FR3045630A1 - PULP COMPOSITE MATERIALS FOR MECHANICAL COUPLING - Google Patents

Abstract

The present invention relates to materials for generating mechanical coupling in elastomeric compositions, particularly used for the manufacture of tire treads. In particular, it relates to a tread comprising a composite material based on an elastomeric matrix, a crosslinking system, a reinforcing filler and a pulp.

Description

Technical area

The present invention relates to materials for generating mechanical coupling in elastomeric compositions, particularly used for the manufacture of tire treads.

STATE OF THE ART Improving the wear resistance of tires is a very important problem, particularly because of the cost of the tires. This problem concerns all types of tires, but is even more important for tires for heavy goods vehicles and civil engineering vehicles because of the economic impact of immobilizing vehicles when replacing worn tires.

Particularly, in the field of civil engineering, and in particular the mining sector, tires are used mainly on ore or coal extraction sites, as well as in quarries. The use consists, in a simplified way, in: - A cycle going in load, generally in rise for the ore and the coal, generally in descent for the quarries, to transport the ore or the sterile material towards the unloading zones (« crusher "for ore," dumping zones "for sterile material); - An empty return cycle, usually downhill for mining use, usually uphill for quarry use, to return to the loading areas.

The tires fitted to the mining dumpers concerned are, as a rule, mounted on the front axle of the vehicle during the first third of their life, and then swapped in twinned on the rear axle for the two thirds of life remaining. The engine torque is transmitted via the rear axle, the braking torque is also almost exclusively transmitted via the rear axle using the engine brake (thermal or electrical in the case of such a transmission).

From the point of view of a mine manager, the transportation of ore and sterile material accounts for a significant portion of the operational costs of the mine, and the share of tires in this contribution is significant. Limiting the speed of wear is therefore a major axis of reduction of operating costs. From the point of view of the tire manufacturer, developing technical solutions to reduce the speed of wear is therefore an important strategic element.

The mining tires of the rear axle of the rigid dumpers are subjected to significant efforts (passage of engine torque and braking) because the slopes of the tracks to leave the open pit mines ("pit" in English) are generally of the order of 8.5 to 10%. This slope value optimizes vehicle productivity with the current available power. These stresses result in a relatively fast wear of the tires. It is therefore a question of proposing a technical solution making it possible to improve the tire wear performance of this axle, both under engine torque under load and under vacuum braking torque.

Many solutions have been sought to increase the wear resistance so as to prolong their life as much as possible and thus reduce operating costs.

In the field of tires for civil engineering vehicles, it is known to use in treads of off-road vehicles, natural rubber, a reinforcing filler of the carbon black type and the additives usually used for these tires. The improvement in the wear resistance of this type of tire is generally achieved by optimizing the nature of its constituents or its sculptures. For example, to improve the wear resistance of off-road tires, WO 2013/041400 proposes to incorporate a certain amount of high vinyl polybutadiene into an isoprenic matrix of a tread composition.

In the field of tires for vehicles traveling on bituminous surfaces such as passenger vehicles or most heavy goods vehicles, a solution to improve the wear resistance has been proposed in US Pat. No. 8,272,412 by integrating, into an elastomeric composition. for tread, glass fibers oriented at 45 degrees to the direction of rolling in the circumferential plane.

However, it is still necessary to provide improved solutions to improve the wear resistance of tires in general, and particularly for tires of heavy goods vehicles or civil engineering vehicles.

Presentation of the invention

Accordingly, the present invention relates to a novel tire formulation for significantly improving their wear resistance.

It particularly relates to a tread comprising at least one tread, said tread comprising a composite material based on an elastomeric matrix, a crosslinking system, a reinforcing filler and pulp, said pulp being present in the matrix. elastomeric compound at a concentration ranging from 5 to 45 parts by weight per hundred parts of elastomer, pce, and being in a material selected from aromatic polyamides, polybenzimidazoles, polybenzothiazoles, polybenzoxazoles, polypyridazoles, polybenzoxadiazoles aromatic polyesters, polyurethanes, polyetheretherketones, polyolefins, polyacrylics and liquid crystal polymers, cellulose, glass and mixtures thereof, said sculpture consisting of a plurality of parallel layers and adjacent to each other, said layers being oriented in sculpture parallel to a plane that is (i) perpendicular to the equatorial plane and (ii) oriented at an angle α expressed in degrees to the radial plane, the angle a being defined by the formula a = 45 +/- x, where x is within a range ranging from 10 to 30.

The tread according to the invention can be either in the green state (before crosslinking or vulcanization), or in the fired state (after crosslinking or vulcanization). It can be in the form of a semi-finished product that can be used in a tire or on a retreaded carcass, or can be already disposed on a tire or a tire casing. Definitions

By the term "part by weight per hundred parts by weight of elastomer" (or phr) is meant for the purposes of the present invention, the part, by weight per hundred parts by weight of elastomer or rubber.

In the present, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass. On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b). In the present invention, when a range of values is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also designated and preferentially.

As used herein, "composition based on" is understood to mean a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of or intended to react between they, at least in part, during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization. By way of example, a composition based on an elastomer and sulfur matrix comprises the elastomeric matrix and the sulfur before firing, whereas after firing the sulfur is no longer detectable because the latter has reacted with the elastomeric matrix while forming disulfide bridges.

Herewith the term "predominantly" includes more than 50%. For example, it may be more than 60%, 70%, 80%, 90% or even 100%.

At a given point of a tire, the circumferential direction, also called the longitudinal direction, is the tangent direction of a circle centered on the axis of rotation of the tire. It is parallel to the rolling direction of the tire. The axis of rotation of the tire is the axis around which it rotates under normal use. At a given point of a tire, the transverse direction, also called the lateral direction, is parallel to the axis of rotation of the tire. At a given point of a tire, the radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it. X is a direction parallel to the circumferential direction, Y is a direction parallel to the transverse direction, and Z is a direction parallel to the radial direction. The XYZ directions form an orthogonal reference (Figure 1).

"Fx" is understood to mean the horizontal component of the forces of the ground on the tire in the running direction of the tire. We speak of motor torque when a positive force Fx is applied and braking torque when a negative force Fx is applied. By "Fy" is meant the horizontal component of the forces of the ground on the tire in the transverse direction of the tire. "Fz" means the vertical component.

The term "coupling ratio" is the ratio of the horizontal component Fx of the forces of the ground on the tire (or of the ground on the specimen) to the vertical component Fz of the forces of the ground on the tire (or of the ground on the tire). test).

A radial plane "YZ", also called meridian plane, is a plane which contains the rotational axis of the tire. A circumferential plane "XZ" is a plane perpendicular to the axis of rotation of the tire. The circumferential mid-plane, also called the equatorial plane, is a plane perpendicular to the axis of rotation of the tire and divides the tire into two halves.

In the present, the term "sculpture" means a more or less complex system of relief elements separated from each other by cutouts. The relief elements of a sculpture can be either ribs or blocks.

By "rib" ("rib" in English) is meant a raised element formed on a tread and extending substantially in the circumferential direction, this element being delimited either by two cutouts or by a cutout and an edge of the tread. A rib comprises two side walls and a contact face, the latter being intended to come into contact with the roadway during driving. This element extends in the circumferential direction and goes around the tire (legend (2) of Figure 1).

By "block" ("tread block" in English) is meant a raised element formed on a tread, this element being delimited by one or more rectilinear, curved or circular cutouts, and possibly by an edge of the tread block. rolling. A block also comprising a contact face, the latter being intended to come into contact with the roadway during taxiing (legend (3) of Figure 1).

The cutouts may be either grooves or incisions according to their thickness, that is to say the distance between the walls of material that delimit and their operation during driving. The thickness of a groove is typically at least 1 mm, while the thickness of an incision is typically at most equal to 1 mm. When rolling the tire, the material walls of a groove do not come into contact with each other, while the material walls of an incision come into contact at least partly with each other. 'other.

In the present, a "cut out" ("eut out" in English) designates a groove and corresponds to the space delimited by material walls facing each other and distant from each other by a non-zero distance, preferably greater than 1 mm, for example greater than 2, 3, 4 or 5 mm (legends (4) and (5) of Figure 1).

According to the invention, the term "composite material", any material based on at least one elastomeric matrix, a crosslinking system, a reinforcing filler and pulp.

In the context of the invention, the carbonaceous products mentioned in the description may be of fossil origin or biobased. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass.

Elastomeric matrix

According to the invention, any elastomeric matrix known to those skilled in the art for the manufacture of tread may be used in the composite material of the sculpture of the tread according to the invention.

For example, the elastomeric matrix may comprise a diene elastomer, preferably an elastomer chosen from isoprenic elastomers, butadiene and styrene copolymers, polybutadienes and their mixtures.

By "diene" elastomer, it is to be understood in a known manner (one or more elastomers) are understood to come from at least a part (ie, a homopolymer or a copolymer) of monomers dienes (monomers carrying two carbon-carbon double bonds, conjugated or not).

These diene elastomers are well known to those skilled in the art and can be classified into two categories: "essentially unsaturated" or "essentially saturated". The term "essentially unsaturated" is generally 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% (mol%); 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 described as "essentially saturated" diene elastomers ( low or very low diene origin, always less than 15%). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer is particularly understood to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

The term "diene elastomer" that may be used in the compositions according to the invention is more particularly understood to mean: a) any homopolymer of a conjugated diene monomer, especially any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 atoms of carbon; b) any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms; c) a ternary copolymer obtained by copolymerization of ethylene, an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, for example elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene; d) a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated versions, in particular chlorinated or brominated, of this type of copolymer.

Although it applies to any type of diene elastomer, the person skilled in the tire art will understand that the present invention is preferably implemented with essentially unsaturated diene elastomers, in particular of the type (a) or (b). ) above. In the case of copolymers of type (b), these contain from 20 to 99% by weight of diene units and from 1 to 80% by weight of vinylaromatic units. As conjugated dienes 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C 1 -C 5) alkyl-1,3-butadienes, such as for example 2 3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1, 3-butadiene, aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene.

By "isoprene elastomer" is meant in 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), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will in particular be made of 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 synthetic cis-1,4 polyisoprene, preferably natural rubber. For example, the synthetic polyisoprene may be a polyisoprene having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%.

The elastomers used in the context of the present invention may for example be block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or starred and / or functionalized with a coupling agent and / or starring and / or functionalization. The isoprene elastomer may be chosen from the group comprising natural rubber, synthetic polyisoprene and their mixture. Preferably, the isoprene elastomer is natural rubber.

For the purposes of the present invention, the term "copolymer of butadiene units and styrenic units" refers to any copolymer obtained by copolymerization of one or more butadiene (s) with one or more styrenic compounds. Suitable styrene compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the "vinyl-toluene" commercial mixture, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene. These elastomers may have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and amounts of modifying and / or randomizing agent used. The elastomers can be, for example, block, random, sequenced, microsequenced, and be prepared in dispersion or in solution.

The butadiene and styrene copolymer may be, for example, butadiene-styrene copolymer (SBR). It may be, for example, an emulsion-prepared SBR ("ESBR") or a solution-prepared SBR ("SSBR"). The levels of vinyl (-1.2), trans-1,4 and cis-1,4 bonds of the butadiene part of SBR can be variable. For example, the vinyl content may be between 15% and 80% (mol%), the content of trans-1,4 bonds between 15% and 80% (mol%). The diene elastomer may also comprise mainly or even exclusively a polybutadiene.

Suitable polybutadienes and in particular those having a content (mol%) in units -1.2 of between 4% and 80% or those having a content (mol%) of cis-1,4 greater than 80%, polyisoprenes, copolymers of butadiene-styrene and in particular those having a Tg (glass transition temperature (Tg, measured according to ASTM D3418) of between 0 ° C. and -70 ° C. and more particularly between -10 ° C. and -60 ° C., 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%) in trans-1,4 bonds of between 10% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a Tg of -40 ° C. to At -80 ° C., the isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg included between at -5 ° C. and -50 ° C. In the case of butadiene-styrene-isoprene copolymers, those having a styrene content of between 5% and 50% by weight and more particularly between 10% and 40% are especially suitable. isoprene content between 15% and 60% by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content (% molar) in units -1,2 of the butadiene part of between 4% and 85%, a content (mol%) in trans-1,4 units of the butadiene part of between 6% and 80%, a content (mol% ) in units -1.2 plus -3.4 of the isoprene part of between 5% and 70% and a content (mol%) in trans units of -1.4 of the isoprenic part of between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg between -5 ° C and -70 ° C.

Crosslinking system

The crosslinking system may be based on sulfur and / or sulfur and / or peroxide and / or bismaleimide donors. The crosslinking system is preferably a vulcanization system, that is to say a system based on sulfur (or a sulfur-donor agent) and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the production phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide. , stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine), or known vulcanization retarders.

The sulfur may be used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The primary vulcanization accelerator is used at a preferred level of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr.

Reinforcing charge

The reinforcing filler is known for its ability to strengthen a rubber composition for use in the manufacture of tires.

According to the invention, the reinforcing filler may comprise carbon black, an organic filler other than carbon black, an inorganic filler or a mixture of at least two of these fillers. Preferably, the reinforcing filler may comprise mainly, or even exclusively, carbon black. The reinforcing filler may also comprise mainly, or even exclusively, a reinforcing inorganic filler.

Such a reinforcing filler typically consists of nanoparticles whose average size (in mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

The carbon black has a BET specific surface preferably of at least 90 m 2 / g, more preferably at least 100 m 2 / g. As such, blacks conventionally used in tires or their treads are suitable ( so-called pneumatic grade blacks). Among the latter, there will be mentioned more particularly the reinforcing carbon blacks of the series 100, 200, 300, or the series blacks 500, 600 or 700 (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 (see for example applications WO 97/36724 or WO 99/16600). The BET surface area of the carbon blacks is measured according to the D6556-10 standard [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range P / PO: 0.1 to 0.3].

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.

"Reinforcing inorganic filler" means any inorganic or mineral filler, irrespective of its color and origin (natural or synthetic), also called "white" filler, "clear" filler or even "non-black" filler. as opposed to carbon black, capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words able to replace, in its function of reinforcement, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferentially silica (SiO 2). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m 2 / g, preferably from 30 to 400 m 2 / g, especially between 60 and 300 m2 / g. As highly dispersible precipitated silicas (called "HDS"), mention may be made, for example, of the "Ultrasil" 7000 and "Ultrasil" 7005 silicas of the Degussa company, the "Zeosil" 1165MP, 1135MP and 1115MP silicas of the Rhodia company. "Hi-Sil" silica EZ150G from the company PPG, the "Zeopol" silicas 8715, 8745 and 8755 from the Huber Company, the high surface area silicas as described in the application WO 03/016387.

In the present description, with regard to silica, the BET surface area is determined in a known manner by gas adsorption using the method of Brunauer-Emmett-Teller described in "The Journal of the American Chemical Society" Flight . 60, page 309, February 1938, specifically according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: time at 160 ° C - relative pressure range p / po: 0.05 at 0.17). The CTAB specific surface is the external surface determined according to the French standard NF T 45-007 of November 1987 (method B).

Reinforcing inorganic fillers are also suitable for mineral fillers of the aluminous type, in particular alumina (Al 2 O 3) or aluminum (oxide) hydroxides, or reinforcing titanium oxides, for example described in US Pat. No. 6,610,261 and US Pat. No. 6,747,087. The physical state in which the reinforcing inorganic filler is present is indifferent whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers as described above.

In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner to ensure a sufficient chemical and / or physical connection between the inorganic filler (surface of its particles) and the diene elastomer. In particular, organosilanes or at least bifunctional polyorganosiloxanes are used.

The content of coupling agent is advantageously less than 12 phr, it being understood that it is generally desirable to use as little as possible. Typically the level of coupling agent is from 0.5% to 15% by weight relative to the amount of inorganic filler. Its level is preferably between 0.5 and 9 phr, more preferably in a range from 3 to 9 phr. This level is easily adjusted by those skilled in the art according to the level of inorganic filler used in the composition.

According to the invention, the level of reinforcing filler can be in a range from 10 to 90 phr, preferably from 10 to 70 phr, preferably from 25 to 60 phr. Advantageously, the level of reinforcing filler is in a range from 10 to 30% by volume fraction, preferably from 15 to 25% by volume fraction, relative to the volume of the composition with low modulus of rigidity.

Pulp

Pulp, also called "pulp" is a material according to BISFA (The International Bureau for the Standardization of Man-Made Fibers) in its 2009 edition of "Terminology of man-made fibers", is a generic term for processed fiber materials for different applications such as fibers, paper or other compounds. The pulp can be produced by mechanical cutting of continuous fibers. The pulp comprises fibrillated fibers, i.e. fibers with fibrils (a subdivision of the fiber) attached to the fibers. The pulp also comprises another form known as a micropulp which can be produced according to the method described in WO 03/044250.

According to the invention, the pulp is in a material chosen from aromatic polyamides, polybenzimidazoles, polybenzothiazoles, polybenzoxazoles, polypyridazoles, polybenzoxadiazoles, aromatic polyesters, polyurethanes, polyetheretherketones, polyolefins, polyacrylics and polymers. liquid crystal, cellulose, glass and their mixtures.

Preferably, the pulp is in a material chosen from aromatic polyamides, polybenzimidazoles, polybenzothiazoles, polybenzoxazoles, polypyridazoles, polybenzoxadiazoles, aromatic polyesters, polyurethanes, polyetheretherketones, polyolefins, polyacrylics and liquid crystals and their mixtures. More preferably, the pulp is in a material selected from aromatic polyamides, polybenzoxazoles and polyolefins.

Advantageously, the pulp is chosen from aramid pulp, ultra-high molecular weight polyethylene pulp (UHMWPE Ultra High Molecular Weight Polyethylene), polybenzoxazole pulp, polypyridazole pulp and more preferably para-aramid pulp and polybenzoxazole pulp. Preferably, the pulp is aramid pulp.

The fibers that make up the pulp generally have a length of between 0.1 and 10 mm, preferably between 0.1 and 8 mm with a diameter between 1 and 40 μm. The micropulpe fibers generally have a length of between 0.01 and 100 μm, preferably between 0.1 and 50 μm.

The pulp may, for example, be a pulp described in EP 0 445 655, US 2004/0191192, WO 03/044250, US 4,871,004, US 2,999,788. By way of example of commercially available pulps, mention may be made of the Kevlar® Aramid pulp marketed by DuPont, Wilmington, Delaware, the Teijin ™ Twaron® pulp aram pulp, the Celanese Vectran® HS pulp sold by Engineering Fibers Technology, Shelton, Conneticut, or CFF Fibrillated Acrylic Fiber pulp marketed by Sterling Fibers Inc., Pace, Florida.

The pulp can be added directly to the elastomeric matrix or is incorporated as a premix, that is to say that the fibers are previously dispersed in an elastomeric matrix to facilitate their incorporation into the final formulation.

According to the invention, the pulp is present in the elastomeric matrix at a concentration ranging from 5 to 45 phr.

Advantageously, the pulp content may range from 5 to 30 phr, preferably from 5 to 20 phr, more preferably from 5 to 15 phr, more preferably from 5 to 10 phr.

Although not required for the practice of the present invention, the pulp may be adhered, i.e. treated to improve its adhesion to the elastomeric matrix. For example, the pulp may be adhered with an adhesive selected from epoxy glues followed by liquid resorcinol-formaldehyde latex (RFL) treatment and formaldehyde-based glues, preferably RFL glues. By way of example of RFL adhesive that can be used to adhere the pulp, mention may be made of those described in patent application WO 2001/057116.

Advantageously, the pulp is mainly oriented in the sculpture parallel to a plane which is (i) perpendicular to the equatorial plane and (ii) oriented at an angle expressed in degrees relative to the radial plane, the angle a being defined by the formula a = 45 +/- x, where x is within a range of 10 to 30. In other words, the pulp is mainly oriented in the sculpture parallel to a plane that is (i) perpendicular to the equatorial plane and (i) ii) oriented at an angle α expressed in degrees relative to the radial plane, the angle a being in the range of 15 to 35 degrees or 55 to 75 degrees. The term "mainly oriented" means the average orientation of the pulp within the sculpture. This main orientation can be achieved by composite material preparation processes described hereinafter, in particular by the fact that the pulp is arranged within oriented layers.

The present invention thus makes available to the skilled person composite materials for transferring a force from the ground on the tire component Fz into different components Fx, and thus generate a significant coupling rate. The skilled person can thus choose the main directions of the pulp in the sculpture of a tire, depending on the conditions of use of the tire.

Various additives

The composite material may also comprise all or part of the usual additives usually used in elastomer compositions intended to constitute treads, such as, for example, plasticizers, pigments, fibers, protective agents such as anti-ozone waxes. chemical antioxidants, anti-oxidants, anti-fatigue agents, well known to those skilled in the art.

Sculpture of the tread

The tread according to the present invention comprises a tread.

According to the invention, the sculpture consists of a plurality of parallel and adjacent layers, the layers being oriented in the sculpture parallel to a plane which is (i) perpendicular to the equatorial plane and (ii) oriented at an angle in degrees with respect to the radial plane, the angle a being defined by the formula a = 45 +/- x, where x is within a range of 10 to 30. In other words, the layers are oriented in the circumferential planes at the same angle expressed in degrees relative to the radial plane, the angle a being in a range of 15 to 35 degrees or 55 to 75 degrees.

Unless otherwise indicated, the orientation of the layers in the tread according to the invention is expressed with respect to a tread disposed on a tire. Those skilled in the art will easily convert the orientation of the layers when the tread is laid flat, for example in the form of a semi-finished. Assuming that the tread is flat, it could be defined in directions parallel to its length, width and thickness which correspond respectively to the circumferential directions "X", transverse "Y" and radial "Z" . The circumferential plane would then be a plane defined by the length and thickness of the tread, the radial plane would be a plane defined by the width and thickness of the tread. Those skilled in the art can measure the angle of the layers within the tread by removing a portion of the tread, preferably by removing half the width of a rib in a plane parallel to the XoZ plane, of in order to reveal an interface containing the layers, and by taking a test piece material by cutting the tread according to Figure 2 and establishing the orientation histogram of the layers in the plane XOZ with respect to the direction Z by optical microscopy in reflection.

According to the invention, the layers can be oriented to the sculpture parallel to a plane which is (i) perpendicular to the equatorial plane and (ii) oriented at an angle α expressed in degrees with respect to the radial plane, the angle a being defined by the formula a = 45 +/- x, where x is within a range of 12.5 to 27.5 (i.e. 17.5 to 35.5 degrees or 57.5 to 72 , 5 degrees), preferably 15 to 25 (i.e., 20 to 30 degrees or 60 to 70 degrees), preferably x is 20 (i.e., 25 degrees). or 65 degrees). Unless otherwise indicated, the angle a is expressed in absolute value. Those skilled in the art understand that when speaking of layers oriented at the same angle α, they may be layers having substantially the same angel a, that is to say that the layers are oriented according to a angle a with a small standard deviation, for example a standard deviation of 3 degrees or less, over at least 80% of the XoZ plane surface.

Whatever the value of the angle α in the range a = 45 +/- 10 to 30 degrees, this orientation gives the composite material the ability to transfer a portion of the component Fz from the forces of the ground on the tire to the ground. Fx component, that is to say, from the vertical component to the horizontal component in the direction of rolling of the tire. This coupling ratio is particularly advantageous for improving the wear resistance of tires for civil engineering vehicles, especially in their specific conditions of use.

Depending on the angle of the layers within the sculpture, the coupling rate is not the same. Thus, when the angle a is between 15 and 35 degrees (i.e., a = 45 - from 10 to 30), the sculpture will transform the component Fz into a positive Fx component. It can be noted that the closer the angle a is to 25 degrees, the higher the coupling rate is. This embodiment is particularly advantageous for improving the wear resistance of tires of vehicles carrying heavy loads uphill.

On the other hand, when the angle a is between 55 and 75 degrees (that is, a = 45 + from 10 to 30), the sculpture will transform the component Fz into a negative Fx component. The closer the angle is to 65 degrees, the higher the coupling rate. This embodiment is particularly advantageous for improving the wear resistance of tires of vehicles traveling downhill empty.

When the angle a is between 35 and 55 degrees, the coupling ratio becomes too low, or even zero around 45 degrees, to give the desired property to the sculpture of the tread according to the invention. The same is true when the angle a is less than 15 degrees or greater than 75 degrees.

According to the invention, the sculpture of the tread may consist of a plurality of parallel layers and adjacent to each other.

According to the invention, the sculpture of the tread may consist entirely of composite material.

According to the invention, the layers of the plurality of layers may be identical or different. Preferably, the layers of the plurality of layers are predominantly, preferably exclusively, identical.

In the present, the term "a group of layers", one or more layers identical to each other. In other words, when the plurality of layers comprises several groups of different layers, these layers may differ from each other by the nature or the concentration of the pulp when it is present, or the nature of the elastomeric matrix, nature or concentration in reinforcing filler, crosslinking system, additives, etc.

According to the invention, the sculpture may comprise, for example, several (i.e. at least two) different layers of composite material. It may also comprise at least one layer of composite material and at least one (that is to say one or more) layer of an elastomeric composition different from the composite material.

When the layers are different, the plurality of layers can be constituted by two groups of different layers, or even more, for example three, four or five groups of different layers from each other. Advantageously, the plurality of layers consists of two groups of different layers.

Any distribution of the layers of different groups can be implemented. For example, the layers of different groups can be distributed alternately or not. For example, when the plurality of layers comprises two groups of different layers (for example called A and B respectively), the distribution can follow the following formula: ((Α) πα (Β) πβ), in which: "nA" and "NB" independently of one another represent an integer selected from 1 to 10, preferably from 1 to 5, preferably from 1 to 2, preferably 1.

When the composite material comprises more than two groups of different layers (for example called A, B, ..., X respectively), the distribution may follow the following formula: ((A) nA (B) nB (-) n. .. (X) nx) i wherein: "nA", "nB", "n" and "nX" independently of one another represent an integer selected from 1 to 10, preferably 1 at 5, preferably from 1 to 2, preferably 1.

The total number of layers within the sculpture is limited by the length of the tread. The skilled person is able to determine this number according to the thickness of the layers and their orientation within the sculpture.

Preferably, when the layers of the plurality of layers are different, the sculpture of the tread consists of two groups of different layers, preferably distributed alternately within the tread pattern.

According to a particular embodiment of the present invention, the plurality of layers comprises layers of composite material and layers of an elastomeric composition different from the composite material which are arranged alternately. Preferably, the plurality of layers comprises a group of layers of composite material and a group of layers of an elastomer composition different from the composite material, the layers of the composite material and the layers of the elastomer composition different from the composite material being arranged alternately ( Figure 2B).

According to the invention, the elastomer composition different from the composite material may comprise an elastomer chosen from any diene elastomer described herein. For example, the different elastomeric composition of the composite material may comprise an elastomer chosen from isoprenic elastomers, butadiene and styrene copolymers, polybutadienes and their mixtures, preferably an elastomer chosen from isoprenic elastomers, preferably natural rubber.

According to the invention, the elastomer composition different from the composite material may advantageously also comprise a crosslinking system and / or a reinforcing filler and / or additives. In particular, the different elastomeric composition of the composite material may comprise any crosslinking system and / or reinforcing filler and / or additives described herein.

Advantageously, the elastomeric composition different from the composite material has an extension stiffness which is at least 5 times less, preferably at least 10 times less, than that of said composite material in the main direction of the pulp. The person skilled in the art is able to determine how the stiffness of the composite material and of the elastomer composition different from the composite material are measured. For example, he can use a method based on the NF ISO 37 standard of December 2005 on a dumbbell type 2 specimen and measure the modulus of elasticity at 5% deformation at 23 ° C. When the extension direction is the main direction of the pulp we will note this extension module EL and when the extension direction is orthogonal to the main direction of the pulp note this extension module AND.

Advantageously, the longitudinal modulus (in the main direction of the pulp) E £ and the transverse modulus (in the direction perpendicular to the main direction of the pulp) EJ define β = Ej / E £, and the volume fraction <J) C of the composite material, and the EM modulus and the volume fraction φΜ (or 1 - φΟ) of the elastomer composition different from the composite material are defined so that the formula

is less than 0.67, preferably between 0.01 and 0.5. The thickness of each of the layers of the composite material may range from 0.1 to 20 mm, preferably from 0.1 to 10 mm. The thickness of each of the layers of the elastomer composition different from the composite material may be in a range from 1 to 20 mm, preferably from 1 to 10 mm.

Advantageously, the volume of layers of the elastomer composition different from the composite material may represent from 50 to 95% by volume, preferably from 60 to 95% by volume, relative to the volume of the tread pattern. Thus, the volume of layers of composite material can represent respectively from 5 to 50% by volume, preferably from 5 to 40% by volume, relative to the volume of the sculpture of the tread.

pneumatic

The present invention can be applied to any type of tire. Thus, the present invention also relates to a tire comprising a tread according to the invention.

Generally speaking, a tire comprises a tread intended to come into contact with the ground via a rolling surface and connected via two sidewalls to two beads intended to provide a mechanical connection. between the tire and the rim on which it is mounted.

A radial tire more particularly comprises a reinforcing reinforcement, comprising a crown reinforcement, radially inner to the tread, and a carcass reinforcement, radially inner to the crown reinforcement.

A tire may be provided with a carcass reinforcement surmounted radially on the outside by a crown reinforcement in order to make a hooping of said carcass reinforcement. The crown reinforcement is generally formed by a stack of a plurality of reinforcing plies, these reinforcements making generally no harm to the circumferential direction.

A tire includes a tread whose tread surface is provided with a tread formed by a plurality of grooves delimiting relief elements (blocks, ribs) so as to generate material edges and troughs. These grooves represent a void volume which, relative to the total tread volume (including both the volume of relief elements and that of all grooves) is expressed as a percentage herein referred to as "rate". of hollow volume ". A trough volume of zero indicates a tread without grooves or recesses.

The present invention is particularly well suited to tires for civil engineering vehicles and heavy goods vehicles, more particularly for civil engineering vehicles whose tires are subject to very specific constraints. Thus, advantageously, the tire according to the invention is a tire for civil engineering vehicles or heavy goods vehicles, preferably civil engineering vehicles.

The tread according to the invention may have one or more grooves with an average depth of 15 to 120 mm, preferably 65 to 120 mm.

The tires according to the invention may have a diameter of from 20 to 63 inches, preferably from 35 to 63 inches.

Furthermore, the average rate of trough on the entire tread according to the invention can be in a range from 5 to 40%, preferably from 5 to 25%.

Preparation of composite materials

The sculptures of the tread can be obtained according to the method defined below. In this case, according to a first variant, the pulp of the composite material is integrated in the form of a premix (pulp dispersed in an elastomeric matrix) in the preparation process during the non-productive phase.

The compositions used in the tire treads of the invention may be manufactured in appropriate mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or mixing thermomechanical system (sometimes referred to as a "non-productive" phase) at a high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed by a second mechanical working phase (sometimes called a "productive" phase) at a lower temperature, typically below 110 ° C, for example between 40 ° C and 100 ° C, finishing phase during which the crosslinking agent is incorporated chemical, in particular the crosslinking system. By way of example, the first (non-productive) phase is carried out in a single thermomechanical step, during which all the necessary constituents, including the pulp, the ingredients, are introduced into a suitable mixer such as a conventional internal mixer. any additional coating or processing agents and other miscellaneous additives, with the exception of the vulcanization system. The total mixing time, in this non-productive phase, is preferably between 2 and 10 min. After cooling the mixture thus obtained during the first non-productive phase, the vulcanization system is then incorporated at low temperature, generally in an external mixer such as a roller mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

According to a second variant, the pulp of the composite material is integrated in the preparation process during the non-productive phase with a previously made mixture containing all the ingredients except for the pulp and crosslinking system which will be called masterbatch.

Masterbatchs (mixtures containing all the ingredients with the exception of the crosslinking system and the pulp) can be manufactured in appropriate mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: first working phase or thermomechanical mixing (sometimes referred to as a "non-productive" phase) at a high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed a second phase of mechanical work (sometimes called "productive" phase) at a lower temperature, typically less than 110 ° C, for example between 40 ° C and 100 ° C, finishing phase during which is incorporated the chemical crosslinking agent, in particular the crosslinking system. In a second step, the masterbatch is taken up in a non-productive phase with the pulp at a lower temperature, typically below 110 ° C for example between 40 and 100 ° C not to start the crosslinking. As an example for obtaining masterbatchs, the first (non-productive) phase is conducted in a single thermomechanical step during which all the necessary constituents are introduced into a suitable mixer such as a conventional internal mixer. , with the exception of the pulp, any additional coating or processing agents and other miscellaneous additives, with the exception of the vulcanization system. The total mixing time, in this non-productive phase, is preferably between 2 and 10 min. After cooling the mixture thus obtained during the first non-productive phase, the vulcanization system is then incorporated at low temperature, generally in an external mixer such as a roller mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min. By way of example, the resumption of the mastarbatch and the addition of the pulp is carried out in a single thermomechanical step in a suitable mixer such as a conventional internal mixer. The total duration of the kneading is preferably between 2 and 5 min.

The sculpting composition thus obtained according to any one of the two variants is then calendered, for example in the form of a layer, so that the pulp is disposed within the layer in a main orientation. This can be achieved for example using for example the method described in WO 2008/027045.

For example, obtaining layers in which the pulp is disposed in a main orientation consists of producing unvulcanized elastomer plates containing pulp by calendering using a roll tool. This first step allows to begin the arrangement of the pulp in the plane of the plate in a main direction in the direction of calendering. For a question of shaping, the plates obtained in the first step are cut out and extruded by means of a micro-nozzle. This second step makes it possible to obtain layers of elastomer in which the pulp is disposed within the layer in a main direction in the direction of extrusion.

Alternatively, the arrangement of the pulp is obtained by producing a non-vulcanized elastomer layer containing pulp by means of calendering using a roll tool (Al and A2) and a receiving roll (B) at the exit of the pulp. the tool as shown in Figure 3. The layer exiting the tool is disposed in contact with the receiving roller (B). The receiving roll is set to have a tangential velocity greater than the tangential velocity of the rolls of the tool without inducing tearing of the layer. This difference in tangential speed makes it possible to arrange the pulp in a main direction in the direction of the calendering within the layer. Those skilled in the art are able to determine the respective tangential speeds of the rolls and the receiving roll.

To obtain the desired orientation of the layers in the tread according to the present invention, any technique that is well known to a person skilled in the art, in particular the method described in application WO 2008/027045, may be used. For example, layers containing the pulp may be assembled flat and cut anywhere appropriate, for example by waterjet cutting, at the desired angle, so as to form elements of sculptures that can be arranged on a raw bandage of in a manner well known to those skilled in the art.

When the sculpture comprises layers of an elastomeric composition different from the composite material, this composition may be prepared according to a method similar to that described above. It may be for example the method according to the second variant described above but not including the pulp addition step. Other advantages may still appear to those skilled in the art on reading the examples below, illustrated by the accompanying figures, given for illustrative and non-limiting.

Brief description of the figures

FIG. 1 is a diagrammatic representation of a tire (1) whose rolling race comprises a rib (2) situated in the central zone of the tire (1), blocks (3), the rib and the blocks being separated. by circumferential grooves (4) and substantially transverse grooves (5).

Figure 2A is a schematic representation of an embodiment of a sculpture according to the invention, seen in section along the XZ plane. This sculpture is composed of a plurality of layers (cl) of composite material according to the invention, parallel, adjacent to each other, and oriented parallel to a plane which is (i) perpendicular to the XZ plane and (ii) oriented at an angle (a) 25 degrees from the YZ plane. The pulp is arranged parallel to the plane of the layers in the XZ plane.

Figure 2B differs from Figure 2A only the plurality of layers comprises layers (c2) of an elastomeric composition different from the composite material, arranged alternately with the layers (cl).

Figure 3 is a schematic representation of a device for orienting the pulp in a main direction within an elastomer layer. "Al" and "A2" represent the cylinders of a shell. "B" represents a receiving roll on which is disposed a layer exiting the calender.

EXAMPLES

Samples with a surface area of 10 cm x 10 cm and a thickness of 3 cm were made according to the process described in application WO 2008/027045 with layers having a thickness of 2 mm from different compositions.

We define below: "X": a direction parallel to the direction of stress of the sample, itself parallel to the length of the sample. This direction corresponds to the direction of the bearing of a tire on which the sample would be present. "Y": a direction parallel to the width of the sample. "Z": a direction parallel to the thickness of the sample.

A control sample was made from a composition A which is a composition conventionally used in tire treads for civil engineering vehicles. This composition A does not include pulp.

Samples were made from compositions B1 and B2 which are composite materials according to the present invention. These compositions differ from the composition A in that they comprise aramid pulp, arranged in layers oriented in the plane defined by the X and Z directions at an angle of 25 degrees with respect to the Z direction.

Each of the samples was prepared with layers parallel to a plane defined by (i) the Y direction and (ii) a line oriented at 25 degrees to Z direction in a plane defined by the X and Z directions.

Measurements of the mechanical properties were carried out after baking the aforementioned compositions at a temperature of 150 ° C. for 30 minutes. The results were obtained from dumbbell type 2 test specimens at 5% deformation at 23 ° C. according to the NF ISO 37 standard of December 2005. When the extension direction is the main orientation direction of the pulp on note this extension module EL and when the extension direction is orthogonal to the main direction of the pulp note this extension module AND. Expansion module results are presented on a 100 basis with respect to the sample extension module EL of the witness A.

To analyze the transfer of the forces of the soil on the specimen of the vertical component (Fz) towards the horizontal component in the running direction (Fx) (the coupling ratio), a force Fz of 900daN corresponding to a pressure was applied. average of 9 bar or 600daN corresponding to an average pressure of 6 bar on the surface of the samples using an electric cylinder and the resulting force Fx was measured using a force sensor. The Fx ratio divided by Fz is called the coupling ratio and is measured at two different average pressures.

The compositions A, B1 and B2 and the experimental results are presented in Table 1 below:

Table 1

(1) Natural rubber (including 77% by weight of pulp masterbatch natural rubber (5)) (2) "Ultrasil VN3" marketed by Evonik (3) Grade N234 carbon black according to ASTM D-1765 ( 4) Umicore industrial grade zinc oxide (5) Kevelar® pre-mix 1F722 aramid pulp from DuPont (includes 77% by weight of natural rubber - eg for 129.9 g of premix on 100 g of NR and 29.9 g of pulp) (6) N-cyclohexyl-2-benzothiazol-sulfenamide, "Santocure CBS", marketed by Flexsys (a) modulus of elasticity at 5% deformation and for compositions based on pulp, the extension direction is in the main direction of the pulp (b) modulus of elasticity at 5% deformation and for pulp-based compositions, the extension direction is orthogonal to the main direction of the pulp

These results show that samples B1 and B2, in accordance with the present invention, have EL and ET extension modules much greater than those of control sample A which does not include pulp. In addition, sample B2 generates a coupling rate compared to control composition A (Table 2).

These results also show that the coupling ratio obtained is the same for the two concentrations of pulp tested. The effect was observed as soon as 5 phr of pulp in the composite material.

A complementary experiment was performed by comparing the coupling rates of samples A and B2, and a sample B1 / A which corresponds to alternating stack of layers A and B1. In sample B1 / A, the thickness of layers A were 3.2 mm so that the volume fraction of pulp within the sample was identical to that of sample B2. The results are shown in Table 2 below.

Table 2

These results show that a coupling rate is obtained for samples B1 / A and B2 which comprise pulp in oriented layers in comparison with sample A which does not include pulp.

The various measurements performed by the Applicants have demonstrated that the coupling ratio obtained was sufficient for the implementation of the present invention when the layers are oriented at an angle of 15 to 35 degrees or 55 to 75 degrees.

The present invention therefore provides treads for transferring a proportion of the ground forces on the tire of the component Fz into different components Fx, to effectively improve the wear resistance of the tires. These results are particularly interesting for vehicles traveling on non-bituminous soils, such as most civil engineering vehicles and some heavy goods vehicles.

Claims (13)

Tread comprising at least one tread, said tread comprising a composite material based on an elastomeric matrix, a crosslinking system, a reinforcing filler and pulp, said pulp being present in the elastomeric matrix at a concentration. in a range from 5 to 45 parts by weight per hundred parts of elastomer, pce, and being in a material selected from aromatic polyamides, polybenzimidazoles, polybenzothiazoles, polybenzoxazoles, polypyridazoles, polybenzoxadiazoles, aromatic polyesters polyurethanes, polyetheretherketones, polyolefins, polyacrylics and liquid crystal polymers, cellulose, glass and mixtures thereof, said sculpture consisting of a plurality of parallel and adjacent layers, said layers being oriented in the sculpture parallel to a plane that is (i) perpendicular to the equatorial lan and (ii) oriented at an angle expressed in degrees relative to the radial plane, the angle a being defined by the formula a = 45 +/- x, where x is within a range of 10 to 30. 2. A tread according to claim 1, wherein the elastomeric matrix comprises a diene elastomer, preferably an elastomer selected from isoprenic elastomers, butadiene and styrenic copolymers, polybutadienes and mixtures thereof. 3. Tread according to claim 1 or 2, wherein the pulp is aramid pulp. 4. Tread according to any one of claims 1 to 3, wherein the pulp concentration is in a range from 5 to 30 phr, preferably from 5 to 15 phr. A tread according to any one of claims 1 to 4, wherein the plurality of layers are layers of said composite material. A tread according to any one of claims 1 to 4, wherein the plurality of layers comprises layers of said composite material and layers of an elastomeric composition different from said composite material. 7. A tread according to claim 6, wherein the longitudinal modulus E £ and the transverse modulus Ej define β = Ej / E £, and the volume fraction of the composite material and the EM module and the volume fraction φΜ (or 1 - φΟ) of the elastomer composition different from the composite material are defined so that the formula less than 0.67. 8. Tread according to claim 6 or 7, wherein the elastomeric composition different from said composite material comprises an elastomer selected from isoprene elastomers, butadiene and styrenic copolymers, polybutadienes and mixtures thereof, preferably natural rubber. 9. Tread according to any one of claims 6 to 8, wherein the layers of the composite material and the elastomeric composition different from said composite material are arranged alternately. 10. Tread according to any one of claims 1 to 9 wherein the layers of the composite material have a thickness in a range from 0.1 to 20 mm, preferably from 0.1 to 10 mm. 11. Tread according to any one of claims 6 to 10, wherein the layers of the elastomeric composition different from said composite material have a thickness in a range of 1 to 20 mm, preferably 1 to 10 mm. 12. A tire comprising a tread as defined in any one of claims 1 to 11. 13. A tire according to claim 12, said tire being a tire for civil engineering vehicles.