EP4648976A1 - Tyre for bicycle wheels - Google Patents

Abstract

The present invention relates to a tyre (100) for bicycle wheels comprising: - a carcass structure (2) comprising at least one carcass ply (3) having ends (3a) turned up around respective bead cores (4a, 4b) to form respective opposite beads (5a, 5b), - a tread band (7) arranged in a radially outside position with respect to said carcass structure (2), and - a layer of vulcanised elastomeric material (8) superimposed, in a radially inside or outside position, to the carcass structure (2), or interposed in the carcass structure (2), said layer of vulcanised elastomeric material (8) axially extending from at least one bead (5a) to the opposite bead (5b), characterised in that said layer of vulcanised elastomeric material (8) is made by vulcanisation of a vulcanisable elastomeric compound comprising micrometre-sized fibrillated polymer fibres.

Description

TITLE

“Tyre for bicycle wheels"

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to a tyre for bicycle wheels with improved performance. The tyre of the present invention may be used on the wheels of racing bicycles, off-road bicycles, and in city bicycles.

PRIOR ART

A tyre for bicycle wheels typically comprises a carcass structure turned around a pair of bead cores at the beads and a tread band arranged in a radially outside position with respect to the carcass structure.

The carcass structure is intended to withstand the inflation pressure and to support the weight of the bicycle and the cyclist. It comprises one or more carcass plies, each comprising a plurality of suitably oriented reinforcing cords. In the case of several carcass plies, they are inclined with respect to each other to form a crossed structure.

The bead cores, also defined as annular anchoring structures, have the task of ensuring the anchoring of the tyre to the wheel rim.

The tread band is designed to guarantee the grip of the tyre to the asphalt or to the ground (or in general to the rolling surface).

In the radially inside position of the carcass structure, an air chamber may be provided in which pressurised air is introduced.

However, there are types of tyres called “tubeless”, i.e. without an inner tube. In these tyres, the pressurised air acts directly on the carcass structure and a layer called “liner” is provided which extends between the pair of bead cores and which is placed radially between the carcass structure and the tread band or, alternatively, in a radial position inside the carcass, to allow air tightness. The carcass structure, the annular anchoring structures and the wheel rim are shaped in such a way that their mutual anchoring guarantees air tightness.

There is a further type of tyre called “tubeless ready”, without an inner tube and in which the liner is replaced by a ply from bead to bead which extends between the pair of bead cores (called “bead to bead”). The bead-to-bead ply is placed radially between the tread band and the carcass structure. The air tightness is guaranteed by a sealant which is inserted between the tyre and the bicycle rim and which forms a thin airtight film. The carcass structure, the annular anchoring structures and the wheel rim are shaped in such a way that their mutual anchoring guarantees air tightness.

To avoid the penetration of debris into the carcass structure and, consequently, the puncturing of any inner tube and/or damage to the carcass structure itself, a protective layer (also known as “anti-puncture layer” or breaker) may be provided at a position radially inside the tread band. This protective layer may be arranged radially inside the carcass structure or be placed radially between the carcass structure and the tread band.

SUMMARY OF THE INVENTION

The Applicant has observed that for the optimisation of the performance of tyres for bicycle wheels, many needs must be taken into account, which are interconnected with each other and in some cases in conflict with each other.

In particular, the Applicant has observed that the requests for tyres for bicycle wheels require good puncture resistance, i.e. good resistance of the tyre to puncture and tearing, at the same time as perfect air tightness, good comfort and manoeuvrability, low rolling resistance and low weight.

The Applicant faced the problem of creating a tyre that best satisfied all the required features.

The Applicant has observed that the use in tyres intended for use without an inner tube, i.e. tubeless or tubeless ready tyres, of a layer made with an elastomeric compound comprising micrometre-sized fibrillated polymer fibres placed in a radially inside position with respect to the carcass structure in place of the liner or “bead-to-bead” ply allowed the aforementioned object to be achieved.

In particular, the Applicant observed that the layer made with an elastomeric compound comprising micrometre-sized fibrillated polymer fibres placed in a radially inside position with respect to the carcass structure allowed good resistance to puncture and good air tightness to be obtained in all the conditions of use, while maintaining good driving comfort and manoeuvrability, and a weight equivalent to or even lower than the weight of a conventional tubeless or tubeless ready tyre. The Applicant has in fact observed that the presence of micrometre-sized fibrillated polymer fibres gave the elastomeric compound of the layer a good impermeability to air such as to guarantee the air tightness of the tyre without the need to use the halogenbutyl compounds typically used in the liner of tubeless tyres.

Furthermore, the Applicant observed that the presence of micrometresized fibrillated polymer fibres gave the elastomeric compound of the layer excellent resistance to puncture.

In addition, the Applicant observed that the elastomeric compound comprising micrometre-sized fibrillated polymer fibres exhibited low hysteresis, predictive of reduced rolling resistance.

Finally, the Applicant observed that the tyre made with an elastomeric compound comprising micrometre-sized fibrillated polymer fibres placed in a radially inside position with respect to the carcass structure had weight, comfort and manoeuvrability features equivalent, if not better, compared to conventional tubeless or tubeless ready tyres.

Continuing with the experimentation, the Applicant also observed that similar results were also found by placing the layer made with an elastomeric compound comprising micrometre-sized fibrillated polymer fibres in a radially outside position with respect to the carcass structure or interposed between the carcass plies.

Therefore, in a first aspect thereof, the present invention relates to a tyre for bicycle wheels comprising

- a carcass structure (2) comprising at least one carcass ply (3) having ends (3a) turned up around respective bead cores (4a, 4b) to form respective opposite beads (5a, 5b),

- a tread band (7) arranged in a radially outside position with respect to said carcass structure (2), and

- a layer of vulcanised elastomeric material (8) superimposed, in a radially inside or outside position, to the carcass structure (2), or interposed in the carcass structure (2), said layer of vulcanised elastomeric material (8) axially extending from at least one bead (5a) to the opposite bead (5b), wherein said layer of vulcanised elastomeric material (8) is made by vulcanisation of a vulcanisable elastomeric compound comprising micrometre-sized fibrillated polymer fibres.

DESCRIPTION OF THE INVENTION

In the present description and following claims, the following definitions apply.

"Racing bicycles" is meant to refer to high performance bicycles for road or track competitions. These bicycles include those that meet the rules established by the Union Cycliste Internationale (UCI) - Title I - General Organization of Cycling Sports - Chapter 3: Equipment Section 2. Within the present scope, recumbent bicycles, time trial bicycles and/or triathlon bicycles are also included. Also included are the so-called fitness bikes (racing bikes for recreational use).

“City bicycles” is meant to refer to bicycles intended for a predominantly urban use for urban journeys on roads or mainly asphalted cycleways (urban bikes, city bikes, trekking bikes and touring bikes, as well as electric or pedal- assisted versions). These bicycles are generally fitted with accessories designed to improve safety and comfort of use, such as good front and rear lighting for good visibility, a crankcase (or chain cover) to protect clothes from the chain, a luggage rack for light luggage or a front basket, and are generally made with 26" or 28" wheels with intermediate covers, neither too smooth as for racing bikes nor with blocks as for off-road bicycles.

“Off-road bicycles” is meant to refer to bicycles intended to cover typically uneven or irregular terrain, that is, grounds very different from each other and different from asphalt, such as muddy, sandy, rocky, compact, soft ground, and so on. These bicycles include those that meet the rules established by the Union Cycliste Internationale (UCI) for the respective specialties and include in particular mountain bikes (MTB) or all terrain bikes (ATB), conventionally divided into the Cross Country (XC), Marathon, Trail, All Mountain, Enduro, Freeride, and Downhill categories, as well as fat bikes, cyclocross, and electric or pedal-assisted versions.

By “equatorial plane” of the tyre it is meant a plane perpendicular to the axis of rotation of the tyre and which divides the tyre into two symmetrically equal parts.

The terms “radial” and “axial” and the expressions “radially inside/outside” and “axially inside/outside” are used referring to a direction perpendicular and a direction parallel to the axis of rotation of the tyre, respectively.

The terms "circumferential" and "circumferentially" are used with reference to the direction of the annular development of the tyre, i.e. to the rolling direction of the tyre, which corresponds to a direction lying on a plane coinciding with or parallel to the equatorial plane of the tyre.

The term “elastomeric compound” is used to designate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such composition further comprises additives such as, for example, a cross-linking agent and/or a plasticiser. Due to the presence of the cross-linking agent, such a compound may be cross-linked (vulcanised) by heating.

The term "elastomeric polymer" or "elastomer" is meant herein to indicate a vulcanisable natural or synthetic polymer which, at room temperature, after being subjected to vulcanisation, is susceptible to deformations due to a force and is capable of recovering rapidly and vigorously the substantially original shape and dimensions after the elimination of the deforming force (according to the definitions of the ASTM D1566-11 Standard terminology relating to Rubber).

The term "cord" or the expression "reinforcing cord" is used to indicate an element consisting of one or more thread-like elements (hereinafter also referred to as "threads") optionally coated with, or incorporated into, an elastomeric compound matrix.

The expression “reinforced ribbon-like element” is meant to indicate an elongated article having a flattened cross-sectional profile and comprising one or more reinforcing cords extended parallel to the longitudinal development of the article and incorporated into, or at least partially coated with, at least one layer of an elastomeric compound matrix.

“Diameter” of a cord or thread means the thickness of the cord or thread measured as prescribed by the BISFA E10 method (The International Bureau For The Standardization Of Man-Made fibres, Internationally Agreed Methods For Testing Steel Tire Cords, 1995 edition).

“Density” or “density of cords” of a layer or a ply or a fabric means the number of reinforcing cords per unit of length present in such a layer/ply/fabric. The density is measurable in TPI (threads per inch).

“Linear density” or “thread count” of a cord or thread means the weight of the reinforcing cord per unit of length. The linear density may be measured in dtex (grams per 10 km in length).

The expression “high elastic modulus fibres” means fibres of a material having elastic modulus or stiffness of not less than 30 GPa, such as Aramid fibres and Lyocell fibres.

For aramid fibres (AR), the elastic modulus is evaluated according to BISFA - Testing methods for para-aramid fibre yarns, 2002 edition, Determination of linear density - Chapter 6, Determination of the tensile properties - Chapter 7 - Test procedures - Paragraph 7.5 - with procedure with initial pretensioning.

For lyocell fibres, the elastic modulus is evaluated according to: BISFA - Testing methods for viscose, cupro, acetate, triacetate and lyocell filament yarns - 2007 edition, Determination of tensile properties - Chapter 7 - Tensile test conditions: oven dry test - Table 7.1 - Test procedure - Paragraph 7.5 - With oven dry test on relaxed samples - Subparagraph 7.5.2.4.

The term “fitting diameter” of a tyre means the diameter of the tyre measured at the internal diameter of the bead cores for anchoring the tyre to the wheel rim, as prescribed in ETRTO (The European Tyre and Rim Technical Organization).

"Axial development of the tread band" or of portions thereof means the development of the radially outermost profile of the tread band or of portions thereof in a cross-section of the tyre performed by means of a plane containing the rotation axis of the tyre.

"Axial development of the tyre" means the development of the radially outermost profile of the tyre in a cross-section of the tyre performed by means of a plane containing the rotation axis of the tyre, such an axial development being measured between the ends of the tyre beads.

"Width" of a tyre means the maximum axial extension of the tyre, Sg width according to the ETRTO standard - Manual Standards 2022 - Cycle and Motorcycle Tyres - M5, such a width being measured between the axially outermost points of the tyre. “Tread camber” of the tyre means the camber measured through a camber radius of a portion of the profile of a cross section of the tyre.

By “camber radius” of a portion of the profile of a cross section of the tyre it is meant the radius of the circumference that best approximates that profile portion.

By “rolling resistance” it is meant the force that opposes the rolling of the tyre and, in more general terms, the energy dissipated by the rolling tyre per unit of distance travelled. The measurement of rolling resistance may be carried out, for example, according to the method described in Example 5.

Tyre for bicycle wheels

A tyre for bicycle wheels typically comprises a carcass structure turned around a pair of bead cores and a tread band arranged in a radially outside position with respect to the carcass structure.

The tyre for bicycle wheels is characterised by a high transverse camber. The tyre may be designed to be mounted on the wheels of a racing bicycle, either off-road or city.

Preferably, in the crown portion of a tyre for racing bicycle, the radius of camber of the tyre is between 10 mm and 18 mm, more preferably between 12 mm and 15 mm, ends included, while in the side portions the radius of camber is between 15 mm and 30 mm, more preferably between 20 mm and 25 mm. For example, the radius of camber in the crown portion may be equal to about 13 mm and the radius of camber in the side portions may be equal to about 25 mm.

Preferably, in the crown portion of a tyre for off-road bicycle, the radius of camber of the tyre is between 15 mm and 50 mm, more preferably between 25 mm and 35 mm, ends included, while in the side portions the radius of camber is between 15 mm and 60 mm, more preferably between 30 mm and 40 mm. For example, the radius of camber in the crown portion may be equal to about 30 mm and the radius of camber in the side portions may be equal to about 35 mm.

Preferably, in the case of a tyre for racing bicycle wheels, the tyre has a weight of less than about 400 g, preferably less than, or equal to, about 350 g-

Preferably, in the case of tyres for wheels of off-road bicycles, the tyre has a weight greater than, or equal to, about 300 g, more preferably greater than, or equal to, about 350 g.

Preferably, in the case of a tyre for city bicycle wheels, the tyre has a weight greater than about 250 g, preferably greater than, or equal to, about 350 g.

Preferably, in the case of a tyre for wheels of off-road or city bikes, the tyre has a weight of less than, or equal to, about 2 kg, more preferably less than, or equal to, about 1.5 kg, even more preferably less than, or equal to, about 750 g, even more preferably less than, or equal to, about 650 g.

In preferred embodiments, in the case of a tyre for off-road bicycle wheels, the tyre has a weight of between about 300 g and about 2 kg, more preferably between about 350 g and about 1.5 kg, more preferably between about 350 g and about 750 g, more preferably between about 350 g and about 650 g, ends included.

Carcass structure

Preferably, the carcass structure of the tyre of the present invention comprises at least one carcass ply engaged, at the axially opposite ends thereof, with a pair of annular anchoring structures, commonly called bead cores, and including a plurality of reinforcing cords inclined, with respect to an equatorial plane of the tyre, by a first angle of between about 30° and about 60°, ends included.

Preferably, the reinforcing cords of said at least one carcass ply are made of a textile material, so as to limit the weight of the tyre as much as possible.

The reinforcing cords are preferably made of a textile material selected from Nylon, Rayon, PET, PEN, Lyocell, Aramid, or combinations thereof, in one or more ends, preferably 1 or 2 ends.

Specific examples of textile materials that may be used for the reinforcing cords are Nylon 930 dtex/1 , Nylon 470 dtex/1 , Nylon 230 dtex/1 , and Aramid 470/1 fibres, where number 1 after dtex indicates the number of ends.

In a first embodiment of the tyre, the carcass structure comprises a single carcass ply. Hereinafter, such a tyre is also referred to as a “single-ply tyre”.

In a second embodiment of the tyre, the carcass structure comprises a first carcass ply comprising a first plurality of reinforcing cords inclined, with respect to said equatorial plane, by said first angle and a second carcass ply arranged in a radially outside position to the first carcass ply and including a second plurality of reinforcing cords inclined, with respect to said equatorial plane, by said first angle on the side opposite to said first plurality of cords, so as to define a crossed, preferably two-ply, carcass structure. Hereinafter, such a tyre is also referred to as a “two-ply tyre”.

In alternative embodiments, the carcass structure may comprise more than two carcass plies, each carcass ply being arranged so as to define a cross-structure with the adjacent radially inside carcass ply, completely identical to that described above with reference to the first and second carcass plies.

The reinforcing cords are inclined, with respect to the equatorial plane of the tyre, by an angle of between about 30° and about 60°, ends included.

Preferably, in the case of a single-ply tyre, the aforementioned angle is approximately 45°, in which case the flaps may exhibit inclinations in the crown portion that are parallel to each other and counter-inclined in proximity to the equatorial plane with respect to the inclination of the reinforcing elements of the first carcass layer (radially innermost).

In the case of a two-ply tyre, on the other hand, a first carcass ply includes a plurality of reinforcing cords inclined, with respect to the equatorial plane of the tyre, by an angle preferably between about 30° and about 60°, ends included, and a second carcass ply, arranged in a position radially outside to the first carcass ply, includes a second plurality of reinforcing cords inclined by the same angle, with respect to said equatorial plane, on the opposite side with respect to the reinforcing cords of the first carcass ply. In the latter case, the reinforcing cords lie on respective planes inclined with respect to the rotation axis, thus defining a crossed carcass structure.

In the case of a tyre for wheels of racing or city bicycles, preferably, the single carcass ply (in the case of a single-ply tyre), or each of the carcass plies (in the case of a tyre with two or more carcass plies), has a density greater than, or equal to, about 20 TPI, more preferably greater than, or equal to, about 30 TPI, even more preferably greater than, or equal to, about 60 TPI, even more preferably greater than, or equal to, about 120 TPI.

In the case of a tyre for wheels of racing or city bicycles, preferably, the single carcass ply (in the case of a single-ply tyre), or each of the carcass plies (in the case of a tyre with two or more carcass plies), has a density of less than, or equal to, about 360 TPI, more preferably less than, or equal to, about 300 TPI, even more preferably less than, or equal to, about 240 TPI, even more preferably less than or equal to, about 200 TPI.

In the case of a tyre for off-road bicycle wheels, preferably, the single carcass ply (in the case of a single-ply tyre), or each of the carcass plies (in the case of a tyre with two or more carcass plies), has a density greater than, or equal to, about 20 TPI, more preferably greater than, or equal to, about 60 TPI.

In the case of a tyre for off-road bicycle wheels, preferably, the single carcass ply (in the case of a single-ply tyre), or each of the carcass plies (in the case of a tyre with two or more carcass plies), has a density of less than, or equal to, about 150 TPI, more preferably less than, or equal to, about 120 TPI.

It is preferable that, in the case of a two-ply (or more than two carcass plies) tyre, the second carcass ply (or at least another carcass ply) has a density substantially identical to that of the first carcass ply.

Preferably, the reinforcing cords of the single carcass ply (in the case of a single-ply tyre) or of each carcass ply (in the case of a two-ply or more than two carcass plies tyre) have a diameter smaller than equal to, about 0.55 mm, more preferably smaller than, or equal to, about 0.35 mm.

Preferably, the reinforcing cords of the single carcass ply (in the case of a single-ply tyre) or of each carcass ply (in the case of a two-ply or more than two carcass plies tyre) have a diameter greater than, or equal to, about 0.10 mm, more preferably greater than, or equal to, about 0.12 mm.

Preferably, the reinforcing cords of the single carcass ply (in the case of a single-ply tyre) or of each carcass ply (in the case of a two-ply or more than two carcass plies tyre) have a linear density greater than, or equal to, about 110 dtex, more preferably greater than, or equal to, about 200 dtex.

Preferably, the reinforcing cords of the single carcass ply (in the case of a single-ply tyre) or of each carcass ply (in the case of a two-ply or more than two carcass plies tyre) have a linear density of less than equal to, about 1300 dtex, more preferably less than, or equal to, about 940 dtex.

Layer comprising fibrillated polymer fibres According to the present invention, the tyre for bicycle wheels comprises a layer of vulcanised elastomeric material superimposed, in a radially inside or outside position, on the carcass structure, or interposed in the carcass structure, wherein said layer of vulcanised elastomeric material is made by vulcanisation of a vulcanisable elastomeric compound comprising micrometre-sized fibrillated polymer fibres.

The elastomeric layer according to the present invention extends at the carcass structure symmetrically with respect to the equatorial plane of the tyre.

According to a preferred embodiment, the elastomeric layer according to the present invention extends up to 100% of the axial development of the tyre from bead to bead, overlapping in a position radially inside the carcass structure, as illustrated in Figures 2-5, and covering the carcass flap at the bead cores.

According to an alternative embodiment, the elastomeric layer according to the present invention extends up to 100% of the axial development of the tyre from bead to bead, interposing itself in the carcass structure, as illustrated in Figures 6 and 7. In particular, in Figure 6 the elastomeric layer according to the present invention is interposed between the two turned up ends of the carcass ply, in a radially outside position with respect to the bead cores, ending at the bead cores. Differently, in Figure 7 the layer according to the present invention is interposed in the carcass structure, in a radially inside position with respect to the bead cores, following the carcass flap around the bead cores.

According to a further alternative embodiment, the elastomeric layer according to the present invention extends up to 100% of the axial development of the tyre from bead to bead, overlapping in a position radially outside the carcass structure, as illustrated in Figure 8, ending at the bead cores.

Preferably, the thickness of the elastomeric layer according to the present invention is between 0.1 mm and 0.7 mm, more preferably from 0.2 mm to 0.6 mm, advantageously from 0.3 mm to 0.5 mm.

The vulcanisable elastomeric compound of the elastomeric layer according to the present invention comprises at least one diene elastomeric polymer, as described below in the present description, and one or more types of micrometre-sized fibrillated polymer fibres, as described below in the present description.

Preferably, the elastomeric layer according to the present invention comprises micrometre-sized fibrillated polymer fibres in an amount equal to or greater than 3 phr, preferably equal to or greater than 4 phr, more preferably equal to or greater than 5 phr.

Preferably, the elastomeric layer according to the present invention comprises micrometre-sized fibrillated polymer fibres in an amount equal to or less than 30 phr, preferably equal to or less than 25 phr, more preferably equal to or less than 20 phr.

Advantageously, the elastomeric layer according to the present invention comprises micrometre-sized fibrillated polymer fibres in an amount ranging from 5 to 20 phr, preferably from 5 to 10 phr.

Micrometre-sized fibrillated polymer fibres

Preferably, the micrometre-sized fibrillated polymer fibres are polymer fibres with a melting temperature of at least 170°C, preferably at least 190°C.

The fibrillated polymer fibres useful in the present invention are represented, for example, by aramid fibres (for example Kevlar® Pulp by DuPont® or Twaron® pulp by Teijin Aramid), polyester fibres (for example Vectran® Pulp by Engineered fibres Technology), acrylic fibres (for example CFF® Fibrillated fibre by Engineered fibres Technology and CFF® Pulp by Sterling fibres), microfibrillated cellulose fibres (for example WMFC Q_ECO, by WEIDMANN fibre TECHNOLOGY), and vegetable fibres (for example Setralit® by ECCO Gleittechnik).

The term "fibrillated polymer fibres" means that the fibres themselves have an irregular and branched shape, with a main trunk from which thinner filaments of frayed fibres branch off, which give the fibre a greater surface area and better anchoring and binding features compared to non-fibrillated fibres. The "fibrillated polymer fibres" are obtained from non-fibrillated fibres through mechanical, thermal and chemical processes.

The term “micrometre-sized” referring to fibres means that the fibres have a diameter or maximum cross-sectional dimension of less than 100 pm (micrometres), typically greater than 500 nm (nanometres).

Aramid fibres are synthetic fibres obtained from aromatic polyamides, i.e. a particular class of nylon obtained by condensation in solution of aromatic diamines and aromatic dicarboxylic acids. The aramid fibres and the preparation process thereof are known in the literature and described, for example, in patents US3006899, US3063966, US3094511 , US3287323, US3322728, US3349062, US3354127, US3380969, US3671542, and US3951914.

Kevlar® is a particular aramid fibre obtained by condensation in solution starting from 1,4-phenylenediamine (para-phenylenediamine) monomers and terephthaloyl chloride.

Kevlar® pulp is a material obtained by fibrillation of Kevlar® fibres according to a DuPont® proprietary technology. Kevlar® pulp typically has fibres with a total length of 0.5-1 mm, surface area of 7-11 m²/g and main fibre diameter of between 10 and 18 micrometres (pm).

Polyester fibres are synthetic fibres obtained from polyesters, or polymers obtained by condensation of monomers comprising at least one carboxyl group (-COOH) and at least one hydroxyl group (-OH).

Vectran® is a completely aromatic-based polyester with melted crystalline liquid features, obtained by condensation of 4-hydroxybenzoic acid with 6- hydroxy-2-carboxy naphthalene acid, produced by Kuraray and Celanese.

Vectran® Pulp is a material obtained by fibrillation of Vectran® fibres, for example from Engineered fibres Technology. Vectran® pulp typically has fibres with an overall length of 1 to 6 mm and fibril diameter of few micrometres.

Acrylic fibres are synthetic fibres obtained from polyacrylates, or polymers obtained by polymerisation, typically radical, of acrylic monomers and in particular of acrylonitrile.

The "CFF® pulp" is obtained by fibrillation of the fibres of specific polyacrylate grades by Engineered fibres Technology, has main fibres with a diameter of about 20 pm and a length up to 7 mm, fibrils of diameter of around 1 pm, and surface area up to 50 m²/g.

Microfibrillated cellulose fibres are natural fibres obtained by cellulose fibrillation, for example from WEIDMANN fibre TECHNOLOGY, generally have a length of 0.05-1 mm, and fibril diameter typically of less than 1 pm.

Setralit® fibrillated natural fibres by ECCO Gleittechnik are obtained by mechanical treatment of plant fibres and have a maximum length of 7-8 mm and a surface area of around 1 m²/g.

The fibrillated polymer fibres preferably used in the present invention consist of a main trunk with a length ranging from about 0.05 to about 8 mm, preferably from about 0.1 to about 2 mm, a diameter of between 5 and 30 pm, and an aspect ratio greater than 30, from which a plurality of fibrils with a diameter smaller than the diameter of the main trunk branch off. The fibrillated polymer fibres have a surface area of between about 0.5 and about 60 m²/g, from about 10 to about 200 times greater than the surface area of an equivalent but not fibrillated polymer fibre.

Elastomeric compound

The vulcanisable elastomeric compound useful in the present invention comprises 100 phr of at least one diene elastomeric polymer.

Preferably, the diene elastomeric polymer which may be used in the present invention may be selected from those commonly used in sulphur- crosslinkable elastomeric compounds, which are particularly suitable for producing tyres and tyre components, i.e. from elastomeric polymers or copolymers with an unsaturated chain characterised by a glass transition temperature (Tg) generally lower than 20°C, preferably in the range of from 0°C to -110°C. These polymers or copolymers may be of natural origin or may be obtained by solution polymerization, emulsion polymerization or gasphase polymerization of one or more conjugated diolefins, optionally mixed with at least one comonomer selected from monovinylarenes and/or polar comonomers in an amount not exceeding 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 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, a-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: 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), 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, and mixtures thereof.

According to a preferred embodiment, said vulcanisable elastomeric compound comprises at least 10% by weight, preferably between 20% by weight and 100% by weight, with respect to the total weight of said at least one diene elastomeric polymer, of natural rubber.

The above vulcanisable elastomeric compound may optionally comprise at least one elastomeric polymer of one or more monoolefins with an olefinic comonomer or derivatives thereof (a¹). The monoolefins may be selected from: ethylene and a-olefins generally containing from 3 to 12 carbon atoms, such as for example propylene, 1 -butene, 1 -pentene, 1 -hexene, 1 -octene and mixtures thereof. The following are preferred: copolymers selected from ethylene and an a-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-ethylidene-2-norbornene, 5- methylene-2-norbornene, vinylnorbornene and mixtures thereof. Among them, the following are particularly preferred: ethylene/propylene (EPR) copolymers or ethylene/propylene/diene (EPDM) copolymers; polyisobutene; butyl rubber; halobutyl rubbers, in particular chlorobutyl or bromobutyl rubbers; or mixtures thereof. A diene elastomeric polymer or an elastomeric polymer functionalised by reaction with suitable terminating agents or coupling agents may also be used. In particular, the diene elastomeric polymers obtained by anionic polymerisation in the presence of an organometallic initiator (in particular, an organolithium initiator) may be functionalised by reacting the residual organometallic groups derived from the initiator with suitable terminating agents or coupling agents such as, for example, imines, carbodiimides, alkyltin halides, substituted benzophenones, alkoxysilanes or aryloxysilanes.

According to an aspect of the present invention, the micrometre-sized fibrillated polymer fibres (for example Kevlar® Pulp) are incorporated into the diene elastomeric polymer together with the other components to give the vulcanisable elastomeric compound with which the layer of vulcanised elastomeric material arranged in a radial position inside the carcass structure is formed.

Preferably, said fibrillated polymer fibres are present in the elastomeric compound in an amount of from 0.1 phr to 20 phr, preferably from 0.5 phr to 10 phr, more preferably from 1 phr to 5 phr.

Preferably, the vulcanisable elastomeric compound comprises a reinforcing filler.

Preferably, the reinforcing filler is selected from carbon black, precipitated amorphous silica, amorphous silica of natural origin, preferably non-modified silicate fibres and mixtures thereof.

Preferably, the reinforcing filler is present in the vulcanisable elastomeric compound in an amount generally ranging between 1 phr and 120 phr, preferably between 20 phr and 90 phr.

Preferably, the overall amount of reinforcing filler present in the vulcanisable elastomeric compound is at least 20 phr, more preferably at least 30 phr.

Preferably, the overall amount of reinforcing filler present in the vulcanisable elastomeric compound is in the range between 20 phr and 120 phr, more preferably between 30 phr and 90 phr.

Preferably, the reinforcing filler is or comprises carbon black having a surface area not smaller than 20 m²/g (as determined by STSA - statistical thickness surface area according to ISO 18852:2005). Preferably, said carbon black reinforcing filler is present in the vulcanisable elastomeric compound in an amount ranging between 1 phr and 120 phr, preferably between 20 phr and 90 phr.

Advantageously, the reinforcing filler is or comprises silica, selected from a pyrogenic silica or, preferably, a precipitated silica, with a BET surface area (measured according to the ISO 5794/1 standard) of between 50 m²/g and 500 m²/g, preferably between 70 m²/g and 200 m²/g.

The vulcanisable elastomeric compound comprises at least one vulcanising agent.

The vulcanising agent most advantageously used is sulphur, or, alternatively, sulphur-containing molecules (sulphur donors), with accelerators, activators and/or retardants known by the man skilled in the art.

Sulphur or derivatives thereof may advantageously be selected, for example, from: (i) soluble sulphur (crystalline sulphur); (ii) insoluble sulphur (polymeric sulphur); (iii) sulphur dispersed in oil (such as 33% sulphur, known by the trade name Crystex OT33 from Eastman); (iv) sulphur donors such as, for example, caprolactam disulphide (OLD), bis[(trialkoxysilyl)propyl]polysulphides, dithiophosphates; and mixtures thereof.

The vulcanising agent is present in the vulcanisable elastomeric compound in an amount of from 0.1 to 15 phr, preferably from 0.5 to 10 phr, even more preferably from 1 to 7 phr.

Preferably, the vulcanising agent is used in combination with accelerators and activators known by the man skilled in the art.

The accelerators which are commonly used may be selected from: dithiocarbamates, guanidine, thiourea, thiazoles, sulphenamides, thiurams, amines, xanthates and mixtures thereof.

Preferably, the vulcanisation accelerators are present in the vulcanisable elastomeric compound in amounts from 0.1 to 8 phr, preferably from 0.3 to 6 phr.

Activators that are particularly effective are zinc compounds, and in particular ZnO, ZnCOs, 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 vulcanisable elastomeric compound from ZnO and fatty acid, as well as Bi2C>3, PbO, PbsC , PbC>2, or mixtures thereof.

Preferably, the vulcanisation activators are present in the vulcanisable elastomeric compound in amounts of from 0.2 to 15 phr, preferably from 0.5 to 10 phr.

The vulcanisable elastomeric compound may optionally further comprise at least one silane coupling agent able to interact with the silica optionally present as reinforcing filler and/or the silicates and to bind it to the diene elastomeric polymer during the vulcanisation.

Preferably, the silane coupling agent which may be used in the present invention is selected from those having at least one hydrolysable silane group, which may be identified, for example, by the following general formula (I):

(R)₃Si-CnH2n-X (I) where the R groups, which may be the same or different, are selected from: alkyl, alkoxy or aryloxy groups or from halogen atoms, provided that at least one of the R groups is an alkoxy or aryloxy group or a halogen; n is an integer of between 1 and 6, inclusive; X is a group selected from: nitrous, mercapto, amino, epoxide, vinyl, imide, chlorine, -(S)mCnH2n-Si-(R)3 and -S- COR, where m and n are integers of between 1 and 6 inclusive and the R groups are as defined above.

Among the silane coupling agents, bis(3-triethoxysilylpropyl)tetrasulphide and bis(3-triethoxysilylpropyl)disulphide are particularly preferred. Said coupling agents may be used as such or as a suitable mixture with an inert filler (such as carbon black) so as to facilitate their incorporation into the vulcanisable elastomeric compound.

Preferably, said silane coupling agent is present in the vulcanisable elastomeric compound in an amount ranging between 0.1 phr and 20 phr, preferably between 0.5 phr and 10 phr.

The vulcanisable elastomeric compounds described above may comprise other commonly used additives, selected on the basis of the specific application for which the compound is intended. For example, said compounds may be admixed with: antioxidants, anti-ageing agents, plasticisers, adhesives, anti-ozone agents, modifying resins, or mixtures thereof.

In particular, in order to further improve the processability, said vulcanisable elastomeric compound may 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. The amount of plasticiser generally ranges from 0 phr and 70 phr, preferably from 5 phr to 30 phr.

The vulcanisable elastomeric compounds described above may be prepared by mixing together the polymeric components with the reinforcing filler and the other additives optionally present according to techniques known in the industry. The mixing may be carried out, for example, using an open mixer of the open-mill type or an internal mixer of the type with tangential rotors (Banbury®) or with interpenetrating rotors (Intermix), or in continuous mixers of the Ko-Kneader™ type (Buss®) or of the twin-screw or multi-screw type.

Tread band

The tread band of the tyre of the present invention comprises a layer of vulcanised elastomeric compound made with a vulcanisable elastomeric compound as described above.

Preferably, the tread band of a tyre may have a thickness of between about 0.8 and about 8 mm depending on the type of tyre.

Preferably, the tread band has a width equal to or less than 50% of the axial development of the tyre, more preferably equal to or less than 45% of the axial development of the tyre.

Preferably, the tread band has a width equal to or greater than 30% of the axial development of the tyre, more preferably equal to or greater than 35% of the axial development of the tyre.

Preferably, the tread band has a width between 30% and 50% of the axial development of the tyre, more preferably between 35% and 50% of the axial development of the tyre, even more preferably between 30% and 45% of the axial development of the tyre, even more preferably between 35% and 45% of the axial development of the tyre, for example about 40% of the axial development of the tyre. In a tyre intended for a racing bicycle wheel, the tread band is generally smooth. In a tyre intended for a city bicycle wheel, the tread band comprises grooves and notches that are more or less angled with respect to each other to promote good grip on the asphalt in all weather conditions of use. In a tyre intended for an off-road bicycle wheel, the tread band comprises a plurality of blocks spaced quite apart from each other to promote good grip on rough terrain.

Protective layer or “breaker”

Advantageously, a protective layer may be arranged in a radially inside position with respect to the carcass structure or be radially interposed between the carcass structure and the tread band. The protective layer is also known as the “breaker”.

Preferably, said protective layer has a width equal to or less than 50% of the axial development of the tyre.

Preferably, the protective layer has a width equal to or greater than 20% of the axial development of the tyre, more preferably equal to or greater than 22% of the axial development of the tyre.

Preferably, said protective layer has a width between 20% and 45% of the axial development of the tyre, more preferably between 22% and 40% of the axial development of the tyre, even more preferably between 22% and 35% of the axial development of the tyre.

In order to allow adequate resistance to puncture of the tyre, while simultaneously containing the weight of the tyre, the Applicant has observed that it is advantageous for said protective layer to have a width equal to, preferably smaller than, the axial development of the tread band.

Preferably, the protective layer has a width equal to or less than 95% of the axial development of the tread band, more preferably equal to or less than 90% of the axial development of the tread band, even more preferably equal to or less than 85% of the development axial of the tread band.

Preferably, the protective layer has a width equal to or greater than 50% of the axial development of the tread band, more preferably equal to or greater than 60% of the axial development of the tread band, more preferably equal to or greater than 70% of the development axial development of the tread band, even more preferably equal to or greater than 75% of the axial development of the tread band.

Preferably, the protective layer has a width between 50% and 95% of the axial development of the tread band, more preferably between 50% and 90% of the axial development of the tread band, even more preferably between 50 % and 85% of the axial development of the tread band.

Preferably, the protective layer is symmetrically arranged with respect to the equatorial plane.

Reinforced ribbon-like element or “chafer”

At the annular anchoring structures, also called bead cores, a reinforced ribbon-like element may be applied in a radially outside position with respect to the carcass structure. The reinforced ribbon-like element is also known as “chafer”.

Such reinforced ribbon-like element is radially interposed between the carcass ply and the wheel rim when the tyre is mounted on such a rim.

The reinforced ribbon-like element has a limited axial extension, preferably between 2% and 15% of the axial development of the tyre. The reinforced ribbon-like element has the purpose of allowing adhesion and friction with the rim, also avoiding possible damage due to abrasion following the rubbing of the carcass ply with the rim.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Further features and advantages of the tyre of the present invention will appear more clearly from the following detailed description of some preferred embodiments thereof, made with reference to the accompanying drawings. In such drawings:

- Figure 1 is a schematic radial sectional view of a tyre for bicycle wheel conventionally known in the art;

- Figures 2-8 show possible schematic construction diagrams of embodiments of tyres according to the invention.

In Figure 1 , reference numeral 100 indicates a tyre for bicycle wheels. The tyre may be designed to be mounted on the wheels of a racing bicycle or offroad (mountain bike or MTB), or city (urban bike or city bike). The tyre 100 in figure 1 comprises a carcass structure 2 comprising a crown portion 2a preferably arranged symmetrically with respect to the equatorial plane X-X and opposite side portions 2b arranged on sides axially opposite to the crown portion 2a.

In the embodiment shown in the accompanying drawings, the carcass structure 2 comprises a single carcass ply 3 (a single-ply tyre), but other embodiments (not shown) are provided in which the carcass structure 2 comprises several carcass plies, preferably two (two-ply tyre).

What is described below with reference to the carcass ply shown in the drawings applies both to the single carcass ply of the single-ply tyre and to each carcass ply of the two-ply tyre, unless explicitly stated otherwise.

The carcass ply 3 extends axially from a side portion 2b of the carcass structure 2 to the opposite side portion 2b.

The carcass ply 3 is engaged, at respective axially opposite ends 3a thereof, with respective annular anchoring structures 4a and 4b, typically called “bead cores".

Each end 3a of the carcass ply 3 is turned up around a respective bead core 4a and 4b.

The bead cores 4a and 4b are preferably made of textile fibres with high elastic modulus, such as for example aramid fibres (common name of the aromatic polyamide fibres) or of metal wires, such as for example steel.

A tapered elastomeric filler may be applied to the external peripheral edge of the bead cores 4a and 4b which occupies the space defined by the carcass flap around the bead cores.

The area of the tyre comprising the bead core 4a and 4b and the optional elastomeric filler forms the so-called “bead”, globally indicated in Figure 1 with reference numeral 5a and 5b, intended for anchoring, by means of elastically forced fitting, the tyre on a corresponding mounting rim, not shown.

On the turned-up end 3a of the carcass ply 3, a reinforced ribbon-like element, not shown in Figure 1 , may be applied at each bead 5a and 5b. Such reinforced ribbon-like element is interposed between the carcass ply 3 and the rim of the wheel when the tyre is mounted on such a rim.

With reference to the tyre in figure 1 , the two edges of the carcass flaps 3a each extend to cover the crown portion 2a overlapping to form three carcass layers in the crown portion 2a with a first radially inside carcass layer.

In a radially outside position with respect to the carcass structure 2 a tread band 7 is provided, whereby the tyre 100 contacts the road surface.

The tread band 7 extends axially and in a radially outside position with respect to the crown structure 2a by a width section which may be less than or at least equal to that of the crown structure 2a.

The tyre 100, if intended for racing bicycle wheels, typically has an axial dimension (herein also indicated as “axial extension” or “width”) preferably between about 19 mm and about 38 mm, more preferably between about 19 mm and about 32 mm, even more preferably between about 23 mm and about 28 mm, ends included. The tyre 100 intended for the various types of bicycles has an external diameter (which, according to the English denomination, is expressed in inches) preferably of between about 24 inches and about 29 inches, more preferably between about 26 inches and about 29 inches, ends included. Correspondingly, the fitting diameter according to the ISO or E.T.R.T.O. convention is preferably about 559 mm (which corresponds to an external diameter of 26 inches for off-road bicycles, MTB), or about 571 mm (which corresponds to an external diameter of 26 inches for road racing bicycles), or about 584 mm (which corresponds to an external diameter of 27.5 inches for off-road bicycles), or about 622 mm (which corresponds to an external diameter of 28 inches for road racing bicycles and to an external diameter of 29 inches for off-road bicycles) or about 630 mm (which corresponds to a particular external diameter of 27 inches for road racing bicycles).

For example, a first embodiment of the tyre 100 of Figure 1 has an external diameter of 26 inches, a second embodiment has an external diameter of 28 inches, and a third embodiment has an external diameter of 29 inches.

In the case of a tyre designed for wheels for off-road bicycles (MTB), the tyre 100 has an axial dimension preferably of between about 37 mm and about 120 mm, ends included.

The tyre 100 intended for city bicycle wheels typically has an axial dimension preferably of between about 32 mm and 62 mm, ends included. The 100 tyre for off-road or city bicycles has an external diameter preferably between about 26 inches and about 29 inches, ends included. Correspondingly, the fitting diameter according to the ISO or E.T.R.T.O. convention is preferably between about 559 mm and about 622 mm.

For example, a first embodiment of the tyre 100 of Figure 1 has an external diameter of 26 inches (fitting diameter equal to 559 mm), a second embodiment has an external diameter of 28 inches (fitting diameter equal to 584 mm), and a third embodiment has an external diameter of 29 inches (fitting diameter equal to 622 mm).

Figures 2-8 illustrate different construction diagrams of tyres according to the present invention.

In the construction diagram of Figure 2, the ends 3a of the carcass ply 3 are partially overlapped with each other at the tread 7 and the protective layer 6.

In the example of Figure 2, a reinforced ribbon-like element 10 is applied to the turned-up end 3a of the carcass ply 3 and the layer 8, in proximity to the bead cores 5.

In the diagram of Figure 2, the layer of elastomeric material comprising fibrillated polymer fibres 8 overlaps, in a radially inside position, on the carcass ply 3, from the bead core 4a to the opposite bead core 4b, with ends 8a and 8b which are interrupted at the flap around the respective bead core 4a and 4b and the reinforced ribbon-like element 10.

The construction diagram of Figure 3 differs from the diagram of Figure 2 in that the ends 3a of the carcass ply 3 are axially spaced from each other.

The construction diagram in Figure 4 differs from the diagram in Figure 2 in that it does not comprise the protective layer 6.

The construction diagram in Figure 5 differs from the diagram in Figure 2 in that it does not comprise the reinforced ribbon-like element 10.

The construction diagram of Figure 6 differs from the diagram of Figure 2 in that it comprises the layer of elastomeric material comprising fibrillated polymer fibres 8 interposed between the two ends 3a and 3b of the carcass ply 3, in a radially outside position with respect to the bead cores 4a and 4b, extending from bead to bead (5a, 5b), with ends 8a and 8b which are interrupted before the flap around the respective bead core 4a and 4b at the reinforced ribbon-like element 10.

The construction diagram of Figure 7 differs from the diagram of Figure 2 in that it comprises the layer of elastomeric material comprising fibrillated polymer fibres 8 interposed in the carcass structure 2, in a radially inside position with respect to the bead cores, extending from bead to bead (5a, 5b), with ends 8a and 8b which are interrupted at the flap around the respective bead 4a and 4b and the reinforced ribbon-like element 10.

The construction diagram of Figure 8 differs from the diagram of Figure 2 in that it comprises the layer of elastomeric material comprising fibrillated polymer fibres 8 superimposed, in a radially outside position, on the carcass structure 2, extending from bead to bead (5a, 5b), with ends 8a and 8b that interrupt before the flap around the respective bead core 4a and 4b at the reinforced ribbon-like element 10.

The present invention will be further illustrated below by means of a number of examples, which are given purely as an indication and without any limitation of the present invention.

EXAMPLE 1 - Preparative test

The elastomeric compounds used to make the layer of elastomeric material radially inside with respect to the carcass structure were prepared as follows (the quantities of the various components are provided in phr).

The compound R1 represents a reference compound for a conventional liner, comprising a mixture of natural rubber and halogen butyl rubber, the compound I2 represents a compound of the invention comprising micrometre-sized fibrillated polymer fibres dispersed in natural rubber, and the compound C3 represents a comparison compound comprising only natural rubber.

All the components, except for sulphur, the retardant (PVI) and the accelerant (CBS) were mixed together in an internal mixer (model Pomini PL 1.6) for about 5 minutes (1^st step). As soon as the temperature reached 145+5°C, the elastomeric compound was unloaded. Sulphur, the retardant and the accelerator (CBS) were then added and mixing was performed in an open roll mixer (2^nd step).

TABLE 1

Natural Rubber STR 20 P 93, SRI Trang Agroindustry;

Halogen Butyl Rubber CHLOROBUTYL 1066, EXXON MOBIL

Fibrillated polymer fibres Kevlar® Pulp comprising 40%Kevlar fibres in natural rubber,

DuPont®;

CB1 Carbon Black N326, Birla;

CB2 Carbon Black N669, Birla;

Stearic acid Undesa;

Zinc Oxide RHENOGRAN® ZnO, Zincol Ossidi; Oil VIVATEC 500 TDAE - Hansen & Rosenthal

6PPD N-(1 ,3-dimethylbutyl)-N'-phenyl-phenylene-diamine, Santoflex;

CBS N-cyclohexyl-2-benzothiazol-sulphenamide Vulkacit® Lanxess;

PVI N-cyclohexylthiophthalimide (Akrochem);

Sulphur Rhenocure® IS 90-33 from Lanxess, a mixture of insoluble/soluble sulphur in a 90:10 ratio plus 33% oil.

EXAMPLE 2 - preparation of the tyre

Racing tyres for bicycles were then prepared, with dimensions 28-622 according to the structure illustrated in Figure 2, comprising a layer of elastomeric material radially inside with respect to the carcass structure made with the elastomeric compounds described in Example 1. The thickness of the layer of elastomeric material radially inside with respect to the carcass structure was approximately 0.35 mm for all tyres.

The tyre PR1 comprised the layer made with the compound R1 , the tyre PI2 comprised the layer made with the compound I2, the tyre PC3 comprised the layer made with the compound C3.

In all cases, the carcass structure was provided with a rubberised carcass ply of 0.4 mm total thickness in nylon 6.6 with a density of 120 TPI and a linear density of 235 dtex, turned up on aramid bead cores and provided with two rubberised non-abrasive square fabrics at the edges.

The tyres were made with a protective layer 6 (extended for the entire axial development of the tread band 7 as illustrated in Figure 2) made of square fabric including as a weft reinforcing cords of aramid fibres, initial modulus 75 GPa and with linear density 220 dtex and density 55TPI and as a warp PET with linear density 330 dtex and density 80TPI oriented with respect to the equatorial plane of the tyre at an angle of 45°.

EXAMPLE 3 - Properties of the compounds

The elastomeric materials prepared in the previous examples were vulcanised to give specimens on which analytical characterisations and the assessment of dynamic mechanical properties were conducted.

Unless otherwise indicated, vulcanisation was carried out in a mould, in hydraulic press at 170 °C and at a pressure of 200 bar for about 10 minutes.

IRHD Hardness: IRHD hardness was measured at 23°C on vulcanised elastomeric compositions according to the ISO 48:2007 standard.

Static moduli: static mechanical properties were measured at 23°C according to the ISO 37:2005 standard on three Dumbell specimens. In particular, the tensile stresses at various elongation levels (10%, 50%, 100% and 300%, named in the order CA0.1 , CAO.5, CA1 and CA3), the elongation at break (AR) and breaking load (CR) were measured on samples of vulcanised elastomeric compositions.

Dynamic moduli: dynamic mechanical properties were measured using an Instron dynamic device in compression and tension operation with the following method. A sample of vulcanised elastomeric cylindrical compositions (length = 25 mm; diameter = 18 mm), preload in compression up to 25% of longitudinal deformation with respect to the initial length and maintained at the predetermined temperature (23°C or 70°C) during the test was subjected to a dynamic sinusoidal voltage with amplitude ± 3.5% with respect to the length of the preload, at a frequency of 10 Hz.

The dynamic mechanical properties are expressed in terms of dynamic elastic modulus (E’), viscous dynamic modulus (E”) and Tan delta (loss factor). The Tan delta value was calculated as the ratio between the viscous dynamic modulus (E”) and the dynamic elastic modulus (E’).

Permeability: permeability was measured, at 23°C, according to the ISO 2782:2006 standard, on specimens with a diameter of 120 mm and a nominal thickness of 1 mm, conditioned at 23°C for 16 hours. The results are summarised in the following Table 2.

TABLE 2

The data in Table 2 demonstrated that the compound 12 of the invention, without halogen butyl rubber but with fibrillated polymer fibres, showed improved mechanical features compared to the reference compound R1 including halogen butyl rubber, excellent dynamic properties, in particular showing reduced hysteresis at both 23°C and 70°C, and sufficient permeability to ensure air tightness in a bicycle tyre. In contrast, the comparison compound C3, without halogenbutyl rubber and without the addition of fibrillated polymer fibres, although showing good mechanical properties and low hysteresis, showed insufficient permeability to ensure air tightness in a bicycle tyre.

EXAMPLE 4 - Anti-puncture test

Samples of vulcanised compounds I2 and C3 of Example 2 of dimensions approximately 200x200x1 mm were subjected to a puncture test according to the DIN EN 14477 standard, adapted to the test conditions, as expressed below.

This test allows evaluating the resistance to perforation of a material by subjecting it to the action of a penetrator (a punch or a screwdriver), which penetrates the sample at a constant speed. The test is carried out with the aid of a dynamometre capable of recording the applied force (measured in N at different depths of penetration) and the elastic deformation of the material (measured in mm).

This applied force is therefore indicative of the resistance opposed by the sample to the penetration of a foreign body (the material is more resistant the higher the force value); and said elastic deformation is an expression of the material's ability to absorb the penetration of a foreign body (the material is the more elastic the higher the value of said deformation for the same force).

The tests were performed in a conditioned environment at a controlled temperature of 23° ± 2°C. The samples were conditioned for 48 hours before the test. The test conditions used were the following:

- test speed = 50 mm/minute;

- initial distance between the tip of the penetrator and the tyre = 10 mm;

- pre-load applied = 0.5 N.

Tests were carried out on 10 samples and the average values obtained are given in the following Table 3.

TABLE 3

The data in Table 3 demonstrated that the compound I2 of the invention, without halogenbutyl rubber, but with fibrillated polymer fibres, showed resistance to puncture (test with punch with round tip) and to laceration (test with punch with blade tip) much greater than that shown by the comparison compound C3, devoid of both the halogenbutyl rubber and the fibrillated polymer fibres.

EXAMPLE 5 - Rolling resistance test

The rolling resistance test was conducted with the tyre of the invention PI2 and with the reference tyre PR1 of Example 2.

To conduct the tyre rolling resistance test, each wheel (19 rim and tyre inflated to 6.0 bar) was mounted above a rotating drum with a diameter of 2000 mm applying a load of 588.4 N (which corresponds to 60 kg). The drum was rotated at a speed of 106 revolutions per minute (which corresponds to 40 km/h). 20 minutes after the drum began to rotate, the driving torque necessary to keep the drum rotating was measured and the average of the last ten seconds of acquisition was calculated (M1). Subsequently, the load was decreased to 100 N for 2 minutes and in the last 10 seconds the average driving torque necessary to keep the drum rotating (M2) was measured. Subsequently, the load was increased up to 588.4 N for 3 minutes and in the last 10 seconds the average driving torque necessary to keep the drum rotating (M3) was measured. Finally, the load was decreased again to 100 N for 2 minutes and in the last 10 seconds the average driving torque necessary to keep the drum (M4) rotating was measured.

After calculating the value of the difference between the first and second measurements (M1-M2) and the value of the difference between the third and fourth measurements (M3-M4), the rolling resistance of the tyre was calculated as the average of the two values, multiplied by the angular velocity of the drum (11.1 rad/s). The rolling resistance of the tyre PI2 of the invention was found to be approximately 20% lower than the rolling resistance of the reference tyre PR1.

The present invention has been described with reference to some preferred embodiments. Various modifications may be made to the embodiments described above, while remaining within the scope of protection of the invention, defined by the following claims.

Claims

1. A tyre (100) for bicycle wheels comprising:

- a carcass structure (2) comprising at least one carcass ply (3) having ends (3a) turned up around respective bead cores (4a, 4b) to form respective opposite beads (5a, 5b),

- a tread band (7) arranged in a radially outside position with respect to said carcass structure (2), and

- a layer of vulcanised elastomeric material (8) superimposed, in a radially inside or outside position, to the carcass structure (2), or interposed in the carcass structure (2), said layer of vulcanised elastomeric material (8) axially extending from at least one bead (5a) to the opposite bead (5b), characterised in that said layer of vulcanised elastomeric material (8) is made by vulcanisation of a vulcanisable elastomeric compound comprising micrometre-sized fibrillated polymer fibres.

2. The tyre (100) according to claim 1, characterised in that said fibrillated polymer fibres are selected from the group consisting of aramid fibres, polyester fibres, acrylic fibres, microfibrillated cellulose fibres, and plant fibres.

3. The tyre (100) according to claim 1, characterised in that said fibrillated polymer fibres have a diameter of less than 100 pm and a length between about 0.05 and about 8 mm.

4. The tyre (100) according to claim 1, characterised in that said fibrillated polymer fibres exhibit a length to diameter aspect ratio of greater than 30:1.

5. The tyre (100) according to claim 1, characterised in that said fibrillated polymer fibres exhibit a surface area between about 0.5 and about 60 m²/g.

6. The tyre (100) according to claim 1 , characterised in that said vulcanisable elastomeric compound comprises:

(a) 100 phr of at least one diene elastomeric polymer;

(b) 0.1 phr to 20 phr of said fibrillated polymer fibres, and (c) 1 to 120 phr of a reinforcing filler.

7. The tyre (100) according to claim 1, characterised in that said fibrillated polymer fibres are present in said elastomeric compound in an amount of from 0.5 phr to 10 phr, preferably from 1 phr to 5 phr.

8. The tyre (100) according to claim 1 , characterised in that said ends (3a) extend until overlapping at said tread band (7).

9. The tyre (100) according to claim 1, characterised in that said layer of vulcanised elastomeric material (8) is superimposed, in a radially inside position, to the carcass structure, and extends from said bead core (4a) to said opposite bead core (4b), with ends (8a, 8b) turned up around said bead cores (4a, 4b).

10. The tyre (100) according to claim 1, characterised in that said layer of vulcanised elastomeric material (8) is superimposed, in a radially outside position, to the carcass structure, and extends from said bead core (4a) to said opposite bead core (4b).

11. The tyre (100) according to claim 1, characterised in that said layer of vulcanised elastomeric material (8) is interposed to the carcass structure, and extends from said bead core (4a) to said opposite bead core (4b), optionally with ends (8a, 8b) turned up around said bead cores (4a, 4b).

12. The tyre (100) according to claim 11 , characterised in that said layer of vulcanised elastomeric material (8) is in a radially outside position with respect to the bead cores (4a, 4b).

13. The tyre (100) according to claim 11 , characterised in that said layer of vulcanised elastomeric material (8) is in a radially inside position with respect to the bead cores (4a, 4b), with ends (8a, 8b) turned up around said bead cores (4a, 4b).

14. The tyre (100) according to claim 1 , characterised in that it comprises, at each bead (5a, 5b), a reinforced ribbon-like element (10) in a radially outside position with respect to said carcass structure (2).

15. The tyre (100) according to claim 1 , characterised in that it comprises, at said tread band (7), a protective layer (6).