Reinforcing cord for tyres for vehicle wheels and process for making such reinforcing cord

Abstract

A reinforcing cord (10) for tyres for vehicle wheels, comprising at least two elongated elements (11a, 11b) made of non-metallic material, wherein at least one elongated element (11a) extends along a helical path around an empty space (10a) with a predetermined helix pitch (E). This reinforcing cord (10) is obtained from a semi-finished product made by winding said at least one elongated element (11a) around at least one sacrificial elongated element with the predetermined helix pitch (E) and, subsequently, removing the at least one sacrificial elongated element from the semi-finished product, thus creating the aforesaid empty space (10a).

Description

[0001] Reinforcing cord for tyres for vehicle wheels and process for making such reinforcing cord

[0002] DESCRIPTION

[0003] The present invention relates to a reinforcing cord for tyres for vehicle wheels.

[0004] The invention also relates to a process for making such a reinforcing cord.

[0005] The invention also relates to a tyre for vehicle wheels comprising such a reinforcing cord.

[0006] The reinforcing cord of the invention has a geometry suitable for achieving a high part load elongation.

[0007] PRIOR ART

[0008] US 10,618,353 B2 describes textile reinforcing cords comprising two or more yarns twisted together and made of aramid fibres. The high modulus of the aramid fibres provides these reinforcing cords with the desired stiffness. In order to increase the part load elongation, while making such reinforcing cords the yarns are spaced apart from each other and a RFL adhesive composition is inserted between them. When these reinforcing cords are subjected to traction, the yarns approach each other, compressing the adhesive composition and achieving the desired part load elongation. As the load increases, the elongation is counteracted by the high modulus of the aramid fibres.

[0009] WO 2012 / 083148 Al, US 2017 / 0274706 Al and US 4,155,394 A describe textile reinforcing cords comprising elongated elements made of a high modulus and low elongation material (aramid), twisted to elongated elements made of a low modulus and high elongation material (nylon).

[0010] KR 20110061110 A describes a reinforcing cord comprising at least one high elongation elongated element made of nylon, at least one medium elongation elongated element made of a material selected among polyester, polyvinyl, PVA, rayon, lyocell, PEN and at least one low elongation elongated element made for example of aramid, carbon fibres or glass fibres.

[0011] SUMMARY OF THE INVENTION

[0012] In this description and in the subsequent claims, when reference is made to certain angle values, these values are to be deemed as absolute values, i.e. both positive and negative values with respect to a reference plane or direction, unless otherwise specified.

[0013] Moreover, when reference is made to any range of values comprised between a minimum value and a maximum value, the aforesaid minimum and maximum values are deemed to be included in the aforesaid range, unless expressly stated to the contrary.

[0014] Moreover, all of the ranges include any combination of the described minimum and maximum values and include any intermediate range, even if not specifically expressly described.

[0015] Even if not expressly indicated, any numerical value is deemed to be preceded by the term "about" to also indicate any numerical value that differs slightly from the one described, for example to take into account the dimensional tolerances typical of the sector of reference.

[0016] Hereinafter, the following definitions apply.

[0017] The term "green tyre" is used to indicate a tyre obtained from the manufacturing process and not yet moulded and vulcanized.

[0018] The term "tyre" or "finished tyre" is used to indicate a tyre obtained by subjecting a green tyre to a moulding and vulcanization process in a vulcanization mould.

[0019] The term "footprint area" of the tyre is used to indicate the portion of the tyre in contact with the ground or road surface when the tyre is mounted on a wheel rim and a predetermined vertical load is exerted on the tyre. The term "parallel" is used to indicate not only a condition of perfect parallelism, but also a condition in which there is a slight deviation from the perfect parallelism, for example by an angle of no more than 5°.

[0020] The term "perpendicular" is used to indicate not only a condition of perfect perpendicularity or orthogonality, but also a condition in which there is a slight deviation from the perfect perpendicularity or orthogonality, for example by an angle of no more than 5°.

[0021] The term "equatorial plane" of the tyre is used to indicate a centreline plane perpendicular to the axis of rotation of the tyre. The equatorial plane subdivides the tyre into two parts that typically are symmetrically equal.

[0022] The term "elastomeric material" or "elastomer" is used to indicate a material comprising a vulcanizable natural or synthetic polymer and a reinforcing filler, wherein said material, at room temperature and after being subjected to vulcanization, is susceptible to deformations caused by a force and is capable of rapidly and energetically recovering the substantially original shape and dimensions after elimination of the deforming force (according to the definitions of ASTM D1566-11 Standard Terminology Relating To Rubber).

[0023] The terms "upstream" and "downstream" are used with reference to a predetermined direction and to a predetermined reference. Therefore, assuming for example a direction from left to right and a reference taken along said direction, a position "downstream" with respect to the reference indicates a position to the right of said reference and a position "upstream" with respect to the reference indicates a position to the left of said reference.

[0024] The terms "circumferential" and "circumferentially" are used, when referred to a tyre, with reference to the rolling direction of the tyre, which corresponds to a direction lying on a plane coincident with or substantially parallel to the equatorial plane of the tyre. The same terms, when referred to a reinforcing cord, are used with reference to a direction that, in any cross section of the reinforcing cord, turns around the centre of the reinforcing cord.

[0025] The terms "radial", "radially inner" and / or "radially outer" are used, when referred to a tyre, with reference to a direction substantially parallel to the equatorial plane of the tyre, i.e. to a direction substantially perpendicular to the axis of rotation of the tyre. The same terms, when referred instead to a reinforcing cord, are used with reference to a direction substantially perpendicular to the longitudinal direction of the reinforcing cord.

[0026] The terms "axial", "axially inner" and / or "axially outer" are used, when referred to a tyre, with reference to a direction substantially perpendicular to the equatorial plane of the tyre, i.e. to a direction substantially parallel to the axis of rotation of the tyre. The same terms, when referred instead to a reinforcing cord, are used with reference to a direction substantially parallel to the longitudinal direction of the reinforcing cord.

[0027] The terms "longitudinal trajectory" and "longitudinal direction" of a reinforcing cord are used to indicate the trajectory and the direction, respectively, along which the centres of the circumferences circumscribing all the cross sections of the reinforcing cord follow each other.

[0028] A longitudinal trajectory is intended as being "non-rectilinear" when, being fixed a reference straight line tangent to the reinforcing cord at the radially outermost point of the reinforcing cord and directed along the longitudinal direction of the reinforcing cord, the distance of the aforesaid centres from said reference straight line varies along the longitudinal direction of the reinforcing cord in such a way that the difference between the maximum distance and the minimum distance is greater than 150 pm.

[0029] The term "substantially axial direction" is used to indicate a direction inclined, with respect to the equatorial plane of the tyre, by an angle comprised between 70° and 90°.

[0030] The term "substantially circumferential direction" is used to indicate a direction oriented, with respect to the equatorial plane of the tyre, at an angle comprised between 0° and 10°.

[0031] The term "reinforcing cord", or more simply "cord" is used to indicate a long-shaped element comprising several elongated elements possibly covered by, or incorporated in, a matrix of elastomeric material.

[0032] The term "elongated element" is used to indicate a wire or yarn.

[0033] The term "wire" is used to indicate an elongated element consisting of a single filament. Therefore, the term "monofilament" is also used to refer to a "wire".

[0034] The term "yarn" is used to indicate an elongated element consisting of the aggregation of a plurality of filaments twisted to each other. Therefore, the term "multifilament" is also used to refer to a "yarn".

[0035] Each filament can also be referred to as "fibre".

[0036] An elongated element may therefore consist of a single wire or of a single yarn or of several yarns twisted together.

[0037] In the case of yarns, the elongated elements can be identified with an abbreviation that represents the textile material, the linear density of the fibre used and the number of yarns that form the elongated element. For example, an elongated element made of PET (polyethylene terephthalate) identified with PET 1672 indicates an elongated element comprising PET fibres having a linear density of 1670 dtex, formed by two yarns twisted together.

[0038] The term "strand" is used to indicate an assembly consisting of at least two elongated elements. The strand may itself define a reinforcing cord or be intended to be twisted to at least another elongated element or to at least another strand to make a reinforcing cord.

[0039] The term "hybrid strand" is used to indicate a strand consisting of at least two elongated elements made of different materials.

[0040] In this description and in the subsequent claims, any reference to a particular plastic material is to be understood as extending both to a plastic material of fossil origin and to a corresponding recycled or biobased material, if any. Thus, for example, when mention is made of PET it is foreseen that such a PET may be of fossil or recycled origin.

[0041] The term "recycled material" is used to indicate a plastic material obtained starting from waste or industrial waste products made of a corresponding plastic material (typically, although not necessarily, of fossil origin) and subjected to appropriate mechanical and / or chemical and / or thermal treatments in order to be able to obtain reusable products.

[0042] The term "non-recycled material" is used to indicate a plastic material of fossil origin.

[0043] The term "bio-based material" is used to indicate a material that is not of fossil origin and is not obtained starting from waste or industrial waste products, but is obtained from renewable sources, such as for example agricultural and forestry products that are cultivated and / or used by the human being for purposes other than those of human or animal nutrition.

[0044] The term "diameter" of a wire is used to indicate the diameter measured as prescribed by the BISFA E10 method (The International Bureau For The Standardization Of Man-Made Fibres, Internationally Agreed Methods For Testing Steel Tyre Cords, 1995 edition).

[0045] By "diameter" of a yarn is intended to mean the diameter of an ideal circumference that circumscribes all the filaments defining the yarn.

[0046] The term "breaking load" of a reinforcing cord is used to indicate the load at which the breakage of the reinforcing cord occurs, evaluated in accordance with the BISFA standard (Bureau International pour la Standardisation des Fibres Artificielles) relating to the material under test as per definition herein below.

[0047] The term "part load elongation" of a reinforcing cord is used to indicate the difference between the percentage elongation obtained by subjecting the reinforcing cord to a traction of 50 N and the percentage elongation obtained by subjecting the reinforcing cord to a traction of 2.5 N. The part load elongation is evaluated with the BISFA E7 method (The International Bureau For The Standardization Of Man-Made Fibres, Internationally Agreed Methods For Testing Steel Tyre Cords, 1995 edition).

[0048] The term "modulus" is used to indicate the ratio between load (or force) and elongation measured at any point of a load-elongation curve according to the BISFA standard. Such a curve is drawn by calculating the first derivative of the load-elongation function that defines the aforesaid curve, normalized to the linear density expressed in Tex. The modulus is therefore expressed in cN / Tex or Mpa. In a load-elongation graph, the modulus is identified by the slope of the aforesaid curve with respect to the X-axis.

[0049] The term "initial modulus" is used to indicate the modulus calculated at the origin point of the load-elongation curve, i.e. for an elongation equal to zero.

[0050] The term "final modulus" is used to indicate the modulus calculated close to the breaking load, before any sudden failure.

[0051] In the context of the present invention, the term "high modulus" is used to indicate a modulus higher than 5 Mpa, while the term "low modulus" is used to indicate a modulus lower than 5 Mpa.

[0052] The term "linear density" or "count" of yarn is used to indicate the weight of the cord / elongated element per unit of length. The linear density is measurable in dtex (grams per 10 km of length).

[0053] For the measurement of the linear density and for the determination of the tensile properties (such as for example the breaking load), flat yarns are referred to, without twists applied during the test phase, according to the tests regulated by the BISFA standard. In particular:

[0054] - for aramid fibres (AR.) reference is made to para-aramidic yarn test methods - 2002 edition:

[0055] • Determination of linear density - Chapter 6;

[0056] • Determination of tensile properties - Chapter 7 - Test Procedure - Paragraph 7.5 - procedure with initial pre-tensioning;

[0057] - for Nylon (NY), reference is made to BISFA - Testing methods for polyamide yarns - 2004 edition:

[0058] • Determination of linear density - Chapter 6 - Procedure A;

[0059] • Determination of tensile properties - Chapter 7 - Procedure A;

[0060] • Preparation of laboratory samples: Preparation of samples under relaxation - paragraph 7.4.1.1 => preparation of samples on collapsible spool;

[0061] • Preparation of laboratory samples and carrying out the test: Manual test - paragraph 7.5.2.1 => c);

[0062] • Start of procedure => e) pretension at start of procedure;

[0063] • Tractions performed with Zwick - Roell Z010 dynamometer;

[0064] - for Polyester (PET), reference is made to BISFA - Methods for testing polyester yarns - 2004 edition:

[0065] • Determination of linear density - Chapter 6 - Procedure A;

[0066] • Determination of tensile properties - Chapter 7 - Procedure A;

[0067] • Preparation of laboratory samples: Preparation of samples under relaxation - paragraph 7.4.1.1 => preparation of samples on collapsible spool;

[0068] • Preparation of laboratory samples and carrying out the test: Manual test - paragraph 7.5.2.1 => c);

[0069] • Start of procedure => e) pretension at start of procedure;

[0070] • Tractions performed with Zwick - Roell Z010 dynamometer.

[0071] Hereinafter, when the adhesion to the elastomeric material of a reinforcing cord or of an elongated element thereof is mentioned, reference is made to the adhesion capacity conferred to the reinforcing cord / elongated element solely by its shape or structure, therefore without considering surface coating treatments through adhesive compositions, such as for example the Resorcinol-Formaldehyde-Latex (RFL) composition typically used in the tyre production sector.

[0072] The term "structural component" of a tyre is used to indicate any tyre ply or layer containing reinforcing cords, such as, for example, a carcass ply of car or motorcycle tyres, or a belt ply of car tyres, or a zerodegree reinforcing layer (or a cross-belt structure) of a motorcycle tyre, or a stiffening layer associated with a carcass ply of car tyres at or close to a respective turned-up end edge of the carcass ply and further below indicated with the terms "flipper" and "chafer".

[0073] The term "mechanical behaviour" of a reinforcing cord or of an elongated element thereof or of a strip-like element that incorporates the cord is used to indicate the reaction offered by the reinforcing cord / strip- like element when subjected to a load (or force). In the case of a traction load, such a load causes an elongation that is variable depending on the amount of the load according to a function identified by a particular loadelongation curve.

[0074] A tyre for vehicle wheels comprises a carcass structure comprising a plurality of reinforcing cords, typically textile. Such reinforcing cords may be incorporated in a single carcass ply or in multiple carcass plies (preferably no more than two) radially superimposed on each other. The carcass structure has a crown portion extended on opposed sides with respect to the equatorial plane and at which the reinforcing cords extend along a substantially axial direction, and two side portions extended on opposed sides with respect to the crown portion, each one in proximity to a respective sidewall of the tyre.

[0075] In a radially outer position with respect to the carcass structure a crown structure comprising a belt structure is provided and, in a radially outer position with respect to the belt structure a tread band made of elastomeric material is provided.

[0076] The belt structure may comprise a cross-belt structure and / or a zero-degree reinforcing layer.

[0077] The cross-belt structure, typically provided in car tyres, comprises several belt layers radially overlapping each other. In particular, it may be provided a first belt layer including reinforcing cords, typically textile or metallic, substantially parallel to each other and inclined, with respect to the equatorial plane of the tyre, by a predetermined angle and at least one second belt layer arranged in a radially outer position with respect to the first belt layer and including reinforcing cords, typically textile or metallic, substantially parallel to each other but oriented, with respect to the equatorial plane of the tyre, with an inclination opposite to that of the reinforcing cords of the first belt layer.

[0078] The "zero-degree reinforcing layer" comprises a plurality of textile reinforcing cords arranged on the belt structure (in the case of car tyres) or on the crown portion of the carcass structure (in the case of motorcycle tyres) according to a substantially circumferential winding direction. In motorcycle tyres, the zero-degree reinforcing layer may itself define the "belt structure" of such tyres or may be replaced by two overlapping reinforcing layers that define a cross-belt structure.

[0079] Typically, the reinforcing cords of the zero-degree reinforcing layer are incorporated into a rubberized fabric strip-like element. This strip-like element is spirally wound on the crown portion of the carcass structure from one end to the other end thereof with a predetermined deposition pulling force.

[0080] The production cycle of a tyre for vehicle wheels generally comprises at first a process for building a green tyre in which the various structural components of the tyre are built and assembled. The green tyre thus shaped is subsequently subjected to a moulding and vulcanization process aimed at defining the structure of the finished tyre according to a desired geometry and tread design.

[0081] Typically, the building and assembling of the various structural components of the tyre takes place on special forming drums having a substantially cylindrical shape. These drums are radially contractible / expandable.

[0082] In particular, the carcass structure is built on a first forming drum, known as first-stage drum, and the crown structure is built on a second forming drum, known as auxiliary or second-stage drum.

[0083] The assembling of the carcass structure to the crown structure may take place on the first forming drum, in which case the first-stage drum is called single stage or "unistage" drum, or on a different forming drum, known as shaping drum. This assembling comprises, after having positioned the crown structure in a coaxially centred and radially outer position with respect to the carcass structure, shaping the green tyre by radially expanding the first-stage and / or shaping drum. This shaping allows the radially outer surface of the carcass structure to be associated with the radially inner surface of the crown structure and the green tyre to take a toroidal configuration.

[0084] The Applicant has observed that during the shaping of the green tyre, the reinforcing cords of the zero-degree reinforcing layer arranged at the axially central portion of the drum (hereinafter also indicated with "centre" of the drum) undergo an elongation greater than that of the reinforcing cords arranged at the opposed shoulder portions of the drum (hereinafter also indicated with "shoulders" of the drum). In other words, during the shaping of the green tyre, the strip-like element that incorporates the aforesaid reinforcing cords elongates more at its portion wound around the centre of the drum (hereinafter indicated with "central portion" of the strip-like element) and less at its opposed side portions wound around the shoulders of the drum (hereinafter indicated with "shoulder portions" of the strip-like element).

[0085] Consequently, at the end of the shaping the strip-like element is more pulled, and thus stiffer, at its central portion and less pulled, and thus less stiff, at its opposed shoulder portions. In particular, the Applicant has found a difference in elongation, and therefore in stiffness, between central portion and shoulder portions of the strip-like element of abpu 2-3%.

[0086] The Applicant has observed that it would instead be desirable the strip-like element to have, at the end of the shaping, a substantially uniform stiffness in the axial direction, so as to avoid an undesired nonuniformity of mechanical behaviour of the zero reinforcing layer in the axial direction at the tyre footprint area.

[0087] The Applicant has considered that a suitable measure to limit the aforesaid difference in elongation or stiffness, thus moving towards the desired uniformity of stiffness in the axial direction, is to wind the striplike element on the drum with a deposition pull force which varies between the shoulders and the centre of the drum. In particular, it is possible to have a greater deposition pull force at the shoulders of the drum and a smaller one at the centre of the drum. In this way, at the end of the deposition of the strip-like element on the drum and before the shaping of the green tyre, the strip-like element is more pulled, and thus stiffer, at the shoulders of the drum and less pulled, and thus less stiff, at the centre of the drum. However, the Applicant has found that the textile reinforcing cords used in the tyre strip-like elements currently on the market have a limited elongation at low loads (such as those which the strip-like element is subjected to as a result of the aforesaid deposition pull force). Therefore, the provision of a deposition pull force that is lower at the centre of the drum and greater at the shoulders of the drum allows to only partially reduce the difference in stiffness typically present at the end of the shaping between central portion and shoulder portions of the strip-like element.

[0088] The Applicant has therefore thought to make reinforcing cords having high part load elongations, so as to be able to achieve a significant elongation of the shoulder portions of the strip-like element when the latter is wound on the drum with a deposition pull force that is greater at the shoulders of the drum and lower at the centre of the drum. In this way, before the shaping of the green tyre, the strip-like element would be more pulled (and thus stiffer) at its shoulder portions and less pulled (and thus less stiff) at its central portion, thus being able to compensate for the inevitable difference in elongation in the axial direction that occurs during the shaping of the green tyre. The desired uniformity of stiffness of the strip-like element in the axial direction would thus be achieved at the end of the shaping of the green tyre.

[0089] Wishing also to contain the rolling resistance of its tyres, in order to reduce CO2 emissions in the atmosphere, the Applicant has oriented itself towards making reinforcing cords that are as light as possible and has therefore decided to use elongated elements made of non-metallic material.

[0090] The Applicant has realised that it is possible to obtain light reinforcing cords having high part load elongations by providing in the reinforcing cord an empty space and at least one elongated element made of non-metallic material and arranged helically around the empty space. The empty space allows, when the reinforcing cord is pulled, stretching of the helix defined by the non-metallic material elongated element(s), thus obtaining a significant elongation of the reinforcing cord.

[0091] In order to achieve the geometry described above, the Applicant has thought of using a sacrificial elongated element, helically winding the at least one elongated element made of non-metallic material around the sacrificial elongated element and subsequently removing the sacrificial elongated element. Following this removal, the at least one elongated element made of non-metallic material is arranged helically around the empty space previously occupied by the sacrificial elongated element. The latter therefore acts as a support for the at least one elongated element of the reinforcing cord while making the latter and, once removed, defines the empty space in the reinforcing cord.

[0092] The maintenance of the empty space in the reinforcing cord is obtained by subjecting the reinforcing cord to a conventional adhesion process before or after the removal of the sacrificial elongated element.

[0093] Therefore, in a first aspect thereof the present invention relates to a reinforcing cord for tyres for vehicle wheels, comprising at least two elongated elements made of non-metallic material.

[0094] Preferably, at least one first elongated element of said at least two elongated elements extends along a helical path around an empty space with a predetermined helix pitch.

[0095] The reinforcing cord of the invention thus has, at a radially inner or core portion thereof, the empty space and at a radially outer or crown portion thereof, at least two elongated elements.

[0096] The empty space may not necessarily be present in all the cross sections of the reinforcing cord, being however sufficient that it is present in a plurality of cross sections distributed along the entire longitudinal extension of the reinforcing cord.

[0097] In a second aspect thereof, the present invention relates to a process for making a reinforcing cord for tyres for vehicle wheels.

[0098] Preferably, at least one semi-finished product is provided.

[0099] Preferably, the semi-finished product comprises at least one sacrificial elongated element.

[0100] Preferably, the semi-finished product comprises at least two elongated elements made of non-metallic material.

[0101] Preferably, at least one first elongated element of said at least two elongated elements extends along a helical path around the at least one sacrificial elongated element with a predetermined helix pitch.

[0102] Preferably, the at least one sacrificial elongated element is removed from the at least one semi-finished product.

[0103] Preferably, following the removal of the at least one sacrificial elongated element, a reinforcing cord is obtained having, in a radially inner position with respect to said at least one first elongated element, an empty space previously occupied by the at least one sacrificial elongated element.

[0104] Preferably, said at least one first elongated element extends along a helical path around the empty space with said predetermined helix pitch.

[0105] The empty space present in the reinforcing cord as a result of the removal of the sacrificial elongated element can occupy, in the crosssections in which it is actually present, an area whose size is not necessarily equal to that of the area previously occupied by the sacrificial elongated element. For example, if following the removal of the sacrificial elongated element a reciprocal displacement of the elongated elements defining the reinforcing cord occurs, the area occupied by the empty space in the relative cross sections of the reinforcing cord may have a size smaller than that of the area previously occupied by the sacrificial elongated element. The size of this area is however such as to allow a significant stretching of the reinforcing cord when subjected to traction, thus achieving a high part load elongation.

[0106] In a further aspect thereof, the invention relates to a tyre for vehicle wheels comprising a plurality of cords in accordance with the first aspect of the invention.

[0107] According to the Applicant, the reinforcing cords of the invention allows the desired uniformity of stiffness of the strip-like element in the axial direction at the end of the shaping of the green tyre to be achieved. This is obtained thanks to the fact that when the strip-like element is wound on the drum with a deposition pull force that is greater at the shoulders of the drum and lower at the centre of the drum, the shoulder portions of the strip-like element can elongate significantly, thus resulting more pulled and stiffer than the central portion of the strip-like element and thus compensating for the greater elongation / pull of the central portion of the strip-like element with respect to the shoulder portions during the shaping of the green tyre.

[0108] The greater stiffness of the shoulder portions of the strip-like element before the shaping of the green tyre causes an increase in stiffness of the entire crown portion of the tyre and, therefore, a uniform and effective transfer of forces between the tyre and the road surface at the tyre footprint area, to the benefit of the tyre's performance and rolling resistance.

[0109] The provision of the empty space also allows an adequate penetration of the elastomeric material into the reinforcing cord, to the benefit of the adhesion between reinforcing cord and elastomeric material.

[0110] The elastomeric material present in the empty space also tends to behave as a structural component of the reinforcing cord and therefore contributes to make it stiffer, to the benefit of the performance of the tyre.

[0111] In addition, the high part load elongation of the reinforcing cords of the invention allows the strip-like element that incorporates them to withstand high pull forces during the shaping of the green tyre, making it possible to deposit the strip-like element on drums having diameters smaller than those typically provided, without any risk of breaking through the belt structure on which the strip-like element is wound.

[0112] The Applicant has observed that depending on the type of elongated elements used in the reinforcing cord (wires, yarns and / or any combination of one or more wires with one or more yarns) and of the non-metallic material (low modulus material, high modulus material or any combination of such materials) it is possible to make reinforcing cords in accordance with the present invention and having characteristics such as to make the reinforcing cords suitable for being used also in structural components of car and motorcycle tyres other than the zero-degree reinforcing layer. In particular:

[0113] - with the same material and diameter, the wires are more suitable than the yarns to withstand compressive stresses and to reduce hysteresis caused by mutual friction between wires and / or filaments of the yarns, while the yarns are more suitable than the wires to withstand bending stresses and to adhere to the surrounding elastomeric material;

[0114] - with the same type of elongated elements and diameter, a high modulus material allows to increase the stiffness, and / or the breaking load, while a low modulus material allows to maximize the part load elongation and / or the elongation at break.

[0115] According to the Applicant, it is preferable to maximize the stiffness and / or the breaking load when the reinforcing cord of the invention are used in the cross-belt structures of the tyres, or in the reinforcing structures of the bead, indicated further below with the terms "chafer" and "flipper", or in the carcass structures of the tyres, while it is preferable to maximize the part load elongation and / or the elongation at break when the reinforcing cord of the invention are used in the zero- degree reinforcing layer.

[0116] In at least one of the aforesaid aspects, the present invention may have at least one of the preferred features described below.

[0117] Preferably, in at least some cross sections of the reinforcing cord said empty space occupies an area greater than, or equal to, 0.018 mm2.

[0118] The Applicant believes that in this case all the benefits and advantages discussed above can be achieved even more clearly and effectively, the other parameters being the same.

[0119] Preferably, in all cross sections of the reinforcing cord the empty space occupies an area greater than, or equal to, 0.018 mm2.

[0120] The Applicant has found that in this case the aforesaid benefits and advantages are maximized.

[0121] Preferably, the predetermined helix pitch is greater than 2 mm, more preferably greater than 3 mm, even more preferably greater than 4 mm.

[0122] Preferably, the predetermined helix pitch is less than 25 mm, more preferably less than 20 mm, even more preferably less than 12.5 mm.

[0123] In preferred embodiments, the predetermined helix pitch is comprised between 2 mm and 25 mm, preferably between 3 mm and 20 mm, even more preferably between 4 mm and 12.5 mm.

[0124] The Applicant has found that in this case the part load elongation and the elongation at break of the reinforcing cords can be maximized, the other parameters being the same. In particular, considering that if the pitch of the helix decreases the diameter of the sacrificial elongated element and therefore the area occupied by the empty space may increase, it is preferable to keep the pitch of the helix within the aforementioned range of values.

[0125] Preferably, at least one second elongated element of said at least two elongated elements extends around the empty space along a respective helical path with a respective helix pitch. This measure contributes to increase the part load elongation and the elongation at break of the reinforcing cords, as well as the penetration of the elastic material and the adherence with the latter.

[0126] Said respective helix pitch may be equal to or different from said predetermined helix pitch.

[0127] Preferably, said respective helix pitch is equal to said predetermined helix pitch.

[0128] In preferred embodiments, said at least one second elongated element is twisted to the at least one first elongated element. In this case, said at least two elongated elements define at least one first strand.

[0129] In preferred embodiments, said at least one first elongated element is defined by at least one yarn and said at least one second elongated element is defined by at least one wire. In this way the typical benefits of both yarns and wires are achieved.

[0130] In some preferred embodiments, the reinforcing cord comprises a single first strand.

[0131] Preferably, said single first strand comprises a single wire twisted to a single yarn.

[0132] In other preferred embodiments, the reinforcing cord comprises two first strands twisted to each other and extending around the empty space along respective helical paths with respective helix pitches.

[0133] Said two first strands may be equal to each other or different from each other.

[0134] Preferably, said two first strands are equal to each other.

[0135] Said respective helix pitches may be equal to or different from said predetermined helix pitch.

[0136] Preferably, said respective helix pitches are equal to said predetermined helix pitch.

[0137] Preferably, each of said two first strands comprises at least one respective wire twisted to at least one respective yarn. Even more preferably, each of the two first strands comprises a single wire twisted to a single yarn.

[0138] In some embodiments, said at least one first elongated element and said at least one second elongated element are made of the same non-metallic material.

[0139] In this case, preferably, said at least two elongated elements are defined by at least one wire and by at least one yarn, respectively, or by at least two wires that may or may not have the same diameter or by respective yarns that may or may not have the same linear density.

[0140] In preferred embodiments, said at least one first elongated element is made of a first non-metallic material and said at least one second elongated element is made of a second non-metallic material different from said first material. In this case, said at least two elongated elements, when twisted to each other, define at least one first hybrid strand.

[0141] In preferred embodiments, said first material and second material are selected among: nylon, rayon, PET, aramid, glass.

[0142] Preferably, said first material is selected among nylon, rayon, PET, aramid, glass.

[0143] Preferably, said second material is selected among nylon, rayon, PET.

[0144] Preferably, it one elongated element is made of a low modulus material and another elongated element is made of a material having a modulus higher than that of the other elongated element.

[0145] Preferably, one elongated element is made of a low modulus material and another elongated element is made of a high modulus material, so as to achieve, in addition to the desired part load elongation, a high stiffness at higher loads.

[0146] The characteristic "double modulus" mechanical behaviour typical of the hybrid reinforcing cords is thus obtained, which translates, in a load-elongation graph, into a curve defined by two segments separated by a connecting knee, in which the segment to the left of the knee (indicative of the part load elongations, which is particularly high in the reinforcing cord of the invention) has an inclination with respect to the axis of the abscissa that is much lower than that of the segment to the right of the knee (indicative of the stiffness). At low loads, the mechanical behaviour of the reinforcing cord is mainly dictated by the reaction offered by the low modulus material (as well as by the empty space), while at high load the mechanical behaviour of the reinforcing cord is mainly dictated by the reaction offered by the high modulus material.

[0147] Preferably, said at least one first elongated element is defined by at least one aramid or glass or PET yarn and said at least one second elongated element is defined by at least one nylon or rayon or PET wire.

[0148] In some specific embodiments, the at least one first elongated element and the at least one second elongated element are defined by nylon yarns. In this case, the greater part load elongation with respect to the conventional reinforcing cords defined by two nylon elongated elements is obtained only thanks to the provision of the empty space.

[0149] In some specific embodiments, the at least one first elongated element and / or the at least one second elongated element are defined by PET wires or yarns. In these cases, the part load elongation is achieved thanks to the provision of the empty space, and the fact that at least one of the two elongated elements is made of PET, provides the reinforcing cord with a greater stiffness than that of the conventional reinforcing cords defined by nylon elongated elements.

[0150] In all of the aforesaid embodiments described above, the reinforcing cord comprises a plurality of substantially circular cross sections.

[0151] In this case, in at least some cross sections of the reinforcing cord the at least two elongated elements can be arranged on diametrically opposite sides with respect to the empty space or arranged circumferentially adjacent to each other, possibly in a condition of substantial mutual contact.

[0152] In some preferred embodiments, the reinforcing cord further comprises at least one third elongated element made of non-metallic material and arranged in a radially inner position with respect to said at least two elongated elements.

[0153] In this case, preferably, said at least two elongated elements extend along respective helical paths around the at least one third elongated element with said predetermined helix pitch.

[0154] The reinforcing cords of these embodiments thus have the empty space and the at least one third elongated element at the respective radially inner or core portions, and at least two elongated elements at the respective radially outer or crown portions.

[0155] Said at least one third elongated element may be made of a non- metallic material which is the same of or different from said first material.

[0156] Preferably, said at least one third elongated element is made of a non-metallic material different from said first material.

[0157] Preferably, said at least one third elongated element is made of a material selected among nylon, rayon, PET.

[0158] Preferably, said at least one third elongated element is defined by at least one wire.

[0159] Preferably, the third elongated element is defined by a single wire.

[0160] In some preferred embodiments, the reinforcing cord comprises at least one fourth elongated element made of non-metallic material and arranged in a radially inner position with respect to said at least two elongated elements.

[0161] The reinforcing cords of such embodiments therefore have the empty space, the at least one third elongated element and the at least one fourth elongated element at the respective radially inner or core portions, and at least two elongated elements at the respective radially outer or crown portions.

[0162] Preferably, said at least one fourth elongated element is twisted to the at least one third elongated element.

[0163] Said at least one fourth elongated element may be made of a non- metallic material which is the same of or different from that of said at least one third elongated element.

[0164] Preferably, said at least one fourth elongated element is made of a non-metallic material different from that of said at least one third elongated element.

[0165] In this case, said at least one third elongated element and at least one fourth elongated element define at least one second hybrid strand, which is preferably arranged in a radially inner position with respect to the first hybrid strand.

[0166] Said second hybrid strand may be equal to or different from said first hybrid strand.

[0167] Preferably, said second hybrid strand is equal to said first hybrid strand.

[0168] Preferably, said at least two elongated elements extend along respective helical paths around the at least one fourth elongated element with said predetermined helix pitch.

[0169] In some preferred embodiments, the reinforcing cord comprises a single second hybrid strand.

[0170] Preferably, said single second hybrid strand comprises a single wire twisted to a single yarn.

[0171] Preferably, said at least one fourth elongated element is made of a material selected among nylon, rayon, PET, aramid, glass.

[0172] Preferably, said at least one fourth elongated element is defined by at least one yarn.

[0173] Preferably, said at least one third elongated element is defined by at least one nylon or rayon or PET wire and said at least one fourth elongated element is defined by at least one aramid or glass yarn.

[0174] More preferably, said at least one third elongated element is defined by a single nylon or rayon or PET wire and said at least one fourth elongated element is defined by a single aramid or glass yarn.

[0175] Preferably, in all the embodiments in which the at least one third elongated element and / or the at least one fourth elongated element is provided, the reinforcing cord comprises a plurality of cross sections having a substantially elliptical shape.

[0176] Preferably, the reinforcing cord has an initial modulus and a final modulus such that the ratio between final modulus and initial modulus is greater than or equal to 9.

[0177] Preferably, the ratio between final modulus and initial modulus is greater than, or equal to, 12, even more preferably greater than, or equal to, 20, even more preferably greater than, or equal to, 30.

[0178] Preferably, the / each wire has a diameter greater than, or equal to, 0.10 mm, more preferably greater than, or equal to, 0.16 mm, even more preferably greater than, or equal to, 0.23 mm.

[0179] Preferably, the / each wire has a diameter less than, or equal to, 0.8 mm, more preferably less than, or equal to, 0.5 mm, even more preferably less than, or equal to, 0.35 mm.

[0180] In preferred embodiments, the / each wire has a diameter comprised between 0.10 mm and 0.8 mm, more preferably comprised between 0.16 mm and 0.5 mm, even more preferably comprised between 0.23 mm and 0.35 mm.

[0181] Preferably, the / each yarn has a linear density greater than or equal to 235 dtex, more preferably greater than or equal to 500 dtex, even more preferably greater than or equal to 940 dtex.

[0182] Preferably, the / each yarn has a linear density less than or equal to 3300 dtex, more preferably less than or equal to 2700 dtex, even more preferably less than or equal to 2200 dtex.

[0183] Preferably, the / each yarn has a linear density comprised between 235 dtex and 3300 dtex, more preferably comprised between 500 dtex and 2700 dtex, even more preferably comprised between 940 dtex and 2200 dtex.

[0184] Preferably, the reinforcing cord extends along a non-rectilinear longitudinal trajectory.

[0185] Preferably, said longitudinal trajectory is substantially undulating. This undulation contributes to increase the part load elongation of the reinforcing cord.

[0186] Preferably, said at least one sacrificial elongated element is a yarn made of a synthetic polymeric material, more preferably a polyvinyl alcohol (PVA) or polyester (PES) yarn. This material is non-toxic, colourless and odourless, and therefore its use does not pose any risk to the operators who handle it or who are in close proximity to it.

[0187] Preferably, the at least one sacrificial elongated element has a linear density greater than or equal to 200 dtex, more preferably greater than or equal to 700 dtex.

[0188] Preferably, the at least one sacrificial elongated element has a linear density less than or equal to 4400 dtex, more preferably less than or equal to 1670 dtex.

[0189] In preferred embodiments, the at least one sacrificial elongated element has a linear density comprised between 200 dtex and 4400 dtex, preferably between 700 dtex and 1670 dtex.

[0190] Preferably, said at least one sacrificial elongated element is obtained by twisting together a number of elongated elements equal to 16 or multiple of 16, for example 32.

[0191] In some embodiments, the material of said at least one sacrificial elongated element is water-soluble, so as to allow removal of the at least one sacrificial elongated element by water bath or water jet. Preferably, in the semi-finished product said at least two elongated elements extend along respective helical paths around the at least one sacrificial elongated element with respective helix pitches.

[0192] Preferably, said respective helix pitches are equal to said predetermined helix pitch.

[0193] In the process for making the reinforcing cord of the invention, the at least one semi-finished product, once made, can be wound in a service reel, from which it is subsequently taken to remove the sacrificial elongated element and, therefore, make the reinforcing cord.

[0194] Alternatively, the at least one semi-finished product can be fed continuously along a predetermined feeding direction to remove the sacrificial elongated element and, therefore, make the reinforcing cord. In the latter case, the removal of the sacrificial elongated element from the at least one takes place continuously while making the semi-finished product and, therefore, continuously while making the reinforcing cord.

[0195] In both the cases discussed above, the at least one sacrificial elongated element and said at least two elongated elements are fed to a twisting device;

[0196] Preferably, said at least one first elongated element is twisted together with the at least one sacrificial elongated element in said twisting device.

[0197] Preferably, the aforesaid twisting takes place with a twisting pitch equal to said predetermined helix pitch.

[0198] Preferably, the aforesaid twisting takes place by winding said at least one elongated element around the sacrificial elongated element so that said at least one sacrificial elongated element is arranged in a radially inner position with respect to said at least one first elongated element.

[0199] In some preferred embodiments, said at least two elongated elements are twisted to each other before being fed to the twisting device. In other preferred embodiments, said at least two elongated elements are fed to the twisting device individually from each other and are twisted together with the sacrificial elongated element in the twisting device with said predetermined twisting pitch.

[0200] In some preferred embodiments, it the at least one sacrificial elongated element, said at least two elongated elements and at least one third elongated element are fed to said twisting device.

[0201] In this case, preferably said at least two elongated elements and the at least one third elongated element are twisted together with the at least one sacrificial elongated element in the twisting device.

[0202] Preferably, said twisting takes place with said predetermined twisting pitch.

[0203] Preferably, said twisting takes place by winding said at least two elongated elements around the sacrificial elongated element and the at least one third elongated element so that the at least one sacrificial elongated element and the at least one third elongated element are arranged in a radially inner position with respect to said at least two elongated elements.

[0204] In further preferred embodiments, the at least one sacrificial elongated element, said at least two elongated elements, said at least one third elongated element and at least one fourth elongated element are fed to said twisting device.

[0205] In this case, preferably, said at least two elongated elements, the at least one third elongated element and the at least one fourth elongated element are twisted together with the at least one sacrificial elongated element in the twisting device.

[0206] Preferably, said twisting takes place with said predetermined twisting pitch.

[0207] Preferably, said twisting takes place by winding said at least two elongated elements around the sacrificial elongated element, the at least one third elongated element and the at least one fourth elongated element so that the at least one sacrificial elongated element, the at least one third elongated element and the at least one fourth elongated element are arranged in a radially inner position with respect to said at least two elongated elements.

[0208] In some preferred embodiments, said at least one third elongated element and said at least one fourth elongated element are twisted together before being fed to the twisting device.

[0209] Preferably, said at least two elongated elements, said at least one third elongated element and said at least one fourth elongated element are twisted together with the at least one sacrificial elongated element in said twisting device with said predetermined twisting pitch so that in the semi-finished product the at least one sacrificial elongated element is arranged in a radially inner position with respect to said at least two elongated elements, said at least one third elongated element and said at least one fourth elongated element or in a radially inner position with respect to said at least two elongated elements and in a radially outer position with respect to said at least one third elongated element and said at least one fourth elongated element.

[0210] In some preferred embodiments, in order to remove said at least one sacrificial elongated element, said at least one semi-finished product is fed to a machine provided with mechanical removal members.

[0211] In other preferred embodiments in which said at least one sacrificial elongated element is made of a water-soluble material, in order to remove said at least one sacrificial elongated element said at least one semi-finished product is immersed in a water bath and / or is hit by a water jet.

[0212] Preferably, after having removed said at least one sacrificial elongated element, the reinforcing cord is hit by a jet of compressed air and dried. Preferably, the reinforcing cord, after the optional drying, is wound on a collection reel from which it is then taken for building the tyre or its structural components.

[0213] Preferably, the reinforcing cords of the invention are used in the zero-degree reinforcing layer of the tyre.

[0214] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0215] Further characteristics and advantages of the tyre of the present invention will become clearer from the following detailed description of preferred embodiments thereof, made with reference to the appended drawings. In such drawings:

[0216] - figure 1 is a schematic partial half-cross section view of a portion of an embodiment of a tyre comprising reinforcing cords in accordance with the present invention;

[0217] - figure 2 is a photo of a segment of a first embodiment of a reinforcing cord in accordance with the present invention;

[0218] - figure 2a is a schematic view of a cross-section of the reinforcing cord of figure 2 taken at the section plane A-A indicated in figure 2;

[0219] - figure 3 is a photo of a segment of a second embodiment of a reinforcing cord in accordance with the present invention;

[0220] - figure 3a is a schematic view of a cross-section of the reinforcing cord of figure 3 taken at the section plane B-B indicated in figure 3;

[0221] - figure 4 shows a load-elongation graph of a conventional textile reinforcing cord and of reinforcing cords made in accordance with the present invention;

[0222] - figure 5 is a schematic view of a first embodiment of an apparatus for making a reinforcing cord in accordance with the present invention, said apparatus performing a continuous process;

[0223] - figures 6a and 6b illustrate a second embodiment of an apparatus for making a reinforcing cord in accordance with the present invention, said apparatus performing a discontinuous process; - figure 7 is a photo of a sacrificial elongated element used for making the reinforcing cord of the present invention.

[0224] For the sake of simplicity, figure 1 shows only a part of an exemplary embodiment of a tyre 100 in accordance with the present invention, the remaining part, which is not shown, being substantially identical and being arranged symmetrically with respect to the equatorial plane M-M of the tyre.

[0225] The tyre 100 shown in figure 1 is, in particular, an exemplary embodiment of a tyre for four-wheeled vehicles.

[0226] Preferably, the tyre 100 is an HP or UHP tyre for sports and / or high and ultra high performance vehicles. This tyre allows to reach speeds higher than 190 km / h, up to over 300 km / h and has one of the following speed codes: "T", "U", "H", "V", "Z","W", "Y", according to the E.T.R.T.O. standard (European Tyre and Rim Technical Organisation). It has a section width equal to or higher than 185 mm, preferably comprised between 195 mm and 385 mm, more preferably comprised between 195 mm and 355 mm and is intended to be mounted on rims having fitting diameters equal to or higher than 13 inches, preferably not higher than 24 inches, more preferably comprised between 16 inches and 23 inches.

[0227] In figure 1 "a" indicates an axial direction, "c" indicates a radial direction, "M-M" indicates the equatorial plane of the tyre 100 and "R-R" indicates the axis of rotation of the tyre 100.

[0228] The tyre 100 comprises a carcass structure 101, in turn comprising at least one carcass ply 111.

[0229] Hereinafter, for the sake of simplicity of disclosure, reference will be made to an embodiment of the tyre 100 comprising a single carcass ply 111. H what is described has analogous application in tyres comprising more than one carcass ply.

[0230] The carcass ply 111 has axially opposite end edges engaged with respective annular anchoring structures 102, called bead cores, possibly associated with an elastomeric filler 104. The area of the tyre 100 comprising the bead core 102 and the possible elastomeric filler 104 forms an annular reinforcing structure 103 called "bead structure" and configured to allow the anchoring of the tyre 100 on a corresponding mounting rim, not shown.

[0231] The carcass ply 111 comprises a plurality of reinforcing cords 10' coated with an elastomeric material or incorporated in a matrix of crosslinked elastomeric material.

[0232] The carcass structure 101 is of the radial type, i.e. the reinforcing cords 10' are arranged on planes comprising the axis of rotation R-R of the tyre 100 and are substantially perpendicular to the equatorial plane M-M of the tyre 100.

[0233] Each annular reinforcing structure 103 is associated with the carcass structure 101 by folding up (or turning up) the opposite end edges of the at least one carcass ply 111 about the bead core 102 and the possible elastomeric filler 104, so as to form the so-called turnings 101a of the carcass structure 101.

[0234] A crown structure is arranged in a radially outer position with respect to the carcass structure 101. The crown structure comprises a cross-belt structure 106 and a zero-degree reinforcing layer 106c, commonly known as a "zero-degree belt".

[0235] The cross-belt structure 106 comprises at least two belt layers 106a, 106b radially overlapping each other.

[0236] The belt layers 106a, 106b respectively comprise a plurality of reinforcing cords 10", 10'". Such reinforcing cords 10", 10'" have an orientation that is inclined with respect to the circumferential direction of the tyre 100, or to the equatorial plane M-M of the tyre 100, by an angle comprised between 15° and 45°, preferably between 20° and 40°. For example, this angle is equal to 30°.

[0237] The reinforcing cords 10", 10'" of one belt layer 106a, 106b are parallel to each other and have a cross orientation with respect to the reinforcing cords 10"', 10" of the other belt layer 106b, 106a.

[0238] The zero-degree reinforcing layer 106c comprises reinforcing cords oriented in a substantially circumferential direction. These reinforcing cords therefore form an angle of a few degrees (typically less than 10°, for example comprised between 0° and 6°) with respect to the equatorial plane M-M of the tyre 100.

[0239] A tread band 109 made of elastomeric material is applied in a radially outer position with respect to the zero-degree reinforcing layer 106c.

[0240] Respective sidewalls 108 made of elastomeric material are also applied on the side surfaces of the carcass structure 101, in an axially outer position with respect to the carcass structure 101 itself. Each sidewall 108 extends from one of the side edges of the tread band 109 up to the respective annular reinforcing structure 103.

[0241] In some specific embodiments, like the one illustrated and described here, the stiffness of the sidewall 108 can be improved by providing a stiffening layer 120, generally known as "flipper" or additional strip-like insert and which has the function of increasing the stiffness and integrity of the annular reinforcing structure 103 and of the sidewall 108.

[0242] The flipper 120 is wound around a respective bead core 102 and elastomeric filler 104 so as to at least partially surround the annular reinforcing structure 103. In particular, the flipper 120 wraps the annular reinforcing structure 103 along the axially inner, axially outer and radially inner zones of the annular reinforcing structure 103.

[0243] The flipper 120 is arranged between the turned-up end edge of the carcass ply 111 and the respective annular reinforcing structure 103. Usually, the flipper 120 is in contact with the carcass ply 111 and the annular reinforcing structure 103.

[0244] In some specific embodiments, like the one illustrated and described here, the bead structure 103 can also comprise a further stiffening layer 121 that is generally known by the term "chafer", or protective strip, and which has the function of increasing the stiffness and integrity of the annular reinforcing structure 103.

[0245] The chafer 121 is associated with a respective turned-up end edge of the carcass ply 111 in an axially outer position with respect to the respective annular reinforcing structure 103 and extends radially towards the sidewall 108 and the tread band 109.

[0246] The flipper 120 and the chafer 121 comprise reinforcing cords 10* (in the attached figures those of the flipper 120 are not visible).

[0247] In the tyre of figure 1, at least some of the reinforcing cords of the zero-degree reinforcing layer 106c (preferably all the cords of the zero-degree reinforcing layer 106c) are reinforcing cords 10 in accordance with the present invention.

[0248] A first embodiment of such reinforcing cords 10 is shown in figures 2 and 2a.

[0249] This reinforcing cord 10 comprises two strands 11, each comprising two elongated elements 11a, lib made of non-metallic material.

[0250] Each of the two strands 11, and therefore each of the respective elongated elements 11a, lib, extends longitudinally along a respective helical path around an empty space 10a with a predetermined helix pitch E. In figure 2 the longitudinal direction L of extension of the individual elongated elements 11a, lib, and therefore of the two strands 11, and therefore of the reinforcing cord 10, is indicated.

[0251] Preferably, the reinforcing cord 10 extends along the longitudinal direction L with a non-rectilinear trajectory, more preferably an undulating trajectory.

[0252] As described below with reference to figures 5, 6a and 6b, the reinforcing cord 10 is obtained by twisting together the two strands 11 and a sacrificial elongated element 20 (of the type for example shown in figure 7 and with dotted lines in figure 2a) with a twisting pitch equal to the aforesaid helix pitch E, to form a semi-finished product 15, leaving the sacrificial elongated element 20 in a radially inner position with respect to the two strands 11.

[0253] Each of the two strands 11 can in turn be obtained by twisting together the respective elongated elements 11a, lib before twisting the two strands 11 together with the sacrificial elongated element 20.

[0254] After having been twisted with the two strands 11, the sacrificial elongated element 20 is removed from the semi-finished product 15, leaving the empty space 10a in the reinforcing cord 10. Following this removal, the two strands 11 maintain a helical geometry and define the reinforcing cord 10, which will also have a helical geometry.

[0255] As shown in figure 2a, each cross-section of the reinforcing cord 10 has a substantially circular shape and has the empty space 10a in the position previously occupied by the sacrificial elongated element 20, and therefore in a radially inner position with respect to the two strands 11. In the specific case illustrated here, the two strands 11 are arranged on diametrically opposite sides with respect to the empty space 10a.

[0256] The sacrificial elongated element 20 is preferably a yarn made of a synthetic, preferably water-soluble, polymeric material, for example polyvinyl alcohol (PVA) or polyester (PES). It can be purchased from specialized producers (such as for example Kuraray Co., Ltd or Sekisui Specialty Chemicals) or be made by twisting together a plurality of PVA or PES elongated elements in a conventional twisting device.

[0257] The helix pitch E is comprised between 2 mm and 25 mm, preferably between 3 mm and 20 mm, more preferably between 4 mm and 12.5 mm.

[0258] The sacrificial elongated element 20 has a linear density comprised between 200 dtex and 4400 dtex, preferably between 700 dtex and 1670 dtex.

[0259] The diameter and / or the linear density of the sacrificial elongated element 20 and the helix pitch E are selected such that, in at least some cross-sections of the reinforcing cord 10, preferably in all the crosssections thereof, the empty space 10a occupies an area greater than, or equal to, 0.018 mm2. In this case, the sacrificial elongated element 20 is made so as to have a diameter greater than or equal to about 0.15 mm.

[0260] In an embodiment of the reinforcing cord 10 of figures 2 and 2a, each of the two elongated elements 11a is defined by a respective yarn, while each of the two elongated elements lib is defined by a respective wire.

[0261] Each wire has a diameter comprised between 0.10 mm and 0.8 mm, preferably comprised between 0.16 mm and 0.5 mm, more preferably comprised between 0.23 mm and 0.35 mm.

[0262] Each yarn has a linear density comprised between 235 dtex and 3300 dtex, preferably comprised between 500 dtex and 2700 dtex, more preferably comprised between 940 dtex and 2200 dtex.

[0263] Each wire is made of a material selected among nylon, rayon, PET.

[0264] Each yarn is made of a material selected among nylon, rayon, PET, aramid, glass.

[0265] Preferably, each wire is made of a low modulus material, in particular nylon or rayon or PET, and each yarn is made of a high modulus material, in particular aramid or glass.

[0266] In those cases where each wire is made of nylon or rayon or PET, each yarn can be made of PET.

[0267] With reference to figure 5, an exemplary embodiment of an apparatus and a process for making the reinforcing cord 10 of figure 2 is described.

[0268] The sacrificial elongated element 20, which in this case is water- soluble, and the two strands 11 are taken from respective reels 40 and 30 and fed to a twisting device 60 to be mutually twisted, so as to form the semi-finished product 15. The twisting device 60 is therefore arranged downstream of the reels 40 and 30 with reference to a feeding direction indicated with A in figure 5. The twisting of the sacrificial elongated element 20 and of the two strands 11 takes place by winding the two strands 11 around the sacrificial elongated element 20 so that the sacrificial elongated element 20 is arranged in a radially inner position with respect to the two strands 11.

[0269] The semi-finished product 15 is fed, along said feeding direction A, to a removal device 70 in which the sacrificial elongated element 20 is removed from the semi-finished product 15, thus making the reinforcing cord 10. The removal device 70 is therefore arranged downstream of the twisting device 60 with reference to the feeding direction A.

[0270] In one embodiment of the invention, the removal device 70 comprises a tank 73 in which the semi-finished product is hit with a jet of hot water in countercurrent while the semi-finished product 15 moves along the feeding direction A. The jet of hot water dissolves the sacrificial elongated element 20 while said jet is crossed by the strands 11, which remain the only constituent elements of the reinforcing cord 10.

[0271] Preferably, the reinforcing cord 10 thus formed then passes through a compressed air feeding and drying device 75 to be subsequently wound in a respective collection reel 50, from which it can then be taken during the building of the tyre 100. The device 75 is therefore arranged downstream of the removal device 70 with reference to the feeding direction A.

[0272] In the process described above with reference to figure 5, the reinforcing cord 10 is made continuously while the semi-finished product 15 is being made (and therefore continuously during the removal of the sacrificial elongated element 20). The reinforcing cord 10 is then made through a continuous process that comprises, in a time sequence without interruptions or stops, making the semi-finished product 15 by mutually twisting the strands 11 and the sacrificial elongated element 20, moving the semi-finished product 15 thus made along the feeding direction A, removing the sacrificial elongated element 20, drying the reinforcing cord 10 thus formed and winding the reinforcing cord 10 in the collection reel 50.

[0273] However, the reinforcing cord 10 can also ne made in two distinct operating steps, i.e. through a discontinuous process such as for example the one illustrated in figures 6a and 6b. This process differs from the one described above with reference to figure 5 only in that the semi-finished product 15, once made, is collected in a service reel 45 (figure 6a), from which it can be taken when it is desired to proceed with making the reinforcing cord 10 as described earlier (figure 6b). The service reel 45 is thus intended to be arranged downstream of the twisting device 60 when the semi-finished product 15 is made and upstream of the removal device 70 when the sacrificial elongated element 20 is removed from the semifinished product 15 to make the reinforcing cord 10.

[0274] Instead of through the removal device 70 described above, the removal of the sacrificial elongated element 20 from the semi-finished product 15 can take place by feeding the semi-finished product 15 to a machine provided with mechanical removal members. These members remove the sacrificial elongated element 20 leaving it intact, so that it can be reused for other purposes.

[0275] Before or after the removal of the sacrificial elongated element 20 the reinforcing cords 10 are subjected to a conventional adhesion process that allows to stabilize the geometry of the reinforcing cord 10, maintaining in the reinforcing cord 10 the empty space 10a discussed above.

[0276] The reinforcing cords 10 are intended to be incorporated into a strip-like element made of elastomeric material and intended to be used for making the zero-degree reinforcing layer 106c of the tyre 100.

[0277] A first example of reinforcing cord 10 of the type shown in figures 2 and 2a has the following construction:

[0278] (32) + 2 x (AR 1680 + NY 0.28) 4.3 wherein moving from left to right:

[0279] - the number in brackets indicates the number of elongated elements of PVA twisted together to obtain the sacrificial elongated element 20 which will then be removed (in this specific case 32 elongated elements);

[0280] - the number after the "+" indicates the number of strands 11 twisted to the sacrificial elongated element 20 (in the specific case 2 strands);

[0281] - the content of the bracket after the "x" indicates the composition of each strand 11, with an indication of the material and linear density of the yarn and of the material and diameter of the wire (in this specific case, each strand 11 is a hybrid strand comprising an aramid yarn having a linear density equal to 1680 dtex and a nylon wire having a diameter equal to 0.28 mm);

[0282] - 4.3 is the helix pitch E of the strands 11.

[0283] In this example the two strands 11 extend along respective helical paths and with a helix pitch E at a crown portion of the reinforcing cord 10, while the empty space 10a is arranged at a core portion of the reinforcing cord 10.

[0284] Another example of reinforcing cord 10 of the type shown in figures 2 and 2a has the following construction:

[0285] (32) + 2 x (AR 1680 + PET 0.16) 4.3.

[0286] This reinforcing cord 10 differs from that of the first example only in that in each strand 11 there is, in addition to the aramid yarn, a PET wire having a diameter equal to 0.16 mm instead of the nylon wire having a diameter equal to 0.33 mm. A non-illustrated example of reinforcing cord in accordance with the present invention and having a construction different from that of figures 2 and 2a has the following construction:

[0287] (32) + 1 x (AR 1680 + NY 0.33) 4.3.

[0288] This reinforcing cord differs from that of the first example only in that a single strand is provided, this strand comprising, in addition to the aramid yarn, a nylon wire having a diameter equal to 0.33 mm. This reinforcing cord can be made with processes similar to those described above with reference to the reinforcing cords of figures 2 and 2a, for example with processes similar to those described and shown in figures 5, 6a and 6b. In this case, however, a single strand 11 is fed (from a respective reel 30) to the twisting device 60, in addition to the sacrificial elongated element (from the reel 40).

[0289] Figures 3 and 3a show a further example of a reinforcing cord 10 in accordance with the present invention.

[0290] This reinforcing cord 10 differs from that of figures 2 and 2a only in that it comprises, in addition to the two strands 11 and to the empty space 10a described above, two further elongated elements 11c made of non-metallic material and arranged in a radially inner position with respect to the two strands 11. Also in this reinforcing cord 10 the two strands 11 extend along respective helical paths and with helix pitch E at the crown portion of the reinforcing cord 10. In this case, however, the reinforcing cord 10 comprises, in the core portion thereof, both the empty space 10a previously occupied by the sacrificial elongated element 20 (illustrated in dotted lines in figure 3a) and the two elongated elements 11c.

[0291] In this case, as shown in figure 3a, each cross-section of the reinforcing cord 10 has a substantially elliptical shape.

[0292] In the specific case shown in figures 3 and 3a, the two strands 11 are arranged circumferentially adjacent to each other around the two elongated elements 11c and the empty space 10a.

[0293] In an embodiment of the reinforcing cord 10 of figures 3 and 3a, each of the two elongated elements 11c is defined by a respective wire having a diameter comprised between 0.10 mm and 0.8 mm, preferably between 0.16 mm and 0.5 mm, more preferably between 0.23 mm and 0.35 mm.

[0294] Each of said wires is made of a material selected among nylon, rayon, PET.

[0295] An example of a reinforcing cord 10 of the type shown in figures 3 and 3a has the following construction:

[0296] (32) + 2 x NY 0.23 + 2x(AR 1680+NY 0.23) 5.3 wherein the two wires 11c are made of nylon and have a diameter equal to 0.23 mm.

[0297] The reinforcing cords of figures 3 and 3a can be made with processes similar to those described above with reference to the reinforcing cords of figures 2 and 2a, for example with processes similar to those described and shown in figures 5, 6a and 6b. In this case, however, two further reels are provided for feeding the elongated elements 11c to the twisting device 60, in addition to the reels 40 and 30 that are shown.

[0298] Another example of reinforcing cord 10 of the type shown in figures 3 and 3a differs from the one mentioned hereinabove only in that the wires 11c are made of PET instead of nylon and / or in that a single wire 11c of nylon or PET is provided instead of two wires 11c and / or in that a single strand 11 is provided instead of two strands 11.

[0299] A further embodiment non-illustrated of a reinforcing cord in accordance with the present invention and having a construction different from that of figures 2 and 2a and from that of figures 3 and 3a is described hereinbelow.

[0300] This reinforcing cord comprises, in addition to the two strands 11 and to the empty space 10a, a further strand arranged in a radially inner position with respect to the two strands 11, said further strand comprising an elongated element 1 lc of the type described above twisted to a further elongated element made of non-metallic material.

[0301] In this case, therefore, the two strands 11 extend, at the crown portion of the reinforcing cord 10, along respective helical paths and with the helix pitch E around a core portion of the reinforcing cord 10 which comprises both the empty space 10a previously occupied by the sacrificial elongated element 20 and the further strand.

[0302] In an embodiment of the reinforcing cord described hereinabove, said further elongated element is defined by a yarn having a linear density comprised between 235 dtex and 3300 dtex, preferably between 500 dtex and 2700 dtex, more preferably between 940 dtex and 2200 dtex.

[0303] This yarn is made of a material selected among nylon, rayon, PET, aramid, glass.

[0304] A construction example of the reinforcing cord described hereinabove is as follows:

[0305] (32) + (AR 1680 + NY 0.28) + (AR 1680 + NY 0.33) 5.3.

[0306] In this specific case, the strand arranged in the core portion of the reinforcing cord comprises an Aramid yarn having a linear density equal to 1680 dtex twisted to a nylon wire having a diameter equal to 0.28 mm. The crown portion instead comprises a single strand comprising an aramid yarn having a linear density equal to 1680 dtex twisted to a nylon wire having a diameter equal to 0.33 mm.

[0307] This reinforcing cord can be made with processes similar to those described above with reference to the reinforcing cords of figures 2 and 2a, for example with processes similar to those described and shown in figures 5, 6a and 6b. In this case, however, the aforesaid further strand is fed (from a reel similar to the reel 30) to the twisting device 60, in addition to the sacrificial elongated element 20 (fed from the reel 40) and to a strand 11 (fed from a reel 30).

[0308] In all the reinforcing cords in accordance with the present invention, it is preferably to provide both at least one elongated element made of a low modulus material and at least one elongated element made of a high modulus material. In particular, the ratio between final modulus and initial modulus is greater than, or equal to, 9.

[0309] The Applicant has made some comparative tensile tests according to the BISFA standard between three reinforcing cords in accordance with the present invention and a conventional reinforcing cord typically used in the zero-degree reinforcing layer of the tyres.

[0310] The conventional reinforcing cord comprised two aramid yarns, each having a linear density equal to 1330 dtex, twisted to a nylon yarn having a linear density equal to 1400 dtex. This cord is indicated herein with STD.

[0311] The reinforcing cords in accordance with the present invention had the following constructions:

[0312] (32) + 2 x (AR. 1680 + NY 0.28), herein indicated with INV1;

[0313] (16) + PET 0.30 + 2 x (AR 1680 + NY 0.23), herein indicated with INV2;

[0314] (32) + 2 x NY 0.23 + 2 x (AR 1680 + NY 0.23), herein indicated with INV3.

[0315] In the three cords INV1, INV2 and INV3 the sacrificial elongated element was made of PVA.

[0316] The results of these comparative tests are shown in figure 4.

[0317] It can be noted that, with the same other parameters, the reinforcing cords in accordance with the present invention have a part load elongation much greater than that of the conventional reinforcing cord, reaching values always greater than 2% and, in the specific case of the cord INV3, close to 8%. It can also be noted that, thanks to the use of the sacrificial elongated element (and therefore to the presence of the empty space left by the sacrificial elongated element when removed), and to the use of low modulus and high modulus elongated elements, the reinforcing cords in accordance with the present invention have the characteristic "double modulus" mechanical behaviour, thus guaranteeing, in addition to the desired part load elongation, a high full load stiffness.

[0318] The present invention has been described with reference to some preferred embodiments. Various modifications can be made to the embodiments described above, still remaining within the scope of protection of the invention as defined by the following claims.

Claims

CLAIMS1. Reinforcing cord (10) for tyres for vehicle wheels, comprising at least two elongated elements (11a, lib) made of non-metallic material, wherein at least one first elongated element (11a) of said at least two elongated elements (11a, lib) extends along a helical path around an empty space (10a) with a predetermined helix pitch (E).

2. Reinforcing cord (10) according to claim 1, wherein in at least some cross sections of the reinforcing cord (10) said empty space (10a) occupies an area greater than, or equal to, 0.018 mm2.

3. Reinforcing cord (10) according to claim 1 or 2, wherein at least one second elongated element (lib) of said at least two elongated elements (11a, lib) extends around the empty space (10a) along a respective helical path with a respective helix pitch (E).

4. Reinforcing cord (10) according to claim 3, wherein said at least one first elongated element (11a) is defined by at least one yarn and said at least one second elongated element (lib) is defined by at least one wire.

5. Reinforcing cord (10) according to claim 3 or 4, wherein said at least one first elongated element (11a) is made of a first non-metallic material and said at least one second elongated element (lib) is made of a second non-metallic material different from said first material.

6. Reinforcing cord (10) according to claim 5, wherein said first material and second material are selected among : nylon, rayon, PET, aramid, glass.

7. Reinforcing cord (10) according to any one of the previous claims, further comprising at least one third elongated element (11c) made of non-metallic material and arranged in a radially inner position with respect to said at least two elongated elements (11a, lib), wherein said at least two elongated elements (11a, lib) extend along respective helical paths around the at least one third elongated element (11c) withsaid predetermined helix pitch (E).

8. Reinforcing cord (10) according to claim 7, wherein said at least one third elongated element (11c) is made of a material selected among nylon, rayon, PET.

9. Reinforcing cord (10) according to claim 7 or 8, wherein said at least one third elongated element (11c) is defined by at least one wire.

10. Reinforcing cord (10) according to any one of the previous claims, wherein said reinforcing cord (10) has an initial modulus and a final modulus such that the ratio between final modulus and initial modulus is greater than, or equal to, 9.

11. Reinforcing cord (10) according to any one of the previous claims, wherein the reinforcing cord (10) extends along a non-rectilinear longitudinal trajectory.

12. Process for making a reinforcing cord for tyres for vehicle wheels, comprising: providing at least one semi-finished product (15) comprising at least one sacrificial elongated element (20) and at least two elongated elements (11a, lib) made of non-metallic material, wherein at least one first elongated element (11a) of said at least two elongated elements (11a, lib) extends along a helical path around the at least one sacrificial elongated element (20) with a predetermined helix pitch (E); removing the at least one sacrificial elongated element (20) from the at least one semi-finished product (15) thus obtaining a reinforcing cord (10) having, in a radially inner position with respect to said at least one first elongated element (11a), an empty space (10a) previously occupied by the at least one sacrificial elongated element (20) and wherein said at least one first elongated element (11a) extends along a helical path around the empty space (10a) with said predetermined helix pitch (E).

13. Process according to claim 12, wherein providing the at leastone semi-finished product (15) comprises:- feeding the at least one sacrificial elongated element (20) and said at least two elongated elements (11a, lib) to a twisting device (60);- twisting said at least one first elongated element (11a) together with the at least one sacrificial elongated element (20) in said twisting device (60) with a twisting pitch equal to said predetermined helix pitch (E) by winding said at least one elongated element (11a) around the sacrificial elongated element (20) so that said at least one sacrificial elongated element (20) is arranged in a radially inner position with respect to said at least one first elongated element (11a).

14. Process according to claim 13, wherein providing said at least one semi-finished product (15) comprises:- feeding the at least one sacrificial elongated element (20), said at least two elongated elements (11a, lib) and at least one third elongated element (11c) to said twisting device (60);- twisting said at least two elongated elements (11a, lib) and the at least one third elongated element (11c) together with the at least one sacrificial elongated element (20) in the twisting device (60) with said predetermined twisting pitch by winding said at least two elongated elements (11a, lib) around the sacrificial elongated element (20) and the at least one third elongated element (11c) so that the at least one sacrificial elongated element (20) and the at least one third elongated element (11c) are arranged in a radially inner position with respect to said at least two elongated elements (11a, lib).

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