EP2373740A1 - Pneumatic object provided with gas-tight layer comprising two thermoplastic elastomers - Google Patents

Abstract

The present invention relates to a pneumatic object provided with an inflation gas-tight elastomer layer and comprises at least: - 50 pce of a polystyrene and polyisobutylene, particularly of a SIBS, block copolymer for the first thermoplastic styrene elastomer; at least 50 pce of an unsaturated thermoplastic styrene, particularly of a SIS, copolymer for the second thermoplastic styrene elastomer; and optionally an extension oil, particularly polybutene, preferably at a level of 5 to 100 pce. Said elastomer gas-tight seal layer has excellent sealing properties and a hysteresis that is comparatively lower than butyl rubber layers. The pneumatic object of the invention is in particular an inner tube or a tire for a vehicle.

Description

 PNEUMATIC OBJECT COMPRISING A GAS-SEALED LAYER BASED ON TWO THERMOPLASTIC ELASTOMERS

The present invention relates to "pneumatic" objects, i.e., by definition, objects that take their usable form when inflated with air or an equivalent inflation gas.

It relates more particularly to gastight layers sealing these pneumatic objects, in particular that of pneumatic tires.

In a conventional pneumatic tire of the "tubeless" type (that is to say without a tube), the radially inner face has an airtight layer (or more generally any inflation gas) which allows the swelling and maintaining the pressure of the tire. Its sealing properties enable it to guarantee a relatively low rate of pressure loss, making it possible to maintain the swollen bandage in normal operating condition for a sufficient duration, normally of several weeks or several months. It also serves to protect the carcass reinforcement from the diffusion of air from the interior space to the bandage.

This function of internal layer or "inner liner" (waterproof inner liner) is now fulfilled by compositions based on butyl rubber (isobutylene and isoprene copolymer), recognized for a long time for their excellent properties of sealing.

However, a well-known disadvantage of compositions based on rubber or butyl elastomer is that they have significant hysteretic losses, moreover over a wide temperature spectrum, a disadvantage that penalizes the rolling resistance of tires.

Decreasing the hysteresis of these internal sealing layers and ultimately the fuel consumption of motor vehicles, is a general objective facing current technology.

However, the Applicants have discovered during their research that an elastomeric layer other than a butyl layer makes it possible to obtain internal sealing layers that respond to such an objective, while offering the latter excellent sealing properties. . Thus, according to a first object, the present invention relates to a pneumatic object provided with an elastomeric layer impervious to inflation gases, characterized in that said elastomeric layer comprises at least:

as the first styrenic thermoplastic elastomer, at least 50 phr of a polystyrene and polyisobutylene block copolymer; as the second styrenic thermoplastic elastomer, at most 50 phr of an unsaturated thermoplastic styrene elastomer.

Compared to a butyl rubber, the above styrenic elastomers have the major advantage, because of their thermoplastic nature, can be worked as such in the molten state (liquid), and therefore to offer a possibility of putting simplified implementation.

The invention particularly relates to pneumatic objects of rubber such as pneumatic tires, or inner tubes, in particular tubes for pneumatic tires.

The invention relates more particularly to pneumatic tires intended to equip tourism-type motor vehicles, SUVs ("Sport Utility Vehicles"), two wheels (in particular motorcycles), planes, such as industrial vehicles such as vans, heavy goods vehicles ( that is, metros, buses, road transport vehicles such as trucks, tractors, trailers, off-the-road vehicles such as agricultural or civil engineering vehicles) and other transport or handling vehicles.

The invention also relates to the use as an inflation-tight layer, in a pneumatic object, of an elastomeric layer as defined above.

The invention as well as its advantages will be readily understood in the light of the description and the following exemplary embodiments, as well as the single figure relating to these examples, which schematizes, in radial section, a tire according to the invention.

I. DETAILED DESCRIPTION OF THE INVENTION

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight. On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b).

Finally, the expression "phr" means parts by weight per hundred parts of elastomer (or "rubber", the two terms being considered synonymous) total, that is to say of the total of the elastomers present in the elastomer composition. forming the gas-tight layer.

I- 1. Elastomeric layer gas-tight

The pneumatic object of the invention has the essential feature of being provided with a gas-tight layer formed of a thermoplastic elastomer composition, said layer or composition comprising at least:

as the first styrenic thermoplastic elastomer, at least 50 phr of a polystyrene and polyisobutylene block copolymer; as second styrenic thermoplastic elastomer, at most 50 phr of a thermoplastic styrene elastomer of the unsaturated type; optionally other additives such as an extension oil or a lamellar filler.

In other words, the level of first elastomer is within a range from 50 phr to less than 100 phr and the level of second elastomer (different from the first elastomer and still present in the gas-tight layer) is included in a range of more than 0 phr to 50 phr maximum.

The formulation of this elastomeric layer is described in detail below.

I-1-A. Styrenic thermoplastic elastomers

It will be recalled first of all that thermoplastic styrene elastomers (abbreviated hereinafter referred to as "TPS") are thermoplastic elastomers in the form of block copolymers based on styrene.

Of intermediate structure between thermoplastic polymers and elastomers, they consist in a known manner of rigid polystyrene blocks connected by flexible elastomer blocks, for example polybutadiene, polyisoprene or poly (ethylene / butylene). They are often triblock elastomers with two rigid segments connected by a flexible segment. The rigid and flexible segments can be arranged linearly, star-shaped or connected. These TPS elastomers may also be diblock elastomers with a single rigid segment connected to a flexible segment. Typically, each of these segments or blocks contains at least more than 5, usually more than 10 base units (e.g., styrene units and isoprene units for a styrene / isoprene / styrene block copolymer).

With this in mind, the term "polystyrene and polyisobutylene block copolymer" is intended to mean any styrenic thermoplastic copolymer comprising at least one polystyrene block (that is to say one or more polystyrene blocks) and at least one polyisobutylene block. (ie one or more polyisobutylene blocks), to which other saturated or unsaturated blocks (e.g. polyethylene and / or polypropylene) and / or other monomer units (e.g. unsaturated dienes).

This polystyrene and polyisobutylene block copolymer, also called "first TPS copolymer" in the present application, is in particular chosen from the group consisting of styrene / isobutylene diblock copolymers (abbreviated to "SIB"), triblock styrene / isobutylene copolymers / styrene (abbreviated as "SIBS") and mixtures of these copolymers SBIB and SIBS, by definition totally saturated. The invention is also applicable to cases where the polyisobutylene block, in the above copolymers, can be interrupted by one or more unsaturated units, in particular one or more diene units such as isoprenic, optionally halogenated.

It has been found that the presence of this first TPS copolymer, in particular SIB or SIBS, provides the elastomeric layer with excellent sealing properties while significantly reducing the hysteresis compared to conventional butyl rubber layers.

Regarding the second styrenic thermoplastic elastomer (also called "second TPS copolymer"), it will first be recalled that, in a manner well known to those skilled in the art, must be understood by unsaturated TPS elastomer a TPS elastomer which is provided with ethylenic unsaturations, that is to say, includes carbon-carbon double bonds (conjugated or otherwise). By saturated TPS elastomer is meant a TPS elastomer which contains no ethylenic unsaturation (Le., No carbon-carbon double bond.

According to a preferred embodiment, the second TPS copolymer is a copolymer comprising styrene blocks and diene blocks, these diene blocks being in particular isoprene or butadiene blocks. More preferably, this second unsaturated TPS copolymer is chosen from the group consisting of styrene / butadiene (SB), styrene / isoprene (SI), styrene / butadiene / butylene (SBB), styrene / butadiene / isoprene (SBI) block copolymers. ), styrene / butadiene / styrene (SBS), styrene / butadiene / butylene / styrene (SBBS), styrene / isoprene / styrene (SIS), styrene / butadiene / isoprene / styrene (SBIS) and mixtures of these copolymers.

It has been found that the presence of this second unsaturated TPS copolymer in the gas-tight layer makes it possible to greatly improve the adhesion of this latter to another layer of unsaturated polymer, present for example in the pneumatic object of the invention. By way of example, another such unsaturated polymer layer is a diene elastomer composition, in particular based on natural rubber, such as those which are commonly used for the carcass reinforcement of tires, generally and in a manner known in the art. direct contact of the inner sealing layer of such tires.

According to a preferred embodiment of the invention, the weight content of styrene in each (first and second) TPS copolymer is between 5% and 50%. Below the minimum indicated, the thermoplastic nature of the elastomers may decrease significantly while above the maximum recommended, the elasticity of the gas-tight layer may be affected. For these reasons, the styrene content is more preferably between 10 and 40%, in particular between 15 and 35%.

By styrene is meant in the present description any monomer containing styrene, unsubstituted as substituted; examples of substituted styrenes are methylstyrenes (for example α-methylstyrene, β-methylstyrene, γ-methylstyrene, tert-butylstyrene) and chlorostyrenes (for example monochlorostyrene, dichlorostyrene).

It is preferred that the Tg (glass transition temperature, measured according to ASTM D3418) of each (first and second) TPS copolymer is less than -20 ° C, especially less than -40 ° C. A value of Tg higher than these minima can reduce the performance of the waterproof layer during use at very low temperatures; for such use, the Tg of the TPS copolymers is more preferably still lower than -50 ^° C.

The number-average molecular weight (denoted Mn) of the first TPS copolymer is preferably between 30,000 and 500,000 g / mol, more preferentially between 40,000 and 400,000 g / mol. Below the minima indicated, the cohesion between the blocks of elastomer chains, especially because of its possible dilution by an extension oil, may be affected. Moreover, a mass Mn that is too high can be detrimental to the flexibility of the gas-tight layer. Thus, it has been found that a value within a range of 50,000 to 300,000 g / mol is particularly well suited, in particular to a use of the composition in a tire. As for the number average molecular weight of the second TPS copolymer, it can be reduced compared to the first TPS elastomer, given the different function and a generally lower proportion of this second copolymer in the sealed composition; preferably, it is between 3000 and 500 000 g / mol, in particular between 4000 and 400 000 g / mol.

The number-average molecular weight (Mn) of the TPS elastomers is determined in known manner by steric exclusion chromatography (SEC). The sample is first solubilized in tetrahydrofuran at a concentration of about 1 g / l; then the solution is filtered on a 0.45 μm porosity filter before injection. The equipment used is a chromatographic chain "WATERS alliance". The elution solvent is tetrahydrofuran, the flow rate 0.7 ml / min, the system temperature 35 ° C and the analysis time 90 min. A set of four WATERS columns in series, of trade names "STYRAGEL" ("HMW7", "HMW6E" and two "HT6E") is used. The injected volume of the solution of the polymer sample is 100 μl. The detector is a differential refractometer "WATERS 2410" and its associated software for the exploitation of chromatographic data is the "WATERS MILLENIUM" system. The calculated average molar masses relate to a calibration curve made with polystyrene standards.

The polydispersity index Ip (booster: Ip = Mw / Mn with Mw weight average molecular weight) of the TPS copolymers is preferably less than 3; more preferably Ip is less than 2.

According to a preferred embodiment, the level of first TPS copolymer is at least 70 phr, that is to say within a range from 70 phr to less than 100 phr.

According to another preferred embodiment, the level of second TPS copolymer is at most 30 phr, that is to say within a range of more than 0 phr to 30 phr maximum.

The minimum amount of TPS (unsaturated) copolymer can be relatively small while producing the intended technical effect (improved adhesion to another layer of unsaturated polymer). Typically, the amount of second TPS copolymer recommended is at least 1 phr (in particular in a range from 1 to 30 phr), more particularly at least 2 phr (in particular in a range from 2 to 25 phr). ).

Thus, according to another particularly preferred embodiment, the amount of first TPS copolymer can be in a range of 70 to 99 phr, in particular in a range of 75 to 98 phr. The gastight layer described above could comprise other elastomers than the two TPS copolymers described above. Such complementary elastomers, minority in weight compared to the first TPS copolymer, could be, for example, diene elastomers such as natural rubber or synthetic polyisoprene, butyl rubber or even other saturated styrenic thermoplastic elastomers, within the limit of the compatibility of their microstructures.

By way of examples of other saturated styrenic thermoplastic elastomers, mention may be made in particular of styrene / ethylene / butylene (SEB), styrene / ethylene / propylene (SEP), styrene / ethylene / ethylene / propylene (SEEP), styrene block copolymers. ethylene / butylene / styrene (SEBS), styrene / ethylene / propylene / styrene (SEPS), styrene / ethylene / ethylene / propylene / styrene (SEEPS).

However, according to a preferred embodiment, the first and second TPS copolymers described above are the only thermoplastic elastomers, and more generally the only elastomers present in the gas-tight elastomeric layer.

These elastomers can be implemented in a conventional manner for TPE, by extrusion or molding, for example from a raw material available in the form of beads or granules.

Unsaturated TPS elastomers which can be used as the second TPS copolymer, such as, for example, SBS, SIS or SBBS, are well known and commercially available, for example from the Kraton company under the name "Kraton D" (eg, products Dl 161, Dl 118 , Dl 116, Dl 163 for examples of elastomers SIS and SBS), from Dynasol under the name "Calprene" (eg, products C405, C41 1, C412 for examples of SBS elastomers) or from Asahi company under the name "Tuftec" (eg, product P 1500 for an example of SBBS elastomer).

Polystyrene and polyisobutylene block copolymers which can be used as the first TPS copolymer, such as, for example, SIBS or SIB elastomers, are also commercially available, sold for example by the company Kaneka under the name "SIBSTAR" (eg "Sibstar 103T", "Sibstar 102T "," Sibstar 073T "or" Sibstar 072T "for SIBS," Sibstar 042D "for SIBs). For example, they have been described, as well as their synthesis, in patent documents EP 731 112, US Pat. No. 4,946,899 and US Pat. No. 5,260,383. They were first developed for biomedical applications and then described in various applications specific to elastomers. TPE, as varied as medical equipment, parts for automobiles or household appliances, sheaths for electrical wires, sealing pieces or elastics (see for example EP 1 431 343, EP 1 561 783, EP 1 566 405, WO 2005/103146) . However, to the knowledge of the applicants, no document of the prior art describes the use as a gas-tight layer in a pneumatic object such as in particular a tire, an elastomeric composition comprising in combination the two copolymers TPS previously described, and optionally an extender oil, which composition has unexpectedly been found to compete with conventional butyl rubber compositions.

I-1-B. Extension oil

The first and second TPS copolymers previously described are sufficient on their own for the gas-tight function to be performed with respect to the pneumatic objects in which they are used.

However, according to a particular embodiment of the invention, the gas-tight layer may also comprise, as a plasticizer, an extension oil (or plasticizing oil) whose function is to facilitate the implementation, particularly the integration into the pneumatic object by a lowering of the module and an increase in the tackifying power of the gas-tight layer, at the cost, however, of a certain loss of tightness.

This optional extender oil is preferably used at a reduced rate, less than 100 phr - less than 100 parts by weight per hundred parts of total elastomer (ie, first and second TPS copolymers above, plus elastomer (s) additional (if applicable).

Any extension oil, preferably of a slightly polar nature, capable of extending and plasticizing elastomers, especially thermoplastics, may be used. At room temperature (23 ° C), these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the ability to eventually take the shape of their container), as opposed especially to resins that are inherently solid.

Preferably, the extender oil is chosen from the group consisting of polyolefinic oils (that is to say derived from the polymerization of olefins, monoolefins or diolefins), paraffinic oils, naphthenic oils (low or high viscosity), aromatic oils, mineral oils, and mixtures of these oils. More preferably, the extender oil is selected from the group consisting of polybutene oils, paraffinic oils and mixtures of these oils.

Polybutene oils, preferably polyisobutylene oils (abbreviated to "PIB"), which have demonstrated the best compromise of properties compared to the other oils tested, in particular paraffinic oils, are particularly used. By way of example, polyisobutylene oils are sold in particular by the company UNIVAR under the name "Dynapak PoIy" (eg "Dynapak PoIy 190"), by BASF under the names "Glissopal" (eg "Glissopal 1000") or "Oppanol "(eg" Oppanol B 12 "), by INEOS Oligomer under the name" Indopol H 1200 ". Paraffinic oils are sold for example by Exxon under the name "Telura 618" or by Repsol under the name "Extensol 51".

The number-average molecular mass (Mn) of the extender oil is preferably between 200 and 25,000 g / mol, more preferably between 300 and

10,000 g / mol. For masses Mn too low, there is a risk of migration of the oil outside the composition, while too large masses can cause excessive stiffening of this composition. A mass Mn between 350 and

4000 g / mol, in particular between 400 and 3000 g / mol, has proved to be an excellent compromise for the intended applications, in particular for use in a tire.

The number average molecular weight (Mn) of the extender oil is determined by SEC, the sample being solubilized beforehand in tetrahydrofuran at a concentration of about 1 g / l; then the solution is filtered on a 0.45 μm porosity filter before injection. The equipment is the chromatographic chain "WATERS alliance". The elution solvent is tetrahydrofuran, the flow rate is 1 ml / min, the temperature of the system is 35 ° C. and the analysis time is 30 minutes. We use a set of two columns "WATERS" of denomination "STYRAGEL HT6E". The injected volume of the solution of the polymer sample is 100 μl. The detector is a differential refractometer "WATERS 2410" and its associated software for the exploitation of chromatographic data is the "WATERS MILLENIUM" system. The calculated average molar masses relate to a calibration curve made with polystyrene standards.

The person skilled in the art will know, in the light of the description and the following exemplary embodiments, how to adjust the amount of extension oil as a function of the particular conditions of use of the gas-tight elastomeric layer, in particular of the pneumatic object in which it is intended to be used.

If an extension oil is used, it is preferred that its level be greater than 5 phr, in particular between 5 and 100 phr. Below the minimum indicated, the elastomeric layer or composition may have too high rigidity for certain applications while beyond the maximum recommended, there is a risk of insufficient cohesion of the composition and loss of tightness may be harmful depending on the application. For these reasons, particularly for use of the airtight layer in a tire, it is preferred that the extender oil content be greater than 10 phr, especially between 10 and 90 phr, more preferably still it is greater than 20 phr, in particular between 20 and 80 phr.

I- 1 -C. Lamellar charge

The use of lamellar filler at a volume ratio preferably greater than 5%, in particular between 5% and 50%, may advantageously make it possible to further reduce the coefficient of permeability (thus increasing the seal) of the elastomer composition. without increasing excessively its module, which keeps the ease of integration of the seal layer in the pneumatic object.

The so-called lamellar fillers (in English "platy fillers") are well known to those skilled in the art. They have been used in particular in pneumatic tires to reduce the permeability of conventional gastight layers based on butyl rubber. In these butyl-based layers, they are generally used at relatively low levels, usually not exceeding 10 to 15 phr (see, for example, US Patent Specification 2004/0194863, WO 2006/047509).

They are generally in the form of plates, platelets, sheets or stacked leaflets, with a more or less marked anisometry. Their aspect ratio (F = L / E) is generally greater than 3, more often greater than 5 or 10, L being the length (or greater dimension) and E the average thickness of these lamellar fillers, these averages being calculated in number. Form ratios of tens or even hundreds are common. Their average length is preferably greater than 1 .mu.m (that is to say that it is then said micrometric lamellar charges), typically between a few microns (for example 5 microns) and a few hundred microns (by 500 or 800 μm example).

Preferably, the lamellar fillers used in accordance with the invention are chosen from the group consisting of graphites, phyllosilicates and mixtures of such fillers. Among the phyllosilicates, there may be mentioned clays, talcs, micas, kaolins, these phyllosilicates may or may not be modified for example by a surface treatment; examples of such modified phyllosilicates include micas coated with titanium oxide, clays modified with surfactants ("organo clays").

Lamellar fillers with a low surface energy, that is to say relatively apolar, are preferably used, such as those chosen from the group consisting of graphites, talcs, micas and mixtures of such fillers, the latter being able to be modified or no, more preferably still in the group consisting of graphites, talcs and mixtures of such fillers. Among the graphites can be mentioned including natural graphites, expanded graphites or synthetic graphites.

Examples of micas include micas marketed by CMMP (Mica-MU®, Mica-Soft®, Briomica® for example), vermiculites (including Shawatec® vermiculite marketed by CMMP or vermiculite Microlite® marketed by WR Grace), modified or processed micas (for example, the Iriodin® range marketed by Merck). As examples of graphites, mention may be made of graphites marketed by Timcal (Timrex® range). As an example of talcs, mention may be made of talcs marketed by Luzenac.

The lamellar charges described above are preferably used at a high level, greater than 5%, more preferably at least 10% by volume of elastomer composition. Such a volume ratio typically corresponds, given the average density of the lamellar charges used (typically between 2.0 and 3.0) and that of the TPS copolymers used, to a weight ratio preferably greater than 20 phr, more preferably at least equal to 40 pce.

To further increase the tightness of the TPS elastomer layer, it is possible to use an even higher layer loading rate, at least equal to 15% or even 20% by volume, which typically corresponds to weight ratios of at least 50% by weight. maybe 80 pce. Weight ratios higher than 100 phr are even advantageously possible.

The level of lamellar filler is, however, preferably less than 50% by volume (typically less than 500 phr), the upper limit from which it may be exposed to problems of increase of the modulus, embrittlement of the composition, difficulties of dispersion. charge and implementation, not to mention a possible penalty for hysteresis.

The introduction of the lamellar fillers into the elastomeric thermoplastic composition may be carried out according to various known methods, for example by mixing in solution, by mass mixing in an internal mixer, or by extrusion mixing.

I-1-D. Various additives

The airtight layer or composition described above may also include the various additives usually present in the airtight layers known to those skilled in the art. For example, reinforcing fillers such as carbon black or silica, non-reinforcing or inert fillers, plasticizers other than the above-mentioned extension oils, protective agents such as antioxidants or antiozonants, anti-UV agents, coloring agents that can be advantageously used for coloring the composition, various setting agents, implement or other stabilizers, or promoters adapted to promote adhesion to the rest of the structure of the pneumatic object.

In addition to the elastomers previously described, the gas-tight composition could also comprise, still in a minority weight fraction relative to the first TPS copolymer, polymers other than elastomers, such as, for example, thermoplastic polymers compatible with TPS elastomers.

The gas-tight layer or composition previously described is a solid (at 23 ° C.) and elastic compound, which is particularly characterized, thanks to its specific formulation, by a very high flexibility and very high deformability.

According to a preferred embodiment of the invention, this gas-tight layer or composition has a secant modulus in extension, at 10% elongation, which is less than 2 MPa, more preferably less than 1.5 MPa (in particular less than at 1 MPa). This quantity is measured at first elongation (ie without accommodation cycle) at a temperature of 23 ° C, with a pulling speed of 500 mm / min (ASTM D412), and reported in section initial test piece.

1-2. Use of the elastomeric layer in a pneumatic object

The elastomeric layer described above can be used as an airtight layer (or any other inflation gas, for example nitrogen) in any type of pneumatic object. Examples of such pneumatic objects include pneumatic boats, balls or balls used for play or sport.

It is particularly well suited for use as an airtight layer in a pneumatic object, finished or semi-finished product, of rubber, especially in a tire for a motor vehicle such as a two-wheeled vehicle, tourism or industrial.

Such an airtight layer is preferentially disposed on the inner wall of the pneumatic object, but it can also be completely integrated into its internal structure.

The thickness of the airtight layer is preferably greater than 0.05 mm, more preferably between 0.1 mm and 10 mm (especially between 0.1 and 1.0 mm). It will be readily understood that, depending on the specific fields of application, the dimensions and the pressures involved, the mode of implementation of the invention may vary, the airtight layer then having several preferential thickness ranges.

For example, for tires of the tourism type, it may have a thickness of at least 0.3 mm, preferably between 0.5 and 2 mm. In another example, for pneumatic tires of heavy goods vehicles or agricultural vehicles, the preferred thickness may be between 1 and 3 mm. According to another example, for tires of vehicles in the field of civil engineering or for aircraft, the preferred thickness may be between 2 and 10 mm.

Compared to a conventional butyl rubber airtight layer, the airtight composition described above has the advantage of having a significantly lower hysteresis, and thus of providing reduced rolling resistance to pneumatic tires, as demonstrated in the following embodiments.

II. EXAMPLES OF CARRYING OUT THE INVENTION

The gas-tight elastomeric layer previously described is advantageously usable in pneumatic tires of all types of vehicles, in particular passenger vehicles or industrial vehicles such as heavy goods vehicles.

By way of example, the single appended figure shows very schematically (without respecting a specific scale), a radial section of a tire according to the invention for a passenger vehicle.

This tire 1 has a crown 2 reinforced by a crown reinforcement or belt 6, two sidewalls 3 and two beads 4, each of these beads 4 being reinforced with a rod 5. The crown 2 is surmounted by a tread represented in this schematic figure. A carcass reinforcement 7 is wound around the two rods 5 in each bead 4, the upturn 8 of this armature 7 being for example disposed towards the outside of the tire 1 which is shown here mounted on its rim 9. The carcass reinforcement 7 is in known manner constituted of at least one sheet reinforced by so-called "radial" cables, for example textile or metal, that is to say that these cables are arranged substantially parallel to each other and s' extend from one bead to the other so as to form an angle of between 80 ° and 90 ° with the median circumferential plane (plane perpendicular to the axis of rotation of the tire which is located halfway between the two beads 4 and goes through the middle of the crown frame 6). The inner wall of the tire 1 comprises an airtight layer 10, for example of thickness equal to about 1 mm, on the side of the internal cavity 11 of the tire 1.

This inner layer (or "inner liner") covers the entire inner wall of the tire, extending from one side to the other, at least to the level of the rim hook when the tire is in the mounted position. It defines the radially inner face of said tire intended to protect the carcass reinforcement from the diffusion of air coming from the space 1 1 inside the bandage. It allows inflation and pressure maintenance of the tire; its sealing properties must enable it to guarantee a relatively low rate of pressure loss, to maintain the swollen bandage, in normal operating condition, for a sufficient duration, normally of several weeks or several months.

In contrast to a conventional tire using a butyl rubber composition, the tire according to the invention uses as airtight layer, in this example, a thermoplastic elastomer composition comprising:

as the first TPS copolymer, 82 phr of an SIBS elastomer ("Sibstar 102T" with a styrene content of about 15%, a Tg of about -65 ° C and an average molecular weight Mn of about 90,000 g / mol);

- As the second TPS copolymer, 18 phr of an SBBS elastomer ("Tuftec P 1500" with a styrene content of about 37%, a Tg of about -75 ° C. and a mass Mn of about 60,000 g / mol); as extension oil, approximately 55 phr of PIB oil ("Dynapak PoIy 190" - Mn of the order of 1000 g / mol);

approximately 40 phr of a lamellar filler (mica "Iriodin 153"), which corresponds to a volume ratio of approximately 7.5% (% by volume of composition).

Layer 10 was prepared as follows. The mixture of the four constituents (SIBS, SBBS, PIB oil and lamellar filler) was conventionally produced using a twin-screw extruder (L / D equal to about 40) at a temperature typically greater than the melting temperature of the composition (about 190 ° C). The extruder used included a feed (hopper) for each TPS copolymer (SIBS and SBBS), another feed (hopper) for the lamellar feed and finally a pressurized liquid injection pump for the polyisobutylene extension oil; it was provided with a die for extruding the product to the desired dimensions.

The tire provided with its airtight layer (10) as described above can be made before or after vulcanization (or cooking). In the first case (ie, before cooking the tire), the airtight layer is simply applied in a conventional manner to the desired location, for formation of the sealing layer 10. The vulcanization is then carried out conventionally. An advantageous manufacturing variant, for those skilled in the tire industry, will for example consist in a first step of laying the airtight layer directly on a manufacturing drum in the form of a flat tire. a layer of suitable thickness, before covering the latter with the rest of the structure of the tire, according to manufacturing techniques well known to those skilled in the art.

In the second case (ie, after firing of the tire), the sealing layer is applied inside the baked tire by any appropriate means, for example by gluing, extrusion, spraying or else by extrusion / blowing. a film of appropriate thickness.

In the following examples, the sealing properties were first analyzed on test specimens of butyl rubber compositions on the one hand, and SIBS and SBBS on the other hand (with and without PIB extension oil). for the second composition based on only two TPS copolymers).

For this analysis, a rigid wall permeameter was used, placed in an oven (temperature of 60 ° C in this case), provided with a pressure sensor (calibrated in the range of 0 to 6 bars) and connected to a tube equipped with an inflation valve. The permeameter can receive standard specimens in the form of a disc (for example 65 mm diameter in this case) and with a uniform thickness of up to 3 mm (0.5 mm in the present case). The pressure sensor is connected to a National Instruments data acquisition card (four-channel analog 0-10V acquisition) which is connected to a computer performing a continuous acquisition with a frequency of 0.5 Hz (1 point every two seconds). The coefficient of permeability (K) is measured from the linear regression line (average over 1000 points) giving the slope α of the pressure loss, through the tested test piece, as a function of time, after stabilization of the system, that is to say obtaining a steady state during which the pressure decreases linearly with time.

At iso-thickness (1 mm), it was noted firstly that the composition comprising only the two TPS copolymers (SIBS and SBBS), that is to say without extension oil or other additive, had a coefficient very low permeability, substantially equal to that of the usual composition based on butyl rubber. This is already a remarkable result for such a composition. As already indicated, if one accepts in return a certain loss of sealing, the addition of an extension oil advantageously facilitates the integration of the elastomeric layer in the pneumatic object, by a lowering of the module and an increase in the tackifying power of the latter.

Thus, using for example 55 phr of extension oil, it was found that the coefficient of permeability was increased (thus the reduced sealing) by about 3 times in the presence of a conventional oil such as paraffinic, whereas this coefficient was only increased by a factor significantly less than two (1.5 times) in the presence of a PIB oil ("Dynapak PoIy 190"), a factor of increase that is ultimately not very penalizing for use in a pneumatic tire. . It is in this respect that the combination of the first and second TPS elastomers and polybutene oil such as PIB has been found to offer the best compromise of properties for the gas-tight layer. On the other hand, by adding, as indicated previously, an appropriate level of lamellar filler (40 phr in this example), it was advantageously possible to compensate for the loss of tightness due to the addition of an extension oil.

On the other hand, adhesion tests (peel tests) were conducted to test the ability of the gas-tight layer to adhere after firing to a diene elastomer layer, more specifically to a conventional rubber composition for tire carcass reinforcement, based on natural rubber (peptized) and N330 carbon black (65 parts per hundred parts of natural rubber), further comprising the usual additives (sulfur, accelerator, ZnO, stearic acid, antioxidant, cobalt naphthenate). It has been found that the addition of the second unsaturated TPS copolymer (for example SBBS) in the gas-tight layer makes it possible to significantly improve, by a factor greater than two, or more in many cases, the adhesion forces between the gas-tight thermoplastic layer and the natural rubber layer.

Following the laboratory tests above, pneumatic tires according to the invention, of the type for passenger vehicle (size 195/65 Rl 5), were manufactured; their inner wall was covered by an airtight layer (10) with a thickness of 1 mm (on the building drum, before making the rest of the tire), and the tires were then vulcanized. Said airtight layer (10) was formed of SIBS (82 phr), SBBS (18 phr), lamellar filler (40 phr of "Iriodin 153"), the whole extended with 55 phr of PIB oil, such as described above.

These pneumatic tires according to the invention were compared to control tires (Michelin "Energy 3" brand) comprising a conventional air-tight layer of the same thickness, based on butyl rubber. The rolling resistance of pneumatic tires was measured on a steering wheel according to ISO 87-67 (1992). It has been found that the pneumatic tires of the invention have a very significant and unexpectedly reduced rolling resistance for those skilled in the art, of nearly 4% compared with the control tires.

In conclusion, the invention offers tire designers the opportunity to significantly reduce the hysteresis of the internal sealing layers, and therefore the fuel consumption of motor vehicles equipped with such tires, without penalty or in any other way. case without prohibitive penalty in the case of the use of an extension oil, sealing properties.

Claims

A pneumatic object provided with an elastomeric layer impervious to inflation gases, characterized in that said elastomeric layer comprises at least: as the first styrenic thermoplastic elastomer, at least 50 phr of a polystyrene and polyisobutylene block copolymer; as the second thermoplastic styrene elastomer, at most 50 phr of an unsaturated thermoplastic styrene copolymer. The pneumatic object according to claim 1, wherein the first elastomer is selected from the group consisting of styrene / isobutylene copolymers, styrene / isobutylene / styrene copolymers and mixtures of these copolymers. The pneumatic object of claim 2, wherein the first elastomer is a styrene / isobutylene / styrene copolymer. 4. Pneumatic object according to any one of claims 1 to 3, wherein the level of first styrenic thermoplastic elastomer is at least 70 phr. 5. Pneumatic object according to any one of claims 1 to 4, wherein the level of second styrenic thermoplastic elastomer is at most 30 phr. 6. Pneumatic object according to claim 5, wherein the level of second styrenic thermoplastic elastomer is in a range of 1 to 30 phr. 7. pneumatic object according to claim 6, wherein the level of second styrenic thermoplastic elastomer is in a range of 2 to 25 phr. 8. Pneumatic object according to any one of claims 1 to 7, wherein the second styrenic thermoplastic elastomer is a copolymer comprising styrene blocks and diene blocks. Pneumatic object according to claim 8, wherein the diene blocks are isoprene or butadiene blocks. The pneumatic object of claim 9, wherein the second styrenic elastomer is selected from the group consisting of styrene / butadiene block copolymers. ("SB"), styrene / isoprene ("SI"), styrene / butadiene / butylene ("SBB"), styrene / butadiene / isoprene ("SBI"), styrene / butadiene / styrene ("SBS"), styrene / butadiene / butylene / styrene ("SBBS"), styrene / isoprene / styrene ("SIS"), styrene / butadiene / isoprene / styrene ("SBIS") and mixtures of these copolymers. 11. Pneumatic object according to any one of claims 1 to 10, wherein each styrenic thermoplastic elastomer comprises between 5 and 50% by weight of styrene. Pneumatic object according to any one of claims 1 to 11, wherein the glass transition temperature of each styrenic thermoplastic elastomer is less than -20 ° C. The pneumatic object according to any one of claims 1 to 12, wherein the number average molecular weight of the first styrenic thermoplastic elastomer is between 30,000 and 500,000 g / mol. The pneumatic object according to any one of claims 1 to 13, wherein the number average molecular weight of the second styrenic thermoplastic elastomer is between 3,000 and 500,000 g / mol. The pneumatic object according to any one of claims 1 to 14, wherein the sealing layer comprises an extension oil. The pneumatic object of claim 15, wherein the extender oil is selected from the group consisting of polyolefin oils, paraffinic oils, naphthenic oils, aromatic oils, mineral oils, and blends thereof. . The pneumatic object of claim 16, wherein the extender oil is selected from the group consisting of polybutene oils. The pneumatic object of claim 17, wherein the extension oil is a polyisobutylene oil. Pneumatic object according to any one of claims 15 to 18, wherein the number average molecular weight of the extender oil is between 200 and 25,000 g / mol. 20. Pneumatic object according to any one of claims 15 to 19, wherein the rate of extension oil is greater than 5 phr. 21. A pneumatic object according to claim 20, wherein the rate of extension oil is between 5 and 100 phr. 22. Pneumatic object according to any one of claims 1 to 21, wherein the sealed elastomeric layer comprises a lamellar filler. 23. A pneumatic object according to any one of claims 1 to 22, wherein the elastomeric layer has a thickness greater than 0.05 mm. Pneumatic object according to claim 23, wherein the elastomeric layer has a thickness of between 0.1 and 10 mm. 25. Pneumatic object according to any one of claims 1 to 24, wherein the elastomeric layer is disposed on the inner wall of the pneumatic object. 26. Pneumatic object according to any one of claims 1 to 25, characterized in that said pneumatic object is a tire. 27. Pneumatic object according to any one of claims 1 to 25, characterized in that said pneumatic object is an air chamber.