Rubber composition

Abstract

The present invention relates to a rubber composition comprising a reinforcing filler, a crosslinking system, an elastomer A, a statistical copolymer comprising monomer units of a 1,3-diene and monomer units of a C4 alkyl methacrylate, wherein the monomer units of the methacrylate represent at least 30 mol % of the monomer units of the elastomer A. The rubber composition makes it possible to improve the reinforcement of treads made of the rubber composition.

Description

[0001] Description

[0002] Title: Rubber composition

[0003] The field of the present invention is that of rubber compositions reinforced by a reinforcing filler, in particular used in the manufacture of tires for vehicles.

[0004] One of the requirements for a tire tread is to withstand wear and tear and ground damage over time. One way to provide good mechanical resistance is to use a rubber compound with good reinforcement for the tire tread. As is well known, those skilled in the art can achieve this type of property by adding reinforcing fillers to the rubber compound.

[0005] But at the same time, the tire tread must also minimize its contribution to the tire's rolling resistance, i.e. be as hysteretic as possible. As is well known, those skilled in the art can achieve this type of property by reducing the amount of reinforcing filler in the rubber composition constituting the tread.

[0006] Another requirement for a tire tread is to ensure optimal grip on the road, especially on wet surfaces. One way to achieve this is to use a rubber compound with a high hysteresis potential for the tire tread.

[0007] Thus the rubber composition of the tread must satisfy potentially contradictory requirements, namely to have maximum reinforcement to satisfy the mechanical resistance requirement, to have as low a hysteresis as possible to satisfy the rolling resistance requirement, and to have high hysteresis to satisfy the wet grip requirement.

[0008] To improve the wet grip performance of a tire while maintaining a good compromise between performance and rolling resistance, it was proposed in patent application WO 2016 / 001052 to introduce elastomers comprising monomer units of a methacrylic acid ester into the rubber compositions constituting tire treads.

[0009] The Applicant, continuing the research efforts, discovered that the choice, as elastomer comprising monomer units of a methacrylic acid ester, of an elastomer comprising monomer units of a 1,3-diene and monomer units of a type of methacrylic acid ester (in this case a methacrylate of an alkyl having 4 carbon atoms) makes it possible to obtain rubber compositions having a better reinforcement index.

[0010] Thus, a first object of the invention is a rubber composition comprising:

[0011] - a reinforcing charge

[0012] - a crosslinking system

[0013] - an elastomer A, a random copolymer comprising monomer units of a 1,3-diene and monomer units of a methacrylic acid ester corresponding to the formula

[0014] CH2= CMe - COOR 1 in which Me is a methyl group and R 1is a C4 alkyl group, the monomer units of methacrylic acid representing at least 30 mol% of the monomer units of elastomer A.

[0015] Another subject of the invention is a semi-finished product, in particular a tread, comprising a rubber composition in accordance with the invention.

[0016] The invention also relates to a tire comprising a rubber composition in accordance with the invention or a semi-finished product, preferably a tread, which is in accordance with the invention. Such a tire has an improved compromise between rolling resistance and wet grip performance on the one hand, and good reinforcement on the other hand.

[0017] Detailed description

[0018] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​from more than a to less than b (i.e., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (i.e., including the strict limits a and b).

[0019] All percentages are by mass unless otherwise stated.

[0020] The abbreviation "pce" means parts by weight per hundred parts of elastomers present in the elastomer matrix.

[0021] The term elastomer matrix refers to all the elastomers present in the rubber composition.

[0022] The compounds mentioned in the description (typically polymers, fillers, plasticizers, coupling agents, vulcanization system, other additives, etc.) may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned may also come from the recycling of materials already in use, that is to say, they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0023] In the present application, carbon chain means a chain which contains one or more carbon atoms.

[0024] In this application, we will denote C xa carbon chain (saturated or unsaturated) comprising x carbon atoms (x being an integer) and C x -C y a carbon chain (saturated or unsaturated) containing from x to y carbon atoms (y also being an integer). The name alkyl C x is used to refer to an alkyl consisting of a carbon chain having x carbon atoms. The name alkyl C x -C y is used to refer to an alkyl consisting of a carbon chain having x to y carbon atoms.

[0025] The invention described in more detail below relates to at least one of the objects defined according to any one of the following listed embodiments: 1- Rubber composition comprising:

[0026] - a reinforcing charge

[0027] - a crosslinking system

[0028] - an elastomer A, a random copolymer comprising monomer units of a 1,3-diene and monomer units of a methacrylic acid ester corresponding to the formula CH2= CMe - COOR 1 in which Me is a methyl group and R 1 is a C4 alkyl group, the monomer units of the methacrylic acid ester representing at least 30 mol% of the monomer units of elastomer A.

[0029] 2- Rubber composition according to embodiment 1 in which R 1 is a linear alkyl group.

[0030] 3- Rubber composition according to any one of embodiments 1 to 2 in which the monomer units of the methacrylic acid ester represent at least 40 mol% of the monomer units of the elastomer A.

[0031] 4- Rubber composition according to any one of embodiments 1 to 3 in which the monomer units of the methacrylic acid ester represent at most 90 mol%, preferably at most 80 mol%, more preferably at most 60 mol% of the monomer units of elastomer A.

[0032] 5- Rubber composition according to any one of embodiments 1 to 3 in which the monomer units of the methacrylic acid ester represent at most 60 mol% of the monomer units of the elastomer A.

[0033] 6- Rubber composition according to any one of embodiments 1 to 5 in which the elastomer A is a copolymer of 1,3-diene and methacrylic acid ester.

[0034] 7- Rubber composition according to any one of embodiments 1 to 6 in which the 1,3-diene is 1,3-butadiene or isoprene or a mixture of 1,3-butadiene and isoprene, preferably 1,3-butadiene.

[0035] 8- Rubber composition according to any one of embodiments 1 to 7 in which the reinforcing filler comprises a silica.

[0036] 9- Rubber composition according to embodiment 8 in which the silica represents more than 50% by mass of the reinforcing filler, preferably more than 80% by mass of the reinforcing filler.

[0037] 10- Rubber composition according to any one of embodiments 1 to 9 in which the crosslinking system is a vulcanization system.

[0038] 11- Semi-finished product comprising a composition according to any one of the preceding embodiments.

[0039] 12- Semi-finished product according to embodiment 11 characterized in that it is a tire tread.

[0040] 13- Tire comprising a semi-finished product according to any one of embodiments 11 to 12 or a rubber composition according to any one of embodiments 1 to 10.

[0041] An essential characteristic of the rubber composition of the invention is to comprise an elastomer A, a random copolymer comprising monomer units of a 1,3-diene and monomer units of a methacrylic acid ester. The methacrylic acid ester whose monomer units constitute the elastomer A corresponds to the following formula (I):

[0042] CH2= CMe - COOR 1 (I) in which Me is a methyl group and R 1 is a C4 alkyl group.

[0043] Preferably, R 1 is a linear alkyl group, and R 1 is then n-butyl.

[0044] The monomer units of the methacrylic acid ester represent at least 30 mol%, preferably at least 40 mol%, of the monomer units of elastomer A.

[0045] According to one embodiment of the invention, the monomer units of the methacrylic acid ester represent at most 90 mol%, preferably at most 80 mol%, and more preferably at most 60 mol% of the monomer units of elastomer A.

[0046] These preferred ranges which relate to the molar percentages of the monomer units of the methacrylic acid ester in the elastomer A can be applied to any of the embodiments of the invention.

[0047] As 1,3-dienes whose monomeric units constitute elastomer A, the following are particularly suitable:

[0048] 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(a C1-C5 alkyl)-1,3-butadienes such as, for example,

[0049] 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. The 1,3-diene is preferably

[0050] 1,3-butadiene, isoprene or a mixture of 1,3-butadiene and isoprene. More preferably, the 1,3-diene is 1,3-butadiene.

[0051] The 1,3-diene monomer units constituting elastomer A preferably represent at least 10 mol% of the monomer units of elastomer A.

[0052] According to one embodiment of the invention, elastomer A is an elastomer obtained by radical polymerization, in particular in bulk, in solution or in dispersed medium, in particular in emulsion, dispersion or suspension. Radical polymerization, in particular in bulk, in solution or in dispersed medium is a process well known to those skilled in the art of polymer synthesis. The choice of one or other of these three processes can be guided for example by the reactivity of the monomers to be polymerized, the polymerization kinetics or the exothermicity of the polymerization reaction. For the choice of the polymerization process, reference can for example be made to the following publications which are Macromolecules, 1998, 31, 2822-2827; Macromolecules, 2006, 39, 923-930; J. Am. Chem. Soc. 1951, 73, 5736. This embodiment may be applied to any of the embodiments of the invention.

[0053] According to a preferred embodiment of the invention, elastomer A is a random copolymer of a 1,3-diene as defined above and of a methacrylic acid ester of formula (I). Elastomer A can then be obtained by radical polymerization of 1,3-diene and of the methacrylic acid ester according to one of the methods mentioned above. According to this preferred embodiment, advantageously the monomer units of the methacrylic acid ester represent from 40 to 60 mol% of the monomer units of the elastomer A, and consequently the monomer units of the 1,3-diene from 40 to 60 mol% of the monomer units of the elastomer A. The elastomer A itself can consist of a single elastomer or of several elastomers which differ from each other by their composition or their macrostructure (in particular the distribution of molar masses of the polymer chains which compose them).

[0054] The rubber composition may comprise, in addition to elastomer A, other elastomers. Other suitable elastomers include, in particular, elastomers usually used in rubber compositions intended for the manufacture of tires, such as polyisoprenes, polybutadienes, isoprene copolymers, butadiene copolymers such as butadiene and styrene copolymers.

[0055] According to any one of the embodiments of the invention, the level of elastomer A in the rubber composition is preferably greater than 50 phr, more preferably greater than 80 phr, even more preferably equal to 100 phr. When elastomer A is used at a level of 100 phr, it is then the only elastomer present in the rubber composition.

[0056] These preferred variants of the rate of elastomer A in the rubber composition can be applied to any of the embodiments of the invention.

[0057] The rubber composition according to the invention comprises a reinforcing filler which, according to one embodiment of the invention, comprises a silica.

[0058] The silica (SiO2) used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica. Examples of highly dispersible precipitated silicas (known as "HDS") include "Ultrasil" 7000 and "Ultrasil" 7005 silicas from Degussa, "Zeosil" 1165MP, 1135MP and 1115MP silicas from Rhodia, "Hi-Sil" EZ150G silica from PPG, "Zeopol" 8715, 8745 and 8755 silicas from Huber, and high specific surface silicas as described in application WO 03 / 016387.

[0059] The physical state in which silica is presented is indifferent, whether in the form of powder, microbeads, granules, or even balls.

[0060] According to one embodiment of the invention, the silica represents more than 50% by mass of the reinforcing filler: the silica is then the majority reinforcing filler by mass. Preferably, the silica represents more than 80% by mass of the reinforcing filler. These preferential ranges of mass proportion of silica in the reinforcing filler can apply to any of the embodiments of the invention.

[0061] It will be noted that the reinforcing filler may contain, in addition to silica, at least one other reinforcing filler which may be a reinforcing inorganic filler or a reinforcing organic filler.

[0062] By "reinforcing inorganic filler" is meant in the present application, by definition, any inorganic or mineral filler (whatever its color and origin (natural or synthetic)), also called "white" filler, "light" filler or even "non-black filler" as opposed to carbon black, capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words capable of replacing, in its reinforcing function, a conventional tire-grade carbon black; such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface.As reinforcing inorganic filler other than silica, mention will also be made of mineral fillers of the aluminous type, in particular alumina (AI2O3) or aluminum (oxide)hydroxides, or even reinforcing titanium oxides, for example described in US 6,610,261 and US 6,747,087.

[0063] If the reinforcing filler contains a reinforcing organic filler, the reinforcing organic filler is preferably a carbon black. This reinforcing organic filler, preferably carbon black, is then preferably present in a weight percentage of less than 50%.

[0064] According to the particular embodiment where the silica represents more than 50% by mass of the reinforcing filler, the carbon black is preferably used at a rate of less than 20 phr, more preferably less than 10 phr (for example between 0.5 and 20 phr, in particular between 2 and 10 phr), even more preferably less than 5 phr. In the indicated ranges, the coloring (black pigmenting agent) and anti-UV properties of the carbon blacks are benefited from, without otherwise penalizing the typical performances provided by the reinforcing inorganic filler.

[0065] Suitable carbon blacks are all carbon blacks, including those conventionally used in tires. Among the latter, we will mention in particular the reinforcing carbon blacks of the 100, 200, 300 series, or the 500, 600 or 700 series blacks (ASTM grades), such as for example 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 certain of the rubber additives used.

[0066] Preferably, the reinforcing filler content in the rubber composition is between 40 and 200 phr. Below 40 phr, the reinforcement of the rubber composition could be insufficient to provide an adequate level of cohesion or wear resistance of the rubber composition. Above 200 phr, there is a risk of increased hysteresis and therefore increased rolling resistance of the tires. More preferably, the reinforcing filler content in the rubber composition is between 60 and 140 phr. These preferred ranges of the reinforcing filler content can apply to any of the embodiments of the invention.

[0067] In embodiments where the reinforcing filler comprises a silica, and in particular in the case where the silica constitutes more than 50% by weight of the reinforcing filler of the rubber composition, a coupling agent (or bonding agent) is typically used in a well-known manner to couple the silica to at least one of the elastomers which constitute the elastomer matrix of the rubber composition.

[0068] As is well known, a coupling agent is an agent capable of establishing a sufficient bond of a chemical and / or physical nature between the filler in question and the elastomer, while facilitating the dispersion of this filler within the elastomer matrix. This at least bifunctional agent is intended to ensure a sufficient connection, of a chemical and / or physical nature, between the inorganic filler, in this case silica, and the elastomer. In particular, organosilanes are used, in particular polysulfurized alkoxysilanes or mercaptosilanes, or even polyorganosiloxanes carrying functions capable of physically and / or chemically bonding to the inorganic filler and functions capable of physically and / or chemically bonding to the elastomer, for example via a sulfur atom.Silica / elastomer bonding agents, in particular, have been described in a large number of documents, the best known being bifunctional alkoxysilanes such as polysulfurized alkoxysilanes. In particular, polysulfurized silanes, called "symmetrical" or "asymmetrical" depending on their particular structure, are used, as described for example in applications WO03 / 002648 (or US 2005 / 016651) and WO03 / 002649 (or US 2005 / 016650).

[0069] As coupling agent other than polysulfurized alkoxysilane, mention will be made in particular of bifunctional POSS (polyorganosiloxanes) or hydroxysilane polysulfides as described in patent applications WO 02 / 30939 (or US 6,774,255) and WO 02 / 31041 (or US 2004 / 051210), or silanes or POSS carrying azo-dicarbonyl functional groups, as described for example in patent applications WO 2006 / 125532, WO 2006 / 125533, WO 2006 / 125534.

[0070] Suitable coupling agents are also alkoxysilanes with an amine function, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 2-aminoethyltriethoxysilane, available for example from the suppliers Sigma-Aldrich, Gelest and Molport.

[0071] The content of coupling agent in the rubber composition according to the invention, whether it is a single compound or a mixture of compounds, is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Typically the level of coupling agent represents from 0.5% to 15% by weight relative to the quantity of silica. Its level is preferably between 0.5 and 12 phr, more preferably within a range of 3 to 10 phr. This level is easily adjusted by a person skilled in the art according to the level of silica used in the composition, and its preferred ranges are applicable to any of the embodiments of the invention.

[0072] Another essential characteristic of the composition according to the invention is to comprise a crosslinking system.

[0073] The crosslinking system may be based on sulfur, peroxides or mixtures thereof. In other words, the crosslinking may be based on reactions involving sulfur or peroxides or both. The level of the compound(s) constituting the crosslinking system introduced into the rubber composition is adjusted by a person skilled in the art depending on the desired degree of crosslinking of the rubber composition and the chemical nature of the crosslinking system. This degree of crosslinking is defined by a person skilled in the art according to the desired rigidity of the rubber composition in the crosslinked state, this rigidity varying according to the intended application of the rubber composition.

[0074] The crosslinking system according to the invention is preferably a vulcanization system, that is to say a system based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. To this basic vulcanization system may be added, incorporated during the first non-productive phase and / or during the productive phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders.As a (primary or secondary) vulcanization accelerator, any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur may be mentioned, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. The sulfur is used at a preferred rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The primary vulcanization accelerator is used in the rubber composition at a preferred rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr. These preferred ranges relating to the sulfur and accelerator levels may apply to any of the embodiments.

[0075] The rubber composition in accordance with the invention may also contain coupling activators, silica covering agents or more generally processing aids capable, in a known manner, thanks to an improvement in the dispersion of the filler in the elastomer matrix and a reduction in the viscosity of the rubber composition, of improving its processability in the raw state, these agents being, for example, hydrolyzable silanes such as alkylalkoxysilanes, polyols, polyethers, hydroxylated or hydrolyzable polyorganosiloxanes.

[0076] The rubber composition in accordance with the invention may also comprise all or part of the usual additives normally used in rubber compositions intended for the manufacture of tires, such as, for example, plasticizers, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents and mixtures of such compounds.

[0077] The rubber composition in accordance with the invention can be manufactured in suitable mixers, generally using two successive preparation phases well known to those skilled in the art: a first phase of thermomechanical working or kneading (so-called "non-productive" phase) at high temperature, up to a maximum temperature of between 110°C and 190°C, preferably between 120°C and 180°C, followed by a second phase of mechanical working (so-called "productive" phase) down to a lower temperature, typically below 110°C, for example between 40°C and 100°C, finishing phase during which the crosslinking system is incorporated.

[0078] The rubber composition in accordance with the invention can be prepared according to a process which comprises the following steps:

[0079] - thermomechanically kneading the elastomer matrix, the reinforcing filler, the coupling agent, and the other additives of the rubber composition with the exception of the crosslinking system, until a maximum temperature of between 110°C and 190°C is reached;

[0080] - cool the assembly to a temperature below 100°C;

[0081] - then incorporate the crosslinking system;

[0082] - knead everything to a maximum temperature below 110°C to obtain a rubber composition.

[0083] After incorporating all the ingredients of the rubber composition, the final composition thus obtained is then calendered, for example in the form of a sheet or plate, in particular for characterization in the laboratory, or extruded, to form for example a rubber profile used as a rubber component or semi-finished product, in particular for the manufacture of a tire. The rubber composition according to the invention can be used in the form of calendering in a tire. The calendering or the extrudate formed from the rubber composition constitutes in whole or in part a semi-finished product, in particular a tire.

[0084] Thus, according to a particular embodiment of the invention, the rubber composition in accordance with the invention, which may be either in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), is in a tire, for example in a tire tread.

[0085] Crosslinking (or curing), and where appropriate vulcanization, is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which may vary, for example, between 5 and 120 min depending in particular on the curing temperature, the crosslinking system adopted and the crosslinking kinetics of the composition in question.

[0086] The semi-finished product in accordance with the invention has the essential characteristic of being made up in whole or in part of the rubber composition in accordance with the invention. It can be manufactured according to the process described above which comprises an additional step of calendering or extrusion of the rubber composition. It is preferably a tire tread.

[0087] The invention also relates to the tread previously described both in the raw state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).

[0088] The invention also relates to the tire comprising a rubber composition or a semi-finished product in accordance with the invention, which tire is both in the raw state and in the cured state, the semi-finished product preferably being a tread. In the present invention, the term "tire" means a pneumatic or non-pneumatic bandage. A pneumatic bandage usually comprises two beads intended to come into contact with a rim, a crown composed of at least one crown reinforcement and a tread, two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic bandage, for its part, usually comprises a base, designed for example for mounting on a rigid rim, a crown reinforcement, ensuring the connection with a tread and a deformable structure, such as spokes, ribs or cells, this structure being arranged between the base and the crown.Such non-pneumatic tires do not necessarily include a sidewall. Non-pneumatic tires are described for example in documents WO 03 / 018332 and FR2898077. According to any one of the embodiments of the invention, the tire according to the invention is preferably a pneumatic tire.

[0089] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative and non-limiting purposes.

[0090] Examples

[0091] I. Measurements and tests used 1.1 Determination of the glass transition temperature of elastomers

[0092] The glass transition temperatures Tg and glass transition widths ATg of polymers are measured using a differential scanning calorimeter according to ASTM D3418-08.

[0093] 1.2. Determination of the microstructure of elastomers by NMR (nuclear magnetic resonance) analysis

[0094] The determination of the methacrylate unit content is carried out by 1H NMR analysis. The spectra are acquired on an Avance 500 MHz BROKER spectrometer equipped with a BBFO z-grad 5 mm "broadband" cryoprobe for soluble samples and a 4 mm HRMAS probe. 1 H / 13 C for insoluble crosslinked samples.

[0095] The quantitative 1H NMR experiment uses a single 30° pulse sequence and a 5-second repetition delay between each acquisition. Samples are solubilized in deuterated chloroform.

[0096] Chemical shifts are calibrated relative to the protonated impurity of chloroform versus tetramethylsilane, TMS (6 ppm 3 H at 0 ppm).

[0097] Attribution of NMR signals 3H used for quantification in butadiene / alkyl methacrylate copolymers:

[0098] 1.3 Determination of the macrostructure of elastomers by SEC analysis

[0099] The SEC (Size Exclusion Chromatography) technique is used to separate macromolecules in solution according to their size through columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first. : the SEC is coupled with a refractometer, in this case it gives relative information. From commercial standard products, the different number-average molar masses (M n ) and in weight (M w ) which characterize the molar mass distribution of the polymer, can be determined and the polymolecularity index (Ip = M w / M n) calculated via a so-called Moore calibration. There is no special treatment of the polymer sample before analysis. It is simply solubilized in the elution solvent at a concentration of approximately 1 g / L. The solution is then filtered through a 0.45 pm porosity filter before injection.

[0100] The equipment used is a "WATERS alliance" chromatographic chain. The elution solvent is tetrahydrofuran, the flow rate is 1 mL / min, the system temperature is 35°C and the analysis time is 45 min. A set of three AGILENT columns (Mixed BLS) is used. The injected volume of the polymer sample solution is 100 pL. The detector is a "WATERS 2414" differential refractometer and the chromatographic data processing software is the "WATERS EMPOWER" system.

[0101] The calculated average molar masses are relative to a calibration curve produced from commercial standard polystyrenes “PSS READY CAL-KIT”.

[0102] 1.4 Determination of the coefficient of friction

[0103] The coefficient of friction was measured on a test piece and is listed in the table of examples under the name “p laboratory”.

[0104] The dynamic friction coefficient measurements were carried out using a method identical to that described by L. Busse, A. Le Gai, and M. Küppel (Modelling of Dry and Wet Friction of Silica Filled Elastomers on Self-Affine Road Surfaces, Elastomere Friction, 2010, 51, p. 8). The specimens are produced by molding and then crosslinking a 6 mm thick square rubber support (50mmx50mm). After closing the mold, it is placed in a press with heated plates at a pressure of 16 bars, at the temperature (typically 150°C) and for the time (typically several tens of minutes) necessary for the material to crosslink. The soil used to carry out these measurements is a core sample taken from a real road surface made of BBTM type bituminous concrete (NF P 98-137 standard).To avoid dewetting phenomena and the appearance of parasitic adhesion forces between the soil and the material, the soil + specimen system is immersed in a 5% aqueous solution of a surfactant (Sinnozon - CAS number: 25155-30-0). The temperature of the aqueous solution is regulated using a thermostatic bath. The specimen is subjected to a sliding movement in translation parallel to the soil plane. The sliding speed Vg is set at 1.2 m / sec. The applied normal stress o. n is 300 kPa. These conditions are described below as "wet soil conditions". The tangential stress o is continuously measured t opposite to the movement of the specimen on the ground. The ratio between the tangential stress o t and the normal stress o ngives the dynamic friction coefficient p. The values ​​of p are measured for an aqueous solution temperature of 5 to 45°C, and obtained in steady state after stabilization of the value of the tangential stress o t .

[0105] The maximum dynamic friction coefficient over the aqueous solution temperature range of 5 to 45°C (denoted "p laboratory max" in the table of examples) is a relevant descriptor of the intrinsic wet grip performance of the rubber composition tested. Since the results are expressed on a base of 100, a value higher than the reference value, arbitrarily set at 100, indicates an improved result.

[0106] 1.5 Determination of the loss factor

[0107] The dynamic properties tan 6 max are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm thick and 400 mm long) is recorded. 2 section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under normal temperature conditions (23°C) according to standard ASTM D 1349-99. A strain amplitude sweep is carried out from 0.1% to 100% (forward cycle), then from 100% to 0.1% (return cycle). The result used is the loss factor tan 6 between the values ​​at 0.1 and 100% strain (Payne effect). For the return cycle, the maximum value of tan 6 observed is indicated, noted tan 6 max return.

[0108] The tan 6 max return is a descriptor of the intrinsic rolling resistance performance of the rubber composition tested. Since the results are expressed on a base of 100, a value lower than the reference value, arbitrarily set at 100, indicates an improved result (lower rolling resistance). 1.6 Determination of reinforcement on a force-elongation curve

[0109] Tensile tests are carried out in accordance with French standard NF T 46-002 of September 1988. The nominal secant modulus (or apparent stress) is measured in MPa, calculated by referring to the initial section of the specimen in MPa, at 100% elongation noted MA100, and 250% elongation noted MA250.

[0110] All these tensile measurements are carried out under normal temperature (23 + / - 2°C) and hygrometry (50 + / - 5% relative humidity) conditions, according to the French standard NF T 40-101 (December 1979). The ratio between the modulus of rigidity under tension at 250% elongation and the modulus of rigidity under tension at 100% elongation, subsequently noted MA250 / MA100, is a descriptor of the reinforcement of the rubber composition tested at large deformations. The results being expressed on a base of 100, a value higher than that of the reference, arbitrarily set at 100, indicates an improved result.

[0111] Preparation of elastomers

[0112] The elastomers used for the examples are prepared as follows:

[0113] Synthesis of 1,3-butadiene and 2-ethylhexyl methacrylate copolymer (Elastomer 1): The reaction takes place in a 100-liter reactor. 0.7 kg (0.5 pce) of sodium dodecyl sulfate (SDS) is dissolved in 15 liters of demineralized water. 6.29 g of cumene hydroperoxide (0.05 equivalent of transfer agent relative to SDS), 2.5 kg of 1,3-butadiene and 3 kg of n-butyl methacrylate are added to the reaction medium. The reactor is heated to 5°C with a stirring speed of 80 rpm, before introducing 0.23 kg (1.2 pce) of potassium persulfate. After 410 minutes of polymerization reaction, 62% conversion of monomers into copolymer is reached. The reaction is then stopped by adding 0.67 kg (3 pce) of resorcinol. The latex is then coagulated in two volumes of an acetone / ethanol mixture. The copolymer is then dried in an oven at 45°C.3.4 kg of 1,3-butadiene and 2-ethylhexyl methacrylate copolymer are recovered with a volatile matter content of less than 1%.

[0114] Synthesis of 1,3-butadiene and n-butyl methacrylate copolymer (Elastomer 2): The reaction takes place in a 10-liter reactor. 67 g (5 pce) of sodium stearate are dissolved in 2.56 liters of demineralized water. 1 g of tert-dodecyl mercaptan (0.05 equivalent of transfer agent relative to potassium persulfate), 369 g of 1,3-butadiene and 990.5 g of n-butyl methacrylate are added to the reaction medium. The reactor is heated to 50°C and stirring is started. 25.6 g (1.2 pce) of potassium persulfate dissolved in 789 ml of water are then added. After 80 minutes of polymerization reaction, 60% conversion of monomers into copolymer is reached. The reaction is then stopped by adding 27.5g of resorcinol (2.6 equivalents of resorcinol relative to potassium persulfate) dissolved in 789ml of water. The latex is then coagulated in two volumes of an acetone / ethanol mixture.The copolymer is then dried in an oven at 45°C. 0.74 kg of butadiene and n-butyl methacrylate copolymer are recovered with a volatile matter content of less than 1%.

[0115] The copolymers obtained have the following characteristics:

[0116] For elastomer 1 (copolymer of 1,3-butadiene and 2-ethylhexyl methacrylate): Tg = -53°C and ATg = 8°C Mn = 238,000 g / mol (PS calibration) and Ip = 2.5

[0117] Mol % (2-ethylhexyl methacrylate monomer unit) = 43.9

[0118] Mol % (butadiene monomer unit) = 56.1

[0119] For elastomer 2 (copolymer of 1,3-butadiene and n-butyl methacrylate):

[0120] Tg = -46°C and ATg = 7°C

[0121] Mn = 356 OOOg / mol (PS calibration) and Ip = 3.4

[0122] Mol % (n-butyl methacrylate monomer unit) = 44.4

[0123] Mol % (butadiene monomer unit) = 55.6

[0124] III Preparation of rubber compositions

[0125] Two rubber compositions C1 and C2 are prepared. The formulations (in pce) of compositions C1 and C2 are described in Table 1.

[0126] Composition C2 is in accordance with the invention; composition C1 is not in accordance with the invention.

[0127] Compositions C1 and C2 also both contain a reinforcing filler, in this case, silica.

[0128] Compositions C1 and C2 both contain an elastomer, a random copolymer comprising monomer units of a 1,3-diene (in this case, monomer units of 1,3-butadiene) and monomer units of a methacrylic acid ester (an alkyl methacrylate), the monomer units of the methacrylic acid ester representing at least 30 mol% (in this case, 44 mol% for elastomer 1 in C1, and 44 mol% for elastomer 2 in C2) of the monomer units of the elastomer. In composition C1, not in accordance with the invention, the alkyl group is 2-ethylhexyl (a C8 alkyl group), the methacrylate being 2-ethylhexyl methacrylate (hereinafter referred to as EHMA). In composition C2, in accordance with the invention, the alkyl group is n-butyl (a C4 alkyl group), the methacrylate being n-butyl methacrylate (hereinafter referred to as BuMA).

[0129] The crosslinking systems of compositions Cl and C2 are vulcanization systems.

[0130] The manufacturing of these compositions is carried out as follows: the elastomer, the silica, the coupling agent, the plasticizer and the various other ingredients, with the exception of the crosslinking system, are successively introduced into an internal mixer (final filling rate: approximately 70% by volume), whose initial tank temperature is approximately 60°C. Thermomechanical work (non-productive phase) is then carried out in one step, lasting a total of 5 minutes, until a maximum "drop" temperature of 165°C is reached.

[0131] The mixture thus obtained is recovered, cooled and then the crosslinking system is incorporated into a mixer (homo-finisher) at 23°C, mixing everything (productive phase) for an appropriate time (for example between 5 and 12 min).

[0132] The compositions thus obtained are then calendered in the form of plates (with a thickness ranging from 2 to 3 mm) or thin sheets of rubber, for the measurement of their physical properties after vulcanization for 30 min at 170°C.

[0133] IV Properties of rubber compositions

[0134] The properties of compositions C1 and C2 are given on a base of 100 relative to C1 in Table 2. Composition C2, in accordance with the invention, has a maximum tan 6 return at 23°C and 10Hz very close to that of composition C1 (97 vs 100), which makes it possible to predict similar rolling resistance performance between a tire for which composition C2 is used in the tread and a tire for which composition C1 is used in the tread.

[0135] In addition, composition C2, in accordance with the invention, has a maximum laboratory p at 3 bars and 1.2 m / s very close to that of composition Cl (98 vs 100), which makes it possible to predict similar wet grip performance between a tire for which composition C2 is used in the tread and a tire for which composition Cl is used in the tread.

[0136] Furthermore, composition C2, in accordance with the invention, has a significantly improved MA250 / MA100 ratio compared to composition Cl (113 vs 100), which makes it possible to predict significantly better reinforcement and wear and attack resistance performance for a tire for which composition C2 is used in the tread than for a tire for which composition Cl is used in the tread.

[0137] The results obtained therefore show that the composition in accordance with the invention makes it possible to solve the technical problem in that it results in improved reinforcement while maintaining a good compromise between rolling resistance and grip on wet ground.

[0138] Table 1

[0139] (1) Copolymer of 1,3-butadiene and 2-ethylhexyl methacrylate (see paragraph IL)

[0140] (2) Copolymer of 1,3-butadiene and n-butyl methacrylate (see paragraph IL)

[0141] (3) Silica "Zeosil 1165 MP" from Solvay-Rhodia in the form of microbeads

[0142] (4) Liquid silane triethoxysilylpropyltetrasulfide (TESPT) “Si69” from Evonik

[0143] (5) Trioctyl phosphate (tri-2-ethylhexyl phosphate) “Disflamoll TOF” from Lanxess

[0144] (6) Diphenylguanidine (“Perkacit” DPG from Flexsys)

[0145] (7) N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (“6PPD” from Flexsys)

[0146] (8) ZnO, industrial grade zinc oxide from Umicore

[0147] (9) N-cyclohexyl-2-benzothiazol-sulfenamide (“Santocure CBS” from Flexsys)

[0148] Table 2

Claims

Claims 1 Rubber composition comprising: - a reinforcing charge - a crosslinking system - an elastomer A, a random copolymer comprising monomer units of a 1,3-diene and monomer units of a methacrylic acid ester corresponding to the formula CH2= CMe - COOR 1 in which Me is a methyl group and R 1 is a C4 alkyl group, the monomer units of the methacrylic acid ester representing at least 30 mol% of the monomer units of elastomer A. 2 Rubber composition according to claim 1 in which R 1 is a linear alkyl group. 3 Rubber composition according to any one of claims 1 to 2 in which the monomer units of the methacrylic acid ester represent at least 40 mol% of the monomer units of elastomer A. 4 Rubber composition according to any one of claims 1 to 3 in which the monomer units of the methacrylic acid ester represent at most 90 mol%, preferably at most 80 mol%, more preferably at most 60 mol% of the monomer units of elastomer A. 5 Rubber composition according to any one of claims 1 to 4 in which the elastomer A is a copolymer of 1,3-diene and methacrylic acid ester. 6 Rubber composition according to any one of claims 1 to 5 in which the 1,3-diene is 1,3-butadiene or isoprene or a mixture of 1,3-butadiene and isoprene, preferably 1,3-butadiene. 7 A rubber composition according to any one of claims 1 to 6 wherein the reinforcing filler comprises a silica. 8 Rubber composition according to claim 7 in which the silica represents more than 50% by mass of the reinforcing filler, preferably more than 80% by mass of the reinforcing filler. 9 Rubber composition according to any one of claims 1 to 8 in which the crosslinking system is a vulcanization system. 10 Semi-finished product comprising a composition according to any one of the preceding claims. 11 Semi-finished product according to claim 10 characterized in that it is a tire tread. 12 A tire comprising a semi-finished product according to any one of claims 10 to 11 or a rubber composition according to any one of claims 1 to 9.

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