizing oil, optionally, said reinforcing inorganic filler and optionally said binding agent, all or part of the other constituents and additives usually used in the compositions rubber, such as pigments, anti-oxidants, antiozonant waxes, a crosslinking system based either on sulfur and / or peroxide and / or bismaleimides, one or more agents for covering the reinforcing inorganic filler such as alkylalkoxysilanes, polyols, amines or amides.

Note that the or at least one diene elastomers used in the composition according to the invention may comprise one or more functional groups specifically active for coupling to said reinforcing filler.

For coupling to a reinforcing inorganic filler, all the functional groups, coupled or stars which are known to those skilled in the art for coupling to silica. Without limitation, suitable - the silanol or polysiloxane having a silanol end, as described in the French patent FR-A-2740778 in the name of the applicant. Specifically, this document teaches the use of a functionalizing agent with a living polymer obtained by anionic polymerization, in order to obtain an active function for coupling to silica. This functionalizing agent comprises a cyclic polysiloxane such as a polymethylcyclo tri, tetra or - deca siloxane, said agent being, preferentially, hexamethylcyclotrisiloxane. The functionalized polymers thus obtained can be separated from the reaction medium resulting in their formation by steam extraction of water from the solvent, without their macrostructure and, consequently, their physical properties changing; and - the alkoxysilane groups. There may be mentioned as such the functionalization reaction disclosed in International Patent WO-A-88/05448 for coupling to silica, which consists in reacting a living polymer obtained anionically a compound alkoxysilane having at least one non-hydrolyzable alkoxyl. This compound is selected from haloalkyl alkoxysilanes.

We may also mention the French patent FR-A-2765882, in respect of obtaining alkoxysilane functions. This document discloses the use of a trialkoxysilane, such as 3-glycidoxypropyltrialkoxysilane, for the functionalization of a living diene polymer, for coupling to the carbon black having silica fixed to its surface as reinforcing filler majority. For coupling with carbon black, can be made, for example functional groups comprising a C-Sn bond. Such groups can be obtained in the known manner by reaction with a organohalotin type functionalizing agent that can meet the general formula R₃SnCl, or with a organodihalotin type coupling agent can respond to the general formula R₂SnCl₂Or with a starring agent of organotrihalotin type that can respond to the general formula RSnCl₃Or tetrahalotin type that can have the formula SnCl (where R is an alkyl, aryl or cycloalkyl).

For a carbon black coupling, may also be made of amino functional groups, for example obtained by using 4,4-bis (diethylaminobenzophenone), also referred DEAB. Examples include patent documents FR-A-2526030 and US Patent 4,848,511.

The compositions according to the invention can be prepared according to methods known to thermomechanical working of the constituents in one or more steps. One can for example be obtained by thermomechanical working in one stage in an internal mixer which lasts from 3 to 7 minutes, with a rotational speed of the blades of 50 revolutions per minute, or in two stages in an internal mixer lasting respectively of 3 to 5 minutes and 2 to 4 minutes, followed by a finishing step conducted at about 80 ° C, during which are incoφorés sulfur and vulcanization accelerators in the case of a composition to be crosslinked with sulfur.

A tread of tire according to the invention is such that it is comprised of said rubber composition according to the invention.

A tire according to the invention comprises this tread. Note that the present invention applies to all types of tires, which may for example be intended to equip motor vehicles or not, such as auto touring or competition or two-wheeled vehicles - including bicycles and light motor vehicles including motorcycles - industrial vehicles selected from among vans, "heavy weight-" - ie buses, road transport vehicles (lorries, tractors, trailers), off-road vehicles - agricultural machinery or of construction machinery, aircraft, other transport or handling.

The aforementioned features of the present invention, as well as others, will be better understood from reading the following description of several embodiments of the invention, illustrative and not restrictive. Determination of the molecular weights of the resins according to the invention by the exclusion chromatography technique by height (SEC):

The exclusion chromatography by size or SEC makes it possible physically to separate macromolecules by their size in the swollen state in columns filled with a porous stationary phase. The macromolecules are separated by their hydrodynamic volume, the bulkiest being eluted first. Without being an absolute method, SEC allows the molecular weight distribution of the resins. From commercially available standards of low molecular weight polystyrene (between 104 and 90000 g / mol), the different average masses Mn and Mw are determined by weight and the polydispersity index Ip calculated. Each resin sample is dissolved in tetrahydrofuran at a concentration of about 1 g / 1.

The equipment used is a chromatograph "WATERS model Alliance 2690". The elution solvent is tetrahydrofuran (mobile phase), the flow rate of 1 ml / min., The system temperature of 35 ° C and the analysis time is 40 min. the stationary phase used for a set of three columns in series respective trade names "WATERS type STYRAGEL HR4E" (mixed-bed column), "WATERS type STYRAGEL HR1" (100 Angstrom pore) and "WATERS STYRAGEL HR0.5 "(porosity 50 Angstrom).

The injected volume of the solution of each resin sample is 100 .mu.l. The detector is a differential refractometer "WATERS model 2410" and the operating software of chromatographic data is the "WATERS MILLENNIUM" (v 3-2).

Measurement of glass transition temperatures of the elastomers and plasticizers:

glass transition temperatures Tg elastomers and plasticizers were measured using a differential scanning calorimeter ( "differential scanning calorimeter").

Regarding measurements of Tg for the rubber compositions incoφorant these elastomers and these plasticizers are conducted dynamic measurements at a frequency of 10 Hz and at two different values ​​of stresses (0.2 MPa to 0.7 MPa), steps "MDC" made in accordance with ISO 4664 (the mode of deformation being shearing and the test pieces being of cylindrical form). Measurement of the rubber compositions of properties:

- Mooney Viscosity ML (l + 4) at 100 ° C measured according to ASTM D 1646 of 1999. - elongation modules MA100 (100%) measured according to ASTM D 412 standard.

Scott index breaking: breaking strength (MPa) and elongation (in%) measured at 23 ° C according to ASTM D 412 of 1998.

- Shore A hardness: measured according to ASTM Standard D 2240 1997.

hysteresis losses (HL): measured in% by rebound at 60 ° C. at the sixth impact, according to the following equation: HL (%) = 100 x (Wo-WjVW, with W₀ : Energy supplied and Wi energy restored.

dynamic shear properties: measured according to ASTM D 2231-71 standard approved again in 1977 (measured in terms of the deformation carried out at 10 Hz with a peak-peak deformation of 0.15% to 50%, and measured as a function temperature carried out at 10 Hz under a repetitive stress of 70 or 20 N / cm² with a temperature sweep from -80 to 100 ° C).

Performance measurement of the tires

We used performance relative indices, compared to a reference index 100 characterizing a "cookie" (a performance index greater than this base 100 indicating a performance superior to that of the envelope corresponding "control" ).

- The rolling resistance of each of the tires tested was measured by running on a wheel at an ambient temperature of 25 ° C, under a load of 392 daN and at a speed of 80 km / h, the internal pressure of the envelope of 2.1 bars, with dimensions of 175/70 R14 envelopes "MXT". - The wear resistance of each tire was determined by means of a relative wear index which is a function of the height of rubber remaining after running on a winding road course at an average speed of 77 km / h and until the wear reaches the wear indicators located in the tread grooves. We got this index wear on comparing the height of rubber remaining a tread according to the invention to the rubber remaining height of a tread "control", which by definition has an index of 100 wear.

- The adhesion of each tire tested was evaluated by the braking distances measured in braking mode "ABS", both on dry ground and on wet ground. Specifically, the braking distance in "ABS" mode was measured on dry ground, passing a speed of 70 km / h to 20 km / h, wet (polished concrete floor with 2 mm of water surface), to a speed of 40 km / h to 10 km / h.

- The behavior on wet ground of each tire was evaluated by the time taken to cover a round winding road circuit and watered, a stated value of 101 corresponds to gain 1 second on that lap.

- The resistance of the tires to the separation of plies was also evaluated by relative performance indices, relative to a reference index 100 characterizing a "cookie" (a performance index greater than this base 100 reflecting a performance superior to that of the envelope corresponding "control").

This resistance was measured by a running test on a wheel, the surface is provided with barriers (bars and "polars" which stress the edges of the belt casing made of two NST1 working crown plies and WCP2 ) at an ambient temperature of 20 ° C, under a load of 490 daN and at a speed of 75 km / h, the internal pressure of the tire being set to 2.5 bar. This test is stopped when detecting a deformation of the casing crown reinforcement.

Each tire had first been "baked" (unmounted) for 4 weeks at 65 ° C. The results are expressed in the form of a mileage performance (base 100 for "control" tire).

EXAMPLE 1

1) First RI resin according to the invention (comprising nearly 100% of units resulting from the polymerization of α-pinene^"):

RI resin, marketed by Hercules as "R2495" presents:

- An aliphatic linkage content of 97%,

- An aromatic linkage content of 0%,

- Number average molecular weights Mn and Mw respectively equal to 820 g / mol and 1060 g / mol, and

- A glass transition temperature Tg of 88 ° C.

2) Synthesis of a second resin RI 'of the invention (homopolvmère limonene^'):

Were weighed in a glove box (under inert atmosphere), 0.42 g of AlCl₃, Which is placed in a "Steinie" bottle under nitrogen. then introduced into this bottle 50 ml of anhydrous toluene, and then 50 ml of pure d-limonene (dextrorotatory enantiomer) and then the bottle is placed under stirring in a thermostated bath at 25 ° C for 4 hours. The reaction was quenched with 3 ml of acetylacetone, and the resin is recovered by coagulation in methanol after addition of 0.4 phr of phenolic antioxidant "Etyl702".

After drying in an oven, a RI resin yellow, pale and translucent obtained with an average yield of 67%, average molecular weights Mn and Mw of 585 g respectively / mol and 866 g / mol and a temperature of glass transition T_g 68 ° C.

This resin RI 'has an aliphatic linkage content of 100% and an aromatic linkage content of 0%, and it consists exclusively of limonene units.

3) Tread compositions according to the invention II, II 'respectively comprising these resins RI. RI 'compared with a "control" composition Tl without resin:

Each of these compositions Tl, II, II 'is intended to constitute a tread of a type of tire "tourism". Table 1 below contains: the formulation of each of these compositions Tl, II, II '; the properties of each composition Tl, II and II 'in the uncrosslinked and crosslinked state and performance of the corresponding tire covers dimension 175/70 R14 "MXT". Table 1

<img id="imgf000018_0001" he="220" wi="162" file="imgf000018_0001.tif" img-format="tif" img-content="table" orientation="portrait" inline="no" /> - With S-SBR A: copolymer of styrene and butadiene prepared in solution having a 1,2 linkage content of 58%, a content of styrene linkages of 25%, a Mooney viscosity ML (l + 4) @ 100 ° C equal to 54, an amount of oil equal to 37.5 phr and a glass transition temperature Tg of -29 ° C.

- With A BR: polybutadiene having a very high cis-1,4 linkage of approximately 93%, a glass transition temperature Tg of -103 ° C and a Mooney viscosity ML (l + 4) at 100 ° C equal to 54.

- With 6PPD: N- (3-dimétyl-butyl) -N'-phenyl-p-phenylenediamine, and

CBS: N-cyclohexyl benzothiazyl sulfenamide.

Note that the respective Tgs of the compositions II and III 'according to the invention under a high modulus of dynamic stress (0.7 MPa) are provided substantially equal to the corresponding Tg of the "control" composition Tl.

As seen in Table 1, the difference between the Tg of Tl compositions, he and II 'that have been measured at a dynamic stress of reduced modulus, equal to 0.2 MPa, is very close to the difference between Tl the Tg of said compositions, he and II 'which were measured under said stress of high modulus.

This lack of difference between the Tg when passing from a stress of high modulus to a reduced modulus expresses the fact that the resin and the resin RI RI 'are each readily miscible in the elastomeric matrix constituted by the S-SBR A and BR A.

This table 1 also shows that the incoφoration of these resins RI or RI 'according to the invention (Mn between 500 and 1000 g / mol and Tg between 60 ° C and 100 ° C) to the respective compositions II and III 'gives envelopes where the treads are made from these compositions a wear resistance much improved over that of the "control" composition Tl devoid of resin, while substantially maintaining the grip performance and resistance to envelopes bearing incoφorant said Tl composition and maintaining or improving the mechanical properties (breaking MA100 and Scott) said composition Tl.

These RI or RI resins' according to the invention also give the corresponding amounts improved endurance, to the extent that they improve the resistance to separation of the triangulation crown plies that each of these tires comprises in its crown reinforcement.

Note also that the compositions II and II 'comprise far less aromatic oil that the composition Tl, which contributes to environmental protection by significantly reducing the pollution resulting from the exudation of this oil by the tires, this exudation furthermore being minimized due to the increased wear resistance to the tires of the invention. EXAMPLE 2

1) The third resin R2 according to the invention (comprising nearly 100% of units resulting from the polymerization of limonene):

The resin R2, sold by DRT under the name "Dercolyte L120" presents:

- An aliphatic linkage content of 100%,

- An aromatic linkage content of 0%,

- Number average molecular weights Mn and Mw respectively of 625 g / mol and 1010 g / mol, and

- A glass transition temperature Tg of 72 ° C.

2) Fourth resin R2 'according to the invention (comprising nearly 100% of units resulting from the polymerization of dipentene^'):

R3 resin, resin sold by Arizona as "Sylvagum TR7125C" presents:

- An aliphatic linkage content of 100%,

- An aromatic linkage content of 0% - number average molecular weights Mn and Mw respectively of 630 g / mol and 950 g / mol, and

- A glass transition temperature Tg of 70 ° C.

3) Tread compositions according to the invention 12, 12 'respectively comprising these resins R2, R2' compared with a "control" composition T2 without resin:

Each of these compositions T2, 12, 12 'is intended to constitute a tread of a type of tire "tourism". The following table 2 contains: the formulation of each of these compositions T2, 12, F 2; - The properties of each composition T2, 12, I'2 in the uncrosslinked state and crosslinked and performance of the corresponding tire envelopes sizes 175/70 R14 "MXT". Table 2

<img id="imgf000021_0001" he="220" wi="159" file="imgf000021_0001.tif" img-format="tif" img-content="table" orientation="portrait" inline="no" /> respective Tg it will be appreciated that compositions 12 and 12 'according to the invention under a high modulus of dynamic stress (0.7 MPa) are provided substantially equal to the corresponding Tg of the "control" composition T2. As seen in Table 2, the difference between the Tg of the compositions T2, 12 and 12 'which have been measured at a dynamic stress of reduced modulus, equal to 0.2 MPa, is very close to the difference between the Tg of said compositions T2, 12 and 12 'which were measured under said stress of high modulus.

This lack of difference between the Tg when passing from a stress of high modulus to a reduced modulus expresses the fact that the resin and the resin R2 R2 are each readily miscible in the elastomeric matrix constituted by the S-SBR A and BR A.

This Table 2 also shows that the incoφoration of R2 or R2 resins 'according to the invention (Mn between 500 and 1000 g / mol and Tg between 60 ° C and 100 ° C) to the respective compositions 12 and 12' gives envelopes where the treads are made from these compositions a wear resistance much improved over that of the "control" composition T2 devoid of resin, practically without adversely affecting the adhesion performance on dry ground and on wet behavior on wet ground and rolling resistance envelopes incoφorant said composition T2, and maintaining or improving the mechanical properties (breaking MA100 and Scott) said composition T2. Note also that the compositions 12 and 12 'comprise far less aromatic oil than T2 composition (composition 12' containing only 1.25 phr of aromatic oil), which contributes to environmental protection in significantly reducing the pollution resulting from the exudation of this oil by the tires, this exudation furthermore being minimized due to the increased wear resistance to the tires of the invention.