RUBBER COMPOSITION COMPRISING A SPECIFIC CRUMB RUBBER

Abstract

A rubber composition is based on at least an elastomer, a reinforcing filler, a crosslinking system and a crumb rubber, in which the crumb exhibits a content of sulfur and a content of accelerator such that their sum is less than or equal to 5 parts by weight per 100 parts by weight of elastomer (phr), the said crumb exhibiting a total sulfur content of less than or equal to 4 parts by weight per 100 parts by weight of elastomer (phr) in the composition of the crumb.

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 exhibits a content of sulfur and a content of accelerator such that a sum of the contents is less than or equal to 5 parts by weight per 100 parts by weight of elastomer (phr), and wherein the crumb rubber exhibits a total sulfur content of less than or equal to 4 parts by weight per 100 parts by weight of elastomer (phr) in the composition of the crumb rubber.

31. The rubber composition according to claim 30, wherein the crumb rubber exhibits a total sulfur content of less than or equal to 3 phr in the composition of the crumb rubber.

32. The rubber composition according to claim 30, wherein the crumb rubber exhibits a content of sulfur and a content of accelerator such that the sum of the contents is less than or equal to 4 phr in the composition of the crumb rubber.

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

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

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

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

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

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

39. The rubber composition according to claim 37, wherein the crumb rubber exhibits a chloroform extract of between 3% and 20% by weight.

40. The rubber composition according to claim 37, wherein the crumb rubber exhibits a ratio of a chloroform extract to an acetone extract, expressed as percentage by weight, of less than 1.5.

41. The rubber composition according to claim 37, wherein the crumb rubber exhibits a chloroform extract, the weight-average molecular weight of which is less than 10,000 g/mol.

42. The rubber composition according to claim 37, wherein the crumb rubber exhibits an average particle size D50 of between 10 and 400 m.

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

44. The rubber composition according to claim 43, wherein the crumb rubber exhibits an acetone extract of between 5% and 20% by weight.

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

46. The rubber composition according to claim 43, wherein the crumb rubber exhibits a ratio of a chloroform extract to an acetone extract, expressed as percentage by weight, of greater than or equal to 1.5.

47. The rubber composition according to claim 43, wherein the crumb rubber exhibits a chloroform extract, the weight-average molecular weight of which is greater than 10,000 g/mol.

48. The rubber composition according to claim 43, wherein the crumb rubber exhibits a Mooney viscosity of between 40 and 90.

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

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

IIIIMPLEMENTATIONAL EXAMPLES OF THE INVENTION

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

[0084] In the examples, the crumb rubbers are characterized as indicated below.

Measurement of the Size of the Particles:

[0085] The size of the particles (in particular the D50) can be measured by a laser particle size analyser of the Mastersizer 3000 type from Malvern. The measurement is carried out by the liquid route, diluted in alcohol after an ultrasound pretreatment for 1 min in order to guarantee the dispersion of the particles. The measurement is carried out in accordance with Standard ISO-13320-1.

Measurement of the Acetone Extract:

[0086] The acetone extract content is measured according to Standard ISO1407 by means of an extractor of Soxhlet type.

[0087] A test sample (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.

[0088] The sample is weighed after extraction. The acetone extract content corresponds to the loss in weight of the sample during the extraction, with respect to its initial weight.

Measurement of the Chloroform Extract:

[0089] The chloroform extract content is measured according to Standard ISO1407 by means of an extractor of Soxhlet type.

[0090] A test sample (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.

[0091] The sample is weighed after extraction. The chloroform extract content corresponds to the loss in weight of the sample during the extraction, with respect to its initial weight.

Measurement of the Average Molecular Weights of the Chloroform Extract:

[0092] The molecular weights are determined by size exclusion chromatography, according to a Moore calibration and according to Standard ISO16014.

[0093] The weight-average molecular weight (Mw) of the chloroform extract is measured by size exclusion chromatography (SEC) with a refractive index (RI) detector. The system is composed of an Alliance 2695 line from Waters, of 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 Agilent. These columns are placed in a column oven thermostatically controlled at 35 C. The mobile phase used is non-antioxidized tetrahydrofuran. The flow rate of the mobile phase is 1 ml/min. The RI detector is also thermostatically controlled at 35 C.

[0094] The chloroform extract is dried under a nitrogen stream. The dry extract is subsequently taken up at 1 g/I in non-antioxidized tetrahydrofuran at 250 ppm with stirring for 2 hours. 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.

[0095] 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 Mooney Viscosity (or Mooney Plasticity)

[0096] Use is made of an oscillating consistometer as described in French Standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state (i.e., before curing) is moulded in a cylindrical chamber heated to 100 C. After preheating for one minute, the rotor rotates within the test specimen at 2 revolutions/minute and the working torque for maintaining this movement is measured after rotating for 4 minutes. The Mooney plasticity (ML 1+4) is expressed in Mooney unit (MU, with 1 MU=0.83 newton.Math.metre). The lower the Mooney value, the lower the viscosity before curing and the better the processability of the composition.

Measurement of the Fraction by Weight of Carbon Black:

[0097] The fraction by weight of carbon black is measured by a thermogravimetric analysis (TGA) according to Standard NF T-46-07, on an appliance from Mettler Toledo, model TGA/DSC1. Approximately 20 g of sample are introduced into the thermal analyser, then subjected to a thermal program from 25 to 600 C. under an inert atmosphere (pyrolysable phase) and then from 400 to 750 C. under an oxidizing 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, with respect to the initial weight of sample.

Measurement of the Total Sulfur Content in the Composition of the Crumb:

[0098] The sulfur content in the composition of the crumb is measured by elemental analysis, using the Thermo Scientific Flash 2000 microanalyser. The analysis comprises a stage of combustion of the sample and then a stage of separation of the compounds formed.

[0099] Approximately 1 mg of sample is introduced into the microanalyser, where it is subjected to a flash combustion of 1000 C. under oxygen. The gases formed are then oxidized by virtue of the excess oxygen and of a tungstic anhydride catalyst. A stage of reduction by passing over copper subsequently makes it possible to trap the excess oxygen and to reduce the nitrogen oxides to give N.sub.2 and also the sulfites to give sulfur to dioxide SO.sub.2. The water is trapped and the compounds N.sub.2, CO.sub.2 and SO.sub.2 formed are subsequently separated on a chromatographic column and then detected by a katharometer. The total sulfur is quantified by measurement of the area of the SO.sub.2 peak, after calibration with standards.

[0100] In the examples, the rubber compositions are characterized, before and/or after curing, as indicated below.

Measurement of the Elongation at Break at 23 C. and at 100 C.:

[0101] The measurement is carried out by tensile tests, which 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. All these tensile measurements are carried out under the standard conditions of temperature (232 C.) or at 100 C., if appropriate, and of hygrometry (5010% relative humidity). The elongations at break (in %) are measured in particular.

[0102] The results are given in base 100 in order to make the results easier to read and understand; that is to say that the value 100 is arbitrarily assigned to the best control, in order to subsequently compare the values of the various solutions tested. In this way, a lower value represents a decrease in tear strength performance (that is to say, a decrease in the elongation at break), whereas a higher value represents a better performance.

III-2 Preparation of the Crumbs

[0103] For the implementational examples, the crumbs used result from the grinding of a heavy-duty vehicle tyre tread composition as presented in Table 1 below. The grinding is carried out on an item of equipment CUM150 from Netzsch using pin diameters of 3 mm and a rotational speed of the mill of 15 000 rpm. The material flow rate is of the order of 50 kg/h and the facility is cooled in order to guarantee a gas temperature at the outlet of the mill of 60 C.

TABLE-US-00001 TABLE 1 Crumb composition P1 P2 NR (1) 100 100 Carbon black (2) 57 57 Antioxidant (3) 1.5 1.5 Stearic acid (4) 2 2 Zinc oxide (5) 3 3 Accelerator (6) 2 1.5 Sulfur 5 1.5 Sulfur + accelerator content 7 3 Total S content (7) 5.6 2.1 Acetone extract 4.6% 4.6% Chloroform extract 6.3% 6.3% Mw (Chloroform extract) 7000 g/mol 7000 g/mol D50 155 m 155 m (1) NR: Natural rubber (2) Carbon black, ASTM N234 grade (3) N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine (Santoflex 6-PPD) from Flexsys (4) Stearin, Pristerene 4931 from Uniqema (5) Zinc oxide, industrial grade - Umicore (6) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from Flexsys) (7) The total sulfur in the composition very predominantly originates from the sulfur added in the crosslinking system but also from the sulfur present in other ingredients of the composition. An amount of the order of 0.5% of sulfur is present in the carbon black. A small amount (0.1%) of sulfur is also contributed by the accelerator CBS.

III-3 Rubber Compositions

[0104] The compositions are manufactured with introduction of all of the constituents onto an internal mixer, with the exception of the vulcanization system. The vulcanization agents (sulfur and accelerator) are introduced onto an external mixer at low temperature (the constituent rollers of the mixer being at approximately 30 C.). The crumbs can be introduced into the internal or external mixer.

[0105] The object of the examples presented in Table 2 is to compare the different rubber properties of the control compositions (C1 and C2) with the properties of the compositions in accordance with the invention (I1 and I2). The properties measured, before and after curing, are presented in Table 3.

TABLE-US-00002 TABLE 2 C1 I1 C2 I2 NR (1) 80 80 100 100 BR (2) 20 20 0 0 Carbon black (3) 48 48 48 48 Crumb P1 40 0 40 0 Crumb P2 0 40 0 40 Antioxidant (4) 3 3 3 3 Stearic acid (5) 2 2 2 2 Zinc oxide (6) 3 3 3 3 Accelerator (7) 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 (1) NR: Natural rubber (2) BR: polybutadiene, CB24 from Lanxess; 96% of cis-1,4; Tg = 107 C. (3) Carbon black, ASTM N234 grade (4) N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine (Santoflex 6-PPD) from Flexsys (5) Stearin, Pristerene 4931 from Uniqema (6) Zinc oxide, industrial grade - Umicore (7) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from Flexsys)

TABLE-US-00003 TABLE 3 C1 I1 C2 I2 Elongation at break at 100 C. (base 100) 100 136 100 140 Elongation at break at 23 C. (base 100) 100 118 100 122

[0106] In comparison with the control composition, it is noted that the composition I in accordance with the invention makes it possible to improve the tear strength, as shown by the measurements of elongation at break at 23 C. and at 100 C.