Tire tread comprising at least one metal chelate and/or a pigment

Abstract

A tire tread is based on one or more diene elastomers, on one or more reinforcing fillers, on a crosslinking system, and on at least one compound (A) selected from a metal chelate comprising at least one ligand and at least one metal, a pigment and their mixture.

Claims

1. A tire tread based on: one or more diene elastomers; a reinforcing filler, wherein the reinforcing filler is carbon black; a crosslinking system; and at least one compound A selected from the group consisting of a metal chelate comprising at least one ligand and at least one metal, a pigment and the mixture thereof, wherein the metal chelate is selected from the group consisting of iron porphyrins, iron hemin, and copper phthalocyanines; wherein the pigment is selected from the group consisting of diketopyrrolopyrroles, anthraquinones, quinacridones, perylenes and pyrazolo-quinazolones; and wherein compound A is present at a content from 1 to 30 phr.

2. The tread according to claim 1, wherein the metal chelate is iron porphines.

3. The tread according to claim 1, wherein the metal chelate is iron hemin of formula (I) below: ##STR00004##

4. The tread according to claim 1, wherein the pigment is a diketopyrrolopyrrole.

5. The tread according to claim 1, wherein the pigment is selected from the group consisting of Red 254, Red 255 and Red 264.

6. The tread according to claim 5, wherein the pigment is Red 254.

7. The tread according to claim 1, wherein compound A is present at a content from 5 to 20 phr.

8. The tread according to claim 1, wherein the one or more diene elastomer is selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures thereof.

9. The tread according to claim 1, wherein the reinforcing filler is present at a content ranging from 20 to 200 phr.

10. The tread according to claim 9, wherein the reinforcing filler is present at a content ranging from 30 to 150 phr.

11. The tread according to claim 10, wherein the reinforcing filler is present at a content ranging from 40 to 80 phr.

12. A process for preparing a tread according to claim 1 comprising the steps of: (a) incorporating compound A and the reinforcing filler into the one or more diene elastomer to make a mixture and kneading the mixture thermomechanically until a maximum temperature ranging from 110 C. to 165 C. is reached; then (b) incorporating the crosslinking system into the mixture and kneading until a maximum temperature of less than 90 C.

13. The process according to claim 12 further comprising the step of: (c) calendering the mixture obtained at the end of step (b).

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

15. A method of improving the grip of a tire on wet roads comprising the step of: incorporating a tread according to claim 1 in the tire.

Description

EXAMPLES

(1) Tests Used

(2) Grip Performance Under Braking on Wet Ground:

(3) The compositions below (A, B and C) are used as treads of radial carcass passenger vehicle tyres. The tyres are denoted respectively as P-A (control tyres), P-B and P-C (tyres according to the invention), with dimensions of 225/55R16, conventionally manufactured and identical in every respect except for the constituent rubber compositions of their tread. The tyres are fitted, at the front and at the rear, under nominal inflation pressure, to a motor vehicle of the BMW make, 530 model, equipped with an ABS system.

(4) The tyres are subjected to a test of braking on wet ground at two different speeds (at 90 km/h and at 30 km/h) that consists in measuring the distance required to come to a stop from 90 km/h (or 30 km/h in the case) during sudden braking in a straight line, on bitumenous concrete with a 1 mm film of water, at ambient temperature. A value greater than that of the control, arbitrarily set at 100, indicates an improved result, that is to say a shorter braking distance. The results obtained are shown in Table 2 below.

(5) Preparation of the Treads

(6) 1) Process for Preparing the Treads

(7) The mixtures for treads are prepared in appropriate mixers using two successive preparation phases according to a general procedure well known to those skilled in the art.

(8) The diene elastomer(s), the optional pigment or optional metal chelate, and the reinforcing filler(s), and then, after kneading for one to two minutes, the various other ingredients, with the exception of the crosslinking system, are introduced into an internal mixer which is 70% filled and which has an initial vessel temperature of approximately 90 C. Thermomechanical working is then carried out (non-productive phase) in one step (total duration of the kneading equal to approximately 5 min), until a maximum dropping temperature of approximately 165 C. is reached. The mixture thus obtained is recovered and cooled and then the crosslinking system is added on an external mixer (homofinisher) at 70 C., everything being mixed (productive phase) for approximately 5 to 6 min.

(9) In this instance, the processing is carried out by means of a mixer of the Haake RM 3000 type of 360 cm.sup.3 with blades of CAM type.

(10) The mixtures thus obtained are then calendered in the form of a tread.

(11) 2) Formulation of the Treads

(12) Two treads according to the invention (treads B and C) and a comparative tread (tread A) were prepared using the ingredients and contents presented in Table 1 below. The contents are expressed in phr.

(13) TABLE-US-00001 TABLE 1 Tread A (Comp) B (Inv) C (Inv) Natural rubber 40 40 40 Styrene butadiene rubber.sup.(1) 40 40 40 Butadiene rubber.sup.(2) 20 20 20 Carbon black.sup.(3) 54 54 54 Stearic acid 2 2 2 ZnO 2 2 2 Antioxidant.sup.(4) 2 2 2 Sulfur 1.1 1.1 1.1 Vulcanization accelerator.sup.(5) 1.1 1.1 1.1 Paraffin 1 1 1 Pigment.sup.(6) 10 Metal chelate.sup.(7) 10 .sup.(1)Styrene-butadiene copolymer, .sup.(2)Polybutadiene with 4% of 1,2-units and 93% of cis-1,4-units (Tg = 106 C.), .sup.(3)Carbon black N234, .sup.(4)N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine, 6-PPD, from Flexsys, .sup.(5)N-Cyclohexyl-2-benzothiazolesulfenamide, Santocure CBS, from Flexsys, .sup.(6)RED 254 .sup.(7)HEMIN

(14) Results

(15) The mechanical properties are presented in Table 2.

(16) TABLE-US-00002 TABLE 2 Tread A (Comp) B (Inv) C (Inv) Braking at 30 km/h 100 105 105 Braking at 90 km/h 100 102 101

(17) The results presented in Table 2 above demonstrate that the treads B and C according to the invention enable a notable improvement in braking at low speed, and at high speed, of the tyres P-B and P-C containing them.