CONSTRUCTION PLANT VEHICLE TIRE WITH LOW ENVIRONMENTAL FOOTPRINT

Abstract

The environmental footprint of a tire for a construction plant vehicle is improved. To do so, the elastomer compounds derived from non-fossil resources represent a mass content greater than or equal to 65% of the total mass of the compounds of the tire, at least 75% of the total mass of the compounds of the tire is made up of elastomer compounds each of which has a viscoelastic loss, measured in terms of tan(δ), less than or equal to 0.065, and an electrical resistivity greater than or equal to 1E+10 ‘Ω.Math.cm.

Claims

1.-15. (canceled)

16. A tire for a heavy-duty vehicle of construction plant type comprising: elastomer compounds derived from non-fossil, fossil, or both non-fossil and fossil resources, any elastomer compound having a viscoelastic loss tan(δ) defined as a ratio of a viscous shear modulus G″ to an elastic shear modulus G′, the modulus values being measured at a frequency of 10 Hz at a temperature of 100° C., and any electrically conductive elastomer compound being defined as having an electrical resistivity less than or equal to 1E+06 ohm-centimeter (‘Ω.Math.cm), measured in accordance with standard ASTM-D257; a tread having two axial end portions that are axially separated by a tread central portion; a crown reinforcement, radially on an inside of the tread, comprising at least one protective reinforcement and a working reinforcement, the reinforcements being formed respectively of protective layers and of working layers containing metal reinforcers coated with an elastomer compound, the layers at their axial ends having a layer of edging compound; a carcass reinforcement, radially on an inside of the crown reinforcement, comprising at least one carcass layer made up of metal reinforcers coated in an electrically conductive coating elastomer compound, the metal reinforcers being substantially mutually parallel and forming, with a circumferential direction, an angle of between 85° and 95°, each carcass layer comprising a main part, connecting two beads to one another and wrapped, within each bead, around a bead wire to form a turn-up; a carcass-crown coupling layer consisting of an electrically conductive elastomer compound and inserted between the carcass reinforcement and the crown reinforcement, axially toward an outside in a shoulder region; and two sidewalls connecting the two axial end portions of the tread to the two beads, the beads comprising a bead chafer layer intended to come into contact with a rim, wherein a mass of the elastomer compounds derived from non-fossil resources is greater than or equal to 65% of a total mass of the elastomer compounds contained in the tire, wherein at least 75% of the total mass of the elastomer compounds contained in the tire is made up of elastomer compounds each of which has a viscoelastic loss tan(δ) less than or equal to 0.065 and an electrical resistivity greater than or equal to 1E+10 ‘Ω.Math.cm, wherein a linking layer, made up of an electrically conductive elastomer compound is inserted radially between the carcass-crown coupling layer and the carcass reinforcement, and is in contact at its axially exterior end with one of the two axial end portions of the tread and at its axially interior end with the carcass layer coating compound, and wherein the one of the two axial end portions of the tread, the linking layer, the carcass layer electrically conductive coating elastomer compound, and the bead chafer layer constitute a preferred conductive pathway for conducting electrical charge between a ground and the rim when the tire is mounted on the rim and compressed onto the ground.

17. The tire according to claim 16, wherein the linking layer is in contact with the on axial end portion of the tread at its radially exterior end over a distance LC1 equal to at least 10 mm, and is in contact at its axially interior end with the carcass layer electrically conductive coating elastomer compound over a distance LC2 equal to at least 10 mm.

18. The tire according to claim 16, wherein a thickness of the linking layer, measured along a straight line normal to the carcass layer passing through the middle of the linking layer is greater than or equal to 2 mm.

19. The tire according to claim 16, wherein the linking layer comprises a rubber composition based on a matrix of polyisoprene natural or synthetic rubber, on a crosslinking system, and on a reinforcing filler at an overall content at most equal to 50 phr, and predominantly comprising carbon black at a content at least equal to 20 phr, and at most equal to 50 phr.

20. The tire according to claim 16, wherein the elastomer compound of at least one axial end portion of the tread is an electrically conductive rubber composition based on at least polyisoprene, on a crosslinking system, and on at least one reinforcing filler comprising carbon black, characterized by a BET surface area at least equal to 110 m.sup.2/g and by a content at least equal to 30 phr and at most equal to 80 phr.

21. The tire according to claim 16, wherein an elastomer compound of the central portion of the tread is a rubber composition based on at least one diene elastomer, on a crosslinking system, and on a reinforcing filler at an overall content at most equal to 40 phr and comprising carbon black and silica.

22. The tire according to claim 16, wherein the edging compound of the protective layers has a rubber composition based on a matrix of polyisoprene natural rubber, on a crosslinking system, and on a reinforcing filler at an overall content at most equal to 50 phr, and predominantly comprising silica at a content at least equal to 30 phr, and at most equal to 50 phr.

23. The tire according to claim 16, wherein the edging compound of the working layers has the same composition as the edging compound of the protective layers.

24. The tire according to claim 16, wherein the electrically conductive elastomer compound of the carcass-crown coupling layer has a rubber composition based on a matrix of polyisoprene natural rubber, on a crosslinking system, and on a reinforcing filler at an overall content at most equal to 55 phr, and predominantly comprising silica at a content at least equal to 35 phr, and at most equal to 55 phr.

25. The tire according to claim 16, wherein the tire further comprises an anti-creep reinforcer, and the elastomer compound of the anti-creep reinforcer has the same composition as the carcass-crown coupling layer.

26. The tire according to claim 16, wherein each bead comprises a filler layer, and the elastomer compound of the filler layer, axially on an outside of the turn-up of the carcass layer, and axially on an inside of a sidewall has the same composition as the carcass-crown coupling layer.

27. The tire according to claim 16, wherein the elastomer compound of each sidewall has a rubber composition based on at least one blend of polyisoprene natural rubber and polybutadiene, on a crosslinking system, and on a reinforcing filler, at an overall content at most equal to 45 phr, and comprising carbon black, at a content at most equal to 5 phr, and, predominantly, silica, at a content at least equal to 20 phr and at most equal to 40 phr.

28. The tire according to claim 16, wherein the elastomer compound of the tread central portion has a viscoelastic loss tan(δ) with a value at most equal to 0.065.

29. The tire according to claim 16, wherein the elastomer compound of each sidewall has a viscoelastic loss tan(δ) with a value at most equal to 0.12.

30. The tire according to claim 16, wherein the elastomer compound of the carcass-crown coupling layer has a viscoelastic loss tan(δ) with a value at most equal to 0.06.

Description

[0084] FIG. 1 schematically shows a tyre 1 according to the invention intended to be used on dumper type vehicles.

[0085] FIG. 2 depicts an enlargement of FIG. 1 in the shoulder region of the tyre. What is meant by the shoulder region is that portion of the tyre comprised between, on the one hand, the straight line D1, normal to the carcass layer and passing through the middle of the sidewall, and, on the other hand, the straight line D2, normal to the carcass layer passing through the point, situated on the tread, positioned at an axial distance equal to 4/5 of its nominal width relative to the equatorial plane.

[0086] FIG. 1 shows, in a meridian plane of a tyre 1 of the invention: [0087] a tread 20 comprising, at each axial end, an axial end portion or tread wings (27, 28); [0088] a crown reinforcement 30, radially on the inside of the tread 20, made up of at least a protective reinforcement 31, and of a working reinforcement 32. The protective reinforcement 31 and working reinforcement 32 are formed of metal reinforcers (311, 322) coated in an elastomer compound; [0089] a layer of edging elastomer compound 37, 35 respectively, is positioned at the axially exterior ends of the protective layers 31 and of the working layers 32, respectively; [0090] a carcass reinforcement 50 comprising at least one carcass layer made up of metal reinforcers 55 coated in an electrically conductive coating elastomer compound 57. The metal reinforcers are substantially parallel to one another and form, with the circumferential direction (XX′), an angle of between 85° and 95°. The carcass layer comprises a main part 90 connecting the two beads 60 to one another and wrapped, in each bead 60, around a bead wire 64. The carcass layer is wrapped around the bead wire 64 from the inside towards the outside of the tyre to form a turn-up 62 comprising an end. The turn-up 62 in each bead 60 allows the carcass reinforcement layer 50 to be anchored to the bead wire 64 of the bead 60; [0091] a layer of compound 45 is inserted between the carcass reinforcement 50 and the crown reinforcement 30 and positioned along the carcass layer 50, axially towards the outside in the shoulder region. This layer of compound 45 couples the carcass reinforcement 50 to the crown reinforcement 30. The pressurizing of the tyre mounted on its rim creates tensions in the reinforcers 55 of the carcass layer 50, and these in turn create shear in the carcass-crown coupling compound 45, which then tensions the reinforcers of the crown reinforcement 30; [0092] two sidewalls 80 connect the tread wings (27, 28) to the two beads 60; [0093] an interior cavity (100), intended to be inflated with a gas, and comprising, working outward from this interior cavity: [0094] an airtight innerliner layer (95) forming the wall of the interior cavity, intended to come into contact with an inflation gas, [0095] an anti-creep layer (90), on the outside of the airtight innerliner layer.

[0096] The top, radially exterior, ends of the tread wings (27, 28) are in contact with the tread central portion 25 over its entire thickness.

[0097] FIG. 2 depicts a detail of FIG. 1 in the shoulder region of the tyre. A layer of electrically conductive linking compound 40 is positioned radially towards the outside on the carcass-crown coupling layer 45. Said linking layer 40 is in contact with the tread wing 27 over a length LC1 at its axially exterior end. At the other, axially interior, end, the layer 40 is in contact with the coating layer 57 that coats the carcass layer over a length LC2.

[0098] The invention was studied more particularly in the case of a tyre for a dumper type vehicle, of size 50/80R57 according to the invention, and as shown in FIG. 1.

[0099] The results of the invention were observed on a tyre produced according to the invention and compared with the simulation results obtained on a reference tyre of the same size, comprising a one-piece tread, according to the prior art.

[0100] The use of natural rubber was standardized across almost all the constituents of the tyre, from the tread to the bead. However, the sidewall, which represents a mass of around 12% of the total mass of the tyre, has a composition containing 50 phr natural rubber and 50 phr butadiene. The very good abrasion-resistance properties of butadiene mean that it is destined for use as the sidewall constituent of the tyre. Antioxidant additives are added to protect it against ageing given its position in the tyre in contact with the ambient air.

[0101] The compounds were reinforced with fillers made of silica except in the case of those belonging to the electrostatic charge removal pathway which themselves remain reinforced using carbon black.

[0102] Plasticizers are added to certain compounds such as the sidewalls to make them easier to process during the manufacture of the tyre. These plasticizers have been selected as not containing petroleum-derived aromatic oils. One example of such a plasticizer is Tetrakis(dimethylamino)ethylene (TDAE). However, in other instances, the plasticizers have been omitted, as in the case of the tread compounds or else the carcass-crown coupling compound.

[0103] More specifically, the inventors have employed the following compositions for the tread:

TABLE-US-00002 TABLE 2 Filler: Elastomer: Black NR Elastomer: Filler: covered Vulcanizing (Natural BR Carbon with Coupling Protective agent Composition Rubber) (Butadiene) black (1) silica (2) agent agent (3) (4) (5) Plasticizer Tread wings 100 0 50 0 1 1.5 6.6 0 Tread 100 0 0 50 1 1.5 6.6 0 central portion (1) N134, sold by Cabot Corporation (2) CRX2125, sold by Cabot Corporation (3) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine, Santoflex 6-PPD, sold by Flexsys (4) Industrial grade zinc oxide, sold by Umicore (5) N-Cyclohexyl-2-benzothiazolesulfenamide, Santocure CBS, sold by Flexsys

[0104] According to the composition of the compound of the central portion of the tread, the mass of natural rubber represents 62.9% of the mass of this compound. Still for the tyre size 50/80 R57, the central portion of the tread represents 54% of the total mass of the compounds of the tyre. In other words, the proportion of non-fossil materials in the composition of the central portion of the tread represents a contribution of 34% of the cumulative mass of the compounds in the tyre. For the tread wings and following the same reasoning, the mass of non-fossil materials is around 3% of the cumulative mass of the compounds in the tyre.

[0105] The properties of the tread compounds measured on test specimens and resulting from the choices of chemical composition are compiled in Table 3:

TABLE-US-00003 TABLE 3 Elastomer compound Elastomer compound of Property of tread wing tread central portion Electrical resistivity 5.7 >11 as Log (Ω .Math. cm) Tan(δ) 0.08 0.065

[0106] The compound of the central portion of the tread has a composition based on an elastomer matrix comprising a diene elastomer and a reinforcing filler predominantly comprising a filler covered at least partially with silica.

[0107] In this embodiment, the tread central portion is electrically insulating. Electrostatic charges are thus removed along the conduction pathway defined by the invention, which passes via the tread wings that are in contact with the ground and are always electrically conductive.

[0108] The tread wings are in contact with the ground when the tyre is running. Reinforcing the basic elastomer using carbon black in adequate quantity ensures an electrical conductivity less than or equal to 1E+06 ohm-centimetre. The volume of this compound is limited to the bare minimum required to ensure conduction of the electrostatic charge. The solution whereby the tread is in three parts allows the content of elastomer derived from natural resources to be increased while at the same time decreasing the hysteresis.

[0109] In a simplified embodiment of the invention, the inventors used the same composition for the edging compounds of the protective layers and of the working layers, as indicated in Table 4 below:

TABLE-US-00004 TABLE 4 Elastomer: Reinforcing NR Elastomer: filler: Reinforcing Coupling (Natural BR Carbon filler: agent: Protective Vulcanizing Composition Rubber) (Butadiene) black Silica Silane agent agent Plasticizer Crown layers 100 0 3 45 6 3.92 13.7 0 edging compound

[0110] According to the composition of the edging compound of the layers of the crown reinforcement, which are listed in Table 4, the proportion of natural rubber is 100 phr and the reinforcing fillers represent 45 phr of silica. In order to maintain the endurance of the crown layers against any migration of oil that is detrimental to the endurance of the crown, the composition of the edging compounds does not include plasticizers. According to the composition of this compound, the mass of natural rubber and of silica amounts to 84% of the mass of the compound, and to around 5.1% of the total mass of the compounds.

[0111] The layer of coupling compound is inserted between the carcass reinforcement and the crown reinforcement. According to the invention, its composition is in the following table:

TABLE-US-00005 TABLE 5 Elastomer: Reinforcing NR Elastomer: filler: Reinforcing Coupling (Natural BR Carbon filler: agent: Protective Vulcanizing Composition Rubber) (Butadiene) black N330 Silica Silane agent agent Plasticizer Carcass- 100 2 35 2 3.8 8.8 0 crown coupling compound

[0112] The coupling layer coupling the carcass reinforcement to the crown reinforcement has a proportion of 100 phr of natural rubber, reinforced with 35 phr of silica and 2 phr of carbon black. The cumulative mass of the natural rubber and of the silica represents a content of 89% of the mass of this compound, and a content of 6.2% of the total mass of the compounds.

[0113] The role played by the coupling compound coupling the carcass reinforcement to the crown reinforcement is essential to the correct operation of the tyre. Specifically, the pressurizing of the tyre mounted on its rim creates tensions in the carcass layer reinforcers, which in turn create shear in the carcass-crown coupling compound, which then tensions the crown reinforcement reinforcers. The mechanical properties of the coupling compound need to be suitable for the operation of the invention. The table below compiles the main mechanical properties of this compound:

TABLE-US-00006 TABLE 6 Carcass-crown coupling compound Property Electrical resistivity Log (Ω .Math. cm) >11 G′ (MPa) 1.15 Tan(δ) 0.06

[0114] The static stiffness modulus of the carcass-crown coupling compound at 10% deformation is 1.15 MPa and the hysteresis loss measured by tan(δ) is 0.06.

[0115] In a drive towards industrial standardization, the inventors found that the coupling compound coupling the carcass reinforcement to the crown reinforcement can also be used in the carcass layer anti-creep reinforcer and in the bead filler. The properties of this compound are compatible with these two constituents of the tyre.

[0116] As regards the tyre sidewalls, which represent, by mass, the second greatest constituent mass of elastomer after the tread, the composition thereof needs also to lead to a reduction in the hysteresis. However, this drop in hysteresis needs to be able to be achieved without adversely affecting the mechanical properties such as fatigue strength and, more particularly, the resistance to cracking. Specifically, the sidewalls of construction plant tyres are subjected to very high stresses, in terms of flexural deformation, attack and also thermal stresses. This prolonged static or dynamic stressing of the sidewalls in the presence of ozone causes more or less pronounced crazing or cracks to arise, of which the propagation, under the effect of the stresses, may give rise to significant damage to the sidewall in question. It is therefore important that the elastomer compounds that make up the sidewalls of tyres have very good mechanical properties, conferred in particular by a high content of reinforcing fillers. The inventors are proposing the following composition:

TABLE-US-00007 TABLE 7 Elastomer: Reinforcing NR Elastomer: filler: Reinforcing Coupling (Natural BR Carbon filler: agent: Protective Vulcanizing Composition Rubber) (Butadiene) black Silica Silane agent agent Plasticizer Sidewall 50 50 3 29 0 4 5.3 10 compound

[0117] The composition of the sidewalls leads to a low hysteresis measured by a tan(δ) value less than or equal to 0.12. The plasticizers for improving industrial workability amount to 10 phr of the oil TDAE. The cumulative mass of natural rubber and of silica represents a proportion of 52.2% of the mass of this compound. Bearing in mind the 12% proportion that the mass of the sidewall represents with respect to the mass of the tyre excluding its metal reinforcers, the mass of the natural rubber combined with that of the silica represents a proportion of 6.3% of the total mass of the compounds of the tyre.

[0118] Table 8 below recaps the proportion of non-fossil materials present in the tyre of the invention. The proportion of each constituent by mass is with respect to the total mass of the tyre without its metal reinforcers:

TABLE-US-00008 TABLE 8 Mass of the constituent as Content (%) of a % of the mass NR + Silica Mass as % of the tyre according to of the non- excluding metal the composition fossil materials Tyre constituent reinforcers of the compound (NR + Silica) Comments Central part of the 54%  62.9% 34.0%  Main part of the tread tread of the tyre in contact with the ground during running, this represents the highest proportion of compound by mass. Tread wing 5% 62.9% 3.1% Part at the axial end of the tread with a volume limited to just enough, in contact with the ground and used as a link in the circuit for the removal of electrostatic charge. Sidewall 12%  52.2% 6.3% By mass, the second constituent of the tyre which connects the tread to the bead that is in contact with the rim. Coupling compound 7% 88.8% 6.2% Internal compound that that mechanically connects the carcass couples the carcass reinforcement to the reinforcement to the crown reinforcement of crown reinforcement the tyre. It transmits the tension generated by the meridian profile of the carcass layer to the crown reinforcement. Anti-creep compound 7% 88.8% 6.2% Layer of compound reinforcing the positioned radially on radially innermost the inside of the carcass airtight innerliner reinforcement to limit the compound layer in creep of the radially the tyre against innermost airtight creep innerliner layer of the tyre. Filler compound in 5% 88.8% 4.4% Layer of compound the bead between contributing to the the turn-up of the operation of the bead. carcass layer and the sidewall Crown layers edging 6% 84.3% 5.1% Layer of compound compound positioned at the axial ends of the crown layers to improve the endurance thereof. Other compounds 4%   0% .sup. 0% Chiefly an airtight innerliner compound, compounds coating the metal layers, a bead chafer compound Total 100%  65.3% 
Table 9 below is a recap of the viscoelastic loss and electrical resistivity measurements for each constituent:

TABLE-US-00009 TABLE 9 Electrical Viscoelastic resistivity Tyre constituent loss (Log) Central part of 0.065 11 the tread Tread wing 0.08 6 Sidewall 0.12 >11 Coupling compound 0.06 >11 that mechanically couples the carcass reinforcement to the crown reinforcement Anti-creep compound 0.06 >11 reinforcing the radially innermost airtight innerliner compound layer in the tyre against creep Filler compound in 0.06 >11 the bead between the turn-up of the carcass layer and the sidewall Crown layers edging 0.065 >11 compound

[0119] The above-described tyre of the invention does therefore indeed meet the claimed objective.

[0120] Table 10 below sets out the overall results obtained on a tyre of the invention:

TABLE-US-00010 TABLE 10 Tyre of the Reference tyre, Property invention routine operation Electrical resistance <8 10 R of the tyre in Log (R) in ohms Temperature in the tread 10 to 15° lower Base 100 Rolling resistance 90 100 

[0121] The electrical resistance of the tyre of the invention is reduced by at least a factor of 100 by comparison with the routine operation reference.

[0122] The objective of the invention has been achieved with a tyre made up of materials not derived from fossil resources, which materials amount to 65% by mass excluding metal components. In use, the environmental impact is significantly reduced by a lower vehicle fuel consumption as a result of a 10% improvement in rolling resistance.