RUBBER COMPOSITION COMPRISING A SPECIFIC CRUMB RUBBER

Abstract

A rubber composition is based on at least one elastomer, a reinforcing filler, a crosslinking system and from 5 to 100 phr of a crumb rubber, the crumb having a mean size D50 of between 100 and 300 μm, and a particle size distribution such that the ratio of the mean sizes D10/D50 is greater than or equal to 0.5; the composition also comprises 1 to 10 phr of a tackifying resin having a number-average molecular weight (Mn) greater than 800 g/mol and a polydispersity index (PI) greater than or equal to 2.0.

Claims

1.-23. (canceled)

24. A rubber composition based on: at least one elastomer; a reinforcing filler; a crosslinking system; from 5 to 100 phr of a crumb rubber, the crumb having a mean size D50 of between 100 and 300 μm, and a particle size distribution such that a mean size ratio D10/D50 is greater than or equal to 0.5; and 1 to 10 phr of a tackifying resin having a number-average molecular weight Mn greater than 800 g/mol and a polydispersity index PI greater than or equal to 2.0.

25. The rubber composition according to claim 24, wherein the mean size ratio D10/D50 of the crumb rubber is between 0.55 and 0.95.

26. The rubber composition according to claim 24, wherein the crumb rubber is present at a content ranging from 10 to 90 phr.

27. The rubber composition according to claim 24, wherein the crumb rubber has an acetone extract of between 3% and 30% by weight.

28. The rubber composition according to claim 24, wherein the crumb rubber has a chloroform extract of between 5% and 85% by weight.

29. The rubber composition according to claim 24, wherein the crumb rubber has not undergone any modification selected from thermal, mechanical, biological, and chemical treatments.

30. The rubber composition according to claim 29, wherein the crumb rubber as an acetone extract of between 3% and 15% by weight.

31. The rubber composition according to claim 30, wherein the crumb rubber has a chloroform extract of between 3% and 20% by weight.

32. The rubber composition according to claim 31, wherein the crumb rubber has a ratio of the chloroform extract to the acetone extract, expressed as percentage by weight, of less than 1.5.

33. The rubber composition according to claim 29, wherein the crumb rubber has a chloroform extract of which the weight-average molecular weight is less than 10 000 g/mol.

34. The rubber composition according to claim 24, wherein the crumb rubber has a carbon black weight fraction ranging from 20% to 40%.

35. The rubber composition according to claim 24, wherein the at least one elastomer predominantly comprises an elastomer selected from the group consisting of essentially unsaturated diene elastomers.

36. The rubber composition according to claim 35, wherein the predominant elastomer is selected from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures thereof.

37. The rubber composition according to claim 36, wherein the predominant elastomer is selected from the group consisting of polybutadienes, butadiene-styrene copolymers, natural or synthetic polyisoprenes and mixtures thereof.

38. The rubber composition according to claim 24, wherein the reinforcing filler is selected from the group consisting of silicas, carbon blacks and mixtures thereof.

39. The rubber composition according to claim 24, wherein the content of tackifying resin is within a range extending from 1 to 8 phr.

40. The rubber composition according to claim 24, wherein the tackifying resin has a number-average molecular weight Mn greater than 1000 g/mol.

41. The rubber composition according to claim 24, wherein the tackifying resin has a polydispersity index PI greater than 2.0.

42. A tire comprising the rubber composition according to claim 24.

43. The tire according to claim 42, wherein a tread of the tire comprises the rubber composition.

Description

[0077] The examples that follow illustrate the invention without, however, limiting it.

III—Implementational Examples of the Invention

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

[0078] In the examples, the crumb rubbers are characterized as indicated below.

Measurement of the Size of the Crumb Particles:

[0079] The crumb particle size weight distribution can be measured by laser particle size analysis, on a mastersizer 3000 device 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 and makes it possible to determine in particular the D10 and the D50, that is to say the mean diameter below which respectively 10% by weight and 50% by weight of the total population of particles are present.

Measurement of the Fraction by Weight of Carbon Black:

[0080] 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 analyser, then subjected to a thermal program from 25 to 600° C. under an inert atmosphere (pyrolysable phase), then from 400 to 750° C. under an oxidizing atmosphere (oxidizable phase). The weight of the sample is measured continuously throughout the thermal program. The organic matter content corresponds to the loss of weight measured during the pyrolysable phase related back to the initial weight of sample. The black content corresponds to the loss of weight measured during the oxidizable phase related back to the initial weight of sample.

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 thereof.

[0084] It is also possible to calculate the content of elastomer, which corresponds to the content of organic matter determined by thermogravimetric analysis from which the content of acetone extract is subtracted.

Measurement of the Chloroform Extract:

[0085] The chloroform extract content is measured according to standard ISO1407 by means of an extractor of soxhlet type.

[0086] 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.

[0087] 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 thereof.

Measurement of the Average Molecular Weights of the Chloroform Extract:

[0088] The molecular weights are determined by size exclusion chromatography, according to a Moore calibration and according to standard ISO16014.

[0089] The measurement of 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, 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 (300×7.5 mm 5 μm) followed by two PL GEL MIXED E columns (300×7.5 mm 3 μm) from the company 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.

[0090] The chloroform extract is dried under a nitrogen stream. The dry extract is subsequently taken up at 1 g/l 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 μm PTFE syringe filter. 100 μl of the filtered solution are injected into the conditioned chromatographic system at 1 ml/min and 35° C.

[0091] 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.

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

[0093] Green Tack (or Tack):

[0094] Tack is the ability of an assembly of unvulcanized mixtures to withstand a tearing stress.

[0095] A test device inspired by the probe tack tester (ASTM D2979-95) is used for measuring the green tack (tack). An Instron tensile testing machine comprising a fixed metal jaw and a mobile metal jaw is used. A first test specimen consisting of a 3 mm thick film of mixture is adhered to the fixed jaw. A second test specimen consisting of a 3 mm thick film of mixture is adhered to the mobile jaw. The films of mixture are adhered to the surface of the metal jaws with a double-sided adhesive (Tesafix® 4970).

[0096] In order to prepare the test specimens of mixture, the films of mixture are obtained by calendering to a thickness of 3 mm. The test specimens are cut by means of a punch of 1 cm diameter.

[0097] The measurement principle consists of bringing the two films of mixture into contact for 16 seconds while applying a compressive force of 30 N. After this contact phase, they are separated by being driven by the crosshead of the tensile testing machine. The rate of displacement of the crosshead in this tearing phase is 60 mm/s. The displacement of the crosshead and the force are measured continuously as a function of time during the contact and tearing phases.

[0098] The green tack result is the measurement of the maximum force (in Newtons, N) reached during tearing. A value of 35 N and above is considered good performance in the context of the present invention.

Percentage of Recycled Material in the Mixture:

[0099] The percentage of recycled material in the mixture is determined taking into account the weight content of crumb rubber relative to the total weight of the mixture comprising the crumb rubber and the other ingredients of the composition. This percentage is 0% in the reference mixture not comprising crumb rubber, and it is calculated as indicated above for each mixture comprising a crumb.

III-2 Preparation of the Crumbs

[0100] Any composition may be suitable for the preparation of these crumbs. For the implementation examples, the crumbs used result from recycling tyres from heavy duty vehicles.

[0101] The crumbs used in the examples of compositions below were prepared by cryogenic grinding according to the process described in document U.S. Pat. No. 7,445,170, comprising the successive and independent steps of granulation, of separation of the metal and textile reinforcements, of cooling and of micronization in order to to obtain a coarse distribution of micronic particles of vulcanized mixture. This micronization is carried out using a conical impact mill as described in document U.S. Pat. No. 7,861,958. The cryogenic input enters the mill, then is transferred by gravity to a rotor rotating at high speed. The cryogenized input is thus projected onto the walls of the rotor chamber multiple times leading to its micronization. The particles then pass through a series of two vibrating screens of the same size (20 mesh) in order to separate the last elements not made of vulcanized mixture. A coarse distribution of micronic particles of vulcanized mixture is obtained.

[0102] An additional step of separation according to a size criterion was carried out to obtain the other crumbs used in composition in the implementation examples. This separation step is carried out using a series of screens stacked in order of size. Thus, the larger particles are retained on the screen while the smaller ones pass to the lower stage on the next screen. Those skilled in the art will understand that the distributions considered below can be composed of all the particles that pass through a given screen or of all the particles retained between 2 stages.

[0103] The size distribution not retained by a 40 mesh screen constitutes “crumb 1” mentioned below.

[0104] The size distribution not retained by a 60 mesh screen constitutes “crumb 2” mentioned below.

[0105] The size distribution between an 80 mesh screen and a 140 mesh screen constitutes “crumb 3” mentioned below.

[0106] The size distributions of the 3 crumbs considered in the composition examples, determined by laser particle size analysis, are shown in table 1 below. This table also presents the composition characteristics of these crumbs.

TABLE-US-00001 TABLE 1 Crumb 1 Crumb 2 Crumb 3 D 10 59 52 112 D 50 161 126 167 D 90 341 257 249 D 10/D 50 0.37 0.41 0.67 Organic matter content (%) 63.2 Acetone extract content (%) 5.7 Elastomer content (%) 57.5 Carbon black content (%) 29.6 Chloroform extract content (%) 7.5 MW (g/mol) of the chloroform 7000 extract

III-3 Rubber Compositions

[0107] The compositions are manufactured with introduction of all of the constituents into 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.).

[0108] The object of the examples presented in table 2 is to compare the various rubber properties of compositions in accordance with the invention (C6 to C9) to the properties of compositions not in accordance with the invention (C0 to C5). The properties are presented in table 3.

TABLE-US-00002 TABLE 2 C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 NR (1) 60 60 60 60 60 60 60 60 60 60 BR (2) 10 10 10 10 10 10 10 10 10 10 SBR (3) 30 30 30 30 30 30 30 30 30 30 Carbon black (4) 62 62 62 62 62 62 62 62 62 62 Crumb 1 (5) 0 46 0 0 0 0 0 0 0 0 Crumb 2 (5) 0 0 46 46 46 46 0 0 0 0 Crumb 3 (5) 0 0 0 0 0 0 46 46 46 46 Oil (6) 10.2 10.2 10.2 10.2 10.2 10.2 10.2 10.2 10.2 10.2 Tack resin (7) 0 0 0 3 6 9 0 3 6 9 Antioxidant (8) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid (9) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Zinc oxide (10) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Accelerator (11) 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Sulfur 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 (1) NR: Natural rubber (2) BR: polybutadiene, CB24 from Lanxess; 96% of cis-1,4; Tg = −107° C. (3) SBR with 26.5% by weight of styrene units and 24% of 1,2-units of the butadiene part (Tg = 48° C.) (4) Carbon black, ASTM N375 grade (5) Crumbs 1 to 3 as presented in table 1 (6) MES (Medium Extracted Solvates) oil (Catenex SNR from Shell) (7) Escorez 1102 tackifying resin from EXXON (Mn 1370 g/mol; PI = 2.3) (8) N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (Santoflex 6-PPD) from Flexsys (9) Pristerene 4931 stearin from Uniqema (10) Zinc oxide, industrial grade - Umicore (11) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from Flexsys)

TABLE-US-00003 TABLE 3 C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 GT (force in N) 59 8 6 21 28 34 37 45 58 64 % by weight of 0.0 22.1 22.1 21.8 21.5 21.2 22.1 21.8 21.5 21.2 recycled material

[0109] It is noted that the compositions comprising a crumb make it possible to integrate into the mixture a large amount of recycled material of approximately 21% to 22%, and therefore to lower the environmental impact. However, it is also noted for the compositions not in accordance with the invention that the green tack (GT) performance is lowered below 35 N, including when adding a tackifying resin. On the other hand, the specific crumb of the invention allows a good green tack, even without tackifying resin, and in the presence of such a resin, makes it possible to achieve a level as efficient as the control, while at the same time having a higher content of recycled material (and therefore a lower environmental impact).