Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
  • B60C1/0016—Compositions of the tread
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/10—Metal compounds
  • C08K3/105—Compounds containing metals of Groups 1 to 3 or of Groups 11 to 13 of the Periodic Table
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/24—Acids; Salts thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L21/00—Compositions of unspecified rubbers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L7/00—Compositions of natural rubber
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons

Definitions

• the invention relates to rubber compositions that can be used as treads of tires, in particular as treads for "winter tires” capable of rolling on floors covered with ice or ice without being provided with nails (also called “studless” tires). ).
• treads of tires specifically adapted for running under so-called "melting ice” conditions encountered in a temperature range typically between -5 ° C and 0 ° C. It is recalled that, in such a field, the pressure of the tires at the passage of a vehicle causes a superficial melting of the ice which is covered with a thin film of water detrimental to the adhesion of these tires.
• solid particles of high hardness such as, for example, silicon carbide (see, for example, US Pat. No. 3,878,147), some of which are flush with the surface of the tread. as it wears, and thus come into contact with the ice.
• Such particles able to act finally as micro-nails on hard ice, thanks to a well known "claw" effect, remain relatively aggressive vis-à-vis the ground; they are not well adapted to driving conditions on melting ice.
• these water-soluble, protruding microparticles on the surface of the tread fulfill the claw function previously described without the disadvantage of being abrasive. Then, in a second step, after progressive expulsion of the rubbery matrix, they release microcavities which act as storage volume and drainage channel of the water film on the surface of the ice; under these conditions, the contact between the surface of the tread and the ice is no longer lubricated and the coefficient of friction is thus improved.
• a first subject of the invention relates to a rubber composition that can be used as a tread of a tire, based on at least one diene elastomer, more than 30 phr of a liquid plasticizer, and between 50 and 150 phr.
• a reinforcing filler between 2 and 40 phr of potassium sulfate microparticles, this composition being characterized in that the volumetric size distribution of said microparticles, measured by laser granulometry according to the ISO 13320-1 standard, satisfies the following relations:
• D 50 is the median particle diameter corresponding to 50% of the cumulative distribution of the microparticles
• Dio and D90 represent the particle diameter corresponding to 10% and 90% respectively of the cumulative particle distribution.
• the invention also relates to the use of such a rubber composition for the manufacture of tire treads, that they are intended for new tires as retreading tires used.
• the invention also relates to these treads and these tires themselves when they comprise a rubber composition according to the invention.
• the tires of the invention are particularly intended for equipping tourism-type motor vehicles, including 4x4 vehicles (four-wheel drive) and SUV vehicles ("Sport Utility Vehicles"), two-wheeled vehicles (especially motorcycles) as vehicles.
• industrial vehicles chosen in particular from vans and "heavy goods vehicles” (eg metro, buses, road transport equipment such as trucks, tractors, trailers).
• any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term “from a to b” means the range from a to b (i.e., including the strict limits a and b).
• the rubber composition of the invention is based on at least one diene elastomer, a liquid plasticizer, a reinforcing filler and potassium sulfate microparticles, which components are described in detail hereinafter.
• a composition comprising the mixture of the various constituents used or, where appropriate, their reaction product, some of these basic constituents being especially capable of or intended to react between they, at least in part, during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization.
• elastomer or rubber, the two terms being synonymous
• dienes monomers carrying two double bonds carbon - carbon, conjugated or not
• the diene elastomers can be classified in known manner into two categories: those known as “essentially unsaturated” and those known as “essentially saturated”. Butyl rubbers, and for example copolymers of dienes and alpha-olefins of the EPDM type, fall into the category of essentially saturated diene elastomers, with a level of diene origin units which is low or very low, still less than 15% (mole%).
• essentially unsaturated diene elastomer is understood to mean a diene elastomer derived at least in part from conjugated diene monomers having a proportion of units or units of diene origin (conjugated dienes) which is greater than 15% (mol%). .
• the term “highly unsaturated” diene elastomer is particularly understood to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%. It is preferred to use at least one diene elastomer of the highly unsaturated type, in particular a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), polybutadienes (BR) and butadiene copolymers, copolymers of isoprene and mixtures of these elastomers.
• NR natural rubber
• IR synthetic polyisoprenes
• BR polybutadienes
• butadiene copolymers copolymers of isoprene and mixtures of these elastomers.
• Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-butadiene-styrene copolymers (SBIR) and mixtures of such copolymers.
• SBR butadiene-styrene copolymers
• BIR isoprene-butadiene copolymers
• SIR isoprene-styrene copolymers
• SBIR isoprene-butadiene-styrene copolymers
• Polybutadienes and in particular those having a content of 1,2-units of between 4% and 80%, or those having a cis-1,4 content of greater than 80%, the polyisoprenes and the butadiene copolymers, are preferably used.
• styrene and in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a 1,2-butadiene content of the butadiene part of between 4% and and 65%>, a content of trans-1,4 bonds of between 20%> and 80%>, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a temperature of glass transition ("Tg" - measured according to ASTM D3418-82) from -40 ° C to -80 ° C, the isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg of -25 ° C to -50 ° C.
• Tg temperature of glass transition
• butadiene-styrene-isoprene copolymers those having a styrene content of between 5% and 50% by weight and more particularly of between 10% and 40%, and an isoprene content of between 15%, are especially suitable.
• the diene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes and polybutadienes having a cis-1,4 bond ratio greater than 90%, butadiene-styrene copolymers and mixtures of these elastomers.
• the diene elastomer used is predominantly, that is to say for more than 50 phr (for recall, "phr” or “phr” in English meaning parts by weight per hundred parts elastomer or rubber), natural rubber (NR) or synthetic polyisoprene (IR). More preferably, said natural rubber or synthetic polyisoprene is then used in blending with a polybutadiene (BR) having a cis-1,4 bond ratio which is preferably greater than 90%.
• BR polybutadiene
• the diene elastomer used is for the most part, that is to say for more than 50 phr, a polybutadiene (BR) having a cis-1,4 bonds greater than 90%. More preferably, said polybutadiene is then used in a blend with natural rubber or synthetic polyisoprene.
• BR polybutadiene
• the diene elastomer used is a binary (mixing) blend of NR (or IR) and BR, or a ternary blend of NR (or IR), BR and SBR.
• the composition comprises between 25 and 75 phr of NR (or IR) and between 75 and 25 phr of BR, to which may be associated or not a third elastomer (ternary cutting) at a lower rate. at 30 phr, especially less than 20 phr.
• This third elastomer is preferably an SBR elastomer, in particular an SBR solution (called "SSBR").
• the composition comprises from 35 to 65 phr of NR (or IR) and from 65 to 35 phr of BR.
• the BR used is preferably a BR having a cis-1,4 bond ratio greater than 90%, more preferably greater than 95%.
• diene elastomers of the compositions of the invention could be associated, in a minor amount, with synthetic elastomers other than diene, or even polymers other than elastomers, for example thermoplastic polymers.
• Another essential feature of the rubber composition of the invention is that it comprises more than 30 phr of a liquid plasticizer (at 23 ° C.) whose function is to soften the matrix by diluting the elastomer and the reinforcing filler; its Tg is preferably less than -20 ° C, more preferably less than -40 ° C.
• any extender oil whether aromatic or non-aromatic, any liquid plasticizer known for its plasticizing properties vis-à-vis diene elastomers, is usable.
• these plasticizers or these oils are liquids (that is to say, as a reminder, substances having the capacity to eventually take on the shape of their container) , in contrast to, in particular, hydrocarbon plasticizing resins which are inherently solid at room temperature.
• Liquid plasticizers selected from the group consisting of polyolefin oils, naphthenic oils, paraffinic oils, DAE (Distillate Aromatic Extracts) oils, MES (Medium Extracted Solvates) oils, Treated Distillate Aromatic Extracts (TDAE) oils are particularly suitable. ), Residual Aromatic Extracts (RAE) oils, Treated Residual Aromatic Extracts (TREE) oils, Safety Residual Aromatic Extracts (SRAE) oils, mineral oils, vegetable oils, ethers plasticizers, ester plasticizers, phosphate plasticizers sulphonate plasticizers and mixtures of these compounds.
• the liquid plasticizer is chosen in the group consisting of MES oils, TDAE oils, naphthenic oils, vegetable oils and mixtures of these oils.
• the liquid plasticizer in particular petroleum oil, is of the non-aromatic type.
• a liquid plasticizer is described as non-aromatic if 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 .
• a liquid plasticizer chosen from the group consisting of MES oils, TDAE oils, naphthenic oils (at low or high viscosity, especially hydrogenated), paraffinic oils and mixtures of these oils.
• RAE oils, TRAE oils and SRAE oils or mixtures thereof which contain low levels of polycyclic compounds.
• phosphate plasticizers for example, mention may be made of those containing from 12 to 30 carbon atoms, for example trioctyl phosphate.
• ester plasticizers mention may be made in particular of compounds selected from the group consisting of trimellitates, pyromellitates, phthalates, 1,2-cyclohexane dicarboxylates, adipates, azelates, sebacates, glycerol and mixtures of these compounds.
• glycerol triesters preferably consisting predominantly (for more than 50%, more preferably more than 80% by weight) of an unsaturated fatty acid Ci 8 is that is to say selected from the group consisting of oleic acid, linoleic acid, linolenic acid and mixtures of these acids. More preferably, whether of synthetic or natural origin (for example vegetable oils of sunflower or rapeseed), the fatty acid used is more than 50% by weight, more preferably still more than 80% by weight. % by weight of oleic acid.
• Such high oleic acid triesters (trioleates) are well known and have been described, for example, in application WO 02/088238, as plasticizers in tire treads.
• the level of liquid plasticizer in the composition of the invention is preferably greater than 40 phr, more preferably within a range of 50 to 100 phr.
• compositions of the invention may also comprise, as solid plasticizer (at 23 ° C.), a hydrocarbon resin having a Tg greater than + 20 ° C., preferably greater than + 30 ° C. C, as described for example in applications WO 2005/087859, WO 2006/061064 and WO 2007/017060.
• Hydrocarbon resins are polymers that are well known to those skilled in the art, essentially based on carbon and hydrogen, which are therefore inherently miscible in nature. diene (s) elastomer compositions (s) when they are further qualified as “plasticizers". They have been described, for example, in the book “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 their applications, in particular pneumatic rubber (5.5 “Rubber Tires and Mechanical Goods”). They may be aliphatic, aromatic or aliphatic / aromatic type that is to say based on aliphatic and / or aromatic monomers. They may be natural or synthetic, whether or not based on petroleum (if so, also known as petroleum resins). They are preferably exclusively hydrocarbon-based, that is to say they contain only carbon and hydrogen atoms.
• the plasticizing hydrocarbon resin has at least one, more preferably all, of the following characteristics: a Tg greater than 20 ° C (more preferably between 40 and 100 ° C);
• Mn a number-average molecular weight (Mn) of between 400 and 2000 g / mol (more preferentially between 500 and 1500 g / mol);
• the Tg of this resin is measured in a known manner by DSC (Differential Scanning Calorimetry), according to the ASTM D3418 standard.
• the macro structure (Mw, Mn and Ip) of the hydrocarbon resin is determined by steric exclusion chromatography (SEC): tetrahydroiuran solvent; temperature 35 ° C; concentration 1 g / 1; flow rate 1 ml / min; filtered solution on 0.45 ⁇ porosity filter before injection; Moore calibration with polystyrene standards; set of 3 "WATERS” columns in series (“STYRAGEL” HR4E, HR1 and HR0.5); differential refractometer detection ("WATERS 2410") and its associated operating software (“WATERS EMPOWER”).
• the plasticizing hydrocarbon resin is chosen from the group consisting of cyclopentadiene homopolymer or copolymer resins (abbreviated to CPD), dicyclopentadiene homopolymer or copolymer resins (abbreviated to DCPD), terpene homopolymer or copolymer resins, homopolymer or C5 cut copolymer resins, homopolymer or C9 cut copolymer resins, alpha-methyl-styrene homopolymer or copolymer resins and mixtures thereof. resins.
• CPD cyclopentadiene homopolymer or copolymer resins
• DCPD dicyclopentadiene homopolymer or copolymer resins
• terpene homopolymer or copolymer resins homopolymer or C5 cut copolymer resins
• homopolymer or C9 cut copolymer resins homopolymer or C9 cut copolymer resins
• copolymer resins are more preferably used those selected from the group consisting of (D) CPD / vinylaromatic copolymer resins, (D) CPD / terpene copolymer resins, copolymer resins (D) CPD / C5 cut, (D) CPD / C9 cut copolymer resins, terpene / vinylaromatic copolymer resins, terpene / phenol copolymer resins, resins of C5 / vinylaromatic cut copolymer, C9 / vinylaromatic cut copolymer resins, and mixtures of these resins.
• pene here combines in a known manner the alpha-pinene, beta-pinene and limonene monomers; preferably, a limonene monomer is used which is present in a known manner in the form of three possible isomers: L-limonene (laevorotatory enantiomer), D-limonene (dextrorotatory enantiomer), or the dipentene, racemic of the dextrorotatory and levorotatory enantiomers. .
• Suitable vinylaromatic monomers are, for example, styrene, alpha-methylstyrene, ortho-, meta-, para-methylstyrene, vinyltoluene, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, hydroxystyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene, any vinylaromatic monomer from a C 9 cut (or more generally from a C 8 to C 10 cut).
• the vinyl-aromatic compound is styrene or a vinylaromatic monomer derived from a C 9 cut (or more generally from a C 8 to C 10 cut).
• the vinylaromatic compound is the minor monomer, expressed as a mole fraction, in the copolymer under consideration.
• the content of hydrocarbon resin is preferably between 3 and 60 phr, more preferably between 3 and 40 phr, especially between 5 and 30 phr.
• the level of total plasticizer i.e., liquid plasticizer plus, where appropriate, solid hydrocarbon resin
• the level of total plasticizer is preferably between 40 and 100 phr, more preferably in a range of 50 to 80 phr.
• reinforcing filler known for its ability to reinforce a rubber composition that can be used for manufacturing tires, for example an organic filler such as carbon black, or a reinforcing inorganic filler such as silica to which is associated in a known manner a coupling agent.
• Such a reinforcing filler typically consists of nanoparticles whose average size (in mass) is less than 500 nm, most often between 20 and 200 nm, in particular and preferably between 20 and 150 nm.
• Suitable carbon blacks are all carbon blacks, especially blacks of the HAF, ISAF, SAF type conventionally used in tire treads (so-called pneumatic grade blacks).
• the reinforcing carbon blacks of the 100, 200 or 300 series for example blacks NI15, N134, N234, N326, N330, N339, N347, N375, will be mentioned more particularly.
• Carbon blacks could for example be already incorporated in the isoprene elastomer in the form of a masterbatch (see for example applications WO 97/36724 or WO 99/16600).
• organic fillers other than carbon blacks mention may be made of functionalized polyvinyl organic fillers as described in applications WO-A-2006/069792 and WO-A-2006/069793, WO-A-2008/003434. and WO-A-2008/003435.
• inorganic filler is to be understood here any inorganic or mineral filler whatever its color and origin (natural or synthetic), also called “white” filler or sometimes “clear” filler or as opposed to black.
• carbon capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words able to replace, in its reinforcing function, a carbon black conventional pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.
• Suitable reinforcing inorganic fillers are, in particular, mineral fillers of the siliceous type, in particular silica (SiO 2), or of the aluminous type, in particular alumina (Al 2 O 3).
• the silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m 2 / g, preferably from 30 to 400 m 2 / g, especially between 60 and 300 m 2 / g.
• HDS highly dispersible precipitated silicas
• reinforcing aluminas examples include the "Baikalox”"Al25” or “CRI 25” aluminas from the company Baikowski, the “APA-100RDX” from Condea, the “Aluminoxid C” from Evonik or the “AKP-G015" from Sumitomo Chemicals.
• the total reinforcing filler content (carbon black and / or reinforcing inorganic filler) is between 60 and 120 phr, in particular between 70 and 100 phr.
• the reinforcing filler comprises predominantly carbon black; in such a case, the carbon black is present at a level preferably greater than 60 phr, associated or not with a reinforcing inorganic filler such as silica in a minority amount.
• the reinforcing filler comprises an inorganic filler, in particular silica, as a majority; in such a case, the inorganic filler, in particular silica, is present at a preferential rate greater than 70 phr, associated or no to carbon black in minority quantity; the carbon black, when present, is preferably used at a level of less than 20 phr, more preferably less than 10 phr (for example between 0.1 and 10 phr).
• the majority use of a reinforcing inorganic filler such as silica is also advantageous from the point of view of adhesion. on wet or snowy ground.
• the reinforcing filler comprises a blend of carbon black and reinforcing inorganic filler such as silica in similar amounts; in such a case, the level of inorganic filler, in particular silica, and the level of carbon black are preferably each between 25 and 75 phr, more particularly each between 30 and 50 phr.
• an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner to ensure a sufficient chemical and / or physical connection between the inorganic filler (surface of its particles) and the diene elastomer.
• organosilanes or bifunctional polyorganosiloxanes are used.
• polysulfide silanes called “symmetrical” or “asymmetrical” silanes according to their particular structure, are used, as described for example in the applications WO03 / 002648 (or US 2005/016651) and WO03 / 002649 (or US 2005/016650).
• x is an integer of 2 to 8 (preferably 2 to 5);
• - A is a divalent hydrocarbon radical (preferably alkylene groups or groups -C IC8 arylene C 6 -C 2, especially in Cl- Cio alkylene, in particular C 1 -C 4, particularly propylene);
• R radicals substituted or unsubstituted, identical or different, represent an alkyl group Ci-Cig, cycloalkyl C 5 -C 8 aryl or C 6 -C 8 (preferably alkyl, Ci-C 6 , cyclohexyl or phenyl, especially C 1 -C 4 alkyl groups, more particularly methyl and / or ethyl).
• R radicals substituted or unsubstituted, identical or different, represent an alkoxy group or Ci-Ci 8 cycloalkoxy, C 5 -C 8 (preferably a group selected from alkoxyls Cg and C cycloalkoxyls 5 -C 8 , more preferably still a group selected from C 1 -C 4 alkoxyls, in particular methoxyl and ethoxyl).
• polysulfurized silanes mention may be made more particularly of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) polysulfides.
• bis (3-triethoxysilylpropyl) tetrasulfide, abbreviated as TESPT, or bis (triethoxysilylpropyl) disulfide, abbreviated as TESPD is especially used.
• polysulfides in particular disulphides, trisulphides or tetrasulfides
• polysulfides of bis- (monoalkoxyl (Ci-C 4 ) -dialkyl (Ci-C 4 ) silylpropyl), more particularly bis-monoethoxydimethylsilylpropyl tetrasulfide.
• polysulfides in particular disulphides, trisulphides or tetrasulfides
• bis-monoethoxydimethylsilylpropyl tetrasulfide as described in patent application WO 02/083782 (or US 2004/132880).
• the content of coupling agent is preferably between 2 and 12 phr, more preferably between 3 and 8 phr.
• Water-soluble sulfate microparticles Another essential feature of the rubber composition of the invention is that it comprises between 2 and 40 phr of potassium sulfate microparticles.
• microparticles By microparticles, it will be recalled that, in a general manner, micrometric particles, that is to say the median size (expressed in weight) of between 1 ⁇ and 1 mm, must be understood, these microparticles being able to present themselves under any densified form, for example in the form of powder, microbeads, granules or beads; a presentation in powder form is here preferred.
• These specific microparticles according to the invention have a specific size distribution: they are characterized on the one hand by a specific median size (D 50 ) and on the other hand by a particularly narrow size distribution, both measured by laser granulometry. , satisfy the following relations: - 50 ⁇ ⁇ 5 ⁇ ⁇ 150 ⁇ ;
• D 50 is the median particle diameter corresponding to 50% by volume of the cumulative particle distribution, i.e., by volume, 50% of the particles have a diameter less than D 50 and 50% of the particles. particles have a diameter greater than D 50 . It is preferred that the size D 50 be between 75 and 125 ⁇ , for an optimized compromise between the desired surface roughness and a good contact between the rubber composition and the ice.
• the narrowness of the volume distribution of particle size is measured in a known manner by the Span parameter, defined according to the following equation: in which :
• Dio and D 90 represent the particle diameter corresponding to 10% and 90% respectively (by volume) of the cumulative particle distribution
• D 50 is the median particle diameter corresponding to 50% (by volume) of the cumulative particle distribution, i.e., by volume, 50% of the particles have a diameter less than D 50 and 50% particles have a diameter greater than D 50 .
• the Span value is between 0.75 and 1.25.
• the value Di 0 is greater than 30 ⁇ , more preferably greater than 40 ⁇ , in particular greater than 50 ⁇ .
• the value D 90 is less than 180 ⁇ , more preferably less than 160 ⁇ , in particular less than 150 ⁇ .
• the microparticle content in the composition of the The invention is preferably between 2 and 30 phr, more preferably between 5 and 20 phr.
• the particle size distribution (or volumetric size distribution) is characterized in a known manner using a laser granulometer, unless otherwise indicated according to ISO 13320-1 (1999).
• a "Partica LA-950V2" laser diffraction granulometer was used from HORIBA, equipped with its data processing software (P2000074001H version 4.1 1).
• the programming parameters of the measurement are as follows: use of the Fraunhofer model; no pre-treatment of the sample with ultrasound; circulation speed in the tank: 6 (corresponds to about 1400 revolutions / min); stirring speed in the cell: 6 (about 2300 rpm); red laser (650 nm); focal length of the objective: 450 mm; prior checking of laser alignment and measurement of background noise (tank with ethanol).
• a suspension of the sample to be tested is first prepared: for this, about 500 mg of sample are placed in an empty beaker (volume about 100 ml); a few drops of ethanol titrated at 95 ° are then used to wet the sample and form a paste having the consistency of a toothpaste; finally, 40 ml of ethanol are added to this preparation, which is then stirred with a magnetic stir bar and a magnetic stirrer (magnetic stirrer IKA® "RET Basic", graduation 750) for about 15 s .
• the suspension thus obtained is gradually injected, using a pipette, into the preparation tank of the granulometer initially filled with ethanol at 95 ° (low level, ie about 180 ml), up to a level of obscuration of the measuring cell, displayed on the apparatus, between 15 and 20% (corresponding to the optimum of concentration).
• the measurement is carried out immediately after stabilization of the level of obscuration, with three successive measurements on the same preparation for a repeatability control.
• a new preparation (suspension) is performed and analyzed according to the same protocol: the two measurements must be identical (reproducibility according to the recommendations of the standard).
• the cell and the preparation tank of the laser granulometer are rinsed twice with deionized water.
• the recorded data are finally exploited by the granulometer software which delivers the volumetric distribution curve of the sizes as well as the desired characteristics of the volumetric distribution (Di 0 , D 50 , D 90 and Span).
• Various additives delivers the volumetric distribution curve of the sizes as
• the rubber compositions of the invention also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tire treads, in particular for winter tires, such as, for example, protective agents such as waxes.
• protective agents such as waxes.
• compositions may also contain coupling activators when a coupling agent is used, inorganic filler recovery agents or, more generally, processing aid agents that are capable in a known manner, by means of an improvement of the dispersion of the filler in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green state;
• these agents are for example hydrolysable silanes such as alkyl-alkoxysilanes, polyols, polyethers, amines, hydroxylated or hydrolysable polyorganosiloxanes.
• the rubber compositions of the invention are manufactured in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes referred to as “non-phase” phase). -productive ”) at high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed by a second phase of mechanical work (sometimes called phase” Producer ”) at a lower temperature, typically below 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system or vulcanization.
• a first phase of work or thermomechanical mixing (sometimes referred to as "non-phase” phase).
• -productive ) at high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C
• a second phase of mechanical work sometimes called phase” Producer ”
• a process that can be used for the manufacture of such compositions comprises, for example, and preferably the following steps: incorporating into the diene elastomer (or the mixture of diene elastomers), in a mixer, more than 30 phr of a liquid plasticizer, between 50 and 150 pce a reinforcing filler, between 2 and 40 phr of potassium sulfate microparticles, by thermomechanically kneading the whole, in one or more times, until a maximum temperature of between 130 ° C. and 200 ° C. is reached; cool the assembly to a temperature below 100 ° C;
• the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, the possible coating agents, are introduced into a suitable mixer such as a conventional internal mixer. or other complementary additives and other additives, with the exception of the crosslinking system.
• a suitable mixer such as a conventional internal mixer. or other complementary additives and other additives, with the exception of the crosslinking system.
• the low temperature crosslinking system is then incorporated, generally in an external mixer such as a roll mill; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.
• the actual crosslinking system is preferably based on sulfur and a primary vulcanization accelerator, in particular a sulfenamide type accelerator.
• a primary vulcanization accelerator in particular a sulfenamide type accelerator.
• various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid, guanidine derivatives (especially diphenylguanidine), etc.
• the sulfur content is preferably between 0.5 and 3.0 phr, that of the primary accelerator is preferably between 0.5 and 5.0 phr.
• accelerator any compound capable of acting as accelerator for vulcanization of diene elastomers in the presence of sulfur, in particular thiazole-type accelerators and their derivatives, accelerators of the thiuram type, zinc dithiocarbamates.
• These accelerators are more preferably selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS”), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated “CBS”), N, N-dicyclohexyl-2-benzothiazyl sulfenamide (“DCBS”), N-tert-butyl-2-benzothiazylsulfenamide (“TBBS”), N-tert-butyl-2-benzothiazylsulfenimide (“TBSI”), zinc dibenzyldithiocarbamate (“ZBEC”) and mixtures thereof. these compounds.
• MBTS 2-mercaptobenzothiazyl disulfide
• CBS N-cyclohexyl-2-benzothiazyl sulfenamide
• DCBS N-dicyclohexyl-2-benzothiazyl sulfenamide
• the final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded, for example in the form of a rubber profile that can be used directly as a strip of tire rolling.
• the vulcanization (or cooking) is conducted in a known manner at a temperature generally between 130 ° C and 200 ° C, for a sufficient time which may vary for example between 5 and 90 min depending in particular on the cooking temperature, the system of vulcanization adopted and the kinetics of vulcanization of the composition under consideration.
• the rubber composition according to the invention can constitute all or only a part of the tread according to the invention, in the case of a tread of composite type which would be formed of several rubber compositions of different formulations. .
• the invention relates to the rubber compositions and treads previously described in both green (i.e., pre-firing) and cooked (i.e., cross-linking or vulcanization) conditions.
• Theromechanical work (non-productive phase) is then carried out in one step, which lasts a total of about 3 to 4 minutes, until a maximum temperature of "fall” of 165 ° C is reached.
• the mixture thus obtained is recovered, cooled and then sulfur and a sulfenamide type accelerator are incorporated on an external mixer (homo-finisher) at 30 ° C., mixing the whole (productive phase) for a suitable time (for example between 5 and 12 minutes).
• compositions thus obtained are then calendered either in the form of plates or thin sheets of rubber for the measurement of their physical or mechanical properties. 5.2. Ice friction tests and water intake tests
• compositions (denoted C-O, Cl, C-2 and C-3) based on diene elastomers (NR and BR cleavage with cis-1,4 bond ratios greater than 95%) are compared, essentially reinforced with silica, in which a fraction is used or not (in this test (20 phr) of microparticles of a water-soluble sulphate of alkaline or alkaline earth metal (in this test, magnesium or potassium sulphate).
• Tables 1 and 2 respectively give the formulation (in phr) of the four compositions and the parameters describing the volumetric size distribution of the microparticles used, this distribution being characterized according to the method detailed above.
• the level of liquid plasticizer was adjusted in the compositions Cl, C-2 and C-3 in order to maintain the rigidity at the same level as that of the control composition C-0 (Shore A hardness equal to about 53 in the four cases). ): in a known manner, identical rigidity is the necessary condition for a rigorous comparison of the ice driving performance.
• the composition C-0 is a control composition, typical of an ice tire tread; it is devoid of microparticles.
• the composition C-1 is the reference composition of the prior art, it uses 20 pce magnesium sulfate microparticles (type A), similar to those described in the application WO 2010/009850 cited in the introduction of this memo.
• the composition C-2 is another composition which does not conform to the invention, it comprises, for its part, potassium sulfate microparticles (type B) similar to those described in the application WO 2012/085063. In these compositions C-1 and C-2, the volumetric particle size distribution does not meet the requirements of the present invention, with a Span value that is not between 0.5 and 1.5.
• composition C-3 is the only composition according to the invention, it comprises 20 phr of potassium sulfate microparticles (type C) with a volumetric distribution of specific size which satisfies all the requirements of the present invention, in particular with a value of Span which is well between 0.5 and 1.5.
• type C microparticles were obtained by filtration, using appropriate sieving, of the above-mentioned type B microparticles, in order to tighten (make narrower) the size distribution appreciably.
• compositions were subjected to a laboratory test consisting in measuring their coefficient of friction on ice.
• the principle is based on a rubber composition slider sliding at a given speed (for example equal to 5 km / h) on an ice track (ice temperature set at -2 C) with an imposed load (for example equal to 3 kg / cm 2 ).
• Fx direction of advance
• Fz perpendicular to the advance
• test pieces (10 cm by 10 cm and 1 mm thick plates) of the C-0 to C-3 rubber compositions were subjected to a wet (90%) moisture treatment. relative) under high temperature (65 ° C) for several days (3 to 20 days); the weight of these specimens was measured before and after storage in order to determine their weight gain (in%) due to the absorption of water.
• the rubber composition according to the invention thanks to the incorporation of potassium sulfate microparticles having a narrow and specific volume distribution, offers the tires and their treads on the one hand an excellent stability to moisture, on the other hand an ice adhesion performance which is still significantly improved over the prior art rubber compositions.
• ice adhesion performance it is also possible to consider significantly reducing the amount of microparticles in the tread compositions, compared to these compositions of the prior art.
• Zerosil 1165MP silica from Rhodia, type “HDS” (BET and CTAB: approximately 160 m 2 / g);
• MN-00 magnesium sulphate
• KSO-25 potassium sulphate
• ASTM N234 grade (Cabot company);

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• 2012
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