RUBBER COMPOSITION COMPRISING A SPECIFIC CRUMB RUBBER

Abstract

A rubber composition is based on at least an elastomer, a reinforcing filler and a crosslinking system and a crumb rubber, said crumb having a particle size distribution such that it comprises less than 35% by weight of particles having a size of less than 50 m and less than 30% by weight of particles having a size of greater than 200 m.

Claims

1.-29. (canceled)

30. A rubber composition based on at least an elastomer, a reinforcing filler, a crosslinking system and a crumb rubber, wherein the crumb rubber has a particle size distribution such that it comprises less than 35% by weight of particles having a size of less than 50 m and less than 30% by weight of particles having a size of greater than 200 m.

31. The rubber composition according to claim 30, wherein the crumb rubber has a particle size distribution such that it comprises less than 25% by weight of particles having a size of less than 50 m and less than 20% by weight of particles having a size of greater than 200 m.

32. The rubber composition according to claim 30, wherein the crumb rubber is present in a content ranging from 5% to 40% by weight.

33. The rubber composition according to claim 30, wherein the crumb rubber is present in a content ranging from 5 to 100 phr.

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

35. The rubber composition according to claim 30, wherein the crumb rubber has a chloroform extract of between 5% and 85% by weight.

36. The rubber composition according to claim 30, wherein the crumb rubber has not undergone any modification by a treatment selected from the group consisting of thermal, mechanical, biological, and chemical treatments and combinations thereof.

37. The rubber composition according to claim 36, wherein the crumb rubber has an acetone extract of between 3% and 15% by weight.

38. The rubber composition according to claim 36, wherein the crumb rubber has a chloroform extract of between 3% and 20% by weight.

39. The rubber composition according to claim 36, wherein the crumb rubber has a ratio of a chloroform extract to an acetone extract, expressed as weight percentage, of less than 1.5.

40. The rubber composition according to claim 36, wherein the crumb rubber has a chloroform extract of which the weight-average molecular weight is less than 10,000 g/mol.

41. The rubber composition according to claim 30, wherein the crumb rubber has a morphology modified by a treatment selected from the group consisting of thermal, mechanical, biological, and chemical treatments and combinations thereof.

42. The rubber composition according to claim 41, wherein the crumb rubber has an acetone extract of between 5% and 20% by weight.

43. The rubber composition according to claim 41, wherein the crumb rubber has a chloroform extract of between 15% and 85% by weight.

44. The rubber composition according to claim 41, wherein the crumb rubber has a ratio of a chloroform extract to an acetone extract, expressed as weight percentage, of greater than or equal to 1.5.

45. The rubber composition according to claim 41, wherein the crumb rubber has a chloroform extract of which the weight-average molecular weight is greater than 10,000 g/mol.

46. The rubber composition according to claim 41, wherein the crumb rubber has a Mooney viscosity of between 40 and 90.

47. The rubber composition according to claim 30, wherein the crumb rubber has a carbon black weight fraction ranging from 20% to 40% by weight.

48. The rubber composition according to claim 30, wherein the crumb rubber has a particle size distribution such that it comprises less than 35% by weight of particles having a size of less than 50 m and less than 30% by weight of particles having a size of greater than 100 m.

49. The rubber composition according to claim 30, wherein the crumb rubber has a particle size distribution such that it comprises less than 35% by weight of particles having a size of less than 100 m and less than 30% by weight of particles having a size of greater than 200 m.

50. The rubber composition according to claim 30, wherein the elastomer predominantly comprises an elastomer selected from the group consisting of essentially unsaturated diene elastomers.

51. The rubber composition according to claim 50, wherein the predominant elastomer is selected from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures thereof.

52. The rubber composition according to claim 51, wherein the predominant elastomer is selected from the group consisting of polybutadienes, polyisoprenes and mixtures thereof.

53. The rubber composition according to claim 30, wherein the reinforcing filler is selected from the group consisting of silicas, carbon blacks, and mixtures thereof.

54. The rubber composition according to claim 30, wherein a content of reinforcing filler is within a range extending from 5 to 200 phr.

55. The rubber composition according to claim 30, wherein a predominant reinforcing filler is carbon black at a content within a range extending from 30 to 90 phr.

56. The rubber composition according to claim 30, wherein a predominant reinforcing filler is silica at a content within a range extending from 30 to 90 phr.

57. A tire comprising the rubber composition according to claim 30.

58. The tire according to claim 57, wherein the rubber composition constitutes all or part of a tread of the tire.

Description

IIIEXEMPLARY EMBODIMENTS OF THE INVENTION

II-1 Characterization of the Crumb Rubbers and the Rubber Compositions of Examples

[0079] In the examples, the crumb rubbers are characterized as indicated below.

Measurement of the Particle Size:

[0080] The particle size weight distribution can be measured using a laser particle size analyzer of the mastersizer 3000 type from the company Malvern. The measurement is carried out by the liquid route, diluted in alcohol after an ultrasound pretreatment for 1 min in order to guarantee particle dispersion. The measurement is carried out in accordance with Standard ISO-13320-1.

Measurement of the Acetone Extract:

[0081] The acetone extract content is measured according to Standard ISO1407 by means of an extractor of soxhlet type.

[0082] A sample test specimen (between 500 mg and 5 g) is introduced into an extraction chamber and then placed in the extractor tube of the soxhlet. A volume of acetone equal to two or three times the volume of the extractor tube is placed in the collector of the soxhlet. The soxhlet is subsequently assembled and then heated for 16 h.

[0083] The sample is weighed after extraction. The acetone extract content corresponds to the loss of weight of the sample during the extraction, related back to the initial weight.

Measurement of the Chloroform Extract:

[0084] The chloroform extract content is measured according to Standard ISO1407 by means of an extractor of soxhlet type.

[0085] A sample test specimen (between 500 mg and 5 g) is introduced into an extraction chamber and then placed in the extractor tube of the soxhlet. A volume of chloroform equal to two or three times the volume of the extractor tube is placed in the collector of the soxhlet. The soxhlet is subsequently assembled and then heated for 16 h.

[0086] The sample is weighed after extraction. The chloroform extract content corresponds to the loss of weight of the sample during the extraction, related back to the initial weight.

Measurement of the Average Molecular Weights of the Chloroform Extract:

[0087] The molecular weights are determined by size exclusion chromatography, according to a Moore calibration and according to Standard ISO16014.

[0088] The weight-average molecular weight (Mw) of the chloroform extract is carried out by size exclusion chromatography (SEC) with a refractive index (RI) detector. The system is composed of an Alliance 2695 system from Waters, a column oven from Waters and also of an RI 410 detector from Waters. The set of columns used is composed of two PL GEL MIXED D columns (3007.5 mm 5 m) followed by two PL GEL MIXED E columns (3007.5 mm 3 m) from the company Agilent. These columns are placed in a column oven thermostated at 35 C. The mobile phase used is non-anti-oxidized tetrahydrofuran. The flow rate of the mobile phase is 1 ml/min. The RI detector is also thermostated at 35 C.

[0089] The chloroform extract is dried under a nitrogen stream. The dry extract is then taken up at 1 g/I in non-anti-oxidized tetrahydrofuran at 250 ppm for 2 hours with stirring. The solution obtained is filtered using a syringe and a single-use 0.45 m PTFE syringe filter. 100 l of the filtered solution are injected into the conditioned chromatographic system at 1 ml/min and 35 C.

[0090] The Mw results are provided by integration of the chromatographic peaks detected by the RI detector above a value of 2000 g/mol. The Mw is calculated from a calibration carried out using polystyrene standards.

Measurement of the Carbon Black Weight Fraction:

[0091] The carbon black weight fraction is measured by thermogravimetric analysis (TGA) according to Standard NF T-46-07, on an instrument from the company Mettler Toledo, model TGA/DSC1. Approximately 20 g of sample are introduced into the thermal analyzer, then subjected to a thermal program from 25 to 600 C. under an inert atmosphere (pyrolyzable phase), then from 400 to 750 C. and an oxidizsing atmosphere (oxidizable phase). The weight of the sample is continuously measured throughout the thermal programme. The black content corresponds to the loss of weight measured during the oxidizable phase related back to the initial weight of sample.

[0092] In the examples, the rubber compositions are characterized, before and/or after curing, as indicated below.

Measurement of the Melt Flow Index:

[0093] This measurement is suitable for the measurement of melt flow index commonly used in the plastics industry for the characterization of the extrudability, in particular of thermoplastics. The measurement is described in Standard ASTM D1238 (or NF T 51-016) and modified as follows.

[0094] The sample of the elastomeric mixture is heated, in a capillary rheometer, to a regulated temperature (approximately 90 deg. C.). The mass which has flowed (extrudate) through a cylindrical die (diameter 2 mm) made of tungsten carbide is subsequently measured using a loaded piston. The melt flow index value corresponds to the displacement of the piston under the effect of the load, in hundredths of a millimetre, for a time of 10 seconds (corresponds to a flow rate). The index 100 is given for the melt flow index of the control composition; an index of greater than 100 indicates a greater melt flow index and a lower index indicates a poorer melt flow index.

Measurement of Elongation at Break (Tensile Tests):

[0095] 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 nominal (or apparent) secant modulus measured in first elongation, calculated by reducing to the initial cross section of the test specimen. The nominal secant moduli (or apparent stresses, in MPa) are measured in first elongation at 50% and 100% elongation, respectively denoted MSA50 and MSA100.

[0096] The breaking stresses (in MPa) and the elongations at break (in %) are measured at 23 C.2 C. according to Standard NF T 46-002 or at 100 C.

III-2 Preparation of the Crumbs

[0097] As indicated above, the specific crumbs of the invention are prepared by cryogenic milling then successive screenings so as to keep only the desired sizes between 50 and 200 microns, and preferentially between 50 and 100 microns or between 100 and 200 microns. Any composition of the crumb may be suitable for the preparation of these crumbs. For the implementation examples, the crumbs used are of a heavy-weight vehicle tyre tread composition as presented in Table 1 below:

TABLE-US-00001 TABLE 1 Crumb composition NR (1) 80 BR (2) 20 Carbon black (3) 48 Antioxidant (4) 3 Stearic acid (5) 2 Zinc oxide (6) 3 Accelerator (7) 1 Sulfur 1.5
(1) NR: Natural rubber
(2) BR: polybutadiene, CB24 from the company Lanxess; 96% of 1,4-cis-; Tg=107 C.
(3) Carbon black, ASTM N234 grade
(4) N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine (Santoflex 6-PPD) from the company Flexsys
(5) Stearin, Pristerene 4931 from the company Uniqema
(6) Zinc oxide, industrial gradethe company Umicore
(7) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from the company Flexsys)

[0098] This composition was milled. The milling is carried out on a piece of equipment, CUM150, from the company Netzsch using spike diameters of 3 mm and a mill rotation speed of 15 000 rpm. The matter flow rate is about 50 kg/h and the equipment is cooled in order to guarantee a mill outlet gas temperature of 60 C. The milled material was then screened as described above, in order to obtain the crumbs 1 to 5 presented in Table 2 below:

[0099] In Table 2 below, a size distribution indicated as 0 to 200 m (respectively 0 to 100 m or 0 to 50 m) means that this crumb has a particle size distribution such that it comprises less than 35% (preferentially less than 25%) by weight of particles having a size of greater than 200 m (or respectively greater than 100 m or greater than 50 m).

[0100] Likewise, a size distribution indicated as 50 to 100 m means that this crumb has a particle size distribution such that it comprises less than 35% (preferably less than 25%) by weight of particles having a size of less than 50 m and less than 30% (preferably less than 20%) by weight of particles having a size of greater than 100 m.

[0101] Likewise, a size distribution indicated as 100 to 200 m means that this crumb has a particle size distribution such that it comprises less than 35% (preferably less than 25%) by weight of particles having a size of less than 100 m and less than 30% (preferably less than 20%) by weight of particles having a size of greater than 200 m.

TABLE-US-00002 TABLE 2 Crumbs Crumb 1 Crumb 2 Crumb 3 Crumb 4 Crumb 5 Size distribution 0 to 200 m 0 to 100 m 0 to 50 m 50 to 100 m 100 to 200 m Acetone extract 4.6% 4.6% 4.6% 4.6% 4.6% Chloroform extract 6.3% 6.3% 6.3% 6.3% 6.3% Mw of the chloroform 7000 g/mol 7000 g/mol 7000 g/mol 7000 g/mol 7000 g/mol extract Carbon black weight 30% 30% 30% 30% 30% fraction

III-3 Rubber Compositions

[0102] The compositions are manufactured with introduction of all of the constituents onto an internal mixer, with the exception of the vulcanization system. The vulcanizing agents (sulfur and accelerator) are introduced into an external mixer at low temperature (the constituent rolls of the mixer being at around 30 C.).

[0103] The object of the examples presented in Table 3 is to compare the different rubber properties of control compositions (T1 to T4) to the properties of compositions in accordance with the invention (C1 and C2). The properties measured, before and after curing, are presented in Table 4.

TABLE-US-00003 TABLE 3 T1 T2 T3 T4 C1 C2 NR (1) 80 80 80 80 80 80 BR (2) 20 20 20 20 20 20 Carbon black (3) 48 48 48 48 48 48 Crumb 1 0 53 0 0 0 0 Crumb 2 0 0 53 0 0 0 Crumb 3 0 0 0 53 0 0 Crumb 4 0 0 0 0 53 0 Crumb 5 0 0 0 0 0 53 Antioxidant (4) 3 3 3 3 3 3 Stearic acid (5) 2.6 2.6 2.6 2.6 2.6 2.6 Zinc oxide (6) 3.3 3.3 3.3 3.3 3.3 3.3 Accelerator (7) 1.15 1.15 1.15 1.15 1.15 1.15 Sulfur 1.9 1.9 1.9 1.9 1.9 1.9 (1) NR: Natural rubber (2) BR: polybutadiene, CB24 from Lanxess; 96% of 1,4-cis-; Tg = 107 C. (3) Carbon black, ASTM N234 grade (4) N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine (Santoflex 6-PPD) from the company Flexsys (5) Stearin, Pristerene 4931 from the company Uniqema (6) Zinc oxide, industrial grade - Umicore (7) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from Flexsys)

TABLE-US-00004 TABLE 4 T1 T2 T3 T4 C1 C2 Melt flow index (base 100 104 85 91 134 128 100) Elongation at break 100 103 106 107 104 106 23 C. (base 100) Elongation at break 100 111 123 86 121 118 100 C. (base 100)

[0104] Compared with the control compositions, it is noted that only compositions C1 and C2 in accordance with the invention make it possible to improve the melt flow index while at the same time preserving very good elongations at break at 23 C. and 100 C.