WO2021105592A1

WO2021105592A1 - Rubber track comprising polyvinyl alcohol fibers

Info

Publication number: WO2021105592A1
Application number: PCT/FR2020/052128
Authority: WO
Inventors: Romain LIBERT; Thomas Ferrand
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2019-11-28
Filing date: 2020-11-19
Publication date: 2021-06-03
Also published as: CA3150699A1; FR3103775B1; FR3103775A1

Abstract

The invention relates to a stress-resistant rubber track, comprising a composition based on at least one elastomer matrix having at least one elastomer, a reinforcing filler, 0.1 to 25 phr of polyvinyl alcohol fiber, and optionally a cross-linking system.

Description

DESCRIPTION

TITLE: RUBBER TRACK INCLUDING POLYVINYL ALCOHOL FIBERS

The present invention relates to rubber tracks, in particular to tracks intended for rolling off the road.

During travel, a rubber track is subjected to mechanical stresses and attacks resulting from direct contact with the ground. A caterpillar rolling on stony ground is very exposed to attacks, and therefore to the initiation of cracks. In the case of a caterpillar mounted on a vehicle moving heavy loads, the mechanical stresses and the attacks undergone by the caterpillar are amplified under the effect of the weight moved.

This has the consequence that the initiators of crack which can be created in the rubber track under the effect of these stresses and these attacks, tend to propagate more on the surface or inside the belt or the pads in rubber of the track, which can cause localized or generalized tearing of material. These stresses can therefore lead to damage to the belt or the pads and therefore reduce their lifespan.

It is therefore important to have rubber tracks, especially those intended for driving on stony ground and moving heavy loads, having a resistance to the initiation and / or to the propagation of crack strong enough to minimize the effect of a crack initiation over the life of the track, and this without penalizing 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 caterpillar can be manifested by a reduction in the endurance (in English “durability”) of the caterpillar. In view of the foregoing, there is a permanent objective of providing rubber compositions which exhibit an improved compromise between resistance to attack and hysteresis.

Continuing its research, the Applicant has unexpectedly discovered that the use of polyvinyl alcohol fibers in a tread composition makes it possible to improve the aforementioned performance compromise.

Thus the subject of the invention is a caterpillar comprising at least one rubber element comprising a composition based on at least one elastomer matrix comprising at least one elastomer, a reinforcing filler, from 0.1 to 25 phr of alcohol fiber. polyvinyl, and optionally a crosslinking system.

In the present document, unless otherwise indicated, the expressions "the composition" or "the composition according to the invention" denote the composition of the at least one rubber element of the track according to the invention.

I- DEFINITIONS

By the expression “composition based on” is meant 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 each other, less partially, during the various phases of manufacture of the composition; the composition may thus be in the fully 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), it is meant within the meaning of the present invention, the part, by mass per hundred parts by mass of elastomer.

In the present document, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass. On the other hand, any interval of values designated by the expression "between a and b" represents the range of values going from more than a to less than b (that is to say limits a and b excluded) while any range of values designated 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 the present 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 understood, within the meaning of the present invention, that this compound is 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 major elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. Likewise, a so-called majority filler is that representing the greatest mass among the fillers of the composition. By way of example, in a system comprising a single elastomer, the latter is in the majority 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, the term “majority” is understood to mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%.

The compounds comprising carbon mentioned in the description can be of fossil origin or biobased. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This concerns in particular polymers, plasticizers, fillers, etc. All the “Tg” glass transition temperature values described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to the ASTM D3418 (1999) standard. II- BRIEF DESCRIPTION OF THE FIGURES

[Fig 1] Figure 1 shows a diagram of a construction vehicle equipped with endless tracks.

[Fig 2] Figure 2 is a schematic representation of a device for orienting short fibers within an elastomer layer. "A1" and "A2" represent the cylinders of a calender. "B" represents a receiving roll on which is disposed a layer emerging from the calender.

III- DESCRIPTION OF THE INVENTION

III- 1 Elastomeric matrix

According to the invention, the composition of the at least one rubber element of the track according to the invention comprises at least one elastomer. The at least one elastomer can be at least one diene elastomer, at least one thermoplastic elastomer or a mixture thereof.

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

These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". In general, the term “essentially unsaturated” is understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a level of units or units of diene origin (conjugated dienes) which is greater than 15% (% by moles); it is thus that diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the preceding definition and can in particular be qualified as “essentially saturated” diene elastomers (content of units of weak or very weak diene origin, always less than 15%). The diene elastomers included in the composition according to the invention are preferably essentially unsaturated. By diene elastomer capable of being used in the compositions in accordance with the invention is particularly meant: 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 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 vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial mixture "vinyl-toluene", para-tert-buty lstyrene.

Suitable aliphatic α-monoolefins are in particular acyclic aliphatic α-monoolefins having from 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-copolymers. butadiene-styrene (SBIR), ethylene-butadiene copolymers (EBR) and mixtures of such copolymers. The above diene elastomers can be, for example, block, random, sequenced, microsequenced, and be prepared in dispersion or in solution; they can be coupled and / or starred or else functionalized with a coupling and / or starring or functionalizing agent, for example epoxidized.

Preferably, when the composition of the at least one rubber element of the caterpillar according to the invention comprises a diene elastomer, the elastomeric matrix comprises at least 50%, preferably at least 70%, preferably at least 90% , preferably 100%, by mass, of at least one isoprene elastomer.

By “isoprene elastomer” is meant in a known manner a homopolymer or a copolymer of isoprene, 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, there may be mentioned in particular the copolymers of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, use is preferably made of polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%.

Advantageously, G 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.

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

It will be noted that the SBR can be prepared in emulsion (ESBR) or in solution (SSBR). Preferably this is an SSBR. Whether it's ESBR or SSBR. Among the copolymers based on styrene and on butadiene, in particular SBR, there may be mentioned in particular those having a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (mol%) in -1,2 bonds of the butadiene part of between 4% and 75%, a content (mol%) of trans-1,4 bonds of 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 from 6% to 30%, by weight relative to the total weight of the copolymer, and a content ( mol%) in -1.2 bonds of the butadiene part of between 4% and 75%, preferably between 15% and 30%.

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

As indicated above, the elastomer of the composition of the at least one rubber element of the track according to the invention may also or alternatively comprise at least one thermoplastic elastomer.

By “thermoplastic elastomer (TPE)” is meant, in a known manner, a polymer of intermediate structure between a thermoplastic polymer and an elastomer. A thermoplastic elastomer consists of one or more rigid "thermoplastic" segments connected to one or more flexible "elastomer" segments.

Thus, the thermoplastic elastomer (s) of the composition of the at least one rubber element of the caterpillar which can be used according to the invention comprise at least one elastomer block and at least one thermoplastic block. Typically, each of these segments or blocks contains at least more than 5, generally more than 10 base units.

Thus, a composition in which a resin or a thermoplastic polymer and an elastomer are mixed does not constitute a thermoplastic elastomer within the meaning of the present invention.

Advantageously, the thermoplastic elastomer comprises, preferably consists of, at least one thermoplastic polyurethane (TPU), which can be any thermoplastic polyurethane, well known to those skilled in the conventional art.

The TPUs that can be used in the context of the present invention advantageously comprise at least one flexible segment and at least one rigid segment. Advantageously, they are block copolymers alternating rigid segments and flexible segments. The rigid segments can in particular be obtained from the reaction of a polyisocyanate (generally a diisocyanate) with a diol or a triol of low molecular weight (preferably within a range ranging from 40 to 350 g / mol), called a chain extender. . By way of example of a low molecular weight diol, mention may be made, without being limited to these examples, of ethylene glycol, diethylene glycol, propanediol, butanediol, Thexane diol, Tisosorbide, Thydroquinone, etc. As an example of a low molecular weight triol, mention may be made, without being limited to these examples, of trimethylol propane, glycerol, etc. Moreover, the polyisocyanate can be aromatic such as MDI (Methylene diphenyl diisocyanate), toluene diisocyanate (TDI), phenylene diisocyanate (PPDI), aliphatic such as Thexamethylene diisocyanate (HDI), Tisoprene diisocyanate (IPDI), alicyclic such as H12 (4,4-dicyclohexyl methane diisocyanate), or combinations thereof. The flexible segments can in particular be obtained from the reaction of a polyisocyanate with a polyol with a long hydrocarbon chain (generally the molecular weight of the hydrocarbon chain of the polyisocyanate is between 600 and 2500 g / mol). The polyol can be of the ether or ester type (generally a polyester glycol or a polyether glycol), but also of the polycarbonate type. For example, for the polyester, there may be mentioned polyadipate or polycaprolactone, for polyether: polypropylene glycol and polytetramethylene glycols, and for polycarbonates: polycarbonates diol. The flexible block of the polyurethane can also be partially crosslinked, for example with a hyper-branched or dendritic polyol.

TPUs exhibit both elastomeric and thermoplastic properties. They exhibit, in a well-known manner, a peak of Tg (flexible segments of the TPU) and a peak of melting temperature (rigid segments of the TPU) (Tf, measured in a well-known manner by DSC according to the standard ASTM D3418). Thus, the flexible segments of TPUs are generally defined by a Tg which can be less than or equal to the ambient temperature (25 ° C), while the rigid segments can have a Tm greater than or equal to 80 ° C.

In the present application, when reference is made to the glass transition temperature of a TPU, it is the glass transition temperature relating to the soft segment (unless stated otherwise).

As examples of TPUs that can be used in the context of the present invention, mention may be made of those described in document FR 2201 320, US 4,124,572, US 4,182,898, US 2003/0032754, CA 2 322093 or CA 2 168 938 for example.

According to the invention, at least one thermoplastic polyurethane advantageously has an elongation at break greater than 500% and a modulus at break greater than 30 MPa, measured according to standard DIN53504. More preferably, at least one thermoplastic polyurethane has an elongation at break greater than 600% and 35 MPa, measured according to standard DIN53504.

As examples of commercially available TPU, mention may be made of DesmopaN® 3378A sold by the company Bayer, Irogran® A85C 4957 from the company Huntsman, Elastollan® 1175AW from the company BASF or Pearlthane® 11T80 from the company. Lubrizol company. When the composition of the at least one rubber element of the track according to the invention comprises a thermoplastic elastomer, preferably a TPU, the elastomeric matrix comprises at least 50%, preferably at least 70%, preferably at least 90 %, preferably 100%, by weight, of at least thermoplastic elastomer, preferably of at least one TPU.

Thus, according to the invention, isoprene telastomer, preferably natural rubber, may be the only elastomer in the composition. In other words, its content in the composition of at least one rubber element of the track according to the invention is preferably 100 phr.

The composition of the at least one rubber element of the track according to the invention may alternatively exclusively comprise one or more thermoplastic elastomer, preferably one or more thermoplastic polyurethanes, in particular TPUs as described above.

The composition of the at least one rubber element of the caterpillar according to the invention may also comprise a mixture of 20 to 90 phr, preferably 30 to 80 phr, more preferably 35 to 70 phr of diene elastomer, preferably isoprene elastomer, and from 10 to 80 phr, preferably 20 to 70 phr, preferably 30 to 65 phr of thermoplastic elastomer, preferably thermoplastic polyurethane.

III-2 Reinforcing charge

The composition of the at least one rubber element of the track according to the invention further comprises a reinforcing filler, known for its ability to reinforce a rubber composition.

The reinforcing filler can comprise carbon black, silica or a mixture thereof. Advantageously, the reinforcing filler mainly comprises, preferably exclusively, 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 black tires of tire grade). Among the latter, there will be mentioned more particularly 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 NI 15, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772). These carbon blacks can be used in the isolated state, as available commercially, or in any other form, for example as a support 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 (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 organic fillers of functionalized polyvinyl as described in applications WO 2006/069792, WO 2006/069793, WO 2008/003434 and WO 2008/003435.

Advantageously, the BET specific surface area of the carbon black is at least 90 m ² / g, preferably between 100 and 150 m ² / g.

The BET specific surface area of carbon blacks is measured according to standard ASTM D6556-10 [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range R / R0: 0.1 to 0.3]

Advantageously, the level of carbon black in the composition of water minus one rubber element of the track according to the invention is between 10 and 70 phr, preferably between 11 and 65 phr, preferably between 12 and 59 phr.

If silica is used in the composition of the at least one rubber element of the caterpillar according to the invention, it may be any silica known to those skilled in the art, in particular any precipitated or pyrogenic silica exhibiting a BET surface as well as a CTAB specific surface both less than 450 m ² / g, preferably from 30 to 400 m ² / g.

The BET specific 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 area 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 "outer" surface of the reinforcing filler.

If silica is used, it advantageously has a BET specific surface area of less than 200 m ² / g and / or a CTAB specific surface area is less than 220 m ² / g, preferably a BET specific surface area within a range ranging from 125 at 200 m ² / g and / or a CTAB specific surface area within a range ranging from 140 to 170 m ² / g.

As silicas which can be used in the context of the present invention, mention will be made, for example, of the highly dispersible precipitated silicas (called “HDS”) “Ultrasil 7000” and “Ultrasil 7005” from the company Evonik, the silicas “Zeosil 1165MP, 1135MP and 1115MP "from the company Rhodia, the silica" Hi-Sil EZ150G "from the company PPG, the silicas" Zeopol 8715, 8745 and 8755 "from the company Huber, silicas with a high specific surface 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 binding 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, the said first functional group being able to interact with the hydroxyl groups of an inorganic charge and a second functional group comprising a sulfur atom, the said second functional group being able to interact with the diene elastomer.

Those skilled in the art can find examples of a 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 the composition of the at least one rubber element of the track according to the invention, is advantageously less than 6% by weight relative to the weight of silica. , less than 2%, preferably 1% by weight relative to the weight of silica. More preferably, when silica is used, the composition of at least one rubber element of the track according to the invention does not include a coupling agent.

Moreover, when the composition of the at least one rubber element of the caterpillar according to the invention comprises silica, the composition advantageously comprises a silica covering agent. Among the silica covering agents, there may be mentioned, for example, hydroxysilanes or hydrolyzable silanes such as hydroxysilanes (see for example WO 2009/062733), alkylalkoxysilanes, in particular alkyltriethoxysilanes such as, for example, 1-octyl-tri- ethoxysilane, polyols (eg diols or triols), polyethers (eg polyethylene glycols), primary, secondary or tertiary amines (eg trialkanol-amines), an optionally substituted guanidine, in particular diphenylguanidine, hydroxylated or hydrolyzable polyorganosiloxanes (for example a, w -dihydroxy-poly-organosilanes (in particular a, w-dihydroxy-polydimethylsiloxanes) (see for example EP 0 784 072), fatty acids such as for example stearic acid. When a silica covering agent is used, it is used at a level of between 0 and 5 phr. Preferably, the covering agent of the silica is polyethylene glycol. When silica is used, the level of covering agent of the silica, preferably polyethylene glycol, in the composition of the at least one rubber element of the track according to the The invention advantageously falls within a field ranging from 1 to 6 phr, preferably from 1.5 to 4 phr.

Whether the composition comprises silica or not, the total rate of reinforcing filler in the composition of the at least one rubber element of the caterpillar 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.

III-3 Free of polyvinyl alcohol

The composition of the at least one rubber element of the track according to the invention has the essential characteristic of comprising from 0.1 to 25 phr of polyvinyl alcohol (PVA) fiber.

Preferably, the amount of polyvinyl alcohol fibers in the composition is within a range ranging from 1 to 25, preferably 3 to 20 phr, preferably 5 to 15 phr.

Advantageously, these polyvinyl alcohol fibers have a length of between 0.5 and 20 mm, preferably between 0.8 and 12 mm, more preferably between 1 and 8 mm. Their average diameter is preferably between 5 and 60 mhi, preferably between 10 and 30 mhi. Preferably, the fibers are coated with an adhesive composition making it possible to improve their adhesion to the rubber composition. This adhesive composition can be a conventional Resorcinol-formaldehyde-latex glue, commonly abbreviated as RFL glue, or even an adhesive composition based on a phenol-aldehyde resin and on 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 on a latex is particularly advantageous because of the non-emission of formaldehyde.

Such PVA fibers are commercially available, in particular Kuralon fibers from Kuraray, PVA fibers from NYCON such as references RSC15, RECS15 or even “Polyvinylalcohol fibers” from STW.

Advantageously, the longitudinal direction of the polyvinyl alcohol fibers is located substantially in a plane parallel to the outer surface of the at least one rubber element.

By "external surface of at least one rubber element" is meant the surface intended to come into contact with the ground when the track is rolling. This is the most radially outer surface with respect to at least one wheel, generally relative to the drive wheel, of the track.

Preferably, the longitudinal direction of the majority of the polyvinyl alcohol fibers has an orientation between -25 degrees and +25 degrees, preferably between -10 degrees and +10 degrees, relative to the outer surface of the at least. a rubber element.

In addition, advantageously, the longitudinal direction of the majority of the polyvinyl alcohol fibers has an orientation of between -40 degrees and +40 degrees, preferably between -20 degrees and +20 degrees, with respect to the circumferential plane of the track. By "circumferential plane" is meant a plane perpendicular to the axis of rotation of the main wheel of the track on which the at least one rubber element is, or is intended to be, mounted.

The orientation of the fibers can be obtained by producing a layer of unvulcanized elastomer containing said fibers by calendering using a roller tool (A1 and A2) and a receiving roller (B) at the outlet of the tool as shown in Figure 3. The layer emerging from the tool is placed in contact with the receiving roller (B). The receiving roller is adjusted so as to have a tangential speed greater than the tangential speed of the tool rolls without inducing tearing of the layer. This tangential speed difference helps orient the short fibers in the calendering direction. Those skilled in the art will be able to determine the respective tangential speeds of the cylinders and of the receiving roller. Those skilled in the art will know how to decrease the angle of the fibers with respect to the longitudinal and circumferential directions, for example by increasing the tangential speed of the take-up roller (B).

Those skilled in the art can measure the angle of the fibers within the at least one rubber element by removing part of said element, preferably by following a plane parallel to the longitudinal plane, so as to reveal an interface containing the fibers. , and by taking a test piece of material by cutting said rubber element and by establishing the orientation histogram of the fibers by optical microscopy in reflection on a sample of at least 100 fibers in accordance with the recommendations of those skilled in the art in " Orientation of short fibers in reinforced thermoplastic parts - Observation of the orientation of the fibers ”, Engineering techniques, Reference AM3729, July 10, 2003, Michel VINCENT.

III-4 Crosslinking system

When the composition of the at least one rubber element of the caterpillar according to the invention comprises at least one diene elastomer, the composition advantageously comprises a crosslinking system. A crosslinking system is not compulsory, in particular when the elastomer of the composition of the at least one rubber element of the track according to the invention is a thermoplastic elastomer, in particular a thermoplastic polyurethane.

The crosslinking system of the composition of the at least one rubber element of the caterpillar according to the invention may be based on molecular sulfur and / or on sulfur donors and / or peroxide, well known to those skilled in the art. job.

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

Whether it comes from molecular sulfur or from the sulfur donor agent, the sulfur, in the composition of the at least one rubber element of the caterpillar according to the invention, is used at a preferential rate of between 0.5 and 10 pce. Advantageously, the sulfur content in the composition of at least one rubber element of the track according to the invention is between 0.5 and 2 phr, preferably between 0.6 and 1.5 phr.

The composition of the at least one rubber element of the caterpillar 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 type. , thioureas and their mixtures. Advantageously, the vulcanization accelerator is chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (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 the composition of the at least one rubber element of the track according to the invention is preferably included in a range from 0.2 to 10 phr, preferably from 0.5 and 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 the composition of the at least one rubber element of the track according to the invention, is within a range ranging from 1.2 to 2, Preferably from 1.4 to 2.

III-5 Possible additives

The compositions of the rubber elements of the track according to the invention may optionally also include all or part of the usual additives usually used in elastomer compositions for rubber tracks, such as, for example, plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, anti-oxidants, anti-fatigue agents, reinforcing resins (such as described for example in application WO 02/10269 ).

III-6 Preparation of rubber compositions

The compositions which 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 thermomechanical working or mixing phase (so-called "non-productive phase). "), Which can be carried out in a single thermomechanical step during which all the necessary constituents, in particular the elastomer matrix, are introduced into a suitable mixer such as a usual internal mixer (for example of the 'Banbury' type), PVA fibers, any other various additives, with the exception of the crosslinking system. The incorporation of the optional filler into the elastomer can be carried out one or more times by thermomechanically mixing. In the case where the filler is already incorporated in whole or in part in the elastomer in the form of a masterbatch 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 is not in the form of a masterbatch, as well as any other various additives other than the crosslinking 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 period 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 less than 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 of a plate, in particular for a characterization in the laboratory, or else extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profile) of rubber which can be used, for example, as a rubber track tread. These products can then be used for the manufacture of rubber belts or rubber pads, 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), can be a semi-finished product which can be used in a rubber track. 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.

III-7 Rubber track

According to the invention, the track comprises at least one rubber element. The at least one rubber element can be an endless rubber belt or a plurality of rubber pads, which are well known to those skilled in the art for equipping tracks (see EPI 120335 or WO2019 / 097834 for example). In Figure 1, there is shown an example of an endless caterpillar 6 fitted to a construction vehicle 10. This vehicle 10 may for example be a bulldozer, a backhoe loader, an excavator or any other type of construction vehicle. In this figure, the construction vehicle 10 comprises a frame 12 supporting a prime mover 14, two sets of tracks 16i, I6 ₂ (called "running gear") and a driver's cab 20 from which an operator can control the construction vehicle 10 for moving it on the ground and performing construction work using a work tool 18. Each track assembly 16 includes an endless rubber belt 22 disposed around a plurality of wheels, comprising a drive wheel 24, a front idler wheel 26, a rear idler wheel 29 and a plurality of roller wheels 28I-282.

IV- PREFERRED EMBODIMENTS

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

A. Track comprising at least one rubber element comprising a composition based on at least one elastomeric matrix comprising at least one elastomer, a reinforcing filler, from 0.1 to 25 phr of polyvinyl alcohol (PVA) fiber, and optionally a crosslinking system.

B. Track according to embodiment A, wherein the at least one rubber member is an endless rubber belt or a plurality of rubber pads.

C. Track according to embodiment A or B, in which the elastomeric matrix comprises at least 50%, preferably at least 70%, preferably at least 90%, preferably 100%, by mass, of at least one isoprene elastomer. D. Track according to embodiment C, in which the isoprene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and their mixtures.

E. Track according to Embodiment C, wherein the isoprene elastomer is natural rubber.

F. Chenille according to embodiment A or B, in which the elastomeric matrix comprises at least 50%, preferably at least 70%, preferably at least 90%, preferably 100%, by weight, of at least one butadiene-styrene copolymer or a mixture of at least one butadiene-styrene copolymer and at least one polybutadiene.

G. Chenille according to embodiment A or B, in which the elastomeric matrix comprises at least 50%, preferably at least 70%, preferably at least 90%, preferably 100%, by mass, of at least one thermoplastic elastomer.

H. Track according to Embodiment G, wherein the thermoplastic elastomer is a thermoplastic polyurethane.

I. Chenille according to any one of the preceding embodiments, in which the composition comprises a mixture of 20 to 90 phr, preferably 30 to 80 phr, more preferably 35 to 70 phr of diene elastomer, preferably of isoprene elastomer, and from 10 to 80 phr, preferably 20 to 70 phr, preferably 30 to 65 phr of thermoplastic elastomer, preferably thermoplastic polyurethane.

J. Chenille according to any of the preceding embodiments, in which the polyvinyl alcohol fibers have a length of between 0.5 and 20 mm, preferably between 0.8 and 12 mm.

K. Chenille according to any of the preceding embodiments, wherein the polyvinyl alcohol fibers have an average diameter of between 5 and 60 µm, preferably between 10 and 30 µm.

L. Chenille according to any one of the preceding embodiments, in which the fibers are coated with an adhesive composition. M. Chenille according to embodiment L, in which the adhesive composition is a Resorcinol-Formaldehyde-Latex adhesive called RFL, or an adhesive composition based on a phenol-aldehyde resin and on a latex.

N. Chenille according to any one of the preceding embodiments, in which the content of polyvinyl alcohol fibers in the composition is within a range ranging from 1 to 25 phr, preferably from 5 to 20 phr.

O. A track according to any of the preceding embodiments, wherein the longitudinal direction of the polyvinyl alcohol fibers is substantially located in a plane parallel to the outer surface of the at least one rubber member.

P. Chenille according to any one of the preceding embodiments, in which the longitudinal direction of the majority of the polyvinyl alcohol fibers has an orientation of between -25 degrees and +25 degrees, preferably between -10 degrees and +10. degrees, relative to the outer surface of the at least one rubber member.

Q. Track according to any of the preceding embodiments, in which the longitudinal direction of the majority of the polyvinyl alcohol fibers has an orientation between -40 degrees and +40 degrees, preferably between -20 degrees and +20. degrees, relative to the circumferential plane of the track.

A. A caterpillar according to any of the preceding embodiments, wherein the reinforcing filler comprises carbon black, silica or a mixture thereof.

S. Chenille according to any of the preceding embodiments, in which the reinforcing filler predominantly comprises carbon black.

T. Chenille according to embodiment R or S, in which the carbon black has a BET specific surface area of at least 90 m2 / g, more preferably between 100 and 150 m2 / g.

U. Caterpillar according to any one of the embodiments R to T, in which the level of carbon black in the composition is between f0 and 70 phr, preferably between 12 and 59 phr. V. Caterpillar according to any one of embodiments R to U, in which the level of silica in the composition is between 2 and 30 phr, preferably between 2 and 24 phr.

W. Chenille according to any one of the preceding embodiments, in which the crosslinking system is a vulcanization system based on molecular sulfur and / or sulfur donor agent.

V- EXAMPLES

V-1 Preparation of the compositions In the examples which follow, the rubbery compositions were produced as described in point III.6 above. In particular, the “non-productive” phase was carried out in a 0.4 liter mixer for 3.5 minutes, for an average pallet speed of 50 revolutions per minute until a maximum drop temperature of 160 ° C was reached. 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 110 ° C and 200 ° C, under pressure. V-2 Measurements and tests used

Dynamic properties

The dynamic properties G * and Max tan (ô) are measured on a viscoanalyst (Metravib VA4000), according to standard ASTM D5992-96. The response of a sample of vulcanized composition (cylindrical test piece 2 mm thick and 79 mm ² in section) is recorded, subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under normal conditions of temperature (23 ° C) according to ASTM D 1349-09. A strain amplitude sweep is carried out from 0.1% to 50% (outward cycle), then from 50% to 0.1% (return cycle). On the return cycle, the value of the loss factor is recorded, noted tan (ô) _max .

The hysteretic performance results (tan (ô) max at 23 ° C) are expressed as a percentage base 100 relative to the control composition T1. A result greater than 100 indicates an improvement in hysteretic performance, i.e. a decrease in hysteresis.

Caterpillar test

This test is representative of resistance to attack. It consists in 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 stones for a certain time. At the end of the ride, the pads are removed and the number of cuts visible to the naked eye on the surface is counted. The lower the number, the better the aggression resistance performance.

To carry out this test, pads of different compositions (see Table 1 below) were manufactured according to the process described in point V-1 above. To obtain a pad, the non-crosslinked composition obtained at point Vl was calendered to a thickness of 5.5 mm, cut from the plates (2 of 260x120 mm, 2 of 250x100 mm and 2 of 235x90 0mm) which were then stacked. in a pyramidal 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 of 235x90 mm in area, and baked at a temperature of 120 ° C for 300 minutes at a pressure of 180 bars, thus allowing crosslinking of the composition.

The pads were then mounted on two X-TRACK10 metal tracks from the Caterpillar company, 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 recut to support the tracks. The tires were inflated to a pressure of 7 bars and carried a load of 4250 kg per tire.

The truck drove on a slope without slope covered with porphyry pebbles of size 30/60 obtained from SONVOLES Murcia, Spain, for 5 hours at a speed of 5 km / h. The density of pebbles on the track was around 1000 to 1500 pebbles per square meter. At the end of the test, the visible cuts on the surface of the pads were counted. The result was averaged on the basis of 6 pads. The results of performance against attacks are expressed as a percentage base 100 relative to the control composition T1. A result greater than 100 indicates an improvement in resistance to attacks.

V-3 Testing of rubber compositions

The purpose of the examples presented below is to compare the resistance to attack and the hysteresis of the tread in accordance with the present invention (C1 and C2) with those of control compositions (T1 to T3).

Table 1 shows the compositions tested (in phr), as well as the results obtained.

Composition C1 differs from composition T1 only by the presence of PVA fibers. Compositions T2 and T3 differ from composition C1 only by the nature of the fibers used. The amount of fiber was adjusted so that the volume fraction of the fibers was 2% in each of compositions C1, T2 and T3, and 5% for composition C2.

The C2 compositions allow to study the impact of increasing the amount of PVA fibers.

[Table 1]

(1) NI 15 grade carbon black according to ASTM D-1765

(2) Silica “Ultrasil VN3” from the company Evonik

(3) “Kuralon 1239” PVA fibers from the company Kuraray

(4) PET fibers “Polyester RFL treated precision had” from the company Bamet (5) PA fibers “Nylon 6.6 RFL treated precision had” from the company Bamet

(6) 1.5 pce of Nl, 3-dimethylbutyl-N-phenylparaphenylenediamine “Santoflex 6-PPD” from the company Flexsys and 1.0 pce of 2,2,4-trimethyl-l, 2-dihydroquinoline (TMQ) from the company Lanxess

(7) “VARAZON 4959” anti-ozone wax from Sasol Wax

(8) “Pristerene 4931” stearic acid from the company Uniqema (9) Zinc oxide of industrial grade from the company Umicore

(10) Polyethylene glycol of Mn 6000-20000 gm / mol sold by SASOL husband

(11) N-cyclohexyl-2-benzothiazyl sulfenamide “Santocure CBS” from the company Flexsys

The results presented in Table 1 above show that the use of PVA fibers in the composition makes it possible to greatly improve the resistance to attack compared to a composition not comprising any, but also compared to compositions comprising fibers. of other nature. It has been found that increasing the level of PVA fiber further improves resistance to attack.

Claims

1. Track comprising at least one rubber element comprising a composition based on at least one elastomeric matrix comprising at least one elastomer, a reinforcing filler, from 0.1 to 25 phr of polyvinyl alcohol (PVA) fiber, and optionally a crosslinking system.

2. The track of claim 1, wherein the at least one rubber member is an endless rubber belt or a plurality of rubber pads.

3. Track according to claim 1 or 2, wherein the elastomeric matrix comprises at least 50%, preferably at least 70%, by weight, of at least one isoprene elastomer.

4. Track according to claim 3, wherein G isoprene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof.

5. Track according to claim 1 or 2, wherein the elastomeric matrix comprises at least 50%, preferably at least 70%, by mass, of at least one butadiene-styrene copolymer or a mixture of at least one copolymer. butadiene-styrene and at least one polybutadiene.

6. Track according to claim 1 or 2, wherein the elastomeric matrix comprises at least 50%, preferably at least 70%, by weight, of at least one thermoplastic elastomer.

7. Track according to claim 6, wherein the thermoplastic elastomer is a thermoplastic polyurethane.

8. A caterpillar according to any one of the preceding claims, in which the polyvinyl alcohol fibers have a length of between 0.5 and 20 mm, preferably between 0.8 and 12 mm.

9. A caterpillar according to any one of the preceding claims, in which the polyvinyl alcohol fibers have an average diameter of between 5 and 60 mhi, preferably between 10 and 30 mhi.

10. Caterpillar according to any one of the preceding claims, in which the content of polyvinyl alcohol fibers in the composition is within a range ranging from 1 to 25 phr, preferably from 5 to 20 phr.

11. A track according to any preceding claim, wherein the longitudinal direction of the polyvinyl alcohol fibers is substantially located in a plane parallel to the outer surface of the at least one rubber member.

12. Track according to any preceding claim, wherein the reinforcing filler comprises carbon black, silica or a mixture thereof.

13. Track according to any one of the preceding claims, in which the reinforcing filler mainly comprises carbon black.

14. Caterpillar according to claim 12 or 13, in which the level of carbon black in the composition is between 10 and 70 phr, preferably between 12 and 59 phr.

15. A caterpillar according to any one of the preceding claims, in which the crosslinking system is a vulcanization system based on molecular sulfur and / or sulfur donor agent.