WO2020084246A1

WO2020084246A1 - Agricultural vehicle tyre

Info

Publication number: WO2020084246A1
Application number: PCT/FR2019/052506
Authority: WO
Inventors: Jean-Luc Cabioch; Anthony MONOD
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2018-10-25
Filing date: 2019-10-22
Publication date: 2020-04-30

Abstract

The invention relates to an agricultural vehicle tyre which has improved grip on wet ground, in which the tread comprises a rubber composition based on an elastomeric matrix comprising in particular at least one butadiene/styrene copolymer which has a glass transition temperature within a range extending from -60°C to -10°C, and from 30 to less than 120 parts by weight per hundred parts by weight of elastomer, phr, of reinforcing filler, wherein the reinforcing filler comprises a mixture of silica and carbon black, and the reinforcing filler comprises between 33% and 100% by weight of silica relative to the total weight of the reinforcing filler, the silica content in the composition being between 10 and 80 phr; and to a crosslinking system.

Description

AGRICULTURAL VEHICLE TIRES

The present invention relates to a tire for a vehicle for agricultural use, such as an agricultural tractor or an agro-industrial vehicle.

The present invention relates more particularly to the tread of such a tire, intended to come into contact with a ground via a tread surface.

In the following, the circumferential, axial and radial directions designate respectively a direction tangent to the running surface of the tire and oriented according to the direction of rotation of the tire, a direction parallel to the axis of rotation of the tire and a direction perpendicular to the axis of rotation of the tire. By “radially interior, respectively radially exterior”, is meant “closer, respectively farther from the axis of rotation of the tire”. By "axially interior, respectively axially exterior" is meant "closer, respectively farther from the equatorial plane of the tire", the equatorial plane of the tire being the plane passing through the middle of the tire rolling surface and perpendicular to the axis of rotation of the tire.

The tread of a tire for an agricultural tractor generally comprises a plurality of bars. The bars are elements in relief with respect to a bottom surface which is a surface of revolution around the axis of rotation of the tire.

A bar generally has a generally elongated parallelepiped shape, consisting of at least one rectilinear or curvilinear portion, and is separated from the adjacent bars by grooves. A bar can be constituted by a succession of rectilinear portions, as described in documents US3603370, US4383567, EP795427 or have a curvilinear shape, as presented in documents US4446902, EP903249, EP1831034.

In the radial direction, a bar extends from the bottom surface to the running surface, the radial distance between the bottom surface and the running surface defining the height of the bar. The radially outer face of the bar, belonging to the running surface, which comes into contact with the ground, during the passage of the bar in the contact area of the tire, is called the contact face of the bar.

In the axial direction, a bar extends inwardly, towards the equatorial plane of the tire, from an axially outer end face to an axially inner end face.

In the circumferential direction, a bar extends, in a preferred direction of rotation of the tire, from a leading face to a trailing face. By preferred direction of rotation is meant the direction of rotation recommended by the tire manufacturer for a optimal use of the tire. By way of example, in the case of a tread comprising two rows of V-shaped or chevron bars, the tire has a preferential direction of rotation according to the point of the chevrons. The leading face is, by definition, the face whose radially outer edge or leading edge first comes into contact with the ground, when the bar passes through the contact surface of the tire with the ground, during the rotation of the tire. The trailing face is, by definition, the side whose radially outer edge or trailing edge comes into final contact with the ground, during the passage of the bar in the contact surface of the tire with the ground, during the rotation of the tire. Depending on the direction of rotation, the leading face is said to be forward with respect to the trailing face.

A bar usually, but not necessarily, has an average angle of inclination, relative to the circumferential direction, close to 45 °. Indeed, this average angle of inclination allows in particular a good compromise between traction in the field and vibratory comfort. The traction in the field is all the better as the bar is axial, that is to say that its mean angle of inclination, relative to the circumferential direction is close to 90 °, while the vibratory comfort is as much better as the bar is circumferential, that is to say that its mean angle of inclination, relative to the circumferential direction, is close to 0 °. It is well known that the traction in the field is more strongly determined by the angle of the bar at the shoulder, which has led some tire designers to propose a very curved bar shape, leading to a bar which is substantially axial with shoulder and substantially circumferential in the middle of the tread.

The tread of a tire for an agricultural tractor generally comprises two rows of bars as previously described. This distribution of bars inclined with respect to the circumferential direction gives the tread a V shape commonly known as a herringbone pattern. The two rows of bars have a symmetry with respect to the equatorial plane of the tire, with most often a circumferential offset between the two rows of bars, resulting from a rotation around the axis of the tire of one half of the strip of rolling compared to the other half of the tread. In addition, the bars can be continuous or discontinuous, and distributed circumferentially with a constant or variable pitch.

The tread of a tire for an agricultural tractor thus comprises two types of elements: the bars, which are the elements in relief, and the grooves, which are the portions of the bottom surface separating the bars. These two types of elements are used in very different ways. The bars are more particularly sensitive to wear in road use and to attack by stones in non-road use or in the field. The furrows, between the bars, are mainly attacked by residual stubble after harvest, in use in the field, and are also sensitive to chemical attack by ozone insofar as these furrows are not subjected to wear. Although not limited to this application, the invention will be more particularly described with reference to a versatile agricultural machine, which can roll both in the fields and on the road, such as an agricultural tractor.

A tire for an agricultural tractor is intended to roll on various types of soil such as the more or less compact earth of the fields, the unpaved paths for access to the fields and the paved surfaces of the roads. Given the diversity of use, in the field and on the road, a tire for an agricultural tractor, and in particular its tread, must present a compromise in performance, in particular between traction in the field, tear resistance, wear resistance on the road, rolling resistance, vibration comfort on the road.

In addition, the demand for tires for agricultural vehicles enabling them to travel at high speeds (which can go around 65 km / h) on paved roads is constantly increasing, in order to reduce travel times between work areas (fields, forest areas, etc.) and warehouse locations (vehicle, agricultural equipment, harvested food, etc.).

However, the increase in speed is accompanied by an increase in fuel consumption. Thus, the impact of rolling resistance is becoming a component that is increasingly considered for agricultural vehicle tires. Solutions have been proposed to reduce the rolling resistance when driving on bituminous soil without impacting the other properties of tires for agricultural vehicles, by adjusting the inflation pressure directly as a function of the nature of the soil on which the agricultural vehicle is traveling. (W02016 / 071158).

The increase in the speed of driving on bituminous ground also generates the need to take into account new performances which must be met by tires for agricultural vehicles intended to run at high speeds on bituminous ground, in particular grip on wet ground.

There is therefore a real need for tires for agricultural vehicles allowing the vehicle to run at high speeds on bituminous soil which has both low rolling resistance, in order to reduce fuel consumption, and good grip, in particular on wet ground, without penalizing the properties specifically linked to tires for agricultural vehicles.

Continuing her research, the Applicant has discovered that the use of a specific elastomeric matrix comprising a mixture of particular reinforcing filler makes it possible to solve the aforementioned technical problem.

Thus, the subject of the present invention is a tire for an agricultural vehicle comprising a tread intended to come into contact with a ground which comprises a plurality of strips separated from each other by grooves, each strip extending radially outwards, over a radial height H, from a bottom surface to a contact face, the grooves being formed by the portions of the bottom surface separating the bars, in which the tread comprises a rubber composition based on:

an elastomeric matrix comprising at least one butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C,

from 30 to less than 120 parts by weight per hundred parts by weight of elastomer, pce, reinforcing filler, the reinforcing filler comprising a mixture of silica and carbon black, the reinforcing filler comprises between 33% and 100% by weight of silica relative to the total weight of the reinforcing filler, the content of silica in the composition being between 10 and 80 phr, and

a crosslinking system.

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 stages of manufacturing the composition; the composition thus being able to 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 to be understood in the sense 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 range of values designated by the expression "between a and b" represents the range of values going from more than a to less than b (ie limits a and b excluded) while any range of values designated by the expression "from a to b" means the range of values from a to b (that is to say including the strict limits a and b). In the present, when describing a range of values by the expression "from a to b", the range represented by the expression "between a and b" is also and preferably described.

When reference is made to a “majority” compound, it is understood within the meaning of the present invention, that this compound is predominant among the compounds of the same type in the composition, that is to say that it is that which represents the greatest amount by mass among compounds of the same type. Thus, for example, a majority elastomer is the elastomer representing the largest mass relative to the total mass of the elastomers in the composition. Likewise, a so-called majority charge is that representing the largest mass among the charges of the composition. For example, in a system comprising a single elastomer, this is 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. Preferably by majority, we mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

The compounds comprising carbon mentioned in the description can be of fossil origin or bio-based. In the latter case, they can be, partially or totally, from biomass or obtained from renewable raw materials from biomass. Are concerned in particular polymers, plasticizers, fillers, etc.

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

II- DESCRIPTION OF THE INVENTION

11-1 Elastomeric matrix

According to the invention, the elastomeric matrix of the composition of the tread of the tire comprises at least one, that is to say one or more, butadiene-styrene copolymer (SBR) having a glass transition temperature (Tg ) included in a range from -60 ° C to -10 ° C.

Advantageously, the glass transition temperature of the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is between -50 ° C and -15 ° C.

The butadiene-styrene copolymer (SBR) having a glass transition temperature (Tg) comprised in a range from -60 ° C. to -10 ° C. can consist exclusively of styrene monomers and butadiene monomers, that is that is, the sum of the molar percentages of styrene monomers and butadiene monomers is 100%. It may also comprise, on a minority basis, monomers other than styrene and butadiene, preferably less than 20%, preferably less than 10%, more preferably less than 5%, by weight relative to the total weight of the copolymer .

Note that the SBR can be prepared in emulsion (ESBR) or in solution (SSBR). Whether ESBR or SSBR, the SBR can be of any microstructure as long as it generates a Tg in a range from -60 ° C to -10 ° C, preferably from -50 ° C at -15 ° C. Use may in particular be made of an SBR having a low styrene content, for example ranging from 35 to 55% by weight of the copolymer, and a vinyl bond content of the butadiene part of between 4% and 70%, preferably between 10 and 40% by weight of the butadiene part of the copolymer. Advantageously, the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is a butadiene-styrene copolymer prepared in solution. The butadiene-styrene copolymer (SBR) having a glass transition temperature (Tg) comprised in a range from -60 ° C. to -10 ° C., which can be used according to the invention, can for example be coupled and / or star-shaped or still functionalized with a coupling and / or star-forming or functionalizing agent. For coupling with carbon black, there may be mentioned for example functional groups comprising a C-Sn bond or amino functional groups such as benzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may, for example, be made of silanol or polysiloxane functional groups having a silanol end (as described for example in FR 2 740 778 or US 6,013,718), alkoxysilane groups (such as described for example in FR 2 765 882 or US 5,977,238), carboxylic groups (as described for example in WO 01/92402 or US 6,815,473, WO 2004/096865 or US 2006/0089445) or also polyether groups (as described for example in EP 1 127 909 or US 6,503,973). Advantageously, the butadiene-styrene copolymer having a glass transition temperature comprised in a range from -60 ° C. to -10 ° C. is functionalized with a coupling agent. Preferably, the coupling agent is 3-Mercaptopropyltriethoxysilane.

According to the invention, the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C can be used alone or in combination with at least one other diene elastomer. By "other diene elastomer" is meant a diene elastomer which is not a butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C.

By "diene" elastomer (or indistinctly rubber), whether natural or synthetic, must be understood in known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of diene monomer units (monomers carrying 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" means a diene elastomer derived at least in part from conjugated diene monomers, having a rate of units or units of diene origin (conjugated dienes) which is greater than 15% (% by moles); This is how diene elastomers such as butyl rubbers or copolymers of dienes and of alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular as “essentially saturated” diene elastomers (content of motifs of diene origin weak or very weak, always less than 15%).

The term “diene elastomer capable of being used in the compositions according to the invention” is understood to mean:

(a) any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms; (b) any copolymer of a diene, conjugated or not, having from 4 to 18 carbon atoms and from at least one other monomer.

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

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

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

Examples of vinyl aromatic compounds are styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tertiobutylstyrene.

As aliphatic α-monoolefins suitable in particular are acyclic aliphatic α-monoolefins having from 3 to 18 carbon atoms.

The at least one other diene elastomer can be chosen from the group consisting of polybutadienes (BR), synthetic polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers and their mixtures . The butadiene copolymers are particularly chosen from the group consisting of butadiene-styrene copolymers (SBR).

The other diene elastomer can be at least one isoprene elastomer. By “isoprene elastomer” is understood, in known manner, an isoprene homopolymer or copolymer, in other words an isoprene elastomer chosen from the group comprising or consisting of natural rubber (NR), which can be plasticized or peptized, synthetic polyisoprenes (IR), the various isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene (butyl rubber IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers ( SBIR).

The isoprene elastomer is preferably chosen from the group consisting of natural rubber, synthetic polyisoprenes and their mixtures. Among these synthetic polyisoprenes, polyisoprenes are preferably used having a rate (mol%) of cis 1,4 bonds greater than 90%, more preferably still greater than 98%. More preferably, the diene elastomer is natural rubber.

Advantageously also, the elastomeric matrix comprises a mixture of butadiene-styrene copolymer having a glass transition temperature comprised in a range ranging from -60 ° C to -10 ° C, polybutadiene and polyisoprene (preferably natural rubber). The level of butadiene-styrene copolymer having a glass transition temperature comprised in a range ranging from -60 ° C. to -10 ° C., in the composition, can be comprised in a range ranging from 35 to 100 phr.

When the composition of the tread of the tire according to the invention does not comprise any other diene elastomer, the level of butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C. to - 10 ° C is thus 100 pce.

When another diene elastomer is present in the composition, its level can be included in a range ranging from 30 to 65 phr, preferably from 40 to 60 phr. In this case, the content of butadiene-styrene copolymer having a glass transition temperature comprised in a range from -60 ° C. to -10 ° C. can also be understood in a range ranging from 35 to 70 phr, preferably from 40 to 60 pce.

Advantageously, the composition of the tread of the tire according to the invention comprises from 5 to 40 phr of polybutadiene. Alternatively or additionally, and just as advantageously, Advantageously, the composition of the tread of the tire according to the invention comprises from 5 to 40 phr of natural rubber and / or synthetic polyisoprene.

In a particularly advantageous manner, the composition of the tread of the tire according to the invention comprises:

from 35 to 65 phr of butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C,

from 20 to 40 phr of polybutadiene, and

from 20 to 40 pce of polyisoprene,

the total level of butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C, polybutadiene and polyisoprene, in the composition, being in a range from 80 at 100 phr, preferably 90 to 100 phr, more preferably being 100 phr.

Reinforcing filler

According to the invention, the composition of the tread of the tire comprises from 30 to less than 120 phr of reinforcing filler, the reinforcing filler comprising a mixture of silica and carbon black, the reinforcing filler comprising between 33% and 100% by weight of silica relative to the total weight of the reinforcing filler, the content of silica in the composition being between 10 and 80 phr.

As carbon blacks, all carbon blacks are suitable, in particular the blacks conventionally used in tires or their treads. Among the latter, there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (grades ASTM D-1765-2017), such as, for example, the blacks. N 115, N 134, N 234, 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 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 WO97 / 36724-A2 or WO99 / 16600-A1). The BET specific surface of carbon blacks is measured according to standard D6556-10 [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range R / R0: 0.1 to 0.3] Advantageously, carbon black has a BET specific surface between 70 and 150 m ² / g, preferably between 100 and 120 m ² / g.

The silica used can be any reinforcing silica known to a person skilled in the art, in particular any precipitated or pyrogenic silica having a BET specific surface as well as a CTAB specific surface both of which are less than 450 m ² / g, preferably included in a field ranging from 30 to 400 m ² / g, in particular from 60 to 300 m ² / g.

In this paper, the BET surface area 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 [multi-point volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160 ° C - relative pressure range w / in: 0.05 to 0.17]

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

Any type of precipitated silica can be used, in particular highly dispersible precipitated silicas (called "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas, highly dispersible or not, are well known to those skilled in the art. Mention may be made, for example, of the silicas described in applications W003 / 016215-A1 and W003 / 016387-A1. Among the commercial HDS silicas, silica "Ultrasil ^® 5000gr" may especially be used, "Ultrasil ^® 7000GR" of Evonik, silicas "Zeosil ^® 1085GR,""Zeosil ^® 1115 MP", "Zeosil ^® 1165 MP", " Zeosil ^® Premium 200MP "," Zeosil ^® HRS 1200 MP "from the company Solvay. As silica non HDS, the following commercial silicas can be used: silicas "Ultrasil ^® VN2GR", "Ultrasil ^® VN3GR" of Evonik, silica "Zeosil ^® 175gr""from Solvay, silicas" Hi -Sil EZ120G (-D) "," Hi-Sil EZ160G (-D) "," Hi-Sil EZ200G (-D) "," Hi-Sil 243LD "," Hi-Sil 210 "," Hi-Sil HDP 320G ”from PPG.

A person skilled in the art will understand that, as a replacement for the reinforcing inorganic filler described above, a reinforcing filler of another nature could be used, since this reinforcing filler of another nature would be covered with an inorganic layer. such as silica, or else would have on its surface functional sites, in particular hydroxyls, requiring the use of a coupling agent to establish the bond between this reinforcing filler and the diene elastomer. Examples include carbon blacks partially or fully covered with silica, or carbon blacks modified with silica, such as, without limitation, "Ecoblack ^® " fillers of the CRX2000 "or" CRX4000 "series from Cabot Corporation.

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

Preferably, the organosilanes are chosen from the group consisting of polysulphurized organosilanes (symmetrical or asymmetrical) such as bis tetrasulphide (3-triethoxysilylpropyl), in short TESPT marketed under the name "Si69" by the company Evonik or bis disulphide - (triethoxysilylpropyle), abbreviated TESPD marketed under the name "Si75" by the company Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S- (3- (triethoxysilyl) propyl) octanethioate marketed by the company Momentary under the name "NXT Silane". More preferably, the organosilane is a polysulfurized organosilane.

Of course, mixtures of the coupling agents previously described could also be used.

Typically the level of coupling agent represents from 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler. Its rate is preferably included in a range ranging from 0.5 to 20 phr, more preferably included in a range ranging from 3 to 3 phr. This rate is easily adjusted by a person skilled in the art according to the rate of reinforcing inorganic filler used in the composition of the invention.

As indicated above, the composition of the tread of the tire according to the invention comprises from 30 to less than 120 phr of reinforcing filler, the reinforcing filler comprising a mixture of silica and carbon black, the reinforcing filler comprises between 33% and 100% by weight of silica relative to the total weight of the reinforcing filler, the level of silica in the composition being between 10 and 80 phr

Advantageously, the reinforcing filler comprises between 33% and 70% by weight, preferably between 35% and 67% by weight, of silica relative to the total weight of the reinforcing filler. More particularly, the reinforcing filler preferably comprises more than 50% by weight, preferably between 50% and 67% by weight of silica relative to the total weight of the reinforcing filler.

Advantageously, the level of silica in the composition is between 15 and 60 phr, and / or the rate of carbon black in the composition is between 5 and 20 phr. Alternatively, advantageously, the level of silica in the composition is between 15 and 60 phr, and / or the rate of carbon black in the composition is between 5 and 35 phr, preferably between 10 and 35 phr, preferably still between 11 and 20 pce.

Whatever the respective levels of carbon black and of silica, the total rate of reinforcing filler in the composition is advantageously between 35 and 90 phr.

Furthermore, the composition of the tread of the tire according to the invention may comprise a non-reinforcing filler, but this is not preferable.

Thus, the composition of the tread of the tire according to the invention advantageously does not comprise a non-reinforcing filler or comprises less than 25 pce, preferably less than 20 pce, more preferably less than 10 pce, and more preferably less than 5 pce. In a particularly preferred manner, the composition of the tread of the tire according to the invention does not include a non-reinforcing filler.

As examples of non-reinforcing fillers (or inert fillers) known to those skilled in the art, mention will be made in particular of those chosen from the group consisting of ash (ie, combustion residues), microparticles of natural calcium carbonates (chalk) or synthetic (synthetic or natural silicates (such as kaolin, talc, mica, cloisite), titanium oxides, aluminas, aluminosilicates (clay, bentonite), and their mixtures.

11-3 Crosslinking system

The crosslinking system can be any type of system known to those skilled in the art in the field of rubber compositions for tires. It can in particular be based on sulfur, and / or peroxide and / or bismaleimides.

Preferably, the crosslinking system is based on sulfur, this is called a vulcanization system. The crosslinking system thus preferably comprises molecular sulfur and / or at least one sulfur donor agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferentially, various known vulcanization activators can be used such as zinc oxide, stearic acid or equivalent compound such as stearic acid salts and salts. of transition metals, guanidine derivatives (in particular diphenylguanidine), or also known vulcanization retardants. Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr.

Any compound capable of acting as an accelerator for vulcanization of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type can be used as accelerator. As examples of such accelerators, mention may be made in particular of the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated to "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N, N-dicyclohexyl- 2-benzothiazyle sulfenamide ("DCBS"), N-ter-butyl-2-benzothiazyle sulfenamide ("TBBS"), N-ter-butyl-2-benzothiazyle sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD") , zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds.

11-4 Other possible additives

The rubber compositions of the tread of the tire according to the invention can optionally also include all or part of the usual additives usually used in elastomer compositions for tires, such as for example plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, anti-ozone chemicals, antioxidants, anti-fatigue agents, reinforcing resins (as described for example in application WO 02/10269 ).

The composition may in particular comprise a plasticizing hydrocarbon resin. The plasticizing hydrocarbon resin is chosen from the group consisting of homopolymer or copolymer resins of cyclopentadiene or dicyclopentadiene, homopolymer or terpene copolymer resins, homopolymer or terpene phenol copolymer resins, homopolymer or copolymer resins of section C5, homopolymer resins or copolymers of section C9, homopolymer resins and copolymers of alpha-methyl-styrene and their mixtures. Advantageously, the level of plasticizing hydrocarbon resin in the composition of the tread of the tire according to the invention is within a range ranging from 2 to 20 phr, preferably from 2 to 10 phr. Such resins are described for example in paragraphs 1-4-1 of the application WO 2016/202968.

Furthermore, the composition of the tread of the tire according to the invention advantageously does not comprise a plasticizing oil or comprises less than 5 phr thereof. By way of example of plasticizing oils, mention may be made of the liquid plasticizers mentioned in paragraph I-4-2 of application WO 2016/202968.

11-5 Preparation of rubber compositions The rubber composition in accordance with the invention can be produced in suitable mixers, using two successive preparation phases well known to those skilled in the art:

a first thermomechanical working or kneading phase (so-called “non-productive” phase), which can be carried out in a single thermomechanical step during which one introduces, into a suitable mixer such as a usual internal mixer (for example of the type 'Banbury'), all the necessary constituents, in particular the elastomeric matrix, any fillers, any other miscellaneous additives, with the exception of the crosslinking system. The incorporation of the optional filler into the elastomer can be carried out once or more times by thermomechanically kneading. The non-productive phase can be carried out at high temperature, up to a maximum temperature between 110 ° C and 200 ° C, preferably between 130 ° C and 185 ° C, for a period generally between 2 and 10 minutes.

a second mechanical working phase (so-called “productive” phase), which is carried out in an external mixer such as a cylinder mixer, after cooling of 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 a plate, in particular for characterization in the laboratory, or else extruded in the form of a semi-finished (or profiled) rubber usable by example as a tire tread for an agricultural vehicle. These products can then be used for the manufacture of tires, 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 cooked state (after crosslinking or vulcanization), can be a semi-finished product which can be used in a tire.

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

11-6 Tires

The present invention relates to a tire for agricultural vehicles.

Agricultural vehicle tires are characterized in particular by their large diameter, generally ranging from 20 to 63 inches, preferably from 28 to 54 inches, more preferably from 36 to 42 inches. In addition, their tread may have one or more grooves, the average depth of which ranges from 15 to 120 mm, preferably 65 to 120 mm. Furthermore, the average rate of volume dip over their entire tread may be within a range ranging from 5 to 40%, preferably from 5 to 25%.

III- BRIEF DESCRIPTION OF THE FIGURES

The present invention will be better understood with the aid of FIG. 1, schematic and not shown to scale, appended hereto, representing a perspective view of a tire 1 for a vehicle for agricultural use, such as a tractor.

In this figure, the tire 1 has a tread 2, intended to come into contact with a ground via a tread surface, and which includes bars 3 separated from each other by grooves 4. Each strip 3 extends radially outwards, from a bottom surface 5 to a contact face 6, positioned in the rolling surface. The grooves 4 are formed by the portions of the bottom surface 5 separating the bars 3.

In particular, in the case of a tire for an agricultural tractor as shown in the figure, the plurality of bars 3 of the tread is distributed in a first row and a second row of bars generally symmetrical with respect to the equatorial plane of the tire, passing through the middle of the tread 2 and perpendicular to the axis of rotation of the tire.

IV- PREFERRED EMBODIMENTS

In view of the above, the preferred embodiments of the invention are described below: A. Tire (1) for an agricultural vehicle comprising a tread (2) intended to come into contact with a ground which comprises a plurality of bars (3) separated from each other by grooves (4), each bar (3) extending radially outwards, over a radial height H, from a bottom surface (5) up to '' to a contact face (6), the grooves (4) being formed by the portions of the bottom surface (5) separating the bars (3),

characterized in that the tread comprises a rubber composition based on:

- an elastomeric matrix comprising at least one butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C,

- from 30 to less than 120 parts by weight per hundred parts by weight of elastomer, pce, reinforcing filler, the reinforcing filler comprising a mixture of silica and carbon black, the reinforcing filler comprises between 33% and 100% weight of silica relative to the total weight of the reinforcing filler, the content of silica in the composition being between 10 and 80 phr, and - a crosslinking system.

B. A tire according to embodiment A, in which the plurality of bars (3) of the tread are distributed in a first row and a second row of bars generally symmetrical with respect to the equatorial plane of the tire, passing through the middle of the tread (2) and perpendicular to the axis of rotation of the tire.

C. A tire according to any one of embodiments A and B, in which the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is a butadiene copolymer -styrene prepared in solution.

D. A tire according to any one of embodiments A to C, in which the glass transition temperature of the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is between -50 ° C and -15 ° C.

E. A tire according to any one of embodiments A to D, in which the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is functionalized with a coupling agent.

F. A tire according to any one of embodiments A to E, in which the content of butadiene-styrene copolymer having a glass transition temperature comprised in a range from -60 ° C to -10 ° C, in the composition, is included in a range from 35 to 100 phr.

G. A tire according to any one of embodiments A to E, in which the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is used in blending with at least one other diene elastomer.

H. A tire according to embodiment G, in which the at least one other diene elastomer is chosen from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and their mixtures.

I. A tire according to embodiment G, in which the composition comprises from 5 to 40 phr of polybutadiene.

J. A tire according to embodiment G or I, in which the composition comprises from 5 to 40 phr of natural rubber and / or synthetic polyisoprene.

K. A tire according to any one of embodiments A to J, in which the composition comprises from 35 to 65 phr of butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to - 10 ° C, from 20 to 40 phr of polybutadiene and from 20 to 40 phr of polyisoprene, the total content of butadiene-styrene copolymer having a glass transition temperature comprised in a range from -60 ° C to -10 ° C, polybutadiene and polyisoprene, in the composition, being included in a range from 80 to 100 phr, preferably from 90 to 100 phr, more preferably being from 100 phr.

L. A tire according to any one of embodiments A to K, in which the reinforcing filler comprises more than 50% by weight, preferably between 50% and 67% by weight, of silica relative to the total weight of the filler reinforcing, or alternatively between 33% and 70% by weight, preferably between 35% and 67% by weight, of silica relative to the total weight of the reinforcing filler.

M. A tire according to any one of embodiments A to L, in which the level of silica in the composition is between 15 and 60 phr.

N. A tire according to any one of embodiments A to M, in which the level of carbon black in the composition is between 5 and 20 phr, or alternatively between 5 and 35 phr, preferably between 10 and 35 phr , preferably between 11 and 20 pce.

O. A tire according to any one of embodiments A to N, in which the carbon black has a BET specific surface of between 70 and 150 m ² / g, preferably between 100 and 120 m ² / g.

P. A tire according to any one of embodiments A to O, in which the total rate of reinforcing filler in the composition is between 35 and 90 phr.

Q. A tire according to any one of embodiments A to P, in which the composition does not comprise a non-reinforcing filler or comprises less than 25 pce, preferably less than 20 pce.

R. A tire according to any one of embodiments A to Q, in which the crosslinking system comprises molecular sulfur and / or at least one sulfur donor.

S. A tire according to any one of embodiments A to R, in which the composition further comprises a plasticizing hydrocarbon resin.

Tire according to any one of embodiments A to S, in which the hydrocarbon plasticizing resin is chosen from the group consisting of homopolymer or copolymer resins of cyclopentadiene or dicyclopentadiene, homopolymer resins or terpene copolymers, terpene phenol homopolymer or copolymer resins, C5 cut homopolymer or copolymer resins, C9 cut homopolymer or copolymer resins, alpha-methyl-styrene homopolymer and copolymer resins and mixtures thereof.

U. A tire according to embodiment S or T, in which the content of plasticizing hydrocarbon resin in the composition is within a range ranging from 2 to 20 phr, preferably from 2 to 10 phr.

V. A tire according to any one of embodiments A to U, in which the composition does not comprise a plasticizing oil or comprises less than 5 phr thereof.

V- EXAMPLES

V-l Measurements and tests used

Determination of the glass transition temperature

The glass transition temperature, Tg, is measured in the present application by the DSC technique (Differential Scanning Calorimetry) on a device called “Setaram DSC 131 ". The temperature program used corresponds to a temperature rise from-120 ° C to 150 ° C at the speed of 10 ° C / min. Reference may be made to the method described in application WO 2007/054224 (page 11).

Dynamic properties

The dynamic properties tan (ô) max at -20 ° C, 0 ° C and 60 ° C are measured on a viscoanalyzer (Metravib VA4000), according to standard ASTM D 5992-96. The response of a sample of crosslinked composition is recorded (cylindrical test piece 4 mm thick and 400 mm ² in section), subjected to a sinusoidal stress in alternating single shear, at the frequency of 10 Hz, under the defined conditions of temperature for example at -20 ° C, 0 ° C or 60 ° C according to standard ASTM D 1349-99, or as the case may be at a different temperature. A deformation amplitude sweep is carried out from 0.1 to 50% (outward cycle), then from 50% to 0.1% (return cycle). The exploited results are the loss factor tan (ô). For the return cycle, we indicate the maximum value of tan (ô) observed, denoted tan (ô) max.

V- 2 Preparation of the compositions

The following tests are carried out as follows: the mixture is introduced into a paddle mixer (final filling rate: approximately 70% by volume), the initial tank temperature of which is approximately 50 ° C., successively, the elastomer, reinforcing fillers, as well as the various other ingredients with the exception of the crosslinking system. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of approximately 4 to 5 min, until a maximum "fall" temperature of 165 ° C. is reached.

The mixture thus obtained is recovered, it is cooled and then the crosslinking system (peroxide or sulfur as the case may be) is incorporated, on a mixer (homo-finisher) between 23 ° C and 50 ° C respectively, mixing the whole (phase productive) in a cylinder tool for an appropriate time (for example between 5 and 12 min).

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or of thin sheets of rubber for the measurement of their physical or mechanical properties.

V-3 Tests of rubber compositions

Six rubber compositions were prepared as indicated in point V-2 above, three in accordance with the invention (noted below C1 to C3) and two non-conforming (control composition noted below T1 and T2). These six formulations all contain, in addition to the elastomeric matrix and the reinforcing fillers presented in Table 1 below: 4 phr of plasticizing resin (C5 / C9 resin, “ECR-373 resin” from the company ExxonMobil), 1, 5 phr of tackifying resin (“Escorez 1102” from the company EXXON (Mn 1370 g / mol; lp = 2.3)), 1.6 phr of sulfur, 1.6 phr of vulcanization accelerator (N-ter-butyl -2-benzothiazyle sulfenamide, "Santocure TBBS" from the company Flexsys), 1.5 pce of industrial grade zinc oxide (company Umicore), 1 pce of stearic acid ("Pristerene 4931" from the company Uniqema), 3 pce of antioxidant (Nl, 3-dimethylbutyl- N-phenylparaphenylenediamine, "Santoflex 6-PPD" from the company Flexsys), 2 pce of anti-ozone wax ("VARAZON 4959" from the company Sasol Wax) and 0.2 pce of "CTP" (N- cyclohexylthiophthalimide sold under the name, "Vulkalent G" by the company Lanxess). The nature and content (in phr) of the elastomeric matrix and of the reinforcing filler system, as well as the properties of these formulations are presented in Table 1 below.

The control composition T1 differs from the compositions according to the invention in that the reinforcing filler system is not according to the invention. The control composition T2 differs from the compositions according to the invention, in addition, in that the glass transition temperature of the butadiene-styrene copolymer used is not included in a range from -60 ° C to -10 ° C .

The results of tan (5) max are presented in "base 100" with respect to the control composition Tl. For the values of tan (5) max at -20 ° C. and 0 ° C., the higher the value, the higher the composition will have improved wet grip. Furthermore, the lower the value of more tan (5) max at 60 ° C., the more the composition will have a low hysteresis and therefore an improved rolling resistance.

Table 1

(1) SBR (star 3-Mercaptopropyltriethoxysilane) with 41% of styrene unit and 24% of unit 1,2 of the butadiene part (Tg -25 ° C)

(2) SBR (starred Sn) with 15.5% of styrene unit and 35% of unit 1,2 of the butadiene part (Tg -65 ° C)

(3) Polybutadiene with 0.5% of 1,2 unit and 97% of 1,4-cis (Tg = -108 ° C)

(4) Natural rubber

(5) N234 carbon black (name according to ASTM D-1765)

(6) “Zeosil 1165 MP” silica from Rhodia type “HDS”

(7) TESPT (“Si69” from Degussa)

These results show that the substitution of a butadiene-styrene copolymer having a glass transition temperature of -25 ° C. with a butadiene-styrene copolymer having a glass transition temperature of -65 ° C improves hysteresis, but greatly penalizes grip on wet surfaces. Thus, only the compositions in accordance with the invention, having at least one butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C and the specific reinforcing filler system in accordance with the invention make it possible to improve both the hysteresis and the grip on wet ground, and this without penalizing the properties expected of a tire for agricultural vehicles.

Claims

1. A tire (1) for an agricultural vehicle comprising a tread (2) intended to come into contact with a ground which comprises a plurality of bars (3) separated from each other by grooves (4), each bar (3 ) extending radially outwards, over a radial height H, from a bottom surface (5) to a contact face (6), the grooves (4) being formed by the portions of the bottom surface (5) separating the bars (3),

characterized in that the tread comprises a rubber composition based on:

- from 30 to less than 120 parts by weight per hundred parts by weight of elastomer, pce, of reinforcing filler, the reinforcing filler comprising a mixture of silica and carbon black, the reinforcing filler comprises between 33% and 100% weight of silica relative to the total weight of the reinforcing filler, the content of silica in the composition being between 10 and 80 phr, and

- a crosslinking system.

2. Tire according to any one of the preceding claims, in which the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is a butadiene-styrene copolymer prepared in solution.

3. Tire according to any one of the preceding claims, in which the glass transition temperature of the butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C is between - 50 ° C and -15 ° C.

4. Tire according to any one of the preceding claims, in which the content of butadiene-styrene copolymer having a glass transition temperature in a range from -60 ° C to -10 ° C, in the composition, is included in an area ranging from 35 to 100 pc.

5. Tire according to any one of the preceding claims, in which the composition comprises from 35 to 65 phr of butadiene-styrene copolymer having a glass transition temperature comprised in a range from -60 ° C to -10 ° C, from 20 to 40 phr of polybutadiene and from 20 to 40 phr of polyisoprene, the total content of butadiene-styrene copolymer having a glass transition temperature comprised in a range from -60 ° C. to -10 ° C., of polybutadiene and polyisoprene, in the composition, being included in a range from 80 to 100 phr, preferably from 90 to 100 phr, more preferably being from 100 phr.

6. Tire according to any one of the preceding claims, in which the reinforcing filler comprises between 33% and 70% by weight, preferably between 35% and 67% by weight, of silica relative to the total weight of the reinforcing filler.

7. A tire according to any one of the preceding claims, in which the level of silica in the composition is between 15 and 60 phr, and the level of carbon black in the composition is between 5 and 35 phr, preferably between 10 and 35 pce.

8. Tire according to any one of the preceding claims, in which the carbon black has a BET specific surface of between 70 and 150 m ² / g, preferably between 100 and 120 m ² / g.

9. Tire according to any one of the preceding claims, in which the total rate of reinforcing filler in the composition is between 35 and 90 phr.

10. Tire according to any one of the preceding claims, in which the composition does not comprise a plasticizing oil or comprises less than 5 phr thereof.