RUBBER COMPOSITION COMPRISING A SPECIFIC REINFORCING FILLER

Abstract

A 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 15 to 70 phr of carbon black having a BET specific surface area of less than 70 m.sup.2/g, and/or a COAN of less than 90 ml/100 g, and from 5 to 20 phr of silica; a salt of an alkaline-earth, alkali or lanthanide metal; and a crosslinking system; in which composition the carbon black to silica ratio is greater than 1.

Claims

1.-34. (canceled)

35. A rubber composition based on at least: a diene elastomer comprising mainly an isoprene elastomer; a reinforcing filler comprising: from 15 to 70 phr of carbon black having a BET specific surface area of less than 70 m.sup.2/g, and from 5 to 20 phr of silica; a salt of an alkaline-earth, alkali or lanthanide metal; and a crosslinking system; wherein the ratio of carbon black to silica is greater than 1.

36. The rubber composition according to claim 35, wherein the content of isoprene elastomer is within a range extending from 60 to 100 phr.

37. The rubber composition according to claim 35, wherein the isoprene elastomer is selected from the group consisting of natural rubber, a synthetic polyisoprene and a mixture thereof.

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

39. The rubber composition according to claim 35, wherein the carbon black has a COAN oil absorption number of less than 90 ml/100 g.

40. The rubber composition according to claim 35, 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.

41. The rubber composition according to claim 35, wherein the carbon black content is within a range extending from 20 to 70 phr.

42. The rubber composition according to claim 35, wherein the silica content is within a range extending from 5 to 15 phr.

43. The rubber composition according to claim 35, wherein the total content of silica and carbon black is within a range extending from 30 to 80 phr.

44. The rubber composition according to claim 35, wherein the carbon black to silica ratio is within a range extending from 2 to 10.

45. The rubber composition according to claim 35 further comprising a coupling agent.

46. The rubber composition according to claim 35, wherein the rubber composition comprises from 0 to less than 11% by weight relative to the weight of silica of coupling agent.

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

48. The rubber composition according to claim 35, 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.

49. The rubber composition according to claim 35, wherein the salt of the alkaline-earth, alkali or lanthanide metal is a magnesium salt or a neodymium salt.

50. The rubber composition according to claim 35, wherein the content of the alkaline-earth, alkali or lanthanide metal salt is within a range extending from 0.1 to 5 phr.

51. The rubber composition according to claim 35 further comprising stearic acid or a salt thereof.

52. The rubber composition according to claim 51, wherein the content of stearic acid or of a salt thereof is within a range extending from 0.5 to 2 phr.

53. The rubber composition according to claim 35 further comprising a cobalt salt.

54. The rubber composition according to claim 53, wherein the cobalt salt is selected from the group consisting of abietates, acetylacetonates, tallates, naphthenates, resinates and mixtures thereof.

55. The rubber composition according to claim 53, wherein the content of cobalt salt is within a range extending from 0.5 to 2 phr.

56. The rubber composition according to claim 35 further comprising an antioxidant selected from the group consisting of substituted p-phenylenediamines, substituted diphenylamines, substituted triphenylamines, quinoline derivatives, and mixtures thereof.

57. The rubber composition according to claim 56, wherein the antioxidant is selected from the group consisting of substituted p-phenylenediamines and mixtures thereof.

58. The rubber composition according to claim 56, wherein the content of antioxidant is within a range extending from 1 to 5 phr.

59. The rubber composition according to claim 35 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.

60. The rubber composition according to claim 59, wherein the metal oxide is a zinc oxide.

61. The rubber composition according to claim 59, wherein the content of metal oxide is within a range extending from 2 to 20 phr.

62. The rubber composition according to claim 59 further comprising stearic acid or a salt thereof, wherein the ratio of metal oxide to stearic acid or a salt thereof is greater than 3.

63. The rubber composition according to claim 35, wherein the crosslinking system comprises molecular sulfur, a sulfur donor, or both molecular sulfur and a sulfur donor.

64. The rubber composition according to claim 63, wherein the sulfur content is greater than 2.5 phr.

65. A finished or semi-finished rubber article comprising a rubber composition according to claim 35.

66. A tire comprising a rubber composition according to claim 35.

67. The tire according to claim 66, wherein the rubber composition is present in at least one internal layer.

68. The tire according to claim 67, wherein the internal layer is selected from the group consisting of carcass plies, crown plies, bead-wire fillings, crown feet, decoupling layers, the tread underlayer and combinations thereof.

Description

EXAMPLES

[0138] I. Measurements and Tests Used

[0139] I.1 Dynamic Properties

[0140] 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 40 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 40 C., the lower will be the hysteresis of the composition and thus the more its rolling resistance will be improved.

[0141] I.2 Adhesion Test

[0142] 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.

[0143] II. Preparation of the Compositions

[0144] 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.

[0145] 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).

[0146] 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.

[0147] III. Tests on Rubber Compositions

[0148] Five rubber compositions were prepared as indicated above, four in accordance with the invention (hereinafter denoted C1 to C4) and one not in accordance (control composition, hereinafter denoted T1). Their formulations (in phr) and their properties have been summarized in Table 1 below. The BET specific surface area and the COAN of the carbon blacks used in these formulations are specified in Table 2.

[0149] The control composition T1 is a composition conventionally used in tyre treads in order to reduce rolling resistance.

[0150] The tan()max results are presented in base 100 relative to the control composition T1. The lower the plus value of tan()max at 40 C. base 100, the lower will be the hysteresis of the composition and thus the more its rolling resistance will be improved.

TABLE-US-00001 TABLE 1 Formulations tested and associated results T1 C1 C2 C3 C4 NR (1) 100 100 100 100 100 N326 (2) 55 N550 (2) 47 57 52 47 Silica (3) 10 10 15 20 DPG (4) 1 1 1 1 6PPD (5) 3 3 3 3 3 Stear. Ac. (6) 0.6 0.6 0.6 0.6 0.6 ZnO (7) 8 8 8 8 8 Acac(Mg) (8) 1.8 1.8 1.8 1.8 1.8 Co salt (9) 1 1 1 1 1 Sulfur 5 5 5 5 5 TBBS (10) 0.8 0.8 0.8 0.8 0.8 Tan()max 100 54 73 65 67 return at 40 C. (1) Natural Rubber (2) Carbon black N326, N550 (name according to ASTM standard D-1765) (3) Zeosil 160MP silica, sold by Rhodia (4) Perkacit DPG diphenylguanidine from Flexsys (5) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys) (6) Stearin (Pristerene 4931 from Uniqema) (7) Zinc oxide (industrial grade - Umicore) (8) Magnesium acetylacetonate NACEM Magnesium (CAS 68488-07-3) from the company Niho Kagaku Sangyo (9) cobalt naphthenate - product No. 60830 from Fluka (10) N-tert-butyl-2-benzothiazylsulfenamide Santocure TBBS from Flexsys

TABLE-US-00002 TABLE 2 Specific surface areas and COAN of the carbon blacks used BET specific surface area COAN Carbon blacks (m.sup.2/g) (ml/100 g) N326 78 68 N550 39 85

[0151] The results presented in Table 1 show that the compositions in accordance with the invention all make it possible to improve the rolling resistance. Moreover, it was noted that the compositions in accordance with the present invention exhibit good adhesion properties.