Inner tire layer based on butyl rubber with low carbon black content and another additional filler

Description

[0001] The invention relates to an inner rubber for a tire having a rubber composition comprising an elastomeric matrix based on butyl rubber and containing a low level of carbon black, as well as a low total level of reinforcing fillers, graphite and specific inert fillers.

[0002] The invention also relates to a tire comprising such a rubber.

[0003] Tubeless tires have an inner surface with low air permeability to prevent the tire from deflating and to protect the internal areas sensitive to the tire from the ingress of oxygen and water, such as layers containing metal cords sensitive to oxidation, this protection improving the tire's endurance. Today, such protection of the inner surface of tires is generally achieved by inner rubbers made of elastomeric compositions based on butyl rubber. However, the air impermeability performance of butyl rubbers is linked to a significant minimum thickness (of the order of a millimeter) and therefore to a certain weight, which is not optimal.

[0004] Thus, it is necessary to add reinforcing fillers, such as carbon black, to the inner rubber compound to improve its waterproofing. However, in large quantities, these reinforcing fillers are detrimental to certain properties of the cured compound: degradation of mechanical properties, in particular reduction of flexural strength as well as rolling resistance properties.

[0005] Document FR 2 925 062 can be cited in particular as an example of a document teaching the use of a high carbon black content.

[0006] However, since fuel economy and the need to protect the environment have become a priority, it is desirable to produce airtight inner rubbers with the lowest possible weight and hysteresis, in order to obtain improved tire rolling resistance.

[0007] The introduction of an oil-type plasticizer makes it possible to overcome the mechanical property problems described above but significantly penalizes impermeability.

[0008] There is therefore a constant need to reduce the hysteresis and weight of the inner rubbers without affecting the other properties essential to these inner rubbers (impermeability and endurance).

[0009] Various solutions have been considered to overcome these drawbacks, in particular by using other types of fillers in addition to the reinforcing fillers, often known as smectites, in particular organophilic smectites. These organophilic smectites improve the waterproofing properties of materials if they are well dispersed in the material. However, this dispersion is often difficult to obtain due to the poor thermodynamic compatibility between elastomers and such fillers.Publication WO 2006 / 047509 of the applicant describes a composition for an inner rubber of a tire, the composition of which is based on butyl rubber and comprising carbon black, and comprises non-reinforcing fillers consisting of organophilic smectites reducing gas permeability, dispersed in the elastomeric matrix, as well as a specific plasticizer consisting of a terpene resin having in particular a glass transition temperature Tg greater than 50°C. This composition actually has mechanical and impermeability properties making it acceptable for use as an inner rubber of a tire, thanks to the combined effect of these organophilic smectites and this high Tg resin.

[0010] Other solutions consist of using lamellar fillers such as graphite in order to improve the impermeability of the composition. However, the presence of graphite can lead to problems with the processability of the mixtures. Thus, application WO 2008 / 145314 describes a rubber composition for the inner rubber of a tire based on at least one butyl rubber, a reinforcing filler, graphite and a plasticizing hydrocarbon resin, making it possible to obtain an inner rubber also having a good compromise of properties.

[0011] Furthermore, if one were to decide to lower the carbon black content to avoid the problems previously discussed associated with a large amount of carbon black, one would expect that this would be detrimental to the tire's endurance.

[0012] The applicant nevertheless discovered, surprisingly and contrary to the knowledge of those skilled in the art, that there was a solution making it possible to obtain an inner rubber with a good compromise of properties and a low carbon black content. This solution consists of producing an inner rubber having a small quantity of carbon black by adding a specific internal additional filler without significantly increasing the total content of reinforcing or semi-reinforcing fillers, such as graphite, in an elastomeric matrix mainly consisting of butyl rubber.

[0013] However, a person skilled in the art expects that such a composition would be detrimental to the endurance properties of a tire having an inner rubber based on this composition.

[0014] However, the applicant discovered that, on the contrary, such a composition made it possible to obtain a tire with good impermeability and good endurance while exhibiting reduced hysteresis.

[0015] The invention therefore relates to an inner rubber for a tire having a rubber composition comprising: an elastomeric matrix comprising at least 50 phr of one or more butyl rubbers, from 5 to 30 phr of carbon black, from 0 to less than 10 phr of a plasticizing agent, at least 5 phr of one or more additional fillers chosen from reinforcing fillers other than carbon black, graphite and inert fillers, said inert fillers being chosen from chalk, clay, bentonite, talc, kaolin, glass microbeads, glass flakes and a mixture of these compounds, the total content of reinforcing fillers and graphite in the rubber composition varying from 5 to 50 phr, the content of the inert filler(s) in the rubber composition varying from 1 to 60 phr.

[0016] Such an inner rubber according to the invention has lower hysteresis than an inner rubber containing more carbon black.

[0017] In addition, it meets the requirements for interior rubbers, namely good permeability.

[0018] Finally, tires made from an inner rubber according to the invention have good endurance.

[0019] The invention also relates to a tire comprising an inner rubber as defined above.

[0020] The invention and its advantages will be easily understood in light of the description and examples of embodiments which follow.

[0021] In this description, unless expressly indicated otherwise, all percentages (%) indicated are % by mass.

[0022] On the other hand, 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 (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 ​​going from a to b (i.e., including the strict limits a and b).

[0023] In the present application, the term "part per cent of elastomer" or "pce" means the part by weight of a constituent per 100 parts by weight of the elastomer(s), i.e. of the total weight of the elastomer(s). Thus, a constituent at 60 pce will mean, for example, 60 g of this constituent per 100 g of elastomer.

[0024] Usually in the present application, the terms “elastomer” and “rubber” are used interchangeably in the text.

[0025] Thus, a first object of the invention is an inner rubber for a tire having a rubber composition comprising: an elastomeric matrix comprising at least 50 phr of one or more butyl rubbers, from 5 to 30 phr of carbon black, from 0 to less than 10 phr of a plasticizing agent, at least 5 phr of one or more additional fillers chosen from reinforcing fillers other than carbon black, graphite and inert fillers, said inert fillers being chosen from chalk, clay, bentonite, talc, kaolin, glass microbeads, glass flakes and a mixture of these compounds, the total content of reinforcing fillers and graphite in the rubber composition varying from 5 to 50 phr, the content of the inert filler(s) in the rubber composition varying from 1 to 60 phr.

[0026] For the purposes of the present invention, the term "elastomeric matrix" means all the elastomers (or rubbers) in the rubber composition. Thus, the elastomeric matrix may in particular consist of a single elastomer but also of a blend of two or more elastomers.

[0027] For the purposes of the present invention, the term "butyl rubber" means a homopolymer of isobutylene or a copolymer of isobutylene and isoprene, as well as halogenated derivatives, in particular generally brominated or chlorinated, of these homopolymers of isobutylene and copolymers of isobutylene and isoprene.

[0028] Particularly preferably, the butyl rubber(s) that can be used in the inner rubber according to the invention are chosen from isobutylene rubbers, isobutylene and isoprene copolymers (IIR), bromobutyl rubbers such as bromobutylene-isoprene copolymer (BIIR) and chlorobutyl rubbers such as chloroisobutylene-isoprene copolymer (CIIR).

[0029] By extension of the previous definition, the term "butyl rubber" will also include copolymers of isobutylene and styrene derivatives such as copolymers of isobutylene and brominated methylstyrene (BIMS) which include the elastomer called EXXPRO marketed by the Exxon company.

[0030] The butyl rubber(s) usable in the inner rubber of the present invention represent at least 50 phr, that is to say they represent at least 50% by weight of the total weight of the elastomeric matrix.

[0031] As other elastomers present in the elastomeric matrix in addition to the butyl rubber(s), mention may in particular be made of diene elastomers other than the butyl elastomers previously mentioned.

[0032] By “diene” elastomer or rubber, one must understand, in a known manner, one or more elastomers derived at least in part (i.e.; a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

[0033] These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”.

[0034] In general, the term "essentially unsaturated" means a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or motifs of diene origin (conjugated dienes) which is greater than 15% (mol %). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer means in particular a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

[0035] This is how diene elastomers such as certain copolymers of dienes and alpha-olefins such as EPDM can be described as “essentially saturated” diene elastomers (low or very low rate of units of diene origin, always less than 15%).

[0036] Given these definitions, the term diene elastomer, whatever the category above, capable of being used in the elastomeric matrix of the inner rubber in accordance with the invention, is understood more particularly to mean: (a) - any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms; (b) - any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more aromatic vinyl compounds having from 8 to 20 carbon atoms; (c) - a ternary copolymer obtained by copolymerization of ethylene, an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, such as for example elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular hexadiene-1,4, ethylidene norbornene, dicyclopentadiene.

[0037] Suitable conjugated dienes include, in particular, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C 1 -C 5 alkyl)-1,3-butadienes such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial mixture "vinyl-toluene", para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene.

[0038] The diene copolymers mentioned above (category (b)) may contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinylaromatic units. The elastomers may have any microstructure which depends on the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used. The elastomers may, for example, be block, random, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or star-shaped or even functionalized with a coupling and / or star-shaped or functionalizing agent.

[0039] Suitable are polybutadienes and in particular those having a content (mol%) of -1,2 units of between 4% and 80% or those having a content (mol%) of cis-1,4 greater than 80%, polyisoprenes, butadiene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content (mol%) of -1,2 bonds of the butadiene part of between 4% and 65%, a content (mol%) of trans-1,4 bonds of between 20% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a glass transition temperature (Tg, measured according to ASTM D3418) of -40°C to -80°C, isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg of between -25°C and -50°C.In the case of butadiene-styrene-isoprene copolymers, those having a styrene content of between 5% and 50% by weight and more particularly between 10% and 40%, an isoprene content of between 15% and 60% by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content (mol%) of -1,2 units in the butadiene part of between 4% and 85%, a content (mol%) of trans -1,4 units in the butadiene part of between 6% and 80%, a content (mol%) of -1,2 plus -3,4 units in the isoprene part of between 5% and 70% and a content (mol%) of trans -1,4 units in the isoprene part of between 5% and 70% between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg between -20°C and -70°C.

[0040] As other elastomers present in the elastomeric matrix in addition to the butyl rubber(s), mention may also be made of isoprene elastomers other than the butyl elastomers previously mentioned.

[0041] The term "isoprene elastomer" is understood to mean, in a known manner, a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and the mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene (SBIR) copolymers. This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used.

[0042] Preferably in the present invention, the butyl rubber(s) have a content varying from 70 to 100 phr, preferably varying from 90 to 100 phr.

[0043] In a first particular embodiment of the invention, the elastomeric matrix comprises a blend of several butyl rubbers.

[0044] In a second particular embodiment of the invention, the elastomeric matrix consists of one or more butyl rubbers.

[0045] In this second particular mode, it is of course understood that the content of butyl rubber alone or of the blend of several butyl rubbers is then 100 pce.

[0046] In the case of a low level of the sum of the reinforcing filler(s) and graphite, and in particular a very low level of the reinforcing filler(s), a person skilled in the art will know how to adapt the molecular mass of the butyl(s) in order to obtain satisfactory raw processability.

[0047] As seen previously, the total content of reinforcing fillers and graphite in the rubber composition usable in the inner rubber according to the invention varies from 5 to 50 pce.

[0048] For the purposes of the present invention, reinforcing fillers are understood to mean any type of filler known for its ability to reinforce a rubber composition that can be used for the manufacture of tires, for example an organic filler such as carbon black or even a reinforcing inorganic filler.

[0049] Thus, in the present invention, the rubber composition usable in the inner rubber according to the invention comprises from 5 to 30 pce of carbon black.

[0050] All carbon blacks are suitable, including HAF, ISAF and SAF type blacks conventionally used in tires (so-called tire grade blacks). Among the latter, we will particularly mention the reinforcing carbon blacks of the 100, 200 or 300 series (ASTI grades), such as blacks N115, N134, N234, N326, N330, N339, N347, N375, or, depending on the intended applications, blacks of higher series (for example N660, N683, N772), or even N990.

[0051] Of course, one can use a single carbon black or a blend of several carbon blacks of different ASTM grades.

[0052] Preferably in the present invention, the carbon black content in the rubber composition varies from 15 to 30 phr, preferably varies from 20 to 30 phr.

[0053] As seen previously, the rubber composition usable in the inner rubber according to the invention comprises at least 5 pce of one or more additional fillers chosen from reinforcing fillers other than carbon black, graphite and inert fillers, said inert fillers being chosen from chalk, clay, bentonite, talc, kaolin, glass microbeads, glass flakes and a mixture of these compounds.

[0054] Thus, the rubber composition usable in the present invention can also comprise one or more reinforcing inorganic fillers.

[0055] 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, "clear" 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.

[0056] The physical state in which the reinforcing inorganic filler is present is indifferent, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term reinforcing inorganic filler also means mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers as described below.

[0057] Suitable reinforcing inorganic fillers are, in particular, mineral fillers of the siliceous type, in particular silica (SiO 2 ), or of the aluminous type, in particular alumina (Al 7 O 3 ). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area and a CTAB specific surface area both of less than 450 m 2 < / g, preferably from 30 to 400 m 2 < / g.

[0058] 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 area silicas as described in application WO 03 / 16837.

[0059] Finally, a person skilled in the art will understand that, as a filler equivalent to the reinforcing inorganic filler described in this paragraph, a reinforcing filler of another nature, in particular organic, could be used, provided that this reinforcing filler is covered with an inorganic layer such as silica, or else comprises functional sites on its surface, in particular hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer.

[0060] It is recalled here that by "coupling agent" we mean, in a known manner, an agent capable of establishing a sufficient bond, of a chemical and / or physical nature, between the inorganic filler and the elastomer.

[0061] Such coupling agents, in particular silica / elastomer, have been described in a very large number of documents, the best known being bifunctional organosilanes carrying alkoxyl functions (i.e., by definition, “alkoxysilanes”) and functions capable of reacting with the elastomer such as, for example, polysulfide functions.

[0062] As seen previously, the additional filler(s) present in the rubber composition which can be used according to the invention can be chosen from graphite.

[0063] Preferably, the content of graphite in the rubber composition usable according to the invention varies from 0 to less than 35 phr, preferably from 1 to less than 35 phr, and even more preferably from 1 to 20 phr.

[0064] Graphite is generally understood to mean a set of non-compact hexagonal sheets of carbon atoms: graphenes. Graphite, a hexagonal crystal system, has an ABAB type stacking where the B plane is translated relative to the A plane; it belongs to the crystal group: space group P63 / mmc.

[0065] Graphite cannot be considered a reinforcing filler unlike carbon black or silica, as it allows an increase in the tensile modulus of a rubber composition in which it is incorporated.

[0066] Given these definitions, graphite capable of being used according to the invention is understood to mean more particularly: (a) any natural graphite, associated with rocks affected by metamorphism, after separation of the impurities accompanying the graphite veins and after crushing; (b) any thermally expandable natural graphite, i.e. in which a chemical compound in the liquid state, for example an acid, is intercalated between its graphene planes; (c) any expanded natural graphite, the latter being produced in two stages: intercalation of a chemical compound in the liquid state, for example an acid, between the graphene planes of a natural graphite by chemical treatment and expansion at high temperature; (d) any synthetic graphite obtained by graphitization of petroleum coke.

[0067] The rubber composition that can be used according to the invention can contain a single graphite or a mixture of several graphites, so it is possible to have a blend of natural graphite and / or expanded graphite and / or synthetic graphite.

[0068] Graphite as defined above can be presented morphologically in a lamellar or non-lamellar form.

[0069] Preferably, the graphite that can be used according to the invention is in lamellar form.

[0070] As seen previously, the additional filler(s) may be chosen from inert fillers, said inert fillers being chosen from chalk, clay, bentonite, talc, kaolin, glass microbeads, glass flakes and a mixture of these compounds.

[0071] In a particularly preferred manner, the content of the inert filler(s) in the rubber composition which can be used according to the invention varies from 1 to 45 pce.

[0072] When the content of the inert filler(s) in the rubber composition which can be used according to the invention preferably varies from 1 to 45 phr, then in a particular embodiment of the invention, the carbon black content in the rubber composition which can be used according to the invention varies from 5 to 15 phr.

[0073] Preferably, the inert filler that can be used according to the invention is chalk.

[0074] Chalk is preferably in the form of microparticles whose average size (by mass) is greater than 1 µm. The median size of chalk microparticles, measured on a sedigraph, is preferably between 0.5 and 200 µm, more particularly between 0.5 and 30 µm and even more preferably between 1 and 20 µm.

[0075] The chalks known to those skilled in the art are natural calcium carbonates (chalk) or synthetic with or without coating (for example with stearic acid).

[0076] Examples of such preferred and commercially available chalks include, for example, the chalk sold under the name “Omya BLS” by the company Omya.

[0077] As explained above, the total content of reinforcing fillers and graphite in the rubber composition usable in the inner rubber according to the invention varies from 5 to 50 phr. More precisely, this means that the sum of the contents of carbon black and other possible reinforcing fillers, for example silica, and the contents of possible graphite, is greater than or equal to 5 and is less than or equal to 50 phr.

[0078] In the present invention, carbon black may advantageously constitute the only reinforcing filler or the majority reinforcing filler.

[0079] As a reminder, in the present invention, the rubber composition usable in the inner rubber comprises from 0 to less than 10 pce of a plasticizing agent.

[0080] As known to those skilled in the art, a “plasticizing agent” by definition is a liquid or solid compound at room temperature (23°C) and atmospheric pressure (1,013.10 5< Pa) which is compatible, i.e. miscible at the rate used with the rubber composition for which it is intended, so as to act as a true diluting agent.

[0081] Preferably in the present invention, the plasticizing agent is chosen from plasticizing oils and plasticizing resins.

[0082] By definition, a plasticizing oil (also called a liquid plasticizer) is liquid at room temperature and atmospheric pressure.

[0083] This or these plasticizing oils generally have a low glass transition temperature, below -20°C (Tg, measured according to ASTM D3418), preferably below -40°C.

[0084] Glass transition temperatures are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418.

[0085] As plasticizing oil usable in the inner rubber according to the invention, all so-called "extender" oils, whether aromatic or non-aromatic in nature, known for their plasticizing properties with respect to the elastomers used in the present invention, can be used.

[0086] Particularly suitable are plasticizing oils selected from the group consisting of liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE (Distillate Aromatic Extracts) oils, MES (Medium Extracted Solvates) oils, TDAE (Treated Distillate Aromatic Extracts) oils, RAE (Residual Aromatic Extracts) oils, TRAE (Treated Residual Aromatic Extracts) oils, SRAE (Safety Residual Aromatic Extracts) oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these compounds.

[0087] Liquid polymers resulting from the polymerization of olefins or dienes are also suitable, such as those selected from the group consisting of polybutenes, polydienes, in particular polybutadienes, polyisoprenes, copolymers of butadiene and isoprene, copolymers of butadiene or isoprene and styrene, and mixtures of these liquid polymers. The number-average molar mass of such liquid polymers is preferably in a range from 500 g / mol to 50,000 g / mol, more preferably from 1,000 g / mol to 10,000 g / mol. Examples include the “Ricon” products from the Sartomer company.

[0088] Also suitable are functionalized or non-functionalized polyisobutylene oils with a molecular mass between 200 g / mol and 40,000 g / mol.

[0089] According to another preferred embodiment of the invention, the plasticizing oil(s) are vegetable oils (such as linseed, safflower, soybean, corn, cottonseed, rapeseed, castor, tung, pine, sunflower, palm, olive, coconut, peanut, grape seed oils, and mixtures of these oils, in particular sunflower oil).

[0090] According to another particular embodiment of the invention, the plasticizing oil(s) are an ether such as, for example, polyethylene glycols or polypropylene glycols.

[0091] Also suitable are plasticizing oils selected from the group consisting of ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these compounds.

[0092] As a reminder, the plasticizing agent can also be chosen from plasticizing resins.

[0093] In contrast to plasticizing oils, a plasticizing resin is a compound that is solid at room temperature (23°C) and atmospheric pressure (1,013.10 5< Pa).

[0094] This or these plasticizing resins generally have a glass transition temperature greater than 20°C (Tg, measured according to ASTM D3418), preferably greater than 30°C.

[0095] Preferably, the plasticizing resins which can be used according to the invention are hydrocarbon plasticizing resins.

[0096] Hydrocarbon resins are polymers well known to those skilled in the art, and are therefore miscible by nature in elastomer compositions when they are also described as “plasticizers”.

[0097] These hydrocarbon plasticizing resins generally have a glass transition temperature above 20°C and a softening temperature below 170°C.

[0098] Softening point temperatures are measured according to ASTM E-28.

[0099] They have been widely described, for example, in the work entitled "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), chapter 5 of which is devoted to their applications, particularly in pneumatic rubber (5.5. "Rubber Tires and Mechanical Goods").

[0100] They can be aliphatic, naphthenic, aromatic or aliphatic / naphthenic / aromatic, i.e. based on aliphatic and / or naphthenic and / or aromatic monomers. They can be natural or synthetic, petroleum-based or not (if this is the case, they are also known as petroleum resins). They are preferably exclusively hydrocarbon-based, i.e. they only contain carbon and hydrogen atoms.

[0101] The content of plasticizing agent in the rubber composition usable according to the invention varies from 0 to less than 10 pce.

[0102] Preferably, the content of plasticizing agent in the rubber composition is less than or equal to 6 pce.

[0103] The rubber composition usable in the inner rubber according to the invention may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tires, such as for example protective agents such as chemical anti-ozonants, antioxidants, anti-fatigue agents, acceptors (for example phenolic novolak resin) or methylene donors (for example HMT or H3M), a crosslinking system based either on sulfur, or on sulfur donors and / or peroxide and / or bismaleimides and / or vulcanizing resins, vulcanization accelerators, vulcanization activators.

[0104] The rubber composition usable in the inner rubber according to the invention can be manufactured in suitable mixers, 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 140°C, preferably between 110°C and 135°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, and finally a finishing phase during which the crosslinking system is incorporated.

[0105] The process for preparing such a composition comprises, for example, the following steps: thermomechanically kneading (for example in one or more stages) the elastomeric matrix with the carbon black, the additional filler(s), the plasticizing system if present, until a maximum temperature of between 110°C and 140°C is reached (so-called “non-productive” phase); cooling the assembly to a temperature below 100°C; then incorporating, during a second stage (so-called “productive”), a crosslinking system; kneading the assembly to a maximum temperature below 110°C.

[0106] For example, the non-productive phase is carried out in a single thermomechanical step during which all the basic constituents (the butyl rubber(s), the other possible elastomer(s), the possible plasticizing system, the carbon black and the additional filler(s)) are introduced into a suitable mixer such as a conventional internal mixer, firstly, then, in a second step, for example after one to two minutes of mixing, the other possible additives, filler covering agents or additional processing agents, with the exception of the crosslinking system. The total mixing time in this non-productive phase is preferably between 1 and 15 min.

[0107] After cooling the mixture thus obtained, the crosslinking system is then incorporated into an external mixer such as a cylinder mixer, maintained at a low temperature (for example between 40°C and 100°C). The whole is then mixed (productive phase) for a few minutes, for example between 2 and 15 min.

[0108] The actual crosslinking system is preferably based on sulfur and a primary vulcanization accelerator, in particular a sulfenamide type accelerator. Added to this vulcanization system, incorporated during the first non-productive phase and / or during the productive phase, are various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), etc. The sulfur content is preferably between 0.5 and 3.0 pce, that of the primary accelerator is preferably between 0.5 and 5.0 pce.

[0109] Any compound capable of acting as a vulcanization accelerator for the elastomers according to the invention in the presence of sulfur may be used as accelerator (primary or secondary), in particular accelerators of the thiazole type and their derivatives, accelerators of the thiuram type, zinc dithiocarbamates. These accelerators are more preferably chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated as “MBTS”), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated as “CBS”), N,N-dicyclohexyl-2-benzothiazyl sulfenamide (abbreviated as “DCBS”), N-tert-butyl-2-benzothiazyl sulfenamide (abbreviated as “TBBS”), N-tert-butyl-2-benzothiazyl sulfenimide (abbreviated as “TBSI”), zinc dibenzyldithiocarbamate (abbreviated as “ZBEC”) and mixtures of these compounds.

[0110] Preferably, a primary accelerator of the sulfenamide type is used.

[0111] The final composition thus obtained can then be calendered, for example in the form of a sheet, a plate in particular for characterization in the laboratory, or even extruded, for example to form a rubber profile used for the manufacture of an interior rubber.

[0112] The inner rubber can be used in any type of inflatable object. Examples of such inflatable objects include inflatable boats, balloons or balls used for games or sports.

[0113] Consequently, the invention also relates to a tire comprising an inner rubber as defined above.

[0114] Generally speaking, the tire according to the invention is intended to equip motor vehicles of the passenger car type, SUVs (“Sport Utility Vehicles”), two-wheelers (in particular motorcycles), airplanes, as well as industrial vehicles such as vans, heavy goods vehicles and other transport or handling vehicles.

[0115] The invention and its advantages will be understood in greater depth in light of the following exemplary embodiments. EXAMPLES: I Measurement and testing methods : 1) Properties after cooking: tensile tests

[0116] These tests make it possible to determine the elastic stresses and the breaking properties.

[0117] Unless otherwise indicated, they are carried out in accordance with French standard NF T 46-002 of September 1988. The breaking stresses (in MPa) and the elongations at break (in %) are measured at a temperature of 23°C. 2) Properties after cooking: dynamic properties

[0118] The dynamic property tan(δ)max is measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen 2 mm thick and 79 mm 2< in cross-section) is recorded, subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at a temperature of 23 ° C according to the ASTM D 1349-99 standard. A strain amplitude sweep is carried out from 0.1 % to 50 % peak-peak (forward cycle), then from 50 % to 0.1 % peak-peak (return cycle). The result used is the loss factor tan(δ). For the return cycle, the maximum value of tan(δ) observed is indicated, noted tan(δ)max. This value is representative of the hysteresis of the material and in this case of the rolling resistance: the lower the value of tan(δ)max, the lower the rolling resistance. 3) Properties after cooking: permeability

[0119] Permeability values ​​are measured using a MOCON OXTRAN 2 / 60 permeability tester at 40°C. Baked samples in the form of discs of a determined thickness (approximately 0.8 to 1 mm) are mounted on the apparatus and sealed with vacuum grease. One side of the disc is maintained under 10 psi of nitrogen while the other side is maintained under 10 psi of oxygen. The increase in oxygen concentration is monitored using a Coulox oxygen detector on the side maintained under nitrogen. The oxygen concentration is recorded on the side maintained under nitrogen to achieve a constant value, which is used to determine the oxygen permeability.

[0120] An arbitrary value of 100 is given for the oxygen permeability of the control, a result less than 100 indicating a decrease in oxygen permeability and therefore better impermeability. 4) Tire tests 4.1) Rolling resistance

[0121] Rolling resistance is measured on a steering wheel, according to the ISO 7-67 (1992) method. In Table III, the rolling resistance indicated corresponds to the difference between the rolling resistance of the reference tire and the rolling resistance of the tire according to the invention. 4.2) Endurance

[0122] The endurance in very long-term driving (40,000 km) under very severe conditions was tested, on an automatic driving machine, according to different predetermined cycles of pressure, load and speed; after which the general condition of each tire is observed. 4.3) Pressure loss

[0123] Measurement tests were conducted to assess tire pressure loss after 4 weeks at 20°C.

[0124] Pneumatic tires in accordance with the invention, of the passenger vehicle type (size 205 / 55 R16), were manufactured, their inner wall being covered by an airtight layer of a given constant thickness (placed on a building drum, before manufacturing the rest of the tire). Then, the tires were vulcanized. These pneumatic tires in accordance with the invention were compared with control pneumatic tires (MICHELIN Energy ™< Saver brand) comprising a conventional airtight layer, of the same thickness, based on butyl rubber. The airtightness of the two types of tires was measured by measuring the pressure loss at 20°C after 4 weeks. The results presented below are presented on a base of 100: an arbitrary value of 100 is given for the airtightness performance of the control, a result greater than 100 indicating better airtightness performance and therefore a reduction in pressure loss after 4 weeks. II Preparation and testing of rubber compositions

[0125] The following tests are carried out as follows: the butyl rubber(s), the elastomer(s) if present, the fillers and the plasticizing agent if present in the rubber composition, as well as the various other ingredients except for the vulcanization 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, which lasts a total of approximately 3 to 4 minutes, until a maximum "drop" temperature of 140°C is reached.

[0126] The mixture thus obtained is recovered, cooled and then sulfur, a sulfenamide type accelerator and the other elements of the vulcanization system are incorporated into a mixer (homo-finisher) at 30°C, mixing everything (productive phase) for an appropriate time (for example between 5 and 12 min).

[0127] The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties, or extruded in the form of inner tire rubbers. Example 1 : rubber composition comprising an inert filler and a plasticizing oil

[0128] Table I below brings together the ingredients and contents (expressed in pce) of a comparative composition (T1) and three compositions which can be used according to the invention (C1 to C3). Tableau I T1 C1 C2 C3 Butyl rubber (1)< 90 90 90 90 Synthetic polyisoprene (2)< 10 10 10 10 Carbon black (3)< 50 25 25 5 Natural graphite - - 15 - Natural chalk 20 20 20 40 Plasticizing agent (4)< 3 3 3 3 Sulfur 1,5 1,5 1,5 1,5 MBTS( 5< ) 1,2 1,2 1,2 1,2 ZnO 1,5 1,5 1,5 1,5 Stearic acid 1,5 1,5 1,5 1,5 (1) Brominated polyisobutylene marketed by EXXON CHEMICAL Co. (2) Synthetic polyisoprene at 97% of cis-1,4 structure sold by Nizhnekamsk company under the reference IR6596 (3) N772 (4) TDAE oil (5) 2-mercaptobenzothiazyl disulfide

[0129] Composition T1 is a control composition, conventionally used in the inner rubbers of tires, which contains 50 pce of carbon black and 20 pce of chalk.

[0130] Composition C1 is in accordance with the invention, and comprises 25 pce of carbon black and 20 pce of chalk.

[0131] Composition C2 is in accordance with the invention, and comprises 25 pce of carbon black, 20 pce of chalk and 15 pce of graphite.

[0132] Composition C3 is in accordance with the invention, and comprises 5 pce of carbon black and 40 pce of chalk.

[0133] The properties of compositions T1 and C1 to C3 after baking have been summarized in Table II below. Table II T1 C1 C2 C3 Breaking stress (in Mpa) 9,3 11,5 8,1 7,3 Elongation at break (in %) 630 835 735 875 Tan(δ)max (at 23°C) 0,37 0,34 0,34 0,33 Oxygen permeability 100 101 75 100

[0134] After cooking, it is found that the elongation and breaking stress properties of compositions C1 to C3 in accordance with the invention are generally equivalent to those of the control composition T1.

[0135] In addition, compositions C1 to C3 in accordance with the invention exhibit lower hysteresis than control composition T1 (tan(δ)max).

[0136] Finally, compositions C1 and C3 in accordance with the invention have an oxygen permeability equivalent to that of the control composition T1. It is even noted that composition C2 in accordance with the invention has a lower permeability (and therefore a better impermeability) to oxygen than that of the control composition T1. Example 2 : rubber composition comprising an inert filler and a plasticizing resin

[0137] Table III below lists the ingredients and contents (expressed in pce) of a T2 composition and a C4 composition. Tableau III T2 C4 Butyl rubber (1)< 100 100 Carbon black (2)< 50 25 Natural graphite 10 10 Plasticizing agent (3)< 8 8 Sulfur 1,5 1,5 MBTS (4)< 1,2 1,2 ZnO 1,5 1,5 Stearic acid 1,5 1,5 (1) Brominated polyisobutylene marketed by EXXON CHEMICAL Co. (2) N772 (3) Plasticizing resin: C5 cut / C9 cut resin marketed by Cray Valley under the name “THER 8644 Resin” (Tg= 44°C) (4) 2-mercaptobenzothiazyl disulfide

[0138] T2 composition is a conventional composition used in tire inner rubbers, which comprises 50 parts carbon black, 10 parts graphite and 8 parts plasticizing resin.

[0139] Composition C4 consists of 25 parts carbon black, 10 parts graphite and 8 parts plasticizing resin.

[0140] The properties of compositions T2 and C4 after curing have been summarized in Table IV below. Table IV T2 C4 Breaking stress (in Mpa) 9,4 9,2 Elongation at break (in %) 725 840 Tan(δ)max (at 23°C) 0,51 0,49 Oxygen permeability 100 100

[0141] After curing, it is found that the elongation and breaking stress properties of composition C4 are generally equivalent to those of composition T2.

[0142] Moreover, composition C4 exhibits lower hysteresis than composition T2 (tan(δ)max).

[0143] Finally, composition C4 has an oxygen permeability equivalent to that of composition T2. Example 3: rubber composition containing neither inert filler nor plasticizer

[0144] Table V below lists the ingredients and contents (expressed in pce) of a T3 composition and a C5 composition. Tableau V T3 C5 Butyl rubber (1)< 100 100 Carbon black (2)< 50 25 Natural graphite 10 10 Sulfur 1,5 1,5 MBTS (3)< 1,2 1,2 ZnO 1,5 1,5 Stearic acid 1,5 1,5 (1) Brominated polyisobutylene marketed by EXXON CHEMICAL Co. (2) N772 (3) 2-Mercaptobenzothiazyl disulfide

[0145] T3 compound is a conventional compound used in tire inner rubbers, which contains 50% carbon black and 10% graphite.

[0146] Composition C5 consists of 25 pce of carbon black and 10 pce of graphite.

[0147] The properties of compositions T3 and C5 after curing have been summarized in Table VI below. Table VI T3 C5 Breaking stress (in Mpa) 9,3 9,5 Elongation at break (in %) 635 780 Tan(δ)max (at 23°C) 0,40 0,37 Oxygen permeability 100 101

[0148] After curing, it is found that the elongation and breaking stress properties of composition C5 are generally equivalent to those of composition T3.

[0149] Moreover, composition C5 exhibits lower hysteresis than composition T3 (tan(δ)max).

[0150] Finally, composition C5 has an oxygen permeability equivalent to that of composition T3. III Tire Rolling Tests

[0151] Table VII below lists the ingredients and contents (expressed in pce) of a comparative composition (T4). The summary of the ingredients and contents of composition C2 which can be used according to the invention is given for information purposes only. Table VII T4 C2 Butyl rubber (1)< 90 90 Synthetic polyisoprene (2)< 10 10 Carbon black (3)< 50 25 Natural graphite 15 15 Natural chalk 20 20 Plasticizing oil (4)< 3 3 Plasticizing resin (5)< 8 - Sulfur 1,5 1,5 MBTS (6)< 1,2 1,2 ZnO 1,5 1,5 Stearic acid 1,5 1,5 (1) Brominated polyisobutylene marketed by EXXON CHEMICAL Co. (2) Synthetic polyisoprene with 97% cis-1,4 structure sold by Nizhnekamsk under the reference IR6596 (3) N772 (4) TDAE oil (5) Plasticizing resin: Plasticizing resin: C5 cut / C9 cut resin marketed by Cray Valley under the name “THER 8644 Resin” (Tg= 44°C) (6) 2-mercaptobenzothiazyl disulfide

[0152] The above T4 and C2 compositions were tested as inner rubber for radial passenger car tyres, size 205 / 55 R16 (speed index H). They were prepared as detailed above and calendered as inner rubber for tyres to a thickness of 0.7 mm.

[0153] The rolling resistance, endurance and pressure loss tests are reported in Table VIII. Table VIII T4 C2 Rolling resistance - gain of 0.12 kg / T Endurance 40,000 km ok ok Loss of pressure 100 100

[0154] These results show that for identical sealing, the tire having as inner rubber the composition C2 in accordance with the invention has improved rolling resistance compared to the tire corresponding to the control composition T4.

[0155] The 40,000 km endurance test for both tires proved positive, meaning that both tires were capable of traveling 40,000 km without showing any significant deterioration.

[0156] It should be noted that this validation of the endurance criteria is all the more remarkable for the tire comprising an inner rubber of composition C2 in accordance with the invention, for which the corresponding composition contains more than half as much carbon black as the control composition T4.

[0157] Finally, we note that the pressure loss of the tire formed from the inner rubber C2 is equivalent to the pressure loss of the tire formed from the inner rubber T4.

Claims

1. Inner liner for tyre having a rubber composition comprising: - an elastomeric matrix comprising at least 50 phr of one or more butyl rubbers, - from 5 to 30 phr of carbon black, - from 0 to less than 10 phr of a plasticizing agent, - at least 5 phr of one or more additional fillers selected from reinforcing fillers other than carbon black, graphite-and inert fillers, said inert fillers is (are) selected from chalk, clay, bentonite, talc, kaolin, glass microbeads, glass flakes, and a mixture of these compounds, the total content of reinforcing fillers and of graphite in the rubber composition varying from 5 to 50 phr, the content of the inert filler(s) in the rubber composition varies from 1 to 60 phr.

2. Inner liner according to Claim 1, in which the butyl rubber(s) is (are) selected from isobutylene rubbers, isobutylene / isoprene copolymers, bromobutyl rubbers and chlorobutyl rubbers.

3. Inner liner according to Claim 1 or 2, in which the content of butyl rubbers of the composition varies from 70 to 100 phr, preferably from 90 to 100 phr.

4. Inner liner according to any one of the preceding claims, in which the elastomeric matrix comprises a blend of several butyl rubbers.

5. Inner liner according to any one of Claims 1 to 3, in which the elastomeric matrix consists of one or more butyl rubbers.

6. Inner liner according to any one of the preceding claims, in which the content of carbon black in the rubber composition varies from 15 to 30 phr, and preferably varies from 20 to 30 phr.

7. Inner liner according to any one of the preceding claims, in which the content of graphite in the rubber composition varies from 0 to less than 35 phr, preferably from 1 to less than 35 phr, and even more preferentially from 1 to 20 phr.

8. Inner liner according to any one of the preceding claims, in which the graphite is in lamellar form.

9. Inner liner according to any one of the preceding claims, in which the content of the inert filler(s) in the rubber composition varies from 1 to 45 phr.

10. Inner liner according to any one of Claim 1 to 5 and 7 to 9, in which the content of carbon black in the rubber composition varies from 5 to 15 phr.

11. Inner liner according to any one of the preceding claims, in which the inert filler is chalk.

12. Inner liner according to any one of the preceding claims, in which the content of plasticizing agent in the rubber composition is less than or equal to 6 phr.

13. Tyre comprising an inner liner as defined in any one of the preceding claims.