FR3015496A1 - RUBBER COMPOSITION COMPRISING NON-REINFORCING INORGANIC LOAD AND REINFORCING LOAD - Google Patents

Abstract

The invention relates to a reinforced rubber composition based on one or more diene elastomers, one or more reinforcing fillers with a specific surface area B ET greater than or equal to 100 m 2 / g, and one or more non-reinforcing fillers. with a BET specific surface area of less than 60 m 2 / g, the reinforcing filler (s) and the non-reinforcing filler (s) being of different chemical natures, the reinforcing filler (s) being predominant in weight relative to the non-reinforcing filler (s).

Description

The present invention relates to a reinforced composition based on a diene elastomer, a reinforcing filler with a BET specific surface area greater than or equal to 100 m 2 / g, and a reinforcing filler comprising a non-reinforcing filler and a reinforcing filler. a minority non-reinforcing filler of a different nature with a BET specific surface area of less than 60 m 2 / g. Since fuel savings and the need to preserve the environment have become priorities, it is desirable to produce blends with good wear resistance properties while having as low a hysteresis as possible in order to be able to use them. in the form of rubber compositions usable for the manufacture of various semi-finished products used in the tire composition, such as, for example, treads, in order to obtain tires having improved wear resistance without penalization of the rolling resistance. Ideally, for example, a tire tread must meet a large number of technical, often antithetical, requirements including high wear resistance while offering the tire low rolling resistance and high adhesion both on the tire and the tire. dry soil only on wet, snowy or icy ground.

To improve the wear resistance, it is known, a certain rigidity of the tread is desirable, this stiffening of the tread can be obtained for example by increasing the rate of reinforcing filler, with a significant surface area or by incorporating certain reinforcing resins into the constituent rubber compositions of these treads. Unfortunately, experience shows that such a stiffening of the tread penalizes in a known manner, most often unacceptably, the rolling resistance properties, accompanied by a significant increase in the hysteretic losses of the composition. of rubber. Improving rigidity performance by keeping rolling resistance low is therefore a constant concern for tire designers. There is therefore a permanent need to provide a rubber composition which makes it possible to obtain tires having improved wear resistance without penalizing the rolling resistance. In view of the foregoing, it is a general object to provide rubber compositions which satisfy a compromise of stiffness / hysteresis properties acceptable for tire use. The applicants have discovered that a reinforced rubber composition based on one or more diene elastomers, one or more reinforcing fillers with a BET surface area greater than or equal to 100 m 2 / g, and one or more non-solid fillers. -Reinforcing minority of different chemical nature of said reinforcing fillers and BET specific surface area less than 60 m2 / g, allowed to achieve a satisfactory level of rigidity maintaining or even improving acceptable hysteresis properties. The subject of the invention is therefore a reinforced rubber composition based on one or more diene elastomers, one or more reinforcing fillers with a BET specific surface area greater than or equal to 100 m 2 / g, and one or more non-solid fillers. reinforcing reinforcements with a BET specific surface area of less than 60 m 2 / g, the reinforcing filler (s) and the non-reinforcing filler (s) being of different chemical natures, the reinforcing filler (s) being predominant in weight with respect to the non-reinforcing filler (s); reinforcing.

The invention also relates to a semi-finished rubber article for a tire, comprising such a crosslinkable or crosslinked rubber composition. The invention also relates to a tire incorporating such a semi-finished article.

Finally, a subject of the invention is a method for preparing a rubber composition for the manufacture of tires as defined above, comprising the following steps: - incorporating in said diene elastomers or, in a first step, said one or more charges reinforcing agents and said one or more non-reinforcing fillers, by thermomechanically kneading the whole, in one or more times, until a maximum temperature of between 110 ° C. and 190 ° C. is reached; - Then incorporate, in a second step, a crosslinking system and knead the whole to a maximum temperature of less than 110 ° C, preferably less than 80 ° C. In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight. On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. the excluded terminals a and b) while any range of values designated by the expression "from a to b" means the range from a to b (i.e., including the strict limits a and b).

"Composition based on" means 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 with one another at least in part. during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization. As explained above, the rubber composition according to the invention is based on one or more diene elastomers. By diene elastomer, should be understood in known manner an elastomer derived at least in part (i.e. a homopolymer or copolymer) of diene monomers (monomers bearing two carbon-carbon double bonds conjugated or not). Preferably, the diene elastomer (s) are chosen from diene elastomers which are essentially unsaturated.

The term "diene elastomer" is generally understood to mean a diene elastomer having a degree of units or units of diene origin (conjugated dienes) which is greater than 15% (mol%).

The essentially unsaturated diene elastomers may themselves be selected from the highly unsaturated diene elastomers. The term "diene elastomer" is generally understood to mean a diene elastomer having a degree of units or units of diene origin (conjugated dienes) which is greater than 50% (mol%). More particularly, diene elastomer is any homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 12 carbon atoms, or any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more vinylaromatic compounds. having from 8 to 20 carbon atoms. In the case of copolymers, these contain from 20% to 99% by weight of diene units, and from 1 to 80% by weight of vinylaromatic units.

Conjugated dienes which can be used in the process according to the invention are especially suitable for 1,3-butadiene, 2-methyl-1,3-butadiene and 2,3-di (C 1 -C 5) alkyl-1,3 butadiene 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-1-butadiene, 3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene, 1,3-pentadiene and 2,4-hexadiene, etc. Examples of suitable vinylaromatic compounds are styrene, ortho-, meta, para-methylstyrene, the commercial "vinyltoluene" mixture, para-tert-butylstyrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene, and the like. The diene elastomer (s) used in the composition according to the invention are preferably chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), copolymers of butadiene, in particular copolymers of butadiene and a vinylaromatic monomer, isoprene copolymers and mixtures of these elastomers. Among the butadiene copolymers, mention may be made of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene-butadiene-styrene copolymers (SBIR). The diene elastomer (s) essentially or strongly unsaturated generally have a glass transition temperature (Tg) of less than 0 ° C. This glass transition temperature is measured in known manner by DSC (Differential Scanning Calorimetry), for example and unless otherwise specified in the present application, according to the ASTM D3418 standard of 1999. As explained above, the composition is also based on one or more reinforcing fillers with a BET specific surface area greater than or equal to 100 m 2 / g, and one or more non-reinforcing fillers with a BET specific surface area of less than or equal to 60 m 2 / g, the chemical nature of the reinforcing filler (s). being different from the chemical nature of the non-reinforcing filler (s).

The BET surface area is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol.60, page 309, February 1938), more precisely according to the standard French NF ISO 9277 from December 1996 [multipoint volumetric method (5 points) - gas: nitrogen - degassing: lh at 160 ° C - relative pressure range p / po: 0.05 to 0.17]. The reinforcing filler (s) with BET specific surface area greater than or equal to 100 m 2 / g may be chosen from reinforcing organic fillers.

According to a preferred embodiment, the reinforcing filler or fillers are carbon black. Suitable carbon blacks are all reinforcing carbon blacks, used individually or in the form of mixtures, in particular the reinforcing blacks conventionally used in tires or their treads (so-called pneumatic grade blacks). Among the latter, the reinforcing carbon blacks of the series 100, 200, 300 (ASTM grades), for example N115, N134, N234, N326, N330, N339, N347 or N375, will be mentioned more particularly. 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. According to another embodiment of the invention, the rubber composition according to the invention may also contain other reinforcing organic fillers which may replace all or part of the reinforcing carbon blacks described above. As examples of reinforcing organic fillers, mention may be made of functionalized polyvinyl organic fillers as described in applications WO-A-2006/069792, WO-A-2006/069793, WO-A2008 / 003434 and WO-A-2008 / 003,435. The reinforcing filler (s) may also be chosen from reinforcing inorganic fillers. Mention may in particular be made of mineral fillers of the siliceous type, preferentially silica (SiO 2). The silica used may be any reinforcing silica known to a person skilled in the art, with a BET specific surface area greater than or equal to 100 m 2 / g. The reinforcing filler or fillers generally represent from 10 to 180 phr, preferably from 30 to 150 phr.

As non-reinforcing minority load must be understood a load whose nature of the surface very different from that of the reinforcing filler. The reinforcing filler or fillers have a BET specific surface area of less than 60 m 2 / g. According to a preferred embodiment, the reinforcing filler (s) have a BET specific surface area of less than or equal to 45 m 2 / g, preferably from 10 to 45 m 2 / g. Non-reinforcing fillers are particularly suitable non-reinforcing inorganic fillers.

Mention may in particular be made of mineral fillers of the siliceous type, preferentially silica (SiO 2). The silica used may be any non-reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area of less than 60 m 2 / g, preferably less than or equal to 45 m 2 / g, preferably 10 at 45 m2 / g. Mention may also be made of mineral fillers with a low specific surface area of the aluminous type, in particular alumina (Al 2 O 3) or aluminum (oxide) hydroxides, or even titanium oxides.

The physical state in which the inorganic non-reinforcing filler is present is indifferent, whether in the form of powder, microbeads, granules or beads. Preferably, the non-reinforcing filler (s) are present at a level ranging from 5 to 50 phr. Advantageously, the reinforcing and non-reinforcing fillers are present at a total content ranging from 15 to 200 phr, preferably from 50 to 150 phr. Preferably, the non-reinforcing fillers represent 5 to 45%, preferably 10 to 40%, more preferably 15 to 35%, by weight of the total weight of the reinforcing and non-reinforcing fillers.

As explained above, the reinforcing fillers or fillers have a different chemical nature from the non-reinforcing fillers. Thus, for example, if the reinforcing filler is a carbon black, the non-reinforcing filler is not a carbon black. It may be, for example, silica. Conversely, if the reinforcing filler is a silica, the non-reinforcing filler is not a silica. It can be a carbon black. When the reinforcing or non-reinforcing fillers comprise a filler requiring the use of a coupling agent to establish the bond between the filler and the elastomer, the rubber composition according to the invention further comprises, in a conventional manner, a agent capable of effectively providing this link. As regards the silica that may be present in the composition as a non-reinforcing filler, it is possible to use as coupling agents organosilanes, in particular polysulfurized alkoxysilanes or mercaptosilanes, or alternatively at least bifunctional polyorganosiloxanes. Silica / elastomer bonding agents, in particular, are well known to those skilled in the art, the best known being bifunctional alkoxysilanes such as polysulfurized alkoxysilanes. In the composition according to the invention, the level of coupling agent is advantageously less than 20 phr. Its level is preferably between 0.3 and 10 phr. The rubber composition according to the invention may also contain, in addition to the coupling agents, coupling activators, charge-recovery agents or, more generally, processing aid agents which can be used in known manner, thanks to an improvement of the dispersion of the filler in the rubber matrix and a lowering of the viscosity of the composition, to improve its ability to use in the green state, these agents being for example hydrolysable silanes such as alkylalkoxysilanes, polyols, polyethers, primary, secondary or tertiary amines, hydroxyl or hydrolyzable polyorganosiloxanes.

The rubber composition according to the invention may also comprise all or part of the usual additives normally used in elastomer compositions intended for the manufacture of tires, for example pigments, protective agents such as anti-ozone waxes, chemical ozonants, anti-oxidants, anti-fatigue agents, plasticizing agents, reinforcing or plasticizing resins, acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M) as described, for example in the application WO 02/10269, a crosslinking system that may be based on either sulfur, or sulfur and / or peroxide donors and / or bismaleimides, vulcanization accelerators, vulcanization activators. The rubber composition according to the invention is manufactured in suitable mixers, generally using two successive preparation phases according to a general procedure well known to those skilled in the art: a first working phase or thermomechanical mixing (sometimes referred to as "non-productive" phase) at high temperature, up to a maximum temperature of between 110 ° C. and 190 ° C., preferably between 115 ° C. and 170 ° C. and even more preferably between 115 ° C. and 160 ° C., followed by a second phase of mechanical work (sometimes called a "productive" phase) at a lower temperature, typically below 110 ° C, for example between 30 ° C and 100 ° C, finishing phase during which can be incorporated the crosslinking system. Thus, according to the invention, the composition according to the invention is prepared according to the process comprising the following steps: - incorporating at or said diene elastomers, during a first step, the reinforcing fill (es) and the said non-reinforcing fillers; -renforçantes, by thermomechanically kneading the whole, in one or more times, until reaching a maximum temperature between 110 ° C and 190 ° C; - Then incorporate, in a second step, a crosslinking system and knead the whole to a maximum temperature of less than 110 ° C, preferably less than 80 ° C. According to a preferred embodiment of the invention, all the basic constituents of the composition used according to the invention, with the exception of the crosslinking system, namely the reinforcing filler (s), the non-reinforcing filler (s), the coupling agent, if appropriate, are intimately incorporated, by kneading, with the diene elastomer or the diene elastomers during the first so-called non-productive phase, that is to say that one introduces in the mixer and thermomechanically kneading, in one or more steps, at least these different basic constituents until the maximum temperature of between 110 ° C. and 190 ° C., preferably between 115 ° C. and 170 ° C. is reached. ° C and more preferably still between 115 ° C and 160 ° C. By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, the possible setting agents, are introduced into a suitable mixer such as a conventional internal mixer. Complementary applications and other various additives, with the exception of the crosslinking system. The total mixing time in this non-productive phase is preferably between 1 and 15 minutes. After cooling the mixture thus obtained during the first non-productive phase, the low temperature crosslinking system is then incorporated, generally in an external mixer such as a roll mill; the whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 min. As an alternative to mixing the elastomer and the dry phase fillers as described above, the mixture of the diene elastomer, the reinforcing filler (s) and the non-reinforcing filler (s) can also be carried out in phase. liquid.

For this purpose, an elastomer in the form of a latex is used which is in the form of elastomer particles dispersed in water, and an aqueous dispersion of the filler, that is to say a filler dispersed in water. , commonly called "slurry". Certain processes in particular, such as those described in US Pat. No. 6,048,923, make it possible to obtain an elastomer and filler masterbatch having a very good dispersion of the filler in the elastomeric matrix. 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 else extruded in the form of a rubber profile that can be used as a tire tread for passenger car or truck. As explained above, the subject of the invention is also a semi-finished article of rubber for a tire, comprising a crosslinkable or crosslinked rubber composition according to the invention. As explained above, the subject of the invention is also a tire comprising a semi-finished article according to the invention.

Due to the improved rigidity which characterizes a reinforced rubber composition according to the invention, without deteriorating the hysteresis properties, it will be noted that a tire whose tread comprises the composition has a wear resistance. advantageously increased without penalizing the rolling resistance. The aforementioned features of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of illustration and not limitation. Examples Measurements and Tests Used The rubber compositions are characterized after curing as indicated below. a) Mechanical properties Tensile tests These tensile tests make it possible to determine the elastic stress and the properties at break. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. It is measured in second elongation (ie, after an accommodation cycle at the extension rate provided for the measurement itself). Nominal secant (or apparent stress, in MPa) at 10% and 100% elongation (respectively denoted MA10 and MA100). The tensile measurements for determining the secant accommodating modules are carried out at a temperature of 60 ° C +/- 2 ° C, and under normal humidity conditions (50 +/- 5% relative humidity). These values are representative of the rigidity: the higher the value of the modules, the higher the rigidity. b) Dynamic properties The dynamic properties G * and tan (8) max are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 599296. The response of a sample of vulcanized composition is recorded (cylindrical specimen of 4 mm d thickness and 400 mm2 section), subjected to sinusoidal stress in alternating simple shear, at the frequency of 10 Hz and at a measurement temperature of 60 ° C. A strain amplitude sweep is carried out from 0.1% to 100% peak-to-peak (forward cycle), then from 100% to 0.1% peak-to-peak (return cycle). The results exploited are the complex dynamic shear modulus (G *) and the loss factor tan (8). For the return cycle, the maximum value of tan (8) observed, denoted tan (8) max, is indicated. This value is representative of the hysteresis of the material and in this case the rolling resistance: the lower the value of tan (8) max, the lower the rolling resistance. The values of G * measured at 60 ° C are representative of the rigidity, that is to say of the resistance to deformation: the higher the value of G *, the greater the rigidity of the material, and therefore the resistance high wear.

Example 1 Four compositions are compared reported in Table 1 below. Three of them are non-compliant comparative compositions with respect to the invention: Composition Ti: a reinforcing reinforcing filler Composition T2: control with unsaturated diene elastomer, carbon black and no non-control filler with elastomer unsaturated diene rigidified via the increase of the carbon black charge rate and no non-reinforcing filler Composition A: composition with an unsaturated diene elastomer, with a mixture of reinforcing fillers, carbon black and silica.

The composition B according to the invention is based on an unsaturated diene elastomer, and a mixture of reinforcing and non-reinforcing fillers, respectively carbon black and "coarse" silica (that is to say silica with BET specific surface area less than or equal to 45 m2 / g). For the following tests, the procedure is as follows: Introduced in an internal mixer (final filling rate: about 70% by volume), the initial vessel temperature is about 80 ° C, successively the elastomer diene, reinforcing fillers (carbon black) and non-reinforcing ("coarse" silica), as well as 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 and a sulfenamide-type accelerator are incorporated on a mixer (homo-finisher) at 30 ° C., mixing the whole (productive phase) for a suitable time (for example a dozen 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. The formulations of the compositions are given in Table 1. The amounts are expressed in parts per 100 parts by weight of elastomer (phr). Table 1 Composition Ti T2 AB Unsaturated elastomer (1) 100 100 100 100 Carbon black (2) 47.5 60 47.5 47.5 Silica (3) 23 Silica (4) Silane (5) 1.90 0, Resin (6) 0.5 0.5 0.5 0.5 Paraffin 1 1 1 1 6-PPD (7) 2 2 2 2 TMQ (8) 1 1 1 1 ZnO 2.7 2.7 2.7 2.7 Stearic acid 2.5 2.5 2.5 2.5 CBS (9) 0.6 0.6 0.6 0.6 HMT3H (10) 0.6 0.6 0.6 0.6 Sulfur 1.5 1.5 1.5 1.5 (1) Natural rubber (2) Reinforcing filler: Carbon black N375 (3) Zéosil 1165 MP silica sold by Rhodia; BET specific surface area of 160 m2 / g; m2 / g; (4) Sidistar R300 silica; BET specific surface area (5) TESPT (Si69 from Degussa) (6) Formophenolic resin (7) N-1,3-dimethylbutyl-N-phenylparaphenylenediamine (8) 2,2,4-trimethyl-1,2- dihydroquinoline (9) N-cyclohexyl-2-benzothiazyl-sulfenamide (10) Hexamethylene tetramine The properties of the compositions are given in Table 2. Table 2 Composition T1 T2 AB tan 8 ', a' 0,19 0,22 0,21 0.16 (60 ° C, 10Hz) G * (MPa) 1.9 2.7 2.6 2.1 (60 ° C, 10Hz, 10%) G * (MPa) 1.3 1.8 1, 1.6 (60 ° C., 10 Hz, 50%) It can be seen that the rigidity at low and medium deformations, respectively 10 and 50% of deformation, of the composition B according to the invention is greater than that of the control composition Ti with less hysteresis. The non-compliant composition A is more rigid than Ti, and close in rigidity with respect to the control composition T2 having a higher loading rate, but the hysteretic properties are penalized with respect to Ti, as well for T2 as for A.

Thus, despite this improvement in rigidity, the composition B according to the invention exhibits hysteretic properties maintained or improved over that of the Ti composition, contrary to what is observed for the control composition T2 and composition A, for which the gain in rigidity is accompanied by a deterioration of the hysteretic properties. The improvement of the mechanical properties translated by the gain in rigidity is favorable in terms of wear resistance of a tire provided with a tread constituted by such a composition.

The improvement of the hysteretic properties is favorable for reducing the rolling resistance of a tire provided with a tread constituted by such a composition. In conclusion, the results of these tests demonstrate that the use of an unsaturated diene elastomer with a BET surface area reinforcing filler mixture greater than or equal to 100 m 2 / g and a non-reinforcing BET surface area of less than or equal to 45 m2 / g significantly improves the rigidity of the rubber compositions according to the invention and therefore improves the wear resistance of tires containing them, while maintaining or decreasing the hysteresis of the compositions and therefore the rolling resistance of the tires compared to a conventional tire.

Claims (14)

REVENDICATIONS1. Reinforced rubber composition based on one or more diene elastomers, one or more reinforcing fillers of BET specific surface area greater than or equal to 100 m 2 / g, and one or more non-reinforcing fillers having a BET specific surface area less than 60 m 2 / g, the reinforcing filler (s) and the non-reinforcing filler (s) being of different chemical natures, the reinforcing filler (s) being predominant in weight relative to the non-reinforcing filler (s). 2. Composition according to claim 1, characterized in that the diene elastomer or elastomers are chosen from diene elastomers which are essentially unsaturated. 3. Composition according to claim 1 or 2 characterized in that the diene elastomer or elastomers are chosen from natural rubber, synthetic polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers. 4. Composition according to any one of claims 1 to 3 characterized in that the reinforcing fillers or fillers are chosen from reinforcing organic fillers. 5. Composition according to claim 4, characterized in that the reinforcing fillers or fillers are carbon black. 6. Composition according to any one of the preceding claims characterized in that the reinforcing fillers or fillers represent from 10 to 180 phr, preferably from 30 to 150 phr. 7. Composition according to any one of the preceding claims, characterized in that the non-reinforcing filler (s) have a BET specific surface area of less than or equal to 45 m 2 / g. 8. Composition according to any one of the preceding claims, characterized in that the non-reinforcing filler or fillers are chosen from mineral fillers of siliceous type, preferably silica. 9. Composition according to any one of the preceding claims, characterized in that the non-reinforcing filler or fillers are present at a rate ranging from 5 to 50 phr. 10. Composition according to any one of the preceding claims, characterized in that the reinforcing and non-reinforcing fillers are present at a total content ranging from 15 to 200 phr, preferably from 50 to 150 phr. 11. Composition according to any one of the preceding claims, characterized in that the non-reinforcing filler (s) represent (s) from 5 to 45%, preferably from 10 to 40%, better still from 15 to 35%, by weight of the total weight of the reinforcing and non-reinforcing fillers. 12. Semi-finished rubber tire article, characterized in that it comprises a crosslinkable or crosslinked rubber composition according to any one of claims 1 to 11. 13. Pneumatic tire, characterized in that it comprises a semi-finished article as defined in claim 12. 14. Process for preparing a rubber composition for the manufacture of tires as defined in any one of claims 1 to 11, characterized in that it comprises the following steps - incorporating at least one of said diene elastomers, during a first step, the one or more reinforcing fillers and the one or more non-reinforcing fillers, by thermomechanically kneading the whole, in one or more times, until a maximum temperature of between 110 ° C. and 190 ° C. is reached; - Then incorporate, in a second step, a crosslinking system and knead the whole to a maximum temperature of less than 110 ° C, preferably less than 80 ° C.