EP1360228A1

EP1360228A1 - Rubber composition used as a safety support for a tyre and said support

Info

Publication number: EP1360228A1
Application number: EP01994828A
Authority: EP
Inventors: François Bataille; Serge Teisseyre; François Masson
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Priority date: 2001-01-02
Filing date: 2001-12-21
Publication date: 2003-11-12
Also published as: JP2004517186A; JP4001552B2; WO2002053637A1; US20040220321A1

Abstract

The invention relates to a rubber composition which can be used in a vulcanised state as a safety support (1) designed to be mounted on a wheel rim inside a tyre cover, one such support (1) which can support a tyre tread on said cover in the event of a drop in tyre pressure, a method of preparing said composition, and a mounted assembly comprising the support (1). The inventive composition, which comprises at least one diene elastomer, is such that it also comprises (pce: parts in weight per 100 parts of diene elastomer(s)): solid or hollow glass microspheres, having a quantity varying between 5 and 50 pce, more than 40 pce of reinforcing filler, and between 3 and 8 pce of sulphur.

Description

Rubber composition usable as a safety support for tires and this support.

The present invention relates to a rubber composition which can be used in the vulcanized state as a safety support intended to be mounted on a wheel rim inside a tire, such support being able to support a tread of said tire. envelope in the event of a drop in inflation pressure, a process for preparing said composition, and a mounted assembly comprising this support.

In known manner, the safety supports for vehicle tires are intended to be mounted on a rim inside the tire, in order to be able to support the tread of this tire in the event of loss of inflation pressure. These supports include in particular a base which is intended to be mounted on the rim, and a top which is intended to come into contact with the tread in the aforementioned case and which leaves a guard with respect to the latter at nominal pressure .

The Japanese patent document JP-A-3/82601 has such a support, the base and the top of which are substantially cylindrical, and which further comprises an annular body connecting said base and said top.

This annular body comprises a support element which is circumferentially continuous, and which comprises:

A plurality of partitions extending axially on either side of said circumferential median plane and distributed over the circumference of said support, and

• junction elements extending substantially circumferentially, each junction element connecting together the two respective ends of two adjacent partitions which are arranged on the same side of the support, said junction elements being arranged successively alternately with on either side of said partitions; in which the partitions and junction elements are substantially rectilinear and the difference between the maximum and minimum values of the area of an axial section of the support element as a function of the azimuth, relative to the sum of these same areas is preferably less than 0.3. Consequently, depending on the azimuth, the area of an axial section of the support element varies by a maximum of a factor of two in order to provide good uniformity in load capacity and limit vibrations during rolling. in support. This support is produced essentially with a hard polymeric material and the whole of the support element is designed to be able to support the load in compression.

Such supports can be produced in the usual way by injection into a mold, for example. European patent document EP-A-1 116 606 in the name of the applicant discloses a rubber composition for safety support comprising (pce: parts by weight per 100 parts of diene elastomer (s)):

- natural rubber or synthetic polyisoprene, in an amount equal to or greater than 60 phr, - more than 60 phr of a reinforcing white filler, and

- from 3 to 8 pce of sulfur.

We also know, from the US patent document US-A-5 141 039 (column

4, lines 18-22), safety supports based on a plastic material or an elastomeric material, such as hard rubber, or else based on a mixture of this elastomeric material and glass fibers , carbon, or the like.

The Applicant has surprisingly discovered that a rubber composition based on at least: (phr: parts by weight per 100 parts of diene elastomer (s)):

- a diene elastomer, solid or hollow glass microbeads, in an amount ranging from 5 to 50 phr,

- more than 40 pce of reinforcing filler, and

- from 3 phr to 8 phr of sulfur,

presents in the unvulcanized state an improved processability compared to that of the known compositions for safety supports and, in the vulcanized state, also improved physical and hysteretic properties making it particularly suitable for constituting 'vulcanized state a safety support intended to be mounted on a wheel rim inside a tire casing. It will be noted that the invention relates both to rubber compositions in the unvulcanized state and in the vulcanized state.

α Concerning said elastomer (s), diene elastomer is understood in known manner to mean an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

Preferably, it will be noted that said elastomer (s) consist of at least one essentially unsaturated diene elastomer. The term “essentially unsaturated diene elastomer” means a diene elastomer which is derived at least in part from conjugated diene monomers having a proportion of units or units of diene origin (conjugated dienes) which is greater than 15% (% by moles), and by example: a) any homopolymer obtained by polymerization of a conjugated diene monomer, such as 1, 3-butadiene, 2-methyl 1, 3-butadiene (or isoprene), 2, 3-di (C1-alkyl) C5) 1, 3-butadiene such as for example 2, 3 dimethyl-1, 3-butadiene, 2, 3-diethyl-1, 3-butadiene, 2-methyl 3-ethyl 1, 3 -butadiene, 2-methyl 3-isopropyl 1, 3 -butadiene, phenyl 1, 3 -butadiene. b) any copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinylaromatic compounds, such as styrene, ortho-, para-, or meta-methylstyrene. Mention may, for example, be made of butadiene-styrene copolymers, or butadiene-isoprene copolymers.

According to an exemplary embodiment of the invention, said composition comprises a single diene elastomer which is entirely made of natural rubber or synthetic polyisoprene. According to an alternative embodiment of the invention, the composition comprises a blend:

- in an amount equal to or greater than 60 phr, of natural rubber or synthetic polyisoprene, and

- in an amount less than or equal to 40 phr, of a homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms, or from a copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms.

Said composition can then comprise, for example, a blend of approximately 60 phr of natural rubber and of approximately 40 phr of polybutadiene.

α The reinforcing filler of a rubber composition according to the invention comprises _. preferentially, a reinforcing white filler on a majority basis, that is to say according to a mass fraction greater than 50%.

White reinforcing filler means a white filler capable of reinforcing on its own, without any other intermediate means than a white filler / elastomer (s) bonding agent, a rubber composition intended for the manufacture of tires, in other words capable to replace in its reinforcement function a conventional load of pneumatic grade carbon black.

Such a reinforcing white filler can for example consist of silica, and it is advantageously present in said composition in an amount ranging from 40 to 80 phr and, even more advantageously, in an amount ranging from 55 to 70 phr.

As silica capable of being used, all precipitated or pyrogenic silicas known to those skilled in the art are suitable, which have a BET or CTAB surface of a value greater than 100 m ² / g, even if the highly precipitated silicas dispersible are preferred. The term “highly dispersible silica” is understood to mean any silica having a very high ability to disaggregate and to disperse in an elastomer matrix, observable in known manner by electron or optical microscopy, on fine sections. As nonlimiting examples of such highly dispersible silicas which can be used for the invention, mention may be made of silicas BN 3370 and BN 3380 from the company Degussa, silicas Zeosil 1165 MP and 1115 MP from the company Rhodia, silica BXR 160 from the company PPG, or Zeopol 8745 M silica from the company Huber.

Preferably, a silica is used whose BET or CTAB surface value is between 110 and 200 m ² / g and, even more preferably, between 140 and 195 m ² / g. Of course, by silica is also meant blends of different silicas. Silica can be used alone or in the presence of other white fillers. The value of the CTAB specific surface is determined according to the method of standard NFT 45007 of November 1987. The value of the BET specific surface is determined according to the method of BRUNAUER, EMMETT and TELLER which is described in "The Journal of the American Chemical Society, vol. 80, p. 309 (1938) ", corresponding to standard NFT 45007 of November 1987.

As reinforcing white filler, it is also possible to use, without limitation,

- aluminas (of formula Al ₂ O ₃ ), such as aluminas with high dispersibility which are described in the European patent document EP-A-810258, or also

- aluminum hydroxides, such as those described in the international patent document WO-A-99/28376.

The reinforcing filler used for the composition of the invention can comprise grade 6 or grade 7 carbon black on a minority basis, that is to say according to a mass fraction of less than 50%. One can for example use for this title the blacks N683 and N772.

Also suitable, as reinforcing filler according to the invention, carbon blacks partially or entirely covered with silica.

α The rubber composition according to the invention also comprises, in a conventional manner, when said reinforcing filler comprises a white reinforcing filler, a white reinforcing filler / elastomer (s) bonding agent (also called coupling agent), which has the function to ensure a sufficient bond (or coupling), of chemical and / or physical nature, between said white charge and said elastomer (s), while facilitating the dispersion of this white charge within this or these latter.

Such a liaison agent, at least bifunctional, has for example as simplified general formula "YTX", in which: Y represents a functional group (“Y” function) which is capable of physically and / or chemically binding to the white charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and surface hydroxyl (OH) groups of the filler (for example surface silanols when it is silica); - X represents a functional group (“function X”) which is capable of physically and / or chemically bonding to the elastomer, for example via a sulfur atom;

- T represents a hydrocarbon group making it possible to link Y and X.

These liaison agents should in particular not be confused with simple agents for recovering the charge in question which, in known manner, may include the active Y function with respect to the charge, but are devoid of the active X function vis-à-vis the elastomer.

Such liaison agents, of variable effectiveness, have been described in a very large number of documents and are well known to those skilled in the art. It is possible in fact to use any binding agent known for or capable of ensuring effectively, in the diene rubber compositions which can be used for the manufacture of tires, the bond between silica and diene elastomer, such as for example organosilanes, in particular polysulphurized alkoxysilanes or mercaptosilanes.

Polysulphurized alkoxysilanes, called "symmetrical" or "asymmetrical" according to their particular structure, are used in particular, as described for example in patents US-A-3,842,111, US-A-3,873,489, US-A-3 978 103, US-A-3 997 581, US-A-4 002 594, US- A-4 072 701, US-A-4 129 585, or in more recent patents US-A-5 580 919, US -A-5 583 245, US-A-5 650 457, US-A-5 663 358, US-A-5 663 395, US-A-5 663 396, US-A-5 674 932, US-A -5,675,014, US-A-5,684,171, US-A-5,684,172, US-A-5,696,197, US-A-5,708,053, US- A-5,892,085, EP-A-1 043 357 which detail such known compounds.

Particularly suitable for the composition of the invention, without the following definition being limiting, so-called "symmetrical" polysulphurized alkoxysilanes corresponding to the following general formula (I):

(I) Z - A - S „- A - Z, in which: - n is an integer from 2 to 8 (preferably from 2 to 5);

- A is a divalent hydrocarbon radical (preferably C _r C ₁₈ alkylene groups or C ₆ -C ₁₂ arylene groups, more particularly C _r C ₁₀ , in particular C ₂ -C ₄ alkylene groups, in particular the propylene); - Z meets one of the formulas below:

R ¹ R ¹ R ²

! I I

- Si— R ¹ ; - Si— R ² ; - If— R ²

IIIR ² R ² R ²

in which:

- the radicals R ¹ , substituted or unsubstituted, identical or different from each other, represent a C _r C ₁₈ alkyl, C ₅ -C ₁₈ cycloalkyl or C ₆ -C ₁₈ aryl group (preferably alkyl groups - , cyclohexyl or phenyl, in particular C ₄ -C ₄ alkyl groups, more particularly methyl and / or ethyl);

- the radicals R ² , substituted or unsubstituted, identical or different from each other, represent a C _r C ₁₈ alkoxyl or C ₅ -C _lc cycloalkoxyl group (preferably 0, -Cg alkoxyl or C ₅ cycloalkoxyl groups -C ₈ , more particularly methoxyl and / or ethoxyl.

In the case of a mixture of polysulphurized alkoxysilanes corresponding to formula (I) above, in particular the usual mixtures commercially available, it will be understood that the average value of "n" is a fractional number, preferably which may vary from 2 to 5. As polysulphurized alkoxysilanes, mention will be made more particularly of polysulphides (in particular tetrasulphides) of bis (alkoxyl (C ₅ -C ₄ ) -silylpropyl), in particular of bis (trialkoxyl (C _r C ₄ ) -silylpropyl), in particular bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) polysulphides. Among these compounds, use is preferably made of bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated as TESPT, of formula [(C ₂ H ₅ O) ₃ Si (CH ₂ ) ₃ S ₂ ] ₂ , marketed for example by the company Degussa under the name Si69 (or X50S when supported at 50% by weight on carbon black), or by the company Witco under the name Silquest Al 289. Those skilled in the art will be able to adjust the content of coupling agent in the compositions of the invention, depending on the intended application, due or the elastomers used and the amount of white reinforcing filler used.

In the rubber compositions in accordance with the invention, the content by weight of coupling agent may be in a range of 2 to 15% relative to the mass of reinforcing white filler and, preferably, in a range of 5 to 12% .

Regarding the sulfur content in the composition according to the invention, it should be noted that it may vary from 3.5 to 5.5 phr.

α The glass microbeads which are used in the composition according to the invention, whether they are solid or hollow (in the latter case, they are sometimes called "glass bubbles" in English) have, by definition, a spherical shape. Of course, microbeads not having exactly a perfectly spherical, but spheroidal geometry, can also be used in the safety support composition according to the invention.

The solid or hollow microbeads which can be used in the composition according to the invention can be based on various constituents.

According to an exemplary embodiment of the invention, microbeads are used which are mainly based on borosilicate of lime and soda, preferably according to a mass fraction of at least 97%. These microbeads also comprise silicon dioxide, according to a mass fraction less than or equal to 3%.

- The hollow microbeads can be used in a composition in accordance with the invention in an amount ranging from 5 phr to 50 phr, preferably from 10 phr to 30 phr and, even more preferably, from 15 phr to 25 phr.

These hollow microbeads have a volume average size (diameter) which is between 10 μm and 400 μm. Preferably, this volume average size is between 10 μm and 100 μm and, even more preferably, between 15 μm and 65 μ. Preferably, the hollow microbeads have before mixing a density equal to or greater than 0.55 g / cm ³ and, even more preferably, equal to or greater than 0.60 g / cm ³ .

- The solid microbeads can also be used in a composition in accordance with the invention in an amount ranging from 5 phr to 50 phr, preferably from 10 phr to 30 phr and, even more preferably, from 15 phr to 25 phr.

These solid microbeads also have a volume average size (diameter) which is between 3 and 400 μm, preferably between 10 and 400 μm and, even more preferably, between 10 and 40 μm.

D A process according to the present invention for preparing said vulcanized rubber composition is such that it essentially consists,

- In a first thermomechanical working step, by kneading said elastomer (s), said reinforcing filler and solid or hollow glass microbeads, the falling temperature being approximately 155 ° C., then

in a second mechanical working step, by adding a sulfur vulcanization system to the mixture obtained at the end of said first step, then

- In a third vulcanization step, by baking the mixture obtained at the end of said second step, so that said microbeads are dispersed in said elastomer (s).

According to an exemplary implementation of the invention, this preparation process consists, - in said first step, in carrying out said mixing for a period of time, for example close to 4 min., Then

- In said second step, to carry out said addition at a temperature below 100 ° C and for a period for example between 2 min. and 2.5 min., then - In said third step, to carry out said cooking at a temperature between 140 ° C and 170 ° C, for example substantially equal to 150 ° C, and for a period for example close to 8 min.

α The rubber compositions according to the invention contain, in addition to said elastomer (s), said reinforcing filler, said glass microbeads and one or more white reinforcing filler / elastomer (s) binding agents, all or part of the other constituents and additives usually used in rubber mixtures, such as plasticizers, pigments, antioxidants, vulcanization accelerators, extension oils, one or more agents for covering the reinforcing white charge, such as alkoxysilanes, polyols, amines, etc. ..

α According to another characteristic of the invention, the rubber composition has a modulus of elasticity M10 at 10% deformation which is greater than 10 MPa and which is preferably greater than 15 MPa, for example equal to 16 MPa, which gives the safety support consisting of this composition a satisfactory rigidity.

α A safety support according to the invention is such that it consists of said rubber composition of the invention.

This support according to the invention is for example of the type comprising:

- a substantially cylindrical base intended to be mounted on the rim,

a substantially cylindrical top intended to come into contact with the tread of the casing in the event of a pressure drop, and leaving a clearance with respect to said strip at nominal pressure, and

an annular body connecting said base and said vertex to each other, said body comprising a circumferentially continuous support element with a circumferential median plane, said support element comprising a plurality of partitions extending axially on either side of said median plane circumferential and distributed over the circumference of said support. According to a first embodiment of this example of support according to the invention, said annular body also comprises, on one of said sides of the support, junction elements extending substantially circumferentially, each junction element connecting the respective ends of two adjacent partitions which are arranged on said side of the support, said junction elements being arranged successively alternately on either side of said partitions. . ^' ,

In this first embodiment, said junction elements are mutually supported, between two adjacent partitions, by a rib extending from said apex to said base of the support, so that said junction elements form a continuous junction wall in the form bellows all over said side of said support.

More specifically, said junction wall comprises a plurality of cells which are each delimited by two adjacent ribs, the bottom of each cell having a substantially dihedral shape whose edge is formed by one of said partitions and whose faces are respectively formed by said alternating junction elements.

/ According to a second embodiment of this example of support according to the invention, said annular body also comprises, on both sides of the support, junction elements extending substantially circumferentially, each junction element connecting the two respective ends of two adjacent partitions which are arranged on the same side of the support, said junction elements being arranged successively alternately on either side of said partitions.

In this second mode, said partitions are adapted in their central part relative to their lateral ends to reinforce the resistance to buckling under a radial load of the annular body.

Indeed, the central part of the partitions of the support element is distant from the junction elements and can be destroyed during rolling in support by the appearance of a repeated buckling deformation. In the case of supports produced essentially with an elastomeric material, such a repeated buckling deformation can cause, on rolling, first an initiation and then a propagation of cracks on the side of the walls in extension. E on the other hand, in the case of supports produced essentially with plastic materials, a buckling deformation results in the appearance of plastic deformations. These irreversible deformations significantly reduce the stiffness of the structure, its load capacity and make it progressively incapable of fulfilling its function.

The ratio between the thickness of the partitions in their central part and their lateral ends is greater than 1.1 and preferably greater than 1.5. This variation in thickness very significantly increases the buckling resistance of the central part of the partitions and thus makes it possible, at a given radial load, to limit the thickness of the junction elements and to reduce the total weight of the support.

These partitions have, from one lateral end to the other, at least one inversion and, preferably, three inversions of the direction of their curvature.

These partitions have, for example, a central part extending substantially axially between two lateral parts, these lateral parts joining the junction elements making an angle γ ranging from 20 to 40 degrees with the circumferential direction.

According to another embodiment, the partitions have, in their central zone, two parts extending substantially axially and offset circumferentially with respect to each other, as well as a third junction part. The variation α of average orientation between this third junction part and the two parts of substantially axial orientation is preferably greater than 20 degrees.

Each junction element may be supported, on one side or on both sides of the support element, by at least one wall extending substantially axially towards the outside of the annular body.

These axial walls are not very sensitive to buckling because they are integral with the support element and relatively short. These axial walls allow, at iso-width of support, to reduce the width of the support element and therefore to increase its buckling resistance. In a preferred embodiment, each junction element forms with an axial wall which shoulder and the lateral ends of the two adjacent partitions a star-shaped assembly with three branches, and the axial width of an axial wall is less or equal to half the axial width of the two adjacent partitions of the support element. The support elements according to the invention may also comprise a substantially cylindrical veil and coaxial with the support, which for example is arranged radially halfway up the support element.

This veil is made of the same material as the rest of the annular body. When it is placed halfway up, it allows the height of the partitions to be halved and thus to increase the buckling limit load by a factor of about four.

To facilitate the production of the supports according to the invention, the different geometries of the support elements are adapted so as to include no undercut part opposing an axial release of the support.

α Preferably, a mounted assembly for a motor vehicle is of the type comprising a wheel rim, a tire casing mounted on said rim and said support according to the invention, said rim comprising in each of its two peripheral edges a rim seat intended to receive a bead of said casing, said rim comprising between its two seats, on the one hand, a bearing surface and, on the other hand, a mounting groove connecting said bearing surface to an axially internal rim of one of said seats, or first seat.

It will be noted that the flat structure which is imparted to said rim by said bearing is such that, when running flat, the entire width of the support supports the load, unlike so-called “hollow” rims.

'The above characteristics of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of illustration and not limitation, in comparison with other examples not in accordance with ^" the invention.

Examples of support architecture according to the invention will be described at the end of this description by means of the appended drawings, in which: Fig. 1 is a side view of a safety support according to an exemplary embodiment of the invention, FIG. 2 is an axial section view of an assembly mounted according to the invention, in which the support of FIG. 1 is mounted on a wheel rim and is in the support position against a tire casing, FIG. 3 is a sectional view, along the line AA in FIG. 1, of a support element according to a first embodiment of the invention, FIG. 4 is a sectional view, along the line AA in FIG. 1, of a support element according to a second embodiment of the invention which comprises partitions connected by alternating circumferential junction elements, FIG. 5, similar to FIG. 4 is a sectional view along the line AA in FIG. 1, of a support element whose partitions have a variable thickness, FIG. 6, similar to FIG. 4 is a sectional view along the line AA in FIG. 1, of a support element, the partitions of which comprise a central connection part which is oriented circumferentially, FIG. 1, similar to FIG. 4 is a sectional view along the line AA in FIG. 1, of a support element whose circumferential junction elements have a variable length, FIG. 8, similar to FIG. 4 is a sectional view along the line AA in FIG. 1, of a support element whose partitions have three curvature inversions in their width, FIG. 9, similar to FIG. 4, is a sectional view along the line AA in FIG. 1, of an annular body including another embodiment of a support element, the partitions of which have three inversions of curvature in their width, FIGS. 10 and 11, similar to FIG. 4, are respectively sectional views, along the line AA of FIG. 1, of annular bodies according to the invention including support elements whose partitions have variable thicknesses, and with axial shoulder walls, FIG. 12 is a side view of a support according to said second embodiment of the invention, the annular body of which comprises a central veil, and FIG. 13 is a perspective view illustrating a known support architecture. α In the following examples, “control” safety supports and safety supports according to the invention were manufactured which differ from each other by the rubber compositions constituting them. The properties of the compositions were measured as follows:

- Mooney MS viscosity (1 + 4) at 100 ° C: measured according to standard ASTM D 1646 of 1999 using a small rotor;

fluidity: measured at the temperature of 90 ° C. in a fluidimeter, by a volume value of the composition having been preheated and premolded,

, which composition flows for a period of 11 seconds in a die of determined geometry and under a load of 300 kg. This volume value is expressed in units or points corresponding to graduations of 1/100 mm on the chamber of the fluidimeter. More specifically, the die consists of a conical upper part of 1 mm in height and a maximum diameter equal to 4.2 mm, which converges at an angle of 45 ° to a cylindrical lower part of 3 mm in height and diameter equal to 2.2 mm. This die is characterized by a roughness parameter Ra equal to 0.1 (Ra, arithmetic mean deviation of the profile to be characterized from the internal face of the wall, being defined in standard NF / E05-015);

- elasticity module M10 (usual abbreviation which designates a secant extension module obtained at a deformation of the order of 10%, at room temperature and in the third stress cycle, according to standard ASTM D 412 of 1998). The corresponding tensile measurements are carried out under normal conditions of temperature and hygrometry, according to standard ASTM D 1349 of 1999. - PH hysteretic losses (60 ° C): measured by rebound at 60 ° C on the sixth shock and expressed as a percentage, according to the following relationship:

PH (%) = 100. (W ₀ -W ₁ ) / Wι, with ₀ : energy supplied and W,: energy restored.

- hysteretic loss factor (tanδ _max ): measured on a sample of vulcanized material using a Schenck machine, according to standard ASTM D 5992 of 1996. The response of this sample is recorded (cylindrical test piece 4 mm thick and 400 mm ² section), subjected to a sinusoidal stress in alternating single shear, at the frequency of 10 Hz, under normal temperature conditions (23 ° C) according to standard ASTM D 1349 of 1999. A sweep is carried out in amplitude of deformation from 0.1 to 50% (outward cycle), then from 50 to 1% (return cycle). For the return cycle, the maximum value of tanδ observed (tanδ _ιnax ) is indicated.

α With reference to Figs. 1 and 2, each of the supports 1 tested (“control” and according to the invention) essentially comprises three parts: - a base 2, of generally annular shape;

a vertex 3, substantially annular, with on its radially outer wall (optionally) longitudinal grooves 5, and

an annular body 4 for connection between the base 2 and the top 3.

Fig. 2 illustrates in particular the function of a support 1 which is to support the tread of the tire in the event of a large loss of inflation pressure thereof.

These “control” supports according to the invention have in common a width of 110 mm, an internal diameter of 460 mm and a height of 60 mm. "WITNESS" EXAMPLES:

I. Example "witness" 1:

α A first “witness” safety support consists of a vulcanized rubber composition as defined below:

- elastomer: natural rubber 100 pce;

- reinforcing filler: silica "ZEOSIL 1165 MP" 70 pce (silica sold by the company Rhodia and having surface values

BET and CTAB of at least 150 to 160 m7g);

- coupling agent: “Si69 / carbon black N330 11 pce;

(including 5.5 phr of Si69 and 5.5 phr of carbon black N330);

- "6PPD": 2 pce; - ZnO: 4 pce;

- stearic acid: 1 pce;

- vulcanization accelerator: "CBS": 3 pce;

- sulfur: 4.5 pce;

where "6PPD" is N- (1,3-dimethyl butyl) -N'-phenyl-p-phenylenediamine, and where

"CBS" is N-cyclohexyl-benzothiazyl-sulfenamide.

This first "witness" support is produced as follows:

- In a first thermomechanical working step implemented in an industrial mixer of 200 liters, one proceeds to a kneading of all the constituents of the necessary composition including the coupling system and the various additives, with the exception of vulcanization system. The elastomer and the reinforcing filler are thus mixed in particular, the dropping temperature being approximately 155 ° C .; - In a second mechanical working step, we proceed, at a temperature below 100 ° C, to an addition of the sulfur vulcanization system to the mixture obtained at the end of said first step;

- In a third vulcanization step implemented in an injection mold at a temperature of 150 ° C, the composition obtained is baked at the end of said second step.

α This first “control” support composition presents, in the unvulcanized state:

- a Mooney MS viscosity (1 + 4) at 100 ° C which is equal to 60, and - a fluidity which is equal to 200.

This composition also presents, in the vulcanized state:

a modulus of elasticity M10 substantially equal to 17.5 MPa, and

- PH hysteretic losses (60 ° C) equal to 23.5, and

- a loss factor tanδ _max (at 40 ° C, return cycle) = 0.25.

α The first "witness" support presents an architecture which is illustrated in FIG. 9, in relation to Figs. 1 and 2 (reference is made to the part of the description entitled "support architectures according to the invention" for a detailed description of this architecture). The section of FIG. 2 shows, for this “witness” support, a first massive part

4a of the annular body 4 as well as a second part 4b consisting of recesses (see also Fig. 1) extending axially over substantially more than half of the annular body

4, opening on the outside in a substantially axial direction. These recesses 4b are regularly distributed over the entire circumference of the annular body 4 and they define partitions 62 (see FIG. 9), which provide a direct radial connection between the apex 2 and the base 3 of the support 1.

This geometry has the advantage of stressing in bending and not in compression these partitions 62 when they are crushed. The recesses 4b and therefore the partitions 62 are numerous enough to provide regular support during rolling under pressure. More precisely, this first “witness” support 1 comprises, on its circumference, 40 partitions 62 which each have a thickness of 15.7 mm, and which are two by two spaced 41.4 mm apart.

In addition, the base 2 and the top 3 have thicknesses which are respectively equal to 7 mm and 8 mm.

The mass of this first "witness" support is 7.3 kg.

IL Example "witness" 2:

A second “control” safety support was made, the composition of which differs only from that of the first “control” safety support, in that it comprises a blend of natural rubber (60 pce) and polybutadiene (40 pce), the architecture, the dimensions and the mass of this support being identical to that of said first "witness" support.

This second “control” support composition is substantially characterized by the same properties in the unvulcanized state (MS (l + 4) and fluidity) and in the vulcanized state (elasticity module M10, hysteretic losses PH (60 ° C) and tanδ _max (40 ° C, return cycle)) that said first support composition "witness".

EXAMPLES OF SAFETY SUPPORTS ACCORDING TO THE INVENTION:

I. Compositions and respective properties of these safety supports:

1) First safety support according to the invention:

α A first safety support according to the invention was manufactured, which consists of a vulcanized rubber composition having the same architecture as that of the abovementioned "control" supports (see FIG. 9). This first support according to the invention is characterized by the following formulation for the vulcanized rubber composition which constitutes it:

- elastomer: natural rubber 100 pce;

- reinforcing filler: silica "ZEOSIL 1165 MP" 63 pce;

- coupling agent: “Si69 / carbon black N330” 10.1 pce; (including 5.5 phr of Si69 and 5.5 phr of carbon black N330);

- hollow glass microbeads: 15 pce; - "6PPD": 2 pce;

- ZnO: 4 pce;

- stearic acid: 1 pce; - vulcanization accelerator: "CBS": 3 pce;

- sulfur: 4.5 pce;

where the hollow glass microbeads which are used are sold by the company 3M under the generic name “3M Scotchlite® Glass Bubbles General Purpose Series”, the particular name of these microbeads being “S60 / 10,000”.

These hollow microbeads have a nominal density (also called absolute or true density) of 0.60 g / cm3, and they are mainly based on borosilicate of lime and soda, present according to a mass fraction ranging from 97% to 100 %.

These microbeads also comprise silicon dioxide, according to a mass fraction less than or equal to 3%. This vulcanized rubber composition is prepared in the following manner:

- In a first thermomechanical working step implemented in an industrial mixer of 200 liters, one proceeds to a kneading of all the constituents of the necessary composition including the coupling system and the various additives, with the exception of vulcanization system. The elastomer, said reinforcing filler and said hollow microbeads are thus mixed in particular for approximately 4 min. at ambient temperature (temperature of introduction of the elastomer), the dropping temperature being approximately 155 ° C .; - In a second mechanical working step, we proceed at a temperature below 100 ° C and for a period of between 2 min. and 2.5 min., to an addition of the sulfur vulcanization system to the mixture obtained at the end of said first step;

- In a third vulcanization step implemented in an injection mold at a temperature of 150 ° C and for about 8 min., the mixture obtained is cooked at the end of said second step.

It will be noted that the size distribution of the microbeads introduced into the internal mixer is as follows (percentages representing cumulative volume fractions; measurements carried out according to standard ASTM D 1214):

- size <15 μm: 10%

- size <30 μm: 50%

- size <55 μm: 90%

- size <65 μm: 95% α This first support composition according to the invention has the following properties:

- Mooney MS viscosity (l + 4) = 51; - fluidity = 220;

- modulus of elasticity Ml 0 = 16 MPa

- hysteretic losses PH (60 ° C) = 19, and

- tanδ _max (at 40 ° C, return cycle) = 0.17

It should be noted that this first support composition according to the invention has:

improved processability for the injection molding operation compared to that of the abovementioned “control” support compositions, because of its Mooney viscosity which is much lower than that of said “control” compositions and of its increased fluidity compared to that of the latter, reduced hysteretic losses compared to those of said “control” compositions. This results in a lower potential heating during rolling on the support consisting of this first composition according to the invention and, consequently, a possibility of increased endurance in running on the flat of this first support according to the invention, and a high rigidity in the vulcanized state.

It will also be noted that the reinforcing white filler, such as silica, which is preferably used in the rubber composition according to the invention, contributes to providing this composition with improved cooked properties, such as cohesion. 2) Second safety support according to the invention:

A second safety support according to the invention was made, which is made of a vulcanized rubber composition having the same architecture as above.

(see Fig. 9), which differs only from said first support according to the invention in that its composition comprises, as an elastomeric matrix, a blend of natural rubber (60 pce) and polybutadiene (40 pce).

The second support composition according to the invention has the following properties: - Mooney MS viscosity (l + 4) = 48;

- modulus of elasticity Ml 0 = 16 MPa; and

- tanδ _max (at 40 ° C, return cycle) = 0.16.

This second composition according to the invention therefore has substantially the same properties in the unvulcanized state (improved processability) and in the vulcanized state (reduced hysteretic losses) as said first composition according to the invention.

3) Third safety support according to the invention:

A third safety support according to the invention was made, which consists of a vulcanized rubber composition having the same architecture as above, and which differs only from said first support according to the invention in that its composition comprises said microbeads. hollow in an amount of 25 pce (instead of 15 pce), and said silica "ZEOSIL-1165 MP" in an amount of 61 pce (instead of 63 pce).

As before, this third support composition according to the invention has substantially the same properties in the unvulcanized state (MS (l + 4)) and in the vulcanized state (M10, PH (60 ° C) and tanδ _max (at 40 ° C., return cycle)) than the preceding compositions according to the invention. 4) Fourth safety support according to the invention:

A fourth safety support according to the invention was made, which consists of a vulcanized rubber composition having the same architecture as above, and which differs only from said second support according to the invention in that its composition comprises said microbeads. hollow in an amount of 25 pce (instead of 15 pce), and said silica "ZEOSIL 1165 MP" in an amount of 61 pce (instead of 63 pce).

As before, this third support composition according to the invention has substantially the same properties in the unvulcanized state (MS (l + 4)) and in the vulcanized state (MIO, PH (60 ° C) and tanδ _max (at 40 ° C., return cycle)) than the preceding compositions according to the invention.

5) Fifth safety support according to the invention

A fifth safety support according to the invention was manufactured, which consists of a vulcanized rubber composition having the same architecture as above, and which differs only from said first support according to the invention in that:

- its composition comprises, according to an amount of 20 phr, microbeads full of glass instead of the 15 phr of hollow microbeads,

- the quantity of coupling agent “Si69 / black N330” is 10.4 phr instead of 10.1 phr, and in that

- the quantity of silica used is 65 phr instead of 63 phr.

These solid microbeads are sold by the company POTTERS BALLOTINI under the name "4-45", and they have a size distribution which is such that their minimum diameter is 4 μm and their maximum diameter is 45 μm. The average density of these solid microbeads is 2.48.

The manufacturing process for this fifth support is similar to that mentioned above in relation to the hollow microbeads. The properties of this fifth support composition are as follows:

- Mooney MS viscosity (l + 4) = 47;

- modulus of elasticity M 10 = 16 MPa;

- PH hysteretic losses (60 ° C) ≈ 20.5; - tanδ _max (at 40 ° C, return cycle) = 0.19.

This fifth composition according to the invention therefore also has an improved processability, as well as hysteretic and physical properties also improved in the vulcanized state, thus making it capable of constituting a safety support having improved endurance.

6) Sixth safety support according to the invention:

A sixth safety support according to the invention was produced, which consists of a vulcanized rubber composition having the same architecture as above, and which differs only from said fifth support according to the invention in that the size distribution of the filled microbeads are such that their minimum diameter is 75 μm and their maximum diameter is 150 μm.

The properties of this sixth support composition are as follows: - Mooney MS viscosity (î + 4) = 47;

- modulus of elasticity M 10 = 16 MPa;

- tanδ _max (at 40 ° C, return cycle) = 0.20.

This sixth composition according to the invention therefore also has an improved processability, as well as hysteretic and physical properties also improved in the vulcanized state, thus making it capable of constituting a safety support having improved endurance. II. Examples of architectures usable for said supports according to the invention:

In addition to the preferred architecture, illustrated in FIG. 9, which was mentioned in paragraph I. and which will be described in this paragraph II, are presented below other advantageous examples of support architectures which can be used for the present invention.

- A first preferred mode of support architecture according to the invention is illustrated in FIG. 3.

As previously indicated in general, with reference to Figs. 1 and 2, a safety support 1 according to FIG. 3 is of the type comprising said base 2, said apex 3 and said annular body 4.

Is shown in Fig. 3 a support element 7 of this preferential support 1 which is circumferentially continuous, said support element comprising a plurality of partitions 6 extending axially on either side of the circumferential median plane P of the support 1 and being distributed over the circumference of said support 1.

We see in Fig. 3 that this support element 7 comprises, on one of said sides of the support 1, junction elements 8 extending substantially circumferentially. Each junction element 8 connects the respective ends 6a of two adjacent partitions 6 which are arranged on said side of the support 1, and said junction elements 8 are arranged successively alternately on either side of said partitions 6.

More specifically, the junction elements 8 are mutually supported, between two adjacent partitions 6, by a rib 8a extending from said apex 3 to said base 2 of the support 1, so that said junction elements 8 form a wall continuous junction 9 in the form of a bellows over all of said side of said support 1.

More specifically, said junction wall 9 comprises a plurality of cells 9a which are each delimited by two adjacent ribs 8a. The bottom of each cell 9a has substantially a dihedral shape, the edge of which is formed by one end 6a of partition 6, and the faces of which are respectively formed by said alternating junction elements 8.

In this preferred example of architecture tested, the partitions 6 of the support 1 are 40 in number on the circumference of said support 1, they each have a thickness of 8 mm, and they are spaced from one another by 40 mm. And as has been said above for each support 1 tested, it has a width of 135 mm, a diameter of 440 mm and a height of 50 mm.

In addition, the base 2 and the top 3 of said support 1 have thicknesses respectively equal to 6 mm and 7 mm. Furthermore, the distance in the axial direction between a plane P ', axially median for said junction elements 8, and the respective free ends of said ribs 8a, is equal to 20 mm in this preferred example.

- A second mode of support architecture 1 according to the invention is illustrated in FIG. 4, the

Figs. 5 to 12, for their part, illustrating variants of this second mode (the structural elements similar to those of FIG. 4 are identified below by numerical references which are increased by 10 in each Fig., This from Fig. 5).

As in said first mode, the supports 1 relating to these FIGS. 4 to 12 are all of the type comprising said base 2, said apex 3 and an annular body 10.

* In Fig. 4 is shown such an annular body 10. This consists of a support element 11 which is circumferentially continuous, which comprises a set of partitions 12 connected in pairs by junction elements 13. The partitions 12 extend laterally on either side of the circumferential median plane P of the support 1, and they are regularly distributed over the circumference of said support 1. They have an inclination Δ, relative to the circumferential direction, which is close to 90 degrees. Their thickness H is constant. In addition, two adjacent partitions 12 have an opposite inclination relative to the axial direction. These junction elements 13 have a thickness e, they are oriented circumferentially and each connect the respective ends of two adjacent partitions 12 which are arranged on the same side of the support 1 (these two ends are the closest one another). The junction elements 13 are thus successively arranged alternately on either side of the partitions 12.

Note that the support element 11 has no undercut element, to facilitate the manufacture of the support 1 with an axial release.

* In Fig. 5 is shown an alternative embodiment of a support element

21, with reference to the support element 11 of FIG. 4.

The partitions 22 of this support element 21 have a thickness H, in their central part, which is greater than their thickness h, at the location of their lateral ends. In this example, H is about twice as large as h. This variation in thickness gives the central parts of the partitions 22 a very good buckling resistance. As for the lateral ends, they are connected to the junction elements 23 continuously, which gives them good buckling resistance.

It should be noted that a variation in thickness of 10% can already have appreciable effects, with a view to delaying the appearance of buckling on overload.

* In Fig. 6 shows another alternative embodiment of a support element 31.

This comprises, as before, a set of partitions 32 which are connected by junction elements 33. The partitions 32 comprise two lateral parts 34 of the same inclination Δ relative to the circumferential direction, which are offset circumferentially and which are connected in the central part of said support element 31 by a third part 35 of substantially circumferential orientation.

The variation α of average orientation between the lateral parts 34 and the central part 35 is here of the order of 80 degrees. As the parts 35 are of circumferential orientation, the angles α and Δ are equal. The presence of this third central part 35, of average orientation very different from that of the two lateral parts, reinforces the buckling resistance of the central part of the partitions 22.

It will be noted that this variation α must, to be effective, be greater than 20 degrees. In this exemplary embodiment, the partitions 32 comprise, from one lateral end to the other, an inversion of the direction of their curvature.

* In Fig. 7 shows another alternative embodiment of a support element 41. The junction elements 43 which are arranged on one side of the support element 41 here have a circumferential length which is less than that of the junction elements 44 , which are arranged on the other side of the support element 41.

It will be noted that the substantially doubled length of the junction elements 44 increases the compression stiffness of the support element 41, on this side of the support 1. This same side is to be placed on the interior side of the vehicle, where the forces undergone by the support 1 in operation are the most important.

* In Fig. 8 shows another alternative embodiment of a support element 51. The junction elements 53 are here practically reduced to the contact surface between the two lateral ends 54 in the form of an arc of a circle of the partitions 52.

These partitions 52 also include a central connecting part 55. It will be noted that the variation α of average orientation between the two lateral parts 56 and the central part 55 is greater than 90 degrees and is of the order of 110 degrees, which increases the average support density of the support element 51 in its central part.

These partitions 52 have, from one lateral end to the other, three inversions of their direction of curvature. * In Fig. 9 shows another alternative embodiment of a support element 61, a variant close to that of FIG. 8 with the following modifications.

The partitions 62 have rectilinear segments and have three inversions of their direction of curvature. They comprise two lateral parts of axial orientation 64, which are connected, on the one hand, to each other by a central part 65 and, on the other hand, to the junction elements 63 by lateral ends 66 of medium orientation γ close 30 degrees from the circumferential direction.

The variation α of average orientation which exists between the two parts of axial orientation 64 of the partitions 62 and the central junction part 65 is of the order of 60 degrees. The junction elements 63 can be defined here as elements of substantially triangular section, which are arranged between two adjacent lateral ends 66.

On both sides of the support element 61, the annular body 60 comprises a set of walls of substantially axial orientation 67 which extends each junction element 63 towards the outside of the support 1. As can be seen in this FIG. . 9, the union of each junction element 63, said adjacent lateral ends 66 and said axial wall 67 thus forms a three-pointed star, which is very resistant to buckling.

* In Fig. 10 shows another alternative embodiment of an annular body 70 and, consequently, of a support element 71.

The latter comprises partitions 72 with central portions 74 of axial orientation which are extended on either side by a lateral end 75, which has an orientation γ close to 30 degrees relative to the circumferential direction.

The joining elements 73 are, on one side of the annular body 70, reduced to the contact surface between the two adjacent lateral ends 75. On the other side, the annular body 70 has side walls 76 which on this side shoulder the joining elements 77, which have a substantially triangular shape.

It will be noted that on this last side, the stiffness in compression of the support element is greater. The length of the side walls 76 is notably less than half the length of the central parts 74 of the partitions 72, so that they are not liable to buckle.

Preferably, the side of the support element 71 whose stiffness in radial compression is the highest is to be placed on the interior side of the vehicle. In fact, it has been found that the forces are highest on this interior side of the vehicle.

The partitions 72 have a thickness H in their central part 74 which is greater than the thickness h of their lateral parts 75, so as to reinforce the buckling resistance of this central part 74.

* In Fig. 11 is shown another alternative embodiment of an annular body 80, a variant very close to said annular body 70 of FIG. 10.

This annular body 80 has axial lateral walls 86 and 87 which shoulder on both sides the support element 81, which is also structurally very close to said support element 71.

For a given width of annular body 80, these side walls 86 and 87 have the advantage of reducing the axial width of the partitions 82 of the continuous support element 81, and thus of improving the buckling resistance of the assembly of the structure. The axial lengths of said walls 86 and 87 may be different, as illustrated in FIG. 11.

* In Fig. 12 is shown an axial view of a support 1 including a support element 91 as described in FIG. 11, but further comprising a continuous circumferential veil 94 which is disposed at mid-height of the annular body 90. This circumferential veil 94, of cylindrical shape, has the advantage of providing a very significant increase, of the order of one factor four, of the buckling limit load of the support structure 1.

Each of the supports 1 described with reference to Figs. 4 to 12 has the following dimensional characteristics.

The partitions 12, ..., 92 are 40 in number on the circumference of each support 1, they each have a thickness of 8 mm, and they are spaced from each other by 40 mm. And as has been said above for each support 1 tested, it has a width of 135 mm, a diameter of 440 mm and a height of 50 mm.

In addition, the base 2 and the top 3 of said support 1 have thicknesses respectively equal to 6 mm and 7 mm.

All the support elements 7, 11, ..., 91 and the annular bodies 4, 10, ..., 90 presented above can be produced by molding techniques. Preferably, they have no undercut part to facilitate axial demoulding.

It will be noted that one could also use, as architecture of supports according to the invention, a support consisting of several rings connected together in the axial direction of said support, its overall structure being unchanged.

One could for example provide for such a support a first ring of substantially rectangular axial section, and one or more annular elements having a plurality of recesses and extending substantially axially over their widths and substantially regularly distributed over their circumferences.

Such a ring support is easier to introduce into a tire, because of the lower bending stiffness of its various annular elements.

Claims

1) Rubber composition, usable in the vulcanized state as a safety support (1) intended to be mounted on a wheel rim inside a tire, said composition comprising at least one diene elastomer, characterized in what it also includes (pce: parts by weight per 100 parts of diene elastomer (s)):

- solid or hollow glass microbeads, in an amount ranging from 5 to 50 phr,

- more than 40 pce of reinforcing filler, and

- from 3 to 8 pce of sulfur.

2) Rubber composition according to claim 1, characterized in that said reinforcing filler mainly comprises a white reinforcing filler.

3) Rubber composition according to claim 2, characterized in that said reinforcing white filler consists of silica, in an amount ranging from 40 to 80 phr.

4) A rubber composition according to claim 2 or 3, characterized in that it comprises a reinforcing white filler / elastomer (s) binding agent which is of the poly-sulfurized alkoxysilane type.

5) Rubber composition according to one of claims 1 to 4, characterized in that said microbeads are solid microbeads which are present in said composition in an amount ranging from 5 phr to 50 phr.

6) Rubber composition according to one of claims 1 to 4, characterized in that said microbeads are hollow microbeads which are present in said composition in an amount ranging from 5 phr to 50 phr.

7) Rubber composition according to claim 6, characterized in that the density of said hollow microbeads is equal to or greater than 0.55 g / cm ³ . 8) Rubber composition according to one of the preceding claims, characterized in that the volume average size of said solid or hollow microbeads is between 10 μm and 400 μm.

9) Rubber composition according to one of the preceding claims, characterized in that it comprises a single diene elastomer which is made of natural rubber or synthetic polyisoprene.

10) Rubber composition according to one of claims 1 to 8, characterized in that it comprises a cutting:

- in an amount less than or equal to 40 phr, of a homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 12 carbon atoms, or of a copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinyl aromatic compounds having 8 to 20 carbon atoms.

11) Rubber composition according to claim 10, characterized in that said cut consists of about 60 phr of natural rubber and about 40 phr of polybutadiene.

12) Rubber composition according to one of the preceding claims, characterized in that it has a modulus of elasticity M10 at 10% deformation which is greater than 10 MPa.

13) Process for preparing a rubber composition in the vulcanized state according to one of the preceding claims, characterized in that it essentially consists, - In a first thermomechanical working step, by kneading said elastomer (s), said reinforcing filler and said solid or hollow glass microbeads, the falling temperature being approximately 155 ° C., then

14) Preparation process according to claim 13, characterized in that it consists,

- in said second step, to carry out said addition, at a temperature below 100 ° C., then

- In said third step, to carry out said cooking at a temperature between 140 ° C and 170 ° C.

15) Safety support (1) intended to be mounted on a wheel rim inside a tire casing for a vehicle, so as to be able to support a tread of said tire in the event of a drop in inflation pressure , characterized in that said support (1) consists of a vulcanized rubber composition according to one of claims 1 to 12. '

16) Safety support (1) according to claim 15, of the type comprising:

- a base (2) intended to be mounted on said rim, - a substantially cylindrical crown (3) intended to come into contact with said tread in the event of a pressure drop, and leaving a guard relative to said strip at the nominal pressure, and

- an annular body (4) connecting said base (2) and said vertex (3) to each other, said body (4) comprising a support element (7) continuous circumferentially with a circumferential median plane (P), said support element (7) comprising: A plurality of partitions (6) extending axially on either side of said circumferential median plane (P) and distributed over the circumference of said support (1),

• junction elements (8) extending substantially circumferentially in one of said sides of the support (1), each junction element connecting together the respective ends (6a) of two adjacent partitions (6) which are arranged on said side of the support (1), said junction elements (8) being successively arranged alternately on either side of said partitions (6), characterized in that, between two adjacent partitions (6), said elements junction (8) are mutually supported by a rib (8a) extending from said top (3) to said base (2) of the support (1), so that said junction elements (8) form a wall of continuous junction (9) in the form of a bellows on all of said side of said support (1).

17) Safety support (1) according to claim 16, characterized in that said continuous wall (9) comprises a plurality of cells (9a) which are each delimited by two adjacent ribs (8a), the bottom of each cell ( 9a) having substantially a dihedral shape, the edge of which is formed by one of said partitions (6) and the faces of which are respectively formed by said alternating junction elements (8).

18) Safety support (1) according to claim 15, of the type comprising:

- a base (2) intended to be mounted on said rim,

- a substantially cylindrical top (3) intended to come into contact with said tread in the event of a pressure drop, and leaving a clearance with respect to said strip at nominal pressure, and - an annular body (10) connecting said base (2) and said top (3) therebetween, said body (10) comprising a support element (11, ..., 91) continuous circumferentially with a circumferential median plane (P), said support element (11 ,. .., 91) including:

A plurality of partitions (12, ..., 92) extending axially on either side of said circumferential median plane (P) and distributed over the circumference of said support (1), and • junction elements (13, ..., 93) extending substantially circumferentially, each junction element (13, ..., 93) connecting together the respective ends of two partitions (12, ..., 92 ) adjacent which are arranged on the same side of the support (1), said junction elements (13, ..., 93) being successively arranged alternately on either side of said partitions (12, .. ., 92), characterized in that said partitions (12, ..., 92) are adapted in their central part relative to their lateral ends to reinforce the resistance to buckling under a radial load of said annular body (10).

19) Safety support (1) according to claim 18, characterized in that the ratio between the thickness of said partitions (22, 72) in their central part and their lateral ends is greater than 1.1.

20) Safety support (1) according to claim 18 or 19, characterized in that said partitions (32) have, from one side end to the other, at least one reversal of the direction of their curvature.

21) Safety support (1) according to claim 20, characterized in that said partitions (62) have a central part (65) extending substantially axially between two side parts (64), said side parts joining the junction elements (63) by making with the circumferential direction an angle γ ranging from 20 to 40 degrees.

22) Safety support (1) according to one of claims 18 to 21, characterized in that said partitions (52) have, from one side end to the other, at least three reversals of the direction of their curvature.

23) Safety support (1) according to one of claims 20 to 22, characterized in that said partitions (32) have, in their central area, two parts (34) extending substantially axially and circumferentially offset one relative to the other, as well as a third part (35) of junction. 24) Safety support (1) according to one of claims 18 to 23, characterized in that, on at least one side of said support element (61, 81, 91), each junction element is supported by at least a wall (67, 87) extending substantially axially towards the outside of said annular body.

25) Safety support (1) according to claim 24, characterized in that each junction element (63) forms with an axial wall (67) which supports the shoulder and the lateral ends (66) of the two adjacent partitions (62) a star-shaped set with three branches.

26) Safety support (1) according to one of claims 18 to 25, characterized in that the support element (91) further comprises a substantially cylindrical web (94) coaxial with the support (1) which is arranged radially at mid-height of said support element (91).

27) Safety support (1) according to one of claims 18 to 26, characterized in that the support element (11) is adapted to include no undercut part opposing an axial release of the '' support (1). I

28) Mounted assembly for a motor vehicle comprising a wheel rim, a tire casing mounted on said rim and a safety support (1) mounted on said rim inside said casing so as to be able to support a tread of said casing in the event of a drop in inflation pressure, said rim comprising in each of its two peripheral edges a rim seat intended to receive a bead of said casing, said rim comprising between its two seats, on the one hand, a seat and , on the other hand, a mounting groove connecting said bearing to an axially internal rim of one of said seats, or first seat, characterized in that said support (1) is as defined in one of claims 15 to 27.