Rubber compound for inner tire rubber containing a rubber powder

Abstract

The present invention relates to a rubber composition comprising a halogenated butyl rubber, a reinforcing filler comprising carbon black, a vulcanization system, and a rubber powder comprising a halogenated butyl rubber, a reinforcing filler comprising carbon black, a vulcanization system, and kaolin. The rubber composition improves the tear resistance after aging of the inner rubber liners of tires comprising the rubber composition.

Description

Title of the invention: Rubber composition for tire inner rubber comprising a rubber powder

[0001] The invention relates to tire rubber compositions comprising a rubber powder.

[0002] Indeed, it is of interest today for tire manufacturers to find solutions to lower the costs of rubber compositions without penalizing the performance of tires using these compositions.

[0003] This need is particularly important for the inner rubbers of tubeless tires. Indeed, in order to improve the tire's durability by preventing deflation and protecting its sensitive internal areas (the plies containing metal cables sensitive to oxidation, for example) against the ingress of oxygen and water, the inner rubbers are currently made of elastomeric compositions based on butyl rubber, which are expensive.

[0004] It is also in the interest of manufacturers to promote the recycling of end-of-life tires into new tires in order to reduce the environmental impact of their activity, for example by incorporating rubber crumbs (or "rubber crumbs") into tire compounds. These crumbs are obtained by grinding or micronizing vulcanized rubber compounds. Tires produced using this type of process are described in the prior art, for example in document WO2020 / 128255.

[0005] Tire manufacturers have sometimes also incorporated rubber powders from tire recycling or curing membranes into tire inner rubber compositions, as described in documents KR100943526, EP1612242 and US6730732.

[0006] However, inner tire rubber compounds must also exhibit good mechanical resistance properties, including after aging. Surprisingly, the Applicant discovered that the use of rubber compositions containing specific rubber powders, in that they contain kaolin, improves the tear resistance properties of inner tire rubber compounds after aging.

[0007] Thus, a first object of the invention is a rubber composition comprising a halogenated butyl rubber Bu2, a reinforcing filler RI comprising carbon black NI, a vulcanization system VI and a rubber powder comprising a halogenated butyl rubber Bu2, a reinforcing filler R2 comprising Carbon black N2, a V2 vulcanization system, and kaolin. Another object of the invention is an inner tire rubber comprising a rubber composition according to the invention. The invention also relates to a tire comprising an inner rubber or a rubber composition according to the invention. Detailed description

[0008] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​going from more than a to less than b (that is to say, bounds a and b excluded) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​going from a to b (that is to say, including the strict bounds a and b).

[0009] The abbreviation "pce" means parts by weight per hundred parts of elastomers present in the elastomer matrix. The elastomer matrix is ​​understood to mean all the elastomers present in the rubber composition according to the invention, excluding the elastomers present in any rubber powder, whether it be the rubber powder useful for the purposes of the invention, or any other rubber powder.

[0010] The compounds mentioned in the description (typically polymers, fillers, plasticizers, coupling agents, the vulcanization system, other additives, etc.) may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already used, 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.

[0011] The invention described in more detail below relates to at least one of the objects defined according to any one of the following embodiments: 1. Rubber composition comprising a halogenated butyl rubber Bul, a reinforcing filler RI comprising carbon black NI, a vulcanization system VI and a rubber powder comprising a halogenated butyl rubber Bu2, a reinforcing filler R2 comprising carbon black N2, a vulcanization system V2 and kaolin. 2. Rubber composition according to embodiment 1 in which the proportion of rubber powder ranges from 5 to less than 40 pieces. 3. Rubber composition according to any one of the preceding embodiments, wherein the rubber powder has a median particle size by volume of between 50 and 500 µm, preferably between 100 and 400 pm. 4. Rubber composition according to any of the preceding embodiments in which halogenated butyl rubber Bu2 represents at least 40% by mass of the total mass of the rubber powder. 5. Rubber composition according to any of the preceding embodiments in which the rubber powder comprises a polyisoprene elastomer representing from 0 to 20% by mass of the total mass of the rubber powder, the polyisoprene elastomer preferably containing more than 90% by mole of 1,4-cis bonding. 6. Rubber composition according to any one of the preceding embodiments wherein the halogenated butyl rubber Bu2 is a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of both. 7. Rubber composition according to any one of the embodiments previous in which the reinforcing charge R2 represents 10 to 40% by mass, preferably 20 to 30% by mass, of the total mass of the gum powder. 8. Rubber composition according to any of the preceding embodiments in which carbon black N2 represents more than 50% by mass, preferably more than 80% by mass, even more preferably 100% by mass of the total mass of the reinforcing filler R2. 9. Rubber composition according to any of the preceding embodiments in which kaolin represents from 3 to 30% by mass, preferably from 5 to 20% by mass of the total mass of the rubber powder. 10. Rubber composition according to any of the preceding embodiments wherein the content of halogenated butyl rubber Bul is greater than or equal to 70 parts per cent. 11. Rubber composition according to any of the preceding embodiments comprising from 0 to 30 pieces of a polyisoprene elastomer preferably containing more than 90 mol% of 1,4-cis bonding. 12. Rubber composition according to any one of the preceding embodiments wherein the halogenated butyl rubber Bul is a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of both. 13. Rubber composition according to any of the preceding embodiments in which the rate of the reinforcing filler RI goes from 20 to 80 pc. 14. Rubber composition according to any one of the embodiments previous ones in which the reinforcing filler RI is composed solely of carbon black. 15. Inner tire rubber comprising a rubber composition according to any of the preceding embodiments. 16. Tire comprising an inner rubber according to embodiment 15 or a rubber composition according to any one of embodiments 1 to 14. Elastomer

[0012] In the usual way, the terms "elastomer" and "rubber" are used interchangeably in the text.

[0013] An essential characteristic of the rubber composition according to the invention is that it contains a halogenated butyl rubber Bul. The halogenated butyl rubber can be used alone or in a mixture with one or more other diene elastomers.

[0014] By butyl rubber, we mean a copolymer of isobutylene and a 1,3-diene, in particular a copolymer of isobutylene and isoprene, as well as halogenated derivatives, in particular generally brominated or chlorinated, of these copolymers.

[0015] Butyl rubbers are well known to those skilled in the art, particularly for their airtightness. Generally, copolymers of isobutylene and a 1,3-diene, particularly isoprene, contain 1 to 5 mole percent of diene units, particularly isoprene, and have a Mooney viscosity (ML 1+8 at 125°C) of 30 to 60. Halogenated copolymers of isobutylene and a 1,3-diene, particularly isoprene, generally have a halogen content of 1 to 4 mass percent of the copolymer mass.

[0016] Examples of halogenated butyl rubbers particularly suitable for the realization of the invention include bromobutyl rubbers such as isobutylene and isoprene brominated copolymer (BIIR), chlorobutyl rubbers such as isobutylene and isoprene chlorinated copolymer (CIIR) and mixtures of these rubbers.

[0017] According to any one of the embodiments of the invention, the halogenated butyl rubber Bul is preferably a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of the two.

[0018] By "diene" elastomer, whether natural or synthetic, a known definition should be understood as an elastomer composed at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers bearing two carbon-carbon double bonds, conjugated or not). Suitable diene elastomers include those commonly used in rubber compositions for the manufacture of tires, such as that polyisoprenes, polybutadienes, isoprene copolymers, butadiene copolymers such as butadiene and styrene copolymers.

[0019] According to one embodiment of the invention, the rubber composition according to the invention comprises from 0 to 30 parts per mol of a diene II elastomer other than a halogenated butyl rubber and selected from the group consisting of polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers, and mixtures thereof. Preferably, the diene II elastomer is a polyisoprene elastomer and, even more preferably, the diene II elastomer contains more than 90 mol% of 1,4-cis bonding. These preferred ranges of elastomer content in the rubber composition according to the invention and of molar percentage of 1,4-cis bonding in the polyisoprene II elastomer as well as these preferred choices of diene elastomer can be applied to any of the embodiments of the invention.

[0020] According to any one embodiment of the invention, the proportion of halogenated butyl rubber (Bul) in the rubber composition according to the invention is preferably greater than or equal to 70 parts per liter. Preferably, the additional rubber used to achieve the 100 parts per liter rubber content in the rubber composition according to the invention is natural rubber. Charge

[0021] The rubber composition according to the invention comprises at least one reinforcing filler RI. Any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition usable in particular for the manufacture of tires, can be used, for example an organic reinforcing filler such as carbon black, an inorganic reinforcing filler such as silica or a mixture of these two types of fillers.

[0022] The reinforcing filler RI of the rubber composition according to the invention comprises carbon black NI. Any carbon black may be suitable, including those conventionally used in tires. These carbon blacks may be used in isolation, as commercially available, or in any other form, for example, as a carrier for some of the rubberizing additives used.

[0023] The carbon black of the rubber composition according to the invention has, in a preferred embodiment, a specific surface area BET ranging from 20 to 60 m² / g. This preferred range of specific surface area BET of carbon black can be applied to any one of the embodiments of the invention.

[0024] The specific surface area BET 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), and more specifically according to a Method adapted from standard NF ISO 5794-1, Annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160°C - relative pressure range w / in: 0.05 to 0.2].

[0025] According to one embodiment of the invention, the proportion of reinforcing filler RI in the rubber composition according to the invention ranges from 20 to 80 parts per liter. Outside this range, the rubber composition may no longer exhibit rigidity compatible with use as an inner tire compound.

[0026] According to a preferred embodiment of the invention, the carbon black NI included in the reinforcing filler of the rubber composition according to the invention is present at a level ranging from 20 to 80 parts per cent. Clearly, the level of carbon black NI in the rubber composition is less than or equal to the level of reinforcing filler RI in the rubber composition. In the even more preferred embodiment where these two levels are equal, the reinforcing filler RI consists solely of carbon black. Vulcanization system

[0027] An essential characteristic of the rubber composition according to the invention is that it comprises a vulcanization system VI, that is to say, a crosslinking system based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. Various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine), or known vulcanization retardants, can be added to this basic vulcanization system. One can cite as a (primary or secondary) vulcanization accelerator any compound capable of acting as a vulcanization accelerator of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithio-phosphate, thio-urea and xanthate types.Sulfur is used at a preferential rate of between 0.5 and 12 parts per annum, particularly between 0.5 and 5 parts per annum. The primary vulcanizing accelerator is used in the rubber composition according to the invention at a preferential rate of between 0.5 and 10 parts per annum, more preferably between 0.5 and 5.0 parts per annum. These preferred ranges for sulfur and accelerator levels can be applied to any one of the embodiments. Gum powder

[0028] Another essential characteristic of the rubber composition according to the invention is that it contains a rubber powder.

[0029] It is recalled that rubber powders are generally in the form of granules (or granules), possibly in the form of a rubber plate. Rubber powders are most often a recycled material product: they are obtained by grinding, particularly micronizing, cured rubber compositions that have already been used in a previous application, for example, as tire curing membranes (as in document US6730732) or as end-of-life tires (as in document KR100943526). Any method or process that does not degrade the rubber during grinding is suitable for grinding rubber compositions. For example, a grinding method using water, such as those described in documents US4374573, US4714201, US5238194, and US5411215, can be chosen: such a method keeps the rubber temperature sufficiently low to prevent reversion, i.e., the degradation of the rubber's cross-linking network. A cryogenic grinding method can also be used.Depending on the resulting object size distribution, the gum powder obtained by the aforementioned processes may undergo an additional sieving step to further control this distribution. Sieving can be performed using various technologies (vibration, centrifugation, aspiration) known to those skilled in the art. Gum powders from the grinding process are generally in the form of microparticles. By "microparticles," we mean particles whose size—namely their diameter in the case of spherical particles or their largest dimension in the case of anisotropic particles—is on the order of tens or hundreds of microns.

[0030] According to one embodiment of the invention, the gum powder useful for the purposes of the invention is in the form of microparticles preferably having a median volume size of the gum powder particles between 50 and 500 pm, preferably between 100 and 400 pm. These particle size ranges can be applied to any one of the embodiments of the invention.

[0031] An essential characteristic of the rubber powder useful for the purposes of the invention is that it contains a halogenated butyl rubber Bu2. The halogenated butyl rubber Bu2 can be used alone or in a mixture with one or more other diene elastomers.

[0032] According to any one of the embodiments of the invention, the halogenated butyl rubber Bu2 is preferably a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of the two.

[0033] According to one embodiment of the invention, the rubber powder used for the purposes of the invention comprises from 0 to 20% by mass of the total mass of the rubber powder of a diene elastomer 12 other than a halogenated butyl rubber and selected from the group consisting of polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures thereof. Preferably, the diene elastomer 12 is a polyisoprene elastomer and, even more preferably, a polyisoprene elastomer. In the reference formulation, diene elastomer 12 is a polyisoprene elastomer containing more than 90 mol% of 1,4-cis bonding. These preferred ranges of mass percentage of elastomer in the gum powder useful for the purposes of the invention and of molar percentage of 1,4-cis bonding in polyisoprene elastomer 12, as well as these preferred choices of diene elastomer, can be applied to any one of the embodiments of the invention.

[0034] According to any one embodiment of the invention, the mass percentage of halogenated butyl rubber Bu2 in the rubber powder used for the purposes of the invention is preferably greater than or equal to 40%, a mass percentage calculated relative to the total mass of the rubber powder. Preferably, the only other rubber present in the rubber powder used for the purposes of the invention is natural rubber.

[0035] The rubber powder useful for the needs of the invention comprises at least one reinforcing filler R2. Any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition usable in particular for the manufacture of tires, can be used, for example an organic reinforcing filler such as carbon black, an inorganic reinforcing filler such as silica or a mixture of these two types of fillers.

[0036] The reinforcing filler R2 of the rubber powder useful for the purposes of the invention comprises carbon black N2. Any carbon black may be suitable, including those conventionally used in tires. These carbon blacks may be used in their isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubberizing additives used.

[0037] According to one embodiment of the invention, the mass percentage of the reinforcing filler R2 in the gum powder useful for the needs of the invention ranges from 20 to 30%, mass percentage calculated in relation to the total mass of the gum powder.

[0038] According to a preferred embodiment of the invention, the carbon black N2 included in the reinforcing filler R2 of the rubber powder used in the invention represents more than 50% by mass, preferably more than 80% by mass, and even more preferably 100% by mass of the reinforcing filler R2 of the rubber powder used in the invention. In this even more preferred embodiment, the reinforcing filler R2 consists solely of carbon black, which is the only reinforcing filler present in the rubber composition of the rubber powder used in the invention.

[0039] An essential characteristic of the gum powder useful for the purposes of the invention is that it comprises a V2 vulcanization system, that is to say a system A sulfur-based (or sulfur-donating) crosslinking agent and a primary vulcanization accelerator are used. Various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid or equivalent compounds, guanidine derivatives (particularly diphenylguanidine), or known vulcanization retarders, can be added to this basic vulcanization system. Examples of vulcanization accelerators (primary or secondary) include any compound capable of accelerating the vulcanization of diene elastomers in the presence of sulfur, notably thiazole-type accelerators and their derivatives, sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea, and xanthate-type accelerators.Sulfur is used in the gum powder relevant to the needs of the invention at a preferential rate of between 0.5 and 12% by mass of the total elastomer mass of the gum powder, in particular between 0.5 and 5% by mass of the total elastomer mass of the gum powder. The primary vulcanization accelerator is used in the gum powder relevant to the needs of the invention at a preferential rate of between 0.5 and 10% by mass, more preferably between 0.5 and 5.0% by mass of the total elastomer mass of the gum powder. These preferential ranges for the sulfur and primary accelerator rates can be applied to any of the embodiments.

[0040] The gum powder useful for the purposes of the invention has as its essential characteristic the presence of kaolin. Kaolin (Al₂O₃ 2SiO₂ 2H₂O) is a non-reinforcing, lamellar mineral filler belonging to the family of natural phyllosilicates.

[0041] According to a preferred embodiment of the invention, kaolin represents from 3 to 30% by mass, preferably from 5 to 20% by mass, of the total mass of the gum powder used for the purposes of the invention. These ranges of mass percentages of kaolin in the gum powder used for the purposes of the invention can be applied to any one of the embodiments of the invention.

[0042] According to one embodiment of the invention, the proportion of the gum powder useful for the purposes of the invention in the rubber composition according to the invention ranges from 5 to less than 40 parts per liter. Below 5 parts per liter of gum powder in the rubber composition, the desired effect may not be sufficiently strong. For a proportion equal to or greater than 40 parts per liter of gum powder in the rubber composition, the industrial implementation of the rubber composition may be hampered. This preferred range for the proportion of gum powder in the rubber composition according to the invention can be applied to any one of the embodiments.

[0043] Advantageously, the rubber composition according to the invention contains less than 1.5 parts per annum of a rubber powder other than the rubber powder useful for The advantageous embodiment, and in particular the more advantageous embodiment, does not contain any gum powder other than the gum powder necessary for the purposes of the invention. The advantageous embodiment, and in particular the more advantageous embodiment, offers a favorable compromise between breaking strength and gas tightness.

[0044] The rubber powder useful for the purposes of the invention can typically be obtained by grinding inner tire rubber. According to this embodiment of the invention, the rubber powder useful for the purposes of the invention consists of particles of inner tire rubber and comprises all the usual ingredients present in a rubber composition for inner tire rubber. Other additives

[0045] The rubber composition according to the invention may include at least one other additive known to improve the processing properties, thermal conductivity, or, in the case of use in a tire inner liner, the impermeability of a rubber composition, such as clay, bentonite, talc, chalk, kaolin, or graphite. This additive is then present in a quantity of 0 to 40 parts per cent in the rubber composition according to the invention.

[0046] The rubber composition according to the invention may also include all or part of the usual additives commonly used in rubber compositions for the manufacture of tires, such as plasticizers, lubricants, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents and mixtures of such compounds. Preparation of compositions

[0047] The rubber composition according to 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 high-temperature thermomechanical working or mixing, up to a maximum temperature between 90°C and 150°C, preferably between 100°C and 130°C, followed by a second phase of mechanical working down to a lower temperature, typically below 110°C, for example between 40°C and 100°C, a finishing and homogenization phase of the rubber composition.

[0048] The rubber composition according to the invention can be prepared according to a process which comprises the following steps: - Thermomechanically mix the ingredients of the rubber composition in accordance with the invention up to a maximum temperature between 90°C and 120°C; - cool the assembly to a temperature below 80°C; - knead everything until a maximum temperature below 90°C to obtain a rubber composition conforming to the invention.

[0049] After incorporating all the ingredients of the rubber composition according to the invention, the resulting final rubber composition is then calendered, for example in the form of a sheet or plate, particularly for laboratory characterization, or extruded, for example to form a rubber profile used as a rubber component or semi-finished product, particularly for the manufacture of a tire. The rubber composition according to the invention can be used in calendered form in a tire. The calendered or extruded product formed from the rubber composition according to the invention constitutes, in whole or in part, a semi-finished product, in particular a tire.

[0050] Thus, according to a particular embodiment of the invention, the rubber composition according to the invention, which can be either in the raw state (before crosslinking or vulcanization) or in the cooked state (after crosslinking or vulcanization), is in a tire, preferably in an inner tire rubber.

[0051] Crosslinking (or curing), in this case vulcanization, is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which can 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 considered. Other objects of the invention

[0052] The inner rubber of a tire according to the invention has as its essential characteristic that it is made up, in whole or in part, of the rubber composition according to the invention. It can be manufactured according to the process described above, which includes an additional step of calendering or extruding the rubber composition. It can be in either a raw state (i.e., before curing) or a cured state (i.e., after cross-linking or vulcanization).

[0053] The invention also relates to a tire comprising a rubber composition or an inner rubber compound according to the invention, which tire is both in its raw and cured states. In the present invention, the term "tire" (in English, "tire") means a pneumatic or non-pneumatic tire. A pneumatic tire usually comprises two beads intended to contact 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 bead sections. A non-pneumatic tire, on the other hand, 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 dimples, 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.

[0054] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration and not limitation. Examples Measurements and tests used

[0055] Determination of the tear resistance properties of rubber compositions

[0056] The tensile strength per unit thickness (hereinafter denoted F^z and expressed in N / mm of thickness) and the elongation at break (hereinafter denoted Ardz and expressed as a percentage) are measured on a specimen stretched at 500 mm / min to cause the specimen to break on a tensile testing machine equipped with a system for measuring and acquiring the force and displacement of the moving crosshead. The tensile specimen consists of a parallelepiped-shaped rubber plate, 2.5 mm thick, 145 mm long, and 10 mm wide. Before the start of the test, three very fine cuts perpendicular to the length of the specimen are made using a razor blade to a depth of 3 mm, on one edge of the specimen, one in the middle and the other two on either side of the first and 6 mm away from it.FRDz is defined as the force (expressed in N per mm of specimen thickness) required to achieve fracture, and Ardz is measured as the elongation (expressed as a percentage) required to achieve fracture. The test was conducted in air at a temperature of 100°C. The tear coefficient (expressed in N / mm) is calculated as the product of FRDz and ARI. High values ​​indicate good cohesion of the rubber composition, even though crack initiation may be present. In the examples below, measurements were performed both on "new" tensile test specimens, i.e., those that had not undergone any prior aging, and on specimens that had been subjected to thermo-oxidative aging. for 21 days in air at 77°C before traction. The results are given on a base of 100: an arbitrary value of 100 is given for the tear resistance coefficient of the control, a result greater than 100 indicates improved tear resistance properties compared to the control.

[0057] Determination of the size of gum powder particles

[0058] The volume size distribution of gum powder particles can be measured by laser granulometry using a Malvern Mastersizer 3000 instrument. A 1-minute ultrasonic treatment is performed prior to measurement to ensure proper dispersion. The measurement is carried out in a liquid state: the gum powder particles are dispersed in alcohol. The measurement is performed in accordance with ISO 13320-1 and, based on the determination of the laser diffraction angles by the gum powder particles, allows for the determination of, in particular, the D10 and D50, i.e., the diameters below which, respectively, 10% and 50% by volume of the total particle population is present. Preparation of rubber compositions

[0059] Four rubber compositions Cl, C2, C3 and C4 are prepared. The formulations (in pieces) of these compositions are described in Table 1.

[0060] Rubber compositions C3 and C4 conform to the invention; rubber compositions Cl and C2 do not conform to the invention. The rubber compositions Cl, C2, C3, and C4 all contain a halogenated butyl rubber Bul (in this case, a brominated butyl rubber), a reinforcing filler RI comprising carbon black NI, a vulcanizing system VI, and a rubber powder (10 parts per unit for the rubber compositions Cl and C3, 30 parts per unit for the rubber compositions C2 and C4) comprising a halogenated butyl rubber Bu2 (in this case, a brominated butyl rubber), a reinforcing filler R2 comprising carbon black N2, and a vulcanizing system V2. In the rubber compositions Cl and C2, which do not conform to the invention, the rubber powder of composition A (given in Table 2) does not contain kaolin; in the rubber compositions C3 and C4, which conform to the invention, the rubber powder of composition B (given in Table 2) contains kaolin.

[0061] The results are considered by comparing the properties of Cl (not in accordance with the invention) and C3 (in accordance with the invention) on the one hand, and those of C2 (not in accordance with the invention) and C4 (in accordance with the invention) on the other hand.

[0062] The tests are carried out as follows: the halogenated butyl rubber is introduced first into an internal mixer, filled to 70% by volume and with an initial tank temperature of approximately 40°C, followed by the reinforcing filler, The rubber powder, the vulcanization system, and other additives in the rubber composition are then processed. A single-stage thermomechanical process is then carried out, lasting approximately 3 to 4 minutes in total, until a maximum "drop" temperature of 115°C is reached.

[0063] The mixture thus obtained is collected, cooled on an external mixer (roller tool) at 30°C, kneading everything to homogenize the mixture for an appropriate time (for example between 5 and 12 min). The resulting compositions are then calendered into sheets (2 to 3 mm thick) or thin sheets of rubber to measure their physical and mechanical properties after vulcanization for 20 minutes at 150 °C. Properties of rubber compositions

[0064] The properties of the Cl, C2, C3 and C4 rubber compositions are given as a basis of 100 relative to Cl in Table 3.

[0065] Rubber composition C3 contains the same proportion of rubber powder as rubber composition Cl, but the rubber powder in C3 includes kaolin (rubber powder composition B), unlike that in rubber composition Cl, which does not (rubber powder composition A). C3 therefore conforms to the invention and exhibits a tear resistance 17% higher than that of rubber composition Cl, which does not conform to the invention. Similarly, rubber compound C4 contains the same proportion of rubber powder as rubber compound C2, but the rubber powder in C4 includes kaolin (rubber powder of compound B), unlike that in rubber compound C2, which does not (rubber powder of compound A). Therefore, C4 conforms to the invention and exhibits higher tear resistance than rubber compound C2, which does not conform to the invention.

[0066] The results obtained therefore show that the rubber compositions according to the invention do indeed solve the technical problem, in that they result in tear resistance properties after aging that are much better than those of the rubber compositions not according to the invention. This result is all the more surprising since, before aging, the rubber compositions according to the invention do not exhibit better tear resistance properties than those of the rubber compositions not according to the invention. [Tables 1] Cl C2 C3 C4 Elastomer (1) 100 100 100 100 Carbon black (2) 40 40 40 40 Kaolin (3) 20 20 20 20 Stearic acid (4) 1.5 1.5 1.5 1.5 Zinc oxide (5) 1.5 1.5 1.5 1.5 Lubricant (6) 2 2 2 2 Accelerator (7) 1.2 1.2 1.2 1.2 Sulfur 1.5 1.5 1.5 1.5 Gum powder 1 (8) 10 30 0 0 Gum powder 2 (9) 0 0 10 30 (1) Brominated butyl X-ButylTM BB2030 from ARLANXEO (2) N770 ASTM grade from ORION company (3) Natural kaolin grade Argirec B24 from the company IMERYS (4) Stearic acid from the company UMICORE (5) Zinc oxide from the company UMICORE (6) Struktol® 40MS from the company STRUKTOL (7) 2-mercaptobenzothiazole disulfide accelerator (“MBTS”) from Solutia (8) Vulcanized inner gum microparticles of composition A with a median size of 280 pm (9) Vulcanized inner gum microparticles of composition B with a median size of 280 pm [Tables 2] AB Elastomer (1) 100 100 Carbon black (2) 50 40 Kaolin (3) 0 20 Stearic acid (4) 1.5 1.5 Zinc oxide (5) 1.5 1.5 Lubricant (6) 2 2 Accelerator (7) 1.2 1.2 Sulfur 1.5 1.5 [Tables 3] C2 C3 C4 Tear strength coefficient when new [N / mm] 100 92 100 89 Tear strength coefficient after aging [N / mm] 100 117 119 130

Claims

Demands

1. Rubber composition comprising a halogenated butyl rubber Bul, a reinforcing filler RI comprising carbon black NI, a vulcanizing system VI and a rubber powder comprising a halogenated butyl rubber Bu2, a reinforcing filler R2 comprising carbon black N2, a vulcanizing system V2 and kaolin.

2. Rubber composition according to claim 1 wherein the proportion of rubber powder ranges from 5 to less than 40 pc.

3. Rubber composition according to any one of the preceding claims wherein the rubber powder has a median volume particle size of between 50 and 500 pm, preferably between 100 and 400 pm.

4. Rubber composition according to any one of the preceding claims wherein halogenated butyl rubber Bu2 represents at least 40% by mass of the total mass of the rubber powder.

5. Rubber composition according to any one of the preceding claims wherein the rubber powder comprises a polyisoprene elastomer representing from 0 to 20% by mass of the total mass of the rubber powder, the polyisoprene elastomer preferably containing more than 90% by mole of 1,4-cis bonding.

6. Rubber composition according to any one of the preceding claims wherein halogenated butyl rubber Bu2 is a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of both.

7. Rubber composition according to any one of the preceding claims wherein the reinforcing filler R2 represents from 10 to 40% by mass, preferably from 20 to 30% by mass, of the total mass of the rubber powder.

8. Rubber composition according to any one of the preceding claims wherein carbon black N2 represents more than 50% by mass, preferably more than 80% by mass, even more preferably 100% by mass of the total mass of the reinforcing filler R?

9. IxZ. Rubber composition according to any one of the preceding claims wherein kaolin represents from 3 to 30% by mass, preferably from 5 to 20% by mass of the total mass of the rubber powder.

10. Rubber composition according to any one of the preceding claims wherein the content of halogenated butyl rubber Bul is greater than or equal to 70 pc.

11. Rubber composition according to any one of the preceding claims comprising from 0 to 30 pieces of a polyisoprene elastomer preferably containing more than 90 mol% of 1,4-cis bonding.

12. Rubber composition according to any one of the preceding claims wherein the halogenated butyl rubber Bul is a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of both.

13. Rubber composition according to any one of the preceding claims wherein the rate of the reinforcing filler RI is from 20 to 80 pc.

14. Rubber composition according to any one of the preceding claims wherein the reinforcing filler RI is composed solely of carbon black.

15. Inner tire rubber comprising a rubber composition according to any one of the preceding claims.

16. A tire comprising an inner rubber according to claim 15 or a rubber composition according to any one of claims 1 to 14.