FR3117122A1 - OFF-ROAD VEHICLE TIRE - Google Patents

Abstract

The invention relates to a pneumatic or non-pneumatic tire, for off-road vehicles, having a good performance compromise between resistance to mechanical attack and hysteresis, the tire comprising a rubber composition based on at least one matrix elastomer comprising at least one diene elastomer, a reinforcing filler, cellulose pulp, and a crosslinking system, in which the cellulose pulp has a length comprised in a range ranging from 0.3 to 5 mm.

Description

OFF-ROAD VEHICLE TIRE

The present invention relates to pneumatic or non-pneumatic off-road tires, in particular tires for civil engineering vehicles and agricultural vehicles.

These tires must have very different technical characteristics from tires intended for vehicles traveling exclusively on the road (i.e. bituminous ground), because the nature of the off-road ground on which they mainly evolve is very different, and notably much more aggressive, due to its stony nature. Furthermore, unlike tires for passenger vehicles, for example, especially for large civil engineering machinery, the tires must be able to support a load which can be extremely heavy. Consequently, the known solutions for tires running on bituminous ground are not directly applicable to off-road tires such as tires for civil engineering vehicles.

The so-called off-road tires, due to their majority off-road use, are provided with treads which have, compared to the thicknesses of the treads of tires for light vehicles, in particular for passenger cars or light trucks, large layers of rubber material. Typically, the wearing part of the tread of a tire for heavy goods vehicles has a thickness of at least 15 mm, that of a civil engineering vehicle at least 30 mm, or even up to 120 mm.

During rolling, a tread undergoes mechanical stresses and attacks resulting from direct contact with the ground. In the case of a tire mounted on a vehicle carrying heavy loads, the mechanical stresses and attacks suffered by the tire are amplified under the effect of the weight it supports.

Tires for mining vehicles in particular are subjected to strong stresses, both at the local level: rolling on the macro-indenters represented by the pebbles which constitute the tracks (crushed rock), and at the global level: passage of significant torque because the slopes of the tracks to enter or exit the "pits", or open-cast mines, are of the order of 10%, and strong stresses on the tires during vehicle U-turns for loading and unloading maneuvers.

This has the consequence that the incipient cracks which are created in the tread of the tire under the effect of these stresses and these attacks tend to spread more on the surface or inside the tread, which may cause localized or general tearing of the tread. These stresses can therefore cause damage to the tread and therefore reduce the life of the tread, and therefore of the tire. A tire rolling on stony ground is very exposed to attacks, and therefore to the onset of cracks and cuts. The very aggressive nature of stony ground not only exacerbates this type of tread aggression, but also its consequences on the tread.

This is particularly true for tires fitted to civil engineering vehicles which generally operate in mines or quarries. This is also true for tires that are mounted on agricultural vehicles due to the stony soil of arable land. The tires that equip heavy-duty construction site vehicles that travel on both stony and bituminous soils are also subject to the same attacks. Due to the two aggravating factors of the weight carried by the tire and the aggressive nature of the road surface, the resistance to crack initiation and/or crack propagation of a tread of a tire for a vehicle of civil engineering, an agricultural vehicle or a heavy construction vehicle proves to be crucial to minimize the impact of the aggressions undergone by the tread. It is therefore important to have a tire for vehicles, in particular those intended to run on stony ground and carrying heavy loads, the tread of which has a resistance to crack initiation and/or crack propagation that is sufficiently strong to minimize the number or effect of crack initiation on tread life. To solve this problem, it is known to those skilled in the art, that for example, the natural rubber in the treads makes it possible to obtain properties of resistance to the initiation and / or the propagation of high cracks .

Furthermore, it remains interesting that the solutions proposed for solving this problem do not penalize the other properties of the rubber composition, in particular the hysteresis reflecting the heat dissipation capacity of the composition. Indeed, the use of a hysteretic composition in a tire can be manifested by an increase in the internal temperature of the tire, which can lead to a reduction in the endurance (in English “durability”) of the tire.

In view of the above, there is a permanent objective to provide rubber compositions which present a good performance compromise between resistance to mechanical attack and hysteresis.

Solutions have been provided to improve this compromise. For example, application WO 2018/104671 A1 proposes using an elastomeric matrix comprising an epoxidized polyisoprene having a molar rate of epoxidation ranging from 5% to less than 50%. Application WO 2016/202970 A1 proposes the use of a specific composition whose elastomeric matrix comprises a diene elastomer chosen from the group consisting of polybutadienes, butadiene copolymers and mixtures thereof, and a styrenic thermoplastic elastomer comprising at least a rigid styrenic segment and at least one flexible diene segment comprising at least 20% by mass of conjugated diene units.

However, manufacturers are always looking for solutions to further improve the performance compromise between resistance to mechanical attack and hysteresis, preferably regardless of the nature of the elastomeric matrix.

Continuing its research, the Applicant discovered unexpectedly that the use of a specific cellulose pulp makes it possible to further improve the above-mentioned performance compromise.

Thus the subject of the invention is a pneumatic or non-pneumatic tire for off-road vehicles, comprising a rubber composition based on at least one elastomeric matrix comprising at least one diene elastomer, a reinforcing filler, pulp of cellulose, and a crosslinking system, in which the cellulose pulp has a length comprised in a range ranging from 0.3 to 5 mm.

I- DEFINITIONS

The expression "composition based on" means a composition comprising the mixture and/or the in situ reaction product of the various constituents used, some of these constituents being able to react and/or being intended to react with one another, less partially, during the various phases of manufacture of the composition; the composition thus possibly being in the totally or partially crosslinked state or in the non-crosslinked state.

By the expression "part by weight per hundred parts by weight of elastomer" (or phr), is meant within the meaning of the present invention, the part, by mass per hundred parts by mass of elastomer.

In the present, unless otherwise expressly indicated, all the percentages (%) indicated are percentages (%) by mass.

On the other hand, any interval of values denoted by the expression "between a and b" represents the domain of values going from more than a to less than b (i.e. limits a and b excluded) while any interval of values denoted by the expression “from a to b” signifies the range of values going from a to b (that is to say including the strict limits a and b). In this document, when an interval of values is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

When reference is made to a "majority" compound, it is meant within the meaning of the present invention that this compound is in the majority among the compounds of the same type in the composition, that is to say that it is the one which represents the greatest amount by mass among compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. In the same way, a so-called majority filler is the one representing the greatest mass among the fillers of the composition. By way of example, in a system comprising a single elastomer, the latter is predominant within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers. On the contrary, a "minority" compound is a compound which does not represent the largest mass fraction among compounds of the same type. Preferably, by majority is meant present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

The compounds mentioned in the description can be of fossil origin or biosourced. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned can also come from the recycling of materials already used, that is to say they can be, partially or totally, from a recycling process, or obtained from materials raw materials themselves from a recycling process. This concerns in particular polymers, plasticizers, fillers, etc.

All the glass transition temperature “Tg” values described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to standard ASTM D3418 (1999).

II- DESCRIPTION OF THE INVENTION

II-1 Elastomeric matrix

The tire according to the invention has the essential characteristic of comprising a rubber composition based on an elastomer matrix comprising at least one diene elastomer.

By “diene elastomer”, it is recalled that should be understood an elastomer which is derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” generally means a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or units of diene origin (conjugated dienes) which is greater than 15% (% in moles); thus diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the above definition and may in particular be qualified as "essentially saturated" diene elastomers (rate of units of low or very low diene origin, always less than 15%). The diene elastomers included in said composition are preferably essentially unsaturated.

By diene elastomer capable of being used in the compositions in accordance with the invention is meant in particular:
a) any homopolymer of a conjugated or non-conjugated diene monomer having from 4 to 18 carbon atoms;
b) any copolymer of a diene, conjugated or not, having from 4 to 18 carbon atoms and of at least one other monomer.

The other monomer can be ethylene, an olefin or a diene, conjugated or not.

Suitable conjugated dienes are conjugated dienes having from 4 to 12 carbon atoms, in particular 1,3-dienes, such as in particular 1,3-butadiene and isoprene.

Suitable olefins are vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms.

Suitable vinylaromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tert-butylstyrene.

Suitable aliphatic α-monoolefins are in particular acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms.

The diene elastomer is preferably a diene elastomer of the highly unsaturated type, in particular a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), polybutadienes (BR), copolymers of butadiene, isoprene copolymers and mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene (SBR) copolymers, isoprene-butadiene (BIR) copolymers, isoprene-styrene (SIR) copolymers, isoprene- styrene-butadiene (SBIR), ethylene-butadiene (EBR) copolymers and mixtures of such copolymers.

The above diene elastomers can, for example, be block, random, sequenced, microsequenced, and be prepared in dispersion or in solution; they can be coupled and/or starred or further functionalized with a coupling and/or starring or functionalizing agent, for example epoxidized.

Preferably, the elastomer matrix of said rubber composition of the tire according to the invention mainly comprises at least one isoprene elastomer.

The term “isoprene elastomer” is understood to mean in known manner an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), various isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of the copolymers of isobutene-isoprene (butyl rubber - IIR), of isoprene-styrene (SIR), of isoprene-butadiene (BIR) or of isoprene-butadiene-styrene (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, are preferably used polyisoprenes having a rate (% molar) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%.

Advantageously, the isoprene elastomer is a polyisoprene comprising a mass content of 1,4-cis bonds of at least 90% of the mass of the polyisoprene. Preferably, the second elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof. More preferably the polyisoprene is a natural rubber.

The isoprene elastomer, preferably natural rubber, can be epoxidized or not.

Alternatively, the elastomer matrix of said rubber composition of the tire according to the invention comprises at least 50%, preferably at least 70%, preferably at least 90%, preferably 100%, by mass, of at least one copolymer of butadiene-styrene (SBR) or a mixture of at least one copolymer of butadiene-styrene (SBR) and of at least one polybutadiene (BR).

It will be noted that the SBR can be prepared in emulsion (ESBR) or in solution (SSBR). Preferably, it is an SSBR. Whether ESBR or SSBR. Among the copolymers based on styrene and butadiene, in particular SBR, mention may be made in particular of those having a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (% molar) in −1,2 bonds of the butadiene part comprised between 4% and 75%, a content (mol %) of trans-1,4 bonds comprised between 10% and 80%. Advantageously, the butadiene-styrene copolymer is an SBR prepared in solution and has a styrene content of between 5% and 60%, preferably 6% to 30%, by weight relative to the total weight of the copolymer, and a content ( % molar) in −1,2 bonds of the butadiene part comprised between 4% and 75%, preferably between 15% and 30%.

Preferably, the polybutadiene has a glass transition temperature comprised in a range ranging from -90 to -120°C, preferably from -100 to -115°C.

In a particularly advantageous manner, said rubber composition comprises from 70 to 100 phr, preferably from 80 to 100 phr, preferably from 90 to 100 phr, of isoprene elastomer, preferably of natural rubber. For example, said rubber composition may comprise from 70 to 99 phr, for example from 80 to 98 phr, for example from 90 to 97 phr, of isoprene elastomer, the balance possibly being another diene elastomer, for example originating from the support cellulose pulp.

II-2 Cellulose pulp

Said rubber composition of the tire according to the invention also has the essential characteristic of comprising cellulose pulp.

By cellulose pulp is meant cellulose fibers having undergone a fibrillation step (also called pulping), well known to those skilled in the art. There are many fibrillation methods described in the state of the art, which are mechanical or chemical, described for example in documents WO 83/003856, WO 2013/049222, EP0677122 and EP0494214. Before fibrillation, a fiber, having a given length and diameter, consists of a plurality of microfibrils essentially parallel to each other, and which are oriented in the direction of the length of the fiber. After fibrillation, certain microfibrils of the fiber have been broken and then emanate from the core of the fiber (and are therefore no longer necessarily oriented in the direction of the length of the fiber).

According to the invention, the cellulose pulp has a length comprised in a range ranging from 0.3 to 5 mm. Below 0.3 mm, the contribution of rigidity in the composition becomes too low, while above 5 mm, the anisotropy increases strongly which implies a shift in rigidity according to the direction of the pulp within the composition. This offset in rigidity is not of interest because of the destination of the rubber article comprising the composition: the mechanical attacks undergone by these articles do not come from a single direction but can come from any direction. On the contrary, it is interesting to have a rigidity without preferential direction. Thus, advantageously, the cellulose pulp has a length comprised in a range ranging from 0.5 to 4 mm, preferably from 1.1 to 3.9 mm. The pulp having these lengths has an anisotropy close to the value 1 and therefore a homogeneous stiffness.

Also preferably, the cellulose pulp has an average diameter comprised in a range ranging from 1 to 40 μm, preferably from 3 to 25 μm, preferably from 5 to 15 μm. These diameters, associated with the aforementioned lengths, make it possible to further increase the homogeneity of the rigidity, i.e. present an anisotropy even closer to the value 1.

In a particularly advantageous manner, the cellulose pulp has a length to average diameter ratio comprised in a range ranging from 12 to 4000, preferably from 40 to 1300, more preferably from 70 to 600.

The length and average diameter of cellulose pulp can easily be measured by light microscope image analysis, scanning electron microscope image analysis, transmission type microscope photograph image analysis, scattering data analysis of X-rays.

When we measure the average diameter of a cellulose pulp, we measure the core diameter made up of all the microfibrils that have retained an orientation in the direction of the main length of the fiber. The average diameter therefore does not take into account the broken microfibrils emanating from the core of the pulp.

The content of the cellulose pulp in the said rubber composition is advantageously within a range ranging from 1 to 25 phr, preferably from 3 to 20 phr. Below 1 phr, no effect is observed on the resistance to mechanical attack, whereas above 25 phr, the composition has limit properties that are too low.

Preferably, the fibers are coated with an adhesive composition to improve their adhesion to the rubber composition. This adhesive composition can be a classic resorcinol-formaldehyde-latex glue, commonly abbreviated RFL glue, or even an adhesive composition based on a phenol-aldehyde resin and a latex, as described in documents WO 2013/017421 , WO 2013/017422, WO 2013/017423, WO 2015/007641 and WO 2015/007642. The use of adhesive compositions based on a phenol-aldehyde resin and a latex is particularly advantageous because of the non-emission of formaldehyde.

Cellulose pulps that can be used in the context of the present invention are commercially available, in particular the “Rhenogran WDP-70/SBR” pulp from the company Lanxess.

II-3 Reinforcing filler

Said rubber composition of the tire according to the invention further comprises a reinforcing filler, known for its ability to reinforce a rubber composition that can be used for the manufacture of rubber articles.

The reinforcing filler can comprise carbon black, silica or a mixture thereof. Advantageously, the reinforcing filler mainly comprises carbon black.

The blacks that can be used in the context of the present invention can be any black conventionally used in pneumatic or non-pneumatic tires or their treads (so-called tire-grade blacks). Among the latter, mention will be made more particularly of the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM grades), such as for example the blacks N115, N134, N234, N326, N330 , N339, N347, N375, N550, N683, N772. These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used. The carbon blacks could for example already be incorporated into the diene elastomer, in particular isoprene in the form of a masterbatch (or “masterbatch” in English) (see for example applications WO 97/36724 or WO 99/16600) .

As examples of organic fillers other than carbon blacks, mention may be made of functionalized polyvinyl organic fillers as described in applications WO 2006/069792, WO 2006/069793, WO 2008/003434 and WO 2008/003435.

Advantageously, the BET specific surface of the carbon black is at least 70 m²/g, preferably at least 90 m²/g, more preferably between 100 and 150 m²/g.

The BET specific surface of carbon blacks is measured according to the ASTM D6556-10 standard [multipoint method (at least 5 points) – gas: nitrogen – relative pressure range P/P0: 0.1 to 0.3].

Advantageously, the content of carbon black in the said rubber composition of the tire according to the invention is comprised from 10 to 70 phr, preferably from 11 to 65 phr, preferably from 12 to 59 phr.

If silica is used in said rubber composition of the tire according to the invention, it may be any silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a specific surface. CTAB both less than 450 m²/g, preferably from 30 to 400 m²/g.

The BET surface area of silica is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), and more precisely according to a method adapted from standard NF ISO 5794-1, appendix E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - vacuum degassing: one hour at 160°C - relative pressure range p/ in: 0.05 to 0.17].

The CTAB specific surface values of silica were determined according to standard NF ISO 5794-1, appendix G of June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-bromide). trimethylammonium) on the "external" surface of the reinforcing filler.

If silica is used, it advantageously has a BET specific surface of less than 200 m²/g and/or a CTAB specific surface of less than 220 m²/g, preferably a BET specific surface comprised in a range from 125 to 200 m² /g and/or a CTAB specific surface comprised in a range ranging from 140 to 170 m²/g.

As silicas that can be used in the context of the present invention, mention will be made, for example, of the highly dispersible precipitated silicas (known as "HDS") "Ultrasil 7000" and "Ultrasil 7005" from the company Evonik, the silicas "Zeosil 1165MP, 1135MP and 1115MP" from Rhodia, "Hi-Sil EZ150G" silica from PPG, "Zeopol 8715, 8745 and 8755" silicas from Huber, high specific surface silicas as described in application WO 03/ 16837.

To couple the reinforcing silica to the diene elastomer, it is possible to use, in a well-known manner, an at least bifunctional coupling agent (or bonding agent) intended to ensure a sufficient connection, of a chemical and/or physical nature, between the silica ( surface of its particles) and the diene elastomer (hereinafter simply referred to as "coupling agent"). In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. By "bifunctional" is meant a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound can comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic filler and a second functional group comprising a sulfur atom, said second group functional being capable of interacting with the diene elastomer.

Those skilled in the art can find examples of coupling agent in the following documents: WO 02/083782, WO 02/30939, WO 02/31041, WO 2007/061550, WO 2006/125532, WO 2006/125533, WO 2006/125534, US 6,849,754, WO 99/09036, WO 2006/023815, WO 2007/098080, WO 2010/072685 and WO 2008/055986.

However, it is advantageous in the context of the present invention not to use a coupling agent. Thus, preferably, when silica is used, the content of coupling agent, in said rubber composition of the tire according to the invention, is advantageously less than 6% by weight relative to the weight of silica, preferably less than 2 %, preferably less than 1% by weight relative to the weight of silica. Preferably again, when silica is used, said rubber composition of the tire according to the invention does not comprise a coupling agent.

Furthermore, when said rubber composition of the tire according to the invention comprises silica, said composition advantageously comprises a silica covering agent. Among the silica covering agents, mention may be made, for example, of hydroxysilanes or hydrolysable silanes such as hydroxysilanes (see for example WO 2009/062733), alkylalkoxysilanes, in particular alkyltriethoxysilanes such as for example 1-octyl-tri- ethoxysilane, polyols (for example diols or triols), polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialkanol-amines), an optionally substituted guanidine, in particular diphenylguanidine, polyorgano -hydroxylated or hydrolysable siloxanes (for example α,ω-dihydroxy-poly-organosilanes, in particular α,ω-dihydroxy-polydimethylsiloxanes) (see for example EP 0 784 072), fatty acids such as for example stearic acid. When a silica capping agent is used, it is used at a level between 0 and 5 phr. Preferably, the silica capping agent is a polyethylene glycol. When silica is used, the level of silica covering agent, preferably polyethylene glycol, in said rubber composition of the tire according to the invention is advantageously within a range ranging from 1 to 6 phr, preferably from 1.5 to 4 pc.

Whether or not the composition comprises silica, the total rate of reinforcing filler in said rubber composition of the tire according to the invention is preferably within a range ranging from 10 and 70 phr, preferably between 11 and 65 phr, preferably between 12 and 59 phr.

II-4 Cross-linking system

The crosslinking system of said rubber composition of the tire according to the invention may be based on molecular sulfur and/or sulfur and/or peroxide donors, well known to those skilled in the art.

The crosslinking system is preferably a sulfur-based vulcanization system (molecular sulfur and/or sulfur-donating agent).

Whether it comes from molecular sulfur or from the sulfur-donating agent, the sulfur, in said rubber composition of the tire according to the invention, is used at a preferential rate of between 0.5 and 10 phr. Advantageously, the sulfur content, in said rubber composition of the tire according to the invention, is between 0.5 and 2 phr, preferably between 0.6 and 1.5 phr.

Said rubber composition of the tire according to the invention advantageously comprises a vulcanization accelerator, which is preferably chosen from the group consisting of accelerators of the thiazole type as well as their derivatives, accelerators of the sulfenamide and thiourea types and their mixtures. Advantageously, the vulcanization accelerator is chosen from the group consisting of 2-mercaptobenzothiazyl disulphide (MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS ), N-ter-butyl-2-benzothiazyl sulfenamide (TBBS), N-ter-butyl-2-benzothiazyl sulfenimide (TBSI), morpholine disulfide, N-morpholino-2-benzothiazyl sulfenamide (MBS), dibutylthiourea (DBTU), and mixtures thereof. Particularly preferably, the primary vulcanization accelerator is N-cyclohexyl-2-benzothiazyl sulfenamide (CBS).

The rate of vulcanization accelerator in said rubber composition of the tire according to the invention is preferably within a range ranging from 0.2 to 10 phr, preferably from 0.5 to 2 phr, preferably between 0.5 and 1.5 phr, more preferably between 0.5 and 1.4 phr.

Advantageously, the sulfur or sulfur donor/vulcanization accelerator weight ratio, in said rubber composition of the tire according to the invention, is within a range ranging from 1.2 to 2.5, preferably from 1.4 to 2.

II-5 Possible additives

Said rubber composition of the tire according to the invention may optionally also comprise all or part of the usual additives usually used in elastomer compositions for pneumatic or non-pneumatic tires, such as for example plasticizers (such as plasticizer oils and/or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, reinforcing resins (as described for example in application WO 02/10269 ).

II-6 Preparation of rubber compositions

The compositions that can be used in the context of the present invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art:
- a first work phase or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which, in a suitable mixer such as a usual internal mixer (for example 'Banbury' type), all the necessary constituents, in particular the elastomeric matrix, the reinforcing filler, the cellulose pulp, any other miscellaneous additives, with the exception of the crosslinking system. The incorporation of the optional filler into the elastomer can be carried out in one or more stages by mixing thermomechanically. In the case where the filler is already incorporated in whole or in part into the elastomer in the form of a masterbatch (“masterbatch” in English) as described for example in applications WO 97/36724 or WO 99 /16600, it is the masterbatch which is mixed directly and, if necessary, the other elastomers or fillers present in the composition which are not in the form of the masterbatch are incorporated, as well as any other various additives other than the cross-linking system. The non-productive phase can be carried out at high temperature, up to a maximum temperature of between 110° C. and 200° C., preferably between 130° C. and 185° C., for a duration generally of between 2 and 10 minutes.
- a second phase of mechanical work (so-called "productive" phase), which is carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120° C., for example between 40° C. and 100° C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min.

Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00/05300 or WO00/05301.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for characterization in the laboratory, or else extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber which can be used in a pneumatic or non-pneumatic tire, a rubber track or a conveyor belt, for example as a tire or non-pneumatic tire tread or as a tire sidewall. These products can then be used for the manufacture of pneumatic or non-pneumatic tires, rubber tracks or conveyor belts, according to techniques known to those skilled in the art.

The composition can be either in the raw state (before crosslinking or vulcanization), or in the cured state (after crosslinking or vulcanization).

The crosslinking of the composition can be carried out in a manner known to those skilled in the art, for example at a temperature of between 130° C. and 200° C., under pressure.

II-7 Pneumatic or non-pneumatic tire

In known manner, the tread of a pneumatic or non-pneumatic tire comprises a rolling surface intended to be in contact with the ground when the tire is rolling. The tread is provided with a sculpture comprising in particular sculpture elements in relief, which may be ribs or elementary blocks delimited by various main, longitudinal or circumferential, transverse or even oblique grooves, the sculpture elements possibly also comprising various incisions or finer lamellae.

The composition in accordance with the invention may be present in the tread of said pneumatic or non-pneumatic tire and/or in the sidewall of said pneumatic tire, preferably in the tread of said pneumatic or non-pneumatic tire. When it is present in the tread, it may be present in the entire tread of the tire according to the invention, or alternatively in part of the tread of the tire.

The present invention is particularly well suited to the treads of tires intended to equip civil engineering vehicles, agricultural vehicles and heavy goods vehicles, more particularly civil engineering vehicles whose tires are subjected to very specific constraints, in particular soils rocks on which they roll. Thus, advantageously, the pneumatic or non-pneumatic tire provided with a tread comprising a composition according to the invention is a tire for a civil engineering, agricultural or heavy goods vehicle, preferably civil engineering.

The tread of the tire according to the invention may have one or more grooves, the average depth of which ranges from 30 to 120 mm, preferably from 45 to 75 mm.

Furthermore, the average rate of volumetric hollows over the entire tread, defined as the ratio between the total volume of the hollows and the total volume of the tread assumed without hollows, can be included in a range from 5 to 40%, preferably 5 to 25%.

The bandages according to the invention can have a diameter ranging from 20 to 63 inches, preferably from 35 to 63 inches.

II-8 Other rubber articles

Said composition of the pneumatic or non-pneumatic tire in accordance with the invention can also be used in rubber articles whose resistance to mechanical attack proves to be particularly advantageous, in particular caterpillars for off-road vehicles or conveyor belts (also called conveying).

Thus, described herein is a caterpillar comprising at least one rubber element comprising said composition of said tire described above, the at least one rubber element preferably being an endless rubber belt or a plurality of rubber pads.

Also disclosed herein is a rubber conveyor belt comprising said tire composition described above.

III- PREFERRED EMBODIMENTS

In view of the foregoing, the preferred embodiments of the invention are described below:

1. Rubber article comprising a rubber composition based on at least one elastomeric matrix comprising at least one diene elastomer, a reinforcing filler, cellulose pulp, and a crosslinking system, in which the cellulose pulp has a length comprised in a range from 0.3 to 5 mm, the rubber article being chosen from the group consisting of tires and not tires for off-road vehicles, tracks comprising at least one rubber element and conveyor belts .

2. Rubber article according to embodiment 1, in which the elastomeric matrix mainly comprises at least one isoprene elastomer.

3. Rubber article according to any one of the preceding embodiments, in which the rubber composition comprises from 70 to 100 phr, preferably from 90 to 100 phr of isoprene elastomer.

4. Rubber article according to embodiment 2 or 3, in which the at least one isoprene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof, preferably the isoprene elastomer is a natural rubber .

5. Rubber article according to any one of the preceding embodiments, in which the cellulose pulp has a length comprised in a range ranging from 0.5 to 4 mm, preferably from 1.1 to 3.9 mm.

6. Rubber article according to any one of the preceding embodiments, in which the cellulose pulp has an average diameter comprised in a range ranging from 1 to 40 μm, preferably from 3 to 25 μm, preferably from 5 to 15 μm .

7. Rubber article according to any one of the preceding embodiments, in which the cellulose pulp has a length to average diameter ratio within a range ranging from 12 to 4000, preferably from 40 to 1300, more preferably 70 at 600.

8. Rubber article according to any one of the preceding embodiments, in which the rate of the cellulose pulp in the rubber composition is within a range from 1 to 25 phr, preferably from 3 to 20 phr.

9. Rubber article according to any of the preceding embodiments, in which the cellulose pulp is coated with an adhesive composition.

10. Rubber article according to embodiment 9, in which the adhesive composition is a Resorcinol-Formaldehyde-Latex glue called RFL, or an adhesive composition based on a phenol-aldehyde resin and a latex.

11. Rubber article according to any one of the preceding embodiments, in which the reinforcing filler comprises carbon black, silica or a mixture thereof.

12. Rubber article according to any one of the preceding embodiments, in which the reinforcing filler mainly comprises carbon black.

13. Rubber article according to embodiment 11 or 12, in which the carbon black has a BET specific surface area of at least 90 m ² /g, more preferably between 100 and 150 m ² /g.

14. Rubber article according to any one of the preceding embodiments, in which the total rate of reinforcing filler, in the rubber composition, is within a range ranging from 10 to 70 phr, preferably from 12 to 59 phr.

15. A rubber article according to any of the preceding embodiments, said rubber article being a pneumatic or non-pneumatic tire for off-road vehicles.

16. A rubber article according to embodiment 15, wherein the rubber composition is present in the tread of said pneumatic or non-pneumatic tire and/or in the sidewall of said pneumatic tire.

17. Rubber article according to embodiment 15 or 16, said rubber article being a pneumatic or non-pneumatic tire for off-road vehicles, the tread of which has one or more grooves, the average depth of which is within a range from 30 to 120 mm, preferably 45 to 75 mm.

18. A rubber article according to any one of embodiments 15 to 17, said rubber article being a pneumatic or non-pneumatic tire for off-road vehicles, having an average rate of volumetric hollowness over the entire tread including in a range ranging from 5% to 40%, preferably from 5% to 25%.

19. A rubber article according to any one of embodiments 15 to 18, said rubber article being a pneumatic or non-pneumatic tire for off-road vehicles, having a diameter ranging from 20 to 63 inches, preferably from 35 to 63 inches.

20. Rubber article according to any one of embodiments 15 to 19, said rubber article being a pneumatic tire, preferably for a civil engineering vehicle or an agricultural vehicle, preferably for a civil engineering vehicle.

21 Rubber article according to any one of the embodiments 1 to 14, said rubber article being a caterpillar comprising at least one rubber element.

22. A rubber article according to embodiment 21, wherein the at least one rubber member of the track is an endless rubber belt or a plurality of rubber pads.

23. A rubber article according to any one of embodiments 1 to 14, said rubber article being a conveyor belt.

IV- EXAMPLES

IV-1 Measurements and tests used

Tensile tests

These tests make it possible to determine the elasticity stresses and the breaking properties. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. We measure in second elongation (i.e. after an accommodation cycle) the so-called "nominal" secant moduli (or apparent stresses, in MPa) at 10% elongation (denoted "MSA10"). All these tensile measurements are carried out under normal temperature (23±2° C.) and hygrometry (50+5% relative humidity) conditions, according to French standard NF T 40-101 (December 1979). The stresses at break (in MPa) and the elongations at break (in %) are also measured at a temperature of 23°C.

In order to determine the anisotropy of the composition, the secant moduli were measured in the direction of the calendering (Direction C) on the one hand and in the direction perpendicular to the calendering (Direction P) on the other hand. The anisotropy criterion is defined as being the MSA10 (Sens C) / MSA10 (Sens P) ratio. The closer this ratio is to 1, the more homogeneous the stiffness of the mixture. On the contrary, the more this ratio moves away from 1, the less the rigidity is homogeneous. For example, a ratio of 5 means that the stiffness in the direction of the liner is five times greater than the stiffness in the direction perpendicular to the liner.

Dynamic properties

The dynamic properties G* and Max tan(δ) are measured on a viscoanalyzer (Metravib VA4000), according to standard ASTM D5992-96. The response of a sample of vulcanized composition (cylindrical test piece 2 mm thick and 79 mm² cross-section) is recorded, subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under normal temperature conditions. (23°C) according to ASTM D 1349-09 or at 60°C. A deformation amplitude scan is carried out from 0.1% to 50% (go cycle), then from 50% to 0.1% (return cycle). On the return cycle, the value of the loss factor, denoted tan(δ) _{max ,} is recorded.

The hysteretic performance results (tan(δ)max at 60° C.) are expressed as a percentage base 100 relative to the control composition T1. A result above 100 indicates an improvement in hysteresis performance, i.e. a decrease in hysteresis.

Caterpillar test

This test is representative of resistance to attacks. It consists of rolling a metal caterpillar mounted on a pneumatic tire mounted on a wheel and vehicle, and inflated, on which rubber pads of a given composition are fixed, on a track filled with pebbles for a certain time. At the end of rolling, the runners are removed and the number of cuts visible to the naked eye on the surface are counted. The lower the number, the better the attack resistance performance.

To carry out this test, pads of different compositions were manufactured (see Table 1 below) according to the method described in point IV-2 below. To obtain a pad, the non-crosslinked composition obtained in point IV-2 was calendered to a thickness of 5.5 mm, cut out from plates (2 of 260x120 mm, 2 of 250x100 mm and 2 of 235x900 mm) that the then stacked in a pyramid fashion. This block of 6 plates was then inserted into a pyramid-shaped mold with a rectangular base of 260x120 mm and a flat top with a surface area of 235x90 mm, and baked at a temperature of 120°C for 300 minutes at a pressure of 180 bars, thus allowing the crosslinking of the composition.

The pads were then mounted on two Caterpillar X-TRACK10 metal tracks, which were themselves mounted on two MICHELIN XMINE D2 12.00R24 tires on the rear axle of a SCANIA R410 truck. The tires have been re-cut to support the tracks. The tires were inflated to a pressure of 7 bars and carried a load of 4,250 kg per tire.

The truck drove on a flat track covered with 30/60 size porphyry pebbles obtained from SONVOLES Murcia, Spain, for 5 hours at a speed of 5 km/h. The density of stones on the track was around 1000 to 1500 stones per square meter.

At the end of the test, the cuts visible on the surface of the pads were counted. The result was averaged on the basis of 6 pads. The aggression performance results are expressed as a percentage base 100 relative to the control composition T1. A result above 100 indicates an improvement in resistance to attacks.

IV-2 Preparation of compositions

In the examples which follow, the rubber compositions were produced as described in point II.6 above. In particular, the "non-productive" phase was carried out in a 0.4 liter mixer for 3.5 minutes, for an average paddle speed of 50 revolutions per minute until reaching a maximum drop temperature of 160° vs. The “productive” phase was carried out in a cylinder tool at 23°C for 5 minutes.

The crosslinking of the composition was carried out at a temperature of between 130° C. and 200° C., under pressure.

IV-3 Testing of rubber compositions

The examples presented below are intended to compare the performance compromise between the resistance to mechanical attack and the hysteresis of a composition in accordance with the present invention (C1) with two control compositions (T1 and T2), as well as the anisotropy criterion generated by the presence of pulp in the composition.

Table 1 presents the compositions tested (in phr, unless otherwise indicated), as well as the results obtained.

T1 T2 C1 natural rubber 100 87.4 95.8 N115(1) 40 40 40 Silica(2) 15 15 15 TMQ(3) 1 1 1 Anti-ozone wax(4) 1 1 1 Antioxidant(5) 1.5 1.5 1.5 PEG(6) 2.5 2.5 2.5 Stearic acid(7) 1 1 1 ZnO(8) 2.5 2.5 2.5 Aramid Pulp(9) - 5% vol Cellulose Pulp(10) - 5% vol CBS(11) 1 1 1 Sulfur 1.5 1.5 1.5 Anisotropy criterion
MSA10 (C) / MSA10 (P) 1 5.7 1.75 Tan(δ)max at 60°C 100 77 100 Resistance to attacks 100 95 120

(1) Grade N115 carbon black according to ASTM D-1765
(2) “Zeosil 1165MP” silica from Solvay
(3) 2,2,4-trimethyl-1,2-dihydroquinoline "Pilnox TMQ" from Nocil
(4) “VARAZON 4959” from Sasol Wax
(5) N-1,3-dimethylbutyl-N-phenylparaphenylenediamine "Santoflex 6-PPD" from the company Flexsys
(6) Polyethylene glycol “CARBOWAX8000” from DOW CORNING
(7) “Pristerene 4931” stearic acid from Uniqema
(8) Industrial grade zinc oxide from Umicore
(9) Aramid pulp supported at 70% by weight in “Rhenogran P91-40/NR” natural rubber from the company Rhein Chemie – Lanxess, Length: 1.5 mm, Diameter 10 µm (5% by volume = 21 pce including 8.4 pce of aramid pulp and 12.6 pce of natural rubber)
(10) Cellulose pulp supported at 70% by weight in “Rhenogran WPD-70/SBR” butadiene-styrene copolymer from Rhein Chemie – Lanxess, Length: 1.5 mm, Diameter 10 µm (5% by volume = 14 phr including 9.8 phr of cellulose pulp and 4.2 phr of butadiene-styrene copolymer)
(11) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from the company Flexsys

The results presented in Table 1 above show first of all that the presence of cellulose pulp in accordance with the invention makes it possible to improve the resistance to mechanical attacks without penalizing the hysteresis. Furthermore, it has been observed that the composition in accordance with the invention containing cellulose pulp has an anisotropy close to 1 and consequently a uniform stiffness compared to a composition comprising aramid pulp.

Claims (15)

Pneumatic or non-pneumatic tire for off-road vehicles, comprising a rubber composition based on at least:

• an elastomer matrix comprising at least one diene elastomer,
• a reinforcing filler,
• cellulose pulp, and
• a cross-linking system,

wherein the cellulose pulp has a length within a range from 0.3 to 5 mm. Bandage according to Claim 1, in which the elastomeric matrix mainly comprises at least one isoprene elastomer. A tire according to any preceding claim, wherein the rubber composition comprises 70 to 100 phr, preferably 90 to 100 phr of isoprene elastomer. Tire according to Claim 2 or 3, in which the at least one isoprene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and their mixtures, preferably the isoprene elastomer is a natural rubber. Bandage according to any one of the preceding claims, in which the cellulose pulp has a length in the range from 0.5 to 4 mm, preferably from 1.1 to 3.9 mm. Bandage according to any one of the preceding claims, in which the cellulose pulp has an average diameter comprised in the range from 1 to 40 µm, preferably from 3 to 25 µm, preferably from 5 to 15 µm. Tire according to any one of the preceding claims, in which the content of the cellulose pulp in the rubber composition is comprised in a range extending from 1 to 25 phr, preferably from 3 to 20 phr. A bandage according to any preceding claim, wherein the cellulose pulp is coated with an adhesive composition. Bandage according to Claim 8, in which the adhesive composition is a Resorcinol-Formaldehyde-Latex glue called RFL, or an adhesive composition based on a phenol-aldehyde resin and a latex. A bandage according to any preceding claim, wherein the reinforcing filler comprises carbon black, silica or a mixture thereof. Bandage according to any one of the preceding claims, in which the reinforcing filler mainly comprises carbon black. Bandage according to Claim 10 or 11, in which the carbon black has a BET specific surface area of at least 90 m ² /g, more preferably between 100 and 150 m ² /g. Tire according to any one of the preceding claims, in which the total rate of reinforcing filler, in the rubber composition, is comprised in a range ranging from 10 to 70 phr, preferably from 12 to 59 phr. A tire according to any preceding claim, wherein the rubber composition is present in the tread of said pneumatic or non-pneumatic tire and/or in the sidewall of said pneumatic tire. Tire according to any one of the preceding claims, said tire being a pneumatic tire, preferably for an earthmoving vehicle or agricultural vehicle, preferably for an earthmoving vehicle.