Tire for vehicle wheels

Abstract

The present invention relates to a tire (100) for vehicle wheels comprising a tire component comprising a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition, wherein said elastomeric composition comprises a polymer blend comprising (a) 50 to 95 percent by weight of a first elastomeric polymer and (b) 5 to 50 percent by weight of a second elastomeric polymer based on the total weight of the polymer blend. The second elastomeric polymer (b) is obtainable by (i) anionic polymerization of at least one conjugated diene monomer and one or more a-olefin monomer(s) in the presence of a polymerization initiator in an organic solvent, and (ii) coupling the polymer chains obtained in (i) by a coupling agent. The second elastomeric polymer (b) has a weight-average molecular weight (Mw) in the range of 5,000-40,000 g/mol and a coupling rate of at least 50 percent by weight.

Claims

1. A tire for vehicle wheels comprising a tire component comprising a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition, wherein the elastomeric composition comprises a polymer blend comprising: (a) from 50 percent to 95 percent by weight of a first elastomeric polymer; and (b) from 5 percent to 50 percent by weight of a second elastomeric polymer; wherein the first elastomeric polymer (a) is obtainable by: (I) anionic polymerization of at least one conjugated diene monomer and one or more α-olefin monomer(s) in the presence of a polymerization initiator in an organic solvent; wherein the second elastomeric polymer (b) is obtainable by: (i) anionic polymerization of at least one conjugated diene monomer and one or more α-olefin monomer(s) in the presence of a polymerization initiator in an organic solvent, and (ii) coupling the polymer chains obtained in (i) by a coupling agent; wherein the first elastomeric polymer (a) has a weight-average molecular weight (Mw) ranging from 300,000 g/mol to 4,000,000 g/mol; wherein the second elastomeric polymer (b) has a weight-average molecular weight (Mw) ranging from 5,000 to g/mol 40,000 g/mol; wherein the at least one conjugated diene monomer of at least one of the first elastomeric polymer and the second elastomeric polymer is chosen from 1,3-butadiene, 2-alkyl-1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, 1,3-hexadiene, 1,3-heptadiene, 1,3-octadiene, 3-butyl-1,3-octadiene, 2-methyl-2,4-pentadiene, cyclopentadiene, 2,4-hexadiene, 2-phenyl-1,3-butadiene, 1,3-cyclooctadiene, and mixtures thereof; wherein the one or more α-olefin monomer of at least one of the first elastomeric polymer and the second elastomeric polymer is chosen from styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, alkyl, cycloalkyl, aryl, alkyl derivative, arylalkyl derivatives of styrene, and mixtures thereof; wherein the first elastomeric polymer (a) is a styrene-butadiene-copolymer and the second elastomeric polymer (b) is a styrene-butadiene-copolymer; wherein an α-olefin content of the first elastomeric polymer ranges from 10% to 50% by weight and the vinyl content of the diene fraction of the first elastomeric copolymers range from 10% to 70% by weight; wherein an α-olefin content of the second elastomeric polymer ranges from 5% to 50% by weight and the vinyl content of the diene fraction of the second elastomeric copolymers ranges from 30% to 75% by weight; wherein a coupling rate of the second elastomeric polymer (b) is at least 50 percent by weight; wherein amounts of components (a) and (b) are based on the total weight of the polymer blend; and a degree of branching of the second elastomeric polymer is between 2 and 4.

2. The tire for vehicle wheels according to claim 1, wherein the polymer blend comprises 10 to 50 percent by weight of the second elastomeric polymer (b) based on the total weight of the polymer blend.

3. The tire for vehicle wheels according to claim 1, wherein the second elastomeric polymer (b) has a weight-average molecular weight (Mw) ranging from 8,000 g/mol to 30,000 g/mol.

4. The tire for vehicle wheels according to claim 1, wherein the polymer blend further comprises (c) from 0 percent to 13 percent by weight of one or more extender oil(s).

5. The tire for vehicle wheels according to claim 1, wherein polymer chain ends of the first elastomeric polymer (a) obtainable in (I) are modified by addition and reaction of at least one compound of formula (1), or formula (12), as defined below:
(R***O).sub.x(R**).sub.ySi-A-S—SiR**.sub.3  formula (1), wherein each of R** is independently chosen from C.sub.1-C.sub.16 alkyl or alkylaryl; R*** is independently chosen from C.sub.1-C.sub.4 alkyl; A is chosen from C.sub.6-C.sub.18 aryl, C.sub.7-C.sub.50 alkylaryl, C.sub.1-C.sub.50 alkyl, and C.sub.2-C.sub.50 dialkylether; x is an integer chosen from 1, 2 and 3; y is an integer chosen from 0, 1 and 2; provided that x+y=3; ##STR00006## wherein R.sup.9e, R.sup.10e, R.sup.11e and R.sup.12e are each independently chosen from hydrogen, (C.sub.1-C.sub.16) alkyl, (C.sub.6-C.sub.16) aryl and (C.sub.7-C.sub.16) aralkyl.

6. The tire for vehicle wheels according to claim 5, wherein the compound represented by formula (1) is chosen from (MeO).sub.3Si—(CH.sub.2).sub.3—S—SiMe.sub.2C(Me).sub.3, (MeO).sub.2(Me)Si—(CH.sub.2).sub.3—S-SiEt.sub.3, (MeO).sub.2(Me)Si—(CH.sub.2).sub.3—S—Si(tBu).sub.3, (MeO).sub.2(Me)Si—(CH.sub.2).sub.3—S—Si(Bn).sub.3 or (MeO).sub.2(Me)Si—(CH.sub.2).sub.3—S—SiMe.sub.2C(Me), and mixtures thereof.

7. The tire for vehicle wheels according to claim 5, wherein the compound represented by formula (12) is N-methyl-2-pyrrolidone.

8. The tire for vehicle wheels according to claim 5, wherein R**, R***, or A may independently be substituted with one or more groups, chosen from C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.6-C.sub.12 aryl, C.sub.7-C.sub.16 alkylaryl, di(C.sub.1-C.sub.7 hydrocarbyl)amino, bis(tri(C.sub.1-C.sub.12 alkyl)silyl)amino, tris(C.sub.1-C.sub.7 hydrocarbyl)silyl and C.sub.1-C.sub.12 thioalkyl.

9. The tire for vehicle wheels according to claim 5, wherein R.sup.9e, R.sup.10e, R.sup.11e are hydrogen and R.sup.12e is methyl.

10. The tire for vehicle wheels according to claim 1, wherein polymer chain ends of the first elastomeric polymer (a) obtainable in (I) are modified by addition and reaction of at least one compound of formula (2), as defined below:
((R.sup.1O).sub.x2′(R.sup.2).sub.y2′Si—R.sup.3—S).sub.s2′M*(R.sup.4).sub.t2′(X*).sub.u2′  formula (2), wherein M* is silicon or tin; x2′ is an integer chosen from 1, 2 and 3; y2′ is an integer chosen from 0, 1, and 2; wherein x2′+y2′=3; s2′ is an integer chosen from 2, 3 and 4; t2′ is an integer chosen from 0, 1 and 2; u2′ is an integer chosen from 0, 1 and 2; wherein s2′+t2′+u2′=4; R.sup.1 is independently chosen from hydrogen and (C.sub.1-C.sub.6) alkyl; R.sup.2 is independently chosen from (C.sub.1-C.sub.16) alkyl, (C.sub.7-C.sub.16) alkylaryl and (C.sub.7-C.sub.16) arylalkyl; R.sup.3 is at least divalent and is independently chosen from (C.sub.1-C.sub.16) alkyl, (C.sub.8-C.sub.16) alkylarylalkyl, (C.sub.7-C.sub.16) arylalkyl and (C.sub.7-C.sub.16) alkylaryl, and each group may be substituted with one or more of the following groups: tertiary amine group, silyl group, (C.sub.7-C.sub.18) aralkyl group and (C.sub.6-C.sub.18) aryl group; R.sup.4 is independently chosen from (C.sub.1-C.sub.16) alkyl and (C.sub.7-C.sub.16) alkylaryl; X* is independently chosen from chloride, bromide and —OR.sup.5*; wherein R.sup.5* is chosen from (C.sub.1-C.sub.16) alkyl and (C.sub.7-C.sub.16) arylalkyl.

11. The tire for vehicle wheels according to claim 1, wherein the coupling agent is at least one compound of formula (16), formula (II) or formula (III), as defined below:
(R.sup.100).sub.a100(Z**).sub.Xb100  formula (16),
(R.sup.100O).sub.a100(Z**)X.sub.b100  formula (II),
(R.sup.100O).sub.b100(Z**)(R.sup.100).sub.a100  formula (III), wherein Z** is tin or silicon; X.sub.b100 is independently chosen from chlorine, bromine and iodine; R.sup.100 is independently chosen from (C.sub.1-C.sub.20) alkyl, (C.sub.3-C.sub.20) cycloalkyl, (C.sub.6-C.sub.16) aryl and (C.sub.7-C.sub.16) aralkyl; a100 is independently an integer ranging from 0 to 1 and b100 is independently an integer from 3 to 4, provided that a+b=4.

12. The tire for vehicle wheels according to claim 1, wherein the coupling agent is chosen from SiCl.sub.4, Si(OCH.sub.3).sub.4 and SnCl.sub.4.

13. The tire for vehicle wheels according to claim 1, wherein the polymerization initiator used in (i) is chosen from n-BuLi, sec-BuLi, and tert-BuLi.

14. The tire for vehicle wheels according to claim 1, wherein the polymerization initiator used in (I) is chosen from n-BuLi, sec-BuLi, tert-BuLi, Li—(CH.sub.2)(Me).sub.2Si—N—(C.sub.4H.sub.9).sub.2, Li—(CH.sub.2)(Me).sub.2Si—N—(C.sub.2H.sub.5).sub.2, a compound of formula (6) or formula (7), a Lewis base adduct thereof, and a mixture thereof; wherein the compound of formula (6) and formula (7) are: ##STR00007## wherein R.sup.3a is independently chosen from —N(R.sup.28)R.sup.29, C.sub.1-C.sub.18 alkyl, C.sub.6-C.sub.18 aryl and (C.sub.7-C.sub.18) aralkyl; R.sup.4a is independently chosen from —N(R.sup.30a)R.sup.31a, (C.sub.1-C.sub.18) alkyl, (C.sub.6-C.sub.18) aryl and (C.sub.7-C.sub.18) aralkyl; R.sup.5 and R.sup.6 are each independently chosen from hydrogen, C.sub.1-C.sub.18 alkyl, C.sub.6-C.sub.18 aryl and C.sub.7-C.sub.18 aralkyl; M.sup.2 is lithium; R.sup.12, R.sup.13, R.sup.14, R.sup.15, R.sup.16, R.sup.17, R.sup.18, R.sup.19, R.sup.20, R.sup.21, R.sup.22, R.sup.23, R.sup.24 and R.sup.25 are each independently chosen from hydrogen, C.sub.1-C.sub.18 alkyl, C.sub.6-C.sub.18 aryl and C.sub.7-C.sub.18 aralkyl; R.sup.26, R.sup.27, R.sup.28, R.sup.29, R.sup.30a and R.sup.31a are each independently chosen from C.sub.1-C.sub.18 alkyl, C.sub.6-C.sub.18 aryl and C.sub.7-C.sub.18 aralkyl; q is chosen from an integer of 1, 2, 3, 4 and 5; r is an integer chosen from 1, 2 and 3; and a1′ is an integer chosen from 0 or 1.

15. The tire for vehicle wheels according to claim 14, wherein a1′ is 1.

16. The tire for vehicle wheels according to claim 1, wherein the first elastomeric polymer (a) and the second elastomeric polymer (b) are random polymers, or the first elastomeric polymer (a) or the second elastomeric polymer (b) is a random polymer.

17. The tire for vehicle wheels according to claim 1, wherein the coupling rate of the second elastomeric polymer (b) is lower than 98% by weight.

18. The tire for vehicle wheels according to claim 1, wherein the crosslinkable elastomeric composition comprises from 20 phr to 80 phr of the polymer blend.

19. The tire for vehicle wheels according to claim 1, wherein the crosslinkable elastomeric composition comprises from 2 phr to 40 phr of the second elastomeric polymer (b).

20. The tire for vehicle wheels according to claim 1, wherein the tire component is chosen from sidewall, mini-sidewall, bead filling, antiabrasive strip, sub-layer arranged between a belt structure, and the tread band.

21. The tire for vehicle wheels according to claim 1, wherein the first elastomeric polymer (a) is obtainable by coupling of the polymer chains obtained in (I) by a coupling agent.

22. The tire for vehicle wheels according to claim 1, wherein the polymer chain ends of the second elastomeric polymer (b) obtained in (i) are modified by addition and reaction of at least one compound of formula (2), as defined below:
((R.sup.1O).sub.x2′(R.sup.2).sub.y2′Si—R.sup.3—S).sub.s2′M*(R.sup.4).sub.t2′(X*).sub.u2′  formula (2), wherein M* is silicon or tin; x2′ is an integer chosen from 1, 2 and 3; y2′ is an integer chosen from 0, 1, and 2; wherein x2′+y2′=3; s2′ is an integer chosen from 2, 3 and 4; t2′ is an integer chosen from 0, 1 and 2; u2′ is an integer chosen from 0, 1 and 2; wherein s2′+t2′+u2′=4; R.sup.1 is independently chosen from hydrogen and (C.sub.1-C.sub.6) alkyl; R.sup.2 is independently chosen from (C.sub.1-C.sub.16) alkyl, (C.sub.7-C.sub.16) alkylaryl and (C.sub.7-C.sub.16) arylalkyl; R.sup.3 is at least divalent and is independently chosen from (C.sub.1-C.sub.16) alkyl, (C.sub.8-C.sub.16) alkylarylalkyl, (C.sub.7-C.sub.16) arylalkyl and (C.sub.7-C.sub.16) alkylaryl, and each group may be substituted with one or more of the following groups: tertiary amine group, silyl group, (C.sub.7-C.sub.18) aralkyl group and (C.sub.6-C.sub.18) aryl group; R.sup.4 is independently chosen from (C.sub.1-C.sub.16) alkyl and (C.sub.7-C.sub.16) alkylaryl; X* is independently chosen from chloride, bromide and —OR.sup.5*; wherein R5* is chosen from (C.sub.1-C.sub.16) alkyl and (C.sub.7-C.sub.16) arylalkyl.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Additional features and advantages of the invention will be better apparent from the following description of a preferred embodiment of a tire according to the invention, made—for illustrating and non-limiting purposes—with reference to the attached drawing FIG. 1 which schematically shows in partial section a winter tire for vehicle wheels in accordance with the present invention.

DESCRIPTION OF A PREFERRED TYRE ACCORDING TO THE INVENTION

(2) Referring to FIG. 1, “a” denotes an axial direction and “x-x”, following an equatorial plane of the tire, denotes a radial direction. For simplicity, FIG. 1 merely shows a portion of the tire, the remaining portion not illustrated being identical and arranged symmetrically with respect to the radial direction “r”.

(3) In FIG. 1, reference numeral 100 denotes a tire, preferably a winter tire, for vehicle wheels according to a preferred embodiment of the invention and formed by a plurality of structural elements.

(4) The tire 100 comprises at least one carcass structure, comprising at least one carcass ply 101 having respectively opposite end flaps attached to respective annular anchoring structures 102, known as bead cores, optionally connected to a bead filling 104.

(5) The region of the tire comprising the bead core 102 and the filling 104 forms an annular reinforcement structure 103, the so-called bead, for anchoring the tire to a corresponding mounting rim, not shown.

(6) The carcass structure is usually radial, in other words, the reinforcement elements of the at least one carcass ply 101 are arranged on planes comprising the rotation axis of the tire and substantially perpendicular to the equatorial plane of the tire.

(7) Said reinforcement elements may be formed by textile strings, for example rayon, nylon, polyester (for example polyethylene naphthalate (PEN)) or by metal strings.

(8) Each annular reinforcement structure is connected to the carcass structure by folding back the opposite lateral edges of the at least one carcass ply 101 around the annular anchoring structure 102 so as to form the so-called folded-back portions of the carcass 101a as shown in FIG. 1.

(9) In one embodiment, the coupling between the carcass structure and the annular reinforcement ring may be provided by way of a second carcass ply (not shown in FIG. 1) applied at an axially external position with respect to the first carcass ply.

(10) Preferably, an antiabrasive strip 105 is arranged at an external position with respect to each annular reinforcement structure 103.

(11) Preferably, each antiabrasive strip 105 is arranged at least at an axially external position on the annular reinforcement structure 103, extending at least between the sidewall 108 and the radially lower portion on the annular reinforcement structure 103.

(12) Preferably, the antiabrasive strip 105 is arranged so as to enclose the annular reinforcement structure 103 along the axially internal, the axially external and the radially inner regions of the reinforcement structure 103 so as to be interposed between said structure and the wheel rim when the tire 100 is mounted thereon.

(13) A belt structure 106, comprising one or more belt layers, for example two layers 106a, 106b placed radially superposed with respect to one another and with respect to the carcass layer, is connected to the carcass structure.

(14) In a preferred embodiment, the belt layers 106a, 106b may comprise reinforcement strings made of metal.

(15) These reinforcement strings may have a crossed orientation with respect to a circumferential direction of progression of the tire 100.

(16) “Circumferential” direction refers herein to a direction generally extending along the rotation direction of the tire.

(17) At a radially external position with respect to the belt layers 106a, 106b, at least one zero-degree reinforcement layer 106c, commonly known as a “0° belt”, may be applied.

(18) The zero-degree reinforcement layer 106c generally incorporates a plurality of reinforcement cords, typically textile or metal cords, optionally combined with one another, oriented along a substantially circumferential direction, meaning with this term that the reinforcement cords form an angle of few degrees (for example an angle between approximately 0° and 6°) with respect to the equatorial plane of the tire.

(19) Preferably, the reinforcement cords are coated with an elastomeric material.

(20) A tread band 109 is applied at a radially external position on the belt structure 106.

(21) The tread band 109 comprises a crosslinked elastomeric composition obtained by vulcanising a crosslinkable elastomeric composition as disclosed herein.

(22) At a radially external position, the tread band 109 has a rolling surface 109a intended to come into contact with the ground.

(23) In a preferred embodiment, the tread band 109 comprises a plurality of grooves and blocks, not illustrated for the sake of simplicity, forming a suitable tread pattern intended to impart to the tire 100 the desired traction, road-holding and water draining characteristics.

(24) Respective sidewalls 108 of elastomeric material are further applied at an axially external position on the axially lateral faces of the carcass structure.

(25) More specifically, each sidewall 108 extend from one of the lateral edges of the tread 109 until in line with the respective reinforcement annular structure 103.

(26) A sub-layer 111 is arranged between the belt structure 106 and the tire tread 109.

(27) A strip formed of elastomeric material 110, commonly known as a “mini-sidewall”, may optionally be present in the joining region between the sidewalls 108 and the tread band 109, this mini-sidewall generally being obtained by co-extrusion with the tread band 109.

(28) The “mini-sidewall” 110 advantageously allows to improve 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.

(29) Typically, a rubber layer 112, generally known as “liner”, which provides the necessary impermeability towards the inflation air of the tire, may also be provided at a radially inner position with respect to the carcass ply 101.

(30) The annular tire reinforcement structure 103 may comprises a further protection layer, generally known by the term “chafer” 121 or protection strip, and having the purpose of increasing the rigidity and integrity of the bead structure 103.

(31) The chafer 121 usually comprises a plurality of strings encased in a cross-linked elastomeric material, which are generally made of textile materials (for example aramid or rayon) or of metal materials (for example steel strings).

(32) The rigidity of the tire sidewalls 108 may be improved by providing the annular reinforcement structure 103 with a reinforcement layer 120 generally known as a “flipper” or additional strip-like insert.

(33) The flipper 120 is a reinforcement layer which is wrapped around the respective annular anchoring structure 102 and the bead filling 104 so as to at least partially enclose the same, the flipper 120 being arranged between the at least one carcass layer 101 and the annular reinforcement structure 103.

(34) Preferably, the flipper 120 is in contact with said at least one carcass layer 101 and said annular reinforcement structure 103.

(35) The flipper 120 preferably comprises a plurality of metal or textile strings encased in a cross-linked elastomeric material.

(36) The production of the winter tire 100 as described above may be implemented in a conventional way by assembling respective semi-finished parts suitable for forming the components of the tire on a forming drum, not shown, to be worked on by at least one assembly device.

(37) On the forming drum, at least some of the components intended to form the carcass structure of the tire may be constructed and/or assembled.

(38) More particularly, the forming drum is suitable for initially receiving the optional liner, and subsequently the carcass structure.

(39) Subsequently, conventional devices, not shown, attach one of the annular anchoring structures coaxially around each of the end flaps, position an external sleeve comprising the belt structure and the tread band at a position coaxially centred about the cylindrical carcass sleeve, and shape the carcass sleeve in a toroidal configuration by radially expanding the carcass structure, so as to connect the latter to a radially inner face of the external sleeve.

(40) After the production of the green tire, a moulding and vulcanisation treatment is carried out to provide structural stabilisation of the tire by cross-linking the elastomeric compositions, in addition to forming a desired tread design on the tread band and forming optional distinctive graphical symbols at the sidewalls.

EXAMPLES

(41) The following examples are provided in order to further illustrate the invention and are not to be construed as limitation of the present invention. “Room temperature” refers to a temperature of about 20° C. All polymerizations were performed in a nitrogen atmosphere under exclusion of moisture and oxygen.

(42) Test Methods

(43) Size Exclusion Chromatography

(44) Molecular weight and molecular weight distribution of the polymer were each measured using size exclusion chromatography (SEC) based on polystyrene standards. Each polymer sample (9 to 11 mg) was dissolved in tetrahydrofuran (10 mL) to form a solution.

(45) The solution was filtered using a 0.45-μm filter. A 100 μL sample was fed into a GPC column (Hewlett Packard system 1100 with 3 PL gel 10 μm MIXED-B columns).

(46) Refraction Index-detection was used as the detector for analyzing the molecular weight.

(47) The molecular weight was calculated as polystyrene based on the calibration with EasiCal PS1 (Easy A and B) Polystyrene standards from Polymer Laboratories.

(48) Figures of weight-average molecular weight (M.sub.w) are given based on the polystyrene standards.

(49) Analysis to Measure Monomer Conversion

(50) Monomer conversion was determined by measuring the solids concentration (TSC) of the polymer solution at the end of the polymerization.

(51) The maximum solid content is obtained at 100 wt % conversion of the charged butadiene (m.sub.Bd) and styrene (m.sub.St) for the final polymer by TSC.sub.max=(m.sub.Bd+m.sub.St)/(m.sub.Bd+m.sub.St+m.sub.polar agent+m.sub.NBL+m.sub.cyclohexane)*100%.

(52) A sample of polymer solution ranging from about 1 g to about 10 g, depending on the expected monomer conversion, was drawn from the reactor directly into a 200 mL Erlenmeyer flask filled with ethanol (50 mL).

(53) The weight of the filled Erlenmeyer flask was determined before sampling (“A”) and after sampling (“B”). The precipitated polymer was removed from the ethanol by filtration on a weighted paper filter (Micro-glass fiber paper, Ø90 mm, MUNKTELL, weight “C”), dried at 140° C., using a moisture analyzer HR73 (Mettler-Toledo) until a mass loss of less than 1 mg within 140 seconds was achieved.

(54) Finally, a second drying period was performed using switch-off at a mass loss of less than 1 mg within 90 seconds to obtain the final mass “D” of the dry sample on the paper filter.

(55) The polymer content in the sample was calculated as TSC=(D−C)/(B−A)*100%. The final monomer conversion was calculated as TSC/TSC.sub.max*100%.

(56) Measurement of the Glass (Transition) Temperature Tg

(57) The glass transition temperature was determined using a DSC Q2000 device (TA instruments), as described in ISO 11357-2 (1999) under the following conditions: Weight: ca. 10-12 mg; Sample container: standard alumina pans; Temperature range: (−140 to 80)° C.; Heating rate: 20 K/min; Cooling rate: free cooling; Purge gas: 20 ml Ar/min; Cooling agent: liquid nitrogen; Evaluation method: inflection method.

(58) Each sample was measured at least once. The measurements contained two heating runs. The 2nd heating run was used to determine the glass transition temperature.

(59) .sup.1H-NMR

(60) Vinyl and total styrene contents were measured using .sup.1H-NMR, following ISO 21561-2005, using a NMR spectrometer BRUKER Avance (400 MHz), and a 5-mm dual probe. CDCl.sub.3/TMS was used as solvent in a weight ratio of 0.05%:99.95%.

(61) The styrene sequences (styrene oligomers) longer than 6 styrene units based on the total styrene units (also referred to as the fraction of the block styrene (BS) in %) was estimated as recommended by Tanaka et al. in Rubber Chem. and Techn. (1981), 54 (4), 685-91, i.e. the fraction of styrene sequences longer than 6 units was determined using the relative intensity of the ortho-phenyl proton signals resonated higher than 6.7 ppm. This is based on the finding that the ortho-phenyl proton, methine proton, and methylene proton signals shift to a higher magnetic field with increasing degree of polymerization. Thus, a block styrene is defined as a styrene sequence longer than 6 units.

(62) Properties of the Cross-Linkable Compositions

(63) The (raw) cross-linkable elastomeric compositions of the examples disclosed herein were subjected to the following evaluations:

(64) Mooney viscosity ML (1+4) at 100° C. was measured, in accordance with standard ISO 289-1:2005.

(65) Scorching time was measured at 127° C. in accordance with standard ISO 289-2:1994.

(66) MDR rheometric analysis (in accordance with standard ISO 6502) using an MDR2000 Alpha Technologies rheometer, the tests were carried out at 170° C. for 20 minutes at an oscillation frequency of 1.66 Hz (100 oscillations per minute) and an oscillation amplitude of ±0.5°, measuring the time required to bring about an increase of two rheometric units (TS2) and the time required to reach 30% (T30) and 90% (T90) respectively of the final torque (Mf). The maximum torque MH and the minimum torque ML are also measured.

(67) Properties of the Cross-Linked Compositions

(68) After cross-linking (vulcanisation), the elastomeric compositions of the examples disclosed herein were subjected to the following evaluations:

(69) The static mechanical properties were measured at 23° C. in accordance with standard ISO 37:2005.

(70) In particular, the tensile stress at various elongation levels (50%, 100% and 300%, referred to in order as T 50%, T 100%, T 300%), the stress at break) TSb and the elongation at break Eb were measured on samples of the aforementioned elastomeric compositions, vulcanised at 170° C. for 10 minutes.

(71) The tension tests were carried out on ring-type samples having a straight axis.

(72) The hardness in IRHD (23° C.) was measured in accordance with standard ISO 48:2007, on samples of the aforementioned elastomeric materials vulcanised at 170° C. for 10 minutes.

(73) The dynamic mechanical properties were measured using a dynamic Instron device in compression-tension operation by the following methods.

(74) A sample of the raw elastomeric compositions of the examples disclosed herein, vulcanised at 170° C. for 10 minutes, having a cylindrical shape (length=25 mm; diameter=14 mm), pre-load compression up to 25% longitudinal deformation with respect to the initial length and kept at the preset temperature (of −10° C., 0° C., 23° C. or 70° C.) throughout the test, was subjected to a sinusoidal dynamic tension having an amplitude of 3.5% with respect to the pre-load length, at a frequency of 10 Hz.

(75) The dynamic mechanical properties are expressed in terms of dynamic modulus of elasticity values (E′) and of tan delta or tan d (dissipation factor). The value of tan delta was calculated as the ratio between the modulus of viscosity (E″) and modulus of elasticity (E′).

(76) Experimental Part

(77) Unless stated otherwise, in the present experimental part the components of the composition are expressed in phr (parts per hundred of rubber).

(78) Comparative High Molecular Weight (HMW) Polymer A

(79) In the examples which follow a comparative high molecular weight elastomeric polymer A coupled with TMS was used.

(80) This polymer is characterized by the following properties:

(81) TABLE-US-00001 HMW Polymer Styrene Vinyl Mw CR cont. cont. TDAE Unit (g/mol) (%) (%) (%) (phr) Polymer A* 883,000 52 25 62 37.5 *SSBR commercial grade SLR 4630 (Trinseo GmbH).

(82) High Molecular Weight Elastomeric Polymer B (Random, Non-Oil-Extended, Coupled with SiCl.sub.4, Coupling Rate 50.2%)

(83) A first high molecular weight elastomeric polymer B (random, non-oil-extended, coupled with SiCl.sub.4 coupling rate 50.2% by weight) was prepared as follows.

(84) 19.597 kg of cyclohexane, 2040 g of butadiene, 693 g of styrene and 2.99 g of DTHFP were charged in a 40 liter reactor. The impurities in the system were titrated by stepwise addition of n-butyl lithium, the addition of butyl lithium was stopped when the yellow color of the polymer solution as recognized. The reaction mixture was heated up to 40° C. (start temperature).

(85) 2.7 g of initiator n-butyl lithium in cyclohexane solution (concentration 3.1 mmol/g) were charged into the reactor to start the polymerization. The temperature increased from 40° C. to 75° C. in 25 minutes. The polymerization mixture was allowed to react for 90 minutes. After this time, 2.67 g of silicon tetrachloride (SiCl.sub.4) in cyclohexane solution were added (0.5942 mmol/g).

(86) 37 g of methanol were then added to stop the reaction. The polymer solution was stabilized with 6.8 g of Irganox 1520 (0.25 phr).

(87) A polymer was obtained having the following characteristics:

(88) Mw=889,000 g/mol (as determined by means of GPC with a polystyrene calibration),

(89) coupling rate=50.2% by weight.

(90) The polymer microstructure (as determined with 1H-NMR) and glass transition temperature of the polymer obtained were:

(91) Styrene content=25%,

(92) Vinyl content=62%,

(93) Block Styrene Content=0%,

(94) Tg=−22.6° C.

(95) High Molecular Weight Elastomeric Polymer C (Random, Coupled with TMS, Coupling Rate 42.1%)

(96) A second high molecular weight elastomeric polymer C (random, coupled with TMS and modified with NMP) was prepared as follows.

(97) 19.597 kg of cyclohexane, 1999 g of butadiene, 693 g of styrene and 2.99 g of DTHFP were charged in a 40 liter reactor. The impurities in the system were titrated by stepwise addition of n-butyl lithium, the addition of butyl lithium was stopped when the yellow color of the polymer solution was recognized. The reaction mixture was heated up to 40° C. (start temperature).

(98) 24.01 g of initiator Li—(CH.sub.2)(Me).sub.2Si—N—(C.sub.4H.sub.9).sub.2 in cyclohexane solution (concentration 0.3329 mmol/g) were charged to the reactor to start the polymerization. The temperature increased from 40° C. to 75° C. in 25 minutes.

(99) The polymerization mixture was allowed to react for 90 minutes.

(100) After this time, 1.5 g of tetramethoxysilane (TMS) in cyclohexane solution was added (0.7659 mmol/g).

(101) After 30 min, 40.8 g of butadiene were added and shortly after 0.9286 g of NMP solution in cyclohexane (concentration: 8.25 mmol/g).

(102) After a reaction time of 30 minutes, 37 g of methanol were added to stop the reaction. The polymer solution was stabilized with 3.45 g of stearylamine (0.13 phr) and 6.8 g of Irganox 1520 (0.25 phr).

(103) A polymer was obtained having the following characteristics:

(104) Mw=984,000 g/mol (as determined by means of GPC with a polystyrene calibration), coupling rate=42.1% by weight.

(105) The polymer microstructure (as determined with 1H-NMR) and glass transition temperature of the polymer obtained were:

(106) Styrene content=24.9%,

(107) Vinyl content=61.4%,

(108) Block Styrene Content=0%,

(109) Tg=−22.6° C.

(110) Low molecular weight elastomeric Dolymer D (random, coupled with TMS)

(111) A first low molecular weight elastomeric polymer D (random, coupled with TMS) was prepared as follows.

(112) 20,555 g cyclohexane, 12.893 g of TMEDA and 31.11 g of butyl lithium solution in cyclohexane (3.1533 mmol/g) were charged in a 10 l reactor and heated up to a start polymerization temperature of 42° C. 327 g of butadiene and 106.4 g of styrene (corresponding to a target molecular weight of 4.0 kg/mol) were charged in the reactor during 30 minutes.

(113) The temperature of the polymerization mixture was kept constant at 42° C. The polymerization mixture was allowed to react for additional 30 minutes. After this time, 175.6 g of TMS solution in cyclohexane (0.1626 mmol/g) was added.

(114) After 60 minutes reaction time, 7 g of methanol were added. The polymer solution was stabilized with 0.88 g of Irganox 1520.

(115) The molecular weight was determined by means of GPC with a polystyrene calibration and a Mw of 16,910 g/mol was obtained.

(116) The following polymer microstructure was determined with .sup.1H-NMR: Styrene content: 28.3%, Vinyl content: 63.6%.

(117) The coupling rate of the polymer was 61.4% by weight.

(118) Low Molecular Weight Elastomeric Polymer E (Random, Coupled with TMS)

(119) A second low molecular weight elastomeric polymer E (random, coupled with TMS) was prepared as follows.

(120) 20,212 g of cyclohexane, 1,517 g of butadiene and 506.6 g of styrene and 33.4 g of DTHFP were charged in a 10 l reactor and heated up to a start polymerization temperature of 42° C.

(121) 178.2 g of butyl lithium solution in cyclohexane (conc. 3.1533 mmol/g) was added to start the polymerization reaction. After 60 minutes, 21.4 g of TMS were added to the reaction mixture. The temperature of the polymer mixture was kept constant at 42° C. After 40 minutes reaction time 36.01 g of methanol were added. The polymer solution was stabilized with 4.05 g of Irganox 1520.

(122) The molecular weight was determined by means of GPC with a polystyrene calibration and a Mw of 17,030 g/mol was obtained.

(123) The following polymer microstructure was determined with 1H-NMR: Styrene content: 25.2%, Vinyl content: 62.9%.

(124) The coupling rate of the polymer was 83% by weight.

(125) Comparative Low Molecular Weight Elastomeric Polymer F (Random, Coupled with TMS)

(126) The comparative low molecular weight elastomeric polymer F (random, coupled with TMS) was prepared by following the preparation procedure of the aforementioned low molecular weight elastomeric polymer E adapting as required the amount of the reagents and of the process conditions.

(127) The molecular weight was determined by means of GPC with a polystyrene calibration and a Mw of 86,000 g/mol was obtained.

(128) The following polymer microstructure was determined with .sup.1H-NMR: Styrene content: 26.3%, Vinyl content: 68.3%.

(129) The coupling rate of the polymer was 87% by weight.

(130) Preparation of an Exemplary Polymer Blend According to the Invention and of a Comparative Polymer Blend

(131) An exemplary polymer blend according to the present invention was prepared using the polymer solutions, as described above.

(132) Specifically, the corresponding polymer solutions of the first high molecular weight elastomeric polymer B and of the low molecular weight elastomeric polymer E were mixed to obtain a polymer blend.

(133) The polymer was then recovered from the solution via steam stripping at 100° C., milled to small crumbs and dried in an oven with air circulation at 70° C. for 30 min.

(134) Finally, the polymer crumbs were dried under ambient conditions on air until a content of residual volatiles was reached below 0.75%.

(135) A comparative blend was prepared following the procedure illustrated above by mixing a polymer solution of the high molecular weight elastomeric polymer B (coupled with TMS) and a solution of the comparative low molecular weight elastomeric polymer F having a Mw higher than the maximum value of 40,000 g/mol.

(136) Details of the inventive and comparative blends are given in Table 1 hereinbelow.

(137) TABLE-US-00002 TABLE 1 Polymer blends P1, P2 Blend P1 according to the invention High Mw polymer B (%) Low Mw polymer E (%) 80 20 Comparative blend P2 High Mw polymer B (%) Low Mw polymer F (%) 85 15

(138) Polymer Compositions (Examples 1-4)

(139) Polymer compositions were prepared using two comparative high molecular weight polymers without any low molecular weight portion, i.e. polymer A (S-SBR, SLR 4630) and BUNA 5025-0 HM (examples 1-2), the inventive polymer blend P1 (example 3) and the comparative polymer blend P2 (example 4).

(140) The polymer compositions were compounded by kneading according to the formulations shown in the following Table 2 (all amounts in phr) in a standard two-step compound recipe with silica and carbon black as fillers in an internal lab mixer comprising a Banbury rotor type with a total chamber volume of 1100 cm.sup.3.

(141) The first mixing step was performed with a filling degree of 73% using an initial temperature of 40° C.

(142) After adding the polymer composition, the filler and all other ingredients described in the formulations for step 1, the rotor speed of the internal mixer is controlled to reach a temperature range between 145° C.-160° C. for up to 4 minutes, so that the silanization reaction can occur.

(143) The total mixing time for the first step is 2′30″. After dumping the compound, the mixture is cooled down and stored for relaxing before adding the curing system in the second mixing step.

(144) The second mixing step was done in the same equipment by using a fill factor of 73% at an initial temperature of 50° C. The compound from first mixing step, sulphur as vulcanizing agent and the accelerators MTBS and CBS were added and mixed for a total time of 2′15″.

(145) TABLE-US-00003 TABLE 2 Ex. 1 Ex. 2 Ex. 3 EX. 4 Comp. Comp. Inv. Comp. Polymer A 68.75 — — — Dry Blend P1 — — 50.00 — Dry Blend P2 50.00 Dry SSBR 50 Dry BR 22 22 22 22 NR 28 28 28 28 TDAE oil 40 58.75 58.75 58.75 Carbon black 8 8 8 8 Silica 95 95 95 95 Silane TESPT 6.7 6.7 6.7 6.7 Wax 2 2 2 2 Stearic acid 3 3 3 3 Zinc oxide 2.5 2.5 2.5 2.5 6-PPD 3 3 3 3 MBTS 1.5 1.5 1.5 1.5 CBS 3 3 3 3 Sulphur 1.5 1.5 1.5 1.5 Total Dry polymer 100 100 100 100 Total oil 58.75 58.75 58.75 58.75
wherein:

(146) Polymer A: Oil-extended S-SBR Sprintan 4630 (Trinseo GmbH);

(147) Dry SSBR: BUNA 5025-0 HM;

(148) Dry BR: polybutadiene Europrene Neocis® BR40 (Versalis S.p.A.);

(149) NR: natural rubber SMR GP (Malaysia);

(150) TDAE Treated Distillate Aromatic Extract oil: Vivatec 500 (Hansen & Rosenthal KG);

(151) Carbon black: N234 (Birla Group);

(152) Silica: Ultrasil 7000 GR (Evonik Industries AG);

(153) Silane TESPT: bis(3-triethoxysilylpropyl)tetrasulphide—Si69 (Evonik Industries AG);

(154) Wax: Riowax bm-01 (SER S.p.A.);

(155) Stearic acid: Radiacid 444 (Oleon NV);

(156) Zinc oxide: (Norzinco GmbH);

(157) 6-PPD: phenyl-p-phenylenediamine (Santoflex 6PPD (Eastman Chemical Co.) (antiozonant);

(158) MBTS: 2,2′ dibenzothiazyl disulphide—Rhenogran MTBS-80 (Rhein Chemie GmbH) (accelerator);

(159) CBS: N-cyclohexyl-2-benzothiazyl-sulphenamide SXCHEM CBS GR (Shandong Sunshine Co. Ltd.) (accelerator);

(160) Sulphur: Multisperse S-IS70P (Omya S.p.A.) (vulcanizing agent).

(161) Results

(162) Table 3 below sets out the results of the static and dynamic mechanical properties for cross-linked samples of the polymer compositions according to Examples 1-4.

(163) TABLE-US-00004 TABLE 3 Unit of Ex. 1 Ex. 2 Ex. 3 Ex. 4 Parameter/Test measure Comp. Comp. Inv. Comp. T 50% MPa 1.09 1.16 1.01 1.11 T 100% MPa 1.72 1.75 1.54 1.90 T 300% MPa 6.62 6.40 5.79 8.00 CR MPa 13.77 13.96 13.77 15.30 AR % 559 589 622 495 IRHD at 23° C. IRHD 68.8 77.0 72.3 84 Mooney ML (1 + 4) MU 66.5 59.8 49.4 41.5 at 100° C. E′ 10 Hz −10° C. MPa 9.43 10.80 9.64 13.49 Tan d 10 Hz −10° C. 0.417 0.437 0.432 0.498 E′ 10 Hz 0° C. MPa 8.18 9.71 8.53 11.25 Tan d 10 Hz 0° C. 0.312 0.361 0.349 0.409 E′ 10 Hz 23° C. MPa 6.86 7.54 6.72 9.01 Tan d 10 Hz 23° C. 0.201 0.235 0.226 0.232 E′ 10 Hz 70° C. MPa 5.80 5.67 5.48 7.03 Tan d 10 Hz 70° C. 0.125 0.159 0.146 0.133

(164) Road Tests

(165) Car winter tyres having a tread band prepared by vulcanising the comparative polymer compositions of Examples 1 and 2 and the polymer composition according to Example 3 (invention) were produced and subjected to road tests.

(166) All of the tyres were of measurement 225/45 R17, with rim 6.0 J and pressure of 2.2 bar for the rear tyres and 2 bar for the front tyres.

(167) Braking tests on a dry and wet road surface and traction and braking tests on a snow-covered road were carried out.

(168) The braking test, both in dry and in wet conditions, takes place using winter tyres equipped on a vehicle provided with a wheel anti-lock braking system (A.B.S).

(169) This braking test was carried out on a straight asphalt passage, in both dry and wet conditions, determining the stopping distance from a preset initial speed, typically 100 km/h in dry conditions and 80 km/h in wet conditions.

(170) The braking test on a snow-covered road was carried out by subjecting the vehicle to deceleration from 50 to 5 km/h using both the anti-lock brake system (A.B.S.) and travel with locked wheels.

(171) The traction test on a snow-covered road was carried out by subjecting the vehicle to acceleration from 0 to 35/40 km/h, wherein accelerometers detect the traction force exerted by the winter tyre on the snow-covered road surface.

(172) The results of the road tests are set out in Table 4, the assessment being reparametrized by setting the assessment for the reference winter tyre (tread composition of Example 1) to 100:

(173) TABLE-US-00005 TABLE 4 Ex. 1 Ex. 2 Ex. 3 Road test Comp. Comp. Inv. Wet braking 100 100 106 Dry braking 100 98 101 Snow traction 100 100 100 Snow braking 100 100 100

(174) In table 4, relating to the results of the road tests, an increase of the value from 100 indicates an improvement in the related parameter (for example 106 vs 100 in the wet braking indicates that this winter tyre behaves better—in other words has a lower braking distance on wet ground—than the tyre having a tread according to reference Example 1). Analogously, a reduction in the value (for example from 100 to 98 in the dry braking between the winter tyre of comparative Example 1 and that of comparative Example 2) represents a worsened performance.

(175) As may be inferred from Table 3, the comparative cross-linked polymer composition of Example 4 obtained using a blend including a coupled low molecular weight elastomeric polymer having a molecular weight outside of the claimed range of 5000-40,000 g/mol, shows an increase of Tan d both at −10° C. (+19.4%) and at 0° C. (+31.1%) (considered predictive of an improved wet behaviour and braking of the tire) which is unable to counterbalance the simultaneous substantial increase of the polymer stiffness E′ at −10° C. (+43.1%) and at 0° C. (+37.5%) (considered predictive of a worsened wet behaviour and braking of the tire), thereby rendering this comparative cross-linked polymer composition hardly suitable to improve the wet/snow balance of a winter tire.

(176) As may be inferred from Table 3, thanks to the presence in the polymer composition of the invention of a blend including a coupled low molecular weight (second) elastomeric polymer having a molecular weight within the range of 5,000-40,000 g/mol and a coupling rate of at least 50 percent by weight, the cross-linked polymer composition according to the invention (Ex. 3) shows a significant increase of Tan d both at −10° C. (+3.6%) and at 0° C. (+11.9%) (considered predictive of an improved wet behaviour and braking of the tire) which counterbalances and overrides the simultaneous limited increase of the polymer stiffness E′ at −10° C. (+2.2%) and at 0° C. (+4.3%) (considered predictive of a worsened wet behaviour and braking of the tire).

(177) The data shown in Table 4 confirm that a winter tire according to the invention has a better performance in terms of wet and dry braking with respect to the reference tires of comparative examples 1 and 2.

(178) On the other hand, such a significant increase of Tan d both at −10° C. and at 0° C. of the winter tire according to the invention also surprisingly allows to counterbalance the simultaneous limited increase of the polymer stiffness E′ predictive of a worsened snow traction and braking due to an increased rigidity of the vulcanized polymer composition.

(179) The data shown in Table 4 therefore confirm that a winter tire according to the invention has a substantially equal performance in terms of snow traction and braking with respect to the reference tires of comparative examples 1 and 2.

(180) Overall, the tires according to the invention therefore achieve a better balance of the tire performances on wet and snow ground and, at the same time, a better performance in terms of braking on dry surfaces.