PNEUMATIC TIRE COMPRISING A RUBBER COMPOSITION CONTAINING A THERMOPLASTIC POLYURETHANE

Abstract

A tire which has improved mechanical properties comprises a rubber composition based on at least one diene elastomer, at least one thermoplastic polyurethane, and a crosslinking system; the composition does not comprise any reinforcing filler or comprises less than 25 parts by weight thereof per hundred parts by weight of elastomer, phr, the carbon black content in the composition being less than 20 phr.

Claims

1.-11. (canceled)

12. A tire comprising a rubber composition based on: at least one diene elastomer; at least one thermoplastic polyurethane; and a crosslinking system, wherein the rubber composition does not comprise any reinforcing filler or comprises less than 25 parts by weight thereof per hundred parts by weight of elastomer, phr, the carbon black content in the rubber composition being less than 20 phr.

13. The tire according to claim 12, wherein the at least one diene elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and mixtures thereof.

14. The tire according to claim 12, wherein the at least one diene elastomer is an isoprene elastomer.

15. The tire according to claim 12, wherein a content of the at least one diene elastomer in the rubber composition is within a range extending from 20 to 90 phr.

16. The tire according to claim 12, wherein a content of the at least one thermoplastic polyurethane in the rubber composition is within a range extending from 10 to 80 phr.

17. The tire according to claim 12, wherein the at least one thermoplastic polyurethane comprises at least one flexible segment and at least one rigid segment, the flexible segment resulting from a reaction of a polyisocyanate with a polyol, the molecular weight of the hydrocarbon-based chain of which is between 600 and 2500 g/mol, and the rigid segment resulting from a reaction of a polyisocyanate with a diol or triol, the molecular weight of which is within a range extending from 40 to 350 g/mol.

18. The tire according to claim 12, wherein the rubber composition does not comprise any reinforcing filler or comprises less than 20 phr.

19. The tire according to claim 12, wherein the carbon black content is within a range extending from more than 0 to 18 phr.

20. The tire according to claim 12, wherein the crosslinking system is based on molecular sulfur, a sulfur-donating agent, or both molecular sulfur and a sulfur-donating agent.

21. The tire according to claim 12, wherein the rubber composition is present in a tread of the tire.

22. The tire according to claim 12, wherein the tire is a tire for civil engineering, agricultural or heavy-duty vehicles.

Description

III—EXAMPLES

[0097] III-1 Measurements and Tests Used

[0098] Dynamic Properties (after Curing): Tensile Test

[0099] These tensile tests make it possible to determine the elasticity stresses and the properties at break. Unless otherwise indicated, they are carried out in accordance with French Standard NF T 46-002 of September 1988. Processing the tensile recordings also makes it possible to plot the curve of modulus as a function of the elongation. The modulus used here is the true secant modulus measured in first elongation, calculated by normalizing to the true cross section of the test specimen at any moment of the test. The nominal secant moduli (or apparent stresses, in MPa) are measured in first elongation at 50%, 100% and 300% elongation, respectively denoted M50, M100 and M300. The MSV300/MSV100 ratio is an indicator of the reinforcement of the rubber composition. The higher this ratio, the stronger the reinforcement of the composition.

[0100] The elongation at break (EB %) and breaking stress (BS) tests are based on Standard NF ISO 37 of December 2005 on an H2 dumbbell test specimen and are measured at a tensile speed of 500 mm/min. The elongation at break is expressed as a percentage of elongation. The breaking stress is expressed in MPa.

[0101] All these tensile measurements are carried out under the standard conditions of temperature (23±2° C.) and hygrometry (50±5% relative humidity), according to French Standard NF T 40-101 (December 1979).

[0102] The dynamic properties G* (25%) and tan(S)max at 60° C. are measured on a viscosity analyser (Metravib VA4000), according to Standard ASTM D 5992-96. The response of a sample of crosslinked composition (cylindrical test specimen with a thickness of 4 mm and a cross section of 400 mm.sup.2), subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, under the defined conditions of temperature, for example at 60° C., according to Standard ASTM D 1349-99 or, as the case may be, at a different temperature, is recorded. A strain amplitude sweep is carried out from 0.1% to 50% (outward cycle) and then from 50% to 1% (return cycle). The results made use of are the complex dynamic shear modulus G* and the loss factor tan(S). The maximum value of tan(6) observed, denoted tan(S)max, and the complex dynamic shear modulus G* at 25% strain, at 60° C., are shown for the return cycle.

[0103] III-2 Preparation of the Compositions

[0104] The tests which follow are carried out in the following way: the thermoplastic polyurethane then the elastomer, the optional reinforcing fillers and also the various other ingredients, with the exception of the crosslinking system, are successively introduced into a blade mixer (final degree of filling: approximately 70% by volume), the initial vessel temperature of which is approximately 175° C. Thermomechanical working (non-productive phase) is then carried out in one step, which lasts in total approximately from 5 to 8 min, until a maximum “dropping” temperature of 175° C. is reached.

[0105] The mixture thus obtained is recovered and cooled and then the crosslinking system is incorporated on a mixer (homofinisher) at 23° C. or 50° C., respectively, everything being mixed (productive phase) in a roll mill for an appropriate time (for example between 5 and 12 min).

[0106] The compositions thus obtained are subsequently calendered, either in the form of plaques (thickness of 2 to 3 mm) or of thin sheets of rubber, for the measurement of their physical or mechanical properties, or extruded in the form of a profiled element.

[0107] III-3 Tests on Rubber Compositions

[0108] The examples presented in Table 1 are intended to compare the mechanical properties and the reinforcement of compositions in accordance with the invention (C1, C2, C3 and C4) with those of control compositions (Ti and T2) which differ from the compositions in accordance with the invention in that they do not comprise diene elastomer and thermoplastic polyurethane concomitantly. The formulations (in phr) and the properties thereof have been summarized in Table 1 below.

TABLE-US-00001 TABLE 1 T1 T2 C1 C2 C3 C4 NR (1) 100 — 60 80 40 60 TPU 1 (2) — 100 40 20 60 40 N234 (3) — — — — — 10 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 CBS (5) 1 1 1 1 1 1 ZnO (6) 2.5 2.5 2.5 2.5 2.5 2.5 Stearic acid (7) 1 1 1 1 1 1 MSV 300/100 100 93 118 107 101 125 MSV break 100 1376 365 278 418 527 % EB 100 145 113 119 113 124 (1) Natural rubber (2) Thermoplastic polyurethane (Desmopan 3378A from the company Bayer) (3) Carbon black, ASTM grade N234 from the company Cabot (5) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from he company Flexsys) (6) Zinc oxide (industrial grade-the company Umicore) (7) Stearin (Pristerene 4931 from the company Uniqema)

[0109] These results show that the compositions in accordance with the invention all make it possible to improve the compromise in mechanical properties without penalizing the reinforcement of the composition, or even while improving it. These results also show that the addition of a small amount of carbon black makes it possible to significantly improve all of the mechanical properties measured.

[0110] A control composition T3 was produced to determine the influence of increasing the carbon black content.

TABLE-US-00002 TABLE 2 T1 C4 T3 NR (1) 100 60 60 TPU 1 (2) — 40 40 N234 (3) — 10 30 Sulfur 1.5 1.5 1.5 CBS (5) 1 1 1 ZnO (6) 2.5 2.5 2.5 Stearic acid (7) 1 1 1 % EB 100 124 100 (1) to (7): see Table 1

[0111] These results show that increasing the amount of carbon black above 25 phr no longer makes it possible to improve the elongation at break of the composition.