RUBBER COMPOSITION FOR TREAD OF AGRICULTURAL VEHICLE TYRE

Abstract

The invention relates to a tire for an agricultural vehicle comprising a tread intended to come into contact with a ground which comprises a plurality of bars separated from each other by grooves, each bar extending radially outwards, over a radial height H, from a bottom surface to a contact face, the grooves being constituted by the portions of the bottom surface separating the bars, the tread comprising a radially external part which comprises a rubber composition based on at least one elastomer matrix comprising at least one polyisoprene, one polybutadiene and one tin-functionalized butadiene-styrene copolymer; a reinforcing filler comprising more than 30% by mass of at least one carbon black having a BET specific surface area in a range from 100 to 130 m² / g;a plasticizing system comprising at least one plasticizing resin having a glass transition temperature above 20°C and at least one liquid plasticizer at 23°C and a crosslinking system. (Figure 1);

Description

Title of the invention: RUBBER COMPOSITION FOR TREAD OF TIRE FOR AGRICULTURAL VEHICLE

[0001] The present invention relates to a tire for a vehicle for agricultural use which can be driven both in fields and on the road, such as a tractor or an agro-industrial vehicle.

[0002] The present invention relates more particularly to a rubber composition located in the radially external part of the tread of such a tire.

[0003] In the following, the circumferential, axial and radial directions respectively designate a direction tangent to the tread surface of the tire and oriented in 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 inner, respectively radially outer" is meant "closer, respectively further from the axis of rotation of the tire". By "axially inner, respectively axially outer" is meant "closer, respectively further from the equatorial plane of the tire", the equatorial plane of the tire being the plane passing through the middle of the tread surface of the tire and perpendicular to the axis of rotation of the tire.

[0004] The tread of a tire for an agricultural vehicle generally comprises a plurality of bars. The bars are elements in relief relative to a base surface which is a surface of revolution around the axis of rotation of the tire.

[0005] A bar generally has a generally elongated parallelepiped shape, consisting of at least one rectilinear or curvilinear portion, and is separated from adjacent bars by grooves. A bar may consist of a succession of rectilinear portions, as described in documents US3603370, US4383567, EP795427 or have a curvilinear shape, as presented in documents US4446902, EP903249, EP1831034.

[0006] In the radial direction, a lug extends from the bottom surface to the rolling surface, the radial distance between the bottom surface and the rolling surface defining the lug height. The radially outer face of the lug, belonging to the rolling surface, which comes into contact with the ground, when the lug passes through the contact patch of the tire, is called the contact face of the lug.

[0007] In the axial direction, a bar extends inwardly, toward the equatorial plane of the tire, from an axially outer end face to an axially inner end face.

[0008] 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, we mean the direction of rotation recommended by the tire manufacturer for optimal use of the tire. For example, in the case of a tread comprising two rows of V-shaped or chevron-shaped bars, the tire has a preferred direction of rotation according to the tip 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 face whose radially outer edge or trailing edge last comes into contact with the ground, when the lug passes through 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 in front of the trailing face.

[0009] A bar usually, but not necessarily, has an average inclination angle, relative to the circumferential direction, close to 45°. Indeed, this average inclination angle allows in particular a good compromise between field traction and vibration comfort. The field traction is all the better when the bar is axial, that is to say that its average inclination angle, relative to the circumferential direction, is close to 90°, while the vibration comfort is all the better when the bar is circumferential, that is to say that its average inclination angle, relative to the circumferential direction, is close to 0°.It is well known that field traction is more strongly determined by the lug angle at the shoulder, which has led some tire designers to propose a very curved lug shape, leading to a lug that is substantially axial at the shoulder and substantially circumferential in the middle of the tread.

[0010] A tire for an agricultural tractor is intended to roll on various types of ground such as more or less compacted earth in fields, unpaved access roads to fields and paved road surfaces.

[0011] Furthermore, the demand for tires for agricultural vehicles allowing travel at high speeds (up to around 65 km / h) on paved roads is constantly increasing, in order to reduce travel times between work areas (fields, forest areas, etc.) and storage locations (for the vehicle, agricultural equipment, harvested produce, etc.).

[0012] However, the increase in speed is accompanied by an increase in the fuel consumption. Thus, the impact of rolling resistance is becoming an increasingly important component for agricultural vehicle tires. Solutions have been proposed to reduce rolling resistance when driving on asphalt without impacting the other properties of agricultural vehicle tires, by adjusting the inflation pressure directly depending on the nature of the soil on which the agricultural vehicle is traveling (WO2016 / 071158).

[0013] The increase in the speed of rolling on bituminous ground also creates the need to take into consideration new performances which must be met by tires for agricultural vehicles intended to roll at high speeds on bituminous ground, in particular resistance to wear.

[0014] There is therefore a real need to have tires for agricultural vehicles allowing the vehicle to travel at high speeds on bituminous ground which have both low rolling resistance, in order to reduce fuel consumption, and resistance to wear, particularly on hard ground, i.e. on tarred road surfaces, and preferably without penalizing the other properties specifically linked to tires for agricultural vehicles.

[0015] Continuing its research, the Applicant has developed a new composition for the tread of such a tire making it possible to further improve the aforementioned performance compromise.

[0016] Thus, the subject of the invention is a tire for a vehicle for agricultural use comprising a tread intended to come into contact with a ground which comprises a plurality of bars separated from each other by grooves, each bar extending radially outwards, over a radial height H, from a bottom surface to a contact face, the grooves being constituted by the portions of the bottom surface separating the bars, the tread comprising a radially external part which comprises a rubber composition based on at least: - an elastomer matrix comprising at least one polyisoprene, one polybutadiene and one tin-functionalized butadiene-styrene copolymer, - a reinforcing filler comprising more than 30% by mass of at least one carbon black having a BET specific surface area in a range from 100 to 130 m2 / g, - a plasticizing system comprising at least one plasticizing resin having a glass transition temperature above 20°C and at least one liquid plasticizer at 23°C, - a crosslinking system.

[0017] As used herein, unless otherwise indicated, the term "the composition" refers to the rubber composition located in the radially outer portion of the strip of rolling of the tire according to the invention. I- DEFINITIONS

[0018] The expression "based on" used to define the constituents of a composition means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other, at least partially, during the different phases of manufacturing the composition. The latter can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0019] By “elastomer matrix” is meant all the elastomers in the composition, including the copolymer defined below.

[0020] Unless otherwise indicated, the rates of units resulting from the insertion of a monomer into a copolymer are expressed as a molar percentage relative to the total monomer units of the copolymer.

[0021] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts of elastomer present in the rubber composition considered and constituting a layer (eg, radially external part of the tread of the tire according to the invention).

[0022] In this document, unless expressly indicated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0023] On the other hand, any interval 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., excluding limits a and b), while any interval of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict limits a and b). In the present document, when an interval of values ​​is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

[0024] The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned may also come from the recycling of materials already used, that is to say they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This concerns in particular polymers, plasticizers, fillers, etc.

[0025] Unless otherwise indicated, all glass transition temperature "Tg" values ​​described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999). II- DESCRIPTION OF THE INVENTION II-1 Elastomeric matrix

[0026] The composition of the radially external part of the tread of the tire according to the invention comprises a specific mixture of several diene elastomers.

[0027] By elastomer (or "rubber", the two terms being considered synonymous) of the "diene" type, it is recalled here that it must be understood in a known manner to mean one (meaning one or more) elastomers derived at least in part (i.e., a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

[0028] Diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". "Essentially unsaturated" generally means a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or patterns 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 such as EPDM do not fall within the preceding definition and can be described in particular as "essentially saturated" diene elastomers (low or very low content of patterns of diene origin, always less than 15%). In the category of "essentially unsaturated" diene elastomers, a "highly unsaturated" diene elastomer is understood to mean in particular a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

[0029] Given these definitions, the rubber composition of the radially external part of the tread of the tire according to the invention is based on an elastomer matrix comprising at least one polyisoprene, one polybutadiene and one tin-functionalized styrene butadiene copolymer.

[0030] Obviously, each of the tin-functionalized polyisoprene, polybutadiene or styrene-butadiene copolymer elastomers may be a mixture of several tin-functionalized polyisoprenes, polybutadienes or styrene-butadiene copolymers respectively.

[0031] Advantageously, the level of polyisoprene in the composition of the radially external part of the tread of the tire according to the invention is within a range from 10 to 40 phr, preferably 15 to 35 phr, more preferably from 15 to 30 phr, more preferably from 15 to 25 phr.

[0032] The level of polybutadiene in the composition of the radially external part of the tread of the tire according to the invention is advantageously within a range from 10 to 40 pce, preferably from 15 to 35 pce, preferably still from 20 to 35 pce, preferably still from 25 to 35 pce.

[0033] As for the level of tin-functionalized styrene butadiene copolymer in the composition of the radially external part of the tread of the tire according to the invention, it is advantageously within a range from 40 to 80 phr, preferably from 45 to 75 phr, more preferably from 45 to 70 phr, more preferably from 45 to 65 phr.

[0034] Preferably, the total content of polyisoprene, polybutadiene and tin-functionalized styrene-butadiene copolymer elastomers is 100 pce, i.e. the composition does not comprise any elastomer other than those previously mentioned.

[0035] Preferably, the polyisoprene comprises a mass content of cis 1,4 monomer unit of at least 90%, more preferably at least 98% relative to the mass of the isoprene elastomer. Preferably, the polyisoprene is chosen from the group comprising or consisting of natural rubber, a synthetic polyisoprene and one of their mixtures, more preferably, the isoprene elastomer is natural rubber.

[0036] According to the invention, the polybutadiene very advantageously has a mass content of cis 1,4 monomer unit of at least 90%, more preferably at least 96% relative to the mass of the polybutadiene.

[0037] The tin (Sn) functionalized styrene butadiene copolymer, i.e. comprising C-Sn bonds (also called Sn functionalization or coupling), can be functionalized simply (C-Sn bonds at the end of the chain) and / or coupled (Sn atom between two chains) and / or star-shaped (Sn atom between 3 or more chains) with a functionalization and / or coupling and / or star-shaped agent. In a generic manner, to bring together all these elastomers linked to tin, we speak of tin-functionalized elastomers. These elastomers are known to those skilled in the art, for example those described in document WO2011 / 042507.

[0038] Other types of functionalization exist for styrenic and butadiene copolymers, such as silanol or polysiloxane functional groups having a silanol end, or epoxidized styrenic and butadiene copolymers. Such functionalizations are possible within the scope of the present invention in addition to that with tin.

[0039] Those skilled in the art are well aware of the functionalizing and / or coupling and / or star-forming agents that can be used in the context of the present invention. As an example of a functionalizing agent, mention may be made of functionalizing agents derived from tin which may correspond to the general formula (X1iR12Sn)-O-(SnR13yX1y) or (X'iR^ Sn)-O-(CH2)nO-(SnR13yX1y), where y represents an integer of value 0 or 1, R1 represents an alkyl, cycloalkyl, aryl, alkaryl or vinyl radical having from 1 to 12 carbon atoms, preferably a butyl, X1 is a halogen atom, preferably chlorine, and n represents an integer from 1 to 20, preferably 4. Furthermore, as tin coupling or star-forming agents, mention may be made of tin derivatives of formula SnRxX4x, x representing an integer of value 0 to 2, R representing an alkyl, cycloalkyl, aryl, alkaryl, aralkyl, vinyl radical having from 1 to 10 carbon atoms, preferably an alkyl radical having from 1 to 4 carbon atoms, and X is a halogen atom, preferably chlorine. As preferred tin derivatives, mention may be made of dibutyltin dichloride or tin tetrachloride, the latter being particularly preferred.

[0040] The tin-functionalized styrene-butadiene copolymer can be obtained in a manner known per se by reacting a tin derivative with the butadiene and styrene copolymer. The preparation of a star-shaped diene elastomer is for example described in US patent 3,393,182.

[0041] The tin-functionalized styrene butadiene copolymer may be an emulsion SBR or ESBR (i.e., prepared by emulsion polymerization), a solution SBR or SSBR (i.e., prepared by solution polymerization), or a mixture of both. Preferably, the tin-functionalized styrene butadiene copolymer is an SSBR.

[0042] Advantageously, the tin-functionalized styrene-butadiene copolymer comprises a styrene content in a range from 5% to less than 30%, preferably from 5% to less than 20%, more preferably from 10% to 19%, by weight relative to the total weight of the tin-functionalized styrene-butadiene copolymer.

[0043] In addition, the tin-functionalized styrene butadiene copolymer comprises a vinyl content in a range from 15 to 50%, preferably from 20 to 35%, by weight relative to the total weight of butadiene unit of the tin-functionalized styrene butadiene copolymer.

[0044] Preferably, the Tg of the tin-functionalized styrene butadiene copolymer is between 0 and -80°C, more particularly between -10°C and -70°C. II-2 Reinforcing charge

[0045] The rubber composition of the radially external part of the tread of the tire according to the invention comprises more than 30% by mass of at least one carbon black having a BET specific surface area within a range from 100 to 130 m2 / g.

[0046] Such a reinforcing filler typically consists of particles whose average size (by 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.

[0047] The BET specific surface area of ​​carbon blacks is measured according to standard D6556-10 [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range P / P0: 0.1 to 0.3].

[0048] Preferably, the level of carbon black in the rubber composition is within a range from 30 to 90 phr, preferably from 35 to 65 phr, more preferably from 50 to 60 phr.

[0049] Furthermore, the carbon black represents more than 50% by mass, preferably more than 80% by mass, of the reinforcing filler.

[0050] According to the invention, the carbon black has a BET specific surface area ranging from 100 to 130 m2 / g, preferably ranging from 105 to 125 m2 / g, more preferably from 110 to 120 m2 / g.

[0051] The blacks that can be used in the context of the present invention can be any black conventionally used in tires or their treads (so-called tire-grade blacks). Among the latter, mention will be made more particularly of the reinforcing carbon blacks of the 200 series (ASTM grades), such as for example blacks N219, N220, N234. These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a support for certain 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).

[0052] Although this is not necessary for the implementation of the present invention, the rubber composition according to the invention may contain, in a minor manner, one or more reinforcing fillers different from the carbon black specifically necessary for the invention (i.e. a reinforcing filler other than carbon black having a BET specific surface area within a range from 100 to 130 m2 / g). This or these different reinforcing fillers are hereinafter referred to as "other reinforcing filler" for the sake of simplification of wording. The other reinforcing filler may, for example, comprise a carbon black different from the carbon black used in the context of the present invention, an organic filler other than carbon black, an inorganic filler or the mixture of at least two of these fillers.

[0053] By "reinforcing inorganic filler" is meant here any inorganic or mineral filler, whatever its color and origin (natural or synthetic), also called "white" filler, "light" filler or even "non-black" filler as opposed to carbon black, capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words capable of replacing, in its reinforcing function, a conventional tire-grade carbon black; such a filler is generally characterized, in a known manner, by the presence of hydroxyl (OH) groups on its surface. In other words, without a coupling agent, the inorganic filler does not reinforce, or does not reinforce sufficiently, the composition and is therefore not included in the definition of “reinforcing inorganic filler”.

[0054] Suitable reinforcing inorganic fillers include, in particular, siliceous-type mineral fillers, preferably silica (SiO2). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area and a CTAB specific surface area both less than 450 m2 / g, preferably from 30 to 400 m2 / g, in particular between 60 and 300 m2 / g. Examples of highly dispersible precipitated silicas (known as "HDS") include "Ultrasil" 7000 and "Ultrasil" 7005 silicas from Degussa, "Zeosil" 1165MP, 1135MP and 1115MP silicas from Rhodia, "Hi-Sil" EZ150G silica from PPG, "Zeopol" 8715, 8745 and 8755 silicas from Huber, and high specific surface silicas as described in application WO 03 / 016387.

[0055] To couple the reinforcing silica to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner, intended to ensure a sufficient connection, of a chemical and / or physical nature, between the silica (surface of its particles) and the diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used.

[0056] Those skilled in the art can find examples of coupling agents in the following documents: WO 02 / 083782, WO 02 / 30939, WO 02 / 31041, WO 2007 / 061550, WO 2006 / 125532, WO 2006 / 125533, WO 2006 / 125534, US 6,849,754, WO 99 / 09036, WO 2006 / 023815, WO 2007 / 098080, WO 2010 / 072685 and WO 2008 / 055986.

[0057] Mention may in particular be made of alkoxysilane-polysulfide compounds, in particular bis-(trialkoxylsilylpropyl) polysulfides, most particularly bis-3-triethoxysilylpropyl disulfide (abbreviated as "TESPD") and bis-3-triethoxysilylpropyl tetrasulfide (abbreviated as "TESPT"). It is recalled that TESPD, of formula [(C2H5O)3Si(CH2)3S]2, is notably marketed by the company Degussa under the names Si266 or Si75 (in the second case, in the form of a mixture of disulfide (75% by weight) and polysulfides). TESPT, with the formula [(C2H5O)3Si(CH2 )3S]4, is marketed in particular by the company Degussa under the name Si69 (or X50S when supported at 50% by weight on carbon black), in the form of a commercial mixture of polysulfides Sx with an average value for x which is close to 4.

[0058] When an inorganic filler is present in the composition, for example silica, the coupling agent content is advantageously less than 10 phr, it being understood that it is generally desirable to use as little as possible. Typically when a reinforcing inorganic filler is present, the level of coupling agent represents from 0.5% to 15% by weight relative to the quantity of inorganic filler. The level is easily adjusted by a person skilled in the art according to the level of inorganic filler used in the composition.

[0059] Advantageously, the composition of the radially external part of the tread of the tire according to the invention does not contain silica, preferably no reinforcing inorganic filler, or comprises less than 20 phr, preferably less than 10 phr, even more preferably less than 5 phr. More preferably, the composition of the radially external part of the tread of the tire according to the invention does not contain any other reinforcing filler (i.e. reinforcing filler other than carbon black having a specific surface area within a range from 100 to 130 m2 / g) or contains less than 20 phr, preferably less than 10 phr, even more preferably less than 5 phr. II-3 Crosslinking system

[0060] The crosslinking system may be based on molecular sulfur and / or sulfur and / or peroxide donors, well known to those skilled in the art.

[0061] The crosslinking system is preferably a sulfur-based vulcanization system (molecular sulfur and / or sulfur donor agent).

[0062] Sulphur is used at a preferential rate of between 0.5 and 10 pce. Advantageously, the sulphur rate is between 0.5 and 2 pce, preferably between 0.5 and 1.8 pce.

[0063] The composition of the tread of the tire according to the invention advantageously comprises a vulcanization accelerator, which is preferably chosen from the group consisting of thiazole type accelerators and their derivatives, sulfenamide and thiourea type accelerators and their mixtures. Advantageously, the vulcanization accelerator is selected from the group consisting of 2-mercaptobenzothiazyl disulfide (MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS), N-tert-butyl-2-benzothiazyl sulfenamide (TBBS), N-tert-butyl-2-benzothiazyl sulfenimide (TBSI), morpholine disulfide, N-morpholino-2-benzothiazyl sulfenamide (MBS), dibutylthiourea (DBTU), and mixtures thereof. Particularly preferably, the primary vulcanization accelerator is N-tert-butyl-2-benzothiazyl sulfenamide (TBBS).

[0064] The vulcanization accelerator content is preferably within a range from 0.2 to 10 pce, preferably from 0.2 to 7 pce, more preferably from 0.6 to 2 pce.

[0065] Advantageously, the weight ratio of sulfur or sulfur donor / vulcanization accelerator varies from 0.8 to 1.2. II-4 Plasticizers

[0066] II-4 Plasticizing resin

[0067] The rubber composition of the radially external part of the tread of the tire according to the invention comprises a plasticizing system comprising at least one plasticizing resin having a glass transition temperature greater than 20°C (hereinafter referred to as "plasticizing resin") and at least one liquid plasticizer at 23°C (hereinafter referred to as "liquid plasticizer").

[0068] The level of plasticizing resin in the rubber composition may be within a range from 2 to 20 pce, preferably from 3 to 10 pce.

[0069] The term "resin" is reserved in the present application, by definition known to those skilled in the art, for a compound which is solid at room temperature (23°C), as opposed to a liquid plasticizing compound such as an oil.

[0070] Hydrocarbon plasticizing resins are polymers well known to those skilled in the art, essentially based on carbon and hydrogen but which may contain other types of atoms, which can be used in particular as plasticizing agents or tackifying agents in polymer matrices. They are by nature miscible (i.e., compatible) at the rates used with the polymer compositions for which they are intended, so as to act as true diluting agents. They have been described, for example, in the work entitled "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), chapter 5 of which is devoted to their applications, in particular in pneumatic rubber (SS "Rubber Tires and Mechanical Goods"). They can be aliphatic, cycloaliphatic, aromatic, hydrogenated aromatic, aliphatic / aromatic type, i.e. based on aliphatic and / or aromatic monomers.They can be natural or synthetic, petroleum-based or not (if so, also known as petroleum resins). Their Tg is preferably above 20°C (most often between 30°C and 95°C).

[0071] In a known manner, these hydrocarbon plasticizing resins can also be described as thermoplastic resins in the sense that they soften upon heating and can thus be molded. They can also be defined by a softening point or temperature. The softening temperature of a hydrocarbon plasticizing resin is generally approximately 50 to 60°C higher than its Tg value. The softening point is measured according to ISO 4625 (“Ring and Bail” method). The macrostructure (Mw, Mn and Ip) is determined by size exclusion chromatography (SEC) as indicated below.

[0072] As a reminder, SEC analysis, for example, consists of separating macromolecules in solution according to their size through columns filled with a porous gel; the molecules are separated according to their hydrodynamic volume, the largest being eluted first. The sample to be analyzed is simply previously solubilized in an appropriate solvent, tetrahydrofuran at a concentration of 1 g / liter. Then the solution is filtered through a 0.45 pm porosity filter, before injection into the apparatus. The apparatus used is, for example, a "Waters alliance" chromatographic chain under the following conditions: - elution solvent is tetrahydrofuran, - temperature 35°C; - concentration 1 g / liter; - flow rate: 1 ml / min; - injected volume: 100 ft; - Moore calibration with polystyrene standards; - set of 3 "Waters" columns in series ("Styragel HR4E", "Styragel HR1" and "Styragel HR 0.5"); - detection by differential refractometer (for example "WATERS 2410") which can be equipped with operating software (for example "Waters Millennium").

[0073] A Moore calibration is carried out with a series of commercial polystyrene standards with low Ip (less than 1.2), of known molar masses, covering the range of masses to be analyzed. The mass-average molar mass (Mw), the number-average molar mass (Mn), as well as the polymolecularity index (Ip = Mw / Mn) are deduced from the recorded data (molar mass mass distribution curve).

[0074] All the molar mass values ​​indicated in the present application are therefore relative to calibration curves produced with polystyrene standards.

[0075] According to a preferred embodiment of the invention, the plasticizing resin has at least one, more preferably all of the following characteristics: - a Tg greater than 25°C (in particular between 30°C and 100°C), more preferably greater than 30°C (in particular between 30°C and 95°C); - a softening point above 50°C (in particular between 50°C and 150°C); - a number-average molar mass (Mn) between 400 and 3000 g / mol, preferably between 500 and 1500 g / mol; - a polymolecularity index (Ip) less than 3, preferably 2 (reminder: Ip = Mw / Mn with Mw average molar mass by weight).

[0076] According to the invention, the plasticizing resin may be chosen from the group comprising or consisting of cyclopentadiene homopolymer or copolymer resins (abbreviated CPD), dicyclopentadiene homopolymer or copolymer resins (abbreviated DCPD), terpene homopolymer or copolymer resins, of C5 cut homopolymer or copolymer resins, C9 cut homopolymer or copolymer resins, alpha-methyl-styrene homopolymer or copolymer resins and mixtures of these plasticizing resins. Preferably, the plasticizing resin is selected from the group comprising or consisting of (D)CPD / vinylaromatic copolymer resins, (D)CPD / terpene copolymer resins, terpene phenol copolymer resins, (D)CPD / C5 cut copolymer resins, (D)CPD / C9 cut copolymer resins, terpene / vinylaromatic copolymer resins, terpene / phenol copolymer resins, C5 cut / vinylaromatic copolymer resins, and mixtures of these plasticizing resins.

[0077] The term "terpene" here groups together in a known manner the monomers alpha-pinene, beta-pinene and limonene; preferably a limonene monomer is used, a compound which is present in a known manner in the form of three possible isomers: L-limonene (levorotatory enantiomer), D-limonene (dextrorotatory enantiomer), or dipentene, racemic of the dextrorotatory and levorotatory enantiomers. Suitable vinylaromatic monomers are, for example, styrene, alpha-methylstyrene, orthomethylstyrene, meta-methylstyrene, para-methylstyrene, vinyltoluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, any vinylaromatic monomer from a C9 cut (or more generally from a C8 to C10 cut).

[0078] More particularly, mention may be made of plasticizing resins chosen from the group consisting of (D)CPD homopolymer resins, (D)CPD / styrene copolymer resins, polylimonene resins, limonene / styrene copolymer resins, limonene / D(CPD) copolymer resins, C5 / styrene cut copolymer resins, C5 / C9 cut copolymer resins, and mixtures of these resins.

[0079] All the above plasticizing resins are well known to those skilled in the art and commercially available, for example sold by the company DRT under the name "Dercolyte" for polylimonene resins, by the company Neville Chemical Company under the name "Super Nevtac", by Kolon under the name "Hikorez" or by the company Exxon Mobil under the name "Oppera" for C5 / styrene cut resins or C5 / C9 cut resins, or by the company Struktol under the name "40 MS" or "40 NS" (mixtures of aromatic and / or aliphatic resins).

[0080] 11-4.2 Liquid plasticizer at 23°C

[0081] Although not necessary for the implementation of the present invention, the rubber composition of the radially outer portion of the tire tread may comprise a plasticizer that is liquid at 23°C.

[0082] When the composition comprises a liquid plasticizer at 23°C, the level of plasticizer liquid at 23°C in the rubber composition is advantageously within a range from more than 0 to less than 10 pce, preferably from 0.5 to 4 pce.

[0083] Any plasticizer that is liquid at 23°C (or extending oil), whether aromatic or non-aromatic, known for its plasticizing properties with respect to diene elastomers, can be used. At room temperature (23°C), these plasticizers or these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the capacity to eventually take the shape of their container), in contrast in particular to hydrocarbon plasticizing resins which are by nature solid at room temperature.

[0084] Particularly suitable are liquid plasticizers at 23°C chosen from the group comprising or consisting of liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE oils, MES (Medium Extracted Solvated) oils, TDAE (Treated Distillate Aromatic Extracts) oils, RAE (Residual Aromatic Extract) oils, TRAE (Treated Residual Aromatic Extract) oils and SRAE (Safety Residual Aromatic Extract) oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these plasticizers liquid at 23°C.

[0085] For example, the liquid plasticizer at 23°C may be a petroleum oil, preferably non-aromatic. A liquid plasticizer is described as non-aromatic when it has a content of polycyclic aromatic compounds, determined with the extract in DMSO according to the IP 346 method, of less than 3% by weight, relative to the total weight of the plasticizer.

[0086] The liquid plasticizer at 23°C may also be a liquid polymer resulting from the polymerization of olefins or dienes, such as polybutenes, polydienes, in particular polybutadienes, polyisoprenes (also known as "LIR") or copolymers of butadiene and isoprene, or copolymers of butadiene or isoprene and styrene or mixtures of these liquid polymers. The number-average molar mass of such liquid polymers is preferably in a range from 500 g / mol to 50,000 g / mol, preferably from 1,000 g / mol to 10,000 g / mol. Examples include the "RICON" products from SARTOMER.

[0087] When the liquid plasticizer at 23°C is a vegetable oil, it may be, for example, an oil chosen from the group comprising or consisting of linseed, safflower, soybean, corn, cottonseed, rapeseed, castor, tung, pine, sunflower, palm, olive, coconut, peanut, grape seed oils and mixtures of these oils. The vegetable oil is preferably rich in oleic acid, that is to say that the fatty acid (or all the fatty acids if several are present) from which it is derived, comprises oleic acid. according to a mass fraction at least equal to 60%, even more preferably according to a mass fraction at least equal to 70%. As vegetable oil, a sunflower oil is advantageously used which is such that all the fatty acids from which it is derived comprise oleic acid according to a mass fraction equal to or greater than 60%, preferably 70% and, according to a particularly advantageous embodiment of the invention, according to a mass fraction equal to or greater than 80%.

[0088] The liquid plasticizer at 23°C may be a triester chosen from the group consisting of carboxylic acid, phosphoric acid, sulfonic acid triesters and mixtures of these triesters.

[0089] Examples of phosphate plasticizers that may be mentioned are those that contain between 12 and 30 carbon atoms, for example trioctyl phosphate. Examples of carboxylic acid ester plasticizers that may be mentioned include compounds chosen from the group consisting of trimellitates, pyromellitates, phthalates, 1,2-cyclohexane dicarboxylates, adipates, azelates, sebacates, glycerol triesters and mixtures of these compounds. Among the above triesters, mention may be made in particular of glycerol triesters, preferably consisting mainly (for more than 50%, more preferably for more than 80% by weight) of an unsaturated C18 fatty acid, that is to say chosen from the group consisting of oleic acid, linoleic acid, linolenic acid and mixtures of these acids. The glycerol triester is preferred.More preferably, whether of synthetic or natural origin (for example, sunflower or rapeseed vegetable oils), the fatty acid used consists of more than 50% by weight, and even more preferably more than 80% by weight, of oleic acid. Such triesters (trioleates) with a high oleic acid content are well known; they have been described, for example, in application WO 02 / 088238, as plasticizing agents in tire treads.

[0090] When the liquid plasticizer at 23°C is an ether plasticizer, it may be, for example, polyethylene glycol or polypropylene glycol.

[0091] The liquid plasticizer at 23°C may be chosen from the group comprising or consisting of MES oils, TDAE oils, naphthenic oils, vegetable oils and mixtures of these mixtures of these liquid plasticizers at 23°C. Advantageously, the liquid plasticizer at 23°C is a TDAE oil. II-5 Possible additives

[0092] The rubber compositions of the radially external part of the tread of the tire according to the invention may optionally also comprise all or part of the usual additives, known to those skilled in the art and usually used in elastomer compositions for tires, such as for example fillers (other than those mentioned above, for example non-reinforcing fillers), pigments, protective agents such as anti-ozone waxes, anti- chemical ozonants, antioxidants, anti-fatigue agents, etc. II-6 Preparation of compositions

[0093] The rubber compositions usable in the context of the present invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: - a first phase of working or thermomechanical mixing (so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents are introduced into a suitable mixer such as a conventional internal mixer (for example of the "Banbury" type), in particular the elastomeric matrix, the reinforcing filler, any other various additives, with the exception of the crosslinking system. The incorporation of the possible filler into the elastomer can be carried out in one or more stages by thermomechanical mixing.In the case where the filler is already incorporated in whole or in part into the elastomer in the form of a masterbatch as described for example in applications WO 97 / 36724 or WO 99 / 16600, it is the masterbatch which is directly mixed and where appropriate the other elastomers or fillers present in the composition which are not in the form of a masterbatch are incorporated, as well as any other various additives other than the crosslinking system. The non-productive phase can be carried out at high temperature, up to a maximum temperature of between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally of between 2 and 10 minutes. - a second phase of mechanical work (so-called "productive" phase), which can be carried out in an external mixer such as a cylinder mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and everything is then mixed for a few minutes, for example between 5 and 15 min.

[0094] Such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

[0095] The final composition thus obtained is then calendered, for example, in the form of a sheet or plate, in particular for laboratory characterization, or extruded (or co-extruded with another rubber composition) in the form of a semi-finished (or profiled) rubber usable, for example, as the radially external part of 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.

[0096] The composition may be either in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), may be a semi-finished product which may be used in a tire.

[0097] 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, for a sufficient duration which can vary for example between 5 and 90 min depending in particular on the curing temperature, the crosslinking system adopted, the crosslinking kinetics of the composition considered or even the size of the tire. II-7 Pneumatics

[0098] The present invention relates to a tire for agricultural vehicles.

[0099] Advantageously, the tire according to the invention has a diameter ranging from 28 to 54 inches, more preferably from 30 to 42 inches.

[0100] The tread of the tire according to the invention comprises a plurality of bars, each bar extending radially outwards, over a radial height H, from a bottom surface (5) to a contact face. Advantageously, the radial height H is within a range from 30 to 90 mm, preferably 40 to 70 mm.

[0101] Furthermore, the average volumetric hollow rate over the entire tread of the tire according to the invention may be within a range from 40% to 85%, preferably from 45% to 80%.

[0102] The tire for an agricultural vehicle according to the invention comprises a tread comprising a radially external portion comprising the rubber composition in accordance with the invention. The tread of the tire for an agricultural vehicle according to the invention advantageously comprises a radially internal portion with a rubber composition different from that of the radially external portion of the tread of the tire according to the invention. For example, the rubber composition of the radially internal portion of the tread of the tire for an agricultural vehicle according to the invention may be based on an elastomer matrix comprising 100% by weight of natural rubber, a reinforcing filler and a vulcanization system.

[0103] In addition, the radially external part of the tread of the tire according to the invention is preferably included in a range from 40 to 85 mm. III- BRIEF DESCRIPTIONS OF THE FIGURES

[0104] The present invention will be better understood with the aid of [Fig.l], schematic and not shown to scale, attached in the appendix, representing a perspective view of a tire 1 for a vehicle for agricultural use, such as a tractor.

[0105] [Fig.l] In this figure, the tire 1 has a tread 2, intended to come into contact with a ground via a rolling surface, and which comprises bars 3 separated from each other by grooves 4. Each bar 3 extends radially outwards, from a bottom surface 5 to a contact face 6, positioned in the rolling surface. The grooves 4 are constituted by the portions of the bottom surface 5 separating the bars 3.

[0106] 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- EXAMPLES IV-1 Measurements and tests used Dynamic properties:

[0107] The dynamic properties G*(10%) and tan(ô)max at 60°C are measured on a screw-coanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of crosslinked composition (cylindrical specimen 4 mm thick and 400 mm2 in cross-section) is recorded, subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under the defined temperature conditions, for example at 60°C according to the ASTM D 1349-99 standard, or depending on the case at a different temperature. A strain amplitude sweep is carried out from 0.1 to 50% (forward cycle), then from 50% to 0.1% (return cycle). The results used are the complex dynamic shear modulus G* and the loss factor tan(ô). For the return cycle, the maximum value of tan(ô) observed, noted tan(ô)max, is indicated, as well as the complex dynamic shear modulus G*(10%) at 10% deformation, at 60°C.

[0108] The tan(ô)max performance results at 60°C are expressed on a base of 100, with the value 100 being assigned to the control. A result greater than 100 indicates that the composition of the example considered is less hysteretic at 60°C, reflecting a reduction in heat dissipation as well as better (lower) rolling resistance of the tread comprising such a composition.

[0109] The performance results G*(10%) at 60°C are expressed on a base of 100, the value 100 being assigned to the control. A result greater than 100 indicates that the composition of the example considered has greater rigidity, reflecting better resistance to wear on hard ground. IV-2 Preparation of compositions

[0110] In the following examples, the rubber compositions were produced as described in point II.6 above. In particular, the “non-productive” phase was carried out in a 0.4 litre mixer for 3.5 minutes, at an average paddle speed of 50 revolutions per minute until a maximum falling temperature of 160°C was reached. The “productive” phase was carried out in a cylinder tool at 23°C for 5 minutes.

[0111] The crosslinking of the composition was carried out at a temperature between 130°C and 200°C, under pressure. IV-3 Rubber composition tests

[0112] In this example, different properties of a tread composition according to the invention (C1) usable in the radially external part of an agricultural tire tread were compared with those of a control composition (T0) which corresponds to a composition conventionally used in agricultural tire treads. The contents (in pce) of the components of these compositions are presented in Table 1 below and the properties obtained in Table 2 below.

[0113] [Tables 1] T0 Cl NR(1) - 20 BR (2) - 30 SBR1 (3) 50 - SBR2 (4) 50 - SBR3 (5) - 50 N347 (6) 67 - N234 (7) - 55 Oil (8) - 3 Oil (9) 10 - Resin (10) - 8 Wax (11) 2 2 Antioxidant (12) 3 3 Stearic acid (13) 0.25 1 ZnO (14) 1.5 1.5 Sulphur 1.15 1.6 Primary accelerator (16) 1 1.6

[0114] (1) Natural rubber (2) Polybutadiene neodymium 98% 1.4 cis - Tg = -108°C (3) SBR1: SBR Emulsion of Tg -48°C, % Styrene 2.25, % Vinyl 18, % Trans 71 (4) SBR2: SBR Tg solution -48°C, % Styrene 26.5, % Vinyl 24, % Trans 50 (5) SBR3: Tin-coupled solution SBR of Tg -65°C, % Styrene 15.5, % Vinyl 35, % Trans 48 (6) Carbon black grade N347 according to ASTM D-1765-21 (7) Carbon black grade N234 according to ASTM D-1765-21 (8) TDAE oil “Vivatec 500” from the company Klaus Dahleke (9) MES / HPD oil “Catenex SNR” from Shell (Tg = -60°C) (10) C5 / C9 cutting resin co “Oppera PR-373” from ExxonMobil -Tg= 44°C (ll) Anti-ozone wax “VARAZON 4959” from Sasol Wax (12) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine “Santoflex 6-PPD” from Flexsys (13) Stearic acid “Pristerene 4931” from Uniqema (14) Industrial grade zinc oxide from Umicore (15) N-ter-butyl-2-benzothiazyl sulfenamide “Santocure TBBS” from Flexsys

[0115] [T ableaux2] T0 Cl Rolling resistance 100 138 Wear resistance 100 107

[0116] The results presented in Table 2 above show that the wear resistance and rolling resistance properties of composition C1 are both improved compared to the control. The tires in accordance with the invention therefore have an improved hard ground wear life and lower fuel consumption than current tires for agricultural vehicles.

Claims

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 constituted by the portions of the bottom surface (5) separating the bars (3), the tread (2) comprising a radially external part which comprises a rubber composition based on at least: • an elastomer matrix comprising at least one polyisoprene, one polybutadiene and one tin-functionalized butadiene-styrene copolymer, • a reinforcing filler comprising more than 30% by mass of at least one carbon black having a BET specific surface area within a range from 100 to 130 m2 / g,• a plasticizing system comprising at least one plasticizing resin having a glass transition temperature above 20°C and at least one liquid plasticizer at 23°C, • a crosslinking system.,

2. A tire according to claim 1, wherein: • the level of polyisoprene in the rubber composition is within a range of 10 to 40 phr, preferably 15 to 35 phr, preferably 15 to 30 phr, • the level of polybutadiene in the rubber composition is within a range of 10 to 40 phr, preferably 15 to 35 phr, preferably 20 to 35 phr and • the level of tin-functionalized butadiene-styrene copolymer in the rubber composition is within a range of 40 to 80 phr, preferably 45 to 75 phr, preferably 45 to 70 phr.

3. A tire according to any preceding claim, wherein the polyisoprene is selected from the group consisting of ca- natural ouchouc, synthetic polyisoprenes and their mixtures.

4. A tire according to any one of the preceding claims, wherein the level of carbon black in the rubber composition is within a range of 30 to 90 phr, preferably 35 to 65 phr, preferably 50 to 60 phr.

5. A tire according to any one of the preceding claims, wherein the carbon black represents more than 50% by mass, preferably more than 80% by mass, of the reinforcing filler.

6. A tire according to any preceding claim, wherein the carbon black has a BET specific surface area of ​​the carbon black in the range of 105 to 125 m2 / g, preferably 110 to 120 m2 / g.

7. A tire according to any one of the preceding claims, wherein the level of plasticizing resin in the rubber composition is within a range of 2 to 20 phr, preferably 3 to 10 phr.

8. A tire according to any one of the preceding claims, wherein the plasticizing resin is selected from the group consisting of cyclopentadiene homopolymer or copolymer resins, dicyclopentadiene homopolymer or copolymer resins, terpene homopolymer or copolymer resins, C5-cut homopolymer or copolymer resins, C9-cut homopolymer or copolymer resins, alpha-methyl-styrene homopolymer or copolymer resins and mixtures thereof.

9. A tire according to any one of the preceding claims, wherein the level of liquid plasticizer at 23°C in the rubber composition is within a range from more than 0 to less than 10 pce, preferably from 0.5 to 4 pce.

10. A tire according to any one of the preceding claims, wherein the plasticizer that is liquid at 23°C is selected from the group consisting of liquid diene polymers, polyolefin oils, naphthenic oils, paraffinic oils, DAE oils, MES oils, TDAE oils, RAE oils, TRAE oils, SRAE oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these plasticizers that are liquid at 23°C.

11. A tire according to any preceding claim, in which the liquid plasticizer at 23°C is a TDAE oil.

12. A tire according to any preceding claim, wherein the crosslinking system is based on molecular sulfur or a sulfur donor agent.

13. A tire according to any preceding claim, wherein the tire diameter is in the range of 28 to 54 inches, preferably 30 to 42 inches.

14. A tire according to any one of the preceding claims, wherein the radial height H is within a range from 30 to 90 mm, preferably from 40 to 70 mm.

15. A tire according to any one of the preceding claims, wherein the average volumetric void rate over the entire tread may be within a range of 40% to 85%, preferably 45% to 80%.

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