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 a radially external position with respect to said carcass ply in a crown portion, at least one liner applied in a radially internal position with respect to said carcass ply, a sealing assembly applied in a radially internal position with respect to said liner and axially extending at least at a part of the crown portion; wherein said sealing assembly comprises a permanent multilayer self-supporting film comprising at least two outer layers of polyamide and at least one inner layer of polyolefin, wherein said multilayer self-supporting film has a residual relaxation strength of between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, and a layer of sealing material associated with and supported by said permanent multilayer self-supporting film; wherein said permanent multilayer self-supporting film is radially internal to the layer of sealing material and said layer of sealing material is placed substantially in contact with said liner.

Description

[0001] “SELF-SEALING TYRE FOR VEHICLE WHEELS”

[0002] The present invention relates to a self-sealing tyre for vehicle wheels, optionally also comprising a noise reducing element. Self-sealing tyres for vehicle wheels are able to delay or prevent the loss of air and the consequent deflation due to a puncture caused by a sharp object such as a nail and / or screw.

[0003] BACKGROUND ART

[0004] A self-sealing tyre comprises at least one layer of sealing elastomeric material which can adhere to the sharp object that punctures the tyre. The sealing polymeric material is made so as to be dragged inside the hole when the sharp object is ejected or removed, thereby sealing the hole itself and preventing air escape from the tyre. The sealing material inside the finished tyre (moulded and vulcanised), even though it has a certain elasticity, is deformable and tacky.

[0005] In the manufacturing process of a self-sealing tyre, the sealing material may be deposited on the radially innermost wall of the already vulcanised tyre, as described for example in US4418093, or it may be applied during the assembly of the green and vulcanised tyre together with the other components. In the latter case, however, due to the tacky and scarcely rigid nature of the sealing material, handling and transport difficulties are encountered. To overcome these drawbacks, protective and supporting layers have been introduced, on which the sealing material is deposited in a uniform layer. Such layers, when arranged as radially innermost layer in the green tyre, facilitate the manufacture of the tyre, preventing any undesired contact of the material with itself, with the handling and assembly equipment and with the other components of the tyre, such as described for example in WO2011064698 in the name of the Applicant.

[0006] Furthermore, the aforesaid layers also perform a support function for the sealing material which, by its nature, has little stiffness, allowing it to be transported and handled on the plants. Therefore, these layers are also called self-supporting layers. The self-supporting protective layer can be temporary and be removed after vulcanisation, as described for example in US2009 / 0084482, or permanent as it can remain in the final structure of the tyre, as occurs for example in WO2011064698 in the name of the Applicant. The self-supporting protective layers used in the industry for this purpose are of various nature and thickness.

[0007] US2009 / 0084482 describes a removable protective layer of nylon or nylon and rubber compounds. The layer is generally removed after vulcanisation and is therefore no longer present in the finished tyre.

[0008] Document EP1435301 describes a self-sealing tyre obtained by arranging an elastomeric composition comprising poly-isobutylene and peroxides at an internal surface of a non-vulcanised tyre. In one embodiment, a protective layer of thermoplastic resin, consisting predominantly of nylon 11 , is disposed on a side radially internal to the sealing layer. The thickness of the layer is 0.1 mm. The elastomeric composition is heated during the vulcanisation of the tyre, causing a decomposition reaction of the polyisobutylene and obtaining an elastomeric sealing layer.

[0009] Document US2012 / 0180923 relates to self-sealing tyres in which the sealing material layer is protected by a removable thermoplastic layer consisting of a block polymer, comprising hard blocks of polyamides and soft blocks of polyethers or copolymers of polyethers / polyesters (Pebax®). The protective layer prevents the sealing layer from sticking to the drum during assembly and subsequently to the vulcanisation membrane.

[0010] Document US2012 / 234449 describes a self-sealing tyre in which the permanent protective layer is based on a chlorinated thermoplastic polymer (PVC, PVDC) and high molecular weight plasticising agents.

[0011] Document WO2011064698 describes self-sealing tyres which allow selective sealing of holes with a diameter smaller than a predetermined value, achieved by virtue of a particular sealing assembly. Said assembly comprises a permanent protective layer in polyamide or polyester - arranged at least in the crown portion thereof so as to be radially more internal in the tyre - and a layer of sealing material, placed directly on the protective layer so as to result, in the tyre, in a radially outermost position with respect to the protective layer.

[0012] This sealing assembly has excellent performance, both in the initial sealing step at the time of perforation and when the sharp object is expelled, by virtue of the cooperation between the thin protective layer and the sealing material. The particular sealing assembly allows the sealing of the perforations in conditions of maximum safety, i.e. the selective sealing only of the holes which, being below a predetermined size, do not risk damaging the structures of the tyre.

[0013] SUMMARY OF THE INVENTION

[0014] Self-sealing tyres provided with a sealing assembly comprising a protective layer of polyamide or polyester, according to WO2011064698, are achieving considerable commercial success as they perform optimally the selective sealing function, allowing a safe driving to the user.

[0015] The Applicant has however observed that the protective layers based on polyamide or polyester make it more difficult to recycle the tyre at the end of its life and / or the semi-finished product comprising the sealing compound, since these layers are difficult to remove from the sealing compound.

[0016] The Applicant has therefore undertaken further studies aimed at further improving the safety of use of these tyres and their eco-sustainability.

[0017] The self-sealing tyre that we wanted to make, in addition to allowing easy recycling, should have offered a sealing capacity at least comparable if not improved compared to existing systems. Furthermore, in the manufacture of the green tyre, the sealing assembly should have been sufficiently self-supporting to allow the storage of the semi-finished product in reel as well as an easy unrolling from the reel itself, an easy transport of the web, it should have been joined in a simple and stable way, it should have be sufficiently deformable not to tear during the expansion step on the building drum and, at the end of this, not return elastically with such a force as to cause instability of the green material, and / or detachment of the sealing material from the protective layer or liner, and finally, it should also have had a thermal resistance such as not to be damaged during vulcanisation and moulding. Furthermore, the Applicant, being aware of the need to have tyres that in addition to being self-sealing are also less noisy, has undertaken studies for the production of self-sealing and soundproofed tyres and has found that the simple coupling of the self-sealing system, i.e. the sealing composition with the self-supporting layer, and of noise reducing elements made for example of foamed materials, did not achieve the desired results in terms of sealing.

[0018] In particular, the Applicant has implemented a tyre comprising a sealing system - consisting of a layer of sealing elastomeric composition, applied on the innermost surface thereof (i.e. on the internal surface of the liner) and of a self-supporting polyamide layer, according to WO2011064698, and a sound-absorbing polyurethane foam adhering to the layer. This tyre sometimes did not achieve the desired sealing performance. In fact, in the dynamic sealing test, it was observed that the conventional noise reducing element interfered with the sealing of the perforations.

[0019] Without wishing to be bound to any interpretative theory, the Applicant believes that the breakage of the self-supporting polyamide layer caused by a puncture causes contact between the sealing material and the porous material of the noise reducing element which would prevent, or at least slow down, the flow of the sealing material towards the hole, aggravating the phenomenon of retention of the intrinsic sealing material of the polyamide. The Applicant also believes that the breakage of the self- supporting polyamide layer and of the porous material layer caused by the puncture generates fragments of polyamide and porous material which can interfere with the sealing of the hole by the sealing material, triggering the formation of microchannels through which the pressurised air contained within the tyre can continue to escape.

[0020] Despite the innumerable constraints imposed by the drawbacks encountered and the absence of teachings in the prior art, the Applicant has found that it was possible to produce a self-sealing tyre with a sealing assembly comprising at least two outer layers of polyamide and at least one inner layer of polyolefin and having a residual relaxation strength of between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, which unexpectedly showed an improved sealing capacity, which resulted in the possibility of reducing the quantities and thicknesses of the sealing material used in the tyre with the same sealing performance, with considerable savings.

[0021] Furthermore, the Applicant has found that the new self-sealing tyres do not have particular production problems such as the instability of the green semi-finished product, the weakness of the joint, the detachment of the sealing material. Furthermore, the use of polyolefin for the self-supporting layer improves the recyclability of the semi-finished product and / or the tyre at the end of its life, with significant improvements in the industrial process and sustainability.

[0022] The present self-sealing tyre therefore comprises a sealing assembly comprising a layer of sealing material in association with a permanent multi-layer self-supporting film.

[0023] More specifically, according to a first aspect, the present invention relates to a selfsealing tyre for vehicle wheels comprising: at least one carcass ply, a tread band applied in a radially external position with respect to said carcass ply in a crown portion. at least one liner applied in a radially internal position with respect to said carcass ply, and a sealing assembly applied in a position radially internal with respect to the liner and extending axially at least at a portion of the crown portion; wherein said sealing assembly comprises a permanent multilayer self-supporting film comprising at least two outer layers of polyamide and at least one inner layer of polyolefin, wherein said multilayer self-supporting film has a residual relaxation strength of between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, and a layer of sealing material associated with and supported by said permanent multilayer self-supporting film; wherein said permanent multilayer self-supporting film is radially internal to the layer of sealing material and said layer of sealing material is placed substantially in contact with said liner.

[0024] The tensile features and the thickness of the permanent multilayer self-supporting film, as well as the viscoelastic and tackiness features of the sealing material and its thickness are arranged in such a way that the assembly reacts to the exit of the perforating element with an effective sealing action in relation to the dimensions of the tyre and its intended use.

[0025] According to a second aspect, the present invention relates to a multilayered ribbonlike composite comprising a sealing assembly and a removable protective film, wherein said sealing assembly comprises a permanent multilayer self-supporting film comprising at least two outer layers of polyamide and at least one inner layer of polyolefin, wherein said multilayer self-supporting film has a residual relaxation strength of between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, and a layer of sealing material having a first and second principal opposing surfaces, said layer of sealing material being associated with and supported by said permanent multilayer self-supporting film, and wherein said removable protective film is placed in contact with the second surface of said sealing material.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are provided for indicative and, thus, non-limiting purpose only.

[0027] Figure 1 schematically shows a radial half-section of a self-sealing tyre for vehicle wheels comprising a sealing assembly according to the present invention;

[0028] Figure 2 shows a section of a sealing assembly intended to form part of the selfsealing tyre of Figure 1 ;

[0029] Figure 3 is a sectional view of a multilayer sealing composite comprising the sealing assembly of Figure 2 and a removable protective film;

[0030] Figure 4 schematically shows a section of the multilayer self-supporting film according to a preferred embodiment of the present invention, comprising an inner layer 11 b of polyethylene, and two outer layers (11 c and 11 c’) of polyamide.

[0031] Figure 5 schematically shows a radial half-section of a soundproof self-sealing tyre for vehicle wheels comprising a sealing assembly and a noise reducing element according to the present invention.

[0032] Figure 6 shows the Cartesian graph of force (MPa) over time (s) with the relaxation curve obtained as described in Example 2 for the multilayer self-supporting film used in the sealing assembly 2 comprising two outer layers of polyamide and an inner layer of polyethylene.

[0033] Figure 7 shows the Cartesian graph of force (MPa) over time (s) with the relaxation curve obtained as described in Example 2 for the self-supporting layer used in the sealing assembly 1 made of Filmon CXS18 polyamide.

[0034] DEFINITIONS

[0035] For the purposes of the present description and the following claims, the term “phr” (acronym for parts per hundreds of rubber) indicates the parts by weight of a given elastomeric compound component per 100 parts by weight of the elastomeric polymer, considered net of any extension oils.

[0036] The term “permanent self-supporting elastomeric layer” means an elastomeric layer capable of supporting the weight of the sealing material during the building of the tyre which remains in the final structure of the tyre after vulcanisation.

[0037] The term “residual relaxation strength” means the residual force observed after 300 seconds on a multilayer self-supporting film specimen using the method described in Example 2.

[0038] The term “elastomeric composition” means a composition comprising at least one diene elastomeric polymer and one or more additives, which by mixing and possible heating provides an elastomeric compound suitable for use in tyres and components thereof.

[0039] The components of the elastomeric composition are not generally introduced simultaneously into the mixer but typically added in sequence. In particular, the vulcanisation additives, such as the vulcanising agent and optionally the accelerant and retardant agents, are usually added in a downstream step with respect to the incorporation and processing of all the other components.

[0040] In the final vulcanisable elastomeric compound, the individual components of the elastomeric composition may be altered or no longer individually traceable as modified, completely or in part, due to the interaction with the other components, of heat and / or mechanical processing. The term “elastomeric composition” herein means to include the set of all the components that are used in the preparation of the elastomeric compound, regardless of whether they are actually present simultaneously, are introduced sequentially or are then traceable in the elastomeric compound or in the final tyre.

[0041] The term “elastomeric polymer” means a natural or synthetic polymer which, after vulcanisation, may be stretched repeatedly at room temperature to at least twice its original length and after removal of the tensile strength substantially immediately returns with force to approximately its original length (according to the definitions of the ASTM D1566-11 Standard terminology relating to Rubber).

[0042] The term “diene polymer” means a polymer or copolymer derived from the polymerisation of one or more different monomers, among which at least one of them is a conjugated diene (conjugated diolefin).

[0043] The term “elastomeric compound” means the compound obtainable by mixing and optionally heating at least one elastomeric polymer with at least one of the additives commonly used in the preparation of tyre compounds.

[0044] The term “expanded vulcanised elastomeric compound” means the material obtainable by vulcanisation of a vulcanisable and expandable elastomeric compound.

[0045] The term “green” means a material, a compound, a composition, a component or a tyre not yet vulcanised.

[0046] The term “vulcanisation” means the cross-linking reaction in a natural or synthetic rubber induced by a sulphur-based cross-linking agent. The term “vulcanising agent” means a product capable of transforming natural or synthetic rubber into elastic and resistant material due to the formation of a three- dimensional network of inter- and intra-molecular bonds. Typical vulcanising agents are sulphur-based compounds such as elemental sulphur, polymeric sulphur, sulphur-donor agents such as bis[(trialkoxysilyl)propyl]polysulphides, thiurams, dithiodimorpholines and caprolactam-disulphide.

[0047] The term “vulcanisation accelerant” means a compound capable of decreasing the duration of the vulcanisation process and / or the operating temperature, such as TBBS, sulphenamides in general, thiazoles, dithiophosphates, dithiocarbamates, guanidines, as well as sulphur donors such as thiurams.

[0048] The term “vulcanisation activating agent” means a product capable of further facilitating the vulcanisation, making it happen in shorter times and possibly at lower temperatures. An example of activating agent is the stearic acid-zinc oxide system. The term “vulcanisation retardant” indicates a product capable of delaying the onset of the vulcanisation reaction and / or suppressing undesired secondary reactions, for example N-(cyclohexylthio)phthalimide (CTP).

[0049] The term “vulcanisation package” means the vulcanising agent and one or more vulcanisation additives selected from among vulcanisation activating agents, accelerants and retardants.

[0050] The term “reinforcing filler” means a reinforcing material typically used in the sector to improve the mechanical properties of tyre rubbers, preferably selected from among carbon black, conventional silica, such as silica from sand precipitated with strong acids, preferably amorphous, diatomaceous earth, calcium carbonate, titanium dioxide, talc, alumina, aluminosilicates, kaolin, silicate fibres and mixtures thereof.

[0051] DETAILED DESCRIPTION OF THE INVENTION

[0052] The self-sealing tyre of the present invention, in at least one of the above aspects thereof, can exhibit one or more of the following preferred features.

[0053] Advantageously, the sealing assembly is placed in the radially innermost position of the tyre to cover its entire circumferential extension for an axial (or transverse) extension of at least 60% of the crown portion of the tyre.

[0054] Preferably, the sealing assembly extends symmetrically from both sides of the equatorial plane of the tyre. Preferably, such assembly extends axially for at least the entire crown portion of the tyre.

[0055] Alternatively, the sealing assembly extends beyond the crown portion, preferably in the area of the edges and sidewalls, up to the bead structures.

[0056] The “crown portion” of a tyre means the portion of the tyre structure corresponding to the region where the tread band is present. As an indication, the extent of the axial development of the crown portion may be identified by the distance between two segments perpendicular to the tread band starting from the edges of the tread band itself.

[0057] According to the present invention, the sealing assembly comprises a permanent multilayer self-supporting film comprising at least two outer layers of polyamide and at least one inner layer of polyolefin having a residual relaxation strength of between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, and a layer of sealing material associated with and supported by said permanent multilayer self- supporting film.

[0058] Advantageously, the permanent multilayer self-supporting film may exhibit any residual relaxation strength value of between 5 MPa and 15 MPa, for example 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa and 15 MPa, including any one or two digit decimal value in between the above values.

[0059] According to an aspect of the present invention, the sealant assembly comprises a permanent multilayer self-supporting film with a tensile strength equal to or less than 50 MPa, preferably equal to or less than 40 MPa.

[0060] According to an aspect of the present invention, the sealant assembly comprises a permanent multilayer self-supporting film with a tensile strength equal to or greater than 10 MPa, preferably equal to or greater than 20 MPa.

[0061] Advantageously, the permanent multilayer self-supporting film may exhibit any tensile strength value of between 20 MPa and 40 MPa, for example 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa, 25 MPa, 26 MPa, 27 MPa, 28 MPa, 29 Mpa, 30 MPa, 31 MPa, 32 MPa, 33 MPa, 34 MPa, 35 MPa, 36 MPa, 37 MPa, 38 MPa, 39 Mpa, and 40 MPa, including any one or two digit decimal value in between the above values. According to an aspect of the present invention, the sealant assembly comprises a permanent multilayer self-supporting film with a strength at 10% strain (CaO.1 ) equal to or less than 40 MPa, preferably equal to or less than 30 MPa.

[0062] According to an aspect of the present invention, the sealant assembly comprises a permanent multilayer self-supporting film with a strength at 10% strain (CaO.1 ) equal to or greater than 5 MPa, preferably equal to or greater than 10 MPa.

[0063] Advantageously, the permanent multilayer self-supporting film may exhibit any tensile strength value of between 10 MPa and 30 MPa, for example 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 Mpa, 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa, 25 MPa, 26 MPa, 27 MPa, 28 MPa, 29 Mpa, and 30 MPa, including any one or two digit decimal value in between the above values. For the purposes of the present invention, the strength and breaking features and Ca0.1 are evaluated by means of a tensile test carried out according to the ASTM D882 standard in the longitudinal direction at the machine exit (MD).

[0064] According to an aspect of the present invention, the sealing assembly comprises a permanent multilayer self-supporting film with a weight per unit area of between 5 and 30 g / m2, preferably between 10 and 25 g / m2, more preferably between 13 and 20 g / m2, measured according to ISO 2286-2:2016.

[0065] The composition and thickness of the layer of sealing material and the thickness of the multilayer self-supporting film are selected, preferably within the aforementioned features, in relation to the type of tyre to be produced in order to provide the optimal tackiness and viscoelastic features for any conditions of use of the tyre itself.

[0066] In fact, the Applicant has taken care to apply the invention to tyres for four-wheeled vehicles for use on the road, such as tyres suitable for equipping medium and high- displacement cars for transporting people (cord sizes from 195 mm to 245 mm) but without any prejudice, the invention is also suitable for tyres for small utility cars or high-performance tyres (HP high performances - UHP ultra high performances) with cord sizes for example from 145 mm to 355 mm. With the necessary adaptations, the present invention may be applied to tyres for different vehicles such as for example motorcycles.

[0067] Preferably, in the finished tyre, said multilayer self-supporting film has a thickness equal to or less than 50 pm, preferably equal to or less than about 40 pm.

[0068] Preferably, in the finished tyre, said self-supporting multilayer film has a thickness equal to or greater than 1 pm, preferably equal to or greater than about 5 pm. Advantageously, in the finished tyre, said multilayer self-supporting film has a thickness of between 5 pm and 40 pm, preferably between about 10 pm and about 30 pm, more preferably 15 pm, 16 pm, 17 pm, 18 pm, 19 pm or 20 pm.

[0069] The thickness of each polyamide layer in the permanent multilayer self-supporting film is preferably between 10% and 40%, preferably between 15% and 35%, more preferably between 20% and 30%, with respect to the overall thickness of the multilayer self-supporting film.

[0070] The thickness of each polyolefin layer in the permanent multilayer self-supporting film is preferably between 20% and 80%, preferably between 30% and 70%, more preferably between 40% and 60%, with respect to the overall thickness of the multilayer self-supporting film.

[0071] Preferably, in the finished tyre, said layer of sealing material has a thickness greater than about 2.0 mm and less than 6.0 mm.

[0072] Preferably, the layer of sealing material has a smaller axial extension than the axial extension of the multilayer self-supporting film, so that the axially opposed edges of the multilayer self-supporting film allow lateral adhesion of the sealing assembly to the liner, thereby enclosing and laterally retaining the sealing material.

[0073] The axially opposite edges of the multilayer self-supporting film retain the sealing material during the tyre shaping and vulcanisation, when the pressure inside the mould presses the carcass against the internal walls of the mould itself.

[0074] According to the present invention, the sealing assembly comprises a permanent multilayer self-supporting film comprising at least two outer layers of polyamide and at least one inner layer of polyolefin.

[0075] The total amount of polyamide in the permanent multilayer self-supporting film is between 20% w / w and 80% w / w, preferably between 30% w / w and 70% w / w, more preferably between 40% w / w and 60% w / w, distributed over at least two outer layers.

[0076] The total amount of polyolefin in the permanent multilayer self-supporting film is between 20% w / w and 80% w / w, preferably between 30% w / w and 70% w / w, more preferably between 40% w / w and 60% w / w, distributed on at least one internal layer. POLYAMIDE

[0077] The term “polyamide” as used herein means any polymer characterised by the amide group -CO-NH- derived from condensation polymerisation of a dicarboxylic acid with a diamine or from polymerisation of a lactam. Preferably, the multilayer self-supporting film according to the present invention comprises a polyamide selected from: nylon 6, nylon 6.6, nylon 4.6, nylon 4.10, nylon 10.10, nylon 11 , nylon 12, nylon 6.10, nylon 6.12, nylon 6 / 6.6 copolymer, nylon 6 / 6.6 / 6.10 copolymer, nylon MXD 6, nylon 6T, nylon 6 / 6T copolymer, nylon 6.6 / PP copolymer, nylon 6.6 / PPS copolymer, alone or in combination.

[0078] Nylon 6 is produced by the polymerisation of caprolactam. It has good mechanical properties, abrasion resistance and heat resistance. Nylon 6.6 is produced by the polymerisation of adipic acid and hexamethylenediamine. It is one of the most common nylons and offers excellent thermal and mechanical resistance, as well as good dimensional stability. Nylon 4.6 is produced by the polymerisation of 1 ,4- diaminobutane with adipic acid. It has good thermal and mechanical resistance, together with high abrasion resistance. Nylon 11 is produced by the polymerisation of undecane-11 -lactam. It has excellent chemical resistance and biocompatibility properties. Nylon 12 is produced by the polymerisation of co-aminolauric acid or laurolactam. It has excellent properties of flexibility, chemical resistance and moisture resistance. Nylon 6.10 is produced by the polymerisation of sebacic acid and hexamethylenediamine. Nylon 6.12 is produced by the polymerisation of dodecanoic acid and hexamethylenediamine. It has a good balance between mechanical resistance and flexibility. Nylon 6 / 66 is a copolymer of nylon 6 and nylon 6.6. It combines the mechanical properties of nylon 6 with the thermal resistance and dimensional stability of nylon 6.6. Nylon 6T is produced by the polymerization of terephthalic acid and hexamethylenediamine. It is known for its thermal and chemical resistance, and is used in industrial applications and in fire-retardant materials.

[0079] The polyamides used in the sealing assembly according to the present invention preferably have a residual relaxation strength of between 20 MPa and 60 MPa, more preferably between 30 MPa and 50 MPa, and even more preferably between 35 MPa and 45 MPa.

[0080] The polyamides used in the sealing assembly according to the present invention preferably have a tensile strength of between 40 MPa and 80 MPa, more preferably between 50 MPa and 70 MPa, and even more preferably between 55 MPa and 65 MPa.

[0081] The polyamides used in the sealing assembly according to the present invention preferably have a strength at 10% strain (Ca0.1 ) of between 45 MPa and 85 MPa, more preferably between 55 MPa and 75 MPa, and even more preferably between 60 MPa and 70 MPa.

[0082] For the purposes of the present invention, the strength and breaking features and Ca0.1 are evaluated by means of a tensile test carried out according to the ASTM D882 standard in the longitudinal direction at the machine exit (MD).

[0083] The polyamides used in the sealing assembly according to the present invention preferably have a weight per unit area of between 5 and 30 g / m2, preferably between 10 and 25 g / m2, more preferably between 14 and 20 g / m2, measured according to 180 2286-2:2016.

[0084] POLYOLEFIN

[0085] The term "polyolefin", as used herein, means any thermoplastic polymer derived from the polymerisation of unsaturated hydrocarbons containing the ethylene or diene function.

[0086] In particular, the term polyolefin includes olefin homopolymers and copolymers and mixtures thereof. Specific examples include ethylene, propylene, butene homopolymers, ethylene-alpha-olefin, propylene-alpha-olefin, butene-alpha-olefin copolymers, polymethylpentenes and modified polymers thereof.

[0087] Preferably, the self-supporting multilayer film according to the present invention comprises a polyolefin selected from homo- and copolymers of ethylene, propylene, C4-C20 alpha-olefins, preferably C4-C10 alpha-olefins, and mixtures thereof, more preferably it is selected from homo- and copolymers of ethylene and mixtures thereof.

[0088] Preferably, the polyolefin is a polyethylene selected from ethylene homopolymers, ethylene copolymers with propylene, ethylene copolymers with a C4-C8 alphaolefin, such as butene and hexene, and ethylene copolymers with vinyl acetate. Advantageously, polyolefin is a homopolymer of ethylene, commonly called polyethylene (PE).

[0089] Polyethylene is generally classified according to density as high density polyethylene (HDPE) when it has density greater than or equal to 0.941 g / cm3, medium density (MDPE) when it has density in the range from 0.926 to 0.940 g / cm3, linear low density (LLDPE) when it has density in the range from 0.915 to 0.925 g / cm3, low density (LDPE) when it has density in the range from 0.910 to 0.940 g / cm3, very low density (VLDPE) when it has density in the range from 0.880 to 0.915 g / cm3. Preferably, the polyethylene of the multilayer self-supporting film is a linear low density polyethylene (LLDPE), or a low density polyethylene (LDPE), or a low density polyethylene copolymerised with vinyl acetate (LDPE-EVA), or medium density polyethylene (MDPE), or mixtures thereof.

[0090] Examples of suitable commercially available polyolefins are produced and distributed by various manufacturers under different trade names, such as, for example, Clearflex™ or Eraclene™ (Versalis SpA), Escorene™ (Exxon Mobil), Purell™ or Petrothene™ or Hostalen™ (LyondellBasell).

[0091] The polyolefins used in the sealant assembly according to the present invention preferably have a residual relaxation strength of less than 10 MPa, a tensile strength of less than 30 MPa, and a tensile strength at 10% strain (Ca0.1 ) of less than 15 MPa.

[0092] For the purposes of the present invention, the strength and breaking features and Ca0.1 are evaluated by means of a tensile test carried out according to the ASTM D882 standard in the longitudinal direction at the machine exit (MD).

[0093] OTHER MATERIALS / LAYERS

[0094] The permanent multilayer self-supporting film used in the sealant assembly according to the present invention may comprise additional layers comprising a polymeric material other than polyamide and polyolefin, such as, for example, polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), thermoplastic elastomeric polyurethane (TPU), fluorinated polymers, such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and ethylene tetrafluoroethylene (ETFE), vinyl polymers, such as ethylene vinyl acetate (EVA), ethylene vinyl alcohol (EVOH), alone or in combination.

[0095] According to an embodiment of the present invention, the additional layers may represent up to 20% w / w, preferably up to 15% w / w, and more preferably up to 10% w / w, of the permanent multilayer self-supporting film used in the sealant assembly. The above polymeric materials should preferably have a residual relaxation strength of less than 10 MPa, a tensile strength of less than 30 MPa, and a tensile strength at 10% strain (Ca0.1 ) of less than 15 MPa.

[0096] PREPARATION

[0097] The permanent multilayer self-supporting film used in the sealing assembly according to the present invention may comprise up to 15 layers, preferably up to 9 layers, and more preferably up to 5 layers with different chemical compositions. The permanent multilayer self-supporting film used in the sealing assembly according to the present invention may be made by the bubble method, otherwise known as film blowing, which is widely known in the art. The process generally takes place according to the following steps.

[0098] 1 . Extrusion of Materials: Each polymer material that will make up a layer of the multilayer film is melted separately in different extruders. Each extruder may contain a different polymer material with specific properties.

[0099] 2. Combination of Layers: After being melted, the different polymer materials are extruded through the extrusion head and joined together. In some cases, the layers may be joined mechanically using rollers or pressure rollers. Alternatively, co-extrusion may be used, where the layers are melted together as they pass through the extrusion head.

[0100] 3. Bubble Formation: The molten multilayer tube is passed through the circumference of the ring-shaped extrusion head, creating a plastic bubble inside. Each layer contributes to the overall properties of the film.

[0101] 4. Cooling and Solidification: The multilayer bubble is cooled using air jets or water circulation cooling systems. This process solidifies the different layers of polymer material, creating a film composed of different but integrated materials.

[0102] 5. Adjusting Properties: The composition and thickness of each layer may be adjusted to achieve the desired properties in the final film. There are many parameters to act on, including the extrusion flow, the extrusion ratio, the extrusion speed, the geometry of the extrusion head, and the air pressure inside the bubble.

[0103] 6. Cutting and Winding: Once the desired size and multilayer structure is achieved, the film is cut from the bubble and wound onto a roll.

[0104] The different layers of the multilayer self-supporting film may be co-cross-linked or non-co-crosslinked. Preferably, the different layers of the multilayer self-supporting film are co-crosslinked using methods known to those skilled in the art, such as radiation, peroxides, anhydrides or ionomers.

[0105] SEALING MATERIAL

[0106] For the purposes of the present invention, the composition of the sealing material is not particularly limiting: for example, the compositions described in document W020091 43895 or in document WO2013093608 in the name of the Applicant may be used.

[0107] By way of example, the sealing material may comprise

[0108] (a) at least one unsaturated styrenic thermoplastic elastomer;

[0109] (b) optionally at least one diene elastomer;

[0110] (c) at least one cross-linking agent;

[0111] (d) at least one tackifying agent.

[0112] The sealing polymeric material comprises, for example, from 20 phr to 100 phr, of at least one unsaturated styrenic thermoplastic elastomer, from 0 to 80 phr of at least one synthetic or natural diene elastomer, from 20 to 200 phr, preferably from 30 phr to 150 phr, of at least one tackifying agent, 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 at 40 phr, preferably from 5 to 30 phr, of at least one reinforcing filler. According to a preferred embodiment, the sealing material may further comprise from about 1 phr to about 20 phr of at least one homogenising agent. In a further embodiment, the sealing material may further comprise from 0.05 phr to 5 phr of at least one peptizer.

[0113] According to a preferred embodiment, the unsaturated styrene thermoplastic elastomer is a styrene polymer selected from styrene I butadiene I styrene (SBS), styrene I isoprene I styrene (SIS), styrene I butadiene I isoprene I styrene (SBIS) block copolymers, and mixtures thereof, optionally also comprising the corresponding diblock thermoplastic elastomers, such as styrene-butadiene (SB) and styrene-isoprene (SI). Particularly preferred are the styrene I isoprene I styrene block copolymer or mixtures of one or more unsaturated styrenic thermoplastic elastomers containing at least 50% of styrene I isoprene I styrene block copolymer. Preferably, the block copolymer has a styrene content of from about 10% to about 30%, more preferably from about 12% to about 18%.

[0114] Preferably, the block copolymer has a percentage of "diblock" of less than 70%, even more preferably less than 60%.

[0115] Preferably, the percentage of "diblock" is of between 15% and 55%.

[0116] By diblock percentage it is meant the percentage of block polymer consisting of only two segments: a polystyrenic one and an elastomeric one.

[0117] While such “diblocks” are present in the block polymers mainly consisting of three segments - styrene-elastomer-styrene and are considered as an impurity due to the imperfect efficiency of the “living polymerization”, the Applicant believes that the presence of diblocks can be advantageously modulated in order to improve the quality of the sealing composition.

[0118] It is believed that a greater percentage of diblock corresponds to greater tackiness, but lower modulus and less cohesion of the sealing material.

[0119] Particularly preferred are styrene I isoprene I styrene block copolymers with a styrene content equal to or less than 20%, more preferably of between 14% and 20%.

[0120] These copolymers are for example marketed under the name Europrene® SOL T190, T9133 of Polimeri Europa, Vector® 4113, 4114 of Dexco Polymers, Kraton® D1111 , D1112 and D1107J of Kraton.

[0121] According to a preferred embodiment, the synthetic or natural diene elastomer included in the sealing material may be selected from those commonly used among the elastomeric materials cross-linkable with sulphur or peroxides, which are particularly suitable for manufacturing tyres, i.e. from the elastomeric polymers or copolymers with an unsaturated chain having a glass transition temperature (Tg) generally below 20°C, preferably in the range from 0°C to -110°C. These polymers or copolymers may be of natural origin or may be obtained by solution polymerisation, emulsion polymerisation or gas phase polymerisation of one or more conjugated diolefins, optionally mixed with at least one comonomer selected from monovinylarenes and / or polar comonomers in an amount not higher than 60% by weight. Conjugated diolefins generally contain from 4 to 12, preferably from 4 to 8 carbon atoms and may 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.

[0122] Polar comonomers that may optionally be used can be selected, for example, from: vinylpyridine, vinylquinoline, acrylic acid and alkylacrylic acid esters, nitriles, or mixtures thereof, such as, for example, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile or mixtures thereof.

[0123] Preferably, the synthetic or natural diene elastomer included in the sealing material can be selected, for example, from: cis-1 ,4-polyisoprene (natural or synthetic rubber, preferably natural rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high content 1 ,4-cis), optionally halogenated isoprene / isobutene copolymers, 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.

[0124] The tackifying agents advantageously used in the present invention may be selected from the group of hydrocarbon resins having a number average molecular weight comprised between several hundreds and several thousands and which provides tackiness when the resin is mixed with natural or synthetic rubber.

[0125] Various types of synthetic resins may be used as resins. The above number average molecular weight (Mn) may be measured according to techniques known in the field, such as for example by gel permeation chromatography (GPC). In particular, hydrocarbon resins, phenolic-based resins, carbon-based resins, xylene-based resins and natural resins such as rosin-based resins or terpene-based resins may be used as tackifying agents.

[0126] Examples of commercial products of hydrocarbon resins include resins based on aromatic petroleum such as PETCOAL manufactured by Tosoh Co., Ltd; resins based on C5 / C9 hydrocarbons such as PETROTACK manufactured by Tosoh Co; resins based on C5 hydrocarbons such as Escorez® 1102 (manufactured by Exxon Mobil).

[0127] Examples of phenol-based resin comprise resins with an alkylphenol-formaldehyde base and derived resins modified with rosin, resins with alkylphenol-acetylene base, modified alkylphenolic and terpene-phenol resins. Specific examples indicated by brand include commercial products such as RESINA SP-1068 (manufactured by SI GROUP Inc.) which is an octylphenol-formaldehyde resin, and KORESIN (manufactured by BASF Company) which is a p-t-butylphenol-acetylene resin.

[0128] Examples of carbon-based resins include coumarone-indene resins. Specific examples include commercial products, cited by brand, such as NOVARES C resins (manufactured by RUTGERS CHEMICAL GmbH), which are synthetic indenecoumarone resins (such as NOVARES C10, C30, and C70).

[0129] Examples of natural resins are rosin resins and terpene resins, which may be as such or modified: examples of these classes are the terpene resins DERCOLYTE manufactured by DRT, resins derived from rosin acids DERTOLINE, GRANOLITE and HYDROGRAL, manufactured by DRT.

[0130] Examples of xylene-based resins include xylene-formaldehyde resins.

[0131] The above adhesive agents may be used alone or mixed together. Suitable cross-linking agents are sulphur or sulphur-containing molecules, in the presence of compounds containing zinc and fatty acids, or peroxides.

[0132] Examples of specific sulphur-containing molecules that can be used as crosslinking agents in the sealing materials for the manufacture of self-sealing tyres are elemental sulphur, thiurams, such as tetraisobutyl thiuram disulphide or tetrabenzyl thiuram disulphide, or dithiophosphates, such as zinc dibutyldithiophosphate, or dithiocarbamates, such as zinc dimethyl dithiocarbamate, together with ZnO or compounds containing zinc, fatty acids and sulphenamides, such as N-t-butyl-2- benzothiazyl sulphenamide (TBBS), or N-cyclohexyl-2-benzothiazyl sulphenamide (CBS), or thiazoles, such as 2,2'-dithiobis-(benzothiazole) (MBTS).

[0133] Specific examples of peroxides that can be used as crosslinking agents in the sealing materials for the manufacture 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.

[0134] Preferably, a peroxide is used as cross-linking agent, even more preferably 2,5- dimethyl-2,5-di(t-butyl-peroxy)hexane (DBPH).

[0135] A specific example of DBPH that can be used is a mixture of 45% DBPH with calcium carbonate and silica marketed under the name Luperox 101 XL45 by Arkema.

[0136] The amount of peroxide preferably ranges from about 0.1 phr to about 6 phr.

[0137] The presence of peroxide or sulphur or other crosslinking agent allows the partial chemical crosslinking of the sealing composition during the vulcanisation of the tyre so as to improve the dynamic sealing features of the layer of sealing material.

[0138] At least one reinforcing filler may be advantageously added to the above sealing elastomeric composition above, generally in an amount of from 0 phr to 120 phr, preferably from 10 phr to 50 phr. The reinforcing filler may be selected from those commonly used for cross-linked products, in particular for tyres, such as carbon black, silica, alumina, aluminosilicates, calcium carbonate, kaolin or mixtures thereof. Carbon black, silica and mixtures thereof are particularly preferred.

[0139] According to a preferred embodiment, said carbon black reinforcement filler can be selected from those having a surface area of not less than 20 m2 / g (as determined by Statistical Thickness Surface Area - STSA - according to ISO 18852:2005).

[0140] According to the second aspect of the present invention, the composite comprises a sealing assembly as previously described, and a removable protective film, which covers the surface of the sealing material opposite to the surface adhering to the multilayer self-supporting film. This protective film preserves the integrity of the sealing material and prevents the sealing assembly from adhering to itself, when wound on a reel, or to machine parts in the unrolling step. This protective film is then removed, usually before the cutting stage, without damaging the integrity of the sealing material.

[0141] Generally, the protective film has a thickness of less than 100 pm, preferably less than 50 pm.

[0142] Preferably, the protective film is wider than the multilayer self-supporting film and also than the sealing material, more preferably it is wider than the total width of the semi-finished product.

[0143] Preferably the film comprises, more preferably it consists of, polymeric materials such as polyesters, polyamides, polycarbonate, polyvinyl chloride, generally made anti-adhesive with a layer of silicone or fluorinated polymer, or it is made of polytetrafluoroethylene, which does not require anti-adhesive treatments. Preferably, the protective film is made of polyester, more preferably of silicone- coated polyester, i.e. of anti-adhesive polyester with a silicone treatment.

[0144] NOISE REDUCING ELEMENT

[0145] The self-sealing tyre according to the present invention preferably comprises a noise reducing element applied to the radially internal surface of the multilayer self- supporting film.

[0146] The expression "noise reducing element" means an element which, once associated with a radially internal surface of a tyre, has the ability to attenuate the noise produced by the cavity (cavity noise) delimited between the tyre and the rim on which it is mounted during use.

[0147] Said cavity noise is generated during the rolling of the tyre on the road, when the air present in the internal annular cavity is placed in vibration, as it is cyclically compressed in the tread crushing step, thus generating sound waves that are amplified by resonance. Cavity noise then propagates to the passenger compartment of the vehicle, by transmission through the rim, the hub, the suspension and the frame, and is perceived as very annoying by passengers.

[0148] The frequencies at which the air resonates in the cavity are inversely proportional to the tyre circumference, and depend, among other things, also on the shape of the cavity itself, on the nature and shape of the materials that internally line it. Indicatively, the resonant frequency can range from about 50 to 400 Hz, typically around 180 - 220 Hz for passenger car tyres, with a diameter from about 600 to 800 mm.

[0149] The ability to attenuate the cavity noise is usually imparted to said element by the type of material, or materials, of which said element is made and / or by the size of the same and / or by the number of elements inserted in the cavity. Such noise reducing elements usually consist of strips or blocks of porous material such as, for example, foamed polymeric material, which are effective in reducing the noise and are compatible with the use in the tyre.

[0150] During use, the noise reducing materials inserted in the inner cavity of tyres are subject to very significant mechanical and thermal stresses.

[0151] In fact, during rolling, on the one hand they are constantly stretched by deformation of the tyre and on the other hand, they are heated well above ambient temperature, due to the heat generated by the tread in the use on the road.

[0152] Therefore, for the specific application, the noise reducing materials in use generally exhibit good thermal and mechanical properties so as not to become degraded and / or deformed due to the combined action of heat and stress.

[0153] Furthermore, due to the fact that the air used to inflate the tyre may contain moisture, and that this moisture may condense and be absorbed by the porous material of the noise reducing element, resulting in a reduction in the noise attenuation capacity, the noise reducing materials in use generally have a low water absorption and are difficult to hydrolyse. Advantageously, the porous material of the noise reducing element can undergo a water-repellent treatment and / or an anti-mould treatment. Preferably, the noise reducing materials are characterised by a water absorption, according to UNI EN 12088 (RH>95% - after 28 days) of less than 6 Kg / m2, more preferably less than 4 Kg / m2, even more preferably less than 3 Kg / m2.

[0154] Furthermore, since noise reducing materials must be easily deformed during driving to avoid detachment phenomena and must not affect driving performance such as steering stability, such materials are preferably lightweight, low-density and flexible materials.

[0155] Preferably the noise reducing materials have a density not higher than 60 Kg / m3, preferably not higher than 40 Kg / m3, more preferably not higher than 35 Kg / m3. Preferably the noise reducing materials have a density of not less than 5 Kg / m3, more preferably not less than 10 Kg / m3, the density of the noise reducing materials being measured according to the ISO 845:2009 standard.

[0156] The expanded polymeric materials preferably used to make the noise reducing element are foamed polyurethanes, such as for example ether-based polyurethane foam and ester-based polyurethane foam, foamed polyolefins, such as, for example, foamed polyethylene, foamed polypropylene, and mixtures thereof, and foamed rubbers, such as for example foamed chloroprene rubber (CR sponge), foamed ethylene-propylene rubber (EDPM sponge), foamed nitrile rubber (NBR sponge), and the like.

[0157] Expanded polymer materials may be open-cell or closed-cell. Expanded polyolefin materials are preferably closed-cell, possibly perforated. Polyurethane materials are preferably open-cell. The cells may have variable dimensions, generally divided into macrocells with average dimensions greater than 1.5 mm, and microcells with average dimensions smaller than 1 .5 mm.

[0158] Useful examples of expanded polymeric materials are described in WO2013182477A1 , EP2457748A1 , EP1661735A1 , EP1876038A1 and

[0159] EP2457720A1 , and also in WO2016051371 A1 and WO2017163219A1 on behalf of the Applicant.

[0160] Further features and advantages will become more apparent from the detailed description of a preferred, but non-exclusive, embodiment of a self-sealing tyre for vehicle wheels and of a composite comprising a sealing assembly according to the present invention.

[0161] Such description is set out below with reference to the drawing of Figure 1 provided for indicative and, therefore, non-limiting purposes only, where “X” indicates the equatorial plane of the finished tyre 1 . For simplicity, Figure 1 shows only a part of the tyre, the remaining part not shown being identical and arranged symmetrically with respect to the equatorial plane “X”.

[0162] The reference numeral 1 indicates in Figure 1 a self-sealing tyre for vehicle wheels, which generally comprises a carcass structure 2 comprising at least a carcass ply 3 having respectively opposite end flaps engaged with respective annular anchoring structures 4, optionally associated with elastomeric fillers 4a, integrated in the areas 5 usually identified by the name of “beads”. The at least one carcass ply 3 comprises a plurality of textile or metal reinforcement cords arranged parallel to each other and at least partially covered with a layer of elastomeric material. The carcass structure 2 is associated with a belt structure 6 comprising one or more belt layers placed in radial superposition with respect to one another and with respect to the carcass ply 3, having typically metal reinforcement cords.

[0163] Such reinforcement cords may have crossed orientation with respect to the circumferential development direction of tyre 1 .

[0164] A tread band 7 is applied in a position radially outer to the belt structure 6, made of an elastomeric compound like other semi-finished products making up tyre 1 . Respective sidewalls 8 of an elastomeric compound are further applied in axially outer position on the lateral surfaces of the carcass structure 2, each extending from one of the lateral edges of the tread band 7 up at the respective annular anchoring structure to beads 5.

[0165] Moreover, a radially internal surface of tyre 1 is preferably internally lined by a layer of substantially airtight elastomeric material, or so-called liner 9.

[0166] In the embodiment shown in figure 1 , tyre 1 is of the type for motor vehicles.

[0167] Typically, in this case, the belt structure 6 further comprises at least one radially outer layer comprising textile or metal cords or textile / metal combinations, arranged according to a substantially zero angle with respect to the circumferential development direction of the tyre.

[0168] According to embodiments of the present invention, the tyre 1 is for motor vehicles. The profile of the straight section of the tyre for motor vehicles (not shown) has a high transversal curvature since it must allow a sufficient footprint area in all the inclination conditions of the motor vehicle. The transverse curvature is defined by the value of the ratio between the distance f of the ridge of the 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. A tyre with high transverse curvature indicates a tyre whose transverse curvature ratio (f / C) is at least 0.20. Preferably, (f / C) is between 0.20 and 0.5 for a rear tyre and between 0.35 and 0.6 for a front tyre, respectively.

[0169] The self-sealing tyre 1 according to the invention further comprises a layer of sealing polymeric material 10 arranged at a crown portion of the tyre 1 and in a radially internal position with respect to the liner 9. The layer of sealing polymeric material 10 extends over the entire circumferential extension of the tyre 1 . The layer of sealing material 10 preferably has a maximum thickness “t1” substantially at the equatorial plane "X" of the finished tyre 1 , i.e. moulded and vulcanised, and tapers towards the axial ends of the crown portion (Figure 1 ). Preferably, said maximum thickness “t1” is comprised between 2 mm and 6 mm, even more preferably between about 2.5 mm and 5 mm.

[0170] In a radially internal position with respect to the sealing polymeric material layer 10 and in contact with said sealing polymeric material layer 10, a multilayer self- supporting film 11 according to the present invention is arranged. As illustrated in Figure 4, the multilayer self-supporting film 11 according to the present invention comprises an inner layer 11 b of polyethylene and two outer layers 11 c and 11 c’ of polyamide. The multilayer self-supporting film 11 extends, like the layer of sealing polymeric material 10, for the entire circumferential extension of the tyre 1 and has a width, i.e. an axial extension, slightly greater than the axial extension of said layer 10.

[0171] Preferably, in the finished tyre, said multilayer self-supporting film 11 has a thickness “t2” preferably of between 5 pm and 40 pm, preferably between about 10 pm and about 30 pm.

[0172] The sealing polymer material layer 10 and the multilayer self-supporting film 11 form a sealing assembly 12. The sealing assembly 12, when a sharp element (such as a nail or a screw) penetrates into the tyre and crosses the layer of sealing polymeric material 10 and the multilayer self-supporting film 11 , is able to adhere to the object penetrated therein and can also flow into the hole when such an object is removed, thus sealing the hole itself and preventing the escape of air from the tyre.

[0173] The sealing assembly 12 is easily perforated by the sharp element while maintaining such deformability and tackiness as to contribute to the transfer of the sealing material while ejecting the sharp element. The perforations thus sealed are clearly visible on the surface of the sealing assembly 12, through the self-supporting multilayer film 11.

[0174] The axially opposed edges 11 a of the multilayer self-supporting film 11 adhere to the radially internal surface of the liner 9 during the building of the green tyre 1 . Two annular strips (not illustrated) made of elastomeric material may also be provided, each positioned near one edge of the sealing assembly 12. An axially inner portion of each elongated element of elastomeric material is superimposed to the sealing assembly 12 and is arranged in a radially inner position within said sealing assembly 12. An axially outer portion of each elongated element of elastomeric material lies in direct contact with the liner 9 and, by co-crosslinking with the latter during the vulcanisation process, secures the sealant assembly 12 to the tyre.

[0175] The building of a precursor of a green tyre 1 as described above, including the sealing assembly 12, is preferably carried out by assembling respective semifinished products on one or more forming supports, not illustrated.

[0176] The carcass structure and the belt structure are generally made separately of each other in respective workstations, to be mutually assembled at a later time.

[0177] More in particular, the building of the carcass structure first provides for the formation of the sealing assembly 12 as a continuous band comprising the layer of sealing material 10 arranged on and supported by 11 with a width such as to leave the axially opposite edges 11 a of the multilayer self-supporting film 11 exposed (Figure 2).

[0178] The sealing layer 10, before incorporating the sealing assembly 12 into the precursor of the tyre 1 and its conformation, has a thickness “t3” between about 3 mm and about 8 mm.

[0179] The multilayer self-supporting film 11 , before incorporating the sealing assembly 12 in the precursor of the tyre 1 and its conformation, has a thickness “t4” equal to or less than 50 pm and preferably less than 40 pm.

[0180] The sealing assembly 12 is cut to size, preferably with an angled (bevel) cut and wrapped around a radially external surface of a building drum, keeping the multilayer self-supporting film 11 in a radially innermost position. Opposite end flaps of the sealing assembly 12 are mutually joined due to the adhesiveness of the sealing compound; preferably, the joint is covered (to avoid leakage of sealing material at the time of vulcanisation) and consolidated by means of, for example, an adhesive tape (joint).

[0181] The liner 9 and the carcass ply or plies 3 are applied on the sealing assembly 12 to form a so-called “carcass sleeve”, typically substantially cylindrical. The annular anchoring structures 4 to beads 5 are fitted or formed on the opposite end flaps of the carcass ply or plies 3, which are then looped back around the annular structures 4 themselves so as to enclose them in a sort of loop.

[0182] A so-called "outer sleeve" is manufactured on a second drum or auxiliary drum, comprising the belt layers 6 applied in reciprocal mutual superimposition, and optionally the tread band 7 applied in a radially outer position to the belt layers 6. The outer sleeve is then picked up from the auxiliary drum to be coupled to the carcass sleeve. To this end, the outer sleeve is arranged coaxially around the carcass sleeve, after which the carcass ply or plies 3 is / are shaped according to a toroidal configuration by mutual axial approach of beads 5 and concurrent introduction of fluid under pressure into the carcass sleeve, so as to cause a radial expansion of the carcass plies 3 up to make them adhere against the internal surface of the outer sleeve.

[0183] The assembly of the carcass sleeve with the outer sleeve can be carried out on the same drum used to make the carcass sleeve, in which case it is called "single step building process" or "unistage process". Building processes of the so-called "two- step" type are also known, in which a so-called "first-step drum" is first used to make the carcass sleeve, while the assembly between the carcass sleeve and the outer sleeve is carried out on a so-called "second-step drum" or "shaping drum", on which the carcass sleeve picked up from the first-step drum and then, the outer sleeve picked up from the auxiliary drum are transferred.

[0184] After building of green tyre 1 , a moulding and vulcanisation treatment is generally carried out in order to determine the structural stabilisation of the tyre through crosslinking of the elastomeric compounds, as well as to impart a desired tread pattern on the tread band 7 and to impart any distinguishing graphic signs at the sidewalls 8. A pattern of covalent bonds develops during vulcanisation between the elastomer macromolecules which, depending on its density, prevents flowing thereof, making the material more and more insoluble, non-melting and elastic. After vulcanisation, the layer of sealing material 10 achieves optimal deformability, tackiness, and cohesion features.

[0185] During vulcanisation, despite the high temperatures used, the multilayer self- supporting film 11 and the sealing material 10 remain intact, do not damage the vulcanisation membrane, and achieve optimal sealing performance.

[0186] In Figure 3, the sealing assembly 10 of Figure 2 is covered with a removable protective film 14 to give the multilayer composite 15. The multilayer composite 15 can be prepared, for example by extrusion of the sealing material 10 on the protective film 14 and mechanical coupling with the multilayer self-supporting film 11 to give the ribbon-like composite, which is cooled and generally stored wound on a reel.

[0187] As shown in Figure 5, the tyre 1 may finally comprise a layer of noise reducing material or element 13, made of expanded polymeric material, applied to the radially - 1 - internal surface of the multilayer self-supporting film 11 , for example by gluing, for the entire circumference of the tyre and axially at at least 40% and up to 90% of the width of the tread band of the tyre, symmetrically with respect to the equatorial plane X. The noise reducing element or layer 13 may be made to adhere to the radially internal surface of the multilayer self-supporting film 11 , by gluing with suitable adhesives such as an acrylic adhesive, or by interlocking or compression, making the noise reducing layer larger than the internal diameter of the tyre.

[0188] The present invention will be further illustrated below by means of a number of preparatory examples, which are provided for indicative purposes only and without any limitation of the present invention.

[0189] EXAMPLES

[0190] Example 1

[0191] For performing the tests, different tyres (size 215 / 55 R17) were made, including different sealing assemblies.

[0192] A sealing assembly 1 obtained according to the teaching of WO2011064698 and comprising a self-supporting layer of Filmon CXS18 polyamide of nominal 15 pm thickness was used as a reference.

[0193] A sealing assembly 2 comprising a 15 pm multilayer self-supporting film made of two outer layers of polyamide, each representing 25% w / w, and an inner layer of polyethylene representing 50% w / w.

[0194] The sealing assemblies 1 -2 comprised the sealing composition of the following Table 1.

[0195] TABLE 1

[0196] IR: cis- 1,4-polyisoprene from Nizhnekamskneftechim Export, Russia;

[0197] SBR: styrene-butadiene copolymer from International Specialty Products (ISP);

[0198] SIS: Styrene-lsoprene-Styrene block copolymer Europrene® SOL T190 from Polimeri Europa;

[0199] NC: Carbon Black N234 from Cabot Corporation;

[0200] Peroxide: Luperox 101 XL45 from Arkema;

[0201] Oil: mineral oil (MES - Mild Extraction Solvated) Catenex SNR from Shell;

[0202] Resin 1: Escorez® 1102 from ExxonMobil;

[0203] Resin 2: Struktol® 40MS from Struktol Corporation;

[0204] Antioxidant: Santoflex® 6PPD from Eastman.

[0205] The layer of sealing material before building the tyre had a thickness of about 4.0 mm and the sealing assembly was arranged in a radially internal position with respect to the liner (as illustrated in Fig. 1 ).

[0206] The sealing assemblies 1 -2 were built and vulcanised with summer tyres (215 / 55R17 Pirelli Cinturato P7TM- P7) with or without a noise reducing element consisting of 6 blocks with dimensions of 120x180x30 mm and 2 blocks with dimensions of 120x240x30 mm made of polyurethane material Cirene 30 (Cires S.p.A.) with density 30± 2 Kg / m3(ISO 845:2009) and applied on the radially internal surface of the self-supporting layer.

[0207] The moulded and vulcanised tyres were mounted on a standard rim and inflated to a pressure of 2.4 bar.

[0208] The tyres were punctured with 15 sharp elements (nails) having a diameter of 3 to 5 mm and a length of 60 mm at the crown portion. The arrangement of the sharp elements included dowels and recesses and was random.

[0209] Tyres without a noise reducing element were subjected to a cold static test and a hot dynamic test. Tyres with noise reducing elements were subjected only to a hot dynamic test.

[0210] Cold static test

[0211] In the cold static test, the tyres with the nails inserted were placed inside a climatic cell at -21 °C for 24 hours, in order to acclimatise. The tyres were then removed from the climate chamber and the 15 nails were removed. For each nail, the air leakage from the holes was evaluated with a soapy water solution.

[0212] The results are summarised in the following Table 2.

[0213] TABLE 2

[0214] From the data shown in Table 2, it is apparent that the tyre according to the present invention, provided with the sealing assembly 2, has significantly improved sealing properties compared to the reference provided with the sealing assembly 1. Hot dynamic test

[0215] In the hot dynamic test, the studded tyres were rolled on a 2.8 m diameter disc at a speed of 120 km / h with a load of 550 kg. The test simulated a 500 km road journey alternating 10-m inute periods with zero drift angle and 10-m inute periods with drift angle oscillating from -6° to +6°. The drift velocity was 1 s, and 25 oscillations were carried out for each drift cycle. The tyres did not lose air throughout the test period.

[0216] At the end of the test, the 15 nails were removed, and each nail was assessed for air leakage from the holes with a soapy water solution.

[0217] The results are summarised in the following Table 3.

[0218] TABLE 3

[0219] From the data shown in Table 3, it is apparent that the tyre according to the present invention, provided with the sealing assembly 2, has sealing properties identical to the reference tyre provided with the sealing assembly 1 in the absence of a noise reducing element, but has significantly improved sealing properties in the presence of a noise reducing element.

[0220] Example 2

[0221] To characterise the self-supporting multilayer film of the sealing assembly 2 with respect to the self-supporting layer of the sealing assembly 1 used in Example 1 , tensile tests were performed on two specimens having dimensions 300x20 mm each according to the ASTM D882 standard measuring the strength at break and the strength at 10% deformation (Ca0.1 ) at a temperature of 23°C and relative humidity of 46% with a tensile speed of 500 mm / minute.

[0222] The results are summarised in the following Table 4.

[0223] TABLE 4

[0224] Furthermore, a stress relaxation test was performed on specimens having the same dimensions using a Zwic model 1445 dynamometer. Before testing, the specimens were conditioned at 23°C for at least 4 hours. The specimens were then installed on the instrument clamps with an initial distance between the clamps of 200 mm by first applying a preload of 0.5 N at a speed of 20 mm / min, and then a deformation (elongation) of 30% at a speed of 500 mm / min, then measuring the residual relaxation strength after 300 seconds of relaxation.

[0225] The results have been summarised in the following Table 5 and Figures 6 and 7.

[0226] TABLE 5

[0227] The low residual strength, as well as the low CaO.1 , of the multilayer self-supporting film according to the present invention describe a less rigid and tough material. The lower rigidity of the sealing assembly 2 allows the sealing composition to flow more at the puncture site when the nail is extracted.

[0228] Similarly, a low residual strength after 300 seconds of relaxation indicates a less elastic material, reducing the elastic return of the film to its equilibrium position upon nail extraction which could drag and push the sealant away from the puncture, and consequently allowing a greater quantity of the sealant composition to remain inside the hole.

Claims

CLAIMS1 . A self-sealing tyre for vehicle wheels comprising: at least one carcass ply, a tread band applied in a radially external position with respect to said carcass ply in a crown portion, at least one liner applied in a radially internal position with respect to said carcass ply, a sealing assembly applied in a radially internal position with respect to said liner and axially extending at least at a part of the crown portion; wherein said sealing assembly comprises a permanent multilayer self- supporting film comprising at least two outer layers of polyamide and at least one inner layer of polyolefin, wherein said multilayer self-supporting film has a residual relaxation strength of between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, and a layer of sealing material associated with and supported by said permanent multilayer self-supporting film; wherein said permanent multilayer self-supporting film is radially internal to the layer of sealing material and said layer of sealing material is placed substantially in contact with said liner.

2. The tyre according to claim 1 wherein said self-supporting multilayer film has a breaking strength between 10 MPa and 50 MPa, preferably between 20 MPa and 40 MPa.

3. The tyre according to claim 1 wherein said self-supporting multilayer film has a strength at 10% strain (Ca0.1 ) between 5 MPa and 40 MPa, preferably between 10 MPa and 30 MPa.

4. The tyre according to any one of claims 1 to 3, wherein said multilayer self- supporting film has a thickness equal to or lower than 50 pm, preferably equal to or lower than about 40 pm.

5. The tyre according to claim 4, wherein said self-supporting multilayer film has a thickness equal to or greater than 1 pm, preferably equal to or greater than about 5 pm.

6. The tyre according to any one of claims 1 to 5, wherein said layer of sealing material has a thickness greater than about 2.0 mm and lower than about 6.0 mm.

7. The tyre according to claim 1 wherein said sealing assembly axially extends for at least 60% of the crown portion of the tyre.

8. The tyre according to claim 7 wherein said sealing assembly axially extends for at least the entire crown portion of the tyre.

9. A multilayered ribbon-like composite comprising a sealing assembly, and a removable protective film, wherein said sealing assembly comprises a permanent multilayer self-supporting film comprising at least two outer layers of polyamide and at least one inner layer of polyolefin, wherein said multilayer self-supporting film has a residual relaxation strength of between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, and a layer of sealing material having a first and second principal opposing surfaces, said layer of sealing material being associated with and supported by said permanent multilayer self-supporting film, at the level of the first surface, and wherein said removable protective film is placed in contact with the second surface of said sealing material.

10. The composite according to claim 9, wherein said removable protective film has a thickness lower than 100 pm, preferably lower than 50 pm.11 . The composite according to any one of claims 9 or 10, wherein said removable protective film comprises a polymeric material selected from polyesters, polyamides, polycarbonates, polyvinyl chlorides, and fluorinated polyolefins.

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