RUBBER COMPOSITION COMPRISING A CRUMB RUBBER

Abstract

A rubber composition is based on at least 50 to 100 phr of a copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing more than 50 mol % of the monomer units of the copolymer, 0.1 to 9% by mass of crumb rubber, a reinforcing filler and a crosslinking system.

Claims

1.-13. (canceled)

14. A rubber composition based on at least: 50 to 100 phr of a copolymer containing ethylene units and 1,3-diene units, the ethylene units in the copolymer representing more than 50 mol % of the monomer units of the copolymer; 0.1% to 9% by mass of crumb rubber; a reinforcing filler; and a crosslinking system.

15. The rubber composition according to claim 14, wherein the copolymer containing ethylene units and 1,3-diene units comprises at least 65 mol % of ethylene units.

16. The rubber composition according to claim 14, wherein the 1,3-diene is 1,3-butadiene.

17. The rubber composition according to claim 14, wherein the content of the copolymer containing ethylene units and 1,3-diene units in the rubber composition is within a range from 80 to 100 phr.

18. The rubber composition according to claim 14, wherein the crumb rubber has an acetone extract of between 3% and 30% by mass.

19. The rubber composition according to claim 14, wherein the crumb rubber has a chloroform extract of between 3% and 85% by mass.

20. The rubber composition according to claim 14, wherein the crumb rubber has a ratio of chloroform extract to acetone extract, expressed as a mass percentage, of less than 1.5.

21. The rubber composition according to claim 14, wherein the crumb rubber has a mean size D50 of between 100 and 300 m.

22. The rubber composition according to claim 14, wherein the crumb rubber has a particle size distribution such that a mean size ratio D10/D50 is greater than or equal to 0.5.

23. The rubber composition according to claim 14, wherein the content of crumb rubber is within a range from 0.5% to 7% by mass.

24. The rubber composition according to claim 14, wherein the reinforcing filler comprises carbon black.

25. A rubber article comprising the rubber composition according to claim 14.

26. A tire comprising the rubber composition according to claim 14.

Description

IIIEXAMPLES OF IMPLEMENTATION OF THE INVENTION

III-1 Characterization of the Rubber Compositions

[0086] In the examples, the rubber compositions are characterized after curing as indicated below.

Fatigue:

[0087] The fatigue strength, expressed as number of cycles or in relative units (r.u.), is measured in a known manner on 12 test specimens subjected to repeated low-frequency tensile strains up to an elongation of 75%, at 23 C., using a Monsanto (MFTR) machine until the test specimen breaks, according to the standards ASTM D4482-85 and ISO40 6943.

[0088] The result is expressed in base 100 for facilitated comparison of the results. A value greater than that of the control, arbitrarily set at 100, indicates an improved result, that is to say a better fatigue strength of the rubber samples.

Dynamic Properties:

[0089] The dynamic properties and more particularly the hysteresis as represented by the tan()max, or also the stiffness as represented by the G*(50%) are measured on a viscoanalyser (Metravib VA4000), according to the standard ASTM D 5992-96. The response of a sample of vulcanized 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 controlled temperature conditions (60 C.), is recorded. A strain amplitude sweep is performed from 0.1% to 100% (outward cycle) and then from 100% to 1% (return cycle). The results used here are, on the one hand, the loss factor tan(), representing the hysteresis of the compositions, and, on the other hand, the stiffness at 50% strain G*(50%). For the outward cycle, the maximum value of tan() observed, denoted tan()max, is indicated.

[0090] The results are expressed in terms of performance in base 100, that is to say that the value 100 is arbitrarily assigned to the best control, in order to calculate and subsequently compare the tan()max and the G*(50%) of the various solutions tested. For the tan()max, a lower value represents a decrease in hysteresis performance (i.e. a larger tan()max value) while a higher value represents a better performance. For the G*(50%), a lower value represents a decrease in stiffness performance (i.e. a lower value of G*(50%)) while a higher value represents a better performance.

III-2 Rubber Compositions

[0091] The elastomer (EBR) is prepared according to the following procedure: 30 mg of metallocene [{Me2SiFlu2Nd(-BH4)2Li(THF)}2, the symbol Flu representing the fluorenyl group of formula C13H8], are introduced into a first Steinie bottle in a glovebox. The co-catalyst, butyloctylmagnesium dissolved beforehand in 300 ml of methylcyclohexane in a second Steinie bottle, is introduced into the first Steinie bottle containing the metallocene in the following proportions: 0.00007 mol/L of metallocene, 0.0004 mol/L of co-catalyst. After contact for 10 minutes at ambient temperature, a catalytic solution is obtained. The catalytic solution is then introduced into the polymerization reactor. The temperature in the reactor is then increased to 80 C. When this temperature is reached, the reaction starts by injection of a gaseous mixture of ethylene and 1,3-butadiene (80/20 mol %) into the reactor. The polymerization reaction proceeds at a pressure of 8 bar. The proportions of metallocene and of co-catalyst are, respectively, 0.00007 mol/L and 0.0004 mol/L. The polymerization reaction is stopped by cooling, degassing of the reactor and addition of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven.

[0092] The rubber compositions, the details of the formulation of which are given in Table 1, were prepared in the following manner:

[0093] The elastomer, the reinforcing filler and the various other ingredients, with the exception of the sulfur and the vulcanization accelerator, are successively introduced into an internal mixer (final degree of filling: about 70% by volume), the initial vessel temperature of which is about 80 C. Thermomechanical working (non-productive phase) is then performed in one step, which lasts in total approximately 3 to 4 min, until a maximum dropping temperature of 165 C. is reached. The mixture thus obtained is recovered and cooled, and sulfur and the vulcanization accelerator are then incorporated on a mixer (homofinisher) at 30 C., the whole being mixed (productive phase) for an appropriate time (for example approximately ten minutes).

[0094] The compositions thus obtained are subsequently calendered, either in the form of slabs (thickness of 2 to 3 mm) or of thin sheets of rubber, for measurement of their physical or mechanical properties, or extruded in the form of a tyre tread.

[0095] Of the compositions shown in Table 1, only composition C2 is in accordance with the invention. Compositions T1 to T3, C1 and C3 are comparative tests to illustrate the effect of the invention. The performance of the compositions is presented in Table 2.

TABLE-US-00001 TABLE 1 Composition T1 T2 T3 C1 C2 C3 NR (1) 60 60 60 SBR (2) 20 20 20 BR (3) 20 20 20 EBR (4) 100 100 100 Crumb (5) 8.5 18 8.5 17 Crumb (m %) 5% 10% 5% 10% Carbon black (6) 54 54 54 40 40 40 Antioxidant (7) 2 2 2 2 Stearic acid (8) 1.5 1.5 1.5 1.5 1.5 1.5 Zinc oxide (9) 2.5 2.5 2.5 2.5 2.5 2.5 Accelerator 1 (10) 1.1 1.1 1.1 0.5 0.5 0.5 Accelerator 2 (11) 0.5 0.5 0.5 Accelerator 3 (12) 0.3 0.3 0.3 Sulfur 1.1 1.1 1.1 0.4 0.4 0.4 (1) NR: Natural rubber (2) SBR with 15.5% by weight of styrene units and, for the butadiene part, 24% of 1,2 units and Tg = 65 C. (3) BR: polybutadiene, CB24 from Lanxess; 96% of cis-1,4; Tg = 107 C. (4) EBR: Elastomer containing 79 mol % of ethylene units, 7 mol % of 1,2-cyclohexanediyl units, 8 mol % of 1,2-butadienyl units, and 6 mol % of 1,4-butadienyl units, prepared as indicated above (5) Polydine PD 80 crumb from the company Lehigh Technologies (6) Carbon black, ASTM N234 grade (7) N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine (Santoflex 6-PPD) from the company Flexsys (8) Pristerene 4931 stearin from the company Uniqema (9) Zinc oxide, industrial grade - from Umicore (10) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from the company Flexsys) (11) Diphenylguanidine (Perkacit DPG from the company Flexsys) (12) Tetrabenzylthiuram disulfide (Perkacit TBZTD from the company Flexsys)

TABLE-US-00002 TABLE 2 Performance T1 T2 T3 C1 C2 C3 Fatigue (base 100) 100 79 68 100 195 11 G*50% 100 105 106 100 104 110 Tan()max 100 103 101 100 100 99

[0096] It is noted that composition C2, alone in accordance with the invention, surprisingly shows a very great improvement in its endurance, as measured by its fatigue strength, while retaining optimum stiffness and hysteresis.