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 5 to 60 phr of carbon black having a BET specific surface area of less than 70 m.sup.2/g, termed coarse carbon black, and from 10 to 30 phr of carbon black having a BET specific surface area of greater than or equal to 70 m.sup.2/g, termed fine carbon black; a salt of an alkali, alkaline-earth or lanthanide metal; and a crosslinking system.

Claims

1.-32. (canceled)

33. A rubber composition based on at least: a diene elastomer comprising mainly an isoprene elastomer; a reinforcing filler comprising: from 5 to 60 phr of coarse carbon black having a BET specific surface area of less than 70 m.sup.2/g, and from 10 to 30 phr of fine carbon black having a BET specific surface area of greater than equal to 70 m.sup.2/g; a salt of an alkali, alkaline-earth or lanthanide metal salt; and a crosslinking system.

34. The rubber composition according to claim 33, wherein the diene elastomer comprises from 60% to 100% by weight of isoprene elastomer relative to the weight of diene elastomer.

35. The rubber composition according to claim 33, wherein the isoprene elastomer comprises a weight content of 1,4-cis bonds of at least 90% of the weight of the isoprene elastomer.

36. The rubber composition according to claim 33, wherein the isoprene elastomer is selected from the group consisting of natural rubber, a synthetic polyisoprene and a mixture thereof.

37. The rubber composition according to claim 33, wherein the coarse carbon black has a BET specific surface area of less than 50 m.sup.2/g.

38. The rubber composition according to claim 33, wherein the coarse carbon black has a COAN oil absorption number of less than 90 ml/100 g.

39. The rubber composition according to claim 33, wherein the fine carbon black has a BET specific surface area within a range extending from 70 to 100 m.sup.2/g.

40. The rubber composition according to claim 33, wherein the fine carbon black has a COAN oil absorption index greater than or equal to 90 ml/100 g.

41. The rubber composition according to claim 33, wherein the coarse carbon black content is within a range extending from 10 to 60 phr.

42. The rubber composition according to claim 33, wherein the content of fine carbon black is within a range extending from 10 to 25 phr.

43. The rubber composition according to claim 33, wherein the total content of carbon black is within a range extending from 30 to 70 phr.

44. The rubber composition according to claim 33, wherein the ratio of coarse carbon black to fine carbon black is within a range extending from 0.5 to 3.

45. The rubber composition according to claim 33, wherein the salt of the alkaline-earth, alkali or lanthanide metal is an acetylacetonate of an alkaline-earth, alkali or lanthanide metal.

46. The rubber composition according to claim 33, wherein the salt is a salt of an alkaline-earth metal.

47. The rubber composition according to claim 46, wherein the salt of an alkaline-earth metal is a magnesium salt.

48. The rubber composition according to claim 33, 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.

49. The rubber composition according to claim 33, wherein the rubber composition comprises 0 to less than 10 phr of silica.

50. The rubber composition according to claim 33, wherein the rubber composition comprises 0 to less than 5% of coupling agent by weight relative to the total weight of the carbon black.

51. The rubber composition according to claim 33 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 3 phr.

53. The rubber composition according to claim 33, wherein the crosslinking system comprises molecular sulfur, a sulfur donor, or both molecular sulfur and a sulfur donor.

54. The rubber composition according to claim 53, wherein the sulfur content is greater than 2.5 phr.

55. The rubber composition according to claim 33 further comprising a cobalt salt.

56. The rubber composition according to claim 55, wherein the cobalt salt is selected from the group consisting of abietates, acetylacetonates, tallates, naphthenates, resinates and the mixtures thereof.

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

58. The rubber composition according to claim 33 further comprising an antioxidant selected from the group consisting of substituted p-phenylenediamines, substituted diphenylamines, substituted triphenylamines, quinoline derivatives, and mixtures thereof.

59. The rubber composition according to claim 58, wherein the antioxidant is selected from the group consisting of substituted p-phenylenediamines and mixtures thereof.

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

61. A finished or semi-finished rubber article comprising a rubber composition according to claim 33.

62. A tire comprising a rubber composition according to claim 33.

63. The tire according to claim 62, wherein the rubber composition is present in at least one internal layer.

64. The tire according to claim 63, 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

[0146] I. Measurements and Tests Used

[0147] I.1 Dynamic Properties

[0148] 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.

[0149] I.2 Tensile Tests

[0150] These tensile tests make it possible to determine the elastic modii and the properties at break and are based on the standard NF ISO 37 of December 2005 on a type-2 dumbbell-shaped test specimen. The elongation at break thus measured at 100 C. is expressed as % elongation.

[0151] I.3 Adhesion Test

[0152] A tearing-out test in accordance with ASTM standard D2229 was carried out on test specimens comprising metal cords of 2.30 NF 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.

[0153] II. Preparation of the Compositions

[0154] 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.

[0155] 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).

[0156] 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.

[0157] III. Tests on Rubber Compositions

[0158] Six rubber compositions were prepared as indicated above, five in accordance with the invention (hereinafter denoted C1 to C5) 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.

[0159] The control composition T1 is a composition conventionally used in tyre treads in order to reduce rolling resistance.

[0160] 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.

[0161] The elongation at break results are indicated in 100, the value 100 being assigned to the control. A result less than 100 indicates a decrease in the value in question, and conversely, a result greater than 100 will indicate an increase in the value in question.

TABLE-US-00001 TABLE 1 Formulations tested and associated results T1 C1 C2 C3 C4 C5 NR (1) 100 100 100 100 100 100 N326 (2) 55 N375 (2) 10 20 10 30 30 N550 (2) 30 25 25 15 5 6PPD (3) 3 3 3 3 3 3 Stear. Ac. (4) 1 1 1 1 1 1 ZnO (5) 8 8 8 8 8 8 Acac(Mg) (6) 1.8 1.8 1.8 1.8 1.8 Co salt (7) 1 1 1 1 1 1 Sulfur 5 5 5 5 5 5 TBBS (8) 0.9 0.9 0.9 0.9 0.9 0.9 Tan()max 100 52 61 42 72 55 return at 40 C. AR % 100 C. 100 116 106 129 111 136 (1) Natural Rubber (2) Carbon black N326, N375, N550 (name according to ASTM standard D-1765) (3) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys) (4) Stearin (Pristerene 4931 from Uniqema) (5) Zinc oxide (industrial grade - Umicore) (6) Magnesium acetylacetonate NACEM Magnesium (CAS 68488-07-3) from the company Niho Kagaku Sangyo (7) cobalt naphthenate - product No. 60830 from Fluka (8) 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 N375 91 96 N550 39 85

[0162] The results presented in Table 1 show that the compositions in accordance with the invention all make it possible to improve the rolling resistance, but also the mechanical properties of the compositions. Moreover, it was noted that the compositions in accordance with the present invention exhibit good adhesion properties.