PROCESS FOR PRODUCING TYRES PROVIDED WITH AUXILIARY COMPONENTS FOR VEHICLE WHEELS

Abstract

A process for producing tyres with auxiliary components for vehicle wheels is described. The process includes i) covering the external surface of an expandable chamber for tyre vulcanisation and moulding apparatuses with a first substantially cross-linkable polysiloxane composition and ii) covering the radially inner surface of the impermeable elastomeric material layer of the green tyre with a second substantially non-cross-linkable polysiloxane composition. An expandable chamber for tyre vulcanisation and moulding apparatuses and, a process for treating the expandable chamber are also described.

Claims

1. A process for producing tyres provided with auxiliary components for vehicle wheels, comprising: a) forming, on a forming drum, a green tyre comprising a carcass structure comprising at least one carcass layer having opposite lateral edges associated with respective bead structures, a pair of sidewalls laterally applied on opposite sides of said carcass structure, a layer of impermeable elastomeric material applied at a radially inner position with respect to said carcass structure, b) arranging an expandable vulcanisation chamber; c) shaping, moulding and vulcanising the green tyre in a manner so as to obtain a finished tyre; d) making an auxiliary component adhere on a first radially inner surface portion of the tyre; wherein arranging an expandable vulcanisation chamber comprises: b1) covering the external surface of said expandable vulcanisation chamber with a first substantially cross-linkable polysiloxane composition A comprising A1) at least one reactive polysiloxane oil having OH groups, A2) at least one cross-linking agent comprising at least two functional groups capable of reacting with the reactive polysiloxane oil A1) b2) cross-linking said first substantially cross-linkable polysiloxane composition A on the expandable chamber; b3) repeating at least once the aforesaid operations b1) and b2), and wherein shaping, moulding and vulcanising the green tyre comprises: c1) selecting at least one green tyre every n green tyres, where n is an integer less than 60; c2) covering at least one second portion of the radially inner surface of said impermeable elastomeric material layer of said at least one selected green tyre with a second substantially non-cross-linkable polysiloxane composition B comprising B1) at least one non-reactive polysiloxane oil, wherein said second portion on the green tyre corresponds with a portion on the finished tyre substantially not superimposing said first portion.

2. The process as claimed in claim 1, wherein the operations b1) and b2) are carried out at least three times.

3. The process as claimed in claim 1, wherein after b1), said process comprises: b11) removing at least one volatile phase of said first substantially cross-linkable polysiloxane composition A.

4. The process as claimed in claim 1, wherein said first polysiloxane composition A that is substantially cross-linkable comprises: A3) at least one non-reactive polysiloxane oil.

5. The process as claimed in claim 4, wherein in said first substantially cross-linkable polysiloxane composition A, the weight ratio between the non-reactive oil A3) and the reactive oil A1) is less than 1.

6. The process as claimed in claim 1, wherein said first substantially cross-linkable polysiloxane composition A comprises: A4) a cross-linking catalyst.

7. The process as claimed in claim 1, wherein said first substantially cross-linkable polysiloxane composition A comprises: A5) at least one polysiloxane resin having condensable hydroxyl groups and siloxylic units.

8. The process as claimed in claim 1, wherein said first substantially cross-linkable polysiloxane composition A comprises: (A6) at least one solvent.

9. The process as claimed in claim 8, wherein said solvent (A6) is a cyclic polysiloxane.

10. The process as claimed in claim 1, wherein said first substantially cross-linkable polysiloxane composition A comprises: at least two different cross-linking agents A2) comprising at least two functional groups capable of reacting with the reactive polysiloxane oil A1).

11. The process as claimed in claim 10, wherein said different cross-linking agents A2) are methyltriethoxysilane and polymethyl-hydrogen-silane.

12. The process as claimed in claim 4, wherein the molecular weight of the reactive oil A1) and/or of the non-reactive oil A3) is greater than 590 Dalton.

13. The process as claimed in claim 1, wherein said first substantially cross-linkable polysiloxane composition A and/or said second substantially non-cross-linkable polysiloxane composition B are applied by means of a sponge, by spraying or spreading.

14. The process as claimed in claim 1, wherein after each application of said first substantially cross-linkable polysiloxane composition A on the external surface of the expandable chamber, the cross-linking b2) of said first polysiloxane composition A can be carried out via heating or at ambient temperature.

15. The process as claimed in claim 1, wherein the cross-linking occurs via heating at a temperature of at least 120 C.

16. The process as claimed in claim 1, wherein the cross-linking occurs for a time comprised between 30 minutes and 2 hours.

17. The process as claimed in claim 1, wherein c2) comprises covering zones, situated at the beads of the radially inner surface of the impermeable elastomeric material layer of said at least one selected green tyre, with said second substantially non-cross-linkable polysiloxane composition B.

18. The process as claimed in claim 17, wherein c2) also comprises covering zones situated at the sidewalls of the tyre.

19. The process as claimed in claim 1, wherein c2) is carried out on one green tyre every n tyres of the production cycle, comprised between 5 and 50.

20. The process as claimed in claim 1, wherein the organic substituents bonded to the silicon atom of the non-reactive polysiloxane oil B1) of the second substantially non-cross-linkable polysiloxane composition B are selected independently from among linear or branched C1-C6 alkyl, C3-C8 cycloalkyl, linear or branched C2-C8 alkenyl, C6-C10 aryl, C6-C15 alkylarylene and C6-C15 arylalkylene.

21. The process as claimed in claim 1, wherein the second substantially non-cross-linkable polysiloxane composition B contains non-reactive polysiloxane oil B1) in a quantity greater than 10%.

22. The process as claimed in claim 1, wherein the molecular weight of the non-reactive polysiloxane oil B1 is greater than 590 Dalton.

23. The process as claimed in claim 1, wherein in d) the auxiliary component is a sound absorbent foam for reducing the transmission of the noise of the tyre and/or a monitoring device and/or a sealing complex.

Description

DESCRIPTION OF THE DRAWINGS

[0136] Further characteristics and advantages will be clearer from the detailed description of a preferred but not exclusive embodiment, of an apparatus for moulding and vulcanising tyres for vehicle wheels, according to the present invention.

[0137] Such description is set forth herein below with reference to the enclosed drawings, provided only as a non-limiting example in which:

[0138] FIG. 1 schematically shows, in diametric section, a vulcanisation mould in an initial step of a moulding and vulcanising process;

[0139] FIG. 2 schematically shows, in radial half-section, a tyre for vehicle wheels;

[0140] FIGS. 3 and 4 show tyres carrying different auxiliary components.

[0141] With reference to FIG. 1, reference number 1 overall indicates a vulcanisation mould belonging to a tyre building plant.

[0142] The vulcanisation and moulding process is executed by introducing the green tyre 100, covered according to the process of the present invention, within a moulding cavity 2 of the vulcanisation mould 1, said cavity 2 having a shape corresponding to the external shaping to be conferred to the tyre 100 once moulded and vulcanised.

[0143] The green tyre 100, once shut in the mould 1, is pressed against the containment walls that have suitable reliefs for determining the formation of a specific tread design.

[0144] Subsequently or at the same time as the pressing step, heat is administered to the green tyre 1 in a manner so as to determine the cross-linking of the elastomeric material constituting the tyre itself.

[0145] As is visible in FIG. 1, the mould 1 has a pair of axially opposite shells 3 that can be mutually coupled at an equatorial plane P. Each of the shells 3 comprises a work surface 4 arranged to operate on beads 103 and on sidewalls 108 of the green tyre 1.

[0146] The mutually adjacent shells 3 on the abovementioned equatorial plane P also define a circumferential surface 7 arranged to operate against the tread band of the green tyre 100 to be vulcanised.

[0147] The green tyre 100, once shut in the mould 1, is pressed against the containment walls due to an expandable vulcanisation chamber 9.

[0148] The expandable chamber for tyre vulcanisation and moulding apparatuses comprises at least one cross-linkable rubber selected from among natural or synthetic rubbers, for example isoprene rubbers. Preferably said expandable chambers comprise a compound with butyl rubber base. Butyl rubber is a copolymer mainly constituted by isobutylene with small quantities of diene monomers, with the purpose of providing sufficient unsaturation for allowing the butyl rubber to cross-link. Preferably, butyl rubber is selected from among isobutyl rubbers; preferably such isobutyl rubbers are selected from among isoolefin monomer homopolymers containing from 4 to 12 carbon atoms, or copolymers obtained by polymerizing a mixture comprising at least one isoolefin monomer containing from 4 to 12 carbon atoms and at least one conjugated diolefin monomer containing from 4 to 12 carbon atoms. Preferably said isoolefin monomer is selected from among compounds C.sub.4-C.sub.12, such as isobutylene, isobutene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, methyl vinyl ether, indene, vinyltrimethylsilane, hexene, 4-methyl-1-pentene, or mixtures thereof. Isobutylene is preferred.

[0149] Preferably, said conjugated diolefin monomer is selected from among the compounds from C.sub.4 to C.sub.14, such as isoprene, 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, myrcene, 6,6-dimethyl-fulvene, hexadiene, cyclopentadiene, piperylene, or mixtures thereof. Isoprene is preferred.

[0150] Other polymerizable monomer, such as styrene, styrene optionally substituted with C.sub.1-C.sub.4-alkyl or halogen groups, such as methylstyrene, dichlorostyrene, can be present in the abovementioned butyl rubbers.

[0151] More preferably, the butyl rubbers are selected from among halogenated and nitrilated butyl rubbers. Still more preferably the butyl rubbers are selected from among halogenated isobutylene and p-alkylstyrene copolymers. Preferably said halogenated isobutylene and p-alkylstyrene copolymers are selected from among copolymers of an olefin containing from 4 to 7 carbon atoms, such as isobutylene, and with a p-alkylstyrene such as for example p-methylstyrene.

[0152] Optionally, said butyl rubber base compound contains conventional additives, including fillers, peptizing agents, stearic acid, accelerators, vulcanising sulfur agents, resins for cross-linking, antiozonants, antioxidants, process oils, activators, initiators, plasticisers, waxes, prevulcanisation inhibitors, diluent oils and the like.

[0153] The expandable vulcanisation chamber 9, covered according to the process of the present invention, has substantially toroidal shape.

[0154] The expandable chamber 9 is subjected to a treatment comprising at least two, preferably at least three successive cycles for covering with the above-described first substantially cross-linkable polysiloxane composition A and subsequent cross-linking of the same in a manner so as to obtain a multilayer film constituted by at least two, preferably at least three layers with cross-linked polysiloxane composition.

[0155] The expandable vulcanization chamber 9 has two circumferential radially inner edges carrying respective anchoring appendages 10, sealingly engageable in the mould 1, for operatively associating the expandable chamber 9 with the same mould

[0156] The anchorage appendages 10 are connected to the mould 1 at more internal anchorage zones of the surfaces of the shells 3 that receive the beads of the green tyre 100.

[0157] A supply duct for vapour, or another operative fluid, obtained in the mould 1 flows inside the expandable chamber 9, so as to allow the expansion of the latter following the introduction of pressurised vapour, in order to compress the green tyre 100 against the containment walls of the mould 1.

[0158] Such compression preferably occurs in a manner such that the radially outer surface 11 of the expandable chamber 9 approaches and contacts the radially inner surface 112 of the green tyre 100, according to a specific approach sequence.

[0159] Preferably, on the inner surface 14 of the expandable chamber 9, a first plurality of grooves 16 is obtained on at least one portion of said expandable chamber 9.

[0160] Preferably said first plurality of grooves 16 is obtained according to trajectories that are substantially parallel to each other.

[0161] The lubricant of one tyre every n tyres to subject to moulding and vulcanisation is selectively carried out only in the portions not affected by the subsequent adhesion of the auxiliary components.

[0162] Preferably the auxiliary component is fixed to the impermeable elastomeric material layer in the crown portion, axially occupying different crown portions which can engage relatively small surfaces, of a few cm.sup.2, such as in the case monitoring devices, or the entire crown portion and possibly also the sidewalls as in the case for example of a sealing complex. Consequently, the covering of the second portions of the radially inner surface 113 of the impermeable elastomeric material layer of said at least one selected green tyre with a second substantially non-cross-linkable polysiloxane composition B is carried out in a manner so as to not cover the radially inner surface of the impermeable elastomeric material layer corresponding to part or all of the crown portion.

[0163] Preferably the covering is carried out in the zones situated at the beads, more preferably also at the zones situated at the sidewalls, still more preferably also at the zones situated at the edges of the tyre and/or beyond the edges at part of the crown portion of the tyre, in any case leaving free of treatment the portion of impermeable elastomeric material layer on which, in the finished tyre, the auxiliary component is made to adhere.

[0164] At the end of the moulding and vulcanisation process, a finished tyre is obtained like that shown in the radial half-section of FIG. 2.

[0165] In FIG. 2, a indicates an axial direction and X indicates a radial direction, in particular with X-X the line of the equatorial plane is indicated.

[0166] The tyre 100 for four-wheel vehicles comprises at least one carcass structure, comprising at least one carcass layer 101 having respectively opposite terminal flaps engaged with respective annular anchoring structures 102, termed bead cores, possibly associated with a bead filler 104. The zone of the tyre comprising the bead core 102 and the filler 104 forms a bead structure 103 intended for the anchorage of the tyre on a corresponding mounting rim, not illustrated.

[0167] The carcass structure is usually of radial type, i.e. the reinforcement elements of the at least one carcass layer 101 are found on planes comprising the rotation axis of the tyre and substantially perpendicular to the equatorial plane of the tyre. Said reinforcement elements are generally constituted by textile cords, for example rayon, nylon, polyesters (e.g. polyethylene naphthalate (PEN)). Each bead structure is associated with the carcass structure by means of bending backward the opposite lateral edges of the at least one carcass layer 101 around the annular anchoring structure 102 in a manner so as to form the so-called turn-ups of the carcass 101a as illustrated in FIG. 2.

[0168] In one embodiment, the coupling between the carcass structure and the bead structure can be provided by means of a second carcass layer (not represented in FIG. 2) applied at an axially outer position with respect to the first carcass layer.

[0169] An anti-abrasive layer 105 made with elastomeric material is arranged at an external position of each bead structure 103.

[0170] The carcass structure is associated with a belt structure 106 comprising one or more belt layers 106a, 106b situated in radial superimposition with respect to each other and with respect to the carcass layer, typically having textile and/or metallic reinforcement cords incorporated within a layer of elastomeric composition.

[0171] Such reinforcement cords can have crossed orientation with respect to a circumferential extension direction of the tyre 100. By circumferential direction it is intended a direction generically directed according to the tyre rotation direction.

[0172] In radially more external position with respect to the belt layers 106a, 106b, at least one circumferential reinforcement layer 106c is applied, commonly known as belt 0, comprising at least one circumferential belt layer.

[0173] The (circumferential belt) reinforcement layer can typically comprise a plurality of textile and/or metallic reinforcement cords.

[0174] In radially outer position with respect to the belt structure 106, a tread band 109 made of elastomeric compound is applied, like other semifinished products forming the tyre 100.

[0175] Respective sidewalls 108 made of elastomeric compound are also applied in axially outer position on the lateral surfaces of the carcass structure, each extended from one of the lateral edges 110 of the tread 109 up to the respective bead structure 103. The tyre portion comprised between the edges 110 identifies the crown C of the tyre. The belt structure 106 is preferably extended at such crown C, hence up to the edges 110 in radially inner position with respect to the tread.

[0176] In radially outer position, the tread band 109 has a rolling surface 109a intended to come into contact with the ground. Circumferential grooves, which are connected by transverse notches (not represented in FIG. 2) in a manner so as to define a plurality of blocks of various shapes and sizes distributed on the rolling surface 109a, are generally obtained in this surface 109a, which for the sake of simplicity is represented smooth in FIG. 2.

[0177] An underlayer 111 can be arranged between the belt structure 106 and the tread band 109.

[0178] An impermeable layer of elastomeric material 112, generally known as liner, provides the necessary impermeability to the tyre inflation air, and is typically arranged in a radially inner position with respect to the carcass layer 101.

[0179] At least one auxiliary component can be adhered to the radially inner surface 113 of the impermeable elastomeric material layer 112, e.g. by means of gluing, for example between a sound absorbent layer comprising a polymer foam for reducing the transmission of the noise of the tyre and/or a monitoring device such as a temperature and/or pressure sensor, and/or a sealing complex.

[0180] The additional component can be made to adhere to the radially inner surface 113 of the impermeable elastomeric material layer by means of gluing with suitable adhesives such as an acrylic adhesive, or by exploiting the adhesive characteristics of the material itself as in the case of the sealing material.

[0181] With reference to FIG. 2, a tyre 100 is shown in radial section bearing, as first auxiliary component embodiment, a sound absorbent layer 301, for example made of expanded polymer material or polymer foam. The sound absorbent layer 301 is made integral with the radially inner surface 113 of the impermeable elastomeric material layer 112 in the crown portion C by means of gluing, occupying in axial extension a part of said crown portion previously not covered by the covering made with the second substantially non-cross-linkable polysiloxane composition B, since not covered directly or by means of transfer of said second composition from the expandable chamber to the tyres vulcanized after the treated tyre.

[0182] FIG. 3 shows a perspective view of a tyre bearing, as second auxiliary component embodiment, a monitoring device 410 adhered to the radially inner surface 113 of the impermeable elastomeric material layer in zone of the crown portion C.

[0183] The monitoring device 410 comprises a housing 411 bearing one or more electronic devices, such as a temperature and/or pressure sensor, or an accelerometer or inertial sensor.

[0184] The housing 411 is provided with a base 411a intended for fixing to the liner of the tyre e.g. by means of gluing. Preferably the housing is made of elastomeric and/or thermoplastic material that is sufficiently elastic to support deformations and forces to which the device is subjected during tyre rolling.

[0185] According to that illustrated in FIG. 3, the device is fixed to the radially inner surface 113 of the impermeable elastomeric material layer 112, preferably in proximity to the equatorial plane of the tyre, therefore requiring that the crown portion lack treatment with the second substantially non-cross-linkable polysiloxane composition B. Nevertheless, other placements of the monitoring device are possible, and consequently other portions of the radially inner surface 113 of the impermeable elastomeric material layer 112 will have to be left free of treatment ahead of time, i.e. not hit directly or by means of transfer of said second polysiloxane composition B from the expandable chamber.

[0186] With reference to FIG. 4, a self-sealing tyre 100 is shown in radial half-section that comprises, as third auxiliary component embodiment, a sealing complex 512 comprising a layer of sealing polymer material 510 arranged at the crown portion of the tyre 100, preferably axially extended up to the edges 110, in radially inner position with respect to the liner 112. The layer of sealing polymer material 510 is extended over the entire circumferential extension of the tyre 100.

[0187] In radially inner position with respect to the layer of sealing polymer material 510 and in direct contact with said layer of sealing polymer material 510, a self-supporting elastomeric film 511 made of thermoplastic or elastomeric-thermoplastic polymer is arranged.

[0188] The tyre 100 also preferably comprises two elongated elements made of elastomeric material 513, each arranged at a circumferential edge of the sealing complex 12. An axially inner portion 513a of each elongated element made of elastomeric material 513 is preferably superimposed on the sealing complex 512 and is arranged in radially inner position with respect to said sealing complex 512.

[0189] An axially outer portion 513b of each elongated element made of elastomeric material 513 lies in direct contact with the radially inner surface 113 of the impermeable elastomeric material layer 112. By axially inner portion 513a, it is intended a portion closer to an equatorial plane X of the tyre 100 with respect to the axially outer portion 513b.

[0190] The sealing complex can be at least partially applied after vulcanisation and is made integral with the radially inner surface 113 of the impermeable elastomeric material layer 112 by means of gluing, e.g. by using the sealing polymer material 510 itself and a specific glue for the zones of the elongated elements 513.

[0191] If the sealing complex also comprises a protective layer in radially outer position with respect to the sealing material, it is such protective layer (not illustrated) to be glued to the radially inner surface 113 of the impermeable elastomeric material layer 112 together with the elongated elements 513.

[0192] The radially inner surface of the impermeable elastomeric material layer at the crown portion and possibly at the edges of the tyre are previously left free of treatment with the second substantially non-cross-linkable polysiloxane composition B.

EXAMPLES

[0193] Two expandable vulcanisation chambers 9 were treated with the first substantially cross-linkable polysiloxane composition A Mono-Lube1100 (ChemTrend Corp.) over 100% of their external surface. Such expandable chambers had a diameter of 540 mm and were obtained via injection moulding and cross-linking of butyl rubber and phenol resins with non-smooth external surface in order to improve the air leakage.

[0194] Before covering, the chambers were cleaned of impurities and prepared for the deposition of the first substantially cross-linkable polysiloxane composition A by means of use of a hydrocarbon solvent. The covering was applied by means of a sponge and about 20 g of composition were applied for each covering, obtaining a residual thickness, after the removal of the volatile phase and after cross-linking, of about 7 micrometres for each covering.

[0195] After each covering, the expandable chamber was left at ambient temperature for about 30 minutes, then placed in the oven at 160 C. for 1 h in order to obtain the cross-linking of the polysiloxane film and cooled at ambient temperature (about 25 C.), leaving it under ambient air for 6 hours. The treatment of covering on the first expandable chamber (comparison chamber) was carried out once (application of only one layer). On the second expandable chamber (chamber according to the invention), the treatment of covering was carried out three successive times.

[0196] The chambers were mounted on a vulcaniser of standing post type, for producing tyres of 215/50 R17 size having as radially inner surface of the impermeable elastomeric material layer a bromobutyl compound and a bead filler compound rich with sulfur (1.2% sulfur in the compound).

[0197] One green tyre every six tyres was treated on the radially inner surface of the impermeable elastomeric material layer, at the beads and at the sidewalls and excluding the crown portion, with the second substantially non-cross-linkable polysiloxane composition B in aqueous solution, Mono-Lube 8186 (ChemTrend Corp.). Before being vulcanised, the green tyre was left at ambient temperature until there was total evaporation of the water; then, normal vulcanisation of the tyres proceeded.

Number of Cycles

[0198] The number of vulcanisation cycles carried out by the second expandable chamber (chamber according to the invention) was greater than 326 cycles, without the chamber having to be replaced and with optimal tyre quality; the tyres were without flaws and without non-uniformities on the radially inner surface of the impermeable elastomeric material layer. The number of total cycles of the comparison expandable chamber, on which only one treatment was applied, was less than 200; the use of the chamber was in fact interrupted when damage of the impermeable elastomeric material layer of the tyres was seen.

Adhesion Force

[0199] A strip of sound absorbent sponge constituted by polyurethane with 35-41 Kg/m.sup.3 density and 2 cm thickness and having, on one side, a layer of pressure-sensitive modified acrylic adhesive by Nitto of Nitto 5015 T(P) type, was made to adhere on the central part of the radially inner surface of the impermeable elastomeric material layer of a tyre in the zone corresponding to the crown, not treated with the second substantially non-cross-linkable polysiloxane composition B. After at least 1 hour from the application, a strip of 19 cm length and 2 cm width was cut from the central zone of the tyre; on such strip, the sponge was made to adhere for a length of 16 cm or for a surface area of 3200 mm.sup.2 while 3 cm were left non-adhered by means of insertion of a film between the sponge and the liner.

[0200] A same strip of sponge was made to adhere to the radially inner surface of the impermeable elastomeric material layer of the tyre in the zone comprised between the edge and the corresponding bead, such zone treated with the second polydimethylsiloxane-based polysiloxane composition B in aqueous solution, Mono-Lube 8186 (ChemTrend Corp.), for a same surface area and applying the same pressure.

[0201] Before gluing the sponge strip, the surface of the impermeable elastomeric material layer between the edge and the bead was cleaned with physical chemical treatment (cleaning with solvent and scraping with scraper) in a manner so as to eliminate the second substantially non-cross-linkable polysiloxane composition B from the surface of the impermeable elastomeric material layer and render the same visibly rough.

[0202] The complete cleaning time for the impermeable elastomeric material layer was about 25 minutes and the inner surface of the tyre was examined in order to verify the absence of damage of the impermeable elastomeric material layer.

[0203] Separation tests were conducted 1 hour after application. The applied forces, measured by means of Instron dynamometer, were substantially equal for the two samples up to the destruction of the component before separation.

[0204] It was thus shown that the tyre according to the invention was directly ready for the application of the auxiliary component without any need for further cleaning treatments and without the presence of fouling and/or damage of the attachment surface.

[0205] The tyre treated with the second substantially non-cross-linkable polydimethylsiloxane-based polysiloxane composition B in aqueous solution, Mono-Lube 8186 (ChemTrend Corp.), only at the zone between each edge and respective bead, and not treated in the crown portion, having the layer of sponge adhered to the central part of the radially inner surface of the impermeable elastomeric material layer in the crown portion, was subjected to an indoor fatigue test that consisted of rolling the tyre at constant speed under constant load on a drum for a predetermined number of hours, verifying at constant intervals the integrity of the sound absorbent layer, upon stoppage and dismantling of the tyre. The tyre according to the invention exceeded the predetermined time without showing any separation and/or damage of the sound absorbent layer.