PNEUMATIC TIRE COMPRISING A RUBBER COMPOSITION BASED ON EPOXIDIZED POLYISOPRENE AND A POLYAMIDE HAVING A LOW MELTING POINT

Abstract

The invention relates to a tyre having improved mechanical properties, comprising a rubber composition based on at least one elastomeric matrix mainly comprising at least one epoxidized polyisoprene having a molar degree of epoxidation greater than 40%, at least one polyamide of which the melting point is less than 170° C., and a crosslinking system.

Claims

1.-15. (canceled)

16. A tire comprising a rubber composition based on: an elastomeric matrix mainly comprising at least one epoxidized polyisoprene having a molar degree of epoxidation greater than 40%; at least one polyamide, the melting point of which is less than 170° C.; and a crosslinking system.

17. The tire according to claim 16, wherein the molar degree of epoxidation of the at least one epoxidized polyisoprene is within a range extending from 40% to 85%.

18. The tire according to claim 16, wherein a content of the at least one epoxidized polyisoprene in the rubber composition is within a range extending from 80 to 100 parts by weight per hundred parts by weight of elastomer, phr.

19. The tire according to claim 16, wherein a content of the at least one polyamide in the rubber composition is within a range extending from 5 to 100 phr.

20. The tire according to claim 16, wherein the at least one polyamide is a copolymer polyamide consisting of at least two different types of monomers selected from the group consisting of lactams or is a copolymer of at least two different types of monomers selected from the group consisting of diacids and of at least two different types of monomers selected from the group consisting of diamines.

21. The tire according to claim 16, wherein the rubber composition does not comprise a plasticizer that is liquid at 23° C.

22. The tire according to claim 16, wherein the rubber composition does not comprise epoxy resin.

23. The tire according to claim 16, wherein the rubber composition is present in a tread of the tire.

24. The tire according to claim 16, wherein the tire is a tire for civil engineering, agricultural or heavy-duty vehicles.

25. A process for preparing a rubber composition for the manufacture of a tire according to claim 16, the process comprising the following steps: (a) bringing into contact and mixing, concomitantly or successively, the at least one epoxidized polyisoprene having a molar degree of epoxidation greater than 40% and the at least one polyamide, the melting point of which is less than 170° C., by thermomechanically kneading until reaching a maximum temperature T1 greater than or equal to the melting point of the at least one polyamide; and (b) reducing the temperature of the mixture obtained in step (a) to a maximum temperature T2 lower than the melting point of the at least one polyamide, then incorporating the crosslinking system into the mixture and kneading the mixture.

26. The process according to claim 25, wherein the at least one polyamide is introduced in a solid state.

27. The process according to claim 25, wherein the maximum temperature T1 is 5 to 20° C. higher than the melting point of the at least one polyamide.

28. The process according to claim 25, wherein the maximum temperature T2 is less than 120° C.

29. A rubber composition obtained by the process according to claim 25.

30. A tire comprising a rubber composition according to claim 29.

Description

IV—EXAMPLES

IV-1 Measurements and Tests Used

Dynamic Properties (After Curing): Tensile Test

[0181] 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 (at any moment) of the test specimen. The true secant moduli (in MPa) are measured in first elongation at 50%, 100% and 300% elongation, respectively denoted M50, M100 and M300.

[0182] The elongation at break (EB%) and breaking stress (BS) tests are based on the standard NF ISO 37 of December 2005 on an H2 dumbbell 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.

[0183] 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).

[0184] The dynamic properties tan(δ)max at 40° C. are measured on a viscosity analyser (Metravib VA4000) according to Standard ASTM D 5992-96. The response of a sample of crosslinked composition (two discs with a thickness of 2 mm and a diameter of 10 mm), subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, under defined temperature conditions, for example 40° C., according to standard ASTM D 1349-99 or, as appropriate, 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). For the return cycle, the maximum value of tan(δ) observed, denoted by tan(δ)max, at 40° C. is indicated.

[0185] The elongation at break and modulus of rupture results are expressed in base 100, the value 100 being assigned to the control. A result of less than 100 indicates improved performance, that is to say that the composition of the example in question reflects better mechanical properties.

[0186] The results for tan(6)Max at 40° C. are expressed in base 100, the value 100 being assigned to the control. A result of less than 100 indicates improved performance, that is to say that the composition of the example in question reflects better hysteresis and therefore reduced rolling resistance.

IV-2 Preparation of the Compositions

[0187] The tests which follow are carried out in the following way: the polyamide then the elastomer 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 170° C. Thermomechanical working (non-productive phase) is then carried out in one step, which lasts in total approximately from 3 to 5 min, until a maximum “dropping” temperature of 180° C. is reached.

[0188] The mixture thus obtained is recovered and cooled and then the crosslinking system is incorporated on a mixer (homofinisher) at 30° C., everything being mixed (productive phase) in a roll mill for an appropriate time (for example between 5 and 12 min).

[0189] 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.

[0190] The samples thus produced were cured for 20 minutes at 170° C. in a bell press. The samples were analysed after having been cooled at ambient temperature for 24 hours.

IV-3 Tests on Rubber Compositions

[0191] The purpose of the examples below is to compare the mechanical properties (elongation at break) of a composition in accordance with the invention (C1) with those of a control composition (T1) of the prior art, and also with a control composition (T2) which differs from the composition Cl only in that the polyisoprene is not epoxidized. 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 NR (1) — 100 — — — ENR50 (2) 100 — 100 100 100 N115 (3) 45 — — — — PA (4) — 27 27 47 74 Sulfur 1.5 1.5 1.5 1.5 1.5 CBS (5) 1 1 1 1 1 % AR 100 173 210 192 207 tan(d)max at 40° C. 100 * 56 60 60 (1) Natural rubber (2) Epoxidized natural rubber at 50 mol % (Epoxyprene 50 from the company Guthrie) (3) Carbon black Grade ASTM N234 (from the company Cabot) (4) Polyamide (Elvamide 8063 from the company Dupont) (5) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from the company Flexsys) * Not measured

[0192] Other examples have been carried out to demonstrate the effect of the molar degree of epoxidation of polyisoprene, and also the effect of the content of polyamide in the composition. The formulations tested (in phr) and the properties thereof have been summarized in Table 2 below.

TABLE-US-00002 TABLE 2 T3 C1 C2 C3 T2 NR (1) — — — — 100 ENR50 (2) — 100 100 100 — ENR25 (6) 100 — — — — PA (4) 29 29 47 74 29 Sulfur 1.5 1.5 1.5 1.5 1.5 CBS (5) 1 1 1 1 1 Modulus of 100 127 156 246 42 rupture (1) to (5): see Table 1 (6) Epoxidized natural rubber at 25 mol % (Epoxyprene 25 from the company Guthrie)

[0193] All of these results show that the concomitant use of epoxidized polyisoprene having a molar degree of epoxidation greater than 40%, and of a polyamide, the melting point of which is less than 170° C., makes it possible to improve the mechanical properties of rubber compositions, in particular compared to compositions comprising a polyisoprene having a molar degree of epoxidation of less than 40% or a non-epoxidized polyisoprene. The compositions according to the invention also exhibit improved hysteresis, and therefore improved rolling resistance. Moreover, it has been observed that increasing the content of polyamide, the melting point of which is less than 170° C., in the composition, makes it possible to further increase the modulus of rupture of the composition, which presents a substantial advantage for the life of the tyre, without penalizing the hysteresis.