WO2015197298A1

WO2015197298A1 - Tyre comprising a buffer zone between the carcass framework and the crown framework

Info

Publication number: WO2015197298A1
Application number: PCT/EP2015/061726
Authority: WO
Inventors: Hichem Rehab; Nathalie Salgues; Jacques Besson
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2014-06-26
Filing date: 2015-05-27
Publication date: 2015-12-30
Also published as: FR3022850B1; FR3022850A1

Abstract

A tyre with radial carcass framework, consisting of at least one layer of metallic reinforcement elements, comprising a crown framework that is radially hooded by a tread layer joined to two beads via two sidewalls, said tyre comprising a first layer G of polymer mixture radially between the carcass framework and the crown framework and a second layer S of polymer mixture axially in contact with the first layer G. Said first layer G consists of a buffer zone provided to trap oxygen outside of said first layer, the axial width of said first layer being at least equal to 70% of the width of the radially smallest crown framework layer, and said second layer S consists of a filled elastomer mixture having a macro dispersion score Z greater than or equal to 65 and a maximum value of tan(δ), denoted tan(δ)max, less than 0.100. A tyre with radial carcass framework, consisting of at least one layer of metallic reinforcement elements, comprising a crown framework that is radially hooded by a tread layer joined to two beads via two sidewalls, said tyre comprising a first layer G of polymer mixture radially between the carcass framework and the crown framework and a second layer S of polymer mixture axially in contact with the first layer G. Said first layer G consists of a buffer zone provided to trap oxygen outside of said first layer, the axial width of said first layer being at least equal to 70% of the width of the radially smallest crown framework layer, and said second layer S consists of a filled elastomer mixture having a macro dispersion score Z greater than or equal to 65 and a maximum value of tan(δ), denoted tan(δ)max, less than 0.100.

Description

PNEUMATIC COMPRISING A BUFFER ZONE

BETWEEN CARCASE FRAME AND REINFORCEMENT

SUMMIT

The present invention relates to a tire, radial carcass reinforcement and more particularly to a tire intended to equip vehicles carrying heavy loads and rolling at a high speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] In general, in heavy-vehicle tires, the carcass reinforcement is anchored on both sides in the bead zone and is radially surmounted by a crown reinforcement consisting of at least two layers, superimposed and formed of son or parallel cables in each layer and crossed from one layer to the next in making with the circumferential direction angles between 10 ° and 45 °. Said working layers, forming the working armature, can still be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcing elements, called elastic elements. It may also comprise a layer of low extensibility wires or metal cables forming with the circumferential direction an angle of between 45 ° and 90 °, this so-called triangulation ply being radially located between the carcass reinforcement and the first ply of plywood. so-called working top, formed of parallel wires or cables having angles at most equal to 45 ° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which presents, under the different stresses it undergoes, few deformations, the triangulation ply having the essential role of taking up the transverse compression forces of which the object all the reinforcing elements in the area of the crown of the tire. In the case of tires for vehicles "heavy-weight", a single protective layer is usually present and its protective elements are, in most cases, oriented in the same direction and with the same angle in absolute value that those reinforcing elements of the working layer radially the more outside and therefore radially adjacent. In the case of civil engineering tires intended for driving on more or less uneven ground, the presence of two layers of protection is advantageous, the reinforcing elements being crossed from one layer to the next and the reinforcement elements of the layer of radially inner protection being crossed with the inextensible reinforcing elements of the radially outer working layer and adjacent to said radially inner protective layer.

Cables are said to be inextensible when said cables have under a tensile force equal to 10% of the breaking force a relative elongation at most equal to 0.2%.

Cables are said elastic when said cables have under a tensile force equal to the breaking load a relative elongation of at least 3% with a maximum tangent modulus of less than 150 GPa.

The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.

The axis of rotation of the tire is the axis around which it rotates in normal use.

[0008] A radial or meridian plane is a plane which contains the axis of rotation of the tire.

The circumferential mid-plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

The transverse or axial direction of the tire is parallel to the axis of rotation of the tire. An axial distance is measured along the axial direction. The expression "axially inner to, respectively axially outside to" means "Whose axial distance measured from the equatorial plane is less than or greater than".

The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular thereto. A radial distance is measured in the radial direction. The expression "radially inner to, respectively radially outside to" means "whose radial distance measured since the axis of rotation of the tire is less than, respectively greater than".

Some current tires, called "road", are intended to run at high speed and on longer and longer journeys, because of the improvement of the road network and the growth of the motorway network in the world. The set of conditions under which such a tire is called to roll, undoubtedly allows an increase in the number of kilometers traveled, the wear of the tire being less; against the endurance of the latter and in particular of the crown reinforcement is penalized. There are indeed constraints at the crown reinforcement and more particularly shear stresses between the crown layers, allied to a significant increase in the operating temperature at the ends of the crown layer. axially the shortest, which result in the appearance and propagation of cracks of the rubber at said ends. This problem exists in the case of edges of two layers of reinforcing elements, said layers not necessarily being radially adjacent.

In order to improve the endurance of the crown reinforcement of the tire type studied, solutions relating to the structure and quality of the layers and / or profiles of rubber compounds which are arranged between and / or around the ends of the tire. plies and more particularly the ends of the axially shortest ply have already been made.

Patent FR 1 389 428, for improving the resistance to degradation of rubber compounds located in the vicinity of the crown reinforcement edges, advocates the use, in combination with a low hysteresis tread, of a rubber profile covering at least the sides and marginal edges of the crown reinforcement and consisting of a low hysteresis rubber mix.

FR 2 222 232, to avoid separations between plies of crown reinforcement, teaches to coat the ends of the frame in a rubber mattress, the hardness Shore A is different from that of the strip rolling overlying said armature, and greater than the Shore A hardness of the rubber mix profile disposed between the edges of crown reinforcement plies and carcass reinforcement. The French application FR 2 728 510 proposes to have, on the one hand between the carcass reinforcement and the crown reinforcement working ply, radially closest to the axis of rotation, an axially continuous ply. formed of inextensible metal ropes forming an angle of at least 60 ° with the circumferential direction, the axial width of which is at least equal to the axial width of the shortest working crown ply, and secondly between the two working crown plies an additional ply formed of metal elements, oriented substantially parallel to the circumferential direction.

The French application WO 99/24269 proposes, on either side of the equatorial plane and in the immediate axial extension of the additional ply of reinforcing elements substantially parallel to the circumferential direction, to couple, on a certain axial distance, the two working crown plies formed of reinforcing elements crossed from one ply to the next to then decouple them by rubber mixing profiles at least over the remainder of the width common to said two working plies . This improvement in the endurance of the tires makes it possible to consider at least the possibility of retreading when the tread is worn. Indeed, when it is desired to retread the tire after wear of the strip of rolling, it is necessary to be able to retread a tire whose aging is not too advanced in order to optimize the use of the new tread.

Moreover, the tires of such vehicles may suffer damage through the tread for example due to the penetration of a nail or bolt. Such perforations of the tread may not be too penalizing, especially if the penetrating object is eliminated rapidly, in particular by a human action as soon as the presence of the object is detected.

On the other hand, if this presence is not detected and if the object penetrates through the crown reinforcement of the tire to the internal cavity of the tire, this causes a loss of inflation air which is slowly drained along the object.

Such a loss of air inflation as slow as it leads to a drop in pressure which must alert the driver and allow to detect the object and eliminate it to repair the tire. Again, if this detection is fast enough damage to the tire can be very limited or nonexistent, retreading the tire is not questioned.

It turns out that today some vehicles are equipped with automatic tire re-inflation device when a drop in pressure is detected by sensors. This reinflation operation is then most often performed without the driver's knowledge. Such an operation involved in the case of a perforation as presented above, it then becomes possible for the tire to continue to roll with a perforating object for a relatively long time allowing for example the inflation air to arrive until to the constituent rubber mixtures of the tire between the cavity thereof and the outer surface of its tread.

The object that can be detected only at the time of the retreading step of the tire then leads to the decision not to perform said retreading, the constituent elements of the tire having been subjected to oxidation for a period of time. unknown. Such oxidation may actually have led to aging premature tire especially by promoting the propagation of cracks within the rubber mixes, said cracks having been initiated during the penetration of the object.

The inventors have thus given themselves the mission of being able to provide tires less vulnerable to the presence of an object having perforated the tread to the tire cavity, particularly in the case of tires intended to to be used on vehicles equipped with automatic re-inflation devices in the event of pressure loss.

This object has been achieved according to the invention by a tire with radial carcass reinforcement, consisting of at least one layer of metal reinforcing elements, said tire comprising a crown reinforcement, itself radially capped. a tread, said tread being joined to two beads by means of two sidewalls, said tire comprising a first layer G of polymeric mixture radially between the carcass reinforcement and the layer of radially reinforcing elements. interior of the crown reinforcement and a second layer S of polymer mixture axially in contact with the first layer G of polymeric mixture, in contact with at least one working crown layer and in contact with the carcass reinforcement, said second layer S of polymeric mixture extending axially to at least the axial end of the tread, said first layer G of polymeric mixture the axial width of said first layer being at least 70% of the width of the radially innermost reinforcing element layer of the reinforcement; of the top and said second layer S of mixed polymer mixture consists of a charged elastomer mixture having a macro dispersion Z score greater than or equal to 65 and a maximum value of tan (δ), denoted tan (δ) max, less than 0.100.

A macro dispersion note Z greater than or equal to 65 of a charged elastomeric mixture means that the filler is dispersed in the elastomer matrix of the composition with a dispersion score Z greater than or equal to 65. In the present description, the charge dispersion in an elastomer matrix is characterized by the note Z, which is measured, after crosslinking, according to the method described by S. Otto and Al in Kautschuk Gummi Kunststoffe, 58 Jahrgang, NR 7 -8/2005, in accordance with ISO 11345. [0029] The calculation of the Z score is based on the percentage of area in which the charge is not dispersed ("% undispersed area"), as measured by the device "disperGRADER +" supplied with its operating mode and its operating software "disperDATA" by the company Dynisco according to the equation:

Z = 100 - (% undispersed area) /0.35 [0030] The percentage of non-dispersed surface is measured by a camera observing the surface of the sample under a 30 ° incident light. The bright spots are associated with filler and agglomerates, while the dark spots are associated with the rubber matrix; digital processing transforms the image into a black and white image, and allows the determination of the percentage of undispersed surface, as described by S. Oto in the aforementioned document.

The higher the note Z is, the better the dispersion of the load in the rubber matrix (a Z score of 100 corresponding to a perfect dispersion and a Z score of 0 to poor dispersion). It will be considered that a note Z greater than or equal to 65 corresponds to a satisfactory dispersion of the charge in the elastomer matrix.

The elastomeric mixtures constituting the layer S are prepared according to known methods.

In order to achieve a Z score of macrodispersion greater than or equal to 65, the elastomer mixture constituting the layer S may advantageously be prepared by forming a masterbatch of diene elastomer and reinforcing filler. For the purposes of the invention, the term "master mix" (commonly referred to by its English name "masterbatch"), an elastomer-based composite into which a charge has been introduced.

There are different methods to obtain a masterbatch of diene elastomer and reinforcing filler. In particular, one type of solution consists in improving the dispersion of the filler in the elastomer matrix by mixing the elastomer and the "liquid" phase filler. To do this, an elastomer in the form of latex has been used in the form of elastomer particles dispersed in water, and an aqueous dispersion of the filler, that is to say a dispersed filler. in water, commonly called "slurry".

Thus, according to one of the variants of the invention, the masterbatch is obtained by mixing in the liquid phase from a diene elastomer latex comprising natural rubber and an aqueous dispersion of a filler comprising carbon black. Even more preferably, the masterbatch according to the invention is obtained according to the following process steps, making it possible to obtain a very good dispersion of the filler in the elastomer matrix:

feeding, with a first continuous stream of a diene elastomer latex, a mixing zone of a coagulation reactor defining an elongate coagulation zone extending between the mixing zone and an outlet,

supplying said mixing zone of the coagulation reactor with a second continuous flow of a fluid comprising a charge under pressure to form a mixture with the elastomer latex by mixing the first fluid and the second fluid in the mixing zone so as to sufficiently energetic to coagulate the elastomer latex with the charge before the exit, said mixture flowing as a continuous flow towards the exit zone and said charge being capable of coagulating the elastomer latex,, recovering at the outlet of the reactor the coagulum obtained previously in the form of a continuous stream and drying it in order to recover the masterbatch.

Such a process for preparing a liquid phase masterbatch is described, for example, in WO 97/36724. Advantageously according to the invention, the elastomer-charge bond of the second layer S of polymeric mixture is characterized by a "bond rubber" rate, measured before crosslinking, greater than 35%.

The so-called "bound rubber" test makes it possible to determine the proportion of elastomer, in a non-vulcanized composition, which is associated with the reinforcing filler so intimately that this proportion of elastomer is insoluble in the usual organic solvents. Knowledge of this insoluble proportion of rubber, fixed by the reinforcing filler during mixing, gives a quantitative indication of the reinforcing activity of the filler in the rubber composition. Such a method has been described, for example, in standard NF-T-45-114 (June 1989) applied to the determination of the level of elastomer bound to carbon black.

This test, well known to those skilled in the art to characterize the quality of reinforcement provided by the reinforcing filler, has for example been described in the following documents: Plastics, Rubber and Composites Processing and Applications, Vol. 25, No 7, p. 327 (1996); Rubber Chemistry and Technology, Vol. 69, p. 325 (1996). In the present case, the level of non-extractable elastomer with toluene is measured after swelling for 15 days of a sample of rubber composition (typically 300-350 mg) in this solvent (for example in 80- 100 cm3 of toluene), followed by a drying step of 24 hours at 100 ° C, under vacuum, before weighing the sample of rubber composition thus treated. Preferably, the above swelling step is conducted at room temperature (about 20 ° C) and away from light, and the solvent (toluene) is changed once, for example after the first five days swelling. The bound rubber content (% by weight) is calculated in a known manner by difference between the initial weight and the final weight of the sample of rubber composition, after taking into account and eliminating, in the calculation, the fraction of the insoluble components by nature, other than the elastomer, initially present in the rubber composition.

The loss factor tan (δ) is a dynamic property of the layer of rubber mixture. It is measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm in thickness and 400 mm ² in section), subjected to sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, at a temperature of 60 is recorded. ° C. A strain amplitude sweep of 0.1 to 50% (forward cycle) and then 50% to 1% (return cycle) are performed. The results used are the complex dynamic shear modulus (G ^* ) and the loss factor tan (δ) measured on the return cycle. For the return cycle, the maximum value of tan (O) observed, denoted tan (O) _max.

As stated above, it is known that the presence of oxygen leads to oxidizing processes, rubber compositions and / or metal or textile reinforcements and / or interfaces between these rubber compositions and these reinforcements.

It is also known to avoid oxidation problems of chemically trapping oxygen by accelerated thermo-oxidation of a rubber composition serving as a buffer, disposed between a main source of oxygen and the zone that the we want to protect against oxidation phenomena. Such a buffer composition is known to be usually used between the rubber forming the inner layer of the tire and the carcass ply to reduce the amount of oxygen that comes into contact with this ply from the inflation air. The inventors have demonstrated that the presence of said first layer G of polymeric mixture radially between the carcass reinforcement and the layer of reinforcing elements radially the innermost of the crown reinforcement with the aforementioned dimensions makes it possible to limit the propagation of cracks in the constitutive polymeric mixtures of the tire in a large number of cases.

The inventors have further shown that the second layer S, consisting of a charged elastomer mixture having a macro dispersion Z score greater than or equal to 65 and a maximum value of tan (δ), denoted tan (δ) max. , less than 0.100, has a sufficiently high cohesion to help limit the propagation of cracks initiated when an object pierces the tread of the tire.

For the purposes of the invention, a cohesive rubbery mixture is a rubbery mixture particularly resistant to cracking. The cohesion of a mixture is thus evaluated by a fatigue cracking test performed on a specimen "PS" (pure shear). It consists in determining, after notching the specimen, the crack propagation speed "Vp" (nm / cycle) as a function of the energy release rate "E" (J / m ² ). The experimental area covered by the measurement is in the range - 20 ° C and + 150 ° C in temperature, with an atmosphere of air or nitrogen. The biasing of the specimen is a dynamic displacement imposed amplitude ranging between 0.1mm and 10mm in the form of impulse-type stress (tangential "haversine" signal) with a rest time equal to the duration of the pulse; the frequency of the signal is of the order of 10 Hz on average. The measurement comprises 3 parts:

• An accommodation of the "PS" test tube, from 1000 cycles to 27% deformation.

• an energetic characterization to determine the law "E" = f (deformation).

The energy release rate "E" is equal to W0 * h0, with W0 = energy supplied to the material per cycle and per unit volume and hO = initial height of the test piece. The exploitation of acquisitions "force / displacement" thus gives the relation between "E" and the amplitude of the solicitation. • The measurement of cracking, after notching of the "PS" test piece. The information collected leads to determining the propagation velocity of the crack "Vp" as a function of the imposed stress level "E".

The tests carried out have shown that the presence of the first layer G of polymer mixture and the second layer S according to the invention limits the propagation of a large number of initialized cracks when an object perforates the tire. . The tests have further shown that it is then possible to envisage a retreading of the tires despite the presence of an object having perforated the tire after repair thereof. Indeed, the tests have shown that a tire according to the invention comprising a perforating object could roll at least 50% more than a conventional pneumatic tire without revealing unacceptable crack propagation to retreading.

According to a preferred embodiment of the invention, the elastomeric mixture of the first layer S comprises, as reinforcing filler, at least one carbon black with a BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g, employed at a rate of between 10 and 50 phr.

More preferably, the reinforcing filler of the elastomeric mixture of the second layer S comprises, as a reinforcing filler, a carbon black blend as described above and a white filler, the overall filler rate being between 10 and 60.degree. pce and the black carbon ratio on white charge being greater than 2.7.

The choice of fillers as described above still allows to confer cohesive properties of the second layer S satisfactory.

According to a preferred embodiment of the invention, the axial width of said first layer G is at most equal to the width of the radially innermost reinforcement element layer of the crown reinforcement. More preferably, the axial width of said first layer G is at least equal to 90% of the width of the radially innermost reinforcement element layer of the crown reinforcement.

A preferred variant of the invention further provides that the thickness, measured in the radial direction, of said first layer G is greater than φ, φ being the diameter of the reinforcing elements of the crown reinforcement layer radially. the most interior.

More preferably, the thickness, measured in the radial direction, of said first layer G is less than 3φ. Such thicknesses lead to a sizing of the first layer G of polymeric mixture offering a compromise between the additional cost related to the polymer mixture and the propagation of cracks initiated during perforation by the object.

Indeed, such polymeric mixtures constituting the first layer G having a significant cost, a limited size of such a first layer G according to the invention allows significant gains in the expectation of retreading for an initial additional cost while acceptable.

Advantageously according to the invention, the thickness of said first layer G, measured in the radial direction, is greater than 1 mm and preferably greater than 1.4 mm. The inventors have demonstrated that such thicknesses provided a limitation of the propagation of cracks in most incidents that may occur by drilling the tread by an object such as a nail or a bolt.

More preferably according to the invention, the constituent polymeric mixture of the first layer G may constitute buffer zones provided for trapping oxygen, comprises a metal salt which catalyzes the oxidation. Advantageously, the metal salt is a cobalt salt. This salt has the effect of activating the homolytic decomposition of hydroperoxides generated during aging caused by the aforementioned oxidation phenomena. This salt is preferably introduced in an amount of 0.2 to 0.3 parts by weight of cobalt equivalent per 100 parts by weight of the elastomer in the buffer composition. This increases the amount of oxygen that can be trapped by this buffer composition by about 50 to 100%, relative to the same composition free of cobalt salt.

European patent document EP-A-507 207 describes, for example, polymeric mixtures comprising a transition metal salt intended to activate the oxygen fixation. As proposed above, the metal salts which are preferentially described are cobalt salts. In the alternative, other metals such as manganese and iron are also contemplated.

The international patent documents WO-A-99/24502 and WO-A-00/68309 and the European patent application EP 1 215 232 describe tires comprising a buffer zone between the polymer mixture forming the tire cavity and the carcass reinforcement. These buffer zones are formed of polymer mixtures comprising at least one specific iron (III) salt intended to activate the oxidation in said composition. These products are obtained by incorporating by mechanical work said salt elastomer or elastomers that comprise said mixtures, for obtaining said buffer zone.

In WO-A-99/24502, said salt belongs to the group consisting of iron (III) acetylacetonate and iron (III) salts of carboxylic acids corresponding to the formula Fe (CnH _2). n0 ₂ ) 3, where n can range from 6 to 23.

In the document WO-A-00/68309, said salt is an iron (III) salt of a carboxylic acid corresponding to the formula Fe (C _n H _2n O ₂ ) 3, where n may range from 2 at 5.

In EP 1 215 232, said salt is an iron salt (III) of a monocarboxylic aromatic acid having one or more aromatic rings. The tires described in these three documents also allow a reduction of hysteretic losses in the buffer zone, in comparison with a buffer zone made for example with a cobalt salt. The selection of these specific iron (III) salts also makes it possible to reduce the self-heating phenomena during rolling and thus improves the life of the tire. In addition, it helps to reduce rolling resistance.

The buffer zones described in these documents correspond to polymeric mixtures for blocking the possible migration of oxygen from the cavity, this oxygen first passing through a layer forming the cavity of the near-sealed tire, usually made of butyl.

The inventors have also been able to demonstrate that this type of polymeric mixture intended to block traces of oxygen could also serve to block the presence of oxygen brought by drainage along the foreign body to perforate the tire until to the cavity thereof from the tread thereof, said oxygen then being present with a pressure corresponding to that of inflation.

The inventors have also shown that increasing the modulus of elasticity of such a polymeric mixture comprising a metal salt relative to a polymeric mixture without it is acceptable. Indeed, the presence of a layer of a polymer mixture between the carcass reinforcement and the crown reinforcement can act as a shock absorber to preserve the integrity of the reinforcing elements of the various constituent layers of the tire. . The slight increase in modulus of elasticity due to the presence of a metal salt allows the first layer to retain this role of shock absorber. According to an alternative embodiment of the invention, the axial width of said first polymeric mixture layer is equal to the width of the radially innermost reinforcing element layer of the crown reinforcement. According to this embodiment of the invention, said first layer G of polymeric mixture advantageously constitutes the radially inner calender layer of the radially innermost crown reinforcement layer.

A layer of reinforcing elements consists of a set of reinforcing elements contained between two layers of polymeric mixtures, called calender layers.

The thickness of the radially inner calender layer of the radially innermost crown reinforcement layer is then defined so that the thickness, measured in the radial direction from the radially innermost point of a cable to the radially inner surface of said calender layer, corresponds to the aforementioned thickness of said first layer. In other words, the calender layer is provided with a thickness greater than the usual calender layer thicknesses so that its thickness, measured in the radial direction, at the back of the cables satisfies the relationships described above and in particular must be between once and three times the diameter of the reinforcing elements of the radially innermost layer. The thickness of the calender layer measured on the back of the cables, which is thus advantageously at least 1 mm, is of the order of at least four times the thicknesses obtained with more usual calendering layers. In addition, this embodiment can lead to a variant in the manufacturing method of the tire when said first polymeric mixture layer G corresponds to the radially inner calender layer of the radially most radially reinforced crown layer. interior. It is indeed possible to prepare a layer of reinforcing elements having two different calendering layers by their nature and by their thickness. Such a reinforcing element layer may then be the radially innermost layer of the tire. In terms of process, it is then possible to eliminate the step in the manufacturing process corresponding to the laying of said first layer of polymer mixture. According to a variant of the invention, the second layer S of polymer mixture constitutes another buffer zone provided for trapping the oxygen outside said second layer S advantageously comprising a metal salt which catalyzes the oxidation. According to this same model, another variant embodiment of the invention provides that the first polymeric mixture layer G consists of a charged elastomer mixture having a macro dispersion score Z greater than or equal to 65 and a maximum value of tan (ô), denoted tan (δ) max, less than 0.100.

According to this alternative embodiment of the invention, the elastomeric mixture of the first layer G advantageously comprises, as reinforcing filler, at least carbon black employed at a level of between 10 and 50 phr and having a BET upper specific surface area. at 90 m ² / g and preferably greater than or equal to 120 m ² / g.

Advantageously again according to this alternative embodiment of the invention, the elastomeric mixture of the first layer G comprises a carbon black cut, BET specific surface area greater than 90 m ² / g and preferably greater than or equal to at 120 m ² / g, and a white filler, the reinforcing filler being used at a rate of between 10 and 60 phr, and the ratio of carbon black on white filler being greater than 2.7. According to one embodiment of the invention, the crown reinforcement of the tire is formed of at least two working crown layers of inextensible reinforcement elements, crossed from one layer to the other by making with the circumferential direction angles between 10 ° and 45 °.

According to other embodiments of the invention, the crown reinforcement also comprises at least one layer of circumferential reinforcing elements.

An embodiment of the invention further provides that the crown reinforcement is completed radially on the outside by at least one additional layer, so-called protection, said elastic reinforcing elements, oriented relative to the circumferential direction with an angle of between 10 ° and 45 ° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent thereto . According to any one of the embodiments of the invention mentioned above, the crown reinforcement can be further completed, radially inwardly between the carcass reinforcement and the nearest radially inner working layer. of said carcass reinforcement, by a triangulation layer of steel non-extensible reinforcing elements making, with the circumferential direction, an angle greater than 60 ° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

Other details and advantageous features of the invention will emerge below from the description of exemplary embodiments of the invention with reference to FIGS. 1 and 2 which represent: - Figural, a meridian view of a diagram of a tire according to the invention, FIG. 2, a diagrammatic representation of a half-view of the tire of the wall, which extends symmetrically with respect to the axis XX 'which represents the circumferential median plane, or equatorial plane. ,

The figures are not represented in scale to simplify understanding.

In FIG. 1, the tire 1, of dimension 275/80 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3, around rods 4. The carcass reinforcement 2 is formed of a single layer of metal cables. The carcass reinforcement 2 is fretted by a crown reinforcement 5, itself capped with a tread 6.

The low areas and beads of the tire 1 are not shown in FIG. 2. In Figure 2, the crown reinforcement 5 is formed radially from the inside to the outside: a triangulation layer 51 formed of unstretchable metal cables 9.28 inextensible, continuous over the entire width of the web , oriented at an angle equal to 65 °, a first working layer 52 formed of unstretchable 11.35 metal cables, continuous over the entire width of the web, oriented by an angle equal to 18 °, of a second working layer 53 formed of unstretchable 11.35 unstretchable metal cables, continuous over the entire width of the web, oriented at an angle equal to 18 ° and crossed with the metal cables of the first working layer, with a protective layer 54 formed of non-woven, elastic, non-shrunk 6.35 wire ropes, continuous across the entire width of the web, oriented at an angle of 18 ° in the same direction as the wire ropes of the working layer 53.

According to the invention, radially between the carcass reinforcement 2 and the triangulation layer 51, there is the first layer G of polymeric mixture which forms a buffer zone for trapping the oxygen which can in particular come from the cavity of the pneumatic 1 when an object such as a nail or bolt pierces the tread 6 and passes through the tire to the cavity.

The thickness, measured in the radial direction, of said polymeric mixture layer G is equal to 1.5 mm. The diameter of the cables of the triangulation layer 51 being equal to 1.07 mm, the thickness of said polymeric mixing layer G is between one and three times the diameter of these cables.

As explained above, when such an object comes to perforate the tire and remains in place, the air leak is limited since the object closes the hole it has formed. Such a leak can be almost invisible to the driver. This is especially true when the vehicle is equipped with an automatic tire refill device to maintain a set pressure. In many cases, if this slight air leak is not visible, it leads to the presence of air passage, or even the formation of air pockets within the constitutive polymeric masses of the tire favoring in particular the propagation of cracks initiated during the penetration of the object. This phenomenon is all the more important that the air present is substantially at the pressure of the inflation air and thus of the order of 8 to 9 bar for a tire equipping a vehicle type heavyweight.

According to the invention also, a second layer S of polymeric mixture is positioned in contact with the first layer of polymeric mixture, in contact with the carcass reinforcement and its axially outer end 9 extends axially beyond the axial end 10 of the tread 6. This second layer S of polymeric mixture has good cohesion and relatively low hysteresis properties. The good cohesion of this second layer S makes it possible according to the invention to also contribute to reducing the propagation speeds of the cracks. Running tests were carried out with a tire according to the invention compared to a reference tire whose architecture is identical but whose layers of polymeric mixtures G and S differ.

The various mixtures used are listed below.

Mixture 1 Mixture 2

N 100 100

Black N330 35

Black N234 35

165G Silica 5

Antioxidant 0.7

1.7

(6PPD)

Stearic acid 1.4 0.5

Zinc oxide 2.1 5 sulfur 2.15 3.13

Accelerator CBS 1 1.10

PTC Delay 0.08

PVI)

MA ₁₀ (MPa) 3.4 3.5 tan (6) ~ 0.074 0.080

P60 (%) 11.3 12

G * 10% at 60 ° C

1.25 1.43

(return cycle)

Note Z 60 65

Bound rubber 27.5 48.1

The values of the constituents are expressed in phr (parts by weight per hundred parts of elastomers.

For each of the mixtures, the following table gives the crack propagation rate "Vp" (nm / cycle) as a function of the energy release rate "E" (J / m ² ) on previously aged samples. for 14 days at 77 ° C under air. The measurements were carried out at 60 ° C. under air.

The reference tire comprises layers G and S consisting of the same polymer mixture corresponding to the mixture 1.

The tire according to the invention comprises firstly a first layer G comprising a cobalt salt; it is the mixture 1 further comprising 1 phr of cobalt hydroxide. On the other hand, the tire according to the invention comprises a second layer S consisting of the mixture 2. Before carrying out the tests, the tires undergo a pretreatment consisting firstly in an artificial wear of the tread to the wear indicators and secondly, accelerated aging in an oven under conditions severe in terms of temperature and oxygen content in the inflation air. [00103] Furthermore, the tires are pierced with a nail with a diameter of 3 mm from the tread to the tire cavity through the layer G, the nail then being held in position. place during the tests.

The tests are performed under defined load and speed conditions to lead to a degradation of the reference tire corresponding to a state of said tire prohibiting its retreading after 15,000 kilometers traveled in said conditions of this test.

[00105] The tests carried out with the tire according to the invention under the same conditions made it possible to run more than 25,000 kilometers, the tire being retreadable after course of repairing the damage caused by the nail.

Claims

1 - Pneumatic radial carcass reinforcement, consisting of at least one layer of metal reinforcing elements, said tire comprising a crown reinforcement, itself capped radially with a tread, said tread being joined to two beads through two sidewalls, said tire comprising a first layer G of polymeric mixture radially between the carcass reinforcement and the radially innermost reinforcing element layer of the crown reinforcement, and a second layer S of polymer mixture axially in contact with the first layer G of polymeric mixture, in contact with at least one working crown layer and in contact with the carcass reinforcement, said second layer S of polymeric mixture extending axially up to at least the axial end of the tread, characterized in that said first layer G of polymeric mixture constitutes a zone buffer provided for trapping oxygen outside said first layer, in that the axial width of said first layer G is at least 70% of the width of the radially innermost reinforcing element layer of the reinforcement of vertex and in that said second layer S of mixed polymeric mixture consists of a charged elastomer mixture having a macro dispersion grade Z greater than or equal to 65 and a maximum value of tan (δ), denoted tan (δ) max less than 0.100.

2 - A tire according to claim 1, characterized in that the elastomeric mixture of the second layer S comprises as reinforcing filler at least carbon black employed at a rate of between 10 and 50 phr, and in that the carbon black has a BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g.

3 - tire according to one of claims 1 or 2, characterized in that the elastomeric mixture of the second layer S comprises a carbon black cut, of BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g, and a white filler, in that the reinforcing filler is used at a level of between 10 and 60 phr, and what the ratio of carbon black on white charge is greater than 2.7. 4 - tire according to one of the preceding claims, characterized in that the axial width of said first layer G is at most equal to the width of the radially innermost reinforcement element layer of the crown reinforcement.

5 - tire according to one of the preceding claims, characterized in that the thickness, measured in the radial direction, of said first layer G is greater than φ, φ being the diameter of the reinforcing elements of the reinforcing layer of radially innermost summit.

6 - tire according to one of the preceding claims, characterized in that the thickness, measured in the radial direction, of said first layer G is less than 3φ, φ being the diameter of the reinforcing elements of the reinforcing layer of radially innermost summit.

7 - A tire according to one of the preceding claims, characterized in that the thickness, measured in the radial direction, of said first layer G is greater than 1 mm, and preferably greater than 1.4 mm.

8 - A tire according to one of the preceding claims, characterized in that said first layer G of polymeric mixture is the radially inner calender layer of the radially innermost crown reinforcement layer.

9 - tire according to one of the preceding claims, characterized in that said first layer G of polymeric mixture constituting a buffer zone comprises a metal salt. 10 - A tire according to claim 9, characterized in that the metal salt is a cobalt salt. 11 - A tire according to one of the preceding claims, characterized in that the second layer S of polymeric mixture is a buffer zone provided for trapping oxygen outside said second layer.

12 - tire according to one of the preceding claims, characterized in that said first layer G of polymeric mixture consists of a charged elastomer mixture having a Z macro dispersion of greater than or equal to 65 and a maximum value of tan (O ), denoted tan (δ) max, less than 0.100.

13 - A tire according to claim 12, characterized in that the elastomeric mixture of the first layer G comprises as reinforcing filler at least carbon black employed at a rate of between 10 and 50 phr, and in that the carbon black present a BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g.

14 - A tire according to claim 12, characterized in that the elastomeric mixture of the first layer G comprises as a carbon black cut, BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g, and a white charge, in that the reinforcing filler is used at a rate of between 10 and 60 phr, and in that the ratio of carbon black on white charge is greater than 2.7.