RUBBER COMPOSITION COMPRISING A SPECIFIC REINFORCING FILLER

Abstract

The invention relates to aA rubber composition has an improved rolling resistance and is based on at least a diene elastomer comprising mainly at least one isoprene elastomer; a reinforcing filler comprising from 10 to 35 phr of carbon black having a BET specific surface area of less than 70 m.sup.2/g, and from 10 to 40 phr of silica; a coupling agent in a content corresponding to a range extending from 5 to 15% by weight relative to the weight of silica; and a crosslinking system; in which composition the total content of carbon black and silica is between 20 and 70 phr, and in which the carbon black to silica weight ratio is greater than 0.3.

Claims

1.-31. (canceled)

32. A rubber composition based on at least: a diene elastomer comprising mainly at least one isoprene elastomer; a reinforcing filler comprising: from 10 to 35 phr of carbon black having a BET specific surface area of less than 70 m.sup.2/g, and from 10 to 40 phr of silica; a coupling agent in a content corresponding to a range extending from 5% to 15% by weight relative to the weight of silica; and a crosslinking system, wherein the total content of carbon black and silica is between 20 and 70 phr, and wherein the weight ratio of carbon black to silica is greater than 0.3.

33. The rubber composition according to claim 32, wherein the content of isoprene elastomer is within a range extending from 60 to 100 phr.

34. The rubber composition according to claim 32, wherein the isoprene elastomer is selected from the group consisting of natural rubber, a synthetic polyisoprene and a mixture thereof.

35. The rubber composition according to claim 32, wherein the carbon black has a BET specific surface area of less than 50 m.sup.2/g.

36. The rubber composition according to claim 32, wherein the carbon black has a COAN oil absorption number of less than 90 ml/100 g.

37. The rubber composition according to claim 32, wherein the silica has a BET specific surface area of less than 200 m.sup.2/g, a CTAB specific surface area of less than 220 m.sup.2/g, or both a BET specific surface area of less than 200 m.sup.2/g and a CTAB specific surface area of less than 220 m.sup.2/g.

38. The rubber composition according to claim 32, wherein the carbon black content is within a range extending from 10 to 30 phr.

39. The rubber composition according to claim 32, wherein the silica content is within a range extending from 15 to 40 phr.

40. The rubber composition according to claim 32, wherein the total content of carbon black and silica is between 30 and 65 phr.

41. The rubber composition according to claim 32, wherein the carbon black to silica weight ratio is within a range extending from 0.3 to 1.5.

42. The rubber composition according to claim 32 further comprising a salt of an alkaline-earth, alkali or lanthanide metal.

43. The rubber composition according to claim 42, wherein the salt of the alkaline-earth, alkali or lanthanide metal is an acetylacetonate of an alkaline-earth, alkali or lanthanide metal.

44. The rubber composition according to claim 42, wherein the salt of the alkaline-earth, alkali or lanthanide metal is selected from the group consisting of lithium, sodium, potassium, calcium, magnesium, lanthanum, cerium, praseodymium, neodymium, samarium, erbium and mixtures thereof.

45. The rubber composition according to claim 44, wherein the salt of an alkaline-earth, alkali or lanthanide metal is a magnesium salt or a neodymium salt.

46. The rubber composition according to claim 42, wherein the content of the salt of the alkaline-earth, alkali or lanthanide metal is within a range extending from 0.1 to 5 phr.

47. The rubber composition according to claim 32 further comprising stearic acid or a salt thereof.

48. The rubber composition according to claim 47, wherein the content of stearic acid or salt thereof is within a range extending from 0.5 to 2 phr.

49. The rubber composition according to claim 32 further comprising a cobalt salt.

50. The rubber composition according to claim 49, wherein the cobalt salt is selected from the group consisting of abietates, acetylacetonates, tallates, naphthenates, resinates and mixtures thereof.

51. The rubber composition according to claim 49, wherein the content of cobalt salt is within a range extending from 0.5 to 2 phr.

52. The rubber composition according to claim 32 further comprising an antioxidant selected from the group consisting of substituted p-phenylenediamines, substituted diphenylamines, substituted triphenylamines, quinoline derivatives, and mixtures thereof

53. The rubber composition according to claim 52, wherein the antioxidant is selected from the group consisting of substituted p-phenylenediamines and mixtures thereof

54. The rubber composition according to claim 52, wherein the content of antioxidant is within a range extending from 1 to 5 phr.

55. The rubber composition according to claim 32 further comprising a metal oxide selected from the group consisting of oxides of group II, IV, V, VI, VII and VIII metals, and mixtures thereof.

56. The rubber composition according to claim 55, wherein the metal oxide is selected from the group consisting of zinc oxide, magnesium oxide, cobalt oxide, nickel oxide and mixtures thereof.

57. The rubber composition according to claim 55, wherein the content of metal oxide is within a range extending from 2 to 20 phr.

58. The rubber composition according to claim 32, wherein the rubber composition comprises from 0 to less than 0.5 phr of reinforcing resin.

59. A finished or semi-finished rubber article comprising a rubber composition according to claim 32.

60. A tire comprising a rubber composition according to claim 32.

61. The tire according to claim 60, wherein the rubber composition is present in at least one internal layer.

62. The tire according to claim 61, wherein the internal layer is selected from the group consisting of carcass plies, crown plies, bead-wire fillings, crown feet, decoupling layers, edge rubbers, the tread underlayer and combinations thereof.

Description

EXAMPLES

[0136] I. Measurements and Tests Used

[0137] I.1 Dynamic Properties

[0138] The dynamic property tan()max was measured on a viscosity analyser (Metravib VA4000) according to ASTM standard 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 and at a temperature of 60 C., according to ASTM standard D 1349-99, is recorded. A strain amplitude sweep was carried out from 0.1% to 50% (outward cycle) and then from 50% to 0.1% (return cycle). The result made use of is the loss factor (tan ). The maximum value of tan observed (tan()max), between the values at 0.1% and at 50% strain (Payne effect), was shown for the return cycle. It is recalled that, in a well-known manner, the lower the value for tan()max at 60 C., the lower will be the hysteresis of the composition and thus the more its rolling resistance will be improved.

[0139] 1.2 Adhesion Test

[0140] A tearing-out test in accordance with ASTM standard D2229 was carried out on test specimens comprising metal cords of 2.30NF structure, a portion of which is inserted between two strips made of a rubber composition and another portion of which is left free. The force necessary to tear the cord out of the two rubber strips was measured. The measurement was carried out for 15 cords. The value retained was the mean of the measurements on these 15 cords. The greater the value of the force, the greater the adhesion between the cord and the rubber composition. The adhesion test described above was carried out with test specimens cured for a period of time of less than 1 hour at a temperature of greater than 100 C. and aged for several days at a temperature of greater than 30 C. and at more than 50% relative humidity.

[0141] 1.3 Tensile (Cohesion) Tests

[0142] These 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. The nominal secant moduli (or apparent stresses, in MPa) at 10% elongation (denoted MA10) and 100% elongation (MA100) are measured in second elongation (i.e., after an accommodation cycle). All these tensile measurements are carried out under the standard conditions of temperature (232 C.) and hygrometry (50+5% relative humidity), according to French Standard NF T 40-101 (December 1979). The breaking stresses (in MPa) and the elongations at break (in %) are also measured, at a temperature of 23 C.

[0143] 1.4 Peel (Adhesion) Test

[0144] The peel test is carried out in accordance with ASTM standard D-4393-98. The metal cord is gradually moved away from the rest of the test specimen at a constant transverse speed of 100 mm/min.

[0145] A score representative of the peel appearance is then assigned, in accordance with Table 1 below. Thus, the better the adhesion, the less the cord is stripped (the more it is covered with rubber), and the higher the appearance score.

TABLE-US-00001 TABLE 1 Mean degree of stripping of the Appearance treated film as % of the surface area score of the film 0 98-100 1 91-97 2 81-90 3 71-80 4 61-70 5 51-60 6 41-50 7 31-40 8 21-30 9 11-20 10 0-10

[0146] II. Preparation of the Compositions

[0147] The tests which follow are carried out in the following way: the diene elastomer, the thermoplastic styrene elastomer, the reinforcing filler and also the various other ingredients, with the exception of the vulcanization system, are successively introduced into an internal mixer (final degree of filling: approximately 70% by volume), the initial vessel temperature of which is approximately 60 C. Thermomechanical working is then carried out (non-productive phase) in one step, which lasts in total approximately from 3 to 4 min, until a maximum dropping temperature of 165 C. is reached.

[0148] The mixture thus obtained is recovered and cooled and then sulfur and an accelerator of sulfenamide type are incorporated on a mixer (homofinisher) at 30 C., everything being mixed (productive phase) for an appropriate time (for example between 5 and 12 min).

[0149] 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. In the case where metal reinforcers are present in the composition, the metal reinforcers were calendered between two layers of rubber composition in the raw (unvulcanized) state, each having a thickness of around 1 mm, in a way well known to those skilled in the art.

[0150] The samples thus produced were cured for 25 minutes at 150 C. or 90 minutes at 160 C. in a bell-shaped press. Some samples also underwent, after curing, a step of thermo-oxidative ageing for a period of 1 or 2 weeks in an oven at a temperature of 77 C., in order to compare the kinetics of the properties measured. All the samples were analysed after having been cooled to ambient temperature for 24 hours.

[0151] III. Tests on Rubber Compositions

[0152] Thirteen rubber compositions were prepared as indicated above, nine in accordance with the invention (hereinafter denoted C1 to C9) and four not in accordance (control composition, hereinafter denoted T1 to T4). Their formulations (in phr) and their properties have been summarized in Table 2 below. The BET specific surface area and the COAN of the carbon blacks used in these formulations are specified in Table 3.

[0153] The control composition T1 is a composition conventionally used in tyre treads in order to reduce rolling resistance.

[0154] The control compositions T2 and T3 differ from the compositions in accordance with the present invention in that the carbon black used has a BET specific surface area of greater than 70 m.sup.2/g.

[0155] The control composition T4 differs from the compositions in accordance with the present invention in that the carbon black to silica weight ratio is less than 0.3.

[0156] The tan()max results are presented in base 100 relative to the control composition T1. The lower the plus value of tan()max at 60 C. base 100, the lower will be the hysteresis of the composition and thus the more its rolling resistance will be improved.

TABLE-US-00002 TABLE 2 Formulations tested and associated results T1 C1 C2 C3 C4 C5 C6 C7 C8 C9 T2 T3 T4 NR (1) 100 100 100 100 100 100 100 100 100 100 100 100 100 N330 (2) 25 N347 (2) 25 N550 (2) 25 20 30 25 10 N683 (2) 20 N772 (2) 25 35 Ecorax S204 (3) 25 30 Silica (4) 48 27 32 22 32 27 27 27 27 27 27 27 40 Carbon / 0.93 0.63 1.36 0.63 0.93 0.93 1.30 0.93 1.11 0.93 0.93 0.25 black/silica weight ratio Coupling agent 8.3 4.7 5.5 3.8 5.5 4.7 4.7 4.7 4.7 4.7 4.7 4.7 7.2 (5) DPG (6) 1 1 1 1 1 1 1 1 1 1 1 1 1 6PPD (7) 3 3 3 3 3 3 3 3 3 3 3 3 3 Stear. Ac. (8) 0.6 0.6 0.6 0.6 0.6 0.4 0.6 0.6 0.6 0.6 0.6 0.6 0.6 ZnO (9) 8 8 8 8 8 8 8 8 8 8 8 8 8 Co salt (10) 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Sulfur 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 TBBS (11) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Tan()max 100 86 86 84 95 90 69 94 61 73 130 106 145 return at 60 C. (1) Natural Rubber (2) Carbon black N330, N347, N550, N683, N772 (name according to ASTM standard D-1765) (3) Carbon black Ecorax S204 from Orion Engineering (4) Zeosil 160MP silica, sold by Rhodia (5) Coupling agent: TESPT Si69 from Evonik (6) Perkacit DPG diphenylguanidine from Flexsys (7) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys) (8) Stearin (Pristerene 4931 from Uniqema) (9) Zinc oxide (industrial grade-Umicore) (10) cobalt naphthenate-product No. 60830 from Fluka (11) N-tert-butyl-2-benzothiazylsulfenamide Santocure TBBS from Flexsys

TABLE-US-00003 TABLE 3 Specific surface areas and COAN of the carbon blacks used BET specific surface area COAN Carbon blacks (m.sup.2/g) (ml/100 g) N330 75 88 N347 83 96 N550 39 85 N683 34 85 N772 30 59 Ecorax S204 20 85

[0157] The results presented in Table 1 show that the compositions in accordance with the invention all make it possible to improve the rolling resistance. Conversely, the use of carbon black having a BET specific surface area higher than the carbon blacks in accordance with the present invention degrades the rolling resistance.

[0158] Moreover, it was noted that the compositions in accordance with the present invention exhibit good adhesion properties. It was observed that the use of stearic acid in a content of greater than or equal to 0.4 phr makes it possible to improve the adhesion of the compositions to metal cords, without penalizing the rolling resistance. Particularly advantageous results were obtained with stearic acid contents within a range extending from 0.5 to 1 phr.

[0159] Finally, particularly advantageous results from the point of view of cohesion/adhesion compromise, in particular after thermo-oxidative ageing, were obtained for compositions according to the invention of which the carbon black to silica ratio is within a range extending from 0.7 to 1.3. Below 0.7, the adhesion properties, although advantageous, are no longer optimal, whereas above 1.3, it is the cohesion properties which are no longer optimal.