TYRE FOR VEHICLE WHEELS

Abstract

The present invention relates to a tyre for vehicle wheels comprising at least one structural element comprising a cross-linked elastomeric material obtained by cross-linking a cross-linkable elastomeric composition comprising carbon nanotubes, wherein said carbon nanotubes are obtained with an iron oxides and/or aluminium oxides based catalyst substantially free of Co, Ni and Mo.

Claims

1-17. (canceled)

18. A tyre for vehicle wheels comprising: at least one structural element with a cross-linked elastomeric material, wherein the crosslinked elastomeric material comprises, before vulcanization, a cross-linkable elastomeric composition comprising carbon nanotubes from a carbon source and iron oxide and/or aluminium oxide catalysts substantially free of Co, Ni, and Mo.

19. The tyre according to claim 18, wherein the tyre comprises at least one carcass structure having opposite lateral edges associated with respective reinforcing annular structures, a belt structure applied in a radially external position with respect to the at least one carcass structure, a tread band applied in a radially external position with respect to the at least one carcass structure, and a pair of sidewalls laterally applied on opposite sides with respect to the at least one carcass structure.

20. The tyre according to claim 18, wherein the structural element is chosen from a tread band, a tread underlayer, a sidewall, a mini-sidewall, a sidewall insert, a bead structure, a rubber coating of the at least one carcass structure, and a rubber coating of the belt structure.

21. The tyre according to claim 18, wherein the cross-linkable elastomeric composition comprises an amount of carbon nanotubes ranging from 0.5 to 5 phr.

22. The tyre according to claim 21, wherein the amount of carbon nanotubes ranges from 1 to 4 phr, or from 2 to 3 phr.

23. The tyre according to claim 18, wherein the carbon nanotubes comprise a carbon percentage equal to or higher than 90% by weight, with respect to the total weight of the carbon nanotubes.

24. The tyre according to claim 23, wherein the carbon percentage is equal to or higher than 95% by weight, equal to or higher than 97% by weight, or equal to or higher than 98% by weight, with respect to the total weight of the carbon nanotubes.

25. The tyre according to claim 18, wherein the carbon nanotubes comprise a residual catalyst percentage lower than 10% by weight, with respect to the total weight of the carbon nanotubes.

26. The tyre according to claim 25, wherein the residual catalyst percentage is lower than 5% by weight, lower than 3% by weight, or lower than 2% by weight, with respect to the total weight of the carbon nanotubes.

27. The tyre according to claim 18, wherein the carbon nanotubes are characterised by a carbon: residual catalyst (C/r) weight ratio higher than 10:1.

28. The tyre according to claim 27, wherein the carbon: residual catalyst (C/r) weight ratio is higher than 20:1, higher than 40:1, or higher than 50:1.

29. The tyre according to claim 18, wherein the carbon nanotubes comprise an amount of Co, Ni, and Mo lower than 0.1 ppm.

30. The tyre according to claim 29, wherein the amount of Co, Ni, and Mo is lower than 0.01 ppm, or lower than 0.001 ppm.

31. A process for producing iron oxide and/or aluminium oxide catalysts substantially free of Co, Ni, and Mo comprising: preparing an aqueous solution (i) comprising a Fe.sup.3+ soluble salt and an Al.sup.3+ soluble salt, wherein the solution (i) comprises a molar concentration of Fe.sup.3+ ranging from 0.3 to 1.5 M and a molar concentration of Al.sup.3+ ranging from 0.8 to 2.4 M, preparing an aqueous solution (ii) comprising ammonium hydroxide, wherein the solution (ii) comprises a molar concentration of NH.sub.3 ranging from 1.8 to 18 M, adding solution (ii) to solution (i), wherein an amount of NH.sub.3 added per minute ranges from 1.3.Math.10.sup.4 to 4.5.Math.10.sup.1 moles per total moles of iron or aluminium or both iron and aluminium, resulting in a combined solution with a pH ranging from 6 to 8, wherein a gel of the combined solution forms, drying the gel at a temperature ranging from 35 C. to 100 C. to obtain a solid, and calcining the obtained solid at a temperature ranging from 250 C. to 750 C. under an atmosphere chosen from air and nitrogen.

32. The process according to claim 31, wherein the Fe.sup.3+ molar concentration ranges from 0.5 to 1.1 M.

33. The process according to claim 31, wherein the Al.sup.3+ molar concentration ranges from 1.2 to 1.8 M.

34. The process according to claim 31, wherein the NH.sub.3 molar concentration ranges from 10 to 18 M.

35. The process according to claim 31, wherein the amount of NH.sub.3 added per minute during the addition of solution (ii) to solution (i) ranges from 2.5.Math.10.sup.4 to 2.Math.10.sup.1 moles per total moles of iron and aluminium.

36. A process for preparing carbon nanotubes comprising: loading a catalyst on a porous material in a reactor chamber, bringing a temperature of the reactor chamber to a reaction temperature, and fluxing a gaseous stream of one or more gaseous hydrocarbons in the reactor chamber, wherein the catalyst is iron oxide and/or aluminium oxide catalyst substantially free of Co, Ni, and Mo obtained by a process comprising: preparing an aqueous solution (i) comprising a Fe.sup.3+ soluble salt and an Al.sup.3+ soluble salt, wherein the solution (i) comprises a molar concentration of Fe.sup.3+ ranging from 0.3 to 1.5 M and a molar concentration of Al.sup.3+ ranging from 0.8 to 2.4 M, preparing an aqueous solution (ii) comprising ammonium hydroxide, wherein the solution (ii) comprises a molar concentration of NH.sub.3 ranging from 1.8 to 18 M, adding solution (ii) to solution (i), wherein an amount of NH.sub.3 added per minute ranges from 1.3.Math.10.sup.4 to 4.5.Math.10.sup.1 moles per total moles of iron or aluminium or both iron and aluminium, resulting in a combined solution with a pH ranging from 6 to 8, wherein a gel of the combined solution forms, drying the gel at a temperature ranging from 35 C. to 100 C. to obtain a solid, and calcining the obtained solid at a temperature ranging from 250 C. to 750 C. under an atmosphere chosen from air and nitrogen.

37. An iron oxide and/or aluminium oxide catalyst substantially free of Co, Ni, and Mo, wherein the catalyst comprises a grain size, expressed as average surface equivalent spherical diameter, ranging from 10 to 150 m, an apparent density ranging from 0.300 to 0.900 g/cm.sup.3, and a surface area ranging from 50 to 500 m.sup.2/g.

38. The catalyst according to claim 37, further comprising a nominal iron content (normalizing the formulation as Fe+Al.sub.2O.sub.3) higher than 30% by weight.

39. The catalyst according to claim 38, wherein the nominal iron content is equal to or higher than 35% by weight, or equal to or higher than 45% by weight.

40. A carbon nanotube comprising an amount of Co, Ni, and Mo lower than 0.1 ppm, and a carbon: residual catalyst (C/r) weight ratio higher than 10:1.

41. The carbon nanotube according to claim 40, wherein the amount of Co, Ni, and Mo is lower than 0.01 ppm, or lower than 0.001 ppm.

42. The carbon nanotube according to claim 40, wherein the carbon: residual catalyst (C/r) weight ratio is higher than 20:1, higher than 40:1, or higher than 50:1.

43. A process for preparing carbon nanotubes comprising: loading a catalyst on a porous material in a reactor chamber, bringing a temperature of the reactor chamber to a reaction temperature, and fluxing a gaseous stream of one or more gaseous hydrocarbons in the reactor chamber, wherein the catalyst is iron oxide and/or aluminium oxide catalyst substantially free of Co, Ni, and Mo, comprising a grain size, expressed as average surface equivalent spherical diameter, ranging from 10 to 150 m, an apparent density ranging from 0.300 to 0.900 g/cm.sup.3, and a surface area ranging from 50 to 500 m.sup.2/g.

Description

DRAWINGS

[0111] The description will be set forth hereinbelow, with reference to the enclosed drawings, provided only as a non-limited example and in which:

[0112] FIG. 1 illustrates, in half cross section, a tyre for motor vehicle wheels according to a first embodiment of the present invention,

[0113] FIG. 2 illustrates, in half cross section, a tyre for motor vehicle wheels according to a second embodiment of the present invention,

[0114] FIG. 3 represents the diffraction spectrum of the catalyst CAT-1SG-35-A obtained as described in example 1,

[0115] FIG. 4 represents the diffraction spectrum of the catalyst CAT-1SG-35-N2 obtained as described in example 1, and

[0116] FIG. 5 represents the diffraction spectrum of the catalyst CAT-2SG-35-N2, obtained as described in example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0117] In FIGS. 1 and 2, a indicates an axial direction and r indicates a radial direction. For the sake of simplicity, FIGS. 1 and 2 only show one portion of the tyre, the remaining not represented portion being identical and symmetrically arranged with respect to the radial direction r.

[0118] 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 anchoring annular structures 102, termed bead cores, possibly associated with a bead filler 104. The zone of the tyre comprising the bead core 102 and the filler 104 forms a reinforcing annular structure 103, the so-called bead, intended for anchoring the tyre on a corresponding mounting rim, not illustrated.

[0119] The reinforcing annular structure 103, and in particular the bead filler 104, are advantageously made with the previously-described elastomeric composition comprising nanotubes, since such elements are particularly subjected to mechanical stresses in use conditions during the rolling of the tyre, since directly in contact with the rim of the wheel.

[0120] The carcass structure is usually of radial type, i.e. the reinforcement elements of the at least one carcass layer 101 are situated on planes comprising the rotation axis of the tyre and substantially perpendicular to the equatorial plane of the tyre. Said reinforcement elements are generally constituted by textile cords, e.g. rayon, nylon, polyester (e.g. polyethylene naphthalate (PEN)). Each reinforcing annular structure is associated with the carcass structure by means of backward bending of the opposite lateral edges of the at least one carcass layer 101 around the anchoring annular structure 102 so as to form the so-called turned-up elements of the carcass 101a as illustrated in FIG. 1.

[0121] In one embodiment, the coupling between carcass structure and reinforcing annular structure can be provided by means of a second carcass layer (not represented in FIG. 1) applied in an axially external position with respect to the first carcass layer.

[0122] An anti-abrasive strip 105 is arranged in an external position of each reinforcing annular structure 103. Preferably each anti-abrasive strip 105 is arranged at least in axially external position with respect to the reinforcing annular structure 103, being extended at least between the sidewall 108 and the portion that is radially lower with respect to the reinforcing annular structure 103.

[0123] Preferably the anti-abrasive strip 105 is arranged so as to enclose the reinforcing annular structure 103 along the axially internal and external and radially lower zones of the reinforcing annular structure 103 in a manner so as to be interposed between the latter and the rim of the wheel when the tyre 100 is mounted on the rim.

[0124] The carcass structure is associated with a belt structure 106 comprising one or more belt layers 106a, 106b situated in radial superimposition with respect to each other and with respect to the carcass layer, having typically metallic reinforcement cords. Such reinforcement cords can have cross orientation with respect to a circumferential extension direction of the tyre 100. By circumferential direction it is intended a direction generally directed according to the tyre rotation direction.

[0125] In radially more external position with respect to the belt layers 106a,106b, at least one zero degree reinforcement layer 106c can be applied, commonly known as 0 belt, 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 (e.g. an angle between about 0 and 6) with respect to the equatorial plane of the tyre, and covered with an elastomeric material.

[0126] In a radially external position with respect to the belt structure 106, a tread band 109 made of elastomeric mixture is applied.

[0127] Respective sidewalls 108 made of elastomeric mixture obtained according to the present invention are also applied in axially external position on the lateral surfaces of the carcass structure, each extended from one of the lateral edges of the tread 109 up to the respective reinforcing annular structure 103.

[0128] In a radially external position, the tread band 109 has a rolling surface 109a intended to come into contact with the ground. Circumferential grooves, which are connected by transverse cuts (not shown in FIG. 1) so as to define a plurality of blocks of various shape and size distributed on the rolling surface 109a, are generally made in this surface 109a, which for the sake of simplicity in FIG. 1 is represented smooth.

[0129] An underlayer 111 is arranged between the belt structure 106 and the tread band 109.

[0130] A strip constituted by elastomeric material 110, commonly known as mini-sidewall, may be present in the zone of connection between the sidewalls 108 and the tread band 109, this mini-sidewall generally being 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 the sidewall 108 directly covers the lateral edge of the tread band 109.

[0131] The tread band, and/or the underlayer, and/or the mini-sidewall and/or the sidewall and/or the anti-abrasive strip and/or the rubber-coating mixtures of the carcass structure and/or belt structure can advantageously be made with the previously described elastomeric composition comprising nanotubes, since a greater tensile strength confers greater tear resistance, and consequently greater resistance and duration of the surface of the sidewall and of the tread, particularly exposed to sudden mechanical stresses during use (due for example to the roughness of the road surface, to impact with sidewalks during parking manoeuvres, and so forth). In addition, the previously described elastomeric composition comprising nanotubes will be electrically conductive even in the presence of silica as main filler, collaborating to construct a conductive path between the rim and the ground.

[0132] In the case of tyres without inner tube, a rubber layer 112, generally known as liner, which provides the necessary impermeability to the tyre inflation air, can also be provided in a radially internal position with respect to the carcass layer 101.

[0133] The self-supporting tyres (100), an example of which being illustrated in FIG. 2, include a support structure capable of supporting the load of the vehicle under a considerable or total loss of pressure. In particular, a sidewall insert (113), made according to the present invention, can be associated with each sidewall. In each side of the self-supporting tyre (100), the sidewall insert (113) is radially extended between the relevant bead structure (103) and the corresponding lateral edge of the tread band (109). Each sidewall insert (113) can be made of one or more portions and is situated in an axially internal or external position with respect to the carcass ply. For example, as represented in FIG. 2, the sidewall insert (113) is situated between the carcass ply (101) and the liner (112).

[0134] Alternatively, if more than one carcass ply is present, a sidewall insert (113) can be situated between two of said carcass plies (not shown in FIG. 2).

[0135] Alternatively, a sidewall insert (113) can be situated between the carcass ply and the sidewall (not shown in FIG. 2).

[0136] The sidewall insert can be advantageously made with the previously described elastomeric composition comprising nanotubes, since in work conditions with the tyre deflated it must have good tear propagation resistance (obtainable when there are higher properties at break, especially higher ultimate elongation properties).

[0137] According to a non-illustrated embodiment, the tyre can be a tyre for wheels for heavy transport vehicles, such as trucks, buses, trailers, vans, and generally for vehicles in which the tyre is subjected to a high load. According to a further non-illustrated embodiment, the tyre can be a tyre for vehicles with two wheels, for example for motorcycles.

[0138] The building of the above-described tyres 100 can be actuated by means of assembly of respective semifinished products on a forming drum, not illustrated, by at least one assembly device.

[0139] On the forming drum, at least one part of the components intended to form the carcass structure of the tyre can be built and/or assembled. More particularly, the forming drum is adapted to receive first the possible liner, then the carcass structure and the anti-abrasive strip. Subsequently, devices (not shown) coaxially engage, around each of the end flaps, one of the anchoring annular structures, position an external sleeve comprising the belt structure and the tread band in a position coaxially centred around the cylindrical carcass sleeve and shape the carcass sleeve according to a toroidal configuration by means of a radial dilation of the carcass structure, so as to determine the application thereof against a radially internal surface of the external sleeve.

[0140] Following the building of the green tyre, a moulding and vulcanisation treatment is executed aimed to determine the structural stabilisation of the tyre by means of cross-linking of the elastomeric mixtures as well as to impart a desired tread design on the tread band and to impart possible distinctive graphic marks at the sidewalls.

[0141] The present invention will be further illustrated hereinbelow by means of a number of preparation examples, which are merely provided as a non-limiting example of this invention.

Example 1

[0142] Preparation of CAT-1SG-50-N2 and CAT-1SG-50-A

[0143] Iron nitrate nonahydrate (126.66 g) and aluminium nitrate nonahydrate (128.77 g) were dissolved in 140 mL of water. A solution of ammonium hydroxide (circa 17 M) was dripped under stirring, up to a pH about 7, at which gelation occurred. The addition of ammonia occurred with constant speed and lasted 30 minutes. The gel was dried at 60 C. for 12 hours, then mildly ground (average surface equivalent spherical diameter (d.sub.s) 37.88 m), then it was divided into 2 aliquots of equal weight, calcining one in a nitrogen current and the other in an air current, at 500 C. for 90 minutes. Thus, 17.86 g of CAT-1SG-50-N2 and 17.40 g of CAT-1SG-50-A were respectively obtained, with an overall yield of 83% with respect to the theoretical.

[0144] Both the catalysts had a nominal catalyst content (normalizing the formulation as Fe+Al.sub.2O.sub.3) equal to 50% by weight with a fraction by weight of iron after calcination equal to 0.412.

[0145] Proceeding in an analogous manner, the catalysts CAT-1SG-35-N2 and CAT-1SG-35-A were obtained, with a nominal catalyst content (normalizing the formulation as Fe+Al.sub.2O.sub.3) equal to 35% by weight with a fraction by weight of iron after calcination equal to 0.304, and the catalysts CAT-1SG-25-N2 and CAT-1SG-25-A, with a nominal catalyst content (normalizing the formulation as Fe+Al.sub.2O.sub.3) equal to 25% by weight with a fraction by weight of iron after calcination equal to 0.226.

[0146] The following table 1 reports some analytical data of the obtained catalysts. The average surface equivalent diameter was obtained starting from the measurements made with an ultrasound granulometer CILAS 1180L. The surface area was obtained by means of BET analysis by using a Micromeritics Tristar II Series instrument. The apparent density was measured in accordance with the EN ISO 60:1977 regulation.

TABLE-US-00001 TABLE 1 Average surface equivalent spherical diameter Apparent density Surface area [m] [g/cm.sup.3] [m.sup.2/g] CAT-1SG-50-N2 87.81 0.503 223 4 CAT-1SG-50-A 83.39 0.637 207 4 CAT-1SG-35-N2 87.55 0.470 245 5 CAT-1SG-35-A 83.65 0.533 241 4 CAT-1SG-25-N2 88.80 0.564 286 5 CAT-1SG-25-A 84.16 0.582. 278 5

[0147] FIGS. 3 and 4 respectively represent the diffraction spectra of the catalyst CAT-1SG-35-A and CAT-1SG-35-N2, obtained by using a Philips X'Pert MPD instrument equipped with a graphite analyser, a radiation source Cu K-alpha and a power of 40 kV+40 mA.

[0148] As shown, phases were found corresponding to alumina (peaks A), hematite (peaks H1), and magnetite (peaks M). The peak P represents the peak of platinum, the material with which the specimen-holder is made.

Example 2

[0149] Preparation of CAT-2SG-35-N2

[0150] Ammonium iron(III) oxalate trihydrate (67.66 g) and aluminium nitrate nonahydrate (119.00 g) were dissolved in 150 mL of water. A solution of ammonium hydroxide (circa 17 M) was dripped under stirring, up to a pH about 7, at which gelation occurred. The addition of ammonia occurred with constant speed and lasted 20 minutes. Such gel was placed on a Buchner filter and carefully washed with 3 aliquots of 50 mL water. It was then dried at 80 C. for 10 hours and then mildly ground (10-100 m). The solid thus obtained was calcined under nitrogen atmosphere at 505 C. for 2 hours, leading to the obtainment of 22.80 g of catalyst, with a yield of 91% with respect to the theoretical.

[0151] The following table 2 reports some analytical data of the obtained catalyst. The measurements were carried out with the same techniques and instruments reported in example 1.

TABLE-US-00002 TABLE 2 Average surface equivalent spherical diameter Apparent density Surface area [m] [g/cm.sup.3] [m.sup.2/g] CAT-2SG-35-N2 37.95 0.486 168 4

[0152] FIG. 5 represents the diffraction spectrum of the catalyst CAT-2SG-35-N2, obtained as described in example 1. The diffraction spectrum of FIG. 5 reveals the presence of a hercynite phase, FeAl.sub.2O.sub.4, represented by the peaks H.

Example 3

[0153] Synthesis of the Carbon Nanotubes

[0154] The synthesis process consists of the CCVD method (catalytic chemical vapour deposition), which is conducted in particular in batch reactors with quartz fluid bed, provided with a porous septum which functions as distributor.

[0155] Nanotubes CNT1-SG1

[0156] 2 grams of catalyst CAT-1SG-50-N2, prepared as in example 1, were fed in the reactor and the temperature was brought to 650 C. by means of a heating ramp of 15 C./min in nitrogen current. Then, the catalyst is reduced in a hydrogen/nitrogen current with the ratio in partial pressures 0.3:0.7 for about 60 minutes. Subsequently, an ethylene/nitrogen mixture was fed, with the ratio under partial pressures 0.2:0.8 for 60 minutes, during which the deposit of carbon occurs. At the end of the experiment, 51 g of product were obtained.

[0157] Nanotubes CNT2-SG1

[0158] The procedure was repeated by using 2 grams of catalyst CAT-1SG-50-A, prepared as in example 1.

[0159] Nanotubes CNT3-SG1

[0160] The procedure was repeated by using 2 grams of catalyst CAT-1SG-35-N2, prepared as in example 1.

[0161] Nanotubes CNT4-SG1

[0162] The procedure was repeated by using 2 grams of catalyst CAT-1SG-35-A, prepared as in example 1.

[0163] Nanotubes CNT5-SG1

[0164] The procedure was repeated by using 2 grams of catalyst CAT-1SG-25-N2, prepared as in example 1.

[0165] Nanotubes CNT6-SG1

[0166] The procedure was repeated by using 2 grams of catalyst CAT-1SG-25-A, prepared as in example 1.

[0167] The nanotubes thus obtained were subjected to thermogravimetric analysis. The following table 3 illustrates the obtained results, expressed as residual percentage (r), carbon percentage (C), carbon over iron weight ratio (C/Fe), and carbon over residue weight ratio (C/r).

TABLE-US-00003 TABLE 3 r C Nanotubes Catalyst [% wt.] [% wt.] C/Fe C/r CNT1-SG1 CAT-1SG-50N2 1.807 97.486 131.072 53.949 CNT2-SG1 CAT-1SG-50A 2.294 97.155 102.895 42.352 CNT3-SG1 CAT-1SG-35N2 4.053 94.981 77.037 23.435 CNT4-SG1 CAT-1SG-35A 4.319 95.036 72.334 22.004 CNT5-SG1 CAT-1SG-25N2 13.596 85.276 27.789 6.272 CNT6-SG1 CAT-1SG-25A 14.414 84.771 26.057 5.881

[0168] The nanotubes thus obtained were conveniently used as is in the mixtures. Alternatively they were used after having subjected them to a humid purification carried out with 20% w/w sulphuric acid at 95 C. so as to further reduce the catalytic residue. In such a manner, purities higher than 98% were attained in all cases.

Example 4

[0169] Nanotubes CNT7-SG2

[0170] 2 grams of catalyst CAT-2SG-35-N2, prepared as in example 2, were fed into the reactor. Subsequently an ethylene/hydrogen/nitrogen mixture was fed, with the ratio under partial pressures 0.2:0.3:0.5 and the temperature was brought to 650 C. by means of a heating ramp of 15 C./min. The system is maintained at such temperature for 60 minutes, during which the carbon deposit occurs. At the end of the experiment, 29 g of product was obtained.

[0171] The nanotubes thus obtained were subjected to thermogravimetric analysis, by using a model TDA SDT Q600 instrument. The following table 4 illustrates the obtained results, expressed as residual percentage (r), carbon percentage (C), carbon over iron weight ratio (C/Fe), and carbon over residue weight ratio (C/r).

TABLE-US-00004 TABLE 4 r C Nanotubes Catalyst [% wt.] [% wt.] C/Fe C/r CNT7-SG2 CAT-2SG-35N2 6.743 93.242 45.457 13.828

Example 5

[0172] The elastomeric materials reported in the following table 5 were prepared in the following manner (the amounts of the various components are indicated in phr).

[0173] All the components, except for sulfur and accelerant (TBBS), were mixed in an internal mixer (Pomini PL 1.6 model) for about 5 minutes (1.sup.a step). As soon as the temperature reached 1455 C., the elastomeric composition was unloaded. Sulfur and accelerant (TBBS) were added and the mixing was carried out in an open roller mixer (2.sup.a step).

TABLE-US-00005 TABLE 5 MIXTURE INGREDIENTS R1 I1 I2 FIRST STEP BR 50 50 50 IR 50 50 50 NC7000 2 purified standard 2 nanotubes Purified CNT2-SG1 2 Stearic acid 1.5 1.5 1.5 VN3 silica 33 33 33 Zinc oxide 4 4 4 6PPD 2 2 2 SECOND STEP TBBS 1.9 1.9 1.9 Insoluble sulfur 3.1 3.1 3.1 R1: Reference I1: Invention I2: Invention [0174] BR is a polybutadiene rubber SKD with Neodymium catalyst having more than 97% cis butadiene, [0175] IR is a high cis-1,4-polyisoprene synthetic rubber, SKI-3, Lee Rubber, [0176] NC7000 is commercial carbon in nanotubes, Nanocyl SA, 90 (wt) % purity in nanotubes, 5.9% Al, 0.2% Co, [0177] Standard nanotubes were prepared according to the patent EP2213369 (B1) and purified with diluted sulphuric acid and have a purity of 95.86 (wt) % in nanotubes, 0.87 (wt) % Al, with Ni, Mo, and Co below the limit of detectability, [0178] purified CNT2_SG1 (purified with diluted sulphuric acid) have a purity of 98.33 (wt) % in nanotubes, 0.01 (wt) % Al, with Ni, Mo, and Co below the limit of detectability, [0179] VN3 silica is a precipitated silica with surface area of 180 m.sup.2/g, Evonik Industries, Germany, [0180] 6PPD is antioxidant aromatic amine N-(1,3-dimethylbutyl)-N-phenyl-p-phenylene-diamine, Lanxess Deutschland GmbH, Germany, [0181] TBBS is a dispersion of N-tert-butyl-2-benzothiazolesulfenamide, Lanxess Deutschland GmbH, Germany.

[0182] The metal content in the nanotubes was measured by means of the ICP/OES (Inductively coupled plasma Optical Emission Spectroscopy) technique, by using a model Perkin Elmer Optima 200DV instrument.

[0183] A specimen of nanotubes to be analysed was mineralised with a mixture of concentrated HNO.sub.3 and H.sub.2O.sub.2. The resulting clear solution was suitably diluted in 1% ultrapure HNO.sub.3 and subjected to ICP/OES analysis.

[0184] The green mixtures were subjected to MDR (Moving Die Rheometer) measurements in order to verify the cross-linking kinetics thereof. The rheometric analysis MDR was carried out by using a MDR Monsanto rheometer. The test was conducted at 170 C. for 20 minutes with an oscillation frequency of 1.66 Hz (100 oscillations per minute) and an oscillation amplitude of 0.5. The minimum torque (ML) and maximum torque (MH) values were measured.

[0185] The Mooney ML (1+4) viscosity at 100 C. was measured, according to the standard ISO 289-1:2005, on non-cross-linked materials, obtained as described above.

[0186] The static mechanical properties according to the standard UNI 6065 were measured at different elongations (CA0550%, CA1100%, and CA3300%) on samples of the abovementioned elastomeric materials, vulcanised at 170 C. for 10 minutes.

[0187] The dynamic mechanical properties E and Tan delta were measured by using a dynamic device Instron model 1341 in the tensile-compression mode according to the following methods. A test piece of cross-linked material (170 C. for 10 minutes) having cylindrical shape (length=25 mm; diameter=14 mm), preloaded under compression up to a longitudinal deformation of 25% with respect to the initial length and maintained at the predetermined temperature (23 C., 70 C. or 100 C.) for the entire duration of the test was subjected to a dynamic sinusoidal stress having an amplitude of 3.5% with respect to the length under pre-loading, with a frequency of 100 Hz. The dynamic mechanical properties are expressed in terms of values of dynamic elastic modulus (E) and Tan delta (loss factor). The Tan delta value was calculated as a ratio between the dynamic viscous modulus (E) and the dynamic elastic modulus (E). The thermoplastic behaviour was evaluated as the difference E between the dynamic elastic modulus values measured at two reference temperatures selected on the basis of the type of elastomeric composition and of its application in the tyre.

[0188] The dynamic mechanical properties G and Tan delta were also measured by using a RPA Alpha Technologies device in shear mode. A disc-shaped specimen (volume=5 cm.sup.3) of cross-linked elastomeric composition (170 C. for 10 minutes) was subjected to the measurement of the dynamic elastic shear modulus (G) at 70 C., frequency 10 Hz, deformation 0.4% to 10%. The dynamic mechanical properties are expressed in terms of values of dynamic elastic shear modulus (G) and Tan delta (loss factor). The Tan delta value was calculated as a ratio between the dynamic viscous shear modulus (G) and the dynamic elastic shear modulus (G).

[0189] The hardness in IRHD degrees (at 23 C. and 100 C.) was measured according to the standard ISO 48:2007, on samples of the mixtures immediately after the cross-linking at 170 C. for 10 minutes. The results were summarised in the following table 6

TABLE-US-00006 TABLE 6 SPECIMEN R1 I1 I2 Mooney ML (1 + 4) viscosity 100 C. 62 60 62 MDR MEASUREMENTS ML (dN m) 2.29 2.13 2.32 MH (dN m) 20.70 19.50 20.55 TS2[min] 1.88 2.05 1.96 T30[min] 2.72 2.88 2.80 T60[min] 3.16 3.34 3.24 T90[min] 4.54 4.51 4.38 STATIC MECHANICAL PROPERTIES Ca0.5[MPa] 1.47 1.33 1.42 Ca1[MPa] 2.71 2.33 2.56 Ca3[MPa] 10.08 9.11 10.04 CR[MPa] 10.67 12.87 13.17 AR[%] 344.7 420.0 411.4 IRHD 23 C. 67.6 66.4 67.4 IRHD 100 C. 65.0 65.1 65.6 DYNAMIC MECHANCAL PROPERTIES E (23 C. - 100 Hz) (MPa) 6.79 6.50 6.88 E (70 C. - 100 Hz) (MPa) 6.32 6.13 6.47 E (100 C. - 100 Hz) (MPa) 6.09 6.10 6.42 Tan delta (23 C.) 0.105 0.100 0.099 Tan delta (70 C.) 0.061 0.057 0.058 Tan delta (100 C.) 0.040 0.037 0.037 RPA MEASUREMENTS G 9% (MPa) 1.18 1.13 1.22 Tan delta (9%) 0.096 0.090 0.090

[0190] The results obtained in the static test of table 6 demonstrated that the mixture of the invention I1 and I2, comprising the nanotubes obtained from an iron oxides and/or aluminium oxides based catalyst substantially free of Co, Ni and Mo, allowed having higher elongation values and above all higher tensile strength with respect to the reference R1, predictive of an improved tear resistance, without substantial variations of the other static, dynamic or rheological characteristics.

[0191] In order to verify if possible residues of Fe in the nanotubes according to the invention give rise to undesired early aging phenomena of the mixtures, the Applicant carried out several thermal aging tests on samples of mixture I1 and I2, maintaining them at 70 C. for 7 days under air. Such tests did not show substantial variations of the mechanical properties of the mixture, in particular of the properties at break, with respect to mixtures lacking nanotubes. The Applicant, without wishing to be tied to any interpretation theory, deems that this is due to the fact that the nanotubes according to the invention are capable of not exposing ferrous particles towards the mixture, instead maintaining them effectively confined inside the structure of the nanotubes themselves.

Example 6

[0192] The elastomeric materials reported in the following table 7 were prepared in the following manner (the amounts of the various components are indicated in phr).

[0193] All the components, except for sulfur and accelerant (TBBS), were mixed in an internal mixer (Pomini model PL 1.6) for about 5 minutes (1.sup.a step). As soon as the temperature reached 1455 C., the elastomeric composition was unloaded. Sulfur and accelerant (TBBS) were added and the mixing was carried out in an open roller mixer (2.sup.a step).

TABLE-US-00007 TABLE 7 MIXTURE INGREDIENTS R2 I3 I4 FIRST STEP BR 50 50 50 IR 50 50 50 NC7000 4 CNT2-SG1 4 Purified CNT2-SG1 4 Stearic acid 1.5 1.5 1.5 Caorso 5.4 5.4 5.4 VN3 silica 27 27 27 Zinc oxide 4 4 4 6PPD 2 2 2 SECOND STEP TBBS 1.9 1.9 1.9 Insoluble sulfur 3.1 3.1 3.1 R2: Reference I3: Invention I4: Invention [0194] BR is a polybutadiene rubber SKD with Neodymium catalyst having more than 97% cis butadiene, [0195] IR is a high cis-1,4-polyisoprene synthetic rubber, SKI-3, Lee Rubber, [0196] NC7000 is commercial carbon in nanotubes, Nanocyl SA, 90 (wt) % purity in nanotubes, 5.9 (wt) % Al, 0.2 (wt) % Co, [0197] CNT2-SG1 has a purity of 91.85 (wt) % in nanotubes, 2.90 (wt) % Al, with Ni, Mo, and Co below the detectability level, [0198] purified CNT2-SG1 was purified with diluted sulphuric acid and has a purity of 98.33 (wt) % in nanotubes, 0.01 (wt) % Al, with Ni, Mo, and Co below the detectability level, [0199] VN3 silica is precipitated silica with surface area of 180 m.sup.2/g, Evonik Industries, Germany, [0200] 6PPD is antioxidant aromatic amine N-(1,3-dimethylbutyl)-N-phenyl-p-phenylene-diamine, Lanxess Deutschland GmbH, Germany, [0201] TBBS is a dispersion of N-tert-butyl-2-benzothiazolesulfenammide, Lanxess Deutschland GmbH, Germany.

[0202] The mixtures (green or cross-linked at 170 C. for 10 minutes) were subjected to the same measurements illustrated in the example 6.

[0203] The volumetric electrical resistivity was measured according to the standard UNI 4288-72 by using the isolation measurement tester NORMA UNILAP ISO X by Siemens. The results were summarised in the following table 8.

TABLE-US-00008 TABLE 8 SPECIMEN R2 I3 I4 Mooney ML (1 + 4) viscosity 100 C. 63 63 64 MDR MEASUREMENTS ML (dN m) 2.35 2.24 2.33 MH (dN m) 20.77 20.14 20.71 TS2[min] 1.99 1.79 1.81 T30[min] 2.81 2.58 2.60 T60[min] 3.23 3.01 3.03 T90[min] 4.39 4.19 4.23 STATIC MECHANICAL PROPERTIES Ca0.5[MPa] 1.62 1.53 1.60 Ca1[MPa] 3.10 2.94 3.05 Ca3[MPa] 10.48 10.99 11.07 CR[MPa] 10.27 12.15 13.50 AR[%] 321.0 333.6 377.6 IRHD 23 C. 68.0 66.4 67.4 IRHD 100 C. 66.1 64.1 64.6 DYNAMIC MECHANCAL PROPERTIES E (23 C. - 100 Hz) (MPa) 6.27 6.07 6.27 E (70 C. - 100 Hz) (MPa) 5.99 5.71 5.96 Tan delta (23 C.) 0.129 0.126 0.130 Tan delta (70 C.) 0.088 0.085 0.086 RPA MEASUREMENTS G 9% (MPa) 1.18 1.12 1.15 Tan delta (9%) 0.107 0.100 0.105 Electrical conductivity Volumetric resistivity (kOhm*m) 6.7 11.0 2.2

[0204] Also the results obtained in the static tests of table 8 confirmed that the mixtures I3 and I4, comprising the nanotubes obtained with the process of the present invention, allowed having higher values of elongation and above all higher tensile strength with respect to the reference R, predictive of an improved tear resistance, without substantial variations of the other static, dynamic and rheological characteristics. Along with this there is a substantial maintenance of the required electrical conductivity level, as confirmed by the volumetric electrical resistivity values reported in table 8 for the reference mixture R2 and for the mixture of the invention I3 and I4, substantially equivalent for the purpose of obtaining a suitable anti-static effect.