TIRE TREAD RUBBER COMPOUND FOR AGRICULTURAL VEHICLES

Abstract

The invention relates to an agricultural vehicle tire 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 base surface to a contact face, the grooves being constituted by the portions of the base 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 specific surface area BET in the range of 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: TIRE TREAD RUBBER COMPOSITE FOR AGRICULTURAL VEHICLES

[0001] The present invention relates to a tire for a vehicle for agricultural use that can drive both in fields and on roads, 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 what follows, the terms circumferential, axial, and radial directions respectively denote a direction tangent to the tire's tread and oriented in the direction of tire rotation, a direction parallel to the tire's axis of rotation, and a direction perpendicular to the tire's axis of rotation. "Radially inside" and "radially outside" respectively mean "closer to, or farther from, the tire's axis of rotation." "Axially inside" and "axially outside" respectively mean "closer to, or farther from, the tire's equatorial plane," the tire's equatorial plane being the plane passing through the midpoint of the tire's tread and perpendicular to the tire's axis of rotation.

[0004] The tread of a tire for agricultural vehicles generally comprises a plurality of lugs. The lugs are raised elements relative to a base surface, which is a surface of revolution around the axis of rotation of the tire.

[0005] A barrette generally has an overall elongated parallelepiped shape, consisting of at least one straight or curved portion, and is separated from adjacent barrettes by grooves. A barrette may consist of a succession of straight portions, as described in documents US3603370, US4383567, EP795427, or have a curved shape, as shown in documents US4446902, EP903249, EP1831034.

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

[0007] According to the axial direction, a bar extends inwards, in the direction of the equatorial plane of the tire, from an axially external end face to an axially internal end face.

[0008] In the circumferential direction, a tread lug extends, in a preferred direction of tire rotation, from a leading edge to a trailing edge. Preferred direction of rotation is defined as the direction of rotation recommended by the tire manufacturer for optimal tire use. For example, in the case of a tread pattern comprising two rows of V-shaped or chevron-shaped lugs, the tire has a preferred direction of rotation along the tips of the chevrons. The leading edge is, by definition, the face whose radially outer edge, or leading edge, first makes contact with the ground as the lug passes through the tire's contact patch with the ground during tire rotation.The trailing edge is, by definition, the face whose radially outer edge, or trailing edge, is the last to come into contact with the ground as the tread passes through the contact patch of the tire with the ground during the tire's rotation. Depending on the direction of rotation, the leading edge is said to be in front of the trailing edge.

[0009] A slat 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. Field traction is better the more axial the slat, that is to say, the closer its average inclination angle, relative to the circumferential direction, is to 90°, while vibration comfort is better the more circumferential the slat, that is to say, the closer its average inclination angle, relative to the circumferential direction, is to 0°.It is well known that field traction is most strongly determined by the angle of the lug at the shoulder, which has led some tire designers to propose a highly curved lug shape, resulting in a lug that is substantially axial at the shoulder and substantially circumferential in the middle of the tread.

[0010] An agricultural tractor tire is intended to run on various types of soil such as the more or less compact soil of fields, unpaved access roads to fields and paved road surfaces.

[0011] Furthermore, the demand for tires for agricultural vehicles that allow driving 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 goods, etc.).

[0012] However, increased speed is accompanied by increased fuel consumption. Therefore, the impact of rolling resistance is becoming an increasingly important factor for agricultural vehicle tires. Solutions have been proposed to reduce rolling resistance when driving on asphalt without affecting other properties of agricultural vehicle tires, by adjusting the inflation pressure in real time according to the type of soil on which the agricultural vehicle is traveling (WO2016 / 071158).

[0013] The increase in driving speed on bituminous soil also creates the need to take into consideration new performance requirements that must be met by tires for agricultural vehicles intended to travel at high speeds on bituminous soil, in particular wear resistance.

[0014] There is therefore a real need for agricultural vehicle tires that allow the vehicle to travel at high speeds on bituminous soil which has 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 other properties specifically related to agricultural vehicle tires.

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

[0016] Thus, the invention relates to a tire for agricultural vehicles comprising a tread intended to come into contact with the ground, comprising a plurality of bars separated from each other by grooves, each bar extending radially outwards, over a radial height H, from a base surface to a contact face, the grooves being formed by the portions of the base surface separating the bars, the tread comprising a radially external portion comprising a rubber composition based on at least: - an elastomeric 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 specific surface area BET in the range of 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] In the present, unless otherwise indicated, the expression "the composition" refers to the rubber composition located in the radially external part of the tread of the tire according to the invention. I- DEFINITIONS

[0018] The expression "based on" used to define the constituents of a composition refers to 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 various stages of manufacturing the composition. The composition may thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0019] By "elastomer matrix" is meant all the elastomers of 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 to be understood in the context of the present invention, the part, by mass per hundred parts of elastomer present in the rubber composition considered and constituting a layer (e.g., radially external part of the tread of the tire according to the invention).

[0022] In this document, unless expressly stated 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 domain of values ​​from greater than a to less than b (i.e., excluding the bounds a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (i.e., including the strict bounds a and b). In the present case, 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 origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, 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 includes, in particular, polymers, plasticizers, fillers, etc.

[0025] Unless otherwise indicated, all glass transition temperature values ​​“Tg” 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 Elastomer 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 is to be understood in a known way as an (we mean one or more) elastomer derived at least in part (i.e., a homopolymer or a copolymer) from diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or not).

[0028] Diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". Generally, "essentially unsaturated" means a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of diene motifs or units (conjugated dienes) greater than 15% (mole percent); thus, diene elastomers such as butyl rubbers or EPDM-type diene-alpha-olefin copolymers do not fall under the preceding definition and can be described in particular as "essentially saturated" diene elastomers (low or very low proportion of diene motifs, always less than 15%). In the category of "essentially unsaturated" diene elastomers, a "highly unsaturated" diene elastomer is defined in particular as a diene elastomer having a rate of diene origin motifs (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 polyisoprene, polybutadiene or tin-functionalized styrene butadiene copolymer elastomers can be a mixture of several polyisoprenes, polybutadienes or tin-functionalized styrene butadiene copolymers respectively.

[0031] Advantageously, the polyisoprene content in the composition of the radially external part of the tread of the tire according to the invention is in a range of 10 to 40 parts per annum, preferably 15 to 35 parts per annum, preferably still 15 to 30 parts per annum, preferably still 15 to 25 parts per annum.

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

[0033] As for the percentage 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 of 40 to 80 parts per annum, preferably from 45 to 75 parts per annum, preferably still from 45 to 70 parts per annum, preferably still from 45 to 65 parts per annum.

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

[0035] Preferably, the polyisoprene comprises a mass percentage of cis 1,4 monomer units of at least 90%, more preferably at least 98%, relative to the mass of the isoprene elastomer. Preferably, the polyisoprene is selected from the group comprising or consisting of natural rubber, a synthetic polyisoprene, and a mixture thereof; more preferably, the isoprene elastomer is natural rubber.

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

[0037] Tin-functionalized (Sn) styrene-butadiene copolymer, i.e., one containing C-Sn bonds (also called Sn functionalization or coupling), can be functionalized simply (C-Sn bonds at the chain ends) and / or coupled (Sn atom between two chains) and / or star-shaped (Sn atom between three or more chains) with a functionalizing and / or coupling and / or star-shaped agent. Generally, all these tin-bonded elastomers are referred to as 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 the tin functionalization.

[0039] A person skilled in the art is well acquainted with the functionalizing and / or coupling and / or star-bonding agents that can be used in the context of the present invention. As an example of a functionalizing agent, one can cite tin-derived functionalizing agents that can conform to the general formula (X1iR12Sn)-O-(SnR13 yX1y) or (X'iR^ Sn)-O-(CH2)nO-(SnR13 yX1y), 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-linking agents, we can mention the tin derivatives of formula SnRxX 4_x, 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. Preferred tin derivatives include dibutyl tin dichloride and 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-styrenic 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 can 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 the two. Preferably, the tin-functionalized styrene-butadiene copolymer is an SSBR.

[0042] Advantageously, the tin-functionalized styrene butadiene copolymer comprises a styrene content in the range of 5% to less than 30%, preferably 5% to less than 20%, more preferably 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 has a vinyl content in the range of 15 to 50%, preferably 20 to 35%, by weight relative to the total weight of butadiene units 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 Load

[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 specific surface area BET in the range of 100 to 130 m2 / g.

[0046] Such a reinforcing charge 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 preferentially between 20 and 150 nm.

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

[0048] Preferably, the carbon black content in the rubber composition is in the range of 30 to 90 parts per annum, preferably 35 to 65 parts per annum, and even more preferably 50 to 60 parts per annum.

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

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

[0051] The blacks usable within the scope of the present invention can be any black conventionally used in tires or their treads (so-called tire-grade blacks). Among these, special mention should be made of reinforcing carbon blacks of the 200 series (ASTM grades), such as N219, N220, and N234. These carbon blacks can be used in isolation, as commercially available, or in any other form, for example, as a carrier for certain rubber additives used. The carbon blacks could, for example, already be incorporated into the diene elastomer, particularly isoprene, in the form of a masterbatch (see, for example, applications WO 97 / 36724 or WO 99 / 16600).

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

[0053] By "reinforcing inorganic filler", herein should be understood any inorganic or mineral filler, whatever its color and origin (natural or synthetic), also called "white" filler, "light" filler or even "non-black" filler. In contrast to carbon black, which is capable of reinforcing, on its own and without any means other than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires—in other words, suitable for replacing, in its reinforcing function, a conventional carbon black of pneumatic grade—such a filler is generally characterized, in a known way, by the presence of hydroxyl (OH) groups on its surface. In other words, without a coupling agent, the inorganic filler does not allow for the reinforcement, or not sufficiently, of the composition and is therefore not included in the definition of "reinforcing inorganic filler."

[0054] Suitable inorganic reinforcing fillers include siliceous 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 pyrogenated 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 from Degussa, "Zeosil" 1165MP, 1135MP and 1115MP from Rhodia, "Hi-Sil" EZ150G from PPG, "Zeopol" 8715, 8745 and 8755 from Huber, and high specific surface area silicas as described in application WO 03 / 016387.

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

[0056] Examples of coupling agents can be found by those skilled in the art 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] Examples include alkoxysilane-polysulfide compounds, particularly bis-(triethoxysilylpropyl) polysulfides, especially bis-3-triethoxysilylpropyl disulfide (abbreviated "TESPD") and bis-3-triethoxysilylpropyl tetrasulfide (abbreviated "TESPT"). It should be noted that TESPD, with the formula [(C2H5O)3Si(CH2)3S]2, is marketed by Degussa under the names Si266 or Si75 (in the latter case, as 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 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 parts per cent, it being understood that it is generally desirable to use as little as possible. Typically, when a reinforcing inorganic filler is present, the coupling agent content represents 0.5% to 15% by weight relative to the amount of inorganic filler. The content is easily adjusted by those skilled in the art according to the amount of inorganic filler used in the composition.

[0059] Advantageously, the composition of the radially outer portion of the tire tread according to the invention does not contain silica, preferably no reinforcing inorganic filler, or contains less than 20 parts per annum, preferably less than 10 parts per annum, and preferably even less than 5 parts per annum. More preferably, the composition of the radially outer portion of the tire tread according to the invention does not contain any other reinforcing filler (i.e., a reinforcing filler other than carbon black having a specific surface area in the range of 100 to 130 m² / g) or contains less than 20 parts per annum, preferably less than 10 parts per annum, and preferably even less than 5 parts per annum. II-3 Crosslinking System

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

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

[0062] Sulfur is used at a preferential rate of between 0.5 and 10 parts per annum. Advantageously, the sulfur content is between 0.5 and 2 parts per annum, preferably between 0.5 and 1.8 parts per annum.

[0063] The tire tread composition according to the invention advantageously comprises a vulcanization accelerator, which is preferably selected from the group consisting of thiazole-type accelerators and their derivatives, sulfenamide-type accelerators, thiourea-type accelerators, and mixtures thereof. 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-ter-butyl-2-benzothiazyl sulfenamide (TBBS), N-ter-butyl-2-benzothiazyl sulfenamide (TBSI), morpholine disulfide, N-morpholino-2-benzothiazyl sulfenamide (MBS), dibutylthiourea (DBTU), and mixtures thereof. In a way The primary vulcanization accelerator, which is particularly preferred, is N-ter-butyl-2-benzothiazyl sulfenamide (TBBS).

[0064] The vulcanization accelerator ratio is preferably in the range of 0.2 to 10 pc, preferably 0.2 to 7 pc, preferably still 0.6 to 2 pc.

[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 including at least one plasticizing resin having a glass transition temperature above 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 proportion of plasticizing resin in the rubber composition can be in the range of 2 to 20 parts per annum, preferably from 3 to 10 parts per annum.

[0069] The term "resin" is reserved in this application, by definition known to the person 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 carbon- and hydrogen-based but potentially containing other types of atoms, and are particularly useful as plasticizing or tackifying agents in polymer matrices. They are inherently miscible (i.e., compatible) at the ratios used with the polymer compositions for which they are intended, so as to act as true diluents. They have been described, for example, in the book 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, particularly in pneumatic rubber (SS "Rubber Tires and Mechanical Goods"). They can be aliphatic, cycloaliphatic, aromatic, hydrogenated aromatic, of the 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] As is known, these hydrocarbon plasticizing resins can also be described as thermoplastic resins in that they soften upon heating and can thus be molded. They can also be defined by a softening point or temperature. The temperature of The softening point of a hydrocarbon plasticizing resin is generally about 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 described below.

[0072] As a reminder, SEC analysis, for example, consists of separating macromolecules in solution according to their size using columns filled with a porous gel; the molecules are separated according to their hydrodynamic volume, with the largest being eluted first. The sample to be analyzed is simply pre-solubilized in a suitable solvent, tetrahydrofuran at a concentration of 1 g / liter. The solution is then filtered through a 0.45 µm porosity filter before being injected into the apparatus. The apparatus used is, for example, a "Waters Alliance" chromatographic system under the following conditions: - elution solvent is tetrahydrofuran, - temperature 35°C; - concentration 1 g / litre; - flow rate: 1 ml / min; - injected volume: 100 ql; - 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 performed with a series of commercial polystyrene standards with a low Ip value (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), and the polymolecularity index (Ip = Mw / Mn) are deduced from the recorded data (mass distribution curve of the molar masses).

[0074] All molar mass values ​​indicated in this application are therefore relative to calibration curves made 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); - an average number 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 can 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, 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 chosen 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 includes in a known way the alpha-pinene, betapinene and limonene monomers; preferably a limonene monomer is used, a compound which is known to exist 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 examples of vinylaromatic monomers include styrene, alpha-methylstyrene, rorthomethylstyrene, meta-methylstyrene, para-methylstyrene, vinyl-toluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, and any vinylaromatic monomer derived from a C9 cut (or more generally from a C8 to C1 cut).

[0078] In particular, we can mention the plasticizing resins chosen from the group consisting of homopolymer (D)CPD resins, (D)CPD / styrene copolymer resins, polylimonene resins, limonene / styrene copolymer resins, limonene / D(CPD) copolymer resins, C5 / styrene copolymer resins, C5 / C9 copolymer resins, and mixtures of these resins.

[0079] All the above-mentioned plasticizing resins are well known to those skilled in the art and are commercially available, for example, sold by DRT under the name "Dercolyte" for polylimonene resins, by Neville Chemical Company under the name "Super Nevtac", by Kolon under the name "Hikorez", or by 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 external part of the tire tread may include a liquid plasticizer at 23 °C.

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

[0083] Any liquid plasticizer at 23°C (or extending oil), whether aromatic or non-aromatic, known for its plasticizing properties with respect to diene elastomers, is usable. At room temperature (23°C), these plasticizers or oils, with varying degrees of viscosity, are liquids (that is to say, substances that eventually take the shape of their container), unlike hydrocarbon plasticizing resins, which are solid at room temperature.

[0084] Particularly suitable are liquid plasticizers at 23 °C selected from the group comprising or consisting of liquid diene polymers, polyolefinic oils, naphthenic oils, paraffinic oils, DAE oils, MES (Medium Extracted Solvates) 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 can be a petroleum oil, preferably non-aromatic. A liquid plasticizer is considered non-aromatic if it has a polycyclic aromatic compound content, determined with the extract in DMSO according to method IP 346, of less than 3% by weight, relative to the total weight of the plasticizer.

[0086] The liquid plasticizer at 23°C can 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 even 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 the range of 500 g / mol to 50,000 g / mol. preferably from 1,000 g / mol to 10,000 g / mol. As an example, the "RICON" products from SARTOMER can be cited.

[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, grapeseed oils and mixtures of these oils. The vegetable oil is preferably rich in oleic acid, that is to say, the fatty acid (or group of fatty acids if several are present) from which it is derived contains oleic acid in a mass fraction of at least 60%, and even more preferably in a mass fraction of at least 70%.As a vegetable oil, sunflower oil is advantageously used which is such that the total fatty acids from which it is derived comprise oleic acid in a mass fraction equal to or greater than 60%, preferably 70% and, according to a particularly advantageous embodiment of the invention, in a mass fraction equal to or greater than 80%.

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

[0089] As an example of phosphate plasticizers, one can cite those containing between 12 and 30 carbon atoms, for example trioctyl phosphate. As examples of carboxylic acid ester plasticizers, one can cite in particular compounds selected 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, one can cite in particular glycerol triesters, preferably consisting predominantly (for more than 50%, more preferably for more than 80% by weight) of a C[8] unsaturated fatty acid, that is to say selected from the group consisting of oleic acid, linoleic acid, linolenic acid and mixtures of these acids. The glycerol triester is preferred.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 can be selected from the group comprising or consisting of by MES oils, TDAE oils, naphthenic oils, vegetable oils and 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 include all or part of the usual additives, known to those skilled in the art and commonly used in elastomer compositions for tires, such as fillers (other than those mentioned above, for example non-reinforcing fillers), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents, etc. II-6 Preparation of compositions

[0093] The rubber compositions usable within the scope of the present invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: - a first thermomechanical working or mixing phase (the so-called "non-productive" phase), which can be carried out in a single thermomechanical step during which all the necessary constituents, including the elastomeric matrix, the reinforcing filler, and any other miscellaneous additives, with the exception of the crosslinking system, are introduced into a suitable mixer such as a standard internal mixer (for example, a "Banbury" type mixer). The incorporation of any filler into the elastomer can be carried out in one or more stages by thermomechanical mixing.In cases 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, the masterbatch is directly mixed, and where applicable, other elastomers or fillers present in the composition that are not in masterbatch form, as well as any other miscellaneous additives other than the crosslinking system, are incorporated. 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 duration generally between 2 and 10 minutes. - a second mechanical working phase (the so-called "productive" phase), which can be carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min.

[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, into a sheet or plate, particularly for laboratory characterization, or extruded (or co-extruded with another rubber composition) into a semi-finished (or profile) rubber product usable, for example, as the outer radial part of a tire tread for an agricultural vehicle. These products can then be used for tire manufacturing, according to techniques known to those skilled in the art.

[0096] 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 that can 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 cooking temperature, the crosslinking system adopted, the crosslinking kinetics of the composition considered or 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, preferably still 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 base surface (5) to a contact face. Advantageously, the radial height H is within a range of 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 can be in a range from 40% to 85%, preferably from 45% to 80%.

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

[0103] Furthermore, 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 the schematic [Fig.1], not shown to scale, attached as an appendix, representing a perspective view of a tire 1 for a vehicle for agricultural use, such as a tractor.

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

[0106] In particular, in the case of an agricultural tractor tire as shown in the figure, the plurality of lugs 3 of the tread is distributed in a first row and a second row of lugs that are 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(φ)max at 60°C are measured on a viscoelastic analyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a cross-linked composite sample (cylindrical specimen 4 mm thick and 400 mm² cross-section) is recorded under sinusoidal alternating simple shear loading at a frequency of 10 Hz, under defined temperature conditions, for example, 60°C according to ASTM D 1349-99, or, as appropriate, at a different temperature. A strain amplitude sweep is performed from 0.1 to 50% (forward cycle), then from 50% to 0.1% (reverse cycle). The results used are the complex dynamic shear modulus G* and the loss factor tan(φ). For the return cycle, we indicate the maximum value of tan(ô) observed, noted tan(ô)max, as well as the complex dynamic shear modulus G*(10%) at 10% strain, at 60°C.

[0108] The tan(φ)max performance results at 60°C are expressed as a base of 100, with 100 being assigned to the control. A result greater than 100 indicates that the composition 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 with such a composition.

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

[0110] In the following examples, the rubbery compositions were produced as described in section II.6 above. In particular, the "non-productive" phase was carried out in a 0.4-liter mixer for 3.5 minutes, at an average paddle speed of 50 revolutions per minute, until a maximum drop temperature of 160°C was reached. The "productive" phase was carried out in a roller 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 Tests of rubber compositions

[0112] In this example, various properties of a tread compound according to the invention (Cl) usable in the radially outer part of an agricultural tire tread were compared with those of a control compound (T0) corresponding to a compound conventionally used in agricultural tire treads. The contents (in parts per kilogram) of the components of these compounds are presented in Table 1 below, and the properties obtained are shown 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 Sulfur 1.15 1.6 Primary accelerator (16) 1 1.6

[0114] (1) Natural rubber (2) Neodymium polybutadiene 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: SBR Tin-coupled solution at Tg -65°C, % Styrene 15.5, % Vinyl 35, % Trans 48 (6) N347 grade carbon black according to ASTM D-1765-21 (7) N234 grade carbon black 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 (11) Anti-ozone wax “VARAZON 4959” from Sasol Wax (12) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine “Santaflex 6-PPD” from Flexsys (13) Stearic acid “Pristerene 4931” from the company Uniqema (14) Industrial grade zinc oxide from Umicore (15) N-ter-butyl-2-benzothiazyl sulfenamide “Santicure TBBS” from Flexsys

[0115] [Tables2] 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 the Cl compound are both improved compared to the control. Tires according to the invention therefore exhibit improved wear life on hard surfaces and lower fuel consumption than current tires for agricultural vehicles.

Claims

Demands

1. A tire (1) for an agricultural vehicle comprising a tread (2) intended to come into contact with the ground, comprising 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 base surface (5) to a contact face (6), the grooves (4) being formed by the portions of the base surface (5) separating the bars (3), the tread (2) comprising a radially outer portion comprising a rubber composition based on at least: • an elastomeric 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 the range of 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. characterized in that • The polyisoprene content in the rubber composition is in the range of 10 to 40 parts per annum, preferably 15 to 35 parts per annum, preferably 15 to 30 parts per annum. • The polybutadiene content in the rubber composition is in the range of 10 to 40 parts per annum, preferably 15 to 35 parts per annum, preferably 20 to 35 parts per annum and • the rate of tin-functionalized butadiene-styrene copolymer in the rubber composition is in the range of 40 to 80 parts per annum, preferably 45 to 75 parts per annum, preferably 45 to 70 parts per annum.

2. Pneumatic according to any one of the preceding claims, wherein the polyisoprene is selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof.

3. Tire according to any one of the preceding claims, wherein the rate of carbon black in the rubber composition is in the range of 30 to 90 pc, preferably 35 to 65 pc, preferably 50 to 60 pc.

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

5. Pneumatic according to any one of the preceding claims, wherein the carbon black has a specific surface area BET of the carbon black is in the range of 105 to 125 m2 / g, preferably 110 to 120 m2 / g.

6. Pneumatic according to any one of the preceding claims, wherein the rate of the plasticizing resin in the rubber composition is in the range of 2 to 20 parts per annum, preferably 3 to 10 parts per annum.

7. Pneumatic 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.

8. Pneumatic according to any one of the preceding claims, wherein the rate of the liquid plasticizer at 23°C in the rubber composition is in the range of more than 0 to less than 10 pc, preferably from 0.5 to 4 pc.

9. A pneumatic system according to any one of the preceding claims, wherein the liquid plasticizer 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, and other plasticizers. phosphates, sulfonate plasticizers and mixtures of these plasticizers liquid at 23 °C.

10. Pneumatic according to any one of the preceding claims, wherein the liquid plasticizer at 23°C is a TDAE oil.

11. Pneumatic according to any one of the preceding claims, wherein the crosslinking system is based on molecular sulfur or a sulfur-donating agent.

12. A tire according to any one of the preceding claims, wherein the diameter of the tire is in a range from 28 to 54 inches, or from 711.2 mm to 1371.6 mm, preferably from 30 to 42 inches, or from 762 mm to 1066.8 mm.

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

14. A tire according to any one of the preceding claims, wherein the average volumetric hollowness rate over the entire tread can be in the range of 40% to 85%, preferably 45% to 80%.

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