TYRE FOR VEHICLE WHEELS

Abstract

The present disclosure relates to a tyre comprising a carcass structure, a tread band, a pair of sidewalls and at least one colored decorative element having a thickness equal to or greater than 200 μm applied by co-vulcanization on at least one side of the pair of sidewalls, wherein the pair of sidewalls comprises an elastomeric composition comprising (i) at least one diene elastomeric polymer, and (ii) an ozone protection system, and the at least one colored decorative element is made with a cross-linkable elastomeric composition comprising (i) 100 phr of elastomeric polymer comprising 30 phr to 70 phr of natural and/or synthetic isoprene rubber, and 30 phr to 70 phr of a rubber chosen from butyl rubber, halobutyl rubber, butadiene rubber, styrene-butadiene rubber, and mixtures thereof, and (ii) 5 phr to 120 phr of at least one reinforcement filler.

Claims

1-28. (canceled)

29. A tyre comprising: a carcass structure comprising a carcass ply having opposite lateral edges associated to respective bead structures; a tread band applied in a radially outer position with respect to the carcass structure; a pair of sidewalls applied laterally on opposite sides of the carcass structure; and at least one colored decorative element having a thickness equal to or greater than 200 μm applied on at least one side of the pair of sidewalls, wherein the pair of sidewalls comprises an elastomeric composition comprising (i) at least one diene elastomeric polymer, and (ii) an ozone protection system, and wherein the at least one colored decorative element is made of a cross-linkable elastomeric composition comprising: (i) 100 phr of elastomeric polymer comprising from 30 phr to 70 phr of natural and/or synthetic isoprene rubber, and from 30 phr to 70 phr of a rubber chosen from butyl rubber, halobutyl rubber, butadiene rubber, styrene-butadiene rubber, and mixtures thereof, and (ii) from 5 phr to 120 phr of at least one reinforcement filler. wherein the at least one colored decorative element is directly applied green or partially vulcanized to the at least one sidewall of the pair of sidewalls of the tyre when green, and co-vulcanized with the tyre.

30. The tyre according to claim 29, wherein the pair of sidewalls comprises an elastomeric composition comprising at least one diene elastomeric polymer and a non-staining ozone protection system.

31. The tyre according to claim 30, wherein the non-staining ozone protection system substantially free of aromatic amine based antioxidants and/or antiozonants.

32. The tyre according to claim 31, wherein the aromatic amine based antioxidants and/or antiozonants are chosen from N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (DMBPPD), N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD), and N-(1,3-dimethylbutyI)-N′-phenyl-phenylene-diamine (6PPD).

33. The tyre according to claim 30, wherein the non-staining ozone protection system is substantially free of (i) waxes and/or (ii) polymeric static protective agents.

34. The tyre according to claim 30, wherein the non-staining ozone protection system consisting essentially of at least one phenolic antioxidant in an amount equal to or greater than 3 phr and/or at least one cyclic acetal or enol-ether antioxidant, in an amount equal to or greater than 1 phr.

35. The tyre according to claim 29, wherein the 100 phr of elastomeric polymer comprises from 40 phr to 60 phr of natural and/or synthetic isoprene rubber.

36. The tyre according to claim 29, wherein the 100 phr of elastomeric polymer comprises 40 phr to 60 phr of butyl and/or halobutyl rubber.

37. The tyre according to claim 29, wherein the 100 phr of elastomeric polymer comprises 40 phr to 60 phr of butadiene and/or styrene-butadiene rubber.

38. The tyre according to claim 29, wherein the 100 phr of elastomeric polymer comprises 40 phr to 60 phr of a mixture of butyl or halobutyl rubber and butadiene and/or styrene-butadiene rubber.

39. The tyre according to claim 29, wherein the cross-linkable elastomeric composition further comprises 5 phr to 120 phr of at least one light reinforcement filler for 100 phr of elastomeric polymer.

40. The tyre according to claim 39, wherein the at least one light reinforcement filler is chosen from silica, alumina, titanium dioxide, aluminosilicates, bentonite, calcium carbonate, kaolin, talc, gypsum, barium sulphate, and mixtures thereof.

41. The tyre according to claim 39, wherein the cross-linkable elastomeric composition further comprises an amount less than or equal to 100 phr of at least one coloring agent for 100 phr of elastomeric polymer.

42. The tyre according to claim 39, wherein the cross-linkable elastomeric composition further comprises 1 phr to 5 phr of carbon black for 100 phr of elastomeric polymer.

43. The tyre according to claim 29, wherein the cross-linkable elastomeric composition further comprises 5 phr to 120 phr of at least one dark reinforcement filler for 100 phr of elastomeric polymer.

44. The tyre according to claim 43, wherein the dark reinforcement filler is carbon black.

45. The tyre according to claim 43, wherein the at least one colored decorative element is molded with at least one rubber-based ink layer.

46. The tyre according to claim 45, wherein the rubber-based ink layer has a thickness equal to or greater than 5 μm.

47. The tyre according to claim 45, wherein the rubber-based ink layer has a thickness equal to or less than 50 μm.

48. The tyre according to one of claims 45, wherein the rubber-based ink comprises a dye or pigment dispersed in a polymeric base comprising a rubber chosen from natural rubber, synthetic rubber, butadiene rubber, styrene-butadiene rubber, butyl rubber, halobutyl rubber, and mixtures thereof.

49. The tyre according to claim 29, wherein the at least one colored decorative element has a thickness equal to or greater than 200 μm.

50. The tyre according to claim 29, wherein the at least one colored decorative element has a thickness equal to or less than 800 μm.

51. A colored decorative element for a tyre comprising at least one layer of cross-linkable elastomeric composition on a plastic support, wherein the elastomeric composition comprises: (i) 100 phr of elastomeric polymer comprising from 30 phr to 70 phr of natural and/or synthetic isoprene rubber, and from 30 phr to 70 phr of a rubber chosen from butyl rubber, halobutyl rubber, butadiene rubber, styrene-butadiene rubber, and mixtures thereof, and (ii) from 5 phr to 120 phr of at least one reinforcement filler.

52. The decorative element according to claim 51, wherein the plastic support consists of a layer of plastic material chosen from polyolefins, polyesters, polyamides, polyimides, perfluorinated polymers, and polyurethanes.

53. The decorative element according to claim 51, wherein the plastic support consists of a layer of polyethylene terephthalate.

54. The decorative element according to claim 51, wherein the plastic support has a thickness ranging from 10 μm to 150 μm.

55. The decorative element according to claim 51, further comprising at least 0.5 phr of at least one coloring agent.

56. A process for preparing a tyre comprising: building a green tyre, introducing the green tyre into a tyre vulcanization apparatus, depositing at least one layer of cross-linkable elastomeric composition on a plastic support, applying the at least one layer on the mold sidewall of the vulcanization device corresponding to the sidewall of the green tyre, closing the tyre vulcanization apparatus bringing into contact the at least one layer with the sidewall, and co-vulcanizing the green tyre and the layer.

57. The tyre according to claim 29, wherein the cross-linkable elastomeric composition further comprises at least 0.5 phr of at least one coloring agent.

58. The tyre according to claim 29, wherein the cross-linkable elastomeric composition further comprises a non-staining ozone protection system.

59. The decorative element according to claim 51, wherein the elastomeric composition further comprises a non-staining ozone protection system.

60. The process according to claim 56, further comprising partially pre-vulcanizing the at least one layer and shaping the at least one layer to remove part of it.

Description

[0117] The present invention will now be described hereinafter with reference to the accompanying drawings, provided only for illustrative and, therefore, non-limiting purposes, in which:

[0118] FIG. 1 shows a cross half-section showing a tyre for motor vehicle wheels according to an embodiment of the present invention;

[0119] FIG. 2 shows a photograph of a tyre according to an embodiment of the present invention at the end of the dynamic ozone test of example 2;

[0120] FIG. 3 shows a photograph of a tyre according to an embodiment of the present invention at the end of the fatigue test of example 3;

[0121] FIG. 4 illustrates the comparison photo of a tyre according to an embodiment of the present invention at the end of the road resistance test of example 4 before and after cleaning.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0122] FIG. 1 shows a tyre 100 having a sidewall 108 on which a colored decorative element 120 (meaning also white as colored) made according to the present invention is present.

[0123] In FIG. 1, the decorative element 120 may cover only a part of the sidewall 108 of the tyre, as for example in the case in which the decorative element 120 comprises drawings, letters, logos, marks, decals applied on the sidewall of the tyre, or it may cover almost the whole sidewall 108, as for example in the case in which said decorative element 120 comprises a layer arranged, in whole or in part, along the circular section of the sidewall 108.

[0124] In FIG. 1, “a” indicates an axial direction and “r” indicates a radial direction.

[0125] With reference to FIG. 1, the tyre 100 for motor vehicle wheels comprises at least one carcass structure, comprising at least one carcass layer 101 having respectively opposite end flaps engaged with respective annular anchoring structures 102, referred to as bead cores, possibly associated to a bead filler 104. The tyre area comprising the bead core 102 and the bead filler 104 forms a reinforcement annular structure 103, the so-called bead, intended for anchoring the tyre onto a corresponding mounting rim, not shown.

[0126] The carcass structure is usually of radial type, i.e. the mutually parallel reinforcement elements of the at least one carcass layer 101 lie on planes comprising the rotational axis of the tyre and substantially perpendicular to the equatorial plane of the tyre.

[0127] Alternatively, tyres are made (not shown) provided with cross-ply carcass structures.

[0128] In such tyres, the carcass structure may comprise at least a first and a second radially overlapping carcass ply, each made of elastomeric material and comprising a plurality of mutually reinforcement elements arranged parallel to one another.

[0129] The carcass plies are radially overlapped so that the reinforcement elements of a ply are inclined with respect to the reinforcement elements of the radially overlapped carcass ply and to the equatorial plane.

[0130] In the carcass ply/plies (both in radial tyres and in cross-ply carcass tyres), the reinforcement elements may consist of metal and/or textile cords, for example steel in the case of metal or rayon cords, lyocell, nylon, polyester [e.g. polyethylene naphthalate (PEN)] in the case of textile cords. Each reinforcement annular structure is associated to the carcass structure by folding back of the opposite lateral edges of the at least one carcass layer 101 around the annular anchoring structure 102 so as to form the so-called carcass flaps 101a as shown in FIG. 1.

[0131] In one embodiment, the coupling between the carcass structure and the reinforcement annular structure can be provided by a second carcass layer (not shown in FIG. 1) applied in an axially outer position with respect to the first carcass layer.

[0132] An anti-abrasive strip 105 is arranged in an outer position of each reinforcement annular structure 103. Preferably each anti-abrasive strip 105 is arranged at least in an axially outer position to the reinforcement annular structure 103 extending at least between the sidewall 108 and the portion radially below the reinforcement annular structure 103.

[0133] Advantageously, the anti-abrasive strip 105 is preferably made with the same elastomeric composition used to make the sidewalls 108 according to the present invention, i.e. a cross-linkable elastomeric composition comprising (i) at least one diene elastomeric polymer, and (ii) a non-staining ozone protection system.

[0134] Preferably, the anti-abrasive strip 105 is arranged so as to enclose the reinforcement annular structure 103 along the axially inner and outer and radially lower areas of the reinforcement annular structure 103 so as to interpose between the latter and the wheel rim when the tyre 100 is mounted to the rim.

[0135] In radial tyres, the carcass structure is associated to a belt structure 106 comprising one or more belt layers 106a, 106b placed in radial superposition with respect to one another and with respect to the carcass layer, having typically metallic reinforcement cords. Such reinforcement cords may have crossed orientation with respect to a direction of circumferential development of tyre 100. By “circumferential” direction it is meant a direction generally facing in the direction of rotation of the tyre.

[0136] At least one zero-degree reinforcement layer 106c, commonly known as a “0° belt”, may be applied in a radially outermost position to the belt layers 106a, 106b, which generally incorporates a plurality of reinforcement cords, typically textile cords, oriented in a substantially circumferential direction, thus forming an angle of a few degrees (such as an angle of between about 0° and 6°) with respect to the equatorial plane of the tyre, and coated with an elastomeric material.

[0137] A tread band 109 of elastomeric blend is applied in a position radially outer to the belt structure 106.

[0138] In some embodiments (for example tyres for motorcycle or scooter wheels), the belt structure may be absent.

[0139] In a radially outer position, the tread band 109 has a rolling surface 109a intended to come in contact with the ground. Circumferential grooves, which are connected by transverse notches (not shown in FIG. 1) so as to define a plurality of blocks of various shapes and sizes distributed over the rolling surface 109a, are generally made on this surface 109a, which for simplicity is represented smooth in FIG. 1.

[0140] An under-layer 111 is arranged between the belt structure 106 and the tread band 109.

[0141] In the case of tubeless tyres, a rubber layer 112, generally known as “liner”, which provides the necessary air-tightness to the inflation air of the tyre, can also be provided in a radially inner position with respect to the carcass layer 101.

[0142] Moreover, respective sidewalls 108, made with a cross-linkable elastomeric composition comprising (i) at least one diene elastomeric polymer, and (ii) a non-staining ozone protection system, are further applied on the lateral surfaces of the carcass structure, each extending from one of the lateral edges of the tread 109 at the respective reinforcement annular structure 103.

[0143] A strip consisting of elastomeric material 110, commonly known as “mini-sidewall”, can optionally be provided in the connecting zone between the sidewalls 108 and the tread band 109, this mini-sidewall being generally obtained by co-extrusion with the tread band 109 and allowing an improvement of the mechanical interaction between the tread band 109 and the sidewalls 108. Preferably, the end portion of sidewall 108 directly covers the lateral edge of the tread band 109.

[0144] Preferably, if present, the mini-sidewall 110 is made like the sidewall with a cross-linkable elastomeric composition comprising (i) at least one diene elastomeric polymer, and (ii) a non-staining ozone protection system.

[0145] On the outer surface of at least one of the two sidewalls 108 (as shown in FIG. 1) at least one decorative element 120 made according to the present invention is applied by co-vulcanisation.

[0146] The building of the tyre 100 according to the present invention may be carried out according to the techniques and using the apparatuses that are known in the art, said building including the manufacture of the green tyre, the manufacture of the green decorative element, the moulding, the vulcanisation of the green tyre and of the green decorative element.

[0147] The application of the green or partially vulcanised decorative element may take place on the green tyre (and in this case the vulcanisation of the decorative element 120 will be simultaneous with that of the tyre 100) or on the finished tyre (and in this case the vulcanisation of the green decorative element will be subsequent to that of the green tyre).

[0148] For the purposes of the present invention, the application of the green or partially vulcanised decorative element takes place on the green tyre.

[0149] In particular, the building of the tyres 100 as described above may be carried out by assembling respective semi-finished products onto a forming drum, not shown, by at least one assembly device.

[0150] At least a part of the components intended to form the carcass structure of the tyre may be built and/or assembled on the forming drum. More particularly, the forming drum is intended to first receive the possible liner, then the carcass structure. Subsequently, devices not shown coaxially engage one of the annular anchoring structures around each of the terminal flaps, and subsequently the sidewalls and the anti-abrasive strip are positioned.

[0151] Thereafter, an outer sleeve comprising the belt structure and the tread band may be positioned 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.

[0152] 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 blends, as well as to impart a desired tread pattern on the tread band and to impart any distinguishing graphic signs at the sidewalls.

[0153] The moulding and vulcanisation treatment is carried out in a vulcanisation apparatus known in the art comprising a toroidal support designed to engage a tyre being processed, a vulcanisation mould designed to receive the toroidal support, pressing means for pressing the outer surface of the tyre against the walls of the moulding cavity comprising a sidewall intended to form the surfaces of the sidewalls and a crown of sectors designed to form the surface of the tread; and heating means for transmitting heat to the tyre closed between the moulding cavity and the toroidal support. The decorative element 120 may be placed directly on the forming drum before assembling the sidewalls, it may be positioned on the green tyre before moulding and vulcanisation, or it may be positioned on the sidewall of the vulcanisation apparatus, and brought into contact with the sidewall of the green tyre during vulcanisation.

[0154] Advantageously, the decorative element 120 coupled with a support layer is positioned on the sidewall of the vulcanisation apparatus, and brought into contact with the sidewall of the green tyre during vulcanisation.

[0155] The Applicant has observed that the application of the decorative element 120 during the moulding and vulcanisation process inside the vulcanisation apparatus allows simplifying the application operations, but above all more easily obtaining the correct positioning of the decorative element 120 on the surface of the sidewall 108 of the tyre 100, avoiding overflows and/or deviations resulting from the application on the green sidewall or on the forming drum.

[0156] In particular, according to an aspect of the present invention, the decorative element 120 is prepared in the form of a layer by deposition of the elastomeric composition of the present invention on a plastic support consisting of polyolefins, such as polyethylene (PE) and polypropylene (PP), polyesters, such as polyethylene terephthalate (PET) and polyethylene terephthalate (PEN), polyamide, polyimide, perfluorinated polymers, such as polytetrafluoroethylene (PTFE), and polyurethanes (PU).

[0157] The plastic support provides the necessary support to the elastomeric composition layer during the subsequent processing steps. The plastic support is selected based on its temperature resistance features, in particular at the vulcanisation temperatures generally of between 150° C. and 180° C.

[0158] The plastic support is preferably made with polyethylene terephthalate (PET) or polyamides, such as, for example Nylon 6 or Nylon 66, with a thickness of between 10 and 150 micrometres (μm), preferably between 20 and 75 micrometres (μm).

[0159] The layer thus formed can be directly applied to the mould sidewall or optionally subjected to a partial pre-vulcanisation.

[0160] The pre-vulcanisation is carried out for a period of at least 1 hour, preferably at least 2 hours, at a temperature equal to or lower than 100° C., preferably lower than 90° C., more preferably lower than 80° C., but equal to or higher than 40° C., preferably higher than 50° C., and more preferably higher than 60° C.

[0161] The partial pre-vulcanisation gives the layer a sufficient consistency for the shaping thereof by removing part of it if the decorative element 120 consists of a plurality of letters, numbers or any discontinuous graphic sign or of significant extension, such as, for example, the mark of the manufacturer and/or the name of the product and/or annular strips. The removal of the layer portions to form the aforesaid words can be carried out with methods known in the art such as, for example, laser ablation or mechanical removal.

[0162] In the case in which the decorative element 120 consists of a more or less wide continuous layer covering a portion of or the whole sidewall, the layer coupled to the support may be directly applied to the mould sidewall, although also in this case it may undergo the pre-vulcanisation treatment.

[0163] The partial pre-vulcanisation of the layer also allows a thin layer of rubber-based inks to be printed on the surface of the layer itself for making the decorative element 120.

[0164] The layer with the plastic support is positioned on the mould sidewall with the exposed surface of elastomeric composition facing towards the inside of the vulcanisation apparatus, at the sidewall of the green tyre, and the plastic support adhered to the surface of the mould sidewall.

[0165] The vulcanisation apparatus is then closed, and the vulcanisation process is started, which consists in bringing the temperature inside the apparatus to a value of between 150° C. and 180° C. for a period of time between 10 seconds and 40 minutes, at the same time pressing the outer surface of the tyre against the walls of the moulding cavity, during which the layer of elastomeric composition of the decorative element and the sidewall of the green tyre co-vulcanise, making a mutual adhesion of the surfaces facing each other.

[0166] Some tests performed on tyres made according to the invention are described below.

EXAMPLE 1

[0167] Tyre Preparation

[0168] The tyres used were Pirelli P ZERO™ 245/35ZR21 (96Y) front (tyre 1), and Pirelli P ZERO™ 285/30ZR21 (100Y) rear (tyre 2).

[0169] The tyres used were made according to the process of the present invention and included the sidewalls made with the compound described in table 1 and the decorative elements, consisting of two continuous strips about one third of the circumference of the sidewall arranged symmetrically one with respect to the other, the writing “PIRELLI”, and the writing “P ZERO”, 300 μm (micrometres) thick, made with the compounds described in table 2.

[0170] The values of tables 1 and 2 are expressed in phr.

TABLE-US-00003 TABLE 1 Component Quantity Natural rubber 40 Butadiene rubber 60 Carbon black 660 50 Tackifying resin  2 Stearic acid  2 Zinc oxide  2.85 Non-staining antioxidant  8 Retardant  0.1 Primary accelerant  0.8 Sulphur  2 Butadiene rubber: Neocis BR40, Versalis Carbon black: N660, Columbian Tackifying resin: Quintone A100, Zeon Corporation Non-staining antioxidant: Irganox 1520L, 4,6-bis[(octylthio)methyl]-o-cresol, BASF Retardant: N-cyclohexylthiophthalimide Primary accelerant: CBS, N-cyclohexyl-2-benzothiazil sulphenamide, Huathai

TABLE-US-00004 TABLE 2 Component Compound A Compound B Natural rubber 50 65 Bromobutyl rubber 50 — Styrene-butadiene rubber — 35 Silica 40 20 Silane Si69  3  6 Titanium oxide 10 20 Talc 15 30 Plasticizer 10 10 Antioxidant 1  3  3 Antioxidant 2  2 Tackifying resin  3 Orange pigment 10 10 Stearic acid  2  2 Zinc oxide  5  3 Primary accelerant  2  1 Thiazolic accelerant  3 Sulphur  0.6 — Sulphur donor  1.5 — Styrene-butadiene rubber: SBR 1502 = ESBR non-extended oil (23.5% Styrene) Plasticiser: wax, paraffinic oil Silica: Zeosil 185 GR by Solvay Primary accelerant: Huathai CBS cyclohexyl benzothiazole sulphenamide Thiazolic accelerant: Rhenogran MBTS 80 by Rheinchemie Antioxidant 1: IRGANOX 1520 L by BASF Antioxidant 2: Vulcazon AFS/LG 3,9-Di-(3-Cyclohexenyl)-2,4,8,10-Tetraoxaspiro(5.5)Undecane by Lanxess Sulphur donor: Vultac TB710 of poly-tert-butylphenoldisulphide and stearic acid by ARKEMA

[0171] The tyres with the decorative elements made with compound A are indicated with 1A and 2A, while the tyres with the decorative elements made with compound B are indicated with 1B and 2B.

EXAMPLE 2

[0172] Dynamic Ozone Tests on the Tyre

[0173] The dynamic test of exposure to ozone was carried out on tyres inflated to a pressure of 2.6 bar (controlled) stressed with a constant vertical load equal to 50% of the load index, and a constant speed of 120 km/h, subjecting it to ozone flow of 3 g/m.sup.3 directly on the sidewall with nozzle at a distance of 7 cm.

[0174] The test was carried out on an Indoor machine with a 1.7-metre road wheel in a conditioned environment with a controlled temperature between 28° C. and 30° C.

[0175] The overall test lasted 200 hours. At the end of the test, the covers were examined to check for defects on the decorative elements (detachments, cracks, change of color), and the results are summarised in the following table 3.

TABLE-US-00005 TABLE 3 Tyre Detachments Cracking Change of color 1A No No No 1B No No No 2A No No No 2B No No No

[0176] FIG. 2 shows a photograph of a tyre at the end of the test. All tested tyres passed the test without any appreciable damage to the decorative elements.

EXAMPLE 3

[0177] Endurance Tests on the Tyre

[0178] The endurance tests consist of a high-speed test and a fatigue test.

[0179] Speed Test

[0180] The high-speed test was carried out on tyres inflated to a pressure of 3.6 bar. The test is carried out on an Indoor machine with a 1.7 m diameter road wheel with camber angle equal to 2° in a conditioned environment with a controlled temperature of 27.5° C.±2.5° C.

[0181] During the test, the tyres were stressed with a constant vertical load of 575 kg (tyre 1) or 650 kg (tyre 2), at speeds varying over time from 240 to 320 km/h.

[0182] The overall test lasted 2 hours and 20 minutes. At the end of the test, the covers were examined to check for defects on the decorative elements (detachments, cracks, change of color), and the results are summarised in the following table 4.

TABLE-US-00006 TABLE 4 Tyre Detachments Cracking Change of color 1A No No No 1B No No No 2A No No No 2B No No No

[0183] All tested tyres passed the test without any appreciable damage to the decorative elements.

[0184] Fatigue Test

[0185] The fatigue test was performed on tyres inflated to a (controlled) pressure of 3 bar stressed with constant vertical load equal to 160% of the load index, and constant speed at 120 km/h.

[0186] The test was carried out on an Indoor machine with a 1.7-metre road wheel in a conditioned environment with a controlled temperature of 27.5° C.±2.5° C. The test included stops for checking the tyres every 12 hours and continued until the cover broke (in the belt end area).

[0187] At the end of the test, the covers were examined to check for defects on the decorative elements (detachments, cracks, change of color), and the results are summarised in the following table 5.

TABLE-US-00007 TABLE 5 Tyre Detachments Cracking Change of color 1A No No No 1B No No No 2A No No No 2B No No No

[0188] FIG. 3 shows a photograph of a tyre at the end of the test. All tested tyres passed the test without any appreciable damage to the decorative elements.

EXAMPLE 4

[0189] Endurance Tests on the Road

[0190] In view of the good results obtained and illustrated in example 3, tests were carried out with tyre engagement on the road.

[0191] The test took place on a private circuit at an average speed of about 200 km/h for a total of about 150 km. The test was performed with a Maserati Ghibli provided with the tyres 1A and 2A inflated to a pressure of 2.5 bar.

[0192] The test allowed evaluating the systems under very high mechanical stress conditions (load, speed and cornering), which led to an increase in the final sidewall temperature up to about 60° C. (external ambient temperature 28° C.).

[0193] At the end of the test, the covers were examined to check for defects on the decorative elements (detachments, cracks, change of color), and the results are summarised in the following table 6.

TABLE-US-00008 TABLE 6 Tyre Detachments Cracking Change of color 1A No No No 2A No No No

[0194] All tested tyres passed the test without any appreciable damage to the decorative elements.

[0195] The decorative elements at the end of the test were dirty, black streaks, resulting from the passage of the tyres on the curbs of the circuit, but a cleaning treatment with heptane solvent brought the decorative elements back to their original appearance without signs of alteration or discoloration. FIG. 4 shows the comparison of a tyre before and after the cleaning operation.