Preferably, in the finished tyre, said self-supporting elastomeric layer has a thickness of less than 2 mm, preferably less than about 1.0 mm.

Preferably, in the finished tyre, said self-supporting elastomeric layer has a thickness greater than 0.1 mm, preferably greater than about 0.2 mm.

Advantageously, in the finished tyre, said self-supporting elastomeric layer has a thickness of between 0.3 mm and 0.9 mm, preferably between about 0.4 mm and about 0.7 mm, more preferably of 0.4 mm, 0.5 mm or 0.6 mm.

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.

Preferably, the layer of sealing material has a smaller axial extension than the axial development of the self-supporting elastomeric layer, so that the axially opposite edges of the self-supporting elastomeric layer guarantee lateral adhesion of the sealing assembly to the liner, so as to enclose and retain the sealing material laterally.

The axially opposite edges of the self-supporting elastomeric layer 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.

The elastomeric compound of the self-supporting elastomeric layer according to the present invention comprises at least one natural or synthetic diene elastomeric polymer derived from the polymerisation of one or more monomers, among which at least one is a conjugated diene.

The synthetic diene elastomeric polymer may be obtained by solution polymerisation, emulsion polymerisation or gas phase polymerisation of at least one conjugated diene, optionally mixed with at least one comonomer selected from monovinylarenes and/or polar comonomers in an amount not exceeding 60% by weight.

The conjugated dienes 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 and mixtures thereof. 1,3-butadiene and isoprene are particularly preferred.

Monovinylarenes, which may optionally be used as comonomers, generally contain from 8 to 20, preferably from 8 to 12 carbon atoms and may be selected, for example, from: styrene; 1-vinylnaphthalene; 2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl derivatives of styrene, such as, for example, α-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-p-tolyl-styrene, 4-(4-phenylbutyl)styrene, and mixtures thereof. Styrene is particularly preferred.

Polar comonomers that may optionally be used, may 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 and mixtures thereof.

Preferably, the diene elastomeric polymer which may be used in the present invention may be selected, for example, from among: cis-1,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high content of 1,4-cis), 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, and mixtures thereof.

The elastomeric compound of the self-supporting elastomeric layer according to the present invention preferably comprises at least one reinforcing filler selected from carbon black, conventional silica, such as sand silica precipitated with strong acids, preferably amorphous, diatomaceous earth, calcium carbonate, titanium dioxide, talc, alumina, aluminosilicates, kaolin, silicate fibres and mixtures thereof.

Preferably, the reinforcing filler is selected from carbon black, conventional silica, silicate fibres, talc and mixtures thereof.

The elastomeric composition for tyres of the invention may optionally comprise one or more reinforcing fillers as defined above in a mixture.

Commercial examples of reinforcing fillers suitable for use in the present elastomeric composition are the carbon black N326 and N375 from Cabot, the carbon black N326 and N375 from Birla, and Minstron HAR lamellar talc produced by Imerys Talc France.

The elastomeric compound of the self-supporting elastomeric layer according to the present invention can comprise at least one vulcanisation agent.

The vulcanisation agent is preferably selected from sulphur, or alternatively, sulphur-containing molecules (sulphur donors), in the presence of compounds containing zinc and fatty acids, or peroxides.

Preferably, the vulcanisation agent is sulphur preferably selected from soluble sulphur (crystalline sulphur), insoluble sulphur (polymeric sulphur), (iii) oil-dispersed sulphur and mixtures thereof.

Alternatively, sulphur donor molecules such as, for example, caprolactam disulphide (CLD), bis[(trialkoxysilyl)propyl]polysulphides, dithiophosphates, phosphoryl polysulphide (SDT) and mixtures thereof can be used.

Commercial examples of suitable vulcanisation agents are the 65% sulphur known under the trade name of Rhenogran from Lanxess, the 67% sulphur known under the trade name of Crystex OT33 from Eastman, the 95% sulphur known under the trade name of SchwefelKC from Solvay, the rhombic crystalline sulphur known under the trade name of Sulphur (1% oil and 0.3% silica) of Zolfindustria.

The vulcanisation agent may be present in the elastomeric composition of the invention in an overall amount generally of from 0.1 to 3 phr, preferably from 0.2 to 2 phr, even more preferably from 0.3 to 0.5 phr.

The vulcanisation agent is preferably used together with adjuvants such as vulcanisation activating agents, accelerants and/or retardants known to the man skilled in the art. The set of vulcanisation activating agents, accelerants and/or retardants constitutes, together with the vulcanisation agent, the so-called “vulcanisation package”.

The vulcanisation activators which are particularly effective are zinc compounds, and in particular ZnO, ZnCO₃, zinc salts of saturated or unsaturated fatty acids containing from 8 to 18 carbon atoms, such as, for example, zinc stearate, which are preferably formed in situ in the elastomeric composition from ZnO and fatty acid, as well as BiO, PbO, Pb₃O₄, PbO₂or mixtures thereof. Commercial examples are Dispersing Agent FS-200 fatty acid zinc salts from Wuhan Jinghe, Palmera B1810 stearic acid from KLK OLEO or grade 203 zinc oxide from U.S. Zinc.

The vulcanisation accelerant is preferably selected from dithiocarbamates, guanidines, thioureas, thiazoles, sulphenamides, sulphenimides, thiurams, amines, xanthates and mixtures thereof.

Preferably, the accelerant is selected from N-cyclohexyl-2-benzothiazol-sulphenamide (CBS), N-tert-butyl-2-benzothiazol-sulphenamide (TBBS) and mixtures thereof.

A commercial example of a suitable accelerant is N-cyclohexyl-2-benzothiazol-sulphenamide Vulkacit® (CBS) marketed by Lanxess.

The vulcanisation accelerant may be present in the vulcanisable elastomeric composition in an overall amount generally ranging between 0.05 phr and 10 phr, preferably between 0.1 phr and 5 phr.

The vulcanisable elastomeric composition may comprise one or more vulcanisation accelerants as defined above in mixture.

The vulcanisation retardant may be selected for example from urea, phthalic anhydride, N-nitrosodiphenylamine N-cyclohexylthiophthalimide (CTP), and mixtures thereof.

A commercial example of a suitable retardant is N-cyclohexylthiophthalimide VULKALENT G from Lanxess.

The retardant may be present in the vulcanisable elastomeric composition in an amount generally ranging between 0.05 phr and 2 phr.

The elastomeric compound of the self-supporting elastomeric layer according to the present invention can comprise other additives commonly used in the production of elastomeric compounds, such as for example antioxidant agents, anti-ageing agents, plasticisers, antiozonants (in particular of the p-phenylenediamine type), waxes, modified resins, lubricants, surfactants, or mixtures thereof.

The antioxidant agent may be selected from the group comprising phenylenediamine, diphenylamine, dihydroquinoline, phenol, benzimidazole, hydroquinone and derivatives thereof, optionally in mixture.

The antioxidant agent is preferably selected from N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD), N-(1,3-dimethyl-butyl)-n′-phenyl-p-phenylenediamine (6PPD), N,N′-bis-(1,4-dimethyl-pentyl)-p-phenylenediamine (77PD), N,N′-bis-(1-ethyl-3-methyl-pentyl)-p-phenylenediamine (DOPD), N,N′-bis-(1,4-dimethyl-pentyl)-p-phenylenediamine, N,N′-diphenyl-p-phenylenediamine (DPPD), N,N′-ditolyl-p-phenylenediamine (DTPD), N,N′-di-beta-naphthyl-p-phenylenediamine (DNPD), N, N′-bis(1-methylheptyl)-p-phenylenediamine, N,N′-Di-sec-butyl-p-phenylenediamine (44PD), N-phenyl-N-cyclohexyl-p-phenylenediamine, N-phenyl-N′-1-methylheptyl-p-phenylenediamine and the like and mixtures thereof, preferably it is N-(1,3-dimethyl-butyl)-N′-phenyl-p-phenylenediamine (6-PPD).

A commercial example of a suitable antioxidant agent is 6PPD from Solutia/Eastman and TMQ 2,2,4-trimethyl-1,2-dihydroquinoline-Vulkanox® HS/LG from Lanxess.

The antioxidant agent may be present in the vulcanisable elastomeric composition in an overall amount generally ranging between 0 phr and 20 phr, preferably between 0.5 phr and 10 phr.

In particular, in order to improve the processability of the compound, the compound may optionally be admixed with at least one plasticiser generally selected from mineral oils, vegetable oils, synthetic oils, polymers with a low molecular weight and mixtures thereof, such as, for example, aromatic oil, naphthenic oil, phthalates, soybean oil and mixtures thereof. Commercial examples of plasticising agents are NYTEX® 4700 naphthenic oil from Nynas, PM Oil paraffinic oil from LLK International, Disflamol® TOF tris(2-ethylhexyl)phosphate from Lanxess, MES Catenex SNR mineral oil from Shell.

Furthermore, in order to improve the anti-adhesive properties and decrease the tackiness of the self-supporting elastomeric layer and therefore reduce its interaction with the self-sealing material, at least one surfactant or a lubricant may be added to the compound, such as for example the amides of fatty acids marketed by Croda Italia SpA under the trade name of Crodamide™ or Incroslip™, such as for example Crodamide™ SR, Crodamide™ ER, Crodamide™ BR, Crodamide™ ORX, Crodamide™ S, Crodamide™ EBS, Crodamide™ OR, Crodamide™ SRV and Incroslip SL™, and by Fine Organics under the trade names of Finawax S, Finawax S 50, Finawax S 70, or a lubricant such as silicones or fluorinated polymers, such as PTFE.

For the purposes of the present invention, the composition of the sealing material is not particularly limiting: for example, the compositions described in document WO2009143895 or in document WO2013093608 in the name of the Applicant may be used.

By way of example, the sealing material may comprise

- (a) at least one unsaturated styrenic thermoplastic elastomer;
- (b) optionally at least one diene elastomer;
- (c) at least one cross-linking agent;
- (d) at least one tackifying agent.

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 agent.

According to a preferred embodiment, the unsaturated styrene thermoplastic elastomer is a styrene polymer selected from styrene/butadiene/styrene (SBS), styrene/isoprene/styrene (SIS), styrene/butadiene/isoprene/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/isoprene/styrene block copolymer or mixtures of one or more unsaturated styrenic thermoplastic elastomers containing at least 50% of styrene/isoprene/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%.

Preferably, the block copolymer has a percentage of “diblock” of less than 70%, even more preferably less than 60%.

Preferably, the percentage of “diblock” is of between 15% and 55%.

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

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.

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

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

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

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.

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.

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 (SBR), styrene/isoprene/1,3-butadiene copolymers, styrene/1,3-butadiene/acrylonitrile copolymers, or mixtures thereof.

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.

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.

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).

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.

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 indene-coumarone resins (such as NOVARES C10, C30, and C70).

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.

Examples of xylene-based resins include xylene-formaldehyde resins.

The above tackifying 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.

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).

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.

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

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 from Arkema.

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

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.

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.

According to a preferred embodiment, said carbon black reinforcing 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).

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 self-supporting elastomeric layer. 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, generally before the cutting step, without damaging the integrity of the sealing material.

Generally the protective film has a thickness of less than 100 μm, preferably less than 50 μm.

Preferably, the protective film is wider than that of the self-supporting elastomeric layer and also that of the sealing material, more preferably it is wider than the total width of the semi-finished product.

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.

The self-sealing tyre according to the present invention preferably comprises a noise reducing element applied to the radially internal surface of the self-supporting elastomeric layer.

The expression “noise reducing element” means an element which, once associated with a radially inner 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.

Said cavity noise is generated during the rolling of the tyre on the road, when the air present in the inner 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.

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.

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.

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

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.

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.

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/m²more preferably less than 4 Kg/m², even more preferably less than 3 Kg/m².

In addition, since noise reducing materials must easily deform during driving to avoid peeling phenomena and must not affect driving performance such as steering stability, such materials are preferably lightweight, low density and flexible materials. 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.

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.

Expanded polymeric materials can be open cell or closed cell. The expanded polyolefin materials are preferably with closed cells, possibly perforated. The polyurethane materials are preferably with open cells. The cells can have variable sizes, generally divided into macrocells with an average size greater than 1.5 mm, and microcells with an average size smaller than 1.5 mm.

Useful examples of expanded polymeric materials are described in WO2013182477A1, EP2457748A1, EP1661735A1, EP1876038A1 and EP2457720A1, and furthermore in WO2016051371A1 and WO2017163219A1 in the name of the Applicant.

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.

Such description is set out below with reference to the drawing of FIG. 1 provided for indicative and, therefore, non-limiting purposes only, where “X” indicates the equatorial plane of the finished tyre 1. For simplicity, FIG. 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”.

The reference numeral 1 indicates in FIG. 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 reinforcing 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 reinforcing cords.

Such reinforcing cords may have crossed orientation with respect to the circumferential development direction of tyre 1.

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.

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

In the embodiment shown in FIG. 1, tyre 1 is of the type for motor vehicles.

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.

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 guarantee 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.

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 (FIG. 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.

A self-supporting elastomeric layer 11 according to the present invention is arranged in a radially internal position with respect to the layer of sealing polymeric material 10 and in contact with said layer of sealing polymeric material 10. The self-supporting elastomeric layer 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.

Preferably, in the finished tyre, said self-supporting elastomeric layer 11 has a thickness “t2” preferably comprised between 0.1 mm and 2.0 mm, advantageously between about 0.2 mm and 1.0 mm.

The sealing polymeric material layer 10 and the self-supporting elastomeric layer 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 self-supporting elastomeric layer 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.

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 elastomeric layer 11.

The axially opposite edges 11a of the self-supporting elastomeric layer 11 adhere to the radially internal surface of the liner 9 during the building of the green tyre 1, and cross-link with it during the vulcanisation process, fixing the sealing assembly 12 to the tyre, while containing the polymeric sealing material 10.

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 semi-finished products on one or more forming supports, not illustrated.

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

More specifically, 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 the self-supporting elastomeric layer 11 with a width such as to leave exposed the axially opposite edges 11a of the self-supporting elastomeric layer 11 (FIG. 2).

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.

The self-supporting elastomeric layer 11, before incorporating the sealing assembly 12 in the precursor of the tyre 1 and its conformation, has a thickness “t4” of less than 2 mm and preferably less than 1 mm.

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 self-supporting elastomeric layer 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).

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.

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 inner surface of the outer sleeve.

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.

After building of green tyre, a moulding and vulcanisation treatment is generally carried out in order to determine the structural stabilisation of the tyre through cross-linking 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.

During vulcanisation, despite the high temperatures used, the self-supporting elastomeric layer 11 and the sealing material 10 remain intact, do not damage the vulcanisation membrane and achieve optimal sealing performance.

In FIG. 3, the sealing assembly 10 of FIG. 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 self-supporting elastomeric layer 11 to give the ribbon-like composite, which is cooled and generally stored wound on a reel.

As shown in FIG. 4, the tyre 1 may finally comprise a layer of noise reducing material or element 13, made of expanded polymeric material, applied to the radially internal surface of the self-supporting layer 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 can be made to adhere to the radially internal surface of the self-supporting layer 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.

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.

EXAMPLES

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

A sealing assembly 1 obtained according to the teaching of WO2011064698 and comprising a self-supporting layer of Filmon CXS18 polyamide of nominal 18 micron thickness was used as a reference.

A sealing assembly 2 comprising a self-supporting layer of 0.5 mm made of elastomeric material obtained with the composition of the following Table 1 was used as a comparison (Compound A).

TABLE 1

Component
Quantity (phr)

BIIR
100

NC
21

Talc
25

Resin
6

Oil 1
3

Oil 2
5

ZnO
3

Stearic acid
2

Accelerant
1.5

Sulphur
0.5

BIIR: bromoisobutyl rubber BIIR 2222 - Exxon;

NC: Carbon Black N234 from Cabot Corporation;

Talc: Minstron HAR produced by Imerys Talc France;

Resin: Struktol ® 40MS from Struktol Corporation;

Oil 1: Paraffin oil PM oil from LLK International

Oil 2: Tris(2-ethylhexyl)phosphate DISFLAMOLL TOF by Lanxess

ZnO: Standard Zn oxide from A-Esse;

Accelerant: Rhenogran MBTS 80 from Rheinchemie

Sulphur: Insoluble sulphur 67%, Sulphotechnics.

A sealing assembly 3 according to the present invention comprises a self-supporting layer of 0.5 mm or 0.4 mm made of elastomeric material obtained with the composition of the following Table 2 (Compound B).

TABLE 2

Component
Quantity (phr)

NR
100

Talc
30

Surfactant
10

ZnO
4

Stearic acid
2

Antioxidant
2

Accelerant 1
1

Accelerant 2
9

Accelerant 3
2.5

Sulphur
0.3

NR: natural rubber (Standard Thai Rubber STR 20 - Thaiteck Rubber);

Talc: Minstron HAR produced by Imerys Talc France;

Surfactant: Crodamide ™ SR from Croda Italia SpA;

ZnO: Standard Zn oxide from A-Esse;

Antioxidant: Santoflex ® 6PPD from Eastman

Accelerant 1: Vulkacit ® CZ/EG-C from Lanxess