High-performance tyre

Abstract

An iso-styrene:diene-terminated copolymer is described which includes (i) a polymeric block of styrene and/or substituted styrene consisting of a sequence of styrene and/or substituted styrene in isotactic configuration, and (ii) a terminal polymeric block consisting of a sequence of one or more dienic monomers.

Claims

1. A iso-styrene:diene-terminated copolymer, wherein said copolymer consists in (i) a polymeric block of at least one of styrene and substituted styrene consisting of a sequence of the at least one of styrene and substituted styrene in isotactic configuration, and (ii) a terminal polymeric block consisting of a sequence of three or more dienic monomers selected from the group comprising isoprene, 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, cyclopentadiene, 1-vinyl-cyclopentene, 2-vinyl-cyclohexene, 4-vinyl-cyclohexene, and mixtures thereof.

2. A copolymer according to claim 1, wherein said dienic monomer is selected from the group comprising isoprene, 1,4-hexadiene, cyclopentadiene, and mixtures thereof.

3. A iso-styrene:diene-terminated copolymer according to claim 1, wherein said substituted styrene is represented by the formula SR, wherein S is a styrene residue and R can be a linear or branched alkyl radical containing from 1 to 20 carbon atoms, a linear or branched alkenyl substituent containing from 2 to 20 carbon atoms, an aryl, even condensed, or alkylaryl substituent containing from 6 to 30 carbon atoms, a halogen or a radical containing one or more silicon atoms.

4. A copolymer according to claim 3, wherein said substituted styrene is selected from the group consisting of p-methylstyrene, o-methylstyrene, p-isopropylstyrene, p-terbutylstyrene, alpha and beta vinylnaphthalene, p-fluorostyrene, p-chlorostyrene, and p-trimethylsilylstyrene.

5. A copolymerization process of at least one of styrene and substituted styrene with one or more dienic monomers comprising (i) to prepare a solution of said one or more dienic monomers in a suitable solvent, (ii) to add to said solution a homogeneous catalytic system, and (iii) to add to said solution said at least one of styrene and substituted styrene, wherein said homogeneous catalytic system comprises a homogeneous catalyst having the following formula (I), ##STR00004## wherein Tr is a transition metal, X and X, equal or different each other, are a halogen atom, R1 and R2, equal or different each other, are a H atom or a linear or branched alkyl group having from 1 to 10 carbon atoms, R3 to R6, equal or different each other, are a H atom or a linear or branched alkyl group having from 1 to 10 carbon atoms, or a linear or branched arylalkyl group having from 7 to 14 carbon atoms, R4 and R6 are linked to the benzene ring in ortho position with respect to the D and D substituent, and R4 and R6 are represented by a linear or branched arylalkyl group having from 7 to 14 carbon atoms, and R3 and R5 are linked to the benzene ring in para position with respect to the D and D substituent, and R3 and R5 are represented by a hydrogen atom or a linear or branched alkyl group having from 1 to 10 carbon atoms, Y and Y, equal or different each other, are an oxygen, sulphur, selenium or tellurium atom, or a NR7 or PR7 group, D and D, equal or different each other, are an oxygen, sulphur, selenium or tellurium atom, or a NR7 or PR7 group, R7 is a H atom or a linear or branched alkyl group having from 1 to 10 carbon atoms, n is an integer from 1 to 10, and wherein said copolymerization process provides the formation of a iso-styrene:diene-terminated copolymer according to claim 1.

6. The copolymerization process according to claim 5, wherein said homogeneous catalyst is represented by the following formula (1): ##STR00005##

Description

DRAWINGS

(1) FIG. 1 shows a view in cross section of a portion of a tyre.

DETAILED DESCRIPTION OF THE INVENTION

(2) The present invention shall be illustrated in further detail by means of an illustrative embodiment with reference to the attached FIG. 1.

(3) a indicates an axial direction and r indicates a radial direction. For simplicity, FIG. 1 shows only part of the tyre, the remaining part not shown being identical and arranged symmetrically with respect to the radial direction r.

(4) The reference number 1 in FIG. 1 indicates a tyre for vehicle wheels, which generally comprises a carcass structure 2 comprising at least one carcass ply 3 having respectively opposite end strips secured to respective annular anchoring structures 4, optionally associated with the elastomeric fillers 4a, Incorporated into the zones 5 usually identified by the name beads.

(5) The carcass structure 2 is associated with a belt structure 6 comprising one or more belt layers 6a, 6b located in radial superpositions relative to each other and relative to the carcass ply 3, having reinforcing cords that are typically metallic. These reinforcing cords may have a crossed orientation relative to a circumferential direction of the tyre 1. The term circumferential direction means a direction generically given according to the direction of rotation of the tyre, or at least slightly inclined relative to the direction of rotation of the tyre.

(6) A tread band 7 made of elastomeric mixture is applied in a radially outer position with respect to the belt structure 6, as are other constituent semi-finished parts of the tyre 1.

(7) Respective side walls 8 made of elastomeric mixture are also applied in axially outer position on the side surfaces of the carcass structure 2, each extending from one of the side edges of the tread band 7 up to the respective annular structure for anchoring to the beads 5.

(8) A radially inner surface of the tyre 1 is also preferably internally lined with a layer of elastomeric material that is substantially impermeable to air, referred to as the liner 9.

(9) The belt structure 6 also comprises at least one reinforcing layer 6c that is radially outer with respect to the belt layers 6a, 6b. The radially outer reinforcing layer 6c comprises textile or metal cords, arranged at a substantially zero angle relative to the circumferential direction of the tyre and immersed in the elastomeric material. Preferably, the cords are arranged substantially parallel and side by side to form a plurality of coils. These coils are substantially oriented in the circumferential direction (typically with an angle of between 0 and 5), this direction usually being said zero degrees with reference to its position relative to the equatorial plane X-X of the tyre. The term equatorial plane of the tyre means a plane perpendicular to the axis of rotation of the tyre and which subdivides the tyre into two symmetrically equal parts.

(10) Preferably, but not exclusively, the tyre 1 for motor vehicles is of the HP (High Performance) or UHP (Ultra-High-Performance) type, i.e. it is a tyre that is capable of withstanding maximum speeds of at least 190 km/h, up to over 300 km/h. Examples of such tyres are those belonging to the classes T, U, H, V, ZR, W, Y.

(11) The manufacture of the tyre 1 as described above is performed by assembling respective semi-finished parts on a moulding drum, not shown, performed by at least one assembling device.

(12) At least a part of the components intended to form the carcass structure 2 of the tyre 1 is constructed and/or assembled on the moulding drum. More particularly, the moulding drum serves to receive first the optional liner 9, and then the carcass ply 3. Next, devices, not shown, engage coaxially around each of the end strips one of the annular anchoring structures 4, position an outer sleeve comprising the belt structure 6 and the tread band 7 in a coaxially centred position around the cylindrical carcass sleeve and conform the carcass sleeve in a toroidal configuration by radial dilation of the carcass ply 3, so as to apply it against a radially internal surface of the outer sleeve.

(13) Following the manufacture of the raw tyre 1, a pressing and vulcanization treatment is performed, aimed at establishing structural stabilization of the tyre 1 by crosslinking of the elastomeric mixtures and also to imprint on the tread band 7 a desired tread pattern and to imprint on the side walls 8 optional distinctive graphic signs.

(14) The present invention shall be further illustrated hereinbelow by means of a certain number of preparative examples, which are given for purely indicative purposes and without any limitation of the present invention.

EXAMPLES

Example 1Synthesis of (Isostyrene/Trans-Butadiene) with 72.8% by Weight of Styrene Free of Polyisoprene End Groups (Polymer S1)

(15) 50 ml of toluene, styrene (9.06 g; 0.087 mol), butadiene (3.1 g; 0.058 mol; 3 M solution in toluene) and MAO (0.0058 mol; 8 ml; 10 wt % solution in toluene) were placed in a 500 ml round-bottomed flask equipped with a magnetic stirrer, under an inert atmosphere. After bringing the solution to the reaction temperature (T=25 C.), the polymerization was initiated by adding the catalyst of formula 1 described previously (0.006 g; 58 mol), dissolved in 1 ml of toluene. The reaction mixture was left stirring for 24 hours.

(16) The polymerization was stopped by pouring the contents of the round-bottomed flask into ethanol acidified with HCl and 2,6-di-tert-butyl-4-methylphenol (BHT) as antioxidant.

(17) The coagulated polymer was washed with ethanol, filtered and dried in a vacuum oven at 30-40 C. The yield was 90%. The resulting polymer had a molecular weight of about 329 000 Da with a polydispersity index equal to about 1.8 and a Tg of about 2 C.

Example 2Synthesis of Iso-Styrene:Isoprene-Terminated with 99.8% by Weight of Styrene and 0.2% by Weight of Terminal Isoprene (Polymer S2)

(18) 50 ml of toluene, isoprene (0.59 g; 0.0087 mol) and MAO (0.0058 mol; 8 ml; solution at 10 wt % in toluene) were placed in a 500 ml round-bottomed flask equipped with a magnetic stirrer, under an inert atmosphere. After bringing the solution to the reaction temperature (T=25 C.), the polymerization was initiated by adding the catalyst of formula 1 (0.006 g; 58 mol), dissolved in 2 ml of toluene. The reaction mixture was left stirring for 2 hours. Next, styrene (7.7 g; 0.074 mol) was added to the reaction mixture, which was left stirring for a further 24 hours.

(19) The polymerization is stopped by pouring the contents of the round-bottomed flask into ethanol acidified with HCl and 2,6-di-tert-butyl-4-methylphenol (BHT) as antioxidant.

(20) The coagulated polymer was washed with ethanol, filtered and dried in a vacuum oven at 30-40 C. The yield was 80%. The resulting polymer had a molecular weight of about 922 000 Da with a polydispersity index equal to about 1.5 and a Tg of about 90 C.

Example 3Synthesis of Isoprene-Terminated Iso-Styrene-Co-Para-Methylstyrene Polymer with 99.8% by Weight of Styrene Including 5% of Para-Methylstyrene and 0.2% by Weight of Terminal Isoprene (Polymer S3)

(21) 70 ml of toluene, 1.66 g (24 mmol) of isoprene, 0.7 g of MAO (toluene solution at 10% by weight, equal to 12 mmol) and finally 6 mg of catalyst of formula 1 (0.01 mmol) dissolved in 2 ml of toluene were placed in a 100 ml round-bottomed flask equipped with a magnetic stirrer, under an inert atmosphere. The reaction was left stirring at room temperature for 2.5 hours. A mixture of 25.4 g of styrene and 2.51 g of p-methylstyrene was then added. The reaction mixture was left stirring at room temperature for 24 hours. The reaction was stopped with ethanol and the polymer was coagulated in ethanol acidified with HCl also containing hydroquinone as antioxidant. After washing with fresh ethanol, the polymer was recovered and dried under vacuum at 40 C.

(22) The resulting polymer had a molecular weight of about 1 060 000 Da with a Tg of about 98.5 C. evaluated by DSC at 10 C./min.

Example 4Preparation of the Elastomeric Compositions (5 phr)

(23) The elastomeric compositions illustrated in Table 1 below were prepared using a styrene-indene resin (Novares TT90, Ruetgers GmbH), a thermoplastic ottylphenolic resin (SP1068, Si Group) and the polymers S1-S2 having the characteristics described above. Composition R1, used as first reference, is free of additives. Composition R2, used as second reference, comprises 5 phr of polymer S1, free of terminal isoprene. The composition used in the tread of a tyre according to the invention 11 comprises 5 phr of polymer S2. The comparative compositions C1 and C2 comprise 5 phr of thermoplastic ottylphenolic resin and styrene-indene resin, respectively.

(24) All the components, with the exception of the vulcanizing agents and accelerators were mixed together for about 5 minutes in a 50 ml Brabender closed mixer, the rotors being maintained at a spin speed of 60 rpm and the temperature being maintained at about 145 C. (first phase). At the end, the elastomeric composition was discharged and left to stand for a few hours at room temperature. The vulcanizing agents and accelerators were then added and mixing was again performed in a 50 ml Brabender closed mixer, the rotors being maintained at a spin speed of about 30 rpm and the temperature being maintained at about 50 C. (second phase). Finally, the elastomeric composition was vulcanized in suitable moulds with a steam press at a temperature of 170 C. for 10 minutes.

(25) All the quantities in Table 1 are expressed in phr.

(26) TABLE-US-00001 TABLE 1 Mixtures R1 R2 I1 C1 C2 S-SBR HP2 110 110 110 110 110 NR 20 20 20 20 20 Corax HP160 4 4 4 4 4 S1 5 S2 5 SP1068 5 Novares TT90 5 Zeosil 1165 50 50 50 50 50 TESPT 4 4 4 4 4 Stearic acid 2 2 2 2 2 ZnO 2.5 2.5 2.5 2.5 2.5 6PPD 2 2 2 2 2 CBS 1.8 1.8 1.8 1.8 1.8 Sulfur 1.5 1.5 1.5 1.5 1.5 S-SBR HP2: solution of styrene-butadiene rubber in TDAE oil, comprising 25% by weight of styrene and 37.5% by weight of oil, produced by Lanxess Deutschland GmbH, Germany NR: natural rubber SIR 20 Corax HP160: carbon black with a high specific surface area produced by Evonik Degussa GmbH, Germany Novares TT90: styrene-indene resin produced by Reutgers Germany GmbH, Germany Zeosil 1165: precipitated silica with a BET surface area equal to about 165 m.sup.2/g (Rhne-Poulenc) TESPT: bis(3-triethoxysilylpropyl) tetrasulfide (Degussa-Hls); 6PPD (antioxidant): N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine CBS (accelerator): N-(cyclohexyl-2-benzothiazylsulfenamide, produced by Lanxess Deutschland GmbH, Germany

Example 5Characterization of the Elastomeric Compositions

(27) The characteristics of each elastomeric composition were evaluated as described below and the results are collated in Table 2 below.

(28) The static mechanical properties (load at 10%, 50%, 100% and 300% of elongation, referred to respectively as CA01, CA05, CA1, CA3, tensile strength and elongation at break) were measured according to the standard ISO 37:2005, on samples of the previously described elastomeric compositions crosslinked at 170 C. for 10 minutes.

(29) The dynamic mechanical properties were measured with a dynamic tensile testing machine of servo-hydraulic type in traction-compression mode according to the following methods. A sample of the crosslinked (at 170 C., for 10 minutes) elastomeric composition of cylindrical form (length=25 mm; diameter=12 mm), pre-compression loaded up to 25% of longitudinal deformation relative to the initial length, and maintained at the preset temperature (100 C.) throughout the test, was subjected to a dynamic sinusoidal elongation having an amplitude of 3.5% relative to the length under preloaded conditions, with a frequency of 100 Hz. The dynamic mechanical properties are expressed in terms of the dynamic elastic modulus (E) and loss factor values (Tan ). The Tan value is calculated in the present case as the ratio between the viscous modulus (E) and the elastic modulus (E).

(30) TABLE-US-00002 TABLE 2 REFERENCE ELASTOMERIC COMPOSITION PARAMETERS R1 R2 I1 C1 C2 STATIC MECHANICAL PROPERTIES CA01 [MPa] 0.27 0.32 0.37 0.32 0.28 CA05 [MPa] 0.7 0.85 0.90 0.79 0.7 CA1 [MPa] 1.3 1.57 1.5 1.31 1.17 CA3 [MPa] 6.99 7.56 6.15 3.09 5.49 Tensile strength 15.2 12.73 16.44 17.42 18.67 [MPa] Elongation at 495.39 446.17 576.80 605.02 650.24 break [%] Energy [J/cm.sup.3] 29.8 23.78 38.75 43.04 46.54 DYNAMIC MECHANICAL PROPERTIES E (0 C.) at 6.481 9.788 8.579 10.259 10.058 100 Hz [MPa] E (23 C.) at 4.017 5.141 4.75 5.325 4.833 100 Hz [MPa] E (70 C.) at 2.855 3.511 3.481 3.561 3.305 100 Hz [MPa] E (100 C.) at 2.811 3.298 3.227 3.448 3.184 100 Hz [MPa] E (0 C.-100C.) 3.670 6.490 5.352 6.811 6.874 at 100 Hz [MPa] Tan (0 C.) at 0.717 0.81 0.846 0.871 0.915 100 Hz Tan (23 C.) at 0.332 0.346 0.355 0.357 0.371 100 Hz Tan (70 C.) at 0.085 0.112 0.14 0.112 0.115 100 Hz Tan (100C.) at 0.067 0.087 0.078 0.086 0.092 100 Hz

(31) According to the Applicant's experience, the parameters that best predict the road behaviour of a tyre are the dynamic-mechanical properties of the elastomeric compositions, in particular the elastic modulus or storage modulus (E), the viscous modulus or dissipative modulus (E) and the ratio between the viscous modulus and the elastic modulus, known as the tangent delta (Tan ), which is an indicator of the hysteretic behaviour of the elastomeric material, and the static-mechanical properties of the elastomeric compositions, in particular the load at various levels of elongation, the tensile strength and the percentage of elongation at break.

(32) As regards the dynamic-mechanical properties, the Applicant considers that a high Tan value at low temperatures (about 0 C.) ensures good road holding on wet ground, whereas a high Tan value at high temperatures (about 100 C.) ensures good road holding when the tyre is used under particularly extreme driving conditions. In addition, to have a low driving resistance of the motor vehicle, i.e. to have a low rolling resistance, and consequently low fuel consumption, the Tan value in the temperature range between 23 C. and 70 C. should be as low as possible. Finally, the elastic modulus (E) undergoes an inevitable reduction in value due to the temperature effects, but the variation should be as limited as possible, so that at low temperature values (typically at 0 C.) the value should not be excessively high, whereas at high temperatures, the value should be as high as possible.

(33) As regards the static-mechanical properties, the Applicant considers that high load values at various levels of elongation and at break give good resistance to laceration and reduction of abrasion. At the same time, to maintain good rigidity, the elongation at break value should not be too high.

(34) The results of Table 2 showed that the elastomeric composition I1 comprising the copolymer as described above had on the whole better mechanical properties, both static and dynamic, relative to the reference elastomeric compositions R1 and R2 and to the comparative elastomeric compositions C1 and C2.

(35) In point of fact, as regards the static mechanical properties, the elastomeric composition I1 showed high load values at each level of elongation (CA01, CA05, CA1, CA3), comparable with and even better than those obtained with the reference compositions R1 and R2, and decidedly better than those obtained with compositions C1 and C2, in which the addition of the resins brings about a drastic drop in the values.

(36) At the same time, the tensile strength and the elongation at break showed optimum values, with a significant improvement relative to the values obtained with the reference compositions R1 and R2, and comparable to those obtained with compositions C1 and C2.

(37) The surprising result of I1 may give a tyre comprising a tread made with such compositions good resistance to laceration, accompanied by good rigidity and less abrasion, with consequent improved durability of the tyre.

(38) On the other hand, as regards the dynamic mechanical properties, the elastomeric composition I1 showed overall elastic modulus (E) values that were higher than the value for the reference R1, but above all composition I1 showed a relatively low E value at 0 C. relative to the value obtained at 100 C., thus obtaining a surprisingly low E(0-100) value.

(39) In addition, the elastomeric composition I1 surprisingly showed high Tan values at high temperatures (100 C.), higher than those obtained by R1 and comparable to those obtained with C1 and C2, and at the same time optimum Tan values in the temperature range between 23 C. and 70 C., comparable to those for R1 and R2.

(40) The surprising result of I1, which is all the more surprising since it is obtained with polymer virtually completely constituted of styrene with a very high Tg (+90 C.), may give a tyre comprising a tread made with such a composition consistent behaviour and optimum road holding both under driving conditions on wet asphalt and under extreme driving conditions at a high speed on dry asphalt, simultaneously giving the tyre low rolling resistance, and consequently low fuel consumption.

Example 6Preparation of the Elastomeric Compositions (10 phr)

(41) The elastomeric compositions illustrated in Table 3 below were prepared using a styrene-indene resin (Novares TT90, Ruetgers GmbH), a thermoplastic ottylphenolic resin (SP1068, Si Group) and the polymer S3 having the characteristics described above. Composition I2 of the invention comprises 10 phr of polymer S3. The comparative compositions C3 and C4 comprise 10 phr of thermoplastic ottylphenolic resin and styrene-indene resin, respectively.

(42) All the components, except for the vulcanizing agents and accelerators, were mixed together for about 5 minutes in a 50 ml Brabender closed mixer, the rotors being maintained at a spin speed of 60 rpm and the temperature at about 145 C. (first phase). At the end, the elastomeric composition was discharged and left to stand for a few hours at room temperature. The vulcanizing agents and accelerators were then added and mixing was again performed in a 50 ml Brabender closed mixer, the rotors being maintained at a spin speed of about 30 rpm and the temperature at about 50 C. (second phase). Finally, the elastomeric composition was vulcanized in suitable moulds using a steam press at a temperature of 170 C. for 10 minutes.

(43) All the quantities in Table 3 are expressed in phr.

(44) TABLE-US-00003 TABLE 3 Mixtures C3 C4 I2 S-SBR HP2 110 110 110 NR 20 20 20 Corax HP160 4 4 4 S3 10 SP1068 10 Novares TT90 10 Zeosil 1165 50 50 50 TESPT 4 4 4 Stearic acid 2 2 2 ZnO 2.5 2.5 2.5 6PPD 2 2 2 CBS 1.8 1.8 1.8 Sulfur 1.5 1.5 1.5

Example 7Characterization of the Elastomeric Compositions

(45) The characteristics of each elastomeric composition were evaluated as described in Example 5 and the results are collated in Table 4 below.

(46) TABLE-US-00004 TABLE 4 ELASTOMERIC COMPOSITION REFERENCE PARAMETERS C3 C4 I2 STATIC MECHANICAL PROPERTIES 10% Modulus (CA0, 1) [MPa] 0.32 0.3 0.45 50% Modulus (CA0, 5) [MPa] 0.78 0.69 1.16 100% Modulus (CA1) [MPa] 1.3 1.1 2 300% Modulus (CA3) [MPa] 5.6 5.09 6.51 Tensile strength [MPa] 13.14 18.26 15.21 Elongation at break [%] 540 667 539 Energy [J/cm.sup.3] 29.3 49.03 34.13 DYNAMIC MECHANICAL PROPERTIES E (0 C.) at 100 Hz [MPa] 9.678 9.637 9.655 E (23 C.) at 100 Hz [MPa] 3.813 3.805 5.27 E (70 C.) at 100 Hz [MPa] 2.581 2.483 3.794 E (100 C.) at 100 Hz [MPa] 2.5 2.359 3.547 E (0 C.-100 C.) at 100 Hz 7.08 7.28 6.108 [MPa] Tan (0 C.) at 100 Hz 1.06 1.01 0.8 Tan (23 C.) at 100 Hz 0.394 0.406 0.302 Tan (70 C.) at 100 Hz 0.21 0.141 0.125 Tan (100 C.) at 100 Hz 0.104 0.12 0.116

(47) The results of Table 4 demonstrated that the elastomeric composition I2 comprising 10 phr of copolymer S3 as described above had on the whole better mechanical properties, both static and dynamic, relative to the comparative elastomeric compositions C3 and C4, confirming the results obtained for the elastomeric composition I1 comprising 5 phr of polymer S2.

(48) In point of fact, as regards the static mechanical properties, the elastomeric composition I2 also showed high load values at each level of elongation (CA01, CA05, CA1, CA3), which were decidedly better than those obtained with compositions C3 and C4, in which the addition of the resin brought about a drastic drop in the values. At the same time, the tensile strength and the elongation at break showed optimum values, comparable to those obtained with compositions C3 and C4.

(49) On the other hand, as regards the dynamic mechanical properties, the elastomeric composition I2 also showed high elastic modulus (E) values, above all at 100 C. compared with 0 C., thus obtaining a surprisingly low E(0-100) value, and high Tan values at high temperatures (100 C.), accompanied by optimum Tan values in the temperature range between 23 C. and 70 C.

(50) All the characteristics that may give a tyre comprising a tread made with such a composition were thus confirmed also for the elastomeric composition I2: on the one hand good resistance to laceration, accompanied by good rigidity and less abrasion, with consequently improved durability of the tyre, and on the other hand consistency of the behaviour and optimum road holding both under driving conditions on wet asphalt and under extreme driving conditions at high speed on dry asphalt, simultaneously giving the tyre low rolling resistance, and consequently low fuel consumption.