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 inner rubber of a tire comprising a rubber powder

[0001] The invention relates to rubber compositions for tires comprising a gum crumb.

[0002] Indeed, it is interesting today for tire manufacturers to find solutions to reduce 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 endurance of the tire by preventing it from deflating and by 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, the cost of which is high.

[0004] It is also of interest to manufacturers to promote the recycling of end-of-life tires into new tires with a view to reducing the environmental impact of their activity, for example by incorporating into rubber compositions for tires rubber crumbs resulting from the grinding or micronization of vulcanized rubber compositions. Tires resulting from this type of process are described in the state of the art, for example in document WO2020 / 128255.

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

[0006] However, the inner rubbers of tires must also have good mechanical resistance properties, including after aging. However, very surprisingly, the Applicant has discovered that the use of rubber compositions containing specific rubber crumbs in that they contain kaolin, makes it possible to improve the tear resistance properties after aging of the inner rubbers of tires.

[0007] Thus, a first subject of the invention is a rubber composition comprising a halogenated butyl rubber Bul, a reinforcing filler RI comprising a carbon black NI, a vulcanization system VI and a gum crumb comprising a halogenated butyl rubber Bu2, a reinforcing filler R2 comprising carbon black N2, a vulcanization system V2 and kaolin. Another subject of the invention is a tire inner rubber comprising a rubber composition in accordance with the invention. The invention also relates to a tire comprising an inner rubber or a rubber composition in accordance with the invention. Detailed description

[0008] 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).

[0009] The abbreviation "pce" means parts by weight per hundred parts of elastomers present in the elastomer matrix. The term "elastomer matrix" means all the elastomers present in the rubber composition in accordance with the invention, excluding the elastomers present in any gum crumb, whether it is the gum crumb useful for the purposes of the invention, or another gum crumb.

[0010] The compounds mentioned in the description (typically the polymers, fillers, plasticizers, coupling agents, the 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 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 has as its object at least one of the objects defined according to any one of the following listed embodiments: 1. A rubber composition comprising a halogenated butyl rubber Bul, a reinforcing filler RI comprising carbon black NI, a vulcanization system VI and a gum crumb 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 content of gum powder ranges from 5 to less than 40 pce. 3. Rubber composition according to any one of the preceding embodiments in which the gum 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 one of the preceding embodiments in which the halogenated butyl rubber Bu2 represents at least 40% by mass of the total mass of the gum crumb. 5. Rubber composition according to any one of the preceding embodiments in which the gum crumb comprises a polyisoprene elastomer representing from 0 to 20% by mass of the total mass of the gum crumb, the polyisoprene elastomer preferably containing more than 90% by mole of 1,4-cis bond. 6. A 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 the two. 7. Rubber composition according to any one of the embodiments previous in which the reinforcing filler R2 represents from 10 to 40% by mass, preferably from 20 to 30% by mass, of the total mass of the gum powder. 8. Rubber composition according to any one of the preceding embodiments in which the 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 one of the preceding embodiments in which the kaolin represents from 3 to 30% by mass, preferably from 5 to 20% by mass of the total mass of the gum powder. 10. Rubber composition according to any one of the preceding embodiments in which the content of halogenated butyl rubber Bul is greater than or equal to 70 pce. 11. Rubber composition according to any one of the preceding embodiments comprising from 0 to 30 pce of a polyisoprene elastomer preferably containing more than 90 mol% of 1,4-cis bond. 12. A 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 the two. 13. Rubber composition according to any one of the preceding embodiments in which the level of reinforcing filler RI ranges from 20 to 80 pce. 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 rubber of a tire comprising a rubber composition according to any one of the preceding embodiments. 16. A tire comprising an inner rubber according to embodiment 15 or a rubber composition according to any one of embodiments 1 to 14. Elastomer

[0012] Usually, the terms “elastomer” and “rubber” are used interchangeably in the text.

[0013] An essential characteristic of the rubber composition according to the invention is to contain 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] Butyl rubber means a copolymer of isobutylene and a 1,3-diene, in particular a copolymer of isobutylene and isoprene, as well as the 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 air-impermeability property. Generally, copolymers of isobutylene and a 1,3-diene, particularly isoprene, contain 1 to 5 mol% of diene units, particularly isoprene units, 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% by mass of the copolymer mass.

[0016] Examples of halogenated butyl rubbers which are particularly suitable for carrying out the invention include bromobutyl rubbers such as brominated isobutylene and isoprene copolymer (BIIR), chlorobutyl rubbers such as chlorinated isobutylene and isoprene 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, is meant in a known manner an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not). As diene elastomers which may be suitable, mention will be made in particular of the diene elastomers usually used in rubber compositions intended for the manufacture of tires, such as such as polyisoprenes, polybutadienes, isoprene copolymers, butadiene copolymers such as butadiene and styrene copolymers.

[0019] According to one embodiment of the invention, the rubber composition in accordance with the invention comprises from 0 to 30 pce of a diene elastomer II other than a halogenated butyl rubber and chosen from the group consisting of polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures thereof. Preferably, the diene elastomer II is a polyisoprene elastomer and, even more preferably, the diene elastomer II contains more than 90 mol% of 1,4-cis bond. These preferred ranges of elastomer content in the rubber composition according to the invention and of molar percentage of 1,4-cis bond 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 of the embodiments of the invention, the content of halogenated butyl rubber Bul in the rubber composition in accordance with the invention is preferably greater than or equal to 70 phr. Preferably, the additional rubber making it possible to reach 100 phr of rubber in the rubber composition in accordance with the invention is natural rubber. Charge

[0021] The rubber composition in accordance with 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 which can be used in particular for the manufacture of tires, may be used, for example a reinforcing organic filler such as carbon black, a reinforcing inorganic 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. All carbon blacks may be suitable as carbon blacks, in particular the blacks conventionally used in tires. These carbon blacks may be used in the isolated state, as commercially available, or in any other form, for example as a support for certain of the rubber additives used.

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

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

[0025] According to one embodiment of the invention, the level of reinforcing filler RI in the rubber composition according to the invention ranges from 20 to 80 pce. Outside this range, the rubber composition may no longer have a rigidity compatible with use as an inner rubber of a tire.

[0026] According to a preferred embodiment of the invention, the carbon black NI included in the reinforcing filler of the rubber composition in accordance with the invention is present at a rate ranging from 20 to 80 phr. Obviously, the rate of carbon black NI in the rubber composition is less than or equal to the rate of reinforcing filler RI in the rubber composition. In the even more preferred embodiment where these two rates are equal, the reinforcing filler RI is composed solely of carbon black. Vulcanization system

[0027] An essential characteristic of the rubber composition according to the invention is to comprise a vulcanization system VI, that is to say a crosslinking system based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. To this basic vulcanization system can be added 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 vulcanization accelerator (primary or secondary) we can cite any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur, 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 0.5 and 5 phr. The primary vulcanization accelerator is used in the rubber composition according to the invention 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 can apply to any of the embodiments. Gum powder

[0028] Another essential characteristic of the rubber composition in accordance with the invention is that it contains a gum powder.

[0029] It is recalled that gum powders are generally presented in the form of granules (or granulates), possibly put in the form of a rubber plate. Most often, rubber crumbs are a product of material recycling: they are produced by grinding, in particular micronization, of cooked rubber compositions already used for a first application, for example as tire curing membranes (as in document US6730732) or as tires that have reached the end of their life (as in document KR100943526). Any method or process that does not degrade the rubber during grinding may be suitable as a method for grinding rubber compositions. For example, a grinding method in the presence of water such as those described in documents US4374573, US4714201, US5238194 and US5411215 may be chosen: such a method makes it possible to keep the temperature of the rubber at a sufficiently low level to avoid reversion, i.e. the degradation of the rubber crosslinking network. A cryogenic grinding method can also be used.Depending on the object size distribution obtained, the gum powder obtained by the processes mentioned may undergo an additional sieving step in order to control this distribution. The sieving may be carried out by different technologies (vibration, centrifugation, suction) known to those skilled in the art. The gum powders resulting from the grinding process are generally in the form of microparticles. By "microparticles" is meant particles which have a size, namely their diameter in the case of spherical particles or their largest dimension in the case of anisotropic particles, of a few 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 size by volume of the particles of the gum powder of between 50 and 500 μm, preferably between 100 and 400 μm. These particle size ranges can be applied to any of the embodiments of the invention.

[0031] An essential characteristic of the gum powder useful for the purposes of the invention is to contain 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 gum crumb useful for the purposes of the invention comprises from 0 to 20% by mass of the total mass of the gum crumb of a diene elastomer 12 other than a halogenated butyl rubber and chosen 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. ferential, the diene elastomer 12 is a polyisoprene elastomer which contains more than 90 mol% of 1,4-cis bond. These preferred ranges of mass percentage of elastomer in the gum crumb useful for the purposes of the invention and of molar percentage of 1,4-cis bond in the polyisoprene elastomer 12 as well as these preferred choices of diene elastomer can be applied to any of the embodiments of the invention.

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

[0035] The gum powder useful for the purposes 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 a reinforcing organic filler such as carbon black, a reinforcing inorganic filler such as silica or a mixture of these two types of fillers.

[0036] The reinforcing filler R2 of the rubber crumb useful for the purposes of the invention comprises carbon black N2. All carbon blacks may be suitable as carbon blacks, in particular the blacks conventionally used in tires. These carbon blacks may be used in the isolated state, as commercially available, or in any other form, for example as a support for certain of the rubber additives used.

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

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

[0039] An essential characteristic of the gum powder useful for the purposes of the invention is to comprise a vulcanization system V2, that is to say a system 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 retarders may be added to this basic vulcanization system. Mention may be made, as a (primary or secondary) vulcanization accelerator, of any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types.Sulfur is used in the gum crumb useful for the purposes of the invention at a preferred rate of between 0.5 and 12% by mass of the total mass of elastomer in the gum crumb, in particular between 0.5 and 5% by mass of the total mass of elastomer in the gum crumb. The primary vulcanization accelerator is used in the gum crumb useful for the purposes of the invention at a preferred rate of between 0.5 and 10% by mass, more preferably between 0.5 and 5.0% by mass of the total mass of elastomer in the gum crumb. These preferred ranges relating to the levels of sulfur and primary accelerator may apply to any of the embodiments.

[0040] The gum powder useful for the purposes of the invention has the essential characteristic of containing kaolin. Kaolin (A12O3 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, the kaolin represents from 3 to 30% by mass, preferably from 5 to 20% by mass of the total mass of the gum powder useful for the purposes of the invention. These ranges of mass percentage of kaolin in the gum powder useful for the purposes of the invention can be applied to any of the embodiments of the invention.

[0042] According to one embodiment of the invention, the level of gum crumb useful for the purposes of the invention in the rubber composition according to the invention ranges from 5 to less than 40 phr. Below 5 phr of gum crumb in the rubber composition, the desired effect might not be sufficiently strong. For a level equal to or greater than 40 phr of gum crumb in the rubber composition, the industrial implementation of the rubber composition could be penalized. This preferential range for the level of gum crumb in the rubber composition according to the invention can apply to any of the embodiments.

[0043] Advantageously, the rubber composition in accordance with the invention contains less than 1.5 pce of a gum powder other than the gum powder useful for needs of the invention, more advantageously does not contain gum crumb other than the gum crumb useful for the needs of the invention. The advantageous embodiment and in particular the more advantageous embodiment are favorable for the compromise between the breaking properties and the gas-tightness properties.

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

[0045] At least one other additive which is known to improve the processing properties, thermal conductivity or, in the case where it is used in an inner rubber of a tire, the impermeability of a rubber composition, such as clay, bentonite, talc, chalk, kaolin or graphite, may be included in the rubber composition according to the invention. This additive is then present at a level of 0 to 40 phr in the rubber composition according to the invention.

[0046] 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, lubricants, pigments, protective agents such as antiozone waxes, chemical antiozonants, antioxidants, anti-fatigue agents and mixtures of such compounds. Preparation of the compositions

[0047] 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 working or thermomechanical mixing at high temperature, up to a maximum temperature of 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 phase of finishing and homogenization of the rubber composition.

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

[0049] After incorporating all the ingredients of the rubber composition according to the invention, the final rubber composition thus obtained is then calendered, for example in the form of a sheet or plate, in particular for laboratory characterization, 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 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 in accordance with the invention, which may be either in the raw state (before crosslinking or vulcanization), or in the cured state (after crosslinking or vulcanization), is in a tire, preferably in an inner rubber of the tire.

[0051] The crosslinking (or curing), in this case the 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 the essential characteristic of being 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 comprises an additional step of calendering or extrusion of the rubber composition. It can be in the raw state (i.e., before curing) as well as in the cured state (i.e., after crosslinking or vulcanization).

[0053] The invention also relates to a tire comprising a rubber composition or an inner rubber according to the invention, which tire is both in the raw state and in the cured state. 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 bandages do not necessarily comprise a sidewall. Non-pneumatic bandages 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 bandage.

[0054] 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. Examples Measures and tests used

[0055] Determination of tear resistance properties of rubber compositions

[0056] The tear breaking force per unit thickness (hereinafter referred to as F^z and expressed in N / mm of thickness) and the tear breaking elongation (hereinafter referred to as Ardz and expressed in %) are measured on a specimen stretched at 500 mm / min to cause the specimen to break on a dynamometric machine for tensile tests, equipped with a system for measuring and acquiring the force and the displacement of the moving crosshead. The tensile specimen consists of a parallelepipedal rubber plate, with a thickness equal to 2.5 mm, a length equal to 145 mm and a width equal to 10 mm. Before starting the test, three very fine notches perpendicular to the length of the test piece are made using a razor blade to a depth of 3 mm, on one edge of the test piece, one in the middle and the other two on either side of the first and 6 mm apart from it.FRDz is determined as the force (expressed in N per mm of specimen thickness) to be exerted to obtain rupture and Ardz is measured as the elongation (expressed in %) to be applied to the specimen to obtain rupture. The test was carried out 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 although there are crack initiations. In the examples below, the measurements were carried out both on "new" tensile specimens, i.e. those which had not undergone any prior aging, and on specimens which had been subjected to thermo-oxidative aging. for 21 days in air at 77°C before traction. The results are given in base 100: an arbitrary value of 100 is given for the tear coefficient of the control, a result greater than 100 indicates improved tear resistance properties compared to the control.

[0057] Determination of the particle size of gum crumbs

[0058] The volume distribution of the size of the gum crumb particles can be measured by laser granulometry, on a mastersizer 3000 type device from Malvern. A 1 minute ultrasonic treatment is carried out prior to the measurement in order to guarantee good dispersion. The measurement is carried out in a liquid method: the gum crumb particles are dispersed in alcohol. The measurement is carried out in accordance with the ISO-13320-1 standard and allows, from the determination of the diffraction angles of the laser by the gum crumb particles, to determine in particular the D10 and the D50, that is to say the diameters below which respectively 10% by volume and 50% by volume of the total particle population is present. Preparation of rubber compositions

[0059] Four rubber compositions C1, C2, C3 and C4 are prepared. The formulations (in pce) of these compositions are described in Table 1.

[0060] Rubber compositions C3 and C4 are in accordance with the invention; rubber compositions C1 and C2 are not in accordance with the invention. The rubber compositions C1, 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 vulcanization system VI and a gum crumb (in an amount of 10 phr for the rubber compositions C1 and C3, 30 phr 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 vulcanization system V2. In the rubber compositions C1 and C2, not in accordance with the invention, the gum crumb of composition A (given in Table 2) does not contain kaolin; in the rubber compositions C3 and C4, in accordance with the invention, the gum crumb of composition B (given in Table 2) contains kaolin.

[0061] The results are considered by comparing the properties of C1 (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 first introduced into an internal mixer, filled to 70% by volume and whose initial tank temperature is approximately 40°C, then the reinforcing filler, the rubber powder, the vulcanization system and the other additives in the rubber composition. A single-stage thermomechanical process is then carried out, lasting a total of approximately 3 to 4 minutes, until a maximum "drop" temperature of 115°C is reached.

[0063] The mixture thus obtained is recovered, cooled on an external mixer (roller tool) to 30°C, mixing everything in order to homogenize the mixture for an appropriate time (for example between 5 and 12 min). The compositions thus obtained are then calendered 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 after vulcanization for 20 min at 150 °C. Properties of rubber compositions

[0064] The properties of rubber compositions C1, C2, C3 and C4 are given on a base of 100 relative to C1 in Table 3.

[0065] Rubber composition C3 contains the same level of gum crumb as rubber composition C1, but the gum crumb included in C3 contains kaolin (gum crumb of composition B), unlike that of rubber composition C1 which does not contain it (gum crumb of composition A). C3 is therefore in accordance with the invention and has a tear resistance 17% higher than that of rubber composition C1, which is not in accordance with the invention. Similarly, rubber composition C4 contains the same level of gum crumb as rubber composition C2, but the gum crumb included in C4 includes kaolin (gum crumb of composition B) unlike that of rubber composition C2 which does not include it (gum crumb of composition A). C4 is therefore in accordance with the invention and has a higher tear resistance than that of rubber composition C2, which is not in accordance with the invention.

[0066] The results obtained therefore show that the rubber compositions in accordance with the invention do indeed make it possible to solve the technical problem here, in that they result in tear resistance properties after aging which are much better than those of the rubber compositions not in accordance with the invention. This result is all the more surprising since, before aging, the rubber compositions in accordance with the invention do not have tear resistance properties which are better than those of the rubber compositions not in accordance with 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 Sulphur 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 UMICORE (5) Zinc oxide from UMICORE (6) Struktol® 40MS from STRUKTOL (7) 2-Mercaptobenzothiazole Disulfide Accelerator (“MBTS”) from Solutia (8) Microparticles of vulcanized internal rubber of composition A with an average size of 280 pm (9) Microparticles of vulcanized internal rubber of composition B with an average 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 Sulphur 1.5 1.5 [Tables 3] Cl C2 C3 C4 Tear coefficient when new [N / mm] 100 92 100 89 Tear coefficient after aging [N / mm] 100 117 119 130

Claims

Claims

1. A rubber composition comprising a halogenated butyl rubber Bul, a reinforcing filler RI comprising carbon black NI, a vulcanization system VI and a gum crumb comprising a halogenated butyl rubber Bu2, a reinforcing filler R2 comprising carbon black N2, a vulcanization system V2 and kaolin.

2. A rubber composition according to claim 1 wherein the gum powder content is from 5 to less than 40 phr.

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

4. A rubber composition according to any preceding claim wherein the halogenated butyl rubber Bu2 represents at least 40% by mass of the total mass of the gum crumb.

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

6. A rubber composition according to any preceding claim 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 preceding claims in which the reinforcing filler R2 represents from 10 to 40% by mass, preferably from 20 to 30% by mass, of the total mass of the gum powder.

8. Rubber composition according to any one of the preceding claims in which the 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 in which the kaolin represents from 3 to 30% by mass, preferably from 5 to 20% by mass of the total mass of the gum powder.

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

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

12. A rubber composition according to any preceding claim 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 in which the level of the reinforcing filler RI ranges from 20 to 80 pce.

14. A rubber composition according to any preceding claim wherein the reinforcing filler RI is composed solely of carbon black.

15. A tire inner 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.