Material for reinforcing against the creep of the inner rubber of a tire for a heavy duty civil engineering vehicle

Abstract

A tire for a civil engineering vehicle the endurance of which has been improved by the addition of an anti-creep layer (30) with a thickness E2 interposed between the airtight inner layer (20), with a thickness E1, and the reinforcer coating layer (46) of the carcass reinforcement (40), with a thickness E3. The thicknesses E1, E2 and E3, being measured in millimetres in a shoulder region forming the transition between the crown and each sidewall of the tire, satisfy the following equations: 2≤E1≤4; 6≤E2+E3 and E1/E2≥0.6. In addition, the viscoelastic loss P60 of the elastomeric mixture M2 of the anti-creep layer (30) is at most equal to 20%.

Claims

1. A tire for a civil engineering vehicle comprising a crown connected to two sidewalls extended by two beads, the assembly delimiting an inner cavity intended to be inflated with a gas, and comprising, starting from the inner cavity: an airtight inner layer forming a wall of the inner cavity, intended to come into contact with an inflation gas, having a thickness E1 and consisting of an elastomeric mixture M1; an anti-creep layer on the outside of the airtight inner layer, having a thickness E2 and consisting of an elastomeric mixture M2 having an elastic loss P60 measured at 60° C., the anti-creep layer and airtight inner layer extending over an entire inner surface of the crown of the tire; a carcass layer, on the outside of the anti-creep layer, consisting, from inside to outside, of an inner carcass coating layer, in contact with the anti-creep layer and having a thickness E3, a layer of metal reinforcers and an outer carcass coating layer, the inner and outer carcass coating layers consisting of an elastomeric mixture M3; the thicknesses E1, E2 and E3 being measured in a shoulder region forming the transition between the crown and each sidewall of the tire, wherein the airtight inner layer has a thickness E1 between two and four millimetres, the sum E2+E3 of the thicknesses E2 of the anti-creep layer and E3 of the inner carcass coating layer, respectively, is at least equal to 6 mm, the ratio E1:E2 between the thickness E1 of the airtight inner layer and the thickness E2 of the anti-creep layer is at most equal to 0.60 and the viscoelastic loss P60 of the elastomeric mixture M2 of the anti-creep layer is at most equal to 20%.

2. The tire according to claim 1, wherein the elastomeric mixture M2 of the anti-creep layer has a viscous shear modulus G″, and the viscous shear modulus G″ of the elastomeric mixture M2 of the anti-creep layer is at most equal to 0.15 MPa.

3. The tire according to claim 1, wherein the elastomeric mixture M2 of the anti-creep layer has a rubber composition based on a matrix of at least one blend of polyisoprene natural or synthetic rubber, polybutadiene, a crosslinking system, and a reinforcing filler at an overall content at most equal to 45 parts by weight per hundred parts by weight of elastomers (phr), and predominantly comprising silica at a content at least equal to 20 phr, and at most equal to 45 phr.

4. The tire according to claim 3, having two sidewalls each consisting of an elastomeric mixture connecting the tread to the bead, wherein the mixture of the sidewalls has the same composition as the anti-creep mixture M2.

5. The tire according to claim 3, each bead comprising a filler element, axially on the inside of the sidewall, and axially on the outside of the turn-up, the filler element consisting of at least one elastomeric mixture, wherein the elastomeric mixture of the filler element has the same composition as the anti-creep mixture M2.

6. The tire according to claim 1, wherein the elastomeric mixture M2 of the anti-creep layer has a rubber composition based on a matrix of polyisoprene natural or synthetic rubber, a crosslinking system, and a reinforcing filler at an overall content at most equal to 45 phr, and predominantly comprising carbon black at a content at least equal to 20 phr, and at most equal to 45 phr.

7. The tire according to claim 6, wherein the elastomeric mixture M2 of the anti-creep layer has a composition comprising a thiosulphate salt, sodium hexamethylene-1,6-bisthiosulphate, in a proportion of 0.5 phr to 2 phr.

8. The tire according to claim 1, wherein the elastomeric mixture M2 of the anti-creep layer has a rubber composition based on a matrix of polyisoprene natural or synthetic rubber, a crosslinking system, and a reinforcing filler at an overall content at most equal to 45 phr, and predominantly comprising silica at a content at least equal to 20 phr, and at most equal to 45 phr.

9. The tire according to claim 8, having a cushion layer positioned along the carcass layer, axially towards the outside, in the shoulder region, consisting of an elastomeric mixture, wherein the elastomeric mixture of the cushion layer has the same composition as the anti-creep mixture M2.

10. The tire according to claim 1, wherein a bonding layer consisting of an elastomeric mixture M4 is interposed between the airtight inner layer and the anti-creep layer.

11. The tire according to claim 10, wherein the bonding layer has a thickness E4 equal to 25% of the thickness E1.

12. The tire according to claim 1 where the anti-creep layer extends across the entire crown of the tire and radially inward along the sidewalls of the tire to points inward of ends of the airtight inner layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features of the invention will be better understood from the description of the attached FIGS. 1 and 2, which are not to scale in order to simplify the presentation thereof.

(2) FIG. 1 represents a schematic view in section on a meridian plane of a tire for a heavy duty civil engineering vehicle according to the invention

(3) FIG. 2 is an enlargement in the shoulder region of the positioning of the carcass layer, the anti-creep layer and the airtight inner layer.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 shows, in a meridian plane of a tire 1 of the invention: A crown 80 connected to two sidewalls 90 extended by two beads 60, the assembly delimiting an inner cavity 100 intended to be inflated with a gas, and comprising, starting from the inner cavity: an airtight inner layer 20 forming the wall of the inner cavity 100, intended to come into contact with an inflation gas, having a thickness E1 and consisting of an elastomeric mixture M1; an anti-creep layer 30, on the outside of the airtight layer, having a thickness E2 and consisting of an elastomeric mixture M2 having an elastic loss P60 measured at 60° C.; a carcass layer 40, on the outside of the anti-creep layer 30, consisting, from inside to outside, of an inner carcass coating layer 46, in contact with the anti-creep layer 30 and having a thickness E3, a layer of metal reinforcers 44 and an outer carcass coating layer 42, the inner and outer carcass coating layers consisting of an elastomeric mixture M3; the bead 60 comprises the turn-up 62 of the carcass layer 40 around the bead wire 64, a filling element 63 of the cavity formed by the main part of the carcass layer 40 and its turn-up 62, and a protection element 65 intended to be in contact with the rim 70; the crown 80 of the tire comprises the crown layers, made up of reinforcers coated in an elastomeric mixture, and each forming an angle with a circumferential direction XX′; the carcass reinforcement 40 is connected to the crown reinforcement 80 by a cushion mixture layer 50 positioned along the carcass layer 40, axially towards the outside in the shoulder region. This cushion mixture, hereafter referred to as the carcass-crown coupling mixture, couples the carcass reinforcement 40 to the crown reinforcement 80. the thicknesses E1, E2 and E3 are measured in a shoulder region in the direction normal to the carcass layer passing through the middle of the cushion layer 50.

(5) FIG. 2 shows the carcass layer 40 comprising, from inside to outside, an inner carcass coating layer 46, in contact with the anti-creep layer 30 and having a thickness E3, a layer of metal reinforcers 44 and an outer carcass coating layer 42 with a thickness E2 and finally the airtight inner layer 20 with a thickness E1, in contact with the internal inflation air. The diameter of the reinforcers of the layer of reinforcers 44 is ϕ.

(6) The invention was studied more particularly on a size 59/80R63 tire for a dumper type vehicle, as shown in FIG. 1. This tire is inflated to 600 KPa for a nominal load of 100,000 kg.

(7) The results of the invention were found on a tire produced according to the invention and compared with the simulation results obtained on a reference tire of the same size according to the prior art, that is, without the presence of a hysteresis-optimized anti-creep layer.

(8) For this tire, the carcass layer has a mean thickness of 7.8 mm, and the thickness E3 of the coating mixture on the back of the reinforcer is approximately 2.5 mm. The airtight inner layer has a thickness E1 of 3.5 mm. The anti-creep layer has a thickness E2 of 6 mm.

(9) Table 1 below gives examples of the composition of the elastomeric mixture M2 of the anti-creep layer interposed between the carcass layer and the airtight inner mixture layer:

(10) TABLE-US-00001 Table 1 Control anti-creep Anti-creep Anti-creep Anti-creep Anti-creep Composition mixture mixture mixture mixture mixture NR elastomer 50 50 100 100 100 BR elastomer 50 50 0 0 0 Carbon black 50 0 35 2 2 N330 Carbon black 0 3 0 0 0 N234 Silica 0 29.5 0 35 35 Plasticizer 18 10 0 0 0 Wax 1 1 0 0 0 Anti-oxidant 3 3 1.50 2 2 Zinc oxide 2.4 2.95 5.00 5 5 Stearic acid 1 1 1.5 1 1 Sulphur 1.3 1.04 1.60 1.75 1.75 Accelerator 0.6 0.8 0.60 0.9 0.9 Silane 0 2.95 0 2 2 PEG 4000 0 0 0 2.5 2.5 DPG 0 0.55 0 0.3 0.3 HTSNa 0 0 2 2 0

(11) The control mixture of the anti-creep layer has a rubber composition based on a matrix of a blend of polyisoprene natural rubber at 50 phr, polybutadiene at 50 phr, a crosslinking system, and a reinforcing filler at an overall content of 50 phr comprising carbon black N330 only.

(12) Mixture A has the same matrix as the control mixture, but with a reinforcing filler comprising carbon black N234 at 3 phr and silica at 29.5 phr.

(13) Mixture B has a rubber composition based on a matrix of polyisoprene natural rubber at 100 phr, a crosslinking system, and a reinforcing filler of carbon black N330 at an overall content equal to 35 phr.

(14) Mixture C has a rubber composition based on a matrix of polyisoprene natural rubber at 100 phr, a crosslinking system, and a reinforcing filler comprising carbon black N330 at 2 phr and silica at 35 phr.

(15) Mixture D is the same as mixture C but without the thiosulphate salt. The comparison between C and D makes it possible to test the effect of the thiosulphate salt.

(16) In summary, the following were tested for the composition of the anti-creep mixture: the effect of the matrix between a blend of natural rubber and polybutadiene and a matrix of natural rubber only, the effect of the reinforcing filler between carbon black and silica, and finally the effect of the thiosulphate salts.

(17) For the tire of the invention, the characterizations of the mixtures tested for the anti-creep layer are shown in Table 2 below:

(18) TABLE-US-00002 TABLE 2 Control anti- Anti-creep Anti-creep Anti-creep Anti-creep creep mixture mixture mixture mixture Results mixture A B C D Mechanical properties after curing MA100 (MPa) 1.1 0.9 1.6 1.6 1.3 MA300 (MPa) 0.9 0.6 15 1.2 1.1 Breaking 720 770 660 650 682 strain (MPa) Elongation at 11 9 15 16 15 break (%) Hysteresis after curing P60 (%) 27 12 15 12 13 G″ (MPa) 0.2 0.1 0.08 0.06 0.06 Ageing: stoving (240 hours at 110° C. NITROGEN) MA100 (MPa) NC NC 1.4 1.2 1.1 MA300 (MPa) NC NC 1.3 1 1 P60 (%) NC NC 17 15 17.5

(19) Anti-creep mixture C is the composition that best minimizes hysteresis with a loss P60 at 60° C. of 12%, and a viscous shear modulus of 0.06 MPa.

(20) The effect of the thiosulphate salts can be seen in the results for mixtures C and D. For mixture C, the hysteresis loss varies between 12% and 15% before and after ageing respectively. In other words, hysteresis deteriorates by 25% with ageing in the presence of thiosulphate salts. For mixture D, without thiosulphate salt, the deterioration in hysteresis is approximately 35% for the same ageing.

(21) Anti-creep mixture C was used for the tire of the invention, and the control anti-creep mixture was used on the reference tire. The results obtained are the mean operating temperature of the tire in the shoulder region, the mean temperature of the internal air in the inflation cavity and the permeability coefficient of the mixture of the airtight inner layer, summarized in Table 3 below:

(22) TABLE-US-00003 TABLE 3 Mean Mean temperature internal air Permeability Composition at shoulder temperature coefficient Control 100 100 100 Tyre of the 103 105 120 to 140 invention

(23) The reduction in the hysteresis of the mixture of the anti-creep layer of the tire of the invention resulted in a 3% reduction in the mean operating temperature of the tire at the shoulder. The temperature of the internal air in the cavity dropped by 5%.

(24) A 20% to 40% improvement in the permeability coefficient of the mixture of the airtight inner layer is observed.

(25) The improvement in the permeability of the airtight inner layer is correlated with the reduction in temperature of the internal air. Permeability is linked to temperature by an Arrhenius law that expresses the exponential decrease in permeability when the temperature increases. A 5° C. reduction in the temperature on the surface of the airtight inner layer thus improves the permeability of the mixture by at least 20%.

(26) The absence of creep of the airtight inner layer was observed on all of the tire solutions provided with an anti-creep mixture layer regardless of the composition of the mixture M2.

(27) The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which includes every combination of any features which are stated in the claims, even if this feature or combination of features is not explicitly stated in the examples.