"SELF-SEALING TYRE COMPRISING A SEALING MATERIAL"

Field of the invention

The present invention relates to a self-sealing tyre for vehicle wheels. More in particular, the present invention relates to a self-sealing tyre for vehicle wheels comprising a sealing material, to the process for manufacturing said tyre, and to said sealing material.

Background of the invention

In the industrial field of tyres for vehicle wheels, various attempts have been made to produce self-sealing tyres, in other words tyres which may retard or prevent the loss of air and consequent deflation of the tyres themselves following a puncture caused e.g. by a sharp object (a nail, for example).

To achieve the above goal, self-sealing tyres are known which are provided with at least one layer comprising a polymeric material which may adhere to the object causing the puncture and may also flow into the puncture site when said object is removed, thus sealing the puncture and preventing the outflow of air from the tyre.

Self-sealing tyres are described, for example, in United States Patent US 3,981 ,342 which discloses a self-sealing tubeless tyre provided with a layer including a composition comprising a mixture of a low molecular weight liquid elastomer and a high molecular weight solid elastomer, and a quantity of a cross-linking agent sufficient to give a partial cross- linking of said mixture, said liquid elastomer being present in a greater quantity than said solid elastomer.

United States Patent US 4,228,839 discloses a self-sealing tyre provided with a layer comprising a mixture of a radiation-degradable polymeric material and a polymeric material which may be cross-linked by radiation and/or by heat.

United States Patent US 4,113,799 discloses a sealant composition comprising a high average molecular weight butyl rubber and a low average molecular weight butyl rubber in a ratio of high to low molecular weight butyl rubber of between about 20/80 to 60/40, in admixture with a tackifier present in an amount between about 55 and 70 weight % of the composition.

Summary of the invention

The Applicant has perceived that one of the major problems encountered in self-sealing tyres is that of finding a correct combination of properties for the sealing material used. In fact, said material must adhere to the object causing the puncture, to be moved rapidly inside the puncture and to not flow out of the puncture, in order to prevent the loss of air and the consequent deflation of the tyre.

Furthermore, the sealing material must maintain its position inside the tyre when the vehicle is halted or during storage. On the other hand, when the tyre is made to move, which could potentially create non- uniformities in the distribution of the sealing material, said sealing material must be capable of maintaining its uniform distribution inside the tyre. In fact, a displacement of the sealing material from its original position and its accumulation in other areas of the tyre would not only cause a loss of balance in the weight distribution within the tyre, but would also make its use as a sealing layer ineffective, or would at least impart an unsatisfactory self-sealing capacity to the tyre.

Additionally, the sealing material must also be capable of being applied during the building of the tyre, thus avoiding the need to subject the finished tyre to further post-production treatments.

Finally, the sealing material must not develop gas during the whole manufacturing process of the tyre, in particular during the vulcanization treatment under heat and pressure, to avoid formation of gas bubbles within the structure of the finished tyre. The Applicant has perceived

that butyl rubbers with low molecular weight are subjected to cracking and developing of gas bubbles during the vulcanization treatment.

The Applicant has now found that it is possible to obtain the desired combination of properties by using a sealing material comprising at least one butyl elastomer, at least one block copolymer elastomer, a low amount of at least one tackifying agent, and, preferably, at least one plasticizer and/or at least one elastomeric polymer different from said at least one butyl elastomer.

The Applicant has observed that said sealing material partially crosslinks and, consequently, it is able to maintain its position inside the finished tyre both when the vehicle is running or is halted and during storage, even maintaining the flowability necessary in order to moving rapidly inside the puncture. The skilled man would be able to select a specific degree of crosslinking with respect to the specific process or product requirements.

Moreover, the Applicant has observed that the use of said at least one tackifying agent in a low amount (e.g., in an amount not higher than or equal to 70 phr) makes the sealing material easily processable in conventional apparatus for rubber mixing such as, for example, a Banbury mixer.

Furthermore, the Applicant has observed that said sealing material does not significantly negatively affect the rolling resistance of the finished tyre.

In a first aspect, therefore, the present invention relates to a tyre for vehicle wheels, comprising:

- a carcass structure of a substantially toroidal shape, having opposite lateral edges terminating in respective bead structures, said carcass structure comprising at least one carcass ply;

- a belt structure applied in a radially external position with respect to said carcass structure, said belt structure comprising at least one belt layer;

- a tread band applied in a radially external position with respect to said belt structure;

- a pair of sidewalls applied laterally on opposite sides with respect to said carcass structure;

- at least one layer of sealing material applied in a radially inner position with respect to said at least one carcass ply; wherein said sealing material comprises: from 20 phr to 99 phr, preferably from 50 phr to 90 phr, of at least one butyl elastomer; from 1 phr to 80 phr, preferably from 10 phr to 50 phr, of at least one block copolymer elastomer; from 10 phr to 70 phr, preferably from 20 phr to 40 phr, of at least one tackifying agent.

For the purposes of the present description and of the claims which follow, the expression "phr" is intended to indicate the parts by weight of a given component per 100 parts by weight of the elastomer(s). For the purposes of the present description and of the claims which follow, except in the operating examples, or where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

In a preferred embodiment, said at least one layer of sealing material is applied between said at least one carcass ply and at least one layer of crosslinked elastomeήc materia] applied in a radially inner position with respect to said at least one carcass ply.

In a further preferred embodiment, a further layer of crosslinked elastomeric material is applied between said at least one layer of sealing material and said at least one carcass ply.

In a further preferred embodiment, said at least one layer of sealing material extends over a surface substantially corresponding to the surface of development of said tread band.

In an alternative preferred embodiment, said at least one layer of sealing material is applied in a radially inner position with respect to said at least one layer of crosslinked elastomeric material. In a further preferred embodiment, a strip of crosslinked elastomeric material, preferably having a substantially triangular cross section, is applied along each outer edge of said at least one layer of sealing material.

In a further preferred embodiment, said at least one layer of sealing material has a thickness in the range of from 1 mm to 5 mm, preferably in the range of from 2 mm to 4 mm.

According to an alternative embodiment, said at least one layer of sealing material is applied onto the inner surface of the finished tyre.

A tyre within the present invention, comprising said at least one layer of sealing material, may be made with no substantial increase of its rolling resistance (such as, for example, not higher than 2% with respect to the same tyre with no such at least one layer of sealing material).

In a further aspect, the present invention relates to a process for producing tyres for vehicle wheels, said process comprising:

- manufacturing a green tyre comprising at least one carcass ply;

- subjecting the green tyre to moulding in a mould cavity formed in a vulcanization mould;

- subjecting said green tyre to crosslinking by heating to a predetermined temperature and for a predetermined period;

wherein said process further comprises the application of, in a radially inner position with respect to said at least one carcass ply, at least one layer of sealing material, wherein said sealing material comprises: from 20 phr to 99 phr, preferably from 50 phr to 90 phr, of at least one butyl elastomer; from 1 phr to 80 phr, preferably from 10 phr to 50 phr, of at least one block copolymer elastomer; from 10 phr to 70 phr, preferably from 20 phr to 40 phr, of at least one tackifying agent.

According to one preferred embodiment, the application of said at least one layer of sealing material is carried out during the manufacturing of the green tyre.

According to an alternative embodiment, the application of said at least one layer of sealing material is carried out by applying the sealing material onto the inner surface of the finished tyre.

In a further preferred embodiment, the application of said at least one layer of sealing material is carried out by winding at least one ribbon- like band consisting of said sealing material in close coils along the cross-sectional profile of a support. Said ribbon-like band may be produced, for example, by extruding said sealing material from an extruder including a die having an extruding hole from which the sealing material is extruded into the desired cross sectional shape. Further details of the methods of forming and/or depositing the various components of the tyre on a support are described, for example, in

European Patent Applications EP 943,421 and EP 919,406, or in International Patent Application WO 01/36185.

In a further aspect, the present invention relates to a sealing material which comprises:

from 20 phr to 99 phr, preferably from 50 phr to 90 phr, of at least one butyl elastomer; from 1 phr to 80 phr, preferably from 10 phr to 50 phr, of at least one block copolymer elastomer; from 10 phr to 70 phr, preferably from 20 phr to 40 phr, of at least one tackifying agent.

According to one preferred embodiment, said sealing material may further comprise an amount of up to 40 phr, preferably of from 10 phr to 20 phr, of at least one plasticizer. According to a further preferred embodiment, said sealing material may further comprise an amount of up to 30 phr, preferably of from 5 phr to 20 phr, of at least one elastomeric polymer different from said butyl elastomer.

The present invention in at least one of the abovementioned aspect, may show one or more of the preferred characteristics hereinafter described.

The butyl elastomers advantageously employed in the present invention may be selected from rubber copolymer comprising, by weight, from 85% to 99.5% combined isoolefin having from 4 to 8 carbon atoms and 0.5% to 15% combined conjugated diolefin having 4 to 8 carbon atoms. Such copolymers and their preparation are well known. The isoolefin, such as isobutylene, is admixed with a conjugated diolefin having about 4 to 8 carbon atoms, such as butadiene or isoprene, preferably isoprene. Isobutylene is the common name for the 2-methyl-1-propene monomer. An inert diluent selected from C ₄ to C ₈ aliphatic alkanes and chlorinated hydrocarbons such as methyl chloride, ethyl chloride, methylene chloride and ethylene dichloride are admixed therewith. The monomers may form from 10% to 50% by weight of the total monomer/diluent mixture. The mixture is cooled and polymerized in a reactor at a temperature in the range from 0 ⁰ C to 165° C using a

cationic catalyst such as aluminum chloride, aluminum bromide, aluminum ethyl dichloride, titanium tetrachloride or boron trifluoride. The polymerization reaction proceeds rapidly to produce a copolymer in the form of a slurry in the diluent. The slurry is removed from the reactor and the copolymer separated therefrom and recovered by well-known methods.

Butyl elastomers which may be used advantageously according to the present invention have a number average molecular weight (M _n ) higher than 150,000, preferably in a range of from 200,000 to 2 or 3 millions or more.

Said number average molecular weight (M _n ) may be measured according to techniques known in the art such as, for example, by gel permeation chromatography (GPC).

Further details regarding butyl elastomers and the methods for their preparation may be found, for example, in United States Patents US 2,356,128, US 3,968,076, US 4,474,924, US 4,068,051 , or US 5,532,312.

Examples of commercially available butyl elastomers which may be used in the present invention are the products Exxon ^® butyl grade of poly(isobutylene-co-isoprene), Exxon ^® Butyl products, Vistanex ^® polyisobutylene rubber, from Exxon, or Bayer Butyl ^® products.

The above described butyl elastomers may be used alone or in a mixture of two or more different butyl elastomers. The total amount of the above described butyl elastomers or the mixture thereof ranges from 20 phr to 99 phr, preferably from 50 phr to 90 phr.

The block copolymer elastomers useful in the present invention comprise at least one segment of a styrenic polymer and at least one segment of an elastomeric saturated olefin polymer. Typically these block copolymer elastomers contain hard segments of styrenic type polymers in combination with soft elastomeric segments of a saturated

olefin polymer. The structure of the block copolymer elastomers useful in the present invention is not critical and may be of the diblock, triblock, radial type, or of a combination of these. Preferably, the predominant structure is that of the triblocks. Methods for the preparation of such block copolymer elastomers are known in the art. Suitable catalysts for the preparation of precursor of the present block copolymer elastomers (block polymers before hydrogenation) include lithium based catalysts and especially lithium- alkyls. United States Patent US 3,595,942 describes suitable hydrogenation methods. The structure of the polymers is determined by their methods of polymerization. For example, linear polymers result by sequential introduction of the desired monomers into the reaction vessel when using such initiators as lithium-alkyls or dilithiostilbene and the like, or by coupling a two segment block copolymer with a difunctional coupling agent. Branched structures, on the other hand, may be obtained by the use of suitable coupling agents having a functionality with respect to the precursor polymers of three or more. Coupling may be effected with multifunctional coupling agents such as dihaloalkanes or alkenes and divinyl benzene as well as certain polar compounds such as silicon halides, siloxanes or esters of monohydric alcohols with carboxylic acids.

Alternatively, selectively hydrogenated block copolymers having the configuration before hydrogenation of the following typical species: polystyrene-polybutadiene-polystyrene (SBS), polystyrene- polyisoprene-polystyrene (SIS), poly(alpha-methylstyrene)- polybutadiene-poly(alpha-methylstyrene) and poly(alpha- methylstyrene)-polyisoprene-poly(alpha-methylstyrene), may be used. The styrenic polymer portion of the block copolymer is preferably a polymer or interpolymer of styrene and its analogs and homohgs including alpha-methylstyrene and ring-substituted styrenes, particularly

ring-methylated styrenes. The preferred styrenics are styrene and alpha-methylstyrene, and styrene is particularly preferred.

Precursor of elastomeric saturated olefin polymer blocks may comprise homopolymers of butadiene or isoprene and copolymers of one or both of these two dienes with a minor amount of styrenic monomer. When the monomer employed is butadiene, it is preferred that between 35 mol percent and 55 mol percent of the condensed butadiene units in the butadiene polymer block have 1 ,2 configuration. Thus, when such a block is hydrogenated, the resulting product is, or resembles, a regular copolymer block of ethylene and 1-butene (EB). If the conjugated diene employed is isoprene, the resulting hydrogenated product is or resembles a regular copolymer block of ethylene and propylene (EP). Preferred examples of such elastomeric saturated olefin polymer blocks include ethylene/butylene or a ethylene/propylene copolymers. Preferred block copolymer elastomers comprise at least one segment of a styrene polymer and at least one segment of an ethylene/butylene or ethylene/propylene copolymer. The most preferred elastomer block copolymer comprises a S-EB-S triblock copolymer, wherein S is a styrene polymer. These block copolymers may be modified by grafting minor amounts of functional groups to them, such as for example maleic anhydride.

Hydrogenation of the precursor block copolymers is preferably effected by use of a catalyst comprising the reaction products of an aluminum alkyl compound with nickel or cobalt carboxylates or alkoxides under such conditions as to substantially completely hydrogenate at least 80% of the aliphatic double bonds while hydrogenating no more than 25% of the styrenic aromatic double bonds.

The proportion of the styrenic blocks is generally between 8% and 65% by weight of the block copolymer. Preferably, the block copolymers

contain from 10 weight percent to 35 weight percent of styrenic polymer segments and from 90 weight percent to 65 weight percent of elastomeric saturated olefin polymer segments, based on the total weight of the block copolymer. The number average molecular weights (M _n ) of the individual blocks may vary within certain limits. In most instances, the styrenic blocks will have number average molecular weights (M _n ) in the order of from 5,000 to 125,000, preferably of from 7,000 to 60,000 while the conjugated diene blocks either before or after hydrogenation will have number average molecular weights (M _n ) in the order of from 10,000 to300,000, preferably of from 30,000 to 150,000. The total number average molecular weight of the block copolymer is typically in the order of from 25,000 to 250,000, preferably of from 35,000 to 200,000. These number average molecular weights (M _n ) may be accurately determined by tritium counting methods or osmotic pressure measurements.

Block copolymers useful in the present invention are commercially available, such as the Kraton ^® G 1600 and G 1700 rubber series available from Kraton Polymers LLC, Houston, Texas. Specific suitable block copolymers are Kraton ^® G1650, G1651 , G1652, G1657, G1702, and G1726M.

The above described block copolymer elastomers may be used alone or in a mixture of two or more different block copolymers. The total amount of the above described block copolymers or the mixture thereof ranges of from 1 phr to 80 phr, preferably of from 10 phr to 50 phr, and most preferably of from 20 phr to 40 phr.

The tackifying agents advantageously employed in the present invention may be selected from the group of hydrocarbon resins. The tackifying agents providing tackiness to the rubber composition means, in general, a hydrocarbon resin which has a number average molecular weight in the range of several hundreds to several thousands and

provides tackiness when the resin is mixed with natural rubber or synthetic rubbers. As the resin, various types of synthetic resins may be used.

Said number average molecular weight (M _n ) may be measured according to techniques known in the art such as, for example, by gel permeation chromatography (GPC).

Specifically, synthetic resins such as petroleum-based resins, phenol-based resins, coal-based resins and xylene-based resins and natural resins such as rosin-based resins and terpene-based resins may be used.

The petroleum-based resin may be obtained by polymerizing a fraction of cracking oil in the presence of a Friedel-Crafts-type catalyst without separating the components. The fraction of cracking oil is formed as a byproduct in the thermal cracking of naphtha in the petrochemical industry in combination with basic materials of the petrochemical industry such as ethylene and propylene and contains unsaturated hydrocarbons such as olefins and diolefins. Examples of the commercial product of the aromatic petroleum resin as shown by the trade name include PETROSIN manufactured by MITSUI SEKIYU KAGAKU Co., Ltd., PETRITE manufactured by MIKUNI KAGAKU Co.,

Ltd., NEOPOLYMER manufactured by NIPPON SEKIYU KAGAKU Co., Ltd., and PETCOAL manufactured by TOYO SODA Co., Ltd.

Examples of the phenol-based resin described above include alkylphenol-formaldehyde-based resins, modified resins thereof with rosin, alkylphenol-acetylene-based resins, modified alkylphenol resins and terpene-phenol resins. Specific examples include commercial products (shown by the trade names) such as HITANOL 1502 (manufactured by HITACHI KASEI Co., Ltd.) which is a novolak-type alkylphenol resin and KORESIN (manufactured by BASF Company) which is a p-t-butylphenol-acetylene resin.

Examples of the coal-based resin include coumarone-indene resins. Specific examples include commercial products (shown by the trade names) such as NOVARES C resins (manufactured by RUTGERS CHEMICAL GmbH) which are purely synthetic indene-coumarone- resins (like NOVARES C 10, C30, and C70) produced by the polymerization of the so-called indene fraction obtained from the distillation of coal tar, or such as NOVARES CA resins, which are phenol-modified indene-coumarone-resins.

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

The tackifying agents advantageously employed in the present invention may also be selected from liquid polymers having a number average molecular weight (M _n ) of from 500 to 50,000, preferably of from 1 ,000 to 10,000. The liquid polymer means a polymer which is fluid at the room temperature. The structure of the liquid polymer is not particularly limited as long as the number average molecular weight (M _n ) is within the above range.

Said number average molecular weight (M _n ) may be measured according to techniques known in the art such as, for example, by gel permeation chromatography (GPC).

Examples of the liquid polymer include styrene-butadiene rubber (SBR), butadiene rubber (BR), and polyisobutylene.

Among these liquid polymers, copolymers of styrene and butadiene having a relatively low molecular weight are preferable. For example, styrene-butadiene copolymers having a number average molecular weight (M _n ) of from 5,000 to 10,000 expressed as the molecular weight of the corresponding polystyrene may be advantageously used. Useful examples of such styrene-butadiene copolymers include RICON 100, 181, and 184 (manufactured by SARTOMER Company). Useful examples of butadiene polymers include RICON 130, 131 , 134, 142,

150, 152, 153, 154, 156, and 157 (manufactured by SARTOMER Company).

The above described tackifying agents may be used alone or in a mixture of two or more different tackifying agents. The total amount of the above described tackifying agents or the mixture thereof ranges from 10 phr to 70 phr, preferably of from 20 phr to 40 phr.

The plasticizer advantageously employed in the present may be selected from: mineral oils, vegetable oils, synthetic oils, or mixtures thereof such as, for example, aromatic oil [such as, for example, mild extraction solvate oils (MES-oils)j, naphthenic oil, phthalates, phosphates, epoxidized oils, soya oil, or mixtures thereof. MES-oils are particularly preferred in the present invention. MES-oils are usually produced by solvent extraction of heavy oil distillates or by treating heavy oil distillates with hydrogen in the presence of catalysts (hydration). Suitable MES oils are available commercially as Catenex ^®

SNR from Shell, Prorex ^® 15 and Flexon ^® 683 from ExxonMobil, VivaTec ^® 200 from BP, Plaxolene ^® MS from TotalFinaElf, Tudalen ^® 4160/4225 from Dahleke, MES-H from Repsol, MES from Z8, and Olio MES S201 from Agip. The plasticizer is preferably added to the sealant material according to the present invention in an amount of up to 40 phr, preferably of from 10 phr to 20 phr.

The elastomeric polymer different from said butyl elastomer advantageously employed in the present invention may be selected from diene elastomers commonly used in sulfur-crosslinkable elastomeric materials, that are particularly suitable for producing tires, that is to say from elastomeric polymers or copolymers with an unsaturated chain having a glass transition temperature (T ₉ ) generally below 20 ⁰ C, preferably in the range of from O ⁰ C to -110 ⁰ C. These polymers or copolymers may be of natural origin or may be obtained by

solution polymerization, emulsion polymerization or gas-phase polymerization of one or more conjugated diolefins, optionally blended with at least one comonomer selected from monovinylarenes and/or polar comonomers in an amount of not more than 60% by weight. The 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.

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, aryi, 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-tolylstyrene, 4-(4-phenylbutyl)styrene, or mixtures thereof. Styrene is particularly preferred.

Polar comonomers which 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, or mixtures thereof.

Preferably, said diene elastomers may be selected, for example, from: cis-1 ,4-polyisoprene (natural or synthetic, preferably synthetic rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high 1 ,4-cis content), 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.

Alternatively, said elastomeric polymer different from said butyl elastomer may be selected, for example, from elastomeric polymers of one or more monoolefins with an olefinic comonomer or derivatives thereof. The monoolefins may be selected, for example, from: ethylene and α-olefins generally containing from 3 to 12 carbon atoms, such as, for example, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof. The following are preferred: copolymers between ethylene and an α-olefin, optionally with a diene; isobutene homopolymers or copolymers thereof with small amounts of a diene, which are optionally at least partially halogenated. The diene optionally present generally contains from 4 to 20 carbon atoms and is preferably selected from: 1 ,3-butadiene, isoprene, 1,4-hexadiene, 1,4- cyclohexadiene, 5-ethyIidene-2-norbornene, 5-methylene-2- norbornene, vinylnorbornene, or mixtures thereof. Among these, the following are particularly preferred: ethylene/propylene copolymers (EPR) or ethylene/propylene/diene copolymers (EPDM) or mixtures thereof.

The above described elastomeric polymers different from said butyl elastomer may be used alone or in a mixture of two or more different elastomeric polymers. The above described elastomeric polymers different from said butyl elastomer or the mixture thereof are preferably added to the sealing material according to the present invention in an amount of up to 30 phr, preferably of from 5 phr to 20 phr.

In a preferred embodiment, the sealing material according to the present invention additionally comprises a reinforcing filler. The reinforcing filler may be selected from carbon black, silica, alumina, aluminosilicates, calcium carbonate, kaolin, or mixtures thereof. Carbon black is preferred.

The types of carbon black which may be used according to the present invention may be selected from those conventionally used in

the production of tyres which generally have a surface area of not lower than 20 m ² /g (determined by absorption of CTAB as described in the ISO 6810 standard). Alternatively, carbon blacks having a surface area lower than 20 m ² /g may also be used. The silica which may be used according to the present invention may generally be a pyrogenic silica or, preferably, a precipitated silica, having a surface area BET (measured according to the ISO 5794/1 standard) in the range of from 50 m ² /g to 500 m ² /g, preferably of from 70 m ² /g to 200 m ² /g. Alternatively, silica having a surface area BET lower than 50 m ² /g may also be used.

The reinforcing filler is preferably added to the sealant material according to the present invention in an amount of from 10 phr to 70 phr, preferably of from 20 phr to 60 phr.

The sealing material according to the present invention may optionally comprise other additives commonly used in elastomeric compositions. For example, antioxidants, anti-ageing agents, adhesives, anti-ozone agents, modifying resins, coupling agents for silica (such as, for example, silanes), or mixtures thereof may be added to said sealing material. As disclosed above, the application of said at least one layer of sealing material may be carried out during the manufacturing of the green tyre.

In this case, for example, the application may be carried out, for example, by applying at least one layer of sealing material onto a support and then superimposing at least one layer of elastomeric material, generally called "liner" which provide the necessary impermeability to the inflation air of the tyre. Said at least one layer of sealing material may be prevented from adhering to the support, for eaxmple, by first applying at least one layer of flexible material onto the support, followed by the application of at least one layer of sealing

material. Thus, said at least one layer of elastomeric material may first be applied onto the support, followed by the application of said at least one layer of sealing material and of at least one carcass ply.

Alternatively, said "liner" may first be applied onto the support, followed by the application of said at least one layer of sealing material and of said at least one carcass ply.

Alternatively, a "liner" may first be applied onto the support, followed by the application of at least one layer of sealing material and of at least one further layer of elastomeric material, generally called "underliner", which may also be provided as an additional means for ensuring the impermeability of the tyre.

As disclosed above, the application of said at least one layer of sealing material may also be carried out by applying the sealing material onto the inner surface of the finished tyre. In order to apply said at least one layer of sealing material onto the inner surface of the finished tyre, the sealing material may be prepared as a solution, for example, as a solution in n-hexane or other suitable volatile organic solvent. This solution may be applied, for example, by spraying or brushing, over the desired area of the inner surface of the finished tyre, using as many coats as required to build up a desired thickness.

Another method is to extrude the sealing material onto the inner surface of the finished tyre at elevated temperature in the form of a layer having the desired thickness. Conveniently, the sealing material may be extruded directly onto the tyre carcass surface from a suitable shaped die extending onto the tyre carcass, while rotating the tyre.

Alternatively, a previously prepared layer such as, for example, an extruded layer of sealing material of suitable width and thickness may be applied by any suitable means to the inner surface of the finished tyre.

The sealing material according to the present invention may be prepared by mixing the components indicated above with the other additives which may be present, according to methods known in the art. The mixing may be carried out, for example, by means of a mixer of the open-mill type, or an internal mixer of the type with tangential rotors

(Banbury) or interlocking rotors (Intermix), or in continuous mixers of the Ko-Kneader (Buss) type or the multiple-screws co-rotating or counter- rotating type.

Brief description of the drawings The present invention will now be illustrated in further detail by means of illustrative embodiments, with reference to the attached Fig. 1 and Fig. 2, which show a view in cross-section of a portion of a tyre made according to the present invention.

Detailed description of the preferred embodiments With reference to Fig. 1 and Fig. 2, "a" indicates an axial direction, and "r" indicates a radial direction. For simplicity, Fig. 1 and Fig. 2 show only a portion of the tyre, the remaining portion, which is not shown, being identical and symmetrically arranged with respect to the radial direction "r". The tyre (100) comprises at least one carcass ply (101) the opposite lateral edges of which are associated with respective bead structures (103) comprising at least one bead core (102) and at least one bead filler (104). The association between the carcass ply (101) and the bead core (102), in this case, is achieved by turning back the opposite lateral edges of the carcass ply (101) around the bead core (102), so as to form the so-called carcass turn-up (101a) as shown in Fig. 1 and Fig. 2. Alternatively, the conventional bead core (102) may be replaced with at least one annular insert formed by rubberized wires arranged in concentric coils (not shown in Fig. 1 and Fig. 2) (see, for example, European Patent Applications EP 928,680, or EP 928,702). In this case,

the carcass ply (101) is not turned-back around said annular inserts, the coupling being provided by a second carcass ply (not shown in Fig. 1 and Fig. 2) applied externally over the first ply.

The carcass ply (101) usually comprises a plurality of reinforcing cords arranged parallel to each other and at least partially coated with a layer of a crosslinked elastomeric material. These reinforcing cords are usually made of textile fibres such as, for example, rayon, nylon, polyethylene terephthalate, or of steel wires which are stranded together, coated with a metal alloy (for example copper/zinc, zinc/manganese, zinc/molybdenum/cobalt alloys and the like).

The carcass ply (101) is usually of the radial type; in other words, it incorporates reinforcing cords arranged in a substantially perpendicular direction with respect to a circumferential direction.

The bead core (102) is enclosed in a bead structure (103), defined along an inner circumferential edge of the tyre (100), with which the tyre engages on a rim (not shown in Fig. 1 and Fig. 2) forming part of a vehicle wheel. The space defined by each carcass turn-up (101a) contains a bead filler (104) usually made of a crosslinked elastomeric material. An antiabrasive strip (105) is usually placed in an axially outer position with respect to the carcass turn-up (101a).

A belt structure (106) is applied along the circumferential development of the carcass ply (101). In the particular embodiment shown in Fig. 1 and Fig. 2, the belt structure (106) comprises two belt layers (106a, 106b) which incorporate a plurality of reinforcing cords, typically metal cords, which are parallel to each other in each layer and intersecting with respect to the adjacent layer, orientated so as to form a predetermined angle with respect to a circumferential direction. On the radially outermost belt layer (106b), at least one zero-degree reinforcing layer (106c), commonly known as a 0° belt", which generally

incorporates a plurality of reinforcing cords, typically textile cords, arranged at an angle of few degrees (e.g. an angle of from 0° to 5°) relative to a circumferential direction, usually coated with a crosslinked elastomeric material. In the particular embodiment shown in Fig. 1 and Fig. 2, two zero-degrees reinforcing layers (106c, 106d).

A sidewall (108), is also applied externally onto the carcass ply (101), this sidewall extending, in an axially external position, from the bead structure (103) to the end of the belt structure (106).

A tread band (109), whose lateral edges are connected to the sidewalls (108), is applied circumferentially in a position radially external with respect to the belt structure (106). Externally, the tread band (109) has a rolling surface (109a) designed to come into contact with the ground. In this surface (109a), shown for simplicity as smooth in Fig. 1 and Fig. 2, there are generally made circumferential grooves which are connected by transverse notches (not shown in Fig. 1 and Fig. 2) so as to define a plurality of blocks of various shapes and sizes distributed over the rolling surface (109a).

In the connecting zone between the sidewalls (108) and the tread band (109) there may optionally be present a strip of crosslinked elastomeric material (110) commonly known as a "mini-sidewaH", which is generally obtained by co-extrusion with the tread band (109) and enables the mechanical interaction between the tread band (109) and the sidewalls (108) to be improved. Alternatively, the end portion of the sidewall (108) is made to directly cover the lateral edge of the tread band (109). Between the belt structure (106) and the tread band (109) there may optionally be present a tread underlayer (not shown in Fig. 1 and Fig. 2).

In the case of tubeless tyres, a layer of crosslinked elastomeric material (111), generally known as a "liner", may also be provided in a

radially inner position with respect to the carcass ply (101), to provide the necessary impermeability to the inflation air of the tyre.

A layer of sealing material (107), according to the present invention, is applied in a radially inner position with respect to said layer of crosslinked elastomeric material (111) (Fig. 1).

A further layer of crosslinked elastomeric material (113), generally known as a "under-liner", may also be provided above the layer of crosslinked elastomeric material (111), as an additional means of ensuring the impermeability of the tyre to an inflating fluid when the tyre is fitted on a rim and inflated: in this case a layer of sealing material

(107), according to the present invention, is applied between said layer of crosslinked elastomeric material (111) and said further layer of crosslinked elastomeric material (113).

Two strips of crosslinked elastomeric material with an essentially triangular cross section (112) may optionally be placed along each outer edge of the layer of sealing material (107), as shown in Fig. 2. Said strips have the function of containing the sealing material in a specified area, thus preventing, for example, infiltrations of the material between the adjacent elements, particularly during the vulcanization of the tyre. Said infiltrations could cause problems of co-vulcanization and detachment of said elements, which would tend to detract from the performance and durability of the finished tyre.

Said layer of sealing material (107) may, if desired, cover the entire inner surface of the tyre from one bead or rim area to the other: in this case the "liner" (111) may be omitted and the layer of sealing material

(107) may act as a "liner".

The present invention is further illustrated below by means of a number of preparation, which are given for purely indicative purposes and without any limitation of this invention.

EXAMPLES 1-4

The compositions given in Table 1 (the amounts of the various components are given in phr) were prepared as follows.

First, the elastomers (Butyl 268 and IR SKI 3) were loaded into an internal mixer of the type with tangential rotors (Banbury), which was rotated at approximately 60 r.p.m for approximately 1 minute. After, the carbon black (N660) the plasticizer (MES oil), and half part of the tackifying agent (Novares C30, and/or Ricon 100, and/or Koresin), were added and the mixing was carried out at approximately 60 r.p.m for approximately 1 minute. Subsequently, the remaining part of the plasticizer were added and the mixing was carried out at approximately 60 r.p.m. After approximately three minutes, but in any case as soon as the temperature reached 120 ⁰ C, the compositions were discharged from the mixer and then transferred to an open mill mixer.

TABLE 1

Butyl 268 is a butyl elastomer having a number average molecular weight (M _n ) of 890,000, manufactured by Exxon;

IR SKI 3 is a cis-1 ,4-polyisoprene rubber manufactured by Nizhnekamsk Neftechim Export;

Kraton ^® G1651 is a styrene-ethylene/butylene-styrene (SEBS) block copolymer elastomer manufactured by Kraton Polymers LLC;

N660 is carbon black;

Catenex ^® SNR is a MES-oils, manufactured by Shell; Novares ^® C30 is a coumarone-indene resin, manufactured by

Rutgers Chemical GmbH;

Ricon ^® 100 is a liquid styrene-butadiene copolymers, manufactured by Sartomer Company;

Koresin ^® is a p-t-butylphenol-acetylene resin, manufactured by BASF Company.

The compositions of Samples 1 to 4 were used to prepare a layer of sealing material for Pirelli Pzero Rosso 235/45R17 tyres. The layer of sealing material had a thickness of about 3.0 mm and was positioned between the liner and the underliner (as represented in Fig. 1) . The tyres were mounted on standard rims and inflated to a pressure of about 2.5 bars.

STATIC TEST

The tyres made as disclosed above were randomly punctured with three pairs of nails having length of 60 mm and diameter of 3, 4, and 5 mm, respectively. A set of tyres was left in storage for 72 hours with the nails inserted, and a set of tyres was left in storage for 72 hours after having extracted the nails. At the end of this period, it was found that all the tyres were still substantially inflated.

DYNAMIC TEST The tyres were randomly punctured as for the static test. The punctured inflated tyres (with and without nails) were run under a load of 350 kg at the speed of 100 km/h for a period of one hour. A drift angle of about 2° was cyclically applied every 5 minutes for the whole duration of the test. After that, they were stored for 72 hours. The tyres, with and without nails, remained inflated for the whole duration of the

test, and did not show any loss of pressure in the subsequent period of 72 hours.

A second dynamic test was made under the same conditions but without application of the drift angle and at a speed of 240 km/h for one hour. The results remained substantially unchanged.