COMPOSITE MATERIALS CONSISTING OF AN ORIENTED STACKING OF HARD-SOFT MIXTURES FOR MECHANICAL COUPLING IN THE PRODUCTION OF TIRE TREADS

Abstract

The present invention relates to materials making it possible to generate mechanical coupling in elastomeric compositions, of use especially for the manufacture of tyre treads. It relates in particular to a tread comprising a stack of layers having high and low stiffness moduli.

Claims

1.-29. (canceled)

30. A tread comprising at least one tread pattern consisting of a plurality of parallel layers adjacent to one another, the layers being oriented within the tread pattern parallel to a plane which is (i) perpendicular to the equatorial plane and (ii) oriented at an angle expressed in degrees relative to the radial plane, the angle being defined by the formula =45+/x, in which x is within a range extending from 10 to 30, wherein the plurality of parallel layers comprise (a) layers formed by a composition having a low stiffness modulus, the modulus of extension at 5% deformation of which is within a range extending from 2 to 8 MPa and (b) layers formed by a composition having a high stiffness modulus, the modulus of extension at 5% deformation of which is within a range extending from 30 MPa to 50 GPa.

31. The tread according to claim 30, wherein the composition having a low stiffness modulus is an elastomeric composition based on an elastomeric matrix, at least one reinforcing filler and at least one crosslinking system.

32. The tread according to claim 31, wherein the elastomeric matrix of the composition having a low stiffness modulus comprises a diene elastomer.

33. The tread according to claim 31, wherein the reinforcing filler of the composition having a low stiffness modulus is selected from the group consisting of carbon black, an inorganic filler, and a combination thereof.

34. The tread according to claim 31, wherein the crosslinking system of the composition having a low stiffness modulus comprises a crosslinking agent selected from the group consisting of sulfur, a sulfur donor, a peroxide, a bismaleimide, and mixtures thereof.

35. The tread according to claim 31, wherein the composition having a low stiffness modulus does not comprise a reinforcing resin.

36. The tread according to claim 31, wherein the reinforcing filler of the composition having a low stiffness modulus is present in the composition having a low stiffness modulus at a concentration ranging from 10 to 160 parts by weight per hundred parts of elastomer, phr.

37. The tread according to claim 31, wherein the crosslinking system of the composition having a low stiffness modulus is present in the composition having a low stiffness modulus at a concentration ranging from 0.1 to 5 phr.

38. The tread according to claim 30, wherein the composition having a high stiffness modulus is an elastomeric composition based on an elastomeric matrix, at least one reinforcing filler and at least one crosslinking system.

39. The tread according to claim 38, wherein the elastomeric matrix of the composition having a high stiffness modulus comprises a diene elastomer.

40. The tread according to claim 38, wherein the reinforcing filler of the composition having a high stiffness modulus predominantly comprises carbon black.

41. The tread according to claim 38, wherein the crosslinking system of the composition having a high stiffness modulus comprises a crosslinking agent selected from the group consisting of sulfur, a sulfur donor, a peroxide, a bismaleimide, and mixtures thereof.

42. The tread according to claim 38, wherein the composition having a high stiffness modulus comprises at least one reinforcing resin.

43. The tread according to claim 42, wherein the reinforcing resin is selected from the group consisting of polyepoxide resins, melamine/formaldehyde resins, phenol/formaldehyde resins, urea/formaldehyde resins, polyurethane resins, unsaturated polyester resins, vinyl ester resins, polyimide resins, diallyl phthalate resins, allyl diglycol carbonate resins and polyorganosiloxane resins.

44. The tread according to claim 38, wherein the reinforcing filler of the composition having a high stiffness modulus is present in the composition having a high stiffness modulus at a concentration ranging from 10 to 160 phr.

45. The tread according to claim 38, wherein the crosslinking system of the composition having a high stiffness modulus is present in the composition having a high stiffness modulus at a concentration ranging from 0.5 to 40 phr.

46. The tread according to claim 30, wherein the composition having a high stiffness modulus is a thermoplastic or comprises a thermoplastic elastomer.

47. The tread according to claim 46, wherein the thermoplastic is selected from polyolefins, vinyl chloride polymers, polystyrenes, polyamides, polyesters, ethylene/vinyl alcohol copolymers, polyacrylates, polyacetals and mixtures thereof.

48. The tread according to claim 46, wherein the thermoplastic is rendered adhesive.

49. The tread according to claim 46, wherein the thermoplastic elastomer is selected from thermoplastic styrene elastomers, ether/amide block copolymers, copolyesters, thermoplastic polyurethane elastomers, vulcanized thermoplastics, thermoplastic polyolefins and mixtures thereof.

50. The tread according to claim 30, wherein the modulus E.sub.H, and the fraction by volume H of the composition having a high modulus, and the modulus E.sub.B, and the fraction by volume B (or 1H) of the composition having a low modulus, are defined such that the formula $\frac{}{\left[.Math..Math.H+\left(1-.Math..Math.H\right).Math.\right]\left[.Math..Math.H.Math..Math.+\left(1-.Math..Math.H\right)\right]},\mathrm{in}.Math..Math.\mathrm{which}.Math..Math.=E_H/E_M,$ is less than 0.67.

51. The tread according to claim 30, wherein the modulus of extension at 5% deformation of the composition having a low stiffness modulus is within a range extending from 3 to 6 MPa.

52. The tread according to claim 30, wherein the modulus of extension at 5% deformation of the composition having a high stiffness modulus is within a range extending from 30 to 300 MPa.

53. The tread according to claim 30, wherein the volume of the layers of the composition having a low stiffness modulus represents from 50 to 95% by volume of the tread pattern of the tread.

54. The tread according to claim 30, wherein the layers of the composition having a low stiffness modulus have a thickness within a range extending from 1 to 20 mm.

55. The tread according to claim 30, wherein the layers of the composition having a high stiffness modulus have a thickness within a range extending from 0.1 to 20 mm.

56. The tread according to claim 30, wherein the layers of the composition having a low stiffness modulus and the layers of the composition having a high stiffness modulus are arranged alternately.

57. A tire comprising a tread according to claim 30.

58. The tire according to claim 57, wherein the tire is a tire for civil engineering vehicles or heavy-duty vehicles.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0173] FIG. 1 is a schematic depiction of a tyre (1), the tread of which comprises a rib (2) located in the central zone of the tyre (1), and tread blocks (3), the rib and the tread blocks being separated by circumferential grooves (4) and substantially transverse grooves (5).

[0174] FIG. 2 is a schematic depiction of several embodiments of a tread pattern according to the invention, viewed in section along the plane XZ. This tread pattern is composed of a plurality of layers (c1) formed of a composition having a high stiffness modulus (thinner) and of layers (c2) formed of a composition having a low stiffness modulus (thicker), which are parallel and adjacent to one another and are oriented parallel to a plane which is (i) perpendicular to the plane XZ and (ii) oriented at an angle (a) of 20 degrees for E1 and E3, of 25 degrees for E4 and of 30 degrees for E2, relative to the plane YZ.

EXAMPLES

[0175] A) Samples with 10 cm10 cm surface area and 3 cm thickness were produced according to the process described in application WO 2008/027045 with layers formed by compositions having low and high stiffness moduli arranged alternately.

[0176] The following definitions apply: [0177] X: a direction parallel to the direction of stress loading of the sample, itself parallel to the length of the sample. [0178] Y: a direction parallel to the width of the sample. [0179] Z: a direction parallel to the thickness of the sample.

[0180] A composition A, which is a composition having a low stiffness modulus, and a composition B, which is a composition having a high stiffness modulus, were prepared. These composition and the associated experimental results are presented in table 1 below:

TABLE-US-00001 TABLE 1 A B NR (1) 100 100 Silica (2) 15 Carbon black (3) 40 Carbon black (4) 75 ZnO (5) 3 8 Stearic acid 1 1 PEG (6) 2.5 FP resin (7) 11 HTT3H (8) 3 H3M72 (9) 6 Sulfur 2 5 Accelerator (10) 1.7 Accelerator (11) 1 Antioxidant (12) 1 1.5 Modulus of extension (a) 4.7 MPa 54 MPa (1) Natural rubber (2) Ultrasil VN3, sold by Evonik (3) Carbon black of N234 grade according to Standard ASTM D-1765 (4) Carbon black of N330 grade according to Standard ASTM D-1765 (5) Zinc oxide of industrial grade from Umicore (6) Polyethylene glycol with an Mn of 6000-20 000 g/mol, sold by Sasol Marl (7) Phenol/formaldehyde resin (8) Hexamethylenetetramine hardener (9) Hexa(methoxymethyl)melamine hardener (10) N-cyclohexyl-2-benzothiazolesulfenamide, Santocure CBS, sold by Flexsys (11) N-tert-butyl-2-benzothiazolesulfenamide, sold under the name TBBS (12) N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine, sold under the name 6PPD (a) Elastic modulus at 5% deformation

[0181] Samples E1, E2, E3 and E4 were produced from compositions A and B in the form of layers arranged alternately and parallel to a plane defined by (i) the direction Y and (ii) a straight line oriented at 20, 25 or 30 degrees relative to the direction Z in a plane defined by the directions X and Z.

[0182] A control sample R1 was produced solely with a composition A, without using oriented layers.

[0183] The mechanical properties were measured after curing the abovementioned compositions at a temperature of 150 C. for 30 minutes. The results were obtained from type 2 dumbbell test specimens at 5% deformation, at 23 C. according to standard NF ISO 37 of December 2005.

[0184] In order to analyse the transfer of ground forces on the test specimen, from the vertical component (Fz) to the horizontal component in the running direction (Fx) (the level of coupling), a force Fz of 900 daN, corresponding to a mean pressure of 9 bar, or of 600 daN, corresponding to a mean pressure of 6 bar, was applied to the surface of the samples using an electric actuating cylinder and the resulting force Fx was measured using a force sensor. The ratio of Fx divided by Fz is referred to as the level of coupling and is measured at two different mean pressures.

[0185] The samples R1, E1, E2, E3 and E4 and the associated experimental results are presented in table 2 below:

TABLE-US-00002 TABLE 2 Samples R1 E1 E2 E3 E4 Angles of the layers * 20 30 20 25 (degrees) Thickness of the layers A and B * 2/0.5 2/0.5 4/0.5 4/0.5 (mm) Volume of composition B .sup.0% 20% 20% 11% 11% (% vol) Level of coupling under a mean 0.0% 5.7% 8.0% 4.0% 5.4% pressure of 6 bar Level of coupling under a mean 0.0% 5.7% 4.0% 3.8% 3.0% pressure of 9 bar * not applicable

[0186] These results show that the samples in accordance with the present invention (comprising layers of composition having low and high stiffness moduli) create a level of coupling compared to a sample comprising solely a composition having a low stiffness modulus. It was observed that the samples which comprise a volume of composition B of 20% (E1 and E2) have a higher level of coupling than the samples comprising a volume of composition B of 11% (E3 and E4).

[0187] B) A similar experiment was carried out using, instead of the abovementioned composition B, a composition C (having a high stiffness modulus) made of a thermoplastic material, namely a polyamide 66 rendered adhesive with an RFL adhesive. The layers made of composition A were 2 mm thick and those of composition C were 1 mm thick. The fraction by volume of the composition C was therefore 33% relative to the volume of the test specimen.

[0188] For this experiment, the layers of compositions A and C were arranged alternately and oriented parallel to a plane defined by (i) the direction Y and (ii) a straight line oriented at 25 or 45 degrees relative to the direction Z in a plane defined by the directions X and Z.

[0189] The results observed have made it possible to demonstrate that no level of coupling is observed when the angle of the layers is 45 degrees, whereas a positive level of coupling is obtained when the angle of the layers is 25 degrees.

[0190] The various measurements carried out by the applicants have demonstrated that the level of coupling obtained was sufficient for implementing the present invention when the layers are oriented according to an angle of 15 to 35 degrees or 55 to 75 degrees.

[0191] The present invention therefore provides treads making it possible to transfer a proportion of the ground forces on the tyre from the component Fz into different components Fx, making it possible to effectively improve the wear resistance of the tyres. These results are particularly beneficial for vehicles running on non-bituminous ground, such as the majority of civil engineering vehicles and some heavy-duty vehicles.