PROCESS FOR PRODUCING TYRES

Abstract

A process for producing tyres including building a green tyre having two bead structures. Each bead structure includes a bead filler. The bead filler or another rigid component of the green tyre includes a final elastomeric compound produced by the following: feeding elastomeric polymer and reinforcement filler to a first batch mixing device; mixing and dispersing the reinforcement filler in the elastomeric polymer and unloading the obtained elastomeric compound; feeding the obtained elastomeric compound, along with at least 5 phr of reinforcement resin, to a continuous mixing device of intermeshing and co-rotating twin-screw or multi-screw type or of planetary type; mixing the reinforcement resin in the elastomeric compound and unloading the obtained elastomeric compound; and feeding the obtained elastomeric compound along with the components capable of facilitating the cross-linking to a second batch mixing device and mixing to obtain the final elastomeric compound. The first and second batch mixing device have two counterrotating rotors.

Claims

1. Process for producing tyres, comprising: building a green tyre comprising two bead structures, each bead structure comprising a bead filler and annular anchoring structures; subjecting the green tyre to moulding and cross-linking to obtain a finished tyre; wherein at least one rigid component of said green tyre selected from among said bead filler, a coating of said annular anchoring structures, an anti-abrasive strip and a sidewall insert, comprises a final elastomeric compound comprising at least one elastomeric polymer, at least one reinforcement filler, components capable of facilitating the cross-linking, and at least 5 phr of reinforcement resin; and wherein said final elastomeric compound is produced by; feeding at least the elastomeric polymer and the reinforcement filler to a first batch mixing device; mixing and dispersing, in said first batch mixing device, said reinforcement filler in said elastomeric polymer, in a manner so as to obtain a first-phase elastomeric compound; unloading said first-phase elastomeric compound from said first batch mixing device; feeding said first-phase elastomeric compound, along with at least 5 phr of said reinforcement resin, to a continuous mixing device, said continuous mixing device being of intermeshing and co-rotating twin-screw or multi-screw type, or of planetary type; mixing and dispersing, in said continuous mixing device, said reinforcement resin in said first-phase elastomeric compound, to obtain an intermediate elastomeric compound, said mixing in said continuous mixing device being executed at a speed from about 40 revolutions per minute to about 400 revolutions per minute; unloading said intermediate elastomeric compound from said continuous mixing device; feeding said intermediate elastomeric compound along with components capable of facilitating the cross-linking to a second batch mixing device; mixing, in said second batch mixing device, said components capable of facilitating the cross-linking in said intermediate elastomeric compound, to obtain said final elastomeric compound, wherein each of said first and second batch mixing device has two counter-rotating rotors and the mixing in said batch mixing devices is executed at a speed from about 5 revolutions per minute to about 80 revolutions per minute; and unloading said final elastomeric compound from said second batch mixing device.

2. The process as claimed in claim 1, wherein said elastomeric polymer is selected from the group consisting of diene elastomeric polymers, mono-olefin elastomeric polymers, and mixtures thereof.

3. The process as claimed in claim 1, wherein an overall content of the reinforcement filler in said final elastomeric compound is greater than 10 phr and less than 120 phr and wherein an entire content of the elastomeric polymer and/or reinforcement filler of the final elastomeric compound is fed into said first batch mixing device.

4. The process as claimed in claim 1, wherein said final elastomeric compound comprises a quantity of components capable of facilitating the cross-linking greater than about 3.5 phr and less than or equal to about 7.5 phr and wherein an entire content of said components capable of facilitating the cross-linking of the final elastomeric compound is fed into said second batch mixing device.

5. The process as claimed in claim 1, wherein an entire content of the reinforcement resin of the final elastomeric compound is solid resin.

6. The process as claimed in claim 1, wherein an entire content of the solid reinforcement resin is fed into said continuous mixing device.

7. The process as claimed in claim 1, wherein at least 70% of the of reinforcement resin of the final elastomeric compound is fed into said continuous mixing device.

8. The process as claimed in claim 1, wherein no other component, except said reinforcement resin, is fed to said continuous mixing device.

9. The process as claimed in claim 1, wherein an overall content of the reinforcement resin in said final elastomeric compound is greater than or equal to 8 phr and/or less than or equal to 25 phr.

10. The process as claimed in claim 1, wherein said reinforcement resin comprises a methylene acceptor compound and wherein the final elastomeric compound comprises a quantity of methylene donor compound greater than about 1 phr and less than about 15 phr.

11. The process as claimed in claim 1, wherein the final elastomeric compound comprises a quantity of methylene acceptor compound greater than about 5 phr and less than about 25 phr.

12. The process as claimed in claim 10, wherein the methylene acceptor compound is selected from the group consisting of: resorcinol; catechol; hydroquinone; pyrogallol; phloroglucinol; 1-naphthol; 2-naphthol phenol resins, obtained from the condensation of a phenol, possibly substituted, with an aldehyde; modified phenol resins; phenol resins derived from products of natural origin; and mixtures of the abovementioned compounds.

13. The process as claimed in claim 1, wherein said final elastomeric compound comprises inorganic fibres of silicates of magnesium and/or aluminium of nanometric size, in a quantity greater than about 5 phr and/or less than about 25 phr.

14. The process as claimed in claim 1, wherein said first and/or second batch mixing device is an internal mixer and wherein said two counter-rotating rotors of the batch mixing device function tangentially with respect to each other or are inter-meshing.

15. The process as claimed in claim 1, wherein said mixing in said first and/or second batch mixing device is executed in a time interval between 50 seconds and 600 seconds.

16. The process as claimed in claim 1, wherein said screws, in the case of twin-screw or multi-screw continuous mixing device, or satellites, in case of continuous mixing device of planetary type, comprise compression and/or shearing mastication elements and transport elements.

17. The process as claimed in claim 1, wherein said continuous mixing device is a ring mixer.

18. The process as claimed in claim 1, wherein said continuous mixing device is of a self-cleaning type.

19. The process as claimed in claim 1, wherein said mixing in said continuous mixing device is executed at a specific energy greater than or equal to about 0.1 kWh/kg and/or less than or equal to about 0.6 kWh/kg.

20. The process as claimed in claim 1, wherein the process further comprises cooling said first-phase elastomeric compound to a temperature ranging from about 15° C. to about 40° C., before feeding said first-phase elastomeric compound to said continuous mixing device.

21. The process as claimed in claim 1, wherein the process further comprises cooling said intermediate elastomeric compound to a temperature ranging from about 15° C. to about 40° C., before feeding said intermediate elastomeric compound to said second batch mixing device.

22. The process as claimed in claim 1, wherein the first-phase elastomeric compound is fed to a conveyer device before being fed to said continuous mixing device, said conveyor being of helical single-screw or counter-rotating helical twin-screw type.

23. The process as claimed in claim 1, wherein said final elastomeric compound is fed to a device for building a semi-finished product, in which said final elastomeric compound is shaped into a strip of elastomeric compound having a size suitable for incorporation into the green tyre as said rigid component.

Description

[0103] The present invention will be illustrated in further detail by means of exemplifying embodiments, with reference to the enclosed figures, in which:

[0104] FIG. 1 schematically shows, in half-section, a tyre for vehicle wheels obtained according to the present invention;

[0105] FIG. 2 is a scheme of an exemplifying plant for producing an elastomeric compound according to the present invention.

[0106] FIG. 1 shows, as an example, a tyre 3 produced with the process according to the present invention

[0107] The tyre 3 essentially comprises at least one carcass ply 4 preferably internally coated with a layer of impermeable elastomeric material or so-called liner 5, two so-called “beads” 6 integrating respective annular anchoring structures 7 associated with a respective bead filler 7a and engaged with the circumferential edges of the carcass ply 4. Typically the annular anchoring structures 7 comprise metallic elements (for example the so-called ‘bead cores’) coated with the elastomeric material produced according to the present invention.

[0108] The tyre 3 also comprises typically a belt structure 8 applied in radially external position with respect to the carcass ply 4, a tread band 9 applied in radially external position with respect to the belt structure 8, in a so-called crown zone of the tyre 3, and two sidewalls 10 applied in laterally opposite positions on the carcass ply 4, each at a lateral zone of the tyre 3, extended from the corresponding bead 6 to the corresponding lateral edge of the tread band 9.

[0109] With reference to FIG. 2, reference number 1 overall indicates a plant for producing elastomeric compound in accordance with the present invention.

[0110] The plant 1 for producing an elastomeric compound includes an internal batch mixing device 101 (e.g. a Banbury® mixer) into which at least the elastomeric polymers 102 and the reinforcement fillers 103 are fed.

[0111] After the mixing has been executed, the obtained first-phase elastomeric compound 104 is fed to the continuous mixing device 106 (e.g. an intermeshing and co-rotating twin-screw self-cleaning extruder) through a feed hopper 105.

[0112] According to the embodiment of FIG. 2, the first-phase elastomeric compound 104 is unloaded from the internal batch mixer 101 to an optional conveyor 301 (e.g. helical single-screw extruder) through a feed hopper 302.

[0113] The first-phase elastomeric compound 104 is delivered by the conveyor 301, for example in the form of a continuous strip or sheet, pumping it through a roller opening or rolling press 303, e.g. by means of a gear pump (not represented in FIG. 2).

[0114] Alternatively (not shown in FIG. 2), the conveyor 301, rather than the roller opening 303, can be equipped with:

[0115] an extrusion opening equipped with a perforated extrusion plate equipped with knives, for the purpose of obtaining the first-phase elastomeric compound in the form of a subdivided product, before feeding it to the continuous mixer 106 (subject to possible storage);

[0116] an open mouth for the purpose of allowing the first-phase elastomeric compound to slide directly in the continuous mixer.

[0117] Alternatively, the conveyor 301 can be substituted with an open mixer (not shown in FIG. 2).

[0118] Alternatively, an open mixer can be arranged between the internal batch mixer 101 and the conveyor 301 (not shown in FIG. 2).

[0119] According to the particular embodiment of FIG. 2, the first-phase elastomeric compound 104 is cooled at the outlet of the conveyor 301, preferably at ambient temperature, by passing it through a cooling device 401 before feeding it to the continuous mixer device 106. Said cooling can be useful for the purpose of increasing the viscosity of the first-phase elastomeric compound before feeding it to said continuous mixer in order to allow an improved mixing of the first-phase elastomeric compound in said continuous mixer 106.

[0120] Alternatively (not shown), the first-phase elastomeric compound 104, at the outlet of the conveyor 301, after having been cooled by passing through the cooling device 401, can be transformed into a subdivided product by means of a cutting device (e.g. rolling mill equipped with rotating blades) before being fed to the continuous mixer 106 (subject to possible storage). Preferably, in this case, the feeding to the continuous mixer 106 can be controlled by means of feeders (volumetric feeders or loss-in-weight feeders) (not shown in FIG. 2).

[0121] In accordance with the present invention, at least 5 phr, preferably at least 8 phr, of reinforcement resin 111 is fed to the continuous mixing device 106 together with the first-phase elastomeric compound 104.

[0122] The continuous mixer 106 of FIG. 2 shows only one feed hopper 105. Nevertheless, more than one feed hopper (not shown in FIG. 2), can be present on the mixer 106. In addition, the continuous mixer 106 can be equipped with gravimetrically-controlled feed pumps (not shown in FIG. 2) which are useful for introducing liquid components, such as plasticising oils, into the mixer extruder.

[0123] The continuous mixer device 106 can optionally be equipped with one or more degassing units 110 for allowing the exit of the gases that can be developed during the mixing of the elastomeric compound.

[0124] After the mixing has been executed, and in particular after the reinforcement resin has been dispersed in the first-phase elastomeric compound in the continuous mixing device, an intermediate elastomeric compound 108 is unloaded from the continuous mixer device 106, for example in the form of a continuous strip, pumping it through a roller opening or rolling press 107, e.g. by means of a gear pump (not shown in FIG. 2).

[0125] Alternatively, the intermediate elastomeric compound 108 can be transformed into a subdivided product by pumping it through an extrusion opening (not shown in FIG. 2) arranged at the head of the continuous mixer, said extrusion opening being equipped with a perforated extrusion plate equipped with knives, by means of a gear pump (not shown in FIG. 2). The product obtained in subdivided form is subsequently cooled, preferably at ambient temperature, for example by conveying it towards a cooling device (not shown in FIG. 2).

[0126] The intermediate elastomeric compound 108 is fed to a second internal batch mixing device 501 (e.g. a Banbury® mixer). In accordance with the present invention, together with the intermediate elastomeric compound, also the components capable of facilitating the cross-linking 113 are fed to said second internal batch mixer 501.

[0127] According to the particular embodiment of FIG. 2, the intermediate elastomeric compound 108 is cooled, preferably at ambient temperature, by making it pass through a cooling device 109 before being fed to said second internal batch mixer 501. Said cooling can be useful for the purpose of increasing the viscosity of the intermediate elastomeric compound before providing it to said second internal batch mixer 501, therefore allowing an improved mixing of the intermediate elastomeric compound in said second internal mixer 501.

[0128] Alternatively (not shown in FIG. 2), the intermediate elastomeric compound 108 can be directly fed, without being cooled, to said second internal batch mixer 501.

[0129] Alternatively (not shown in FIG. 2), the intermediate elastomeric compound 108 can be obtained in the form of a subdivided product, as described above and subsequently fed to said second internal batch mixer 501.

[0130] In the second batch mixing device the components capable of facilitating the cross-linking are mixed and dispersed in the intermediate elastomeric compound, in a manner so as to obtain the final elastomeric compound 112 useful for incorporation in the bead filler of the green tyre, upon suitable shaping.

[0131] The final elastomeric compound 112 is then unloaded from said second batch mixing device 501, preferably by using a conveyor, not shown, combined with the second mixer 501 as described above with reference to the conveyor 301. The final elastomeric compound 112 is typically unloaded from the conveyor in sheet form, pumping it through an extrusion opening or a roller opening (not shown). Usually, the obtained sheet is subsequently subjected to a cooling treatment, usually by means of water and/or forced air. The sheet thus treated is then usually arranged on benches or reels, while awaiting further processing.

[0132] Typically the final elastomeric compound 112 is fed to a device for building a semi-finished element (not shown in FIG. 2), for example a single-screw short cylinder extruder with hot feeding, in a manner so as to obtain the bead filler ready for incorporation in the green tyre.

[0133] The present invention will be further illustrated hereinbelow by means of a number of test examples, which are given for merely exemplifying purposes and without any limitation of this invention.

EXAMPLES 1-6

[0134] Preparation of the Elastomeric Compounds

[0135] Tables 1 and 2 report the recipe of the components mixed in the batch mixer in the first step and in the final step, respectively, for all the examples 1-6 (the quantities are given in phr).

TABLE-US-00001 TABLE 1 COMPONENT phr high cis polybutadiene, SKD-neodymium, Nizhnekamsk 30 high cis-1,4-polyisoprene synthetic rubber, SKI-3, Nizhnekamsk 70 mineral oil, MES (Mild Extraction Solvate), ENI SPA 2 Carbon black, N375, Cabot 62 Stearic acid, Sogis 2 Zinc oxide, Zincol Ossidi 8 bonding tertbutylphenol resin, Koresin, Basf 2

TABLE-US-00002 TABLE 2 COMPONENT phr 50% Silane TESPT (bis[3-(triethoxysilyl)propyl]tetrasulfide) 3 supported on carbon black, X 50-S, Evonik Industries 65% HMMM hexamethoxymethylmelamine (65%) on inert carrier, 8 Cyrez 964 P.C., Cytec CTP cyclohexylthiophthalimide, Vulkalent G, Lanxess 0.3 TBBS:N-tert-butyl-2-benzothiazylsulfenamide, Vulkacit ® NZ/EG 1.5 C, Lanxess; Sulfur, Redball Superfine, International Sulphur Inc. 8

Example 1

Reference 1

[0136] First Step

[0137] All the components listed in Table 1, with the addition of 18 phr of reinforcement resin (4 phr of liquid reinforcement phenol resin (CELLOBOND J 3111 L, Momentive Specialty Chemicals UK Limited) and 14 phr of solid reinforcement phenol resin (DUREZ 12686, Sumitomo Bakelite Europe)), were mixed together in a Banbury® mixer (model F270), operating at the following work conditions: [0138] mixing time: 270 seconds; [0139] fill factor: 70%; [0140] rotor speed: 60 revolutions per minute; [0141] unloading temperature: 160° C.

[0142] Second Step

[0143] The elastomeric compound obtained in the first step, cooled at ambient temperature (23° C.), along with all the components of Table 2, were fed into a Banbury® mixer (model F270) and a further mixing was executed, operating at the following work conditions: [0144] mixing time: 180 seconds; [0145] fill factor: 70%; [0146] rotor speed: 20 revolutions per minute; [0147] unloading temperature: 90° C.

[0148] The elastomeric compound unloaded from the Banbury® mixer was subsequently cooled at ambient temperature (23° C.).

Example 2

Comparative 1

[0149] Like Example 1 with additionally, between the first and the second step, an intermediate step in which the elastomeric compound obtained in the first step was cooled at ambient temperature (23° C.) and was subsequently fed into a Banbury® mixer (model F270). A further mixing was executed, without adding any further component, operating at the following work conditions: [0150] mixing time: 150 seconds; [0151] fill factor: 70%; [0152] rotor speed: 35 revolutions per minute; [0153] unloading temperature: 120° C.

[0154] The elastomeric compound thus obtained was then subjected to the aforesaid second step of Example 1.

Example 3

Comparative 2

[0155] Like Example 1 with additionally, between the first and the second step, an intermediate step in which the elastomeric compound obtained in the first step was cooled at ambient temperature (23° C.) and was subsequently fed to an intermeshing and co-rotating twin-screw mixer Maris TM92HT having nominal screw diameter of 92 mm and L/D ratio of 32. A further mixing was executed, without adding any further component, operating at the following work conditions: [0156] feeding speed: 200 kg/h; [0157] speed of the double screw: 100 revolutions per minute; [0158] temperature profile: 40-50-60-50-20-10-10-10° C. [0159] specific energy: 0.3 kWh/kg [0160] temperature of elastomeric compound measured at the outlet of the extruder: 115° C.

[0161] The elastomeric compound thus obtained was then subjected to the aforesaid second step of Example 1.

Example 4

Comparative 3

[0162] Like Example 1 with additionally, after the second step, a further step in which the elastomeric compound obtained in the second step was cooled to ambient temperature (23° C.) and was subsequently fed to the aforesaid intermeshing and co-rotating twin-screw mixer Maris TM92HT. A further mixing was executed, without adding any further component, operating at the following work conditions: [0163] feeding speed: 200 kg/h; [0164] speed of the double screw: 100 revolutions per minute; [0165] temperature profile: 40-50-60-50-20-10-10-10° C. [0166] specific energy: 0.3 kWh/kg [0167] temperature of elastomeric compound measured at the outlet of the mixer: 125° C.

Example 5

Invention 1

[0168] First Step

[0169] All the components listed in Table 1, with the addition of 4 phr of liquid reinforcement phenol resin (CELLOBOND J 3111 L, Momentive Specialty Chemicals UK Limited), were mixed together in a Banbury® mixer (model F270), operating at the following work conditions: [0170] mixing time: 270 seconds; [0171] fill factor: 70%; [0172] rotor speed: 60 revolutions per minute; [0173] unloading temperature: 160° C.

[0174] Intermediate Step

[0175] The elastomeric compound obtained in accordance with the first step was cooled at ambient temperature (23° C.) and subsequently fed to the aforesaid continuous mixer Maris TM92HT, together with further 14 phr of solid reinforcement phenol resin (DUREZ 12686, Sumitomo Bakelite Europe), continuously fed.

[0176] The continuous mixer operated at the following work conditions: [0177] feeding speed: 200 kg/h; [0178] speed of the double screw: 100 revolutions per minute; [0179] temperature profile: (°C.): 40-50-60-50-20-10-10-10 [0180] specific energy: 0.3 kWh/kg [0181] temperature of elastomeric compound measured at the outlet of the mixer: 125° C.

[0182] The intermediate elastomeric compound unloaded from the continuous twin-screw mixer was subsequently cooled at ambient temperature (23° C.) and then subjected to the aforesaid second step of Example 1 in the second batch mixer in order to obtain a final elastomeric compound according to the present invention.

Example 6

Invention 2

[0183] First Step

[0184] All the components listed in Table 1, without any reinforcement resin, were mixed together in a Banbury® mixer (model F270), operating at the following work conditions: [0185] mixing time: 270 seconds; [0186] fill factor: 70%; [0187] rotor speed: 60 revolutions per minute; [0188] unloading temperature: 160° C.

[0189] Intermediate Step

[0190] The elastomeric compound obtained in accordance with the first step was cooled at ambient temperature (23° C.) and subsequently continuously fed to the aforesaid continuous mixer Maris TM92HT, together with further 17 phr of only solid reinforcement phenol resin (DUREZ 12686, Sumitomo Bakelite Europe)), continuously fed.

[0191] The continuous mixer operating at the following work conditions: [0192] feeding speed: 200 kg/h; [0193] speed of the double screw: 120 revolutions per minute; [0194] temperature profile: (° C.): 40-50-60-50-20-10-10-10 [0195] specific energy: 0.3 kWh/kg [0196] temperature of elastomeric compound measured at the outlet of the mixer: 125° C.

[0197] The intermediate elastomeric compound unloaded from the continuous twin-screw mixer was subsequently cooled at ambient temperature (23° C.) and then subjected to the aforesaid second step of Example 1 in the second batch mixer in order to obtain a final elastomeric compound according to the present invention.

EXAMPLES 7-8

[0198] Preparation of the Elastomeric Compounds

[0199] Tables 1 a and 2a report the recipe of the components mixed in the batch mixer in the first step and in the second step, respectively, for both examples 7 and 8.

TABLE-US-00003 TABLE 1a COMPONENT phr IR high synthetic rubber cis-1,4-polyisoprene, SKI-3, 100 Nizhnekamsk Mineral oil, MES (Mild Extraction Solvate), ENI SPA 3 Carbon black, N375, Cabot 75 Sepiolite, Pangel B5, Tolsa Group: sepiolite modified 13 with quaternary ammonium salt of about 20% by weight, fibres of length comprised between 0.2 μm and 2 μm and diameter comprised between 5 nm and 30 nm (13 phr of Pangel B5 corresponds to about 10 phr of mineral filler) Stearic acid, Sogis 2 Zinc oxide, Zincol Ossidi 8 Bonding octylphenol resin, SP1068, Si Group 2

TABLE-US-00004 TABLE 2a COMPONENT phr 50% Silane TESPT (bis[3- 4 (triethoxysilyl)propyl]tetrasulfide) supported on carbon black, X 50-S, Evonik Industries 65% HMMM hexamethoxymethylmelamine (65%) 8 on inert carrier, Cyrez 964 P.C., Cytec CTP cyclohexylthiophthalimide, Vulkalent G, 0.3 Lanxess TBBS:N-tert-butyl-2-benzothiazylsulfenamide, 1.5 Vulkacit ® NZ/EG C, Lanxess; Sulfur, Redball Superfine, International Sulphur 5.3 Inc.

Example 7

Reference 2

[0200] First Step

[0201] All the components listed in Table 1 a, with the addition of 15 phr overall of solid reinforcement phenol resin (DUREZ 12686, Sumitomo Bakelite Europe), were mixed together in a Banbury® mixer (model F270).

[0202] Second Step

[0203] The elastomeric compound obtained in the first step, cooled at ambient temperature (23° C.), along with all the components of Table 2a, were fed into a Banbury® mixer (model F270) and a further mixing was executed.

[0204] The elastomeric compound unloaded from the mixer Banbury® was subsequently cooled at ambient temperature (23° C.).

Example 8

Invention 3

[0205] First Step

[0206] All the components listed in Table 1 a, without any reinforcement resin, were mixed together in a Banbury® mixer (model F270).

[0207] Intermediate Step

[0208] The elastomeric compound obtained in accordance with the first step was cooled at ambient temperature (23° C.) and subsequently continuously fed to the aforesaid continuous mixer Maris TM92HT, together with 15 phr of only solid reinforcement phenol resin (DUREZ 12686, Sumitomo Bakelite Europe), continuously fed.

[0209] The continuous mixer operating at the following work conditions: [0210] feeding speed: 200Kg/h; [0211] speed of the double screw: 100 revolutions per minute; [0212] temperature profile (° C.): 40-50-60-50-20-10-10-10 (° C.) [0213] specific energy: 0.27 kWh/kg [0214] temperature of the elastomeric compound measured at the outlet of the mixer: 120° C.;

[0215] Second Step

[0216] The intermediate elastomeric compound unloaded from the continuous mixer was subsequently cooled at ambient temperature (23° C.) and then subjected to the second step in the second batch mixer, like in Example 7, in order to obtain a final elastomeric compound according to the present invention.

[0217] All the elastomeric compounds obtained in the Examples were tested in order to evaluate the following properties: Mooney (ML 1+4) viscosity, dynamic mechanical properties: the obtained results were given in the Tables 3 and 4 in arbitrary units and relative to the value obtained for the reference sample.

[0218] Mooney Viscosity

[0219] The Mooney ML(1+4) viscosity at 100° C. was measured, according to the standard ISO 289-1: 2005, on the non-cross-linked elastomeric compounds obtained as described above.

[0220] Mechanical Properties

[0221] Tables 3 and 4 also show the dynamic mechanical properties, measured by using a dynamic Instron device in the traction-compression mode, according to the following methods. A test sample of cross-linked elastomeric compounds (vulcanised at 170° C., for 10 min.), having cylindrical form (length=25 mm, diameter=14 mm) compression preloaded up to 10% longitudinal deformation with respect to the initial length, and held at the predetermined temperature (23° C. and 70° C.) for the entire duration of the test, was subjected to sinusoidal dynamic stress having an amplitude of ±3.5% with respect to the length under preload, with a frequency of 10 Hz. The dynamic mechanical properties are expressed in terms of dynamic elastic modulus (E′) and Tan delta (loss factor) values. The value of

[0222] Tan delta is calculated as a ratio between the viscous modulus (E″) and the elastic modulus (E′).

TABLE-US-00005 TABLE 3 Mooney Tan Tan Viscosity E′ delta E′ delta EXAMPLE (ML 1 + 4) (23° C.) (23° C.) (70° C.) (70° C.) Example 1 100 100 100 100 100 (Reference 1) Example 2 96 100 100 103  99 (Comparative 1) Example 3 90 98 100 NA NA (Comparative 2) Example 4 88 99 102  95 103 (Comparative 3) Example 5 86 116 101 118 103 (Invention 1) Example 6 84 121 103 125 105 (Invention 2)

TABLE-US-00006 TABLE 4 Mooney Tan Tan Viscosity E′ delta E′ delta EXAMPLE (ML 1 + 4) (23° C.) (23° C.) (70° C.) (70° C.) Example 7 100 100 100 100 100 (Reference 2) Example 8 94 115 103 110 101 (Invention 3)

[0223] The data reported in the above Tables 3 and 4 shows that the elastomeric compounds obtained in accordance with the present invention (Examples 5, 6 and 8), in which at least a substantial part of the content of reinforcement resin is incorporated in an intermediate step of continuous mixing, have both an improved viscosity for the purpose of workability and, after cross-linking, an improved rigidity at all temperatures, with respect to all the other compounds (Examples 1-4 and 7) made with alternative techniques.

[0224] In particular, the use of only solid reinforcement resin, at least a substantial part of the content thereof incorporated in the continuous mixer, is particularly advantageous in terms of characteristics of the resulting compound and of the corresponding cross-linked material.

[0225] Even if the invention has been exemplified with regard to the achievement of a bead structure of a tyre, this allows attaining the described results also with other particularly rigid components of the tyre, such as the coating (or rubber-coating) of the annular anchoring structures, the anti-abrasive strip or the sidewall insert for self-supporting tyres.