EP2373739A1 - Pneumatic object provided with a gas-tight layer comprising a thermoplastic elastomer and expanded thermoplastic microspheres - Google Patents

Abstract

The invention relates to a pneumatic object provided with an elastomer layer sealed against an inflation gas such as air, said layer comprising at least, as the predominant elastomer, a thermoplastic polystyrene and polyisobutylene block copolymer, such as a SIBS (styrene/isobutylene/styrene) copolymer, and expanded thermoplastic microspheres at a level preferably from 1 to 30 pce. Said copolymer contains preferably from 5 to 50 wt % of styrene, the number-average molecular weight thereof is from 30000 to 500000 g/mol, and the Tg thereof is less than -20°C. Optionally, the sealed elastomer layer also comprises, as a plasticizer, an extension oil, particularly a polybutene oil, at a level preferably between 5 and 100 pce. Said sealed layer has not only excellent sealing properties but also a density and a hysteresis that are both comparatively lower than butyl rubber layers. The invention particularly relates to a tire for an automobile.

Description

 PNEUMATIC OBJECT COMPRISING A GAS TIGHT LAYER

BASED ON A THERMOPLASTIC ELASTOMER AND MICROSPHERES

EXPANDED THERMOPLASTICS

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 butyl rubber-based compositions is that they have significant hysteretic losses, moreover over a wide temperature spectrum, a disadvantage which penalizes the rolling resistance of pneumatic 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 elastomer layer impervious to inflation gases, characterized in that said elastomer layer comprises at least, as majority elastomer, a thermoplastic block copolymer polystyrene and polyisobutylene and expanded thermoplastic microspheres.

Compared to a butyl rubber, the thermoplastic copolymer above has the major advantage, because of its thermoplastic nature, to be worked as such in the molten state (liquid) and thus to offer improved processability; such a copolymer makes it possible in particular to prepare very thin layers of tight layer, easily integrate relatively difficult or relatively fragile fillers such as thermoplastic microspheres, significantly reducing the risk of degradation of such charges.

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, for sealing the inflating gases of a pneumatic object, of a thermoplastic copolymer elastomer with polystyrene and polyisobutylene blocks and thermally expandable thermoplastic microspheres.

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).

I- 1. Elastomeric layer gas-tight

The pneumatic object of the invention has the essential feature of being provided with a gastight layer formed of an elastomer composition (or "rubber", both of which are considered in a known manner as synonyms) of the thermoplastic type, said layer or composition comprising at least, as majority elastomer, a thermoplastic copolymer elastomer with polystyrene and polyisobutylene blocks, expanded thermoplastic microspheres and optionally an extension oil and any other additives. All of these components are described in detail below.

I-1-A. Styrenic thermoplastic elastomer

It will be recalled first of all that thermoplastic styrene elastomers (abbreviated 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 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 block copolymer polystyrene and polyisobutylene, also called "copolymer

TPS "in the present application, is in particular chosen from the group consisting of styrene / isobutylene diblock copolymers (abbreviated as" SIB "), styrene triblock copolymers / isobutylene / styrene (abbreviated "SIBS") and mixtures of these copolymers SIB and SIBS, by definition fully 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 the TPS copolymer, particularly SIB or SIBS, provides the gastight layer with excellent sealing properties while significantly reducing hysteresis compared to conventional butyl rubber layers.

According to a preferred embodiment of the invention, the weight content of styrene in the TPS copolymer is between 5% and 50%. Below the minimum indicated, the thermoplastic nature of the elastomer may decrease significantly while above the maximum recommended, the elasticity of the seal 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, any styrene-based monomer, whether unsubstituted as substituted, should be understood in the present description; among the substituted styrenes may be mentioned, for example, methylstyrenes (for example α-methylstyrene, β-methylstyrene, p-methylstyrene, tert-butylstyrene) and chlorostyrenes (for example monochlorostyrene, dichlorostyrene).

It is preferred that the glass transition temperature (Tg, measured according to ASTM D3418) of the TPS copolymer is less than -20 ^° C., more preferably 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 copolymer is more preferably still lower than -50 ° C.

The number-average molecular weight (denoted Mn) of the TPS copolymer is preferably between 30,000 and 500,000 g / mol, more preferably between 40,000 and 400,000 g / mol. Below the minimum indicated, the cohesion between the chains of the elastomer may be affected, particularly because of a possible dilution of the latter by an extension oil. Moreover, a mass that is too high can be detrimental to the flexibility of the gas-tight layer. Thus, it has been found that a Mn value within a range of 50,000 to 300,000 g / mol is particularly well suited, especially to a use of the composition in a tire.

The number-average molecular weight (Mn) of the TPS copolymer 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 copolymer is preferably less than 3; more preferably Ip is less than 2.

The TPS copolymer and the expanded thermoplastic microspheres may alone constitute the gas-tight elastomeric layer or may be associated in the elastomeric composition with other elastomers in a minor amount relative to the TPS copolymer.

If any other elastomers are used in the composition, the TPS copolymer constitutes the majority elastomer by weight. Its level is then preferably greater than 70 phr, in particular within a range of 80 to 100 phr (as a reminder, "phr" means parts by weight per hundred parts of total elastomer, that is to say of the total of elastomers present in the composition forming the gas-tight layer). Such complementary elastomers, minority by weight, could be, for example, diene elastomers such as natural rubber or synthetic polyisoprene, butyl rubber or thermoplastic elastomers other than styrenic, within the limit of the compatibility of their microstructures.

Such complementary elastomers, which are minor in weight, could also be other styrenic thermoplastic elastomers, whether of the unsaturated type as saturated (that is to say in known manner, provided or not with ethylenic unsaturations or double bonds carbon-carbon).

As examples of unsaturated TPS elastomers, there may be mentioned, for example, those comprising styrene blocks and diene blocks, in particular those chosen from the group consisting of styrene / butadiene block copolymers (SB) and styrene / isoprene block copolymers (IS). ), 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. As examples of saturated TPS elastomers, mention may be made, for example, of those selected from the group consisting of styrene / ethylene / butylene (SEB), styrene / ethylene / propylene (SEP), styrene / ethylene / ethylene / block copolymers. propylene (SEEP), styrene / ethylene / butylene / styrene (SEBS), styrene / ethylene / propylene / styrene (SEPS), styrene / ethylene / ethylene / propylene / styrene (SEEPS) and mixtures of these copolymers.

However, according to a particularly preferred embodiment, the gas-tight layer is devoid of such complementary elastomers; in other words, the TPS copolymer, in particular SIB or SIBS, previously described is the only thermoplastic elastomer and more generally the only elastomer present in the elastomeric composition of the gas-tight layer.

The polystyrene and polyisobutylene block copolymers are commercially available, they can be implemented conventionally for TPS elastomers, by extrusion or molding, for example from a raw material available in the form of beads or granules. They are sold for example with regard to the SIB or SIBS by the company

KANEKA under the name "SIBSTAR" (e.g. "Sibstar 103T", "Sibstar 102T", "Sibstar

073T "or" Sibstar 072T "for SIBS," Sibstar 042D "for SIBs), for example, have been described, as well as their synthesis, in patent documents EP 731 1 12, US 4 946 899, US 5

260 383. They were first developed for biomedical applications then described in various applications specific to TPE elastomers, as varied as medical equipment, parts for automobiles or household appliances, sleeves for electrical wires, sealing parts 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 state of the art describes the use in a pneumatic object such as in particular a tire, an elastomeric composition comprising in combination a polystyrene and polyisobutylene block copolymer and expanded thermoplastic microspheres, a composition which has been found, quite unexpectedly, able to compete with conventional butyl rubber compositions as a sealing layer in pneumatic objects.

I-1-B. Expanded thermoplastic microspheres

The thermoplastic microspheres used here are well known, they are spherical, resilient particles composed of a thermoplastic polymer capsule containing a liquid and / or a gas depending on their state of expansion. They can be used in an unexpanded form (for example as a "blowing agent") or in an expanded form. In unexpanded form, their average diameter is generally in a range of 5 to 50 microns. The shells of these capsules are for example based on copolymers of acrylonitrile monomers, methyl methacrylate, vinylidene chloride; the liquid acting as swelling agent is typically an alkane (eg isobutane or isopentane).

Under the effect of heat, typically at temperatures of 80 to 190 ° C depending on the selected microspheres, the pressure inside the sphere increases, causing the irreversible expansion of the capsule, by plastic deformation. The final volume can thus reach several tens of times the initial volume. These expanded microspheres can be used in various applications, they are used in particular very low density lightening fillers in paints, sealants, adhesives, coatings, etc. They can also improve certain properties of use of the matrices comprising them; in particular, they have recently been described in compositions based on butyl rubber for pneumatic tires, with a view to improving the tightness of these compositions (see in particular application EP 1 967 543).

For more details on these thermoplastic microspheres, we can refer to the many technical documents available from their suppliers (see for example Expancel Technical Bulletin No. 40 entitled "Expancel® Microspheres -A Technical Presentation", published by Akzo Nobel the 24/07/2006).

As commercial examples of expandable thermoplastic microspheres that can be used in the present invention, mention may be made for example of the products offered by Expancel under the names "Expancel 091DU-80", "Expancel 091DU-140", "Expancel 092DU-120" .

Preferably, the level of thermoplastic microspheres foamed in the gas-tight layer is between 0.1 and 30 phr, preferably between 0.5 and 10 phr, particularly in a range of 1 to 8 phr. Below the minima indicated, the desired technical effect may be insufficient while beyond the recommended maxima, there is a risk of embrittlement and loss of endurance of the layer, not to mention its increase in cost.

In the thermoplastic elastomer composition forming the gastight layer, the thermoplastic microspheres are preferentially introduced in the initial state in unexpanded form. They are then foamed, in whole or in part, during the various mixing operations (with the TPS copolymer), of extrusion (of the elastomer composition forming the gas-tight layer) and / or of final cooking or vulcanization (by example of the tire), at the moment in fact when they reach a temperature sufficient for the expansion phase to be triggered.

I- 1 -C. Extension oil

The TPS copolymer, in particular SIB or SIBS, and the expanded thermoplastic microspheres 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.

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 capacity to eventually take on the shape of their container), as opposed to 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 H1200 ". 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 of 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 molecular weight M n of the extension oil is determined by SEC, the sample being solubilized beforehand in tetrahydrofuran at a concentration of approximately 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 extender oil is used, it is preferred that its level be greater than 5 phr, more preferably 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 all 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 than greater than 20 phr, in particular between 20 and 80 phr.

I-1-D. Various additives

The airtight layer or composition described above may furthermore comprise the various additives usually present in the airtight layers known to the man in the air. job. For example, reinforcing fillers such as carbon black or silica, non-reinforcing or inert fillers, lamellar fillers that further improve the seal (eg phyllosilicates such as kaolin, talc, mica, graphite, clays or modified clays) may be mentioned. ("organo clays ^" ), 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 agents for implementing or other stabilizers, or promoters capable of promoting adhesion to the rest of the structure of the pneumatic object.

The use of lamellar fillers in the gas-tight layer advantageously makes it possible to further reduce the coefficient of permeability (and therefore of increasing the seal) of the thermoplastic elastomer composition, without excessively increasing its modulus, which makes it possible to preserve the ease of integration of the sealing layer in the pneumatic object. Such fillers are generally in the form of plates, platelets, sheets or stacked sheets, with a more or less marked anisometry, whose average length is for example between a few microns and a few hundred microns. They can be used at variable weight rates according to the applications, for example greater than 20 phr, especially greater than 50 phr.

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

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

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

It 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.

In addition, thanks to the presence of its expanded thermoplastic microspheres, its density is significantly reduced compared to butyl rubber-based sealing layers. Preferably, the density of the sealed layer is less than 1 g / cm ³ , more preferably less than 0.9 g / cm ³ ; it can be in many cases less than 0.8 g / cm ³ .

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 1.1 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 10, in this example, a thermoplastic elastomer composition comprising the following components:

a single 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); 2.5 parts of expanded thermoplastic microspheres (Expancel ^® 09 Idul 40) per 100 parts by weight of elastomer SIBS (2.5 phr);

65 parts of PIB oil ("Dynapak PoIy 190" - mass Mn of the order of 1000 g / mol) per 100 parts by weight of SIBS elastomer (ie 65 phr).

Layer 10 was prepared as follows. The mixture of the three constituents (SIBS, thermoplastic microspheres and PIB) was made conventionally, using a twin-screw extruder (LfD equal to about 40), at a temperature typically above the melting temperature of the composition (about 190 ° C). The extruder used had a feed (hopper) for the SIBS, another feed (hopper) for the thermoplastic microspheres (powdered, in unexpanded form) and 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 (i.e., prior to firing the tire), the airtight layer is simply conventionally applied to the desired location, for formation of the layer 10. Vulcanization is then performed 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 baking the tire), the sealing layer is applied inside the baked tire by any appropriate means, for example by gluing, extrusion, spraying or else extrusion / blowing of a tire. film of appropriate thickness.

In the following examples, the sealing properties were first analyzed on test specimens of butyl rubber-based compositions, on the one hand, and thermoplastic expanded SIBS and microspheres on the other hand (with and without oil). extension PIB, for the second composition based on SIBS and microspheres).

For this analysis, a rigid wall permeameter was used, placed in an oven (temperature of 60 ^° C. in the present case), provided with a pressure sensor (calibrated in the range of 0 to 6 bar) 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.

Firstly, it was noted that the composition comprising only the SIBS copolymer and the expanded thermoplastic microspheres, that is to say without extension oil or other additive, had a very low permeability coefficient, substantially equal to that of the usual composition based on butyl rubber, for the same thickness. 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 tackifiant power of the latter.

Thus, using 65 phr of extension oil, it was found that the coefficient of permeability was increased (and thus reduced) by about 2.3 times in the presence of a conventional oil such as paraffinic, then that this coefficient was only increased by 1.5 times in the presence of a PIB oil ("Dynapak PoIy 190"), increase finally not penalizing for use in a tire. It is in this that the combination of the TPS copolymer (in particular SIB or SIBS), expanded thermoplastic microspheres and polybutene oil (especially PIB) has been found to offer the best compromise of properties for the gas-tight 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 1.1 mm

(On the manufacture drum, before manufacturing the rest of the tire), then the tires were vulcanized. Said airtight layer (10) was formed of SIBS

(100 phr), expanded thermoplastic microspheres (2.5 phr), and 65 phr of PIB oil, 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 gas-tight layer of the pneumatic object of the invention not only has excellent sealing properties, but also a density and a hysteresis which are both reduced compared to butyl rubber-based layers. .

The invention thus offers tire designers the opportunity to reduce the fuel consumption of motor vehicles equipped with such tires, while reducing the density of the sealing layers.

Claims

1. A pneumatic object provided with an elastomeric layer impervious to inflation gases, characterized in that said elastomeric layer comprises at least, as a majority elastomer, a thermoplastic copolymer with polystyrene and polyisobutylene blocks and expanded thermoplastic microspheres. The pneumatic object according to claim 1, wherein the thermoplastic copolymer is selected from the group consisting of styrene / isobutylene copolymers, styrene / isobutylene / styrene copolymers and mixtures of these copolymers. 3. Pneumatic object according to claim 1 or 2, wherein the thermoplastic copolymer comprises between 5 and 50% by weight of styrene. 4. Pneumatic object according to any one of claims 1 to 3, wherein the glass transition temperature of the thermoplastic copolymer is less than - 20 ° C. The pneumatic object according to any one of claims 1 to 4, wherein the number average molecular weight of the thermoplastic copolymer is between 30,000 and 500,000 g / mol. The pneumatic object of any one of claims 1 to 5, wherein the seal layer comprises an extender oil of the thermoplastic copolymer. The pneumatic object of claim 6, 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 7, wherein the extension oil is selected from the group consisting of polybutenes. The pneumatic object of claim 8, wherein the extender oil is a polyisobutylene oil. The pneumatic object according to any one of claims 6 to 9, wherein the number average molecular weight of the extender oil is between 200 and 25,000 g / mol. 11. Pneumatic object according to claim 10, wherein the rate of extension oil is greater than 5 phr. 12. Pneumatic object according to claim 11, wherein the rate of extension oil is between 5 and 100 phr. 13. Pneumatic object according to any one of claims 1 to 12, wherein the sealed layer comprises a lamellar filler. 14. Pneumatic object according to any one of claims 1 to 13, wherein the level of expanded thermoplastic microspheres is between 0.1 and 30 phr. 15. Pneumatic object according to claim 14, wherein the level of expanded thermoplastic microspheres is between 0.5 and 10 phr. Pneumatic object according to any one of claims 1 to 15, wherein the density of the sealed elastomeric layer is less than 1.0 g / cm ³ . Pneumatic object according to any one of claims 1 to 16, wherein the density of the gas-tight layer is less than 0.9 g / cm ³ . The pneumatic object according to any one of claims 1 to 17, wherein the gas-tight layer has a thickness greater than 0.05 mm. Pneumatic object according to claim 18, wherein the waterproof layer has a thickness of between 0.1 mm and 10 mm. 20. Pneumatic object according to any one of claims 1 to 19, wherein the gas-tight layer is disposed on the inner wall of the pneumatic object. 21. pneumatic object according to any one of claims 1 to 20, characterized in that said object is rubber. 22. Pneumatic object according to claim 21, characterized in that said rubber object is a tire. 23. Pneumatic object according to claim 21, characterized in that said pneumatic object is an air chamber. 24. Use, for sealing the inflating gases of a pneumatic object, a thermoplastic copolymer elastomer polystyrene and polyisobutylene blocks and thermally expandable thermoplastic microspheres.