SELF-SEALING TYRE FOR VEHICLE WHEELS

Abstract

The present invention relates to a self-sealing tyre for vehicle wheels comprising at least one carcass ply, a tread band applied in radially outer position to said carcass ply in a crown zone, optionally a liner applied in radially inner position to said carcass ply, a sealing composite applied in radially inner position to the liner and axially extended at least at a part of the crown portion of the tyre; wherein said sealing composite comprises a self-supporting thermoplastic film comprising at least 50% by weight with respect to the weight of the film itself of at least one or more polyolefins, wherein the at least one polyolefin has a fluidity index (MFI) of less than 4 gram per 10 minutes, and a sealing composition layer associated with and supported by said self-supporting thermoplastic film.

Claims

1. A green or at least partially vulcanised tyre comprising at least: a carcass structure (2), a tread band (7) applied in radially outer position to said carcass structure (2), optionally a layer of elastomeric material substantially impermeable to air, liner (9), applied in radially inner position to said carcass structure (2), a sealing composite (12) applied to the radially more internal surface of said tyre axially extended at least at a crown portion of the tyre; wherein said sealing composite (12) comprises at least a self-supporting thermoplastic film (11) and a sealing composition layer (10) associated with and supported by said self-supporting thermoplastic film (11); characterised in that the self-supporting thermoplastic film (11) comprises at least 50% by weight with respect to the weight of the film itself of at least one or more polyolefins, wherein the at least one polyolefin is characterised by a fluidity index (MFI) less than 4, preferably less than 2, more preferably less than 1.5, still more preferably less than 1 gram per 10 minutes evaluated according to ASTM D1238 at 190 C./2.16 Kg, and it is radially inside the sealing composition layer (10) and said sealing composition layer (10) is placed substantially in contact with the radially more internal surface of the tyre.

2. The tyre according to claim 1 wherein said at least one polyolefin is characterised by a fluidity index (MFI) greater than 0.1, more preferably greater than 0.2 grams per 10 minutes evaluated according to ASTM D1238 at 190 C./2.16 Kg.

3. The tyre according to claim 1 or 2 wherein the at least one or more polyolefins in the mixture of the self-supporting thermoplastic film has a melting point less than 160 C., 150 C., preferably less than 140 C. or 130 C. or 120 C.

4. The tyre according to any one of the preceding claims wherein said self-supporting thermoplastic film comprises at least 50%, 60%, 70%, 80% or 90% or more than 90%, 95% or 98% by weight with respect to the weight of the film itself of said at least one or more polyolefins and/or from 1 to 50%, preferably from 10 to 40%, more preferably from 15 to 35% by weight of one or more polar polymers selected from among polyvinyl acetate, ethylene-vinyl acetate copolymers, EVOH, polyvinyl acetate with a high level of hydrolysis, polyvinyl alcohol (PVA, PVOH) or mixtures thereof.

5. The tyre according to any one of the preceding claims wherein the at least one polyolefin of said self-supporting thermoplastic film is selected from among homopolymers and copolymers of ethylene, of propylene, of C4-C20 alpha-olefin and mixtures thereof, preferably it is a polyethylene selected from among homopolymers of ethylene, copolymers of ethylene with propylene, copolymers of ethylene with a C4-C8 alpha-olefin and copolymers of ethylene with vinyl acetate and mixtures thereof.

6. The tyre according to claim 5 wherein the at least one polyolefin is a polyethylene (PE), preferably selected from among linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), low-density polyethylene copolymerised with vinyl acetate (LDPE-EVA), medium-density polyethylene (MDPE) or mixtures thereof and/or a PE having a melting temperature less than 135 C.

7. The tyre according to any one of the preceding claims wherein said self-supporting thermoplastic film has one or more of the following parameters: a) a load for elongation at break greater than 15 MPa, preferably greater than 20 MPa and/or a load for 5% elongation greater than 6 MPa, preferably greater than 8 MPa, more preferably comprised between 9 and 16 MPa, evaluated according to ASTM D882 on a sample with 12.57 mm width deformed at the speed of 500 mm/min at 23 C.; b) an elongation at break (AR) greater than 100% in the longitudinal direction, preferably greater than 150%, more preferably equal to or greater than 200%, evaluated according to ASTM D882 on a sample with 12.57 mm width deformed at the speed of 500 mm/min at 23 C.; c) a residual elastic force per linear centimetre of width of the film, about 5 minutes after reaching 50% deformation, that is generally less than 3.6 N/cm, preferably less than 3.0 N/cm, more preferably less than 2.8 N/cm, preferably comprised between 2.75 and 1.75 N/cm.

8. The tyre according to any one of the preceding claims, wherein said self-supporting thermoplastic film, before shaping, has a thickness less than 100 m, preferably less than 50 m, more preferably less than 40 m or 30 m.

9. The tyre according to any one of the claims 1 to 7 wherein the sealing composition has a dynamic modulus value G* measured at 10 Hz and at 60 C. that is greater than 0.03 MPa, preferably greater than 0.04 MPa, still more preferably greater than 0.06 MPa

10. The tyre according to any one of the preceding claims, wherein said sealing composition layer, before shaping, has a thickness less than 8 mm, preferably less than 7 mm, more preferably less than 6 mm.

11. The tyre according to any one of the preceding claims wherein the sealing composition comprises one or more plasticisers in an overall quantity of less than 200 phr, more preferably less than 100 phr, still more preferably less than 80 phr.

12. A self-sealing tyre for vehicle wheels obtained by vulcanisation of a green or partially vulcanised tyre according to any one of the claims 1 to 11.

13. Process for producing a self-sealing tyre for vehicle wheels according to claim 12, comprising: a) forming, on a forming drum, a green tyre comprising a carcass structure (2), a tread band (7) applied in radially outer position to said carcass structure (2), optionally a layer of elastomeric material substantially impermeable to air (liner) (9) applied in radially inner position to said carcass structure (2), a sealing composite (12) applied to the radially more internal surface of said tyre, axially extended at least at a crown portion of the tyre, b) arranging an expandable vulcanisation chamber; c) expanding said expandable vulcanisation chamber within said green tyre in a manner so as to shape, mould and vulcanise the green tyre and to obtain a finished self-sealing tyre, wherein said sealing composite (12) comprises a self-supporting thermoplastic film (11) comprising at least 50% by weight with respect to the weight of the film itself of at least one or more polyolefins, wherein the at least one polyolefin is characterised by a fluidity index (MFI) less than 4, preferably less than 2, more preferably less than 1.5, still more preferably less than 1 gram per 10 minutes evaluated according to ASTM D1238 at 190 C./2.16 Kg, and a sealing composition layer (10) associated with and supported by said self-supporting thermoplastic film (11); wherein the self-supporting thermoplastic film (11) is radially inside the sealing composition layer (10) and said sealing composition layer (10) is placed substantially in contact with the radially more internal surface of said tyre.

14. A sealing composite (12) for tyres comprising at least a self-supporting thermoplastic film (11) comprising at least 50% by weight with respect to the weight of the film itself of at least one or more polyolefins, wherein the at least one polyolefin is characterised by a fluidity index (MFI) less than 4, preferably less than 2, more preferably less than 1.5, still more preferably less than 1 gram per 10 minutes evaluated according to ASTM D1238 at 190 C./2.16 Kg), and a sealing composition layer (10) associated with and supported by said self-supporting thermoplastic film (11).

15. A sealing composite according to claim 14 wherein: said self-supporting thermoplastic film also comprises from 1 to 50%, preferably from 10 to 40%, more preferably from 15 to 35% by weight of one or more polar polymers selected from among polyvinyl acetate, ethylene-vinyl acetate copolymers, EVOH, polyvinyl acetate with a high level of hydrolysis, polyvinyl alcohol (PVA, PVOH) or mixtures thereof; and/or said self-supporting thermoplastic film comprises at least 50%, 60%, 70%, 80%, 90% of a polyethylene having a fluidity index (MFI) less than 4.0, preferably less than 2.0, more preferably less than 1.5, still more preferably less than 1 gram per 10 minutes according to ASTM D1238, 190 C./2.16 Kg, and/or said sealing composition comprises one or more plasticisers in an overall quantity of less than 200 phr, more preferably less than 100 phr, still more preferably less than 80 phr; and/or said sealing composition has a dynamic modulus value G* measured at 10 Hz and at 60 C. greater than 0.03 MPa, more preferably greater than 0.04 MPa, still more preferably greater than 0.06 MPa.

Description

[0190] Such description will be set forth hereinbelow with reference to the enclosed drawings, provided only by way of a non-limiting example, in which:

[0191] FIG. 1 schematically shows, in radial half-section, a self-sealing tyre for vehicle wheels;

[0192] FIG. 2 shows a section of a sealing composite associated with two elongated elements made of elastomeric material and intended to form part of the self-sealing tyre of FIG. 1;

[0193] FIG. 3 represents a section of a multilayer sealing composite comprising the sealing composite of FIG. 2 and a second removable protective film;

[0194] FIG. 4 is the comparative graphical representation of the relaxation under stress of two self-supporting films, one with polyamide base (comparative example C of the prior art) and the other with polyolefin base (according to the invention, example 1);

[0195] FIG. 5 is a photograph which shows the corrugations of the self-supporting film, the deformation and the separation of the joint of a green semifinished product comprising a sealing composite with polyamide film;

[0196] FIGS. 6a and 6b are photographs which frame corresponding portions of a comparative tyre (6a film made of polyamide C) and of a tyre of the invention (6b film made of polyolefin), and show that the holes are decidedly more evident in the tyre of the invention.

[0197] In FIG. 1, reference number 1 indicates a self-sealing tyre for vehicle wheels, which generally comprises a carcass structure 2 comprising at least one carcass ply 3 having respectively opposite end flaps engaged with respective anchoring annular structures 4, possibly associated with elastomeric fillers 4a, integrated in the zones 5 normally identified with the name beads. The at least one carcass ply 3 comprises a plurality of textile or metallic reinforcing cords arranged parallel to each other and at least partially covered with a layer of elastomeric material.

[0198] The carcass structure 2 is associated with a belt structure 6 comprising one or more belt layers, situated radially superimposed with respect to each other and with respect to the carcass ply 3, typically having metallic reinforcing cords.

[0199] Such reinforcing cords may have crossed orientation with respect to the direction of circumferential extension of the tyre 1.

[0200] In radially outer position with respect to the belt structure 6, a tread band 7 is applied that is made of elastomeric composition, like other semifinished products constituting the tyre 1.

[0201] Respective sidewalls 8 made of elastomeric composition are also applied in an axially outer position on the lateral surfaces of the carcass structure 2, each extended from one of the lateral edges of the tread band 7 up to the respective anchoring annular structure to the beads 5.

[0202] A radially inner surface of the tyre 1 is also preferably internally covered with a layer of elastomeric material substantially impermeable to air, or so-called liner 9.

[0203] In the embodiment illustrated in FIG. 1, the tyre 1 is of the type for motor vehicles.

[0204] Typically, in this case the belt structure 6 further comprises at least one radially outer layer comprising textile or metallic cords or a combination of textile/metallic cords, arranged according to an angle that is substantially zero with respect to the circumferential extension direction of the tyre.

[0205] In accordance with alternative embodiments of the present invention, the tyre 1 is of the type intended for heavy vehicle use.

[0206] In accordance with further embodiments of the present invention, the tyre 1 is for motorcycles. The profile of the cross section of the tyre for motorcycles (not illustrated) has a high transverse curvature since it must ensure a sufficient footprint area in all motorcycle tilt conditions. The transverse curvature is defined by the value of the ratio between the distance f of the top of tread from the line passing through the laterally opposite ends of the tread itself, measured on the equatorial plane of the tyre, and the width C defined by the distance between the laterally opposite ends of the tread itself. With tyre with high transverse curvature, a tyre is indicated whose transverse curvature ratio (f/C) is at least 0.20.

[0207] The self-sealing tyre 1 according to the invention also comprises a sealing composition layer 10 arranged at a crown zone of the tyre 1 and in radially inner position with respect to the liner 9. The sealing composition layer 10 is extended for the entire circumferential extension of the tyre 1. The sealing composition layer 10 has preferably a maximum thickness t1 substantially at the equatorial plane X of the finished tyre 1, i.e. moulded and vulcanised, and is thinned towards the axial ends of the crown zone (FIG. 1). Preferably, said maximum thickness t1 is comprised between about 2 mm and about 6 mm still more preferably between about 2.5 mm and 4.0 mm.

[0208] In the present description, with the term phr (acronym of parts per hundred of rubbers) it is intended to indicate parts by weight per 100 parts by weight of total elastomer base. For the calculation of 100 parts of total elastomer base, possible additives are not considered (such as possible elastomeric resins or extension oils).

[0209] The sealing composition comprises, according to a first preferred embodiment, from 55 to 95 phr of one or more natural or synthetic elastomers, from 5 to 45 phr of a pre-cross-linked elastomer, from 5 to 50 phr of at least one bonding resin and from 1 to 40 phr of at least one reinforcing filler. According to a particularly preferred embodiment, the sealing composition also comprises from 25 to 65 phr of plasticiser (oil or liquid polymer), from 0.05 phr to 1 phr of at least one peptising agent and from 0.1 to 6 phr of at least one cross-linking agent; in addition, the sealing composition can comprise from about 1 phr to about 20 phr of at least one homogenising agent.

[0210] According to a second preferred embodiment, the sealing composition comprises from 20 phr to 100 phr of at least one unsaturated styrene thermoplastic elastomer, from 0 to 80 phr of at least one synthetic or natural elastomer, from 20 to 200 phr, preferably from 30 phr to 150 phr, of at least one bonding resin, from 0.1 to 6 phr of at least one cross-linking agent, from 10 phr to 200 phr, preferably from 20 phr to 60 phr, of plasticiser (oil or liquid polymer), and preferably from 1 to 40 phr, preferably from 5 to 30 phr, of at least one reinforcing filler.

[0211] According to a preferred embodiment the sealing composition can also comprise from about 1 phr to about 20 phr of at least one homogenising agent. In a further embodiment the sealing composition can also comprise from 0.05 phr to 5 phr of at least one peptising agent.

[0212] Preferably, the synthetic or natural elastomers included in the sealing composition can be selected from among those commonly used from among the elastomeric materials cross-linkable with sulfur or peroxides, which are particularly suitable for producing tyres, i.e. from the elastomeric polymers or copolymers with an unsaturated chain having a vitreous transition temperature (Tg) generally below 20 C., preferably in the range from 0 C. to 110 C. These polymers or copolymers can be of natural origin or they can be obtained by means of polymerisation in solution, polymerisation in emulsion or polymerisation in gaseous phase of one or more conjugated diolefins, optionally mixed with at least one comonomer selected from among monovinylarenes and/or polar comonomers in a quantity not greater than 60% by weight. The conjugated diolefins generally contain from 4 to 12, preferably from 4 to 8 carbon atoms and can be selected, for example, from the group comprising: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, or mixtures thereof. 1,3-Butadiene or isoprene are particularly preferred.

[0213] The polar comonomers that can be possibly used can be selected, for example, from among: vinylypyridine, vinylquinoline, acrylic acid esters and alkylacrylic acid esters, nitriles, or mixtures thereof, such as methylacrylate, ethylacrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, or mixtures thereof.

[0214] Preferably, the synthetic or natural elastomer included in the sealing composition can be selected, for example, from among: cis-1,4-polyisoprene (natural or synthetic rubber, preferably natural rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high content of 1,4-cis), isoprene/isobutene copolymers, possibly halogenated, 1,3-butadiene/acrylonitrile copolymers, styrene/1,3-butadiene copolymers, styrene/isoprene/1,3-butadiene copolymers, styrene/1,3-butadiene/acrylonitrile copolymers, or mixtures thereof.

[0215] According to a preferred embodiment, the pre-cross-linked elastomer is a butadiene-styrene copolymer produced with a process of polymerisation under hot emulsion, with a styrene content from 2 to 50% by weight, preferably from 15% to 35%. Particularly preferred are the grades SBR1009, 1009AF and 4503C produced by Lion Elastomers.

[0216] According to a preferred embodiment, the unsaturated styrene thermoplastic elastomer is a styrene-diene-styrene polymer, preferably selected from among styrene/butadiene/styrene (SBS) block copolymer, styrene/isoprene/styrene (SIS) block copolymer, styrene/butadiene/isoprene/styrene (SBIS) block copolymer, and mixtures thereof, also optionally comprising the corresponding diblock thermoplastic elastomers, such as styrene-butadiene (SB) and styrene-isoprene (SI). Particularly preferred are the styrene/isoprene/styrene block copolymer or mixtures of one or more unsaturated styrene thermoplastic elastomers containing at least 50% of styrene/isoprene/styrene block copolymer.

[0217] Preferably the block copolymer has a content of styrene from about 10% to about 30%, more preferably from about 12% to about 18%.

[0218] Preferably the block copolymer has a percentage of diblock less than 70%, still more preferably less than 60%.

[0219] Preferably the percentage of diblock is comprised between 15% and 55%.

[0220] With diblock percentage, it is intended the percentage of block polymer constituted by only two segments: a polystyrene segment and an elastomeric segment.

[0221] Even if such diblocks are present in the block polymers mainly constituted by three segmentsstyrene-elastomer-styrene and are considered to be an impurity due to the imperfect efficiency of the living polymerisation, the Applicant deems that the presence of diblocks can be advantageously modulated in order to improve the quality of the sealing composition.

[0222] It is deemed that with an increased percentage of diblock, there is a corresponding greater stickiness, but smaller modulus and lesser cohesion of the sealing composition.

[0223] Particularly preferred are styrene/isoprene/styrene block copolymers with a content of styrene equal to or less than 20%, more preferably comprised between 14% and 20%.

[0224] Such copolymers are for example sold with the name Europrene SOL T190, T9133 by Polymers Europa, Vector 4113, 4114 by Dexco Polymers, Kraton D1111, D1112 and D1107J by Kraton.

[0225] The bonding agents advantageously used in the present invention can be selected from the group of hydrocarbon resins, phenol-based resins, coal-based resins, xylene-based resins and natural resins such as rosin-based resins or terpene-based resins, having an average molecular weight comprised between 200 and 50000, typically between 500 and 10000 and which provides stickiness when the resin is mixed with natural or synthetic rubber.

[0226] The aforesaid average numeric molecular weight (Mn) can be measured according to techniques known in the field, such as by means of gel permeation chromatography (GPC). Examples of hydrocarbon resin commercial products comprise resins based on aromatic petrols such as PETCOAL produced by Tosoh Co., Ltd; C5/C9 hydrocarbon-based resins such as PETROTACK produced by Tosoh Co; C5 hydrocarbon-based resins such as Escorez 1102 (produced by Exxon Mobil).

[0227] Examples of phenol-based resins comprise resins with alkylphenol-formaldehyde base, and derived resins modified with rosin, resins with alkylphenol-acetylene base, modified alkylphenol and terpene-phenol resins. Specific examples indicated by brand comprise commercial products such as RESINA SP-1068 (produced by SI GROUP Inc.) which is an octylphenol-formaldehyde resin, and KORESIN (produced by BASF Company) which is a p-t-butylphenol-acetylene resin.

[0228] Examples of coal-based resins include coumarone-indene resins. Specific examples comprise commercial products, mentioned by brand, such as NOVARES C resins (produced by RUTGERS CHEMICAL GmbH) which are indene-coumarone synthetic resins (such as NOVARES C10, C30, and C70).

[0229] Examples of natural resins are the rosin resins and the terpene resins, which can be as is or modified: examples of these classes are the terpene resins DERCOLYTE produced by DRT, the resins derived from rosin acids DERTOLINE, GRANOLITE and HYDROGRAL produced by DRT.

[0230] Examples of xylene-based resins comprise the xylene-formaldehyde resins.

[0231] The aforesaid bonding agents can be used on their own or mixed with each other.

[0232] Suitable cross-linking agents are sulfur or molecules containing sulfur, in the presence of compounds containing zinc and fatty acids, or peroxides.

[0233] Specific examples of molecules containing sulfur usable as cross-linking agents in the sealing materials for the obtainment of self-sealing tyres are elementary sulfur, thiurams, such as tetraisobutyl thiuram disulfide or tetrabenzyl thiuram disulfide, or dithiophosphates, such as zinc dibutyldithiophosphate, or dithiocarbamates, such as zinc dimethyl dithiocarbamate, together with ZnO or compounds containing zinc, fatty acids and sulfenamides, such as N-t-butyl-2-benzothiazyl sulfenamide (TBBS) or N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), or thiazoles, such as 2,2-dithiobis-(benzothiazole) (MBTS).

[0234] Specific examples of peroxides usable as cross-linking agents in the sealing materials for the obtainment of self-sealing tyres are organic peroxides such as dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane (DBPH), bis-(2,4-dichlorobenzoyl) peroxide (DCBP), di-t-butyl-peroxide. Preferably, a peroxide is used as cross-linking agent, still more preferably 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane (DBPH).

[0235] A specific example of usable DBPH is a mixture of 45% DBPH with calcium carbonate and silica sold with the name Luperox 101 XL45 by Arkema.

[0236] The quantity of peroxide is preferably comprised between about 0.1 phr and about 6 phr.

[0237] The presence of peroxide or sulfur or another cross-linking agent allows the partial chemical cross-linking of the sealing composition during the vulcanisation of the tyre in a manner so as to improve the dynamic sealing characteristics of the sealing composition layer.

[0238] At least one reinforcing filler can be advantageously added to the abovementioned sealing composition, in a quantity generally from 1 phr to 40 phr, preferably from 5 phr to 15 phr. The reinforcing filler can be selected from among those commonly used for cross-linked products, in particular for tyres, such as carbon black, silica, aluminium, aluminosilicates, calcium carbonate, kaolin or mixtures thereof. Particularly preferred are carbon black, silica and mixtures thereof.

[0239] At least one or more plasticisers can be added to the sealing composition selected from among the oils (extender oils) or liquid polymers commonly used in the field, in an overall quantity preferably less than 200 phr, more preferably less than 100 phr, still more preferably less than 80 phr.

[0240] Examples of suitable plasticiser oils are polyolefin oils, paraffin oils, naphthenic oils, aromatic oils, mineral oils and mixtures thereof.

[0241] Examples of suitable liquid polymers are the liquid polymers with butadiene base (BR), isoprene base (IR), isoprene/butadiene base (IBR), styrene/butadiene base (SBR), possibly hydroxy and epoxy functionalisation, or depolymerised natural liquid polymers (NR).

[0242] According to a preferred embodiment, said reinforcing filler of carbon black can be selected from among those which have a surface area not less than 20 m.sup.2/g (determined by the STSAStatistical Thickness Surface Areaaccording to ISO 18852:2005).

[0243] In radially inner position with respect to the sealing composition layer 10 and in contact with said sealing composition layer 10, a self-supporting thermoplastic film 11 made of polyolefin is arranged. The self-supporting thermoplastic film 11 is extended, as the sealing composition layer 10, over the entire circumferential extension of the tyre 1 and has a width or an axial extension slightly less than the axial extension of said layer 10.

[0244] Preferably, said self-supporting thermoplastic film 11 is essentially constituted by a polyolefin characterised by a fluidity index (MFI) less than 4, preferably less than 2, more preferably less than 1.5, still more preferably less than 1 gram per 10 minutes (ASTM D1238, 190 C./2.16 Kg), preferably by a polyethylene selected from among those sold with the name Exxon LL 1201 KG [LLDPE MFI 0.70 g/10 min @190 C./2.16 Kg; 1250 ppm slip agent], Exxon Enable 20-05 HH [m-PE MFI 0.50 g/10 min @190 C./2.16 Kg, no slip agent], Exxon Exceed 1012 MK [m-VLDPE MFI 0.50 g/10 min @190 C./2.16 Kg, 1000 ppm slip agent]) or mixtures thereof.

[0245] Alternatively, said self-supporting thermoplastic film 11 comprises at least 50%, at least 60%, at least 70% of a polyolefin or multiple polyolefins.

[0246] Alternatively, said self-supporting thermoplastic film 11 is constituted by 1 to 50%, preferably from 10 to 30%, more preferably from 15 to 25% by weight of one or more polar polymers selected from among polyvinyl acetate, ethylene-vinyl acetate copolymers, EVOH, polyvinyl acetate with a high level of hydrolysis, polyvinyl alcohol (PVA, PVOH) or mixtures thereof, the remainder up to 100% by weight being constituted by a polyolefin or by two or more polyolefins mixed together.

[0247] More preferably the self-supporting thermoplastic film 11 is a film overall containing 80% polyolefins and 20% polyvinyl alcohol, with MFI equal to 0.60 grams per 10 minutes (ASTM D1238, 190 C./2.16 Kg), melting peaks at 107 C., 119 C. and 170 C. (the latter relative to PVOH) measured as maximums in the DSC trace obtained in a scan from 50 C. to 200 C. at 10 C./min.

[0248] Preferably, the self-supporting thermoplastic film 11 has an elongation at break greater than 100%, more preferably greater than 150%, still more preferably equal to or greater than 200% in longitudinal direction, evaluated according to ASTM D882 on a sample with 12.57 mm width deformed at the speed of 500 mm/min at 23 C.

[0249] Preferably, in the finished tyre, said self-supporting thermoplastic film 11 has a thickness t2 comprised between about 10 m and about 40 m.

[0250] The sealing composition layer 10 and the self-supporting thermoplastic film 11 form a sealing composite 12. The sealing composite 12, when a pointed element (such as a nail) penetrates into the tyre and traverses the sealing composition layer 10 and the self-supporting thermoplastic film 11, is able to adhere to the object inserted therein and can also flow into the hole when such object is removed, thus sealing the hole itself and preventing the outflow of air from the tyre. The sealing composite 12 can be easily perforated by the pointed element, while maintaining a deformability and stickiness such to contribute the transfer of the sealing composition during the expulsion of the pointed element. The perforations thus sealed are clearly visible on the surface of the sealing composite, through the self-supporting film 11 (FIG. 6b).

[0251] The tyre 1 also comprises preferably two elongated elements made of elastomeric material 13, each arranged at a circumferential edge of the sealing composite 12. An axially inner portion 13a of each elongated element made of elastomeric material 13 is preferably superimposed on the sealing composite 12 and is arranged in radially inner position with respect to said sealing composite 12. An axially outer portion 13b of each elongated element made of elastomeric material 13 lies in contact with the liner 9. By axially inner portion 13a, it is intended a portion closer to an equatorial plane X of the tyre 1 with respect to the axially outer portion 13b.

[0252] More in detail, the radially inner portion 13a in turn preferably has an axially inner zone applied directly on the self-supporting thermoplastic film 11 and an axially outer zone directly applied on a surface of the sealing composition layer 10. In fact, the sealing composition layer 10 preferably has an axial extension greater than the axial extension of the self-supporting thermoplastic film 11. It follows that each elongated element made of elastomeric material 13 is in contact both with the sealing composition layer 10 and with the self-supporting thermoplastic film 11.

[0253] The building of a precursor of a tyre 1, as described above, including the sealing composite 12, is preferably actuated by means of assembly of respective semifinished products on one or more forming supports, not shown.

[0254] The carcass structure and the belt structure are generally made separately from each other in respective work stations, in order to be mutually assembled at a later time.

[0255] More particularly, the obtainment of the carcass structure first provides for the formation of the sealing composite 12 as a continuous belt comprising the sealing composition layer 10 arranged on the and supported by the self-supporting thermoplastic film 11 joined to the elongated elements in elastomeric material 13 associated with opposite longitudinal edges of the abovementioned sealing composite 12 (FIG. 2). Preferably, before incorporation of the sealing composite 12 in the precursor of the tyre 1 and the shaping thereof, each elongated element 13 is in contact with the self-supporting thermoplastic film 11 for a first width L1 and with the sealing composition layer 10 for a second width L2. Said widths are preferably substantially equal to each other.

[0256] The sealing layer 10, before incorporation of the sealing composite 12 in the precursor of the tyre 1 and the shaping thereof, has a thickness t3 comprised between about 3 mm and about 7 mm.

[0257] The self-supporting thermoplastic film 11, before incorporation of the sealing composite 12 in the precursor of the tyre 1 and the shaping thereof, has a thickness t4 less than 50 m and preferably comprised between about 15 and 30 m.

[0258] The sealing composite 12 provided with the respective elongated elements made of elastomeric material 13 is cut to size, preferably with angled (chamfer) cutting and wound around a radially outer surface of a building drum, maintaining the thermoplastic film 11 in a radially more internal position. Opposite end flaps of the sealing composite 12 are mutually joined due to the adhesivity of the sealing composition; preferably the joint is covered (in order to prevent the outflow of sealing composition at the time of vulcanisation) and consolidated by means of (for example) an adhesive tape (joint). Preferably the aforesaid adhesive tape is made via coupling of an adhesive to a self-supporting thermoplastic film, similar or equal to that used in the sealing composite itself; preferably therefore a thermoplastic adhesive film will be used. In such a manner, one avoids a concentration of stress at the edge of the thermoplastic adhesive film itself, and one reduces the possibilities of separation of the thermoplastic adhesive film after shaping and of local tearing of the self-supporting film close to the edge of the thermoplastic adhesive film, as could instead occur in the case of a generic adhesive tape, typically much more rigid than the self-supporting thermoplastic film that is the object of the invention. As adhesives, the following can be used: the adhesive produced by 3M with the name 9472 LE, or the adhesive produced by NITTO with the name 5015T.

[0259] The liner 9 and the carcass ply or plies 3 are applied on the sealing composite 12 to form a so-called carcass sleeve, typically substantially cylindrical. The anchoring annular structures 4 to the beads 5 are fit or formed on the opposite end flaps of the carcass ply or plies 3, which are subsequently turned up around the annular structures 4 themselves so as to enclose them in a kind of noose.

[0260] On a second drum or auxiliary drum, a so-called outer sleeve is obtained comprising the belt layers 6 applied in mutual radial superimposition, and possibly the tread band 7 applied in radially outer position to the belt layers 6. The outer sleeve is then picked up from the auxiliary drum in order to be coupled to the carcass sleeve. The outer sleeve is for such purpose arranged coaxially around the carcass sleeve, after which the carcass ply or plies 3 are shaped according to a toroidal configuration by means of mutual axial approaching of the beads 5 and simultaneous introduction of pressurised fluid within the carcass sleeve, so as to cause a radial expansion of the carcass plies 3 until they are made to adhere against the inner surface of the outer sleeve.

[0261] Following the shaping, the thermoplastic film shows a tension relaxation such that the residual elastic tension does not cause deformation of the green tyre or cause the separation of its radially inner layers. The residual elastic tension of the film about 5 minutes after reaching 50% deformation (using a speed of deformation of 500 mm/min, on a 200 mm20 mm rectilinear test piece preloaded to 0.4 N) must preferably be less than 3.6 N/cm (Newton per linear centimetre of width of the film), more preferably less than 3.0 N/cm, still more preferably less than 2.8 N/cm.

[0262] The assembly of the carcass sleeve with the outer sleeve can be actuated on the same drum used for making the carcass sleeve, and in such case is termed single-stage building process or unistage process. Building processes are also known of the so-called two-stage type, in which a so-called first-stage drum is employed for making the carcass sleeve, while the assembly between the carcass structure and the outer sleeve is actuated on a so-called second-stage drum or shaping drum, onto which the carcass sleeve picked up from the first-stage drum and subsequently the outer sleeve picked up from the auxiliary drum are transferred.

[0263] Following the building of the green tyre 1, a moulding and vulcanisation treatment is executed, aimed to determine the structural stabilisation of the tyre 1 by means of cross-linking of the elastomeric compositions as well as to impart, on the tread band 7, a desired tread pattern and at the sidewalls 8 possible distinctive graphic marks. During vulcanisation, between the elastomer macromolecules of the sealing composition, a network of covalent bonds is created which, in accordance with its density, prevents the sliding thereof, rendering the material increasingly insoluble, infusible and elastic. After vulcanisation, the sealing composition layer 10 attains optimal characteristics of deformability, cohesion and stickiness.

[0264] During vulcanisation, notwithstanding the high temperatures employed, the self-supporting thermoplastic film 11 and the sealing composition 10 remain integral, they do not damage the vulcanisation chamber and they attain optimal sealing performances.

[0265] Alternatively, the sealing composite can be applied to the radially more internal surface of the tyre partially or completely vulcanised and optionally be subjected to subsequent thermal and/or chemical consolidation treatments.

[0266] In FIG. 3, the sealing composite 10 of FIG. 2 is covered with a second removable protective film 14 in order to make the multilayer sealing composite 15. The multilayer sealing composite 15 can be prepared, for example via extrusion of the sealing composition 10 on the second protective film 14 and mechanical coupling with the self-supporting thermoplastic film 11 and the lateral elongated elements 13 to give the strip-like composite, which is cooled and generally preserved wound in a reel.

EXAMPLES

[0267] Traction Test

[0268] In order to characterise the self-supporting film, a traction test was executed on two test pieces of film A and on two test pieces of film B according to provision ASTM D882, in the following test conditions: [0269] test temperature 23 C. [0270] relative humidity 46% [0271] test speed=500 mm/min [0272] test piece width 12.57 mm

[0273] The results of the test are reported in the following table 1.

TABLE-US-00001 TABLE 1 Elongation Film Composition Properties at break (%) A-Exxon Polyethylene d: 0.920 g/cm3 400 Enable 20-05 MFI: 0.50 25 m Melting Temp peak 114 C. B Polyolefins 80% MFI: 0.60, 245 25 m Polyvinyl Melting Temp alcohol 20% peaks at 107 C., 119 C. and 170 C. (the latter relative to PVOH) MFI: g/10 min, ASTM D1238, 190 C./2.16 Kg Melting temperature peaks: measured as maximums in the DSC trace obtained in a scan from 50 C. to 200 C. at 10 C./min.

[0274] Mechanical Stability of the Sealing Composite

[0275] In the scope of the above-described test (ASTM D882), the force was also measured for an elongation of 5% per cm of width of various film samples, comparison C and according to the invention A and B, as an indication of the mechanical stability of the semifinished product, i.e. of the sealing composite comprising the self-supporting film, the sealing composition and, preferably, the two elongated elements.

[0276] The types of self-supporting film tested and the respective measured force values are shown in the following Table 2:

TABLE-US-00002 TABLE 2 Normalised force for 5% elongation Nominal vs. thickness Force thickness Film Composition (micron) (N/cm) (MPa) A Exxon Enable Polyethylene 25 2.5 10 20-05 HH B Polyolefins 80% 25 3 12 Polyvinyl alcohol 20% C Filmon CXS18 Polyamide 18 7.2 40

[0277] It is indicated that all the tested materials have good rigidity at low elongation. A typical sealing composite with 20 cm width and 5 mm thickness has a linear weight of about 1 Kg per m, and hence due to its weight is able to exert forces on the order of 10N on the self-supporting thermoplastic film for a meter of non-supported semifinished product.

[0278] From the data reported in table 2, it is inferred that the three above-considered films are deformed (5% elongation deformation) only with very high forces, between 50 N and 144 N (7.2 N/cm*20 cm of width). The forces detected for 5% elongation of the test piece are indicative of the forces necessary for inducing smaller deformations, shown in FIG. 4 by the initial slope of the curve. Even if the polyolefin films A and B are less rigid than the polyamide C, such lower rigidity does not negatively affect the behaviour.

[0279] Test for Evaluating the Residual Force

[0280] A comparative test was also executed by comparing residual force on two samples of self-supporting film (200 mm20 mm, cut in longitudinal direction with respect to the extension of the film reel and preloaded to 0.4 N), the first made of polyolefin according to the invention (film B with 25 micron nominal thickness) and the second the comparative sample made of polyamide C (Filmon CXS18, with 18 micron nominal thickness). The test piece was conditioned for 24 hours at 23 C. and 45% relative humidity.

[0281] The test was executed by means of dynamometer Zwic model 1445, the force values encountered in the test, which led to an elongation up to 50% at the speed of 500 mm/sec and the subsequent maintenance of such deformation for overall 5 minutes, are reported in FIG. 4.

[0282] With the sample made of polyolefin according to the invention (example 1), the residual force exerted in the step of maintaining the deformation after traction is always less than that of the sample made of polyamide (comparative example), notwithstanding the greater thickness of the test piece according to the invention, and it settles on values below 6 N (i.e. less than 3 N/cm of width, that is less than 12 MPa) while for the test piece made of polyamide values greater than 7.2 N are observed (i.e. greater than 3.6 N/cm and 20 MPa).

[0283] Notwithstanding a moderate reduction of the residual force of the film made of polyolefin with respect to that made of polyamide, there is a considerable improvement of the stability over time of the green tyre, and in particular of the joint of the semifinished product, which passes from several hours (after 16 hours the semifinished products with polyamide film have extensive detachments at the joint and at the elongated elements) to a time greater than 48 h (with polyolefin films, no significant openings of the joint were observed, nor was any separation observed at the elongated elements for at least 2-3 days).

[0284] Sealing Composition

[0285] The sealing composition of the following table 3, according to the patent application WO2009143895, was used for the preparation of the sealing layer.

TABLE-US-00003 TABLE 3 Components phr IR 60 SBR 1502 30 SBR 1009 10 Luperox 101 XL45 0.56 Process oil 45 6-PPD 2 Escorez 1102 40 Struktol 40MS 7 N326 12 IR is a cis-1,4-polyisoprene elastomer produced by Nizhnekamskneftechim Export, Russia; SBR 1502 is a styrene-butadiene elastomeric copolymer produced by Lanxess and sold as Buna SE 1502 SBR 1009 is a butadiene-styrene pre-cross-linked elastomeric copolymer produced with a process of polymerisation under hot emulsion by Lion Polymers; Luperox 101 XL45 is a peroxide produced by Arkema Process oil is (MES-mild extraction solvates) mineral-based oil that is highly refined with solvent and/or via hydrotreatment (Catenex SNR produced by Shell); Escorez 1102 is an aliphatic bonding resin produced by ExxonMobil; 6-PPD is N-(1,3-Dimethylbuty1)-N'-phenyl-p-phenylenediamine, antioxidant and antiozonant produced by Eastman; Struktol 40MS is a mixture of aromatic aliphatic-napthenic hydrocarbon resins (Struktol Corporation); N326 is carbon black produced by Birla.

[0286] Dynamic Properties

[0287] The dynamic properties of the sealing composition were measured with a rheometer RPA 2000 by Alpha Technologies. The samples were placed in a chamber between two striated biconical plates. After closure, the volume of the chamber is about 4.5 cm.sup.3. One of the plates is fixed, the other in sinusoidal oscillation around its centre. A deformation of 20% was set and a frequency scan between 0.1 and 20 Hz carried out. The temperature inside the chamber was set at 60 C. The quantities evaluated were the dynamic shear modulus G* and the tan delta loss factor, wherein:

[0288] G*=root sum of the squares of G and G, dynamic shear modulus in MPa;

[0289] G: elastic dynamic shear modulus in MPa;

[0290] G: viscous dynamic shear modulus in MPa;

[0291] Delta (D)=displacement between the set deformation and the measured stress;

Tan delta=G/G

The sealing compositions according to the invention showed (at 10 Hz and at 60 C., 10% deformation) a value of G* equal to 0.07 and a tan delta of 0.35.

[0292] Preparation of Self-Sealing Tyres

[0293] The sealing composition layer, before building the tyre, had a thickness of about 4.8 mm and the sealing composite was deposited in radially inner position on the liner (as illustrated in FIG. 1).

[0294] The moulded and vulcanised tyres were mounted on a standard rim and inflated to the pressure of 2.4 bar.

Example 1

[0295] The sealing composition according to the formulation of table 3 was used for preparing, via extrusion, two sealing composites with thickness of about 5 mm, comprising a removable film made of siliconised polyester, 251 mm lateral elongated elements made of rubber and, respectively, according to the invention, the self-supporting film made of polyolefins (film B) with 25 micron nominal thickness, and the self-supporting film made of Nylon (C) with 18 micron nominal thickness for comparison.

[0296] The two composites were used for preparing self-sealing tyres of size 215/60R16 comprising a sealing composite with thickness of about 3 mm comprising a sealing composition as in table 3, together with a self-supporting thermoplastic film made of polyolefins (film B, invention) and self-sealing tyres of size 215/60R16 comprising a sealing composite with thickness of about 3 mm, with the same composition but comprising a self-supporting film made of polyamide (C).

[0297] Dynamic Sealing Test Under Cold Conditions

[0298] The sealing capacity in low temperature conditions was verified according to the following procedure:

[0299] 1) Through the tread of the above-described self-sealing tyres 215/60R16, mounted on standard rims and inflated to the pressure of 2.4 bar, 3 nails of 3, 4 and 5 mm diameter were inserted, having length of 40 mm, for a total of 9 nails per tyre (3 for each diameter). The zone of the tread to be perforated corresponded with the belts. The arrangement of the nails comprised blocks and notches and it was circumferentially random.

[0300] 2) A VW Tiguan car was equipped with 4 self-sealing tyres 215/60R16 according to the invention, each perforated with 3 nails for each diameter as described above, while a second car VW Tiguan was equipped with 4 self-sealing tyres 215/60R16 with sealing composite comprising a self-supporting film made of aliphatic polyamide (Nylon), perforated in the manner.

[0301] 3) 1000 km were travelled on roads, mostly snowy, at the maximum speed of 120 km/h in environmental temperature conditions between 10 C. and 1 C. The tyres did not lose air for the entire period of the test.

[0302] 4) The tyres were dismounted from the cars and placed in a climatic chamber at 25 C. for 24 h.

[0303] 5) The tyres were removed from the climatic chamber and the nails were extracted while the tyres were still very cold and the loss of air was controlled with a solution of soapy water. The obtained results are summarised in the following table 4a, in the form of percentage of holes sealed (e.g. 83% signifies that 10 holes out of 12 total were sealed)

TABLE-US-00004 TABLE 4a 1000 km travel with nails, 24 hours at 25 C., extraction Percentage of holes Test sealed (hole diameter) Tyre size temperature Film (3 mm) (4 mm) (5 mm) 215/60 R16 25 C. Nylon- 83% 83% 58% comparison 215/60 R16 25 C. Polyolefin- 100% 100% 75% invention

[0304] 6) The cars were equipped with the tyres from which the nails were removed, the tyres were re-inflated and another 300 km were travelled at the maximum speed of 120 km/h in environmental conditions between 10 C. and 1 C. The air loss from the holes was further controlled with a solution of soapy water. The obtained results are summarised in the following table 4b, in the form of percentage of holes sealed:

TABLE-US-00005 TABLE 4b 1000 Km travel with nails, extraction, inflation, 300 km travel without nails Percentage of holes sealed (hole diameter) Size Film (3 mm) (4 mm) (5 mm) 215/60 R16 Nylon- 100% 100% 92% comparison 215/60 R16 Polyolefin- 100% 100% 100% invention

[0305] From the data of the tables 4a and 4b, it is indicated that a tyre according to the present invention, given the same composition and thickness of the sealing composition of the sealing composite, has a greater sealing capacity at low temperatures with respect to a tyre equipped with self-supporting film made of aliphatic polyamide (Nylon).

[0306] Recycling of the Semifinished Product

[0307] In the experience of the Applicant, it has been technically difficult and onerous to recycle the strip-like semifinished product comprising the sealing composition, the self-supporting film and preferably the lateral elongated elements (hence lacking the second removable protective film), when the support film has polyamide base. Indeed, it was found that pieces of film of size between several mm.sup.2 and a few cm.sup.2 pollute the resulting composition, not allowing the correct extrusion thereof. The removal of these polyamide fragments by filtration has proven very difficult and little effective.

[0308] The present thermoplastic film made of polyolefin allows an easy recycling of the semifinished product.

[0309] It is observed that, by introducing in the formulation of the sealing composition an aliquot of sealing composite (comprising the sealing composition, the self-supporting polyolefin film and the elongated elements, but lacking the second removable protective film) equal to about 10-20% by weight with respect to the original formulation, one obtains a composition that is not polluted by macroscopic film fragmentssubjecting it to filtration through two steel meshes with 18 mesh density (opening of 0.88 mm2) mounted at 45, no material was found to be retainedand that has sealing performances comparable to those of the original composition.

Example 2

[0310] The sealing composite according to the invention to be recycled, constituted by the thermoplastic film made of polyolefins (film B) with 25 micron nominal thickness, by the sealing composition (as in table 3, thickness 4.8 mm) and by 251 mm lateral elongated elements made of rubber, was added in a Banbury in a quantity of 25 phr (about 10% with respect to the finished composition) to the Master composition constituted by the polymers, by the carbon black CB, and by the 6-PPD and by the Struktol 40MS; the resulting masterbatch was then used for preparing a sealing composition according to the overall recipe reported in the following table 5. Analogously, a comparative sealing composition was prepared comprising a recycled sealing composite with film with polyamide base (C), according to the final recipe reported in Table 5:

TABLE-US-00006 TABLE 5 Composition Composition with recycled with recycled polyolefin film, Nylon film, 25 m (phr) 18 m (phr) (INVENTION) (COMPARISON) IR 60 60 SBR 1502 30 30 SBR 1009 10 10 Recycled 25 composite (Nylon) Recycled 25 composite (PO) N 326 12 12 6-PPD 2 2 Struktol 40MS 7 7 MES 45 45 Escorez 1102 40 40 Luperox 101 XL45 0.65 0.65 Key: IR is a cis-1,4-polyisoprene elastomer produced by Nizhnekamskneftechim Export, Russia; SBR 1502 is a styrene-butadiene elastomeric copolymer produced by Lanxess and sold as Buna SE 1502 SBR 1009 is a butadiene-styrene pre-cross-linked elastomeric copolymer produced with a process of polymerisation under hot emulsion by Lion Polymers; Luperox 101 XL45 is a peroxide produced by Arkema; N 326 is carbon black; 6-PPD is N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine, antioxidant and antiozonant produced by Eastman; Struktol 40MS is a mixture of aromatic aliphatic-napthenic hydrocarbon resins (Struktol Corporation); Process oil is (MES-mild extraction solvates) mineral-based oil that is highly refined with solvent and/or for hydrotreatment (Catenex SNR produced by Shell); Escorez 1102 is an aliphatic bonding resin produced by ExxonMobil.

[0311] The two sealing compositions were used for preparing two strip-like sealing composites with thickness of 4.8 mm, respectively comprising a self-supporting film made of polyolefins (film B) with 25 micron nominal thickness, according to the invention, and a self-supporting film made of Nylon with 18 micron (C) for comparison and lateral elongated elements made of rubber. The two semifinished products were used for the preparation of self-sealing tyres of size 215/55 R17, which showed the dynamic sealing performance reported in tables 6a and 6b.

[0312] Dynamic Sealing Test with Sealing Materials Comprising Recycled Materials

[0313] 1) Nails with 3, 4, 5 mm diameter, having 40 mm length, were inserted in the tread of a self-sealing tyre according to the invention (film B made of polyolefins with 25 micron nominal thickness and about 3 mm of sealing composition) and of a tyre comprising a self-supporting film made of polyamide, Filmon CXS18, 18 micron nominal thickness (C) and about 3 mm of sealing composition) inflated to the pressure of 2.4 bar. For both tyres, the sealing composition was obtained by using 25 phr (about 10% by weight) of recycled material of the semifinished product with the elongated elements and the respective film, as described above in Table 5.

[0314] The zone of the tread to be perforated corresponded with the belts. The arrangement of the nails comprised blocks and grooves and it was circumferentially random.

[0315] 12 nails were inserted for each of the 3 selected sizes (3, 4 and 5 mm diameter per 4 cm length) in each tyre.

[0316] The tyres were rolled, with the nails inserted, on a so-called road wheel, a disc with 2.8 m diameter, at the speed of 120 k m/h with a load of 550 kg.

[0317] 2) 500 km were travelled with the two tyres, alternating periods of 10 minutes with zero slip angle with periods of 10 minutes with slip angle oscillating from 6 to +6. The slip speed was 1/s: for each slip cycle, 25 oscillations were completed.

[0318] The tyres did not lose air for the entire testing period.

[0319] 3) The inserted nails were extracted and the air loss from the holes was controlled with a solution of soapy water. The obtained results are summarised in the following table 6a

TABLE-US-00007 TABLE 6 500 km of travel with nails Percentage of holes Sealing sealed (hole diameter) Tyre size composition Film (3 mm) (4 mm) (5 mm) 215/55R17 Comparative C-Nylon Filmon 100% 83% 92% composition CXS18- Table 5, comparison 10% recycled 215/55R17 Invention B-Polyolefins 100% 100% 92% composition invention Table 5, 10% recycled

[0320] 4) Another 10 km were travelled with 550 kg of load and slip angle oscillating from 2 to +2. The air loss from the holes was further controlled with a solution of soapy water. The obtained results are summarised in the following table 6b

TABLE-US-00008 TABLE 6b 500 km of travel with nails, extraction, 10 km travel without nails Percentage of holes Sealing sealed (hole diameter) Tyre size composition Film (3 mm) (4 mm) (5 mm) 215/55R17 Comparative C-Nylon 100% 83% 92% composition Filmon Table 5 CXS18- 10% recycled comparison 215/55R17 Invention B-Polyolefins 100% 100% 100% composition invention Table 5 10% recycled

[0321] From the data reported in table 6a and 6b, it is indicated that even in a recycled condition of the sealing composite, the tyre according to the present invention has a greater sealing capacity.

[0322] Visual Evaluation Test for the Perforations

[0323] The two tyres subjected to the above-described dynamic test, of the same size and structure, except for the self-supporting film, were subjected to observation of the radially more internal surface, in order to verify if and how many perforations were easily identifiable by visual inspection.

[0324] In a visual test, three observers provided the following evaluations:

TABLE-US-00009 TABLE 7 holes detected over 36 present Tyre of the invention Comparative tyre (polyolefin film) (polyamide film) Observer A 35 (97%) 12 (33%) Observer B 36 (100%) 18 (50%) Observer C 32 (89%) 22 (61%)

[0325] The self-sealing tyre of the invention was equipped with sealing composite with self-supporting polyolefin film (B) while the comparative tyre with polyamide film (C) (Filmon CXS18).

[0326] The photographs of FIGS. 6a and 6b frame corresponding portions, which contain the same perforations, of the two tyres 215/55R17 for the purpose of the above-described test: it is clear that the holes are decidedly more evident in the tyre of the invention.

[0327] The collected data allow concluding that a self-sealing tyre according to the present invention allows detecting the perforations present by simple visual inspection much more effectively than what occurs for known self-sealing tyres.