SELF-SUPPORTING TIRE FOR VEHICLE WHEELS

Abstract

The present invention relates to a self-supporting tire for vehicle wheels comprising a carcass structure comprising at least one carcass ply having a plurality of hybrid reinforcing cords (10) each comprising at least two strands (20) twisted to each other with a predetermined stranding pitch (P), wherein each of said at least two strands (20) comprises at least one monofilament textile thread (21) at least partially embedded in the filaments (22a) of at least one multifilament textile yarn (22) and a pair of sidewall reinforcement inserts (113), where at least one of said sidewall reinforcement inserts comprises a vulcanised elastomeric compound which has a dynamic shear modulus value G equal to or less than 1.25 MPa measured at 70° C., 10 Hz, 9% deformation according to the RPA method reported in the present description.

Claims

1-18. (canceled)

19. A self-supporting tire for vehicle wheels comprising: a carcass structure comprising at least one carcass ply having opposing side edges associated with respective bead structures; a belt structure applied in a radially external position with respect to the carcass structure; a tread band applied in a radially external position with respect to the belt structure; a pair of sidewalls respectively applied in an axially external position on side surfaces of the carcass structure; a layer of air-impermeable elastomeric material extending at least in correspondence with the tread band in a radially internal position with respect to the carcass structure; and a pair of sidewall reinforcement inserts respectively embedded in correspondence with the pair of sidewalls in an axially internal position with respect to the pair of sidewalls, wherein the carcass ply comprises a plurality of hybrid reinforcing cords, each hybrid reinforcing cord has at least two strands corded to each other with a predetermined twisting pitch (P), wherein each of the at least two strands comprises: at least one monofilament textile thread; at least one multifilament textile yarn comprising a plurality of textile filaments; wherein, in any cross-section of the hybrid reinforcing cord, the at least one monofilament textile thread is at least partially embedded in the filaments of the at least one multifilament textile yarn, and at least one sidewall reinforcement insert of the pair of sidewall reinforcement inserts comprises a vulcanised elastomeric compound having a value of elastic dynamic shear modulus G′ equal to or lower than 1.25 MPa measured at 70° C., 10 Hz, 9% strain according to a rubber process analyzer (RPA) method.

20. The self-supporting tire for vehicle wheels according to claim 19, wherein the vulcanised elastomeric compound is obtained by mixing and vulcanising a vulcanisable elastomeric composition comprising 100 phr of at least one diene elastomeric polymer, a total amount of less than 30% by weight of a total weight relative to the total weight of the composition of at least one reinforcing filler, and at least 0.1 phr of at least one vulcanising agent.

21. The self-supporting tire for vehicle wheels according to claim 19, wherein the at least one sidewall reinforcement insert of the pair of sidewall reinforcement inserts comprises a vulcanised elastomeric compound having a value of elastic dynamic shear modulus G′ ranging from 0.50 MPa to 1.25 MPa measured at 70° C., 10 Hz, 9% deformation according to the RPA method.

22. The self-supporting tire for vehicle wheels according to claim 19, wherein the vulcanised elastomeric compound has a value of elastic dynamic shear modulus G′ ranging from 0.55 MPa to 1.20 MPa, measured at 70° C., 10 Hz, 9% deformation according to the RPA method.

23. The self-supporting tire for vehicle wheels according to claim 19, wherein the vulcanised elastomeric compound has a value of elastic dynamic compression modulus E ranging from 2.50 to 7.50 MPa measured at 70° C., 10 Hz, 9% deformation according to the RPA method.

24. The self-supporting tire for vehicle wheels according to claim 19, wherein the vulcanised elastomeric compound has a Tan Delta value ranging from 0.030 to 0.080, measured at 70° C., 10 Hz according to the RPA method.

25. The self-supporting tire for vehicle wheels according to claim 19, wherein the vulcanised elastomeric compound is comprised in both sidewall reinforcement inserts of the pair of sidewall reinforcement inserts.

26. The self-supporting tire for vehicle wheels according to claim 19, wherein the sidewall reinforcement inserts have a maximum axial extension ranging from 3 mm to 14 mm, measured in a direction perpendicular to the plane tangent to the external surface of each sidewall reinforcement insert.

27. The self-supporting tire for vehicle wheels according to claim 20, wherein the at least one reinforcing filler is selected from carbon black, silica, modified silica, silicates, modified silicates, silicate fibres, modified silicate fibres, and mixtures thereof.

28. The self-supporting tire for vehicle wheels according to claim 27, wherein the silicate fibres are selected from sepiolite fibres, paligorskite fibres, wollastonite fibres, imogolite fibres, and mixtures thereof.

29. The self-supporting tire for vehicle wheels according to claim 27, wherein the modified silicate fibres are selected from fibres modified by acid treatment with partial magnesium removal, fibres modified by deposition of amorphous silica on the surface, fibres organically modified by reaction with quaternary ammonium salts, fibres modified by reaction with a silanising agent, and mixtures thereof.

30. The Self-supporting tire for vehicle wheels according to claim 20, wherein the vulcanisable elastomeric composition comprises the at least one reinforcing filler in a total amount ranging from 5% to 30% by weight relative to the total weight of the vulcanisable elastomeric composition.

31. The self-supporting tire according to claim 19, wherein in any cross-section of at least one segment of the hybrid reinforcing cord, the at least one monofilament textile thread is completely embedded in the filaments of the at least one multifilament textile yarn.

32. The self-supporting tire according to claim 19, wherein the at least one monofilament textile thread has a diameter ranging from 0.15 mm to 0.50 mm.

33. The self-supporting tire according to claim 19, wherein the at least one multifilament textile yarn has a linear density ranging from 400 dTex to 4000 dTex.

34. The self-supporting tire according to claim 19, wherein the at least one carcass ply has a thread count ranging from 70 cords/dm to 95 cords/dm.

35. The self-supporting tire according to claim 19, wherein the at least one carcass ply has a thickness ranging from 0.7 mm to 1.5 mm.

36. The self-supporting tire according to claim 19, wherein the carcass structure comprises a single carcass ply.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0285] Further features and advantages of the tyre of the present invention will appear more clearly from the following detailed description of preferred embodiments thereof, made with reference to the accompanying drawings. In such drawings:

[0286] FIG. 1 is a schematic partial cross half-sectional view of a portion of a self-supporting tire according to an embodiment of the present invention;

[0287] FIG. 2 is a side schematic view of a segment of a first embodiment of a hybrid reinforcing cord used in the carcass structure of the tire of FIG. 1;

[0288] FIG. 3 is an enlarged schematic view of a cross section of the hybrid reinforcing cord of FIG. 2 embedded in a portion of the carcass structure of the tire of FIG. 1, such cross section being taken on the sectional plane S—S drawn in FIG. 2;

[0289] FIG. 4 is a schematic perspective view of the hybrid reinforcing cord of FIG. 2 in which part of its components have been removed to show other otherwise hidden components;

[0290] FIG. 5 is a schematic perspective view of a second embodiment of the hybrid reinforcing cord of FIG. 2 in which part of its components have been removed to show other otherwise hidden components;

[0291] FIG. 6 is an enlarged schematic view of a cross section of a further embodiment of a hybrid reinforcing cord usable in the carcass structure of the tire of FIG. 1.

[0292] For simplicity, FIG. 1 shows only a part of an exemplary embodiment of a tire 100 according to the present invention, the remaining part, which is not shown, being substantially identical and being symmetrically arranged with respect to the equatorial plane M-M of the tire.

DESCRIPTION OF AN EMBODIMENT OF THE TYRE ACCORDING TO THE INVENTION

[0293] The tire 100 illustrated in FIG. 1 is, in particular, an exemplary embodiment of a self-supporting tire for four-wheeled vehicles.

[0294] In FIG. 1, “a” indicates an axial direction, “c” indicates a radial direction, “M-M” indicates the equatorial plane of the tire 100 and “R—R” indicates the rotation axis of tire 100.

[0295] The tire 100 comprises a carcass structure 101 of the radial type, comprising in turn at least one carcass ply 111.

[0296] Hereinafter, for simplicity of explanation, reference will be made to an embodiment of the tire 100 comprising a single carcass ply 111 (single-ply tire), it being however understood that what is described with reference to the carcass ply 111 also applies to each carcass ply of tyres comprising more than one carcass ply, unless otherwise indicated. In fact, embodiments of the tire 100 of the invention are contemplated in which the carcass structure 101 comprises for example two carcass plies 111 (double-ply tire).

[0297] The carcass ply 111 comprises a plurality of reinforcing cords 10′ coated with, or embedded into, a layer of cross-linked elastomeric material.

[0298] The reinforcing cords 10′ of the carcass structure 101 (preferably all the reinforcing cords 10′) comprise hybrid reinforcing cords 10 of the type illustrated in FIGS. 2-6 and described below.

[0299] In the case where the tire 100 is double ply, the reinforcing cords of a first carcass ply can be substantially parallel to those of the other carcass ply or inclined with respect to those of the other carcass ply by an angle of less than 40°.

[0300] The carcass ply 111 preferably has a thread count greater than 70 cords/dm and less than, or equal to, 95 cords/dm, more preferably in the range from 75 cords/dm to 90 cords/dm. For example, in a preferred embodiment of the tire 100 of the invention, the aforementioned thread count is equal to 85 cords/dm.

[0301] The carcass ply 111 preferably has a thickness in the range from 0.7 mm to 1.5 mm, more preferably from 0.9 mm to 1.3 mm. For example, in the aforementioned preferred embodiment of the tire 100 of the invention, the aforesaid thickness is equal to 1.1 mm.

[0302] The carcass ply 111 has axially opposite end flaps engaged with respective annular anchoring structures 102, called bead cores, possibly associated with an elastomeric filler 104. The area of the tire 100 comprising the bead core 102 and the possible elastomeric filler 104 forms an annular reinforcement structure 103 called “bead structure” and intended to allow anchoring of the tire 100 on a corresponding mounting rim, not shown.

[0303] Each annular reinforcement structure 103 is associated with the carcass structure 101 by folding backwards (or turning up) the opposite end flaps of the at least one carcass ply 111 around the bead core 102 and the possible elastomeric filler 104, so as to form the so-called flaps 101a of the carcass structure 101.

[0304] In one embodiment, the coupling between the carcass structure 101 and the annular reinforcement structure 103 can be achieved by means of a (not shown in FIG. 1) applied in a radially external position with respect to the carcass ply 111.

[0305] An anti-abrasive strip 105 is arranged at each annular reinforcement structure 103 so as to enclose the annular reinforcement structure 103 along the axially internal, axially external and radially internal areas of the annular reinforcement structure 103, thus interposing between the latter and the wheel rim when the tire 100 is mounted on the rim. However, such anti-abrasive strip 105 may not be provided.

[0306] The tire 100 comprises, in a position radially external to the carcass structure 101, a crossed belt structure 106 comprising at least two belt layers 106a, 106b placed in radial overlap with respect to each other.

[0307] The belt layers 106a, 106b respectively comprise a plurality of reinforcing cords 10a, 10b. Such reinforcing cords 10a, 10b have an inclined orientation with respect to the circumferential direction of the tire 100, or to the equatorial plane M-M of the tire 100, by an angle in the range from 15° to 45°, preferably from 20° to 40°. For example, such angle is 30°.

[0308] The tyre 100 can also comprise a further belt layer (not shown) disposed between the carcass structure 101 and the radially innermost belt layer of the aforementioned belt layers 106a, 106b and comprising a plurality of reinforcing cords having an inclined orientation with respect to the circumferential direction of the tyre 100, or to the equatorial plane M-M of the tyre 100, by an angle equal to 90°.

[0309] The reinforcing cords 10a, 10b of a belt layer 106a, 106b are parallel to each other and have a cross orientation with respect to the reinforcing cords of the other belt layer 106b, 106a.

[0310] In ultra-high performance tires, the belt structure 106 may be a turned up cross belt structure. Such belt structure is made by arranging at least one belt layer on a support element and turning up the opposite lateral end flaps of said at least one belt layer. Preferably, initially a first belt layer is deposited on the support element, subsequently the support element expands radially, subsequently a second belt layer is deposited on the first belt layer and finally the opposing axial end flaps of the first belt layer are turned up on the second belt layer to at least partially cover the second belt layer, which is the radially outermost one. In some cases, a third belt layer may be placed on the second belt layer. Advantageously, the turn-up of the axially opposing end flaps of a belt layer on another belt layer radially external thereto imparts a greater reactivity and readiness of response of the tire when entering a bend.

[0311] The tire 100 comprises, in a position radially outermost to the crossed belt structure 106, at least one zero degree reinforcing layer 106c, commonly known as a “zero degree belt”. It comprises reinforcing cords 10c oriented in a substantially circumferential direction. These reinforcing cords 10c therefore form an angle of a few degrees (typically less than 10°, for example ranging from 0° to 6°) with respect to the equatorial plane M-M of the tire 100.

[0312] The reinforcing cords 10a, 10b, 10c are coated with an elastomeric material or embedded in a matrix of cross-linked elastomeric material. The reinforcing cords 10a, 10b, 10c and 10d can also be hybrid reinforcing cords 10 of the type illustrated in FIGS. 2-6 or reinforcing cords of a different type.

[0313] In a radially external position to the zero-degree reinforcing layer 106c, a tread band 109 of elastomeric material is applied.

[0314] Respective sidewalls 108 made of elastomeric material are also applied on the lateral surfaces of the carcass structure 101, in a position axially external to the carcass structure 101 itself. Each sidewall 108 extends from one of the lateral edges of the tread band 109 to the respective annular reinforcement structure 103.

[0315] The anti-abrasive strip 105, if present, extends at least as far as the respective sidewall 108.

[0316] In some specific embodiments, such as the one illustrated and described herein, the rigidity and integrity of the annular reinforcement structure 103 and of the side 108 can be improved by providing a stiffening layer 120, generally known as a “flipper” or additional strip-like insert.

[0317] The flipper 120 is wrapped around a respective bead 102 and the elastomeric filler 104 so as to at least partially surround the annular reinforcement structure 103. In particular, the flipper 120 encloses the annular reinforcement structure 103 along the axially internal, axially external and radially internal areas of the annular reinforcement structure 103.

[0318] The flipper 120 is arranged between the turned up end flap of the carcass ply 111 and the respective annular reinforcement structure 103. Usually, the flipper 120 is in contact with the carcass ply 111 and the annular reinforcement structure 103.

[0319] In some specific embodiments, such as the one illustrated and described herein, the bead structure 103 may further comprise a further stiffening layer 121 which is generally known by the term “chafer”, or protective strip, and which has the function to increase the rigidity and integrity of the annular reinforcement structure 103.

[0320] The chafer 121 is associated with a respective turned up end flap of the carcass ply 111 in an axially outermost position with respect to the respective annular reinforcement structure 103 and extends radially towards the sidewall 108 and the tread band 109.

[0321] The flipper 120 and the chafer 121 comprise reinforcing cords 10d (those of the flipper 120 are not visible in the accompanying figures) coated with an elastomeric material or embedded in a matrix of cross-linked elastomeric material.

[0322] The tread band 109 has, in a radially external position, a rolling surface 109a intended to come into contact with the ground. Circumferential grooves (not shown in FIG. 1) are formed on the rolling surface 109a, which are connected by transverse notches (not shown in FIG. 1) so as to define on the rolling surface 109a a plurality of blocks of various shapes and sizes (not shown in FIG. 1).

[0323] An underlayer 107 is disposed between the crossed belt structure 106 and the tread band 109.

[0324] In some specific embodiments, such as the one illustrated and described herein, a strip 110 made of elastomeric material, commonly known as a “mini-sidewall”, may possibly be present in the connection area between the sidewall 108 and the tread band 109. The mini-sidewall 110 is generally obtained by co-extrusion with the tread band 109 and allows an improvement of the mechanical interaction between the tread band 109 and the sidewalls 108.

[0325] Preferably, an end portion of the sidewall 108 directly covers the lateral edge of the tread band 109.

[0326] In the case of tubeless tires, such as the one illustrated and described herein, a layer of rubber 112, generally known as a “liner”, is provided in a radially internal position with respect to the carcass ply 111 to provide the necessary impermeability to the inflation air of the tyre 100.

[0327] A layer of elastomeric material, underliner 112a, can also be provided in a radially external position to said liner 112, according to a preferred embodiment of the invention.

[0328] In an axially external position with respect to the liner 112 and the underliner 112a and axially internal to the sidewall 108 there is a sidewall reinforcement insert made of elastomeric material 113 comprising a vulcanised elastomeric compound according to the invention intended to prevent sagging or swelling of the sidewall 108 when the tire is flat.

[0329] The liner 112 and the underliner 112a can extend throughout the internal structure of the tire from bead to bead, as illustrated in FIG. 1, or they can extend only at the crown structure of the tread, in the case in which the sidewall reinforcement insert 113 imparts the necessary impermeability to the inflation air of the tire 100. With reference to FIGS. 2-4, the hybrid reinforcing cord 10 comprises two strands 20a, 20b twisted to each other with a predetermined twisting pitch P. Preferably, the two strands 20a, 20b are identical.

[0330] As illustrated in FIGS. 3 and 4, each strand 20a, 20b comprises a single monofilament textile thread 21a, 21b and a single multifilament textile yarn 22a, 22b defined by a plurality of filaments 23a, 23b. Each strand 20a, 20b could however comprise more than one monofilament textile thread and more than one multifilament textile yarn.

[0331] In any cross section of the reinforcing cord 10, the monofilament textile thread 21a, 21b is embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b.

[0332] In the embodiment illustrated in FIGS. 3 and 4, the monofilament textile thread 21a, 21b is, in any cross section of the reinforcing cord 10, completely embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b and, therefore, the aforesaid filaments 23a, 23b are arranged around the respective monofilament textile thread 21a, 21b so as to completely enclose the monofilament textile thread 21a, 21b.

[0333] Therefore, in FIG. 2, the monofilament textile threads 21a, 21b are not visible as they are entirely covered by the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b.

[0334] Although the embodiment of FIGS. 2-4 (and as will be seen later also that of FIG. 5) in which the monofilament textile thread 21a, 21b is, in any cross section of the reinforcing cord 10, completely embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b is particularly preferred, also preferred are embodiments in which, in any cross section of the reinforcing cord 10, the monofilament textile thread 21a, 21b is only partially embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b, and in particular those in which at least 50% of the external surface of the monofilament textile thread 21a, 21b is embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b.

[0335] The monofilament textile threads 21a, 21b extend along a longitudinal direction A, illustrated in FIG. 2.

[0336] The mutual arrangement of the monofilament textile threads 21a, 21b and of the filaments 23a, 23b of the multifilament textile yarn 22a, 22b along the longitudinal direction A can be such that the monofilament textile threads 21a, 21b extend substantially parallel to the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b, as illustrated in FIG. 4, or such that the filaments 23a, 23b of the multifilament textile yarn 22a, 22b are helically wound on the respective monofilament textile thread 21a, 21b with a predetermined winding pitch W which, preferably, is equal to the twisting pitch P.

[0337] In the latter case, the direction of the twisting of the two strands 20a, 20b is preferably the same as that of the winding of the filaments 23a, 23b of the multifilament textile yarn 22a, 22b on the monofilament textile thread 21a, 21b, but it is possible to provide opposite directions.

[0338] The twisting pitch P is preferably in the range from 1 mm to 20 mm, more preferably from 2 mm to 15 mm, for example equal to 12.5 mm.

[0339] FIG. 5 illustrates an embodiment of a hybrid reinforcing cord 10 which differs from that illustrated in FIGS. 2-4 only in that the monofilament textile threads 21a, 21b are twisted on themselves with a predetermined torsion pitch T.

[0340] Preferably, the torsion pitch T is equal to the twisting pitch P.

[0341] The direction of the torsion of the monofilament textile threads 21a, 21b can be the same or opposite to that of the twisting of the two strands 20a, 20b.

[0342] The monofilament textile threads 21a, 21b are made of polyester fibres, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or mixtures thereof.

[0343] The filaments 23a, 23b of each multifilament textile yarn 22a, 22b are made of aramid fibres or polyester fibres, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or rayon fibres, or in any mixture of the aforesaid fibres.

[0344] Irrespective of the specific type of textile material used for the filaments 23a, 23b of the multifilament textile yarns 22a, 22b, such material is suitably adhered to the surface so as to provide adequate adhesion to the surrounding elastomeric material.

[0345] Typically, the adhesion can be accomplished by coating with an adhesive substance or by a chemical or physical treatment.

[0346] For example, the adhesion is performed by immersion of the hybrid reinforcing cord 10 in a solution comprising the adhesive substance after having twisted the two strands 20a, 20b together.

[0347] The monofilament textile threads 21a, 21b preferably have a diameter in the range from 0.15 mm to 0.50 mm, more preferably from 0.20 mm to 0.40 mm. For example, in a preferred embodiment of the carcass structure 101 of the tire 100, the aforementioned diameter is equal to 0.30 mm.

[0348] The multifilament textile yarns 22a, 22b preferably have a linear density in the range from 840 dtex to 2100 dtex, preferably from 940 dtex to 1840 dtex. For example, in a preferred embodiment of the carcass structure 101 of the tire 100, the aforesaid linear density is equal to 1100 dtex.

[0349] In a preferred embodiment of the hybrid reinforcing cord 10 illustrated in FIGS. 2-5 and used in the above preferred embodiment of the carcass structure 101 of the tire 100, the hybrid reinforcing cord 10 has two strands 20a, 20b stranded together. In each strand 20a, 20b, the monofilament textile threads 21a, 21b are made of PET fibres and have a diameter of 0.30 mm, while the multifilament textile yarns 22a, 22b are made of aramid and have a linear density equal to 1110 dtex. In such hybrid reinforcing cord 10, for example, the multifilament textile yarn 22a, 22b and the monofilament textile thread 21a, 21b of each of the two strands 20a, 20b were imparted 310 twists in the right-hand direction (Z), while each of the two strands 20a, 20b were imparted 180 twists in a left-hand direction (S). Such a reinforcing cord can therefore be indicated with (PET0.30+AR1100)×2 310Z/180S.

[0350] Another preferred embodiment of the hybrid reinforcing cord 10 illustrated in FIGS. 2-5 differs from the one described above only in that the multifilament textile yarns 22a, 22b are made of rayon and have a linear density equal to 1840 dtex. In such hybrid reinforcing cord 10, for example, the multifilament textile yarn 22a, 22b and the monofilament textile thread 21a, 21b of each of the two strands 20a, 20b were imparted 300 or 310 twists in the right-hand direction (Z), while each of the two strands 20a, 20b were imparted 180 twists in a left-hand direction (S). Such reinforcing cords can therefore be indicated with (PET0.30+RY1840)×2 300Z/1805 and (PET0.30+RY1840)×2 310Z/1805, respectively.

[0351] Another preferred embodiment of the hybrid reinforcing cord 10 illustrated in FIGS. 2-5 differs from the one described above in that the multifilament textile yarns 22a, 22b made of rayon have a linear density equal to 1220 dtex. In such hybrid reinforcing cord 10, for example, the multifilament textile yarn 22a, 22b and the monofilament textile thread 21a, 21b of each of the two strands 20, 20b were imparted 300 twists in the right-hand direction (Z), while each of the two strands 20a, 20b were imparted 150 twists in a left-hand direction (5). Such a reinforcing cord can therefore be indicated with (PET0.30+RY1220)×2 300Z/150S.

[0352] In another preferred embodiment of the hybrid reinforcing cord 10 illustrated in FIGS. 2-5, the two strands 20a, 20b are not identical. For example, while in both strands 20a, 20b the monofilament textile threads 21a, 21b are made of PET fibres and have a diameter of 0.30 mm, the multifilament textile yarn 22a of a strand 20a is made of rayon and has a linear density equal to 1220 dtex and the multifilament textile yarn 22b of the other strand 20b is made of rayon and has a linear density equal to 1840 dtex. In such hybrid reinforcing cord 10, for example, the multifilament textile yarn 22a, 22b and the monofilament textile thread 21a, 21b of each of the two strands 20a and 20b were imparted 300 twists in the right-hand direction (Z), while each of the two strands 20a, 20b were imparted 150 twists in a left-hand direction (5). Such a reinforcing cord can therefore be indicated with (PET0.30+RY1220)+(PET0.30+RY1840) 300Z/150S.

[0353] The Applicant has also made hybrid reinforcing cords according to the present invention by twisting three strands together. For example, an embodiment of this type of hybrid reinforcing cord provides that each strand comprises a monofilament textile thread made of PET fibres and having a diameter of 0.30 mm and a multifilament textile yarn made of rayon and having a linear density equal, for example, to 1220 dtex. In such hybrid reinforcing cords, for example, the multifilament textile yarn and the monofilament textile thread of each of the three strands were imparted 300 twists in the right-hand direction (Z), while each of the three strands were imparted 150 twists in a left-hand direction (S). Such a reinforcing cord can therefore be indicated with (PET0.30+RY1220)×3 300Z/150S.

[0354] FIG. 6 shows another preferred embodiment of a hybrid reinforcing cord 10 usable in the carcass structure 101 of tires 100 according to the present invention, preferably of the self-supporting type.

[0355] The hybrid reinforcing cord 10 of FIG. 6 differs from that illustrated in FIGS. 2-4 only in that the strand 20a comprises two monofilament textile threads 21a of the type described above and two multifilament textile yarns 22a of the type described above. Similarly, the strand 20b comprises two monofilament textile threads 21b of the type described above and two multifilament textile yarns 22b of the type described above. The empty space in the centre of the hybrid reinforcing cord 10 illustrated in FIG. 6 will in reality be occupied by the filaments 23a and 23b of the multifilament textile yarns 22a, 22b.

[0356] The strand 20a comprises two ends 20a′ twisted together with a twisting pitch which can be equal to, or different from, the twisting pitch of the two strands 20a, 20b. Similarly, the strand 20b comprises two ends 20b′ twisted together with a twisting pitch which can be equal to, or different from, the twisting pitch of the two ends 20a′. Each of the two ends 20a′ of the strand 20a comprises a monofilament textile thread 21a at least partially embedded in the filaments 23a of a multifilament textile yarn 22a. Similarly, each of the two ends 20b′ of the strand 20bcomprising a monofilament textile thread 21b at least partially embedded in the filaments 23b of a multifilament textile yarn 22b.

[0357] In a preferred embodiment of the hybrid reinforcing cord 10 illustrated in FIG. 6, the monofilament textile threads 21a, 21b are made of PET fibres and have a diameter of 0.30 mm, while the multifilament textile yarns 22a, 22b are made of aramid and have a linear density equal to 1110 dtex. In this hybrid reinforcing cord 10, for example, 310 twists in the right direction (Z) were imparted to the ends 20a′, 20b′ of each strand 20a, and 20b, while 280 twists in the left direction (S) were imparted to each of the two strands the ends 20a′, 20b′. The reinforcing cord can therefore be indicated with 2×2 (PET0.30+AR1100) 310Z/280S.

[0358] The building of the tyre (100) as described above, can be carried out by assembling respective semi-finished products adapted to form the components of the tyre, on a forming drum, not shown, by at least one assembling device.

[0359] At least a part of the components intended to form the carcass structure of the tyre can be built and/or assembled on the forming drum. More specifically, the forming drum is suitable for receiving first liners and underliner, then the sidewall reinforcement inserts and subsequently the carcass structure. Thereafter, devices non shown coaxially engage one of the annular anchoring structures around each of the end flaps, position an outer sleeve comprising the belt structure and the tread band in a coaxially centred position around the cylindrical carcass sleeve and shape the carcass sleeve according to a toroidal configuration through a radial expansion of the carcass structure, so as to cause the application thereof against a radially inner surface of the outer sleeve.

[0360] After the building of the green tyre, a moulding and vulcanisation treatment is generally carried out in order to determine the structural stabilisation of the tyre through cross-linking of the elastomeric compositions, as well as to impart a desired tread pattern on the tread band and at any distinguishing graphic signs at the sidewalls.

[0361] The following examples are now provided for merely illustrative and non-limiting purposes.

Experimental Part

Evaluation Methods

[0362] The static mechanical properties (CA1 load at 100% elongation, CR tensile strength, AR % elongation at break) according to the UNI 6065:2001 standard were measured at 23° C. on samples of elastomeric materials, vulcanised at 170° C. for 10 minutes.

[0363] The compressive dynamic mechanical properties E′ and Tan delta were measured using an Instron model 1341 dynamic device in the tension-compression mode according to the following methods. A test piece of cross-linked material (170° C. for 10 minutes) having a cylindrical shape (length=25 mm; diameter=14 mm), preloaded in compression up to a longitudinal strain of 25% with respect to the initial length and maintained at the predetermined temperature (23° C.) for the whole duration of the test was subjected to a dynamic sinusoidal strain having an amplitude of ±3.5% with respect to the length under pre-load, with a frequency of 10 Hz. The dynamic mechanical properties are expressed in terms of dynamic elastic modulus)(E′ and Tan delta (loss factor). The Tan delta value was calculated as the ratio between the viscous dynamic module (E″) and the dynamic elastic modulus (E′).

[0364] The dynamic mechanical properties of shear and Tan delta dynamic modulus G′ were evaluated using an Alpha Technologies R.P.A. 2000 oscillating chamber rheometer (Rubber Process Analyser) with chamber geometry as described in ASTM D6601-19 FIG. 1, applying the following method:

1) an approximately cylindrical test sample with a volume in the range from 4.6 to 5 cm.sup.3 was obtained by punching a sheet with a thickness of at least 5 mm of the green vulcanisable elastomeric compound to be characterised;
2) the chambers of the RPA apparatus were preliminarily preheated to 170° C.;
3) the sample was loaded between the chambers of the RPA apparatus and the chambers were closed. Between the sample of the green vulcanisable elastomeric compound and each chamber of the RPA apparatus, two films were interposed to protect the chamber itself: in contact with the compound, a film of Nylon 6.6 cast of about 25 microns and in contact with the chamber of the RPA apparatus a polyester film of about 23 microns;
4) the sample was then vulcanised for a fixed time of 10 min at a temperature of 170° C. while recording the vulcanisation curve, i.e. subjecting the sample to a sinusoidal deformation of 7% amplitude and 1.67 Hz frequency for the entire duration of the vulcanisation;
5) the temperature of the chambers of the RPA apparatus was then brought to 70° C.; 10 minutes after the chamber temperature was set at 70° C., a sequence of dynamic measurements was performed at a constant temperature of 70° C. by sinusoidally stressing the sample in torsion at a fixed frequency of 10 Hz and amplitude progressively increasing from 0.3% to 10%, carrying out 10 stabilisation cycles and 10 measurement cycles for each condition;
6) again at 70° C., a dynamic measurement was then performed by sinusoidally stressing the sample in torsion at the fixed frequency of 10 Hz and amplitude of 9%, carrying out 10 stabilisation cycles and 20 measurement cycles: the result was expressed as average of what measured in the 20 measurement cycles, as dynamic shear modulus G′ and as Tan Delta (ratio between viscous modulus G″ and G′, Tan Delta=G″/G′).

[0365] Rolling Resistance (RR) Assessment

[0366] Rolling resistance (RR) measurements were carried out on the sample tyres according to the UNECE reg. 117 Rev.4 annex 6—ISO 28580:2018 (par. 4b (torque method))—Notification No. 2011-237 (Korea). The rolling resistance coefficient was expressed in N/kN.

[0367] The tyres thus tested were then assigned a relative rolling resistance index equal to the ratio of the rolling resistance measured for the tyre in question with respect to the reference tyre. The lower the value of this index, the lower the rolling resistance of the tyre under test and therefore the better its performance.

[0368] The results of the tests carried out are reported in Table 3. In such Table 3, a reduction in value (e.g. from 100 to 92) in the RR results represented improved performance while an increase in value (e.g. from 100 to 104) indicated deterioration.

[0369] Evaluation of the Distance Travelled in Deflation Conditions (Run Flat Test)

[0370] A BMW 5 Series car was equipped with four tyres, reference or invention, depending on the tyre group under consideration (see Example 3, sample tyre preparation P1-P4).

[0371] A flat ride test was performed for each group of tyres by completely deflating the left rear tyre and driving on a mixed route at a travel speed not exceeding 80 km/h until the tyre was evidently damaged.

[0372] The test was repeated twice for each tyre group and the results averaged.

[0373] In order to compare the performance of the tyres, an “RF” distance index of 100 was assigned to a reference tyre for each group of tyres being compared.

[0374] A relative “RF” index was then assigned to the other tyres of the same group, corresponding to the ratio between the distance in flat running conditions measured for the test tyres compared to that of the reference tyre, set at 100, said distances having been measured in close comparison.

[0375] The results are shown in Table 3.

[0376] In such Table 3, maintaining or moderately decreasing the value (e.g. from 100 to 75) in flat driving results represented comparable or entirely acceptable performance even if slightly worsened. An increase in the value (e.g. from 100 to 120) indicated an improved performance, i.e. a longer distance while a significant decrease in the value (e.g. less than 50) indicated an unacceptable performance.

Example 1

[0377] Preparation of Elastomeric Compounds for Sidewall Reinforcement Insert

[0378] The reference compositions and according to the invention reported in the following Table 1 were prepared as elastomeric compositions for the sidewall reinforcement insert:

TABLE-US-00001 TABLE 1 Compositions Reference (R) Invention (I) NR — 80.0 IR 40.0 20.0 BR 60.0 — N-550 32.0 — SilSep1 20.0 — SilSep1 — 16.0 Stearic acid 2.0 2.0 Zinc oxide 4.0 4.0 TESPT 50% on CB 5.0 4.0 TMQ 1.0 1.0 6-PPD 2.0 2.0 TBBS 2.5 1.9 Isobutyl TUADS 0.5 0.3 Sulphur 2.3 3.6 Total Phr 171.3 134.8 Total filler (%) 32% 13% NR: natural rubber (Standard Thai Rubber STR 20 - Thaiteck Rubber); IR: synthetic polyisoprene: (SKI-3 Nizhnekamskneftekhim); BR: polybutadiene (Europrene Neocis ® - Polymers Europe); TESPT 50% on CB: Mixture of Bis(triethoxysilylpropyl)tetrasulphide (TESPT 50%) supported on carbon black (50%), produced by Evonik Industries AG, Germany; N550: carbon black (N550 Birla Carbon); Silica: ZEOSIL 1115 HP (Solvay); SilSep1: white filler in microbeads M2 prepared according to Example 1 of patent application WO2019106562A1; SilSep2: white filler in microbeads M6 prepared according to Example 3 of patent application WO2019106562A1; Stearic acid: STEARINA N (SOGIS) Zinc oxide: Rhenogran ® ZnO-80 (RheinChemie); TMQ (anti-ageing): Polymerised NAUGARD Q (CHEMTURA CORPORATION); 6-PPD (antioxidant): N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylene-diamine (Santoflex ™ 6PPD - Eastman); TBBS (accelerant): N-tert-butyl-2-benzothiazylsulphenamide (Vulkacit ® NZ/EGC - Lanxess); Isobutil TUADS (Isobutylthiuram disulphide) accelerant produced by RTVanderbilt; Sulphur (vulcaniser): insoluble 67%, Solfotecnica.

[0379] Starting from the elastomeric compositions shown in Table 1, the corresponding elastomeric compounds were prepared according to the following process.

[0380] The mixing of the components was carried out in two steps using an internal mixer (Banbury, Intermix or Brabender) In the first step (1), all the ingredients were introduced with the exception of vulcanisers and accelerants. The mixing was continued for a maximum time of 5 minutes, reaching a temperature of approximately 145° C. Subsequently, in the second test (2), again carried out using an internal mixer, the vulcanisers and accelerants were added, and the mixing was continued for about 4 minutes while maintaining the temperature below 100° C. The compounds were then unloaded.

[0381] After cooling and at least 12 hours from preparation, some samples of the compounds were vulcanised in a press at 170° C. for 10 min to give the specimens useful for mechanical characterisations.

Example 2

[0382] Characterisation of the Compounds

[0383] The main static and dynamic properties of the aforementioned elastomeric compounds, measured by the methods described above, are shown in the following Table 2

TABLE-US-00002 TABLE 2 Reference Invention compound (R) compound (I) Dynamic mechanical properties E′ 23° C. 10 Hz 9.32 4.68 Tanδ 23° C. 10 Hz 0.072 0.036 G′ 70° C. 10 Hz (RPA) 1.81 0.74 Tanδ 70° C. 10 Hz (RPA) 0.090 0.049 Static mechanical properties CA1 (MPa) 5.14 3.39 CR (MPa) 12.3 8.30 AR % 244 275

[0384] By comparing the mechanical properties of the compound used in the invention (I) with those of the compound used in the reference sidewall reinforcement insert (R), it is observed that the compound (I) shows a Tan δ value at 23° C. and 70° C. extremely low, predictive of low rolling resistance and reduced fuel consumption.

[0385] The compound (I) also shows dynamic mechanical properties, in particular the dynamic shear modulus (G′) and the dynamic compression modulus (E′), particularly low compared to the compound (R), indicative of a lower rigidity of the sidewall reinforcement insert.

Example 3

[0386] Preparation of Sample Tyres

[0387] In order to evaluate the performance of tyres with sidewall reinforcement inserts according to the present invention with respect to reference tyres, in terms of rolling resistance and maximum mileage in run flat conditions, sets of tyres were prepared having the features shown below.

[0388] Each tire comprised a carcass structure comprising a carcass ply and two sidewall reinforcement inserts, axially internal to each of the sidewalls, as shown in FIG. 1, said two sidewall reinforcement inserts having identical composition, same thickness and same shape.

[0389] In each set, tyres were compared under the same operating conditions, modified only in terms of carcass structure and/or elastomeric compound of the sidewall reinforcement inserts and/or their thickness, all other features of the sidewall reinforcement inserts and tyres being equal.

[0390] The sample tires included the Applicant's self-supporting RunFlat tires in size 245/45 R18 100Y XL configured as follows: [0391] commercial self-supporting tire comprising carcass structure comprising non-hybrid reinforcing cords, as described below, and sidewall reinforcement inserts having a thickness of 7 mm consisting of the reference elastomeric compound, hereinafter reference tyre P1; [0392] self-supporting tire like P1 but comprising sidewall reinforcement inserts with a thickness of 6.5 mm consisting of the reference elastomeric compound, hereinafter comparative tire P2; [0393] self-supporting tire like P2 but comprising carcass structure comprising hybrid reinforcing cords, as described below, hereinafter comparison tire P3; and [0394] self-supporting tyre like P3 but comprising sidewall reinforcement inserts with a thickness of 8 mm made up of the elastomeric compound of the invention, hereinafter invention tyre P4.

[0395] The non-hybrid reinforcing cords of the carcass structure of the tyres P1 and P2 were of the type RY1840x2 (48Zx48S), i.e. they each comprised two multifilament rayon textile yarns twisted together, in which each multifilament textile yarn was imparted 48 right-handed twists (Z) and 48 twists in left-hand direction (S) were imparted to the reinforcing cord. These reinforcing cords were arranged in the carcass structure with a thread count equal to 120 cords/dm.

[0396] The hybrid reinforcing cords of the carcass structure of the tyres P3 and P4 were of the following type: (PET0.30+AR1680)×2 310Z/180S, i.e. they each comprised two strands, each strand comprising two PET monofilament textile threads having a diameter of 0.30 mm and an aramid multifilament textile yarn having a linear density of 1680 dtex. The two strands were twisted together by imparting 310 twists in the right direction (Z), while each multifilament textile yarn was twisted to the respective monofilament textile thread imparting 180 twists in the left direction (S). These hybrid reinforcing cords were arranged in the carcass structure with a thread count equal to 85 cords/dm.

Example 4

[0397] Characterisation of Tires

[0398] The main features of the self-supporting tyres P1-P4 and their rolling resistance and maximum mileage performance in run flat conditions, evaluated according to the methods described above, are shown in the following Table 3:

TABLE-US-00003 TABLE 3 Tyre Reference Comparison Comparison Invention P1 P2 P3 P4 Compound IRF Reference Reference Reference Invention Carcass cords Non-hybrid Non-hybrid Hybrid Hybrid Relative IRF 100 93 93 114 thickness Relative RR 100 97 98  95 Relative RF 100 27 83 102 IRF = sidewall reinforcement inserts; Relative IRF thickness = thickness normalising the value of the reference tire P1 to 100; RR = absolute and relative rolling resistance by normalising the value of the reference tyre P1 to 100; RF = maximum distance in flat run conditions, absolute and relative driving conditions by normalising the value of the reference tire P1 to 100.

[0399] By comparing the performance of the comparison tire P2 with that of the reference tire P1 it is observed that even a modest reduction in the thickness of the sidewall reinforcement insert leads to a drastic reduction in the distance travelled in run flat conditions, although a moderate benefit is obtained in terms of rolling resistance.

[0400] By comparing the performance of the comparison tire P3 with that of the comparison tire P2, it is observed that the use of a carcass ply including the hybrid cords allows to recover a large part of the distance travelled in run flat conditions, without excessively penalising the rolling resistance, however better than the value of the reference tire P1.

[0401] Finally, by comparing the performance of the tire of the invention P4 with that of the reference tire P1 and comparison tire P2 and P3, it can be observed that all the distance lost by the tires P2 and P3 has been recovered, obtaining an even better result than that obtained with the tire P1, and that at the same time a significantly lower value of rolling resistance was obtained, despite the use of a slightly greater thickness of the sidewall reinforcement insert.

[0402] In conclusion, from the above tests it was found that by reducing the rigidity of the sidewall reinforcement inserts of self-supporting tires in the presence of a carcass structure made with hybrid cords according to the invention it was possible to achieve an overall advantageous result, with an appreciable improvement in terms of mileage in run flat conditions, but above all surprisingly improved in rolling resistance compared to self-supporting tires of the prior art.

Example 5

[0403] Tire Performance

[0404] In a second series of tests, aimed at evaluating the performance of the tire of the present invention, the Applicant compared a reference tire P1b of the type 215/45 R17 91Y XL, RunFlat made by the Applicant, having a carcass structure and a sidewall reinforcement insert as described for the tire P1, with a tire of the invention P4b similar to the tire P1b, but having a carcass structure and a sidewall reinforcement insert as described for the tyre P4.

[0405] The reference tire P1b is a tire appreciated by customers for its excellent behaviour on dry and wet road surfaces in terms of driveability and braking.

[0406] The tyres P1b and P4b were mounted on a Mini Cooper S, inflated to 2.6 bar at the front and 2.2 bar at the rear and submitted to the evaluation of an evaluator who made a series of laps of a circuit.

[0407] The rating given by the evaluator is shown in Table 4 below, where the symbol indicates an excellent rating and the symbol “+” indicates an improvement compared to the reference tires.

TABLE-US-00004 TABLE 4 Tyre Reference P1b Invention P4b Straight drive on uneven surface = + Straight drive on smooth surface = + Steering response = + Steering torque = + Steering angle required = + Change of direction = + Comfort = + Rolling noise = + Insertion = + Understeer = + Oversteer = + Release = + Progressive loss of grip = + Recovery = + Controllability = + Lateral seal = +

[0408] Table 4 shows that the tire of the invention gave improved results with respect to the already excellent results of the reference tire in all performance items.

[0409] 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.