FR3083542A1 - INTERIOR GUM INCLUDING CARBON BLACK AND KAOLIN - Google Patents

Abstract

The invention relates to an inner rubber for a tire, having a rubber composition based on at least one butyl rubber with a content ranging from 60 to 100 phr, parts per hundred parts of elastomer, of carbon black with a content ranging from 12 to 45 phr, kaolin with a rate ranging greater than or equal to 10 phr and a plasticizer with a rate ranging from 0 to 8 phr.

Description

The present invention relates to a rubber composition for the manufacture of an inner layer of an airtight tire, commonly called an "inner rubber" of a tire.

Tubeless tires indeed have an interior surface of low air permeability in order to avoid deflation of the tire and to protect the sensitive internal zones of the latter against the arrival of oxygen and water, such as the plies containing metallic cables sensitive to oxidation, this protection making it possible to improve the endurance of the tire. Today, such protection of the interior surface of tires is carried out by interior gums constituted by elastomeric compositions based on butyl rubber.

However, since fuel economy and the need to protect the environment have become a priority, it is desirable to produce interior gums which are airtight and which have as low a weight and hysteresis as possible, in order to obtain a improved rolling resistance of the tire. However, the performance in terms of air impermeability of butyl rubbers is linked to a non-negligible minimum thickness (of the order of a millimeter) and therefore to a certain weight, which does not make it possible to respond effectively to these new requirements.

Thus, it is necessary to add reinforcing fillers, such as carbon black, to the elastomeric composition of inner rubber to improve its impermeability. However, in large quantities, these reinforcing fillers harm certain properties of the composition, both raw: difficulty in processing the raw composition, commonly called “processability”, when cooked: degradation of mechanical properties, in particular reduction in resistance to bending. The introduction of an oil-type plasticizer overcomes these aspects of processing and mechanical properties, but greatly penalizes impermeability.

Various solutions have been envisaged to remedy these drawbacks in particular by using other types of fillers which are added to the reinforcing fillers, often known under the name of smectites and in particular of organophilic smectites. These organophilic smectites improve the waterproofing properties of materials if they are well dispersed in the material, that is to say both a homogeneous distribution of these charges within the material and good compatibility with the latter. This dispersion is often difficult to obtain because of the poor thermodynamic compatibility existing between the elastomers and such fillers.

The publication WO 2006/047509 of the applicant describes a composition for an inner tire rubber, the composition based on butyl rubber and

-2 comprising carbon black, contains non-reinforcing fillers constituted by organophilic smectites reducing gas permeability, dispersed in the elastomeric matrix as well as a specific plasticizer constituted by a terpene resin having in particular a higher glass transition temperature, Tg, at 50 ° C. This composition effectively has mechanical and waterproof properties making it acceptable for use as an inner tire rubber, thanks to the combined effect of these organophilic smectites and this high Tg resin.

Other solutions consist in using lamellar fillers such as graphite in order to improve the waterproofing of the composition. However, the presence of graphite can lead to problems of processability of the mixtures. Thus, application WO 2008/145314 describes a rubber composition for an internal 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 internal rubber also having a good compromise of properties.

The Applicant has discovered, in its application WO2016001226 and contrary to the knowledge of a person skilled in the art, that there exists a solution making it possible to obtain an interior rubber with a good compromise of properties with good impermeability and good endurance while presenting reduced hysteresis, and a low carbon black content by adding an additional filler without significantly increasing the total content of reinforcing or semi-reinforcing fillers in an elastomeric matrix mainly consisting of butyl rubber.

However, by continuing its research, the Applicant has discovered that the use of a specific inert filler in a composition for an inner tire of a tire with a low carbon black content, made it possible to have a “burn-out time” of the composition clearly. longer.

Indeed, a person skilled in the art knows that it is important to allow crosslinking of the rubber compositions in industrially acceptable times, while preserving a minimum safety period ("roasting time") during which the compositions can be put fit without risk of premature crosslinking ("roasting").

Thus, the subject of the invention is an interior rubber for a tire, having a rubber composition based on at least one butyl rubber with a rate ranging from 60 to 100 phr, parts per hundred parts of elastomer, carbon black with a rate ranging from 12 to 45 phr, kaolin with a rate ranging greater than or equal to 10 phr and a plasticizer with a rate ranging from 0 to 8 phr.

-3 Preferably the carbon black content of this composition ranges from 15 to 45 phr, more preferably from 20 to 40 phr and even more preferably from 20 to 35 phr and the plasticizer content of the composition ranges from 0 to 6 phr , preferably from 0 to 3 pce.

Advantageously, the kaolin content of the composition ranges from 10 to 80 phr, preferably from 10 to 70 phr and more preferably from 20 to 70 phr.

According to one embodiment of the invention, the composition comprises at least one diene elastomer chosen from polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, copolymers of isoprene, and mixtures of these elastomers.

The subject of the invention is also a tire comprising an inner rubber as defined above.

I. MEASUREMENTS AND TESTS USED

The rubber compositions are characterized, after curing, as indicated below.

Permeability

The permeability values are measured using a MOCON OXTRAN 2/60 permeability “tester” at 40 ° C. Samples baked 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 kept under 10 psi of nitrogen while the other side is kept under 10 psi of oxygen (1 psi = 6894.76 Pa). The increase in oxygen concentration is controlled by using a “Coulox” oxygen detector on the side kept under nitrogen. The oxygen concentration is noted on the face maintained under nitrogen allowing a constant value to be reached, used to determine the oxygen permeability.

An arbitrary value of 100 is given for the oxygen permeability of the control, a result less than 100 indicating a reduction in the oxygen permeability therefore a better impermeability.

Toasting time (or fixing time)

The measurements are carried out at 130 ° C, in accordance with French standard NF T 43-005. The evolution of the consistometric index as a function of time makes it possible to determine the toasting time of the rubber compositions, assessed in accordance with the aforementioned standard by parameter T5 (case of a large rotor), expressed in minutes, and defined

-4 as the time required to obtain an increase in the consistometric index (expressed in MU) by 5 units above the minimum value measured for this index.

An arbitrary value of 100 is given for the toasting time (parameter T5) of the conventional control, a result greater than 100 indicating an increase in the toasting time therefore an advantageous property.

Tensile tests

These tensile tests make it possible to determine the elasticity stresses and the breaking properties. Unless otherwise indicated, they are carried out in accordance with French standard NF T 46-002 of September 1988. The module is measured at second extension (ie, after an accommodation cycle at the rate of extension provided for the measurement itself). nominal secant (or apparent stress, in MPa) at 100% elongation (noted M100).

The stresses at break (in MPa) and the elongations at break (in%) are also measured. All these tensile measurements are carried out at a temperature of 100 ° C ± 2 ° C, and under normal humidity conditions (50 ± 5% relative humidity), according to French standard NF T 40-101 (December 1979 ).

Thus, one can determine the energy to cause the rupture (Energie Rupture) of the test-tube which is the product of the stress at break and the elongation at break (Energie Rupture = stress at break * elongation at the Out).

The results are shown in base 100; the arbitrary value 100 being attributed to the witness respectively for the stress at rupture and for the Energy Rupture. A result less than 100 for the breaking stress or for the Rupture Energy indicates a decrease in the value concerned, which corresponds to a decrease in the performance of breaking strength and conversely, a result greater than 100, indicates an increase of this value, which corresponds to an improvement in this performance.

II. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an inner rubber for a tire, having a rubber composition based on at least one butyl rubber with a rate ranging from 60 to 100 phr, parts per hundred parts of elastomer, of carbon black with a rate ranging from 12 to 45 phr, kaolin with a rate ranging greater than or equal to 10 phr and a plasticizer with a rate ranging from 0 to 8 phr.

By the expression composition based on, is meant a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some

-5 of these constituents which can react and / or which are intended to react with each other, at least partially, during the various stages of manufacturing the composition; the composition thus being able to be in the fully or partially crosslinked state or in the non-crosslinked state.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass. On the other hand, any range of values designated by the expression between a and b represents the range of values going from more than a to less than b (i.e. limits a and b excluded) while any range of values designated by the expression from a to b signifies the range of values going from a to b (that is to say including the strict limits a and b).

By the expression part by weight per hundred parts by weight of elastomer (or phr), it is understood within the meaning of the present invention, the part, by mass per hundred parts by mass of elastomer.

When reference is made to a majority compound, it is understood within the meaning of the present invention, that this compound is predominant among the compounds of the same type in the composition, that is to say that it is that which represents the most large mass amount among compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the largest mass relative to the total mass of the elastomers in the composition. In the same way, a so-called majority charge is that representing the largest mass among the charges of the composition. For example, in a system comprising a single elastomer, the latter is predominant within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers.

The compounds comprising carbon mentioned in the description can be of fossil origin or bio-based. In the latter case, they can be, partially or totally, from biomass or obtained from renewable raw materials from biomass. Are concerned in particular polymers, plasticizers, fillers, etc.

Diene elastomer

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

-6The composition according to the invention for a sealed inner rubber of a tubeless tire contains at least 60 phr of a butyl rubber, used alone, in combination with one or more other butyl rubber or diene elastomers.

By butyl rubber is meant a homopolymer of poly (isobutylene) or a copolymer of poly (isobutylene) with isoprene (in this case this butyl rubber is one of the diene elastomers), as well as the halogenated derivatives, in particular generally brominated or chlorinated, of these poly (isobutylene) homopolymers and copolymers of poly (isobutylene) and isoprene.

Examples of butyl rubber that are particularly suitable for carrying out the invention are: copolymers of isobutylene and isoprene (IIR), bromo-butyl rubbers such as the bromoisobutylene-isoprene copolymer (BIIR), chlorobutyl rubbers such as the chloroisbutylene-isoprene copolymer (CIIR) and isobutylene rubbers.

By extension of the preceding definition, the term “butyl rubber” will also include copolymers of isobutylene and styrene derivatives such as copolymers of isobutylene and brominated methylstyrene (BIMS) of which the elastomer called EXXPRO is in particular a part. marketed by the company Exxon.

By diene elastomer (or indistinctly rubber), whether natural or synthetic, must be understood in known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of diene monomer units (monomers carrying two double carbon-carbon bonds, conjugated or not).

These diene elastomers can be classified into two categories: essentially unsaturated or essentially saturated. Generally understood by essentially unsaturated, a diene elastomer derived at least in part from conjugated diene monomers, having a rate of units or units of diene origin (conjugated dienes) which is greater than 15% (% by moles); This is how diene elastomers such as certain butyl rubbers or the copolymers of dienes and of alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular as essentially saturated diene elastomers (rate of units d weak or very weak diene origin, always less than 15%).

The expression “diene elastomer capable of being used in the compositions in accordance with the invention” is particularly understood:

(a) - any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms;

-7 (b) - any copolymer of a diene, conjugated or not, having from 4 to 18 carbon atoms and from at least one other monomer.

The other monomer can be ethylene, an olefin or a diene, conjugated or not.

By way of conjugated dienes, conjugated dienes having from 4 to 12 carbon atoms are suitable, in particular 1,3-dienes, such as in particular 1,3-butadiene and isoprene.

As olefins suitable are vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms.

Examples of vinyl aromatic compounds are styrene, ortho-, meta-, para-methylstyrene, the commercial vinyl-toluene mixture, paratertiobuty 1 styrene.

As aliphatic α-monoolefins suitable in particular are acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms.

Preferably, the diene elastomer is chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these. elastomers. The butadiene copolymers are particularly chosen from the group consisting of butadiene-styrene copolymers (SBR).

The diene elastomer can be modified, that is to say either coupled and / or starred, or functionalized, or coupled and / or starred and simultaneously functionalized.

Thus, the diene elastomer can be coupled and / or star-shaped, for example by means of a silicon or tin atom which links the elastomer chains together.

The diene elastomer can be simultaneously or alternately functionalized and comprise at least one functional group. The term "functional group" means a group comprising at least one heteroatom chosen from Si, N, S, O, P. Particularly suitable as functional groups are those comprising at least one function such as: silanol, an alkoxysilane, a primary amine , secondary or tertiary, cyclic or not, a thiol, an epoxide.

In summary, the butyl rubber of the composition in accordance with the invention is preferably chosen from the group of essentially saturated diene elastomers constituted by the copolymers of isobutene and isoprene and their halogenated derivatives, this essentially saturated elastomer being able to be used in cutting with an elastomer chosen from the group of highly unsaturated diene elastomers constituted by

- 8 polybutadienes (abbreviated BR), synthetic polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers, butadiene-styrene copolymers (SBR), isoprene copolymers -butadiene (BIR), isoprene-styrene copolymers (SIR) and isoprene-butadiene-styrene copolymers (SBIR) and mixtures of these elastomers.

Preferably, the butyl rubber content ranges from 60 to 100 phr, preferably from 70 to 100 phr, more preferably from 80 to 100 phr.

According to an alternative embodiment of the invention, the composition also comprises a diene elastomer as mentioned above with a level of 0 to 40 phr of these elastomers, preferably from 0 to 30 phr more preferably from 0 to 20 phr.

According to another preferred variant of the invention, the composition only comprises a butyl rubber or a mixture of butyl rubbers.

Loads and coupling agents

By filler is meant here any type of filler, whether it is reinforcing or whether it is non-reinforcing or inert.

The rubber composition of the invention comprises at least one reinforcing filler. Any type of reinforcing filler can be used, known for its capacity to reinforce a rubber composition which can be used in particular for the manufacture of tires, for example an organic filler such as carbon black, an inorganic filler such as silica or else a mixture of these two types of charges.

As carbon blacks, all carbon blacks are suitable, in particular the blacks conventionally used in tires or their treads. Among the latter, there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (grades ASTM D-1765-2017), such as, for example, the blacks NI 15, N134 , N234, N326, N330, N339, N347, N375, N550, N683, N772, N774). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a support for some of the rubber additives used. The carbon blacks could for example already be incorporated into the diene elastomer, in particular isoprene, in the form of a masterbatch (see for example applications WO97 / 36724-A2 or WO99 / 16600Al).

-9By "reinforcing inorganic filler" should be understood here any inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also called "white" filler, "clear" filler or even "non-filler" black "as opposed to carbon black, capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires. In known manner, certain reinforcing inorganic fillers can be characterized in particular by the presence of hydroxyl groups (DOH) on their surface.

As reinforcing inorganic fillers, in particular mineral fillers of the siliceous type, preferably silica (SiO2) or of the aluminous type, in particular alumina (A12O3), are suitable. The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET specific surface as well as a CTAB specific surface both of which are less than 450 m 2 / g, preferably included in a range ranging from 30 to 400 m2 / g, in particular from 60 to 300 m2 / g.

Any type of precipitated silica can be used, in particular highly dispersible precipitated silicas (called "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas, highly dispersible or not, are well known to those skilled in the art. Mention may be made, for example, of the silicas described in applications W003 / 016215-A1 and W003 / 016387-A1. Among the commercial HDS silicas, it is possible in particular to use the “Ultrasil® 5000GR”, “Ultrasil® 7000GR” silicas from the company Evonik, the “Zeosil® 1085GR”, “Zeosil® 1115 MP”, “Zeosil® 1165MP”, “ Zeosil® Premium 200MP ”,“ Zeosil® HRS 1200 MP ”from the company Solvay. As non-HDS silica, the following commercial silicas can be used: "Ultrasil ® VN2GR", "Ultrasil ® VN3GR" from Evonik, silica, "Hi-Sil EZ120G (-D)", " Hi-Sil EZ160G (-D) "," Hi-Sil EZ200G (D) "," Hi-Sil 243LD "," Hi-Sil 210 "," Hi-Sil HDP 320G "from PPG.

The physical state in which the reinforcing inorganic filler is present is immaterial, whether in the form of powder, microbeads, granules, or even balls or any other suitable densified form. Of course, the term reinforcing inorganic filler is also understood to mean mixtures of different reinforcing inorganic fillers, in particular of silicas as described above.

Those skilled in the art will understand that, as a replacement for the reinforcing inorganic filler described above, a reinforcing filler of another nature could be used, since this reinforcing filler of another nature would be covered with an inorganic layer. such as silica, or else would have on its surface functional sites, in particular hydroxyls, requiring the use of a coupling agent for

- 10 establish the connection between this reinforcing filler and the diene elastomer. By way of example, there may be mentioned carbon blacks partially or entirely covered with silica, or carbon blacks modified with silica, such as, without limitation, fillers of the “Ecoblack®” type from the series CRX2000 ”or from the“ CRX4000 ”series from Cabot Corporation.

In this paper, the BET surface area is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938) , and more precisely according to a method adapted from standard NF ISO 5794-1, appendix E of June 2010 [multi-point volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160 ° C - relative pressure range p / in: 0.05 to 0.2],

For inorganic fillers such as silica for example, the CTAB specific surface values were determined according to standard NF ISO 5794-1, appendix G of June 2010. The process is based on the adsorption of CTAB (bromide of N- hexadecyl-N, N, Ntrimethylammonium) on the "external" surface of the reinforcing filler.

For carbon blacks, the specific surface area STSA is determined according to standard ASTM D6556-2016.

To couple the reinforcing inorganic filler to the diene elastomer, it is possible to use, in a well known manner, an at least bifunctional coupling agent (or bonding agent) intended to ensure a sufficient connection, of chemical and / or physical nature, between the filler inorganic (surface of its particles) and the diene elastomer. In particular organosilanes or polyorganosiloxanes which are at least bifunctional are used. By "bifunctional" is meant a compound having a first functional group capable of interacting with the inorganic charge and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound can comprise a first functional group comprising a silicon atom, the said first functional group being capable of interacting with the hydroxyl groups of an inorganic charge and a second functional group comprising a sulfur atom, the so-called second functional group capable of interacting with the diene elastomer.

Preferably, the organosilanes are chosen from the group consisting of polysulphurized organosilanes (symmetrical or asymmetrical) such as bis tetrasulphide (3-triethoxysilylpropyl), in short TESPT marketed under the name "Si69" by the company Evonik or bis disulphide - (triethoxysilylpropyle), abbreviated as TESPD marketed under the name "Si75" by the company Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as

- 11 "NXT-Silane" marketed by Momentive. More preferably, the organosilane is a polysulfurized organosilane.

Of course, mixtures of the coupling agents described above could also be used.

The content of coupling agent in the composition of the invention is advantageously less than or equal to 20 phr, it being understood that it is generally desirable to use as little as possible. Typically, the level of coupling agent represents from 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler. Its rate is preferably included in a range from 0.5 to 12 phr, more preferably included in a range ranging from 3 to 10 phr. This level is easily adjusted by a person skilled in the art according to the level of reinforcing inorganic filler used in the composition. Any type of reinforcing filler known for its capacity to reinforce a rubber composition which can be used for the manufacture of tires, for example an organic filler such as carbon black, an inorganic reinforcing filler such as silica, or a cutting of these two types of filler, in particular a cutting of carbon black and silica.

As reinforcing filler, carbon black is preferably used in a range from 12 to 45 phr. In fact, beyond this rate, the penalty in terms of rigidity of the composition is too great for an application as an inner tire rubber. Preferably, the carbon black content ranges from 20 to 40 phr, and more preferably from 20 to 35 phr.

It is clear that carbon blacks of very high ASTM grade, such as carbon black N990, are less reinforcing than carbon blacks of grade 700, and a fortiori 600, and that it is necessary for an identical reinforcement of '' use higher levels of carbon black in the case of carbon blacks of grade 900 than in the case of blacks of grade 600 or 700.

Carbon black can advantageously constitute the only reinforcing filler or the majority reinforcing filler, that is to say that it comprises more than 50% (> 50%) by weight of carbon black relative to the total weight of the filler reinforcing. Of course, it is possible to use a single carbon black or a blend of several carbon blacks of different ASTM grades.

Carbon black can also be used in blending with other reinforcing fillers and in particular reinforcing inorganic fillers as described above, and in particular silica. In this case, the total rate of reinforcing filler ranges from 13 to 50 phr, the rate of inorganic filler ranging from 1 to 38 phr.

- 12 The composition according to the invention comprises kaolin, which is an inert filler, that is to say non-reinforcing, with a rate greater than or equal to 10 phr, preferably ranging from 10 to 80 phr, more preferably from 10 to 70 pce and even more preferably from 20 to 70 pce.

The composition according to the invention may comprise an inert filler other than kaolin, such as clay particles, bentonite, talc, chalk with a rate preferably ranging from 0 to 50 phr, preferably from 0 to 40 phr, or even comprise a semi-reinforcing filler such as graphite with a rate ranging from 0 to 4 pc.

Preferably, the composition does not include other inert or semi-reinforcing fillers.

The plasticizer

The composition according to the invention may comprise a plasticizer with a rate ranging from 0 to 8 phr, preferably from 0 to 6 phr, more preferably still from 0 to 3 phr.

Beyond the maximums indicated, the tackiness of compositions in the raw state, on the mixing tools, can in certain cases become prohibitive from an industrial point of view.

In a manner known to those skilled in the art of rubber compositions for tires, this plasticizer is preferably chosen from hydrocarbon resins with a high glass transition temperature (Tg), plasticizing oils and their mixtures.

By definition, a high Tg hydrocarbon resin is by definition a solid at room temperature and pressure (20 ° C, 1 atm), while a plasticizer oil is liquid at room temperature and a low Tg hydrocarbon resin is viscous at room temperature.

Hydrocarbon resins, also called plasticizing hydrocarbon resins, are polymers well known to those skilled in the art, essentially based on carbon and hydrogen but which may contain other types of atoms, for example oxygen, which can be used in particular as plasticizers or tackifiers in polymeric matrices. They are by nature at least partially miscible (i.e., compatible) at the levels used with the polymer compositions for which they are intended, so as to act as true diluents. They have been 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, especially in pneumatic rubber (5.5. Rubber

- 13 Tires and Mechanical Goods). In known manner, these hydrocarbon resins can also be qualified as thermoplastic resins in the sense that they soften by heating and can thus be molded.

The softening point of hydrocarbon resins is measured according to ISO standard 4625 (Ring and Bail method). The Tg is measured according to standard ASTM D3418 (1999). The macrostructure (Mw, Mn and Ip) of the hydrocarbon resin is determined by steric exclusion chromatography (SEC): tetrahydrofuran solvent; temperature 35 ° C; concentration 1 g / 1; flow 1 ml / min; solution filtered on a 0.45 μm porosity filter before injection; Moore calibration with polystyrene standards; set of 3 WATERS columns in series (STYRAGEL HR4E, HR1 and HR0.5); detection by differential refractometer (WATERS 2410) and its associated operating software (WATERS EMPOWER).

The hydrocarbon resins can be aliphatic, or aromatic or else of the aliphatic / aromatic type, that is to say based on aliphatic and / or aromatic monomers. They can be natural or synthetic, based on petroleum or not (if this is the case, also known as petroleum resins).

As aromatic monomers suitable, for example, styrene, alphamethylstyrene, indene, ortho-, meta-, para-methylstyrene, vinyl-toluene, paratertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene , vinylnaphthalene, any vinyl aromatic monomer resulting from a C9 cut (or more generally from a C8 to C10 cut). Preferably, the vinyl aromatic monomer is styrene or a vinyl aromatic monomer derived from a C9 cut (or more generally from a C8 to C10 cut). Preferably, the vinyl aromatic monomer is the minority monomer, expressed in molar fraction, in the copolymer considered.

In known manner, high Tg hydrocarbon resins are thermoplastic hydrocarbon resins, the Tg of which is greater than 20 ° C.

Preferably, the high Tg hydrocarbon plasticizing resin has at least any of the following characteristics:

- a Tg greater than 30 ° C;

a number average molecular mass (Mn) of between 300 and 2000 g / mol, more preferably between 400 and 1500 g / mol;

- a polymolecularity index (Ip) less than 3, more preferably less than 2 (reminder: Ip = Mw / Mn with Mw average molecular weight by weight).

- 14 More preferably, this high Tg hydrocarbon plasticizing resin has all of the above preferred characteristics.

As examples of other preferred resins, mention may also be made of modified phenol alpha-methyl-styrene resins.

The plasticizer can also contain an extension oil (or plasticizing oil) liquid at 20 ° C, called "low Tg", that is to say which by definition has a Tg below 20 ° C, preferably lower at 40 ° C.

Any extension oil, whether of an aromatic or non-aromatic nature known for its plasticizing properties with respect to elastomers, can be used. At room temperature (20 ° C), these oils, more or less viscous, are liquids (that is to say, substances having the capacity to eventually take the form of their container), by difference especially with high Tg hydrocarbon resins which are by nature solid at room temperature.

Particularly suitable are the plasticizing oils chosen from the group consisting of naphthenic oils (low or high viscosity, in particular hydrogenated or not), paraffinic oils, MES oils (Medium Extracted Solvates), TDAE oils (Treated Distillate Aromatic Extracts), RAE oils (Residual Aromatic Extract oils), TRAE oils (Treated Residual Aromatic Extract) and SRAE oils (Safety Residual Aromatic Extract oils), mineral oils, vegetable oils, plasticizers ethers, plasticizers esters, plasticizers phosphates , sulfonate plasticizers and mixtures of these compounds.

More particularly suitable as plasticizing oils, MES oils or TDAE oils.

Crosslinking system

The crosslinking system can be any type of system known to those skilled in the art in the field of rubber compositions. It can in particular be based on sulfur, and / or peroxide and / or bismaleimides.

Preferably, the crosslinking system is based on sulfur, this is called a vulcanization system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or of a sulfur donor. At least one vulcanization accelerator is also preferably present, and, optionally, also preferentially, various known vulcanization activators can be used such as zinc oxide, stearic acid or equivalent compound such as the salts

-15 stearic acid and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or also known vulcanization retarders.

Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr.

Any compound capable of acting as an accelerator for 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 type can be used as accelerator. Examples of such accelerators include the following compounds: 2mercaptobenzothiazyl disulfide (abbreviated to MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS ), N-ter-butyl-2benzothiazyl sulfenamide (TBBS), N-ter-butyl-2-benzothiazyl sulfenimide (TBSI), tetrabenzylthiuram disulfide (TBZTD), zinc dibenzyldithiocarbamate (ZBEC) and mixtures of these compounds. Miscellaneous additives.

Miscellaneous additives:

The rubber compositions in accordance with the invention may also comprise all or part of the usual additives and processing agents known to those skilled in the art and usually used in rubber compositions, such as for example pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants.

In particular, the composition may comprise from 0 to 10 pce of processing agent, preferably from 0 to 5 pce.

Manufacture of rubber compositions:

The rubber compositions of the invention are produced in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first working phase or thermomechanical kneading (sometimes qualified as a non-working phase). productive) on a suitable mixer (for example "Banbury" type mixer) at high temperature, up to a maximum temperature of between 110 ° C and 200 ° C, preferably between 135 ° C and 185 ° C, followed by a second mechanical working phase (sometimes called a productive phase) at a lower temperature, typically below 120 ° C, for example

- 16 between 40 ° C and 100 ° C, finishing phase during which the crosslinking or vulcanization system is incorporated.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for characterization in the laboratory, or else extradited in the form of a semi-finished (or profiled) rubber usable as snowshoe sole.

The crosslinking of the composition can be carried out in a manner known to a person skilled in the art, for example at a temperature between 130 ° C. and 200 ° C., under pressure.

III- EXAMPLES OF IMPLEMENTATION OF THE INVENTION

The examples which follow make it possible to illustrate the invention, the latter cannot however be limited to these examples only.

Preparation of rubber compositions

The tests are carried out as follows: an internal mixer, filled to 70% and whose initial tank temperature is around 60 ° C, is introduced, successively the reinforcing filler, the graphite, the plasticizing system, the rubber butyl as well as various other possible ingredients with the exception of the vulcanization system. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of approximately 3 to 4 minutes, until a maximum "fall" temperature of 150 ° C is reached.

The mixture thus obtained is recovered, it is cooled and then sulfur and a sulfenamide-type accelerator are incorporated on an external mixer (homo-finisher) at 30 ° C., mixing the whole (productive phase) for an appropriate time (for example between 5 and 12 min).

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 internal rubber compounds for tires.

- 17 Example

The purpose of this test is to show the improvement in performance in terms of rubber properties of several compositions according to the invention compared to a conventional control composition and to compositions of the prior art.

All of the compositions were prepared in accordance with the process detailed in the previous paragraph. These compositions are defined as follows:

the control composition T1 is a composition of “conventional” tire inner rubber including a conventional carbon black content and an inert filler,

the control composition T2 comprises a low level of carbon black and of chalk,

the composition C2 in accordance with the present invention is identical to the composition T2 with the exception of the nature of the inert filler which is kaolin,

the control composition T3 comprises a low level of carbon black and of chalk with a rate different from the composition T2,

the composition C3 in accordance with the present invention is identical to the composition T3 with the exception of the nature of the inert filler which is kaolin,

the control composition T4 comprises a low level of carbon black and of chalk with a different level of the compositions T2 and T3,

- Composition C4 according to the present invention is identical to composition T4 with the exception of the nature of the inert filler which is kaolin.

The rates of the various constituents of the compositions expressed in phr, part by weight per hundred parts by weight of elastomer, are presented in Table 1 which follows:

- 18 Table 1

tl T2 T3 T4 C2 C3 C4 Butyl rubber (1) 90 90 90 90 90 90 90 Natural rubber 10 10 10 10 10 10 10 Black (2) 60 30 30 30 30 30 30 Chalk 20 15 30 60 - - - Kaolin (3) - - - - 15 30 60 Agent (4) 3 3 3 3 3 Sulfur 1 1 1 1 1 1 1 MBTS (5) 1 1 1 1 1 1 1 ZnO 1 1 1 1 1 1 1 Stearic acid 1 1 1 1 1 1 1

(1) Browned polyisobutylene sold under the reference BB2222 by the company EXXON Mobile CHEMICAL.

(2) Carbon black N772 REGAL @ SRF marketed by Cabot Ravenne.

(3) PolwhiteTM KL natural kaolin marketed by Imerys, with a specific surface of 13m2 / g (4) AMO40 processing agent marketed by the company

Struktol Company of America (5) 2-Mercaptobenzothiazyl disulfide marketed by General Quimica SAU

The rubber properties of these compositions are measured before baking and after baking at 150 ° C. for 60 minutes, the results obtained are shown in Table 2.

Table 2

tl T2 T3 T4 C2 C3 C4 Permeability 100 129 125 125 117 100 85 Toasting time 100 120 112 103 127 131 136 Breaking energy 100 190 170 130 183 157 123

It is seen from Table 2, that the compositions according to the invention have a comparable or improved seal compared to the conventional control composition Tl (lower permeability value), and a significantly improved seal

- 19 for each composition in accordance with the invention relative to the control composition including a level of chalk identical to the level of kaolin (C2 vs T2, C3 vs T3 and C4 vs T4).

In addition, as expected, the compositions T2 to T4 and C2 to C4 exhibit a much better energy at break than the conventional control composition T1, the compositions C according to the invention having energies of rupture similar to the compositions T having a rate identical with inert charge (i.e. C2 vs T2, C3 vs T3 and C4 vs T4).

However, it is surprisingly found that the compositions in accordance with the invention 10 have a significantly improved roasting time with respect to the conventional control composition T1 as well as with respect to the compositions T having an identical rate of inert filler ( i.e. C2 vs T2, C3 vs T3 and C4 vs T4). In addition, surprisingly we note that the increase in the inert load rate has a negative effect on the toasting time when it is chalk (transition from T2 to T3 then to T4) whereas on the contrary 15 l he effect is positive for kaolin (transition from C2 to C3 then to C4).

Claims (14)

1) Inner rubber for a tire, having a rubber composition based on at least one butyl rubber with a rate ranging from 60 to 100 phr, parts per hundred parts of elastomer, of carbon black with a rate ranging from 12 to 45 pce, kaolin with a rate greater than or equal to 10 pce and a plasticizer with a rate ranging from 0 to 8 pce. 2) Inner rubber according to claim 1, in which the carbon black content ranges from 15 to 45 phr, preferably from 20 to 40 phr and more preferably from 20 to 35 phr. 3) Inner compound according to any one of the preceding claims, in which the level of plasticizer ranges from 0 to 6 phr, preferably from 0 to 3 phr. 4) Inner compound according to any one of the preceding claims, in which the level of kaolin ranges from 10 to 80 phr, preferably from 10 to 70 phr and more preferably from 20 to 70 phr. 5) Inner rubber according to any one of the preceding claims, in which the composition comprises at least one diene elastomer. 6) Inner rubber according to claim 5, in which the diene elastomer is chosen from polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. 7) Inner compound according to any one of claims 5 or 6, in which the butyl rubber content ranges from 70 to 100 phr, preferably from 80 to 100 phr. 8) Inner compound according to any one of the preceding claims, in which the butyl rubber is a copolymer of isobutene and isoprene, preferably a copolymer of isobutene and halogenated isoprene. 9) Inner rubber according to any one of the preceding claims, in which the composition comprises a reinforcing inorganic filler with a level ranging from 1 to 38 phr. 10) Inner rubber according to claim 9, in which the reinforcing inorganic reinforcing filler is silica. 11) Inner compound according to any one of the preceding claims, in which the composition contains one or more other inert fillers with a level of less than 50 phr. 12) Inner rubber according to any one of the preceding claims, in which the plasticizer comprises a plasticizing oil, preferably the plasticizer is a plasticizing oil. 5 13) Inner compound according to any one of the preceding claims, in which the composition comprises an implementing agent with a level ranging from 0 to 10 phr, preferably from 0 to 5 phr. 14) A tire comprising an inner rubber according to any one of claims 10 to 13.