Composite materials based on oriented orthotropic fiber mixtures for imparting mechanical coupling

Abstract

Materials make it possible to generate mechanical coupling in elastomeric compositions, of use especially for the manufacture of tyre treads. In particular, a tread comprises a composite material based on an elastomeric matrix, a crosslinking system, a reinforcing filler and oriented short fibres.

Claims

1. A tread comprising a tread pattern, said tread pattern comprising a composite material based on an elastomeric matrix, a crosslinking system, a reinforcing filler and short fibers, wherein the short fibers have a thickness within a range extending from 5 to 40 μm, a length within a range extending from 0.5 to 10 mm, and a Young's modulus within a range extending from 0.5 to 800 GPa, wherein the short fibers are present in the elastomeric matrix at a concentration within a range extending from 5 to 30 parts by weight per hundred parts by weight of elastomer, phr, wherein the short fibers are oriented in circumferential planes according to the same angle α expressed in degrees relative to the radial plane, the angle α being defined by the formula α=45+/−x, in which x is within a range extending from 10 to 30, wherein the tread pattern is composed of a plurality of parallel layers adjacent to one another, and wherein the layers of the plurality of layers are oriented in the tread pattern parallel to the plane defined by the orientation of the short fibers in the tread pattern and the axial direction.

2. The tread according to claim 1, wherein the elastomeric matrix comprises a diene elastomer.

3. The tread according to claim 1, wherein the thickness of the short fibers is within a range extending from 5 to 35 μm.

4. The tread according to claim 1, wherein the length of the short fibers is within a range extending from 1 to 9 mm.

5. The tread according to claim 1, wherein the ratio between the length and the thickness of the short fibers s within a range extending from 12.5 to 2000.

6. The tread according to claim 1, wherein the Young's modulus of the short fibers is within a range extending from 0.5 to 500 GPa.

7. The tread according to claim 1, wherein the short fibers are fibers selected from PET, nylon, PBT, aramid, PBO, natural fibers and mixtures thereof.

8. The tread according to claim 1, wherein the short fibers are rendered adhesive.

9. The tread according to claim 1, wherein the concentration of short fibers is within a range extending from 5 to 20 phr.

10. The tread according to claim 1, wherein each of the layers of the plurality of layers is formed by the composite material.

11. The tread according to claim 10, wherein the layers of the composite material have a thickness within a range extending from 1 to 20 mm.

12. The tread according to claim 1, wherein the plurality of layers comprises layers of the composite material and layers of an elastomeric composition different from the elastomeric composition of the composite material.

13. The tread according to claim 12, wherein the layers of the composite material and the layers of the elastomeric composition different from the elastomeric composition of the composite material are arranged alternately.

14. The tread according to claim 12, wherein the elastomeric composition different from the elastomeric composition of the composite material comprises an elastomer selected from isoprene elastomers, butadiene and styrene copolymers, polybutadienes and mixtures thereof.

15. The tread according to claim 12, wherein the longitudinal modulus E.sup.L.sub.C and the transverse modulus E.sup.T.sub.C define β=E.sup.T.sub.C/E.sup.L.sub.C, and the fraction by volume ϕC of the composite material and the modulus EM and the fraction by volume ϕM (or 1−ϕC) of the elastomeric composition different from the elastomeric composition of the composite material are defined such that the formula $\frac{\alpha \beta }{\left[\varphi C+\left(1-\varphi C\right)\alpha \beta \right]\left[\varphi C\alpha +\left(1-\varphi C\right)\right]},\mathrm{in}\mathrm{which}\alpha =E_C^T,$ is less than 0.67.

16. The tread according to claim 12, wherein the layers of the elastomeric composition different from the elastomeric composition of the composite material have a thickness within a range extending from 1 to 20 mm.

17. The tread according to claim 1, wherein the layers of the plurality of layers are parallel to the equatorial plane.

18. The tread according to claim 17, wherein each of the layers of the plurality of layers is formed by the composite material.

19. A tire comprising a tread according to claim 1.

20. The tire according to claim 19, wherein the tire is a tire for civil engineering vehicles or heavy-duty vehicles.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) 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).

(2) FIG. 2A is a schematic depiction of an embodiment of a tread pattern according to the invention, viewed in perspective. This tread pattern is composed of several layers (c) of composite material according to the invention, which are parallel and adjacent to one another and oriented parallel to a plane XZ in which X corresponds to the running direction of the tyre and Z corresponds to the thickness of the composite material. The short fibres (f) are oriented parallel to the plane XZ according to an angle (a) of 25 degrees relative to the plane YZ or Y corresponding to the transverse direction of the tread pattern.

(3) FIG. 2B differs from FIG. 1A solely in that the short fibres (f) are oriented according to an angle (b) of 65 degrees relative to the plane YZ.

(4) FIG. 3A is a schematic depiction of an embodiment of a tread pattern according to the invention, viewed in section along the plane XZ. This tread pattern is composed of several layers of composite material according to the invention, which are parallel and adjacent to one another and oriented parallel to a plane which is (i) perpendicular to the plane XZ and (ii) oriented at an angle (a) of 25 degrees relative to the plane YZ. The short fibres are arranged parallel to the plane of the layers in the plane XZ.

(5) FIG. 3B differs from FIG. 2A solely in that the layers are oriented according to an angle (b) of 65 degrees relative to the plane YZ.

(6) FIG. 4A is a schematic depiction of an embodiment 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) of composite material according to the invention and of layers (c2) of an elastomeric composition other than the composite material, which are parallel and adjacent to one another and arranged alternately and oriented parallel to a plane which is (i) perpendicular to the plane XZ and (ii) oriented at an angle (a) of 25 degrees relative to the plane YZ. The short fibres are arranged parallel to the plane of the layers in the plane XZ.

(7) FIG. 3B differs from FIG. 4A solely in that the layers are oriented according to an angle (b) of 65 degrees relative to the plane YZ.

(8) FIG. 5 is a schematic depiction of a device making it possible to orient short fibres within an elastomer layer. “A1” and “A2” represent the cylinders of a calender. “B” represents a receiving roll, on which a layer leaving the calender is arranged.

EXAMPLES

(9) Samples with 10 cm×10 cm surface area and 3 cm thickness were produced according to the process described in application WO 2008/027045 with layers with a thickness of 2 mm, from different compositions.

(10) The following definitions apply: “X”: a direction parallel to the direction of stress loading of the sample, itself parallel to the length of the sample. “Y”: a direction parallel to the width of the sample. “Z”: a direction parallel to the thickness of the sample.

(11) A control sample was produced from a composition A which is a composition conventionally used in tyre treads for civil engineering vehicles. This composition A does not comprise short fibres or any other type of fibres.

(12) Samples were produced from compositions B1 and B2 which are composite materials in accordance with the present invention. These compositions differ from the composition A in that they comprise short aramid fibres, oriented in the plane defined by the directions X and Z according to an angle of 25 degrees relative to the direction Z.

(13) Each of the samples was prepared according to two embodiments: with layers parallel to a plane defined by the directions X and Z, and with layers parallel to a plane defined by (i) the direction Y and (ii) a straight line oriented at 25 degrees relative to the direction Z in a plane defined by the directions X and Z.

(14) 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 type test specimens at 5% deformation, at 23° C. according to standard NF ISO 37 of December 2005. When the direction of extension is the main direction of orientation of the fibres, this modulus of extension will be denoted EL, and when the direction of extension is orthogonal to the main direction of the fibres, this modulus of extension will be denoted ET. The modulus of extension results are presented to a base 100, relative to the modulus of extension of the sample EL of control A.

(15) 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.

(16) The compositions A, B1 and B2 and the experimental results are presented in table 1 below.

(17) TABLE-US-00001 TABLE 1 A B1 B2 NR (1) 100 100 100 Silica (2) 15 15 15 Carbon black (3) 40 40 40 ZnO (4) 3 3 3 Stearic acid 1 1 1 Short fibres (5) — 11 23.5 Sulfur 2 2 2 Accelerator (6) 1.7 1.7 1.7 Modulus of extension EL (a) 100 3210 5870 Modulus of extension ET (b) 115 276 584 EL/ET ratio 0.87 11.65 10.05 Level of coupling under a 0.0% 18.4% 18.9% mean pressure of 6 bar Level of coupling under a 0.0% 21.4% 21.5% mean pressure of 9 bar (1) Natural rubber (2) Ultrasil VN3, sold by Evonik (3) Carbon black of N234 grade according to standard ASTM D-1765 (4) Zinc oxide of industrial grade from Umicore (5) Short aramid fibres treated with RFL, from Barnet, 5 mm long and 15 μm in diameter (6) N-cyclohexyl-2-benzothiazolesulfenamide, Santocure CBS, sold by Flexsys (a) Elastic modulus at 5% deformation and, for the fibre-based compositions, the direction of extension is in the main direction of the fibres (b) Elastic modulus at 5% deformation and, for the fibre-based compositions, the direction of extension is orthogonal to the main direction of the fibres

(18) These results show that the samples B1 and B2 in accordance with the present invention have moduli of extension EL and ET that are far greater than those of the control sample A which does not comprise oriented short fibres. Moreover, the samples B1 and B2 generate a level of coupling compared to the control composition A.

(19) These results also show that the level of coupling obtained is the same for the two concentrations of short fibres tested. The effect was observed from 5 phr of short fibres in the composite material.

(20) An additional experiment was carried out, comparing the level of coupling of the sample B1 above with that of the sample A and that of a sample C1 which only differs from the sample B1 in that the short fibres are oriented at 65 degrees (as opposed to 25 degrees for sample B1). The results are presented in table 2 below.

(21) TABLE-US-00002 TABLE 2 A B1 C1 (25 degrees) (25 degrees) (65 degrees) Level of coupling under a 0.0% 29.3% −8.4% mean pressure of 6 bar Level of coupling under a 0.0% 31.5% −10.1% mean pressure of 9 bar

(22) These results show that the level of coupling obtained with an orientation of the short fibres at 65 degrees is in an opposite direction to that obtained with an orientation of the short fibres at 25 degrees. This clearly demonstrates that there is an angle for which the level of coupling is zero between 25 and 65 degrees, especially at 45 degrees.

(23) 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 fibres are oriented according to an angle of 15 to 35 degrees or 55 to 75 degrees.

(24) 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.